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Sample records for chirp transform techniques

  1. Gravitational Waves from Rotating Neutron Stars and Evaluation of fast Chirp Transform Techniques

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

    2000-01-01

    X-ray observations suggest that neutron stars in low mass X-ray binaries (LMXB) are rotating with frequencies from 300 - 600 Hz. These spin rates are significantly less than the break-up rates for essentially all realistic neutron star equations of state, suggesting that some process may limit the spin frequencies of accreting neutron stars to this range. If the accretion induced spin up torque is in equilibrium with gravitational radiation losses, these objects could be interesting sources of gravitational waves. I present a brief summary of current measurements of neutron star spins in LMXBs based on the observations of high-Q oscillations during thermonuclear bursts (so called 'burst oscillations'). Further measurements of neutron star spins will be important in exploring the gravitational radiation hypothesis in more detail. To this end I also present a study of fast chirp transform (FCT) techniques as described by Jenet and Prince in the context of searching for the chirping signals observed during X-ray bursts.

  2. Temperature profile measurements within a chirped fiber Bragg grating using a Fourier transform technique

    NASA Astrophysics Data System (ADS)

    Nand, Anbhawa; Kitcher, Daniel J.; Wade, Scott A.; Collins, Stephen F.; Baxter, Gregory W.

    2005-05-01

    The use of reflected power spectra arising from a chirped fiber Bragg grating (CFBG) to extract a nonuniform temperature distribution along the grating has been investigated. The technique uses a discrete Fourier transform (FFT) in which the measured spectrum of the CFBG due to a localised temperature change was simulated using the FFT grating design model. The model operated on the reference spectrum and hypothesis temperature distributions, T(z), to generate a spectrum representative of a localised temperature disturbance. The simulated spectrum was fitted to the measured spectrum using a three-parameter disturbance function operating on position, width and amplitude of temperature change. The rms deviation of the applied value for position of a localised temperature change was 0.14 mm.

  3. Adaptive chirp-Fourier transform for chirp estimation with applications in ISAR imaging of maneuvering targets

    NASA Astrophysics Data System (ADS)

    Xia, Xiang-Gen; Wang, Genyuan; Chen, Victor C.

    2001-03-01

    This paper first reviews some basic properties of the discrete chirp-Fourier transform and then present an adaptive chirp- Fourier transform, a generalization of the amplitude and phase estimation of sinusoids (APES) algorithm proposed by Li and Stoica for sinusoidal signals. We finally applied it to the ISAR imaging of maneuvering targets.

  4. 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.

  5. Optical chirp z-transform processor with a simplified architecture.

    PubMed

    Ngo, Nam Quoc

    2014-12-29

    Using a simplified chirp z-transform (CZT) algorithm based on the discrete-time convolution method, this paper presents the synthesis of a simplified architecture of a reconfigurable optical chirp z-transform (OCZT) processor based on the silica-based planar lightwave circuit (PLC) technology. In the simplified architecture of the reconfigurable OCZT, the required number of optical components is small and there are no waveguide crossings which make fabrication easy. The design of a novel type of optical discrete Fourier transform (ODFT) processor as a special case of the synthesized OCZT is then presented to demonstrate its effectiveness. The designed ODFT can be potentially used as an optical demultiplexer at the receiver of an optical fiber orthogonal frequency division multiplexing (OFDM) transmission system. PMID:25607197

  6. Error analysis of the chirp-z transform when implemented using waveform synthesizers and FFTs

    SciTech Connect

    Bielek, T.P.

    1990-11-01

    This report analyzes the effects of finite-precision arithmetic on discrete Fourier transforms (DFTs) calculated using the chirp-z transform algorithm. An introduction to the chirp-z transform is given together with a description of how the chirp-z transform is implemented in hardware. Equations for the effects of chirp rate errors, starting frequency errors, and starting phase errors on the frequency spectrum of the chirp-z transform are derived. Finally, the maximum possible errors in the chirp rate, the starting frequencies, and starting phases are calculated and used to compute the worst case effects on the amplitude and phase spectrums of the chirp-z transform. 1 ref., 6 figs.

  7. 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.

  8. [Study on Differential Optical Absorption Spectroscopy Data Processing Based on Chirp-Z Transformation].

    PubMed

    Zheng, Hai-ming; Li, Guang-jie; Wu, Hao

    2015-06-01

    Differential optical absorption spectroscopy (DOAS) is a commonly used atmospheric pollution monitoring method. Denoising of monitoring spectral data will improve the inversion accuracy. Fourier transform filtering method is effectively capable of filtering out the noise in the spectral data. But the algorithm itself can introduce errors. In this paper, a chirp-z transform method is put forward. By means of the local thinning of Fourier transform spectrum, it can retain the denoising effect of Fourier transform and compensate the error of the algorithm, which will further improve the inversion accuracy. The paper study on the concentration retrieving of SO2 and NO2. The results show that simple division causes bigger error and is not very stable. Chirp-z transform is proved to be more accurate than Fourier transform. Results of the frequency spectrum analysis show that Fourier transform cannot solve the distortion and weakening problems of characteristic absorption spectrum. Chirp-z transform shows ability in fine refactoring of specific frequency spectrum. PMID:26601381

  9. 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.

  10. Fiber dispersion measurement using chirped laser dispersion spectroscopy technique.

    PubMed

    Plant, Genevieve; Hangauer, Andreas; Wang, Ting; Wysocki, Gerard

    2015-11-20

    Utilizing the fundamentals of chirped laser dispersion spectroscopy, an alternative method of fiber dispersion measurement is presented. The dispersion of the device under test is probed through the interaction of copropagating electromagnetic waves and subsequent heterodyne detection and frequency demodulation. Measurement of the dispersion parameter, D, is possible with this direct measurement scheme. PMID:26836547

  11. Chirped dissipative double-kink and fractional-transform quadratic solitons induced by localized nonlinear gain

    NASA Astrophysics Data System (ADS)

    Raju, Thokala Soloman; Hegde, Tejaswi; Kumar, C. N.; Panigrahi, Prasanta K.

    2015-06-01

    We demonstrate that the localized nonlinear gain induces stable chirped dissipative double-kink, fractional-transform, bell, and kink type solitons in optical mediawith quadratic nonlinearity. To compensate spatially uniform loss in both fundamental-frequency (FF) and second-harmonic (SH) component of the system, a strongly localized 'hot-spot', carrying the nonlinear gain, is added, acting either on FF component or on the SH one.

  12. a Study of 4,4-DIMETHYLAMINOBEZONITRILE by Chirped-Pulsed Fourier Transform Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bird, Ryan G.; Alstadt, Valerie J.; Pratt, David W.; Neill, Justin L.; Pate, Brooks H.

    2010-06-01

    The ground state rotational spectrum of 4,4-dimethylaminobenzonitrile (DMABN) was studied using chirped-pulsed Fourier transform microwave spectroscopy (CP-FTMW). The rotational spectrum from 6.5 to 18 GHz was collected using a compilation of 250 MHz chirped pulses and pieced together. DMABN is widely known as an important model for excited state twisted intramolecular charge transfer dynamics. It has been previously studied in our group using high resolution electronic spectroscopy, in which a strong coupling between methyl group internal rotation and overall rotation was discovered. We have recently determined that these couplings are not present in the ground state spectrum. The ground state structure and nuclear quadrupole coupling terms will also be discussed.

  13. Room temperature chirped-pulse Fourier transform microwave spectroscopy of anisole

    NASA Astrophysics Data System (ADS)

    Reinhold, B.; Finneran, I. A.; Shipman, S. T.

    2011-12-01

    The room-temperature rotational spectrum of anisole from 8.7 to 18.3 GHz was collected with a waveguide-based chirped-pulse Fourier transform microwave spectrometer whose operating principles are described. Three spectra were assigned, corresponding to the vibrational ground state and the first and second excited states of the lowest frequency torsional mode. Results for the ground state and first excited state are in agreement with prior millimeter wave studies of this molecule. Microwave-microwave double resonance measurements also confirm these assignments.

  14. Broadband Chirped-Pulse Fourier Transform Microwave Spectroscopy and Molecular Structure of the ARGON-{ {(Z)}}-1-CHLORO-2-FLUOROETHYLENE Complex

    NASA Astrophysics Data System (ADS)

    Marshall, Mark D.; Leung, Helen O.

    2012-06-01

    A chirped-pulse Fourier transform microwave spectrometer is used to obtain the 6--18 GHz rotational spectrum of the gas-phase complex formed between argon and (Z)-1-chloro-2-fluoroethylene. Both the 35Cl and 37Cl isotopologues are observed in natural abundance, and analysis of these spectra provides predictions for both singly-substituted 13C species with sufficient precision to allow their observation with minimal searching using the more sensitive narrow band Balle-Flygare cavity technique. The non-planar structure of the complex is similar to previously observed argon-fluoroethylene complexes with the argon atom closer to the fluorine than to the chlorine. In contrast to the argon-vinyl chloride and argon-cis-1,2-difluoroethylene complexes, tunneling of the argon atom between the two equivalent, non-planar geometries is not observed.

  15. A broadband Fourier transform microwave spectrometer based on chirped pulse excitation.

    PubMed

    Brown, Gordon G; Dian, Brian C; Douglass, Kevin O; Geyer, Scott M; Shipman, Steven T; Pate, Brooks H

    2008-05-01

    Designs for a broadband chirped pulse Fourier transform microwave (CP-FTMW) spectrometer are presented. The spectrometer is capable of measuring the 7-18 GHz region of a rotational spectrum in a single data acquisition. One design uses a 4.2 Gsampless arbitrary waveform generator (AWG) to produce a 1 mus duration chirped pulse with a linear frequency sweep of 1.375 GHz. This pulse is sent through a microwave circuit to multiply the bandwidth of the pulse by a factor of 8 and upconvert it to the 7.5-18.5 GHz range. The chirped pulse is amplified by a traveling wave tube amplifier and broadcast inside the spectrometer by using a double ridge standard gain horn antenna. The broadband molecular free induction decay (FID) is received by a second horn antenna, downconverted, and digitized by a 40 Gsampless (12 GHz hardware bandwidth) digital oscilloscope. The second design uses a simplified pulse generation and FID detection scheme, employing current state-of-the-art high-speed digital electronics. In this spectrometer, a chirped pulse with 12 GHz of bandwidth is directly generated by using a 20 Gsampless AWG and upconverted in a single step with an ultrabroadband mixer. The amplified molecular emission is directly detected by using a 50 Gsampless digital oscilloscope with 18 GHz bandwidth. In both designs, fast Fourier transform of the FID produces the frequency domain rotational spectrum in the 7-18 GHz range. The performance of the CP-FTMW spectrometer is compared to a Balle-Flygare-type cavity-FTMW spectrometer. The CP-FTMW spectrometer produces an equal sensitivity spectrum with a factor of 40 reduction in measurement time and a reduction in sample consumption by a factor of 20. The CP-FTMW spectrometer also displays good intensity accuracy for both sample number density and rotational transition moment. Strategies to reduce the CP-FTMW measurement time by another factor of 90 while simultaneously reducing the sample consumption by a factor of 30 are demonstrated. PMID:18513057

  16. Waveguide Chirped-Pulse Fourier Transform Microwave Spectroscopy of Allyl Bromide

    NASA Astrophysics Data System (ADS)

    McCabe, Morgan N.; Shipman, Steven

    2014-06-01

    The rotational spectrum of allyl bromide was recorded from 8.7 to 26.5 GHz at -20 °C with a waveguide chirped-pulse Fourier transform microwave spectrometer. The rotational spectrum of allyl bromide has been previously studied by Niide and coworkers. However, previous assignments of this spectrum only extended to J = 12 and K_a = 1. Newly acquired data from our spectrometer has allowed us to extend the previous work to higher values of J and K_a, leading to significant improvements in the distortion constants in particular. Comparisons between the spectra and conformational preferences of the allyl halides will also be discussed. Y. Niide, M, Takano,T. Satoh, and Y. Sasada J. Mol. Spectrosc., 63, 108(1976) Niide, Yuzuru, J. Sci. Hiroshima Univ., Ser. A, 48, 1(1984)

  17. Microwave spectral taxonomy: A semi-automated combination of chirped-pulse and cavity Fourier-transform microwave spectroscopy

    NASA Astrophysics Data System (ADS)

    Crabtree, Kyle N.; Martin-Drumel, Marie-Aline; Brown, Gordon G.; Gaster, Sydney A.; Hall, Taylor M.; McCarthy, Michael C.

    2016-03-01

    Because of its structural specificity, rotational spectroscopy has great potential as an analytical tool for characterizing the chemical composition of complex gas mixtures. However, disentangling the individual molecular constituents of a rotational spectrum, especially if many of the lines are entirely new or unknown, remains challenging. In this paper, we describe an empirical approach that combines the complementary strengths of two techniques, broadband chirped-pulse Fourier transform microwave spectroscopy and narrowband cavity Fourier transform microwave spectroscopy, to characterize and assign lines. This procedure, called microwave spectral taxonomy, involves acquiring a broadband rotational spectrum of a rich mixture, categorizing individual lines based on their relative intensities under series of assays, and finally, linking rotational transitions of individual chemical compounds within each category using double resonance techniques. The power of this procedure is demonstrated for two test cases: a stable molecule with a rich spectrum, 3,4-difluorobenzaldehyde, and products formed in an electrical discharge through a dilute mixture of C2H2 and CS2, in which spectral taxonomy has enabled the identification of propynethial, HC(S)CCH.

  18. Microwave spectral taxonomy: A semi-automated combination of chirped-pulse and cavity Fourier-transform microwave spectroscopy.

    PubMed

    Crabtree, Kyle N; Martin-Drumel, Marie-Aline; Brown, Gordon G; Gaster, Sydney A; Hall, Taylor M; McCarthy, Michael C

    2016-03-28

    Because of its structural specificity, rotational spectroscopy has great potential as an analytical tool for characterizing the chemical composition of complex gas mixtures. However, disentangling the individual molecular constituents of a rotational spectrum, especially if many of the lines are entirely new or unknown, remains challenging. In this paper, we describe an empirical approach that combines the complementary strengths of two techniques, broadband chirped-pulse Fourier transform microwave spectroscopy and narrowband cavity Fourier transform microwave spectroscopy, to characterize and assign lines. This procedure, called microwave spectral taxonomy, involves acquiring a broadband rotational spectrum of a rich mixture, categorizing individual lines based on their relative intensities under series of assays, and finally, linking rotational transitions of individual chemical compounds within each category using double resonance techniques. The power of this procedure is demonstrated for two test cases: a stable molecule with a rich spectrum, 3,4-difluorobenzaldehyde, and products formed in an electrical discharge through a dilute mixture of C2H2 and CS2, in which spectral taxonomy has enabled the identification of propynethial, HC(S)CCH. PMID:27036440

  19. Headspace Analysis of Volatile Compounds Using Segemented Chirped-Pulse Fourier Transform Mm-Wave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Harris, Brent; Steber, Amanda; Pate, Brooks

    2014-06-01

    A chirped-pulse Fourier transform mm-wave spectrometer has been tested in analytical chemistry applications of headspace analysis of volatile species. A solid-state mm-wave light source (260-290 GHz) provides 30-50 mW of power. This power is sufficient to achieve optimal excitation of individual transitions of molecules with dipole moments larger than about 0.1 D. The chirped-pulse spectrometer has near 100% measurement duty cycle using a high-speed digitizer (4 GS/s) with signal accumulation in an FPGA. The combination of the ability to perform optimal pulse excitation and near 100% measurement duty cycle gives a spectrometer that is fully optimized for trace detection. The performance of the instrument is tested using an EPA sample (EPA VOC Mix 6 - Supelco) that contains a set of molecules that are fast eluting on gas chromatographs and, as a result, present analysis challenges to mass spectrometry. The ability to directly analyze the VOC mixture is tested by acquiring the full bandwidth (260-290 GHz) spectrum in a "high dynamic range" measurement mode that minimizes spurious spectrometer responses. The high-resolution of molecular rotational spectroscopy makes it easy to analyze this mixture without the need for chemical separation. The sensitivity of the instrument for individual molecule detection, where a single transition is polarized by the excitation pulse, is also tested. Detection limits in water will be reported. In the case of chloromethane, the detection limit (0.1 microgram/L), matches the sensitivity reported in the EPA measurement protocol (EPA Method 524) for GC/MS.

  20. Using the inverse Chirp-Z transform for time-domain analysis of simulated radar signals

    SciTech Connect

    Frickey, D.A.

    1995-01-01

    There exists a need to develop a method to locate underground voids, or caches. In the past, ground penetrating radar (GPR) operating in the time domain mode has been used. In this paper, we turn our attention to stepped frequency radar, capable of making frequency domain reflection coefficient measurements. We then apply the inverse Chirp-Z transform (ICZT) to this data, generating a time domain response. The scenario under consideration is that of an airborne radar passing over the surface of the earth. The radar is directed toward the surface and is capable of measuring the reflection coefficient, seen looking toward the earth, as a function of frequency. The frequency domain -data in this work is simulated and is generated from a transmission line model of the problem. Using the ICZT we convert this frequency domain data to the time domain. Once in the time domain, reflections due to discontinuities appear at times indicating their relative distance from the source. The discontinuities occurring beyond the surface of the earth could be indicative of underground structures. The ICZT allows a person to zoom in on the time span of interest by specifying the starting time, the time resolution, and the number of time steps.

  1. 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.

  2. 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.

  3. 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).

  4. The Marriage of Spectroscopy and Dynamics: Chirped-Pulse Fourier-Transform Mm-Wave Cp-Ft Spectroscopy in Pulsed Uniform Supersonic Flows

    NASA Astrophysics Data System (ADS)

    Abeysekera, Chamara; Oldham, James M.; Suits, Arthur G.; Park, G. Barratt; Field, Robert W.

    2012-06-01

    A new experimental scheme is presented that combines two powerful emerging technologies: chirped-pulse Fourier-transform mm-Wave 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. Chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy, pioneered by Pate and coworkers, allows rapid acquisition of broadband microwave spectrum through advancements in waveform generation and oscilloscope technology. This revolutionary approach has successfully been adapted to higher frequencies by the Field group at MIT. Our new apparatus will exploit amplified chirped pulses in the range of 26-40 GHz, in combination with a pulsed uniform supersonic flow from a Laval nozzle. This nozzle source, pioneered by Rowe, Sims, and Smith for low temperature kinetics studies, produces thermalized reactants at high densities and low temperatures perfectly suitable for reaction dynamics experiments studied using the CP-mmW approach. This combination of techniques shall enhance the thousand-fold improvement in data acquisition rate achieved in the CP method by a further 2-3 orders of magnitude. A pulsed flow alleviates the challenges of continuous uniform flow, e.g. large gas loads and reactant consumption rates. In contrast to other pulsed Laval systems currently in use, we will use a fast piezo valve and small chambers to achieve the desired pressures while minimizing the gas load, so that a 10 Hz repetition rate can be achieved with one turbomolecular pump. The proposed technique will be suitable for many diverse fields, including fundamental studies in spectroscopy and reaction dynamics, reaction kinetics, combustion, atmospheric chemistry, and astrochemistry. We expect a significant advancement in the ability to detect absolute populations of complex reaction products under near-nascent conditions, providing the powerful method of reaction dynamics with a universal spectroscopic probe capable of capturing the details of complex chemistry for specific product isomers and conformers.

  5. 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.

  6. 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).

  7. Multipath interference test method using synthesized chirped signal from directly modulated DFB-LD with digital-signal-processing technique.

    PubMed

    Aida, Kazuo; Sugie, Toshihiko

    2011-12-12

    We propose a method of testing transmission fiber lines and distributed amplifiers. Multipath interference (MPI) is detected as a beat spectrum between a multipath signal and a direct signal using a synthesized chirped test signal with lightwave frequencies of f(1) and f(2) periodically emitted from a distributed feedback laser diode (DFB-LD). This chirped test pulse is generated using a directly modulated DFB-LD with a drive signal calculated using a digital signal processing technique (DSP). A receiver consisting of a photodiode and an electrical spectrum analyzer (ESA) detects a baseband power spectrum peak appearing at the frequency of the test signal frequency deviation (f(1)-f(2)) as a beat spectrum of self-heterodyne detection. Multipath interference is converted from the spectrum peak power. This method improved the minimum detectable MPI to as low as -78 dB. We discuss the detailed design and performance of the proposed test method, including a DFB-LD drive signal calculation algorithm with DSP for synthesis of the chirped test signal and experiments on single-mode fibers with discrete reflections. PMID:22274099

  8. A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. I. The low-temperature flow system

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    We report the development of a new instrument that combines chirped-pulse microwave spectroscopy with a pulsed uniform supersonic flow. This combination promises a nearly universal detection method that can deliver isomer and conformer specific, quantitative detection and spectroscopic characterization of unstable reaction products and intermediates, product vibrational distributions, and molecular excited states. This first paper in a series of two presents a new pulsed-flow design, at the heart of which is a fast, high-throughput pulsed valve driven by a piezoelectric stack actuator. Uniform flows at temperatures as low as 20 K were readily achieved with only modest pumping requirements, as demonstrated by impact pressure measurements and pure rotational spectroscopy. The proposed technique will be suitable for application in diverse fields including fundamental studies in spectroscopy, kinetics, and reaction dynamics.

  9. Study on DFB semiconductor laser array integrated with grating reflector based on reconstruction-equivalent-chirp technique.

    PubMed

    Zhang, Yunshan; Zheng, Jilin; Zhang, Fangzheng; Shi, Yuechun; Zheng, Junshou; Lu, Jun; Liu, Shengping; Qiu, Bocang; Chen, Xiangfei

    2015-02-01

    A 4-channel distributed feedback (DFB) semiconductor laser array with incorporation of a grating reflector utilizing reconstruction-equivalent-chirp technique is theoretically studied and experimentally demonstrated. By integrating with a grating reflector, 40% increase of slope efficiency, about 10mA decrease of threshold current and 7dB increase of side mode suppression ratio (SMSR) are achieved with a deviation of wavelength spacing being less than 0.07nm. The SMSRs of all the lasers are higher than 60dB. PMID:25836150

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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 vibrational state of the molecule are corrected to provide equilibrium values of these constants for all four isotopologues. The equilibrium constants are used for structure determination via both Kraitchman substitution coordinates and least squares fits to equilibrium moments of inertia. Both experiment and theory give a structure in which all but two fluorine atoms in the terminal -CF 3 group are coplanar. A substantial barrier to internal rotation of this group is predicted by ab initio calculation, and no evidence of internal rotation is seen in the spectra. A detailed description of the new spectrometer is given.

  11. 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.

  12. 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.

  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. Spectral Taxonomy: a Semi-Automated Combination of Chirped-Pulse and Cavity Fourier Transform Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Crabtree, Kyle N.; McCarthy, Michael C.

    2014-06-01

    Chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW) has proven to be a powerful tool for broadband spectral surveys in the cm-wave band. In conjunction with a non-specific production source, such as an electrical discharge, new, unexpected molecules can be detected by their rotational spectra provided that they can be disentangled from other species that may be present. As an example, we have recently used a CP-FTMW spectrometer operating in the 8--18 GHz band to detect and identify two new silicon nitrides, HSiNSi and H_3SiNSi, in a discharge of dilute silane and nitrogen, although neither species had been the subject of prior experimental or theoretical study. However, of the ˜100 lines that are observed in this plasma, only ˜20 have been assigned to known species. To further investigate unassigned lines in CP-FTMW spectra, we take advantage of the higher sensitivity of a traditional cavity FTMW spectrometer to rapidly perform follow-up assays in an approach we call "spectral taxonomy." Lines are classified according to whether their intensities are significantly altered by, for instance, turning off the discharge, applying a magnetic field, or removing a precursor gas; lines that show the same behavior for all tests may arise from a common carrier. After taxonometric classification, lines within each group are exhaustively tested with double resonance methods in an attempt to establish linkages which would identify lines arising from a shared quantum state and give clues as to the structure of the carrier. Using newly-designed control software for our cavity spectrometer, this entire procedure can be performed with minimal human intervention.

  15. Dynamic chirp control and pulse compression for attosecond high-order harmonic emission.

    PubMed

    Zheng, Yinghui; Zeng, Zhinan; Zou, Pu; Zhang, Li; Li, Xiaofang; Liu, Peng; Li, Ruxin; Xu, Zhizhan

    2009-07-24

    We propose a scheme to compensate dynamically the intrinsic chirp of the attosecond harmonic pulses. By adding a weak second harmonic laser field to the driving laser field, the chirp compensation can be varied from the negative to the positive continuously by simply adjusting the relative time delay between the two-color pulses. Using this technique, the compensation of the negative chirp in harmonic emission is demonstrated experimentally for the first time and the nearly transform-limited attosecond pulse trains are obtained. PMID:19659355

  16. Dynamic Chirp Control and Pulse Compression for Attosecond High-Order Harmonic Emission

    SciTech Connect

    Zheng Yinghui; Zeng Zhinan; Zou Pu; Zhang Li; Li Xiaofang; Liu Peng; Li Ruxin; Xu Zhizhan

    2009-07-24

    We propose a scheme to compensate dynamically the intrinsic chirp of the attosecond harmonic pulses. By adding a weak second harmonic laser field to the driving laser field, the chirp compensation can be varied from the negative to the positive continuously by simply adjusting the relative time delay between the two-color pulses. Using this technique, the compensation of the negative chirp in harmonic emission is demonstrated experimentally for the first time and the nearly transform-limited attosecond pulse trains are obtained.

  17. Ultrabroadband optical chirp linearization for precision metrology applications.

    PubMed

    Roos, Peter A; Reibel, Randy R; Berg, Trenton; Kaylor, Brant; Barber, Zeb W; Babbitt, Wm Randall

    2009-12-01

    We demonstrate precise linearization of ultrabroadband laser frequency chirps via a fiber-based self-heterodyne technique to enable extremely high-resolution, frequency-modulated cw laser-radar (LADAR) and a wide range of other metrology applications. Our frequency chirps cover bandwidths up to nearly 5 THz with frequency errors as low as 170 kHz, relative to linearity. We show that this performance enables 31-mum transform-limited LADAR range resolution (FWHM) and 86 nm range precisions over a 1.5 m range baseline. Much longer range baselines are possible but are limited by atmospheric turbulence and fiber dispersion. PMID:19953164

  18. A Segmented Chirped-Pulse Fourier Transform Mm-Wave Spectrometer (260-295 Ghz) with Real-Time Signal Averaging Capability

    NASA Astrophysics Data System (ADS)

    Harris, Brent J.; Steber, Amanda L.; Pate, Brooks H.

    2013-06-01

    The design and performance of a 260-295 GHz segmented chirped-pulse Fourier transform mm-wave spectrometer is presented. The spectrometer uses an arbitrary waveform generator to create an excitation and detection waveform. The excitation waveform is a series of chirped pulses with 720 MHz bandwidth at mm-wave and about 200 ns pulse duration. The excitation pulses are produced using an x24 active multiplier chain with a peak power of 30 mW. Following a chirped pulse excitation, the molecular emission from all transitions in the excitation bandwidth is detected using heterodyne detection. The free induction decay (FID) is collected for about 1.5 microseconds and each segment measurement time period is 2 microseconds. The local oscillator for the detection in each segment is also created from the arbitrary waveform generator. The full excitation waveform contains 50 segments that scan the chirped pulse frequency and LO frequency across the 260-295 GHz frequency range in a total measurement time of 100 microseconds. The FID from each measurement segment is digitized at 4 GSamples/s, for a record length of 400 kpts. Signal averaging is performed by accumulating the FID signals from each sweep through the spectrum in a 32-bit FPGA. This allows the acquisition of 16 million sequential 260-295 GHz spectra in real time. The final spectrum is produced from fast Fourier transform of the FID in each measurement segment with the frequency calculated using the segment's LO frequency. The agility of the arbitrary waveform generator light source makes it possible to perform several coherent spectroscopic measurements to speed the analysis of the spectrum. In particular, high-sensitivity double-resonance measurements can be performed by applying a "pi-pulse" to a selected molecular transition and observing the changes to all other transitions in the 260-295 GHz frequency range of the spectrometer. In this mode of operation, up to 50 double-resonance frequencies can be used in each segment with the double-resonance signal collection taking place in real time.

  19. Methyl rotors in the gas phase: A study of o- and m-toluidine by chirped-pulse Fourier transform microwave spectroscopy

    NASA Astrophysics Data System (ADS)

    Bird, Ryan G.; Pratt, David W.

    2011-04-01

    Microwave spectra of o- and m-toluidine were recorded in a pulsed supersonic jet using chirped pulse techniques. The spectra show both torsional and 14N quadrupole splittings at high resolution. From the torsional splittings, barrier heights were determined of 531 cm -1 and 2.0 cm -1 respectively. Using the quadrupole splittings, orbital occupancy numbers of the amino-nitrogen atoms were calculated. An apparent relationship between these values and the barriers to internal rotation of the methyl groups is discussed.

  20. Chirp-modulated visual evoked potential as a generalization of steady state visual evoked potential

    NASA Astrophysics Data System (ADS)

    Tu, Tao; Xin, Yi; Gao, Xiaorong; Gao, Shangkai

    2012-02-01

    Visual evoked potentials (VEPs) are of great concern in cognitive and clinical neuroscience as well as in the recent research field of brain-computer interfaces (BCIs). In this study, a chirp-modulated stimulation was employed to serve as a novel type of visual stimulus. Based on our empirical study, the chirp stimuli visual evoked potential (Chirp-VEP) preserved frequency features of the chirp stimulus analogous to the steady state evoked potential (SSVEP), and therefore it can be regarded as a generalization of SSVEP. Specifically, we first investigated the characteristics of the Chirp-VEP in the time-frequency domain and the fractional domain via fractional Fourier transform. We also proposed a group delay technique to derive the apparent latency from Chirp-VEP. Results on EEG data showed that our approach outperformed the traditional SSVEP-based method in efficiency and ease of apparent latency estimation. For the recruited six subjects, the average apparent latencies ranged from 100 to 130 ms. Finally, we implemented a BCI system with six targets to validate the feasibility of Chirp-VEP as a potential candidate in the field of BCIs.

  1. 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.

  2. Multiplexed chirp waveform synthesizer

    DOEpatents

    Dudley, Peter A.; Tise, Bert L.

    2003-09-02

    A synthesizer for generating a desired chirp signal has M parallel channels, where M is an integer greater than 1, each channel including a chirp waveform synthesizer generating at an output a portion of a digital representation of the desired chirp signal; and a multiplexer for multiplexing the M outputs to create a digital representation of the desired chirp signal. Preferably, each channel receives input information that is a function of information representing the desired chirp signal.

  3. Optimal chirped probe pulse length for terahertz pulse measurement.

    PubMed

    Peng, Xiao-Yu; Willi, Oswald; Chen, Min; Pukhov, Alexander

    2008-08-01

    A detailed analysis of the relationship between the duration of the chirped probe pulse and the bipolar terahertz (THz) pulse length in the spectral encoding technique is carried out. We prove that there is an optimal chirped probe pulse length (or an optimal chirp rate of the chirped probe pulse) matched to the input THz pulse length and derive a rigorous relationship between them. We find that only under this restricted condition the THz signal can be correctly retrieved. PMID:18679511

  4. The symmetry in a chirp filter and its application to LPI communication

    NASA Astrophysics Data System (ADS)

    Lam, Larry

    The even phase symmetry property of a chirp filter is discussed. It is known that significant spectral lines are produced at the output when a binary-phase-shift keyed (BPSK) signal is applied to a squaring circuit (SC) or a delay-and-multiply circuit. These spectral lines can be suppressed by using an even phase symmetric filter. One application of a chirp filter is to transform a conventional direct-sequence-spread-spectrum (DS-SS) low probability of intercept (LPI) signal into a form that is more difficult to detect. Computer simulation results are presented to show the effectiveness of the proposed technique.

  5. Precise linearization of broadband frequency chirp for coherent optical frequency domain reflectometry

    NASA Astrophysics Data System (ADS)

    Qin, Jie; Shi, Hongxiao; Xie, Weilin; Zhou, Qian; Dong, Yi; Hu, Weisheng

    2015-08-01

    Optical frequency domain reflectometry is a suitable and promising measurement technique for optical network components characterization; however its performance is severely limited by sweep nonlinearity of the laser chirp. We demonstrate precise linearization of broadband optical frequency chirp using optoelectronic feedback loop. The sweep rate and the laser chirp shape is locked to and determined by the frequency of a reference electronic signal, an agile, high coherence swept-frequency semiconductor laser source with a bandwidth of 66GHz in 100ms is achieved. The laser source is applied to a coherent optical frequency domain reflectometry; a transform-limited spatial resolution of 1.5mm at a distance of 200 meters is demonstrated.

  6. 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.

  7. 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.

  8. Wavelet transform techniques and signal analysis

    SciTech Connect

    Perez, R.B.; Mattingly, J.K. |; Perez, J.S.

    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.

  9. Tapered and linearly chirped fiber Bragg gratings with co-directional and counter-directional resultant chirps

    NASA Astrophysics Data System (ADS)

    Osuch, Tomasz

    2016-05-01

    A method of spectral width tailoring of tapered fiber Bragg gratings is theoretically analyzed and experimentally verified. This concept is based on inscription grating structures in which synthesis of chirps comes from both taper profile and a linearly chirped phase mask used for grating inscription. It is shown that under UV exposure and depending on the orientation of the optical fiber taper relative to the variable-pitch phase mask, tapered and linearly chirped fiber Bragg gratings (TCFBG) with resultant co-directional or counter-directional chirps are achieved. Thus, both effects, those of reduction and enhancement of the grating chirp, as well as their influence on the grating spectral response, are presented. In particular, using the above approach TCFBG with significantly narrowed spectral width are shown. Moreover, fused tapered chirped FBG with relatively large waist diameter are shown having broad spectrum, something that prior to now was not attainable using previously developed techniques.

  10. Hadamard transform spectrometry: A new analytical technique

    SciTech Connect

    Hall, W.

    1989-11-10

    The following four projects were expanded during the second year of this three year program. (a) Construction of a stationary interferometer for possible use in the Hadamard transform Raman high performance liquid chromatography (HPLC) experiment. (b) Construction of a dispersive Hadamard transform spectrometer with concave holographic gratings for possible application as a HPLC detector. (c) Investigation of both colloidal-dispersed and polymer-dispersed liquid crystal materials as efficient optical shutters for making improved Hadamard encoding masks. (d) Improvement of the software necessary to recover a spectrum from the Hadamard encoded data. 1 fig.

  11. 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.

  12. High-performance, high-chip-count optical code division multiple access encoders-decoders based on a reconstruction equivalent-chirp technique.

    PubMed

    Dai, Yitang; Chen, Xiangfei; Sun, Jie; Yao, Yu; Xie, Shizhong

    2006-06-01

    Fiber Bragg grating-based, 511 chip, 500 Gchip/s encoders-decoders are experimentally demonstrated by the reconstruction equivalent-chirp (REC) method. Encoding-decoding efficiency close to the theoretical value is achieved. Without any real phase shifts, the encoders-decoders are fabricated by use of the traditional setup. Highly precise phase control requires only submicrometer precision. The encoding-decoding performance can be further improved by REC-based correction. PMID:16688239

  13. Tunable-chirp pulse compression in quasi-phase-matched second-harmonic generation.

    PubMed

    Schober, A M; Imeshev, G; Fejer, M M

    2002-07-01

    We demonstrate continuously tunable compensation of linear chirp on a first-harmonic pump pulse to produce a near-transform-limited second-harmonic output pulse through the use of a chirped, fanned, periodically poled lithium niobate quasi-phase-matching grating. Compensation of positive and negative chirps is possible through reversal of device orientation. The device is simple and monolithic and can be applied to compensation of a higher-order phase with minor modification. PMID:18026383

  14. Chirp and polarization control of femtosecond molecular fragmentation

    PubMed Central

    Goswami, T; Das, D K; Kumar, S K Karthick; Goswami, D

    2013-01-01

    We explore the simultaneous effect of chirp and polarization as the two control parameters for non-resonant photo-dissociation of n-propyl benzene. Experiments performed over a wide range of laser intensities show that these two control knobs behave mutually exclusively. Specifically, for the coherently enhanced fragments (C3H3+, C5H5+) with negatively chirped pulses and C6H5+ with positively chirped pulses, polarization effect is the same as compared to that in the case of transform-limited pulses. Though a change in polarization affects the overall fragmentation efficiency, the fragmentation pattern of n-propyl benzene molecule remains unaffected in contrast to the chirp case. PMID:24115807

  15. Evolution of chirped laser pulses in a magnetized plasma channel

    SciTech Connect

    Jha, Pallavi; Hemlata,; Mishra, Rohit Kumar

    2014-12-15

    The propagation of intense, short, sinusoidal laser pulses in a magnetized plasma channel has been studied. The wave equation governing the evolution of the radiation field is set up and a variational technique is used to obtain the equations describing the evolution of the laser spot size, pulse length and chirp parameter. Numerical methods are used to analyze the simultaneous evolution of these parameters. The effect of the external magnetic field on initially chirped as well as unchirped laser pulses on the spot size, pulse length and chirping has been analyzed.

  16. Evolution of chirped laser pulses in a magnetized plasma channel

    NASA Astrophysics Data System (ADS)

    Jha, Pallavi; Hemlata; Mishra, Rohit Kumar

    2014-12-01

    The propagation of intense, short, sinusoidal laser pulses in a magnetized plasma channel has been studied. The wave equation governing the evolution of the radiation field is set up and a variational technique is used to obtain the equations describing the evolution of the laser spot size, pulse length and chirp parameter. Numerical methods are used to analyze the simultaneous evolution of these parameters. The effect of the external magnetic field on initially chirped as well as unchirped laser pulses on the spot size, pulse length and chirping has been analyzed.

  17. Real-Time Optical Hough Transform and Morphological Inspection Techniques.

    NASA Astrophysics Data System (ADS)

    Richards, Jeffrey Scott

    A real-time optical Hough transform inspection processor is described and applied to the industrial case study of the inspection of cigarette packages. The inspections are performed in real-time using a color Epson liquid crystal television as the input spatial light modulator. A new selective, real-time edge-enhancement technique is used to enhance edges only at the selected orientations which will Hough transform to peaks (this maximizes the signal to noise ratio in the Hough transform output). Several slices of the Hough transform are generated in parallel with a new computer generated hologram utilizing 1D modulated error diffusion. We benchmark our Hough transform processor with the inspection of 100 sample cigarette packages. Correct classification of all the packages (with defects that we intended to inspect for) was attained. We also discuss the confidence with which we can apply our laboratory sample set results to the industrial installation of our inspection processor. Extensions of the Hough transform are also described which generalize the Hough space to recognize shapes other than straight lines (e.g. circles, ellipses). We propose a new high speed acousto-optic architecture to implement these generalized Hough transforms. We also describe how the exact position of input lines can be extracted from Hough transform peak data. Typically, only the contour on which an input line resides is extracted from Hough data. Digital simulations illustrating both generalized Hough transformations and determination of input line position from Hough data are presented. Basic morphological transformations and their real-time optical implementation are discussed. We describe how morphological transformations are useful in inspection and show digital simulations and optical results of an inspection application (string detection in chopped tobacco) where morphological transformations are used.

  18. Control of Ultracold Collisions with Frequency-Chirped Light

    SciTech Connect

    Wright, M.J.; Gould, P.L.; Gensemer, S.D.; Vala, J.; Kosloff, R.

    2005-08-05

    We report on ultracold atomic collision experiments utilizing frequency-chirped laser light. A rapid chirp below the atomic resonance results in adiabatic excitation to an attractive molecular potential over a wide range of internuclear separation. This leads to a transient inelastic collision rate which is large compared to that obtained with fixed-frequency excitation. The combination of high efficiency and temporal control demonstrates the benefit of applying the techniques of coherent control to the ultracold domain.

  19. Characterization and compensation of the residual chirp in a Mach-Zehnder-type electro-optical intensity modulator.

    PubMed

    Rogers, C E; Carini, J L; Pechkis, J A; Gould, P L

    2010-01-18

    We utilize various techniques to characterize the residual phase modulation of a waveguide-based Mach-Zehnder electro-optical intensity modulator. A heterodyne technique is used to directly measure the phase change due to a given change in intensity, thereby determining the chirp parameter of the device. This chirp parameter is also measured by examining the ratio of sidebands for sinusoidal amplitude modulation. Finally, the frequency chirp caused by an intensity pulse on the nanosecond time scale is measured via the heterodyne signal. We show that this chirp can be largely compensated with a separate phase modulator. The various measurements of the chirp parameter are in reasonable agreement. PMID:20173940

  20. Characterization and compensation of the residual chirp in a Mach-Zehnder-type electro-optical intensity modulator

    NASA Astrophysics Data System (ADS)

    Rogers, C. E., III; Carini, J. L.; Pechkis, J. A.; Gould, P. L.

    2010-01-01

    We utilize various techniques to characterize the residual phase modulation of a fiber-based Mach-Zehnder electro-optical intensity modulator. A heterodyne technique is used to directly measure the phase change due to a given change in intensity, thereby determining the chirp parameter of the device. This chirp parameter is also measured by examining the ratio of sidebands for sinusoidal amplitude modulation. Finally, the frequency chirp caused by an intensity pulse on the nanosecond time scale is measured via the heterodyne signal. We show that this chirp can be largely compensated with a separate phase modulator. The various measurements of the chirp parameter are in reasonable agreement.

  1. Complex heterodyne for undersampled chirped sinusoidal signals.

    PubMed

    Niebauer, T M; Schiel, A; van Westrum, D

    2006-11-10

    We describe a method for analyzing frequency-chirped sinusoidal signals using a complex heterodyne, sometimes also known as complex demodulation on the digitized waveform. This method allows one to use prior knowledge of the signal to reduce the effective bandwidth of the signal. The method can be used to extract a frequency-chirped signal even when it is sampled well below the Nyquist criterion. Accordingly, the method facilitates the use of less-expensive data acquisition and signal processing hardware than has traditionally been used for these applications. This technique is particularly useful for high-precision (parts in 10(9)) interferometer applications in which there exists a differential acceleration between the two arms (commonly found in absolute gravity meters or gradiometers). PMID:17068577

  2. Complex heterodyne for undersampled chirped sinusoidal signals

    NASA Astrophysics Data System (ADS)

    Niebauer, T. M.; Schiel, A.; van Westrum, D.

    2006-11-01

    We describe a method for analyzing frequency-chirped sinusoidal signals using a complex heterodyne, sometimes also known as complex demodulation on the digitized waveform. This method allows one to use prior knowledge of the signal to reduce the effective bandwidth of the signal. The method can be used to extract a frequency-chirped signal even when it is sampled well below the Nyquist criterion. Accordingly, the method facilitates the use of less-expensive data acquisition and signal processing hardware than has traditionally been used for these applications. This technique is particularly useful for high-precision (parts in 109) interferometer applications in which there exists a differential acceleration between the two arms (commonly found in absolute gravity meters or gradiometers).

  3. Excitation of chirping whistler waves in a laboratory plasma

    NASA Astrophysics Data System (ADS)

    An, Xin

    2015-11-01

    Whistler mode chorus emissions with a characteristic frequency chirp largely control the dynamic variability of the Earth's outer radiation belt. They are 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 gyrating beam of energetic electrons injected into a cold plasma. It is shown that there is an optimal beam density for frequency chirps, which indicates the existence of optimum wave amplitude for the generation of chirps. Also, frequency chirps only occur for a very narrow range of ratio of fpe /fce , similar to that observed in space. Strong magnetic field gradient, which prohibits the formation of phase space electron hole, disrupts frequency chirps as expected. Broadband whistler waves similar to magnetospheric hiss are also observed at relatively high plasma density. Their mode structures are identified by the phase-correlation technique. It is demonstrated that broadband whistlers are excited through Landau resonance, cyclotron resonance and anomalous cyclotron resonance. Wave growth rate and wave normal angle given by linear theory are consistent with experimental results in general. Preliminary particle-in-cell simulation captures the linear theory prediction of broadband whistlers and also gives important information on the evolution of electron distribution function. Supported by NSF/DOE Plasma Partnership grant DE-SC0010578.

  4. 5 Hz, >250 mJ Optical Parametric Chirped-Pulse Amplifier at 1053 nm

    SciTech Connect

    Bagnoud, V.; Begishev, I.A.; Guardalben, M.J.; Puth, J.; Zuegel, J.D.

    2005-07-15

    A 250 mJ, 5 Hz repetition rate optical parametric chirped-pulse amplifier with near-Fourier-transform-limited, 430 fs pulses and a beam that can be focused to near the diffraction limit is demonstrated.

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

    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 C3H 3 + and C5H 5 + in the case of negatively chirped pulses and C6H 5 + 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.

  7. 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.

  8. 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

  9. An analysis of spectral transformation techniques on graphs

    NASA Astrophysics Data System (ADS)

    Djurović, Igor; Sejdić, Ervin; Bulatović, Nikola; Simeunović, Marko

    2015-05-01

    Emerging methods for the spectral analysis of graphs are analyzed in this paper, as graphs are currently used to study interactions in many fields from neuroscience to social networks. There are two main approaches related to the spectral transformation of graphs. The first approach is based on the Laplacian matrix. The graph Fourier transform is defined as an expansion of a graph signal in terms of eigenfunctions of the graph Laplacian. The calculated eigenvalues carry the notion of frequency of graph signals. The second approach is based on the graph weighted adjacency matrix, as it expands the graph signal into a basis of eigenvectors of the adjacency matrix instead of the graph Laplacian. Here, the notion of frequency is then obtained from the eigenvalues of the adjacency matrix or its Jordan decomposition. In this paper, advantages and drawbacks of both approaches are examined. Potential challenges and improvements to graph spectral processing methods are considered as well as the generalization of graph processing techniques in the spectral domain. Its generalization to the time-frequency domain and other potential extensions of classical signal processing concepts to graph datasets are also considered. Lastly, it is given an overview of the compressive sensing on graphs concepts.

  10. Control of two-photon double ionization of helium with intense chirped attosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Barmaki, S.; Lanteigne, P.; Laulan, S.

    2014-06-01

    We study the two-photon double-ionization process of the helium atom by solving numerically the nonrelativistic, time-dependent Schrödinger equation in its full dimensionality. We investigate with intense chirped attosecond laser pulses of 23.5-nm wavelength the two-photon absorption near and above the sequential threshold. We show how it is possible by adjusting the chirp parameter to control the electronic transitions inside the atom, thereby reinforcing or weakening the ionization process. Attosecond chirped laser pulses offer a promising way to probe and control the two-photon double ionization of helium when compared with attosecond transform-limited pulses.

  11. Fast Discrete Fourier Transform Computations Using the Reduced Adder Graph Technique

    NASA Astrophysics Data System (ADS)

    Meyer-Bäse, Uwe; Natarajan, Hariharan; Dempster, Andrew G.

    2007-12-01

    It has recently been shown that thse[InlineEquation not available: see fulltext.]-dimensional reduced adder graph (RAG-[InlineEquation not available: see fulltext.]) technique is beneficial for many DSP applications such as for FIR and IIR filters, where multipliers can be grouped in multiplier blocks. This paper highlights the importance of DFT and FFT as DSP objects and also explores how the RAG-[InlineEquation not available: see fulltext.] technique can be applied to these algorithms. This RAG-[InlineEquation not available: see fulltext.] DFT will be shown to be of low complexity and possess an attractively regular VLSI data flow when implemented with the Rader DFT algorithm or the Bluestein chirp-[InlineEquation not available: see fulltext.] algorithm. ASIC synthesis data are provided and demonstrate the low complexity and high speed of the design when compared to other alternatives.

  12. The performance of methods based on the fractional Fourier transform for detecting marine mammal vocalizations.

    PubMed

    Locke, Jonathan; White, Paul R

    2011-10-01

    The analysis of cetacean vocalizations is considered using Fourier-based techniques that employ chirp functions in their decomposition. In particular, the paper considers a short-time methods based on the fractional Fourier transform for detecting frequency modulated narrow-band signals, such as dolphin whistles, and compares this to the classical short-time Fourier methods. The fractional Fourier technique explored computes transforms associated with a range of chirp rates and automatically selects the rate for the final analysis. This avoids the need for prior knowledge of signal's chirp rate. An analysis is presented that details the performance of both methods as signal detectors and allows one to determine their detection thresholds. These thresholds are then used to measure the detectability of synthetic signals. This principle is then extended to measure performance on a set of recordings of narrow-band vocalizations from a range of cetacean species. PMID:21973352

  13. High-order-harmonic generation driven by pulses with angular spatial chirp

    NASA Astrophysics Data System (ADS)

    Hernández-García, Carlos; Jaron-Becker, Agnieszka; Hickstein, Daniel D.; Becker, Andreas; Durfee, Charles G.

    2016-02-01

    We present and analyze a technique to drive high-order harmonics by laser pulses with an angular spatial chirp. Results of our numerical simulations show that each harmonic is emitted with an angular chirp which scales inversely with the harmonic order and leads to additional control of the spatial and temporal resolution of the spectrum. In particular, the use of angular chirp leads to separation of the harmonics in two dimensions where (i) high spectral resolution can be achieved and (ii) the temporal periodicity of the harmonic pulse trains can be controlled. We show that this technique does not require carrier-envelope-phase stabilization when using few-cycle laser pulses.

  14. 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

  15. 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.

  16. Computer-Aided Diagnosis System for Alzheimer's Disease Using Different Discrete Transform Techniques.

    PubMed

    Dessouky, Mohamed M; Elrashidy, Mohamed A; Taha, Taha E; Abdelkader, Hatem M

    2016-05-01

    The different discrete transform techniques such as discrete cosine transform (DCT), discrete sine transform (DST), discrete wavelet transform (DWT), and mel-scale frequency cepstral coefficients (MFCCs) are powerful feature extraction techniques. This article presents a proposed computer-aided diagnosis (CAD) system for extracting the most effective and significant features of Alzheimer's disease (AD) using these different discrete transform techniques and MFCC techniques. Linear support vector machine has been used as a classifier in this article. Experimental results conclude that the proposed CAD system using MFCC technique for AD recognition has a great improvement for the system performance with small number of significant extracted features, as compared with the CAD system based on DCT, DST, DWT, and the hybrid combination methods of the different transform techniques. PMID:26371347

  17. Chirped pulse amplification: Present and future

    SciTech Connect

    Maine, P.; Strickland, D.; Pessot, M.; Squier, J.; Bado, P.; Mourou, G.; Harter, D.

    1988-01-01

    Short pulses with ultrahigh peak powers have been generated in Nd: glass and Alexandrite using the Chirped Pulse Amplification (CPA) technique. This technique has been successful in producing picosecond terawatt pulses with a table-top laser system. In the near future, CPA will be applied to large laser systems such as NOVA to produce petawatt pulses (1 kJ in a 1 ps pulse) with focused intensities exceeding 10/sup /plus/21/ W/cm/sup 2/. These pulses will be associated with electric fields in excess of 100 e/a/sub o//sup 2/ and blackbody energy densities equivalent to 3 /times/ 10/sup 10/ J/cm/sup 3/. This petawatt source will have important applications in x-ray laser research and will lead to fundamentally new experiments in atomic, nuclear, solid-state, plasma, and high-energy density physics. A review of present and future designs are discussed. 17 refs., 5 figs.

  18. Effective temporal resolution in pump-probe spectroscopy with strongly chirped pulses

    SciTech Connect

    Polli, D.; Lanzani, G.; Brida, D.; Cerullo, G.; Mukamel, S.

    2010-11-15

    This paper introduces a general theoretical description of femtosecond pump-probe spectroscopy with chirped pulses whose joint spectral and temporal profile is expressed by Wigner spectrograms. We demonstrate that the actual experimental time resolution intimately depends on the pulse-sample interaction and that the commonly used instrumental response function needs to be replaced by a sample-dependent effective response function. We also show that, using the proper configurations in excitation and/or detection, it is possible to overcome the temporal smearing of the measured dynamics due to chirp-induced pulse broadening and recover the temporal resolution that would be afforded by the transform-limited pulses. We verify these predictions with experiments using broadband chirped pump and probe pulses. Our results allow optimization of the temporal resolution in the common case when the chirp of the pump and/or probe pulse is not corrected and may be extended to a broad range of time-resolved experiments.

  19. 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.

  20. SAR impulse response with residual chirps.

    SciTech Connect

    Doerry, Armin Walter

    2009-06-01

    A Linear Frequency-Modulated (LFM) chirp is a function with unit amplitude and quadratic phase characteristic. In a focused Synthetic Aperture Radar (SAR) image, a residual chirp is undesired for targets of interest, as it coarsens the manifested resolution. However, for undesired spurious signals, a residual chirp is often advantageous because it spreads the energy and thereby diminishes its peak value. In either case, a good understanding of the effects of a residual LFM chirp on a SAR Impulse Response (IPR) is required to facilitate system analysis and design. This report presents an analysis of the effects of a residual chirp on the IPR. As reference, there is a rich body of publications on various aspects of LFM chirps. A quick search reveals a plethora of articles, going back to the early 1950s. We mention here purely as trivia one of the earlier analysis papers on this waveform by Klauder, et al.

  1. Analytic signal demodulation of phase-modulated frequency-chirped signals.

    PubMed

    Niebauer, T M

    2013-03-20

    Both interferometers and frequency-modulated (FM) radios create sinusoidal signals with phase information that must be recovered. Often these two applications use narrow band signals but some applications create signals with a large bandwidth. For example, accelerated mirrors in an interferometer naturally create a chirped frequency that linearly increases with time. Chirped carriers are also used for spread-spectrum, FM transmission to reduce interference or avoid detection. In both applications, it is important to recover the underlying phase modulations that are superimposed on the chirped carrier. A common way to treat a chirped waveform is to fit zero crossings of the signal. For lower signal-to-noise applications, however, it is helpful to have a technique that utilizes data over the entire waveform (not just at zero crossings). We present a technique called analytic signal demodulation (ASD), which employs a complex heterodyne of the analytic signal to fully demodulate the chirped waveform. ASD has a much higher sensitivity for recovering phase information than is possible using a chirp demodulation on the raw data. This paper introduces a phase residual function, R(θ), that forms an analytic signal and provides a complex demodulation from the received signal in one step. The function defines a phase residual at each point on the chirped waveform, not just at the zero crossings. ASD allows sensitive detection of phase-modulated signals with a very small modulation index (much less than 0.01) that would otherwise be swamped by noise if the raw signal were complex demodulated. The mathematics used to analyze a phase-modulated chirped signal is quite general and can easily be extended for frequency profiles more complicated than a simple chirp. PMID:23518726

  2. Blind data hiding technique using the Fresnelet transform.

    PubMed

    Muhammad, Nazeer; Bibi, Nargis; Mahmood, Zahid; Kim, Dai-Gyoung

    2015-01-01

    A new blind data hiding scheme is proposed in which data is decomposed using the Fresnelet transform. The inverse Fresnelet transform is performed on decomposed subbands by choosing different key parameters, and the coded pattern of the information data is obtained. This coded pattern is embedded into particular subbands of the cover image using the wavelets. The proposed method has good imperceptibility and large capacity of the information embedded data. Using the Fresnelet transform with a family of wavelet transforms makes the scheme more efficient in terms of extracted accuracy of hidden information. Moreover, the hidden data can be recovered without access to the original cover data. The proposed method is used to resolve privacy and security issues raised with respect to emerging internet applications for the effective handling of confidential data. PMID:26753119

  3. 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.

  4. Chirp reduction and on/off contrast enhancement via optical injection locking and coherent carrier manipulation

    NASA Astrophysics Data System (ADS)

    Slavík, Radan; Kakande, Joseph; Phelan, Richard; O'Carroll, John; Kelly, Brian; Richardson, David J.

    2013-05-01

    The most cost-effective solution for modulating data onto an optical carrier is via direct modulation of a semiconductor laser. Unfortunately, this approach suffers from high chirp. The chirp can be reduced by reducing the on/off modulation contrast ratio (i.e. by keeping the signaling laser well above threshold when generating both logical `0' and `1' bits), but the low contrast ratio itself compromises performance. Other techniques can better suppress chirp, e,g., based on selfinjection or optical injection locking of the directly-modulated laser (slave) to another laser (master) that emits CW light. However, this technique although very efficient at eliminating chirp, also requires the slave laser be operated well above threshold. We show however that the issue of the limited on/off modulation contrast can be addressed in this instance by subtraction of the carrier using a component of the master beam and an interferometric arrangement.

  5. Chirped pulse amplification of 300 fs pulses in an Alexandrite regenerative amplifier

    SciTech Connect

    Pessot, M.; Squier, J.; Bado, P.; Mourou, G. ); Harter, D.J. )

    1989-01-01

    The authors demonstrate the amplification of femtosecond dye laser pulses up to the 3.5 mJ level in an alexandrite regenerative amplifier. An expansion/compression system using diffraction gratings allows chirped pulse amplification techniques to be used to produce peak powers upwards of 1 GW. Limitations in the chirped pulse amplification of ultrashort pulses due to intracavity dispersive elements are discussed.

  6. Time Resolved Optical Nonlinearities Using Long Chirped Pulses

    NASA Astrophysics Data System (ADS)

    Sutherland, R. L.; Tang, N.; Fleitz, P. A.; McLean, D. G.

    1997-03-01

    We have developed a novel technique for resolving optical nonlinearities with response time much shorter than the interrogating laser pulse. The method employs a simple two- wave mixing geometry in a time-delayed pump-probe scheme using chirped pulses. Although the pulse width is long compared to the material response time, the pulse chirp magnifies the time scale of the material response and allows measurement of very fast mechanisms. The transmission of the probe pulse as a function of delay time exhibits a Lorentzian dispersion-like curve. The time difference between the peak and valley yields the time response of the medium, while the peak-to-valley swing gives the refractive nonlinearity, and the deviation of the mean transmission from unity gives the two-photon absorption coefficient. We illustrate our technique by measuring nonlinearities in molten diphenyl butadiene referenced to carbon disulfide.

  7. Spectral property of ultrashort chirped pulsed Gaussian beams diffracted by Gaussian aperture in dispersive media

    NASA Astrophysics Data System (ADS)

    Zou, Qihui; Hu, Qianhuan; Guo, Jie; Duan, Xi; Tong, Shihong

    2015-10-01

    Based on the Fresnel-Kirchhoff diffraction integral and Fourier transform, the propagation equation and its Fourier spectrum for ultra-short chirped pulsed Gaussian beams diffracted by Gaussian aperture are derived in dispersive medium, and the frequency-domain analytical electric field are presented. The effects of relative aperture, transmission distance and chirp parameter on the axial spectral properties are illustrated with numerical calculation results, and the variations of off-axis power spectrum with relative aperture, transmission distance and off-axis radius are given. It is found that the axial power spectrum of ultra-short chirped pulsed Gaussian increases with increasing relative aperture, the axial spectral blue-shift increases and approaches an asymptotic value associated with chirp parameter and propagation distance. The axial spectra of ultra-short chirped pulsed Gaussian become broadened with increasing the absolute value of the chirp parameter. With increasing off-axis radius, the off-axis power spectrum reduce rapidly, and the distribution of spectra shifts to the left. The off-axis spectral redshift increases with increasing off-axis radius.

  8. 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.

  9. Population inversion by chirped pulses

    SciTech Connect

    Lu Tianshi

    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.

  10. Chirp signal generator feasibility study

    NASA Astrophysics Data System (ADS)

    Chomiki, M.; Genauzeau, F.

    1983-03-01

    The feasibility of a signal generator with 100 microsec temporal dispersion, and 330 MHz frequency dispersion, for the ERS-1 (ESA satellite) radar altimeter, with a solid state transmitter, is demonstrated. Two surface wave dispersive filters (20 and 80 microsec dispersion) are cascaded with a frequency multiplier to give a 900 MHz output signal. The first filter receives an impulse which ensures an output signal to noise ratio 20 dB. The chirp signal output level is 0 dBm; amplitude fluctuation 2 dBcc, phase error compared with theory 10 deg rms; short term jitter 100 psec. The generator model occupies 0.5 l, and consumes 7 W.

  11. Synthesis of fiber Bragg grating for gain-narrowing compensation in high-power Nd: Glass chirped pulse amplification system

    NASA Astrophysics Data System (ADS)

    Liu, Qiong; Ye, Qing; Pan, Zhengqing; Luo, Aiping; Cai, Haiwen; Qu, Ronghui; Fang, Zujie

    2011-05-01

    We propose and analyze theoretically a method to compensate gain-narrowing effect by using the spectral shaping technology based on superstructure fiber Bragg grating (SSFBG) in high-power Nd:glass chirped pulse amplification system. The target spectrum is firstly calculated from hundreds joules amplified chirped Gaussian or super-Gaussian pulse by an inverse engineering operation. A genetic algorithm is used to design the SSFBG and obtain the index modulation distribution of grating which can transform the initial seed pulse to the target spectrum. The numerically simulations show that the spectral narrowing effect of chirped pulse amplification will be reduced largely and the ideal pulse spectrum (Gaussian or super-Gaussian) is also obtained. It is believed that this proposed method will provide a theoretical direction for the following experiment. Moreover, it will also be useful and flexible for the spectral transform in other chirped pulse application areas.

  12. Short-range harmonic radar: chirp waveform, electronic targets

    NASA Astrophysics Data System (ADS)

    Mazzaro, Gregory J.; Gallagher, Kyle A.; Martone, Anthony F.; Sherbondy, Kelly D.; Narayanan, Ram M.

    2015-05-01

    Radio-frequency (RF) electronic targets, such as man-portable electronics, cannot be detected by traditional linear radar because the radar cross section of those targets is much smaller than that of nearby clutter. One technology that is capable of separating RF electronic targets from naturally-occurring clutter is nonlinear radar. Presented in this paper is the evolution of nonlinear radar at the United States Army Research Laboratory (ARL) and recent results of short-range over-the-air harmonic radar tests there. For the present implementation of ARL's nonlinear radar, the transmit waveform is a chirp which sweeps one frequency at constant amplitude over an ultra-wide bandwidth (UWB). The receiver captures a single harmonic of this entire chirp. From the UWB received harmonic, a nonlinear frequency response of the radar environment is constructed. An inverse Fourier Transform of this nonlinear frequency response reveals the range to the nonlinear target within the environment. The chirped harmonic radar concept is validated experimentally using a wideband horn antenna and commercial off-the-shelf electronic targets.

  13. 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

  14. 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.

  15. Pulse compression of an FM chirped CO(2) laser.

    PubMed

    Halmos, M J; Henderson, D M; Duvall Iii, R L

    1989-09-01

    A CO(2) laser has been FM chirp modulated by a CdTe intracavity modulator. A frequency deviation-of-100 MHz in 2 micros was attained in this fashion. Following heterodyne detection the chirped pulse was compressed to 15 ns using a surface acoustic wave compression filter. This corresponded to a compression factor of 130. The suppression of unwanted sidelobes with a weighting filter was demonstrated. We have explored the use of this technique for laser radar systems and described an electrooptically FM modulated CO(2) waveguide laser with postdetection pulse compression by a surface acoustic wave compressive filter. To our knowledge this is the first report of the successful operation of this important system. PMID:20555743

  16. 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.

  17. 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…

  18. Redox transformations in peroxidases studied by pulse radiolysis technique

    NASA Astrophysics Data System (ADS)

    Gȩbicka, L.; Gȩbicki, J. L.

    By means of pulse radiolysis technique, redox processes in two heme enzymes, horseradish peroxidase (HRP) and lactoperoxidase (LPO) have been studied. It has been found that both hydrated electron and hydroxyl radical reduce HRP and LPO to their ferrous forms. The formation of compound III (an oxyform of the heme enzyme) in a two-step reaction of LPO and HRP with superoxide anion has been proposed.

  19. Transionospheric signal detection with chirped wavelets

    SciTech Connect

    Doser, A.B.; Dunham, M.E.

    1997-11-01

    Chirped wavelets are utilized to detect dispersed signals in the joint time scale domain. Specifically, pulses that become dispersed by transmission through the ionosphere and are received by satellites as nonlinear chirps are investigated. Since the dispersion greatly lowers the signal to noise ratios, it is difficult to isolate the signals in the time domain. Satellite data are examined with discrete wavelet expansions. Detection is accomplished via a template matching threshold scheme. Quantitative experimental results demonstrate that the chirped wavelet detection scheme is successful in detecting the transionospheric pulses at very low signal to noise ratios.

  20. Chirped-Pulse Microwave Spectroscopy in the Undergraduate Chemistry Curriculum

    NASA Astrophysics Data System (ADS)

    Gaster, Sydney A.; Hall, Taylor M.; Arnold, Sean; Brown, Gordon G.

    2015-06-01

    The use of chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy as a tool for training undergraduates will be discussed. Coker College's inexpensive, versatile CP-FTMW spectrometer has been applied both in the undergraduate teaching laboratory and the undergraduate research laboratory. In both cases, the education of the students is a central priority of the project. The study of 3-iodopyridine, a project recently completed by Coker undergraduate students, will be discussed. Details of the Coker CP-FTMW spectrometer will also be presented.

  1. Adaptive Chirp Beamforming for Direction-of-Arrival Estimation of Wideband Chirp Signals in Sensor Arrays

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Soo; Choi, Byung-Woong; Bae, Eun-Hyon; Lee, Kyun-Kyung

    An adaptive chirp beamforming method is proposed to solve the bias problem in the direction-of-arrival (DOA) estimation of wideband chirp signals that have identical time-frequency parameters yet emanate from different directions. The proposed method, based on the steered minimum variance (STMV) method, exploits the time-frequency structure of a chirp signal to improve the DOA estimation performance by effectively suppressing the wideband chirp interferences causing the bias. Simulations are performed to demonstrate the effectiveness of the proposed method.

  2. Incipient fault diagnosis of power transformers using optical spectro-photometric technique

    NASA Astrophysics Data System (ADS)

    Hussain, K.; Karmakar, Subrata

    2015-06-01

    Power transformers are the vital equipment in the network of power generation, transmission and distribution. Mineral oil in oil-filled transformers plays very important role as far as electrical insulation for the winding and cooling of the transformer is concerned. As transformers are always under the influence of electrical and thermal stresses, incipient faults like partial discharge, sparking and arcing take place. As a result, mineral oil deteriorates there by premature failure of the transformer occurs causing huge losses in terms of revenue and assets. Therefore, the transformer health condition has to be monitored continuously. The Dissolved Gas Analysis (DGA) is being extensively used for this purpose, but it has some drawbacks like it needs carrier gas, regular instrument calibration, etc. To overcome these drawbacks, Ultraviolet (UV) -Visible and Fourier Transform Infrared (FTIR) Spectro-photometric techniques are used as diagnostic tools for investigating the degraded transformer oil affected by electrical, mechanical and thermal stresses. The technique has several advantages over the conventional DGA technique.

  3. 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.

  4. A chirp modem incorporating interference excision

    NASA Astrophysics Data System (ADS)

    Darbyshire, E. P.; Gott, G. F.

    1992-08-01

    The paper describes an experimental 75-baud chirp modem designed to operate at high frequency (HF), which is able to reject interference from other HF users by adaptive filtering at the receiver. It also has inherently good performance in multipath preparation and in white noise, and is thus capable of robust digital communication. The system has been tested over a 170 km point-to-point HF skywave link, in which short chirp messages (approximately 30 s duration) were alternated in time with frequency-exchange keyed (FEK) messages. The total duration of the tests was 72 hours, and included day and night operation. In these tests, the chirp system had an overall performance which was superior to that of FEK. FEK occasionally suffered from long periods (e.g., 1 hour) of severe failure, essentially due to interference, whereas the chirp modem achieved more continuous useful operation.

  5. Ultrashort-attosecond-pulse generation by reducing harmonic chirp with a spatially inhomogeneous electric field

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Chen, Gao; Li, Su-Yu; Ding, Da-Jun; Chen, Ji-Gen; Guo, Fu-Ming; Yang, Yu-Jun

    2015-09-01

    We theoretically study high-order harmonic generation from an inhomogeneous field originated by the interaction between an ultrashort laser pulse and a gold nanostructure and demonstrate that ultrashort isolated attosecond pulses can be generated by reducing the harmonic chirp with the spatially inhomogeneous electric field. It can be found that the instants of ionized electrons coming back to the core are highly concentrated in the case of the spatially inhomogeneous electric field and a broadband supercontinuum harmonic spectrum with less chirp can be produced. Then an isolated 127-as pulse close to the Fourier transform limit can be directly generated without phase compensation.

  6. Photodissociation of Methyl Isothiocyanate Studied Using Chirped Pulse Uniform Flow Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ariyasingha, Nuwandi M.; Zack, Lindsay N.; Abeysekera, Chamara; Joalland, Baptiste; Suits, Arthur

    2015-06-01

    Chirped-Pulse Fourier-transform microwave spectroscopy has been applied in a uniform supersonic flow (Chirped-pulse/Uniform flow, CPUF) to study the 193 nm photodissociation of methyl isothiocyanate (MITC). Several products (CH3NC, NCS, H2CS, HCN and HNC) were identified via their pure rotational spectra. Observation of CH3NC and NCS are consistent with previous studies of this system, however it is the first detection of H2CS and HCN/HNC. Branching ratios were obtained from these data and will be discussed.

  7. Control of the two-Photon Double Ionization of Helium with Intense Chirped Attosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Barmaki, Samira; Laulan, Stephane

    2014-05-01

    We study the two-photon double ionization process of the helium atom by solving numerically the nonrelativistic time-dependent Schrödinger equation in its full dimensionality. We investigate with an intense chirped attosecond laser pulse of central carrier frequency that corresponds to the 29th harmonic of a Ti-sapphire laser the direct and sequential processes in helium. We show how it is possible by adjusting the chirp parameter to control the dominance of one process over the other within the atom. Attosecond chirped laser pulses offer a promising way to probe and control the two-photon double ionization of helium when compared with attosecond transform-limited pulses.

  8. 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

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

    PubMed

    Illias, Hazlee Azil; Chai, Xin Rui; Abu Bakar, Ab Halim; Mokhlis, Hazlie

    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

  10. 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.

  11. [The applications for Fourier transform infrared spectrum analysis technique in preventive medicine field].

    PubMed

    Yang, Jiao-lan; Luo, Tian

    2002-08-01

    This paper expatriated the applications for Fourier transform infrared spectrum analysis technique in preventive medicine field from four aspects of environmental pollution, life science, and the latest infrared analysis methods and near infrared analysis technique. In the environmental pollution field, it mainly described the advantages, the limitations and the solutions of the combined applications for gas chromatograph and Fourier transform infrared spectrum. In the life science field, it described the application for Fourier transform infrared spectrum analysis technique on protein secondary structure, membrane protein, phospholipid, nucleic acid, cell, tissue. In addition, it also introduced a few latest infrared analysis methods and the applications for near infrared spectrum analysis technique in food, cosmetic, drug. PMID:12938378

  12. Interplay of the Chirps and Chirped Pulse Compression in a High-gain Seeded Free-electron Laser

    SciTech Connect

    Wu, Juhao; Murphy, J.B.; Emma, P.J.; Wang, X.J.; Watanabe, T.; Zhong, Xinming; /Beijing Normal U.

    2007-01-03

    In a seeded high-gain Free-electron Laser (FEL), where a coherent laser pulse interacts with an ultra-relativistic electron beam, the seed laser pulse can be frequency chirped, and the electron beam can be energy chirped. Besides these two chirps, the FEL interaction introduces an intrinsic frequency chirp in the FEL even if the above mentioned two chirps are absent. In this paper we examine the interplay of these three chirps. The problem is formulated as an initial value problem, and solved via a Green function approach. Besides the chirp evolution, we also give analytical expressions for the pulse duration and bandwidth of the FEL, which remains fully longitudinally coherent in the high gain exponential growth regime. Because the chirps are normally introduced for a final compression of the FEL pulse, some conceptual issues are discussed. We show that in order to get a short pulse duration, an energy chirp in the electron beam is necessary.

  13. Efficient Formation of Ultracold Molecules with Chirped Nanosecond Pulses.

    PubMed

    Carini, J L; Kallush, S; Kosloff, R; Gould, P L

    2016-05-19

    We describe experiments and associated quantum simulations involving the production of ultracold (87)Rb2 molecules with nanosecond pulses of frequency-chirped light. With appropriate chirp parameters, the formation is dominated by coherent processes. For a positive chirp, excited molecules are produced by photoassociation early in the chirp, and then transferred into high vibrational levels of the lowest triplet state by stimulated emission later in the chirp. Generally good agreement is seen between the data and the simulations. Shaping of the chirp can lead to a significant enhancement of the formation rate. Further improvements using higher intensities and different intermediate states are predicted. PMID:26652642

  14. 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.

  15. Development of broad spectrum technologies for high energy chirped pulse amplification

    NASA Astrophysics Data System (ADS)

    Hays, Gregory Ross

    We have developed several broad-spectrum technologies for high-intensity chirped pulse amplification. We present the design and performance of two 20 TW laser systems. THOR is a Ti:sapphire, 10 Hz, ultra-fast laser that produces femtosecond pulses with a peak intensity of 18.4 TW. The laser operates near the bandwidth limit of the medium maintaining sufficient spectrum to produce 38 fs pulses. This equates to a near transform limited time-bandwidth product of 0.490. The second laser system was developed to study broad-spectrum pulse amplification in mixed Neodymium-doped laser glasses. Our efforts were to produce a multi-Joule laser with sufficient bandwidth to compress near 100 fs using mixed-glasses in the final amplifier. We present the GHOST laser with modeling and experimental analysis of the precise gain ratios between the mixed glasses. GHOST examines the bandwidth limit of the mixed-glass architecture in order to produce the broadest amplified spectrum with the shortest compressed pulsewidth. The laser has a total gain of 4x109 with a net gain of 260 from glass. The measured optimum gain ratio of 3.3 (G phos/Gsil) produced 14.4 nm (FWHM) of bandwidth with a 103 fs pulsewidth. This constitutes a time-bandwidth product of 0.398. Additionally we have investigated two novel laser glasses in an effort to generate high energy (>1 kJ), broad spectrum pulses from a chirped-pulse amplification Nd:glass laser. Both glasses have significantly broader spectra (>38 nm FWHM) than currently available Nd:phosphate and Nd:silicate glasses. We present calculations for small signal pulse amplification to simulate spectral gain narrowing. The technique of spectral shaping using mixed-glass architecture with an optical parametric chirped-pulse amplification front-end is evaluated. Our modeling shows amplified pulses with energies exceeding 10 kJ with sufficient bandwidth to achieve 120 fs pulse widths are achievable with the use of the new laser glasses. With further development of current technologies, a laser system could be scaled to generate one exawatt in peak power. Finally we report controlled enhancement of optical third harmonic generation from hydrodynamically expanding clusters of noble gas atoms several hundred femtoseconds following ionization and heating by ultrashort pump pulses.

  16. An efficient coordinate transformation technique for unsteady, transonic aerodynamic analysis of low aspect-ratio wings

    NASA Technical Reports Server (NTRS)

    Guruswamy, G. P.; Goorjian, P. M.

    1984-01-01

    An efficient coordinate transformation technique is presented for constructing grids for unsteady, transonic aerodynamic computations for delta-type wings. The original shearing transformation yielded computations that were numerically unstable and this paper discusses the sources of those instabilities. The new shearing transformation yields computations that are stable, fast, and accurate. Comparisons of those two methods are shown for the flow over the F5 wing that demonstrate the new stability. Also, comparisons are made with experimental data that demonstrate the accuracy of the new method. The computations were made by using a time-accurate, finite-difference, alternating-direction-implicit (ADI) algorithm for the transonic small-disturbance potential equation.

  17. Inverse synthetic aperture radar imaging of targets with complex motions based on modified chirp rate-quadratic chirp rate distribution for cubic phase signal

    NASA Astrophysics Data System (ADS)

    Yanyan, Li; Tao, Su; Jibin, Zheng

    2015-01-01

    For targets with complex motions, the time-varying Doppler frequency deteriorates inverse synthetic aperture radar (ISAR) images. After range alignment and phase adjustment, azimuth echoes in a range cell can be modeled as multicomponent cubic phase signals (CPSs). The chirp rate and the quadratic chirp rate of the CPS are identified as the causes of the time-varying Doppler frequency; thus, it is necessary to estimate these two parameters correctly to obtain a well-focused ISAR image. The parameter-estimation algorithm based on the modified chirp rate-quadratic chirp rate distribution (M-CRQCRD) is proposed for the CPS and applied to the ISAR imaging of targets with complex motions. The computational cost of M-CRQCRD is low, because it can be implemented by the fast Fourier transform (FFT) and the nonuniform FFT easily. Compared to two representative parameter-estimation algorithms, the M-CRQCRD can acquire a higher antinoise performance due to the introduction of an optimal lag-time. Through simulations and analyses for the synthetic radar data, the effectiveness of the M-CRQCRD and the imaging algorithm based on the M-CRQCRD are verified.

  18. 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

  19. Plasma absorption evidence via chirped pulse spectral transmission measurements

    SciTech Connect

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

    2015-06-08

    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.

  20. Optical cryptographic system employing multiple reference-based joint transform correlation technique

    NASA Astrophysics Data System (ADS)

    Islam, Mohammed Nazrul; Karim, Mohammad Ataul; Alam, Mohammad Showkat; Asari, K. Vijayan

    2011-06-01

    An optical joint transform correlation-based cryptographic system is a used to feed multiple phase-shifted encryption keys into four parallel channels along with a to-be-encrypted signal in the form of an image. The resulting joint power spectra (JPS) signals are phase-shifted and then combined to yield a modified JPS signal. Inverse Fourier transformation of the modified JPS signal yields the secured encrypted image. For decryption purpose, the received encrypted signal is first Fourier transformed and multiplied by the encryption key used in encryption. The derived signal is then inverse Fourier transformed to generate the output signal. The proposed system offers a nonlinear encryption without the involvement of any complex mathematical operation on the encryption key otherwise required in similar encryption techniques and is invariant to noise. Computer simulation results are presented to show the effectiveness of the proposed scheme with binary, as well as gray images in both noise-free and noisy environment.

  1. Multiple color images encryption by triplets recombination combining the phase retrieval technique and Arnold transform

    NASA Astrophysics Data System (ADS)

    Shi, Xiaoyan; Zhao, Daomu; Huang, Yinbo; Pan, Jianjiang

    2013-10-01

    We propose a new method for multiple color images encryption by using triplets recombination. In this proposed technique, triplet (R, G and B) components of the secret color image are recorded simultaneously as a real and positive gray image exploiting parallel multi-wavelength recording technology. Arnold transform and phase retrieval algorithm adapted to Fresnel transform domain are used to encode the parallel hybrid result. By using of the proposed technique, each color image is encrypted into a pure phase distribution and combined by superposition. Phase modulation is introduced to eliminate the cross-talk caused by multiple images superposition. The wavelength and transform parameters are provided as keys to enhance the system security. In addition, computer simulations are performed and numerical results are presented to show the validity and efficiency of the proposed method.

  2. A frequency based encoding technique for transformation of categorical variables in mixed IVF dataset.

    PubMed

    Uyar, Asli; Bener, Ayse; Ciray, H; Bahceci, Mustafa

    2009-01-01

    Implantation prediction of in-vitro fertilization (IVF) embryos is critical for the success of the treatment. In this study, Support Vector Machine (SVM) method has been used on an original IVF dataset for classification of embryos according to implantation potentials. The dataset we analyzed includes both categorical and continuous feature values. Transformation of categorical variables into numeric attributes is an important pre-processing stage for SVM affecting the performance of the classification. We have proposed a frequency based encoding technique for transformation of categorical variables. Experimental results revealed that, the proposed technique significantly improved the performance of IVF implantation prediction in terms of Area Under ROC curve (0.712+/-0.032) compared to common binary encoding and expert judgement based transformation methods (0.676+/-0.033 and 0.696 +/- 0.024, respectively). PMID:19964898

  3. Diagnostic techniques and apparatus for detecting faults in perfluorocarbon liquid immersed transformers

    SciTech Connect

    Mizuno, K.; Ogawa, A.; Ooe, E.; Mori, E.

    1996-04-01

    This paper deals with techniques and an apparatus designed to diagnosis transformer faults by detecting C{sub 2}F{sub 4}, C{sub 2}F{sub 6} and C{sub 3}F{sub 6} gases contained in perfluorocarbon (PFC) liquid. The authors first established fault diagnostic techniques that employ gas patterns, gas composition ratios and fault diagnostic diagram and flow chart, based on the C{sub 2}F{sub 4}, C{sub 2}F{sub 6} and C{sub 3}F{sub 6} gases generated by overheating, partial discharges and arc discharges. Then, the authors verified the possibility of diagnosing internal faults in PFC liquid-immersed transformers when internal fault simulation tests on transformer model are conducted. The C{sub 2}F{sub 4} and C{sub 3}F{sub 6} gases generated there are detected with the gas diagnostic apparatus equipped with a gas sensor.

  4. Control of the Atomic Ionization with Short and Intense Chirped Laser Pulses

    NASA Astrophysics Data System (ADS)

    Hennani, Salima; Laulan, Stephane; Barmaki, Samira

    2014-05-01

    We investigate a two-photon ionization process in a real hydrogen atom by short and intense chirped laser pulses. Our simulation of the laser-atom interaction consists on numerically solving the three-dimensional time-dependent Schrödinger equation with a spectral method. The unperturbed wave functions and electronic energies of the atomic system were found by using an accurate L2 discretization technique based on the expansion of the wave functions on B-spline functions. We show the efficiency of chirped laser pulses to control the ionization yield and the transfer of the population to the 2 p bound state involved in the ionization path.

  5. Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal

    SciTech Connect

    Trull, J.; Wang, B.; Parra, A.; Vilaseca, R.; Cojocaru, C.; Sola, I.; Sheng, Y.

    2015-06-01

    Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.

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

    SciTech Connect

    Yang Xihua; Zhang Zhenhua; Yan Xiaona; Li Chunfang

    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. Computer-Assisted Techniques to Enhance Transformative Learning in First-Year Literature Courses.

    ERIC Educational Resources Information Center

    Jamieson, Marguerite; Kajs, Rebecca; Agee, Anne

    1996-01-01

    Illustrates techniques to foster transformative learning in computer-assisted literature classes: (1) a lesson plan on John Donne's "A Valediction: Forbidding Mourning"; (2) a plan to analyze "Oedipus Rex" using the "Daedalus" Interactive Writing Environment; and (3) a demonstration of how students engage in "meta-reflection" as they explore

  8. Computer-Assisted Techniques to Enhance Transformative Learning in First-Year Literature Courses.

    ERIC Educational Resources Information Center

    Jamieson, Marguerite; Kajs, Rebecca; Agee, Anne

    1996-01-01

    Illustrates techniques to foster transformative learning in computer-assisted literature classes: (1) a lesson plan on John Donne's "A Valediction: Forbidding Mourning"; (2) a plan to analyze "Oedipus Rex" using the "Daedalus" Interactive Writing Environment; and (3) a demonstration of how students engage in "meta-reflection" as they explore…

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

    PubMed

    Csehi, Andrs; Halsz, Gbor J; Cederbaum, Lorenz S; Vibk, gnes

    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

  10. Chirp- and random-based coded ultrasonic excitation for localized blood-brain barrier opening.

    PubMed

    Kamimura, H A S; Wang, S; Wu, S-Y; Karakatsani, M E; Acosta, C; Carneiro, A A O; Konofagou, E E

    2015-10-01

    Chirp- and random-based coded excitation methods have been proposed to reduce standing wave formation and improve focusing of transcranial ultrasound. However, no clear evidence has been shown to support the benefits of these ultrasonic excitation sequences in vivo. This study evaluates the chirp and periodic selection of random frequency (PSRF) coded-excitation methods for opening the blood-brain barrier (BBB) in mice. Three groups of mice (n  =  15) were injected with polydisperse microbubbles and sonicated in the caudate putamen using the chirp/PSRF coded (bandwidth: 1.5–1.9 MHz, peak negative pressure: 0.52 MPa, duration: 30 s) or standard ultrasound (frequency: 1.5 MHz, pressure: 0.52 MPa, burst duration: 20 ms, duration: 5 min) sequences. T1-weighted contrast-enhanced MRI scans were performed to quantitatively analyze focused ultrasound induced BBB opening. The mean opening volumes evaluated from the MRI were mm3, mm3and mm3 for the chirp, random and regular sonications, respectively. The mean cavitation levels were V.s, V.s and V.s for the chirp, random and regular sonications, respectively. The chirp and PSRF coded pulsing sequences improved the BBB opening localization by inducing lower cavitation levels and smaller opening volumes compared to results of the regular sonication technique. Larger bandwidths were associated with more focused targeting but were limited by the frequency response of the transducer, the skull attenuation and the microbubbles optimal frequency range. The coded methods could therefore facilitate highly localized drug delivery as well as benefit other transcranial ultrasound techniques that use higher pressure levels and higher precision to induce the necessary bioeffects in a brain region while avoiding damage to the surrounding healthy tissue. PMID:26394091

  11. Multispectral image sharpening using wavelet transform techniques and spatial correlation of edges

    USGS Publications Warehouse

    Lemeshewsky, George P.; Schowengerdt, Robert A.

    2000-01-01

    Several reported image fusion or sharpening techniques are based on the discrete wavelet transform (DWT). The technique described here uses a pixel-based maximum selection rule to combine respective transform coefficients of lower spatial resolution near-infrared (NIR) and higher spatial resolution panchromatic (pan) imagery to produce a sharpened NIR image. Sharpening assumes a radiometric correlation between the spectral band images. However, there can be poor correlation, including edge contrast reversals (e.g., at soil-vegetation boundaries), between the fused images and, consequently, degraded performance. To improve sharpening, a local area-based correlation technique originally reported for edge comparison with image pyramid fusion is modified for application with the DWT process. Further improvements are obtained by using redundant, shift-invariant implementation of the DWT. Example images demonstrate the improvements in NIR image sharpening with higher resolution pan imagery.

  12. Cr4+ : YAG chirped-pulse oscillator

    PubMed Central

    Sorokin, Evgeni; Kalashnikov, Vladimir L; Mandon, Julien; Guelachvili, Guy; Picqué, Nathalie; Sorokina, Irina T

    2010-01-01

    We demonstrate chirped-pulse operation of a Cr : YAG passively mode-locked laser. Different operation regimes of the laser are extensively investigated in the vicinity of zero dispersion both experimentally and numerically. It is shown that for a given laser configuration, transition to the positive dispersion regime allows a 5-fold increase in the output pulse energy, which is otherwise limited by the onset of the multipulsing or ‘chaotic’ mode-locking. The output pulses have 1.4 ps duration and are compressible down to 120 fs in a 3 m piece of silica fiber, enabling supercontinuum generation in a nonlinear fiber. The spectrum shape and operation stability of the chirped-pulse regime depend strongly on the amount and shape of the intracavity dispersion. The numerical model predicts the existence of the minimum amount of the positive dispersion, above which the chirped-pulse regime can be realized. Once located, the chirped-pulse regime can be reliably reproduced and is sufficiently stable for applications. PMID:21151831

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

    SciTech Connect

    Xu Junjie; Zeng Bin; Yu Yongli

    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.

  14. Robust modulation formats recognition technique using wavelet transform for high speed optical networks

    NASA Astrophysics Data System (ADS)

    Guesmi, Latifa; Hraghi, Abir; Menif, Mourad

    2015-09-01

    There is a need, for high speed optical communication networks, in the monitoring process, to determine the modulation format type of a received signal. In this paper, we present a new achievement of modulation format recognition technique, where we proposed the use of wavelet transform of the detected signal in conjunction with the artificial neural network (ANN) algorithm. Besides, wavelet transform is one of the most popular candidates of the time-frequency transformations, where the wavelets are generated from a basic wavelet function by dilations and translations. We proved that this technique is capable of recognizing the multi-carriers modulation scheme with high accuracy under different transmission impairments such as chromatic dispersion (CD), differential group delay (DGD) and accumulated amplified spontaneous emission (ASE) noise with different ranges. Both the theoretical analysis and the simulation results showed that the wavelet transform not only can be used for modulation identification of optical communication signals, but also has a better classification accuracies under appropriate OSNR (optical signal-to-noise ratio) values.

  15. Filter implementation technique for multicriteria characterization of coding domains in the joint transform correlator.

    PubMed

    Bigué, L; Ambs, P

    1999-07-10

    An improved method for implementing correlation filters in the joint transform correlator architecture is proposed. We derived the method from computer-generated holography techniques. It allows us to use any correlation filters, especially ones that provide an optimal trade-off between noise robustness, peak sharpness, and optical efficiency, with any spatial light modulator (SLM). This method also allows for an objective comparison of the performance of the coding domains of various SLM's. PMID:18323915

  16. 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.

  17. 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

  18. Color enhancement of highly correlated images. II - Channel ratio and 'chromaticity' transformation techniques

    NASA Technical Reports Server (NTRS)

    Gillespie, Alan R.; Kahle, Anne B.; Walker, Richard E.

    1987-01-01

    Two techniques for enhancing the color of multispectral images are described; both involve ratioing of data from different image channels. In the first technique, the ratioed data are assigned the primary color for display as color ratio pictures, and in the second method, image data are transformed to RGB chromaticity coordinates by ratioing the data acquired in three channels to the sum of their intensities. The two techniques are applied to a NASA Thermal-IR Multispectral Scanner (TIMS) image of Death Valley and to a Landsat MSS image of the Mojave Desert. The basic principles of ratioing are discussed, and the effects of atmospheric path radiances on the interpretation of ratioed images are investigated. It is observed that the color pictures produced using these two enhancement techniques are similar to the pictures enhanced by decorrelation and hue-saturation-intensity methods.

  19. Techniques for Handling Channeling in High Resolution Fourier Transform Spectra Recorded with Synchrotron Sources

    SciTech Connect

    Ibrahim, Amr; PredoiCross, Adriana; Teillet, P. M.

    2010-10-29

    Seven different techniques in dealing the problem of channel spectra in Fourier transform Spectroscopy utilizing synchrotron source were examined and compared. Five of these techniques deal with the artifacts (spikes) in the recorded interferogram which in turn result in channel spectra within the spectral domain. Such interferogram editing method include replacing these spikes with zeros, straight line, fitted polynomial curve, rescaled spike and spike reduced with Gauss Function. Another two techniques try to target this issue in the spectral domain instead by either generating a synthetic background simulating the channels or measuring the channels parameters (amplitude, spacing and phase) to use in the spectral fitting program. Results showed spectral domain techniques produces higher quality results in terms of signal to noise and fitting residual. The effect of each method on the line parameters such as position, intensity are air broadening are also measured and discussed.

  20. TRANSFORMATION

    SciTech Connect

    LACKS,S.A.

    2003-10-09

    Transformation, which alters the genetic makeup of an individual, is a concept that intrigues the human imagination. In Streptococcus pneumoniae such transformation was first demonstrated. Perhaps our fascination with genetics derived from our ancestors observing their own progeny, with its retention and assortment of parental traits, but such interest must have been accelerated after the dawn of agriculture. It was in pea plants that Gregor Mendel in the late 1800s examined inherited traits and found them to be determined by physical elements, or genes, passed from parents to progeny. In our day, the material basis of these genetic determinants was revealed to be DNA by the lowly bacteria, in particular, the pneumococcus. For this species, transformation by free DNA is a sexual process that enables cells to sport new combinations of genes and traits. Genetic transformation of the type found in S. pneumoniae occurs naturally in many species of bacteria (70), but, initially only a few other transformable species were found, namely, Haemophilus influenzae, Neisseria meningitides, Neisseria gonorrheae, and Bacillus subtilis (96). Natural transformation, which requires a set of genes evolved for the purpose, contrasts with artificial transformation, which is accomplished by shocking cells either electrically, as in electroporation, or by ionic and temperature shifts. Although such artificial treatments can introduce very small amounts of DNA into virtually any type of cell, the amounts introduced by natural transformation are a million-fold greater, and S. pneumoniae can take up as much as 10% of its cellular DNA content (40).

  1. TRANSFORMER

    DOEpatents

    Baker, W.R.

    1959-08-25

    Transformers of a type adapted for use with extreme high power vacuum tubes where current requirements may be of the order of 2,000 to 200,000 amperes are described. The transformer casing has the form of a re-entrant section being extended through an opening in one end of the cylinder to form a coaxial terminal arrangement. A toroidal multi-turn primary winding is disposed within the casing in coaxial relationship therein. In a second embodiment, means are provided for forming the casing as a multi-turn secondary. The transformer is characterized by minimized resistance heating, minimized external magnetic flux, and an economical construction.

  2. Fractional Fourier plane image encryption technique using radial hilbert-, and Jigsaw transform

    NASA Astrophysics Data System (ADS)

    Joshi, Madhusudan; Shakher, Chandra; Singh, Kehar

    2010-07-01

    A new method for image encryption using integral order radial Hilbert transform (RHT) filter in the fractional Fourier transform (FRT) domain has been proposed. The technique is implemented using the popular double random phase encoding method in the fractional Fourier domain. The random phase masks (RPMs), integral orders of the RHT, fractional orders of FRT, and indices of the Jigsaw transform (JT) have been used as keys for encryption and decryption. Simulation results have been presented and the schematic representation for optical implementation has been proposed. The mean-square-error and signal-to-noise ratio between the decrypted image and the input image have been calculated for the correct as well as incorrect orders of the RHT. Effect of occlusion and noise on the performance of the proposed scheme has also been studied. The robustness of the technique has been verified against attack using partial windows of the correct random phase masks. Similar investigations have also been carried out for the chosen-, and the known-plain-text attacks.

  3. Inverse synthetic aperture radar imaging of maneuvering target based on cubic chirps model with time-varying amplitudes

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Zhang, Qingxiang; Zhao, Bin

    2016-01-01

    Inverse synthetic aperture radar (ISAR) imaging of maneuvering target is a main topic in the field of radar signal processing, and the received signal in a range bin can usually be characterized as multicomponent cubic chirps with constant amplitudes after motion compensation. In fact, the phenomenon of migration through resolution cell (MTRC) often occurs for the target's complex motion, and this will induce the time-varying character for the amplitudes of cubic chirps. An algorithm for the parameters estimation of multicomponent cubic chirps with time-varying amplitudes based on the extension form of match Fourier transform is proposed, and by using it in ISAR imaging of maneuvering target, the quality of images can be improved significantly compared with the constant amplitudes model. Results of simulated and real data validate the effectiveness of the algorithm in this paper.

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

    SciTech Connect

    Carrera, Juan J.; Chu, Shih-I

    2007-03-15

    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 cutoff extension can be achieved through the optimization of the chirping rate parameters. The HHG power spectrum is calculated by solving accurately and efficiently the time-dependent Schroedinger equation by means of the time-dependent generalized pseudospectral method. The time-frequency characteristics of the HHG power spectrum are analyzed in detail by means of the wavelet transform of the time-dependent induced dipole acceleration. In addition, we perform classical trajectory simulation of the strong-field electron dynamics and electron return map. It is found that the quantum and classical results provide complementary and consistent information regarding the underlying mechanisms responsible for the substantial extension of the cutoff region.

  5. Coherent control of ultracold collisions with chirped light: Direction matters

    SciTech Connect

    Wright, M. J.; Pechkis, J. A.; Carini, J. L.; Gould, P. L.; Kallush, S.; Kosloff, R.

    2007-05-15

    We demonstrate the ability to coherently control ultracold atomic Rb collisions using frequency-chirped light on the nanosecond time scale. For certain center frequencies of the chirp, the rate of inelastic trap-loss collisions induced by negatively chirped light is dramatically suppressed compared to the case of a positive chirp. We attribute this to a fundamental asymmetry in the system: an excited wave packet moves inward on the attractive molecular potential. For a positive chirp, the resonance condition moves outward in time, while for a negative chirp, it moves inward, in the same direction as the excited wave packet; this allows multiple interactions between the wave packet and the light, enabling the wave packet to be returned coherently to the ground state. Classical and quantum calculations support this interpretation.

  6. 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

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

    PubMed Central

    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

  8. 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.

  9. Next generation techniques in the high resolution spectroscopy of biologically relevant molecules.

    PubMed

    Neill, Justin L; Douglass, Kevin O; Pate, Brooks H; Pratt, David W

    2011-04-28

    Recent advances in the technology of test and measurement equipment driven by the computer and telecommunications industries have made possible the development of a new broadband, Fourier-transform microwave spectrometer that operates on principles similar to FTNMR. This technique uses a high sample-rate arbitrary waveform generator to construct a phase-locked chirped microwave pulse that gives a linear frequency sweep over a wide frequency range in 1 μs. The chirped pulse efficiently polarizes the molecular sample at all frequencies lying within this band. The subsequent free induction decay of this polarization is measured with a high-speed digitizer and then fast Fourier-transformed to yield a broadband, frequency-resolved rotational spectrum, spanning up to 11.5 GHz and containing lines that are as narrow as 100 kHz. This new technique is called chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The technique offers the potential to determine the structural and dynamical properties of very large molecules solely from fully resolved pure rotational spectra. FTMW double resonance techniques employing a low-resolution UV laser facilitate an easy assignment of overlapping spectra produced by different conformers in the sample. Of particular interest are the energy landscapes of conformationally flexible molecules of biological importance, including studies of their interaction with solvent and/or other weakly bound molecules. An example is provided from the authors' work on p-methoxyphenethylamine, a neurotransmitter, and its complexes with water. PMID:21394332

  10. Mechanism of electron acceleration by chirped laser pulse

    SciTech Connect

    Wu, X. Y.; Wang, P. X.; Kawata, S.

    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.

  11. 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.

  12. 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.

  13. Single image orthogonal fringe technique for resolution enhancement of the Fourier transform fringe analysis method

    NASA Astrophysics Data System (ADS)

    Tavares, Paulo J.; Vaz, Mário A. P.

    2013-03-01

    Gradient range and spatial resolution in Fourier Transform Profilometry depend on the size of the filter window in reciprocal space. The proposed methods to date for the elimination of the fundamental frequency and enlargement of the filter window are either too computationally complex or depend on the possibility of using two frames, thus disabling the method's ability to cope with dynamic situations and subjecting the results to possible intensity changes between the two frame acquisitions. This article describes a simple method for using a single crossed fringe pattern to accomplish that objective, greatly improving the previously reported technique, whilst retaining its main advantages.

  14. Fast Fourier transform scanning spreading resistance microscopy: a novel technique to overcome the limitations of classical conductive AFM techniques.

    PubMed

    Eyben, P; Bisiaux, P; Schulze, A; Nazir, A; Vandervorst, W

    2015-09-01

    A new atomic force microscopy (AFM)-based technique named fast Fourier transform scanning spreading-resistance microscopy (FFT-SSRM) has been developed. FFT-SSRM offers the ability to isolate the local spreading resistance (Sr) from the parasitic series resistance (probe, bulk, and back contact). The parasitic series resistance limits the use of classical SSRM in confined volumes and on very highly doped materials, two increasingly important situations in nanoelectronic components. This is realized via a force modulation at controlled frequency (affecting the SR component) and the extraction of the resistance amplitude at the modulation frequency, performing an FFT-based lock-in deconvolution. A systematic evaluation of the FFT-SSRM performances (i.e., resolution, dynamic range, sensitivity, and repeatability) is presented. The impact of various parameters (i.e., modulation frequency and amplitude or cutoff frequency of the current amplifier) on the performances of FFT-SSRM has been evaluated. We demonstrate the possibility to overcome sensitivity losses due to tip saturation in highly doped material and the utility of the technique in two different structures, presenting isolated and confined volumes. PMID:26245715

  15. [A new automatic quasars recognition technique based on PCA and Hough transform].

    PubMed

    Huang, Ling-yun; Hu, Zhan-yi

    2003-02-01

    The main purpose of quasar recognition is to determine the observed quasar spectrum's redshift value. Previously the template of quasar rest frame in the literature was basically constructed based on astronomers' hypotheses. Due to the inaccuracy of such a template, it is hard to determine the redshift value by matching the observed quasar spectrum with the template directly. This paper's main contributions are two-fold: Firstly, the template in our paper is constructed by the principal component analysis (PCA) method from some selected spectra with known redshift values, hence the obtained template is more realistic. Secondly, a 2D standard Hough transform, rather than a 1D Hough transform, is used. This is because although only redshift needs to be determined in our system, based on our observations, the magnitude of emission peak is also changed, hence a new parameter, namely scale parameter, is also introduced to the Hough transform to enhance the reliability of the recognition. The experiments show that the proposed technique is workable and the correct recognition rate can reach about as high as 90%. PMID:12940004

  16. 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.

  17. 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.

    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.

  18. Nonlinear frequency chirp measurement of frequency sweeping lasers for FD-OCT applications

    NASA Astrophysics Data System (ADS)

    Ahn, Tae-Jung; Kim, Dug Young

    2006-02-01

    A noble measurement method by using a homodyne interferometer and Hilbert transform has been proposed for characterizing frequency sweeping light sources used in traditional optical frequency domain reflectometer (OFDR) and optical frequency domain imaging (OFDI). A Michelson interferometer with a tunable laser generates a sinusoidal beating signal. A phase of measured beating signal as a function of time is approximately proportional to optical frequency of the swept light source during frequency tuning and can be obtained by the Hilbert transformation. Thus, optical frequency chirp can be determined by a simple equation related with the phase of the beating signal from the interferometer. We have demonstrated the effectiveness and the simplicity of our proposed method by testing a temperature-tuned frequency sweeping DFB-LD and a commercial external cavity tunable laser source as practical examples. In the case of DFB-LD, the frequency sweep becomes more linear while the amount of frequency sweep saturates as the amplitude of the control voltage applied to a TEC driver increases, and the frequency-tuning rate increases as the repetition rate decreases. We also found that a commercial frequency-sweeping laser has a feed back control to adjust its frequency-sweeping rate such that the tuning rate oscillates around an intended value as a function of time. We have demonstrated the possibility of using a self-homodyne interferometer as a powerful tool for characterizing frequency sweeping laser sources. We expect this method will be useful for improving the performance of many optical frequency domain measurement techniques such as OFDR, FD-OCT or OFDI.

  19. Transformation

    PubMed Central

    Knauer, Stefan H.; Rösch, Paul; Artsimovitch, Irina

    2012-01-01

    The textbook view that a primary sequence determines the unique fold of a given protein has been challenged by identification of proteins with variant structures, such as prions. Our recent studies revealed that the transcription factor RfaH simultaneously changes its topology and function. RfaH is a two-domain protein whose N-terminal domain binds to transcribing RNA polymerase, stimulating its processivity. The α-helical C-terminal domain masks the RNA polymerase-binding site of the N-terminal domain, preventing unwarranted recruitment to genes lacking a specific DNA sequence. Upon binding to its DNA target, RfaH domains dissociate, and the C-terminal domain refolds into a β-barrel. This dramatic transformation allows binding to the ribosomal protein S10 and subsequent recruitment of a ribosome, coupling transcription and translation. We define RfaH as first example of “transformer proteins”, in which two alternative structural states have distinct cellular functions and hypothesize that transformer proteins may be widespread in nature. PMID:23131843

  20. Impact of chirp on soliton trapping of dispersive waves in photonic crystal fiber with two zero dispersive wavelengths

    NASA Astrophysics Data System (ADS)

    Yang, Hua; Zeng, Qilin; Hu, Hui; Wang, Boyan; Wang, Weibin

    2014-08-01

    We present a numerical study of soliton trapping of dispersive waves with the effect of chirp during supercontinuum generation in photonic crystal fibers (PCF) pumped with femtosecond pulses in the anomalous dispersion region. For different propagation length along the PCF, we can see that the evolution of pulse can be divided into three stages: initial broadening stage, dramatic broadening stage and saturation broadening stage. We find a fascinating phenomenon that the intensity of blue-shifted dispersive waves (B-DWs) and red-shifted dispersive waves (R-DWs) will be enhanced with positive chirped. It reveals that the coupling between the Raman soliton and the DW under suitable chirp conditions may be a key mechanism in controlling the spectral broadening and soliton trapping of DW. Numerical study shows that initial chirp dramatically influences both the DW generation, spectral recoil and soliton trapping of DW. In order to clearly display the evolution of soliton trapping of DW by chirped pulses, we observed the spectrogram of output pulses using cross-correlation frequency-resolved optical gating technique (XFROG).

  1. Chirped femtosecond pulses in the higher-order nonlinear Schrödinger equation with non-Kerr nonlinear terms and cubic-quintic-septic nonlinearities

    NASA Astrophysics Data System (ADS)

    Triki, Houria; Biswas, Anjan; Milović, Daniela; Belić, Milivoj

    2016-05-01

    We consider a high-order nonlinear Schrödinger equation with competing cubic-quintic-septic nonlinearities, non-Kerr quintic nonlinearity, self-steepening, and self-frequency shift. The model describes the propagation of ultrashort (femtosecond) optical pulses in highly nonlinear optical fibers. A new ansatz is adopted to obtain nonlinear chirp associated with the propagating femtosecond soliton pulses. It is shown that the resultant elliptic equation of the problem is of high order, contains several new terms and is more general than the earlier reported results, thus providing a systematic way to find exact chirped soliton solutions of the septic model. Novel soliton solutions, including chirped bright, dark, kink and fractional-transform soliton solutions are obtained for special choices of parameters. Furthermore, we present the parameter domains in which these optical solitons exist. The nonlinear chirp associated with each of the solitonic solutions is also determined. It is shown that the chirping is proportional to the intensity of the wave and depends on higher-order nonlinearities. Of special interest is the soliton solution of the bright and dark type, determined for the general case when all coefficients in the equation have nonzero values. These results can be useful for possible chirped-soliton-based applications of highly nonlinear optical fiber systems.

  2. 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.

  3. 90 mJ parametric chirped pulse amplification of 10 fs pulses.

    PubMed

    Tavella, Franz; Marcinkevicius, Andrius; Krausz, Ferenc

    2006-12-25

    We demonstrate the amplification of broadband pulses from a Ti:Sapphire oscillator by non-collinear optical parametric chirped-pulse amplification technique in a type-I BBO crystal to energies of 90 mJ. Partial compression of the amplified pulses is demonstrated down to a 10 fs duration. These parameters come in combination with good spatial quality and focusability of the amplified beam. PMID:19532173

  4. Fiber grating compression of giant-chirped nanosecond pulses from an ultra-long nanotube mode-locked fiber laser.

    PubMed

    Woodward, R I; Kelleher, E J R; Runcorn, T H; Loranger, S; Popa, D; Wittwer, V J; Ferrari, A C; Popov, S V; Kashyap, R; Taylor, J R

    2015-02-01

    We demonstrate that the giant chirp of coherent, nanosecond pulses generated in an 846 m long, all-normal dispersion, nanotube mode-locked fiber laser can be compensated using a chirped fiber Bragg grating compressor. Linear compression to 11 ps is reported, corresponding to an extreme compression factor of ∼100. Experimental results are supported by numerical modeling, which is also used to probe the limits of this technique. Our results unequivocally conclude that ultra-long cavity fiber lasers can support stable dissipative soliton attractors and highlight the design simplicity for pulse-energy scaling through cavity elongation. PMID:25680054

  5. Phase and intensity characterization of femtosecond pulses from a chirped-pulse amplifier by frequency-resolved optical gating

    SciTech Connect

    Kohler, B.; Yakovlev, V.V.; Wilson, K.R.; Squier, J.; DeLong, K.W.; Trebino, R.

    1995-03-01

    Frequency-resolved optical gating (FROG) measurements were made to characterize pulses from a Ti:sapphire chirped-pulse amplified laser system. By characterizing both the pulse intensity and the phase, the FROG data provided the first direct observation to our knowledge of residual phase distortion in a chirped-pulse amplifier. The FROG technique was also used to measure the regenerative amplifier dispersion and to characterize an amplitude-shaped pulse. The data provide an experimental demonstration of the value of FROG for characterizing complex pulses, including tailored femtosecond pulses for quantum control.

  6. 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.

  7. Measurements of solar magnetic fields by Fourier transform techniques. II - Saturated and blended lines

    NASA Technical Reports Server (NTRS)

    Tarbell, T. D.; Title, A. M.

    1976-01-01

    Fourier techniques have been exhaustively calibrated using Unno's (1956) results for the absorption profile of a simple Zeeman triplet. If a simple transformation is applied to the normalized line depths, then magnetic-field strengths and inclination angles can be measured very accurately from noisy saturated line profiles. Systematic errors caused by saturation effects can be estimated and reduced by varying one parameter. When a significant fraction of the line profile is unsplit and unpolarized, large errors may be made in measurements of low fields, unless the line is sufficiently weak. For a weak line, a vertical field of 1600 gauss can be measured to 10% accuracy even when 70% of the line profile is stray light. These stray-light errors are troublesome in measuring fields of gaps and pores but not sunspots. Numerical results of the error analysis are presented graphically.

  8. A carrier removal technique for Fourier transform profilometry based on principal component analysis

    NASA Astrophysics Data System (ADS)

    Feng, Shijie; Chen, Qian; Zuo, Chao; Sun, Jiasong; Tao, Tianyang; Hu, Yan

    2015-11-01

    We present a carrier removal method for Fourier transform profilometry using the principal component analysis. The proposed approach is able to decompose the phase map into several principal components, in which the phase of the carrier can be extracted from the first dominant component acquired. It can cope well with the nonlinear carrier problem resulted from the divergent illumination which is commonly adopted in the fringe projection profilometry. It is effective, fully automatic and does not require the estimation for system geometrical parameters or the prior knowledge on the measured object. Further, the influence of the lens distortion is considered thus the carrier can be determined more accurately. The principle of the technique is verified by our experiments, showing that it performs well in both static and dynamic measurements.

  9. Prepreg cure monitoring using diffuse reflectance-FTIR. [Fourier Transform Infrared Technique

    NASA Technical Reports Server (NTRS)

    Young, P. R.; Chang, A. C.

    1984-01-01

    An in situ diffuse reflectance-Fourier transform infrared technique was developed to determine infrared spectra of graphite fiber prepregs as they were being cured. A bismaleimide, an epoxy, and addition polyimide matrix resin prepregs were studied. An experimental polyimide adhesive was also examined. Samples were positioned on a small heater at the focal point of diffuse reflectance optics and programmed at 15 F/min while FTIR spectra were being scanned, averaged, and stored. An analysis of the resulting spectra provided basic insights into changes in matrix resin molecular structure which accompanied reactions such as imidization and crosslinking. An endo-exothermal isomerization involving reactive end-caps was confirmed for the addition polyimide prepregs. The results of this study contribute to a fundamental understanding of the processing of composites and adhesives. Such understanding will promote the development of more efficient cure cycles.

  10. Chirped fiber Bragg grating detonation velocity sensing.

    PubMed

    Rodriguez, G; Sandberg, R L; McCulloch, Q; Jackson, S I; Vincent, S W; Udd, E

    2013-01-01

    An all optical-fiber-based approach to measuring high explosive detonation front position and velocity is described. By measuring total light return using an incoherent light source reflected from a linearly chirped fiber Bragg grating sensor in contact with the explosive, dynamic mapping of the detonation front position and velocity versus time is obtained. We demonstrate two calibration procedures and provide several examples of detonation front measurements: PBX 9502 cylindrical rate stick, radial detonation front in PBX 9501, and PBX 9501 detonation along curved meridian line. In the cylindrical rate stick measurement, excellent agreement with complementary diagnostics (electrical pins and streak camera imaging) is achieved, demonstrating accuracy in the detonation front velocity to below the 0.3% level when compared to the results from the pin data. Finally, an estimate on the linear spatial and temporal resolution of the system shows that sub-mm and sub-?s levels are attainable with proper consideration of the recording speed, detection sensitivity, spectrum, and chirp properties of the grating. PMID:23387683

  11. Chirp- and random-based coded ultrasonic excitation for localized blood-brain barrier opening

    NASA Astrophysics Data System (ADS)

    Kamimura, H. A. S.; Wang, S.; Wu, S.-Y.; Karakatsani, M. E.; Acosta, C.; Carneiro, A. A. O.; Konofagou, E. E.

    2015-10-01

    Chirp- and random-based coded excitation methods have been proposed to reduce standing wave formation and improve focusing of transcranial ultrasound. However, no clear evidence has been shown to support the benefits of these ultrasonic excitation sequences in vivo. This study evaluates the chirp and periodic selection of random frequency (PSRF) coded-excitation methods for opening the blood-brain barrier (BBB) in mice. Three groups of mice (n  =  15) were injected with polydisperse microbubbles and sonicated in the caudate putamen using the chirp/PSRF coded (bandwidth: 1.5-1.9 MHz, peak negative pressure: 0.52 MPa, duration: 30 s) or standard ultrasound (frequency: 1.5 MHz, pressure: 0.52 MPa, burst duration: 20 ms, duration: 5 min) sequences. T1-weighted contrast-enhanced MRI scans were performed to quantitatively analyze focused ultrasound induced BBB opening. The mean opening volumes evaluated from the MRI were 9.38+/- 5.71 mm3, 8.91+/- 3.91 mm3and 35.47+/- 5.10 mm3 for the chirp, random and regular sonications, respectively. The mean cavitation levels were 55.40+/- 28.43 V.s, 63.87+/- 29.97 V.s and 356.52+/- 257.15 V.s for the chirp, random and regular sonications, respectively. The chirp and PSRF coded pulsing sequences improved the BBB opening localization by inducing lower cavitation levels and smaller opening volumes compared to results of the regular sonication technique. Larger bandwidths were associated with more focused targeting but were limited by the frequency response of the transducer, the skull attenuation and the microbubbles optimal frequency range. The coded methods could therefore facilitate highly localized drug delivery as well as benefit other transcranial ultrasound techniques that use higher pressure levels and higher precision to induce the necessary bioeffects in a brain region while avoiding damage to the surrounding healthy tissue.

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

    PubMed

    Kaprálová-Žďánská, Petra Ruth; Moiseyev, Nimrod

    2014-07-01

    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. PMID:25005289

  13. Temporal compression and shaping of chirped biphotons using Fresnel-inspired binary phase shaping

    NASA Astrophysics Data System (ADS)

    Li, Baihong; Xu, Yonggang; Zhu, Haifei; Lin, Fukun; Li, Yongfang

    2015-02-01

    Chirped biphotons generated via spontaneous parametric down-conversion in chirped quasi-phase-matched nonlinear crystals have ultrabroadband frequency spectra, while their correlation times are not ultranarrow, due to the nonlinear frequency dependence of the phase factor. Based on the idea of Fresnel zone lenses, we propose a Fresnel-inspired binary phase-shaping scheme for tailoring broadband biphoton spectra. By applying binary phase masks to the biphoton spectrum, a Fresnel zone lens was produced in the frequency domain, compressing the broadband temporal wave packets of the chirped biphotons to the Fourier-transform limit due to the effective removal of the quadratic phase. Furthermore, biphoton correlation trains can also be generated by properly shaping the biphoton spectrum with this scheme. This provides a method for biphoton compression and shaping, which avoids the length dependence and the impact of higher-order dispersion in a dispersive medium by using the phase compensation method. Our results could prove useful in quantum metrology, lithography, and coding of entangled photons.

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

    SciTech Connect

    Kaprálová-Žďánská, Petra Ruth; Moiseyev, Nimrod

    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.

  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-μm 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. Characterization of strong fiber Bragg gratings using an applied thermal chirp and iterative algorithm.

    PubMed

    Miller, Gary A; Peele, John R; Askins, Charles G; Cranch, Geoffrey A

    2011-12-20

    Coupling coefficients of various grating types and strengths are calculated from measurements of the complex reflectivity using an applied thermal chirp and optical frequency domain reflectometry (OFDR). The complex reflectivity is then utilized by a layer peeling algorithm to determine the coupling coefficient of the thermally chirped grating. A guess of the temperature profile enables the coupling coefficient of the unchirped grating to be estimated. An iterative algorithm is then used to converge on the exact coupling coefficient, employing an error minimization method applied to the reflectivity spectra. This technique removes the need for a reference grating while preserving the spatial resolution obtained with the initial OFDR measurement. Successful reconstruction of gratings with integrated |κ|L ~ 9.0 are demonstrated with a spatial resolution of less than 100 μm. PMID:22193191

  17. 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.

  18. Direct Excitation of High-Amplitude Chirped Bucket-BGK Modes

    NASA Astrophysics Data System (ADS)

    Bertsche, William

    2004-11-01

    Using a low amplitude, chirped-frequency localized potential drive(W. Bertsche, J. Fajans and L. Friedland, Direct Excitation of High-Amplitude Chirped Bucket-BGK Modes, Phys. Rev. Lett., 91: 265003, 2003. ), we excited undamped large amplitude electrostatic plasma waves in a relatively hot plasma. We believe these waves to be BGK waves, stationary, non-linear kinetic waves which are untouched by classical Landau damping. Even though BGK modes underpin much of kinetic wave theory, direct experimental evidence of undamped BGK waves has proven elusive. Large-amplitude responses have been observed in the past, however such structures have generally been unstable and short-lived. Other excitations generated during continuous driving have resulted in stable but low-amplitude waves. Our technique generates a tailored distribution function along with a self-consistent field, yielding large oscillations long after the drive has been removed. A theory for this excitation has been developed, which agrees with many features observed experimentally(L. Friedland, F. Peinetti, W. Bertsche, J. Fajans, and J. Wurtele, Driven Phase Space Holes and Synchronized Bernstein, Green, and Kruskal (BGK) Modes , Phys. Plasmas (accepted, 2004).). Restricted two-dimensional PIC simulations of an electron plasma column with a localized chirped drive are in close agreement with experimental data. This technique may lend laboratory insight to physical phenomena observed in other fields such as laser plasma interactions.

  19. 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

  20. Infrared sequence transformation technique for in situ measurement of thermal diffusivity and monitoring of thermal diffusion

    NASA Astrophysics Data System (ADS)

    Dong, Huilong; Zheng, Boyu; Chen, Feifan

    2015-11-01

    An infrared (IR) sequence transformation technique for visualization of thermal diffusion process and in situ measurement of radial thermal diffusivity is reported. It consists of heating the sample surface instantaneously by an angle-adjustable Gaussian beam and recording the temperature evolution by an IR camera. Compared to common techniques requiring the excitation beam to be fixed approximately perpendicular to the measurement surface, the proposed method allows a dynamic adjustment of the excitation incidence angle according to the actual operating space, which contributes to a fast and efficient in situ measurement approach. To achieve this, a new heat transfer model considering the elliptical distortion of the Gaussian beam caused by tilted incidence is established. Through decoupling analysis it is discovered that the area s surrounded by the maximum temperature curve rTmax (θ) grows linearly over time. The thermal diffusivity can be obtained from the growth rate at any incidence angle. Based on this s-time relation, an automatic thermal diffusivity characterization framework which involves extracting the rTmax (θ) sequence through a distance regularized level set evolution (DRLSE) formulation is proposed. For verification, samples of 304 stainless steel, titanium and zirconium are measured with the excitation incidence angles ranging from 30 ° to 60 ° , and the relative deviations from the literature values are - 6.28 % to 3.27 %, - 3.22 % to 5.79%, and - 1.61 % to 4.03% respectively. Besides, the thermal diffusion process of two typical printed circuit boards (PCBs) are monitored and analyzed visually with this technique.

  1. Chirped-Superlattice, Blocked-Intersubband QWIP

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath; Ting, David; Bandara, Sumith

    2004-01-01

    An Al(x)Ga(1-x)As/GaAs quantum-well infrared photodetector (QWIP) of the blocked-intersubband-detector (BID) type, now undergoing development, features a chirped (that is, aperiodic) superlattice. The purpose of the chirped superlattice is to increase the quantum efficiency of the device. A somewhat lengthy background discussion is necessary to give meaning to a brief description of the present developmental QWIP. A BID QWIP was described in "MQW Based Block Intersubband Detector for Low-Background Operation" (NPO-21073), NASA Tech Briefs Vol. 25, No. 7 (July 2001), page 46. To recapitulate: The BID design was conceived in response to the deleterious effects of operation of a QWIP at low temperature under low background radiation. These effects can be summarized as a buildup of space charge and an associated high impedance and diminution of responsivity with increasing modulation frequency. The BID design, which reduces these deleterious effects, calls for a heavily doped multiple-quantum-well (MQW) emitter section with barriers that are thinner than in prior MQW devices. The thinning of the barriers results in a large overlap of sublevel wave functions, thereby creating a miniband. Because of sequential resonant quantum-mechanical tunneling of electrons from the negative ohmic contact to and between wells, any space charge is quickly neutralized. At the same time, what would otherwise be a large component of dark current attributable to tunneling current through the whole device is suppressed by placing a relatively thick, undoped, impurity-free AlxGa1 x As blocking barrier layer between the MQW emitter section and the positive ohmic contact. [This layer is similar to the thick, undoped Al(x)Ga(1-x)As layers used in photodetectors of the blocked-impurity-band (BIB) type.] Notwithstanding the aforementioned advantage afforded by the BID design, the responsivity of a BID QWIP is very low because of low collection efficiency, which, in turn, is a result of low electrostatic- potential drop across the superlattice emitter. Because the emitter must be electrically conductive to prevent the buildup of space charge in depleted quantum wells, most of the externally applied bias voltage drop occurs across the blocking-barrier layer. This completes the background discussion. In the developmental QWIP, the periodic superlattice of the prior BID design is to be replaced with the chirped superlattice, which is expected to provide a built-in electric field. As a result, the efficiency of collection of photoexcited charge carriers (and, hence, the net quantum efficiency and thus responsivity) should increase significantly.

  2. Multiscale Transient Signal Detection: Localizing Transients in Geodetic Data Through Wavelet Transforms and Sparse Estimation Techniques

    NASA Astrophysics Data System (ADS)

    Riel, B.; Simons, M.; Agram, P.

    2012-12-01

    Transients are a class of deformation signals on the Earth's surface that can be described as non-periodic accumulation of strain in the crust. Over seismically and volcanically active regions, these signals are often challenging to detect due to noise and other modes of deformation. Geodetic datasets that provide precise measurements of surface displacement over wide areas are ideal for exploiting both the spatial and temporal coherence of transient signals. We present an extension to the Multiscale InSAR Time Series (MInTS) approach for analyzing geodetic data by combining the localization benefits of wavelet transforms (localizing signals in space) with sparse optimization techniques (localizing signals in time). Our time parameterization approach allows us to reduce geodetic time series to sparse, compressible signals with very few non-zero coefficients corresponding to transient events. We first demonstrate the temporal transient detection by analyzing GPS data over the Long Valley caldera in California and along the San Andreas fault near Parkfield, CA. For Long Valley, we are able to resolve the documented 2002-2003 uplift event with greater temporal precision. Similarly for Parkfield, we model the postseismic deformation by specific integrated basis splines characterized by timescales that are largely consistent with postseismic relaxation times. We then apply our method to ERS and Envisat InSAR datasets consisting of over 200 interferograms for Long Valley and over 100 interferograms for Parkfield. The wavelet transforms reduce the impact of spatially correlated atmospheric noise common in InSAR data since the wavelet coefficients themselves are essentially uncorrelated. The spatial density and extended temporal coverage of the InSAR data allows us to effectively localize ground deformation events in both space and time with greater precision than has been previously accomplished.

  3. Optimization and characterization of dual-chirped optical parametric amplification

    NASA Astrophysics Data System (ADS)

    Fu, Yuxi; Takahashi, Eiji J.; Zhang, Qingbin; Lu, Peixiang; Midorikawa, Katsumi

    2015-12-01

    We report optimization and characterization of a dual-chirped optical parametric amplification (DC-OPA) scheme (2011 Opt. Express 19 7190). By increasing a pump pulse energy to 100 mJ, a total (signal + idler) output energy exceeding 30 mJ was recorded with higher than 30% conversion efficiency. The feasibility of further increasing the output energy to a higher scale using the DC-OPA scheme was confirmed by a proof-of-principle experiment, in which 30%-40% conversion efficiency was observed. The signal pulse with the center wavelength of 1.4 μm was compressed to 27 fs (FWHM), which was very close to a transform-limited pulse duration of 25 fs. Since the DC-OPA scheme is efficient for generating high-energy infrared (IR) pulses with excellent scaling ability, the design parameters for obtaining hundred-mJ-level and even joule-level IR pulses are discussed and presented in detail. Invited contribution to the special issue on optical parametric processes.

  4. Dispersion compensation in chirped pulse amplification systems

    SciTech Connect

    Bayramian, Andrew James; Molander, William A.

    2014-07-15

    A chirped pulse amplification system includes a laser source providing an input laser pulse along an optical path. The input laser pulse is characterized by a first temporal duration. The system also includes a multi-pass pulse stretcher disposed along the optical path. The multi-pass pulse stretcher includes a first set of mirrors operable to receive input light in a first plane and output light in a second plane parallel to the first plane and a first diffraction grating. The pulse stretcher also includes a second set of mirrors operable to receive light diffracted from the first diffraction grating and a second diffraction grating. The pulse stretcher further includes a reflective element operable to reflect light diffracted from the second diffraction grating. The system further includes an amplifier, a pulse compressor, and a passive dispersion compensator disposed along the optical path.

  5. Transient water age distributions in environmental flow systems: The time-marching Laplace transform solution technique

    NASA Astrophysics Data System (ADS)

    Cornaton, F. J.

    2012-03-01

    Environmental fluid circulations are very often characterized by analyzing the fate and behavior of natural and anthropogenic tracers. Among these tracers, age is taken as an ideal tracer which can yield interesting diagnoses, as for example the characterization of the mixing and renewal of water masses, of the fate and mixing of contaminants, or the calibration of hydrodispersive parameters used by numerical models. Such diagnoses are of great interest in atmospheric and ocean circulation sciences, as well in surface and subsurface hydrology. The temporal evolution of groundwater age and its frequency distributions can display important changes as flow regimes vary due to natural change in climate and hydrologic conditions and/or human induced pressures on the resource to satisfy the water demand. Groundwater age being nowadays frequently used to investigate reservoir properties and recharge conditions, special attention needs to be put on the way this property is characterized, would it be using isotopic methods or mathematical modeling. Steady state age frequency distributions can be modeled using standard numerical techniques since the general balance equation describing age transport under steady state flow conditions is exactly equivalent to a standard advection-dispersion equation. The time-dependent problem is however described by an extended transport operator that incorporates an additional coordinate for water age. The consequence is that numerical solutions can hardly be achieved, especially for real 3-D applications over large time periods of interest. A novel algorithm for solving the age distribution problem under time-varying flow regimes is presented and, for some specific configurations, extended to the problem of generalized component exposure time. The algorithm combines the Laplace transform technique applied to the age (or exposure time) coordinate with standard time-marching schemes. The method is validated and illustrated using analytical and numerical solutions considering 1-D, 2-D, and 3-D theoretical groundwater flow domains.

  6. Research on the technique of public watermarking system based on wavelet transform and neural network

    NASA Astrophysics Data System (ADS)

    Xu, Li; Tao, Gu

    2007-04-01

    A hybrid algorithm of using a wavelet transform and a neural network is presented which solves the problems confronted in public watermarking systems. First, to get the wavelet coefficients, db1 wavelet is used to decompose the selected image. Second, to ensure better quality of the watermarked image, some wavelet coefficients and their closely relevant wavelet coefficients are randomly selected from the wavelet coefficients decomposed by the low pass filter and used to establish the relational model by using a neural network. Third, the bit information of the watermark is also enlarged by increasing the amount of zeros or ones and then one bit of the results is embedded by adjusting the polarity between a chosen wavelet coefficient and the output value of the model. Finally, a new image with watermark information is reconstructed by using the modified wavelet coefficients and other unmodified wavelet coefficients. On the other hand, the process of retrieving the watermark is the inverse of the embedding process. The embedded watermark can also be retrieved by using the hybrid algorithm and the restore function without knowing the original image and watermark. Experimental results show that the proposed technique is very robust against some image processing operations and JPEG lossy compression. Meanwhile, the extracted watermark can be proved by the proposed method. Because of the neural network, the proposed method is also robust against attack of false authentication. Therefore, the hybrid algorithm can be used to protect the copyright of one important image.

  7. New technique of distinguishing rock from coal based on statistical analysis of wavelet transform

    NASA Astrophysics Data System (ADS)

    Li, Xu; Gu, Tao

    2009-04-01

    A hybrid algorithm of distinguishing rock from coal based on statistical analysis of Wavelet Transform (WT) is presented which can be used in the process of caving coal. First, eight groups of sound signals sampled with the speed 8192 samples/sec during caving are decomposed by db3 wavelet. Second, the WT results are analyzed by using the variance analytical method in the second-level details (D2). Third, the typical values i.e. the detail-level coefficient variances (Dvar) of the sound of the coal bumping the transporting coal armor plate, the rock bumping the armor plate and the mixing of coal and rock bumping the armor plate are calculated. Finally, the threshold value of distinguishing rock from coal is evaluated by the typical values and used to direct the opportunity for caving. We can learn by the experimental results that the proposed technique can depict effectively the different characteristics of the sampled signals. The experimental results also show that we can distinguish effectively different bumping sounds of coal, rock and the mixing of them by the characteristics when adjusting the appropriate threshold value. Meanwhile, the proposed method has strong ability to resist the noise occurred during mining. Therefore, the algorithm can be used to improve the miners' productivity and promote the construction of digital mine.

  8. 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.

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

    PubMed

    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. PMID:21806220

  10. ABCD-matrix elements for a chirped diffraction grating

    NASA Astrophysics Data System (ADS)

    April, Alexandre; McCarthy, Nathalie

    2007-03-01

    The ABCD-matrix elements for a chirped diffraction grating, used at an arbitrary angle of incidence and in an arbitrary diffraction order, are derived both for the tangential and sagittal planes. The derivation is based on the notion of optical path difference and assumes a spherical chirped grating used in reflection in air or vacuum, but the results apply to transmission grating as well. The matrix elements are then employed to establish the effective focal length of the chirped grating and the position of its cardinal points. In this paper, by chirped gratings (also called varied line-space gratings or varied pitch gratings), it is meant gratings whose grooves are straight and parallel but not equally spaced.

  11. Single attosecond pulse generation from multicycle nonlinear chirped pulses

    SciTech Connect

    Niu Yueping; Qi Yihong; Gong Shangqing; Xiang Yang

    2009-12-15

    We present a method of producing single attosecond pulses by high-order harmonic generation with multicycle nonlinear chirped driver laser pulses. The symmetry of the laser field in several optical cycles near the pulse center is broken, and then the photons near the cutoff burst only in half optical cycle. By selecting out the harmonics near the cutoff, an isolated attosecond pulse could be obtained. The results are almost independent of the length and chirp form of the driver laser pulse.

  12. Chirping for efficiency enhancement of the free-electron laser

    SciTech Connect

    Moore, G.T.; Goldstein, J.C.

    1988-01-01

    One-dimensional numerical studies have been made of free-electron laser oscillators in which the incident electron energy varies (chirps) as a function of time over each micropulse. Optical radiation resonant with such micropulses is chirped in frequency. Highest calculated efficiency (up to 8.1% for wavelengths near 10 ..mu..m) has been obtained in cases where the optical pulse at saturation is short compared to the slippage. 8 refs., 7 figs., 1 tab.

  13. Iterative direction-of-arrival estimation with wideband chirp signals

    NASA Astrophysics Data System (ADS)

    Wang, Genyuan; Xia, Xiang-Gen; Chen, Victor C.

    1999-11-01

    Amin et. al. recently developed a time-frequency MUSIC algorithm with narrow band models for the estimation of direction of arrival (DOA) when the source signals are chirps. In this research, we consider wideband models. The joint time-frequency analysis is first used to estimate the chirp rates of the source signals and then the DOA is estimated by the MUSIC algorithm with an iterative approach.

  14. Optical transformation based image encryption and data embedding techniques using MATLAB

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Debalina; Ghosh, Ajay

    2015-06-01

    The proposed work describes optical transformations such as Fourier transformation and Fresnel transformation based encryption and decryption of images using random phase masks (RPMs). The encrypted images have been embedded in some secret cover files of other formats like text files, word files, audio files etc to increase the robustness in the security applications. So, if any one wants to send confidential documents, it will be difficult for the interloper to unhide the secret information. The whole work has been done in MATLAB®

  15. Sampled chirped fiber gratings as distributed pressure sensors

    NASA Astrophysics Data System (ADS)

    Tjin, Swee Chuan; Mohanty, Lipi; Ngo, Nam Quoc

    2004-09-01

    Fiber gratings have been studied for their applications in sensing and communications. Many sensing applications of the uniform fiber Bragg grating, chirped fiber grating and long period grating have been studied, proposed and commercialized. Sampled chirped gratings have been studied for multichannel dispersion compensation in DWDM systems. In this paper, we show that the sampled chirped fiber grating can be used as a distributed pressure sensor. The chirp provides ease of manufacture of many gratings. The sampling results in many small, uniform grating-like structures. This fact can be used to simulate a distributed sensor over the length of the sampled chirped grating. When a surface comes into contact with the sensor, the distribution of the pressure determines the shift in central wavelength of the various sub-gratings. The sub-grating that experiences the maximum pressure will show maximum wavelength shift whereas adjacent sub-gratings will show less shift. This can also give the location of the pressure. The sensor design comprises of a sampled chirped grating embedded in unidirectional fiber-reinforced composite prepreg. The prepreg enhances the mechanical strength and the unidirectional embedding reduces birefringence. The number of layers in the prepreg stack varies the sensitivity. Such distributed pressure sensors can be applied in robotics, ergonomics, and in the biomedical field.

  16. Broadband spectroscopy of dynamic impedances with short chirp pulses.

    PubMed

    Min, M; Land, R; Paavle, T; Parve, T; Annus, P; Trebbels, D

    2011-07-01

    An impedance spectrum of dynamic systems is time dependent. Fast impedance changes take place, for example, in high throughput microfluidic devices and in operating cardiovascular systems. Measurements must be as short as possible to avoid significant impedance changes during the spectrum analysis, and as long as possible for enlarging the excitation energy and obtaining a better signal-to-noise ratio (SNR). The authors propose to use specific short chirp pulses for excitation. Thanks to the specific properties of the chirp function, it is possible to meet the needs for a spectrum bandwidth, measurement time and SNR so that the most accurate impedance spectrogram can be obtained. The chirp wave excitation can include thousands of cycles when the impedance changes slowly, but in the case of very high speed changes it can be shorter than a single cycle, preserving the same excitation bandwidth. For example, a 100 kHz bandwidth can be covered by the chirp pulse with durations from 10 s to 1 s; only its excitation energy differs also 10(5) times. After discussing theoretical short chirp properties in detail, the authors show how to generate short chirps in the microsecond range with a bandwidth up to a few MHz by using digital synthesis architectures developed inside a low-cost standard field programmable gate array. PMID:21646703

  17. Flat focusing lens designs having minimized reflection based on coordinate transformation techniques.

    PubMed

    Kwon, Do-Hoon; Werner, Douglas H

    2009-05-11

    Two-dimensional far-zone focusing lenses are designed using the coordinate transformation approach that feature minimized reflections from the lens boundaries. A flat lens of trapezoidal cross section completely converts incident waves with cylindrical wavefronts into transmitted waves with planar wavefronts. A rectangular lens with reduced non-magnetic material parameters that incorporates a nonlinear coordinate transformation features a significantly reduced amount of reflections compared with the non-magnetic lens based on a linear transformation. The improved reflection performance of each new lens design is verified using a full-wave finite-element analysis and compared with previously reported transformation optical lenses. PMID:19434112

  18. Single-stripe tunable laser with chirped sampled gratings fabricated by nanoimprint lithography

    NASA Astrophysics Data System (ADS)

    Yoshinaga, Hiroyuki; Yanagisawa, Masaki; Kaneko, Toshimitsu; Akiyama, Kan; Tajima, Mikio; Shoji, Daisei; Fujii, Takuya; Shoji, Hajime

    2014-08-01

    The fabrication of diffraction gratings of a chirped sampled gratings distributed reflector (CSG-DR) laser by nanoimprint lithography (NIL) has been demonstrated. The diffraction gratings with highly uniform linewidth and period have been successfully fabricated by the combination of the reverse-tone NIL and precise etching techniques. The CSG-DR laser fabricated by NIL shows a sufficiently wide tuning range of 40 nm as we designed. The results of this study indicate that our fabrication process for the sampled gratings utilizing the NIL technique has a high potential for the fabrication of a CSG-DR laser.

  19. Propagation effects of isolated attosecond pulse generation with a multicycle chirped and chirped-free two-color field

    SciTech Connect

    Du Hongchuan; Hu Bitao

    2011-08-15

    We present a theoretical study of isolated attosecond pulse generation with a multicycle chirped and chirped-free two-color field. We show that the bandwidth of the extreme ultraviolet supercontinuum can be extended by combining a multicycle chirped pulse and a multicycle chirped-free pulse. Also, the broadband supercontinuum can still be generated when the macroscopic effects are included. Furthermore, the macroscopic effects can ameliorate the temporal characteristic of the broadband supercontinuum of the single atom, and eliminate the modulations of the broadband supercontinuum. Thus a very smooth broadband supercontinuum and a pure isolated 102-as pulse can be directly obtained. Moreover, the structure of the broadband supercontinuum can be steadily maintained for a relative long distance after a certain distance.

  20. Development and Experimental Validation of a Numerical Tool for Structural Health and Usage Monitoring Systems Based on Chirped Grating Sensors

    PubMed Central

    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 sensorsDraw Tower Grating arrayshas 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

  1. 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.

  2. Distortion-invariant face recognition using multiple phase-shifted reference-based joint transform correlation technique

    NASA Astrophysics Data System (ADS)

    Islam, Mohammed Nazrul; Asari, K. Vijayan; Karim, Mohammad A.

    2011-09-01

    We have developed a novel face recognition technique utilizing optical joint transform correlation (JTC) technique which provides with a number of salient features as compared to similar other digital techniques, including fast operation, simple architecture and capability of updating the reference image in real time. The proposed technique incorporates a synthetic discriminant function (SDF) of the target face estimated from a set of different training faces to make the face recognition performance invariant to noise and distortion. The technique then involves four different phase-shifted versions of the same SDF reference face, which are individually joint transform correlated with the given input scene with unknown faces and other objects. Appropriate combination of correlation signals yields a single cross-correlation peak corresponding to each potential face image. The technique also involves a fringe-adjusted filter to generate a delta-like correlation peak with high discrimination between the target face and the non-target face and background objects. Performance of the proposed face recognition technique is investigated through computer simulation where it is observed to be efficient and successful in different complex environments.

  3. 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.

  4. ORGANIC ACID DERIVATIZATION TECHNIQUES APPLIED TO PETROLEUM HYDROCARBON TRANSFORMATIONS IN SUBSURFACE ENVIRONMENTS

    EPA Science Inventory

    Evidence for the natural microbial remediation of subsurface fuel contamination situations should include identification and analysis of transformation or degradation products. In this way. u mass balance between fuel constituents and end products may be approached to monitor cle...

  5. 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...

  6. ORGANIC ACID DERIVATIZATION TECHNIQUES APPLIED TO PETROLEUM HYDROCARBON TRANSFORMATIONS IN SUBSURFACE ENVIRONMENT

    EPA Science Inventory

    Evidence for the natural microbial remediation of subsurface fuel contamination situations should include identification and analysis of transformation or degradation products. n this way, a mass balance between fuel constituents and end products may be approached to monitor clea...

  7. Effective technique for solving the reconstruction problems in tomography using the 2D Hartley transform

    NASA Astrophysics Data System (ADS)

    Karimov, Magomed G.; Batyrov, Rustam M.; Halilulayev, Gusein M.

    1999-02-01

    One of major aspects of a problem of restoration (reconstruction) of the internal structure of various objects and other information about their properties considers the reception of the information on distribution of some physical characteristic from their experimentally obtained spectrum of integral projective data received by various methods (emissive, transmissive -- by a physical principle; acoustical, optical, laser, radiological -- by the type of used radiation, etc.). The given branch of investigation is known as a reconstructive tomography. The majority of methods for restoration of the images from their integral projections in reconstructive tomography are based on a fundamental generalized projective theorem with use of Fourier transform. The main difficulty in practical processing of the complex Fourier-like transforms (Laplace, Mellin transforms, etc.) despite of their convenience in analytical calculations and algebra becomes the insufficient speed of data processing for reception of the dynamic distribution image of an investigated physical characteristic. In the present work we examined the possibilities of application in various areas of a reconstructive tomography of the real-domain integral transform offered by Ralph Vinton Lyon Hartley in 1942 for study of a spectra of electrosignals, lastly named in his honor by Hartley transform. Some examples of an effective applications and basic properties of Hartley transform are presented in works of Ronald N. Bracewell. From middle of the 1960-the years there were offered various fast algorithms of calculation of discrete Fourier transform (FFT) which characterized by some advantage in speed of data processing in comparison with discrete FT, but however owing to its complexity and asymmetry FFT concedes in speed of processing to fast algorithms based on Hartley transform.

  8. Chirped Pulse and Cavity FT Microwave Spectroscopy of the HCCH-2,6-DIFLUOROPYRIDINE Weakly Bound Complex

    NASA Astrophysics Data System (ADS)

    Dewberry, Chris; Mackenzie, Becca; Leopold, Ken

    2015-06-01

    The microwave spectrum of the HCCH-2,6-difluoropyrine complex has been observed using a chirped pulse and conventional cavity-type Fourier transform microwave spectroscopy. The acetylene moiety forms a hydrogen bond to the nitrogen of the 2,6-difluoropyridine, and this structure is contrasted with several systems involving HCCH or CO2 bound to pyridine or 2,6-difluoropyridine. The results of DFT calculations support the experimental observations and are reported as well. The chirped pulse spectrometer is new in our laboratory and is built in tandem with our cavity-type spectrometer with a design that allows for switching between the two modes of operation without having to break vacuum. Pertinent details of the spectrometer will also be given.

  9. Cpuf: Chirped-Pulse Microwave Spectroscopy in Pulsed Uniform Supersonic Flows

    NASA Astrophysics Data System (ADS)

    Suits, Arthur; Abeysekera, Chamara; Zack, Lindsay N.; Joalland, Baptiste; Ariyasingha, Nuwandi M.; Park, Barratt; Field, Robert W.; Sims, Ian

    2015-06-01

    Chirped-pulse Fourier-transform microwave spectroscopy has stimulated a resurgence of interest in rotational spectroscopy owing to the dramatic reduction in spectral acquisition time it enjoys when compared to cavity-based instruments. This suggests that it might be possible to adapt the method to study chemical reaction dynamics and even chemical kinetics using rotational spectroscopy. The great advantage of this would be clear, quantifiable spectroscopic signatures for polyatomic products as well as the possibility to identify and characterize new radical reaction products and transient intermediates. To achieve this, however, several conditions must be met: 1) products must be thermalized at low temperature to maximize the population difference needed to achieve adequate signal levels and to permit product quantification based on the rotational line strength; 2) a large density and volume of reaction products is also needed to achieve adequate signal levels; and 3) for kinetics studies, a uniform density and temperature is needed throughout the course of the reaction. These conditions are all happily met by the uniform supersonic flow produced from a Laval nozzle expansion. In collaboration with the Field group at MIT we have developed a new instrument we term a CPUF (Chirped-pulse/Uniform Flow) spectrometer in which we can study reaction dynamics, photochemistry and kinetics using broadband microwave and millimeter wave spectroscopy as a product probe. We will illustrate the performance of the system with a few examples of photodissociation and reaction dynamics, and also discuss a number of challenges unique to the application of chirped-pulse microwave spectroscopy in the collisional environment of the flow. Future directions and opportunities for application of CPUF will also be explored.

  10. Spatial-spectral characterization of focused spatially chirped broadband laser beams.

    PubMed

    Greco, Michael J; Block, Erica; Meier, Amanda K; Beaman, Alex; Cooper, Samuel; Iliev, Marin; Squier, Jeff A; Durfee, Charles G

    2015-11-20

    Proper alignment is critical to obtain the desired performance from focused spatially chirped beams, for example in simultaneous spatial and temporal focusing (SSTF). We present a simple technique for inspecting the beam paths and focusing conditions for the spectral components of a broadband beam. We spectrally resolve the light transmitted past a knife edge as it was scanned across the beam at several axial positions. The measurement yields information about spot size, M2, and the propagation paths of different frequency components. We also present calculations to illustrate the effects of defocus aberration on SSTF beams. PMID:26836543

  11. Deterministic implementations of quantum gates with circuit QEDs via Stark-chirped rapid adiabatic passages

    NASA Astrophysics Data System (ADS)

    Chen, Jingwei; Wei, L. F.

    2015-10-01

    We show that a set of universal quantum gates could be implemented robustly in a circuit QED system by using Stark-chirped rapid adiabatic passage (SCRAP) technique. Under the adiabatic limit we find that the population transfers could be deterministically passaged from one selected quantum states to the others, and thus the desired quantum gates can be implemented. The proposed SCRAP-based gates are insensitive to the details of the operations and thus relax the designs of the applied pulses, operational imperfections, and the decoherence of the system.

  12. Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system.

    PubMed

    Jullien, Aurélie; Ricci, Aurélien; Böhle, Frederik; Rousseau, Jean-Philippe; Grabielle, Stéphanie; Forget, Nicolas; Jacqmin, Hermance; Mercier, Brigitte; Lopez-Martens, Rodrigo

    2014-07-01

    We present the first carrier-envelope-phase stable chirped-pulse amplifier (CPA) featuring high temporal contrast for relativistic intensity laser-plasma interactions at 1 kHz repetition rate. The laser is based on a double-CPA architecture including cross-polarized wave (XPW) filtering technique and a high-energy grism-based compressor. The 8 mJ, 22 fs pulses feature 10⁻¹¹ temporal contrast at -20  ps and a carrier-envelope-phase drift of 240 mrad root mean square. PMID:24978734

  13. Hadamard transform spectrometry: A new analytical technique: Progress report, March 15, 1988--March 14, 1989

    SciTech Connect

    Fateley, W.G.

    1988-01-01

    The following four projects were initiated during the first year of this three year program: construction of a stationary interferometer for possible use in the Hadamard transform Raman HPLC experiment; construction of a dispersive Hadamard transform spectrometer with concave holographic gratings for possible application as a HPLC detector; investigation of new polymer-dispersed liquid crystal films as efficient optical shutters for making improved Hadamard encoding masks; and improvement of the software necessary to recover a spectrum from the Hadamard encoded data. This paper covers these topics. 5 refs., 3 figs.

  14. Ultra-fast dynamic compression technique to study kinetics of phase transformations in Bismuth

    SciTech Connect

    Smith, R F; Kane, J O; Eggert, J H; Saculla, M D; Jankowski, A F; Bastea, M; Hicks, D G; Collins, G W

    2007-12-28

    Pre-heated Bi was ramp compressed within 30 ns to a peak stress of {approx}11 GPa to explore structural phase transformation kinetics under dynamic loading conditions. Under these ultra-fast compression time-scales the equilibrium Bi I-II phase boundary is overpressurized by {Delta}P {approx} 0.8 GPa. {Delta}P is observed to increase logarithmically with strain rate, {var_epsilon}, above 10{sup 6} s{sup -1}. Estimates from a kinetics model predict that the Bi I phase is fully transformed within 3 ns.

  15. A non-intrusive and continuous-in-space technique to investigate the wave transformation and breaking over a breakwater

    NASA Astrophysics Data System (ADS)

    Ferrari, Simone; Grazia Badas, Maria; Querzoli, Giorgio

    2016-03-01

    To design longshore breakwaters, the evaluation of the wave motion transformations over the structures and of the energy they are able to absorb, dissipate and reflect is necessary. To characterize features and transformations of monochromatic wave trains above a breakwater, both submerged and emerged, we have designed and developed a non-intrusive and continuous-in-space technique, based on Image Analysis, and carried out an experimental campaign, in a laboratory flume equipped with a wave-maker, in order to test it. The investigation area was lighted with a light sheet and images were recorded by a video-camera. The working fluid was seeded with non buoyant particles to make it bright and clearly distinct from dark background and breakwater. The technique, that is based on a robust algorithm to identify the free surface, has showed to properly work also in prohibitive situations for traditional resistive probes (e.g., very shallow waters and/or breaking waves) and to be able to measure the free surface all over the investigation field in a non-intrusive way. Two kind of analysis were mainly performed, a statistical and a spectral one. The peculiarities of the measurement technique allowed to describe the whole wave transformation and to supply useful information for design purposes.

  16. Transformation of Resources to Reserves: Next Generation Heavy-Oil Recovery Techniques

    SciTech Connect

    Stanford University; Department of Energy Resources Engineering Green Earth Sciences

    2007-09-30

    This final report and technical progress report describes work performed from October 1, 2004 through September 30, 2007 for the project 'Transformation of Resources to Reserves: Next Generation Heavy Oil Recovery Techniques', DE-FC26-04NT15526. Critical year 3 activities of this project were not undertaken because of reduced funding to the DOE Oil Program despite timely submission of a continuation package and progress on year 1 and 2 subtasks. A small amount of carried-over funds were used during June-August 2007 to complete some work in the area of foamed-gas mobility control. Completion of Year 3 activities and tasks would have led to a more thorough completion of the project and attainment of project goals. This progress report serves as a summary of activities and accomplishments for years 1 and 2. Experiments, theory development, and numerical modeling were employed to elucidate heavy-oil production mechanisms that provide the technical foundations for producing efficiently the abundant, discovered heavy-oil resources of the U.S. that are not accessible with current technology and recovery techniques. Work fell into two task areas: cold production of heavy oils and thermal recovery. Despite the emerging critical importance of the waterflooding of viscous oil in cold environments, work in this area was never sanctioned under this project. It is envisioned that heavy oil production is impacted by development of an understanding of the reservoir and reservoir fluid conditions leading to so-called foamy oil behavior, i.e, heavy-oil solution gas drive. This understanding should allow primary, cold production of heavy and viscous oils to be optimized. Accordingly, we evaluated the oil-phase chemistry of crude oil samples from Venezuela that give effective production by the heavy-oil solution gas drive mechanism. Laboratory-scale experiments show that recovery correlates with asphaltene contents as well as the so-called acid number (AN) and base number (BN) of the crude oil. A significant number of laboratory-scale tests were made to evaluate the solution gas drive potential of West Sak (AK) viscous oil. The West Sak sample has a low acid number, low asphaltene content, and does not appear foamy under laboratory conditions. Tests show primary recovery of about 22% of the original oil in place under a variety of conditions. The acid number of other Alaskan North Slope samples tests is greater, indicating a greater potential for recovery by heavy-oil solution gas drive. Effective cold production leads to reservoir pressure depletion that eases the implementation of thermal recovery processes. When viewed from a reservoir perspective, thermal recovery is the enhanced recovery method of choice for viscous and heavy oils because of the significant viscosity reduction that accompanies the heating of oil. One significant issue accompanying thermal recovery in cold environments is wellbore heat losses. Initial work on thermal recovery found that a technology base for delivering steam, other hot fluids, and electrical heat through cold subsurface environments, such as permafrost, was in place. No commercially available technologies are available, however. Nevertheless, the enabling technology of superinsulated wells appears to be realized. Thermal subtasks focused on a suite of enhanced recovery options tailored to various reservoir conditions. Generally, electrothermal, conventional steam-based, and thermal gravity drainage enhanced oil recovery techniques appear to be applicable to 'prime' Ugnu reservoir conditions to the extent that reservoir architecture and fluid conditions are modeled faithfully here. The extent of reservoir layering, vertical communication, and subsurface steam distribution are important factors affecting recovery. Distribution of steam throughout reservoir volume is a significant issue facing thermal recovery. Various activities addressed aspects of steam emplacement. Notably, hydraulic fracturing of horizontal steam injection wells and implementation of steam trap control that limits steam entry into horizontal production wells overcomes many of the problems associated with implementation of thermal gravity drainage processes in heterogeneous sands. In a steam-assisted gravity drainage (SAGD) well pattern, hydraulically fractured injectors were able to achieve significantly improved reservoir heating and improvements to oil-steam ratio. On the opposite side of the steam injection spectrum, steam often channels through high-permeability zones. Foamed steam stabilized by aqueous surfactants is promising to alter steam flow, but has yet to be tested and simulated under SAGD conditions. The mechanistic population balance method for describing foam flow was extended to a local equilibrium framework that reduces computational costs and is promising for simulation of the effects of foamed steam in 3D.

  17. 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.

  18. Excitation of Chirping Whistler Waves in a Laboratory Plasma.

    PubMed

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

    2015-06-19

    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. PMID:26196981

  19. Thomson scattering in high-intensity chirped laser pulses

    NASA Astrophysics Data System (ADS)

    Holkundkar, Amol R.; Harvey, Chris; Marklund, Mattias

    2015-10-01

    We consider the Thomson scattering of an electron in an ultra-intense laser pulse. It is well known that at high laser intensities, the frequency and brilliance of the emitted radiation will be greatly reduced due to the electron losing energy before it reaches the peak field. In this work, we investigate the use of a small frequency chirp in the laser pulse in order to mitigate this effect of radiation reaction. It is found that the introduction of a negative chirp means the electron enters a high frequency region of the field while it still has a large proportion of its original energy. This results in a significant enhancement of the frequency and intensity of the emitted radiation as compared to the case without chirping.

  20. Effects of collisions on energetic particle-driven chirping bursts

    SciTech Connect

    Lesur, M.

    2013-05-15

    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.

  1. Time-frequency signature sparse reconstruction using chirp dictionary

    NASA Astrophysics Data System (ADS)

    Nguyen, Yen T. H.; Amin, Moeness G.; Ghogho, Mounir; McLernon, Des

    2015-05-01

    This paper considers local sparse reconstruction of time-frequency signatures of windowed non-stationary radar returns. These signals can be considered instantaneously narrow-band, thus the local time-frequency behavior can be recovered accurately with incomplete observations. The typically employed sinusoidal dictionary induces competing requirements on window length. It confronts converse requests on the number of measurements for exact recovery, and sparsity. In this paper, we use chirp dictionary for each window position to determine the signal instantaneous frequency laws. This approach can considerably mitigate the problems of sinusoidal dictionary, and enable the utilization of longer windows for accurate time-frequency representations. It also reduces the picket fence by introducing a new factor, the chirp rate α. Simulation examples are provided, demonstrating the superior performance of local chirp dictionary over its sinusoidal counterpart.

  2. Chirped pulse inverse free-electron laser vacuum accelerator

    DOEpatents

    Hartemann, Frederic V.; Baldis, Hector A.; Landahl, Eric C.

    2002-01-01

    A chirped pulse inverse free-electron laser (IFEL) vacuum accelerator for high gradient laser acceleration in vacuum. By the use of an ultrashort (femtosecond), ultrahigh intensity chirped laser pulse both the IFEL interaction bandwidth and accelerating gradient are increased, thus yielding large gains in a compact system. In addition, the IFEL resonance condition can be maintained throughout the interaction region by using a chirped drive laser wave. In addition, diffraction can be alleviated by taking advantage of the laser optical bandwidth with negative dispersion focusing optics to produce a chromatic line focus. The combination of these features results in a compact, efficient vacuum laser accelerator which finds many applications including high energy physics, compact table-top laser accelerator for medical imaging and therapy, material science, and basic physics.

  3. Experimental investigation of chirp properties induced by signal amplification in quantum-dot semiconductor optical amplifiers.

    PubMed

    Matsuura, Motoharu; Ohta, Hiroaki; Seki, Ryota

    2015-03-15

    We experimentally show the dynamic frequency chirp properties induced by signal amplification in a quantum-dot semiconductor optical amplifier (QD-SOA) for the first time. We also compare the red and blue chirp peak values and temporal chirp changes while changing the gain and injected signal powers of the QD-SOA with those of a common SOA. PMID:25768145

  4. Temperature insensitive accelerometer based on a strain-chirped FBG

    NASA Astrophysics Data System (ADS)

    Zhou, Wenjun; Dong, Xinyong; Ni, Kai; Chan, C. C.; Shum, P.

    2009-10-01

    A novel accelerometer based on a strain-chirped optical fiber Bragg grating (FBG) is proposed. The FBG is glued in a slanted direction onto the lateral side of a right-angled triangle cantilever beam with a mass bonded on its free end. Vertical acceleration applied to the cantilever beam leads to a uniform bending along the beam length. As a result, the FBG is chirped and its reflection bandwidth changes linearly with the applied acceleration. A high sensitivity of 0.684 nm/g has been achieved in the experiment. This sensor is temperature insensitive, owning to the temperatureindependence nature of reflection bandwidth of the FBG.

  5. 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.

  6. A technique for increasing the accuracy of the numerical inversion of the Laplace transform with applications

    NASA Technical Reports Server (NTRS)

    Berger, B. S.; Duangudom, S.

    1973-01-01

    A technique is introduced which extends the range of useful approximation of numerical inversion techniques to many cycles of an oscillatory function without requiring either the evaluation of the image function for many values of s or the computation of higher-order terms. The technique consists in reducing a given initial value problem defined over some interval into a sequence of initial value problems defined over a set of subintervals. Several numerical examples demonstrate the utility of the method.

  7. Discrete Walsh Hadamard transform based visible watermarking technique for digital color images

    NASA Astrophysics Data System (ADS)

    Santhi, V.; Thangavelu, Arunkumar

    2011-10-01

    As the size of the Internet is growing enormously the illegal manipulation of digital multimedia data become very easy with the advancement in technology tools. In order to protect those multimedia data from unauthorized access the digital watermarking system is used. In this paper a new Discrete walsh Hadamard Transform based visible watermarking system is proposed. As the watermark is embedded in transform domain, the system is robust to many signal processing attacks. Moreover in this proposed method the watermark is embedded in tiling manner in all the range of frequencies to make it robust to compression and cropping attack. The robustness of the algorithm is tested against noise addition, cropping, compression, Histogram equalization and resizing attacks. The experimental results show that the algorithm is robust to common signal processing attacks and the observed peak signal to noise ratio (PSNR) of watermarked image is varying from 20 to 30 db depends on the size of the watermark.

  8. Single-shot real-time characterization of chirped-pulse amplification systems by spectral phase interferometry for direct electric-field reconstruction.

    PubMed

    Dorrer, C; de Beauvoir, B; Le Blanc, C; Ranc, S; Rousseau, J P; Rousseau, P; Chambaret, J P; Salin, F

    1999-11-15

    We characterize chirped-pulse amplification systems by using spectral phase interferometry for direct electric-field reconstruction. For the first time to the authors' knowledge, single-shot real-time operation has been obtained for this technique, leading to a fast and accurate optimization of these systems. PMID:18079891

  9. Experimental verification and analysis of wavelength effect on pulse stretching and compressing in mid-IR chirped-pulse amplification

    NASA Astrophysics Data System (ADS)

    Zhong, Haizhe; Yuan, Peng; Zhao, Kun; Zhang, Lifu; Ma, Jingui; Li, Ying; Fan, Dianyuan

    2016-02-01

    As a consequence of the general experimental challenge to detect signals in mid-IR range, taking dispersive chirped near-IR laser pulses as the injected signal source seems to be an artistic route avoiding the daunting mid-IR stretcher and constantly was applied in moderate energy mid-IR optical parametric chirped-pulse amplifications (OPCPA) systems. In this paper we study the wavelength effect on pulse stretching and compressing in detail. Beginning with the theoretical analysis on each dispersion term of grating pairs, we evaluate the residual dispersions when pulse stretcher and compressor work at distinct wavelengths, which shows that this wavelength effect will result in poorly compressed pulses far from transform-limited. Via proof-of-principle experiments based on mid-IR OPCPAs and corresponding numerical simulations, we show that this artful configuration led to un-compressible pulses of ∼2 ps with a time-bandwidth product of ∼ 10 when the chirped-pulse duration is ∼400 ps. To overcome this effect, we demonstrate a simple design of pulse stretcher and compressor. The presented design consisted of a reflection grism-pair compressor can simultaneously cancel the quadric and cubic dispersions of conventional grating based stretcher, showing a potential ability of supporting high-contrast, sub-100-fs pulse-duration and 10,000× of pulse expansion.

  10. (2+1)-dimensional dissipation nonlinear Schrödinger equation for envelope Rossby solitary waves and chirp effect

    NASA Astrophysics Data System (ADS)

    Jin-Yuan, Li; Nian-Qiao, Fang; Ji, Zhang; Yu-Long, Xue; Xue-Mu, Wang; Xiao-Bo, Yuan

    2016-04-01

    In the past few decades, the (1+1)-dimensional nonlinear Schrödinger (NLS) equation had been derived for envelope Rossby solitary waves in a line by employing the perturbation expansion method. But, with the development of theory, we note that the (1+1)-dimensional model cannot reflect the evolution of envelope Rossby solitary waves in a plane. In this paper, by constructing a new (2+1)-dimensional multiscale transform, we derive the (2+1)-dimensional dissipation nonlinear Schrödinger equation (DNLS) to describe envelope Rossby solitary waves under the influence of dissipation which propagate in a plane. Especially, the previous researches about envelope Rossby solitary waves were established in the zonal area and could not be applied directly to the spherical earth, while we adopt the plane polar coordinate and overcome the problem. By theoretical analyses, the conservation laws of (2+1)-dimensional envelope Rossby solitary waves as well as their variation under the influence of dissipation are studied. Finally, the one-soliton and two-soliton solutions of the (2+1)-dimensional NLS equation are obtained with the Hirota method. Based on these solutions, by virtue of the chirp concept from fiber soliton communication, the chirp effect of envelope Rossby solitary waves is discussed, and the related impact factors of the chirp effect are given. Project supported by the National Natural Science Foundation of China (Grant No. 41406018).

  11. Flexible generation of coherent rectangular pulse from an ultrafast fiber laser based on dispersive Fourier transformation technique.

    PubMed

    Wang, Fu-Zao; Liu, Hao; Huang, Yu-Qi; Liu, Meng; Luo, Ai-Ping; Luo, Zhi-Chao; Xu, Wen-Cheng

    2015-10-19

    We propose a new solution to flexibly generate the coherent rectangular pulse from an ultrafast fiber laser based on the dispersive Fourier transformation (DFT) technique. The rectangular dissipative soliton (DS) spectra emitted from a net-normal dispersion mode-locked fiber laser is mapped into a time-domain coherent rectangular waveform through the DFT technique. The rectangular pulse can be broadened flexibly with the adjustments of the pump power. The coherence and shot-to-shot fluctuations of the achieved rectangular pulses are further verified by the Mach-Zehnder interference experiment and the recorded single-shot pulse train, respectively. The results demonstrate that the combination of DS mode-locked laser and DFT technique might be indeed an effective and flexible way to achieve highly coherent rectangular pulses. PMID:26480392

  12. Fourier transform infrared spectrometry: a versatile technique for real world samples.

    PubMed

    Rintoul, L; Panayiotou, H; Kokot, S; George, G; Cash, G; Frost, R; Bui, T; Fredericks, P

    1998-04-01

    The versatility of FTIR spectrometry was explored by considering a variety of samples drawn from industrial applications, materials science and biomedical research. These samples included polymeric insulators, bauxite ore, clay, human hair and human skin. A range of sampling techniques suitable for these samples is discussed, in particular FTIR microscopy, FTIR emission spectroscopy, attenuated total reflectance and photoacoustic FTIR spectrometry. The power of modern data processing techniques, particularly multivariate analysis, to extract useful information from spectral data is also illustrated. PMID:9684399

  13. Electron heating enhancement by frequency-chirped laser pulses

    SciTech Connect

    Yazdani, E.; Afarideh, H.; Sadighi-Bonabi, R.; Riazi, Z.; Hora, H.

    2014-09-14

    Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2. Furthermore, it is noticed that for a chirped laser pulse with a₀=5, because of increasing the plasma transparency length, the laser pulse can penetrate up to about n{sub e}≈6n{sub c}, where n{sub c} is plasma critical density. It shows 63% increase in the effective critical density compared to the relativistic induced transparency regime for an unchirped condition.

  14. Generating nonlinear FM chirp radar signals by multiple integrations

    DOEpatents

    Doerry, Armin W.

    2011-02-01

    A phase component of a nonlinear frequency modulated (NLFM) chirp radar pulse can be produced by performing digital integration operations over a time interval defined by the pulse width. Each digital integration operation includes applying to a respectively corresponding input parameter value a respectively corresponding number of instances of digital integration.

  15. Chirped frequency transfer: a tool for synchronization and time transfer.

    PubMed

    Raupach, Sebastian M F; Grosche, Gesine

    2014-06-01

    We propose and demonstrate the phase-stabilized transfer of a chirped frequency as a tool for synchronization and time transfer. Technically, this is done by evaluating remote measurements of the transferred, chirped frequency. The gates of the frequency counters, here driven by a 10-MHz oscillation derived from a hydrogen maser, play a role analogous to the 1-pulse per second (PPS) signals usually employed for time transfer. In general, for time transfer, the gates consequently must be related to the external clock. Synchronizing observations based on frequency measurements, on the other hand, only requires a stable oscillator driving the frequency counters. In a proof of principle, we demonstrate the suppression of symmetrical delays, such as the geometrical path delay. We transfer an optical frequency chirped by around 240 kHz/s over a fiber link of around 149 km. We observe an accuracy and simultaneity, as well as a precision (Allan deviation, 18,000 s averaging interval) of the transferred frequency of around 2 × 10(-19). We apply chirped frequency transfer to remote measurements of the synchronization between two counters' gate intervals. Here, we find a precision of around 200 ps at an estimated overall uncertainty of around 500 ps. The measurement results agree with those obtained from reference measurements, being well within the uncertainty. In the present setup, timing offsets up to 4 min can be measured unambiguously. We indicate how this range can be extended further. PMID:24859656

  16. Technique for gray-scale visual light and infrared image fusion based on non-subsampled shearlet transform

    NASA Astrophysics Data System (ADS)

    Kong, Weiwei

    2014-03-01

    A novel image fusion technique based on NSST (non-subsampled shearlet transform) is presented, aiming at resolving the fusion problem of spatially gray-scale visual light and infrared images. NSST, as a new member of MGA (multi-scale geometric analysis) tools, possesses not only flexible direction features and optimal shift-invariance, but much better fusion performance and lower computational costs compared with several current popular MGA tools such as NSCT (non-subsampled contourlet transform). We specifically propose new rules for the fusion of low and high frequency sub-band coefficients of source images in the second step of the NSST-based image fusion algorithm. First, the source images are decomposed into different scales and directions using NSST. Then, the model of region average energy (RAE) is proposed and adopted to fuse the low frequency sub-band coefficients of the gray-scale visual light and infrared images. Third, the model of local directional contrast (LDC) is given and utilized to fuse the corresponding high frequency sub-band coefficients. Finally, the final fused image is obtained by using inverse NSST to all fused sub-images. In order to verify the effectiveness of the proposed technique, several current popular ones are compared over three different publicly available image sets using four evaluation metrics, and the experimental results demonstrate that the proposed technique performs better in both subjective and objective qualities.

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

    SciTech Connect

    Afhami, Saeedeh; Eslami, Esmaeil

    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.

  18. Feature extraction and classification for EEG signals using wavelet transform and machine learning techniques.

    PubMed

    Amin, Hafeez Ullah; Malik, Aamir Saeed; Ahmad, Rana Fayyaz; Badruddin, Nasreen; Kamel, Nidal; Hussain, Muhammad; Chooi, Weng-Tink

    2015-03-01

    This paper describes a discrete wavelet transform-based feature extraction scheme for the classification of EEG signals. In this scheme, the discrete wavelet transform is applied on EEG signals and the relative wavelet energy is calculated in terms of detailed coefficients and the approximation coefficients of the last decomposition level. The extracted relative wavelet energy features are passed to classifiers for the classification purpose. The EEG dataset employed for the validation of the proposed method consisted of two classes: (1) the EEG signals recorded during the complex cognitive task--Raven's advance progressive metric test and (2) the EEG signals recorded in rest condition--eyes open. The performance of four different classifiers was evaluated with four performance measures, i.e., accuracy, sensitivity, specificity and precision values. The accuracy was achieved above 98 % by the support vector machine, multi-layer perceptron and the K-nearest neighbor classifiers with approximation (A4) and detailed coefficients (D4), which represent the frequency range of 0.53-3.06 and 3.06-6.12 Hz, respectively. The findings of this study demonstrated that the proposed feature extraction approach has the potential to classify the EEG signals recorded during a complex cognitive task by achieving a high accuracy rate. PMID:25649845

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

    DOEpatents

    Bennett, Corey Vincent

    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.

  20. 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.

  1. Techniques for computing the discrete Fourier transform using the quadratic residue Fermat number systems

    NASA Technical Reports Server (NTRS)

    Truong, T. K.; Chang, J. J.; Hsu, I. S.; Pei, D. Y.; Reed, I. S.

    1986-01-01

    The complex integer multiplier and adder over the direct sum of two copies of finite field developed by Cozzens and Finkelstein (1985) is specialized to the direct sum of the rings of integers modulo Fermat numbers. Such multiplication over the rings of integers modulo Fermat numbers can be performed by means of two integer multiplications, whereas the complex integer multiplication requires three integer multiplications. Such multiplications and additions can be used in the implementation of a discrete Fourier transform (DFT) of a sequence of complex numbers. The advantage of the present approach is that the number of multiplications needed to compute a systolic array of the DFT can be reduced substantially. The architectural designs using this approach are regular, simple, expandable and, therefore, naturally suitable for VLSI implementation.

  2. Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy.

    PubMed

    Segawa, Takuya F; Doll, Andrin; Pribitzer, Stephan; Jeschke, Gunnar

    2015-07-28

    The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclear modulation spectrum. PMID:26233121

  3. High-energy infrared femtosecond pulses generated by dual-chirped optical parametric amplification.

    PubMed

    Fu, Yuxi; Takahashi, Eiji J; Midorikawa, Katsumi

    2015-11-01

    We demonstrate high-energy infrared femtosecond pulse generation by a dual-chirped optical parametric amplification (DC-OPA) scheme [Opt. Express19, 7190 (2011)]. By employing a 100 mJ pump laser, a signal pulse energy exceeding 20 mJ at a wavelength of 1.4 μm was achieved before dispersion compensation. A total output energy of 33 mJ was recorded. Under a further energy scaling condition, the signal pulse was compressed to an almost transform-limited duration of 27 fs using a fused silica prism compressor. Since the DC-OPA scheme is efficient and energy scalable, design parameters for obtaining 100 mJ level infrared pulses are presented, which are suitable as driver lasers for the energy scaling of high-order harmonic generation with sub-keV photon energy. PMID:26512524

  4. Coherence rephasing combined with spin-wave storage using chirped control pulses

    NASA Astrophysics Data System (ADS)

    Demeter, Gabor

    2014-06-01

    Photon-echo based optical quantum memory schemes often employ intermediate steps to transform optical coherences to spin coherences for longer storage times. We analyze a scheme that uses three identical chirped control pulses for coherence rephasing in an inhomogeneously broadened ensemble of three-level Λ systems. The pulses induce a cyclic permutation of the atomic populations in the adiabatic regime. Optical coherences created by a signal pulse are stored as spin coherences at an intermediate time interval, and are rephased for echo emission when the ensemble is returned to the initial state. Echo emission during a possible partial rephasing when the medium is inverted can be suppressed with an appropriate choice of control pulse wave vectors. We demonstrate that the scheme works in an optically dense ensemble, despite control pulse distortions during propagation. It integrates conveniently the spin-wave storage step into memory schemes based on a second rephasing of the atomic coherences.

  5. Radio crickets: chirping jets from black hole binaries entering their gravitational wave inspiral

    NASA Astrophysics Data System (ADS)

    Kulkarni, Girish; Loeb, Abraham

    2016-03-01

    We study a novel electromagnetic signature of supermassive black hole (BH) binaries whose inspiral starts being dominated by gravitational wave (GW) emission. Recent simulations suggest that the binary's member BHs can continue to accrete gas from the circumbinary accretion disc in this phase of the binary's evolution, all the way until coalescence. If one of the binary members produces a radio jet as a result of accretion, the jet precesses along a biconical surface due to the binary's orbital motion. When the binary enters the GW phase of its evolution, the opening angle widens, the jet exhibits milliarcsecond-scale wiggles, and the conical surface of jet precession is twisted due to apparent superluminal motion. The rapidly increasing orbital velocity of the binary gives the jet an appearance of a `chirp'. This helical chirping morphology of the jet can be used to infer the binary parameters. For binaries with mass 107-1010 M⊙ at redshifts z < 0.5, monitoring these features in current and archival data will place a lower limit on sources that could be detected by Evolved Laser Interferometer Space Antenna and Pulsar Timing Arrays. In the future, microarcsecond interferometry with the Square Kilometre Array will increase the potential usefulness of this technique.

  6. Damage Modes Recognition and Hilbert-Huang Transform Analyses of CFRP Laminates Utilizing Acoustic Emission Technique

    NASA Astrophysics Data System (ADS)

    WenQin, Han; Ying, Luo; AiJun, Gu; Yuan, Fuh-Gwo

    2015-08-01

    Discrimination of acoustic emission (AE) signals related to different damage modes is of great importance in carbon fiber-reinforced plastic (CFRP) composite materials. To gain a deeper understanding of the initiation, growth and evolution of the different types of damage, four types of specimens for different lay-ups and orientations and three types of specimens for interlaminar toughness tests are subjected to tensile test along with acoustic emission monitoring. AE signals have been collected and post-processed, the statistical results show that the peak frequency of AE signal can distinguish various damage modes effectively. After a AE signal were decomposed by Empirical Mode Decomposition (EMD) method, it may separate and extract all damage modes included in this AE signal apart from damage mode corresponding to the peak frequency. Hilbert-Huang Transform (HHT) of AE signals can clearly illustrate the frequency distribution of Intrinsic Mode Functions (IMF) components in time-scale in different damage stages, and can calculate accurate instantaneous frequency for damage modes recognition to help understanding the damage process.

  7. Damage Modes Recognition and Hilbert-Huang Transform Analyses of CFRP Laminates Utilizing Acoustic Emission Technique

    NASA Astrophysics Data System (ADS)

    WenQin, Han; Ying, Luo; AiJun, Gu; Yuan, Fuh-Gwo

    2016-04-01

    Discrimination of acoustic emission (AE) signals related to different damage modes is of great importance in carbon fiber-reinforced plastic (CFRP) composite materials. To gain a deeper understanding of the initiation, growth and evolution of the different types of damage, four types of specimens for different lay-ups and orientations and three types of specimens for interlaminar toughness tests are subjected to tensile test along with acoustic emission monitoring. AE signals have been collected and post-processed, the statistical results show that the peak frequency of AE signal can distinguish various damage modes effectively. After a AE signal were decomposed by Empirical Mode Decomposition (EMD) method, it may separate and extract all damage modes included in this AE signal apart from damage mode corresponding to the peak frequency. Hilbert-Huang Transform (HHT) of AE signals can clearly illustrate the frequency distribution of Intrinsic Mode Functions (IMF) components in time-scale in different damage stages, and can calculate accurate instantaneous frequency for damage modes recognition to help understanding the damage process.

  8. Regularization techniques on least squares non-uniform fast Fourier transform.

    PubMed

    Gibiino, Fabio; Positano, Vincenzo; Landini, Luigi; Santarelli, Maria Filomena

    2013-05-01

    Non-Cartesian acquisition strategies are widely used in MRI to dramatically reduce the acquisition time while at the same time preserving the image quality. Among non-Cartesian reconstruction methods, the least squares non-uniform fast Fourier transform (LS_NUFFT) is a gridding method based on a local data interpolation kernel that minimizes the worst-case approximation error. The interpolator is chosen using a pseudoinverse matrix. As the size of the interpolation kernel increases, the inversion problem may become ill-conditioned. Regularization methods can be adopted to solve this issue. In this study, we compared three regularization methods applied to LS_NUFFT. We used truncated singular value decomposition (TSVD), Tikhonov regularization and L?-regularization. Reconstruction performance was evaluated using the direct summation method as reference on both simulated and experimental data. We also evaluated the processing time required to calculate the interpolator. First, we defined the value of the interpolator size after which regularization is needed. Above this value, TSVD obtained the best reconstruction. However, for large interpolator size, the processing time becomes an important constraint, so an appropriate compromise between processing time and reconstruction quality should be adopted. PMID:23408698

  9. An efficient watermarking technique for satellite images using discrete cosine transform

    NASA Astrophysics Data System (ADS)

    AL-Mansoori, Saeed

    2012-10-01

    Due to the significant progress in science and technology, the digital world became an interesting topic for many studies. "Data Security" is one of the main concepts related to the digital world especially in the field of remote sensing. Therefore, to deal with this matter the "Watermarking" concept was introduced. The idea of digital image watermarking is to embed the information within a signal (i.e. image, video, etc.), which cannot be easily extracted by a third party. This will generate a copyright protection and authentication for the owner(s). Emirates Institution for Advanced Science and Technology (EIAST) as an owner provides satellite images captured by DubaiSat-1 satellite to customers. The aim of this study is to implement a robust algorithm to hide EIAST logo within any delivered image in order to increase the data security and protect the ownership of DubaiSat-1 images. In addition, it is necessary to provide a high quality images to the end-user; nevertheless, adding any information (logo) to these images will affect its quality. Therefore, the model will be designed to keep the observable difference between the watermarked and original image at minimum. Moreover, the watermark should be difficult to remove or alter without the degradation of the host image. This study will be based on Discrete Cosine Transform (DCT) to provide an excellent and highly robust protection in cases such as noise addition, cropping, rotation and JPEG compression attacks.

  10. Writing trace identification using ultraviolet Fourier-transform imaging spectroscopy technique

    NASA Astrophysics Data System (ADS)

    Lyu, Hang; Liao, Ningfang; Wu, Wenmin; Li, Yasheng; Cao, Bin

    2015-08-01

    Conventional identification methods of writing traces commonly utilize imaging or spectroscopic techniques which work in visible to near infrared range or short-wave infrared range. Yet they cannot be applied in identifying the erased writing traces. In this study, we perform a research in identification of erased writing traces applying an ultraviolet Fouriertransform imaging spectrometer. Experiments of classifying the reflected ultraviolet spectra of erasable pens are made. The resulting hyperspectral images demonstrate that the erased writing traces on printing paper can be clearly identified by this ultraviolet imaging spectrometer.

  11. ISAR imaging of maneuvering targets based on the range centroid Doppler technique.

    PubMed

    Lv, Xiaolei; Xing, Mengdao; Wan, Chunru; Zhang, Shouhong

    2010-01-01

    A new inverse synthetic aperture radar (ISAR) imaging approach is presented for application in situations where the maneuverability of noncooperative target is not too severe and the Doppler variation of subechoes from scatterers can be approximated as a first-order polynomial. The proposed algorithm is referred to as the range centroid Doppler (RCD) ISAR imaging technique and is based on the stretch Keystone-Wigner transform (SKWT). The SKWT introduces a stretch weight factor containing a range of chirp rate into the autocorrelation function of each cross-range profile and uses a 1-D interpolation of the phase history which we call stretch keystone formatting. The processing simultaneously eliminates the effects of linear frequency migration for all signal components regardless of their unknown chirp rate in time-frequency plane, but not for the noise or for the cross terms. By utilizing this novel technique, clear ISAR imaging can be achieved for maneuvering targets without an exhaustive search procedure for the motion parameters. Performance comparison is carried out to evaluate the improvement of the RCD technique versus other methods such as the conventional range Doppler (RD) technique, the range instantaneous Doppler (RID) technique, and adaptive joint time-frequency (AJTF) technique. Examples provided demonstrate the effectiveness of the RCD technique with both simulated and experimental ISAR data. PMID:19775968

  12. 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, Bjrg; Jrgensen, Kjetil; Lien, Sigbjrn; 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

  13. 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.

  14. Chirped-pulse terahertz spectroscopy for broadband trace gas sensing.

    PubMed

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

    2011-04-25

    We report the first demonstration of a broadband trace gas sensor based on chirp-pulse terahertz spectroscopy. The advent of newly developed solid state sources and sensitive heterodyne detectors for the terahertz frequency range have made it possible to generate and detect precise arbitrary waveforms at THz frequencies with ultra-low phase noise. In order to maximize sensitivity, the sample gas is first polarized using sub-μs chirped THz pulses and the free inductive decays (FIDs) are then detected using a heterodyne receiver. This approach allows for a rapid broadband multi-component sensing with low parts in 10(9) (ppb) sensitivities and spectral frequency accuracy of <20 kHz in real-time. Such a system can be configured into a portable, easy to use, and relatively inexpensive sensing platform. PMID:21643150

  15. Hyper dispersion pulse compressor for chirped pulse amplification systems

    SciTech Connect

    Barty, Christopher P. J.

    2011-11-29

    A grating pulse compressor configuration is introduced for increasing the optical dispersion for a given footprint and to make practical the application for chirped pulse amplification (CPA) to quasi-narrow bandwidth materials, such as Nd:YAG. The grating configurations often use cascaded pairs of gratings to increase angular dispersion an order of magnitude or more. Increased angular dispersion allows for decreased grating separation and a smaller compressor footprint.

  16. Multimodal nonlinear Raman microspectroscopy with ultrashort chirped laser pulses

    NASA Astrophysics Data System (ADS)

    Lanin, A. A.; Stepanov, E. A.; Tikhonov, R. A.; Sidorov-Biryukov, D. A.; Fedotov, A. B.; Zheltikov, A. M.

    2015-05-01

    We demonstrate the physical principles of multimodal nonlinear optical microspectroscopy, integrating methods of coherent and stimulated Raman scattering of ultrashort chirped laser pulses in a single optical scheme. Nonlinear phase distortions of ultrashort laser pulses are accurately compensated within a broad spectral range in this scheme to enable a high-spectral-resolution laser microspectroscopy that can reliably resolve groups of fingerprint molecular vibrations with close frequencies, thus facilitating an analysis of complex multicomponent systems.

  17. Learning-based computing techniques in geoid modeling for precise height transformation

    NASA Astrophysics Data System (ADS)

    Erol, B.; Erol, S.

    2013-03-01

    Precise determination of local geoid is of particular importance for establishing height control in geodetic GNSS applications, since the classical leveling technique is too laborious. A geoid model can be accurately obtained employing properly distributed benchmarks having GNSS and leveling observations using an appropriate computing algorithm. Besides the classical multivariable polynomial regression equations (MPRE), this study attempts an evaluation of learning based computing algorithms: artificial neural networks (ANNs), adaptive network-based fuzzy inference system (ANFIS) and especially the wavelet neural networks (WNNs) approach in geoid surface approximation. These algorithms were developed parallel to advances in computer technologies and recently have been used for solving complex nonlinear problems of many applications. However, they are rather new in dealing with precise modeling problem of the Earth gravity field. In the scope of the study, these methods were applied to Istanbul GPS Triangulation Network data. The performances of the methods were assessed considering the validation results of the geoid models at the observation points. In conclusion the ANFIS and WNN revealed higher prediction accuracies compared to ANN and MPRE methods. Beside the prediction capabilities, these methods were also compared and discussed from the practical point of view in conclusions.

  18. Auditory brainstem responses to chirps delivered by an insert earphone with equalized frequency response

    PubMed Central

    Elberling, Claus; Don, Manuel; Kristensen, Sinnet G. B.

    2012-01-01

    Recently it has been demonstrated that auditory brainstem responses, ABRs, to chirps are larger with the ER-2 than with the ER-3A insert earphone due to differences between the corresponding amplitude-frequency responses. Therefore a modified chirp, which equalizes the amplitude-frequency response of the ER-3A, is constructed and subsequently compared to the unmodified chirp. ABRs are recorded from 20 normal-hearing subjects in response to the two chirps delivered by the ER-3A earphone at a wide range of levels. The results confirm that the modified chirp generates significantly larger ABRs than the unmodified chirp at levels below 60 dB nHL. PMID:22894314

  19. Chirped pulse control of CsI fragmentation: an experimental possibility

    NASA Astrophysics Data System (ADS)

    Amstrup, Bjarne; Szabó, Gábor; Sauerbrey, Roland A.; Lörincz, András

    1994-10-01

    The strength of chirped pulse optimal control as an experimental possibility is demonstrated in this paper. The suggested experiment is a pump-dump experiment that first creates an unstable - dissociating - molecule on a repulsive level and then stops fragmentation. The experiment is envisioned by using a start pulse (a doubled green pulse) that inverts the population. The control pulse - that stops the fragmentation - is the chirp optimized green pulse itself. Optimization includes second and third order chirp expansion terms. Optimization is made for the weak and strong field limits with the help of the simulated annealing method. Weak field optimization shows the expected red chirp results. Strong field optimization, on the other hand, gives rise to blue chirp as optimal solution. It is argued, that the blue chirp is the consequence of the need for locking the upper and lower state wavefunctions for efficient population inversion.

  20. 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.

  1. Study on the technique of distinguishing rock from coal based on statistical analysis of fast Fourier transform

    NASA Astrophysics Data System (ADS)

    Li, Xu; Gu, Tao

    2010-04-01

    An algorithm of distinguishing rock from coal based on statistical analysis of Fast Fourier Transform (FFT) is presented which can be used in the mechanized caving coal locales. First, eight groups of sound signals sampled with the speed 8192 samples/sec during caving are transformed by FFT. Second, the FFT results are analyzed and the ratios of the low frequency energy to the high frequency energy(ER) defined in the FFT results are calculated by using the variance analytical method (Var). Third, the typical values of the sound of the coal bumping the transporting coal armor plate, the rock bumping the armor plate and the mixing of coal and rock bumping the armor plate are calculated with the variances and the ratios(EV= ER *Var). Finally, the threshold of distinguishing rock from coal is evaluated by using the typical values and used to direct the opportunity for caving. We can learn by the experimental results that the proposed technique can depict effectively the different characteristics of the sampled signals. The experimental results also show that we can distinguish effectively different bumping sounds of coal, rock and the mixing of them by the characteristics when adjusting the threshold value. Therefore the algorithm can be used to improve the miners' productivity and promote the construction of digital mine.

  2. Chirped pulse Raman amplification in warm plasma: towards controlling saturation.

    PubMed

    Yang, X; Vieux, G; Brunetti, E; Ersfeld, B; Farmer, J P; Hur, M S; Issac, R C; Raj, G; Wiggins, S M; Welsh, G H; Yoffe, S R; Jaroszynski, D A

    2015-01-01

    Stimulated Raman backscattering in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers because plasma is fully broken down and withstands extremely high electric fields. Plasma also has unique nonlinear optical properties that allow simultaneous compression of optical pulses to ultra-short durations. However, current measured efficiencies are limited to several percent. Here we investigate Raman amplification of short duration seed pulses with different chirp rates using a chirped pump pulse in a preformed plasma waveguide. We identify electron trapping and wavebreaking as the main saturation mechanisms, which lead to spectral broadening and gain saturation when the seed reaches several millijoules for durations of 10's - 100's fs for 250 ps, 800 nm chirped pump pulses. We show that this prevents access to the nonlinear regime and limits the efficiency, and interpret the experimental results using slowly-varying-amplitude, current-averaged particle-in-cell simulations. We also propose methods for achieving higher efficiencies. PMID:26290153

  3. Shear wave speed and dispersion measurements using crawling wave chirps.

    PubMed

    Hah, Zaegyoo; Partin, Alexander; Parker, Kevin J

    2014-10-01

    This article demonstrates the measurement of shear wave speed and shear speed dispersion of biomaterials using a chirp signal that launches waves over a range of frequencies. A biomaterial is vibrated by two vibration sources that generate shear waves inside the medium, which is scanned by an ultrasound imaging system. Doppler processing of the acquired signal produces an image of the square of vibration amplitude that shows repetitive constructive and destructive interference patterns called "crawling waves." With a chirp vibration signal, successive Doppler frames are generated from different source frequencies. Collected frames generate a distinctive pattern which is used to calculate the shear speed and shear speed dispersion. A special reciprocal chirp is designed such that the equi-phase lines of a motion slice image are straight lines. Detailed analysis is provided to generate a closed-form solution for calculating the shear wave speed and the dispersion. Also several phantoms and an ex vivo human liver sample are scanned and the estimation results are presented. PMID:24658144

  4. Chirped pulse Raman amplification in warm plasma: towards controlling saturation

    PubMed Central

    Yang, X.; Vieux, G.; Brunetti, E.; Ersfeld, B.; Farmer, J. P.; Hur, M. S.; Issac, R. C.; Raj, G.; Wiggins, S. M.; Welsh, G. H.; Yoffe, S. R.; Jaroszynski, D. A.

    2015-01-01

    Stimulated Raman backscattering in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers because plasma is fully broken down and withstands extremely high electric fields. Plasma also has unique nonlinear optical properties that allow simultaneous compression of optical pulses to ultra-short durations. However, current measured efficiencies are limited to several percent. Here we investigate Raman amplification of short duration seed pulses with different chirp rates using a chirped pump pulse in a preformed plasma waveguide. We identify electron trapping and wavebreaking as the main saturation mechanisms, which lead to spectral broadening and gain saturation when the seed reaches several millijoules for durations of 10’s – 100’s fs for 250 ps, 800 nm chirped pump pulses. We show that this prevents access to the nonlinear regime and limits the efficiency, and interpret the experimental results using slowly-varying-amplitude, current-averaged particle-in-cell simulations. We also propose methods for achieving higher efficiencies. PMID:26290153

  5. Evaluation of adaptive/nonadaptive filtering and wavelet transform techniques for noise reduction in EMG mobile acquisition equipment.

    PubMed

    Ortolan, Rodrigo Lcio; Mori, Ricardo Naoki; Pereira, Roberto R Jnior; Cabral, Cristina M N; Pereira, Jos Carlos; Cliquet, Alberto Jnior

    2003-03-01

    The myoelectric signal can be used to control many rehabilitation systems, for instance, prostheses and artificial neuromuscular electrical stimulation toward restoring movement to spinal cord injured subjects. These mobile systems are usually used in different environments and thus are being exposed to different noise levels with characteristics not completely known. In this article, three main techniques for noise reduction were evaluated: wavelet transform (WT), adaptive digital filters, and nonadaptive digital filters. The WT was used to reconstruct the signal with the components without noise information. Adaptive filters were designed using least mean square (LMS) and recursive least square (RLS) algorithms. Finite-impulse response (FIR) and infinite-impulse response (IIR) nonadaptive filters were used for comparison to both the adaptive filters and the signal reconstruction through the WT. PMID:12797727

  6. Controlling the femtosecond laser-driven transformation of dicyclopentadiene into cyclopentadiene

    PubMed Central

    Goswami, Tapas; Das, Dipak K.; Goswami, Debabrata

    2013-01-01

    Dynamics of the chemical transformation of dicyclopentadiene into cyclopentadiene in a supersonic molecular beam is elucidated using femtosecond time-resolved degenerate pump–probe mass spectrometry. Control of this ultrafast chemical reaction is achieved by using linearly chirped frequency modulated pulses. We show that negatively chirped femtosecond laser pulses enhance the cyclopentadiene photoproduct yield by an order of magnitude as compared to that of the unmodulated or the positively chirped pulses. This demonstrates that the phase structure of femtosecond laser pulse plays an important role in determining the outcome of a chemical reaction. PMID:24098059

  7. Spectral characteristics of draw-tower step-chirped fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Idrisov, Ravil F.; Varzhel, Sergey V.; Kulikov, Andrey V.; Meshkovskiy, Igor K.; Rothhardt, Manfred; Becker, Martin; Schuster, Kay; Bartelt, Hartmut

    2016-06-01

    This paper presents research results on the spectral properties of step-chirped fiber Bragg grating arrays written during the fiber drawing process into a birefringent optical fiber with an elliptical stress cladding. The dependences of resonance shift of the step-chirped fiber Bragg grating on bending, on applied tensile stress and on temperature have been investigated. A usage of such step-chirped fiber Bragg gratings in fiber-optic sensing elements creation has been considered.

  8. Generating nonlinear FM chirp waveforms for radar.

    SciTech Connect

    Doerry, Armin Walter

    2006-09-01

    Nonlinear FM waveforms offer a radar matched filter output with inherently low range sidelobes. This yields a 1-2 dB advantage in Signal-to-Noise Ratio over the output of a Linear FM waveform with equivalent sidelobe filtering. This report presents design and implementation techniques for Nonlinear FM waveforms.

  9. Compression and collisions of chirped pulses in a dense two-level medium

    NASA Astrophysics Data System (ADS)

    Novitsky, Denis V.

    2016-01-01

    Using numerical simulations, we study propagation of linearly-chirped optical pulses in a homogeneously broadened two-level medium. We pay attention to the three main topics - validity of the rotating-wave approximation (RWA), pulse compression, and collisions of counter-propagating pulses. The cases of long and single-cycle pulses are considered and compared with each other. We show that the RWA does not give a correct description of chirped pulse interaction with the medium. The compression of the chirp-free single-cycle pulse is stronger than of the chirped one, while the opposite is true for long pulses. We demonstrate that the influence of chirp on the collisions of the long pulses allows us to control the state of the transmitted radiation: the transmission of the chirp-free pulse can be dramatically changed under collision with the chirped counter-propagating one, in sharp contrast to the case when both pulses are chirped. On the other hand, the collisions of the chirped single-cycle pulses can be used for precise control of medium excitation in a narrow spatial region.

  10. Transit time of chirped pulses through one-dimensional, nonabsorbing barriers.

    PubMed

    D'Aguanno, G; Centini, M; Bloemer, M J; Myneni, K; Scalora, M; Bowden, C M; Sibilia, C; Bertolotti, M

    2002-02-01

    Experiments show that the transit times of chirped, narrow-band pulses that move across nonabsorbing, one-dimensional barriers are modified dramatically by the interplay between the chirp and the transmission function of the sample. In an experiment we monitored 0.9-ns chirped, nearly Gaussian pulses as they traversed a 450-mum GaAs etalon. At certain wavelengths pulse transit times can be superluminal or even negative. To explain these phenomena we have proposed a generalization of the transit time for chirped pulses that is still meaningful even when the transit times are superluminal or negative. Our predictions agree well with the experimental results. PMID:18007747

  11. The use of the fractional Fourier transform with coded excitation in ultrasound imaging.

    PubMed

    Bennett, Michael J; McLaughlin, Steve; Anderson, Tom; McDicken, Norman

    2006-04-01

    Medical ultrasound systems are limited by a tradeoff between axial resolution and the maximum imaging depth which may be achieved. The technique of coded excitation has been used extensively in the field of RADAR and SONAR for some time, but has only relatively recently been exploited in the area of medical ultrasound. This technique is attractive because allows the relationship between the pulse length and the maximum achievable spatial resolution to be changed. The work presented here explores the possibility of using the fractional Fourier transform as an effective means for the processing of signals received after the transmission of linear frequency modulated chirps. Results are presented which demonstrate that this technique is able to offer spatial resolutions similar to those obtained with a single cycle duration signal. PMID:16602583

  12. Application of the windowed-Fourier-transform-based fringe analysis technique for investigating temperature and concentration fields in fluids.

    PubMed

    Mohanan, Sharika; Srivastava, Atul

    2014-04-10

    The present work is concerned with the development and application of a novel fringe analysis technique based on the principles of the windowed-Fourier-transform (WFT) for the determination of temperature and concentration fields from interferometric images for a range of heat and mass transfer applications. Based on the extent of the noise level associated with the experimental data, the technique has been coupled with two different phase unwrapping methods: the Itoh algorithm and the quality guided phase unwrapping technique for phase extraction. In order to generate the experimental data, a range of experiments have been carried out which include cooling of a vertical flat plate in free convection conditions, combustion of mono-propellant flames, and growth of organic as well as inorganic crystals from their aqueous solutions. The flat plate and combustion experiments are modeled as heat transfer applications wherein the interest is to determine the whole-field temperature distribution. Aqueous-solution-based crystal growth experiments are performed to simulate the mass transfer phenomena and the interest is to determine the two-dimensional solute concentration field around the growing crystal. A Mach-Zehnder interferometer has been employed to record the path-integrated quantity of interest (temperature and/or concentration) in the form of interferometric images in the experiments. The potential of the WFT method has also been demonstrated on numerically simulated phase data for varying noise levels, and the accuracy in phase extraction have been quantified in terms of the root mean square errors. Three levels of noise, i.e., 0%, 10%, and 20% have been considered. Results of the present study show that the WFT technique allows an accurate extraction of phase values that can subsequently be converted into two-dimensional temperature and/or concentration distribution fields. Moreover, since WFT is a local processing technique, speckle patterns and the inherent noise in the interferometric data do not affect the resultant phase values. Brief comparisons of the accuracy of the WFT with other standard techniques such as conventional Fourier-filtering methods are also presented. PMID:24787402

  13. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy: An analytical technique to understand therapeutic responses at the molecular level

    PubMed Central

    Kalmodia, Sushma; Parameswaran, Sowmya; Yang, Wenrong; Barrow, Colin J.; Krishnakumar, Subramanian

    2015-01-01

    Rapid monitoring of the response to treatment in cancer patients is essential to predict the outcome of the therapeutic regimen early in the course of the treatment. The conventional methods are laborious, time-consuming, subjective and lack the ability to study different biomolecules and their interactions, simultaneously. Since; mechanisms of cancer and its response to therapy is dependent on molecular interactions and not on single biomolecules, an assay capable of studying molecular interactions as a whole, is preferred. Fourier Transform Infrared (FTIR) spectroscopy has become a popular technique in the field of cancer therapy with an ability to elucidate molecular interactions. The aim of this study, was to explore the utility of the FTIR technique along with multivariate analysis to understand whether the method has the resolution to identify the differences in the mechanism of therapeutic response. Towards achieving the aim, we utilized the mouse xenograft model of retinoblastoma and nanoparticle mediated targeted therapy. The results indicate that the mechanism underlying the response differed between the treated and untreated group which can be elucidated by unique spectral signatures generated by each group. The study establishes the efficiency of non-invasive, label-free and rapid FTIR method in assessing the interactions of nanoparticles with cellular macromolecules towards monitoring the response to cancer therapeutics. PMID:26568521

  14. The Optoelectronic Swept-Frequency Laser and Its Applications in Ranging, Three-Dimensional Imaging, and Coherent Beam Combining of Chirped-Seed Amplifiers

    NASA Astrophysics Data System (ADS)

    Vasilyev, Arseny

    This thesis explores the design, construction, and applications of the optoelectronic swept-frequency laser (SFL). The optoelectronic SFL is a feedback loop designed around a swept-frequency (chirped) semiconductor laser (SCL) to control its instantaneous optical frequency, such that the chirp characteristics are determined solely by a reference electronic oscillator. The resultant system generates precisely controlled optical frequency sweeps. In particular, we focus on linear chirps because of their numerous applications. We demonstrate optoelectronic SFLs based on vertical-cavity surface-emitting lasers (VCSELs) and distributed-feedback lasers (DFBs) at wavelengths of 1550 nm and 1060 nm. We develop an iterative bias current predistortion procedure that enables SFL operation at very high chirp rates, up to 1016 Hz/sec. We describe commercialization efforts and implementation of the predistortion algorithm in a stand-alone embedded environment, undertaken as part of our collaboration with Telaris, Inc. We demonstrate frequency-modulated continuous-wave (FMCW) ranging and three-dimensional (3-D) imaging using a 1550 nm optoelectronic SFL. We develop the technique of multiple source FMCW (MS-FMCW) reflectometry, in which the frequency sweeps of multiple SFLs are "stitched" together in order to increase the optical bandwidth, and hence improve the axial resolution, of an FMCW ranging measurement. We demonstrate computer-aided stitching of DFB and VCSEL sweeps at 1550 nm. We also develop and demonstrate hardware stitching, which enables MS-FMCW ranging without additional signal processing. The culmination of this work is the hardware stitching of four VCSELs at 1550 nm for a total optical bandwidth of 2 THz, and a free-space axial resolution of 75 microns. We describe our work on the tomographic imaging camera (TomICam), a 3-D imaging system based on FMCW ranging that features non-mechanical acquisition of transverse pixels. Our approach uses a combination of electronically tuned optical sources and low-cost full-field detector arrays, completely eliminating the need for moving parts traditionally employed in 3-D imaging. We describe the basic TomICam principle, and demonstrate single-pixel TomICam ranging in a proof-of-concept experiment. We also discuss the application of compressive sensing (CS) to the TomICam platform, and perform a series of numerical simulations. These simulations show that tenfold compression is feasible in CS TomICam, which effectively improves the volume acquisition speed by a factor ten. We develop chirped-wave phase-locking techniques, and apply them to coherent beam combining (CBC) of chirped-seed amplifiers (CSAs) in a master oscillator power amplifier configuration. The precise chirp linearity of the optoelectronic SFL enables non-mechanical compensation of optical delays using acousto-optic frequency shifters, and its high chirp rate simultaneously increases the stimulated Brillouin scattering (SBS) threshold of the active fiber. We characterize a 1550 nm chirped-seed amplifier coherent-combining system. We use a chirp rate of 5*1014 Hz/sec to increase the amplifier SBS threshold threefold, when compared to a single-frequency seed. We demonstrate efficient phase-locking and electronic beam steering of two 3 W erbium-doped fiber amplifier channels, achieving temporal phase noise levels corresponding to interferometric fringe visibilities exceeding 98%.

  15. 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 μm 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

  16. Chirped laser dispersion spectroscopy for remote open-path trace-gas sensing.

    PubMed

    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 μm 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

  17. 2-microm Doppler lidar transmitter with high frequency stability and low chirp.

    PubMed

    Wulfmeyer, V; Randall, M; Brewer, A; Hardesty, R M

    2000-09-01

    A coherent Doppler lidar system was frequency stabilized in a master-slave configuration by a phase-modulation technique. The short-term frequency stability, ~0.2 MHz rms, was maintained in a vibrational environment on a ship during a field campaign in the tropical Pacific Ocean. The long-term frequency stability was <2.6 kHz/h. Thus, in many applications, shot-to-shot frequency correction can be disregarded, which will result in increased speed and simplicity of the data-acquisition system. A frequency chirp could not be detected. These properties permit Doppler wind measurements with high efficiency and duty cycles to be made, even on airborne and spaceborne platforms. PMID:18066175

  18. Limitations on the fidelity of 100 fs pulses produced by chirped pulse amplification

    NASA Astrophysics Data System (ADS)

    White, W. E.; Patterson, F. G.; Vanwoerkom, L. D.; Price, D. F.; Shepherd, R. L.

    1993-05-01

    A system for continuously variable independent tuning of the higher order frequency dependent phase of ultrashort laser pulses was developed. This technique relies on geometric aberrations that arise from adjustments to the relative alignment of the elements of an air spaced doublet lens in systems such as a diffraction grating stretcher in which the spectral components of the optical pulses are spatially dispersed. Modeling results are compared to experimental measurements for a nonoptimized pulse stretcher/compressor combination showing the higher order phase aberrations that limit the performance of a chirped pulse amplification system. Numerical results are presented indicating these higher order phase terms can be compensated by a properly adjusted air spaced doublet design within the pulse stretcher.

  19. Pulsed heterodyne CO(2) laser rangefinder and velocimeter with chirp correction.

    PubMed

    Cohen, L H; van Eijk, A M; de Leeuw, G

    1994-08-20

    A pulsed hybrid CO(2) transversely excited atmosphere (TEA) laser has been used in a bistatic laser rangefinder-velocimeter system with heterodyne detection. Several techniques have been applied to improve the performance of the system. These include the stabilization of the hybrid CO(2) TEA-laser and the stabilization of the frequency offset of the local oscillator (better than ±74 kHz peak to peak), phase-front matching at the detector surface resulting in a heterodyne beat efficiency of 0.4-0.6, and chirp correction. With this system, targets at distances of up to 25 km can be detected with an accuracy of 15 m. The velocity of the targets can be estimated with an accuracy of approximately ±0.5 m/s. PMID:20935966

  20. Chirped-pulsed FTMW spectra of valeric acid, 5-aminovaleric acid, and δ-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 δ-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 → π* 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.

  1. Hadamard transform spectrometry: A new analytical technique; Progress report, Second year, March 15, 1992--November 15, 1992

    SciTech Connect

    Fateley, W.G.; Hammaker, R.M.

    1992-11-15

    The document is divided into 4 parts: Hadamard transform photoacoustic spectrometry and depth profiling; Hadamard transform imaging with a 2D Hadamard encoding mask (Raman image using pararosaniline hydrochloride); Hadamard transform Raman spectrometry; and work on the growth of VO{sub 2}(s) crystals for Hadamard masking material. 13 figs, refs.

  2. Gd(III)-Gd(III) distance measurements with chirp pump pulses.

    PubMed

    Doll, Andrin; Qi, Mian; Wili, Nino; Pribitzer, Stephan; Godt, Adelheid; Jeschke, Gunnar

    2015-10-01

    The broad EPR spectrum of Gd(III) spin labels restricts the dipolar modulation depth in distance measurements between Gd(III) pairs to a few percent. To overcome this limitation, frequency-swept chirp pulses are utilized as pump pulses in the DEER experiment. Using a model system with 3.4 nm Gd-Gd distance, application of one single chirp pump pulse at Q-band frequencies leads to modulation depths beyond 10%. However, the larger modulation depth is counteracted by a reduction of the absolute echo intensity due to the pump pulse. As supported by spin dynamics simulations, this effect is primarily driven by signal loss to double-quantum coherence and specific to the Gd(III) high spin state of S=7/2. In order to balance modulation depth and echo intensity for optimum sensitivity, a simple experimental procedure is proposed. An additional improvement by 25% in DEER sensitivity is achieved with two consecutive chirp pump pulses. These pulses pump the Gd(III) spectrum symmetrically around the observation position, therefore mutually compensating for dynamical Bloch-Siegert phase shifts at the observer spins. The improved sensitivity of the DEER data with modulation depths on the order of 20% is due to mitigation of the echo reduction effects by the consecutive pump pulses. In particular, the second pump pulse does not lead to additional signal loss if perfect inversion is assumed. Moreover, the compensation of the dynamical Bloch-Siegert phase prevents signal loss due to spatial dependence of the dynamical phase, which is caused by inhomogeneities in the driving field. The new methodology is combined with pre-polarization techniques to measure long distances up to 8.6 nm, where signal intensity and modulation depth become attenuated by long dipolar evolution windows. In addition, the influence of the zero-field splitting parameters on the echo intensity is studied with simulations. Herein, larger sensitivity is anticipated for Gd(III) complexes with zero-field splitting that is smaller than for the employed Gd-PyMTA complex. PMID:26340436

  3. Gd(III)-Gd(III) distance measurements with chirp pump pulses

    NASA Astrophysics Data System (ADS)

    Doll, Andrin; Qi, Mian; Wili, Nino; Pribitzer, Stephan; Godt, Adelheid; Jeschke, Gunnar

    2015-10-01

    The broad EPR spectrum of Gd(III) spin labels restricts the dipolar modulation depth in distance measurements between Gd(III) pairs to a few percent. To overcome this limitation, frequency-swept chirp pulses are utilized as pump pulses in the DEER experiment. Using a model system with 3.4 nm Gd-Gd distance, application of one single chirp pump pulse at Q-band frequencies leads to modulation depths beyond 10%. However, the larger modulation depth is counteracted by a reduction of the absolute echo intensity due to the pump pulse. As supported by spin dynamics simulations, this effect is primarily driven by signal loss to double-quantum coherence and specific to the Gd(III) high spin state of S = 7/2. In order to balance modulation depth and echo intensity for optimum sensitivity, a simple experimental procedure is proposed. An additional improvement by 25% in DEER sensitivity is achieved with two consecutive chirp pump pulses. These pulses pump the Gd(III) spectrum symmetrically around the observation position, therefore mutually compensating for dynamical Bloch-Siegert phase shifts at the observer spins. The improved sensitivity of the DEER data with modulation depths on the order of 20% is due to mitigation of the echo reduction effects by the consecutive pump pulses. In particular, the second pump pulse does not lead to additional signal loss if perfect inversion is assumed. Moreover, the compensation of the dynamical Bloch-Siegert phase prevents signal loss due to spatial dependence of the dynamical phase, which is caused by inhomogeneities in the driving field. The new methodology is combined with pre-polarization techniques to measure long distances up to 8.6 nm, where signal intensity and modulation depth become attenuated by long dipolar evolution windows. In addition, the influence of the zero-field splitting parameters on the echo intensity is studied with simulations. Herein, larger sensitivity is anticipated for Gd(III) complexes with zero-field splitting that is smaller than for the employed Gd-PyMTA complex.

  4. Determination of the far-field from measured near-field data, theory and measuring technique of the near-field far-field transformation

    NASA Astrophysics Data System (ADS)

    Schrott, A.; Stein, V.

    1980-12-01

    Methods are described for measuring the far field of antennas at distances that are small compared to the wavelength of the field. The so called compact test range is explained and the principle of the near field far field transformation is described. The advantages and disadvantages of the planar, cylindrical, and spherical transformation techniques are discussed. Theory and measuring technique for the spherical method are treated extensively. An assessment of the influence of errors is given and the acceptable tolerances are presented. A proposal is given for the construction of a near field test range. Finally the performance of the method is demonstrated with the aid of some examples.

  5. Generation of two-color ultra-short radiation pulses from two electron bunches and a chirped seeded free-electron laser

    NASA Astrophysics Data System (ADS)

    Feng, Chao; Wang, Zhen; Wang, Xingtao; Huang, Dazhang

    2016-01-01

    In this paper we describe a new method for the realization of two-color femtosecond radiation pulses in a seeded free-electron laser (FEL). The two-color pulses are obtained from two electron bunches and a chirped seeding laser. Compared to the previous methods based on seeded FELs, our method has the advantages of producing two-color FEL pulses with more flexible tunability both in the pulse durations and separations. Numerical simulations for the Dalian Coherent Light Source confirm that femtosecond XUV pulses with variable pulse durations and time delay can be directly generated from a chirped seed laser at 250 nm by using this technique. We also show the possibility of performing a proof-of-principle experiment of this technique based on the Shanghai Deep-Ultraviolet FEL facility.

  6. Auditory brainstem responses to chirps delivered by different insert earphones

    PubMed Central

    Elberling, Claus; Kristensen, Sinnet G. B.; Don, Manuel

    2012-01-01

    The frequency response and sensitivity of the ER-3A and ER-2 insert earphones are measured in the occluded-ear simulator using three ear canal extensions. Compared to the other two extensions, the DB 0370 (Brüel & Kjær), which is recommended by the international standards, introduces a significant resonance peak around 4500 Hz. The ER-3A has an amplitude response like a band-pass filter (1400 Hz, 6 dB/octave – 4000 Hz, −36 dB/octave), and a group delay with “ripples” of up to ±0.5 ms, while the ER-2 has an amplitude response, and a group delay which are flat and smooth up to above 10000 Hz. Both earphones are used to record auditory brainstem responses, ABRs, from 22 normal-hearing ears in response to two chirps and a click at levels from 20 to 80 dB nHL. While the click-ABRs are slightly larger for ER-2 than for ER-3A, the chirp-ABRs are much larger for ER-2 than for ER-3A at levels below 60 dB nHL. With a simulated amplitude response of the ER-3A and the smooth group delay of the ER-2 it is shown that the increased chirp-ABR amplitude with the ER-2 is caused by its broader amplitude response and not by its smoother group delay. PMID:22423705

  7. Effect of pulse profile and chirp on a laser wakefield generation

    SciTech Connect

    Zhang Xiaomei; Shen Baifei; Ji Liangliang; Wang Wenpeng; Xu Jiancai; Yu Yahong; Yi Longqing; Wang Xiaofeng; Hafz, Nasr A. M.; Kulagin, V.

    2012-05-15

    A laser wakefield driven by an asymmetric laser pulse with/without chirp is investigated analytically and through two-dimensional particle-in-cell simulations. For a laser pulse with an appropriate pulse length compared with the plasma wavelength, the wakefield amplitude can be enhanced by using an asymmetric un-chirped laser pulse with a fast rise time; however, the growth is small. On the other hand, the wakefield can be greatly enhanced for both positively chirped laser pulse having a fast rise time and negatively chirped laser pulse having a slow rise time. Simulations show that at the early laser-plasma interaction stage, due to the influence of the fast rise time the wakefield driven by the positively chirped laser pulse is more intense than that driven by the negatively chirped laser pulse, which is in good agreement with analytical results. At a later time, since the laser pulse with positive chirp exhibits opposite evolution to the one with negative chirp when propagating in plasma, the wakefield in the latter case grows more intensely. These effects should be useful in laser wakefield acceleration experiments operating at low plasma densities.

  8. Small signal analysis of frequency chirping in injection-locked semiconductor lasers

    SciTech Connect

    Piazzolla, S.; Spano, P.; Tamburrini, M.

    1986-12-01

    A theoretical and experimental investigation of frequency chirping in injection-locked semiconductor lasers under a condition of small signal modulation is presented. It shows that a substantial reduction of frequency chirping can be obtained which, however, is effective only up to modulation frequencies of the order of the locking bandwidth and is strongly dependent on the frequency detuning between master and slave.

  9. 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

  10. 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.

  11. Chirped nonlinear cavity for digital quantum state readout without switching

    NASA Astrophysics Data System (ADS)

    Naaman, Ofer; Aumentado, José.; Friedland, Lazar; Wurtele, Jonathan; Siddiqi, Irfan

    2009-03-01

    We observe a new phase-locking effect in a high-Q cavity embedding a Josephson junction driven with a chirped microwave signal. Above a critical drive amplitude, the cavity phase-locks to the drive and its oscillation amplitude grows with time. Below threshold, the cavity dephases from the drive and its amplitude remains small. The transition to phase-locking is associated with a sharp threshold sensitive to the junction I0, and can be used for digital detection of quantum states. This detector smoothly evolves into one oscillation state or the other without relying on any switching process.

  12. Optimal control of quantum systems by chirped pulses

    NASA Astrophysics Data System (ADS)

    Amstrup, B.; Doll, J. D.; Sauerbrey, R. A.; Szabó, G.; Lorincz, A.

    1993-11-01

    Research on optimal control of quantum systems has been severely restricted by the lack of experimentally feasible control pulses. Here, to overcome this obstacle, optimal control is considered with the help of chirped pulses. Simulated annealing is used as the optimizing procedure. The examples treated are pulsed population inversion between electronic levels, and optimization of vibronic excitation in the presence of another electronic level. In the problem of population inversion effective potentials of displaced harmonic oscillators are used. For optimizing vibronic excitation the CsI model potential is used.

  13. High-order dispersion in chirped-pulse oscillators.

    PubMed

    Kalashnikov, Vladimir L; Fernández, Alma; Apolonski, Alexander

    2008-03-17

    The effects of high-order dispersion on a chirped-pulse oscillator operating in the positive dispersion regime were studied both theoretically and experimentally. It was found that odd and negative even high-order dispersions impair the oscillator stability owing to resonance with the dispersion waves, but can broaden the spectrum as in the case of continuum generation in the fibers. Positive fourth-order dispersion enhances the stability and shifts the stability range into negative dispersion. The destabilization mechanism was found to be a parametrical instability which causes noisy mode locking around zero dispersion. PMID:18542516

  14. Oxidation of carbon monoxide at a platinum film electrode studied by Fourier transform infrared spectroscopy with attenuated total reflection technique

    SciTech Connect

    Zhu, Yimin; Uchida, Hiroyuki; Watanabe, Masahiro

    1999-12-07

    Fourier transform infrared reflection absorption spectroscopy with the attenuated total reflection technique (ATR-FTIR), coupled with cyclic voltammetry (CV) measurement, is used to observe the oxidation process of adsorbed CO at Pt film sputtered on a silicon prism. The interesting bipolar shape of the linearly bonded CO band is observed at high coverage of CO, although no CO band is included in the reference spectrum. This asymmetric shape is ascribed to Fano resonance. In addition to a linear CO and bridged CO, a new absorption band presumably assigned to a carboxyl radical, was detected. This band may be formed by a heterogeneous reaction between adsorbed CO and H{sub 2}O on the Pt surface in the hydrogen adsorption potential region. The adsorbed carboxyl radical was oxidized at a less positive potential than the adsorbed CO, which can be ascribed to a presumable origin for the pre-peak that appeared in a CV reading prior to the oxidation of such a linear or bridged CO. This oxidation led to the rearrangement of CO ad-layers, especially at high coverage of CO. In the case of the low coverage of CO, the conversion from the bridged CO to the linear CO is ascribed to the potential induced electronic effects of the electrode surface on the adsorption states. A consumption of adsorbed H{sub 2}O and a production of CO{sub 2} were also clearly indicated by the spectroscopy when COOH of CO disappeared from the surface.

  15. Measuring Temperature-Dependent Propagating Disturbances in Coronal Fan Loops Using Multiple SDO-AIA Channels and Surfing Transform Technique

    NASA Technical Reports Server (NTRS)

    Uritskiy, Vadim M.; Davila, Joseph M.; Viall, Nicholeen M.; Ofman, Leon

    2013-01-01

    A set of co-aligned high resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) 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 quantitative description of sub visual 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-timeplots 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 which 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 the slow mode magneto-acoustic wave which seems to be the dominating wave mode in the studied loop structures. This result extends recent observations by Kiddie et al. (2012) to a more general class of fan loop systems not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

  16. Effect of nonlinear chirped Gaussian laser pulse on plasma wake field generation

    SciTech Connect

    Afhami, Saeedeh; Eslami, Esmaeil

    2014-08-15

    An ultrashort laser pulse propagating in plasma can excite a nonlinear plasma wake field which can accelerate charged particles up to GeV energies within a compact space compared to the conventional accelerator devices. In this paper, the effect of different kinds of nonlinear chirped Gaussian laser pulse on wake field generation is investigated. The numerical analysis of our results depicts that the excitation of plasma wave with large and highly amplitude can be accomplished by nonlinear chirped pulses. The maximum amplitude of excited wake in nonlinear chirped pulse is approximately three times more than that of linear chirped pulse. In order to achieve high wake field generation, chirp parameters and functions should be set to optimal values.

  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. Control of Brillouin short-pulse seed amplification by chirping the pump pulse

    SciTech Connect

    Lehmann, G.; Spatschek, K. H.

    2015-04-15

    Seed amplification via Brillouin backscattering of a long pump pulse is considered. Similar to Raman amplification, several obstructive effects may occur during short-pulse Brillouin amplification. One is the spontaneous Raman backscattering of the pump before interacting with the seed. Preforming the plasma and/or chirping the pump will reduce unwanted pump backscattering. Optimized regions for low-loss pump propagation were proposed already in conjunction with Raman seed amplification. Hence, the influence of the chirp of the pump during Brillouin interaction with the seed becomes important and will be considered here. Both, the linear as well as the nonlinear evolution phases of the seed caused by Brillouin amplification under the action of a chirped pump are investigated. The amplification rate as well as the seed profiles are presented as function of the chirping rate. Also the dependence of superradiant scaling rates on the chirp parameter is discussed.

  19. Isolated short attosecond pulse generation in an orthogonally polarized multicycle chirped laser field

    SciTech Connect

    Xu Junjie

    2011-03-15

    We theoretically demonstrate the generation of a high-order harmonic and isolated attosecond pulse in an orthogonally polarized laser field, which is synthesized by an 800-nm chirped laser pulse and an 800-nm chirp-free laser pulse. Owing to the instantaneous frequency increasingly reducing close to the center of the driving pulse, the extreme ultraviolet supercontinuum for the chirped synthesized field is even broader than that for an orthogonal chirp-free two-color laser field. It is found that the broadband supercontinuum spectrum can be achieved for the driving pulse with ten and above optical cycles. After phase compensation an isolated attosecond pulse with a duration of {approx}16 as is produced. Furthermore, the optimization of the chirping rate parameters is investigated to achieve cutoff extension and an isolated short attosecond pulse.

  20. Perturbation-theory analysis of ionization by a chirped few-cycle attosecond pulse

    SciTech Connect

    Pronin, E. A.; Starace, Anthony F.; Peng Liangyou

    2011-07-15

    The angular distribution of electrons ionized from an atom by a chirped few-cycle attosecond pulse is analyzed using perturbation theory (PT), keeping terms in the transition amplitude up to second order in the pulse electric field. The dependence of the asymmetry in the ionized electron distributions on both the chirp and the carrier-envelope phase (CEP) of the pulse are explained using a simple analytical formula that approximates the exact PT result. This approximate formula (in which the chirp dependence is explicit) reproduces reasonably well the chirp-dependent oscillations of the electron angular distribution asymmetries found numerically by Peng et al. [Phys. Rev. A 80, 013407 (2009)]. It can also be used to determine the chirp rate of the attosecond pulse from the measured electron angular distribution asymmetry.

  1. Enhancement of proton acceleration by frequency-chirped laser pulse in radiation pressure mechanism

    NASA Astrophysics Data System (ADS)

    Vosoughian, H.; Riazi, Z.; Afarideh, H.; Yazdani, E.

    2015-07-01

    The transition from hole-boring to light-sail regime of radiation pressure acceleration by frequency-chirped laser pulses is studied using particle-in-cell simulation. The penetration depth of laser into the plasma with ramped density profile increases when a negatively chirped laser pulse is applied. Because of this induced transparency, the laser reflection layer moves deeper into the target and the hole-boring stage would smoothly transit into the light-sail stage. An optimum chirp parameter which satisfies the laser transparency condition, a 0 ≈ π n e l / n c λ , is obtained for each ramp scale length. Moreover, the efficiency of conversion of laser energy into the kinetic energy of particles is maximized at the obtained optimum condition. A relatively narrow proton energy spectrum with peak enhancement by a factor of 2 is achieved using a negatively chirped pulse compared with the un-chirped pulse.

  2. New genetic techniques for group B streptococci: high-efficiency transformation, maintenance of temperature-sensitive pWV01 plasmids, and mutagenesis with Tn917.

    PubMed Central

    Framson, P E; Nittayajarn, A; Merry, J; Youngman, P; Rubens, C E

    1997-01-01

    Three techniques were developed to improve the genetic manipulation of group B streptococci (GBS). We first optimized a protocol for transformation of GBS by electroporation, which provided transformation efficiencies of 10(5) CFU/microgram. Variables that influenced the transformation efficiency were the glycine content of the competent cell growth media, the electric field strength during electroporation, the electroporation buffer composition, the host origin of the transforming plasmid, and the concentration of selective antibiotic at the final plating. Our transformation protocol provides an efficiency sufficient for cloning from ligation reactions directly into GBS, obviating an intermediate host such as Escherichia coli. Second, temperature-sensitive plasmids of the pWV01 lineage were shown to transform GBS, and their temperature-sensitive replication was confirmed. Lastly, the temperature-sensitive pWV01 plasmid pTV1OK, which contains Tn917, was used as a transposon delivery vector for the construction of genomic Tn917 mutant libraries. We have shown, for the first time, that Tn917 transposes to the GBS chromosome and at a frequency of 10(-3)/CFU. Furthermore, representative clones from a Tn917 library contained single transposon insertions that were randomly located throughout the chromosome. These techniques should provide useful methods for cloning, mutagenesis, and characterization of genes from GBS. PMID:9293004

  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. Modification of chirped laser pulses via delayed rotational nonlinearity

    NASA Astrophysics Data System (ADS)

    Romanov, D. A.; Odhner, J. H.; Levis, R. J.

    2016-03-01

    To interpret single-shot measurements of rotational revival patterns in molecular gases excited by an ultrashort laser pulse, an analytical description of the probe pulse modulation by the impulsively excited medium is developed. A femtosecond pump laser pulse prepares a rotational wavepacket in a gas-phase sample, and the resulting periodic revivals are mapped into the frequency domain by using a substantially chirped continuum probe pulse. Since the standard approximate descriptions of probe pulse propagation are inapplicable (such as the slowly varying envelope approximation and the slowly evolving wave approximation), we propose an approach capable of incorporating both the substantial chirp of the pulse and the temporal dispersion of the medium response. Theory is presented for the case where the frequency change of the probe during the probe pulse duration is comparable with the carrier frequency. Analytical expressions are obtained for the probe signal modulation over the pump-probe interaction region and for the resulting heterodyned transient birefringence spectra. The approach is illustrated using the case of nitrogen gas.

  5. 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.

  6. Modification of chirped laser pulses via delayed rotational nonlinearity.

    PubMed

    Romanov, D A; Odhner, J H; Levis, R J

    2016-03-28

    To interpret single-shot measurements of rotational revival patterns in molecular gases excited by an ultrashort laser pulse, an analytical description of the probe pulse modulation by the impulsively excited medium is developed. A femtosecond pump laser pulse prepares a rotational wavepacket in a gas-phase sample, and the resulting periodic revivals are mapped into the frequency domain by using a substantially chirped continuum probe pulse. Since the standard approximate descriptions of probe pulse propagation are inapplicable (such as the slowly varying envelope approximation and the slowly evolving wave approximation), we propose an approach capable of incorporating both the substantial chirp of the pulse and the temporal dispersion of the medium response. Theory is presented for the case where the frequency change of the probe during the probe pulse duration is comparable with the carrier frequency. Analytical expressions are obtained for the probe signal modulation over the pump-probe interaction region and for the resulting heterodyned transient birefringence spectra. The approach is illustrated using the case of nitrogen gas. PMID:27036454

  7. 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.; Aldama-Reyna, W.; Lara-Rodriguez, A.G.; Garcia-Fernandez, T.; Pulos, G.; Trivi, M.; Villagran-Muniz, M.

    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.

  8. Effect of wavelet transform techniques upon the estimation of sugar content in apple with near-infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Ying, Yibin B.; Liu, Yande; Fu, Xiaping; Lu, Huishan

    2004-11-01

    Wavelet transform (WT) has proven a powerful and efficient tool for dealing with chemical data due to its characteristic of dual localization and has been widely used in analytical chemistry. This paper aims at serving three purposes: First, it gives a review of the applications of the wavelet transform in infrared spectroscopy; Second, it gives a quick summary of aspects and properties of wavelets and wavelet transforms which are needed in order to understand how to (pre-) process data from spectrometry with wavelet methods; Third, it shows on a typical example (apple NIR spectra) how wavelet transforms can be used in order to extract quantitative information. The sugar content of intact apple was measured by NIRS and analyzed by wavelet transform, which is a new development in signal treatment method in recent years. The results show that the spectra treated with wavelet transform indicate more effectively the relationship with sugar content in intact apple. Compared with original spectra, wavelet transform of three-size has the most marked relation with sugar content. The predicting precision of five-element regression is the best and the scale 3 is the best for its 0.904 correlation efficient of determination and the 0.777 in standard error of prediction which is less than that of primitive spectra. Therefore, the conclusion of improved predicting precision for quantitative detection of sugar content in intact apple with wavelet transform can be drawn.

  9. Tunable optoelectronic oscillator based on a chirped Mach-Zehnder modulator

    NASA Astrophysics Data System (ADS)

    Wei, Zhihu; Pan, Shilong; Wang, Rong; Pu, Tao; Fang, Tao; Sun, Guodan; Zheng, Jilin

    2013-05-01

    Realization of a wideband tunable optoelectronic oscillator based on a chirped Mach-Zehnder modulator (MZM) and a chirped fiber Bragg grating is proposed and demonstrated. By simply adjusting the direct-current bias of the chirped MZM, the frequency of the oscillating signal is tuned. A theoretical model is established, then verified by an experiment. A high-purity microwave signal with a tunable frequency from 5.8 to 11.8 GHz is generated. The single-sideband phase noise of the generated signal is -112.6 dBc/Hz at a frequency offset of 10 kHz.

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

    SciTech Connect

    Song, Q.; Wu, X. Y.; Wang, J. X.; Kawata, S.; Wang, P. X.

    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.

  11. 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.

  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. Intrinsic chirp of attosecond pulses: Single-atom model versus experiment

    SciTech Connect

    Kazamias, S.; Balcou, Ph.

    2004-06-01

    We demonstrate and evaluate the importance of an intrinsic chirp inherent to attosecond pulse creation accompanying high-order harmonic generation in recently published experimental data by Dinu et al. [Phys. Rev. Lett. 91, 063901 (2003)]. We present an analytical model, from which the atomic origin of the harmonic chirp is clearly understood. Moreover, the behavior of the chirp as a function of experimental parameters such as laser intensity is inferred. The comparison between our model and the experimental data provides us with useful information about the conditions in which the high-order harmonics is generated.

  14. Hydrogen-induced structural transformation of AuCu nanoalloys probed by synchrotron X-ray diffraction techniques.

    PubMed

    Yamauchi, M; Okubo, K; Tsukuda, T; Kato, K; Takata, M; Takeda, S

    2014-04-21

    In situ X-ray diffraction measurements reveal that the transformation of a AuCu nanoalloy from a face-centered-cubic to an L10 structure is accelerated under a hydrogen atmosphere. The structural transformation rate for the AuCu nanoalloy under hydrogen above 433 K was found to be 100 times faster than that in a vacuum, which is the first quantitative observation of hydrogen-induced ordering of nanoalloys. PMID:24608274

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

    SciTech Connect

    Lemery, F.; Mihalcea, D.; Prokop, C.R.; 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.

  16. 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.; Błaszkiewicz, 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.

  17. Robust Volume Assessment of Brain Tissues for 3-Dimensional Fourier Transformation MRI via a Novel Multispectral Technique

    PubMed Central

    Chai, Jyh-Wen; Chen, Clayton C.; Wu, Yi-Ying; Chen, Hung-Chieh; Tsai, Yi-Hsin; Chen, Hsian-Min; Lan, Tsuo-Hung; Ouyang, Yen-Chieh; Lee, San-Kan

    2015-01-01

    A new TRIO algorithm method integrating three different algorithms is proposed to perform brain MRI segmentation in the native coordinate space, with no need of transformation to a standard coordinate space or the probability maps for segmentation. The method is a simple voxel-based algorithm, derived from multispectral remote sensing techniques, and only requires minimal operator input to depict GM, WM, and CSF tissue clusters to complete classification of a 3D high-resolution multislice-multispectral MRI data. Results showed very high accuracy and reproducibility in classification of GM, WM, and CSF in multislice-multispectral synthetic MRI data. The similarity indexes, expressing overlap between classification results and the ground truth, were 0.951, 0.962, and 0.956 for GM, WM, and CSF classifications in the image data with 3% noise level and 0% non-uniformity intensity. The method particularly allows for classification of CSF with 0.994, 0.961 and 0.996 of accuracy, sensitivity and specificity in images data with 3% noise level and 0% non-uniformity intensity, which had seldom performed well in previous studies. As for clinical MRI data, the quantitative data of brain tissue volumes aligned closely with the brain morphometrics in three different study groups of young adults, elderly volunteers, and dementia patients. The results also showed very low rates of the intra- and extra-operator variability in measurements of the absolute volumes and volume fractions of cerebral GM, WM, and CSF in three different study groups. The mean coefficients of variation of GM, WM, and CSF volume measurements were in the range of 0.03% to 0.30% of intra-operator measurements and 0.06% to 0.45% of inter-operator measurements. In conclusion, the TRIO algorithm exhibits a remarkable ability in robust classification of multislice-multispectral brain MR images, which would be potentially applicable for clinical brain volumetric analysis and explicitly promising in cross-sectional and longitudinal studies of different subject groups. PMID:25710499

  18. 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.

  19. Compression of chirp pulses from a femtosecond fiber based amplifier

    NASA Astrophysics Data System (ADS)

    Ito, Rumi; Takiuchi, Ken-ichi; Tei, Kazuyoku; Yamaguchi, Shigeru; Enokidani, Jyun; Sumida, Shin

    2015-03-01

    We demonstrate a single mode fiber based master oscillator power amplifier (MOPA) with a single polarization and a fully monolithic design. We have built a passive mode-locked polarization maintaining Yb doped fiber as the master oscillator contains a semiconductor saturable absorber mirror and a chirped fiber Bragg grating for the dispersion management. The net intracavity dispersion was managed to be slightly anomalous. The oscillator generates the 150 fs (sech2) pulses at the center wavelength of 1065 nm, and the repetition rate of 42 MHz. The oscillator output was amplified to 1.4 W from 80 mW in the single stage fiber amplifier which results in pulse shape distortion. The pulse shaping with a band pass filter and a compressor was applied to the amplified pulses. The shaping pulses have the pulse width of 90 fs and the pulse energy of 16 nJ.

  20. Femtosecond Chirp-Free Transient Absorption Method And Apparatus

    DOEpatents

    McBranch, Duncan W.; Klimov, Victor I.

    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.

  1. Synchronously pumped femtosecond optical parametric oscillator with broadband chirped mirrors

    NASA Astrophysics Data System (ADS)

    Stankevičiūte, Karolina; Melnikas, Simas; Kičas, Simonas; Trišauskas, Lukas; Vengelis, Julius; Grigonis, Rimantas; Vengris, Mikas; Sirutkaitis, Valdas

    2015-05-01

    We present results obtained during investigation of synchronously pumped optical parametric oscillator (SPOPO) with broadband complementary chirped mirror pairs (CMP). The SPOPO based on β-BBO nonlinear crystal is pumped by second harmonic of femtosecond Yb:KGW laser and provides signal pulses tunable over spectral range from 625 to 980 nm. More than 500 mW are generated in the signal beam, giving up to 27 % pump power to signal power conversion efficiency. The plane SPOPO cavity mirror pairs were specially designed to provide 99 % reflection in broad spectral range corresponding to signal wavelength tuning (630-1030 nm) and to suppress group delay dispersion (GDD) oscillations down to +/-10 fs2. Dispersion properties of designed mirrors were tested with white light interferometer (WLI) and attributed to the SPOPO tuning behaviour.

  2. Active stabilization for optically synchronized optical parametric chirped pulse amplification.

    PubMed

    Schwarz, Alexander; Ueffing, Moritz; Deng, Yunpei; Gu, Xun; Fattahi, Hanieh; Metzger, Thomas; Ossiander, Marcus; Krausz, Ferenc; Kienberger, Reinhard

    2012-02-27

    The development of new high power laser sources tends toward optical parametric chirped pulse amplification (OPCPA) in recent years. One of the difficulties in OPCPA is the the temporal overlap between pump and seed pulses. In this work we characterize our timing jitter on a single-shot basis using spectrally resolved cross-correlation in combination with a position sensitive detector. A commercial beam stabilization is adapted to actively enhance temporal overlap. This delay-stabilizer reduces the RMS jitter from σ = 127 fs down to σ = 24 fs. The enhanced temporal overlap is demonstrated in our frontend and we propose the scheme to be applicable in many optically synchronized high-repetition-rate OPCPA systems. PMID:22418362

  3. Orbit-based analysis of nonlinear energetic ion dynamics in tokamaks. II. Mechanisms for rapid chirping and convective amplification

    NASA Astrophysics Data System (ADS)

    Bierwage, Andreas; Shinohara, Kouji

    2016-04-01

    The nonlinear interactions between shear Alfvén modes and tangentially injected beam ions in the 150-400 keV range are studied numerically in realistic geometry for a JT-60U tokamak scenario. In Paper I, which was reported in the companion paper, the recently developed orbit-based resonance analysis method was used to track the resonant frequency of fast ions during their nonlinear evolution subject to large magnetic and electric drifts. Here, that method is applied to map the wave-particle power transfer from the canonical guiding center phase space into the frequency-radius plane, where it can be directly compared with the evolution of the fluctuation spectra of fast-ion-driven modes. Using this technique, we study the nonlinear dynamics of strongly driven shear Alfvén modes with low toroidal mode numbers n = 1 and n = 3. In the n = 3 case, both chirping and convective amplification can be attributed to the mode following the resonant frequency of the radially displaced particles, i.e., the usual one-dimensional phase locking process. In the n = 1 case, a new chirping mechanism is found, which involves multiple dimensions, namely, wave-particle trapping in the radial direction and phase mixing across velocity coordinates.

  4. Influence of chirping the Raman lasers in an atom gravimeter: Phase shifts due to the Raman light shift and to the finite speed of light

    NASA Astrophysics Data System (ADS)

    Cheng, B.; Gillot, P.; Merlet, S.; Pereira Dos Santos, F.

    2015-12-01

    We present here an analysis of the influence of the frequency dependence of the Raman laser light shifts on the phase of a Raman-type atom gravimeter. Frequency chirps are applied to the Raman lasers in order to compensate gravity and ensure the resonance of the Raman pulses during the interferometer. We show that the change in the Raman light shift when this chirp is applied only to one of the two Raman lasers is enough to bias the gravity measurement by a fraction of μ Gal (1 μ Gal =10-8m /s2). We also show that this effect is not compensated when averaging over the two directions of the Raman wave vector k . This thus constitutes a limit to the rejection efficiency of the k -reversal technique. Our analysis allows us to separate this effect from the effect of the finite speed of light, which we find in perfect agreement with expected values. This study highlights the benefit of chirping symmetrically the two Raman lasers.

  5. Fast Hearing-Threshold Estimation Using Multiple Auditory Steady-State Responses with Narrow-Band Chirps and Adaptive Stimulus Patterns

    PubMed Central

    Mühler, Roland; Mentzel, Katrin; Verhey, Jesko

    2012-01-01

    This paper describes the estimation of hearing thresholds in normal-hearing and hearing-impaired subjects on the basis of multiple-frequency auditory steady-state responses (ASSRs). The ASSR was measured using two new techniques: (i) adaptive stimulus patterns and (ii) narrow-band chirp stimuli. ASSR thresholds in 16 normal-hearing and 16 hearing-impaired adults were obtained simultaneously at both ears at 500, 1000, 2000, and 4000 Hz, using a multiple-frequency stimulus built up of four one-octave-wide narrow-band chirps with a repetition rate of 40 Hz. A statistical test in the frequency domain was used to detect the response. The recording of the steady-state responses was controlled in eight independent recording channels with an adaptive, semiautomatic algorithm. The average differences between the behavioural hearing thresholds and the ASSR threshold estimate were 10, 8, 13, and 15 dB for test frequencies of 500, 1000, 2000, and 4000 Hz, respectively. The average overall test duration of 18.6 minutes for the threshold estimations at the four frequencies and both ears demonstrates the benefit of an adaptive recording algorithm and the efficiency of optimised narrow-band chirp stimuli. PMID:22619622

  6. Development and characterization of a high average power, single-stage regenerative chirped pulse amplifier

    NASA Astrophysics Data System (ADS)

    Ramanathan, Vidya

    Ultrashort pulses have revolutionized the field of optical science making it possible to investigate highly nonlinear processes in atomic, molecular, plasma and solid-state physics and to access previously unexplored states of matter. Although ultrashort pulses make an extremely useful tool, the generation of these highly energetic but short pulses is by no means trivial. Amplified ultrashort pulses are generated by the technique of chirped pulse amplification (CPA). Pulses with peak powers of the order of 1012 W from the CPA lasers when focused down to a surface area that correspond to a few square-microns generates high intensities capable of ionizing the medium or generate spectacular non-linear electromagnetic phenomena. This dissertation details the design, fabrication and complete characterization of a high average power, high repetition rate, and single-stage chirped pulse amplifier system capable of delivering 40-45 fs pulses in the milli-joule range at multikilohertz repetition rate. In order to achieve millijoule level pulses from a single amplifier stage, the CPA systems need to be pumped with high average power sources. This introduces a host of thermal issues and thermal management then becomes necessary to increase the efficiency of such systems. In this work, we have carried out a systematic investigation of the thermal loading effects in a high average power, regenerative CPA system. We experimentally characterize the thermal aberrations using a variety of different techniques (interferometry, pump-probe thermal lens power, and M2 analysis). We compute the temperature distribution, the optical path deformations (OPDs) and the corresponding thermal lens focal powers using Finite Element Analysis (FEA) for different pumping conditions. The validation of the experimental results with the FEA model allowed us to use the model to design an effective regenerative amplifier cavity that is stable over a wide range of thermal lens focal length and hence over a wide range of repetition rates. The model could also predict optimal pumping conditions for minimizing thermal aberrations for a variety of geometries and pumping schemes. The regenerative amplifier is capable of generating 40-45 fs, ˜1mJ pulses at 5 kHz repetition rate and ˜300 muJ at 12 kHz repetition rate with minimal fluctuations (0.9% of mean pulse energy) in the shot-to-shot pulse energy and good beam quality (average M 2 of 1.42 at 5 kHz).

  7. Few-cycle attosecond pulse chirp effects on asymmetries in ionized electron momentum distributions

    SciTech Connect

    Peng Liangyou; Tan Fang; Gong Qihuang; Pronin, Evgeny A.; Starace, Anthony F.

    2009-07-15

    The momentum distributions of electrons ionized from H atoms by chirped few-cycle attosecond pulses are investigated by numerically solving the time-dependent Schroedinger equation. The central carrier frequency of the pulse is chosen to be 25 eV, which is well above the ionization threshold. The asymmetry (or difference) in the yield of electrons ionized along and opposite to the direction of linear laser polarization is found to be very sensitive to the pulse chirp (for pulses with fixed carrier-envelope phase), both for a fixed electron energy and for the energy-integrated yield. In particular, the larger the pulse chirp, the larger the number of times the asymmetry changes sign as a function of ionized electron energy. For a fixed chirp, the ionized electron asymmetry is found to be sensitive also to the carrier-envelope phase of the few-cycle pulse.

  8. Bubble-Based Acoustic Radiation Force Using Chirp Insonation to Reduce Standing Wave Effects

    PubMed Central

    Erpelding, Todd N.; Hollman, Kyle W.; ODonnell, 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 Youngs 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

  9. 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.

  10. Nonlinear chirped-pulse propagation and supercontinuum generation in photonic crystal fibers.

    PubMed

    Hu, Xiaohong; Wang, Yishan; Zhao, Wei; Yang, Zhi; Zhang, Wei; Li, Cheng; Wang, Hushan

    2010-09-10

    Based on the generalized nonlinear Schrödinger equation and waveguiding properties typical of the photonic crystal fiber structure, nonlinear chirped-pulse propagation and supercontinua generation in the femtosecond and picosecond regimes are investigated numerically. The simulation results indicate that an input chirp parameter mainly affects the initial stage of spectral broadening caused by the self-phase modulation (SPM) effect. In the femtosecond regime where the SPM effect plays an important role in the process of spectral broadening, an input positive chirp can enhance the supercontinuum bandwidth through a modified pulse compression phase and a decreased propagation distance required by soliton fission. In the picosecond regime, where the SPM effect contributes less to the continuum bandwidth and four-wave mixing process or modulational instability dominates the initial stage of spectral and temporal evolution, the output spectral shape and bandwidths are less sensitive to the input chirp parameters. PMID:20830188

  11. Quantum dynamics of a two-state system induced by a chirped zero-area pulse

    NASA Astrophysics Data System (ADS)

    Lee, Han-gyeol; Song, Yunheung; Kim, Hyosub; Jo, Hanlae; Ahn, Jaewook

    2016-02-01

    It is well known that area pulses make Rabi oscillation and chirped pulses in the adiabatic interaction regime induce complete population inversion of a two-state system. Here we show that chirped zero-area pulses could engineer an interplay between the adiabatic evolution and Rabi-like rotations. In a proof-of-principle experiment utilizing spectral chirping of femtosecond laser pulses with a resonant spectral hole, we demonstrate that the chirped zero-area pulses could induce, for example, complete population inversion and return of the cold rubidium atom two-state system. Experimental result agrees well with the theoretically considered overall dynamics, which could be approximately modeled to a Ramsey-like three-pulse interaction, where the x and z rotations are driven by the hole and the main pulse, respectively.

  12. Generation and direct measurement of giant chirp in a passively mode-locked laser.

    PubMed

    Kelleher, E J R; Travers, J C; Ippen, E P; Sun, Z; Ferrari, A C; Popov, S V; Taylor, J R

    2009-11-15

    We evaluate the shape and chirp of nanosecond pulses from a fiber laser passively mode locked with a nanotube-based saturable absorber by using a synchronously scanning streak camera and a monochromator to directly measure the pulse spectrogram. We show that the stable sech(2) output pulse possesses a predominantly linear chirp, with a residual quartic phase and low noise. Comparison with analytical mode-locking theory shows a good quantitative agreement with the master equation mode-locking model. PMID:19927199

  13. 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. ...

  14. Evaluating auditory brainstem responses to different chirp stimuli at three levels of stimulation

    PubMed Central

    Elberling, Claus; Callø, Johannes; Don, Manuel

    2010-01-01

    Auditory brainstem responses (ABRs) are recorded in ten normal-hearing adults (20 ears) in response to a standard 100 μs click and five chirps having different durations (sweeping rates). The chirps are constructed from five versions of a power function model of the cochlear-neural delay that is based on derived-band ABR latencies from N=81 normal-hearing adults [Elberling, C., and Don, M. (2008). J. Acoust. Soc. Am. 124, 3022–3037]. The click and the chirps have identical amplitude spectra and, in general, for each of the three stimulus levels 60, 40, and 20 dB nHL, the ABRs to the chirps are significantly larger than the ABRs to the click. However, the shorter chirps are the most efficient at higher levels of stimulation whereas the longer chirps are the most efficient at lower levels. It is suggested that two different mechanisms are responsible for these observed changes with stimulus level—(1) upward spread of excitation at higher levels, and (2) an increased change of the cochlear-neural delay with frequency at lower levels. PMID:20649217

  15. 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.

  16. Combining harmonic generation and laser chirping to achieve high spectral density in Compton sources

    DOE PAGESBeta

    Terzić, Balša; Reeves, Cody; Krafft, Geoffrey A.

    2016-04-25

    Recently various laser-chirping schemes have been investigated with the goal of reducing or eliminating ponderomotive line broadening in Compton or Thomson scattering occurring at high laser intensities. Moreover, as a next level of detail in the spectrum calculations, we have calculated the line smoothing and broadening expected due to incident beam energy spread within a one-dimensional plane wave model for the incident laser pulse, both for compensated (chirped) and unchirped cases. The scattered compensated distributions are treatable analytically within three models for the envelope of the incident laser pulses: Gaussian, Lorentzian, or hyperbolic secant. We use the new results tomore » demonstrate that the laser chirping in Compton sources at high laser intensities: (i) enables the use of higher order harmonics, thereby reducing the required electron beam energies; and (ii) increases the photon yield in a small frequency band beyond that possible with the fundamental without chirping. We found that this combination of chirping and higher harmonics can lead to substantial savings in the design, construction and operational costs of the new Compton sources. This is of particular importance to the widely popular laser-plasma accelerator based Compton sources, as the improvement in their beam quality enters the regime where chirping is most effective.« less

  17. Coherent control of ultracold {sup 85}Rb trap-loss collisions with nonlinearly frequency-chirped light

    SciTech Connect

    Pechkis, J. A.; Carini, J. L.; Rogers, C. E. III; Gould, P. L.; Kallush, S.; Kosloff, R.

    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. Chromatin Isolation by RNA Purification (ChIRP)

    PubMed Central

    Chu, Ci; Quinn, Jeffrey; Chang, Howard Y.

    2012-01-01

    Long noncoding RNAs are key regulators of chromatin states for important biological processes such as dosage compensation, imprinting, and developmental gene expression 1,2,3,4,5,6,7. The recent discovery of thousands of lncRNAs in association with specific chromatin modification complexes, such as Polycomb Repressive Complex 2 (PRC2) that mediates histone H3 lysine 27 trimethylation (H3K27me3), suggests broad roles for numerous lncRNAs in managing chromatin states in a gene-specific fashion 8,9. While some lncRNAs are thought to work in cis on neighboring genes, other lncRNAs work in trans to regulate distantly located genes. For instance, Drosophila lncRNAs roX1 and roX2 bind numerous regions on the X chromosome of male cells, and are critical for dosage compensation 10,11. However, the exact locations of their binding sites are not known at high resolution. Similarly, human lncRNA HOTAIR can affect PRC2 occupancy on hundreds of genes genome-wide 3,12,13, but how specificity is achieved is unclear. LncRNAs can also serve as modular scaffolds to recruit the assembly of multiple protein complexes. The classic trans-acting RNA scaffold is the TERC RNA that serves as the template and scaffold for the telomerase complex 14; HOTAIR can also serve as a scaffold for PRC2 and a H3K4 demethylase complex 13. Prior studies mapping RNA occupancy at chromatin have revealed substantial insights 15,16, but only at a single gene locus at a time. The occupancy sites of most lncRNAs are not known, and the roles of lncRNAs in chromatin regulation have been mostly inferred from the indirect effects of lncRNA perturbation. Just as chromatin immunoprecipitation followed by microarray or deep sequencing (ChIP-chip or ChIP-seq, respectively) has greatly improved our understanding of protein-DNA interactions on a genomic scale, here we illustrate a recently published strategy to map long RNA occupancy genome-wide at high resolution 17. This method, Chromatin Isolation by RNA Purification (ChIRP) (Figure 1), is based on affinity capture of target lncRNA:chromatin complex by tiling antisense-oligos, which then generates a map of genomic binding sites at a resolution of several hundred bases with high sensitivity and low background. ChIRP is applicable to many lncRNAs because the design of affinity-probes is straightforward given the RNA sequence and requires no knowledge of the RNA's structure or functional domains. PMID:22472705

  19. Bimolecular Pyrolysis Reactions Studied by Chirped-Pulse Millimeter-Wave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Prozument, Kirill; Vasiliou, Angayle K.; Shaver, Rachel G.; Park, G. Barratt; Muenter, John S.; Stanton, John F.; Ellison, G. Barney; Field, Robert W.

    2013-06-01

    The feasibility of using Chirped-Pulse Millimeter-Wave (CPmmW) spectroscopy for studies of pyrolysis reactions is demonstrated. The molecules under investigation were mixed with a source of H-atoms (methyl nitrite) and put through a heated silicon carbide micro-reactor (2 cm x 1 mm). More efficient paths of thermal cracking of (i) acetaldehyde and (ii) acetone are demonstrated when using, as a catalyst, the free H-atoms released from methyl nitrite compared to cracking of neat acetaldehyde or acetone. CPmmW spectra of (i) formaldehyde and (ii) acetaldehyde were observed, suggesting that the following bimolecular reactions took place in the micro-reactor: i) CH_3CHO + H → CH_3 + CH_2O ii) CH_3COCH_3 + H → CH_3 + CH_3CHO. The vibrational population distributions (VPDs) of the formaldehyde and acetaldehyde products of the pyrolysis reactions are measured using the broad bandwidth capability of the CPmmW technique. Although we found that the VPDs of the molecules convey little information about the pyrolysis reaction transition state(s), they provide insight to the vibrational collisional cooling mechanisms in different molecules. The relevance of the observed catalytic reactions to biomass decomposition is discussed and other bimolecular pyrolysis reactions are proposed for study by CPmmW spectroscopy. KP thanks the Petroleum Research Fund for support of this work.

  20. Mismatch characteristics of optical parametric chirped pulse amplification

    NASA Astrophysics Data System (ADS)

    Novák, O.; Turčičová, H.; Divoký, M.; Huynh, J.; Straka, P.

    2014-02-01

    The stability of an optical parametric chirped pulse amplifier (OPCPA) is influenced by time and the angular matching of the input beams. We derived the Gaussian dependence of the monochromatic signal gain on the small mismatch between the signal and pump beams. Gain characteristics were also calculated for polychromatic amplification and the impact of different beam mismatches and interaction geometries was explained. The asymmetry of the energy gain, and the square root dependence of the phase matched wavelength on beam angles were found. The predicted dependences were verified in a noncollinear OPCPA system with LBO and KDP crystal amplifying pulses of a Ti:sapphire laser around a central wavelength of 800 nm, pumped by the third harmonic frequency of an iodine gas laser at a wavelength of 438 nm. The widths of the gain curves in the dependence on both the pump-signal or the phase matching angles varied from several tenths to a few milliradians. The gain curve widths dependent on the pump-signal pulse delay were about two thirds of the pump pulse width for moderate pumping and about a half of the pump pulse width for pumping on the order of GW cm-2. A stable gain output is achieved if angular and temporal fluctuations are fractions of the measured gain curve widths, and when the signal direction is between the pump and the crystal principal axis (i.e. in the psz geometry).

  1. Low voltage integrated optics electro-optical modulator applied to optical voltage transformer based on WLI technique

    NASA Astrophysics Data System (ADS)

    Santos, J. C.; Rubini, J.; Silva, L. P. C.; Caetano, R. E.

    2015-09-01

    The use of two electro-optical modulators linked in series, one for sensing and one for recovering signals, was formerly presented by some of the authors as a solution for interrogation of optical fiber sensor systems based on WLI method. A key feature required from such systems is that half-wave voltage (Vπ) of recovering modulator must be as small as possible. Aiming at meeting this requirement, in this paper it is presented the use of an unbalanced Michelson Interferometer implemented using an integrated optics component as recover interferometer in an optical voltage transformer intended for high voltage measurements.

  2. Evaluation of oxide layers formed during the decarburisation of grain-oriented electrical steel using a Fourier transform infrared (FTIR) technique

    NASA Astrophysics Data System (ADS)

    Poultney, Darren; Snell, David

    Electrical steels are highly specialised, magnetically soft materials, used to form the cores that carry the magnetic flux in electrical machines such as motors, generators and transformers. During the production of GO electrical steel, the strip passes through a decarburisation furnace, which promotes the formation of a thin surface oxide layer consisting of predominantly fayalite (Fe 2SiO 4) and silica (SiO 2). During a subsequent high temperature anneal, this layer reacts with magnesia (MgO) to form a forsterite 'glass film' layer, which applies a tensile stress to the steel. This reduces the magnetic losses of the material on which the final product is routinely graded. Due to the effect that the oxide layer has on the quality of the final material, it would be beneficial to possess a technique that can rapidly assess its composition and/or morphology. This paper details the assessment of Fourier transform infrared (FTIR) and electrochemical potential (ECP) analysis, and a technique of combining the two. FTIR analysis of the decarburisation oxide layer exhibited evidence of just fayalite, with silica only being observed on the spectra following brief acid etching. To refine the etching process, samples were removed from the acid at various intervals based on the output of the ECP technique. It was established that there was a clear link between the position reached on the ECP profile and absorption bands observed on the corresponding FTIR spectra.

  3. A 32x32 pixel focal plane array ladar system using chirped amplitude modulation

    NASA Astrophysics Data System (ADS)

    Stann, Barry L.; Aliberti, Keith; Carothers, Daniel; Dammann, John; Dang, Gerard; Giza, Mark M.; Lawler, William B.; Redman, Brian C.; Simon, Deborah R.

    2004-09-01

    The Army Research Laboratory is researching system architectures and components required to build a 32x32 pixel scannerless ladar breadboard. The 32x32 pixel architecture achieves ranging based on a frequency modulation/continuous wave (FM/cw) technique implemented by directly amplitude modulating a near-IR diode laser transmitter with a radio frequency (RF) subcarrier that is linearly frequency modulated (i.e. chirped amplitude modulation). The backscattered light is focused onto an array of metal-semiconductor-metal (MSM) detectors where it is detected and mixed with a delayed replica of the laser modulation signal that modulates the responsivity of each detector. The output of each detector is an intermediate frequency (IF) signal (a product of the mixing process) whose frequency is proportional to the target range. Pixel read-out is achieved using code division multiple access techniques as opposed to the usual time-multiplexed techniques to attain high effective frame rates. The raw data is captured with analog-to-digital converters and fed into a PC to demux the pixel data, compute the target ranges, and display the imagery. Last year we demonstrated system proof-of-principle for the first time and displayed an image of a scene collected in the lab that was somewhat corrupted by pixel-to-pixel cross-talk. This year we report on system modifications that reduced pixel-to-pixel cross-talk and new hardware and display codes that enable near real-time stereo display of imagery on the ladar's control computer. The results of imaging tests in the laboratory will also be presented.

  4. 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

  5. Optimizational 6-bit all-optical quantization with positive or negative pre-chirp based on photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Li, Sha; Wang, Jianping; Kang, Zhe; Yu, Chongxiu

    2015-10-01

    In this paper, we optimize a proposed 6-bit all-optical quantization approach based on soliton self-frequency shift (SSFS) and spectral compression techniques. A 10 m-long high nonlinear photonic crystal fiber (PCF) is still used as an SSFS medium relevant to the power of the sampled optical pulses. Furthermore, a 10 m-long dispersion flattened hybrid cladding hexagonal-octagonal PCF (6/8-PCF) is utilized as a spectral compression medium to realize resolution enhancement after positive or negative pre-chirp process. Simulation results show that the 6-bit quantization is still obtained when a 100 m-long dispersion-increasing fiber (DIF) is replaced by a hybrid cladding 6/8-PCF in spectral compression module.

  6. Algorithm for high-resolution single-shot THz measurement using in-line spectral interferometry with chirped pulses

    NASA Astrophysics Data System (ADS)

    Yellampalle, B.; Kim, K. Y.; Rodriguez, G.; Glownia, J. H.; Taylor, A. J.

    2005-11-01

    Z. P. Jiang and X. C. Zhang demonstrated a single-shot THz diagnostic based on spectral encoding of a chirped optical probe pulse [Appl. Phys. Lett. 72, 1945 (1998)]. This technique is thought to have an inherent uncertainty principle-imposed temporal resolution limitations. In this letter, we describe a method to recover the THz field without distortions, surpassing previous resolution limitations. Our approach is based on interpreting the spectral encoding experiment as in-line spectral interferometry, analogous to Gabor's in-line spatial holography [D. Gabor, Nature (London) 161, 777 (1948)]. We recover the THz field from the interferogram and the characterized probe by using Tikhonov regularization combined with lower and upper triangular decomposition.

  7. a Chirped Pulse Ftmw Study of the Structure of Phenol Dimer

    NASA Astrophysics Data System (ADS)

    Steber, Amanda L.; Neill, Justin L.; Zaleski, Daniel P.; Pate, Brooks H.; Lesarri, Alberto

    2011-06-01

    Phenol dimer has been studied extensively and is considered a benchmark molecular complex for ab initio theory due to a long range dispersion interaction between the rings as well as an intermolecular hydrogen bond. Previously, the structure had been determined using RCS and high resolution UV measurements; however, several assumptions were integrated into the structure because a full isotopically substituted structure could not be determined. In this study, the rotational spectrum of the dimer as well as 13C and 18O isotopologue spectra that were seen in natural abundance were obtained using chirped pulse Fourier transform microwave spectroscopy (CP-FTMW). The structure was determined using both linear least squares fitting (r_0 structure) and the Kraitchman substitution analysis (r_s structure). Ab initio calculations were performed for the dimer using MP2/cc-pVTZ cp, B3LYP/6-31G(d,p), M06-2X/6-31G(d,p), and M06-2X/6-311++G(d,p), while CCSD calculations are currently under way. Changing the level of theory and the basis set dramatically changes the structure. The MP2 calculation underestimates the hinge angle (C-O-O-C dihedral angle), while the B3LYP overestimates it. The M06-2X calculations seem to give the best cost-to-benefit ratio when compared to the r_s structure, but they show poorer agreement with increasing basis set size. L. L. Connell, S. M. Ohline, P. W. Joireman, T. C. Corcoran, and P. M. Felker, J.Chem.Phys. 96, 2585 (1992) A. Weichert, C. Riehn, and B. Brutschy, J. Phys. Chem. A 105, 5679 (2001) M. Schmitt, M. Böhm, C. Ratzer, D. Krügler, K. Kleinermanns, I. Kalkman, G. Berden, and W. L. Meerts, Chem. Phys. Chem. 7, 1241 (2006) P. Jurecka, J. Sponer, J. Cerny, and P. Hobza, Phys. Chem. Chem. Phys. 8, 1985 (2006)

  8. The Chirped Pulse and Cavity Fourier Transform Microwave Cp-Ftmw and Ftmw) Spectrum of Bromoperfluoroacetone

    NASA Astrophysics Data System (ADS)

    Force, Nicholas; Gillcrist, David Joseph; Hurley, Cassandra C.; Marshall, Frank E.; Payton, Nicholas A.; Persinger, Thomas D.; Shreve, N. E.; Grubbs, G. S., II

    2014-06-01

    The microwave spectrum of the molecule bromoperfluoroacetone has been measured on a newly constructed CP-FTMW spectrometer along with a FTMW spectrometer relocated from Oxford University to Missouri S&T. Rotational constants, centrifugal distortion parameters, and nuclear quadrupole coupling constants will be discussed. Comparisons to the previously studied halogen analogues perfluoroacetone and chloroperfluoroacetone will be discussed. J.-U. Grabow, N. Heineking, and W. Stahl, Z. Naturforsch. 46a (1991) 229. G. Kadiwar, C. T. Dewberry, G. S. Grubbs II and S. A. Cooke, Talk RH11, 65th International Symposium on Molecular Spectroscopy (2010).

  9. Validation of a high-resolution precipitation database (CHIRPS) over Cyprus for a 30-year period

    NASA Astrophysics Data System (ADS)

    Katsanos, Dimitrios; Retalis, Adrianos; Michaelides, Silas

    2016-03-01

    A study for a 30-year period (1981-2010) for a new precipitation database is performed over the island of Cyprus. Climate Hazards Group Infrared Precipitation with Station data (CHIRPS) is a more than 30-year quasi-global rainfall dataset, spanning 50°S-50°N (and all longitudes). Starting in 1981 to near-present, CHIRPS incorporates 0.05° resolution satellite imagery with in situ station data to create gridded rainfall time series. In this study, CHIRPS database is firstly compared to other precipitation databases over the Mediterranean basin. In the following, this study focuses over Cyprus, where a dense and reliable network of rain gauges is available. CHIRPS data are compared for the first time with in situ measurements in this area, for the aforementioned 30-year period. Monthly and annual comparisons are presented for each of the 0.05 × 0.05 degree cells overlaying the island of Cyprus. Results showed good correlation between CHIRPS values and recorded precipitation, although an overestimation of the in situ rainfall data has been noted during the last decade.

  10. 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.

  11. Efficient broadband 400  nm noncollinear second-harmonic generation of chirped femtosecond laser pulses in BBO and LBO.

    PubMed

    Gobert, O; Mennerat, G; Maksimenka, R; Fedorov, N; Perdrix, M; Guillaumet, D; Ramond, C; Habib, J; Prigent, C; Vernhet, D; Oksenhendler, T; Comte, M

    2014-04-20

    We report on 400 nm broadband type I frequency doubling in a noncollinear geometry with pulse-front-tilted and chirped femtosecond pulses (λ =800  nm; Fourier transform limited pulse duration, 45 fs). With moderate power densities (2 to 10  GW/cm2) thus avoiding higher-order nonlinear phenomena, the energy conversion efficiency was up to 65%. Second-harmonic pulses of Fourier transform limited pulse duration shorter than the fundamental wave were generated, exhibiting good beam quality and no pulse-front tilt. High energy (20 mJ/pulse) was produced in a 40 mm diameter and 6 mm thick LBO crystal. To the best of our knowledge, this is the first demonstration of this optical configuration with sub-100-fs pulses. Good agreement between experimental results and simulations is obtained. PMID:24787591

  12. Time-domain measurement of a self-amplified spontaneous emission free-electron laser with an energy-chirped electron beam and undulator tapering

    SciTech Connect

    Marcus, G.; Rosenzweig, J. B.; Artioli, M.; Ciocci, F.; Del Franco, M.; Giannessi, L.; Petralia, A.; Quattromini, M.; Bacci, A.; Bellaveglia, M.; Chiadroni, E.; Di Pirro, G.; Ferrario, M.; Filippetto, D.; Gatti, G.; Rossi, A. R.; Cianchi, A.; Labat, M.; Mostacci, A.; Petrillo, V.; and others

    2012-09-24

    We report, with an unequivocal time-domain measurement, that an appropriately chosen undulator taper can compensate for an electron beam longitudinal energy-chirp in a free-electron laser amplifier, leading to the generation of single-spike radiation close to the Fourier limit. The measurements were taken using the frequency-resolved optical gating technique by employing an advanced transient-grating diagnostic geometry. The reconstructed longitudinal radiation characteristics are compared in detail to prediction from time-dependent three-dimensional simulations.

  13. Use of the Fourier transform infrared (FTIR) technique for determination of the composition of final phosphate coatings on grain-oriented electrical steel

    NASA Astrophysics Data System (ADS)

    Poultney, Darren; Snell, David

    Electrical steels are highly specialised, magnetically soft materials, used to form the cores that carry the magnetic flux in electrical machines such as motors, generators and transformers. The steel strip is coated with a phosphate-based solution, which, on curing, provides an electrically insulating layer that also imparts a tension onto the strip. It has previously been shown that the magnetic losses of the material are affected by the ratio of phosphate and silica within the coating solution [O. Tanaka, H. Kobayashi, E. Minematsu, New insulating coating for grain-oriented electrical steel, J. Mater. Eng. 13 (1991) 161-168.]. It would therefore be highly beneficial to possess an analytical technique that can be used to accurately and rapidly determine the composition of this coating. This paper details the evaluation of the Fourier transform infrared (FTIR) technique for this purpose. Analysing each of the important constituents separately enabled their specific absorption bands to be identified, and laboratory trials produced spectra that exhibited a good agreement with theoretical predictions. Analysis of samples coated under production conditions was found to be more challenging due to the detection of an underlying forsterite layer. However, there is potential for FTIR analysis when using regions of the spectra that were unaffected by this compound.

  14. Examination of the Thermal Transformation of Chrysotile by Using Dispersion Staining and Conventional X-ray Diffraction Techniques

    NASA Astrophysics Data System (ADS)

    Crummett, C. D.; Candela, P. A.; Wylie, A. G.; Earnest, D. J.

    2004-12-01

    Chrysotile has been used industrially as a component of refractory products, and in friction products, such as brake linings. Examining the decomposition or transformation of chrysotile as a function of time and temperature will help clarify the characteristics of particulates released during processes such as automotive braking. Previous studies have reported that the thermal treatment of chrysotile alters both its surface and structure, resulting in deviations from its natural properties, possibly reducing its biological activity (Langer, 2003: Reg Tox Pharm, v38, p71). In past studies, the nonequilibrium thermal decomposition of chrysotile has been investigated by using static dehydration, X-ray diffraction, differential thermal analysis, and thermogravimetric analysis. These studies suggest that the thermal transformation of chrysotile follows a two step sequence of dehydroxylation/dehydration and recrystallization where (1) chrysotile yields forsterite + silica + water with (2) forsterite + silica later forming enstatite (Ball and Taylor, 1963: Mineral. Mag. v33, p467, Brindley and Hayami, 1965: Mineral. Mag. v35, p189). In this research the decomposition of chrysotile from Thetford Quebec was studied. Samples were heated isothermally in air at temperatures from 200° C to 1000° C. After heating for up to 24 hours the refractive indices of remaining chrysotile fibers were measured by using dispersion staining. In addition, reaction products were identified by optical methods, electron probe microanalysis, and X-ray diffraction performed after the termination of the experiment. Preliminary results show that there is no change in optical properties of chrysotile heated to 400° C for 24 hours. From 400° C to 575° C for 24 hours, the index of refraction increases parallel to the length of the fiber from 1.552 to 1.560. From 400° C to 575° C for 24 hours, the index of refraction perpendicular to the length of the fiber varies irregularly from 1.538-1.548. The variability of the refractive indices, both parallel and perpendicular, observed in unheated chrysotile reduces from approximately ± 0.04 to ± 0.01 when heated to 575° C for 24 hours. Chrysotile heated to 575° C for 24 hours shows an overall loss of X-ray intensity for the main chrysotile peaks and possible growth of forsterite. At 800° C, although the fibrous morphology remains, X-ray diffraction analysis of the run products shows no remaining chrysotile and the index of refraction parallel to the length of the fiber is approximately 1.594. Initial data show that the reaction rates associated with the dehydroxylation/dehydration and recrystallization of chrysotile are dependent upon the texture of individual fibers.

  15. A direct approach for the design of chirp stimuli used for the recording of auditory brainstem responses

    PubMed Central

    Elberling, Claus; Don, Manuel

    2010-01-01

    A recent study evaluates auditory brainstem responses (ABRs) evoked by chirps of different durations (sweeping rates) [Elberling et al. (2010). J. Acoust. Soc. Am. 128, 215–223]. The study demonstrates that shorter chirps are most efficient at higher levels of stimulation whereas longer chirps are most efficient at lower levels. Mechanisms other than the traveling wave delay, in particular, upward spread of excitation and changes in cochlear-neural delay with level, are suggested to be responsible for these findings. As a consequence, delay models based on estimates of the traveling wave delay are insufficient for the design of chirp stimuli, and another delay model based on a direct approach is therefore proposed. The direct approach uses ABR-latencies from normal-hearing subjects in response to octave-band chirps over a wide range of levels. The octave-band chirps are constructed by decomposing a broad-band chirp, and constitute a subset of the chirp. The delay compensations of the proposed model are similar to those found in the previous experimental study, which thus verifies the results of the proposed model. PMID:21110591

  16. UTILIZING A CHIRP SONAR TO ACCURATELY CHARACTERIZE NEWLY DEPOSITED MATERIAL AT THE CALCASIEU OCEAN DREDGED MATERIAL DISPOSAL SITE, LOUISIANA

    EPA Science Inventory

    The distribution of dredged sediments is measured at the Calcasieu Ocean Dredged Material Disposal Site (ODMDS) using a chirp sonar immediately after disposal and two months later. ubbottom reflection data, generated by a chirp sonar transmitting a 4 to 20 kHz FM sweep, is proces...

  17. Frequency chirped light at large detuning with an injection-locked diode laser

    SciTech Connect

    Teng, K.; Disla, M.; Dellatto, J.; Limani, A.; Kaufman, B.; Wright, M. J.

    2015-04-15

    We have developed a laser system to generate frequency-chirped light at rapid modulation speeds (∼100 MHz) with a large frequency offset. Light from an external cavity diode laser with its frequency locked to an atomic resonance is passed through a lithium niobate electro-optical phase modulator. The phase modulator is driven by a ∼6 GHz signal whose frequency is itself modulated with a RF MHz signal (<200 MHz). A second injection locked diode laser is used to filter out all of the light except the frequency-chirped ±1 order by more than 30 dB. Using this system, it is possible to generate a 1 GHz frequency chirp in 5 ns.

  18. Attosecond XUV sources generation from polarized gating two-color chirped pulse

    NASA Astrophysics Data System (ADS)

    Feng, Liqiang; Liu, Hang; Chu, Tianshu

    2015-07-01

    A promising method to generate the attosecond XUV sources from the high-order harmonic has been theoretically presented by controlling the polarized gating two-color chirped pulse. The results show that with the introduction of the chirps, the harmonic has been remarkably extended. Moreover, the harmonic interferences are very sensitive to the polarization angle between the two lasers. Particularly, when the polarization angle is equal to 0.2π, the supercontinuum with a single quantum path contribution is achieved, and a series of isolated attosecond pulses with the duration of 33 as are directly obtained. Further, by testing the influences of other laser parameters on the supercontinuum, we found that this polarized two-color chirped scheme can also be achieved in the multi-cycle pulse region, which is much better for experimental realization.

  19. Note: Directly measuring the direct digital synthesizer frequency chirp-rate for an atom interferometer

    SciTech Connect

    Tao, Juan-Juan; Zhou, Min-Kang E-mail: zmk@hust.edu.cn; Zhang, Qiao-Zhen; Cui, Jia-Feng; Duan, Xiao-Chun; Shao, Cheng-Gang; Hu, Zhong-Kun E-mail: zmk@hust.edu.cn

    2015-09-15

    During gravity measurements with Raman type atom interferometry, the frequency of the laser used to drive Raman transition is scanned by chirping the frequency of a direct digital synthesizer (DDS), and the local gravity is determined by precisely measuring the chip rate α of DDS. We present an effective method that can directly evaluate the frequency chirp rate stability of our DDS. By mixing a pair of synchronous linear sweeping signals, the chirp rate fluctuation is precisely measured with a frequency counter. The measurement result shows that the relative α instability can reach 5.7 × 10{sup −11} in 1 s, which is neglectable in a 10{sup −9} g level atom interferometry gravimeter.

  20. Low chirp and high-speed operation of transverse coupled cavity VCSEL

    NASA Astrophysics Data System (ADS)

    Hu, Shanting; Ahmed, Moustafa; Bakry, Ahmed; Koyama, Fumio

    2015-09-01

    We present the modeling on the modulation bandwidth and frequency chirp of transverse-coupled-cavity vertical-cavity surface-emitting lasers (VCSELs), which enable us to tailor the transfer function of intensity and frequency modulations thanks to an optical feedback effect. The simulation shows the 3-dB-modulation bandwidth can be doubled and the chirp can be reduced by a factor of more than three. These improvements could be explained by an increase in differential net gain in coupled cavities. The result shows a possibility of high-speed and low-chirp operations of transverse coupled cavity VCSELs for higher data rates and longer link lengths of single-mode fiber transmissions.

  1. Deexcitation of high-Rydberg-state atoms with a chirped train of half-cycle pulses

    SciTech Connect

    Kopyciuk, T.; Parzynski, R.

    2007-05-15

    Encouraged by the experiments on production of antihydrogen atoms in high Rydberg states we have calculated the effect of deexcitation towards lower states by a chirped train of identical unidirectional half-cycle pulses. The calculations exploit both the one-dimensional and impulse approximations providing convenient analytical formulas for the Rydberg-to-Rydberg transition amplitudes. The calculated deexcitation is shown in terms of the mean value of localization of the Rydberg wave packet in the coordinate space, the Rydberg-state population distribution, the Husimi phase-space distribution function, and the probability density distribution, each of these measures vs the length of the applied train of half-cycle pulses. The results for chirped trains are compared with those for periodic trains and examples of higher deexcitation efficiency of the chirped trains are given.

  2. Period-chirped gratings fabricated by laser interference lithography with a concave Lloyd's mirror.

    PubMed

    Kim, Hanbit; Jung, Hyunho; Lee, Dong-Hyun; Lee, Kyu Back; Jeon, Heonsu

    2016-01-10

    We developed a laser interference lithography (LIL) system for fabrication of period-chirped gratings, which would be useful for sophisticated optical components. Despite its simplicity, the developed LIL system, based on a Lloyd's mirror interferometer with a cylindrically concave mirror, can generate chirped gratings, yet over a large area at high throughput owing to the nature of LIL. We have derived exact theoretical equations needed for system design, built the LIL system, and subsequently realized period-chirped gratings. A fabricated sample whose center period is Λ≈600  nm exhibits a continuous period variation of ΔΛ=92  nm across 17 mm width. PMID:26835772

  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. First results of a deep tow CHIRP sonar seafloor imaging system

    USGS Publications Warehouse

    Parent, M.; Fang, Changle; O'Brien, Thomas F.; Danforth, William W.

    1993-01-01

    The latest and most innovative technology has been applied towards the development of a full-ocean depth multi-sensor sonar system using linear swept-FM (Chirp) technology. The seafloor imaging system (SIS- 7000) described herein uses Chirp sidescan sonar to provide high resolution imagery at long range, and Chirp subbottom sonar to provide high resolution profiles in both the near bottom and deeper subbottom. The tow vehicle contains a suite of full-ocean depth instrumentation for measuring various oceanographic parameters and for monitoring vehicle status. Top side systems include a sonar display and data logging system as well as real-time sensor status display and tow vehicle control system. This paper will present an overview of this system, describe its technology and capabilities, and present some initial results. 

  5. Photonic generation of low phase noise arbitrary chirped microwave waveforms with large time-bandwidth product.

    PubMed

    Xie, Weilin; Xia, Zongyang; Zhou, Qian; Shi, Hongxiao; Dong, Yi; Hu, Weisheng

    2015-07-13

    We present a photonic approach for generating low phase noise, arbitrary chirped microwave waveforms based on heterodyne beating between high order correlated comb lines extracted from frequency-agile optical frequency comb. Using the dual heterodyne phase transfer scheme, extrinsic phase noises induced by the separate optical paths are efficiently suppressed by 42-dB at 1-Hz offset frequency. Linearly chirped microwave waveforms are achieved within 30-ms temporal duration, contributing to a large time-bandwidth product. The linearity measurement leads to less than 90 kHz RMS frequency error during the entire chirp duration, exhibiting excellent linearity for the microwave and sub-THz waveforms. The capability of generating arbitrary waveforms up to sub-THz band with flexible temporal duration, long repetition period, broad bandwidth, and large time-bandwidth product is investigated and discussed. PMID:26191866

  6. Frequency chirped light at large detuning with an injection-locked diode laser.

    PubMed

    Teng, K; Disla, M; Dellatto, J; Limani, A; Kaufman, B; Wright, M J

    2015-04-01

    We have developed a laser system to generate frequency-chirped light at rapid modulation speeds (∼100 MHz) with a large frequency offset. Light from an external cavity diode laser with its frequency locked to an atomic resonance is passed through a lithium niobate electro-optical phase modulator. The phase modulator is driven by a ∼6 GHz signal whose frequency is itself modulated with a RF MHz signal (<200 MHz). A second injection locked diode laser is used to filter out all of the light except the frequency-chirped ±1 order by more than 30 dB. Using this system, it is possible to generate a 1 GHz frequency chirp in 5 ns. PMID:25933848

  7. Flexible time domain averaging technique

    NASA Astrophysics Data System (ADS)

    Zhao, Ming; Lin, Jing; Lei, Yaguo; Wang, Xiufeng

    2013-09-01

    Time domain averaging(TDA) is essentially a comb filter, it cannot extract the specified harmonics which may be caused by some faults, such as gear eccentric. Meanwhile, TDA always suffers from period cutting error(PCE) to different extent. Several improved TDA methods have been proposed, however they cannot completely eliminate the waveform reconstruction error caused by PCE. In order to overcome the shortcomings of conventional methods, a flexible time domain averaging(FTDA) technique is established, which adapts to the analyzed signal through adjusting each harmonic of the comb filter. In this technique, the explicit form of FTDA is first constructed by frequency domain sampling. Subsequently, chirp Z-transform(CZT) is employed in the algorithm of FTDA, which can improve the calculating efficiency significantly. Since the signal is reconstructed in the continuous time domain, there is no PCE in the FTDA. To validate the effectiveness of FTDA in the signal de-noising, interpolation and harmonic reconstruction, a simulated multi-components periodic signal that corrupted by noise is processed by FTDA. The simulation results show that the FTDA is capable of recovering the periodic components from the background noise effectively. Moreover, it can improve the signal-to-noise ratio by 7.9 dB compared with conventional ones. Experiments are also carried out on gearbox test rigs with chipped tooth and eccentricity gear, respectively. It is shown that the FTDA can identify the direction and severity of the eccentricity gear, and further enhances the amplitudes of impulses by 35%. The proposed technique not only solves the problem of PCE, but also provides a useful tool for the fault symptom extraction of rotating machinery.

  8. Assessment of nitrous oxide emission from cement plants: real data measured with both Fourier transform infrared and nondispersive infrared techniques.

    PubMed

    Mosca, Silvia; Benedetti, Paolo; Guerriero, Ettore; Rotatori, Mauro

    2014-11-01

    Nitrous oxide (N2O) is the third most important greenhouse gas after carbon dioxide and methane, and contributes about 6% to the greenhouse effect. Nitrous oxide is a minor component of the atmosphere, and it is a thousand times less than carbon dioxide (CO2). Nevertheless, it is much more potent than CO2 and methane, owing to its long stay in the atmosphere of approximately 120 yr and the high global warmingpotential (GWP) of298 times that of CO2. Although greenhouse gases are natural in the atmosphere, human activities have changed the atmospheric concentrations. Most of the values of emission of nitrous oxide are still obtained by means ofemission factors and not actually measured; the lack ofreal data may result in an underestimation ofcurrent emissions. The emission factors used for the calculation of N2O can be obtained from the "Guidelines for the implementation of the national inventory of emissions" of the Intergovernmental Panel on Climate Change, which refer to all nations for the realization of their inventory. This study will present real data, measured in several Italian cement plants with different characteristics. The work also shows a comparison between N2O concentration measured with in situ-Fourier transform IR (FTIR) and the reference method EN ISO 21258 based on nondispersive IR (NDIR), in order to investigate the interfering compounds in the measurement with NDIR. PMID:25509548

  9. 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

  10. Best chirplet chain: Near-optimal detection of gravitational wave chirps

    NASA Astrophysics Data System (ADS)

    Chassande-Mottin, Éric; Pai, Archana

    2006-02-01

    The list of putative sources of gravitational waves possibly detected by the ongoing worldwide network of large scale interferometers has been continuously growing in the last years. For some of them, the detection is made difficult by the lack of a complete information about the expected signal. We concentrate on the case where the expected gravitational wave (GW) is a quasiperiodic frequency modulated signal i.e., a chirp. In this article, we address the question of detecting an a priori unknown GW chirp. We introduce a general chirp model and claim that it includes all physically realistic GW chirps. We produce a finite grid of template waveforms which samples the resulting set of possible chirps. If we follow the classical approach (used for the detection of inspiralling binary chirps, for instance), we would build a bank of quadrature matched filters comparing the data to each of the templates of this grid. The detection would then be achieved by thresholding the output, the maximum giving the individual which best fits the data. In the present case, this exhaustive search is not tractable because of the very large number of templates in the grid. We show that the exhaustive search can be reformulated (using approximations) as a pattern search in the time-frequency plane. This motivates an approximate but feasible alternative solution which is clearly linked to the optimal one. The time-frequency representation and pattern search algorithm are fully determined by the reformulation. This contrasts with the other time-frequency based methods presented in the literature for the same problem, where these choices are justified by “ad hoc” arguments. In particular, the time-frequency representation has to be unitary. Finally, we assess the performance, robustness and computational cost of the proposed method with several benchmarks using simulated data.

  11. Generation of an isolated sub-40-as pulse using two-color laser pulses: Combined chirp effects

    SciTech Connect

    Feng, Liqiang; Chu, Tianshu

    2011-11-15

    In this paper, we theoretically discuss the combined chirp effects on the isolated attosecond generation when a model Ar is exposed to an intense 5-fs, 800-nm fundamental chirped pulse combined with a weak 10-fs, 1200-nm controlling chirped pulse. It shows that for the case of the chirp parameters {beta}{sub 1} = 6.1 (corresponding to the 800-nm field) and {beta}{sub 2} = 4.0 (corresponding to the 1200-nm field), both the harmonic cutoff energy and the supercontinuum can be remarkably extended resulting in a 663-eV bandwidth. Moreover, due to the introduction of the chirps, the short quantum path is selected to contribute to the harmonic spectrum. Finally, by superposing a properly selected harmonic spectrum in the supercontinuum region, an isolated pulse as short as 31 as (5 as) is generated without (with) phase compensation.

  12. Some refractometric features of dual-core chirped microstructured optical fibers

    NASA Astrophysics Data System (ADS)

    Velasquez-Botero, Fabian; Reyes-Vera, Erick; Torres, Pedro

    2015-09-01

    Refractometric features of dual-core transversally chirped microstructured optical fibers (MOF) are evaluated. It is shown from numerical results that the chirped MOF could act as a structure with decoupled cores, forming a Mach- Zehnder interferometer in which the analyte directly modulates the device transmittance by its differential influence on the effective refractive index of each core mode. We investigate the influence of the MOF parameters and the analyte refractive index on sensor performance. This novel structure is suitable for measuring refractive indices in the 1.33-1.44 range.

  13. Control of spectral aberrations in a monochromator using a chirped grating

    NASA Astrophysics Data System (ADS)

    April, A.; McCarthy, N.

    2008-06-01

    A method is proposed to minimize the impact of spectral aberrations in a monochromator based on a rectilinear translation of a plane chirped grating. The chirped grating, that has a spatially variable groove spacing, is used to diffract and to spectrally focus the radiation. The expression of the width of the instrument line shape due to aberrations have been developed in order to obtain the optimal rectilinear trajectory required to operate the monochromator without significant spectral aberrations. Experimental measurements of the emission spectrum of a five-wavelength Helium-Neon laser are presented, as well as the sensitivity of the monochromator performance to different geometrical parameters.

  14. Reflectivity of linear and nonlinear gamma radiated apodized chirped Bragg grating under ocean

    SciTech Connect

    Hamdalla, Taymour A.

    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.

  15. Transformational Learners: Transformational Teachers

    ERIC Educational Resources Information Center

    Jones, Marguerite

    2009-01-01

    Transformational learning, according to Mezirow (1981), involves transforming taken-for-granted frames of reference into more discriminating, flexible "habits of mind". In teacher education, transformative learning impacts on the development of students' action theories, self-efficacy and professional attributes. Although considered imperative to

  16. LC-MS screening techniques for wastewater analysis and analytical data handling strategies: Sartans and their transformation products as an example.

    PubMed

    Letzel, Thomas; Bayer, Anne; Schulz, Wolfgang; Heermann, Alexandra; Lucke, Thomas; Greco, Giorgia; Grosse, Sylvia; Schüssler, Walter; Sengl, Manfred; Letzel, Marion

    2015-10-01

    A large number of anthropogenic trace contaminants such as pharmaceuticals, their human metabolites and further transformation products (TPs) enter wastewater treatment plants on a daily basis. A mixture of known, expected, and unknown molecules are discharged into the receiving aquatic environment because only partial elimination occurs for many of these chemicals during physical, biological and chemical treatment processes. In this study, an array of LC-MS methods from three collaborating laboratories was applied to detect and identify anthropogenic trace contaminants and their TPs in different waters. Starting with theoretical predictions of TPs, an efficient workflow using the combination of target, suspected-target and non-target strategies for the identification of these TPs in the environment was developed. These techniques and strategies were applied to study anti-hypertensive drugs from the sartan group (i.e., candesartan, eprosartan, irbesartan, olmesartan, and valsartan). Degradation experiments were performed in lab-scale wastewater treatment plants, and a screening workflow including an inter-laboratory approach was used for the identification of transformation products in the effluent samples. Subsequently, newly identified compounds were successfully analyzed in effluents of real wastewater treatment plants and river waters. PMID:26246044

  17. Characterization of ancient glass excavated in Enez (Ancient Ainos) Turkey by combined Instrumental Neutron Activation Analysis and Fourier Transform Infrared spectrometry techniques

    NASA Astrophysics Data System (ADS)

    Akyuz, Sevim; Akyuz, Tanil; Mukhamedshina, Nuranya M.; Mirsagatova, A. Adiba; Basaran, Sait; Cakan, Banu

    2012-05-01

    Ancient glass fragments excavated in the archaeological district Enez (Ancient Ainos)-Turkey were investigated by combined Instrumental Neutron Activation Analysis (INAA) and Fourier Transform Infrared (FTIR) spectrometry techniques. Multi-elemental contents of 15 glass fragments that belong to Hellenistic, Roman, Byzantine, and Ottoman Periods, were determined by INAA. The concentrations of twenty six elements (Na, K, Ca, Sc, Cr, Mn, Fe, Co, Cu, Zn, As, Rb, Sr, Sb, Cs, Ba, Ce, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Au and Th), which might be present in the samples as flux, stabilizers, colorants or opacifiers, and impurities, were examined. Chemometric treatment of the INAA data was performed and principle component analysis revealed presence of 3 distinct groups. The thermal history of the glass samples was determined by FTIR spectrometry.

  18. Assessment of low-frequency hearing with narrow-band chirp-evoked 40-Hz sinusoidal auditory steady-state response.

    PubMed

    Wilson, Uzma S; Kaf, Wafaa A; Danesh, Ali A; Lichtenhan, Jeffery T

    2016-04-01

    Objective To determine the clinical utility of narrow-band chirp-evoked 40-Hz sinusoidal auditory steady state responses (s-ASSR) in the assessment of low-frequency hearing in noisy participants. Design Tone bursts and narrow-band chirps were used to respectively evoke auditory brainstem responses (tb-ABR) and 40-Hz s-ASSR thresholds with the Kalman-weighted filtering technique and were compared to behavioral thresholds at 500, 2000, and 4000 Hz. A repeated measure ANOVA and post-hoc t-tests, and simple regression analyses were performed for each of the three stimulus frequencies. Study sample Thirty young adults aged 18-25 with normal hearing participated in this study. Results When 4000 equivalent response averages were used, the range of mean s-ASSR thresholds from 500, 2000, and 4000 Hz were 17-22 dB lower (better) than when 2000 averages were used. The range of mean tb-ABR thresholds were lower by 11-15 dB for 2000 and 4000 Hz when twice as many equivalent response averages were used, while mean tb-ABR thresholds for 500 Hz were indistinguishable regardless of additional response averaging. Conclusion Narrow-band chirp-evoked 40-Hz s-ASSR requires a ∼15 dB smaller correction factor than tb-ABR for estimating low-frequency auditory threshold in noisy participants when adequate response averaging is used. PMID:26795555

  19. Optical pulse chirp modification in degenerate four-wave mixing at finite pump powers

    NASA Astrophysics Data System (ADS)

    Shockley, R. C.

    1982-06-01

    Exact solutions of the linearized transient envelope equations for degenerate four-wave mixing in a finite-length cell show that reflection coefficients near unity severely restrict the conditions under which chirp reversal occurs, and can lead to nulls in the amplitude of the reflected and transmitted fields.

  20. 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.

  1. Transporting near-circular Bohr-like wave packets using chirped pulse trains

    NASA Astrophysics Data System (ADS)

    Yoshida, S.; Burgdörfer, J.; Reinhold, C. O.; Wyker, B.; Ye, S.; Dunning, F. B.

    2011-05-01

    Protocols for driving localized high- n (n 300) wave packets in near-circular Bohr-like orbits to higher n states using chirped sine waves are described. While Rydberg wave packets involving several n levels are known to be dispersive, circular wave packets can be stabilized by the application of a circularly- or linearly-polarized resonant sine wave. A similar stabilization mechanism is known for the formation of the Trojan asteroids in celestial mechanics. We demonstrate that by slowly chirping the drive frequency parent high- n wave packets can be transported to a narrow distribution of much higher n states because the motion of the wave packet remains locked to the sine wave during the chirping. Use of a chirped HCP train instead of a sine wave allows similar transport but also provides some control of the orbit eccentricity. Research supported by the NSF, the Robert A. Welch Foundation, the OBES US DoE to ORNL, and by the FWF (Austria)

  2. Female giant panda (Ailuropoda melanoleuca) chirps advertise the caller's fertile phase.

    PubMed

    Charlton, Benjamin D; Keating, Jennifer L; Rengui, Li; Huang, Yan; Swaisgood, Ronald R

    2010-04-01

    Although female mammal vocal behaviour is known to advertise fertility, to date, no non-human mammal study has shown that the acoustic structure of female calls varies significantly around their fertile period. Here, we used a combination of hormone measurements and acoustic analyses to determine whether female giant panda chirps have the potential to signal the caller's precise oestrous stage (fertile versus pre-fertile). We then used playback experiments to examine the response of male giant pandas to female chirps produced during fertile versus pre-fertile phases of the caller's reproductive cycle. Our results show that the acoustic structure of female giant panda chirps differs between fertile and pre-fertile callers and that male giant pandas can perceive differences in female chirps that allow them to determine the exact timing of the female's fertile phase. These findings indicate that male giant pandas could use vocal cues to preferentially associate and copulate with females at the optimum time for insemination and reveal the likely importance of female vocal signals for coordinating reproductive efforts in this critically endangered species. PMID:19955154

  3. Female giant panda (Ailuropoda melanoleuca) chirps advertise the caller's fertile phase

    PubMed Central

    Charlton, Benjamin D.; Keating, Jennifer L.; Rengui, Li; Huang, Yan; Swaisgood, Ronald R.

    2010-01-01

    Although female mammal vocal behaviour is known to advertise fertility, to date, no non-human mammal study has shown that the acoustic structure of female calls varies significantly around their fertile period. Here, we used a combination of hormone measurements and acoustic analyses to determine whether female giant panda chirps have the potential to signal the caller's precise oestrous stage (fertile versus pre-fertile). We then used playback experiments to examine the response of male giant pandas to female chirps produced during fertile versus pre-fertile phases of the caller's reproductive cycle. Our results show that the acoustic structure of female giant panda chirps differs between fertile and pre-fertile callers and that male giant pandas can perceive differences in female chirps that allow them to determine the exact timing of the female's fertile phase. These findings indicate that male giant pandas could use vocal cues to preferentially associate and copulate with females at the optimum time for insemination and reveal the likely importance of female vocal signals for coordinating reproductive efforts in this critically endangered species. PMID:19955154

  4. A mode-locked fiber laser with a chirped grating mirror

    NASA Astrophysics Data System (ADS)

    Haus, J. W.; Hayduk, M.; Kaechele, W.; Shaulov, G.; Theimer, J.; Teegarden, K.; Wicks, G.

    2000-01-01

    A novel fiber laser was built using a multiple-quantum well mode-locking element and a chirped fiber grating to balance dispersion and nonlinearity. Energetic pulses as short as 2 ps were generated in the cavity and propagated in a fiber to determine the pulse characteristics. Laser cavity modeling and pulse propagation simulations are in good agreement with experiments.

  5. Designing Fresnel microlenses for focusing astigmatic multi-Gaussian beams by using fractional order Fourier transforms

    NASA Astrophysics Data System (ADS)

    Patiño, A.; Durand, P.-E.; Fogret, É.; Pellat-Finet, P.

    2011-01-01

    According to a scalar theory of diffraction, light propagation can be expressed by two-dimensional fractional order Fourier transforms. Since the fractional Fourier transform of a chirp function is a Dirac distribution, focusing a light beam is optically achieved by using a diffractive screen whose transmission function is a two-dimensional chirp function. This property is applied to designing Fresnel microlenses, and the orders of the involved Fourier fractional transforms depend on diffraction distances as well as on emitter and receiver radii of curvature. If the emitter is astigmatic (with two principal radii of curvature), the diffraction phenomenon involves two one-dimensional fractional Fourier transforms whose orders are different. This degree of freedom allows us to design microlenses that can focus astigmatic Gaussian beams, as produced by a line-shaped laser diode source.

  6. 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.

  7. 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.

  8. 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

  9. Assessment of natural radioactivity and function of minerals in soils of Yelagiri hills, Tamilnadu, India by Gamma Ray spectroscopic and Fourier Transform Infrared (FTIR) techniques with statistical approach.

    PubMed

    Chandrasekaran, A; Ravisankar, R; Rajalakshmi, A; Eswaran, P; Vijayagopal, P; Venkatraman, B

    2014-10-28

    Gamma Ray and Fourier Transform Infrared (FTIR) spectroscopic techniques were used to evaluate the natural radioactivity due to natural radionuclides and mineralogical characterization in soils of Yelagiri hills, Tamilnadu, India. Various radiological parameters were calculated to assess the radiation hazards associated with the soil. The distribution pattern of activity due to natural radionuclides is explained by Kriging method of mapping. Using FTIR spectroscopic technique the minerals such as quartz, microcline feldspar, orthoclase feldspar, kaolinite, montmorillonite, illite, and organic carbon were identified and characterized. The extinction coefficient values were calculated to know the relative distribution of major minerals such as quartz, microcline feldspar, orthoclase feldspar and kaolinite. The calculated values indicate that the amount of quartz is higher than orthoclase feldspar, microcline feldspar and much higher than kaolinite. Crystallinity index was calculated to know the crystalline nature of quartz. The result indicates that the presence of disordered crystalline quartz in soils. The relation between minerals and radioactivity was assessed by multivariate statistical analysis (Pearson's correlation and cluster analysis). The statistical analysis confirms that the clay mineral kaolinite and non-clay mineral quartz is the major factor than other major minerals to induce the important radioactivity variables and concentrations of uranium and thorium. PMID:25467664

  10. Assessment of natural radioactivity and function of minerals in soils of Yelagiri hills, Tamilnadu, India by Gamma Ray spectroscopic and Fourier Transform Infrared (FTIR) techniques with statistical approach

    NASA Astrophysics Data System (ADS)

    Chandrasekaran, A.; Ravisankar, R.; Rajalakshmi, A.; Eswaran, P.; Vijayagopal, P.; Venkatraman, B.

    2015-02-01

    Gamma Ray and Fourier Transform Infrared (FTIR) spectroscopic techniques were used to evaluate the natural radioactivity due to natural radionuclides and mineralogical characterization in soils of Yelagiri hills, Tamilnadu, India. Various radiological parameters were calculated to assess the radiation hazards associated with the soil. The distribution pattern of activity due to natural radionuclides is explained by Kriging method of mapping. Using FTIR spectroscopic technique the minerals such as quartz, microcline feldspar, orthoclase feldspar, kaolinite, montmorillonite, illite, and organic carbon were identified and characterized. The extinction coefficient values were calculated to know the relative distribution of major minerals such as quartz, microcline feldspar, orthoclase feldspar and kaolinite. The calculated values indicate that the amount of quartz is higher than orthoclase feldspar, microcline feldspar and much higher than kaolinite. Crystallinity index was calculated to know the crystalline nature of quartz. The result indicates that the presence of disordered crystalline quartz in soils. The relation between minerals and radioactivity was assessed by multivariate statistical analysis (Pearson's correlation and cluster analysis). The statistical analysis confirms that the clay mineral kaolinite and non-clay mineral quartz is the major factor than other major minerals to induce the important radioactivity variables and concentrations of uranium and thorium.

  11. Amplitude modulated chirp excitation to reduce grating lobes and maintain ultrasound intensity at the focus of an array

    PubMed Central

    Karunakaran, Chandra P; Oelze, Michael L

    2013-01-01

    During application of high intensity focused ultrasound (HIFU) with therapy arrays, the existence of grating lobes can cause heating at unintended tissue regions. Therefore, the reduction of grating lobes in therapeutic arrays is an important goal. One way to reduce the grating lobes in therapy arrays is to excite the arrays with broadband signals (defined here as >10% fractional bandwidth). To achieve a reduction in grating lobe levels in an ultrasonic array, coded waveforms can be utilized that reduce the grating lobe levels while maintaining the spatial peak temporal average intensity. In this study, a 5-MHz, 9-element, 1.25 mm inter-elemental spacing linear array was excited by a sinusoidal waveform, a conventional linear chirp, and a modified linear chirp. Both chirps spanned the −3-dB bandwidth of the transducer. The conventional chirp was a broadband signal with a linear sweep of frequencies between 2.5 and 7.5 MHz, with all frequency components excited with equal amplitude. The modified chirp signal also swept the frequencies between 2.5 and 7.5 MHz, but the amplitude was weighted such that the edges (low and high frequencies of the band) were excited with more energy than the center of the band. In simulations, the field patterns for the sinusoidal, conventional chirp and modified chirp excitations were produced from the array using Field II and compared. For experiments, the beam pattern from a 5-MHz single-element transducer was mapped using a hydrophone for the sinusoidal, conventional chirp and modified chirp excitation. Each field from the transducer was repeated and summed to produce a field from an array of 9 elements. The difference in the time averaged intensity (in dB) in the main lobe and grating lobes were estimated for each excitation and compared. The results demonstrated that the chirp signals resulted in decreases in grating lobe levels compared to the main lobe, i.e. 10 dB down for focusing and 6 dB down for focusing and steering. A further 1 dB decrease in grating lobe levels was observed for the modified chirp excitation compared to the conventional chirp excitation, which corresponds to ~21% reduction in energy deposition at the grating lobe location. PMID:23648212

  12. Multi-resonance effects within a single chirp in broadband rotational spectroscopy: The rapid adiabatic passage regime for benzonitrile

    NASA Astrophysics Data System (ADS)

    Schmitz, David; Alvin Shubert, V.; Betz, Thomas; Schnell, Melanie

    2012-10-01

    We report here pronounced, stepwise multi-resonance excitations in benzonitrile arising from a single 1 μs broadband 2-8.3 GHz microwave chirp, observed with our new chirped-pulse broadband rotational spectrometer, COMPACT. Such multi-resonance excitations significantly alter the relative intensity patterns and are a strong indication that, for the given experimental conditions and using benzonitrile as a polar test molecule (μA = 4.5152 D), the rapid adiabatic passage (RAP) regime for strong coupling must be applied. This finding is contrary to previous discussions of chirped-pulse rotational spectroscopy, where the linear fast passage regime of weak coupling has been assumed.

  13. Development of a Fourier transform infrared spectroscopy coupled to UV-Visible analysis technique for aminosides and glycopeptides quantitation in antibiotic locks.

    PubMed

    Sayet, G; Sinegre, M; Ben Reguiga, M

    2014-01-01

    Antibiotic Lock technique maintains catheters' sterility in high-risk patients with long-term parenteral nutrition. In our institution, vancomycin, teicoplanin, amikacin and gentamicin locks are prepared in the pharmaceutical department. In order to insure patient safety and to comply to regulatory requirements, antibiotic locks are submitted to qualitative and quantitative assays prior to their release. The aim of this study was to develop an alternative quantitation technique for each of these 4 antibiotics, using a Fourier transform infrared (FTIR) coupled to UV-Visible spectroscopy and to compare results to HPLC or Immunochemistry assays. Prevalidation studies permitted to assess spectroscopic conditions used for antibiotic locks quantitation: FTIR/UV combinations were used for amikacin (1091-1115cm(-1) and 208-224nm), vancomycin (1222-1240cm(-1) and 276-280nm), and teicoplanin (1226-1230cm(-1) and 278-282nm). Gentamicin was quantified with FTIR only (1045-1169cm(-1) and 2715-2850cm(-1)) due to interferences in UV domain of parabens, preservatives present in the commercial brand used to prepare locks. For all AL, the method was linear (R(2)=0.996 to 0.999), accurate, repeatable (intraday RSD%: from 2.9 to 7.1% and inter-days RSD%: 2.9 to 5.1%) and precise. Compared to the reference methods, the FTIR/UV method appeared tightly correlated (Pearson factor: 97.4 to 99.9%) and did not show significant difference in recovery determinations. We developed a new simple reliable analysis technique for antibiotics quantitation in locks using an original association of FTIR and UV analysis, allowing a short time analysis to identify and quantify the studied antibiotics. PMID:24438668

  14. Human visual quality image/video compression techniques based on integer wavelet packet transform and SPIHT, and their application to mobile communications

    NASA Astrophysics Data System (ADS)

    Asdornwised, Widhyakorn; Jitapunkul, Somchai

    2004-07-01

    In this paper, we present an efficient compression technique that is suitable for image/video communications over wireless (mobile) channel. Our technique uses basic directional differences operators to estimate corresponding detail subband images/videos from their approximation subband images/videos. We empirically found that the detail subband images/videos can be well approximated by the estimate subband images/videos. In this work, image and video are first decomposed using integer wavelet packet transformation. Having established that detail subband images/video can be estimated from the approximation subbands, the information needed to send over the wireless channel is only the most important subband images/video, where we selected them via best basis selection algorithm. Next, after best basis selection, the selection subband components are encoded using either SPIHT (JPEG) for image or 3-D SPIHT for video and then the encoded data are sent over the wireless channel. The advantages of our algorithms are two folds. First, most of the computation used in our technique is performed in integer for the purpose of coding speed improvement. Second, the computation of our algorithm (either SPIHT (JPEG) or 3-D SPIHT) is reduced from its original computation by an order of magnitude. The reason is that in our algorithm either SPIHT (JPEG) or 3-D SPIHT is performed only on the set of important components (two or a few subband image/videos) instead of the whole image/video. Finally, we show that our proposed algorithm using SPIHT (3-D SPIHT) are better that pure JPEG (MPEG-2) both in terms of human visual image and computation complexity.

  15. An Operator Method for Evaluating Laplace Transforms

    ERIC Educational Resources Information Center

    Lanoue, B. G.; Yurekli, O.

    2005-01-01

    This note discusses a simple operator technique based on the differentiation and shifting properties of the Laplace transform to find Laplace transforms for various elementary functions. The method is simpler than known integration techniques to evaluate Laplace transforms.

  16. 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

  17. Rolling element bearing defect detection using the generalized synchrosqueezing transform guided by time-frequency ridge enhancement.

    PubMed

    Li, Chuan; Sanchez, Vinicio; Zurita, Grover; Cerrada Lozada, Mariela; Cabrera, Diego

    2016-01-01

    Healthy rolling element bearings are vital guarantees for safe operation of the rotating machinery. Time-frequency (TF) signal analysis is an effective tool to detect bearing defects under time-varying shaft speed condition. However, it is a challenging work dealing with defective characteristic frequency and rotation frequency simultaneously without a tachometer. For this reason, a technique using the generalized synchrosqueezing transform (GST) guided by enhanced TF ridge extraction is suggested to detect the existence of the bearing defects. The low frequency band and the resonance band are first chopped from the Fourier spectrum of the bearing vibration measurements. The TF information of the lower band component and the resonance band envelope are represented using short-time Fourier transform, where the TF ridge are extracted by harmonic summation search and ridge candidate fusion operations. The inverse of the extracted TF ridge is subsequently used to guide the GST mapping the chirped TF representation to the constant one. The rectified TF pictures are then synchrosqueezed as sharper spectra where the rotation frequency and the defective characteristic frequency can be identified, respectively. Both simulated and experimental signals were used to evaluate the present technique. The results validate the effectiveness of the suggested technique for the bearing defect detection. PMID:26542359

  18. 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.

  19. Dependence of plasma wake wave amplitude on the shape of Gaussian chirped laser pulse propagating in a plasma channel

    NASA Astrophysics Data System (ADS)

    Akou, H.; Asri, M.

    2016-04-01

    The generation of longitudinal electrostatic plasma waves (wakefields) due to the propagation of a chirped laser pulse through a parabolic plasma channel is studied. The wakes generated by a temporally symmetric Gaussian laser pulse are compared with those generated by asymmetric one. The main interest in this paper is to investigate the effects of a laser pulse shape with of sharp rising and slow falling time scales on the excited wakefield amplitude. Moreover, positive, negative and un-chirped laser pulses are employed in numerical codes to evaluate the influence of the initial chirp on wakefield excitation. Numerical results showed that for an appropriate laser pulse length compared with the plasma wavelength, the wakefield amplitude can be enhanced for a positively chirped asymmetric Gaussian laser pulse with a fast rise time.

  20. Generation of isolated sub-40-attosecond pulse with a multicycle chirped laser and a static electric field

    NASA Astrophysics Data System (ADS)

    Mohebbi, Masoud

    2016-02-01

    We numerically investigate the high-order harmonic generation and isolated attosecond pulse generation in a waveform that linearly produced by chirped laser pulse, chirp-free laser pulse, and static electric field. When a chirp-free laser pulse is added to the produced field of the chirped driving pulse and the static electric field, the plateau harmonic yield is enhanced by two orders. The spectral modulation is also significantly decreased, and the bandwidth of XUV spectrum is further broadened. An intense and a clean isolated 38-as pulse can be produced from the intense broadband XUV supercontinuum. After proper phase compensation, an isolated sub-8-attosecond pulse can be obtained. Furthermore, quantum time-frequency analysis reveals that the selection of the short quantum path can be achieved in this scheme.

  1. Thermally tunable dispersion compensator in 40-Gb/s system using FBG fabricated with linearly chirped phase mask.

    PubMed

    Sun, Jie; Dai, Yitang; Chen, Xiangfei; Zhang, Yejin; Xie, Shizhong

    2006-01-01

    An improved design and fabrication method of nonlinearly chirped fiber Bragg gratings is demonstrated. Based on reconstruction-equivalent- chirp method, the nonlinearly chirped fiber Bragg grating is realized with a linearly chirped phase mask instead of a uniform one, which improves the performance of the device. Coated with uniform thin metal film, the obtained grating works as a tunable dispersion compensator with a tuning range ~200ps/nm, peak-to-peak group delay ripple <14ps and 3-dB bandwidth approximately 2nm. Employing this device, the power penalty in a 40- Gb/s X5/10km conventional single mode fiber using carrier suppressed return-to-zero format is less than 0.7dB at a BER=10-10. PMID:19503314

  2. A pulse compressor for a chirped-pulse amplification system based on a frequency-doubling crystal and grating

    NASA Astrophysics Data System (ADS)

    Chen, Ying; Zhou, Yuan; Yuan, Peng; Qian, Liejia

    2016-05-01

    The limited damage threshold of the last compression grating in a general compressor is still an obstruction that limits the output capability of a high-energy laser facility. We propose and theoretically study a novel pulse compressor consisting of a pair of gratings and a nonlinear crystal, which is applied to chirped-pulse amplification (CPA) or optical parametric CPA (OPCPA) systems. The obstruction in the high-energy laser facility is alleviated substantially in our proposed compressor because the nonlinear crystal with a much higher damage threshold can withstand more high energy of the chirped pulse. We prove that, by means of a pair of anti-parallel gratings and noncollinear frequency doubling, it is possible to obtain a compressed second-harmonic pulse without chirp and angular dispersion. A hypothetical example of a 1 μm linear chirped pulse compression is discussed.

  3. Simultaneous ranging and velocimetry of fast moving targets using oppositely chirped pulses from a mode-locked laser.

    PubMed

    Piracha, Mohammad U; Nguyen, Dat; Ozdur, Ibrahim; Delfyett, Peter J

    2011-06-01

    A lidar system based on the coherent detection of oppositely chirped pulses generated using a 20 MHz mode locked laser and chirped fiber Bragg gratings is presented. Sub millimeter resolution ranging is performed with > 25 dB signal to noise ratio. Simultaneous, range and Doppler velocity measurements are experimentally demonstrated using a target moving at > 330 km/h inside the laboratory. PMID:21716350

  4. 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.

  5. A simple, sensitive and non-destructive technique for characterizing bovine dental enamel erosion: attenuated total reflection Fourier transform infrared spectroscopy

    PubMed Central

    Kim, In-Hye; Son, Jun Sik; Min, Bong Ki; Kim, Young Kyoung; Kim, Kyo-Han; Kwon, Tae-Yub

    2016-01-01

    Although many techniques are available to assess enamel erosion in vitro, a simple, non-destructive method with sufficient sensitivity for quantifying dental erosion is required. This study characterized the bovine dental enamel erosion induced by various acidic beverages in vitro using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Deionized water (control) and 10 acidic beverages were selected to study erosion, and the pH and neutralizable acidity were measured. Bovine anterior teeth (110) were polished with up to 1 200-grit silicon carbide paper to produce flat enamel surfaces, which were then immersed in 20 mL of the beverages for 30 min at 37 °C. The degree of erosion was evaluated using ATR-FTIR spectroscopy and Vickers' microhardness measurements. The spectra obtained were interpreted in two ways that focused on the ν1, ν3 phosphate contour: the ratio of the height amplitude of ν3 PO4 to that of ν1 PO4 (Method 1) and the shift of the ν3 PO4 peak to a higher wavenumber (Method 2). The percentage changes in microhardness after the erosion treatments were primarily affected by the pH of the immersion media. Regression analyses revealed highly significant correlations between the surface hardness change and the degree of erosion, as detected by ATR-FTIR spectroscopy (P<0.001). Method 1 was the most sensitive to these changes, followed by surface hardness change measurements and Method 2. This study suggests that ATR-FTIR spectroscopy is potentially advantageous over the microhardness test as a simple, non-destructive, sensitive technique for the quantification of enamel erosion. PMID:27025266

  6. A simple, sensitive and non-destructive technique for characterizing bovine dental enamel erosion: attenuated total reflection Fourier transform infrared spectroscopy.

    PubMed

    Kim, In-Hye; Son, Jun Sik; Min, Bong Ki; Kim, Young Kyoung; Kim, Kyo-Han; Kwon, Tae-Yub

    2016-01-01

    Although many techniques are available to assess enamel erosion in vitro, a simple, non-destructive method with sufficient sensitivity for quantifying dental erosion is required. This study characterized the bovine dental enamel erosion induced by various acidic beverages in vitro using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Deionized water (control) and 10 acidic beverages were selected to study erosion, and the pH and neutralizable acidity were measured. Bovine anterior teeth (110) were polished with up to 1 200-grit silicon carbide paper to produce flat enamel surfaces, which were then immersed in 20 mL of the beverages for 30 min at 37 °C. The degree of erosion was evaluated using ATR-FTIR spectroscopy and Vickers' microhardness measurements. The spectra obtained were interpreted in two ways that focused on the ν1, ν3 phosphate contour: the ratio of the height amplitude of ν3 PO4 to that of ν1 PO4 (Method 1) and the shift of the ν3 PO4 peak to a higher wavenumber (Method 2). The percentage changes in microhardness after the erosion treatments were primarily affected by the pH of the immersion media. Regression analyses revealed highly significant correlations between the surface hardness change and the degree of erosion, as detected by ATR-FTIR spectroscopy (P<0.001). Method 1 was the most sensitive to these changes, followed by surface hardness change measurements and Method 2. This study suggests that ATR-FTIR spectroscopy is potentially advantageous over the microhardness test as a simple, non-destructive, sensitive technique for the quantification of enamel erosion. PMID:27025266

  7. Fourier transform infrared photoacoustic spectroscopy study of physicochemical interaction between human dentin and etch-&-rinse adhesives in a simulated moist bond technique

    NASA Astrophysics Data System (ADS)

    Ubaldini, Adriana L. M.; Baesso, Mauro L.; Sehn, Elizandra; Sato, Francielle; Benetti, Ana R.; Pascotto, Renata C.

    2012-06-01

    The purpose of this study was to provide the physicochemical interactions at the interfaces between two commercial etch-&-rinse adhesives and human dentin in a simulated moist bond technique. Six dentin specimens were divided into two groups (n=3) according to the use of two different adhesive systems: (a) 2-hydroxyethylmethacrylate (HEMA) and 4-methacryloxyethyl trimellitate anhydrate (4-META), and (b) HEMA. The Fourier transform infrared photoacoustic spectroscopy was performed before and after dentin treatment with 37% phosphoric acid, with adhesive systems and also for the adhesive systems alone. Acid-conditioning resulted in a decalcification pattern. Adhesive treated spectra subtraction suggested the occurrence of chemical bonding to dentin expressed through modifications of the OH stretching peak (3340 cm-1) and symmetric CH stretching (2900 cm-1) for both adhesives spectra; a decrease of orthophosphate absorption band (1040 to 970 cm-1) for adhesive A and a better resolved complex band formation (1270 to 970 cm-1) for adhesive B were observed. These results suggested the occurrence of chemical bonding between sound human dentin and etch-&-rinse adhesives through a clinical typical condition.

  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; Davila, Joseph M.; Viall, Nicholeen M.

    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. A new Fourier transform photo-modulation spectroscopic technique for narrow band-gap materials in the mid- to far-infra-red

    NASA Astrophysics Data System (ADS)

    Hosea, T. J. C.; Merrick, M.; Murdin, B. N.

    2005-05-01

    There is a large number of technologically important semiconducting optoelectronic materials with narrow band-gaps in the finger-print region of the infra-red (IR) spectrum. However, in many instances their band-structures have not been very well characterised, making it difficult to engineer their properties. Part of the reason is that the key non-destructive optical characterisation tool, modulation spectroscopy, becomes increasingly difficult as one attempts to look further out into the IR. To date, conventional diffraction-grating-based modulation spectroscopy has been applied predominantly below 4 μm. We have developed a new photo-modulation system, based on a Fourier transform spectrometer, that permits such measurements out to much longer wavelengths. We discuss the advantages and technical difficulties of implementing such a system, and give the results obtained so far for narrower-gap materials, including bulk-like GaSb, InAs and InSb, comparing these with what can be obtained with conventional modulation spectroscopy arrangements. We apply our new technique to measure the bandgap in dilute-N InSbN, achieving what we believe are the first modulation spectroscopy measurements in the mid-IR beyond 6 μm.

  10. The response of phospholipid-encapsulated microbubbles to chirp-coded excitation: implications for high-frequency nonlinear imaging.

    PubMed

    Shekhar, Himanshu; Doyley, Marvin M

    2013-05-01

    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

  11. Ultrafast chirped optical waveform recorder using a time microscope

    DOEpatents

    Bennett, Corey Vincent

    2015-04-21

    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. By also including a variety of possible demultiplexing techniques, this process is scalable to recoding continuous signals.

  12. Making ultracold molecules in a two-color pump-dump photoassociation scheme using chirped pulses

    SciTech Connect

    Koch, Christiane P.; Luc-Koenig, Eliane; Masnou-Seeuws, Francoise

    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.

  13. Curvature-Induced Bunch Self-Interaction for an Energy-Chirped Bunch in Magnetic Bends

    SciTech Connect

    Rui Li

    2006-01-04

    The curvature-induced bunch collective interaction in magnetic bends can be studied using effective forces in the canonical formulation of the coherent synchrotron radiation (CSR) effect. In this paper, for an electron distribution moving ultrarelativistically in a bending system, the dynamics of a particle in the electron distribution is derived from the Hamiltonian of the particle in terms of the bunch internal coordinates. The consequent Vlasov equation manifests explicitly how the phase space distribution is perturbed by the effective CSR forces. In particular, we study the impact of an initial linear energy chirp of the bunch on the behavior of the effective longitudinal CSR force, which arises due to the modification of the retardation relation as a result of the energy-chirping-induced longitudinal-horizontal correlation of the bunch distribution (bunch tilt) in dispersive regions.

  14. Modeling of coherent beam combining from multimillijoule chirped pulse tapered fiber amplifiers

    NASA Astrophysics Data System (ADS)

    Andrianov, A. V.; Kim, A. V.; Anashkina, E. A.; Meyerov, I. B.; Lebedev, S. A.; Sergeev, A. M.; Koenig, K.; Mourou, G.

    2015-10-01

    The amplification of high energy chirped pulses in Large Mode Area tapered fiber amplifiers and their coherent combining have been investigated numerically. We have developed a three-dimensional model of strongly chirped nanosecond pulse amplification and compression back to femtosecond duration fully taking into account transverse and longitudinal variations of refractive index profile and distribution of active ions in the fiber, wavelength dependence of emission and absorption cross sections, gain saturation and Kerr nonlinearity. Modeling of Yb-doped fiber amplifier shows that up to 3 mJ of output energy can be extracted in 1 ns pulse with single-mode beam quality. Finally, we have investigated numerically the capabilities of compression and coherent combining of up to 36 perturbed amplifying channels in which high-order modes were excited and have obtained more than 70% combining efficiency and 380 fs compressed pulse duration.

  15. Fully distributed chirped FBG sensor and application in laser-induced interstitial thermotherapy

    NASA Astrophysics Data System (ADS)

    Li, Chenglin; Chen, Na; Chen, Zhenyi; Wang, Tingyun

    2009-11-01

    In the laser induced interstitial thermotherapy (LITT), real-timely detecting the temperature distribution of the cured tissue is a bottleneck. In this paper, a fully distributed chirped Fiber Bragg grating (FBG) sensor, which is of small size, immune from electromagnetic interference (EMI) and high sensitivity, is proposed to solve this problem. An experiment simulation of LITT is set up, and only one chirped FBG is used to detect the dynamic spectral variation with different laser power. Meanwhile, a high-efficiency spectra inversion algorithm named MSAE of FBG is utilized to demodulate the system and obtain the temperature distribution. The spatial resolution is 0.25mm and the running time of demodulation is tens of seconds, which can help doctors control the laser parameters such as the laser power and the treatment time to guarantee the security of the therapy.

  16. FEMTOSECOND X-RAY PULSES FROM A FREQUENCY CHIRPED SASE FEL.

    SciTech Connect

    KRINSKY,S.HUANG,Z.

    2004-01-07

    We discuss the temporal and spectral properties of self-amplified spontaneous emission (SASE) utilizing an energy-chirped electron beam. A short temporal pulse is generated by using a monochromator to select a narrow radiation bandwidth from the frequency chirped SASE. For the filtered radiation, the minimum pulse length is limited by the intrinsic SASE bandwidth, while the number of modes and the energy fluctuation can be controlled through the monochromator bandwidth. Two cases are considered: (1) placing the monochromator at the end of a single long undulator; (2) placing the monochromator after an initial undulator and amplifying the short-duration output in a second undulator. We analyze these cases and show that tens of femtosecond x-ray pulses may be generated for the linac coherent light source.

  17. On the conditions for the onset of nonlinear chirping structures in NSTX

    NASA Astrophysics Data System (ADS)

    Duarte, Vinicius; Podesta, Mario; Berk, Herbert; Gorelenkov, Nikolai

    2015-11-01

    The nonlinear dynamics of phase space structures is a topic of interest in tokamak physics in connection with fast ion loss mechanisms. The onset of phase-space holes and clumps has been theoretically shown to be associated with an explosive solution of an integro-differential, nonlocal cubic equation that governs the early mode amplitude evolution in the weakly nonlinear regime. The existence and stability of the solutions of the cubic equation have been theoretically studied as a function of Fokker-Planck coefficients for the idealized case of a single resonant point of a localized mode. From realistic computations of NSTX mode structures and resonant surfaces, we calculate effective pitch angle scattering and slowing-down (drag) collisional coefficients and analyze NSTX discharges for different cases with respect to chirping experimental observation. Those results are confronted to the theory that predicts the parameters region that allow for chirping to take place.

  18. Frequency chirp and pulse shape effects in self-modulated laser wakefield accelerators

    SciTech Connect

    Schroeder, C.B.; Esarey, E.; Geddes, C.G.R.; Toth, Cs.; Shadwick, B.A.; van Tilborg, J.; Faure, J.; Leemans, W.P.

    2002-11-07

    The effect of asymmetric laser pulses on plasma wave excitation in a self-modulated laser wakefield accelerator is examined. Laser pulse shape and frequency chirp asymmetries, controlled experimentally in the laser system through a grating pair compressor, are shown to strongly enhance measured electron yields for certain asymmetries. It is shown analytically that a positive (negative) frequency chirp enhances (suppresses) the growth rate of the Raman forward scattering and near-forward Raman sidescatter instabilities, but is of minimal importance for the experimental parameters. Temporal laser pulse shapes with fast rise times (< plasma period) are shown to generate larger wakes (compared to slow rise time pulses) which seed the growth of the plasma wave, resulting in enhanced electron yield.

  19. Note: A concrete erosion sensor based on a chirped fibre optic Bragg grating

    NASA Astrophysics Data System (ADS)

    Kanopoulos, Patrick; Xia, Kaiwen; Gu, Xijia; Amirchoupani, Ardavan; Yao, Wei

    2015-12-01

    Erosion of concrete surfaces in major civil structures is a common problem, which in certain circumstances can undermine the structural and operational integrities of the structure. The manual monitoring of the erosion process can be difficult and dangerous under certain circumstances (such as within hydrotunnels and spillways of dams). This paper describes a concrete erosion sensor based on a chirped fibre Bragg grating (FBG) which is able to monitor the extent of concrete erosion at a single point to sub-millimetre accuracy. The chirped FBG length embedded below the concrete surface decreases as a result of concrete erosion and consequently the reflected light spectrum bandwidth narrows. A simple procedure is presented to determine the extent of erosion, and this procedure is applied to an experimental demonstration of the sensing device.

  20. Minimization of dispersion in an ultrafast chirped pulse amplifier using adaptive learning

    NASA Astrophysics Data System (ADS)

    Efimov, A.; Moores, M. D.; Mei, B.; Krause, J. L.; Siders, C. W.; Reitze, D. H.

    Minimizing residual frequency dispersion that accompanies pulse stretching, amplification, and recompression is an important consideration in ultrashort chirped-pulse amplifiers. Here we show how an adaptive learning algorithm can be used in conjunction with a pulse shaper to compensate for higher-order and nonlinear dispersion in a chirped-pulse amplifier. Using spectral blueshifting as a sensitive diagnostic for pulse shape, we implement a `learning loop' comprised of the pulse shaper, strong field laser ionization, and a genetic algorithm to minimize dispersion through the amplifier. We verify our optimization results using frequency-resolved optical gating (FROG) measurements and also show theoretically and experimentally that spectral blueshifting is indeed a sensitive diagnostic for pulse shape, and specifically, for higher-order dispersion.

  1. 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)

  2. Electron acceleration in moving laser-induced gratings produced by chirped femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Kozák, Martin

    2015-10-01

    We propose nonrelativistic electron acceleration in a vacuum using interaction with two crossed chirped femtosecond laser pulses at different frequencies. Electron energy gain is optimized by the phase-matching of accelerated electron velocity to a maximum of ponderomotive force in the moving intensity grating by linear chirping of both pulses. Particle tracking simulations show acceleration gradients as high as 40 GeV m-1 (energy gain of hundreds of keV) using 25 fs pulses with peak power ≤500 GW. The dependence of electron energy gain and the deflection angle on experimental parameters (the amplitude of the electric field of laser pulses, and the initial phase shift between the electron and intensity grating) was studied in detail.

  3. Chirp-free ultra-short pulses in complex nonlinear optical fibers

    NASA Astrophysics Data System (ADS)

    Jiang, Xiance; Liang, Jianchu; Cao, Jianzhong; Song, Jinxiang; Cai, Zebin

    2016-04-01

    Chirp-free ultra-short pulses propagating in optical fiber with complex parameters are investigated for the first time. The existence condition for such chirp-free ultrashort pulses is that the imaginary parts of the nonlinear terms, i.e., the nonlinear absorption coefficient (a2i), nonlinear dispersion coefficient (a4i) and imaginary Raman coefficient (a2i) fulfill a linear relationship a2i = a4i ω = -2/3 a5i ω . Bight solitons can stably propagate in such complex nonlinear optical fiber. It is found that the single Jacobi elliptic function solutions have two free parameters while hybrid Jacobi elliptic function solutions have only one free parameter.

  4. Coherent control of broadband isolated attosecond pulses in a chirped two-color laser field

    SciTech Connect

    Zou Pu; Zeng Zhinan; Zheng Yinghui; Lu Yingying; Liu Peng; Li Ruxin; Xu Zhizhan

    2010-03-15

    A theoretical investigation is presented that uses a strong two-color laser field composed of a linearly chirped fundamental (900 nm) and its subharmonic (1800-nm) laser pulses to control coherently the broadband isolated attosecond pulses in high-order harmonic generations. After the subharmonic field is added, the intrinsic chirp of harmonic emission can be reduced significantly, and consequently, the temporal synchronization of harmonic emission with different photon energies at the level of the single-atom response can be realized. In addition, the scheme is robust against the carrier envelope phase variation to produce a twin pulse of stable sub-100-as duration, and the relative intensity of the twin pulses can be changed just by adjusting the relative time delay of the two driving pulses, which is of benefit in general pump-probe experiments.

  5. 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; Baik, Moon-Gu

    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.

  6. Near-field-smoothing of periodic chirped pulse with applied angular dispersion

    NASA Astrophysics Data System (ADS)

    Cheng, Wenyong; Zhang, Xiaomin; Su, Jingqin; Zhang, Rui; Gong, Mali

    2011-03-01

    Periodic chirped pulse (PCP) with applied angular dispersion has been approved to be an efficient beam smoothing method in inertial confinement fusion. In this paper, the propagation characteristics of dispersed PCP in near field is analyzed theoretically and calculated numerically, and the results indict dispersed PCP is a motion beam, which can be applied to improve beam uniformity in near field. An experiment is carried out to validate the near-field-intensity smoothing effect of PCP.

  7. Ultrahigh contrast from a frequency-doubled chirped-pulse-amplification beamline.

    PubMed

    Hillier, David; Danson, Colin; Duffield, Stuart; Egan, David; Elsmere, Stephen; Girling, Mark; Harvey, Ewan; Hopps, Nicholas; Norman, Michael; Parker, Stefan; Treadwell, Paul; Winter, David; Bett, Thomas

    2013-06-20

    This paper describes frequency-doubled operation of a high-energy chirped-pulse-amplification beamline. Efficient type-I second-harmonic generation was achieved using a 3 mm thick 320 mm aperture KDP crystal. Shots were fired at a range of energies achieving more than 100 J in a subpicosecond, 527 nm laser pulse with a power contrast of 10(14). PMID:23842168

  8. New stretcher scheme for a parametric amplifier of chirped pulses with frequency conversion

    SciTech Connect

    Freidman, Gennadii I; Yakovlev, I V

    2007-02-28

    The properties of hybrid prism-grating dispersion systems are studied. The scheme of a prism-grating stretcher matched to a standard compressor in the phase dispersion up to the fourth order inclusive is developed for a petawatt laser complex based on the optical parametric chirped-pulse amplification. The stretcher was used to obtain the {approx}200-TW peak power of laser radiation. (control of laser radiation parameters)

  9. Chirped multiphoton adiabatic passage for a four-level ladder-type Rydberg excitation

    NASA Astrophysics Data System (ADS)

    Qian, Jing; Zhai, Jingjing; Zhang, Lu; Zhang, Weiping

    2015-01-01

    We develop a multiphoton adiabatic passage to realize a highly efficient Rydberg excitation in a four-level ladder-type atomic system. The adiabatic passage is based on the existence of a novel quasidark state in the cascade excitation system where the frequencies of the lasers are appropriately chirped with time. We also investigate the influence of the interatomic Rydberg interaction on the passage and extend its application to the preparation of antiblockade Rydberg atom pairs in the Rydberg blockade regime.

  10. Tunable optical delay line in SOI implemented with step chirped Bragg gratings and serial grating arrays

    NASA Astrophysics Data System (ADS)

    Spasojevic, Mina; Chen, Lawrence R.

    2013-10-01

    Tunable optical delay devices have numerous applications in optical communications [1] and have been successfully implemented using slow light elements and fiber or waveguide gratings. There has been considerable interest in siliconon- insulator (SOI) as a technology platform for compact integration of optical signal processing systems. SOI-based delay lines have been realized using coupled ring resonators [2], photonic crystals [3], and various Bragg grating-based configurations including single or coupled chirped sidewall gratings [4,5] as well as tapered rib waveguide gratings [6]. By linearly chirping the period in sidewall gratings, relatively small delays (a few ps) over a bandwidth of tens of nm were demonstrated [4]; with tapered waveguides, significantly larger delays (300-500 ps) were obtained, albeit over a narrower bandwidth (< 2 nm) [6]. On the other hand, some signal processing applications may require large delays (e.g., tens to hundreds of ps) over large bandwidths (several to tens of nm). Several designs have been proposed to meet these requirements, e.g., a step-chirped rib waveguide grating providing 50 ps delay over 15 nm [7] or complementary apodized sidewall gratings providing up to 275 ps over 3 nm [8], however, they have not been realized experimentally. In this paper, we demonstrate discretely tunable optical delay lines that provide tens of ps delay (up to 65 ps) in steps of 15-32 ps over bandwidths of several tens of nm (35-70 nm). The devices are fabricated on SOI using electron beam lithography and implemented through two different approaches: serial sidewall Bragg grating arrays and the step-chirped sidewall Bragg gratings.

  11. Modeling interface roughness scattering in a layered seabed for normal-incident chirp sonar signals.

    PubMed

    Tang, Dajun; Hefner, Brian T

    2012-04-01

    Downward looking sonar, such as the chirp sonar, is widely used as a sediment survey tool in shallow water environments. Inversion of geo-acoustic parameters from such sonar data precedes the availability of forward models. An exact numerical model is developed to initiate the simulation of the acoustic field produced by such a sonar in the presence of multiple rough interfaces. The sediment layers are assumed to be fluid layers with non-intercepting rough interfaces. PMID:22502485

  12. Synchronous optical sampling with chirped optical pulse based on high nonlinear spiral photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Li, Sha; Wang, Jianping; Shi, Zhiguo; Zhang, Xianting; Kang, Zhe; Yu, Chongxiu

    2015-05-01

    We optimize a proposed multicast parametric synchronous sampling scheme. Two segments of 1 cm high nonlinear spiral photonic crystal fiber are utilized as a nonlinear medium in parametric processors. Meanwhile, a segment of 1.8 km dispersion compensation fiber is used to obtain linear chirped sampling pulses instead of a 5 km single-mode fiber. The experimental results show that a 120 GSa/s equivalent sampling rate, high power of sampling copies, and low variance are obtained.

  13. Two and Three Beam Pumped Optical Parametric Amplifier of Chirped Pulses

    NASA Astrophysics Data System (ADS)

    Ališauskas, S.; Butkus, R.; Pyragaitė, V.; Smilgevičius, V.; Stabinis, A.; Piskarskas, A.

    2010-04-01

    We present two and three beam pumped optical parametric amplifier of broadband chirped pulses. The seed pulses from Ti:sapphire oscillator were stretched and amplified in a non-collinear geometry pumping with up to three beams derived from independent laser amplifiers. The signal with ˜90 nm bandwidth was amplified up to 0.72 mJ. The conversion efficiency dependence on intersection angles of pump beams is also revealed.

  14. Influence of chirp on laser-pulse amplification in Brillouin backscattering schemes

    NASA Astrophysics Data System (ADS)

    Lehmann, Goetz; Schluck, Friedrich; Spatschek, Karl-Heinz

    2015-11-01

    Plasma-based amplification of laser pulses is currently discussed as a key component for the next generation of high-intensity laser systems, possibly enabling the generation of ultra-short pulses in the exawatt-zetawatt regime. In these scenarios the energy of a long pump pulse (several ps to ns of duration) is transferred to a short seed pulse via a plasma oscillation. Weakly- and strongly-coupled (sc) Brillouin backscattering have been identified as potential candidates for robust amplification scenarios. With the help of three-wave interaction models, we investigate the influence of a chirp of the pump beam on the seed amplification. We show that chirp can mitigate deleterious spontaneous Raman backscattering of the pump off noise and that at the same time the amplification dynamics due to Brillouin scattering is still intact. For the experimentally very interesting case of sc-Brillouin we find a dependence of the efficiency on the sign of the chirp. Funding provided by project B10 of SFB TR18 of the Deutsche Forschungsgemeinschaft (DFG).

  15. Increasing the sonoporation efficiency of targeted polydisperse microbubble populations using chirp excitation.

    PubMed

    McLaughlan, James; Ingram, Nicola; Smith, Peter R; Harput, Sevan; Coletta, P Louise; Evans, Stephen; Freear, Steven

    2013-12-01

    The therapeutic use of microbubbles for targeted drug or gene delivery is a highly active area of research. Phospholipid- encapsulated microbubbles typically have a polydisperse size distribution over the 1 to 10 μm range and can be functionalized for molecular targeting and loaded with drugcarrying liposomes. Sonoporation through the generation of shear stress on the cell membrane by microbubble oscillations is one mechanism that results in pore formation in the cell membrane and can improve drug delivery. A microbubble oscillating at its resonant frequency would generate maximum shear stress on a membrane. However, because of the polydisperse nature of phospholipid microbubbles, a range of resonant frequencies would exist in a single population. In this study, the use of linear chirp excitations was compared with equivalent duration and acoustic pressure tone excitations when measuring the sonoporation efficiency of targeted microbubbles on human colorectal cancer cells. A 3 to 7 MHz chirp had the greatest sonoporation efficiency of 26.9 ± 5.6%, compared with 16.4 ± 1.1% for the 1.32 to 3.08 MHz chirp. The equivalent 2.2- and 5-MHz tone excitations have efficiencies of 12.8 ± 2.1% and 15.6 ± 1.1%, respectively, which were all above the efficiency of 4.1 ± 3.1% from the control exposure. PMID:24297017

  16. Multiple slow waves and relevant transverse transmission and confinement in chirped photonic crystals.

    PubMed

    Serebryannikov, Andriy E; Cakmak, A Ozgur; Colak, Evrim; Caglayan, Humeyra; Kurt, Hamza; Ozbay, Ekmel

    2014-09-01

    The dispersion properties of rod-type chirped photonic crystals (PhCs) and non-channeled transmission in the direction of the variation of structural parameters from one cell of such a PhC to another are studied. Two types of configurations that enable multiple slow waves but differ in the utilized chirping scheme are compared. It is demonstrated that the multiple, nearly flat bands with a group index of refraction exceeding 180 can be obtained. For these bands, transmission is characterized by multiple narrow peaks of perfect transmission, strong field enhancement inside the slab, and large values of the Q-factor. Among the bands, there are some that show negative phase velocity. Symmetry with respect to the slab mid-plane must be kept in order to obtain constructive interferences that are necessary for reflection-free transmission. It is shown that 15 and more slow wave bands can be obtained in one configuration. The corresponding transmission peaks are well separated from each other, being the only significant feature of the transmission spectrum, while the Q-factor can exceed 10⁵. The observed features are preserved in a wide range of the incidence angle variation. They can be used for tuning the locations and spectral widths of the transmission peaks. Some comparisons with the chirped multilayer structures have been carried out. PMID:25321556

  17. 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.

  18. Electron acceleration by a chirped laser pulse in vacuum under the influence of magnetic field

    NASA Astrophysics Data System (ADS)

    Ghotra, Harjit Singh; Kant, Niti

    2015-08-01

    A linearly polarized (LP) chirped laser pulse is employed for electron acceleration to GeV energy under the influence of azimuthal magnetic field in vacuum. LP laser pulse supports the trapping of pre-accelerated electron during laser-electron interaction in vacuum. The electron gains energy from LP laser pulse and gets accelerated in the direction of propagation of laser pulse. Additionally, the chirping increases the electron laser interaction for longer duration while the azimuthal magnetic field having pinching effect keeps the motion of electron parallel to the direction of propagation of laser pulse leads to enhance the electron acceleration. The combined effect of chirping of laser pulse and pinching of azimuthal magnetic field not only enhances the electron energy gain but also supports in retaining of gained energy by the electron for longer distances. The accelerating distance is observed to be of three times the Rayleigh length where the Rayleigh length is about 6.78 μm. We observe electron energy gain of about 1.47 GeV in the presence of azimuthal magnetic field of about 438 kG with an intense LP laser pulse of peak intensity of about 3.4 × 1021 W/cm2. Higher electron energy gain may be obtained with highly intense laser pulse.

  19. Broadband excitation by chirped pulses: application to single electron spins in diamond

    NASA Astrophysics Data System (ADS)

    Niemeyer, I.; Shim, J. H.; Zhang, J.; Suter, D.; Taniguchi, T.; Teraji, T.; Abe, H.; Onoda, S.; Yamamoto, T.; Ohshima, T.; Isoya, J.; Jelezko, F.

    2013-03-01

    Pulsed excitation of broad spectra requires very high field strengths if monochromatic pulses are used. If the corresponding high power is not available or not desirable, the pulses can be replaced by suitable low-power pulses that distribute the power over a wider bandwidth. As a simple case, we use microwave pulses with a linear frequency chirp. We use these pulses to excite spectra of single nitrogen-vacancy centres in a Ramsey experiment. Compared to the conventional Ramsey experiment, our approach increases the bandwidth by at least an order of magnitude. Compared to the conventional continuous wave-ODMR experiment, the chirped Ramsey experiment does not suffer from power broadening and increases the resolution by at least an order of magnitude. As an additional benefit, the chirped Ramsey spectrum contains not only ‘allowed’ single quantum transitions, but also ‘forbidden’ zero- and double quantum transitions, which can be distinguished from the single quantum transitions by phase-shifting the readout pulse with respect to the excitation pulse or by variation of the external magnetic field strength.

  20. Synthetic aperture acoustic imaging of canonical targets with a 2-15 kHz linear FM chirp

    NASA Astrophysics Data System (ADS)

    Vignola, Joseph F.; Judge, John A.; Good, Chelsea E.; Bishop, Steven S.; Gugino, Peter M.; Soumekh, Mehrdad

    2011-06-01

    Synthetic aperture image reconstruction applied to outdoor acoustic recordings is presented. Acoustic imaging is an alternate method having several military relevant advantages such as being immune to RF jamming, superior spatial resolution, capable of standoff side and forward-looking scanning, and relatively low cost, weight and size when compared to 0.5 - 3 GHz ground penetrating radar technologies. Synthetic aperture acoustic imaging is similar to synthetic aperture radar, but more akin to synthetic aperture sonar technologies owing to the nature of longitudinal or compressive wave propagation in the surrounding acoustic medium. The system's transceiver is a quasi mono-static microphone and audio speaker pair mounted on a rail 5meters in length. Received data sampling rate is 80 kHz with a 2- 15 kHz Linear Frequency Modulated (LFM) chirp, with a pulse repetition frequency (PRF) of 10 Hz and an inter-pulse period (IPP) of 50 milliseconds. Targets are positioned within the acoustic scene at slant range of two to ten meters on grass, dirt or gravel surfaces, and with and without intervening metallic chain link fencing. Acoustic image reconstruction results in means for literal interpretation and quantifiable analyses. A rudimentary technique characterizes acoustic scatter at the ground surfaces. Targets within the acoustic scene are first digitally spotlighted and further processed, providing frequency and aspect angle dependent signature information.

  1. Recognition of Sediments from Marine High Resolution Seismic Reflection (Chirp) Data

    NASA Astrophysics Data System (ADS)

    Jiang, D.; Song, G.

    2012-12-01

    Chirp sonar echo sounder is based on the frequency conversion of the transmission of electrical impulses, and it`s signal transmission frequency was gradually increased from the received signal being tackled by the original emitted signal to do each other comparison (correlation), to obtain high-resolution seabed sonar echo profile, use the amplitude and frequency conversion of the chirp features observed wave energy changes, shoot out and reflected wave energy to do comparison, get the change of the reflected energy change, different substrate will produce a different pass depletion, when a sound wave incident in the sea water to the seabed, the acoustic energy through the interface and transmitted by pressure waves and shear waves in the sea-bed, so different acoustic properties of the bottom material will produce different pass, the use of this nature to identify the substrate. the conditions in the water are quite large impact for acoustic detection, specifically, by the sound pass depletion performance, sound transfer loss will be affected by the hydrological environment, sediment characteristics, seabed topography, surface roughness and other factors, so chirp sonar data is the more complete the more accurate the more able to grasp the actual situation of the underwater acoustic transmission, and thus a comprehensive understanding of the actual situation of the background texture for the marine environment. Collect sediment data in two ways, one for the core sampling for sediment acoustic parameters of operational difficulties and only a little bit of information, and the second anti-algorithm, in theory, the chirp signal bandwidth is very wide, has a high SNR penetration ratio and substrate have different reactions for each frequency of the broadband rectifiable more accurate sediment attenuation coefficient (k) , In contrast, core sampling unable to obtain a wide range of information, and the sampling data is not enough depth, data variables and the results are not easy to control, use recognition of sediments from chirp data can get more comprehensive geological data, large amounts of data collated can provide Taiwan acoustic research help. The results showed that different sediments will have a different energy changes, the establishment of the collection into areas where the continuous variable frequency sonar data to do the calculation to obtain the acoustic attenuation coefficient in the sediment. Summarized a variety of sediment produced by the attenuation coefficient can be used to identify the bottom material, or can be used to exploration, search more information of the seabed.

  2. Thermoanalytical and Fourier transform infrared spectral curve-fitting techniques used to investigate the amorphous indomethacin formation and its physical stability in Indomethacin-Soluplus® solid dispersions.

    PubMed

    Lin, Shan-Yang; Lin, Hong-Liang; Chi, Ying-Ting; Huang, Yu-Ting; Kao, Chi-Yu; Hsieh, Wei-Hsien

    2015-12-30

    The amorphous form of a drug has higher water solubility and faster dissolution rate than its crystalline form. However, the amorphous form is less thermodynamically stable and may recrystallize during manufacturing and storage. Maintaining the amorphous state of drug in a solid dosage form is extremely important to ensure product quality. The purpose of this study was to quantitatively determine the amount of amorphous indomethacin (INDO) formed in the Soluplus® solid dispersions using thermoanalytical and Fourier transform infrared (FTIR) spectral curve-fitting techniques. The INDO/Soluplus® solid dispersions with various weight ratios of both components were prepared by air-drying and heat-drying processes. A predominate IR peak at 1683cm(-1) for amorphous INDO was selected as a marker for monitoring the solid state of INDO in the INDO/Soluplus® solid dispersions. The physical stability of amorphous INDO in the INDO/Soluplus® solid dispersions prepared by both drying processes was also studied under accelerated conditions. A typical endothermic peak at 161°C for γ-form of INDO (γ-INDO) disappeared from all the differential scanning calorimetry (DSC) curves of INDO/Soluplus® solid dispersions, suggesting the amorphization of INDO caused by Soluplus® after drying. In addition, two unique IR peaks at 1682 (1681) and 1593 (1591)cm(-1) corresponded to the amorphous form of INDO were observed in the FTIR spectra of all the INDO/Soluplus® solid dispersions. The quantitative amounts of amorphous INDO formed in all the INDO/Soluplus® solid dispersions were increased with the increase of γ-INDO loaded into the INDO/Soluplus® solid dispersions by applying curve-fitting technique. However, the intermolecular hydrogen bonding interaction between Soluplus® and INDO were only observed in the samples prepared by heat-drying process, due to a marked spectral shift from 1636 to 1628cm(-1) in the INDO/Soluplus® solid dispersions. The INDO/Soluplus® solid dispersions prepared by both drying processes could keep the amorphous state of INDO in the INDO/Soluplus® solid dispersions at the accelerated storage condition. PMID:26481469

  3. Kinetics of electrochemically controlled surface reactions on bulk and thin film metals studied with Fourier transform impedance spectroscopy and surface plasmon resonance techniques

    NASA Astrophysics Data System (ADS)

    Assiongbon, Kankoe A.

    2005-07-01

    In the work presented in this thesis, the surface sensitive electrochemical techniques of cyclic voltametry (CV), potential step (PS) and Fourier transform impedance spectroscopy (FT-EIS), as well as the optical technique of surface plasmon resonance (SPR), were used to probe a wide variety of surface processes at various metal/liquid interface. Three polycrystalline metals (Au, Ta and Cu) and a Cr-coated gold film were used for these studies in different aqueous environments. A combination of CV with FT-EIS and PS was used to investigate electronic and structural proprieties of a modified bulk electrode of Au. This experimental system involved under potential deposition (UPD) of Bi3+ on Au in a supporting aqueous electrolyte containing ClO-4 . UPD range of Bi3+ was determined, and adsorption kinetics of Bi3+ in the presence of coadsorbing anion, ClO-4 were quantified. Potentiodynamic growth of oxide films of Ta in the following electrolytes NaNO3, NaNO3 + 5wt% H2O2, NaOH and NaOH + 5wt% H2O2 had been investigated. The oxide films were grown in the range -0.1 → +0.4V (high electric field) at a scan rate of 10 mV/s. Time resolved A.C. impedance spectroscopy measurements in the frequency range (0.1--20 KHz) were performed to characterize the surface reactions of oxide formation. The results are interpreted in terms of charge conductivity O2- through the oxide film, and disintegration of H2O2 into OH-. In a high pH medium (pH 12), dissociation of H2O2 was catalytically enhanced. This led to destabilization of the electrogenerated tantalum oxide surface film in the form of a soluble hexatantalate species. In contrast with the electrolytes, NaNO3, NaNO3 + 5wt% H2O2, NaOH, where only the oxide growth was observed, the A.C. impedance spectroscopy measurements in NaOH + 5wt% H 2O2 showed competition between oxide formation and its removal. These results are relevant for chemical slurry design in chemical mechanical polishing (CMP) of Ta. Further investigations were performed by studying potential galvanic corrosion effects that are susceptible to occur during planarization process in CMP technology. A combination of FT-EIS with potentiodynamic polarization and galvanic current measurements showed evidence of these effects when Cu (interconnected material in integrated circuits) and Ta (barrier material) were brought into electrical contact via abrasive-free polishing solutions. Quantitative analyses of kinetics of these effects were performed. Catalytic activity of a thin film Au (˜40 nm) toward methanol oxidation in alkaline medium for direct methanol fuel cell (DMFC) was carried out in this part of the work. A relatively unique combined technique of FT-EIS and SPR was used to perform this study. The FT-EIS data provided detailed kinetic parameters that characterize electro-oxidation of methanol. This led to a quantitative understanding of the mechanism of the probed surface reactions. At the same time, the SPR data provided with high accuracy the optical parameters and electronic characteristics of the thin film Au. The combined technique provided a complete understanding of the observed surface reactions, and showed consistency in data.

  4. 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.

  5. Code synchronization based on lumped time-delay compensation scheme with a linearly chirped fiber Bragg grating in all-optical analog-to-digital conversion

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Kang, Zhe; Yuan, Jin-Hui; Tian, Ye; Yan, Bin-Bin; Sang, Xin-Zhu; Yu, Chong-Xiu

    2014-10-01

    We propose a novel lumped time-delay compensation scheme for all-optical analog-to-digital conversion based on soliton self-frequency shift and optical interconnection techniques. A linearly chirped fiber Bragg grating is optimally designed and used to compensate for the entire time-delays of the quantized pulses precisely. Simulation results show that the compensated coding pulses are well synchronized with a time difference less than 3.3 ps, which can support a maximum sampling rate of 151.52 GSa/s. The proposed scheme can efficiently reduce the structure complexity and cost of all-optical analog-to-digital conversion compared to the previous schemes with multiple optical time-delay lines.

  6. Jarosite as a Storage Mineral for Small Organic Molecules: Investigations of Natural Samples Using an 'In Situ' Laser Desorption Fourier Transform Mass Spectrometry Technique

    NASA Astrophysics Data System (ADS)

    Kotler, J. M.; Hinman, N. W.; Yan, B.; Stoner, D. L.; Scott, J. R.

    2007-03-01

    The use of laser desorption Fourier transform mass spectrometry has revealed the presence of organic matter in several jarosite samples from various locations worldwide including jarosite precipitated in the lab by acidothiobacillus ferroxidans.

  7. Energy and angular differential probabilities for photoionization of He using chirped attosecond soft-x-ray pulses

    SciTech Connect

    Lee, Teck-Ghee; Pindzola, M. S.; Robicheaux, F.

    2009-05-15

    Based on the time-dependent close-coupling method, energy and angular differential probabilities for various ionization processes of He atoms subjected to intense attosecond soft-x-ray pulses with a photon energy of 91.6 eV and a peak intensity of 10{sup 15} W/cm{sup 2} are calculated to explore their dependence on the duration and the chirp of the pulse. It is found that the single and the double electron energy distributions for two-photon double ionization are rather sensitive to chirps. That is, both the magnitudes and locations of the sequential peaks in the single electron energy distributions vary strongly with chirps and the two-electron energy distributions being broadened and stretched along the equal energy sharing direction as opposed to the usual total excess energy direction for the case of zero chirp. In addition, our calculation also reveals an unexpected structure formed between the two sequential peaks. In order to better understand the chirp effects on both independent-electron and correlated electron emissions and their relations to the origin of the structure, we analyzed the corresponding probability differential in energy and angle.

  8. Generation of green frequency comb from chirped χ(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) χ(2) nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 μm to 7.1 μm. 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.

  9. Generation of green frequency comb from chirped χ{sup (2)} nonlinear photonic crystals

    SciTech Connect

    Lai, C.-M.; Chang, K.-H.; Yang, Z.-Y.; Fu, S.-H.; Tsai, S.-T.; Hsu, C.-W.; Peng, L.-H.; Yu, N. E.; Boudrioua, A.; Kung, A. H.

    2014-12-01

    Spectrally broad frequency comb generation over 510–555 nm range was reported on chirped quasi-phase-matching (QPM) χ{sup (2)} nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 μm to 7.1 μm. 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.

  10. Brewster-angled chirped mirrors for high-fidelity dispersion compensation and bandwidths exceeding one optical octave

    NASA Astrophysics Data System (ADS)

    Steinmeyer, G.

    2003-09-01

    A novel design approach for dispersion-compensating chirped mirrors with greater-than-octave bandwidth is proposed. The commonly encountered problem of dispersion ripple is overcome by impedance matching via Brewster incidence in respect to the top-layer coating material. This approach totally suppresses undesired reflections off the interface to the ambient medium without any need for complicated matching sections. It is shown that Brewster-angled chirped mirrors can deliver ultrabroadband dispersion compensation over a much wider bandwidth than conventional doublechirped mirrors and without the mechanical complexity of back-deposition approaches. Due to their relatively simple structure, the sensitivity of the dispersion of the Brewster-angled designs towards growth errors is greatly reduced. Therefore, this new generation of chirped mirrors appears ideal for compression of continuum pulses with a potential of pulse durations in the single-cycle regime.

  11. Isolated few-cycle radiation from chirped-pulse compression of a superradiant free-electron laser

    NASA Astrophysics Data System (ADS)

    Huang, Yen-Chieh; Zhang, Zhen; Chen, Chia-Hsiang; Wu, Ming-Hsiung

    2015-08-01

    When a short electron bunch traverses an undulator to radiate a wavelength longer than the bunch length, intense superradiance from the electron bunch can quickly deplete the electron's kinetic energy and lead to generation of an isolated chirped radiation pulse. Here, we develop a theory to describe this novel chirped pulse radiation in a superradiant free-electron laser and show the opportunity to generate isolated few-cycle high-power radiation through chirped-pulse compression after the undulator. The theory is completely characterized by how fast the electron energy is depleted for a given length of an undulator. We further present two design examples at the THz and extreme-ultraviolet wavelengths and numerically generate isolated three- and nine-cycle radiation pulses, respectively.

  12. Ultrafast single-electron transfer in coupled quantum dots driven by a few-cycle chirped pulse

    SciTech Connect

    Yang, Wen-Xing; Chen, Ai-Xi; Bai, Yanfeng; Lee, Ray-Kuang

    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.

  13. Spectroscopy of the hydrogen 1 S -3 S transition with chirped laser pulses

    NASA Astrophysics Data System (ADS)

    Yost, D. C.; Matveev, A.; Grinin, A.; Peters, E.; Maisenbacher, L.; Beyer, A.; Pohl, R.; Kolachevsky, N.; Khabarova, K.; Hänsch, T. W.; Udem, Th.

    2016-04-01

    We identify a systematic present in two-photon direct frequency comb spectroscopy (DFCS) which is a result of chirped laser pulses and is a manifestation of the first-order Doppler effect. We carefully analyze this systematic and propose methods for its mitigation within the context of our measurement of the hydrogen 1 S -3 S transition. We also report on our determination of the absolute frequency of this transition, which is comparable to a previous measurement using continuous-wave spectroscopy [O. Arnoult et al., Eur. Phys. J. D 60, 243 (2010), 10.1140/epjd/e2010-00249-6], but was obtained with a different experimental method.

  14. Inducing changes in the bond length of diatomic molecules by time-symmetric chirped pulses

    SciTech Connect

    Chang, Bo Y.; Shin, Seokmin; Sola, Ignacio R.

    2010-12-15

    We show numerically that it is possible to change the structure of a simple molecule, that is, a diatomic molecule, where the bond length is modified at a precise timing with symmetrically chirped laser pulses. In the adiabatic regime, the process is fully time reversible, making it possible to design slow vibrations with large bond elongations. The scheme relies on the preparation of a separable state of both nuclear and electronic degrees of freedom with predominant amplitude on the dissociative (antibonding) electronic wave function. Shorter laser pulses can be used to dynamically induce larger bond elongations, preparing a highly excited vibrational wave packet in the ground potential as the laser is switched off.

  15. Controlling the spectral shape of nonlinear Thomson scattering with proper laser chirping

    NASA Astrophysics Data System (ADS)

    Rykovanov, S. G.; Geddes, C. G. R.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.

    2016-03-01

    Effects of nonlinearity in Thomson scattering of a high intensity laser pulse from electrons are analyzed. Analytic expressions for laser pulse shaping in frequency (chirping) are obtained which control spectrum broadening for high laser pulse intensities. These analytic solutions allow prediction of the spectral form and required laser parameters to avoid broadening. Results of analytical and numerical calculations agree well. The control over the scattered radiation bandwidth allows narrow bandwidth sources to be produced using high scattering intensities, which in turn greatly improves scattering yield for future x- and gamma-ray sources.

  16. Degenerated optical parametric chirped-pulse amplification with cesium lithium borate

    NASA Astrophysics Data System (ADS)

    Zhao, Baozhen; Liang, Xiaoyan; Leng, Yuxin; Jiang, Yongliang; Wang, Cheng; Lu, Haihe; Du, Juan; Xu, Zhizhan; Shen, Dezhong

    2006-01-01

    A gain amplifier for degenerated optical parametric chirped-pulse amplification (OPCPA) with lithium triborate and cesium lithium borate (CLBO) crystals was demonstrated in a near-collinear configuration. The signal gain of the final energy amplifier with CLBO was ˜6. After compression, the 123 fs pulse duration was obtained. Compared with potassium dihydrogen phosphate, it is confirmed that CLBO is more effective as a nonlinear crystal in a final power amplifier for terawatt or petawatt OPCPA systems. To our knowledge, this is the first demonstration of OPCPA with CLBO.

  17. Degenerated optical parametric chirped-pulse amplification with cesium lithium borate.

    PubMed

    Zhao, Baozhen; Liang, Xiaoyan; Leng, Yuxin; Jiang, Yongliang; Wang, Cheng; Lu, Haihe; Du, Juan; Xu, Zhizhan; Shen, Dezhong

    2006-01-20

    A gain amplifier for degenerated optical parametric chirped-pulse amplification (OPCPA) with lithium triborate and cesium lithium borate (CLBO) crystals was demonstrated in a near-collinear configuration. The signal gain of the final energy amplifier with CLBO was approximately 6. After compression, the 123 fs pulse duration was obtained. Compared with potassium dihydrogen phosphate, it is confirmed that CLBO is more effective as a nonlinear crystal in a final power amplifier for terawatt or petawatt OPCPA systems. To our knowledge, this is the first demonstration of OPCPA with CLBO. PMID:16463743

  18. Chirped laser dispersion spectroscopy using a directly modulated quantum cascade laser

    SciTech Connect

    Hangauer, Andreas Nikodem, Michal; Wysocki, Gerard; Spinner, Georg; Institute for Quantum Electronics, ETH Zurich, 8093 Zurich

    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.

  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. High-power pre-chirp managed amplification of femtosecond pulses at high repetition rates

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Li, Wenxue; Zhao, Jian; Bai, Dongbi; Luo, Daping; Zeng, Heping

    2015-06-01

    Femtosecond pulses at 250 MHz repetition rate from a mode-locked fiber laser are amplified to high power in a pre-chirp managed amplifier. The experimental strategy offers a potential towards high-power ultrashort laser pulses at high repetition rates. By investigating the laser pulse evolution in the amplification processes, we show that self-similar evolution, finite gain bandwidth and mode instabilities determine pulse characteristics in different regimes. Further average power scaling is limited by the mode instabilities. Nevertheless, this laser system enables us to achieve sub-50 fs pulses with an average power of 93 W.

  1. High-Gain Regenerative Chirped-Pulse Amplifier Using Photonic Crystal Rod Fiber

    NASA Astrophysics Data System (ADS)

    Ogino, Jumpei; Sueda, Keiichi; Kurita, Takashi; Kawashima, Toshiyuki; Miyanaga, Noriaki

    2013-12-01

    We have demonstrated a high-gain regenerative chirped-pulse amplifier (CPA) using an Yb-doped photonic crystal rod fiber of 100 µm core diameter. The input pulse energy is 150 nJ in a pulse width of 2.5 ns at a repetition rate of 1 kHz with a central wavelength of 1053 nm. At a pump power of 13.2 W, the amplified pulse energy is 0.26 mJ, yielding a gain of 1700.

  2. Long-period grating assisted fractional differentiation of highly chirped light pulses

    NASA Astrophysics Data System (ADS)

    Poveda-Wong, L.; Carrascosa, A.; Cuadrado-Laborde, C.; Cruz, J. L.; Díez, A.; Andrés, M. V.

    2016-03-01

    We experimentally demonstrate the possibility to perform a fractional differentiation of arbitrary order on a given light pulse by propagation through a single long-period grating. A simple analytical expression is obtained also, relating the fractional order of differentiation with the parameters of the long-period grating. A secant hyperbolic like pulse of 23 ps time width with a chirp parameter of -30 was successfully fractionally differentiated to the 0.5th order. The proposal was corroborated experimentally and numerically. The device may find applications in real time phase recovery.

  3. Laser Control of Chemical Dynamics. I. Control of Electronic Transitions by Quadratic Chirping

    NASA Astrophysics Data System (ADS)

    Zou, S.; Kondorskiy, A.; Mil'nikov, G.; Nakamura, H.

    An effective scheme for the laser control of wavepacket dynamics applicable to systems with many degrees of freedom is discussed. It is demonstrated that specially designed quadratically chirped pulses can be used to achieve fast and near-complete excitation of the wavepacket without significantly distorting its shape. The parameters of the laser pulse can be estimated analytically from the Zhu-Nakamura (ZN) theory of nonadiabatic transitions. The scheme is applicable to various processes, such as simple electronic excitations, pump-dumps, and selective bond-breaking, and, taking diatomic and triatomic molecules as examples, it is actually shown to work well.

  4. 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

  5. Intensity-modulated refractometer with long period fiber grating cascaded by chirped fiber grating

    NASA Astrophysics Data System (ADS)

    Yang, Jingyi; Dong, Xinyong; Chen, Li Han; Zheng, Yangzi; Chan, Chi Chu; So, Ping Lam

    2015-09-01

    An intensity-modulated refractometer is proposed and experimentally demonstrated by using a long period fiber grating (LPG) cascaded with a chirped-fiber Bragg grating (CFBG). The reflection wavelength band of the CFBG was properly selected to contain the most sensitive spectral part of the LPG. As a result, intensity of the reflected signal was modulated linearly by refractive index (RI) of surrounding liquid outside the LPG. RI measurement in a range from 1.33 to ~1.45 was realized with enhanced sensitivity up to 48.93 μW/R.I.U.

  6. Electron acceleration by a bichromatic chirped laser pulse in underdense plasmas

    NASA Astrophysics Data System (ADS)

    Pocsai, M. A.; Varró, S.; Barna, I. F.

    2016-02-01

    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 nm . 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 λ = 800 nm wavelength pulse. We performed calculations both for plane wave and Gaussian pulses.

  7. Effects of Detuning on Control of Intersubband Quantum Well Transitions with Chirped Electromagnetic Pulses

    SciTech Connect

    Blekos, Konstantinos; Terzis, Andreas F.; Simserides, Constantinos; Paspalakis, Emmanuel

    2010-11-10

    We study the interaction of a chirped electromagnetic pulse with intersubband transitions of a double semiconductor quantum well. We specifically consider the interaction of the ground and first excited subbands with the electromagnetic field and use the nonlinear density matrix equations for the description of the system dynamics. These equations are solved numerically for various values of the electron sheet density for a realistic double GaAs/AlGaAs quantum well, and the efficiency of population transfer is discussed with emphasis given to the effects of the detuning of the central frequency of the electromagnetic field from resonance.

  8. High-energy noncollinear optical parametric-chirped pulse amplification in LBO at 800 nm.

    PubMed

    Xu, Lu; Yu, Lianghong; Liang, Xiaoyan; Chu, Yuxi; Hu, Zhanggui; Ma, Lin; Xu, Yi; Wang, Cheng; Lu, Xiaoming; Lu, Haihe; Yue, Yinchao; Zhao, Ying; Fan, Feidi; Tu, Heng; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan

    2013-11-15

    The optical parametric-chirped pulse amplification (OPCPA) based on large-aperture nonlinear optical crystals is promising for implementation of an ultrahigh peak-power laser system of 10 PW and beyond. We demonstrated the highest energy broadband OPCPA at 800 nm, to the best of our knowledge, by using an 80 mm in diameter LiB(3)O(5)(LBO) amplifier, with an output energy of 28.68 J, a bandwidth of 80 nm (FWHM), and conversion efficiency of 25.38%. After compression, a peak power of 0.61 PW with 33.8 fs pulse duration is produced. PMID:24322145

  9. Covariance-Based Direction-of-Arrival Estimation of Wideband Coherent Chirp Signals via Sparse Representation

    PubMed Central

    Sha, Zhichao; Liu, Zhengmeng; Huang, Zhitao; Zhou, Yiyu

    2013-01-01

    This paper addresses the problem of direction-of-arrival (DOA) estimation of multiple wideband coherent chirp signals, and a new method is proposed. The new method is based on signal component analysis of the array output covariance, instead of the complicated time-frequency analysis used in previous literatures, and thus is more compact and effectively avoids possible signal energy loss during the hyper-processes. Moreover, the a priori information of signal number is no longer a necessity for DOA estimation in the new method. Simulation results demonstrate the performance superiority of the new method over previous ones. PMID:23995096

  10. 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...

  11. Generation of 0.3 mW high-power broadband terahertz pulses from GaP crystal pumped by negatively chirped femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Li, Jiang; Chai, Lu; Shi, Junkai; Liu, Feng; Liu, Bowen; Xu, Baozhong; Hu, Minglie; Li, Yanfeng; Xing, Qirong; Wang, Chingyue; Fedotov, A. B.; Zheltikov, A. M.

    2013-12-01

    Based on optical rectification in a 3 mm GaP crystal with a femtosecond photonic crystal fiber amplifier as the pump source, a detailed experimental investigation on the influence of the chirp characteristics of the pump pulses on the THz wave generation efficiency is conducted. It is shown that a higher THz generation efficiency can be achieved using negatively chirped pulses rather than de-chirped pulses. In the chosen geometry, using 21 W pump pulses with a negative chirp of -2.3 10-3 ps2, broadband THz radiation with an average power of 0.3 mW is obtained, which is, to the best of our knowledge, the highest value reported so far for high-repetition-rate THz pulses generated by collinear optical rectification. The higher THz generation efficiency by negatively chirped pulses is explained by a pulse-narrowing mechanism in the nonlinear crystal.

  12. Spectrum bandwidth narrowing of Thomson scattering X-rays with energy chirped electron beams from laser wakefield acceleration

    SciTech Connect

    Xu, Tong; Chen, Min Li, Fei-Yu; Yu, Lu-Le; Sheng, Zheng-Ming; SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG ; Zhang, Jie; Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190

    2014-01-06

    We study incoherent Thomson scattering between an ultrashort laser pulse and an electron beam accelerated from a laser wakefield. The energy chirp effects of the accelerated electron beam on the final radiation spectrum bandwidth are investigated. It is found that the scattered X-ray radiation has the minimum spectrum width and highest intensity as electrons are accelerated up to around the dephasing point. Furthermore, it is proposed that the electron acceleration process inside the wakefield can be studied by use of 90° Thomson scattering. The dephasing position and beam energy chirp can be deduced from the intensity and bandwidth of the scattered radiation.

  13. Processing advantages of linear chirped fiber Bragg gratings in the time domain realization of optical frequency-domain reflectometry.

    PubMed

    Saperstein, R E; Alic, N; Zamek, S; Ikeda, K; Slutsky, B; Fainman, Y

    2007-11-12

    The inclusion of a linear chirped fiber Bragg grating for short pulse dispersion is shown to enhance the time domain realization of optical frequency-domain reflectometry. A low resolution demonstrator is constructed with single surface scans containing 140 resolvable spots. The system dynamic range meets that shown in earlier demonstrations without digital post-processing for signal linearization. Using a conjugate pair of chirped pulses created by the fiber grating, ranging is performed with position and velocity information decoupled. Additionally, by probing the target with short pulses and introducing grating dispersion just before photodetection, velocity immune ranging is demonstrated. PMID:19550832

  14. Full-Field Spectroscopy at Megahertz-frame-rates: Application of Coherent Time-Stretch Transform

    NASA Astrophysics Data System (ADS)

    DeVore, Peter Thomas Setsuda

    Outliers or rogue events are found extensively in our world and have incredible effects. Also called rare events, they arise in the distribution of wealth (e.g., Pareto index), finance, network traffic, ocean waves, and e-commerce (selling less of more). Interest in rare optical events exploded after the sighting of optical rogue waves in laboratory experiments at UCLA. Detecting such tail events in fast streams of information necessitates real-time measurements. The Coherent Time-Stretch Transform chirps a pulsed source of radiation so that its temporal envelope matches its spectral profile (analogous to the far field regime of spatial diffraction), and the mapped spectral electric field is slow enough to be captured by a real-time digitizer. Combining this technique with spectral encoding, the time stretch technique has enabled a new class of ultra-high performance spectrometers and cameras (30+ MHz), and analog-to-digital converters that have led to the discovery of optical rogue waves and detection of cancer cells in blood with one in a million sensitivity. Conventionally, the Coherent Time-Stretch Transform maps the spectrum into the temporal electric field, but the time-dilation process along with inherent fiber losses results in reduction of peak power and loss of sensitivity, a problem exacerbated by extremely narrow molecular linewidths. The loss issue notwithstanding, in many cases the requisite dispersive optical device is not available. By extending the Coherent Time-Stretch Transform to the temporal near field, I have demonstrated, for the first time, phase-sensitive absorption spectroscopy of a gaseous sample at millions of frames per second. As the Coherent Time-Stretch Transform may capture both near and far field optical waves, it is a complete spectro-temporal optical characterization tool. This is manifested as an amplitude-dependent chirp, which implies the ability to measure the complex refractive index dispersion at megahertz frame rates. This technique is not only four orders of magnitude faster than even the fastest (kHz) spectrometers, but will also enable capture of real-time complex dielectric function dynamics of plasmas and chemical reactions (e.g. combustion). It also has applications in high-energy physics, biology, and monitoring fast high-throughput industrial processes. Adding an electro-optic modulator to the Time-Stretch Transform yields time-to-time mapping of electrical waveforms. Known as TiSER, it is an analog slow-motion processor that uses light to reduce the bandwidth of broadband RF signals for capture by high-sensitivity analog-to-digital converters (ADC). However, the electro-optic modulator limits the electrical bandwidth of TiSER. To solve this, I introduced Optical Sideband-only Amplification, wherein electro-optically generated modulation (containing the RF information) is amplified at the expense of the carrier, addressing the two most important problems plaguing electro-optic modulators: (1) low RF bandwidth and (2) high required RF drive voltages. I demonstrated drive voltage reductions of 5x at 10 GHz and 10x at 50 GHz, while simultaneously increasing the RF bandwidth.

  15. Chirped pulse amplification in x-ray free-electron lasers

    NASA Astrophysics Data System (ADS)

    Dacasa, Hugo; Mahieu, Benoît; Fajardo, Marta; Le, Thuy T. T.; Li, Lu; Oliva, Eduardo; Zeitoun, Philippe

    2015-09-01

    X-ray free-electron lasers (FELs) are powerful tools for probing matter properties down to sub-nanometer scales with femtosecond time resolution, allowing a growing number of physical, chemical, biological and medical investigations to be carried out. FELs operating in seeding mode intrinsically present enhanced temporal coherence properties with respect to those relying on the self-amplified spontaneous emission (SASE) process. They are however limited, for the moment, to extreme ultraviolet (XUV) wavelengths, or in some cases to soft X-rays, and durations of tens of femtoseconds. We studied how these limits can be overcome by means of X-ray chirped pulse amplification, inspired by infrared lasers. As a matter of fact, the use of a seed enables a fine control of the chirp and a spectro-temporal shaping of the FEL emission. Moreover, ultrashort wavelengths can be envisaged through schemes of high-gain harmonic generation and echo-enabled harmonic generation. We will present FEL simulations coupled with the study of a compressor in conical diffraction geometry.

  16. Curvature-Induced Bunch Self-Interaction for an Energy-Chirped Bunch in Magnetic Bends

    SciTech Connect

    Li, Rui

    2008-02-01

    Within the realm of classical electrodynamics, the curvature-induced bunch collective interaction in magnetic bends can be studied using effective forces in the canonical formulation of the coherent synchrotron radiation (CSR) effect. As an application of this canonical formulation, in this paper, for an electron distribution moving ultrarelativistically in a bending system, the dynamics of the particles in the distribution is derived from the Hamiltonian of the particles in terms of the bunch internal coordinates. The consequent Vlasov equation manifests explicitly how the phase-space distribution is perturbed by the effective CSR forces. In particular, we study the impact of an initial linear energy chirp of the bunch on the behavior of the effective longitudinal CSR force, which arises due to the modification of the retardation relation as a result of the energy-chirping- induced longitudinal-horizontal correlation of the bunch distribution (bunch tilt) in dispersive regions. Our study demonstrates clearly the time delay (or retardation) of the behavior of the effective longitudinal CSR force on a bunch in responding to the change of the bunch length in a magnetic bend. Our result also shows that the effective longitudinal CSR force for a bunch under full compression can have sensitive dependence on the transverse position of the test particle in the bunch for certain parameter regimes.

  17. Power limitations and pulse distortions in an Yb : KGW chirped-pulse amplification laser system

    SciTech Connect

    Kim, G H; Yang, J; Kulik, A V; Sall, E G; Chizhov, S A; Kang, U; Yashin, V E

    2013-08-31

    We have studied self-action effects (self-focusing and self-phase modulation) and stimulated Raman scattering in an Yb : KGW chirped-pulse amplification laser system. The results demonstrate that self-focusing in combination with thermal lensing may significantly limit the chirped pulse energy in this system (down to 200 μJ) even at a relatively long pulse duration (50 ps). Nonlinear lenses in the laser crystals in combination with thermal lenses bring the regenerative amplifier cavity in the laser system to the instability zone and limit the average output power at pulse repetition rates under 50 kHz. Self-phase modulation, a manifestation of self-action, may significantly distort a recompressed femtosecond pulse at energies near the self-focusing threshold. Stimulated Raman scattering in such a laser has a weaker effect on output parameters than do self-focusing and thermal lensing, and Raman spectra are only observed in the case of pulse energy instability. (nonlinear optical phenomena)

  18. Acetylene measurement in flames by chirp-based quantum cascade laser spectrometry.

    PubMed

    Quine, Zachary R; McNesby, Kevin L

    2009-06-01

    We have designed and characterized a mid-IR spectrometer built around a pulsed distributed-feedback quantum cascade laser using the characteristic frequency down-chirp to scan through the spectral region 6.5 cm(-1) spectral region. The behavior of this chirp is extensively measured. The accuracy and detection limits of the system as an absorption spectrometer are demonstrated first by measuring spectra of acetylene through a single pass 16 cm absorption cell in real time at low concentrations and atmospheric pressure. The smallest detectable peak is measured to be approximately 1.5 x 10(-4) absorbance units, yielding a minimum detectable concentration length product of 2.4 parts per million meter at standard temperature and pressure. This system is then used to detect acetylene within an ethylene-air opposed flow flame. Measurements of acetylene content as a function of height above the fuel source are presented, as well as measurements of acetylene produced in fuel breakdown as a function of preinjection fuel temperature. PMID:19488121

  19. Compact, all-PM fiber-CPA system based on a chirped volume Bragg grating

    NASA Astrophysics Data System (ADS)

    Sobon, Grzegorz; Krzempek, Karol; Tarka, Jan; Sotor, Jaroslaw

    2016-01-01

    We demonstrate the chirped pulse amplification (CPA) of ultrashort pulses in a compact setup utilizing a chirped volume Bragg grating (CVBG) at 1560 nm wavelength. The system comprises a seed laser, dual-stage fiber amplifier and one CVBG, which is used as a stretcher and compressor simultaneously. The pulses from the low-power oscillator were amplified to 1 W of average power at a 50 MHz repetition rate with a pulse duration of 2.44 ps. The setup utilizes only polarization maintaining (PM) fibers and components, which ensures excellent stability and immunity to external disturbances. The output beam is linearly polarized with excellent geometrical quality (M 2 parameter close to 1). The usage of CVBG instead of classical grating-based stretchers and compressors allows the reduction of the complexity of the CPA system and minimizes its footprint. Such a simple and compact setup might be used as a pump source for nonlinear frequency conversion or mid-infrared supercontinuum generation.

  20. High flatness optical frequency comb generator based on the chirping of modulators

    NASA Astrophysics Data System (ADS)

    Qu, Kun; Zhao, Shanghong; Liang, Dan Ya; Zhu, Zihang; Dong, Chen; Li, Xuan

    2016-04-01

    A novel scheme for generation of an optical frequency comb (OFC) based on the chirping of two cascaded modulators is proposed. The first modulator is a dual-electrode Mach-Zehnder modulator (MZM), while the other modulator is an integrated MZM composed of two parallel MZMs that increases the number of comb lines. Our modified scheme can generate a large number of frequency lines with excellent flatness by simply modifying the chirp factor, and it is shown that up to 54 frequency lines could be observed. Theoretical analysis and simulation results show that under the variety of conditions that can be used in this scheme, the power fluctuations of the OFC lines are less than 0.5 dB in all cases; these results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness. Additionally, our modified scheme has the merit of tunable frequency spacing, which is practical for experimental realization of the OFC.

  1. Optical frequency comb generation based on chirping of Mach-Zehnder Modulators

    NASA Astrophysics Data System (ADS)

    Hmood, Jassim K.; Emami, Siamak D.; Noordin, Kamarul A.; Ahmad, Harith; Harun, Sulaiman W.; Shalaby, Hossam M. H.

    2015-06-01

    A new approach for the generation of an optical frequency comb, based on chirping of modulators, is proposed and numerically demonstrated. The setup includes two cascaded Mach-Zehnder Modulators (MZMs), a sinusoidal wave oscillator, and an electrical time delay. The first MZM is driven directly by a sinusoidal wave, while the second MZM is driven by a delayed replica of the sinusoidal wave. A mathematical model of the proposed system is formulated and modeled using the Matlab software. It is shown that the number of the frequency lines is directly proportional to the chirp factor. In order to achieve the highest number of frequency comb lines with the best flatness, the time delay between the driving voltages of the two MZMs is optimized. Our results reveal that at least 51 frequency lines can be observed at the output spectrum. In addition, 27 of these lines have power fluctuations of less than 1 dB. The performance of the proposed system is also simulated using a split-step numerical analysis. An optical frequency comb, with tunable frequency spacing ranging from 5 to 40 GHz, is successfully generated.

  2. Gas Analysis by Fourier Transform Mm-Wave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Harris, Brent J.; Steber, Amanda L.; Lehmann, Kevin K.; Pate, Brooks H.

    2013-06-01

    Molecular rotational spectroscopy of low pressure, room temperature gases offers high chemical selectivity and sensitivity with the potential for a wide range of applications in gas analysis. A strength of the technique is the potential to identify molecules that have not been previously studied by rotational spectroscopy by comparing experimental results to predictions of the spectroscopic parameters from quantum chemistry -6 so called library-free detection. The development of Fourier transform mm-wave spectrometers using high peak power (30 mW) active multiplier chain mm-wave sources brings new measurement capabilities to the analysis of complex gas mixtures. Strategies for gas analysis based on high-throughput mm-wave spectroscopy and arbitrary waveform generator driven mm-wave sources are described. Several new measurement capabilities come from the intrinsic time-domain measurement technique. High-sensitivity double-resonance measurements can be performed to speed the analysis of a complex gas sample containing several species. This technique uses a "pi-pulse" to selectively invert the population of two selected rotational energy levels and the effect of this excitation pulse on all other transitions in the spectrometer operating range is monitored using segmented chirped-pulse Fourier transform spectroscopy. This method can lead to automated determination of the molecular rotational constants. Rapid pulse duration scan experiments can be used to estimate the magnitude and direction of the dipole moment of the molecule from an unknown spectrum. Coherent pulse echo experiments, using the traditional Hahn sequence or two-color population recovery methods, can be used to determine the collisional relaxation rate of the unknown molecule. This rate determination improves the ability to estimate the mass of the unknown molecule from the determination of the Doppler dephasing rate. By performing a suite of automated, high-throughput measurements, there is the potential to determine the shape (via the rotational constant), electric properties (the dipole moments and its direction in the principal axis system), and the mass of the molecule to aid its identification.

  3. Conformers of β-aminoisobutyric acid probed by jet-cooled microwave and matrix isolation infrared spectroscopic techniques

    NASA Astrophysics Data System (ADS)

    Kuş, N.; Sharma, A.; Peña, I.; Bermúdez, M. C.; Cabezas, C.; Alonso, J. L.; Fausto, R.

    2013-04-01

    β-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. Novel Applications of Chirp Managed Laser in Optical Fiber Communication Systems

    NASA Astrophysics Data System (ADS)

    Jia, Wei

    Nowadays, with the dramatically growing bandwidth requirement of Internet, the number of wavelength division multiplexing (WDM) channels of the optical fiber communication systems is increasing rapidly. Hence, optical transmitters with cost effectiveness, high power efficiency, and excellent transmission performance are necessary. Especially, for access and metropolitan applications, simple configuration is the essential factor. The conventional optical transmitter is composed of a laser as continuous-wave (CW) source and one or more external modulators for modulation. However, the high insertion loss, large driving voltage, and extra cost of external modulator make it relatively bulky and power-hungry. Chirp managed laser (CML), comprising a directly modulated semiconductor laser (DML) and a passive optical filter, is an alternative promising transmitter candidate. It has the merits of smaller device size, lower cost, less power consumption, and higher fiber chromatic dispersion (CD) tolerance, compared with that based on external modulator. In this thesis, we have investigated several novel applications of CML in optical fiber communication systems, taking advantage of its unique phase modulating and spectral reshaping properties. These topics include optical return-to-zero (RZ) pulses generation using CML, M-ary RZ differential phase-shift-keying (RZ-DPSK) signals generation using CML, and enhanced CD tolerance of CML with pre-emphasis. These CML-based designs consume low power for less electrical pre-coding, require reduced or no external modulator, and show notable transmission performances. Optical RZ pulses generation using CML: RZ pulses have been widely used in optical fiber communication systems together with on-off-keying (OOK) and DPSK modulation formats, for its high robustness towards inter symbol interference (ISI) and nonlinear distortions. In this thesis, we propose and experimentally demonstrate the technique of 10-Gb/s optical RZ pulses generation using CML. No external modulator is used for pulse carving. The frequency of the sinusoidal driving signal is half the output RZ pulse rate. 70-km and 50-km error-free SSMF transmissions have been achieved for the 10-Gb/s 33%-duty-cycle and 67%-duty-cycle CML-RZ- pulses based RZ-DPSK signals, respectively. Later, we extend to demonstrate the scheme of 20-Gb/s RZ pulses generation using CML driven at one-fourth the output pulse rate and investigate the transmission performance of the 20-Gb/s CML-RZ-pulses based RZ-OOK signal. M-ary RZ-DPSK signals generation using CML: M-ary RZ-DPSK is an attractive modulation format in optical fiber long-haul transmission systems, due to the advantages of high receiver sensitivity, increased spectral efficiency, and strong robustness against fiber nonlinearities. In this thesis, we propose and experimentally demonstrate the techniques of RZ-DPSK, ¾-RZ-DQPSK, and RZ-DQPSK signals generation using CML. First, we generate the 10-Gb/s RZ-DPSK signal using CML and pulse carver. It does not require any differential encoder or phase modulator (PM). The CML-based RZ-DPSK signal shows 3-dB higher receiver sensitivity after 70-km SSMF transmission without dispersion compensation and comparable nonlinear tolerance performance, compared with that generated by PM. Next, this proposal is generalized to generate the 10-Gbaud RZ-DQPSK signal using CML and pulse carver. Compared with the complex pre-coding required for the MZM-based RZ-DQPSK transmitter, only a simple exclusive-or (XOR) encoder is needed for that based on CML. Later, we demonstrate the scheme of 10-Gbaud ¾-RZ-DQPSK signal generation using single CML, without the need for external pulse carver. In this new signal format, the symbols with a differential phase shift of 0 remain non-return-to-zero (NRZ), while those with differential phase shifts of 0.5pi, pi, and 1.5pi are RZ. Error-free transmission is realized over 60-km SSMF without optical signal-noise-ratio (OSNR) penalty. Finally, we demonstrate the technique of 10.709-Gbaud RZ-DQPSK signal generation using single CML, without the need for differential encoder, external modulator, or pulse carver. The full RZ-shape is orientated from the combined effect of the designated driving signal and the narrow-bandwidth filter in CML. It realizes 40-km SSMF transmission at bit-error-rate (BER) of 10-9 . Enhanced CD tolerance of CML with pre-emphasis: For optical access and metropolitan networks, CML is a promising transmitter for its low cost, compact footprint, low power consumption, and high CD tolerance. In this thesis, we propose and experimentally realize the 10-Gb/s 300-km SSMF transmission at BER of 10-9 using CML with a simple and passive pre-emphasis driver. The 10-Gb/s standard CML signal without pre-emphasis can only be transmitted up to 220 km, in comparison. No expensive optical dispersion compensation module (DCM) or power-hungry electronic dispersion compensation (EDC) technique is used. Later, we further demonstrate the 20-Gb/s 100-km SSMF transmission at BER of 10-9, using CML with pre-emphasis.

  5. Improved techniques for measuring physical and chemical transformations in the atmosphere: observations of pollution transport, wind shear, and profile evolution using controlled meteorological balloons.

    NASA Astrophysics Data System (ADS)

    Voss, P. B.; Zaveri, R. A.; Berkowitz, C. M.; Riddle, E. E.; Talbot, R. W.; Stohl, A.; Holcombe, D.; Hartley, T.

    2005-12-01

    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 long-range transport and transformation of urban pollution plumes. Balloon and aircraft observations (e.g., companion presentation by Zaveri et al.) in the quasi-Lagrangian reference frame shed light on photochemical processes (nighttime ozone loss) and show direct thermal effects of aerosols of sufficient magnitude to impact cloud formation, precipitation, and regional climate. Repeated balloons soundings in the core of the plumes provide measurements of transport, shear, and dispersion necessary interpret and quasi-Lagrangian observations. Implications for upcoming campaigns focused on the transport and transformation of urban air pollution (e.g., Mirage-Mex) will be discussed.

  6. Simple detuning method for low-chirp operation in polymer-based tunable external-cavity lasers.

    PubMed

    Choi, Byung-Seok; Jeong, Jong Sool; Lee, Hak-Kyu; Chung, Yun C

    2015-11-30

    We propose and demonstrate a simple detuning method for the low-chirp operation of a polymer-based tunable external-cavity laser (ECL). To ensure the low-chirp operation of this directly-modulated ECL, we first obtain the optimum values of the heater current applied to the polymer Bragg grating reflector (PBR) and the operating temperature of this ECL. For this purpose, we sweep the current applied to the phase control heater until the peak output power measured from the high-reflection (HR) coated facet reaches the minimum value. We then operate this ECL with minimum chirp by tuning the lasing mode to the longer wavelength limit of the stable operation region. This is because the detuned loading effect is maximized at this limit as the in-phase condition between the lights reflected from the PBR and anti-reflection (AR) coated facet of the gain medium is satisfied. Thus, by using this method together with conventional wavelength-locking algorithm, we can operate this ECL with minimum chirp at any wavelength. PMID:26698698

  7. Application of the newly constructed Chirp raw data recording system for shallow gas in the Korea Strait shelf mud off SE Korea

    NASA Astrophysics Data System (ADS)

    Kim, Young-Jun; Koo, Nam-Hyung; Chun, Jong-Hwa; Shin, Sung-Ryul; Cheong, Snons; Kim, Jeong-Ki; Lee, Ho-Young

    2014-05-01

    Chirp is a marine high-resolution sub-bottom profiling system applied in a variety of marine geological and geophysical fields. Chirp source systems generate the sweep pulse with a frequency modulation of 2 - 7 kHz bandwidth. Commercial Chirp data acquisition systems provide the seismic data of the envelope type without polarity and phase information after real-time processing. To record the raw data preserving the polarity and phase information, we constructed the new data acquisition system and acquired the field data in the southeastern coast of Korea using the newly constructed system and the conventional Chirp system simultaneously. The survey data contains the acoustic blanking caused by shallow gas and the feature of rough seafloor in KSSM(Korea Strait shelf mud) off SE Korea. We performed the correlation of raw seismic data with the estimated sweep signature, deconvolution, swell effect correction and migration to compare the resolution of Chirp SBP sections and to enhance the features associated with shallow gas. When we compare Chirp SBP section preserving polarity and phase information with the conventional envelope section, the new section shows better continuity of the sedimentary layers and higher resolution than conventional section. Through the thorough examination of the Chirp sections after the data processing, a possible gas related acoustic anomaly was found at the rough seafloor and underlying sediments. The low P-wave velocity was identified among the physical properties measured from a piston core recovered at the survey area.

  8. A real-time chirp-coded imaging system with tissue attenuation compensation.

    PubMed

    Ramalli, A; Guidi, F; Boni, E; Tortoli, P

    2015-07-01

    In ultrasound imaging, pulse compression methods based on the transmission (TX) of long coded pulses and matched receive filtering can be used to improve the penetration depth while preserving the axial resolution (coded-imaging). The performance of most of these methods is affected by the frequency dependent attenuation of tissue, which causes mismatch of the receiver filter. This, together with the involved additional computational load, has probably so far limited the implementation of pulse compression methods in real-time imaging systems. In this paper, a real-time low-computational-cost coded-imaging system operating on the beamformed and demodulated data received by a linear array probe is presented. The system has been implemented by extending the firmware and the software of the ULA-OP research platform. In particular, pulse compression is performed by exploiting the computational resources of a single digital signal processor. Each image line is produced in less than 20 μs, so that, e.g., 192-line frames can be generated at up to 200 fps. Although the system may work with a large class of codes, this paper has been focused on the test of linear frequency modulated chirps. The new system has been used to experimentally investigate the effects of tissue attenuation so that the design of the receive compression filter can be accordingly guided. Tests made with different chirp signals confirm that, although the attainable compression gain in attenuating media is lower than the theoretical value expected for a given TX Time-Bandwidth product (BT), good SNR gains can be obtained. For example, by using a chirp signal having BT=19, a 13 dB compression gain has been measured. By adapting the frequency band of the receiver to the band of the received echo, the signal-to-noise ratio and the penetration depth have been further increased, as shown by real-time tests conducted on phantoms and in vivo. In particular, a 2.7 dB SNR increase has been measured through a novel attenuation compensation scheme, which only requires to shift the demodulation frequency by 1 MHz. The proposed method characterizes for its simplicity and easy implementation. PMID:25749529

  9. 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.

  10. Broadband and broadangle SPP antennas based on plasmonic crystals with linear chirp

    NASA Astrophysics Data System (ADS)

    Bouillard, J.-S.; Vilain, S.; Dickson, W.; Wurtz, G. A.; Zayats, A. V.

    2012-11-01

    Plasmonic technology relies on the coupling of light to surface electromagnetic modes on smooth or structured metal surfaces. While some applications utilise the resonant nature of surface polaritons, others require broadband characteristics. We demonstrate unidirectional and broadband plasmonic antennas with large acceptance angles based on chirped plasmonic gratings. Near-field optical measurements have been used to visualise the excitation of surface plasmon polaritons by such aperiodic structures. These weakly aperiodic plasmonic crystals allow the formation of a trapped rainbow-type effect in a two-dimensional geometry as surface polaritons of different frequencies are coherently excited in different locations over the plasmonic structure. Both the crystal's finite size and the finite lifetime of plasmonic states are crucial for the generation of broadband surface plasmon polaritons. This approach presents new opportunities for building unidirectional, broadband and broad-angle plasmonic couplers for sensing purposes, information processing, photovoltaic applications and shaping and manipulating ultrashort optical pulses.

  11. Precision short-pulse damage test station utilizing optical parametric chirped-pulse amplification

    SciTech Connect

    Jovanovic, I; Brown, C; Wattellier, B; Nielsen, N; Molander, W; Stuart, B; Pennington, D; Barty, C J

    2004-03-22

    The next generation of high-energy petawatt (HEPW)-class lasers will utilize multilayer dielectric diffraction gratings for pulse compression, due to their high efficiency and high damage threshold for picosecond pulses. The peak power of HEPW lasers will be determined by the aperture and damage threshold of the final dielectric grating in the pulse compressor and final focusing optics. We have developed a short-pulse damage test station for accurate determination of the damage threshold of the optics used on future HEPW lasers. Our damage test station is based on a highly stable, high-beam-quality optical parametric chirped-pulse amplifier (OPCPA) operating at 1053 nm at a repetition rate of 10 Hz. We present the design of our OPCPA system pumped by a commercial Q-switched pump laser and the results of the full system characterization. Initial short-pulse damage experiments in the far field using our system have been performed.

  12. Short ring cavity swept source based on a highly reflective chirped FBG

    NASA Astrophysics Data System (ADS)

    Stancu, Radu-Florin; Podoleanu, Adrian

    2015-09-01

    An optical akinetic swept source (AKSS) at 1060 nm, comprising a 5 m length fiber ring cavity, a semiconductor optical amplifier (SOA) as gain medium, and a 98% reflective chirped fiber Bragg grating as a dispersive element, is described. Active mode-locking was achieved by directly modulating the current of the SOA with sinusoidal signal of frequency equal to 10 times and 20 times the cavity resonance frequency. In the static regime, linewidths as narrow as 60 pm and a tuning bandwidth of 30 nm were achieved, while a 2 mW output power, without any optical booster, was measured dynamically at a sweep speed of 100 kHz. The axial range of the AKSS was evaluated by scanning through the channeled spectrum of a Mach-Zehnder interferometer.

  13. An optical parametric chirped-pulse amplifier for seeding high repetition rate free-electron lasers

    SciTech Connect

    Höppner, H.; Tanikawa, T.; Schulz, M.; Riedel, R.; Teubner, U.; Faatz, B.; Tavella, F.

    2015-05-15

    High repetition rate free-electron lasers (FEL), producing highly intense extreme ultraviolet and x-ray pulses, require new high power tunable femtosecond lasers for FEL seeding and FEL pump-probe experiments. A tunable, 112 W (burst mode) optical parametric chirped-pulse amplifier (OPCPA) is demonstrated with center frequencies ranging from 720–900 nm, pulse energies up to 1.12 mJ and a pulse duration of 30 fs at a repetition rate of 100 kHz. Since the power scalability of this OPCPA is limited by the OPCPA-pump amplifier, we also demonstrate a 6.7–13.7 kW (burst mode) thin-disk OPCPA-pump amplifier, increasing the possible OPCPA output power to many hundreds of watts. Furthermore, third and fourth harmonic generation experiments are performed and the results are used to simulate a seeded FEL with high-gain harmonic generation.

  14. Direct Digital Synthesis Chirped Pulse Microwave Spectrometers for the Classroom and Research

    NASA Astrophysics Data System (ADS)

    Blake, Geoffrey; Carroll, Brandon; Finneran, Ian A.

    2015-06-01

    By combining the rapid development in direct digital synthesis circuitry and Field Programmable Gate Arrays (FPGAs) coupled to fast A/D samplers, it is possible to construct high performance chirped pulse microwave spectrometers suitable for gas-phase rotational spectroscopy experiments in undergraduate physical chemistry labs as well as graduate level research. The technology is highly tailorable, and sufficiently robust that extensive experimentation is feasible in the teaching environment. The time domain nature of the experiment has strong ties to concepts in Nuclear Magnetic Resonance (NMR) widely discussed in undergraduate curricula, and the software environment for the instrument control and spectral assignment can be integrated with ab initio quantum chemistry predictions of molecular structure and dynamics.

  15. Population transfer in the Na s-p Rydberg ladder by a chirped microwave pulse

    SciTech Connect

    Maeda, H.; Gurian, J. H.; Gallagher, T. F.

    2011-12-15

    While quantum defects of nl Rydberg states of Na with l{>=}2 are nearly equal to zero, the quantum defects of ns and np states of Na are quite large due to the finite size of its ionic core. Since the Na ns and np states are energetically isolated from the higher angular momentum states of the same n, we can think of the Na ns and np Rydberg states as a specific example of a simple multilevel ladder system consisting of only alternating s and p angular momentum states. Here we report that population transfer in the Na s-p Rydberg ladder can be effectively achieved using a frequency-chirped microwave pulse, which couples only s and p states under suitable conditions.

  16. Second Stokes component generation in the SRS of chirped laser pulses

    SciTech Connect

    Konyashchenko, Aleksandr V; Losev, Leonid L; Tenyakov, S Yu

    2011-05-31

    An experimental investigation was made of optical schemes for the generation of the second Stokes component in the SRS of broadband chirped laser pulses in high-pressure gases. Measurements were made of the energy conversion efficiency and the spatial characteristics of the light beam of the second Stokes component for one- and two-fold focusing of the pump radiation into the gas-filled cell as well as in schemes involving a quartz capillary and two gas-filled cells. The highest energy efficiency of conversion to the second Stokes component was attained in the case of cascade generation in the optical scheme with two pressurised-gas cells. In the SRS in hydrogen in this scheme, the Ti:sapphire laser radiation with a wavelength of 0.79 {mu}m was converted to the 2.3-{mu}m second Stokes component with an efficiency of 8.5%. (nonlinear-optics phenomena)

  17. Design considerations for a high power, ultrabroadband optical parametric chirped-pulse amplifier.

    PubMed

    Prandolini, M J; Riedel, R; Schulz, M; Hage, A; Höppner, H; Tavella, F

    2014-01-27

    A conceptual design of a high power, ultrabroadband optical parametric chirped-pulse amplifier (OPCPA) was carried out comparing nonlinear crystals (LBO and BBO) for 810 nm centered, sub-7.0 fs pulses with energies above 1 mJ. These amplifiers are only possible with a parallel development of kilowatt-level OPCPA-pump amplifiers. It is therefore important to know good strategies to use the available OPCPA-pump energy efficiently. Numerical simulations, including self- and cross-phase modulation, were used to investigate the critical parameters to achieve sufficient spectral and spatial quality. At high output powers, thermal absorption in the nonlinear crystals starts to degrade the output beam quality. Strategies to minimize thermal effects and limits to the maximum average power are discussed. PMID:24515165

  18. Broadband and broadangle SPP antennas based on plasmonic crystals with linear chirp.

    PubMed

    Bouillard, J-S; Vilain, S; Dickson, W; Wurtz, G A; Zayats, A V

    2012-01-01

    Plasmonic technology relies on the coupling of light to surface electromagnetic modes on smooth or structured metal surfaces. While some applications utilise the resonant nature of surface polaritons, others require broadband characteristics. We demonstrate unidirectional and broadband plasmonic antennas with large acceptance angles based on chirped plasmonic gratings. Near-field optical measurements have been used to visualise the excitation of surface plasmon polaritons by such aperiodic structures. These weakly aperiodic plasmonic crystals allow the formation of a trapped rainbow-type effect in a two-dimensional geometry as surface polaritons of different frequencies are coherently excited in different locations over the plasmonic structure. Both the crystal's finite size and the finite lifetime of plasmonic states are crucial for the generation of broadband surface plasmon polaritons. This approach presents new opportunities for building unidirectional, broadband and broad-angle plasmonic couplers for sensing purposes, information processing, photovoltaic applications and shaping and manipulating ultrashort optical pulses. PMID:23170197

  19. Analysis of 808nm centered optical parametric chirped pulse amplifier based on DKDP crystals

    NASA Astrophysics Data System (ADS)

    Sun, Meizhi; Cui, Zijian; Kang, Jun; Zhang, Yanli; Zhang, Junyong; Cui, Ying; Xie, Xinglong; Liu, Cheng; Liu, Dean; Zhu, Jianqiang; Lin, Zunqi

    2015-08-01

    The non-collinear phase-matching in Potassium Dideuterium Phosphate (DKDP) crystal is analyzed in detail with signal pulse of center wavelength at 808 nm and pump pulse of wavelength at 526.5 nm. By numerical analysis, parametric bandwidths for various DKDP crystals of different deuteration level are presented. In particularly for DKDP crystals of 95% deuteration level, the optimal non-collinear angles, phase-matching angles, parametric bandwidths, walk-off angles, acceptance angles, efficiency coefficients, gain and gain bandwidths are provided based on the parameter concepts. Optical parametric chirped pulse amplifier based on DKDP crystal is designed and the output characteristics are simulated by OPA coupled wave equations for further discuss. It is concluded that DKDP crystals higher than 90% deuteration level can be utilized in ultra-short high power laser systems with compressed pulses broader than 30fs. The disadvantage is that the acceptance angles are small, increasing the difficulty of engineering regulation.

  20. Non-invasive monitoring of underground power cables using Gaussian-enveloped chirp reflectometry

    NASA Astrophysics Data System (ADS)

    Lee, Chun Ku; Lee, Sin Ho; Chang, Seung Jin; Park, Jin Bae; Yoon, Tae Sung

    2013-10-01

    In this paper, we introduce non-invasive Gaussian-enveloped linear chirp (GELC) reflectometry for the diagnosis of live underground power cables. The GELC reflectometry system transmits the incident signal to live underground power cables via an inductive coupler. To improve the spatial resolution of the GELC reflectometry, we used the multiple signal classification method, which is a super-resolution method. An equalizer, which is based on Wiener filtering, is used to compensate for the signal distortion due to the propagation characteristics of underground power cables and inductive couplers. The proposed method makes it possible to detect impedance discontinuities in live underground power cables with high spatial resolution. Experiments to find the impedance discontinuity in a live underground power cable were conducted to verify the performance of the proposed method.