Sample records for chirp transform techniques

  1. Chirp technique approach for objects' identification

    Microsoft Academic Search

    V. Genis; I. Oboznenko; J. M. Reid; P. A. Lewin; K. Soetanto

    1991-01-01

    Identification of inhomogeneities is of importance in the areas of tissue characterization, nondestructive evaluation and underwater acoustics. An approach to the identification of inhomogeneities by using a pulsed swept frequency technique (chirping) is presented. This technique allows frequency domain data to be determined directly from time domain data without using a Fourier transform algorithm and vice versa. The combined information

  2. Chirp Z-transform spectral zoom optimization with MATLAB.

    SciTech Connect

    Martin, Grant D.

    2005-11-01

    The MATLAB language has become a standard for rapid prototyping throughout all disciplines of engineering because the environment is easy to understand and use. Many of the basic functions included in MATLAB are those operations that are necessary to carry out larger algorithms such as the chirp z-transform spectral zoom. These functions include, but are not limited to mathematical operators, logical operators, array indexing, and the Fast Fourier Transform (FFT). However, despite its ease of use, MATLAB's technical computing language is interpreted and thus is not always capable of the memory management and performance of a compiled language. There are however, several optimizations that can be made within the chirp z-transform spectral zoom algorithm itself, and also to the MATLAB implementation in order to take full advantage of the computing environment and lower processing time and improve memory usage. To that end, this document's purpose is two-fold. The first demonstrates how to perform a chirp z-transform spectral zoom as well as an optimization within the algorithm that improves performance and memory usage. The second demonstrates a minor MATLAB language usage technique that can reduce overhead memory costs and improve performance.

  3. Project Summary MRI: Development of a Chirped-Pulse, Fourier-Transform mm-Wave Pulsed

    E-print Network

    Baskaran, Mark

    Project Summary MRI: Development of a Chirped-Pulse, Fourier-Transform mm-Wave Pulsed Uniform technologies: chirped-pulse Fourier-transform mm-wave spectroscopy and pulsed uniform supersonic flows: The instrument will leverage the ultra-broadband Chirped-pulse Fourier-transform Microwave (CP

  4. Edge effects in chirped-pulse Fourier transform microwave spectra

    NASA Astrophysics Data System (ADS)

    Park, G. Barratt; Field, Robert W.

    2015-06-01

    Recent applications of chirped-pulse Fourier transform microwave and millimeter wave spectroscopy have motivated the use of short (10-50 ns) chirped excitation pulses. In this regime, individual transitions within the chirped pulse bandwidth do not all, in effect, experience the same frequency sweep through resonance from far above to far below (or vice versa), and "edge effects" may dominate the relative intensities. We analyze this effect and provide simplifying expressions for the linear fast passage polarization response in the limit of long and short excitation pulses. In the long pulse limit, the polarization response converges to a rectangular function of frequency, and in the short pulse limit, the polarization response morphs into a form proportional to the window function of the Fourier-transform-limited excitation pulse.

  5. On a Pseudo-Subspace Framework for Discrete Fractional Fourier Transform Based Chirp

    E-print Network

    Santhanam, Balu

    On a Pseudo-Subspace Framework for Discrete Fractional Fourier Transform Based Chirp Parameter to develop a pseudo-subspace approach towards chirp parameter estimation. Keywords: Discrete Fractional to the pseudo signal subspace and small values corresponding to the pseudo noise subspace. transform based chirp

  6. A high-resolution chirp transform spectrometer for microwave measurements

    Microsoft Academic Search

    P. Hartogh; G. K. Hartmann

    1990-01-01

    A microwave heterodyne spectrometer consists of a radiometer front-end and a real-time spectrum analyzer back-end. Common spectrometer types are filterbanks, autocorrelators and acousto-optic spectrometers (AOS). In this paper a high-resolution chirp transform spectrometer using reflective array compressor (RAC) filters with a time bandwidth product of 6400 is presented. The spectrometer has 1600 channels within a 40 MHz input bandwidth and

  7. Progress Towards Chirped-Pulse Fourier Transform Thz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Douglass, Kevin O.; Plusquellic, David F.; Gerecht, Eyal

    2010-06-01

    New opportunities are provided by the development of higher power THz frequency multiplier sources, the development of a broadband Chirped-Pulse FTMW spectroscopy technique at microwave and mm Wave frequencies, and recently demonstrated heterodyne hot electron bolometer detection technology in the THz frequency region with near quantum noise-limited performance and high spectral resolution. Combining these three technologies and extending the chirped-pulse technique to 0.85 THz enables a host of new applications. NIST is currently pursing applications as a point sensor for greenhouse gases, volatile organic compounds, and potentially human breath. The generation and detection of phase stable chirped pulses at 850 GHz will be demonstrated. A description of the experimental setup and preliminary data will be presented for nitrous oxide. G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S. Shipman and B.H. Pate, Rev.Sci.Instrum. 79 (2008) 053103. E. Gerecht, D. Gu, L. You, K.S. Yngvesson, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES. 56, (2008) 1083.

  8. Chirped-Pulse Fourier Transform Microwave Spectroscopy of 3-VINYLBENZALDEHYDE

    NASA Astrophysics Data System (ADS)

    Smith, Miranda; Brown, Gordon G.

    2013-06-01

    The pure rotational spectrum of 3-vinylbenzaldehyde (3VBA) has been measured and assigned. Coker College's chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer was used to measure the rotational spectrum of 3VBA in the 7.5 - 18.5 GHz region of the microwave spectrum. The results have been analyzed to discover the rotational constants and centrifugal distortion constants of four distinct conformations of 3VBA: cis,cis-, cis,trans-, trans,cis-, and trans,trans-3VBA. The experimental rotational constants have been compared to the results of ab initio calculations. The performance of Coker's CP-FTMW spectrometer will also be discussed.

  9. Frequency Correction for MIRO Chirp Transformation Spectroscopy Spectrum

    NASA Technical Reports Server (NTRS)

    Lee, Seungwon

    2012-01-01

    This software processes the flyby spectra of the Chirp Transform Spectrometer (CTS) of the Microwave Instrument for Rosetta Orbiter (MIRO). The tool corrects the effect of Doppler shift and local-oscillator (LO) frequency shift during the flyby mode of MIRO operations. The frequency correction for CTS flyby spectra is performed and is integrated with multiple spectra into a high signal-to-noise averaged spectrum at the rest-frame RF frequency. This innovation also generates the 8 molecular line spectra by dividing continuous 4,096-channel CTS spectra. The 8 line spectra can then be readily used for scientific investigations. A spectral line that is at its rest frequency in the frame of the Earth or an asteroid will be observed with a time-varying Doppler shift as seen by MIRO. The frequency shift is toward the higher RF frequencies on approach, and toward lower RF frequencies on departure. The magnitude of the shift depends on the flyby velocity. The result of time-varying Doppler shift is that of an observed spectral line will be seen to move from channel to channel in the CTS spectrometer. The direction (higher or lower frequency) in the spectrometer depends on the spectral line frequency under consideration. In order to analyze the flyby spectra, two steps are required. First, individual spectra must be corrected for the Doppler shift so that individual spectra can be superimposed at the same rest frequency for integration purposes. Second, a correction needs to be applied to the CTS spectra to account for the LO frequency shifts that are applied to asteroid mode.

  10. Waveguide Chirped-Pulse Fourier Transform Microwave Spectroscopy of 2-ETHOXYETHANOL

    NASA Astrophysics Data System (ADS)

    Phillips, Maria A.; Shipman, Steven T.

    2013-06-01

    The pure rotational spectrum of 2-ethoxyethanol was recorded from 8.7 to 26.5 GHz at 250 K with a waveguide chirped-pulse Fourier transform microwave spectrometer. The full spectrum contains contributions from multiple vibrational states. Preliminary assignments have been made with a combination of ab initio calculations and an automated spectral fitting program that accelerates the initial fitting process.

  11. a Low-Cost Chirped-Pulse Fourier Transform Microwave Spectrometer for Undergraduate Physical Chemistry Lab

    NASA Astrophysics Data System (ADS)

    Carroll, Brandon; Finneran, Ian; Blake, Geoffrey

    2014-06-01

    We present the design and construction of a simple and low-cost waveguide chirped pulse Fourier transform microwave (CP-FTMW) spectrometer suitable for gas-phase rotational spectroscopy experiments in undergraduate physical chemistry labs as well as graduate level research. The spectrometer operates with modest bandwidth, using phased locked loop (PLL) microwave sources and a direct digital synthesis (DDS) chirp source, making it an affordable for undergraduate labs. The performance of the instrument is benchmarked by acquiring the pure rotational spectrum of the J = 1 - 0 transition OCS and its isotopologues from 11-12.5 GHz.

  12. Chirped-Pulse Fourier Transform Microwave Spectroscopy of 3-METHOXYPROPYLAMINE

    NASA Astrophysics Data System (ADS)

    McCabe, Morgan N.; Shipman, Steven; Arnold, Sean; Chewning, J. Chase; Smith, Miranda; Brown, Gordon

    2014-06-01

    The rotational spectrum of 3-methoxypropylamine was collected from 8.0 to 18.5 GHz with the Coker College chirped-pulse FTMW molecular beam spectrometer. Ab initio predictions using the B3LYP-D3 dispersion-corrected density functional gave high quality starting geometries, enabling us to quickly assign the spectrum of the lowest energy conformer, which has a g'gt configuration (moving from the amine end to the methoxy end of the molecule). Attempts were also made to collect the spectrum of this molecule in the room-temperature waveguide instrument at New College, but these attempts were unsuccessful as the molecule rapidly reacts with the copper walls of the waveguide to produce ammonia.

  13. High-resolution chirp transform spectrometer for middle atmospheric microwave sounding

    Microsoft Academic Search

    Paul Hartogh

    1997-01-01

    The development of microwave heterodyne receiver technologies like Superconductor-Insulator-Superconductor-(SIS) mixer and Hot-Electron-Bolometer (HEB) offers the possibility to detect a large number of minor atmospheric constituents, which have been under the detection limit before. The requirements on the functional performance of spectrometers have increased at the same time. The Chirp Transform Spectrometer (CTS) fulfills these requirements, because of its high resolution,

  14. Source of metastable H(2s) atoms using the Stark chirped rapid-adiabatic-passage technique

    Microsoft Academic Search

    L. P. Yatsenko; B. W. Shore; T. Halfmann; K. Bergmann

    1999-01-01

    We propose the use of Stark chirped rapid-adiabatic-passage method, a technique in which the energy of a target state is swept through resonance by a slowly varying dynamic Stark shift to induce complete population transfer from the ground 1s state to the metastable 2 s state of the hydrogen atom. Parasitic ionization pro- cesses are strongly reduced by using a

  15. REMOVAL OF RESIDUAL CHIRP IN COMPRESSED BEAMS USING A PASSIVE WAKEFIELD TECHNIQUE

    E-print Network

    Brookhaven National Laboratory

    of Bane and Stupakov [1], in RF-free residual chirp mitigation using only passive techniques. Beam in papers by Bane, Stupakov, and Emma [2] [3]. The longitudinal wakefield generated by a single electron and the circular pipe that was used in Stupakov and Bane's original derivation [4]. The wakefield produced

  16. a Chirped-Pulse Fourier Transform Spectrometer Operating from 110 TO 170 GHZ

    NASA Astrophysics Data System (ADS)

    Bernier, Lauren E.; Shipman, Steven

    2014-06-01

    A chirped-pulse Fourier transform spectrometer operating from 110 - 170 GHz was constructed. The design of this spectrometer is directly adapted from that of the 260 - 295 GHz chirped-pulse spectrometer built by Steber and co-workers at the University of Virginia. In this instrument, an arbitrary waveform generator (AWG) produces a chirped pulse which is frequency shifted to a range between 9.2 and 14.1 GHz and then multiplied by a factor of 12 via an active multiplier chain to a range between 110 and 170 GHz. As in the Pate lab design, the AWG also serves as a local oscillator (LO) source; this LO is multiplied and used to downconvert the molecular emission, allowing it to be collected by a 40 GS/s digitizer. Benchmark measurements were taken for methanol at room temperature, and details of the instrument's performance will be discussed. A.L. Steber, B.J. Harris, J.L. Neill, and B.H. Pate, J. Mol. Spectrosc., 280, 3 (2012)

  17. A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. II. Performance and applications for reaction dynamics.

    PubMed

    Abeysekera, Chamara; Zack, Lindsay N; Park, G Barratt; Joalland, Baptiste; Oldham, James M; Prozument, Kirill; Ariyasingha, Nuwandi M; Sims, Ian R; Field, Robert W; Suits, Arthur G

    2014-12-01

    This second paper in a series of two reports on the performance of a new instrument for studying chemical reaction dynamics and kinetics at low temperatures. Our approach employs chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy to probe photolysis and bimolecular reaction products that are thermalized in pulsed uniform flows. Here we detail the development and testing of a new K(a)-band CP-FTMW spectrometer in combination with the pulsed flow system described in Paper I [J. M. Oldham, C. Abeysekera, B. Joalland, L. N. Zack, K. Prozument, I. R. Sims, G. B. Park, R. W. Field, and A. G. Suits, J. Chem. Phys. 141, 154202 (2014)]. This combination delivers broadband spectra with MHz resolution and allows monitoring, on the ?s timescale, of the appearance of transient reaction products. Two benchmark reactive systems are used to illustrate and characterize the performance of this new apparatus: the photodissociation of SO2 at 193 nm, for which the vibrational populations of the SO product are monitored, and the reaction between CN and C2H2, for which the HCCCN product is detected in its vibrational ground state. The results show that the combination of these two well-matched techniques, which we refer to as chirped-pulse in uniform flow, also provides insight into the vibrational and rotational relaxation kinetics of the nascent reaction products. Future directions are discussed, with an emphasis on exploring the low temperature chemistry of complex polyatomic systems. PMID:25481137

  18. Waveguide Chirped-Pulse Fourier Transform Microwave Spectroscopy of 1-PROPANETHIOL

    NASA Astrophysics Data System (ADS)

    Gordon, Brittany P.; Shipman, Steven T.

    2013-06-01

    The rotational spectrum of 1-propanethiol was measured from 8.7 to 26.5 GHz at 250 K with a waveguide chirped-pulse Fourier transform microwave spectrometer. This thiol has a dense spectrum containing contributions from multiple conformers, excited vibrational states, and singly-substituted isotopomers (^{34}S and ^{13}C) in natural abundance. Further, the spectrum shows complications due to the presence of internal rotation. Despite this complexity, some progress has been made, and preliminary work on this molecule will be presented.

  19. A chirped pulse Fourier transform microwave study of the refrigerant alternative 2,3,3,3-tetrafluoropropene

    Microsoft Academic Search

    Mark D. Marshall; Helen O. Leung; Benjamin Q. Scheetz; Jonathan E. Thaler; John S. Muenter

    2011-01-01

    Fourier transform microwave, rotational spectra in the 6–18GHz band of the low global warming potential, low ozone depletion potential refrigerant alternative, 2,3,3,3-tetrafluoropropene (HFO-1234yf), and in natural abundance, its three singly substituted 13C isotopologues are obtained using a newly constructed chirped pulse spectrometer. Employing anharmonic vibration–rotation interaction alpha constants from ab initio calculations, the rotational constants determined for the ground vibrational

  20. A chirped pulse Fourier transform microwave study of the refrigerant alternative 2,3,3,3-tetrafluoropropene

    Microsoft Academic Search

    Mark D. Marshall; Helen O. Leung; Benjamin Q. Scheetz; Jonathan E. Thaler; John S. Muenter

    2011-01-01

    Fourier transform microwave, rotational spectra in the 6-18 GHz band of the low global warming potential, low ozone depletion potential refrigerant alternative, 2,3,3,3-tetrafluoropropene (HFO-1234yf), and in natural abundance, its three singly substituted 13C isotopologues are obtained using a newly constructed chirped pulse spectrometer. Employing anharmonic vibration-rotation interaction alpha constants from ab initio calculations, the rotational constants determined for the ground

  1. Probing Chemical Dynamics with High Resolution Spectroscopy: Chirped-Pulse Fourier-Transform Microwave Spectroscopy Coupled with a Hyperthermal Source

    NASA Astrophysics Data System (ADS)

    Kidwell, Nathanael M.; Vara, Vanesa Vaquero; Mehta-Hurt, Deepali N.; Korn, Joseph A.; Dian, Brian C.; Zwier, Timothy S.

    2013-06-01

    Chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy has proven to be a well-suited technique for the rapid study and spectral identification of molecular species due to its ultra-broadband capability and excellent specificity to molecular structure from high-resolution rotational transitions. This talk will describe initial results from combining CP-FTMW detection with a hyperthermal nozzle source. This source has the advantage of producing traditionally high thermal product densities in a pulsed supersonic expansion with a short contact time compared to conventional pyrolysis. Used in tandem, CP-FTMW spectroscopy and the hyperthermal nozzle in a supersonic expansion is a powerful method that can produce and detect changes in conformation and isomer populations, and characterize important intermediates on the reaction surface of a precursor. In particular, we show its utility to provide insight into the unimolecular decomposition pathways of model lignin compounds and alternative biofuels. Preliminary results will be discussed including spectroscopic evidence for formation of cyclopentadienone in the pyrolysis of a lignin derivative guaiacol (o-methoxyphenol).

  2. Perfluorobutyric Acid and its Monohydrate: a Chirped Pulse and Cavity Based Fourier Transform Microwave Spectroscopic Study

    NASA Astrophysics Data System (ADS)

    Thomas, Javix; Serrato, Agapito, III; Lin, Wei; Jaeger, Wolfgang; Xu, Yunjie

    2014-06-01

    Perfluorobutyric acid (PFBA) is highly soluble in water and is a molecule of environmental importance. Rotational spectra of PFBA and its monohydrate were studied using a broadband chirped pulse and a narrow band cavity based Fourier transform microwave spectrometers and high level ab initio calculations. Extensive conformational search was performed for both the acid and its monohydrate at the MP2/6-311++G(2d,p) level of theory. Two and three conformers were predicted for PFBA and its monohydrate, respectively. One set of rotational transitions of PFBA and its mono-hydrate in each case was observed and assigned. Based on the broadband spectra obtained, one can confidently conclude that only one dominate conformer exists in each case. The orientation of the hydroxyl group in PFBA was determined using isotopic analysis. Comparison of the observed transition intensities and the calculated electric dipole moment components allowed one to identify the most stable monohydrate conformation which takes on the insertion hydrogen-bonding topology. Comparison to the shorter chain analogues, i.e. trifluoroacetic acid, perfluoropropionic acid, and their monohydrates, was made to elucidate the general trend in their conformational preference and binding topologies.

  3. Microwave Frequency Transitions Requiring Laser Ablated Uranium Metal Discovered Using Chirp-Pulse Fourier Transform Spectroscopy

    NASA Astrophysics Data System (ADS)

    Long, B. E.; Cooke, S. A.

    2014-06-01

    A rod of depleted uranium metal (mp = 1,132° C) has been ablated with the fundamental operating frequency of a Nd:YAG laser. The resulting ablation plume of uranium was then mixed with argon gas and expanded between the transmit/receive horn antennae of a chirp-pulse Fourier transform microwave spectrometer. The recorded spectra show nine strong transitions which are not present when the laser is not used in the experimental procedure. A series of experiments in which the backing gas conditions were altered provides evidence that the nine observed transitions are carried by the same species. Should the transitions be from one species it is most likely an asymmetric top. The transitions persist even when ultra-pure argon is used as the sole backing gas. The oxide coating of the uranium metal likely provides a source of oxygen and, presently, the ``top" candidate for the unknown molecule is UO_3, which is known to have C_2v symmetry. Double resonance experiments are planned to aid transition assignments. A plausible explanation for an elusive assignment to date is the presence of pseudo-rotation.

  4. Chirped Pulse-Fourier Transform Microwave Spectroscopy of Ethyl 3-METHYL-3-PHENYLGLYCIDATE (strawberry Aldehyde)

    NASA Astrophysics Data System (ADS)

    Shipman, Steven T.; Neill, Justin L.; Muckle, Matt T.; Suenram, Richard D.; Pate, Brooks H.

    2009-06-01

    Strawberry aldehyde (C_{12} O_3 H_{14}), a common artificial flavoring compound, has two non-interconvertible conformational families defined by the relative stereochemistry around its epoxide carbons. In one family, referred to as the trans because the two large substituents (a phenyl ring and an ethyl ester) are on opposite sides of the epoxide ring, these two substituents are unable to interact with each other. However, in the cis family, there is a long-range interaction that is difficult to accurately capture in electronic structure calculations. Three trans and two cis conformations have been assigned by broadband chirped pulse Fourier transform microwave spectroscopy, along with the C-13 isotopomers in natural abundance for one conformer from each of the families. The agreement of the rotational constants, relative dipole moments, and relative energies between theory and experiment is excellent, even at relatively crude levels of theory, for the trans family, but is quite poor for the cis conformers. In addition, due to the reactivity of strawberry aldehyde and the high temperature to which it must be heated to yield a suitable vapor pressure, several decomposition products have been assigned, and more, as of yet unassigned, are likely to be present. This project demonstrates some of the challenges in performing large-molecule rotational spectroscopy.

  5. Joint transform time-integrating acousto-optic correlator for chirp spectrum analysis

    Microsoft Academic Search

    P. S. Guilfoyle; D. L. Hecht; D. L. Steinmetz

    1980-01-01

    A time-integrating optical processor is configured for one-dimensional chirp correlation spectrum analysis. A unique optical implementation, utilizing TeO2 shear wave acousto-optic cells, is designed to operate in a configuration which allows wide bandwidth diffraction to both the positive and negative first diffraction orders. The result is high optical throughput efficiency, excellent fringe visibility, and a coaxial system design. Chirp linearity

  6. Techniques for High-Bandwidth (?30 GHz) Chirped-Pulse Submillimeter-Wave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Neill, Justin L.; Steber, Amanda L.; Harris, Brent J.; Pate, Brooks H.; Douglass, Kevin O.; Plusquellic, David F.; Gerecht, Eyal

    2011-06-01

    Due to the increased availability of active multiplier chains for converting microwave pulses into the millimeter/submillimeter with reasonably high power (?1 mW), chirped pulses with high phase stability and complete arbitrary waveform generator (AWG) frequency agility can be created and employed for high-sensitivity molecular spectroscopy, as demonstrated at the Symposium in the past few years. The bandwidths of multiplier chains, however, can exceed the current limitations on digitizer bandwidth. Therefore, in order to obtain ?30 GHz spectra in ~1 ms or less, techniques are being developed in which a two-channel AWG creates both the chirped pulses for molecular irradiation and a local oscillator pulse for heterodyne detection. These approaches reduce the digitizer bandwidths to 500 MHz or less to collect a high-bandwidth spectrum. A single instrument design can be used to measure both absorption and emission spectra, only requiring that the AWG pulses are changed. Due to the phase stability of the pulse generation and detection, coherent time-domain signal averaging can be performed to enhance sensitivity as desired. Preliminary results from prototype instruments designed at UVa and NIST will be presented, with sensitivity, frequency accuracy, and measurement speed comparisons to current millimeter/submillimeter-wave spectrometers. G.B. Park, A.H. Steeves, K. Kuyanov-Prozument, A.P. Colombo, R.W. Field, J.L. Neill, and B.H. Pate, RH07, 64th International Symposium on Molecular Spectroscopy (2009) K.O. Douglass, D.F. Plusquellic, and E. Gerecht, WH09, 65th International Symposium on Molecular Spectroscopy (2010).

  7. Chirped-Pulse Fourier Transform Microwave Spectroscopy of 2-CHLORO-3-FLUOROPYRIDINE and 2-CHLORO-6-FLUOROPYRIDINE

    NASA Astrophysics Data System (ADS)

    Arnold, Sean; Chewning, J. Chase; Brown, Gordon

    2014-06-01

    The pure rotational spectra of 2-chloro-3-fluoropyridine and 2-chloro-6-fluoropyridine were measured on a chirped-pulsed Fourier transform microwave (CP-FTMW) spectrometer in the 8 - 18.5 GHz frequency range. The spectra were analyzed to find the rotational constants of the molecules for both the 35Cl and the 37Cl isotopologues. The measured rotational transitions exhibit hyperfine splitting, from which the nuclear quadrupole coupling constants have been assigned. The rotational constants and the nuclear quadrupole coupling constants have been compared to ab initio calculations performed using the Gaussian 03W software package.

  8. Barley Transformation Using Biolistic Techniques

    NASA Astrophysics Data System (ADS)

    Harwood, Wendy A.; Smedley, Mark A.

    Microprojectile bombardment or biolistic techniques have been widely used for cereal transformation. These methods rely on the acceleration of gold particles, coated with plasmid DNA, into plant cells as a method of directly introducing the DNA. The first report of the generation of fertile, transgenic barley plants used biolistic techniques. However, more recently Agrobacterium-mediated transformation has been adopted as the method of choice for most cereals including barley. Biolistic procedures are still important for some barley transformation applications and also provide transient test systems for the rapid checking of constructs. This chapter describes methods for the transformation of barley using biolistic procedures and also highlights the use of the technology in transient assays.

  9. Broadband Chirped-Pulse Fourier Transform Microwave Spectroscopy and Molecular Structure of the ARGON-1-CHLORO-1-FLUOROETHYLENE Complex

    NASA Astrophysics Data System (ADS)

    Marshall, Mark D.; Leung, Helen O.

    2013-06-01

    Previous studies of argon complexes with fluoroethylenes have revealed a preference for a geometry that maximizes the contact of the argon atom with heavy atoms on the fluoroethylene. We have observed a continuation of this trend when one of the fluorine atoms is replaced by chlorine. As part of a systematic study of the effect of chlorine substitution on intermolecular interactions, we have examined the argon-1-chloro-1-fluoroethylene complex, and obtained the 5.6 - 18.1 GHz chirped-pulse Fourier transform microwave spectrum of this species. Transitions for both the ^{35}Cl and ^{37}Cl isotopologues are observed and analyzed to provide geometric parameters for this non-planar complex. The structure is found to be similar to those of analogous complexes and agrees well with ab initio predictions. Z. Kisiel, P.W. Fowler, and A.C. Legon, J. Chem. Phys. {95,} 2283 (1991).

  10. Chirped-Pulse Fourier-Transform Microwave/pulsed Uniform Flow Spectrometer: the Low-Temperature Pulsed Uniform Supersonic Flow System

    NASA Astrophysics Data System (ADS)

    Abeysekera, Chamara; Prozument, Kirill; Oldham, James; Joalland, Baptiste; Zack, Lindsay; Park, Barratt; Field, Robert W.; Sims, Ian; Suits, Arthur

    2014-06-01

    Traditional techniques (e.g. REMPI, imaging, etc.) that are used to study reaction dynamics are able to provide a great deal of fundamental information about systems containing atoms and smaller molecules. However, as larger molecules and more complex systems are targeted, it becomes more of a challenge to determine isomer- and vibrational level-specific information and accurate branching ratios. In order to complement existing methods and obtain information about larger systems, a Ka-band (26-40 GHz) chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer has been has been constructed. The system integrates a pulsed uniform supersonic flow (PUSF) source to ensure that experimental conditions, such as temperature and density, are well-known and constant. This PUSF system is based around a high-throughput piezoelectric stack valve, a Laval nozzle, and simple pumping scheme. This system is able to produce cold, uniform flows with densities on the order of 1016 cm-3 that persist for up to 20 cm from the nozzle exit. A description of this system and its characterization will be presented.

  11. A single isolated sub-50 attosecond pulse generation with a two-color laser field by a frequency-chirping technique

    NASA Astrophysics Data System (ADS)

    Zhao, Kun; Chu, Tianshu

    2011-07-01

    We discuss the possibility of using the frequency-chirping technique to shorten the duration of the generated single attosecond pulse (SAP) by a two-color laser field of 800 and 1600 nm with few-cycle pulses. By adopting various combinations of the two frequency-chirped laser fields in our numerical simulation of ionizing He atom, we demonstrate that the best possible condition to obtain the shortest SAP is using the same chirping in both the fundamental and the half-harmonic laser fields without any phase effect and any delay time. There is a maximum increment of about 40 eV in the bandwidth of the XUV super-continuum in the cutoff (the second plateau) region. A single isolated attosecond pulse of 48 as can be generated that is further reduced to 9.7 as by phase compensation.

  12. An optically controlled microwave phase shifter based on self-heterodyning technique using chirped fiber gratings and an optical frequency shifter

    Microsoft Academic Search

    Wataru Chujo; Yoshihiro Tomiyama

    2000-01-01

    A novel optically controlled microwave phase shifter based on self-heterodyne technique using chirped fiber gratings (CFG's) and optical frequency shifter (OFS) is demonstrated experimentally. The phase shifter is able to provide a wide bandwidth and beam scanning capability over a wide angle. Calculated results of an investigation into the beam scanning properties of a nine-element phased array antenna at 5

  13. Chirped-Pulse and Cavity Based Fourier Transform Microwave Spectroscopy of the Methyl Lactate-Ammonia Adduct

    NASA Astrophysics Data System (ADS)

    Thomas, Javix; Sukhorukov, Oleksandr; Jaeger, Wolfgang; Xu, Yunjie

    2012-06-01

    The hydrogen bonded complex of ammonia with methyl lactate, a chiral alpha-hydroxyester, has been studied using rotational spectroscopy and high level ab initio calculations. Previous studies showed that methyl lactate can exist in a number of conformers. However, only the most stable one which has an intramolecular hydrogen bonded ring formed with its alcoholic hydroxyl and its carbonyl oxygen atom was detected experimentally An extensive ab initio search has been performed to locate all possible low energy conformers of the methyl lactate-ammonia contact pair. Five lowest energy conformers have been identified at the MP2/6-311++G(d,p) level. The lowest energy conformer favors an insertion arrangement, where ammonia is inserted into the existing intramolecular hydrogen bonded ring in the most stable methyl lactate conformer. Broadband scans for the rotational spectra of possible binary conformers have been carried out using a chirped-pulse Fourier transform microwave (FTMW) instrument. The most stable binary adduct was identified and assigned. The final frequency measurements have been done with a cavity based FTMW instrument. The spectrum observed shows complicated fine and hyperfine splitting patterns, likely due to the internal rotations of the methyl groups of methyl lactate and that of ammonia, as well as the 14N quadrupolar nucleus. The binary adduct with 15NH3 has also been studied to simplify the splitting pattern and to aid the assignments of the extensive splittings. The isotopic data and the fine and hyperfine structures will be discussed in terms of internal rotation dynamics and geometry of the hydrogen bonded adduct.

  14. Barley Transformation Using Agrobacterium-Mediated Techniques

    NASA Astrophysics Data System (ADS)

    Harwood, Wendy A.; Bartlett, Joanne G.; Alves, Silvia C.; Perry, Matthew; Smedley, Mark A.; Leyland, Nicola; Snape, John W.

    Methods for the transformation of barley using Agrobacterium-mediated techniques have been available for the past 10 years. Agrobacterium offers a number of advantages over biolistic-mediated techniques in terms of efficiency and the quality of the transformed plants produced. This chapter describes a simple system for the transformation of barley based on the infection of immature embryos with Agrobacterium tumefaciens followed by the selection of transgenic tissue on media containing the antibiotic hygromycin. The method can lead to the production of large numbers of fertile, independent transgenic lines. It is therefore ideal for studies of gene function in a cereal crop system.

  15. Bulk chirped Bragg reflectors for light pulse compression and expansion

    NASA Astrophysics Data System (ADS)

    Tournois, Pierre; Hartemann, Pierre

    1995-02-01

    Bulk chirped Bragg reflectors are proposed as optical dispersive devices for the chirp pulse amplification technique. These transversal filters allow to synthesize any monotonous group delay time law versus optical frequency with a positive or negative slope.

  16. Interferogram analysis using Fourier transform techniques

    NASA Technical Reports Server (NTRS)

    Roddier, Claude; Roddier, Francois

    1987-01-01

    A method of interferogram analysis is described in which Fourier transform techniques are used to map the complex fringe visibility in several types of interferograms. Algorithms are developed for estimation of both the amplitude and the phase of the fringes (yielding the modulus and the phase of the holographically recorded object Fourier transform). The algorithms were applied to the reduction of interferometric seeing measurements (i.e., the estimation of the fringe amplitude only), and the reduction of interferometric tests (i.e., estimation of the fringe phase only). The method was used to analyze scatter-plate interferograms obtained at NOAO.

  17. Development of a Reduced-Cost Chirped Pulse Microwave Spectrometer

    NASA Astrophysics Data System (ADS)

    Finneran, Ian A.; Holland, Daniel B.; Carroll, P. Brandon; Blake, Geoffrey A.

    2013-06-01

    Chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy has become a ubiquitous technique in the high-resolution molecular spectroscopy community. Unfortunately, many components of CP-FTMW spectrometers are extremely expensive. Here we report of the development of an inexpensive microwave circuit and we present spectra of tetrahydrofuran and methanol collected between 8-16 GHz. Possible applications in remote sensing will also be discussed.

  18. Monitoring the Reaction Products of Perfluoropropionic Acid and Allyl Phenyl Ether Using Chirped-Pulse Fourier Transform Microwave Cp-Ftmw Spectroscopy

    NASA Astrophysics Data System (ADS)

    Frank, Derek S.; Obenchain, Daniel A.; Lin, Wei; Novick, Stewart E.; Cooke, S. A.; Grubbs, G. S., II

    2014-06-01

    The pure rotational spectra of the reaction mixture of perfluoropropionic acid, CF3CF2COOH, and allyl phenyl ether, C6H5OCH2CH=CH2, have been studied by a pulsed nozzle, chirped-pulse Fourier transform microwave spectrometer in the frequency range of 8-14 GHz. Transitions corresponding to multiple species, two of which being starting materials allyl phenyl ether and perfluoropropionic acid, have been observed and analyzed. Determination of the reaction products was carried out by matching observed rotational constants with ab initio quantum chemical calculations of predicted products and will be discussed. Rotational constants, centrifugal distortion constants and the assignment of allyl phenyl ether and reaction products spectra will all be discussed.

  19. High spectral resolution multiplex CARS spectroscopy using chirped pulses

    E-print Network

    Cohen, Ronald C.

    . This new chirped (c-CARS) technique should prove useful for chemically-selective imaging applicationsHigh spectral resolution multiplex CARS spectroscopy using chirped pulses K.P. Knutsen, J (CARS) spectra with a fem- tosecond laser system is presented. A linearly chirped and stretched ($10 ps

  20. Chirped-Pulse Fourier-Transform Microwave Spectroscopy of the Prototypical C-H\\cdots? Interaction: the BENZENE\\cdotsACETYLENE Weakly Bound Dimer

    NASA Astrophysics Data System (ADS)

    Ulrich, Nathan; Seifert, Nathan A.; Dorris, Rachel E.; Peebles, Rebecca A.; Peebles, Sean A.; Pate, Brooks

    2014-06-01

    The rotational spectrum of the CH\\cdots? bonded complex between benzene and acetylene has been measured in the 6-20 GHz range using chirped-pulse Fourier-transform microwave spectroscopy. The spectra for the normal isotopologue, three unique 13C substituted species, and the d_1-benzene\\cdotsHCCH species have allowed determination of the dimer structure. The spectrum is that of a symmetric top, with effective C6v symmetry, and a CH\\cdots? distance of 2.4921(1) Å. The dipole moment has been measured using the Stark effect, and is 0.438(11) D. In addition to the ground state spectrum, three additional sets of transitions corresponding to similar rotational constants have been observed, likely due to excitation of the three low energy intermolecular vibrational modes of the dimer. Analysis of these excited state transitions is in progress. Comparison of the binding energy and structure of the benzene\\cdotsHCCH dimer with other H\\cdots? complexes will be presented.

  1. Chirped pulse enhancement of multiphoton absorption in molecular iodine Vladislav V. Yakovlev, Christopher J. Bardeen, Jianwe Che, Jianshu Cao,

    E-print Network

    Cao, Jianshu

    are observed for chirped pulses with respect to transform-limited, zero chirp pulses. Theoretical a negatively chirped pulse has the opposite ordering. A transform-limited pulse is of the shortest possible relative to the shortest, transform- limited pulse. Preliminary calculations suggest that this en

  2. Chirping the probe pulse in a coherent transients experiment

    SciTech Connect

    Weber, Sebastien; Girard, Bertrand; Chatel, Beatrice [CNRS-Universite de Toulouse, UPS, Laboratoire Collisions, Agregats Reactivite, IRSAMC, F-31062 Toulouse (France)

    2010-02-15

    Coherent transients occur when a chirped pump pulse excites a two-level transition. They have been observed with an ultrashort probe pulse. Several studies have been dedicated to using various pump shapes. In this study, the roles of the pump and the probe pulses are reversed. With a Fourier-transform-limited pump pulse followed by a chirped-probe pulse, similar effects can be observed. Finally, the case of two pulses with opposite chirps is considered.

  3. pathChirp: Efficient Available Bandwidth Estimation for Network Paths

    SciTech Connect

    Cottrell, Les

    2003-04-30

    This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing rate within each chirp, pathChirp obtains a rich set of information from which to dynamically estimate the available bandwidth. Since it uses only packet interarrival times for estimation, pathChirp does not require synchronous nor highly stable clocks at the sender and receiver. We test pathChirp with simulations and Internet experiments and find that it provides good estimates of the available bandwidth while using only a fraction of the number of probe bytes that current state-of-the-art techniques use.

  4. Wavelet transform techniques and signal analysis

    SciTech Connect

    Perez, R.B.; Mattingly, J.K. (Oak Ridge National Lab., TN (United States) Tennessee Univ., Knoxville, TN (United States). Dept. of Nuclear Engineering); Perez, J.S. (Universidad Politecnica de Madrid (Spain). Facultad de Informatica)

    1993-01-01

    Traditionally, the most widely used signal analysis tool is the Fourier transform which, by producing power spectral densities (PSDs), allows time dependent signals to be studied in the frequency domain. However, the Fourier transform is global -- it extends over the entire time domain -- which makes it ill-suited to study nonstationary signals which exhibit local temporal changes in the signal's frequency content. To analyze nonstationary signals, the family of transforms commonly designated as short-time Fourier transforms (STFTs), capable of identifying temporally localized changes in the signal's frequency content, were developed by employing window functions to isolate temporal regions of the signal. For example, the Gabor STFT uses a Gaussian window. However, the applicability of STFTs is limited by various inadequacies. The Wavelet transform (NW), recently developed by Grossman and Morlet and explored in depth by Daubechies (2) and Mallat, remedies the inadequacies of STFTs. Like the Fourier transform, the WT can be implemented as a discrete transform (DWT) or as a continuous (integral) transform (CWT). This paper briefly illustrates some of the potential applications of the wavelet transform algorithms to signal analysis.

  5. Wavelet transform techniques and signal analysis

    SciTech Connect

    Perez, R.B.; Mattingly, J.K. [Oak Ridge National Lab., TN (United States)]|[Tennessee Univ., Knoxville, TN (United States). Dept. of Nuclear Engineering; Perez, J.S. [Universidad Politecnica de Madrid (Spain). Facultad de Informatica

    1993-03-01

    Traditionally, the most widely used signal analysis tool is the Fourier transform which, by producing power spectral densities (PSDs), allows time dependent signals to be studied in the frequency domain. However, the Fourier transform is global -- it extends over the entire time domain -- which makes it ill-suited to study nonstationary signals which exhibit local temporal changes in the signal`s frequency content. To analyze nonstationary signals, the family of transforms commonly designated as short-time Fourier transforms (STFTs), capable of identifying temporally localized changes in the signal`s frequency content, were developed by employing window functions to isolate temporal regions of the signal. For example, the Gabor STFT uses a Gaussian window. However, the applicability of STFTs is limited by various inadequacies. The Wavelet transform (NW), recently developed by Grossman and Morlet and explored in depth by Daubechies (2) and Mallat, remedies the inadequacies of STFTs. Like the Fourier transform, the WT can be implemented as a discrete transform (DWT) or as a continuous (integral) transform (CWT). This paper briefly illustrates some of the potential applications of the wavelet transform algorithms to signal analysis.

  6. Wavelet transform domain filters: a spatially selective noise filtration technique

    Microsoft Academic Search

    Yansun Xu; John B. Weaver; Dennis M. Healy Jr.; Jian Lu

    1994-01-01

    Wavelet transforms are multiresolution decompositions that can be used to analyze signals and images. They describe a signal by the power at each scale and position. Edges can be located very effectively in the wavelet transform domain. A spatially selective noise filtration technique based on the direct spatial correlation of the wavelet transform at several adjacent scales is introduced. A

  7. A Transformed Lagged Ensemble Forecasting Technique for Increasing Ensemble Size

    E-print Network

    Hansens, Jim

    A Transformed Lagged Ensemble Forecasting Technique for Increasing Ensemble Size Andrew. R.Lawrence@ecmwf.int #12;Abstract An ensemble-based data assimilation approach is used to transform old en- semble. The impact of the transformations are propagated for- ward in time over the ensemble's forecast period

  8. Towards Solvation of a Chiral Alpha-Hydroxy Ester: Broadband Chirp and Narrow Band Cavity Fouirier Transform Microwave Spectroscopy of Methyl Lactate-Water Clusters

    NASA Astrophysics Data System (ADS)

    Thomas, Javix; Sukhorukov, Oleksandr; Jaeger, Wolfgang; Xu, Yunjie

    2013-06-01

    Methyl lactate (ML), a chiral alpha-hydroxy ester, has attracted much attention as a prototype system in studies of chirality transfer,[1] solvation effects on chiroptical signatures,[2] and chirality recognition.[3] It has multiple functional groups which can serve both as a hydrogen donor and acceptor. By applying rotational spectroscopy and high level ab initio calculations, we examine the delicate competition between inter- and intramolecular hydrogen-bonding in the ML-water clusters. Broadband rotational spectra obtained with a chirp Fourier transform microwave (FTMW) spectrometer, reveal that the insertion conformations are the most favourable ones in the binary and ternary solvated complexes. In the insertion conformations, the water molecule(s) inserts itself (themselves) into the existing intramolecular hydrogen-bonded ring formed between the alcoholic hydroxyl group and the oxygen of the carbonyl group of ML. The final frequency measurements have been carried out using a cavity based FTMW instrument where internal rotation splittings due to the ester methyl group have also been detected. A number of insertion conformers with subtle structural differences for both the binary and ternary complexes have been identified theoretically. The interconversion dynamics of these conformers and the identification of the most favorable conformers will be discussed. 1. C. Merten, Y. Xu, Angew. Chem. Int. Ed., 2013, 52, 2073 -2076. 2. M. Losada, Y. Xu, Phys. Chem. Chem. Phys., 2007, 9, 3127-3135; Y. Liu, G. Yang, M. Losada, Y. Xu, J. Chem. Phys., 2010, 132, 234513/1-11. 3. A. Zehnacker, M. Suhm, Angew. Chem. Int. Ed. 2008, 47, 6970 - 6992.

  9. Wavelet transform techniques and signal analysis

    SciTech Connect

    Perez, R.B. (Oak Ridge National Lab., TN (United States)); Mattingly, J.K. (Univ. of Tennessee, Knoxville (United States)); Segovia-Perez, J. (Univ. of Madrid (Spain))

    1993-01-01

    Traditionally, the most widely used signal analysis tool is the Fourier transform, which, by producing power spectral densities (PSDs), allows time-dependent signals to be studied in the frequency domain. However, the Fourier transform is global-it extends over the entire time domain-which makes it ill suited to study nonstationary signals that exhibit local temporal changes in the signal's frequency content. To analyze nonstationary signals, the family of transforms commonly designated as short-time Fourier transforms (STFTs), capable of identifying temporally localized changes in the signal's frequency content, was developed by employing window functions to isolate temporal regions of the signal. For example, the Garborl STFT uses a Gaussian window. However, the applicability of STFTs is limited by various inadequacies. The wavelet transform (WT), recently developed by Grossman and Morlet and explored in depth by Daubechies and Mallat remedies the inadequacies of STFTS. Like the Fourier trans- form, the WT can be implemented as a discrete transform (DWT) or as a continuous (integral) transform (CWT).

  10. Detection of a chirping electromagnetic signal

    SciTech Connect

    Stearns, S.D.

    1989-01-01

    A matched chirp transform (MCT) method for detecting a dispersive electromagnetic pulse is described. The unique feature of this transform is that it gives a distribution of signal amplitude over time rather than frequency, and thereby simplifies signal detection and identification in the case described here. In the MCT method, the incoming signal is matched to a set of signal segments that chirp in accordance with an expected model of the dispersive medium. The performance of the MCT method is compared with that of a standard periodogram method of frequency measurement. 6 refs., 5 figs.

  11. Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics.

    PubMed

    Harput, Sevan; McLaughlan, James; Cowell, David M J; Freear, Steven

    2014-11-01

    Superharmonic imaging improves the spatial resolution by using the higher order harmonics generated in tissue. The superharmonic component is formed by combining the third, fourth, and fifth harmonics, which have low energy content and therefore poor SNR. This study uses coded excitation to increase the excitation energy. The SNR improvement is achieved on the receiver side by performing pulse compression with harmonic matched filters. The use of coded signals also introduces new filtering capabilities that are not possible with pulsed excitation. This is especially important when using wideband signals. For narrowband signals, the spectral boundaries of the harmonics are clearly separated and thus easy to filter; however, the available imaging bandwidth is underused. Wideband excitation is preferable for harmonic imaging applications to preserve axial resolution, but it generates spectrally overlapping harmonics that are not possible to filter in time and frequency domains. After pulse compression, this overlap increases the range side lobes, which appear as imaging artifacts and reduce the Bmode image quality. In this study, the isolation of higher order harmonics was achieved in another domain by using the fan chirp transform (FChT). To show the effect of excitation bandwidth in superharmonic imaging, measurements were performed by using linear frequency modulated chirp excitation with varying bandwidths of 10% to 50%. Superharmonic imaging was performed on a wire phantom using a wideband chirp excitation. Results were presented with and without applying the FChT filtering technique by comparing the spatial resolution and side lobe levels. Wideband excitation signals achieved a better resolution as expected, however range side lobes as high as -23 dB were observed for the superharmonic component of chirp excitation with 50% fractional bandwidth. The proposed filtering technique achieved >50 dB range side lobe suppression and improved the image quality without affecting the axial resolution. PMID:25389159

  12. Transionospheric chirp event classifier

    SciTech Connect

    Argo, P.E.; Fitzgerald, T.J.; Freeman, M.J.

    1995-09-01

    In this paper we will discuss a project designed to provide computer recognition of the transionospheric chirps/pulses measured by the Blackbeard (BB) satellite, and expected to be measured by the upcoming FORTE satellite. The Blackbeard data has been perused by human means -- this has been satisfactory for the relatively small amount of data taken by Blackbeard. But with the advent of the FORTE system, which by some accounts might ``see`` thousands of events per day, it is important to provide a software/hardware method of accurately analyzing the data. In fact, we are providing an onboard DSP system for FORTE, which will test the usefulness of our Event Classifier techniques in situ. At present we are constrained to work with data from the Blackbeard satellite, and will discuss the progress made to date.

  13. Image watermarking technique based on the steerable pyramid transform

    E-print Network

    Baskurt, Atilla

    of the steerable pyramid transform. This makes possible to hide watermarks with more energy in an image and alsoImage watermarking technique based on the steerable pyramid transform Fadoua DRIRA, Florence DENIS@liris.cnrs.fr fdenis@liris.cnrs.fr atilla.baskurt@liris.cnrs.fr ABSTRACT The application of the steerable pyramid

  14. Chirp Multiplication by Four Wave Mixing for Wideband Swept-Frequency Sources for High Resolution Imaging

    Microsoft Academic Search

    Naresh Satyan; George Rakuljic; Amnon Yariv

    2010-01-01

    We present an analysis and demonstration of the doubling of the chirp rate and total chirp bandwidth of a frequency chirped optical signal by the process of four-wave mixing in a non-linear optical medium. The effects of chromatic dispersion and input power on the maximum achievable output bandwidth are analyzed, and a dispersion compensation technique for phase matching is described.

  15. Chirped Pulse Microwave Spectroscopy in Pulsed Uniform Supersonic Flows

    NASA Astrophysics Data System (ADS)

    Abeysekera, Chamara; Oldham, James; Prozument, Kirill; Joalland, Baptiste; Park, Barratt; Field, Robert W.; Sims, Ian; Suits, Arthur; Zack, Lindsay

    2014-06-01

    We present preliminary results describing the development of a new instrument that combines two powerful techniques: Chirped Pulse-Fourier Transform MicroWave (CP-FTMW) spectroscopy and pulsed uniform supersonic flows. It promises a nearly universal detection method that can deliver quantitative isomer, conformer, and vibrational level specific detection, characterization of unstable reaction products and intermediates and perform unique spectroscopic, kinetics and dynamics measurements. We have constructed a new high-power K_a-band, 26-40 GHz, chirped pulse spectrometer with sub-MHz resolution, analogous to the revolutionary CP-FTMW spectroscopic technique developed in the Pate group at University of Virginia. In order to study smaller molecules, the E-band, 60-90 GHz, CP capability was added to our spectrometer. A novel strategy for generating uniform supersonic flow through a Laval nozzle is introduced. High throughput pulsed piezo-valve is used to produce cold (30 K) uniform flow with large volumes of 150 cm^3 and densities of 1014 molecules/cm3 with modest pumping facilities. The uniform flow conditions for a variety of noble gases extend as far as 20 cm from the Laval nozzle and a single compound turbo-molecular pump maintains the operating pressure. Two competing design considerations are critical to the performance of the system: a low temperature flow is needed to maximize the population difference between rotational levels, and high gas number densities are needed to ensure rapid cooling to achieve the uniform flow conditions. At the same time, collision times shorter than the chirp duration will give inaccurate intensities and reduced signal levels due to collisional dephasing of free induction decay. Details of the instrument and future directions and challenges will be discussed.

  16. Optimized pulse source employing an externally injected gain-switched laser diode in conjunction with a nonlinearly chirped grating

    Microsoft Academic Search

    P. M. Anandarajah; C. Guignard; A. Clarke; D. Reid; M. Rensing; L. P. Barry; G. Edvell; J. D. Harvey

    2006-01-01

    In this paper, we demonstrate the generation of transform-limited short optical pulses, which display excellent spectral and temporal qualities by employing a novel technology, based on an externally injected gain-switched laser in conjunction with a nonlinearly chirped grating. Using this technique, 3.5-ps optical pulses exhibiting a time-bandwidth product (TBP) of 0.45 are generated, which are suitable for use in high-speed

  17. Detection of Partial Discharges in Transformers Using Acoustic Emission Techniques

    Microsoft Academic Search

    E. Howells; E. T. Norton

    1978-01-01

    Partial discharges in transformers cause high frequency (ultrasonic) pressure pulses to propagate through the insulating media. These are similar in character to stress waves propagated in solids during crack formation (acoustic emission). The techniques involved in the detection of acoustic emission (AE) are shown to be well suited to the detection of emissions from partial discharges.

  18. Remote sensing image denoising by using discrete multiwavelet transform techniques

    NASA Astrophysics Data System (ADS)

    Wang, Haihui; Wang, Jun; Zhang, Jian

    2006-01-01

    We present a new method by using GHM discrete multiwavelet transform in image denoising on this paper. The developments in wavelet theory have given rise to the wavelet thresholding method, for extracting a signal from noisy data. The method of signal denoising via wavelet thresholding was popularized. Multiwavelets have recently been introduced and they offer simultaneous orthogonality, symmetry and short support. This property makes multiwavelets more suitable for various image processing applications, especially denoising. It is based on thresholding of multiwavelet coefficients arising from the standard scalar orthogonal wavelet transform. It takes into account the covariance structure of the transform. Denoising of images via thresholding of the multiwavelet coefficients result from preprocessing and the discrete multiwavelet transform can be carried out by treating the output in this paper. The form of the threshold is carefully formulated and is the key to the excellent results obtained in the extensive numerical simulations of image denoising. We apply the multiwavelet-based to remote sensing image denoising. Multiwavelet transform technique is rather a new method, and it has a big advantage over the other techniques that it less distorts spectral characteristics of the image denoising. The experimental results show that multiwavelet based image denoising schemes outperform wavelet based method both subjectively and objectively.

  19. New real time needle segmentation technique using grayscale Hough transformation

    NASA Astrophysics Data System (ADS)

    Qiu, Wu; Zhou, Hua; Ding, Mingyue; Zhang, Songgeng

    2007-12-01

    Real-time needle segmentation and tracking is very important in image-guided surgery, biopsy, and therapy. In this paper, we described an automated technique to provide real-time needle segmentation from a sequence of 2-D ultrasound images for the use of guidance of a needle to the target in soft tissues. The Hough transform is used to find straight lines or analytic curves in binary image. Hough transform is applied usually to binary images. Hence one needs to convert, initially, the gray level image to a binary one (through thresholding, edge detection, or thinning) in order to apply the HT. While in the process of binarization, some information about line segments in the image may be lost when an inappropriate threshold is used. Gray-Scale Hough Transform can detect the line without binarization. Unfortunately, its high computational cost often prevents it from being applied in real-time applications without the help of specially designed hardware. In this paper, we proposed a needle segmentation technique based on a real-time gray-scale Hough transform. It is composed of an improved Gray Hough Transformation and a coarse-fine search strategy. Furthermore, the RTGHT (Real-Time Gray-Scale Hough Transform) technique is evaluated by patient breast biopsy images. Experiments with patient breast biopsy ultrasound (US) image sequences showed that our approach can segment the biopsy needle in real time (i.e., less than 60 ms) with the angular rms error of about 1° and the position rms error of about 0.5 mm an affordable PC computer without the help of specially designed hardware.

  20. Transform-limited 100 microJ, 340 MW pulses from a nonlinear-fiber chirped-pulse amplifier using a mismatched grating stretcher-compressor.

    PubMed

    Zaouter, Y; Boullet, J; Mottay, E; Cormier, E

    2008-07-01

    We report on a compact double-stage ytterbium-doped-fiber chirped-pulse amplifier system delivering high temporal quality 270 fs pulses of 100 microJ energy at a repetition rate of 300 kHz resulting in a peak power of 340 MW. The recompression down to 1.1 times the Fourier limit is based on the exploitation of nonlinear phase shifts associated with mismatched stretcher-compressor units. A 1-m-long ytterbium-doped 80 mum core diameter photonic crystal fiber is implemented as the power amplifier and allows the production of 143 microJ pulses before compression with an accumulated B integral of 17 rad throughout the amplification stages. PMID:18594687

  1. Minimax Techniques For Optimizing Non-Linear Image Algebra Transforms

    NASA Astrophysics Data System (ADS)

    Davidson, Jennifer L.

    1989-08-01

    It has been well established that the Air Force Armament Technical Laboratory (AFATL) image algebra is capable of expressing all linear transformations [7]. The embedding of the linear algebra in the image algebra makes this possible. In this paper we show a relation of the image algebra to another algebraic system called the minimax algebra. This system is used extensively in economics and operations research, but until now has not been investigated for applications to image processing. The relationship is exploited to develop new optimization methods for a class of non-linear image processing transforms. In particular, a general decomposition technique for templates in this non-linear domain is presented. Template decomposition techniques are an important tool in mapping algorithms efficiently to both sequential and massively parallel architectures.

  2. Mode-selective excitation using ultrafast chirped laser pulses

    NASA Astrophysics Data System (ADS)

    Malinovskaya, S. A.

    2006-03-01

    We propose a method to control population transfer and coherence in a multimode system using a transform-limited pump and a linearly chirped Stokes pulse in stimulated Raman scattering. Simultaneously applied pump and Stokes pulse are shown to induce the ac Stark shifts that result in nonadiabatic coupling of the dressed states, through which the pulse chirp governs population distribution. The method may be applied to selectively excite Raman transitions having the frequency difference less than the bandwidth of a transform-limited pulse.

  3. Transforming spatial entanglement using a domain-engineering technique.

    PubMed

    Yu, X Q; Xu, P; Xie, Z D; Wang, J F; Leng, H Y; Zhao, J S; Zhu, S N; Ming, N B

    2008-12-01

    We study the spatial correlation of a two-photon entangled state produced in a multistripe periodically poled LiTaO3 crystal by spontaneous parametric down-conversion. The far-field diffraction-interference experiments reveal that the transverse modulation of domain patterns transforms the spatial mode function of the two-photon state. This result offers an approach to prepare a novel type of two-photon state with a unique spatial entanglement by using a domain-engineering technique. PMID:19113550

  4. Chirped-pulsed frequency modulation (C-PFM) for fiber Bragg grating sensors multiplexing

    Microsoft Academic Search

    G. Breglio; A. Irace; A. Cusano; A. Cutolo

    2006-01-01

    In this paper, we present experimental demonstration of using chirped-pulsed frequency modulation technique (C-PFM) in order to increase the multiplexing capability of a multipoint fiber Bragg grating (FBG) sensor network without increasing the hardware complexity of the acquisition system. This technique, extensively used in radar applications, is based on the amplitude modulation of the emitted signal (pulsed) by a chirped

  5. Recent EISCAT heating results using chirped ISR

    Microsoft Academic Search

    B. Isham; C. La Hoz; H. Kohl; T. Hagfors; T. B. Leyser; M. T. Rietveld

    1996-01-01

    The chirp technique has recently become fully operational on the EISCAT UHF radar system and has been used for daytime observations of the HF-modified ionosphere over Ramfjordmoen in November 1992 and March 1993. During certain periods the UHF observations show a difference in the frequencies of the photoelectron-enhanced plasma line and the HF-enhanced plasma line (HFPL) similar to the one

  6. Chirp Tunable Pure Dispersion Slope Compensator using Two Chirp FBG

    E-print Network

    Park, Namkyoo

    Chirp Tunable Pure Dispersion Slope Compensator using Two Chirp FBG *1),2) , 2) , 1) 1 , , , . , , . , . 1 . , S . , . , , FBG1 , FBG2 . beam , (a) Movable pivot Fixed pivot Uniform FBG Metal Beam L/2 1/3L Metal beam supporter ` FBG 1

  7. MULTICOMPONENT SUBSPACE CHIRP PARAMETER ESTIMATION USING DISCRETE FRACTIONAL FOURIER ANALYSIS

    E-print Network

    Santhanam, Balu

    MULTICOMPONENT SUBSPACE CHIRP PARAMETER ESTIMATION USING DISCRETE FRACTIONAL FOURIER ANALYSIS Albuquerque, NM, USA: 87131 jpeacock,bsanthan@unm.edu ABSTRACT The Discrete Fractional Fourier Transform- processing, and presents a quantitative analysis of its per- formance as compared to the Cram´er-Rao lower

  8. SAR vibrometry using fractional Fourier transform processing

    NASA Astrophysics Data System (ADS)

    Wang, Qi; Hayat, Majeed M.; Santhanam, Balu; Atwood, Tom

    2009-05-01

    A novel signal-processing approach is reported for vibrometry in synthetic aperture radar (SAR) imaging systems. The approach exploits the conventional deramp process; however, in place of Fourier-transform processing we utilize the fractional Fourier transform (FRFT) as a processing tool. The FRFT is geared toward non-stationary signals and chirped sinusoids particularly. A simplified mathematical expression is developed to describe the reflectivity of the aimed patch of ground containing vibrating targets as a function of space and time. Under the approximation that the velocities of vibrating point targets are constant during each probing chirped pulse, it is shown that the returned echo after the deramp process is a superposition of sinusoids that are chirped according to the Doppler effects induced by the vibrating point targets. By applying the multiangle centered discrete fractional Fourier transform (MA-CDFRFT) to the demodulated echoes, the instantaneous velocities of the vibrating point targets are estimated from the two coordinates of each peak in the MA-CDFRFT's frequency-angle plane. By repeating this process where a sequence of successive pulses are used to interrogate the vibrating targets, the velocities of the targets are estimated in each pulse, thereby generating a piecewise-linear estimate of the history of the vibration velocity in time. Theoretical performance evaluation of the proposed technique is carried out using real SAR-system parameters and simulated vibrating targets. The interplay amongst minimum detectable velocity, maximum detectable vibration frequency, pulse duration and chirp rate is determined analytically.

  9. Control of laser induced molecular fragmentation of n-propyl benzene using chirped femtosecond laser pulses

    PubMed Central

    Goswami, Tapas; Karthick Kumar, S.K.; Dutta, Aveek; Goswami, Debabrata

    2009-01-01

    We present the effect of chirping a femtosecond laser pulse on the fragmentation of n-propyl benzene. An enhancement of an order of magnitude for the relative yields of C3H3+ and C5H5+ in the case of negatively chirped pulses and C6H5+ in the case of positively chirped pulses with respect to the transform-limited pulse indicates that in some fragmentation channel, coherence of the laser field plays an important role. For the relative yield of all other heavier fragment ions, resulting from the interaction of the intense laser field with the molecule, there is no such enhancement effect with the sign of chirp, within experimental errors. The importance of the laser phase is further reinforced through a direct comparison of the fragmentation results with the second harmonic of the chirped laser pulse with identical bandwidth. PMID:19696899

  10. Transform Coding Techniques for Lossy Hyperspectral Data Compression

    Microsoft Academic Search

    Barbara Penna; Tammam Tillo; Enrico Magli; Gabriella Olmo

    2007-01-01

    Transform-based lossy compression has a huge potential for hyperspectral data reduction. Hyperspectral data are 3-D, and the nature of their correlation is different in each dimension. This calls for a careful design of the 3-D transform to be used for compression. In this paper, we investigate the transform design and rate allocation stage for lossy compression of hyperspectral data. First,

  11. Linear frequency-modulated signal detection using Radon-ambiguity transform

    Microsoft Academic Search

    Minsheng Wang; Andrew K. Chan; Charles K. Chui

    1998-01-01

    A novel time-frequency technique for linear frequency modulated (LFM) signal detection is proposed. The design of the proposed detectors is based on the Radon transform of the modulus square or the envelope amplitude of the ambiguity function (AF) of the signal. A practical assumption is made that the chirp rate is the only parameter of interest. Since the AF of

  12. Improved technique for one-way transformation of information

    DOEpatents

    Cooper, J.A.

    1987-05-11

    Method and apparatus are provided for one-way transformation of data according to multiplication and/or exponentiation modulo a prime number. An implementation of the invention permits the one way residue transformation, useful in encryption and similar applications, to be implemented by n-bit computers substantially with no increase in difficulty or complexity over a natural transformation thereby, using a modulus which is a power of two. 9 figs.

  13. Off\\/on-line FRA condition monitoring technique for power transformer

    Microsoft Academic Search

    S. Birlasekaran; Fred Fetherston

    1999-01-01

    This letter presents a novel and sensitive frequency response analysis (FRA) technique for off\\/on-line condition monitoring of expensive power apparatus. The main objective is to investigate the applicability of this predictive maintenance technique to diagnosing power transformer failures, to characterize the transformer in a frequency plane for safe operation, and to develop on-line monitoring technique. The effectiveness of this technique

  14. Techniques for increasing throughput in HEVC transform coefficient coding

    NASA Astrophysics Data System (ADS)

    Joshi, Rajan L.; Sole, Joel; Chen, Jianle; Chien, Wei-Jung; Karczewicz, Marta

    2012-10-01

    Transform coefficient coding in HEVC encompasses the scanning patterns and the coding methods for the last significant coefficient, significance map, coefficient levels and sign data. Unlike H.264/AVC, HEVC has a single entropy coding mode based on the context adaptive binary arithmetic coding (CABAC) engine. Due to this, achieving high throughput for transform coefficient coding was an important design consideration. This paper analyzes the throughput of different components of transform coefficient coding with special emphasis on the explicit coding of the last significant coefficient position and high throughput binarization. A comparison with H.264/AVC transform coefficient coding is also presented, demonstrating that HEVC transform coefficient coding achieves higher average and worst case throughput.

  15. Coherent multiple-frequency chirp exciter for L band radars

    Microsoft Academic Search

    Zdzislaw Sawicki

    2004-01-01

    This work presents design examples of coherent multiple-frequency chirp exciter for long distance L band surveillance radars. The implemented technique for pulse compression is the use of linear frequency modulation during the pulse. Long-duration linear FM pulses are obtained by the use of cascade two dispersive SAW delay lines and are converted to the desired carrier frequency. The set of

  16. Temporal self-imaging effect for chirped laser pulse sequences: Repetition rate and duty cycle tunability

    Microsoft Academic Search

    J. Lancis; J. Caraquitena; P. Andrés; M. A. Muriel

    2005-01-01

    We express parabolic-dispersion-induced transformations of a linearly chirped signal in terms of those suffered by the unchirped version of the same input signal. Specifically, we unveil that any amount of chirping and dispersion produces, aside from a scale factor, the same pulse-distortion effect as a certain parabolic dispersion in the unchirped input. This relevant result allows us to derive, as

  17. Lossless Image Compression Using Burrows Wheeler Transform (Methods and Techniques)

    Microsoft Academic Search

    Elfitrin Syahrul; Julien Dubois; Vincent Vajnovszki; Taoufik Saidani; Mohamed Atri

    2008-01-01

    The burrows-wheeler transform (BWT) is a combinatorial algorithm originally created for text compression such as bzip2, and that has been recently applied to image compression field. This paper focuses on the impact of compression scheme based on the combinatorial transform on high-level resolution medical images. It overviews the original scheme and some improvements that have been develop in post processing

  18. Embedded wavelet packet transform technique for texture compression

    NASA Astrophysics Data System (ADS)

    Li, Jin; Cheng, Po-Yuen; Kuo, C.-C. Jay

    1995-09-01

    A highly efficient texture compression scheme is proposed in this research. With this scheme, energy compaction of texture images is first achieved by the wavelet packet transform, and an embedding approach is then adopted for the coding of the wavelet packet transform coefficients. By comparing the proposed algorithm with the JPEG standard, FBI wavelet/scalar quantization standard and the EZW scheme with extensive experimental results, we observe a significant improvement in the rate-distortion performance and visual quality.

  19. Brain chirps: spectrographic signatures of epileptic seizures

    Microsoft Academic Search

    Steven J Schiff; David Colella; Gary M Jacyna; Elizabeth Hughes; Joseph W Creekmore; Angela Marshall; Maribeth Bozek-Kuzmicki; George Benke; William D Gaillard; Joan Conry; Steven R Weinstein

    2000-01-01

    Objective: A chirp is a brief signal within which the frequency content changes rapidly. Spectrographic chirps are found in signals produced from many biological and physical phenomena. In radar and sonar engineering, signals with chirps are used to localize direction and range to the signal source. Although characteristic frequency changes during epileptic seizures have long been observed, the correlation with

  20. Chirped-pulse millimeter-wave spectroscopy, dynamics, and manipulation of Rydberg-Rydberg Transitions

    E-print Network

    Colombo, Anthony P. (Anthony Paul)

    2013-01-01

    The chirped-pulse millimeter-wave (CPmmW) technique is applied to transitions between Rydberg states, and calcium atoms are used as the initial test system. The unique feature of Rydberg{Rydberg transitions is that they ...

  1. A Study of Mexican Free-Tailed Bat Chirp Syllables: Bayesian Functional Mixed Models for Nonstationary Acoustic Time Series

    PubMed Central

    MARTINEZ, Josue G.; BOHN, Kirsten M.; CARROLL, Raymond J.

    2013-01-01

    We describe a new approach to analyze chirp syllables of free-tailed bats from two regions of Texas in which they are predominant: Austin and College Station. Our goal is to characterize any systematic regional differences in the mating chirps and assess whether individual bats have signature chirps. The data are analyzed by modeling spectrograms of the chirps as responses in a Bayesian functional mixed model. Given the variable chirp lengths, we compute the spectrograms on a relative time scale interpretable as the relative chirp position, using a variable window overlap based on chirp length. We use 2D wavelet transforms to capture correlation within the spectrogram in our modeling and obtain adaptive regularization of the estimates and inference for the regions-specific spectrograms. Our model includes random effect spectrograms at the bat level to account for correlation among chirps from the same bat, and to assess relative variability in chirp spectrograms within and between bats. The modeling of spectrograms using functional mixed models is a general approach for the analysis of replicated nonstationary time series, such as our acoustical signals, to relate aspects of the signals to various predictors, while accounting for between-signal structure. This can be done on raw spectrograms when all signals are of the same length, and can be done using spectrograms defined on a relative time scale for signals of variable length in settings where the idea of defining correspondence across signals based on relative position is sensible. PMID:23997376

  2. Frequency-chirped subwavelength nanoantennas.

    PubMed

    Yaacobi, Ami; Watts, Michael R

    2012-12-01

    Herein we propose, theoretically investigate, and numerically demonstrate the first use to our knowledge of frequency chirping to achieve broadband, efficient subwavelength vertical emission from a dielectric waveguide. We demonstrate this unique and effective approach in the telecom C band in a nanophotonic frequency-chirped dipole antenna. The structure utilizes a plasmonic antenna placed above an Si3N4 waveguide and a ground plane to enhance emission efficiency. Three-dimensional finite-difference time-domain simulations reveal up to 55% vertical emission efficiency, and a bandwidth of 500 nm is possible in a structure less than half a wavelength long. The design methodology and theoretical underpinnings of frequency-chirped nanophotonic antennas coupled to dielectric waveguides are presented. PMID:23202110

  3. XPM and SPM response of a chirped DFBSOA all-optical flip-flop

    Microsoft Academic Search

    M. Jabbari; M. K. Moravvej-Farshi; R. Ghayour; A. Zarifkar

    2008-01-01

    In this paper, deriving a dynamic model based on the coupled-mode and carrier rate equations, we have proposed a new technique to switch ON and OFF of a chirped DFB-SOA all-optical flip-flop based on self phase modulation (SPM) and cross phase modulation (XPM). We have shown that with this technique in an optimized condition into a DFB-SOA with chirped grating

  4. Multi-secondary transformer: A modeling technique for simulation

    Microsoft Academic Search

    A. Patel; N. P. Singh; B. Raval; A. Roy; A. Thakar; D. Parmar; H. Dhola; R. Dave; S. Gajjar; V. Gupta; U. Baruah; V. Tripathi; L. N. Gupta; P. Patel

    2011-01-01

    Pulse Step Modulation based High voltage power supply has played significant role in fusion research. Multi- Secondary transformers are invariably used for generation of tens of kV range outputs with fast (µS order) transient response. In this scheme, large numbers of isolated voltage sources are connected in series to generate the output. Isolated voltage sources can be achieved by large

  5. Comparing Parameter Estimation Techniques for an Electrical Power Transformer Oil Temperature Prediction Model

    NASA Technical Reports Server (NTRS)

    Morris, A. Terry

    1999-01-01

    This paper examines various sources of error in MIT's improved top oil temperature rise over ambient temperature model and estimation process. The sources of error are the current parameter estimation technique, quantization noise, and post-processing of the transformer data. Results from this paper will show that an output error parameter estimation technique should be selected to replace the current least squares estimation technique. The output error technique obtained accurate predictions of transformer behavior, revealed the best error covariance, obtained consistent parameter estimates, and provided for valid and sensible parameters. This paper will also show that the output error technique should be used to minimize errors attributed to post-processing (decimation) of the transformer data. Models used in this paper are validated using data from a large transformer in service.

  6. Structured Chirped Fiber Bragg Gratings

    Microsoft Academic Search

    Marco Pisco; Agostino Iadicicco; Stefania Campopiano; Antonello Cutolo; Andrea Cusano

    2008-01-01

    In this paper, a theoretical and numerical analysis of novel in-fiber photonic devices based on a structured chirped fiber Bragg gratings (CFBGs) for sensing and communication applications is presented. The investigated structure consists in a CFBG with single or multiple defects obtained by a deep and localized stripping of the cladding layer along the grating structure. The thinning of the

  7. A transformation technique to estimate the process capability index for non-normal processes

    Microsoft Academic Search

    S. Z. Hosseinifard; Babak Abbasi; S. Ahmad; M. Abdollahian

    2009-01-01

    Estimating the process capability index (PCI) for non-normal processes has been discussed by many researches. There are two\\u000a basic approaches to estimating the PCI for non-normal processes. The first commonly used approach is to transform the non-normal\\u000a data into normal data using transformation techniques and then use a conventional normal method to estimate the PCI for transformed\\u000a data. This is

  8. Superconducting current transformer for testing Nb3Sn cable splicing technique

    SciTech Connect

    Nicolai Andreev et al.

    2002-09-10

    To provide a quick feedback on different approaches to superconducting cable splicing design and assembly techniques, a superconducting current transformer that can deliver more than 20 kA for testing splice samples has been designed and fabricated. The existing infrastructure of the Short Sample Test Facility at Fermilab, including its cryostat, power supply, and data acquisition system, was used for housing and operating the transformer. This report presents the design features of the transformer and the main results of cable splice tests.

  9. Novel combinatorial probabilistic Hough transform technique for detection of underwater bubbles

    Microsoft Academic Search

    John Y. Goulermas; Panos Liatsis

    1997-01-01

    Combinatorial Probabilistic Hough Transforms (CPHTs) are a class of HTs that transform minimal subsets of points required to define an instance of the sought shape to single parameter cells, thus reducing redundant evidence. Existing CPHTs discard valuable information contained in the gradient of the object outlines. This research proposes a novel HT technique for detection of circular instances, called the

  10. MICROARRAY IMAGE ENHANCEMENT TECHNIQUES USING THE DISCRETE WAVELET TRANSFORM

    Microsoft Academic Search

    Emmanouil Athanasiadis; Dimitris Glotsos; Antonis Daskalakis; Panagiotis Bougioukos; Pantelis Theocharakis; Panagiota Spyridonos; Kalatzis Ioannis; George Nikiforidis; Dionisis Cavouras

    The objective of this work was to perform a comparative evaluation of five different wavelet-based filtering techniques in the task of microarray image denoising and enhancement. Clinical material comprised microarray images collected from the Oak Ridge National Laboratory. Image processing was performed in two stages: In the first stage an Exponential Histogram Equalization filter was applied in order to increase

  11. Transforming Student Health Services through Purpose-Driven Assessment Techniques

    ERIC Educational Resources Information Center

    Knoll, Dorothy; Meiers, Chris; Honeck, Sara

    2006-01-01

    The University of Kansas Medical Center did a comprehensive review of the services provided in the Student Health Center (SHC). Using purpose-driven assessment techniques, areas needing improvement were identified. The results of the survey were presented to students and, with student support, student health fees were increased to fund desired…

  12. Alias-free image reconstruction using Fresnel transform in the phase-scrambling Fourier imaging technique.

    PubMed

    Ito, Satoshi; Yamada, Yoshifumi

    2008-08-01

    An image reconstruction technique that reduces aliasing artifacts by scalable image reconstruction in magnetic resonance imaging (MRI) is proposed. The signal obtained by the phase-scrambling Fourier transform (PSFT) imaging technique can be transformed to the signal described in the Fresnel transform equation of the objects. Therefore, image reconstruction can be performed not only by inverse FT but also by inverse Fresnel transform. When a phase-scrambling coefficient is given in a certain range, image reconstruction by inverse Fresnel transform allows shrinking of images over rather wide scales. Thus, reduced aliasing images can be reconstructed even from signals that produce serious aliasing artifacts by standard inverse FT reconstruction. Simulation and experimental studies reveal that the proposed method can be used to produce reduced aliasing images. PMID:18666133

  13. Pulse-shaping and Fourier Transform Techniques in Multiphoton Microscopy

    Microsoft Academic Search

    Jennifer Ogilvie; Delphine D'Barre; Emmanuel Beaurepaire; Antigoni Alexandrou; Manuel Joffre

    2006-01-01

    Multiphoton microscopy is an important tool that is increasingly used in biological research. The ease with which broadband femtosecond pulses can be created and manipulated has opened up new directions for enhancing multiphoton microscopy. In particular, pulse-shaping techniques can tailor broadband light to selectively excite fluorescent species.[1] Here we demonstrate the use of pulse-shaped excitation to enhance multiphoton fluorescence imaging

  14. Conversion of chirp in fiber compression.

    PubMed

    Dombi, Péter; Rácz, Péter; Veisz, Laszlo; Baum, Peter

    2014-04-15

    Focusing positively chirped femtosecond pulses into nonlinear fibers provides significant spectral broadening and compression at higher pulse energies than achievable conventionally because self-focusing and damage are avoided. Here, we investigate the transfer of input to output chirp in such an arrangement. Our measurements show that the group delay dispersion of the output pulse, originating from the nonlinearities, is considerably reduced as compared to the initial value, by about a factor of 10. The mechanism of chirp reduction is understood by an interplay of self-phase modulation with initial chirp within the fiber. A simple model calculation based on this picture yields satisfactory agreement with the observations and predicts significant chirp reduction for input pulses up to the ?J regime. In practice, the reduction of chirp observed here allows for compressing the spectrally broadened intense pulses by ultrabroadband dispersive multilayer mirrors of quite moderate dispersion. PMID:24978959

  15. Scale Invariant Feature Transform Technique for Weed Classification in Oil Palm Plantation

    Microsoft Academic Search

    Kamarul Hawari Ghazali; Mohd. Marzuki Mustafa; Aini Hussain; Saifudin Razali

    2008-01-01

    This study presents a new and robust technique using Scale Invariant Feature Transform (SIFT) for weed classification in oil palm plantation. The proposed SIFT classification technique was developed to overcome problem in real application of image processing such as varies of lighting densities, resolution and target range which contributed to classification accuracy. In this study, SIFT classification algorithm is used

  16. Effective switching mode power supplies common mode noise cancellation technique with zero equipotential transformer models

    Microsoft Academic Search

    Yick Po Chan; Man Hay Pong; Ngai Kit Poon; Chui Pong Liu

    2010-01-01

    In this paper a transformer construction technique is proposed that effectively cut off the Common Mode (CM) noise voltage passing across the isolated primary and secondary windings. This technique employs the Zero Equipotential Line theory to construct an anti-phase winding. It effectively cuts down CM noise by eliminating the noise voltage across the isolated primary and secondary windings. The concept

  17. Continuous wavelet transform technique for fault signal diagnosis of internal combustion engines

    Microsoft Academic Search

    Jian-Da Wu; Jien-Chen Chen

    2006-01-01

    A fault signal diagnosis technique for internal combustion engines that uses a continuous wavelet transform algorithm is presented in this paper. The use of mechanical vibration and acoustic emission signals for fault diagnosis in rotating machinery has grown significantly due to advances in the progress of digital signal processing algorithms and implementation techniques. The conventional diagnosis technology using acoustic and

  18. Hybrid chirped pulse amplification system

    DOEpatents

    Barty, Christopher P.; Jovanovic, Igor

    2005-03-29

    A hybrid chirped pulse amplification system wherein a short-pulse oscillator generates an oscillator pulse. The oscillator pulse is stretched to produce a stretched oscillator seed pulse. A pump laser generates a pump laser pulse. The stretched oscillator seed pulse and the pump laser pulse are directed into an optical parametric amplifier producing an optical parametric amplifier output amplified signal pulse and an optical parametric amplifier output unconverted pump pulse. The optical parametric amplifier output amplified signal pulse and the optical parametric amplifier output laser pulse are directed into a laser amplifier producing a laser amplifier output pulse. The laser amplifier output pulse is compressed to produce a recompressed hybrid chirped pulse amplification pulse.

  19. Transformer Incipient Fault Prediction Using Combined Artificial Neural Network and Various Particle Swarm Optimisation Techniques

    PubMed Central

    2015-01-01

    It is important to predict the incipient fault in transformer oil accurately so that the maintenance of transformer oil can be performed correctly, reducing the cost of maintenance and minimise the error. Dissolved gas analysis (DGA) has been widely used to predict the incipient fault in power transformers. However, sometimes the existing DGA methods yield inaccurate prediction of the incipient fault in transformer oil because each method is only suitable for certain conditions. Many previous works have reported on the use of intelligence methods to predict the transformer faults. However, it is believed that the accuracy of the previously proposed methods can still be improved. Since artificial neural network (ANN) and particle swarm optimisation (PSO) techniques have never been used in the previously reported work, this work proposes a combination of ANN and various PSO techniques to predict the transformer incipient fault. The advantages of PSO are simplicity and easy implementation. The effectiveness of various PSO techniques in combination with ANN is validated by comparison with the results from the actual fault diagnosis, an existing diagnosis method and ANN alone. Comparison of the results from the proposed methods with the previously reported work was also performed to show the improvement of the proposed methods. It was found that the proposed ANN-Evolutionary PSO method yields the highest percentage of correct identification for transformer fault type than the existing diagnosis method and previously reported works. PMID:26103634

  20. Identification of biological tissue using chirped probe THz imaging

    Microsoft Academic Search

    B. Ferguson; S. Wang; D. Gray; D. Abbott; X.-C Zhang

    2002-01-01

    We consider the application of pulsed THz imaging systems in biomedical diagnostics and mail\\/packaging inspection. The sub-millimetre spectroscopic measurements obtained from T-ray systems contain a wealth of information about the sample under test. We demonstrate that different types of tissue can be classified based on their terahertz response measured with the chirped probe pulse technique. We demonstrate the performance of

  1. Double-image encryption by using chaos-based local pixel scrambling technique and gyrator transform

    NASA Astrophysics Data System (ADS)

    Li, Huijuan; Wang, Yurong; Yan, Haitao; Li, Liben; Li, Qiuze; Zhao, Xiaoyan

    2013-12-01

    A novel double-image encryption algorithm is proposed by using chaos-based local pixel scrambling technique and gyrator transform. Two original images are first regarded as the amplitude and phase of a complex function. Arnold transform is used to scramble pixels at a local area of the complex function, where the position of the scrambled area and the Arnold transform frequency are generated by the standard map and logistic map respectively. Then the changed complex function is converted by gyrator transform. The two operations mentioned will be implemented iteratively. The system parameters in local pixel scrambling and gyrator transform serve as the keys of this encryption algorithm. Numerical simulation has been performed to test the validity and the security of the proposed encryption algorithm.

  2. Micro-diffuse reflectance and matrix isolation Fourier transform infrared techniques for the identification of tetrachlorodibenzodioxins

    Microsoft Academic Search

    Donald F. Gurka; Jimmie W. Brasch; Russell H. Barnes; Charles J. Riggle; Sidney Bourne

    1986-01-01

    Micro-diffuse reflectance Fourier transform infrared (DRIFT) and matrix isolation (MI) Fourier transform infrared spectra of the 22 tetrachlorodibenzodioxin (TCDD) isomers have been recorded. The DRIFT and MI techniques required about four minutes and one-half minute, respectively, of signal averaging to produce high signal-to-noise (S\\/N) spectra on low-nanogram-level samples. Spectral subtraction was employed to remove DRIFT solvent impurity interferences. The validity

  3. Detection and frequency tracking of chirping signals

    SciTech Connect

    Elliott, G.R.; Stearns, S.D.

    1990-08-01

    This paper discusses several methods to detect the presence of and track the frequency of a chirping signal in broadband noise. The dynamic behavior of each of the methods is described and tracking error bounds are investigated in terms of the chirp rate. Frequency tracking and behavior in the presence of varying levels of noise are illustrated in examples. 11 refs., 29 figs.

  4. Coherent chirped pulse laser network with Mickelson phase conjugator.

    PubMed

    Okulov, A Yu

    2014-04-10

    The mechanisms of nonlinear phase-locking of a large fiber amplifier array are analyzed. The preference is given to the most suitable configuration for a coherent coupling of thousands of fundamental spatial mode fiber beams into a single smooth beam ready for chirped pulse compression. It is shown that a Michelson phase-conjugating configuration with double passage through an array of fiber amplifiers has the definite advantage compared to a one-way fiber array coupled in a Mach-Zehnder configuration. Regardless of the amount of synchronized fiber amplifiers, the Michelson phase-conjugating interferometer is expected to do a perfect compensation of the phase-piston errors and collimation of backwardly amplified fiber beams on an entrance/output beam splitter. In both configurations, the nonlinear transformation of the stretched pulse envelope, due to gain saturation, is capable of randomizing the position of chirp inside an envelope; thus it may reduce the visibility of the interference pattern at an output beam splitter. Certain advantages are inherent to the sech-form temporal envelope because of the exponential precursor and self-similar propagation in gain medium. The Gaussian envelope is significantly compressed in a deep gain saturation regime, and the frequency chirp position inside pulse envelope is more deformed. PMID:24787398

  5. Population inversion by chirped pulses

    SciTech Connect

    Lu Tianshi [Department of Mathematics and Statistics, Wichita State University, Wichita, Kansas 67260-0033 (United States)

    2011-09-15

    In this paper, we analyze the condition for complete population inversion by a chirped pulse over a finite duration. The nonadiabatic transition probability is mapped in the two-dimensional parameter space of coupling strength and detuning amplitude. Asymptotic forms of the probability are derived by the interference of nonadiabatic transitions for sinusoidal and triangular pulses. The qualitative difference between the maps for the two types of pulses is accounted for. The map is used for the design of stable inversion pulses under specific accuracy thresholds.

  6. A Robust Transform Domain Narrowband Interference Suppression Technique in Wireless Communications

    Microsoft Academic Search

    Li-Ping Zhu; Zhihong Chen; Xiaodong Yan; Yi-Sheng Zhu

    2008-01-01

    In this paper, we propose a robust narrowband interference excision technique in wireless communications based on modulated lapped biorthogonal transform (MLBT), including the Malvar's MLBT and the MLBT constructed by Matviyenko's optimized window. First, we study the bit error rate (BER) performance of the MLBT-based exciser in direct sequence spread spectrum (DSSS) system theoretically. Then we study the application of

  7. High quality switched wavelet packet and discrete cosine transform audio coding technique

    Microsoft Academic Search

    Pao-Chi Chang; Tzung-Hung Wu; Kong-Yueh Ho

    2005-01-01

    We propose a hybrid coding system that utilizes both wavelet packet (WP) and DCT techniques. To process each audio frame, the system selects either WP or DCT as the transform based on the frame flatness measures in the wavelet domain and the frequency domain. If DCT is chosen, all DCT coefficients are quantized by a non-uniform quantizer according to the

  8. Chirped-Pulse Millimeter-Wave Spectroscopy of Rydberg-Rydberg Transitions

    SciTech Connect

    Prozument, Kirill; Colombo, Anthony P.; Zhou Yan; Park, G. Barratt; Petrovic, Vladimir S.; Coy, Stephen L.; Field, Robert W. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2011-09-30

    Transitions between Rydberg states of Ca atoms, in a pulsed, supersonic atomic beam, are directly detected by chirped-pulse millimeter-wave spectroscopy. Broadband, high-resolution spectra with accurate relative intensities are recorded instantly. Free induction decay (FID) of atoms, polarized by the chirped pulse, at their Rydberg-Rydberg transition frequencies, is heterodyne detected, averaged in the time domain, and Fourier transformed into the frequency domain. Millimeter-wave transient nutations are observed, and the possibility of FID evolving to superradiance is discussed.

  9. December 15, 1994 / Vol. 19, No. 24 / OPTICS LETTERS 2149 Self-phasemodulation in chirped-pulse amplification

    E-print Network

    Ditmire, Todd

    assume that the initial low-energy pulse is transform limited with a field distribution, Eo(z, t), and a Fourier transform, Eo(z, co- coo). This pulse is stretched by a grating-based stretcher with a phaseDecember 15, 1994 / Vol. 19, No. 24 / OPTICS LETTERS 2149 Self-phasemodulation in chirped-pulse

  10. Fully programmable spectrum sliced chirped microwave photonic filter.

    PubMed

    Leitner, Peter; Yi, Xiaoke; Li, Liwei; Huang, Thomas X H

    2015-02-23

    A novel chirped microwave photonic filter (MPF) capable of achieving a large radio frequency (RF) group delay slope and a single passband response free from high frequency fading is presented. The design is based upon a Fourier domain optical processor (FD-OP) and a single sideband modulator. The FD-OP is utilized to generate both constant time delay to tune the filter and first order dispersion to induce the RF chirp, enabling full software control of the MPF without the need for manual adjustment. An optimized optical parameter region based on a large optical bandwidth >750 GHz and low slicing dispersion < ± 1 ps/nm is introduced, with this technique greatly improving the RF properties including the group delay slope magnitude and passband noise. Experimental results confirm that the structure simultaneously achieves a large in-band RF chirp of -4.2 ns/GHz, centre frequency invariant tuning and independent reconfiguration of the RF amplitude and phase response. Finally, a stochastic study of the device passband noise performance under tuning and reconfiguration is presented, indicating a low passband noise <-120 dB/Hz. PMID:25836442

  11. Chirp control of a single-mode, good beam quality, zigzag dye laser

    SciTech Connect

    Mandl, A.; Zavriyev, A.; Klimek, D.E. [Textron Systems Div., Wilmington, MA (United States)] [Textron Systems Div., Wilmington, MA (United States)

    1997-03-01

    The authors report a substantial reduction of frequency chirp of a single-mode laser-pumped zigzag dye laser. A linear optical cavity using counterpropagating orthogonally polarized waves was injection-seeded at 568 nm and operated with a laser output of about 1 J. The chirp was controlled by an intracavity Pockels cell that was configured to add optical density at a rate which counterbalanced the decrease in optical density due to dye-solvent heating during the {approximately}1-{micro}s laser pulse. Heterodyne measurements were used to determine that the bandwidth was near the transform limit and chirp rate of {approximately}1 MHz/{micro}s. The beam quality of the laser was measured at 10 Hz as 1.7 XDL.

  12. Characteristics of nonlinear imaging of broadband laser stacked by chirped pulses

    NASA Astrophysics Data System (ADS)

    Wang, Youwen; You, Kaiming; Chen, Liezun; Lu, Shizhuan; Dai, Zhiping; Ling, Xiaohui

    2014-11-01

    Nanosecond-level pulses of specific shape is usually generated by stacking chirped pulses for high-power inertial confinement fusion driver, in which nonlinear imaging of scatterers may damage precious optical elements. We present a numerical study of the characteristics of nonlinear imaging of scatterers in broadband laser stacked by chirped pulses to disclose the dependence of location and intensity of images on the parameters of the stacked pulse. It is shown that, for sub-nanosecond long sub-pulses with chirp or transform-limited sub-pulses, the time-mean intensity and location of images through normally dispersive and anomalously dispersive self-focusing medium slab are almost identical; While for picosecond-level short sub-pulses with chirp, the time-mean intensity of images for weak normal dispersion is slightly higher than that for weak anomalous dispersion through a thin nonlinear slab; the result is opposite to that for strong dispersion in a thick nonlinear slab; Furthermore, for given time delay between neighboring sub-pulses, the time-mean intensity of images varies periodically with chirp of the sub-pulse increasing; for a given pulse width of sub-pulse, the time-mean intensity of images decreases with the time delay between neighboring sub-pulses increasing; additionally, there is a little difference in the time-mean intensity of images of the laser stacked by different numbers of sub-pulses. Finally, the obtained results are also given physical explanations.

  13. High-Fidelity Adiabatic Passage by Composite Sequences of Chirped Pulses

    NASA Astrophysics Data System (ADS)

    Torosov, Boyan T.; Guérin, Stéphane; Vitanov, Nikolay V.

    2011-06-01

    We present a method for optimization of the technique of adiabatic passage between two quantum states by composite sequences of frequency-chirped pulses with specific relative phases: composite adiabatic passage (CAP). By choosing the composite phases appropriately the nonadiabatic losses can be canceled to any desired order with sufficiently long sequences, regardless of the nonadiabatic coupling. The values of the composite phases are universal for they do not depend on the pulse shapes and the chirp. The accuracy of the CAP technique and its robustness against parameter variations make CAP suitable for high-fidelity quantum information processing.

  14. A novel fault-detection technique of high-impedance arcing faults in transmission lines using the wavelet transform

    Microsoft Academic Search

    Chul-Hwan Kim; Hyun Kim; Young-Hun Ko; Sung-Hyun Byun; Raj K. Aggarwal; Allan T. Johns

    2002-01-01

    This paper describes a novel fault-detection technique of high-impedance faults (HIFs) in high-voltage transmission lines using the wavelet transform. The wavelet transform (WT) has been successfully applied in many fields. The technique is based on using the absolute sum value of coefficients in multiresolution signal decomposition (MSD) based on the discrete wavelet transform (DWT). A fault indicator and fault criteria

  15. Optical chirped beam amplification and propagation

    DOEpatents

    Barty, Christopher P.

    2004-10-12

    A short pulse laser system uses dispersive optics in a chirped-beam amplification architecture to produce high peak power pulses and high peak intensities without the potential for intensity dependent damage to downstream optical components after amplification.

  16. Categorical perception of nonspeech chirps and bleats

    Microsoft Academic Search

    Richard E. Pastore; Xiao-Feng Li; Jody Kaplan Layer

    1990-01-01

    Mattingly, Liberman, Syrdal, and Halwes, (1971) claimed to demonstrate that subjects cannot classify nonspeech chirp and bleat\\u000a continua, but that they can classify into three categories a syllable place continuum whose variation is physically identical\\u000a to the nonspeech chirp and bleat continua. This finding for F2 transitions, as well as similar findings for F3 transitions,\\u000a has been cited as one

  17. Image hiding in Fourier domain by use of joint transform correlator architecture and holographic technique.

    PubMed

    Shi, Xiaoyan; Zhao, Daomu

    2011-02-10

    Based on joint transform correlator (JTC) architecture and holographic techniques, a new method for image hiding is presented. A hidden image encrypted by JTC architecture is embedded in the Fourier hologram of the host image. Inverse Fourier transform can be used to obtain the watermarked image, and JTC architecture is used to decode the hidden image from the watermarked hologram. Unlike other watermarking techniques, by prechoosing information, the noise added to the recovered hidden image by the host can be reduced. Unlike other watermarking systems based on double random-phase encoding, no conjugate key is used to recover the hidden image. Theoretical analyses have shown the system's feasibility. Computer simulations are presented to verify the system's validity and efficiency. Numerical simulations also show that the proposed system is robust enough to resist attacks, such as occlusion, noise, and filtering. PMID:21343999

  18. A Hilbert transform method for parameter identification of time-varying structures with observer techniques

    Microsoft Academic Search

    Zuo-Cai Wang; Wei-Xin Ren; Gen-Da Chen

    2012-01-01

    This paper presents a recursive Hilbert transform method for the time-varying property identification of large-scale shear-type buildings with limited sensor deployments. An observer technique is introduced to estimate the building responses from limited available measurements. For an n-story shear-type building with l measurements (l ? n), the responses of other stories without measurements can be estimated based on the first

  19. Analyzing laser plasma interferograms with a continuous wavelet transform ridge extraction technique: the method

    Microsoft Academic Search

    Paolo Tomassini; Antonio Giulietti; Leonida A. Gizzi; Marco Galimberti; Danilo Giulietti; Marco Borghesi; Oswald Willi

    2001-01-01

    Laser plasma interferograms are currently analyzed by extraction of the phase-shift map with fast Fourier transform (FFT) techniques [Appl. Opt. 18, 3101 (1985)]. This methodology works well when interferograms are only marginally affected by noise and reduction of fringe visibility, but it can fail to produce accurate phase-shift maps when low-quality images are dealt with. We present a novel procedure

  20. Weighted fuzzy interpolative reasoning for sparse fuzzy rule-based systems based on transformation techniques

    Microsoft Academic Search

    Yuan-Kai Ko; Shyi-Ming Chen; Jeng-Shyang Pan

    2008-01-01

    In this paper, we present a new weighted fuzzy interpolative reasoning method for sparse fuzzy rule-based systems. For multiple antecedent variables interpolation, the proposed method allows each condition appearing in the antecedent parts of fuzzy rules associated with a weighting factor. The alpha-cuts and transformation techniques are extended to handle the weighted fuzzy interpolative reasoning in sparse fuzzy rule-based systems.

  1. Optical image encryption based on multistage fractional Fourier transforms and pixel scrambling technique

    NASA Astrophysics Data System (ADS)

    Zhao, Jianlin; Lu, Hongqiang; Song, Xiaoshan; Li, Jifeng; Ma, Yanghua

    2005-05-01

    A novel encryption for optical image based on multistage fractional Fourier transforms (FRTs) and pixel scrambling technique is presented in this paper. The principle of pixel scrambling is described and an optical approach to realize the pixel scrambling and decoding is also proposed. Numerical simulation results are given to verify the algorithm, and relative error (RE) between the decoded images and the original image versus the deviation of fractional orders is discussed. Comparing with single FRT encryption, the security using this method for optical image encryption is greatly improved due to the introduction of the pixel scrambling technique.

  2. Fast X-ray microdiffraction techniques for studying irreversible transformations in materials

    PubMed Central

    Kelly, Stephen T.; Trenkle, Jonathan C.; Koerner, Lucas J.; Barron, Sara C.; Walker, Nöel; Pouliquen, Philippe O.; Tate, Mark W.; Gruner, Sol M.; Dufresne, Eric M.; Weihs, Timothy P.; Hufnagel, Todd C.

    2011-01-01

    A pair of techniques have been developed for performing time-resolved X-ray microdiffraction on irreversible phase transformations. In one technique capillary optics are used to focus a high-flux broad-spectrum X-ray beam to a 60?µm spot size and a fast pixel array detector is used to achieve temporal resolution of 55?µs. In the second technique the X-rays are focused with Kirkpatrick–Baez mirrors to achieve a spatial resolution better than 10?µm and a fast shutter is used to provide temporal resolution better than 20?µs while recording the diffraction pattern on a (relatively slow) X-ray CCD camera. Example data from experiments are presented where these techniques are used to study self-propagating high-temperature synthesis reactions in metal laminate foils. PMID:21525656

  3. Unraveling the nature of electric field- and stress- induced structural transformations in soft PZT by a new powder poling technique.

    PubMed

    Kalyani, Ajay Kumar; V, Lalitha K; James, Ajit R; Fitch, Andy; Ranjan, Rajeev

    2015-02-25

    A 'powder-poling' technique was developed to study electric field induced structural transformations in ferroelectrics exhibiting a morphotropic phase boundary (MPB). The technique was employed on soft PZT exhibiting a large longitudinal piezoelectric response (d(33) ? 650 pC N(-1)). It was found that electric poling brings about a considerable degree of irreversible tetragonal to monoclinic transformation. The same transformation was achieved after subjecting the specimen to mechanical stress, which suggests an equivalence of stress and electric field with regard to the structural mechanism in MPB compositions. The electric field induced structural transformation was also found to be accompanied by a decrease in the spatial coherence of polarization. PMID:25629264

  4. Attenuated total reflectance spectroscopy with chirped-pulse upconversion.

    PubMed

    Shirai, Hideto; Duchesne, Constance; Furutani, Yuji; Fuji, Takao

    2014-12-01

    Chirped-pulse upconversion technique has been applied to attenuated total reflectance (ATR) infrared spectroscopy. An extremely broadband infrared pulse was sent to an ATR diamond prism and the reflected pulse was converted to the visible by using four-wave mixing in krypton gas. Absorption spectra of liquids in the range from 200 to 5500 cm(-1) were measured with a visible spectrometer on a single-shot basis. The system was applied to observe the dynamics of exchanging process of two solvents, water and acetone, which give clear vibrational spectral contrast. We observed that the exchange was finished within ? 10 ms. PMID:25606893

  5. Plasma absorption evidence via chirped pulse spectral transmission measurements

    NASA Astrophysics Data System (ADS)

    Jedrkiewicz, Ottavia; Minardi, Stefano; Couairon, Arnaud; Jukna, Vytautas; Selva, Marco; Di Trapani, Paolo

    2015-06-01

    This work aims at highlighting the plasma generation dynamics and absorption when a Bessel beam propagates in glass. We developed a simple diagnostics allowing us to retrieve clear indications of the formation of the plasma in the material, thanks to transmission measurements in the angular and wavelength domains. This technique featured by the use of a single chirped pulse having the role of pump and probe simultaneously leads to results showing the plasma nonlinear absorption effect on the trailing part of the pulse, thanks to the spectral-temporal correspondence in the measured signal, which is also confirmed by numerical simulations.

  6. Selective and efficient control of coherent population transfer with time-separated chirped pulses

    SciTech Connect

    Yang Xihua; Zhang Zhenhua; Yan Xiaona; Li Chunfang [Department of Physics, Shanghai University, Shanghai 200444 (China)

    2010-03-15

    We propose a selective, efficient, and robust way to realize control of coherent population transfer in a {Lambda}-type four-level system with a closely spaced doublet in the final state with time-separated chirped pump pulse and Stokes pulse pair by merging stimulated Raman adiabatic passage, temporal coherent control, and chirped adiabatic passage techniques. Moreover, an arbitrary coherent superposition between the final doublet, or between the intermediate state and either of the doublets can be created. This method holds the ability to 'control with control' and has potential applications in coherent control of chemical reactions and quantum information processing.

  7. Femtosecond mode-locked Yb fiber laser for single-mode fiber chirped pulse amplification system

    Microsoft Academic Search

    K. Sumimura; H. Yoshida; H. Fujita; M. Nakatsuka

    2007-01-01

    High-peak-power laser systems are based on the chirped pulse amplification (CPA) technique. CPA laser system needs a mode-locked\\u000a laser oscillator for stable ultrashort pulse laser generation. We report a single-mode fiber CPA system which consists of\\u000a stable mode-locked Yb-doped fiber laser oscillator with a wide tuning range, chirped fiber Bragg grating stretcher, and two\\u000a Yb-doped fiber amplifiers. The single-mode fibers

  8. Adaptive narrow-band interference rejection in a DS spread-spectrum intercept receiver using transform domain signal processing techniques

    NASA Technical Reports Server (NTRS)

    Gevargiz, John; Das, Pankaj K.; Milstein, Laurence B.

    1989-01-01

    An intercept receiver which uses a transform-domain-processing filter is described. This receiver detects direct-sequence BPSK spread-spectrum signals in the presence of narrowband interference by employing adaptive narrowband interference rejection techniques. The improvement in the system performance over that of conventional detection techniques is shown by presenting the results of experimental measurements of probability of detection versus false alarm for an enhanced total power detector. Also presented are certain results corresponding to detection of the spectral lines generated at twice the carrier frequency, wherein the goal is often not just signal detection, but also carrier frequency estimation. The receiver uses one of two transform-domain-processing techniques for adaptive narrowband interference rejection. In the first technique, the narrowband interference is detected and excised in the transform domain by using an adaptive notch filter. In the second technique, the interference is suppressed using soft-limiting in the transform domain.

  9. Seismic coherent and random noise attenuation using the undecimated discrete wavelet transform method with WDGA technique

    NASA Astrophysics Data System (ADS)

    Goudarzi, Alireza; Riahi, Mohammad Ali

    2012-12-01

    One of the most crucial challenges in seismic data processing is the reduction of the noise in the data or improving the signal-to-noise ratio. In this study, the 1D undecimated discrete wavelet transform (UDWT) has been acquired to attenuate random noise and ground roll. Wavelet domain ground roll analysis (WDGA) is applied to find the ground roll energy in the wavelet domain. The WDGA will be a substitute method for thresholding in seismic data processing. To compare the effectiveness of the WDGA method, we apply the 1D double density discrete wavelet transform (DDDWT) using soft thresholding in the random noise reduction and ground roll attenuation processes. Seismic signals intersect with ground roll in the time and frequency domains. Random noise and ground roll have many undesirable effects on pre-stack seismic data, and result in an inaccurate velocity analysis for NMO correction. In this paper, the UDWT by using the WDGA technique and DDDWT (using the soft thresholding technique) and the regular Fourier based method as f-k transform will be used and compared for seismic denoising.

  10. End effect analysis of linear induction motor based on the wavelet transform technique

    SciTech Connect

    Mori, Yoshihiko; Torii, Susumu; Ebihara, Daiki

    1999-09-01

    HSST (High Speed Surface Transport) is currently being developed for the railway systems of urban transportation in Japan. It is used in the electromagnetic suspension and short-stator Linear Induction Motor (LIM) for the HSST. The performance of LIM is degraded due to the influence of the end effects. LIM is analyzed using the Fourier series expansion to throw light on this problem. However, to obtain the high-accuracy in this technique, the number of times for calculating is increased. In case of the Wavelet transform technique, as the Wavelet coefficients converge rapidly to zero, this technique has been applied to analyze the end effects of LIM. In this paper, the authors investigated the method for determining of mother wavelet.

  11. Experimental Demonstration of Energy-Chirp Compensation by a Tunable Dielectric-Based Structure

    NASA Astrophysics Data System (ADS)

    Antipov, S.; Baturin, S.; Jing, C.; Fedurin, M.; Kanareykin, A.; Swinson, C.; Schoessow, P.; Gai, W.; Zholents, A.

    2014-03-01

    A tunable energy-chirp compensator was used to remove a correlated energy chirp from the 60-MeV beam at the Brookhaven National Laboratory Accelerator Test Facility. The compensator operates through the interaction of the wakefield of the electron bunch with itself and consists of a planar structure comprised of two alumina bars with copper-plated backs separated by an adjustable beam aperture. By changing the gap size, the correlated energy chirp of the electron bunch was completely removed. Calculations show that this device, properly scaled to account for the electron bunch charge and length, can be used to remove residual correlated energy spread at the end of the linacs used for free-electron lasers. The experimental results are shown to be in good agreement with numerical simulations. Application of this technique can significantly simplify linac design and improve free-electron lasers performance.

  12. Chirp signal matching and signal power optimization in pulse-echo mode ultrasonic nondestructive testing

    Microsoft Academic Search

    Martin Pollakowski; Helmut Ermert

    1994-01-01

    Chirp pulse compression is a signal correlation technique that uses frequency modulated pulses as transmitted signals. Usually, signals with linear frequency modulation are applied. They can be generated rather easily, but their spectra are not totally matched to the transfer function of ultrasonic systems. In pulse-echo mode operation, with signal duration and consequently the time-bandwidth product being critical parameters, waveforms

  13. Scheme for measuring dispersion of chirped FBG using loop mirror configuration

    Microsoft Academic Search

    A. K. Atieh; I. Golub

    2001-01-01

    A novel scheme for measuring dispersion of chirped fiber Bragg gratings is demonstrated using loop mirror configuration. The measurement is insensitive to polarization or temperature variation. The technique is relatively simple, inexpensive, and requires only a broad-band light source

  14. Pattern Transformation of Heat-Shrinkable Polymer by Three-Dimensional (3D) Printing Technique

    NASA Astrophysics Data System (ADS)

    Zhang, Quan; Yan, Dong; Zhang, Kai; Hu, Gengkai

    2015-03-01

    A significant challenge in conventional heat-shrinkable polymers is to produce controllable microstructures. Here we report that the polymer material fabricated by three-dimensional (3D) printing technique has a heat-shrinkable property, whose initial microstructure can undergo a spontaneous pattern transformation under heating. The underlying mechanism is revealed by evaluating internal strain of the printed polymer from its fabricating process. It is shown that a uniform internal strain is stored in the polymer during the printing process and can be released when heated above its glass transition temperature. Furthermore, the internal strain can be used to trigger the pattern transformation of the heat-shrinkable polymer in a controllable way. Our work provides insightful ideas to understand a novel mechanism on the heat-shrinkable effect of printed material, but also to present a simple approach to fabricate heat-shrinkable polymer with a controllable thermo-structural response.

  15. Pattern transformation of heat-shrinkable polymer by three-dimensional (3D) printing technique.

    PubMed

    Zhang, Quan; Yan, Dong; Zhang, Kai; Hu, Gengkai

    2015-01-01

    A significant challenge in conventional heat-shrinkable polymers is to produce controllable microstructures. Here we report that the polymer material fabricated by three-dimensional (3D) printing technique has a heat-shrinkable property, whose initial microstructure can undergo a spontaneous pattern transformation under heating. The underlying mechanism is revealed by evaluating internal strain of the printed polymer from its fabricating process. It is shown that a uniform internal strain is stored in the polymer during the printing process and can be released when heated above its glass transition temperature. Furthermore, the internal strain can be used to trigger the pattern transformation of the heat-shrinkable polymer in a controllable way. Our work provides insightful ideas to understand a novel mechanism on the heat-shrinkable effect of printed material, but also to present a simple approach to fabricate heat-shrinkable polymer with a controllable thermo-structural response. PMID:25757881

  16. Image encryption based on extended fractional Fourier transform and digital holography technique

    NASA Astrophysics Data System (ADS)

    Wang, Xiaogang; Zhao, Daomu; Chen, Linfei

    2006-04-01

    We present a new optical image encryption algorithm that is based on extended fractional Fourier transform (FRT) and digital holography technique. We can perform the encryption and decryption with more parameters compared with earlier similar methods in FRT domain. In the extended FRT encryption system, the input data to be encrypted is extended fractional Fourier transformed two times and random phase mask is placed at the output plane of the first extended FRT. By use of an interference with a wave from another random phase mask, the encrypted data is stored as a digital hologram. The data retrieval is operated by all-digital means. Computer simulations are presented to verify its validity and efficiency.

  17. CHIRP's potential to introduce a new USAF space acquisition paradigm

    Microsoft Academic Search

    Joseph Simonds; George Sullivan

    2012-01-01

    The objectives of this paper are: (1) to explore lessons learned from the United States Air Force's (USAF) Commercially Hosted Infrared Payload (CHIRP); and (2) how those lessons can be applied to acquire operational space assets quickly and less expensively in the future. CHIRP is a payload configured with a SES-WorldSkies comsat. The goals of the CHIRP program are to

  18. Chirped Brillouin dynamic gratings for storing and compressing light.

    PubMed

    Winful, Herbert G

    2013-04-22

    We demonstrate theoretically that chirped dynamic gratings can be created in optical fibers through stimulated Brillouin scattering with frequency-chirped "signal" and "write" pulses. When the grating is interrogated with a third pulse of the opposite chirp, a compressed signal pulse is retrieved. This provides a method to regenerate stored pulses and enhance signal levels for communications applications. PMID:23609709

  19. Optical image encryption based on multichannel fractional Fourier transform and double random phase encoding technique

    NASA Astrophysics Data System (ADS)

    Jin, Weimin; Yan, Caijie

    2007-01-01

    The optical image encryption based on multichannel fractional Fourier transform (FRT) and double random phase encoding technique is proposed. Optical principles of encoding and decoding are analyzed in detail. With this method, one can encrypt different parts of input image, respectively. The system security can be improved to some extent, not only because fractional orders and random phase masks in every channel can be set with freedom, but also because the system parameters among all channels are independent. Numerical simulation results of optical image encryption based on four channel FRT and double random phase encoding are given to verify the feasibility of the method.

  20. On the utility of fast transforms in parity-mixed PDEs: Part I. Numerical techniques and analysis

    E-print Network

    Julien, Keith

    for computing these complicated projections exactly up to some arbitrary degree using fast Fourier transformsOn the utility of fast transforms in parity-mixed PDEs: Part I. Numerical techniques and analysis Sciences & JILA, University of Colorado, Boulder, CO 80309, United States bDepartment of Astrophysical

  1. Photodissociation of D2 (+) induced by linearly chirped laser pulses.

    PubMed

    Csehi, András; Halász, Gábor J; Cederbaum, Lorenz S; Vibók, Ágnes

    2015-07-01

    Recently, it has been revealed that so-called light-induced conical intersections (LICIs) can be formed both by standing or by running laser waves even in diatomic molecules. Due to the strong nonadiabatic couplings, the existence of such LICIs has significant impact on the dynamical properties of a molecular system. In our former studies, the photodissociation process of the D2 (+) molecule was studied initiating the nuclear dynamics both from individual vibrational levels and from the superposition of all the vibrational states produced by ionizing D2. In the present work, linearly chirped laser pulses were used for initiating the dissociation dynamics of D2 (+). In contrast to the constant frequency (transform limited) laser fields, the chirped pulses give rise to LICIs with a varying position according to the temporal frequency change. To demonstrate the impact of these LICIs on the dynamical properties of diatomics, the kinetic energy release spectra, the total dissociation probabilities, and the angular distributions of the D2 (+) photofragments were calculated and discussed. PMID:26156481

  2. The fiber optic device for signal positive chirping by interferential method with tuning of chirp size

    NASA Astrophysics Data System (ADS)

    Vinogradova, Irina L.; Sultanov, Albert K.; Meshkov, Ivan K.; Andrianova, Anna V.; Abdrahmanova, Guzel I.; Gorodetsky, Ivan I.; Nizamov, Timir R.; Chirikov, Roman Y.

    2015-03-01

    The device for positive chirping of a signal in a fiber optical line is offered. The device is based on two Fabry-Perot resonator with additional fiber optical cannels. If to execute the amalgamator from an erbium doped material, the device will supply amplification of a target signal, which is important for distribution access systems (for example, Radio-over- Fiber systems (RoF)). The device provides selectivity for spectral components of entrance radiation, that allows to operate of chirp. Built-in the converter of length provides in additional fiber optical cannels tuning the chirp under the given size.

  3. Dilatometric technique for evaluation of the kinetics of solid-state transformation of maraging steel

    SciTech Connect

    Viswanathan, U.K.; Kutty, T.R.G.; Ganguly, C. [Bhabha Atomic Research Centre, Bombay (India). Radiometallurgy Div.

    1993-12-01

    Solid-state transformation kinetics of a 350 grad commercial maraging steel were investigated using a nonisothermal dilatometric technique. Two solid-state reactions -- namely, precipitation of intermetallic phases from supersaturated martensite and reversion of martensite to austenite -- were identified. Determination was made of the temperatures at which the rates of these reactions reached a maximum at different heating rates. The kinetics of the individual reactions in terms of activation energy were analyzed by simplified procedures based on the Kissinger equation. An estimated activation energy of 145 {+-} 4 kJ/mol for the precipitation of intermetallic phase was in good agreement with reported results based on the isothermal hardness measurement technique. Martensite to austenite reversion was associated with an activation energy of 224 {+-} 4 kJ/mol, which is very close to the activation energy for diffusion of substitutional elements in ferrite. Results were supplemented with microstructural analysis.

  4. Fourier transform infrared spectroscopy techniques for the analysis of drugs of abuse

    NASA Astrophysics Data System (ADS)

    Kalasinsky, Kathryn S.; Levine, Barry K.; Smith, Michael L.; Magluilo, Joseph J.; Schaefer, Teresa

    1994-01-01

    Cryogenic deposition techniques for Gas Chromatography/Fourier Transform Infrared (GC/FT-IR) can be successfully employed in urinalysis for drugs of abuse with detection limits comparable to those of the established Gas Chromatography/Mass Spectrometry (GC/MS) technique. The additional confidence of the data that infrared analysis can offer has been helpful in identifying ambiguous results, particularly, in the case of amphetamines where drugs of abuse can be confused with over-the-counter medications or naturally occurring amines. Hair analysis has been important in drug testing when adulteration of urine samples has been a question. Functional group mapping can further assist the analysis and track drug use versus time.

  5. On the relationship between pump chirp and single-photon chirp in spontaneous parametric downconversion

    E-print Network

    X. Sanchez-Lozano; A. B. U'Ren; J. L. Lucio

    2012-06-04

    We study the chronocyclic character, i.e. the joint temporal and spectral properties, of the single-photon constituents of photon pairs generated by spontaneous parametric down conversion. In particular we study how single photon properties, including purity and single-photon chirp, depend on photon pair properties, including the type of signal-idler spectral and correlations and the level of pump chirp.

  6. Chirped pulse amplification with a nonlinearly chirped fiber Bragg grating matched to the Treacy compressor

    NASA Astrophysics Data System (ADS)

    Imeshev, G.; Hartl, I.; Fermann, M. E.

    2004-04-01

    We demonstrate a fiber chirped pulse amplification system that uses an engineered nonlinearly chirped fiber Bragg grating stretcher dispersion matched to the Treacy compressor. The seed pulses at 1558 nm are stretched to 720 ps, amplified by more than 50 dB to 6.5-µJ energy, and recompressed to 940 fs. After almost 1000 times compression the pulses are within 30% of the bandwidth limit and have a contrast ratio of better than 30 dB.

  7. Transformers

    NSDL National Science Digital Library

    Kuphaldt, Tony R.

    All About Circuits is a website that â??provides a series of online textbooks covering electricity and electronics.â? Written by Tony R. Kuphaldt, the textbooks available here are wonderful resources for students, teachers, and anyone who is interested in learning more about electronics. This specific section, Transformers, is the ninth chapter in Volume II â??Alternating Current (AC). A few of the topics covered in this chapter include: Mutual inductance and basic operation; Step-up and Step-down transformers; Electrical isolation; Phasing; Winding configurations; Voltage Regulation; and finally, Special transformers and applications.. Diagrams and detailed descriptions of concepts are included throughout the chapter to provide users with a comprehensive lesson. Visitors to the site are also encouraged to discuss concepts and topics using the All About Circuits discussion forums (registration with the site is required to post materials).

  8. Extension of harmonic cutoff in a multicycle chirped pulse combined with a chirp-free pulse

    SciTech Connect

    Xu Junjie; Zeng Bin; Yu Yongli [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800 (China)

    2010-11-15

    We demonstrate high-order harmonic generation in a wave form synthesized by a multicycle 800-nm chirped laser pulse and a chirp-free laser pulse. Compared with the case of using only a chirped pulse, both the harmonic cutoff and the extreme ultraviolet supercontinuum can be extended when a weak chirp-free pulse is combined with the chirped pulse. When chirp-free pulse intensity grows, the cutoff energy and bandwidth of the supercontinuum grow as well. It is found that the broad supercontinuum can be achieved for a driving pulse with long duration even though the driving pulse reaches 10 optical cycles. An isolated attosecond pulse with duration of about 59 as is obtained, and after appropriate phase compensation with a duration of about 11 as. In addition, by performing time-frequency analyses and the classical trajectory simulation, the difference in supercontinuum generation between the preceding wave form and a similar wave form synthesized by an 800-nm fundamental pulse and a 1600-nm subharmonic pulse is investigated.

  9. Coherent control of terahertz harmonic generation by a chirped few-cycle pulse in a quantum well

    NASA Astrophysics Data System (ADS)

    Cui, Ni; Xiang, Yang; Niu, Yueping; Gong, Shangqing

    2010-01-01

    We present results on the occurrence of ultrashort terahertz harmonic generation (THG) driven by a millimeter nonlinear chirped few-cycle laser pulse in a symmetric double quantum well. By solving the effective nonlinear Bloch equations, THG with a generic plateau and cutoff can be produced. The time-frequency characteristic of the ultrashort terahertz harmonic spectrum is analyzed in detail by means of the wavelet transform of induced dipole acceleration. Furthermore, an ultrabroad supercontinuum terahertz harmonic spectrum can be generated and an isolated ultrashort terahertz pulse can be obtained at the cutoff region by choosing the appropriate chirping rate parameters.

  10. Chirped-Pulse millimeter-Wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions.

    PubMed

    Prozument, Kirill; Park, G Barratt; Shaver, Rachel G; Vasiliou, AnGayle K; Oldham, James M; David, Donald E; Muenter, John S; Stanton, John F; Suits, Arthur G; Ellison, G Barney; Field, Robert W

    2014-08-14

    A Chirped-Pulse millimeter-Wave (CPmmW) spectrometer is applied to the study of chemical reaction products that result from pyrolysis in a Chen nozzle heated to 1000-1800 K. Millimeter-wave rotational spectroscopy unambiguously determines, for each polar reaction product, the species, the conformers, relative concentrations, conversion percentage from precursor to each product, and, in some cases, vibrational state population distributions. A chirped-pulse spectrometer can, within the frequency range of a single chirp, sample spectral regions of up to ?10 GHz and simultaneously detect many reaction products. Here we introduce a modification to the CPmmW technique in which multiple chirps of different spectral content are applied to a molecular beam pulse that contains the pyrolysis reaction products. This technique allows for controlled allocation of its sensitivity to specific molecular transitions and effectively doubles the bandwidth of the spectrometer. As an example, the pyrolysis reaction of ethyl nitrite, CH3CH2ONO, is studied, and CH3CHO, H2CO, and HNO products are simultaneously observed and quantified, exploiting the multi-chirp CPmmW technique. Rotational and vibrational temperatures of some product molecules are determined. Subsequent to supersonic expansion from the heated nozzle, acetaldehyde molecules display a rotational temperature of 4 ± 1 K. Vibrational temperatures are found to be controlled by the collisional cooling in the expansion, and to be both species- and vibrational mode-dependent. Rotational transitions of vibrationally excited formaldehyde in levels ?4, 2?4, 3?4, ?2, ?3, and ?6 are observed and effective vibrational temperatures for modes 2, 3, 4, and 6 are determined and discussed. PMID:24756159

  11. 850 OPTICS LETTERS / Vol. 25, No. 11 / June 1, 2000 Chirp control in the direct space-to-time pulse shaper

    E-print Network

    Purdue University

    is manipulated. These properties are fundamentally different than in the well-known Fourier-transform pulse this geometry and the well- known Fourier-transform (FT) pulse-shaper geome- try4,5 is that the state of each850 OPTICS LETTERS / Vol. 25, No. 11 / June 1, 2000 Chirp control in the direct space-to-time pulse

  12. Analysis of cochlear implant artifact removal techniques using the continuous wavelet transform.

    PubMed

    Sinkiewicz, Daniel; Friesen, Lendra; Ghoraani, Behnaz

    2014-01-01

    When patients with cochlear implants (CI) undergo cortical auditory evoked potential (CAEP) tests to evaluate their hearing, a large electrical artifact introduced by the CI obscures the relevant information in the signal. Several methods have been developed for the purpose of removing the CI artifact; however, there is no gold standard (i.e., patient's auditory response before the CI) to assess the effectiveness of these methods in terms of successful removal of artifact. To address this crucial shortcoming, we employ time-frequency (TF) signal representation (i.e., continuous wavelet transform (CWT)) to evaluate the effectiveness of two recent CI removal techniques, known as the subtraction and polynomial methods. Our results show that polynomial method consistently outperforms the subtraction method in the presence of tone stimulus. These results also indicate a possible CWT-based method for removing the CI artifact from a speech stimuli response, which the subtraction and polynomial methods cannot do. PMID:25571235

  13. The Climate Hazards group InfraRed Precipitation (CHIRP) with Stations (CHIRPS): Development and Validation

    NASA Astrophysics Data System (ADS)

    Peterson, P.; Funk, C. C.; Husak, G. J.; Pedreros, D. H.; Landsfeld, M.; Verdin, J. P.; Shukla, S.

    2013-12-01

    CHIRP and CHIRPS are new quasi-global precipitation products with daily to seasonal time scales, a 0.05° resolution, and a 1981 to near real-time period of record. Developed by the Climate Hazards Group at UCSB and scientists at the U.S. Geological Survey Earth Resources Observation and Science Center specifically for drought early warning and environmental monitoring, CHIRPS provides moderate latency precipitation estimates that place observed hydrologic extremes in their historic context. Three main types of information are used in the CHIRPS: (1) global 0.05° precipitation climatologies, (2) time-varying grids of satellite-based precipitation estimates, and (3) in situ precipitation observations. CHIRP: The global grids of long-term (1980-2009) average precipitation were estimated for each month based on station data, averaged satellite observations, and physiographic parameters. 1981-present time-varying grids of satellite precipitation were derived from spatially varying regression models based on pentadal cold cloud duration (CCD) values and TRMM V7 training data. The CCD time-series were derived from the CPC and NOAA B1 datasets. Pentadal CCD-percent anomaly values were multiplied by pentadal climatology fields to produce low bias pentadal precipitation estimates. CHIRPS: The CHG station blending procedure uses the satellite-observed spatial covariance structure to assign relative weights to neighboring stations and the CHIRP values. The CHIRPS blending procedure is based on the expected correlation between precipitation at a given target location and precipitation at the locations of the neighboring observation stations. These correlations are estimated using the CHIRP fields. The CHG has developed an extensive archive of in situ daily, pentadal and monthly precipitation totals. The CHG database has over half a billion daily rainfall observations since 1980 and another half billion before 1980. Most of these observations come from four sets of global climate observations: the monthly Global Historical Climate Network version 2 archive, the daily Global Historical Climate Network archive, the Global Summary of the Day dataset (GSOD), and the daily Global Telecommunication System (GTS) archive provided by NOAA's Climate Prediction Center (CPC). A screening procedure was developed to flag and remove potential false zeros from the daily data, since these potentially spurious data can artificially suppress rainfall totals. Validation: Our validation focused on precipitation products with global coverage, long periods of record and near real-time availability: CHIRP, CHIRPS, CPC-Unified, CFS Reanalysis and ECMWF datasets were compared to GPCC and high quality datasets from Uganda, Colombia and the Sahel. The CHIRP and CHIRPS are shown to have low systematic errors (bias) and low mean absolute errors. Analyses in Uganda, Colombia and the Sahel indicate that the ECMWF, CPC-Unified and CFS-Reanalysis have large inhomogeneities, making them unsuitable for drought monitoring. The CHIRPS performance appears quite similar to research quality products like the GPCC and GPCP, but with higher resolution and lower latency.

  14. High Sensitivity EMAT System using Chirp Pulse Compression and Its Application to Crater End Detection in Continuous Casting

    NASA Astrophysics Data System (ADS)

    Iizuka, Y.; Awajiya, Y.

    2014-06-01

    A high sensitivity EMAT system using chirp pulse compression technique was developed. The system uses a high power gated amplifier having 2kVpp output to transmit chirp waves. Pulse compression of the received signals are performed digitally in a PC after amplification and analog-to-digital conversion. A 20dB improvement of the signal-to-noise ratio was achieved by chirp pulse compression and synchronous averaging. A new surface cooling technique was also developed to improve the signal amplitude of the bulk shear wave with hot steel, and its effectiveness was demonstrated. An actual plant test of crater end detection by the developed EMAT system was conducted at a continuous caster, and clear detection by non-contact EMATs was achieved.

  15. Studies on Nephrite and Jadeite Jades by Fourier Transform Infrared (ftir) and Raman Spectroscopic Techniques

    NASA Astrophysics Data System (ADS)

    Tan, T. L.; Ng, L. L.; Lim, L. C.

    2013-10-01

    The mineralogical properties of black nephrite jade from Western Australia are studied by Fourier transform infrared (FTIR) spectroscopy using both transmission and specular reflectance techniques in the 4000-400 cm-1 wavenumber region. The infrared absorption peaks in the 3700-3600 cm-1 region which are due to the O-H stretching mode provides a quantitative analysis of the Fe/(Fe+Mg) ratio in the mineral composition of jade samples. The Fe/(Fe+Mg) percentage in black nephrite is found to be higher than that in green nephrite, but comparable to that of actinolite (iron-rich nephrite). This implies that the mineralogy of black nephrite is closer to actinolite than tremolite. The jade is also characterized using Raman spectroscopy in the 1200-200 cm-1 region. Results from FTIR and Raman spectroscopic data of black nephrite jade are compared with those of green nephrite jade from New Zealand and jadeite jade from Myanmar. Black nephrite appears to have a slightly different chemical composition from green nephrite. Spectra from FTIR and Raman spectroscopic techniques were found to be useful in differentiating black nephrite, green nephrite, and green jadeite jades. Furthermore, data on refractive index, specific gravity, and hardness of black nephrite jade are measured and compared with those of green nephrite and of jadeite jade.

  16. Design constraints of optical parametric chirped pulse amplification based on chirped quasi-phase-matching gratings.

    PubMed

    Phillips, C R; Mayer, B W; Gallmann, L; Fejer, M M; Keller, U

    2014-04-21

    Chirped quasi-phase-matching (QPM) gratings offer efficient, ultra-broadband optical parametric chirped pulse amplification (OPCPA) in the mid-infrared as well as other spectral regions. Only recently, however, has this potential begun to be realized [1]. In this paper, we study the design of chirped QPM-based OPCPA in detail, revealing several important constraints which must be accounted for in order to obtain broad-band, high-quality amplification. We determine these constraints in terms of the underlying saturated nonlinear processes, and explain how they were met when designing our mid-IR OPCPA system. The issues considered include gain and saturation based on the basic three-wave mixing equations; suppression of unwanted non-collinear gain-guided modes; minimizing and characterizing nonlinear losses associated with random duty cycle errors in the QPM grating; avoiding coincidentally-phase-matched nonlinear processes; and controlling the temporal/spectral characteristics of the saturated nonlinear interaction in order to maintain the chirped-pulse structure required for OPCPA. The issues considered place constraints both on the QPM devices as well as the OPCPA system. The resulting experimental guidelines are detailed. Our results represent the first comprehensive discussion of chirped QPM devices operated in strongly nonlinear regimes, and provide a roadmap for advancing and experimentally implementing OPCPA systems based on these devices. PMID:24787850

  17. Propagation stability of a chirped soliton in birefringent fibers

    NASA Astrophysics Data System (ADS)

    Zheng, Hongjun; Liu, Shanliang; Li, Xin; Wu, Chongqing

    2011-02-01

    The propagation stability of a chirped soliton at anomalous dispersion region in birefringent fibers is numerically studied by using the split-step Fourier-method. It is found that initial linear chirp can change obviously the threshold value Ath above which soliton stably propagates in birefringent fibers, the Ath increases with the decrease of the polarization angle | /4- |. The positive chirp makes obviously the Ath smaller for group velocity mismatch parameter >0.5, the negative one makes the Ath larger for <0.5. The effect of initial positive chirp on the Ath is greater than that of negative chirp for high birefringent fibers, is less than that of negative chirp for low birefringent fibers.

  18. Supercontinuum spectrum control in microstructure fibers by initial chirp management.

    PubMed

    Driben, Rodislav; Zhavoronkov, Nickolai

    2010-08-01

    Experiments and numerical simulation were performed for verification of the role of femtosecond pulse chirp for supercontinuum generation in photonic crystal fiber. We demonstrate that injection of high power negatively chirped pulses near zero dispersion point brings an advantage over positively chirped pulses resulting in additional collision between solitons and in development of a significantly broader spectrum. Coupling between Raman induced solitons and dispersive waves generated by higher order dispersion was proven to be the key mechanism behind the results. PMID:20721063

  19. The generation of group delay ripple of chirped fiber gratings

    NASA Astrophysics Data System (ADS)

    Tan, Zhongwei; Liu, Yan; Ning, Tigang; Jian, Shuisheng

    2004-01-01

    The analysis of the group delay ripple (GDR) generated by chirped fiber gratings is developed based on the Fabry-Perot (F-P) resonator. It shows clearly how the GDR is generated and why the periods of GDR varies along the chirped fiber gratings. It could also explain why apodization could suppress the GDR and how apodization affects the chirp of the grating. The theory could be used to devise the apodization of fiber gratings.

  20. Mechanism of electron acceleration by chirped laser pulse

    SciTech Connect

    Wu, X. Y.; Wang, P. X. [Department of Nuclear Science and Technology, Institute of Modern Physics, Fudan University, Shanghai 200433, China and Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education (China); Kawata, S. [Department of Advanced Interdisciplinary Science, Center for Optical Research and Education, Graduate School of Engineering, Utsunomiya University, Utsunomiya 321-8585 (Japan)

    2012-05-28

    We studied the mechanism of electron acceleration by a chirped laser pulse. We found that, because of the chirp effect, a region exists where the laser wave phase experienced by the electron varies slowly, so that the electron can be accelerated for a long time. The mechanism of chirped laser acceleration is different to that of the capture and acceleration scenario, although both of them have a main acceleration stage in which the electrons are trapped for long periods.

  1. Program Transformation Techniques Applied to Languages Used in High Performance Computing

    E-print Network

    Gray, Jeffrey G.

    Parallelization Transformations Specified in SPOT Meta-level Transformation Code Antlr3 + StringTemplate Rose Code and program transformation OpenFortran Meta-Level Program Variable Method Base-Level Program MetaC Targeted Hardware Architectures Using parallel programming models to convert serial programs into parallel

  2. Measurement of neutral currents in a power transformer and fault detection using wavelet techniques

    Microsoft Academic Search

    A. Bhoomaiah; P. Krishna Reddyl; K. S. Linga Murthyl; P. Appla Naidu; B. P. Singh

    2004-01-01

    Fault analysis and diagnosis of a transformer are essential, as power quality is one of the primary concerns of the electric power utilities. Insulation failure within transformer windings is considered to be one of the most important causes of the failure of power transformers. A comparison of neutral currents at reduced and full voltages is carried out for detection of

  3. Categorical perception of nonspeech chirps and bleats.

    PubMed

    Pastore, R E; Li, X F; Layer, J K

    1990-08-01

    Mattingly, Liberman, Syrdal, and Halwes, (1971) claimed to demonstrate that subjects cannot classify nonspeech chirp and bleat continua, but that they can classify into three categories a syllable place continuum whose variation is physically identical to the nonspeech chirp and bleat continua. This finding for F2 transitions, as well as similar findings for F3 transitions, has been cited as one source of support for theories that different modes or modules underlie the perception of speech and nonspeech acoustic stimuli. However, this pattern of finding for speech and nonspeech continua may be the result of research methods rather than a true difference in subject ability. Using tonal stimuli based on the nonspeech stimuli of Mattingly et al., we found that subjects, with appropriate practice, could classify nonspeech chirp, short bleat, and bleat continua with boundaries equivalent to the syllable place continuum of Mattingly et al. With the possible exception of the higher frequency boundary for both our bleats and the Mattingly syllables, ABX discrimination peaks were clearly present and corresponded in location to the given labeling boundary. PMID:2385489

  4. SAR processing with stepped chirps and phased array antennas.

    SciTech Connect

    Doerry, Armin Walter

    2006-09-01

    Wideband radar signals are problematic for phased array antennas. Wideband radar signals can be generated from series or groups of narrow-band signals centered at different frequencies. An equivalent wideband LFM chirp can be assembled from lesser-bandwidth chirp segments in the data processing. The chirp segments can be transmitted as separate narrow-band pulses, each with their own steering phase operation. This overcomes the problematic dilemma of steering wideband chirps with phase shifters alone, that is, without true time-delay elements.

  5. Phase transformation of nanostructured titanium dioxide from anatase-to-rutile via combined ultrasound assisted sol–gel technique

    Microsoft Academic Search

    Krishnamurthy Prasad; D. V. Pinjari; A. B. Pandit; S. T. Mhaske

    2010-01-01

    An effort was made to synthesize nanostructured TiO2 via sol–gel technique to obtain a 100% rutile polymorph of nanostructured TiO2. The sol–gel synthesis technique was suitably modified by incorporating ultrasound to study the effect of cavitation on the phase transformation, crystallite size, crystallinity and morphological (scanning electron microscopy) properties of the obtained nano-TiO2. It was observed that using ultrasound, yield

  6. Chirped pulse amplification with a nonlinearly chirped fiber Bragg grating matched to the Treacy compressor.

    PubMed

    Imeshev, G; Hartl, I; Fermann, M E

    2004-04-01

    We demonstrate a fiber chirped pulse amplification system that uses an engineered nonlinearly chirped fiber Bragg grating stretcher dispersion matched to the Treacy compressor. The seed pulses at 1558 nm are stretched to 720 ps, amplified by more than 50 dB to 6.5-microJ energy, and recompressed to 940 fs. After almost 1000 times compression the pulses are within 30% of the bandwidth limit and have a contrast ratio of better than 30 dB. PMID:15072356

  7. Color image encryption based on fractional Fourier transforms and pixel scrambling technique

    NASA Astrophysics Data System (ADS)

    Zhao, Jianlin; Lu, Hongqiang; Fan, Qi

    2007-01-01

    Color image encryption based on fractional Fourier transform (FRT) and pixel scrambling technique is presented in this paper. In general, color (RGB) image cannot be directly encrypted using a traditional setup for optical information processing, because which is only adapted to process two-dimensional gray image. In the proposed method, a three-dimensional RGB image is decomposed to three two-dimensional gray images (R, G and B values of the color image), and the encryption operation will be done on each two-dimensional gray image, then the encoded color image is available by composing the three two-dimensional encrypted images. The decryption process is an inverse of the encryption. The optical encrypting systems based on the presented method is proposed and simulated. Some results of computer simulation are presented to verify the flexibility and the reliability of this method. The quality of decrypted images would be debased with the difference of the fractional order. The frustrated decryption of monochromic image will affect the color of decrypted image. At the end of this paper, an all-optical and photoelectric encryption/decryption systems solution are presented, and the principle of selecting optical devices are also given.

  8. Generation of two attosecond pulses with tunable delay using orthogonally-polarized chirped laser pulses.

    PubMed

    Miao, Jing; Zeng, Zhinan; Liu, Peng; Zheng, Yinghui; Li, Ruxin; Xu, Zhizhan; Platonenko, V T; Strelkov, V V

    2012-02-27

    We investigate theoretically the high-order harmonic generation (HHG) by two orthogonally-polarized linearly chirped laser pulses. We show that such generating field has a specific temporal variation of the ellipticity which provides generation of two XUV attosecond pulses with tunable delay between them. This delay is controlled by the delay between the two generating pulses. Perspectives of application of this technique for the attosecond pump - attosecond probe experiments are discussed. PMID:22418325

  9. Experimental photonic generation of chirped pulses using nonlinear dispersion-based incoherent processing.

    PubMed

    Rius, Manuel; Bolea, Mario; Mora, José; Ortega, Beatriz; Capmany, José

    2015-05-18

    We experimentally demonstrate, for the first time, a chirped microwave pulses generator based on the processing of an incoherent optical signal by means of a nonlinear dispersive element. Different capabilities have been demonstrated such as the control of the time-bandwidth product and the frequency tuning increasing the flexibility of the generated waveform compared to coherent techniques. Moreover, the use of differential detection improves considerably the limitation over the signal-to-noise ratio related to incoherent processing. PMID:26074613

  10. Demonstration of stable raman fibre laser with asymmetrical laser cavity including broadband chirped FBG

    NASA Astrophysics Data System (ADS)

    Im, Young-Eun; Chun, Kyungwon; Kim, Hangeul; Hann, Swook; Kim, Dong-Hwan; Chung, Youngjoo; Park, Chang-Soo

    2009-10-01

    We experimentally and theoretically demonstrated a novel technique to generate a stable multi-wavelength Raman fibre laser (RFL) based on an asymmetrical all-fibre Raman laser cavity by using a broadband chirped fibre Bragg grating (CFBG). The output power variations from detuning the center wavelength of in/out reflectors are studied with symmetrical and asymmetrical RFL cavities. The RFL output with asymmetrical cavity is more stable than that of symmetrical cavity.

  11. Shaping of clean, femtosecond pulses at 1.053 micron for chirped-pulse amplification

    Microsoft Academic Search

    Jean-Luc Tapie; Gerard Mourou

    1992-01-01

    The generation of 200-fs optical pulses at 1.053 micron using two stages of fiber-grating compressors is reported. The usual intensity background associated with this compression technique has been reduced to less than 10(exp-7) of the peak intensity by using nonlinear birefringence in the second fiber. These pulses are used at the front end of the chirped-pulse amplification terawatt Nd:glass laser

  12. Extinction-ratio-independent electrical method for measuring chirp parameters of Mach-Zehnder modulators using frequency-shifted heterodyne.

    PubMed

    Zhang, Shangjian; Wang, Heng; Zou, Xinhai; Zhang, Yali; Lu, Rongguo; Liu, Yong

    2015-06-15

    An extinction-ratio-independent electrical method is proposed for measuring chirp parameters of Mach-Zehnder electric-optic intensity modulators based on frequency-shifted optical heterodyne. The method utilizes the electrical spectrum analysis of the heterodyne products between the intensity modulated optical signal and the frequency-shifted optical carrier, and achieves the intrinsic chirp parameters measurement at microwave region with high-frequency resolution and wide-frequency range for the Mach-Zehnder modulator with a finite extinction ratio. Moreover, the proposed method avoids calibrating the responsivity fluctuation of the photodiode in spite of the involved photodetection. Chirp parameters as a function of modulation frequency are experimentally measured and compared to those with the conventional optical spectrum analysis method. Our method enables an extinction-ratio-independent and calibration-free electrical measurement of Mach-Zehnder intensity modulators by using the high-resolution frequency-shifted heterodyne technique. PMID:26076279

  13. Tunable dispersion slope compensation for WDM systems using a single non-channelized third-order-chirped FBG

    Microsoft Academic Search

    Y. W. Song; S. M. R. Motoghian; D. Starodubov; J. E. Rothenberg; Z. Pan; H. Li; R. Wilcox; J. Popelek; R. Caldwell; V. Grubsky; A. E. Willner

    2002-01-01

    We demonstrate a novel technique for tunable dispersion slope compensation that relies on a single nonchannelized chirped fiber Bragg grating (FBG). This grating is unique in that it is written such that the time delay as a function of wavelength is a third-order profile that covers several WDM channels over a continuous bandwidth of many nanometers. The dispersion range provided

  14. FY07 LDRD Final Report Precision, Split Beam, Chirped-Pulse, Seed Laser Technology

    SciTech Connect

    Dawson, J W; Messerly, M J; Phan, H H; Crane, J K; Beach, R J; Siders, C W; Barty, C J

    2009-11-12

    The goal of this LDRD ER was to develop a robust and reliable technology to seed high-energy laser systems with chirped pulses that can be amplified to kilo-Joule energies and recompressed to sub-picosecond pulse widths creating extremely high peak powers suitable for petawatt class physics experiments. This LDRD project focused on the development of optical fiber laser technologies compatible with the current long pulse National Ignition Facility (NIF) seed laser. New technologies developed under this project include, high stability mode-locked fiber lasers, fiber based techniques for reduction of compressed pulse pedestals and prepulses, new compact stretchers based on chirped fiber Bragg gratings (CFBGs), new techniques for manipulation of chirped pulses prior to amplification and new high-energy fiber amplifiers. This project was highly successful and met virtually all of its goals. The National Ignition Campaign has found the results of this work to be very helpful. The LDRD developed system is being employed in experiments to engineer the Advanced Radiographic Capability (ARC) front end and the fully engineered version of the ARC Front End will employ much of the technology and techniques developed here.

  15. Power-Combining Transformer Techniques for Fully-Integrated CMOS Power Amplifiers

    Microsoft Academic Search

    Kyu Hwan An; Ockgoo Lee; Hyungwook Kim; Dong Ho Lee; Jeonghu Han; Ki Seok Yang; Younsuk Kim; Jae Joon Chang; Wangmyong Woo; Chang-Ho Lee; Haksun Kim; Joy Laskar

    2008-01-01

    Fully integrated CMOS power amplifiers (PAs) with parallel power-combining transformer are presented. For the high power CMOS PA design, two types of transformers, series-combining and parallel-combining, are fully analyzed and compared in detail to show the parasitic resistance and the turn ratio as the limiting factor of power combining. Based on the analysis, two kinds of parallel-combining transformers, a two-primary

  16. Discrete techniques for 3D digital images and patterns under transformations

    Microsoft Academic Search

    Zi C. Li

    1993-01-01

    Three dimensional (3-D) digital images and patterns under transformations are facilitated by the splitting-shooting method (SSM) and the splitting-integrating method (SIM). The combination (CSIM) of SSM and SIM and the combination (CIIM) of SIM and SIM are proposed for a cycle conversion T-1T, where T is a nonlinear transformation, and T-1 is its inverse transformation. This paper focuses on exploitation

  17. Failure statistics and power transformer condition evaluation by dissolved gas analysis technique

    Microsoft Academic Search

    Thanapong Suwanasri; Ekkachai Chaidee; Cattareeya Adsoongnoen

    2008-01-01

    Due to the degradation of power transformer under its normal and abnormal operating conditions, maintenance activities are vital to restore the condition. However, the preventive maintenance costs are now of primary concern. The scattering failure data are systematically recorded and analyzed to determine the critical component of power transformer. Two transformer models of rated voltage 115\\/22 kV and 230\\/115\\/22 kV

  18. Review of high-throughput techniques for detecting solid phase Transformation from material libraries produced by combinatorial methods

    NASA Technical Reports Server (NTRS)

    Lee, Jonathan A.

    2005-01-01

    High-throughput measurement techniques are reviewed for solid phase transformation from materials produced by combinatorial methods, which are highly efficient concepts to fabricate large variety of material libraries with different compositional gradients on a single wafer. Combinatorial methods hold high potential for reducing the time and costs associated with the development of new materials, as compared to time-consuming and labor-intensive conventional methods that test large batches of material, one- composition at a time. These high-throughput techniques can be automated to rapidly capture and analyze data, using the entire material library on a single wafer, thereby accelerating the pace of materials discovery and knowledge generation for solid phase transformations. The review covers experimental techniques that are applicable to inorganic materials such as shape memory alloys, graded materials, metal hydrides, ferric materials, semiconductors and industrial alloys.

  19. Direct optical techniques for the measurement of water content in oil-paper insulation in power transformers

    NASA Astrophysics Data System (ADS)

    Rodríguez-Rodríguez, Joaquín H.; Martínez-Piñón, Fernando; Álvarez-Chávez, José A.; Jaramillo-Vigueras, David; Robles-Pimentel, Edgar G.

    2011-06-01

    Paper-oil insulation in power transformers is degraded and gradually damaged due to electrical, chemical, mechanical and moisture factors. It is well established from several studies that moisture is a major source of insulation failure in high voltage power transformers. Measurement and monitoring of moisture is essential to predict life and operation condition for power transformers. This paper presents direct optical measurement of water content at paper insulation immersed in transformer oil inside a test cell, which contains a water source, and a capillary paper bridge to transfer water to the paper inside an oil reservoir. Optical measurement of water content was carried out in the near infrared from 900 to 1500 nm band. Experimental studies of light transmission in transformer oil and water are discussed. The criteria to establish the best optical bands for maximum sensitivities are given. The measurement limitations, calibration procedures and an error analysis are presented. The resulting technique can be used for on-line measurements in electrical apparatus that use oil-paper insulation under large electrical field gradients. The presented method has advantages, since it is a direct and fast technique to measure the water transfer to paper immersed in oil, and it could be applied in compact portable equipment at a low cost.

  20. Chirped optical solitons in single-mode birefringent fibers

    NASA Astrophysics Data System (ADS)

    Mahmood, M. F.

    1996-12-01

    The trapping behavior of two chirped solitons forming a bound state in a single-mode birefringent fiber is investigated on the basis of a model of coupled nonlinear Schroedinger equations. The positive initial chirp plays an important role in controlling the threshold amplitude for soliton trapping without causing excessive pulse broadening.

  1. Chirping noise of laser diodes under small signal modulation

    Microsoft Academic Search

    Zang Huai-quan; Duan Hui

    2009-01-01

    Distributed feedback laser diodes are of high modulation frequency response. They can be used as light sources and be directly modulated for high bit rate optical communication. As the case of conventional laser diodes, direct intensity modulation of DFB laser diodes brings about chirping, which affects the performance of optical transmission systems. In this paper, chirping characteristics of DFB laser

  2. MULTICOMPONENT CHIRP DEMODULATION USING DISCRETE FRACTIONAL FOURIER ANALYSIS

    E-print Network

    Santhanam, Balu

    MULTICOMPONENT CHIRP DEMODULATION USING DISCRETE FRACTIONAL FOURIER ANALYSIS Lakshmikanth Reddy S, there has been significant interest in the area of discrete fractional Fourier analysis (DFRFT) because of multicomponent chirp demodulation using the recently introduced multi angle-centered discrete fractional fourier

  3. Frequency chirping in semiconductor-optical fiber ring laser

    SciTech Connect

    Zhang, Jiangping; Ye, Peida (Beijing Univ. of Posts and Telecommunications (China))

    1990-01-01

    In this letter, a complete small-signal analysis for frequency chirping in the semiconductor-optical fiber ring laser is presented. It shows that chirp-to-power ratio (CPR) strongly depends on the junction phase shift, the optical coupling, and the phase detuning between two cavities, especially if the modulation frequency is below the gigahertz range. 7 refs.

  4. Chirp and cw linewidth measurements of integrated external cavity lasers

    NASA Astrophysics Data System (ADS)

    Dutta, N. K.; Cella, T.; Piccirilli, A. B.; Brown, R. L.; Green, C.

    1988-01-01

    Single-frequency integrated external cavity distributed Bragg reflector lasers emitting near 1.5 ?m have been fabricated. The chirp and cw linewidth measurements of these devices show that lasers with long external cavity exhibit lower chirp and lower cw linewidth compared to lasers with short external cavity. The experimental data are explained by using theoretical calculations.

  5. Interferometric fiber sensor with a chirped Bragg grating sensing element

    NASA Astrophysics Data System (ADS)

    Kersey, Alan D.; Davis, Michael A.

    1994-09-01

    An interferometric sensor based on the use of a chirped Bragg grating reflector is described. It is shown that strain applied to the chirped grating can induce a large path length change in an interferometer, equivalent to that obtained with a multi-meter length of fiber when strained directly.

  6. Hyperspectral Imaging with Stimulated Raman Scattering by Chirped Femtosecond Lasers

    E-print Network

    Xie, Xiaoliang Sunney

    Hyperspectral Imaging with Stimulated Raman Scattering by Chirped Femtosecond Lasers Dan Fu, Gary imaging system using chirped femtosecond lasers to achieve rapid Raman spectra acquisition while retaining laser beams with an energy difference tuned to the vibrational frequency of the molecule of interest

  7. A chirp scaling approach for processing squint mode SAR data

    Microsoft Academic Search

    G. W. Davidson; I. G. Cumming; M. R. Ito

    1996-01-01

    Image formation from squint mode synthetic aperture radar (SAR) is limited by image degradations caused by neglecting the range-variant filtering required by secondary range compression (SRC). Introduced here is a nonlinear FM chirp scaling, an extension of the chirp scaling algorithm, as an efficient and accurate approach to range variant SRC. Two methods of implementing the approach are described. The

  8. Chirp: a practical global filesystem for cluster and Grid computing

    Microsoft Academic Search

    Douglas Thain; Christopher Moretti; Jeffrey Hemmes

    2009-01-01

    Traditional distributed £lesystem technologies designed for local and campus area networks do not adapt well to wide area grid computing environments. To address this problem, we have designed the Chirp distributed £lesystem, which is designed from the ground up to meet the needs of grid computing. Chirp is easily deployed without special privileges, provides strong andexible security mechanisms, tunable consistency

  9. Helium in chirped laser fields as a time-asymmetric atomic switch

    SciTech Connect

    Kaprálová-Ž?ánská, Petra Ruth, E-mail: kapralova@jh-inst.cas.cz [Department of Radiation and Chemical Physics, Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic); J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8 (Czech Republic); Moiseyev, Nimrod, E-mail: nimrod@tx.technion.ac.il [Schulich Faculty of Chemistry and Faculty of Physics, Technion – Israel Institute of Technology, Haifa 32000 (Israel)

    2014-07-07

    Tuning the laser parameters exceptional points in the spectrum of the dressed laser helium atom are obtained. The weak linearly polarized laser couples the ground state and the doubly excited P-states of helium. We show here that for specific chirped laser pulses that encircle an exceptional point one can get the time-asymmetric phenomenon, where for a negative chirped laser pulse the ground state is transformed into the doubly excited auto-ionization state, while for a positive chirped laser pulse the resonance state is not populated and the neutral helium atoms remains in the ground state as the laser pulse is turned off. Moreover, we show that the results are very sensitive to the closed contour we choose. This time-asymmetric state exchange phenomenon can be considered as a time-asymmetric atomic switch. The optimal time-asymmetric switch is obtained when the closed loop that encircles the exceptional point is large, while for the smallest loops, the time-asymmetric phenomenon does not take place. A systematic way for studying the effect of the chosen closed contour that encircles the exceptional point on the time-asymmetric phenomenon is proposed.

  10. Estimation of high-resolution brightness temperature from auxiliary remote sensing products using transformation techniques

    NASA Astrophysics Data System (ADS)

    Cheney, T. H.; Nagarajan, K.; Judge, J.

    2010-12-01

    Passive microwave observations of brightness temperature (TB) at the L-band (1.4 GHz) are highly sensitive to near-surface soil moisture and have been widely used to retrieve them. The European Space Agency-Soil Moisture and Ocean Salinity (ESA-SMOS) and the near-future NASA-Soil Moisture Active Passive (SMAP) missions will provide global observations of TB at 1.4 GHz every 3 days at spatial resolutions in the order of 40-50 kilometers . These observations need to be downscaled to 1 km to merge them with hydrometeorological models for data assimilation and to study the effects of land surface heterogeneity such as dynamic vegetation conditions. However, downscaling is an ill-posed problem and additional information regarding TB is required at finer scales. In this study, we investigate two methodologies that provide this information by transforming auxiliary remote sensing (RS) products such as Land Surface Temperature (LST), Vegetation Water Content (VWC), and Land Cover (LC), which are readily available at 1km, into initial estimates of TB at 1km. In the first method, a non-parametric probabilistic technique based on Baye's rule was used to estimate TB by embedding its functional relationship to the RS products in terms of conditional probability density functions. In the second method, the principle of local correlation was used to estimate TB by extracting structural information between TB and the RS products within local neighborhoods. Field observations obtained during the intensive field experiments conducted over growing seasons of corn and cotton in North Central Florida were used to compare and analyze the performance of the two methodologies. The impacts of limited training data on the accuracy and reliability of the two methodologies were also investigated.

  11. Review of modern diagnostic techniques for assessing insulation condition in aged transformers

    Microsoft Academic Search

    Tapan K. Saha

    2003-01-01

    Cellulosic paper and oil insulation in a transformer degrade at higher operating temperatures. Degradation is accelerated in the presence of oxygen and moisture. Power transformers being expensive items need to be carefully monitored throughout their operation. Well established time-based maintenance and conservative replacement planning is not feasible in a current market driven electricity industry. Condition based maintenance and online monitoring

  12. Verification Techniques for Model Transformations Dept. of Informatics, King's College London

    E-print Network

    Lano, Kevin Charles

    or medical device software, patient records, need assurance of transformation correctness. 2 #12-driven development (MDD) approaches for software construction. Transformations are used for: · Refinement: eg., code Process Model notation to another · Analysis: eg., identifying hazardous states in drug dispenser device

  13. CHIRPED PULSE AMPLIFICATION OF HGHG-FEL FACILITY AT BNL.

    SciTech Connect

    DOYURAN,A.ET AL.

    2003-09-08

    The DUV-FEL facility has been in operation in High Gain Harmonic Generation (HGHG) mode for one year producing 266 nm output from 177 MeV electrons. In this paper we present preliminary results of the Chirped Pulse Amplification (CPA) of HGHG radiation. In the normal HGHG process, a 1 ps electron beam is seeded by chirped 9 ps long 800 nm Ti:Sapphire laser. The electron beam sees only a narrow fraction of the seed laser bandwidth. However, in the CPA case the seed laser pulse length is reduced to 1 ps, and the electron beam sees the full bandwidth. We introduce an energy chirp on electron beam to match the chirp of the seed pulse, enabling the resonant condition for the whole beam. We present measurements of the spectrum bandwidth for various chirp conditions.

  14. Frequency chirping during a fishbone burst

    NASA Astrophysics Data System (ADS)

    Marchenko, V. S.; Reznik, S. N.

    2011-12-01

    It is shown that frequency chirping during fishbone activity can be attributed to the reactive torque exerted on the plasma during the instability burst, which slows down plasma rotation inside the q = 1 surface and reduces the mode frequency in the lab frame. Estimates show that the peak value of this torque can exceed the neutral beam torque in modern tokamaks. The simple line-broadened quasilinear burst model (Berk et al 1995 Nucl. Fusion 35 1661), properly adapted for the fishbone case, is capable of reproducing the key features of the bursting mode.

  15. Impact of modulator chirp in 100 Gbps class optical discrete multi-tone transmission system

    NASA Astrophysics Data System (ADS)

    Nishihara, Masato; Tanaka, Toshiki; Takahara, Tomoo; Li, Lei; Tao, Zhenning; Rasmussen, Jens C.

    2012-12-01

    Discrete multi-tone (DMT) technology is an attractive modulation technique for short reach optical transmission system. One of the main factors that limit the performance of the 1.5-?m band DMT system is the interplay between the chromatic dispersion of the transmission fiber and the chirp characteristic of the transmitter. We experimentally measured and compared the chirp characteristics of various modulator configurations, which are lithium-niobate Mach-Zehnder modulator, directly modulated laser, and electro-absorption modulator, by the frequency discriminator method using MZ interferometer. We also measured and compared the transmission characteristics of the transmitters using above-mentioned modulators and discuss the suitable transmitter configuration for DMT technology.

  16. Applying image transformation and classification techniques to airborne hyperspectral imagery for mapping Ashe juniper infestations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ashe juniper (Juniperus ashei Buchholz), in excessive coverage, reduces forage production, interferes with livestock management, and degrades watersheds and wildlife habitat in infested rangelands. The objective of this study was to apply minimum noise fraction (MNF) transformation and different cla...

  17. Monitoring of high voltage power transformer using direct optical partial discharge detection technique

    Microsoft Academic Search

    S. Karmakar; N. K. Roy; P. Kumbhakar

    2009-01-01

    In electrical power systems, high voltage power transformers are used to transfer the power from one substation to another.\\u000a The insulation of the high voltage power transformers are gradually deteriorated due to electrical, chemical and mechanical\\u000a stresses caused by the partial discharges (PDs). It is well established from several studies that PDs are the major source\\u000a of insulation failure in

  18. A GA based Window Selection Methodology to Enhance Window based Multi wavelet transformation and thresholding aided CT image denoising technique

    Microsoft Academic Search

    Syed Amjad Ali; Srinivasan Vathsal; K. Lal kishore

    2010-01-01

    Image denoising is getting more significance, especially in Computed\\u000aTomography (CT), which is an important and most common modality in medical\\u000aimaging. This is mainly due to that the effectiveness of clinical diagnosis\\u000ausing CT image lies on the image quality. The denoising technique for CT images\\u000ausing window-based Multi-wavelet transformation and thresholding shows the\\u000aeffectiveness in denoising, however, a

  19. Detection of delta-ferrite to sigma transformation using metallographic techniques involving ferromagnetic colloid, color etching, and microprobe analysis

    Microsoft Academic Search

    R. J. Gray; V. K. Sikka; R. T. King

    1976-01-01

    The mechanical properties of ferrite-containing austenitic stainless steel base metal and weldments are usually adversely affected by prolonged exposure to temperatures in the 482 to 900°C (900 to 1652°F) range. One cause of the property alteration is related to the transformation of relatively ductile delta-ferrite to less ductile sigma-phase. Attempts to identify sigma and delta-ferrite phases by color staining techniques

  20. Characterization of Silicon Sulfides by Chirped-Pulse Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    McCarthy, Michael C.; Crabtree, Kyle N.; Martinez, Oscar; , Jr.

    2013-06-01

    Chirped-pulse Fourier transform microwave spectroscopy is used to characterize the electrical discharge products that are formed in a supersonic molecular beam through a dilute gas mixture of silane and hydrogen sulfide. The spectrum between 6 and 18 GHz is dominated by SiS: more than 175 transitions have been assigned to either its isotopic species, its vibrationally excited states, or both, on the basis of previous cavity measurements. Owing to the flat instrument response function and extensive vibrational excitation that has been observed, it is possible to derive a precise vibrational temperature for SiS, and determine the relative abundances of SiS, HSiS, and H_2SiS. Although rotational lines from more than 15 other silicon or sulfur molecules have been identified in the same discharge, more than 50% of lines that have been detected with a signal-to-noise ratio of three or greater are presently unassigned. Attempts to assign these many remaining lines, and efforts to benchmark the performance of our spectrometer will be highlighted as well.

  1. Three-Dimensional Analysis of Frequency-Chirped FELs

    SciTech Connect

    Huang, Z.

    2010-09-14

    Frequency-chirped free-electron lasers (FELs) are useful to generate a large photon bandwidth or a shorter x-ray pulse duration. In this paper, we present a three-dimensional analysis of a high-gain FEL driven by the energy-chirped electron beam. We show that the FEL eigenmode equation is the same for a frequency-chirped FEL as for an undulator-tapered FEL. We study the transverse effects of such FELs including mode properties and transverse coherence.

  2. Highly depth-resolved chirped pulse photothermal radar for bone diagnostics

    NASA Astrophysics Data System (ADS)

    Kaiplavil, Sreekumar; Mandelis, Andreas

    2011-07-01

    A novel chirped pulse photothermal (PT) radiometric radar with improved sensitivity over the conventional harmonically modulated thermal-wave radar technique and alternative pulsed laser photothermal radiometry is introduced for the diagnosis of biological samples, especially bones with tissue and skin overlayers. The constraints imposed by the laser safety (maximum permissible exposure) ceiling on pump laser energy and the strong attenuation of thermal-wave signals in tissues significantly limit the photothermally active depth in most biological specimens to a level which is normally insufficient for practical applications (a few mm below the skin surface). A theoretical approach for improvement of signal-to-noise ratio (SNR), minimizing the static (dc) component of the photothermal signal and making use of the photothermal radiometric nonlinearity has been introduced and verified by comparing the SNR of four distinct excitation wave forms (sine-wave, square-wave, constant-width and constant duty-cycle pulses) for chirping the pump laser, under constant exposure energy. At low frequencies fixed-pulsewidth chirps of large peak power were found to be superior to all other equal-energy modalities, with an SNR improvement up to two orders of magnitude. Distinct thickness-dependent characteristic delay times in a goat bone were obtained, establishing an active depth resolution range of ˜2.8 mm in a layered skin-fat-bone structure, a favorable result compared to the maximum reported pulsed photothermal radiometric depth resolution <1 mm in turbid biological media.

  3. Time resolved chirp measurements of gain switched semiconductor laser using a polarization based optical differentiator.

    PubMed

    Consoli, Antonio; Tijero, Jose Manuel G; Esquivias, Ignacio

    2011-05-23

    We present a novel implementation of the "phase reconstruction using optical ultra fast differentiation" (PROUD) technique and apply it to characterize the time resolved chirp of a gain switched semiconductor laser. The optical temporal differentiator is a fiber based polarization interferometer. The method provides a fast and simple recovery of the instantaneous frequency from two temporal intensity measurements, obtained by changing the spectral response of the interferometer. Pulses with different shapes and durations of hundreds of picoseconds are fully characterized in amplitude and phase. The technique is validated by comparing the measured pulse spectra with the reconstructed spectra obtained from the intensity and the recovered phase. PMID:21643337

  4. Study on adaptive thresholding technique of image denoising based on wavelet transform

    Microsoft Academic Search

    Xi'an Zhu; Xiao Xie

    2010-01-01

    It is studied in the paper that an adaptive soft and hard thresholding image denoising method, in which image pyramid decomposing is realized by wavelet transform, and the mean value, mid-value and root mean square value of different sub bands are calculated as thresholding. The image is added into different kinds and different intensities noise, and processed by different wavelet

  5. Measurement and communication techniques for remote condition monitoring of high voltage transformer bushings

    Microsoft Academic Search

    D. Cornforth; G. Ledwich

    1998-01-01

    The insulation used in high voltage transformer bushings experiences an aging process, which reduces its effectiveness and ultimately may lead to catastrophic breakdown. The progress of aging can be estimated by measuring various parameters of the insulator material. The most easily obtainable parameters are electrical, and this fact has led to the introduction of commercial automated measurement systems suitable for

  6. Transformation pressure of ZnS by a new primary pressure technique

    NASA Technical Reports Server (NTRS)

    Ruoff, A. L.; Chan, K. S.

    1979-01-01

    An experiment designed to measure the transformation pressure of zinc sulfide by a primary pressure method using an indentor-anvil system made of single-crystal diamond is discussed. A nonsorting electrode-grid which can be applied directly to the anvil using optical lithography is described, together with the procedures used for positioning.

  7. Turn to -turn fault localization of power transformers using neural network techniques

    Microsoft Academic Search

    Hormatollah FIROOZI; Mohammad KHAREZI; Hasan BAKHSHI

    2009-01-01

    Power transformers are considered as one of the essential elements in electrical networks. Any failure in these equipments directly reduces network reliability and increases maintenance costs. Therefore, quick and precise diagnosis of faults is very important. One of the main faults in this regards is turn-to-turn fault that its localization is very useful and vital. This paper has been presented

  8. Quantum Fluctuations in the Chirped Pendulum

    E-print Network

    K. W. Murch; R. Vijay; I. Barth; O. Naaman; J. Aumentado; L. Friedland; I. Siddiqi

    2010-08-26

    An anharmonic oscillator when driven with a fast, frequency chirped voltage pulse can oscillate with either small or large amplitude depending on whether the drive voltage is below or above a critical value-a well studied classical phenomenon known as autoresonance. Using a 6 GHz superconducting resonator embedded with a Josephson tunnel junction, we have studied for the first time the role of noise in this non-equilibrium system and find that the width of the threshold for capture into autoresonance decreases as the square root of T, and saturates below 150 mK due to zero point motion of the oscillator. This unique scaling results from the non-equilibrium excitation where fluctuations, both quantum and classical, only determine the initial oscillator motion and not its subsequent dynamics. We have investigated this paradigm in an electrical circuit but our findings are applicable to all out of equilibrium nonlinear oscillators.

  9. Development and experimental validation of a numerical tool for structural health and usage monitoring systems based on chirped grating sensors.

    PubMed

    Bettini, Paolo; Guerreschi, Erika; Sala, Giuseppe

    2015-01-01

    The interest of the aerospace industries in structural health and usage monitoring systems is continuously increasing. Among the techniques available in literature those based on Fibre Bragg Grating sensors are much promising thanks to their peculiarities. Different Chirped Bragg Grating sensor configurations have been investigated in this paper. Starting from a numerical model capable of simulating the spectral response of a grating subjected to a generic strain profile (direct problem), a new code has been developed, allowing strain reconstruction from the experimental validation of the program, carried out through different loading cases applied on a chirped grating. The wavelength of the reflection spectrum for a chirped FBG has a one-to-one correspondence to the position along the gauge section, thus allowing strain reconstruction over the entire sensor length. Tests conducted on chirped FBGs also evidenced their potential for SHM applications, if coupled with appropriate numerical strain reconstructions tools. Finally, a new class of sensors-Draw Tower Grating arrays-has been studied. These sensors are applicable to distributed sensing and load reconstruction over large structures, thanks to their greater length. Three configurations have been evaluated, having different spatial and spectral characteristics, in order to explore possible applications of such sensors to SHM systems. PMID:25587979

  10. The word length influence on waveform coding techniques based on wavelet transform applied to disturbance compression

    Microsoft Academic Search

    M. V. Ribeiro; C. A. Duque

    2002-01-01

    The paper focuses on the influence of the finite precision in the wavelet filters and disturbance signals to demand a low computational complexity and efficient use of DSP solution applied to disturbance data compression technique, which depends on the finite precision, stability and convergence of the used techniques. The results show that the finite precision produces low degradation level with

  11. Chirp signalling offers modulation scheme for underwater communications

    Microsoft Academic Search

    Wireless communication can be conducted in the underwater acoustic (UWA) channel through sonar signalling. We propose using the frequency-vs-time slope of sonar 'chirps' to transmit information in a robust scheme for a spread-spectrum underwa- ter communications system. Digitaldatacanberepresented bytheslope of chirpsignals.In the simplest binary case, an 'up' chirp (i.e., a signal with instan- taneous frequency that linearly increases with time)

  12. Discerning Some Tylenol Brands Using Attenuated Total Reflection Fourier Transform Infrared Data and Multivariate Analysis Techniques

    Microsoft Academic Search

    Huggins Z. Msimanga; Robert J. Ollis Jr.

    2010-01-01

    Principal component anal. (PCA) and partial least squares discriminant anal. (PLS-DA) were used to classify acetaminophen-contg. medicines using their attenuated total reflection Fourier transform IR (ATR-FT-IR) spectra. Four formulations of Tylenol (Arthritis Pain Relief, Extra Strength Pain Relief, 8 H Pain Relief, and Extra Strength Pain Relief Rapid Release) along with 98% pure acetaminophen were selected for this study because

  13. A GA based Window Selection Methodology to Enhance Window based Multi wavelet transformation and thresholding aided CT image denoising technique

    E-print Network

    Ali, Syed Amjad; kishore, K Lal

    2010-01-01

    Image denoising is getting more significance, especially in Computed Tomography (CT), which is an important and most common modality in medical imaging. This is mainly due to that the effectiveness of clinical diagnosis using CT image lies on the image quality. The denoising technique for CT images using window-based Multi-wavelet transformation and thresholding shows the effectiveness in denoising, however, a drawback exists in selecting the closer windows in the process of window-based multi-wavelet transformation and thresholding. Generally, the windows of the duplicate noisy image that are closer to each window of original noisy image are obtained by the checking them sequentially. This leads to the possibility of missing out very closer windows and so enhancement is required in the aforesaid process of the denoising technique. In this paper, we propose a GA-based window selection methodology to include the denoising technique. With the aid of the GA-based window selection methodology, the windows of the ...

  14. Fourier transform image processing techniques for grid-based phase contrast imaging

    NASA Astrophysics Data System (ADS)

    Tahir, Sajjad; Bashir, Sajid; Petruccelli, Jonathan C.; MacDonald, C. A.

    2014-09-01

    A recently developed technique for phase imaging using table top sources is to use multiple fine-pitch gratings. However, the strict manufacturing tolerences and precise alignment required have limited the widespread adoption of grating-based techniques. In this work, we employ a technique recently demonstrated by Bennett et al.1 that ultilizes a single grid of much coarser pitch. Phase is extracted using Fourier processing on a single raw image taken using a focused mammography grid. The effects on the final image of varying grid, object, and detector distances, window widths, and of a variety of windowing functions, used to separate the harmonics, were investigated.

  15. Modified Fourier-Hankel method based on analysis of errors in Abel inversion using Fourier transform techniques.

    PubMed

    Ma, Shuiliang; Gao, Hongming; Wu, Lin

    2008-03-20

    Errors in discrete Abel inversion methods using Fourier transform techniques have been analyzed. The Fourier expansion method is very accurate but sensitive to noise. The Fourier-Hankel method has a significant systematic negative deviation, which increases with the radius; inversion error of the method can be reduced by adjusting the value of a factor. With a decrease of the factor both methods show a noise filtering property. Based on the analysis, a modified Fourier-Hankel method that is accurate, computationally efficient, and has the ability to filter noise in the inversion process is proposed for applying to experimental data. PMID:18709083

  16. Advanced Techniques for In-Situ Monitoring of Phase Transformations During Welding Using Synchrotron-Based X-Ray Diffraction

    SciTech Connect

    Elmer, J W; Palmer, T A; Zhang, W; DebRoy, T

    2005-06-05

    Understanding the evolution of microstructure in welds is an important goal of welding research because of the strong correlation between weld microstructure and weld properties. To achieve this goal it is important to develop a quantitative measure of phase transformations encountered during welding in order to ultimately develop methods for predicting weld microstructures from the characteristics of the welding process. To aid in this effort, synchrotron radiation methods have been developed at Lawrence Livermore National Laboratory (LLNL) for direct observation of microstructure evolution during welding. Using intense, highly collimated synchrotron radiation, the atomic structure of the weld heat affected and fusion zones can be probed in real time. Two synchrotron-based techniques, known as spatially resolved (SRXRD) and time resolved (TRXRD) x-ray diffraction, have been developed for these investigations. These techniques have now been used to investigate welding induced phase transformations in titanium alloys, low alloy steels, and stainless steel alloys. This paper will provide a brief overview of these methods and will discuss microstructural evolution during the welding of low carbon (AISI 1005) and medium carbon (AISI 1045) steels where the different levels of carbon influence the evolution of microstructures during welding.

  17. Pulse compression over a 170-THz bandwidth in the visible by use of only chirped mirrors.

    PubMed

    Zavelani-Rossi, M; Cerullo, G; De Silvestri, S; Gallmann, L; Matuschek, N; Steinmeyer, G; Keller, U; Angelow, G; Scheuer, V; Tschudi, T

    2001-08-01

    We report on double-chirped mirrors with custom-tailored dispersion characteristics over a bandwidth of 170 THz in the visible. The mirrors are used in a prismless compressor for a noncollinear optical parametric amplifier in the visible. The compressed pulses, characterized for the what is believed to be first time by use of the spectral phase interferometry for direct electric field reconstruction technique, display a nearly flat phase from 510 to 710 nm and have a duration of 5.7 fs. PMID:18049547

  18. Chirp and self-phase modulation in induced-grating autocorrelation measurements of ultrashort pulses.

    PubMed

    Trebino, R; Hayden, C C; Johnson, A M; Simpson, W M; Levine, A M

    1990-10-01

    We show that induced-grating/four-wave-mixing ultrashort-pulse autocorrelation techniques that use slowly responding media offer the same phase information as interferometric second-harmonic generation. We also show that autocorrelation traces from nearly all possible induced-grating/four-wave-mixing beam geometries provide this information, with all yielding the same theoretical result, an integral of a fourth-order electric-field coherence function. Such traces clearly reveal chirp and self-phase-modulation effects without high-frequency fringes. Experiments using a two-beam-coupling arrangement in photorefractive media illustrate these effects. PMID:19771003

  19. Chirp and self-phase modulation in induced-grating autocorrelation measurements of ultrashort pulses

    SciTech Connect

    Trebino, R.; Hayden, C.C. (Combustion Research Facility, Sandia National Laboratories, Livermore, CA (USA)); Johnson, A.M.; Simpson, W.M. (AT T Bell Laboratories, Holmdel, NJ (USA)); Levine, A.M. (The College of Staten Island, City University of New York, Staten Island, NY (USA))

    1990-10-01

    We show that induced-grating/four-wave-mixing ultrashort-pulse autocorrelation techniques that use slowly responding media offer the same phase information as interferometric second-harmonic generation. We also show that autocorrelation traces from nearly all possible induced-grating/four-wave-mixing beam geometries provide this information, with all yielding the same theoretical result, an integral of a fourth-order electric-field coherence function. Such traces clearly reveal chirp and self-phase-modulation effects without high-frequency fringes. Experiments using a two-beam-coupling arrangement in photorefractive media illustrate these effects.

  20. Building requirements Repository Using Requirements Transformation Techniques to Support Requirements Reuse

    Microsoft Academic Search

    Sami M. Homod; David C. Rine

    Software reuse is introduced to increase software development process productivity, improve software quality and reduce development time and cost. So applying the reuse techniques at the requirements engineering phase of the software development life cycle will help get complete and accurate requirements with less effort and time. The goal of this research is to develop an approach for building a

  1. FD-CHIRP: hosted payload system engineering lessons

    NASA Astrophysics Data System (ADS)

    Schueler, Carl F.

    2012-10-01

    The Commercially Hosted Infrared Payload (CHIRP) Flight Demonstration (FD-CHIRP) launched 21 Sept 2011 was designated a "resounding success" as the first Wide Field-of-View (WFOV) staring infrared (IR) sensor flown in geostationary earth orbit (GEO) with a primary mission of Missile Warning (MW). FD-CHIRP was an Air Force research and development project initiated in July 2008 via an unsolicited industry proposal aimed to mature and reduce the risk of WFOV sensors and ground processing technologies. Unlike the Defense Support Program (DSP) and the Space Based Infrared System (SBIRS) which were acquired via traditional integrated sensor and satellite design, FDCHIRP was developed using the "commercially hosted" approach. The FD-CHIRP host spacecraft and sensor were independently designed, creating significant development risk to the industry proposer, especially under a Firm Fixed Price contract. Yet, within 39 months of contract initiation, FD-CHIRP was launched and successfully operated in GEO to 30 June 2012 at a total cost of 111M including the 82.9M CHIRP commercial-hosting contract and a $28M sensor upgrade. The commercial-hosting contract included sensor and spacecraft modifications, integration and test, design and development of secure Mission Operations and Analysis Centers, launch, and nearly a year of GEO operations with 70 Mbps secure data acquisition. The Air Force extended the contract for six months to continue operations through the end of calendar 2012. This paper outlines system engineering challenges FD-CHIRP overcame and key lessons to smooth development of future commercially hosted missions.

  2. Study on adaptive thresholding technique of image denoising based on wavelet transform

    NASA Astrophysics Data System (ADS)

    Zhu, Xi'an; Xie, Xiao

    2011-05-01

    It is studied in the paper that an adaptive soft and hard thresholding image denoising method, in which image pyramid decomposing is realized by wavelet transform, and the mean value, mid-value and root mean square value of different sub bands are calculated as thresholding. The image is added into different kinds and different intensities noise, and processed by different wavelet decomposing levels and thresholding selected algorithms, the total 27 kinds of thresholding combination schemes are completed in the research process. The SNR (signal noise ratio) and PSNR (peak signal noise ratio) of denoised image are compared and analyzed and benefited results are achieved. Furthermore, the algorithm in reference is realized by MATLAB program, the results of reference are compared with that of the paper to demonstrate the significance and correctness of the results in the paper.

  3. Study on adaptive thresholding technique of image denoising based on wavelet transform

    NASA Astrophysics Data System (ADS)

    Zhu, Xi'an; Xie, Xiao

    2010-12-01

    It is studied in the paper that an adaptive soft and hard thresholding image denoising method, in which image pyramid decomposing is realized by wavelet transform, and the mean value, mid-value and root mean square value of different sub bands are calculated as thresholding. The image is added into different kinds and different intensities noise, and processed by different wavelet decomposing levels and thresholding selected algorithms, the total 27 kinds of thresholding combination schemes are completed in the research process. The SNR (signal noise ratio) and PSNR (peak signal noise ratio) of denoised image are compared and analyzed and benefited results are achieved. Furthermore, the algorithm in reference is realized by MATLAB program, the results of reference are compared with that of the paper to demonstrate the significance and correctness of the results in the paper.

  4. Tunable RF-power-fading compensation of multiple-channel double-sideband SCM transmission using a nonlinearly chirped FBG

    Microsoft Academic Search

    H. Sun; M. C. Cardakli; K.-M. Feng; J.-X. Cai; H. Long; M. I. Hayee; A. E. Willner

    2000-01-01

    We demonstrate that a nonlinearly chirped fiber Bragg grating can compensate RF power degradation in subcarrier-multiplexed (SCM) systems that is caused by fiber dispersion. Our all-optical technique provides tunable dispersion that compensates for multiple SCM channels simultaneously. We achieve RF-power-fading compensation for two SCM\\/BPSK 156-Mb\\/s channels in which the fading is reduced from 15 and 6 dB, respectively, to <0.5

  5. Modified isotope pairing technique to study N transformations in polluted aquatic systems: theory.

    PubMed

    Master, Y; Shavit, U; Shaviv, A

    2005-03-15

    Denitrification of nitrate in sediments of polluted aquatic systems has the potential to release considerable nitrogen amounts into the atmosphere in the form of dinitrogen (N2) and/or nitrous oxide (N2O). Nitrate may diffuse into the anoxic sediment layer either from the oxic sediment layer (after being produced there by nitrifiers) or directly from the overlying water. Currently, the most common technique that explicitly distinguishes between the two main nitrate sources is the Isotope Pairing Technique (IPT). 15N-labeled nitrate is added to the water column, and formation of 15N labeled N2 molecules is subsequently monitored. The main shortcoming of the IPT is that the formation of N20 is ignored, thus resulting in an underestimation of sediment denitrification. Another limitation is the inability to account for a possible influx of nitrate through the hyporheic zone (e.g., nitrate-polluted groundwater) into the anoxic sediment layer. We have further developed and analyzed the theoretical basis of the original IPT. The two important factors that we took into account are the isotopic composition of N20 and the input of an external source of nitrate. We also examined the option of adding 15N-labeled ammonium to the water column to specifically adjustthe technique to field studies. The presented modified technique allows us to (i) improve the estimation of sediment denitrification capacity, (ii) gain an insight into the N20 formation mechanism(s) and fluxes, and (iii) assess inputs of nitrate-polluted water through the hyporheic zone. PMID:15819234

  6. Velocity measurements using a single transmitted linear frequency-modulated chirp.

    PubMed

    Levy, Yoav; Azhari, Haim

    2007-05-01

    Velocity measurement is a challenge for a variety of remote sensing systems such as ultrasonic and radar scanners. However, current Doppler-based techniques require a comparatively long data acquisition time. It has been suggested to use coded signals, such as linear frequency-modulated signals (chirp), for ultrasonic velocity estimation by extracting the needed information from a set of several sequential coded pulses. In this study, a method for velocity estimation using a single linear frequency-modulated chirp transmission is presented and implemented for ultrasonic measurements. The complex cross-correlation function between the transmitted and reflected signals is initially calculated. The velocity is then calculated from the phase of the peak of the envelope of this cross-correlation function. The suggested method was verified using computer simulations and experimental measurements in an ultrasonic system. Applying linear regression to the data has yielded very good correlation (r = 0.989). With the suggested technique, higher frame rates of velocity mapping can be potentially achieved relative to current techniques. Also, the same data can be utilized for both velocity mapping and image reconstruction. PMID:17412485

  7. PI film property analysis in the application of infrared image transform technique

    NASA Astrophysics Data System (ADS)

    Li, Yanhong; Zhang, Li; Li, Zhuo

    2013-09-01

    Modern infrared focal plane arrays (IR FPA) with high dynamic range, and multiband versions are being deployed in fielded systems. It needs to develop advanced scene projection technology to operate both in laboratory testing for hardware-in-the-loop simulation and validation of fielded units immediately prior to mission use. One of the fiber array visible to infrared imaging transducer is introduced. Different from the fiber bundle, the fiber array is etched on the substrate material. The property of transducer is determined by the substrate material. Polyimide (PI) film has the property of high dynamic range for temperature resistant, electric insulating, radiation resistant, good thermosetting and thermomechanical effect. The heat diffusion property of PI film is analyzed by experimental study. For experimental study, samples of with sputtered graphite on surface and different thickness of PI film were made. Using the visible light irradiate on the film and a high speed infrared camera capture the temperature information. The time of raising temperature process and the max temperature were recorded. The different energy of visible light was tried for the max temperature for samples. The result show the PI film can be achieved to 600K and has high thermal efficiency. And the surface film with good absorptivity is also important for heat transforming. PI film can be used as one of the material in the Infrared imaging transducer for high dynamic range and multiband radiation.

  8. Quasimonoenergic collimated electrons from the ionization of nitrogen by a chirped intense laser pulse

    SciTech Connect

    Singh, Kunwar Pal [Singh Simutech Pvt. Ltd., Bharatpur, Rajasthan 321201 (India); Sajal, Vivek [Department of Physics, Jaypee Institute of Information Technology University, Noida 201 307, Uttar Pradesh (India)

    2009-04-15

    A scheme is proposed for quasimonoenergic collimated GeV electrons generated during ionization of nitrogen by a chirped intense laser pulse. The electrons accelerated by a laser pulse without a frequency chirp are known for poor-quality beams. If a suitable frequency chirp is introduced, then the energy of the electrons increases significantly. It is shown that quasimonoenergic collimated GeV electrons can be produced using a right choice of laser spot size, frequency chirp, and pulse duration.

  9. Partial discharge localization in power transformers based on the sequential quadratic programming-genetic algorithm adopting acoustic emission techniques

    NASA Astrophysics Data System (ADS)

    Liu, Hua-Long; Liu, Hua-Dong

    2014-10-01

    Partial discharge (PD) in power transformers is one of the prime reasons resulting in insulation degradation and power faults. Hence, it is of great importance to study the techniques of the detection and localization of PD in theory and practice. The detection and localization of PD employing acoustic emission (AE) techniques, as a kind of non-destructive testing, plus due to the advantages of powerful capability of locating and high precision, have been paid more and more attention. The localization algorithm is the key factor to decide the localization accuracy in AE localization of PD. Many kinds of localization algorithms exist for the PD source localization adopting AE techniques including intelligent and non-intelligent algorithms. However, the existed algorithms possess some defects such as the premature convergence phenomenon, poor local optimization ability and unsuitability for the field applications. To overcome the poor local optimization ability and easily caused premature convergence phenomenon of the fundamental genetic algorithm (GA), a new kind of improved GA is proposed, namely the sequence quadratic programming-genetic algorithm (SQP-GA). For the hybrid optimization algorithm, SQP-GA, the sequence quadratic programming (SQP) algorithm which is used as a basic operator is integrated into the fundamental GA, so the local searching ability of the fundamental GA is improved effectively and the premature convergence phenomenon is overcome. Experimental results of the numerical simulations of benchmark functions show that the hybrid optimization algorithm, SQP-GA, is better than the fundamental GA in the convergence speed and optimization precision, and the proposed algorithm in this paper has outstanding optimization effect. At the same time, the presented SQP-GA in the paper is applied to solve the ultrasonic localization problem of PD in transformers, then the ultrasonic localization method of PD in transformers based on the SQP-GA is proposed. And localization results based on the SQP-GA are compared with some algorithms such as the GA, some other intelligent and non-intelligent algorithms. The results of calculating examples both stimulated and spot experiments demonstrate that the localization method based on the SQP-GA can effectively prevent the results from getting trapped into the local optimum values, and the localization method is of great feasibility and very suitable for the field applications, and the precision of localization is enhanced, and the effectiveness of localization is ideal and satisfactory.

  10. Effect of chirped gratings on reflective optical bistability in DFB semiconductor laser amplifiers

    Microsoft Academic Search

    Drew N. Maywar; Govind P. Agrawal

    1998-01-01

    We use spatial chirp of the built-in grating to improve optical bistability on reflection from distributed feedback semiconductor laser amplifiers. We show that improvements in the on-off switching ratio occur because spatial chirp greatly affects the saturation behavior of the reflectivity resonances, allowing access to states of low reflection during bistable switching. We also show that spatial chirp modifies the

  11. An efficient Non-Linear Chirp Scaling method of focusing bistatic SAR images

    Microsoft Academic Search

    Yew Lam Neo; Frank Wong; Ian Cumming

    Bistatic SAR data processing parameters, unlike monostatic SAR data, are generally azimuth-variant. The Non-Linear Chirp Scaling (NLCS) algorithm introduced in this paper is able to handle the azimuth variance. It focuses a bistatic image by first introducing a bulk linear range cell migration correction followed by a chirp scaling process to equalize the azimuth chirp rates for all targets in

  12. Frequency chirp and pulse shape effects in self-modulated laser wakefield acceleratorsa...

    E-print Network

    Geddes, Cameron Guy Robinson

    Frequency chirp and pulse shape effects in self-modulated laser wakefield acceleratorsa... C. B excitation in a self-modulated laser wakefield accelerator is examined. Laser pulse shape and frequency chirp negative frequency chirp enhances suppresses the growth rate of the Raman forward scattering and near

  13. Fiber Bragg grating strain sensor demodulator using a chirped fiber grating

    Microsoft Academic Search

    Sungchul Kim; Seungwoo Kim; Jaejoon Kwon; Byoungho Lee

    2001-01-01

    A fiber Bragg grating (FBG) sensor demodulator using a chirped fiber grating is proposed. The demodulator uses UV-induced birefringence of chirped fiber grating to interrogate the wavelength shift of a sensor FBG. The demodulator is composed of a polarizing beam splitter, a polarization controller, a single-mode fiber, and a chirped fiber grating. The proposed demodulator is immune to light power

  14. A signal processing approach to exploit chirp excitation in Lamb wave defect detection and localization procedures

    NASA Astrophysics Data System (ADS)

    De Marchi, Luca; Perelli, Alessandro; Marzani, Alessandro

    2013-08-01

    A non-linear Lamb wave signal processing strategy aimed at extending the capability of active-passive networks of PZT transducers for defect detection is proposed. In particular, the proposed signal processing allows to use chirp shaped pulses in actuation, instead of classically applied spiky pulses, requiring thus lower input voltages. To such aim, the acquired Lamb waves are processed by means of a two-step procedure: a warped frequency transform (WFT) to compensate for the dispersion due to the traveled distance, followed by a compression procedure to remove from the signals the induced chirp frequency modulation. Next, the resulting signals are exploited to feed an imaging algorithm aimed at providing the position of the defect on the plate. The potential of the procedure is demonstrated and validated by analyzing experimental Lamb waves propagating in an aluminum plate where defects were emulated by posing an added mass on the plate. The proposed automatic procedure is suitable to locate defect-induced reflections and can be easily implemented in real applications for structural health monitoring.

  15. Technique for infrared and visible image fusion based on non-subsampled shearlet transform and spiking cortical model

    NASA Astrophysics Data System (ADS)

    Kong, Weiwei; Wang, Binghe; Lei, Yang

    2015-07-01

    Fusion of infrared and visible images is an active research area in image processing, and a variety of relevant algorithms have been developed. However, the existing techniques commonly cannot gain good fusion performance and acceptable computational complexity simultaneously. This paper proposes a novel image fusion approach that integrates the non-subsampled shearlet transform (NSST) with spiking cortical model (SCM) to overcome the above drawbacks. On the one hand, using NSST to conduct the decompositions and reconstruction not only consists with human vision characteristics, but also effectively decreases the computational complexity compared with the current popular multi-resolution analysis tools such as non-subsampled contourlet transform (NSCT). On the other hand, SCM, which has been considered to be an optimal neuron network model recently, is responsible for the fusion of sub-images from different scales and directions. Experimental results indicate that the proposed method is promising, and it does significantly improve the fusion quality in both aspects of subjective visual performance and objective comparisons compared with other current popular ones.

  16. Feature-Based Adaptive Tolerance Tree (FATT): An Efficient Indexing Technique for Content-Based Image Retrieval Using Wavelet Transform

    E-print Network

    AnandhaKumar, Dr P

    2010-01-01

    This paper introduces a novel indexing and access method, called Feature- Based Adaptive Tolerance Tree (FATT), using wavelet transform is proposed to organize large image data sets efficiently and to support popular image access mechanisms like Content Based Image Retrieval (CBIR).Conventional database systems are designed for managing textual and numerical data and retrieving such data is often based on simple comparisons of text or numerical values. However, this method is no longer adequate for images, since the digital presentation of images does not convey the reality of images. Retrieval of images become difficult when the database is very large. This paper addresses such problems and presents a novel indexing technique, Feature Based Adaptive Tolerance Tree (FATT), which is designed to bring an effective solution especially for indexing large databases. The proposed indexing scheme is then used along with a query by image content, in order to achieve the ultimate goal from the user point of view that ...

  17. Schwinger vacuum pair production in chirped laser pulses

    SciTech Connect

    Dumlu, Cesim K. [Department of Physics, University of Connecticut, Storrs Connecticut 06269-3046 (United States)

    2010-08-15

    The recent developments of high intensity ultrashort laser pulses have raised the hopes of observing Schwinger vacuum pair production which is one of the important nonperturbative phenomena in QED. The quantitative analysis of realistic high intensity laser pulses is vital for understanding the effect of the field parameters on the momentum spectrum of the produced particles. In this study, we analyze chirped laser pulses with a subcycle structure, and investigate the effects of the chirp parameter on the momentum spectrum of the produced particles. The combined effect of the chirp and carrier phase of the laser pulse is also analyzed. These effects are qualitatively explained by investigating the turning-point structure of the potential within the framework of the complex WKB scattering approach to pair production.

  18. Excitation of Chirping Whistler Waves in a Laboratory Plasma

    NASA Astrophysics Data System (ADS)

    Van Compernolle, B.; An, X.; Bortnik, J.; Thorne, R. M.; Pribyl, P.; Gekelman, W.

    2015-06-01

    Whistler mode chorus emissions with a characteristic frequency chirp are important magnetospheric waves, responsible for the acceleration of outer radiation belt electrons to relativistic energies and also for the scattering loss of these electrons into the atmosphere. Here, we report on the first laboratory experiment where whistler waves exhibiting fast frequency chirping have been artificially produced using a beam of energetic electrons launched into a cold plasma. Frequency chirps are only observed for a narrow range of plasma and beam parameters, and show a strong dependence on beam density, plasma density, and magnetic field gradient. Broadband whistler waves similar to magnetospheric hiss are also observed, and the parameter ranges for each emission are quantified.

  19. Effects of collisions on energetic particle-driven chirping burstsa)

    NASA Astrophysics Data System (ADS)

    Lesur, M.

    2013-05-01

    In the presence of an energetic particle population in a dissipative plasma, self-trapped structures in phase-space (holes and clumps) emerge from nonlinear wave-particle interactions. Their dynamics can lead to a nonlinear continuous shifting of the wave frequency (chirping). The effects of collisions on chirping characteristics are investigated, with a one-dimensional kinetic model. Existing analytic theory is extended to account for Krook-like collisions, which quantitatively explains a significant departure from widely accepted square-root time dependency. Relaxation oscillations, associated with chirping bursts, are investigated in the presence of dynamical friction and velocity-diffusion. The period increases with decreasing drag and weakly increases with decreasing diffusion. The mechanism is clarified with a simple semi-analytic model of hole/clump pair, which satisfies a Fokker-Planck equation. The model shows that the linear growth rate cannot be obtained simply by fitting an exponential to the amplitude time-series.

  20. Predicting the fatty acid composition of milk: a comparison of two Fourier transform infrared sampling techniques.

    PubMed

    Afseth, Nils Kristian; Martens, Harald; Randby, Ashild; Gidskehaug, Lars; Narum, Bjørg; Jørgensen, Kjetil; Lien, Sigbjørn; Kohler, Achim

    2010-07-01

    In the present study a novel approach for Fourier transform infrared (FT-IR) characterization of the fatty acid composition of milk based on dried film measurements has been presented and compared to a standard FT-IR approach based on liquid milk measurements. Two hundred and sixty-two (262) milk samples were obtained from a feeding experiment, and the samples were measured with FT-IR as dried films as well as liquid samples. Calibrations against the most abundant fatty acids, CLA (i.e., 18:2cis-9, trans-11), 18:3cis-9, cis-12, cis-15, and summed fatty acid parameters were obtained for both approaches. The estimation errors obtained in the dried film calibrations were overall lower than the corresponding liquid sample calibrations. Similar and good calibrations (i.e., R(2) ranges from 0.82 to 0.94 (liquid samples) and from 0.88 to 0.97 (dried films)) for short-chain fatty acids (6:0-14:0), 18:1cis-9, SAT, MUFA, and iodine value were obtained by both approaches. However, the dried film approach was the only approach for which feasible calibrations (i.e., R(2) ranges from 0.78 to 0.93) were obtained for the major saturated fatty acids 16:0 and 18:0, the minor fatty acid features 4:0, CLA (i.e., 18:2cis-9, trans-11), PUFA, and the summed 18:1 trans isomers. For the dried film approach, logical spectral features were found to dominate the respective fatty acid calibration models. The preconcentration step of the dried film approach could be expected to account for a major part of the prediction improvements going from predictions in liquid milk to predictions in dried films. The dried film approach has a significant potential for use in high-throughput applications in industrial environments and might also serve as a valuable supplement for determination of genetic and breeding factors within research communities. PMID:20615281

  1. Effects of frequency chirp on magnetron injection locking

    SciTech Connect

    Pengvanich, P.; Lau, Y. Y.; Luginsland, J. W.; Gilgenbach, R. M.; Cruz, E. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Schamiloglu, E. [Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131 (United States)

    2008-07-15

    The injection locking of a magnetron is theoretically analyzed when either the free running oscillator or the drive signal has a frequency chirp. It is found that complete phase locking of the signal cannot be achieved in either case. However, as long as the locking condition of Adler is well-satisfied instantaneously, a high degree of locking occurs during a major duration of the frequency chirps. The expected output phase variation is computed in terms of the noise in the free-running magnetron oscillator for the case of constant drive frequency.

  2. Dense Monoenergetic Proton Beams from Chirped Laser-Plasma Interaction

    NASA Astrophysics Data System (ADS)

    Galow, Benjamin J.; Salamin, Yousef I.; Liseykina, Tatyana V.; Harman, Zoltán; Keitel, Christoph H.

    2011-10-01

    Interaction of a frequency-chirped laser pulse with single protons and a hydrogen gas target is studied analytically and by means of particle-in-cell simulations, respectively. The feasibility of generating ultraintense (107 particles per bunch) and phase-space collimated beams of protons (energy spread of about 1%) is demonstrated. Phase synchronization of the protons and the laser field, guaranteed by the appropriate chirping of the laser pulse, allows the particles to gain sufficient kinetic energy (around 250 MeV) required for such applications as hadron cancer therapy, from state-of-the-art laser systems of intensities of the order of 1021W/cm2.

  3. Chirped pulse excitation of two-atom Rydberg states

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Elena

    2015-07-01

    We analyze the excitation of two ground state atoms to a double Rydberg state by a two-photon chirped optical pulse in the regime of adiabatic rapid passage (ARP). For intermediate Rydberg–Rydberg interaction strengths relevant for atoms separated by ?ten ?m, adiabatic excitation can be achieved at experimentally feasible Rabi frequencies and chirp rates of the pulses, resulting in high transfer efficiencies. We also study the adiabatic transfer between ground and Rydberg states as a means to realize a controlled phase gate between atomic qubits.

  4. Ultrafast chirped optical waveform recording using referenced heterodyning and a time microscope

    DOEpatents

    Bennett, Corey Vincent

    2010-06-15

    A new technique for capturing both the amplitude and phase of an optical waveform is presented. This technique can capture signals with many THz of bandwidths in a single shot (e.g., temporal resolution of about 44 fs), or be operated repetitively at a high rate. That is, each temporal window (or frame) is captured single shot, in real time, but the process may be run repeatedly or single-shot. This invention expands upon previous work in temporal imaging by adding heterodyning, which can be self-referenced for improved precision and stability, to convert frequency chirp (the second derivative of phase with respect to time) into a time varying intensity modulation. By also including a variety of possible demultiplexing techniques, this process is scalable to recoding continuous signals.

  5. Ultrafast chirped optical waveform recorder using referenced heterodyning and a time microscope

    DOEpatents

    Bennett, Corey Vincent (Livermore, CA)

    2011-11-22

    A new technique for capturing both the amplitude and phase of an optical waveform is presented. This technique can capture signals with many THz of bandwidths in a single shot (e.g., temporal resolution of about 44 fs), or be operated repetitively at a high rate. That is, each temporal window (or frame) is captured single shot, in real time, but the process may be run repeatedly or single-shot. This invention expands upon previous work in temporal imaging by adding heterodyning, which can be self-referenced for improved precision and stability, to convert frequency chirp (the second derivative of phase with respect to time) into a time varying intensity modulation. By also including a variety of possible demultiplexing techniques, this process is scalable to recoding continuous signals.

  6. Optical screening of diabetes mellitus using non-invasive Fourier-transform infrared spectroscopy technique for human lip.

    PubMed

    Yoshida, Satoshi; Yoshida, Makoto; Yamamoto, Mayumi; Takeda, Jun

    2013-03-25

    The Fourier-transform mid-infrared spectroscopy (FTIR) technique has not been used for diabetes diagnosis so far in clinical practice. We attempted to predict non-invasively blood hemoglobin A1c (HbA1c) levels by FTIR to enable evaluation and screening for diabetes. Twenty eight patients from age 20s to 80s, 14 males and 14 females, with and without diabetes, were examined in hospital as a pilot study, and their biochemical data were analyzed with infrared (IR) spectral data of the lip surface by FTIR spectroscopy. Some IR peaks of lip surface had significant correlations with blood glucose and HbA1c levels. Among several peaks in the spectra of lip, peaks at around 1300-1400cm(-1) discriminated groups with higher or lower HbA1c levels, suggesting the observation of lip surface advanced glycation end-products with carboxymethyl group. The application of partial least squares (PLS) regression analysis to the correlation between HbA1c levels and lip FTIR spectra resulted in highly significant prediction of HbA1c values for the subjects. Comparison of some IR peaks with predicted HbA1c values served to remove false-negative data effectively. This study with FTIR technique proposed here was effective for screening of diabetes patients with higher HbA1c levels. PMID:23333685

  7. SAR vibrometry using fractional Fourier transform processing

    Microsoft Academic Search

    Qi Wang; Majeed M. Hayat; Balu Santhanam; Tom Atwood

    2009-01-01

    A novel signal-processing approach is reported for vibrometry in synthetic aperture radar (SAR) imaging systems. The approach exploits the conventional deramp process; however, in place of Fourier-transform processing we utilize the fractional Fourier transform (FRFT) as a processing tool. The FRFT is geared toward non-stationary signals and chirped sinusoids particularly. A simplified mathematical expression is developed to describe the reflectivity

  8. Injection and acceleration of electron bunch in a plasma wakefield produced by a chirped laser pulse

    SciTech Connect

    Afhami, Saeedeh; Eslami, Esmaeil, E-mail: eeslami@iust.ac.ir [Department of Physics, Iran University of Science and Technology (IUST), Narmak, Tehran 16846-13114 (Iran, Islamic Republic of)

    2014-06-15

    An ultrashort laser pulse propagating in plasma can excite a nonlinear plasma wakefield which can trap and accelerate charged particles up to GeV. One-dimensional analysis of electron injection, trapping, and acceleration by different chirped pulses propagating in plasma is investigated numerically. In this paper, we inject electron bunches in front of the chirped pulses. It is indicated that periodical chirped laser pulse can trap electrons earlier than other pulses. It is shown that periodical chirped laser pulses lead to decrease the minimum momentum necessary to trap the electrons. This is due to the fact that periodical chirped laser pulses are globally much efficient than nonchirped pulses in the wakefield generation. It is found that chirped laser pulses could lead to much larger electron energy than that of nonchirped pulses. Relative energy spread has a lower value in the case of periodical chirped laser pulses.

  9. Optimization of apodized linearly chirped fiber gratings for optical communications

    Microsoft Academic Search

    Karin Ennser; N. Zervas; Richard I. Laming

    1998-01-01

    The dispersion characteristics of apodized, linearly chirped fiber Bragg gratings and their potential as dispersion compensators have been studied systematically. It is shown that the positive hyperbolic-tangent profile results in an overall superior performance, as it provides highly linearized time-delay characteristics with minimum reduction in the linear dispersion. To compensate for the linear dispersion of 100 km of standard telecom

  10. Focusing Bistatic SAR Images using Non-Linear Chirp Scaling

    Microsoft Academic Search

    Y. L. Neo; F. H. Wong; I. Cumming

    2004-01-01

    Non-Linear Chirp Scaling is an innovative way to focus bistatic SAR images and has been demonstrated to work on the configuration where the transmitter imaging on broadside and the receiver is stationary. This paper improves and extends the method to the configuration where both the receiver and the transmitter are imaging at a squint angle and moving in a parallel

  11. Pulse compression on the Mark III FEL using energy chirping

    Microsoft Academic Search

    Eric B. Szarmes; Stephen V. Benson; John M. J. Madey

    1990-01-01

    We have performed preliminary simulations of the optical-pulse formation in the Mark III FEL using electron micropulses which exhibit a linear energy dependence on time, and have demonstrated optical pulses whose frequency chirps agree fairly well with those obtained analytically by assuming that the resonance condition determines the lasing wavelength during the pulse. In a typical case, we project pulse

  12. Influence of nonideal chirped fiber grating characteristics on dispersion cancellation

    Microsoft Academic Search

    K. Ennser; M. Ibsen; M. Durkin; M. N. Zervas; R. I. Laming

    1998-01-01

    The effect of nonideal dispersion and reflection characteristics of chirped fiber gratings on the performance of 10-Gb\\/s nonreturn-to-zero-transmission systems operating over standard fiber is investigated. The system penalty for different amplitude and period ripples are quantified. Analyses of an experimental grating confirm that current fabrication technology can meet the requirements for <1-dB-penalty operation

  13. Effects of Frequency Chirping in Electro-Magnetically Induced Transparency

    NASA Astrophysics Data System (ADS)

    Narducci, Frank A.; Davis, Jon P.

    2006-05-01

    Under the right conditions, electro-magnetically induced transparency can lead to ultra-narrow resonances. In this paper, we explore theoretically the effects of rapidly chirping the frequency of the probe laser on the observed lineshapes. For a proper choice of parameters, the lineshape can become distorted and show asymmetric ringing-like behavior. Experimental results will also be discussed.

  14. Numerical studies of driven, chirped Bernstein, Greene, and Kruskal modes

    E-print Network

    Wurtele, Jonathan

    Numerical studies of driven, chirped Bernstein, Greene, and Kruskal modes F. Peinetti University-amplitude periodic density fluctuations, were induced by driving the plasma with a weak oscillating drive, whose in plasmas. These waves are usually strongly Landau damped; however, if destabilizing mecha- nisms

  15. High Squint SAR Processing Using Modified Extended Chirp Scaling

    Microsoft Academic Search

    Duan Shizhong; Li Junxian

    2006-01-01

    This paper proposes a novel approach for high squint missile borne SAR raw data processing using a modified extended chirp scaling algorithm to accommodate the condition of high squint and short wave wavelength. Compared with the tradition synthesis aperture radar (SAR), the missile borne SAR has important characteristics including high flight speed, non-straight movement with non-constant velocity and big squint

  16. Chirped microlens arrays for diode laser circularization and beam expansion

    NASA Astrophysics Data System (ADS)

    Schreiber, Peter; Dannberg, Peter; Hoefer, Bernd; Beckert, Erik

    2005-08-01

    Single-mode diode lasers are well-established light sources for a huge number of applications but suffer from astigmatism, beam ellipticity and large manufacturing tolerances of beam parameters. To compensate for these shortcomings, various approaches like anamorphic prism pairs and cylindrical telescopes for circularization as well as variable beam expanders based on zoomed telescopes for precise adjustment of output beam parameters have been employed in the past. The presented new approach for both beam circularization and expansion is based on the use of microlens arrays with chirped focal length: Selection of lenslets of crossed cylindrical microlens arrays as part of an anamorphic telescope enables circularization, astigmatism correction and divergence tolerance compensation of diode lasers simultaneously. Another promising application of chirped spherical lens array telescopes is stepwise variable beam expansion for circular laser beams of fiber or solid-state lasers. In this article we describe design and manufacturing of beam shaping systems with chirped microlens arrays fabricated by polymer-on-glass replication of reflow lenses. A miniaturized diode laser module with beam circularization and astigmatism correction assembled on a structured ceramics motherboard and a modulated RGB laser-source for photofinishing applications equipped with both cylindrical and spherical chirped lens arrays demonstrate the feasibility of the proposed system design approach.

  17. Wide-band nonlinear chirp transducers for planar acoustooptic deflectors

    Microsoft Academic Search

    K. Anemogiannis; P. Russer; R. Weigel

    1989-01-01

    The design, fabrication, and performance characteristics of LiNbO 3-based wideband nonlinear interdigital chirp transducers are reported. A 54% bandwidth centered at 720 MHz has been obtained for a collinear deflector on a YX substrate. A 66% bandwidth at a midband frequency of 600 MHz has been designed for a Bragg deflector on a YZ substrate with electrodes tilted to satisfy

  18. The Theta Laser A Low Noise Chirped Pulse Laser

    E-print Network

    Van Stryland, Eric

    The Theta Laser A Low Noise Chirped Pulse Laser Dimitrios Mandridis dmandrid@creol.ucf.edu April 29, 2011 CREOL Affiliates Day 2011 #12;2 Objective: Frequency Swept (FM) Mode-locked Laser · Develop a frequency swept laser, · linear f-sweep, · uniform-intensity, · low noise, · with long-term stability

  19. Chirped-Pulse Broadband Microwave Spectra and Structures of the OCS Trimer and Tetramer

    NASA Astrophysics Data System (ADS)

    Evangelisti, Luca; Perez, Cristobal; Seifert, Nathan A.; Pate, Brooks; Dehghany, Mehdi; Moazzen-Ahmadi, Nasser; McKellar, Bob

    2014-06-01

    Structure determination of weakly bound OCS clusters is a challenging problem due to many low energy isomers on the potential energy surface. The premier tool for studying these clusters is high-resolution infrared spectroscopy, as it can be used to analyze non-polar clusters. Following the analysis of high-resolution IR spectra of clusters formed in a molecular beam expansion of OCS there were some outstanding questions about the structures of the observed clusters. The chirped-pulse Fourier transform microwave spectrum in the 3-9 GHz frequency range was measured for a pulsed molecular beam of OCS in neon (1%). All 13C, 18O and 34S isotopologues of the previously detected OCS trimer have been observed in natural abundance in the 3-9 GHz band using chirped-pulse Fourier transform microwave spectroscopy. The structure of this trimer features a barrel-shaped structure with two aligned and one anti-aligned OCS monomers. A new OCS trimer is also observed for the first time, and its structure is consistent with a barrel-shaped structure with 3 aligned monomers. Using the infrared spectrum for guidance, a spectrum corresponding to a polar OCS tetramer has been assigned. This cluster has a similar barrel-like structure but with an additional tilted OCS monomer added to the top of the barrel. All 13C and 34S isotopologues have been assigned for the tetramer. However, due to sign ambiguities in Kraitchman's equations, and small rotational constant differences between aligned and anti-aligned combinations of OCS molecules in the trimer barrel, absolute structural assignment is indeterminate without additional constraints. Therefore a combinatoric approach was used to compute the most reasonable tetramer structure using distance and sign constraints between pairs of carbon and sulfur coordinates, assuming the experimental OCS monomer structure. Results of this approach will be presented, as well as a comparison of the experimental results with the most recent ab initio structures for the OCS tetramer.

  20. Direct optical techniques for the measurement of water content in oil-paper insulation in power transformers

    Microsoft Academic Search

    Joaquín H. Rodríguez-Rodríguez; Fernando Martínez-Piñón; José A. Álvarez-Chávez; David Jaramillo-Vigueras; Edgar G. Robles-Pimentel

    2011-01-01

    Paper-oil insulation in power transformers is degraded and gradually damaged due to electrical, chemical, mechanical and moisture factors. It is well established from several studies that moisture is a major source of insulation failure in high voltage power transformers. Measurement and monitoring of moisture is essential to predict life and operation condition for power transformers. This paper presents direct optical

  1. Spin-wave storage using chirped control fields in atomic frequency comb-based quantum memory

    NASA Astrophysics Data System (ADS)

    Miná?, Ji?í; Sangouard, Nicolas; Afzelius, Mikael; de Riedmatten, Hugues; Gisin, Nicolas

    2010-10-01

    It has been shown that an inhomogeneously broadened optical transition shaped into an atomic frequency comb can store a large number of temporal modes of the electromagnetic field at the single-photon level without the need to increase the optical depth of the storage material. The readout of light modes is made efficient thanks to the rephasing of the optical-wavelength coherence similar to photon-echo-type techniques, and the reemission time is given by the comb structure. For on-demand readout and long storage times, two control fields are used to transfer the optical coherence back and forth into a spin wave. Here, we present a detailed analysis of the spin-wave storage based on chirped adiabatic control fields. In particular, we verify that chirped fields require significantly weaker intensities than ? pulses. The price to pay is a reduction of the multimode storage capacity that we quantify for realistic material parameters associated with solids doped with rare-earth-metal ions.

  2. Fiber laser sensor based on a phase-shifted chirped grating for acoustic sensing of partial discharges

    NASA Astrophysics Data System (ADS)

    Lima, Sanderson E. U.; Farias, Rubem G.; Araújo, Francisco M.; Ferreira, Luís A.; Santos, José L.; Miranda, Vladimiro; Frazão, Orlando

    2013-03-01

    Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in the high voltage apparatus. Partial discharges are a major source of insulation failure in electric power transformers, and the differentiation from other sources of acoustic emission is of the utmost importance. This paper reports the development of a new sensor concept — a fiber laser sensor based on a phase-shifted chirped fiber grating — for the acoustic emission detection of incipient faults in oil-filled power transformers. These sensors can be placed in the inner surface of the transformer tank wall, not affecting the insulation integrity of the structure and improving fault detection and location. The performance of the sensing head is characterized and compared for different surrounding media: air, water, and oil. The results obtained indicate the feasibility of this sensing approach for the industrial development of practical solutions.

  3. Alignment of a tiled-grating compressor in a high-power chirped-pulse amplification laser system.

    PubMed

    Hornung, Marco; Bödefeld, Ragnar; Siebold, Mathias; Schnepp, Matthias; Hein, Joachim; Sauerbrey, Roland; Kaluza, Malte C

    2007-10-20

    We present a novel technique to align a tiled grating in all five relevant degrees of freedom utilized in the compressor of the high-power chirped-pulse amplification laser system POLARIS at the Institute for Optics and Quantum Electronics, Jena, Germany. With this technique, alignment errors of the two gratings with respect to each other can be detected with an accuracy of 1 microrad for the rotational and 40 nm for the translational degrees of freedom. This is well sufficient to recompress 1030 nm pulses, which were stretched to 2.2 ns before amplification, to their bandwith limit of 150 fs. PMID:17952178

  4. Detection and tracking of platforms above sea-level in infrared and visual band videos using Bag-of-Features technique with scale invariant feature transform

    Microsoft Academic Search

    Tolga Can; A. Onur Karali; Tayfun Aytac

    2011-01-01

    In this study, platforms above sea-level are detected and tracked using Bag-of-Features technique (BoF) with scale-invariant fea- ture transform (SIFT) in infrared (IR) and visual (VIS) band videos. Features in the training set corresponding to platforms above sea-level and background are firstly clustered in offline mode and these features are used for target detection using BoF technique. With these features,

  5. Detection and tracking of sea-surface targets in infrared and visual band videos using the bag-of-features technique with scale-invariant feature transform

    Microsoft Academic Search

    Tolga Can; A. Onur Karali; Tayfun Aytac

    2011-01-01

    Sea-surface targets are automatically detected and tracked using the bag-of-features (BOF) technique with the scale-invariant feature transform (SIFT) in infrared (IR) and visual (VIS) band videos. Features corresponding to the sea-surface targets and background are first clustered using a training set offline, and these features are then used for online target detection using the BOF technique. The features corresponding to

  6. Broadband sum-frequency generation using cascaded processes via chirped quasi-phase-matching

    NASA Astrophysics Data System (ADS)

    Rangelov, A. A.; Vitanov, N. V.

    2012-04-01

    An efficient broadband sum-frequency generation (SFG) technique using the two cascaded optical parametric processes ?3=?1+?2 and ?4=?1+?3 is proposed. The technique uses chirped quasi-phase-matched gratings, which, in the undepleted pump approximation, make SFG analogous to adiabatic population transfer in three-state systems with crossing energies in quantum physics. If the local modulation period first makes the phase match occur for ?3 and then for ?4 SFG processes then the energy is converted adiabatically to the ?4 field. Efficient SFG of the ?4 field is also possible by the opposite direction of the local modulation sweep; then transient SFG of the ?3 field is strongly reduced. Most of these features remain valid in the nonlinear regime of depleted pump.

  7. Spectral Characterizations of the Clouds and the Earth's Radiant Energy System (CERES) Thermistor Bolometers using Fourier Transform Spectrometer (FTS) Techniques

    NASA Technical Reports Server (NTRS)

    Thornhill, K. Lee; Bitting, Herbert; Lee, Robert B., III; Paden, Jack; Pandey, Dhirendra K.; Priestley, Kory J.; Thomas, Susan; Wilson, Robert S.

    1998-01-01

    Fourier Transform Spectrometer (FTS) techniques are being used to characterize the relative spectral response, or sensitivity, of scanning thermistor bolometers in the infrared (IR) region (2 - >= 100-micrometers). The bolometers are being used in the Clouds and the Earth's Radiant Energy System (CERES) program. The CERES measurements are designed to provide precise, long term monitoring of the Earth's atmospheric radiation energy budget. The CERES instrument houses three bolometric radiometers, a total wavelength (0.3- >= 150-micrometers) sensor, a shortwave (0.3-5-micrometers) sensor, and an atmospheric window (8-12-micrometers) sensor. Accurate spectral characterization is necessary for determining filtered radiances for longwave radiometric calibrations. The CERES bolometers spectral response's are measured in the TRW FTS Vacuum Chamber Facility (FTS - VCF), which uses a FTS as the source and a cavity pyroelectric trap detector as the reference. The CERES bolometers and the cavity detector are contained in a vacuum chamber, while the FTS source is housed in a GN2 purged chamber. Due to the thermal time constant of the CERES bolometers, the FTS must be operated in a step mode. Data are acquired in 6 IR spectral bands covering the entire longwave IR region. In this paper, the TRW spectral calibration facility design and data measurement techniques are described. Two approaches are presented which convert the total channel FTS data into the final CERES spectral characterizations, producing the same calibration coefficients (within 0.1 percent). The resulting spectral response curves are shown, along with error sources in the two procedures. Finally, the impact of each spectral response curve on CERES data validation will be examined through analysis of filtered radiance values from various typical scene types.

  8. Study of the Q Branch Structure of the 14N and 15N Isotopologues of the ?4 Band of Ammonia Using Frequency Chirped Quantum Cascade Lasers

    NASA Astrophysics Data System (ADS)

    Duxbury, Geoffrey; Wilson, David; Hay, Kenneth; Langford, Nigel

    2013-10-01

    Intrapulse quantum cascade (QC) laser spectrometers are able to produce both saturation and molecular alignment of a gas sample owing to the rapid sweep of the radiation through the absorption features. In the QC lasers used to study the 14N and 15N isotopologues of the -4 band of ammonia centered near 1625 cm-1, the variation of the chirp rate during the scan is very large, from ca. 85 to ca. 15 MHz ns-1. In the rapid chirp zone the collisional interaction time of the laser radiation with the gas molecules is short, and large rapid passage effects are seen, whereas at the slow chirp end the line shape resembles that of a Doppler broadened line. The total scan range of the QC laser of ca. 10 cm-1 is sufficient to allow the spectra of both isotopologues to be recorded and the rapid and slow interactions with the laser radiation to be seen. The rapid passage effects are enhanced by the use of an off axis Herriott cell with an effective path length of 62 m, which allows a buildup of polarization to occur. The effective resolution of the chirped QC laser is ca. 0.012 cm-1 full width at half-maximum in the 1625 cm-1 region. The results of these experiments are compared with those of other studies of the -4 band of ammonia carried out using Fourier transform and Laser Stark spectroscopy. They also demonstrate the versatility of the down chirped QC laser for investigating collisional effects in low pressure gases using long absorbing path lengths.

  9. Use of time history speckle pattern and pulsed photoacoustic techniques to detect the self-accommodating transformation in a Cu-Al-Ni shape memory alloy

    SciTech Connect

    Sanchez-Arevalo, F.M., E-mail: fsanchez@iim.unam.mx [CCADET - Universidad Nacional Autonoma de Mexico, A.P. 70-186, Mexico D.F., C.P. 04510 (Mexico); Aldama-Reyna, W. [Departamento Academico de Fisica, Universidad Nacional de Trujillo, Trujillo (Peru); Lara-Rodriguez, A.G. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico (Mexico); Garcia-Fernandez, T. [Universidad Autonoma de la Ciudad de Mexico (UACM), Prolongacion San Isidro 151, Col. San Lorenzo Tezonco, Mexico DF, C.P. 09790 (Mexico); Pulos, G. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico (Mexico); Trivi, M. [Centro de Investigaciones Opticas, Universidad de la Plata (Argentina); Villagran-Muniz, M. [CCADET - Universidad Nacional Autonoma de Mexico, A.P. 70-186, Mexico D.F., C.P. 04510 (Mexico)

    2010-05-15

    Continuous and pulsed electromagnetic radiation was used to detect the self-accommodation mechanism on a polycrystalline Cu-13.83 wt.%Al-2.34 wt.%Ni shape memory alloy. Rectangular samples of this alloy were mechanically polished to observe the austenite and martensite phases. The samples were cooled in liquid nitrogen prior to the experiments to obtain the martensite phase. Using a dynamic speckle technique with a continuous wave laser we obtained the time history of the speckle pattern image and monitored the surface changes caused by the self-accommodation mechanism during the inverse (martensitic to austenitic) transformation. Using a photoacoustic technique based on a pulsed laser source it was also possible to detect the self-accommodation phenomena in a bulk sample. For comparison purposes, we used differential scanning calorimetry (DSC) to detect the critical temperatures of transformation and use these as reference to evaluate the performance of the optical and photoacoustical techniques. In all cases, the same range of temperature was obtained during the inverse transformation. From these results, we conclude that time history speckle pattern (THSP) and pulsed photoacoustic are complementary techniques; they are non-destructive and useful to detect surface and bulk martensitic transformation induced by a temperature change.

  10. Exact solution of axially symmetric Rayleigh scattering transport equation by Laplace transform and Wiener-Hopf technique and new expression of HL and HR function

    Microsoft Academic Search

    R. N. Das

    1978-01-01

    An exact solution of the transport equation in radiative transfer for an axially symmetric Rayleigh scattering problem in a semiinfinite planetary atmosphere for both emergent intensity and intensity at any optical depth has been derived with the aid of the Laplace transform and the Wiener-Hopf technique, and by use of the constancy of net flux. Chandrasekhar's (1950) results for emergent

  11. Suppression of reflection from the grid boundary in solving the time-dependent Schroedinger equation by split-step technique with fast Fourier transform

    Microsoft Academic Search

    A. A. Gonoskov; I. A. Gonoskov

    2006-01-01

    We present an approach to numerically solving the time-dependent Schroedinger equation and other parabolic equations by the split-step technique with fast Fourier transform, which suppresses the backreflection of waves from the grid boundaries with any specified accuracy. Most importantly, all known methods work well only for a narrow region of incident waves spectrum, and the proposed method provides absorption of

  12. From Chirps to Random-FM Excitations in Pulse Compression Ultrasound Systems

    E-print Network

    Callegari, Sergio; Caporale, Salvatore; Monticelli, Marcello; Eroli, Massimiliano; Senni, Luca; Rovatti, Riccardo; Setti, Gianluca; Burrascano, Pietro

    2013-01-01

    Pulse compression is often practiced in ultrasound Non Destructive Testing (NDT) systems using chirps. However, chirps are inadequate for setups where multiple probes need to operate concurrently in Multiple Input Multiple Output (MIMO) arrangements. Conversely, many coded excitation systems designed for MIMO miss some chirp advantages (constant envelope excitation, easiness of bandwidth control, etc.) and may not be easily implemented on hardware originally conceived for chirp excitations. Here, we propose a system based on random-FM excitations, capable of enabling MIMO with minimal changes with respect to a chirp-based setup. Following recent results, we show that random-FM excitations retain many advantages of chirps and provide the ability to frequency-shape the excitations matching the transducers features.

  13. ATOMIC AND MOLECULAR PHYSICS: Ionization of atoms by chirped attosecond pulses

    NASA Astrophysics Data System (ADS)

    Tan, Fang; Peng, Liang-You; Gong, Qi-Huang

    2009-11-01

    We investigate the ionization dynamics of atoms by chirped attosecond pulses using the strong field approximation method. The pulse parameters are carefully chosen in the regime where the strong field approximation method is valid. We analyse the effects of the chirp of attosecond pulses on the energy distributions and the corresponding left-right asymmetry of the ionized electrons. For a single chirped attosecond pulse, the ionized electrons can be redistributed and the left-right asymmetry shows oscillations because of the introduction of the chirp. For time-delayed double attosecond pulses at different intensities with the weaker one chirped, exchanging the order of the two pulses shows a relative shift of the energy spectra, which can be explained by the different effective time delays of different frequency components because of the chirp.

  14. Chirped-pulsed FTMW spectra of valeric acid, 5-aminovaleric acid, and ?-valerolactam: A study of amino acid mimics in the gas phase

    NASA Astrophysics Data System (ADS)

    Bird, Ryan G.; Vaquero-Vara, Vanesa; Zaleski, Daniel P.; Pate, Brooks H.; Pratt, David W.

    2012-10-01

    The lowest energy conformations of valeric acid (VA) and ?-valerolactam (DVL) were determined using chirped-pulsed Fourier transform microwave spectroscopy. DVL was produced by heating 5-aminovaleric acid (AVA) in a metal nozzle. A study of the reaction pathway leading to DVL identified the preferred structure of AVA and demonstrated that an n ? ?* interaction plays the key role in the transformation of reactant into product. An inverse kinetic isotope effect was detected for this process. Additionally, the spectra of single and double water complexes of DVL along with the 13C and 15N-substituted species (in natural abundance) were collected and analyzed.

  15. Steady state heat transfer in a SF6. gas cooled-insulated power transformer using finite element technique

    Microsoft Academic Search

    M. M. Abdel Aziz; M. B. Eteiba; J. H. Shazly

    2006-01-01

    In this paper, the finite element analysis approach is utilized to perform heat transfer analysis to obtain the steady state temperature distribution of SF6 gas cooled-insulated power transformer resulting from conditions imposed on its boundaries, which represents how temperature varies with position in the transformer. The obtained results are compared with measured temperature data collected during the testing program carried

  16. A novel iron loss reduction technique for distribution transformers based on a combined genetic algorithm - neural network approach

    Microsoft Academic Search

    Pavlos S. Georgilakis; Nikolaos D. Doulamis; Anastasios D. Doulamis; Nikos D. Hatziargyriou; Stefanos D. Kollias

    2001-01-01

    The paper presents an effective method to reduce the iron losses of wound core distribution transformers based on a combined neural network\\/genetic algorithm approach. The originality of the work presented is that it tackles the iron loss reduction problem during the transformer production phase, while previous works concentrated on the design phase. More specifically, neural networks effectively use measurements taken

  17. A Novel Iron Loss Reduction Technique for Distribution Transformers Based on a Combined Genetic Algorithm - Neural Network Approach

    Microsoft Academic Search

    Palvos S. Georgilakis; Nikolaos D. Doulamis; Anastasios D. Doulamis; Nikos D. Hatziargyriou; Stefanos D. Kollias

    2001-01-01

    This paper presents an effective method to reduce the iron losses of wound core distribution transformers based on a combined neural network - genetic algorithm approach. The originality of the work presented in this paper is that it tackles the iron loss reduction problem during the transformer production phase, while previous works were concentrated on the design phase. More specifically,

  18. An analysis of As_(2)S_(3) chirped fiber grating formed by two-photon absorption effect

    NASA Astrophysics Data System (ADS)

    Wang, Huaisheng; Zhang, Zhigang; Chai, Lu; Wang, Qingyue

    2003-06-01

    When femtosecond laser pulses interfere with chirped femtosecond laser pulses in As_(2)S_(3) fiber, a chirped fiber grating is formed. An analytical expression is given to describe the chirped grating, and its Bragg reflectivity is calculated. Because of the high photosensitive effect of As_(2)S_(3) material, the chirped fiber grating has a wide Bragg reflective spectrum and high reflectivity by choosing proper parameters. This indicates that the chirped fiber grating can be used as a stretcher in the femtosecond chirped pulse amplification (CPA) system.

  19. Pulse compression on the Mark III FEL using energy chirping

    NASA Astrophysics Data System (ADS)

    Szarmes, Eric B.; Benson, Stephen V.; Madey, John M. J.

    1990-10-01

    We have performed preliminary simulations of the optical-pulse formation in the Mark III FEL using electron micropulses which exhibit a linear energy dependence on time, and have demonstrated optical pulses whose frequency chirps agree fairly well with those obtained analytically by assuming that the resonance condition determines the lasing wavelength during the pulse. In a typical case, we project pulse compression by a factor of 13.3, from an initial pulse width of 3.13 ps to a final pulse width of 236 fs, at a wavelength of 3.35 ?m and an electron energy chirp of +2% (energy increasing towards the back of the pulse). This represents an optical pulse less than half as short as the slippage length of 47 magnet periods for this wavelength.

  20. Excitation of the Morse oscillator by an ultrashort chirped pulse

    SciTech Connect

    Astapenko, V. A., E-mail: astval@mail.ru; Romadanovskii, M. S. [Moscow Institute of Physics and Technology (Russian Federation)

    2010-03-15

    The excitation of the classic Morse oscillator by an ultrashort electromagnetic pulse with a linear frequency chirp is studied theoretically. Formulas are derived for the oscillation amplitude and the radiation power averaged over a period as functions of the excitation energy for free oscillations of the Morse oscillator. Analytical expressions for describing the oscillator motion after the end of the pulse are obtained in the harmonic limit. In the general case of arbitrary parameters of the problem, the specific features of an excited Morse oscillator are analyzed numerically. Prominence is given to the effect of chirp on the excitation energy. The consideration is performed in terms of dimensionless variables, which makes it possible to apply the results obtained to a wide range of molecular systems and exciting-pulse parameters.

  1. Interaction of strongly chirped pulses with two-level atoms

    SciTech Connect

    Ibanez, S.; Peralta Conde, A.; Muga, J. G. [Departamento de Quimica Fisica, Universidad del Pais Vasco - Euskal Herriko Unibertsitatea, Apdo. 644, Bilbao (Spain); Guery-Odelin, D. [Laboratoire Collisions Agregats Reactivite, CNRS UMR 5589, IRSAMC, Universite Paul Sabatier, 118 Route de Narbonne, F-31062 Toulouse CEDEX 4 (France)

    2011-07-15

    We study the effect of ultrachirped pulses on the population inversion of two-level atoms. Ultrachirped pulses are defined as those for which the frequency chirp is of the order of the transition frequency of the two-level atom. When the chirp is large enough, the resonance may be crossed twice, for positive and negative frequencies. In fact the decomposition of the field into amplitude and phase factors, and the corresponding definition of the instantaneous frequency, are not unique. The interaction pictures for different decomposition are strictly equivalent, but only as long as approximations are not applied. The domain of validity of the formal rotating wave approximation is dramatically enhanced by a suitable choice, the so-called analytic signal representation.

  2. Radial-modulation chirp imaging for high-resolution contrast detection

    Microsoft Academic Search

    Meng-Lin Li; Yu-Chen Kuo; Chih-Kuang Yeh

    2008-01-01

    In this study, we propose a radial-modulation chirp imaging method for contrast detection with high frequency ultrasound. This method detects microbubbles by extracting and then selectively compressing the radial-modulated chirp component of the response. The amplitude of the imaging chirp signal will be radial modulated at the resonance frequency due to the high-amplitude oscillation of the microbubble wall which are

  3. Design Of Chirped Grating Lenses In Planar Optical Waveguides

    Microsoft Academic Search

    William S. C. Chang; Siamak Forouhar; Jean-Marc Delavaux; Ron-Xin Lu

    1982-01-01

    Theoretical designs of chirped grating lenses have yielded very high efficiency and moderately large angular fields of view. Experimentally, high efficiency (0.7dB insertion loss) and large angular field of view (0.1 radians) have been obtained in low index glass waveguides. Performance in high index waveguides such as LiNbO 3 will be limited by the n eff-n\\/subs\\/, the index of the

  4. Beam focusing in reflection from flat chirped mirrors

    NASA Astrophysics Data System (ADS)

    Cheng, Y. C.; Peckus, M.; Kicas, S.; Trull, J.; Cojocaru, C.; Vilaseca, R.; Drazdys, R.; Staliunas, K.

    2013-04-01

    We propose and show by proof-of-principle calculations and experiments that beam focusing and imaging can be obtained in reflection from a flat interface of a micromodulated dielectric structure. We show, in particular, that a one-dimensionally modulated and chirped structure can focus a beam, performing an imaging of a light pattern, i.e., can act as a transversely invariant flat focusing mirror.

  5. Pulse transformer design study

    Microsoft Academic Search

    H. Aslin

    1977-01-01

    This final report describes the design, development of fabrication techniques, fabrication, and testing of two uniform field, air core pulse transformers. The described transformer design minimizes the volume of dielectric material, which provides turn-to-turn insulation, reduces stray series inductance, and thus improves the transformer high frequency response in comparison to conventional pulse transformers. The described pulse transformers are intended for

  6. Harmonic chirp imaging method for ultrasound contrast agent.

    PubMed

    Borsboom, Jerome M G; Chin, Chien Ting; Bouakaz, Ayache; Versluis, Michel; de Jong, Nico

    2005-02-01

    Coded excitation is currently used in medical ultrasound to increase signal-to-noise ratio (SNR) and penetration depth. We propose a chirp excitation method for contrast agents using the second harmonic component of the response. This method is based on a compression filter that selectively compresses and extracts the second harmonic component from the received echo signal. Simulations have shown a clear increase in response for chirp excitation over pulse excitation with the same peak amplitude. This was confirmed by two-dimensional (2-D) optical observations of bubble response with a fast framing camera. To evaluate the harmonic compression method, we applied it to simulated bubble echoes, to measured propagation harmonics, and to B-mode scans of a flow phantom and compared it to regular pulse excitation imaging. An increase of approximately 10 dB in SNR was found for chirp excitation. The compression method was found to perform well in terms of resolution. Axial resolution was in all cases within 10% of the axial resolution from pulse excitation. Range side-lobe levels were 30 dB below the main lobe for the simulated bubble echoes and measured propagation harmonics. However, side-lobes were visible in the B-mode contrast images. PMID:15801312

  7. Spontaneous parametric down conversion in chirped, aperiodically-poled crystals

    E-print Network

    X. Sanchez-Lozano; Jose Luis Lucio

    2015-03-23

    We present a theoretical analysis of the process of spontaneous parametric down conversion (SPDC) in a non-linear crystal characterized by a linearly-chirped X(2) grating along the direction of propagation. Our analysis leads to an expression for the joint spectral amplitude, based on which we can derive various spectral-temporal properties of the photon pairs and of the heralded single photons obtained from the photon pairs, including: the single photon spectrum, the chronocyclic Wigner function and the Schmidt number. The simulations that we present are for the specific case of a collinear SPDC source based on a PPLN crystal with the signal and idler photons emitted close to the telecom window. We discuss the mechanism for spectral broadening due to the presence of a linearly chirped X(2) grating, showing that not only the width but also to some extent the shape of the SPDC spectrum maybe controlled. Also, we discuss how the fact that the different spectral components are emitted on different planes in the crystal leads to single-photon chirp.

  8. Chirped Laser Dispersion Spectroscopy for Remote Open-Path Trace-Gas Sensing

    PubMed Central

    Nikodem, Michal; Wysocki, Gerard

    2012-01-01

    In this paper we present a prototype instrument for remote open-path detection of nitrous oxide. The sensor is based on a 4.53 ?m quantum cascade laser and uses the chirped laser dispersion spectroscopy (CLaDS) technique for molecular concentration measurements. To the best of our knowledge this is the first demonstration of open-path laser-based trace-gas detection using a molecular dispersion measurement. The prototype sensor achieves a detection limit down to the single-ppbv level and exhibits excellent stability and robustness. The instrument characterization, field deployment performance, and the advantages of applying dispersion sensing to sensitive trace-gas detection in a remote open-path configuration are presented. PMID:23443389

  9. Generation of ultrabroadband energetic laser pulses by noncollinear optical parametric chirped pulse amplification

    NASA Astrophysics Data System (ADS)

    Figueira, Gonçalo; Imran, Tayyab; João, Celso P.; Pires, Hugo; Cardoso, Luís.

    2013-11-01

    Optical parametric chirped pulse amplification (OPCPA) is currently one of the leading techniques for the generation of ultra-powerful laser pulses, from the multi-terawatt to the petawatt range, with extremely high peak intensities. A properly designed OPCPA setup is able to provide gain over bandwidths extending hundreds of nanometers in the visible and near-infrared, allowing the generation of high-quality, energetic, few-cycle pulses. In this paper we describe the design and performance of a compact laser amplifier that makes use of noncollinear, ultrabroadband amplification in the nonlinear crystal yttrium-calcium oxyborate (YCOB). The pump and the supercontinuum seed pulses are generated from a common diode-pumped amplifier, ensuring their optical synchronization. This laser will be used as a source of ultrashort (~20 fs), energetic (~20 mJ), tunable pulses in the near infrared.

  10. Chirped Probe Pulse Femtosecond Coherent Anti-Stokes Raman Scattering for Turbulent Combustion Diagnostics

    NASA Astrophysics Data System (ADS)

    Fineman, Claresta N.; Lucht, Robert P.

    2014-06-01

    Chirped probe pulse (CPP) femtosecond (fs) coherent anti-Stokes Raman scattering (CARS) thermometry at 5 kHz has been successfully applied for single-laser-shot flame temperature measurements in a mildly turbulent hydrogen-air jet diffusion flame, sooting methane-air jet diffusion flame, and most recently a turbulent combustor of practical interest. Measurements were performed at various heights and radial locations within each flame and resulted in temperatures ranging from 300 K to 2400 K. In the turbulent combustor every laser shot produced some resonant CARS signal; no loss of signal due to beam steering, pressure fluctuations, or shear layer density gradients was noticeable. Furthermore, the measurement volume spatial resolution is better than has previously been reported for other CARS experiments. Flame temperature measurements compare well with those previously reported in similar flames. These results indicate high repetition rate CPP fs-CARS is an excellent technique for the study of turbulent combustion.

  11. Target diagnostics for commissioning the AWE HELEN Laser Facility 100 TW chirped pulse amplification beam

    SciTech Connect

    Eagleton, R. T.; Clark, E. L.; Davies, H. M.; Edwards, R. D.; Gales, S.; Girling, M. T.; Hoarty, D. J.; Hopps, N. W.; James, S. F.; Kopec, M. F.; Nolan, J. R.; Ryder, K. [AWE Aldermaston, Reading, Berks RG7 4PR (United Kingdom)

    2006-10-15

    The capability of the HELEN laser at the Atomic Weapons Establishment Aldermaston has been enhanced by the addition of a short-pulse laser beam to augment the twin opposing nanosecond time scale beams. The short-pulse beam utilizes the chirped pulse amplification (CPA) technique and is capable of delivering up to 60 J on target in a 500 fs pulse, around 100 TW, at the fundamental laser wavelength of 1.054 {mu}m. During the commissioning phase a number of diagnostic systems have been fielded, these include: x-ray pinhole imaging of the laser heated spot, charged particle time of flight, thermoluminescent dosimeter array, calibrated radiochromic film, and CR39 nuclear track detector. These diagnostic systems have been used to verify the performance of the CPA beam to achieve a focused intensity of around 10{sup 19} W cm{sup -2} and to underwrite the facility radiological safety system.

  12. Computation of the response function in chirp-pulse microwave computerized tomography

    NASA Astrophysics Data System (ADS)

    Bertero, M.; Conte, F.; Miyakawa, M.; Piana, M.

    2001-06-01

    Chirp-pulse microwave computerized tomography (CP-MCT) is a technique designed to image temperature variations inside a body. In the prototype developed at Niigata University images are obtained by means of the basic algorithm of tomography, namely filtered backprojection. The purpose of this paper is to develop an improved linear model for data reduction. We introduce a method, based on scattering theory, for computing the projections of a small phantom and we use these projections for defining the response function of the system. Our results also indicate that CP-MCT data are related to the variations of the attenuation constant inside a body. We conclude that, if these variations are sufficiently smooth, then CP-MCT projections can depend linearly on the distribution of the attenuation constant through the response function of the system.

  13. Experimental Demonstration of Energy Chirp Compensation by a Tunable Dielectric Based Structure

    E-print Network

    Antipov, S; Jing, C; Fedurin, M; Kanareykin, A; Swinson, C; Schoessow, P; Gai, W; Zholents, A

    2013-01-01

    A 60 MeV beam at the BNL Accelerator Test Facility (ATF) was manipulated by a planar tunable de-chirper made out of two 10 cm long dielectric slabs with copper plated backs. While the gap was changed from 5.8 mm to 1 mm, the correlated energy chirp of the low charge electron bunch was reduced from approximately 330 keV/mm to zero. This result is in agreement with simulations. Calculations show that similar devices, properly scaled to account for the expected electron bunch charge and length, can be used to remove residual correlated energy spread at the end of the linacs used for free-electron lasers (FEL). Potentially, this technique could significantly simplify linac design and improve FEL performance.

  14. Hough Transform from the Radon Transform

    Microsoft Academic Search

    Stanley R. Deans

    1981-01-01

    An appropriate special case of a transform developed by J. Radon in 1917 is shown to have the major properties of the Hough transform which is useful for finding line segments in digital pictures. Such an observation may be useful in further efforts to generalize the Hough transform. Techniques for applying the Radon transform to lines and pixels are developed

  15. Time dependent measurements of nitrous oxide and carbon dioxide collisional relaxation processes by a frequency down-chirped quantum cascade laser: rapid passage signals and the time dependence of collisional processes.

    PubMed

    Tasinato, Nicola; Hay, Kenneth G; Langford, Nigel; Duxbury, Geoffrey; Wilson, David

    2010-04-28

    Intrapulse quantum cascade laser spectrometers are able to produce both saturation and molecular alignment of the gas sample. This is due to the rapid sweep of the radiation through the absorption features. The intrapulse time domain spectra closely resemble those recorded in coherent optical nutation experiments. In the present paper, the frequency down-chirped technique is employed to investigate the nitrous oxide-foreign gas collisions. We have demonstrated that the measurements may be characterized by the induced polarization dominated and collision dominated measurement limits. The first of these is directly related to the time dependence of the long range collision cross sections. Among the collisional partners considered, carbon dioxide shows a very unusual behavior of rapid polarization damping, resulting in the production of symmetrical line shapes at very low gas buffer pressures. In the collision dominated regime, the pressure broadening parameters, which we have derived, are comparable at slow chirp rates, with those derived from other experimental methods. By comparing the pressure broadening coefficients of Ar, N(2), and CO(2) with those of He, making use of the chirp rate independence of the pressure broadening by helium, we have shown that at higher chirp rates there is clear evidence of the chirp-rate dependence of the pressure broadening parameters of N(2) and CO(2). PMID:20441269

  16. Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques

    SciTech Connect

    Lemery, F.; Mihalcea, D.; Prokop, C.R.; /Northern Illinois U.; Piot, P.; /Northern Illinois U. /Fermilab

    2012-07-08

    In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (> 2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration.

  17. Morphological and lithological transformation records of the Lake Czechowskie basin on the basis of paleogeography and GIS techniques analysis

    NASA Astrophysics Data System (ADS)

    Kramkowski, M. A.; B?aszkiewicz, M.; Tyszkowski, S.; Kordowski, J.

    2014-12-01

    The analyses of the annually laminated lacustrine sediments are particularly important in the studies of global climate change. They provide information about the ecosystem response to environmental and climate changes. The condition for the laminated sedimentation with the annual resolution is a calm sedimentation environment where there is no mixing and thus there are anaerobic conditions in the benthic zone. Below a certain depth there is no wave induced mixing and temperature is constant, which causes water stagnation. In shallower areas such conditions are favoured by the morphology of the lake basin and the long presence of ice cover (bradymictic). The combination of these environmental features predispose to the deposition of laminated sediments. Lake Czechowskie is located within the limit of the Scandinavian Ice Sheet during the Last Glaciation in the Central European Lowland (northern Poland - 53°52"N 18°14"E) in a deep kettle-hole type. Taking into account the thickness of the lacustrine sediments, the maximum depth of the basin exceeds 70 m. Detailed surveying as well as geological drilling using the GIS techniques made it possible to reconstruct the morphology of the basin of Lake Czechowskie and its adjacent areas before the biogenic sedimentation started in Allerød. At that time water level was 2 m higher than in the modern times. Following climate changes initiated the natural processes of the lake basin transformation. The analysis of the morphology of the lake basin is the basis for modelling the sedimentation conditions considering, inter alia, the wind direction and wind velocity, fluctuations of the water levels and the degree of filling the basin with the deposits in different periods of the Late Glacial and Holocene. It allows specifying the variability and sedimentation rate within the basin. The analysis shows the spatial variation of the erosion and accumulation zones, and enables to determine the zones of calm sedimentation revealing places particularly predisposed to accumulate annually laminated lacustrine sediments. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution (ICLEA) of the Helmholtz Association and the research project no. 2011/01/B/ST10/07367 Polish Ministry of Science and Higher Education.

  18. Suppression of reflection from the grid boundary in solving the time-dependent Schroedinger equation by split-step technique with fast Fourier transform

    E-print Network

    Gonoskov, A A

    2006-01-01

    We present an approach to numerically solving the time-dependent Schroedinger equation and other parabolic equations by the split-step technique with fast Fourier transform, which suppresses the backreflection of waves from the grid boundaries with any specified accuracy. Most importantly, all known methods work well only for a narrow region of incident waves spectrum, and the proposed method provides absorption of any wave whose length is large enough in comparison with the size of absorption region.

  19. Extension of high-order harmonic generation cutoff via coherent control of intense few-cycle chirped laser pulses

    E-print Network

    Carrera, Juan J.; Chu, Shih-I

    2007-03-16

    We present an ab initio quantum investigation of the high-order harmonic generation (HHG) cutoff extension using intense few-cycle chirped laser pulses. For a few-cycle chirped driving laser pulse, it is shown that significant ...

  20. Chirp excitation of ultrasonic probes and algorithm for filtering transit times in high-rangeability gas flow metering.

    PubMed

    Folkestad, T; Mylvaganam, K S

    1993-01-01

    The signal processing used in an ultrasonic high-rangeability gas flow meter using times of flight is presented. The flow meter under discussion uses a combination of continuous wave and chirp signals to measure at low flow velocities, below 20 m/s, and chirp signals alone to measure high flow velocities, above 20 m/s. Because of the need for a pulse compression technique in the signal waveform design the technique of pulse compression and the choice of signal waveforms are discussed. The advantages and disadvantages of amplitude weighting vis-a-vis frequency domain manipulations of the waveforms are also discussed. To eliminate spurious times of flight, a special filtering technique is used, based on assessing the gradient of ascendingly ordered time series of time-of-flight measurements. A summary of user experience with high-rangeability gas flow meters in use on different offshore platforms and in refineries is given. Long-term tests that examined the accuracy of the high-rangeability flow meter are also described. PMID:18263174

  1. Chirped Pulse Adiabatic Passage in CARS for Imaging of Biological Structure and Dynamics

    Microsoft Academic Search

    Svetlana A. Malinovskaya; Svetlana A

    2007-01-01

    We propose the adiabatic passage control scheme implementing chirped femtosecond laser pulses to maximize coherence in a predetermined molecular vibrational mode using two-photon Raman transitions. We investigate vibrational energy relaxation and collisional dephasing as factors of coherence loss, and demonstrate the possibility for preventing decoherence by the chirped pulse train. The proposed method may be used to advance noninvasive biological

  2. Fine-Grained Access Control in the Chirp Distributed File System Patrick Donnelly and Douglas Thain

    E-print Network

    Thain, Douglas

    Fine-Grained Access Control in the Chirp Distributed File System Patrick Donnelly and Douglas Thain filesystem. We have implemented this system in the context of the Chirp user-level distributed filesystem distributed computing systems such as clus- ters, clouds, and grids provide end users with access to virtually

  3. Classification of nonstationary narrowband signals using segmented chirp features and hidden Gauss-Markov models

    Microsoft Academic Search

    Phillip L. Ainsleigh; Stephen G. Greineder; Nasser Kehtarnavaz

    2005-01-01

    A method is provided for classifying finite-duration signals with narrow instantaneous bandwidth and dynamic instantaneous frequency (IF). In this method, events are partitioned into nonoverlapping segments, and each segment is modeled as a linear chirp, forming a piecewise-linear IF model. The start frequency, chirp rate, signal energy, and noise energy are estimated in each segment. The resulting sequences of frequency

  4. Phase-locking and coherent power combining of broadband linearly chirped optical waves.

    PubMed

    Satyan, Naresh; Vasilyev, Arseny; Rakuljic, George; White, Jeffrey O; Yariv, Amnon

    2012-11-01

    We propose, analyze and demonstrate the optoelectronic phase-locking of optical waves whose frequencies are chirped continuously and rapidly with time. The optical waves are derived from a common optoelectronic swept-frequency laser based on a semiconductor laser in a negative feedback loop, with a precisely linear frequency chirp of 400 GHz in 2 ms. In contrast to monochromatic waves, a differential delay between two linearly chirped optical waves results in a mutual frequency difference, and an acoustooptic frequency shifter is therefore used to phase-lock the two waves. We demonstrate and characterize homodyne and heterodyne optical phase-locked loops with rapidly chirped waves, and show the ability to precisely control the phase of the chirped optical waveform using a digital electronic oscillator. A loop bandwidth of ~ 60 kHz, and a residual phase error variance of < 0.01 rad(2) between the chirped waves is obtained. Further, we demonstrate the simultaneous phase-locking of two optical paths to a common master waveform, and the ability to electronically control the resultant two-element optical phased array. The results of this work enable coherent power combining of high-power fiber amplifiers-where a rapidly chirping seed laser reduces stimulated Brillouin scattering-and electronic beam steering of chirped optical waves. PMID:23187338

  5. Chirped fiber-Bragg grating as self-temperature referenced strain sensor in nonisothermal thermoset processing

    Microsoft Academic Search

    Andrea Cusano; Patrizio Capoluongo; Antonello Cutolo; Michele Giordano

    2006-01-01

    A partially embedded chirped fiber-Bragg grating (FBG) has been used to monitor the strain build up during nonisothermal curing of a model thermoset resin. The particular feature of the spectrum of a linearly chirped and strongly apodized FBG to encode position along the sensor has been used to simultaneously measure temperature and strain during the cure cycle of an epoxy-based

  6. Temperature-independent strain sensor using a chirped grating partially embedded in a glass tube

    Microsoft Academic Search

    Sungchul Kim; Jaejoong Kwon; Sungwoo Kim; Byoungho Lee

    2000-01-01

    A novel intensity-based temperature-independent strain sensor using a chirped grating is demonstrated. The longer reflection wavelength part of the chirped grating is fixed to a glass tube and, hence, the reflected power from the grating decreases linearly with strain and is independent of temperature perturbation

  7. Optimal Particle Filters for Tracking a Time-Varying Harmonic or Chirp Signal

    Microsoft Academic Search

    Efthimios E. Tsakonas; Nicholas D. Sidiropoulos; Ananthram Swami

    2008-01-01

    We consider the problem of tracking the time-varying (TV) parameters of a harmonic or chirp signal using particle fil- tering (PF) tools. Similar to previous PF approaches to TV spec- tral analysis, we assume that the model parameters (complex am- plitude, frequency, and frequency rate in the chirp case) evolve ac- cording to a Gaussian AR(1) model; but we concentrate

  8. Airborne SAR processing of highly squinted data using a chirp scaling approach with integrated motion compensation

    Microsoft Academic Search

    A. Moreira; Yonghong Huang

    1994-01-01

    Proposes a new approach for high-resolution airborne SAR data processing, which uses a modified chirp scaling algorithm to accommodate the correction of motion errors, as well as the variations of the Doppler centroid in range and azimuth. By introducing a cubic phase term in the chirp scaling phase, data acquired with a squint angle up to 30° can be processed

  9. Chirped Pulse Adiabatic Passage in CARS for Imaging of Biological Structure and Dynamics

    Microsoft Academic Search

    Svetlana A. Malinovskaya

    2008-01-01

    We propose the adiabatic passage control scheme implementing chirped femtosecond laser pulses to maximize coherence in a predetermined molecular vibrational mode using two-photon Raman transitions. We investigate vibrational energy relaxation and coUisional dephasing as factors of coherence loss, and demonstrate the possibility for preventing decoherence by the chirped pulse train. The proposed method may be used to advance noninvasive biological

  10. Effects of Energy Chirp on Echo-Enabled Harmonic Generation Free-Electron Lasers

    SciTech Connect

    Huang, Z.; Ratner, D.; Stupakov, G.; Xiang, D.; /SLAC

    2009-02-23

    We study effects of energy chirp on echo-enabled harmonic generation (EEHG). Analytical expressions are compared with numerical simulations for both harmonic and bunching factors. We also discuss the EEHG free-electron laser bandwidth increase due to an energy-modulated beam and its pulse length dependence on the electron energy chirp.

  11. Application of the constant exposure time technique to transformation experiments with fission neutrons; failure to demonstrate dose-rate dependence

    SciTech Connect

    Balcer-Kubiczek, E.K.; Harrison, G.H.; McCready, W.A.

    1994-12-31

    A direct comparison of the effectiveness of fission neutron at high or several low dose-rates was carried out under identical conditions. Monolayers of exponentially growing C3H/10T1/2 cells were exposed at 37 deg C to reactor-produced neutrons. Survival or transformation induction were studied at five doses from 10(exp 5) to 94 cGy. In low dose-rate irradiations, these doses were protracted over 0.5, 1, 3 or 4.5 h, resulting in 17 different dose-rates. Up to six experiments were performed at each of five exposure times. Concurrently with transformation the authors studied cell proliferation in control versus cells irradiated at 40 cGY acute and a 4.5-h protraction and found no evidence of a shift in the cell cycle distribution among these cells. At a given dose and dose-rate, the effect of dose protraction on survival or transformation was assessed by the dose-rate modifying factor DRMF, defined as the low:high dose-rate effect ratio at the same dose. Survival or transformation induction curves were nearly linear with initial slopes, respectively, of about 6.5 x 10(exp {minus}3) or 6.2 x 10(exp {minus}6) /cGY. Consistent with dose response curves, DRMFs were independent of the dose and dose-rate. The mean values of the dRMF with their uncertainties and 99 deg confidence intervals, based on measurements in individual doses and dose-rates for survival or transformation were, respectively: 1.01 {+-} 0.03, 0.92, 1.09 or 0.98 {+-} 0.04, 0.83, 1.08 indicating a similar precision in determining DRMF for survival or transformation, and no dose or dose-rate influence on these end points.

  12. A novel broadband asynchronous histogram technique for optical performance monitoring [optical fibre communication

    Microsoft Academic Search

    Sarah D. Dods; Don F. Hewitt; P. M. Farrell; Kerry Hinton

    2005-01-01

    We combine tunable narrowband filtering with asynchronous sampling to produce broadband histograms that measure frequency-resolved signal distortion. We demonstrate the technique using chirped WDM signals affected by filter detuning, dispersion and nonlinear effects.

  13. Chirped-pulse amplification system based on chirp reversal and near-field spatial reversal with common tiled grating pair as stretcher and compressor.

    PubMed

    Wang, Xiao; Wei, Xiaofeng; Hu, Yao; Zeng, Xiaoming; Zuo, Yanlei; Hao, Xin; Zhou, Kainan; Xie, Na; Zhang, Ying

    2012-08-10

    Chirped-pulse amplification system based on chirp reversal in optical parametric chirped-pulse amplification is proposed and experimentally demonstrated. The operation of this system can be described as negative stretching-temporal chirp reversal-energy amplification-negative compression, in which the pulse is stretched and compressed with the same gratings. Stand-alone stretcher adopting lenses or concave mirrors with large aperture can be omitted. Simulations showed that this work mode can also increase the cut-off band-pass of the whole system and increase the output energy by 15-17%. In addition, the stability of a tiled-grating compressor can be improved with this work mode. PMID:22885574

  14. Chirped time-resolved CARS microscopy with square-pulse excitation.

    PubMed

    Upputuri, Paul Kumar; Gong, Li; Wang, Haifeng

    2014-04-21

    Time-resolved coherent anti-Stokes Raman scattering (T-CARS) microscopy is a technique known for suppressing non-resonant background by utilizing the different temporal responses of virtual electronic transitions and Raman transitions. However, the previous use of femtosecond excitations in T-CARS microscopy has led to low spectral resolution and difficulty in selectively exciting a single Raman band. Here, we report an improved T-CARS imaging technique with chirped pump and Stokes excitations, and the Stokes pulses were shaped into square pulses. Using a femtosecond probe, we acquired T-CARS images with a high spectral resolution, suppressed non-resonant background, and high resonant signal level. We experimentally demonstrated the selective excitation of two close Raman bands of polystyrene at 1005 cm(-1) and 1035 cm(-1) using our technique; conventional T-CARS would inevitably excite them both with little selectivity. Our novel technique could become an ideal method for high-sensitivity, background-free imaging of single Raman bands for a wide variety of samples. PMID:24787849

  15. Fast estimation of dispersion and initial chirp penalties by using TRC parameters

    NASA Astrophysics Data System (ADS)

    Coskun, Tamer H.; Klein, Jackson

    2003-08-01

    We have developed a wavelength domain simulation approach that can estimate the dispersion penalty due to initial chirp. This method only requires estimation of two parameters, i.e. effective chirp duration and effective chirp peak value, from the measured time resolved chirp (TRC) data. It is very fast comparing to full time domain simulation since it does not require the calculation of the time domain signal propagation in fiber. The method is based on a simple phenomenological model that is capable to predict the dispersion/chirp-induced eye-closure penalty. Model can estimate other system performance indicators such as BER and Q factor by taking into account the effects such as ASE, thermal and shot noise, extinction ratio etc. We have compared our results with published experimental data and full time domain simulations and have observed very good agreement.

  16. Backward Raman amplification in plasmas with chirped wideband pump and seed pulses

    NASA Astrophysics Data System (ADS)

    Wu, Zhao-Hui; Wei, Xiao-Feng; Zuo, Yan-Lei; Liu, Lan-Qin; Zhang, Zhi-Meng; Li, Min; Zhou, Yu-Liang; Su, Jing-Qin

    2015-01-01

    Chirped wideband pump and seed pulses are usually considered for backward Raman amplification (BRA) in plasmas to achieve an extremely high-power laser pulse. However, current theoretical models only contain either a chirped pump or a chirped seed. In this paper, modified three-wave coupling equations are proposed for the BRA in the plasmas with both chirped wideband pump and seed. The simulation results can more precisely describe the experiments, such as the Princeton University experiment. The optimized chirp and bandwidth are determined based on the simulation to enhance the output intensity and efficiency. Project supported by the National Natural Science Foundation of China (Grant No. 11305157) and the Development Foundation of China Academy of Engineering Physics Laboratory (CAEPL) (Grant No. 2013A0401019).

  17. Transverse-to-longitudinal Emittance-exchange with an Energy Chirped Beam

    SciTech Connect

    Thangaraj, J.; Ruan, J.; Johnson, A.S.; Thurman-Keup, R.; Lumpkin, A.H.; Santucci, J.; Sun, Y.-E; Maxwell, T.; Edwards, H.; /Fermilab

    2012-05-01

    Emittance exchange has been proposed to increase the performance of free electron lasers by tailoring the phase space of an electron beam. The principle of emittance exchange - where the transverse phase space of the electron beam is exchanged with the longitudinal phase space - has been demonstrated recently at the A0 photoinjector. The experiment used a low charge bunch (250 pC) with no energy chirp. Theory predicts an improvement in the emittance exchange scheme when the incoming beam has an energy chirp imparted on it. The energy chirp helps to overcome the thick lens effect of the deflecting mode cavity and other second order effects that might lead to an incomplete emittance exchange at higher charges. In this work, we report experimental and simulation results from operating the emittance exchange beam line using an energy chirped beam with higher charge (500 pC) at different RF-chirp settings.

  18. Analytical solution of the advection-diffusion transport equation using a change-of-variable and integral transform technique

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This paper presents a formal exact solution of the linear advection-diffusion transport equation with constant coefficients for both transient and steady-state regimes. A classical mathematical substitution transforms the original advection-diffusion equation into an exclusively diffusive equation. ...

  19. From the Unity of Truth to Technique and Back Again: The Transformation of Curriculum and Professionalism within Higher Education

    ERIC Educational Resources Information Center

    Nguyen, Roselynn H.; Null, J. Wesley

    2008-01-01

    Upon reviewing the story of higher education from the early eighteenth to the late twentieth century, the authors are able to evaluate the ideals of knowledge and how they have been transformed during this time period. Considering the implications education has on the training of students who become leaders in society, individuals should pay…

  20. Chirped laser dispersion spectroscopy with differential frequency generation source.

    PubMed

    Nikodem, Michal; Krzempek, Karol; Karwat, Renata; Dudzik, Grzegorz; Abramski, Krzysztof; Wysocki, Gerard

    2014-08-01

    A feasibility study of open-path methane detection at 3.4 ?m using chirped laser dispersion spectroscopy (CLaDS) based on nonlinear differential frequency generation (DFG) laser source is performed. Application of a DFG source based on telecom laser sources and modulators allows mid-infrared CLaDS system to be optimized for measurements of gases at atmospheric conditions for which modulation in the GHz range is required. Excellent agreement between observed CLaDS signals and spectroscopic models has been observed. PMID:25078192

  1. First-harmonic approximation in nonlinear chirped-driven oscillators.

    PubMed

    Uzdin, Raam; Friedland, Lazar; Gat, Omri

    2014-01-01

    Nonlinear classical oscillators can be excited to high energies by a weak driving field provided the drive frequency is properly chirped. This process is known as autoresonance (AR). We find that for a large class of oscillators, it is sufficient to consider only the first harmonic of the motion when studying AR, even when the dynamics is highly nonlinear. The first harmonic approximation is also used to relate AR in an asymmetric potential to AR in a "frequency equivalent" symmetric potential and to study the autoresonance breakdown phenomenon. PMID:24580292

  2. First-harmonic approximation in nonlinear chirped-driven oscillators

    NASA Astrophysics Data System (ADS)

    Uzdin, Raam; Friedland, Lazar; Gat, Omri

    2014-01-01

    Nonlinear classical oscillators can be excited to high energies by a weak driving field provided the drive frequency is properly chirped. This process is known as autoresonance (AR). We find that for a large class of oscillators, it is sufficient to consider only the first harmonic of the motion when studying AR, even when the dynamics is highly nonlinear. The first harmonic approximation is also used to relate AR in an asymmetric potential to AR in a "frequency equivalent" symmetric potential and to study the autoresonance breakdown phenomenon.

  3. Chirped CPMG for well-logging NMR applications.

    PubMed

    Casabianca, Leah B; Mohr, Daniel; Mandal, Soumyajit; Song, Yi-Qiao; Frydman, Lucio

    2014-05-01

    In NMR well-logging, the measurement apparatus typically consists of a permanent magnet which is inserted into a bore, and the sample is the rock surrounding the borehole. When compared to the conditions of standard NMR experiments, this application is thus challenged by relatively weak and invariably inhomogeneous B0 and B1 fields. Chemical shift information is not generally obtained in these measurements. Instead, diffusivity, porosity and permeability information is collected from multi-echo decay measurements - most often using a Carr-Purcell Meiboom-Gill (CPMG) pulse sequence to enhance the experiment's limited sensitivity. In this work, we explore the consequences of replacing the hard square pulses used in a typical CPMG sequence with chirped pulses sweeping a range of frequencies. The greater bandwidths that for a maximum B1 level can be excited by chirped pulses translates into marked expansion of the detection volume, and thus significant signal-to-noise improvements when compared to standard CPMG acquisitions using hard pulses. This improvement, usually amounting to signal enhancements ?3, can be used to reduce the experimental time of NMR well-logging measurements, for measuring T2 even when B0 and B1 inhomogenieties complicate the measurements, and opening new opportunities in the determination of diffusional properties. PMID:24674888

  4. Chirped CPMG for well-logging NMR applications

    NASA Astrophysics Data System (ADS)

    Casabianca, Leah B.; Mohr, Daniel; Mandal, Soumyajit; Song, Yi-Qiao; Frydman, Lucio

    2014-05-01

    In NMR well-logging, the measurement apparatus typically consists of a permanent magnet which is inserted into a bore, and the sample is the rock surrounding the borehole. When compared to the conditions of standard NMR experiments, this application is thus challenged by relatively weak and invariably inhomogeneous B0 and B1 fields. Chemical shift information is not generally obtained in these measurements. Instead, diffusivity, porosity and permeability information is collected from multi-echo decay measurements - most often using a Carr-Purcell Meiboom-Gill (CPMG) pulse sequence to enhance the experiment’s limited sensitivity. In this work, we explore the consequences of replacing the hard square pulses used in a typical CPMG sequence with chirped pulses sweeping a range of frequencies. The greater bandwidths that for a maximum B1 level can be excited by chirped pulses translates into marked expansion of the detection volume, and thus significant signal-to-noise improvements when compared to standard CPMG acquisitions using hard pulses. This improvement, usually amounting to signal enhancements ?3, can be used to reduce the experimental time of NMR well-logging measurements, for measuring T2 even when B0 and B1 inhomogenieties complicate the measurements, and opening new opportunities in the determination of diffusional properties.

  5. Evolution of the frequency chirp of Gaussian pulses and beams when passing through a pulse compressor.

    PubMed

    Li, Derong; Lv, Xiaohua; Bowlan, Pamela; Du, Rui; Zeng, Shaoqun; Luo, Qingming

    2009-09-14

    The evolution of the frequency chirp of a laser pulse inside a classical pulse compressor is very different for plane waves and Gaussian beams, although after propagating through the last (4th) dispersive element, the two models give the same results. In this paper, we have analyzed the evolution of the frequency chirp of Gaussian pulses and beams using a method which directly obtains the spectral phase acquired by the compressor. We found the spatiotemporal couplings in the phase to be the fundamental reason for the difference in the frequency chirp acquired by a Gaussian beam and a plane wave. When the Gaussian beam propagates, an additional frequency chirp will be introduced if any spatiotemporal couplings (i.e. angular dispersion, spatial chirp or pulse front tilt) are present. However, if there are no couplings present, the chirp of the Gaussian beam is the same as that of a plane wave. When the Gaussian beam is well collimated, the introduced frequency chirp predicted by the plane wave and Gaussian beam models are in closer agreement. This work improves our understanding of pulse compressors and should be helpful for optimizing dispersion compensation schemes in many applications of femtosecond laser pulses. PMID:19770925

  6. Effect of atomic density on propagation and spectral property of femtosecond chirped Gaussian pulses

    NASA Astrophysics Data System (ADS)

    Wang, Zhendong; Gao, Feng

    2015-05-01

    We theoretically investigate the effect of the atomic densities N on propagation and spectral property of femtosecond chirped Gaussian pulse in a three-level ?-type atomic medium by using the numerical solution of the full Maxwell- Bloch equations. It is shown that, when the positive chirped pulse with area 3?, propagate in the medium with smaller N, pulse splitting doesn't occur and many small oscillations at the trailing edge of the pulse appear, in addition, the level |2< population ?22 of the pulse exhibits an oscillation feature with time evolution, moreover, the spectral component near the central frequency of the pulse shows an oscillation characteristic too, and the propagation and spectral property of the negative chirped 3? pulse is very similar to that of the positive chirped 3? pulse. For the positive chirped 3? pulse pulses, propagate in the medium with larger N, pulse splitting also doesn't occur but many small oscillations both at leading edge and the trailing edge of the pulse appear, and the population ?22 of the pulse only exhibits an scarcely oscillation feature with time evolution, at the same time many oscillations both in blue shift and red shift components of the pulse appear but the spectral component near the central frequency of the pulse oscillate more severely, and the propagation and spectral property of the negative chirped 3? pulse is very similar to that of the positive chirped 3? pulse, but comparing with the case of the negative chirped 3? pulse, the propagation of the positive chirped 3? pulse is delayed at the same distance and the delayed time becomes longer with the distance increasing.

  7. Isolated attosecond pulse generation from pre-excited medium with a chirped and chirped-free two-color field.

    PubMed

    Du, Hongchuan; Luo, Laoyong; Wang, Xiaoshan; Hu, Bitao

    2012-04-23

    We theoretically investigate the isolated attosecond pulse generation from pre-excited medium with a chirped and chirped-free two-color field. It is found that the large initial population of the excited state can lead to the high density of the free electrons in the medium and the large distortion of the driving laser field after propagation, though it benefits large enhancement of harmonic intensity in single atom response. These effects can weaken the phase-match of the macroscopic supercontinuum. On the contrary, the small initial population of 4% can generate well phase-match intense supercontinuum. We also investigate an isolated attosecond pulse generation by using a filter centered on axis to select the harmonics in the far field. Our results reveal that the radius of the spatial filter should be chosen to be small enough to reduce the duration of the isolated attosecond pulse due to the curvature effect of spatiotemporal profiles of the generated attosecond pulses in the far field. PMID:22535063

  8. Optimal water and waste-load allocations in rivers using a fuzzy transformation technique: a case study.

    PubMed

    Nikoo, Mohammad Reza; Kerachian, Reza; Karimi, Akbar; Azadnia, Ali Asghar

    2013-03-01

    In this paper, a new methodology is developed for integrated allocation of water and waste-loads in river basins utilizing a fuzzy transformation method (FTM). The fuzzy transformation method is used to incorporate the existing uncertainties in model inputs. In the proposed methodology, the FTM, as a simulation model, is utilized in an optimization framework for constructing a fuzzy water and waste-loads allocation model. In addition, economic as well as environmental impacts of water allocation to different water users are considered. For equitable water and waste load allocation, all possible coalition of water users are considered and total benefit of each coalition, which is a fuzzy number, is reallocated to water users who are participating in the coalition. The fuzzy cost savings are reallocated using a fuzzy nucleolus cooperative game and the FTM. As a case study, the Dez River system in south-west of Iran is modeled and analyzed using the methodology developed here. The results show the effectiveness of the methodology in optimal water and waste-loads allocations under uncertainty. PMID:22773144

  9. Peculiarities of laser phase behavior associated with the accelerated electron in a chirped laser pulse

    SciTech Connect

    Song, Q.; Wu, X. Y. [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); Wang, J. X. [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); State Key Laboratory of Precision Spectroscopy and Department of Physics, East China Normal University, Shanghai 200062 (China); Kawata, S. [Center for Optical Research and Education, Department of Advanced Interdisciplinary Science, Graduate School of Engineering, Utsunomiya University, Utsunomiya 321-8585 (Japan); Wang, P. X., E-mail: wpx@fudan.edu.cn [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); Center for Optical Research and Education, Department of Advanced Interdisciplinary Science, Graduate School of Engineering, Utsunomiya University, Utsunomiya 321-8585 (Japan)

    2014-05-15

    In this paper, we qualitatively analyzed peculiarities of laser phase behavior associated with the accelerated electron in a chirped laser pulse. We unveiled the relationship between the changes in the orientation of the electron trajectory and the cusps in magnitude of the phase velocity of the optical field along the electron trajectory in a chirped laser pulse. We also explained how the chirp effect induced the singular point of the phase velocity. Finally, we discussed the phase velocity and phase witnessed by the electron in the particle's moving instantaneous frame.

  10. Positive and negative chirping of laser pulses shorter than 100 fsec in a saturable absorber

    SciTech Connect

    Miranda, R.S.; Jacobovitz, G.R.; Brito Cruz, C.H.; Scarparo, M.A.F.

    1986-04-01

    We present a calculation of the chirp generated in laser pulses shorter than 100 fsec on propagation through a saturable absorber (DODCI in ethylene glycol). The calculation takes into account the absorber saturation and the solvent nonlinear refractive index. At pulse energies greater than 10 nJ the chirp tends to be predominantly positive, and it increases rapidly as the pulse duration becomes shorter than 50 fsec. At pulse energies in the 1--7-nJ range the chirp is mostly negative for pulses longer than 30 fsec.

  11. Multiscale modeling of vibrational predissociation spectra under a chirped laser pulse

    NASA Astrophysics Data System (ADS)

    Calvo, F.; Parneix, P.

    2012-06-01

    The vibrational predissociation spectrum of the argon-tagged ionic cluster (NaCl)32 due to exposure to a chirped infrared laser was theoretically calculated in a time multiscale framework. The response to the laser field is modeled explicitly by molecular dynamics simulations, and statistical rate theories are used to evaluate the long-time dissociation probability. Due to anharmonicities and multiphoton processes, the predissociation spectrum shows some small but systematic red shift in the main absorption line. Negative chirping toward lower frequencies further enhances this effect, and also alters the band intensity and the band width. Positive chirping attenuates the dissociation efficiency.

  12. Rate equation analysis of frequency chirp in optically injection-locked quantum cascade lasers

    NASA Astrophysics Data System (ADS)

    Wang, C.; Grillot, F.; Kovanis, V. I.; Bodyfelt, J. D.; Even, J.

    2014-03-01

    The frequency chirp characteristics of an optically injection-locked quantum cascade laser are theoretically investigated. The key parameter chirp-to-power ratio (CPR) is analytically derived from a full rate equation model. The CPR value can be efficiently reduced by increasing optical injection strength, especially at modulation frequencies less than 10 GHz. In contrast to interband lasers, both positive and negative frequency detuning increase the CPR. Since the frequency detuning is also predicted to enhance the intensity modulation response, a trade-off is required in the optical injection to simultaneously obtain a large modulation bandwidth and low frequency chirp.

  13. Self-deflecting plasmonic lattice solitons and sur-face modes in chirped plasmonic arrays

    E-print Network

    Li, Chunyan; Ye, Fangwei; Kartashov, Yaroslav V; Torner, Lluis; Chen, Xianfeng

    2015-01-01

    We show that chirped metal-dielectric waveguide arrays with focusing cubic nonlinearity can support plasmonic lattice solitons that undergo self-deflection in the transverse plane. Such lattice solitons are deeply-subwavelength self-sustained excitations, although they cover several periods of the array. Upon propagation,the excitations accelerate in the transverse plane and follow trajectories curved in the direction in which the separation between neighboring metallic layers decreases, a phenomenon that yields considerable deflection angles. The deflection angle can be controlled by varying the array chirp. We also reveal the existence of surface modes at the boundary of truncated plasmonic chirped arraythat form even in the absence of nonlinearity.

  14. Relation between chirp and linewidth reduction in external Bragg reflector semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Olsson, N. A.; Henry, C. H.; Kazarinov, R. F.; Lee, H. J.; Johnson, B. H.

    1987-07-01

    A 1.5-?m single longitudinal mode semiconductor laser, formed by butt coupling an external Bragg reflector to a standard Fabry-Perot laser, is shown to have greatly reduced wavelength chirp and emission linewidth. The linewidth reduction is found to be proportional to the square of the chirp reduction, in agreement with a previous theoretical prediction. The linewidth and chirp reduction factor can be varied by changing the operating point of the laser. With a 3-mm-long Bragg reflector, a linewidth of 1 MHz at 5 mW has been achieved.

  15. Concepts, performance review, and prospects of table-top, few-cycle optical parametric chirped-pulse amplification

    NASA Astrophysics Data System (ADS)

    Vaupel, Andreas; Bodnar, Nathan; Webb, Benjamin; Shah, Lawrence; Richardson, Martin

    2014-05-01

    More than 20 years after the first presentation of optical parametric chirped-pulse amplification (OPCPA), the technology has matured as a powerful technique to produce high-intensity, few-cycle, and ultrashort laser pulses. The output characteristics of these systems cover a wide range of center wavelengths, pulse energies, and average powers. The current record performance of table-top, few-cycle OPCPA systems are 16 TW peak power and 22 W average power, which show that OPCPA is able to directly compete with Ti:sapphire chirped-pulse amplification-based systems as source for intense optical pulses. Here, we review the concepts of OPCPA and present the current state-of-the art performance level for several systems reported in the literature. To date, the performance of these systems is most generally limited by the employed pump laser. Thus, we present a comprehensive review on the recent progress in high-energy, high-average-power, picosecond laser systems, which provide improved performance relative to OPCPA pump lasers employed to date. From here, the impact of these novel pump lasers on table-top, few-cycle OPCPA is detailed and the prospects for next-generation OPCPA systems are discussed.

  16. A privacy-preserving technique for Euclidean distance-based mining algorithms using Fourier-related transforms

    Microsoft Academic Search

    Shibnath Mukherjee; Zhiyuan Chen; Aryya Gangopadhyay

    2006-01-01

    Privacy preserving data mining has become increasingly popular because it allows sharing of privacy-sensitive data for analysis purposes. However, existing techniques such as random perturbation do not fare well for simple yet widely used and efficient Euclidean distance-based mining algorithms. Although original data distributions can be pretty accurately reconstructed from the perturbed data, distances between individual data points are not

  17. Fourier transform-infrared spectroscopy and Gas chromatography-mass spectroscopy: Reliable techniques for analysis of Parthenium mediated vermicompost

    NASA Astrophysics Data System (ADS)

    Rajiv, P.; Rajeshwari, Sivaraj; Venckatesh, Rajendran

    2013-12-01

    Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography-mass spectroscopy have been carried out to investigate the chemical composition of Parthenium mediated vermicompost. Four different concentrations of Parthenium and cow dung mixtures were vermicomposted using the earthworms (Eudrilus eugeniae). FT-IR spectra reveal the absence of Parthenin toxin (sesquiterpene lactone) and phenols in vermicompost which was obtained from high concentration of cow dung mixed treatments. GC-MS analysis shows no phenolic compounds and predominant level of intermediate metabolites such as 4,8,12,16-Tetramethylheptadecan-4-olide (7.61%), 2-Pentadecanone, 6,10,14-trimethyl- (5.29%) and Methyl 16-methyl-heptadecanoate (4.69%) during the vermicomposting process. Spectral results indicated that Parthenin toxin and phenols can be eradicated via vermicomposting if mixed with appropriate quantity of cow dung.

  18. Fourier transform-infrared spectroscopy and Gas chromatography-mass spectroscopy: reliable techniques for analysis of Parthenium mediated vermicompost.

    PubMed

    Rajiv, P; Rajeshwari, Sivaraj; Venckatesh, Rajendran

    2013-12-01

    Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography-mass spectroscopy have been carried out to investigate the chemical composition of Parthenium mediated vermicompost. Four different concentrations of Parthenium and cow dung mixtures were vermicomposted using the earthworms (Eudrilus eugeniae). FT-IR spectra reveal the absence of Parthenin toxin (sesquiterpene lactone) and phenols in vermicompost which was obtained from high concentration of cow dung mixed treatments. GC-MS analysis shows no phenolic compounds and predominant level of intermediate metabolites such as 4,8,12,16-Tetramethylheptadecan-4-olide (7.61%), 2-Pentadecanone, 6,10,14-trimethyl- (5.29%) and Methyl 16-methyl-heptadecanoate (4.69%) during the vermicomposting process. Spectral results indicated that Parthenin toxin and phenols can be eradicated via vermicomposting if mixed with appropriate quantity of cow dung. PMID:23998948

  19. Femtosecond Chirp-Free Transient Absorption Method And Apparatus

    DOEpatents

    McBranch, Duncan W. (Santa Fe, NM); Klimov, Victor I. (White Rock, NM)

    2001-02-20

    A method and apparatus for femtosecond transient absorption comprising phase-sensitive detection, spectral scanning and simultaneous controlling of a translation stage to obtain TA spectra information having at least a sensitivity two orders of magnitude higher than that for single-shot methods, with direct, simultaneous compensation for chirp as the data is acquired. The present invention includes a amplified delay translation stage which generates a splittable frequency-doubled laser signal at a predetermined frequency f, a controllable means for synchronously modulating one of the laser signals at a repetition rate of f/2, applying the laser signals to a material to be sample, and acquiring data from the excited sample while simultaneously controlling the controllable means for synchronously modulating.

  20. Experimental demonstration of fiber optical parametric chirped-pulse amplification

    NASA Astrophysics Data System (ADS)

    Zhou, Yue; Cheung, Kim K. Y.; Chui, P. C.; Wong, Kenneth K. Y.

    2010-02-01

    A fiber optical parametric chirped-pulse amplifier (FOPCPA) is experimentally demonstrated. A 1.76 ps signal at 1542 nm with a peak power of 20 mW is broadened to 40 ps, and then amplified by a 100-ps pulsed pump at 1560 nm. The corresponding idler at 1578 nm is generated as the FOPCPA output. The same medium used to stretch the signal is deployed to compress the idler to 3.8 ps, and another spool of fiber is deployed to further compress the idler to 1.87 ps. The peak power of the compressed idler is 2 W, which corresponds to a gain of 20 dB.

  1. Fuzzy Interpolative Reasoning for Sparse Fuzzy Rule-Based Systems Based on bm alpha-Cuts and Transformations Techniques

    Microsoft Academic Search

    Shyi-ming Chen; Yaun-kai Ko

    2008-01-01

    In sparse fuzzy rule-based systems, the fuzzy rule bases are usually incomplete. In this situation, the system may not properly perform fuzzy reasoning to get reasonable consequences. In order to overcome the drawback of sparse fuzzy rule-based systems, there is an increasing demand to develop fuzzy interpolative reasoning techniques in sparse fuzzy rule-based systems. In this paper, we present a

  2. Fabry-Pérot cavity based on chirped sampled fiber Bragg gratings.

    PubMed

    Zheng, Jilin; Wang, Rong; Pu, Tao; Lu, Lin; Fang, Tao; Li, Weichun; Xiong, Jintian; Chen, Yingfang; Zhu, Huatao; Chen, Dalei; Chen, Xiangfei

    2014-02-10

    A novel kind of Fabry-Pérot (FP) structure based on chirped sampled fiber Bragg grating (CSFBG) is proposed and demonstrated. In this structure, the regular chirped FBG (CFBG) that functions as reflecting mirror in the FP cavity is replaced by CSFBG, which is realized by chirping the sampling periods of a sampled FBG having uniform local grating period. The realization of such CSFBG-FPs having diverse properties just needs a single uniform pitch phase mask and sub-micrometer precision moving stage. Compared with the conventional CFBG-FP, it becomes more flexible to design CSFBG-FPs of diverse functions, and the fabrication process gets simpler. As a demonstration, based on the same experimental facilities, FPs with uniform FSR (~73 pm) and chirped FSR (varying from 28 pm to 405 pm) are fabricated respectively, which shows good agreement with simulation results. PMID:24663569

  3. A Multiterawatt Laser Using a High-Contrast, Optical Parametric Chirped-Pulse Presamplifier

    SciTech Connect

    Bagnoud, V.; Puth, J.; Begishev, I.; Guardalben, M.; Zuegel, J.D.; Forget, N.; LeBlanc, C.

    2005-09-30

    A laser has been built that uses optical parametric chirped-pulse preamplification and a glass booster amplifier. We review the performance of the 5-Hz, multijoule OPCPA pump laser, the 370-mJ OPCPA, and the overall laser.

  4. Bubble-Based Acoustic Radiation Force Using Chirp Insonation to Reduce Standing Wave Effects

    PubMed Central

    Erpelding, Todd N.; Hollman, Kyle W.; O’Donnell, Matthew

    2007-01-01

    Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young’s modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200, and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size. PMID:17306697

  5. Chirp Frequency-Translated Reference Ultra-Wideband (UWB) Wireless Communication System

    Microsoft Academic Search

    Zhang Jian; Hu Han-Ying; Liu Luo-Kun; Wang Tao

    2008-01-01

    A chirp frequency-translated reference ultra-wideband system is proposed based on the time-domain and code-domain transmitted-reference impulse radio UWB systems. Mathematic derivation and simulation results show that while this system has similar performance to pulse-based UWB system without losing the merits, it has the advantages of chirp communication system as well. Meanwhile, this system not only offers a solution of simple

  6. Practical design of optical diagnostics for chirped-pulse free-electron lasers

    Microsoft Academic Search

    Eric B. Szarmes; John M. J. Madey

    1992-01-01

    In recent years there have been several proposals to operate rf-linac-driven FELs with chirped electron and optical micropulses for use in fast time-resolved experiments. We have been actively pursuing this application on the Mark-III infrared FEL at Duke University, and have designed and procured an apparatus to achieve broad-band compression of chirped optical pulses between roughly 2.5 mum and 4.1

  7. Spectral transmission characteristics of weakly tilted and tilted chirped fiber gratings: comparative studies

    NASA Astrophysics Data System (ADS)

    Osuch, Tomasz; Jurek, Tomasz; Jedrzejewski, Kazimierz

    2013-10-01

    In this paper the comparative study of spectral transmission characteristics of tilted Bragg gratings made using uniform phase mask and chirped phase mask are presented. Results are focused on low tilt angles with special interest on cladding modes behavior. The spectral characteristic shape for simultaneously tilted and chirped Bragg gratings point out its potential applications as amplitude discriminator in fiber sensing applications and gain flattening element for EDFA.

  8. Spatial-chirp compensation in dynamical holograms reconstructed with ultrafast lasers

    NASA Astrophysics Data System (ADS)

    Martínez-León, Lluís; Clemente, Pere; Tajahuerce, Enrique; Mínguez-Vega, Gladys; Mendoza-Yero, Omel; Fernández-Alonso, Mercedes; Lancis, Jesús; Climent, Vicent; Andrés, Pedro

    2009-01-01

    A computer generated hologram (CGH) reconstructed with a sub-100-fs laser pulse at the focal plane of a conventional refractive lens experiences a large amount of spatial chirp. We report the shaping of a 12 fs laser pulsed beam by means of a Fourier CGH implemented onto a spatial light modulator, using a hybrid diffractive-refractive lens triplet that provides spatial-chirp compensation. Experimental results demonstrate that parallel, arbitrary, and high-resolution patterning is possible with the proposed device.

  9. Widely Tunable Negative-Chirp SG-DBR Laser/EA-Modulated Transmitter

    NASA Astrophysics Data System (ADS)

    Raring, J. W.; Skogen, E. J.; Johansson, L. A.; Sysak, M. N.; Denbaars, S. P.; Coldren, L. A.

    2005-01-01

    Ten Gb/s low power penalty (< 0.5 dB) error-free transmission was achieved through 75 km using a high-performance sampled-grating (SG) distributed Bragg reflector (DBR) laser/EAM transmitter. Large signal chirp measurements show negative chirp operation across the entire tuning range of the devices. An integration-oriented quantum-well-intermixing (QWI) process was employed for the realization of these devices.

  10. Fiber Ring Laser Operated by Dynamic Local Phase Shifting of a Chirped Grating

    Microsoft Academic Search

    Ana Gonzalez-Segura; Pere Perez-Millan; JosÉ Luis Cruz; Miguel V. Andres

    2009-01-01

    An ultranarrow linewidth erbium-doped fiber ring laser is presented. It is based on the filtering properties of a phase-shifted chirped fiber Bragg grating, which is inserted inside the cavity of the laser. A dynamic control of the phase shifting, which is induced by a magnetostrictive transducer, permits both tunable continuous-wave and actively Q-switched operation. The use of a chirped grating

  11. A coupling-of-modes analysis of chirped transducers containing reflective electrode geometries

    Microsoft Academic Search

    B. P. Abbott; C. S. Hartmann; D. C. Malocha

    1989-01-01

    An accurate and numerically efficient model for analyzing chirped transducers incorporating internal reflections is presented. The model results in a complete three-port characterization of the transducer. The three-port description of the transducer (two acoustic ports and one electric port) is obtained by representing the response of the chirped transducer as that of a set of cascaded uniform sections. The three-port

  12. Fourier Transform Rheology as an innovative morphological characterization technique for the emulsion volume average radius and its distribution.

    PubMed

    Reinheimer, K; Grosso, M; Hetzel, F; Kübel, J; Wilhelm, M

    2012-08-15

    This article extends previous works on emulsion characterization via Fourier Transform Rheology. The interest here is on the effects of (i) polydispersity and (ii) high volume fraction (often associated with commercial samples) on the nonlinear rheological behavior. To analyze the effects of polydispersity on the LAOS measurements, the investigated samples were characterized with respect to their volume average radius, [R](43), and the polydispersity index of the distribution. As the nonlinear mechanical emulsion value E(0) introduced in the literature is a function of both nonlinear rheological parameters, such as I(5/3), as well as emulsion properties including the volume average radius, interfacial tension and viscosities of the matrix and dispersed phase, it is, therefore, a useful tool for emulsion characterization. In addition, the analysis of the higher harmonic ratios, I(7/5), has been demonstrated to provide information about the width of the distribution. With respect to the characterization of the high volume fraction samples, these first experiments on commercial w/o-emulsions were shown to relate nonlinear rheological properties to the droplet size and droplet size distribution of highly filled systems, demonstrating that LAOS experiments can give useful insights on the average droplet size and its distribution. PMID:22633109

  13. Transforming traditional Tai Ji Quan techniques into integrative movement therapy—Tai Ji Quan: Moving for Better Balance

    PubMed Central

    Li, Fuzhong

    2014-01-01

    Tai Ji Quan, developed as a martial art, has traditionally served multiple purposes, including self-defense, competition/performance, and health promotion. With respect to health, the benefits historically and anecdotally associated with Tai Ji Quan are now being supported by scientific and clinical research, with mounting evidence indicating its potential value in preventing and managing various diseases and improving well-being and quality of life in middle-aged and older adults. The research findings produced to date have both public health significance and clinical relevance. However, because of its roots in the martial arts, transforming traditional Tai Ji Quan movements and training approaches into contemporary therapeutic programs and functional applications is needed to maximize its ultimate utility. This paper addresses this issue by introducing Tai Ji Quan: Moving for Better Balance, a functional therapy that involves the use of Tai Ji Quan principles and Yang-style-based movements to form an innovative, contemporary therapeutic approach that integrates motor, sensory, and cognitive components to improve postural control, gait, and mobility for older adults and those who have neurodegenerative movement impairments. It provides a synergy of traditional and contemporary Tai Ji Quan practice with the ultimate goal of improving balance and gait, enhancing performance of daily functional tasks, and reducing incidence of falls among older adults. PMID:25126445

  14. Recovering strain readings from chirping fiber Bragg gratings in composite overwrapped pressure vessels

    NASA Astrophysics Data System (ADS)

    Strutner, Scott M.; Pena, Frank; Piazza, Anthony; Parker, Allen R.; Richards, W. Lance; Carman, Gregory P.

    2014-04-01

    This study reports on signal recovery of optical fiber Bragg gratings embedded in a carbon fiber composite overwrapped pressure vessel's (COPV) structure which have become chirped due to microcracks. COPVs are commonly used for the storage of high pressure liquids and gases. They utilize a thin metal liner to seal in contents, with a composite overwrap to strengthen the vessel with minimal additional mass. A COPV was instrumented with an array of surface mounted and embedded fiber Bragg gratings (FBGs) for structural health monitoring (SHM) via strain sensing of the material. FBGs have been studied as strain sensors for the last couple decades. Many of the embedded FBGs reflected a multi-peak, chirped response which was not able to be interpreted well by the current monitoring algorithm. Literature and this study found that the chirping correlated with microcracks. As loading increases, so does the number of chirped FBGs and microcracks. This study uses optical frequency domain reflectometry (OFDR) to demultiplex the array of FBGs, and then sub- divide individual FBGs. When a FBG is sub-divided using OFDR, the gratings' strain along its length is recovered. The sub-divided chirped FBGs have strain gradients along their length from microcracks. Applying this to all chirped gratings, nearly the entirety of the embedded sensors' readings can be recovered into a series of single peak responses, which show very large local strains throughout the structure. This study reports on this success in recovering embedded FBGs signal, and the strain gradient from microcracks.

  15. Detection and tracking of sea-surface targets in infrared and visual band videos using the bag-of-features technique with scale-invariant feature transform.

    PubMed

    Can, Tolga; Karali, A Onur; Aytaç, Tayfun

    2011-11-20

    Sea-surface targets are automatically detected and tracked using the bag-of-features (BOF) technique with the scale-invariant feature transform (SIFT) in infrared (IR) and visual (VIS) band videos. Features corresponding to the sea-surface targets and background are first clustered using a training set offline, and these features are then used for online target detection using the BOF technique. The features corresponding to the targets are matched to those in the subsequent frame for target tracking purposes with a set of heuristic rules. Tracking performance is compared with an optical-flow-based method with respect to the ground truth target positions for different real IR and VIS band videos and synthetic IR videos. Scenarios are composed of videos recorded/generated at different times of day, containing single and multiple targets located at different ranges and orientations. The experimental results show that sea-surface targets can be detected and tracked with plausible accuracies by using the BOF technique with the SIFT in both IR and VIS band videos. PMID:22108891

  16. Spectrum transformation for divergent iterations

    NASA Technical Reports Server (NTRS)

    Gupta, Murli M.

    1991-01-01

    Certain spectrum transformation techniques are described that can be used to transform a diverging iteration into a converging one. Two techniques are considered called spectrum scaling and spectrum enveloping and how to obtain the optimum values of the transformation parameters is discussed. Numerical examples are given to show how this technique can be used to transform diverging iterations into converging ones; this technique can also be used to accelerate the convergence of otherwise convergent iterations.

  17. Coherent control of ultracold {sup 85}Rb trap-loss collisions with nonlinearly frequency-chirped light

    SciTech Connect

    Pechkis, J. A. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Currently with the Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375 (United States); Carini, J. L.; Rogers, C. E. III; Gould, P. L. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Kallush, S. [Department of Physics and Optical Engineering, ORT Braude, P.O. Box 78, Karmiel (Israel); Kosloff, R. [Department of Physical Chemistry and the Fritz Haber Research Center for Molecular Dynamics, Hebrew University, IL-91094 Jerusalem (Israel)

    2011-06-15

    We present results on coherent control of ultracold trap-loss collisions using 40-ns pulses of nonlinearly frequency-chirped light. The chirps, either positive or negative, sweep {approx}1 GHz in 100 ns and are centered at various detunings below the D{sub 2} line of {sup 85}Rb. At each center detuning, we compare the collisional rate constant {beta} for chirps that are linear in time, concave-down, and concave-up. For positive chirps, we find that {beta} generally depends very little on the shape of the chirp. For negative chirps, however, we find that {beta} can be enhanced by up to 50(20)% for the case of the concave-down shape. This occurs at detunings where the evolution of the wave packet is expected to be coherent. An enhancement at these detunings is also seen in quantum-mechanical simulations of the collisional process.

  18. Optical Extinction Ratio Monitoring Techniques Using Optical Spectrum Analysis

    Microsoft Academic Search

    Chun-Liang Yang; San-Liang Lee

    2007-01-01

    Abstrac An optical extinction ratio monitoring technique for wavelength-division-multiplexed passive optical network systems is proposed. This technique is based on the optical spectrum analysis. It can accurately measure the optical extinction ratio of optical signals and does not change with the transmission distance. In our experiments, the transient chirp hardly affects the measured results if the optical extinction ratio is

  19. Swept Frequency Technique For Classification Of The Scatterer Structure

    Microsoft Academic Search

    V. Genis; I. Oboznenko; J. M. Reid; P. Lewin

    1991-01-01

    Identification of inhomogeneities is of importance in the areas of tissue characterization, nondestructive evaluation and underwater acoustics. This paper presents a specific approach to the identification and classification of inhomogeneities by using a pulsed swept frequency technique (chirping). The unique feature of this technique is that it allows frequency domain data to be determined directly from time domain data without

  20. Detection of linear features using a localized Radon transform with a wavelet filter

    Microsoft Academic Search

    Abbie L. Warrick; Pamela A. Delaney

    1997-01-01

    One problem of interest to the oceanic engineering community is the detection and enhancement of internal wakes in open water synthetic aperture radar (SAR) images. Internal wakes, which occur when a ship travels in a stratified medium, have a “V” shape extending from the ship, and a chirp-like feature across each arm. The Radon transform has been applied to the

  1. Comparison of chirp scaling and wavenumber domain algorithms for airborne low-frequency SAR

    NASA Astrophysics Data System (ADS)

    Potsis, Athanasios; Reigber, Andreas; Alivizatos, Emmanouil; Moreira, Alberto; Uzunoglou, Nikolaos K.

    2003-03-01

    In recent years a new class of Synthetic Aperture Radar (SAR) systems, using low frequencies, have emerged. The combination of low frequencies with high bandwidths allows a variety of new applications. Several new fields arise in forestry, biomass estimation and in archaeological and geological exploration. The P-band SAR technology benefits from technological advances in antenna design, low noise amplifiers, band pass filters, digital receiver technology, as well as new processing algorithms. For all the new applications of an airborne P-band SAR system, the high-resolution imaging is an important parameter, but it cannot be easily achieved with conventional processing techniques. In this paper, the performance and limitations of the Extended Chirp Scaling (ECS) algorithm and wavenumber domain Omega-K processing algorithm are analysed and discussed. Additionally, modifications of both algorithms are proposed, which optimise the respective algorithm for processing low frequency, wide-beam and wide-band SAR data. Despite of the inherent limitations of the above mentioned processing algorithms, a deterministic phase error, called "digital phase error", due to digital signal processing characteristics is formulated and its effect to the processed SAR data is analytically described. The analysis is carried out, using simulated low frequency airborne SAR data.

  2. Higher order chirp compensation of femtosecond mode-locked semiconductor lasers using optical fibers with different group-velocity dispersions

    Microsoft Academic Search

    Shin Arahira; Satoko Kutsuzawa; Yasuhiro Matsui; Yoh Ogawa

    1996-01-01

    Higher order chirp compensation of optical short pulses by using two types of optical fibers with different group-velocity dispersions was theoretically and experimentally investigated in detail. By optimizing the lengths of two types of optical fibers, both second- and third-order dispersion of chirped optical pulses were found to be simultaneously compensated. Pulse-compression experiments with chirped optical pulses from a mode-locked

  3. Generation of isolated attosecond pulses of sub-atomic-time durations with multi-cycle chirped polarization gating pulses.

    PubMed

    Zhang, Chaojin; Yao, Jinping; Ni, Jielei

    2012-10-22

    We theoretically investigate the X-ray supercontinuum generated by interaction of multi-cycle, chirped polarization gating pulses with the helium gas. It is shown that with this scheme, an isolated sub-50-attosecond pulse can be obtained straightforwardly without any phase compensation. Interestingly, if one selects an extremely broad spectral range near the high-order harmonic cutoff, an isolated and intense sub-24-attosecond pulse can be generated after phase compensation, which could be used to detect and control the electronic dynamics inside the atoms. Furthermore, it is found that the generation of such a broad and smooth X-ray supercontinuum is not so stringent on the selection of the simulated parameters, allowing for the experimental demonstration of this technique in the future. PMID:23187227

  4. Derivatization technique to increase the spectral selectivity of two-dimensional Fourier transform infrared focal plane array imaging: analysis of binder composition in aged oil and tempera paint.

    PubMed

    Zumbühl, Stefan; Scherrer, Nadim C; Eggenberger, Urs

    2014-01-01

    The interpretation of standard Fourier transform infrared spectra (FT-IR) on oil-based paint samples often suffers from interfering bands of the different compounds, namely, binder, oxidative aging products, carboxylates formed during aging, and several pigments and fillers. The distinction of the aging products such as ketone and carboxylic acid functional groups pose the next problem, as these interfere with the triglyceride esters of the oil. A sample preparation and derivatization technique using gaseous sulfur tetrafluoride (SF4), was thus developed with the aim to discriminate overlapping signals and achieve a signal enhancement on superposed compounds. Of particular interest in this context is the signal elimination of the broad carboxylate bands of the typical reaction products developing during the aging processes in oil-based paints, as well as signal interference originating from several typical pigments in this spectral range. Furthermore, it is possible to distinguish the different carbonyl-containing functional groups upon selective alteration. The derivatization treatment can be applied to both microsamples and polished cross sections. It increases the selectivity of the infrared spectroscopy technique in a fundamental manner and permits the identification and two-dimensional (2D) localization of binder components in aged paint samples at the micrometer scale. The combination of SF4 derivatization with high-resolution 2D FT-IR focal plane array (FPA) imaging delivers considerable advances to the study of micro-morphological processes involving organic compounds. PMID:24694702

  5. Spectra resolution for simultaneous spectrophotometric determination of lamivudine and zidovudine components in pharmaceutical formulation of human immunodeficiency virus drug based on using continuous wavelet transform and derivative transform techniques.

    PubMed

    Sohrabi, Mahmoud Reza; Tayefeh Zarkesh, Mahshid

    2014-05-01

    In the present paper, two spectrophotometric methods based on signal processing are proposed for the simultaneous determination of two components of an anti-HIV drug called lamivudine (LMV) and zidovudine (ZDV). The proposed methods are applied to synthetic binary mixtures and commercial pharmaceutical tablets without the need for any chemical separation procedures. The developed methods are based on the application of Continuous Wavelet Transform (CWT) and Derivative Spectrophotometry (DS) combined with the zero cross point technique. The Daubechies (db5) wavelet family (242 nm) and Dmey wavelet family (236 nm) were found to give the best results under optimum conditions for simultaneous analysis of lamivudine and zidovudine, respectively. In addition, the first derivative absorption spectra were selected for the determination of lamivudine and zidovudine at 266 nm and 248 nm, respectively. Assaying various synthetic mixtures of the components validated the presented methods. Mean recovery values were found to be between 100.31% and 100.2% for CWT and 99.42% and 97.37% for DS, respectively for determination of LMV and ZDV. The results obtained from analyzing the real samples by the proposed methods were compared to the HPLC reference method. One-way ANOVA test at 95% confidence level was applied to the results. The statistical data from comparing the proposed methods with the reference method showed no significant differences. PMID:24720987

  6. A chirp-compensated, injection-seeded alexandrite laser

    NASA Astrophysics Data System (ADS)

    Bakule, P.; Baird, P. E. G.; Boshier, M. G.; Cornish, S. L.; Heller, D. F.; Jungmann, K.; Lane, I. C.; Meyer, V.; Sandars, P. H. G.; Toner, W. T.; Towrie, M.; Walling, J. C.

    2000-07-01

    A Q-switched alexandrite laser suitable for high-resolution spectroscopy is described which produces pulses of 35 mJ energy in a 10 MHz bandwidth, with a high-purity TEM00 mode. The laser can be synchronised to external event to within 100 ns. The output pulse length is 120 ns and the repetition rate 25 Hz. The laser is injection-seeded by a Ti:sapphire laser operating around 730 nm. To preserve single-mode seeding under external triggering conditions, and to obtain small time-jitter, active cavity length control was used. In order to achieve the 10 MHz output bandwidth, intra-cavity electro-optic modulators were used to compensate for the frequency chirp. The refractive index of alexandrite was found to vary linearly with inversion density with a constant of proportionality equal to 1.6×10-24 cm3. In pulsed operation at 730 nm, the index change due to this effect is only partially compensated by changes due to ground state phonon relaxation.

  7. Chirped and divided-pulse Sagnac fiber amplifier

    NASA Astrophysics Data System (ADS)

    Guichard, Florent; Zaouter, Yoann; Hanna, Marc; Mai, Khanh-Lin; Morin, Franck; Hönninger, Clemens; Mottay, Eric; Georges, Patrick

    2015-03-01

    Femtosecond fiber chirped pulse amplifiers have numerous advantages, but are limited in energy because of the small interaction area with the fiber core. In this contribution, we create two orthogonally-polarized stretched pulse replicas in the time domain, following the divided-pulse amplification (DPA) principle. This beam is subsequently separated into two counter-propagating beams in a Sagnac interferometer to finally generate four pulse replicas. These pulses are amplified in two state-of-the-art large mode area rod-type fiber amplifiers in series, before final coherent combination and compression. Because the stretched-pulse duration is of the order of hundreds of picoseconds, the DPA delay is induced using a freespace interferometer with reasonable arm lengths of few tens of centimeters. The use of a common interferometer to divide and recombine temporal pulse replicas, together with the Sagnac geometry, results in an identical optical path for all four replicas. Therefore, the whole spatio-temporal combining architecture is passive, avoiding the need for active electronic stabilization systems. Because we only use two temporal replicas, the system is immune to differential saturation levels or B-integrals between successive pulses: this is compensated by controlling the amplitude of both pulses at the input of the amplifying setup. This setup allows the generation of 1 mJ, 300 fs compressed pulses at 50 kHz repetition rate, corresponding to 50 W output average power, with a combining efficiency above 90% at all power levels.

  8. Analysis of Dynamic Stall Through Chirp Signal Pitch Excursions

    NASA Astrophysics Data System (ADS)

    Heintz, Kyle; Coleman, Dustin; Wicks, Michael; Corke, Thomas; Thomas, Flint

    2013-11-01

    An augmentation of the typical pitching airfoil experiment has been performed where the pitching frequency and amplitude are dynamically varied in a short-time event to produce a ``chirp'' trajectory, ? (t) =?0 +?1 (t) sin (t? (t)) . The frequency evolution followed a Schroeder-phase relation, ? (t) =?min + K (?max -?min) . The frequencies ranged from 0.5 Hz to 30 Hz, resulting in reduced frequencies from 0.02 to 0.1. The free-stream Mach number ranged from Mach 0.4 to 0.6, giving chord Reynolds numbers from 5 ×105 to 3 ×106 . The airfoil was a NACA 23012 section shape that was fully instrumented with 31 flush-mounted high-bandwidth pressure transducers. The pressure transducer outputs were simultaneously sampled with the instantaneous angle of attack, ? (t) . The motivation for this study was to compare dynamic stall under non-equilibrium conditions. A particular interest is on the flow features that occur when dynamically passing between light and deep stall regimes. The results include phase analysis of aerodynamic loads, wavelet-based spectral analysis, and the determination of the intra-cycle aerodynamic damping factors.

  9. Chirped-pulse millimeter-wave spectroscopy: Spectrum, dynamics, and manipulation of Rydberg-Rydberg transitions

    SciTech Connect

    Colombo, Anthony P.; Zhou Yan; Prozument, Kirill; Coy, Stephen L.; Field, Robert W. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2013-01-07

    We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of Rydberg-Rydberg transitions is that they have enormous electric dipole transition moments ({approx}5 kiloDebye at n*{approx} 40, where n* is the effective principal quantum number), so they interact strongly with the mm-wave radiation. After polarization by a mm-wave pulse in the 70-84 GHz frequency region, the excited transitions re-radiate free induction decay (FID) at their resonant frequencies, and the FID is heterodyne-detected by the CPmmW spectrometer. Data collection and averaging are performed in the time domain. The spectral resolution is {approx}100 kHz. Because of the large transition dipole moments, the available mm-wave power is sufficient to polarize the entire bandwidth of the spectrometer (12 GHz) in each pulse, and high-resolution survey spectra may be collected. Both absorptive and emissive transitions are observed, and they are distinguished by the phase of their FID relative to that of the excitation pulse. With the combination of the large transition dipole moments and direct monitoring of transitions, we observe dynamics, such as transient nutations from the interference of the excitation pulse with the polarization that it induces in the sample. Since the waveform produced by the mm-wave source may be precisely controlled, we can populate states with high angular momentum by a sequence of pulses while recording the results of these manipulations in the time domain. We also probe the superradiant decay of the Rydberg sample using photon echoes. The application of the CPmmW technique to transitions between Rydberg states of molecules is discussed.

  10. Phase retrieval with unknown sampling factors via the two-dimensional chirp z-transform

    E-print Network

    Fienup, James R.

    in fine phasing of the James Webb Space Telescope (JWST) [4]. These algorithms work by modeling the system. Jurling and James R. Fienup* Institute of Optics, University of Rochester, Rochester, New York 14627, USA

  11. Chirped Pulse-Fourier Transform Microwave Spectroscopy of Ethyl 3METHYL3-PHENYLGLYCIDATE (strawberry Aldehyde)

    Microsoft Academic Search

    Steven T. Shipman; Justin L. Neill; Matt T. Muckle; Richard D. Suenram; Brooks H. Pate

    2009-01-01

    Strawberry aldehyde (C_{12} O_3 H_{14}), a common artificial flavoring compound, has two non-interconvertible conformational families defined by the relative stereochemistry around its epoxide carbons. In one family, referred to as the trans because the two large substituents (a phenyl ring and an ethyl ester) are on opposite sides of the epoxide ring, these two substituents are unable to interact with

  12. A Chirp Transform Algorithm for Processing Squint Mode FMCW SAR Data

    Microsoft Academic Search

    Zhi-Hong Jiang; Kan Huang-Fu; Jian-Wei Wan

    2007-01-01

    Frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) is a lightweight cost-effective high-resolution airborne imaging radar. In squint case, the frequency scaling algorithm, which is suitable for processing nonchirped raw data, cannot be used directly in FMCW SAR data processing because of low system sampling frequency. On the other hand, the continuous antenna motion of FMCW SAR can cause serious distortions

  13. Beam Sharpening of Delay\\/Doppler Altimeter Data Through Chirp Zeta Transform

    Microsoft Academic Search

    Pietro Guccione

    2008-01-01

    The main goal of a satellite radar altimeter is to measure the height of the reflecting surface scanned by the passage of the instrument overhead. A delay\\/Doppler altimeter reduces the along-track footprint size by exploiting the coherence of the emitted pulses to synthetize a narrower antenna. Doppler beam formation is then a straightforward procedure that implies application of the discrete

  14. Millimeter wave detection of mesospheric ozone using a high resolution chirp transform spectrometer backend

    Microsoft Academic Search

    P. Hartogh; C. Jarchow

    1994-01-01

    The diurnal variation of mesospheric ozone can be measured by groundbased millimeter wave radiometry. Due to the narrow linewidth of the millimeter wave emissions of ozone from the upper mesosphere not only a low noise radiometer frontend, but also a high resolution spectrometer backend is required. Since end of 1992 the authors are monitoring the 142 GHz ozone line using

  15. Sub-picosecond chirped pulse propagation in concave-dispersion-flattened fibers

    NASA Astrophysics Data System (ADS)

    Li, Xin; Zheng, Hong-jun; Yu, Hui-shan; Liu, Shan-liang

    2012-01-01

    Tianjin University of Technology and Springer-Verlag Berlin Heidelberg 2012 C We propose the sub-picosecond chirped soliton pulse propagation in concave-dispersion-flattened fibers (CDFF). The effects of pulse characteristics and the fiber dispersion parameters on propagation characteristics of the chirped soliton pulse are numerically investigated in the CDFF by the split-step Fourier method (SSFM). The unchirped soliton pulse can stably propagate with unchanged pulse width in the CDFF. The temporal full width at half maximum (FWHM) of the chirped soliton performs a damped oscillation with the increase of propagation distance. The period and amplitude of the oscillation increase with the increase of the chirp parameter | C|. The effect of high-order dispersion ( ? 3- ? 6) on soliton propagation characteristics can be neglected. The soliton pulse slightly broadens with the increase of propagation distance and still maintains soliton characteristics when the fiber loss (ATT) is further considered. The variation of root-meansquare (RMS) spectral width with propagation distance is opposite to that of the temporal width. The output spectrum of soliton has a single peak for the unchirped case, while has multi-peak for chirped case. The temporal width of the soliton obviously increases with the increase of the initial width, decreases with the increase of dispersion peak D 0 of the fiber, and slightly increases with the decrease of dispersion coefficients k 1 and k 2 of the fiber.

  16. Extended chirp scaling algorithm for air- and spaceborne SAR data processing in stripmap and ScanSAR imaging modes

    Microsoft Academic Search

    A. Moreira; J. Mittermayer; R. Scheiber

    1996-01-01

    Presents a generalized formulation of the extended chirp scaling (ECS) approach for high precision processing of air- and spaceborne SAR data. Based on the original chirp scaling function, the ECS algorithm incorporates a new azimuth scaling function and a subaperture approach, which allow an effective phase-preserving processing of ScanSAR data without interpolation for azimuth geometric correction. The azimuth scaling can

  17. Seed Laser Chirping for Enhanced Backward Raman Amplification in Plasmas Z. Toroker, V. M. Malkin, and N. J. Fisch

    E-print Network

    Seed Laser Chirping for Enhanced Backward Raman Amplification in Plasmas Z. Toroker, V. M. Malkin is that, by chirping the seed pulse, the group velocity dispersion may in fact be used advantageously elements will likely have to be replaced by plasma. In a plasma, a short counter-propagating seed pulse

  18. Tuning range extension by active mode-locking of external cavity laser including a linearly chirped fiber Bragg grating

    Microsoft Academic Search

    Aurélien Bergonzo; Estelle Gohin; Jean Landreau; Olivier Durand; Romain Brenot; Guang-Hua Duan; Joel Jacquet

    2003-01-01

    We demonstrate electrical wavelength tuning by mode locking of an external cavity laser (ECL) with linearly chirped fiber Bragg grating (LCFBG). The configuration consists of a laser chip providing the gain coupled to an LCFBG with a large chip rate of 10 or 55 nm\\/cm providing the counter-reaction for laser oscillation. The laser chirp is electrically modulated by a sinusoidal

  19. High-repetition-rate optical parametric chirped-pulse amplifier producing 1-J, sub-100-fs pulses

    E-print Network

    Keller, Ursula

    a high-repetition-rate, femtosecond optical parametric chirped pulse amplifier (OPCPA). Its seed signal. Limpert, and A. Tünnermann, "High repetition rate fiber amplifier pumped sub-20 fs optical parametric, G. H. C. New, and K. Osvay, "Analysis and optimization of optical parametric chirped pulse

  20. Effects of pump laser chirp in high-order harmonics generated from various solid surfaces using femtosecond lasers

    Microsoft Academic Search

    C A Popovici; R A Ganeev; F Vidal; T Ozaki

    2012-01-01

    We investigate the effects of the pump laser chirp on high-order harmonic generation from solid surfaces of aluminium, indium and C60 film targets. Chirped pulses were produced by varying the distance between the two gratings of the laser compressor. We optimized the nanosecond contrast of our femtosecond laser pump (? = 35 fs, ? = 793 nm, I ? 1018

  1. Frequency modulation coherent anti-Stokes Raman scattering (FM-CARS) microscopy based on spectral focusing of chirped laser pulses

    Microsoft Academic Search

    Bi-Chang Chen; Jiha Sung; Sang-Hyun Lim

    2010-01-01

    We demonstrate a new CARS microscopy method based on fast switching of effective vibrational excitation frequency from chirped femtosecond laser pulses. Broadband pump and Stokes pulses excite a single vibrational mode with a high spectral resolution when the two pulses are identically chirped and their pulse durations are approaching the dephasing time of the excited vibrational state. This \\

  2. Effects of pump laser chirp in high-order harmonics generated from various solid surfaces using femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Popovici, C. A.; Ganeev, R. A.; Vidal, F.; Ozaki, T.

    2012-02-01

    We investigate the effects of the pump laser chirp on high-order harmonic generation from solid surfaces of aluminium, indium and C60 film targets. Chirped pulses were produced by varying the distance between the two gratings of the laser compressor. We optimized the nanosecond contrast of our femtosecond laser pump (? = 35 fs, ? = 793 nm, I ˜ 1018 W cm-2) for surface harmonic generation by adjusting the trigger timing of the Pockels cell. Harmonics up to the 18th order (? = 44 nm) were observed. We show experimentally that for chirped pulses with the same pulse duration, those with negative chirp produced stronger harmonics, compared to those with positive chirp. This effect is attributed to the different rise time of the leading edge of the pulse due to the presence of high-order dispersion terms. We also show experimentally that the peak wavelength of the harmonics presents blueshift for pump lasers with negative chirp and redshift for those with positive chirp. This phenomenon appears to be due to the shift in the instantaneous wavelength of the pump laser at the maximum intensity for the different chirped pulses.

  3. Self-deflecting plasmonic lattice solitons and surface modes in chirped plasmonic arrays.

    PubMed

    Li, Chunyan; Cui, Ran; Ye, Fangwei; Kartashov, Yaroslav V; Torner, Lluis; Chen, Xianfeng

    2015-03-15

    We show that chirped metal-dielectric waveguide arrays with focusing cubic nonlinearity can support plasmonic lattice solitons that undergo self-deflection in the transverse plane. Such lattice solitons are deeply subwavelength self-sustained excitations, although they cover several periods of the array. Upon propagation, the excitations accelerate in the transverse plane and follow trajectories curved in the direction in which the separation between neighboring metallic layers decreases, a phenomenon that yields considerable deflection angles. The deflection angle can be controlled by varying the array chirp. We also reveal the existence of surface modes at the boundary of truncated plasmonic chirped array that form even in the absence of nonlinearity. PMID:25768141

  4. Factorization of numbers with Gauss sums: II. Suggestions for implementations with chirped laser pulses

    E-print Network

    W. Merkel; S. Wölk; W. P. Schleich; I. Sh. Averbukh; B. Girard; G. G. Paulus

    2012-10-24

    We propose three implementations of the Gauss sum factorization schemes discussed in part I of this series: (i) a two-photon transition in a multi-level ladder system induced by a chirped laser pulse, (ii) a chirped one-photon transition in a two-level atom with a periodically modulated excited state, and (iii) a linearly chirped one-photon transition driven by a sequence of ultrashort pulses. For each of these quantum systems we show that the excitation probability amplitude is given by an appropriate Gauss sum. We provide rules how to encode the number N to be factored in our system and how to identify the factors of N in the fluorescence signal of the excited state.

  5. Greatly enhanced slow and fast light in chirped pulse semiconductor optical amplifiers: theory and experiments.

    PubMed

    Pesala, Bala; Sedgwick, Forrest; Uskov, Alexander V; Chang-Hasnain, Connie

    2009-02-16

    Chirped pulse scheme is shown to be highly effective to attain large tunable time shifts via slow and fast light for an ultra-short pulse through a semiconductor optical amplifier (SOA). We show for the first time that advance can be turned into delay by simply reversing the sign of the chirp. A large continuously tunable advance-bandwidth product (ABP) of 4.7 and delay-bandwidth product (DBP) of 4.0 are achieved for a negatively and positively chirped pulse in the same device, respectively. We show that the tunable time shift is a direct result of self-phase modulation (SPM). Theoretical simulation agrees well with experimental results. Further, our simulation results show that by proper optimization of the SOA and chirper design, a large continuously tunable DBP of 55 can be achieved. PMID:19219122

  6. Femtosecond X-ray Pulses from a Spatially Chirped Electron Bunch in a SASE FEL

    SciTech Connect

    Emma, P.

    2003-01-14

    We propose a simple method to produce short x-ray pulses using a spatially chirped electron bunch in a SASE FEL. The spatial chirp is generated using an rf deflector which produces a transverse offset (in y and/or y') correlated with the longitudinal bunch position. Since the FEL gain is very sensitive to an initial offset in the transverse phase space at the entrance of the undulator, only a small portion of the electron bunch with relatively small transverse offset will interact significantly with the radiation, resulting in an x-ray pulse length much shorter than the electron bunch length. The x-ray pulse is also naturally phase locked to the rf deflector and so allows high precision timing synchronization. We discuss the generation and transport of such a spatially chirped electron beam and show that tens of femtosecond long pulse can be generated for the linac coherent light source (LCLS).

  7. A simple photonic generation of linearly chirped microwave pulse with large time-bandwidth product and high compression ratio.

    PubMed

    Gao, Hongbiao; Lei, Cheng; Chen, Minghua; Xing, Fangjian; Chen, Hongwei; Xie, Shizhong

    2013-10-01

    Based on the heterodyne beating between the pre-chirped optical pulse and the continuous wave (CW) light in a wideband photodetector (PD), linearly chirped microwave pulse with time duration of 3.2ns and bandwidth of 33GHz, which yields a large time-bandwidth product (TBWP) of 106 and high compression ratio of 160, is generated in our experiment. Dispersion compensation fiber (DCF) with uniform response across broad bandwidth is used for providing the original linear chirp in our method, which shows the promise to generate linearly chirped microwave pulse with bandwidth of up to THz. The flexibility of the center frequency and the stability of the time-frequency performance are demonstrated by generating different types of linearly chirped microwave pulses. The range resolution of our generated microwave pulse is also verified by off-line processing. PMID:24104226

  8. Measuring temperature-dependent propagating disturbances in coronal fan loops using multiple SDO/AIA channels and the surfing transform technique

    SciTech Connect

    Uritsky, Vadim M.; Ofman, Leon [Catholic University of America, Washington, D.C. 20064 (United States); Davila, Joseph M.; Viall, Nicholeen M. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2013-11-20

    A set of co-aligned high-resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling a quantitative description of subvisual coronal motions with low signal-to-noise ratios of the order of 0.1%. The technique operates with a set of one-dimensional 'surfing' signals extracted from position-time plots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency-velocity space that exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square-root dependence predicted for slow mode magneto-acoustic waves which seem to be the dominating wave mode in the loop structures studied. This result extends recent observations by Kiddie et al. to a more general class of fan loop system not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

  9. Measuring Temperature-dependent Propagating Disturbances in Coronal Fan Loops Using Multiple SDO/AIA Channels and the Surfing Transform Technique

    NASA Astrophysics Data System (ADS)

    Uritsky, Vadim M.; Davila, Joseph M.; Viall, Nicholeen M.; Ofman, Leon

    2013-11-01

    A set of co-aligned high-resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling a quantitative description of subvisual coronal motions with low signal-to-noise ratios of the order of 0.1%. The technique operates with a set of one-dimensional "surfing" signals extracted from position-time plots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency-velocity space that exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square-root dependence predicted for slow mode magneto-acoustic waves which seem to be the dominating wave mode in the loop structures studied. This result extends recent observations by Kiddie et al. to a more general class of fan loop system not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

  10. Numerical studies of driven, chirped Bernstein, Greene, and Kruskal modes

    NASA Astrophysics Data System (ADS)

    Peinetti, F.; Bertsche, W.; Fajans, J.; Wurtele, J.; Friedland, L.

    2005-06-01

    Recent experiments showed the possibility of creating long-lived, nonlinear kinetic structures in a pure-electron plasma. These structures, responsible for large-amplitude periodic density fluctuations, were induced by driving the plasma with a weak oscillating drive, whose frequency was adiabatically decreased in time [W. Bertsche, J. Fajans, and L. Friedland, Phys. Rev. Lett. 91, 265003 (2003)]. A one-dimensional analytical model of the system was developed [L. Friedland, F. Peinetti, W. Bertsche, J. Fajans, and J. Wurtele, Phys. Plasmas 11, 4305 (2004)], which pointed out the phenomenon responsible for the modifications induced by the weak drive in the phase-space distribution of the plasma (initially Maxwellian). In order to validate the theory and to perform quantitative comparisons with the experiments, a more accurate description of the system is developed and presented here. The new detailed analysis of the geometry under consideration allows for more precise simulations of the excitation process, in which important physical and geometrical parameters (such as the length of the plasma column) are evaluated accurately. The numerical investigations probe properties and features of the modes not accessible to direct measurement. Due to the presence of two distinct time scales (because of the adiabatic chirp of the drive frequency), a fully two-dimensional numerical study of the system is expected to be rather time consuming. This becomes particularly important when, as here, a large number of comparisons (covering a wide range of drive parameters) are performed. For this reason, a coupled one-dimensional, radially averaged model is derived and implemented in a particle-in-cell code.

  11. Reflectivity of linear and nonlinear gamma radiated apodized chirped Bragg grating under ocean

    SciTech Connect

    Hamdalla, Taymour A. [Faculty of Science, Alexandria University, Alexandria (Egypt); Faculty of Science, Tabuk University, Tabuk (Saudi Arabia)

    2012-09-06

    In this paper, the effect Co{sup 60} gamma radiation is investigated on the effective refractive index of apodized chirped Bragg grating. Nine apodization profiles are considered. Comparison between the reflectivity of the gamma radiated and non radiated fiber Bragg grating has been carried out. The electric field of signals propagating through the apodized chirped fiber Bragg grating (ACFBG) is first calculated from which, new values for the refractive index are determined. The nonlinear effects appear on the ACFBG reflectivity. The effect of nonlinearity and undersea temperature and pressure on the grating is also studied.

  12. Injection-seeded optical parametric amplifier for generating chirped nanosecond pulses.

    PubMed

    Miyake, Shinichirou; Ohshima, Yasuhiro

    2013-03-11

    We constructed an optical parametric amplifier with BiBO crystals, which was injection seeded by a phase-modulated cw beam in the 1,040-1,070 nm region. Two-stage pre-amplification by Yb-doped fibers were implemented for stable injection to the OPA. The frequency chirp in the OPA pulse was actively controlled by adjusting the RF wave for the phase modulation and its synchronization to the OPA firing. Down/up chirps with up to 500 MHz shift were demonstrated. The output pulse energy was ~40 mJ, which is sufficient for future application of frequency conversion and coherent population transfer. PMID:23482098

  13. Practical design of optical diagnostics for chirped-pulse free-electron lasers

    NASA Astrophysics Data System (ADS)

    Szarmes, Eric B.; Madey, John M. J.

    1992-07-01

    In recent years there have been several proposals to operate rf-linac-driven FELs with chirped electron and optical micropulses for use in fast time-resolved experiments. We have been actively pursuing this application on the Mark-III infrared FEL at Duke University, and have designed and procured an apparatus to achieve broad-band compression of chirped optical pulses between roughly 2.5 ?m and 4.1 ?m, with subsequent measurement of pulse widths as short as 200 fs. The principles of design for this experiment will be reviewed, and extensions of the design to other wavelengths will be considered.

  14. Amplification of optical delay by use of matched linearly chirped fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Yang, Changhuei; Yazdanfar, Siavash; Izatt, Joseph

    2004-04-01

    We describe the use of a matched linearly chirped fiber Bragg grating (FBG) pair as a key element in an adjustable optical delay line. This delay line has the unique property that the achievable optical group delay is orders of magnitude greater (factor of 10 2 in our experiment) than the actual physical displacement. We demonstrate operation of such an optical delay line over a delay range of 3.5 mm using a pair of matched 1300-nm chirped FBGs with a bandwidth of 20 nm each.

  15. Chirped and phase-sampled fiber Bragg grating for tunable DBR fiber laser

    NASA Astrophysics Data System (ADS)

    Xu, Ximing; Dai, Yitang; Chen, Xiangfei; Jiang, Dianjie; Xie, Shizhong

    2005-05-01

    Chirped and phase-sampled fiber Bragg gratings are fabricated and used as reflectors in tunable DBR fiber laser for the first time. By controlling the phase of each sampling section, sampled Bragg gratings (SBG) with different channel spacing can be obtained using only a single chirped phase mask. A 30nm-wide tunable Erbium-doped fiber (EDF) laser is designed and experimentally demonstrated by utilizing the vernier effect of two such SBGs with channel spacing of 3.2nm and 3.6nm, respectively. The lasers' output power of different channels is almost identical (difference less than 1dB) within the tunable range.

  16. Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water

    NASA Astrophysics Data System (ADS)

    Milián, Carles; Jarnac, Amélie; Brelet, Yohann; Jukna, Vytautas; Houard, Aurélien; Mysyrowicz, André; Couairon, Arnaud

    2014-11-01

    We analyze numerically and experimentally the effect of the input pulse chirp on the nonlinear energy deposition from $5\\ \\mu$J fs-pulses at $800$ nm to water. Numerical results are also shown for pulses at $400$ nm, where linear losses are minimized, and for different focusing geometries. Input chirp is found to have a big impact on the deposited energy and on the plasma distribution around focus, thus providing a simple and effective mechanism to tune the electron density and energy deposition. We identify three relevant ways in which plasma features may be tuned.

  17. Nonlinear energy deposition in water from fs-laser pulses: effect of the input chirp

    NASA Astrophysics Data System (ADS)

    Milián, C.; Jarnac, Amelie; Brelet, Y.; Jukna, V.; Houard, A.; Mysyrowicz, A.; Couairon, A.

    2014-05-01

    We present numerical and experimental investigation of the effect that the input pulse chirp has on the energy transfer from 5 ?J fs-pulses at 800 nm to water. The chirp is seen to control efficiently the energy transfer and the geometrical properties of the excited plasma volumes. Agreement between simulations and experiments is obtained via a parametric study, the details of which are presented here. These results may find applications in the control of underwater bubble and sound wave formation, and also in laser surgery involving aqueous media.

  18. Coherent XUV pulse generation using a chirped pulse combined with a unipolar pulse

    NASA Astrophysics Data System (ADS)

    Feng, Liqiang; Liu, Hang

    2015-01-01

    High-order harmonic emission and attosecond XUV source generation have been theoretically investigated using a chirped pulse combined with a unipolar pulse. It shows that the harmonic plateau is very sensitive to the chirp parameter and the intensity, pulse duration and relative position of the unipolar pulse. Further, by optimizing the laser parameters, a 714?eV supercontinuum bandwidth with a single short quantum path contribution has been obtained. Finally, by superposing the selected harmonic spectrum from the 70th to the 470th orders, an isolated attosecond pulse with a duration of 36 as can be obtained.

  19. Generation of a widely tunable linearly chirped microwave waveform based on spectral filtering and unbalanced dispersion.

    PubMed

    Zhang, Hao; Zou, Weiwen; Chen, Jianping

    2015-03-15

    We propose a method to generate a widely tunable linearly chirped microwave waveform based on spectral filtering and unbalanced dispersion. Heterodyne beating between two differently dispersed optical pulses in a photodetector produces the linearly chirped microwave waveform. Desired waveforms with flexible and independent control of the center frequency and sweep bandwidth can be obtained by simply tuning two optical filters. Simulation and experimental investigations are carried out, and the results are in good agreement. The measured microwave waveform has ?5.2-ns pulse duration and ?64-GHz sweep bandwidth, corresponding to a time-bandwidth product of ?166.4 and a compression ratio of ?248. PMID:25768188

  20. ATOMIC AND MOLECULAR PHYSICS: Lithium atom population transfer by population trapping in a chirped microwave pulse

    NASA Astrophysics Data System (ADS)

    Jia, Guang-Rui; Zhang, Xian-Zhou; Ren, Zhen-Zhong; Wu, Su-Ling

    2009-12-01

    Using a time-dependent multilevel approach, we demonstrate that lithium atoms can be transferred to states of lower principle quantum number by exposing them to a frequency chirped microwave pulse. The population transfer from n = 79 to n = 70 states of lithium atoms with more than 80% efficiency is achieved by means of the sequential two-photon ?n = -1 transitions. It is shown that the coherent control of the population transfer can be accomplished by the optimization of the chirping parameters and microwave field strength. The calculation results agree well with the experimental ones and novel explanations have been given to understand the experimental results.

  1. Substitution Structures of Multiple Silicon-Containing Species by Chirped Pulse Ftmw Spectroscopy

    NASA Astrophysics Data System (ADS)

    Seifert, Nathan A.; Lobsiger, Simon; Pate, Brooks H.; Guirgis, Gamil A.; Overby, Jason S.; Durig, James R.

    2013-06-01

    The structures of CH_{3}SiHF-NCO, 1-X-silacyclopropane (X = cyano, isocyanato), 1,1,3,3-tetrafluoro-1,3-disilacyclopentane and its hydrogen analogue (1,3-disilacyclopentane), and 1-isocyanato-silacyclohexane have been studied by chirped pulse FTMW spectroscopy in the 6-18 GHz band. Multiple conformers for some of the species were also detected: anti and gauche for both silacyclopropyl species, and axial and equatorial for the silacyclohexane. Heavy atom substitution structures were determined, with all possible single ^{13}C, ^{29}Si/^{30}Si and most ^{15}N isotopologues assigned in natural abundance. Nitrogen hyperfine and distortion parameters for all species have been determined, and the barrier for methyl internal rotation for CH_{3}SiHF-NCO has been determined as 481(20) cm^{-1}, close to the B3LYP/6-311++g(d,p) barrier of 450 cm^{-1}. A summary of the microwave and structural results for the aforementioned molecules will be presented. In addition, emphasis will be placed on the use of previously discussed automated fitting techniques as a means of efficient and fast assignment of isotopologues in spectra with increasingly large line densities. A. L. Steber, J. L. Neill, M. T. Muckle, B. H. Pate, D. F. Plusquellic, V. Lattanzi, S. Spezzano, M. C. McCarthy. 65th OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 2010, TC10. E. B. Kent, M. N. McCabe, M. A. Phillips, B. P. Gordon, S. T. Shipman. 66th OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 2011, RH01.

  2. High-energy, diode-pumped, picosecond Yb:YAG chirped-pulse regenerative amplifier for pumping optical parametric chirped-pulse amplification.

    PubMed

    Akahane, Y; Aoyama, M; Ogawa, K; Tsuji, K; Tokita, S; Kawanaka, J; Nishioka, H; Yamakawa, K

    2007-07-01

    A diode-pumped, cryogenic-cooled Yb:YAG regenerative amplifier utilizing gain-narrowing has been developed. A 1.2-ns chirped-seed pulse was simultaneously amplified and compressed in the regenerative amplifier, which generated a 35-ps pulse with ~8-mJ of energy without a pulse compressor. Second-harmonics of the amplified pulse was used to pump picosecond two-color optical parametric amplification. PMID:17603607

  3. Conformers of ?-aminoisobutyric acid probed by jet-cooled microwave and matrix isolation infrared spectroscopic techniques

    NASA Astrophysics Data System (ADS)

    Ku?, N.; Sharma, A.; Peña, I.; Bermúdez, M. C.; Cabezas, C.; Alonso, J. L.; Fausto, R.

    2013-04-01

    ?-aminoisobutyric acid (BAIBA) has been studied in isolation conditions: in the gas phase and trapped into a cryogenic N2 matrix. A solid sample of the compound was vaporized by laser ablation and investigated through their rotational spectra in a supersonic expansion using two different spectroscopic techniques: broadband chirped pulse Fourier transform microwave spectroscopy and conventional molecular beam Fourier transform microwave spectroscopy. Four conformers with structures of two types could be successfully identified by comparison of the experimental rotational and 14N nuclear quadruple coupling constants with those predicted theoretically: type A, bearing an OH⋯N intramolecular hydrogen bond and its carboxylic group in the trans geometry (H-O-C=O dihedral ˜180°), and type B, having an NH⋯O bond and the cis arrangement of the carboxylic group. These two types of conformers could also be trapped from the gas phase into a cryogenic N2 matrix and probed by Fourier transform infrared (IR) spectroscopy. In situ irradiation of BAIBA isolated in N2 matrix of type B conformers using near-IR radiation tuned at the frequency of the O-H stretching 1st overtone (˜6930 cm-1) of these forms allowed to selectively convert them into type A conformers and into a new type of conformers of higher energy (type D) bearing an NH⋯O=C bond and a O-H "free" trans carboxylic group.

  4. Effect of chromatic dispersion induced chirp on the temporal coherence property of individual beam from spontaneous four wave mixing

    E-print Network

    Xiaoxin Ma; Xiaoying Li; Liang Cui; Xueshi Guo; Lei Yang

    2011-05-18

    Temporal coherence of individual signal or idler beam, determined by the spectral correlation property of photon pairs, is important for realizing quantum interference among independent sources. To understand the effect of chirp on the temporal coherence property, two series of experiments are investigated by introducing different amount of chirp into either the pulsed pump or individual signal (idler) beam. In the first one, based on spontaneous four wave mixing in a piece of optical fiber, the intensity correlation function of the filtered individual signal beam, which characterizes the degree of temporal coherence, is measured as a function of the chirp of pump. The results demonstrate that the chirp of pump pulses decreases the degree of temporal coherence. In the second one, a Hong-Ou-Mandel type two-photon interference experiment with the signal beams generated in two different fibers is carried out. The results illustrate that the chirp of individual beam does not change the temporal coherence degree, but affect the temporal mode matching. To achieve high visibility, apart from improving the coherence degree by minimizing the chirp of pump, mode matching should be optimized by managing the chirps of individual beams.

  5. The FAST technique: a simplified Agrobacterium-based transformation method for transient gene expression analysis in seedlings of Arabidopsis and other plant species

    Microsoft Academic Search

    Jian-Feng Li; Eunsook Park; Albrecht G von Arnim; Andreas Nebenführ

    2009-01-01

    BACKGROUND: Plant genome sequencing has resulted in the identification of a large number of uncharacterized genes. To investigate these unknown gene functions, several transient transformation systems have been developed as quick and convenient alternatives to the lengthy transgenic assay. These transient assays include biolistic bombardment, protoplast transfection and Agrobacterium-mediated transient transformation, each having advantages and disadvantages depending on the research

  6. Active phase control and frequency chirp effects on supercontinuum generation in high birefringence photonic crystal fiber

    Microsoft Academic Search

    Y. Jiang; Y. Leng; X. Chen; X. Li; Z. Xu

    2008-01-01

    An acoustic-optics programmable dispersive filter (AOPDF) was first employed to actively control the linearly polarized femtosecond pump pulse frequency chirp for supercontinuum (SC) generation in a high birefringence photonic crystal fiber (PCF). By accurately controlling the second order phase distortion and polarization direction of incident pulses, the output SC spectrum can be tuned to various spectral energy distributions and bandwidths.

  7. Chirp-induced dynamics of femtosecond filaments Rachel Nuter, Stefan Skupin,* and Luc Berg

    E-print Network

    Skupin, Stefan

    the influence of a chirped phase on femtosecond pulses propagating in air. Pulses with an initially negative-power laser pulses self-focus under the Kerr re- sponse of air until their intensity exceeds the ioniza- tion, many practical applications have been suggested, such as lidar remote sensing and lightning protection

  8. Comparison of methods of determining meteoroid range rates from linear frequency modulated chirped pulses

    E-print Network

    Oppenheim, Meers

    frequency modulated (LFM) chirped pulse data from the ALTAIR radar. The first method is based on the simple capability of ALTAIR to solve for range rates based on the difference in the measured ranges due to range, are given for a large set of meteoroid head echoes taken from a data collection conducted with ALTAIR

  9. Effectiveness of nonlinear optical loop mirrors in chirped fiber gratings compensated

    E-print Network

    Wai, Ping-kong Alexander

    in CFGs randomly varies along the transmission line, which includes the amplifier noise in a 40 Gb/s DMJTuC1 Effectiveness of nonlinear optical loop mirrors in chirped fiber gratings compensated dispersion-managed transmission systems Y. H. C. Kwan, t K. Nakkeeran, and P. K. A. Wai Photonics Research

  10. TONE AND CHIRP DETECTION USING SUMS OF CONJUGATE PRODUCTS I. Vaughan L. Clarkson

    E-print Network

    Clarkson, Vaughan

    ] to perform an asymptotic analysis. We compare the performance of the detectors with the en- ergy detector call sums of conjugate products, for the purpose of detecting tones and chirps in noise their asymptotic statistics and compare their discriminating power against the energy detector. We find

  11. The monitoring and multiplexing of fiber optic sensors using chirped laser sources 

    E-print Network

    Wan, Xiaoke

    2004-09-30

    A wide band linearly chirped erbium-doped fiber laser has been developed. The erbium-doped fiber laser using a rotating mirror/grating combination as one of the reflectors in a Fabry-Perot laser cavity has been tuned over a 46 nm spectral range...

  12. Fundamental limitations in the performance of chirped grating lenses on planar optical waveguides

    Microsoft Academic Search

    J.-M. Delavaux; W. S. Chang

    1985-01-01

    The fundamental limitations in the performance of chirped grating lenses on planar optical waveguides caused by diffraction and by fabrication tolerances have been analyzed based on the generalized coupled mode theory (GCMT). The two most crucial lens parameters that affect the performance have been identified as the minimum grating periodicity and the maximum coupling coefficient. They have a strong effect

  13. Spectral and Noise Purity of Coherent Multiple-Frequency Chirp Exciter for L Band Radars

    Microsoft Academic Search

    Tomasz Cegielski; Zdzislaw Sawicki

    2006-01-01

    This paper presents results of spectral analysis and design performance of the up-converter module of the coherent multiple-frequency chirp exciter for long distance L Band surveillance radars. Some measured results of spectral and noise purity of the exciter with coherent frequency synthesizer driven from high stability oscillator source are included. The experimental results are in good agreement with requested values.

  14. Chirped porous silicon reflectors for thin-film epitaxial silicon solar cells

    Microsoft Academic Search

    Izabela J. Kuzma-Filipek; Filip Duerinckx; Emmanuel van Kerschaver; Kris van Nieuwenhuysen; Guy Beaucarne; Jef Poortmans

    2008-01-01

    The studies of porous silicon as a one-dimensional photonic crystal have led to solutions allowing the fabrication of broad photonic band gaps as large as several hundreds nanometers for various types of applications. In this work we demonstrate the use of the chirping process, i.e., the gradual increase in the spatial period of the structure, as it is used in

  15. Optical multi-coset sampling of GHz-band chirped signals

    NASA Astrophysics Data System (ADS)

    Valley, George C.; Sefler, George A.; Shaw, T. J.; Smith, Stephen L.

    2015-03-01

    Direct digitization of long, wideband chirped RF signals in the GHz band requires power hungry ADCs and produces large data sets. Here we present an optical scheme to perform multi-coset sampling of such signals with reduced power consumption and smaller data sets. In our scheme a repetitively pulsed femtosecond laser is dispersed to the interpulse time, the RF is modulated on the optical field, and the field is directed to a pair of wavelength-division demultiplexers (WDM). The channels of the WDM are attenuated with a pseudo-random sequence to form a coset pattern that repeats at the laser repetition rate. After a photodiode, the photocurrent is integrated for the duration of the dispersed optical pulse so that the coset pattern non-uniformly samples the RF signal. Since the laser repetition rate is uncorrelated with the RF, each coset provides an independent measurement of the RF. Experimental and numerical results show that 4 properties of the RF chirp pulse can be determined from the multiple coset samples: carrier frequency, chirp rate, start time, and pulse duration. Results are presented for a 20MHz chirp on a 13 microsecond pulse at a carrier of 2.473 GHz.

  16. Dynamics and performance of hybrid distributed Bragg reflector lasers including a chirped fiber grating

    NASA Astrophysics Data System (ADS)

    Duan, GuangHua; Helmers, H.; Leroy, A.; Brosson, Philippe; Jacquet, Joel

    2002-06-01

    In this work, we report the spectral and modulation characteristics, as well as bit-error-rate performances of stabilized hybrid distributed Bragg reflector lasers including a chirped fiber grating. An original analysis of such lasers based on a modified second order rate equation will also be presented to explain the observed stability behavior.

  17. Proposal of high-yield widely-tunable DBR lasers with equivalent-chirp grating reflectors

    Microsoft Academic Search

    Yitang Dai; Kun Xu; Jian Wu; Yan Li; Xiaobin Hong; Hongxiang Guo; Yong Zuo; Wei Li; Jintong Lin

    2010-01-01

    Equivalent-chirp technology is demonstrated to enable fabrication of flat-top-envelop comb gratings with conventional two-beam-interference lithography, instead of e-beam. Widely-tunable DBR semiconductor lasers using such gratings are studied numerically, showing excellent uniformity and SMSR during tuning.

  18. Characterization of a fiber-optic direct modulation analog link with chirp radar signals

    Microsoft Academic Search

    Rossano Pardini; Umberto Bruno; Roberto Izzo

    2009-01-01

    This paper describes the experimental investigations carried out to evaluate the behaviour of a fiber-optic direct modulation analog link as a substitute of traditional transmission means, like coaxial cables or waveguides, for X-band chirp modulated radar signals. First of all, the link has been completely characterized, and the spurious frequency modulation has been measured in presence of pulsed signals. Afterwards,

  19. Quantum Phenomena in a Chirped Parametric Anharmonic Oscillator I. Barth and L. Friedland

    E-print Network

    Friedland, Lazar

    is the oscillator governed by the Hamiltonian H ¼ p2 2 þ ð1 þ cos Þ x2 2 þ x4 4 ð1Þ (here all variables and parameters are dimensionless). The frequency of the modulation is chirped, d=dt ¼ 2 þ t, passing the linear

  20. Analysis and modeling of click and chirp evoked auditory steady state responses

    Microsoft Academic Search

    Yuce Hekimoglu

    2003-01-01

    This study aims to investigate the possible advantages of using cochlear chirp stimulus instead of click for recording auditory steady-state responses (ASSRs), and to test the validity of the superposition hypothesis for the generation of the ASSRs through simulations, and modeling. Simulation of the ASSRs at different stimulation rates was achieved by shifting and adding of the transient auditory evoked

  1. Past applications and future uses of chirped ISR plasma line observations

    Microsoft Academic Search

    T. Hagfors; B. Isham

    1989-01-01

    The method of chirped incoherent scatter plasma wave observation is described. Applications of the method to the determination of electron density profiles, ionospheric irregularities, electron temperatures, electron gas vertical motion, field aligned currents, and plasma line enhancements caused by photoelectrons and precipitating auroral electrons are discussed. In all of these observations there is a large increase in the signal-to-noise ratio

  2. Fiber optical parametric chirped-pulse amplification in the femtosecond regime

    E-print Network

    Paris-Sud XI, Université de

    . J. Russell, "Continuous-wave tunable optical parametric generation in a photonic-crystal fiber," J to conventional OPCPA operating in bulk crystals, the fiber geometry offers a greater interaction lengthFiber optical parametric chirped-pulse amplification in the femtosecond regime Marc Hanna, Fr

  3. BreezChirp: Energy Efficient Wi-Fi Bandwidth Estimator for Smartphones

    E-print Network

    Boutaba, Raouf

    and Engineering, Hochiminh City University of Technology, Vietnam email: nhatminhhcmut@gmail.com Abstract--Mobile. Index Terms--Energy Saving, Smartphones, Measurement I. INTRODUCTION The proliferation of mobileBreezChirp: Energy Efficient Wi-Fi Bandwidth Estimator for Smartphones Jian Li, Jin Xiao, Huu Nhat

  4. Transform picture coding

    Microsoft Academic Search

    P. A. Wintz

    1972-01-01

    Picture coding by first dividing the picture into sub-pictures and then performing a linear transformation on each sub-picture cud quantizing and coding the resulting coefficients is introduced from a heuristic point of view. Various transformation, quantization, and coding strategies are discussed. A survey of all known applications of these techniques to monochromatic image coding is presented along with a summary

  5. Numerical analysis of the optimal length and profile of a linearly chirped fiber Bragg grating for dispersion compensation

    NASA Astrophysics Data System (ADS)

    Thibault, Simon; Lauzon, Jocelyn; Cliche, Jean-Francois; Martin, Jean; Duguay, Michel A.; Têtu, Michel

    1995-03-01

    We propose a theoretical investigation of the length and coupling profile of a linearly chirped fiber Bragg grating for maximum dispersion compensation in a repeaterless optical communication system. The system consists of 100 km of standard optical fiber in which a 1550-nm signal, directly modulated at 2.5 Gbits / s, is launched. We discuss the results obtained with 6-, 4.33-, and 1-cm-long linearly chirped fiber Bragg gratings having Gaussian and uniform coupling profiles. We numerically show that a 4.33-cm-long chirped fiber Bragg grating having a uniform coupling profile is capable of compensating efficiently for the dispersion of our optical communication system.

  6. Effects of the initial chirp and fibre loss on the soliton mechanism of picosecond pulse compression in optical fibres

    SciTech Connect

    Yang Xingyu; Yang Guangqiang [Department of Physics, Inner Mongolia University, Huhhot (China)

    2001-08-31

    The effect of the initial chirp and fibre loss on the efficiency of soliton-effect picosecond pulse compression are analysed by simulating numerically the transmission of picosecond pulse in fibres by the split-step Fourier method. Analysis of changes in the compression factor, the optimum fibre length, and the compression efficiency showed that the initial chirp and fibre loss affect the compression of a picosecond pulse in opposite ways. A further study revealed that an additional properly created initial chirp provides good pulse compression. (nonlinear optical phenomena)

  7. Relaxed dispersion requirement in the generation of chirped RF signals based on frequency-to-time mapping

    NASA Astrophysics Data System (ADS)

    Xu, Yuxiao; Shi, Zhiguo; Chi, Hao; Jin, Xiaofeng; Zheng, Shilie; Zhang, Xianmin

    2014-11-01

    Photonic generation of chirped RF signal based on frequency-to-time mapping (FTM) is investigated in this paper. A new criterion on system parameters (dispersion amounts and pulse duration) for the generation of well-shaped linearly chirped signals is given, which is proved to be less restrictive than the currently known conditions. Therefore, requirement on the dispersion amount can be relaxed, which is highly desired in practical implementation of the FTM-based system. Theoretical results are presented, the correctness of which is verified by numerical and experimental results. The reported theory is a good guidance in designing the photonic system for the generation of chirped signals based on FTM.

  8. Combined effect of tight-focusing and frequency-chirping on laser acceleration of an electron in vacuum

    SciTech Connect

    Gupta, Devki Nandan; Jang, Hyo Jae; Suk, Hyyong [Advanced Photonics Research Institute (APRI) and School of Photon Science and Technology, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of)

    2009-05-15

    The investigation [Gupta et al., Appl. Phys. Lett. 91, 211101 (2007)] for electron acceleration by a tightly focused laser beam is revisited by including the effect of laser frequency chirping. The frequency chirping plays an important role to enhance the electron energy if the laser is tightly focused. Due to the combined effect of frequency chirping and tight focusing of a laser beam, an electron can be accelerated for a longer time in vacuum. As a result, from the proposed investigation, the electron energy gain during the laser acceleration is found to be considerably higher.

  9. Direct DPSK modulation of chirp-managed laser as cost-effective downstream transmitter for symmetrical 10-Gbit/s WDM PONs.

    PubMed

    Le, Quang Trung; Emsia, Ali; Briggmann, Dieter; Küppers, Franko

    2012-12-10

    This paper proposes the use of chirp-managed lasers (CML) as cost-effective downstream (DS) transmitters for next generation access networks. As the laser bandwidth is as high as 10 GHz, the CML could be directly modulated at 10 Gbit/s for downstream transmission in future wavelength division multiplexing passive optical networks (WDM PON). The laser adiabatic chirp, which is the main drawback limiting the transmission performance of directly modulated lasers, is now utilized to generate phase-shift keying (PSK) modulation format by direct modulation. At the user premise, the wavelength reuse technique based on reflective colorless upstream transmitter is applied. The optical network unit (ONU) reflects and orthogonally remodulates the received light with upstream data. A full-duplex transmission with symmetrical 10-Gbit/s bandwidth is demonstrated. Bit-error-rate measurement showed that optical power budgets of 29 dB at BER of 10(-9) or of 36 dB at BER of 10(-3) could be obtained with direct phase-shift-keying modulation of CML which proves that the proposed solution is a viable candidate for future WDM-PONs. PMID:23262890

  10. Building Climate Service Capacities in Eastern Africa with CHIRP and GeoCLIM

    NASA Astrophysics Data System (ADS)

    Pedreros, D. H.; Magadzire, T.; Funk, C. C.; Verdin, J. P.; Peterson, P.; Landsfeld, M.; Husak, G. J.

    2013-12-01

    In developing countries there is a great need for capacity building within national and regional climate agencies to develop and analyze historical and real time gridded rainfall datasets. These datasets are of key importance for monitoring climate and agricultural food production at decadal and seasonal time scales, and for informing local decision makers. The Famine Early Warning Systems Network (FEWS NET), working together with the U.S. Geological Survey (USGS) and the Climate Hazards Group (CHG) of the University of California Santa Barbara, has developed an integrated set of data products and tools to support the development of African climate services. The core data product is the Climate Hazards Group Infrared Precipitation (CHIRP) dataset. The CHIRP is a new rainfall dataset resulting from the blending of satellite estimated precipitation with high resolution precipitation climatology. The CHIRP depicts rainfall on five day totals at 5km spatial resolution from 1981 to present. The CHG is developing and deploying a standalone tool - the GeoCLIM - which will allow national and regional meteorological agencies to blend the CHIRP with station observations, run simple crop water balance models, and conduct climatological, trend, and time series analysis. Blending satellite estimates and gauge data helps overcome limited in situ observing networks. Furthermore, the GeoCLIM combines rainfall, soil, and evapotranspiration data with crop hydrological requirements to calculate agricultural water balance, presented as the Water Requirement Satisfaction Index (WRSI). The WRSI is a measurement of the degree in which a crop's hydrological requirements have been satisfied by rainfall. We present the results of a training session for personnel of the East African Intergovernmental Authority on Development Climate Prediction and Applications Center. The two week training program included the use of the GeoCLIM to improve CHIRP using station data, and to calculate and analyze trends in rainfall, WRSI, and drought frequency in the region.

  11. Heterodyne technique for measuring the amplitude and phase transfer functions of an optical modulator

    Microsoft Academic Search

    Francis P. Romstad; D. Birkedal; J. Mork; J. A. Hvam

    2002-01-01

    We propose a technique based on heterodyne detection for accurately and simultaneously measuring the amplitude and phase transfer functions of an optical modulator. The technique is used to characterize an InGaAsP multiple quantum-well electroabsorption modulator. From the measurements we derive the small-signal ?-parameter and the time-dependent chirp for different operation conditions

  12. An AWG-based 10 Gbit/s colorless WDM-PON system using a chirp-managed directly modulated laser

    NASA Astrophysics Data System (ADS)

    Latif, Abdul; Yu, Chong-xiu; Xin, Xiang-jun; Husain, Aftab; Hussain, Ashiq; Munir, Abid; Khan, Yousaf

    2012-09-01

    We propose an arrayed waveguide grating (AWG)-based 10 Gbit/s per channel full duplex wavelength division multiplexing passive optical network (WDM-PON). A chirp managed directly modulated laser with return-to-zero (RZ) differential phase shift keying (DPSK) modulation technique is utilized for downlink (DL) direction, and then the downlink signal is re-modulated for the uplink (UL) direction using intensity modulation technique with the data rate of 10 Gbit/s per channel. A successful WDM-PON transmission operation with the data rate of 10 Gbit/s per channel over a distance of 25 km without any optical amplification or dispersion compensation is demonstrated with low power penalty.

  13. Efficiency droop suppression in GaN-based light-emitting diodes by chirped multiple quantum well structure at high current injection

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Kun; Li, Yu-Feng; Huang, Ya-Ping; Wang, Hong; Su, Xi-Lin; Ding, Wen; Yun, Feng

    2015-05-01

    Gallium nitride (GaN) based light-emitting diodes (LEDs) with chirped multiple quantum well (MQW) structures have been investigated experimentally and numerically in this paper. Compared to conventional LEDs with uniform quantum wells (QWs), LEDs with chirped MQW structures have better internal quantum efficiency (IQE) and carrier injection efficiency. The droop ratios of LEDs with chirped MQW structures show a remarkable improvement at 600 mA/mm2, reduced down from 28.6% (conventional uniform LEDs) to 23.7% (chirped MQWs-a) and 18.6% (chirped MQWs-b), respectively. Meanwhile, the peak IQE increases from 76.9% (uniform LEDs) to 83.7% (chirped MQWs-a) and 88.6% (chirped MQWs-b). The reservoir effect of chirped MQW structures is the significant reason as it could increase hole injection efficiency and radiative recombination. The leakage current and Auger recombination of chirped MQW structures can also be suppressed. Furthermore, the chirped MQWs-b structure with lower potential barriers can enhance the reservoir effect and obtain further improvement of the carrier injection efficiency and radiative recombination, as well as further suppressing efficiency droop. Project suppored by the National High Technology Research and Development Program of China (Grant No. 2014AA032608), the Key Laboratory for Mechanical Behavior of Material of Xi’an Jiaotong University, China (Grant No. 20121201), and the Fundamental Research Funds for the Central Universities, China.

  14. Transform coding of images

    NASA Astrophysics Data System (ADS)

    Clarke, R. J.

    The theoretical and practical aspects of transform coding systems for processing still or moving images are discussed. Among the specific topics considered are: the statistical properties of images; orthogonal transforms for image coding; and transform coefficient quantization and bit allocation. Some practical methods of image coding are described, including: interframe coding; intraframe coding; and transform coding of color data. The application of human visual models to the assessment of image quality is also discussed. Techniques for measuring rms error in coded images are given in an appendix.

  15. Chloroplast transformation.

    PubMed

    Lu, Xiao-Mei; Yin, Wei-Bo; Hu, Zan-Min

    2006-01-01

    In this chapter we briefly review the developmental history and current research status of chloroplast transformation and introduce the merits of chloroplast transformation as compared with the nuclear genome transformation. Furthermore, according to the chloroplast transformation achieved in oilseed rape (Brassica napus), we introduce the preparation of explants, transformation methods, system selection, identification methods of the transplastomic plants, and experimental results. The technical points, the bottleneck, and the further research directions of the chloroplast transformation are discussed in the notes. PMID:16673924

  16. 660 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 3, MARCH 2005 Optical Generation of Linearly Chirped Microwave

    E-print Network

    Horowitz, Moshe

    fiber or by using a fiber Bragg grating (FBG). The FBG was used to generate pulses with a constant optical delay line. AT is an attenuator. FBG1 and FBG2 are chirped FBGs. can be much broader than can

  17. Pulse chirping and ionization of O2 molecules for the filamentation of femtosecond laser pulses in air

    NASA Astrophysics Data System (ADS)

    Nuter, Rachel; Bergé, Luc

    2006-05-01

    We examine two analytical models describing the photoionization of O2 molecules in both tunnel and multiphoton regimes. Applying these models to the nonlinear propagation of chirped laser beams in the atmosphere, we demonstrate how chirp phases can be used as a tool to monitor the self-guiding range of femtosecond filaments or even to shorten the pulse duration. The good agreement between simulations and experimental measurements validates our numerical code for ultrashort-pulse propagation in air.

  18. Performance limitations of an optical RZ-DPSK transmission system affected by frequency chirp, chromatic dispersion and polarization mode dispersion

    Microsoft Academic Search

    Lazhar Kassa-Baghdouche; Lotfy Mokhtar Simohamed

    2011-01-01

    The performance limitations due to the combined effects of frequency chirp and CD or PMD in a 40 Gbit\\/s optical Return-to-Zero Differential Phase-Shift-Keying (RZDPSK) transmission system are numerically simulated. By means of numerical simulations, we optimize the bandwidths of the optical and electrical receiver’s filters. Then, the impact of the Chirp factor (C) on the Bit Error Rate (BER) performance

  19. A new and efficient theoretical model to analyze chirped grating distributed feedback lasers

    NASA Astrophysics Data System (ADS)

    Arif, Muhammad

    Threshold conditions of a distributed feedback (DFB) laser with a linearly chirped grating are investigated using a new and efficient method. DFB laser with chirped grating is found to have significant effects on the lasing characteristics. The coupled wave equations for these lasers are derived and solved using a power series method to obtain the threshold condition. A Newton- Raphson routine is used to solve the threshold conditions numerically to obtain threshold gain and lasing wavelengths. To prove the validity of this model, it is applied to both conventional index-coupled and complex- coupled DFB lasers. The threshold gain margins are calculated as functions of the ratio of the gain coupling to index coupling (|?g|/|? n|), and the phase difference between the index and gain gratings. It was found that for coupling coefficient |?|l < 0.9, the laser shows a mode degeneracy at particular values of the ratio |? g|/|?n|, for cleaved facets. We found that at phase differences ?/2 and 3?/2, between the gain and index grating, for an AR-coated complex-coupled laser, the laser becomes multimode and a different mode starts to lase. We also studied the effect of the facet reflectivity (both magnitude and phase) on the gain margin of a complex- coupled DFB laser. Although, the gain margin varies slowly with the magnitude of the facet reflectivity, it shows large variations as a function of the phase. Spatial hole burning was found to be minimum at phase difference n?, n = 0, 1, ... and maximum at phase differences ?/2 and 3?/2. The single mode gain margin of an index-coupled linearly chirped CG-DFB is calculated for different chirping factors and coupling constants. We found that there is clearly an optimum chirping for which the single mode gain margin is maximum. The gain margins were calculated also for different positions of the cavity center. The effect of the facet reflectivities and their phases on the gain margin was investigated. We found the gain margin is maximum and the Spatial Hole Burning (SHB) is minimum for the cavity center at the middle of the laser cavity. Effect of chirping on the threshold gain, gain margin and spatial hole burning (SHB) for different parameters, such as the coupling coefficients, facet reflectivities, etc., of these lasers are studied. Single mode yield of these lasers are calculated and compared with that of a uniform grating DFB laser.

  20. Deriving Criteria-supporting Benchmark Values from Empirical Response Relationships: Comparison of Statistical Techniques and Effect of Log-transforming the Nutrient Variable

    EPA Science Inventory

    In analyses supporting the development of numeric nutrient criteria, multiple statistical techniques can be used to extract critical values from stressor response relationships. However there is little guidance for choosing among techniques, and the extent to which log-transfor...

  1. Generalized Transforms and Special Functions

    E-print Network

    G. Dattoli; E. Sabia

    2010-10-08

    We study the properties of different type of transforms by means of operational methods and discuss the relevant interplay with many families of special functions. We consider in particular the binomial transform and its generalizations. A general method, based on the use of the Fourier transform technique, is proposed for the study of the properties of functions of operators.

  2. The response of phospholipid-encapsulated microbubbles to chirp-coded excitation: Implications for high-frequency nonlinear imaging

    PubMed Central

    Shekhar, Himanshu; Doyley, Marvin M.

    2013-01-01

    The current excitation strategy for harmonic and subharmonic imaging (HI and SHI) uses short sine-bursts. However, alternate pulsing strategies may be useful for enhancing nonlinear emissions from ultrasound contrast agents. The goal of this study was to corroborate the hypothesis that chirp-coded excitation can improve the performance of high-frequency HI and SHI. A secondary goal was to understand the mechanisms that govern the response of ultrasound contrast agents to chirp-coded and sine-burst excitation schemes. Numerical simulations and acoustic measurements were conducted to evaluate the response of a commercial contrast agent (Targestar-P®) to chirp-coded and sine-burst excitation (10?MHz frequency, peak pressures 290 kPa). The results of the acoustic measurements revealed an improvement in signal-to-noise ratio by 4 to 14?dB, and a two- to threefold reduction in the subharmonic threshold with chirp-coded excitation. Simulations conducted with the Marmottant model suggest that an increase in expansion-dominated radial excursion of microbubbles was the mechanism responsible for the stronger nonlinear response. Additionally, chirp-coded excitation detected the nonlinear response for a wider range of agent concentrations than sine-bursts. Therefore, chirp-coded excitation could be a viable approach for enhancing the performance of HI and SHI. PMID:23654417

  3. Laboratory demonstrations of interferometric and spotlight synthetic aperture ladar techniques.

    PubMed

    Crouch, Stephen; Barber, Zeb W

    2012-10-22

    A variety of synthetic-aperture ladar (SAL) imaging techniques are investigated on a table-top laboratory setup using an ultra-broad bandwidth (>3 THz) actively linearized chirp laser centered at 1.55 microns. Stripmap and spotlight mode demonstrations of SAL in monstatic and bistatic geometries are presented. Interferometric SAL for 3D topographical relief imaging is demonstrated highlighting the coherent properties of the SAL imaging technique. PMID:23187186

  4. CSR Interaction for a 2D Energy-Chirped Bunch on a General Orbit

    SciTech Connect

    Rui Li

    2009-05-01

    When an electron bunch with initial linear energy chirp traverses a bunch compression chicane, the bunch interacts with itself via coherent synchrotron radiation (CSR) and space charge force. The effective longitudinal CSR force for such kind of 2D bunch on a circular orbit has been analyzed earlier [1]. In this paper, we present the analytical results of the effective longitudinal CSR force for a 2D energy-chirped bunch going through a general orbit, which includes the entrance and exit of a circular orbit. In particular, we will show the behavior of the force in the last bend of a chicane when the bunch is under extreme compression. This is the condition when bifurcation of bunch phase space occurs in many CSR measurements. [1] R. Li, Phys. Rev. ST Accel. Beams 11, 024401 (2008)

  5. Making ultracold molecules in a two-color pump-dump photoassociation scheme using chirped pulses

    SciTech Connect

    Koch, Christiane P. [Laboratoire Aime Cotton, CNRS, Bat. 505, Campus d'Orsay, 91405 Orsay Cedex (France); Department of Physical Chemistry and Fritz Haber Research Center, Hebrew University, Jerusalem 91904 (Israel); Luc-Koenig, Eliane; Masnou-Seeuws, Francoise [Laboratoire Aime Cotton, CNRS, Bat. 505, Campus d'Orsay, 91405 Orsay Cedex (France)

    2006-03-15

    This theoretical paper investigates the formation of ground state molecules from ultracold cesium atoms in a two-color scheme. Following previous work on photoassociation with chirped picosecond pulses [Luc-Koenig et al., Phys. Rev. A, 70, 033414 (2004)], we investigate stabilization by a second (dump) pulse. By appropriately choosing the dump pulse parameters and time delay with respect to the photoassociation pulse, we show that a large number of deeply bound molecules are created in the ground triplet state. We discuss (i) broad-bandwidth dump pulses which maximize the probability to form molecules while creating a broad vibrational distribution as well as (ii) narrow-bandwidth pulses populating a single vibrational ground state level, bound by 113 cm{sup -1}. The use of chirped pulses makes the two-color scheme robust, simple, and efficient.

  6. Cluster explosion investigated by linearly chirped spectral scattering of an expanding plasma sphere

    SciTech Connect

    Liu Jiansheng; Wang Cheng; Liu Bingchen; Shuai Bin; Wang Wentao; Cai Yi; Li Hongyu; Ni Guoquan; Li Ruxin; Xu Zhizhan [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800 (China)

    2006-03-15

    Femtosecond explosive processes of argon clusters irradiated by linearly chirped ultraintense laser pulses have been investigated by 90 deg. side spectral scattering. The spectral redshift and blueshift, which correlate with the cluster explosion processes have been measured for negatively and positively chirped driving laser pulses, respectively. The evolution of the heated-cluster polarizability indicates that the core of the cluster is shielded from the laser field in the beginning of the explosion and enhanced scattering occurs after the fast explosion initiates. Evidence of resonant heating is found from the coincidence of enhanced scattering with enhanced absorption measured using the transmitted spectra. Anomalously large-size clusters with very low gas density have been observed in this way and can be used as clean and important cluster targets.

  7. 1.5 ?m asymmetric Fabry-Perot modulators with two distinct modulation and chirp characteristics

    NASA Astrophysics Data System (ADS)

    Yoo, S. J. B.; Koza, M. A.; Bhat, Raj; Caneau, Catherine

    1998-06-01

    This letter discusses the design and the realization of asymmetric Fabry-Perot modulators with InP/InGaAsP distributed Bragg reflectors and 80 AlInGaAs quantum wells. We demonstrate two types of modulators utilizing two different top reflectors: an InP to air interface and a Si/SiO2/Si coating. The first modulator showed a monotonic reduction in the reflectivity as the bias voltage increased, and achieved a 2.2 dB insertion loss and a 15 dB contrast ratio at the resonant wavelength. The second modulator showed an initial reduction and then an increase in the reflectivity as the bias changed from 0 to -10 V. The chirp calculation based on the measured data reveals that the second modulator exhibits two distinct positive and negative chirp characteristics.

  8. Highly chirped single-bandpass microwave photonic filter with reconfiguration capabilities.

    PubMed

    Bolea, Mario; Mora, José; Ortega, Beatriz; Capmany, José

    2011-02-28

    We propose a novel photonic structure to implement a chirped single-bandpass microwave photonic filter based on the amplitude modulation of a broadband optical signal transmitted by a non-linear dispersive element and an interferometric system prior to balanced photodetection. A full reconfigurability of the filter is achieved since amplitude and phase responses can be independently controlled. We have experimentally demonstrated chirp values up to tens of ns/GHz, which is, as far as we know, one order of magnitude better than others achieved by electrical approaches and furthermore, without restrictions in terms of frequency tuning since a frequency operation range up to 40 GHz has been experimentally demonstrated. PMID:21369289

  9. Study on the influence of dispersion and chirp on femtosecond Airy pulse propagation in Kerr media

    NASA Astrophysics Data System (ADS)

    Song, Zhenming; Lin, Yuxian

    2015-05-01

    We present the influence of second order dispersion(GVD), third-order dispersion(TOD), and initial chirp on femtosecond Airy pulse propagation in Kerr media by solving the Nonlinear Schrodinger Equation with the split-step Fourier Method. In the time duration of femtosecond pulse, the effect of TOD should not be neglected. TOD can lead to waveform distortion and lower the quality of optical pulses. We also study the propagation of femtoscond Airy pulse in anomalous dispersion Kerr media. According to the numerical results, we show that when the parameter of the TOD and the propagation distance are selected as some typical values, the pulses will broadening first and then appear a process of compression. Finally, we discussed the influence of the initial pulse chirp on the propagation of the pulse profile and broadening factor.

  10. All optical quantum storage based on spatial chirp of the control field

    E-print Network

    Xiwen Zhang; Alexey Kalachev; Olga Kocharovskaya

    2014-10-21

    We suggest an all-optical quantum memory scheme which is based on the off-resonant Raman interaction of a signal quantum field and a strong control field in a three-level atomic medium in the case, when the control field has a spatially varying frequency across the beam, called a spatial chirp. We show that the effect of such a spatial chirp is analogous to the effect of a controllable reversible inhomogeneous broadening (CRIB) of the atomic transition used in the gradient echo memory (GEM) scheme. However, the proposed scheme does not require temporal modulation of the control field or the atomic levels, and can be realized without additional electric or magnetic fields. It means that materials demonstrating neither linear Stark nor Zeeman effects can be used and/or materials which are placed in specific external fields remain undisturbed.

  11. Single sub-50-attosecond pulse generation from chirp-compensated harmonic radiation using material dispersion

    SciTech Connect

    Kim, Kyung Taec; Kim, Chul Min; Umesh, G.; Nam, Chang Hee [Department of Physics and Coherent X-ray Research Center, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of); Baik, Moon-Gu [Department of Physics, Kyungwon University, Seongnam, Gyeonggi-do 461-701 (Korea, Republic of)

    2004-05-01

    A method for obtaining a single sub-50-attosecond pulse using harmonic radiation is proposed. For the generation of broad harmonic radiation during a single half-optical cycle, atoms are driven by a femtosecond laser pulse with intensity above the saturation intensity for optical field ionization and hence experience a large nonadiabatic increase of the laser electric field between optical cycles. Although the chirped structure of the harmonic radiation imposes a limit on the minimum achievable pulse duration, we demonstrate that its positive chirp can be compensated by the negative group delay dispersion of an appropriately selected x-ray filter material, used also for the spectral selection, resulting in a single attosecond pulse with a duration less than 50 as.

  12. Short-Circuit Current Densities Exceeding 30 by Use of Chirped Porous-Silicon Reflectors and Shallow Emitters in Thin-Film (20- ) Epitaxial Silicon Solar Cells

    Microsoft Academic Search

    Izabela Kuzma-Filipek; Kris Van Nieuwenhuysen; Jan Van Hoeymissen; Guy Beaucarne; Emmanuel Van Kerschaver; Jef Poortmans; Robert Mertens

    2009-01-01

    We demonstrate the use of chirped porous-silicon broadband optical reflectors for thin-film epitaxial silicon solar cells. The benefits of chirped multilayer structures over conventional Bragg reflectors on the cell level are presented. By combining these chirped reflectors with shallow emitters, we show that both low- and high-energy photons are more effectively absorbed in the thin (20-mum ) epitaxial active layer

  13. High average power and energetic femtosecond fiber laser using chirped- and divided-pulse amplification

    NASA Astrophysics Data System (ADS)

    Zaouter, Yoann; Guichard, Florent; Hanna, Marc; Morin, Franck; Hönninger, Clemens; Druon, Frédéric; Mottay, Eric; Georges, Patrick

    2014-03-01

    We implement, in the same femtosecond fiber amplifier setup, both chirped pulse amplification and divided pulse amplification. With the generation of temporally delayed replicas this scheme allows an equivalent stretched pulse duration of more than 1ns in a compact tabletop system. The generation of 45 W of compressed average power at 100 kHz, together with 320 fs and 450 ?J pulses, is demonstrated using a rod-type ytterbium-doped fiber.

  14. Impact of Mach-Zehnder Modulator Chirp on Radio over Fiber Links

    Microsoft Academic Search

    Xiaogang Chen; Shengqin Feng; Dexiu Huang

    2009-01-01

    The impact of Mach-Zehnder modulator (MZM) chirp on single sideband (SSB) and carrier suppressed double sideband (CS-DSB)\\u000a modulation radio over fiber (RoF) links are investigated and simulated. Finite extinction ratio and drive signal unbalanced\\u000a ratio of non-ideal MZM are considered, power variation of target microwave signal and harmonic suppression are calculated\\u000a and evaluated. Our results suggest that unbalanced ratio could

  15. Spectral broadening and self-compression of negatively chirped visible femtosecond pulses in fused silica

    SciTech Connect

    Aristov, A I; Grudtsyn, Ya V; Mikheev, L D; Polivin, A V; Stepanov, S G; Trofimov, V A; Yalovoi, V I

    2012-12-31

    This paper describes a new effect: spectral broadening and self-compression of negatively chirped visible femtosecond pulses as a result of nonlinear interaction of large-aperture beams with fused silica. We assume that the likely mechanism of the observed spectral broadening is the combined effect of self-phase modulation and four-wave mixing. (special issue devoted to the 90th anniversary of n.g. basov)

  16. Electro-optic measurement of THz field pulses with a chirped optical beam

    Microsoft Academic Search

    Zhiping Jiang; X.-C. Zhang

    1998-01-01

    Using a linearly chirped optical probe pulse in free-space electro-optic measurements, a temporal wave form of a co-propagating THz field is linearly encoded onto the frequency spectrum of the optical probe pulse, and then decoded by dispersing the probe beam from a grating to a detector array. We achieve acquisition of picosecond THz field pulses without using mechanical time-delay device.

  17. Experimental validation of a linear model for data reduction in Chirp-Pulse microwave CT

    Microsoft Academic Search

    M. Miyakawa; K. Orikasa; M. Bertero; P. Boccacci; F. Conte; M. Piana

    2002-01-01

    Chirp-pulse microwave computerized tomography (CP-MCT) is an imaging modality developed at the Department of Biocybernetics, University of Niigata (Niigata, Japan), which intends to reduce the microwave-tomography problem to an X-ray-like situation. We have recently shown that data acquisition in CP-MCT can be described in terms of a linear model derived from scattering theory. In this paper, we validate this model

  18. Open-path sensor for atmospheric methane based on chirped laser dispersion spectroscopy

    NASA Astrophysics Data System (ADS)

    Nikodem, Michal; Plant, Genevieve; Sonnenfroh, David; Wysocki, Gerard

    2015-04-01

    The design and characterization of a near-IR Chirped Laser Dispersion Spectroscopy (CLaDS) sensor for atmospheric methane detection are reported. The near-IR CLaDS system exhibits the benefits of the prior mid-IR CLaDS systems implemented for open-path sensing while taking advantage of the robust fiber-optic components available in the near-IR. System noise, long-term stability, and comparison with existing technology for methane detection are presented.

  19. Longitudinal mode control of an erbium ring fibre laser containing an intracavity chirped Bragg grating etalon

    NASA Astrophysics Data System (ADS)

    Forster, R. J.; Langford, N.; Gloag, A.; Zhang, L.; Williams, J. A. R.; Bennion, I.

    1997-02-01

    We present preliminary data which show that it is possible to prevent longitudinal mode hops in a unidirectional erbium ring fibre laser by including an all fibre etalon formed from chirped fibre Bragg reflectors. A reduction in the relative intensity noise of ˜ 10 dB is observed when the laser is frequency stabilised. A resolution limited linewidth of 170 kHz is observed from the laser.

  20. Wavelength-division multiplexing isolation filter using concatenated chirped long period gratings

    NASA Astrophysics Data System (ADS)

    Das, Mini; Thyagarajan, Krishna

    2001-09-01

    We propose the use of concatenated chirped long period gratings as an efficient wavelength-division multiplexing (WDM) isolation filter. The proposed filter not only works in the transmission mode but also has almost equispaced pass bands with high isolation at the stop bands. The filter has negligible dispersion effects in the pass band, which should make such a device suitable for use in WDM fiber optic communication links.

  1. FY07 LDRD Final Report Precision, Split Beam, Chirped-Pulse, Seed Laser Technology

    Microsoft Academic Search

    J W Dawson; M J Messerly; H H Phan; J K Crane; R J Beach; C W Siders; C J Barty

    2009-01-01

    The goal of this LDRD ER was to develop a robust and reliable technology to seed high-energy laser systems with chirped pulses that can be amplified to kilo-Joule energies and recompressed to sub-picosecond pulse widths creating extremely high peak powers suitable for petawatt class physics experiments. This LDRD project focused on the development of optical fiber laser technologies compatible with

  2. Space weather and HF propagation along different paths of the Russian chirp sounders network

    Microsoft Academic Search

    V. I. Kurkin; G. I. Litovkin; S. M. Matyushonok; G. G. Vertogradov; V. A. Ivanov; I. N. Poddelsky; S. V. Rozanov; V. P. Uryadov

    2004-01-01

    This paper presents experimental data obtained on long paths (from 2200 km to 5700 km range) of Russian frequency modulated continues wave (chirp) sounders network for the period from 1998 to 2003. Four transmitters (near Magadan, Khabarovsk, Irkutsk, Norilsk) and four receivers (near Irkutsk, Yoshkar-Ola, Nizhny Novgorod, Rostov-on-Don) were combined into single network to investigate a influence of geomagnetic storms

  3. Chirping a two-photon transition in a multi-state ladder

    E-print Network

    Wolfgang Merkel; Holger Mack; Wolfgang P. Schleich; Eric Lutz; Gerhard G. Paulus; Bertrand Girard

    2007-02-13

    We consider a two-photon transition in a specific ladder system driven by a chirped laser pulse. In the weak field limit, we find that the excited state probability amplitude arises due to interference of multiple quantum paths which are weighted by quadratic phase factors. The excited state population has the form of a Gauss sum which plays a prominent role in number theory.

  4. Measurement and characterization of laser chirp of multiquantum-well distributed-feedback lasers

    Microsoft Academic Search

    Eva Peral; Amnon Yariv

    1999-01-01

    Measurements of relative intensity noise and modulation response, before and after propagation in optical fiber, of the output field of multiquantum-well distributed-feedback (MQW-DFB) lasers are used to determine the influence of the intraband damping mechanisms, the DFB structure and the carrier transport and carrier capture into the QWs on the laser chirp. The power dependence of the linewidth enhancement factor

  5. Optical equalization to combat the effects of laser chirp and fiber dispersion

    Microsoft Academic Search

    LEONARD J. CIMINI; L. J. Greenstein; A. A. M. Saleh

    1990-01-01

    Optical equalizers capable of combating the effects of laser chirp and fiber chromatic dispersion on high-speed long-haul fiber-optic communication links at 1.5 ?m are described. They consist of both reflective and transmissive cavity structures. The equalizers are adaptive in the sense that the position of their periodic frequency responses are optimally adjusted in real time. The equalizers are evaluated by

  6. Short-term transformation and long-term replacement of branchial chloride cells in killifish transferred from seawater to freshwater, revealed by morphofunctional observations and a newly established 'time-differential double fluorescent staining' technique.

    PubMed

    Katoh, Fumi; Kaneko, Toyoji

    2003-11-01

    Short- and long-term responses to direct transfer from seawater to freshwater were examined in gill chloride cells of killifish, which developed distinct freshwater- and seawater-type chloride cells in the respective environments. In a short-term response within 24 h after transfer, seawater-type chloride cells forming a pit structure on the apical surface were transformed into freshwater-type cells equipped with developed microvilli on the flat or projecting apical membrane, via the intermediate type. The transformation process was accompanied by the disappearance of apically located Cl- channel (cystic fibrosis transmembrane conductance regulator) and neighboring accessory cells. Chloride cell replacement was also examined as a long-term adaptation to freshwater transfer, using a newly established 'time-differential double fluorescent staining (TDS)' technique. In the TDS technique, in vivo labeling of chloride cells was performed on two separate days, using two distinguishable mitochondria-specific fluorescent probes. For 3 days after freshwater transfer, 14.7% of seawater-type cells were replaced with newly differentiated freshwater-type cells, whereas these ratios of chloride cell replacement were much lower (1.2% and 1.8%) in seawater- and freshwater-maintained groups, respectively. In consequence, following direct transfer of killifish from seawater to freshwater, seawater-type chloride cells were transformed morphologically and functionally into freshwater-type cells as a short-term response, followed by the promotion of chloride cell replacement as a long-term response. PMID:14555751

  7. Reconfigurable optical-force-drive chirp and delay line in micro- or nanofiber Bragg grating

    NASA Astrophysics Data System (ADS)

    Luo, Wei; Xu, Fei; Lu, Yan-qing

    2015-05-01

    The emergence of optical micro- or nanofibers (MNFs) with subwavelength diameter, which have ultralight mass and an intense light field, provides an opportunity for developing fiber-based optomechanical systems. In this study we show theoretically an optomechanical effect in silica MNF Bragg gratings (MNFBGs). The light-induced mechanical effect results in continuously distributed strain along the grating and the power-related strain introduces an optically reconfigurable chirp in the grating period. We develop optomechanical coupled-mode equations and analyze theoretically the influence of the optical-force-induced nonlinearity and chirp on the grating performance. Compared with the weak Kerr effect, the optomechanical effect dominates in the properties' evolution of MNFBGs. Significant group-velocity reduction and switching effect have been demonstrated theoretically at medium power level. This kind of optomechanical MNFBG with optically reconfigurable chirp may offer a path toward an all-optical tunable bandwidth of Bragg resonance and may lead to useful applications such as all-optical switching, optically controlled dispersion, and slow or fast light.

  8. Study of nonlinear propagation of chirped optical pulses in laser amplifying medium

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaohong; Gao, Xiaorong; Wang, Li; Wang, Zeyong; Luo, Bin; Li, Jinlong

    2012-10-01

    In chirped pulse amplification, the amplification of an optical pulse in laser amplifying medium is a very important link. After considering dispersion, Kerr nonlinear effect, gain distribution and loss of the medium, the physical model that the optical pulse propagates in the medium has been established, which is suitable for the general situation where the optical pulse propagates in the amplifying medium. Using a split-step Fourier method, the propagation state of a chirped optical pulse in the amplifying medium has been numerically simulated, and the influences of the gain dispersion of the medium and the frequency detuning of the pulse on the optical pulse have been discussed emphatically. The results show that, with the amplification and propagation of the ultrashort chirped pulse in the amplifying medium, gain saturation and Kerr nonlinear effect of the medium will cause distortion of the optical pulse. For the optical pulse with a wideband spectrum, gain dispersion will cause the gain narrowing effect, so it is equivalent to a loss mechanism. The frequency detuning of the optical pulse will cause distortion of the pulse, which can be used to weaken the impact of gain saturation, thus reshaping the optical pulse.

  9. Chirp-pulse-compression three-dimensional lidar imager with fiber optics.

    PubMed

    Pearson, Guy N; Ridley, Kevin D; Willetts, David V

    2005-01-10

    A coherent three-dimensional (angle-angle-range) lidar imager using a master-oscillator-power-amplifier concept and operating at a wavelength of 1.5 microm with chirp-pulse compression is described. A fiber-optic delay line in the local oscillator path enables a single continuous-wave semiconductor laser source with a modulated drive waveform to generate both the constant-frequency local oscillator and the frequency chirp. A portion of this chirp is gated out and amplified by a two-stage fiber amplifier. The digitized return signal was compressed by cross correlating it with a sample of the outgoing pulse. In this way a 350-ns, 10-microJ pulse with a 250-MHz frequency sweep is compressed to a width of approximately 8 ns. With a 25-mm output aperture, the lidar has been used to produce three-dimensional images of hard targets out to a range of approximately 2 km with near-diffraction-limited angular resolution and submeter range resolution. PMID:15678779

  10. A novel symmetric 10 Gbit/s architecture with a single feeder fiber for WDM-PON based on chirp-managed laser

    NASA Astrophysics Data System (ADS)

    Hussain, Aftab; Xin, Xiang-jun; Latif, Abdul; Hussain, Ashiq; Yu, Chong-xiu; Munir, Abid; Khan, Yousaf; Afridi, Muhammad Idrees

    2012-11-01

    We propose the single feeder fiber architecture for wavelength division multiplexing passive optical network (WDM-PON) based on directly modulated chirp managed laser (CML). The downlink (DL) signal output from the laser is converted to return-to-zero (RZ) differential phase shift signal using a pulse carver. The downstream signal is reused as a carrier for the upstream using intensity modulation technique. Simulation results show the error-free performance at symmetric data rate of 10 Gbit/s per channel with negligible power penalty and improved receiver sensitivity for the uplink (UL), over 25 km standard single-mode fiber (SSMF). A low-cost and reduced circuitry network design is implemented on a single feeder fiber with the elimination of differential encoder and one external modulator.

  11. IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 47, NO. 7, JULY 1999 1309 Photonic Time Stretch and Its Application

    E-print Network

    Jalali. Bahram

    -stretch preprocessor and a 1-Gsample/s electronic ADC is demonstrated. This technique is promising for A/D conversion-to-digital conversion, chirp pulses, mode-locked laser, time stretching. I. INTRODUCTION IT IS WIDELY recognizedIEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 47, NO. 7, JULY 1999 1309 Photonic Time

  12. APPLICATION OF PULSE COMPRESSION SIGNAL PROCESSING TECHNIQUES TO ELECTROMAGNETIC ACOUSTIC TRANSDUCERS (EMATS) FOR NON-CONTACT THICKNESS MEASUREMENTS AND IMAGING

    Microsoft Academic Search

    T. H. Gan; K. S. Ho; D. A. Hutchins; D. R. Billson

    A pair of non-contact EMATs has been used for thickness measurements and imaging of metallic plates. This was performed using wide bandwidth EMATs and pulse- compression signal processing techniques, using chirp excitation. This gives a greatly improved Signal to Noise Ratio (SNR) for non-contact experiments, increasing the speed of data acquisition. A numerical simulation of the technique has confirmed the

  13. Intelligent Transformer Monitoring System Utilizing Neuro-Fuzzy

    E-print Network

    Intelligent Transformer Monitoring System Utilizing Neuro-Fuzzy Technique Approach Intelligent Center Intelligent Transformer Monitoring System Utilizing Neuro-Fuzzy Technique Approach Final Project neuro-fuzzy techniques is used for non-linear system identification, output estimation, and fault

  14. Using a surface-sensitive chemical probe and a bulk structure technique to monitor the ?- to ?-Al2O3 phase transformation

    SciTech Connect

    Kwak, Ja Hun; Peden, Charles HF; Szanyi, Janos

    2011-06-30

    In this work, we investigated the phase transformation of ? Al2O3 to ? Al2O3 by ethanol TPD and XRD. Ethanol TPD showed remarkable sensitivity toward the surface structures of the aluminas studied. Maximum desorption rates for the primary product of ethanol adsorption, ethylene, were observed at 225°C, 245°C and 320°C over ?-, ?-, and ?-Al2O3, respectively. Ethanol TPD over a ? Al2O3 sample calcined at 800 °C clearly show that the surface of the resulting material possesses ?-alumina characteristics, even though only the ?-alumina phase was detected by XRD. These results strongly suggest that the ?-to-? phase transformation of alumina initiates at oxide particle surfaces. The results obtained are also consistent with our previous finding that the presence of penta-coordinated Al3+ sites, formed on the (100) facets of the alumina surface, are strongly correlated with the thermal stability of ?-alumina.

  15. Improved techniques for measuring physical and chemical transformations in the atmosphere: observations of pollution transport, wind shear, and profile evolution using controlled meteorological balloons

    Microsoft Academic Search

    P. B. Voss; R. A. Zaveri; C. M. Berkowitz; E. E. Riddle; R. W. Talbot; A. Stohl; D. Holcombe; T. Hartley

    2005-01-01

    Controlled Meteorological (CMET) balloons are small altitude-controlled platforms that can be commanded via satellite to perform soundings, track constant-level, adiabatic, or terrain-following trajectories, or target specific layers in the atmosphere. During the International Consortium for Atmospheric Research on Transport and Transformations (ICARTT) campaign in 2004 and Southeast Texas Tetroon Study (SETTS) in 2005, CMET balloons were used to study the

  16. Monolithic optical parametric oscillator using chirped quasi-phase matching

    E-print Network

    , 2007 We describe a highly efficient monolithic, Q-switched, nanosecond optical parametric oscillator ranging, three-dimensional laser terrain mapping, and burst-illumination imaging, which require pulse burst-illumination techniques [3], and both can be implemented at microjoule levels [1­3]. In burst

  17. Transformation of Yeast

    Microsoft Academic Search

    Albert Hinnen; James B. Hicks; Gerald R. Fink

    1978-01-01

    A stable leu2- yeast strain has been transformed to LEU2+ by using a chimeric ColE1 plasmid carrying the yeast leu2 gene. We have used recently developed hybridization and restriction endonuclease mapping techniques to demonstrate directly the presence of the transforming DNA in the yeast genome and also to determine the arrangement of the sequences that were introduced. These studies show

  18. Clinical evaluation of chirp-coded excitation in medical ultrasound

    Microsoft Academic Search

    Morten H. Pedersen; Thanassis X. Misaridis; Jørgen A. Jensen

    2003-01-01

    Despite the enormous development in medical ultrasound (US) imaging over the last decades, penetration depth with satisfying image quality is often a problem in clinical practice. Coded excitation, used for years in radar techniques to increase signal-to-noise ratio (SNR), has recently been introduced in medical US scanning. In the present study, coded excitation using frequency-modulated US signals is implemented and

  19. transformations: representations

    E-print Network

    Nguyen, Dat H.

    Overview 1. Number transformations: from one base to another 2. Integer representations 3. Real rate, caches... #12; ECS 50, Discussion on 4/25 2 Integer Transformation: From Decimal to Binary Let, Discussion on 4/25 3 Integer Transformation: From Binary to Decimal Compute the weight of each digit position

  20. Transformation Composition

    E-print Network

    Drewes, Frank

    Proc. AGTIVE'99, to appear in LNCS Graph Transformation Modules and their Composition ? Frank,knirsch,kreo,kuskeg@informatik.uni-bremen.de Abstract. In this paper, we investigate the notion of transformation modules as a structuring principle. Based on the notion of transformation units, a concept that allows to specify binary relations on graphs

  1. Optical coordinate transformations.

    PubMed

    Davidson, N; Friesem, A A; Hasman, E

    1992-03-10

    A novel technique for designing holographic optical elements that can perform general types of coordinate transformation is presented. The design is based on analytic ray-tracing techniques for finding the grating vector of the element, from which the holographic grating function is obtained as a solution of a Poissonlike equation. The grating function can be formed either as a computer-generated or as a computer-originated hologram. The design and realization procedure are illustrated for a specific holographic element that performs a logarithmic coordinate transformation on two-dimensional patterns. PMID:20720723

  2. Statistical denoising of signals in the S-transform domain

    NASA Astrophysics Data System (ADS)

    Weishi, Man; Jinghuai, Gao

    2009-06-01

    In this paper, the denoising of stochastic noise in the S-transform (ST) and generalized S-transform (GST) domains is discussed. First, the mean power spectrum (MPS) of white noise is derived in the ST and GST domains. The results show that the MPS varies linearly with the frequency in the ST and GST domains (with a Gaussian window). Second, the local power spectrum (LPS) of red noise is studied by employing the Monte Carlo method in the two domains. The results suggest that the LPS of Gaussian red noise can be transformed into a chi-square distribution with two degrees of freedom. On the basis of the difference between the LPS distribution of signals and noise, a denoising method is presented through hypothesis testing. The effectiveness of the method is confirmed by testing synthetic seismic data and a chirp signal.

  3. Structures of storage-induced transformation products of the beer's bitter principles, revealed by sophisticated NMR spectroscopic and LC-MS techniques.

    PubMed

    Intelmann, Daniel; Kummerlöwe, Grit; Haseleu, Gesa; Desmer, Nina; Schulze, Kerstin; Fröhlich, Roland; Frank, Oliver; Luy, Burkhard; Hofmann, Thomas

    2009-12-01

    Besides undesirable changes in the attractive aroma, a significant decrease in the intensity of the bitterness as well as a change of the taste into a lingering, harsh bitterness has long been known as a shelf-life limiting factor of beer. Multiple studies have demonstrated that the aging of beer induces a decrease of the total amount of cis- and trans-iso-alpha-acids, the well-known bitter principles of beer. Although the trans-iso-alpha-acids exclusively, not the cis-iso-alpha-acids, were found to be degraded upon storage of beer, the key transformation products formed exclusively from the trans isomers in beer are not known. In the present study, suitable model experiments followed by LC-MS/MS and sophisticated NMR spectroscopic experiments, including the measurement of residual dipolar couplings (RDCs) in gel-based alignment media as well as a novel broadband and B(1)-field-compensated incredible natural abundance double-quantum transfer experiment (INADEQUATE) pulse sequence, enabled the identification of a series of previously unknown trans-specific iso-alpha-acid transformation products, namely, tricyclocohumol, tricyclocohumene, isotricyclocohumene, tetracyclocohumol, and epitetracyclocohumol, respectively. HPLC-MS/MS analysis of these compounds, which exhibit the aforementioned harsh lingering bitter taste and have threshold concentrations ranging from 5 to 70 micromol L(-1), confirmed their generation during aging of beer and, for the first time, explained the storage-induced changes of the beer's bitter taste on a molecular level. PMID:19876978

  4. X-ray kinematography of phase transformations of three-component lipid mixtures: a time-resolved synchrotron X-ray scattering study using the pressure-jump relaxation technique.

    PubMed

    Jeworrek, Christoph; Pühse, Matthias; Winter, Roland

    2008-10-21

    By using the pressure-jump relaxation technique in combination with time-resolved synchrotron small-angle X-ray diffraction (TRSAXS), the kinetics of lipid phase transformations of ternary lipid mixtures serving as model systems of heterogeneous raftlike membranes were investigated. To this end, we first established the temperature-pressure phase diagram of a model lipid raft mixture, 1,2-dioleoyl- sn-glycero-3-phosphatidylcholine (DOPC)/1,2-dipalmitoyl- sn-glycero-3-phosphatidylcholine (DPPC)/cholesterol (1:2:1), using Fourier transform infrared spectroscopy and SAXS, covering the pressure range from 1 bar to 10 kbar at temperatures in the range from 7 to 80 degrees C. We then studied the kinetics of interlamellar phase transitions of the ternary lipid system involving transitions from the fluidlike (liquid-disordered, l d) phase to the liquid-ordered (l o)/liquid-disordered (l d) two-phase coexistence region as well as between the two- and three-phase coexistence regions of the system, where also solid-ordered phases (s o) are involved. The phase transition from the all-fluid l d phase to the l o+l d two-phase coexistence region turns out to be rather rapid. Phases appear or disappear within the 25 ms time resolution of the technique, followed by a slow lattice relaxation process, which, depending on the pressure-jump amplitude, takes several seconds. Contrary to many one-component phospholipid phase transitions, the kinetics of the l d <--> l o+l d transition follows a similar time scale and mechanism for the pressurization and depressurization direction. A similar behavior is observed for the phase transition kinetics of the s o+l o+l d <--> l o+l d transformation and even for the s o+l o+l d <--> l d transformation, jumping across the l o+l d two-phase region. All transitions are fully reversible, and no intermediate states are populated. As indicated by the complex relaxation profiles observed, the overall rates observed seem to reflect the effect of coupling of various dynamical processes through the transformation, involving fast conformational changes in the sub-millisecond time regime and slow relaxation of the lattices growing, probably being largely controlled by the transport and redistribution of water into and in the new phases of the multilamellar vesicle assemblies. PMID:18767826

  5. Ultrafast single-electron transfer in coupled quantum dots driven by a few-cycle chirped pulse

    SciTech Connect

    Yang, Wen-Xing, E-mail: wenxingyang2@126.com [Department of Physics, Southeast University, Nanjing 210096 (China); Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China); Chen, Ai-Xi [Department of Applied Physics, School of Basic Science, East China Jiaotong University, Nanchang 330013 (China); Bai, Yanfeng [Department of Physics, Southeast University, Nanjing 210096 (China); Lee, Ray-Kuang [Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China)

    2014-04-14

    We theoretically study the ultrafast transfer of a single electron between the ground states of a coupled double quantum dot (QD) structure driven by a nonlinear chirped few-cycle laser pulse. A time-dependent Schrödinger equation without the rotating wave approximation is solved numerically. We demonstrate numerically the possibility to have a complete transfer of a single electron by choosing appropriate values of chirped rate parameters and the intensity of the pulse. Even in the presence of the spontaneous emission and dephasing processes of the QD system, high-efficiency coherent transfer of a single electron can be obtained in a wide range of the pulse parameters. Our results illustrate the potential to utilize few-cycle pulses for the excitation in coupled quantum dot systems through the nonlinear chirp parameter control, as well as a guidance in the design of experimental implementation.

  6. Nonuniform injection current induced unusual chirp behavior of a four-electrode bistable distributed Bragg reflector laser

    NASA Astrophysics Data System (ADS)

    Landais, Pascal; Duan, Guang-Hua; Keller, Stefan; Jacquet, Joel

    1995-06-01

    A complete analysis of the chirp of a four-electrode bistable distributed Bragg reflector laser is given in theory and by experiment. Experimentally, the chirp investigation is realized by a Mach-Zehnder interferometer. In small-signal regime, the modulus and phase of 2 beta/m, frequency and amplitude modulation index ratio, is measured for different injection currents and shows an unusual behavior against the modulation frequency. A theoretical model including nonuniform injection current shows the same behavior of 2 beta/m against the modulation frequency and proves that the nonuniform carrier distribution inside the cavity is the origin of the specific behavior. The large-signal analysis provides a study of the instantaneous chirp behavior during optical switching.

  7. Generation of green frequency comb from chirped ?(2) nonlinear photonic crystals

    NASA Astrophysics Data System (ADS)

    Lai, C.-M.; Chang, K.-H.; Yang, Z.-Y.; Fu, S.-H.; Tsai, S.-T.; Hsu, C.-W.; Yu, N. E.; Boudrioua, A.; Kung, A. H.; Peng, L.-H.

    2014-12-01

    Spectrally broad frequency comb generation over 510-555 nm range was reported on chirped quasi-phase-matching (QPM) ?(2) nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 ?m to 7.1 ?m. When pumped with nanosecond infrared (IR) frequency comb derived from a QPM optical parametric oscillator (OPO) and spanned over 1040 nm to 1090 nm wavelength range, the 520 nm to 545 nm up-converted green spectra were shown to consist of contributions from (a) second-harmonic generation among the signal or the idler modes, and (b) sum-frequency generation (SFG) from the neighboring pairs of the signal or the idler modes. These mechanisms led the up-converted green frequency comb to have the same mode spacing of 450 GHz as that in the IR-OPO pump comb. As the pump was further detuned from the aforementioned near-degeneracy point and moved toward the signal (1020-1040 nm) and the idler (1090-1110 nm) spectral range, the above QPM parametric processes were preserved in the chirped QPM devices to support up-converted green generation in the 510-520 nm and the 545-555 nm spectral regime. Additional 530-535 nm green spectral generation was also observed due to concurrence of multi-wavelength SFG processes between the (signal, idler) mode pairs. These mechanisms facilitate the chirped QPM device to support a single-pass up-conversion efficiency ˜10% when subject to an IR-OPO pump comb with 200 mW average power operated near- or off- the degeneracy point.

  8. 3D-printed slit nozzles for Fourier transform microwave spectroscopy

    NASA Astrophysics Data System (ADS)

    Dewberry, Christopher T.; Mackenzie, Rebecca B.; Green, Susan; Leopold, Kenneth R.

    2015-06-01

    3D printing is a new technology whose applications are only beginning to be explored. In this report, we describe the application of 3D printing to the design and construction of supersonic nozzles. Nozzles can be created for 0.50 or less, and the ease and low cost can facilitate the optimization of nozzle performance for the needs of any particular experiment. The efficacy of a variety of designs is assessed by examining rotational spectra of OCS (carbonyl sulfide) and Ar-OCS using a Fourier transform microwave spectrometer with tandem cavity and chirped-pulse capabilities. A slit geometry which, to the best of our knowledge has not been used in conjunction with Fourier transform microwave spectrometers, was found to increase the signal-to-noise ratio for the J = 1?0 transition of OCS, by a factor of three to four compared with that obtained using our standard circular nozzle. Corresponding gains for the Ar-OCS complex were marginal, at best, but further optimization of nozzle geometry should be possible. The spectrometer itself is designed to allow rapid switching between cavity and chirped-pulse modes of operation without the need to break vacuum. This feature, as well as the newly incorporated chirped-pulse capability, is described in detail.

  9. An incremental-learning-by-navigation approach to vision-based autonomous land vehicle guidance in indoor environments using vertical line information and multiweighted generalized Hough transform technique.

    PubMed

    Chen, G Y; Tsai, W H

    1998-01-01

    An incremental learning by navigation approach to vision based autonomous land vehicle (ALV) guidance in indoor environments is proposed. The approach consists of three stages: initial learning, navigation, and model updating. In the initial learning stage, the ALV is driven manually, and environment images and other status data are recorded automatically. Then, an offline procedure is performed to build an initial environment model. In the navigation stage, the ALV moves along the learned environment automatically, locates itself by model matching, and records necessary information for model updating. In the model updating stage, an offline procedure is performed to refine the learned model. A more precise model is obtained after each navigation-and-update iteration. Used environment features are vertical straight lines in camera views. A multiweighted generalized Hough transform is proposed for model matching. A real ALV was used as the testbed, and successful navigation experiments show the feasibility of the proposed approach. PMID:18255993

  10. Broadband supercontinuum generation method combining mid-infrared chirped-pulse modulation and generalized polarization gating.

    PubMed

    Du, Hongchuan; Hu, Bitao

    2010-12-01

    We present a method to control the harmonic process by a mid-infrared modulated generalized polarization gating for the generation of the broadband supercontinuum. Using a mid-IR generalized polarization gating modulated by a weaker mid-IR linearly polarized chirped field, the ionization, acceleration and recombination steps in the HHG process are simultaneously controlled, leading to the efficient generation of an ultra-broadband supercontinuum covered by the spectral range from ultraviolet to water window x-ray. Using this method we expect that isolated sub-100 attosecond pulses with tunable wavelength could be obtained straightforwardly. PMID:21164942

  11. Cooling of a mirror in cavity optomechanics with a chirped pulse

    SciTech Connect

    Liao, Jie-Qiao; Law, C. K. [Department of Physics and Institute of Theoretical Physics, The Chinese University of Hong Kong, Shatin, Hong Kong Special Administrative Region (China)

    2011-11-15

    We investigate the response of a harmonically confined mirror to an optical pulse in cavity optomechanics. We show that when the pulsed coupling strength takes the form of a chirped pulse, thermal fluctuations of the mirror can be significantly transferred to the cavity field. In addition, the frequency modulation of the pulse could enable a better cooling performance by suppressing the sensitivity of the dependence of detuning and pulse areas. Using numerical investigations, we find that the pulsed cooling is mainly limited by the cavity-field decay rate.

  12. Power scaling of supercontinuum seeded megahertz-repetition rate optical parametric chirped pulse amplifiers.

    PubMed

    Riedel, R; Stephanides, A; Prandolini, M J; Gronloh, B; Jungbluth, B; Mans, T; Tavella, F

    2014-03-15

    Optical parametric chirped-pulse amplifiers with high average power are possible with novel high-power Yb:YAG amplifiers with kW-level output powers. We demonstrate a compact wavelength-tunable sub-30-fs amplifier with 11.4 W average power with 20.7% pump-to-signal conversion efficiency. For parametric amplification, a beta-barium borate crystal is pumped by a 140 W, 1 ps Yb:YAG InnoSlab amplifier at 3.25 MHz repetition rate. The broadband seed is generated via supercontinuum generation in a YAG crystal. PMID:24690803

  13. Design of a monolithic tunable laser based on equivalent-chirp grating reflectors.

    PubMed

    Dai, Yitang; Xu, Kun; Wu, Jian; Li, Yan; Hong, Xiaobin; Guo, Hongxiang; Lin, Jintong

    2010-12-01

    A Vernier-tuned distributed Bragg reflector (DBR) semiconductor laser is an effective monolithic approach for wide wavelength tunability, at the expense, however, of costly electron-beam lithography during fabrication. In this Letter, a tunable laser design with equivalent-chirp based, flat-top envelope grating reflectors is proposed that can be implemented easily by conventional two-beam interference lithography. The principle is described, and a detailed design shows uniform output power (0.08 dB variation) and excellent side-mode suppression ratio (47 dB minimum) within a wide tuning range (>32 nm) through numerical simulation. PMID:21124552

  14. Optical beam focusing by a single subwavelength metal slit surrounded by chirped dielectric surface gratings

    SciTech Connect

    Kim, Seyoon; Lim, Yongjun; Kim, Hwi; Park, Junghyun; Lee, Byoungho [National Creative Research Center for Active Plasmonics Application Systems, Inter-University Semiconductor Research Center and School of Electrical Engineering, Seoul National University, Gwanak-Gu Sillim-Dong, Seoul 151-774 (Korea, Republic of)

    2008-01-07

    A method for optical beam focusing by a single subwavelength metal slit surrounded by surface gratings is proposed. In our proposed method, the period of each surface grating is chirped so that the radiation fields of surface plasmon polaritons can be controlled to make a beam spot at the desired focal length. Through our proposed method, it is numerically shown that we can make a beam spot which is located at the several times of wavelength distance from the slit, and its focal length can be controlled.

  15. Electron Acceleration by a Bichromatic Chirped Laser Pulse in Underdense Plasmas

    E-print Network

    Pocsai, Mihály András; Varró, Sándor

    2015-01-01

    A theoretical study of laser and plasma based electron acceleration is presented. An effective model has been used, in which the presence of an underdense plasma has been taken account via its index of refraction $n_{m}$. In the confines of this model, the basic phenomena can be studied by numerically solving the classical relativistic equations of motion. The key idea of this paper is the application of chirped, bichromatic laser fields. We investigated the advantages and disadvantages of mixing the second harmonic to the original $\\lambda = 800 \\, \\mathrm{nm}$ wavelength pulse. We performed calculations both for plane wave and Gaussian pulses.

  16. Chirped laser dispersion spectroscopy using a directly modulated quantum cascade laser

    SciTech Connect

    Hangauer, Andreas, E-mail: hangauer@princeton.edu; Nikodem, Michal; Wysocki, Gerard, E-mail: gwysocki@princeton.edu [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States)] [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States); Spinner, Georg [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States) [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States); Institute for Quantum Electronics, ETH Zurich, 8093 Zurich (Switzerland)

    2013-11-04

    Chirped laser dispersion spectroscopy (CLaDS) utilizing direct modulation of a quantum cascade laser (QCL) is presented. By controlling the laser bias nearly single- and dual-sideband CLaDS operation can be realized in an extremely simplified optical setup with no external optical modulators. Capability of direct single-sideband modulation is a unique feature of QCLs that exhibit a low linewidth enhancement factor. The developed analytical model shows excellent agreement with the experimental, directly modulated CLaDS spectra. This method overcomes major technical limitations of mid-infrared CLaDS systems by allowing significantly higher modulation frequencies and eliminating optical fringes introduced by external modulators.

  17. RF-photonic chirp encoder and compressor for seamless analysis of information flow.

    PubMed

    Zalevsky, Zeev; Shemer, Amir; Zach, Shlomo

    2008-05-26

    In this paper we realize an RF photonic chirp compression system that compresses a continuous stream of incoming RF data (modulated on top of an optical carrier) into a train of temporal short pulses. Each pulse in the train can be separated and treated individually while being sampled by low rate optical switch and without temporal loses of the incoming flow of information. Each such pulse can be filtered and analyzed differently. The main advantage of the proposed system is its capability of being able to handle, seamlessly, high rate information flow with all-optical means and with low rate optical switches. PMID:18545501

  18. Two-photon adiabatic passage in ultracold Rb interacting with a single nanosecond, chirped pulse

    E-print Network

    Liu, Gengyuan

    2015-01-01

    A semiclassical, four-level model of a nanosecond, chirped pulse interacting with all optically accessible hyperfine states in the ultracold Rb atom is analyzed aiming at population inversion within $5S_{1/2}$ electronic state. The nature of two-photon adiabatic passage performed by such a single pulse having a bandwidth smaller than the hyperfine splitting of $5S_{1/2}$ state is investigated in the framework of the dressed state picture. It is shown that two dressed states are involved in the adiabatic dynamics of population inversion. The excited state manifold appeared to play an important mediating role in the mechanism of population transfer.

  19. Optical Parametric Chirped-Pulse-Amplification Contrast Enhancement by Regenerative Pump Spectral Filtering

    SciTech Connect

    Dorrer, C.; Okishev, A.V.; Begishev, I.A.; Zuegel, J.D.; Smirnov, V.I.; Glebov, L.B.

    2007-08-17

    We demonstrate an approach to fundamentally improve the contrast of optical parametric chirped-pulse amplifiers (OPCPA). The instantaneous parametric gain couples the temporal variations of the pump-pulse intensity to spectral variations of the intensity of the stretched signal pulse being amplified, which significantly degrade the temporal contrast of the amplified pulse after recompression. Simple and efficient pump-intensity noise reduction in an OPCPA system using a volume Bragg grating in a regenerative amplifier demonstrates contrast improvements up to 30 dB.

  20. ATOMIC AND MOLECULAR PHYSICS: Observation of the near transform-limited high-resolution tunable far-ultraviolet light

    NASA Astrophysics Data System (ADS)

    Zheng, Huai-Bin; Zhang, Yan-Peng; Nie, Zhi-Qiang; Li, Chang-Biao; Song, Jian-Ping; Li, Chuang-She; Lu, Ke-Qing

    2009-07-01

    This paper studies the near transform-limited high-resolution tunable far-ultraviolet light which is generated by narrow-band tunable light both theoretically and experimentally. It shows the theoretical work about conversion efficiency of sum-frequency, which is restricted by phase-matching angle, walk-off angle and phase distortion and so on, and sets experiment to check this work successfully. Also the origin of chirp of dye laser is analysed.