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Sample records for broad band photon

  1. Broadening of effective photonic band gaps in biological chiral structures: From intrinsic narrow band gaps to broad band reflection spectra

    NASA Astrophysics Data System (ADS)

    Vargas, W. E.; Hernández-Jiménez, M.; Libby, E.; Azofeifa, D. E.; Solis, Á.; Barboza-Aguilar, C.

    2015-09-01

    Under normal illumination with non-polarized light, reflection spectra of the cuticle of golden-like and red Chrysina aurigans scarabs show a structured broad band of left-handed circularly polarized light. The polarization of the reflected light is attributed to a Bouligand-type left-handed chiral structure found through the scarab's cuticle. By considering these twisted structures as one-dimensional photonic crystals, a novel approach is developed from the dispersion relation of circularly polarized electromagnetic waves traveling through chiral media, to show how the broad band characterizing these spectra arises from an intrinsic narrow photonic band gap whose spectral position moves through visible and near-infrared wavelengths.

  2. Efficient photon extraction from a quantum dot in a broad-band planar cavity antenna

    SciTech Connect

    Ma, Yong Kremer, Peter E.; Gerardot, Brian D.

    2014-01-14

    We analyse the extraction of photons emitted from single InAs quantum dots embedded in planar microcavities. The structures are designed to achieve broad-band operation and high-collection efficiency from a device requiring straightforward fabrication, even with electrical contacts. The designs consist of a quantum dot in a GaAs membrane with asymmetric top and bottom mirrors and a top-side solid immersion lens (SIL). Four separate cases are considered in our design: a GaAs membrane only (case 1), GaAs membrane with a glass SIL on top (case 2), a GaAs membrane with a glass SIL on top and a back mirror consisting of Au (case 3), a GaAs membrane with a glass SIL on top of a distribute Bragg reflector mirror and Au back mirror (case 4). Both finite difference time domain and analytical simulations are used to calculate the electric field, power density, and far-field radiation pattern. For optimized structures (case 4), we obtain significant extraction efficiencies (>50%) with modest Purcell enhancements (∼20%) and a large spectral full-width-half-maximum (>100 nm). The high-extraction efficiency, broad-band operation, and facile fabrication make the proposed structures promising for realistic quantum dot devices.

  3. Efficient photon extraction from a quantum dot in a broad-band planar cavity antenna

    NASA Astrophysics Data System (ADS)

    Ma, Yong; Kremer, Peter E.; Gerardot, Brian D.

    2014-01-01

    We analyse the extraction of photons emitted from single InAs quantum dots embedded in planar microcavities. The structures are designed to achieve broad-band operation and high-collection efficiency from a device requiring straightforward fabrication, even with electrical contacts. The designs consist of a quantum dot in a GaAs membrane with asymmetric top and bottom mirrors and a top-side solid immersion lens (SIL). Four separate cases are considered in our design: a GaAs membrane only (case 1), GaAs membrane with a glass SIL on top (case 2), a GaAs membrane with a glass SIL on top and a back mirror consisting of Au (case 3), a GaAs membrane with a glass SIL on top of a distribute Bragg reflector mirror and Au back mirror (case 4). Both finite difference time domain and analytical simulations are used to calculate the electric field, power density, and far-field radiation pattern. For optimized structures (case 4), we obtain significant extraction efficiencies (>50%) with modest Purcell enhancements (˜20%) and a large spectral full-width-half-maximum (>100 nm). The high-extraction efficiency, broad-band operation, and facile fabrication make the proposed structures promising for realistic quantum dot devices.

  4. Broad-band optical parametric gain on a silicon photonic chip

    NASA Astrophysics Data System (ADS)

    Foster, Mark A.; Turner, Amy C.; Sharping, Jay E.; Schmidt, Bradley S.; Lipson, Michal; Gaeta, Alexander L.

    2006-06-01

    Developing an optical amplifier on silicon is essential for the success of silicon-on-insulator (SOI) photonic integrated circuits. Recently, optical gain with a 1-nm bandwidth was demonstrated using the Raman effect, which led to the demonstration of a Raman oscillator, lossless optical modulation and optically tunable slow light. A key strength of optical communications is the parallelism of information transfer and processing onto multiple wavelength channels. However, the relatively narrow Raman gain bandwidth only allows for amplification or generation of a single wavelength channel. If broad gain bandwidths were to be demonstrated on silicon, then an array of wavelength channels could be generated and processed, representing a critical advance for densely integrated photonic circuits. Here we demonstrate net on/off gain over a wavelength range of 28nm through the optical process of phase-matched four-wave mixing in suitably designed SOI channel waveguides. We also demonstrate wavelength conversion in the range 1,511-1,591nm with peak conversion efficiencies of +5.2dB, which represents more than 20 times improvement on previous four-wave-mixing efficiencies in SOI waveguides. These advances allow for the implementation of dense wavelength division multiplexing in an all-silicon photonic integrated circuit. Additionally, all-optical delays, all-optical switches, optical signal regenerators and optical sources for quantum information technology, all demonstrated using four-wave mixing in silica fibres, can now be transferred to the SOI platform.

  5. Broad band waveguide spectrometer

    DOEpatents

    Goldman, Don S.

    1995-01-01

    A spectrometer for analyzing a sample of material utilizing a broad band source of electromagnetic radiation and a detector. The spectrometer employs a waveguide possessing an entry and an exit for the electromagnetic radiation emanating from the source. The waveguide further includes a surface between the entry and exit portions which permits interaction between the electromagnetic radiation passing through the wave guide and a sample material. A tapered portion forms a part of the entry of the wave guide and couples the electromagnetic radiation emanating from the source to the waveguide. The electromagnetic radiation passing from the exit of the waveguide is captured and directed to a detector for analysis.

  6. Kind of broad-band photonic valve and its application to silicon solar cells.

    PubMed

    Le Perchec, J

    2012-09-10

    We investigate the dual optical behaviour of a photonic grating interface presenting a more or less important index contrast, showing either efficient broadband reflectivity, either high transmittance within the same spectral window, depending on the direction of the incident light. This behaviour is reminiscent of a diode one and could find interesting applications. A typical example is given for thin crystalline silicon solar cells where the rear side is directly nano-textured to trap light without metal reflector (bifacial device), well compatible with an integration in a photovoltaic module. PMID:23037524

  7. Broad-band beam buncher

    DOEpatents

    Goldberg, David A.; Flood, William S.; Arthur, Allan A.; Voelker, Ferdinand

    1986-01-01

    A broad-band beam buncher is disclosed, comprising an evacuated housing, an electron gun therein for producing an electron beam, a buncher cavity having entrance and exit openings through which the beam is directed, grids across such openings, a source providing a positive DC voltage between the cavity and the electron gun, a drift tube through which the electron beam travels in passing through such cavity, grids across the ends of such drift tube, gaps being provided between the drift tube grids and the entrance and exit grids, a modulator for supplying an ultrahigh frequency modulating signal to the drift tube for producing velocity modulation of the electrons in the beam, a drift space in the housing through which the velocity modulated electron beam travels and in which the beam is bunched, and a discharge opening from such drift tube and having a grid across such opening through which the bunched electron beam is discharged into an accelerator or the like. The buncher cavity and the drift tube may be arranged to constitute an extension of a coaxial transmission line which is employed to deliver the modulating signal from a signal source. The extended transmission line may be terminated in its characteristic impedance to afford a broad-band response and the device as a whole designed to effect broad-band beam coupling, so as to minimize variations of the output across the response band.

  8. Photonic band gap materials

    SciTech Connect

    Soukoulis, C.M. |

    1993-12-31

    An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented.

  9. Broad-band beam buncher

    DOEpatents

    Goldberg, D.A.; Flood, W.S.; Arthur, A.A.; Voelker, F.

    1984-03-20

    A broad-band beam bunther is disclosed, comprising an evacuated housing, an electron gun therein for producing an electron beam, a buncher cavity having entrance and exit openings through which the beam is directed, grids across such openings, a source providing a positive DC voltage between the cavity and the electron gun, a drift tube through which the electron beam travels in passing through such cavity, grids across the ends of such drift tube, gaps being provided between the drift tube grids and the entrance and exit grids, a modulator for supplying an ultrahigh frequency modulating signal to the drift tube for producing velocity modulation of the electrons in the beam, a drift space in the housing through which the velocity modulated electron beam travels and in which the beam is bunched, and a discharge opening from such drift tube and having a grid across such opening through which the bunched electron beam is discharged into an accelerator or the like. The buncher cavity and the drift tube may be arranged to constitute an extension of a coaxial transmission line which is employed to deliver the modulating signal from a signal source. The extended transmission line may be terminated in its characteristic impedance to afford a broad-

  10. Demonstration of broad photonic crystal stop band in a freely-suspended microfiber perforated by an array of rectangular holes.

    PubMed

    Yu, Yang; Ding, Wei; Gan, Lin; Li, Zhi-Yuan; Luo, Qiang; Andrews, Steve

    2014-02-10

    It is shown that photonic crystal (PhC) optical reflectors with reflectance in excess of 60% and fractional bandwidths greater than 10% can be fabricated by ion beam milling of fewer than ten periods of rectangular cross section through-holes in micron-scale tapered fibers. The optical characteristics agree well with numerical simulations when allowance is made for fabrication artefacts and we show that the radiation loss, which is partly determined by optical interference, can be suppressed by design. The freely-suspended devices are compact and robust and could form the basic building block of optical cavities and filters. PMID:24663545

  11. Silicon micromachined broad band light source

    NASA Technical Reports Server (NTRS)

    George, Thomas (Inventor); Jones, Eric (Inventor); Tuma, Margaret L. (Inventor); Eastwood, Michael (Inventor); Hansler, Richard (Inventor)

    2004-01-01

    A micro electromechanical system (MEMS) broad band incandescent light source includes three layers: a top transmission window layer; a middle filament mount layer; and a bottom reflector layer. A tungsten filament with a spiral geometry is positioned over a hole in the middle layer. A portion of the broad band light from the heated filament is reflective off the bottom layer. Light from the filament and the reflected light of the filament are transmitted through the transmission window. The light source may operate at temperatures of 2500 K or above. The light source may be incorporated into an on board calibrator (OBC) for a spectrometer.

  12. The GREGOR Broad-Band Imager

    NASA Astrophysics Data System (ADS)

    von der Lühe, O.; Volkmer, R.; Kentischer, T. J.; Geißler, R.

    2012-11-01

    The design and characteristics of the Broad-Band Imager (BBI) of GREGOR are described. BBI covers the visible spectral range with two cameras simultaneously for a large field and with critical sampling at 390 nm, and it includes a mode for observing the pupil in a Foucault configuration. Samples of first-light observations are shown.

  13. A broad-band scalar vortex coronagraph

    NASA Astrophysics Data System (ADS)

    Errmann, R.; Minardi, S.; Pertsch, T.

    2013-10-01

    Broad-band coronagraphy with deep nulling and small inner working angle has the potential of delivering images and spectra of exoplanets and other faint objects. In recent years, many coronagraphic schemes have been proposed, the most promising being the optical vortex phase mask coronagraphs. In this paper, a new scheme of broad-band optical scalar vortex coronagraph is proposed and characterized experimentally in the laboratory. Our setup employs a pair of computer-generated phase gratings (one of them containing a singularity) to control the chromatic dispersion of phase plates and achieves a constant peak-to-peak attenuation below 1 × 10-3 over a bandwidth of 120 nm centred at 700 nm. An inner working angle of ˜λ/D is demonstrated along with a raw contrast of 11.5 mag at 2λ/D.

  14. Broad-band UHF dipole array

    NASA Technical Reports Server (NTRS)

    Bailey, M. C.

    1985-01-01

    A 6X6 array of fan-dipoles was designed to operate in the 510 to 660 MHz frequency range for aircraft flight test and evaluation of a UHF radiometer system. A broad-band dipole design operating near the first resonance is detailed. Measured VSWR and radiation patterns for the dipole array demonstrate achievable bandwidths in the 35 percent to 40 percent range.

  15. Broad-band acoustic Doppler current profiler

    USGS Publications Warehouse

    Cobb, E.D.

    1993-01-01

    The broad-band acoustic Doppler current profiler is an instrument that determines velocity based on the Doppler principle by reflecting acoustic signals off sediment particles in the water. The instrument is capable of measuring velocity magnitude and direction throughout a water column and of measuring water depth. It is also capable of bottom tracking and can, therefore, keep track of its own relative position as it is moved across a channel. Discharge measurements can be made quickly and, based on limited tests, accurately with this instrument. ?? 1993.

  16. Ultra-Broad-Band Optical Parametric Amplifier or Oscillator

    NASA Technical Reports Server (NTRS)

    Strekalov, Dmitry; Matsko, Andrey; Savchenkov, Anatolly; Maleki, Lute

    2009-01-01

    A concept for an ultra-broad-band optical parametric amplifier or oscillator has emerged as a by-product of a theoretical study in fundamental quantum optics. The study was originally intended to address the question of whether the two-photon temporal correlation function of light [in particular, light produced by spontaneous parametric down conversion (SPDC)] can be considerably narrower than the inverse of the spectral width (bandwidth) of the light. The answer to the question was found to be negative. More specifically, on the basis of the universal integral relations between the quantum two-photon temporal correlation and the classical spectrum of light, it was found that the lower limit of two-photon correlation time is set approximately by the inverse of the bandwidth. The mathematical solution for the minimum two-photon correlation time also provides the minimum relative frequency dispersion of the down-converted light components; in turn, the minimum relative frequency dispersion translates to the maximum bandwidth, which is important for the design of an ultra-broad-band optical parametric oscillator or amplifier. In the study, results of an analysis of the general integral relations were applied in the case of an optically nonlinear, frequency-dispersive crystal in which SPDC produces collinear photons. Equations were found for the crystal orientation and pump wavelength, specific for each parametric-down-converting crystal, that eliminate the relative frequency dispersion of collinear degenerate (equal-frequency) signal and idler components up to the fourth order in the frequency-detuning parameter

  17. Broad-Band Activatable White-Opsin

    PubMed Central

    Batabyal, Subrata; Cervenka, Gregory; Ha, Ji Hee; Kim, Young-tae; Mohanty, Samarendra

    2015-01-01

    Currently, the use of optogenetic sensitization of retinal cells combined with activation/inhibition has the potential to be an alternative to retinal implants that would require electrodes inside every single neuron for high visual resolution. However, clinical translation of optogenetic activation for restoration of vision suffers from the drawback that the narrow spectral sensitivity of an opsin requires active stimulation by a blue laser or a light emitting diode with much higher intensities than ambient light. In order to allow an ambient light-based stimulation paradigm, we report the development of a ‘white-opsin’ that has broad spectral excitability in the visible spectrum. The cells sensitized with white-opsin showed excitability at an order of magnitude higher with white light compared to using only narrow-band light components. Further, cells sensitized with white-opsin produced a photocurrent that was five times higher than Channelrhodopsin-2 under similar photo-excitation conditions. The use of fast white-opsin may allow opsin-sensitized neurons in a degenerated retina to exhibit a higher sensitivity to ambient white light. This property, therefore, significantly lowers the activation threshold in contrast to conventional approaches that use intense narrow-band opsins and light to activate cellular stimulation. PMID:26360377

  18. Photonic band gap structure simulator

    DOEpatents

    Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.

    2006-10-03

    A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.

  19. Multimode Broad-Band Patch Antennas

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.

    2003-01-01

    Microstrip patch antennas of a proposed type would be tunable over broad wavelength ranges. These antennas would be attractive for use in a variety of microwave communication systems in which there are requirements for transmission and/or reception at multiple, widely separated frequencies. Prior efforts to construct tunable microstrip patch antennas have involved integration of microstrip circuitry with, variously, ferrite films with magneticfield tuning, solid-state electronic tuning devices, or piezoelectric tuning actuators. Those efforts have been somewhat successful, but have yielded tuning ranges of 20 percent and smaller much smaller than needed in typical practical cases. Like prior microstrip patch antennas (both tunable and non-tunable), the proposed antennas would have instantaneous bandwidths of about 1 percent of their nominal or resonance frequencies. However, these would be tunable over much broader frequency ranges as much as several octaves, depending on specific designs. They could be fabricated relatively simply and inexpensively by use of conventional photolithography, and without need for integration with solid-state electronic or piezoelectric control devices. An antenna as proposed (see figure) would include a microstrip patch radiating element on a thin ferroelectric film on a semiconductor substrate with a ground-plane conductor on the underside of the substrate. The ferroelectric film could be, for example, SrTiO3 with a thickness of the order of 1 or 2 micrometers.

  20. Broad band airborne water vapor radiometry

    NASA Astrophysics Data System (ADS)

    Kuhn, Peter M.

    An infrared radiometer with a pass band of 280 to 520 cm-1 (35.7 to 19.2 µm) is employed on the NASA Ames Research Center U-2 and C-141A aircraft in the measurement of water vapor burden in the upper troposphere and stratosphere. Coincidentally with altitude changes the water vapor mass mixing ratio is also inferred by observing the change in optical depth over a known vertical distance. Data from the December 1980 U-2 Water Vapor Exchange Experiment over the Panama Canal Zone adds to the concept that overshooting cumulonimbus towers “moisten” the lower stratosphere. The average mass mixing ratio in close proximity to or above such towers ranges from 3.5 to 5.0 parts per million above 18 km while the average background mass mixing ratio is only 2.9 parts per million. Generally the lowest background mixing ratios, averaging 2.6 parts per million occurred in the 18 to 21 km layer. For the same levels background Panama mass mixing ratios averaged from 1.0 to 3.0 parts per million higher than in middle latitudes.

  1. Optically tuneable blue phase photonic band gaps

    SciTech Connect

    Liu, H.-Y.; Wang, C.-T.; Hsu, C.-Y.; Lin, T.-H.; Liu, J.-H.

    2010-03-22

    This study investigates an optically switchable band gap of photonic crystal that is based on an azobenzene-doped liquid crystal blue phase. The trans-cis photoisomerization of azobenzene deforms the cubic unit cell of the blue phase and shifts the photonic band gap. The fast back-isomerization of azobenzene was induced by irradiation with different wavelengths light. The crystal structure is verified using Kossel diffraction diagram. An optically addressable blue phase display, based on Bragg reflection from the photonic band gap, is also demonstrated. The tunable ranges are around red, green, and blue wavelengths and exhibit a bright saturated color.

  2. Ultra high vacuum broad band high power microwave window

    DOEpatents

    Nguyen-Tuong, V.; Dylla, H.F. III

    1997-11-04

    An improved high vacuum microwave window has been developed that utilizes high density polyethylene coated on two sides with SiOx, SiNx, or a combination of the two. The resultant low dielectric and low loss tangent window creates a low outgassing, low permeation seal through which broad band, high power microwave energy may be passed. No matching device is necessary and the sealing technique is simple. The features of the window are broad band transmission, ultra-high vacuum compatibility with a simple sealing technique, low voltage standing wave ratio, high power transmission and low cost. 5 figs.

  3. Ultra high vacuum broad band high power microwave window

    DOEpatents

    Nguyen-Tuong, Viet; Dylla, III, Henry Frederick

    1997-01-01

    An improved high vacuum microwave window has been developed that utilizes high density polyethylene coated on two sides with SiOx, SiNx, or a combination of the two. The resultant low dielectric and low loss tangent window creates a low outgassing, low permeation seal through which broad band, high power microwave energy may be passed. No matching device is necessary and the sealing technique is simple. The features of the window are broad band transmission, ultra-high vacuum compatibility with a simple sealing technique, low voltage standing wave ratio, high power transmission and low cost.

  4. A planar broad-band flared microstrip slot antenna

    NASA Astrophysics Data System (ADS)

    Povinelli, Mark J.

    1987-08-01

    Experimental results have been obtained on a planar multioctave bandwidth flared microstrip slot. When crossed, the element is capable of horizontal, vertical, or circular polarization. A design was fabricated and measurements were taken to define the performance. The input impedance and radiation characteristics are shown to have a broad-band response when configured as a cavity-backed element.

  5. Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures

    SciTech Connect

    Perina, Jan Jr.; Centini, Marco; Sibilia, Concita; Bertolotti, Mario; Scalora, Michael

    2006-03-15

    We have developed a rigorous quantum model of spontaneous parametric down-conversion in a nonlinear 1D photonic-band-gap structure based upon expansion of the field into monochromatic plane waves. The model provides a two-photon amplitude of a created photon pair. The spectra of the signal and idler fields, their intensity profiles in the time domain, as well as the coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are determined both for cw and pulsed pumping regimes in terms of the two-photon amplitude. A broad range of parameters characterizing the emitted down-converted fields can be used. As an example, a structure composed of 49 layers of GaN/AlN is analyzed as a suitable source of photon pairs having high efficiency.

  6. Robust photonic band gap from tunable scatterers

    PubMed

    Zhang; Lei; Wang; Zheng; Tam; Chan; Sheng

    2000-03-27

    We show theoretically and experimentally that photonic band gaps can be realized using metal or metal-coated spheres as building blocks. Robust photonic gaps exist in any periodic structure built from such spheres when the filling ratio of the spheres exceeds a threshold. The frequency and the size of the gaps depend on the local order rather than on the symmetry or the global long range order. Good agreement between theory and experiment is obtained in the microwave regime. Calculations show that the approach can be scaled up to optical frequencies even in the presence of absorption. PMID:11018959

  7. Broad-Band Spectroscopy of Hercules X-1 with Suzaku

    NASA Technical Reports Server (NTRS)

    Asami, Fumi; Enoto, Teruaki; Iwakiri, Wataru; Yamada, Shin'ya; Tamagawa, Toru; Mihara, Tatehiro; Nagase, Fumiaki

    2014-01-01

    Hercules X-1 was observed with Suzaku in the main-on state from 2005 to 2010. The 0.4- 100 keV wide-band spectra obtained in four observations showed a broad hump around 4-9 keV in addition to narrow Fe lines at 6.4 and 6.7 keV. The hump was seen in all the four observations regardless of the selection of the continuum models. Thus it is considered a stable and intrinsic spectral feature in Her X-1. The broad hump lacked a sharp structure like an absorption edge. Thus it was represented by two different spectral models: an ionized partial covering or an additional broad line at 6.5 keV. The former required a persistently existing ionized absorber, whose origin was unclear. In the latter case, the Gaussian fitting of the 6.5-keV line needs a large width of sigma = 1.0-1.5 keV and a large equivalent width of 400-900 eV. If the broad line originates from Fe fluorescence of accreting matter, its large width may be explained by the Doppler broadening in the accretion flow. However, the large equivalent width may be inconsistent with a simple accretion geometry.

  8. Broad band invisibility cloak made of normal dielectric multilayer

    NASA Astrophysics Data System (ADS)

    Xu, Xiaofei; Feng, Yijun; Xiong, Shuai; Fan, Jinlong; Zhao, Jun-Ming; Jiang, Tian

    2011-10-01

    We present the design, fabrication, and performance test of a quasi three-dimensional carpet cloak made of normal dielectric in the microwave regime. Taking advantage of a simple linear coordinate transformation, we design a carpet cloak with homogeneous anisotropic medium and then practically realize the device with multilayer of alternating normal dielectric slabs based on the effective medium theory. As a proof-of-concept example, we fabricate the carpet cloak with multilayer of FR4 dielectric slabs with air spacing. The performance of the fabricated design is verified through full-wave numerical simulation and measurement of the far-field scattering electromagnetic waves in a microwave anechoic chamber. Experimental results have demonstrated pronounced cloaking effect in a very broad band from 8 GHz to 18 GHz (whole X and Ku band) due to the low loss, non-dispersive feature of the multilayer dielectric structure.

  9. Assessment of autonomic response by broad-band respiration

    NASA Technical Reports Server (NTRS)

    Berger, R. D.; Saul, J. P.; Cohen, R. J.

    1989-01-01

    We present a technique for introducing broad-band respiratory perturbations so that the response characteristics of the autonomic nervous system can be determined noninvasively over a wide range of physiologically relevant frequencies. A subject's respiratory bandwidth was broadened by breathing on cue to a sequence of audible tones spaced by Poisson intervals. The transfer function between the respiratory input and the resulting instantaneous heart rate was then computed using spectral analysis techniques. Results using this method are comparable to those found using traditional techniques, but are obtained with an economy of data collection.

  10. Effect of size of silica microspheres on photonic band gap

    SciTech Connect

    Dhiman, N. Sharma, A. Gathania, A. K.; Singh, B. P.

    2014-04-24

    In present work photonic crystals of different size of silica microspheres have been fabricated. The optical properties of these developed photonic crystals have been studied using UV-visible spectroscopy. UV-visible spectroscopy shows that they have photonic band gap that can be tuned in visible and infrared regime by changing the size of silica microspheres. The photonic band gap structures of these photonic crystals have been calculated using MIT photonic band gap package. It also reveals that with the increase in size of silica microspheres the photonic band gap shifts to lower energy region.

  11. Fabrication of photonic band gap materials

    DOEpatents

    Constant, Kristen; Subramania, Ganapathi S.; Biswas, Rana; Ho, Kai-Ming

    2002-01-15

    A method for forming a periodic dielectric structure exhibiting photonic band gap effects includes forming a slurry of a nano-crystalline ceramic dielectric or semiconductor material and monodisperse polymer microspheres, depositing a film of the slurry on a substrate, drying the film, and calcining the film to remove the polymer microspheres therefrom. The film may be cold-pressed after drying and prior to calcining. The ceramic dielectric or semiconductor material may be titania, and the polymer microspheres may be polystyrene microspheres.

  12. Fabrication of Photonic band gap Materials

    SciTech Connect

    Constant, Kristen; Subramania, Ganapathi S.; Biswas, Rana; Ho, Kai-Ming

    2000-01-05

    A method for forming a periodic dielectric structure exhibiting photonic band gap effects includes forming a slurry of a nano-crystalline ceramic dielectric or semiconductor material and monodisperse polymer microsphere, depositing a film of the slurry on a substrate, drying the film, and calcining the film to remove the polymer microsphere there from. The film may be cold-pressed after drying and prior to calcining. The ceramic dielectric or semiconductor material may be titania, and the polymer microsphere may be polystyrenemicrosphere.

  13. Calculation of effective doses for broad parallel photon beams.

    PubMed

    Kim, C H; Reece, W D; Poston, J W

    1999-02-01

    Values of effective dose (E) were calculated for the entire range of incident directions of broad parallel photon beams for selected photon energies using the Monte Carlo N-Particle (MCNP) transport code with a hermaphroditic phantom. The calculated results are presented in terms of conversion coefficients transforming air kerma to effective dose. This study also compared the numerical values of E and H(E) over the entire range of incident beam directions. E was always less than H(E) considering all beam directions and photon energies, but the differences were not significant except when a photon beam approaches some specific directions (overhead and underfoot). This result suggests that the current H(E) values can be directly interpreted as E or, at least, as a conservative value of E without knowing the details of irradiation geometries. Finally, based on the distributions of H(E) and E over the beam directions, this study proposes ideal angular response factors for personal dosimeters that can be used to improve the angular response properties of personal dosimeters for off-normal incident photons. PMID:9929126

  14. Turbulent boundary layer flow over broad-banded roughness

    NASA Astrophysics Data System (ADS)

    Pawlak, Geno; Aghsaee, Payam; Mazrouei, Saeed; Leonardi, Stefano; Rajagopalan, Krishnakumar; Kobayashi, Marcelo

    2014-11-01

    The response of the boundary layer to a regular roughness is often parameterized in terms of the length scales defining the roughness. Difficulty arises in the case of broad-banded and highly irregular roughness distributions such as over coral reefs or urban canopies where the length scale that determines the response of the boundary layer is not clear. Here we use a spectral description for roughness to create idealized two-dimensional irregular roughness profiles, using square waves as a basis function. Laboratory experiments along with Direct Numerical Simulations (DNS) are used to examine the hydrodynamic response to the broad-banded roughness and flow characteristics are related to geometric characteristics of the boundary. The simulations and experiments show that the nature of the flow over two-dimensional irregular walls can be determined as a function of the hydrodynamic origin, which, in turn, can be determined as a function of a mean cavity shape. Results are interpreted in terms of the spectral characteristics of the roughness. The contribution of the various spectral components to the total drag is analyzed for each case. The roughness spectrum influences the flow through the shape of the cavities on the wall and can provide some guidance in predicting the nature of the flow.

  15. Highly dispersive photonic band-gap prism.

    PubMed

    Lin, S Y; Hietala, V M; Wang, L; Jones, E D

    1996-11-01

    We propose the concept of a photonic band-gap (PBG) prism based on two-dimensional PBG structures and realize it in the millimeter-wave spectral regime. We recognize the highly nonlinear dispersion of PBG materials near Brillouin zone edges and utilize the dispersion to achieve strong prism action. Such a PBG prism is very compact if operated in the optical regime, ~20 mm in size for lambda ~ 700 nm, and can serve as a dispersive element for building ultracompact miniature spectrometers. PMID:19881796

  16. Dual-band photon sorting plasmonic MIM metamaterial sensor

    NASA Astrophysics Data System (ADS)

    Jung, Young Uk; Bendoym, Igor; Golovin, Andrii B.; Crouse, David T.

    2014-06-01

    We propose plasmonic metal-insulator-metal (MIM) metamaterial designs for the sensing of two infrared wavelength bands, the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) band by using a photon sorting technique. The proposed structures can capture light effectively on the metasurfaces based on coupling of free space energy to a subwavelength plasmonic mode. Photon sorting can be performed such that the incident light with a broad spectrum upon the metasurfaces can be "split" according to wavelength, channeling different spectral bands to different physical regions of the array on the surface where it is then absorbed by the insulator. Two different structures described in this work are (1) Square-type structure which consists of MIM resonators being periodically arranged to form a polarization independent sensor and (2) Meander-type structure which consists of MIM resonators being connected to form the meander shaped sensor. Mercury Cadmium Telluride (HgCdTe) posts are used as absorbing material within the MIM structure to generate free carriers and allow for collection of carrier charges. The proposed structures have compact designs and exhibit efficient light splitting and absorption for the IR spectral band. Structural and material properties, the electric field distribution and Poynting vector fields at the resonance frequencies are provided. Applications include thermal imaging, night vision systems, rifle sights, missile detection and discrimination, dual bandwidth optical filters, light trapping, and electromagnetically induced transparency.

  17. Phase Modulation of Photonic Band Gap Signal

    PubMed Central

    Wang, Zhiguo; Gao, Mengqin; Mahesar, Abdul Rasheed; Zhang, Yanpeng

    2016-01-01

    We first investigate the probe transmission signal (PTS) and the four wave mixing band gap signal (FWM BGS) modulated simultaneously by the relative phase and the nonlinear phase shift in the photonic band gap (PBG) structure. The switch between the absorption enhancement of PTS and the transmission enhancement of PTS with the help of changing the relative phase and the nonlinear phase shift is obtained in inverted Y-type four level atomic system experimentally and theoretically. The corresponding switch in PTS can be used to realize all optical switches. On other hand, the relative phase and the nonlinear phase shift also play the vital role to modulate the intensity of FWM BGS reflected from the PBG structure. And it can be potentially used to realize the optical amplifier. PMID:27323849

  18. Phase Modulation of Photonic Band Gap Signal.

    PubMed

    Wang, Zhiguo; Gao, Mengqin; Mahesar, Abdul Rasheed; Zhang, Yanpeng

    2016-01-01

    We first investigate the probe transmission signal (PTS) and the four wave mixing band gap signal (FWM BGS) modulated simultaneously by the relative phase and the nonlinear phase shift in the photonic band gap (PBG) structure. The switch between the absorption enhancement of PTS and the transmission enhancement of PTS with the help of changing the relative phase and the nonlinear phase shift is obtained in inverted Y-type four level atomic system experimentally and theoretically. The corresponding switch in PTS can be used to realize all optical switches. On other hand, the relative phase and the nonlinear phase shift also play the vital role to modulate the intensity of FWM BGS reflected from the PBG structure. And it can be potentially used to realize the optical amplifier. PMID:27323849

  19. Introducing Defects in Photonic Band-Gap (PBG) Crystals

    SciTech Connect

    Johnson, Elliott C.; /North Dakota State U. /SLAC

    2007-11-07

    Photonic Band-Gap (PBG) fibers are a periodic array of optical materials arranged in a lattice called a photonic crystal. The use of PBG fibers for particle acceleration is being studied by the Advanced Accelerator Research Department (AARD) at SLAC. By introducing defects in such fibers, e.g. removing one or more capillaries from a hexagonal lattice, spatially confined modes suitable for particle acceleration may be created. The AARD has acquired several test samples of PBG fiber arrays with varying refractive index, capillary size, and length from an external vendor for testing. The PBGs were inspected with a microscope and characteristics of the capillaries including radii, spacing, and errors in construction were determined. Transmission tests were performed on these samples using a broad-range spectrophotometer. In addition, detailed E-field simulations of different PBG configurations were done using the CUDOS and RSOFT codes. Several accelerating modes for different configurations were found and studied in detail.

  20. Two photon absorption in high power broad area laser diodes

    NASA Astrophysics Data System (ADS)

    Dogan, Mehmet; Michael, Christopher P.; Zheng, Yan; Zhu, Lin; Jacob, Jonah H.

    2014-03-01

    Recent advances in thermal management and improvements in fabrication and facet passivation enabled extracting unprecedented optical powers from laser diodes (LDs). However, even in the absence of thermal roll-over or catastrophic optical damage (COD), the maximum achievable power is limited by optical non-linear effects. Due to its non-linear nature, two-photon absorption (TPA) becomes one of the dominant factors that limit efficient extraction of laser power from LDs. In this paper, theoretical and experimental analysis of TPA in high-power broad area laser diodes (BALD) is presented. A phenomenological optical extraction model that incorporates TPA explains the reduction in optical extraction efficiency at high intensities in BALD bars with 100μm-wide emitters. The model includes two contributions associated with TPA: the straightforward absorption of laser photons and the subsequent single photon absorption by the holes and electrons generated by the TPA process. TPA is a fundamental limitation since it is inherent to the LD semiconductor material. Therefore scaling the LDs to high power requires designs that reduce the optical intensity by increasing the mode size.

  1. Broad Band Intra-Cavity Total Reflection Chemical Sensor

    DOEpatents

    Pipino, Andrew C. R.

    1998-11-10

    A broadband, ultrahigh-sensitivity chemical sensor is provided that allows etection through utilization of a small, extremely low-loss, monolithic optical cavity. The cavity is fabricated from highly transparent optical material in the shape of a regular polygon with one or more convex facets to form a stable resonator for ray trajectories sustained by total internal reflection. Optical radiation enters and exits the monolithic cavity by photon tunneling in which two totally reflecting surfaces are brought into close proximity. In the presence of absorbing material, the loss per pass is increased since the evanescent waves that exist exterior to the cavity at points where the circulating pulse is totally reflected, are absorbed. The decay rate of an injected pulse is determined by coupling out an infinitesimal fraction of the pulse to produce an intensity-versus-time decay curve. Since the change in the decay rate resulting from absorption is inversely proportional to the magnitude of absorption, a quantitative sensor of concentration or absorption cross-section with 1 part-per-million/pass or better sensitivity is obtained. The broadband nature of total internal reflection permits a single device to be used over a broad wavelength range. The absorption spectrum of the surrounding medium can thereby be obtained as a measurement of inverse decay time as a function of wavelength.

  2. Broad-band Lg attenuation modelling in the Middle East

    NASA Astrophysics Data System (ADS)

    Pasyanos, Michael E.; Matzel, Eric M.; Walter, William R.; Rodgers, Arthur J.

    2009-06-01

    We present a broad-band tomographic model of Lg attenuation in the Middle East derived from source- and site-corrected amplitudes. Absolute amplitude measurements are made on hand-selected and carefully windowed seismograms for tens of stations and thousands of crustal earthquakes resulting in excellent coverage of the region. A conjugate gradient method is used to tomographically invert the amplitude data set of over 8000 paths over a 45° × 40° region of the Middle East. We solve for Q variation, as well as site and source terms, for a wide range of frequencies ranging from 0.5 to 10 Hz. We have modified the standard attenuation tomography technique to more explicitly define the earthquake source expression in terms of the seismic moment. This facilitates the use of the model to predict the expected amplitudes of new events, an important consideration for earthquake hazard or explosion monitoring applications. The attenuation results have a strong correlation to tectonics. Shields have low attenuation, whereas tectonic regions have high attenuation, with the highest attenuation at 1 Hz found in eastern Turkey. The results also compare favourably to other studies in the region made using Lg propagation efficiency, Lg/Pg amplitude ratios and two-station methods. We tomographically invert the amplitude measurements for each frequency independently. In doing so, it appears the frequency dependence of attenuation in all regions is not compatible with the power-law representation of Q(f), an assumption that is often made.

  3. Measurement of photonic band diagram in non-crystalline photonic band gap (PBG) materials

    NASA Astrophysics Data System (ADS)

    Man, Weining; Williamson, Eric; Hashemizad, Seyed; Yadak, Polin; Florescu, Marian

    2011-03-01

    Non-crystalline PBG materials have received increasing attention recently and sizeable PBGs have been reported in quasi-crystalline structures or even in disordered structures. Band calculations for periodic structures produce accurate dispersion relations in them and refraction properties at their surfaces. However, band calculations for non-periodic structures employ large super-cells of N >100 building blocks, and provide little useful information other than the PBG frequency and width. Since band is folded into N bands, within the first Brillouin zone of the supper-cell. Using stereolithography, we construct various quasi-crystalline or disordered PBG materials and perform transmission measurements. The dispersion relations of EM wave (band diagrams) are reconstructed from the measured phase data. Our experiments not only verify the existence of sizeable PBGs in these structures, but also provide detailed information of the effective band diagrams, dispersion relation, group velocity vector, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study presents a powerful tool to investigate photonic properties of non-crystalline structures and provides important dispersion information, which is otherwise impossible to obtain.

  4. Ground Based Test Results for Broad Band LIDAR

    NASA Astrophysics Data System (ADS)

    Heaps, W. S.; Georgieva, E.; Huang, W.; Baldauf, B.; McComb, T.

    2010-12-01

    Our team of personnel from Northrop Grumman Aerospace Systems (NGAS) and Goddard Space Flight Center (GSFC) is developing two new lidar systems for column CO2 measurement based on an innovative new lidar technique using a Fabry-Perot based detector and a broadband laser source which replaces the narrow band laser commonly used. Our lidar is capable of mitigating inaccuracy associated with atmospherically induced variations in CO2 absorption line shape and strength and reduces the number of individual different wavelength lasers required from three or more to only one.It also reduces the requirement for source wavelength stability, instead putting this responsibility on the Fabry-Perot based receiver. There is a great need for measurements of atmospheric carbon dioxide concentration with high spatial and temporal resolution for global and regional studies of the carbon cycle. Such measurements will better resolve the linkage between global warming and anthropogenic CO2 emissions. In the Decadal Survey of Earth Science the National Research Council recommended that NASA develop, build, and fly a laser based system for precision measurement of total carbon dioxide column (the ASCENDS mission). The mission demands measurements of CO2 to a precision of 1 ppm out of the total ~400 ppm column in order to locate sources and sinks. Achieving this 400:1 precision is made more difficult due to the strong dependence on changes in atmospheric pressure and temperature of atmospheric carbon dioxide absorption line position, shape, and strength. Most lidar systems currently under development for remote sensing of atmospheric CO2 require multiple lasers operating at different, very narrow bandwidth wavelengths in order to resolve these effects. Our approach requires only a single laser and the wavelength stability requirements are much less stringent than those for the multiple laser approaches. Since 2007 GSFC has been developing a lidar using their broadband detection scheme and

  5. Highly dispersive photonic band-gap-edge optofluidic biosensors

    NASA Astrophysics Data System (ADS)

    Xiao, S.; Mortensen, N. A.

    2006-11-01

    Highly dispersive photonic band-gap-edge optofluidic biosensors are studied theoretically. We demonstrate that these structures are strongly sensitive to the refractive index of the liquid, which is used to tune dispersion of the photonic crystal. The upper frequency band-gap edge shifts about 1.8 nm for δ n=0.002, which is quite sensitive. Results from transmission spectra agree well with those obtained from the band structure theory.

  6. Quantum electrodynamics near a photonic band-gap

    NASA Astrophysics Data System (ADS)

    Liu, Yanbing; Houck, Andrew

    Quantum electrodynamics predicts the localization of light around an atom in photonic band-gap (PBG) medium or photonic crystal. Here we report the first experimental realization of the strong coupling between a single artificial atom and an one dimensional PBG medium using superconducting circuits. In the photonic transport measurement, we observe an anomalous Lamb shift and a large band-edge avoided crossing when the artificial atom frequency is tuned across the band-edge. The persistent peak within the band-gap indicates the single photon bound state. Furthermore, we study the resonance fluorescence of this bound state, again demonstrating the breakdown of the Born-Markov approximation near the band-edge. This novel architecture can be directly generalized to study many-body quantum electrodynamics and to construct more complicated spin chain models.

  7. Toward broad-band x-ray detected ferromagnetic resonance in longitudinal geometry

    SciTech Connect

    Ollefs, K.; Meckenstock, R.; Spoddig, D.; Römer, F. M.; Hassel, Ch.; Schöppner, Ch.; Farle, M.; Ney, V.; Ney, A.

    2015-06-14

    An ultrahigh-vacuum-compatible setup for broad-band X-ray detected ferromagnetic resonance (XFMR) in longitudinal geometry is introduced which relies on a low-power, continuous-wave excitation of the ferromagnetic sample. A simultaneous detection of the conventional ferromagnetic resonance via measuring the reflected microwave power and the XFMR signal of the X-ray absorption is possible. First experiments on the Fe and Co L{sub 3}-edges of a permalloy film covered with Co nanostripes as well as the Fe and Ni K-edges of a permalloy film are presented and discussed. Two different XFMR signals are found, one of which is independent of the photon energy and therefore does not provide element-selective information. The other much weaker signal is element-selective, and the dynamic magnetic properties could be detected for Fe and Co separately. The dependence of the latter XFMR signal on the photon helicity of the synchrotron light is found to be distinct from the usual x-ray magnetic circular dichroism effect.

  8. Designer disordered materials with large, complete photonic band gaps

    PubMed Central

    Florescu, Marian; Torquato, Salvatore; Steinhardt, Paul J.

    2009-01-01

    We present designs of 2D, isotropic, disordered, photonic materials of arbitrary size with complete band gaps blocking all directions and polarizations. The designs with the largest band gaps are obtained by a constrained optimization method that starts from a hyperuniform disordered point pattern, an array of points whose number variance within a spherical sampling window grows more slowly than the volume. We argue that hyperuniformity, combined with uniform local topology and short-range geometric order, can explain how complete photonic band gaps are possible without long-range translational order. We note the ramifications for electronic and phononic band gaps in disordered materials. PMID:19918087

  9. Quantum information processing with narrow band two-photon state

    NASA Astrophysics Data System (ADS)

    Lu, Yajun

    Application of quantum sources in communication and information processing are believed to bring a new revolution to the on-going information age. The generation of applicable quantum sources such as single photon state and two-photon state, appears to be one of the most difficult in experimental quantum optics. Spontaneous Parametric Down-Conversion (PDC) is known to generate two-photon state, but bandwidth problem makes it less applicable in quantum information processing. The aim of this work is to generate a narrow band two-photon state and apply it to quantum information processing. We start by developing a cavity enhanced PDC device to narrow the bandwidth of the two-photon state. Direct measurement of the bandwidth of the generated state has been made and the quantum theory of such a device has been investigated. An application of this narrow band two-photon state is to generate anti-bunched photons for quantum cryptography, based on the quantum interference between the two-photon state and a coherent state. The feasibility of this scheme for pulsed pump is also investigated. When applying the concept of mode locking in lasers to a two-photon state, we have mode-locked two-photon state which exhibits a comb-like correlation function and may be used for engineering of quantum states in time domain. Other applications such as demonstration of single photon nonlocality, nonlinear sign gate in quantum computation, and direct measurement of quantum beating, will also be addressed.

  10. Broad band spectral energy distribution studies of Fermi bright blazars

    NASA Astrophysics Data System (ADS)

    Monte, C.; Giommi, P.; Cavazzuti, E.; Gasparrini, D.; Rainò, S.; Fuhrmann, L.; Angelakis, E.; Villata, M.; Raiteri, C. M.; Perri, M.; Richards, J.

    2011-02-01

    The Fermi Gamma-ray Space Telescope was successfully launched on June 11, 2008 and has already opened a new era for gamma-ray astronomy. The Large Area Telescope (LAT), the main instrument on board Fermi, presents a significant improvement in sensitivity over its predecessor EGRET, due to its large field of view and effective area, combined with its excellent timing capabilities. The preliminary results of the Spectral Energy Distribution Analysis performed on a sample of bright blazars are presented. For this study, the data from the first three months of data collection of Fermi have been used. The analysis is extended down to radio, mm, near-IR, optical, UV and X-ray bands and up to TeV energies based on unprecedented sample of simultaneous multi-wavelength observations by GASP-WEBT.

  11. Parallel Processing of Broad-Band PPM Signals

    NASA Technical Reports Server (NTRS)

    Gray, Andrew; Kang, Edward; Lay, Norman; Vilnrotter, Victor; Srinivasan, Meera; Lee, Clement

    2010-01-01

    A parallel-processing algorithm and a hardware architecture to implement the algorithm have been devised for timeslot synchronization in the reception of pulse-position-modulated (PPM) optical or radio signals. As in the cases of some prior algorithms and architectures for parallel, discrete-time, digital processing of signals other than PPM, an incoming broadband signal is divided into multiple parallel narrower-band signals by means of sub-sampling and filtering. The number of parallel streams is chosen so that the frequency content of the narrower-band signals is low enough to enable processing by relatively-low speed complementary metal oxide semiconductor (CMOS) electronic circuitry. The algorithm and architecture are intended to satisfy requirements for time-varying time-slot synchronization and post-detection filtering, with correction of timing errors independent of estimation of timing errors. They are also intended to afford flexibility for dynamic reconfiguration and upgrading. The architecture is implemented in a reconfigurable CMOS processor in the form of a field-programmable gate array. The algorithm and its hardware implementation incorporate three separate time-varying filter banks for three distinct functions: correction of sub-sample timing errors, post-detection filtering, and post-detection estimation of timing errors. The design of the filter bank for correction of timing errors, the method of estimating timing errors, and the design of a feedback-loop filter are governed by a host of parameters, the most critical one, with regard to processing very broadband signals with CMOS hardware, being the number of parallel streams (equivalently, the rate-reduction parameter).

  12. Very-high-energy blazars: A broad(band) perspective

    NASA Astrophysics Data System (ADS)

    Furniss, Amy Kathryn

    emitted spectra, allowing insight into the acceleration mechanisms at work within the blazar jets and the propagation of gamma-ray photons through intergalactic space.

  13. Bimetallic Nanoshells for Metal - Enhanced Fluorescence with Broad Band Fluorophores.

    PubMed

    Zhang, Jian; Fu, Yi; Mahdavi, Farhad

    2012-11-15

    In this article, we reported the near-field interactions between the Ru(bpy)(3) (2+) complexes and plasmon resonances from the bimetallic nanoshells. The metallic nanoshells were fabricated on 20 nm silica spheres as cores by depositing 10 nm monometallic or bimetallic shells. There were approx. 15 Ru(bpy)(3) (2+) complexes in the silica core. The metal shells were constituted of silver or/and gold. The bimetallic shells could be generated in homogeneous or heterogeneous geometries. The homogeneous bimetallic shells contained 10 nm silver-gold alloys. The heterogeneous bimetallic shells contained successive 5 nm gold and 5 nm silver shells, or alternatively, 5 nm silver and 5 nm gold shells. Optical properties of metal nanoshells were studied on both the ensemble spectra and single nanoparticle imaging measurements. The heterogeneous bimetallic shells were found to have a large scale of metal-enhanced emission relative to the monometallic or homogeneous bimetallic shells. It is because the heterogeneous bimetallic shells may display split dual plasmon resonances which can interact with the excitation and emission bands of the Ru(bpy)(3) (2+) complexes in the silica cores leading to more efficient near-field interactions. The prediction can be demonstrated by the lifetimes. Therefore, it is suggested that both the compositions and geometries of the metal shells can influence the interactions with the fluorophores in the cores. This observation also offers us an opportunity for developing plasmon-based fluorescence metal nanoparticles as novel nanoparticle imaging agents which have high performances in fluorescence cell or tissue imaging. PMID:23230456

  14. Large Format Narrow-Band, Multi-Band, and Broad-Band LWIR QWIP Focal Planes for Space and Earth Science Applications

    NASA Technical Reports Server (NTRS)

    Gunapala, S. D.; Bandara, S. V.

    2004-01-01

    A 640x512 pixel, long-wavelength cutoff, narrow-band (delta(lambda)/approx. 10%) quantum well infrared photodetector (QWIP) focal plane array (FPA), a four-band QWIP FPA in the 4-16 m spectral region, and a broad-band (delta(lambda)/approx. 42%) QWIP FPA having 15.4 m cutoff have been demonstrated.

  15. Replication technology for photonic band gap applications

    NASA Astrophysics Data System (ADS)

    Grigaliunas, V.; Kopustinskas, V.; Meskinis, S.; Margelevicius, M.; Mikulskas, I.; Tomasiunas, R.

    2001-06-01

    Replication technology was applied for photonic structure fabrication in silicon substrate. It was revealed, that thin thermoplastic polymer layers on silicon substrates may be patterned by hot embossing technique for dry etching masking. Ni mold used for plain hot embossing into polymer layers was fabricated by Ni electrochemical deposition on the reference silicon surface structure, which was obtained by direct electron beam (EB) writing and SF 6/N 2 reactive ion etching (RIE) technique. It is shown that the shape of replicated photonic structures is determined by RIE parameters.

  16. Recent Results from Broad-Band Intensity Mapping Measurements of Cosmic Large Scale Structure

    NASA Astrophysics Data System (ADS)

    Zemcov, Michael B.; CIBER, Herschel-SPIRE

    2016-01-01

    Intensity mapping integrates the total emission in a given spectral band over the universe's history. Tomographic measurements of cosmic structure can be performed using specific line tracers observed in narrow bands, but a wealth of information is also available from broad-band observations performed by instruments capable of capturing high-fidelity, wide-angle images of extragalactic emission. Sensitive to the continuum emission from faint and diffuse sources, these broad-band measurements provide a view on cosmic structure traced by components not readily detected in point source surveys. After accounting for measurement effects and astrophysical foregrounds, the angular power spectra of such data can be compared to predictions from models to yield powerful insights into the history of cosmic structure formation. This talk will highlight some recent measurements of large scale structure performed using broad-band intensity mapping methods that have given new insights on faint, distant, and diffuse components in the extragalactic background light.

  17. Effect of disorder on photonic band gaps

    NASA Astrophysics Data System (ADS)

    Sigalas, M. M.; Soukoulis, C. M.; Chan, C. T.; Biswas, R.; Ho, K. M.

    1999-05-01

    We study the transmission of electromagnetic waves propagating in three-dimensional disordered photonic crystals that are periodic on the average with a diamond symmetry. The transmission has been calculated using the transfer matrix method. We study two different geometries for the scatterers: spheres and rods connecting nearest neighbors. We find that the gaps of the periodic structure survive to a higher amount of disorder in the rods' case than in the spheres' case. We argue that this is due to the connectivity of the rod structure that exists for any amount of disorder.

  18. Photonic band-edge-induced enhancement in absorption and emission

    NASA Astrophysics Data System (ADS)

    Ummer, Karikkuzhi Variyath; Vijaya, Ramarao

    2015-01-01

    An enhancement in photonic band-edge-induced absorption and emission from rhodamine-B dye doped polystyrene pseudo gap photonic crystals is studied. The band-edge-induced enhancement in absorption is achieved by selecting the incident angle of the excitation beam so that the absorption spectrum of the emitter overlaps the photonic band edge. The band-edge-induced enhancement in emission, on the other hand, is possible with and without an enhancement in band-edge-induced absorption, depending on the collection angle of emission. Through a simple set of measurements with suitably chosen angles for excitation and emission, we achieve a maximum enhancement of 70% in emission intensity with band-edge-induced effects over and above the intrinsic emission in the case of self-assembled opals. This is a comprehensive effort to interpret tunable lasing in opals as well as to predict the wavelength of lasing arising as a result of band-edge-induced distributed feedback effects.

  19. On the affinities of lambda 5778 and other broad diffuse interstellar bands

    NASA Technical Reports Server (NTRS)

    Mcintosh, Alan; Webster, Adrian

    1994-01-01

    The authors examined the broad band 5778 A because of the quantity and quality of data that exists in literature. To investigate the affinity of that band with the bands of Family 1, the ratio W(sub lambda)(4430)/W(sub lambda)(5797) was formed. If the two band belong to the same family then the ratio should be a constant from star to star and it should not be possible to find an independent variable with which the ratio is correlated. If, however, a variable is found which does produce a statistically significant correlation with the ratio of equivalent widths then the bands cannot be in the same family. To test the affinity of the band at 5778 A with the other families the procedure was repeated using the bands at 5780 and 5787 A as being representative of Families 2 and 3 respectively. The measurement results of this test are shown using 21 stars taken from Herbig. Statistically significant correlations resulted when the band at 5778 A was tested against the bands of Families 1 and 2 but there was no correlation with Family 3. It is concluded that lambda 5778 is unlikely a member of Family 1 and so all the broad bands do not have their origin in a single carrier. Also, lambda 5778 does not appear to be a member of Family 2 either, but may be a member of Family 3. It appears that either a single carrier can be the origin of both broad and narrow bands or that the bands are produced by different carriers which exist in similar interstellar habitats. This latter possibility would require the introduction of a fourth family of bands.

  20. Fully confined photonic band gap and guided modes in a two-dimensional photonic crystal slab

    SciTech Connect

    Chow, K.C.; Lin, S.Y.; Johnson, S.G.; Villeneuve, P.R.; Joannopoulos, J.D.

    1999-12-15

    A new two-dimensional photonic crystal (2D PC) slab structure was created with a full three-dimensional light confinement. Guided modes with broad bandwidth and high transmission within the band gap are also observed. As an optical analog to electronic crystals, PC promises a revolution in the photonic world similar to the electronic revolution created by the electronic band gap engineering in semiconductor. 2D PC has an advantage of being easier to fabricate at optical wavelength ({lambda}) comparing with 3D PC. However, the light leakage in the vertical direction has been the main problem for using 2D PC in opto-electronic application. In this study, the authors solve this problem by combining traditional 2D PC with strong vertical index guiding between the waveguide layer (GaAs) and the cladding layer (Al{sub x}O{sub y}). A set of triangular lattice holes 2D PC's were fabricated with lattice constant a=460nm, hole diameter (d=0.6a) and waveguide layer thickness (t = 0.5a). Those parameters were chosen to maximize the TE photonic band gap (PBG) around {lambda} = 1.55{micro}m. The depth of etched holes is {approximately}0.6{micro}m and the 2{micro}m thick Al{sub x}O{sub y} cladding layer is obtained by thermal oxidation of Al{sub 0.9}Ga{sub 0.1}As. PC waveguides were also created by introducing line defects along {Gamma}K direction. The authors perform transmission measurement by coupling light to PC with 3{micro}m wide waveguides which extends {approximately}0.6mm on both sides of PC. An aspheric lens with NA = 0.4 is used to focus the collimated light from tunable diode laser into the input waveguide. Another identical lens is used to collect the transmitted light and focus to an infrared (IR) camera and a calibrated photo-detector with a beamsplitter. The Gaussian waveguide mode indicates that the signal detected by the photodetector comes only from the light interacting with PC and propagating along the waveguide. The absolute transmittance is obtained by

  1. Special purpose modes in photonic band gap fibers

    SciTech Connect

    Spencer, James; Noble, Robert; Campbell, Sara

    2013-04-02

    Photonic band gap fibers are described having one or more defects suitable for the acceleration of electrons or other charged particles. Methods and devices are described for exciting special purpose modes in the defects including laser coupling schemes as well as various fiber designs and components for facilitating excitation of desired modes. Results are also presented showing effects on modes due to modes in other defects within the fiber and due to the proximity of defects to the fiber edge. Techniques and devices are described for controlling electrons within the defect(s). Various applications for electrons or other energetic charged particles produced by such photonic band gap fibers are also described.

  2. Random sized plasmonic nanoantennas on Silicon for low-cost broad-band near-infrared photodetection.

    PubMed

    Nazirzadeh, Mohammad Amin; Atar, Fatih Bilge; Turgut, Berk Berkan; Okyay, Ali Kemal

    2014-01-01

    In this work, we propose Silicon based broad-band near infrared Schottky barrier photodetectors. The devices operate beyond 1200 nm wavelength and exhibit photoresponsivity values as high as 3.5 mA/W with a low dark current density of about 50 pA/µm(2). We make use of Au nanoislands on Silicon surface formed by rapid thermal annealing of a thin Au layer. Surface plasmons are excited on Au nanoislands and this field localization results in efficient absorption of sub-bandgap photons. Absorbed photons excite the electrons of the metal to higher energy levels (hot electron generation) and the collection of these hot electrons to the semiconductor results in photocurrent (internal photoemission). Simple and scalable fabrication makes these devices suitable for ultra-low-cost NIR detection applications. PMID:25407509

  3. Estimating carbon dioxide fluxes from temperate mountain grasslands using broad-band vegetation indices

    PubMed Central

    Wohlfahrt, G.; Pilloni, S.; Hörtnagl, L.; Hammerle, A.

    2013-01-01

    The broad-band normalised difference vegetation index (NDVI) and the simple ratio (SR) were calculated from measurements of reflectance of photosynthetically active and short-wave radiation at two temperate mountain grasslands in Austria and related to the net ecosystem CO2 exchange (NEE) measured concurrently by means of the eddy covariance method. There was no significant statistical difference between the relationships of midday mean NEE with narrow- and broad-band NDVI and SR, measured during and calculated for that same time window, respectively. The skill of broad-band NDVI and SR in predicting CO2 fluxes was higher for metrics dominated by gross photosynthesis and lowest for ecosystem respiration, with NEE in between. A method based on a simple light response model whose parameters were parameterised based on broad-band NDVI allowed to improve predictions of daily NEE and is suggested to hold promise for filling gaps in the NEE time series. Relationships of CO2 flux metrics with broad-band NDVI and SR however generally differed between the two studied grassland sites indicting an influence of additional factors not yet accounted for. PMID:24339832

  4. High-Power Fiber Lasers Using Photonic Band Gap Materials

    NASA Technical Reports Server (NTRS)

    DiDomenico, Leo; Dowling, Jonathan

    2005-01-01

    High-power fiber lasers (HPFLs) would be made from photonic band gap (PBG) materials, according to the proposal. Such lasers would be scalable in the sense that a large number of fiber lasers could be arranged in an array or bundle and then operated in phase-locked condition to generate a superposition and highly directed high-power laser beam. It has been estimated that an average power level as high as 1,000 W per fiber could be achieved in such an array. Examples of potential applications for the proposed single-fiber lasers include welding and laser surgery. Additionally, the bundled fibers have applications in beaming power through free space for autonomous vehicles, laser weapons, free-space communications, and inducing photochemical reactions in large-scale industrial processes. The proposal has been inspired in part by recent improvements in the capabilities of single-mode fiber amplifiers and lasers to produce continuous high-power radiation. In particular, it has been found that the average output power of a single strand of a fiber laser can be increased by suitably changing the doping profile of active ions in its gain medium to optimize the spatial overlap of the electromagnetic field with the distribution of active ions. Such optimization minimizes pump power losses and increases the gain in the fiber laser system. The proposal would expand the basic concept of this type of optimization to incorporate exploitation of the properties (including, in some cases, nonlinearities) of PBG materials to obtain power levels and efficiencies higher than are now possible. Another element of the proposal is to enable pumping by concentrated sunlight. Somewhat more specifically, the proposal calls for exploitation of the properties of PBG materials to overcome a number of stubborn adverse phenomena that have impeded prior efforts to perfect HPFLs. The most relevant of those phenomena is amplified spontaneous emission (ASE), which causes saturation of gain and power

  5. Quantum interference of independently generated telecom-band single photons

    SciTech Connect

    Patel, Monika; Altepeter, Joseph B.; Huang, Yu-Ping; Oza, Neal N.; Kumar, Prem

    2014-12-04

    We report on high-visibility quantum interference of independently generated telecom O-band (1310 nm) single photons using standard single-mode fibers. The experimental data are shown to agree well with the results of simulations using a comprehensive quantum multimode theory without the need for any fitting parameter.

  6. Photonic Band Gap structures: A new approach to accelerator cavities

    SciTech Connect

    Kroll, N. |; Smith, D.R.; Schultz, S.

    1992-12-31

    We introduce a new accelerator cavity design based on Photonic Band Gap (PGB) structures. The PGB cavity consists of a two-dimensional periodic array of high dielectric, low loss cylinders with a single removal defect, bounded on top and bottom by conducting sheets. We present the results of both numerical simulations and experimental measurements on the PGB cavity.

  7. W-band active imaging by photonics-based synthesizer

    NASA Astrophysics Data System (ADS)

    Kanno, Atsushi; Sekine, Norihiko; Kasamatsu, Akifumi; Yamamoto, Naokatsu

    2016-05-01

    We demonstrate a nondestructive electromagnetic-wave imaging system with a photonics-based W-band synthe- sizer, traveling-wave tube amplifier and focal-plane transistor array in real time manner. High-power amplifier with multi-watts output will enhance the quality of obtained images under transmission and reflection imaging configurations.

  8. Broad-band opsin for effective stimulation of cells by white light

    NASA Astrophysics Data System (ADS)

    Batabyal, Subrata; Cervenka, Gregory; Kim, Young-Tae; Mohanty, Samarendra

    2015-03-01

    Currently, use of optogenetic sensitization of retinal cells combined with activation/inhibition has potential as alternative to retinal implants that would have required electrodes inside every single neuron for high visual resolution. However, clinical translation of optogenetic activation for restoration of vision suffers from the drawback that narrow spectral sensitivity of opsin requires active stimulation by blue laser or LED having intensity much higher than ambient light. In order to allow ambient-light based stimulation paradigm, here we report development of broad-band opsin that has broad spectral excitability in the entire visible spectrum. The cells sensitized with the broad-band opsin showed order of magnitude higher excitability with white light as compared to that using only the narrow-band light components. The use of broad-band opsin construct will allow higher sensitivity of the opsin-sensitized neurons in degenerated retina to ambient white light, and therefore, significantly lower activation-threshold in contrast to conventional approach of intense, narrow-band light based active-stimulation.

  9. A study on broad-banding the tuning ratio for varactor-tuned oscillators

    NASA Astrophysics Data System (ADS)

    Sinha, M. P.

    1992-12-01

    A bipolar-based varactor-tuned oscillator (VTO) is analyzed which is based on two varactors in the tuning circuit with a back-to-back configuration and a varactor in the feedback circuit. It is shown that two varactors in the tuning circuit make it possible to broad-band the tuning ratio by using a varactor in the feedback circuit.

  10. Analysis of tunable photonic band structure in an extrinsic plasma photonic crystal

    NASA Astrophysics Data System (ADS)

    King, Tzu-Chyang; Yang, Chih-Chiang; Hsieh, Pei-Hung; Chang, Tsung-Wen; Wu, Chien-Jang

    2015-03-01

    In this work, we theoretically investigate the tunable photonic band structure (PBS) for an extrinsic plasma photonic crystal (PPC). The extrinsic PPC is made of a bulk cold plasma layer which is influenced by an externally periodic static magnetic field. The PBS can be tuned by the variation of the magnitude of externally applied magnetic field. In addition, we also show that the PBS can be changed as a function of the electron density as well as the thickness variation.

  11. Broad working bandwidth and "endlessly" single-mode guidance within hybrid silicon photonics.

    PubMed

    Bougot-Robin, K; Hugonin, J-P; Besbes, M; Benisty, H

    2015-08-01

    The successes of nonlinear photonics and hybrid silicon photonics with a growing variety of functional materials entail ever-enlarging bandwidths. It is best exemplified by parametric comb frequency generation. Such operation challenges the dielectric channel waveguide as the basis for guidance, because of the adverse advent of higher order modes at short wavelengths. Surprisingly, the popular mechanism of endlessly single-mode guidance [Opt. Lett.22, 961 (1997).] operating in photonic crystal fibers has not been transposed within silicon photonics yet. We outline here the strategy and potential of this approach within planar and hybrid silicon photonics, whereby in-plane and vertical confinement are shown to be amenable to near-single-mode behavior in the typical silicon band, i.e., λ=1.1  μm to ∼5  μm. PMID:26258345

  12. Optical properties of silver nanocomposites and photonic band gap - Pressure dependence

    NASA Astrophysics Data System (ADS)

    Ramanujam, N. R.; Wilson, K. S. Joseph

    2016-06-01

    We theoretically investigate the effect of photonic band gaps in one dimensional photonic crystals based on nanocomposite of silver nanoparticles. The dielectric permittivity is computed based on the pressure dependence of plasma frequency and damping constant of silver nanoparticle. It leads to the tuning of photonic band gap. We have also investigated the change in photonic band gap due to the influence of filling factor and the size of the nanoparticles. Our results provide a guideline for designing potential photonic devices.

  13. Photonic Band Gap resonators for high energy accelerators

    SciTech Connect

    Schultz, S.; Smith, D.R.; Kroll, N. |

    1993-12-31

    We have proposed that a new type of microwave resonator, based on Photonic Band Gap (PBG) structures, may be particularly useful for high energy accelerators. We provide an explanation of the PBG concept and present data which illustrate some of the special properties associated with such structures. Further evaluation of the utility of PBG resonators requires laboratory testing of model structures at cryogenic temperatures, and at high fields. We provide a brief discussion of our test program, which is currently in progress.

  14. Two-pattern compound photonic crystals with a large complete photonic band gap

    SciTech Connect

    Jia Lin; Thomas, Edwin L.

    2011-09-15

    We present a set of two-dimensional aperiodic structures with a large complete photonic band gap (PBG), which are named two-pattern photonic crystals. By superposing two substructures without regard to registration, we designed six new aperiodic PBG structures having a complete PBG larger than 15% for {epsilon}{sub 2}/{epsilon}{sub 1} = 11.4. The rod-honeycomb two-pattern photonic crystal provides the largest complete PBG to date. An aperiodic structure becomes the champion structure with the largest PBG. Surprisingly, the TM and TE gaps of a two-pattern photonic crystal are much less interdependent than the PBGs of conventional photonic crystals proposed before, affording interesting capabilities for us to tune the TM and TE PBGs separately. By altering the respective substructures, optical devices for different polarizations (TE, TM, or both) can readily be designed.

  15. Photonic Crystal and Photonic Band-Gap Structures for Light Extraction and Emission Control

    NASA Astrophysics Data System (ADS)

    de La Rue, Richard M.

    Research into photonic crystal (PhC) and photonic band-gap (PBG) structures has been motivated, from the start, by their possible use in controlling, modifying and enhancing the light emission process from high refractive index solid materials. This chapter considers the possible role of such structures when incorporated into semiconductor diode based light-emitting devices. Both light-emitting diodes (LEDs) and lasers will be considered. In order to provide a proper framework for discussion and analysis, space is devoted to the historical development of III-V semiconductor based LEDs — and to competing alternative approaches that have been demonstrated for enhanced light extraction. The possible advantages of photonic quasi-crystal (PQC) structures over regularly periodic photon crystal structures for advanced LED designs are also considered. Photonic crystal structures potentially provide major enhancements in the performance of laser diodes (LDs) — and progress towards this performance enhancement will be reviewed.

  16. CAN H{sub 2}CCC BE THE CARRIER OF BROAD DIFFUSE BANDS?

    SciTech Connect

    Krelowski, J.; Galazutdinov, G.; Kolos, R. E-mail: runizag@gmail.com

    2011-07-10

    The recent assignment of two broad diffuse interstellar bands (DIBs) near 4882 and 5450 A to the propadienylidene (l-C{sub 3}H{sub 2}) molecule is examined using a statistically meaningful sample of targets. Our spectra clearly show that the strength ratio of two broad DIBs is strongly variable, contrary to what should be observed if both features are due to l-C{sub 3}H{sub 2}, since the proposed transitions are lifetime broadened and start from the same level. Moreover, even in directions where the 4882 DIB and 5450 DIB are strong, the third expected l-C{sub 3}H{sub 2} band, in the 5165-5185 A region, is absent. Another puzzling characteristic of l-C{sub 3}H{sub 2} as the proposed carrier of both broad diffuse bands is its column density of several 10{sup 14} cm{sup -2}, inferred from the equivalent width of the 5450 DIB. This value is one order of magnitude higher than N(CH) toward the same objects and two to three orders of magnitude higher than N(H{sub 2}CCC), measured at radio frequencies in absorption, for comparable samples of the diffuse medium. We conclude that the proposed identification of broad DIBs is unjustified.

  17. Nonorthogonal FDTD simulations for photonic band structures, states density, and transmission/reflection of photonic crystals

    NASA Astrophysics Data System (ADS)

    Le, Zichun; Yang, Yang; Quan, Bisheng; Wang, Weibiao; Wang, Xiaoxiao; Chi, Yongjiang; Ma, Lingfang

    2005-01-01

    Photonic crystals have been widely studied in the fields of physics, material science and optical information technology. In general, the standard rectangular finite difference time domain (FDTD) method is used to predict the performances of photonic crystals. It is however very time consuming and inefficient. The current authors developed a software called GCFE, which is based on a non-orthogonal FDTD method. The software can be used to predict the photonic band structures, photonic states density and transmission and/or reflection coefficients for one-dimensional to three-dimensional photonic crystals. In the present paper, the derivations of the discrete Maxwell"s equations in time-domain and space-domain and the derivation of the discrete transfer matrix in real-space domain are briefly described firstly. In addition, the design idea and the functions of GCFE version 2.0.00 are introduced. Moreover, the band structures, transmission and reflection coefficients and photonic states density for the photonic crystal with cube lattice are calculated by our GCFE software, and numerical application results are also shown.

  18. Hollow-Core Photonic Band Gap Fibers for Particle Acceleration

    SciTech Connect

    Noble, Robert J.; Spencer, James E.; Kuhlmey, Boris T.; /Sydney U.

    2011-08-19

    Photonic band gap (PBG) dielectric fibers with hollow cores are being studied both theoretically and experimentally for use as laser driven accelerator structures. The hollow core functions as both a longitudinal waveguide for the transverse-magnetic (TM) accelerating fields and a channel for the charged particles. The dielectric surrounding the core is permeated by a periodic array of smaller holes to confine the mode, forming a photonic crystal fiber in which modes exist in frequency pass-bands, separated by band gaps. The hollow core acts as a defect which breaks the crystal symmetry, and so-called defect, or trapped modes having frequencies in the band gap will only propagate near the defect. We describe the design of 2-D hollow-core PBG fibers to support TM defect modes with high longitudinal fields and high characteristic impedance. Using as-built dimensions of industrially-made fibers, we perform a simulation analysis of the first prototype PBG fibers specifically designed to support speed-of-light TM modes.

  19. Band gaps of two-dimensional antiferromagnetic photonic crystal

    NASA Astrophysics Data System (ADS)

    Song, Yu-Ling; Ta, Jin-Xing; Wang, Xuan-Zhang

    2011-07-01

    In an external magnetic field, the band structure of a two-dimensional photonic crystal (PC) composed of parallel antiferromagnetic cylinders in a background dielectric is investigated with a Green's function method. The cylinders with two resonant frequencies form a square lattice and are characterized by a magnetic permeability tensor. In our numerical calculation, we find that this method allows fast convergence and is available in both the resonant and non-resonant frequency ranges. In the non-resonant range, the PC is similar in band structure to an ordinary dielectric PC. Two electromagnetic band gaps, however, appear in the resonant frequency region, and their frequency positions and widths are governed by the external field. The dependence of the electromagnetic gaps on the cylinder radius also is discussed.

  20. Photonic band gaps in one-dimensional magnetized plasma photonic crystals with arbitrary magnetic declination

    SciTech Connect

    Zhang Haifeng; Liu Shaobin; Kong Xiangkun

    2012-12-15

    In this paper, the properties of photonic band gaps and dispersion relations of one-dimensional magnetized plasma photonic crystals composed of dielectric and magnetized plasma layers with arbitrary magnetic declination are theoretically investigated for TM polarized wave based on transfer matrix method. As TM wave propagates in one-dimensional magnetized plasma photonic crystals, the electromagnetic wave can be divided into two modes due to the influence of Lorentz force. The equations for effective dielectric functions of such two modes are theoretically deduced, and the transfer matrix equation and dispersion relations for TM wave are calculated. The influences of relative dielectric constant, plasma collision frequency, incidence angle, plasma filling factor, the angle between external magnetic field and +z axis, external magnetic field and plasma frequency on transmission, and dispersion relation are investigated, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that plasma collision frequency cannot change the locations of photonic band gaps for both modes, and also does not affect the reflection and transmission magnitudes. The characteristics of photonic band gaps for both modes can be obviously tuned by relative dielectric constant, incidence angle, plasma filling factor, the angle between external magnetic field and +z axis, external magnetic field and plasma frequency, respectively. These results would provide theoretical instructions for designing filters, microcavities, and fibers, etc.

  1. Unfolding the band structure of non-crystalline photonic band gap materials

    NASA Astrophysics Data System (ADS)

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-08-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain.

  2. Unfolding the band structure of non-crystalline photonic band gap materials.

    PubMed

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-01-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434

  3. Unfolding the band structure of non-crystalline photonic band gap materials

    PubMed Central

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-01-01

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain. PMID:26289434

  4. Ray-based geoacoustic inversion for high frequency broad band data

    NASA Astrophysics Data System (ADS)

    Siderius, Martin; Hursky, Paul; Porter, Michael

    2003-04-01

    One of the difficulties in making reliable acoustic propagation predictions in shallow water is the lack of good information about the seabed type. In recent years, matched field processing- (MFP-) based geoacoustic inversion has been shown as a practical technique for estimating properties of the seabed. The MFP inversion method compares measured acoustic fields to those generated using an acoustic propagation model. Often, thousands of forward model calculations are required to find a set of seabed parameters that correlate well with the measured data. The large number of forward model calculations is computationally demanding and this is made worse when matching at higher frequencies or over broad band data. Ray-based propagation modeling relieves some of the computational burden since the calculation time is fairly insensitive to frequency and is inherently broad band. Further, the ray arrival amplitudes and delays are well suited for interpolation and this allows the seabed parameter search space to be explored using just a few ray trace calculations. The broad band nature of the modeled data provides flexibility in choosing correlation functions and this allows for more robust inversions. In this presentation, techniques using ray-based propagation modeling will be applied to the geoacoustic inversion problem.

  5. Modeling of Photonic Band Gap Crystals and Applications

    SciTech Connect

    Ihab Fathy El-Kady

    2002-08-27

    In this work, the authors have undertaken a theoretical approach to the complex problem of modeling the flow of electromagnetic waves in photonic crystals. The focus is to address the feasibility of using the exciting phenomena of photonic gaps (PBG) in actual applications. The authors start by providing analytical derivations of the computational electromagnetic methods used in their work. They also present a detailed explanation of the physics underlying each approach, as well as a comparative study of the strengths and weaknesses of each method. The Plane Wave expansion, Transfer Matrix, and Finite Difference time Domain Methods are addressed. They also introduce a new theoretical approach, the Modal Expansion Method. They then shift the attention to actual applications. They begin with a discussion of 2D photonic crystal wave guides. The structure addressed consists of a 2D hexagonal structure of air cylinders in a layered dielectric background. Comparison with the performance of a conventional guide is made, as well as suggestions for enhancing it. The studies provide an upper theoretical limit on the performance of such guides, as they assumed no crystal imperfections and non-absorbing media. Next, they study 3D metallic PBG materials at near infrared and optical wavelengths. The main objective is to study the importance of absorption in the metal and the suitability of observing photonic band gaps in such structures. They study simple cubic structures where the metallic scatters are either cubes or interconnected metallic rods. Several metals are studied (aluminum, gold, copper, and silver). The effect of topology is addressed and isolated metallic cubes are found to be less lossy than the connected rod structures. The results reveal that the best performance is obtained by choosing metals with a large negative real part of the dielectric function, together with a relatively small imaginary part. Finally, they point out a new direction in photonic crystal

  6. Study of LEO-SAT microwave link for broad-band mobile satellite communication system

    NASA Technical Reports Server (NTRS)

    Fujise, Masayuki; Chujo, Wataru; Chiba, Isamu; Furuhama, Yoji; Kawabata, Kazuaki; Konishi, Yoshihiko

    1993-01-01

    In the field of mobile satellite communications, a system based on low-earth-orbit satellites (LEO-SAT's) such as the Iridium system has been proposed. The LEO-SAT system is able to offer mobile telecommunication services in high-latitude areas. Rain degradation, fading and shadowing are also expected to be decreased when the system is operated at a high elevation angle. Furthermore, the propagation delay generated in the LEO-SAT system is less pronounced than that in the geostationary orbit satellite (GEO-SAT) system and, in voice services, the effect of the delay is almost negligible. We proposed a concept of a broad-band mobile satellite communication system with LEO-SAT's and Optical ISL. In that system, a fixed L-band (1.6/1.5 GHz) multibeam is used to offer narrow band service to the mobile terminals in the entire area covered by a LEO-SAT and steerable Ka-band (30/20 GHz) spot beams are used for the wide band service. In this paper, we present results of a study of LEO-SAT microwave link between a satellite and a mobile terminal for a broad-band mobile satellite communication system. First, the results of link budget calculations are presented and the antennas mounted on satellites are shown. For a future mobile antenna technology, we also show digital beamforming (DBF) techniques. DBF, together with modulation and/or demodulation, is becoming a key technique for mobile antennas with advanced functions such as antenna pattern calibration, correction, and radio interference suppression. In this paper, efficient DBF techniques for transmitting and receiving are presented. Furthermore, an adaptive array antenna system suitable for this LEO-SAT is presented.

  7. Achieving omnidirectional photonic band gap in sputter deposited TiO2/SiO2 one dimensional photonic crystal

    NASA Astrophysics Data System (ADS)

    Jena, S.; Tokas, R. B.; Sarkar, P.; Haque, S. Maidul; Misal, J. S.; Rao, K. D.; Thakur, S.; Sahoo, N. K.

    2015-06-01

    The multilayer structure of TiO2/SiO2 (11 layers) as one dimensional photonic crystal (1D PC) has been designed and then fabricated by using asymmetric bipolar pulse DC magnetron sputtering technique for omnidirectional photonic band gap. The experimentally measured photonic band gap (PBG) in the visible region is well matched with the theoretically calculated band structure (ω vs. k) diagram. The experimentally measured omnidirectional reflection band of 44 nm over the incident angle range of 0°-70° is found almost matching within the theoretically calculated band.

  8. Phononic and photonic band gap structures: modelling and applications

    NASA Astrophysics Data System (ADS)

    Armenise, Mario N.; Campanella, Carlo E.; Ciminelli, Caterina; Dell'Olio, Francesco; Passaro, Vittorio M. N.

    2010-01-01

    Photonic crystals (PhCs) are artificial materials with a permittivity which is a periodic function of the position, with a period comparable to the wavelength of light. The most interesting characteristic of such materials is the presence of photonic band gaps (PBGs). PhCs have very interesting properties of light confinement and localization together with the strong reduction of the device size, orders of magnitude less than the conventional photonic devices, allowing a potential very high scale of integration. These structures possess unique characteristics enabling to operate as optical waveguides, high Q resonators, selective filters, lens or superprism. The ability to mould and guide light leads naturally to novel applications in several fields. Band gap formation in periodic structures also pertains to elastic wave propagation. Composite materials with elastic coefficients which are periodic functions of the position are named phononic crystals. They have properties similar to those of photonic crystals and corresponding applications too. By properly choosing the parameters one may obtain phononic crystals (PhnCs) with specific frequency gaps. An elastic wave, whose frequency lies within an absolute gap of a phononic crystal, will be completely reflected by it. This property allows realizing non-absorbing mirrors of elastic waves and vibration-free cavities which might be useful in high-precision mechanical systems operating in a given frequency range. Moreover, one can use elastic waves to study phenomena such as those associated with disorder, in more or less the same manner as with electromagnetic waves. The authors present in this paper an introductory survey of the basic concepts of these new technologies with particular emphasis on their main applications, together with a description of some modelling approaches.

  9. Ultra-broad band and dual-band highly efficient polarization conversion based on the three-layered chiral structure

    NASA Astrophysics Data System (ADS)

    Xu, Kai-kai; Xiao, Zhong-yin; Tang, Jing-yao; Liu, De-jun; Wang, Zi-hua

    2016-07-01

    In the paper, a novel three-layered chiral structure is proposed and investigated, which consists of a split-ring resonator sandwiched between two layers of sub-wavelength gratings. This designed structure can achieve simultaneously asymmetric transmission with an extremely broad bandwidth and high amplitude as well as multi-band 90° polarization rotator with very low dispersion. Numerical simulations adopted two kinds of softwares with different algorithms demonstrate that asymmetric parameter can reach a maximum of 0.99 and over than 0.8 from 4.6 to 16.8 GHz, which exhibit magnitude and bandwidth improvement over previous chiral metamaterials in microwave bands (S, C, X and Ku bands). Specifically, the reason of high amplitude is analyzed in detail based on the Fabry-perot like resonance. Subsequently, the highly efficient polarization conversion with very low dispersion between two orthogonal linearly polarized waves is also analyzed by the optical activity and ellipticity. Finally, the electric fields are also investigated and further demonstrate the correctness of the simulated and calculated results.

  10. Relationship of Aerial Broad Band Reflectance to Meloidogyne incognita Density in Cotton

    PubMed Central

    Wheeler, T. A.; Kaufman, H. W.

    2003-01-01

    Aerial images were obtained on 22 July 1999 and 4 August 2000 from five cotton sites infested with Meloidogyne incognita. Images contained three broad bands representing the green (500-600 nm), red (600-700 nm), and near-infrared (700-900 nm) spectrum. Soil samples were collected and assayed for nematodes in the fall at these sites. Sampling locations were identified from images, by locating the coordinates of a wide range of light intensity (measured as a digital number) for each single band, and combinations of bands. There was no single band or band combination in which reflectance consistently predicted M. incognita density. In all 10 site-year combinations, the minimum number of samples necessary to estimate M. incognita density within 25% of the population mean was greater when sampling by reflectance-based classes (3 to 4 per site) than sampling based on the entire site as one unit. Two sites were sampled at multiple times during the growing season. At these sites, there was no single time during the growing season optimal to take images for nematode sampling. Aerial infrared photography conducted during the growing season could not be used to accurately determine fall population densities of M. incognita. PMID:19265974

  11. Relationship of Aerial Broad Band Reflectance to Meloidogyne incognita Density in Cotton.

    PubMed

    Wheeler, T A; Kaufman, H W

    2003-03-01

    Aerial images were obtained on 22 July 1999 and 4 August 2000 from five cotton sites infested with Meloidogyne incognita. Images contained three broad bands representing the green (500-600 nm), red (600-700 nm), and near-infrared (700-900 nm) spectrum. Soil samples were collected and assayed for nematodes in the fall at these sites. Sampling locations were identified from images, by locating the coordinates of a wide range of light intensity (measured as a digital number) for each single band, and combinations of bands. There was no single band or band combination in which reflectance consistently predicted M. incognita density. In all 10 site-year combinations, the minimum number of samples necessary to estimate M. incognita density within 25% of the population mean was greater when sampling by reflectance-based classes (3 to 4 per site) than sampling based on the entire site as one unit. Two sites were sampled at multiple times during the growing season. At these sites, there was no single time during the growing season optimal to take images for nematode sampling. Aerial infrared photography conducted during the growing season could not be used to accurately determine fall population densities of M. incognita. PMID:19265974

  12. Nonlinear Bloch waves in metallic photonic band-gap filaments

    SciTech Connect

    Kaso, Artan; John, Sajeev

    2007-11-15

    We demonstrate the occurrence of nonlinear Bloch waves in metallic photonic crystals (PCs). These periodically structured filaments are characterized by an isolated optical pass band below an effective plasma gap. The pass band occurs in a frequency range where the metallic filament exhibits a negative, frequency-dependent dielectric function and absorption loss. The metallic losses are counterbalanced by gain in two models of inhomogeneously broadened nonlinear oscillators. In the first model, we consider close-packed quantum dots that fill the void regions of a two-dimensional (2D) metallic PC, and whose inhomogeneously broadened emission spectrum spans the original optical pass band of the bare filament. In the second model, we consider thin (10-50 nm) layers of inhomogeneously broadened two-level resonators, with large dipole oscillator strength, that cover the interior surfaces of 2D metallic (silver and tungsten) PCs. These may arise from localized surface plasmon resonances due to small metal particles or an otherwise rough metal surface. For simplicity, we treat electromagnetic modes with electric field perpendicular to the plane of metal periodicity. In both models, a pumping threshold of the resonators is found, above which periodic nonlinear solutions of Maxwell's equations with purely real frequency within the optical pass band emerge. These nonlinear Bloch waves exhibit a laserlike input pumping to output amplitude characteristic. For strong surface resonances, these nonlinear waves may play a role in light emission from a hot tungsten (suitably microstructured) filament.

  13. The composite broad band spectrum of Cir X-1 at the periastron: a peculiar Z-source

    NASA Astrophysics Data System (ADS)

    Iaria, R.; di Salvo, T.; Burderi, L.; La Barbera, N.; Robba, N. R.

    2001-09-01

    We report on the spectral analysis of the peculiar source Cir X-1 observed by the BeppoSAX satellite when the X-ray source was near the periastron. A flare lasting ~6×103s is present at the beginning of the observation. We produced broad band (0.1 - 100 keV) energy spectra during the flare and the persistent emission. At low energies the continuum is well fitted by a model consisting of Comptonization of soft photons, with a temperature of ~0.4 keV, by electrons at a temperature of ~1 keV. Out of the flare a power-law component, with photon index ~3, is dominant at energies higher than 10 keV. This component contributes to ~4% of the total luminosity. During the flare its addition is not statistically significant. Similar hard components have been recently observed in other Z-sources, sometimes related to the position of the source in the color-color diagram. An interesting possibility is that these components are due to the presence of jet emission.

  14. Photonic crystals composed of virtual pillars with magnetic walls: Photonic band gaps and double Dirac cones

    NASA Astrophysics Data System (ADS)

    Kim, Seong-Han; Kim, Soeun; Kee, Chul-Sik

    2016-08-01

    Photonic crystals composed of virtual pillars with magnetic walls are proposed. A virtual pillar with a magnetic wall can be created inside a parallel perfect electric conductor plate waveguide by introducing a circular perfect magnetic conductor patch in the upper perfect electric conductor plate of the waveguide. The virtual pillar mimics a perfect magnetic conductor pillar with a radius less than that of the circular patch because electromagnetic waves can slightly penetrate the wall. Furthermore, the photonic band structures of a triangular photonic crystal composed of virtual pillars for the transverse electromagnetic modes of the waveguide are investigated. They are very similar to those of a triangular photonic crystal composed of infinitely long perfect electric conductor cylinders for transverse magnetic modes. The similarity between the two different photonic crystals is well understood by the boundary conditions of perfect electric and magnetic conductor surfaces. A double Dirac cone at the center of the Brillouin zone is observed and thus the virtual pillar triangular photonic crystal can act a zero-refractive-index material at the Dirac point frequency.

  15. Broad-band near-field ground motion simulations in 3-dimensional scattering media

    NASA Astrophysics Data System (ADS)

    Imperatori, W.; Mai, P. M.

    2013-02-01

    The heterogeneous nature of Earth's crust is manifested in the scattering of propagating seismic waves. In recent years, different techniques have been developed to include such phenomenon in broad-band ground-motion calculations, either considering scattering as a semi-stochastic or purely stochastic process. In this study, we simulate broad-band (0-10 Hz) ground motions with a 3-D finite-difference wave propagation solver using several 3-D media characterized by von Karman correlation functions with different correlation lengths and standard deviation values. Our goal is to investigate scattering characteristics and its influence on the seismic wavefield at short and intermediate distances from the source in terms of ground motion parameters. We also examine scattering phenomena, related to the loss of radiation pattern and the directivity breakdown. We first simulate broad-band ground motions for a point-source characterized by a classic ω2 spectrum model. Fault finiteness is then introduced by means of a Haskell-type source model presenting both subshear and super-shear rupture speed. Results indicate that scattering plays an important role in ground motion even at short distances from the source, where source effects are thought to be dominating. In particular, peak ground motion parameters can be affected even at relatively low frequencies, implying that earthquake ground-motion simulations should include scattering also for peak ground velocity (PGV) calculations. At the same time, we find a gradual loss of the source signature in the 2-5 Hz frequency range, together with a distortion of the Mach cones in case of super-shear rupture. For more complex source models and truly heterogeneous Earth, these effects may occur even at lower frequencies. Our simulations suggests that von Karman correlation functions with correlation length between several hundred metres and few kilometres, Hurst exponent around 0.3 and standard deviation in the 5-10 per cent range

  16. Predicting spectral features in galaxy spectra from broad-band photometry

    NASA Astrophysics Data System (ADS)

    Abdalla, F. B.; Mateus, A.; Santos, W. A.; Sodrè, L., Jr.; Ferreras, I.; Lahav, O.

    2008-07-01

    We explore the prospects of predicting emission-line features present in galaxy spectra given broad-band photometry alone. There is a general consent that colours, and spectral features, most notably the 4000 Å break, can predict many properties of galaxies, including star formation rates and hence they could infer some of the line properties. We argue that these techniques have great prospects in helping us understand line emission in extragalactic objects and might speed up future galaxy redshift surveys if they are to target emission-line objects only. We use two independent methods, Artificial Neural Networks (based on the ANNz code) and Locally Weighted Regression (LWR), to retrieve correlations present in the colour N-dimensional space and to predict the equivalent widths present in the corresponding spectra. We also investigate how well it is possible to separate galaxies with and without lines from broad-band photometry only. We find, unsurprisingly, that recombination lines can be well predicted by galaxy colours. However, among collisional lines some can and some cannot be predicted well from galaxy colours alone, without any further redshift information. We also use our techniques to estimate how much information contained in spectral diagnostic diagrams can be recovered from broad-band photometry alone. We find that it is possible to classify active galactic nuclei and star formation objects relatively well using colours only. We suggest that this technique could be used to considerably improve redshift surveys such as the upcoming Fibre Multi Object Spectrograph (FMOS) survey and the planned Wide Field Multi Object Spectrograph (WFMOS) survey.

  17. On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing

    SciTech Connect

    Gerrits, Thomas; Lita, Adriana E.; Calkins, Brice; Tomlin, Nathan A.; Fox, Anna E.; Linares, Antia Lamas; Mirin, Richard P.; Nam, Sae Woo; Thomas-Peter, Nicholas; Metcalf, Benjamin J.; Spring, Justin B.; Langford, Nathan K.; Walmsley, Ian A.; Gates, James C.; Smith, Peter G. R.

    2011-12-15

    Integration is currently the only feasible route toward scalable photonic quantum processing devices that are sufficiently complex to be genuinely useful in computing, metrology, and simulation. Embedded on-chip detection will be critical to such devices. We demonstrate an integrated photon-number-resolving detector, operating in the telecom band at 1550 nm, employing an evanescently coupled design that allows it to be placed at arbitrary locations within a planar circuit. Up to five photons are resolved in the guided optical mode via absorption from the evanescent field into a tungsten transition-edge sensor. The detection efficiency is 7.2{+-}0.5 %. The polarization sensitivity of the detector is also demonstrated. Detailed modeling of device designs shows a clear and feasible route to reaching high detection efficiencies.

  18. Dual-etalon cavity ring-down frequency-comb spectroscopy with broad band light source

    DOEpatents

    Chandler, David W; Strecker, Kevin E

    2014-04-01

    In an embodiment, a dual-etalon cavity-ring-down frequency-comb spectrometer system is described. A broad band light source is split into two beams. One beam travels through a first etalon and a sample under test, while the other beam travels through a second etalon, and the two beams are recombined onto a single detector. If the free spectral ranges ("FSR") of the two etalons are not identical, the interference pattern at the detector will consist of a series of beat frequencies. By monitoring these beat frequencies, optical frequencies where light is absorbed may be determined.

  19. Synchronous fluctuation in broad-band processes and application to the electroencephalographic brain data

    NASA Astrophysics Data System (ADS)

    Lin, D. C.; Perez Velazquez, J. L.; Nenadovic, V.

    2012-02-01

    We propose phase-like characteristics in the broad-band process and introduce a novel wavelet-based method to analyze fluctuation in synchrony (FIS) in a wide frequency range. We demonstrate FIS between multifractal processes and a modeled dynamical system in phase transition. We then apply the idea to analyze surface scalp electroencephalographic data from normal subjects and traumatic brain-injured (TBI) patients. Our results show that FIS in normal subjects is more pronounced and exhibits more dynamic spatiotemporal patterns. Moreover, we find an intrinsic synchrony-variability relationship underlying these FIS characteristics.

  20. Broad-band polarization in molecular spectra. [Zeeman effect in magnetic stars

    NASA Technical Reports Server (NTRS)

    Illing, R. M. E.

    1981-01-01

    The rotational lines of the CN(0,0) red system have been observed to show a strongly asymmetric Zeeman profile. Certain molecules are very susceptible to magnetic perturbation because of the weakness of their spin-rotation coupling; a fairly weak magnetic field can cause a complete Paschen-Back effect. The calculation of transition probabilities incorporating this effect into the Hamiltonian is discussed, and the detailed calculation is then given. The resulting transition probabilities are transformed into synthetic line profiles by using the Unno (1956) model of polarized radiation transfer. The dependence of the net polarized flux on magnetic field and equivalent width is investigated. It is shown that entire band systems may be significantly polarized. Broad-band circular polarization of sunspots may be due, in part, to molecular bands. Analysis of the CH G band indicates a magnetic field of 0.25-0.50 x 10 to the 6th gauss in the white dwarf G99-37, an order of magnitude lower than previous estimates.

  1. Study of transmission line attenuation in broad band millimeter wave frequency range

    NASA Astrophysics Data System (ADS)

    Pandya, Hitesh Kumar B.; Austin, M. E.; Ellis, R. F.

    2013-10-01

    Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmospheric water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively.

  2. A Hard Tail in Broad Band Spectrum of Cir X-1: a clue for a Z-source behavior

    NASA Astrophysics Data System (ADS)

    Iaria, R.; Di Salvo, T.; La Barbera, A.; Burderi, L.; Robba, N. R.

    2000-10-01

    We report on the spectral analysis of the peculiar source Cir X--1 observed by the BeppoSAX satellite when the X-ray source was near the periastron. A flare lasting ~ 6 x 103 s is present at the beginning of the observation. The luminosity during the persistent emission is 1 x 1038 erg s-1, while during the flare is 2 x 1038 erg s-1. The broad band (0.1--100 keV) energy spectrum is well fitted by a model consisting of Comptonization of soft photons, with a temperature of ~ 0.4 keV, by electrons at a temperature of ~ 1 keV, and a power-law component, with photon index ~ 3, dominant at energies higher than 10 keV. This component is present out the flare, contributing to ~ 4% of the total luminosity, while during the flare its addition is not statistically significant. An absorption edge at ~ 8.4 keV, with optical depth ~ 1, corresponding to the K-edge of Fe XXIII--XXV, and an iron emission line at 6.7 keV are also present. The iron line energy is in agreement with the ionization level of the absorbtion edge. The hydrogen column deduced from the absorption edge is ~ 1024 cm-2,two order of magnitude larger than the absorption measured in this source. We calculated the radius of the region originating the comptonized seed photons, RW ~ 150 km. We propose a scenario where RW is the inner disk radius, a highly ionized torus surrounds the accretion disk and a magnetospere is large up to RW. The absorption edge, the emission line could originate in the photoionized torus present in the outer edge of the accretion disk, while the comptonized component originates in an inner region of the disk.

  3. Association of broad icosahedral Raman bands with substitutional disorder in SiB{sub 3} and boron carbide

    SciTech Connect

    Aselage, T.L.; Tallant, D.R.

    1998-02-01

    The structure of silicon boride, SiB{sub 3}, is based on 12-atom, boron-rich icosahedra in which silicon atoms substitute for some boron atoms. Raman bands associated with vibrations of icosahedral atoms in SiB{sub 3} are quite broad, reflecting this substitutional disorder. Comparing the Raman spectra of other icosahedral borides with SiB{sub 3}, only boron carbides have similarly broad icosahedral Raman bands. The direct correlation of broad icosahedral Raman bands with substitutional disorder supports the proposition that carbon atoms replace icosahedral boron atoms in boron carbides of all compositions. {copyright} {ital 1998} {ital The American Physical Society}

  4. Broad Band X-Ray Telescope (BBXRT) Work Station in the Spacelab Payload Operations Control Center

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The primary objective of the STS-35 mission was round the clock observation of the celestial sphere in ultraviolet and X-Ray astronomy with the Astro-1 observatory which consisted of four telescopes: the Hopkins Ultraviolet Telescope (HUT); the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE); the Ultraviolet Imaging Telescope (UIT); and the Broad Band X-Ray Telescope (BBXRT). The Huntsville Operations Support Center (HOSC) Spacelab Payload Operations Control Center (SL POCC) at the Marshall Space Flight Center (MSFC) was the air/ground communication channel used between the astronauts and ground control teams during the Spacelab missions. Teams of controllers and researchers directed on-orbit science operations, sent commands to the spacecraft, received data from experiments aboard the Space Shuttle, adjusted mission schedules to take advantage of unexpected science opportunities or unexpected results, and worked with crew members to resolve problems with their experiments. Due to loss of data used for pointing and operating the ultraviolet telescopes, MSFC ground teams were forced to aim the telescopes with fine tuning by the flight crew. This photo captures the activity of WUPPE (Wisconsin Ultraviolet Photo-Polarimeter Experiment) data review at the Science Operations Area during the mission. This image shows mission activities at the Broad Band X-Ray Telescope (BBXRT) Work Station in the Science Operations Area (SOA).

  5. Wide-Band Microwave Receivers Using Photonic Processing

    NASA Technical Reports Server (NTRS)

    Matsko, Andrey; Maleki, Lute; Itchenko, Vladimir; Yu, Nan; Strekalov, Dmitry; Savchenkov, Anatoliy

    2008-01-01

    In wide-band microwave receivers of a type now undergoing development, the incoming microwave signals are electronically preamplified, then frequency-up-converted to optical signals that are processed photonically before being detected. This approach differs from the traditional approach, in which incoming microwave signals are processed by purely electronic means. As used here, wide-band microwave receivers refers especially to receivers capable of reception at any frequency throughout the range from about 90 to about 300 GHz. The advantage expected to be gained by following the up-conversion-and-photonic-processing approach is the ability to overcome the limitations of currently available detectors and tunable local oscillators in the frequency range of interest. In a receiver following this approach (see figure), a preamplified incoming microwave signal is up-converted by the method described in the preceeding article. The frequency up-converter exploits the nonlinearity of the electromagnetic response of a whispering gallery mode (WGM) resonator made of LiNbO3. Up-conversion takes place by three-wave mixing in the resonator. The WGM resonator is designed and fabricated to function simultaneously as an electro-optical modulator and to exhibit resonance at the microwave and optical operating frequencies plus phase matching among the microwave and optical signals circulating in the resonator. The up-conversion is an efficient process, and the efficiency is enhanced by the combination of microwave and optical resonances. The up-converted signal is processed photonically by use of a tunable optical filter or local oscillator, and is then detected. Tunable optical filters can be made to be frequency agile and to exhibit high resonance quality factors (high Q values), thereby making it possible to utilize a variety of signal-processing modalities. Therefore, it is anticipated that when fully developed, receivers of this type will be compact and will be capable of both

  6. Observation of localized flat-band modes in a quasi-one-dimensional photonic rhombic lattice.

    PubMed

    Mukherjee, Sebabrata; Thomson, Robert R

    2015-12-01

    We experimentally demonstrate the photonic realization of a dispersionless flat band in a quasi-one-dimensional photonic lattice fabricated by ultrafast laser inscription. In the nearest neighbor tight binding approximation, the lattice supports two dispersive and one nondispersive (flat) band. We experimentally excite superpositions of flat-band eigenmodes at the input of the photonic lattice and show the diffractionless propagation of the input states due to their infinite effective mass. In the future, the use of photonic rhombic lattices, together with the successful implementation of a synthetic gauge field, will enable the observation of Aharonov-Bohm photonic caging. PMID:26625021

  7. Recent progress on photonic band gap accelerator cavities

    SciTech Connect

    Smith, D.R.; Li, D.; Vier, D.C.

    1997-02-01

    We report on the current status of our program to apply Photonic Band Gap (PBG) concepts to produce novel high-energy, high-intensity accelerator cavities. The PBG design on which we have concentrated our initial efforts consists of a square array of metal cylinders, terminated by conducting or superconducting sheets, and surrounded by microwave absorber on the periphery of the structure. A removed cylinder from the center of the array constitutes a site defect where a localized electromagnetic mode can occur. In previous work, we have proposed that this structure could be utilized as an accelerator cavity, with advantageous properties over conventional cavity designs. In the present work, we present further studies, including MAFIA-based numerical calculations and experimental measurements, demonstrating the feasibility of using the proposed structure in a real accelerator application.

  8. Effect of implementation of a Bragg reflector in the photonic band structure of the Suzuki-phase photonic crystal lattice.

    PubMed

    Martinez, Luis Javier; Alija, Alfonso Rodriguez; Postigo, Pablo Aitor; Galisteo-López, J F; Galli, Matteo; Andreani, Lucio Claudio; Seassal, Christian; Viktorovitch, Pierre

    2008-06-01

    We investigate the change of the photonic band structure of the Suzuki-phase photonic crystal lattice when the horizontal mirror symmetry is broken by an underlying Bragg reflector. The structure consists of an InP photonic crystal slab including four InAsP quantum wells, a SiO(2) bonding layer, and a bottom high index contrast Si/SiO(2) Bragg mirror deposited on a Si wafer. Angle- and polarization-resolved photoluminescence spectroscopy has been used for measuring the photonic band structure and for investigating the coupling to a polarized plane wave in the far field. A drastic change in the k-space photonic dispersion between the structure with and without Bragg reflector is measured. An important enhancement on the photoluminescence emission up to seven times has been obtained for a nearly flat photonic band, which is characteristic of the Suzuki-phase lattice. PMID:18545565

  9. Control of lateral divergence in high-power, broad-area photonic crystal lasers

    NASA Astrophysics Data System (ADS)

    Rong, Jiamin; Xing, Enbo; Wang, Lijie; Shu, Shili; Tian, Sicong; Tong, Cunzhu; Wang, Lijun

    2016-07-01

    One-dimensional photonic bandgap crystal (PBC) lasers have demonstrated ultra-low vertical divergence and record brightness; however, their future development is limited by their lateral beam quality. In this paper, a fishbone microstructure is proposed to control the lateral modes in broad-area PBC lasers. The findings reveal that the introduction of the microstructure improves the full width at half maximum of the lateral far field by 22.2% and increases the output power to a small extent. The detailed measurements show that the lateral beam parameter product decreases by 15.9%.

  10. Wake-field studies on photonic band gap accelerator cavities

    NASA Astrophysics Data System (ADS)

    Li, Derun; Kroll, N.; Smith, D. R.; Schultz, S.

    1997-03-01

    We have studied the wake-field of several metal Photonic Band Gap (PBG) cavities which consist of either a square or a hexagonal array of metal cylinders, bounded on top and bottom by conducting or superconducting sheets, surrounded by placing microwave absorber at the periphery or by replacing outer rows of metal cylinders with lossy dielectric ones, or by metallic walls. A removed cylinder from the center of the array constitutes a site defect where a localized electromagnetic mode can occur. While both monopole and dipole wake-fields have been studied, we confine our attention here mainly to the dipole case. The dipole wake-field is produced by modes in the propagation bands which tend to fill the entire cavity more or less uniformly and are thus easy to damp selectively. MAFIA time domain simulation of the transverse wake-field has been compared with that of a cylindrical pill-box comparison cavity. Even without damping the wake-field of the metal PBG cavity is substantially smaller than that of the pill-box cavity and may be further reduced by increasing the size of the lattice. By introducing lossy material at the periphery we have been able to produce Q factors for the dipole modes in the 40 to 120 range without significantly degrading the accelerating mode.

  11. Tunable complete photonic band gap in anisotropic photonic crystal slabs with non-circular air holes using liquid crystals

    NASA Astrophysics Data System (ADS)

    Fathollahi Khalkhali, T.; Bananej, A.

    2016-06-01

    In this study, we analyze the tunability of complete photonic band gap of square and triangular photonic crystal slabs composed of square and hexagonal air holes in anisotropic tellurium background with SiO2 as cladding material. The non-circular holes are infiltrated with liquid crystal. Using the supercell method based on plane wave expansion, we study the variation of complete band gap by changing the optical axis orientation of liquid crystal. Our numerical results show that noticeable tunability of complete photonic band gap can be obtained in both square and triangular structures with non-circular holes.

  12. Broad-band X-ray emission and the reality of the broad iron line from the neutron star-white dwarf X-ray binary 4U 1820-30

    NASA Astrophysics Data System (ADS)

    Mondal, Aditya S.; Dewangan, G. C.; Pahari, M.; Misra, R.; Kembhavi, A. K.; Raychaudhuri, B.

    2016-09-01

    Broad relativistic iron lines from neutron star X-ray binaries are important probes of the inner accretion disc. The X-ray reflection features can be weakened due to strong magnetic fields or very low iron abundances such as is possible in X-ray binaries with low mass, first generation stars as companions. Here, we investigate the reality of the broad iron line detected earlier from the neutron-star low-mass X-ray binary 4U 1820-30 with a degenerate helium dwarf companion. We perform a comprehensive, systematic broad-band spectral study of the atoll source using Suzaku and simultaneous NuSTAR and Swift observations. We have used different continuum models involving accretion disc emission, thermal blackbody and thermal Comptonization of either disc or blackbody photons. The Suzaku data show positive and negative residuals in the region of Fe K band. These features are well described by two absorption edges at 7.67 ± 0.14 keV and 6.93 ± 0.07 keV or partial covering photoionized absorption or by blurred reflection. Though, the simultaneous Swift and NuSTAR data do not clearly reveal the emission or absorption features, the data are consistent with the presence of either absorption or emission features. Thus, the absorption based models provide an alternative to the broad iron line or reflection model. The absorption features may arise in winds from the inner accretion disc. The broad-band spectra appear to disfavour continuum models in which the blackbody emission from the neutron-star surface provides the seed photons for thermal Comptonization. Our results suggest emission from a thin accretion disc (kTdisc ˜ 1 keV), Comptonization of disc photons in a boundary layer most likely covering a large fraction of the neutron-star surface and innermost parts of the accretion disc, and blackbody emission (kTbb ˜ 2 keV) from the polar regions.

  13. Etched distributed Bragg reflectors as three-dimensional photonic crystals: photonic bands and density of states.

    PubMed

    Pavarini, E; Andreani, L C

    2002-09-01

    The photonic band dispersion and density of states (DOS) are calculated for the three-dimensional (3D) hexagonal structure corresponding to a distributed Bragg reflector patterned with a 2D triangular lattice of circular holes. Results for the Si/SiO(2) and GaAs/Al(x)Ga(1-x)As systems determine the optimal parameters for which a gap in the 2D plane occurs and overlaps the 1D gap of the multilayer. The DOS is considerably reduced in correspondence with the overlap of 2D and 1D gaps. Also, the local density of states (i.e., the DOS weighted with the squared electric field at a given point) has strong variations depending on the position. Both results imply substantial changes of spontaneous emission rates and patterns for a local emitter embedded in the structure and make this system attractive for the fabrication of a 3D photonic crystal with controlled radiative properties. PMID:12366275

  14. The Photonic Band Gaps in the Two-Dimensional Plasma Photonic Crystals with Rhombus Lattice

    NASA Astrophysics Data System (ADS)

    Zhang, Kaiming; Sun, Dongsheng

    2016-06-01

    In this paper, under two different electromagnetic modes, the photonic band gaps (PBGs) in the two-dimensional plasma photonic crystals (PPCs) are theoretically investigated based on the plane wave expansion method. The proposed PPCs are arranged in rhombus lattices, in which the homogeneous unmagnetized plasma rods are immersed in the isotropic dielectric background. The computed results showed that PBGs can be easily tuned by the angle of rhombus lattices, and a cutoff frequency and a flatbands region can be observed under the TM and TE polarized waves, respectively. The relationships between the relative bandwidths of first PBGs and the parameters of PPCs in two such cases also are discussed. The numerical simulations showed that the PBGs can be manipulated obviously by the parameters as mentioned above. The proposed results can be used to design the waveguide and filter based on the PPCs.

  15. Photonic band structures of one-dimensional photonic crystals doped with plasma

    NASA Astrophysics Data System (ADS)

    Guo, B.; Xie, M. Q.; Peng, L.

    2012-07-01

    The photonic band structures (PBSs) of oblique incidence propagation in one-dimensional plasma-doped photonic crystals (PCs) are investigated carefully. When the lattice constant of plasma-doped PCs is less than the incident wavelength, the PC becomes anisotropic. Therefore, the dielectric constant of PC is converted into a complex tensor dielectric constant. This determines the PBSs of PCs. In the present paper, one-dimensional PCs are taken as an example to study both normal and absorption PBSs. Using both the effective medium approximation and the transfer matrix method, we can derive the dispersion relation for PCs. The dependence of the plasma filling factor on the effective dielectric constant and PBSs is calculated and discussed.

  16. Results on the Performance of a Broad Band Focussing Cherenkov Counter

    DOE R&D Accomplishments Database

    Cester, R.; Fitch, V. L.; Montag, A.; Sherman, S.; Webb, R. C.; Witherell, M. S.

    1980-01-01

    The field of ring imaging (broad band differential) Cherenkov detectors has become a very active area of interest in detector development at several high energy physics laboratories. Our group has previously reported on a method of Cherenkov ring imaging for a counter with large momentum and angular acceptance using standard photo multipliers. Recently, we have applied this technique to the design of a set of Cherenkov counters for use in a particle search experiment at Fermi National Accelerator Laboratory (FNAL). This new detector operates over the range 0.998 < ..beta.. < 1.000 in velocity with a delta..beta.. approx. 2 x 10{sup -4}. The acceptance in angle is +- 14 mrad in the horizontal and +- 28 mrad in the vertical. We report here on the performance of this counter.

  17. How to adapt broad-band gravitational-wave searches for r-modes

    SciTech Connect

    Owen, Benjamin J.

    2010-11-15

    Up to now there has been no search for gravitational waves from the r-modes of neutron stars in spite of the theoretical interest in the subject. Several oddities of r-modes must be addressed to obtain an observational result: The gravitational radiation field is dominated by the mass current (gravitomagnetic) quadrupole rather than the usual mass quadrupole, and the consequent difference in polarization affects detection statistics and parameter estimation. To astrophysically interpret a detection or upper limit it is necessary to convert the gravitational-wave amplitude to an r-mode amplitude. Also, it is helpful to know indirect limits on gravitational-wave emission to gauge the interest of various searches. Here I address these issues, thereby providing the ingredients to adapt broad-band searches for continuous gravitational waves to obtain r-mode results. I also show that searches of existing data can already have interesting sensitivities to r-modes.

  18. Compressive Broad-Band Hyperspectral Sum Frequency Generation Microscopy to Study Functionalized Surfaces.

    PubMed

    Zheng, Desheng; Lu, Liyang; Li, Yun; Kelly, Kevin F; Baldelli, Steven

    2016-05-19

    A broad-band sum frequency generation microscope has been developed for the study of molecular monolayers on surfaces. Because sum frequency generation is a vibrational spectroscopy based on a second-order optical process, it is uniquely sensitive to detecting a molecule's vibrational fingerprints specifically at interfaces. In this microscope, a structured illumination beam generated by a spatial light modulator is used to irradiate the sample with a series of sparsifying pseudorandom patterns. The spectra associated with each pattern are then input into a reconstruction algorithm to compressively recover the full hyperspectral image cube. As a proof-of-principle, this system performed molecule-specific imaging of a microcontact-printed self-assembled monolayer of alkanethiolate on copper. This hyperspectral compressive imaging effectively recovered both spatial and spectral surface features with compression greater than 80%, meaning more than a 5-fold decrease in acquisition time compared to traditional methods. PMID:27121296

  19. Broad-band analysis of the spectral evolution of GX 339-4

    NASA Astrophysics Data System (ADS)

    Clavel, M.; Rodriguez, J.; Corbel, S.

    2015-07-01

    Black Hole X-ray binaries display large outbursts during which their spectral properties are strongly variable. Their high-energy emission includes the contribution of thermal and non-thermal components that are respectively attributed to the emission of an accretion disk and the one of a jet. How these structures form and evolve over time is still under investigation. The aim of our group is to provide the most up to date generic properties of these objects, as observed along the course of their outbursts, in order to constrain the theoretical models. Therefore, I will present the systematic broad-band analysis of the spectral properties of black hole binaries that we are currently developing, using the 2010 outburst of GX 339-4 as an example. I will give an overview of the results we obtained using observations at all wavelengths from proprietary radio data to hard X-rays.

  20. Anomalously Broad Diffuse Interstellar Bands and Excited CH+ Absorption in the Spectrum of Herschel 36

    NASA Astrophysics Data System (ADS)

    York, D. G.; Dahlstrom, J.; Welty, D. E.; Oka, T.; Hobbs, L. M.; Johnson, S.; Friedman, S. D.; Jiang, Z.; Rachford, B. L.; Snow, T. P.; Sherman, R.; Sonnentrucker, P.

    2014-02-01

    Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, an O star system next to the bright Hourglass nebula of the Hii region Messier 8. Excited lines of CH and CH+ are seen as well. We show that the region is very compact and itemize other anomalies of the gas. An infrared-bright star within 400 AU is noted. The combination of these effects produces anomalous DIBs, interpreted by Oka et al. (2013, see also this volume) as being caused predominantly by infrared pumping of rotational levels of relatively small molecules.

  1. Cerebral oxygenation monitoring during cardiac bypass surgery in infants with broad band spatially resolved spectroscopy

    NASA Astrophysics Data System (ADS)

    Soschinski, Jan; Ben Mine, Lofti; Geraskin, Dmitri; Bennink, Gerardus; Kohl-Bareis, Matthias

    2007-07-01

    Neurological impairments following cardio-pulmonary bypass (CPB) during open heart surgery can result from microembolism and ischaemia. Here we present results from monitoring cerebral haemodynamics during CPB with near infrared spatially resolved broadband spectroscopy. In particular, the study has the objective (a) to monitor oxy- and deoxy-hemoglobin concentrations (oxy-Hb, deoxy-Hb) and their changes as well as oxygen saturation during CPB surgery and (b) to develop and test algorithms for the calculation of these parameters from broad band spectroscopy. For this purpose a detection system was developed based on an especially designed lens imaging spectrograph with optimised sensitivity of recorded reflectance spectra for wavelengths between 600 and 1000 nm. The high f/#-number of 1:1.2 of the system results in about a factor of 10 higher light throughput combined with a lower astigmatism and crosstalk between channels when compared with a commercial mirror spectrometers (f/# = 1:4). For both hemispheres two independent channels each with three source-detector distances (ρ = 25 . 35 mm) were used resulting in six spectra. The broad band approach allows to investigate the influence of the wavelength range on the calculated haemoglobin concentrations and their changes and oxygen saturation when the attenuation A(λ) and its slope ΔA(λ)/Δρ are evaluated. Furthermore, the different depth sensitivities of these measurement parameters are estimated from Monte Carlo simulations and exploited for an optimization of the cerebral signals. It is demonstrated that the system does record cerebral oxygenation parameters during CPB in infants. In particular, the correlation of haemoglobin concentrations with blood supply (flow, pressure) by the heart-lung machine and the significant decreases in oxygen saturation during cardiac arrest is discussed.

  2. Broad-band soft x-ray diagnostic instruments at the LLNL Novette laser facility

    SciTech Connect

    Tirsell, K.G.; Lee, P.H.Y.; Nilson, D.G.; Medecki, H.

    1983-09-15

    Complementary broad-band instruments have been developed to measure time dependent, absolute soft x-ray spectra at the Lawrence Livermore National Laboratory (LLNL) Nd glass laser irradiation facilities. Absolute flux measurements of x rays emitted from laser-produced plasmas are important for understanding laser absorption and energy transport. We will describe two new 10-channel XRD systems that have been installed at the LLNL Novette facility for use in the 0.15- to 1.5-keV range. Since XRD channel time response is limited by available oscilloscope performance to 120 ps, a soft x-ray streak camera has been developed for better time resolution (20 ps) and greater dynamic range (approx.10/sup 3/) in the same x-ray energy region. Using suitable filters, grazing incidence mirrors, and a gold or cesium-iodide transmission cathode, this streak camera instrument has been installed at Novette to provide one broad and four relatively narrow channels. It can also be used in a single channel, spatially discriminating mode by means of pinhole imaging. The complementary nature of these instruments has been enhanced by locating them in close proximity and matching their channel energy responses. As an example of the use of these instruments, we present results from Novette 2..omega..(0.53 ..mu..m) gold disk irradiations at 1 ns and 10/sup 14/ to 10/sup 15/ W/cm/sup 2/.

  3. A class of supported membranes: formation of fluid phospholipid bilayers on photonic band gap colloidal crystals.

    PubMed

    Brozell, Adrian M; Muha, Michelle A; Sanii, Babak; Parikh, Atul N

    2006-01-11

    We report the formation of a new class of supported membranes consisting of a fluid phospholipid bilayer coupled directly to a broadly tunable colloidal crystal with a well-defined photonic band gap. For nanoscale colloidal crystals exhibiting a band gap at the optical frequencies, substrate-induced vesicle fusion gives rise to a surface bilayer riding onto the crystal surface. The bilayer is two-dimensionally continuous, spanning multiple beads with lateral mobilities which reflect the coupling between the bilayer topography and the curvature of the supporting colloidal surface. In contrast, the spreading of vesicles on micrometer scale colloidal crystals results in the formation of bilayers wrapping individual colloidal beads. We show that simple UV photolithography of colloidal crystals produces binary patterns of crystal wettabilities, photonic stopbands, and corresponding patterns of lipid mono- and bilayer morphologies. We envisage that these approaches will be exploitable for the development of optical transduction assays and microarrays for many membrane-mediated processes, including transport and receptor-ligand interactions. PMID:16390122

  4. High sensitivity ultra-broad-band absorption spectroscopy of inductively coupled chlorine plasma

    NASA Astrophysics Data System (ADS)

    Marinov, Daniil; Foucher, Mickaël; Campbell, Ewen; Brouard, Mark; Chabert, Pascal; Booth, Jean-Paul

    2016-06-01

    We propose a method to measure the densities of vibrationally excited Cl2(v) molecules in levels up to v  =  3 in pure chlorine inductively coupled plasmas (ICPs). The absorption continuum of Cl2 in the 250–450 nm spectral range is deconvoluted into the individual components originating from the different vibrational levels of the ground state, using a set of ab initio absorption cross sections. It is shown that gas heating at constant pressure is the major depletion mechanism of the Cl2 feedstock in the plasma. In these line-integrated absorption measurements, the absorption by the hot (and therefore rarefied) Cl2 gas in the reactor centre is masked by the cooler (and therefore denser) Cl2 near the walls. These radial gradients in temperature and density make it difficult to assess the degree of vibrational excitation in the centre of the reactor. The observed line-averaged vibrational distributions, when analyzed taking into account the radial temperature gradient, suggest that vibrational and translational degrees of freedom in the plasma are close to local equilibrium. This can be explained by efficient vibrational-translational (VT) relaxation between Cl2 and Cl atoms. Besides the Cl2(v) absorption band, a weak continuum absorption is observed at shorter wavelengths, and is attributed to photodetachment of Cl‑ negative ions. Thus, line-integrated densities of negative ions in chlorine plasmas can be directly measured using broad-band absorption spectroscopy.

  5. Multiwavelength observations of the energetic GRB 080810: detailed mapping of the broad-band spectral evolution

    NASA Astrophysics Data System (ADS)

    Page, K. L.; Willingale, R.; Bissaldi, E.; Postigo, A. De Ugarte; Holland, S. T.; McBreen, S.; O'Brien, P. T.; Osborne, J. P.; Prochaska, J. X.; Rol, E.; Rykoff, E. S.; Starling, R. L. C.; Tanvir, N. R.; van der Horst, A. J.; Wiersema, K.; Zhang, B.; Aceituno, F. J.; Akerlof, C.; Beardmore, A. P.; Briggs, M. S.; Burrows, D. N.; Castro-Tirado, A. J.; Connaughton, V.; Evans, P. A.; Fynbo, J. P. U.; Gehrels, N.; Guidorzi, C.; Howard, A. W.; Kennea, J. A.; Kouveliotou, C.; Pagani, C.; Preece, R.; Perley, D.; Steele, I. A.; Yuan, F.

    2009-11-01

    GRB 080810 was one of the first bursts to trigger both Swift and the Fermi Gamma-ray Space Telescope. It was subsequently monitored over the X-ray and UV/optical bands by Swift, in the optical by Robotic Optical Transient Search Experiment (ROTSE) and a host of other telescopes, and was detected in the radio by the Very Large Array. The redshift of z = 3.355 +/- 0.005 was determined by Keck/High Resolution Echelle Spectrometer (HIRES) and confirmed by RTT150 and NOT. The prompt gamma/X-ray emission, detected over 0.3-103 keV, systematically softens over time, with Epeak moving from ~600 keV at the start to ~40 keV around 100s after the trigger; alternatively, this spectral evolution could be identified with the blackbody temperature of a quasi-thermal model shifting from ~60 to ~3keV over the same time interval. The first optical detection was made at 38s, but the smooth, featureless profile of the full optical coverage implies that this is originated from the afterglow component, not from the pulsed/flaring prompt emission. Broad-band optical and X-ray coverage of the afterglow at the start of the final X-ray decay (~8ks) reveals a spectral break between the optical and X-ray bands in the range of 1015-2 × 1016Hz. The decay profiles of the X-ray and optical bands show that this break initially migrates blueward to this frequency and then subsequently drifts redward to below the optical band by ~3 × 105s. GRB 080810 was very energetic, with an isotropic energy output for the prompt component of 3 × 1053 and 1.6 × 1052 erg for the afterglow; there is no evidence for a jet break in the afterglow up to 6d following the burst. This paper is dedicated to the memory of Professor Martin Turner, who sadly passed away during its writing. Martin was an influential figure in X-ray Astronomy and an excellent PhD supervisor. He will be greatly missed. E-mail: kpa@star.le.ac.uk ‡ NASA postdoctoral program fellow.

  6. A broad-standard technique for correcting for band broadening in size-exclusion chromatography.

    PubMed

    Zhang, Peng; Mazoyer, Paul; Gilbert, Robert G

    2016-04-22

    Band broadening in size-exclusion chromatography (SEC) is always present to some extent. Broadening effects on averages such as the weight- and number average molecular weights (MW¯ and Mn¯ respectively) are minimal with modern SEC systems. However, broadening distorts the shape of the true molecular weight distribution (MWD), which causes problems if one wants to compare the detailed form of the MWD to a model. An addition to current methods for overcoming this problem is presented. One starts with a sufficiently wide range of samples whose exact values of Mn¯ andMW¯ have been measured by non-SEC methods (e.g. by fluorimetry and light scattering, respectively, of the sample without size separation). A true (unbroadened) molecular weight distribution for a sample can be obtained by deconvolution (here using a maximum-entropy algorithm) by fitting SEC data for these samples to these exact Mn¯ and MW¯ values to find the values of the parameters in a sufficiently flexible assumed broadening function. This was modelled using simulated band broadening and subsequent deconvolution, with the broadening parameters least-squares fitted to the "exact" sets of values of Mn¯ and MW¯. The results show that if these Mn¯ and MW¯ values are for a series of broad (not narrow) standards covering a sufficient range of molecular weight, then after deconvolution, a good representation of the original molecular weight distribution used in the simulation is obtained. The method should prove useful for water-soluble polymers, for which it is often difficult to obtain narrow standards of a wide range of molecular weight, as required in a number of well-established methods for correcting for band broadening. PMID:27016112

  7. Geometric phase and entanglement of Raman photon pairs in the presence of photonic band gap

    SciTech Connect

    Berrada, K.; Ooi, C. H. Raymond; Abdel-Khalek, S.

    2015-03-28

    Robustness of the geometric phase (GP) with respect to different noise effects is a basic condition for an effective quantum computation. Here, we propose a useful quantum system with real physical parameters by studying the GP of a pair of Stokes and anti-Stokes photons, involving Raman emission processes with and without photonic band gap (PBG) effect. We show that the properties of GP are very sensitive to the change of the Rabi frequency and time, exhibiting collapse phenomenon as the time becomes significantly large. The system allows us to obtain a state which remains with zero GP for longer times. This result plays a significant role to enhance the stabilization and control of the system dynamics. Finally, we investigate the nonlocal correlation (entanglement) between the pair photons by taking into account the effect of different parameters. An interesting correlation between the GP and entanglement is observed showing that the PBG stabilizes the fluctuations in the system and makes the entanglement more robust against the change of time and frequency.

  8. Communication: excitation band modulation with high-order photonic band gap in PMMA:Eu(TTA)3(TPPO)2 opals.

    PubMed

    Xu, Wen; Bai, Xue; Zhu, Yongsheng; Liu, Tong; Xu, Sai; Dong, Biao; Song, Hongwei

    2013-05-14

    Changes in the excitation spectra of luminescent species inserted in photorefractive crystals as a function of changes in the high-order photonic band gap (PBG) have not been previously observed. In this communication, we present our results monitoring the excitation band of Eu(TTA)3(TPPO)2 inserted in the PMMA opal photonic crystals as a function of the changes in the high-order PBG of the crystals. We find shifts in the complex excitation band and changes in the integrated emission intensity that correlates with shifts in the high-order PBG through coupling to the excitation transition. PMID:23676019

  9. Communication: Excitation band modulation with high-order photonic band gap in PMMA:Eu(TTA)3(TPPO)2 opals

    NASA Astrophysics Data System (ADS)

    Xu, Wen; Bai, Xue; Zhu, Yongsheng; Liu, Tong; Xu, Sai; Dong, Biao; Song, Hongwei

    2013-05-01

    Changes in the excitation spectra of luminescent species inserted in photorefractive crystals as a function of changes in the high-order photonic band gap (PBG) have not been previously observed. In this communication, we present our results monitoring the excitation band of Eu(TTA)3(TPPO)2 inserted in the PMMA opal photonic crystals as a function of the changes in the high-order PBG of the crystals. We find shifts in the complex excitation band and changes in the integrated emission intensity that correlates with shifts in the high-order PBG through coupling to the excitation transition.

  10. High-power narrow-vertical-divergence photonic band crystal laser diodes with optimized epitaxial structure

    SciTech Connect

    Liu, Lei; Qu, Hongwei; Liu, Yun; Zhang, Yejin; Zheng, Wanhua; Wang, Yufei; Qi, Aiyi

    2014-12-08

    900 nm longitudinal photonic band crystal (PBC) laser diodes with optimized epitaxial structure are fabricated. With a same calculated fundamental-mode divergence, stronger mode discrimination is achieved by a quasi-periodic index modulation in the PBC waveguide than a periodic one. Experiments show that the introduction of over 5.5 μm-thick PBC waveguide contributes to only 10% increment of the internal loss for the laser diodes. For broad area PBC lasers, output powers of 5.75 W under continuous wave test and over 10 W under quasi-continuous wave test are reported. The vertical divergence angles are 10.5° at full width at half maximum and 21.3° with 95% power content, in conformity with the simulated angles. Such device shows a prospect for high-power narrow-vertical-divergence laser emission from single diode laser and laser bar.

  11. Hypersonic modulation of light in three-dimensional photonic and phononic band-gap materials.

    PubMed

    Akimov, A V; Tanaka, Y; Pevtsov, A B; Kaplan, S F; Golubev, V G; Tamura, S; Yakovlev, D R; Bayer, M

    2008-07-18

    The elastic coupling between the a-SiO2 spheres composing opal films brings forth three-dimensional periodic structures which besides a photonic stop band are predicted to also exhibit complete phononic band gaps. The influence of elastic crystal vibrations on the photonic band structure has been studied by injection of coherent hypersonic wave packets generated in a metal transducer by subpicosecond laser pulses. These studies show that light with energies close to the photonic band gap can be efficiently modulated by hypersonic waves. PMID:18764257

  12. Photonic bands in two-dimensional microplasma arrays. I. Theoretical derivation of band structures of electromagnetic waves

    SciTech Connect

    Sakai, Osamu; Sakaguchi, Takui; Tachibana, Kunihide

    2007-04-01

    Two theoretical approaches appropriate for two-dimensional plasma photonic crystals reveal dispersions of propagating waves including photonic (electromagnetic) band gaps and multiflatbands. A modified plane-wave expansion method yields dispersions of collisional periodical plasmas, and the complex-value solution of a wave equation by a finite difference method enables us to obtain dispersions with structure effects in an individual microplasma. Periodical plasma arrays form band gaps as well as normal photonic crystals, and multiflatbands are present below the electron plasma frequency in the transverse electric field mode. Electron elastic collisions lower the top frequency of the multiflatbands but have little effect on band gap properties. The spatial gradient of the local dielectric constant resulting from an electron density profile widens the frequency region of the multiflatbands, as demonstrated by the change of surface wave distributions. Propagation properties described in dispersions including band gaps and flatbands agree with experimental observations of microplasma arrays.

  13. Photonic-Band-Gap Traveling-Wave Gyrotron Amplifier

    PubMed Central

    Nanni, E. A.; Lewis, S. M.; Shapiro, M. A.; Griffin, R. G.; Temkin, R. J.

    2014-01-01

    We report the experimental demonstration of a gyrotron traveling-wave-tube amplifier at 250 GHz that uses a photonic band gap (PBG) interaction circuit. The gyrotron amplifier achieved a peak small signal gain of 38 dB and 45 W output power at 247.7 GHz with an instantaneous −3 dB bandwidth of 0.4 GHz. The amplifier can be tuned for operation from 245–256 GHz. The widest instantaneous −3 dB bandwidth of 4.5 GHz centered at 253.25 GHz was observed with a gain of 24 dB. The PBG circuit provides stability from oscillations by supporting the propagation of transverse electric (TE) modes in a narrow range of frequencies, allowing for the confinement of the operating TE03-like mode while rejecting the excitation of oscillations at nearby frequencies. This experiment achieved the highest frequency of operation for a gyrotron amplifier; at present, there are no other amplifiers in this frequency range that are capable of producing either high gain or high output power. This result represents the highest gain observed above 94 GHz and the highest output power achieved above 140 GHz by any conventional-voltage vacuum electron device based amplifier. PMID:24476286

  14. Photonic-band-gap traveling-wave gyrotron amplifier.

    PubMed

    Nanni, E A; Lewis, S M; Shapiro, M A; Griffin, R G; Temkin, R J

    2013-12-01

    We report the experimental demonstration of a gyrotron traveling-wave-tube amplifier at 250 GHz that uses a photonic band gap (PBG) interaction circuit. The gyrotron amplifier achieved a peak small signal gain of 38 dB and 45 W output power at 247.7 GHz with an instantaneous -3  dB bandwidth of 0.4 GHz. The amplifier can be tuned for operation from 245-256 GHz. The widest instantaneous -3  dB bandwidth of 4.5 GHz centered at 253.25 GHz was observed with a gain of 24 dB. The PBG circuit provides stability from oscillations by supporting the propagation of transverse electric (TE) modes in a narrow range of frequencies, allowing for the confinement of the operating TE03-like mode while rejecting the excitation of oscillations at nearby frequencies. This experiment achieved the highest frequency of operation for a gyrotron amplifier; at present, there are no other amplifiers in this frequency range that are capable of producing either high gain or high output power. This result represents the highest gain observed above 94 GHz and the highest output power achieved above 140 GHz by any conventional-voltage vacuum electron device based amplifier. PMID:24476286

  15. A 250 GHz Photonic Band Gap Gyrotron Amplifier

    NASA Astrophysics Data System (ADS)

    Nanni, Emilio A.; Lewis, Samantha M.; Shapiro, Michael A.; Temkin, Richard J.

    2012-10-01

    Initial results for a high power 250 GHz gyrotron traveling wave tube (gyro-TWT) amplifier will be presented. The amplifier uses a novel photonic band gap (PBG) interaction circuit that confines the TE03-like mode for operation. Stability from oscillations in lower order modes is provided by the PBG circuit. At 26.6 kV and 0.25 A the gyro-TWT operates with peak small signal gain of 27.3 dB at 251 GHz. The instantaneous -3 dB bandwidth of the amplifier at peak gain is 0.4 GHz. The amplifier can be tuned for operation from 245-254 GHz. A peak output power of 7.5 W has been measured. Experimental results taken over a wide range of parameters, 15-30 kV and 0.25-0.5 A, show good agreement with a theoretical model in the small signal gain regime. The theoretical model incorporates cold test measurements for the transmission line, input coupler, PBG waveguide and mode converter.

  16. A Lunar Broad Band Seismometer on SELENE-2 / LUNETTE missions: Focus on VBB technical improvements

    NASA Astrophysics Data System (ADS)

    Nebut, T.; Gagnepain-Beyneix, J.; Lognonne, P.; Kobayashi, N.; Giardini, D.; Christensen, U. R.; de Raucourt, S.; Bierwirth, M.; Mimoun, D.; Zweifel, P.; Tillier, S.; Robert, O.; Escande, N.; Gabsi, T.; Lecomte, B.; Pot, O.; Mance, D.; Roll, R.; Shiraishi, H.; Garcia, R. F.; Yamada, R.; Mocquet, A.; Banerdt, B.; Tanaka, S.

    2010-12-01

    The Moon will be explored during the next decade by a series of missions, especially from Japan, China, India and USA. We present here the status of the development of space qualified Very Broad Band seismometer in Europe. This instrument, completed by Japanese Short Period Seismometers, is called Lunar Broad Band Seismometer (LBBS). It is considered for the Japanese project SELENE-2 and US project LUNETTE. The main scientific goals are to determine the internal structure of the whole Moon and more specifically the composition and size of the lunar core. The LBBS instrument is the result of an international consortium: A 3 axis short period (SP) seismometer (ISAS/JAXA) A 3 axis very broad band (VBB) seismometer (IPGP) A deployment system (DPL) (MPS) A data acquisition system (SEIS-AC) (ETHZ) Both SP and VBB development rely on technical heritage of cancelled space missions (LUNAR-A for the SP, Netlander & Humboldt/ExoMars for the VBB). This technical development lead VBB to reach a Technical Readiness Level (TRL) above 5 (ESA ExoMars PDR), and we aim at TRL 6 within the next few months. The adaptation of the VBB from Mars to Moon conditions and environment is challenging. The resolution has to be improved by a factor of ten and should be inferior to 2.10-11m/s^2/sqrt(Hz) @ 0.1 Hz while the Instrument are supporting very large temperature variations (several 10s of degrees) compared to those of typical VBB seismometers. Using Netlander & ExoMars heritage, It appeared that a trade-off between resolution and VBB thermal sensibility was possible. A passive thermal compensation device was designed and tested at IPGP reducing VBB thermal sensitivity by a factor of 12, and we aim at a factor of 20. It will be possible to improve the resolution consequently if thermal sensitivity is reduced. For Moon missions VBB developments, efforts have been made both on mechanical design and Displacement Capacitive Sensor (DCS). The mechanical part of VBB is an inverted pendulum; the

  17. Broad Band Polarimetry with the Soft Gamma-ray Detector on board Hitomi (ASTRO-H)

    NASA Astrophysics Data System (ADS)

    Mizuno, Tsunefumi

    2016-07-01

    X-ray and gamma-ray polarization can arise from synchrotron emission in ordered magnetic fields, photon propagation in extremely strong magnetic fields and anisotropic Compton scattering. Polarization measurement provides vital information (often inaccessible even with the current best imaging instruments) on magnetic field and accretion disk around astrophysical objects, hence is a powerful probe to investigate emission mechanism and geometries of the sources. The Soft Gamma-ray Detector (SGD) on board Hitomi (ASTRO-H) satellite is a highly-sensitive spectrometer in the 40-600 keV energy band. Since the SGD is a Si/CdTe Compton camera surrounded by a thick BGO shield, it also works as a very sensitive polarimeter in wide energy range. We have verified the SGD polarization measurement capability through extensive beam tests at a synchrotron facility SPring-8 in 2008 (Takeda et al. 2010) and 2015 (Katsuta et al. in preparation). In addition, we have examined possible sciences provided by the SGD polarimetry based on the expected performance (Coppi et al. 2014). In this contribution, we will present the SGD instrumentation, the latest beam test results and expected sciences provided by the polarization measurements. The results based on the initial observations will also be reported.

  18. A comparison between two permanent broad band ocean bottom seismometers in the western Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Frontera, T.; Deschamps, A.; Ugalde, A.; Jara, J. A.; Hello, Y.; Goula, X.; Olivera, C.

    2009-04-01

    The aim of this work is to compare two permanent broad band ocean bottom seismometers (OBS) in terms of noise conditions by taking to account their similar instrumentation types, but their very different site characteristics. Both OBS stations have Güralp CMG-3T three component broad band sensors and differential pressure gauges (DPG). The first sensor operates since August 2005 under the framework of a research project that aims to improve the knowledge of the seismicity and seismic risk in the Tarragona region (north eastern Spain). This pioneering project in Spain is being carried out by the Institut Geològic de Catalunya (IGC) and the Observatori de l'Ebre, in collaboration with the Spanish oil company Repsol Investigaciones Petrolíferas, and is being financed by the Ministerio de Educación y Ciencia (CASABLANCA REN2003-06577), FEDER funding, the IGC and the Institut Cartogràfic de Catalunya. The OBS is installed inside the security perimeter of the Casablanca oil platform, which is located 40 km offshore Tarragona. The sensors are submerged at about 400 m to the SW of the oil platform at about 150 m in depth. Data are digitized on-site and are transmitted through a submarine cable to the platform, where they are recorded. In July 2007 some improvements were made: i) the OBS was completely buried and the DPG was moved about 10 m away from the OBS; and ii) via satellite signal transmission was implemented, which allowed to have continuous and real time data in Barcelona so that the OBS could be integrated into the Catalan Seismic Network. The second seismometer operates in the frame of the Antares neutrino telescope project developed in Liguria Sea. Geoazur is carrying out the project of deployment of a broad band seismological instrument in the aim of developing the permanent sea floor observation knowledge necessary to characterize Ligurian Sea seismicity and seismic risk along French Riviera coast (SE France). The operation was facilitated by the

  19. Integrable optical-fiber source of polarization-entangled photon pairs in the telecom band

    SciTech Connect

    Li Xiaoying; Liang Chuang; Fook Lee, Kim; Chen, Jun; Voss, Paul L.; Kumar, Prem

    2006-05-15

    We demonstrate an optical-fiber-based source of polarization-entangled photon pairs with improved quality and efficiency, which has been integrated with off-the-shelf telecom components and is, therefore, well suited for quantum communication applications in the 1550-nm telecom band. Polarization entanglement is produced by simultaneously pumping a loop of standard dispersion-shifted fiber with two orthogonally polarized pump pulses, one propagating in the clockwise and the other in the counterclockwise direction. We characterize this source by investigating two-photon interference between the generated signal-idler photon pairs under various conditions. The experimental parameters are carefully optimized to maximize the generated photon-pair correlation and to minimize contamination of the entangled photon pairs from extraneously scattered background photons that are produced by the pump pulses for two reasons: (i) spontaneous Raman scattering causes uncorrelated photons to be emitted in the signal and idler bands and (ii) broadening of the pump-pulse spectrum due to self-phase modulation causes pump photons to leak into the signal and idler bands. We obtain two-photon interference with visibility >90% without subtracting counts caused by the background photons (only dark counts of the detectors are subtracted), when the mean photon number in the signal (idler) channel is about 0.02/pulse, while no interference is observed in direct detection of either the signal or idler photons.

  20. The solar wind control of Jupiter's broad-band kilometric radio emission

    NASA Technical Reports Server (NTRS)

    Barrow, C. H.; Leblanc, Y.; Desch, M. D.

    1988-01-01

    Observations of the solar wind close to Jupiter are compared with the broad-band kilometric radio emission (bKOM), using data recorded by Voyager 1 and Voyager 2 during 1979. The lower bKOM frequencies, less than about 300 kHz, are found to correlate with the solar wind density and pressure and with the interplanetary magnetic field (IMF) magnitude during periods when there is a well-defined magnetic sector structure. The results suggest that lower frequency bKOM events are most likely to occur after a sector boundary has passed Jupiter during the period when the solar wind density and the IMF magnitude are increasing towards the sector center. The average bKOM energy per Jovian rotation tends to have lower values soon after the sector center has passed. Higher-frequency/higher-energy bKOM emission may be contaminated by hectometric emission (HOM) and differently correlated with solar activity. The solar wind control may also be obscured by some stronger control. It is suggested that electron density fluctuations in the Io torus, where the source is believed to be located, may be responsible for variations in the beaming and hence variations in the observed emission.

  1. Development of polyurethane/epoxy interpenetrating networks as broad band damping materials

    SciTech Connect

    Coughlin, C.S.; Samuels, M.Q.; Capps, R.N.

    1993-12-31

    Several series of polyurethane/epoxy IPN`s were prepared for possible use as broad band damping materials. The polyurethane component contained a poly(caprolactone) soft segment and a carbodiimide-modified MDI hard segment chain extended with trimethylolpropane. The epoxy component was a standard bisphenol-A resin cured with either a BCl{sub 3}-amine complex or BF{sub 3}-etherate. All IPN`s showed apparent true IPN behavior with no or very small scale phase separation. Dynamic mechanical data revealed that the systems prepared with BCl{sub 3} as the epoxy curative are too stiff with a Tg too high for the damping application. BF{sub 3}-etherate cured IPN`s showed good damping ability but the epoxy component was not fully incorporated and could be leached out yielding an unstable system. Ongoing work is focusing on incorporating a more flexible epoxy component and/or a plasticizer to increase damping and lower the Tg.

  2. Broad band X-ray telescope (BBXRT) displacement monitor system (DMS) testing and calibration

    NASA Technical Reports Server (NTRS)

    Hagopian, John G.; Northcutt, William

    1989-01-01

    NASA's shuttle-borne Broad Band X-Ray Telescope (BBXRT) consists of two glancing incidence imaging mirror assemblies mounted on an optical bench which is bolted to the primary structure of the instrument. The X-ray detectors are located in the focal plane of the mirror assemblies approximately 3.5 meters away. It is desirable to monitor the relative alignment of these components throughout ground testing, and to determine the magnitude of launch or thermally induced perturbations to the alignment during flight. The Displacement Monitor System (DMS) was designed to accomplish this task. This paper describes the design of the DMS, the development and optimization of the DMS calibration facility, and the characterization of the system. The characterization of the DMS includes environmental qualification, displacement vs output calibration over the operating temperature range, a detailed error analysis, and the generation of a calibration polynomial which utilizes DMS detector output and thermocouple data to optimize system performance. The DMS accuracy exceeded the requirements of a 15 arc second limit of error, and passed the stringent environmental tests. As such, the DMS is one of the first flight qualified displacement monitor systems with this accuracy to be flown in space.

  3. A Broad-Band Phase-Contrast Wave-Front Sensor

    NASA Technical Reports Server (NTRS)

    Bloemhof, Eric; Wallace, J. Kent

    2005-01-01

    A broadband phase-contrast wave-front sensor has been proposed as a real-time wave-front sensor in an adaptive-optics system. The proposed sensor would offer an alternative to the Shack-Hartmann wave-front sensors now used in high-order adaptive-optics systems of some astronomical telescopes. Broadband sensing gives higher sensitivity than does narrow-band sensing, and it appears that for a given bandwidth, the sensitivity of the proposed phase-contrast sensor could exceed that of a Shack-Hartmann sensor. Relative to a Shack-Hartmann sensor, the proposed sensor may be optically and mechanically simpler. As described below, an important element of the principle of operation of a phase-contrast wave-front sensor is the imposition of a 90deg phase shift between diffracted and undiffracted parts of the same light beam. In the proposed sensor, this phase shift would be obtained by utilizing the intrinsic 90 phase shift between the transmitted and reflected beams in an ideal (thin, symmetric) beam splitter. This phase shift can be characterized as achromatic or broadband because it is 90deg at every wavelength over a broad wavelength range.

  4. Very-broad-band seismology in Northern Africa under the M EDN ET project

    NASA Astrophysics Data System (ADS)

    Giardini, D.; Boschi, E.; Mazza, S.; Morelli, A.; Sari, D. Ben; Najid, D.; Benhallou, H.; Bezzeghoud, M.; Trabelsi, H.; Hfaidh, M.; Kebeasy, R. M.; Ibrahim, E. M.

    1992-08-01

    The Mediterranean and North African regions are characterized by strong seismicity and active, complex tectonics, which are often poorly monitored and understood owing to a lack of high-quality seismic recordings. To increase the instrumental coverage in the Mediterranean region, the Istituto Nazionale di Geofisica began in 1987 the deployment in this area of a network of 12 Very-Broad-Band seismic stations, termed M EDN ET. Motivated both by research interests and by considerations on seismic hazard monitoring, M EDN ET has been designed following the highest technical standards. Its geometry will provide a homogeneous coverage of the Mediterranean and North African area, with installations in most countries and an average spacing between stations of 800-1000 km; the network should be completed by 1992. Three stations are now installed in North African countries (Morocco, Tunisia and Egypt) and one is in preparation in Algeria. Great care is being taken in choosing isolated, underground sites for the installations, to ensure optimal signal-to-noise ratios at all frequencies. The noise level at these stations overlaps, and at low frequencies is sometimes better than, the current Low Noise Model. Data are recorded locally and forwarded to the M EDN ET Data Centre in Rome for collection and distribution

  5. MSFC Reviews Data from the Broad Band X-Ray Telescope (BBXRT) During STS-35 Mission

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The primary objective of the STS-35 mission was round the clock observation of the celestial sphere in ultraviolet and X-Ray astronomy with the Astro-1 observatory which consisted of four telescopes: the Hopkins Ultraviolet Telescope (HUT); the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE); the Ultraviolet Imaging Telescope (UIT); and the Broad Band X-Ray Telescope (BBXRT). The Huntsville Operations Support Center (HOSC) Spacelab Payload Operations Control Center (SL POCC) at the Marshall Space Flight Center (MSFC) was the air/ground communication channel used between the astronauts and ground control teams during the Spacelab missions. Teams of controllers and researchers directed on-orbit science operations, sent commands to the spacecraft, received data from experiments aboard the Space Shuttle, adjusted mission schedules to take advantage of unexpected science opportunities or unexpected results, and worked with crew members to resolve problems with their experiments. Due to loss of data used for pointing and operating the ultraviolet telescopes, MSFC ground teams were forced to aim the telescopes with fine tuning by the flight crew. This photo captures the activity of BBKRT data review in the Science Operations Area during the mission.

  6. Absolute radical densities in etching plasmas determined by broad-band UV absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Booth, Jean-Paul; Cunge, Gilles; Neuilly, François; Sadeghi, Nader

    1998-08-01

    Broad-band UV absorption spectroscopy was used to determine radical densities in reactive gas plasmas generated in a 13.56 MHz capacitively coupled parallel plate reactor. Five radical species were detected: 0963-0252/7/3/021/img1, CF, AlF, 0963-0252/7/3/021/img2 and 0963-0252/7/3/021/img3. Absolute (line-integrated) 0963-0252/7/3/021/img1 densities were determined in 0963-0252/7/3/021/img5 and 0963-0252/7/3/021/img6 plasmas, as were the 0963-0252/7/3/021/img1 vibrational and rotational temperatures in the latter case. In 0963-0252/7/3/021/img5 plasmas the CF radical was also detected, along with the etch products AlF (from the Al powered electrode) and 0963-0252/7/3/021/img2 (when an Si substrate was present). The fraction that 0963-0252/7/3/021/img2 comprises of the total etch products was estimated. Finally, the 0963-0252/7/3/021/img3 dimer was detected in an 0963-0252/7/3/021/img12 plasma in the presence of an Si substrate. This simple technique allows absolute concentrations of many key reactive species to be determined in reactive plasmas, without the need to analyse the complex rotational spectra of these polyatomic molecules.

  7. Broad band tunable quantum cascade lasers for stand-off detection of explosives

    NASA Astrophysics Data System (ADS)

    Hinkov, Borislav; Fuchs, Frank; Kaster, Jan M.; Yang, Quankui; Bronner, Wolfgang; Aidam, Rolf; Köhler, Klaus

    2009-09-01

    We present experimental results on a Quantum cascade laser (QC laser) embedded in an external cavity. These results were obtained with a broadly tunable laser exceeding 80 cm-1 covering a characteristic absorption band of trinitrotoluene (TNT). By combining the laser source with a high performance IR imager a stand-off detection setup based on multi- spectral MIR backscattering spectroscopy has been realized. With this technique TNT surface-contaminations of as low as 10 μg/cm2 could be detected on surfaces such as an aluminum-sheet and standard car paint. The contrast of the detection technique depends on the reflectance of the surface. A surface leading to mirror-like reflectance of the IR laser radiation leads to absorbance-like signatures of the TNT contamination, while surfaces showing high absorbance of the laser light may induce a contrast-reversal in the resulting image of the TNT coverage. This effect can be explained by a theoretical model for thin film coated substrates taking into account differences in the reflectance. Limitations and further work needed to explore the full potential of the IR backscattering technique are also discussed.

  8. Multiplexed Volume Bragg Gratings in Narrowand Broad-band Spectral Systems: Analysis and Application

    NASA Astrophysics Data System (ADS)

    Ingersoll, Gregory B.

    Volume Bragg gratings (VBGs) are important holographic optical elements in many spectral systems. Using multiple volume gratings, whether multiplexed or arranged sequentially, provides advantages to many types of systems in overall efficiency, dispersion performance, flexibility of design, etc. However, the use of multiple gratings---particularly when the gratings are multiplexed in a single holographic optical element (HOE)---is subject to inter-grating coupling effects that ultimately limit system performance. Analyzing these coupling effects requires a more complex mathematical model than the straightforward analysis of a single volume grating. We present a matrix-based algorithm for determining diffraction efficiencies of significant coupled waves in these multiplexed grating holographic optical elements (HOEs). Several carefully constructed experiments with spectrally multiplexed gratings in dichromated gelatin verify our conclusions. Applications of this theory to broad- and narrow-band systems are explored in detailed simulations. Broadband systems include spectrum splitters for diverse-bandgap photovoltaic (PV) cells. Volume Bragg gratings can serve as effective spectrum splitters, but the inherent dispersion of a VBG can be detrimental given a broad-spectrum input. The performance of a holographic spectrum splitter element can be improved by utilizing multiple volume gratings, each operating in a slightly different spectral band. However, care must be taken to avoid inter-grating coupling effects that limit ultimate performance. We explore broadband multi-grating holographic optical elements (HOEs) in sandwiched arrangements where individual single-grating HOEs are placed in series, and in multiplexed arrangements where multiple gratings are recorded in a single HOE. Particle swarm optimization (PSO) is used to tailor these systems to the solar spectrum taking into account both efficiency and dispersion. Both multiplexed and sandwiched two-grating systems

  9. Broad-band spectrophotometry of HAT-P-32 b: Search for a scattering signature in the planetary spectrum

    NASA Astrophysics Data System (ADS)

    Mallonn, M.; Bernt, I.; Herrero, E.; Hoyer, S.; Kirk, J.; Wheatley, P. J.; Seeliger, M.; Mackebrandt, F.; von Essen, C.; Strassmeier, K. G.; Granzer, T.; Künstler, A.; Dhillon, V. S.; Marsh, T. R.; Gaitan, J.

    2016-08-01

    Multi-colour broad-band transit observations offer the opportunity to characterise the atmosphere of an extrasolar planet with small- to medium-sized telescopes. One of the most favourable targets is the hot Jupiter HAT-P-32 b. We combined 21 new transit observations of this planet with 36 previously published light curves for a homogeneous analysis of the broad-band transmission spectrum from the Sloan u' band to the Sloan z' band. Our results rule out cloud-free planetary atmosphere models of solar metallicity. Furthermore, a discrepancy at reddest wavelengths to previously published results makes a recent tentative detection of a scattering feature less likely. Instead, the available spectral measurements of HAT-P-32 b favour a completely flat spectrum from the near-UV to the near-IR. A plausible interpretation is a thick cloud cover at high altitudes.

  10. Photonic band gap of three dimensional magnetized photonic crystal with Voigt configuration

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun; Li, Bing-Xiang

    2013-08-01

    In this paper, the properties of two types of three-dimensional magnetized plasma photonic crystals (MPPCs) composed of homogeneous magnetized plasma and dielectric with simple-cubic lattices are theoretically studied by a modified plane wave expansion (PWE) method, as the magneto-optical Voigt effects of magnetized plasma are considered. The equations for type-1 structures with simple-cubic lattices (dielectric spheres immersed in magnetized plasma background), are theoretically deduced. The influences of dielectric constant of dielectric, plasma collision frequency, filling factor, the external magnetic field and plasma frequency on the properties of photonic band gaps (PBGs) for both types of MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. The characteristics of flatbands regions are also discussed. From the numerical results, it has been shown that the PBGs of both types of three-dimensional MPPCs can be manipulated by plasma frequency, filling factor, the external magnetic field and the relative dielectric constant of dielectric, respectively. However, the plasma collision frequency has no effects on the PBGs for two types of three-dimensional MPPCs. The locations of flatbands regions can not be tuned by any parameters except for plasma frequency and the external magnetic field.

  11. Simultaneous existence of phononic and photonic band gaps in periodic crystal slabs.

    PubMed

    Pennec, Y; Djafari Rouhani, B; El Boudouti, E H; Li, C; El Hassouani, Y; Vasseur, J O; Papanikolaou, N; Benchabane, S; Laude, V; Martinez, A

    2010-06-21

    We discuss the simultaneous existence of phononic and photonic band gaps in a periodic array of holes drilled in a Si membrane. We investigate in detail both the centered square lattice and the boron nitride (BN) lattice with two atoms per unit cell which include the simple square, triangular and honeycomb lattices as particular cases. We show that complete phononic and photonic band gaps can be obtained from the honeycomb lattice as well as BN lattices close to honeycomb. Otherwise, all investigated structures present the possibility of a complete phononic gap together with a photonic band gap of a given symmetry, odd or even, depending on the geometrical parameters. PMID:20588565

  12. A comparison between two permanent broad band ocean bottom seismometers in the western Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Frontera, T.; Deschamps, A.; Ugalde, A.; Jara, J. A.; Hello, Y.; Goula, X.; Olivera, C.

    2009-04-01

    The aim of this work is to compare two permanent broad band ocean bottom seismometers (OBS) in terms of noise conditions by taking to account their similar instrumentation types, but their very different site characteristics. Both OBS stations have Güralp CMG-3T three component broad band sensors and differential pressure gauges (DPG). The first sensor operates since August 2005 under the framework of a research project that aims to improve the knowledge of the seismicity and seismic risk in the Tarragona region (north eastern Spain). This pioneering project in Spain is being carried out by the Institut Geològic de Catalunya (IGC) and the Observatori de l'Ebre, in collaboration with the Spanish oil company Repsol Investigaciones Petrolíferas, and is being financed by the Ministerio de Educación y Ciencia (CASABLANCA REN2003-06577), FEDER funding, the IGC and the Institut Cartogràfic de Catalunya. The OBS is installed inside the security perimeter of the Casablanca oil platform, which is located 40 km offshore Tarragona. The sensors are submerged at about 400 m to the SW of the oil platform at about 150 m in depth. Data are digitized on-site and are transmitted through a submarine cable to the platform, where they are recorded. In July 2007 some improvements were made: i) the OBS was completely buried and the DPG was moved about 10 m away from the OBS; and ii) via satellite signal transmission was implemented, which allowed to have continuous and real time data in Barcelona so that the OBS could be integrated into the Catalan Seismic Network. The second seismometer operates in the frame of the Antares neutrino telescope project developed in Liguria Sea. Geoazur is carrying out the project of deployment of a broad band seismological instrument in the aim of developing the permanent sea floor observation knowledge necessary to characterize Ligurian Sea seismicity and seismic risk along French Riviera coast (SE France). The operation was facilitated by the

  13. X-Ray Emitting GHz-Peaked Spectrum Galaxies: Testing a Dynamical-Radiative Model with Broad-Band Spectra

    SciTech Connect

    Ostorero, L.; Moderski, R.; Stawarz, L.; Diaferio, A.; Kowalska, I.; Cheung, C.C.; Kataoka, J.; Begelman, M.C.; Wagner, S.J.; /Heidelberg Observ.

    2010-06-07

    In a dynamical-radiative model we recently developed to describe the physics of compact, GHz-Peaked-Spectrum (GPS) sources, the relativistic jets propagate across the inner, kpc-sized region of the host galaxy, while the electron population of the expanding lobes evolves and emits synchrotron and inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the expanding lobes, and photoionized by the active nucleus, are responsible for the radio spectral turnover through free-free absorption (FFA) of the synchrotron photons. The model provides a description of the evolution of the GPS spectral energy distribution (SED) with the source expansion, predicting significant and complex high-energy emission, from the X-ray to the {gamma}-ray frequency domain. Here, we test this model with the broad-band SEDs of a sample of eleven X-ray emitting GPS galaxies with Compact-Symmetric-Object (CSO) morphology, and show that: (i) the shape of the radio continuum at frequencies lower than the spectral turnover is indeed well accounted for by the FFA mechanism; (ii) the observed X-ray spectra can be interpreted as non-thermal radiation produced via IC scattering of the local radiation fields off the lobe particles, providing a viable alternative to the thermal, accretion-disk dominated scenario. We also show that the relation between the hydrogen column densities derived from the X-ray (N{sub H}) and radio (N{sub HI}) data of the sources is suggestive of a positive correlation, which, if confirmed by future observations, would provide further support to our scenario of high-energy emitting lobes.

  14. The broad-band fractal nature of heterogeneity in the upper crust from petrophysical logs

    NASA Astrophysics Data System (ADS)

    Dolan, Sean; Bean, Christopher; Riollet, Bruno

    1998-03-01

    In situ measurements of petrophysical properties of the upper crust from wire-line logs provide a direct means of assessing fluctuations in these properties with depth, and thus allow for the statistical characterization of crustal heterogeneity. Wire-line logs from a cluster of nine boreholes (1000-1500m deep) have been analysed using four different techniques: autocorrelation, semi-variogram, rescaled range and power spectra. Six of the boreholes are vertical, the remainder inclined. All penetrate clastic and pyroclastic rock. The analysis techniques have been tested on synthetic data, for which we have precise control on the scaling, in order to assess their robustness. The results, for the borehole data, show broad-band fractal scaling with a fractal dimension of 1.62 to 1.97 (autocorrelation), 1.59 to 1.79 (rescaled range) and 1.61 to 2.0 (power spectra). The use of different techniques to estimate the fractal dimension provides an excellent constraint on the results. Furthermore, it allows us to determine which model for crustal heterogeneity best describes the data: a `band-limited' von Kármán function or `unbounded' fractal scaling. In order to test the possible anisotropy in the scaling parameters, the horizontal scaling properties for this area have been calculated by correlation-spectra analysis of neighbouring wells. This suggests that upper-crustal correlation lengths are of the order of kilometres and anisotropic, being over four times greater in the horizontal direction. The origins of the observed power-law scaling are complex. Analysis of long-term correlations between logs and televiewer data points towards the influence of fracture porosity within the pyroclastics. But a fractal distribution of pore spaces within the clastics also controls the log fluctuations. Separating the logs into clastic and pyroclastic subsets reveals slight differences in fractal scaling, as determined by autocorrelation and semi-variogram. These differences are

  15. Azimuthal anisotropy beneath southern Africa from very broad-band surface-wave dispersion measurements

    NASA Astrophysics Data System (ADS)

    Adam, Joanne M.-C.; Lebedev, Sergei

    2012-10-01

    Seismic anisotropy within the lithosphere of cratons preserves an important record of their ancient assembly. In southern Africa, anisotropy across the Archean Kaapvaal Craton and Limpopo Belt has been detected previously by observations of SKS-wave splitting. Because SKS-splitting measurements lack vertical resolution, however, the depth distribution of anisotropy has remained uncertain. End-member interpretations invoked the dominance of either anisotropy in the lithosphere (due to the fabric formed by deformation in Archean or Palaeoproterozoic orogenies) or that in the asthenosphere (due to the fabric formed by the recent plate motion), each with significant geodynamic implications. To determine the distribution of anisotropy with depth, we measured phase velocities of seismic surface waves between stations of the Southern African Seismic Experiment. We applied two complementary measurement approaches, very broad-band cross-correlation and multimode waveform inversion. Robust, Rayleigh- and Love-wave dispersion curves were derived for four different subregions of the Archean southern Africa in a period range from 5 s to 250-400 s (Rayleigh) and 5 s to 100-250 s (Love), depending on the region. Rayleigh-wave anisotropy was determined in each region at periods from 5 s to 150-200 s, sampling from the upper crust down to the asthenosphere. The jackknife method was used to estimate uncertainties, and the F-test to verify the statistical significance of anisotropy. We detected strong anisotropy with a N-S fast-propagation azimuth in the upper crust of the Limpopo Belt. We attribute it to aligned cracks, formed by the regional, E-W extensional stress associated with the southward propagation of the East African Rift. Our results show that it is possible to estimate regional stress from short-period, surface wave anisotropy, measured in this study using broad-band array recordings of teleseismic surface waves. Rayleigh-wave anisotropy at 70-120 s periods shows that

  16. X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment

    SciTech Connect

    Marsh, Roark A.; Shapiro, Michael A.; Temkin, Richard J.; Dolgashev, Valery A.; Laurent, Lisa L.; Lewandowski, James R.; Yeremian, A.Dian; Tantawi, Sami G.; /SLAC

    2012-06-11

    In order to understand the performance of photonic band-gap (PBG) structures under realistic high gradient, high power, high repetition rate operation, a PBG accelerator structure was designed and tested at X band (11.424 GHz). The structure consisted of a single test cell with matching cells before and after the structure. The design followed principles previously established in testing a series of conventional pillbox structures. The PBG structure was tested at an accelerating gradient of 65 MV/m yielding a breakdown rate of two breakdowns per hour at 60 Hz. An accelerating gradient above 110 MV/m was demonstrated at a higher breakdown rate. Significant pulsed heating occurred on the surface of the inner rods of the PBG structure, with a temperature rise of 85 K estimated when operating in 100 ns pulses at a gradient of 100 MV/m and a surface magnetic field of 890 kA/m. A temperature rise of up to 250 K was estimated for some shots. The iris surfaces, the location of peak electric field, surprisingly had no damage, but the inner rods, the location of the peak magnetic fields and a large temperature rise, had significant damage. Breakdown in accelerator structures is generally understood in terms of electric field effects. These PBG structure results highlight the unexpected role of magnetic fields in breakdown. The hypothesis is presented that the moderate level electric field on the inner rods, about 14 MV/m, is enhanced at small tips and projections caused by pulsed heating, leading to breakdown. Future PBG structures should be built to minimize pulsed surface heating and temperature rise.

  17. Model atmospheres broad-band colors, bolometric corrections and temperature calibrations for O - M stars

    NASA Astrophysics Data System (ADS)

    Bessell, M. S.; Castelli, F.; Plez, B.

    1998-05-01

    Broad band colors and bolometric corrections in the Johnson-Cousins-Glass system (Bessell, 1990; Bessell & Brett, 1988) have been computed from synthetic spectra from new model atmospheres of Kurucz (1995a), Castelli (1997), Plez, Brett & Nordlund (1992), Plez (1995-97), and Brett (1995a,b). These atmospheres are representative of larger grids that are currently being completed. We discuss differences between the different grids and compare theoretical color-temperature relations and the fundamental color temperature relations derived from: (a) the infrared-flux method (IRFM) for A-K stars (Blackwell & Lynas-Gray 1994; Alonso et al. 1996) and M dwarfs (Tsuji et al. 1996a); (b) lunar occultations (Ridgway et al. 1980) and (c) Michelson interferometry (Di Benedetto & Rabbia 1987; Dyck et al. 1996; Perrin et al. 1997) for K-M giants, and (d) eclipsing binaries for M dwarfs. We also compare color - color relations and color - bolometric correction relations and find good agreement except for a few colors. The more realistic fluxes and spectra of the new model grids should enable accurate population synthesis models to be derived and permit the ready calibration of non-standard photometric passbands. As well, the theoretical bolometric corrections and temperature - color relations will permit reliable transformation from observed color magnitude diagrams to theoretical HR diagrams. Tables 1-6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

  18. Precision Column CO2 Measurement from Space Using Broad Band LIDAR

    NASA Technical Reports Server (NTRS)

    Heaps, William S.

    2009-01-01

    In order to better understand the budget of carbon dioxide in the Earth's atmosphere it is necessary to develop a global high precision understanding of the carbon dioxide column. To uncover the missing sink" that is responsible for the large discrepancies in the budget as we presently understand it, calculation has indicated that measurement accuracy of 1 ppm is necessary. Because typical column average CO2 has now reached 380 ppm this represents a precision on the order of 0.25% for these column measurements. No species has ever been measured from space at such a precision. In recognition of the importance of understanding the CO2 budget to evaluate its impact on global warming the National Research Council in its decadal survey report to NASA recommended planning for a laser based total CO2 mapping mission in the near future. The extreme measurement accuracy requirements on this mission places very strong constraints on the laser system used for the measurement. This work presents an overview of the characteristics necessary in a laser system used to make this measurement. Consideration is given to the temperature dependence, pressure broadening, and pressure shift of the CO2 lines themselves and how these impact the laser system characteristics. We are examining the possibility of making precise measurements of atmospheric carbon dioxide using a broad band source of radiation. This means that many of the difficulties in wavelength control can be treated in the detector portion of the system rather than the laser source. It also greatly reduces the number of individual lasers required to make a measurement. Simplifications such as these are extremely desirable for systems designed to operate from space.

  19. The use of broad-band prior covariance for inverse palaeoclimate estimation

    NASA Astrophysics Data System (ADS)

    Şerban, Delia Zemira; Jacobsen, Bo Holm

    2001-09-01

    The determination of ground surface temperature history (GSTH) from present borehole temperature defines an ill-posed inverse problem for which the required regularization must reflect the stochastic properties of both measurement noise and ground surface temperature. The timescales of interest in the study of climate changes range from a few decades to hundreds of thousands of years. This makes climate a very broad-banded process. This paper presents a multiple-scale stochastic prior model for GSTH, which overcomes several problems in previous commonly applied single-scale modes of regularization. The von Karmann power-law stochastic processes come out as special cases. Should other information warrant uneven prior variation bounds on different frequency intervals, the multiple-scale formulation can readily incorporate this. The practical computation of the prior covariances between past temperature node values is achieved through an elementary function space projection formulation. This projection approach is generally applicable for arbitrary base functions underlying the discretization. The superior robustness of this multiple-scale prior model is demonstrated by comparison to previously used single-scale models for the classic test case by Beck (1977) where the multiple-scale prior model allows simultaneous estimation of temperature history from decade scale to glaciation scale. Moreover, the function space projection method ensures that GSTH estimates are insensitive to discretization, provided that discretization is finer than the inherent resolution limit. A test on two very different experimental data sets confirms the merits of the proposed stochastic model. For maximum consistency between GSTH estimates across timescales, borehole depths scales and groups of investigators, we propose that a covariance function with a uniform variance of (5 K)2 per frequency decade be used as a standard prior for inverse ground surface temperature history problems.

  20. Broad Band Antireflection Coating on Zinc Sulphide Window for Shortwave infrared cum Night Vision System

    NASA Astrophysics Data System (ADS)

    Upadhyaya, A. S.; Bandyopadhyay, P. K.

    2012-11-01

    In state of art technology, integrated devices are widely used or their potential advantages. Common system reduces weight as well as total space covered by its various parts. In the state of art surveillance system integrated SWIR and night vision system used for more accurate identification of object. In this system a common optical window is used, which passes the radiation of both the regions, further both the spectral regions are separated in two channels. ZnS is a good choice for a common window, as it transmit both the region of interest, night vision (650 - 850 nm) as well as SWIR (0.9 - 1.7 μm). In this work a broad band anti reflection coating is developed on ZnS window to enhance the transmission. This seven layer coating is designed using flip flop design method. After getting the final design, some minor refinement is done, using simplex method. SiO2 and TiO2 coating material combination is used for this work. The coating is fabricated by physical vapour deposition process and the materials were evaporated by electron beam gun. Average transmission of both side coated substrate from 660 to 1700 nm is 95%. This coating also acts as contrast enhancement filter for night vision devices, as it reflect the region of 590 - 660 nm. Several trials have been conducted to check the coating repeatability, and it is observed that transmission variation in different trials is not very much and it is under the tolerance limit. The coating also passes environmental test for stability.

  1. The Low Band Observatory (LOBO): Expanding the VLA Low Frequency Commensal System for Continuous, Broad-band, sub-GHz Observations

    NASA Astrophysics Data System (ADS)

    Kassim, Namir E.; Clarke, Tracy E.; Helmboldt, Joseph F.; Peters, Wendy M.; Brisken, Walter; Hyman, Scott D.; Polisensky, Emil; Hicks, Brian

    2015-01-01

    The Naval Research Laboratory (NRL) and the National Radio Astronomy Observatory (NRAO) are currently commissioning the VLA Low Frequency Ionosphere and Transient Experiment (VLITE) on a subset of JVLA antennas at modest bandwidth. Its bounded scientific goals are to leverage thousands of JVLA on-sky hours per year for ionospheric and transient studies, and to demonstrate the practicality of a prime-focus commensal system on the JVLA. Here we explore the natural expansion of VLITE to a full-antenna, full-bandwidth Low Band Observatory (LOBO) that would follow naturally from a successful VLITE experience. The new Low Band JVLA receivers, coupled with the existing primary focus feeds, can access two frequency bands: 4 band (54 - 86 MHz) and P band (236-492 MHz). The 4 band feeds are newly designed and now undergoing testing. If they prove successful then they can be permanently mounted at the primary focus, unlike their narrow band predecessors. The combination of Low Band receivers and fixed, primary-focus feeds could provide continuous, broad-band data over two complimentary low-frequency bands. The system would also leverage the relatively large fields-of-view of ~10 degrees at 4 band, and ~2.5 degrees at P band, coupling an excellent survey capability with a natural advantage for serendipitous discoveries. We discuss the compelling science case that flows from LOBO's robust imaging and time domain capabilities coupled with thousands of hours of wide-field, JVLA observing time each year. We also touch on the possibility to incorporate Long Wavelength Array (LWA) stations as additional 'dishes' through the LOBO backend, to improve calibration and sensitivity in LOBO's 4 band.

  2. Low-energy broad-beam photon shielding data for constituents of concrete.

    PubMed

    Ogundare, Folorunso O; Ogundele, Samuel A; Akerele, Olumide O; Balogun, Fatai A

    2012-01-01

    The ability of concrete to attenuate ionizing radiation intensity is assessed using its linear or mass attenuation coefficient. In this work, the broad-beam linear and mass attenuation coefficients of different types of soils and cements used for making concrete were measured at different photon energies (60-1333 keV), nearly spanning the diagnostic photon energy range, using a NaI detector. The mass attenuation coefficients of cement decreased from 0.133 ± 0.002 at 60 keV to 0.047 ± 0.003 at 1332.5 keV. For soils, the mass attenuation coefficient of those collected from the beach was the highest, decreasing from 0.176 ± 0.003 cm²/g at 60 keV to 0.054 ± 0.001 cm²/g at 1332.5 keV. Land soils had the least value, decreasing from 0.124 ± 0.002 cm²/g at 60 keV to 0.044 ± 0.003 cm²/g at 1332.5 keV. Limestone had smaller mass attenuation coefficients than the cement produced using it. The implication of the above is that for making concrete, beach sand should be preferred as the sand component of the concrete. Models of the form μ(L) = A(E) exp[B(E)ρ] and μ(m) = αln(E)+β are proposed for fitting the linear attenuation coefficient and mass attenuation coefficient data, respectively. PMID:22402377

  3. Fabrication of 3-D Photonic Band Gap Crystals Via Colloidal Self-Assembly

    NASA Technical Reports Server (NTRS)

    Subramaniam, Girija; Blank, Shannon

    2005-01-01

    The behavior of photons in a Photonic Crystals, PCs, is like that of electrons in a semiconductor in that, it prohibits light propagation over a band of frequencies, called Photonic Band Gap, PBG. Photons cannot exist in these band gaps like the forbidden bands of electrons. Thus, PCs lend themselves as potential candidates for devices based on the gap phenomenon. The popular research on PCs stem from their ability to confine light with minimal losses. Large scale 3-D PCs with a PBG in the visible or near infra red region will make optical transistors and sharp bent optical fibers. Efforts are directed to use PCs for information processing and it is not long before we can have optical integrated circuits in the place of electronic ones.

  4. Investigation on the properties of omnidirectional photonic band gaps in two-dimensional plasma photonic crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Li, Bing-Xiang

    2016-01-01

    The properties of omnidirectional photonic band gaps (OBGs) in two-dimensional plasma photonic crystals (2D PPCs) are theoretically investigated by the modified plane wave expansion method. In the simulation, we consider the off-plane incident wave vector. The configuration of 2D PPCs is the triangular lattices filled with the nonmagnetized plasma cylinders in the homogeneous and isotropic dielectric background. The calculated results show that the proposed 2D PPCs possess a flatbands region and the OBGs. Compared with the OBGs in the conventional 2D dielectric-air PCs, it can be obtained more easily and enlarged in the 2D PPCs with a similar structure. The effects of configurational parameters of the PPCs on the OBGs also are studied. The simulated results demonstrate that the locations of OBGs can be tuned easily by manipulating those parameters except for changing plasma collision frequency. The achieved OBGs can be enlarged by optimizations. The OBGs of two novel configurations of PPCs with different cross sections are computed for a comparison. Both configurations have the advantages of obtaining the larger OBGs compared with the conventional configuration, since the symmetry of 2D PPCs is broken by different sizes of periodically inserted plasma cylinders or connected by the embedded plasma cylinders with thin veins. The analysis of the results shows that the bandwidths of OBGs can be tuned by changing geometric and physical parameters of such two PPCs structures. The theoretical results may open a new scope for designing the omnidirectional reflectors or mirrors based on the 2D PPCs.

  5. Field demonstration of X-band photonic antenna remoting in the Deep Space Network

    NASA Technical Reports Server (NTRS)

    Yao, X. S.; Lutes, G.; Logan, R. T., Jr.; Maleki, L.

    1994-01-01

    We designed a photonic link for antenna remoting based on our integrated system analysis. With this 12-km link, we successfully demonstrated photonic antenna-remoting capability at X-band (8.4 GHz) at one of NASA's Deep Space Stations while tracking the Magellan spacecraft.

  6. Measurement of the Zak phase of photonic bands through the interface states of a metasurface/photonic crystal

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Xiao, Meng; Liu, Hui; Zhu, Shining; Chan, C. T.

    2016-01-01

    The Zak phase labels the topological property of one-dimensional Bloch bands. Here we propose a scheme and experimentally measure the Zak phase in a photonic system. The Zak phase of a bulk band is related to the topological properties of the two band gaps sandwiching this band, which in turn can be inferred from the existence or absence of an interface state. Using a reflection spectrum measurement, we determined the existence of interface states in the gaps and then obtained the Zak phases. The knowledge of Zak phases can also help us predict the existence of interface states between a metasurface and a photonic crystal. By manipulating the property of the metasurface, we can further tune the excitation frequency and the polarization of the interface state.

  7. Generation of narrow-band hyperentangled nondegenerate paired photons.

    PubMed

    Yan, Hui; Zhang, Shanchao; Chen, J F; Loy, M M T; Wong, G K L; Du, Shengwang

    2011-01-21

    We report the generation of nondegenerate narrow-bandwidth paired photons with time-frequency and polarization entanglements from laser cooled atoms. We observe the two-photon interference caused by Rabi splitting with a coherence time of about 30 ns and a visibility of 81.8% which verifies the time-frequency entanglement of the paired photons. The polarization entanglement is confirmed by polarization correlation measurements which exhibit a visibility of 89.5% and characterized by quantum-state tomography with a fidelity of 90.8%. Taking into account the transmission losses and duty cycle, we estimate that the system generates hyperentangled paired photons into opposing single-mode fibers at a rate of 320 pairs per second. PMID:21405274

  8. Generation of Narrow-Band Hyperentangled Nondegenerate Paired Photons

    NASA Astrophysics Data System (ADS)

    Yan, Hui; Zhang, Shanchao; Chen, J. F.; Loy, M. M. T.; Wong, G. K. L.; Du, Shengwang

    2011-01-01

    We report the generation of nondegenerate narrow-bandwidth paired photons with time-frequency and polarization entanglements from laser cooled atoms. We observe the two-photon interference caused by Rabi splitting with a coherence time of about 30 ns and a visibility of 81.8% which verifies the time-frequency entanglement of the paired photons. The polarization entanglement is confirmed by polarization correlation measurements which exhibit a visibility of 89.5% and characterized by quantum-state tomography with a fidelity of 90.8%. Taking into account the transmission losses and duty cycle, we estimate that the system generates hyperentangled paired photons into opposing single-mode fibers at a rate of 320 pairs per second.

  9. 0.8-5.2GHz Broad-Band SiGe-MMIC Quadrature Mixer for Software Defined Radio Receiver

    NASA Astrophysics Data System (ADS)

    Murakami, Keishi; Suematsu, Noriharu; Tsutsumi, Koji; Kanazawa, Gakushi; Sekine, Tomotsugu; Kubo, Hiroshi; Isota, Yoji

    For the next generation wireless terminals used in the software defined radio (SDR), multi-band / multi-mode transceivers and their MMIC are required which cover the wide RF frequency range from several hundreds MHz up to several GHz. In this paper, 0.8-5.2GHz broad-band SiGe-MMIC quadrature mixer (Q-MIX) for multi-band / multi-mode direct conversion receiver has been developed. By using a static type frequency divider as a 90 degrees local (LO) power divider, measured error vector magnitude (EVM) of less than 3.1% can be achieved in the cases of 0.8/2.1GHz W-CDMA and 5.2GHz wireless Local Area Network (LAN) (IEEE 802.11a) reception. This Q-MIX also shows broad-band characteristic for base-band signal and is applicable for 4G cellular. By using fabricated Q-MIX, a multi-band / multi-mode (1.9GHz (3rd generation cellular (W-CDMA)) / 5.2GHz (4th generation cellular (Multi-Carrier (MC)-CDMA))) receiver has been developed and it has firstly demonstrated the successful reception of motion picture via W-CDMA and MC-CDMA.

  10. The Broad-Band Seismic Noise Wavefield at the Larderello-Travale Geothermal Field (Italy)

    NASA Astrophysics Data System (ADS)

    Zupo, M.; Saccorotti, G.; Piccinini, D.

    2013-12-01

    Cross-correlation of ambient noise wave-field between a pair of receivers (NCF), provides an estimate of the Green's Function between the two sites, thus allowing extraction of the associated group velocity dispersion curve. This is valid under the assumption that noise sources and/or scatterers are isotropically distributed and uncorrelated each other. These conditions are usually met once the cross-correlations are averaged over long time intervals. At frequencies lower than 1 Hz, ambient noise wavefield is essentially composed by surface waves that are mostly associated with oceanic sources; as a consequence, the noise wavefield may exhibit marked directional properties over short (day) to intermediate (weeks) time scales. A detailed assessment of the nature and duration of these sources is therefore required in order to define the optimal conditions for retrieving the Green's functions from NCF analysis. This study presents ambient noise analysis for the Larderello-Travale Geothermal Field (Italy). We use data collected by a temporary seismic array consisting of 20 broad-band instruments, with station spacing ranging from 6 to 50 Km. Below 1 Hz, the most energetic sources are those associated with both primary and secondary microseisms, with dominant spectral peaks spanning the 0.05-0.5 Hz frequency range. Focusing on the secondary microseism sources (f > 0.1 Hz), we test the validity of the isotropic-wavefield assumption by determining the kinematic properties of the wavefield using frequency-domain beamforming. For the May-November 2012 time span, our results show that the most energetic and persistent wavefield components propagate from WNW (Gulf of Marseille and Genova) and SW (Sardinia channel). In the late part of the observation period, additional wavefield components are observed to propagate from the NE-SE azimuthal range, corresponding to sources located throughout the Adriatic sea. This suggests that the conditions for the application of the NCF

  11. Reducing magnetic field induced noise in broad-band seismic recordings

    NASA Astrophysics Data System (ADS)

    Forbriger, Thomas

    2007-04-01

    Seismic broad-band sensors are known to be sensitive to the magnetic field. Magnetic storms and man-made disturbances of the magnetic field can produce significant noise in seismic recordings. I show that variations in the magnetic field translate directly into apparent acceleration of the seismic sensor within the period range from 60 to 1200s for all leaf-spring sensors under investigation. For a Streckeisen STS-1V this is shown even for periods down to 1s. The sensitivity is quantified in magnitude and direction. Both are quite stable over many time windows and signal periods. The sensitivities obtained by linear regression of the acceleration signal on magnetic field recordings during a magnetic storm can effectively be applied to reduce noise in seismic signals. The sensitivity varies in magnitude from sensor to sensor but all are in the range from 0.05 to 1.2ms-2T-1. Seismograms from sensors at Black Forest Observatory (BFO) and stations of the German Regional Seismic Network were investigated. Although these are mainly equipped with leaf-spring sensors, the problem is not limited to this type of instrument. The effect is not observable on the horizontal component STS-1s at BFO while it is significant in the recordings of the vertical STS-1. The main difference between these instruments is the leaf-spring suspension in the vertical component that appears to be the source of the trouble. The suspension springs are made of temperature compensated Elinvar alloys that inherently are ferromagnetic and may respond to the magnetic field in various ways. However, the LaCoste Romberg ET-19 gravimeter at BFO, which uses this material too, does not respond to magnetic storms at a similar magnitude neither do the Invar-wire strainmeters. An active shielding, composed of three Helmholtz coils and a feedback system, is installed at station Stuttgart and provides an improvement of signal-to-noise ratio by almost a factor of 20 at this particular station. The passive

  12. Metallic photonic-band-gap filament architectures for optimized incandescent lighting

    NASA Astrophysics Data System (ADS)

    John, Sajeev; Wang, Rongzhou

    2008-10-01

    We identify an optimized three-dimensional metallic photonic-band-gap filament architecture for electrically pumped, quasithermal, visible light emission. This identification is based on extensive band structure and finite-difference time-domain calculations of metallic photonic crystals. The optimum structure consists of an inverse square-spiral photonic crystal, exhibiting a large bandwidth optical passband below the effective plasma screening frequency of the periodically structured metal. Light emission from the interior surfaces of the filament to the interior air channels occurs exclusively into the passband modes, enabling high-efficiency conversion of electrical energy into visible light.

  13. Photocurrent induced by two-photon excitation in ZnTeO intermediate band solar cells

    NASA Astrophysics Data System (ADS)

    Tanaka, Tooru; Miyabara, Masaki; Nagao, Yasuhiro; Saito, Katsuhiko; Guo, Qixin; Nishio, Mitsuhiro; Yu, Kin M.; Walukiewicz, Wladek

    2013-02-01

    Intermediate band (IB) solar cell structures based on ZnTeO highly mismatched alloy were examined to demonstrate a photocurrent induced by a two-photon excitation (TPE) process. Two types of the devices, with and without a blocking layer for the IB, are prepared. The device with a blocked IB exhibits small external quantum efficiency (EQE) in photon energy range in which electron transitions from valence band (VB) to IB take place, implying the electron accumulation in IB. The enhancement of EQE is observed in TPE experiments as a result of electron transition from VB to conduction band via IB.

  14. Analysis of plasma-magnetic photonic crystal with a tunable band gap

    SciTech Connect

    Mehdian, H.; Mohammadzahery, Z.; Hasanbeigi, A.

    2013-04-15

    In this paper, electromagnetic wave propagation through the one-dimensional plasma-magnetic photonic crystal in the presence of external magnetic field has been analyzed. The dispersion relation, transmission and reflection coefficients have been obtained by using the transfer matrix method. It is investigated how photonic band gap of photonic crystals will be tuned when both dielectric function {epsilon} and magnetic permeability {mu} of the constitutive materials, depend on applied magnetic field. This is shown by one dimensional photonic crystals consisting of plasma and ferrite material layers stacked alternately.

  15. Photonic Band Gap Structures as a Gateway to Nano-Photonics

    SciTech Connect

    FRITZ, IAN J.; GOURLEY, PAUL L.; HAMMONS, G.; HIETALA, VINCENT M.; JONES, ERIC D.; KLEM, JOHN F.; KURTZ, SHARON L.; LIN, SHAWN-YU; LYO, SUNGKWUN K.; VAWTER, GREGORY A.; WENDT, JOEL R.

    1999-08-01

    This LDRD project explored the fundamental physics of a new class of photonic materials, photonic bandgap structures (PBG), and examine its unique properties for the design and implementation of photonic devices on a nano-meter length scale for the control and confinement of light. The low loss, highly reflective and quantum interference nature of a PBG material makes it one of the most promising candidates for realizing an extremely high-Q resonant cavity, >10,000, for optoelectronic applications and for the exploration of novel photonic physics, such as photonic localization, tunneling and modification of spontaneous emission rate. Moreover, the photonic bandgap concept affords us with a new opportunity to design and tailor photonic properties in very much the same way we manipulate, or bandgap engineer, electronic properties through modern epitaxy.

  16. Low index-contrast aperiodically ordered photonic quasicrystals for the development of isotropic photonic band-gap devices

    NASA Astrophysics Data System (ADS)

    Priya Rose, T.; Di Gennaro, E.; Andreone, A.; Abbate, G.

    2010-05-01

    Photonic quasicrystals (PQCs) have neither true periodicity nor translational symmetry, however they can exhibit symmetries that are not achievable by conventional periodic structures. The arbitrarily high rotational symmetry of these materials can be practically exploited to manufacture isotropic band gap materials, which are perfectly suitable for hosting waveguides or cavities. In this work, formation and development of the photonic bandgap (PBG) in twodimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low dielectric contrast (0.4-0.6) were measured in the microwave region and compared with the PBG properties of a conventional hexagonal crystal. Band-gap properties were also investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0° to 30° were used in order to investigate the isotropic nature of the band-gap.

  17. Two-photon photoemission from a copper cathode in an X -band photoinjector

    NASA Astrophysics Data System (ADS)

    Li, H.; Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.; Dunning, M.; Jobe, K.; Raubenheimer, T.; Vrielink, A.; Vecchione, T.; Wang, F.; Weathersby, S.

    2016-02-01

    This paper presents two-photon photoemission from a copper cathode in an X -band photoinjector. We experimentally verified that the electron bunch charge from photoemission out of a copper cathode scales with laser intensity (I) square for 400 nm wavelength photons. We compare this two-photon photoemission process with the single photon process at 266 nm. Despite the high reflectivity (R ) of the copper surface for 400 nm photons (R =0.48 ) and higher thermal energy of photoelectrons (two-photon at 200 nm) compared to 266 nm photoelectrons, the quantum efficiency of the two-photon photoemission process (400 nm) exceeds the single-photon process (266 nm) when the incident laser intensity is above 300 GW /cm2 . At the same laser pulse energy (E ) and other experimental conditions, emitted charge scales inversely with the laser pulse duration. A thermal emittance of 2.7 mm-mrad per mm root mean square (rms) was measured on our cathode which exceeds by sixty percent larger compared to the theoretical predictions, but this discrepancy is similar to previous experimental thermal emittance on copper cathodes with 266 nm photons. The damage of the cathode surface of our first-generation X -band gun from both rf breakdowns and laser impacts mostly explains this result. Using a 400 nm laser can substantially simplify the photoinjector system, and make it an alternative solution for compact pulsed electron sources.

  18. Accidental degeneracy in photonic bands and topological phase transitions in two-dimensional core-shell dielectric photonic crystals

    NASA Astrophysics Data System (ADS)

    Xu, Lin; Wang, Hai-Xiao; Xu, Ya-Dong; Chen, Huan-Yang; Jiang, Jian-Hua

    2016-08-01

    A simple core-shell two-dimensional photonic crystal is studied where the triangle lattice symmetry and $C_{6v}$ rotation symmetry leads to rich physics in the study of accidental degeneracy's in photonic bands. We systematically evaluate different types of accidental nodal points, depending on the dispersions around them and their topological properties, when the geometry and permittivity are continuously changed. These accidental nodal points can be the critical states lying between a topological phase and a normal phase and are thus important for the study of topological photonic states. In time-reversal systems, this leads to the photonic quantum spin Hall insulator where the spin is defined upon the orbital angular momentum for transverse-magnetic polarization. We study the topological phase transition as well as the properties of the edge and bulk states and their application potentials in optics.

  19. Tandem photonic-crystal thin films surpassing Lambertian light-trapping limit over broad bandwidth and angular range

    SciTech Connect

    Oskooi, Ardavan Tanaka, Yoshinori; Noda, Susumu

    2014-03-03

    Random surface texturing of an optically thick film to increase the path length of scattered light rays, first proposed nearly thirty years ago, has thus far remained the most effective approach for photon absorption over the widest set of conditions. Here, using recent advances in computational electrodynamics, we describe a general strategy for the design of a silicon thin film applicable to photovoltaic cells based on a quasi-resonant approach to light trapping where two partially disordered photonic-crystal slabs, stacked vertically on top of each other, have large absorption that surpasses the Lambertian limit over a broad bandwidth and angular range.

  20. Photonic-band-gap effects in two-dimensional polycrystalline and amorphous structures

    SciTech Connect

    Yang, Jin-Kyu; Noh, Heeso; Liew, Seng-Fatt; Schreck, Carl; Guy, Mikhael I.; O'Hern, Corey S.; Cao, Hui

    2010-11-15

    We study numerically the density of optical states (DOS) in two-dimensional photonic structures with short-range positional order and observe a transition from polycrystalline to amorphous photonic systems. In polycrystals, photonic band gaps (PBGs) are formed within individual domains, which leads to a depletion of the DOS similar to that in periodic structures. In amorphous photonic media, the domain sizes are too small to form PBGs, thus the depletion of the DOS is weakened significantly. The critical domain size that separates the polycrystalline and amorphous regimes is determined by the attenuation length of Bragg scattering, which depends not only on the degree of positional order but also the refractive-index contrast of the photonic material. Even with relatively low-refractive-index contrast, we find that modest short-range positional order in photonic structures enhances light confinement via collective scattering and interference.

  1. Achieving omnidirectional photonic band gap in sputter deposited TiO{sub 2}/SiO{sub 2} one dimensional photonic crystal

    SciTech Connect

    Jena, S. Tokas, R. B.; Sarkar, P.; Thakur, S.; Sahoo, N. K.; Haque, S. Maidul; Misal, J. S.; Rao, K. D.

    2015-06-24

    The multilayer structure of TiO{sub 2}/SiO{sub 2} (11 layers) as one dimensional photonic crystal (1D PC) has been designed and then fabricated by using asymmetric bipolar pulse DC magnetron sputtering technique for omnidirectional photonic band gap. The experimentally measured photonic band gap (PBG) in the visible region is well matched with the theoretically calculated band structure (ω vs. k) diagram. The experimentally measured omnidirectional reflection band of 44 nm over the incident angle range of 0°-70° is found almost matching within the theoretically calculated band.

  2. Broad-band linear polarization in late-type active dwarfs

    NASA Astrophysics Data System (ADS)

    Patel, Manoj K.; Pandey, Jeewan C.; Karmakar, Subhajeet; Srivastava, D. C.; Savanov, Igor S.

    2016-04-01

    We present recent polarimetric results of magnetically active late-type dwarfs. The polarization in these stars is found to be wavelength dependent, decreasing towards the longer wavelength. The average values of degree of polarization in these active dwarfs are found to be 0.16 ± 0.01, 0.080 ± 0.006, 0.056 ± 0.004 and 0.042 ± 0.003 per cent in B, V, R, and I bands, respectively. Present results indicate that polarization in the majority of active dwarfs are primarily due to sum of the polarization by magnetic intensification and scattering. However, supplementary sources of the polarization are also found to be present in some active stars. The correlations between the degree of polarization and various activity parameters like Rossby number, chromospheric activity indicator and coronal activity indicator are found to be stronger in B band and weaker in I band.

  3. Broad-band radio behaviour of flaring BL Lac (J2202+4216)

    NASA Astrophysics Data System (ADS)

    Angelakis, E.; Fuhrmann, L.; Nestoras, I.; Schmidt, R.; Zensus, J. A.; Krichbaum, T. P.; Ungerechts, H.; Sievers, A.; Riquelme, D.

    2011-05-01

    Responding to the ATels #3368, #3371, #3375 and #3377 reporting the recent activity of BL Lac (J2202+4216, RA= 22:02:43, DEC=+42:16:39 in J2000) at different high energy bands, we here report its behaviour in the cm-to-mm radio bands as observed by the F-GAMMA program. Recent activity: Observations performed with the Effelsberg 100-m and the IRAM 30-m telescope over the last months on May 1, 7, 20 and 25, show a persistent increase in the flux at all frequencies observed.

  4. Tuning of full band gap in anisotropic photonic crystal slabs using a liquid crystal

    NASA Astrophysics Data System (ADS)

    Khalkhali, T. Fathollahi; Rezaei, B.; Ramezani, A. H.

    2012-11-01

    We analyze the tunability of full band gap in photonic crystal slabs created by square and triangular lattices of air holes in anisotropic tellurium background, considering that the regions above and below the slab are occupied by SiO2 and the holes are infiltrated with liquid crystals. Using the supercell method based on plane wave expansion, we study the variation of full band gap by changing the optical axis orientation of liquid crystal. Our results demonstrate the existence and remarkable tunability of full band gap in both square and triangular lattices, largest band gap and tunability being obtained for the triangular lattice.

  5. Photonic band gaps and planar cavity of two-dimensional eightfold symmetric void-channel photonic quasicrystals

    NASA Astrophysics Data System (ADS)

    Zhou, Guangyong; Gu, Min

    2007-05-01

    By using the femtosecond laser induced microexplosion method, high-quality two-dimensional eightfold photonic quasicrystals have been fabricated in a solid transparent polymer material. Multiorder band gaps have been observed in a 25-layer structure with a suppression rate of up to 72% for the fundamental gap. Polarization measurements show that the photonic quasicrystal has a strong anisotropic effect, showing that the transverse electric is the favorite polarization. Fabry-Pérot cavities have been fabricated by removing the central layer of channels. Based on the cavity mode position, the order of the mode and the effective cavity size have been determined.

  6. Fabrication of Ceramic Layer-by-Layer Infrared Wavelength Photonic Band Gap Crystals

    SciTech Connect

    Henry Hao-Chuan Kang

    2004-12-19

    Photonic band gap (PBG) crystals, also known as photonic crystals, are periodic dielectric structures which form a photonic band gap that prohibit the propagation of electromagnetic (EM) waves of certain frequencies at any incident angles. Photonic crystals have several potential applications including zero-threshold semiconductor lasers, the inhibition of spontaneous emission, dielectric mirrors, and wavelength filters. If defect states are introduced in the crystals, light can be guided from one location to another or even a sharp bending of light in micron scale can be achieved. This generates the potential for optical waveguide and optical circuits, which will contribute to the improvement in the fiber-optic communications and the development of high-speed computers.

  7. Energy transfer from Rhodamine-B to Oxazine-170 in the presence of photonic stop band

    NASA Astrophysics Data System (ADS)

    Kedia, Sunita; Sinha, Sucharita

    2015-03-01

    Photonic crystals can effectively suppress spontaneous emission of embedded emitter in the direction were photonic stop band overlaps emission band of emitter. This property of PhC has been successfully exploited to enhance energy transfer from a donor Rhodamine-B dye to an acceptor Oxazine-170 dye by inhibiting the fluorescence emission of donor in a controlled manner. Self-assembled PhC were synthesized using RhB dye doped polystyrene microspheres subsequently infiltrated with O-170 dye molecules dissolved in ethanol. An angle dependent enhancement of emission intensity of acceptor via energy transfer in photonic crystal environment was observed. These results were compared with observations made on a dye mixture solution of the same two dyes. Restricted number of available modes in photonic crystal inhibited de-excitation of donor thereby enabling efficient transfer of energy from excited donor to acceptor dye molecules.

  8. Experimental Work With Photonic Band Gap Fiber: Building A Laser Electron Accelerator

    SciTech Connect

    Lincoln, Melissa; Ischebeck, Rasmus; Nobel, Robert; Siemann, Robert; /SLAC

    2006-09-29

    In the laser acceleration project E-163 at the Stanford Linear Accelerator Center, work is being done toward building a traveling wave accelerator that uses as its accelerating structure a length of photonic band gap fiber. The small scale of the optical fiber allows radiation at optical wavelengths to be used to provide the necessary accelerating energy. Optical wavelength driving energy in a small structure yields higher accelerating fields. The existence of a speed-of-light accelerating mode in a photonic band gap fiber has been calculated previously [1]. This paper presents an overview of several of the experimental challenges posed in the development of the proposed photonic band gap fiber accelerator system.

  9. Method of manufacturing flexible metallic photonic band gap structures, and structures resulting therefrom

    DOEpatents

    Gupta, Sandhya; Tuttle, Gary L.; Sigalas, Mihail; McCalmont, Jonathan S.; Ho, Kai-Ming

    2001-08-14

    A method of manufacturing a flexible metallic photonic band gap structure operable in the infrared region, comprises the steps of spinning on a first layer of dielectric on a GaAs substrate, imidizing this first layer of dielectric, forming a first metal pattern on this first layer of dielectric, spinning on and imidizing a second layer of dielectric, and then removing the GaAs substrate. This method results in a flexible metallic photonic band gap structure operable with various filter characteristics in the infrared region. This method may be used to construct multi-layer flexible metallic photonic band gap structures. Metal grid defects and dielectric separation layer thicknesses are adjusted to control filter parameters.

  10. Band structure of germanium carbides for direct bandgap silicon photonics

    NASA Astrophysics Data System (ADS)

    Stephenson, C. A.; O'Brien, W. A.; Penninger, M. W.; Schneider, W. F.; Gillett-Kunnath, M.; Zajicek, J.; Yu, K. M.; Kudrawiec, R.; Stillwell, R. A.; Wistey, M. A.

    2016-08-01

    Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge1-xCx (x = 0.78%) using density functional theory with HSE06 hybrid functionals predicts a splitting of the conduction band at Γ and a strongly direct bandgap, consistent with band anticrossing. Photoreflectance of Ge0.998C0.002 shows a bandgap reduction supporting these results. Growth of Ge0.998C0.002 using tetrakis(germyl)methane as the C source shows no signs of C-C bonds, C clusters, or extended defects, suggesting highly substitutional incorporation of C. Optical gain and modulation are predicted to rival III-V materials due to a larger electron population in the direct valley, reduced intervalley scattering, suppressed Auger recombination, and increased overlap integral for a stronger fundamental optical transition.

  11. Zero-coupling-gap degenerate band edge resonators in silicon photonics.

    PubMed

    Burr, Justin R; Reano, Ronald M

    2015-11-30

    Resonances near regular photonic band edges are limited by quality factors that scale only to the third power of the number of periods. In contrast, resonances near degenerate photonic band edges can scale to the fifth power of the number periods, yielding a route to significant device miniaturization. For applications in silicon integrated photonics, we present the design and analysis of zero-coupling-gap degenerate band edge resonators. Complex band diagrams are computed for the unit cell with periodic boundary conditions that convey characteristics of propagating and evanescent modes. Dispersion features of the band diagram are used to describe changes in resonance scaling in finite length resonators. Resonators with non-zero and zero coupling gap are compared. Analysis of quality factor and resonance frequency indicates significant reduction in the number of periods required to observe fifth power scaling when degenerate band edge resonators are realized with zero-coupling-gap. High transmission is achieved by optimizing the waveguide feed to the resonator. Compact band edge cavities with large optical field distribution are envisioned for light emitters, switches, and sensors. PMID:26698725

  12. CW-pumped telecom band polarization entangled photon pair generation in a Sagnac interferometer

    NASA Astrophysics Data System (ADS)

    Li, Yan; Zhou, Zhi-Yuan; Ding, Dong-Sheng; Shi, Bao-Sen

    2015-11-01

    A polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum swapping, quantum computation and high precision quantum metrology. Here, we report on the generation of a continuous-wave pumped degenerated 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II phase-matched periodically poled KTiOPO4 crystal in a Sagnac interferometer. Hong-Ou-Mandel-type interference measurement shows the photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The wavelength of photons can be tuned over a broad range by changing the temperature of crystal or pump power without losing the quality of entanglement. This source will be useful for building up long-distance quantum networks.

  13. Accidental degeneracy in photonic bands and topological phase transitions in two-dimensional core-shell dielectric photonic crystals.

    PubMed

    Xu, Lin; Wang, Hai-Xiao; Xu, Ya-Dong; Chen, Huan-Yang; Jiang, Jian-Hua

    2016-08-01

    A simple core-shell two-dimensional photonic crystal is studied where the triangular lattice symmetry and the C6 point group symmetry give rich physics in accidental touching points of photonic bands. We systematically evaluate different types of accidental nodal points at the Brillouin zone center for transverse-magnetic harmonic modes when the geometry and permittivity of the core-shell material are continuously tuned. The accidental nodal points can have different dispersions and topological properties (i.e., Berry phases). These accidental nodal points can be the critical states lying between a topological phase and a normal phase of the photonic crystal. They are thus very important for the study of topological photonic states. We show that, without breaking time-reversal symmetry, by tuning the geometry of the core-shell material, a phase transition into the photonic quantum spin Hall insulator can be achieved. Here the "spin" is defined as the orbital angular momentum of a photon. We study the topological phase transition as well as the properties of the edge and bulk states and their application potentials in optics. PMID:27505772

  14. True-time-delay photonic beamformer for an L-band phased array radar

    NASA Astrophysics Data System (ADS)

    Zmuda, Henry; Toughlian, Edward N.; Payson, Paul M.; Malowicki, John E.

    1995-10-01

    The problem of obtaining a true-time-delay photonic beamformer has recently been a topic of great interest. Many interesting and novel approaches to this problem have been studied. This paper examines the design, construction, and testing of a dynamic optical processor for the control of a 20-element phased array antenna operating at L-band (1.2-1.4 GHz). The approach taken here has several distinct advantages. The actual optical control is accomplished with a class of spatial light modulator known as a segmented mirror device (SMD). This allows for the possibility of controlling an extremely large number (tens of thousands) of antenna elements using integrated circuit technology. The SMD technology is driven by the HDTV and laser printer markets so ultimate cost reduction as well as technological improvements are expected. Optical splitting is efficiently accomplished using a diffractive optical element. This again has the potential for use in antenna array systems with a large number of radiating elements. The actual time delay is achieved using a single acousto-optic device for all the array elements. Acousto-optic device technologies offer sufficient delay as needed for a time steered array. The topological configuration is an optical heterodyne system, hence high, potentially millimeter wave center frequencies are possible by mixing two lasers of slightly differing frequencies. Finally, the entire system is spatially integrated into a 3D glass substrate. The integrated system provides the ruggedness needed in most applications and essentially eliminates the drift problems associated with free space optical systems. Though the system is presently being configured as a beamformer, it has the ability to operate as a general photonic signal processing element in an adaptive (reconfigurable) transversal frequency filter configuration. Such systems are widely applicable in jammer/noise canceling systems, broadband ISDN, and for spread spectrum secure communications

  15. Threshold for formation of atom-photon bound states in a coherent photonic band-gap reservoir

    NASA Astrophysics Data System (ADS)

    Wu, Yunan; Wang, Jing; Zhang, Hanzhuang

    2016-05-01

    We study the threshold for the formation of atom-photon bound (APB) states from a two-level atom embedded in a coherent photonic band-gap (PBG) reservoir. It is shown that the embedded position of the atom plays an important role in the threshold. By varying the atomic embedded position, a part of formation range of APB states can be moved from inside to outside the band gap. The direct link between the steady-state entanglement and APB states is also investigated. We show that the values of entanglement between reservoir modes reflect the amount of bounded energy caused by APB states. The feasible experimental systems for verifying the above phenomena are discussed. Our results provide a clear clue on how to form and control APB states in PBG materials.

  16. Broad-band characterization of the complex permittivity and permeability of materials

    SciTech Connect

    Avalle, C.A.

    1994-11-01

    By employment of state-of-the-art Vector Network Analyzers, and other wide-band measurement equipment and techniques, the authors have the capability of measuring the complex permittivity and permeability of materials, for frequencies ranging from several tens of Kilohertz up to several Gigahertz. Measurement methods and equations for numerical determination are based on recommendations by the National Institute of Standards and Technology (NIST). Types of materials which can be analyzed are dielectric or magnetic RF and radar absorbers; thin sheets, paints, coatings; castable resins; foams and low density materials; ceramics and ferrites; carbonized fabrics; and composites.

  17. A broad-band VLF-burst associated with ring-current electrons. [geomagnetic storms

    NASA Technical Reports Server (NTRS)

    Maeda, K.

    1982-01-01

    Frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma is known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type broadening of VLF emission lasting less than ten minutes was observed by Explorer 45 in a similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasielectrostatic whistler mode emission of short wavelength by hot bimaxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of this event.

  18. Omnidirectional photonic band gap enlarged by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure

    SciTech Connect

    Zhang Haifeng; Liu Shaobin; Kong Xiangkun; Bian Borui; Dai Yi

    2012-11-15

    In this paper, an omnidirectional photonic band gap realized by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure, which is composed of homogeneous unmagnetized plasma and two kinds of isotropic dielectric, is theoretically studied by the transfer matrix method. It has been shown that such an omnidirectional photonic band gap originates from Bragg gap in contrast to zero-n gap or single negative (negative permittivity or negative permeability) gap, and it is insensitive to the incidence angle and the polarization of electromagnetic wave. From the numerical results, the frequency range and central frequency of omnidirectional photonic band gap can be tuned by the thickness and density of the plasma but cease to change with increasing Fibonacci order. The bandwidth of omnidirectional photonic band gap can be notably enlarged. Moreover, the plasma collision frequency has no effect on the bandwidth of omnidirectional photonic band gap. It is shown that such new structure Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of frequency range of omnidirectional photonic band gap compared with the conventional ternary and conventional Fibonacci quasiperiodic ternary plasma photonic crystals.

  19. Comparison of UV-B measurements performed with a Brewer spectrophotometer and a new UVB-1 broad band detector

    NASA Technical Reports Server (NTRS)

    Bais, Alkiviadis F.; Zerefos, Christos S.; Meleti, Charicleia; Ziomas, Ioannis C.

    1994-01-01

    Measurements of the UV-B erythemal dose, based on solar spectra acquired with a Brewer spectrophotometer at Thessaloniki, Greece, are compared to measurements performed with the recently introduced, by the Yankee Environmental Systems, (Robertson type) broad band solar UV-B detector. The spectral response function of this detector, when applied to the Brewer spectral UV-B measurements, results in remarkably comparable estimates of the erythemal UV-B dose. The two instruments provide similar information on the UV-B dose when they are cross-examined under a variety of meteorological and atmospheric conditions and over the a large range of solar zenith angles and total ozone.

  20. Broad-band properties of the CfA Seyfert galaxies. III - Ultraviolet variability

    NASA Technical Reports Server (NTRS)

    Edelson, R. A.; Pike, G. F.; Krolik, J. H.

    1990-01-01

    A total of 657 archived IUE spectra are used to study the UV variability properties of six members of the CfA Seyfert I galaxy sample. All show strong evidence for continuum and line variations and a tendency for less luminous objects to be more strongly variable. Most objects show a clear correlation at zero lag between UV spectral index and luminosity, evidence that the variable component is an accretion disk around a black hole which is systematically smaller in less luminous sources. No correlation is seen between the continuum luminosity and equivalent width of the C IV, Mg II, and semiforbidden C III emission lines when the entire sample is examined, but a clear anticorrelation is present when only repeated observations of individual objects are considered. This is due to a combination of light-travel time effects in the broad-line region and the nonlinear responses of lines to continuum fluctuations.

  1. A compact planar multi-broad band monopole antenna for mobile devices

    NASA Astrophysics Data System (ADS)

    Zhong, Xiaoqing; Yao, Bin; Zheng, Qinhong; Yang, Jikong; Cao, Xiangqi

    2015-10-01

    A Multiple-frequency broadband planar monopole antenna is proposed in this Paper. The antenna is stimulated and numerically optimized by HFSS13.0 (High Frequency Structure Simulator). The size of it is 39mm×22mm×1.7mm. The antenna resonates at many frequencies. The parameter S11<=-6dB means the proposed antenna matches well with its feed-line and covers many useful operation frequency bands, including 2G(DCS1800 and PCS1900), 3G(UMTS), 4G(LTE2300 and LTE2500), ISM, WLAN. It is quiet appropriate for the present ultra-thin smart phones

  2. Research on Shore-Ship Photonic Link Performance for Two- Frequency-Band Signals

    NASA Astrophysics Data System (ADS)

    Zuo, Yanqin; Cong, Bo

    2016-02-01

    Ka and Ku bands links for shore-ship communications suffer limited bandwidth and high loss. In this paper, photonics-based links are proposed and modeled. The principle of phase modulation (PM) is elaborated and analyzed. It is showed that PM can effectively suppress high-order inter-modulation distortion (IMD), reduce the insert loss and improve the reliability of the system.

  3. Planar Defect Modes Excited at the Band Edge of Three-dimensional Photonic Crystals

    NASA Astrophysics Data System (ADS)

    Iida, Masaru; Tani, Masahiko; Sakai, Kiyomi; Watanabe, Masayoshi; Kitahara, Hideaki; Tohme, Takuya; Wada Takeda, Mitsuo

    2004-09-01

    We experimentally and numerically studied planar defect modes excited at band-edge resonant mode frequencies in three-dimensional photonic crystals. We identified the observed peaks as the defect modes using the spectrum calculated at the defect layer. The spectrum also clarifies the difference between these modes and ordinary band-edge resonant modes. The calculated spatial distribution of the electric field in the defect modes shows that the defect modes have a characteristic field concentration in the band-edge resonant mode.

  4. Band gap of two-dimensional fiber-air photonic crystals

    NASA Astrophysics Data System (ADS)

    Yang, Shu; Li, Masha

    2016-04-01

    A two-dimensional photonic crystal (PC) composed of textile fiber and air is initially discussed in this paper. Textile materials are so called soft materials, which are different from the previous PCs composed of rigid materials. The plain wave expansion method is used to calculate band structure of different PCs by altering component properties or structural parameters. Results show that the dielectric constant of textile fibers, fiber filling ratio and lattice arrangement are effective factors which influence PCs' band gap. Yet lattice constant and fiber diameter make inconspicuous influence on the band gap feature.

  5. Air and dielectric bands photonic crystal microringresonator for refractive index sensing.

    PubMed

    Urbonas, Darius; Balčytis, Armandas; Vaškevičius, Konstantinas; Gabalis, Martynas; Petruškevičius, Raimondas

    2016-08-01

    We present the experimental and numerical analysis of a microring resonator with an integrated one-dimensional photonic crystal fabricated on a silicon-on-insulator platform and show its applicability in bulk refractive index sensing. The photonic crystal is formed by periodically patterned, partially etched cylindrical perforations, whose induced photonic bandgap is narrower than the range of measurable wavelengths (1520-1620 nm). Of particular interest is that the microring operates in both air and dielectric bands, and the sensitivities of the resonances on both edges of the bandgap were investigated. We showed that a higher field localization inside the volume of the perforations for the air band mode leads to an increase in sensitivity. PMID:27472642

  6. Wide-Band Spatially Tunable Photonic Bandgap in Visible Spectral Range and Laser based on a Polymer Stabilized Blue Phase.

    PubMed

    Lin, Jia-De; Wang, Tsai-Yen; Mo, Ting-Shan; Huang, Shuan-Yu; Lee, Chia-Rong

    2016-01-01

    This work successfully develops a largely-gradient-pitched polymer-stabilized blue phase (PSBP) photonic bandgap (PBG) device with a wide-band spatial tunability in nearly entire visible region within a wide blue phase (BP) temperature range including room temperature. The device is fabricated based on the reverse diffusion of two injected BP-monomer mixtures with a low and a high chiral concentrations and afterwards through UV-curing. This gradient-pitched PSBP can show a rainbow-like reflection appearance in which the peak wavelength of the PBG can be spatially tuned from the blue to the red regions at room temperature. The total tuning spectral range for the cell is as broad as 165 nm and covers almost the entire visible region. Based on the gradient-pitched PSBP, a spatially tunable laser is also demonstrated in this work. The temperature sensitivity of the lasing wavelength for the laser is negatively linear and approximately -0.26 nm/°C. The two devices have a great potential for use in applications of photonic devices and displays because of their multiple advantages, such as wide-band tunability, wide operated temperature range, high stability and reliability, no issue of hysteresis, no need of external controlling sources, and not slow tuning speed (mechanically). PMID:27456475

  7. Wide-Band Spatially Tunable Photonic Bandgap in Visible Spectral Range and Laser based on a Polymer Stabilized Blue Phase

    PubMed Central

    Lin, Jia-De; Wang, Tsai-Yen; Mo, Ting-Shan; Huang, Shuan-Yu; Lee, Chia-Rong

    2016-01-01

    This work successfully develops a largely-gradient-pitched polymer-stabilized blue phase (PSBP) photonic bandgap (PBG) device with a wide-band spatial tunability in nearly entire visible region within a wide blue phase (BP) temperature range including room temperature. The device is fabricated based on the reverse diffusion of two injected BP-monomer mixtures with a low and a high chiral concentrations and afterwards through UV-curing. This gradient-pitched PSBP can show a rainbow-like reflection appearance in which the peak wavelength of the PBG can be spatially tuned from the blue to the red regions at room temperature. The total tuning spectral range for the cell is as broad as 165 nm and covers almost the entire visible region. Based on the gradient-pitched PSBP, a spatially tunable laser is also demonstrated in this work. The temperature sensitivity of the lasing wavelength for the laser is negatively linear and approximately −0.26 nm/°C. The two devices have a great potential for use in applications of photonic devices and displays because of their multiple advantages, such as wide-band tunability, wide operated temperature range, high stability and reliability, no issue of hysteresis, no need of external controlling sources, and not slow tuning speed (mechanically). PMID:27456475

  8. Wide-Band Spatially Tunable Photonic Bandgap in Visible Spectral Range and Laser based on a Polymer Stabilized Blue Phase

    NASA Astrophysics Data System (ADS)

    Lin, Jia-De; Wang, Tsai-Yen; Mo, Ting-Shan; Huang, Shuan-Yu; Lee, Chia-Rong

    2016-07-01

    This work successfully develops a largely-gradient-pitched polymer-stabilized blue phase (PSBP) photonic bandgap (PBG) device with a wide-band spatial tunability in nearly entire visible region within a wide blue phase (BP) temperature range including room temperature. The device is fabricated based on the reverse diffusion of two injected BP-monomer mixtures with a low and a high chiral concentrations and afterwards through UV-curing. This gradient-pitched PSBP can show a rainbow-like reflection appearance in which the peak wavelength of the PBG can be spatially tuned from the blue to the red regions at room temperature. The total tuning spectral range for the cell is as broad as 165 nm and covers almost the entire visible region. Based on the gradient-pitched PSBP, a spatially tunable laser is also demonstrated in this work. The temperature sensitivity of the lasing wavelength for the laser is negatively linear and approximately ‑0.26 nm/°C. The two devices have a great potential for use in applications of photonic devices and displays because of their multiple advantages, such as wide-band tunability, wide operated temperature range, high stability and reliability, no issue of hysteresis, no need of external controlling sources, and not slow tuning speed (mechanically).

  9. High-performance broad-band spectroscopy for breast cancer risk assessment

    NASA Astrophysics Data System (ADS)

    Pawluczyk, Olga; Blackmore, Kristina; Dick, Samantha; Lilge, Lothar

    2005-09-01

    Medical diagnostics and screening are becoming increasingly demanding applications for spectroscopy. Although for many years the demand was satisfied with traditional spectrometers, analysis of complex biological samples has created a need for instruments capable of detecting small differences between samples. One such application is the measurement of absorbance of broad spectrum illumination by breast tissue, in order to quantify the breast tissue density. Studies have shown that breast cancer risk is closely associated with the measurement of radiographic breast density measurement. Using signal attenuation in transillumination spectroscopy in the 550-1100nm spectral range to measure breast density, has the potential to reduce the frequency of ionizing radiation, or making the test accessible to younger women; lower the cost and make the procedure more comfortable for the patient. In order to determine breast density, small spectral variances over a total attenuation of up to 8 OD have to be detected with the spectrophotometer. For this, a high performance system has been developed. The system uses Volume Phase Holographic (VPH) transmission grating, a 2D detector array for simultaneous registration of the whole spectrum with high signal to noise ratio, dedicated optical system specifically optimized for spectroscopic applications and many other improvements. The signal to noise ratio exceeding 50,000 for a single data acquisition eliminates the need for nitrogen cooled detectors and provides sufficient information to predict breast tissue density. Current studies employing transillumination breast spectroscopy (TIBS) relating to breast cancer risk assessment and monitoring are described.

  10. Development of inexpensive optical broad- and narrow-band sensors for ecosystem research

    NASA Astrophysics Data System (ADS)

    Mollenhauer, Hannes; Cuntz, Thomas; Bumberger, Jan

    2014-05-01

    The observation and monitoring of ecosystem processes are great challenges in environmental science, due to the dynamic and complexity of such procedures. To describe and understand biotic and abiotic processes and their interaction it is necessary to acquire multiple parameters, which are influencing the natural regime. Essential issues are: the detection of spatial heterogeneities and scale overlapping procedures in the environment. To overcome these problems an adequate monitoring system should cover a representative area as well as have a sufficient resolution in time and space. Hence, the needed quantity of sensors (depending on the observed parameters or processes) can be enormous. According to these issues, there is a high demand on low-cost sensor technologies (with adequate performances) to realize a delicate monitoring platform. In the case of vegetation processes, one key feature is to characterize photosynthetic activity of the plants in detail. Common investigation methods are based on optical measurements. Here photosynthetically active radiation (PAR) sensors and hyperspectral sensors are in major use. Photosynthetically active radiation (solar radiation from 400 to 700 nanometers) designates the spectral range that photosynthetic organisms are able to use in the process of photosynthesis. PAR sensors enable the detection of the reflected solar light of the vegetation in whole the PAR wave band. The amount of absorption indicates photosynthetic activity of the plant. Hyperspectral sensors observe specific parts of the solar light spectrum and facilitate the determination of the main pigment classes (Chlorophyll, Carotenoid and Anthocyanin). Due to absorption of pigments they producing a specific spectral signature in the visible part of the electromagnetic spectrum (narrow-band peaks). If vegetation is affected by water or nutritional deficience the proportion of light-absorbing pigments is reduced which finally results in an overall reduced light

  11. Light reflector, amplifier, and splitter based on gain-assisted photonic band gaps

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Liu, Yi-Mou; Zheng, Tai-Yu; Wu, Jin-Hui

    2016-07-01

    We study both the steady and the dynamic optical response of cold atoms trapped in an optical lattice and driven to the three-level Λ configuration. These atoms are found to exhibit gain without population inversion when an incoherent pump is applied to activate spontaneously generated coherence. Gain-assisted double photonic band gaps characterized by reflectivities over 100% then grow up near the probe resonance due to the periodic distribution of the atomic density. These band gaps along with the neighboring allowed bands of transmissivities over 100% can be tuned by modulating the control field in amplitude, frequency, and, especially, phase. Consequently it is viable to realize a reflector, an amplifier, or a splitter when a weak incident light pulse is totally reflected in the photonic band gaps, totally transmitted in the allowed bands, or equally reflected and transmitted in the intersecting regions. Our results have potential applications in all-optical networks with respect to fabricating dynamically switchable devices for manipulating photon flows at low-light levels.

  12. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    SciTech Connect

    Kevin Jerome Sutherland

    2001-05-01

    Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.

  13. Geoacoustic inversion of broad-band ambient noise data using undersampled and short aperture arrays

    NASA Astrophysics Data System (ADS)

    Siderius, Martin; Porter, Michael; Harrison, Chris

    2001-05-01

    Ocean ambient noise is generated in many ways such as from winds, rain and shipping. A technique has recently been developed [Harrison and Simons, J. Acoust. Soc. Am. 112 (2002)] that uses the vertical directionality of ambient noise to determine seabed properties. The ratio of beams steered towards the surface to those steered towards the bottom produces the bottom reflection loss curve. This technique was applied to data in the 200-1500-Hz band using a 16-m array. Extending this to higher frequencies allows the array length to be substantially shortened and greatly reduces interference from shipping. However, this limits the low end of the frequency spectrum since reduced aperture increases beam widths and the up/down beam ratio no longer produces reflection loss. Similarly, for high frequencies, if hydrophone spacing is greater than half-wavelength, the beamformed output is aliased and again the up/down ratio produces erroneous results. In general, frequencies much below the array design will suffer from large beams and frequencies above from undersampling. In this paper, we describe techniques for obtaining seabed properties from ambient noise measured on short or undersampled arrays. Results will be presented from the KauaiEx (July 2003) and ElbaEx (October 2003) experiments.

  14. A photonic crystal waveguide with silicon on insulator in the near-infrared band

    NASA Astrophysics Data System (ADS)

    Tang, Hai-Xia; Zuo, Yu-Hua; Yu, Jin-Zhong; Wang, Qi-Ming

    2007-07-01

    A two-dimensional (2D) photonic crystal waveguide in the Γ-K direction with triangular lattice on a silicon-on-insulator (SOI) substrate in the near-infrared band is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. Its transmission characteristics are analysed from the stimulated band diagram by the effective index and the 2D plane wave expansion (PWE) methods. In the experiment, the transmission band edge in a longer wavelength of the photonic crystal waveguide is about 1590 nm, which is in good qualitative agreement with the simulated value. However, there is a disagreement between the experimental and the simulated results when the wavelength ranges from 1607 to 1630 nm, which can be considered as due to the unpolarized source used in the transmission measurement.

  15. Modeling and Design of Two-Dimensional Guided-Wave Photonic Band-Gap Devices

    NASA Astrophysics Data System (ADS)

    Ciminelli, Caterina; Peluso, Francesco; Armenise, Mario N.

    2005-02-01

    The model of two-dimensional (2-D) guided-wave photonic band-gap structures based on the Bloch-Floquet theory is proposed for the first time for both infinite and finite length devices. The efficient computation of dispersion curves and field distribution is carried out in very short computer time. Both guided and radiated modes can be easily identified to give a physical insight, even in defective structures. The accuracy of the model has been tested through the design of a very compact narrow-band 2-D guided-wave photonic band-gap filter at 1.55 μm. The filter has a channel isolation of 22 dB, a large number of channel (>80) with a channel spacing of 50 GHz, and a very short length (24 μm).

  16. Fabrication and characterization of photonic crystals with well-controlled thickness and stop-band attenuation

    NASA Astrophysics Data System (ADS)

    Gates, B.; Lu, Y.; Li, Z. Y.; Xia, Y.

    Photonic crystals with stop bands located in the visible region have been fabricated by crystallizing monodispersed spherical colloids (made of polystyrene or silica) into cubic-close-packed lattices within specially designed packing cells. These crystals were oriented with their (111) planes parallel to their solid supports, and the number of these planes could be conveniently controlled from 13 to 127 layers by varying the thickness of packing cells. In accordance, the stop-band attenuation of these crystals monotonically increased from 1 to 21 dB. Our transmission spectral measurements indicated that there exists a non-linear dependence between the stop-band attenuation and the total number of (111) planes, and this dependence could be quantitatively simulated using the dynamic light scattering model or the photonic analogy to KKR method. The colloidal crystals presented here should find use as components in fabricating optical devices that include sensors, mirrors, filters, switches and waveguides.

  17. Deep Broad-Band Infrared Nulling Using A Single-Mode Fiber Beam Combiner and Baseline Rotation

    NASA Technical Reports Server (NTRS)

    Mennesson, Bertrand; Haguenauer, P.; Serabyn, E.; Liewer, K.

    2006-01-01

    The basic advantage of single-mode fibers for deep nulling applications resides in their spatial filtering ability, and has now long been known. However, and as suggested more recently, a single-mode fiber can also be used for direct coherent recombination of spatially separated beams, i.e. in a 'multi-axial' nulling scheme. After the first successful demonstration of deep (<2e-6) visible LASER nulls using this technique (Haguenauer & Serabyn, Applied Optics 2006), we decided to work on an infrared extension for ground based astronomical observations, e.g. using two or more off-axis sub-apertures of a large ground based telescope. In preparation for such a system, we built and tested a laboratory infrared fiber nuller working in a wavelength regime where atmospheric turbulence can be efficiently corrected, over a pass band (approx.1.5 to 1.8 micron) broad enough to provide reasonable sensitivity. In addition, since no snapshot images are readily accessible with a (single) fiber nuller, we also tested baseline rotation as an approach to detect off-axis companions while keeping a central null. This modulation technique is identical to the baseline rotation envisioned for the TPF-I space mission. Within this context, we report here on early laboratory results showing deep stable broad-band dual polarization infrared nulls <5e-4 (currently limited by detector noise), and visible LASER nulls better than 3e-4 over a 360 degree rotation of the baseline. While further work will take place in the laboratory to achieve deeper stable broad-band nulls and test off-axis sources detection through rotation, the emphasis will be put on bringing such a system to a telescope as soon as possible. Detection capability at the 500:1 contrast ratio in the K band (2.2 microns) seem readily accessible within 50-100 mas of the optical axis, even with a first generation system mounted on a >5m AO equipped telescope such as the Palomar Hale 200 inch, the Keck, Subaru or Gemini telescopes.

  18. Harvesting Broad Frequency Band Blue Energy by a Triboelectric-Electromagnetic Hybrid Nanogenerator.

    PubMed

    Wen, Zhen; Guo, Hengyu; Zi, Yunlong; Yeh, Min-Hsin; Wang, Xin; Deng, Jianan; Wang, Jie; Li, Shengming; Hu, Chenguo; Zhu, Liping; Wang, Zhong Lin

    2016-07-26

    Ocean wave associated energy is huge, but it has little use toward world energy. Although such blue energy is capable of meeting all of our energy needs, there is no effective way to harvest it due to its low frequency and irregular amplitude, which may restrict the application of traditional power generators. In this work, we report a hybrid nanogenerator that consists of a spiral-interdigitated-electrode triboelectric nanogenerator (S-TENG) and a wrap-around electromagnetic generator (W-EMG) for harvesting ocean energy. In this design, the S-TENG can be fully isolated from the external environment through packaging and indirectly driven by the noncontact attractive forces between pairs of magnets, and W-EMG can be easily hybridized. Notably, the hybrid nanogenerator could generate electricity under either rotation mode or fluctuation mode to collect energy in ocean tide, current, and wave energy due to the unique structural design. In addition, the characteristics and advantages of outputs indicate that the S-TENG is irreplaceable for harvesting low rotation speeds (<100 rpm) or motion frequencies (<2 Hz) energy, which fits the frequency range for most of the water wave based blue energy, while W-EMG is able to produce larger output at high frequencies (>10 Hz). The complementary output can be maximized and hybridized for harvesting energy in a broad frequency range. Finally, a single hybrid nanogenerator unit was demonstrated to harvest blue energy as a practical power source to drive several LEDs under different simulated water wave conditions. We also proposed a blue energy harvesting system floating on the ocean surface that could simultaneously harvest wind, solar, and wave energy. The proposed hybrid nanogenerator renders an effective and sustainable progress in practical applications of the hybrid nanogenerator toward harvesting water wave energy offered by nature. PMID:27267558

  19. Hydrogen production by Tuning the Photonic Band Gap with the Electronic Band Gap of TiO2

    NASA Astrophysics Data System (ADS)

    Waterhouse, G. I. N.; Wahab, A. K.; Al-Oufi, M.; Jovic, V.; Anjum, D. H.; Sun-Waterhouse, D.; Llorca, J.; Idriss, H.

    2013-10-01

    Tuning the photonic band gap (PBG) to the electronic band gap (EBG) of Au/TiO2 catalysts resulted in considerable enhancement of the photocatalytic water splitting to hydrogen under direct sunlight. Au/TiO2 (PBG-357 nm) photocatalyst exhibited superior photocatalytic performance under both UV and sunlight compared to the Au/TiO2 (PBG-585 nm) photocatalyst and both are higher than Au/TiO2 without the 3 dimensionally ordered macro-porous structure materials. The very high photocatalytic activity is attributed to suppression of a fraction of electron-hole recombination route due to the co-incidence of the PBG with the EBG of TiO2 These materials that maintain their activity with very small amount of sacrificial agents (down to 0.5 vol.% of ethanol) are poised to find direct applications because of their high activity, low cost of the process, simplicity and stability.

  20. Theoretical aspects of photonic band gap in 1D nano structure of LN: MgLN periodic layer

    SciTech Connect

    Sisodia, Namita

    2015-06-24

    By using the transfer matrix method, we have analyzed the photonic band gap properties in a periodic layer of LN:MgLN medium. The Width of alternate layers of LN and MgLN is in the range of hundred nanometers. The birefringent and ferroelectric properties of the medium (i.e ordinary, extraordinary refractive indices and electric dipole moment) is given due considerations in the formulation of photonic band gap. Effect of electronic transition dipole moment of the medium on photonic band gap is also taken into account. We find that photonic band gap can be modified by the variation in the ratio of the width of two medium. We explain our findings by obtaining numerical values and the effect on the photonic band gap due to variation in the ratio of alternate medium is shown graphically.

  1. Broad-band ambient noise surface wave tomography: Technique development and application across the United States

    NASA Astrophysics Data System (ADS)

    Bensen, Gregory David

    2007-05-01

    In recent years, it has been shown that surface wave signals can be extracted from high-quality empirical Green functions (EGF) obtained through cross-correlation of long ambient noise timeseries. Early work showed that Rayleigh wave components of EGFs could be created in a narrow period band under certain background noise characteristics. Such Rayleigh wave signals were used to develop shear wave tomography models of several geographic regions with unprecedented high resolution. However, questions remained regarding the robustness of these signals and their range of applicability. My work focuses on two problems. The first is researching the best method for computing, measuring and selecting high-quality EGFs. The second is to use this new technique to create a three-dimensional (3D) velocity model of the continental United States. Testing a variety of temporal and spectral normalization techniques yields an optimal method of creating EGFs. These signals are evaluated for robustness in a variety of noise environments effectively broadening the bandwidth from 7.5-20 s period to 6-100 s period. An automated dispersion measurement technique is presented as well as a preferred method of measurement selection and certain "best practices" are proposed for future study. Applying this method across the continental United States I develop Rayleigh and Love wave group and phase speed dispersion maps from 8-70 s period. The resulting set of dispersion maps possesses unprecedented high resolution and bandwidth for continental scale surface wave investigations and unites diverse tectonic regions into a coherent model. I invert the dispersion maps for a 3D shear velocity model with resolution from the surface to 150 km depth using a two-step procedure. First is a linearized inversion for the best fitting velocity model. Second is a Monte-Carlo re-sampling to develop an ensemble of models of sufficient quality and to generate uncertainty estimates at all points. The resulting

  2. Experimental and Theoretical Studies of Photonic Band gaps in Artificial Opals

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Yin, Ming; Arammash, Fouzi; Datta, Timir

    2014-03-01

    Photonic band structure and band gap were numerically computed for a number of closed packed simple cubic and Hexagonal arrangements of non-conducting spheres using ``Finite Difference Time Domain Method''. Photonic gaps were found to exist in the simple cubic overlapping spheres with index of refraction (n) >3.2. Gap increased linearly from 0.117- 0.161 (1/micron) as lattice constant decreased from 0.34 to 0.18 (micron). For less than 3.2 no gap was obtained. Also, no gaps were obtained for hexagonal packing. UV-VIS reflectivity and transmission measurements of polycrystalline bulk artificial opals of silica (SiO2) spheres, ranging from 250nm to 300nm in sphere diameter indicate a reflection peak in the 500-600 nm regimes. Consistent with photonic band gap behavior we find that reflectivity is enhanced in the same wavelength where transmission is reduced. To the best of our knowledge this is the first observation of photonic gap in the visible wave length under ambient conditions. The wave length at the reflectance peak increases with the diameter of the SiO2 spheres, and is approximately twice the diameter following Bragg reflection. DOD Award No 60177-RT-H from ARO.

  3. Silvered three-dimensional polymeric photonic crystals having a large mid-infrared stop band

    NASA Astrophysics Data System (ADS)

    Kuebler, Stephen M.; Tal, Amir; Chen, Yun-Sheng

    2007-02-01

    Interest in three-dimensional (3D) metal photonic crystals (MPCs) has grown considerably given their potential applications in optics and photonics. Yet, experimental studies of such materials remain few because of the difficulties associated with fabricating 3D micron- and sub-micron-scale metallic structures. We report a route to MPCs based on metallization of 3D polymeric photonic crystals fabricated by multi-photon direct laser writing. Polymeric photonic crystals (PCs) having simple-cubic symmetry with periodicities varying from 1.6 to 3.2 microns were created using a cross-linkable acrylate pre-polymer. The resulting dielectric PCs were metallized by electroless deposition of silver. Analysis of the metallized structures in cross-section by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy shows that silver deposited conformally onto the entire micro-porous lattice. The dielectric and metallized PCs were characterized by Fourier transform infrared (FTIR) spectroscopy in the (001) direction. The polymer photonic crystals exhibit a stop band resulting in circa 60% reflectance centered at 3.2 to 6.4 microns, depending upon the lattice period, with a full-width at half-maximum (FWHM) of 500 nm. Interestingly, FTIR spectra of the metallized PCs show widened stop bands of nearly 6 microns FWHM, while the center wavelengths were red shifted and ranged from 6 to 7 microns. The appreciable broadening of the stop band due to the presence of the deposited silver is a result consistent with previously reported theoretical and experimental data for all-metallic 3D PCs. Thus, the approach described here appears suitable for fabricating 3D MPCs of many symmetries and basis sets and provides a path for integrating such structures with other micron-scale optical elements.

  4. Parametric analysis of 2D guided-wave photonic band gap structures

    NASA Astrophysics Data System (ADS)

    Ciminelli, C.; Peluso, F.; Armenise, M. N.

    2005-11-01

    The parametric analysis of the electromagnetic properties of 2D guided wave photonic band gap structures is reported with the aim of providing a valid tool for the optimal design. The modelling approach is based on the Bloch-Floquet method. Different lattice configurations and geometrical parameters are considered. An optimum value for the ratio between the hole (or rod) radius and the lattice constant does exist and the calculation demonstrated that it is almost independent from the etching depth, only depending on the lattice type. The results are suitable for the design optimisation of photonic crystal reflectors to be used in integrated optical devices.

  5. Parametric analysis of 2D guided-wave photonic band gap structures.

    PubMed

    Ciminelli, C; Peluso, F; Armenise, M

    2005-11-28

    The parametric analysis of the electromagnetic properties of 2D guided wave photonic band gap structures is reported with the aim of providing a valid tool for the optimal design. The modelling approach is based on the Bloch-Floquet method. Different lattice configurations and geometrical parameters are considered. An optimum value for the ratio between the hole (or rod) radius and the lattice constant does exist and the calculation demonstrated that it is almost independent from the etching depth, only depending on the lattice type. The results are suitable for the design optimisation of photonic crystal reflectors to be used in integrated optical devices. PMID:19503180

  6. Isotropic properties of the photonic band gap in quasicrystals with low-index contrast

    NASA Astrophysics Data System (ADS)

    Priya Rose, T.; di Gennaro, E.; Abbate, G.; Andreone, A.

    2011-09-01

    We report on the formation and development of the photonic band gap in two-dimensional 8-, 10-, and 12-fold symmetry quasicrystalline lattices of low-index contrast. Finite-size structures made of dielectric cylindrical rods were studied and measured in the microwave region, and their properties were compared with a conventional hexagonal crystal. Band-gap characteristics were investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0∘ to 30∘ were used to investigate the isotropic nature of the band gap. The arbitrarily high rotational symmetry of aperiodically ordered structures could be practically exploited to manufacture isotropic band-gap materials, which are perfectly suitable for hosting waveguides or cavities.

  7. Broad-band, multi-kilowatt, vacuum, HOM waveguide loads for the PEP-II RF cavity

    SciTech Connect

    Pendleton, R.; Ko, K.; Ng, C.; Schwarz, H.; Corlett, J.; Johnson, J.; Rimmer, R.

    1994-06-01

    For the HOM damping waveguides in the PEP-II RF cavity to work effectively as high-pass filters a broad-band, low-reflection, load is required with a VSWR less than 2:1 in the frequency range 700 MHz to 2500 Mhz. Additional design constraints are vacuum operation, thus eliminating an RF window and a potential source of reflections, and the capability of dissipating up to 10 kill of HOM power. A compact baseline design using a lossy dielectric is proposed which fulfills these requirements based on results from numerical simulations. We present the electrical properties of such a load, discuss its thermal properties under high power conditions, and detail a fabrication technique for brazing the lossy dielectric onto the copper walls of the HOM waveguide. Finally, simulation results of an alternative design utilizing ferrites are presented.

  8. Broad-band linear polarization in cool stars. II - Amplitude and wavelength dependence for magnetic and scattering regions

    NASA Technical Reports Server (NTRS)

    Saar, Steven H.; Huovelin, Juhani

    1993-01-01

    We have developed a model to estimate the amplitude and wavelength dependence of broad-band linear polarization (BLP) from magnetic regions on cool stars. The model includes corrections both for line blends and for the partial cancellation of polarization in the vector sum over the stellar disk. Our results agree with recent calculations of BLP in the red, but show larger amplitudes and a different wavelength dependence in the blue. We find that the detailed wavelength dependence of the polarization is complex and varies with effective temperature and gravity due to changes in line blanketing. The BLP amplitudes depend strongly on field strength, blanketing, and magnetic region filling factor and geometry. We make rough estimates of the maximum BLP for stars of various spectral types and demonstrate a method for deriving a lower limit to the filling factor from the maximum observed BLP. This lower limit is related to the fractional area covered by the spatially asymmetric component of magnetic regions.

  9. Phase velocities of Rayleigh and Love waves in central and northern Europe from automated, broad-band, interstation measurements

    NASA Astrophysics Data System (ADS)

    Soomro, R. A.; Weidle, C.; Cristiano, L.; Lebedev, S.; Meier, T.; Passeq Working Group

    2016-01-01

    The increasingly dense coverage of Europe with broad-band seismic stations makes it possible to image its lithospheric structure in great detail, provided that structural information can be extracted effectively from the very large volumes of data. We develop an automated technique for the measurement of interstation phase velocities of (earthquake-excited) fundamental-mode surface waves in very broad period ranges. We then apply the technique to all available broad-band data from permanent and temporary networks across Europe. In a new implementation of the classical two-station method, Rayleigh and Love dispersion curves are determined by cross-correlation of seismograms from a pair of stations. An elaborate filtering and windowing scheme is employed to enhance the target signal and makes possible a significantly broader frequency band of the measurements, compared to previous implementations of the method. The selection of acceptable phase-velocity measurements for each event is performed in the frequency domain, based on a number of fine-tuned quality criteria including a smoothness requirement. Between 5 and 3000 single-event dispersion measurements are averaged per interstation path in order to obtain robust, broad-band dispersion curves with error estimates. In total, around 63,000 Rayleigh- and 27,500 Love-wave dispersion curves between 10 and 350 s have been determined, with standard deviations lower than 2 per cent and standard errors lower than 0.5 per cent. Comparisons of phase-velocity measurements using events at opposite backazimuths and the examination of the variance of the phase-velocity curves are parts of the quality control. With the automated procedure, large data sets can be consistently and repeatedly measured using varying selection parameters. Comparison of average interstation dispersion curves obtained with different degrees of smoothness shows that rough perturbations do not systematically bias the average dispersion measurement. They

  10. Flight qualified solid argon cooler for the BBXRT instrument. [Broad Band X Ray Telescope for ASTRO-1 payload

    NASA Technical Reports Server (NTRS)

    Cygnarowicz, Thomas A.; Schein, Michael E.; Lindauer, David A.; Scarlotti, Roger; Pederson, Robert

    1990-01-01

    A solid argon cooler (SAC) for attached Shuttle payloads has been developed and qualified to meet the need for low cost cooling of flight instruments to the temperature range of 60-120 K. The SACs have been designed and tested with the intent of flying them up to five times. Two coolers, as part of the Broad Band X-ray Telescope (BBXRT) instrument on the ASTRO-1 payload, are awaiting launch on Space Shuttle mission STS-35. This paper describes the design, testing and performance of the SAC and its vacuum maintenance system (VMS), used to maintain the argon as a solid during launch delays of up to 5 days. BBXRT cryogen system design features used to satisfy Shuttle safety requirements are discussed, along with SAC ground servicing equipment (GSE) and procedures used to fill, freeze and subcool the argon.

  11. Comparison of M46 broad-band visible data with ELF data from the Sprites `96 campaign

    SciTech Connect

    Mitchell, E.A.

    1997-10-01

    Lightning data, recorded with satellite optical sensors, are compared with extremely low frequency (ELF) and Schumann resonance (SR) data from the Sprites `96 Campaign. The satellite data are broad-band visible events recorded by the M46 satellite payload. Full width at half maximum and optical tail durations from the satellite data are compared with ELF slow tail features and Schumann resonance spectral color. In addition, continuing current estimates were computed for several positive cloud-to-ground (PCG) strokes. These estimates were derived using relative optical intensities from the satellite data and a peak current measurement from National Lightning Detection Network (NLDN) data. This assessment of M46 lightning data supports correlations between visible and ELF signatures. More data must be studied for compelling proof.

  12. A flexible experimental setup for femtosecond time-resolved broad-band ellipsometry and magneto-optics

    SciTech Connect

    Boschini, F.; Hedayat, H.; Piovera, C.; Dallera, C.; Gupta, A.; Carpene, E.

    2015-01-15

    A versatile experimental setup for femtosecond time-resolved ellipsometry and magneto-optical Kerr effect measurements in the visible light range is described. The apparatus is based on the pump-probe technique and combines a broad-band probing beam with an intense near-infrared pump. According to Fresnel scattering matrix formalism, the analysis of the reflected beam at different polarization states of the incident probe light allows one to determine the diagonal and the off-diagonal elements of the dielectric tensor in the investigated sample. Moreover, the pump-probe method permits to study the dynamics of the dielectric response after a short and intense optical excitation. The performance of the experimental apparatus is tested on CrO{sub 2} single crystals as a benchmark.

  13. A flexible experimental setup for femtosecond time-resolved broad-band ellipsometry and magneto-optics.

    PubMed

    Boschini, F; Hedayat, H; Piovera, C; Dallera, C; Gupta, A; Carpene, E

    2015-01-01

    A versatile experimental setup for femtosecond time-resolved ellipsometry and magneto-optical Kerr effect measurements in the visible light range is described. The apparatus is based on the pump-probe technique and combines a broad-band probing beam with an intense near-infrared pump. According to Fresnel scattering matrix formalism, the analysis of the reflected beam at different polarization states of the incident probe light allows one to determine the diagonal and the off-diagonal elements of the dielectric tensor in the investigated sample. Moreover, the pump-probe method permits to study the dynamics of the dielectric response after a short and intense optical excitation. The performance of the experimental apparatus is tested on CrO2 single crystals as a benchmark. PMID:25638099

  14. A flexible experimental setup for femtosecond time-resolved broad-band ellipsometry and magneto-optics

    NASA Astrophysics Data System (ADS)

    Boschini, F.; Hedayat, H.; Piovera, C.; Dallera, C.; Gupta, A.; Carpene, E.

    2015-01-01

    A versatile experimental setup for femtosecond time-resolved ellipsometry and magneto-optical Kerr effect measurements in the visible light range is described. The apparatus is based on the pump-probe technique and combines a broad-band probing beam with an intense near-infrared pump. According to Fresnel scattering matrix formalism, the analysis of the reflected beam at different polarization states of the incident probe light allows one to determine the diagonal and the off-diagonal elements of the dielectric tensor in the investigated sample. Moreover, the pump-probe method permits to study the dynamics of the dielectric response after a short and intense optical excitation. The performance of the experimental apparatus is tested on CrO2 single crystals as a benchmark.

  15. Swiss AlpArray: deployment of the Swiss AlpArray temporary broad-band stations and their noise characterization

    NASA Astrophysics Data System (ADS)

    Molinari, Irene; Kissling, Edi; Clinton, John; Hetényi, György; Šipka, Vesna; Stipćević, Josip; Dasović, Iva; Solarino, Stefano; Wéber, Zoltán; Gráczer, Zoltán; Electronics Lab, SED

    2016-04-01

    One of the main actions of the AlpArray European initiative is the deployment of a dense seismic broad-band network, that complements the existing permanent stations. This will ensure a spatially homogeneous seismic coverage of the greater Alpine area for at least two years, allowing a great number of innovative scientific works to be carried out. Our contribution to the AlpArray Seismic Network consists in the deployment of 24 temporary broad-band stations: three in Switzerland, twelve in Italy, three in Croatia, three in Bosnia and Herzegovina and three in Hungary. This deployment is lead by ETH Zurich and founded by the Swiss-AlpArray Sinergia programme by SNSF, and is the result of a fruitful collaboration between five research institutes. Stations were installed between Autumn and Winter 2015. Our installations are both free field and in-house and consist of 21 STS-2 and 3 Trillium Compact sensors equipped with Taurus digitizers and 3G telemetry sending data in real time to the ETH EIDA node. In this work, we present sites and stations setting and we discuss in details the characteristics in terms of site effects and noise level of each station. In particular we analyse the power spectral density estimates investigating the major source of noise and the background noise related to seasons, time of the day, human activities and type of installation. In addition we will show examples of data usage - i.e. earthquake locations, noise cross correlations, measures of surface wave dispersion curves. We thanks the Swiss AlpArray Field Team: Blanchard A., Erlanger E. D., Jarić D., Herak D., M. Herak, Hermann M., Koelemeijer P. J., Markušić S., Obermann A., Sager K., Šikman S., Singer J., Winterberg S. SED Electronic Lab: Barman S., Graf P., Hansemann R., Haslinger F., Hiemer S., Racine R., Tanner R., Weber F.

  16. Dual-band bandpass tunable microwave photonic filter based on stimulated Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Li, Jia-qi; Xiao, Yong-chuan; Dong, Wei; Zhang, Xin-dong

    2016-07-01

    A dual-band bandpass microwave photonic filter (MPF) based on stimulated Brillouin scattering (SBS) is theoretically analyzed and experimentally demonstrated. Two separated tunable laser sources (TLSs) are employed to generate two passbands by implementing phase modulation to amplitude modulation conversion by using SBS induced sideband amplification. The center frequencies of both passbands can be independently tuned ranging from 1 GHz to 19 GHz. High resolution with 3 dB bandwidth less than 30 MHz and large out-of-band rejection about 40 dB under 25 mW optical pump power are achieved.

  17. Photonic Generation of Dual-Band Power-Efficient Millimeter-Wave UWB Signals

    NASA Astrophysics Data System (ADS)

    Xiang, Peng; Guo, Hao; Chen, Dalei; Zhou, Hua

    2015-05-01

    Ultra-wideband (UWB) technology has attracted great interest because it can provide a promising solution of future radar and short-range broadband wireless communications. The generation of millimeter-wave UWB signals using photonic approaches can reduce the high cost of the millimeter-wave electrical circuits. Moreover, it is well compatible with fiber transmission, which can effectively extend its signal coverage. In this paper, a novel approach to the photonic generation of millimeter-wave UWB signals with dual-band operation consideration is proposed. The proposed scheme can simultaneously generate millimeter-wave UWB signals in both 24 GHz and 60 GHz millimeter band, and can efficiently exploit the spectrum limit allowed by the FCC mask by using the linear combination pulse design concept. A model describing the proposed system is developed and the generation of 24/60 GHz millimeter-wave UWB signals is demonstrated via computer simulations.

  18. Influence of structural parameters on tunable photonic band gaps modulated by liquid crystals

    NASA Astrophysics Data System (ADS)

    Huang, Aiqin; Zheng, Jihong; Jiang, Yanmeng; Zhou, Zengjun; Tang, Pingyu; Zhuang, Songlin

    2011-10-01

    Tunable photonic crystals (PCs), which are infiltrated with nematic liquid crystals (LCs), tune photonic band gap (PBG) by rotating directors of LCs when applied with the external electrical field. Using the plane wave expansion method, we simulated the PBG structure of two-dimensional tunable PCs with a triangular lattice of circular column, square column and hexagon column, respectively. When PCs are composed of LCs and different substrate materials such as germanium (Ge) and silicon (Si), the influence of structural parameters including column shape and packing ration on PBG is discussed separately. Numerical simulations show that absolute PBG can't be found at any conditions, however large tuning range of polarized wave can be achieved by rotating directors of LCs. The simulation results provide theoretical guidance for the fabrication of field-sensitive polarizer with big tunable band range.

  19. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, E.; Tuttle, G.; Michel, E.; Ho, K.M.; Biswas, R.; Chan, C.T.; Soukoulis, C.

    1995-04-11

    A method is disclosed for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap. 42 figures.

  20. Optimization of band gap of photonic crystals fabricated by holographic lithography

    NASA Astrophysics Data System (ADS)

    Yang, X.-L.; Cai, L.-Z.; Wang, Y.-R.; Feng, C.-S.; Dong, G.-Y.; Shen, X.-X.; Meng, X.-F.; Hu, Y.

    2008-01-01

    Generally the photonic band gap (PBG) is a multi-variable function of several parameters related to the shape and size of the dielectric columns of photonic crystals (PhCs), and a time-consuming step-by-step scanning process for each parameter has to be used to find their best combination yielding maximum PBG. In this letter, the widely used Nelder-Mead simplex algorithm is introduced to optimize these parameters simultaneously to find a larger PBG for a new kind of two-dimensional (2D) hexagonal GaAs-Air PhC. This structure can be conveniently produced by the single-exposure holographic lithography, and the specific holographic design is also systematically investigated. This study reveals that the band gaps of PhCs made by holographic lithography may be widened by introducing irregularity of the columns and lowering the symmetry of the structure.

  1. UV-VIS regime band gap in a 3-d photonic system

    NASA Astrophysics Data System (ADS)

    Yin, Ming; Arammash, Fouzi; Datta, Timir; Tsu, Ray

    2013-03-01

    Synthetic opals are self-organized bulk, close packed systems that are three-dimensionally ordered with periodicity determined by the sphere diameter. These materials have been used as templates for nano devices with novel properties. For example, in carbon inverse opals show quantum hall effect and related magneto electric responses. Inverse are also reported to show photonic band gap. It is expected that devices based on these materials will be an alternative to electronic devices. These opal specimens were hexagonal or face centered cubic crystals with silica sphere diameter ranging between 220 nm and 270nm. Here we will present results of structural and imaging studies such as SEM, AFM and XRD. In addition results of the (UV-VIS) optical behavior will be provided. The optical response will be analyzed in terms of photonic band gaps in the sub-micrometer optical and UV regime.

  2. Excitation, Ionization, and Desorption: How Sub-band gap Photons Modify the Structure of Oxide Nanoparticles

    SciTech Connect

    Trevisanutto, P. E.; Sushko, Petr V.; Beck, Kenneth M.; Joly, Alan G.; Hess, Wayne P.; Shluger, Alexander L.

    2009-01-29

    Nanoparticles of wide-band-gap materials MgO and CaO, subjected to low-intensity ultraviolet irradiation with 266 nm (4.66 eV) photons, emit hyperthermal oxygen atoms with kinetic energies up to ~ 0.4 eV. We use ab initio embedded cluster methods to study theoretically a variety of elementary photoinduced processes at both ideal and defect-containing surfaces of these nanoparticles and develop a mechanism for the desorption process. The proposed mechanism includes multiple local photoexcitations resulting in sequential formation of localized excitons, their ionization, and further excitations. It is suggested that judicious choice of sub-band-gap photon energies can be used to selectively modify surfaces of nanomaterials.

  3. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, Ekmel; Tuttle, Gary; Michel, Erick; Ho, Kai-Ming; Biswas, Rana; Chan, Che-Ting; Soukoulis, Costas

    1995-01-01

    A method for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap.

  4. Spatially graded TiO₂-SiO₂ Bragg reflector with rainbow-colored photonic band gap.

    PubMed

    Singh, Dhruv Pratap; Lee, Seung Hee; Choi, Il Yong; Kim, Jong Kyu

    2015-06-29

    A simple single-step method to fabricate spatially graded TiO2-SiO2 Bragg stack with rainbow colored photonic band gap is presented. The gradation in thickness of the Bragg stack was accomplished with a modified glancing angle deposition (GLAD) technique with dynamic shadow enabled by a block attached to one edge of the rotating substrate. A linear gradation in thickness over a distance of about 17 mm resulted in a brilliant colorful rainbow pattern. Interestingly, the photonic band gap position can be changed across the whole visible wavelength range by linearly translating the graded Bragg stack over a large area substrate. The spatially graded Bragg stack may find potential applications in the tunable optical devices, such as optical filters, reflection gratings, and lasers. PMID:26191764

  5. INTERACTION BETWEEN THE BROAD-LINED TYPE Ic SUPERNOVA 2012ap AND CARRIERS OF DIFFUSE INTERSTELLAR BANDS

    SciTech Connect

    Milisavljevic, Dan; Margutti, Raffaella; Crabtree, Kyle N.; Soderberg, Alicia M.; Sanders, Nathan E.; Drout, Maria R.; Kamble, Atish; Chakraborti, Sayan; Kirshner, Robert P.; Foster, Jonathan B.; Fesen, Robert A.; Parrent, Jerod T.; Pickering, Timothy E.; Cenko, S. Bradley; Silverman, Jeffrey M.; Marion, G. H. Howie; Vinko, Jozsef; Filippenko, Alexei V.; Mazzali, Paolo; Maeda, Keiichi; and others

    2014-02-10

    Diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond to electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova SN 2012ap that exhibit changes in equivalent width over short (≲ 30 days) timescales. The 4428 Å and 6283 Å DIB features get weaker with time, whereas the 5780 Å feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique information about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers.

  6. Interaction Between the Broad-Lined Type Ic Supernova 2012ap and Carriers of Diffuse Interstellar Bands

    NASA Technical Reports Server (NTRS)

    Milisavljevic, Dan; Margutti, Raffaella; Crabtree, Kyle N.; Foster, Jonathan B.; Soderberg, Alicia M.; Fesen, Robert A.; Parrent, Jerod T.; Sanders, Nathan E.; Drout, Maria R.; Kamble, Atish; Cenko, S. Bradley

    2014-01-01

    The diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond with electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad- lined Type Ic supernova SN2012ap that exhibit changes in equivalent width over short (. 30 days) timescales. The 4428 A and 6283 A DIB features get weaker with time, whereas the 5780 A feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of the DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique information about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers.

  7. High brightness photonic band crystal semiconductor lasers in the passive mode locking regime

    SciTech Connect

    Rosales, R.; Kalosha, V. P.; Miah, M. J.; Bimberg, D.; Posilović, K.; Pohl, J.; Weyers, M.

    2014-10-20

    High brightness photonic band crystal lasers in the passive mode locking regime are presented. Optical pulses with peak power of 3 W and peak brightness of about 180 MW cm{sup −2} sr{sup −1} are obtained on a 5 GHz device exhibiting 15 ps pulses and a very low beam divergence in both the vertical and horizontal directions.

  8. A versatile optical junction using photonic band-gap guidance and self collimation

    SciTech Connect

    Gupta, Man Mohan; Medhekar, Sarang

    2014-09-29

    We show that it is possible to design two photonic crystal (PC) structures such that an optical beam of desired wavelength gets guided within the line defect of the first structure (photonic band gap guidance) and the same beam gets guided in the second structure by self-collimation. Using two dimensional simulation of a design made of the combination of these two structures, we propose an optical junction that allows for crossing of two optical signals of same wavelength and same polarization with very low crosstalk. Moreover, the junction can be operated at number of frequencies in a wide range. Crossing of multiple beams with very low cross talk is also possible. The proposed junction should be important in future integrated photonic circuits.

  9. Photonic band gap in (Pb,La)(Zr,Ti)O3 inverse opals

    NASA Astrophysics Data System (ADS)

    Li, Bo; Zhou, Ji; Hao, Lifeng; Hu, Wei; Zong, Ruilong; Cai, Minmin; Fu, Min; Gui, Zhilun; Li, Longtu; Li, Qi

    2003-05-01

    (Pb,La)(Zr,Ti)O3 (PLZT) inverse opal photonic crystals were synthesized by a process of self-assembly in combination with a sol-gel technique. In this process, PLZT precursors were infiltrated into the interstices of the opal template assembled by monodisperse submicron polystyrene spheres, and then gelled in a humid environment. Polystyrene template was removed by calcining the specimen at a final temperature of 700 °C accompanied with the crystallization of perovskite phase in PLZT inverse opal network. Scanning electron microscope images show that the inverse opals possess a fcc structure with a lattice constant of 250 nm. A wide photonic band gap in the visible range is observed from transmission spectra of the sample. Such PLZT inverse opals as photonic crystals should be of importance in device applications.

  10. Synchronous chaos and broad band gamma rhythm in a minimal multi-layer model of primary visual cortex.

    PubMed

    Battaglia, Demian; Hansel, David

    2011-10-01

    Visually induced neuronal activity in V1 displays a marked gamma-band component which is modulated by stimulus properties. It has been argued that synchronized oscillations contribute to these gamma-band activity. However, analysis of Local Field Potentials (LFPs) across different experiments reveals considerable diversity in the degree of oscillatory behavior of this induced activity. Contrast-dependent power enhancements can indeed occur over a broad band in the gamma frequency range and spectral peaks may not arise at all. Furthermore, even when oscillations are observed, they undergo temporal decorrelation over very few cycles. This is not easily accounted for in previous network modeling of gamma oscillations. We argue here that interactions between cortical layers can be responsible for this fast decorrelation. We study a model of a V1 hypercolumn, embedding a simplified description of the multi-layered structure of the cortex. When the stimulus contrast is low, the induced activity is only weakly synchronous and the network resonates transiently without developing collective oscillations. When the contrast is high, on the other hand, the induced activity undergoes synchronous oscillations with an irregular spatiotemporal structure expressing a synchronous chaotic state. As a consequence the population activity undergoes fast temporal decorrelation, with concomitant rapid damping of the oscillations in LFPs autocorrelograms and peak broadening in LFPs power spectra. We show that the strength of the inter-layer coupling crucially affects this spatiotemporal structure. We predict that layer VI inactivation should induce global changes in the spectral properties of induced LFPs, reflecting their slower temporal decorrelation in the absence of inter-layer feedback. Finally, we argue that the mechanism underlying the emergence of synchronous chaos in our model is in fact very general. It stems from the fact that gamma oscillations induced by local delayed

  11. Broad-band spectral energy distribution of 3000 Å break quasars from the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Meusinger, H.; Schalldach, P.; Mirhosseini, A.; Pertermann, F.

    2016-03-01

    Context. In past decades, huge surveys have confirmed the existence of populations of exotic and hitherto unknown quasar types. The discovery and investigation of these rare peculiar objects is important because they may represent links to special evolutionary stages and hold clues to the evolution of quasars and galaxies. Aims: The Sloan Digital Sky Survey (SDSS) discovered the unusual quasars J010540.75-003313.9 and J220445.27+003141.8 and a small number of similar objects. Their spectra are characterised by a break in the continuum around 3000 Å that neither shows the typical structure of broad absorption line (BAL) troughs nor is explained by typical intrinsic dust reddening. The main aim of the present paper was twofold. First, a new target-oriented search was performed in the spectra database of the SDSS to construct a sizable sample of such 3000 Å break quasars. Second, their broad-band spectral energy distribution (SED) was compared with SEDs of BAL quasars. Methods: We used the method of Kohonen self-organising maps for data mining in the SDSS spectra archive to search for more quasars with properties comparable to the prototypes J010540.75-003313.9 and J220445.27+003141.8. We constructed a sample of 3000 Å break quasars and comparison samples of quasars with similar properties, to some extent, but also showing indications for typical BAL features. Particular attention was payed to a possible contamination by rare stellar spectral types, in particular DQ white dwarfs. We construct ensemble-averaged broad-band SEDs based on archival data from SDSS, GALEX, 2MASS, UKIDSS, WISE, and other surveys. The SEDs were corrected for dust absorption at the systemic redshifts of the quasars by the comparison with the average SED of normal quasars. Results: We compiled a list of 23 quasars classified as 3000 Å break quasars with properties similar to 010540.75-003313.9 and J220445.27+003141.8. Their de-reddened arithmetic median composite SED is indistinguishable

  12. Isotropic band gaps and freeform waveguides observed in hyperuniform disordered photonic solids

    PubMed Central

    Man, Weining; Florescu, Marian; Williamson, Eric Paul; He, Yingquan; Hashemizad, Seyed Reza; Leung, Brian Y. C.; Liner, Devin Robert; Torquato, Salvatore; Chaikin, Paul M.; Steinhardt, Paul J.

    2013-01-01

    Recently, disordered photonic media and random textured surfaces have attracted increasing attention as strong light diffusers with broadband and wide-angle properties. We report the experimental realization of an isotropic complete photonic band gap (PBG) in a 2D disordered dielectric structure. This structure is designed by a constrained optimization method, which combines advantages of both isotropy due to disorder and controlled scattering properties due to low-density fluctuations (hyperuniformity) and uniform local topology. Our experiments use a modular design composed of Al2O3 walls and cylinders arranged in a hyperuniform disordered network. We observe a complete PBG in the microwave region, in good agreement with theoretical simulations, and show that the intrinsic isotropy of this unique class of PBG materials enables remarkable design freedom, including the realization of waveguides with arbitrary bending angles impossible in photonic crystals. This experimental verification of a complete PBG and realization of functional defects in this unique class of materials demonstrate their potential as building blocks for precise manipulation of photons in planar optical microcircuits and has implications for disordered acoustic and electronic band gap materials. PMID:24043795

  13. Isotropic band gaps and freeform waveguides observed in hyperuniform disordered photonic solids.

    PubMed

    Man, Weining; Florescu, Marian; Williamson, Eric Paul; He, Yingquan; Hashemizad, Seyed Reza; Leung, Brian Y C; Liner, Devin Robert; Torquato, Salvatore; Chaikin, Paul M; Steinhardt, Paul J

    2013-10-01

    Recently, disordered photonic media and random textured surfaces have attracted increasing attention as strong light diffusers with broadband and wide-angle properties. We report the experimental realization of an isotropic complete photonic band gap (PBG) in a 2D disordered dielectric structure. This structure is designed by a constrained optimization method, which combines advantages of both isotropy due to disorder and controlled scattering properties due to low-density fluctuations (hyperuniformity) and uniform local topology. Our experiments use a modular design composed of Al2O3 walls and cylinders arranged in a hyperuniform disordered network. We observe a complete PBG in the microwave region, in good agreement with theoretical simulations, and show that the intrinsic isotropy of this unique class of PBG materials enables remarkable design freedom, including the realization of waveguides with arbitrary bending angles impossible in photonic crystals. This experimental verification of a complete PBG and realization of functional defects in this unique class of materials demonstrate their potential as building blocks for precise manipulation of photons in planar optical microcircuits and has implications for disordered acoustic and electronic band gap materials. PMID:24043795

  14. All-optical dynamical Casimir effect in a three-dimensional terahertz photonic band gap

    NASA Astrophysics Data System (ADS)

    Hagenmüller, David

    2016-06-01

    We identify an architecture for the observation of all-optical dynamical Casimir effect in realistic experimental conditions. We suggest that by integrating quantum wells in a three-dimensional (3D) photonic band-gap material made out of large-scale (˜200 -μ m ) germanium logs, it is possible to achieve ultrastrong light-matter coupling at terahertz frequencies for the cyclotron transition of a two-dimensional electron gas interacting with long-lived optical modes, in which vacuum Rabi splitting is comparable to the Landau level spacing. When a short, intense electromagnetic transient of duration ˜250 fs and carrying a peak magnetic field ˜5 T is applied to the structure, the cyclotron transition can be suddenly tuned on resonance with a desired photon mode, switching on the light-matter interaction and leading to a Casimir radiation emitted parallel to the quantum well plane. The radiation spectrum consists of sharp peaks with frequencies coinciding with engineered optical modes within the 3D photonic band gap, and its characteristics are extremely robust to the nonradiative damping which can be large in our system. Furthermore, the absence of continuum with associated low-energy excitations for both electromagnetic and electronic quantum states can prevent the rapid absorption of the photon flux which is likely to occur in other proposals for all-optical dynamical Casimir effect.

  15. Precision X-Band Linac Technologies for Nuclear Photonics Gamma-Ray Sources

    SciTech Connect

    Hartemann, F V; Albert, F; Anderson, S G; Bayramian, A J; Cross, R R; Ebbers, C A; Gibson, D J; Houck, T L; Marsh, R A; Messerly, M J; Siders, C W; McNabb, D P; Barty, C J; Adolphsen, C E; Chu, T S; Jongewaard, E N; Tantawi, S G; Vlieks, A E; Wang, F; Wang, J W; Raubenheimer, T O; Ighigeanu, D; Toma, M; Cutoiu, D

    2011-08-31

    Nuclear photonics is an emerging field of research requiring new tools, including high spectral brightness, tunable gamma-ray sources; high photon energy, ultrahigh-resolution crystal spectrometers; and novel detectors. This presentation focuses on the precision linac technology required for Compton scattering gamma-ray light sources, and on the optimization of the laser and electron beam pulse format to achieve unprecedented spectral brightness. Within this context, high-gradient X-band technology will be shown to offer optimal performance in a compact package, when used in conjunction with the appropriate pulse format, and photocathode illumination and interaction laser technologies. The nascent field of nuclear photonics is enabled by the recent maturation of new technologies, including high-gradient X-band electron acceleration, robust fiber laser systems, and hyper-dispersion CPA. Recent work has been performed at LLNL to demonstrate isotope-specific detection of shielded materials via NRF using a tunable, quasi-monochromatic Compton scattering gamma-ray source operating between 0.2 MeV and 0.9 MeV photon energy. This technique is called Fluorescence Imaging in the Nuclear Domain with Energetic Radiation (or FINDER). This work has, among other things, demonstrated the detection of {sup 7}Li shielded by Pb, utilizing gamma rays generated by a linac-driven, laser-based Compton scattering gamma-ray source developed at LLNL. Within this context, a new facility is currently under construction at LLNL, with the goal of generating tunable {gamma}-rays in the 0.5-2.5 MeV photon energy range, at a repetition rate of 120 Hz, and with a peak brightness in the 10{sup 20} photons/(s x mm{sup 2} x mrad{sup 2} x 0.1% bw).

  16. Analogy of transistor function with modulating photonic band gap in electromagnetically induced grating

    PubMed Central

    Wang, Zhiguo; Ullah, Zakir; Gao, Mengqin; Zhang, Dan; Zhang, Yiqi; Gao, Hong; Zhang, Yanpeng

    2015-01-01

    Optical transistor is a device used to amplify and switch optical signals. Many researchers focus on replacing current computer components with optical equivalents, resulting in an optical digital computer system processing binary data. Electronic transistor is the fundamental building block of modern electronic devices. To replace electronic components with optical ones, an equivalent optical transistor is required. Here we compare the behavior of an optical transistor with the reflection from a photonic band gap structure in an electromagnetically induced transparency medium. A control signal is used to modulate the photonic band gap structure. Power variation of the control signal is used to provide an analogy between the reflection behavior caused by modulating the photonic band gap structure and the shifting of Q-point (Operation point) as well as amplification function of optical transistor. By means of the control signal, the switching function of optical transistor has also been realized. Such experimental schemes could have potential applications in making optical diode and optical transistor used in quantum information processing. PMID:26349444

  17. Analogy of transistor function with modulating photonic band gap in electromagnetically induced grating

    NASA Astrophysics Data System (ADS)

    Wang, Zhiguo; Ullah, Zakir; Gao, Mengqin; Zhang, Dan; Zhang, Yiqi; Gao, Hong; Zhang, Yanpeng

    2015-09-01

    Optical transistor is a device used to amplify and switch optical signals. Many researchers focus on replacing current computer components with optical equivalents, resulting in an optical digital computer system processing binary data. Electronic transistor is the fundamental building block of modern electronic devices. To replace electronic components with optical ones, an equivalent optical transistor is required. Here we compare the behavior of an optical transistor with the reflection from a photonic band gap structure in an electromagnetically induced transparency medium. A control signal is used to modulate the photonic band gap structure. Power variation of the control signal is used to provide an analogy between the reflection behavior caused by modulating the photonic band gap structure and the shifting of Q-point (Operation point) as well as amplification function of optical transistor. By means of the control signal, the switching function of optical transistor has also been realized. Such experimental schemes could have potential applications in making optical diode and optical transistor used in quantum information processing.

  18. Spherical silicon-shell photonic band gap structures fabricated by laser-assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, H.; Yang, Z. Y.; Lu, Y. F.

    2007-02-01

    Laser-assisted chemical vapor deposition was applied in fabricating three-dimensional (3D) spherical-shell photonic band gap (PBG) structures by depositing silicon shells covering silica particles, which had been self-assembled into 3D colloidal crystals. The colloidal crystals of self-assembled silica particles were formed on silicon substrates using the isothermal heating evaporation approach. A continuous wave Nd:YAG laser (1064nm wavelength) was used to deposit silicon shells by thermally decomposing disilane gas. Periodic silicon-shell/silica-particle PBG structures were obtained. By removing the silica particles enclosed in the silicon shells using hydrofluoric acid, hollow spherical silicon-shell arrays were produced. This technique is capable of fabricating structures with complete photonic band gaps, which is predicted by simulations with the plane wave method. The techniques developed in this study have the potential to flexibly engineer the positions of the PBGs by varying both the silica particle size and the silicon-shell thickness. Ellipsometry was used to investigate the specific photonic band gaps for both structures.

  19. Broad-band efficiency calibration of ITER bolometer prototypes using Pt absorbers on SiN membranes.

    PubMed

    Meister, H; Willmeroth, M; Zhang, D; Gottwald, A; Krumrey, M; Scholze, F

    2013-12-01

    The energy resolved efficiency of two bolometer detector prototypes for ITER with 4 channels each and absorber thicknesses of 4.5 μm and 12.5 μm, respectively, has been calibrated in a broad spectral range from 1.46 eV up to 25 keV. The calibration in the energy range above 3 eV was performed against previously calibrated silicon photodiodes using monochromatized synchrotron radiation provided by five different beamlines of Physikalische Technische Bundesanstalt at the electron storage rings BESSY II and Metrology Light Source in Berlin. For the measurements in the visible range, a setup was realised using monochromatized halogen lamp radiation and a calibrated laser power meter as reference. The measurements clearly demonstrate that the efficiency of the bolometer prototype detectors in the range from 50 eV up to ≈6 keV is close to unity; at a photon energy of 20 keV the bolometer with the thick absorber detects 80% of the photons, the one with the thin absorber about 50%. This indicates that the detectors will be well capable of measuring the plasma radiation expected from the standard ITER scenario. However, a minimum absorber thickness will be required for the high temperatures in the central plasma. At 11.56 keV, the sharp Pt-L3 absorption edge allowed to cross-check the absorber thickness by fitting the measured efficiency to the theoretically expected absorption of X-rays in a homogeneous Pt-layer. Furthermore, below 50 eV the efficiency first follows the losses due to reflectance expected for Pt, but below 10 eV it is reduced further by a factor of 2 for the thick absorber and a factor of 4 for the thin absorber. Most probably, the different histories in production, storage, and operation led to varying surface conditions and additional loss channels. PMID:24387428

  20. Broad-band efficiency calibration of ITER bolometer prototypes using Pt absorbers on SiN membranes

    NASA Astrophysics Data System (ADS)

    Meister, H.; Willmeroth, M.; Zhang, D.; Gottwald, A.; Krumrey, M.; Scholze, F.

    2013-12-01

    The energy resolved efficiency of two bolometer detector prototypes for ITER with 4 channels each and absorber thicknesses of 4.5 μm and 12.5 μm, respectively, has been calibrated in a broad spectral range from 1.46 eV up to 25 keV. The calibration in the energy range above 3 eV was performed against previously calibrated silicon photodiodes using monochromatized synchrotron radiation provided by five different beamlines of Physikalische Technische Bundesanstalt at the electron storage rings BESSY II and Metrology Light Source in Berlin. For the measurements in the visible range, a setup was realised using monochromatized halogen lamp radiation and a calibrated laser power meter as reference. The measurements clearly demonstrate that the efficiency of the bolometer prototype detectors in the range from 50 eV up to ≈6 keV is close to unity; at a photon energy of 20 keV the bolometer with the thick absorber detects 80% of the photons, the one with the thin absorber about 50%. This indicates that the detectors will be well capable of measuring the plasma radiation expected from the standard ITER scenario. However, a minimum absorber thickness will be required for the high temperatures in the central plasma. At 11.56 keV, the sharp Pt-L3 absorption edge allowed to cross-check the absorber thickness by fitting the measured efficiency to the theoretically expected absorption of X-rays in a homogeneous Pt-layer. Furthermore, below 50 eV the efficiency first follows the losses due to reflectance expected for Pt, but below 10 eV it is reduced further by a factor of 2 for the thick absorber and a factor of 4 for the thin absorber. Most probably, the different histories in production, storage, and operation led to varying surface conditions and additional loss channels.

  1. Inverse dispersion method for calculation of complex photonic band diagram and PT symmetry

    NASA Astrophysics Data System (ADS)

    Rybin, Mikhail V.; Limonov, Mikhail F.

    2016-04-01

    We suggest an inverse dispersion method for calculating a photonic band diagram for materials with arbitrary frequency-dependent dielectric functions. The method is able to calculate the complex wave vector for a given frequency by solving the eigenvalue problem with a non-Hermitian operator. The analogy with PT -symmetric Hamiltonians reveals that the operator corresponds to the momentum as a physical quantity, and the singularities at the band edges are related to the branch points and responses for the features on the band edges. The method is realized using a plane wave expansion technique for a two-dimensional periodic structure in the case of TE and TM polarizations. We illustrate the applicability of the method by the calculation of the photonic band diagrams of an infinite two-dimensional square lattice composed of dielectric cylinders using the measured frequency-dependent dielectric functions of different materials (amorphous hydrogenated carbon, silicon, and chalcogenide glass). We show that the method allows one to distinguish unambiguously between Bragg and Mie gaps in the spectra.

  2. Broad beam attenuation of kilovoltage photon beams: effect of ion chambers.

    PubMed

    Das, I J

    1998-01-01

    In kilovoltage X-ray treatment, beam shaping and shielding normal tissue are accomplished by thin sheets of lead cutout, the thickness of which is selected based upon either published data or measurements. Available broad beam attenuation (BBA) data are found to be unsatisfactory and are the subject of this investigation. BBA is defined as the ratio of intensity with (I) and without (I0) attenuating medium for a large field in a phantom. BBA = I(x,t,E)/I0(x,0,E), where x is the depth of measurement, t is the thickness of attenuator, and E is the beam energy. The depth x should be zero for kilovoltage beams and dmax for megavoltage beams. Unfortunately, x is limited by the window thickness which is the core of this study. A Farmer-type cylindrical ion chamber and three parallel plate ion chambers (Capintec, PS-033; Markus; and Holt) were used to measure BBA for kilovoltage beams from a Siemens Stabilipan unit. Results indicate that attenuation is strongly dependent on the window thickness. For the 240 kVp beam, the thickness of lead for 5% and 1% transmissions are 3.1 mm, and 5.2 mm, respectively, with the Capintec chamber. The corresponding values of lead thickness for the Markus chamber are 2.3 mm and 4.0 mm; for the Holt chamber the values are 1.1 mm and 2.2 mm; and for the cylindrical chambers the values are 1.1 mm and 2.3 mm, respectively. Similar variabilities in lead thickness with ion chambers were also noted for the other kilovoltage beams. The large differences in lead thicknesses produce enormous clinical errors, especially for shielding eye and other critical structures. For small thickness of lead (< 0.1 mm), a 20-fold increase in surface dose could be observed instead of usual beam attenuation. This is due to intense low energy photoelectrons liberated from lead sheets in the contact with tissue. It is concluded that the lead thickness required to shield normal tissue varies with ion chamber. Until national or international guidelines for broad beam

  3. Photonic band-gap modulation of blue phase liquid crystal (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Lin, Tsung-Hsien

    2015-10-01

    Blue phase liquid crystals (BPLCs) are self-assembled 3D photonic crystals exhibiting high susceptibility to external stimuli. Two methods for the photonic bandgap tuning of BPs were demonstrated in this work. Introducing a chiral azobenzene into a cholesteric liquid crystal could formulate a photoresponsive BPLC. Under violet irradiation, the azo dye experiences trans-cis isomerization, which leads to lattice swelling as well as phase transition in different stages of the process. Ultrawide reversible tuning of the BP photonic bandgap from ultraviolet to near infrared has been achieved. The tuning is reversible and nonvolatile. We will then demonstract the electric field-induced bandgap tuning in polymer-stabilized BPLCs. Under different BPLCs material preparation conditions, both red-shift and broadening of the photonic bandgaps have been achieved respectively. The stop band can be shifted over 100 nm. The bandwidth can be expanded from ~ 30 nm to ~ 250 nm covering nearly the full visible range. It is believed that the developed approaches could strongly promote the use of BPLC in photonic applications.

  4. Low-threshold photonic-band-edge laser using iron-nail-shaped rod array

    SciTech Connect

    Choi, Jae-Hyuck; No, You-Shin; Hwang, Min-Soo; Jeong, Kwang-Yong; Park, Hong-Gyu E-mail: hgpark@korea.ac.kr; Kwon, Soon-Yong; Yang, Jin-Kyu E-mail: hgpark@korea.ac.kr; Kwon, Soon-Hong

    2014-03-03

    We report the experimental demonstration of an optically pumped rod-type photonic-crystal band-edge laser. The structure consists of a 20 × 20 square lattice array of InGaAsP iron-nail-shaped rods. A single-mode lasing action is observed with a low threshold of ∼90 μW and a peak wavelength of 1451.5 nm at room temperature. Measurements of the polarization-resolved mode images and lasing wavelengths agree well with numerical simulations, which confirm that the observed lasing mode originates from the first Γ-point transverse-electric-like band-edge mode. We believe that this low-threshold band-edge laser will be useful for the practical implementation of nanolasers.

  5. Photoswitching properties of photonic band gap materials containing azo-polymer liquid crystal

    NASA Astrophysics Data System (ADS)

    Moritsugu, Masaki; Shirota, Tomomi; Kubo, Shoichi; Kim, Sun-nam; Ogata, Tomonari; Nonaka, Takamasa; Sato, Osamu; Kurihara, Seiji

    2008-08-01

    Photochemically tunable photonic band gap materials were prepared by infiltration of liquid crystal polymers having azobenzene groups into voids of SiO2 inverse opal films. Linearly polarized light irradiation resulted in transformation from a random to an anisotropic molecular orientation of azobenzene side chains in the voids of the SiO2 inverse opal film, leading to the reversible and stable shift of the reflection band to longer wavelength more than 15 nm. In order to improve switching properties, we used copolymers with azobenzene monomer and tolane monomer, which indicate higher birefringence, as infiltration materials into the voids. The azo-tolane copolymers were found to show the higher birefringence than azobenzene homopolymers by the linearly polarized light irradiation. Thus, the reflection band of the SiO2 inverse opal film infiltrated with the azo-tolane copolymers was shifted to long wavelength region more than 55 nm by the irradiation of linearly polarized light.

  6. Broad-Band Continuum and Line Emission of the gamma-Ray Blazar PKS 0537-441

    NASA Technical Reports Server (NTRS)

    Pian, E.; Falomo, R.; Hartman, R. C.; Maraschi, L.; Tavecchio, F.; Tornikoski, M.; Treves, A.; Urry, C. M.; Ballo, L.; Mukherjee, R.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    PKS 0537-441, a bright gamma ray emitting blazar was observed at radio, optical, UV and X-ray frequencies during various EGRET paintings, often quasi-simultaneously. In 1995 the object was found in an intense emission state at all wavelengths. BeppoSAX observations made in 1998, non-simultaneously with exposures at other frequencies, allow us to characterize precisely the spectral shape of the high energy blazer component, which we attribute to inverse Compton scatter in The optical-to-gamma-ray spectral energy distributions at the different epochs show that the gamma-ray luminosity dominates the barometric output. This, together with the presence of optical and UV line emission, suggests that, besides the synchrotron self-Compton mechanism, the Compton upscattering of photons external to the jet (e.g., in the broad line region) may have a significant role for high energy radiation. The multiwavelength variability can be reproduced by changes of the plasma bulk Lorentz factor. The spectrum secured by ICE in 1995 appears to be partially absorbed shortward of approximately 1700 Angstroms. However, this signature is not detected in the HST spectrum taker during a lower state of the source. The presence of intervening absorbers is not supported by optical imaging and spectroscopy of the field.

  7. The Seismic Broad Band Western Mediterranean (wm) Network and the Obs Fomar Pool: Current state and Obs activities.

    NASA Astrophysics Data System (ADS)

    Pazos, Antonio; Davila, Jose Martin; Buforn, Elisa; Bezzeghoud, Mourad; Harnafi, Mimoun; Mattesini, Mauricio; Caldeira, Bento; Hanka, Winfried; El Moudnib, Lahcen; Strollo, Angelo; Roca, Antoni; Lopez de Mesa, Mireya; Dahm, Torsten; Cabieces, Roberto

    2016-04-01

    The Western Mediterranean (WM) seismic network started in 1996 as an initiative of the Royal Spanish Navy Observatory (ROA) and the Universidad Complutense de Madrid (UCM), with the collaboration of the GeoForschungsZentrum (GFZ) of Potsdam. A first broad band seismic station (SFUC) was installed close to Cádiz (South Spain). Since then, additional stations have been installed in the Ibero-Moghrebian region. In 2005, the "WM" code was assigned by the FDSN and new partners were jointed: Evora University (UEVO, Portugal), the Scientifique Institute of Rabat (ISRABAT, Morocco), and GFZ. Now days, the WM network is composed by 15 BB stations, all of them with Streckaisen STS-2 or STS-2.5 sensors, Quanterra or Earthdata digitizers and SeiscomP. Most them have co-installed a permanent geodetic GPS stations, and some them also have an accelerometer. There are 10 stations deployed in Spanish territory (5 in the Iberian peninsula, 1 in Balearic islands and 4 in North Africa Spanish places) with VSAT or Internet communications, 2 in Portugal (one of them without real time), and 3 in Morocco (2 VSAT and 1 ADSL). Additionally, 2 more stations (one in South Spain and one in Morocco) will be installed along this year. Additionally ROA has deployed a permanent real time VBB (CMG-3T: 360s) station at the Alboran Island. Due to the fact that part of the seismic activity is located at marine areas, and also because of the poor geographic azimuthal coverage at some zones provided by the land stations (specially in the SW of the San Vicente Cape area), ROA and UCM have acquired six broad band "LOBSTERN" OBS, manufactured by KUM (Kiel, Germany), conforming the OBS FOMAR pool. Three of them with CMG-40T sensor and the other with Trillium 120. These OBS were deployed along the Gibraltar strait since January to November 2014 to study the microseismicity in the Gibraltar strait area. In September 2015 FOMAR network has been deployed in SW of the San Vicente Cape for 8 months as a part of

  8. CW-pumped telecom band polarization entangled photon pair generation in a Sagnac interferometer.

    PubMed

    Li, Yan; Zhou, Zhi-Yuan; Ding, Dong-Sheng; Shi, Bao-Sen

    2015-11-01

    Polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum communications, quantum computation and high precision quantum metrology. We report on the generation of a continuous-wave pumped 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II periodically poled KTiOPO(4) (PPKTP) crystal in a Sagnac interferometer. Hong-Ou-Mandel (HOM) interference measurement yields signal and idler photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The source can be tuned over a broad range against temperature or pump power without loss of visibilities. This source will be used in our future experiments such as generation of orbital angular momentum entangled source at telecom wavelength for quantum frequency up-conversion, entanglement based quantum key distributions and many other quantum optics experiments at telecom wavelengths. PMID:26561148

  9. Investigation of anisotropic photonic band gaps in three-dimensional magnetized plasma photonic crystals containing the uniaxial material

    SciTech Connect

    Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun

    2013-09-15

    In this paper, the dispersive properties of three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic photonic band gaps (PBGs) in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatbands regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field on the dispersive properties of the 3D MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D MPPCs with fcc lattices and the complete PBGs can be found compared to the conventional 3D MPPCs doped by the isotropic material. The bandwidths of PBGs can be tuned by introducing the magnetized plasma into 3D PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field, respectively. The locations of flatbands regions cannot be manipulated by any parameters except for the plasma frequency and external magnetic field. Introducing the uniaxial material can obtain the complete PBGs as the 3D MPPCs with high symmetry and also provides a way to design the tunable devices.

  10. Monolithically integrated broad-band Mach-Zehnder interferometers for highly sensitive label-free detection of biomolecules through dual polarization optics

    PubMed Central

    Psarouli, A.; Salapatas, A.; Botsialas, A.; Petrou, P. S.; Raptis, I.; Makarona, E.; Jobst, G.; Tukkiniemi, K.; Sopanen, M.; Stoffer, R.; Kakabakos, S. E.; Misiakos, K.

    2015-01-01

    Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated. PMID:26825114

  11. Monolithically integrated broad-band Mach-Zehnder interferometers for highly sensitive label-free detection of biomolecules through dual polarization optics.

    PubMed

    Psarouli, A; Salapatas, A; Botsialas, A; Petrou, P S; Raptis, I; Makarona, E; Jobst, G; Tukkiniemi, K; Sopanen, M; Stoffer, R; Kakabakos, S E; Misiakos, K

    2016-01-01

    Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated. PMID:26825114

  12. Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at Z greater than 1

    NASA Technical Reports Server (NTRS)

    VanDerWel, A.; Straughn, A. N.; Rix, H.-W.; Finkelstein, S. L.; Koekemoer, A. M.; Weiner, B. J.; Wuyts, S.; Bell, E. F.; Faber, S. M.; Trump, J. R.; Koo, D.; Ferguson, H. C.; Scarlata, C.; Hathi, N. P.; Dunlop, J. S.; Newman, J. A.; Kocevski, D. D.; Lai, K.; Grogin, N. A.; Rodney, S. A.; Lee, K.-S.; Guo, Y.

    2011-01-01

    We identify an abundant population of extreme emission line galaxies at redshift z=1.6 - 1.8 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). 69 candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared, broad-band fluxes. Supported by spectroscopic confirmation of strong [OIII] emission lines - with equivalent widths approximately 1000A - in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are dwarf galaxies with approximately 10(exp 8) solar mass in stellar mass, undergoing an enormous star-burst phase with M*/M* of only approximately 10 Myr. The star formation activity and the co-moving number density (3.7 x 10(exp -4) Mpc(exp -3)) imply that strong, short-lived bursts play a significant, perhaps even dominant role in the formation and evolution of dwarf galaxies at z greater than 1. The observed star formation activity can produce in less than 5 Gyr the same amount of stellar mass density as is presently contained in dwarf galaxies. Therefore, our observations provide a strong indication that the stellar populations of present-day dwarf galaxies formed mainly in strong, short-lived bursts, mostly at z greater than 1.

  13. Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at Z greater than 1

    NASA Technical Reports Server (NTRS)

    vanderWel, A.; Straughn, A. N.; Rix, H.-W.; Finkelstein, S. L.; Koekemoer, A. M.; Weiner, B. J.; Wuyts, S.; Bell, E. F.; Faber, S. M.; Trump, J. R.; Koo, D. C.; Ferguson, H. C.; Scarlata, C.; Hathi, N. P.; Dunlop, J. S.; Newman, J. A.; Dickinson, M.; Jahnke, K.; Salmon, B. W.; deMello, D. F.; Kkocevski, D. D.; Lai, K.; Grogin, N. A.; Rodney, S. A.; Guo, Yicheng

    2012-01-01

    We identify an abundant population of extreme emission line galaxies (EELGs) at redshift z approx. 1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). 69 EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broad-band magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission lines . with rest-frame equivalent widths approx. 1000A in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with approx.10(exp 8) Solar Mass in stellar mass, undergoing an enormous starburst phase with M*/M* of only approx. 15 Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the co-moving number density (3.7x10(exp -4) Mpc(sup -3) can produce in approx.4 Gyr much of the stellar mass density that is presently contained in 10(exp 8) - 10(exp 9) Solar Mass dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z > 1.

  14. High-resolution line-shape spectroscopy during a laser pulse based on Dual-Broad-Band-CARS interferometry

    SciTech Connect

    Vereschagin, Konstantin A; Vereschagin, Alexey K; Smirnov, Valery V; Stelmakh, O M; Fabelinskii, V I; Clauss, W; Klimenko, D N; Oschwald, M E-mail: Al_Vereshchagin@mail.r E-mail: stelmakh@kapella.gpi.r

    2006-07-31

    A high-resolution spectroscopic method is developed for recording Raman spectra of molecular transitions in transient objects during a laser pulse with a resolution of {approx}0.1 cm{sup -1}. The method is based on CARS spectroscopy using a Fabry-Perot interferometer for spectral analysis of the CARS signal and detecting a circular interferometric pattern on a two-dimensional multichannel photodetector. It is shown that the use of the Dual-Broad-Band-CARS configuration to obtain the CARS process provides the efficient averaging of the spectral-amplitude noise of the CARS signal generated by a laser pulse and, in combination with the angular integration of the two-dimensional interference pattern, considerably improves the quality of interferograms. The method was tested upon diagnostics of the transient oxygen-hydrogen flame where information on the shapes of spectral lines of the Q-branch of hydrogen molecules required for measuring temperature was simultaneously obtained and used. (special issue devoted to the 90th anniversary of a.m. prokhorov)

  15. High resolution broad-band spectroscopy in the NIR using the Triplespec externally dispersed interferometer at the Hale telescope

    NASA Astrophysics Data System (ADS)

    Erskine, David J.; Edelstein, J.; Sirk, M.; Wishnow, E.; Ishikawa, Y.; McDonald, E.; Shourt, W. V.

    2014-07-01

    High resolution broad-band spectroscopy at near-infrared wavelengths has been performed using externally dis- persed interferometry (EDI) at the Hale telescope at Mt. Palomar. The EDI technique uses a field-widened Michelson interferometer in series with a dispersive spectrograph, and is able to recover a spectrum with a resolution 4 to 10 times higher than the existing grating spectrograph. This method increases the resolution well beyond the classical limits enforced by the slit width and the detector pixel Nyquist limit and, in principle, decreases the effect of pupil variation on the instrument line-shape function. The EDI technique permits arbi- trarily higher resolution measurements using the higher throughput, lower weight, size, and expense of a lower resolution spectrograph. Observations of many stars were performed with the TEDI interferometer mounted within the central hole of the 200 inch primary mirror. Light from the interferometer was then dispersed by the TripleSpec near-infrared echelle spectrograph. Continuous spectra between 950 and 2450 nm with a resolution as high as ~27,000 were recovered from data taken with TripleSpec at a native resolution of ˜2,700. Aspects of data analysis for interferometric spectral reconstruction are described. This technique has applications in im- proving measurements of high-resolution stellar template spectra, critical for precision Doppler velocimetry using conventional spectroscopic methods. A new interferometer to be applied for this purpose at visible wavelengths is under construction.

  16. Broad band X-ray Telescope observations of the hot interstellar media in NGC 1399 and NGC 4472

    NASA Technical Reports Server (NTRS)

    Serlemitsos, P. J.; Loewenstein, M.; Mushotzky, R. F.; Marshall, F. E.; Petre, R.

    1993-01-01

    We present our analysis and interpretation of spatially resolved X-ray spectroscopy of the elliptical galaxies NGC 1399 and NGC 4472 obtained with the Broad Band X-Ray Telescope. The X-ray emission from both galaxies is dominated by thermal emission from a hot interstellar medium. The temperature of the plasma in NGC 1399 is 1.0-1.2 keV with a mild positive temperature gradient; for NGC 4472 the average temperature is 0.7-1.0 keV. The temperature of NGC 1399, when combined with other X-ray and optical data, implies that, if the gas is gravitationally confined, about 70 percent of the mass inside a radius of about 8.6 arcmin (38 kpc) is nonluminous. The derived metallicities and metallicity gradients are consistent with optically determined stellar metallicities, and allow surprisingly small upper limits to be placed on Type Ia supernovae rates in both galaxies. The implications of this for the gasdynamical evolution of the two galaxies are discussed. Limits on the oxygen-to-iron ratio and the line-of-sight column density are derived. There is a possible detection of cold gas in the line of sight to NGC 1399 that exceeds the Galactic value. Constraints on the contribution from a harder spectral component are placed, and likely candidates for the origin of this secondary component are evaluated.

  17. Transverse acceleration of oxygen ions by electromagnetic ion cyclotron resonance with broad band left-hand polarized waves

    NASA Technical Reports Server (NTRS)

    Chang, T.; Crew, G. B.; Hershkowitz, N.; Jasperse, J. R.; Retterer, J. M.

    1986-01-01

    Central plasma sheet (CPS) ion conics are oxygen-dominated, with peak energies ranging from tens to hundreds of eV centered around pitch-angles between 115 and 130 degrees. Because of the lack of correlation between the CPS conics and the observed currents and/or electron beam-like structures, it is not likely that all of these conics are generated by interactions with electrostatic ion cyclotron waves or lower hybrid waves. Instead, it is suggested that the observed intense broad band electric field fluctuations in the frequency range between 0 and 100 Hz can be responsible for the transverse energization of the ions through cyclotron resonance heating with the left-hand polarized electromagnetic waves. This process is much more efficient for heating the oxygen ions than hydrogen ions, thus providing a plausible explanation of the oxygen dominance in CPS conics. Simple algebraic expressions are given from which estimates of conic energy and pitch angle can be easily calculated. This suggested mechanism can also provide some preheating of the oxygen ions in the boundary plasma sheet (BPS) where discrete aurorae form.

  18. The properties of photonic band gaps for three-dimensional plasma photonic crystals in a diamond structure

    SciTech Connect

    Zhang Haifeng; Liu Shaobin; Kong Xiangkun, Chenchen; Bian Borui

    2013-04-15

    In this paper, the properties of photonic band gaps (PBGs) for two types of three-dimensional plasma photonic crystals (PPCs) composed of isotropic dielectric and unmagnetized plasma with diamond lattices are theoretically investigated for electromagnetic waves based on a modified plane wave expansion method. The equations for type-1 structure are theoretically deduced, which depend on the diamond lattices realization (dielectric spheres immersed in plasma background). The influences of dielectric constant of dielectric, plasma collision frequency, filling factor, and plasma frequency on PBGs are investigated, respectively, and some corresponding physical explanations and the possible methods to realize the three-dimensional PPCs in experiments are also given. From the numerical results, it has been shown that not only the locations but also the gap/midgap ratios of the PBGs for two types of PPCs can be tuned by plasma frequency, filling factor, and the relative dielectric constant, respectively. However, the plasma collision frequency has no effect on the frequency ranges and gap/midgap ratios of the PBGs for two types of PPCs.

  19. Analysis of photonic band gap in dispersive properties of tunable three-dimensional photonic crystals doped by magnetized plasma

    SciTech Connect

    Zhang HaiFeng; Liu Shaobin; Yang Huan; Kong Xiangkun

    2013-03-15

    In this paper, the magnetooptical effects in dispersive properties for two types of three-dimensional magnetized plasma photonic crystals (MPPCs) containing homogeneous dielectric and magnetized plasma with diamond lattices are theoretically investigated for electromagnetic (EM) wave based on plane wave expansion (PWE) method, as incidence EM wave vector is parallel to the external magnetic field. The equations for two types of MPPCs with diamond lattices (dielectric spheres immersed in magnetized plasma background or vice versa) are theoretically deduced. The influences of dielectric constant, plasma collision frequency, filling factor, the external magnetic field, and plasma frequency on the dispersive properties for both types of structures are studied in detail, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that the photonic band gaps (PBGs) for both types of MPPCs can be manipulated by plasma frequency, filling factor, the external magnetic field, and the relative dielectric constant of dielectric, respectively. Especially, the external magnetic field can enlarge the PBG for type-2 structure (plasma spheres immersed in dielectric background). However, the plasma collision frequency has no effect on the dispersive properties of two types of three-dimensional MPPCs. The locations of flatbands regions for both types of structures cannot be tuned by any parameters except for plasma frequency and the external magnetic field. The analytical results may be informative and of technical use to design the MPPCs devices.

  20. The properties of photonic band gaps for three-dimensional plasma photonic crystals in a diamond structure

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun; Chen-Chen; Bian, Bo-Rui

    2013-04-01

    In this paper, the properties of photonic band gaps (PBGs) for two types of three-dimensional plasma photonic crystals (PPCs) composed of isotropic dielectric and unmagnetized plasma with diamond lattices are theoretically investigated for electromagnetic waves based on a modified plane wave expansion method. The equations for type-1 structure are theoretically deduced, which depend on the diamond lattices realization (dielectric spheres immersed in plasma background). The influences of dielectric constant of dielectric, plasma collision frequency, filling factor, and plasma frequency on PBGs are investigated, respectively, and some corresponding physical explanations and the possible methods to realize the three-dimensional PPCs in experiments are also given. From the numerical results, it has been shown that not only the locations but also the gap/midgap ratios of the PBGs for two types of PPCs can be tuned by plasma frequency, filling factor, and the relative dielectric constant, respectively. However, the plasma collision frequency has no effect on the frequency ranges and gap/midgap ratios of the PBGs for two types of PPCs.

  1. Photonic-band-gap engineering for volume plasmon polaritons in multiscale multilayer hyperbolic metamaterials

    NASA Astrophysics Data System (ADS)

    Zhukovsky, Sergei V.; Orlov, Alexey A.; Babicheva, Viktoriia E.; Lavrinenko, Andrei V.; Sipe, J. E.

    2014-07-01

    We study theoretically the propagation of large-wave-vector waves (volume plasmon polaritons) in multilayer hyperbolic metamaterials with two levels of structuring. We show that when the parameters of a subwavelength metal-dielectric multilayer (substructure) are modulated (superstructured) on a larger, wavelength scale, the propagation of volume plasmon polaritons in the resulting multiscale hyperbolic metamaterials is subject to photonic-band-gap phenomena. A great degree of control over such plasmons can be exerted by varying the superstructure geometry. When this geometry is periodic, stop bands due to Bragg reflection form within the volume plasmonic band. When a cavity layer is introduced in an otherwise periodic superstructure, resonance peaks of the Fabry-Pérot nature are present within the stop bands. More complicated superstructure geometries are also considered. For example, fractal Cantor-like multiscale metamaterials are found to exhibit characteristic self-similar spectral signatures in the volume plasmonic band. Multiscale hyperbolic metamaterials are shown to be a promising platform for large-wave-vector bulk plasmonic waves, whether they are considered for use as a kind of information carrier or for far-field subwavelength imaging.

  2. Micro-metric electronic patterning of a topological band structure using a photon beam

    NASA Astrophysics Data System (ADS)

    Golden, Mark; Frantzeskakis, Emmanouil; de Jong, Nick; Huang, Yingkai; Wu, Dong; Pan, Yu; de Visser, Anne; van Heumen, Erik; van Bay, Tran; Zwartsenberg, Berend; Pronk, Pieter; Varier Ramankutty, Shyama; Tytarenko, Alona; Xu, Nan; Plumb, Nick; Shi, Ming; Radovic, Milan; Varkhalov, Andrei

    2015-03-01

    The only states crossing EF in ideal, 3D TIs are topological surface states. Single crystals of Bi2Se3andBi2Te3 are too defective to exhibit bulk-insulating behaviour, and ARPES shows topologically trivial 2DEGs at EF in the surface region due to downward band bending. Ternary & quaternary alloys of Bi /Te /Se /Sb hold promise for obtaining bulk-insulating crystals. Here we report ARPES data from quaternary, bulk-insulating, Bi-based TIs. Shortly after cleavage in UHV, downward band bending pulls the bulk conduction band below EF, once again frustrating the ``topological only'' ambition for the Fermi surface. However, there is light at the end of the tunnel: we show that a super-band-gap photon beam generates a surface photovoltage sufficient to flatten the bands, thereby recovering the ideal, ``topological only'' situation. In our bulk-insulating quaternary TIs, this effect is local in nature, and permits the writing of arbitrary, micron-sized patterns in the topological energy landscape at the surface. Support from FOM, NWO and the EU is gratefully acknowledged.

  3. Robust topology optimization of three-dimensional photonic-crystal band-gap structures.

    PubMed

    Men, H; Lee, K Y K; Freund, R M; Peraire, J; Johnson, S G

    2014-09-22

    We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for robust topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors. PMID:25321732

  4. Photonic-band-gap properties for two-component slow light

    SciTech Connect

    Ruseckas, J.; Kudriasov, V.; Juzeliunas, G.; Unanyan, R. G.; Otterbach, J.; Fleischhauer, M.

    2011-06-15

    We consider two-component ''spinor'' slow light in an ensemble of atoms coherently driven by two pairs of counterpropagating control laser fields in a double tripod-type linkage scheme. We derive an equation of motion for the spinor slow light (SSL) representing an effective Dirac equation for a massive particle with the mass determined by the two-photon detuning. By changing the detuning the atomic medium acts as a photonic crystal with a controllable band gap. If the frequency of the incident probe light lies within the band gap, the light experiences reflection from the sample and can tunnel through it. For frequencies outside the band gap, the transmission and reflection probabilities oscillate with the increasing length of the sample. In both cases the reflection takes place into the complementary mode of the probe field. We investigate the influence of the finite excited state lifetime on the transmission and reflection coefficients of the probe light. We discuss possible experimental implementations of the SSL using alkali-metal atoms such as rubidium or sodium.

  5. Robust topology optimization of three-dimensional photonic-crystal band-gap structures

    NASA Astrophysics Data System (ADS)

    Men, H.; Lee, K. Y. K.; Freund, R. M.; Peraire, J.; Johnson, S. G.

    2014-09-01

    We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for \\emph{robust} topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors.

  6. Efficient heralding of O-band passively spatial-multiplexed photons for noise-tolerant quantum key distribution.

    PubMed

    Liu, Mao Tong; Lim, Han Chuen

    2014-09-22

    When implementing O-band quantum key distribution on optical fiber transmission lines carrying C-band data traffic, noise photons that arise from spontaneous Raman scattering or insufficient filtering of the classical data channels could cause the quantum bit-error rate to exceed the security threshold. In this case, a photon heralding scheme may be used to reject the uncorrelated noise photons in order to restore the quantum bit-error rate to a low level. However, the secure key rate would suffer unless one uses a heralded photon source with sufficiently high heralding rate and heralding efficiency. In this work we demonstrate a heralded photon source that has a heralding efficiency that is as high as 74.5%. One disadvantage of a typical heralded photon source is that the long deadtime of the heralding detector results in a significant drop in the heralding rate. To counter this problem, we propose a passively spatial-multiplexed configuration at the heralding arm. Using two heralding detectors in this configuration, we obtain an increase in the heralding rate by 37% and a corresponding increase in the heralded photon detection rate by 16%. We transmit the O-band photons over 10 km of noisy optical fiber to observe the relation between quantum bit-error rate and noise-degraded second-order correlation function of the transmitted photons. The effects of afterpulsing when we shorten the deadtime of the heralding detectors are also observed and discussed. PMID:25321795

  7. Zero- n bar band gap in two-dimensional metamaterial photonic crystals

    NASA Astrophysics Data System (ADS)

    Mejía-Salazar, J. R.; Porras-Montenegro, N.

    2015-04-01

    We have theoretically studied metamaterial photonic crystals (PCs) composed by air and double negative (DNG) material. Numerical data were obtained by means of the finite difference time-domain (FDTD) method, with results indicating the possibility for the existence of the zero- n bar non-Bragg gap in two-dimensional metamaterial PCs, which has been previously observed only in one-dimensional photonic superlattices. Validity of the present FDTD algorithm for the study of one-dimensional metamaterial PCs is shown by comparing with results for the transmittance spectra obtained by means of the well known transfer matrix method (TMM). In the case of two-dimensional metamaterial PCs, we have calculated the photonic band structure (PBS) in the limiting case of a one-dimensional photonic superlattice and for a nearly one-dimensional PC, showing a very similar dispersion relation. Finally, we show that due to the strong electromagnetic field localization on the constitutive rods, the zero- n bar non-Bragg gap may only exist in two-dimensional systems under strict geometrical conditions.

  8. Spectral modification of the laser emission of a terahertz quantum cascade laser induced by broad-band double pulse injection seeding

    SciTech Connect

    Markmann, Sergej Nong, Hanond Hekmat, Negar; Jukam, Nathan; Pal, Shovon; Scholz, Sven; Kukharchyk, Nadezhda; Ludwig, Arne; Wieck, Andreas D.; Dhillon, Sukhdeep; Tignon, Jérôme; Marcadet, Xavier; Bock, Claudia; Kunze, Ulrich

    2015-09-14

    We demonstrate by injection seeding that the spectral emission of a terahertz (THz) quantum cascade laser (QCL) can be modified with broad-band THz pulses whose bandwidths are greater than the QCL bandwidth. Two broad-band THz pulses delayed in time imprint a modulation on the single THz pulse spectrum. The resulting spectrum is used to injection seed the THz QCL. By varying the time delay between the THz pulses, the amplitude distribution of the QCL longitudinal modes is modified. By applying this approach, the QCL emission is reversibly switched from multi-mode to single mode emission.

  9. Acousto-optic modulation of a photonic crystal nanocavity with Lamb waves in microwave K band

    SciTech Connect

    Tadesse, Semere A.; Li, Huan; Liu, Qiyu; Li, Mo

    2015-11-16

    Integrating nanoscale electromechanical transducers and nanophotonic devices potentially can enable acousto-optic devices to reach unprecedented high frequencies and modulation efficiency. Here, we demonstrate acousto-optic modulation of a photonic crystal nanocavity using Lamb waves with frequency up to 19 GHz, reaching the microwave K band. The devices are fabricated in suspended aluminum nitride membrane. Excitation of acoustic waves is achieved with interdigital transducers with period as small as 300 nm. Confining both acoustic wave and optical wave within the thickness of the membrane leads to improved acousto-optic modulation efficiency in these devices than that obtained in previous surface acoustic wave devices. Our system demonstrates a scalable optomechanical platform where strong acousto-optic coupling between cavity-confined photons and high frequency traveling phonons can be explored.

  10. Applicability of effective medium description to photonic crystals in higher bands: Theory and numerical analysis

    NASA Astrophysics Data System (ADS)

    Markel, Vadim A.; Tsukerman, Igor

    2016-06-01

    We consider conditions under which photonic crystals (PCs) can be homogenized in the higher photonic bands and, in particular, near the Γ point. By homogenization we mean introducing some effective local parameters ɛeff and μeff that describe reflection, refraction, and propagation of electromagnetic waves in the PC adequately. The parameters ɛeff and μeff can be associated with a hypothetical homogeneous effective medium. In particular, if the PC is homogenizable, the dispersion relations and isofrequency lines in the effective medium and in the PC should coincide to some level of approximation. We can view this requirement as a necessary condition of homogenizability. In the vicinity of a Γ point, real isofrequency lines of two-dimensional PCs can be close to mathematical circles, just like in the case of isotropic homogeneous materials. Thus, one may be tempted to conclude that introduction of an effective medium is possible and, at least, the necessary condition of homogenizability holds in this case. We, however, show that this conclusion is incorrect: complex dispersion points must be included into consideration even in the case of strictly nonabsorbing materials. By analyzing the complex dispersion relations and the corresponding isofrequency lines, we have found that two-dimensional PCs with C4 and C6 symmetries are not homogenizable in the higher photonic bands. We also draw a distinction between spurious Γ -point frequencies that are due to Brillouin-zone folding of Bloch bands and "true" Γ -point frequencies that are due to multiple scattering. Understanding of the physically different phenomena that lead to the appearance of spurious and "true" Γ -point frequencies is important for the theory of homogenization.

  11. Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

    SciTech Connect

    Askari, Nasim; Eslami, Esmaeil; Mirzaie, Reza

    2015-11-15

    The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

  12. Linear-Circular Dichroism of Four-Photon Absorption of Light in Semiconductors with a Complex Valence Band

    NASA Astrophysics Data System (ADS)

    Rasulov, R. Ya.; Rasulov, V. R.; Eshboltaev, I.

    2016-04-01

    Matrix elements of optical transitions occuring between the subbands of the valence band of a p-GaAs type semiconductor are calculated. Transitions associated with the non-simultaneous absorption of single photons and simultaneous absorption of two photons are taken into account. The expressions are obtained for the average values of the square modulus of matrix elements calculated with respect to the solid angle of the wave vector of holes. Linear-circular dichroism of four-photon absorption of light in semiconductors with a complex valence band is theoretically studied.

  13. Waveguides in three-dimensional metallic photonic band-gap materials

    SciTech Connect

    Sigalas, M.M.; Biswas, R.; Ho, K.M.; Soukoulis, C.M.; Crouch, D.D.

    1999-08-01

    We theoretically investigate waveguide structures in three-dimensional metallic photonic band-gap (MPBG) materials. The MPBG materials used in this study consist of a three-dimensional mesh of metallic wires embedded in a dielectric. An {ital L}-shaped waveguide is created by removing part of the metallic wires. Using finite difference time domain simulations, we found that an 85{percent} transmission efficiency can be achieved through the 90{degree} bend with just three unit cell thickness MPBG structures. thinsp {copyright} {ital 1999} {ital The American Physical Society}

  14. Design and testing of photonic band gap channel-drop-filters

    SciTech Connect

    Shchegolkov, Dmitry; Earley, Lawrence M; Health, Cynthia E; Smirnova, Evgenya I

    2009-01-01

    We have designed, fabricated and tested several novel passive mm-wave spectrometers based on Photonic Band Gap (PBG) structures. Our spectrometers were designed to operate in the frequency ranges of 90-130 and 220-300 GHz. We built and tested both metallic and dielectric silicon Channel-Drop-Filter (CDF) structures at 90-130 GHz. We are currently fabricating a dielectric CDF structure to operate at 220-300 GHz. The complete recent test results for the metal version and preliminary test results for the higher frequency silicon versions will be presented at the conference.

  15. Exceptional Contours and Band Structure Design in Parity-Time Symmetric Photonic Crystals

    NASA Astrophysics Data System (ADS)

    Cerjan, Alexander; Raman, Aaswath; Fan, Shanhui

    2016-05-01

    We investigate the properties of two-dimensional parity-time symmetric periodic systems whose non-Hermitian periodicity is an integer multiple of the underlying Hermitian system's periodicity. This creates a natural set of degeneracies that can undergo thresholdless P T transitions. We derive a k .p perturbation theory suited to the continuous eigenvalues of such systems in terms of the modes of the underlying Hermitian system. In photonic crystals, such thresholdless P T transitions are shown to yield significant control over the band structure of the system, and can result in all-angle supercollimation, a P T -superprism effect, and unidirectional behavior.

  16. A Broad-band Spectral and Timing Study of the X-Ray Binary System Centaurus X-3

    NASA Technical Reports Server (NTRS)

    Audley, Michael Damian

    1998-01-01

    This dissertation describes a multi-mission investigation of the high mass X-ray binary pulsar Centaurus X-3. Cen X-3 was observed with the Broad Band X-Ray Telescope (BBXRT) in December 1990. This was the first high-resolution solid state X-ray spectrometer to cover the iron K fluorescence region. The Fe K emission feature was resolved into two components for the first time. A broad 6.7 keV feature was found to be a blend of lines from Fe XXI-Fe XXVI with energies ranging from 6.6 to 6.9 keV due to photoionization of the companion's stellar wind. A narrow line at 6.4 keV due to fluorescence of iron in relatively low ionization states was also found. The quasi-periodic oscillations (QPO) at about 40 mHz were used to estimate the surface magnetic field of Cen X-3 as approx. 2.6 x 10(exp 12) G and to predict that there should be a cyclotron scattering resonance absorption feature (CSRF) near 30 keV. In order to further resolve the iron line complex and to investigate the pulse-phase dependence of the iron line intensities, Cen X-3 was observed with the Advanced Satellite for Cosmology and Astrophysics (ASCA). Using ASCA's state-of-the-art non-dispersive X-ray spectrometers the 6.4 keV fluorescent iron line was found to be pulsing while the intensities of the 6.7 and 6.9 keV recombination lines do not vary with pulse phase. This confirms that the 6.4 keV line is due to reflection by relatively neutral matter close to the neutron star while the recombination lines originate in the extended stellar wind. The continuum spectrum was found to be modified by reflection from matter close to the neutron star. Observations with the EXOSAT GSPC were used to search for a CSRF. The EXOSAT spectra were consistent with the presence of a CSRF but an unambiguous detection was not possible because of a lack of sensitivity at energies higher than the cyclotron energy. Cen X-3 was then observed with the Rossi X-Ray Timing Explorer (RXTE) and evidence for a CSRF at 25.1 +/- 0.3 keV was

  17. Suzaku broad-band spectrum of 4U 1705-44: probing the reflection component in the hard state

    NASA Astrophysics Data System (ADS)

    Di Salvo, T.; Iaria, R.; Matranga, M.; Burderi, L.; D'Aí, A.; Egron, E.; Papitto, A.; Riggio, A.; Robba, N. R.; Ueda, Y.

    2015-05-01

    Iron emission lines at 6.4-6.97 keV, identified with Kα radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disc. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM-Newton observation performed in the soft state. In particular, we find that the inner disc radius is Rin = 17 ± 5Rg (where Rg is the gravitational radius, GM/c2), the emissivity dependence from the disc radius is r-2.5 ± 0.5, the inclination angle with respect to the line of sight is i = 43° ± 5°, and the outer radius of the emitting region in the disc is Rout > 200Rg. We note that the accretion disc does not appear to be truncated at large radii, although the source is in a hard state at ˜3 per cent of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 ± 0.03 keV, compatible with emission from mildly ionized argon (Ar XVI-XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low-energy line appears compatible with being smeared by the same inner disc parameters found for the reflection component.

  18. Research of dual-band microwave photonic filter for WLAN based on optical frequency comb.

    PubMed

    Zhang, Qi; Li, Jiaqi; Jiang, Lingke; Pan, Linbing; Dong, Wei; Zhang, Xindong; Ruan, Shengping

    2016-07-20

    This paper presents a dual-band microwave photonic filter for a wireless local area networks with independently tunable passband center frequencies and bandwidths. The two bands of the filter were 2.4 GHz and 5.725 GHz, respectively. The filter was based on a stimulated Brillouin scattering and an optical frequency comb (OFC) scheme. We created this filter using OFC pumps instead of a single pump. The OFC scheme consists of a cascaded Mach-Zehnder modulator (MZM) and a dual-parallel MZM (DPMZM) hybrid modulation that generated seven and 11 lines. The experimental results show that the two passbands of the filter were 80 and 130 MHz. PMID:27463899

  19. Cross-phase-modulation-instability band gap in a birefringence-engineered photonic-crystal fiber

    NASA Astrophysics Data System (ADS)

    Kibler, B.; Amrani, F.; Morin, P.; Kudlinski, A.

    2016-01-01

    We report the cancellation of the cross-phase-modulation-instability (XPMI) gain over a large spectral window (which we term the XPMI band gap) in a highly birefringent photonic-crystal fiber with zero group birefringence. The XPMI ceases to occur when single-frequency pumping of orthogonally polarized modes takes place in such a spectral band gap whose frequency bandwidth depends on the pump power itself. The suppression of XPMI sidebands is confirmed experimentally when Raman scattering remains negligible. At high powers the Raman Stokes wave, generated by the pump, implies novel dual-frequency pump configurations with large group-velocity mismatch, thus leading to another type of Raman-induced XPMI sidebands. The experimental results are in good agreement with analytical phase-matching calculations and numerical simulations.

  20. Band-edge lasing and miniband lasing in 1-D dual-periodic photonic crystal

    NASA Astrophysics Data System (ADS)

    Ying, Cui-Feng; Zhou, Wen-Yuan; Li, Yi; Ye, Qing; Zhang, Chun-Ping; Tian, Jian-Guo

    2012-06-01

    Herein, we report two different dual-periodic Photonic Crystals (PCs) in dichromated gelatin emulsion which are fabricated by four-beam holography and double-exposure holography. The minibands with high Q-factors have been evidently located in both two structures. By taking into account the non-uniform distribution of material, the numerical results agree quite well with the experimental results. We also compared the band-edge lasing in single-periodic PC and miniband lasing in Moiré dual-periodic PC. Due to extremely flat dispersion and large mode volume of the miniband, high optical conversion efficiency in miniband lasing is achieved as compared with that of band-edge lasing. Such effect may provide potential applications in low-threshold lasers and ultra-sensitive fluorescent probes in biological assays.

  1. Observation of wakefields in a beam-driven photonic band gap accelerating structure.

    SciTech Connect

    Conde, M.; Yusof, Z.; Power, J. G.; Jing, C.; Gao, F.; Antipov, S.; Xu, P.; Zheng, S.; Chen, H.; Tang, C.; Gai, W.; High Energy Physics; Euclid Techlabs LLC; Tsinghua Univ.

    2009-12-01

    Wakefield excitation has been experimentally studied in a three-cell X-band standing wave photonic band gap (PBG) accelerating structure. Major monopole (TM{sub 01}- and TM{sub 02}-like) and dipole (TM{sub 11}- and TM{sub 12}-like) modes were identified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be {approx}10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to {approx} 30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.

  2. Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure

    SciTech Connect

    Liao, Chen; Zhang, Huichao; Tang, Luping; Zhou, Zhiqiang; Lv, Changgui; Cui, Yiping; Zhang, Jiayu

    2014-04-28

    Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO{sub 2} sol, were utilized to fabricate a SiO{sub 2}:NCs/TiO{sub 2} all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n{sub 2}) of the PBG structure was nearly triple of that of the SiO{sub 2}:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (Δn) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ∼17 folds of that of the SiO{sub 2}:NCs film. Under excitation of a 30 GW/cm{sup 2} femtosecond laser beam, a transmission decrease of 80% was realized.

  3. Role of Short-Range Order and Hyperuniformity in the Formation of Band Gaps in Disordered Photonic Materials

    NASA Astrophysics Data System (ADS)

    Froufe-Pérez, Luis S.; Engel, Michael; Damasceno, Pablo F.; Muller, Nicolas; Haberko, Jakub; Glotzer, Sharon C.; Scheffold, Frank

    2016-07-01

    We study photonic band gap formation in two-dimensional high-refractive-index disordered materials where the dielectric structure is derived from packing disks in real and reciprocal space. Numerical calculations of the photonic density of states demonstrate the presence of a band gap for all polarizations in both cases. We find that the band gap width is controlled by the increase in positional correlation inducing short-range order and hyperuniformity concurrently. Our findings suggest that the optimization of short-range order, in particular the tailoring of Bragg scattering at the isotropic Brillouin zone, are of key importance for designing disordered PBG materials.

  4. Role of Short-Range Order and Hyperuniformity in the Formation of Band Gaps in Disordered Photonic Materials.

    PubMed

    Froufe-Pérez, Luis S; Engel, Michael; Damasceno, Pablo F; Muller, Nicolas; Haberko, Jakub; Glotzer, Sharon C; Scheffold, Frank

    2016-07-29

    We study photonic band gap formation in two-dimensional high-refractive-index disordered materials where the dielectric structure is derived from packing disks in real and reciprocal space. Numerical calculations of the photonic density of states demonstrate the presence of a band gap for all polarizations in both cases. We find that the band gap width is controlled by the increase in positional correlation inducing short-range order and hyperuniformity concurrently. Our findings suggest that the optimization of short-range order, in particular the tailoring of Bragg scattering at the isotropic Brillouin zone, are of key importance for designing disordered PBG materials. PMID:27517772

  5. Spectral and polarization structure of field-induced photonic bands in cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Palto, S. P.; Barnik, M. I.; Geivandov, A. R.; Kasyanova, I. V.; Palto, V. S.

    2015-09-01

    Transmission of planar layers of cholesteric liquid crystals is studied in pulsed electric fields perpendicular to the helix axis at normal incidence of both linearly polarized and unpolarized light. Spectral and light polarization properties of the primary photonic band and the field-induced bands up to fourth order of Bragg selective reflection are studied in detail. In our experiments we have achieved an electric field strength several times higher than the theoretical values corresponding to the critical field of full helix unwinding. However, the experiments show that despite the high strength of the electric field applied the helix does not unwind, but strongly deforms, keeping its initial spatial period. Strong helix deformation results in distinct spectral band splitting, as well as very high field-induced selective reflectance that can be applied in lasers and other optoelectronic devices. Peculiarities of inducing and splitting the bands are discussed in terms of the scattering coefficient approach. All observed effects are confirmed by numerical simulations. The simulations also show that liquid crystal surface anchoring is not the factor that prevents the helix unwinding. Thus, the currently acknowledged concept of continuous helix unwinding in the electric field should be reconsidered.

  6. An ATCA survey of Sagittarius B2 at 7 mm: chemical complexity meets broad-band interferometry

    NASA Astrophysics Data System (ADS)

    Corby, Joanna F.; Jones, Paul A.; Cunningham, Maria R.; Menten, Karl M.; Belloche, Arnaud; Schwab, Frederic R.; Walsh, Andrew J.; Balnozan, Egon; Bronfman, Leonardo; Lo, Nadia; Remijan, Anthony J.

    2015-10-01

    We present a 30-50 GHz survey of Sagittarius B2(N) conducted with the Australia Telescope Compact Array with ˜5-10 arcsec resolution. This work releases the survey data and demonstrates the utility of scripts that perform automated spectral line fitting on broad-band line data. We describe the line-fitting procedure, evaluate the performance of the method, and provide access to all data and scripts. The scripts are used to characterize the spectra at the positions of three H II regions, each with recombination line emission and molecular line absorption. Towards the most line-dense of the three regions characterized in this work, we detect ˜500 spectral line components of which ˜90 per cent are confidently assigned to H and He recombination lines and to 53 molecular species and their isotopologues. The data reveal extremely sub-thermally excited molecular gas absorbing against the continuum background at two primary velocity components. Based on the line radiation over the full spectra, the molecular abundances and line excitation in the absorbing components appear to vary substantially towards the different positions, possibly indicating that the two gas clouds are located proximate to the star-forming cores instead of within the envelope of Sgr B2. Furthermore, the spatial distributions of species including CS, OCS, SiO, and HNCO indicate that the absorbing gas components likely have high UV-flux. Finally, the data contain line-of-sight absorption by ˜15 molecules observed in translucent gas in the Galactic Centre, bar, and intervening spiral arm clouds, revealing the complex chemistry and clumpy structure of this gas. Formamide (NH2CHO) is detected for the first time in a translucent cloud.

  7. A source model of the 2014 South Napa Earthquake by the EGF broad-band strong ground motion simulation

    NASA Astrophysics Data System (ADS)

    Iwata, T.; Asano, K.; Kubo, H.

    2014-12-01

    The source model of the 2014 South Napa earthquake (Mw6.0) is estimated using broad band strong ground motion simulation by the empirical Green's function method (Irikura, 1986, Irikura et al., 1997). We used the CESMD strong motion data. Aftershock ground motion records of Mw3.6 which occurred at 05:33 on 24th August (PDT), are used as an empirical Green's function. We refer to the finite source model by Dreger et al. (2014) for setting the geometry of the source fault plane and the rupture velocity. We assume a single rectangular strong motion generation area (e.g. Miyake et al., 2003; Asano and Iwata, 2012). The seismic moment ratio between the target and EGF events is fixed from the moment magnitudes. As only five station data are available for the aftershock records, the size of SMGA area, rupture starting point, and the rise time on the SMGA are determined by the trial and error. Preliminary SMGA model is 6x6km2 and the rupture mainly propagates WNW and shallower directions. The SMGA size we obtained follows the empirical relationship of Mw and SMGA size for the inland crustal events (Irikura and Miyake, 2011). Waveform fittings are fairly well at the near source station NHC (Huichica creek) and 68150 (Napa Collage), where as the fitting is not good at the south-side stations, 68206 (Crockett - Carquinez Br. Geotech Array) and 68310 (Vallejo - Hwy 37/Napa River E Geo. Array). Particularly, we did not succeed in explaining the high PGA at the 68206 surface station. We will try to improve our SMGA model and will discuss the origin of the high PGA observed at that station.

  8. Periodic dielectric structure for production of photonic band gap and devices incorporating the same

    DOEpatents

    Ho, Kai-Ming; Chan, Che-Ting; Soukoulis, Costas

    1994-08-02

    A periodic dielectric structure which is capable of producing a photonic band gap and which is capable of practical construction. The periodic structure is formed of a plurality of layers, each layer being formed of a plurality of rods separated by a given spacing. The material of the rods contrasts with the material between the rods to have a refractive index contrast of at least two. The rods in each layer are arranged with their axes parallel and at a given spacing. Adjacent layers are rotated by 90.degree., such that the axes of the rods in any given layer are perpendicular to the axes in its neighbor. Alternating layers (that is, successive layers of rods having their axes parallel such as the first and third layers) are offset such that the rods of one are about at the midpoint between the rods of the other. A four-layer periocity is thus produced, and successive layers are stacked to form a three-dimensional structure which exhibits a photonic band gap. By virtue of forming the device in layers of elongate members, it is found that the device is susceptible of practical construction.

  9. Fabrication of ceramic layer-by-layer infrared wavelength photonic band gap crystals

    NASA Astrophysics Data System (ADS)

    Kang, Henry Hao-Chuan

    Photonic band gap (PBG) crystals, also known as photonic crystals, are periodic dielectric structures which form a photonic band gap that prohibit the propagation of electromagnetic (EM) waves of certain frequencies at any incident angles. Photonic crystals have several potential applications including zero-threshold semiconductor lasers, the inhibiting spontaneous emission, dielectric mirrors, and wavelength filters. If defect states are introduced in the crystals, light can be guided from one location to another or even a sharp bending of light in submicron scale can be achieved. This generates the potential for optical waveguide and optical circuits, which will contribute to the improvement in the fiber-optic communications and the development of high-speed computers. The goal of this dissertation research is to explore techniques for fabricating 3D ceramic layer-by-layer (LBL) photonic crystals operating in the infrared frequency range, and to characterize the infilling materials properties that affect the fabrication process as well as the structural and optical properties of the crystals. While various approaches have been reported in literature for the fabrication of LBL structure, the uniqueness of this work ties with its cost-efficiency and relatively short process span. Besides, very few works have been reported on fabricating ceramic LBL crystals at mid-IR frequency range so far. The fabrication techniques reported here are mainly based on the concepts of microtransfer molding with the use of polydimethyl siloxane (PDMS) as molds/stamps. The infilling materials studied include titanium alkoxide precursors and aqueous suspensions of nanosize titania particles (slurries). Various infilling materials were synthesized to determine viscosities, effects on drying and firing shrinkages, effects on film surface roughness, and their moldability. Crystallization and phase transformation of the materials were also monitored using DTA, TGA and XRD. Mutilayer crystal

  10. Self-induced transparency solitary waves in a doped nonlinear photonic band gap material

    NASA Astrophysics Data System (ADS)

    Aközbek, Neşet; John, Sajeev

    1998-09-01

    We derive the properties of self-induced transparency (SIT) solitary waves in a one-dimensional periodic structure doped uniformly with resonance two-level atoms. In our model, the electromagnetic field is treated classically and the dopant atoms are described quantum mechanically. The resulting solitary waves take the form of ultrashort (picosecond) laser pulses which propagate near the band edge of the nonlinear photonic band gap (PBG) material doped with rare-earth atoms such as erbium. Solitary wave formation involves the combined effects of group velocity dispersion (GVD), nonresonant Kerr nonlinearity, and resonant interaction with dopant atoms. We derive the general Maxwell-Bloch equations for a nonlinear PBG system and then demonstrate the existence of elementary solitary wave solutions for frequencies far outside the gap where GVD effects are negligible and for frequencies near the photonic band edge where GVD effects are crucial. We find two distinct new types of propagating SIT solitary wave pulses. Far from Bragg resonance, we recapture the usual McCall-Hahn soliton with hyperbolic secant profile when the nonlinear Kerr coefficient χ(3)=0. However, when the host nonresonant Kerr coefficient is nonzero, we obtain the first new type of soliton. In this case, the optical soliton envelope function deviates from the hyperbolic secant profile and pulse propagation requires nontrivial phase modulation (chirping). We derive the dependence of the solitary wave structure on the Kerr coefficient χ(3), the resonance impurity atom density, and the detuning of the average laser frequency from the atomic transition. When the laser frequency and the atomic transition frequencies are near the photonic band edge we obtain the second type of soliton. To illustrate the second type of soliton we consider two special cases. In the first case, GVD facilitates the propagation of an unchirped SIT-gap soliton moving at a velocity fixed by the material's parameters. The soliton

  11. High-frequency homogenization of zero-frequency stop band photonic and phononic crystals

    NASA Astrophysics Data System (ADS)

    Antonakakis, T.; Craster, R. V.; Guenneau, S.

    2013-10-01

    We present an accurate methodology for representing the physics of waves, in periodic structures, through effective properties for a replacement bulk medium: this is valid even for media with zero-frequency stop bands and where high-frequency phenomena dominate. Since the work of Lord Rayleigh in 1892, low-frequency (or quasi-static) behaviour has been neatly encapsulated in effective anisotropic media; the various parameters come from asymptotic analysis relying upon the ratio of the array pitch to the wavelength being sufficiently small. However, such classical homogenization theories break down in the high-frequency or stop band regime whereby the wavelength to pitch ratio is of order one. Furthermore, arrays of inclusions with Dirichlet data lead to a zero-frequency stop band, with the salient consequence that classical homogenization is invalid. Higher-frequency phenomena are of significant importance in photonics (transverse magnetic waves propagating in infinite conducting parallel fibres), phononics (anti-plane shear waves propagating in isotropic elastic materials with inclusions) and platonics (flexural waves propagating in thin-elastic plates with holes). Fortunately, the recently proposed high-frequency homogenization (HFH) theory is only constrained by the knowledge of standing waves in order to asymptotically reconstruct dispersion curves and associated Floquet-Bloch eigenfields: it is capable of accurately representing zero-frequency stop band structures. The homogenized equations are partial differential equations with a dispersive anisotropic homogenized tensor that characterizes the effective medium. We apply HFH to metamaterials, exploiting the subtle features of Bloch dispersion curves such as Dirac-like cones, as well as zero and negative group velocity near stop bands in order to achieve exciting physical phenomena such as cloaking, lensing and endoscope effects. These are simulated numerically using finite elements and compared to predictions

  12. Wave propagation in ordered, disordered, and nonlinear photonic band gap materials

    SciTech Connect

    Lidorikis, Elefterios

    1999-12-10

    Photonic band gap materials are artificial dielectric structures that give the promise of molding and controlling the flow of optical light the same way semiconductors mold and control the electric current flow. In this dissertation the author studied two areas of photonic band gap materials. The first area is focused on the properties of one-dimensional PBG materials doped with Kerr-type nonlinear material, while, the second area is focused on the mechanisms responsible for the gap formation as well as other properties of two-dimensional PBG materials. He first studied, in Chapter 2, the general adequacy of an approximate structure model in which the nonlinearity is assumed to be concentrated in equally-spaced very thin layers, or 6-functions, while the rest of the space is linear. This model had been used before, but its range of validity and the physical reasons for its limitations were not quite clear yet. He performed an extensive examination of many aspects of the model's nonlinear response and comparison against more realistic models with finite-width nonlinear layers, and found that the d-function model is quite adequate, capturing the essential features in the transmission characteristics. The author found one exception, coming from the deficiency of processing a rigid bottom band edge, i.e. the upper edge of the gaps is always independent of the refraction index contrast. This causes the model to miss-predict that there are no soliton solutions for a positive Kerr-coefficient, something known to be untrue.

  13. Reverberation Mapping with Intermediate-band Photometry: Detection of Broad-line Hα Time Lags for Quasars at 0.2 < z < 0.4

    NASA Astrophysics Data System (ADS)

    Jiang, Linhua; Shen, Yue; McGreer, Ian D.; Fan, Xiaohui; Morganson, Eric; Windhorst, Rogier A.

    2016-02-01

    We present a reverberation mapping (RM) experiment that combines broad- and intermediate-band photometry; it is the first such attempt targeting 13 quasars at 0.2 < z < 0.9. The quasars were selected to have strong Hα or Hβ emission lines that are located in one of three intermediate bands (with FWHM around 200 Å) centered at 8045, 8505, and 9171 Å. The imaging observations were carried out in the intermediate bands and the broad i and z bands using the prime-focus imager 90Prime on the 2.3 m Bok telescope. Because of the large (˜1 deg2) field of view (FOV) of 90Prime, we included the 13 quasars within only five telescope pointings or fields. The five fields were repeatedly observed over 20-30 epochs that were unevenly distributed over a duration of 5-6 months. The combination of the broad- and intermediate-band photometry allows us to derive accurate light curves for both optical continuum emission (from the accretion disk) and line emission (from the broad-line region, or BLR). We detect Hα time lags between the continuum and line emission in six quasars. These quasars are at relatively low redshifts 0.2 < z < 0.4. The measured lags are consistent with the current BLR size-luminosity relation for Hβ at z < 0.3. While this experiment appears successful in detecting lags of the bright Hα line, further investigation is required to see if it can also be applied to the fainter Hβ line for quasars at higher redshifts. Finally we demonstrate that, by using a small telescope with a large FOV, intermediate-band photometric RM can be efficiently executed for a large sample of quasars at z > 0.2.

  14. Experimental Demonstration of a Hybrid-Quantum-Emitter Producing Individual Entangled Photon Pairs in the Telecom Band

    PubMed Central

    Chen, Geng; Zou, Yang; Zhang, Wen-Hao; Zhang, Zi-Huai; Zhou, Zong-Quan; He, De-Yong; Tang, Jian-Shun; Liu, Bi-Heng; Yu, Ying; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can

    2016-01-01

    Quantum emitters generating individual entangled photon pairs (IEPP) have significant fundamental advantages over schemes that suffer from multiple photon emission, or schemes that require post-selection techniques or the use of photon-number discriminating detectors. Quantum dots embedded within nanowires (QD-NWs) represent one of the most promising candidate for quantum emitters that provide a high collection efficiency of photons. However, a quantum emitter that generates IEPP in the telecom band is still an issue demanding a prompt solution. Here, we demonstrate in principle that IEPPs in the telecom band can be created by combining a single QD-NW and a nonlinear crystal waveguide. The QD-NW system serves as the single photon source, and the emitted visible single photons are split into IEPPs at approximately 1.55 μm through the process of spontaneous parametric down conversion (SPDC) in a periodically poled lithium niobate (PPLN) waveguide. The compatibility of the QD-PPLN interface is the determinant factor in constructing this novel hybrid-quantum-emitter (HQE). Benefiting from the desirable optical properties of QD-NWs and the extremely high nonlinear conversion efficiency of PPLN waveguides, we successfully generate IEPPs in the telecom band with the polarization degree of freedom. The entanglement of the generated photon pairs is confirmed by the entanglement witness. Our experiment paves the way to producing HQEs inheriting the advantages of multiple systems. PMID:27225881

  15. Experimental Demonstration of a Hybrid-Quantum-Emitter Producing Individual Entangled Photon Pairs in the Telecom Band

    NASA Astrophysics Data System (ADS)

    Chen, Geng; Zou, Yang; Zhang, Wen-Hao; Zhang, Zi-Huai; Zhou, Zong-Quan; He, De-Yong; Tang, Jian-Shun; Liu, Bi-Heng; Yu, Ying; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can

    2016-05-01

    Quantum emitters generating individual entangled photon pairs (IEPP) have significant fundamental advantages over schemes that suffer from multiple photon emission, or schemes that require post-selection techniques or the use of photon-number discriminating detectors. Quantum dots embedded within nanowires (QD-NWs) represent one of the most promising candidate for quantum emitters that provide a high collection efficiency of photons. However, a quantum emitter that generates IEPP in the telecom band is still an issue demanding a prompt solution. Here, we demonstrate in principle that IEPPs in the telecom band can be created by combining a single QD-NW and a nonlinear crystal waveguide. The QD-NW system serves as the single photon source, and the emitted visible single photons are split into IEPPs at approximately 1.55 μm through the process of spontaneous parametric down conversion (SPDC) in a periodically poled lithium niobate (PPLN) waveguide. The compatibility of the QD-PPLN interface is the determinant factor in constructing this novel hybrid-quantum-emitter (HQE). Benefiting from the desirable optical properties of QD-NWs and the extremely high nonlinear conversion efficiency of PPLN waveguides, we successfully generate IEPPs in the telecom band with the polarization degree of freedom. The entanglement of the generated photon pairs is confirmed by the entanglement witness. Our experiment paves the way to producing HQEs inheriting the advantages of multiple systems.

  16. Experimental Demonstration of a Hybrid-Quantum-Emitter Producing Individual Entangled Photon Pairs in the Telecom Band.

    PubMed

    Chen, Geng; Zou, Yang; Zhang, Wen-Hao; Zhang, Zi-Huai; Zhou, Zong-Quan; He, De-Yong; Tang, Jian-Shun; Liu, Bi-Heng; Yu, Ying; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can

    2016-01-01

    Quantum emitters generating individual entangled photon pairs (IEPP) have significant fundamental advantages over schemes that suffer from multiple photon emission, or schemes that require post-selection techniques or the use of photon-number discriminating detectors. Quantum dots embedded within nanowires (QD-NWs) represent one of the most promising candidate for quantum emitters that provide a high collection efficiency of photons. However, a quantum emitter that generates IEPP in the telecom band is still an issue demanding a prompt solution. Here, we demonstrate in principle that IEPPs in the telecom band can be created by combining a single QD-NW and a nonlinear crystal waveguide. The QD-NW system serves as the single photon source, and the emitted visible single photons are split into IEPPs at approximately 1.55 μm through the process of spontaneous parametric down conversion (SPDC) in a periodically poled lithium niobate (PPLN) waveguide. The compatibility of the QD-PPLN interface is the determinant factor in constructing this novel hybrid-quantum-emitter (HQE). Benefiting from the desirable optical properties of QD-NWs and the extremely high nonlinear conversion efficiency of PPLN waveguides, we successfully generate IEPPs in the telecom band with the polarization degree of freedom. The entanglement of the generated photon pairs is confirmed by the entanglement witness. Our experiment paves the way to producing HQEs inheriting the advantages of multiple systems. PMID:27225881

  17. Broad-band calibration of marine seismic sources used by R/V Polarstern for academic research in polar regions

    NASA Astrophysics Data System (ADS)

    Breitzke, Monika; Boebel, Olaf; El Naggar, Saad; Jokat, Wilfried; Werner, Berthold

    2008-08-01

    Air guns and air-gun arrays of different volumes are used for scientific seismic surveys with R/V Polarstern in polar regions. To assess the potential risk of these research activities on marine mammal populations, knowledge of the sound pressure field of the seismic sources is essential. Therefore, a broad-band (0-80 kHz) calibration study was conducted at the Heggernes Acoustic Range, Norway. A GI (2.4 l), a G (8.5 l) and a Bolt gun (32.8 l) were deployed as single sources, 3 GI (7.4 l), 3 G (25.6 l) and 8 VLF™ Prakla-Seismos air guns (24.0 l) as arrays. Each configuration was fired along a line of 3-4 km length running between two hydrophone chains with receivers in 35, 100, 198 and 263 m depth. Peak-to-peak, zero-to-peak, rms and sound exposure levels (SEL) were analysed as functions of range. They show the typical dipole-like directivity of marine seismic sources with amplitude cancellation close to the sea surface, higher amplitudes in greater depths, and sound pressure levels which continuously decrease with range. Levels recorded during the approach are lower than during the departure indicating a shadowing effect of Polarsterns's hull. Backcalculated zero-to-peak source levels range from 224-240 dB re 1 μPa @ 1 m. Spectral source levels are highest below 100 Hz and amount to 182-194 dB re 1 μPa Hz-1. They drop off continuously with range and frequency. At 1 kHz they are ~30 dB, at 80 kHz ~60 dB lower than the peak level. Above 1 kHz amplitude spectra are dominated by Polarstern's self-noise. From the rms and sound exposure levels of the deepest hydrophone radii for different thresholds are derived. For a 180 dB rms-level threshold radii maximally vary between 200 and 600 m, for a 186 dB SEL threshold between 50 and 300 m.

  18. The broad-band X-ray spectrum of IC 4329A from a joint NuSTAR/Suzaku observation

    SciTech Connect

    Brenneman, L. W.; Elvis, M.; Madejski, G.; Fuerst, F.; Harrison, F. A.; Grefenstette, B. W.; Madsen, K. K.; Rivers, E.; Walton, D. J.; Matt, G.; Marinucci, A.; Ballantyne, D. R.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.; Fabian, A. C.; Hailey, C. J.; Stern, D.; Zhang, W. W.

    2014-06-10

    We have obtained a deep, simultaneous observation of the bright, nearby Seyfert galaxy IC 4329A with Suzaku and NuSTAR. Through a detailed spectral analysis, we are able to robustly separate the continuum, absorption, and distant reflection components in the spectrum. The absorbing column is found to be modest (∼6×10{sup 21} cm{sup −2} ), and does not introduce any significant curvature in the Fe K band. We are able to place a strong constraint on the presence of a broadened Fe Kα line (E{sub rest}=6.46{sub −0.07}{sup +0.08} keV with σ=0.33{sub −0.07}{sup +0.08} keV and EW=34{sub −7}{sup +8} eV), though we are not able to constrain any of the parameters of a relativistic reflection model. These results highlight the range in broad Fe K line strengths observed in nearby, bright, active galactic nuclei (roughly an order of magnitude), and imply a corresponding range in the physical properties of the inner accretion disk in these sources. We have also updated our previously reported measurement of the high-energy cutoff of the hard X-ray emission using both observatories rather than just NuSTAR alone: E {sub cut} = 186 ± 14 keV. This high-energy cutoff acts as a proxy for the temperature of the coronal electron plasma, enabling us to further separate this parameter from the plasma's optical depth and to update our results for these parameters as well. We derive kT=50{sub −3}{sup +6} keV with τ=2.34{sub −0.11}{sup +0.16} using a spherical geometry, kT = 61 ± 1 keV with τ = 0.68 ± 0.02 for a slab geometry, with both having an equivalent goodness-of-fit.

  19. Frequency-selective plasmonic wave propagation through the overmoded waveguide with photonic-band-gap slab arrays

    SciTech Connect

    Shin, Young-Min

    2012-05-15

    Confined propagation of guided waves through the periodically corrugated channel sandwiched between two staggered dielectric photonic-band-gap slab arrays is investigated with the band-response analysis. Numerical simulations show that longitudinally polarized evanescent waves within the band gap propagate with insertion loss of {approx}-0.2 to 1 dB (-0.05 to 0.4 dB/mm at G-band) in the hybrid band filter. This structure significantly suppresses low energy modes and higher-order-modes beyond the band-gap, including background noises, down to {approx}-45 dB. This would enable the single-mode propagation in the heavily over-moded waveguide (TEM-type), minimizing abnormal excitation probability of trapped modes. This band filter could be integrated with active and passive RF components for electron beam and optoelectronic devices.

  20. Design of full-k-space flat bands in photonic crystals beyond the tight-binding picture

    PubMed Central

    Xu, Changqing; Wang, Gang; Hang, Zhi Hong; Luo, Jie; Chan, C. T.; Lai, Yun

    2015-01-01

    Based on a band engineering method, we propose a theoretical prescription to create a full-k-space flat band in dielectric photonic crystals covering the whole Brillouin Zone. With wave functions distributed in air instead of in the dielectrics, such a flat band represents a unique mechanism for achieving flat dispersions beyond the tight-binding picture, which can enormously reduce the requirement of permittivity contrast in the system. Finally, we propose and numerically demonstrate a unique application based on the full-k-space coverage of the flat band: ultra-sensitive detection of small scatterers. PMID:26656882

  1. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    SciTech Connect

    Kevin Jerome Sutherland

    2001-06-27

    Over the last ten years, photonic band gap (PBG) theory and technology have become an important area of research because of the numerous possible applications ranging from high-efficiency laser diodes to optical circuitry. This research concentrates on reducing the length scale in the fabrication of layered photonic band gap structures and developing procedures to improve processing consistency. Various procedures and materials have been used in the fabrication of layered PBG structures. This research focused on an economical micro transfer molding approach to create the final PBG structure. A poly dimethylsiloxane (PDMS) rubber mold was created from a silicon substrate. It was filled with epoxy and built layer-by-layer to create a 3-D epoxy structure. This structure was infiltrated with nanoparticle titania or a titania sol-gel, then fired to remove the polymer mold, leaving a monolithic ceramic inverse of the epoxy structure. The final result was a lattice of titania rolds that resembles a face-centered tetragonal structure. The original intent of this research was to miniaturize this process to a bar size small enough to create a photonic band gap for wavelengths of visible electro-magnetic radiation. The factor limiting progress was the absence of a silicon master mold of small enough dimensions. The Iowa State Microelectronics Research Center fabricated samples with periodicities of 2.5 and 1.0 microns with the existing technology, but a sample was needed on the order of 0.3 microns or less. A 0.4 micron sample was received from Sandia National Laboratory, which was made through an electron beam lithography process, but it contained several defects. The results of the work are primarily from the 2.5 and 1.0 micron samples. Most of the work focused on changing processing variables in order to optimize the infiltration procedure for the best results. Several critical parameters were identified, ranging from the ambient conditions to the specifics of the

  2. Tunability of photonic band gaps in one- and two-dimensional photonic crystals based on ZnS particles embedded in TiO2 matrix

    NASA Astrophysics Data System (ADS)

    Labbani, Amel; Benghalia, Abdelmadjid

    2012-06-01

    Using the Maxwell-Garnett theory, the evolution of the refractive index of titanium dioxide (TiO2) doped with zinc sulfide (ZnS) particles is presented. The presence of the nano-objects in the host matrix allows us to obtain a new composite material with tunable optical properties. We find that the filling factor of ZnS nanoparticles greatly alters photonic band gaps (PBGs). We have calculated also the photonic band structure for electromagnetic waves propagating in a structure consisting of ZnS rods covered with the air shell layer in 2D hexagonal and square lattices by the finite difference time domain (FDTD) method. The rods are embedded in the TiO2 background medium with a high dielectric constant. Such photonic lattices present complete photonic band gaps (CPBGs). Our results show that the existence of the air shell layer leads to larger complete photonic gaps. We believe that the present results are significant to increase the possibilities for experimentalists to realize a sizeable and larger CPBG.

  3. Large-area 2D periodic crystalline silicon nanodome arrays on nanoimprinted glass exhibiting photonic band structure effects.

    PubMed

    Becker, C; Lockau, D; Sontheimer, T; Schubert-Bischoff, P; Rudigier-Voigt, E; Bockmeyer, M; Schmidt, F; Rech, B

    2012-04-01

    Two-dimensional silicon nanodome arrays are prepared on large areas up to 50 cm² exhibiting photonic band structure effects in the near-infrared and visible wavelength region by downscaling a recently developed fabrication method based on nanoimprint-patterned glass, high-rate electron-beam evaporation of silicon, self-organized solid phase crystallization and wet-chemical etching. The silicon nanodomes, arranged in square lattice geometry with 300 nm lattice constant, are optically characterized by angular resolved reflection measurements, allowing the partial determination of the photonic band structure. This experimentally determined band structure agrees well with the outcome of three-dimensional optical finite-element simulations. A 16% photonic bandgap is predicted for an optimized geometry of the silicon nanodome arrays. By variation of the duration of the selective etching step, the geometry as well as the optical properties of the periodic silicon nanodome arrays can be controlled systematically. PMID:22422473

  4. Large full band gaps for photonic crystals in two dimensions computed by an inverse method with multigrid acceleration

    NASA Astrophysics Data System (ADS)

    Chern, R. L.; Chang, C. Chung; Chang, Chien C.; Hwang, R. R.

    2003-08-01

    In this study, two fast and accurate methods of inverse iteration with multigrid acceleration are developed to compute band structures of photonic crystals of general shape. In particular, we report two-dimensional photonic crystals of silicon air with an optimal full band gap of gap-midgap ratio Δω/ωmid=0.2421, which is 30% larger than ever reported in the literature. The crystals consist of a hexagonal array of circular columns, each connected to its nearest neighbors by slender rectangular rods. A systematic study with respect to the geometric parameters of the photonic crystals was made possible with the present method in drawing a three-dimensional band-gap diagram with reasonable computing time.

  5. Large full band gaps for photonic crystals in two dimensions computed by an inverse method with multigrid acceleration.

    PubMed

    Chern, R L; Chang, C Chung; Chang, Chien C; Hwang, R R

    2003-08-01

    In this study, two fast and accurate methods of inverse iteration with multigrid acceleration are developed to compute band structures of photonic crystals of general shape. In particular, we report two-dimensional photonic crystals of silicon air with an optimal full band gap of gap-midgap ratio Deltaomega/omega(mid)=0.2421, which is 30% larger than ever reported in the literature. The crystals consist of a hexagonal array of circular columns, each connected to its nearest neighbors by slender rectangular rods. A systematic study with respect to the geometric parameters of the photonic crystals was made possible with the present method in drawing a three-dimensional band-gap diagram with reasonable computing time. PMID:14525145

  6. CCT- and CRI-tuning of white light-emitting diodes using three-dimensional non-close-packed colloidal photonic crystals with photonic stop-bands.

    PubMed

    Lai, Chun-Feng; Chang, Chung-Chieh; Wang, Ming-Jye; Wu, Mau-Kuen

    2013-07-01

    This study exhibited the correlated color temperature (CCT)- and color-rendering index (CRI)-tuning behavior of light emission from white light-emitting diodes (WLEDs) using three-dimensional non-close-packed (3D NCP) colloidal photonic crystals (CPhCs). The CCT of approximately 5300 K (characteristic of cold WLEDs) of white light propagated through the NCP CPhCs dropped to 3000 K (characteristic of warm WLEDs) because of the photonic stop-bands based on the photonic band structures of NCP CPhCs. This study successfully developed a novel technique that introduces lower-cost CCT- and CRI-tuning cold WLEDs with a CRI of over 90 that of warm WLEDs by using 3D NCP CPhCs. PMID:24104495

  7. Theoretical investigation of the broad one-photon absorption line-shape of a flexible symmetric carbazole derivative.

    PubMed

    Liu, Yanli; Cerezo, Javier; Santoro, Fabrizio; Rizzo, Antonio; Lin, Na; Zhao, Xian

    2016-08-17

    The one-photon absorption spectrum of a carbazole derivative has been studied by employing density functional response theory combined with a mixed quantum/classical (QC) approach to simulate the spectral shape. In a first step of our analysis we employed the vertical gradient (VG) vibronic model to investigate the role of Franck-Condon (FC) profiles of the first ten electronic excited states of the system, underlying most of the range of the experimental spectrum. We then focussed on the first six excited states covering the low-energy region of the spectrum, and investigated the effect of inter-state electronic couplings on the spectral shapes within Herzberg-Teller (HT) theory. Furthermore, in order to introduce the broadening effects due to the two inter-ring torsions, we employed a QC approach, adopting VG vibronic models for high-frequency modes and computing the contribution of the torsions to the spectrum from the distribution of the excitation energies along a two-dimensional relaxed potential energy. Finally, we estimated the solvent inhomogeneous broadening by computing the solvent reorganization energy using a polarizable continuum model. Our calculations allow us to obtain a non-phenomenological description of the low-energy part of the spectrum in semi-quantitative agreement with experiment and to dissect the relative importance of solvent, torsional flexibility, FC vibronic progressions, and inter-state couplings in determining its broad spectral shapes and the modulation of its intensity. Our analysis also clearly highlights that the investigated carbazole represents a big challenge for available methodologies due to the existence of many close-lying excited electronic states coupled by internal low-frequency and high-frequency motions and by solvent fluctuations. The study of their impact on the spectra at the HT level is only approximate and more refined treatments would require a fully quantum-dynamical calculation on the manifold of the coupled

  8. Pressure, temperature and plasma frequency effects on the band structure of a 1D semiconductor photonic crystal

    NASA Astrophysics Data System (ADS)

    González, Luz E.; Porras-Montenegro, N.

    2012-01-01

    In this work using the transfer-matrix formalism we study pressure, temperature and plasma frequency effects on the band structure of a 1D semiconductor photonic crystal made of alternating layers of air and GaAs. We have found that the temperature dependence of the photonic band structure is negligible, however, its noticeable changes are due mainly to the variations of the width and the dielectric constant of the layers of GaAs, caused by the applied hydrostatic pressure. On the other hand, by using the Drude's model, we have studied the effects of the hydrostatic pressure by means of the variation of the effective mass and density of the carriers in n-doped GaAs, finding firstly that increasing the amount of n-dopants in GaAs, namely, increasing the plasma frequency, the photonic band structure is shifted to regions of higher frequencies, and secondly the appearance of two regimes of the photonic band structure: one above the plasma frequency with the presence of usual Bragg gaps, and the other, below this frequency, where there are no gaps regularly distributed, with their width diminishing with the increasing of the plasma frequency as well as with the appearance of more bands, but leaving a wide frequency range in the lowest part of the spectrum without accessible photon states. Also, we have found characteristic frequencies in which the dielectric constant equals for different applied pressures, and from which to higher or lower values the photonic band structure inverts its behavior, depending on the value of the applied hydrostatic pressure. We hope this work may be taken into account for the development of new perspectives in the design of new optical devices.

  9. Broad self-trapped and slow light bands based on negative refraction and interference of magnetic coupled modes.

    PubMed

    Fang, Yun-Tuan; Ni, Zhi-Yao; Zhu, Na; Zhou, Jun

    2016-01-13

    We propose a new mechanism to achieve light localization and slow light. Through the study on the coupling of two magnetic surface modes, we find a special convex band that takes on a negative refraction effect. The negative refraction results in an energy flow concellation effect from two degenerated modes on the convex band. The energy flow concellation effect leads to forming of the self-trapped and slow light bands. In the self-trapped band light is localized around the source without reflection wall in the waveguide direction, whereas in the slow light band, light becomes the standing-waves and moving standing-waves at the center and the two sides of the waveguide, respectively. PMID:26647772

  10. Electrotunable band gaps of one- and two-dimensional photonic crystal structures based on silicon and liquid crystals

    NASA Astrophysics Data System (ADS)

    Arriaga, J.; Dobrzynski, L.; Djafari-Rouhani, B.

    2008-09-01

    One- and two-dimensional photonic crystals based on silicon with infiltrated liquid crystals are investigated in this paper. We show that the photonic band gap can be continuously tuned changing the orientation of the director of the liquid crystal. For the one-dimensional case, we considered arbitrary direction of propagation of the electromagnetic waves, and we show that it is possible to tune the photonic band gap by an adequate orientation of the liquid crystal. For the two-dimensional case and propagation in the plane of periodicity, we show that there exists no complete photonic band gap in the system for both polarizations. We consider two different configurations, square array of solid Si cylinders in liquid crystal background and a triangular array of liquid crystal cylinders surrounded by Si. We show that for the triangular array it is possible to tune the photonic band gap only for the transversal electric modes. We used the plane wave expansion method to solve the Maxwell equations for anisotropic systems.

  11. Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure

    DOE PAGESBeta

    Simakov, Evgenya I.; Arsenyev, Sergey A.; Buechler, Cynthia E.; Edwards, Randall L.; Romero, William P.; Conde, Manoel; Ha, Gwanghui; Power, John G.; Wisniewski, Eric E.; Jing, Chunguang

    2016-02-10

    We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic band gap (PBG) accelerating structure at 11.700 GHz. It has been long recognized that PBG structures have potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. Wemore » conducted an experiment at the Argonne Wakefield Accelerator (AWA) test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Lastly, excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test.« less

  12. Accessing quadratic nonlinearities of metals through metallodielectric photonic-band-gap structures.

    PubMed

    D'Aguanno, Giuseppe; Mattiucci, Nadia; Bloemer, Mark J; Scalora, Michael

    2006-09-01

    We study second harmonic generation in a metallodielectric photonic-band-gap structure made of alternating layers of silver and a generic, dispersive, linear, dielectric material. We find that under ideal conditions the conversion efficiency can be more than two orders of magnitude greater than the maximum conversion efficiency achievable in a single layer of silver. We interpret this enhancement in terms of the simultaneous availability of phase matching conditions over the structure and good field penetration into the metal layers. We also give a realistic example of a nine-period, Si3/N4Ag stack, where the backward conversion efficiency is enhanced by a factor of 50 compared to a single layer of silver. PMID:17025762

  13. Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure.

    PubMed

    Simakov, Evgenya I; Arsenyev, Sergey A; Buechler, Cynthia E; Edwards, Randall L; Romero, William P; Conde, Manoel; Ha, Gwanghui; Power, John G; Wisniewski, Eric E; Jing, Chunguang

    2016-02-12

    We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic-band-gap (PBG) accelerating structure at 11.700 GHz. It has been long recognized that PBG structures have the potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. We conducted an experiment at the Argonne Wakefield Accelerator test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test. PMID:26918995

  14. Multiwavelength L-band fiber laser with bismuth-oxide EDF and photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Ramzia Salem, A. M.; Al-Mansoori, M. H.; Hizam, H.; Mohd Noor, S. B.; Abu Bakar, M. H.; Mahdi, M. A.

    2011-05-01

    A multiwavelength laser comb using a bismuth-based erbium-doped fiber and 50 m photonic crystal fiber is demonstrated in a ring cavity configuration. The fiber laser is solely pumped by a single 1455 nm Raman pump laser to exploit its higher power delivery compared to that of a single-mode laser diode pump. At 264 mW Raman pump power and 1 mW Brillouin pump power, 38 output channels in the L-band have been realized with an optical signal-to-noise ratio above 15 dB and a Stokes line spacing of 0.08 nm. The laser exhibits a tuning range of 12 nm and produces stable Stokes lines across the tuning range between Brillouin pump wavelengths of 1603 nm and 1615 nm.

  15. Pushing the Gradient Limitations of Superconducting Photonic Band Gap Structure Cells

    SciTech Connect

    Simakov, Evgenya I.; Haynes, William B.; Kurennoy, Sergey S.; Shchegolkov, Dmitry; O'Hara, James F.; Olivas, Eric R.

    2012-06-07

    Superconducting photonic band gap resonators present us with unique means to place higher order mode couples in an accelerating cavity and efficiently extract HOMs. An SRF PBG resonator with round rods was successfully tested at LANL demonstrating operation at 15 MV/m. Gradient in the SRF PBG resonator was limited by magnetic quench. To increase the quench threshold in PBG resonators one must design the new geometry with lower surface magnetic fields and preserve the resonator's effectiveness for HOM suppression. The main objective of this research is to push the limits for the high-gradient operation of SRF PBG cavities. A NCRF PBG cavity technology is established. The proof-of-principle operation of SRF PBG cavities is demonstrated. SRF PBG resonators are effective for outcoupling HOMs. PBG technology can significantly reduce the size of SRF accelerators and increase brightness for future FELs.

  16. Structural Coloration of Colloidal Fiber by Photonic Band Gap and Resonant Mie Scattering.

    PubMed

    Yuan, Wei; Zhou, Ning; Shi, Lei; Zhang, Ke-Qin

    2015-07-01

    Because structural color is fadeless and dye-free, structurally colored materials have attracted great attention in a wide variety of research fields. In this work, we report the use of a novel structural coloration strategy applied to the fabrication of colorful colloidal fibers. The nanostructured fibers with tunable structural colors were massively produced by colloidal electrospinning. Experimental results and theoretical modeling reveal that the homogeneous and noniridescent structural colors of the electrospun fibers are caused by two phenomena: reflection due to the band gap of photonic structure and Mie scattering of the colloidal spheres. Our unprecedented findings show promise in paving way for the development of revolutionary dye-free technology for the coloration of various fibers. PMID:26066732

  17. New method for computation of band structures in 1D photonic crystals based on the Fresnel equations

    NASA Astrophysics Data System (ADS)

    Roshan Entezar, S.

    2013-02-01

    In this paper, we present a new method for calculation of band structure in one-dimensional bilayer photonic crystals, based on the Fresnel equations. We derive a new relation to obtain the band structure without using the Floquet theorem. It is shown that this relation can be simplified under the assumption that the single-path phase-shift acquired through the individual layers of the photonic crystal be equal to ? . The results obtained by our method are compared with the ones obtained from the transfer matrix method to show that they are exactly identical.

  18. Experimental high gradient testing of a 17.1 GHz photonic band-gap accelerator structure

    NASA Astrophysics Data System (ADS)

    Munroe, Brian J.; Zhang, JieXi; Xu, Haoran; Shapiro, Michael A.; Temkin, Richard J.

    2016-03-01

    We report the design, fabrication, and high gradient testing of a 17.1 GHz photonic band-gap (PBG) accelerator structure. Photonic band-gap (PBG) structures are promising candidates for electron accelerators capable of high-gradient operation because they have the inherent damping of high order modes required to avoid beam breakup instabilities. The 17.1 GHz PBG structure tested was a single cell structure composed of a triangular array of round copper rods of radius 1.45 mm spaced by 8.05 mm. The test assembly consisted of the test PBG cell located between conventional (pillbox) input and output cells, with input power of up to 4 MW from a klystron supplied via a TM01 mode launcher. Breakdown at high gradient was observed by diagnostics including reflected power, downstream and upstream current monitors and visible light emission. The testing procedure was first benchmarked with a conventional disc-loaded waveguide structure, which reached a gradient of 87 MV /m at a breakdown probability of 1.19 ×10-1 per pulse per meter. The PBG structure was tested with 100 ns pulses at gradient levels of less than 90 MV /m in order to limit the surface temperature rise to 120 K. The PBG structure reached up to 89 MV /m at a breakdown probability of 1.09 ×10-1 per pulse per meter. These test results show that a PBG structure can simultaneously operate at high gradients and low breakdown probability, while also providing wakefield damping.

  19. Wide-band acousto-optic deflectors for large field of view two-photon microscope.

    PubMed

    Jiang, Runhua; Zhou, Zhenqiao; Lv, Xiaohua; Zeng, Shaoqun

    2012-04-01

    Acousto-optic deflector (AOD) is an attractive scanner for two-photon microscopy because it can provide fast and versatile laser scanning and does not involve any mechanical movements. However, due to the small scan range of available AOD, the field of view (FOV) of the AOD-based microscope is typically smaller than that of the conventional galvanometer-based microscope. Here, we developed a novel wide-band AOD to enlarge the scan angle. Considering the maximum acceptable acoustic attenuation in the acousto-optic crystal, relatively lower operating frequencies and moderate aperture were adopted. The custom AOD was able to provide 60 MHz 3-dB bandwidth and 80% peak diffraction efficiency at 840 nm wavelength. Based on a pair of such AOD, a large FOV two-photon microscope was built with a FOV up to 418.5 μm (40× objective). The spatiotemporal dispersion was compensated simultaneously with a single custom-made prism. By means of dynamic power modulation, the variation of laser intensity within the FOV was reduced below 5%. The lateral and axial resolution of the system were 0.58-2.12 μm and 2.17-3.07 μm, respectively. Pollen grain images acquired by this system were presented to demonstrate the imaging capability at different positions across the entire FOV. PMID:22559541

  20. Two-photon absorption cross section measurement in the gamma band system of nitric oxide

    SciTech Connect

    Burris, J.F. Jr.

    1982-01-01

    A dye laser with a single longitudinal mode and very stable spatial mode structure has been constructed. With this laser system a four-wave mixing experiment was done in the gamma bands of nitric oxide using two photon resonance. Another four-wave mixing experiment was done in nitrogen using coherent anti-Stokes Raman scattering (CARS) and the two signals ratioed. Using accurately known values of the Raman scattering cross section, the third order susceptibility in NO was determined without needing to know the spatial and temporal properties of the dye lasers. From this susceptibility, the two photon absorption cross section was calculated with the explicit dependence of sigma/sup (2)/ upon X/sup (3)/ shown. For the R/sub 22/ + S/sub 12/(J'' = 9 1/2) (A/sup 2/..sigma..+(v' = 0) -- X/sup 2/..pi..(v'' = 0)) line, sigma/sup (2)/ = (1.0 +/- 0.6) x 10/sup -38/cm/sup 4/g(2/sub 1/-Vertical Barsub f/ is the normalized lineshape. Branching ratios for the A/sup 2/..sigma..+(v' = n) ..-->.. X/sup 2/..omega..(v'' = n)(n = o,...9) transitions of NO were also measured, Franck-Condon factors calculated and the lifetime of the A state determined.

  1. High-power picosecond pulse delivery through hollow core photonic band gap fibers

    NASA Astrophysics Data System (ADS)

    Michieletto, Mattia; Johansen, Mette M.; Lyngsø, Jens K.; Lægsgaard, Jesper; Bang, Ole; Alkeskjold, Thomas T.

    2016-03-01

    We demonstrated robust and bend insensitive fiber delivery of high power laser with diffraction limited beam quality for two different kinds of hollow core band gap fibers. The light source for this experiment consists of ytterbium-doped double clad fiber aeroGAIN-ROD-PM85 in a high power amplifier setup. It provided 22ps pulses with a maximum average power of 95W, 40MHz repetition rate at 1032nm (~2.4μJ pulse energy), with M2 <1.3. We determined the facet damage threshold for a 7-cells hollow core photonic bandgap fiber and showed up to 59W average power output for a 5 meters fiber. The damage threshold for a 19-cell hollow core photonic bandgap fiber exceeded the maximum power provided by the light source and up to 76W average output power was demonstrated for a 1m fiber. In both cases, no special attention was needed to mitigate bend sensitivity. The fibers were coiled on 8 centimeters radius spools and even lower bending radii were present. In addition, stimulated rotational Raman scattering arising from nitrogen molecules was measured through a 42m long 19 cell hollow core fiber.

  2. 2D photonic crystal complete band gap search using a cyclic cellular automaton refination

    NASA Astrophysics Data System (ADS)

    González-García, R.; Castañón, G.; Hernández-Figueroa, H. E.

    2014-11-01

    We present a refination method based on a cyclic cellular automaton (CCA) that simulates a crystallization-like process, aided with a heuristic evolutionary method called differential evolution (DE) used to perform an ordered search of full photonic band gaps (FPBGs) in a 2D photonic crystal (PC). The solution is proposed as a combinatorial optimization of the elements in a binary array. These elements represent the existence or absence of a dielectric material surrounded by air, thus representing a general geometry whose search space is defined by the number of elements in such array. A block-iterative frequency-domain method was used to compute the FPBGs on a PC, when present. DE has proved to be useful in combinatorial problems and we also present an implementation feature that takes advantage of the periodic nature of PCs to enhance the convergence of this algorithm. Finally, we used this methodology to find a PC structure with a 19% bandgap-to-midgap ratio without requiring previous information of suboptimal configurations and we made a statistical study of how it is affected by disorder in the borders of the structure compared with a previous work that uses a genetic algorithm.

  3. Photon path length distributions for cloudy skies  oxygen A-Band measurements and model calculations

    NASA Astrophysics Data System (ADS)

    Funk, O.; Pfeilsticker, K.

    2003-03-01

    This paper addresses the statistics underlying cloudy sky radiative transfer (RT) by inspection of the distribution of the path lengths of solar photons. Recent studies indicate that this approach is promising, since it might reveal characteristics about the diffusion process underlying atmospheric radiative transfer (Pfeilsticker, 1999). Moreover, it uses an observable that is directly related to the atmospheric absorption and, therefore, of climatic relevance. However, these studies are based largely on the accuracy of the measurement of the photon path length distribution (PPD). This paper presents a refined analysis method based on high resolution spectroscopy of the oxygen A-band. The method is validated by Monte Carlo simulation atmospheric spectra. Additionally, a new method to measure the effective optical thickness of cloud layers, based on fitting the measured differential transmissions with a 1-dimensional (discrete ordinate) RT model, is presented. These methods are applied to measurements conducted during the cloud radar inter-comparison campaign CLARE’98, which supplied detailed cloud structure information, required for the further analysis. For some exemplary cases, measured path length distributions and optical thicknesses are presented and backed by detailed RT model calculations. For all cases, reasonable PPDs can be retrieved and the effects of the vertical cloud structure are found. The inferred cloud optical thicknesses are in agreement with liquid water path measurements.

  4. Observation of nonlinear bands in near-field scanning optical microscopy of a photonic-crystal waveguide

    SciTech Connect

    Singh, A.; Huisman, S. R.; Ctistis, G. Mosk, A. P.; Pinkse, P. W. H.; Korterik, J. P.; Herek, J. L.

    2015-01-21

    We have measured the photonic bandstructure of GaAs photonic-crystal waveguides with high resolution in energy as well as in momentum using near-field scanning optical microscopy. Intriguingly, we observe additional bands that are not predicted by eigenmode solvers, as was recently demonstrated by Huisman et al. [Phys. Rev. B 86, 155154 (2012)]. We study the presence of these additional bands by performing measurements of these bands while varying the incident light power, revealing a non-linear power dependence. Here, we demonstrate experimentally and theoretically that the observed additional bands are caused by a waveguide-specific near-field tip effect not previously reported, which can significantly phase-modulate the detected field.

  5. Observation of nonlinear bands in near-field scanning optical microscopy of a photonic-crystal waveguide

    NASA Astrophysics Data System (ADS)

    Singh, A.; Ctistis, G.; Huisman, S. R.; Korterik, J. P.; Mosk, A. P.; Herek, J. L.; Pinkse, P. W. H.

    2015-01-01

    We have measured the photonic bandstructure of GaAs photonic-crystal waveguides with high resolution in energy as well as in momentum using near-field scanning optical microscopy. Intriguingly, we observe additional bands that are not predicted by eigenmode solvers, as was recently demonstrated by Huisman et al. [Phys. Rev. B 86, 155154 (2012)]. We study the presence of these additional bands by performing measurements of these bands while varying the incident light power, revealing a non-linear power dependence. Here, we demonstrate experimentally and theoretically that the observed additional bands are caused by a waveguide-specific near-field tip effect not previously reported, which can significantly phase-modulate the detected field.

  6. Broad-band photometric colors and effective temperature calibrations for late-type giants. II. Z < 0.02

    NASA Astrophysics Data System (ADS)

    Kučinskas, A.; Hauschildt, P. H.; Brott, I.; Vansevičius, V.; Lindegren, L.; Tanabé, T.; Allard, F.

    2006-06-01

    We investigate the effects of metallicity on the broad-band photometric colors of late-type giants, and make a comparison of synthetic colors with observed photometric properties of late-type giants over a wide range of effective temperatures (T_eff=3500-4800 K) and gravities (log g=0.0-2.5), at [M/H]=-1.0 and -2.0. The influence of metallicity on the synthetic photometric colors is small at effective temperatures above 3800 K, but the effects grow larger at lower T_eff, due to the changing efficiency of molecule formation which reduces molecular opacities at lower [M/H]. To make a detailed comparison of the synthetic and observed photometric colors of late type giants in the T_eff-color and color-color planes (which is done at two metallicities, [M/H]=-1.0 and -2.0), we derive a set of new T_eff-log g-color relations based on synthetic photometric colors, at [M/H]=-0.5, -1.0, -1.5, and -2.0. These relations are based on the T_eff-log g scales that we derive employing literature data for 178 late-type giants in 10 Galactic globular clusters (with metallicities of the individual stars between [M/H]=-0.7 and -2.5), and synthetic colors produced with the PHOENIX, MARCS and ATLAS stellar atmosphere codes. Combined with the T_eff-log g-color relations at [M/H]=0.0 (Kučinskas et al. 2005), the set of new relations covers metallicities [M/H]=0.0dots-2.0 (Δ[M/H]=0.5), effective temperatures T_eff=3500dots4800 K (Δ T_eff=100 K), and gravities log g=-0.5dots3.0. The new T_eff-log g-color relations are in good agreement with published T_eff-color relations based on observed properties of late-type giants, both at [M/H]=-1.0 and -2.0. The differences in all T_eff-color planes are typically well within 100 K. We find, however, that effective temperatures predicted by the scales based on synthetic colors tend to be slightly higher than those resulting from the T_eff-color relations based on observations, with the offsets up to 100 K. This is clearly seen both at [M/H]=-1

  7. Photonically enabled Ka-band radar and infrared sensor subscale testbed

    NASA Astrophysics Data System (ADS)

    Lohr, Michele B.; Sova, Raymond M.; Funk, Kevin B.; Airola, Marc B.; Dennis, Michael L.; Pavek, Richard E.; Hollenbeck, Jennifer S.; Garrison, Sean K.; Conard, Steven J.; Terry, David H.

    2014-10-01

    A subscale radio frequency (RF) and infrared (IR) testbed using novel RF-photonics techniques for generating radar waveforms is currently under development at The Johns Hopkins University Applied Physics Laboratory (JHU/APL) to study target scenarios in a laboratory setting. The linearity of Maxwell's equations allows the use of millimeter wavelengths and scaled-down target models to emulate full-scale RF scene effects. Coupled with passive IR and visible sensors, target motions and heating, and a processing and algorithm development environment, this testbed provides a means to flexibly and cost-effectively generate and analyze multi-modal data for a variety of applications, including verification of digital model hypotheses, investigation of correlated phenomenology, and aiding system capabilities assessment. In this work, concept feasibility is demonstrated for simultaneous RF, IR, and visible sensor measurements of heated, precessing, conical targets and of a calibration cylinder. Initial proof-of-principle results are shown of the Ka-band subscale radar, which models S-band for 1/10th scale targets, using stretch processing and Xpatch models.

  8. A super narrow band filter based on silicon 2D photonic crystal resonator and reflectors

    NASA Astrophysics Data System (ADS)

    Wang, Yuanyuan; Chen, Deyuan; Zhang, Gang; Wang, Juebin; Tao, Shangbin

    2016-03-01

    In this paper, a novel structure of super narrow band filter based on two-dimensional square lattice photonic crystals of silicon rods in air for 1.5 um communication is proposed and studied. COMSOL Multiphysics4.3b software is used to simulate the optical behavior of the filter. The filter consists of one point-defect-based resonator and two line-defect-based reflectors. The resonance frequency, transmission coefficient and quality factor are investigated by varying the parameters of the structure. In design, a silicon rod is removed to form the resonator; for the rows of rods above and below the resonator, a part of the rods are removed to form the reflectors. By optimizing the parameters of the filter, the quality factor and transmission coefficient of the filter at the resonance frequency of 2e14 Hz can reach 1330 and 0.953, respectively. The super narrow band filter can be integrated into optical circuit for its micron size. Also, it can be used for wavelength selection and noise filtering of optical amplifier in future communication application.

  9. Photonic vector signal generation at W-band employing an optical frequency octupling scheme enabled by a single MZM

    NASA Astrophysics Data System (ADS)

    Li, Xinying; Yu, Jianjun; Zhang, Ziran; Xiao, Jiangnan; Chang, Gee-Kung

    2015-08-01

    We propose photonic vector signal generation at millimeter-wave (mm-wave) bands enabled by a single Mach-Zehnder modulator (MZM) and phase-precoding technique, which can realize photonic frequency multiplication of the precoded microwave vector signal used for the drive of the single MZM. We also experimentally demonstrate the generation of quadrature-phase-shift-keying (QPSK) modulated vector signal at W-band adopting photonic frequency octupling (×8) based on our proposed scheme. The MZM is driven by a 12-GHz QPSK modulated precoded vector signal. Up to 4-Gbaud QPSK-modulated electrical vector signal at 96 GHz is generated and then delivered over 3-m wireless transmission distance.

  10. Influence of photonic stop band effect on photoluminescence of Y 2O 3:Eu 3+ inverse opal films

    NASA Astrophysics Data System (ADS)

    Qu, Xuesong; Dong, Biao; Pan, Guohui; Bai, Xue; Dai, Qilin; Zhang, Hui; Qin, Ruifei; Song, Hongwei

    2011-06-01

    Y 2O 3:Eu 3+ inverse opal films were fabricated by the self-assembly technique, which had a lattice parameter of ˜260 nm and a photonic stop band at 520 nm. Near the center of the photonic stop band, both the emission intensity and the spontaneous transition rate of 5D 1- 7F 1 transitions were modified. At the band gap edge, no obvious change was observed for the 5D 0- 7F J spontaneous transition rate, however, the emission intensity of 5D 0- 7F J ( J = 0, 1) was depressed in contrast to the 5D 0- 7F 2, which improved the color purity of the red emission.

  11. Plasmonic coupling with most of the transition metals: a new family of broad band and near infrared nanoantennas

    NASA Astrophysics Data System (ADS)

    Manchon, Delphine; Lermé, Jean; Zhang, Taiping; Mosset, Alexis; Jamois, Cécile; Bonnet, Christophe; Rye, Jan-Michael; Belarouci, Ali; Broyer, Michel; Pellarin, Michel; Cottancin, Emmanuel

    2014-12-01

    In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be controlled through morphological variation of the NAs (size, shape, interparticle distance). First, accurate calculations using the generalized Mie theory on spherical dimers demonstrate that we can take advantage of the plasmonic coupling to enhance LSPRs over a broad spectral range for many transition metals (Pt, Pd, Cr, Ni etc.). The LSPR remains broad for low interparticle distances and masks the various hybridized modes within the overall resonance. However, an analysis of the charge distribution on the surface of the nanoparticles reveals these modes and their respective contributions to the observed LSPR. In the case of spherical dimers, the transfer of the oscillator strengths from the ``dipolar'' mode to higher orders involves a maximum extinction cross-section for intermediate interparticle distances of a few nanometers. The emergence of the LSPR has been then experimentally illustrated with parallelepipedal NAs (monomers and dimers) made of various transition metals (Pt, Pd and Cr) and elaborated by nanolithography. Absolute extinction cross-sections have been measured with the spatial modulation spectroscopy technique over a broad spectral range (300-900 nm) for individual NAs, the morphology of which has been independently characterized by electron microscopy imaging. A clear enhancement of the LSPR has been revealed for a longitudinal excitation and plasmonic coupling has been clearly evidenced in dimers by an induced redshift and broadening of the LSPR compared to monomers. Furthermore, the LSPR has been shown to be highly sensitive to slight modifications of the interparticle distance. All the experimental

  12. Relations between broad-band linear polarization and Ca II H and K emission in late-type dwarf stars

    NASA Technical Reports Server (NTRS)

    Huovelin, Juhani; Saar, Steven H.; Tuominen, Ilkka

    1988-01-01

    Broadband UBV linear polarization data acquired for a sample of late-type dwarfs are compared with contemporaneous measurements of Ca II H and K line core emission. A weighted average of the largest values of the polarization degree is shown to be the best parameter for chromospheric activity diagnosis. The average maximum polarization in the UV is found to increase from late-F to late-G stars. It is noted that polarization in the U band is considerably more sensitive to activity variations than that in the B or V bands. The results indicate that stellar magnetic fields and the resulting saturation in the Zeeman-sensitive absorption lines are the most probably source of linear polarization in late-type main-sequence stars.

  13. Comparing Broad-Band and Red Edge-Based Spectral Vegetation Indices to Estimate Nitrogen Concentration of Crops Using Casi Data

    NASA Astrophysics Data System (ADS)

    Wang, Yanjie; Liao, Qinhong; Yang, Guijun; Feng, Haikuan; Yang, Xiaodong; Yue, Jibo

    2016-06-01

    In recent decades, many spectral vegetation indices (SVIs) have been proposed to estimate the leaf nitrogen concentration (LNC) of crops. However, most of these indices were based on the field hyperspectral reflectance. To test whether they can be used in aerial remote platform effectively, in this work a comparison of the sensitivity between several broad-band and red edge-based SVIs to LNC is investigated over different crop types. By using data from experimental LNC values over 4 different crop types and image data acquired using the Compact Airborne Spectrographic Imager (CASI) sensor, the extensive dataset allowed us to evaluate broad-band and red edge-based SVIs. The result indicated that NDVI performed the best among the selected SVIs while red edge-based SVIs didn't show the potential for estimating the LNC based on the CASI data due to the spectral resolution. In order to search for the optimal SVIs, the band combination algorithm has been used in this work. The best linear correlation against the experimental LNC dataset was obtained by combining the 626.20nm and 569.00nm wavebands. These wavelengths correspond to the maximal chlorophyll absorption and reflection position region, respectively, and are known to be sensitive to the physiological status of the plant. Then this linear relationship was applied to the CASI image for generating an LNC map, which can guide farmers in the accurate application of their N fertilization strategies.

  14. Second-harmonic generation at angular incidence in a negative-positive index photonic band-gap structure.

    PubMed

    D'Aguanno, Giuseppe; Mattiucci, Nadia; Scalora, Michael; Bloemer, Mark J

    2006-08-01

    In the spectral region where the refractive index of the negative index material is approximately zero, at oblique incidence, the linear transmission of a finite structure composed of alternating layers of negative and positive index materials manifests the formation of a new type of band gap with exceptionally narrow band-edge resonances. In particular, for TM-polarized (transverse magnetic) incident waves, field values that can be achieved at the band edge may be much higher compared to field values achievable in standard photonic band-gap structures. We exploit the unique properties of these band-edge resonances for applications to nonlinear frequency conversion, second-harmonic generation, in particular. The simultaneous availability of high field localization and phase matching conditions may be exploited to achieve second-harmonic conversion efficiencies far better than those achievable in conventional photonic band-gap structures. Moreover, we study the role played by absorption within the negative index material, and find that the process remains efficient even for relatively high values of the absorption coefficient. PMID:17025558

  15. Plasmonic coupling with most of the transition metals: a new family of broad band and near infrared nanoantennas.

    PubMed

    Manchon, Delphine; Lermé, Jean; Zhang, Taiping; Mosset, Alexis; Jamois, Cécile; Bonnet, Christophe; Rye, Jan-Michael; Belarouci, Ali; Broyer, Michel; Pellarin, Michel; Cottancin, Emmanuel

    2015-01-21

    In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be controlled through morphological variation of the NAs (size, shape, interparticle distance). First, accurate calculations using the generalized Mie theory on spherical dimers demonstrate that we can take advantage of the plasmonic coupling to enhance LSPRs over a broad spectral range for many transition metals (Pt, Pd, Cr, Ni etc.). The LSPR remains broad for low interparticle distances and masks the various hybridized modes within the overall resonance. However, an analysis of the charge distribution on the surface of the nanoparticles reveals these modes and their respective contributions to the observed LSPR. In the case of spherical dimers, the transfer of the oscillator strengths from the "dipolar" mode to higher orders involves a maximum extinction cross-section for intermediate interparticle distances of a few nanometers. The emergence of the LSPR has been then experimentally illustrated with parallelepipedal NAs (monomers and dimers) made of various transition metals (Pt, Pd and Cr) and elaborated by nanolithography. Absolute extinction cross-sections have been measured with the spatial modulation spectroscopy technique over a broad spectral range (300-900 nm) for individual NAs, the morphology of which has been independently characterized by electron microscopy imaging. A clear enhancement of the LSPR has been revealed for a longitudinal excitation and plasmonic coupling has been clearly evidenced in dimers by an induced redshift and broadening of the LSPR compared to monomers. Furthermore, the LSPR has been shown to be highly sensitive to slight modifications of the interparticle distance. All the experimental

  16. Plasmonic coupling with most of the transition metals: a new family of broad band and near infrared nanoantennas

    NASA Astrophysics Data System (ADS)

    Manchon, Delphine; Lermé, Jean; Zhang, Taiping; Mosset, Alexis; Jamois, Cécile; Bonnet, Christophe; Rye, Jan-Michael; Belarouci, Ali; Broyer, Michel; Pellarin, Michel; Cottancin, Emmanuel

    2014-12-01

    In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be controlled through morphological variation of the NAs (size, shape, interparticle distance). First, accurate calculations using the generalized Mie theory on spherical dimers demonstrate that we can take advantage of the plasmonic coupling to enhance LSPRs over a broad spectral range for many transition metals (Pt, Pd, Cr, Ni etc.). The LSPR remains broad for low interparticle distances and masks the various hybridized modes within the overall resonance. However, an analysis of the charge distribution on the surface of the nanoparticles reveals these modes and their respective contributions to the observed LSPR. In the case of spherical dimers, the transfer of the oscillator strengths from the ``dipolar'' mode to higher orders involves a maximum extinction cross-section for intermediate interparticle distances of a few nanometers. The emergence of the LSPR has been then experimentally illustrated with parallelepipedal NAs (monomers and dimers) made of various transition metals (Pt, Pd and Cr) and elaborated by nanolithography. Absolute extinction cross-sections have been measured with the spatial modulation spectroscopy technique over a broad spectral range (300-900 nm) for individual NAs, the morphology of which has been independently characterized by electron microscopy imaging. A clear enhancement of the LSPR has been revealed for a longitudinal excitation and plasmonic coupling has been clearly evidenced in dimers by an induced redshift and broadening of the LSPR compared to monomers. Furthermore, the LSPR has been shown to be highly sensitive to slight modifications of the interparticle distance. All the experimental

  17. Low-voltage broad-band electroabsorption from thin Ge/SiGe quantum wells epitaxially grown on silicon.

    PubMed

    Edwards, Elizabeth H; Lever, Leon; Fei, Edward T; Kamins, Theodore I; Ikonic, Zoran; Harris, James S; Kelsall, Robert W; Miller, David A B

    2013-01-14

    We demonstrate electroabsorption contrast greater than 5 dB over the entire telecommunication S- and C-bands with only 1V drive using a new Ge/SiGe QW epitaxy design approach; further, this is demonstrated with the thinnest Ge/SiGe epitaxy to date, using a virtual substrate only 320-nm-thick. We use an eigenmode expansion method to model the optical coupling between SOI waveguides and both vertically and butt-coupled Ge/SiGe devices, and show that this reduction in thickness is expected to lead to a significant improvement in the insertion loss of waveguide-integrated devices. PMID:23388980

  18. Investigation of the validity of quasilinear theory for electron Landau damping in a tokamak using a broad-band wave effect

    SciTech Connect

    Lee, Jungpyo; Bonoli, Paul; Wright, John

    2011-01-01

    The quasilinear diffusion coefficient assuming a constant magnetic field along the electron orbit is widely used to describe electron Landau damping of waves in a tokamak where the magnitude of the magnetic field varies on a flux surface. To understand the impact of violating the constant magnetic field assumption, we introduce the effect of a broad-bandwidth wave spectrum which has been used in the past to validate quasilinear theory for the fast decorrelation process between resonances. By the reevaluation of the diffusion coefficient through the level of the phase integral for the tokamak geometry with the broad-band wave effect included, we identify the three acceptable errors for the use of the quasilinear diffusion coefficient.

  19. Investigation of the validity of quasilinear theory for electron Landau damping in a tokamak using a broad-band wave effect

    DOE PAGESBeta

    Lee, Jungpyo; Bonoli, Paul; Wright, John

    2011-01-01

    The quasilinear diffusion coefficient assuming a constant magnetic field along the electron orbit is widely used to describe electron Landau damping of waves in a tokamak where the magnitude of the magnetic field varies on a flux surface. To understand the impact of violating the constant magnetic field assumption, we introduce the effect of a broad-bandwidth wave spectrum which has been used in the past to validate quasilinear theory for the fast decorrelation process between resonances. By the reevaluation of the diffusion coefficient through the level of the phase integral for the tokamak geometry with the broad-band wave effect included,more » we identify the three acceptable errors for the use of the quasilinear diffusion coefficient.« less

  20. Investigation of the validity of quasilinear theory for electron Landau damping in a tokamak using a broad-band wave effect

    SciTech Connect

    Lee, Jungpyo; Bonoli, Paul; Wright, John

    2011-01-15

    The quasilinear diffusion coefficient assuming a constant magnetic field along the electron orbit is widely used to describe electron Landau damping of waves in a tokamak where the magnitude of the magnetic field varies on a flux surface. To understand the impact of violating the constant magnetic field assumption, we introduce the effect of a broad-bandwidth wave spectrum which has been used in the past to validate quasilinear theory for the fast decorrelation process between resonances. By the reevaluation of the diffusion coefficient through the level of the phase integral for the tokamak geometry with the broad-band wave effect included, we identify the three acceptable errors for the use of the quasilinear diffusion coefficient.

  1. Enhanced 2 μm broad-band emission and NIR to visible frequency up-conversion from Ho3+/Yb3+ co-doped Bi2O3-GeO2-ZnO glasses.

    PubMed

    Biswas, Kaushik; Sontakke, Atul D; Sen, R; Annapurna, K

    2013-08-01

    In this work, a new and non-conventional oxide glass composition based on Bi2O3-GeO2-ZnO system has been formulated with an aim to realize low phonon oxide glass and elucidate its performance when co-doped with Ho(3+)/Yb(3+) for the energy transfer based NIR emission at 2 μm from Ho(3+) ions under Yb(3+) excitation. The glass with 1.0 mol% Ho2O3 and 0.5 mol% Yb2O3 has exhibited maximum energy transfer rate (3602 s(-1)) and energy transfer efficiency (65.92%). Important radiative properties have been predicted for emission transitions of Ho(3+) ions using intensity parameters derived from measured absorption spectra using standard Judd-Ofelt theory. At lower acceptor ion concentration (0.1 mol%), an efficient NIR to visible up-conversion emission has been observed based on two photon absorption process which has found to be reduced significantly at higher Ho(3+) concentrations with simultaneous enhancement in 2 μm emission. Hence, this newly developed glass codoped with Yb(3+)/Ho(3+) is promising glass for sensitized 2 μm emission applications as broad band tunable lasers because of the combination of low phonon energy (707 cm(-1)), high energy transfer efficiency, moderately high emission cross-section (5.33×10(-21) cm(2)) and larger effective half-width of the emission band value of 169 nm. PMID:23685797

  2. Relationship between the broad OH stretching band of methanol and hydrogen-bonding patterns in the liquid phase.

    PubMed

    Ohno, Keiichi; Shimoaka, Takafumi; Akai, Nobuyuki; Katsumoto, Yukiteru

    2008-08-14

    The OH stretching (nu(OH)) band of methanol observed in condensed phase has been analyzed in terms of hydrogen-bonding patterns. Quantum chemical calculations for methanol clusters have revealed that broadening of the nu(OH) envelope is reasonably reproduced by considering nearest and next-nearest neighbor interactions through hydrogen bonding. Because the hydrogen bond formed between donor (D) and acceptor (A) is cooperatively strengthened or weakened by a newly formed hydrogen bond at D or A, we have proposed the following notation for hydrogen-bonding patterns of monohydric alcohols: a(D)DAd(A)a(A), where a is the number of protons accepted by D (a(D)) or A (a(A)), and d(A) is the number of protons donated by A. The indicator of the hydrogen-bond strength, which is given by M(OH) = a(D) + d(A) - a(A), is correlated well with the nu(OH) wavenumber of the methanol molecule D participating in the a(D)DAd(A)a(A) pattern. The correlation between M(OH) and the hydrogen-bonding energy of the a(D)DAd(A)a(A) pattern has also been deduced from the calculation results for the clusters. The nu(OH) bands of methanol measured in the CCl4 solution and pure liquid have been successfully analyzed by the method proposed here. PMID:18636720

  3. The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band

    SciTech Connect

    Visser, P. J. de; Yates, S. J. C.; Guruswamy, T.; Goldie, D. J.; Withington, S.; Neto, A.; Llombart, N.; Baryshev, A. M.; Klapwijk, T. M.; Baselmans, J. J. A.

    2015-06-22

    We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on, the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice, this is a measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.

  4. The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band

    NASA Astrophysics Data System (ADS)

    de Visser, P. J.; Yates, S. J. C.; Guruswamy, T.; Goldie, D. J.; Withington, S.; Neto, A.; Llombart, N.; Baryshev, A. M.; Klapwijk, T. M.; Baselmans, J. J. A.

    2015-06-01

    We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on, the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice, this is a measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.

  5. Correlation between the local OH stretching vibration wavenumber and the hydrogen bonding pattern of water in a condensed phase: Quantum chemical approach to analyze the broad OH band

    NASA Astrophysics Data System (ADS)

    Shimoaka, Takafumi; Hasegawa, Takeshi; Ohno, Keiichi; Katsumoto, Yukiteru

    2012-12-01

    A study of the chemical origin of the broad IR absorption band of the O-H stretching vibration (νOH) of liquid water is mentioned. The study is performed by measuring the local νOH mode of the half-deuterated water (HDO) dissolved in deuterated water (D2O) with an aid of quantum chemical calculation. The band position of a local νOH mode is analyzed as a function of hydrogen (H)-bond coordination pattern, which is taken into account by using a useful index of MOH based on the DA3 pattern method. The DA3 method focuses on a HDO-D2O (donor-accepter; DA) molecular pair, and the hydration about the DA pair is categorized into 36 patterns with respect to the H-bond coordination pattern. The MOH index summarizes the patterns by considering the positive and negative contributions of the hydration to the H-bond in the DA pair. The calculated band position of the H-bonded νOH in the pair is readily grouped by using the MOH index, which can also be used as an index for evaluating H-bonding energy. This paper demonstrates the potential of the DA3 method to analyze the νOH band and H-bonding energy of liquid water and ice by referring to QC calculation results for relatively small water clusters.

  6. Notes on a broad-band variant of the NCER seismic data multiplex system for use with field tape recorders

    USGS Publications Warehouse

    Eaton, Jerry P.

    1976-01-01

    Tests of the standard NCER multiplex system recorded and played back on both the Bell and Howell 3700B (about 0.1% tape speed variation) and on the Sony TC-126 cassette recorder (about 1% tape speed variation) showed that subtractive compensation employing a reference frequency multiplexed on the data track was remarkably effective in reducing tape-speed-variation-induced noise 1 and, hence, in increasing the dynamic range of the record/playback system. Further tests suggested that the 0 to 30 Hz bandwidth of the standard system (8 data channels) might be increased substantially, at the 'price' of reducing the number of data channels to 3 or 4, without serious loss of dynamic range if subtractive compensation could be implemented effectively with the broader-band system.

  7. Band structure of cavity-type hypersonic phononic crystals fabricated by femtosecond laser-induced two-photon polymerization

    NASA Astrophysics Data System (ADS)

    Rakhymzhanov, A. M.; Gueddida, A.; Alonso-Redondo, E.; Utegulov, Z. N.; Perevoznik, D.; Kurselis, K.; Chichkov, B. N.; El Boudouti, E. H.; Djafari-Rouhani, B.; Fytas, G.

    2016-05-01

    The phononic band diagram of a periodic square structure fabricated by femtosecond laser pulse-induced two photon polymerization is recorded by Brillouin light scattering (BLS) at hypersonic (GHz) frequencies and computed by finite element method. The theoretical calculations along the two main symmetry directions quantitatively capture the band diagrams of the air- and liquid-filled structure and moreover represent the BLS intensities. The theory helps identify the observed modes, reveals the origin of the observed bandgaps at the Brillouin zone boundaries, and unravels direction dependent effective medium behavior.

  8. Spin-wave band-pass filters based on yttrium iron garnet films for tunable microwave photonic oscillators

    NASA Astrophysics Data System (ADS)

    Ustinov, A. B.; Drozdovskii, A. V.; Nikitin, A. A.; Kalinikos, B. A.

    2015-12-01

    The paper reports on development of tunable band-pass microwave filters for microwave photonic generators. The filters were fabricated with the use of epitaxial yttrium iron garnet films. Principle of operation of the filters was based on excitation, propagation, and reception of spin waves. In order to obtain narrow pass band, the filtering properties of excitation and reception antennas were exploited. The filters demonstrated insertion losses of 2-3 dB, bandwidth of 25-35 MHz, and tuning range of up to 1.5 GHz in the range 3-7 GHz.

  9. Imaging of the Deep Structure by Long Term Broad Band OBSs \\ \\ -- Trans-PHS Profile and NW Pacific WP-2 site --

    NASA Astrophysics Data System (ADS)

    Shiobara, H.; Sugioka, H.; Yoneshima, S.; Mochizuki, K.; Mochizuki, M.; Kodaira, S.; Hino, R.; Shinohara, M.; Kanazawa, T.; Fukao, Y.

    2001-12-01

    As an important part of the Ocean Hemisphere network Project, long term ocean bottom seismic observations have been started and some of their data have been retrieved already. One of them, the trans-Philippine Sea profile observation (15 Long Term OBSs, Nov. 1999 -- July 2000) was preliminarily reported at the last AGU fall meeting (S51B-02, 2000). Other long term broad band observations had been performed twice at the northwestern Pacific (Broad Band OBS, NWPAC1: Aug. 1999 -- May 2000, NWPAC2: May 2000 -- Nov. 2000), where the borehole seismic observatory (WP-2) has been activated in Nov. 2000. The LTOBS and the BBOBS contain a semi broad band sensor (WB2023LP, PMD) which has the pass band from 30s to 50Hz and a broad band sensor (CMG-1T, Guralp) which has the pass band from 360s to 80Hz, respectively. The seismic data is recorded continuously with a sampling frequency of 128Hz by a 20bit ADC on four 2.5 inch 6.5 GB HDDs. The direction of horizontal components are determined from the data of the direct water wave during the airgun shooting or P-SV converted waves at the sediment-basement interface. Running acceleration power spectra (0dB=1m2/s4/Hz) of these data during the whole observation period indicate followings; 1) sufficiently low noise band exists in the frequency range of 10--100mHz and the lowest level is close to the NLNM, but the horizontal noise level varies about 20--30dB with a dominant 12 hours interval, 2) high level micro seismic noise in the range of 0.1--1Hz is always near the NHNM and varies about 30--40dB. In this presentation, preliminary results of the deep structure imaging from these vast data by a receiver function analysis is shown. To perform this analysis with the OBS data, removal of water column reverberations and reduction of high level micro seismic noise should be necessary. The former process has a difficulty in the estimation of the water-sea bottom reflection coefficient and requires the data of higher sampling frequency, more

  10. Tuning the photonic stop bands of nanoporous anodic alumina-based distributed bragg reflectors by pore widening.

    PubMed

    Rahman, Mohammad Mahbubur; Marsal, Lluis F; Pallarès, Josep; Ferré-Borrull, Josep

    2013-12-26

    A distributed Bragg reflector based on nanoporous anodic alumina was fabricated using an innovative cyclic anodization voltage approach, which resulted in an in-depth modulation of the pore geometry and the refractive index. The effect of a pore-widening wet-etching step on the structure's photonic stop-band properties was studied. From transmittance measurements, it was shown that by changing the pore-widening time it is possible to modulate the photonic stop band in the range of visible to near infrared. With the help of a theoretical model, we were able to obtain information about the evolution with the pore widening of the material effective refractive indexes. This opens the possibility of obtaining several optoelectronic devices based on nanoporous anodic alumina. PMID:24283602

  11. Spontaneous emission from a two-level atom in anisotropic one-band photonic crystals: A fractional calculus approach

    SciTech Connect

    Wu, J.-N.; Huang, C.-H.; Cheng, S.-C.; Hsieh, W.-F.

    2010-02-15

    Spontaneous emission (SE) from a two-level atom in an anisotropic photonic crystal (PC) is investigated by the fractional calculus. Physical phenomena of the SE are studied analytically by solving the fractional kinetic equations of the SE. There is a dynamical discrepancy between the SE of anisotropic and isotropic PCs. We find that, contrary to the SE phenomenon of the isotropic PC, the SE near the band edge of an anisotropic PC shows no photon-atom bound state. It is consistent with the experimental results of Barth, Schuster, Gruber, and Cichos [Phys. Rev. Lett. 96, 243902 (2006)] that the anisotropic property of the system enhances the SE. We also study effects of dispersion curvatures on the changes of the photonic density of states and the appearance of the diffusion fields in the SE.

  12. The KLT (Karhunen-Loève Transform) to extend SETI searches to broad-band and extremely feeble signals

    NASA Astrophysics Data System (ADS)

    Maccone, Claudio

    2010-12-01

    The KLT (acronym for Karhunen-Loève Transform) is a mathematical algorithm superior to the classical FFT in many regards: The KLT can filter signals out of the background noise over both wide and narrow bands. This is in sharp contrast to the FFT that rigorously applies to narrow-band signals only. The KLT can be applied to random functions that are non-stationary in time, i.e. whose autocorrelation is a function of the two independent variables t1 and t2 separately. Again, this is a sheer advantage of the KLT over the FFT, inasmuch as the FFT rigorously applies to stationary processes only, i.e. processes whose autocorrelation is a function of the absolute value of the difference of t1 and t2 only. The KLT can detect signals embedded in noise to unbelievably small values of the Signal-to-Noise Ratio (SNR), like 10 -3 or so. This particular feature of the KLT is studied in detail in this paper. An excellent filtering algorithm like the KLT, however, comes with a cost that one must be ready to pay for especially in SETI: its computational burden is much higher than for the FFT. In fact, it can be shown that no fast KLT transform can possibly exist and, for an autocorrelation matrix of size N, the calculations must be of the order of N2, rather than N log( N). Nevertheless, for moderate values of N (in the hundreds), the KLT dominates over the FFT, as shown by the numerical simulations. Finally, an important and recent (2007-2008) development in the KLT theory, called the "Bordered Autocorrelation Method" (BAM), is presented. This BAM-KLT method gets around the difficulty of the N2 brunt calculations and ends up in the following unexpected theorem: the KLT of a feeble sinusoidal carrier embedded into a lot of white stationary noise is given by the Fourier transform of the derivative of the largest KLT eigenvalue with respect to the bordering index. This basic result is fully proved analytically in the final sections of this paper by virtue of a new theorem

  13. Ultrasensitive solution-processed broad-band photodetectors using CH3NH3PbI3 perovskite hybrids and PbS quantum dots as light harvesters

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Wang, Kai; Du, Pengcheng; Wang, Enmin; Gong, Xiong; Heeger, Alan J.

    2015-10-01

    Sensing from ultraviolet-visible to infrared is critical for both scientific and industrial applications. In this work, we demonstrate solution-processed ultrasensitive broad-band photodetectors (PDs) utilizing organolead halide perovskite materials (CH3NH3PbI3) and PbS quantum dots (QDs) as light harvesters. Through passivating the structural defects on the surface of PbS QDs with diminutive molecular-scaled CH3NH3PbI3, both trap states in the bandgap of PbS QDs for charge carrier recombination and the leakage currents occurring at the defect sites are significantly reduced. In addition, CH3NH3PbI3 itself is an excellent light harvester in photovoltaics, which contributes a great photoresponse in the ultraviolet-visible region. Consequently, operated at room temperature, the resultant PDs show a spectral response from 375 nm to 1100 nm, with high responsivities over 300 mA W-1 and 130 mA W-1, high detectivities exceeding 1013 Jones (1 Jones = 1 cm Hz1/2 W-1) and 5 × 1012 Jones in the visible and near infrared regions, respectively. These device performance parameters are comparable to those from pristine inorganic counterparts. Thus, our results offer a facile and promising route for advancing the performance of broad-band PDs.

  14. Ultrasensitive solution-processed broad-band photodetectors using CH₃NH₃PbI₃ perovskite hybrids and PbS quantum dots as light harvesters.

    PubMed

    Liu, Chang; Wang, Kai; Du, Pengcheng; Wang, Enmin; Gong, Xiong; Heeger, Alan J

    2015-10-21

    Sensing from ultraviolet-visible to infrared is critical for both scientific and industrial applications. In this work, we demonstrate solution-processed ultrasensitive broad-band photodetectors (PDs) utilizing organolead halide perovskite materials (CH3NH3PbI3) and PbS quantum dots (QDs) as light harvesters. Through passivating the structural defects on the surface of PbS QDs with diminutive molecular-scaled CH3NH3PbI3, both trap states in the bandgap of PbS QDs for charge carrier recombination and the leakage currents occurring at the defect sites are significantly reduced. In addition, CH3NH3PbI3 itself is an excellent light harvester in photovoltaics, which contributes a great photoresponse in the ultraviolet-visible region. Consequently, operated at room temperature, the resultant PDs show a spectral response from 375 nm to 1100 nm, with high responsivities over 300 mA W(-1) and 130 mA W(-1), high detectivities exceeding 10(13) Jones (1 Jones = 1 cm Hz(1/2) W(-1)) and 5 × 10(12) Jones in the visible and near infrared regions, respectively. These device performance parameters are comparable to those from pristine inorganic counterparts. Thus, our results offer a facile and promising route for advancing the performance of broad-band PDs. PMID:26395642

  15. Amplification of broad-band chirped pulses up to the 100-mJ level using alexandrite-pumped neodymium-doped glasses

    SciTech Connect

    Gamache, C.; Husson, D.; Seznec, S.; Descamps, D.; Migus, A. |

    1996-08-01

    In this work, the authors are concerned by the amplification of broad-band energetic pulses in laser-pumped Nd:glasses, with obvious applications to ultrashort pulse technology, but also to a front end for the envisioned Megajoules Nd:glass laser facility devoted to inertial confinement fusion (ICF) studies and ignition demonstration. An alexandrite laser is used to longitudinally end-pump mixed Nd:glass rods in a multipass arrangement in order to amplify chirped pulses in the 50--100-mJ range at a 1-Hz repetition rate. This system has a broad-band capability of up to 8--10 nm output bandwidth. The authors have developed a model, which in the specific case of amplification of chirped-pulse, takes into account the exact configuration of the rods, their spectral properties, and the longitudinal pumping geometry. An agreement between experiment and theory is obtained by assuming a pump quantum efficiency of the order of 60%.

  16. The effect of broad-band Alfven-cyclotron waves spectra on the preferential heating and differential acceleration of He{sup ++} ions in the solar wind

    SciTech Connect

    Maneva, Y. G.; Ofman, L.; Vinas, A. F.

    2013-06-13

    In anticipation of results from inner heliospheric missions such as the Solar Orbiter and the Solar Probe we present the results from 1.5D hybrid simulations to study the role of magnetic fluctuations for the heating and differential acceleration of He{sup ++} ions in the solar wind. We consider the effects of nonlinear Alfven-cyclotron waves at different frequency regimes. Monochromatic nonlinear Alfven-alpha-cyclotron waves are known to preferentially heat and accelerate He{sup ++} ions in collisionless low beta plasma. In this study we demonstrate that these effects are preserved when higherfrequency monochromatic and broad-band spectra of Alfven-proton-cyclotron waves are considered. Comparison between several nonlinear monochromatic waves shows that the ion temperatures, anisotropies and relative drift are quantitatively affected by the shift in frequency. Including a broad-band wave-spectrum results in a significant reduction of both the parallel and the perpendicular temperature components for the He{sup ++} ions, whereas the proton heating is barely influenced, with the parallel proton temperature only slightly enhanced. The differential streaming is strongly affected by the available wave power in the resonant daughter ion-acoustic waves. Therefore for the same initial wave energy, the relative drift is significantly reduced in the case of initial wave-spectra in comparison to the simulations with monochromatic waves.

  17. Dual-function photonic integrated circuit for frequency octo-tupling or single-side-band modulation.

    PubMed

    Hasan, Mehedi; Maldonado-Basilio, Ramón; Hall, Trevor J

    2015-06-01

    A dual-function photonic integrated circuit for microwave photonic applications is proposed. The circuit consists of four linear electro-optic phase modulators connected optically in parallel within a generalized Mach-Zehnder interferometer architecture. The photonic circuit is arranged to have two separate output ports. A first port provides frequency up-conversion of a microwave signal from the electrical to the optical domain; equivalently single-side-band modulation. A second port provides tunable millimeter wave carriers by frequency octo-tupling of an appropriate amplitude RF carrier. The circuit exploits the intrinsic relative phases between the ports of multi-mode interference couplers to provide substantially all the static optical phases needed. The operation of the proposed dual-function photonic integrated circuit is verified by computer simulations. The performance of the frequency octo-tupling and up-conversion functions is analyzed in terms of the electrical signal to harmonic distortion ratio and the optical single side band to unwanted harmonics ratio, respectively. PMID:26030542

  18. Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12

    NASA Astrophysics Data System (ADS)

    Ge, Xianghong; Mao, Yanchao; Liu, Xiansheng; Cheng, Yongguang; Yuan, Baohe; Chao, Mingju; Liang, Erjun

    2016-04-01

    In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices.

  19. Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12.

    PubMed

    Ge, Xianghong; Mao, Yanchao; Liu, Xiansheng; Cheng, Yongguang; Yuan, Baohe; Chao, Mingju; Liang, Erjun

    2016-01-01

    In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices. PMID:27098924

  20. Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12

    PubMed Central

    Ge, Xianghong; Mao, Yanchao; Liu, Xiansheng; Cheng, Yongguang; Yuan, Baohe; Chao, Mingju; Liang, Erjun

    2016-01-01

    In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices. PMID:27098924

  1. Tunable all-angle negative refraction and photonic band gaps in two-dimensional plasma photonic crystals with square-like Archimedean lattices

    SciTech Connect

    Zhang, Hai-Feng E-mail: lsb@nuaa.edu.cn; Liu, Shao-Bin E-mail: lsb@nuaa.edu.cn; Jiang, Yu-Chi

    2014-09-15

    In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.

  2. Tunable all-angle negative refraction and photonic band gaps in two-dimensional plasma photonic crystals with square-like Archimedean lattices

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Jiang, Yu-Chi

    2014-09-01

    In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.

  3. Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9-2021

    NASA Astrophysics Data System (ADS)

    Pintore, F.; Sanna, A.; Di Salvo, T.; Del Santo, M.; Riggio, A.; D'Aì, A.; Burderi, L.; Scarano, F.; Iaria, R.

    2016-04-01

    We analysed a 115-ks XMM-Newton observation and the stacking of 8 d of INTEGRAL observations, taken during the raise of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021. The source showed numerous type-I burst episodes during the XMM-Newton observation, and for this reason we studied separately the persistent and burst epochs. We described the persistent emission with a combination of two soft thermal components, a cold thermal Comptonization component (˜2 keV) and an additional hard X-ray emission described by a power law (Γ ˜ 2.3). The continuum components can be associated with an accretion disc, the neutron star (NS) surface and a thermal Comptonization emission coming out of an optically thick plasma region, while the origin of the high-energy tail is still under debate. In addition, a number of broad (σ = 0.1-0.4 keV) emission features likely associated with reflection processes have been observed in the XMM-Newton data. The estimated 1.0-50 keV unabsorbed luminosity of the source is ˜5 × 1037 erg s-1, about 25 per cent of the Eddington limit assuming a 1.4 M⊙ NS. We suggest that the spectral properties of SAX J1748.9-2021 are consistent with a soft state, differently from many other accreting X-ray millisecond pulsars which are usually found in the hard state. Moreover, none of the observed type-I burst reached the Eddington luminosity. Assuming that the burst ignition and emission are produced above the whole NS surface, we estimate an NS radius of ˜7-8 km, consistent with previous results.

  4. Broad Balmer Wings in BA Hyper/Supergiants Distorted by Diffuse Interstellar Bands: Five Examples in the 30 Doradus Region from the VLT-FLAMES Tarantula Survey

    NASA Astrophysics Data System (ADS)

    Walborn, Nolan R.; Sana, Hugues; Evans, Christopher J.; Taylor, William D.; Sabbi, Elena; Barbá, Rodolfo H.; Morrell, Nidia I.; Maíz Apellániz, Jesús; Sota, Alfredo; Dufton, Philip L.; McEvoy, Catherine M.; Clark, J. Simon; Markova, Nevena; Ulaczyk, Krzysztof

    2015-08-01

    Extremely broad emission wings at Hβ and Hα have been found in VLT-FLAMES Tarantula Survey data for five very luminous BA supergiants in or near 30 Doradus in the Large Magellanic Cloud. The profiles of both lines are extremely asymmetrical, which we have found to be caused by very broad diffuse interstellar bands (DIBs) in the longward wing of Hβ and the shortward wing of Hα. These DIBs are well known to interstellar but not to many stellar specialists, so that the asymmetries may be mistaken for intrinsic features. The broad emission wings are generally ascribed to electron scattering, although we note difficulties for that interpretation in some objects. Such profiles are known in some Galactic hyper/supergiants and are also seen in both active and quiescent Luminous Blue Variables (LBVs). No prior or current LBV activity is known in these 30 Dor stars, although a generic relationship to LBVs is not excluded; subject to further observational and theoretical investigation, it is possible that these very luminous supergiants are approaching the LBV stage for the first time. Their locations in the HRD and presumed evolutionary tracks are consistent with that possibility. The available evidence for spectroscopic variations of these objects is reviewed, while recent photometric monitoring does not reveal variability. A search for circumstellar nebulae has been conducted, with an indeterminate result for one of them.

  5. Lunar BroadBand Seismometer System in the Japanese lunar landing mission SELENE-2: its science goals and instrument details

    NASA Astrophysics Data System (ADS)

    Shiraishi, H.; Kobayashi, N.; Takeuchi, N.; Murakami, H.; Lognonne, P.; Giardini, D.; Christensen, U. R.; Okamoto, T.; Kuge, K.; Zhao, D.; Mocquet, A.; Mimoun, D.; de Raucourt, S.; Nebut, T.; Tillier, S.; Kawamura, T.; Mance, D.; Zweifel, P.; Bierwirth, M.; Roll, R.; Ishihara, Y.; Araki, E.; Ogawa, K.; Yamada, R.; Shirai, K.; Iijima, Y.; Hayakawa, M.; Tanaka, S.; Kakuma, H.; Yamada, I.

    2010-12-01

    SELENE-2 is the first lunar landing mission of Japan. We are developing a broadband seismometer system as a powerful candidate for a payload instrument. In this paper, we demonstrate the necessity of broadband seismometer observation and its scientific targets. The Apollo projects in 1970's installed an equilateral triangle seismograph network at apexes where Apollo 12,14,15 and 16 landed. The passive seismic observation had lasted for over 7 years and it provided us with the first information on the lunar seismicity and the lunar structure down to a depth of 1,000km. It, however, had two drawbacks: (1) the size of the network is limited within 1,000km, and (2) the sensitivity of the seismometers with a limited narrow band of 0.17Hz is marginal to detect the small deep moonquakes which occurred frequently. In addition, due to the strong scattering of seismic waves, P and S wave arrivals could not be picked up accurately, and the typical picking error is up to 10sec. Because of these problems, the lunar velocity models obtained so far are less certain, in particular, at depths greater than 200km. In the SELENE-2 project we plan to have only one landing site and so we cannot run a seismic network observation by the project alone. Thus, we need to obtain more information from the feeble seismic waveforms using a broadband (0.02-50Hz) seismometer having 10 times higher sensitivity than that of the Apollo seismometers to overcome the drawback (2) as mentioned above. The characteristic frequency of the shallow layer is about 0.12Hz for the seismic velocity model of Nakamura(1981). Below that frequency, we expect clear detection of seismic phases reflected and converted at an internal discontinuity such as the core-mantle boundary. The long-period seismic waveforms may provide us not only information on the depth of an internal discontinuity but also seismic velocity contrast at the boundary. Another scientific target is to determine the corner frequency of deep

  6. One-photon band gap engineering of borate glass doped with ZnO for photonics applications

    SciTech Connect

    Abdel-Baki, Manal; Abdel-Wahab, Fathy A.; El-Diasty, Fouad

    2012-04-01

    Lithium tungsten borate glass of the composition (0.56-x)B{sub 2}O{sub 3}-0.4Li{sub 2}O-xZnO-0.04WO{sub 3} (0 {<=}x{<=} 0.1 mol. %) is prepared for photonics applications. The glass is doped with ZnO to tune the glass absorption characteristics in a wide spectrum range (200-2500 nm). Chemical bond approach, including chemical structure, electronegativity, bond ionicity, nearest-neighbor coordination, and other chemical bonding aspect, is used to analyze and to explain the obtained glass properties such as: transmittance, absorption, electronic structure parameters (bandgap, Fermi level, and Urbach exciton-phonon coupling), Wannier free excitons excitation (applying Elliott's model), and two-photon absorption coefficient as a result of replacement of B{sub 2}O{sub 3} by ZnO.

  7. One-photon band gap engineering of borate glass doped with ZnO for photonics applications

    NASA Astrophysics Data System (ADS)

    Abdel-Baki, Manal; Abdel-Wahab, Fathy A.; El-Diasty, Fouad

    2012-04-01

    Lithium tungsten borate glass of the composition (0.56-x)B2O3-0.4Li2O-xZnO-0.04WO3 (0 ≤ x ≤ 0.1 mol. %) is prepared for photonics applications. The glass is doped with ZnO to tune the glass absorption characteristics in a wide spectrum range (200-2500 nm). Chemical bond approach, including chemical structure, electronegativity, bond ionicity, nearest-neighbor coordination, and other chemical bonding aspect, is used to analyze and to explain the obtained glass properties such as: transmittance, absorption, electronic structure parameters (bandgap, Fermi level, and Urbach exciton-phonon coupling), Wannier free excitons excitation (applying Elliott's model), and two-photon absorption coefficient as a result of replacement of B2O3 by ZnO.

  8. Broad band simulation of Gamma Ray Bursts (GRB) prompt emission in presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Ziaeepour, Houri; Gardner, Brian

    2011-12-01

    The origin of prompt emission in GRBs is not yet well understood. The simplest and most popular model is Synchrotron Self-Compton (SSC) emission produced by internal shocks inside an ultra-relativistic jet. However, recent observations of a delayed high energy component by the Fermi-LAT instrument have encouraged alternative models. Here we use a recently developed formulation of relativistic shocks for GRBs to simulate light curves and spectra of synchrotron and self-Compton emissions in the framework of internal shock model. This model takes into account the evolution of quantities such as densities of colliding shells, and fraction of kinetic energy transferred to electrons and to induced magnetic field. We also extend this formulation by considering the presence of a precessing external magnetic field. These simulations are very realistic and present significant improvement with respect to previous phenomenological GRB simulations. They reproduce light curves of separate peaks of real GRBs and variety of spectral slopes at E > Epeak observed by the Fermi-LAT instrument. The high energy emission can be explained by synchrotron emission and a subdominant contribution from inverse Compton. We also suggest an explanation for extended tail emission and relate it to the screening of the magnetic field and/or trapping of accelerated electrons in the electromagnetic energy structure of the plasma in the shock front. Spectral slopes of simulated bursts at E << Epeak are consistent with theoretical prediction and at E < Epeak can be flatter if the spectrum of electrons is roughly flat or has a shallow slope at low energies. The observed flat spectra at soft gamma-ray and hard x-ray bands is the evidence that there is a significant contribution at E < Epeak from lower Lorentz factor wing of electron distribution which have a roughly random acceleration rather than being thermal. This means that the state of matter in the jet at the time of ejection is most probably

  9. Surface passivation of a photonic crystal band-edge laser by atomic layer deposition of SiO2 and its application for biosensing

    NASA Astrophysics Data System (ADS)

    Cha, Hyungrae; Lee, Jeongkug; Jordan, Luke R.; Lee, Si Hoon; Oh, Sang-Hyun; Kim, Hyo Jin; Park, Juhun; Hong, Seunghun; Jeon, Heonsu

    2015-02-01

    We report on the conformal surface passivation of photonic crystal (PC) laser devices with an ultrathin dielectric layer. Air-bridge-type Γ-point band-edge lasers (BELs) are fabricated by forming a honeycomb lattice two-dimensional PC structure into an InGaAsP multiple-quantum-well epilayer. Atomic layer deposition (ALD) is employed for conformal deposition of a few-nanometer-thick SiO2 layer over the entire device surface, not only on the top and bottom surfaces of the air-bridge membrane but also on the air-hole sidewalls. Despite its extreme thinness, the ALD passivation layer is found to protect the InGaAsP BEL devices from harsh chemicals. In addition, the ALD-SiO2 is compatible with the silane-based surface chemistry, which allows us to use ALD-passivated BEL devices as label-free biosensors. The standard streptavidin-biotin interaction shifts the BEL lasing wavelength by ~1 nm for the dipole-like Γ-point band-edge mode. A sharp lasing line (<0.2 nm, full width at half-maximum) and a large refractive index sensitivity (~163 nm per RIU) produce a figure of merit as high as ~800 for our BEL biosensor, which is at least an order of magnitude higher than those of more common biosensors that rely on a broad resonance peak, showing that our nanolaser structures are suitable for highly sensitive biosensor applications.

  10. Electron cyclotron resonance plasma source by using Ku-band traveling-wave tube amplifier for broad ion-beam processing

    NASA Astrophysics Data System (ADS)

    Asaji, Toyohisa; Sasaki, Hiroshi; Kato, Yushi; Sato, Fuminobu; Iida, Toshiyuki; Saito, Junji

    2006-03-01

    A new electron cyclotron resonance (ECR) plasma source has been developed for broad ion-beam processing. A Ku-band traveling-wave tube amplifier (11-13GHz) is adopted to generate high-density plasma under low-pressure conditions. An eight-pole magnetic field is selected to improve good uniformity and plasma confinement. The ECR zone for 11GHz microwaves, i.e., 0.393T, is formed within 6.5mm of the inner wall of a chamber. The ECR plasma is generated by low microwave power (˜200W). The radial profile of plasma density and electron temperature is measured with a Langmuir probe. The plasma density is approximately 3×1017m-3 at the microwave power of 200W. The uniformity of the density is within ±12.6% over 140mm in diameter.

  11. Photonic band structures of periodic arrays of pores in a metallic host: tight-binding beyond the quasistatic approximation

    NASA Astrophysics Data System (ADS)

    Kim, Kwangmoo; Stroud, David

    2014-03-01

    We have calculated the photonic band structures of metallic inverse opals and of periodic linear chains of spherical pores in a metallic host, below a plasma frequency ωp. In both cases, we use a tight-binding approximation, assuming a Drude dielectric function for the metallic component, but without making the quasistatic approximation. The tight-binding modes are linear combinations of the single-cavity transverse magnetic (TM) modes. For the inverse-opal structures, the lowest modes are analogous to those constructed from the three degenerate atomic p-states in fcc crystals. For the linear chains, in the limit of small spheres compared to a wavelength, the results bear some qualitative resemblance to the dispersion relation for metal spheres in an insulating host, as calculated by Brongersma et al. [Phys. Rev. B 62, R16356 (2000)]. Because the electromagnetic fields of these modes decay exponentially in the metal, there are no radiative losses, in contrast to the case of arrays of metallic spheres in air. We suggest that this tight-binding approach to photonic band structures of such metallic inverse materials may be a useful approach for studying photonic crystals containing metallic components. This work was supported by KIAS, by NSF-MRSEC at OSU (DMR-0820414), and by DOE Grant No. DE-FG02-07ER46424. Computing resources were provided by OSC and by Abacus at KIAS.

  12. Photonic band structures of periodic arrays of pores in a metallic host: tight-binding beyond the quasistatic approximation.

    PubMed

    Kim, Kwangmoo; Stroud, D

    2013-08-26

    We have calculated the photonic band structures of metallic inverse opals and of periodic linear chains of spherical pores in a metallic host, below a plasma frequency ωp. In both cases, we use a tight-binding approximation, assuming a Drude dielectric function for the metallic component, but without making the quasistatic approximation. The tight-binding modes are linear combinations of the single-cavity transverse magnetic (TM) modes. For the inverse-opal structures, the lowest modes are analogous to those constructed from the three degenerate atomic p-states in fcc crystals. For the linear chains, in the limit of small spheres compared to a wavelength, the results bear some qualitative resemblance to the dispersion relation for metal spheres in an insulating host, as calculated by Brongersma et al. [Phys. Rev. B 62, R16356 (2000)]. Because the electromagnetic fields of these modes decay exponentially in the metal, there are no radiative losses, in contrast to the case of arrays of metallic spheres in air. We suggest that this tight-binding approach to photonic band structures of such metallic inverse materials may be a useful approach for studying photonic crystals containing metallic components, even beyond the quasistatic approximation. PMID:24105532

  13. Ground-based Photon Path Measurements from Solar Absorption Spectra of the O2 A-band

    NASA Technical Reports Server (NTRS)

    Yang, Z.; Wennberg, P. O.; Cageao, R. P.; Pongetti, T. J.; Toon, G. C.; Sander, S. P.

    2005-01-01

    High-resolution solar absorption spectra obtained from Table Mountain Facility (TMF, 34.38degN, 117.68degW, 2286 m elevation) have been analyzed in the region of the O2 A-band. The photon paths of direct sunlight in clear sky cases are retrieved from the O2 absorption lines and compared with ray-tracing calculations based on the solar zenith angle and surface pressure. At a given zenith angle, the ratios of retrieved to geometrically derived photon paths are highly precise (approx.0.2%), but they vary as the zenith angle changes. This is because current models of the spectral lineshape in this band do not properly account for the significant absorption that exists far from the centers of saturated lines. For example, use of a Voigt function with Lorentzian far wings results in an error in the retrieved photon path of as much as 5%, highly correlated with solar zenith angle. Adopting a super-Lorentz function reduces, but does not completely eliminate this problem. New lab measurements of the lineshape are required to make further progress.

  14. Tunable all-optical single-bandpass photonic microwave filter based on spectrally sliced broad optical source and phase modulation.

    PubMed

    Chen, Ming; Pan, Wei; Zou, Xihua; Luo, Bin; Yan, Lianshan; Liu, Xinkai

    2013-01-10

    A tunable all-optical single-bandpass photonic microwave filter (PMF) based on spectrally sliced broadband optical source and phase modulation is proposed and experimentally demonstrated. A broadband optical source and a Mach-Zehnder interferometer (MZI) are used to generate continuous optical spectral samples, which are employed to form a finite impulse response filter with a single-bandpass response with the help of a single-mode fiber. A phase modulator is then adopted to eliminate the baseband components in the filtering response. The center frequency of the PMF can be tuned by changing the free spectral range of the MZI. An experiment is performed, and the results demonstrate that the proposed PMF has a single-bandpass without baseband components and a tuning range of 5-15 GHz. PMID:23314649

  15. Quantification of magnetic nanoparticles with broad-band-frequency magnetic susceptibility measurements: a case study of an upper loess/palaeosol succession at Luochuan, Chinese Loess Plateau

    NASA Astrophysics Data System (ADS)

    Kodama, Kazuto; An, Zhisheng; Chang, Hong; Qiang, Xiaoke

    2014-11-01

    Broad-band magnetic susceptibility (MS) measurement, a novel magnetic method capable of quantifying a narrow grain size distribution (GSD) of superparamagnetic (SP) particles by measuring low-field MS at a number of frequency steps spanning four orders of magnitude, has been tested in a loess/palaeosol section at Luochuan in the Chinese Loess Plateau. The studied succession consists of sequences from the latest palaeosol unit (S0) to the upper part of the loess unit (L2), spanning the last glacial-interglacial cycle. Reconstructed GSDs consist of volume fractions on the order of 10-24 m3, and the mean GSDs are modal but with distinctive skewness among the loess, the weakly developed palaeosols (weak palaeosols), and the mature palaeosols. This indicates that the mean volume of SP particles in this loess/palaeosol sequence tends to increase during the transition from loess → weak palaeosol → palaeosol, an indication of grain growth as pedogenesis progresses. Total frequency dependence, or TFD(per cent), the difference between χ130 at the lowest (130 Hz) and χ500k at the highest (500 kHz) frequencies normalized to χ130, is judged to be a more suitable index than previous frequency dependence parameters for the concentration of SP particles. TFD(per cent) has a strong correlation with χ130, showing a continuous `growth curve' with the rate of increase being highest for the loess, moderate for the weak palaeosols, and saturated for the palaeosols. The characteristic curve suggests that smaller SP particles are preferentially formed in the earlier stage of pedogenesis rather than the later phase when even larger particles are formed in mature palaeosols. These results demonstrate that the broad-band MS measurement method will be useful for the quantitative assessment of magnetic nanoparticles in soils and sediments.

  16. Wavelength-resolved optical extinction measurements of aerosols using broad-band cavity-enhanced absorption spectroscopy over the spectral range of 445-480 nm.

    PubMed

    Zhao, Weixiong; Dong, Meili; Chen, Weidong; Gu, Xuejun; Hu, Changjin; Gao, Xiaoming; Huang, Wei; Zhang, Weijun

    2013-02-19

    Despite the significant progress in the measurements of aerosol extinction and absorption using spectroscopy approaches such as cavity ring-down spectroscopy (CRDS) and photoacoustic spectroscopy (PAS), the widely used single-wavelength instruments may suffer from the interferences of gases absorption present in the real environment. A second instrument for simultaneous measurement of absorbing gases is required to characterize the effect of light extinction resulted from gases absorption. We present in this paper the development of a blue light-emitting diode (LED)-based incoherent broad-band cavity-enhanced spectroscopy (IBBCEAS) approach for broad-band measurements of wavelength-resolved aerosol extinction over the spectral range of 445-480 nm. This method also allows for simultaneous measurement of trace gases absorption present in the air sample using the same instrument. On the basis of the measured wavelength-dependent aerosol extinction cross section, the real part of the refractive index (RI) can be directly retrieved in a case where the RI does not vary strongly with the wavelength over the relevant spectral region. Laboratory-generated monodispersed aerosols, polystyrene latex spheres (PSL) and ammonium sulfate (AS), were employed for validation of the RI determination by IBBCEAS measurements. On the basis of a Mie scattering model, the real parts of the aerosol RI were retrieved from the measured wavelength-resolved extinction cross sections for both aerosol samples, which are in good agreement with the reported values. The developed IBBCEAS instrument was deployed for simultaneous measurements of aerosol extinction coefficient and NO(2) concentration in ambient air in a suburban site during two representative days. PMID:23320530

  17. Broad-band modelling of short gamma-ray bursts with energy injection from magnetar spin-down and its implications for radio detectability

    NASA Astrophysics Data System (ADS)

    Gompertz, B. P.; van der Horst, A. J.; O'Brien, P. T.; Wynn, G. A.; Wiersema, K.

    2015-03-01

    The magnetar model has been proposed to explain the apparent energy injection in the X-ray light curves of short gamma-ray bursts (SGRBs), but its implications across the full broad-band spectrum are not well explored. We investigate the broad-band modelling of four SGRBs with evidence for energy injection in their X-ray light curves, applying a physically motivated model in which a newly formed magnetar injects energy into a forward shock as it loses angular momentum along open field lines. By performing an order of magnitude search for the underlying physical parameters in the blast wave, we constrain the characteristic break frequencies of the synchrotron spectrum against their manifestations in the available multiwavelength observations for each burst. The application of the magnetar energy injection profile restricts the successful matches to a limited family of models that are self-consistent within the magnetic dipole spin-down framework. We produce synthetic light curves that describe how the radio signatures of these SGRBs ought to have looked given the restrictions imposed by the available data, and discuss the detectability of these signatures with present-day and near-future radio telescopes. Our results show that both the Atacama Large Millimeter Array (ALMA) and the upgraded Very Large Array are now sensitive enough to detect the radio signature within two weeks of trigger in most SGRBs, assuming our sample is representative of the population as a whole. We also find that the upcoming Square Kilometre Array will be sensitive to depths greater than those of our lower limit predictions.

  18. Broad-band monitoring tracing the evolution of the jet and disc in the black hole candidate X-ray binary MAXI J1659-152

    NASA Astrophysics Data System (ADS)

    van der Horst, A. J.; Curran, P. A.; Miller-Jones, J. C. A.; Linford, J. D.; Gorosabel, J.; Russell, D. M.; de Ugarte Postigo, A.; Lundgren, A. A.; Taylor, G. B.; Maitra, D.; Guziy, S.; Belloni, T. M.; Kouveliotou, C.; Jonker, P. G.; Kamble, A.; Paragi, Z.; Homan, J.; Kuulkers, E.; Granot, J.; Altamirano, D.; Buxton, M. M.; Castro-Tirado, A.; Fender, R. P.; Garrett, M. A.; Gehrels, N.; Hartmann, D. H.; Kennea, J. A.; Krimm, H. A.; Mangano, V.; Ramirez-Ruiz, E.; Romano, P.; Wijers, R. A. M. J.; Wijnands, R.; Yang, Y. J.

    2013-12-01

    MAXI J1659-152 was discovered on 2010 September 25 as a new X-ray transient, initially identified as a gamma-ray burst, but was later shown to be a new X-ray binary with a black hole as the most likely compact object. Dips in the X-ray light curves have revealed that MAXI J1659-152 is the shortest period black hole candidate identified to date. Here we present the results of a large observing campaign at radio, submillimetre, near-infrared (nIR), optical and ultraviolet (UV) wavelengths. We have combined this very rich data set with the available X-ray observations to compile a broad-band picture of the evolution of this outburst. We have performed broad-band spectral modelling, demonstrating the presence of a spectral break at radio frequencies and a relationship between the radio spectrum and X-ray states. Also, we have determined physical parameters of the accretion disc and put them into context with respect to the other parameters of the binary system. Finally, we have investigated the radio-X-ray and nIR/optical/UV-X-ray correlations up to ˜3 yr after the outburst onset to examine the link between the jet and the accretion disc, and found that there is no significant jet contribution to the nIR emission when the source is in the soft or intermediate X-ray spectral state, consistent with our detection of the jet break at radio frequencies during these states.

  19. Simultaneous microwave photonic and phononic band gaps in piezoelectric-piezomagnetic superlattices with three types of domains in a unit cell

    NASA Astrophysics Data System (ADS)

    Tang, Zheng-hua; Jiang, Zheng-Sheng; Chen, Tao; Lei, Da-Jun; Yan, Wen-Yan; Qiu, Feng; Huang, Jian-Quan; Deng, Hai-Ming; Yao, Min

    2016-04-01

    A novel phoxonic crystal using the piezoelectric (PMN-PT) and piezomagnetic (CoFe2O4) superlattices with three types of domains in a unit cell (PPSUC) is present, in which dual microwave photonic and phononic band gaps can be obtained simultaneously. Two categories of phononic band gaps, originating from both the Bragg scattering of acoustic waves in periodic structures at the Brillouin zone boundary and the electromagnetic wave-lattice vibration couplings near the Brillouin zone center, can be observed in the phononic band structures. The general characteristics of the microwave photonic band structures are similar to those of pure piezoelectric or piezomagnetic superlattices, with the major discrepancy being the appearance of nearly dispersionless branches within the microwave photonic band gaps, which show an extremely large group velocity delay. Thus, the properties may also be applied to compact acoustic-microwave devices.

  20. Experimental evidence of the photonic band gap in hybrid one-dimensional photonic crystal based on a mixture of (HMDSO, O2)

    NASA Astrophysics Data System (ADS)

    Amri, R.; Sahel, S.; Manaa, C.; Bouaziz, L.; Gamra, D.; Lejeune, M.; Clin, M.; Zellama, K.; Bouchriha, H.

    2016-08-01

    Hybrid One-dimensional photonic crystal coated from a mixture of an organic compound (HMDSO) and oxygen (O2) is elaborated by PECVD technique. The originality of the method consists in obtaining layers of different permittivity with the same gas mixture, but with different flow. The change in flow is optimized to obtain organic/inorganic layers of good quality with high and low refractive index of 2.1 and 1.4 corresponding respectively to HMDSO and SiO2 materials as assigned by IR measurement. Evidence of the photonic band gap is obtained by measuring the transmissions and reflections spectra which show that it appears only after 13 periods with a width of 325 nm corresponding to energy 3.8 eV. We have also introduced a defect in this photonic structure by changing the thickness of central layer, and observed the presence of a frequency mode corresponding to this defect. Our results are interpreted by using a theoretical model based on transfer matrix wich well reproduced the experimental data.

  1. Femtosecond Pulse Characterization as Applied to One-Dimensional Photonic Band Edge Structures

    NASA Technical Reports Server (NTRS)

    Fork, Richard L.; Gamble, Lisa J.; Diffey, William M.

    1999-01-01

    The ability to control the group velocity and phase of an optical pulse is important to many current active areas of research. Electronically addressable one-dimensional photonic crystals are an attractive candidate to achieve this control. This report details work done toward the characterization of photonic crystals and improvement of the characterization technique. As part of the work, the spectral dependence of the group delay imparted by a GaAs/AlAs photonic crystal was characterized. Also, a first generation an electrically addressable photonic crystal was tested for the ability to electronically control the group delay. The measurement technique, using 100 femtosecond continuum pulses was improved to yield high spectral resolution (1.7 nanometers) and concurrently with high temporal resolution (tens of femtoseconds). Conclusions and recommendations based upon the work done are also presented.

  2. The Voigt effects in the anisotropic photonic band gaps of three-dimensional magnetized plasma photonic crystals doped by the uniaxial material

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Li, Bing-Xiang

    2013-10-01

    In this paper, the properties of photonic band gaps (PBGs) for three-dimensional magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with simple-cubic lattices are theoretically investigated by the plane wave expansion (PWE) method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic PBGs in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatband regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency and plasma cyclotron frequency on the characteristics of anisotropic PBGs for the three-dimensional MPPCs are studied in detail and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in simple-cubic lattices and the complete PBGs can be found compared to the conventional three-dimensional MPPCs doped by the isotropic material. The bandwidths of PBGs can be enlarged by introducing the magnetized plasma into three-dimensional PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency and plasma cyclotron frequency. The locations of flatband regions cannot be tuned by any parameters except for the plasma frequency and plasma cyclotron frequency. Introducing the uniaxial material in three-dimensional magnetized plasma-dielectric photonic crystals can enlarge the PBGs and also provide a way to obtain the complete PBGs as the three-dimensional MPPCs with high symmetry.

  3. Characterization of toxins from the broad-banded water snake Helicops angulatus (Linnaeus, 1758): isolation of a cysteine-rich secretory protein, Helicopsin.

    PubMed

    Estrella, Amalid; Sánchez, Elda E; Galán, Jacob A; Tao, W Andy; Guerrero, Belsy; Navarrete, Luis F; Rodríguez-Acosta, Alexis

    2011-04-01

    Helicops angulatus (broad-banded water snake) according to recent proposals is presently cited in the family Dipsadidae, subfamily Xenodontinae, forming the tribe Hydropsini along with the genera Hydrops and Pseudoeryx. The current work characterizes the proteolytic and neurotoxic activities of H. angulatus crude toxins from salivary excretion (SE) and describes the isolation and identification of a cysteine-rich secretory protein (CRISP) called helicopsin. The SE lethal dose (LD₅₀) was 5.3 mg/kg; however, the SE did not contain hemorrhagic activity. Helicopsin was purified using activity-guided, Superose 12 10/300 GL molecular exclusion, Mono Q10 ion exchange, and Protein Pak 60 molecular exclusion. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a highly purified band of approximately 20 kDa. The minimal lethal dose for helicopsin was 0.4 mg/kg. Liquid chromatography mass spectrometry (LC-MS/MS) analysis identified 2 unique peptides MEWYPEAAANAER and YTQIVWYK, representing a protein sequence (deleted homology) belonging to cysteine-rich secretory proteins, which are conserved in snake venoms (CRISPs). CRISPs are a large family of cysteine-rich secretory proteins found in various organisms and participate in diverse biological processes. Helicopsin exhibited robust neurotoxic activity as evidenced by immediate death (~8 min) due to respiratory paralysis in NIH mice. These observations for helicopsin purified from H. angulatus provide further evidence of the extensive distribution of highly potent neurotoxins in the Colubroidea superfamily of snakes than previously described. PMID:20931174

  4. High Internal Gain Axial SiOx-In2-xO3-y/Au Heterostructure Nanocolumnar Array Based Schottky Detector for Broad Band Recognition.

    PubMed

    Singh, Naorem Khelchand; Mondal, Aniruddha

    2015-08-01

    Glancing angle deposition (GLAD) was employed to fabricate the SiOx-In2-xO3-y axial heterostructure nanocolumn. The fabricated heterostructure nanocolumn was annealed at 550 °C for 1 hour at open air condition. The XRD analysis revealed the polycrystalline nature of the annealed SiOx-In2-xO3-y nanocolumn. The emission at 378 nm (~3.3 eV, FWHM 39.101 nm) from Photoluminescence (PL), corresponds to main band gap of In2O3. The In2-xO3-y-SiOx nanocolumn based Schottky detector processed maximum photoresponsivity of 199 A/W at 375 nm, as well as UV-Vis broad band detection. The high internal gain of ~659 at UV region (375 nm) was calculated for the device. The detector exhibited increase in photoresponsivity with decrease in room temperature upto 160 K, which further reduced at low temperature. A very sharp rise time (~1.82 s) and decay time (~1.78 s) was recorded at the applied potential of -2 V and -3 V. PMID:26369205

  5. Constraints on cosmic ray production from broad-band observations and modeling of the supernova remnant G347.3-0.5

    NASA Astrophysics Data System (ADS)

    Ellison, D.; Slane, P.; Gaensler, M. B.

    2001-08-01

    The supernova remnant G347.3 0.5 emits a featureless power-law in X-rays, thought to indicate shock-acceleration of electrons to high energies. We here produce a broad-band spectrum of the bright NW limb of this source by combin-ing radio observations from the Australia Telescope Compact Array (ATCA), X-ray observations from the Advanced Satellite for Cosmology and Astro-physics (ASCA), and TeV γ-ray observations from the CANGAROO imaging Cerenkov telescope. We assume this emission is produced by an electron popu-lation generated by diffusive shock acceleration at the remnant forward shock. The nonlinear aspects of the particle acceleration force a connection between the widely different wavelength bands and between the electrons and the unseen ions, presumably accelerated simultaneously with the electrons. This allows us to infer the relativistic proton spectrum and estimate ambient parameters such as the supernova explosion energy, magnetic field, matter density, and efficiency of the shock acceleration process. We find convincing evidence that the shock acceleration is efficient, placing > 20% of the shock kinetic energy ux into rel-ativistic ions. However, we find that the maximum electron and proton energies depend somewhat on assumptions for the compression of the magnetic field in the shock, but are generally well below the observed knee at ˜ 1015 eV in the galactic cosmic-ray spectrum. We discuss implications of this for theories of cosmic-ray origin.

  6. Detailed optical and near-infrared polarimetry, spectroscopy and broad-band photometry of the afterglow of GRB 091018: polarization evolution

    NASA Astrophysics Data System (ADS)

    Wiersema, K.; Curran, P. A.; Krühler, T.; Melandri, A.; Rol, E.; Starling, R. L. C.; Tanvir, N. R.; van der Horst, A. J.; Covino, S.; Fynbo, J. P. U.; Goldoni, P.; Gorosabel, J.; Hjorth, J.; Klose, S.; Mundell, C. G.; O'Brien, P. T.; Palazzi, E.; Wijers, R. A. M. J.; D'Elia, V.; Evans, P. A.; Filgas, R.; Gomboc, A.; Greiner, J.; Guidorzi, C.; Kaper, L.; Kobayashi, S.; Kouveliotou, C.; Levan, A. J.; Rossi, A.; Rowlinson, A.; Steele, I. A.; de Ugarte Postigo, A.; Vergani, S. D.

    2012-10-01

    Follow-up observations of large numbers of gamma-ray burst (GRB) afterglows, facilitated by the Swift satellite, have produced a large sample of spectral energy distributions and light curves, from which their basic micro- and macro-physical parameters can in principle be derived. However, a number of phenomena have been observed that defy explanation by simple versions of the standard fireball model, leading to a variety of new models. Polarimetry can be a major independent diagnostic of afterglow physics, probing the magnetic field properties and internal structure of the GRB jets. In this paper we present the first high-quality multi-night polarimetric light curve of a Swift GRB afterglow, aimed at providing a well-calibrated data set of a typical afterglow to serve as a benchmark system for modelling afterglow polarization behaviour. In particular, our data set of the afterglow of GRB 091018 (at redshift z = 0.971) comprises optical linear polarimetry (R band, 0.13-2.3 d after burst); circular polarimetry (R band) and near-infrared linear polarimetry (Ks band). We add to that high-quality optical and near-infrared broad-band light curves and spectral energy distributions as well as afterglow spectroscopy. The linear polarization varies between 0 and 3 per cent, with both long and short time-scale variability visible. We find an achromatic break in the afterglow light curve, which corresponds to features in the polarimetric curve. We find that the data can be reproduced by jet break models only if an additional polarized component of unknown nature is present in the polarimetric curve. We probe the ordered magnetic field component in the afterglow through our deep circular polarimetry, finding Pcirc < 0.15 per cent (2σ), the deepest limit yet for a GRB afterglow, suggesting ordered fields are weak, if at all present. Our simultaneous R- and Ks-band polarimetry shows that dust-induced polarization in the host galaxy is likely negligible.

  7. A semi-analytical model for the approximation of plasmonic bands in arrays of metal wires in photonic crystal fibers.

    PubMed

    Spittel, Ron; Bartelt, Harmut; Schmidt, Markus A

    2014-05-19

    We present a highly efficient semi-analytical and straightforward-to-implement model for the determination of plasmonic band edges of metallic nanowire arrays inside photonic crystal fibers. The model relies on the approximation of the hexagonal unit cell by a circle and using particular boundary conditions, showing an accurate agreement with finite element simulations. The model reduces simulation time by a factor of 100, thus representing an efficient tool for structure design. It further allows the calculation of all relevant modes in the system by slight changes of the entries in a 4 × 4 matrix. PMID:24921296

  8. Band gap control using electric field of photonic gel cells fabricated with block copolymer and hydrogel.

    PubMed

    Lee, Sung Nam; Baek, Young Bin; Shin, Dong Myung

    2014-08-01

    Optical and electrical characteristics of the devices using photonic gel film and hydrogel electrolyte were studied. Poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) lamellar film with alternating hydrophobic block and hydrophilic polyelectrolyte block polymers (52 kg/mol-b-57 kg/mol) were prepared for the photonic gel. Poly(isobutylene-co-maleic acid) sodium salts were prepared for the hydrogel. This hydrogel fiber is common water swelling material and it owned ions for a device has conductivity. Photonic gel and hydrogel was spin coating onto Indium-tin-oxide (ITO) glass for make electric fields. The reflectance maximum wavelength of photonic crystal device shifted from 538 nm and reached to 557 nm, 585 nm and 604 nm during 30 min voltage applying time. The bandwidth variation was very limited. Loss of electrolyte was much less with hydrogel compared to the pure water. We can control color of hydrogel used photonic device by electric field with reasonable time range under moderate electric field by applying 2 V between two facing electrodes. PMID:25936055

  9. A high peak power S-band switching system for the Advanced Photon Source (APS) Linear Accelerator (Linac).

    SciTech Connect

    Grelick, A. E.

    1998-09-11

    An S-band linear accelerator is the source of particles and front end of the Advanced Photon Source [1] injector. Additionally, it will be used to support a low-energy undulator test line (LEUTL) and to drive a free-electron laser (FEL). To provide maximum linac availability for all uses, an additional modulator-klystron subsystem has been built,and a waveguide-switching and distribution subsystem is now under construction. The combined subsystems provide a hot spare for any of the five S-band transmitters that power the lina cand have been given the additional function of powering an rf gun test stand whenever they are not otherwise needed. Design considerations for the waveguide-switching subsystem, topology selection, timing, control, and system protection provisions are described.

  10. Low-light-level nonlinear optics with rubidium atoms in hollow-core photonic band-gap fibers

    NASA Astrophysics Data System (ADS)

    Bhagwat, Amar Ramdas

    Low-light-level optical nonlinearities are of significant interest for performing operations such as single-photon switching and quantum non-demolition measurements on single-photons. To evoke strong nonlinearities from single-photons, one can enhance the matter-photon interaction using strongly nonlinear materials such as alkali vapors in combination with an appropriate geometry such as a waveguide, which provides a long interaction length while maintaining a small light mode area. We demonstrate for the first time that such a system can be experimentally realized by loading rubidium vapor inside a hollow-core photonic band-gap fiber. Using the technique of light-induced atomic desorption in this geometry, we have generated optical depths greater than 1000. As a proof of principle, we demonstrate electromagnetically induced transparency (EIT) with control powers 1000 times lower than those used for hot vapor cells in a focused beam geometry. Working with such a high aspect ratio geometry requires us to identify and measure the various sources of decoherence via spectroscopy of desorbed atoms in the fiber. Using such techniques, we also estimate the temperature of the desorbing atoms inside the fiber. The desorption mechanism is studied, and we show that pulsed desorption beams of the right amplitude and duration can be used for generating precisely controlled optical depths. Finally, we investigate the use of various buffer gas techniques for increasing the effective transverse path of the atoms as they move across the fiber in order to reduce their ground state decoherence and map this effect as a function of buffer gas pressure.

  11. Complete photonic band gaps and tunable self-collimation in the two-dimensional plasma photonic crystals with a new structure

    SciTech Connect

    Zhang, Hai-Feng; Ding, Guo-Wen; Li, Hai-Ming; Liu, Shao-Bin

    2015-02-15

    In this paper, the properties of complete photonic band gaps (CPBGs) and tunable self-collimation in two-dimensional plasma photonic crystals (2D PPCs) with a new structure in square lattices, whose dielectric fillers (GaAs) are inserted into homogeneous and nomagnetized plasma background are theoretically investigated by a modified plane wave expansion (PWE) method with a novel technique. The novel PWE method can be utilized to compute the dispersion curves of 2D PPCs with arbitrary-shaped cross section in any lattices. As a comparison, CPBGs of PPCs for four different configurations are numerically calculated. The computed results show that the proposed design has the advantages of achieving the larger CPBGs compared to the other three configurations. The influences of geometric parameters of filled unit cell and plasma frequency on the properties of CPBGs are studied in detail. The calculated results demonstrate that CPBGs of the proposed 2D PPCs can be easily engineered by changing those parameters, and the larger CPBGs also can be obtained by optimization. The self-collimation in such 2D PPCs also is discussed in theory under TM wave. The theoretical simulations reveal that the self-collimation phenomena can be found in the TM bands, and both the frequency range of self-collimation and the equifrequency surface contours can be tuned by the parameters as mentioned above. It means that the frequency range and direction of electromagnetic wave can be manipulated by designing, as it propagates in the proposed PPCs without diffraction. Those results can hold promise for designing the tunable applications based on the proposed PPCs.

  12. Surface wave tomography of North America and the Caribbean using global and regional broad-band networks: Phase velocity maps and limitations of ray theory

    USGS Publications Warehouse

    Godey, S.; Snieder, R.; Villasenor, A.; Benz, H.M.

    2003-01-01

    We present phase velocity maps of fundamental mode Rayleigh waves across the North American and Caribbean plates. Our data set consists of 1846 waveforms from 172 events recorded at 91 broad-band stations operating in North America. We compute phase velocity maps in four narrow period bands between 50 and 150 s using a non-linear waveform inversion method that solves for phase velocity perturbations relative to a reference Earth model (PREM). Our results show a strong velocity contrast between high velocities beneath the stable North American craton, and lower velocities in the tectonically active western margin, in agreement with other regional and global surface wave tomography studies. We perform detailed comparisons with global model results, which display good agreement between phase velocity maps in the location and amplitude of the anomalies. However, forward modelling shows that regional maps are more accurate for predicting waveforms. In addition, at long periods, the amplitude of the velocity anomalies imaged in our regional phase velocity maps is three time larger than in global phase velocity models. This amplitude factor is necessary to explain the data accurately, showing that regional models provide a better image of velocity structures. Synthetic tests show that the raypath coverage used in this study enables one to resolve velocity features of the order of 800-1000 km. However, only larger length-scale features are observed in the phase velocity maps. The limitation in resolution of our maps can be attributed to the wave propagation theory used in the inversion. Ray theory does not account for off-great-circle ray propagation effects, such as ray bending or scattering. For wavelengths less than 1000 km, scattering effects are significant and may need to be considered.

  13. Electro-tuning of the photonic band gap in SOI-based structures infiltrated with liquid crystal

    NASA Astrophysics Data System (ADS)

    Tolmachev, V. A.; Grudinkin, S. A.; Zharova, J. A.; Melnikov, V. A.; Astrova, E. V.; Perova, T. S.

    2008-04-01

    One dimensional periodic and non-periodic silicon photonic structures have been designed and fabricated on silicon-on-insulator substrate for the investigation of the electro-tuning effect in composite system Photonic Crystal - Liquid Crystal. The reflection spectra registered for non-periodic structures demonstrate the phase polarisation shift for bands of high reflection, while for the periodic structure the shift of the photonic band gap edge was observed. Under an applied electric field in the range from 2V to 10V, the shift of the polarised reflection spectra, caused by reorientation of the LC director from planar to homeotropic alignment, has been obtained. A significant change in the refractive index close to Δn=0.2, which is a characteristic feature for LC E7, has been achieved due to LC reorientation in all structures just after LC infiltration. It was found that after switching-off the applied electric field the initial planar orientation of LC molecules is not restored. This effect is related to weak anchoring of LC molecules to the silicon side-walls which results in the transition of LC to the pseudo-isotropic alignment after the applied voltage is off. A relatively smaller (with Δn=0.07), but highly reproducible electro-tuning effect was revealed during the LC reorientation from pseudo-isotropic to homeotropic alignment. The shift of the edge of PBG by Δλ=0.16 or by Δλ/λ=1.6% in relative shift units was observed in this case. The response time estimated under applied square shaped ac pulses of various frequencies was found to be around 30 ms.

  14. Comparison of broad band time series recorded parallel by FGI type interferometric water level and Lippmann type pendulum tilt meters at Conrad observatory, Austria

    NASA Astrophysics Data System (ADS)

    Ruotsalainen, Hannu; Papp, Gabor; Leonhardt, Roman; Ban, Dora; Szücs, Eszter; Benedek, Judith

    2016-04-01

    The Finnish Geodetic Institute (FGI) the progenitor of Finnish Geospatial Research Institute of NLS designed and built a 5.5m long prototype of interferometric water level tiltmeter (iWT) in early 2014. Geodetic and Geophysical Institute (GGI), Sopron, Hungary bought the instrument and started tilt measurement in August 2014 at the Conrad observatory (COBS), Austria to monitor geodynamical phenomena like microseisms, free oscillations of the Earth, earth tides, mass loading effects and crustal deformations in cooperation with Austrian Central Institute for Meteorology and Geodynamics (ZAMG) and the FGI. On the July 16 2015 a Lippmann-type 2D tilt sensor (LTS) was also installed by GGI on the 6 m long pier where iWT was set up previously. This situation opens a possibility to do broad band (from secular to seismic variations up to 15 Hz) geophysical signal analysis comparing the responses of long (several meters) and short (a few decimeters) base instruments implementing different physical principles (relative height change of a level surface and inclination change of the plumb line). The characteristics of the sensors are studied by the evaluation of the spectra of recorded signals dominated by microseisms. The iWT has internal interferometric calibration and it can be compared to Lippmanns tilt meter one. Both instruments show good long term ( > 1 day) stability when earth tides and ocean and air mass loading tilts are modelled.

  15. Modelling the variable broad-band optical/UV/X-ray spectrum of PG1211+143: implications for the ionized outflow

    NASA Astrophysics Data System (ADS)

    Papadakis, I. E.; Nicastro, F.; Panagiotou, C.

    2016-06-01

    Context. We present the results from a detailed analysis of the 2007 Swift monitoring campaign of the quasar PG1211+143. Aims: We study its broad-band optical/UV-X-ray spectral energy distribution and its variations, with the use of physically motivated models. Methods: We constructed broad-band, optical/UV-X-ray spectral energy distributions over three X-ray flux intervals, and we fitted them with a model which accounts for the disc and the X-ray coronal emission. We also added a spectral model component to account for the presence of the warm absorber which has been well established from past observations of the source. Results: We detected no optical/UV variations over the two-month period of the monitoring campaign. On the other hand, the X-rays are highly variable in a correlated way in the soft and hard X-ray bands with an amplitude larger than has been commonly observed in nearby Seyferts, even on longer time scales. The three flux spectra are well fitted by the model we considered. The disc inner temperature remains constant at ~2 eV, while X-rays are variable in slope and normalization. The absorber covers almost 90% of the central source. It is outflowing with a velocity less than 2.3 × 104 km s-1 (3σ upper limit), and has a column density of log NH ~ 23.2. Its ionization parameter varies by a factor of 1.6, and it is in photo-ionizing equilibrium with the ionizing flux. It is located at a distance of less than 0.35 pc from the central source, and its relative thickness, ΔR/R, is less than 0.1. The absorber's ionization parameter variations can explain the larger than average amplitude of the X-ray variations. Conclusions: The absence of optical/UV variations are consistent with the high black hole mass estimate of ~108M⊙ for this object, which implies variability time scales longer than the period of the Swift observations. It argues against the presence of inward propagating fluctuations in the disc as the reason for the flux variability in this

  16. Photonic band gap response of structurally modified non-close-packed inverse opals by template directed multilayer atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Graugnard, Elton; Gaillot, Davy P.; King, Jeffrey S.; Summers, Christopher J.

    2006-04-01

    We report the controllable and tunable fabrication of structurally modified non-close-packed inverse shell opals using multi-layer atomic layer deposition and present a model and simulation algorithm to calculate the structural parameters critical to fabrication. This powerful, flexible and unique technique enables opal inversion, structural modification and backfilling and was applied to the fabrication of TiO II non-close-packed inverse opals. Using successive conformal backfilling it was possible to tune the Bragg peak over 600 nm and enhance the Bragg peak width by >50%. Additionally, band structure calculations, using dielectric functions approximating the true network topology, were used to predict the optical properties during the fabrication process. 3D finite-difference-time-domain results predict experimentally achievable structures with a complete band gap as large as 7.2%. Additionally, the refractive index requirement was predicted to decrease from 3.3 in an 86% infiltrated inverse shell opal to 3.0 in an optimized non-close-packed inverse shell opal. It was also shown for these structures that the complete photonic band gap peak can be statically tuned by over 70% by increasing the backfilled thickness.

  17. Surface passivation of a photonic crystal band-edge laser by atomic layer deposition of SiO2 and its application for biosensing.

    PubMed

    Cha, Hyungrae; Lee, Jeongkug; Jordan, Luke R; Lee, Si Hoon; Oh, Sang-Hyun; Kim, Hyo Jin; Park, Juhun; Hong, Seunghun; Jeon, Heonsu

    2015-02-28

    We report on the conformal surface passivation of photonic crystal (PC) laser devices with an ultrathin dielectric layer. Air-bridge-type Γ-point band-edge lasers (BELs) are fabricated by forming a honeycomb lattice two-dimensional PC structure into an InGaAsP multiple-quantum-well epilayer. Atomic layer deposition (ALD) is employed for conformal deposition of a few-nanometer-thick SiO2 layer over the entire device surface, not only on the top and bottom surfaces of the air-bridge membrane but also on the air-hole sidewalls. Despite its extreme thinness, the ALD passivation layer is found to protect the InGaAsP BEL devices from harsh chemicals. In addition, the ALD-SiO2 is compatible with the silane-based surface chemistry, which allows us to use ALD-passivated BEL devices as label-free biosensors. The standard streptavidin-biotin interaction shifts the BEL lasing wavelength by ∼1 nm for the dipole-like Γ-point band-edge mode. A sharp lasing line (<0.2 nm, full width at half-maximum) and a large refractive index sensitivity (∼163 nm per RIU) produce a figure of merit as high as ∼800 for our BEL biosensor, which is at least an order of magnitude higher than those of more common biosensors that rely on a broad resonance peak, showing that our nanolaser structures are suitable for highly sensitive biosensor applications. PMID:25631610

  18. Fast Purcell-enhanced single photon source in 1,550-nm telecom band from a resonant quantum dot-cavity coupling

    NASA Astrophysics Data System (ADS)

    Birowosuto, Muhammad Danang; Sumikura, Hisashi; Matsuo, Shinji; Taniyama, Hideaki; van Veldhoven, Peter J.; Nötzel, Richard; Notomi, Masaya

    2012-03-01

    High-bit-rate nanocavity-based single photon sources in the 1,550-nm telecom band are challenges facing the development of fibre-based long-haul quantum communication networks. Here we report a very fast single photon source in the 1,550-nm telecom band, which is achieved by a large Purcell enhancement that results from the coupling of a single InAs quantum dot and an InP photonic crystal nanocavity. At a resonance, the spontaneous emission rate was enhanced by a factor of 5 resulting a record fast emission lifetime of 0.2 ns at 1,550 nm. We also demonstrate that this emission exhibits an enhanced anti-bunching dip. This is the first realization of nanocavity-enhanced single photon emitters in the 1,550-nm telecom band. This coupled quantum dot cavity system in the telecom band thus provides a bright high-bit-rate non-classical single photon source that offers appealing novel opportunities for the development of a long-haul quantum telecommunication system via optical fibres.

  19. Higher order mode damping in a five-cell superconducting rf cavity with a photonic band gap coupler cell

    NASA Astrophysics Data System (ADS)

    Arsenyev, Sergey A.; Temkin, Richard J.; Shchegolkov, Dmitry Yu.; Simakov, Evgenya I.; Boulware, Chase H.; Grimm, Terry L.; Rogacki, Adam R.

    2016-08-01

    We present a study of higher order mode (HOM) damping in the first multicell superconducting radio-frequency (SRF) cavity with a photonic band gap (PBG) coupler cell. Achieving higher average beam currents is particularly desirable for future light sources and particle colliders based on SRF energy-recovery linacs (ERLs). Beam current in ERLs is limited by the beam breakup instability, caused by parasitic HOMs interacting with the beam in accelerating cavities. A PBG cell incorporated in an accelerating cavity can reduce the negative effect of HOMs by providing a frequency selective damping mechanism, thus allowing significantly higher beam currents. The five-cell cavity with a PBG cell was designed and optimized for HOM damping. Monopole and dipole HOMs were simulated. The SRF cavity was fabricated and tuned. External quality factors for some HOMs were measured in a cold test. The measurements agreed well with the simulations.

  20. Suzaku broad-band spectroscopy of RX J1347.5-1145: constraints on the extremely hot gas and non-thermal emission

    NASA Astrophysics Data System (ADS)

    Ota, N.; Murase, K.; Kitayama, T.; Komatsu, E.; Hattori, M.; Matsuo, H.; Oshima, T.; Suto, Y.; Yoshikawa, K.

    2008-11-01

    shows that the SE component is consistent with being thermal. We measure the 3σ upper limit to the non-thermal flux, F<8×10-12 erg s-1 cm^{-2} in the 12-60 keV band, which provides a limit on the inverse Compton scattering of relativistic electrons off the CMB photons. Combining this limit with the discovery of a radio mini halo in this cluster at 1.4 GHz, which measures the synchrotron radiation, we find a lower limit to the strength of the intracluster magnetic field, such that B>0.007 {μ G}.

  1. Optical broad-band photometry and reference image for APMUKS(BJ) B215839.70-615403.9 / ASASSN-15lh from the Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Melchior, Peter; Drlica-Wagner, Alexander; Bechtol, Keith; Rykoff, Eli; Hartley, William; Dark Energy Survey Collaboration

    2015-07-01

    We report optical broad-band photometry of the host galaxy APMUKS(BJ) B215839.70-615403.9 of SLSN ASASSN-15lh (ATel #7642; Dong et al., arXiv:1507.03010). The images were obtained using the DECam imager on the Blanco 4-m telescope at NOAO's Cerro Tololo Inter-American Observatory during Year-2 observations of the Dark Energy Survey (DES). A preliminary reduction of the images was performed by the DES Data Management pipeline (Mohr et al. 2012, SPIE Conference Series, 84510D; Desai et al. 2012, ApJ, 757, 83). The photometry was measured using SExtractor with additional calibration via stellar locus regression to provide magnitude zero points with 2-3% calibration uncertainty for point sources (relative to 2MASS) and mildly increased uncertainties for extended sources. We fit the DES g-r, r-i, and i-z colors to a red-sequence model from redMaPPer (Rykoff et al. 2014, ApJ, 785, 104) and obtain a redshift 0.25±0.02, consistent with the spectroscopic redshift of z = 0.2326 (ATel #7774). Fixed to that redshift, the host photometry is fully consistent with a red-sequence galaxy. We combine photometry from DES grizY with VHS NIR (ATel #7776) and WISE IR and fit a linear combination of single stellar populations with a variety of ages. We find that the fit is dominated by an old (5 Gyr) component, consistent with those of elliptical galaxies. We further compare with dusty SEDs taken from the latest set of templates in EAZY (Brammer, van Dokkum & Coppi, 2008, ApJ, 686, 1503). The combined host photometry is not well described by any of the dusty templates.

  2. Broad-band strong motion simulations coupling k-square kinematic source models with empirical Green's functions: the 2009 L'Aquila earthquake

    NASA Astrophysics Data System (ADS)

    Del Gaudio, Sergio; Causse, Mathieu; Festa, Gaetano

    2015-10-01

    The use of simulated accelerograms may improve the evaluation of the seismic hazard when an accurate modelling of both source and propagation is performed. In this paper, we performed broad-band simulations of the 2009, M 6.3 L'Aquila earthquake, coupling a k-2 kinematic model for the seismic source with empirical Green's functions (EGFs) as propagators. We extracted 10 EGFs candidates from a database of aftershocks satisfying quality criteria based on signal-to-noise ratio, fault proximity, small magnitude, similar focal mechanism and stress drop. For comparison with real observations, we also derived a low-frequency kinematic model, based on inversion of ground displacement as integrated from strong motion data. Kinematic properties of the inverted model (rupture velocity, position of the rupture nucleation, low-frequency slip and roughness degree of slip heterogeneity) were used as constraints in the k-2 model, to test the use of a single specific EGF against the use of the whole set of EGFs. Comparison to real observations based on spectral and peak ground acceleration shows that the use of all available EGFs improves the fit of simulations to real data. Moreover the epistemic variability related to the selection of a specific EGF is significantly larger (two to three times) than recent observations of between event variability, that is the variability associated with the randomness of the rupture process. We finally performed `blind' simulations releasing all the information on source kinematics and only considering the fault geometry and the magnitude of the target event as known features. We computed peak ground acceleration, acceleration Fourier and response spectra. Simulations follow the same trend with distance as real observations. In most cases these latter fall within one sigma from predictions. Predictions with source parameters constrained at low frequency do not perform better than `blind' simulations, showing that extrapolation of the low

  3. Spectral and Temporal Behavior of Low Mass X-ray Binaries Observed by the Einstein SSS and MPC, and the Broad Band X-ray Telescope

    NASA Astrophysics Data System (ADS)

    Christian, D. J.; Swank, J. H.

    1992-12-01

    An extensive survey of 50 low mass X-ray binaries was carried out using the HEAO-2 Einstein Solid State Spectrometer data (0.5-4.5 keV) with the Monitor Proportional Counter data (1.2-20.0 keV) and the Broad Band X-Ray Telescope (BBXRT) (0.5-12 keV). Spectra were selected on the basis of intensity and fit with a set of simple and complex spectral models. For all the subclasses, including Eddington-limited bulge sources, bursters, dippers, the soft spectrum black hole candidates, and a few transients in decline, the spectra could be fit acceptably with combinations of thermal bremsstrahlung and blackbody spectra or a Comptonized spectrum and a blackbody. The results rule out optically thick disk models for the bright Z sources and power law models for bursters. There is a progression of spectra as a function of X-ray luminosity for the bursters, Atoll and Z sources. Interpretation is discussed in terms of separate emission regions, one due to radial accretion onto a neutron star and the optically thick component that appears for higher luminosity due to a boundary layer or to high optical depth to scattering in the flow. A lower temperature blackbody required in some cases could be an expected contribution from the accretion disk. The soft spectrum sources are dominated by blackbody spectra, but for two, low effective area is a problem for the black hole interpretation. The strongest of previously reported low energy X-ray lines due to OVIII or Fe L transitions are confirmed. Similar line emission is seen for several other sources, in particular X0614+091. The photoionized gas in the inner part of an accretion disk corona can give Fe K lines from Fe XXV. BBXRT obtained upper limits for X0614+091 and M15 which are consistent with the coronal model.

  4. Broad-band spectrophotometry of the hot Jupiter HAT-P-12b from the near-UV to the near-IR

    NASA Astrophysics Data System (ADS)

    Mallonn, M.; Nascimbeni, V.; Weingrill, J.; von Essen, C.; Strassmeier, K. G.; Piotto, G.; Pagano, I.; Scandariato, G.; Csizmadia, Sz.; Herrero, E.; Sada, P. V.; Dhillon, V. S.; Marsh, T. R.; Künstler, A.; Bernt, I.; Granzer, T.

    2015-11-01

    Context. The detection of trends or gradients in the transmission spectrum of extrasolar planets is possible with observations at very low spectral resolution. Transit measurements of sufficient accuracy using selected broad-band filters allow for an initial characterization of the atmosphere of the planet. Aims: We want to investigate the atmosphere of the hot Jupiter HAT-P-12b for an increased absorption at the very blue wavelength regions caused by scattering. Furthermore, we aim for a refinement of the transit parameters and the orbital ephemeris. Methods: We obtained time series photometry of 20 transit events and analyzed them homogeneously, along with eight light curves obtained from the literature. In total, the light curves span a range from 0.35 to 1.25 microns. During two observing seasons over four months each, we monitored the host star to constrain the potential influence of starspots on the derived transit parameters. Results: We rule out the presence of a Rayleigh slope extending over the entire optical wavelength range, a flat spectrum is favored for HAT-P-12b with respect to a cloud-free atmosphere model spectrum. A potential cause of such gray absorption is the presence of a cloud layer at the probed latitudes. Furthermore, in this work we refine the transit parameters, the ephemeris and perform a TTV analysis in which we found no indication for an unseen companion. The host star showed a mild non-periodic variability of up to 1%. However, no stellar rotation period could be detected to high confidence.

  5. Density of resonant states and a manifestation of photonic band structure in small clusters of spherical particles

    NASA Astrophysics Data System (ADS)

    Yamilov, Alexey; Cao, Hui

    2003-08-01

    We introduce a numerical recipe for calculating the density of the resonant states of the clusters of dielectric spheres. Using truncated multipole expansions (generalized multisphere Mie solution) we obtain the scattering matrix of the problem. By introducing an infinitesimal absorption in the spheres we express the dwell time of the electromagnetic wave in terms of the elements of the scattering matrix. Using the parameters in recent light localization experiments [Phys. Rev. Lett. 87, 153901 (2001)], we demonstrate that the density of the resonant states, related to the dwell time, shows the formation of the photonic band structure in small clusters of dielectric spheres as the small as five particles. Density of resonant states of a cluster of 32 spheres exhibits a well defined structure similar to the density of electromagnetic states of the infinite photonic crystal. Our results suggest that, due to the formation of small ordered clusters, a significant modification of the density of electromagnetic states can occur in a random collection of monodisperse spheres.

  6. Micro-metric electronic patterning of a topological band structure using a photon beam.

    PubMed

    Frantzeskakis, E; De Jong, N; Zwartsenberg, B; Huang, Y K; Bay, T V; Pronk, P; Van Heumen, E; Wu, D; Pan, Y; Radovic, M; Plumb, N C; Xu, N; Shi, M; De Visser, A; Golden, M S

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi(2-x)Sb(x)Te(3-y)Se(y) with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi(2-x)Sb(x)Te(3-y)Se(y) crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by 'writing' micron-sized letters in the Dirac point energy of the system. PMID:26543011

  7. Micro-metric electronic patterning of a topological band structure using a photon beam

    PubMed Central

    Frantzeskakis, E.; De Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; Van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; De Visser, A.; Golden, M. S.

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2−xSbxTe3−ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2−xSbxTe3−ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system. PMID:26543011

  8. Micro-metric electronic patterning of a topological band structure using a photon beam

    NASA Astrophysics Data System (ADS)

    Frantzeskakis, E.; de Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; de Visser, A.; Golden, M. S.

    2015-11-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2-xSbxTe3-ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2-xSbxTe3-ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system.

  9. Optimization of pump spectra for gain-flattened photonic crystal fiber Raman amplifiers operating in C-band.

    PubMed

    Sasaki, Kazuya; Varshney, Shailendra K; Wada, Keisuke; Saitoh, Kunimasa; Koshiba, Masanori

    2007-03-01

    This paper focuses on the optimization of pump spectra to achieve low Raman gain ripples over C-band in ultra-low loss photonic crystal fiber (PCF) and dispersion compensating PCFs (DCPCFs). Genetic algorithm (GA), a multivariate stochastic optimization algorithm, is applied to optimize the pump powers and the wavelengths for the aforesaid fiber designs. In addition, the GA integrated with full-vectorial finite element method with curvilinear edge/nodal elements is used to optimize the structural parameters of DCPCF. The optimized DCPCF provides broadband dispersion compensation over C-band with low negative dispersion coefficient of -530 ps/nm/km at 1550 nm, which is five times larger than the conventional dispersion compensating fibers with nearly equal effective mode area (21.7 mum(2)). A peak gain of 8.4 dB with +/-0.21 dB gain ripple is achieved for a 2.73 km long DCPCF module when three optimized pumps are used in the backward direction. The lowest gain ripple of +/-0.36 dB is attained for a 10 km long ultra-low loss PCF with three backward pumps. Sensitivity analysis has been performed and it is found that within the experimental fabrication tolerances of +/-2%, the absolute magnitude of dispersion may vary by +/-16%, while the Raman gain may change by +/-7%. Through tolerance study, it is examined that the ring core's hole-size is more sensitive to the structural deformations. PMID:19532502

  10. An organic dye with very large Stokes-shift and broad tunability of fluorescence: Potential two-photon probe for bioimaging and ultra-sensitive solid-state gas sensor

    NASA Astrophysics Data System (ADS)

    He, Tingchao; Wang, Yue; Tian, Xiaoqing; Gao, Yang; Zhao, Xin; Grimsdale, Andrew C.; Lin, Xiaodong; Sun, Handong

    2016-01-01

    Light-emitting nonlinear optical molecules, especially those with large Stokes shifts and broad tunability of their emission wavelength, have attracted considerable attention for various applications including biomedical imaging and fluorescent sensors. However, most fluorescent chromophores have only limited potential for such applications due to small Stokes shifts, narrow tunability of fluorescence emissions, and small optical nonlinearity in highly polar solvents. In this work, we demonstrate that a two-photon absorbing stilbene chromophore exhibits a large two-photon absorption action cross-section (ηδ = 320 GM) in dimethylsulfoxide (DMSO) and shows broad fluorescence tunability (125 nm) by manipulating the polarity of the surrounding medium. Importantly, a very large Stokes shift of up to 227 nm is achieved in DMSO. Thanks to these features, this chromophore can be utilized as a two-photon probe for bioimaging applications and in an ultrasensitive solid-state gas detector.

  11. Ultrathin, high-efficiency, broad-band, omni-acceptance, organic solar cells enhanced by plasmonic cavity with subwavelength hole array.

    PubMed

    Chou, Stephen Y; Ding, Wei

    2013-01-14

    Three of central challenges in solar cells are high light coupling into solar cell, high light trapping and absorption in a sub-absorption-length-thick active layer, and replacement of the indium-tin-oxide (ITO) transparent electrode used in thin-film devices. Here, we report a proposal and the first experimental study and demonstration of a new ultra-thin high-efficiency organic solar cell (SC), termed "plasmonic cavity with subwavelength hole-array (PlaCSH) solar cell", that offers a solution to all three issues with unprecedented performances. The ultrathin PlaCSH-SC is a thin plasmonic cavity that consists of a 30 nm thick front metal-mesh electrode with subwavelength hole-array (MESH) which replaces ITO, a thin (100 nm thick) back metal electrode, and in-between a polymer photovoltaic active layer (P3HT/PCBM) of 85 nm thick (1/3 average absorption-length). Experimentally, the PlaCSH-SCs have achieved (1) light coupling-efficiency/absorptance as high as 96% (average 90%), broad-band, and Omni acceptance (light coupling nearly independent of both light incident angle and polarization); (2) an external quantum efficiency of 69% for only 27% single-pass active layer absorptance; leading to (3) a 4.4% power conversion efficiency (PCE) at standard-solar-irradiation, which is 52% higher than the reference ITO-SC (identical structure and fabrication to PlaCSH-SC except MESH replaced by ITO), and also is among the highest PCE for the material system that was achievable previously only by using thick active materials and/or optimized polymer compositions and treatments. In harvesting scattered light, the Omni acceptance can increase PCE by additional 81% over ITO-SC, leading to a total 175% increase (i.e. 8% PCE). Furthermore, we found that (a) after formation of PlaCSH the light reflection and absorption by MESH are reduced by 2 to 6 fold from the values when it is alone; and (b) the sheet resistance of a 30 nm thick MESH is 2.2 ohm/sq or less-4.5 fold or more lower

  12. Dynamics of the 2007 Eruptions of Piton de la Fournaise and the Related Caldera Collapse from a Single Very Broad-band Seismic Station

    NASA Astrophysics Data System (ADS)

    Fontaine, Fabrice R.; Roult, Geneviève; Michon, Laurent; Barruol, Guilhem; Ferrazzini, Valérie; Di Muro, Andrea; Reymond, Dominique; Peltier, Aline; Staudacher, Thomas

    2014-05-01

    Seismic records from the RER very broad-band seismic station (La Réunion Island) belonging to the GEOSCOPE network are investigated to understand the eruptive succession (February to May) of Piton de la Fournaise and the caldera collapse episode of April 2007. Data first indicate that the short-lived, small volume, summit eruption of February 18 occurred during a phase of continuous inflation initiated in January 2007. Inflation decelerated around 2 weeks before a second short-lived small volume eruption on March 30-31 on the SE flank, almost simultaneous with a sudden, large deflation of the edifice. Deflation rate, which had stabilized at a relatively low level, increased anew on April 1 while no magma was emitted, followed on April 2 by a more distant and one of the most voluminous eruptions of the last two centuries at La Réunion Island. The RER station shows that very long period (VLP) and ultra long period (ULP) events developed during this period. Seven ULP events preceded the caldera collapse and 48 ones occurred during the caldera collapse over 9 days, most of which during the first 30 hours. A thorough examination of the seismic signals corrected for tide effects shows that each collapse event was coeval with VLP and ULP signals. Each individual collapse showed similar ULP and VLP signals characterized by periods of ~ 500 s and ~ 7 s, respectively. The back-azimuth of most ULP signals related to the caldera collapse points clearly toward the Dolomieu caldera. The strikingly constant duration of the VLP signals (around 20 s) related to the collapse events and their occurrence before the collapse initiation suggest a physical control of the volcanic edifice. Waveforms and spectrograms of the various caldera collapse events show very homogeneous patterns, suggesting a similar and repeating volcano-tectonic process for the formation of the VLP signals events. Although tilt may be responsible of part of the ULP signals observed during the collapse events, we

  13. Chaotic noise in superconducting microbridge 4-photon, x-band parametric amplifier

    SciTech Connect

    Andresen, J.E.; Christiansen, B.; Levinsen, M.T. )

    1989-06-01

    The anomalous noise rise observed in nearly all types of parametric amplifiers based on Josephson junctions has been an intriguing as well as annoying problem for many years. This phenomenon has been most spectacular in microbridge amplifiers. Here they present measurements on externally pumped single microbridge 4-photon unbiased amplifiers, where the slit with the bridge is used as a slotline resonantly coupled to the waveguide in an exceptionally simple coupling scheme. This scheme may be of interest in itself, particularly if the noise problem can be overcome, and in other connections. Up to 16 dB gain was obtained at the top of the waveguide. However, the noise rise was observed as usual. An analog computer study on a model including an input/output circuit was performed. The results are in very good agreement with the experiments. The amplification is heralded by a seemingly chaotic noise rise. This noise is then amplified linearly when gain occurs. Amplification is found to take place very close to where the supercurrent is completely suppressed by the pump. The cause of the noise rise has previously been interpreted as loss of phaselock. However, the power spectra of the time-derivative of the phase show this still to be locked in the region of positive gain. Furthermore, computations of the Lyapunov exponents show one to be positive in the region where gain occurs, reaching a maximum value at the parameters corresponding to maximum gain. They therefore conclude that chaotic noise is indeed present in Josephson junction parametric amplifiers where low-impedance devices such as microbridges with negligible capacitance are used as the active elements.

  14. Measurement of the resonant polaron effect in the Reststrahlen band of GaAs:Si using far-infrared two-photon excitation

    SciTech Connect

    Wenckebach, W.Th.; Planken, P.C.M.; Son, P.C. van

    1995-12-31

    We present the results of photoconductivity measurements of the resonant electron-phonon interaction in the middle of the Reststrahlen band using two-photon excitation with intense picosecond pulses with frequency around 143 cm{sup -1} (70 {mu}m). We use two photons rather than a single photon for the excitation of the resonant-polaron to avoid the problems of strong reflection and dielectric artifacts encountered in direct single-photon excitation in the Reststrahlen band. The sample is a 10 {mu}m thick Si-doped GaAs epitaxial layer on a 400 {mu}m semi-insulating GaAs substrate. The electronic levels of the Si shallow donor can be tuned by the application of a magnetic field. Intense tunable picosecond pulses with a frequency of around 143 cm{sup -1} from the Dutch free-electron laser FELIX are weakly focussed onto the sample, which is kept at 8 K. Electrons excited to the 3d{sup +2} state via the electric-dipole allowed two-photon transition out of the 1s{sub 0-} ground state, decay to the conduction band and give rise to an increase in the photoconductivity. The figure shows the energy-peak position of the 3d{sup +2} transition thus obtained as a function of the magnetic-field strength. The figure clearly shows the avoided crossing around the LO-phonon energy where the coupling shows the avoided crossing around the LO-phonon energy where the coupling between the 3d{sup +2} state and the LO phonon is strongest. Note that the data between 267 cm{sup -1} and 296 cm{sup -1} are extremely difficult to obtain with single-photon excitation because of their position in the middle of the Reststrahlen band.

  15. Effect of the inclusion of small metallic components in a two-dimensional dielectric photonic crystal with large full band gap

    NASA Astrophysics Data System (ADS)

    Chang, Chien C.; Chi, J. Y.; Chern, R. L.; Chang, C. Chung; Lin, C. H.; Chang, C. O.

    2004-08-01

    In this study, we investigate the effect of metallic inclusion modeled as perfect conductor on a dielectric photonic crystal (silicon/air) with large full band gap. The dielectric crystal consists of a hexagonal array of circular dielectric columns, each connected to its nearest neighbors by slender rectangular rods. It is found that inclusion of small metallic components inside the circular dielectrics sharply “turns off“ the full band gap of the dielectric photonic crystal. By increasing the radius of metallic inclusion above a threshold value, the full band gap (of the metallodielectric photonic crystal) makes its appearance again and continues to grow in size. On the other hand, metallic inclusion in the air region shows an opposite trend that the full band gap is not turned off, and its size diminishes gradually to zero with increasing the radius of inclusion. These peculiar behaviors can be explained on a unified basis by examining different types of boundary conditions for TM and TE modes, and employing variational arguments based on Rayleigh’s quotients. Moreover, the free-electron model for metallic components is also considered for TM modes. At large plasma frequencies, these modes show very close band structures to those described above for the case of perfect conductors.

  16. Switching of the photonic band gap in three-dimensional film photonic crystals based on opal-VO{sub 2} composites in the 1.3-1.6 {mu}m spectral range

    SciTech Connect

    Pevtsov, A. B. Grudinkin, S. A.; Poddubny, A. N.; Kaplan, S. F.; Kurdyukov, D. A.; Golubev, V. G.

    2010-12-15

    The parameters of three-dimensional photonic crystals based on opal-VO{sub 2} composite films in the 1.3-1.6 {mu}m spectral range important for practical applications (Telecom standard) are numerically calculated. For opal pores, the range of filling factors is established (0.25-0.6) wherein the composite exhibits the properties of a three-dimensional insulator photonic crystal. On the basis of the opal-VO{sub 2} composites, three-dimensional photonic film crystals are synthesized with specified parameters that provide a maximum shift of the photonic band gap in the vicinity of the wavelength {approx}1.5 {mu}m ({approx}170 meV) at the semiconductor-metal transition in VO{sub 2}.

  17. Spectral and temporal behavior of low mass X ray binaries observed with the Einstein SSS and MPC, and the Broad Band X Ray Telescope

    NASA Astrophysics Data System (ADS)

    Christian, Damian Joseph

    An extensive survey of 50 low mass X-ray binaries was carried out using the HEAO-2 Einstein Solid State Spectrometer data (0.5-4.5 keV) with the Monitor Proportional Counter data (1.2-20.0 keV). The SSS provided 160 eV resolution below 4.5 keV with about 200 sq cm of area, 100 times that of grating instruments on Einstein and EXOSAT. Additional observations were obtained with the Broad Band X-Ray Telescope (0.5-12 keV). Although LMXRB are some of the most luminous X-ray sources and include one of the first X-ray sources discovered, the nature of their emission regions has remained uncertain. Spectra were selected on the basis of intensity and fit with a set of simple and complex spectral models. For all the subclasses, including Eddington-limited bulge sources, bursters, dippers, the soft spectrum black hole candidates, and a few transients in decline, the spectra could be fit acceptably with combinations of thermal bremsstrahlung and blackbody spectra or a Comptonized spectrum and a blackbody. The results rule out optically thick disk models for the bright Z sources and power law models for bursters. The results suggest a progression of spectra as a function of X-ray luminosity for the bursters, Atoll, and Z sources, in which there are separate emission regions, one optically thin to scattering. The optically thick component that appears for higher luminosity may be due to a boundary layer or to high optical depth to scattering in the flow. A lower temperature blackbody indicated in some cases could be an expected contribution from the accretion disk. The soft spectrum sources are dominated by blackbody spectra, but for two, low effective area of emission is a problem for the black hole interpretation. There did not appear to be any clear selection between models for the sources with high binary orbit inclinations. Column densities for absorption by cold gas were determined simultaneously with the fits. They give distance estimates for the galactic bulge sources

  18. Temperature dependence of beat-length and confinement loss in an air-core photonic band-gap fiber

    NASA Astrophysics Data System (ADS)

    Xu, Zhenlong; Li, Xuyou; Hong, Yong; Liu, Pan; Yang, Hanrui; Ling, Weiwei

    2016-05-01

    The temperature dependence of polarization-maintaining (PM) property and loss in a highly-birefringent air-core photonic band-gap fiber (PBF) is investigated. The effects of temperature variation on the effective index, beat-length and confinement loss are studied numerically by using the full-vector finite element method (FEM). It is found that, the PM property of this PBF is insensitive to the temperature, and the temperature-dependent beat-length coefficient can be as low as 2.86×10-8 m/°C, which is typically 200 times less than those of conventional panda fibers, the PBF has a stable confinement loss of 0.01 dB/m over the temperature range of -30 to 20 °C for the slow axis at the wavelength of 1.55 μm. The PBF with ultra-low temperature-dependent PM property and low loss can reduce the thermally induced polarization instability apparently in interferometric applications such as resonant fiber optic gyroscope (RFOG), optical fiber sensors, and so on.

  19. Effects of electron beam parameters and velocity spread on radio frequency output of a photonic band gap cavity gyrotron oscillator

    SciTech Connect

    Singh, Ashutosh; Jain, P. K.

    2015-09-15

    In this paper, the effects of electron beam parameters and velocity spread on the RF behavior of a metallic photonic band gap (PBG) cavity gyrotron operating at 35 GHz with TE{sub 041}–like mode have been theoretically demonstrated. PBG cavity is used here to achieve a single mode operation of the overmoded cavity. The nonlinear time-dependent multimode analysis has been used to observe the beam-wave interaction behavior of the PBG cavity gyrotron, and a commercially available PIC code “CST Particle Studio” has been reconfigured to obtain 3D simulation results in order to validate the analytical values. The output power for this typical PBG gyrotron has been obtained ∼108 kW with ∼15.5% efficiency in a well confined TE{sub 041}–like mode, while all other competing modes have significantly low values of power output. The output power and efficiency of a gyrotron depend highly on the electron beam parameters and velocity spread. The influence of several electron beam parameters, e.g., beam voltage, beam current, beam velocity pitch factor, and DC magnetic field, on the PBG gyrotron operations has been investigated. This study would be helpful in optimising the electron beam parameters and estimating accurate RF output power of the high frequency PBG cavity based gyrotron oscillators.

  20. Effects of electron beam parameters and velocity spread on radio frequency output of a photonic band gap cavity gyrotron oscillator

    NASA Astrophysics Data System (ADS)

    Singh, Ashutosh; Jain, P. K.

    2015-09-01

    In this paper, the effects of electron beam parameters and velocity spread on the RF behavior of a metallic photonic band gap (PBG) cavity gyrotron operating at 35 GHz with TE041-like mode have been theoretically demonstrated. PBG cavity is used here to achieve a single mode operation of the overmoded cavity. The nonlinear time-dependent multimode analysis has been used to observe the beam-wave interaction behavior of the PBG cavity gyrotron, and a commercially available PIC code "CST Particle Studio" has been reconfigured to obtain 3D simulation results in order to validate the analytical values. The output power for this typical PBG gyrotron has been obtained ˜108 kW with ˜15.5% efficiency in a well confined TE041-like mode, while all other competing modes have significantly low values of power output. The output power and efficiency of a gyrotron depend highly on the electron beam parameters and velocity spread. The influence of several electron beam parameters, e.g., beam voltage, beam current, beam velocity pitch factor, and DC magnetic field, on the PBG gyrotron operations has been investigated. This study would be helpful in optimising the electron beam parameters and estimating accurate RF output power of the high frequency PBG cavity based gyrotron oscillators.

  1. Plant lighting system with five wavelength-band light-emitting diodes providing photon flux density and mixing ratio control

    PubMed Central

    2012-01-01

    Background Plant growth and development depend on the availability of light. Lighting systems therefore play crucial roles in plant studies. Recent advancements of light-emitting diode (LED) technologies provide abundant opportunities to study various plant light responses. The LED merits include solidity, longevity, small element volume, radiant flux controllability, and monochromaticity. To apply these merits in plant light response studies, a lighting system must provide precisely controlled light spectra that are useful for inducing various plant responses. Results We have developed a plant lighting system that irradiated a 0.18 m2 area with a highly uniform distribution of photon flux density (PFD). The average photosynthetic PFD (PPFD) in the irradiated area was 438 micro-mol m–2 s–1 (coefficient of variation 9.6%), which is appropriate for growing leafy vegetables. The irradiated light includes violet, blue, orange-red, red, and far-red wavelength bands created by LEDs of five types. The PFD and mixing ratio of the five wavelength-band lights are controllable using a computer and drive circuits. The phototropic response of oat coleoptiles was investigated to evaluate plant sensitivity to the light control quality of the lighting system. Oat coleoptiles irradiated for 23 h with a uniformly distributed spectral PFD (SPFD) of 1 micro-mol m–2 s–1 nm–1 at every peak wavelength (405, 460, 630, 660, and 735 nm) grew almost straight upwards. When they were irradiated with an SPFD gradient of blue light (460 nm peak wavelength), the coleoptiles showed a phototropic curvature in the direction of the greater SPFD of blue light. The greater SPFD gradient induced the greater curvature of coleoptiles. The relation between the phototropic curvature (deg) and the blue-light SPFD gradient (micro-mol m–2 s–1 nm–1 m–1) was 2 deg per 1 micro-mol m–2 s–1 nm–1 m–1. Conclusions The plant lighting system, with a computer with a graphical user interface

  2. Band structure of a 2D photonic crystal based on ferrofluids of Co(1-x)Znx Fe2O4 nanoparticles under perpendicular applied magnetic field

    NASA Astrophysics Data System (ADS)

    Lopez, Javier; Gonzalez, Luz Esther; Quinonez, Mario; Porras, Nelson; Zambrano, Gustavo; Gomez, Maria Elena

    2014-03-01

    Using a ferrfluid of cobalt-zinc ferrite nanoparticles Co(1 - x)ZnxFe2O4 coated with oleic acid and suspended in ethanol, we have fabricated a 2D photonic crystal (PC) by the application of an external magnetic field perpendicular to the plane of the ferrofluid. The 2D PC is made by rods of nanoparticles organized in a hexagonal structure. By means of the plane-wave expansion method, we study its photonic band structure (PBS) which depends on the effective permittivity and on the area ratio of the liquid phase. Additionaly, taking into account the Maxwell-Garnett theory we calculated the effective permittivity of the rods. We have found that the effective refractive index of the ferrofluid increases with its magnetization. Using these results we calculate the band structure of the photonic crystal at different applied magnetic fields, finding that the increase of the applied magnetic field shifts the band structure to lower frequencies with the appearance of more band gaps. Departamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia

  3. Cascaded Mach-Zehnder wavelength filters in silicon photonics for low loss and flat pass-band WDM (de-)multiplexing.

    PubMed

    Horst, Folkert; Green, William M J; Assefa, Solomon; Shank, Steven M; Vlasov, Yurii A; Offrein, Bert Jan

    2013-05-20

    We present 1-to-8 wavelength (de-)multiplexer devices based on a binary tree of cascaded Mach-Zehnder-like lattice filters, and manufactured using a 90 nm CMOS-integrated silicon photonics technology. We demonstrate that these devices combine a flat pass-band over more than 50% of the channel spacing with low insertion loss of less than 1.6 dB, and have a small device size of approximately 500 × 400 µm. This makes this type of filters well suited for application as WDM (de-)multiplexer in silicon photonics transceivers for optical data communication in large scale computer systems. PMID:23736388

  4. Band alignment and photon extraction studies of Na-doped MgZnO/Ga-doped ZnO heterojunction for light-emitter applications

    NASA Astrophysics Data System (ADS)

    Pandey, Sushil Kumar; Awasthi, Vishnu; Sengar, Brajendra Singh; Garg, Vivek; Sharma, Pankaj; Kumar, Shailendra; Mukherjee, C.; Mukherjee, Shaibal

    2015-10-01

    Ultraviolet photoelectron spectroscopy is carried out to measure the energy discontinuity at the interface of p-type Na-doped MgZnO (NMZO)/n-type Ga-doped ZnO (GZO) heterojunction grown by dual ion beam sputtering. The offset values at valence band and conduction band of NMZO/GZO heterojunction are calculated to be 1.93 and -2.36 eV, respectively. The p-type conduction in NMZO film has been confirmed by Hall measurement and band structure. Moreover, the effect of Ar+ ion sputtering on the valence band onset values of NMZO and GZO thin films has been investigated. This asymmetric waveguide structure formed by the lower refractive index of GZO than that of NMZO indicates that easy extraction of photons generated in GZO through the NMZO layer into free space. The asymmetric waveguide structure has potential applications to produce ZnO-based light emitters with high extraction efficiency.

  5. Electronic band structure of highly mismatched GaN{sub 1−x}Sb{sub x} alloys in a broad composition range

    SciTech Connect

    Segercrantz, N.; Yu, K. M.; Ting, M.; Sarney, W. L.; Svensson, S. P.; Novikov, S. V.; Foxon, C. T.; Walukiewicz, W.

    2015-10-05

    In this letter, we study the optical properties of GaN{sub 1−x}Sb{sub x} thin films. Films with an Sb fraction up to 42% were synthesized by alternating GaN-GaSb layers at a constant temperature of 325 °C. The measured optical absorption data of the films are interpreted using a modified band anticrossing model that is applicable to highly mismatched alloys such as GaN{sub 1−x}Sb{sub x} in the entire composition range. The presented model allows us to more accurately determine the band gap as well as the band edges over the entire composition range thereby providing means for determining the composition for, e.g., efficient spontaneous photoelectrochemical cell applications.

  6. A program for calculating photonic band structures, Green's functions and transmission/reflection coefficients using a non-orthogonal FDTD method

    NASA Astrophysics Data System (ADS)

    Ward, A. J.; Pendry, J. B.

    2000-06-01

    In this paper we present an updated version of our ONYX program for calculating photonic band structures using a non-orthogonal finite difference time domain method. This new version employs the same transparent formalism as the first version with the same capabilities for calculating photonic band structures or causal Green's functions but also includes extra subroutines for the calculation of transmission and reflection coefficients. Both the electric and magnetic fields are placed onto a discrete lattice by approximating the spacial and temporal derivatives with finite differences. This results in discrete versions of Maxwell's equations which can be used to integrate the fields forwards in time. The time required for a calculation using this method scales linearly with the number of real space points used in the discretization so the technique is ideally suited to handling systems with large and complicated unit cells.

  7. Effect of temperature on terahertz photonic and omnidirectional band gaps in one-dimensional quasi-periodic photonic crystals composed of semiconductor InSb.

    PubMed

    Singh, Bipin K; Pandey, Praveen C

    2016-07-20

    Engineering of thermally tunable terahertz photonic and omnidirectional bandgaps has been demonstrated theoretically in one-dimensional quasi-periodic photonic crystals (PCs) containing semiconductor and dielectric materials. The considered quasi-periodic structures are taken in the form of Fibonacci, Thue-Morse, and double periodic sequences. We have shown that the photonic and omnidirectional bandgaps in the quasi-periodic structures with semiconductor constituents are strongly depend on the temperature, thickness of the constituted semiconductor and dielectric material layers, and generations of the quasi-periodic sequences. It has been found that the number of photonic bandgaps increases with layer thickness and generation of the quasi-periodic sequences. Omnidirectional bandgaps in the structures have also been obtained. Results show that the bandwidths of photonic and omnidirectional bandgaps are tunable by changing the temperature and lattice parameters of the structures. The generation of quasi-periodic sequences can also change the properties of photonic and omnidirectional bandgaps remarkably. The frequency range of the photonic and omnidirectional bandgaps can be tuned by the change of temperature and layer thickness of the considered quasi-periodic structures. This work will be useful to design tunable terahertz PC devices. PMID:27463924

  8. Doppler-free two-photon spectroscopy on the S 1 ← S 0 origin band of 1,4-diazabicyclo[2,2,2]octane (DABCO)

    NASA Astrophysics Data System (ADS)

    Berden, Giel; Groot, Tim; van der Veldt, Tony; Meijer, Gerard

    1997-01-01

    The rotationally resolved two-photon excitation spectrum of the Q-branch ( ΔJ = 0) of the O 00 band in the S 1 ← S 0 transition of DABCO was recorded in a cell at room temperature. Two counterpropagating narrow bandwidth laser beams were used for Doppler-free excitation. The observed linewidth was 20 MHz. Analysis of the spectra provides the change upon electronic excitation of the rotational constants.

  9. Application of Novel High Order Time Domain Vector Finite Element Method to Photonic Band-Gap Waveguides

    SciTech Connect

    Rieben, R; White, D; Rodrigue, G

    2004-01-13

    In this paper we motivate the use of a novel high order time domain vector finite element method that is of arbitrary order accuracy in space and up to 5th order accurate in time; and in particular, we apply it to the case of photonic band-gap (PBG) structures. Such structures have been extensively studied in the literature with several practical applications; in particular, for the low loss transmission of electromagnetic energy around sharp 90 degree bends [1]. Typically, such structures are simulated via a numerical solution of Maxwell's equations either in the frequency domain or directly in the time domain over a computational grid. The majority of numerical simulations performed for such structures make use of the widely popular finite difference time domain (FDTD) method [2], where the time dependent electric and magnetic fields are discretized over a ''dual'' grid to second order accuracy in space and time. However, such methods do not generalize to unstructured, non-orthogonal grids or to higher order spatial discretization schemes. To simulate more complicated structures with curved boundaries, such as the structure of [3], a cell based finite element method with curvilinear elements is preferred over standard stair-stepped Cartesian meshes; and to more efficiently reduce the effects of numerical dispersion, a higher order method is highly desirable. In this paper, the high order basis functions of [5] are used in conjunction with the high order energy conserving symplectic time integration algorithms of [6] resulting in a high order, fully mimetic, mixed vector finite element method.

  10. Design optimization of a low-loss and wide-band sharp 120° waveguide bend in 2D photonic crystals

    NASA Astrophysics Data System (ADS)

    Yuan, Jianhua; Yang, Jian; Shi, Dan; Ai, Wenbao; Shuai, Tianping

    2016-05-01

    For two dimensional photonic crystals containing finite cylinders on triangle lattice, a 120° waveguide bend with low-loss and wide-band is obtained in this paper. The optimal process can be divided into two steps: firstly, a conventional waveguide bend can be introduced by maximizing the photonic bandgap; then further optimization involves shifting the position and modifying the radius of only one air hole near the bend. An optimization problem at a given frequency or over a frequency range needs to be solved. It depends on both the field solutions obtained by using the finite element method and the optimization of photonic bandgap obtained by using the plane wave expansion method. With the proposed optimal technique, the result of our optimized design for sharp 120° waveguide bends shows that an obvious low-loss transmission at wavelength 1550 nm can be observed and the maximum value of objective function is able to be rapidly obtained.

  11. High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide.

    PubMed

    Marichy, Catherine; Muller, Nicolas; Froufe-Pérez, Luis S; Scheffold, Frank

    2016-01-01

    Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold refractive index contrast that depends on the crystal structure. In the case of the so-called woodpile photonic crystals this threshold is comparably low, approximately 1.9 for the direct structure. Therefore direct or inverted woodpiles made of high refractive index materials like silicon, germanium or titanium dioxide are sought after. Here we show that, by combining multiphoton lithography and atomic layer deposition, we can achieve a direct inversion of polymer templates into TiO2 based photonic crystals. The obtained structures show remarkable optical properties in the near-infrared region with almost perfect specular reflectance, a transmission dip close to the detection limit and a Bragg length comparable to the lattice constant. PMID:26911540

  12. High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide

    PubMed Central

    Marichy, Catherine; Muller, Nicolas; Froufe-Pérez, Luis S.; Scheffold, Frank

    2016-01-01

    Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold refractive index contrast that depends on the crystal structure. In the case of the so-called woodpile photonic crystals this threshold is comparably low, approximately 1.9 for the direct structure. Therefore direct or inverted woodpiles made of high refractive index materials like silicon, germanium or titanium dioxide are sought after. Here we show that, by combining multiphoton lithography and atomic layer deposition, we can achieve a direct inversion of polymer templates into TiO2 based photonic crystals. The obtained structures show remarkable optical properties in the near-infrared region with almost perfect specular reflectance, a transmission dip close to the detection limit and a Bragg length comparable to the lattice constant. PMID:26911540

  13. High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide

    NASA Astrophysics Data System (ADS)

    Marichy, Catherine; Muller, Nicolas; Froufe-Pérez, Luis S.; Scheffold, Frank

    2016-02-01

    Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold refractive index contrast that depends on the crystal structure. In the case of the so-called woodpile photonic crystals this threshold is comparably low, approximately 1.9 for the direct structure. Therefore direct or inverted woodpiles made of high refractive index materials like silicon, germanium or titanium dioxide are sought after. Here we show that, by combining multiphoton lithography and atomic layer deposition, we can achieve a direct inversion of polymer templates into TiO2 based photonic crystals. The obtained structures show remarkable optical properties in the near-infrared region with almost perfect specular reflectance, a transmission dip close to the detection limit and a Bragg length comparable to the lattice constant.

  14. A 0.2-0.5 THz single-band heterodyne receiver based on a photonic local oscillator and a superconductor-insulator-superconductor mixer

    NASA Astrophysics Data System (ADS)

    Kohjiro, Satoshi; Kikuchi, Kenichi; Maezawa, Masaaki; Furuta, Tomofumi; Wakatsuki, Atsushi; Ito, Hiroshi; Shimizu, Naofumi; Nagatsuma, Tadao; Kado, Yuichi

    2008-09-01

    We have demonstrated that a superconductor-insulator-superconductor (SIS) mixer pumped by a photonic local oscillator (LO) covers the whole frequency range of 0.2-0.5THz. In the bandwidth of 74% of the center frequency, this single-band receiver exhibits noise temperature of TRX⩽20hf/kB, where h is Planck's constant, f is the frequency, and kB is Boltzmann's constant. Resultant TRX is almost equal to TRX of the identical SIS mixer pumped by three conventional frequency-multiplier-based LOs which share the 0.2-0.5THz band. This technique will contribute to simple, wide-band, and low-noise heterodyne receivers in the terahertz region.

  15. Lattice dynamics and broad-band dielectric properties of multiferroic Pb(Fe{sub 1/2}Nb{sub 1/2})O{sub 3} ceramics

    SciTech Connect

    Mackeviciute, R.; Greicius, S.; Grigalaitis, R.; Banys, J.; Goian, V.; Nuzhnyy, D.; Kamba, S.; Holc, J.

    2015-02-28

    Complex dielectric properties of Pb(Fe{sub 1/2}Nb{sub 1/2})O{sub 3} ceramics were investigated in a broad frequency range from 100 Hz up to 90 THz. A broad dielectric anomaly was observed near the temperature of the ferroelectric phase transition (T{sub C1} = 376 K). Below 1 MHz, the anomaly is strongly influenced by conductivity of the sample, but higher frequency data taken up to 81 MHz reveal a broad and frequency independent peak at T{sub C1} typical for a diffuse ferroelectric phase transition. Surprisingly, dielectric permittivity measured at 37 GHz exhibits a peak shifted by 25 K above T{sub C1}, which indicates polar nanoregions with dynamics in microwave frequency region. A dielectric relaxation, which appears in THz region below 700 K, slows down towards T{sub C1} and again hardens below T{sub C2} = 356 K. This central mode drives both phase transitions, so they belong to order–disorder type, although the polar phonons exhibit anomalies near both phase transitions. In the paraelectric phase, infrared reflectivity spectra correspond to local Fm3{sup ¯}m structure due to short-range chemical ordering of Fe and Nb cations on the B perovskite sites. Moreover, each polar phonon is split due to two different cations on the B sites. Recently, Manley et al. [Nat. Commun. 5, 3683 (2014)] proposed a new mechanism of creation of polar nanoregions in relaxor ferroelectrics. They argued, based on their inelastic neutron scattering studies of PMN–PT, that the TO1 phonon is split and interaction of both components gives rise to so called Anderson phonon localization, which can produce regions of trapped standing waves and these waves induce polar nanoregions in relaxors. We cannot exclude or confirm this mechanism, but we show that the splitting of polar phonons is a common feature for all complex perovskites with relaxor ferroelectric behavior and it can be also observed in canonical ferroelectric BaTiO{sub 3}, where the soft mode is split in

  16. Lattice dynamics and broad-band dielectric properties of multiferroic Pb(Fe1/2Nb1/2)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Mackeviciute, R.; Goian, V.; Greicius, S.; Grigalaitis, R.; Nuzhnyy, D.; Holc, J.; Banys, J.; Kamba, S.

    2015-02-01

    Complex dielectric properties of Pb(Fe1/2Nb1/2)O3 ceramics were investigated in a broad frequency range from 100 Hz up to 90 THz. A broad dielectric anomaly was observed near the temperature of the ferroelectric phase transition (TC1 = 376 K). Below 1 MHz, the anomaly is strongly influenced by conductivity of the sample, but higher frequency data taken up to 81 MHz reveal a broad and frequency independent peak at TC1 typical for a diffuse ferroelectric phase transition. Surprisingly, dielectric permittivity measured at 37 GHz exhibits a peak shifted by 25 K above TC1, which indicates polar nanoregions with dynamics in microwave frequency region. A dielectric relaxation, which appears in THz region below 700 K, slows down towards TC1 and again hardens below TC2 = 356 K. This central mode drives both phase transitions, so they belong to order-disorder type, although the polar phonons exhibit anomalies near both phase transitions. In the paraelectric phase, infrared reflectivity spectra correspond to local F m 3 ¯ m structure due to short-range chemical ordering of Fe and Nb cations on the B perovskite sites. Moreover, each polar phonon is split due to two different cations on the B sites. Recently, Manley et al. [Nat. Commun. 5, 3683 (2014)] proposed a new mechanism of creation of polar nanoregions in relaxor ferroelectrics. They argued, based on their inelastic neutron scattering studies of PMN-PT, that the TO1 phonon is split and interaction of both components gives rise to so called Anderson phonon localization, which can produce regions of trapped standing waves and these waves induce polar nanoregions in relaxors. We cannot exclude or confirm this mechanism, but we show that the splitting of polar phonons is a common feature for all complex perovskites with relaxor ferroelectric behavior and it can be also observed in canonical ferroelectric BaTiO3, where the soft mode is split in paraelectric phase due to a strong lattice anharmonicity.

  17. Photonic crystal scene projector development

    NASA Astrophysics Data System (ADS)

    Wilson, J. A.; Burckel, B.; Caulfield, J.; Cogan, S.; Massie, M.; Lamott, R.; Snyder, D.; Rapp, R.

    2010-04-01

    This paper describes results from the Extremely High Temperature Photonic Crystal System Technology (XTEMPS) program. The XTEMPS program is developing projector technology based on photonic crystals capable of high dynamic range, multispectral emission from SWIR to LWIR, and realistic band widths. These Photonics Crystals (PhC) are fabricated from refractory materials to provide high radiance and long device lifetime. Cyan is teamed with Sandia National Laboratories, to develop photonics crystals designed for realistic scene projection systems and Nova sensors to utilize their advanced Read In Integrated Circuit (RIIC). PhC based emitters show improved in-band output power efficiency when compared to broad band "graybody" emitters due to the absence of out-of-band emission. Less electrical power is required to achieve high operating temperature, and the potential for nonequilibrium pumping exists. Both effects boost effective radiance output. Cyan has demonstrated pixel designs compatible with Nova's medium format RIIC, ensuring high apparent output temperatures, modest drive currents, and low operating voltages of less than five volts. Unit cell pixel structures with high radiative efficiency have been demonstrated, and arrays using PhC optimized for up to four spectral bands have been successfully patterned.

  18. Broad-band dielectric spectroscopy and ferroelectric soft-mode response in the Ba(0.6)Sr(0.4)TiO(3) solid solution.

    PubMed

    Ostapchuk, T; Petzelt, J; Hlinka, J; Bovtun, V; Kužel, P; Ponomareva, I; Lisenkov, S; Bellaiche, L; Tkach, A; Vilarinho, P

    2009-11-25

    Ceramic Ba(0.6)Sr(0.4)TiO(3) (BST-0.6) samples were studied in the broad spectral range of 10(6)-10(14) Hz by using several dielectric techniques in between 20 and 800 K. The dominant dielectric dispersion mechanism in the paraelectric phase was shown to be of strongly anharmonic soft-phonon origin. The whole soft-mode response in the vicinity of the ferroelectric transition was shown to consist of two coupled overdamped THz excitations, which show classical features of a coupled soft and central mode, known from many ferroelectric crystals with a dynamics near the displacive and order-disorder crossover. Similar behaviour has been recently revealed and theoretically simulated in pure BaTiO(3) (see Ponomareva et al 2008 Phys. Rev. B 77 012102 and Hlinka et al 2008 Phys. Rev. Lett. 101 167402). Also for the BST system, this feature was confirmed by the theory based on molecular dynamics simulations with an effective first-principles Hamiltonian. In all the ferroelectric phases, additional relaxation dispersion appeared in the GHz range, assigned to ferroelectric domain-wall dynamics. The microwave losses were analysed from the point of view of applications. The paraelectric losses above 1 GHz are comparable with those in single crystals and appear to be of intrinsic multi-phonon origin. The ceramic BST system is therefore well suited for applications in the whole microwave range. PMID:21832494

  19. Telecommunication Wavelength-Band Single-Photon Emission from Single Large InAs Quantum Dots Nucleated on Low-Density Seed Quantum Dots.

    PubMed

    Chen, Ze-Sheng; Ma, Ben; Shang, Xiang-Jun; He, Yu; Zhang, Li-Chun; Ni, Hai-Qiao; Wang, Jin-Liang; Niu, Zhi-Chuan

    2016-12-01

    Single-photon emission in the telecommunication wavelength band is realized with self-assembled strain-coupled bilayer InAs quantum dots (QDs) embedded in a planar microcavity on GaAs substrate. Low-density large QDs in the upper layer active for ~1.3 μm emission are fabricated by precisely controlling the indium deposition amount and applying a gradient indium flux in both QD layers. Time-resolved photoluminescence (PL) intensity suggested that the radiative lifetime of their exciton emission is 1.5~1.6 ns. The second-order correlation function of g (2)(0) < 0.5 which demonstrates a pure single-photon emission. PMID:27576522

  20. High-quality lowest-frequency normal mode strain observations at the Black Forest Observatory (SW-Germany) and comparison with horizontal broad-band seismometer data and synthetics

    NASA Astrophysics Data System (ADS)

    Zürn, W.; Ferreira, A. M. G.; Widmer-Schnidrig, R.; Lentas, K.; Rivera, L.; Clévédé, E.

    2015-12-01

    We present spectra concentrating on the lowest-frequency normal modes of the Earth obtained from records of the invar-wire strainmeters and STS-1 broad-band seismometers located in the Black Forest Observatory, Germany after the disastrous earthquakes off the NW coast of Sumatra in 2004 and off the coast near Tohoku, Japan in 2011. We compare the spectra to ones obtained from synthetic seismograms computed using a mode summation technique for an anelastic, elliptical, rotating, spherically symmetric Earth model. The synthetics include strain-strain-coupling effects by using coupling coefficients obtained from comparisons between Earth tide signals recorded by the strainmeters and synthetic tidal records. We show that for the low-frequency toroidal and spheroidal modes up to 1 mHz, the strainmeters produce better signal-to-noise ratios than the broad-band horizontal seismometers. Overall, the comparison with the synthetics is satisfactory but not as good as for vertical accelerations. In particular, we demonstrate the high quality of the strainmeter data by showing the Coriolis splitting of toroidal modes for the first time in individual records, the first clear observation of the singlet _2S_1^0 and the detection of the fundamental radial mode 0S0 with good signal-to-noise ratio and with a strain amplitude of 10-11. We also identify the latter mode in a record of the Isabella strainmeter after the great Chilean quake in 1960, the detection of which was missed by the original studies.

  1. Wide-field broad-band radio imaging with phased array feeds: a pilot multi-epoch continuum survey with ASKAP-BETA

    NASA Astrophysics Data System (ADS)

    Heywood, I.; Bannister, K. W.; Marvil, J.; Allison, J. R.; Ball, L.; Bell, M. E.; Bock, D. C.-J.; Brothers, M.; Bunton, J. D.; Chippendale, A. P.; Cooray, F.; Cornwell, T. J.; De Boer, D.; Edwards, P.; Gough, R.; Gupta, N.; Harvey-Smith, L.; Hay, S.; Hotan, A. W.; Indermuehle, B.; Jacka, C.; Jackson, C. A.; Johnston, S.; Kimball, A. E.; Koribalski, B. S.; Lenc, E.; Macleod, A.; McClure-Griffiths, N.; McConnell, D.; Mirtschin, P.; Murphy, T.; Neuhold, S.; Norris, R. P.; Pearce, S.; Popping, A.; Qiao, R. Y.; Reynolds, J. E.; Sadler, E. M.; Sault, R. J.; Schinckel, A. E. T.; Serra, P.; Shimwell, T. W.; Stevens, J.; Tuthill, J.; Tzioumis, A.; Voronkov, M. A.; Westmeier, T.; Whiting, M. T.

    2016-04-01

    The Boolardy Engineering Test Array is a 6 × 12 m dish interferometer and the prototype of the Australian Square Kilometre Array Pathfinder (ASKAP), equipped with the first generation of ASKAP's phased array feed (PAF) receivers. These facilitate rapid wide-area imaging via the deployment of simultaneous multiple beams within an ˜30 deg2 field of view. By cycling the array through 12 interleaved pointing positions and using nine digitally formed beams, we effectively mimic a traditional 1 h × 108 pointing survey, covering ˜150 deg2 over 711-1015 MHz in 12 h of observing time. Three such observations were executed over the course of a week. We verify the full bandwidth continuum imaging performance and stability of the system via self-consistency checks and comparisons to existing radio data. The combined three epoch image has arcminute resolution and a 1σ thermal noise level of 375 μJy beam-1, although the effective noise is a factor of ˜3 higher due to residual sidelobe confusion. From this we derive a catalogue of 3722 discrete radio components, using the 35 per cent fractional bandwidth to measure in-band spectral indices for 1037 of them. A search for transient events reveals one significantly variable source within the survey area. The survey covers approximately two-thirds of the Spitzer South Pole Telescope Deep Field. This pilot project demonstrates the viability and potential of using PAFs to rapidly and accurately survey the sky at radio wavelengths.

  2. Simple Experimental Verification of the Relation between the Band-Gap Energy and the Energy of Photons Emitted by LEDs

    ERIC Educational Resources Information Center

    Precker, Jurgen W.

    2007-01-01

    The wavelength of the light emitted by a light-emitting diode (LED) is intimately related to the band-gap energy of the semiconductor from which the LED is made. We experimentally estimate the band-gap energies of several types of LEDs, and compare them with the energies of the emitted light, which ranges from infrared to white. In spite of…

  3. An approach to control tuning range and speed in 1D ternary photonic band gap material nano-layered optical filter structures electro-optically

    NASA Astrophysics Data System (ADS)

    Zia, Shahneel; Banerjee, Anirudh

    2016-05-01

    This paper demonstrates a way to control spectrum tuning capability in one-dimensional (1D) ternary photonic band gap (PBG) material nano-layered structures electro-optically. It is shown that not only tuning range, but also tuning speed of tunable optical filters based on 1D ternary PBG structures can be controlled Electro-optically. This approach finds application in tuning range enhancement of 1D Ternary PBG structures and compensating temperature sensitive transmission spectrum shift in 1D Ternary PBG structures.

  4. Theoretical analysis of a palladium-based one-dimensional metallo-dielectric photonic band gap structure for applications to H2 sensors

    NASA Astrophysics Data System (ADS)

    Vincenti, Maria Antonietta; Trevisi, Simona; De Sario, Marco; Petruzzelli, Vincenzo; D'Orazio, Antonella; Prudenzano, Francesco; Cioffi, Nicola; de Ceglia, Domenico; Scalora, Michael

    2008-03-01

    In this paper we report a numerical study of a palladium-based metallo-dielectric photonic band gap structure for the purpose of detecting H2. In particular, and as an example, we will explore applications to the diagnosis of lactose malabsorption, more commonly known as lactose intolerance condition. This pathology occurs as a result of an incomplete absorption or digestion of different substances, causing an increased spontaneous emission of H2 in human breath. Palladium is considered in order to exploit its well known ability to absorb hydrogen spontaneously. The proposed structure is particularly able to detect the lactose malabsorption level of the patient with relatively high sensitivity and rapidity.

  5. High-precision broad-band linear polarimetry of early-type binaries. I. Discovery of variable, phase-locked polarization in HD 48099

    NASA Astrophysics Data System (ADS)

    Berdyugin, A.; Piirola, V.; Sadegi, S.; Tsygankov, S.; Sakanoi, T.; Kagitani, M.; Yoneda, M.; Okano, S.; Poutanen, J.

    2016-06-01

    Aims: We investigate the structure of the O-type binary system HD 48099 by measuring linear polarization that arises due to light scattering process. High-precison polarimetry provides independent estimates of the orbital parameters and gives important information on the properties of the system. Methods: Linear polarization measurements of HD 48099 in the B, V and R passbands with the high-precision Dipol-2 polarimeter have been carried out. The data have been obtained with the 60 cm KVA (Observatory Roque de los Muchachos, La Palma, Spain) and T60 (Haleakala, Hawaii, USA) remotely controlled telescopes during 31 observing nights. Polarimetry in the optical wavelengths has been complemented by observations in the X-rays with the Swift space observatory. Results: Optical polarimetry revealed small intrinsic polarization in HD 48099 with ~0.1% peak to peak variation over the orbital period of 3.08 d. The variability pattern is typical for binary systems, showing strong second harmonic of the orbital period. We apply our model code for the electron scattering in the circumstellar matter to put constraints on the system geometry. A good model fit is obtained for scattering of light on a cloud produced by the colliding stellar winds. The geometry of the cloud, with a broad distribution of scattering particles away from the orbital plane, helps in constraining the (low) orbital inclination. We derive from the polarization data the inclination i = 17° ± 2° and the longitude of the ascending node Ω = 82° ± 1° of the binary orbit. The available X-ray data provide additional evidence for the existence of the colliding stellar winds in the system. Another possible source of the polarized light could be scattering from the stellar photospheres. The models with circumstellar envelopes, or matter confined to the orbital plane, do not provide good constraints on the low inclination, better than i ≤ 27°, as is already suggested by the absence of eclipses. The

  6. Eight-band k·p modeling of InAs/InGaAsSb type-II W-design quantum well structures for interband cascade lasers emitting in a broad range of mid infrared

    SciTech Connect

    Ryczko, K.; Sęk, G.; Misiewicz, J.

    2013-12-14

    Band structure properties of the type-II W-design AlSb/InAs/GaIn(As)Sb/InAs/AlSb quantum wells have been investigated theoretically in a systematic manner and with respect to their use in the active region of interband cascade laser for a broad range of emission in mid infrared between below 3 to beyond 10 μm. Eight-band k·p approach has been utilized to calculate the electronic subbands. The fundamental optical transition energy and the corresponding oscillator strength have been determined in function of the thickness of InAs and GaIn(As)Sb layers and the composition of the latter. There have been considered active structures on two types of relevant substrates, GaSb and InAs, introducing slightly modified strain conditions. Additionally, the effect of external electric field has been taken into account to simulate the conditions occurring in the operational devices. The results show that introducing arsenic as fourth element into the valence band well of the type-II W-design system, and then altering its composition, can efficiently enhance the transition oscillator strength and allow additionally increasing the emission wavelength, which makes this solution prospective for improved performance and long wavelength interband cascade lasers.

  7. Band alignment and photon extraction studies of Na-doped MgZnO/Ga-doped ZnO heterojunction for light-emitter applications

    SciTech Connect

    Pandey, Sushil Kumar; Awasthi, Vishnu; Sengar, Brajendra Singh; Garg, Vivek; Sharma, Pankaj; Mukherjee, Shaibal; Kumar, Shailendra; Mukherjee, C.

    2015-10-28

    Ultraviolet photoelectron spectroscopy is carried out to measure the energy discontinuity at the interface of p-type Na-doped MgZnO (NMZO)/n-type Ga-doped ZnO (GZO) heterojunction grown by dual ion beam sputtering. The offset values at valence band and conduction band of NMZO/GZO heterojunction are calculated to be 1.93 and −2.36 eV, respectively. The p-type conduction in NMZO film has been confirmed by Hall measurement and band structure. Moreover, the effect of Ar{sup +} ion sputtering on the valence band onset values of NMZO and GZO thin films has been investigated. This asymmetric waveguide structure formed by the lower refractive index of GZO than that of NMZO indicates that easy extraction of photons generated in GZO through the NMZO layer into free space. The asymmetric waveguide structure has potential applications to produce ZnO-based light emitters with high extraction efficiency.

  8. Wide Band to ''Double Band'' upgrade

    SciTech Connect

    Kasper, P.; Currier, R.; Garbincius, P.; Butler, J.

    1988-06-01

    The Wide Band beam currently uses electrons obtained from secondary photon conversions to produce the photon beam incident on the experimental targets. By transporting the positrons produced in these conversions as well as the electrons it is possible to almost double the number of photons delivered to the experiments per primary beam proton. 11 figs.

  9. Temperature dependence of band gap ratio and Q-factor defect mode in a semiconductor quaternary alloy hexagonal photonic-crystal hole slab

    NASA Astrophysics Data System (ADS)

    Sánchez-Cano, R.; Porras-Montenegro, N.

    2016-04-01

    We present numerical predictions for the photonic TE-like band gap ratio and the quality factors of symmetric localized defect as a function of the thickness slab and temperature by the use of plane wave expansion and the finite-difference time-domain methods. The photonic-crystal hole slab is composed of a 2D hexagonal array with identical air holes and a circular cross section, embedded in a non-dispersive III-V semiconductor quaternary alloy slab, which has a high value of dielectric function in the near-infrared region, and the symmetric defect is formed by increasing the radius of a single hole in the 2D hexagonal lattice. We show that the band gap ratio depends linearly on the temperature in the range 150-400 K. Our results show a strong temperature dependence of the quality factor Q, the maximum (Q = 7000) is reached at T = 350 hbox {K}, but if the temperature continues to increase, the efficiency drops sharply. Furthermore, we present numerical predictions for the electromagnetic field distribution at T = 350 hbox {K}.

  10. Optimal focusing for maximal collection of entangled narrow-band photon pairs into single-mode fibers

    SciTech Connect

    Ljunggren, Daniel; Tengner, Maria

    2005-12-15

    We present a theoretical and experimental investigation of the emission characteristics and the flux of photon pairs generated by spontaneous parametric downconversion in quasi-phase matched bulk crystals for the use in quantum communication sources. We show that, by careful design, one can attain well defined modes close to the fundamental mode of optical fibers and obtain high coupling efficiencies also for bulk crystals, these being more easily aligned than crystal waveguides. We distinguish between singles coupling, {gamma}{sub s} and {gamma}{sub i}, conditional coincidence, {mu}{sub i|s}, and pair coupling, {gamma}{sub c}, and show how each of these parameters can be maximized by varying the focusing of the pump mode and the fiber-matched modes using standard optical elements. Specifically we analyze a periodically poled KTP-crystal pumped by a 532 nm laser creating photon pairs at 810 nm and 1550 nm. Numerical calculations lead to coupling efficiencies above 93% at optimal focusing, which is found by the geometrical relation L/z{sub R} to be {approx_equal}1 to 2 for the pump mode and {approx_equal}2 to 3 for the fiber-modes, where L is the crystal length and z{sub R} is the Rayleigh-range of the mode-profile. These results are independent on L. By showing that the single-mode bandwidth decreases {proportional_to}1/L, we can therefore design the source to produce and couple narrow bandwidth photon pairs well into the fibers. Smaller bandwidth means both less chromatic dispersion for long propagation distances in fibers, and that telecom Bragg gratings can be utilized to compensate for broadened photon packets--a vital problem for time-multiplexed qubits. Longer crystals also yield an increase in fiber photon flux {proportional_to}{radical}(L), and so, assuming correct focusing, we can only see advantages using long crystals.

  11. Characteristic investigation of 2D photonic crystals with full material anisotropy under out-of-plane propagation and liquid-crystal-filled photonic-band-gap-fiber applications using finite element methods.

    PubMed

    Hsu, Sen-ming; Chang, Hung-chun

    2008-12-22

    To effectively investigate the fundamental characteristics of two-dimensional (2D) photonic crystals (PCs) with arbitrary 3D material anisotropy under the out-of-plane wave propagation, we establish a full-vectorial finite element method based eigenvalue algorithm to perform related analysis correctly. The band edge diagrams can be conveniently constructed from the band structures of varied propagation constants obtained from the algorithm, which is helpful for the analysis and design of photonic ban gap (PBG) fibers. Several PCs are analyzed to demonstrate the correctness of this numerical model. Our analysis results for simple PCs are checked with others' ones using different methods, including the transfer matrix method, the finite-difference frequency-domain (FDFD) method, and the plane-wave expansion method. And the validity of those for the most complex PC with arbitrary 3D anisotropy is supported by related liquid-crystal-filled PBG fiber mode analysis, which demonstrates the dependence of transmission properties on the PBGs, employing a full-vectorial finite element beam propagation method (FE-BPM). PMID:19104565

  12. Graphene-channel FETs for photonic frequency double-mixing conversion over the sub-THz band

    NASA Astrophysics Data System (ADS)

    Kawasaki, Tetsuya; Sugawara, Kenta; Dobroiu, Adrian; Eto, Takanori; Kurita, Yuki; Kojima, Kazuki; Yabe, Yuhei; Sugiyama, Hiroki; Watanabe, Takayuki; Suemitsu, Tetsuya; Ryzhii, Victor; Iwatsuki, Katsumi; Fukada, Youichi; Kani, Jun-ichi; Terada, Jun; Yoshimoto, Naoto; Kawahara, Kenji; Ago, Hiroki; Otsuji, Taiichi

    2015-01-01

    We report on photonic frequency double-mixing conversion utilizing a graphene-channel FET (G-FET). Optoelectronic properties of graphene are exploited to perform single-chip photonic double-mixing functionality, which is greatly advantageous in future broadband technological conversion between optical fiber and sub-terahertz wireless communications. A 1 GHz modulation signal on a 125 GHz carrier is electrically input to the gate, whereas a 1.58 μm dual wavelength CW laser beam having a frequency difference of 112.5 GHz impinges on the G-FET. The G-FET works as a photomixer generating a 112.5 GHz local signal which is then electrically mixed to the 1 GHz modulated 125 GHz carrier signal, resulting in the down-conversion of the 1 GHz signal to a 12.5 GHz intermediate frequency (IF) signal.

  13. Modelling the channel-wise count response of a photon-counting spectral CT detector to a broad x-ray spectrum

    NASA Astrophysics Data System (ADS)

    Liu, Xuejin; Chen, Han; Bornefalk, Hans; Danielsson, Mats; Karlsson, Staffan; Persson, Mats; Xu, Cheng; Huber, Ben

    2015-03-01

    Variations among detector channels in CT very sensitively lead to ring artefacts in the reconstructed images. For material decomposition in the projection domain, the variations can result in intolerable biases in the material line integral estimates. A typical way to overcome these effects is to apply calibration methods that try to unify spectral responses from different detector channels to an ideal response from a detector model. However, the calibration procedure can be rather complex and require excessive calibration measurements for a multitude of combinations of x-ray shapes, tissue combinations and thicknesses. In this paper, we propose a channel-wise model for a multibin photon-counting detector for spectral CT. Predictions of this channel-wise model match well with their physical performances, which can thus be used to eliminate ring artefacts in CT images and achieve projection-basis material decomposition. In an experimental validation, image data show significant improvement with respect to ring artefacts compared to images calibrated with flat-fielding data. Projection-based material decomposition gives basis material images showing good separation among individual materials and good quantification of iodine and gadolinium contrast agents. The work indicates that the channel-wise model can be used for quantitative CT with this detector.

  14. Design and demonstration of ultra-fast W-band photonic transmitter-mixer and detectors for 25 Gbits/sec error-free wireless linking.

    PubMed

    Chen, Nan-Wei; Shi, Jin-Wei; Tsai, Hsuan-Ju; Wun, Jhih-Min; Kuo, Fong-Ming; Hesler, Jeffery; Crowe, Thomas W; Bowers, John E

    2012-09-10

    A 25 Gbits/s error-free on-off-keying (OOK) wireless link between an ultra high-speed W-band photonic transmitter-mixer (PTM) and a fast W-band envelope detector is demonstrated. At the transmission end, the high-speed PTM is developed with an active near-ballistic uni-traveling carrier photodiode (NBUTC-PD) integrated with broadband front-end circuitry via the flip-chip bonding technique. Compared to our previous work, the wireless data rate is significantly increased through the improvement on the bandwidth of the front-end circuitry together with the reduction of the intermediate-frequency (IF) driving voltage of the active NBUTC-PD. The demonstrated PTM has a record-wide IF modulation (DC-25 GHz) and optical-to-electrical fractional bandwidths (68-128 GHz, ~67%). At the receiver end, the demodulation is realized with an ultra-fast W-band envelope detector built with a zero-bias Schottky barrier diode with a record wide video bandwidth (37 GHz) and excellent sensitivity. The demonstrated PTM is expected to find applications in multi-gigabit short-range wireless communication. PMID:23037246

  15. Broad band tunable dye laser development

    NASA Astrophysics Data System (ADS)

    Lee, Jong Min; Kim, Jung Bog; Kim, Sung Ho; Go, Do Kyung; Lim, Chang Hwan; Rho, Si Pyo; Song, Kyu Seok; Lee, Byung Cheol; Rhi, Jong Hoon; Han, Jae Min

    1992-12-01

    The technical goal and objectives are the development of a tunable laser which can be tuned from UV to near IR and commercialization for uses in various fields. Two kinds of resonators are developed. The user can select one resonator and change into the other without changing other parts. GIM type has a linewidth of 5 GHz which is able to be used usually, and a SLM type which has a very narrow linewidth of less than 1 GHz. Each system can have one or two amplifiers depending on output power or cost. High stability and safety, cost-down, and modules into about 30 components have been tried. We hope that this laser can help developments in researches of university, industry, and institute.

  16. Broad band sound from wind turbine generators

    NASA Technical Reports Server (NTRS)

    Hubbard, H. H.; Shepherd, K. P.; Grosveld, F. W.

    1981-01-01

    Brief descriptions are given of the various types of large wind turbines and their sound characteristics. Candidate sources of broadband sound are identified and are rank ordered for a large upwind configuration wind turbine generator for which data are available. The rotor is noted to be the main source of broadband sound which arises from inflow turbulence and from the interactions of the turbulent boundary layer on the blade with its trailing edge. Sound is radiated about equally in all directions but the refraction effects of the wind produce an elongated contour pattern in the downwind direction.

  17. Broad-band multisection electrooptic modulators

    NASA Astrophysics Data System (ADS)

    Lax, Benjamin; Marino, Richard M.; Eng, Richard S.

    1988-10-01

    A general solution has been derived for expressing the conversion of power from a base frequency to a modulation sideband using a multisection electrooptic modulator. The objective is to obtain broadband frequency modulation of a laser by the use of multiple collinear electrooptic crystals with microwave power levels well below the breakdown threshold. It is found that segmented structures lead to greater bandwidths, which increase with the number of modulator sections. This is achieved by adjusting the phases of microwaves between sections to maximize the single-sideband conversion efficiency. It is shown that a 10.6-micron CO2 laser modulator with six geometrically identical CdTe sections can potentially achieve a 3-dB bandwidth of nearly 6 GHz using a 10-kW traveling-wave tube operating at 16-GHz center frequency.

  18. High average power, high energy 1.55 μm ultra-short pulse laser beam delivery using large mode area hollow core photonic band-gap fiber.

    PubMed

    Peng, Xiang; Mielke, Michael; Booth, Timothy

    2011-01-17

    We demonstrate high average power, high energy 1.55 μm ultra-short pulse (<1 ps) laser delivery using helium-filled and argon-filled large mode area hollow core photonic band-gap fibers and compare relevant performance parameters. The ultra-short pulse laser beam-with pulse energy higher than 7 μJ and pulse train average power larger than 0.7 W-is output from a 2 m long hollow core fiber with diffraction limited beam quality. We introduce a pulse tuning mechanism of argon-filled hollow core photonic band-gap fiber. We assess the damage threshold of the hollow core photonic band-gap fiber and propose methods to further increase pulse energy and average power handling. PMID:21263632

  19. Analysis of one-dimensional photonic band gap structures with a liquid crystal defect towards development of fiber-optic tunable wavelength filters.

    PubMed

    Del Villar, Ignacio; Matias, Ignacio; Arregui, Francisco; Claus, Richard

    2003-03-10

    A theoretical analysis of a fiber optical photonic band gap based tunable wavelength filter is presented. The design presented here is based on the quarter wave reflector with a liquid crystal defect layer in the middle of the structure. The filter generated by the structure is shifted in wavelength as the voltage applied to the structure is modified. Some critical parameters are analyzed: the effect of the consideration of fiber as the first layer and not the input medium in the shape of the filter, the number of layers of the structure, and the thickness of the defect layer. This last parameter determines the width of the wavelength sweep of the filter, but is limited by the creation of more defects. Some rules of practical implementation of this device are also given. PMID:19461749

  20. Cryogenic testing of the 2.1 GHz five-cell superconducting RF cavity with a photonic band gap coupler cell

    NASA Astrophysics Data System (ADS)

    Arsenyev, Sergey A.; Temkin, Richard J.; Haynes, W. Brian; Shchegolkov, Dmitry Yu.; Simakov, Evgenya I.; Tajima, Tsuyoshi; Boulware, Chase H.; Grimm, Terrence L.; Rogacki, Adam R.

    2016-05-01

    We present results from cryogenic tests of the multi-cell superconducting radio frequency (SRF) cavity with a photonic band gap (PBG) coupler cell. Achieving high average beam currents is particularly desirable for future light sources and particle colliders based on SRF energy-recovery-linacs (ERLs). Beam current in ERLs is limited by the beam break-up instability, caused by parasitic higher order modes (HOMs) interacting with the beam in accelerating cavities. A PBG cell incorporated in an accelerating cavity can reduce the negative effect of HOMs by providing a frequency selective damping mechanism, thus allowing significantly higher beam currents. The multi-cell cavity was designed and fabricated of niobium. Two cryogenic (vertical) tests were conducted. The high unloaded Q-factor was demonstrated at a temperature of 4.2 K at accelerating gradients up to 3 MV/m. The measured value of the unloaded Q-factor was 1.55 × 108, in agreement with prediction.

  1. Strong interlayer coupling mediated giant two-photon absorption in MoS e2 /graphene oxide heterostructure: Quenching of exciton bands

    NASA Astrophysics Data System (ADS)

    Sharma, Rituraj; Aneesh, J.; Yadav, Rajesh Kumar; Sanda, Suresh; Barik, A. R.; Mishra, Ashish Kumar; Maji, Tuhin Kumar; Karmakar, Debjani; Adarsh, K. V.

    2016-04-01

    A complex few-layer MoS e2 /graphene oxide (GO) heterostructure with strong interlayer coupling was prepared by a facile hydrothermal method. In this strongly coupled heterostructure, we demonstrate a giant enhancement of two-photon absorption that is in stark contrast to the reverse saturable absorption of a weakly coupled MoS e2 /GO heterostructure and saturable absorption of isolated MoS e2 . Spectroscopic evidence of our study indicates that the optical signatures of isolated MoS e2 and GO domains are significantly modified in the heterostructure, displaying a direct coupling of both domains. Furthermore, our first-principles calculations indicate that strong interlayer coupling between the layers dramatically suppresses the MoS e2 excitonic bands. We envision that our findings provide a powerful tool to explore different optical functionalities as a function of interlayer coupling, which may be essential for the development of device technologies.

  2. Tellurite glass defect-core spiral photonic crystal fiber with low loss and large negative flattened dispersion over S + C + L + U wavelength bands.

    PubMed

    Hasan, Md Rabiul; Hasan, Md Imran; Anower, Md Shamim

    2015-11-10

    A defected-core spiral photonic crystal fiber is proposed to achieve very large negative flattened dispersion and small confinement loss. Simulation results reveal that the designed structure exhibits very large flattened dispersion over S+C+L+U wavelength bands and an average dispersion of about -720.7  ps nm(-1) km(-1) with an absolute dispersion variation of 12.7  ps nm(-1)  km(-1) over the wavelength ranging from 1.45 to 1.65 μm. The proposed fiber has five air-hole rings in the cladding leading to very small confinement loss of 0.00111  dB/km at the excitation wavelength of 1.55 μm. The tolerance of the fiber dispersion of ±2% changing in the structural parameters is investigated for practical conditions. PMID:26560773

  3. Photonic frequency-quadrupling and balanced pre-coding technologies for W-band QPSK vector mm-wave signal generation based on a single DML

    NASA Astrophysics Data System (ADS)

    Wang, Yanyi; Yang, Chao; Chi, Nan; Yu, Jianjun

    2016-05-01

    We propose a novel scheme for high-frequency quadrature phase shift keying (QPSK) photonic vector signal generation based on a single directly modulated laser (DML) employing photonic frequency quadrupling and balanced pre-coding technologies. In order to realize frequency quadrupling, a wavelength selective switch (WSS) is intruded in our experiment. The intruded WSS combined with DML can not only realize high-frequency vector signal generation but also simplify the architecture. We experimentally demonstrate 1-or 2-Gbaud QPSK vector signal generation at 88 GHz based on our proposed scheme. The generated 1-Gbaud balanced pre-coded QPSK vector signal is transmitted 0.5-m wireless distance with the bit-error-ratio (BER) below hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10-3. To our knowledge, this is the first time to demonstrate W-band mm-wave vector signal based on a single DML with quadrupling frequency and pre-coding technologies.

  4. Optical parametric chirped pulse amplification and spectral shaping of a continuum generated in a photonic band gap fiber.

    PubMed

    Hugonnot, E; Somekh, M; Villate, D; Salin, F; Freysz, E

    2004-05-31

    A chirped pulse, spectrally broadened in a photonic bandgap optical fiber by 120 fs Ti:Sapphire laser pulses, is parametrically amplified in a BBO crystal pumped by a frequency doubled nanosecond Nd:YAG laser pulse. Without changing the frequency of the Ti:Sapphire, a spectral tunability of the amplified pulses is demonstrated. The possibility to achieve broader spectral range amplification is confirmed for a non-collinear pump-signal interaction geometry. For optimal non-collinear interaction geometry, the pulse duration of the original and amplified pulse are similar. Finally, we demonstrate that the combination of two BBO crystals makes it possible to spectrally shape the amplified pulses. PMID:19475076

  5. A heuristic approach to the realization of the wide-band optical diode effect in photonic crystal waveguides

    NASA Astrophysics Data System (ADS)

    Khavasi, Amin; Rezaei, Mohsen; Fard, Ali P.; Mehrany, Khashayar

    2013-07-01

    In this paper a highly efficient optical diode is demonstrated in photonic crystal waveguides with broken spatial symmetry. The structure is made of isotropic linear materials and does not need high power optical beams or strong magnetic fields. While the proposed structure shows almost complete light transmission (>99%) in one direction, it blocks light transmission in the opposite direction. This unidirectional transmission is retained within a wide range of frequencies (>4% of central frequency). In order to achieve an optical diode effect, the optical mode of the waveguide is manipulated by designing an ultra-compact mode converter and an efficient mode filter. The dimensions of the proposed mode converter are less than two wavelengths long.

  6. Band gap engineered P3HT/CdPbS composites for utilization of low energy photons.

    PubMed

    Arora, Leena; Singh, Vidya Nand; Gupta, Poonam; Chhikara, Nitu; Jain, Kiran; Chand, S

    2014-07-01

    In the present study, CdPbS composite has been synthesized in the P3HT matrix in a single step. The synthesis has been carried out at a temperature of 120 degrees C by the decomposition of xanthate compound in the polymer matrix. This synthesis method helps in proper distribution of nanoparticles in the polymer matrix. The synthesized materials were characterized using UV-Vis spectroscopy, X-ray diffraction, transmission electron microcopy, photoluminescence (PL) and time resolved florescence spectroscopy. The P3HT/CdPbS nanoparticle composite can absorb photon in the range of 0.7 eV to 2.7 eV and a charge transfer between CdPbS and P3HT has been observed. It has been proposed that this composite may increase both the Voc as well as Jsc by better utilization of solar spectrum and increased charge transfer. PMID:24757972

  7. The very-broad-band long-base tiltmeters of Grotta Gigante (Trieste, Italy): Secular term tilting and the great Sumatra-Andaman islands earthquake of December 26, 2004

    NASA Astrophysics Data System (ADS)

    Braitenberg, Carla; Romeo, Giovanni; Taccetti, Quintilio; Nagy, Ildikò

    2006-01-01

    The horizontal pendulums of the Grotta Gigante (Giant Cave) in the Trieste Karst, are long-base tiltmeters with Zöllner type suspension. The instruments have been continuously recording tilt and shear in the Grotta Gigante since the date of their installation by Prof. Antonio Marussi in 1966. Their setup has been completely overhauled several times since installation, restricting the interruptions of the measurements though to a minimum. The continuous recordings, apart from some interruptions, cover thus almost 40 years of measurements, producing a very noticeable long-term tiltmeter record of crustal deformation. The original recording system, still in function, was photographic with a mechanical timing and paper-advancing system, which has never given any problems at all, as it is very stable and not vulnerable by external factors as high humidity, problems in power supply, lightning or similar. In December 2003 a new recording system was installed, based on a solid-state acquisition system intercepting a laser light reflected from a mirror mounted on the horizontal pendulum beam. The sampling rate is 30 Hz, which turns the long-base instrument to a very-broad-band tiltmeter, apt to record the tilt signal on a broad-band of frequencies, ranging from secular deformation rate through the earth tides to seismic waves. Here we describe the acquisition system and present two endline members of the instrumental observation, the up to date long-term recording, and the observation of the great Sumatra-Andaman Islands earthquake of December 26, 2004, seismic moment magnitude Mw = 9.1-9.3 [Lay, T., Kanamori, H., Ammon, C.J., Nettles, M., Ward, S.N., Aster, R.C., Beck, S.L., Bilek, S.L., Brudzinski, M.L., Butler, R., DeShon, H.R., Ekström, G., Satake, K., Sipkin, S., 2005. The Great Sumatra-Andaman Earthquake of 26 December 2004. Science. 308, 1127-1133.]. The secular-term observations indicate an average tilting over the last four decades towards NW of 23.4 nrad

  8. Competitive behavior of photons contributing to junction voltage jump in narrow band-gap semiconductor multi-quantum-well laser diodes at lasing threshold

    NASA Astrophysics Data System (ADS)

    Feng, Liefeng; Yang, Xiufang; Li, Yang; Li, Ding; Wang, Cunda; Yao, Dongsheng; Hu, Xiaodong; Li, Hongru

    2015-04-01

    The junction behavior of different narrow band-gap multi-quantum-well (MQW) laser diodes (LDs) confirmed that the jump in the junction voltage in the threshold region is a general characteristic of narrow band-gap LDs. The relative change in the 1310 nm LD is the most obvious. To analyze this sudden voltage change, the threshold region is divided into three stages by Ithl and Ithu, as shown in Fig. 2; Ithl is the conventional threshold, and as long as the current is higher than this threshold, lasing exists and the IdV/dI-I plot drops suddenly; Ithu is the steady lasing point, at which the separation of the quasi-Fermi levels of electron and holes across the active region (Vj) is suddenly pinned. Based on the evolutionary model of dissipative structure theory, the rate equations of the photons in a single-mode LD were deduced in detail at Ithl and Ithu. The results proved that the observed behavior of stimulated emission suddenly substituting for spontaneous emission, in a manner similar to biological evolution, must lead to a sudden increase in the injection carriers in the threshold region, which then causes the sudden increase in the junction voltage in this region.

  9. Competitive behavior of photons contributing to junction voltage jump in narrow band-gap semiconductor multi-quantum-well laser diodes at lasing threshold

    SciTech Connect

    Feng, Liefeng E-mail: lihongru@nankai.edu.cn; Yang, Xiufang; Wang, Cunda; Yao, Dongsheng; Li, Yang; Li, Ding; Hu, Xiaodong; Li, Hongru E-mail: lihongru@nankai.edu.cn

    2015-04-15

    The junction behavior of different narrow band-gap multi-quantum-well (MQW) laser diodes (LDs) confirmed that the jump in the junction voltage in the threshold region is a general characteristic of narrow band-gap LDs. The relative change in the 1310 nm LD is the most obvious. To analyze this sudden voltage change, the threshold region is divided into three stages by I{sub th}{sup l} and I{sub th}{sup u}, as shown in Fig. 2; I{sub th}{sup l} is the conventional threshold, and as long as the current is higher than this threshold, lasing exists and the IdV/dI-I plot drops suddenly; I{sub th}{sup u} is the steady lasing point, at which the separation of the quasi-Fermi levels of electron and holes across the active region (V{sub j}) is suddenly pinned. Based on the evolutionary model of dissipative structure theory, the rate equations of the photons in a single-mode LD were deduced in detail at I{sub th}{sup l} and I{sub th}{sup u}. The results proved that the observed behavior of stimulated emission suddenly substituting for spontaneous emission, in a manner similar to biological evolution, must lead to a sudden increase in the injection carriers in the threshold region, which then causes the sudden increase in the junction voltage in this region.

  10. Optical microfiber-based photonic crystal cavity

    NASA Astrophysics Data System (ADS)

    Yu, Yang; Sun, Yi-zhi; Andrews, Steve; Li, Zhi-yuan; Ding, Wei

    2016-01-01

    Using a focused ion beam milling technique, we fabricate broad stop band (∼10% wide) photonic crystal (PhC) cavities in adiabatically-tapered silica fibers. Abrupt structural design of PhC mirrors efficiently reduces radiation loss, increasing the cavity finesse to ∼7.5. Further experiments and simulations verify that the remaining loss is mainly due to Ga ion implantation. Such a microfiber PhC cavity probably has potentials in many light-matter interaction applications.

  11. Green photonics

    NASA Astrophysics Data System (ADS)

    Quan, Frederic

    2012-02-01

    Photonics, the broad merger of electronics with the optical sciences, encompasses such a wide swath of technology that its impact is almost universal in our everyday lives. This is a broad overview of some aspects of the industry and their contribution to the ‘green’ or environmental movement. The rationale for energy conservation is briefly discussed and the impact of photonics on our everyday lives and certain industries is described. Some opinions from industry are presented along with market estimates. References are provided to some of the most recent research in these areas.

  12. Sub-GHz-resolution C-band Nyquist-filtering interleaver on a high-index-contrast photonic integrated circuit.

    PubMed

    Zhuang, Leimeng; Zhu, Chen; Corcoran, Bill; Burla, Maurizio; Roeloffzen, Chris G H; Leinse, Arne; Schröder, Jochen; Lowery, Arthur J

    2016-03-21

    Modern optical communications rely on high-resolution, high-bandwidth filtering to maximize the data-carrying capacity of fiber-optic networks. Such filtering typically requires high-speed, power-hungry digital processes in the electrical domain. Passive optical filters currently provide high bandwidths with low power consumption, but at the expense of resolution. Here, we present a passive filter chip that functions as an optical Nyquist-filtering interleaver featuring sub-GHz resolution and a near-rectangular passband with 8% roll-off. This performance is highly promising for high-spectral-efficiency Nyquist wavelength division multiplexed (N-WDM) optical super-channels. The chip provides a simple two-ring-resonator-assisted Mach-Zehnder interferometer, which has a sub-cm2 footprint owing to the high-index-contrast Si3N4/SiO2 waveguide, while manifests low wavelength-dependency enabling C-band (> 4 THz) coverage with more than 160 effective free spectral ranges of 25 GHz. This device is anticipated to be a critical building block for spectrally-efficient, chip-scale transceivers and ROADMs for N-WDM super-channels in next-generation optical communication networks. PMID:27136769

  13. Three dimensional reflectance properties of superconductor-dielectric photonic crystal

    NASA Astrophysics Data System (ADS)

    Pandey, G. N.; Pandey, J. P.; Pandey, U. K.; Sancheti, Bhagyashree; Ojha, S. P.

    2016-05-01

    In this present communication, we have studied the optical properties of Photonics Crystals with super conducting constituent using the TMM method for a stratified medium. We also studied the three dimensional reflectance property of superconductor-dielectric photonic crystal at different temperature and thickness. From above study we show that the superconductor-dielectric photonic crystal may be used as broad band reflector and omnidirectional reflector at low temperature below to the critical temperature. Such property may be applied to make of the reflector which can be used in low temperature region.

  14. Investigation on the magneto-optical Voigt effects in surface plasmon modes and anisotropic photonic band gap in the three-dimensional magnetized plasma photonic crystals as the mixed polarized modes considered

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Ding, Guo-Wen

    2014-10-01

    In this paper, the magneto-optical Voigt effects in surface plasmon modes and anisotropic photonic band gaps (PBGs) of the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with face-centered-cubic lattices are theoretically investigated based on the modified plane wave expansion (PWE) method, which are the homogeneous Te (tellurium) spheres immersed in the homogeneous magnetized plasma background, as the mixed polarized modes are considered. The more general condition is considered, and the anisotropic PBGs are not only for the extraordinary and ordinary modes but also for mixed polarized modes. The equations for computing such anisotropic PBGs are theoretically deduced. Theoretical simulations show that the anisotropic PBGs and a flatbands region can be observed in the dispersive curve. Compared to the similar 3D MPPCs containing the isotropic dielectric or uniaxial material spheres, the larger PBGs can be obtained as the extraordinary axis of the inserted uniaxial material is along the Г-H symmetry line although the region of flatbands is also different. However, the relative bandwidths of PBGs for such two cases are almost the same. The interesting properties of surface plasmon modes can also be found, which are that the upper edge of flatbands region cannot be tuned by the filling factor but can almost linearly increase on increasing the plasma frequency and plasma cyclotron frequency (the external magnetic field), respectively. The effects of the filling factor, plasma frequency and plasma cyclotron frequency on the anisotropic PBGs are investigated in detail, respectively. Theoretical calculations also show that such PBGs can be manipulated by the parameters as mentioned above.

  15. Modeling of optical wireless scattering communication channels over broad spectra.

    PubMed

    Liu, Weihao; Zou, Difan; Xu, Zhengyuan

    2015-03-01

    The air molecules and suspended aerosols help to build non-line-of-sight (NLOS) optical scattering communication links using carriers from near infrared to visible light and ultraviolet bands. This paper proposes channel models over such broad spectra. Wavelength dependent Rayleigh and Mie scattering and absorption coefficients of particles are analytically obtained first. They are applied to the ray tracing based Monte Carlo method, which models the photon scattering angle from the scatterer and propagation distance between two consecutive scatterers. Communication link path loss is studied under different operation conditions, including visibility, particle density, wavelength, and communication range. It is observed that optimum communication performances exist across the wavelength under specific atmospheric conditions. Infrared, visible light and ultraviolet bands show their respective features as conditions vary. PMID:26366662

  16. Photonic E-field sensor

    SciTech Connect

    Savchenkov, A. A.; Liang, W.; Ilchenko, V. S.; Dale, E.; Savchenkova, E. A.; Matsko, A. B. Seidel, D.; Maleki, L.

    2014-12-15

    We report on both theoretical and experimental studies of a photonic implementation of the electric (E-) field sensor using a probe made with all-dielectric RF-transparent elements. The geometrical dimensions of the electric field probe can be smaller than the wavelength of the measured electromagnetic field in the material. Our theoretical calculations show that the sensor allows detecting electric fields in a broad frequency range (100 Hz-20 GHz) with sensitivity better than 1 μV/[Hz{sup 1/2} m]. We demonstrate the sensor operating at X-band and validate the theoretical predictions.

  17. Photonic crystal light source

    DOEpatents

    Fleming, James G.; Lin, Shawn-Yu; Bur, James A.

    2004-07-27

    A light source is provided by a photonic crystal having an enhanced photonic density-of-states over a band of frequencies and wherein at least one of the dielectric materials of the photonic crystal has a complex dielectric constant, thereby producing enhanced light emission at the band of frequencies when the photonic crystal is heated. The dielectric material can be a metal, such as tungsten. The spectral properties of the light source can be easily tuned by modification of the photonic crystal structure and materials. The photonic crystal light source can be heated electrically or other heating means. The light source can further include additional photonic crystals that exhibit enhanced light emission at a different band of frequencies to provide for color mixing. The photonic crystal light source may have applications in optical telecommunications, information displays, energy conversion, sensors, and other optical applications.

  18. Light scattering in opal-based photonic crystals

    NASA Astrophysics Data System (ADS)

    Limonov, M. F.

    2010-05-01

    We present a new light scattering pattern in low-contrast opal-based photonic crystals (PhCs). The structure of real opals is always imperfect because of the a-SiO2 particles being inherently inhomogeneous and nonuniform in size and average dielectric permittivity. We found that opals possess all predictable properties of multi-component PhCs, which we define as periodic structures consisting of inhomogeneous or multiple (three or more) components. By theory, by properly tuning the permittivity of one of the components in ordered, low-contrast multi-component PhCs (for instance, of the filler ɛf in an opal), one can produce selective disappearance of any non-resonant (hkl) stop band. A study of transmission spectra of opals revealed that stop bands exhibit different (including resonant) behavior under variation of ɛf. Experiment did not, however, substantiate complete disappearance of stop bands predicted by theory for an ordered PhC. In the region of the predicted disappearance, a new effect has been observed, namely flip-over of the Bragg band, i.e., transformation of the Bragg dip into a Bragg rise. The flip-over effect, which has been studied in considerable detail in the particular example of the (111) stop band, originates from the nonuniformity of a-SiO2 particles. This nonuniformity leads to additional broad-band light scattering, the character of which is determined by Mie scattering. Thus, Mie scattering is responsible for two components in opal transmission spectra, more specifically, narrow Bragg bands and broad-band background. Their interference gives rise to formation of the Fano resonance, which in opal spectra becomes manifest, first, in a Bragg band asymmetry, and, second, in the flip-over effect, i.e., transformation of a photonic stop band into a photonic pass band.

  19. Function photonic crystals

    NASA Astrophysics Data System (ADS)

    Wu, Xiang-Yao; Zhang, Bai-Jun; Yang, Jing-Hai; Liu, Xiao-Jing; Ba, Nuo; Wu, Yi-Heng; Wang, Qing-Cai

    2011-07-01

    In this paper, we present a new kind of function photonic crystals (PCs), whose refractive index is a function of space position. Conventional PCs structure grows from two materials, A and B, with different dielectric constants εA and εB. Based on Fermat principle, we give the motion equations of light in one-dimensional, two-dimensional and three-dimensional function photonic crystals. For one-dimensional function photonic crystals, we give the dispersion relation, band gap structure and transmissivity, and compare them with conventional photonic crystals, and we find the following: (1) For the vertical and non-vertical incidence light of function photonic crystals, there are band gap structures, and for only the vertical incidence light, the conventional PCs have band gap structures. (2) By choosing various refractive index distribution functions n( z), we can obtain more wider or more narrower band gap structure than conventional photonic crystals.

  20. Broad-band spectroscopy of the transient X-ray binary pulsar KS 1947+300 during 2013 giant outburst: Detection of pulsating soft X-ray excess component

    NASA Astrophysics Data System (ADS)

    Epili, Prahlad; Naik, Sachindra; Jaisawal, Gaurava K.

    2016-05-01

    We present the results obtained from detailed timing and spectral studies of the Be/X-ray binary pulsar KS 1947+300 during its 2013 giant outburst. We used data from Suzaku observations of the pulsar at two epochs, i.e. on 2013 October 22 (close to the peak of the outburst) and 2013 November 22. X-ray pulsations at ∼18.81 s were clearly detected in the light curves obtained from both observations. Pulse periods estimated during the outburst showed that the pulsar was spinning up. The pulse profile was found to be single-peaked up to ∼10 keV beyond which a sharp peak followed by a dip-like feature appeared at hard X-rays. The dip-like feature has been observed up to ∼70 keV. The 1–110 keV broad-band spectroscopy of both observations revealed that the best-fit model was comprised of a partially absorbed Negative and Positive power law with EXponential cutoff (NPEX) continuum model along with a blackbody component for the soft X-ray excess and two Gaussian functions at 6.4 and 6.7 keV for emission lines. Both the lines were identified as emission from neutral and He-like iron atoms. To fit the spectra, we included the previously reported cyclotron absorption line at 12.2 keV. From the spin-up rate, the magnetic field of the pulsar was estimated to be ∼1.2×1012 G and found to be comparable to that obtained from the detection of the cyclotron absorption feature. Pulse-phase resolved spectroscopy revealed the pulsating nature of the soft X-ray excess component in phase with the continuum flux. This confirms that the accretion column and/or accretion stream are the most probable regions of the soft X-ray excess emission in KS1947+300. The presence of the pulsating soft X-ray excess in phase with continuum emission may be the possible reason for not observing the dip at soft X-rays.