Unusual large-pitch banding in poly(L-lactic acid): Effects of composition and geometry confinement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woo, Eamor M.; Lugito, Graecia; Hsieh, Ya-Ting

2014-02-24

Lamellar patterns and orientations in blends of two crystalline polymers: poly(ethylene oxide) (PEO) and low-molecular-weight poly(L-lactic acid) (PLLA) were investigated using polarizing light optical microscopy (POM), and atomic and scanning electron microscopy (AFM, SEM). Specific etching off of PEO was used to reveal the complex earlier-grown PLLA lamellae patterns with various PEO content in blends. Banding of extremely long pitch (50 μm) in crystallized PLLA spherulites was induced by two kinetic factors: geometry confinement by top cover and introduction of diluent such as PEO. The mechanisms and correlation among the lamellar assembly, ring bands, and cracks are exemplified. Lamellar patternsmore » and ring-band types in blends were found to vary with respect to not only blend compositions, but also confinement of top-cover.« less

FINAL REPORT: Scalable Methods for Electronic Excitations and Optical Responses of Nanostructures: Mathematics to Algorithms to Observables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chelikowsky, James R.

2013-04-01

Work in nanoscience has increased substantially in recent years owing to its potential technological applications and to fundamental scientific interest. A driving force for this activity is to capitalize on new phenomena that occurs at the nanoscale. For example, the physical confinement of electronic states, i.e., quantum confinement, can dramatically alter the electronic and optical properties of matter. A prime example of this occurs for the optical properties of nanoscale crystals such as those composed of elemental silicon. Silicon in the bulk state is optically inactive due to the small size of the optical gap, which can only be accessedmore » by indirect transitions. However, at the nanoscale, this material becomes optically active. The size of the optical gap is increased by confinement and the conservation of crystal momentum ceases to hold, resulting in the viability of indirect transitions. Our work associated with this grant has focused on developing new scalable algorithms for describing the electronic and optical properties of matter at the nanoscale such as nano structures of silicon and related semiconductor properties.« less

Enhanced optical confinement of dye-doped dielectric nanoparticles using a picosecond-pulsed near-infrared laser

NASA Astrophysics Data System (ADS)

Kittiravechote, A.; Chiang, W.-Y.; Usman, A.; Liau, I.; Masuhara, H.

2014-07-01

We demonstrate a novel strategy to increase the capability of confining numerous dye-doped polymeric nanobeads (diameter 100 nm) with laser trapping. Unlike most classical works of optical trapping that address mainly the stiffness of the optical trap, our work concerns an increase in the number of particles confined near the laser focus. We developed an imaging system of light scattering in which a condenser lamp was employed to illuminate the focal plane of the objective lens, and the scattering of the incoherent light was specifically measured to determine the number of confined nanobeads. In contrast to preceding work that used mainly continuous-wave or femtosecond-pulsed lasers, we employed a picosecond-pulsed laser with the half-wavelength of the laser particularly falling within the absorption band of the dopant. Our results show that the number of doped nanobeads held by the laser is significantly greater than that of the bare nanobeads of the same dimension. In striking contrast, the confinement of the nanobeads of the two types was comparable when a continuous-wave laser of the same wavelength and power was employed. The number of confined dye-doped nanobeads increased nonlinearly with the power of the pulsed laser; this dependence was fitted satisfactorily with a second-order polynomial. Supported by theoretical analysis, we attribute the enhanced confinement of doped nanobeads in part to an increased effective refractive index resulting from two-photon resonance between the optical field of the laser and the dopant of the nanobead. We envisage that our findings would evoke applications that benefit from controlled confinement or aggregation of nanomaterials with the employment of near-infrared pulsed lasers.

Application of Optical Forces in Microphotonic Systems

DTIC Science & Technology

2013-05-01

Experiments are carried out to optically characterize the high-Q guided resonance modes with slot confinement. The evolution of the measured wavelengths...the guided resonant device. Two cross polarizers (PC) are applied before and after the device to cancel out Fabry-Perot noise. TL: tunable laser; MO...carried out to optically characterize the high-Q guided resonance modes with slot confinement. The evolution of the measured wavelengths and quality

Optical properties of Si and Ge nanocrystals: Parameter-free calculations

NASA Astrophysics Data System (ADS)

Ramos, L. E.; Weissker, H.-Ch.; Furthmüller, J.; Bechstedt, F.

2005-12-01

The cover picture of the current issue refers to the Edi-tor's Choice article of Ramos et al. [1]. The paper gives an overview of the electronic and optical properties of silicon and germanium nanocrystals determined by state-of-the-art ab initio methods. Nanocrystals have promising applications in opto-electronic devices, since they can be used to confine electrons and holes and facilitate radiative recombination. Since meas-urements for single nanoparticles are difficult to make, ab initio theoretical investigations become important to understand the mechanisms of luminescence.The cover picture shows nanocrystals of four sizes with tetrahedral coordination whose dangling bonds at the surface are passivated with hydrogen. As often observed in experiments, the nanocrystals are not perfectly spherical, but contain facets. Apart from the size of the nanocrystals, which determines the quantum confinement, the way their dangling bonds are passivated is relevant for their electronic and optical properties. For instance, the passivation with hydroxyls reduces the quantum confine-ment. On the other hand, the oxidation of the silicon nanocrys-tals increases the quantum confinement and reduces the effect of single surface terminations on the gap. Due to the oscillator strengths of the lowest-energy optical transitions, Ge nanocrys-tals are in principle more suitable for opto-electronic applica-tions than Si nanocrystals.The first author, Luis E. Ramos, is a postdoc at the Institute of Solid-State Physics and Optics (IFTO), Friedrich-Schiller University Jena, Germany. He investigates electronic and optical properties of semiconductor nanocrystallites and is a member of the European Network of Excellence NANO-QUANTA and of the European Theoretical Spectroscopy Facility (ETSF).

Heterostructure Quantum Confined Stark Effect Electrooptic Modulators Operating at 938 nm

DTIC Science & Technology

1993-12-01

type of modulator, suitable for use in optical interconnects, is an asymmetric Fabry-Perot reflection modulator (ARM). This type of an intensity ...calibrated spectrometer/diode array (Princeton Instruments Model ST-100) used in conjunction with an optical multichannel analyzer (OMA). The transmission...AD-A279 342 -" RL-TR-93-259 In -House Report December 1993N~I HETEROSTRUCTURE QUANTUM CONFINED STARK EFFECT ELECTRO- OPTIC MODULATORS OPERATING AT 938

Performance analysis of all-optical XOR gate with photonic crystal semiconductor optical amplifier-assisted Mach-Zehnder interferometer at 160 Gb/s

NASA Astrophysics Data System (ADS)

Kotb, Amer; Zoiros, Kyriakos E.

2017-11-01

The photonic crystal (PC) can be used to prohibit, confine, or control the propagation of light in a photonic band-gap. The performance of an ultrafast exclusive disjunction (XOR) gate-implemented with a photonic crystal semiconductor optical amplifier (PC-SOA)-assisted Mach-Zehnder interferometer (MZI) is numerically investigated and analyzed at a data rate of 160 Gb/s. The impact of the data signals and PC-SOA's critical parameters on the output quality factor (Q-factor) is examined and assessed. The simulation results demonstrate that the XOR gate which is based on the proposed scheme is capable of operating at the target data rate with logical correctness and high quality. This is achieved with better performance than when having conventional SOAs in the MZI, which justifies employing PC-SOAs as nonlinear elements.

Optical measures of dust velocities and direction during loss of vacuum accidents in confined environment and correlation between dust positions and properties with the resuspension degrees and the velocity modules

NASA Astrophysics Data System (ADS)

Andrea, Malizia; Rossi, Riccardo; Gaudio, Pasquale

2017-08-01

Dust explosions are dangerous events that still today represent a risk to all the industries that produce and/or handle combustible dust like the agro-alimentary, pharmaceutical and energy ones. When a dust cloud is dispersed in an oxidant gas, like air, it may reach the explosive concentration range. A model to predict the dust critical conditions, that can cause explosions, is a key factor for safety of operators and the security of the plants. The key point to predict this dust resuspension is to measure the velocity vectors of dust under the accidental conditions. In order to achieve this goal the authors have developed an experimental facility, STARDUST-U, which allow to obtain different conditions of temperature and pressurization rates characteristic of accidents in confined environment. The authors have developed also optical methods and software to analyse different dust resuspension phenomena under different conditions in confined environment. In this paper, the author will present how they measure the dust velocity vectors in different experimental conditions (and for different type of dusts) and how they have related the dust characteristics and positions inside STARDUST-U with the resuspension degree and the velocity values.

Particle trapping in 3-D using a single fiber probe with an annular light distribution.

PubMed

Taylor, R; Hnatovsky, C

2003-10-20

A single optical fiber probe has been used to trap a solid 2 ìm diameter glass bead in 3-D in water. Optical confinement in 2-D was produced by the annular light distribution emerging from a selectively chemically etched, tapered, hollow tipped metalized fiber probe. Confinement of the bead in 3-D was achieved by balancing an electrostatic force of attraction towards the tip and the optical scattering force pushing the particle away from the tip.

Electronic and optical properties of exciton, trions and biexciton in II-VI parabolic quantum dot

NASA Astrophysics Data System (ADS)

Sujanah, P.; John Peter, A.; Woo Lee, Chang

2015-08-01

Binding energies of exciton, trions and biexciton and their interband optical transition energies are studied in a CdTe/ZnTe quantum dot nanostructure taking into consideration the geometrical confinement effect. The radial spread of the wavefunctions, binding energies, optical transition energies, oscillator strength, radiative life time and the absorption coefficients of exciton, positively and negatively charged excitons and biexciton are carried out. It is found that the ratio of the radiative life time of exciton with the trions and biexciton enhances with the reduction of geometrical confinement. The results show that (i) the binding energies of exciton, positive and negative trions and the biexciton have strong influence on the reduction of geometrical confinement effect, (ii) the binding energy is found to decrease from the binding energies of exciton to positive trion through biexciton and negative trion binding energies, (iii) the oscillator strength of trions is found to be lesser than exciton and the biexciton and (iv) the electronic and optical properties of exciton, trions and the biexciton are considerably dependent on the spatial confinement, incident photon energy and the radiative life time. The obtained results are in good agreement with the other existing literature.

Controlling the state of polarization via optical nanoantenna feeding with surface plasmon polaritons

NASA Astrophysics Data System (ADS)

Xie, Yu-Bo; Liu, Zheng-Yang; Wang, Qian-Jin; Sun, Guang-Hou; Zhang, Xue-Jin; Zhu, Yong-Yuan

2016-03-01

Optical nanoantennas, usually referring to metal structures with localized surface plasmon resonance, could efficiently convert confined optical energy to free-space light, and vice versa. But it is difficult to manipulate the confined visible light energy for its nanoscale spatial extent. Here, a simple method is proposed to solve this problem by controlling surface plasmon polaritons to indirectly manipulate the localized plasmons. As a proof of principle, we demonstrate an optical rotation device which is a grating with central circular polarization optical nanoantenna. It realized the arbitrary optical rotation of linear polarized light by controlling the retard of dual surface plasmon polaritons sources from both side grating structures. Furthermore, we use a two-parameter theoretical model to explain the experimental results.

Strong confinement of optical fields using localized surface phonon polaritons in cubic boron nitride.

PubMed

Chatzakis, Ioannis; Krishna, Athith; Culbertson, James; Sharac, Nicholas; Giles, Alexander J; Spencer, Michael G; Caldwell, Joshua D

2018-05-01

Phonon polaritons (PhPs) are long-lived electromagnetic modes that originate from the coupling of infrared (IR) photons with the bound ionic lattice of a polar crystal. Cubic-boron nitride (cBN) is such a polar, semiconductor material which, due to the light atomic masses, can support high-frequency optical phonons. Here we report on random arrays of cBN nanostructures fabricated via an unpatterned reactive ion etching process. Fourier-transform infrared reflection spectra suggest the presence of localized surface PhPs within the reststrahlen band, with quality factors in excess of 38 observed. These can provide the basis of next-generation IR optical components such as antennas for communication, improved chemical spectroscopies, and enhanced emitters, sources, and detectors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slipchenko, S. O., E-mail: serghpl@mail.ioffe.ru; Podoskin, A. A.; Pikhtin, N. A.

Threshold conditions for generation of a closed mode in the crystal of the Fabry-Perot semiconductor laser with a quantum-well active region are analyzed. It is found that main parameters affecting the closed mode lasing threshold for the chosen laser heterostructure are as follows: the optical loss in the passive region, the optical confinement factor of the closed mode in the gain region, and material gain detuning. The relations defining the threshold conditions for closed mode lasing in terms of optical and geometrical characteristics of the semiconductor laser are derived. It is shown that the threshold conditions can be satisfied atmore » a lower material gain in comparison with the Fabry-Perot cavity mode due to zero output loss for the closed mode.« less

Laser absorption spectroscopy of oxygen confined in highly porous hollow sphere xerogel.

PubMed

Yang, Lin; Somesfalean, Gabriel; He, Sailing

2014-02-10

An Al2O3 xerogel with a distinctive microstructure is studied for the application of laser absorption spectroscopy of oxygen. The xerogel has an exceptionally high porosity (up to 88%) and a large pore size (up to 3.6 µm). Using the method of gas-in-scattering media absorption spectroscopy (GASMAS), a long optical path length (about 3.5m) and high enhancement factor (over 300 times) are achieved as the result of extremely strong multiple-scattering when the light is transmitted through the air-filled, hollow-sphere alumina xerogel. We investigate how the micro-physical feature influences the optical property. As part of the optical sensing system, the material's gas exchange dynamics are also experimentally studied.

Generation of highly confined photonic nanojet using crescent-shape refractive index profile in microsphere

NASA Astrophysics Data System (ADS)

Patel, H. S.; Kushwaha, P. K.; Swami, M. K.

2018-05-01

Photonic nanojets (PNJs) owing to their sub-wavelength near-field features have found many interesting applications like nanoscopy, nano photolithography, high density optical storage, enhancement of Raman signal and single molecule spectroscopy etc. More recently, the focus of research has been on tailoring of PNJs either for better confinement and thus higher peak intensity or for elongation of nanojet for high resolution far field applications. In this paper, we show that crescent-shape refractive index profile (CSRP) of microspheres can be used to generate highly confined PNJ. By optimizing the refractive index of different layers in CSRP microsphere, we show a free space confinement down to ∼ λ / 4 . 5 (FWHM ∼ 110 nm for excitation with 500 nm wavelength). Further, it was observed that the optical properties of substrates also modulate the PNJ characteristics and lead to a further improvement in the transverse confinement to ∼ λ / 6 . 7.

Intraband Raman laser gain in a boron nitride coupled quantum well

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moorthy, N. Narayana; Peter, A. John, E-mail: a.john.peter@gmail.com

2016-05-23

On-centre impurity related electronic and optical properties are studied in a Boron nitride coupled quantum well. Confined energies for the intraband transition are investigated by studying differential cross section of electron Raman scattering taking into consideration of spatial confinement in a B{sub 0.3}Ga{sub 0.7}N/BN coupled quantum well. Raman gain as a function of incident optical pump intensity is computed for constant well width. The enhancement of Raman gain is observed with the application of pump power. The results can be applied for the potential applications for fabricating some optical devices such as optical switches, infrared photo-detectors and electro-optical modulator.

Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kushwaha, Manvir S.

2014-12-15

Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes) – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorptionmore » in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level transitions are seen to be forbidden. The spherical quantum dots have an edge over the strictly two-dimensional quantum dots in that the additional (magnetic) quantum number makes the physics richer (but complex). A deeper grasp of the Coulomb blockade, quantum coherence, and entanglement can lead to a better insight into promising applications involving lasers, detectors, storage devices, and quantum computing.« less

Split-wedge antennas with sub-5 nm gaps for plasmonic nanofocusing

DOE PAGES

Chen, Xiaoshu; Lindquist, Nathan C.; Klemme, Daniel J.; ...

2016-11-22

Here, we present a novel plasmonic antenna structure, a split-wedge antenna, created by splitting an ultrasharp metallic wedge with a nanogap perpendicular to its apex. The nanogap can tightly confine gap plasmons and boost the local optical field intensity in and around these opposing metallic wedge tips. This three-dimensional split-wedge antenna integrates the key features of nanogaps and sharp tips, i.e., tight field confinement and three-dimensional nanofocusing, respectively, into a single platform. We fabricate split-wedge antennas with gaps that are as small as 1 nm in width at the wafer scale by combining silicon V-grooves with template stripping and atomicmore » layer lithography. Computer simulations show that the field enhancement and confinement are stronger at the tip–gap interface compared to what standalone tips or nanogaps produce, with electric field amplitude enhancement factors exceeding 50 when near-infrared light is focused on the tip–gap geometry. The resulting nanometric hotspot volume is on the order of λ 3/10 6. Experimentally, Raman enhancement factors exceeding 10 7 are observed from a 2 nm gap split-wedge antenna, demonstrating its potential for sensing and spectroscopy applications.« less

Split-Wedge Antennas with Sub-5 nm Gaps for Plasmonic Nanofocusing

PubMed Central

2016-01-01

We present a novel plasmonic antenna structure, a split-wedge antenna, created by splitting an ultrasharp metallic wedge with a nanogap perpendicular to its apex. The nanogap can tightly confine gap plasmons and boost the local optical field intensity in and around these opposing metallic wedge tips. This three-dimensional split-wedge antenna integrates the key features of nanogaps and sharp tips, i.e., tight field confinement and three-dimensional nanofocusing, respectively, into a single platform. We fabricate split-wedge antennas with gaps that are as small as 1 nm in width at the wafer scale by combining silicon V-grooves with template stripping and atomic layer lithography. Computer simulations show that the field enhancement and confinement are stronger at the tip–gap interface compared to what standalone tips or nanogaps produce, with electric field amplitude enhancement factors exceeding 50 when near-infrared light is focused on the tip–gap geometry. The resulting nanometric hotspot volume is on the order of λ3/106. Experimentally, Raman enhancement factors exceeding 107 are observed from a 2 nm gap split-wedge antenna, demonstrating its potential for sensing and spectroscopy applications. PMID:27960527

Optical gain in 1.3-μm electrically driven dilute nitride VCSOAs

PubMed Central

2014-01-01

We report the observation of room-temperature optical gain at 1.3 μm in electrically driven dilute nitride vertical cavity semiconductor optical amplifiers. The gain is calculated with respect to injected power for samples with and without a confinement aperture. At lower injected powers, a gain of almost 10 dB is observed in both samples. At injection powers over 5 nW, the gain is observed to decrease. For nearly all investigated power levels, the sample with confinement aperture gives slightly higher gain. PMID:24417791

Fabrication and Testing of Microfluidic Optomechanical Oscillators

PubMed Central

Han, Kewen; Kim, Kyu Hyun; Kim, Junhwan; Lee, Wonsuk; Liu, Jing; Fan, Xudong; Carmon, Tal; Bahl, Gaurav

2014-01-01

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained. PMID:24962013

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bissa, Shivangi; Naruka, Preeti; Bishnoi, Nidhi

In the present study the dielectric optical response of various nanostructures of ZnO deposited on silica substrate has been studied using Maxwell-Garnett Effective Medium Theory. Using the volume filling factors for different nanostructures of ZnO the effective dielectric constant has been evaluated. The variation of this effective dielectric constant with the frequency of applied signal has been investigated. Moreover, the reflectance of the film, power absorption and variation of refractive index with frequency has been studied. The results obtained show that the quantum confinement effects in ZnO nano-structural films deposited on silica substrate give rise to distinct optical properties makingmore » it an ideal choice for high power THz generation.« less

Magneto-optical mode conversion in a hybrid glass waveguide made by sol-gel and ion-exchange techniques

NASA Astrophysics Data System (ADS)

Royer, François; Amata, Hadi; Parsy, François; Jamon, Damien; Ghibaudo, Elise; Broquin, Jean-Emmanuel; Neveu, Sophie

2012-01-01

The integration of magneto-optical materials with classical technologies being still a difficult problem, this study explores the possibility to realize a mode converter based on a hybrid structure. A composite magneto-optical layer made of a silica/zirconia matrix doped by magnetic nanoparticles is coated on the top face of ion-exchanged glass waveguides. Optical characterizations that have been carried out demonstrated the efficiency of these hybrid structures in terms of lateral confinement. Furthermore, TE to TM mode conversion has been observed when a longitudinal magnetic field is applied to the device. The amount of this conversion is analysed taking into account the magneto-optical confinement and the modal birefringence of the structure.

Progress and challenges in electrically pumped GaN-based VCSELs

NASA Astrophysics Data System (ADS)

Haglund, A.; Hashemi, E.; Bengtsson, J.; Gustavsson, J.; Stattin, M.; Calciati, M.; Goano, M.

2016-04-01

ABSTRACT The Vertical-Cavity Surface-Emitting Laser (VCSEL) is an established optical source in short-distance optical communication links, computer mice and tailored infrared power heating systems. Its low power consumption, easy integration into two-dimensional arrays, and low-cost manufacturing also make this type of semiconductor laser suitable for application in areas such as high-resolution printing, medical applications, and general lighting. However, these applications require emission wavelengths in the blue-UV instead of the established infrared regime, which can be achieved by using GaN-based instead of GaAs-based materials. The development of GaN-based VCSELs is challenging, but during recent years several groups have managed to demonstrate electrically pumped GaN-based VCSELs with close to 1 mW of optical output power and threshold current densities between 3-16 kA/cm2. The performance is limited by challenges such as achieving high-reflectivity mirrors, vertical and lateral carrier confinement, efficient lateral current spreading, accurate cavity length control and lateral optical mode confinement. This paper summarizes different strategies to solve these issues in electrically pumped GaN-VCSELs together with state-of-the-art results. We will highlight our work on combined transverse current and optical mode confinement, where we show that many structures used for current confinement result in unintentionally optically anti-guided resonators. Such resonators can have a very high optical loss, which easily doubles the threshold gain for lasing. We will also present an alternative to the use of distributed Bragg reflectors as high-reflectivity mirrors, namely TiO2/air high contrast gratings (HCGs). Fabricated HCGs of this type show a high reflectivity (>95%) over a 25 nm wavelength span.

Molecular Dynamics of Flexible Polar Cations in a Variable Confined Space: Toward Exceptional Two-Step Nonlinear Optical Switches.

PubMed

Xu, Wei-Jian; He, Chun-Ting; Ji, Cheng-Min; Chen, Shao-Li; Huang, Rui-Kang; Lin, Rui-Biao; Xue, Wei; Luo, Jun-Hua; Zhang, Wei-Xiong; Chen, Xiao-Ming

2016-07-01

The changeable molecular dynamics of flexible polar cations in the variable confined space between inorganic chains brings about a new type of two-step nonlinear optical (NLO) switch with genuine "off-on-off" second harmonic generation (SHG) conversion between one NLO-active state and two NLO-inactive states. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optical properties of monolayer MoS2 nanoribbons

NASA Astrophysics Data System (ADS)

Wei, Guohua; Lenferink, Erik J.; Stern, Nathaniel P.

Confinement of carriers in semiconductors is a powerful mechanism for manipulating optical and electronic properties of materials. Although atomically-thin monolayer semiconductors such as transition metal dichalcogenides naturally confine carriers in the out-of-plane direction, achieving appreciable confinement effects in the in-plane dimensions is less well-studied because their optical processes are dominated by tightly bound excitons. In earlier work, we have shown that lateral confinement effects can be controlled in monolayer MoS2 using high-resolution top-down nanopatterning. Here, we use similar techniques to create monolayer MoS2 nanoribbons that exhibit size-tunable photoluminescence and anisotropic Raman scattering. Our process also allows characterization of transport properties of the nanoribbons. This approach demonstrates how dimensionality influences monolayer semiconductors, which could impact charge and valley dynamics relevant to nano-scale opto-electronic devices. This work is supported by ISEN and ONR (N00014-16-1-3055). Use of the Center for Nanoscale Materials was supported by DOE Contract No. DE-AC02-06CH11357. N.P.S. is an Alfred P. Sloan Research Fellow.

Active material, optical mode and cavity impact on nanoscale electro-optic modulation performance

NASA Astrophysics Data System (ADS)

Amin, Rubab; Suer, Can; Ma, Zhizhen; Sarpkaya, Ibrahim; Khurgin, Jacob B.; Agarwal, Ritesh; Sorger, Volker J.

2017-10-01

Electro-optic modulation is a key function in optical data communication and possible future optical compute engines. The performance of modulators intricately depends on the interaction between the actively modulated material and the propagating waveguide mode. While a variety of high-performance modulators have been demonstrated, no comprehensive picture of what factors are most responsible for high performance has emerged so far. Here we report the first systematic and comprehensive analytical and computational investigation for high-performance compact on-chip electro-optic modulators by considering emerging active materials, model considerations and cavity feedback at the nanoscale. We discover that the delicate interplay between the material characteristics and the optical mode properties plays a key role in defining the modulator performance. Based on physical tradeoffs between index modulation, loss, optical confinement factors and slow-light effects, we find that there exist combinations of bias, material and optical mode that yield efficient phase or amplitude modulation with acceptable insertion loss. Furthermore, we show how material properties in the epsilon near zero regime enable reduction of length by as much as by 15 times. Lastly, we introduce and apply a cavity-based electro-optic modulator figure of merit, Δλ/Δα, relating obtainable resonance tuning via phase shifting relative to the incurred losses due to the fundamental Kramers-Kronig relations suggesting optimized device operating regions with optimized modulation-to-loss tradeoffs. This work paves the way for a holistic design rule of electro-optic modulators for high-density on-chip integration.

High quality factor surface Fabry-Perot cavity of acoustic waves

NASA Astrophysics Data System (ADS)

Xu, Yuntao; Fu, Wei; Zou, Chang-ling; Shen, Zhen; Tang, Hong X.

2018-02-01

Surface acoustic wave (SAW) resonators are critical components in wireless communications and many sensing applications. They have also recently emerged as a subject of study in quantum acoustics at the single phonon level. Acoustic loss reduction and mode confinement are key performance factors in SAW resonators. Here, we report the design and experimental realization of high quality factor Fabry-Perot SAW resonators formed in between the tapered phononic crystal mirrors patterned on a GaN-on-sapphire material platform. The fabricated SAW resonators are characterized by both an electrical network analyzer and an optical heterodyne vibrometer. We observed standing Rayleigh waves inside the cavity, with an intrinsic quality factor exceeding 1.3 × 104 at ambient conditions.

Probing the ultimate plasmon confinement limits with a van der Waals heterostructure.

PubMed

Alcaraz Iranzo, David; Nanot, Sébastien; Dias, Eduardo J C; Epstein, Itai; Peng, Cheng; Efetov, Dmitri K; Lundeberg, Mark B; Parret, Romain; Osmond, Johann; Hong, Jin-Yong; Kong, Jing; Englund, Dirk R; Peres, Nuno M R; Koppens, Frank H L

2018-04-20

The ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing, and nanoscale lasers. Although plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the length scale of one atom. This is achieved through far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric spacer between graphene and metal rods. A theoretical model that takes into account the nonlocal optical response of both graphene and metal is used to describe the results. These ultraconfined plasmonic modes, addressed with far-field light excitation, enable a route to new regimes of ultrastrong light-matter interactions. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tadesse, Semere A.; School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455; Li, Huan

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. Ourmore » system demonstrates a scalable optomechanical platform where strong acousto-optic coupling between cavity-confined photons and high frequency traveling phonons can be explored.« less

Micromanipulation and physiological monitoring of cells using two-photon excited fluorescence in cw laser tweezers

NASA Astrophysics Data System (ADS)

Sonek, Gregory J.; Liu, Yagang; Berns, Michael W.; Tromberg, Bruce J.

1996-05-01

We report the observation of two-photon fluorescence excitation and cell confinement, simultaneously, in a continuous-wave (cw) single-beam gradient force optical trap, and demonstrate its use as an in-situ probe to study the physiological state of an optically confined cell sample. At the wavelength of 1064 nm, a single focused gaussian laser beam is used to simultaneously confine, and excite visible fluorescence from, a human sperm cell that has been tagged with propidium iodide, a exogenous fluorescent dye that functions as a viability assay of cellular physiological state. The intensity at the dye peak emission wavelength of 620 nm exhibits a near-square-law dependence on incident trapping beam photon laser power, a behavior consistent with a two-photon absorption process. In addition, for a sperm cell held stationary in the optical tweezers for a period of several minutes at a constant trapping power, red fluorescence emission was observed to increase the time, indicating that the cell has gradually transitioned between a live and dead state. Two-photon excited fluorescence was also observed in chinese hamster ovary cells that were confined by cw laser tweezers and stained with either propidium iodide or Snarf, a pH-sensitive dye probe. These results suggest that, for samples suitably tagged with fluorescent probes and vital stains, optical tweezers can be used to generate their own in-situ diagnostic optical probes of cellular viability or induced photodamage, via two-photon processes.

Quantum Confined Semiconductors

DTIC Science & Technology

2015-02-01

diodes [8-10], metamaterials [11-13], and solar cells [14,15]. As a consequence, the optical and electrical stability of colloidal quantum dots...PbS quantum dot solar cells with high fill factor,” ACS Nano, 4 (7), 3743–3752 (2010). [15] Gur, I., Fromer, N. A., Geier, M. L. and Alivisatos, A...P., “Air-stable all-inorganic nanocrystal solar cells processed from solution,” Sci. 310, 462–465 (2005). [16] Dai, Q., Wang, Y. N., Zhang, Y

Imaging of the 3D dynamics of flagellar beating in human sperm.

PubMed

Silva-Villalobos, F; Pimentel, J A; Darszon, A; Corkidi, G

2014-01-01

The study of the mechanical and environmental factors that regulate a fundamental event such as fertilization have been subject of multiple studies. Nevertheless, the microscopical size of the spermatozoa and the high beating frequency of their flagella (up to 20 Hz) impose a series of technological challenges for the study of the mechanical factors implicated. Traditionally, due to the inherent characteristics of the rapid sperm movement, and to the technological limitations of microscopes (optical or confocal) to follow in three dimensions (3D) their movement, the analysis of their dynamics has been studied in two dimensions, when the head is confined to a surface. Flagella propel sperm and while their head can be confined to a surface, flagellar movement is not restricted to 2D, always displaying 3D components. In this work, we present a highly novel and useful tool to analyze sperm flagella dynamics in 3D. The basis of the method is a 100 Hz oscillating objective mounted on a bright field optical microscope covering a 16 microns depth space at a rate of ~ 5000 images per second. The best flagellum focused subregions were associated to their respective Z real 3D position. Unprecedented graphical results making evident the 3D movement of the flagella are shown in this work and supplemental material illustrating a 3D animation using the obtained experimental results is also included.

Determining the confined optical length of high index vertical Si nanoforest arrays for photonic applications

NASA Astrophysics Data System (ADS)

Chaliyawala, Harsh A.; Purohit, Zeel; Khanna, Sakshum; Ray, Abhijit; Pati, Ranjan K.; Mukhopadhyay, Indrajit

2018-06-01

The structural and the optical properties of different Si nanostructures have been compared. Detailed optical properties of Si nanowires arrays of different optical lengths, fabricated by facile electroless etching technique, have been reported. The theoretical calculation of exponential sine profile at constant λ = 600 nm shows a better explanation in terms of gradient index with optical length for vertical nanowires. The observations signify the possibility of strong light trapping due to an exponential gradient towards the high index along the nanowires and the existence of dense subwavelength features. The optical admittance (Ƶ) shows a strong impact on optical distance (Z) for Z < H, owing to the electromagnetic wave interaction with the nanowires that perceive a different Ƶ at the oblique angle of incidence (AOI). In addition, the experimental reflectance data and the theoretical model for transverse electric and transverse magnetic modes predict that an optical length of 5 μm can exhibit a very low reflectance value. This indicates that the Si nanowires are polarization insensitive over a wide range of AOI (0°-80°). Moreover, Raman spectra showed a very strong light confinement effect in the first order transverse optical band with increasing etching depths. The morphological dependent resonance theory predicts a strong localized light field confinement in the lower wavelength regime for SiNWs. The effect on the strong resonant absorption modes was further correlated with the simulation results obtained by using COMSOL. The obtained results are likely to enhance the maximum absorption of SiNWs for various photonic applications.

Theory for n-type doped, tensile-strained Ge-Si(x)Ge(y)Sn1-x-y quantum-well lasers at telecom wavelength.

PubMed

Chang, Guo-En; Chang, Shu-Wei; Chuang, Shun Lien

2009-07-06

We propose and develop a theoretical gain model for an n-doped, tensile-strained Ge-Si(x)Ge(y)Sn(1-x-y) quantum-well laser. Tensile strain and n doping in Ge active layers can help achieve population inversion in the direct conduction band and provide optical gain. We show our theoretical model for the bandgap structure, the polarization-dependent optical gain spectrum, and the free-carrier absorption of the n-type doped, tensile-strained Ge quantum-well laser. Despite the free-carrier absorption due to the n-type doping, a significant net gain can be obtained from the direct transition. We also present our waveguide design and calculate the optical confinement factors to estimate the modal gain and predict the threshold carrier density.

Tuning direct bandgap GeSn/Ge quantum dots' interband and intraband useful emission wavelength: Towards CMOS compatible infrared optical devices

NASA Astrophysics Data System (ADS)

Baira, Mourad; Salem, Bassem; Madhar, Niyaz Ahamad; Ilahi, Bouraoui

2018-05-01

In this work, interband and intraband optical transitions from direct bandgap strained GeSn/Ge quantum dots are numerically tuned by evaluating the confined energies for heavy holes and electrons in D- and L-valley. The practically exploitable emission wavelength ranges for efficient use in light emission and sensing should fulfill specific criteria imposing the electrons confined states in D-valley to be sufficiently below those in L-valley. This study shows that GeSn quantum dots offer promising opportunity towards high efficient group IV based infrared optical devices operating in the mid-IR and far-IR wavelength regions.

An Optical Trap for Relativistic Plasma

NASA Astrophysics Data System (ADS)

Zhang, Ping

2002-11-01

Optical traps have achieved remarkable success recently in confining ultra-cold matter.Traps capable of confining ultra-hot matter, or plasma, have also been built for applications such as basic plasma research and thermonuclear fusion. For instance, low-density plasmas with temperature less than 1 keV have been confined with static magnetic fields in Malmberg-Penning traps. Low-density 10-50 keV plasmas are confined in magnetic mirrors and tokamaks. High density plasmas have been trapped in optical traps with kinetic energies up to 10 keV [J. L. Chaloupka and D. D. Meyerhofer, Phys. Rev. Lett. 83, 4538 (1999)]. We present the results of experiment, theory and numerical simulation on an optical trap capable of confining relativistic plasma. A stationary interference grating with submicron spacing is created when two high-power (terawatt) laser pulses of equal wavelength (1-micron) are focused from orthogonal directions to the same point in space and time in high density underdense plasma. Light pressure gradients bunch electrons into sheets located at the minima of the interference pattern. The density of the bunched electrons is found to be up to ten times the background density, which is orders-of-magnitude above that previously reported for other optical traps or plasma waves. The amplitudes and frequencies of multiple satellites in the scattered spectrum also indicate the presence of a highly nonlinear ion wave and an electron temperature about 100 keV. Energy transfer from the stronger beam to the weaker beam is also observed. Potential applications include a test-bed for detailed studies of relativistic nonlinear scattering, a positron source and an electrostatic wiggler. This research is also relevant to fast igniter fusion or ion acceleration experiments, in which laser pulses with intensities comparable to those used in the experiment may also potentially beat [Y. Sentoku, et al., Appl. Phys. B 74, 207215 (2002)]. The details of a specific application, the injection of electrons into laser-driven plasma waves, will also be presented. With crossed beams, the energy of a laser-accelerated electron beam is increased and its emittance is decreased compared with a single beam, potentially paving the way towards an all-optical monoenergetic electron injector.

Tailoring the Spectroscopic Properties of Semiconductor Nanowires via Surface-Plasmon-Based Optical Engineering

PubMed Central

2014-01-01

Semiconductor nanowires, due to their unique electronic, optical, and chemical properties, are firmly placed at the forefront of nanotechnology research. The rich physics of semiconductor nanowire optics arises due to the enhanced light–matter interactions at the nanoscale and coupling of optical modes to electronic resonances. Furthermore, confinement of light can be taken to new extremes via coupling to the surface plasmon modes of metal nanostructures integrated with nanowires, leading to interesting physical phenomena. This Perspective will examine how the optical properties of semiconductor nanowires can be altered via their integration with highly confined plasmonic nanocavities that have resulted in properties such as orders of magnitude faster and more efficient light emission and lasing. The use of plasmonic nanocavities for tailored optical absorption will also be discussed in order to understand and engineer fundamental optical properties of these hybrid systems along with their potential for novel applications, which may not be possible with purely dielectric cavities. PMID:25396030

Optically controlled resonant tunneling in a double-barrier diode

NASA Astrophysics Data System (ADS)

Kan, S. C.; Wu, S.; Sanders, S.; Griffel, G.; Yariv, A.

1991-03-01

The resonant tunneling effect is optically enhanced in a GaAs/GaAlAs double-barrier structure that has partial lateral current confinement. The peak current increases and the valley current decreases simultaneously when the device surface is illuminated, due to the increased conductivity of the top layer of the structure. The effect of the lateral current confinement on the current-voltage characteristic of a double-barrier resonant tunneling structure was also studied. With increased lateral current confinement, the peak and valley current decrease at a different rate such that the current peak-to-valley ratio increases up to three times. The experimental results are explained by solving the electrostatic potential distribution in the structure using a simple three-layer model.

Effects of quantum confinement and shape on band gap of core/shell quantum dots and nanowires

NASA Astrophysics Data System (ADS)

Gao, Faming

2011-05-01

A quantum confinement model for nanocrystals developed is extended to study for the optical gap shifts in core/shell quantum dots and nanowires. The chemical bond properties and gap shifts in the InP/ZnS, CdSe/CdS, CdSe/ZnS, and CdTe/ZnS core/shell quantum dots are calculated in detail. The calculated band gaps are in excellent agreement with experimental values. The effects of structural taping and twinning on quantum confinement of InP and Si nanowires are elucidated. It is found theoretically that a competition between the positive Kubo energy-gap shift and the negative surface energy shift plays the crucial role in the optical gaps of these nanosystems.

High power diode laser Master Oscillator-Power Amplifier (MOPA)

NASA Technical Reports Server (NTRS)

Andrews, John R.; Mouroulis, P.; Wicks, G.

1994-01-01

High power multiple quantum well AlGaAs diode laser master oscillator - power amplifier (MOPA) systems were examined both experimentally and theoretically. For two pass operation, it was found that powers in excess of 0.3 W per 100 micrometers of facet length were achievable while maintaining diffraction-limited beam quality. Internal electrical-to-optical conversion efficiencies as high as 25 percent were observed at an internal amplifier gain of 9 dB. Theoretical modeling of multiple quantum well amplifiers was done using appropriate rate equations and a heuristic model of the carrier density dependent gain. The model gave a qualitative agreement with the experimental results. In addition, the model allowed exploration of a wider design space for the amplifiers. The model predicted that internal electrical-to-optical conversion efficiencies in excess of 50 percent should be achievable with careful system design. The model predicted that no global optimum design exists, but gain, efficiency, and optical confinement (coupling efficiency) can be mutually adjusted to meet a specific system requirement. A three quantum well, low optical confinement amplifier was fabricated using molecular beam epitaxial growth. Coherent beam combining of two high power amplifiers injected from a common master oscillator was also examined. Coherent beam combining with an efficiency of 93 percent resulted in a single beam having diffraction-limited characteristics. This beam combining efficiency is a world record result for such a system. Interferometric observations of the output of the amplifier indicated that spatial mode matching was a significant factor in the less than perfect beam combining. Finally, the system issues of arrays of amplifiers in a coherent beam combining system were investigated. Based upon experimentally observed parameters coherent beam combining could result in a megawatt-scale coherent beam with a 10 percent electrical-to-optical conversion efficiency.

Highly selective surface-wave resonators for terahertz frequency range formed by metallic Bragg gratings

NASA Astrophysics Data System (ADS)

Ginzburg, N. S.; Malkin, A. M.; Sergeev, A. S.; Fil'chenkov, S. E.; Zaslavsky, V. Yu.

2018-04-01

In the frame of the quasi-optical approach we solve the diffraction problem and describe surface modes confined at a metallic plate with a shallow grating of finite length. We prove that such planar grating can form a highly selective surface-wave Bragg resonator. For a given material conductivity and grating length, we find the optimum corrugation depth that provides the maximum value of Q factor. These results are applicable for developing resonators for terahertz frequency bands.

Photonic heterostructure High Contrast Grating as a novel polarization control and light confinement system in HCG VCSEL

NASA Astrophysics Data System (ADS)

Gebski, M.; Dems, M.; Chen, J.; Qijie, W.; Dao Hua, Z.; Czyszanowski, T.

2014-05-01

In this paper we present results of computer optical simulations of VCSEL with modified high refractive index contrast grating (HCG) as a top mirror. We consider the HCG of two different designs which determine the lateral aperture. Such HCG mirror provides selective guiding effect. We show that proper design of aperture of HCG results in almost sixfold increase in cavity Q-factor for zero order mode and a discrimination of higher order modes.

Linear and nonlinear magneto-optical properties of an off-center single dopant in a spherical core/shell quantum dot

NASA Astrophysics Data System (ADS)

Feddi, E.; Talbi, A.; Mora-Ramos, M. E.; El Haouari, M.; Dujardin, F.; Duque, C. A.

2017-11-01

Using the effective mass approximation and a variational procedure, we have investigated the nonlinear optical absorption coefficient and the relative refractive index changes associated to a single dopant confined in core/shell quantum dots considering the influences of the core/shell dimensions, externally applied magnetic field, and dielectric mismatch. The results show that the optical absorption coefficient and the coefficients of relative refractive index change depend strongly on the core/shell sizes and they are blue shifted when the spatial confinement increases so this effect is magnified by higher structural dimensions. Additionally, it is obtained that both studied optical properties are sensitive to the dielectric environment in such a way that their amplitudes are very affected by the local field corrections.

Dynamics of an optically confined nanoparticle diffusing normal to a surface.

PubMed

Schein, Perry; O'Dell, Dakota; Erickson, David

2016-06-01

Here we measure the hindered diffusion of an optically confined nanoparticle in the direction normal to a surface, and we use this to determine the particle-surface interaction profile in terms of the absolute height. These studies are performed using the evanescent field of an optically excited single-mode silicon nitride waveguide, where the particle is confined in a height-dependent potential energy well generated from the balance of optical gradient and surface forces. Using a high-speed cmos camera, we demonstrate the ability to capture the short time-scale diffusion dominated motion for 800-nm-diam polystyrene particles, with measurement times of only a few seconds per particle. Using established theory, we show how this information can be used to estimate the equilibrium separation of the particle from the surface. As this measurement can be made simultaneously with equilibrium statistical mechanical measurements of the particle-surface interaction energy landscape, we demonstrate the ability to determine these in terms of the absolute rather than relative separation height. This enables the comparison of potential energy landscapes of particle-surface interactions measured under different experimental conditions, enhancing the utility of this technique.

Optical Microfibre Based Photonic Components and Their Applications in Label-Free Biosensing

PubMed Central

Wang, Pengfei; Bo, Lin; Semenova, Yuliya; Farrell, Gerald; Brambilla, Gilberto

2015-01-01

Optical microfibre photonic components offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These unique features have been exploited in a range of applications such as telecommunication, sensing, optical manipulation and high Q resonators. Optical microfibre biosensors, as a class of fibre optic biosensors which rely on small geometries to expose the evanescent field to interact with samples, have been widely investigated. Due to their unique properties, such as fast response, functionalization, strong confinement, configurability, flexibility, compact size, low cost, robustness, ease of miniaturization, large evanescent field and label-free operation, optical microfibres based biosensors seem a promising alternative to traditional immunological methods for biomolecule measurements. Unlabeled DNA and protein targets can be detected by monitoring the changes of various optical transduction mechanisms, such as refractive index, absorption and surface plasmon resonance, since a target molecule is capable of binding to an immobilized optical microfibre. In this review, we critically summarize accomplishments of past optical microfibre label-free biosensors, identify areas for future research and provide a detailed account of the studies conducted to date for biomolecules detection using optical microfibres. PMID:26287252

Optical Microfibre Based Photonic Components and Their Applications in Label-Free Biosensing.

PubMed

Wang, Pengfei; Bo, Lin; Semenova, Yuliya; Farrell, Gerald; Brambilla, Gilberto

2015-07-22

Optical microfibre photonic components offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These unique features have been exploited in a range of applications such as telecommunication, sensing, optical manipulation and high Q resonators. Optical microfibre biosensors, as a class of fibre optic biosensors which rely on small geometries to expose the evanescent field to interact with samples, have been widely investigated. Due to their unique properties, such as fast response, functionalization, strong confinement, configurability, flexibility, compact size, low cost, robustness, ease of miniaturization, large evanescent field and label-free operation, optical microfibres based biosensors seem a promising alternative to traditional immunological methods for biomolecule measurements. Unlabeled DNA and protein targets can be detected by monitoring the changes of various optical transduction mechanisms, such as refractive index, absorption and surface plasmon resonance, since a target molecule is capable of binding to an immobilized optical microfibre. In this review, we critically summarize accomplishments of past optical microfibre label-free biosensors, identify areas for future research and provide a detailed account of the studies conducted to date for biomolecules detection using optical microfibres.

Strong coupling between 0D and 2D modes in optical open microcavities

NASA Astrophysics Data System (ADS)

Trichet, A. A. P.; Dolan, P. R.; Smith, J. M.

2018-02-01

We present a study of the coupling between confined modes and continuum states in an open microcavity system. The confined states are the optical modes of a plano-concave Fabry-Pérot cavity while the continuum states are the propagating modes in a surrounding planar cavity. The length tunability of the open cavity system allows to study the evolution of localised modes as they are progressively deconfined and coupled to the propagating modes. We observe an anti-crossing between the confined and propagating modes proving that mode-mixing takes place in between these two families of modes, and identify 0D-2D mixed modes which exhibit reduced loss compared with their highly localised counterparts. For practical design, we investigate the details of the microcavity shape that can be used to engineer the degree of mode-mixing. This study discusses for the first time experimentally and theoretically how light confinement arises in planar micromirrors and is of interest for the realisation of chip-based extended microphotonics using open cavities.

Ultrasensitive plano-concave optical microresonators for ultrasound sensing

NASA Astrophysics Data System (ADS)

Guggenheim, James A.; Li, Jing; Allen, Thomas J.; Colchester, Richard J.; Noimark, Sacha; Ogunlade, Olumide; Parkin, Ivan P.; Papakonstantinou, Ioannis; Desjardins, Adrien E.; Zhang, Edward Z.; Beard, Paul C.

2017-11-01

Highly sensitive broadband ultrasound detectors are needed to expand the capabilities of biomedical ultrasound, photoacoustic imaging and industrial ultrasonic non-destructive testing techniques. Here, a generic optical ultrasound sensing concept based on a novel plano-concave polymer microresonator is described. This achieves strong optical confinement (Q-factors > 105) resulting in very high sensitivity with excellent broadband acoustic frequency response and wide directivity. The concept is highly scalable in terms of bandwidth and sensitivity. To illustrate this, a family of microresonator sensors with broadband acoustic responses up to 40 MHz and noise-equivalent pressures as low as 1.6 mPa per √Hz have been fabricated and comprehensively characterized in terms of their acoustic performance. In addition, their practical application to high-resolution photoacoustic and ultrasound imaging is demonstrated. The favourable acoustic performance and design flexibility of the technology offers new opportunities to advance biomedical and industrial ultrasound-based techniques.

Optical analysis of AlGaInP laser diodes with real refractive index guided self-aligned structure

NASA Astrophysics Data System (ADS)

Xu, Yun; Zhu, Xiaopeng; Ye, Xiaojun; Kang, Xiangning; Cao, Qing; Guo, Liang; Chen, Lianghui

2004-05-01

Optical modes of AlGaInP laser diodes with real refractive index guided self-aligned (RISA) structure were analyzed theoretically on the basis of two-dimension semivectorial finite-difference methods (SV-FDMs) and the computed simulation results were presented. The eigenvalue and eigenfunction of this two-dimension waveguide were obtained and the dependence of the confinement factor and beam divergence angles in the direction of parallel and perpendicular to the pn junction on the structure parameters such as the number of quantum wells, the Al composition of the cladding layers, the ridge width, the waveguide thickness and the residual thickness of the upper P-cladding layer were investigated. The results can provide optimized structure parameters and help us design and fabricate high performance AlGaInP laser diodes with a low beam aspect ratio required for optical storage applications.

Single-Mode, Distributed Feedback Interband Cascade Lasers

NASA Technical Reports Server (NTRS)

Frez, Clifford F. (Inventor); Borgentun, Carl E. (Inventor); Briggs, Ryan M. (Inventor); Bagheri, Mahmood (Inventor); Forouhar, Siamak (Inventor)

2016-01-01

Single-mode, distributed feedback interband cascade lasers (ICLs) using distributed-feedback gratings (e.g., lateral Bragg gratings) and methods of fabricating such ICLs are provided. The ICLs incorporate distributed-feedback gratings that are formed above the laser active region and adjacent the ridge waveguide (RWG) of the ICL. The ICLs may incorporate a double-ridge system comprising an optical confinement structure (e.g., a RWG) disposed above the laser active region that comprises the first ridge of the double ridge system, a DFB grating (e.g., lateral Bragg grating) disposed above the laser active region and adjacent the optical confinement structure, and an electric confinement structure that passes at least partially through the laser active region and that defines the boundary of the second ridge comprises and the termination of the DFB grating.

Temperature and excitation power influence on the velocity-selective optical pumping resonances of 133Cs atoms confined in an extremely thin cell

NASA Astrophysics Data System (ADS)

Vartanyan, T.; Polishchuk, V.; Sargsyan, A.; Krasteva, A.; Cartaleva, St.; Todorov, G.

2018-03-01

Linear and nonlinear absorption spectra of 133Cs vapor confined in an extremely thin cell were computed via iterations with respect to the resonance radiation intensity. When the incident radiation intensity is low, the transient polarization of the atoms that undergo frequent collisions with the cell walls leads to sub-Doppler features in the absorption spectra. Higher incident radiation intensities result in the appearance of velocity-selective optical pumping resonances. The theory developed agrees quantitatively with the experimental findings.

Optical pumping in a whispering mode optical waveguide

DOEpatents

Kurnit, Norman A.

1984-01-01

A device and method for optical pumping in a whispering mode optical waveguide. Both a helical ribbon and cylinder are disclosed which incorporate an additional curvature for confining the beam to increase intensity. An optical pumping medium is disposed in the optical path of the beam as it propagates along the waveguide. Optical pumping is enhanced by the high intensities of the beam and long interaction pathlengths which are achieved in a small volume.

Mapping Nanoscale Hotspots with Single-Molecule Emitters Assembled into Plasmonic Nanocavities Using DNA Origami.

PubMed

Chikkaraddy, Rohit; Turek, V A; Kongsuwan, Nuttawut; Benz, Felix; Carnegie, Cloudy; van de Goor, Tim; de Nijs, Bart; Demetriadou, Angela; Hess, Ortwin; Keyser, Ulrich F; Baumberg, Jeremy J

2018-01-10

Fabricating nanocavities in which optically active single quantum emitters are precisely positioned is crucial for building nanophotonic devices. Here we show that self-assembly based on robust DNA-origami constructs can precisely position single molecules laterally within sub-5 nm gaps between plasmonic substrates that support intense optical confinement. By placing single-molecules at the center of a nanocavity, we show modification of the plasmon cavity resonance before and after bleaching the chromophore and obtain enhancements of ≥4 × 10 3 with high quantum yield (≥50%). By varying the lateral position of the molecule in the gap, we directly map the spatial profile of the local density of optical states with a resolution of ±1.5 nm. Our approach introduces a straightforward noninvasive way to measure and quantify confined optical modes on the nanoscale.

Transparent electrode for optical switch

DOEpatents

Goldhar, J.; Henesian, M.A.

1984-10-19

The invention relates generally to optical switches and techniques for applying a voltage to an electro-optical crystal, and more particularly, to transparent electodes for an optical switch. System architectures for very large inertial confinement fusion (ICF) lasers require active optical elements with apertures on the order of one meter. Large aperture optical switches are needed for isolation of stages, switch-out from regenerative amplifier cavities and protection from target retroreflections.

In situ microparticle analysis of marine phytoplankton cells with infrared laser-based optical tweezers

NASA Astrophysics Data System (ADS)

Sonek, G. J.; Liu, Y.; Iturriaga, R. H.

1995-11-01

We describe the application of infrared optical tweezers to the in situ microparticle analysis of marine phytoplankton cells. A Nd:YAG laser (lambda=3D 1064 nm) trap is used to confine and manipulate single Nannochloris and Synechococcus cells in an enriched seawater medium while spectral fluorescence and Lorenz-Mie backscatter signals are simultaneously acquired under a variety of excitation and trapping conditions. Variations in the measured fluorescence intensities of chlorophyll a (Chl a) and phycoerythrin pigments in phytoplankton cells are observed. These variations are related, in part, to basic intrasample variability, but they also indicate that increasing ultraviolet-exposure time and infrared trapping power may have short-term effects on cellular physiology that are related to Chl a photobleaching and laser-induced heating, respectively. The use of optical tweezers to study the factors that affect marine cell physiology and the processes of absorption, scattering, and attenuation by individual cells, organisms, and particulate matter that contribute to optical closure on a microscopic scale are also described. (c)1995 Optical Society of America

Micro/Nanofibre Optical Sensors: Challenges and Prospects

PubMed Central

Tong, Limin

2018-01-01

Micro/nanofibres (MNFs) are optical fibres with diameters close to or below the vacuum wavelength of visible or near-infrared light. Due to its wavelength- or sub-wavelength scale diameter and relatively large index contrast between the core and cladding, an MNF can offer engineerable waveguiding properties including optical confinement, fractional evanescent fields and surface intensity, which is very attractive to optical sensing on the micro and nanometer scale. In particular, the waveguided low-loss tightly confined large fractional evanescent fields, enabled by atomic level surface roughness and extraordinary geometric and material uniformity in a glass MNF, is one of its most prominent merits in realizing optical sensing with high sensitivity and great versatility. Meanwhile, the mesoporous matrix and small diameter of a polymer MNF, make it an excellent host fibre for functional materials for fast-response optical sensing. In this tutorial, we first introduce the basics of MNF optics and MNF optical sensors, and review the progress and current status of this field. Then, we discuss challenges and prospects of MNF sensors to some extent, with several clues for future studies. Finally, we conclude with a brief outlook for MNF optical sensors.

Electronic and Optical Properties of Two-Dimensional GaN from First-Principles.

PubMed

Sanders, Nocona; Bayerl, Dylan; Shi, Guangsha; Mengle, Kelsey A; Kioupakis, Emmanouil

2017-12-13

Gallium nitride (GaN) is an important commercial semiconductor for solid-state lighting applications. Atomically thin GaN, a recently synthesized two-dimensional material, is of particular interest because the extreme quantum confinement enables additional control of its light-emitting properties. We performed first-principles calculations based on density functional and many-body perturbation theory to investigate the electronic, optical, and excitonic properties of monolayer and bilayer two-dimensional (2D) GaN as a function of strain. Our results demonstrate that light emission from monolayer 2D GaN is blueshifted into the deep ultraviolet range, which is promising for sterilization and water-purification applications. Light emission from bilayer 2D GaN occurs at a similar wavelength to its bulk counterpart due to the cancellation of the effect of quantum confinement on the optical gap by the quantum-confined Stark shift. Polarized light emission at room temperature is possible via uniaxial in-plane strain, which is desirable for energy-efficient display applications. We compare the electronic and optical properties of freestanding two-dimensional GaN to atomically thin GaN wells embedded within AlN barriers in order to understand how the functional properties are influenced by the presence of barriers. Our results provide microscopic understanding of the electronic and optical characteristics of GaN at the few-layer regime.

Confined detection volume of fluorescence correlation spectroscopy by bare fiber probes.

PubMed

Lu, Guowei; Lei, Franck H; Angiboust, Jean-François; Manfait, Michel

2010-04-01

A fiber-tip-based near-field fluorescence correlation spectroscopy (FCS) has been developed for confining the detection volume to sub-diffraction-limited dimensions. This near-field FCS is based on near-field illumination by coupling a scanning near-field optical microscope (SNOM) to a conventional confocal FCS. Single-molecule FCS analysis at 100 nM Rhodamine 6G has been achieved by using bare chemically etched, tapered fiber tips. The detection volume under control of the SNOM system has been reduced over one order of magnitude compared to that of the conventional confocal FCS. Related factors influencing the near-field FCS performance are investigated and discussed in detail. In this proof-of-principle study, the preliminary experimental results suggest that the fiber-tip-based near-field FCS might be a good alternative to realize localized analysis at the single-molecule level.

The influence of mesoscopic confinement on the dynamics of imidazolium-based room temperature ionic liquids in polyether sulfone membranes.

PubMed

Thomaz, Joseph E; Bailey, Heather E; Fayer, Michael D

2017-11-21

The structural dynamics of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C n mimNTf 2 , n = 2, 4, 6, 10: ethyl-Emim; butyl-Bmim; hexyl-Hmim; decyl-Dmim) room temperature ionic liquids confined in the pores of polyether sulfone (PES 200) membranes with an average pore size of ∼350 nm and in the bulk liquids were studied. Time correlated single photon counting measurements of the fluorescence of the fluorophore coumarin 153 (C153) were used to observe the time-dependent Stokes shift (solvation dynamics). The solvation dynamics of C153 in the ionic liquids are multiexponential decays. The multiexponential functional form of the decays was confirmed as the slowest decay component of each bulk liquid matches the slowest component of the liquid dynamics measured by optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments, which is single exponential. The fact that the slowest component of the Stokes shift matches the OHD-OKE data in all four liquids identifies this component of the solvation dynamics as arising from the complete structural randomization of the liquids. Although the pores in the PES membranes are large, confinement on the mesoscopic length scale results in substantial slowing of the dynamics, a factor of ∼4, for EmimNTf 2 , with the effect decreasing as the chain length increases. By DmimNTf 2 , the dynamics are virtually indistinguishable from those in the bulk liquid. The rotation relaxation of C153 in the four bulk liquids was also measured and showed strong coupling between the C153 probe and its environment.

The influence of mesoscopic confinement on the dynamics of imidazolium-based room temperature ionic liquids in polyether sulfone membranes

NASA Astrophysics Data System (ADS)

Thomaz, Joseph E.; Bailey, Heather E.; Fayer, Michael D.

2017-11-01

The structural dynamics of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (CnmimNTf2, n = 2, 4, 6, 10: ethyl—Emim; butyl—Bmim; hexyl—Hmim; decyl—Dmim) room temperature ionic liquids confined in the pores of polyether sulfone (PES 200) membranes with an average pore size of ˜350 nm and in the bulk liquids were studied. Time correlated single photon counting measurements of the fluorescence of the fluorophore coumarin 153 (C153) were used to observe the time-dependent Stokes shift (solvation dynamics). The solvation dynamics of C153 in the ionic liquids are multiexponential decays. The multiexponential functional form of the decays was confirmed as the slowest decay component of each bulk liquid matches the slowest component of the liquid dynamics measured by optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments, which is single exponential. The fact that the slowest component of the Stokes shift matches the OHD-OKE data in all four liquids identifies this component of the solvation dynamics as arising from the complete structural randomization of the liquids. Although the pores in the PES membranes are large, confinement on the mesoscopic length scale results in substantial slowing of the dynamics, a factor of ˜4, for EmimNTf2, with the effect decreasing as the chain length increases. By DmimNTf2, the dynamics are virtually indistinguishable from those in the bulk liquid. The rotation relaxation of C153 in the four bulk liquids was also measured and showed strong coupling between the C153 probe and its environment.

Optical studies of quantum confined nanostructures

NASA Astrophysics Data System (ADS)

Vamivakas, Anthony Nickolas

Recent advances in material growth techniques have led to the laboratory realization of quantum confined nanostructures. By engineering the geometry of these systems it is possible to tailor their optical, electrical and vibrational properties. We now envision integrated electronic and optical devices potentially harnessing quantum mechanical properties of photons, electrons or even phonons. The realization of these next generation devices requires parallel advances in both electrical and optical characterization techniques. In this dissertation we study the optical properties of both zero-dimensional (0D) InAs/GaAs semiconductor quantum dots (QDs) and one-dimensional (1D) single wall carbon nanotubes (SWNTs). We utilize high resolution optical microscopy and spectroscopy techniques to experimentally study both individual QDs and SWNTs. The effect of quantum confinement on light-matter interaction in SWNTs is theoretically investigated. InAs QDs grown by Stranski-Krastanow self-assembly are buried in a GaAs matrix. The planar barriers presented by the dielectric boundary between the GaAs and the host medium limits the optical access to the InAs QDs. Incorporating a numerical aperture increasing microlens (NAIL) into a fiber-based confocal microscope we demonstrate improved ability to couple photons to and from a single InAs QD. With such immersion lens techniques we measure a record 12% extinction of a far-field laser by a single InAs QD. Even typical QD extinction of 6% is visible using a dc power-meter without the need for phase sensitive lock-in detection. This experimental advance will make possible the study of single QDs interacting with engineered vector laser beams. In the optical characterization of SWNTs, one-phonon resonant Raman scattering is employed to measure a tube's electronic resonances and determine the physical diameter and chirality of the tube under study. Recent work has determined excitons dominate the optical response of semiconducting SWNTs. We develop a theory to model the exciton mediated resonant Raman scattering cross-section from a 1D system looking for excitonic signatures in the scattering line shape. Additionally, we theoretically study phonon confinement to a 1D SWNT and use these results to extract the electron-phonon coupling in SWNTs from our Raman measurements. Knowledge of the electron-phonon coupling is a crucial piece of information to characterize a SWNTs electrical transport properties.

Electrons and Phonons in Semiconductor Multilayers

NASA Astrophysics Data System (ADS)

Ridley, B. K.

1996-11-01

This book provides a detailed description of the quantum confinement of electrons and phonons in semiconductor wells, superlattices and quantum wires, and shows how this affects their mutual interactions. It discusses the transition from microscopic to continuum models, emphasizing the use of quasi-continuum theory to describe the confinement of optical phonons and electrons. The hybridization of optical phonons and their interactions with electrons are treated, as are other electron scattering mechanisms. The book concludes with an account of the electron distribution function in three-, two- and one-dimensional systems, in the presence of electrical or optical excitation. This text will be of great use to graduate students and researchers investigating low-dimensional semiconductor structures, as well as to those developing new devices based on these systems.

Optical pumping in a whispering-mode optical waveguide

DOEpatents

Kurnit, N.A.

1981-08-11

A device and method for optical pumping in a whispering mode optical waveguide are described. Both a helical ribbon and cylinder are disclosed which incorporate an additional curvature for confining the beam to increase intensity. An optical pumping medium is disposed in the optical path of the beam as it propagates along the waveguide. Optical pumping is enhanced by the high intensities of the beam and long interaction path lengths which are achieved in a small volume.

Quantum Computation with Neutral Atoms at Addressable Optical Lattice Sites and Atoms in Confined Geometries

DTIC Science & Technology

2014-10-13

include doublon dissolution, quantum distillation , and confinement of vacancies in a doublon sea, can be 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND...include doublon dissolution, quantum distillation , and confinement of vacancies in a doublon sea, can be qualitatively understood even in the intermediate...with a deep enough lattice that isolated doublons are stable; the quantum distillation of singlons out of the doublon sea; and the long term

A new perspective on plasmonics: Confinement and propagation length of surface plasmons for different materials and geometries [A new perspective on materials for plasmonics

DOE PAGES

Dastmalchi, Babak; Tassin, Philippe; Koschny, Thomas; ...

2015-09-21

Surface-plasmon polaritons are electromagnetic waves propagating on the surface of a metal. Thanks to subwavelength confinement, they can concentrate optical energy on the micrometer or even nanometer scale, enabling new applications in bio-sensing, optical interconnects, and nonlinear optics, where small footprint and strong field concentration are essential. The major obstacle in developing plasmonic applications is dissipative loss, which limits the propagation length of surface plasmons and broadens the bandwidth of surface-plasmon resonances. Here, a new analysis of plasmonic materials and geometries is presented which fully considers the tradeoff between propagation length and degree of confinement. It is based on amore » two-dimensional analysis of two independent figures of merit and the analysis is applied to relevant plasmonic materials, e.g., noble metals, aluminum, silicon carbide, doped semiconductors, graphene, etc. Furthermore, the analysis provides guidance on how to improve the performance of any particular plasmonic application and substantially eases the selection of the plasmonic material.« less

Transverse Anderson Localization in Disordered Glass Optical Fibers: A Review.

PubMed

Mafi, Arash; Karbasi, Salman; Koch, Karl W; Hawkins, Thomas; Ballato, John

2014-07-28

Disordered optical fibers show novel waveguiding properties that can be used for various device applications, such as beam-multiplexed optical communications and endoscopic image transport. The strong transverse scattering from the transversely disordered optical fibers results in transversely confined beams that can freely propagate in the longitudinal direction, similar to conventional optical fibers, with the advantage that any point in the cross section of the fiber can be used for beam transport. For beam multiplexing and imaging applications, it is highly desirable to make the localized beam radius as small as possible. This requires large refractive index differences between the materials that define the random features in the disordered fiber. Here, disordered glass-air fibers are briefly reviewed, where randomly placed airholes in a glass matrix provide the sufficiently large refractive index difference of 0.5 for strong random transverse scattering. The main future challenge for the fabrication of an optimally disordered glass-air fibers is to increase the fill-fraction of airholes to nearly 50% for maximum beam confinement.

Transverse Anderson Localization in Disordered Glass Optical Fibers: A Review

PubMed Central

Mafi, Arash; Karbasi, Salman; Koch, Karl W.; Hawkins, Thomas; Ballato, John

2014-01-01

Disordered optical fibers show novel waveguiding properties that can be used for various device applications, such as beam-multiplexed optical communications and endoscopic image transport. The strong transverse scattering from the transversely disordered optical fibers results in transversely confined beams that can freely propagate in the longitudinal direction, similar to conventional optical fibers, with the advantage that any point in the cross section of the fiber can be used for beam transport. For beam multiplexing and imaging applications, it is highly desirable to make the localized beam radius as small as possible. This requires large refractive index differences between the materials that define the random features in the disordered fiber. Here, disordered glass-air fibers are briefly reviewed, where randomly placed airholes in a glass matrix provide the sufficiently large refractive index difference of 0.5 for strong random transverse scattering. The main future challenge for the fabrication of an optimally disordered glass-air fibers is to increase the fill-fraction of airholes to nearly 50% for maximum beam confinement. PMID:28788142

Sub-natural width resonances in Cs vapor confined in micrometric thickness optical cell

NASA Astrophysics Data System (ADS)

Cartaleva, S.; Krasteva, A.; Sargsyan, A.; Sarkisyan, D.; Slavov, D.; Vartanyan, T.

2013-03-01

We present here the behavior of Electromagnetically Induced Transparency (EIT), Velocity Selective Optical Pumping (VSOP) resonances and Velocity Selective Excitation (VSE) resonances observed in Cs vapor confined in а micrometric optical cell (MC) with thickness L = 6λ, λ = 852nm. For comparison of behavior of VSE resonance another conventional optical cell with thickness L=2.5 cm is used. Cells are irradiated in orthogonal to their windows directions by probe beam scanned on the Fg = 4 → Fe= 3, 4, 5 set of transitions and pump beam fixed at the Fg = 3 → Fe = 4 transition, on the D2 line of Cs. The enhanced absorption (fluorescence) narrow VSOP resonance at the closed transition transforms into reduced absorption (fluorescence) one with small increase of atomic concentration or light intensity. A striking difference appears between the VSE resonance broadening in L = 6λ and conventional L = 2.5cm cells.

Mapping Nanoscale Hotspots with Single-Molecule Emitters Assembled into Plasmonic Nanocavities Using DNA Origami

PubMed Central

2017-01-01

Fabricating nanocavities in which optically active single quantum emitters are precisely positioned is crucial for building nanophotonic devices. Here we show that self-assembly based on robust DNA-origami constructs can precisely position single molecules laterally within sub-5 nm gaps between plasmonic substrates that support intense optical confinement. By placing single-molecules at the center of a nanocavity, we show modification of the plasmon cavity resonance before and after bleaching the chromophore and obtain enhancements of ≥4 × 103 with high quantum yield (≥50%). By varying the lateral position of the molecule in the gap, we directly map the spatial profile of the local density of optical states with a resolution of ±1.5 nm. Our approach introduces a straightforward noninvasive way to measure and quantify confined optical modes on the nanoscale. PMID:29166033

FIBER AND INTEGRATED OPTICS: Directional pattern and other output properties of a quantum-well injection laser for the 780-nm spectral region

NASA Astrophysics Data System (ADS)

Davydova, Evgeniya I.; Drakin, A. E.; Eliseev, P. G.; Pak, G. T.; Popovichev, V. V.; Uspenskiĭ, M. B.; Khlopotin, S. E.; Shishkin, Viktor A.

1992-10-01

An optical model is constructed for a GaAlAs/GaAs stripe-geometry laser heterostructure with a ridge-waveguide configuration in the p-type emitter layer. This waveguide configuration provides lateral optical confinement. The directional characteristics of the output are found as a function of the parameters of the structure. The quantum-well active layer is in a three-layer waveguide (in a separate-confinement structure). Laser structures were fabricated experimentally by MOCVD epitaxy followed by ion-chemical etching and vacuum deposition of zinc selenide on the mesa stripes. Low-threshold lasers with a cw, single-frequency power up to 40 μW were obtained. In single-spatial-mode operation, a power up to 80 μW was achieved at a wavelength of 780 nm. Windows of ZnSe were grown on the laser facets to improve the optical strength.

Mapping Nanoscale Hotspots with Single-Molecule Emitters Assembled into Plasmonic Nanocavities Using DNA Origami

NASA Astrophysics Data System (ADS)

Chikkaraddy, Rohit; Turek, V. A.; Kongsuwan, Nuttawut; Benz, Felix; Carnegie, Cloudy; van de Goor, Tim; de Nijs, Bart; Demetriadou, Angela; Hess, Ortwin; Keyser, Ulrich F.; Baumberg, Jeremy J.

2018-01-01

Fabricating nanocavities in which optically-active single quantum emitters are precisely positioned, is crucial for building nanophotonic devices. Here we show that self-assembly based on robust DNA-origami constructs can precisely position single molecules laterally within sub-5nm gaps between plasmonic substrates that support intense optical confinement. By placing single-molecules at the center of a nanocavity, we show modification of the plasmon cavity resonance before and after bleaching the chromophore, and obtain enhancements of $\\geq4\\times10^3$ with high quantum yield ($\\geq50$%). By varying the lateral position of the molecule in the gap, we directly map the spatial profile of the local density of optical states with a resolution of $\\pm1.5$ nm. Our approach introduces a straightforward non-invasive way to measure and quantify confined optical modes on the nanoscale.

Optical response in a laser-driven quantum pseudodot system

NASA Astrophysics Data System (ADS)

Kilic, D. Gul; Sakiroglu, S.; Ungan, F.; Yesilgul, U.; Kasapoglu, E.; Sari, H.; Sokmen, I.

2017-03-01

We investigate theoretically the intense laser-induced optical absorption coefficients and refractive index changes in a two-dimensional quantum pseudodot system under an uniform magnetic field. The effects of non-resonant, monochromatic intense laser field upon the system are treated within the framework of high-frequency Floquet approach in which the system is supposed to be governed by a laser-dressed potential. Linear and nonlinear absorption coefficients and relative changes in the refractive index are obtained by means of the compact-density matrix approach and iterative method. The results of numerical calculations for a typical GaAs quantum dot reveal that the optical response depends strongly on the magnitude of external magnetic field and characteristic parameters of the confinement potential. Moreover, we have demonstrated that the intense laser field modifies the confinement and thereby causes remarkable changes in the linear and nonlinear optical properties of the system.

Avalanches and plasticity for colloids in a time dependent optical trap

DOE PAGES

Olson Reichhardt, Cynthia Jane; McDermott, Danielle Marie; Reichhardt, Charles

2015-08-25

Here, with the use of optical traps it is possible to confine assemblies of colloidal particles in two-dimensional and quasi-one-dimensional arrays. Here we examine how colloidal particles rearrange in a quasi-one-dimensional trap with a time dependent confining potential. The particle motion occurs both through slow elastic uniaxial distortions as well as through abrupt large-scale two-dimensional avalanches associated with plastic rearrangements. During the avalanches the particle velocity distributions extend over a broad range and can be fit to a power law consistent with other studies of plastic events mediated by dislocations.

Optical Field-Strength Polarization of Two-Mode Single-Photon States

ERIC Educational Resources Information Center

Linares, J.; Nistal, M. C.; Barral, D.; Moreno, V.

2010-01-01

We present a quantum analysis of two-mode single-photon states based on the probability distributions of the optical field strength (or position quadrature) in order to describe their quantum polarization characteristics, where polarization is understood as a significative confinement of the optical field-strength values on determined regions of…

Investigating axial diffusion in cylindrical pores using confocal single-particle fluorescence correlation spectroscopy.

PubMed

Chen, Fang; Neupane, Bhanu; Li, Peiyuan; Su, Wei; Wang, Gufeng

2016-08-01

We explored the feasibility of using confocal fluorescence correlation spectroscopy to study small nanoparticle diffusion in hundred-nanometer-sized cylindrical pores. By modeling single particle diffusion in tube-like confined three-dimensional space aligned parallel to the confocal optical axis, we showed that two diffusion dynamics can be observed in both original intensity traces and the autocorrelation functions (ACFs): the confined two-dimensional lateral diffusion and the unconfined one-dimensional (1D) axial diffusion. The separation of the axial and confined lateral diffusion dynamics provides an opportunity to study diffusions in different dimensions separately. We further experimentally studied 45 nm carboxylated polystyrene particles diffusing in 300 nm alumina pores. The experimental data showed consistency with the simulation. To extract the accurate axial diffusion coefficient, we found that a 1D diffusion model with a Lorentzian axial collection profile needs to be used to analyze the experimental ACFs. The diffusion of the 45 nm nanoparticles in polyethyleneglycol-passivated 300 nm pores slowed down by a factor of ∼2, which can be satisfactorily explained by hydrodynamic frictions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct optical mapping of transcription factor binding sites on field-stretched λ-DNA in nanofluidic devices

PubMed Central

Sriram, K. K.; Yeh, Jia-Wei; Lin, Yii-Lih; Chang, Yi-Ren; Chou, Chia-Fu

2014-01-01

Mapping transcription factor (TF) binding sites along a DNA backbone is crucial in understanding the regulatory circuits that control cellular processes. Here, we deployed a method adopting bioconjugation, nanofluidic confinement and fluorescence single molecule imaging for direct mapping of TF (RNA polymerase) binding sites on field-stretched single DNA molecules. Using this method, we have mapped out five of the TF binding sites of E. coli RNA polymerase to bacteriophage λ-DNA, where two promoter sites and three pseudo-promoter sites are identified with the corresponding binding frequency of 45% and 30%, respectively. Our method is quick, robust and capable of resolving protein-binding locations with high accuracy (∼ 300 bp), making our system a complementary platform to the methods currently practiced. It is advantageous in parallel analysis and less prone to false positive results over other single molecule mapping techniques such as optical tweezers, atomic force microscopy and molecular combing, and could potentially be extended to general mapping of protein–DNA interaction sites. PMID:24753422

One-dimensional Tamm plasmons: Spatial confinement, propagation, and polarization properties

NASA Astrophysics Data System (ADS)

Chestnov, I. Yu.; Sedov, E. S.; Kutrovskaya, S. V.; Kucherik, A. O.; Arakelian, S. M.; Kavokin, A. V.

2017-12-01

Tamm plasmons are confined optical states at the interface of a metal and a dielectric Bragg mirror. Unlike conventional surface plasmons, Tamm plasmons may be directly excited by an external light source in both TE and TM polarizations. Here we consider the one-dimensional propagation of Tamm plasmons under long and narrow metallic stripes deposited on top of a semiconductor Bragg mirror. The spatial confinement of the field imposed by the stripe and its impact on the structure and energy of Tamm modes are investigated. We show that the Tamm modes are coupled to surface plasmons arising at the stripe edges. These plasmons form an interference pattern close to the bottom surface of the stripe that involves modification of both the energy and loss rate for the Tamm mode. This phenomenon is pronounced only in the case of TE polarization of the Tamm mode. These findings pave the way to application of laterally confined Tamm plasmons in optical integrated circuits as well as to engineering potential traps for both Tamm modes and hybrid modes of Tamm plasmons and exciton polaritons with meV depth.

Fiber-Coupled Acousto-Optical-Filter Spectrometer

NASA Technical Reports Server (NTRS)

Levin, Kenneth H.; Li, Frank Yanan

1993-01-01

Fiber-coupled acousto-optical-filter spectrometer steps rapidly through commanded sequence of wavelengths. Sample cell located remotely from monochromator and associated electronic circuitry, connected to them with optical fibers. Optical-fiber coupling makes possible to monitor samples in remote, hazardous, or confined locations. Advantages include compactness, speed, and no moving parts. Potential applications include control of chemical processes, medical diagnoses, spectral imaging, and sampling of atmospheres.

Optical properties of voltage sensitive hemicyanine dyes of variable hydrophobicity confined within surfactant micelles

NASA Astrophysics Data System (ADS)

Naeem, Kashif; Naseem, Bushra; Shah, S. S.; Shah, Syed W. H.

2017-11-01

The optical properties of amphiphilic hemicyanine dyes with variable hydrophobicity, confined within anionic micelles of sodium dodecylbenzenesulfonate (NaDDBS) have been studied by UV-visible absorption spectroscopy. The confinement constant, K conf has been determined for each entrapped dye. The ion-pair formation between dye and surfactant causes a decline in electronic transition energy (ΔE T) when dye alkyl chains are smaller due to stabilization of both the ground and excited state. ΔE T values gradually increase with increase in dye hydrophobicity that hampers the electrostatic interaction with dialkylammonium moiety and consequently excited state stabilization is compromised. The average number of dye molecules trapped in a single micelle was also determined. The negative values of Gibbs free energy indicate that the dye entrapment within micelles is energetically favored. These findings have significance for developing functional materials with peculiar luminescent properties, especially for more effective probing of complex biological systems.

Resonantly enhanced second-harmonic generation using III–V semiconductor all-dielectric metasurfaces

DOE PAGES

Liu, Sheng; Sinclair, Michael B.; Saravi, Sina; ...

2016-08-08

Nonlinear optical phenomena in nanostructured materials have been challenging our perceptions of nonlinear optical processes that have been explored since the invention of lasers. For example, the ability to control optical field confinement, enhancement, and scattering almost independently allows nonlinear frequency conversion efficiencies to be enhanced by many orders of magnitude compared to bulk materials. Also, the subwavelength length scale renders phase matching issues irrelevant. Compared with plasmonic nanostructures, dielectric resonator metamaterials show great promise for enhanced nonlinear optical processes due to their larger mode volumes. Here, we present, for the first time, resonantly enhanced second-harmonic generation (SHG) using galliummore » arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical resonators we observe SHG enhancement factors as large as 10 4 relative to unpatterned GaAs. At the magnetic dipole resonance, we measure an absolute nonlinear conversion efficiency of ~2 × 10 –5 with ~3.4 GW/cm 2 pump intensity. In conclusion, the polarization properties of the SHG reveal that both bulk and surface nonlinearities play important roles in the observed nonlinear process.« less

Formation of contour optical traps using a four-channel liquid crystal focusing device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korobtsov, A V; Kotova, S P; Losevsky, N N

2014-12-31

The capabilities and specific features of the formation and dynamic control of so-called contour optical traps using a fourchannel liquid crystal modulator are studied theoretically and experimentally. Circular, elliptical and C-shaped traps are formed. Trapping and confinement of absorbing micro-objects by the formed traps are demonstrated. (optical traps)

Continuous parametric feedback cooling of a single atom in an optical cavity

NASA Astrophysics Data System (ADS)

Sames, C.; Hamsen, C.; Chibani, H.; Altin, P. A.; Wilk, T.; Rempe, G.

2018-05-01

We demonstrate a feedback algorithm to cool a single neutral atom trapped inside a standing-wave optical cavity. The algorithm is based on parametric modulation of the confining potential at twice the natural oscillation frequency of the atom, in combination with fast and repetitive atomic position measurements. The latter serve to continuously adjust the modulation phase to a value for which parametric excitation of the atomic motion is avoided. Cooling is limited by the measurement backaction which decoheres the atomic motion after only a few oscillations. Nonetheless, applying this feedback scheme to an ˜5 -kHz oscillation mode increases the average storage time of a single atom in the cavity by a factor of 60 to more than 2 s. In contrast to previous feedback schemes, our algorithm is also capable of cooling a much faster ˜500 -kHz oscillation mode within just microseconds. This demonstrates that parametric cooling is a powerful technique that can be applied in all experiments where optical access is limited.

On-chip hybrid photonic-plasmonic light concentrator for nanofocusing in an integrated silicon photonics platform.

PubMed

Luo, Ye; Chamanzar, Maysamreza; Apuzzo, Aniello; Salas-Montiel, Rafael; Nguyen, Kim Ngoc; Blaize, Sylvain; Adibi, Ali

2015-02-11

The enhancement and confinement of electromagnetic radiation to nanometer scale have improved the performances and decreased the dimensions of optical sources and detectors for several applications including spectroscopy, medical applications, and quantum information. Realization of on-chip nanofocusing devices compatible with silicon photonics platform adds a key functionality and provides opportunities for sensing, trapping, on-chip signal processing, and communications. Here, we discuss the design, fabrication, and experimental demonstration of light nanofocusing in a hybrid plasmonic-photonic nanotaper structure. We discuss the physical mechanisms behind the operation of this device, the coupling mechanisms, and how to engineer the energy transfer from a propagating guided mode to a trapped plasmonic mode at the apex of the plasmonic nanotaper with minimal radiation loss. Optical near-field measurements and Fourier modal analysis carried out using a near-field scanning optical microscope (NSOM) show a tight nanofocusing of light in this structure to an extremely small spot of 0.00563(λ/(2n(rmax)))(3) confined in 3D and an exquisite power input conversion of 92%. Our experiments also verify the mode selectivity of the device (low transmission of a TM-like input mode and high transmission of a TE-like input mode). A large field concentration factor (FCF) of about 4.9 is estimated from our NSOM measurement with a radius of curvature of about 20 nm at the apex of the nanotaper. The agreement between our theory and experimental results reveals helpful insights about the operation mechanism of the device, the interplay of the modes, and the gradual power transfer to the nanotaper apex.

Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber.

PubMed

Minn, Khant; Anopchenko, Aleksei; Yang, Jingyi; Lee, Ho Wai Howard

2018-02-05

We report a novel optical waveguide design of a hollow step index fiber modified with a thin layer of indium tin oxide (ITO). We show an excitation of highly confined waveguide mode in the proposed fiber near the wavelength where permittivity of ITO approaches zero. Due to the high field confinement within thin ITO shell inside the fiber, the epsilon-near-zero (ENZ) mode can be characterized by a peak in modal loss of the hybrid waveguide. Our results show that such in-fiber excitation of ENZ mode is due to the coupling of the guided core mode to the thin-film ENZ mode. We also show that the phase matching wavelength, where the coupling takes place, varies depending on the refractive index of the constituents inside the central bore of the fiber. These ENZ nanostructured optical fibers have many potential applications, for example, in ENZ nonlinear and magneto-optics, as in-fiber wavelength-dependent filters, and as subwavelength fluid channel for optical and bio-photonic sensing.

Ultra-low threshold gallium nitride photonic crystal nanobeam laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niu, Nan, E-mail: nanniu@fas.harvard.edu; Woolf, Alexander; Wang, Danqing

2015-06-08

We report exceptionally low thresholds (9.1 μJ/cm{sup 2}) for room temperature lasing at ∼450 nm in optically pumped Gallium Nitride (GaN) nanobeam cavity structures. The nanobeam cavity geometry provides high theoretical Q (>100 000) with small modal volume, leading to a high spontaneous emission factor, β = 0.94. The active layer materials are Indium Gallium Nitride (InGaN) fragmented quantum wells (fQWs), a critical factor in achieving the low thresholds, which are an order-of-magnitude lower than obtainable with continuous QW active layers. We suggest that the extra confinement of photo-generated carriers for fQWs (compared to QWs) is responsible for the excellent performance.

Electronic band structure and optical gain of GaN{sub x}Bi{sub y}As{sub 1−x−y}/GaAs pyramidal quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Zhi-Gang; State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083; Bose, Sumanta

The electronic band structure and optical gain of GaN{sub x}Bi{sub y}As{sub 1−x−y}/GaAs pyramidal quantum dots (QDs) are investigated using the 16-band k ⋅ p model with constant strain. The optical gain is calculated taking both homogeneous and inhomogeneous broadenings into consideration. The effective band gap falls as we increase the composition of nitrogen (N) and bismuth (Bi) and with an appropriate choice of composition we can tune the emission wavelength to span within 1.3 μm–1.55 μm, for device application in fiber technology. The extent of this red shift is more profound in QDs compared with bulk material due to quantum confinement. Othermore » factors affecting the emission characteristics include virtual crystal, strain profile, band anticrossing (BAC), and valence band anticrossing (VBAC). The strain profile has a profound impact on the electronic structure, specially the valence band of QDs, which can be determined using the composition distribution of wave functions. All these factors eventually affect the optical gain spectrum. With an increase in QD size, we observe a red shift in the emission energy and emergence of secondary peaks owing to transitions or greater energy compared with the fundamental transition.« less

Optical study of xanthene-type dyes in nano-confined liquid

NASA Astrophysics Data System (ADS)

Mahdi Shavakandi, Seyyed; Alizadeh, Khalil; Sharifi, Soheil; Marti, Othmar; Amirkhani, Masoud

2017-04-01

The optical activity of dye molecules in different environments is of great interest for many applications such as laser system or biological imaging. We investigate the fluorescence and absorption spectrum of nano-confined xanthene dyes (RhB and fluorescein sodium salt) in a two-phase liquid. Each show very distinct optical behavior in the water phase of a reverse microemulsion. Their optical properties such as absorption and fluorescence for different concentrations of dye and nanodroplets are investigated. We show that for the same concentration of dye in the microemulsion the peak of fluorescence intensity is varied by altering the concentration of nanodroplets. However, the trend of the change is widely different depending on the hydrophobicity of dyes. Quantum-mechanical second order perturbation theory is used to calculate the ratio of dipole moments in the ground and excited states, which accounts for the Stokes shift in fluorescence peak. Photon correlation spectroscopy is employed to check the trace of the dye in the oil phase of the microemulsion.

Reversible optical switching of highly confined phonon-polaritons with an ultrathin phase-change material

NASA Astrophysics Data System (ADS)

Li, Peining; Yang, Xiaosheng; Maß, Tobias W. W.; Hanss, Julian; Lewin, Martin; Michel, Ann-Katrin U.; Wuttig, Matthias; Taubner, Thomas

2016-08-01

Surface phonon-polaritons (SPhPs), collective excitations of photons coupled with phonons in polar crystals, enable strong light-matter interaction and numerous infrared nanophotonic applications. However, as the lattice vibrations are determined by the crystal structure, the dynamical control of SPhPs remains challenging. Here, we realize the all-optical, non-volatile, and reversible switching of SPhPs by controlling the structural phase of a phase-change material (PCM) employed as a switchable dielectric environment. We experimentally demonstrate optical switching of an ultrathin PCM film (down to 7 nm, <λ/1,200) with single laser pulses and detect ultra-confined SPhPs (polariton wavevector kp > 70k0, k0 = 2π/λ) in quartz. Our proof of concept allows the preparation of all-dielectric, rewritable SPhP resonators without the need for complex fabrication methods. With optimized materials and parallelized optical addressing we foresee application potential for switchable infrared nanophotonic elements, for example, imaging elements such as superlenses and hyperlenses, as well as reconfigurable metasurfaces and sensors.

Fabrication of microlens array with controllable high NA and tailored optical characteristics using confined ink-jetting

NASA Astrophysics Data System (ADS)

Wang, Li; Luo, Yu; Liu, ZengZeng; Feng, Xueming; Lu, Bingheng

2018-06-01

This work presents an economic and controllable fabricating method of high numerical aperture (NA) polymer microlens array (MLA) based on ink-jetting technology. The MLAs are ink-jetted to align on micro platforms patterned flexible PDMS substrate. The shape of a sole lens is constructed by the ink-jetted pre-cured polymer volume confined on a micro platform. In this way, MLAs with targeted geometries-as well as tailored optical characteristics-can be printed, leading to freely designed optical properties. High NA from 0.446 to 0.885 and focal lengths between 99.26 μm and 39.45 μm are demonstrated, confirming theoretical predictions. Particularly, both the simulations and experimental measurements in optical properties are carried out, demonstrating that microlenses with shapes beyond a hemisphere (CA > 90°) exhibits higher light utilization efficiency and wider viewing angle. Meanwhile, the MLAs are fabricated on flexible PDMS substrates and can be attached to other curved surfaces for wider field of view imaging and higher sensitivity.

Slow light enhanced optical nonlinearity in a silicon photonic crystal coupled-resonator optical waveguide.

PubMed

Matsuda, Nobuyuki; Kato, Takumi; Harada, Ken-Ichi; Takesue, Hiroki; Kuramochi, Eiichi; Taniyama, Hideaki; Notomi, Masaya

2011-10-10

We demonstrate highly enhanced optical nonlinearity in a coupled-resonator optical waveguide (CROW) in a four-wave mixing experiment. Using a CROW consisting of 200 coupled resonators based on width-modulated photonic crystal nanocavities in a line defect, we obtained an effective nonlinear constant exceeding 10,000 /W/m, thanks to slow light propagation combined with a strong spatial confinement of light achieved by the wavelength-sized cavities.

Anomalous Faraday effect of a system with extraordinary optical transmittance.

PubMed

Khanikaev, Alexander B; Baryshev, Alexander V; Fedyanin, Andrey A; Granovsky, Alexander B; Inoue, Mitsuteru

2007-05-28

It is shown theoretically that the Faraday rotation becomes anomalously large and exhibits extraordinary behavior near the frequencies of the extraordinary optical transmittance through optically thick perforated metal film with holes filled with a magneto-optically active material. This phenomenon is explained as result of strong confinement of the evanescent electromagnetic field within magnetic material, which occurs due to excitation of the coupled plasmon-polaritons on the opposite surfaces of the film.

Molecular Insights into Division of Single Human Cancer Cells in On-Chip Transparent Microtubes

PubMed Central

2016-01-01

In vivo, mammalian cells proliferate within 3D environments consisting of numerous microcavities and channels, which contain a variety of chemical and physical cues. External environments often differ between normal and pathological states, such as the unique spatial constraints that metastasizing cancer cells experience as they circulate the vasculature through arterioles and narrow capillaries, where they can divide and acquire elongated cylindrical shapes. While metastatic tumors cause most cancer deaths, factors impacting early cancer cell proliferation inside the vasculature and those that can promote the formation of secondary tumors remain largely unknown. Prior studies investigating confined mitosis have mainly used 2D cell culture systems. Here, we mimic aspects of metastasizing tumor cells dividing inside blood capillaries by investigating single-cell divisions of living human cancer cells, trapped inside 3D rolled-up, transparent nanomembranes. We assess the molecular effects of tubular confinement on key mitotic features, using optical high- and super-resolution microscopy. Our experiments show that tubular confinement affects the morphology and dynamics of the mitotic spindle, chromosome arrangements, and the organization of the cell cortex. Moreover, we reveal that membrane blebbing and/or associated processes act as a potential genome-safety mechanism, limiting the extent of genomic instability caused by mitosis in confined circumstances, especially in tubular 3D microenvironments. Collectively, our study demonstrates the potential of rolled-up nanomembranes for gaining molecular insights into key cellular events occurring in tubular 3D microenvironments in vivo. PMID:27267364

Enhanced ionic liquid mobility induced by confinement in 1D CNT membranes

NASA Astrophysics Data System (ADS)

Berrod, Q.; Ferdeghini, F.; Judeinstein, P.; Genevaz, N.; Ramos, R.; Fournier, A.; Dijon, J.; Ollivier, J.; Rols, S.; Yu, D.; Mole, R. A.; Zanotti, J.-M.

2016-04-01

Water confined within carbon nanotubes (CNT) exhibits tremendous enhanced transport properties. Here, we extend this result to ionic liquids (IL) confined in vertically aligned CNT membranes. Under confinement, the IL self-diffusion coefficient is increased by a factor 3 compared to its bulk reference. This could lead to high power battery separators.Water confined within carbon nanotubes (CNT) exhibits tremendous enhanced transport properties. Here, we extend this result to ionic liquids (IL) confined in vertically aligned CNT membranes. Under confinement, the IL self-diffusion coefficient is increased by a factor 3 compared to its bulk reference. This could lead to high power battery separators. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01445c

Relative merits of phononics vs. plasmonics: the energy balance approach

NASA Astrophysics Data System (ADS)

Khurgin, Jacob B.

2018-01-01

The common feature of various plasmonic schemes is their ability to confine optical fields of surface plasmon polaritons (SPPs) into subwavelength volumes and thus achieve a large enhancement of linear and nonlinear optical properties. This ability, however, is severely limited by the large ohmic loss inherent to even the best of metals. However, in the mid- and far-infrared ranges of the spectrum, there exists a viable alternative to metals - polar dielectrics and semiconductors, in which dielectric permittivity (the real part) turns negative in the Reststrahlen region. This feature engenders the so-called surface phonon polaritons, capable of confining the field in a way akin to their plasmonic analogs, the SPPs. Since the damping rate of polar phonons is substantially less than that of free electrons, it is not unreasonable to expect that phononic devices may outperform their plasmonic counterparts. Yet a more rigorous analysis of the comparative merits of phononics and plasmonics reveals a more nuanced answer, namely, that while phononic schemes do exhibit narrower resonances and can achieve a very high degree of energy concentration, most of the energy is contained in the form of lattice vibrations so that enhancement of the electric field and, hence, the Purcell factor is rather small compared to what can be achieved with metal nanoantennas. Still, the sheer narrowness of phononic resonances is expected to make phononics viable in applications where frequency selectivity is important.

Wavelength stabilized DBR high power diode laser using EBL optical confining grating technology

NASA Astrophysics Data System (ADS)

Paoletti, R.; Codato, S.; Coriasso, C.; Gotta, P.; Meneghini, G.; Morello, G.; De Melchiorre, P.; Riva, E.; Rosso, M.; Stano, A.; Gattiglio, M.

2018-02-01

This paper reports a DBR High Power Diode Laser (DBR-HPDL) realization, emitting up to 10W in the 920 nm range. High spectral purity (90% power in about 0.5 nm), and wavelength stability versus injected current (about 5 times more than standard FP laser) candidates DBR-HPDL as a suitable device for wavelength stabilized pump source, and high brightness applications exploiting Wavelength Division Multiplexing. Key design aspect is a multiple-orders Electron Beam Lithography (EBL) optical confining grating, stabilizing on same wafer multiple wavelengths by a manufacturable and reliable technology. Present paper shows preliminary demonstration of wafer with 3 pitches, generating DBRHPDLs 2.5 nm spaced.

Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robert, C., E-mail: cedric.robert@insa-rennes.fr, E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.

The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

One-dimensional self-confinement promotes polymorph selection in large-area organic semiconductor thin films.

PubMed

Giri, Gaurav; Li, Ruipeng; Smilgies, Detlef-M; Li, Er Qiang; Diao, Ying; Lenn, Kristina M; Chiu, Melanie; Lin, Debora W; Allen, Ranulfo; Reinspach, Julia; Mannsfeld, Stefan C B; Thoroddsen, Sigurdur T; Clancy, Paulette; Bao, Zhenan; Amassian, Aram

2014-04-16

A crystal's structure has significant impact on its resulting biological, physical, optical and electronic properties. In organic electronics, 6,13(bis-triisopropylsilylethynyl)pentacene (TIPS-pentacene), a small-molecule organic semiconductor, adopts metastable polymorphs possessing significantly faster charge transport than the equilibrium crystal when deposited using the solution-shearing method. Here, we use a combination of high-speed polarized optical microscopy, in situ microbeam grazing incidence wide-angle X-ray-scattering and molecular simulations to understand the mechanism behind formation of metastable TIPS-pentacene polymorphs. We observe that thin-film crystallization occurs first at the air-solution interface, and nanoscale vertical spatial confinement of the solution results in formation of metastable polymorphs, a one-dimensional and large-area analogy to crystallization of polymorphs in nanoporous matrices. We demonstrate that metastable polymorphism can be tuned with unprecedented control and produced over large areas by either varying physical confinement conditions or by tuning energetic conditions during crystallization through use of solvent molecules of various sizes.

Lamb-Dicke spectroscopy of atoms in a hollow-core photonic crystal fibre

PubMed Central

Okaba, Shoichi; Takano, Tetsushi; Benabid, Fetah; Bradley, Tom; Vincetti, Luca; Maizelis, Zakhar; Yampol'skii, Valery; Nori, Franco; Katori, Hidetoshi

2014-01-01

Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom–atom and atom–wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturization. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kagome-lattice hollow-core photonic crystal fibre are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom–atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the 1S0−3P1(m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibres improve the optical depth while preserving atomic coherence time. PMID:24934478

The size-quantized oscillations of the optical-phonon-limited electron mobility in AlN/GaN/AlN nanoscale heterostructures

NASA Astrophysics Data System (ADS)

Pokatilov, E. P.; Nika, D. L.; Askerov, A. S.; Zincenco, N. D.; Balandin, A. A.

2007-12-01

nanometer scale thickness by taking into account multiple quantized electron subbands and the confined optical phonon dispersion. It was shown that the inter-subband electronic transitions play an important role in limiting the electron mobility in the heterostructures when the energy separation between one of the size-quantized excited electron subbands and the Fermi energy becomes comparable to the optical phonon energy. The latter leads to the oscillatory dependence of the electron mobility on the thickness of the heterostructure conduction channel layer. This effect is observable at room temperature and over a wide range of the carrier densities. The developed formalism and calculation procedure are readily applicable to other material systems. The described effect can be used for fine-tuning the confined electron and phonon states in the nanoscale heterostructures in order to achieve performance enhancement of the nanoscale electronic and optoelectronic devices.

Active Control of Charge Density Waves at Degenerate Semiconductor Interfaces

NASA Astrophysics Data System (ADS)

Vinnakota, Raj; Genov, Dentcho

We present numerical modeling of an active electronically controlled highly confined charge-density waves, i.e. surface plasmon polaritons (SPPs) at the metallurgic interfaces of degenerate semiconductor materials. An electro-optic switching element for fully-functional plasmonic circuits based on p-n junction semiconductor Surface Plasmon Polariton (SPP) waveguide is shown. Two figures of merits are introduced and parametric study has been performed identifying the device optimal operation range. The Indium Gallium Arsenide (In0.53Ga0.47As) is identified as the best semiconductor material for the device providing high optical confinement, reduced system size and fast operation. The electro-optic SPP switching element is shown to operate at signal modulation up to -24dB and switching rates surpassing 100GHz, thus potentially providing a new pathway toward bridging the gap between electronic and photonic devices. The current work is funded by the NSF EPSCoR CIMM project under award #OIA-1541079.

Bohmian Photonics for Independent Control of the Phase and Amplitude of Waves

NASA Astrophysics Data System (ADS)

Yu, Sunkyu; Piao, Xianji; Park, Namkyoo

2018-05-01

The de Broglie-Bohm theory is one of the nonstandard interpretations of quantum phenomena that focuses on reintroducing definite positions of particles, in contrast to the indeterminism of the Copenhagen interpretation. In spite of intense debate on its measurement and nonlocality, the de Broglie-Bohm theory based on the reformulation of the Schrödinger equation allows for the description of quantum phenomena as deterministic trajectories embodied in the modified Hamilton-Jacobi mechanics. Here, we apply the Bohmian reformulation to Maxwell's equations to achieve the independent manipulation of optical phase evolution and energy confinement. After establishing the deterministic design method based on the Bohmian approach, we investigate the condition of optical materials enabling scattering-free light with bounded or random phase evolutions. We also demonstrate a unique form of optical confinement and annihilation that preserves the phase information of incident light. Our separate tailoring of wave information extends the notion and range of artificial materials.

Au10(SG)10: A Chiral Gold Catenane Nanocluster with Zero Confined Electrons. Optical Properties and First-Principles Theoretical Analysis.

PubMed

Bertorelle, Franck; Russier-Antoine, Isabelle; Calin, Nathalie; Comby-Zerbino, Clothilde; Bensalah-Ledoux, Amina; Guy, Stephan; Dugourd, Philippe; Brevet, Pierre-François; Sanader, Željka; Krstić, Marjan; Bonačić-Koutecký, Vlasta; Antoine, Rodolphe

2017-05-04

We report facile synthesis of the Au 10 (SG) 10 nanoclusters, where SG stands for glutathione, found to be promising as a new class of radiosensitizers for cancer radiotherapy. The homoleptic catenane structure with two Au 5 SG 5 interconnected rings, among different isomer structures, gives the best agreement between theoretical and experimental optical spectra and XRD patterns. This catenane structure exhibits a centrosymmetry-broken structure, resulting in enhanced second harmonic response and new characteristic circular dichroism signals in the spectral region of 250-400 nm. This is the first determination of the nonlinear optical properties of a ligated cluster with an equal Au-to-ligand ratio, thus without a metallic core and therefore zero confined electrons. Insight into the nonlinear and chiroptical efficiencies arising from interplay between structural and electronic properties is provided by the TD-DFT approach.

Extreme triple asymmetric (ETAS) epitaxial designs for increased efficiency at high powers in 9xx-nm diode lasers

NASA Astrophysics Data System (ADS)

Kaul, T.; Erbert, G.; Maaßdorf, A.; Martin, D.; Crump, P.

2018-02-01

Broad area lasers that are tailored to be most efficient at the highest achievable optical output power are sought by industry to decrease operation costs and improve system performance. Devices using Extreme-Double-ASymmetric (EDAS) epitaxial designs are promising candidates for improved efficiency at high optical output powers due to low series resistance, low optical loss and low carrier leakage. However, EDAS designs leverage ultra-thin p-side waveguides, meaning that the optical mode is shifted into the n-side waveguide, resulting in a low optical confinement in the active region, low gain and hence high threshold current, limiting peak performance. We introduce here explicit design considerations that enable EDAS-based devices to be developed with increased optical confinement in the active layer without changing the p-side layer thicknesses. Specifically, this is realized by introducing a third asymmetric component in the vicinity of the quantum well. We call this approach Extreme-Triple-ASymmetric (ETAS) design. A series of ETAS-based vertical designs were fabricated into broad area lasers that deliver up to 63% power conversion efficiency at 14 W CW optical output power from a 100 μm stripe laser, which corresponds to the operation point of a kW optical output power in a laser bar. The design process, the impact of structural changes on power saturation mechanisms and finally devices with improved performance will be presented.

MOCVD-Grown InGaAsP Double Heterostructure Diode Lasers

DTIC Science & Technology

1993-08-01

assuming refractive index and its dispersion for InGaAsP and InGaP corresponding to the known values for AIGaAs compounds with the same bandgap [13...in the refractive index between the waveguide and cladding layers provides light confinement within the optical cavity. Separate optical and

Mott glass from localization and confinement

NASA Astrophysics Data System (ADS)

Chou, Yang-Zhi; Nandkishore, Rahul M.; Radzihovsky, Leo

2018-05-01

We study a system of fermions in one spatial dimension with linearly confining interactions and short-range disorder. We focus on the zero-temperature properties of this system, which we characterize using bosonization and the Gaussian variational method. We compute the static compressibility and ac conductivity, and thereby demonstrate that the system is incompressible, but exhibits gapless optical conductivity. This corresponds to a "Mott glass" state, distinct from an Anderson and a fully gapped Mott insulator, arising due to the interplay of disorder and charge confinement. We argue that this Mott glass phenomenology should persist to nonzero temperatures.

Electron-phonon interactions in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Yu, Segi

In this dissertation, electron-phonon interactions are studied theoretically in semiconductor nanoscale heterostructures. Interactions of electrons with interface optical phonons dominate over other electron-phonon interactions in narrow width heterostructures. Hence, a transfer matrix method is used to establish a formalism for determining the dispersion relations and electrostatic potentials of the interface phonons for multiple-interface heterostructure within the macroscopic dielectric continuum model. This method facilitates systematic calculations for complex structures where the conventional method is difficult to implement. Several specific cases are treated to illustrate advantages of the formalism. Electrophonon resonance (EPR) is studied in cylindrical quantum wires using the confined/interface optical phonons representation and bulk phonon representation. It has been found that interface phonon contribution to EPR is small compared with confined phonon. Different selection rules for bulk phonons and confined phonons result in different EPR behaviors as the radius of cylindrical wire changes. Experiment is suggested to test which phonon representation is appropriate for EPR. The effects of phonon confinement on elect ron-acoustic-phonon scattering is studied in cylindrical and rectangular quantum wires. In the macroscopic elastic continuum model, the confined-phonon dispersion relations are obtained for several crystallographic directions with free-surface and clamped-surface boundary conditions in cylindrical wires. The scattering rates due to the deformation potential are obtained for these confined phonons and are compared with those of bulk-like phonons. The results show that the inclusion of acoustic phonon confinement may be crucial for calculating accurate low-energy electron scattering rates. Furthermore, it has been found that there is a scaling rule governing the directional dependence of the scattering rates. The Hamiltonian describing the deformation-potential of confined acoustic phonons is derived by quantizing the appropriate, experimentally verified approximate compressional acoustic-phonon modes in a free-standing rectangular quantum wire. The scattering rate is obtained for GaAs quantum wires with a range of cross-sectional dimensions. The results demonstrate that a proper treatment of confined acoustic phonons may be essential to correctly model electron scattering rates at low energies in nanoscale structures.

Lithographically Defined, Room Temperature Low Threshold Subwavelength Red-Emitting Hybrid Plasmonic Lasers.

PubMed

Liu, Ning; Gocalinska, Agnieszka; Justice, John; Gity, Farzan; Povey, Ian; McCarthy, Brendan; Pemble, Martyn; Pelucchi, Emanuele; Wei, Hong; Silien, Christophe; Xu, Hongxing; Corbett, Brian

2016-12-14

Hybrid plasmonic lasers provide deep subwavelength optical confinement, strongly enhanced light-matter interaction and together with nanoscale footprint promise new applications in optical communication, biosensing, and photolithography. The subwavelength hybrid plasmonic lasers reported so far often use bottom-up grown nanowires, nanorods, and nanosquares, making it difficult to integrate these devices into industry-relevant high density plasmonic circuits. Here, we report the first experimental demonstration of AlGaInP based, red-emitting hybrid plasmonic lasers at room temperature using lithography based fabrication processes. Resonant cavities with deep subwavelength 2D and 3D mode confinement of λ 2 /56 and λ 3 /199, respectively, are demonstrated. A range of cavity geometries (waveguides, rings, squares, and disks) show very low lasing thresholds of 0.6-1.8 mJ/cm 2 with wide gain bandwidth (610 nm-685 nm), which are attributed to the heterogeneous geometry of the gain material, the optimized etching technique, and the strong overlap of the gain material with the plasmonic modes. Most importantly, we establish the connection between mode confinements and enhanced absorption and stimulated emission, which plays critical roles in maintaining low lasing thresholds at extremely small hybrid plasmonic cavities. Our results pave the way for the further integration of dense arrays of hybrid plasmonic lasers with optical and electronic technology platforms.

Vibrational nonlinear optical properties of spatially confined weakly bound complexes.

PubMed

Zaleśny, Robert; Chołuj, Marta; Kozłowska, Justyna; Bartkowiak, Wojciech; Luis, Josep M

2017-09-13

This study focuses on the theoretical description of the influence of spatial confinement on the electronic and vibrational contributions to (hyper)polarizabilities of two dimeric hydrogen bonded systems, namely HCNHCN and HCNHNC. A two-dimensional analytical potential is employed to render the confining environment (e.g. carbon nanotube). Based on the results of the state-of-the-art calculations, performed at the CCSD(T)/aug-cc-pVTZ level of theory, we established that: (i) the influence of spatial confinement increases with increasing order of the electrical properties, (ii) the effect of spatial confinement is much larger in the case of the electronic than vibrational contribution (this holds for each order of the electrical properties) and (iii) the decrease in the static nuclear relaxation first hyperpolarizability upon the increase of confinement strength is mainly due to changes in the harmonic term, however, in the case of nuclear relaxation second hyperpolarizability the anharmonic terms contribute more to the drop of this property.

Influence of confinement layers in the emitting layer of the blue phosphorescent organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Ji, Chang-Yan; Gu, Zheng-Tian; Kou, Zhi-Qi

2016-10-01

The electrical and optical properties of the blue phosphorescent organic light-emitting diodes (PHOLEDs) can be affected by the various structure of confinement layer in the emitting layer (EML). A series of devices with different electron or hole confinement layer (TCTA or Bphen) are fabricated, it is more effective to balance charge carriers injection for the device with the double electron confinement layers structure, the power efficiency and luminance can reach 17.7 lm/W (at 103 cd/m2) and 3536 cd/m2 (at 8 V). In case of the same double electron confinement layers, another series of devices with different profile of EML are fabricated by changing the confinement layers position, the power efficiency and luminance can be improved to 21.7 lm/W (at 103 cd/m2) and 7674 cd/m2 (at 8 V) when the thickness of EML separated by confinement layers increases gradually from the hole injection side to the electron injection side, the driving voltage can also be reduced.

Integrated optical isolators using magnetic surface plasmon (Presentation Recording)

NASA Astrophysics Data System (ADS)

Shimizu, Hiromasa; Kaihara, Terunori; Umetsu, Saori; Hosoda, Masashi

2015-09-01

Optical isolators are one of the essential components to protect semiconductor laser diodes (LDs) from backward reflected light in integrated optics. In order to realize optical isolators, nonreciprocal propagation of light is necessary, which can be realized by magnetic materials. Semiconductor optical isolators have been strongly desired on Si and III/V waveguides. We have developed semiconductor optical isolators based on nonreciprocal loss owing to transverse magneto-optic Kerr effect, where the ferromagnetic metals are deposited on semiconductor optical waveguides1). Use of surface plasmon polariton at the interface of ferromagnetic metal and insulator leads to stronger optical confinement and magneto-optic effect. It is possible to modulate the optical confinement by changing the magnetic field direction, thus optical isolator operation is proposed2, 3). We have investigated surface plasmons at the interfaces between ferrimagnetic garnet/gold film, and applications to waveguide optical isolators. We assumed waveguides composed of Au/Si(38.63nm)/Ce:YIG(1700nm)/Si(220nm)/Si , and calculated the coupling lengths between Au/Si(38.63nm)/Ce:YIG plasmonic waveguide and Ce:YIG/Si(220nm)/Si waveguide for transversely magnetized Ce:YIG with forward and backward directions. The coupling length was calculated to 232.1um for backward propagating light. On the other hand, the coupling was not complete, and the length was calculated to 175.5um. The optical isolation by using the nonreciprocal coupling and propagation loss was calculated to be 43.7dB when the length of plasmonic waveguide is 700um. 1) H. Shimizu et al., J. Lightwave Technol. 24, 38 (2006). 2) V. Zayets et al., Materials, 5, 857-871 (2012). 3) J. Montoya, et al, J. Appl. Phys. 106, 023108, (2009).

Heterogeneous microring and Mach-Zehnder modulators based on lithium niobate and chalcogenide glasses on silicon

DOE PAGES

Rao, Ashutosh; Patil, Aniket; Chiles, Jeff; ...

2015-08-20

In this study, thin films of lithium niobate are wafer bonded onto silicon substrates and rib-loaded with a chalcogenide glass, Ge 23Sb 7S 70, to demonstrate strongly confined single-mode submicron waveguides, microring modulators, and Mach-Zehnder modulators in the telecom C band. The 200 μm radii microring modulators present 1.2 dB/cm waveguide propagation loss, 1.2 × 10 5 quality factor, 0.4 GHz/V tuning rate, and 13 dB extinction ratio. The 6 mm long Mach-Zehnder modulators have a half-wave voltage-length product of 3.8 V.cm and an extinction ratio of 15 dB. The demonstrated work is a key step towards enabling wafer scalemore » dense on-chip integration of high performance lithium niobate electro-optical devices on silicon for short reach optical interconnects and higher order advanced modulation schemes.« less

Multiple coherent light scattering in ultracold rubidium

NASA Astrophysics Data System (ADS)

Kulatunga, P.; Sukenik, C. I.; Havey, M. D.; Kupriyanov, D. V.; Sokolov, I. M.

2001-11-01

We report investigation of multiple coherent light scattering from ^85Rb atoms confined in a magneto-optic trap. In a theoretical study of intensity enhancement of near-resonant backscattered light from cold ^85,87Rb atoms, we consider the dominant mode of double scattering only. Enhancement factors are calculated for all D1 and D2 hyperfine components and for both isotopes. In experimental studies, measurements are made of coherent backscattering of a low-intensity probe beam tuned near the F = 3 - F' = 4 transition in ^85Rb atoms. Polarization of backscattered light is determined by a backscattering polarimeter; the spatial distribution of light intensity is measured by a liquid-nitrogen cooled CCD camera set in the focal plane of the analyzing optics. The instrument has angular resolution of about 100 micro-radians, and a polarization analyzing power of roughly 1000. In this paper we describe the instrument details, including calibration procedures, and progress towards observation of atomic coherent backscattering.

Multiple coherent light scattering in ultracold rubidium

NASA Astrophysics Data System (ADS)

Havey, M. D.; Sukenik, C. I.; Kulatunga, P.; Kupriyanov, D. V.; Sokolov, I. M.

2001-05-01

We report investigation of multiple coherent light scattering from ^85Rb atoms confined in a magneto-optic trap. In a theoretical study of intensity enhancement of near-resonant backscattered light from cold ^85,87Rb atoms, we consider the dominant mode of double scattering only. Enhancement factors are calculated for all D1 and D2 hyperfine components and for both isotopes. In experimental studies, measurements are made of coherent backscattering of a low-intensity probe beam tuned near the F = 3 - F' = 4 transition in ^85Rb atoms. Polarization of backscattered light is determined by a backscattering polarimeter; the spatial distribution of light intensity is measured by a liquid-nitrogen cooled CCD camera set in the focal plane of the analyzing optics. The instrument has angular resolution of about 100 micro-radians, and a polarization analyzing power of roughly 1000. In this paper we describe the instrument details, including calibration procedures, and progress towards observation of atomic coherent backscattering.

Heterogeneous microring and Mach-Zehnder modulators based on lithium niobate and chalcogenide glasses on silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rao, Ashutosh; Patil, Aniket; Chiles, Jeff

In this study, thin films of lithium niobate are wafer bonded onto silicon substrates and rib-loaded with a chalcogenide glass, Ge 23Sb 7S 70, to demonstrate strongly confined single-mode submicron waveguides, microring modulators, and Mach-Zehnder modulators in the telecom C band. The 200 μm radii microring modulators present 1.2 dB/cm waveguide propagation loss, 1.2 × 10 5 quality factor, 0.4 GHz/V tuning rate, and 13 dB extinction ratio. The 6 mm long Mach-Zehnder modulators have a half-wave voltage-length product of 3.8 V.cm and an extinction ratio of 15 dB. The demonstrated work is a key step towards enabling wafer scalemore » dense on-chip integration of high performance lithium niobate electro-optical devices on silicon for short reach optical interconnects and higher order advanced modulation schemes.« less

Design of a terahertz parametric oscillator based on a resonant cavity in a terahertz waveguide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saito, K., E-mail: k-saito@material.tohoku.ac.jp; Oyama, Y.; Tanabe, T.

We demonstrate ns-pulsed pumping of terahertz (THz) parametric oscillations in a quasi-triply resonant cavity in a THz waveguide. The THz waves, down converted through parametric interactions between the pump and signal waves at telecom frequencies, are confined to a GaP single mode ridge waveguide. By combining the THz waveguide with a quasi-triply resonant cavity, the nonlinear interactions can be enhanced. A low threshold pump intensity for parametric oscillations can be achieved in the cavity waveguide. The THz output power can be maximized by optimizing the quality factors of the cavity so that an optical to THz photon conversion efficiency, η{submore » p}, of 0.35, which is near the quantum-limit level, can be attained. The proposed THz optical parametric oscillator can be utilized as an efficient and monochromatic THz source.« less

Alpha Radiation Effects on Silicon Oxynitride Waveguides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morichetti, Francesco; Grillanda, Stefano; Manandhar, Sandeep

2016-09-21

Photonic technologies are today of great interest for use in harsh environments, such as outer space, where they can potentially replace current communication systems based on radiofrequency components. However, very much alike to electronic devices, the behavior of optical materials and circuits can be strongly altered by high-energy and high-dose ionizing radiations. Here, we investigate the effects of alpha () radiation with MeV-range energy on silicon oxynitride (SiON) optical waveguides. Irradiation with a dose of 5×1015 cm-2 increases the refractive index of the SiON core by nearly 10-2, twice as much that of the surrounding silica cladding, leading to amore » significant increase of the refractive index contrast of the waveguide. The higher mode confinement induced by -radiation reduces the loss of tightly bent waveguides. We show that this increases the quality factor of microring resonators by 20%, with values larger than 105 after irradiation.« less

Passive isolation/damping system for the Hubble space telescope reaction wheels

NASA Technical Reports Server (NTRS)

Hasha, Martin D.

1987-01-01

NASA's Hubble Space Telescope contain large, diffraction limited optics with extraordinary resolution and performance for surpassing existing observatories. The need to reduce structural borne vibration and resultant optical jitter from critical Pointing Control System components, Reaction Wheels, prompted the feasibility investigation and eventual development of a passive isolation system. Alternative design concepts considered were required to meet a host of stringent specifications and pass rigid tests to be successfully verified and integrated into the already built flight vehicle. The final design employs multiple arrays of fluid damped springs that attenuate over a wide spectrum, while confining newly introduced resonances to benign regions of vehicle dynamic response. Overall jitter improvement of roughly a factor of 2 to 3 is attained with this system. The basis, evolution, and performance of the isolation system, specifically discussing design concepts considered, optimization studies, development lessons learned, innovative features, and analytical and ground test verified results are presented.

High-fidelity quantum gates on quantum-dot-confined electron spins in low-Q optical microcavities

NASA Astrophysics Data System (ADS)

Li, Tao; Gao, Jian-Cun; Deng, Fu-Guo; Long, Gui-Lu

2018-04-01

We propose some high-fidelity quantum circuits for quantum computing on electron spins of quantum dots (QD) embedded in low-Q optical microcavities, including the two-qubit controlled-NOT gate and the multiple-target-qubit controlled-NOT gate. The fidelities of both quantum gates can, in principle, be robust to imperfections involved in a practical input-output process of a single photon by converting the infidelity into a heralded error. Furthermore, the influence of two different decay channels is detailed. By decreasing the quality factor of the present microcavity, we can largely increase the efficiencies of these quantum gates while their high fidelities remain unaffected. This proposal also has another advantage regarding its experimental feasibility, in that both quantum gates can work faithfully even when the QD-cavity systems are non-identical, which is of particular importance in current semiconductor QD technology.

Lasing from active optomechanical resonators

PubMed Central

Czerniuk, T.; Brüggemann, C.; Tepper, J.; Brodbeck, S.; Schneider, C.; Kamp, M.; Höfling, S.; Glavin, B. A.; Yakovlev, D. R.; Akimov, A. V.; Bayer, M.

2014-01-01

Planar microcavities with distributed Bragg reflectors (DBRs) host, besides confined optical modes, also mechanical resonances due to stop bands in the phonon dispersion relation of the DBRs. These resonances have frequencies in the 10- to 100-GHz range, depending on the resonator’s optical wavelength, with quality factors exceeding 1,000. The interaction of photons and phonons in such optomechanical systems can be drastically enhanced, opening a new route towards the manipulation of light. Here we implemented active semiconducting layers into the microcavity to obtain a vertical-cavity surface-emitting laser (VCSEL). Thereby, three resonant excitations—photons, phonons and electrons—can interact strongly with each other providing modulation of the VCSEL laser emission: a picosecond strain pulse injected into the VCSEL excites long-living mechanical resonances therein. As a result, modulation of the lasing intensity at frequencies up to 40 GHz is observed. From these findings, prospective applications of active optomechanical resonators integrated into nanophotonic circuits may emerge. PMID:25008784

Properties of Type-II ZnTe/ZnSe Submonolayer Quantum Dots Studied via Excitonic Aharonov- Bohm Effect and Polarized Optical Spectroscopy

NASA Astrophysics Data System (ADS)

Ji, Haojie

In this thesis I develop understanding of the fundamental physical and material properties of type-II ZnTe/ZnSe submonolayer quantum dots (QDs), grown via combination of molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). I use magneto-photoluminescence, including excitonic Aharonov-Bohm (AB) effect and polarized optical spectroscopy as the primary tools in this work. I present previous studies as well as the background of optical and magneto-optical processes in semiconductor nanostructures and introduce the experimental methods in Chapters 1 - 3. In Chapter 4 I focus on the excitonic AB effect in the type-II QDs. I develop a lateral tightly-bound exciton model for ZnTe/ZnSe type-II QDs, using analytical methods and numerical calculations. This explained the magneto-PL observation and allowed for establishing the size and density of the QDs in each sample based on the results of PL and magneto-PL measurements. For samples with larger QDs, I observe behaviors that fall between properties of quantum-dot and quantum-well-like systems due to increased QD densities and their type-II nature. Finally, the decoherence mechanisms of the AB excitons are investigated via the temperature dependent studies of the magneto-PL. It is determined that the AB exciton decoherence is due to transport-like (acoustic phonon) scattering of the electrons moving in the ZnSe barriers, but with substantially smaller magnitude of electron-phonon coupling constant due to relatively strong electron-hole coupling within these type-II QDs. In Chapter 5 I discuss the results of circularly polarized magneto-PL measurements. A model with ultra-long spin-flip time of holes confined to submonolayer QDs is proposed. The g-factor of type-II excitons was extracted from the Zeeman splitting and the g-factor of electrons was obtained by fitting the temperature dependence of the degree of circular polarization (DCP), from which g-factor of holes confined within ZnTe QDs was found. It is shown that it is about three times larger than that of bulk ZnTe. In Chapter 6 I study the optical anisotropy in QDs. I show that all samples exhibit such an effect, and explain it based on non-spherical shape of the QDs. Numerical calculation is applied to calculate degree of linear polarization, and estimate the aspect ratio. The exciton anisotropic exchange splitting is calculated from the magnetic field dependence of the DCP. In the last two chapters I show my achievement on the growth of ZnO nanorods as a core for type-II 1D systems and propose an outlook for future research on the type-II semiconductor heterostructures.

Simulation of optically pumped intersubband laser in magnetic field

NASA Astrophysics Data System (ADS)

Erić, Marko; Milanović, Vitomir; Ikonić, Zoran; Indjin, Dragan

2007-06-01

Simulations of an optically pumped intersubband laser in magnetic field up to 60 T are performed within the steady-state rate equations model. The electron-polar optical phonon scattering is calculated using the confined and interface phonon model. A strong oscillatory optical gain vs. magnetic field dependence is found, with two dominant gain peaks occurring at 20 and 40 T, the fields which bring appropriate states into resonance with optical phonons and thus open additional relaxation paths. The peak at 20 T exceeds the value of gain achieved at zero field.

Acoustic trapping of active matter

NASA Astrophysics Data System (ADS)

Takatori, Sho C.; de Dier, Raf; Vermant, Jan; Brady, John F.

2016-03-01

Confinement of living microorganisms and self-propelled particles by an external trap provides a means of analysing the motion and behaviour of active systems. Developing a tweezer with a trapping radius large compared with the swimmers' size and run length has been an experimental challenge, as standard optical traps are too weak. Here we report the novel use of an acoustic tweezer to confine self-propelled particles in two dimensions over distances large compared with the swimmers' run length. We develop a near-harmonic trap to demonstrate the crossover from weak confinement, where the probability density is Boltzmann-like, to strong confinement, where the density is peaked along the perimeter. At high concentrations the swimmers crystallize into a close-packed structure, which subsequently `explodes' as a travelling wave when the tweezer is turned off. The swimmers' confined motion provides a measurement of the swim pressure, a unique mechanical pressure exerted by self-propelled bodies.

Acoustic trapping of active matter

PubMed Central

Takatori, Sho C.; De Dier, Raf; Vermant, Jan; Brady, John F.

2016-01-01

Confinement of living microorganisms and self-propelled particles by an external trap provides a means of analysing the motion and behaviour of active systems. Developing a tweezer with a trapping radius large compared with the swimmers' size and run length has been an experimental challenge, as standard optical traps are too weak. Here we report the novel use of an acoustic tweezer to confine self-propelled particles in two dimensions over distances large compared with the swimmers' run length. We develop a near-harmonic trap to demonstrate the crossover from weak confinement, where the probability density is Boltzmann-like, to strong confinement, where the density is peaked along the perimeter. At high concentrations the swimmers crystallize into a close-packed structure, which subsequently ‘explodes' as a travelling wave when the tweezer is turned off. The swimmers' confined motion provides a measurement of the swim pressure, a unique mechanical pressure exerted by self-propelled bodies. PMID:26961816

An efficient method for the creation of tunable optical line traps via control of gradient and scattering forces.

PubMed

Tietjen, Gregory T; Kong, Yupeng; Parthasarathy, Raghuveer

2008-07-07

Interparticle interaction energies and other useful physical characteristics can be extracted from the statistical properties of the motion of particles confined by an optical line trap. In practice, however, the potential energy landscape, U(x), imposed by the line provides an extra, and in general unknown, influence on particle dynamics. We describe a new class of line traps in which both the optical gradient and scattering forces acting on a trapped particle are designed to be linear functions of the line coordinate and in which their magnitude can be counterbalanced to yield a flat U(x). These traps are formed using approximate solutions to general relations concerning non-conservative optical forces that have been the subject of recent investigations [Y. Roichman, B. Sun, Y. Roichman, J. Amato-Grill, and D. G. Grier, Phys. Rev. Lett. 100, 013602-4 (2008).]. We implement the lines using holographic optical trapping and measure the forces acting on silica microspheres, demonstrating the tunability of the confining potential energy landscape. Furthermore, we show that our approach efficiently directs available laser power to the trap, in contrast to other methods.

Symposium on New Materials for Nonlinear Optics

DTIC Science & Technology

1991-01-01

C. B. Aakeroy, N. Azoz, P. D. Calvert, M. Kadim, A. J. McCaffery, and K. R. Seddon 35 . Clathrasils: New Materials for Nonlinear Optical...of Quantum Confined Semiconductor Structures - D.S. Chemla 2: 35 Preparation and Characterization of Small Semiconductor Particulates - Norman Herron 3...presiding 2:00 Opening Remarks - John Sohn 2:05 Approaches for the Design of Materials for Nonlinear Optics - M. Lahav 2: 35 Control of Symmetry and Asymmetry

Probing plasmonic breathing modes optically

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krug, Markus K., E-mail: markus.krug@uni-graz.at; Reisecker, Michael; Hohenau, Andreas

2014-10-27

The confinement of surface plasmon modes in flat nanoparticles gives rise to plasmonic breathing modes. With a vanishing net dipole moment, breathing modes do not radiate, i.e., they are optically dark. Having thus escaped optical detection, breathing modes were only recently revealed in silver nanodisks with electron energy loss spectroscopy in an electron microscope. We show that for disk diameters >200 nm, retardation induced by oblique optical illumination relaxes the optically dark character. This makes breathing modes and thus the full plasmonic mode spectrum accessible to optical spectroscopy. The experimental spectroscopy data are in excellent agreement with numerical simulations.

A Review of Multimode Interference in Tapered Optical Fibers and Related Applications.

PubMed

Wang, Pengfei; Zhao, Haiyan; Wang, Xianfan; Farrell, Gerald; Brambilla, Gilberto

2018-03-14

In recent years, tapered optical fibers (TOFs) have attracted increasing interest and developed into a range of devices used in many practical applications ranging from optical communication, sensing to optical manipulation and high-Q resonators. Compared with conventional optical fibers, TOFs possess a range of unique features, such as large evanescent field, strong optical confinement, mechanical flexibility and compactness. In this review, we critically summarize the multimode interference in TOFs and some of its applications with a focus on our research project undertaken at the Optoelectronics Research Centre of the University of Southampton in the United Kingdom.

A Review of Multimode Interference in Tapered Optical Fibers and Related Applications

PubMed Central

Wang, Pengfei; Zhao, Haiyan; Wang, Xianfan; Brambilla, Gilberto

2018-01-01

In recent years, tapered optical fibers (TOFs) have attracted increasing interest and developed into a range of devices used in many practical applications ranging from optical communication, sensing to optical manipulation and high-Q resonators. Compared with conventional optical fibers, TOFs possess a range of unique features, such as large evanescent field, strong optical confinement, mechanical flexibility and compactness. In this review, we critically summarize the multimode interference in TOFs and some of its applications with a focus on our research project undertaken at the Optoelectronics Research Centre of the University of Southampton in the United Kingdom. PMID:29538333

Fluorescent fluid interface position sensor

DOEpatents

Weiss, Jonathan D.

2004-02-17

A new fluid interface position sensor has been developed, which is capable of optically determining the location of an interface between an upper fluid and a lower fluid, the upper fluid having a larger refractive index than a lower fluid. The sensor functions by measurement, of fluorescence excited by an optical pump beam which is confined within a fluorescent waveguide where that waveguide is in optical contact with the lower fluid, but escapes from the fluorescent waveguide where that waveguide is in optical contact with the upper fluid.

Remote optical sensing on the nanometer scale with a bowtie aperture nano-antenna on a fiber tip of scanning near-field optical microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atie, Elie M.; Xie, Zhihua; El Eter, Ali

2015-04-13

Plasmonic nano-antennas have proven the outstanding ability of sensing chemical and physical processes down to the nanometer scale. Sensing is usually achieved within the highly confined optical fields generated resonantly by the nano-antennas, i.e., in contact to the nanostructures. In this paper, we demonstrate the sensing capability of nano-antennas to their larger scale environment, well beyond their plasmonic confinement volume, leading to the concept of “remote” (non contact) sensing on the nanometer scale. On the basis of a bowtie-aperture nano-antenna (BNA) integrated at the apex of a SNOM (Scanning Near-field Optical Microscopy) fiber tip, we introduce an ultra-compact, moveable, andmore » background-free optical nanosensor for the remote sensing of a silicon surface (up to distance of 300 nm). Sensitivity of the BNA to its large scale environment is high enough to expect the monitoring and control of the spacing between the nano-antenna and a silicon surface with sub-nanometer accuracy. This work paves the way towards an alternative class of nanopositioning techniques, based on the monitoring of diffraction-free plasmon resonance, that are alternative to nanomechanical and diffraction-limited optical interference-based devices.« less

A comprehensive simulation model of the performance of photochromic films in absorbance-modulation-optical-lithography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majumder, Apratim; Helms, Phillip L.; Menon, Rajesh, E-mail: rmenon@eng.utah.edu

2016-03-15

Optical lithography is the most prevalent method of fabricating micro-and nano-scale structures in the semiconductor industry due to the fact that patterning using photons is fast, accurate and provides high throughput. However, the resolution of this technique is inherently limited by the physical phenomenon of diffraction. Absorbance-Modulation-Optical Lithography (AMOL), a recently developed technique has been successfully demonstrated to be able to circumvent this diffraction limit. AMOL employs a dual-wavelength exposure system in conjunction with spectrally selective reversible photo-transitions in thin films of photochromic molecules to achieve patterning of features with sizes beyond the far-field diffraction limit. We have developed amore » finite-element-method based full-electromagnetic-wave solution model that simulates the photo-chemical processes that occur within the thin film of the photochromic molecules under illumination by the exposure and confining wavelengths in AMOL. This model allows us to understand how the material characteristics influence the confinement to sub-diffraction dimensions, of the transmitted point spread function (PSF) of the exposure wavelength inside the recording medium. The model reported here provides the most comprehensive analysis of the AMOL process to-date, and the results show that the most important factors that govern the process, are the polarization of the two beams, the ratio of the intensities of the two wavelengths, the relative absorption coefficients and the concentration of the photochromic species, the thickness of the photochromic layer and the quantum yields of the photoreactions at the two wavelengths. The aim of this work is to elucidate the requirements of AMOL in successfully circumventing the far-field diffraction limit.« less

Electrical control of second-harmonic generation in a WSe 2 monolayer transistor

DOE PAGES

Seyler, Kyle L.; Schaibley, John R.; Gong, Pu; ...

2015-04-20

Nonlinear optical frequency conversion, in which optical fields interact with a nonlinear medium to produce new field frequencies, is ubiquitous in modern photonic systems. However, the nonlinear electric susceptibilities that give rise to such phenomena are often challenging to tune in a given material and, so far, dynamical control of optical nonlinearities remains confined to research laboratories as a spectroscopic tool. In this paper, we report a mechanism to electrically control second-order optical nonlinearities in monolayer WSe 2, an atomically thin semiconductor. We show that the intensity of second-harmonic generation at the A-exciton resonance is tunable by over an ordermore » of magnitude at low temperature and nearly a factor of four at room temperature through electrostatic doping in a field-effect transistor. Such tunability arises from the strong exciton charging effects in monolayer semiconductors, which allow for exceptional control over the oscillator strengths at the exciton and trion resonances. The exciton-enhanced second-harmonic generation is counter-circularly polarized to the excitation laser due to the combination of the two-photon and one-photon valley selection rules, which have opposite helicity in the monolayer. Finally, our study paves the way towards a new platform for chip-scale, electrically tunable nonlinear optical devices based on two-dimensional semiconductors.« less

Dispersion of the electron g factor anisotropy in InAs/InP self-assembled quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belykh, V. V., E-mail: vasilii.belykh@tu-dortmund.de; P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991; Yakovlev, D. R.

The electron g factor in an ensemble of InAs/InP quantum dots with emission wavelengths around 1.4 μm is measured using time-resolved pump-probe Faraday rotation spectroscopy in different magnetic field orientations. Thereby, we can extend recent single dot photoluminescence measurements significantly towards lower optical transition energies through 0.86 eV. This allows us to obtain detailed insight into the dispersion of the recently discovered g factor anisotropy in these infrared emitting quantum dots. We find with decreasing transition energy over a range of 50 meV a strong enhancement of the g factor difference between magnetic field normal and along the dot growth axis, namely, frommore » 1 to 1.7. We argue that the g factor cannot be solely determined by the confinement energy, but the dot asymmetry underlying this anisotropy therefore has to increase with increasing dot size.« less

Dynamic Failure Processes Under Confining Stress in AlON, a Transparent Polycrystalline Ceramic

DTIC Science & Technology

2008-12-01

axes, the dynamic loading is imposed (using MKB) along the second specimen axis and the third axis is used for the ultra-high-speed photography. The...to its optically isotropic cubic crystal structure, fully dense, polycrystalline bodies can be rendered completely transparent, making it a viable... tribological loading conditions. During indentation, the region beneath the indenter is effectively confined due to the surrounding medium, and it

Intrinsic optical confinement for ultrathin InAsN quantum well superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakri, A.; Robert, C.; Pedesseau, L.

We study energy-band engineering with InAsN monolayer in GaAs/GaP quantum well structure. A tight-binding calculation indicates that both type I alignment along with direct band-gap behavior can be obtained. We show that the optical transitions are less sensitive to the position of the probe.

Collective phenomena in photonic, plasmonic and hybrid structures.

PubMed

Boriskina, Svetlana V; Povinelli, Michelle; Astratov, Vasily N; Zayats, Anatoly V; Podolskiy, Viktor A

2011-10-24

Preface to a focus issue of invited articles that review recent progress in studying the fundamental physics of collective phenomena associated with coupling of confined photonic, plasmonic, electronic and phononic states and in exploiting these phenomena to engineer novel devices for light generation, optical sensing, and information processing. © 2011 Optical Society of America

Quantum interference in plasmonic circuits.

PubMed

Heeres, Reinier W; Kouwenhoven, Leo P; Zwiller, Valery

2013-10-01

Surface plasmon polaritons (plasmons) are a combination of light and a collective oscillation of the free electron plasma at metal/dielectric interfaces. This interaction allows subwavelength confinement of light beyond the diffraction limit inherent to dielectric structures. As a result, the intensity of the electromagnetic field is enhanced, with the possibility to increase the strength of the optical interactions between waveguides, light sources and detectors. Plasmons maintain non-classical photon statistics and preserve entanglement upon transmission through thin, patterned metallic films or weakly confining waveguides. For quantum applications, it is essential that plasmons behave as indistinguishable quantum particles. Here we report on a quantum interference experiment in a nanoscale plasmonic circuit consisting of an on-chip plasmon beamsplitter with integrated superconducting single-photon detectors to allow efficient single plasmon detection. We demonstrate a quantum-mechanical interaction between pairs of indistinguishable surface plasmons by observing Hong-Ou-Mandel (HOM) interference, a hallmark non-classical interference effect that is the basis of linear optics-based quantum computation. Our work shows that it is feasible to shrink quantum optical experiments to the nanoscale and offers a promising route towards subwavelength quantum optical networks.

Light emission from silicon: Some perspectives and applications

NASA Astrophysics Data System (ADS)

Fiory, A. T.; Ravindra, N. M.

2003-10-01

Research on efficient light emission from silicon devices is moving toward leading-edge advances in components for nano-optoelectronics and related areas. A silicon laser is being eagerly sought and may be at hand soon. A key advantage is in the use of silicon-based materials and processing, thereby using high yield and low-cost fabrication techniques. Anticipated applications include an optical emitter for integrated optical circuits, logic, memory, and interconnects; electro-optic isolators; massively parallel optical interconnects and cross connects for integrated circuit chips; lightwave components; high-power discrete and array emitters; and optoelectronic nanocell arrays for detecting biological and chemical agents. The new technical approaches resolve a basic issue with native interband electro-optical emission from bulk Si, which competes with nonradiative phonon- and defect-mediated pathways for electron-hole recombination. Some of the new ways to enhance optical emission efficiency in Si diode devices rely on carrier confinement, including defect and strain engineering in the bulk material. Others use Si nanocrystallites, nanowires, and alloying with Ge and crystal strain methods to achieve the carrier confinement required to boost radiative recombination efficiency. Another approach draws on the considerable progress that has been made in high-efficiency, solar-cell design and uses the reciprocity between photo- and light-emitting diodes. Important advances are also being made with silicon-oxide materials containing optically active rare-earth impurities.

Transition Behaviors of Configurations of Colloidal Particles at a Curved Oil-Water Interface

PubMed Central

Lee, Mina; Xia, Ming; Park, Bum Jun

2016-01-01

We studied the transition behaviors of colloidal arrangements confined at a centro-symmetrically curved oil-water interface. We found that assemblies composed of several colloidal particles at the curved interface exhibit at least two unique patterns that can be attributed to two factors: heterogeneity of single-colloid self-potential and assembly kinetics. The presence of the two assembly structures indicates that an essential energy barrier between the two structures exists and that one of the structures is kinetically stable. This energy barrier can be overcome via external stimuli (e.g., convection and an optical force), leading to dynamic transitions of the assembly patterns. PMID:28773263

Photonic crystal nanofiber air-mode cavity with high Q-factor and high sensitivity for refractive index sensing

NASA Astrophysics Data System (ADS)

Ma, Xiaoxue; Chen, Xin; Nie, Hongrui; Yang, Daquan

2018-01-01

Recently, due to its superior characteristics and simple manufacture, such as small size, low loss, high sensitivity and convenience to couple, the optical fiber sensor has become one of the most promising sensors. In order to achieve the most effective realization of light propagation by changing the structure of sensors, FOM(S •Q/λres) ,which is determined by two significant variables Q-factor and sensitivity, as a trade-off parameter should be optimized to a high value. In typical sensors, a high Q can be achieved by confining the optical field in the high refractive index dielectric region to make an interaction between analytes and evanescent field of the resonant mode. However, the ignored sensitivity is relatively low with a high Q achieved, which means that the resonant wavelength shift changes non-obviously when the refractive index increases. Meanwhile, the sensitivity also leads to a less desirable FOM. Therefore, a gradient structure, which can enhance the performance of sensors by achieving high Q and high sensitivity, has been developed by Kim et al. later. Here, by introducing parabolic-tapered structure, the light field localized overlaps strongly and sufficiently with analytes. And based on a one-dimensional photonic-crystal nanofiber air-mode cavity, a creative optical fiber sensor is proposed by combining good stability and transmission characteristics of fiber and strengths of tapered structure, realizing excellent FOM {4.7 x 105 with high Q-factors (Q{106) and high sensitivities (<700 nm/RIU).

Slow quench dynamics of a one-dimensional Bose gas confined to an optical lattice.

PubMed

Bernier, Jean-Sébastien; Roux, Guillaume; Kollath, Corinna

2011-05-20

We analyze the effect of a linear time variation of the interaction strength on a trapped one-dimensional Bose gas confined to an optical lattice. The evolution of different observables such as the experimentally accessible on site particle distribution are studied as a function of the ramp time by using time-dependent numerical techniques. We find that the dynamics of a trapped system typically displays two regimes: For long ramp times, the dynamics is governed by density redistribution, while at short ramp times, local dynamics dominates as the evolution is identical to that of an homogeneous system. In the homogeneous limit, we also discuss the nontrivial scaling of the energy absorbed with the ramp time.

First-principles real-space study of electronic and optical excitations in rutile TiO 2 nanocrystals

DOE PAGES

Hung, Linda; Baishya, Kopinjol; Öğüt, Serdar

2014-10-17

We model rutile titanium dioxide nanocrystals (NCs) up to ~1.5 nm in size to study the effects of quantum confinement on their electronic and optical properties. Ionization potentials (IPs) and electron affinities (EAs) are obtained via the perturbative GW approximation (G 0W 0) and ΔSCF method for NCs up to 24 and 64 TiO 2 formula units, respectively. These demanding GW computations are made feasible by using a real-space framework that exploits quantum confinement to reduce the number of empty states needed in GW summations. Time-dependent density functional theory (TDDFT) is used to predict the optical properties of NCs upmore » to 64 TiO 2 units. For a NC containing only 2 TiO 2 units, the offsets of the IP and the EA from the corresponding bulk limits are of similar magnitude. However, as NC size increases, the EA is found to converge more slowly to the bulk limit than the IP. The EA values computed at the G 0W 0 and ΔSCF levels of theory are found to agree fairly well with each other, while the IPs computed with ΔSCF are consistently smaller than those computed with G 0W 0 by a roughly constant amount. TDDFT optical gaps exhibit weaker size dependence than GW quasiparticle gaps, and result in exciton binding energies on the order of eV. Finally, altering the dimensions of a fixed-size NC can change electronic and optical excitations up to several tenths of an eV. The largest NCs modeled are still quantum confined and do not yet have quasiparticle levels or optical gaps at bulk values. Nevertheless, we find that classical Mie-Gans theory can quite accurately reproduce the line shape of TDDFT absorption spectra, even for (anisotropic) TiO 2 NCs of subnanometer size.« less

First-principles real-space study of electronic and optical excitations in rutile TiO2 nanocrystals

NASA Astrophysics Data System (ADS)

Hung, Linda; Baishya, Kopinjol; Ã-ǧüt, Serdar

2014-10-01

We model rutile titanium dioxide nanocrystals (NCs) up to ˜1.5 nm in size to study the effects of quantum confinement on their electronic and optical properties. Ionization potentials (IPs) and electron affinities (EAs) are obtained via the perturbative GW approximation (G0W0) and ΔSCF method for NCs up to 24 and 64 TiO2 formula units, respectively. These demanding GW computations are made feasible by using a real-space framework that exploits quantum confinement to reduce the number of empty states needed in GW summations. Time-dependent density functional theory (TDDFT) is used to predict the optical properties of NCs up to 64 TiO2 units. For a NC containing only 2 TiO2 units, the offsets of the IP and the EA from the corresponding bulk limits are of similar magnitude. However, as NC size increases, the EA is found to converge more slowly to the bulk limit than the IP. The EA values computed at the G0W0 and ΔSCF levels of theory are found to agree fairly well with each other, while the IPs computed with ΔSCF are consistently smaller than those computed with G0W0 by a roughly constant amount. TDDFT optical gaps exhibit weaker size dependence than GW quasiparticle gaps, and result in exciton binding energies on the order of eV. Altering the dimensions of a fixed-size NC can change electronic and optical excitations up to several tenths of an eV. The largest NCs modeled are still quantum confined and do not yet have quasiparticle levels or optical gaps at bulk values. Nevertheless, we find that classical Mie-Gans theory can quite accurately reproduce the line shape of TDDFT absorption spectra, even for (anisotropic) TiO2 NCs of subnanometer size.

Monolithic subwavelength high refractive-index-contrast grating VCSELs

NASA Astrophysics Data System (ADS)

Gebski, Marcin; Dems, Maciej; Lott, James A.; Czyszanowski, Tomasz

2016-03-01

In this paper we present optical design and simulation results of vertical-cavity surface-emitting lasers (VCSELs) that incorporate monolithic subwavelength high refractive-index-contrast grating (MHCG) mirrors - a new variety of HCG mirror that is composed of high index material surrounded only on one side by low index material. We show the impact of an MHCG mirror on the performance of 980 nm VCSELs designed for high bit rate and energy-efficient optical data communications. In our design, all or part of the all-semiconductor top coupling distributed Bragg reflector mirror is replaced by an undoped gallium-arsenide MHCG. We show how the optical field intensity distribution of the VCSEL's fundamental mode is controlled by the combination of the number of residual distributed Bragg reflector (DBR) mirror periods and the physical design of the topmost gallium-arsenide MHCG. Additionally, we numerically investigate the confinement factors of our VCSELs and show that this parameter for the MHCG DBR VCSELs may only be properly determined in two or three dimensions due to the periodic nature of the grating mirror.

Field enhancement in plasmonic nanostructures

NASA Astrophysics Data System (ADS)

Piltan, Shiva; Sievenpiper, Dan

2018-05-01

Efficient generation of charge carriers from a metallic surface is a critical challenge in a wide variety of applications including vacuum microelectronics and photo-electrochemical devices. Replacing semiconductors with vacuum/gas as the medium of electron transport offers superior speed, power, and robustness to radiation and temperature. We propose a metallic resonant surface combining optical and electrical excitations of electrons and significantly reducing powers required using plasmon-induced enhancement of confined electric field. The properties of the device are modeled using the exact solution of the time-dependent Schrödinger equation at the barrier. Measurement results exhibit strong agreement with an analytical solution, and allow us to extract the field enhancement factor at the surface. Significant photocurrents are observed using combination of {{W}} {{{c}}{{m}}}-2 optical power and 10 V DC excitation on the surface. The model suggests optical field enhancement of 3 orders of magnitude at the metal interface due to plasmonic resonance. This simple planar structure provides valuable evidence on the electron emission mechanisms involved and it can be used for implementation of semiconductor compatible vacuum devices.

Optically switchable photonic metasurfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waters, R. F.; MacDonald, K. F.; Hobson, P. A.

2015-08-24

We experimentally demonstrate an optically switchable gallium-based metasurface, in which a reversible light-induced transition between solid and liquid phases occurring in a confined nanoscale surface layer of the metal drives significant changes in reflectivity and absorption. The metasurface architecture resonantly enhances the metal's “active plasmonic” phase-change nonlinearity by an order of magnitude, offering high contrast all-optical switching in the near-infrared range at low, μW μm{sup −2}, excitation intensities.

Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bose, Sumanta; Fan, W. J., E-mail: ewjfan@ntu.edu.sg; Zhang, D. H.

2016-04-14

The effect of lateral size and vertical thickness of CdSe and CdS nanoplatelets (NPLs) on their electronic structure and optical properties are investigated using an effective-mass envelope function theory based on the 8-band k ⋅ p model with valence force field considerations. Volumetrically larger NPLs have lower photon emission energy due to limited quantum confinement, but a greater transition matrix element (TME) due to larger electron-hole wavefunction overlap. The optical gain characteristics depend on several factors such as TME, Fermi factor, carrier density, NPL dimensions, material composition, and dephasing rate. There is a red shift in the peak position, moremore » so with an increase in thickness than lateral size. For an increasing carrier density, the gain spectrum undergoes a slight blue shift due to band filling effect. For a fixed carrier density, the Fermi factor is higher for volumetrically larger NPLs and so is the difference between the quasi-Fermi level separation and the effective bandgap. The transparency injection carrier density (and thus input current density threshold) is dimension dependent and falls for volumetrically larger NPLs, as they can attain the requisite exciton count for transparency with a relatively lower density. Between CdSe and CdS, CdSe has lower emission energy due to smaller bandgap, but a higher TME due to lower effective mass. CdS, however, has a higher so hole contribution due to a lower spin-orbit splitting energy. Both CdSe and CdS NPLs are suitable candidates for short-wavelength LEDs and lasers in the visible spectrum, but CdSe is expected to exhibit better optical performance.« less

Localized excitations at the Mott insulator-superfluid interfaces for confined Bose-Einstein condensates.

PubMed

Mariani, Eros; Stern, Ady

2005-12-31

In this Letter, we derive the dispersion relation of the surface waves at the interfaces between Mott-insulating and superfluid domains for a two-dimensional Bose-Einstein condensate in an optical lattice subjected to a confining potential. We then calculate their contribution to the heat capacity of the system and show how its low-temperature scaling allows an experimental test of the existence and properties of Mott insulator-superfluid domains.

Trapping of a microsphere pendulum resonator in an optical potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ward, J. M.; Photonics Centre, Tyndall National Institute, Prospect Row, Cork; Wu, Y.

We propose a method to spatially confine or corral the movements of a micropendulum via the optical forces produced by two simultaneously excited optical modes of a photonic molecule comprising two microspherical cavities. We discuss how the cavity-enhanced optical force generated in the photonic molecule can create an optomechanical potential of about 10 eV deep and 30 pm wide, which can be used to trap the pendulum at any given equilibrium position by a simple choice of laser frequencies. This result presents opportunities for very precise all-optical self-alignment of microsystems.

Liquid crystal emulsion micro-droplet WGM resonators

NASA Astrophysics Data System (ADS)

Ježek, Jan; Pilát, Zdeněk.; Brzobohatý, Oto; Jonáš, Alexandr; Aas, Mehdi; Kiraz, Alper; Zemánek, Pavel

2014-12-01

We introduce tunable optofluidic microlasers based on optically stretched or thermally modified, dye-doped emulsion droplets of liquid crystals (LC) confined in a dual-beam optical trap. Droplets were created in microfluidic chips or by shaking. Optically trapped microdroplets emulsified in water and stained with fluorescent dye act as an active ultrahigh-Q optical resonant cavity hosting whispering gallery modes (WGMs). Tuning of the laser emission wavelength was achieved by a controlled deformation of the droplet shape using light-induced forces generated by dual-beam optical trap and by thermal changing of the order in the LC.

Radio Frequency Magneto-Optical Trapping of CaF with High Density.

PubMed

Anderegg, Loïc; Augenbraun, Benjamin L; Chae, Eunmi; Hemmerling, Boerge; Hutzler, Nicholas R; Ravi, Aakash; Collopy, Alejandra; Ye, Jun; Ketterle, Wolfgang; Doyle, John M

2017-09-08

We demonstrate significantly improved magneto-optical trapping of molecules using a very slow cryogenic beam source and either rf modulated or dc magnetic fields. The rf magneto-optical trap (MOT) confines 1.0(3)×10^{5} CaF molecules at a density of 7(3)×10^{6}  cm^{-3}, which is an order of magnitude greater than previous molecular MOTs. Near Doppler-limited temperatures of 340(20)  μK are attained. The achieved density enables future work to directly load optical tweezers and create optical arrays for quantum simulation.

Rings Around the Sun and Moon: Coronae and Diffraction

ERIC Educational Resources Information Center

Cowley, Les; Laven, Philip; Vollmer, Michael

2005-01-01

Atmospheric optical effects can teach much about physics and especially optics. Coronae--coloured rings around the sun or moon--are large-scale consequences of diffraction, which is often thought of as only a small effect confined to the laboratory. We describe coronae, how they are formed and experiments that can be conducted on ones in the sky.…

Supramolecular Nanocomposites Under Confinement: Chiral Optically Active Nanoparticle Assemblies and Beyond

NASA Astrophysics Data System (ADS)

Bai, Peter; Yang, Sui; Bao, Wei; Salmeron, Miquel; Zhang, Xiang; Xu, Ting

2015-03-01

Block copolymer-based supramolecules provide a versatile platform to direct the self-assembly of nanoparticles (NPs) into precisely controlled nanostructures in bulk and thin film geometries. A supramolecule, PS-b-P4VP(PDP), composed of the small molecule 3-pentadecylphenol (PDP) hydrogen bonded to a diblock copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP), was subjected to 2-D volume confinement in cylindrical anodic aluminum oxide (AAO) membrane pores. TEM and 3-D TEM tomography reveal that the morphologies accessible by the supramolecule and supramolecule/NP composites, such as NP clusters, arrays, stacked rings, and single and double helical ribbons, are significantly different from those in the bulk or thin film. Furthermore, single molecule dark field scattering measurements demonstrate strong chiral optical response of single helical Au NP ribbon nanostructures in the near infrared wavelength regime. These studies demonstrate 2-D confinement to be an effective means to tailor self-assembled NP structure within supramolecule nanocomposites and pave the way for this assembly approach to be applied towards next generation chiral metamaterials and optoelectronic devices.

Enhancement of the sensitivity of gas sensor based on microstructure optical fiber

NASA Astrophysics Data System (ADS)

Morshed, Monir; Hasan, Md. Imran; Razzak, S. M. Abdur

2015-12-01

This paper proposes the design and characterization of microstructure optical fiber for gas sensing applications. The aim is to detect toxic and colorless gases over a wide transmission band covering 0.80 µm to 2.00 µm wavelength. Numerical investigation is carried out by using the finite element method (FEM). The numerical study shows that sensitivity of the proposed sensor is moderately increased by introducing four non-circular holes around the defected core of photonic crystal fiber and the confinement loss is also reduced. Furthermore, we confirm that increasing the diameter of central air core and size of the non-circular holes can improve the relative sensitivity and the confinement loss is reduced by increasing the diameter of air holes in the cladding. The enhancement of the relative sensitivity is more than 27.58% (0.1323 to 0.1688) at the wavelength λ=1.33µm that is the absorption line of methane (CH4) and hydrogen fluoride (HF) gases. The confinement loss of the fiber is 1.765×10-8 dB/m.

Estimating the effect of selected predictors on agricultural confined-space hazard perceptions of Utah farm owner/operators.

PubMed

Pate, M L; Dai, X

2014-04-01

The purpose of this study was to assess how selected variables affect the confined-space hazard perceptions of farmers in Utah. A confined space was defined as "any space found in an agricultural workplace that was not designed or intended as a regular workstation, has limited or restricted means of entry or exit, and contains potential physical and toxic hazards to workers who intentionally or unintentionally enter the space" (proposed by NCERA-197, 18 May 2011, draft copy). A total of 303 out of 327 farm owner/operators provided complete surveys that were used in the analysis. The state of Utah was grouped into five regions in this study: central, east, northeast, northwest, and southwest. Grain and dairy production comprised 48.7% of the operations responding to the survey. The general linear modeling (GLM) procedure in SAS 9.3 was used to select the models on hazard perception scores for the five studied regions. Interested predictors included response type, production type, safety planning, and injury concerns. Animal production operations had the highest average number of confined spaces (micro = 4, SD = 2.7). Regionally, the northwest region had the highest average number of confined spaces (micro = 4, SD = 2.5). The variables contributing most to confined-space hazard perceptions were injury and death concerns while working alone in confined spaces. Three factors were generated using principle factor analysis (PFA) with orthogonal varimax rotation. Results suggested that factors affect hazard perceptions differently by region. We conclude that outreach and educational efforts to change safety behaviors regarding confined-space hazards should be strategically targeted for each region based on predicting factors. The result can assist agricultural safety and health professionals in targeting agricultural producers' social networks to address human factors such as worker attitudes and/or lack of skills or knowledge that effect hazard perceptions of confined spaces in agriculture.

Nonlinear graphene plasmonics

PubMed Central

2017-01-01

The rapid development of graphene has opened up exciting new fields in graphene plasmonics and nonlinear optics. Graphene's unique two-dimensional band structure provides extraordinary linear and nonlinear optical properties, which have led to extreme optical confinement in graphene plasmonics and ultrahigh nonlinear optical coefficients, respectively. The synergy between graphene's linear and nonlinear optical properties gave rise to nonlinear graphene plasmonics, which greatly augments graphene-based nonlinear device performance beyond a billion-fold. This nascent field of research will eventually find far-reaching revolutionary technological applications that require device miniaturization, low power consumption and a broad range of operating wavelengths approaching the far-infrared, such as optical computing, medical instrumentation and security applications. PMID:29118665

Nonlinear graphene plasmonics

NASA Astrophysics Data System (ADS)

Ooi, Kelvin J. A.; Tan, Dawn T. H.

2017-10-01

The rapid development of graphene has opened up exciting new fields in graphene plasmonics and nonlinear optics. Graphene's unique two-dimensional band structure provides extraordinary linear and nonlinear optical properties, which have led to extreme optical confinement in graphene plasmonics and ultrahigh nonlinear optical coefficients, respectively. The synergy between graphene's linear and nonlinear optical properties gave rise to nonlinear graphene plasmonics, which greatly augments graphene-based nonlinear device performance beyond a billion-fold. This nascent field of research will eventually find far-reaching revolutionary technological applications that require device miniaturization, low power consumption and a broad range of operating wavelengths approaching the far-infrared, such as optical computing, medical instrumentation and security applications.

Spatial and Temporal Confined Photothermolysis of Cancer Cells Mediated by Hollow Gold Nanospheres Targeted to Epidermal Growth Factor Receptors

PubMed Central

2018-01-01

To date, a few studies have investigated the potential use of a short-pulsed laser in selective tumor cell destruction or its mechanism of cell killing. Computer simulation of the spatial and temporal profiles of temperature elevation after pulsed laser irradiation on an infinitesimal point source estimated that the temperature reached its highest point at ∼35 ns after a single 15 ns laser pulse. Moreover, temperature elevation was confined to a radius of sub-micrometer and returned to baseline within 100 ns. To investigate the effect of 15 ns laser pulses on A431 tumor cells, we conjugated hollow gold nanospheres (HAuNSs) to an antibody (C225) directed at the epithelial growth factor receptor. The resulting nanoparticles, C225-HAuNSs, bound to the cell membrane, internalized, and distributed throughout the cytoplasm, with some nanoparticles transported to the vicinity of the nuclear membrane. On using an optical microscope mounted to a tunable pulsed Ti:sapphire laser, rapid and extensive damage of live cancer cells was observed, whereas irradiation of A431 cells pretreated with nontargeted HAuNSs with a pulsed laser or pretreated with C225-HAuNSs with a continuous-wave laser-induced minimal cellular damage. Furthermore, after a single 15 ns laser pulse, C225-HAuNS-treated A431 cells cocultured with 3T3 fibroblasts showed signs of selective destruction. Thus, compared with a continuous-wave laser, shots of a short-pulsed laser were the most damaging to tumor cells that bound HAuNSs and generated the least heat to the surrounding environment. This mode of action by a short-pulsed laser on cancer cells (i.e., confined photothermolysis) may have potential applications in selective tumor cell destruction. PMID:29876540

Spatial and Temporal Confined Photothermolysis of Cancer Cells Mediated by Hollow Gold Nanospheres Targeted to Epidermal Growth Factor Receptors.

PubMed

Ku, Geng; Huang, Qian; Wen, Xiaoxia; Ye, John; Piwnica-Worms, David; Li, Chun

2018-05-31

To date, a few studies have investigated the potential use of a short-pulsed laser in selective tumor cell destruction or its mechanism of cell killing. Computer simulation of the spatial and temporal profiles of temperature elevation after pulsed laser irradiation on an infinitesimal point source estimated that the temperature reached its highest point at ∼35 ns after a single 15 ns laser pulse. Moreover, temperature elevation was confined to a radius of sub-micrometer and returned to baseline within 100 ns. To investigate the effect of 15 ns laser pulses on A431 tumor cells, we conjugated hollow gold nanospheres (HAuNSs) to an antibody (C225) directed at the epithelial growth factor receptor. The resulting nanoparticles, C225-HAuNSs, bound to the cell membrane, internalized, and distributed throughout the cytoplasm, with some nanoparticles transported to the vicinity of the nuclear membrane. On using an optical microscope mounted to a tunable pulsed Ti:sapphire laser, rapid and extensive damage of live cancer cells was observed, whereas irradiation of A431 cells pretreated with nontargeted HAuNSs with a pulsed laser or pretreated with C225-HAuNSs with a continuous-wave laser-induced minimal cellular damage. Furthermore, after a single 15 ns laser pulse, C225-HAuNS-treated A431 cells cocultured with 3T3 fibroblasts showed signs of selective destruction. Thus, compared with a continuous-wave laser, shots of a short-pulsed laser were the most damaging to tumor cells that bound HAuNSs and generated the least heat to the surrounding environment. This mode of action by a short-pulsed laser on cancer cells (i.e., confined photothermolysis) may have potential applications in selective tumor cell destruction.

Interfacial behavior of confined mesogens at smectic-C*-water boundary.

PubMed

Chandran, Achu; Khanna, P K; Haranath, D; Biradar, Ashok M

2018-02-01

In this paper, we have investigated the behavior of mesogens at smectic-C*-water interface confined in a liquid crystal (LC) cell with interfacial geometry. Polarized optical microscopy was used to probe the appearance of various smectic-C* domain patterns at water interface owing to the reorientation of mesogens. The undulated stripe domains observed at the air interface of smectic-C* meniscus vanished as the water entered into the smectic layers and focal conical domain patterns appeared at smectic-C*-water boundary. A spatially variable electro-optical switching of LC molecules was also observed outside the electrode area of the interfacial cell. The electrode region at the interface, as well as on the water side, was damaged upon application of an electric field of magnitude more than 150 kV/m. The change in dielectric parameters of mesogens was extensively studied at interface after evaporating the water. These studies give fundamental insights into smectic-C*-water interface and also will be helpful in fabricating better LC devices for electro-optical and sensing applications.

Compact nanomechanical plasmonic phase modulators [Ultracompact nano-mechanical plasmonic phase modulators

DOE PAGES

Dennis, B. S.; Haftel, M. I.; Czaplewski, D. A.; ...

2015-03-30

Highly confined optical energy in plasmonic devices is advancing miniaturization in photonics. However, for mode sizes approaching ≈10 nm, the energy increasingly shifts into the metal, raising losses and hindering active phase modulation. Here, we propose a nanoelectromechanical phase-modulation principle exploiting the extraordinarily strong dependence of the phase velocity of metal–insulator–metal gap plasmons on dynamically variable gap size. We experimentally demonstrate a 23-μm-long non-resonant modulator having a 1.5π rad range, with 1.7 dB excess loss at 780 nm. Analysis shows that by simultaneously decreasing the gap, length and width, an ultracompact-footprint π rad phase modulator can be realized. This ismore » achieved without incurring the extra loss expected for plasmons confined in a decreasing gap, because the increasing phase-modulation strength from a narrowing gap offsets rising propagation losses. Here, such small, high-density electrically controllable components may find applications in optical switch fabrics and reconfigurable plasmonic optics.« less

Blue-detuned optical ring trap for Bose-Einstein condensates based on conical refraction.

PubMed

Turpin, A; Polo, J; Loiko, Yu V; Küber, J; Schmaltz, F; Kalkandjiev, T K; Ahufinger, V; Birkl, G; Mompart, J

2015-01-26

We present a novel approach for the optical manipulation of neutral atoms in annular light structures produced by the phenomenon of conical refraction occurring in biaxial optical crystals. For a beam focused to a plane behind the crystal, the focal plane exhibits two concentric bright rings enclosing a ring of null intensity called the Poggendorff ring. We demonstrate both theoretically and experimentally that the Poggendorff dark ring of conical refraction is confined in three dimensions by regions of higher intensity. We derive the positions of the confining intensity maxima and minima and discuss the application of the Poggendorff ring for trapping ultra-cold atoms using the repulsive dipole force of blue-detuned light. We give analytical expressions for the trapping frequencies and potential depths along both the radial and the axial directions. Finally, we present realistic numerical simulations of the dynamics of a ⁸⁷Rb Bose-Einstein condensate trapped inside the Poggendorff ring which are in good agreement with corresponding experimental results.

Polaronic effects due to quasi-confined optical phonons in wurtzite nitride nanowire in the presence of an electric field

NASA Astrophysics Data System (ADS)

Vardanyan, Karen A.; Asatryan, Anna L.; Vartanian, Arshak L.

2015-07-01

Considering the effect of an external electric field in wurtzite nitride cylindrical nanowire (NW), the polaron self-energy and effective mass due to the electron interaction with the quasi-confined optical phonons are studied theoretically by means of Lee-Low-Pines variational approach. The analytical expressions for the quasi-one-dimensional Fröhlich polaron self-energy and effective mass are obtained as functions of the wire radius and the strength of the electric field applied perpendicular to the wire axis. It is found that the main contribution to polaron basic parameters is from higher frequency optical phonon modes. The numerical results on the GaN material show that the polaron self-energy increases with the increase of the electric field and is more sensitive to the field when the wire radius is larger. It is also found that the polaron self-energy in GaN NWs is higher than that in zinc-blende GaAs-based cylindrical NWs.

Interfacial behavior of confined mesogens at smectic-C*-water boundary

NASA Astrophysics Data System (ADS)

Chandran, Achu; Khanna, P. K.; Haranath, D.; Biradar, Ashok M.

2018-02-01

In this paper, we have investigated the behavior of mesogens at smectic-C*-water interface confined in a liquid crystal (LC) cell with interfacial geometry. Polarized optical microscopy was used to probe the appearance of various smectic-C* domain patterns at water interface owing to the reorientation of mesogens. The undulated stripe domains observed at the air interface of smectic-C* meniscus vanished as the water entered into the smectic layers and focal conical domain patterns appeared at smectic-C*-water boundary. A spatially variable electro-optical switching of LC molecules was also observed outside the electrode area of the interfacial cell. The electrode region at the interface, as well as on the water side, was damaged upon application of an electric field of magnitude more than 150 kV/m. The change in dielectric parameters of mesogens was extensively studied at interface after evaporating the water. These studies give fundamental insights into smectic-C*-water interface and also will be helpful in fabricating better LC devices for electro-optical and sensing applications.

Faraday spectroscopy of ultracold atoms guided in hollow core optical fibers

NASA Astrophysics Data System (ADS)

Fatemi, Fredrik; Pechkis, Joseph

2013-05-01

We have performed spatially and temporally resolved magnetometry using Faraday spectroscopy of ultracold rubidium atoms confined in hollow core optical fibers. We first guide 105 Rb atoms into a 3-cm-long, 100-micron-core hollow fiber using blue-detuned hollow waveguide modes. Inside the fiber, the atoms are exposed to an optical pumping pulse, and the Larmor precession is monitored by the polarization rotation of a probe laser beam detuned by 50 GHz. The intense guide beams can perturb the detected Larmor precession frequencies, but we show that by confining the atoms to the intensity null of higher order blue-detuned hollow modes, these perturbations are reduced by over 95% compared to red-detuned guides. By adjusting the guide beam detuning and polarization, the deleterious effects of both photon scattering and frequency shifts can be suppressed such that multiple magnetic field measurements with sensitivity of 30 nT per sampling pulse can be obtained throughout the length of the fiber in a single loading cycle. Work supported by ONR and DARPA.

Optical Field Confinement Enhanced Single ZnO Microrod UV Photodetector

NASA Astrophysics Data System (ADS)

Wei, Ming; Xu, Chun-Xiang; Qin, Fei-Fei; Gowri Manohari, Arumugam; Lu, Jun-Feng; Zhu, Qiu-Xiang

2017-07-01

ZnO microrods are synthesized using the vapor phase transport method, and the magnetron sputtering is used to decorate the Al nanoparticles (NPs) on a single ZnO microrod. The micro-PL and I-V responses are measured before and after the decoration of Al NPs. The FDTD stimulation is also carried out to demonstrate the optical field distribution around the decoration of Al NPs on the surface of a ZnO microrod. Due to an implementation of Al NPs, the ZnO microrod exhibits an improved photoresponse behavior. In addition, Al NPs induced localized surface plasmons (LSPs) as well as improved optical field confinement can be ascribed to an enhancement of ultraviolet (UV) response. This research provides a method for improving the responsivity of photodetectors. Supported by the National Natural Science Foundation of China under Grant Nos 61475035 and 61275054, the Science and Technology Support Program of Jiangsu Province under Grant No BE2016177, and the Collaborative Innovation Center of Suzhou Nano Science and Technology.

Optical phase conjugation (OPC)-assisted isotropic focusing.

PubMed

Jang, Mooseok; Sentenac, Anne; Yang, Changhuei

2013-04-08

Isotropic optical focusing - the focusing of light with axial confinement that matches its lateral confinement, is important for a broad range of applications. Conventionally, such focusing is achieved by overlapping the focused beams from a pair of opposite-facing microscope objective lenses. However the exacting requirements for the alignment of the objective lenses and the method's relative intolerance to sample turbidity have significantly limited its utility. In this paper, we present an optical phase conjugation (OPC)-assisted isotropic focusing method that can address both challenges. We exploit the time-reversal nature of OPC playback to naturally guarantee the overlap of the two focused beams even when the objective lenses are significantly misaligned (up to 140 microns transversely and 80 microns axially demonstrated). The scattering correction capability of OPC also enabled us to accomplish isotropic focusing through thick scattering samples (demonstrated with samples of ~7 scattering mean free paths). This method can potentially improve 4Pi microscopy and 3D microstructure patterning.

In situ TEM near-field optical probing of nanoscale silicon crystallization.

PubMed

Xiang, Bin; Hwang, David J; In, Jung Bin; Ryu, Sang-Gil; Yoo, Jae-Hyuck; Dubon, Oscar; Minor, Andrew M; Grigoropoulos, Costas P

2012-05-09

Laser-based processing enables a wide variety of device configurations comprising thin films and nanostructures on sensitive, flexible substrates that are not possible with more traditional thermal annealing schemes. In near-field optical probing, only small regions of a sample are illuminated by the laser beam at any given time. Here we report a new technique that couples the optical near-field of the laser illumination into a transmission electron microscope (TEM) for real-time observations of the laser-materials interactions. We apply this technique to observe the transformation of an amorphous confined Si volume to a single crystal of Si using laser melting. By confinement of the material volume to nanometric dimensions, the entire amorphous precursor is within the laser spot size and transformed into a single crystal. This observation provides a path for laser processing of single-crystal seeds from amorphous precursors, a potentially transformative technique for the fabrication of solar cells and other nanoelectronic devices.

Nanoantennas for enhancing and confining the magnetic optical field

NASA Astrophysics Data System (ADS)

Grosjean, Thierry; Mivelle, Mathieu; Baida, Fadi I.; Burr, Geoffrey W.; Fischer, Ulrich C.

2011-05-01

We propose different optical antenna structures for enhancing and confining the magnetic optical field. A common feature of these structures are concave corners in thin metal films as locations of the enhanced magnetic field. This proposal is inspired by Babinet's principle as the concave edges are the complementary structures to convex metal corners, which are known to be locations of a strongly enhanced electric field. Bowtie antennas and the bowtie apertures of appropriate size were shown to exhibit resonances in the infrared frequency range with an especially strong enhancement of the electrical field in the gap between 2 convex metal corners. We show by numerical calculations, that the complementary structures, the complementary bowtie aperture - the diabolo antenna - and the complementary bow tie antenna - two closely spaced triangular apertures in a metal film with a narrow gap between two opposing concave corners - exhibit resonances with a strongly enhanced magnetic field at the narrow metal constriction between the concave corners. We suggest sub-wavelength circuits of concave and convex corners as building blocks of planar metamaterials.

Generation of various partially coherent beams and their propagation properties in turbulent atmosphere: a review

NASA Astrophysics Data System (ADS)

Cai, Yangjian

2011-03-01

Partially coherent beams, such as Gaussian Schell-model beam, partially coherent dark hollow beam, partially coherent flat-topped beam and electromagnetic Gaussian Schell-model beam, have important applications in free space optical communications, optical imaging, optical trapping, inertial confinement fusion and nonlinear optics. In this paper, experimental generations of various partially coherent beams are introduced. Furthermore, with the help of a tensor method, analytical formulae for such beams propagating in turbulent atmosphere are derived, and the propagation properties of such beams in turbulent atmosphere are reviewed.

Sensitive liquid refractive index sensors using tapered optical fiber tips.

PubMed

Tai, Yi-Hsin; Wei, Pei-Kuen

2010-04-01

An optical fiber sensor based on the change of optical confinement in a subwavelength tip is presented. The optical spot is substantially increased when the environmental refractive index (RI) increases from 1.3 to 1.4. By measuring the intensity of low angular spectral components, an intensity sensitivity up to 8000% per RI unit is achieved. The fiber tip sensors take advantage of the small detection volume and real-time responses. We demonstrate the application of the nanofiber sensors for measuring concentrations of acids and evaporation rates of aqueous mixtures.

Infrared rectification in a nanoantenna-coupled metal-oxide-semiconductor tunnel diode.

PubMed

Davids, Paul S; Jarecki, Robert L; Starbuck, Andrew; Burckel, D Bruce; Kadlec, Emil A; Ribaudo, Troy; Shaner, Eric A; Peters, David W

2015-12-01

Direct rectification of electromagnetic radiation is a well-established method for wireless power conversion in the microwave region of the spectrum, for which conversion efficiencies in excess of 84% have been demonstrated. Scaling to the infrared or optical part of the spectrum requires ultrafast rectification that can only be obtained by direct tunnelling. Many research groups have looked to plasmonics to overcome antenna-scaling limits and to increase the confinement. Recently, surface plasmons on heavily doped Si surfaces were investigated as a way of extending surface-mode confinement to the thermal infrared region. Here we combine a nanostructured metallic surface with a heavily doped Si infrared-reflective ground plane designed to confine infrared radiation in an active electronic direct-conversion device. The interplay of strong infrared photon-phonon coupling and electromagnetic confinement in nanoscale devices is demonstrated to have a large impact on ultrafast electronic tunnelling in metal-oxide-semiconductor (MOS) structures. Infrared dispersion of SiO2 near a longitudinal optical (LO) phonon mode gives large transverse-field confinement in a nanometre-scale oxide-tunnel gap as the wavelength-dependent permittivity changes from 1 to 0, which leads to enhanced electromagnetic fields at material interfaces and a rectified displacement current that provides a direct conversion of infrared radiation into electric current. The spectral and electrical signatures of the nanoantenna-coupled tunnel diodes are examined under broadband blackbody and quantum-cascade laser (QCL) illumination. In the region near the LO phonon resonance, we obtained a measured photoresponsivity of 2.7 mA W(-1) cm(-2) at -0.1 V.

Terahertz quantum cascade lasers based on resonant phonon scattering for depopulation.

PubMed

Hu, Qing; Williams, Benjamin S; Kumar, Sushil; Callebaut, Hans; Reno, John L

2004-02-15

We report our development of terahertz (THz) quantum cascade lasers (QCLs), in which the depopulation of the lower radiative level is achieved through resonant longitudinal optical (LO) phonon scattering. This depopulation mechanism, similar to that implemented in all the QCLs operating at mid-infrared frequencies, is robust at high temperatures and high injection levels. The unique feature of resonant LO-phonon scattering in our THz QCL structures allows a highly selective depopulation of the lower radiative level with a sub-picosecond lifetime, while maintaining a relatively long upper level lifetime (more than 5 ps) that is due to upper-to-ground-state scattering. The first QCL based on this mechanism achieved lasing at 3.4 THz (lambda approximately 87 microm) up to 87 K for pulsed operations, with peak power levels exceeding 10 mW at ca. 40 K. Using a novel double-sided metal waveguide for mode confinement, which yields a unity mode confinement factor and therefore a low total cavity loss at THz frequencies, we have also achieved lasing at wavelengths longer than 100 microm.

Raman scattering in a whispering mode optical waveguide

DOEpatents

Kurnit, Norman A.

1982-01-01

A device and method for Raman scattering in a whispering mode optical waveguide. Both a helical ribbon and cylinder are disclosed which incorporate an additional curvature .rho. p for confining the beam to increase intensity. A Raman scattering medium is disposed in the optical path of the beam as it propagates along the waveguide. Raman scattering is enhanced by the high intensities of the beam and long interaction path lengths which are achieved in a small volume.

Mode structure of planar optical antennas on dielectric substrates

DOE PAGES

Word, Robert C.; Konenkamp, Rolf

2016-08-08

Here, we report a numerical study, supported by photoemission electron microscopy (PEEM), of sub-micron planar optical antennas on transparent substrate. We find these antennas generate intricate near-field spatial field distributions with odd and even numbers of nodes. We show that the field distributions are primarily superpositions of planar surface plasmon polariton modes confined to the metal/substrate interface. The mode structure provides opportunities for coherent switching and optical control in sub-micron volumes.

Confinement of gigahertz sound and light in Tamm plasmon resonators

NASA Astrophysics Data System (ADS)

Villafañe, V.; Bruchhausen, A. E.; Jusserand, B.; Senellart, P.; Lemaître, A.; Fainstein, A.

2015-10-01

We demonstrate theoretically and by pump-probe picosecond acoustics experiments the simultaneous confinement of light and gigahertz sound in Tamm plasmon resonators, formed by depositing a thin layer of Au onto a GaAs/AlGaAs Bragg reflector. The cavity has InGaAs quantum dots (QDs) embedded at the maximum of the confined optical field in the first GaAs layer. The different sound generation and detection mechanisms are theoretically analyzed. It is shown that the Au layer absorption and the resonant excitation of the QDs are the more efficient light-sound transducers for the coupling of near-infrared light with the confined acoustic modes, while the displacement of the interfaces is the main back-action mechanism at these energies. The prospects for the compact realization of optomechanical resonators based on Tamm plasmon cavities are discussed.

Hybrid photonic-plasmonic crystal nanocavity sensors

NASA Astrophysics Data System (ADS)

Cheng, Pi-Ju; Chiang, Chih-Kai; Chou, Bo-Tsun; Huang, Zhen-Ting; Ku, Yun-Cheng; Kuo, Mao-Kuen; Hsu, Jin-Chen; Lin, Tzy-Rong

2018-02-01

We have investigated a hybrid photonic-plasmonic crystal nanocavity consisting of a silicon grating nanowire adjacent to a metal surface with a gain gap between them. The hybrid plasmonic cavity modes are highly confined in the gap due to the strong coupling of the photonic crystal cavity modes and the surface plasmonic gap modes. Using finite-element method (FEM), guided modes of the hybrid plasmonic waveguide (WG) were numerically determined at a wavelength of 1550 nm. The modal characteristics such as WG confinement factors and modal losses of the fundamental hybrid plasmonic modes were obtained as a function of groove depth at various gap heights. Furthermore, the band structure of the hybrid crystal modes corresponding to a wide band gap of 17.8 THz is revealed. To enclose the optical energy effectively, a single defect was introduced into the hybrid crystal. At a deep subwavelength defect length as small as 270 nm, the resonant mode exhibits a high quality factor of 567 and an ultrasmall mode volume of 1.9 × 10- 3 ( λ/ n eff)3 at the resonance wavelength of 1550 nm. Compared to conventional photonic crystal nanowire cavities in the absence of a metal surface, the factor Q/ V m is significantly enhanced by about 15 times. The designed hybrid photonic-plasmonic cavity sensors exhibit distinguished characteristics such as sensitivity of 443 nm/RIU and figure of merit of 129. The proposed nanocavities open new possibilities for various applications with strong light-matter interaction, such as biosensors and nanolasers.

Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties

NASA Technical Reports Server (NTRS)

Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher

1995-01-01

One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.

Electron mobility limited by optical phonons in wurtzite InGaN/GaN core-shell nanowires

NASA Astrophysics Data System (ADS)

Liu, W. H.; Qu, Y.; Ban, S. L.

2017-09-01

Based on the force-balance and energy-balance equations, the optical phonon-limited electron mobility in InxGa1-xN/GaN core-shell nanowires (CSNWs) is discussed. It is found that the electrons tend to distribute in the core of the CSNWs due to the strong quantum confinement. Thus, the scattering from first kind of the quasi-confined optical (CO) phonons is more important than that from the interface (IF) and propagating (PR) optical phonons. Ternary mixed crystal and size effects on the electron mobility are also investigated. The results show that the PR phonons exist while the IF phonons disappear when the indium composition x < 0.047, and vice versa. Accordingly, the total electron mobility μ first increases and then decreases with indium composition x, and reaches a peak value of approximately 3700 cm2/(V.s) when x = 0.047. The results also show that the mobility μ increases as increasing the core radius of CSNWs due to the weakened interaction between the electrons and CO phonons. The total electron mobility limited by the optical phonons exhibits an obvious enhancement as decreasing temperature or increasing line electron density. Our theoretical results are expected to be helpful to develop electronic devices based on CSNWs.

Optical spectroscopy to study confined and semi-closed explosions of homogeneous and composite charges

NASA Astrophysics Data System (ADS)

Maiz, Lotfi; Trzciński, Waldemar A.; Paszula, Józef

2017-01-01

Confined and semi-closed explosions of new class of energetic composites as well as TNT and RDX charges were investigated using optical spectroscopy. These composites are considered as thermobarics when used in layered charges or enhanced blast explosives when pressed. Two methods to estimate fireball temperature histories of both homogeneous and metallized explosives from the spectroscopic data are also presented, compared and analyzed. Fireball temperature results of the charges detonated in a small explosion chamber under air and argon atmospheres, and detonated in a semi-closed bunker are presented and compared with theoretical ones calculated by a thermochemical code. Important conclusions about the fireball temperatures and the physical and chemical phenomena occurring after the detonation of homogeneous explosives and composite formulations are deduced.

Effects of an external magnetic field in pulsed laser deposition

NASA Astrophysics Data System (ADS)

García, T.; de Posada, E.; Villagrán, M.; Ll, J. L. Sánchez; Bartolo-Pérez, P.; Peña, J. L.

2008-12-01

Thin films were grown by pulsed laser deposition, PLD, on Si (1 0 0) substrates by the ablation of a sintered ceramic SrFe 12O 19 target with and without the presence of a nonhomogeneous magnetic field of μ0H = 0.4 T perpendicular to substrate plane and parallel to the plasma expansion axis. The field was produced by a rectangular-shaped Nd-Fe-B permanent magnet and the substrate was just placed on the magnet surface (Aurora method). An appreciable increment of optical emission due to the presence of the magnetic field was observed, but no film composition change or thickness increment was obtained. It suggests that the increment of the optical emission is due mainly to the electron confinement rather than confinement of ionic species.

Electrically tunable robust edge states in graphene-based topological photonic crystal slabs

NASA Astrophysics Data System (ADS)

Song, Zidong; Liu, HongJun; Huang, Nan; Wang, ZhaoLu

2018-03-01

Topological photonic crystals are optical structures supporting topologically protected unidirectional edge states that exhibit robustness against defects. Here, we propose a graphene-based all-dielectric photonic crystal slab structure that supports two-dimensionally confined topological edge states. These topological edge states can be confined in the out-of-plane direction by two parallel graphene sheets. In the structure, the excitation frequency range of topological edge states can be dynamically and continuously tuned by varying bias voltage across the two parallel graphene sheets. Utilizing this kind of architecture, we construct Z-shaped channels to realize topological edge transmission with diffrerent frequencies. The proposal provides a new degree of freedom to dynamically control topological edge states and potential applications for robust integrated photonic devices and optical communication systems.

Nanomaterial-enhanced frequency combs (Conference Presentation)

NASA Astrophysics Data System (ADS)

Armani, Andrea M.; Castro-Beltran, Rigoberto; Diep, Vinh; Gungor, Eda; Shen, Xiaoqin; Soltani, Soheil

2017-02-01

Optical cavities are able to confine and store specific wavelengths of light, acting as optical amplifiers at those wavelengths. Because the amount of amplification is directly related to the cavity quality factor (Q) (or the cavity finesse), frequency comb research has focused on high-Q and ultra-high Q microcavities fabricated from a range of materials using a variety of methods. In all cases, the comb generation relies on a nonlinear process known as parametric frequency conversion which is based on a third order nonlinear interaction and which results in four wave mixing (FWM). Clearly, this approach requires significant optical power, which was the original motivation for using ultra-high-Q cavities. In fact, the majority of research to date has focused on pursuing increasingly high Q factors. However, another strategy is to improve the nonlinearity of the resonator through intelligently designing materials for this application. In the present work, a suite of nanomaterials (organic and inorganic) have been intelligently designed with the explicit purpose to enhance the nonlinearity of the resonator and reducing the threshold for frequency comb generation in the near-IR. The nanomaterials do not change the structure of the comb and only act to reduce the comb threshold. The silica microcavity is used as a testbed for initial demonstration and verification purposes. However, the fundamental strategy is translatable to other whispering gallery mode cavities.

Can Tauc plot extrapolation be used for direct-band-gap semiconductor nanocrystals?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Y., E-mail: yu.feng@unsw.edu.au; Lin, S.; Huang, S.

Despite that Tauc plot extrapolation has been widely adopted for extracting bandgap energies of semiconductors, there is a lack of theoretical support for applying it to nanocrystals. In this paper, direct-allowed optical transitions in semiconductor nanocrystals have been formulated based on a purely theoretical approach. This result reveals a size-dependant transition of the power factor used in Tauc plot, increasing from one half used in the 3D bulk case to one in the 0D case. This size-dependant intermediate value of power factor allows a better extrapolation of measured absorption data. Being a material characterization technique, the generalized Tauc extrapolation givesmore » a more reasonable and accurate acquisition of the intrinsic bandgap, while the unjustified purpose of extrapolating any elevated bandgap caused by quantum confinement is shown to be incorrect.« less

Engineering 1D Quantum Stripes from Superlattices of 2D Layered Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gruenewald, John H.; Kim, Jungho; Kim, Heung Sik

Dimensional tunability from two dimensions to one dimension is demonstrated for the first time using an artificial superlattice method in synthesizing 1D stripes from 2D layered materials. The 1D confinement of layered Sr2IrO4 induces distinct 1D quantum-confined electronic states, as observed from optical spectroscopy and resonant inelastic X-ray scattering. This 1D superlattice approach is generalizable to a wide range of layered materials.

Decreasing the electronic confinement in layered perovskites through intercalation.

PubMed

Smith, Matthew D; Pedesseau, Laurent; Kepenekian, Mikaël; Smith, Ian C; Katan, Claudine; Even, Jacky; Karunadasa, Hemamala I

2017-03-01

We show that post-synthetic small-molecule intercalation can significantly reduce the electronic confinement of 2D hybrid perovskites. Using a combined experimental and theoretical approach, we explain structural, optical, and electronic effects of intercalating highly polarizable molecules in layered perovskites designed to stabilize the intercalants. Polarizable molecules in the organic layers substantially alter the optical and electronic properties of the inorganic layers. By calculating the spatially resolved dielectric profiles of the organic and inorganic layers within the hybrid structure, we show that the intercalants afford organic layers that are more polarizable than the inorganic layers. This strategy reduces the confinement of excitons generated in the inorganic layers and affords the lowest exciton binding energy for an n = 1 perovskite of which we are aware. We also demonstrate a method for computationally evaluating the exciton's binding energy by solving the Bethe-Salpeter equation for the exciton, which includes an ab initio determination of the material's dielectric profile across organic and inorganic layers. This new semi-empirical method goes beyond the imprecise phenomenological approximation of abrupt dielectric-constant changes at the organic-inorganic interfaces. This work shows that incorporation of polarizable molecules in the organic layers, through intercalation or covalent attachment, is a viable strategy for tuning 2D perovskites towards mimicking the reduced electronic confinement and isotropic light absorption of 3D perovskites while maintaining the greater synthetic tunability of the layered architecture.

Superfocusing terahertz waves below lambda/250 using plasmonic parallel-plate waveguides.

PubMed

Zhan, Hui; Mendis, Rajind; Mittleman, Daniel M

2010-04-26

We experimentally demonstrate complete two-dimensional (2-D) confinement of terahertz (THz) energy in finite-width parallel-plate waveguides, defying conventional wisdom in the century-old field of microwave waveguide technology. We find that the degree of energy confinement increases exponentially with decreasing plate separation. We propose that this 2-D confinement is mediated by the mutual coupling of plasmonic edge modes, analogous to that observed in slot waveguides at optical wavelengths. By adiabatically tapering the width and the separation, we focus THz waves down to a size of 10 microm (approximately lambda/260) by 18 microm ( approximately lambda/145), which corresponds to a mode area of only 2.6 x 10(-5) lambda(2).

Efficient production of spin singlets in lattice-confined spinor condensates

NASA Astrophysics Data System (ADS)

Zhao, Lichao; Chen, Zihe; Tang, Tao; Liu, Yingmei

2017-04-01

We present an efficient experimental scheme for a production of spin singlets in an antiferromagnetic spinor condensate confined by a cubic optical lattice. Via two independent detection methods, we demonstrate that about 80 percent of atoms in the lattice-confined spinor condensate can form spin singlets, immediately after the atoms cross a first-order superfluid to Mott-insulator phase transition in a sufficiently low microwave dressing field. We also discuss a good agreement between our data and the mean field theory, and two applications of spin singlets in quantum information science. We thank the National Science Foundation and the Oklahoma Center for the Advancement of Science and Technology for financial support.

Panoramic lens designed with transformation optics.

PubMed

Wang, Huaping; Deng, Yangyang; Zheng, Bin; Li, Rujiang; Jiang, Yuyu; Dehdashti, Shahram; Xu, Zhiwei; Chen, Hongsheng

2017-01-06

The panoramic lens is a special kind of lens, which is applied to observe full view. In this letter, we theoretically present a panoramic lens (PL) using transformation optics method. The lens is designed with inhomogeneous and anisotropic constitutive parameters, which has the ability to gather light from all directions and confine light within the visual angle of observer. Simulation results validate our theoretical design.

Nonpolar InGaN/GaN Core-Shell Single Nanowire Lasers.

PubMed

Li, Changyi; Wright, Jeremy B; Liu, Sheng; Lu, Ping; Figiel, Jeffrey J; Leung, Benjamin; Chow, Weng W; Brener, Igal; Koleske, Daniel D; Luk, Ting-Shan; Feezell, Daniel F; Brueck, S R J; Wang, George T

2017-02-08

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.

Nonpolar InGaN/GaN core–shell single nanowire lasers

DOE PAGES

Li, Changyi; Wright, Jeremy Benjamin; Liu, Sheng; ...

2017-01-24

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core–shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core–shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core–shell nanowires, despite significantly shorter cavity lengths and reducedmore » active region volume. Mode simulations show that due to the core–shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. Furthermore, the results show the viability of this p-i-n nonpolar core–shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV–visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.« less

Absorption and emission spectroscopy of individual semiconductor nanostructures

NASA Astrophysics Data System (ADS)

McDonald, Matthew P.

The advent of controllable synthetic methods for the production of semiconductor nanostructures has led to their use in a host of applications, including light-emitting diodes, field effect transistors, sensors, and even television displays. This is, in part, due to the size, shape, and morphologically dependent optical and electrical properties that make this class of materials extremely customizable; wire-, rod- and sphere-shaped nanocrystals are readily synthesized through common wet chemical methods. Most notably, confining the physical dimension of the nanostructure to a size below its Bohr radius (aB) results in quantum confinement effects that increase its optical energy gap. Not only the size, but the shape of a particle can be exploited to tailor its optical and electrical properties. For example, confined CdSe quantum dots (QDs) and nanowires (NWs) of equivalent diameter possess significantly different optical gaps. This phenomenon has been ascribed to electrostatic contributions arising from dielectric screening effects that are more pronounced in an elongated (wire-like) morphology. Semiconducting nanostructures have thus received significant attention over the past two decades. However, surprisingly little work has been done to elucidate their basic photophysics on a single particle basis. What has been done has generally been accomplished through emission-based measurements, and thus does not fully capture the full breadth of these intriguing systems. What is therefore needed then are absorption-based studies that probe the size and shape dependent evolution of nanostructure photophysics. This thesis summarizes the single particle absorption spectroscopy that we have carried out to fill this knowledge gap. Specifically, the diameter-dependent progression of one-dimensional (1D) excitonic states in CdSe NWs has been revealed. This is followed by a study that focuses on the polarization selection rules of 1D excitons within single CdSe NWs. Finally, shape effects are explored by probing the absorption spectra of CdSe nanowires and nanorods of varying length. All experimental studies are complemented by theoretical predictions from an effective mass model that takes electrostatic interactions into account. Thus, this thesis seeks to show the delicate interplay between quantum confinement and dielectric screening effects in single CdSe nanostructures.

Highly-reliable operation of 638-nm broad stripe laser diode with high wall-plug efficiency for display applications

NASA Astrophysics Data System (ADS)

Yagi, Tetsuya; Shimada, Naoyuki; Nishida, Takehiro; Mitsuyama, Hiroshi; Miyashita, Motoharu

2013-03-01

Laser based displays, as pico to cinema laser projectors have gathered much attention because of wide gamut, low power consumption, and so on. Laser light sources for the displays are operated mainly in CW, and heat management is one of the big issues. Therefore, highly efficient operation is necessitated. Also the light sources for the displays are requested to be highly reliable. 638 nm broad stripe laser diode (LD) was newly developed for high efficiency and highly reliable operation. An AlGaInP/GaAs red LD suffers from low wall plug efficiency (WPE) due to electron overflow from an active layer to a p-cladding layer. Large optical confinement factor (Γ) design with AlInP cladding layers is adopted to improve the WPE. The design has a disadvantage for reliable operation because the large Γ causes high optical density and brings a catastrophic optical degradation (COD) at a front facet. To overcome the disadvantage, a window-mirror structure is also adopted in the LD. The LD shows WPE of 35% at 25°C, highest record in the world, and highly stable operation at 35°C, 550 mW up to 8,000 hours without any catastrophic optical degradation.

Photonic Devices and Systems for Optical Signal Processing

DTIC Science & Technology

1993-08-01

efficiency can either increase or decrease with improving mirror quality depending on the relative amounts of optical loss due to the mirror...Gs is dependent on the degree of confinement of the TE and TM modes in the wave guide and the average intensity of light in the cavity. It is given...Approximately 80% of the optical power from the main laser with the 36 mA threshold can be quenched. Note the linear decrease in main laser intensity as the

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coles, David M.; Lidzey, David G.

We construct a microcavity in which the extended optical path length of the cavity (5.9 μm) permits a series of closely spaced optical modes to be supported. By placing a J-aggregated cyanine dye into the cavity, we reach the strong-coupling regime and evidence a simultaneous optical hybridization between the organic-exciton and a number of the confined cavity modes, forming an effective ladder of polariton branches. We explore the emission from such cavities and evidence a polariton-population on adjacent polariton branches around k{sub ∥} = 0.

Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives

PubMed Central

Bergmair, Michael; Bruno, Giovanni; Cattelan, Denis; Cobet, Christoph; de Martino, Antonello; Fleischer, Karsten; Dohcevic-Mitrovic, Zorana; Esser, Norbert; Galliet, Melanie; Gajic, Rados; Hemzal, Dušan; Hingerl, Kurt; Humlicek, Josef; Ossikovski, Razvigor; Popovic, Zoran V.; Saxl, Ottilia

2009-01-01

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures. PMID:21170135

Athermal operation of silicon waveguides: spectral, second order and footprint dependencies.

PubMed

Raghunathan, Vivek; Ye, Winnie N; Hu, Juejun; Izuhara, Tomoyuki; Michel, Jurgen; Kimerling, Lionel

2010-08-16

We report the design criteria and performance of Si ring resonators for passive athermal applications in wavelength division multiplexing (WDM). The waveguide design rules address i) positive-negative thermo-optic (TO) composite structures, ii) resonant wavelength dependent geometry to achieve constant confinement factor (Gamma), and iii) observation of small residual second order effects. We develop exact design requirements for a temperature dependent resonant wavelength shift (TDWS) of 0 pm/K and present prototype TDWS performance of 0.5 pm/K. We evaluate the materials selection tradeoffs between high-index contrast (HIC) and low-index contrast (LIC) systems and show, remarkably, that FSR and footprint become comparable under the constraint of athermal design.

Determination of the effective refractive index spectrum of a quantum-well semiconductor laser diode from the measured modal gain spectrum

NASA Astrophysics Data System (ADS)

Wu, Linzhang; Tian, Wei; Gao, Feng

2004-09-01

This paper presents a self-consistent method to directly determine the effective refractive-index spectrum of a semiconductor quantum-well (QW) laser diode from the measured modal gain spectrum for a given current. The dispersion spectra of the optical waveguide confinement factor and the strongly carrier-density-dependent refractive index of the QW active layer of the test laser are also accurately obtained. The experimental result from a single QW GaInP/AlGaInP laser diode, which has 6 nm thick compressively strained Ga0.4InP active layer sandwiched by two 80 nm thick Al0.33GaInP, is presented.

High-sensitivity liquid refractive-index sensor based on a Mach-Zehnder interferometer with a double-slot hybrid plasmonic waveguide.

PubMed

Sun, Xu; Dai, Daoxin; Thylén, Lars; Wosinski, Lech

2015-10-05

A Mach-Zehnder Interferometer (MZI) liquid sensor, employing ultra-compact double-slot hybrid plasmonic (DSHP) waveguide as active sensing arm, is developed. Numerical results show that extremely large optical confinement factor of the tested analytes (as high as 88%) can be obtained by DSHP waveguide with optimized geometrical parameters, which is larger than both, conventional SOI waveguides and plasmonic slot waveguides with same widths. As for MZI sensor with 40μm long DSHP active sensing area, the sensitivity can reach as high value as 1061nm/RIU (refractive index unit). The total loss, excluding the coupling loss of the grating coupler, is around 4.5dB.

The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots.

PubMed

Askari, Sadegh; Svrcek, Vladmir; Maguire, Paul; Mariotti, Davide

2015-12-22

Hydrogenation in amorphous silicon quantum dots (QDs) has a dramatic impact on the corresponding optical properties and band energy structure, leading to a quantum-confined composite material with unique characteristics. The synthesis of a-Si:H QDs is demonstrated with an atmospheric-pressure plasma process, which allows for accurate control of a highly chemically reactive non-equilibrium environment with temperatures well below the crystallization temperature of Si QDs. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electric field induced optical gain of a hydrogenic impurity in a Cd{sub 0.8}Zn{sub 0.2}Se/ZnSe parabolic quantum dot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jasmine, P. Christina Lily; Peter, A. John, E-mail: a.john.peter@gmail.com

The dependence of electric field on the electronic and optical properties is investigated in a Cd{sub 0.8}Zn{sub 0.2}Se/ZnSe quantum dot. The hydrogenic binding energy, in the presence of electric field, is calculated with the spatial confinement effect. The electric field dependent optical gain with the photon energy is found using compact density matrix method. The results show that the electric field has a great influence on the optical properties of II-VI semiconductor quantum dot.

Near-field scanning magneto-optical spectroscopy of Wigner molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mintairov, A. M., E-mail: amintair@nd.edu; Rouvimov, S.; Ioffe Physical-Technical Institute of the Russian Academy of Sciences, Saint Petersburg, 194021

We study the emission spectra of single self-organized InP/GaInP QDs (size 100-220 nm) using high-spatial-resolution, low-temperature (5 K) near-field scanning optical microscope (NSOM) operating at magnetic field strength B=0-10 T. The dots contain up to twenty electrons and represent natural Wigner molecules (WM). We observed vibronic-type shake-up structure in single electron QDs manifesting formation of two electron (2e) WM in photo-excited state. We found that relative intensities of the shake-up components described well by vibronic Frank-Condon factors giving for dots having parabolic confinement energy ħω{sub 0}=1.2-4 meV molecule bond lengths 40-140 nm. We used measurements of magnetic-field-induced shifts to distinguishmore » emission of 2e-WM and singly charged exciton (trion). We also observed magnetic-field-induced molecular-droplet transition for two electron dot, emitting through doubly charge exciton (tetron) at zero magnetic field.« less

Nanoscale optical positioning of single quantum dots for bright and pure single-photon emission

PubMed Central

Sapienza, Luca; Davanço, Marcelo; Badolato, Antonio; Srinivasan, Kartik

2015-01-01

Self-assembled, epitaxially grown InAs/GaAs quantum dots (QDs) are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of QDs, presenting a challenge in creating devices that exploit the strong interaction of single QDs with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single QDs with respect to alignment features with an average position uncertainty <30 nm (<10 nm when using a solid-immersion lens), which represents an enabling technology for the creation of optimized single QD devices. To that end, we create QD single-photon sources, based on a circular Bragg grating geometry, that simultaneously exhibit high collection efficiency (48%±5% into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50%), low multiphoton probability (g(2)(0) <1%), and a significant Purcell enhancement factor (≈3). PMID:26211442

Observation of coherent backscattering of light in ultracold ^85Rb

NASA Astrophysics Data System (ADS)

Kulatunga, P.; Sukenik, C. I.; Havey, M. D.; Kupriyanov, D. V.; Sokolov, I. M.

2002-05-01

We report investigation of multiple coherent light scattering from ^85Rb atoms confined in a magneto-optic trap. In experimental studies, measurements are made of coherent backscattering of a low-intensity probe beam tuned near the F = 3 - F' = 4 transition in ^85Rb atoms. Polarization of backscattered light is determined by a backscattering polarimeter; the spatial distribution of light intensity is measured by a liquid-nitrogen cooled CCD camera set in the focal plane of the analyzing optics. The instrument has angular resolution of about 100 micro-radians, and a polarization analyzing power of roughly 1000. In this paper we describe the instrument details, including calibration procedures, and our measurements of atomic coherent backscattering. In a theoretical study of intensity enhancement of near-resonant backscattered light from cold ^85,87Rb atoms, we consider scattering orders up to 8 and a Gaussian atom distribution in the MOT. Enhancement factors are calculated for all D1 and D2 hyperfine components and for both isotopes.

High-Speed Photography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paisley, D.L.; Schelev, M.Y.

1998-08-01

The applications of high-speed photography to a diverse set of subjects including inertial confinement fusion, laser surgical procedures, communications, automotive airbags, lightning etc. are briefly discussed. (AIP) {copyright} {ital 1998 Society of Photo-Optical Instrumentation Engineers.}

Quench-induced resonant tunneling mechanisms of bosons in an optical lattice with harmonic confinement

NASA Astrophysics Data System (ADS)

Mistakidis, Simeon; Koutentakis, Georgios; Schmelcher, Peter; Theory Group of Fundamental Processes in Quantum Physics Team

2017-04-01

The non-equilibrium dynamics of small boson ensembles in one-dimensional optical lattices is explored upon a sudden quench of an additional harmonic trap from strong to weak confinement. We find that the competition between the initial localization and the repulsive interaction leads to a resonant response of the system for intermediate quench amplitudes, corresponding to avoided crossings in the many-body eigenspectrum with varying final trap frequency. In particular, we show that these avoided crossings can be utilized to prepare the system in a desired state. The dynamical response is shown to depend on both the interaction strength as well as the number of atoms manifesting the many-body nature of the tunneling dynamics. Deutsche Forschungsgemeinschaft (DFG) in the framework of the SFB 925 ``Light induced dynamics and control of correlated quantum systems''.

Localized surface plasmons in vibrating graphene nanodisks

NASA Astrophysics Data System (ADS)

Wang, Weihua; Li, Bo-Hong; Stassen, Erik; Mortensen, N. Asger; Christensen, Johan

2016-02-01

Localized surface plasmons are confined collective oscillations of electrons in metallic nanoparticles. When driven by light, the optical response is dictated by geometrical parameters and the dielectric environment and plasmons are therefore extremely important for sensing applications. Plasmons in graphene disks have the additional benefit of being highly tunable via electrical stimulation. Mechanical vibrations create structural deformations in ways where the excitation of localized surface plasmons can be strongly modulated. We show that the spectral shift in such a scenario is determined by a complex interplay between the symmetry and shape of the modal vibrations and the plasmonic mode pattern. Tuning confined modes of light in graphene via acoustic excitations, paves new avenues in shaping the sensitivity of plasmonic detectors, and in the enhancement of the interaction with optical emitters, such as molecules, for future nanophotonic devices.

Stiffness of RBC optical confinement affected by optical clearing

NASA Astrophysics Data System (ADS)

Grishin, Oleg V.; Fedosov, Ivan V.; Tuchin, Valery V.

2017-03-01

In vivo optical trapping is a novel applied direction of an optical manipulation, which enables one to noninvasive measurement of mechanical properties of cells and tissues in living animals directly. But an application area of this direction is limited because strong scattering of many biological tissues. An optical clearing enables one to decrease the scattering and therefore increase a depth of light penetration, decrease a distortion of light beam, improve a resolution in imaging applications. Now novel methods had appeared for a measurement an optical clearing degree at a cellular level. But these methods aren't applicable in vivo. In this paper we present novel measurement method of estimate of the optical clearing, which are based on a measurement of optical trap stiffness. Our method may be applicable in vivo.

Confinement of active systems: trapping, swim pressure, and explosions

NASA Astrophysics Data System (ADS)

Takatori, Sho; de Dier, Raf; Vermant, Jan; Brady, John

2015-11-01

We analyze the run-and-tumble dynamics and motion of living bacteria and self-propelled Janus motors confined in an acoustic trap. Since standard optical tweezers are far too weak, we developed an acoustic trap strong enough to confine swimmers over distances large compared to the swimmers' size and run length. The external trap behaves as an ``osmotic barrier'' that confines the swimmers inside the trapping region, analogous to semipermeable membranes that confine passive Brownian particles inside a boundary. From the swimmers' restricted motion inside the trap, we calculate the unique swim pressure generated by active systems originating from the force required to confine them by boundaries. We apply a strong trap to collect the swimmers into a close-packed active crystal and then turn off the trap which causes the crystal to ``explode'' due to an imbalance of the active pressure. We corroborate all experimental results with Brownian dynamics simulations and analytical theory. ST is supported by a Gates Millennium Scholars fellowship and a NSF Fellowship No. DGE-1144469. RDD is supported by a doctoral fellowship of the fund for scientific research (FWO-Vlaanderen). This work is also supported by NSF Grant CBET 1437570.

Distributed feedback imprinted electrospun fiber lasers.

PubMed

Persano, Luana; Camposeo, Andrea; Del Carro, Pompilio; Fasano, Vito; Moffa, Maria; Manco, Rita; D'Agostino, Stefania; Pisignano, Dario

2014-10-01

Imprinted, distributed feedback lasers are demonstrated on individual, active electrospun polymer nanofibers. In addition to advantages related to miniaturization, optical confinement and grating nanopatterning lead to a significant threshold reduction compared to conventional thin-film lasers. The possibility of imprinting arbitrary photonic crystal geometries on electrospun lasing nanofibers opens new opportunities for realizing optical circuits and chips. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Longwave Silicon Chip - Integrated Plasma-Photonics in Group IV And III-V Semiconductors

DTIC Science & Technology

2013-10-01

infrared applications; SiGeSn heterostructure photonics; group IV plasmonics with silicides , germanicides, doped Si, Ge or GeSn; Franz-Keldysh...SPP waveguide in which localized silicide or germanicide “conductors” are introduced to give local plasmonic confinement. Therefore, guided-wave...reconfigurable integrated optoelectronics, electro-optical logic in silicon, silicides for group IV plasmonics, reviews of third-order nonlinear optical

Exciton diamagnetic shift and optical properties in CdSe nanocrystal quantum dots in magnetic fields

NASA Astrophysics Data System (ADS)

Wu, Shudong; Cheng, Liwen

2018-04-01

The magnetic field dependence of the optical properties of CdSe nanocrystal quantum dots (NQDs) is investigated theoretically using a perturbation method within the effective-mass approximation. The results show that the magnetic field lifts the degeneracy of the electron (hole) states. A blue-shift in the absorption spectra of m ≥ 0 exciton states is observed while the absorption peak of m < 0 exciton states is first red-shifted and then blue-shifted with increasing the magnetic field strength B. This is attributed to the interplay of the orbital Zeeman effect and the additive confinement induced by the magnetic field. The excitonic absorption coefficient is almost independent of B in the strong confinement regime. The applied magnetic field causes the splitting of degenerated exciton states, resulting in the new absorption peaks. Based on the first-order perturbation theory, we propose the analytical expressions for the exciton binding energy, exciton transition energy and exciton diamagnetic shift of 1s, 1p-1, 1p0, 1p1, 1d-2, 1d-1, 1d0, 1d1, 1d2 and 2s exciton states on the applied magnetic field in the strong confinement regime.

Quantum bright solitons in a quasi-one-dimensional optical lattice

NASA Astrophysics Data System (ADS)

Barbiero, Luca; Salasnich, Luca

2014-06-01

We study a quasi-one-dimensional attractive Bose gas confined in an optical lattice with a superimposed harmonic potential by analyzing the one-dimensional Bose-Hubbard Hamiltonian of the system. Starting from the three-dimensional many-body quantum Hamiltonian, we derive strong inequalities involving the transverse degrees of freedom under which the one-dimensional Bose-Hubbard Hamiltonian can be safely used. To have a reliable description of the one-dimensional ground state, which we call a quantum bright soliton, we use the density-matrix-renormalization-group (DMRG) technique. By comparing DMRG results with mean-field (MF) ones, we find that beyond-mean-field effects become relevant by increasing the attraction between bosons or by decreasing the frequency of the harmonic confinement. In particular, we find that, contrary to the MF predictions based on the discrete nonlinear Schrödinger equation, average density profiles of quantum bright solitons are not shape-invariant. We also use the time-evolving-block-decimation method to investigate the dynamical properties of bright solitons when the frequency of the harmonic potential is suddenly increased. This quantum quench induces a breathing mode whose period crucially depends on the final strength of the superimposed harmonic confinement.

Experimental demonstration of subwavelength domino plasmon devices for compact high-frequency circuit.

PubMed

Ma, Y G; Lan, L; Zhong, S M; Ong, C K

2011-10-24

In optical frequency, surface plasmons of metal provide us a prominent way to build compact photonic devices or circuits with non-diffraction limit. It is attributed by their extraordinary electromagnetic confining effect. But in the counterpart of lower frequencies, plasmonics behavior of metal is screened by eddy current induced in a certain skin depth. To amend this, spoof plasmons engineered by artificial structures have been introduced to mimic surface plasmons in these frequencies. But it is less useful for practical application due to their weak field confinement as manifested by large field decaying length in the upper dielectric space. Recently, a new type of engineered plasmons, domino plasmon was theoretically proposed to produce unusual field confinement and waveguiding capabilities that make them very attractive for ultra-compact device applications [Opt. Exp. 18, 754-764 (2010)]. In this work, we implemented these ideas and built three waveguiding devices based on domino plasmons. Their strong capabilities to produce versatile and ultra-compact devices with multiple electromagnetic functions have been experimentally verified in microwaves. And that can be extended to THz regime to pave the way for a new class of integrated wave circuits. © 2011 Optical Society of America

Nanofiber quantum photonics

NASA Astrophysics Data System (ADS)

Nayak, Kali P.; Sadgrove, Mark; Yalla, Ramachandrarao; Le Kien, Fam; Hakuta, Kohzo

2018-07-01

Recent advances in the coherent control of single quanta of light, photons, is a topic of prime interest, and is discussed under the banner of quantum photonics. In the last decade, the subwavelength diameter waist of a tapered optical fiber, referred to as an optical nanofiber, has opened promising new avenues in the field of quantum optics, paving the way toward a versatile platform for quantum photonics applications. The key feature of the technique is that the optical field can be tightly confined in the transverse direction while propagating over long distances as a guided mode and enabling strong interaction with the surrounding medium in the evanescent region. This feature has led to surprising possibilities to manipulate single atoms and fiber-guided photons, e.g. the efficient channeling of emission from single atoms and solid-state quantum emitters into the fiber-guided modes, high optical depth with a few atoms around the nanofiber, trapping atoms around a nanofiber, and atomic memories for fiber-guided photons. Furthermore, implementing a moderate longitudinal confinement in nanofiber cavities has enabled the strong coupling regime of cavity quantum electrodynamics to be reached, and the long-range dipole–dipole interaction between quantum emitters mediated by the nanofiber offers a platform for quantum nonlinear optics with an ensemble of atoms. In addition, the presence of a longitudinal component of the guided field has led to unique capabilities for chiral light–matter interactions on nanofibers. In this article, we review the key developments of the nanofiber technology toward a vision for quantum photonics on an all-fiber interface.

Relating quark confinement and chiral symmetry breaking in QCD

NASA Astrophysics Data System (ADS)

Suganuma, Hideo; Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro

2017-12-01

We study the relation between quark confinement and chiral symmetry breaking in QCD. Using lattice QCD formalism, we analytically express the various ‘confinement indicators’, such as the Polyakov loop, its fluctuations, the Wilson loop, the inter-quark potential and the string tension, in terms of the Dirac eigenmodes. In the Dirac spectral representation, there appears a power of the Dirac eigenvalue {λ }n such as {λ }n{Nt-1}, which behaves as a reduction factor for small {λ }n. Consequently, since this reduction factor cannot be cancelled, the low-lying Dirac eigenmodes give negligibly small contribution to the confinement quantities, while they are essential for chiral symmetry breaking. These relations indicate that there is no direct one-to-one correspondence between confinement and chiral symmetry breaking in QCD. In other words, there is some independence of quark confinement from chiral symmetry breaking, which can generally lead to different transition temperatures/densities for deconfinement and chiral restoration. We also investigate the Polyakov loop in terms of the eigenmodes of the Wilson, the clover and the domain-wall fermion kernels, and find similar results. The independence of quark confinement from chiral symmetry breaking seems to be natural, because confinement is realized independently of quark masses and heavy quarks are also confined even without the chiral symmetry.

A novel liquid-filled microstructured polymer optical fiber as bio-sensing platform for Raman spectroscopy

NASA Astrophysics Data System (ADS)

Azkune, Mikel; Arrospide, Eneko; Berganza, Amaia; Bikandi, Iñaki; Aldabaldetreku, Gotzon; Durana, Gaizka; Zubia, Joseba

2018-02-01

One approach to overcome the poor efficiency of the Raman scattering as a sensing platform is to use microstructured optical fibers. In this type of fibers with a longitudinal holey structure, light interacts with the target sample, which is confined in the core, giving rise to a light intensity increase of the obtained Raman spectra due to the large interaction distances and the guidance of the scattered light. In this work, we present an ad-hoc fabricated liquid-core microstructured polymer optical fiber (LC-mPOF) as a bio-sensing platform for Raman Spectroscopy. Arising from an initial simulation stage, we create the desired preform using the drilling technique and afterwards the LC-mPOF is drawn in our fiber drawing tower. The guiding mechanism of the light through the solution has a major importance, being a key factor to obtain appreciable enhancements in Raman scattering. In this case, in order to optimize the Raman scattering signal of dissolved glucose (target molecule), we have filled the core with an aqueous solution of the target molecule, enabling in this way the modified total internal reflection mechanism. Experimental Raman measurements are performed and results are discussed.

Extrinsic curvature, geometric optics, and lamellar order on curved substrates

NASA Astrophysics Data System (ADS)

Kamien, Randall D.; Nelson, David R.; Santangelo, Christian D.; Vitelli, Vincenzo

2009-11-01

When thermal energies are weak, two-dimensional lamellar structures confined on a curved substrate display complex patterns arising from the competition between layer bending and compression in the presence of geometric constraints. We present broad design principles to engineer the geometry of the underlying substrate so that a desired lamellar pattern can be obtained by self-assembly. Two distinct physical effects are identified as key factors that contribute to the interaction between the shape of the underlying surface and the resulting lamellar morphology. The first is a local ordering field for the direction of each individual layer, which tends to minimize its curvature with respect to the three-dimensional embedding. The second is a nonlocal effect controlled by the intrinsic geometry of the surface that forces the normals to the (nearly incompressible) layers to lie on geodesics, leading to caustic formation as in optics. As a result, different surface morphologies with predominantly positive or negative Gaussian curvature can act as converging or diverging lenses, respectively. By combining these ingredients, as one would with different optical elements, complex lamellar morphologies can be obtained. This smectic optometry enables the manipulation of lamellar configurations for the design of materials.

Measurement of nanoparticle size, suspension polydispersity, and stability using near-field optical trapping and light scattering (Conference Presentation)

NASA Astrophysics Data System (ADS)

Schein, Perry; O'Dell, Dakota; Erickson, David

2017-02-01

Nanoparticles are becoming ubiquitous in applications including diagnostic assays, drug delivery and therapeutics. However, there remain challenges in the quality control of these products. Here we present methods for the orthogonal measurement of these parameters by tracking the motion of the nanoparticle in all three special dimensions as it interacts with an optical waveguide. These simultaneous measurements from a single particle basis address some of the gaps left by current measurement technologies such as nanoparticle tracking analysis, ζ-potential measurements, and absorption spectroscopy. As nanoparticles suspended in a microfluidic channel interact with the evanescent field of an optical waveguide, they experience forces and resulting motion in three dimensions: along the propagation axis of the waveguide (x-direction) they are propelled by the optical forces, parallel to the plane of the waveguide and perpendicular to the optical propagation axis (y-direction) they experience an optical gradient force generated from the waveguide mode profile which confines them in a harmonic potential well, and normal to the surface of the waveguide they experience an exponential downward optical force balanced by the surface interactions that confines the particle in an asymmetric well. Building on our Nanophotonic Force Microscopy technique, in this talk we will explain how to simultaneously use the motion in the y-direction to estimate the size of the particle, the comparative velocity in the x-direction to measure the polydispersity of a particle population, and the motion in the z-direction to measure the potential energy landscape of the interaction, providing insight into the colloidal stability.

Soft exfoliation of 2D SnO with size-dependent optical properties

NASA Astrophysics Data System (ADS)

Singh, Mandeep; Della Gaspera, Enrico; Ahmed, Taimur; Walia, Sumeet; Ramanathan, Rajesh; van Embden, Joel; Mayes, Edwin; Bansal, Vipul

2017-06-01

Two-dimensional (2D) materials have recently gained unprecedented attention as potential candidates for next-generation (opto)electronic devices due to their fascinating optical and electrical properties. Tin monoxide, SnO, is an important p-type semiconductor with applications across photocatalysis (water splitting) and electronics (transistors). However, despite its potential in several important technological applications, SnO remains underexplored in its 2D form. Here we present a soft exfoliation strategy to produce 2D SnO nanosheets with tunable optical and electrical properties. Our approach involves the initial synthesis of layered SnO microspheres, which are readily exfoliated through a low-power sonication step to form high quality SnO nanosheets. We demonstrate that the properties of 2D SnO are strongly dependent on its dimensions. As verified through optical absorption and photoluminescence studies, a strong size-dependent quantum confinement effect in 2D SnO leads to substantial variation in its optical and electrical properties. This results in a remarkable (>1 eV) band gap widening in atomically thin SnO. Through photoconductivity measurements, we further validate a strong correlation between the quantum-confined properties of 2D SnO and the selective photoresponse of atomically thin sheets in the high energy UV light. Such tunable semiconducting properties of 2D SnO could be exploited for a variety of applications including photocatalysis, photovoltaics and optoelectronics in general.

Coherence-limited solar power conversion: the fundamental thermodynamic bounds and the consequences for solar rectennas

NASA Astrophysics Data System (ADS)

Mashaal, Heylal; Gordon, Jeffrey M.

2014-10-01

Solar rectifying antennas constitute a distinct solar power conversion paradigm where sunlight's spatial coherence is a basic constraining factor. In this presentation, we derive the fundamental thermodynamic limit for coherence-limited blackbody (principally solar) power conversion. Our results represent a natural extension of the eponymous Landsberg limit, originally derived for converters that are not constrained by the radiation's coherence, and are irradiated at maximum concentration (i.e., with a view factor of unity to the solar disk). We proceed by first expanding Landsberg's results to arbitrary solar view factor (i.e., arbitrary concentration and/or angular confinement), and then demonstrate how the results are modified when the converter can only process coherent radiation. The results are independent of the specific power conversion mechanism, and hence are valid for diffraction-limited as well as quantum converters (and not just classical heat engines or in the geometric optics regime). The derived upper bounds bode favorably for the potential of rectifying antennas as potentially high-efficiency solar converters.

Tunable cavity coupling of the zero phonon line of a nitrogen-vacancy defect in diamond

NASA Astrophysics Data System (ADS)

Johnson, S.; Dolan, P. R.; Grange, T.; Trichet, A. A. P.; Hornecker, G.; Chen, Y. C.; Weng, L.; Hughes, G. M.; Watt, A. A. R.; Auffèves, A.; Smith, J. M.

2015-12-01

We demonstrate the tunable enhancement of the zero phonon line of a single nitrogen-vacancy colour centre in diamond at cryogenic temperature. An open cavity fabricated using focused ion beam milling provides mode volumes as small as 1.24 μm3 (4.7 {λ }3) and quality factor Q≃ 3000. In situ tuning of the cavity resonance is achieved with piezoelectric actuators. At optimal coupling to a TEM00 cavity mode, the signal from individual zero phonon line transitions is enhanced by a factor of 6.25 and the overall emission rate of the NV- centre is increased by 40% compared with that measured from the same centre in the absence of cavity field confinement. This result represents a step forward in the realisation of efficient spin-photon interfaces and scalable quantum computing using optically addressable solid state spin qubits.

Plasmon-emitter interaction using integrated ring grating-nanoantenna structures.

PubMed

Rahbany, Nancy; Geng, Wei; Bachelot, Renaud; Couteau, Christophe

2017-05-05

Overcoming the diffraction limit to achieve high optical resolution is one of the main challenges in the fields of plasmonics, nanooptics and nanophotonics. In this work, we introduce novel plasmonic structures consisting of nanoantennas (nanoprisms, single bowtie nanoantennas and double bowtie nanoantennas) integrated in the center of ring diffraction gratings. Propagating surface plasmon polaritons (SPPs) are generated by the ring grating and coupled with localized surface plasmons (LSPs) at the nanoantennas exciting emitters placed in their gap. SPPs are widely used for optical waveguiding but provide low resolution due to their weak spatial confinement. In contrast, LSPs provide excellent sub-wavelength confinement but induce large losses. The phenomenon of SPP-LSP coupling witnessed in our structures allows for achieving more precise focusing at the nanoscale, causing an increase in the fluorescence emission of the emitters. Finite-difference time-domain simulations as well as experimental fabrication and optical characterization results are presented to study plasmon-emitter coupling between an ensemble of dye molecules and our integrated plasmonic structures. A comparison is given to highlight the importance of each structure on the photoluminescence and radiative decay enhancement of the molecules.

Nanostructuring-induced modification of optical properties of p-GaAs (1 0 0)

NASA Astrophysics Data System (ADS)

Naddaf, M.; Saloum, S.

2009-10-01

A pulsed anodic etching method has been utilized for nanostructuring of p-type GaAs (1 0 0) surface, using HCl-based solution as electrolyte. The resulting porous GaAs layer is characterized by atomic force microscopy (AFM), room temperature photoluminescence (PL), Raman spectroscopy and optical reflectance measurements. AFM imaging reveals that the porous GaAs layer is consisted of a pillar-like of few nm in width distributed between more-reduced size nanostructures. In addition to the “infrared” PL band of un-etched GaAs, a strong “green” PL band is observed in the etched sample. The broad visible PL band of a high-energy (3.82 eV) excitation is found to compose of two PL band attributed to excitons confinement in two different sizes distribution of GaAs nanocrystals. The quantum confinement effects in GaAs nanocrystallites is also evidenced from Raman spectroscopy through the pronounced appearance of the transverse optical (TO) phonon line in the spectra of the porous sample. Porosity-induced a significant reduction of the specular reflection, in the spectral range (400-800 nm), is also demonstrated.

Elliptical As2Se3 filled core ultra-high-nonlinearity and polarization-maintaining photonic crystal fiber with double hexagonal lattice cladding

NASA Astrophysics Data System (ADS)

Li, Feng; He, Menghui; Zhang, Xuedian; Chang, Min; Wu, Zhizheng; Liu, Zheng; Chen, Hua

2018-05-01

A high birefringence and ultra-high nonlinearity photonic crystal fiber (PCF) is proposed, which is composed of an elliptical As2Se3-doped core and an inner cladding with hexagonal lattice. Optical properties of the PCF are simulated by the full-vector finite element method. The simulation results show that the high birefringence of ∼0.33, ultra-high-nonlinearity coefficient of 300757 W-1km-1 and the low confinement loss can be achieved in the proposed PCF simultaneously at the wavelength of 1.55 μm. Furthermore, by comparison with the other two materials (80PbO•20Ga2O3, As2S3) filled in the core, the As2Se3-doped PCF is found to have the highest birefringence and nonlinearity due to its higher refractive index and nonlinear refractive index. The flattened dispersion feature, as well as the low confinement loss of the proposed PCF structure make it suitable as a wide range of applications, such as the coherent optical communications, polarization-maintaining and nonlinear optics, etc.

Influence of image charge effect on impurity-related optical absorption coefficients and refractive index changes in a spherical quantum dot

NASA Astrophysics Data System (ADS)

Vartanian, A. L.; Asatryan, A. L.; Vardanyan, L. A.

2017-03-01

We have investigated the influence of an image charge effect (ICE) on the energies of the ground and first few excited states of a hydrogen-like impurity in a spherical quantum dot (QD) in the presence of an external electric field. The oscillator strengths of transitions from the 1 s -like state to excited states of 2px and 2pz symmetries are calculated as the functions of the strengths of the confinement potential and the electric field. Also, we have studied the effect of image charges on linear and third-order nonlinear optical absorption coefficients and refractive index changes (RICs). The results show that image charges lead to the decrease of energies for all the hydrogen-like states, to the significant enhancement of the oscillator strengths of transitions between the impurity states, and to comparatively large blue shifts in linear, nonlinear, and total absorption coefficients and refractive index changes. Our results indicate that the total optical characteristics can be controlled by the strength of the confinement and the electric field.

Plasmon-emitter interaction using integrated ring grating-nanoantenna structures

NASA Astrophysics Data System (ADS)

Rahbany, Nancy; Geng, Wei; Bachelot, Renaud; Couteau, Christophe

2017-05-01

Overcoming the diffraction limit to achieve high optical resolution is one of the main challenges in the fields of plasmonics, nanooptics and nanophotonics. In this work, we introduce novel plasmonic structures consisting of nanoantennas (nanoprisms, single bowtie nanoantennas and double bowtie nanoantennas) integrated in the center of ring diffraction gratings. Propagating surface plasmon polaritons (SPPs) are generated by the ring grating and coupled with localized surface plasmons (LSPs) at the nanoantennas exciting emitters placed in their gap. SPPs are widely used for optical waveguiding but provide low resolution due to their weak spatial confinement. In contrast, LSPs provide excellent sub-wavelength confinement but induce large losses. The phenomenon of SPP-LSP coupling witnessed in our structures allows for achieving more precise focusing at the nanoscale, causing an increase in the fluorescence emission of the emitters. Finite-difference time-domain simulations as well as experimental fabrication and optical characterization results are presented to study plasmon-emitter coupling between an ensemble of dye molecules and our integrated plasmonic structures. A comparison is given to highlight the importance of each structure on the photoluminescence and radiative decay enhancement of the molecules.

Generating a stationary infinite range tractor force via a multimode optical fibre

NASA Astrophysics Data System (ADS)

Ebongue, C. A.; Holzmann, D.; Ostermann, S.; Ritsch, H.

2017-06-01

Optical fibres confine and guide light almost unattenuated and thus convey light forces to polarizable nano-particles over very long distances. Radiation pressure forces arise from scattering of guided photons into free space while gradient forces are based on coherent scattering between different fibre modes or propagation directions. Interestingly, even scattering between co-propagating modes induces longitudinal forces as the transverse confinement of the light modes creates mode dependent longitudinal wave-vectors and photon momenta. We generalize a proven scattering matrix based approach to calculate single as well as inter-particle forces to include several forward and backward propagating modes. We show that an injection of the higher order mode only in a two mode fibre will induce a stationary tractor force against the injection direction, when the mode coupling to the lower order mode dominates against backscattering and free space losses. Generically this arises for non-absorbing particles at the centre of a waveguide. The model also gives improved predictions for inter-particle forces in evanescent nanofibre fields as experimentally observed recently. Surprisingly strong tractor forces can also act on whole optically bound arrays.

Deep-UV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures

NASA Astrophysics Data System (ADS)

Islam, S. M.; Protasenko, Vladimir; Lee, Kevin; Rouvimov, Sergei; Verma, Jai; Xing, Huili Grace; Jena, Debdeep

2017-08-01

Deep ultraviolet (UV) optical emission below 250 nm (˜5 eV) in semiconductors is traditionally obtained from high aluminum containing AlGaN alloy quantum wells. It is shown here that high-quality epitaxial ultrathin binary GaN quantum disks embedded in an AlN matrix can produce efficient optical emission in the 219-235 nm (˜5.7-5.3 eV) spectral range, far above the bulk bandgap (3.4 eV) of GaN. The quantum confinement energy in these heterostructures is larger than the bandgaps of traditional semiconductors, made possible by the large band offsets. These molecular beam epitaxy-grown extreme quantum-confinement GaN/AlN heterostructures exhibit an internal quantum efficiency of 40% at wavelengths as short as 219 nm. These observations together with the ability to engineer the interband optical matrix elements to control the direction of photon emission in such binary quantum disk active regions offer unique advantages over alloy AlGaN quantum well counterparts for the realization of deep-UV light-emitting diodes and lasers.

Mach-Zehnder Fiber-Optic Links for ICF Diagnostics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, E. K., Hermann, H. W.

2012-11-01

This article describes the operation and evolution of Mach-Zehnder links for single-point detectors in inertial confinement fusion experimental facilities, based on the Gamma Reaction History (GRH) diagnostic at the National Ignition Facility.

Optical Refrigeration

DTIC Science & Technology

2007-12-01

confined to either glasses and crystals doped with rare-earth (RE) elements or direct-bandgap semiconductors such as gallium arsenide. Although laser...condition. Highly controlled epitaxial growth techniques, such as metal–organic chemical vapour deposition (MOCVD) can produce very low surface

Renormalization of optical transition strengths in semiconductor nanoparticles due to band mixing

DOE PAGES

Velizhanin, Kirill A.

2016-05-25

We report that unique optical properties of semiconductor nanoparticles (SN) make them very promising in the multitude of applications including lasing, light emission and photovoltaics. In many of these applications it is imperative to understand the physics of interaction of electrons in a SN with external electromagnetic fields on the quantitative level. In particular, the strength of electron–photon coupling determines such important SN parameters as the radiative lifetime and absorption cross section. This strength is often assumed to be fully encoded by the so called Kane momentum matrix element. This parameter, however, pertains to a bulk semiconductor material and, asmore » such, is not sensitive to the quantum confinement effects in SNs. In this work we demonstrate that the quantum confinement, via the so called band mixing, can result in a significant suppression of the strength of electron interaction with electromagnetic field. Within the envelope function formalism we show how this suppression can be described by introducing an effective energy-dependent Kane momentum. Then, the effect of band mixing on the efficiencies of various photoinduced processes can be fully captured by the conventional formulae (e.g., spontaneous emission rate), once the conventional Kane momentum is substituted with the renormalized energy-dependent Kane momentum introduced in here. Lastly, as an example, we evaluate the energy-dependent Kane momentum for spherical PbSe and PbS SNs (i.e., quantum dots) and show that neglecting band mixing in these systems can result in the overestimation of absorption cross sections and emission rates by a factor of ~2.« less

Microfiber Optical Sensors: A Review

PubMed Central

Lou, Jingyi; Wang, Yipei; Tong, Limin

2014-01-01

With diameter close to or below the wavelength of guided light and high index contrast between the fiber core and the surrounding, an optical microfiber shows a variety of interesting waveguiding properties, including widely tailorable optical confinement, evanescent fields and waveguide dispersion. Among various microfiber applications, optical sensing has been attracting increasing research interest due to its possibilities of realizing miniaturized fiber optic sensors with small footprint, high sensitivity, fast response, high flexibility and low optical power consumption. Here we review recent progress in microfiber optical sensors regarding their fabrication, waveguide properties and sensing applications. Typical microfiber-based sensing structures, including biconical tapers, optical gratings, circular cavities, Mach-Zehnder interferometers and functionally coated/doped microfibers, are summarized. Categorized by sensing structures, microfiber optical sensors for refractive index, concentration, temperature, humidity, strain and current measurement in gas or liquid environments are reviewed. Finally, we conclude with an outlook for challenges and opportunities of microfiber optical sensors. PMID:24670720

22 W coherent GaAlAs amplifier array with 400 emitters

NASA Technical Reports Server (NTRS)

Krebs, D.; Herrick, R.; No, K.; Harting, W.; Struemph, F.

1991-01-01

Greater than 22 W of optical power has been demonstrated from a multiple-emitter, traveling-wave semiconductor amplifier, with approximately 87 percent of the output at the frequency of the injection source. The device integrates, in AlGaAs graded-index separate-confinement heterostructure single quantum well (GRINSCH-SQW) epitaxy, 400 ridge waveguide amplifiers with a coherent optical signal distribution circuit on a 12 x 6 mm chip.

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, Richard P.; Lott, James A.

1994-01-01

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors.

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, R.P.; Lott, J.A.

1994-09-27

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors. 5 figs.

Quantum Simulation of the Hubbard Model Using Ultra-Cold Atoms

DTIC Science & Technology

2008-11-01

explore phases that do not yet have analogous behavior in QCD . ..,.. Ultracold fennions in optical lattices . The evolution from BCS to BEC...trimer states. The three-component Fermi gas we have created will, when confined in an optical lattice , be an experimental realization of the SU(3...chromodynamics ( QCD ): the color superconducting phase and the formation of baryons. Our initial investigations have focused on understanding three-body

Double high refractive-index contrast grating VCSEL

NASA Astrophysics Data System (ADS)

Gebski, Marcin; Dems, Maciej; Wasiak, Michał; Sarzała, Robert P.; Lott, J. A.; Czyszanowski, Tomasz

2015-03-01

Distributed Bragg reflectors (DBRs) are typically used as the highly reflecting mirrors of vertical-cavity surface-emitting lasers (VCSELs). In order to provide optical field confinement, oxide apertures are often incorporated in the process of the selective wet oxidation of high aluminum-content DBR layers. This technology has some potential drawbacks such as difficulty in controlling the uniformity of the oxide aperture diameters across a large-diameter (≥ 6 inch) production wafers, high DBR series resistance especially for small diameters below about 5 μm despite elaborate grading and doping schemes, free carrier absorption at longer emission wavelengths in the p-doped DBRs, reduced reliability for oxide apertures placed close to the quantum wells, and low thermal conductivity for transporting heat away from the active region. A prospective alternative mirror is a high refractive index contrast grating (HCG) monolithically integrated with the VCSEL cavity. Two HCG mirrors potentially offer a very compact and simplified VCSEL design although the problems of resistance, heat dissipation, and reliability are not completely solved. We present an analysis of a double HCG 980 nm GaAs-based ultra-thin VCSEL. We analyze the optical confinement of such a structure with a total optical thickness is ~1.0λ including the optical cavity and the two opposing and parallel HCG mirrors.

High-birefringence photonic crystal fiber structures based on the binary morse-thue fractal sequence

NASA Astrophysics Data System (ADS)

Al-Muraeb, Ahmed; Abdel-Aty-Zohdy, Hoda

2016-09-01

A novel index-guiding Silica glass-core hexagonal High-Birefringence Photonic Crystal Fiber (HB-PCF) is proposed, with five rings of standard cladding air circular holes arranged in four formations inspired by the Binary Morse-Thue fractal Sequence (BMTS). The form birefringence, confinement loss, chromatic dispersion, effective mode area, and effective normalized frequency are evaluated for the four PCFs operating within (1.8 - 2 μm) eye-safe wavelength range. Modeling and analysis of the four PCF formations are performed deploying full-vector analysis in Finite Element Method (FEM) using COMSOL Multiphysics. Respecting fabrication and in light of commercial availability in designing the proposed PCF structures, a high birefringence of up to (6.549 × 10-3 at 2 μm) is achieved with dispersionfree single-mode operation. Confinement loss as low as (3.2 × 10-5 - 6.5 × 10-4 dB/m for 1.8 - 2 μm range) is achieved as well. Comparison against previously reported PCF structures reveals the desirably higher birefringence of our BMTS HB-PCF. The proposed PCFs are of vital use in various optical systems (e.g.: multi-wavelength fiber ring laser systems, and tunable lasers), catering for applications such as: optical sensing, LIDAR systems, material processing, optical signal processing, and optical communication.

Beyond dipolar regime in high-order plasmon mode bowtie antennas

NASA Astrophysics Data System (ADS)

Cuche, Aurélien; Viarbitskaya, Sviatlana; Kumar, Upkar; Sharma, Jadab; Arbouet, Arnaud; Girard, Christian; Dujardin, Erik

2017-03-01

Optical nanoantennas have shown their great potential for far-field to near-field coupling and for light confinement in subwavelength volumes. Here, we report on a multimodal configuration for bright and polarization-dependent bowtie antenna based on large and highly crystalline gold prisms. Each individual prism constituting an antenna arm sustains high order plasmon modes in the visible and near infrared range that allow for high field confinement and two-dimensional optical information propagation. We demonstrate by scanning two-photon luminescence (TPL) microscopy and numerical simulations based on the Green dyadic method that these bowtie antennas result in intense hot spots in different antenna locations as a function of the incident polarization. Finally, we quantify the local field enhancement above the antennas by computing the normalized total decay rate of a molecular system placed in the near field of the antenna gap as a function of the dipole orientation. We demonstrate the existence of a subtle relation between antenna geometry, polarization dependence and field enhancement. These new multimodal optical antennas are excellent far field to near field converter and they open the door for new strategies in the design of coplanar optical components for a wide range of applications including sensing, energy conversion or integrated information processing.

Quantum confinement and magnetic field effects on the electron Landé g factor in GaAs-(Ga,Al)As double quantum wells

NASA Astrophysics Data System (ADS)

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

2011-12-01

Nowadays the spin-related phenomena have attracted great attention for the possible spintronic and optoelectronic applications. The manipulation of the Landé g factor by means of the control of the electron confinement, applied magnetic field and hydrostatic pressure offers the possibility of having a wide range of ways to control single qubit operation and to have pure spin states to guarantee that no losses occur when the electron spins transport information. In this work we have performed a theoretical study of the quantum confinement (geometrical and barrier potential confinements) and growth direction applied magnetic field effects on the conduction-electron effective Landé g factor in GaAs-(Ga,Al)As double quantum wells. Our calculations of the Landé g factor are performed by using the Ogg-McCombe effective Hamiltonian, which includes non-parabolicity and anisotropy effects for the conduction-band electrons. Our theoretical results are given as function of the central barrier widths for different values of the applied magnetic fields. We have found that in this type of heterostructure the geometrical confinement commands the behavior of the electron effective Landé g factor as compared to the effect of the applied magnetic field. Present theoretical reports are in very good agreement with previous experimental and theoretical results.

Confining standing waves in optical corrals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babayan, Y.; McMahon, J. M.; Li, S.

2009-03-01

Near-field scanning optical microscopy images of solid wall, circular, and elliptical microscale corrals show standing wave patterns confined inside the structures with a wavelength close to that of the incident light. The patterns inside the corrals can be tuned by changing the size and material of the walls, the wavelength of incident light, and polarization direction for elliptical corrals. Finite-difference time-domain calculations of the corral structures agree with the experimental observations and reveal that the electric and magnetic field intensities are out of phase inside the corral. A theoretical modal analysis indicates that the fields inside the corrals can bemore » attributed to p- and s-polarized waveguide modes, and that the superposition of the propagating and evanescent modes can explain the phase differences between the fields. These experimental and theoretical results demonstrate that electromagnetic fields on a dielectric surface can be controlled in a predictable manner.« less

Theoretical study of low-frequency noise and amplitude – frequency characteristics of a semiconductor laser with a fiber Bragg grating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurnosov, V D; Kurnosov, K V

2013-09-30

Using the rate equations for the density of photons and charge carriers, we have studied the amplitude low-frequency noise of a fibre Bragg grating semiconductor laser. The calculations rely on two versions of the rate equation for the carriers, characterised by the presence of the optical confinement coefficient for the term, which takes into account the rate of stimulated recombination. It is shown that the relative noise intensity, which is calculated by using the rate equation for the carriers without optical confinement, agrees better with the experimental results. The calculation of the amplitude – frequency characteristics (AFCs) has shown thatmore » it is impossible to give preference to any one of these systems, since the AFCs for the two versions of the rate equations for the carriers coincide. (lasers)« less

High data rate atom interferometric device

DOEpatents

Biedermann, Grant; McGuinness, Hayden James Evans; Rakholia, Akash

2015-07-21

A light-pulse atomic interferometry (LPAI) apparatus is provided. The LPAI apparatus comprises a vessel, two sets of magnetic coils configured to magnetically confine an atomic vapor in two respective magneto-optical traps (MOTs) within the vessel when activated, and an optical system configured to irradiate the atomic vapor within the vessel with laser radiation that, when suitably tuned, can launch atoms previously confined in each of the MOTs toward the other MOT. In embodiments, the magnetic coils are configured to produce a magnetic field that is non-zero at the midpoint between the traps. In embodiments, the time-of-flight of the launched atoms from one MOT to the other is 12 ms or less. In embodiments, the MOTs are situated approximately 36 mm apart. In embodiments, the apparatus is configured to activate the magnetic coils according to a particular temporal magnetic field gradient profile.

Multiscale Study of Plasmonic Scattering and Light Trapping Effect in Silicon Nanowire Array Solar Cells.

PubMed

Meng, Lingyi; Zhang, Yu; Yam, ChiYung

2017-02-02

Nanometallic structures that support surface plasmons provide new ways to confine light at deep-subwavelength scales. The effect of light scattering in nanowire array solar cells is studied by a multiscale approach combining classical electromagnetic (EM) and quantum mechanical simulations. A photovoltaic device is constructed by integrating a silicon nanowire array with a plasmonic silver nanosphere. The light scatterings by plasmonic element and nanowire array are obtained via classical EM simulations, while current-voltage characteristics and optical properties of the nanowire cells are evaluated quantum mechanically. We found that the power conversion efficiency (PCE) of photovoltaic device is substantially improved due to the local field enhancement of the plasmonic effect and light trapping by the nanowire array. In addition, we showed that there exists an optimal nanowire number density in terms of optical confinement and solar cell PCE.

Confinement and Diffusion Effects in Dynamical Nuclear Polarization in Low Dimensional Nanostructures

NASA Astrophysics Data System (ADS)

Henriksen, Dan; Tifrea, Ionel

2012-02-01

We investigate the dynamic nuclear polarization as it results from the hyperfine coupling between nonequilibrium electronic spins and nuclear spins in semiconductor nanostructures. The natural confinement provided by low dimensional nanostructures is responsible for an efficient nuclear spin - electron spin hyperfine coupling [1] and for a reduced value of the nuclear spin diffusion constant [2]. In the case of optical pumping, the induced nuclear spin polarization is position dependent even in the presence of nuclear spin diffusion. This effect should be measurable via optically induced nuclear magnetic resonance or time-resolved Faraday rotation experiments. We discuss the implications of our calculations for the case of GaAs quantum well structures.[4pt] [1] I. Tifrea and M. E. Flatt'e, Phys. Rev. B 84, 155319 (2011).[0pt] [2] A. Malinowski and R. T. Harley, Solid State Commun. 114, 419 (2000).

GaSb/AlGaSb VCSEL structures and microcavities in the 1.5 μm wavelength range

NASA Astrophysics Data System (ADS)

Koeth, J.; Dietrich, R.; Reithmaier, J. P.; Forchel, A.

Vertical cavity surface emitting laser structures for 1.5 μm wavelength applications were realized by growing AlSb/AlGaSb Bragg mirrors on GaAs substrates with solid source molecular beam epitaxy. Due to the high refractive index contrast between GaSb and AlSb high quality resonators can be made by only 15 layer pairs for each Bragg mirror. Laser operation could be demonstrated by optical pumping with threshold excitation densities of about 500 W/cm2. In laterally deeply etched microcavities with diameters of 5 μm a clear discretization of the optical modes was observed. The lateral confinement effects are compared with results of AlAs/GaAs microcavities designed for 0.9 μm emission wavelength. Due to the longer wavelength a stronger confinement effect can be achieved in AlSb/AlGaSb microcavities for the same lateral dimensions.

Manipulation of metal-dielectric core-shell particles in optical fields

NASA Astrophysics Data System (ADS)

Chvátal, Lukáš; Šiler, Martin; Zemánek, Pavel

2014-12-01

Metal-dielectric core-shell particles represent promising tools in nanoplasmonics. In combination with optical tweezers they can be manipulated in a contactless way through fluid and their plasmonic properties can be used to probe or modify the local environment. We perform a numerical parametric study to find the particle geometry and material parameters under which such particle can be stably confined in optical tweezers. We use the theory based on Mie scattering in the focal field of an ideal water immersion objective of numerical aperture NA=1.2. For very thin metal layers we find that strong trapping on the optical axis can be achieved.

Engineering 1D Quantum Stripes from Superlattices of 2D Layered Materials.

PubMed

Gruenewald, John H; Kim, Jungho; Kim, Heung Sik; Johnson, Jared M; Hwang, Jinwoo; Souri, Maryam; Terzic, Jasminka; Chang, Seo Hyoung; Said, Ayman; Brill, Joseph W; Cao, Gang; Kee, Hae-Young; Seo, Sung S Ambrose

2017-01-01

Dimensional tunability from two dimensions to one dimension is demonstrated for the first time using an artificial superlattice method in synthesizing 1D stripes from 2D layered materials. The 1D confinement of layered Sr 2 IrO 4 induces distinct 1D quantum-confined electronic states, as observed from optical spectroscopy and resonant inelastic X-ray scattering. This 1D superlattice approach is generalizable to a wide range of layered materials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modal Analysis of β -Ga2O3:Cr Widely Tunable Luminescent Optical Microcavities

NASA Astrophysics Data System (ADS)

Alonso-Orts, M.; Nogales, E.; San Juan, J. M.; Nó, M. L.; Piqueras, J.; Méndez, B.

2018-06-01

Optical microcavities are key elements in many photonic devices, and those based on distributed Bragg reflectors (DBRs) enhance dramatically the end reflectivity, allowing for higher quality factors and finesse values. Besides, they allow for wide wavelength tunability, needed for nano- and microscale light sources to be used as photonic building blocks in the micro- and nanoscale. Understanding the complete behavior of light within the cavity is essential to obtaining an optimized design of properties and optical tunability. In this work, focused ion-beam fabrication of high refractive-index contrast DBR-based optical cavities within Ga2O3:Cr microwires grown and doped by the vapor-solid mechanism is reported. Room-temperature microphotoluminescence spectra show strong modulations from about 650 nm up to beyond 800 nm due to the microcavity resonance modes. Selectivity of the peak wavelength is achieved for two different cavities, demonstrating the tunability of this kind of optical system. Analysis of the confined modes is carried out by an analytical approximation and by finite-difference-time-domain simulations. A good agreement is obtained between the reflectivity values of the DBRs calculated from the experimental resonance spectra, and those obtained by finite-difference-time-domain simulations. Experimental reflectivities up to 70% are observed in the studied wavelength range and cavities, and simulations demonstrate that reflectivities up to about 90% could be reached. Therefore, Ga2O3:Cr high-reflectivity optical microcavities are shown as good candidates for single-material-based, widely tunable light emitters for micro- and nanodevices.

Reverse-absorbance-modulation-optical lithography for optical nanopatterning at low light levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majumder, Apratim, E-mail: apratim.majumder@utah.edu; Wan, Xiaowen; Masid, Farhana

2016-06-15

Absorbance-Modulation-Optical Lithography (AMOL) has been previously demonstrated to be able to confine light to deep sub-wavelength dimensions and thereby, enable patterning of features beyond the diffraction limit. In AMOL, a thin photochromic layer that converts between two states via light exposure is placed on top of the photoresist layer. The long wavelength photons render the photochromic layer opaque, while the short-wavelength photons render it transparent. By simultaneously illuminating a ring-shaped spot at the long wavelength and a round spot at the short wavelength, the photochromic layer transmits only a highly confined beam at the short wavelength, which then exposes themore » underlying photoresist. Many photochromic molecules suffer from a giant mismatch in quantum yields for the opposing reactions such that the reaction initiated by the absorption of the short-wavelength photon is orders of magnitude more efficient than that initiated by the absorption of the long-wavelength photon. As a result, large intensities in the ring-shaped spot are required for deep sub-wavelength nanopatterning. In this article, we overcome this problem by using the long-wavelength photons to expose the photoresist, and the short-wavelength photons to confine the “exposing” beam. Thereby, we demonstrate the patterning of features as thin as λ/4.7 (137 nm for λ = 647 nm) using extremely low intensities (4-30 W/m{sup 2}, which is 34 times lower than that required in conventional AMOL). We further apply a rigorous model to explain our experiments and discuss the scope of the reverse-AMOL process.« less

Low-index discontinuity terahertz waveguides

NASA Astrophysics Data System (ADS)

Nagel, Michael; Marchewka, Astrid; Kurz, Heinrich

2006-10-01

A new type of dielectric THz waveguide based on recent approaches in the field of integrated optics is presented with theoretical and experimental results. Although the guiding mechanism of the low-index discontinuity (LID) THz waveguide is total internal reflection, the THz wave is predominantly confined in the virtually lossless low-index air gap within a high-index dielectric waveguide due to the continuity of electric flux density at the dielectric interface. Attenuation, dispersion and single-mode confinement properties of two LID structures are discussed and compared with other THz waveguide solutions. The new approach provides an outstanding combination of high mode confinement and low transmission losses currently not realizable with any other metal-based or photonic crystal approach. These exceptional properties might enable the breakthrough of novel integrated THz systems or endoscopy applications with sub-wavelength resolution.

Optical fiber tips for biological applications: From light confinement, biosensing to bioparticles manipulation.

PubMed

Paiva, Joana S; Jorge, Pedro A S; Rosa, Carla C; Cunha, João P S

2018-05-01

The tip of an optical fiber has been considered an attractive platform in Biology. The simple cleaved end of an optical fiber can be machined, patterned and/or functionalized, acquiring unique properties enabling the exploitation of novel optical phenomena. Prompted by the constant need to measure and manipulate nanoparticles, the invention of the Scanning Near-field Optical Microscopy (SNOM) triggered the optimization and development of novel fiber tip microfabrication methods. In fact, the fiber tip was soon considered a key element in SNOM by confining light to sufficiently small extensions, challenging the diffraction limit. As result and in consequence of the newly proposed "Lab On Tip" concept, several geometries of fiber tips were applied in three main fields: imaging (in Microscopy/Spectroscopy), biosensors and micromanipulation (Optical Fiber Tweezers, OFTs). These are able to exert forces on microparticles, trap and manipulate them for relevant applications, as biomolecules mechanical study or protein aggregates unfolding. This review presents an overview of the main achievements, most impactful studies and limitations of fiber tip-based configurations within the above three fields, along the past 10 years. OFTs could be in future a valuable tool for studying several cellular phenomena such as neurodegeneration caused by abnormal protein fibrils or manipulating organelles within cells. This could contribute to understand the mechanisms of some diseases or biophenomena, as the axonal growth in neurons. To the best of our knowledge, no other review article has so far provided such a broad view. Despite of the limitations, fiber tips have key roles in Biology/Medicine. Copyright © 2018 Elsevier B.V. All rights reserved.

Confinement and Ordering of Au Nanorods in Polymer Films

NASA Astrophysics Data System (ADS)

Hore, Michael J. A.; Mills, Eric; Liu, Yu; Composto, Russell J.

2009-03-01

Ordered arrays of gold nanorods (Au NRs) possess interesting optical properties that might be utilized in future devices. Au NRs functionalized with a poly(ethylene glycol)-thiol brush are incorporated into homopolymer or block copolymer (BCP) films. NR distribution and orientational correlations are studied as a function of nanorod concentration and spacial confinement via Rutherford backscattering spectrometry (RBS) and transmission electron microscopy, respectively. In particular, differences in the degree of nanorod ordering are presented for PMMA homopolymer films (d ˜ 45 nm) versus PS-b-PMMA BCP films (L/2 ˜ 40 nm), where higher ordering is seen in the case of BCP films. At moderate volume fractions of NRs, φ = 1% to 10%, the degree of ordering is moderate, and increases with increasing φ . However, coexistence between regions of higher ordering and isotropic orientations is observed. In addition to the planar confinement considered above, orientation of Au NRs confined to cylindrical P2VP domains is studied in PS-b-P2VP BCP films.

Current density characteristics in the studies of electromagnetically induced transparency in a GaAs/GaAlAs quantum well

NASA Astrophysics Data System (ADS)

Jayarubi, J.; Peter, A. John

2017-05-01

Confinement potential profiles due to conduction and valence bands are obtained in a Ga0.7Al0.3As/ GaAs/ Ga0.7Al0.3As using variation formulism. The free electron distribution is carried out. The confined energy eigenvalue and its corresponding wavefunctions of charge carriers are found using self-consistent method. The confined energies with the geometrical confinement are computed. The potentials due to charges are done by Poisson equation. The effects of dielectric mismatch between the GaAs and GaAlAs semiconductors are introduced in the effective potential expressions. Transfer matrix method is employed to obtain the respective energies. The transmission probability is obtained for a constant well size. The high current density characteristics as a function of applied voltage is investigated. This investigation on the electromagnetically induced transparency in the photonic material will exploit in fabricating novel nonlinear optical devices in future.

Photonic confinement in laterally structured metal-organic microcavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mischok, Andreas, E-mail: andreas.mischok@iapp.de; Brückner, Robert; Sudzius, Markas

2014-08-04

We investigate the formation of optical modes in organic microcavities with an incorporated perforated silver layer. The metal leads to a formation of Tamm-plasmon-polaritons and thus separates the sample into metal-free or metal-containing areas, supporting different resonances. This mode splitting is exploited to confine photons in elliptic holes and triangular cuts, forming distinctive standing wave patterns showing the strong lateral confinement. A comparison with a Maxwell-Bloch based rate equation model clearly shows the nonlinear transition into the lasing regime. The concentration of the electric field density and inhibition of lateral loss channels in turn decreases the lasing threshold by upmore » to one order of magnitude, to 0.1 nJ. By spectroscopic investigation of such a triangular wedge, we observe the transition from the unperturbed cavity state to a strongly confined complex transversal mode. Such a structured silver layer can be utilized in future for charge carrier injection in an electrically driven organic solid state laser.« less

Hollow waveguide cavity ringdown spectroscopy

NASA Technical Reports Server (NTRS)

Dreyer, Chris (Inventor); Mungas, Greg S. (Inventor)

2012-01-01

Laser light is confined in a hollow waveguide between two highly reflective mirrors. This waveguide cavity is used to conduct Cavity Ringdown Absorption Spectroscopy of loss mechanisms in the cavity including absorption or scattering by gases, liquid, solids, and/or optical elements.

Observability of localized magnetoplasmons in quantum dots: Scrutinizing the eligibility of far-infrared, Raman, and electron-energy-loss spectroscopies

NASA Astrophysics Data System (ADS)

Kushwaha, Manvir S.

2016-03-01

We investigate a one-component, quasi-zero dimensional, quantum plasma exposed to a parabolic potential and an applied magnetic field in the symmetric gauge. If the size of such a system as can be realized in the semiconducting quantum dots is on the order of the de-Broglie wavelength, the electronic and optical properties become highly tunable. Then the quantum size effects challenge the observation of many-particle phenomena such as the magneto-optical absorption, Raman intensity, and electron energy-loss spectrum. An exact analytical solution of the problem leads us to infer that these many-particle phenomena are, in fact, dictated by the generalized Kohn's theorem (GKT) in the long-wavelength limit. Maneuvering the confinement and/or the magnetic field furnishes the resonance energies capable of being explored with the FIR, Raman, and/or electron-energy-loss spectroscopy. This implies that either of these probes is competent in observing the localized magnetoplasmons in the system. As an application of the rigorous analytical diagnosis of the system, we have presented various pertinent single-particle, such as Fock-Darwin spectrum, Fermi energy, zigzag excitation spectrum, and magneto-optical transitions, and the many-particle phenomena, such as magneto-optical absorption, Raman intensity, and electron energy-loss probability. In the latter, the energy position of the resonance peaks is observed to be independent of the electron-electron interactions and hence of the number of electrons in the quantum dot in compliance with the GKT. It is found that both confinement potential and magnetic field play a decisive role in influencing the aforementioned many-particle phenomena. Specifically, increasing (decreasing) the strength of the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots and results into a blue (red) shift in the respective spectra. Intensifying the magnetic field has two-fold effects in the resonance spectra associated with all three spectroscopies considered here: the lower resonance peak observes a red shift, whereas the higher one experiences a blue shift. This is a unique and intriguing behavior observed in the quantum dots with complete confinement. A deeper insight into the physics of the quantum dots is paving the way for their implementation in such diverse fields as quantum computing and medical imaging.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kushwaha, Manvir S.

We investigate a one-component, quasi-zero dimensional, quantum plasma exposed to a parabolic potential and an applied magnetic field in the symmetric gauge. If the size of such a system as can be realized in the semiconducting quantum dots is on the order of the de-Broglie wavelength, the electronic and optical properties become highly tunable. Then the quantum size effects challenge the observation of many-particle phenomena such as the magneto-optical absorption, Raman intensity, and electron energy-loss spectrum. An exact analytical solution of the problem leads us to infer that these many-particle phenomena are, in fact, dictated by the generalized Kohn’s theoremmore » (GKT) in the long-wavelength limit. Maneuvering the confinement and/or the magnetic field furnishes the resonance energies capable of being explored with the FIR, Raman, and/or electron-energy-loss spectroscopy. This implies that either of these probes is competent in observing the localized magnetoplasmons in the system. As an application of the rigorous analytical diagnosis of the system, we have presented various pertinent single-particle, such as Fock-Darwin spectrum, Fermi energy, zigzag excitation spectrum, and magneto-optical transitions, and the many-particle phenomena, such as magneto-optical absorption, Raman intensity, and electron energy-loss probability. In the latter, the energy position of the resonance peaks is observed to be independent of the electron-electron interactions and hence of the number of electrons in the quantum dot in compliance with the GKT. It is found that both confinement potential and magnetic field play a decisive role in influencing the aforementioned many-particle phenomena. Specifically, increasing (decreasing) the strength of the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots and results into a blue (red) shift in the respective spectra. Intensifying the magnetic field has two-fold effects in the resonance spectra associated with all three spectroscopies considered here: the lower resonance peak observes a red shift, whereas the higher one experiences a blue shift. This is a unique and intriguing behavior observed in the quantum dots with complete confinement. A deeper insight into the physics of the quantum dots is paving the way for their implementation in such diverse fields as quantum computing and medical imaging.« less

Position and Momentum Entanglement of Dipole-Dipole Interacting Atoms in Optical Lattices

NASA Astrophysics Data System (ADS)

Opatrný, T.; Kolář, M.; Kurizki, G.

We consider a possible realization of the position- and momentum-correlated atomic pairs that are confined to adjacent sites of two mutually shifted optical lattices and are entangled via laser-induced dipole-dipole interactions. The Einstein-Podolsky-Rosen (EPR) "paradox" [Einstein 1935] with translational variables is then modified by lattice-diffraction effects. We study a possible mechanism of creating such diatom entangled states by varying the effective mass of the atoms.

Spatio-temporal Theory of Lasing Action in Optically-Pumped Rotationally Excited Molecular Gases

DTIC Science & Technology

2011-04-11

17. A. E. Siegman , Lasers (Univ. Science Books, 1986). 18. R. Bansal (ed.), Handbook of Engineering Electromagnetics (Marcel Dekker, Inc., 2004). 19... laser emission from optically-pumped rota- tionally excited molecular gases confined in a metallic cavity. To this end, we have developed a...the operation of this class of lasers . The effect on the main lasing features of the spatial variation of the electric field intensity and the ohmic

Kinect the dots: 3D control of optical tweezers

NASA Astrophysics Data System (ADS)

Shaw, Lucy; Preece, Daryl; Rubinsztein-Dunlop, Halina

2013-07-01

Holographically generated optical traps confine micron- and sub-micron sized particles close to the center of focused light beams. They also provide a way of trapping multiple particles and moving them in three dimensions. However, in many systems the user interface is not always advantageous or intuitive especially for collaborative work and when depth information is required. We discuss and evaluate a set of multi-beam optical tweezers that utilize off the shelf gaming technology to facilitate user interaction. We use the Microsoft Kinect sensor bar as a way of getting the user input required to generate arbitrary optical force fields and control optically trapped particles. We demonstrate that the system can also be used for dynamic light control.

Optical response tuning in nanorod-on-semicontinous film systems: A computational study

NASA Astrophysics Data System (ADS)

Mokkath, Junais Habeeb

2018-01-01

Strongly confined and intense optical fields within the plasmonic metal nanocavities show outstanding potential for a wide range of functionalities in nanophotonics. Using time dependent density functional theory calculations, we investigate the optical response evolution as a function of the gap separation distances in nanorod-on-film systems comprised of a nanorod (NR) made of Al or Na on top of an Al film. Huge optical field modulations emerged in the chemically distinct Na NR - Al film system in comparison to the Al NR - Al film system, indicating the vital role of metals involved. We further study the optical response modifications by placing a conducting molecule in the gap region, finding strong spectral modulations via through-molecule electron tunneling.

Measuring forces and dynamics for optically levitated 20μm PS particles in air using electrostatic modulation

NASA Astrophysics Data System (ADS)

Park, Haesung; LeBrun, Thomas W.

2015-08-01

We demonstrate the simultaneous measurement of optical trap stiffness and quadrant-cell photodetector (QPD) calibration of optically trapped polystyrene particle in air. The analysis is based on the transient response of particles, confined to an optical trap, subject to a pulsed electrostatic field generated by parallel indium tin oxide (ITO) coated substrates. The resonant natural frequency and damping were directly estimated by fitting the analytical solution of the transient response of an underdamped harmonic oscillator to the measured particle displacement from its equilibrium position. Because, the particle size was estimated independently with video microscopy, this approach allowed us to measure the optical force without ignoring the effects of inertia and temperature changes from absorption.

Characteristics of gradient-interface-structured ZnCdSSe quantum dots with modified interface and its application to quantum-dot-sensitized solar cells

NASA Astrophysics Data System (ADS)

Jeong, Da-Woon; Kim, Jae-Yup; Seo, Han Wook; Lim, Kyoung-Mook; Ko, Min Jae; Seong, Tae-Yeon; Kim, Bum Sung

2018-01-01

Colloidal quantum dots (QDs) are attractive materials for application in photovoltaics, LEDs, displays, and bio devices owing to their unique properties. In this study, we synthesized gradient-interface-structured ZnCdSSe QDs and modified the interface based on a thermodynamic simulation to investigate its optical and physical properties. In addition, the interface was modified by increasing the molar concentration of Se. QDs at the modified interface were applied to QD-sensitized solar cells, which showed a 25.5% increase in photoelectric conversion efficiency owing to the reduced electron confinement effect. The increase seems to be caused by the excited electrons being relatively easily transferred to the level of TiO2 owing to the reduced electron confinement effect. Consequently, the electron confinement effect was observed to be reduced by increasing the ZnSe (or Zn1-xCdxSe)-rich phase at the interface. This means that, based on the thermodynamic simulation, the interface between the core QDs and the surface of the QDs can be controlled. The improvement of optical and electronic properties by controlling interfaces and surfaces during the synthesis of QDs, as reported in this work, can be useful for many applications beyond solar cells.

Intraband magneto-optical absorption in InAs/GaAs quantum dots: Orbital Zeeman splitting and the Thomas-Reiche-Kuhn sum rule

NASA Astrophysics Data System (ADS)

Zhang, J.-Z.; Galbraith, I.

2008-05-01

Using perturbation theory, intraband magneto-optical absorption is calculated for InAs/GaAs truncated pyramidal quantum dots in a magnetic field applied parallel to the growth direction z . The effects of the magnetic field on the electronic states as well as the intraband transitions are systematically studied. Selection rules governing the intraband transitions are discussed based on the symmetry properties of the electronic states. While the broadband z -polarized absorption is almost insensitive to the magnetic field, the orbital Zeeman splitting is the dominant feature in the in-plane polarized spectrum. Strong in-plane polarized magneto-absorption features are located in the far-infrared region, while z -polarized absorption occurs at higher frequencies. This is due to the dot geometry (the base length is much larger than the height) yielding different quantum confinement in the vertical and lateral directions. The Thomas-Reiche-Kuhn sum rule, including the magnetic field effect, is applied together with the selection rules to the absorption spectra. The orbital Zeeman splitting depends on both the dot size and the confining potential—the splitting decreases as the dot size or the confining potential decreases. Our calculated Zeeman splittings are in agreement with experimental data.

Photonic structures based on hybrid nanocomposites

NASA Astrophysics Data System (ADS)

Husaini, Saima

In this thesis, photonic structures embedded with two types of nanomaterials, (i) quantum dots and (ii) metal nanoparticles are studied. Both of these exhibit optical and electronic properties different from their bulk counterpart due to their nanoscale physical structure. By integrating these nanomaterials into photonic structures, in which the electromagnetic field can be confined and controlled via modification of geometry and composition, we can enhance their linear and nonlinear optical properties to realize functional photonic structures. Before embedding quantum dots into photonic structures, we study the effect of various host matrices and fabrication techniques on the optical properties of the colloidal quantum dots. The two host matrices of interest are SU8 and PMMA. It is shown that the emission properties of the quantum dots are significantly altered in these host matrices (especially SU8) and this is attributed to a high rate of nonradiative quenching of the dots. Furthermore, the effects of fabrication techniques on the optical properties of quantum dots are also investigated. Finally a microdisk resonator embedded with quantum dots is fabricated using soft lithography and luminescence from the quantum dots in the disk is observed. We investigate the absorption and effective index properties of silver nanocomposite films. It is shown that by varying the fill factor of the metal nanoparticles and fabrication parameters such as heating time, we can manipulate the optical properties of the metal nanocomposite. Optimizing these parameters, a silver nanocomposite film with a 7% fill factor is prepared. A one-dimensional photonic crystal consisting of alternating layers of the silver nanocomposite and a polymer (Polymethyl methacrylate) is fabricated using spin coating and its linear and nonlinear optical properties are investigated. Using reflectivity measurements we demonstrate that the one-dimensional silver-nanocomposite-dielectric photonic crystal exhibits a 200% enhancement of the reflection band which is attributed to the interplay between the plasmon resonance of the silver nanoparticles and the Bloch modes of the photonic crystal. Nonlinear optical studies on this one-dimensional silver-nanocomposite-dielectric structure using z-scan measurements are conducted. These measurements indicate a three-fold enhancement in the nonlinear absorption coefficient when compared to a single film of comparable metal composite thickness.

Nonlinear optical switching and optical limiting in colloidal CdSe quantum dots investigated by nanosecond Z-scan measurement

NASA Astrophysics Data System (ADS)

Valligatla, Sreeramulu; Haldar, Krishna Kanta; Patra, Amitava; Desai, Narayana Rao

2016-10-01

The semiconductor nanocrystals are found to be promising class of third order nonlinear optical materials because of quantum confinement effects. Here, we highlight the nonlinear optical switching and optical limiting of cadmium selenide (CdSe) quantum dots (QDs) using nanosecond Z-scan measurement. The intensity dependent nonlinear absorption and nonlinear refraction of CdSe QDs were investigated by applying the Z-scan technique with 532 nm, nanosecond laser pulses. At lower intensities, the nonlinear process is dominated by saturable absorption (SA) and it is changed to reverse saturable absorption (RSA) at higher intensities. The SA behaviour is attributed to the ground state bleaching and the RSA is ascribed to free carrier absorption (FCA) of CdSe QDs. The nonlinear optical switching behaviour and reverse saturable absorption makes CdSe QDs are good candidate for all-optical device and optical limiting applications.

Optical gain for the interband optical transition in InAsP/InP quantum well wire in the influence of laser field intensity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saravanan, S.; Peter, A. John, E-mail: a.john.peter@gmail.com

Intense high frequency laser field induced electronic and optical properties of heavy hole exciton in the InAs{sub 0.8}P{sub 0.2}/InP quantum wire is studied taking into account the geometrical confinement effect. Laser field related exciton binding energies and the optical band gap in the InAs{sub 0.8}P{sub 0.2}/InP quantum well wire are investigated. The optical gain, for the interband optical transition, as a function of photon energy, in the InAs{sub 0.8}P{sub 0.2}/InP quantum wire, is obtained in the presence of intense laser field. The compact density matrix method is employed to obtain the optical gain. The obtained optical gain in group III-Vmore » narrow quantum wire can be applied for achieving the preferred telecommunication wavelength.« less

Preparation of nanocrystals and nanocomposites of nanocrystal-conjugated polymer, and their photophysical properties in confined geometries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Jun

2007-01-01

Semiconductors nanocrystals (NCs), also called quantum dots (QDs), have attracted tremendous interest over the past decade in the fields of physics, chemistry, and engineering. Due to the quantum-confined nature of QDs, the variation of particle size provides continuous and predictable changes in fluorescence emission. On the other hand, conjugated polymers (CPs) have been extensively studied for two decades due to their semiconductor-like optical and electronic properties. The electron and energy transfer between NCs and CPs occur in solar cells and light emitting diodes (LEDs), respectively. Placing CPs in direct contact with a NC (i.e., preparing NC-CP nanocomposites) carries advantage overmore » cases where NC aggregation dominates. Such NC-CP nanocomposites possess a well-defined interface that significantly promotes the charge or energy transfer between these two components. However, very few studies have centered on such direct integration. We prepared NCs and NC-CP nanocomposites based on heck coupling and investigated the energy and charge transfer between semiconductor NCs (i.e., CdSe QDs), CPs (i.e., poly(3-hexyl thiophene) (P3HT)) in the nanocomposites in confined geometries. Two novel strategies were used to confine NC and/or NC-CP nanocomposites: (a) directly immobilizing nanohybrids, QDs and nanorods in nanoscopic porous alumina membrane (PAM) , and (b) confining the QDs and CPs in sphere-on-flat geometry to induce self-assembly. While investigating the confinement effect, gradient concentric ring patterns of high regularity form spontaneously simply by allowing a droplet of solution containing either conjugated polymer or semiconductor nanocrystal in a consecutive stick-slip mothion in a confined geometry. Such constrained evaporation can be utilized as a simple, cheap, and robust strategy for self-assembling various materials with easily tailored optical and electronic properties into spatially ordered, two-dimensional patterns. These self-organized patterns of functional nanoscale materials over large areas offer a tremendous potential for applications in optoelectronic devices, LEDs, solar cells, and biosensors. Meanwhile, spherical nanocrystals (i.e. CdSe/ZnS core/shell QDs) were placed in a hexagonal array of highly ordered cylindrical nanopores of PAMs by a simple dip-coating method and vacuum suction process, respectively. The fluorescence of CdSe/ZnS QD was retained after being filled inside PAMs and the filling contents were obtained via transmission UV-vis measurements.« less

High refractive index substrates for fluorescence microscopy of biological interfaces with high z contrast

PubMed Central

Ajo-Franklin, Caroline M.; Kam, Lance; Boxer, Steven G.

2001-01-01

Total internal reflection fluorescence microscopy is widely used to confine the excitation of a complex fluorescent sample very close to the material on which it is supported. By working with high refractive index solid supports, it is possible to confine even further the evanescent field, and by varying the angle of incidence, to obtain quantitative information on the distance of the fluorescent object from the surface. We report the fabrication of hybrid surfaces consisting of nm layers of SiO2 on lithium niobate (LiNbO3, n = 2.3). Supported lipid bilayer membranes can be assembled and patterned on these hybrid surfaces as on conventional glass. By varying the angle of incidence of the excitation light, we are able to obtain fluorescent contrast between 40-nm fluorescent beads tethered to a supported bilayer and fluorescently labeled protein printed on the surface, which differ in vertical position by only tens of nm. Preliminary experiments that test theoretical models for the fluorescence-collection factor near a high refractive index surface are presented, and this factor is incorporated into a semiquantitative model used to predict the contrast of the 40-nm bead/protein system. These results demonstrate that it should be possible to profile the vertical location of fluorophores on the nm distance scale in real time, opening the possibility of many experiments at the interface between supported membranes and living cells. Improvements in materials and optical techniques are outlined. PMID:11717428

Plasmonic Antennas for Optical Nanocrystallography and Femtosecond Spatio-Temporal Control

NASA Astrophysics Data System (ADS)

Berweger, Samuel

Controlling optical fields on nanometer length scales has been a long standing problem in optics, driven by the desire to image spatial inhomogeneities of condensed matter on the natural length scales of molecular, electronic, or lattice correlations. The concept of optical antennas based on plasmon resonant nanostructures has emerged as an attractive solution for concentrating and confining light to the nanoscale with a high degree of spatial confinement achieved in the evanescent field. This dissertation focuses on the fundamental characteristics of the antenna properties of plasmonic metal tips and their application for nanometer-resolved optical scanning probe spectroscopy and imaging. First this work demonstrates the extension of tip-enhanced Raman scattering (TERS) to optical nanocrystallography in order to study ferroelectric domain order by using the symmetry selective Raman selection rules for polar phonon modes in combination with the polarization-dependent TERS enhancement. After the derivation of the polar phonon TERS selection rules, ferroelectric domains arising from finite size effects within individual BaTiO3 nanorods are imaged. The second part of this work explores the fundamental characteristics and applications of adiabatic surface plasmon polariton (SPP) nanofocusing as an optical antenna for far- to near-field mode transformation. This process, resulting from the radius-dependent index of refraction experienced by SPP's propagating on tapered waveguides, is shown to result in a nanoconfined optical excitation at the apex of Au tips 10's of nm in size. To demonstrate the general application for background-free spectroscopy, adiabatic nanofocusing TERS is shown to improve contrast and sensitivity, and enables the extension to the near-IR spectral range. Lastly, due to the phase, wavelength, and amplitude independent nanofocusing mechanism, the independent and simultaneous nanometer-femtosecond spatio-temporal control of ultrafast pulses is possible. Combining the frequency domain shaping of optical transients with nanofocusing, we demonstrate the deterministic control of pulses as short as 16 fs and the generation of arbitrary waveforms at the tip apex. These results demonstrate the capability of these plasmonic optical antennas to not only generate enhanced optical fields for the study of matter on the nanoscale, but also to control ultrafast nano-optical excitations with applications for imaging and spectroscopy.

Dark optical lattice of ring traps for cold atoms

NASA Astrophysics Data System (ADS)

Courtade, Emmanuel; Houde, Olivier; Clément, Jean-François; Verkerk, Philippe; Hennequin, Daniel

2006-09-01

We propose an optical lattice for cold atoms made of a one-dimensional stack of dark ring traps. It is obtained through the interference pattern of a standard Gaussian beam with a counterpropagating hollow beam obtained using a setup with two conical lenses. The traps of the resulting lattice are characterized by a high confinement and a filling rate much larger than unity, even if loaded with cold atoms from a magneto-optical trap. We have implemented this system experimentally, and demonstrated its feasibility. Applications in statistical physics, quantum computing, and Bose-Einstein condensate dynamics are conceivable.

Robust calibration of an optical-lattice depth based on a phase shift

NASA Astrophysics Data System (ADS)

Cabrera-Gutiérrez, C.; Michon, E.; Brunaud, V.; Kawalec, T.; Fortun, A.; Arnal, M.; Billy, J.; Guéry-Odelin, D.

2018-04-01

We report on a method to calibrate the depth of an optical lattice. It consists of triggering the intrasite dipole mode of the cloud by a sudden phase shift. The corresponding oscillatory motion is directly related to the interband frequencies on a large range of lattice depths. Remarkably, for a moderate displacement, a single frequency dominates the oscillation of the zeroth and first orders of the interference pattern observed after a sufficiently long time of flight. The method is robust against atom-atom interactions and the exact value of the extra weak external confinement superimposed to the optical lattice.

High-resolution laser spectroscopy of hot Cs and Rb vapor confined in a thin optical cell

NASA Astrophysics Data System (ADS)

Todorov, P.; Krasteva, A.; Vartanyan, T.; Todorov, G.; Sarkisyan, D.; Cartaleva, S.

2018-03-01

We propose a novel use of an optical cell of micrometer thickness filled with Cs vapor in view of studying the collisions between two different alkali atoms of strongly different densities. We demonstrate narrow and good-contrast sub-Doppler resonances at the Rb D2 line for a mean-free-path of the Cs atoms comparable to the optical cell longitudinal dimension; the resonances are completely destroyed when the mean-free-path of the Cs atoms is more than two orders of magnitude shorter than the longitudinal dimension of the thin cell.

Measurement of the complex transmittance of large optical elements with Ptychographical Iterative Engine.

PubMed

Wang, Hai-Yan; Liu, Cheng; Veetil, Suhas P; Pan, Xing-Chen; Zhu, Jian-Qiang

2014-01-27

Wavefront control is a significant parameter in inertial confinement fusion (ICF). The complex transmittance of large optical elements which are often used in ICF is obtained by computing the phase difference of the illuminating and transmitting fields using Ptychographical Iterative Engine (PIE). This can accurately and effectively measure the transmittance of large optical elements with irregular surface profiles, which are otherwise not measurable using commonly used interferometric techniques due to a lack of standard reference plate. Experiments are done with a Continue Phase Plate (CPP) to illustrate the feasibility of this method.

Quantum memory with optically trapped atoms.

PubMed

Chuu, Chih-Sung; Strassel, Thorsten; Zhao, Bo; Koch, Markus; Chen, Yu-Ao; Chen, Shuai; Yuan, Zhen-Sheng; Schmiedmayer, Jörg; Pan, Jian-Wei

2008-09-19

We report the experimental demonstration of quantum memory for collective atomic states in a far-detuned optical dipole trap. Generation of the collective atomic state is heralded by the detection of a Raman scattered photon and accompanied by storage in the ensemble of atoms. The optical dipole trap provides confinement for the atoms during the quantum storage while retaining the atomic coherence. We probe the quantum storage by cross correlation of the photon pair arising from the Raman scattering and the retrieval of the atomic state stored in the memory. Nonclassical correlations are observed for storage times up to 60 mus.

Large-pitch kagome-structured hollow-core photonic crystal fiber

NASA Astrophysics Data System (ADS)

Couny, F.; Benabid, F.; Light, P. S.

2006-12-01

We report the fabrication and characterization of a new type of hollow-core photonic crystal fiber based on large-pitch (˜12μm) kagome lattice cladding. The optical characteristics of the 19-cell, 7-cell, and single-cell core defect fibers include broad optical transmission bands covering the visible and near-IR parts of the spectrum with relatively low loss and low chromatic dispersion, no detectable surface modes and high confinement of light in the core. Various applications of such a novel fiber are also discussed, including gas sensing, quantum optics, and high harmonic generation.

How the stiffness of the optical trap depends on the proximity of the dielectric interface

NASA Astrophysics Data System (ADS)

Jákl, Petr; Šerý, Mojmír; Liška, Miroslav; Zemánek, Pavel

2005-09-01

When a probe confined in a single focused laser beam approaches the surface, it is getting more influenced by the retroreflected beam. This beam interferes with the incident one and a weak standing wave (SW) is created, which slightly modulates the incident beam. We studied experimentally how this phenomena influences the optical trap properties if SW is created using surfaces of two different reflectivities. We used polystyrene probes of diameters 690 nm and 820 nm, tracked their positions with quadrant photodiode (QPD) and analysed their thermal motion to get the axial trap stiffness along optical axis.

Electric-dipole absorption resonating with longitudinal optical phonon-plasmon system and its effect on dispersion relations of interface phonon polariton modes in metal/semiconductor-stripe structures

NASA Astrophysics Data System (ADS)

Sakamoto, Hironori; Takeuchi, Eito; Yoshida, Kouki; Morita, Ken; Ma, Bei; Ishitani, Yoshihiro

2018-01-01

Interface phonon polaritons (IPhPs) in nano-structures excluding metal components are thoroughly investigated because they have lower loss in optical emission or absorption and higher quality factors than surface plasmon polaritons. In previous reports, it is found that strong infrared (IR) absorption is based on the interaction of p-polarized light and materials, and the resonance photon energy highly depends on the structure size and angle of incidence. We report the optical absorption by metal/semiconductor (bulk-GaAs and thin film-AlN)-stripe structures in THz to mid-IR region for the electric field of light perpendicular to the stripes, where both of s- and p-polarized light are absorbed. The absorption resonates with longitudinal optical (LO) phonon or LO phonon-plasmon coupling (LOPC) modes, and thus is independent of the angle of incidence or structure size. This absorption is attributed to the electric dipoles by the optically induced polarization charges at the metal/semiconductor, heterointerfaces, or interfaces of high electron density layers and depression ones. The electric permittivity is modified by the formation of these dipoles. It is found to be indispensable to utilize our form of altered permittivity to explain the experimental dispersion relations of metal/semiconductor-IPhP and SPhP in these samples. This analysis reveals that the IPhPs in the stripe structures of metal/AlN-film on a SiC substrate are highly confined in the AlN film, while the permittivity of the structures of metal/bulk-GaAs is partially affected by the electric-dipoles. The quality factors of the electric-dipole absorption are found to be 42-54 for undoped samples, and the value of 62 is obtained for Al/AlN-IPhP. It is thought that metal-contained structures are not obstacles to mode energy selectivity in phonon energy region of semiconductors.

Optical nonlinearity of CdSe-PMMA hybrid nanocomposite investigated via Z-scan technique and semi-empirical relations

NASA Astrophysics Data System (ADS)

Kaur, Ramneek; Tripathi, S. K.

2016-04-01

CdSe-PMMA nanocomposite has been synthesized by ex-situ technique. The effect of different Ag doping concentrations on its structural and optical properties has been studied. X-ray diffraction reveals the hexagonal wurtzite structure of the polymer nanocomposites with preferential growth of the nanocrystals along (1 0 0) direction. Transmission electron micrograph shows the spherical CdSe nanoparticles embedded in polymer matrix. The nonlinear refractive index of the nanocomposites has been calculated using Tichy & Ticha semi-empirical relations and Z-scan technique. Z-scan results disclose the two photon absorption process in the hybrid nanocomposites with self focussing behaviour. With Ag doping, the nonlinearity is found to be increased up to 0.2% Ag doping concentration due to the confined effect of Surface Plasmon, Quantum confinement and thermal lensing. Above 0.2% Ag concentration, its value decreases due to the declined linear refractive index of the nanocomposites. Maximum two photon figure of merit is 76 for 0.2% Ag doped CdSe-PMMA hybrid nanocomposite. The present results accentuate the possibility of tuning the optical non-linearity of CdSe-PMMA hybrid nanocomposite by adjusting the doping concentration.

Design of a hybrid As₂S₃-Ti:LiNbO₃ optical waveguide for phase-matched difference frequency generation at mid-infrared.

PubMed

Wang, Xin; Madsen, Christi K

2014-11-03

Based on arsenic tri-sulfide films on titanium-diffused lithium niobate, we designed a hybrid optical waveguide for efficient mid-infrared emission by phase-matched difference frequency generation (DFG). The hybrid waveguide structure possesses a low-index magnesium fluoride buffer layer sandwiched between two high-index As(2)S(3) slabs, so that pump and signal waves are tightly confined by titanium-diffused waveguide while the DFG output idler wave at mid-infrared is confined by the whole hybrid waveguide structure. On a 1 mm-long hybrid waveguide pumped at 50 mW powers, a normalized power conversion efficiency of 20.52%W(-1)cm(-2) was theoretically predicted, which is the highest record for mid-infrared DFG waveguides based on lithium niobate crystal, to the best of our knowledge. Using a tunable near-infrared pump laser at 1.38-1.47 µm or a tunable signal laser at 1.95-2.15 µm, a broad mid-infrared tuning range from 4.0 µm to 4.9 µm can be achieved. Such hybrid optical waveguides are feasible for mid-infrared emission with mW powers and sub-nanometer linewidths.

Cavity-enhanced optical bottle beam as a mechanical amplifier

NASA Astrophysics Data System (ADS)

Freegarde, Tim; Dholakia, Kishan

2002-07-01

We analyze the resonant cavity enhancement of a hollow ``optical bottle beam'' for the dipole-force trapping of dark-field-seeking species. We first improve upon the basic bottle beam by adding further Laguerre-Gaussian components to deepen the confining potential. Each of these components itself corresponds to a superposition of transverse cavity modes, which are then enhanced simultaneously in a confocal cavity to produce a deep optical trap needing only a modest incident power. The response of the trapping field to displacement of the cavity mirrors offers an unusual form of mechanical amplifier in which the Gouy phase shift produces an optical Vernier scale between the Laguerre-Gaussian beam components.

Electro-optical resonance modulation of vertical-cavity surface-emitting lasers.

PubMed

Germann, Tim David; Hofmann, Werner; Nadtochiy, Alexey M; Schulze, Jan-Hindrik; Mutig, Alex; Strittmatter, André; Bimberg, Dieter

2012-02-27

Optical and electrical investigations of vertical-cavity surface-emitting lasers (VCSEL) with a monolithically integrated electro-optical modulator (EOM) allow for a detailed physical understanding of this complex compound cavity laser system. The EOM VCSEL light output is investigated to identify optimal working points. An electro-optic resonance feature triggered by the quantum confined Stark effect is used to modulate individual VCSEL modes by more than 20 dB with an extremely small EOM voltage change of less than 100 mV. Spectral mode analysis reveals modulation of higher order modes and very low wavelength chirp of < 0.5 nm. Dynamic experiments and simulation predict an intrinsic bandwidth of the EOM VCSEL exceeding 50 GHz.

Optical ridge waveguides preserving the thermo-optic features in LiNbO3 crystals fabricated by combination of proton implantation and selective wet etching.

PubMed

Tan, Yang; Chen, Feng

2010-05-24

We report on a new, simple method to fabricate optical ridge waveguides in a z-cut LiNbO3 wafer by using proton implantation and selective wet etching. The measured modal field is well confined in the ridge waveguide region, which is also confirmed by the numerical simulation. With thermal annealing treatment at 400 degrees C, the propagation loss of the ridge waveguides is determined to be as low as approximately 0.9 dB/cm. In addition, the measured thermo-optic coefficients of the waveguides are in good agreement with those of the bulk, suggesting potential applications in integrated photonics.

Design of novel SOI 1 × 4 optical power splitter using seven horizontally slotted waveguides

NASA Astrophysics Data System (ADS)

Katz, Oded; Malka, Dror

2017-07-01

In this paper, we demonstrate a compact silicon on insulator (SOI) 1 × 4 optical power splitter using seven horizontal slotted waveguides. Aluminum nitride (AIN) surrounded by silicon (Si) was used to confine the optical field in the slot region. All of the power analysis has been done in transverse magnetic (TM) polarization mode and a compact optical power splitter as short as 14.5 μm was demonstrated. The splitter was designed by using full vectorial beam propagation method (FV-BPM) simulations. Numerical investigations show that this device can work across the whole C-band (1530-1565 nm) with excess loss better than 0.23 dB.

Twinkle, Twinkle, Little Laser by Ben Bova

NASA Astrophysics Data System (ADS)

Bova, Ben

2000-03-01

Radio astronomers have had no success in the search for extraterrestrial intelligence (SETI). Astronomers are now studying the heavens for signals that intelligent beings might send using lasers. Laser lights have the advantage of directionality, monochromaticity, and coherence. This research, called "optical SETI," looks for optical or infrared pulses with detectors that can pick up a broad spectrum of frequencies. By confining the search to stars similar to the Sun, scientists hope to find evidence of life other than ours.

The thickness design of unintentionally doped GaN interlayer matched with background doping level for InGaN-based laser diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.; Zhao, D. G., E-mail: dgzhao@red.semi.ac.cn; Jiang, D. S.

2016-03-15

In order to reduce the internal optical loss of InGaN laser diodes, an unintentionally doped GaN (u-GaN) interlayer is inserted between InGaN/GaN multiple quantum well active region and Al{sub 0.2}Ga{sub 0.8}N electron blocking layer. The thickness design of u-GaN interlayer matching up with background doping level for improving laser performance is studied. It is found that a suitably chosen u-GaN interlayer can well modulate the optical absorption loss and optical confinement factor. However, if the value of background doping concentration of u-GaN interlayer is too large, the output light power may decrease. The analysis of energy band diagram of amore » LD structure with 100 nm u-GaN interlayer shows that the width of n-side depletion region decreases when the background concentration increases, and may become even too small to cover whole MQW, resulting in a serious decrease of the output light power. It means that a suitable interlayer thickness design matching with the background doping level of u-GaN interlayer is significant for InGaN-based laser diodes.« less

Size-dependent optical properties of colloidal PbS quantum dots.

PubMed

Moreels, Iwan; Lambert, Karel; Smeets, Dries; De Muynck, David; Nollet, Tom; Martins, José C; Vanhaecke, Frank; Vantomme, André; Delerue, Christophe; Allan, Guy; Hens, Zeger

2009-10-27

We quantitatively investigate the size-dependent optical properties of colloidal PbS nanocrystals or quantum dots (Qdots), by combining the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient epsilon increases with the Qdot volume d(3) and agrees with theoretical calculations using the Maxwell-Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on epsilon in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, epsilon only increases with d(1.3), and values are comparable to the epsilon of PbSe Qdots. The data are related to the oscillator strength f(if) of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of f(if) on d. For both PbS and PbSe Qdots, the exciton lifetime tau is calculated from f(if). We find values ranging between 1 and 3 mus, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems.

TYPE 3 NEOVASCULARIZATION IMAGED WITH CROSS-SECTIONAL AND EN FACE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY.

PubMed

Tan, Anna C S; Dansingani, Kunal K; Yannuzzi, Lawrence A; Sarraf, David; Freund, K Bailey

2017-02-01

To study the cross-sectional and en face optical coherence tomography angiography (OCTA) findings in Type 3 neovascularization (NV). Optical coherence tomography angiography imaging of 27 eyes of 23 patients with Type 3 NV was analyzed with 9 eyes having consecutive follow-up OCTA studies. Type 3 NV appeared as a linear high-flow structure on cross-sectional OCTA corresponding to a high-flow tuft of vessels seen on en face OCTA. Cross-sectional OCTA seemed to enable the distinction between vascular and nonvascular intraretinal hyperreflective foci. Two patterns of flow were observed; Pattern 1 (11%): a flow signal confined to the neurosensory retina and Pattern 2 (74%): a flow signal extending through the retinal pigment epithelium. No definitive retinal-choroidal anastomosis was observed; however, projection artifacts confounded the interpretation of deeper structures. An increase in the intensity of the high-flow tuft was seen during the progression or recurrence of Type 3 NV. Intravitreal anti-vascular endothelial growth factor therapy caused a reduction in the intensity of the high-flow tuft which was not sustained. Compared with conventional imaging, OCTA may improve detection and delineation of vascular changes occurring in Type 3 NV. Cross-sectional and en face OCTA may prove useful in studying the pathogenesis and guiding the management of these lesions.

Confinement factor, near and far field patterns in InGaN MQW laser diodes

NASA Astrophysics Data System (ADS)

Martín, J.; Sánchez, M.

2005-07-01

In this work the influence of the QW number in the active region on spectral characteristics in InGaN multi quamtun well lasers is analyzed. A comparison between the abrupt index step structure (Step) and a graded-index structure (GRIN) is done. The effect of the introduction of a p-AlxGa1-xN electron blocking layer, placed above the last InGaN barrier in the Step structure is also analyzed. Calculations of the confinement factor, near and far field patterns were carried out. We found that with the adequate aluminum content in this layer, the confinement factor, near and far field patterns are improved, and values similar to those obtained with GRIN structure can be reached.

Quantum confinement-induced tunable exciton states in graphene oxide.

PubMed

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-01-01

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology.

Spin interactions in InAs quantum dots

NASA Astrophysics Data System (ADS)

Doty, M. F.; Ware, M. E.; Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

2006-03-01

Fine structure splittings in optical spectra of self-assembled InAs quantum dots (QDs) generally arise from spin interactions between particles confined in the dots. We present experimental studies of the fine structure that arises from multiple charges confined in a single dot [1] or in molecular orbitals of coupled pairs of dots. To probe the underlying spin interactions we inject particles with a known spin orientation (by using polarized light to perform photoluminescence excitation spectroscopy experiments) or use a magnetic field to orient and/or mix the spin states. We develop a model of the spin interactions that aids in the development of quantum information processing applications based on controllable interactions between spins confined to QDs. [1] Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot, Phys. Rev. Lett. 95, 177403 (2005)

Rolled-up Functionalized Nanomembranes as Three-Dimensional Cavities for Single Cell Studies

PubMed Central

2014-01-01

We use micropatterning and strain engineering to encapsulate single living mammalian cells into transparent tubular architectures consisting of three-dimensional (3D) rolled-up nanomembranes. By using optical microscopy, we demonstrate that these structures are suitable for the scrutiny of cellular dynamics within confined 3D-microenvironments. We show that spatial confinement of mitotic mammalian cells inside tubular architectures can perturb metaphase plate formation, delay mitotic progression, and cause chromosomal instability in both a transformed and nontransformed human cell line. These findings could provide important clues into how spatial constraints dictate cellular behavior and function. PMID:24598026

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koyanagi, T.; Lance, M. J.; Katoh, Y.

Raman spectra from polycrystalline beta-silicon carbide (SiC) were collected following neutron irradiation at 380–1180 °C to 0.011–1.87 displacement per atom. The longitudinal optical (LO) peak shifted to a lower frequency and broadened as a result of the irradiation. The changes observed in the LO phonon line shape and position in neutron-irradiated SiC are explained by a combination of changes in the lattice constant and Young's modulus, and the phonon confinement effect. The phonon confinement model reasonably estimates the defect-defect distance in the irradiated SiC, which is consistent with results from previous experimental studies and simulations.

Whispering gallery effect in relativistic optics

NASA Astrophysics Data System (ADS)

Abe, Y.; Law, K. F. F.; Korneev, Ph.; Fujioka, S.; Kojima, S.; Lee, S.-H.; Sakata, S.; Matsuo, K.; Oshima, A.; Morace, A.; Arikawa, Y.; Yogo, A.; Nakai, M.; Norimatsu, T.; d'Humières, E.; Santos, J. J.; Kondo, K.; Sunahara, A.; Gus'kov, S.; Tikhonchuk, V.

2018-03-01

relativistic laser pulse, confined in a cylindrical-like target, under specific conditions may perform multiple scattering along the internal target surface. This results in the confinement of the laser light, leading to a very efficient interaction. The demonstrated propagation of the laser pulse along the curved surface is just yet another example of the "whispering gallery" effect, although nonideal due to laser-plasma coupling. In the relativistic domain its important feature is a gradual intensity decrease, leading to changes in the interaction conditions. The proccess may pronounce itself in plenty of physical phenomena, including very efficient electron acceleration and generation of relativistic magnetized plasma structures.

1300 nm wavelength InAs quantum dot photodetector grown on silicon.

PubMed

Sandall, Ian; Ng, Jo Shien; David, John P R; Tan, Chee Hing; Wang, Ting; Liu, Huiyun

2012-05-07

The optical and electrical properties of InAs quantum dots epitaxially grown on a silicon substrate have been investigated to evaluate their potential as both photodiodes and avalanche photodiodes (APDs) operating at a wavelength of 1300 nm. A peak responsivity of 5 mA/W was observed at 1280 nm, with an absorption tail extending beyond 1300 nm, while the dark currents were two orders of magnitude lower than those reported for Ge on Si photodiodes. The diodes exhibited avalanche breakdown at 22 V reverse bias which is probably dominated by impact ionisation occurring in the GaAs and AlGaAs barrier layers. A red shift in the absorption peak of 61.2 meV was measured when the reverse bias was increased from 0 to 22 V, which we attributed to the quantum confined stark effect. This shift also leads to an increase in the responsivity at a fixed wavelength as the bias is increased, yielding a maximum increase in responsivity by a factor of 140 at the wavelength of 1365 nm, illustrating the potential for such a structure to be used as an optical modulator.

Predicting scattering scanning near-field optical microscopy of mass-produced plasmonic devices

NASA Astrophysics Data System (ADS)

Otto, Lauren M.; Burgos, Stanley P.; Staffaroni, Matteo; Ren, Shen; Süzer, Özgün; Stipe, Barry C.; Ashby, Paul D.; Hammack, Aeron T.

2018-05-01

Scattering scanning near-field optical microscopy enables optical imaging and characterization of plasmonic devices with nanometer-scale resolution well below the diffraction limit. This technique enables developers to probe and understand the waveguide-coupled plasmonic antenna in as-fabricated heat-assisted magnetic recording heads. In order to validate and predict results and to extract information from experimental measurements that is physically comparable to simulations, a model was developed to translate the simulated electric field into expected near-field measurements using physical parameters specific to scattering scanning near-field optical microscopy physics. The methods used in this paper prove that scattering scanning near-field optical microscopy can be used to determine critical sub-diffraction-limited dimensions of optical field confinement, which is a crucial metrology requirement for the future of nano-optics, semiconductor photonic devices, and biological sensing where the near-field character of light is fundamental to device operation.

Silicon Photonics: All-Optical Devices for Linear and Nonlinear Applications

NASA Astrophysics Data System (ADS)

Driscoll, Jeffrey B.

Silicon photonics has grown rapidly since the first Si electro-optic switch was demonstrated in 1987, and the field has never grown more quickly than it has over the past decade, fueled by milestone achievements in semiconductor processing technologies for low loss waveguides, high-speed Si modulators, Si lasers, Si detectors, and an enormous toolbox of passive and active integrated devices. Silicon photonics is now on the verge of major commercialization breakthroughs, and optical communication links remain the force driving integrated and Si photonics towards the first commercial telecom and datacom transceivers; however other potential and future applications are becoming uncovered and refined as researchers reveal the benefits of manipulating photons on the nanoscale. This thesis documents an exploration into the unique guided-wave and nonlinear properties of deeply-scaled high-index-contrast sub-wavelength Si waveguides. It is found that the tight confinement inherent to single-mode channel waveguides on the silicon-on-insulator platform lead to a rich physics, which can be leveraged for new devices extending well beyond simple passive interconnects and electro-optic devices. The following chapters will concentrate, in detail, on a number of unique physical features of Si waveguides and extend these attributes towards new and interesting devices. Linear optical properties and nonlinear optical properties are investigated, both of which are strongly affected by tight optical confinement of the guided waveguide modes. As will be shown, tight optical confinement directly results in strongly vectoral modal components, where the electric and magnetic fields of the guided modes extend into all spatial dimensions, even along the axis of propagation. In fact, the longitudinal electric and magnetic field components can be just as strong as the transverse fields, directly affecting the modal group velocity and energy transport properties since the longitudinal fields are shown to contribute no time-averaged momentum. Furthermore, the vectoral modal components, in conjunction with the tensoral nature of the third-order susceptibility of Si, lead to nonlinear properties which are dependent on waveguide orientation with respect to the Si parent crystal and the construction of the modal electric field components. This consideration is used to maximize effective nonlinearity and realize nonlinear Kerr gratings along specific waveguide trajectories. Tight optical confinement leads to a natural enhancement of the intrinsically large effective nonlinearty of Si waveguides, and in fact, the effective nonlinearty can be made to be almost 106 times greater in Si waveguides than that of standard single-mode fiber. Such a large nonlinearity motivates chip-scale all-optical signal processing techniques. Wavelength conversion by both four-wave-mixing (FWM) and cross-phase-modulation (XPM) will be discussed, including a technique that allows for enhanced broadband discrete FWM over arbitrary spectral spans by modulating both the linear and nonlinear waveguide properties through periodic changes in waveguide geometry. This quasi-phase-matching approach has very real applications towards connecting mature telecom sources detectors and components to other spectral regimes, including the mid-IR. Other signal processing techniques such as all-optical modulation format conversion via XPM will also be discussed. This thesis will conclude by looking at ways to extend the bandwidth capacity of Si waveguide interconnects on chip. As the number of processing cores continues to scale as a means for computational performance gains, on-chip link capacity will become an increasingly important issue. Metallic traces have severe limitations and are envisioned to eventually bow to integrated photonic links. The aggregate bandwidth supported by a single waveguide link will therefore become a crucial consideration as integrated photonics approaches the CPU. One way to increase aggregate bandwidth is to utilize different eigen-modes of a multimode waveguide, and integrated waveguide mode-muxes and demuxes for achieving simultaneous mode-division-multiplexing and wavelength-division-multiplexing will be demonstrated.

Biomolecule-assisted hydrothermal synthesis of silver bismuth sulfide with nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaowphong, Sulawan, E-mail: sulawank@gmail.com; Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200

2012-05-15

Silver bismuth sulfide (AgBiS{sub 2}) nanostructures were successfully prepared via a simple biomolecule-assisted hydrothermal synthesis at 200 Degree-Sign C for 12-72 h. Silver nitrate, bismuth nitrate and L-cysteine were used as starting materials. Here, the biomolecule, L-cysteine, was served as the sulfide source and a complexing agent. The products, characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were cubic AgBiS{sub 2} nanoparticles with a diameter range of about 20-75 nm. It was found that their crystallinity and particle size increased with increasing reaction time. The energy dispersive X-ray spectroscopy (EDX) and inductively coupledmore » plasma optical emission spectrophotometry (ICP-OES) analyses were used to confirm the stoichiometry of AgBiS{sub 2}. The optical band gap of the AgBiS{sub 2} nanoparticles, calculated from UV-vis spectra, was 3.0 eV which indicated a strong blue shift because of the quantum confinement effect. A possible formation mechanism of the AgBiS{sub 2} nanoparticles was also discussed. - Graphical abstract: The optical band gap of the as-prepared AgBiS{sub 2} nanoparticles displays a strong blue shift comparing to the 2.46 eV of bulk AgBiS{sub 2} caused by the quantum confinement effects. Highlights: Black-Right-Pointing-Pointer A simple biomolecule-assisted hydrothermal method is developed to prepare AgBiS{sub 2}. Black-Right-Pointing-Pointer L-Cysteine is served as the sulfide source and a complexing agent. Black-Right-Pointing-Pointer Increase in band gap of the AgBiS{sub 2} nanoparticles attributes to the quantum confinement effects.« less

Suppressed power saturation due to optimized optical confinement in 9xx nm high-power diode lasers that use extreme double asymmetric vertical designs

NASA Astrophysics Data System (ADS)

Kaul, T.; Erbert, G.; Maaßdorf, A.; Knigge, S.; Crump, P.

2018-03-01

Broad area lasers with novel extreme double asymmetric structure (EDAS) vertical designs featuring increased optical confinement in the quantum well, Γ, are shown to have improved temperature stability without compromising series resistance, internal efficiency or losses. Specifically, we present here vertical design considerations for the improved continuous wave (CW) performance of devices operating at 940 nm, based on systematically increasing Γ from 0.26% to 1.1%, and discuss the impact on power saturation mechanisms. The results indicate that key power saturation mechanisms at high temperatures originate in high threshold carrier densities, which arise in the quantum well at low Γ. The characteristic temperatures, T 0 and T 1, are determined under short pulse conditions and are used to clarify the thermal contribution to power limiting mechanisms. Although increased Γ reduces thermal power saturation, it is accompanied by increased optical absorption losses in the active region, which has a significant impact on the differential external quantum efficiency, {η }{{diff}}. To quantify the impact of internal optical losses contributed by the quantum well, a resonator length-dependent simulation of {η }{{diff}} is performed and compared to the experiment, which also allows the estimation of experimental values for the light absorption cross sections of electrons and holes inside the quantum well. Overall, the analysis enables vertical designs to be developed, for devices with maximized power conversion efficiency at high CW optical power and high temperatures, in a trade-off between absorption in the well and power saturation. The best balance to date is achieved in devices using EDAS designs with {{Γ }}=0.54 % , which deliver efficiencies of 50% at 14 W optical output power at an elevated junction temperature of 105 °C.

Hybrid plasmonic electro-optical absorption modulator based on epsilon-near-zero characteristics of ITO

NASA Astrophysics Data System (ADS)

Abdelatty, M. Y.; Badr, M. M.; Swillam, M. A.

2018-03-01

Using transparent conducting oxides (TCOs), like indium-tin-oxide (ITO), for optical modulation attracted research interest because of their epsilon-near-zero (ENZ) characteristics at telecom wavelengths. Utilizing indium-tin-oxide (ITO) in multilayer structure modulators, optical absorption of the active ITO layer can be electrically modulated over a large spectrum range. Although they show advances over common silicon electro-optical modulators (EOMs), they suffer from high insertion losses. To reduce insertion losses and device footprints without sacrificing bandwidth and modulation strength, slot waveguides are promising options because of their high optical confinement. In this paper, we present the study and the design of an electro-optical absorption modulator based on electrically tuning ITO carrier density inside a MOS structure. The device structure is based on dielectric slot waveguide with an ITO plasmonic waveguide modulation section. By changing the dimensions, the effective refractive indices for the slot mode and the off-sate mode of the plasmonic section can be matched. When applying electric field to the plasmonic section (on-state), carriers are generated at the ITO-dielectric interface that result in changing the layer where the electric field is confined from a transparent layer into a lossy layer. A finite difference time domain method with perfect matching layer (PML) absorbing boundary conditions is taken up to simulate and analyze this design. An extinction ratio of 2.3 dB is achieved for a 1-μm-short modulation section, at the telecommunications wavelength (1.55 μm). This EOM has advantages of simple design, easy fabrication, compact size, compatibility with existing silicon photonics platforms, as well as broadband performance.

Fundamental limit of nanophotonic light trapping in solar cells.

PubMed

Yu, Zongfu; Raman, Aaswath; Fan, Shanhui

2010-10-12

Establishing the fundamental limit of nanophotonic light-trapping schemes is of paramount importance and is becoming increasingly urgent for current solar cell research. The standard theory of light trapping demonstrated that absorption enhancement in a medium cannot exceed a factor of 4n(2)/sin(2)θ, where n is the refractive index of the active layer, and θ is the angle of the emission cone in the medium surrounding the cell. This theory, however, is not applicable in the nanophotonic regime. Here we develop a statistical temporal coupled-mode theory of light trapping based on a rigorous electromagnetic approach. Our theory reveals that the conventional limit can be substantially surpassed when optical modes exhibit deep-subwavelength-scale field confinement, opening new avenues for highly efficient next-generation solar cells.

A functional probe with bowtie aperture and bull's eye structure for nanolithograph

NASA Astrophysics Data System (ADS)

Wang, Shuo; Li, Xu-Feng; Wang, Qiao; Guo, Ying-Yan; Pan, Shi

2012-10-01

The bowtie aperture surrounded by concentric gratings (the bull's eye structure) integrated on the near-field scanning optical microscopy (NSOM) probe (aluminum coated fiber tip) for nanolithography has been investigated using the finite-difference time domain (FDTD) method. By modifying the parameters of the bowtie aperture and the concentric gratings, a maximal field enhancement factor of 391.69 has been achieved, which is 18 times larger than that obtained from the single bowtie aperture. Additionally, the light spot depends on the gap size of the bowtie aperture and can be confined to sub-wavelength. The superiority of the combination of the bowtie aperture and the bull's eye structure is confirmed, and the mechanism for the electric field enhancement in this derived structure is analyzed.

Intrinsic polarization control in rectangular GaN nanowire lasers

DOE PAGES

Li, Changyi; Liu, Sheng; Luk, Ting S.; ...

2016-02-01

In this study, we demonstrate intrinsic, linearly polarized lasing from single GaN nanowires using cross-sectional shape control. A two-step top-down fabrication approach was employed to create straight nanowires with controllable rectangular cross-sections. A clear lasing threshold of 444kW/cm 2 and a narrow spectral line width of 0.16 nm were observed under optical pumping at room temperature, indicating the onset of lasing. The polarization was along the short dimension (y-direction) of the nanowire due to the higher transverse confinement factors for y-polarized transverse modes resulting from the rectangular nanowire cross-section. The results show that cross-sectioned shape control can enable inherent controlmore » over the polarization of nanowire lasers without additional environment requirements, such as placement onto lossy substrates.« less

Interacting Electrons and Holes in Quasi-2D Quantum Dots in Strong Magnetic Fields

NASA Astrophysics Data System (ADS)

Hawrylak, P.; Sheng, W.; Cheng, S.-J.

2004-09-01

Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and of excitonic quantum Hall droplets at a filling factorν=2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons.

Physiological Monitoring of Optically Trapped Cells: Studying the Effects of Confinement by 1064 NM Lazer Tweezers Using Microfluorometry

NASA Astrophysics Data System (ADS)

Liu, Yagang

A novel technique that combines microfluorometric detection and optical laser trapping has been developed for in-situ assessing the physiological state of an optically trapped biological sample. This optical diagnostic technique achieves high sensitivity (>30 dB signal -to-noise ratio) and high spatial resolution (~ 1 μm) over a broad spectral range (>400 nm). The fluorescence spectra derived from exogenous fluorescent probes, including laurdan, acridine orange, propidium iodide and Snarf, are used to assess the effects of optical confinement with respect to temperature, DNA structure, cell viability, and intracellular pH, respectively. In the latter three cases, fluorescence is excited via a two-photon absorption process, using the cw laser trap itself as the fluorescence excitation source. This enables the cw near infrared laser trapping beam to be used simultaneously as an optical diagnostic probe as well as an optical micromanipulator. Using microfluorometry, a temperature increase of less than several degrees centigrade was measured for test samples, including liposomes, Chinese hamster ovary (CHO) cells and human sperm cells that were held stationary by 1064 nm optical tweezers having a power density of ~10^7 W/cm^2. Additional physiological monitoring experiments indicated that there is no observable denaturation of DNA, or change of intracellular pH under typical continuous wave laser trapping conditions (P <= 400 mW). Under some circumstances, however, it was possible to achieve a decrease in cell viability with cw trapping, as monitored by a live/dead vital stain. In comparison, significant DNA denaturation and cellular physiological changes (e.g. cell death) were observed when a Q-switched pulsed laser at a threshold of ~30mu J/pulse was used as trapping source. These results generally support the conclusion that cw laser trapping at 1064 nm wavelength is a safe, non-invasive process and should prove to be of great value for understanding the mechanisms of laser microirradiation effects on living cells held stationary in a near-infrared trapping beam.

Engineering photonic and plasmonic light emission enhancement

NASA Astrophysics Data System (ADS)

Lawrence, Nathaniel

Semiconductor photonic devices are a rapidly maturing technology which currently occupy multi-billion dollar markets in the areas of LED lighting and optical data communication. LEDs currently demonstrate the highest luminous efficiency of any light source for general lighting. Long-haul optical data communication currently forms the backbone of the global communication network. Proper design of light management is required for photonic devices, which can increase the overall efficiency or add new device functionality. In this thesis, novel methods for the control of light propagation and confinement are developed for the use in integrated photonic devices. The first part of this work focuses on the engineering of field confinement within deep subwavelength plasmonic resonators for the enhancement of light-matter interaction. In this section, plasmonic ring nanocavities are shown to form gap plasmon modes confined to the dielectric region between two metal layers. The scattering properties, near-field enhancement and photonic density of states of nanocavity devices are studied using analytic theory and 3D finite difference time domain simulations. Plasmonic ring nanocavities are fabricated and characterized using photoluminescence intensity and decay rate measurements. A 25 times increase in the radiative decay rate of Er:Si02 is demonstrated in nanocavities where light is confined to volumes as small as 0.01( ln )3. The potential to achieve lasing, due to the enhancement of stimulated emission rate in ring nanocavities, is studied as a route to Si-compatible plasmon-enhanced nanolasers. The second part of this work focuses on the manipulation of light generated in planar semiconductor devices using arrays of dielectric nanopillars. In particular, aperiodic arrays of nanopillars are engineered for omnidirectional light extraction enhancement. Arrays of Er:SiNx, nanopillars are fabricated and a ten times increase in light extraction is experimentally demonstrated, while simultaneously controlling far-field radiation patterns in ways not possible with periodic arrays. Additionally, analytical scalar diffraction theory is used to study light propagation from Vogel spiral arrays and demonstrate generation of OAM. Using phase shifting interferometry, the presence of OAM is experimentally verified. The use of Vogel spirals presents a new method for the generation of OAM with applications for secure optical communications.

Design and Development of Nanostructured Surfaces for Enhanced Optical Sensing

NASA Astrophysics Data System (ADS)

Santiago Cordoba, Miguel A.

At smaller size regimes, materials' physicochemical properties change with respect to bulk analogs. In the case of metal nanoparticles like gold or silver, specific wavelengths of light can induce a coherent oscillation of their conduction electrons, generating an optical field confined to the nanoparticle surface. This phenomenon is termed surface plasmon, and has been used as an enhancing mechanism in optical sensing, allowing the detection of foreign materials at small concentrations. The goal of this dissertation is to develop nanostructured materials relying on surface plasmons that can be combined with different optical sensing platforms in order to enhance current detection limits. Initially, we focus on the development of surfactant free, stimuli responsive nanoparticle thin films, which undergo an active release when exposed to a stimulus such as a change in pH. These nanoparticle thin films provide faster analyte particle transport and direct electronic coupling with the analyte molecule, all without attenuating the evanescent wave from the optical transducer to the particle. These stimuli responsive nanostructured substrates are tested within a surface enhanced Raman platform for the detection of biomolecular probes at sub-nanomolar concentrations and microL sample sizes. Furthermore, the developed nanosubstrates can be patterned, providing a versatile nanoparticle thin film for multiplexing analysis, offering a substantial advantage over conventional surface based nanoparticle detection methods. Our results encouraged further optimization of light-matter interactions in optical detection platforms. It is for that reason that this dissertation evolves towards confined optical systems. Particularly, whispering gallery microcavities confine electromagnetic waves - at high volumes - at the boundary of a dielectric resonator. In this dissertation, we examined the sensitivity of whispering gallery modes combining optical microcavities with plasmonic nanoparticles in analogy to a "nanoantenna". First, our hybrid methodology is tested by analyzing the resonant wavelength displacement of a whispering gallery mode cavity upon perturbation with a gold nanoparticle layer containing a model protein. Next, we developed a real-time optical sensing platform relying on whispering gallery microcavities and surface plasmons, and then tested it for the detection of a model protein at fM concentration (less than 1000 protein molecules). Finally, this plasmonic-photonic coupling process involving whispering gallery modes is studied via a self-referenced methodology relying on the mode splitting of a whispering gallery resonance. Specifically, we studied the mode splitting evolution of a resonant whispering gallery microcavity as a function of gold nanoparticle adherence with varying diameters. Mode splitting increases as the localized surface plasmon wavelength of the nanoparticle approaches the spectral line of the whispering gallery mode. Plasmonic-photonic coupling observed in this study provides a novel alternative to achieve single particle detection using mode splitting, as well as understanding optimization of particle size for plasmonic-photonic coupling. The study described herein opens a new way to optimize current optical sensing technology, enabling not only the detection of an analyte, but also the execution of fundamental studies of analyte interactions at ultralow concentrations.

NRMC - A GPU code for N-Reverse Monte Carlo modeling of fluids in confined media

NASA Astrophysics Data System (ADS)

Sánchez-Gil, Vicente; Noya, Eva G.; Lomba, Enrique

2017-08-01

NRMC is a parallel code for performing N-Reverse Monte Carlo modeling of fluids in confined media [V. Sánchez-Gil, E.G. Noya, E. Lomba, J. Chem. Phys. 140 (2014) 024504]. This method is an extension of the usual Reverse Monte Carlo method to obtain structural models of confined fluids compatible with experimental diffraction patterns, specifically designed to overcome the problem of slow diffusion that can appear under conditions of tight confinement. Most of the computational time in N-Reverse Monte Carlo modeling is spent in the evaluation of the structure factor for each trial configuration, a calculation that can be easily parallelized. Implementation of the structure factor evaluation in NVIDIA® CUDA so that the code can be run on GPUs leads to a speed up of up to two orders of magnitude.

A trapped mercury 199 ion frequency standard

NASA Technical Reports Server (NTRS)

Cutler, L. S.; Giffard, R. P.; Mcguire, M. D.

1982-01-01

Mercury 199 ions confined in an RF quadrupole trap and optically pumped by mercury 202 ion resonance light are investigated as the basis for a high performance frequency standard with commercial possibilities. Results achieved and estimates of the potential performance of such a standard are given.

Ultrafast atomic-scale visualization of acoustic phonons generated by optically excited quantum dots

PubMed Central

Vanacore, Giovanni M.; Hu, Jianbo; Liang, Wenxi; Bietti, Sergio; Sanguinetti, Stefano; Carbone, Fabrizio; Zewail, Ahmed H.

2017-01-01

Understanding the dynamics of atomic vibrations confined in quasi-zero dimensional systems is crucial from both a fundamental point-of-view and a technological perspective. Using ultrafast electron diffraction, we monitored the lattice dynamics of GaAs quantum dots—grown by Droplet Epitaxy on AlGaAs—with sub-picosecond and sub-picometer resolutions. An ultrafast laser pulse nearly resonantly excites a confined exciton, which efficiently couples to high-energy acoustic phonons through the deformation potential mechanism. The transient behavior of the measured diffraction pattern reveals the nonequilibrium phonon dynamics both within the dots and in the region surrounding them. The experimental results are interpreted within the theoretical framework of a non-Markovian decoherence, according to which the optical excitation creates a localized polaron within the dot and a travelling phonon wavepacket that leaves the dot at the speed of sound. These findings indicate that integration of a phononic emitter in opto-electronic devices based on quantum dots for controlled communication processes can be fundamentally feasible. PMID:28852685

Quantum phase transition modulation in an atomtronic Mott switch

NASA Astrophysics Data System (ADS)

McLain, Marie A.; Carr, Lincoln D.

2018-07-01

Mott insulators provide stable quantum states and long coherence times due to small number fluctuations, making them good candidates for quantum memory and atomic circuits. We propose a proof-of-principle for a 1D Mott switch using an ultracold Bose gas and optical lattice. With time-evolving block decimation simulations—efficient matrix product state methods—we design a means for transient parameter characterization via a local excitation for ease of engineering into more complex atomtronics. We perform the switch operation by tuning the intensity of the optical lattice, and thus the interaction strength through a conductance transition due to the confined modifications of the ‘wedding cake’ Mott structure. We demonstrate the time-dependence of Fock state transmission and fidelity of the excitation as a means of tuning up the device in a double well and as a measure of noise performance. Two-point correlations via the g (2) measure provide additional information regarding superfluid fragments on the Mott insulating background due to the confinement of the potential.

Experimental Studies of the Brownian Diffusion of Boomerang Colloidal Particle in a Confined Geometry

NASA Astrophysics Data System (ADS)

Chakrabarty, Ayan; Wang, Feng; Joshi, Bhuwan; Wei, Qi-Huo

2011-03-01

Recent studies shows that the boomerang shaped molecules can form various kinds of liquid crystalline phases. One debated topic related to boomerang molecules is the existence of biaxial nematic liquid crystalline phase. Developing and optical microscopic studies of colloidal systems of boomerang particles would allow us to gain better understanding of orientation ordering and dynamics at ``single molecule'' level. Here we report the fabrication and experimental studies of the Brownian motion of individual boomerang colloidal particles confined between two glass plates. We used dark-field optical microscopy to directly visualize the Brownian motion of the single colloidal particles in a quasi two dimensional geometry. An EMCCD was used to capture the motion in real time. An indigenously developed imaging processing algorithm based on MatLab program was used to precisely track the position and orientation of the particles with sub-pixel accuracy. The experimental finding of the Brownian diffusion of a single boomerang colloidal particle will be discussed.

Engineering of frustration in colloidal artificial ice (Conference Presentation)

NASA Astrophysics Data System (ADS)

Ortiz-Ambriz, Antonio; Tierno, Pietro

2016-09-01

Artificial spin-ice systems have been used to date as microscopic models of frustration induced by lattice topology, as they allow for the direct visualization of spin arrangements and textures. However, the engineering of frustrated ice states in which individual spins can be manipulated in situ and the real-time observation of their collective dynamics remain both challenging tasks. Recently, an analogue system has been proposed theoretically, where an optical landscape confined colloidal particles that interacted electrostatically. Here we realize experimentally another version of a colloidal artificial ice system using interacting magnetically polarizable particles confined to lattices of bistable gravitational traps. We show quantitatively that ice-selection rules emerge in this frustrated soft matter system by tuning the strength of the pair-interactions between the microscopic units. By using optical tweezers, we can control particle positioning and dipolar coupling, we introduce monopole-like defects and strings and use loops with defined chirality as an elementary unit to store binary information.

Effects of multiple organic ligands on size uniformity and optical properties of ZnSe quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archana, J., E-mail: archana.jayaram@yahoo.com; Navaneethan, M.; Hayakawa, Y.

2012-08-15

Highlights: ► Highly monodispersed ZnSe quantum dots have been synthesized by wet chemical route. ► Strong quantum confinement effect have been observed in ∼ 4 nm ZnSe quantum dots. ► Enhanced ultraviolet near band emission have been obtained using long chain polymer. -- Abstract: The effects of multi-ligands on the formation and optical transitions of ZnSe quantum dots have been investigated. The dots are synthesized using 3-mercapto-1,2-propanediol and polyvinylpyrrolidone ligands, and have been characterized by X-ray diffraction, transmission electron microscopy (TEM), UV–visible absorption spectroscopy, photoluminescence spectroscopy, and Fourier transform infrared spectroscopy. TEM reveals high monodispersion with an average size ofmore » 4 nm. Polymer-stabilized, organic ligand-passivated ZnSe quantum dots exhibit strong UV emission at 326 nm and strong quantum confinement in the UV–visible absorption spectrum. Uniform size and suppressed surface trap emission are observed when the polymer ligand is used. The possible growth mechanism is discussed.« less

Cooling the Motion of Diamond Nanocrystals in a Magneto-Gravitational Trap in High Vacuum.

PubMed

Hsu, Jen-Feng; Ji, Peng; Lewandowski, Charles W; D'Urso, Brian

2016-07-22

Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamond nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. We demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K.

Cooling the motion of diamond nanocrystals in a magneto-gravitational trap in high vacuum

DOE PAGES

Hsu, Jen -Feng; Ji, Peng; Lewandowski, Charles W.; ...

2016-07-22

Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamondmore » nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. Furthermore, we demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K.« less

Cooling the Motion of Diamond Nanocrystals in a Magneto-Gravitational Trap in High Vacuum

PubMed Central

Hsu, Jen-Feng; Ji, Peng; Lewandowski, Charles W.; D’Urso, Brian

2016-01-01

Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamond nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. We demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K. PMID:27444654

Optical lattice clock with atoms confined in a shallow trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemonde, Pierre; Wolf, Peter; Bureau International des Poids et Mesures, Pavillon de Breteuil, 92312 Sevres Cedex

2005-09-15

We study the trap depth requirement for the realization of an optical clock using atoms confined in a lattice. We show that site-to-site tunneling leads to a residual sensitivity to the atom dynamics hence requiring large depths [(50-100)E{sub r} for Sr] to avoid any frequency shift or line broadening of the atomic transition at the 10{sup -17}-10{sup -18} level. Such large depths and the corresponding laser power may, however, lead to difficulties (e.g., higher-order light shifts, two-photon ionization, technical difficulties) and therefore one would like to operate the clock in much shallower traps. To circumvent this problem we propose themore » use of an accelerated lattice. Acceleration lifts the degeneracy between adjacents potential wells which strongly inhibits tunneling. We show that using the Earth's gravity, much shallower traps (down to 5E{sub r} for Sr) can be used for the same accuracy goal.« less

Type-II GaSb/GaAs quantum-dot intermediate band with extended optical absorption range for efficient solar cells

NASA Astrophysics Data System (ADS)

Boustanji, Hela; Jaziri, Sihem

2018-02-01

GaSb/GaAs type-II quantum-dot solar cells (QD SCs) have attracted attention as highly efficient intermediate band SCs due to their infrared absorption. Type-II QDs exhibited a staggered confinement potential, where only holes are strongly confined within the dots. Long wavelength light absorption of the QDSCs is enhanced through the improved carriers number in the IB. The absorption of dots depends on their shape, material quality, and composition. Therefore, the optical properties of the GaSbGaAs QDs before and after thermal treatment are studied. Our intraband studies have shown an extended absorption into the long wavelength region 1.77 μ {m}. The annealed QDs have shown significantly more infrared response of 7.2 μ {m} compared to as-grown sample. The photon absorption and hole extraction depend strongly on the thermal annealing process. In this context, emission of holes from localized states in GaSb QDs has been studied using conductance-voltage ( G- V ) characteristics.

An overview of optical diagnostics developed for the Lockheed Martin compact fusion reactor

NASA Astrophysics Data System (ADS)

Sommers, Bradley; Raymond, Anthony; Gucker, Sarah; Lockheed Martin Compact Fusion Reactor Team

2017-10-01

The T4B experiment is a linear, encapsulated ring cusp confinement device, designed to develop a physics and technology basis for a follow-on high beta machine as part of the compact fusion reactor program. Toward this end, a collection of non-invasive optical diagnostics have been developed to investigate confinement, neutral beam heating, and source behavior on the T4B device. These diagnostics include: (1) a multipoint Thomson scattering system employing a 532 nm Nd:YAG laser and high throughput spectrometer to measure 1D profiles of electron density and temperature, (2) a dispersion interferometer utilizing a continuous-wave CO2 laser (10.6 μm) to measure time resolved, line-integrated electron density, and (3) a bolometer suite utilizing four AXUV photodiodes with 64 lines of sight to generate 2D reconstructions of total radiative power and soft x-ray emission (via beryllium filters). An overview of design methods, including laser systems, detection schemes, and data analysis techniques is presented as well as results to date.

Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations

DOE PAGES

Wood, R. M.; Saha, D.; McCarthy, L. A.; ...

2014-10-29

A combined experimental-theoretical study of optically pumped NMR (OPNMR) has been performed in a GaAs/Al 0.1Ga 0.9As quantum well film with thermally induced biaxial strain. The photon energy dependence of the Ga-71 OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from differential absorption to spin-up and spin-down states of the conduction band using a modified Pidgeon Brown model. Reasonable agreement between theory and experiment is obtained, facilitating assignment of features in the OPNMR energy dependence to specific interband transitions. Despitemore » the approximations made in the quantum-mechanical model and the inexact correspondence between the experimental and calculated observables, the results provide insight into how effects of strain and quantum confinement are manifested in OPNMR signals« less

Boosting infrared energy transfer in 3D nanoporous gold antennas.

PubMed

Garoli, D; Calandrini, E; Bozzola, A; Ortolani, M; Cattarin, S; Barison, S; Toma, A; De Angelis, F

2017-01-05

The applications of plasmonics to energy transfer from free-space radiation to molecules are currently limited to the visible region of the electromagnetic spectrum due to the intrinsic optical properties of bulk noble metals that support strong electromagnetic field confinement only close to their plasma frequency in the visible/ultraviolet range. In this work, we show that nanoporous gold can be exploited as a plasmonic material for the mid-infrared region to obtain strong electromagnetic field confinement, co-localized with target molecules into the nanopores and resonant with their vibrational frequency. The effective optical response of the nanoporous metal enables the penetration of optical fields deep into the nanopores, where molecules can be loaded thus achieving a more efficient light-matter coupling if compared to bulk gold. In order to realize plasmonic resonators made of nanoporous gold, we develop a nanofabrication method based on polymeric templates for metal deposition and we obtain antenna arrays resonating at mid-infrared wavelengths selected by design. We then coat the antennas with a thin (3 nm) silica layer acting as the target dielectric layer for optical energy transfer. We study the strength of the light-matter coupling at the vibrational absorption frequency of silica at 1240 cm -1 through the analysis of the experimental Fano lineshape that is benchmarked against identical structures made of bulk gold. The boost in the optical energy transfer from free-space mid-infrared radiation to molecular vibrations in nanoporous 3D nanoantenna arrays can open new application routes for plasmon-enhanced physical-chemical reactions.

Analysis of waveguide architectures of InGaN/GaN diode lasers by nearfield optical microscopy

NASA Astrophysics Data System (ADS)

Friede, Sebastian; Tomm, Jens W.; Kühn, Sergei; Hoffmann, Veit; Wenzel, Hans

2017-02-01

Waveguide (WG) architectures of 420-nm emitting InAlGaN/GaN diode lasers are analyzed by photoluminescence (PL) and photocurrent (PC) spectroscopy using a nearfield scanning optical microscope (NSOM) for excitation and detection. The measurements with a spatial resolution of 100 nm are implemented by scanning the fiber tip along the unprepared front facets of standard devices. PL is collected by the fiber tip, whereas PCs are extracted from the contacts that are anyway present for power supply. The mechanisms of signal generation are addressed in detail. The components of the `optical active region', multiple quantum wells (MQW), WGs, and cladding layers are separately inspected. Even separate analysis of p- and n-sections of the WG become possible. Defect levels are detected in the p-part of the WG. Their presence is consistent with the doping by Mg. An increased efficiency of carrier capture into InGaN/GaN WGs compared to GaN WGs is observed. Thus, beyond the improved optical confinement, the electrical confinement is improved, as well. NSOM PL and PC at GaN based devices do not reach the clarity and spatial resolution for WG mode analysis as seen before for GaAs based devices. This is due to higher modal absorption and higher WG losses. NSOM based optical analysis turns out to be an efficient tool for analysis of single layers grown into InAlGaN/GaN diode laser structures, even if this analysis is done at a packaged ready-to-work device.

A 980 nm pseudomorphic single quantum well laser for pumping erbium-doped optical fiber amplifiers

NASA Technical Reports Server (NTRS)

Larsson, A.; Forouhar, S.; Cody, J.; Lang, R. J.; Andrekson, P. A.

1990-01-01

The authors have fabricated ridge waveguide pseudomorphic InGaAs/GaAs/AlGaAs GRIN-SCH SQW (graded-index separate-confinement-heterostructure single-quantum-well) lasers, emitting at 980 nm, with a maximum output power of 240 mW from one facet and a 22 percent coupling efficiency into a 1.55-micron single-mode optical fiber. These lasers satisfy the requirements on efficient and compact pump sources for Er3+-doped fiber amplifiers.

Proposal for Translational Entanglement of Dipole-Dipole Interacting Atoms in Optical Lattices

NASA Astrophysics Data System (ADS)

Opatrný, Tomáš; Deb, Bimalendu; Kurizki, Gershon

2003-06-01

We propose and investigate a realization of the position- and momentum-correlated Einstein-Podolsky-Rosen (EPR) states [

Semiconductor lasers with a continuous tuning range above 100 nm in the nearest IR spectral region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostin, Yu O; Lobintsov, A A; Shramenko, M V

2015-08-31

We have developed two new types of lasers based on quantum-confined semiconductor optical amplifiers with an acousto-optic tunable filter in an external fibre ring cavity. The lasers offer continuous wavelength tuning ranges from 780 to 885 and from 880 to 1010 nm, 20 mW of cw output power, and a tuning rate up to 10{sup 4} nm s{sup -1} at an instantaneous spectral linewidth less than 0.1 nm. (lasers)

Magnetic and Optical Properties of Submicron-Size Hollow Spheres

PubMed Central

Ye, Quan-Lin; Yoshikawa, Hirofumi; Awaga, Kunio

2010-01-01

Magnetic hollow spheres with a controlled diameter and shell thickness have emerged as an important class of magnetic nanomaterials. The confined hollow geometry and pronouncedly curved surfaces induce unique physical properties different from those of flat thin films and solid counterparts. In this paper, we focus on recent progress on submicron-size spherical hollow magnets (e.g., cobalt- and iron-based materials), and discuss the effects of the hollow shape and the submicron size on magnetic and optical properties.

Luminescence and related properties of nanocrystalline porous silicon

NASA Astrophysics Data System (ADS)

Koshida, N.

This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses luminescence and related properties of nanocrystalline porous silicon. Topics include an overview of nanostructured silicon, its fabrication technology, and properties of nanocrystalline porous silicon such as confinement effects, photoluminescence, electroluminesce, carrier charging effects, ballistic transport and emission, and thermally induced acoustic emission.

Spectroscopic Feedback for High Density Data Storage and Micromachining

DOEpatents

Carr, Christopher W.; Demos, Stavros; Feit, Michael D.; Rubenchik, Alexander M.

2008-09-16

Optical breakdown by predetermined laser pulses in transparent dielectrics produces an ionized region of dense plasma confined within the bulk of the material. Such an ionized region is responsible for broadband radiation that accompanies a desired breakdown process. Spectroscopic monitoring of the accompanying light in real-time is utilized to ascertain the morphology of the radiated interaction volume. Such a method and apparatus as presented herein, provides commercial realization of rapid prototyping of optoelectronic devices, optical three-dimensional data storage devices, and waveguide writing.

Infiltrated photonic crystal cavity as a highly sensitive platform for glucose concentration detection

NASA Astrophysics Data System (ADS)

Arafa, Safia; Bouchemat, Mohamed; Bouchemat, Touraya; Benmerkhi, Ahlem; Hocini, Abdesselam

2017-02-01

A Bio-sensing platform based on an infiltrated photonic crystal ring shaped holes cavity-coupled waveguide system is proposed for glucose concentration detection. Considering silicon-on-insulator (SOI) technology, it has been demonstrated that the ring shaped holes configuration provides an excellent optical confinement within the cavity region, which further enhances the light-matter interactions at the precise location of the analyte medium. Thus, the sensitivity and the quality factor (Q) can be significantly improved. The transmission characteristics of light in the biosensor under different refractive indices that correspond to the change in the analyte glucose concentration are analyzed by performing finite-difference time-domain (FDTD) simulations. Accordingly, an improved sensitivity of 462 nm/RIU and a Q factor as high as 1.11х105 have been achieved, resulting in a detection limit of 3.03х10-6 RIU. Such combination of attributes makes the designed structure a promising element for performing label-free biosensing in medical diagnosis and environmental monitoring.

Induced high-order resonance linewidth shrinking with multiple coupled resonators in silicon-organic hybrid slotted two-dimensional photonic crystals for reduced optical switching power in bistable devices

NASA Astrophysics Data System (ADS)

Hoang, Thu Trang; Ngo, Quang Minh; Vu, Dinh Lam; Le, Khai Q.; Nguyen, Truong Khang; Nguyen, Hieu P. T.

2018-01-01

Shrinking the linewidth of resonances induced by multiple coupled resonators is comprehensively analyzed using the coupled-mode theory (CMT) in time. Two types of coupled resonators under investigation are coupled resonator optical waveguides (CROWs) and side-coupled resonators with waveguide (SCREW). We examine the main parameters influencing on the spectral response such as the number of resonators (n) and the phase shift (φ) between two adjacent resonators. For the CROWs geometry consisting of n coupled resonators, we observe the quality (Q) factor of the right- and left-most resonant lineshapes increases n times larger than that of a single resonator. For the SCREW geometry, relying on the phase shift, sharp, and asymmetric resonant lineshape of the high Q factor a narrow linewidth of the spectral response could be achieved. We employ the finite-difference time-domain (FDTD) method to design and simulate two proposed resonators for practical applications. The proposed coupled resonators in silicon-on-insulator (SOI) slotted two-dimensional (2-D) photonic crystals (PhCs) filled and covered with a low refractive index organic material. Slotted PhC waveguides and cavities are designed to enhance the electromagnetic intensity and to confine the light into small cross-sectional area with low refractive index so that efficient optical devices could be achieved. A good agreement between the theoretical CMT analysis and the FDTD simulation is shown as an evidence for our accurate investigation. All-optical switches based on the CROWs in the SOI slotted 2-D PhC waveguide that are filled and covered by a nonlinear organic cladding to overcome the limitations of its well-known intrinsic properties are also presented. From the calculations, we introduce a dependency of the normalized linewidth of the right-most resonance and its switching power of the all-optical switches on number of resonator, n. This result might provide a guideline for all-optical signal processing on a silicon PhC chip design.

Impact of physical confinement on nuclei geometry and cell division dynamics in 3D spheroids.

PubMed

Desmaison, Annaïck; Guillaume, Ludivine; Triclin, Sarah; Weiss, Pierre; Ducommun, Bernard; Lobjois, Valérie

2018-06-08

Multicellular tumour spheroids are used as a culture model to reproduce the 3D architecture, proliferation gradient and cell interactions of a tumour micro-domain. However, their 3D characterization at the cell scale remains challenging due to size and cell density issues. In this study, we developed a methodology based on 3D light sheet fluorescence microscopy (LSFM) image analysis and convex hull calculation that allows characterizing the 3D shape and orientation of cell nuclei relative to the spheroid surface. By using this technique and optically cleared spheroids, we found that in freely growing spheroids, nuclei display an elongated shape and are preferentially oriented parallel to the spheroid surface. This geometry is lost when spheroids are grown in conditions of physical confinement. Live 3D LSFM analysis of cell division revealed that confined growth also altered the preferential cell division axis orientation parallel to the spheroid surface and induced prometaphase delay. These results provide key information and parameters that help understanding the impact of physical confinement on cell proliferation within tumour micro-domains.

Confinement effects on lyotropic nematic liquid crystal phases of graphene oxide dispersions

NASA Astrophysics Data System (ADS)

Al-Zangana, Shakhawan; Iliut, Maria; Turner, Michael; Vijayaraghavan, Aravind; Dierking, Ingo

2017-12-01

Graphene oxide (GO) forms well ordered liquid crystal (LC) phases in polar solvents. Here, we map the lyotropic phase diagram of GO as a function of the lateral dimensions of the GO flakes, their concentration, geometrical confinement configuration and solvent polarity. GO flakes were prepared in water and transferred into other polar solvents. Polarising optical microscopy (POM) was used to determine the phase evolution through the isotropic-biphasic-nematic transitions of the GO LC. We report that the confinement volume and geometry relative to the particle size is critical for the observation of the lyotropic phase, specifically, this determines the low-end concentration limit for the detection of the GO LC. Additionally, a solvent with higher polarisability stabilises the LC phases at lower concentrations and smaller flake sizes. GO LCs have been proposed for a range of applications from display technologies to conductive fibres, and the behaviour of LC phase formation under confinement imposes a limit on miniaturisation of the dimensions of such GO LC systems which could significantly impact on their potential applications.

Quasi-one-dimensional density of states in a single quantum ring.

PubMed

Kim, Heedae; Lee, Woojin; Park, Seongho; Kyhm, Kwangseuk; Je, Koochul; Taylor, Robert A; Nogues, Gilles; Dang, Le Si; Song, Jin Dong

2017-01-05

Generally confinement size is considered to determine the dimensionality of nanostructures. While the exciton Bohr radius is used as a criterion to define either weak or strong confinement in optical experiments, the binding energy of confined excitons is difficult to measure experimentally. One alternative is to use the temperature dependence of the radiative recombination time, which has been employed previously in quantum wells and quantum wires. A one-dimensional loop structure is often assumed to model quantum rings, but this approximation ceases to be valid when the rim width becomes comparable to the ring radius. We have evaluated the density of states in a single quantum ring by measuring the temperature dependence of the radiative recombination of excitons, where the photoluminescence decay time as a function of temperature was calibrated by using the low temperature integrated intensity and linewidth. We conclude that the quasi-continuous finely-spaced levels arising from the rotation energy give rise to a quasi-one-dimensional density of states, as long as the confined exciton is allowed to rotate around the opening of the anisotropic ring structure, which has a finite rim width.

Size-tunable Lateral Confinement in Monolayer Semiconductors

DOE PAGES

Wei, Guohua; Czaplewski, David A.; Lenferink, Erik J.; ...

2017-06-12

Three-dimensional confinement allows semiconductor quantum dots to exhibit size-tunable electronic and optical properties that enable a wide range of opto-electronic applications from displays, solar cells and bio-medical imaging to single-electron devices. Additional modalities such as spin and valley properties in monolayer transition metal dichalcogenides provide further degrees of freedom requisite for information processing and spintronics. In nanostructures, however, spatial confinement can cause hybridization that inhibits the robustness of these emergent properties. Here in this paper, we show that laterally-confined excitons in monolayer MoS 2 nanodots can be created through top-down nanopatterning with controlled size tunability. Unlike chemically-exfoliated monolayer nanoparticles, themore » lithographically patterned monolayer semiconductor nanodots down to a radius of 15 nm exhibit the same valley polarization as in a continuous monolayer sheet. The inherited bulk spin and valley properties, the size dependence of excitonic energies, and the ability to fabricate MoS 2 nanostructures using semiconductor-compatible processing suggest that monolayer semiconductor nanodots have potential to be multimodal building blocks of integrated optoelectronics and spintronics systems« less

Temporal waveguides for optical pulses

DOE PAGES

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

2016-05-12

Here we discuss, temporal total internal reflection (TIR), in analogy to the conventional TIR of an optical beam at a dielectric interface, is the total reflection of an optical pulse inside a dispersive medium at a temporal boundary across which the refractive index changes. A pair of such boundaries separated in time acts as the temporal analog of planar dielectric waveguides. We study the propagation of optical pulses inside such temporal waveguides, both analytically and numerically, and show that the waveguide supports a finite number of temporal modes. We also discuss how a single-mode temporal waveguide can be created inmore » practice. In contrast with the spatial case, the confinement can occur even when the central region has a lower refractive index.« less

Observer for a thick layer of solid deuterium-tritium using backlit optical shadowgraphy and interferometry.

PubMed

Choux, Alexandre; Busvelle, Eric; Gauthier, Jean Paul; Pascal, Ghislain

2007-11-20

Our work is in the context of the French "laser mégajoule" project, about fusion by inertial confinement. The project leads to the problem of characterizing the inner surface, of the approximately spherical target, by optical shadowgraphy techniques. Our work is entirely based on the basic idea that optical shadowgraphy produces "caustics" of systems of optical rays, which contain a great deal of 3D information about the surface to be characterized. We develop a method of 3D reconstruction based upon this idea plus a "small perturbations" technique. Although computations are made in the special "spherical" case, the method is in fact general and may be extended to several other situations.

Microstructure of squarylium dye J aggregate films examined on the basis of optical behavior at low temperature

NASA Astrophysics Data System (ADS)

Tatsuura, Satoshi; Tian, Minquan; Furuki, Makoto; Sato, Yasuhiro; Iwasa, Izumi; Pu, Lyong Sun; Kawashima, Hitoshi; Ishikawa, Hiroshi

2002-10-01

The microstructure of a spin-coated film of squarylium dye J aggregates is examined on the basis of the measurement of the optical properties and the third-order nonlinear optical susceptibility χ(3) at low temperature. The absorption maximum of J aggregates shifted to lower energies as the film temperature decreased, while χ(3) was independent of the temperature. The latter finding indicates that the coherent length of J aggregates is confined by a structural boundary rather than by phonons; consequently, the observed peak energy shift can be due to temperature-dependent conformational change of the aggregates. The small aggregation size may contribute to the ultrahigh-speed optical response of squarylium dye J aggregates.

Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands.

PubMed

Carroll, Gerard M; Limpens, Rens; Neale, Nathan R

2018-05-09

The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups-alkyls, amides, and alkoxides-on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative to alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands-not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals-are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. These results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.

Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands

DOE PAGES

Carroll, Gerard M.; Limpens, Rens; Neale, Nathan R.

2018-04-16

The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups - alkyls, amides, and alkoxides - on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative tomore » alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands - not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals - are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. Furthermore, these results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.« less

Free-standing membrane polymer laser on the end of an optical fiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhai, Tianrui, E-mail: trzhai@bjut.edu.cn, E-mail: zhangxinping@bjut.edu.cn; Li, Songtao; Hu, Yujie

2016-01-25

One- and two-dimensional distributed feedback cavities were constructed on free-standing polymer membranes using spin-coating and lift-off techniques. Low threshold lasing was generated through feedback amplification when the 290-nm membrane device was optically pumped, which was attributed to the strong confinement mechanism provided by the active waveguide layer without a substrate. The free-standing membrane polymer laser is flexible and can be transplanted. Single- and dual-wavelength fiber lasers were achieved by directly attaching the membrane polymer laser on the optical fiber end face. This technique provides potential to fabricate polymer lasers on surfaces with arbitrary shapes.

Broadband light funneling in ultrasubwavelength channels having periodic connected unfilled apertures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Subramania, Ganapathi Subramanian; Brener, Igal; Foteinopoulou, Stavroula

2017-08-01

A structure for broadband light funneling comprises a two-dimensional periodic array of connected ultrasubwavelength apertures, each aperture comprising a large sub-aperture that aids in the coupling of the incoming incident light and a small sub-aperture that funnels a significant fraction of the incident light power. The structure possesses all the capabilities of prior extraordinary optical transmission platforms, yet operates nonresonantly on a distinctly different mechanism. The structure demonstrates efficient ultrabroadband funneling of optical power confined in an area as small as .about.(.lamda./500).sup.2, where optical fields are enhanced, thus exhibiting functional possibilities beyond resonant platforms.

Effect of CTAB on structural and optical properties of CuO nanoparticles prepared by coprecipitation route

NASA Astrophysics Data System (ADS)

Varghese, Donna; Tom, Catherine; Krishna Chandar, N.

2017-11-01

CuO (Copper Oxide) nanoparticles were synthesized by a simple coprecipitation route by using copper acetate, sodium hydroxide as precursors and cetyltrimethyl ammonium bromide (CTAB) as surfactant. For the purpose of the study, the surfactant-CTAB treated and non-treated samples were synthesized separately. Both the synthesized samples were studied to understand their structural and optical properties. The formation of CuO and its crystallinity was confirmed by XRD. Further, the optical studies showed a defined blue shift in CTAB treated sample which is clear evidence that the particles undergo confinement when they are nano-regime.

Applications of ultrafast laser direct writing: from polarization control to data storage

NASA Astrophysics Data System (ADS)

Donko, A.; Gertus, T.; Brambilla, G.; Beresna, M.

2018-02-01

Ultrafast laser direct writing is a fascinating technology which emerged more than two decades from fundamental studies of material resistance to high-intensity optical fields. Its development saw the discovery of many puzzling phenomena and demonstration of useful applications. Today, ultrafast laser writing is seen as a technology with great potential and is rapidly entering the industrial environment. Whereas, less than 10 years ago, ultrafast lasers were still confined within the research labs. This talk will overview some of the unique features of ultrafast lasers and give examples of its applications in optical data storage, polarization control and optical fibers.

Investigation of the spatial distribution of second-order nonlinearity in thermally poled optical fibers.

PubMed

An, Honglin; Fleming, Simon

2005-05-02

The spatial distribution of second-order nonlinearity in thermally poled optical fibers was characterized by second-harmonic microscopy. The second-order nonlinearity was found to be confined to a thin layer close to the anode surface and progressed further into the silica as the poling time increased. Position uncertainty of the anode metal wire was observed to have an effect, as the nonlinear layers were found not always symmetrically located around the nearest points between the anode and cathode. Optical microscopy results were obtained on etched poled fiber cross-sections and compared with those from second-harmonic microscopy.

Magnetic force micropiston: an integrated force/microfluidic device for the application of compressive forces in a confined environment.

PubMed

Fisher, J K; Kleckner, N

2014-02-01

Cellular biology takes place inside confining spaces. For example, bacteria grow in crevices, red blood cells squeeze through capillaries, and chromosomes replicate inside the nucleus. Frequently, the extent of this confinement varies. Bacteria grow longer and divide, red blood cells move through smaller and smaller passages as they travel to capillary beds, and replication doubles the amount of DNA inside the nucleus. This increase in confinement, either due to a decrease in the available space or an increase in the amount of material contained in a constant volume, has the potential to squeeze and stress objects in ways that may lead to changes in morphology, dynamics, and ultimately biological function. Here, we describe a device developed to probe the interplay between confinement and the mechanical properties of cells and cellular structures, and forces that arise due to changes in a structure's state. In this system, the manipulation of a magnetic bead exerts a compressive force upon a target contained in the confining space of a microfluidic channel. This magnetic force microfluidic piston is constructed in such a way that we can measure (a) target compliance and changes in compliance as induced by changes in buffer, extract, or biochemical composition, (b) target expansion force generated by changes in the same parameters, and (c) the effects of compression stress on a target's structure and function. Beyond these issues, our system has general applicability to a variety of questions requiring the combination of mechanical forces, confinement, and optical imaging.

Magnetic force micropiston: An integrated force/microfluidic device for the application of compressive forces in a confined environment

NASA Astrophysics Data System (ADS)

Fisher, J. K.; Kleckner, N.

2014-02-01

Cellular biology takes place inside confining spaces. For example, bacteria grow in crevices, red blood cells squeeze through capillaries, and chromosomes replicate inside the nucleus. Frequently, the extent of this confinement varies. Bacteria grow longer and divide, red blood cells move through smaller and smaller passages as they travel to capillary beds, and replication doubles the amount of DNA inside the nucleus. This increase in confinement, either due to a decrease in the available space or an increase in the amount of material contained in a constant volume, has the potential to squeeze and stress objects in ways that may lead to changes in morphology, dynamics, and ultimately biological function. Here, we describe a device developed to probe the interplay between confinement and the mechanical properties of cells and cellular structures, and forces that arise due to changes in a structure's state. In this system, the manipulation of a magnetic bead exerts a compressive force upon a target contained in the confining space of a microfluidic channel. This magnetic force microfluidic piston is constructed in such a way that we can measure (a) target compliance and changes in compliance as induced by changes in buffer, extract, or biochemical composition, (b) target expansion force generated by changes in the same parameters, and (c) the effects of compression stress on a target's structure and function. Beyond these issues, our system has general applicability to a variety of questions requiring the combination of mechanical forces, confinement, and optical imaging.

Anisotropic Failure Strength of Shale with Increasing Confinement: Behaviors, Factors and Mechanism.

PubMed

Cheng, Cheng; Li, Xiao; Qian, Haitao

2017-11-15

Some studies reported that the anisotropic failure strength of shale will be weakened by increasing confinement. In this paper, it is found that there are various types of anisotropic strength behaviors. Four types of anisotropic strength ratio ( S A 1 ) behaviors and three types of anisotropic strength difference ( S A 2 ) behaviors have been classified based on laboratory experiments on nine groups of different shale samples. The cohesion c w and friction angle ϕ w of the weak planes are proven to be two dominant factors according to a series of bonded-particle discrete element modelling analyses. It is observed that shale is more prone to a slight increase of S A 1 and significant increase of S A 2 with increasing confinement for higher cohesion c w and lower to medium friction angle ϕ w . This study also investigated the mechanism of the anisotropic strength behaviors with increasing confinement. Owing to different contributions of c w and ϕ w under different confinements, different combinations of c w and ϕ w may have various types of influences on the minimum failure strength with the increasing confinement; therefore, different types of anisotropic behaviors occur for different shale specimens as the confinement increases. These findings are very important to understand the stability of wellbore and underground tunneling in the shale rock mass, and should be helpful for further studies on hydraulic fracture propagations in the shale reservoir.

Anisotropic Failure Strength of Shale with Increasing Confinement: Behaviors, Factors and Mechanism

PubMed Central

Cheng, Cheng; Li, Xiao; Qian, Haitao

2017-01-01

Some studies reported that the anisotropic failure strength of shale will be weakened by increasing confinement. In this paper, it is found that there are various types of anisotropic strength behaviors. Four types of anisotropic strength ratio (SA1) behaviors and three types of anisotropic strength difference (SA2) behaviors have been classified based on laboratory experiments on nine groups of different shale samples. The cohesion cw and friction angle ϕw of the weak planes are proven to be two dominant factors according to a series of bonded-particle discrete element modelling analyses. It is observed that shale is more prone to a slight increase of SA1 and significant increase of SA2 with increasing confinement for higher cohesion cw and lower to medium friction angle ϕw. This study also investigated the mechanism of the anisotropic strength behaviors with increasing confinement. Owing to different contributions of cw and ϕw under different confinements, different combinations of cw and ϕw may have various types of influences on the minimum failure strength with the increasing confinement; therefore, different types of anisotropic behaviors occur for different shale specimens as the confinement increases. These findings are very important to understand the stability of wellbore and underground tunneling in the shale rock mass, and should be helpful for further studies on hydraulic fracture propagations in the shale reservoir. PMID:29140292

Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field

DOE PAGES

Piazza, L.; Lummen, T. T. A.; Quiñonez, E.; ...

2015-03-02

Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinducedmore » near-field is imaged synchronously with its spatial interference pattern. In conclusion, this methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.« less

Scattering of particles in the presence of harmonic confinement perturbed by a complex absorbing potential

NASA Astrophysics Data System (ADS)

Maghari, A.; Kermani, M. M.

2018-04-01

A system of two interacting atoms confined in 1D harmonic trap and perturbed by an absorbing boundary potential is studied using the Lippmann-Schwinger formalism. The atom-atom interaction potential was considered as a nonlocal separable model. The perturbed absorbing boundary potential was also assumed in the form of Scarf II complex absorbing potential. The model is used for the study of 1D optical lattices that support the trapping of a pair atom within a unit cell. Moreover, it allows to describe the scattering particles in a tight smooth trapping surface and to analyze the bound and resonance states. The analytical expressions for wavefunctions and transition matrix as well as the absorption probabilities are calculated. A demonstration of how the complex absorbing potential affecting the bound states and resonances of particles confined in a harmonic trap is described.

Controllable Fabrication of Au Nanocups by Confined-Space Thermal Dewetting for OCT Imaging.

PubMed

Gao, Aiqin; Xu, Wenjing; Ponce de León, Yenisey; Bai, Yaocai; Gong, Mingfu; Xie, Kongliang; Park, Boris Hyle; Yin, Yadong

2017-07-01

Here, this study reports a novel confined-space thermal dewetting strategy for the fabrication of Au nanocups with tunable diameter, height, and size of cup opening. The nanocup morphology is defined by the cup-shaped void space created by a yolk-shell silica template that spontaneously takes an eccentric configuration during annealing. Thermal dewetting of Au, which is sandwiched between the yolk and shell, leads to the desired nanocup morphology. With strong scattering in near infrared, the Au nanocups exhibit superior efficiency as contrast agents for spectral-domain optical coherence tomography imaging. This confined-space thermal dewetting strategy is scalable and general, and can be potentially extended to the synthesis of novel anisotropic nanostructures of various compositions that are difficult to produce by conventional wet chemical or physical methods, thus opening up opportunities for many new applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum confinement-induced tunable exciton states in graphene oxide

PubMed Central

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M.; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-01-01

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology. PMID:23872608

Three-dimensional spatiotemporal focusing of holographic patterns

PubMed Central

Hernandez, Oscar; Papagiakoumou, Eirini; Tanese, Dimitrii; Fidelin, Kevin; Wyart, Claire; Emiliani, Valentina

2016-01-01

Two-photon excitation with temporally focused pulses can be combined with phase-modulation approaches, such as computer-generated holography and generalized phase contrast, to efficiently distribute light into two-dimensional, axially confined, user-defined shapes. Adding lens-phase modulations to 2D-phase holograms enables remote axial pattern displacement as well as simultaneous pattern generation in multiple distinct planes. However, the axial confinement linearly degrades with lateral shape area in previous reports where axially shifted holographic shapes were not temporally focused. Here we report an optical system using two spatial light modulators to independently control transverse- and axial-target light distribution. This approach enables simultaneous axial translation of single or multiple spatiotemporally focused patterns across the sample volume while achieving the axial confinement of temporal focusing. We use the system's capability to photoconvert tens of Kaede-expressing neurons with single-cell resolution in live zebrafish larvae. PMID:27306044

Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field

PubMed Central

Piazza, L; Lummen, T.T.A.; Quiñonez, E; Murooka, Y; Reed, B.W.; Barwick, B; Carbone, F

2015-01-01

Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits. PMID:25728197

Confinement and surface effects on the physical properties of rhombohedral-shape hematite (α-Fe{sub 2}O{sub 3}) nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luna, Carlos, E-mail: carlos.lunacd@uanl.edu.mx; Cuan-Guerra, Aída D.; Barriga-Castro, Enrique D.

2016-08-15

Highlights: • Uniform rhombohedral hematite nanocrystals (RHNCs) have been obtained. • A detailed formation mechanism of these HNCS has been proposed. • Phonon confinement effects were revealed in the RHNCS vibrational bands. • Quantum confinement effects on the optical and electronic properties were found. - Abstract: Morphological, microstructural and vibrational properties of hematite (α-Fe{sub 2}O{sub 3}) nanocrystals with a rhombohedral shape and rounded edges, obtained by forced hydrolysis of iron(III) solutions under a fast nucleation, have been investigated in detail as a function of aging time. These studies allowed us to propose a detailed formation mechanism and revealed that thesemore » nanocrystals are composed of four {104} side facets, two {110} faces at the edges of the long diagonal of the nanocrystals and two {−441} facets as the top and bottom faces. Also, the presence of nanoscopic pores and fissures was evidenced. The vibrational bands of such nanocrystals were shifted to lower frequencies in comparison with bulk hematite ones as the nanocrystal size was reduced due to phonon confinement effects. Also, the indirect and direct transition band gaps displayed interesting dependences on the aging time arising from quantum confinement and surface effects.« less

Spatially confined low-power optically pumped ultrafast synchrotron x-ray nanodiffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Joonkyu; Zhang, Qingteng; Chen, Pice

2015-08-27

The combination of ultrafast optical excitation and time-resolved synchrotron x-ray nanodiffraction provides unique insight into the photoinduced dynamics of materials, with the spatial resolution required to probe individual nanostructures or small volumes within heterogeneous materials. Optically excited x-ray nanobeam experiments are challenging because the high total optical power required for experimentally relevant optical fluences leads to mechanical instability due to heating. For a given fluence, tightly focusing the optical excitation reduces the average optical power by more than three orders of magnitude and thus ensures sufficient thermal stability for x-ray nanobeam studies. Delivering optical pulses via a scannable fiber-coupled opticalmore » objective provides a well-defined excitation geometry during rotation and translation of the sample and allows the selective excitation of isolated areas within the sample. Finally, experimental studies of the photoinduced lattice dynamics of a 35 nm BiFeO 3 thin film on a SrTiO 3 substrate demonstrate the potential to excite and probe nanoscale volumes.« less

Nanophotonic Optical Isolator Controlled by the Internal State of Cold Atoms

NASA Astrophysics Data System (ADS)

Sayrin, Clément; Junge, Christian; Mitsch, Rudolf; Albrecht, Bernhard; O'Shea, Danny; Schneeweiss, Philipp; Volz, Jürgen; Rauschenbeutel, Arno

2015-10-01

The realization of nanophotonic optical isolators with high optical isolation even at ultralow light levels and low optical losses is an open problem. Here, we employ the link between the local polarization of strongly confined light and its direction of propagation to realize low-loss nonreciprocal transmission through a silica nanofiber at the single-photon level. The direction of the resulting optical isolator is controlled by the spin state of cold atoms. We perform our experiment in two qualitatively different regimes, i.e., with an ensemble of cold atoms where each atom is weakly coupled to the waveguide and with a single atom strongly coupled to the waveguide mode. In both cases, we observe simultaneously high isolation and high forward transmission. The isolator concept constitutes a nanoscale quantum optical analog of microwave ferrite resonance isolators, can be implemented with all kinds of optical waveguides and emitters, and might enable novel integrated optical devices for fiber-based classical and quantum networks.

Experimental Study of Damage Evolution in Circular Stirrup-Confined Concrete

PubMed Central

Li, Zuohua; Peng, Zhihan; Teng, Jun; Wang, Ying

2016-01-01

This paper presents an experimental study on circular stirrup-confined concrete specimens under uniaxial and monotonic load. The effects of stirrup volume ratio, stirrup yield strength and concrete strength on damage evolution of stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, the concrete damage evolution can be relatively restrained with the increase of the stirrup volume ratio. Secondly, higher stirrup yield strength usually causes larger confining pressures and slower concrete damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates the concrete damage evolution. A plastic strain expression is obtained through curve fitting, and a damage evolution equation for circular stirrup-confined concrete is proposed by introducing a confinement factor (C) based on the experimental data. The comparison results demonstrate that the proposed damage evolution model can accurately describe the experimental results. PMID:28773402

Experimental Study of Damage Evolution in Circular Stirrup-Confined Concrete.

PubMed

Li, Zuohua; Peng, Zhihan; Teng, Jun; Wang, Ying

2016-04-08

This paper presents an experimental study on circular stirrup-confined concrete specimens under uniaxial and monotonic load. The effects of stirrup volume ratio, stirrup yield strength and concrete strength on damage evolution of stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, the concrete damage evolution can be relatively restrained with the increase of the stirrup volume ratio. Secondly, higher stirrup yield strength usually causes larger confining pressures and slower concrete damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates the concrete damage evolution. A plastic strain expression is obtained through curve fitting, and a damage evolution equation for circular stirrup-confined concrete is proposed by introducing a confinement factor ( C ) based on the experimental data. The comparison results demonstrate that the proposed damage evolution model can accurately describe the experimental results.

Impurity confinement and transport in high confinement regimes without edge localized modes on DIII-D [Impurity confinement and transport in high confinement regimes without ELMs on DIII-D

DOE PAGES

Grierson, Brian A.; Burrell, Keith H.; Nazikian, Raffi M.; ...

2015-04-17

Here, impurity transport in the DIII-D tokamak is investigated in stationary high confinement (H-mode) regimes without edge localized modes (ELMs). In plasmas maintained by resonant magnetic perturbation (RMP) ELM-suppression and QH-mode the confinement time of fluorine (Z=9) is equivalent to that in ELMing discharges with 40 Hz ELMs. For selected discharges with impurity injection the impurity particle confinement time compared to the energy confinement time is in the range of τ p/τ e ≈ 2 $-$ 3. In QH-mode operation the impurity confinement time is shown to be smaller for intense, coherent magnetic and density fluctuations of the edge harmonicmore » oscillation than weaker fluctuations. Transport coefficients are derived from the time evolution of the impurity density profile and compared to neoclassical and turbulent transport models NEO and TGLF. Neoclassical transport of fluorine is found to be small compared to the experimental values. In the ELMing and RMP ELM-suppressed plasma the impurity transport is affected by the presence of tearing modes. For radii larger than the mode radius the TGLF diffusion coefficient is smaller than the experimental value by a factor of 2-3, while the convective velocity is within error estimates. Low levels of diffusion are observed for radii smaller than the tearing mode radius. In the QH-mode plasma investigated, the TGLF diffusion coefficient higher inside of ρ = 0.4 and lower outside of 0.4 than the experiment, and the TGLF convective velocity is more negative by a factor of approximately 1.7.« less

Effect of substrates and thickness on optical properties in atomic layer deposition grown ZnO thin films

NASA Astrophysics Data System (ADS)

Pal, Dipayan; Singhal, Jaya; Mathur, Aakash; Singh, Ajaib; Dutta, Surjendu; Zollner, Stefan; Chattopadhyay, Sudeshna

2017-11-01

Atomic Layer Deposition technique was used to grow high quality, very low roughness, crystalline, Zinc Oxide (ZnO) thin films on silicon (Si) and fused quartz (SiO2) substrates to study the optical properties. Spectroscopic ellipsometry results of ZnO/Si system, staggered type-II quantum well, demonstrate that there is a significant drop in the magnitudes of both the real and imaginary parts of complex dielectric constants and in near-band gap absorption along with a blue shift of the absorption edge with decreasing film thickness at and below ∼20 nm. Conversely, UV-vis absorption spectroscopy of ZnO/SiO2, thin type-I quantum well, consisting of a narrower-band gap semiconductor grown on a wider-band gap (insulator) substrate, shows the similar thickness dependent blue-shift of the absorption edge but with an increase in the magnitude of near-band gap absorption with decreasing film thickness. Thickness dependent blue shift, energy vs. 1/d2, in two different systems, ZnO/Si and ZnO/SiO2, show a difference in their slopes. The observed phenomena can be consistently explained by the corresponding exciton (or carrier/s) deconfinement and confinement effects at the ZnO/Si and ZnO/SiO2 interface respectively, where Tanguy-Elliott amplitude pre-factor plays the key role through the electron-hole overlap factor at the interface.

State-dependent fluorescence of neutral atoms in optical potentials

NASA Astrophysics Data System (ADS)

Martinez-Dorantes, M.; Alt, W.; Gallego, J.; Ghosh, S.; Ratschbacher, L.; Meschede, D.

2018-02-01

Recently we have demonstrated scalable, nondestructive, and high-fidelity detection of the internal state of 87Rb neutral atoms in optical dipole traps using state-dependent fluorescence imaging [M. Martinez-Dorantes, W. Alt, J. Gallego, S. Ghosh, L. Ratschbacher, Y. Völzke, and D. Meschede, Phys. Rev. Lett. 119, 180503 (2017), 10.1103/PhysRevLett.119.180503]. In this paper we provide experimental procedures and interpretations to overcome the detrimental effects of heating-induced trap losses and state leakage. We present models for the dynamics of optically trapped atoms during state-dependent fluorescence imaging and verify our results by comparing Monte Carlo simulations with experimental data. Our systematic study of dipole force fluctuations heating in optical traps during near-resonant illumination shows that off-resonant light is preferable for state detection in tightly confining optical potentials.

Deep cooling of optically trapped atoms implemented by magnetic levitation without transverse confinement.

PubMed

Li, Chen; Zhou, Tianwei; Zhai, Yueyang; Xiang, Jinggang; Luan, Tian; Huang, Qi; Yang, Shifeng; Xiong, Wei; Chen, Xuzong

2017-05-01

We report a setup for the deep cooling of atoms in an optical trap. The deep cooling is implemented by eliminating the influence of gravity using specially constructed magnetic coils. Compared to the conventional method of generating a magnetic levitating force, the lower trap frequency achieved in our setup provides a lower limit of temperature and more freedoms to Bose gases with a simpler solution. A final temperature as low as ∼6nK is achieved in the optical trap, and the atomic density is decreased by nearly two orders of magnitude during the second stage of evaporative cooling. This deep cooling of optically trapped atoms holds promise for many applications, such as atomic interferometers, atomic gyroscopes, and magnetometers, as well as many basic scientific research directions, such as quantum simulations and atom optics.

Deep cooling of optically trapped atoms implemented by magnetic levitation without transverse confinement

NASA Astrophysics Data System (ADS)

Li, Chen; Zhou, Tianwei; Zhai, Yueyang; Xiang, Jinggang; Luan, Tian; Huang, Qi; Yang, Shifeng; Xiong, Wei; Chen, Xuzong

2017-05-01

We report a setup for the deep cooling of atoms in an optical trap. The deep cooling is implemented by eliminating the influence of gravity using specially constructed magnetic coils. Compared to the conventional method of generating a magnetic levitating force, the lower trap frequency achieved in our setup provides a lower limit of temperature and more freedoms to Bose gases with a simpler solution. A final temperature as low as ˜ 6 nK is achieved in the optical trap, and the atomic density is decreased by nearly two orders of magnitude during the second stage of evaporative cooling. This deep cooling of optically trapped atoms holds promise for many applications, such as atomic interferometers, atomic gyroscopes, and magnetometers, as well as many basic scientific research directions, such as quantum simulations and atom optics.

Hyperpolarizability and Operational Magic Wavelength in an Optical Lattice Clock

NASA Astrophysics Data System (ADS)

Brown, R. C.; Phillips, N. B.; Beloy, K.; McGrew, W. F.; Schioppo, M.; Fasano, R. J.; Milani, G.; Zhang, X.; Hinkley, N.; Leopardi, H.; Yoon, T. H.; Nicolodi, D.; Fortier, T. M.; Ludlow, A. D.

2017-12-01

Optical clocks benefit from tight atomic confinement enabling extended interrogation times as well as Doppler- and recoil-free operation. However, these benefits come at the cost of frequency shifts that, if not properly controlled, may degrade clock accuracy. Numerous theoretical studies have predicted optical lattice clock frequency shifts that scale nonlinearly with trap depth. To experimentally observe and constrain these shifts in an 171Yb optical lattice clock, we construct a lattice enhancement cavity that exaggerates the light shifts. We observe an atomic temperature that is proportional to the optical trap depth, fundamentally altering the scaling of trap-induced light shifts and simplifying their parametrization. We identify an "operational" magic wavelength where frequency shifts are insensitive to changes in trap depth. These measurements and scaling analysis constitute an essential systematic characterization for clock operation at the 10-18 level and beyond.

Applications of Optical Microcavity Resonators in Analytical Chemistry

PubMed Central

Wade, James H.; Bailey, Ryan C.

2018-01-01

Optical resonator sensors are an emerging class of analytical technologies that use recirculating light confined within a microcavity to sensitively measure the surrounding environment. Bolstered by advances in microfabrication, these devices can be configured for a wide variety of chemical or biomolecular sensing applications. The review begins with a brief description of optical resonator sensor operation followed by discussions regarding sensor design, including different geometries, choices of material systems, methods of sensor interrogation, and new approaches to sensor operation. Throughout, key recent developments are highlighted, including advancements in biosensing and other applications of optical sensors. Alternative sensing mechanisms and hybrid sensing devices are then discussed in terms of their potential for more sensitive and rapid analyses. Brief concluding statements offer our perspective on the future of optical microcavity sensors and their promise as versatile detection elements within analytical chemistry. PMID:27049629

Terraced-heterostructure large-optical-cavity AlGaAs diode laser - A new type of high-power CW single-mode device

NASA Technical Reports Server (NTRS)

Botez, D.; Connolly, J. C.

1982-01-01

A new terraced lateral wave confining structure is obtained by liquid phase epitaxy over channeled substrates misoriented perpendicular to the channels' direction. Single spatial and longitudinal mode CW operation is achieved to 50 mW from one facet, in large spot sizes (2 x 7.5 micron, 1/e squared points in intensity) and narrow beams (6 deg x 23 deg), full width half-power). At 70 C ambient temperature CW lasing is obtained to 15 mW from one facet. Weak mode confinement in an asymmetric lateral waveguides provides discrimination against high-order mode oscillation.

A vacuum gauge based on an ultracold gas

NASA Astrophysics Data System (ADS)

Makhalov, V. B.; Turlapov, A. V.

2017-06-01

We report the design and application of a primary vacuum gauge based on an ultracold gas of atoms in an optical dipole trap. The pressure is calculated from the confinement time for atoms in the trap. The relationship between pressure and confinement time is established from the first principles owing to elimination of all channels introducing losses, except for knocking out an atom from the trap due to collisions with a residual gas particle. The method requires the knowledge of the gas chemical composition in the vacuum chamber, and, in the absence of this information, the systematic error is less than that of the ionisation sensor.

An extraordinary directive radiation based on optical antimatter at near infrared.

PubMed

Mocella, Vito; Dardano, Principia; Rendina, Ivo; Cabrini, Stefano

2010-11-22

In this paper we discuss and experimentally demonstrate that in a quasi- zero-average-refractive-index (QZAI) metamaterial, in correspondence of a divergent source in near infrared (λ = 1.55 μm) the light scattered out is extremely directive (Δθ(out) = 0.06°), coupling with diffraction order of the alternating complementary media grating. With a high degree of accuracy the measurements prove also the excellent vertical confinement of the beam even in the air region of the metamaterial, in absence of any simple vertical confinement mechanism. This extremely sensitive device works on a large contact area and open news perspective to integrated spectroscopy.

Tailoring growth conditions for efficient tuning of band edge of CdS nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Susha, N.; Nair, Swapna S., E-mail: swapna.s.nair@gmail.com; Aravind, P. B.

2015-06-24

CdS nanoparticles are successively synthesized by chemical precipitation method. The samples prepared at different reaction time and temperature are characterized by X-ray diffraction, Diffuse reflectance spectroscopy, Photoluminescence spectroscopy ans Energy dispersive x-ray analysis. Visible color variation is noted from light yellow to orange, indicates the quantum confinement effect and the results are again got confirmed from the optical studies. A shift in absorption peak is observed towards the lower region of the visible spectra - the “blue shift”- upon decrease in reaction time and temperature. Blue emission observed in the photoluminescence spectrum confirms the grain size induced confinement.

Growth of group II-VI semiconductor quantum dots with strong quantum confinement and low size dispersion

NASA Astrophysics Data System (ADS)

Pandey, Praveen K.; Sharma, Kriti; Nagpal, Swati; Bhatnagar, P. K.; Mathur, P. C.

2003-11-01

CdTe quantum dots embedded in glass matrix are grown using two-step annealing method. The results for the optical transmission characterization are analysed and compared with the results obtained from CdTe quantum dots grown using conventional single-step annealing method. A theoretical model for the absorption spectra is used to quantitatively estimate the size dispersion in the two cases. In the present work, it is established that the quantum dots grown using two-step annealing method have stronger quantum confinement, reduced size dispersion and higher volume ratio as compared to the single-step annealed samples. (

Quantification of irradiation defects in beta-silicon carbide using Raman spectroscopy

DOE PAGES

Koyanagi, T.; Lance, M. J.; Katoh, Y.

2016-08-11

Raman spectra from polycrystalline beta-silicon carbide (SiC) were collected following neutron irradiation at 380–1180 °C to 0.011–1.87 displacement per atom. The longitudinal optical (LO) peak shifted to a lower frequency and broadened as a result of the irradiation. The changes observed in the LO phonon line shape and position in neutron-irradiated SiC are explained by a combination of changes in the lattice constant and Young's modulus, and the phonon confinement effect. The phonon confinement model reasonably estimates the defect-defect distance in the irradiated SiC, which is consistent with results from previous experimental studies and simulations.

Electronic states and optical properties of single donor in GaN conical quantum dot with spherical edge

NASA Astrophysics Data System (ADS)

El Aouami, A.; Feddi, E.; El-Yadri, M.; Aghoutane, N.; Dujardin, F.; Duque, C. A.; Phuc, Huynh Vinh

2018-02-01

In this paper we present a theoretical investigation of quantum confinement effects on the electron and single donor states in GaN conical quantum dot with spherical edge. In the framework of the effective mass approximation, the Schrödinger equations of electron and donor have been solved analytically in an infinite potential barrier model. Our calculations show that the energies of electron and donor impurity are affected by the two characteristic parameters of the structure which are the angle Ω and the radial dimension R. We show that, despite the fact that the reduction of the two parameters Ω and R leads to the same confinement effects, the energy remains very sensitive to the variation of the radial part than the variation of the angular part. The analysis of the photoionization cross-section corresponding to optical transitions between the conduction band and the first donor energy level shows clearly that the reduction of the radius R causes a shift in resonance peaks towards the high energies. On the other hand, the optical transitions between 1 s - 1 p , 1 p - 1 d and 1 p - 2 s show that the increment of the conical aperture Ω (or reduction of R) implies a displacement of the excitation energy to higher energies.

Tuning a circular p-n junction in graphene from quantum confinement to optical guiding

NASA Astrophysics Data System (ADS)

Jiang, Yuhang; Mao, Jinhai; Moldovan, Dean; Masir, Massoud Ramezani; Li, Guohong; Watanabe, Kenji; Taniguchi, Takashi; Peeters, Francois M.; Andrei, Eva Y.

2017-11-01

The photon-like propagation of the Dirac electrons in graphene, together with its record-high electronic mobility, can lead to applications based on ultrafast electronic response and low dissipation. However, the chiral nature of the charge carriers that is responsible for the high mobility also makes it difficult to control their motion and prevents electronic switching. Here, we show how to manipulate the charge carriers by using a circular p-n junction whose size can be continuously tuned from the nanometre to the micrometre scale. The junction size is controlled with a dual-gate device consisting of a planar back gate and a point-like top gate made by decorating a scanning tunnelling microscope tip with a gold nanowire. The nanometre-scale junction is defined by a deep potential well created by the tip-induced charge. It traps the Dirac electrons in quantum-confined states, which are the graphene equivalent of the atomic collapse states (ACSs) predicted to occur at supercritically charged nuclei. As the junction size increases, the transition to the optical regime is signalled by the emergence of whispering-gallery modes, similar to those observed at the perimeter of acoustic or optical resonators, and by the appearance of a Fabry-Pérot interference pattern for junctions close to a boundary.

Optical and structural characterization of InAs/GaAs quantum wells

NASA Technical Reports Server (NTRS)

Ksendzov, A.; George, T.; Grunthaner, F. J.; Liu, J. K.; Rich, D. H.; Terhune, R. W.; Wilson, B. A.; Pollak, F. H.; Huang, Y.-S.

1991-01-01

Three InAs/GaAs single quantum wells of two-, three-, and four-monolayer thickness were characterized using optical and structural techniques. The results of high-resolution transmission electron (HRTEM) microscopy and optical studies which combine absorption, photoluminescence (PL), photoreflectance, and cathodoluminescence are presented. Using the polarization modulated absorptance technique, we observed two absorption features in our samples at 77 K. On the basis of their polarization properties and comparison with an envelope function calculation, these structures are assigned to transitions between the confined heavy-hole and confined and unconfined electron levels. Photoreflectance spectra of the three-monolayer sample in 77-300 K range show only the fundamental quantum well transition. The temperature dependence of this transition is approximately linear with a slope of 2.2 x 10 exp -4 eV/K, which is significantly lower than in both constituent materials. Comparison to the absorption data reveals that the PL spectra are affected by the carrier diffusion and therefore do not provide direct measure of the exciton density of states. The HRTEM images indicate that, while the interfaces of the two-monolayer sample are smooth and the well thickness is uniform, the four-monolayer sample has uneven interfaces and contains domains of two, three, and four monolayers.

Dissolved organic carbon in coral-reef lagoons, by high temperature catalytic oxidation and UV spectrometry

NASA Astrophysics Data System (ADS)

Pagès, Jean; Torréton, Jean-Pascal; Sempéré, Richard

1997-06-01

Two surveys were carried out on ten atolls in the Tuamotu archipelago (French Polynesia, Pacific Ocean). In vitro UV (250-400 nm) spectra of water samples gave absorption at 254 nm, A 254, and spectrum slope, S ⋆ (computed from In A λ versus λ).These two descriptors are negatively correlated, and data points are arrayed along a hyperbola spanned between an oceanic pole (high S ⋆, low A 254) and a confined pole (low 5 ⋆, high A 254). Dissolved organic carbon (DOC) concentrations, [C], as assessed by HTCO, exhibit a narrow range (0.7-1.0 mg C.L -1 for most lagoons) contrasting with the wide diversity of optical characteristics. [C] and A 254 are positively correlated, with a significant intercept (0.5 mg C.L -1) representing non-chromophoric DOC. Carbon-specific absorption, ɛ 254 increases (from 0.4 to 1.3 m 2.g -1) with increasing [C], mainly according to the literature) owing to increased average molecular weight (MW) of the chromophoric DOC fraction, which also lowers S ⋆. Our optical data thus illustrate a gradient of confinement (or residence time) that corresponds to a continuum in DOC nature, especially in MW and hence in bioavailability. Optical methods are confirmed as quick and effective means of assessing DOM distribution.

Interferometric optical online dosimetry for selective retina treatment (SRT)

NASA Astrophysics Data System (ADS)

Stoehr, Hardo; Ptaszynski, Lars; Fritz, Andreas; Brinkmann, Ralf

2007-07-01

Selective retina treatment (SRT) is a new laser based method to treat retinal diseases associated with disorders of the retinal pigment epithelium (RPE). Applying microsecond laser pulses tissue damage spatially confined to the retinal pigment epithelium (RPE) is achieved. The RPE cell damage is caused by transient microbubbles emerging at the strongly absorbing melanin granules inside the RPE cells. Due to the spatial confinement to the RPE the photoreceptors can be spared and vision can be maintained in the treated retinal areas. A drawback for effective clinical SRT is that the laser induced lesions are ophthalmoscopically invisible. Therefore, a real-time feedback system for dosimetry is necessary in order to avoid undertreatment or unwanted collateral damage to the adjacent tissue. We develop a dosimetry system which uses optical interferometry for the detection of the transient microbubbles. The system is based on an optical fiber interferometer operated with a laser diode at 830nm. We present current results obtained with a laser slit lamp using porcine RPE explants in vitro and complete porcine eye globes ex vivo. The RPE cell damage is determined by Calcein fluorescence viability assays. With a threshold criterium for RPE cell death derived from the measured interferometric signal transients good agreement with the results of the viability assays is achieved.

Acoustic Events and “Optophonic” Cochlear Responses Induced by Pulsed Near-Infrared LASER

PubMed Central

Maier, Hannes; Richter, Claus-Peter; Kral, Andrej

2012-01-01

Optical stimulation of neural tissue within the cochlea was described as a possible alternative to electrical stimulation. Most optical stimulation was performed with pulsed lasers operating with near-infrared (NIR) light and in thermal confinement. Under these conditions, the coexistence of laser-induced optoacoustic stimulation of the cochlea (“optophony”) has not been analyzed yet. This study demonstrates that pulsed 1850-nm laser light used for neural stimulation also results in sound pressure levels up to 62 dB peak-to-peak equivalent sound pressure level (SPL) in air. The sound field was confined to a small volume along the laser beam. In dry nitrogen, laser-induced acoustic events disappeared. Hydrophone measurements demonstrated pressure waves for laser fibers immersed in water. In hearing rats, laser-evoked signals were recorded from the cochlea without targeting neural tissue. The signals showed a two-domain response differing in amplitude and latency functions, as well as sensitivity to white-noise masking. The first component had characteristics of a cochlear microphonic potential, and the second component was characteristic for a compound action potential. The present data demonstrate that laser-evoked acoustic events can stimulate a hearing cochlea. Whenever optical stimulation is used, care must be taken to distinguish between such “optophony” and the true optoneural response. PMID:21278011

Progress Toward an Neutral Yb Frequency Standard

NASA Astrophysics Data System (ADS)

Cramer, Claire; Hong, Tao; Nagourney, Warren; Fortson, Norval

2004-05-01

We report recent progress toward a direct observation of the ^1S_0^ -- ^3P0 clock transition at 578 nm in atomic Yb and review the experimental path to an optical frequency standard based on neutral Yb confined in a Stark-free optical lattice. Lamb-Dicke confinement in an optical lattice at the ``magic wavelength'' (λ _M) at which ground and excited state light shifts cancel will free the spectrum from Doppler and recoil shifts, providing an optimal environment for a clock consisting of an ensemble of cold, trapped atoms. In^171Yb the ^3P0 level has a hfs induced lifetime of 21 s. With this isotope in a Stark-free lattice at λ M ng 750 nm, perturbations to the clock energy levels can be held below the mHz level, providing an accuracy of a few parts in 10^18[1]. To observe the clock transition we use a shelving scheme that creates a leak in a MOT on the ^1S_0^ -- ^1P1 transition. A laser resonant with the clock transition drives atoms into the ^3P0 state, in which they can escape the MOT, leading to an observable decrease in MOT fluorescence. [1] S. Porsev and A. Derevianko, to be published in PRA

Extraordinary Effects in Quasi-Periodic Gold Nanocavities: Enhanced Transmission and Polarization Control of Cavity Modes.

PubMed

Dhama, Rakesh; Caligiuri, Vincenzo; Petti, Lucia; Rashed, Alireza R; Rippa, Massimo; Lento, Raffaella; Termine, Roberto; Caglayan, Humeyra; De Luca, Antonio

2018-01-23

Plasmonic quasi-periodic structures are well-known to exhibit several surprising phenomena with respect to their periodic counterparts, due to their long-range order and higher rotational symmetry. Thanks to their specific geometrical arrangement, plasmonic quasi-crystals offer unique possibilities in tailoring the coupling and propagation of surface plasmons through their lattice, a scenario in which a plethora of fascinating phenomena can take place. In this paper we investigate the extraordinary transmission phenomenon occurring in specifically patterned Thue-Morse nanocavities, demonstrating noticeable enhanced transmission, directly revealed by near-field optical experiments, performed by means of a scanning near-field optical microscope (SNOM). SNOM further provides an intuitive picture of confined plasmon modes inside the nanocavities and confirms that localization of plasmon modes is based on size and depth of nanocavities, while cross talk between close cavities via propagating plasmons holds the polarization response of patterned quasi-crystals. Our performed numerical simulations are in good agreement with the experimental results. Thus, the control on cavity size and incident polarization can be used to alter the intensity and spatial properties of confined cavity modes in such structures, which can be exploited in order to design a plasmonic device with customized optical properties and desired functionalities, to be used for several applications in quantum plasmonics.

Non-linear optical response of an impurity in a cylindrical quantum dot under the action of a magnetic field

NASA Astrophysics Data System (ADS)

Portacio, Alfonso A.; Rodríguez, Boris A.; Villamil, Pablo

2017-04-01

The linear and nonlinear optical response in a cylindrical quantum dot (CQD) of GaAs / Ga0.6Al0.4 As with a donor impurity in a uniform magnetic field applied in the axial direction of the cylinder is studied theoretically. The calculations were carried out in approximations of effective mass and two-level quantum systems. Using the variational method, the binding energies and the wave functions of the 1s-like y 2pz-like states for different positions of the impurity inside the CQD were found. It was found that the binding energy is greatest in the center of the CQD and diminishes as the impurity moves radially and/or axially. The optical rectification, the change in the refractive index, and the optical absorption were studied as functions of the energy of a photon incident on the CQD and different intensities of the magnetic field, with an impurity located at various positions. It was found that in a CDQ with an impurity inside, the effect of the variation of the intensity of the magnetic field on the optical response is much less than the effect produced by the variation of the position of the impurity. The physical reason for this behavior is that in nanostructures with impurities the Coulomb confinement is stronger than the magnetic confinement. It was also found that when the impurity is in the center of the quantum dot, the optical rectification coefficient is zero, due to the symmetry that the wave function of the impurity exhibits at this geometric point. When the impurity moves in the axial direction, the symmetry is broken and the optical rectification coefficient is different from zero, and its value increases as the impurity moves away from the center of the CQD.

A High-Power Broadband Terahertz Source Enabled by Three-Dimensional Light Confinement in a Plasmonic Nanocavity.

PubMed

Yardimci, Nezih Tolga; Cakmakyapan, Semih; Hemmati, Soroosh; Jarrahi, Mona

2017-06-23

The scope and potential uses of time-domain terahertz imaging and spectroscopy are mainly limited by the low optical-to-terahertz conversion efficiency of photoconductive terahertz sources. State-of-the-art photoconductive sources utilize short-carrier-lifetime semiconductors to recombine carriers that cannot contribute to efficient terahertz generation and cause additional thermal dissipation. Here, we present a novel photoconductive terahertz source that offers a significantly higher efficiency compared with terahertz sources fabricated on short-carrier-lifetime substrates. The key innovative feature of this source is the tight three-dimensional confinement of the optical pump beam around the terahertz nanoantennas that are used as radiating elements. This is achieved by means of a nanocavity formed by plasmonic structures and a distributed Bragg reflector. Consequently, almost all of the photo-generated carriers can be routed to the terahertz nanoantennas within a sub-picosecond time-scale. This results in a very strong, ultrafast current that drives the nanoantennas to produce broadband terahertz radiation. We experimentally demonstrate that this terahertz source can generate 4 mW pulsed terahertz radiation under an optical pump power of 720 mW over the 0.1-4 THz frequency range. This is the highest reported power level for terahertz radiation from a photoconductive terahertz source, representing more than an order of magnitude of enhancement in the optical-to-terahertz conversion efficiency compared with state-of-the-art photoconductive terahertz sources fabricated on short-carrier-lifetime substrates.

A High-Power Broadband Terahertz Source Enabled by Three-Dimensional Light Confinement in a Plasmonic Nanocavity

DOE PAGES

Yardimci, Nezih Tolga; Cakmakyapan, Semih; Hemmati, Soroosh; ...

2017-06-23

The scope and potential uses of time-domain terahertz imaging and spectroscopy are mainly limited by the low optical-to-terahertz conversion efficiency of photoconductive terahertz sources. State-of-theart photoconductive sources utilize short-carrier-lifetime semiconductors to recombine carriers that cannot contribute to efficient terahertz generation and cause additional thermal dissipation. Here, we present a novel photoconductive terahertz source that offers a significantly higher efficiency compared with terahertz sources fabricated on short-carrier-lifetime substrates. The key innovative feature of this source is the tight three-dimensional confinement of the optical pump beam around the terahertz nanoantennas that are used as radiating elements. This is achieved by means ofmore » a nanocavity formed by plasmonic structures and a distributed Bragg reflector. Consequently, almost all of the photo-generated carriers can be routed to the terahertz nanoantennas within a sub-picosecond time-scale. This results in a very strong, ultrafast current that drives the nanoantennas to produce broadband terahertz radiation. We experimentally demonstrate that this terahertz source can generate 4 mW pulsed terahertz radiation under an optical pump power of 720 mW over the 0.1–4 THz frequency range. This is the highest reported power level for terahertz radiation from a photoconductive terahertz source, representing more than an order of magnitude of enhancement in the optical-to-terahertz conversion efficiency compared with state-of-the-art photoconductive terahertz sources fabricated on shortcarrier- lifetime substrates.« less

Thin film lithium niobate electro-optic modulator with terahertz operating bandwidth.

PubMed

Mercante, Andrew J; Shi, Shouyuan; Yao, Peng; Xie, Linli; Weikle, Robert M; Prather, Dennis W

2018-05-28

We present a thin film crystal ion sliced (CIS) LiNbO 3 phase modulator that demonstrates an unprecedented measured electro-optic (EO) response up to 500 GHz. Shallow rib waveguides are utilized for guiding a single transverse electric (TE) optical mode, and Au coplanar waveguides (CPWs) support the modulating radio frequency (RF) mode. Precise index matching between the co-propagating RF and optical modes is responsible for the device's broadband response, which is estimated to extend even beyond 500 GHz. Matching the velocities of these co-propagating RF and optical modes is realized by cladding the modulator's interaction region in a thin UV15 polymer layer, which increases the RF modal index. The fabricated modulator possesses a tightly confined optical mode, which lends itself to a strong interaction between the modulating RF field and the guided optical carrier; resulting in a measured DC half-wave voltage of 3.8 V·cm -1 . The design, fabrication, and characterization of our broadband modulator is presented in this work.

Comparative study between the reflective optics and lens based system for microwave imaging system on KSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, W.; Yun, G. S.; Nam, Y.

2010-10-15

Recently, two-dimensional microwave imaging diagnostics such as the electron cyclotron emission imaging (ECEI) system and microwave imaging reflectometry (MIR) have been developed to study magnetohydrodynamics instabilities and turbulence in magnetically confined plasmas. These imaging systems utilize large optics to collect passive emission or reflected radiation. The design of this optics can be classified into two different types: reflective or refractive optical systems. For instance, an ECEI/MIR system on the TEXTOR tokamak [Park et al., Rev. Sci. Instrum. 75, 3787 (2004)] employed the reflective optics which consisted of two large mirrors, while the TEXTOR ECEI upgrade [B. Tobias et al., Rev.more » Sci. Instrum. 80, 093502 (2009)] and systems on DIII-D, ASDEX-U, and KSTAR adopted refractive systems. Each system has advantages and disadvantages in the standing wave problem and optical aberrations. In this paper, a comparative study between the two optical systems has been performed in order to design a MIR system for KSTAR.« less

Coherent multi-dimensional spectroscopy at optical frequencies in a single beam with optical readout

NASA Astrophysics Data System (ADS)

Seiler, Hélène; Palato, Samuel; Kambhampati, Patanjali

2017-09-01

Ultrafast coherent multi-dimensional spectroscopies form a powerful set of techniques to unravel complex processes, ranging from light-harvesting, chemical exchange in biological systems to many-body interactions in quantum-confined materials. Yet these spectroscopies remain complex to implement at the high frequencies of vibrational and electronic transitions, thereby limiting their widespread use. Here we demonstrate the feasibility of two-dimensional spectroscopy at optical frequencies in a single beam. Femtosecond optical pulses are spectrally broadened to a relevant bandwidth and subsequently shaped into phase coherent pulse trains. By suitably modulating the phases of the pulses within the beam, we show that it is possible to directly read out the relevant optical signals. This work shows that one needs neither complex beam geometries nor complex detection schemes in order to measure two-dimensional spectra at optical frequencies. Our setup provides not only a simplified experimental design over standard two-dimensional spectrometers but its optical readout also enables novel applications in microscopy.

Dynamics of water confined in lyotropic liquid crystals: Molecular dynamics simulations of the dynamic structure factor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantha, Sriteja; Yethiraj, Arun

2016-02-24

The properties of water under confinement are of practical and fundamental interest. Here in this work we study the properties of water in the self-assembled lyotropic phases of gemini surfactants with a focus on testing the standard analysis of quasi-elastic neutron scattering (QENS) experiments. In QENS experiments the dynamic structure factor is measured and fit to models to extract the translational diffusion constant, D T , and rotational relaxation time, τ R. We test this procedure by using simulation results for the dynamic structure factor, extracting the dynamic parameters from the fit as is typically done in experiments, and comparingmore » the values to those directly measured in the simulations. We find that the decoupling approximation, where the intermediate scattering function is assumed to be a product of translational and rotational contributions, is quite accurate. The jump-diffusion and isotropic rotation models, however, are not accurate when the degree of confinement is high. In particular, the exponential approximations for the intermediate scattering function fail for highly confined water and the values of D T and τ R can differ from the measured value by as much as a factor of two. Other models have more fit parameters, however, and with the range of energies and wave-vectors accessible to QENS, the typical analysis appears to be the best choice. In the most confined lamellar phase, the dynamics are sufficiently slow that QENS does not access a large enough time scale and neutron spin echo measurements would be a valuable technique in addition to QENS.« less

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

NASA Astrophysics Data System (ADS)

Alireza, Samavati; Othaman, Z.; K. Ghoshal, S.; K. Mustafa, M.

2015-02-01

The influences of thermal annealing on the structural and optical features of radio frequency (rf) magnetron sputtered self-assembled Ge quantum dots (QDs) on Si (100) are investigated. Preferentially oriented structures of Ge along the (220) and (111) directions together with peak shift and reduced strain (4.9% to 2.7%) due to post-annealing at 650 °C are discerned from x-ray differaction (XRD) measurement. Atomic force microscopy (AFM) images for both pre-annealed and post-annealed (650 °C) samples reveal pyramidal-shaped QDs (density ˜ 0.26× 1011 cm-2) and dome-shape morphologies with relatively high density ˜ 0.92 × 1011 cm-2, respectively. This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity. The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role. The observed red-shift ˜ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing, and is related to the effect of quantum confinement. Furthermore, the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots. Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart. An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes. A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established. Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated. Project supported by Ibnu Sina Institute for Fundamental Science Study, Universiti Teknologi Malaysia through Vote Q.J130000.2526.02H94, O5 and Postdoctoral Research Grant.

Quantum Dots and Their Multimodal Applications: A Review

PubMed Central

Bera, Debasis; Qian, Lei; Tseng, Teng-Kuan; Holloway, Paul H.

2010-01-01

Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

Nematicons and Their Electro-Optic Control: Light Localization and Signal Readdressing via Reorientation in Liquid Crystals

PubMed Central

Piccardi, Armando; Alberucci, Alessandro; Assanto, Gaetano

2013-01-01

Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely “nematicons”. Nematicons can guide other light signals and interact with inhomogeneities and other beams. Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing. Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing. PMID:24108367

Scalable photonic quantum computing assisted by quantum-dot spin in double-sided optical microcavity.

PubMed

Wei, Hai-Rui; Deng, Fu-Guo

2013-07-29

We investigate the possibility of achieving scalable photonic quantum computing by the giant optical circular birefringence induced by a quantum-dot spin in a double-sided optical microcavity as a result of cavity quantum electrodynamics. We construct a deterministic controlled-not gate on two photonic qubits by two single-photon input-output processes and the readout on an electron-medium spin confined in an optical resonant microcavity. This idea could be applied to multi-qubit gates on photonic qubits and we give the quantum circuit for a three-photon Toffoli gate. High fidelities and high efficiencies could be achieved when the side leakage to the cavity loss rate is low. It is worth pointing out that our devices work in both the strong and the weak coupling regimes.

Circular heat and momentum flux radiated by magneto-optical nanoparticles

NASA Astrophysics Data System (ADS)

Ott, A.; Ben-Abdallah, P.; Biehs, S.-A.

2018-05-01

In the present article we investigate the heat and momentum fluxes radiated by a hot magneto-optical nanoparticle in its surroundings under the action of an external magnetic field. We show that the flux lines circulate in a confined region at a nanometric distance from the particle around the axis of the magnetic field in a vortexlike configuration. Moreover we prove that the spatial orientation of these vortices (clockwise or counterclockwise) is associated with the contribution of optical resonances with topological charges m =+1 or m =-1 to the thermal emission. This work paves the way for a geometric description of heat and momentum transport in lattices of magneto-optical particles. Moreover it could have important applications in the field of energy storage as well as in thermal management at nanoscale.

Quantum optical circulator controlled by a single chirally coupled atom

NASA Astrophysics Data System (ADS)

Scheucher, Michael; Hilico, Adèle; Will, Elisa; Volz, Jürgen; Rauschenbeutel, Arno

2016-12-01

Integrated nonreciprocal optical components, which have an inherent asymmetry between their forward and backward propagation direction, are key for routing signals in photonic circuits. Here, we demonstrate a fiber-integrated quantum optical circulator operated by a single atom. Its nonreciprocal behavior arises from the chiral interaction between the atom and the transversally confined light. We demonstrate that the internal quantum state of the atom controls the operation direction of the circulator and that it features a strongly nonlinear response at the single-photon level. This enables, for example, photon number-dependent routing and novel quantum simulation protocols. Furthermore, such a circulator can in principle be prepared in a coherent superposition of its operational states and may become a key element for quantum information processing in scalable integrated optical circuits.

Large-scale atomistic simulations demonstrate dominant alloy disorder effects in GaBixAs1 -x/GaAs multiple quantum wells

NASA Astrophysics Data System (ADS)

Usman, Muhammad

2018-04-01

Bismide semiconductor materials and heterostructures are considered a promising candidate for the design and implementation of photonic, thermoelectric, photovoltaic, and spintronic devices. This work presents a detailed theoretical study of the electronic and optical properties of strongly coupled GaBixAs1 -x /GaAs multiple quantum well (MQW) structures. Based on a systematic set of large-scale atomistic tight-binding calculations, our results reveal that the impact of atomic-scale fluctuations in alloy composition is stronger than the interwell coupling effect, and plays an important role in the electronic and optical properties of the investigated MQW structures. Independent of QW geometry parameters, alloy disorder leads to a strong confinement of charge carriers, a large broadening of the hole energies, and a red-shift in the ground-state transition wavelength. Polarization-resolved optical transition strengths exhibit a striking effect of disorder, where the inhomogeneous broadening could exceed an order of magnitude for MQWs, in comparison to a factor of about 3 for single QWs. The strong influence of alloy disorder effects persists when small variations in the size and composition of MQWs typically expected in a realistic experimental environment are considered. The presented results highlight the limited scope of continuum methods and emphasize on the need for large-scale atomistic approaches to design devices with tailored functionalities based on the novel properties of bismide materials.

Effect of X-ray irradiation on the optical absorption of СdSe1-xTex nanocrystals embedded in borosilicate glass

NASA Astrophysics Data System (ADS)

Prymak, M. V.; Azhniuk, Yu. M.; Solomon, A. M.; Krasilinets, V. M.; Lopushansky, V. V.; Bodnar, I. V.; Gomonnai, A. V.; Zahn, D. R. T.

2012-07-01

The effect of X-ray irradiation on the optical absorption spectra of CdSe1-xTex nanocrystals embedded in a borosilicate matrix is studied. The observed blue shift of the absorption edge and bleaching of the confinement-related features in the spectra are related to X-ray induced negative ionization of the nanocrystals with charge transfer across the nanocrystal/matrix interface. The radiation-induced changes are observed to recover after longer post-irradiation storage at room temperature.

A Noninvasive Miniaturized-Wireless Laser-Doppler Fiber-Optic Sensor for Understanding Distal Fingertip Injuries in Astronauts

NASA Technical Reports Server (NTRS)

Ansari, Rafat R.; Jones, Jeffrey A.; Pollonini, Luca; Rodriquez, Mikael; Opperman, Roedolph; Hochstein, Jason

2009-01-01

During extra-vehicular activities (EVAs) or spacewalks astronauts over use their fingertips under pressure inside the confined spaces of gloves/space suits. The repetitive hand motion is a probable cause for discomfort and injuries to the fingertips. We describe a new wireless fiber-optic probe that can be integrated inside the astronaut glove for noninvasive blood perfusion measurements in distal fingertips. In this preliminary study, we present blood perfusion measurements while performing hand-grip exercises simulating the use of space tools.

Study of electron-related intersubband optical properties in three coupled quantum wells wires with triangular transversal section

NASA Astrophysics Data System (ADS)

Tiutiunnyk, A.; Tulupenko, V.; Akimov, V.; Demediuk, R.; Morales, A. L.; Mora-Ramos, M. E.; Radu, A.; Duque, C. A.

2015-11-01

This work concerns theoretical study of confined electrons in a low-dimensional structure consisting of three coupled triangular GaAs/AlxGa1-xAs quantum wires. Calculations have been made in the effective mass and parabolic band approximations. In the calculations a diagonalization method to find the eigenfunctions and eigenvalues of the Hamiltonian was used. A comparative analysis of linear and nonlinear optical absorption coefficients and the relative change in the refractive index was made, which is tied to the intersubband electron transitions.

Creation of long-term coherent optical memory via controlled nonlinear interactions in Bose-Einstein condensates.

PubMed

Zhang, Rui; Garner, Sean R; Hau, Lene Vestergaard

2009-12-04

A Bose-Einstein condensate confined in an optical dipole trap is used to generate long-term coherent memory for light, and storage times of more than 1 s are observed. Phase coherence of the condensate as well as controlled manipulations of elastic and inelastic atomic scattering processes are utilized to increase the storage fidelity by several orders of magnitude over previous schemes. The results have important applications for creation of long-distance quantum networks and for generation of entangled states of light and matter.

The tug-of-war behavior of a Brownian particle in an asymmetric double optical trap with stochastic fluctuations

NASA Astrophysics Data System (ADS)

Long, Fei; Zhu, Jia-Pei

2018-07-01

A Brownian particle optically trapped in an asymmetric double potential surrounded by a thermal bath was simulated. Under the cooperative action of the resultant deterministic optical force and the stochastic fluctuations of the thermal bath, the confined particle undergoes Kramers transition, and oscillates between the two traps with a probability of trap occupancy that is asymmetrically distributed about the midpoint. The simulation results obtained at different temperatures indicate that the oscillation behavior of the particle can be treated as the result of a tug-of-war game played between the resultant deterministic force and the random force. We also employ a bistable model to explain the observed phenomena.

Pulse shaping system

DOEpatents

Skeldon, Mark D.; Letzring, Samuel A.

1999-03-23

Temporally shaped electrical waveform generation provides electrical waveforms suitable for driving an electro-optic modulator (EOM) which produces temporally shaped optical laser pulses for inertial confinement fusion (ICF) research. The temporally shaped electrical waveform generation is carried out with aperture coupled transmission lines having an input transmission line and an aperture coupled output transmission line, along which input and output pulses propagate in opposite directions. The output electrical waveforms are shaped principally due to the selection of coupling aperture width, in a direction transverse to the lines, which varies along the length of the line. Specific electrical waveforms, which may be high voltage (up to kilovolt range), are produced and applied to the EOM to produce specifically shaped optical laser pulses.

Pulse shaping system

DOEpatents

Skeldon, M.D.; Letzring, S.A.

1999-03-23

Temporally shaped electrical waveform generation provides electrical waveforms suitable for driving an electro-optic modulator (EOM) which produces temporally shaped optical laser pulses for inertial confinement fusion (ICF) research. The temporally shaped electrical waveform generation is carried out with aperture coupled transmission lines having an input transmission line and an aperture coupled output transmission line, along which input and output pulses propagate in opposite directions. The output electrical waveforms are shaped principally due to the selection of coupling aperture width, in a direction transverse to the lines, which varies along the length of the line. Specific electrical waveforms, which may be high voltage (up to kilovolt range), are produced and applied to the EOM to produce specifically shaped optical laser pulses. 8 figs.

VCSELs for datacom applications

NASA Astrophysics Data System (ADS)

Wipiejewski, Torsten; Wolf, Hans-Dieter; Korte, Lutz; Huber, Wolfgang; Kristen, Guenter; Hoyler, Charlotte; Hedrich, Harald; Kleinbub, Oliver; Albrecht, Tony; Mueller, Juergen; Orth, Andreas; Spika, Zeljko; Lutgen, Stephan; Pflaeging, Hartwig; Harrasser, Joerg; Droegemueller, Karsten; Plickert, Volker; Kuhl, Detlef; Blank, Juergen; Pietsch, Doris; Stange, Herwig; Karstensen, Holger

1999-04-01

The use of oxide confined VCSELs in datacom applications is demonstrated. The devices exhibit low threshold currents of approximately 3 mA and low electrical series resistance of about 50 (Omega) . The emission wavelength is in the 850 nm range. Life times of the devices are several million hours under normal operating conditions. VCSEL arrays are employed in a high performance parallel optical link called PAROLITM. This optical ink provides 12 parallel channels with a total bandwidth exceeding 12 Gbit/s. The VCSELs optimized for the parallel optical link show excellent threshold current uniformity between channels of < 50 (mu) A. The array life time drops compared to a single device, but is still larger than 1 million hours.

Measuring the charge density of a tapered optical fiber using trapped microparticles.

PubMed

Kamitani, Kazuhiko; Muranaka, Takuya; Takashima, Hideaki; Fujiwara, Masazumi; Tanaka, Utako; Takeuchi, Shigeki; Urabe, Shinji

2016-03-07

We report the measurements of charge density of tapered optical fibers using charged particles confined in a linear Paul trap at ambient pressure. A tapered optical fiber is placed across the trap axis at a right angle, and polystyrene microparticles are trapped along the trap axis. The distance between the equilibrium position of a positively charged particle and the tapered fiber is used to estimate the amount of charge per unit length of the fiber without knowing the amount of charge of the trapped particle. The charge per unit length of a tapered fiber with a diameter of 1.6 μm was measured to be 2-1+3×10 -11 C/m.

Whispering gallery mode laser based on cholesteric liquid crystal microdroplets as temperature sensor

NASA Astrophysics Data System (ADS)

Zhao, Liyuan; Wang, Yan; Yuan, Yonggui; Liu, Yongjun; Liu, Shuangqiang; Sun, Weimin; Yang, Jun; Li, Hanyang

2017-11-01

We developed a tunable whispering gallery mode (WGM) microlaser based on dye-doped cholesteric liquid crystal (CLC) microdroplets with controllable size in an aqueous environment. An individual dye-doped CLC microdroplet confined at the tip of a microcapillary was optically pumped via a tapered optical fiber tip positioned within its vicinity. Numerical simulations and various spectral characteristics verify the WGM resonance of the lasing in microdroplets. Thermal tuning of the lasing modes is realized due to the thermo-optic effect of CLC. The proposed CLC microdroplet-based WGM resonator was applied as a temperature sensor and exhibited maximum temperature sensitivity up to 0.96 nm/°C.

Surface plasmons and Bloch surface waves: Towards optimized ultra-sensitive optical sensors

DOE PAGES

Lereu, Aude L.; Zerrad, M.; Passian, Ali; ...

2017-07-07

In photonics, the field concentration and enhancement have been major objectives for achieving size reduction and device integration. Plasmonics offers resonant field confinement and enhancement, but ultra-sharp optical resonances in all-dielectric multi-layer thin films are emerging as a powerful contestant. Thus, applications capitalizing upon stronger and sharper optical resonances and larger field enhancements could be faced with a choice for the superior platform. Here in this paper, we present a comparison between plasmonic and dielectric multi-layer thin films for their resonance merits. We show that the remarkable characteristics of the resonance behavior of optimized dielectric multi-layers can outweigh those ofmore » their metallic counterpart.« less

Optical properties of in-vitro biomineralised silica.

PubMed

Polini, Alessandro; Pagliara, Stefano; Camposeo, Andrea; Cingolani, Roberto; Wang, Xiaohong; Schröder, Heinz C; Müller, Werner E G; Pisignano, Dario

2012-01-01

Silicon is the second most common element on the Earth's crust and its oxide (SiO(2)) the most abundant mineral. Silica and silicates are widely used in medicine and industry as well as in micro- and nano-optics and electronics. However, the fabrication of glass fibres and components requires high temperature and non-physiological conditions, in contrast to biosilica structures in animals and plants. Here, we show for the first time the use of recombinant silicatein-α, the most abundant subunit of sponge proteins catalyzing biosilicification reactions, to direct the formation of optical waveguides in-vitro through soft microlithography. The artificial biosilica fibres mimic the natural sponge spicules, exhibiting refractive index values suitable for confinement of light within waveguides, with optical losses in the range of 5-10 cm(-1), suitable for application in lab-on-chips systems. This method extends biosilicification to the controlled fabrication of optical components by physiological processing conditions, hardly addressed by conventional technologies.

Acousto-optical interaction of surface acoustic and optical waves in a two-dimensional phoxonic crystal hetero-structure cavity.

PubMed

Ma, Tian-Xue; Zou, Kui; Wang, Yue-Sheng; Zhang, Chuanzeng; Su, Xiao-Xing

2014-11-17

Phoxonic crystal is a promising material for manipulating sound and light simultaneously. In this paper, we theoretically demonstrate the propagation of acoustic and optical waves along the truncated surface of a two-dimensional square-latticed phoxonic crystal. Further, a phoxonic crystal hetero-structure cavity is proposed, which can simultaneously confine surface acoustic and optical waves. The interface motion and photoelastic effects are taken into account in the acousto-optical coupling. The results show obvious shifts in eigenfrequencies of the photonic cavity modes induced by different phononic cavity modes. The symmetry of the phononic cavity modes plays a more important role in the single-phonon exchange process than in the case of the multi-phonon exchange. Under the same deformation, the frequency shift of the photonic transverse electric mode is larger than that of the transverse magnetic mode.

Comparative optical study of epitaxial InGaAs quantum rods grown with As{sub 2} and As{sub 4} sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nedzinskas, Ramūnas; Čechavičius, Bronislovas; Kavaliauskas, Julius

2013-12-04

Photoreflectance and photoluminescence (PL) spectroscopies are used to examine the optical properties and electronic structure of InGaAs quantum rods (QRs), embedded within InGaAs quantum well (QW). The nanostructures studied were grown by molecular beam epitaxy using As{sub 2} or As{sub 4} sources. The impact of As source on spectral features associated with interband optical transitions in the QRs and the surrounding QW are demonstrated. A red shift of the QR- and a blue shift of the QW-related optical transitions, along with a significant increase in PL intensity, have been observed if an As{sub 4} source is used. The changes inmore » optical properties are attributed mainly to carrier confinement effects caused by variation of In content contrast between the QR material and the surrounding well.« less

Effective bichromatic potential for ultra-high Q-factor photonic crystal slab cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alpeggiani, Filippo, E-mail: filippo.alpeggiani01@ateneopv.it; Andreani, Lucio Claudio; Gerace, Dario

2015-12-28

We introduce a confinement mechanism in photonic crystal slab cavities, which relies on the superposition of two incommensurate one-dimensional lattices in a line-defect waveguide. It is shown that the resulting photonic profile realizes an effective quasi-periodic bichromatic potential for the electromagnetic field confinement yielding extremely high quality (Q) factor nanocavities, while simultaneously keeping the mode volume close to the diffraction limit. We apply these concepts to pillar- and hole-based photonic crystal slab cavities, respectively, and a Q-factor improvement by over an order of magnitude is shown over existing designs, especially in pillar-based structures. Thanks to the generality and easy adaptationmore » of such confinement mechanism to a broad class of cavity designs and photonic lattices, this work opens interesting routes for applications where enhanced light–matter interaction in photonic crystal structures is required.« less

High quality factor GaAs microcavity with buried bullseye defects

NASA Astrophysics Data System (ADS)

Winkler, K.; Gregersen, N.; Häyrynen, T.; Bradel, B.; Schade, A.; Emmerling, M.; Kamp, M.; Höfling, S.; Schneider, C.

2018-05-01

The development of high quality factor solid-state microcavities with low mode volumes has paved the way towards on-chip cavity quantum electrodynamics experiments and the development of high-performance nanophotonic devices. Here, we report on the implementation of a new kind of solid-state vertical microcavity, which allows for confinement of the electromagnetic field in the lateral direction without deep etching. The confinement originates from a local elongation of the cavity layer imprinted in a shallow etch and epitaxial overgrowth technique. We show that it is possible to improve the quality factor of such microcavities by a specific in-plane bullseye geometry consisting of a set of concentric rings with subwavelength dimensions. This design results in a smooth effective lateral photonic potential and therefore in a reduction of lateral scattering losses, which makes it highly appealing for experiments in the framework of exciton-polariton physics demanding tight spatial confinement.

Structural characteristics of hydrated protons in the conductive channels: effects of confinement and fluorination studied by molecular dynamics simulation.

PubMed

Zhang, Ning; Song, Yuechun; Ruan, Xuehua; Yan, Xiaoming; Liu, Zhao; Shen, Zhuanglin; Wu, Xuemei; He, Gaohong

2016-09-21

The relationship between the proton conductive channel and the hydrated proton structure is of significant importance for understanding the deformed hydrogen bonding network of the confined protons which matches the nanochannel. In general, the structure of hydrated protons in the nanochannel of the proton exchange membrane is affected by several factors. To investigate the independent effect of each factor, it is necessary to eliminate the interference of other factors. In this paper, a one-dimensional carbon nanotube decorated with fluorine was built to investigate the independent effects of nanoscale confinement and fluorination on the structural properties of hydrated protons in the nanochannel using classical molecular dynamics simulation. In order to characterize the structure of hydrated protons confined in the channel, the hydrogen bonding interaction between water and the hydrated protons has been studied according to suitable hydrogen bond criteria. The hydrogen bond criteria were proposed based on the radial distribution function, angle distribution and pair-potential energy distribution. It was found that fluorination leads to an ordered hydrogen bonding structure of the hydrated protons near the channel surface, and confinement weakens the formation of the bifurcated hydrogen bonds in the radial direction. Besides, fluorination lowers the free energy barrier of hydronium along the nanochannel, but slightly increases the barrier for water. This leads to disintegration of the sequential hydrogen bond network in the fluorinated CNTs with small size. In the fluorinated CNTs with large diameter, the lower degree of confinement produces a spiral-like sequential hydrogen bond network with few bifurcated hydrogen bonds in the central region. This structure might promote unidirectional proton transfer along the channel without random movement. This study provides the cooperative effect of confinement dimension and fluorination on the structure and hydrogen bonding of the slightly acidic water in the nanoscale channel.

General approach to polymer chains confined by interacting boundaries

NASA Astrophysics Data System (ADS)

Freed, Karl F.; Dudowicz, Jacek; Stukalin, Evgeny B.; Douglas, Jack F.

2010-09-01

Polymer chains, confined to cavities or polymer layers with dimensions less than the chain radius of gyration, appear in many phenomena, such as gel chromatography, rubber elasticity, viscolelasticity of high molar mass polymer melts, the translocation of polymers through nanopores and nanotubes, polymer adsorption, etc. Thus, the description of how the constraints alter polymer thermodynamic properties is a recurrent theoretical problem. A realistic treatment requires the incorporation of impenetrable interacting (attractive or repulsive) boundaries, a process that introduces significant mathematical complications. The standard approach involves developing the generalized diffusion equation description of the interaction of flexible polymers with impenetrable confining surfaces into a discrete eigenfunction expansion, where the solutions are normally truncated at the first mode (the "ground state dominance" approximation). This approximation is mathematically well justified under conditions of strong confinement, i.e., a confinement length scale much smaller than the chain radius of gyration, but becomes unreliable when the polymers are confined to dimensions comparable to their typically nanoscale size. We extend a general approach to describe polymers under conditions of weak to moderate confinement and apply this semianalytic method specifically to determine the thermodynamics and static structure factor for a flexible polymer confined between impenetrable interacting parallel plate boundaries. The method is first illustrated by analyzing chain partitioning between a pore and a large external reservoir, a model system with application to chromatography. Improved agreement is found for the partition coefficients of a polymer chain in the pore geometry. An expression is derived for the structure factor S(k ) in a slit geometry to assist in more accurately estimating chain dimensions from scattering measurements for thin polymer films.

Summary and evaluation of hydraulic property data available for the Hanford Site upper basalt confined aquifer system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spane, F.A. Jr.; Vermeul, V.R.

Pacific Northwest Laboratory, as part of the Hanford Site Ground-Water Surveillance Project, examines the potential for offsite migration of contamination within the upper basalt confined aquifer system. For the past 40 years, hydrologic testing of the upper basalt confined aquifer has been conducted by a number of Hanford Site programs. Hydraulic property estimates are important for evaluating aquifer flow characteristics (i.e., ground-water flow patterns, flow velocity, transport travel time). Presented are the first comprehensive Hanford Site-wide summary of hydraulic properties for the upper basalt confined aquifer system (i.e., the upper Saddle Mountains Basalt). Available hydrologic test data were reevaluated usingmore » recently developed diagnostic test analysis methods. A comparison of calculated transmissivity estimates indicates that, for most test results, a general correspondence within a factor of two between reanalysis and previously reported test values was obtained. For a majority of the tests, previously reported values are greater than reanalysis estimates. This overestimation is attributed to a number of factors, including, in many cases, a misapplication of nonleaky confined aquifer analysis methods in previous analysis reports to tests that exhibit leaky confined aquifer response behavior. Results of the test analyses indicate a similar range for transmissivity values for the various hydro-geologic units making up the upper basalt confined aquifer. Approximately 90% of the calculated transmissivity values for upper basalt confined aquifer hydrogeologic units occur within the range of 10{sup 0} to 10{sup 2} m{sup 2}/d, with 65% of the calculated estimate values occurring between 10{sup 1} to 10{sup 2} m{sup 2}d. These summary findings are consistent with the general range of values previously reported for basalt interflow contact zones and sedimentary interbeds within the Saddle Mountains Basalt.« less

Interband emission energy in a dilute nitride quaternary semiconductor quantum dot for longer wavelength applications

NASA Astrophysics Data System (ADS)

Mageshwari, P. Uma; Peter, A. John; Lee, Chang Woo; Duque, C. A.

2016-07-01

Excitonic properties are studied in a strained Ga1-xInxNyAs1-y/GaAs cylindrical quantum dot. The optimum condition for the desired band alignment for emitting wavelength 1.55 μm is investigated using band anticrossing model and the model solid theory. The band gap and the band discontinuities of a Ga1-xInxNyAs1-y/GaAs quantum dot on GaAs are computed with the geometrical confinement effect. The binding energy of the exciton, the oscillator strength and its radiative life time for the optimum condition are found taking into account the spatial confinement effect. The effects of geometrical confinement and the nitrogen incorporation on the interband emission energy are brought out. The result shows that the desired band alignment for emitting wavelength 1.55 μm is achieved for the inclusion of alloy contents, y=0.0554% and x=0.339% in Ga1-xInxNyAs1-y/GaAs quantum dot. And the incorporation of nitrogen and indium shows the red-shift and the geometrical confinement shows the blue-shift. And it can be applied for fibre optical communication networks.

Recovering Galaxy Rotation Speeds from Irregular Emission Profiles

NASA Astrophysics Data System (ADS)

Lavezzi, T. E.; Dickey, J. M.

1997-12-01

We simulate extragalactic emission spectra in order to determine whether the spectra of molecular gas measure the full velocity of disk rotation, despite their confined gas distributions. We present synthetic emission profiles to determine the effects on profile shapes due to factors such as telescope beam size. gas distribution, opacity, and pointing errors. We find that linewidths cease to be useful if the telescope beam resolves the solid body rotation region of the galaxy disk, or if the disk is very optically thick. Opacity is more problematic for edge-on galaxies; at lower optical depths, we find that very often a trough is created in the center of the emission line. We establish guidelines for rejecting spectra as unreliable disk-velocity indicators, and determine what corrections to the measured line widths at 20% and 50% of the peak intensity are best to recover twice the disk rotation velocity. Following the procedure of Bicay & Giovanelli (1986, AJ, 91, 705) we find that the 50% of peak intensity threshold for measuring linewidths (W50p, or FWHM) is the most robust, yielding the smallest measurement errors as a function of signal to noise, and requires the smallest turbulence corrections.

Structural, optical, electrochemical and photovoltaic studies of spider web like Silver Indium Diselenide Quantum dots synthesized by ligand mediated colloidal sol-gel approach

NASA Astrophysics Data System (ADS)

Adhikari, Tham; Pathak, Dinesh; Wagner, Tomas; Jambor, Roman; Jabeen, Uzma; Aamir, Muhammad; Nunzi, Jean-Michel

2017-11-01

Silver indium diselenide quantum dots were successively synthesized by colloidal sol-gel method by chelating with organic ligand oleylamine (OLA). The particle size was studied by transmission electron microscopy (TEM) and the size was found about 10 nm. X-ray diffraction (XRD) was used to study crystalline structure of the nanocrystals. The grain size and morphology were further studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elemental composition was studied by X-ray photon electron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDAX). The capping property of OLA in nanocrystal was also demonstrated by Fourier Transform Infrared spectroscopy (FTIR). The band gap was calculated from both cyclic voltammetry and optical absorption and suggest quantum confinement. The solution processed bilayer thin film solar cells were fabricated with n-type Zinc oxide using doctor blading/spin coating method and their photovoltaic performance was studied. The best device sintered at 450 °C showed an efficiency 0.75% with current density of 4.54 mAcm-2, open-circuit voltage 0.44 V and fill factor 39.4%.

Remote Sensing of Global Fire Patterns, Aerosol Optical Thickness, and Carbon Monoxide During April 1994

NASA Technical Reports Server (NTRS)

Christopher, Sundar A.; Wang, Min; Klich, Donna V.; Welch, Ronald M.; Nolf, Scott; Connors, Vickie S.

1997-01-01

Fires play a crucial role in several ecosystems. They are routinely used to burn forests in order to accommodate the needs of the expanding population, clear land for agricultural purposes, eliminate weeds and pests, regenerate nutrients in grazing and crop lands and produce energy for cooking and heating purposes. Most of the fires on earth are related to biomass burning in the tropics, although they are not confined to these latitudes. The boreal and tundra regions also experience fires on a yearly basis. The current study examines global fire patterns, Aerosol Optical Thickness (AOT) and carbon monoxide concentrations during April 9-19, 1994. Recently, global Advanced Very High Resolution Radiometer (AVHRR) data at nadir ground spatial resolution of 1 km are made available through the NASA/NOAA Pathfinder project. These data from April 9-19, 1994 are used to map fires over the earth. In summary, our analysis shows that fires from biomass burning appear to be the dominant factor for increased tropospheric CO concentrations as measured by the MAPS. The vertical transport of CO by convective activities, along with horizontal transport due to the prevailing winds, are responsible for the observed spatial distribution of CO.

Confined high-pressure chemical deposition of hydrogenated amorphous silicon.

PubMed

Baril, Neil F; He, Rongrui; Day, Todd D; Sparks, Justin R; Keshavarzi, Banafsheh; Krishnamurthi, Mahesh; Borhan, Ali; Gopalan, Venkatraman; Peacock, Anna C; Healy, Noel; Sazio, Pier J A; Badding, John V

2012-01-11

Hydrogenated amorphous silicon (a-Si:H) is one of the most technologically important semiconductors. The challenge in producing it from SiH(4) precursor is to overcome a significant kinetic barrier to decomposition at a low enough temperature to allow for hydrogen incorporation into a deposited film. The use of high precursor concentrations is one possible means to increase reaction rates at low enough temperatures, but in conventional reactors such an approach produces large numbers of homogeneously nucleated particles in the gas phase, rather than the desired heterogeneous deposition on a surface. We report that deposition in confined micro-/nanoreactors overcomes this difficulty, allowing for the use of silane concentrations many orders of magnitude higher than conventionally employed while still realizing well-developed films. a-Si:H micro-/nanowires can be deposited in this way in extreme aspect ratio, small-diameter optical fiber capillary templates. The semiconductor materials deposited have ~0.5 atom% hydrogen with passivated dangling bonds and good electronic properties. They should be suitable for a wide range of photonic and electronic applications such as nonlinear optical fibers and solar cells. © 2011 American Chemical Society

Silicon carbide transparent chips for compact atomic sensors

NASA Astrophysics Data System (ADS)

Huet, L.; Ammar, M.; Morvan, E.; Sarazin, N.; Pocholle, J.-P.; Reichel, J.; Guerlin, C.; Schwartz, S.

2017-11-01

Atom chips [1] are an efficient tool for trapping, cooling and manipulating cold atoms, which could open the way to a new generation of compact atomic sensors addressing space applications. This is in particular due to the fact that they can achieve strong magnetic field gradients near the chip surface, hence strong atomic confinement at moderate electrical power. However, this advantage usually comes at the price of reducing the optical access to the atoms, which are confined very close to the chip surface. We will report at the conference experimental investigations showing how these limits could be pushed farther by using an atom chip made of a gold microcircuit deposited on a single-crystal Silicon Carbide (SiC) substrate [2]. With a band gap energy value of about 3.2 eV at room temperature, the latter material is transparent at 780nm, potentially restoring quasi full optical access to the atoms. Moreover, it combines a very high electrical resistivity with a very high thermal conductivity, making it a good candidate for supporting wires with large currents without the need of any additional electrical insulation layer [3].

An integrated platform for surface forces measurements and fluorescence correlation spectroscopy

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Ashis; Zhao, Jiang; Bae, Sung Chul; Granick, Steve

2003-06-01

We describe an apparatus to measure the diffusion of dilute fluorophores in molecularly thin liquid films within a surface forces apparatus (SFA). The design is a significant modification of the traditional SFA in that it allows one to combine nanorheology with the single-molecule sensitive technique of fluorescence correlation spectroscopy. The primary enabling idea was to place a miniaturized SFA onto the stage of an optical microscope equipped with a long working distance objective and illuminated by a femtosecond laser. A secondary enabling idea was that the silver coating on the backside of mica, normally used in the traditional SFA design for interferometric measurements of the film thickness, was replaced by multilayer dielectric coatings that allowed simultaneous interferometry and fluorescence measurements in different regions of the optical spectrum. To illustrate the utility of this instrument, we contrast the translational diffusion of rhodamine dye molecules (in the solvent, 1,2-propane diol), in the unconfined bulk state and confined between mica sheets to the thickness 2.5 nm. The diffusion coefficient is found to decrease by 2 orders of magnitude under confinement.

Assessing the performance of a motion tracking system based on optical joint transform correlation

NASA Astrophysics Data System (ADS)

Elbouz, M.; Alfalou, A.; Brosseau, C.; Ben Haj Yahia, N.; Alam, M. S.

2015-08-01

We present an optimized system specially designed for the tracking and recognition of moving subjects in a confined environment (such as an elderly remaining at home). In the first step of our study, we use a VanderLugt correlator (VLC) with an adapted pre-processing treatment of the input plane and a postprocessing of the correlation plane via a nonlinear function allowing us to make a robust decision. The second step is based on an optical joint transform correlation (JTC)-based system (NZ-NL-correlation JTC) for achieving improved detection and tracking of moving persons in a confined space. The proposed system has been found to have significantly superior discrimination and robustness capabilities allowing to detect an unknown target in an input scene and to determine the target's trajectory when this target is in motion. This system offers robust tracking performance of a moving target in several scenarios, such as rotational variation of input faces. Test results obtained using various real life video sequences show that the proposed system is particularly suitable for real-time detection and tracking of moving objects.

Continuous plasma laser. [method and apparatus for producing intense, coherent, monochromatic light from low temperature plasma

NASA Technical Reports Server (NTRS)

Libby, W. F.; Jensen, C. A.; Wood, L. L. (Inventor)

1977-01-01

The apparatus includes a housing for confining a gas at subatmospheric pressure and including a set of reflectors defining an optical cavity. At least one anode and cathode are positioned within the gas. First control means control the voltage applied to the anode and second control means independently control the temperature of the cathode. The pressure of the gas is controlled by a third control means. An intense monochromatic output is achieved by confining the gas in the housing at a controlled pre-determined reduced pressure, independently controlling the temperature of the electron emitting cathode and applying predetermined controlled low voltage to the anode.

Simulations of inertial confinement fusion driven by a novel synchrotron-radiation-based x-ray igniter

NASA Astrophysics Data System (ADS)

Shlyaptsev, Vyacheslav N.; Tatchyn, Roman O.

2004-01-01

The advantages and challenges of using a powerful x-ray source for the fast ignition of compressed Inertial Confinement Fusion (ICF) targets have been considered. The requirements for such a source together with the optics to focus the x-rays onto compressed DT cores lead to a conceptual design based on Energy Recovery Linacs (ERLs) and long wigglers to produce x-ray pulses with the appropriate phase space properties. A comparative assessment of the parameters of the igniter system indicates that the technologies for building it, although expensive, are physically achievable. Our x-ray fast ignition (XFI) scheme requires substantially smaller energy for the initiation of nuclear fusion reactions than other methods.

Linear and ultrafast nonlinear plasmonics of single nano-objects

NASA Astrophysics Data System (ADS)

Crut, Aurélien; Maioli, Paolo; Vallée, Fabrice; Del Fatti, Natalia

2017-03-01

Single-particle optical investigations have greatly improved our understanding of the fundamental properties of nano-objects, avoiding the spurious inhomogeneous effects that affect ensemble experiments. Correlation with high-resolution imaging techniques providing morphological information (e.g. electron microscopy) allows a quantitative interpretation of the optical measurements by means of analytical models and numerical simulations. In this topical review, we first briefly recall the principles underlying some of the most commonly used single-particle optical techniques: near-field, dark-field, spatial modulation and photothermal microscopies/spectroscopies. We then focus on the quantitative investigation of the surface plasmon resonance (SPR) of metallic nano-objects using linear and ultrafast optical techniques. While measured SPR positions and spectral areas are found in good agreement with predictions based on Maxwell’s equations, SPR widths are strongly influenced by quantum confinement (or, from a classical standpoint, surface-induced electron scattering) and, for small nano-objects, cannot be reproduced using the dielectric functions of bulk materials. Linear measurements on single nano-objects (silver nanospheres and gold nanorods) allow a quantification of the size and geometry dependences of these effects in confined metals. Addressing the ultrafast response of an individual nano-object is also a powerful tool to elucidate the physical mechanisms at the origin of their optical nonlinearities, and their electronic, vibrational and thermal relaxation processes. Experimental investigations of the dynamical response of gold nanorods are shown to be quantitatively modeled in terms of modifications of the metal dielectric function enhanced by plasmonic effects. Ultrafast spectroscopy can also be exploited to unveil hidden physical properties of more complex nanosystems. In this context, two-color femtosecond pump-probe experiments performed on individual bimetallic heterodimers are discussed in the last part of the review, demonstrating the existence of Fano interferences in the optical absorption of a gold nanoparticle under the influence of a nearby silver one.

["Tied down"--the process of becoming bedridden through gradual local confinement].

PubMed

Zegelin, Angelika

2005-10-01

To be bedridden is a common phenomenon in nursing. However, there is no solid base of knowledge on reasons, types, development of and coping with this situation. The concept of being bedridden is applied in an arbitrary manner and the state of being bedridden is far from being clearly defined. A literature review revealed that only pathophysiological effects of this state are sufficiently explained. The aim of this study was to gain knowledge of the development of being confined to bed. Thirty-two interviews with elderly, bedridden people (nineteen women, thirteen men) were conducted. They were asked about their perspective on and their experience of the development of being confined to bed. Half of the interviewees lived in a nursing home, the others were cared for at home. Data collection and analysis were performed by using a Grounded Theory approach as developed by Strauss and Corbin. "Gradual local fixation" was identified as the core category. Becoming bedridden is a slow process by which the person is increasingly confined to one location. This development is related to an increasing need for support and to negative consequences such as a pathology of immobility, narrowing of interests, and loss of time. These consequences again are responsible for a downward spiral development. This study reveals phases of development and a range of factors influencing them. Many of these factors arise from the person and his/her interactional behaviour in the circumstances, other influences are structural factors such as external pressure caused by time constraints of professional nursing services or unfavourable arrangements of furniture. A lot of factors of being confined to bed are changeable. Long periods of being bedridden can be prevented in many cases, if early warning signs are being recognized and preventive measures are taken in time.

Designer Disordered Complex Media: Hyperuniform Photonic and Phononic Band Gap Materials

NASA Astrophysics Data System (ADS)

Amoah, Timothy

In this thesis we investigate designer disordered complex media for photonics and phononics applications. Initially we focus on the photonic properties and we analyse hyperuniform disordered structures (HUDS) using numerical simulations. Photonic HUDS are a new class of photonic solids, which display large, isotropic photonic band gaps (PBG) comparable in size to the ones found in photonic crystals (PC). We review their complex interference properties, including the origin of PBGs and potential applications. HUDS combine advantages of both isotropy due to disorder (absence of long-range order) and controlled scattering properties from uniform local topology due to hyperuniformity (constrained disorder). The existence of large band gaps in HUDS contradicts the longstanding intuition that Bragg scattering and long-range translational order is required in PBG formation, and demonstrates that interactions between Mie-like local resonances and multiple scattering can induce on their own PBGs. The discussion is extended to finite height effects of planar architectures such as pseudo-band-gaps in photonic slabs as well as the vertical confinement in the presence of disorder. The particular case of a silicon-on-insulator compatible hyperuniform disordered network structure is considered for TE polarised light. We address technologically realisable designs of HUDS including localisation of light in point-defect-like optical cavities and the guiding of light in freeform PC waveguide analogues. Using finite-difference time domain and band structure computer simulations, we show that it is possible to construct optical cavities in planar hyperuniform disordered solids with isotropic band gaps that effciently confine TE polarised radiation. We thus demonstrate that HUDS are a promising general-purpose design platform for integrated optical micro-circuitry. After analysing HUDS for photonic applications we investigate them in the context of elastic waves towards phononics applications. We demonstrate the first phononic band gaps (PnBG) for HUDS. We find that PnBGs in phononic HUDS can confine and guide elastic waves similar to photonic HUDS for EM radiation.

Microshell-tipped optical fibers as sensors of high-pressure pulses in adverse environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benjamin, R.F.; Mayer, F.J.; Maynard, R.L.

1984-01-01

An optical-fiber sensor for detecting the arrival of strong pressure pulses was developed. The sensor consists of an optical fiber, tipped with a gas-filled microballoon. They have been used successfully in adverse environments including explosives, ballistics and electromagnetic pulses (EMP). The sensor produces a bright optical pulse caused by the rapid shock-heating of a gas, typically argon or xenon, which is confined in the spherical glass or plastic microballoon. The light pulse is transmitted via the optical fiber to a photo detector, usually a streak camera or photomultiplier tube. The microballoon optical sensor (called an optical pin by analogy tomore » standard electrical pins), was originally developed for diagnosing an explosive, pulsed-power generator. Optical pins are required due to the EMP. The optical pins are economical arrival-time indicators because many channels can be recorded by one streak camera. The generator tests and related experiments, involving projectile velocities and detonation velocities of several kilometers per sec have demonstrated the usefulness of the sensors in explosives and ballistics applications. The technical and cost advantages of this optical pin make it potentially useful for many electromagnetic, explosive, and ballistics applications.« less

Long-Range Repulsion Between Spatially Confined van der Waals Dimers

NASA Astrophysics Data System (ADS)

Sadhukhan, Mainak; Tkatchenko, Alexandre

2017-05-01

It is an undisputed textbook fact that nonretarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial dimensionality. The universality of vdW attraction is attributed to the dipolar coupling between fluctuating electron charge densities. Here, we demonstrate that the long-range interaction between spatially confined vdW dimers becomes repulsive when accounting for the full Coulomb interaction between charge fluctuations. Our analytic results are obtained by using the Coulomb potential as a perturbation over dipole-correlated states for two quantum harmonic oscillators embedded in spaces with reduced dimensionality; however, the long-range repulsion is expected to be a general phenomenon for spatially confined quantum systems. We suggest optical experiments to test our predictions, analyze their relevance in the context of intermolecular interactions in nanoscale environments, and rationalize the recent observation of anomalously strong screening of the lateral vdW interactions between aromatic hydrocarbons adsorbed on metal surfaces.

Decoupling the effects of confinement and passivation on semiconductor quantum dots.

PubMed

Rudd, Roya; Hall, Colin; Murphy, Peter J; Reece, Peter J; Charrault, Eric; Evans, Drew

2016-07-20

Semiconductor (SC) quantum dots (QDs) have recently been fabricated by both chemical and plasma techniques for specific absorption and emission of light. Their optical properties are governed by the size of the QD and the chemistry of any passivation at their surface. Here, we decouple the effects of confinement and passivation by utilising DC magnetron sputtering to fabricate SC QDs in a perfluorinated polyether oil. Very high band gaps are observed for fluorinated QDs with increasing levels of quantum confinement (from 4.2 to 4.6 eV for Si, and 2.5 to 3 eV for Ge), with a shift down to 3.4 eV for Si when oxygen is introduced to the passivation layer. In contrast, the fluorinated Si QDs display a constant UV photoluminescence (3.8 eV) irrespective of size. This ability to tune the size and passivation independently opens a new opportunity to extending the use of simple semiconductor QDs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Guohua; Czaplewski, David A.; Lenferink, Erik J.

Three-dimensional confinement allows semiconductor quantum dots to exhibit size-tunable electronic and optical properties that enable a wide range of opto-electronic applications from displays, solar cells and bio-medical imaging to single-electron devices. Additional modalities such as spin and valley properties in monolayer transition metal dichalcogenides provide further degrees of freedom requisite for information processing and spintronics. In nanostructures, however, spatial confinement can cause hybridization that inhibits the robustness of these emergent properties. Here in this paper, we show that laterally-confined excitons in monolayer MoS 2 nanodots can be created through top-down nanopatterning with controlled size tunability. Unlike chemically-exfoliated monolayer nanoparticles, themore » lithographically patterned monolayer semiconductor nanodots down to a radius of 15 nm exhibit the same valley polarization as in a continuous monolayer sheet. The inherited bulk spin and valley properties, the size dependence of excitonic energies, and the ability to fabricate MoS 2 nanostructures using semiconductor-compatible processing suggest that monolayer semiconductor nanodots have potential to be multimodal building blocks of integrated optoelectronics and spintronics systems« less

Highly non-linear solid core photonic crystal fiber with one nano hole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gangwar, Rahul Kumar, E-mail: rahul0889@gmail.com; Bhardwaj, Vanita, E-mail: bhardwajphy12@gmail.com; Singh, Vinod Kumar, E-mail: singh.vk.ap@ismdhanbad.co.in

2015-08-28

The numerical study of newly designed solid core photonic crystal fiber (SCPCF) having three hexagonal air hole rings in cladding region and one small nano hole at the center are presented. By using full vectorial finite element method (FV-FEM), we analyses the optical properties like effective area, nonlinearity and confinement loss of the proposed PCF. Results show that the change in core diameter controls the effective area, nonlinearity and confinement loss. A low effective area (3.34 µm{sup 2}), high nonlinearity (36.34 W{sup −1}km{sup −1}) and low confinement loss (0.00106 dB/km) are achieved at the communication wavelength 1.55 µm for themore » SCPCF having core air hole diameter 0.10 µm, cladding air holes diameter 1.00 µm and pitch 2.50 µm. This type of PCF is very useful in non-linear applications such as supercontinuum generation, four wave mixing, second harmonic generation etc.« less

Conical Refraction Bottle Beams for Entrapment of Absorbing Droplets.

PubMed

Esseling, Michael; Alpmann, Christina; Schnelle, Jens; Meissner, Robert; Denz, Cornelia

2018-03-22

Conical refraction (CR) optical bottle beams for photophoretic trapping of airborne absorbing droplets are introduced and experimentally demonstrated. CR describes the circular split-up of unpolarised light propagating along an optical axis in a biaxial crystal. The diverging and converging cones lend themselves to the construction of optical bottle beams with flexible entry points. The interaction of single inkjet droplets with an open or partly open bottle beam is shown implementing high-speed video microscopy in a dual-view configuration. Perpendicular image planes are visualized on a single camera chip to characterize the integral three-dimensional movement dynamics of droplets. We demonstrate how a partly opened optical bottle transversely confines liquid objects. Furthermore we observe and analyse transverse oscillations of absorbing droplets as they hit the inner walls and simultaneously measure both transverse and axial velocity components.

Structural and optical properties of nanostructured CdSe thin films prepared by electrochemical deposition

NASA Astrophysics Data System (ADS)

Bai, Rekha; Chaudhary, Sujeet; Pandya, Dinesh K.

2018-05-01

Cadmium selenide (CdSe) nanostructured thin films have been grown on fluorine doped tin oxide (FTO) coated glass substrates by potentiostatic electrochemical deposition (ECD) technique for use in solar energy conversion devices. The effect of bath temperature on the structural, morphological and optical properties of prepared CdSe films has been explored. X-ray diffraction (XRD) and Raman spectroscopy clearly show that the CdSe films are polycrystalline and exhibit phase transformation from wurtzite to zincblende structure with increase in bath temperature. Optical spectra reveal that the nanostructured CdSe films have high absorbance in visible region and the films show a red shift in direct optical energy band gap from 1.90 to 1.65 eV with increase in bath temperature due to change in phase and bandgap tuning related to quantum confinement effect.

Near- and far-field spectroscopic imaging investigation of resonant square-loop infrared metasurfaces.

PubMed

D' Archangel, Jeffrey; Tucker, Eric; Kinzel, Ed; Muller, Eric A; Bechtel, Hans A; Martin, Michael C; Raschke, Markus B; Boreman, Glenn

2013-07-15

Optical metamaterials have unique properties which result from geometric confinement of the optical conductivity. We developed a series of infrared metasurfaces based on an array of metallic square loop antennas. The far-field absorption spectrum can be designed with resonances across the infrared by scaling the geometric dimensions. We measure the amplitude and phase of the resonant mode as standing wave patterns within the square loops using scattering-scanning near-field optical microscopy (s-SNOM). Further, using a broad-band synchrotron-based FTIR microscope and s-SNOM at the Advanced Light Source, we are able to correlate far-field spectra to near-field modes of the metasurface as the resonance is tuned between samples. The results highlight the importance of multi-modal imaging for the design and characterization of optical metamaterials.

Topological Switching and Orbiting Dynamics of Colloidal Spheres Dressed with Chiral Nematic Solitons

PubMed Central

Porenta, T.; Čopar, S.; Ackerman, P. J.; Pandey, M. B.; Varney, M. C. M.; Smalyukh, I. I.; Žumer, S.

2014-01-01

Metastable configurations formed by defects, inclusions, elastic deformations and topological solitons in liquid crystals are a promising choice for building photonic crystals and metamaterials with a potential for new optical applications. Local optical modification of the director or introduction of colloidal inclusions into a moderately chiral nematic liquid crystal confined to a homeotropic cell creates localized multistable chiral solitons. Here we induce solitons that “dress” the dispersed spherical particles treated for tangential degenerate boundary conditions, and perform controlled switching of their state using focused optical beams. Two optically switchable distinct metastable states, toron and hopfion, bound to colloidal spheres into structures with different topological charges are investigated. Their structures are examined using Q-tensor based numerical simulations and compared to the profiles reconstructed from the experiments. A topological explanation of observed multistability is constructed. PMID:25477195

Topological switching and orbiting dynamics of colloidal spheres dressed with chiral nematic solitons.

PubMed

Porenta, T; Copar, S; Ackerman, P J; Pandey, M B; Varney, M C M; Smalyukh, I I; Žumer, S

2014-12-05

Metastable configurations formed by defects, inclusions, elastic deformations and topological solitons in liquid crystals are a promising choice for building photonic crystals and metamaterials with a potential for new optical applications. Local optical modification of the director or introduction of colloidal inclusions into a moderately chiral nematic liquid crystal confined to a homeotropic cell creates localized multistable chiral solitons. Here we induce solitons that "dress" the dispersed spherical particles treated for tangential degenerate boundary conditions, and perform controlled switching of their state using focused optical beams. Two optically switchable distinct metastable states, toron and hopfion, bound to colloidal spheres into structures with different topological charges are investigated. Their structures are examined using Q-tensor based numerical simulations and compared to the profiles reconstructed from the experiments. A topological explanation of observed multistability is constructed.

Holographic optical tweezers for object manipulations at an air-liquid surface.

PubMed

Jesacher, Alexander; Fürhapter, Severin; Maurer, Christian; Bernet, Stefan; Ritsch-Marte, Monika

2006-06-26

We investigate holographic optical tweezers manipulating micro-beads at a suspended air-liquid interface. Axial confinement of the particles in the two-dimensional interface is maintained by the interplay between surface tension and gravity. Therefore, optical trapping of the micro-beads is possible even with a long distance air objective. Efficient micro-circulation of the liquid can be induced by fast rotating beads, driven by the orbital angular momentum transfer of incident Laguerre-Gaussian (doughnut) laser modes. Our setup allows various ways of creating a tailored dynamic flow of particles and liquid within the surface. We demonstrate examples of surface manipulations like efficient vortex pumps and mixers, interactive particle flow steering by arrays of vortex pumps, the feasibility of achieving a "clocked" traffic of micro beads, and size-selective guiding of beads along optical "conveyor belts".

Compact and low power operation optical switch using silicon-germanium/silicon hetero-structure waveguide.

PubMed

Sekiguchi, Shigeaki; Kurahashi, Teruo; Zhu, Lei; Kawaguchi, Kenichi; Morito, Ken

2012-04-09

We proposed a silicon-based optical switch with a carrier-plasma-induced phase shifter which employs a silicon-germanium (SiGe) / silicon (Si) hetero-structure in the waveguide core. A type-I hetero-interface formed by SiGe and Si is expected to confine carriers effectively in the SiGe waveguide core. The fabricated Mach-Zehnder optical switch shows a low switching power of only 1.53 mW with a compact phase shifter length of 250 μm. The switching time of the optical switch is less than 4.6 ns for the case of a square waveform driving condition, and 1 ns for the case of a pre-emphasis electric driving condition. These results show that our proposed SiGe/Si waveguide structure holds promise for active devices with compact size and low operation power.

Time-resolved absolute measurements by electro-optic effect of giant electromagnetic pulses due to laser-plasma interaction in nanosecond regime

PubMed Central

Consoli, F.; De Angelis, R.; Duvillaret, L.; Andreoli, P. L.; Cipriani, M.; Cristofari, G.; Di Giorgio, G.; Ingenito, F.; Verona, C.

2016-01-01

We describe the first electro-optical absolute measurements of electromagnetic pulses (EMPs) generated by laser-plasma interaction in nanosecond regime. Laser intensities are inertial-confinement-fusion (ICF) relevant and wavelength is 1054 nm. These are the first direct EMP amplitude measurements with the detector rather close and in direct view of the plasma. A maximum field of 261 kV/m was measured, two orders of magnitude higher than previous measurements by conductive probes on nanosecond regime lasers with much higher energy. The analysis of measurements and of particle-in-cell simulations indicates that signals match the emission of charged particles detected in the same experiment, and suggests that anisotropic particle emission from target, X-ray photoionization and charge implantation on surfaces directly exposed to plasma, could be important EMP contributions. Significant information achieved on EMP features and sources is crucial for future plants of laser-plasma acceleration and inertial-confinement-fusion and for the use as effective plasma diagnostics. It also opens to remarkable applications of laser-plasma interaction as intense source of RF-microwaves for studies on materials and devices, EMP-radiation-hardening and electromagnetic compatibility. The demonstrated extreme effectivity of electric-fields detection in laser-plasma context by electro-optic effect, leads to great potential for characterization of laser-plasma interaction and generated Terahertz radiation. PMID:27301704

Time-resolved absolute measurements by electro-optic effect of giant electromagnetic pulses due to laser-plasma interaction in nanosecond regime

NASA Astrophysics Data System (ADS)

Consoli, F.; de Angelis, R.; Duvillaret, L.; Andreoli, P. L.; Cipriani, M.; Cristofari, G.; di Giorgio, G.; Ingenito, F.; Verona, C.

2016-06-01

We describe the first electro-optical absolute measurements of electromagnetic pulses (EMPs) generated by laser-plasma interaction in nanosecond regime. Laser intensities are inertial-confinement-fusion (ICF) relevant and wavelength is 1054 nm. These are the first direct EMP amplitude measurements with the detector rather close and in direct view of the plasma. A maximum field of 261 kV/m was measured, two orders of magnitude higher than previous measurements by conductive probes on nanosecond regime lasers with much higher energy. The analysis of measurements and of particle-in-cell simulations indicates that signals match the emission of charged particles detected in the same experiment, and suggests that anisotropic particle emission from target, X-ray photoionization and charge implantation on surfaces directly exposed to plasma, could be important EMP contributions. Significant information achieved on EMP features and sources is crucial for future plants of laser-plasma acceleration and inertial-confinement-fusion and for the use as effective plasma diagnostics. It also opens to remarkable applications of laser-plasma interaction as intense source of RF-microwaves for studies on materials and devices, EMP-radiation-hardening and electromagnetic compatibility. The demonstrated extreme effectivity of electric-fields detection in laser-plasma context by electro-optic effect, leads to great potential for characterization of laser-plasma interaction and generated Terahertz radiation.

Modelling debris and shrapnel generation in inertial confinement fusion experiments

DOE PAGES

Eder, D. C.; Fisher, A. C.; Koniges, A. E.; ...

2013-10-24

Modelling and mitigation of damage are crucial for safe and economical operation of high-power laser facilities. Experiments at the National Ignition Facility use a variety of targets with a range of laser energies spanning more than two orders of magnitude (~14 kJ to ~1.9 MJ). Low-energy inertial confinement fusion experiments are used to study early-time x-ray load symmetry on the capsule, shock timing, and other physics issues. For these experiments, a significant portion of the target is not completely vaporized and late-time (hundreds of ns) simulations are required to study the generation of debris and shrapnel from these targets. Damagemore » to optics and diagnostics from shrapnel is a major concern for low-energy experiments. Here, we provide the first full-target simulations of entire cryogenic targets, including the Al thermal mechanical package and Si cooling rings. We use a 3D multi-physics multi-material hydrodynamics code, ALE-AMR, for these late-time simulations. The mass, velocity, and spatial distribution of shrapnel are calculated for three experiments with laser energies ranging from 14 to 250 kJ. We calculate damage risk to optics and diagnostics for these three experiments. For the lowest energy re-emit experiment, we provide a detailed analysis of the effects of shrapnel impacts on optics and diagnostics and compare with observations of damage sites.« less

Quantum dots and nanocomposites.

PubMed

Mansur, Herman Sander

2010-01-01

Quantum dots (QDs), also known as semiconducting nanoparticles, are promising zero-dimensional advanced materials because of their nanoscale size and because they can be engineered to suit particular applications such as nonlinear optical devices (NLO), electro-optical devices, and computing applications. QDs can be joined to polymers in order to produce nanocomposites which can be considered a scientific revolution of the 21st century. One of the fastest moving and most exciting interfaces of nanotechnology is the use of QDs in medicine, cell and molecular biology. Recent advances in nanomaterials have produced a new class of markers and probes by conjugating semiconductor QDs with biomolecules that have affinities for binding with selected biological structures. The nanoscale of QDs ensures that they do not scatter light at visible or longer wavelengths, which is important in order to minimize optical losses in practical applications. Moreover, at this scale, quantum confinement and surface effects become very important and therefore manipulation of the dot diameter or modification of its surface allows the properties of the dot to be controlled. Quantum confinement affects the absorption and emission of photons from the dot. Thus, the absorption edge of a material can be tuned by control of the particle size. This paper reviews developments in the myriad of possibilities for the use of semiconductor QDs associated with molecules producing novel hybrid nanocomposite systems for nanomedicine and bioengineering applications.

Low-dimensional systems: quantum size effects and electronic properties of semiconductor microcrystallites (zero-dimensional systems) and some quasi-two-dimensional systems

NASA Astrophysics Data System (ADS)

Yoffe, A. D.

2002-03-01

This review is concerned with quantum confinement effects in low-dimensional semiconductor systems. The emphasis is on the optical properties, including luminescence, of nanometre-sized microcrystallites, also referred to as zerodimensional systems. There is some discussion on certain of the two-dimensional systems, such as thin films and layer structures. The increase in energy of excitation peaks (blue shift) as the radius R of a microcrystallite is reduced is treated theoretically, and experimental data when they are available are used to assess the reliability of the different models that have been used. These experiments normally make use of microcrystallites dispersed in a large-bandgap matrix such as glass, rocksalt, polymers, zeolites or liquids. Exciton binding energies Eb are larger than for bulk semiconductors, and oscillator strengths are higher for the microcrystallites. The regimes of direct interest are as follows. Firstly there is the so-called weak-confinement regime where R is greater than the bulk exciton Bohr radius aB. Experimentally, semiconductors such as CuCl with aB , 7 Å, are suitable for study in this case. Secondly there is the moderate-confinement regime, where R , aB, and ah < R < ae, ah and ae being the hole and electron Bohr radii, respectively. Finally there is the strong-confinement regime, with R < aB, and R < ah, ae. For this case we are concerned with a ladder of discrete energy levels, as in molecular systems, rather than energy bands. The electrons and holes are treated as independent particles, and for excited states we refer to electron-hole pairs rather than excitons. Suitable materials for investigation in this regime are the II-VI semiconductors, and also GaAs and Ge, for which aB is relatively large. Although a number of different theoretical models have been used, none can be described as completely first-principles calculations, and there is room for improvement on this aspect. However, useful expressions have been developed by Brus and by Lippens and Lannoo, giving the energy of excited states as a function of R, in terms of the bulk energy gap, kinetic energy, Coulomb energy and correlation energy. Other phenomena discussed are firstly biexciton formation by the use of high intensity laser beams and secondly nonlinear optical effects. Strong nonlinearities and short decay times for excited states have been predicted, and the models developed cover both the resonant and the non-resonant cases. The possibility of using microcrystallites embedded at reasonable concentrations in a glass matrix in the field of optical communications and optical switching is also considered.