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1

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

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

2

Two-Dimensional Chirped-Pulse Fourier Transform Microwave Spectroscopy: Introduction to Two-Dimensional Broadband Techniques  

Microsoft Academic Search

There is a gap in the electromagnetic spectrum where the microwave region is located when considering broadband two-dimensional spectroscopy. We introduce two-dimensional chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy as a way to directly identify coherences between coupled rotational levels. The theory and application of these experiments is a direct extension of traditional two-dimensional NMR techniques. Several different pulse sequences will

Amanda J. Shirar; Kelly M. Hotopp; David S. Wilcox; Brian C. Dian

2010-01-01

3

The interlaced chirp Z transform  

Microsoft Academic Search

In this paper we introduce the interlaced chirp Z transform (Interlaced CZT). It is based on the computation of several carefully staggered CZT that are progressively interlaced to result in a spectrum that has denser frequency samples where needed. This simple modification of the CZT is shown to result in significant computational savings over the regular CZT, as well as

Indranil Sarkar; Adly T. Fam

2006-01-01

4

Superconductive chirp-transform spectrum analyzer  

SciTech Connect

Spectral analysis over an instantaneous bandwidth of 2.4 GHz was demonstrated, utilizing superconductive dispersive delay lines in a chirp-transform configuration. Two-tone resolution of 43 MHz and + or - 1.2 dB amplitude uniformity was achieved.

Withers, R.S.; Reible, S.A.

1985-06-01

5

Superconductive Chirp-Transform Spectrum Analyzer.  

National Technical Information Service (NTIS)

Spectral analysis over an instantaneous bandwidth of 2.4 GHz has been demonstrated utilizing superconductive dispersive delay lines in a chirp-transform configuration. Two-tone resolution of 43 MHz and + or - 1.2 dB amplitude uniformity was achieved.

R. S. Withers S. A. Reible

1985-01-01

6

Spectral analysis using the CCD Chirp Z-transform  

NASA Technical Reports Server (NTRS)

The charge coupled device (CCD) Chirp Z transformation (CZT) spectral analysis techniques were reviewed and results on state-of-the-art CCD CZT technology are presented. The CZT algorithm was examined and the advantages of CCD implementation are discussed. The sliding CZT which is useful in many spectral analysis applications is described, and the performance limitations of the CZT are studied.

Eversole, W. L.; Mayer, D. J.; Bosshart, P. W.; Dewit, M.; Howes, C. R.; Buss, D. D.

1978-01-01

7

Chirp Z-transform spectral zoom optimization with MATLAB.  

SciTech Connect

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.

Martin, Grant D.

2005-11-01

8

A Programmable Radar Pulse Compression Filter Utilizing Chirp Transform Correlation  

Microsoft Academic Search

A programmable matched Elter for pulse compression of large TB product chirp radar waveforms is described. This Elter is based on SAW chirp transform correlation, CTC. Pulse compression is achieved through cross- correlation of the radar return with a reference waveform. Correlation processing is superior to conventional SAW matched filtering in three ways. First, a single processor is capable of

H. M. Gerard; O. W. Otto

1976-01-01

9

Phase-shifted distributed feedback laser with linearly chirped grating fabricated by reconstruction equivalent chirp technique  

NASA Astrophysics Data System (ADS)

The phase-shifted distributed feedback (DFB) semiconductor laser with linearly chirped grating based on reconstruction equivalent chirp (REC) technique is theoretically analyzed and experimentally demonstrated for the first time. The asymmetric property of the lasing spectrum is analyzed according to the normalized threshold gain, and the different spectra from each facet of the laser are compared. Due to the low cost and fabrication flexibility, REC technique provides a promising way for the future practical applications of DFB lasers with chirped gratings.

Li, Lianyan; Lu, Linlin; Li, Simin; Guo, Renjia; Shi, Yuechun; Chen, Xiangfei

2014-09-01

10

Discrete chirp-Fourier transform and its application to chirp rate estimation  

Microsoft Academic Search

The discrete Fourier transform (DFT) has found tremendous applications in almost all fields, mainly because it can be used to match the multiple frequencies of a stationary signal with multiple harmonics. In many applications, wideband and nonstationary signals, however, often occur. One of the typical examples of such signals is chirp-type signals that are usually encountered in radar signal processing,

Xiang-Gen Xia

2000-01-01

11

Carrier-Compatible Chirp-Z Transform Device.  

National Technical Information Service (NTIS)

The patent application relates to a surface acoustic wave (SAW) device useful in band-limited TV systems, and suitable for carrier-compatible chirp-Z transform Fourier analysis. It includes apparatus for taking the discrete Fourier transform of a complex ...

J. M. Alsup H. J. Whitehouse

1976-01-01

12

A stepped chirp technique for range resolution enhancement  

Microsoft Academic Search

A novel stepped frequency chirp waveform concept for increasing the range resolution of an existing pulse compression radar is presented. The stepped frequency chirp technique is ideally suited to obtaining high range resolution in a radar system that has a limited instantaneous bandwidth, but a large tunable bandwidth. To achieve high range resolution using these given bandwidths, two or more

F. McGroary; K. Lindell

1991-01-01

13

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

National Technical Information Service (NTIS)

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 transf...

T. P. Bielek

1990-01-01

14

A direct digital synthesis chirped pulse Fourier transform microwave spectrometer  

NASA Astrophysics Data System (ADS)

Chirped pulse Fourier transform microwave (CP-FTMW) spectrometers have become the instrument of choice for acquiring rotational spectra, due to their high sensitivity, fast acquisition rate, and large bandwidth. Here we present the design and capabilities of a recently constructed CP-FTMW spectrometer using direct digital synthesis (DDS) as a new method for chirped pulse generation, through both a suite of extensive microwave characterizations and deep averaging of the 10-14 GHz spectrum of jet-cooled acetone. The use of DDS is more suited for in situ applications of CP-FTMW spectroscopy, as it reduces the size, weight, and power consumption of the chirp generation segment of the spectrometer all by more than an order of magnitude, while matching the performance of traditional designs. The performance of the instrument was further improved by the use of a high speed digitizer with dedicated signal averaging electronics, which facilitates a data acquisition rate of 2.1 kHz.

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

2013-08-01

15

CHIRP Versus BURST Sonar Resolution Techniques for Classification during Detection.  

National Technical Information Service (NTIS)

A previous Dalmo Victor report, R-2850-2931, proposed the CHIRP pulse compression technique as most adequately resolving detection range, classification and range rate problems for search sonars. This report qualitatively evaluates the effects of propagat...

R. E. Baker

1969-01-01

16

The chirp z-transform algorithm  

Microsoft Academic Search

A computational algorithm for numerically evaluating thez-transform of a sequence ofNsamples is discussed. This algorithm has been named the chirpz-transform (CZT) algorithm. Using the CZT algorithm one can efficiently evaluate thez-transform atMpoints in thez-plane which lie on circular or spiral contours beginning at any arbitrary point in thez-plane. The angular spacing of the points is an arbitrary constant, andMandNare arbitrary

L. R. RABINER; R. Schafer; C. Rader

1969-01-01

17

A digital dispersive matching network for SAW devices in chirp transform spectrometers  

Microsoft Academic Search

The performance of a chirp transform spectrometer can be significantly improved through a digital dispersive matching network. In this paper, we present the development of a new design, the adaptive digital chirp processor (ADCP), which generates an expander chirp signal with dispersive characteristics matching those of the surface acoustic wave filter behaving as a compressor\\/convolver. This matching signal (i.e., the

Geronimo Luis Villanueva; Paul Hartogh; Leonhard M. Reindl

2006-01-01

18

Room-Temperature Chirped-Pulse Fourier Transform Microwave Cp-Ftmw Spectrum of 2-METHYLFURAN  

Microsoft Academic Search

The microwave spectrum of 2-methylfuran has been measured at temperatures between 0°C and 50°C from 8.7--18.3 GHz with waveguide chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). Using the enhanced sensitivity of this technique relative to that of prior measurements from Stark-modulated instruments, we have been able to extend the assignments of the lowest energy A- and E-states from Norris and Krisher

Ian A. Finneran; Steven T. Shipman

2011-01-01

19

Progress Towards Chirped-Pulse Fourier Transform Thz Spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

20

A direct digital synthesis chirped pulse Fourier transform microwave spectrometer.  

PubMed

Chirped pulse Fourier transform microwave (CP-FTMW) spectrometers have become the instrument of choice for acquiring rotational spectra, due to their high sensitivity, fast acquisition rate, and large bandwidth. Here we present the design and capabilities of a recently constructed CP-FTMW spectrometer using direct digital synthesis (DDS) as a new method for chirped pulse generation, through both a suite of extensive microwave characterizations and deep averaging of the 10-14 GHz spectrum of jet-cooled acetone. The use of DDS is more suited for in situ applications of CP-FTMW spectroscopy, as it reduces the size, weight, and power consumption of the chirp generation segment of the spectrometer all by more than an order of magnitude, while matching the performance of traditional designs. The performance of the instrument was further improved by the use of a high speed digitizer with dedicated signal averaging electronics, which facilitates a data acquisition rate of 2.1 kHz. PMID:24007050

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

2013-08-01

21

Chirped-Pulse Fourier Transform Microwave Spectroscopy of 3-VINYLBENZALDEHYDE  

NASA Astrophysics Data System (ADS)

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

Smith, Miranda; Brown, Gordon G.

2013-06-01

22

The Study of Small Biomolecules Using Chirped-Pulse Fourier Transform Microwave Cp-Ftmw Spectrometer in the Gas Phase  

Microsoft Academic Search

The microwave spectra of a large molecule is sensitive to both the structure of the molecule and as well as its motion along different vibrational coordinates. Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is an exciting new technique that makes possible the reading of the complete microwave spectrum of a gas phase sample using a single 1 -s pulse. In this

Ryan G. Bird; David W. Pratt; Justin L. Neill; Brooks H. Pate

2009-01-01

23

Structrural Determination of Silacyclobutane and Silacyclopentane Using Fourier Transform Microwave (ftmw) and Chirped Pulse Fourier Transform Microwave (cp-FTMW) Spectroscopy  

Microsoft Academic Search

The pure rotational spectra of the ground states of silacyclobutane (SCB) and silacyclopentane (SCP) were measured in a supersonic jet in the 6-24 GHz range using Fourier transform microwave spectroscopy and the chirped-pulse variant of this technique. Heavy atom isotopic substitution for the silicon and each of the carbon atoms within the rings enabled the accurate determination of the RS

Ziqiu Chen; Cody Van Dijk; Jennifer Van Wijngaarden

2011-01-01

24

Programmable convolution via the chirp Z-transform with CCD's  

NASA Technical Reports Server (NTRS)

Technique filtering by convolution in frequency domain rather than in time domain presents possible solution to problem of programmable transversal filters. Process is accomplished through utilization of chip z-transform (CZT) with charge-coupled devices

Buss, D. D.

1977-01-01

25

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

Microsoft Academic Search

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

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

2010-01-01

26

a KA-BAND Chirped-Pulse Fourier Transform Microwave Spectrometer  

Microsoft Academic Search

The design and performance of a new chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer operating from 25-40 GHz will be discussed. A 10.5-3 GHz linear frequency sweep, generated by a 24 GS\\/s arbitrary waveform generator, is upconverted by a 23.00 GHz phase-locked oscillator, then fed into an active doubler to create a 25-40 GHz chirped pulse. After amplification with a 60-80

Daniel P. Zaleski; Justin L. Neill; Matthew T. Muckle; Brooks H. Pate; P. Brandon Carroll; Susanna L. Widicus Weaver

2010-01-01

27

Frequency Correction for MIRO Chirp Transformation Spectroscopy Spectrum  

NASA Technical Reports Server (NTRS)

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.

Lee, Seungwon

2012-01-01

28

Application of a Newly Built Chirped-Pulse Fourier Transform Microwave (CP-FTMW) Spectrometer to Study Biomolecules in the Gas Phase  

Microsoft Academic Search

Chirped-pulse Fourier Transform Microwave (CP-FTMW) spectroscopy is an exciting new technique that makes possible the recording of the complete microwave spectrum of a gas phase sample using a single 1 mus pulse. In this report, we will describe the recent introduction of a laser ablation nozzle for the study of small biomolecules using this technique. Potential applications to samples such

Ryan Bird; David Pratt; Justin Neill; Brooks Pate

2009-01-01

29

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

NASA Astrophysics Data System (ADS)

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

Phillips, Maria A.; Shipman, Steven T.

2013-06-01

30

Multiband chirp transform spectrometer for the microwave remote sensing of middle atmospheric trace gases  

Microsoft Academic Search

A new generation of submillimeter wave limb sounders require multiband real time spectrometer backends with high constraints on mass, size and power consumption. A new concept, the multiband chirp transform spectrometer (MBCTS) was developed for this purpose. The MBCTS was chosen to be suitable for the Advanced Microwave Atmospheric Sounder (AMAS), a European instrument, which is currently in the breadboarding

Paul Hartogh; Klaus Osterschek

1995-01-01

31

Application of the chirped Z-transform to processing frequency hopping spread spectrum signals  

Microsoft Academic Search

Charge coupled device\\/chirped Z transform (CCD\\/CZT) oriented detection schemes for a frequency-hopped spread spectrum (FHSS) signal in the presence of white Gaussian noise and radio frequency interference are derived. For the case when an FHSS signal is corrupted by white Gaussian noise, the frequency-hopped complex exponents representing a binary symbol are assumed to have partial coherence. The optimum receiver structures

S. Mahmood

1980-01-01

32

The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave spectroscopy  

Microsoft Academic Search

The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is presented. A new CP-FTMW spectrometer capable of measuring the entire 7.5–18.5GHz spectrum with a single polarizing pulse is described briefly. The CP-FTMW spectrometer takes advantage of recent advances in digital electronics by utilizing a 4.2GS\\/s arbitrary waveform generator as a frequency source and a 12GHz digital

Gordon G. Brown; Brian C. Dian; Kevin O. Douglass; Scott M. Geyer; Brooks H. Pate

2006-01-01

33

Microsolvation of beta-PROPIOLACTONE as Revealed by Chirped-Pulse Fourier Transform Microwave Spectroscopy  

Microsoft Academic Search

Microwave spectra of water clusters of beta-propiolactone with up to five water molecules attached are presented. Helium or neon carrier gas with 3 atm of backing pressure is flowed over a room-temperature water reservoir, then over a room-temperature sample of beta-propiolactone before being expanded into a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer operating between 6.5 and 18.5 GHz. A very

Justin L. Neill; Matt T. Muckle; Brooks H. Pate; I. Pena; C. Perez; J. L. Alonso

2010-01-01

34

Room temperature chirped-pulse Fourier transform microwave spectroscopy of anisole  

Microsoft Academic Search

The room-temperature rotational spectrum of anisole from 8.7 to 18.3GHz 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

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

35

Waveguide Chirped-Pulse Fourier Transform Microwave Cp-Ftmw Spectrum of Allyl Chloride  

Microsoft Academic Search

The microwave spectrum of allyl chloride at 0° C was measured from 8.7--18.3 GHz with waveguide chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). The spectrum consists of contributions from 35Cl and 37Cl isotopomers of the cis and skew isomers. As the vibrational partition function for each of these conformers is approximately 4, the microwave spectrum contains a few thousand transitions with

Erin B. Kent; Morgan N. McCabe; Maria A. Phillips; Brittany P. Gordon; Steven T. Shipman

2011-01-01

36

Waveguide Chirped-Pulse Fourier Transform Microwave Cp-Ftmw Spectrum of Ortho-Fluorotoluene  

Microsoft Academic Search

The microwave spectrum of o-fluorotoluene has been measured at 0°C from 8.7--18.3 GHz with waveguide chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). We have extended previous assignments of the lowest energy A- and E-states by Susskind and Mäder and report on preliminary assignments of vibrationally excited states. This molecule also serves as a proof-of-principle for ``coarse\\

Ian A. Finneran; Steven T. Shipman

2011-01-01

37

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

NASA Astrophysics Data System (ADS)

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

Gordon, Brittany P.; Shipman, Steven T.

2013-06-01

38

Chirped-Pulse Fourier Transform Microwave Spectroscopy of Meta-Chlorobenzaldehyde  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of meta-chlorobenzaldehyde (m-ClBA) has been measured from 8 - 18.5 GHz by chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The spectrum has been analyzed to discover the presence of two conformations of m-ClBA in the free jet expansion. For each conformation the rotational constants, the centrifugal distortion constants, and the nuclear quadrupole coupling constants have been found for both the ^{35}Cl and the ^{37}Cl isotopologue. The rotational constants and the nuclear quadrupole coupling constants have been compared to ab initio calculations performed using the Gaussian 03W software package.

Arnold, Sean T.; Garrett, Jessica A.; Brown, Gordon G.

2013-06-01

39

Waveguide Chirped-Pulse Fourier Transform Microwave Cp-Ftmw Spectrum of Allyl Chloride  

NASA Astrophysics Data System (ADS)

The microwave spectrum of allyl chloride at 0° C was measured from 8.7--18.3 GHz with waveguide chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). The spectrum consists of contributions from 35Cl and 37Cl isotopomers of the cis and skew isomers. As the vibrational partition function for each of these conformers is approximately 4, the microwave spectrum contains a few thousand transitions with intensities above a 3:1 S/N ratio after a few hours of averaging. We will discuss our progress on the analysis of this spectrum, which has been aided with an automated strategy to find candidate assignments.

Kent, Erin B.; McCabe, Morgan N.; Phillips, Maria A.; Gordon, Brittany P.; Shipman, Steven T.

2011-06-01

40

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

NASA Astrophysics Data System (ADS)

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.

Marshall, Mark D.; Leung, Helen O.

2012-06-01

41

An arbitrary waveform generator based chirped pulse Fourier transform spectrometer operating from 260 to 295 GHz  

NASA Astrophysics Data System (ADS)

The performance of a chirped-pulse Fourier transform millimeter-wave spectrometer operating from 260 to 295 GHz is described. The spectrometer uses a high-speed arbitrary waveform generator (AWG) to create both a chirped excitation pulse and the single-frequency local oscillator (LO) used for the final down conversion detection stage. The mm-wave excitation source is an active multiplier chain (factor of 24 frequency multiplication) with power output of greater than 10 mW across the 260-295 GHz frequency range. The LO, produced by a separate active multiplier chain (factor of 12 frequency multiplication), drives a subharmonic mixer which downconverts the molecular emission to the microwave region for digitization on a 100 GS/s digital oscilloscope. All frequency sources in the experiment are locked to a 10 MHz Rb-disciplined oscillator providing direct frequency calibration for molecular transitions in the Fourier transform frequency-domain spectrum. Benchmark measurements are presented on ethyl cyanide and 1-butyne and are used to illustrate advantages and tradeoffs compared with direct absorption millimeter-wave spectroscopy.

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

2012-10-01

42

Evaluation of an ultrabroadband high-gain amplification technique for chirped pulse amplification facilities.  

PubMed

Recently, an amplification technique for ultrashort pulses was explored in detail in a theoretical paper by Ross et al. [Opt. Commun. 144, 125 (1997)]. The technique, based on nonlinear optics, is called optical parametric chirped pulse amplification. It has a number of features that, in principle, make it highly attractive. It primarily offers extremely large gains simultaneously with extremely large bandwidths. Additional attractions are virtually no spatial and temporal phase distortion of the amplified pulse, high efficiencies and a low thermal loading, reduced amplified spontaneous emission levels, small optical material lengths, and an inherent simplicity of implementation. We present an evaluation of the technique as a front end amplifier for the ultrashort pulse amplification chain of the Vulcan laser system. Such a device could replace some of the existing amplification in Nd:glass and additionally have a wider effect as a direct replacement of Ti:sapphire regenerative amplifiers on large-scale chirped pulse amplification scale facilities. PMID:18324304

Collier, J; Hernandez-Gomez, C; Ross, I N; Matousek, P; Danson, C N; Walczak, J

1999-12-20

43

a KA-BAND Chirped-Pulse Fourier Transform Microwave Spectrometer.  

NASA Astrophysics Data System (ADS)

The design and performance of a new chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer operating from 25-40 GHz will be discussed. A 10.5-3 GHz linear frequency sweep, generated by a 24 GS/s arbitrary waveform generator, is upconverted by a 23.00 GHz phase-locked oscillator, then fed into an active doubler to create a 25-40 GHz chirped pulse. After amplification with a 60-80 W pulsed traveling wave tube amplifier, the pulse is broadcast across a molecular beam chamber where it interacts with a molecular sample. The molecular FID signal is downconverted with the 23 GHz oscillator so that it can be digitized on a 50 GS/s oscilloscope with 16 GHz hardware bandwidth. The sensitivity and phase stability of this spectrometer is comparable to that of the previously reported 6.5-18.5 CP-FTMW spectrometer. On propyne (?=0.78 D), a single-shot signal to noise ratio of approximately 200:1 is observed on the J=2-1 rotational transition at 34183 MHz when the full bandwidth is swept; optimal excitation is observed for this transition with a 250 MHz bandwidth sweep. The emission has a T_2 lifetime of 4 ?s. Early results from this spectrometer, particularly in the study of species of astrochemical interest, will be presented. G.G. Brown et al., Rev. Sci. Instrum. 79 (2008) 053103.

Zaleski, Daniel P.; Neill, Justin L.; Muckle, Matthew T.; Pate, Brooks H.; Carroll, P. Brandon; Weaver, Susanna L. Widicus

2010-06-01

44

Broadband Chirped-Pulse FourierTransform Microwave Spectroscopic Investigation of the Structures of Three Diethylsilane Conformers  

Microsoft Academic Search

The rotational spectrum of diethylsilane has been assigned using broadband chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy. Previously, Fourier-transform microwave rotational spectra were observed using a Balle-Flygare type instrument for the ^{28}Si isotopologues of the gauche-gauche, trans-gauche, and trans-trans conformers. In the present study, a broadband microwave spectrum was obtained at the University of Virginia, taking advantage of the ability to perform

Amanda L. Steber; Daniel A. Obenchain; Rebecca A. Peebles; Sean A. Peebles; Justin L. Neill; Matt T. Muckle; Brooks H. Pate; Gamil A. Guirgis

2009-01-01

45

Real-time chirp diagnostic for ultrashort laser pulses.  

PubMed

Using a real-time Fourier-transform algorithm, we present a simple technique for measuring the chirp of femtosecond laser pulses. We demonstrate significantly enhanced sensitivity compared with standard autocorrelation measurements. PMID:18007952

Hirayama, Toshiyuki; Sheik-Bahae, Mansoor

2002-05-15

46

Design and Initial Optimisation of a Broadband (6.5-18 GHz) Chirped-Pulse Fourier Transform Microwave Spectrometer  

Microsoft Academic Search

A chirped-pulse, Fourier transform microwave spectrometer has been constructed to allow the measurement of broadband microwave spectra from 6.5 GHz to 18 GHz. The design of the new instrument, developed from the original model of Pate and co-workers, and the results of tests using different experimental conditions and a wide range of molecules will be described. The PGOPHER program has

N. R. Walker; S. L. Stephens

2010-01-01

47

A Ka-band chirped-pulse Fourier transform microwave spectrometer  

NASA Astrophysics Data System (ADS)

The design and performance of a new chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer operating from 25 to 40 GHz (Ka-band) is presented. This spectrometer is well-suited for the study of complex organic molecules of astronomical interest in the size range of 6-10 atoms that have strong rotational transitions in Ka-band under pulsed jet sample conditions (Trot = 1-10 K). The spectrometer permits acquisition of the full spectral band in a single data acquisition event. Sensitivity is enhanced by using two pulsed jet sources and acquiring 10 broadband measurements for each sample injection cycle. The spectrometer performance is benchmarked by measuring the pure rotational spectrum of several isotopologues of acetaldehyde in natural abundance. The rotational spectra of the singly substituted 13C and 18O isotopologues of the two lowest energy conformers of ethyl formate have been analyzed and the resulting substitution structures for these conformers are compared to electronic structure theory calculations.

Zaleski, Daniel P.; Neill, Justin L.; Muckle, Matt T.; Seifert, Nathan A.; Brandon Carroll, P.; Widicus Weaver, Susanna L.; Pate, Brooks H.

2012-10-01

48

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

SciTech Connect

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.

Frickey, D.A.

1995-01-01

49

Perfluorobutyric acid and its monohydrate: a chirped pulse and cavity based fourier transform microwave spectroscopic study.  

PubMed

Rotational spectra of perfluorobutyric acid (PFBA) and its monohydrate were studied with a broadband chirped pulse and a narrow-band cavity based Fourier transform microwave spectrometer, and high-level ab initio calculations. Extensive conformational searches were performed for both the acid and its monohydrate at the MP2/6-311++G(2d,p) level of theory. Two and three conformers were predicted to exist for PFBA and its monohydrate, respectively. One set of rotational transitions was observed and assigned for each, PFBA and its monohydrate. Based on the measured broadband spectra, we confidently conclude that only one dominant conformer exists in each case. The orientation of the hydroxyl group in PFBA was determined by using isotopic analysis. Comparison of the observed transition intensities and the calculated electric dipole moment components allowed us to identify the most stable monohydrate conformation, which takes on an insertion hydrogen-bonding topology. Comparisons to the shorter chain analogues, that is, trifluoroacetic acid, perfluoropropionic acid, and their monohydrates, are made to elucidate the general trend in their conformational preference and binding topologies. PMID:24756992

Thomas, Javix; Serrato, Agapito; Lin, Wei; Jäger, Wolfgang; Xu, Yunjie

2014-05-12

50

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

NASA Astrophysics Data System (ADS)

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.

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

2009-06-01

51

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

NASA Astrophysics Data System (ADS)

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).

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

2013-06-01

52

a 480 MHz Chirped-Pulse FourierTransform Microwave Spectrometer: Construction and Measurement of the Rotational Spectra of Divinyl Silane and 3,3-DIFLUOROPENTANE  

Microsoft Academic Search

A chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer based on the original Pate design has been constructed to allow analysis of any 480 MHz region in the 7 - 18 GHz range. A 1 mus chirped-pulse (0 - 240 MHz) from an arbitrary function generator is mixed with output from a microwave synthesizer and used to polarize a supersonic gas expansion; the

Daniel A. Obenchain; Amanda L. Steber; Ashley A. Elliott; Rebecca A. Peebles; Sean A. Peebles; Charles J. Wurrey; Gamil A. Guirgis

2010-01-01

53

Conformational analysis of n-butanal by Chirped-Pulse Fourier Transform Microwave spectroscopy  

NASA Astrophysics Data System (ADS)

The rotational spectrum of n-butanal was obtained in the 7.5-18.5 GHz range using Chirped-Pulse Fourier Transform Microwave (CP-FTMW) spectroscopy. In addition to the previously observed cis/trans and cis/gauche conformers, a new conformer gauche/gauche was assigned; tentative assignments were also made on a second new conformer, gauche/trans. Density functional theory calculations using GAUSSIAN03 allowed us to predict the four most stable geometries (cis/trans, cis/gauche, gauche/trans, and gauche/gauche), which were verified as local minima in vibrational calculations. We also performed relaxed potential energy scans and found internal methyl rotor torsional barriers of V3 = 8.4 kJ/mol (cis/trans), 11.6 kJ/mol (cis/gauche), 12.5 kJ/mol (gauche/trans), and 11.8 kJ/mol (gauche/gauche). The program XIAM was used to determine a V3 barrier 6.3 ± 0.2 kJ/mol for the gauche/gauche structure, which is significantly smaller than the lowest V3 barrier predicted by ab initio calculations of 8.4 kJ/mol. Because of the high signal-to-noise of the CP-FTMW spectrometer, we assigned the 13C n-butanal isotopologues of cis/trans and cis/gauche in natural abundance. Kraitchman analysis was performed to determine the carbon-carbon bond angles and bond distances in these structures based on our observed data.

Hotopp, Kelly M.; Vara, Vanesa Vaquero; Dian, Brian C.

2012-10-01

54

The complete iodine and nitrogen nuclear electric quadrupole coupling tensors for fluoroiodoacetonitrile determined by chirped pulse Fourier transform microwave spectroscopy.  

PubMed

Molecular pulsed jet, chirped-pulse Fourier transform microwave spectroscopy has been used to record 499 transitions for the title molecule. Measurements have been made in the 8-16 GHz regions. Vibrational and electronic ground state rotational constants A, B, and C have been obtained, together with centrifugal distortion terms. The complete iodine and nitrogen nuclear quadrupole coupling tensors have been determined for the first time. Quantum chemical calculations have been performed to aid with analyses and, in particular, to aid in determining the signs of the off-diagonal components of the nuclear quadrupole coupling tensors. An experimentally determined relative electronegativity scale for several polyhalomethyl groups is proposed. PMID:20095677

Grubbs, G S; Kadiwar, G; Bailey, W C; Cooke, S A

2010-01-14

55

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

56

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)

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.

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

2012-06-01

57

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

NASA Astrophysics Data System (ADS)

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).

Marshall, Mark D.; Leung, Helen O.

2013-06-01

58

Investigation of structural trends in difluoropyridine rings using chirped-pulse Fourier transform microwave spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

The ground state rotational spectra of 2,3-, 2,4-, 2,5-, 2,6- and 3,5-difluoropyridine have been investigated using both Balle-Flygare type Fourier transform microwave (FTMW) and chirped pulse Fourier transform microwave (cp-FTMW) spectroscopies. In addition to the parent species, the spectra of the 13C and 15N singly-substituted isotopologues were recorded in the 5-23 GHz region in natural abundance. The rotational constants determined from heavy atom substitution were used to determine the bond lengths and angles within the pyridine backbone of each species. A more pronounced deviation from the pyridine ring geometry is observed when the fluorine substituent is ortho to nitrogen which is consistent with ab initio predictions of the structures at the MP2 (6-311G++2d2p) level of theory. Analyses of the observed 14N hyperfine splitting patterns provided a key source of information about the electronic structure surrounding the nitrogen atom as a function of the various fluorine substitutions. Together, the experimental results are consistent with bonding models that involve subtle changes in the hybridization of the carbon atom that bears the fluorine substituent as well as donation of electron density from the lone pair of fluorine into the ?-system of pyridine.

van Dijk, Cody W.; Sun, Ming; van Wijngaarden, Jennifer

2012-10-01

59

Experimental demonstration of the three phase shifted DFB semiconductor laser based on Reconstruction-Equivalent-Chirp technique.  

PubMed

A three phase shifted (3PS) distributed feedback (DFB) semiconductor laser based on Reconstruction-Equivalent-Chirp (REC) technique is experimentally demonstrated for the first time. The simulation results show that the performances of the equivalent 3PS DFB semiconductor laser are nearly the same as that of the true 3PS laser. However, it only changes the ?m-level sampling structures but the seed grating is uniform. So, its cost of fabrication is low. The measurement results exhibit its good single longitudinal mode (SLM) operation even at high bias current and surrounding temperature. PMID:23038289

Shi, Yuechun; Chen, Xiangfei; Zhou, Yating; Li, Simin; Li, Lianyan; Feng, Yijun

2012-07-30

60

Chirped-Pulse Fourier Transform Microwave Spectrum of the Low Global Warming Potential Refrigerant Alternative, 2,3,3,3-TETRAFLUOROPROPENE  

Microsoft Academic Search

A newly-constructed, chirped-pulse Fourier transform microwave spectrometer is used to obtain the microwave spectrum of 2,3,3,3-tetrafluoropropene, which has been proposed as an alternative to HFC-134a for use as a mobile air conditioning refrigerant. With a bandwidth of 6 GHz, this instrument has the potential to provide complete coverage of the microwave spectrum from 6 to 18 GHz in two steps,

Mark D. Marshall; Helen O. Leung; John S. Muenter

2010-01-01

61

Rotational spectroscopy of iodobenzene and iodobenzene–neon with a direct digital 2–8 GHz chirped-pulse Fourier transform microwave spectrometer  

Microsoft Academic Search

The design of a chirped-pulse Fourier transform microwave spectrometer operating in the 2–8GHz frequency range is presented. The linear frequency sweep is generated by an arbitrary waveform generator with a sampling rate of 20 GS\\/s. After amplification, the microwave pulse is broadcast into a vacuum chamber where it interacts with a supersonically expanded molecular sample. The resulting molecular free induction

Justin L. Neill; Steven T. Shipman; Leonardo Alvarez-Valtierra; Alberto Lesarri; Zbigniew Kisiel; Brooks H. Pate

2011-01-01

62

Chirped Attosecond Photoelectron Spectroscopy  

SciTech Connect

We study analytically the photoionization of a coherent superposition of electronic states and show that chirped pulses can measure attosecond time scale electron dynamics just as effectively as transform-limited attosecond pulses of the same bandwidth. The chirped pulse with a frequency-dependent phase creates the interfering photoelectron amplitudes that measure the electron dynamics. We show that at a given pump-probe time delay the differential asymmetry oscillates as a function of photoelectron energy. Our results suggest that the important parameter for attosecond science is not the pulse duration, but the bandwidth of phased radiation.

Yudin, G.L. [Laboratoire de Chimie Theorique, Universite de Sherbrooke, Sherbrooke, Quebec J1K 2R1 (Canada); National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada); Bandrauk, A.D. [Laboratoire de Chimie Theorique, Universite de Sherbrooke, Sherbrooke, Quebec J1K 2R1 (Canada); Corkum, P.B. [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada)

2006-02-17

63

Issues in Information Hiding Transform Techniques.  

National Technical Information Service (NTIS)

This paper gives a review of prevailing transform embedding techniques for information hiding, and discusses the robustness and detectability of two specific methods. Spatial embedding inserts messages into image pixels. Transform embedding embeds a messa...

L. Chang

2002-01-01

64

An iterative template matching algorithm using the Chirp-Z transform for digital image watermarking  

Microsoft Academic Search

INTRODUCTIONThe popularity of the World Wide Web has clearly demonstrated the commercial potential of the digital multimediamarket. Unfortunately however, digital networks and multimedia also afford virtually unprecedented opportunitiesto pirate copyrighted material. As a result, digital image watermarking has become a an active area of research.Techniques for hiding watermarks have grown steadily more sophisticated and increasingly robust to standard imageprocessing techniques.

Shelby Pereira; Thierry Pun

2000-01-01

65

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

NASA Astrophysics Data System (ADS)

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.

Zhao, Kun; Chu, Tianshu

2011-07-01

66

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

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

67

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

SciTech Connect

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.

Zheng Yinghui; Zeng Zhinan; Zou Pu; Zhang Li; Li Xiaofang; Liu Peng; Li Ruxin; Xu Zhizhan [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, 201800 (China)

2009-07-24

68

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

69

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

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

70

Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70-102 GHz region  

Microsoft Academic Search

Chirped-pulse millimeter-wave (CPmmW) spectroscopy is the first broadband (multi-GHz in each shot) Fourier-transform technique for high-resolution survey spectroscopy in the millimeter-wave region. The design is based on chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy [G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, and B. H. Pate, Rev. Sci. Instrum. 79, 053103 (2008)], which is described

G. Barratt Park; Adam H. Steeves; Kirill Kuyanov-Prozument; Justin L. Neill; Robert W. Field

2011-01-01

71

Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70–102 GHz region  

Microsoft Academic Search

Chirped-pulse millimeter-wave (CPmmW) spectroscopy is the first broadband (multi-GHz in each shot) Fourier-transform technique for high-resolution survey spectroscopy in the millimeter-wave region. The design is based on chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy [G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, and B. H. Pate, Rev. Sci. Instrum. 79, 053103 (2008)], which is described

G. Barratt Park; Adam H. Steeves; Kirill Kuyanov-Prozument; Justin L. Neill; Robert W. Field

2011-01-01

72

Chirp-compensated 40GHz mode-locked lasers integrated with electroabsorption modulators and chirped gratings  

Microsoft Academic Search

40-GHz short-pulse generation of monolithic mode-locked lasers integrated with electroabsorption modulators and chirped gratings is reported. Theoretical analysis of active mode-locking based on a Gaussian model is described. Chirped gratings are shown to compensate the optical-frequency chirp and extend the repetition frequency range. Nearly transform-limited pulses of less than 4 ps are experimentally generated over a wide range of repetition

Kenji Sato; Akira Hirano; Hiroyuki Ishii

1999-01-01

73

Measurement and analysis of the pure rotational spectra of tin monochloride, SnCl, using laser ablation equipped chirped pulse and cavity Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of tin monochloride, SnCl, has been measured and analyzed using chirped pulse and cavity Fourier transform microwave spectrometers equipped with a laser ablation source. SnCl, in its X2? electronic state, has been measured in the 8-17 GHz region. Rotational constants, centrifugal distortion constants, ?-doubling constants, magnetic hyperfine constants, and nuclear electric quadrupole coupling constants for multiple isotopologues have been determined and are reported. The bond length, nuclear magnetic and quadrupole constants have been analyzed and compared against the family of tetral halides. Analysis of the bond length and hyperfine interactions point to a Sn-Cl single bond which is largely ionic in nature.

Grubbs, G. S.; Frohman, Daniel J.; Novick, Stewart E.; Cooke, S. A.

2012-10-01

74

Development of a Reduced-Cost Chirped Pulse Microwave Spectrometer  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

75

Chirped microwave pulse generation using a tilted fiber Bragg grating  

Microsoft Academic Search

A technique to generate a chirped microwave waveform based on spectral-shaping and wavelength-to-time-mapping using a tilted fiber Bragg grating (TFBG) is proposed. A 24.21-GHz chirped microwave pulse with a chirp-rate of 0.0070 GHz\\/ps is generated.

Ming Li; Liyang Shao; Jacques Albert; Jianping Yao

2010-01-01

76

Optimal chirped probe pulse length for terahertz pulse measurement.  

PubMed

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

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

2008-08-01

77

Analysis and transformation of image using spectral transformation technique  

Microsoft Academic Search

Image processing is a rapidly growing field. There are several transforms that do image transformation i.e image enhancement and segmentation. Among all the transformations spectral transformation is the simplest one because it is similar to the commonly used geometric coordinate transformation except that the geometric coordinate are replaced with the spectral bands. I can perform spectral transformation by different algorithms,

V. Singh; M. Singh

2010-01-01

78

Chirped Pulse Amplification: Present and Future.  

National Technical Information Service (NTIS)

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 th...

P. Maine D. Strickland M. Pessot J. Squier P. Bado

1988-01-01

79

Molecular structure of the argon-(Z)-1-chloro-2-fluoroethylene complex from chirped-pulse and narrow-band Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

Broadband chirped pulse, Fourier transform microwave spectra in the 6-18 GHz region are obtained for the 35Cl and 37Cl isotopomers of the complex formed between argon and (Z)-1-chloro-2-fluoroethylene. Analysis of the spectra provides predictions of rotational transition frequencies for the two singly substituted 13C isotopomers of Ar-35ClHCCHF sufficient to narrow the search range required for observation in a more sensitive, narrow band cavity Fourier transform instrument. Only a non-planar structure with the argon atom maximizing the number of its contacts with preferably heavy atoms is consistent with the rotational constants for all four isotopomers, and no evidence of tunneling between the two equivalent minima on either side of the ethylene plane is found. Rotational transitions for four isotopomers of (Z)-1-chloro-2-fluoroethylene itself, appearing in the broadband spectrum, are analyzed to determine the complete chlorine nuclear quadrupole coupling tensor for this molecule, and when these are combined with the hyperfine constants determined for the complex with argon, the sign ambiguity of the measured off-diagonal tensor components is removed.

Marshall, Mark D.; Leung, Helen O.; Calvert, Catherine E.

2012-10-01

80

Transmission performance of chirp-controlled signal by using semiconductor optical amplifier  

Microsoft Academic Search

We examine the fiber transmission performance of the optical signal whose chirp is controlled by utilizing phase modulation in semiconductor optical amplifier (SOA) with both simulations and experiments. This chirp control technique converts a positive chirp created by electroabsorption (EA) modulator into negative chirp, which reduces the waveform degradation due to the chromatic dispersion in transmission over standard single-mode fiber

Toshio Watanabe; Norio Sakaida; Hiroshi Yasaka; Fumiyoshi Kano; Masafumi Koga

2000-01-01

81

Fiber Bragg gratings with various chirp profiles made in etched tapers  

NASA Astrophysics Data System (ADS)

We have studied, both theoretically and experimentally, fiber Bragg gratings with a number of different chirp profiles. These chirp profiles can easily be achieved by a recently demonstrated technique involving a taper of desired profile etched into the cladding of a fiber. The performances of gratings with linear, quadratic, periodically modulated, and step-chirp profiles are analyzed numerically. The versatility of the technique was demonstrated when linearly and quadratically chirped gratings were made as examples of continuous chirp, and gratings with step chirps were made as examples of discontinuously chirped structures.

Cruz, J. L.; Dong, L.; Barcelos, S.; Reekie, L.

1996-12-01

82

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

NASA Astrophysics Data System (ADS)

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.

Lam, Larry

83

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)

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.

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

2013-06-01

84

The Pure Rotational Spectra of Acetaldehyde and Glycolaldehyde Isotopologues Measured in Natural Abundance by Chirped-Pulse Fourier Transform Microwave Spectroscopy  

NASA Astrophysics Data System (ADS)

Complex organic molecules (COMs) such as glycolaldehyde (HOCH_2CHO) and acetaldehyde (CH_3CHO) have now been detected in numerous interstellar sources. Glycolaldehyde has been detected in two hot cores, Sgr B2(N) and G31.41+0.31. Acetaldehyde has been observed in various sources, including the translucent clouds CB 17 and CB 24, cold molecular clouds such as TMC-1 and L134N, and hot cores such as Sgr B2(N), NGC 6334F, and the Orion Compact Ridge. Such COMs are known to have rich and complex spectra that add to the line confusion problem faced in observations of molecule-rich sources. Laboratory studies of excited vibrational states and isotopologues for known COMs therefore provide important guidance for sorting out the interstellar line confusion problem. Detection of isotopologues and determination of their abundance relative to the main isotopic species would also provide important constraints on interstellar chemical models, as these isotopic ratios are dependent on the formation mechanism for each species. The isotopic ratios for 13C/12C, 18O/16O, and D/H are known in various interstellar environments for simple molecules, but remain relatively unexplored for more complex species such as glycolaldehyde and acetaldehyde. The rotational spectra of the main isotopologues for glycolaldehyde and acetaldehyde have been well-characterized through microwave, millimeter, and submillimeter laboratory spectroscopy. Here we present the laboratory characterization of the isotopologues of acetaldehyde and glycolaldehyde in natural abundance by chirped pulse Fourier transform microwave spectroscopy (CP-FTMW). This spectroscopic information lays the groundwork for additional higher-frequency studies that can be directly applied to the interpretation of millimeter and submillimeter observations.

Carroll, P. Brandon; McGuire, Brett A.; Weaver, Susanna L. Widicus; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.

2011-06-01

85

Transionospheric chirp event classifier  

SciTech Connect

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.

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

1995-09-01

86

A filter design technique for steerable pyramid image transforms  

Microsoft Academic Search

We describe a novel recursive filter design technique for multi-scale “pyramid” transforms. The recursion in the design technique follows that of the pyramid construction, and allows us to solve a reduced design problem at each step. We demonstrate the use of this technique by designing filters of various orientation bandwidths for use in a “steerable pyramid” image transform

Anestis Karasaridis; Eero Simoncelli

1996-01-01

87

Hadamard transform spectrometry: A new analytical technique  

Microsoft Academic Search

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

Hall

1989-01-01

88

An improved processing sequence for uncorrelated Chirp sonar data  

NASA Astrophysics Data System (ADS)

Chirp sonar systems can be used to obtain high resolution seismic reflection images of the sub-seafloor during marine surveys. The exact knowledge of the Chirp signature allows the use of deterministic algorithms to process the data, similarly to that applied to Vibroseis data on land. Here, it is described an innovative processing sequence to be applied to uncorrelated Chirp data, which can improve vertical and lateral resolution compared to conventional methods. It includes application of a Wiener filter to transform a frequency-modulated sweep into a minimum-phase pulse sequence. In this way, the data become causal and can undergo predictive deconvolution to reduce ringing and enhance vertical resolution. Afterwards, FX-deconvolution and Stolt migration can be applied to obtain an improved imaging of the subsurface. The result of this procedure is a seismic reflection image with higher resolution than traditional ones, which are normally represented using the envelope function of the signal. This technique can be particularly useful for engineering-geotechnical surveys and archaeological investigations that require a fine detail imaging of the uppermost meters of the sub-seafloor.

Baradello, Luca

2014-03-01

89

Wavelet transform domain filters: a spatially selective noise filtration technique  

Microsoft Academic Search

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

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

1994-01-01

90

A Static Analysis Technique for Graph Transformation Systems  

Microsoft Academic Search

In this paper we introduce a static analysis technique for graph transformation systems. We present an algorithm which, given a graph transformation system and a start graph, produces a nite struc- ture consisting of a hypergraph decorated with transitions (Petri graph) which can be seen as an approximation of the Winskel style unfolding of the graph transformation system. The fact

Paolo Baldan; Andrea Corradini; Barbara König

2001-01-01

91

Hadamard transform spectrometry: A new analytical technique  

SciTech Connect

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.

Hall, W.

1989-11-10

92

Hadamard transform techniques in photothermal spectroscopy  

NASA Astrophysics Data System (ADS)

Hadamard transform imaging is shown to be generally applicable to any linear spectroscopy and to be useful where locally high power densities are undesirable. Application to transverse photothermal deflection and Raman spectroscopies is reviewed. The modulation transfer functions (MTF) of both source-encoded and signal-encoded Hadamard imagers are described. Preliminary results from a signal-encoded imager are presented.

Treado, Patrick J.; Morris, Michael D.

1989-10-01

93

Hadamard transform techniques in photothermal spectroscopy  

Microsoft Academic Search

Hadamard transform imaging is shown to be generally applicable to any linear spectroscopy and to be useful where locally high power densities are undesirable. Application to transverse photothermal deflection and Raman spectroscopies is reviewed. The modulation transfer functions (MTF) of both source-encoded and signal-encoded Hadamard imagers are described. Preliminary results from a signal-encoded imager are presented.

Patrick J. Treado; Michael D. Morris

1989-01-01

94

Intrinsic chirp of single-cycle pulses  

SciTech Connect

The Fourier transform-limited electromagnetic pulse has been regarded to be free of chirps for a long time. This is no longer true if the pulse duration goes down to or less than one optical cycle. We report the experimental observation of intrinsic chirps in such pulses with the sub-single-cycle terahertz (THz) waveforms obtained with a standard THz time-domain spectroscopy system. The results confirm the break down of the carrier-envelope (CE) expression for single-cycle optical pulses, and may influence the experimental measurements and theoretical modeling with single-cycle pulses.

Lin Qiang; Zheng Jian [Institute of Optics, Department of Physics, Zhejiang University, Hangzhou 310027 (China); Dai Jianming; Ho, I-Chen; Zhang, X.-C. [Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

2010-04-15

95

Wideband chirp modulation for FH-CDMA wireless systems: coherent and non-coherent receiver structures  

Microsoft Academic Search

In this paper, we propose a novel signaling scheme based on wideband time-varying chirp signals for frequency-hopped code division multiple access (FH-CDMA) techniques. Our new method has been motivated by the inherent resistance of chirp signals against channel imposed distortions as chirps are bandwidth efficient and robust to fading. Specifically, we combine FH-CDMA with chirp modulation such that every user

C. Gupta; T. Mumtaz; M. Zaman; A. Papandreou-Suppappola

2003-01-01

96

Compression of amplified chirped optical pulses  

Microsoft Academic Search

A system is reported which transposes a short-pulse amplification technique employed in radar to the optical regime and that, in principle, should be capable of producing short (1 pc or less) pulses with energies at the Joule level. The technique involves stretching a chirped optical pulse and then amplifying it before recompression. To date, 2-ps pulses with an energy of

D. Strickland; G. Mourou

1985-01-01

97

Advanced techniques for Fourier transform wavefront reconstruction  

NASA Astrophysics Data System (ADS)

The performance of Fourier transform (FT) reconstructors in large adaptive optics systems with Shack-Hartmann sensors and a deformable mirror is analyzed. FT methods, which are derived for point-based geometries, are adapted for use on continuous systems. Analysis and simulation show how to compensate for effects such as misalignment of the deformable mirror and wavefront sensor gain. Further filtering methods to reduce noise and improve performance are presented. These modifications can be implemented at the filtering stage, preserving the speed of FT reconstruction and providing flexibility by allowing on-the-fly filter adaptation. Simulation of a large system shows how compensated FT methods can have equivalent or better performance to slower vector-matrix-multiply methods. The best-performing FT method is the fastest to compute, has lower noise propagation and does not suffer from waffle errors.

Poyneer, Lisa A.

2003-02-01

98

Linear fm chirp laser  

SciTech Connect

The method is described of operating a laser radar system comprising the steps of: actuating a transmitter laser to emit laser light at approximately a preselected center frequency; frequency modulating the light of the transmitter laser in linear chirps by passing it through an electro-optical crystal disposed within the cavity of the transmitter and driving the crystal with linear chirp drive signal from a precision linear driver; and actuating a local oscillator laser to emit laser light at a predetermined frequency offset from the center frequency by a frequency substantially greater than the maximum frequency shift of the transmitter laser.

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

1987-05-19

99

Calibration of optical detectors using discrete Fourier transform techniques  

NASA Technical Reports Server (NTRS)

A method for determining the detector electrooptical transfer function (DEOTF) at different discrete frequencies simultaneously is presented. It involves simulation of the detector with a waveform of unknown frequency composition, such as a square wave or impulse function. The DEOTF is calculated as the ratio of the discrete Fourier transform of the detector output to the transform of the input waveform. This technique was successfully applied to Golay cell and bolometer detectors and can be used for other linear detector systems.

Hagopian, John G.; Eichhorn, William

1990-01-01

100

Bright chirp-free and chirped nonautonomous solitons under dispersion and nonlinearity management  

NASA Astrophysics Data System (ADS)

We present a series of chirp-free and chirped analytical nonautonomous soliton solutions to the generalized nonlinear Schrodinger equation (NLSE) with distributed coefficients by Darboux transformation from a trivial seed. For chirpfree nonautonomous soliton, the dispersion management term can change the motion of nonautonomous soliton and do not affect its shape at all. Especially,the classical optical soliton can be presented with variable dispersion term and nonlinearity when there is no gain. For chirped nonautonomous soliton, dispersion management can affect the shape and motion of nonautonomous solitons meanwhile. The periodic dispersion term can be used to control its "breathing" shape, and it does not affect the trajectory of nonautonomous soliton center with a certain condition.

Yang, Zhan-Ying; Zhao, Li-Chen; Zhang, Tao; Yue, Rui-Hong

2011-02-01

101

Fourier fringe processing using a regressive Fourier-transform technique  

NASA Astrophysics Data System (ADS)

Since the introduction of a fourier fringe algorithm by Takeda, it has been possible to determine the phase of a particular light source impinging on an object from one sole image. This has led to applications in many whole field optical measurement techniques such as ESPI, holography, profilometry and so on. However, the basic processing technique, in case of the 2D-Fourier transform, is subject to a major drawback. Because this technique supposes periodicity in a fringe image, the so-called leakage effects occur. This gives rise to non-negligible errors, which can be resolved by using a regressive Fourier transformation technique. In the method introduced in this article, the fringe signal is represented by a model using sines and cosines where the frequency is not fixed (which is the case for classical FFT-techniques). The coefficients of those sines and cosines together with the frequency components are then estimated locally by means of a frequency domain system identification technique. This allows the fringe pattern to be unwrapped without any distortion. This method will be applied in particular to Fourier-transform profilometry (determines object geometry using shifts of projected fringes) although it can be used in any of the techniques mentioned above. Moreover, it will be shown that the proposed method can deal with other distortions that occur in practice such as over-modulation and varying fringe visibility. The proposed technique will be validated on both simulations and on a profile measurement of a pipe section.

Vanherzeele, J.; Guillaume, Patrick; Vanlanduit, Steve

2005-06-01

102

Hybrid Chirped Pulse Amplification  

SciTech Connect

We present a novel chirped pulse amplification method which combines optical parametric amplification and laser amplification. We have demonstrated this hybrid CPA concept with a combination of beta-barium borate and Ti:sapphire. High-efficiency, multi-terawatt compatible amplification is achieved without gain narrowing and without electro-optic modulators using a simple commercial pump laser.

Jovanovic, I; Barty, C P J

2002-05-07

103

Image watermarking technique based on the steerable pyramid transform  

NASA Astrophysics Data System (ADS)

The application of the steerable pyramid transform in image watermarking has many useful properties. In this paper, we will try to address some properties of steerable pyramid transform that are relevant for use in image watermarking; these properties include: (1) invariance properties; (2) multiresolution aspect; (3) capture of multi-scale and multiresolution structures in the image. All the above mentioned properties make this steerable pyramid transform appropriate for the design of a robust watermarking scheme. This paper proposes an image watermarking scheme based on steerable pyramid transform to embed invisible and robust watermark. We can summarize the basic principles of our method as follow: a host image is first transformed by the steerable pyramid transform. The different features are then extracted by thresolding the different subbands. The watermark sequence is inserted into disjoint blocks centered on the extracted feature points. The original host image is needed in watermark detection mainly for extracting the featured coefficients necessary for robust detection and determining the value of one bit of the watermark spread into a block. It has been confirmed by experiments and comparisons with many existing non-blind techniques that the watermark information embedded by the proposed technique is robust to JPEG compression, additive noise, and median filtering.

Drira, Fadoua; Denis, Florence; Baskurt, Atilla M.

2004-11-01

104

Detection of Partial Discharges in Transformers Using Acoustic Emission Techniques  

Microsoft Academic Search

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

E. Howells; E. T. Norton

1978-01-01

105

Approximate Fast Fourier Transform Technique for Vernier Spectral Analysis.  

National Technical Information Service (NTIS)

An approximate and quick fast Fourier transform technique for vernier spectral analysis is derived and tested for several candidate time-and delay-weightings, and for overlaps of the time weightings. For 50 percent overlap, the use of a simple cosine lobe...

A. H. Nuttall

1974-01-01

106

Propagation of chirped laser pulses in a plasma channel  

SciTech Connect

Propagation of an initially chirped, Gaussian laser pulse in a preformed parabolic plasma channel is analyzed. A variational technique is used to obtain equations describing the evolution of the phase shift and laser spot size. The effect of initial chirp on the laser pulse length and intensity of a matched laser beam propagating in a plasma channel has been analyzed. The effective pulse length and chirp parameter of the laser pulse due to its interaction with plasma have been obtained and graphically depicted. The resultant variation in laser frequency across the laser pulse is discussed.

Jha, Pallavi; Malviya, Amita; Upadhyay, Ajay K. [Department of Physics, University of Lucknow, Lucknow 226007 (India)

2009-06-15

107

Linear FM chirp laser  

SciTech Connect

The method is described of operating a laser radar system comprising: actuating a transmitter laser and a local oscillator laser to emit laser light at approximately a preselected common base frequency; frequency modulating the light of the transmitter laser in linear chirps by passing it through an electro-optical crystal disposed within the cavity of the transmitter and driving crystal with a linear chirp drive signal from a precision linear driver; sensing a portion of the laser light from the transmitter laser and the local oscillator laser to determine the base frequency thereof and adjusting the piezoelectric translators of the two lasers as a function of the sensed portion to maintain the lasers emitting at exactly the preselected base frequency; and using the balance of the light from the transmitter laser as the transmitted laser beam.

Duvall, R.L. III; Halmos, M.J.; Henderson, D.M.

1987-05-05

108

Frequency chirping in external modulators  

Microsoft Academic Search

A general formula is given that expresses frequency chirping in some types of external intensity modulators, such as the loss modulator, directional-coupler-type modulator, Mach-Zehnder interferometry-type modulator, and total-internal-reflection-type modulator. The chirping phenomenon treated is caused by the phase modulation due to an accompanied refractive index change. It is uniquely expressed in terms of an ?-parameter that contributes to frequency chirping

Fumio Koyama; KENICHI IGA

1988-01-01

109

Measuring optically thick molecular samples using chirped laser dispersion spectroscopy.  

PubMed

In this Letter, a dispersion-based gas sensing method applied to detection of optically thick samples is presented. We show that chirped laser dispersion spectroscopy (CLaDS) technique provides perfectly linear signal response over a wide range of target analyte concentrations. Using the most convenient chirp-modulated CLaDS detection scheme, it enables spectroscopic measurements in a line-locked mode from the minimum detection limit up to >99% peak molecular absorption. PMID:24081065

Nikodem, Michal; Wysocki, Gerard

2013-10-01

110

Image fusion in discrete cosine transform domain using masking techniques  

NASA Astrophysics Data System (ADS)

Image fusion is the process of combining two or more images of the same scene into a single image which is suitable for human perception and practical applications. This paper investigates the effect of use of different types of masks in discrete cosine transform (DCT) domain for image fusion applications. Here we have used different types of masks such as rectangular, triangular, strip and fan shaped mask. In the proposed scheme, the DCT of both the images are taken and mask and its complimentary mask are applied on two transformed images respectively. The masked images are then fused in the transform domain and inverse DCT is applied to obtain the fused image. Simulation results of the proposed technique are also presented and it is observed that fusion based on the fan shaped mask gives better quality of fused image than other masks consider in this paper as well as some of the methods existing in the literature.

Sharma, K. K.; Priti, K.

2013-01-01

111

Pattern recognition using versatile hybrid joint transform correlators: some techniques for improving the performance  

NASA Astrophysics Data System (ADS)

This paper reports the outcome of research studies carried out by us in the area of Optical Pattern Recognition. A hybrid JTC architecture has been used to evaluate correlation performance of four different types of JTCs in a non-cooperative situation. A non-zero order JTC has been proposed based on the principle of differential processing of joint power spectrum and its sensitivity to illumination variation has been investigated. A hybrid wavelet transform based JTC has been proposed and demonstrated to achieve high image discrimination. Hartley transform has been introduced in joint-transform correlation. Chirp modulation in HJTC has been demonstrated to extract information on object correlation and absolute object position from correlation output. A discrimination sensitive rotation-invariant JTC has been proposed based on gradient preprocessing and circular harmonic decomposition.

Pati, G. S.; Singh, Kehar

1999-04-01

112

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

PubMed

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

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

2010-01-18

113

Recent EISCAT heating results using chirped ISR  

Microsoft Academic Search

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

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

1996-01-01

114

Precision SAR processing using chirp scaling  

Microsoft Academic Search

A space-variant interpolation is required to compensate for the migration of signal energy through range resolution cells when processing synthetic aperture radar (SAR) data, using either the classical range\\/Doppler (R\\/D) algorithm or related frequency domain techniques. In general, interpolation requires significant computation time, and leads to loss of image quality, especially in the complex image. The new chirp scaling algorithm

R. Keith Raney; H. Runge; Richard Bamler; Ian G. Cumming; Frank H. Wong

1994-01-01

115

Dynamic chirped microwave photonic filter  

Microsoft Academic Search

A chirped single bandpass microwave photonic filter based on a broadband optical source, a Mach-Zehnder interferometer and a dispersive element is proposed. Special and unique features are shown such as the capacity of modifying the chirp in the passband using the dispersive element together in combination with the possibility of tunability and reconfigurability. The later features are achieved by means

M. Bolea; J. Mora; B. Ortega; J. Capmany; L. Chen

2009-01-01

116

Improved Chirp Filters/Signals.  

National Technical Information Service (NTIS)

A discrete chirp generator produces discrete chirp signals which correspond to either of two exponential functions, namely the functions exp (j pi (m sq + alpha)/N) or exp (j pi (m(m+beta)+alpha)/N), where m equal 0, 1, 2, ..., M. Typically, M and N might...

J. N. Alsup

1980-01-01

117

Bayesian Spectrum And Chirp Analysis  

Microsoft Academic Search

: We seek optimal methods of estimating power spectrum and chirp (frequency change)rate for the case that one has incomplete noisy data on values y(t) of a time series. The Schusterperiodogram turns out to be a "sufficient statistic" for the spectrum, a generalization playing thesame role for chirped signals. However, the optimal processing is not a linear filtering operation likethe

E. T. Jaynes; Wayman Crow

1987-01-01

118

Continuously tunable chirped microwave waveform generation using an optically pumped linear chirped fiber Bragg grating  

Microsoft Academic Search

A novel approach to generat ing a chirped microwave waveform with continuously tunable chirp rate using an optically pumped linearly chirped fiber Bragg grating (LCFBG) based on a temporal interferometer is proposed and demonstrated. A theoretical analys is is performed which is verified by an experiment. A linearly chirped microwave waveform with a tunable chirp rate from 79 to 64

Ming Li; Weilin Liu; Jianping Yao

2011-01-01

119

Complex heterodyne for undersampled chirped sinusoidal signals  

NASA Astrophysics Data System (ADS)

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).

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

2006-11-01

120

Complex heterodyne for undersampled chirped sinusoidal signals.  

PubMed

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

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

2006-11-10

121

Propagation dependence of chirp in Gaussian pulses and beams due to angular dispersion.  

PubMed

The chirp acquired by a Gaussian ultrashort pulse due to angular dispersion, unlike that of plane waves, increases nonlinearly with propagation distance and eventually asymptotes to a constant. However, this interesting result has never been directly measured. In this Letter, we use two-dimensional spectral interferometry to measure the propagation dependence of the chirp for Gaussian ultrashort pulses and beams with angular dispersion. The measured chirp as a function of propagation distance agreed well with theory. This work verifies both an equation and a measurement technique that will be useful for predicting or determining the pulse's chirp in ultrafast optics experiments that contain angular dispersion. PMID:19340185

Li, Derong; Zeng, Shaoqun; Luo, Qingming; Bowlan, Pamela; Chauhan, Vikrant; Trebino, Rick

2009-04-01

122

Error-resilient video coding technique based on wavelet transform  

NASA Astrophysics Data System (ADS)

In this paper, we propose a zerotree wavelet image/video coding technique with resilience to transmission errors which typically occur on noisy channels. A key tool that we employ is the bit partitioning algorithm and the bit reorganization algorithm which is called the EREC (Error Resilient Entropy Code). In order to take full advantage of the bit reorganization algorithm, the bit partitioning algorithm composes the data as separate code-blocks although the zerotree wavelet coding algorithm is not block-based compression technique. The bit reorganization algorithm requires a very low redundancy for the sequential transmission of variable length blocks that offer virtually guaranteed code and block synchronization. We present simulation results verifying the error resiliency of the proposed algorithm both for image coding which uses the wavelet transform and for video coding which uses the 3D wavelet transform. Experimental results show that the proposed coders outperform the existing error resilient coders for both noise-free channels and noisy channels. In addition, we confirm that the proposed algorithm is more error-resilient than the previously reported error-resilient coders for various channel error conditions.

Sohn, Kwang-Hoon; Lee, Chulhee; Jang, Woo-Young

2000-05-01

123

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

SciTech Connect

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

Malinovskaya, Svetlana A. [Department of Physics and Engineering Physics, Stevens Institute of Technology Hoboken, NJ 07030 (United States)

2007-12-26

124

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

PubMed Central

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.

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

2009-01-01

125

The Pure Rotational Spectrum of Perfluorooctanonitrile, C_7F15CN, Studied Using - and Chirped-Pulsed Fourier Transform Microwave Spectroscopies  

NASA Astrophysics Data System (ADS)

Fourier transform rotational spectroscopy has been used to collect the spectrum of perfluooctanonitrile. The spectrum was weak and only one conformer was observed. The assigned spectrum currently consists of both a- and b-type transitions spanning J = 8 to 40. The rotational constants are small, A = 681.37155(18) MHz, B = 126.116097(48) MHz, and C = 124.284824(49) MHz. The spectroscopic constants together with quantum chemical calculations have been used to identify the structure of the observed conformer. Notably the helical nature of the perfluoro alkyl chain is fully in evidence. Further calculations confirm that the nitrogen quadrupole coupling tensor is such that nitrogen hyperfine splitting will not be observable at the high J transitions recorded in our experiments. Spectroscopic constants and a discussion of the molecular structure will be presented.

Dewberry, C. T.; Grubbs, G. S. Grubbs, II; Cooke, S. A.; Bailey, W. C.

2011-06-01

126

Image Watermark Technique Based on Digital Holography and Ridgelet Transform  

Microsoft Academic Search

A novel image watermark algorithm based on digital holography and ridgelet transform was designed by taking the advantage that ridgelet transform domain is a most suitable representation of image's linear outline edge features. Firstly, the image was divided into blocks, and each block was transformed by finite ridgelet transformation. Secondly, the digital holography watermark is embedded into the most energetic

Jian-Ping Huang

2010-01-01

127

Solving Molodensky's series by fast Fourier transform techniques  

NASA Astrophysics Data System (ADS)

The use of the fast Fourier transform algorithm in the evaluation of the Molodensky series terms is demonstrated in this paper. The solution by analytical continuation to point level has been reformulated to obtain convolution integrals in planar approximation which can be efficiently evaluated in the frequency domain. Preliminary results show that the solution by Faye anomalies is not sufficient for highly accurate deflections of the vertical and height anomalies. The Molodensky solution up to at least the second-order term must be carried out. Part of the unrecovered deflection and height anomaly signal appears to be due to density variations, verifying the essential role of density modelling. A remove-restore technique for the terrain effects can improve the convergence of the series and minimize the interpolation errors.

Sideris, M. G.; Schwarz, K. P.

1986-03-01

128

Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70-102 GHz region  

NASA Astrophysics Data System (ADS)

Chirped-pulse millimeter-wave (CPmmW) spectroscopy is the first broadband (multi-GHz in each shot) Fourier-transform technique for high-resolution survey spectroscopy in the millimeter-wave region. The design is based on chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy [G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, and B. H. Pate, Rev. Sci. Instrum. 79, 053103 (2008)], which is described for frequencies up to 20 GHz. We have built an instrument that covers the 70-102 GHz frequency region and can acquire up to 12 GHz of spectrum in a single shot. Challenges to using chirped-pulse Fourier-transform spectroscopy in the millimeter-wave region include lower achievable sample polarization, shorter Doppler dephasing times, and problems with signal phase stability. However, these challenges have been partially overcome and preliminary tests indicate a significant advantage over existing millimeter-wave spectrometers in the time required to record survey spectra. Further improvement to the sensitivity is expected as more powerful broadband millimeter-wave amplifiers become affordable. The ability to acquire broadband Fourier-transform millimeter-wave spectra enables rapid measurement of survey spectra at sufficiently high resolution to measure diagnostically important electronic properties such as electric and magnetic dipole moments and hyperfine coupling constants. It should also yield accurate relative line strengths across a broadband region. Several example spectra are presented to demonstrate initial applications of the spectrometer.

Park, G. Barratt; Steeves, Adam H.; Kuyanov-Prozument, Kirill; Neill, Justin L.; Field, Robert W.

2011-07-01

129

Rotational spectrum of three conformers of 3,3-difluoropentane: Construction of a 480 MHz bandwidth chirped-pulse Fouriertransform microwave spectrometer  

Microsoft Academic Search

The rotational spectra for three conformers of 3,3-difluoropentane have been measured using both a newly constructed narrow bandwidth chirped-pulse Fourier-transform microwave spectrometer and a Balle–Flygare resonant cavity Fourier-transform microwave spectrometer. The chirped-pulse instrument produces a microwave pulse spanning up to 480MHz bandwidth in the 7–18GHz region by mixing a 1?s chirped pulse (of up to 240MHz bandwidth) from an arbitrary

Daniel A. Obenchain; Ashley A. Elliott; Amanda L. Steber; Rebecca A. Peebles; Sean A. Peebles; Charles J. Wurrey; Gamil A. Guirgis

2010-01-01

130

Rotational spectrum of three conformers of 3,3-difluoropentane: Construction of a 480 MHz bandwidth chirped-pulse Fouriertransform microwave spectrometer  

Microsoft Academic Search

The rotational spectra for three conformers of 3,3-difluoropentane have been measured using both a newly constructed narrow bandwidth chirped-pulse Fourier-transform microwave spectrometer and a Balle-Flygare resonant cavity Fourier-transform microwave spectrometer. The chirped-pulse instrument produces a microwave pulse spanning up to 480 MHz bandwidth in the 7-18 GHz region by mixing a 1 mus chirped pulse (of up to 240 MHz

Daniel A. Obenchain; Ashley A. Elliott; Amanda L. Steber; Rebecca A. Peebles; Sean A. Peebles; Charles J. Wurrey; Gamil A. Guirgis

2010-01-01

131

High-resolution imaging with advanced chirp optical coherence tomography  

NASA Astrophysics Data System (ADS)

Chirp optical coherence tomography (Chirp OCT) has been introduced as an alternative solution for imaging scattering media or biotissues. The basic principle of Chirp OCT is well-known by the FMCW radar technique and is adapted to the optical regime. This method uses a frequency modulated laser source in the near IR frequency range. Fast imaging can be performed by an electrical tuned diode laser without the disadvantage of any mechanical moved elements but retaining the properties of optical tomographic tools for contact less, non-ionizing, non-invasive and high depth resolved scanning. The demand of high resolution imaging for media application requires a large frequency tuning range. Covering the whole lasing bandwidth of an external cavity laser by the frequency Chirp, non-linear terms as well as mode-hopping reduce the depth resolution and the dynamic range, if equidistant sampling in the time domain is performed. To restore the resolution given by the Chirp bandwidth a reference detector has been implemented, which allows the detection of mode-hopping quantitatively and the correction of the non-linearity. The reference detector can be used for real-time laser frequency measurements and offers the possibility to determine the location of discrete reflectors more accurate. Images with a high dynamic range demonstrate an increased penetration depth.

Hoelscher, Dominik; Kemmer, Claude; Rupp, Florian; Blazek, Vladimir

2000-04-01

132

SAR Impulse Response with Residual Chirps.  

National Technical Information Service (NTIS)

A residual chirp waveform is a quadratic phase error that broadens the Impulse Response (IPR) and diminishes its peak value in a predictable manner. This report qualitatively and quantitatively analyzes the effects of a residual chirp on the IPR. .

A. W. Doerry

2009-01-01

133

Chirped four-wave mixing  

NASA Astrophysics Data System (ADS)

We will demonstrate that four-wave mixing with linearly chirped (phase-modulated) pulses is a unique tool for obtaining information on the dynamics and level structure of a system. Especially, it will be shown that the transient-grating-scattering type of experiment with chirped pulses provides an immediate answer to the question of whether the dynamics of a system occurs on a fast and/or slow time scale. In addition, we present compelling evidence that chirped four-wave mixing in a molecular system is a viable method for measuring excited-state vibrational frequencies. Double-sided Feynman diagrams are used for a third-order perturbative calculation of two-level four-wave-mixing effects and chirped coherent Raman scattering. The diagrams provide a visual representation of the quantum-mechanical pathways that the system can take as a result of the different field interactions. The number of quantum-mechanical pathways that contribute to the signal is shown to depend on the chirp rate compared to the time scale(s) of the system dynamics. A stochastic model is used to describe the optical dynamics of the system. The resulting expressions for the third-order nonlinear polarization are so complex that numerical calculations are necessary to simulate the time dependence of the optical response. It will also be shown that our theoretical results in the appropriate limits converge to those obtained for impulsive or continuous-wave excitation.

Duppen, Koos; de Haan, Foppe; Nibbering, Erik T. J.; Wiersma, Douwe A.

1993-06-01

134

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

135

Chirp Scaling Algorithms for SAR Processing  

NASA Technical Reports Server (NTRS)

The chirp scaling SAR processing algorithm is both accurate and efficient. Successful implementation requires proper selection of the interval of output samples, which is a function of the chirp interval, signal sampling rate, and signal bandwidth. Analysis indicates that for both airborne and spaceborne SAR applications in the slant range domain a linear chirp scaling is sufficient. To perform nonlinear interpolation process such as to output ground range SAR images, one can use a nonlinear chirp scaling interpolator presented in this paper.

Jin, M.; Cheng, T.; Chen, M.

1993-01-01

136

Frequency-chirped subwavelength nanoantennas.  

PubMed

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

Yaacobi, Ami; Watts, Michael R

2012-12-01

137

Photonic microwave matched filters for chirped microwave pulse compression  

Microsoft Academic Search

In this paper, a technique to design and implement a photonic microwave matched filter for chirped microwave pulse compression is presented. To realize matched filtering, the filter should have a spectral response that is matched to that of the input pulse, which is implemented in this paper using a photonic system that consists of an optical single-sideband (SSB) modulator and

Chao Wang; Jianping Yao

2008-01-01

138

Improved technique for one-way transformation of information  

DOEpatents

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.

Cooper, J.A.

1987-05-11

139

Wideband true-time-delay beam former that employs a tunable chirped fiber grating prism.  

PubMed

A fiber grating prism that consists of four tunable chirped-grating delay lines for wideband true-time-delay beam forming is proposed and demonstrated. The chirped gratings are produced by use of the grating bending technique in which a uniform grating is surface mounted on a simply supported beam. We obtained chirped gratings with different chirp rates by bending the uniform gratings with different beam deflections. Four linear chirped fiber gratings with identical spectral width but linearly increased grating length are fabricated. The spectra and time-delay responses of the tunable chirped gratings are measured. A chirped-grating prism for wideband true-time-delay beam forming by use of four chirped gratings is constructed and tested experimentally. We obtained different time delays by tuning the wavelength of the optical carrier. The proposed true-time-delay beam former with a four-element phased-array steerer is suitable for continuous beam forming at microwave frequencies up to 20 GHz. PMID:12737457

Liu, Yunqi; Yao, Jianping; Yang, Jianliang

2003-05-01

140

Linear frequency-modulated signal detection using Radon-ambiguity transform  

Microsoft Academic Search

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

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

1998-01-01

141

a Fourier Transform Technique for Estimating Bioelectric Currents from Magnetic Field Measurements  

Microsoft Academic Search

This dissertation presents a new noniterative technique for estimating current densities from magnetic field measurements. This Fourier-transform technique starts by forming a set of linear equations from the Fourier-transformed Maxwell equations. The set of equations is sampled according to the Whittaker-Shannon sampling theorem and solved by matrix methods. Two variations of the technique are extensions of a Fourier-transform method developed

Heidi Anne Schlitt

1992-01-01

142

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

PubMed Central

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.

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

2013-01-01

143

Image watermarking technique based on the steerable pyramid transform  

Microsoft Academic Search

The application of the steerable pyramid transform in image watermarking has many useful properties. In this paper, we will try to address some properties of steerable pyramid transform that are relevant for use in image watermarking; these properties include: (1) invariance properties; (2) multiresolution aspect; (3) capture of multi-scale and multiresolution structures in the image. All the above mentioned properties

Fadoua Drira; Florence Denis; Atilla M. Baskurt

2004-01-01

144

Techniques of on-line monitoring and diagnosis for transformer  

Microsoft Academic Search

The transformer is crucial for the energy conversion and transmission in the process of power transmission and distribution, and plays an important role in the security of grid. On-line monitoring and diagnostics provides a promising platform not only to help the operators to manage transformer in a targeted fault repair and maintenance manner, but also to avoid fatal accidents. This

GuangMing Zhang; GuoLian Jiang; ZhiXun Xie

2011-01-01

145

Techniques for increasing throughput in HEVC transform coefficient coding  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

146

A hybrid semi-blind digital image watermarking technique using lifting wavelet transform — Singular value decomposition  

Microsoft Academic Search

The lifting wavelet transform (LWT) is a recent approach to wavelet transform and singular value decomposition (SVD) is a valuable transform technique for robust digital watermarking. While LWT allows generating an infinite number of discrete biorthogonal wavelets starting from an initial one, singular values (SV) allow us to make changes in an image without affecting the image quality much. This

Meenakshi S Arya; Rajesh Siddavatam; S P Ghrera

2011-01-01

147

Hadamard Transform Spectrometry: A New Analytical Technique. Progress Report.  

National Technical Information Service (NTIS)

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) Con...

W. Hall

1989-01-01

148

Bandwidth-Tunable Fiber Bragg Gratings Based on UV Glue Technique  

NASA Astrophysics Data System (ADS)

In this study, we have demonstrated that a uniform fiber Bragg grating (FBG) can be transformed into a chirped fiber grating by a simple UV glue adhesive technique without shifting the reflection band with respect to the center wavelength of the FBG. The technique is based on the induced strain of an FBG due to the UV glue adhesive force on the fiber surface that causes a grating period variation and an effective index change. This technique can provide a fast and simple method of obtaining the required chirp value of a grating for applications in the dispersion compensators, gain flattening in erbium-doped fiber amplifiers (EDFAs) or optical filters.

Fu, Ming-Yue; Liu, Wen-Feng; Chen, Hsin-Tsang; Chuang, Chia-Wei; Bor, Sheau-Shong; Tien, Chuen-Lin

2007-07-01

149

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

SciTech Connect

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.

Polli, D.; Lanzani, G. [IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); CNST, Istituto Italiano di Tecnologia, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Brida, D.; Cerullo, G. [IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Mukamel, S. [Chemistry Department, University of California, Irvine, Irvine, California 92697-2025 (United States)

2010-11-15

150

A Robust Wavelet Transform Based Technique for Video Text Detection  

Microsoft Academic Search

In this paper, we propose a new method based on wavelet transform, statistical features and central moments for both graphics and scene text detection in video images. The method uses wavelet single level decomposition LH, HL and HH subbands for computing features and the computed features are fed to k means clustering to classify the text pixel from the background

Palaiahnakote Shivakumara; Trung Quy Phan; Chew Lim Tan

2009-01-01

151

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

PubMed

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(?), 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

Niebauer, T M

2013-03-20

152

Frequency chirp stabilization in semiconductor distributed feedback lasers with external control  

NASA Astrophysics Data System (ADS)

It is well known that current modulation in diode lasers generates amplitude (AM) and optical frequency (FM) modulations. The frequency chirp under direct current modulation originates from variations in the carrier density and from the finite difference in carrier density between the laser on and off states. Modulation of the carrier density modulates the gain and the optical index causing the resonant mode to shift. This frequency chirp broadens the spectrum, which is a serious limitation for high-speed applications and optical fiber communications. At low frequencies, thermal effects also alter the frequency chirp. The aim of this paper is to show that the laser's frequency chirp can be modified using an external control technique. The chirp response is evaluated via the determination of the chirp-to-power ratio (CPR) through a Mach-Zehnder interferometer. Experiments demonstrate that when an external optical feedback is properly adjusted, the CPR can be severely decreased over a wide range of modulation frequencies as compared to the free-running case. These preliminary results obtained on quantum well distributed feedback lasers (QW DFB) with low normalized coupling coefficient (?L) demonstrate how to stabilize the CPR through the DFB facet phase effects or parameters such as the linewidth enhancement factor. In order to confirm this frequency chirp engineering, selfconsistent calculations based on the transfer matrix method are also presented.

Grillot, F.; Provost, J. G.; Kechaou, K.; Thedrez, B.; Erasme, D.

2012-02-01

153

SAR impulse response with residual chirps.  

SciTech Connect

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.

Doerry, Armin Walter

2009-06-01

154

Nonlinearly chirped microwave pulse generation using a spatially discrete chirped fiber Bragg grating  

Microsoft Academic Search

In this paper, we propose an optical approach to generating nonlinearly chirped microwave pulses based on space-to-frequency-to-time mapping using a spatially discrete chirped fiber Bragg grating (SD-CFBG). The SD-CFBG functions to perform simultaneous spectral slicing, frequency-to-time mapping and temporal shifting. The generation of a nonlinearly chirped microwave pulse with a chirp rate varying from 93.6 to 11.2 GHz\\/ns is experimentally

Chao Wang; Jianping Yao

2009-01-01

155

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

NASA Technical Reports Server (NTRS)

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.

Morris, A. Terry

1999-01-01

156

Reconfigurable and single-shot chirped microwave pulse compression using a time-spectrum convolution system  

Microsoft Academic Search

An approach for reconfigurable single-shot chirped microwave pulse compression is proposed and experimentally demonstrated based on a time-spectrum convolution (TSC) system, for the first time to our knowledge. This proposed technique has three key features. The first feature is that non-periodic input chirped microwave pulses can be single-shot compressed. The second one is that the compression system is reconfigurable by

Ming Li; Antonio Malacarne; Sophie LaRochelle; Jianping Yao; Jose Azana

2011-01-01

157

Analysis of a digital chirp synthesizer  

SciTech Connect

Definite advantages are gained by using a chirp (linear-FM) waveform for radar pulse compression. Digital generation of this waveform provides programmability, predictability, and repeatability. Of the digital implementations considered, the digital chirp synthesizer is shown to have the most flexibility and is more readily miniaturized than the arbitrary waveform generator design. Elements and features of the digital chirp synthesizer are examined and design considerations are presented. A TTL breadboard circuit that was built demonstrates the soundness of the fundamental design of the digital chirp synthesizer concept. 10 refs., 18 figs., 10 tabs.

Allen, C.T.

1988-08-01

158

Accumulation of copper in Trichoderma reesei transformants, constructed with the modified Agrobacterium tumefaciens -mediated transformation technique  

Microsoft Academic Search

A modified Agrobacterium tumefaciens-mediated transformation method was established for the construction of mutants with improved copper tolerance and accumulation\\u000a capability in Trichoderma reesei. One transformant, AT01, exhibited the highest copper accumulation capability. With copper at 0.7 mM, AT01 removed 13 mg\\u000a copper\\/g biomass (removal rate of 96%), whereas the wild-type strain removed only 6 mg copper\\/g biomass (removal rate of 50%).\\u000a Optimal conditions

Kehe Fu; Lixing Liu; Lili Fan; Tong Liu; Jie Chen

2010-01-01

159

Wide-band superconductive Chirp filters  

SciTech Connect

Chirp filters are described that consist of miniature tapped superconductive stripline. The stripline consists of 40-micron-wide niobium thin films in a spiral pattern on 125-micron-thick silicon wafers, and tapping is effected by backward-wave couplers between neighboring lines. Sophisticated fabrication and packaging techniques have led to a now mature technology. Devices with 2.6-GHz bandwidth and time-bandwidth products of 98 are routinely fabricated that exhibit amplitude errors within a few tenths of a decibel and phase errors within a fractions of a degree of theoretical. In pulse-compression tests, matched amplitude-weighted devices yield peak relative side-lobe levels of -32 dB.

DiIorio, M.S.; Withers, R.S.; Anderson, A.C.

1989-04-01

160

Harnessing modified manganin technique to study processes of explosive transformation in pyrotechnic compositions  

Microsoft Academic Search

The paper reviews results of the experimental study of explosive transformation in pyrotechnic compositions with modified manganin technique. In particular, experimental data on pressure profiles recorded with tiny manganin sensors are cited to characterize the effect of parameters of the loading pulse, dispersion and density on peculiarities of explosive transformation in studied pyrotechnic pieces under shock-wave initiation. In the paper

Sergei Batalov

2005-01-01

161

Generation of ultrahigh peak power pulses by chirped pulse amplification  

Microsoft Academic Search

Single picosecond pulses have been amplified to the terawatt level by a table-top-size Nd:glass amplifier by using the technique of chirped pulse amplification (CPA). The divergence of the beam is twice the diffraction limit, making the brightness of this source equal to 2 x 10 to the 18th W\\/(cm-sr), which is thought to be the highest brightness yet reported. The

P. Maine; D. Strickland; P. Bado; M. Pessot; G. Mourou

1988-01-01

162

Identification of biological tissue using chirped probe THz imaging  

Microsoft Academic Search

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

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

2002-01-01

163

Highly Chirped Reconfigurable Microwave Photonic Filter  

Microsoft Academic Search

A photonic structure is proposed to implement a chirped single-bandpass filter based on a broadband optical source, an inteferometric structure, and a nonlinear dispersive element. The ability of controlling a quasi-linear chirp in the pass- band by using the dispersive element in addition to the possibility of tuning and reconfiguring the passband by means of a proper configuration of the

Mario Bolea; José Mora; Lawrence R. Chen; José Capmany

2011-01-01

164

Chirped-microwave assisted magnetization reversal  

Microsoft Academic Search

This paper reports simulation results on microwave-assisted magnetization reversal in magnetic thin films with perpendicular anisotropy. In comparison with frequency-fixed microwaves, frequency-chirped microwaves have higher efficiency in pumping magnetization precession and, therefore, can lead to more significant reduction in switching fields. Through the use of chirped microwaves, switching with low fields is also possible for large damping films.

Zihui Wang; Mingzhong Wu

2009-01-01

165

Detection and frequency tracking of chirping signals.  

National Technical Information Service (NTIS)

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....

G. R. Elliott S. D. Stearns

1990-01-01

166

Detection and frequency tracking of chirping signals  

SciTech Connect

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.

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

1990-08-01

167

High-frequency subharmonic emission with chirp-coded excitation: implications for imaging  

NASA Astrophysics Data System (ADS)

There is growing interest in developing techniques to assess the structure and function of microvasculature, to enable clinical diagnosis and to gain insights into disease pathology. High-frequency subharmonic imaging is an emerging technique that can visualize the microvasculature with high specificity. However, the sensitivity of high-frequency subharmonic imaging is compromised because of the pressure threshold for subharmonic behavior, which may limit its potential for preclinical and clinical imaging. The goal of this work was to demonstrate that the sensitivity of subharmonic imaging could be improved by rectangular apodization and chirp-coding of the excitation pulse. We report an experimental study carried out at 20-MHz transmit frequency to compare the efficacy of narrowband sine bursts and coded-chirps towards generating subharmonics. It was demonstrated that chirp-coding of the excitation pulse could generate stable subharmonic signals for excitation bandwidths of 10-20%. The threshold for onset of subharmonic behavior was lowest when rectangularwindowed excitation pulses were employed. The subharmonic to fundamental ratio of RF spectra using coded chirps was up to 5.7 dB higher for sine bursts, and the axial resolution obtained with chirp-coded excitation was up to twofold better compared to that obtained using sine bursts. At 20-MHz transmit frequency, 20% bandwidth rectangular chirp-coded pulse appears to be a good tradeoff between sensitivity and axial resolution.

Shekhar, Himanshu; Doyley, Marvin M.

2012-02-01

168

Population inversion by chirped pulses  

SciTech Connect

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.

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

2011-09-15

169

Raman forward scattering of chirped laser pulses  

SciTech Connect

Raman scattering of a high-intensity, short duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatio-temporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all regimes of forward scattering, it is shown that the growth rate increases (decreases) for positive (negative) frequency chirp. The effect of chirp on the growth rate is relatively minor, i.e., a few percent chirp yields few percent changes in the growth rates. Numerical solutions based on fully nonlinear cold Maxwell-fluid model are presented which confirm analytical predictions. Relation of these results to recent experiments is discussed.

Schroeder, C.B.; Esarey, E.; Shadwick, B.A.; Leemans, W.P.

2002-12-05

170

Coherent chirped pulse laser network with Mickelson phase conjugator.  

PubMed

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

Okulov, A Yu

2014-04-10

171

Pulse compression of an FM chirped CO sub 2 Laser  

SciTech Connect

A CO{sub 2} laser has been FM chirp modulated by a CdTe intracavity modulator. A frequency deviation-of-100 MHz in 2 {mu}s 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{sub 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.

Halmos, M.J.; Henderson, D.M.; Duvall, R.,III (Hughes Aircraft Company, Laser Sensors Laboratories, Tactical Engineering Division, Electro-Optical Data Systems Group, P.O. Box 902, El Segundo, California 90245 (US))

1989-09-01

172

A sliding-window transform-domain technique for denoising of DSPI phase maps  

NASA Astrophysics Data System (ADS)

We have developed a technique for denoising speckle pattern fringes, which makes use of an overcomplete expansion in transform domain combined with suitable thresholding of transform-domain coefficients related with the speckle size. In this paper, we modify the technique to work on noisy phase maps obtained by Phase Shifting Digital Speckle Pattern Interferometry (PSDSPI). The modified version utilizes a complex-valued representation for the phase maps and consequently employs Discrete Fourier transform in sliding window mode for obtaining the sought overcomplete expansion. We discuss issues related of the window size and local threshold value selection. We compare this approach with two state of the art denoising techniques on simulated speckle pattern phase maps. Furthermore, we demonstrate the performance of our technique for denoising of real phase maps, obtained through PSDSPI in an out-of-plane sensitive set-up.

Shulev, Assen A.; Gotchev, Atanas

2014-02-01

173

Transformation techniques for cross-sectional and longitudinal endocrine data: application to salivary cortisol concentrations.  

PubMed

Endocrine time series often lack normality and homoscedasticity most likely due to the non-linear dynamics of their natural determinants and the immanent characteristics of the biochemical analysis tools, respectively. As a consequence, data transformation (e.g., log-transformation) is frequently applied to enable general linear model-based analyses. However, to date, data transformation techniques substantially vary across studies and the question of which is the optimum power transformation remains to be addressed. The present report aims to provide a common solution for the analysis of endocrine time series by systematically comparing different power transformations with regard to their impact on data normality and homoscedasticity. For this, a variety of power transformations of the Box-Cox family were applied to salivary cortisol data of 309 healthy participants sampled in temporal proximity to a psychosocial stressor (the Trier Social Stress Test). Whereas our analyses show that un- as well as log-transformed data are inferior in terms of meeting normality and homoscedasticity, they also provide optimum transformations for both, cross-sectional cortisol samples reflecting the distributional concentration equilibrium and longitudinal cortisol time series comprising systematically altered hormone distributions that result from simultaneously elicited pulsatile change and continuous elimination processes. Considering these dynamics of endocrine oscillations, data transformation prior to testing GLMs seems mandatory to minimize biased results. PMID:23063878

Miller, Robert; Plessow, Franziska

2013-06-01

174

Chirped femtosecond pulse scattering by spherical particles  

NASA Astrophysics Data System (ADS)

Generalized Lorentz-Mie formulas are used to study the scattering characteristics when a chirped femtosecond pulse illuminates a spherical particle. For a linear chirped Gaussian pulse with the envelope function g( tau ) = exp[- pi (1 + ib) tau 2], dimensionless parameter b is defined as a chirp. The calculation illustrated that even for pulses with a constant carrier wavelength ( lambda 0 = 0.5 mu m) and pulse-filling coefficient (l0 = 1.98), the efficiencies for extinction and scattering differ very much between the carrier wave and the different chirped pulses. The slowly varying background of the extinction and the scattering curves is damped by the chirp. When the pulse is deeply chirped, the maxima and minima of the background curves reduce to the point where they disappear, and the efficiency curves illustrate a steplike dependence on the sphere size. Another feature is that the only on the amount of chirp (|b|), regardless of upchirp (b greater than 0) or downchirp (b less than 0).

Kim, Dal-Woo; Xiao, Gang-Yao; Lee, Tong-Nyong

1996-05-01

175

Polar format agorithm using chirp scaling for spotlight SAR image formation  

Microsoft Academic Search

A novel implementation of the polar format algorithm (PFA) using the principle of chirp scaling (PCS) for spotlight synthetic aperture radar (SAR) image formation is addressed. A PFA completely free of interpolation has been achieved in moderate squinted imaging geometry. The presented approach consists of the range and azimuth scaling of the polar samples, in which only fast Fourier transforms

Daiyin Zhu; Shaohua Ye; Zhaoda Zhu

2008-01-01

176

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

177

15 N isotope dilution techniques to study soil nitrogen transformations and plant uptake  

Microsoft Academic Search

The use of15N as a tracer in soil\\/plant research is examined. The limitations of the so-called Ndff approach are discussed to show the need to consider not just the fate of the added label but also the path that was followed and the rate of the transformation. The development of15N isotope dilution techniques to determine gross rates of nitrogen transformation

D. Barraclough

1995-01-01

178

Transionospheric signal detection with chirped wavelets  

SciTech Connect

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.

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

1997-11-01

179

CHIRP  

Cancer.gov

Skip to Main Content Headlines Pediatric Oncology Branch Home > Pediatric Psycho-Oncology Professionals > Training Headline Title Pediatric Psycho-Oncology Professionals Pediatric Psychology Postdoctoral Fellowship University of Louisville School of

180

Chaotic chirped-pulse oscillators.  

PubMed

We present results of experimental investigation of the chaotic and quasi-periodic regime in the chirped-pulsed (dissipative soliton) Cr:ZnS and Cr:ZnSe mid-IR oscillators with significant third-order dispersion. The instability develops when the spectrum edge approaches resonance with a linear wave either due to power increase or by dispersion adjustment. In practice, this occurs when the spectrum edge reaches zero dispersion wavelength. The analysis suggests a three-oscillator chaos model, which is confirmed by numerical simulations. The regime is long-term stable and can be easily overlooked in similar systems. We show that chaotic regime is accompanied by a characteristic spectral shape and can be reliably recognized by using wavelength-skewed filters and by second-harmonic or two-photon absorption detectors. PMID:24514508

Sorokin, Evgeni; Tolstik, Nikolai; Kalashnikov, Vladimir L; Sorokina, Irina T

2013-12-01

181

Self-referenced characterization of femtosecond laser pulses by chirp scan.  

PubMed

We investigate a variant of the d-scan technique, an intuitive pulse characterization method for retrieving the spectral phase of ultrashort laser pulses. In this variant a ramp of quadratic spectral phases is applied to the input pulses and the second harmonic spectra of the resulting pulses are measured for each chirp value. We demonstrate that a given field envelope produces a unique and unequivocal chirp-scan map and that, under some asymptotic assumptions, both the spectral amplitude and phase of the measured pulse can be retrieved analytically from only two measurements. An iterative algorithm can exploit the redundancy of the information contained in the chirp-scan map to discard experimental noise, artifacts, calibration errors and improve the reconstruction of both the spectral intensity and phase. This technique is compared to two reference characterization techniques (FROG and SRSI). Finally, we perform d-scan measurements with a simple grating-pair compressor. PMID:24150331

Loriot, Vincent; Gitzinger, Gregory; Forget, Nicolas

2013-10-21

182

Chirped-pulse manipulated carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs  

NASA Astrophysics Data System (ADS)

Chirped pulse controlled carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs are investigated by degenerate pump-probe technique. Varying the chirped condition of excited pulse from negative to positive increases the carrier relaxation time so as to modify the dispersion and reshape current pulse in time domain. The spectral dependence of carrier dynamics is analytically derived and explained by Shockley-Read Hall model. This observation enables the new feasibility of controlling carrier dynamics in ultrafast optical devices via the chirped pulse excitations.

Lee, Chao-Kuei; Lin, Yuan-Yao; Lin, Sung-Hui; Lin, Gong-Ru; Pan, Ci-Ling

2014-04-01

183

Terahertz surface plasmon on chirped groove grating  

Microsoft Academic Search

The excitation of terahertz surface plasmon on metallized chirped groove gratings is studied in time- and frequency-domain. These gratings have a potential to launch and decouple broadband terahertz surface plasmon necessary for integrated optical circuits.

M. Martl; J. Darmo; K. Unterrainer; E. Gornik

2008-01-01

184

Residual chirp in integrated-optic modulators  

Microsoft Academic Search

The authors have analyzed and measured the dispersion effects of residual chirp arising from asymmetry in field overlap in Mach-Zehnder structures. A clear influence of chirp was seen at 7 Gb\\/s and a propagation length of 75-km nondispersion shifted fiber at ?=1.55 ?m. It is shown that a MZ-modulator with field overlap in one arm only and operated in the

Anders Djupsjobacka

1992-01-01

185

Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges.  

PubMed

We present a simple and robust technique to retrieve the phase of ultrashort laser pulses, based on a chirped mirror and glass wedges compressor. It uses the compression system itself as a diagnostic tool, thereby making unnecessary the use of complementary diagnostic tools. We used this technique to compress and characterize 7.1 fs laser pulses from an ultrafast laser oscillator. PMID:22274393

Miranda, Miguel; Fordell, Thomas; Arnold, Cord; L'Huillier, Anne; Crespo, Helder

2012-01-01

186

High-Fidelity Adiabatic Passage by Composite Sequences of Chirped Pulses  

SciTech Connect

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

Torosov, Boyan T. [Department of Physics, Sofia University, 5 James Bourchier Boulevard, 1164 Sofia (Bulgaria); Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 5209, BP 47870, F-21078 Dijon (France); Guerin, Stephane [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 5209, BP 47870, F-21078 Dijon (France); Vitanov, Nikolay V. [Department of Physics, Sofia University, 5 James Bourchier Boulevard, 1164 Sofia (Bulgaria)

2011-06-10

187

Ultrashort pulse characterization by spectral shearing interferometry with spatially chirped ancillae.  

PubMed

We report a new version of spectral phase interferometry for direct electric field reconstruction (SPIDER), in which two spatially chirped ancilla fields are used to generate a spatially encoded SPIDER interferogram. We dub this new technique Spatially Encoded Arrangement for Chirped ARrangement for SPIDER (SEA-CAR-SPIDER). The single shot interferogram contains multiple shears, the spectral amplitude of the test pulse, and the reference phase, which is accurate for broadband pulses. The technique enables consistency checking through the simultaneous acquisition of multiple shears and offers a simple and precise calibration method. All calibration parameters--the shears, and the upconversionfrequency--can be accurately obtained from a single calibration trace. PMID:20372632

Witting, Tobias; Austin, Dane R; Walmsley, Ian A

2009-10-12

188

Pattern recognition techniques screening for drugs of abuse with gas chromatography–Fourier transform infrared spectroscopy  

Microsoft Academic Search

As many drugs of abuse are relatively volatile substances, gas chromatography–mass spectrometry (GC–MS), and more recently gas chromatography–Fourier transform infrared spectroscopy (GC–FTIR) became the most powerful techniques applied for their identification. We are presenting a combination of pattern recognition techniques discriminating illicit amphetamines according to the substitution pattern associated with the psychotropic activity (stimulants and hallucinogens) for which they are

M. Praisler; I. Dirinck; J. Van Bocxlaer; A. De Leenheer; D. L. Massart

2000-01-01

189

Comparison of different current transformer modeling techniques for protection system studies  

Microsoft Academic Search

If current transformer (CT) characteristics are not properly selected for fault conditions, saturation will occur and relays can have delayed response or even fail to trip. To verify that CT saturation will not cause mis-coordination with other protection devices a study needs to be performed, which requires CT modeling. This paper compares different CT computer modeling techniques. Models of a

Lj. A. Kojovic

2002-01-01

190

Superconducting current transformer for testing Nb3Sn cable splicing technique  

Microsoft Academic Search

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 was 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

N. Andreev; E. Barzi; S. Bhashyam; C. Boffo; D. R. Chichili; S. Yadav; I. Terechkine; A. V. Zlobin

2003-01-01

191

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

ERIC Educational Resources Information Center

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…

Jamieson, Marguerite; Kajs, Rebecca; Agee, Anne

1996-01-01

192

Space curve recognition based on the wavelet transform and string-matching techniques  

Microsoft Academic Search

A technique for representing and recognising 3-D or space curves is presented. In the proposed algorithm, the space curves are represented by a set of two zero-crossing representations which are constructed based on the dyadic wavelet transform. These representations are then described in the form of an ordered set of complex numbers which is referred to as the compact representation

Quang Minh Tieng; Wageeh W. Boles; Mohamed Deriche

1995-01-01

193

On the POCS-based postprocessing technique to reduce the blocking artifacts in transform coded images  

Microsoft Academic Search

We propose a novel postprocessing technique, based on the theory of projections onto convex sets (POCS), to reduce the blocking artifacts in transform coded images. It is assumed, in our approach, that the original image is highly correlated. Thus, the global frequency characteristics in two adjacent blocks are similar to the local ones in each block. We consider the high-frequency

Hoon Paek; Rin-Chul Kim; Sang-Uk Lee

1998-01-01

194

A new robust digital image watermarking technique based on the Discrete Cosine Transform and Neural Network  

Microsoft Academic Search

This paper presents a new robust digital image watermarking technique based on discrete cosine transform (DCT) and neural network. The neural network is full counter propagation neural network (FCNN). FCNN has been used to simulate the perceptual and visual characteristics of the original image. The perceptual features of the original image have been used to determine the highest changeable threshold

Ahmad R Naghsh Nilchi; Ayoub Taheri

2008-01-01

195

Chirped excitation of optically dense inhomogeneously broadened media using Eu3+:Y2SiO5  

NASA Astrophysics Data System (ADS)

We describe experimentally accessible diagnostics for the excitation of optically dense frequency-selective media by linear frequency-chirped pulses using a sensitive pump-probe technique on the 7F0 to 5D0 transitions of 1.0% Eu3+:Y2SiO5. Distinct features within a transmitted cw probe pulse are used to identify the combination of linear chirp rate and optical power needed to produce an average Bloch-vector rotation of 90°. The resulting superposition state is thus an equal mixture of the ground and excited states on average. We find experimentally a linear relationship between the applied chirp-pulse intensity and chirp rate required to produce this half-inversion, a conclusion supported by both analytical calculations made using a Landau-Zener approach, and detailed computer simulations using the Maxwell-Bloch model. The numerical simulations predict experimentally observed phenomena such as the reshaping of probe pulses by stimulated emission or absorption. Finally, we quantify the relationship between chirp rate and optical power for half-inversion as a function of the optical density of the medium. The pump-probe experimental techniques and simulation analysis techniques developed here can be extended to produce an arbitrary mixture of ground and excited states, on average, in media spanning a wide range of optical density. Preparation of such media by chirped pulses for applications in quantum computing, photon-echo-based time-domain storage, and signal processing will be aided by these techniques.

Harris, Todd L.; Tian, Mingzhen; Babbitt, W. Randall; Burr, Geoffrey W.; Hoffnagle, John A.; Jefferson, C. Michael

2004-04-01

196

Interplay of the chirps and chirped pulse compression in a high-gain seeded free-electron laser  

SciTech Connect

In a seeded high-gain free-electron laser (FEL), where a coherent laser pulse interacts with an ultrarelativistic 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. 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 to get a short pulse duration, an energy chirp in the electron beam is important.

Wu Juhao; Murphy, James B.; Emma, Paul J.; Wang Xijie; Watanabe, Takahiro; Zhong Xinming [Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States); National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States); Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States); National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States); Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875 (China)

2007-03-15

197

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

SciTech Connect

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.

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

2007-01-03

198

Interaction of free charged particles with a chirped electromagnetic pulse.  

PubMed

We study the effect of chirp on electromagnetic (EM) pulse interaction with a charged particle. Both the one-dimensional (1D) and 3D cases are considered. It is found that, in contrast to the case of a nonchirped pulse, the charged particle energy can be changed after the interaction with a 1D EM chirped pulse. Different types of chirp and pulse envelopes are considered. In the case of small chirp, an analytical expression is found for arbitrary temporal profiles of the chirp and the pulse envelope. In the 3D case, the interaction with a chirped pulse results in a polarization-dependent scattering of charged particles. PMID:15697564

Khachatryan, A G; van Goor, F A; Boller, K-J

2004-12-01

199

Interaction of free charged particles with a chirped electromagnetic pulse  

SciTech Connect

We study the effect of chirp on electromagnetic (EM) pulse interaction with a charged particle. Both the one-dimensional (1D) and 3D cases are considered. It is found that, in contrast to the case of a nonchirped pulse, the charged particle energy can be changed after the interaction with a 1D EM chirped pulse. Different types of chirp and pulse envelopes are considered. In the case of small chirp, an analytical expression is found for arbitrary temporal profiles of the chirp and the pulse envelope. In the 3D case, the interaction with a chirped pulse results in a polarization-dependent scattering of charged particles.

Khachatryan, A.G.; Goor, F.A. van; Boller, K.-J. [Department of Applied Science, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands)

2004-12-01

200

Analytical chirped solutions to the (3 + 1)-dimensional Gross-Pitaevskii equation for various diffraction and potential functions.  

PubMed

Analytical solutions to the (3 + 1)-dimensional Gross-Pitaevskii equation in the presence of chirp and for different diffraction and potential functions are found. We utilize a method we formulated to solve the Riccati equation for the chirp function that arises when the F-expansion technique and the homogeneous balance principle are applied to the Gross-Pitaevskii equation. Three specific examples of physical interest are considered in some detail. PMID:21867333

Al Bastami, Anas; Beli?, Milivoj R; Milovi?, Daniela; Petrovi?, Nikola Z

2011-07-01

201

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

USGS Publications Warehouse

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.

Lemeshewsky, George, P.; Schowengerdt, Robert, A.

2000-01-01

202

Harnessing modified manganin technique to study processes of explosive transformation in pyrotechnic compositions  

NASA Astrophysics Data System (ADS)

The paper reviews results of the experimental study of explosive transformation in pyrotechnic compositions with modified manganin technique. In particular, experimental data on pressure profiles recorded with tiny manganin sensors are cited to characterize the effect of parameters of the loading pulse, dispersion and density on peculiarities of explosive transformation in studied pyrotechnic pieces under shock-wave initiation. In the paper are shown the experimental pressure profiles, characteristic for processes of explosive transformation of extended delay. The experimental results prove the effect of density variation of the specimens under study on the process of the explosive transformation. It is felt that for given range of pressures of the incoming shock wave the difference of the explosive transformation history, at equal parameters of loading pulse, is caused also by different dispersion of the initial powder and final porosity of studied specimens. The experimental results provide support for possibility of use of tiny manganin and constantan sensors in studying processes of explosive transformation of pyrotechnic compositions under initiation by divergent shock waves of large curve front and slumping pressure profile.

Batalov, Sergei

2005-07-01

203

High Accuracy Evaluation of the Finite Fourier Transform Using Sampled Data  

NASA Technical Reports Server (NTRS)

Many system identification and signal processing procedures can be done advantageously in the frequency domain. A required preliminary step for this approach is the transformation of sampled time domain data into the frequency domain. The analytical tool used for this transformation is the finite Fourier transform. Inaccuracy in the transformation can degrade system identification and signal processing results. This work presents a method for evaluating the finite Fourier transform using cubic interpolation of sampled time domain data for high accuracy, and the chirp Zeta-transform for arbitrary frequency resolution. The accuracy of the technique is demonstrated in example cases where the transformation can be evaluated analytically. Arbitrary frequency resolution is shown to be important for capturing details of the data in the frequency domain. The technique is demonstrated using flight test data from a longitudinal maneuver of the F-18 High Alpha Research Vehicle.

Morelli, Eugene A.

1997-01-01

204

High Resolution Pulse Compression Imaging Using Super Resolution FM-Chirp Correlation Method (SCM)  

NASA Astrophysics Data System (ADS)

This study addresses the issue of the super-resolution pulse compression technique (PCT) for ultrasound imaging. Time resolution of multiple ultrasonic echoes using the FM-Chirp PCT is limited by the bandwidth of the sweep-frequency. That is, the resolution depends on the sharpness of auto-correlation function. We propose the Super resolution FM-Chirp correlation Method (SCM) and evaluate its performance. This method is based on the multiple signal classification (MUSIC) algorithm. Our simulations were made for the model assuming multiple signals reflected from some scatterers. We confirmed that SCM detects time delay of complicated reflected signals successfully with high resolution.

Fujiwara, M.; Okubo, K.; Tagawa, N.

205

Chirped pulse shadowgraphy for single shot time resolved plasma expansion measurements  

SciTech Connect

The dynamics of ultrashort laser plasmas demand single shot temporal measurements on fast time scales. We describe a method to record the plasma expansion on picosecond (ps) timescales continuously over hundreds of ps, in single shot. The method uses the chirp of a Ti:sapphire laser as a time-resolved optical diagnostic tool. Using this technique, the evolution of the plasma expansion had been recorded with ps time resolutions, by probing with a chirped laser pulse of 200 ps duration. A peak expansion velocity of 1.8x10{sup 7} cm/s is observed and its evolution in time is obtained for approx300 ps.

Prasad, Y. B. S. R.; Barnwal, S.; Naik, P. A.; Chakera, J. A.; Khan, R. A.; Gupta, P. D. [Laser Plasma Division, RRCAT, Indore, 452 013 Madhya Pradesh (India)

2010-05-31

206

Experimental demonstration of energy-chirp compensation by a tunable dielectric-based structure.  

PubMed

A tunable energy-chirp compensator was used to remove a correlated energy chirp from the 60-MeV beam at the Brookhaven National Laboratory Accelerator Test Facility. The compensator operates through the interaction of the wakefield of the electron bunch with itself and consists of a planar structure comprised of two alumina bars with copper-plated backs separated by an adjustable beam aperture. By changing the gap size, the correlated energy chirp of the electron bunch was completely removed. Calculations show that this device, properly scaled to account for the electron bunch charge and length, can be used to remove residual correlated energy spread at the end of the linacs used for free-electron lasers. The experimental results are shown to be in good agreement with numerical simulations. Application of this technique can significantly simplify linac design and improve free-electron lasers performance. PMID:24702378

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

2014-03-21

207

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

PubMed

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

Shi, Xiaoyan; Zhao, Daomu

2011-02-10

208

Joint transform correlator based on CIELAB model with encoding technique for color pattern recognition  

NASA Astrophysics Data System (ADS)

The CIELAB standard color vision model instead of the traditional RGB color model is utilized for polychromatic pattern recognition. The image encoding technique is introduced. The joint transform correlator is set to be the optical configuration. To achieve the distortion invariance in discrimination processes, we have used the minimum average correlation energy approach to yield sharp correlation peak. From the numerical results, it is found that the recognition ability based on CIELAB color specification system is accepted.

Lin, Tiengsheng; Chen, Chulung; Liu, Chengyu; Chen, Yuming

2010-05-01

209

Fast classification and compositional analysis of cornstover fractions using Fourier transform near-infrared techniques  

Microsoft Academic Search

The objectives of this research were to determine the variation of chemical composition across botanical fractions of cornstover, and to probe the potential of Fourier transform near-infrared (FT-NIR) techniques in qualitatively classifying separated cornstover fractions and in quantitatively analyzing chemical compositions of cornstover by developing calibration models to predict chemical compositions of cornstover based on FT-NIR spectra. Large variations of

X. Philip Ye; Lu Liu; Douglas Hayes; Alvin Womac; Kunlun Hong; Shahab Sokhansanj

2008-01-01

210

Multiplexed Wavelet Transform Technique for Detection of Microcalcification in Digitized Mammograms  

Microsoft Academic Search

Wavelet transform (WT) is a potential tool for the detection of microcalcifications, an early sign of breast cancer. This article describes the implementation and evaluates the performance of two novel WT-based schemes for the automatic detection of clustered microcalcifications in digitized mammograms. Employing a one-dimensional WT technique that utilizes the pseudo-periodicity property of image sequences, the proposed algorithms achieve high

M. G. Mini; V. P. Devassia; Tessamma Thomas

2004-01-01

211

Techniques for Handling and Removal of Spectral Channels in Fourier Transform Synchrotron-Based Spectra  

SciTech Connect

Channel spectra are a big problem for those attempting to use synchrotron-based Fourier transform spectra for spectral lineshape studies. Due to the layout of the optical system at the CLS far-infrared beamline, the synchrotron beam undergoes unavoidable multiple reflections on the steering mirrors, beam splitter, several sets of windows, and filters. We present a method for eliminating channel spectra and compare the results of our technique with other methods available in the literature.

Ibrahim, Amr; Predoi-Cross, Adriana; Teillet, Philippe M. [University of Lethbridge, Department of Physics and Astronomy, 4401 University Drive, Lethbridge, AB, T1K 3M4 (Canada)

2010-02-03

212

Coherent chirped pulse laser network with Mickelson phase conjugator  

NASA Astrophysics Data System (ADS)

The mechanisms of nonlinear phase-locking of a large fiber amplifier array are analyzed. It is shown that Michelson phase conjugating configuration with double passage through array of fiber amplifiers have the definite advantages compared to one-way fiber array coupled in a Mach-Zehnder configuration. Regardless to amount of synchronized fiber amplifiers Michelson phase-conjugating interferometer is expected to do a perfect compensation of the phase-piston errors and collimation of backwardly amplified fiber beams on entrance/output beamsplitter. In both configurations the nonlinear transformation of the stretched pulse envelope due to gain saturation is capable to randomize the position of chirp inside envelope thus it may reduce the visibility of interference pattern at output beamsplitter. A certain advantages are inherent to the $sech$-form temporal envelope because of exponential precursor and self-similar propagation in gain medium. The Gaussian envelope is significantly compressed in a deep gain saturation regime and frequency chirp position inside pulse envelope is more deformed.

Okulov, A. Yu.

2014-04-01

213

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

Microsoft Academic Search

Chirp-pulse microwave computerized tomography (CP-MCT) is a technique designed to image temperature variations inside a body. In the prototype developed at Niigata University images are obtained by means of the basic algorithm of tomography, namely filtered backprojection. The purpose of this paper is to develop an improved linear model for data reduction. We introduce a method, based on scattering theory,

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

2001-01-01

214

Velocity Measurements Using a Single Transmitted Linear Frequency-Modulated Chirp  

Microsoft Academic Search

Velocity measurement is a challenge for a variety of remote sensing systems such as ultrasonic and radar scanners. However, current Doppler-based techniques require a comparatively long data acquisition time. It has been suggested to use coded signals, such as linear frequency-modulated signals (chirp), for ultrasonic velocity estimation by extracting the needed information from a set of several sequential coded pulses.

Yoav Levy; Haim Azhari

2007-01-01

215

A precision chirp scaling SAR processor extension to sub-aperture implementation on massively parallel supercomputers  

Microsoft Academic Search

A new concept in SAR raw data focusing algorithms is discussed. The so called “chirp scaling” (CS) technique has allowed the complete elimination of the interpolation step required in conventional ?-K wave domain processing algorithms. This drives to high performance the implementation of aberrationless 2D processors, both for SAR focusing and for analogue problems (seismic wave migration, tomography, etc.). Furthermore

Fabr izio Impagnatiello

1995-01-01

216

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

Microsoft Academic Search

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

Martin Pollakowski; Helmut Ermert

1994-01-01

217

Powerful femtosecond pulse generation by chirped and stretched pulse parametric amplification in BBO crystal  

Microsoft Academic Search

Chirped pulses have been parametrically amplified by a factor of ~2×104 without bandwidth limitation in BBO crystal. Pulses were compressed down to 70 fs, and ~0.9 GW output power has been obtained. A special technique to match temporal profiles of signal and pump pulses was used.

A. Dubietis; G. Jonusauskas; A. Piskarskas

1992-01-01

218

All-Optical High-Frequency Electrical Chirped Pulse Generation using a Nonlinearly Chirped Fiber Bragg Grating  

Microsoft Academic Search

In this paper, two novel approaches to optically generating high-frequency chirped electrical pulses with tunable chirp rate using a tunable nonlinearly chirped fiber Bragg grating (NL-CFBG) are proposed. In the first approach, a high-frequency electrical chirped pulse is generated based on optical spectral shaping and nonlinear wavelength-to-time conversion using a tunable NL-CFBG. In the second approach, two ultrashort pulses at

Chao Wang; Jianping Yao

2007-01-01

219

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

PubMed Central

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.

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

2011-01-01

220

TRANSFORMATION  

SciTech Connect

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).

LACKS,S.A.

2003-10-09

221

Slit Function Measurement of An Imaging Spectrograph Using Fourier Transform Techniques  

NASA Technical Reports Server (NTRS)

Knowledge of a spectrograph slit function is necessary to interpret the unresolved lines in an observed spectrum. A theoretical slit function can be calculated from the sizes of the entrance slit, the detector aperture when it functions as an exit slit, the dispersion characteristic of the disperser, and the point spread function of the spectrograph. A measured slit function is preferred to the theoretical one for the correct interpretation of the spectral data. In a scanning spectrometer with a single exit slit, the slit function is easily measured. In a fixed grating/or disperser spectrograph, illuminating the entrance slit with a near monochromatic light from a pre-monochrmator or a tunable laser and varying the wavelength of the incident light can measure the slit function. Even though the latter technique had been used successfully for the slit function measurements, it had been very laborious and it would be prohibitive to an imaging spectrograph or a multi-object spectrograph that has a large field of view. We explore an alternative technique that is manageable for the measurements. In the proposed technique, the imaging spectrograph is used as a detector of a Fourier transform spectrometer. This method can be applied not only to an IR spectrograph but also has a potential to a visible/UV spectrograph including a wedge filter spectrograph. This technique will require a blackbody source of known temperature and a bolometer to characterize the interferometer part of the Fourier Transform spectrometer. This pa?er will describe the alternative slit function measurement technique using a Fourier transform spectrometer.

Park, Hongwoo; Swimyard, Bruce; Jakobsen, Peter; Moseley, Harvey; Greenhouse, Matthew

2004-01-01

222

Above-threshold ionization by chirped laser pulses  

SciTech Connect

We theoretically investigate above-threshold ionization by chirped laser pulses. By comparing the photoelectron energy spectra and the photoelectron angular distributions of Na for the laser pulses with different chirp rates but with the identical spectral profile, we find that the ionization processes have a clear dependence on the chirp rate. Further calculations without excited bound states during the time propagation of the wave function reveal practically no chirp dependence, which is clear evidence that the origin of the chirp dependence in above-threshold ionization is the excited bound states.

Nakajima, Takashi [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)

2007-05-15

223

Photonic Generation of Chirped Microwave Pulses Using Superimposed Chirped Fiber Bragg Gratings  

Microsoft Academic Search

A novel approach to generating linearly chirped microwave pulses in the optical domain based on spectral shaping and linear frequency-to-time mapping is proposed and experimentally demonstrated. In the proposed system, the spectrum of a femtosecond pulse generated by a mode-locked fiber laser is spectrum-shaped by an optical filter that consists of two superimposed chirped fiber Bragg gratings (SI-CFBGs) with different

Chao Wang; Jianping Yao

2008-01-01

224

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

NASA Astrophysics Data System (ADS)

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

Goudarzi, Alireza; Riahi, Mohammad Ali

2012-12-01

225

Coherent control of atomic quantum states by single frequency-chirped laser pulses  

SciTech Connect

We present a scheme of population transfer between two metastable (ground) states of the {lambda} atom without considerable excitation of the atom using single frequency-chirped laser pulses. The physics of the process is generation of the 'trapped' superposition of the ground states by the laser pulse at sufficiently high laser peak intensity. The main conditions for realization of this regime are the following: The width of the transform-limited laser pulse envelope frequency spectrum (without chirp) must be smaller and the peak Rabi frequency of the pulse must be larger than the frequency interval between the two ground states of the {lambda} atom. During the frequency chirp, the laser pulse must first come into resonance with the transition from the initially occupied ground state to the excited state and after that with the transition between the excited and second initially empty ground states. In the case when the envelope frequency spectrum width (without chirp) of the pulse exceeds the frequency interval between the two ground states, we show a possibility of controllable generation of superposition of the ground states with a controllable excitation of the {lambda} atom.

Djotyan, G.P.; Bakos, J.S.; Soerlei, Zs.; Szigeti, J. [Research Institute for Particle and Nuclear Physics, XII. Konkoly Thege ut 29-33, P.O. Box 49, H-1525, Budapest (Hungary)

2004-12-01

226

An enhanced Hilbert-Huang transform technique for bearing condition monitoring  

NASA Astrophysics Data System (ADS)

A new technique, enhanced Hilbert-Huang transform (eHHT), is proposed in this work for fault detection in rolling element bearings. It includes two processes: firstly, the collected vibration signal is denoised to highlight defect-related impulses; and secondly the denoised signal is further processed by the use of the proposed eHHT technique to identify the defect features for bearing fault detection. Signal denoising is carried out by the use of the minimum entropy deconvolution filter to reduce impedance effect of the transmission path of the measured signal. In the proposed eHHT, a novel strategy is proposed to enhance feature extraction based on the analysis of correlation and mutual information. The effectiveness of the proposed eHHT technique in feature extraction and analysis is verified by a series of experimental tests corresponding to different bearing conditions. Its robustness is examined by using data sets from a different resource.

Osman, Shazali; Wang, Wilson

2013-08-01

227

Optimization of laser processing techniques and parameters for laser transformation hardening with multi-objectives  

NASA Astrophysics Data System (ADS)

The new idea of the optimum controlling of laser processing technique and parameters with multi-objectives and multi-variables was put forth. With the comprehensive discussion about the quality index of laser transformation hardening (LTH), a hierarchical structure of the LTH quality index system and a decision-making framework model of the quality control were set up. Then, based on the conclusions of the sensitivities of LTH parameters' influences on the case indexes, the principle of LTH's parameters optimization was discussed by means of fuzzy decision method. With the combination of the principle and the sectionlly changing scanning velocity technique, which can effectively the uniformity of longitudinal case-distribution, a decision-making framework for optimal controlling on the laser scanning technique and the parameters with multi-objectives were put forward. An optimization model was developed and the validity of the model was verified both by theoretical computation and experimental results.

Wu, Gang; Hong, Lei

2008-03-01

228

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

SciTech Connect

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

Mori, Yoshihiko; Torii, Susumu; Ebihara, Daiki

1999-09-01

229

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

SciTech Connect

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.

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

2010-11-15

230

Cr4+ : YAG chirped-pulse oscillator  

PubMed Central

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.

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

2010-01-01

231

Parameter estimation for superimposed chirp signals  

Microsoft Academic Search

Parameter estimation for superimposed chirp signals is a difficult signal processing problem that shows up in many applications. Cramer-Rao lower bounds are derived here for the error variance in the parameter estimates. The approach reported uses global Hankel rank reduction to estimate instantaneous frequencies followed by total least squares fitting to obtain initial estimates of the parameters. These estimates are

R. M. Liang; K. S. Arun

1992-01-01

232

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

PubMed

Laser plasma interferograms are currently analyzed by extraction of the phase-shift map with fast Fourier transform (FFT) techniques [Appl. Opt. 18, 3101 (1985)]. This methodology works well when interferograms are only marginally affected by noise and reduction of fringe visibility, but it can fail to produce accurate phase-shift maps when low-quality images are dealt with. We present a novel procedure for a phase-shift map computation that makes extensive use of the ridge extraction in the continuous wavelet transform (CWT) framework. The CWT tool is flexible because of the wide adaptability of the analyzing basis, and it can be accurate because of the intrinsic noise reduction in the ridge extraction. A comparative analysis of the accuracy performances of the new tool and the FFT-based one shows that the CWT-based tool produces phase maps considerably less noisy and that it can better resolve local inhomogeneties. PMID:18364963

Tomassini, P; Giulietti, A; Gizzi, L A; Galimberti, M; Giulietti, D; Borghesi, M; Willi, O

2001-12-10

233

Imaging based symptomatic classification using a combination of trace transform, fuzzy technique and multitude of features  

US Patent & Trademark Office Database

Characterization of carotid atherosclerosis and classification of plaque into symptomatic or asymptomatic and risk score estimation are of clinical value. A statistical system is described for symptomatic versus asymptomatic plaque automated classification of carotid ultrasound images and cardiovascular risk score computation. The technique is applicable for the following types of modalities for carotids: 2D Ultrasound, 3D Ultrasound, CT, MR. Wall region is segmented and features are extracted consisting of type 1 combination consisting of: (a) Higher Order Spectra; (b) Discrete Wavelet Transform (DWT); (c) Texture and (d) Wall Variability; type 2 combination consisting of: (a) Local Binary Pattern; (b) Law's Mask Energy and (c) Wall Variability and type 3 combination: (a) Trace Transform; (b) Fuzzy Grayscale Level Co-occurrence Matrix and (c) Wall Variability. These features are trained using a training classifier on training images and the coefficients are applied to on-line test patient images. The system yields the cardiovascular risk score value using the feature combinations.

2013-09-10

234

Photoreflectance spectroscopy with a step-scan Fourier-transform infrared spectrometer: technique and applications.  

PubMed

We report on a new technique of realizing photoreflectance (PR) spectroscopy with a step-scan Fourier-transform infrared spectrometer. The experimental configuration is briefly described and a detailed theoretical analysis is conducted. The results reveal two distinct features of this PR technique that (i) the PR related signal is enhanced by a factor of at least 100 relative to those of the conventional PR techniques and (ii) the unwanted spurious signal introduced by either diffuse reflected pump beam or pump-beam induced material's photoluminescence reaching the photodetector of the PR configuration is eliminated without any special consideration of normalization for deducing the final PR spectrum. Applications are given as examples in the study of GaNAs/GaAs single quantum wells and GaInP/AlGaInP multiple quantum wells, respectively, under different pump-beam excitation energy and/or power. The experimental results approve the theoretically predicted features and illustrate the possibility of investigating weak PR features by using high pump-beam power. A brief comparison of this technique with the conventional PR techniques is given, and the extendibility of this technique to long-wavelength spectral regions is pointed out. PMID:17503911

Shao, Jun; Lu, Wei; Yue, Fangyu; Lü, Xiang; Huang, Wei; Li, Zhifeng; Guo, Shaoling; Chu, Junhao

2007-01-01

235

The complete gravity gradient tensor derived from the vertical component of gravity: a Fourier transform technique  

NASA Astrophysics Data System (ADS)

A technique has been to developed to determine the complete gravity gradient tensor from pre-existing vertical gravity data using the fast Fourier Transform (FFT). Since direct measurement of the entire gravity gradient tensor is generally unavailable, our technique provides an alternative determination of the gravity gradient tensor components. Traditionally, derivatives of vertical gravity ( gz,x, gz,y, and gz,z) have been the only gravity gradient tensor components that have been computed directly. Gravity gradient tensor components are computed for four different, three-dimensional (3-D), idealized horst-and-graben models, with varying depths to the horst. Comparing the FFT results with calculated gradient components from the 3-D models shows that the RMS error for each component, between the two results, is at most ˜3.3 Eötvos Units. In addition, measured gravity gradient components from an airborne survey over the Wichita Uplift and Anadarko Basin region of southwest Oklahoma compare favorably with the FFT-derived results using available vertical gravity data. No error analysis was attempted between the two results due to a low signal-to-noise ratio in the measured data. Our technique offers a novel way to transform and visualize the available data, and it also offers an inexpensive and previously unavailable subsurface mapping capability.

Mickus, Kevin L.; Hinojosa, Juan Homero

2001-03-01

236

Transformers  

NSDL National Science Digital Library

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

Kuphaldt, Tony R.

2008-07-03

237

Chirped fiber Brillouin frequency-domain distributed sensing  

NASA Astrophysics Data System (ADS)

A frequency-domain distributed temperature/strain sensor based on a longitudinally graded optical fiber (LGF) is proposed and evaluated. In an LGF, the Brillouin scattering frequency, ?, changes (i.e., is chirped) lengthwise monotonically and thus every position along the fiber has a unique ?. Any change locally (at some position) in the fiber environment will result in a measurable change in the shape of the Brillouin gain spectrum (BGS) near the frequency component mapped to that position. This is demonstrated via measurements and modeling for an LGF with local heating. The LGF is one with ˜100 MHz Brillouin frequency gradient over 16.7 m, with 1.1 and 1.7 m segments heated up to 40 K above ambient. A measurement of the BGS can enable the determination of a thermal (or strain) distribution along a sensor fiber, thus rendering the system one that is in the frequency domain. A sensitivity analysis is also presented for both coherent and pump-probe BGS measurement schemes. The modeling results suggest that the frequency-domain systems based on fibers with a chirped Brillouin frequency are highly suited as inexpensive event sensors (alarms) and have the potential to reach submeter position determination with sub-1-K temperature accuracies at >1 kHz sampling rates. Limitations to the technique are discussed.

Dragic, Peter D.; Mangognia, Anthony; Ballato, John

2014-05-01

238

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

239

Chirped-pulse millimeter-wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions.  

PubMed

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

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

2014-07-01

240

Analysis of tokamak data using a novel Hilbert transform based technique  

NASA Astrophysics Data System (ADS)

A novel data analysis technique based on the ``empirical mode decomposition'' and Hilbert transform is applied to the analysis of edge fluctuation data and Mirnov coil data from the ADITYA tokamak [S. B. Bhatt et al., Ind. J. Pure Appl. Phys. 27, 710 (1989)]. It is shown that the edge fluctuations can be well represented by a finite number of about 10 discrete modes. Their instantaneous energies show intermittent bursts and the high frequency modes are nonstationary. The technique is further developed to study three-mode interactions and employed to show that triplet interactions are statistically significant among high frequency modes of the fluctuation data. A general critique of the method is presented and its utility for the analysis of nonlinear phenomena in complex systems like plasma turbulence is highlighted.

Jha, R.; Raju, D.; Sen, A.

2006-08-01

241

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

NASA Astrophysics Data System (ADS)

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.

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

1994-01-01

242

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

SciTech Connect

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.

Carrera, Juan J.; Chu, Shih-I [Chemistry Department, University of Kansas and Kansas Center for Advanced Scientific Computing, Lawrence, Kansas 66045 (United States)

2007-03-15

243

Spatially adaptive wavelet transform speckle noise-smoothing technique for SAR images  

NASA Astrophysics Data System (ADS)

In this work we propose a new wavelet transform based speckle denoising algorithm for SAR images. The algorithm will explicitly account for the signal dependent nature of the noise by studying the variances of detail wavelet coefficients. The algorithm will use the analysis of variance ANOVA technique to check if variances are due to means belonging to the same population or not. If neighboring variances indicate belonging to the same population, then it's a smooth region and coefficient should be smoothed. If neighboring variances indicate the presence of two different populations, then coefficient is due to image feature and should be preserved. This approach will provide the flexibility of adjusting to region intensity level and thus no need for the fixed threshold concept. The algorithm will take advantage of the fact that wavelet transform creates three detail sub-images and a coarse sub-image. Each detail sub-image is associated with frequency contents due to certain edge location and orientation. The algorithm will also consider using cross-information from all three-detail sub-images to decide whether coefficients are due to a feature and thus should be preserved, or they are due to noise and should be smoothed. Simulations will show that our algorithm will provide better performance in terms of PSNR, ENL , and visually than currently existing techniques.

Hawwar, Yousef; Reza, Ali

2001-11-01

244

Catalytic transformations of supercoiled DNA as studied by flow linear dichroism technique.  

PubMed

A catalytic turnover of supercoiled DNA (scDNA) transformation mediated by topoisomerases leads to changes in the linking number (Lk) of the polymeric substrate by 1 or 2 per cycle. As a substrate of the topoisomerization reaction it is chemically identical to its product; even a single catalytic event results in the quantum leap in the scDNA topology. Non-intrusive continuous assay to measure the kinetics of the scDNA topoisomerization was performed. The development of such a technique was hindered because of multiple DNA species of intermediate topology present in the reaction mixture. The interrelation of DNA topology, its hydrodynamics, and optical anisotropy enable us to use the flow linear dichroism technique (FLD) for continuous monitoring of the scDNA topoisomerization reaction. This approach permits us to study the kinetics of DNA transformation catalyzed by eukaryotic topoisomerases I and II, as well as mechanistic characteristics of these enzymes and their interactions with anticancer drugs. Moreover, FLD assay can be applied to any enzymatic reaction that involves scDNA as a substrate. It also provides a new way of screening drugs dynamically and is likely to be potent in various biomedical applications. PMID:16336270

Gabibov, Alexander; Yakubovskaya, Elena; Lukin, Mark; Favorov, Peter; Reshetnyak, Andrey; Monastyrsky, Michael

2005-12-01

245

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

PubMed

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

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

2014-04-21

246

Coherent Stark nonlinear spectroscopy with chirped pulses  

NASA Astrophysics Data System (ADS)

Quantum control of the four-wave mixing produced by two-color ?-3? femtosecond laser pulses propagating in a two-level system is accomplished by varying the relative phase between the two laser pulses. The phase sensitivity of the spectral 5? anti-Stokes component is cancelled when the ac Stark shift produced by the ? and 3? pulses is compensated. We apply perturbation theory and provide simple analytical formulas for the phase-sensitivity cancellation in the 5? anti-Stokes component. We demonstrate that this quantum interference effect is robust against chirping of the pulses and show that asymmetric chirping results in phase-sensitive shaping of the four-wave mixing spectra.

Serrat, C.; Loiko, Yu.; de La Cruz, R.; Cela, J. M.

2007-01-01

247

Coherent control of ultracold collisions with chirped light: Direction matters  

SciTech Connect

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.

Wright, M. J.; Pechkis, J. A.; Carini, J. L.; Gould, P. L. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Kallush, S.; Kosloff, R. [Department of Physical Chemistry and the Fritz Haber Research Center for Molecular Dynamics, The Hebrew University, 91094, Jerusalem (Israel)

2007-05-15

248

Spectral shaping in chirped-pulse amplification  

SciTech Connect

The role of spectral shaping in the production of subpicosecond, high-contrast pulses using chirped-pulse amplification in Nd:glass lasers is described. Spectral shaping has been used to produce 3.2-TW pulses at 750 fsec with an energy contrast of better than 10{sup 3}:1. In the absence of shaping, compression of the 1053-nm pulses yielded only 1.5 psec and a contrast ratio of approximately 10:1.

Perry, M.D.; Patterson, F.G. (Lawrence Livermore National Laboratory, P.O. Box 808, L-473, Livermore, California 94550 (USA)); Weston, J.; Pax, P. (Continuum, 3150 Central Expressway, Santa Clara, California 95051 (USA))

1990-04-01

249

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

NASA Astrophysics Data System (ADS)

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

Iizuka, Y.; Awajiya, Y.

2014-06-01

250

Reduced chirping in coupled-cavity-semiconductor lasers  

Microsoft Academic Search

Chirping in coupled-cavity lasers is studied experimentally and theoretically. Using a conventional and a cleaved-coupled-cavity (C3) laser obtained from the same wafer, we find that the chirp for a C3 laser is typically reduced by a factor of 2. A simple rate equation model is presented to account for reduced chirping. Mode selectivity arising from the cavity coupling is incorporated

G. P. Agrawal; N. A. Olsson; N. K. Dutta

1984-01-01

251

Reduced chirping in coupled-cavity-semiconductor lasers  

Microsoft Academic Search

Chirping in coupled-cavity lasers is studied experimentally and theoretically. Using a conventional and a cleaved-coupled-cavity (C³) laser obtained from the same wafer, we find that the chirp for a C³ laser is typically reduced by a factor of 2. A simple rate equation model is presented to account for reduced chirping. Mode selectivity arising from the cavity coupling is incorporated

G. P. Agrawal; N. A. Olsson; N. K. Dutta

1984-01-01

252

Reduced chirping in coupled-cavity-semiconductor lasers  

SciTech Connect

Chirping in coupled-cavity lasers is studied experimentally and theoretically. Using a conventional and a cleaved-coupled-cavity (C/sup 3/) laser obtained from the same wafer, we find that the chirp for a C/sup 3/ laser is typically reduced by a factor of 2. A simple rate equation model is presented to account for reduced chirping. Mode selectivity arising from the cavity coupling is incorporated through wavelength-dependent cavity-loss variations.

Agrawal, G.P.; Olsson, N.A.; Dutta, N.K.

1984-07-15

253

Coherent Control of Stimulated Raman Scattering Using Chirped Laser Pulses  

Microsoft Academic Search

A novel method for the control of stimulated Raman scattering in short-pulse laser-plasma interactions is proposed. Linear frequency chirp in a non-bandwidth limited pulse is used to selectively increase or decrease the instability growth rate, depending on the sign of the chirp. Theoretical calculations show that a chirped pulse with 12% bandwidth is needed to eliminate forward Raman scattering. The

Evan Dodd; Donald Umstadter

1999-01-01

254

The effect of laser chirping on lightwave system performance  

Microsoft Academic Search

Directly modulated semiconductor lasers exhibit a dynamic wavelength shift (chirping) arising from gain-induced variations of the laser refractive index. The effect of laser chirping on the performance of multi-Gb\\/s lightwave systems operating at a wavelength of 1550 nm is investigated. Models suitable for computer-aided analysis are used to describe the dynamic response of the laser and the propagation of chirped

J. C. Cartledge; G. S. Burley

1989-01-01

255

Mechanism of electron acceleration by chirped laser pulse  

SciTech Connect

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.

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

2012-05-28

256

Fast matching pursuit with a multiscale dictionary of Gaussian chirps  

Microsoft Academic Search

We introduce a modified matching pursuit algorithm, called fast ridge pursuit, to approximate N-dimensional signals with M Gaussian chirps at a computational cost O(MN) instead of the expected O(MN2 logN). At each iteration of the pursuit, the best Gabor atom is first selected, and then, its scale and chirp rate are locally optimized so as to get a “good” chirp

Rémi Gribonval

2001-01-01

257

pathChirp: Efficient Available Bandwidth Estimation for Network Paths  

Microsoft Academic Search

This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing

Les

2003-01-01

258

Chirp pulse microwave computed tomography(CP-MCT) equipped with a fan beam scanner for high-speed imaging of a biological target  

Microsoft Academic Search

Recently, microwave imaging aiming at early-stage-tumor detection has become of major interest because of its relatively high contrast resolution in the image. Chirp pulse microwave computed tomography (CP-MCT) obtains the attenuation and\\/or phase shift images of biological targets by use of a chirp pulse signal from 1 GHz to 2 GHz and signal processing techniques. The experimental- and computational-studies show

M. Miyakawa; E. Harada; Wu Jing

2003-01-01

259

Analysis of intrapulse chirp in CO2 oscillators  

NASA Technical Reports Server (NTRS)

Pulsed single-frequency CO2 laser oscillators are often used as transmitters for coherent lidar applications. These oscillators suffer from intrapulse chirp, or dynamic frequency shifting. If excessive, such chirp can limit the signal-to-noise ratio of the lidar (by generating excess bandwidth), or limit the velocity resolution if the lidar is of the Doppler type. This paper describes a detailed numerical model that considers all known sources of intrapulse chirp. Some typical predictions of the model are shown, and simple design rules to minimize chirp are proposed.

Moody, Stephen E.; Berger, Russell G.; Thayer, William J., III

1987-01-01

260

Visible imaging Fourier transform spectrometer based on a beam-folding technique  

NASA Astrophysics Data System (ADS)

A low-cost visible to Near-infrared Imaging Fourier Transform Spectrometer (IFTS) using a beam-folding technique instead of the spectral folding technique is presented. The retroreflectors are used to replace the plane mirrors to maintain the optical alignments without the adoption of complex active-alignment measures. Fast-scanning mechanism is adopted to avoid the high-cost precise-position control system. The interferogram images at sequential sampling points, spectral images at different wavenumbers and pixel interferograms and spectra of the multimode fiber ends illuminated by a He- Ne laser and a red LED source respectively, are given. The experimental results show that the IFTS based on the beamfolding technique can achieve a spectral resolution of ~15cm-1 (~0.5nm) when measuring the bright coherent light source (the end of a 600 ?m fiber coupled with the He-Ne laser). The resolution is mainly limited by the nonlinearity of the CCD output, the memory size of the PC and the data-transferring speed between the PC and the CCD camera PL-A741. Preliminary results showed that it is suited to the measurement of bright object sources. This restriction is only due to the poor performance of the CCD detector array used in the experiment. A fast-scanning visible-Near infrared IFTS for the objects of low light intensity is feasible when the high-sensitivity CCD camera is adopted.

Wang, Xuzhu; Chan, Robert K. Y.

2009-07-01

261

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

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

262

Accurate sizing of closed crack using nonlinear ultrasound of SPACE with high voltage transformer pulser technique  

NASA Astrophysics Data System (ADS)

As the improvement of the detectability of crack tip echo in ultrasonic inspection with low S/N ratio, we developed SPACE (Subharmonic Phased Array Crack Evaluation) as a subharmonic ultrasound imaging technique. Although the pulser of conventional SPACE could incident large displacement ultrasound to a crack, availability of the SPACE measurement was limited for only closed crack. In order to use the SPACE system for wider industrial inspection fields, we have been developed the larger displacement ultrasound incidence equipment considering the crack opening supposed to be several nm to sub- ?m in order. In this study, we developed new SPACE combining high voltage transformer to a low cost pulser. The availability of the developed system in ultrasonic inspection was investigated using several model cracks.

Mihara, Tsuyoshi; Konishi, Goki; Miura, Yusuke; Ishida, Hitoshi

2014-02-01

263

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

NASA Astrophysics Data System (ADS)

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).

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

2014-08-01

264

Spectral shearing interferometry with spatially chirped replicas for measuring ultrashort pulses.  

PubMed

A new spectral shearing interferometry technique for ultrashort pulse characterization is demonstrated. The method makes use of a spectral shear that varies across the test pulse beam profile to generate a two-dimensional interferogram that allows simultaneous reference phase measurement and pulse-field reconstruction from a single data set. The method uses a new configuration for upconversion of a single (non-spatially chirped) test pulse with two spatially chirped ancillary pulses in a medium with a highly asymmetric phase matching function. This technique is particularly suited for spectral regions where second harmonic is much easier detectable that the fundamental wavelength, such as telecom band around 1.5 ?m, since all the data are available from the measurement at the upconverted wavelength. The high degree of redundancy in the two-dimensional interferogram provides a built-in check of the consistency of the reconstruction. PMID:19550800

Gorza, S P; Wasylczyk, P; Walmsley, I A

2007-11-12

265

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

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

266

Image restoration in chirp-pulse microwave CT (CP-MCT)  

Microsoft Academic Search

Chirp-pulse microwave computed tomography (CP-MCT) is a technique for imaging the distribution of temperature variations inside biological tissues. Even if resolution and contrast are adequate to this purpose, a further improvement of image quality is desirable. In this paper, we discuss the blur of CP-MCT images and we propose a method for estimating the corresponding point spread function (PSF). To

Mario Bertero; Michio Miyakawa; Patrizia Boccacci; Francesco Conte; Kentaroh Orikasa; Masatoshi Furutani

2000-01-01

267

A linear model for chirp-pulse microwave computerized tomography: applicability conditions  

Microsoft Academic Search

Chirp-pulse microwave computerized tomography (CP-MCT) represents an innovative medical imaging technique. One of the advantages of CP-MCT is that data reduction is based on the standard algorithm of x-ray tomography, namely filtered back-projection and therefore is very fast, even if not very accurate. For this reason we recently proposed a modification of this algorithm based on a linear model, hence

A. M. Massone; M. Miyakawa; M. Piana; F. Conte; M. Bertero

2006-01-01

268

Coherent Control of Lithium Atom by Adiabatic Rapid Passage with Chirped Microwave Pulses  

Microsoft Academic Search

Using the time-dependent multilevel approach and the B-spline technique, populations of Rydberg lithium atoms in chirped microwave pulses are demonstrated. Firstly the populations of two energy levels are controlled by the microwave pulse parameters. Secondly the atoms experience the consequence 70s-71p-72s-73p-74s in a microwave field using optimized microwave field parameters. It is shown that the coherent control of the population

Jiang Li-Juan; Zhang Xian-Zhou; Ma Huan-Qiang; Xia Li-Hua; Jia Guang-Rui

2012-01-01

269

Nonuniformly spaced photonic microwave delay-line filter using a spatially discrete chirped fiber Bragg grating  

Microsoft Academic Search

A new technique to implement a nonuniformly-spaced photonic microwave delay-line filter using a spatially discrete chirped fiber Bragg grating (SD-CFBG) is proposed and investigated. It is different from a regular nonuniformly-spaced photonic microwave delay-line filter where a laser array with nonuniformly spaced wavelengths is used to provide nonuniformly-spaced filter taps, the proposed method employs a single incoherent broadband optical source.

Chao Wang; Jianping Yao

2011-01-01

270

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

Microsoft Academic Search

We show that induced-grating\\/four-wave-mixing ultrashort-pulse autocorrelation techniques that use slowly responding media offer the same phase information as interferometric second-harmonic generation. We also show that autocorrelation traces from nearly all possible induced-grating\\/four-wave-mixing beam geometries provide this information, with all yielding the same theoretical result, an integral of a fourth-order electric-field coherence function. Such traces clearly reveal chirp and self-phase-modulation effects

Rick Trebino; Carl C. Hayden; Anthony M. Johnson; Wayne M. Simpson; Alfred M. Levine

1990-01-01

271

Performance scaling via passive pulse shaping in cavity-enhanced optical parametric chirped-pulse amplification.  

PubMed

We show that an enhancement cavity seeded at the full repetition rate of the pump laser can automatically reshape small-signal gain across the interacting pulses in an optical parametric chirped-pulse amplifier for close-to-optimal operation, significantly increasing both the gain bandwidth and the conversion efficiency, in addition to boosting gain for high-repetition-rate amplification. Applied to a degenerate amplifier, the technique can provide an octave-spanning gain bandwidth. PMID:20548342

Siddiqui, Aleem M; Moses, Jeffrey; Hong, Kyung-Han; Lai, Chien-Jen; Kärtner, Franz X

2010-06-15

272

Virtual Gires-Tournois etalons realized with phase-modulated wideband chirped fiber gratings.  

PubMed

We propose and demonstrate novel virtual Gires-Tournois (GT) etalons based on fiber gratings. By introducing an additional phase modulation in wideband linearly chirped fiber Bragg gratings, we have successfully generated GT resonance with only one grating. This technique can simplify the fabrication procedure while retaining the normal advantages of distributed etalons, including their full compatibility with optical fiber, low insertion loss, and low cost. Such etalons can be used as dispersion compensation devices in optical transmission systems. PMID:18087537

Shu, Xuewen; Sugden, Kate; Bennion, Ian

2007-12-15

273

Enhanced four-wave mixing in mercury isotopes, prepared by stark-chirped rapid adiabatic passage  

Microsoft Academic Search

We demonstrate significant enhancement of four-wave mixing in coherently driven mercury isotopes to generate vacuum-ultraviolet radiation at 125nm. The enhancement is accomplished by preparation of the mercury atoms in a state of maximum coherence, i.e. maximum nonlinear-optical polarization, driven by Stark-chirped rapid adiabatic passage (SCRAP). In this technique, a pump laser at 313nm excites the two-photon transition between the ground

Martin Oberst; Jens Klein; Thomas Halfmann

2006-01-01

274

Decrease of pulse-contrast in nonlinear chirped-pulse amplification systems due to high-frequency spectral phase ripples.  

PubMed

It is analytically shown that weak initial spectral phase modulations cause a pulse-contrast degradation at the output of nonlinear chirped-pulse amplification systems. The Kerr-nonlinearity causes an energy-transfer from the main pulse to side-pulses during nonlinear amplification. The relative intensities of these side-pulses can be described in terms of Bessel-functions. It is shown that the intensities of the pulses are dependent on the magnitude of the accumulated nonlinear phase-shift (i.e., the B-integral), the depth and period of the initial spectral phase-modulation and the slope of the linear stretching chirp. The results are applicable to any type of laser amplifier that is based on the technique of chirped-pulse amplification. The analytical results presented in this paper are of particular importance for high peak-power laser applications requiring high pulse-contrasts, e.g. high field physics. PMID:18545600

Schimpf, Damian; Seise, Enrico; Limpert, Jens; Tünnermann, Andreas

2008-06-01

275

Multivariation calibration techniques applied to NIRA (near infrared reflectance analysis) and FTIR (Fourier transform infrared) data  

NASA Astrophysics Data System (ADS)

Multivariate calibration techniques can reduce the time required for routine testing and can provide new methods of analysis. Multivariate calibration is commonly used with near infrared reflectance analysis (NIRA) and Fourier transform infrared (FTIR) spectroscopy. Two feasibility studies were performed to determine the capability of NIRA, using multivariate calibration techniques, to perform analyses on the types of samples that are routinely analyzed at this laboratory. The first study performed included a variety of samples and indicated that NIRA would be well-suited to perform analyses on selected materials properties such as water content and hydroxyl number on polyol samples, epoxy content on epoxy resins, water content of desiccants, and the amine values of various amine cure agents. A second study was performed to assess the capability of NIRA to perform quantitative analysis of hydroxyl numbers and water contents of hydroxyl-containing materials. Hydroxyl number and water content were selected for determination because these tests are frequently run on polyol materials and the hydroxyl number determination is time consuming. This study pointed out the necessity of obtaining calibration standards identical to the samples being analyzed for each type of polyol or other material being analyzed. Multivariate calibration techniques are frequently used with FTIR data to determine the composition of a large variety of complex mixtures. A literature search indicated many applications of multivariate calibration to FTIR data. Areas identified where quantitation by FTIR would provide a new capability are quantitation of components in epoxy and silicone resins, polychlorinated biphenyls (PCBs) in oils, and additives to polymers.

Long, C. L.

1991-02-01

276

Frequency chirping in semiconductor-optical fiber ring laser  

SciTech Connect

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

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

1990-01-01

277

Some focusing properties of chirped gratings at microwave frequencies  

Microsoft Academic Search

The paper presents theoretical and experimental analyses of the focusing properties of metallic chirped gratings. It is shown that chirped gratings can be used to focus microwave energy at a predetermined position. The focal point depends on the exact width and space variations of the grating, as well as on the angle of incidence.

C. G. Christodoulou; J. C. Schmidt

1993-01-01

278

Phase-Locking Transition in a Chirped Superconducting Josephson Resonator  

Microsoft Academic Search

We observe a sharp threshold for dynamic phase locking in a high-Q transmission line resonator embedded with a Josephson tunnel junction, and driven with a purely ac, chirped microwave signal. When the drive amplitude is below a critical value, which depends on the chirp rate and is sensitive to the junction critical current I0, the resonator is only excited near

O. Naaman; J. Aumentado; L. Friedland; J. S. Wurtele; I. Siddiqi

2008-01-01

279

A chirp scaling approach for processing squint mode SAR data  

Microsoft Academic Search

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

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

1996-01-01

280

Electron acceleration by a chirped Gaussian laser pulse in vacuum  

SciTech Connect

Electron acceleration by a chirped Gaussian laser pulse is investigated numerically. A linear and negative chirp is employed in this study. At first, a simple analytical description for the chirp effect on the electron acceleration in vacuum is provided in one-dimensional model. The chirp mechanism is then extended to the interaction of a femtosecond laser pulse and electron. The electron final energy is obtained as a function of laser beam waist, laser intensity, chirp parameter, and initial phase of the laser pulse. It is shown that the electron final energy depends strongly on the chirp parameter and the initial phase of the laser pulse. There is an optimal value for the chirp parameter in which the electron acceleration takes place effectively. The energy gain increases with laser beam waist and intensity. It is also shown that the electron is accelerated within a few degrees to the axial direction. Emphasis is on the important aspect of the chirp effect on the energy gained by an electron from the electromagnetic wave.

Sohbatzadeh, F.; Mirzanejhad, S.; Ghasemi, M. [Physics Department, Science Faculty, Mazandaran University, Babolsar (Iran, Islamic Republic of)

2006-12-15

281

Hadamard Transform Spectrometry: A New Analytical Technique: Progress Report, March 15, 1988-March 14, 1989.  

National Technical Information Service (NTIS)

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 spec...

W. G. Fateley

1988-01-01

282

Comparison differential transformation technique with Adomian decomposition method for linear and nonlinear initial value problems  

Microsoft Academic Search

In this paper, we will compare the differential transformation method DTM and Adomian decomposition method ADM to solve partial differential equations (PDEs). The definition and operations of differential transform method was introduced by Zhou [Zhou JK. Differential transformation and its application for electrical circuits. Wuuhahn, China: Huarjung University Press; 1986 [in Chinese

I. H. Abdel-Halim Hassan

2008-01-01

283

Power transformer design using magnetic circuit theory and finite element analysis — A comparison of techniques  

Microsoft Academic Search

This paper summarises a reverse method of transformer design where the construction details of the transformer are directly specified and are used to determine the device performance and ratings. Two magnetic models are presented for the inductive-reactance components of the Steinmetz 'exact' transformer equivalent circuit. The first model, based on magnetic circuit theory, is frequently taught in undergraduate power system

Simon C. Bell; Pat S. Bodger

2007-01-01

284

Beam homogenizers based on chirped microlens arrays.  

PubMed

Lens array arrangements are commonly used for the homogenization of highly coherent laser beams. These fly's eye condenser configurations can be used to shape almost arbitrary input intensity distributions into a top hat. Due to the periodic structure of regular arrays the output intensity distribution is modulated by equidistant sharp intensity peaks which are disturbing the homogeneity. As a new approach we apply chirped microlens arrays to the beam shaping system. These are non-regular arrays consisting of individually shaped lenses defined by a parametric description which can be derived completely from analytical functions. The advantages of the new concept and design rules are presented. PMID:19546927

Wippermann, Frank; Zeitner, Uwe-D; Dannberg, Peter; Bräuer, Andreas; Sinzinger, Stefan

2007-05-14

285

CHIRPED PULSE AMPLIFICATION OF HGHG-FEL FACILITY AT BNL.  

SciTech Connect

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

DOYURAN,A.ET AL.

2003-09-08

286

Raman forward scattering of high-intensity chirped laser pulses  

SciTech Connect

Raman forward scattering of a high-intensity, short-duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatio-temporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all regimes of forward scattering, it is shown that the growth rate increases (decreases) for positive (negative) frequency chirp. The effect of chirp on the growth rate is relatively minor, i.e., a few percent chirp yields few percent changes in the growth rates. Relation of these results to recent experiments is discussed.

Schroeder, C.B.; Esarey, E.; Shadwick, B.A.; Leemans, W.P.

2002-06-23

287

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

NASA Astrophysics Data System (ADS)

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.

Cornaton, F. J.

2012-03-01

288

Fast classification and compositional analysis of cornstover fractions using Fourier transform near-infrared techniques.  

PubMed

The objectives of this research were to determine the variation of chemical composition across botanical fractions of cornstover, and to probe the potential of Fourier transform near-infrared (FT-NIR) techniques in qualitatively classifying separated cornstover fractions and in quantitatively analyzing chemical compositions of cornstover by developing calibration models to predict chemical compositions of cornstover based on FT-NIR spectra. Large variations of cornstover chemical composition for wide calibration ranges, which is required by a reliable calibration model, were achieved by manually separating the cornstover samples into six botanical fractions, and their chemical compositions were determined by conventional wet chemical analyses, which proved that chemical composition varies significantly among different botanical fractions of cornstover. Different botanic fractions, having total saccharide content in descending order, are husk, sheath, pith, rind, leaf, and node. Based on FT-NIR spectra acquired on the biomass, classification by Soft Independent Modeling of Class Analogy (SIMCA) was employed to conduct qualitative classification of cornstover fractions, and partial least square (PLS) regression was used for quantitative chemical composition analysis. SIMCA was successfully demonstrated in classifying botanical fractions of cornstover. The developed PLS model yielded root mean square error of prediction (RMSEP %w/w) of 0.92, 1.03, 0.17, 0.27, 0.21, 1.12, and 0.57 for glucan, xylan, galactan, arabinan, mannan, lignin, and ash, respectively. The results showed the potential of FT-NIR techniques in combination with multivariate analysis to be utilized by biomass feedstock suppliers, bioethanol manufacturers, and bio-power producers in order to better manage bioenergy feedstocks and enhance bioconversion. PMID:18249535

Philip Ye, X; Liu, Lu; Hayes, Douglas; Womac, Alvin; Hong, Kunlun; Sokhansanj, Shahab

2008-10-01

289

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

NASA Astrophysics Data System (ADS)

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

Zhao, Jianlin; Lu, Hongqiang; Fan, Qi

2007-01-01

290

Chirped fiber Bragg grating detonation velocity sensing  

NASA Astrophysics Data System (ADS)

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.

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

2013-01-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

292

Comparison between headspace and vacuum gas extraction techniques for the gas chromatographic determination of dissolved gases from transformer insulating oils  

Microsoft Academic Search

The conventional headspace sampling technique is highly efficient for analyzing dissolved gases in transformer oil apart from the relatively long time that the analytes take to equilibrate between the sample and vapor phases. By mixing the sample during the equilibration period, the equilibration time was shortened by a factor of 15. Under these conditions, analysis of the gases of the

Jocelyn Jalbert; Roland Gilbert

1994-01-01

293

A New Robust Digital Image Watermarking Technique Based on Joint DWT-DCT Transformation  

Microsoft Academic Search

In this paper, a new robust digital image watermarking algorithm based on Joint DWT-DCT Transformation is proposed. The imperceptibility is provided as well as higher robustness against common signal processing attacks. A binary watermarked image is embedded in certain sub-bands of a 3-level DWT transformed of a host image. Then, DCT transform of each selected DWT sub-band is computed and

Saied Amirgholipour Kasmani; Ahmadreza Naghsh-Nilchi

2008-01-01

294

Chirped-Pulse Amplification Near the Gain-Narrowing Limit of an Yb-Doped Fiber Amplifier Using a Reflection Grism Compressor  

Microsoft Academic Search

Chirped-pulse amplification near the Yb gain-narrowing limit is studied numerically and experimentally. An inhomogeneous gain lineshape is consistent with experiments. With a grism compressor, transform-limited 120-fs pulses are generated with energy up to 0.7 muJ.

L. Kuznetsova; F. W. Wise; S. Kane; J. Squier

2007-01-01

295

Determination of nuclear spin–rotation coupling constants in CF 3I by chirped-pulse Fouriertransform microwave spectroscopy  

Microsoft Academic Search

The rotational spectrum of CF3I in the ground vibrational state has been re-measured using a chirped-pulse Fourier-transform microwave spectrometer recently constructed at the University of Bristol. The new spectrometer provides the capability to acquire broadband rotational spectra throughout an operational frequency range of 7–18GHz. The frequencies of ninety-nine F1?–F1? transitions in three distinct JK?–JK? bands have been recorded during an

Susanna L. Stephens; Nicholas R. Walker

2010-01-01

296

Determination of nuclear spin-rotation coupling constants in CF3I by chirped-pulse Fouriertransform microwave spectroscopy  

Microsoft Academic Search

The rotational spectrum of CF3I in the ground vibrational state has been re-measured using a chirped-pulse Fourier-transform microwave spectrometer recently constructed at the University of Bristol. The new spectrometer provides the capability to acquire broadband rotational spectra throughout an operational frequency range of 7-18 GHz. The frequencies of ninety-nine F1'-F1\\

Susanna L. Stephens; Nicholas R. Walker

2010-01-01

297

Chirped pulse amplification in single mode Tm:fiber using a chirped Bragg grating  

NASA Astrophysics Data System (ADS)

We report femtosecond pulse generation and chirped pulse amplification in Tm:fiber. A mode-locked oscillator operating in the soliton regime produced 800 fs pulses with 5 nm spectral bandwidth, at 40 pJ pulse energy. This oscillator seeded a pre-amplifier that utilizes a Raman soliton self-frequency shift to produce wavelength tunable pulses with 3 nJ energy, reduced pulse duration of 150 fs, and increased bandwidth of 30 nm. For further amplification, the pulses were stretched up to 160 ps using a chirped Bragg grating (CBG). Stretched pulses were amplified to 85 nJ after compression in single-mode Tm:fiber and recompressed with the CBG as short as 400 fs. Compressed pulses were coupled into a highly nonlinear tellurite fiber to investigate the potential of this ultrashort pulse 2-?m fiber source as a pump for mid-IR supercontinuum generation.

Sims, R. Andrew; Kadwani, Pankaj; Ebendorff-Heideprem, Heike; Shah, Lawrence; Monro, Tanya M.; Richardson, Martin

2013-05-01

298

Finite difference time domain analysis of chirped dielectric gratings  

NASA Technical Reports Server (NTRS)

The finite difference time domain (FDTD) method for solving Maxwell's time-dependent curl equations is accurate, computationally efficient, and straight-forward to implement. Since both time and space derivatives are employed, the propagation of an electromagnetic wave can be treated as an initial-value problem. Second-order central-difference approximations are applied to the space and time derivatives of the electric and magnetic fields providing a discretization of the fields in a volume of space, for a period of time. The solution to this system of equations is stepped through time, thus, simulating the propagation of the incident wave. If the simulation is continued until a steady-state is reached, an appropriate far-field transformation can be applied to the time-domain scattered fields to obtain reflected and transmitted powers. From this information diffraction efficiencies can also be determined. In analyzing the chirped structure, a mesh is applied only to the area immediately around the grating. The size of the mesh is then proportional to the electric size of the grating. Doing this, however, imposes an artificial boundary around the area of interest. An absorbing boundary condition must be applied along the artificial boundary so that the outgoing waves are absorbed as if the boundary were absent. Many such boundary conditions have been developed that give near-perfect absorption. In this analysis, the Mur absorbing boundary conditions are employed. Several grating structures were analyzed using the FDTD method.

Hochmuth, Diane H.; Johnson, Eric G.

1993-01-01

299

Characterization of Silicon Sulfides by Chirped-Pulse Rotational Spectroscopy  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

300

Walking assistance system for sight impaired people based on a multimodal information transformation technique  

Microsoft Academic Search

A multimodal information transformation system is proposed in this paper to provide sight impaired people with scene information of walking areas and obstacles. The scene information is first acquired as images using a single CCD camera, and then image information is transformed into voice information so that sight impaired people can obtain by hearing instead of seeing. During scene image

JaeHyoung Yu; Hwan-Ik Chung; Hernsoo Hahn

2009-01-01

301

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

Microsoft Academic Search

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

Fateley

1988-01-01

302

A Wavelet Transform Based Technique For The Recognition Of The Human Iris  

Microsoft Academic Search

A new approach for the recognition of the iris of human eyes based on the wavelet transform is presented. It specifically uses the zero-crossings of the wavelet transform of the unique features obtained from the grey level profiles of the ins. The recognition process is performed in two stages. The fxst stage consists of building a one-dimensional representation of the

W. W. Boles

1996-01-01

303

Personal identification technique based on human iris recognition with wavelet transform  

Microsoft Academic Search

This paper presents a biometric recognition system, based on the iris of a human eye, using a wavelet transform. The proposed system includes three modules: image preprocessing, feature extraction, and recognition. The feature extraction module adopts the gradient direction (i.e., angle) of the wavelet transform as the discriminating texture features. The system encodes the features to generate its iris feature

Wen-Shiung Chen; Kun-Huei Chih; Sheng-Wen Shih; Chih-Ming Hsieh

2005-01-01

304

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

305

Three-Dimensional Analysis of Frequency-Chirped FELs  

SciTech Connect

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

Zhirong, Huang

2010-09-14

306

Chirped-Superlattice, Blocked-Intersubband QWIP  

NASA Technical Reports Server (NTRS)

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.

Gunapala, Sarath; Ting, David; Bandara, Sumith

2004-01-01

307

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

NASA Technical Reports Server (NTRS)

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.

Lee, Jonathan A.

2005-01-01

308

Coherent strong-field control of multiple states by a single chirped femtosecond laser pulse  

NASA Astrophysics Data System (ADS)

We present a joint experimental and theoretical study on strong-field photo-ionization of sodium atoms using chirped femtosecond laser pulses. By tuning the chirp parameter, selectivity among the population in the highly excited states 5p, 6p, 7p and 5f, 6f is achieved. Different excitation pathways enabling control are identified by simultaneous ionization and measurement of photoelectron angular distributions employing the velocity map imaging technique. Free electron wave packets at an energy of around 1 eV are observed. These photoelectrons originate from two channels. The predominant 2 + 1 + 1 resonance enhanced multi-photon ionization (REMPI) proceeds via the strongly driven two-photon transition 4s<--<--3s, and subsequent ionization from the states 5p, 6p and 7p whereas the second pathway involves 3 + 1 REMPI via the states 5f and 6f. In addition, electron wave packets from two-photon ionization of the non-resonant transiently populated state 3p are observed close to the ionization threshold. A mainly qualitative five-state model for the predominant excitation channel is studied theoretically to provide insights into the physical mechanisms at play. Our analysis shows that by tuning the chirp parameter the dynamics is effectively controlled by dynamic Stark shifts and level crossings. In particular, we show that under the experimental conditions the passage through an uncommon three-state 'bow-tie' level crossing allows the preparation of coherent superposition states.

Krug, M.; Bayer, T.; Wollenhaupt, M.; Sarpe-Tudoran, C.; Baumert, T.; Ivanov, S. S.; Vitanov, N. V.

2009-10-01

309

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

PubMed

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

Kaiplavil, Sreekumar; Mandelis, Andreas

2011-07-01

310

Highly depth-resolved chirped pulse photothermal radar for bone diagnostics  

NASA Astrophysics Data System (ADS)

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.

Kaiplavil, Sreekumar; Mandelis, Andreas

2011-07-01

311

A parameter extraction technique for FMCW radar signals using Wigner-Hough-Radon transform  

Microsoft Academic Search

An autonomous parameter extraction algorithm for frequency modulated continuous wave (FMCW) radar signals using Wigner-Ville Distribution (WVD)-Hough transform was investigated in [1] and extraction of polyphase radar modulation parameters using a Wigner-Ville distribution-Radon transform was investigated in [2]. The algorithm in [1] produced very dependable results with as low as ?6 dB SNR levels, however some degradation has been observed

T. O. Gulum; A. Y. Erdogan; T. Yildirim; P. E. Pace

2012-01-01

312

A wavelet-based technique for discrimination between faults and magnetizing inrush currents in transformers  

Microsoft Academic Search

This paper presents the development of a wavelet-based scheme, for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast, and computationally efficient tool. The operating time of the scheme is less than half the power frequency cycle (based on a 5-kHz sampling rate). In this work, a wavelet transform concept is presented.

Omar A. S. Youssef

2003-01-01

313

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

Microsoft Academic Search

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

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

2009-01-01

314

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

NASA Astrophysics Data System (ADS)

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.

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

1999-02-01

315

Optical linear sideband chirp compression for microwave arbitrary waveform generation  

Microsoft Academic Search

A novel approach for the practical implementation of photonic arbitrary waveform generation of microwave signals is explored. Here we describe and demonstrate linear sideband chirp compression over 1 GHz bandwidth with a compression factor of >4000.

Randy R. Reibel; Tiejun Chang; Mingzhen Tian; W. Randall Babbitt

2004-01-01

316

Giant-chirp oscillators for short-pulse fiber amplifiers.  

PubMed

A new regime of pulse parameters in a normal-dispersion fiber laser is identified. Dissipative solitons exist with remarkably large pulse duration and chirp, along with large pulse energy. A low-repetition-rate oscillator that generates pulses with large and linear chirp can replace the standard oscillator, stretcher, pulse-picker, and preamplifier in a chirped-pulse fiber amplifier. The theoretical properties of such a giant-chirp oscillator are presented. A fiber laser designed to operate in the new regime generates approximately 150 ps pulses at a 3 MHz repetition rate. Amplification of these pulses to 1 microJ energy with pulse duration as short as 670 fs demonstrates the promise of this new approach. PMID:19079529

Renninger, William H; Chong, Andy; Wise, Frank W

2008-12-15

317

Giant-chirp oscillators for short-pulse fiber amplifiers  

PubMed Central

A new regime of pulse parameters in a normal-dispersion fiber laser is identified. Dissipative solitons exist with remarkably large pulse duration and chirp, along with large pulse energy. A low-repetition-rate oscillator that generates pulses with large and linear chirp can replace the standard oscillator, stretcher, pulse-picker, and pre-amplifier in a chirped-pulse fiber amplifier. The theoretical properties of such a giant-chirp oscillator are presented. A fiber laser designed to operate in the new regime generates ~150-ps pulses at 3-MHz repetition rate. Amplification of these pulses to 1-?J energy with pulse duration as short as 670 fs demonstrates the promise of this new approach.

Renninger, William H.; Chong, Andy; Wise, Frank W.

2011-01-01

318

Chirped Microwave Pulse Generation Based on Optical Spectral Shaping and Wavelength-to-Time Mapping Using a Sagnac Loop Mirror Incorporating a Chirped Fiber Bragg Grating  

Microsoft Academic Search

In this paper, we propose and demonstrate an approach to optically generating chirped microwave pulses with tunable chirp profile based on optical spectral shaping using a Sagnac loop filter incorporating a chirped fiber Bragg grating (CFBG) and linear wavelength-to-time mapping in a dispersive element. In the proposed approach, the optical power spectrum of an ultrashort optical pulse is shaped by

Chao Wang; Jianping Yao

2009-01-01

319

Photonic Generation of Continuously Tunable Chirped Microwave Waveforms Based on a Temporal Interferometer Incorporating an Optically Pumped Linearly Chirped Fiber Bragg Grating  

Microsoft Academic Search

A novel approach to generating a chirped microwave waveform with continuously tunable chirp rate based on a temporal interferometer incorporating an optically pumped linearly chirped fiber Bragg grating (LCFBG) is proposed and demonstrated. The temporal interferometer is realized using a Mach–Zehnder interferometer (MZI) that incorporates an LCFBG and a dispersion compensating fiber to generate a temporal interference pattern with an

Ming Li; Jianping Yao

2011-01-01

320

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

PubMed

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

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

2011-05-23

321

Microwave multiphoton transitions between Rydberg states driven by chirped pulses  

Microsoft Academic Search

We observe microwave multiphoton transitions in Rydberg states of potassium using intense pulses of chirped microwave radiation. Pulses of microwaves with frequencies between 0.6 and 0.9 GHz with frequency chirp times from 5 ns (4 cycles) to 200 ns (150 cycles) are generated with peak fields of 15 V\\/cm. We are able to drive high order multiphoton transitions using these

C. W. S. Conover; M. C. Doogue; D. A. Perry

1998-01-01

322

Pulse-front tilt caused by spatial and temporal chirp.  

PubMed

Pulse-front tilt in an ultrashort laser pulse is generally considered to be a direct consequence of, and equivalent to, angular dispersion. We show, however, that, while this is true for certain types of pulse fields, simultaneous temporal chirp and spatial chirp also yield pulse-front tilt, even in the absence of angular dispersion. We verify this effect experimentally using GRENOUILLE. PMID:19483989

Akturk, Selcuk; Gu, Xun; Zeek, Erik; Trebino, Rick

2004-09-20

323

Dispersion penalty reduction using an optical modulator with adjustable chirp  

Microsoft Academic Search

Using a unique Ti:LiNbO3 modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb\\/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m

A. H. Gnauck; S. K. Korotky; J. J. Veselka; J. Nagel; C. T. Kemmerer; W. J. Minford; D. T. Moser

1991-01-01

324

Low chirp observed in directly modulated quantum dot lasers  

Microsoft Academic Search

We have examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) lasers at room temperature. A novel characteristic of low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers. This is more than one order of magnitude less than the typical chirp (0.2-nm) found in a conventional quantum well laser that we used as

Hideaki Saito; Kenichi Nishi; Akio Kamei; Shigeo Sugou

2000-01-01

325

Single attosecond pulse generation from multicycle nonlinear chirped pulses  

SciTech Connect

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.

Niu Yueping; Qi Yihong; Gong Shangqing [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800 (China); Xiang Yang [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800 (China); College of Computer Science and Technology, Henan Polytechnic University, Jiaozuo 454000 (China)

2009-12-15

326

Photonic generation of microwave waveforms with wide chirp tuning range  

NASA Astrophysics Data System (ADS)

We show analytically as well as demonstrate experimentally an approach to generate microwave waveforms with wide chirp tuning range. The approach is based on the interference of two temporally-stretched pulses which are time-delayed with respect to each other and having different frequency chirp. This approach is realized by an unbalanced Mach Zehnder Interferometer (MZI) incorporating a linearly-chirped fiber-Bragg-grating (LCFBG) whose group-delay-dispersion (GDD) can be tuned across a wide range. In general, tuning the GDD of the LCFBG changes the chirp rate of the generated microwave waveform and tuning the relative time-delay between the interferometer arms changes the center frequency of the generated microwave waveform. Balanced photodetection is also implemented to obtain DC-free microwave waveforms. Based on this approach, we demonstrate the generation of microwave waveforms with different center frequencies and with the chirp rates ranging from˜-126.7 GHz/ns to ˜+120.8 GHz/ns, including the zero-chirp case.

Wong, Jia Haur; Liu, Huan Huan; Lam, Huy Quoc; Aditya, Sheel; Zhou, Junqiang; Lim, Peng Huei; Lee, Kenneth Eng Kian; Wu, Kan; Chow, Kin Kee; Shum, Perry Ping

2013-09-01

327

Sampled chirped fiber gratings as distributed pressure sensors  

NASA Astrophysics Data System (ADS)

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.

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

2004-09-01

328

A novel tunable polarization mode dispersion compensation of linear chirped Bragg grating without shift of central wavelength by variable magnetic field  

Microsoft Academic Search

A novel technique to introduce tunable linear chirp to a uniform fiber Bragg grating (FBG) without shift of central Bragg wavelength based on a magnetic field applied to a magnetostrictive rod capable of tuning polarization mode dispersion (PMD) is proposed. This all-fiber PMD compensation technique is cost-effective and flexible in designing the differential group delay (DGD). Based on the numerical

Yumin Liu; Zhongyuan Yu; Xiaoguang Zhang

2005-01-01

329

Filtering in the joint time/chirp-rate domain for separation of quadratic and cubic phase chirp signals  

NASA Astrophysics Data System (ADS)

This article investigates the possibility and convenience of a filtering operation in the joint time/chirp-rate (TCR) domain, and proposes a novel linear TCR filter for decomposing multicomponent signals into their quadratic and/or cubic phase chirp components with monotonic instantaneous chirp-rate (ICR) laws only. The TCR domain mask of the filter is selected on a display of a TCR representation of an input signal to isolate the desired chirp component. Projecting the input signal onto the phase signal associated with the TCR mask and approximating the phase difference in this projection operation in terms of ICR values result in the proposed TCR filter that recovers the selected component. Simulations illustrate the proposed filtering in recovery of undersampled cubic phase signals and in resolving back-to-back objects from in-line holograms for which cases it is easier to design filter masks in the TCR domain than in the time-frequency domain.

Özgen, Mehmet Tankut

2012-12-01

330

Time-Frequency Transform Techniques Applied to Ultra-wideband Ground-Penetrating Radar  

NASA Astrophysics Data System (ADS)

Background Recently, Dauvignac et al [1] utilized a ground penetrating radar unit consisting of an exponentially tapered slot antenna (ETSA) of the Vivaldi type, connected to an Agilent vector network analyzer to obtain a densely-sampled profile in the anti-blast tunnel of LSBB (Low-Noise inter-Disciplinary Underground Science & Technology Laboratory) located in Rustrel, France. The frequency data, from 150 MHz to 2 GHz, was inverse Fourier-transformed to obtain the time dependent data. Simultaneously, the same profile was obtained using a RAMAC 500 MHz ground-penetrating radar unit. Initial comparison of both data sets was done in the time-domain. Data obtained from the ETSA will be inverted using a constrained least squares algorithm, in order that the depth-dependent permittivity can be inferred. As a quality control, the RAMAC data will also be inverted. The resulting permittivity profiles obtained in both inversions will be used to image water content over a depth of several meters. Proposed Research It is well-known, qualitatively in the ground penetrating radar literature that high frequencies appear at early times, but generally are attenuated at later times, essentially due to the skin effect. However, a signal-processing verification of this well-known result is needed. We propose to use the Stockwell or S transform [2] to determine the temporal location of frequencies in both of the foregoing datasets. The S transform, a short-time Fourier transform with a frequency-dependent window, will be described and applied to synthetic data. Then the application of the S transform to the RAMAC and ETSA data will be presented, after each data set has undergone the same pre-processing. The S transform is completely linear and preserves the phase of the data, which allows for easy interpretation of the operations of filtering, due to the linear inverse of the forward S transform. Thus the S transform is ideal for comparing the temporal distribution of frequency in these two datasets. BIBLIOGRAPHY [1] DAUVIGNAC J.-Y., N. FORTINO, G. SENECHAL, A. CRESP, M. YEDLIN, S. GAFFET, D. ROUSSET, and C. PICHOT, "Ultra-Wideband GPR Imaging of the Vaucluse Karst Aquifer", American Geophysical Union, Fall Meeting 2008, Abstract #NS51A-08. [2] STOCKWELL R. G., L. MANSINHA, R. P. LOWE, "Localization of the complex spectrum: the S transform", IEEE Transactions on Signal Processing, vol.44, n°4, pp 998-1001, April 1996.

Yedlin, M.; Cresp, A.; Dauviganc, J. Y.; Gaffet, S.; Sénéchal, G.; Fortino, N.; Pichot, C.; Aliferis, I.

2009-04-01

331

Application of wavelet transform techniques to spread spectrum demodulation and jamming  

NASA Astrophysics Data System (ADS)

This project has investigated the application of wavelet methods in spread spectrum communications. Use of the wavelet transform as an alternative to the short-time Fourier and quadratic time-frequency transforms for measuring critical parameters of intercepted slow frequency hopping communication signals has been explored. Direct application of the wavelet transform was found to not offer performance advantages over the Fourieer transform in this application. However, use of the wavelet transform in conjunction with Fourier methods provided an efficient hybrid framework for precise measurement of hopping times and frequencies. A new approach to multiple-access spread spectrum communications was also developed in this project. This approach employs orthogonal wavelets as symbols for encoding digital communication signals. Several users can transmit simultaneously in the same medium using channels defined by wavelet scale in much the same way that channels are defined by frequency in traditional frequency division multiple access. Appropriate choices of wavelet symbols make the transmitted signals robust with respect to detection and jamming.

Cochran, Douglas

1993-02-01

332

Digital watermarking technique based on integer Harr transforms and visual properties  

NASA Astrophysics Data System (ADS)

In this paper, a new method is proposed to hide watermark image based on the discrete integer Haar wavelet transform. This method utilizes excellent properties of the discrete integer Haar wavelet transform and some characteristics of human visual system(HSV). The watermark are processed the discrete Haar wavelet transforms as a grey-value image, and are decomposed and synthesized the image of the watermark and hiding. The algorithm of the discrete integer Haar wavelet is simple and viable. Algorithmic operation is also small .The speed of algorithmic operation is quick. The algorithm is of parallel structure. The experimental results using this algorithm shows that the method of this paper implement that be added watermark and be hidden processing to image. This method can improve robustness of watermarking.

Tao, Hongjiu; Liu, Jianguo; Tian, Jinwen

2001-09-01

333

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

SciTech Connect

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.

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

334

A technique to improve the empirical mode decomposition in the Hilbert-Huang transform  

Microsoft Academic Search

The Hilbert-based time-frequency analysis has promising capacity to reveal the time-variant behaviors of a system. To admit\\u000a well-behaved Hilbert transforms, component decomposition of signals must be performed beforehand. This was first systematically\\u000a implemented by the empirical mode decomposition (EMD) in the Hilbert-Huang transform, which can provide a time-frequency representation\\u000a of the signals. The EMD, however, has limitations in distinguishing different

Yangbo Chen; Maria Q. Feng

2003-01-01

335

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

SciTech Connect

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.

Fateley, W.G.

1988-01-01

336

Slippage effect on energy modulation in seeded free-electron lasers with frequency chirped seed laser pulses  

NASA Astrophysics Data System (ADS)

Free-electron lasers (FELs) seeded with external lasers hold great promise for generating high power radiation with nearly transform-limited bandwidth in the soft x-ray region. However, it has been pointed out that the initial seed laser phase error will be amplified by the frequency up-conversion process, which may degrade the quality of the output radiation produced by a harmonic generation scheme. In this paper, theoretical and simulation studies on frequency chirp amplification in seeded FEL schemes with slippage effect taken into account are presented. It is found that the seed laser imperfection experienced by the electron beam can be significantly smoothed by the slippage effect in the modulator when the slippage length is comparable to the seed laser pulse length. This smoothing effect allows one to preserve the excellent temporal coherence of seeded FELs in the presence of large frequency chirp in the seed laser. Our studies show that the tolerance on frequency chirp in the seed laser for generating nearly transform-limited soft x-ray pulses in seeded FELs is much looser than previously thought and fully coherent radiation at nanometer wavelength may be reached with current technologies.

Feng, Chao; Deng, Haixiao; Wang, Guanglei; Wang, Dong; Zhao, Zhentang; Xiang, Dao

2013-06-01

337

Generator fault detection technique using detailed coefficients ratio by daubechies wavelet transform  

Microsoft Academic Search

An AC (alternating current) generator is one of the important components in producing a electric power and so it requires highly reliable protection relays to minimize the possiblity of demage occurring under fault conditions. Conventionally, a RDR (ratio differential relaying) based on DFT (discrete Fourier transform) has been used for protecting the stator winding of a generator. However, when DFTs

Chul-Won Park; Kwang-Chul Shin; Sang-Seung Lee; Jong-Keun Park; Myong-Chul Shin

2009-01-01

338

A human identification technique using images of the iris and wavelet transform  

Microsoft Academic Search

A new approach for recognizing the iris of the human eye is presented. Zero-crossings of the wavelet transform at various resolution levels are calculated over concentric circles on the iris, and the resulting one-dimensional (1-D) signals are compared with model features using different dissimilarity functions

W. W. Boles; B. Boashash

1998-01-01

339

Optoelectronic fractal scanning technique for wavelet transform and neural net pattern classifiers  

Microsoft Academic Search

A 1D scan which follows Peano's curve to a desired resolution is demonstrated to preserve the 2D proximity relationship and is furthermore shown to be efficient for wavelet transform (WT) processing and artificial neural network pattern recognition. This deterministic fractal sampling method can be implemented in real time using optoelectronic scanning. For example, 2D texture patterns are analyzed by using

Sonlinh Phuvan; Tae Kwan Oh; Nick Caviris; Yao Li; H. Szu

1992-01-01

340

Ultrashort pulses from an all-fiber ring laser incorporating a pair of chirped fiber Bragg gratings.  

PubMed

By incorporating two linearly chirped ultrabroadband fiber Bragg gratings of opposite dispersion in an all-fiber ring laser, we demonstrate a mode-locking regime in which a femtosecond pulse evolving in the normal dispersion gain segment is locally transformed into a highly chirped picosecond pulse that propagates in the remaining section of the cavity. By minimizing nonlinear effects and avoiding soliton pulse shaping in this anomalous-dispersion section, low repetition rate fiber lasers can be made to produce high-energy ultrashort pulses. Using this approach, 98 fs pulses with 0.96 nJ of energy are obtained from an erbium-doped fiber laser operated in the highly anomalous dispersion regime at a repetition rate of 9.4 MHz. PMID:24562259

Duval, Simon; Olivier, Michel; Bernier, Martin; Vallée, Réal; Piché, Michel

2014-02-15

341

FD-CHIRP: hosted payload system engineering lessons  

NASA Astrophysics Data System (ADS)

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.

Schueler, Carl F.

2012-10-01

342

Fast Quantum Gates Using Chirped Pulses  

NASA Astrophysics Data System (ADS)

A common method to implement quantum gates is based on the Rabi solution regime of a two-level system excited by external field. To construct a quantum gate one uses the exact form of evolution operator of the qubit under the external excitation. In the case of Rabi solution the qubit evolution has very simple and easily interpreted form. In essence, the whole dynamics of the qubit wave function is governed by the pulse area and it exhibits Rabi oscillations for the time less than the decoherence time. Various implementations of the quantum gates employ relatively weak pulses that results in slow gate operations of order microseconds. To make quantum gates faster one may use strong femtosecond pulses. However, direct implementation schemes are not so obvious because of strong field effects and large bandwidth of the pulses might give rise to unwanted excitations. Here we propose a scheme which provides a possibility to utilize strong pulses while keeps all advantages of Rabi solution regime. We design fast quantum gates (picosecond time scale) by choosing proper parameters of the chirped pulses as a way to control nonadiabatic terms and to satisfy the adiabaticity conditions. Proposed Hadamard and phase-shift gate allow us to construct universal set of single qubit gates by controlling the effective pulse area and two-photon detuning. The proposed excitation scheme can be also used to implement CNOT gate.

Malinovsky, Vladimir

2008-05-01

343

Data reconstructing for windowing broom Fourier transform imaging spectrometers based on multi-core techniques  

NASA Astrophysics Data System (ADS)

The windowing broom Fourier transform imaging spectrometer, based on space-time modulation, has the characteristics of high luminous flux, static interference part etc. However, the large amount of raw data and the data reconstruction increase the difficulty of the whole data processing and extend the computing time. In this paper, a parallel calculation algorithm for reconstruction of raw data is proposed. The proposed algorithm is achieved by using Task Parallel Library (TPL), which is provided by .NET framework, and a visualized processing system is further established. A set of data collected from a windowing broom Fourier transform imaging spectrometer is processed using both the proposed method and the ordinary serial algorithm. The scalability of this presented algorithm is verified by employing it on computers with different number of cores. The experimental results show that, compared to the serial algorithm, the proposed method can greatly speed up the processing with the same hardware condition, and it also has ideal scalability with different hardware.

Dong, Zhi-gang; Liao, Ning-fang; Qu, Liang; Lv, Hang

2013-08-01

344

Benchmarking techniques for evaluation of compression transform performance in ATR applications  

NASA Astrophysics Data System (ADS)

Image compression is increasingly employed in applications such as medical imaging, for reducing data storage requirement, and Internet video transmission, to effectively increase channel bandwidth. Similarly, military applications such as automated target recognition (ATR) often employ compression to achieve storage and communication efficiencies, particularly to enhance the effective bandwidth of communication channels whose throughput suffers, for example, from overhead due to error correction/detection or encryption. In the majority of cases, lossy compression is employed due the resultant low bit rates (high compression ratio). However, lossy compression produces artifacts in decompressed imagery that can confound ATR processes applied to such imagery, thereby reducing the probability of detection (Pd) and possibly increasing the rate or number of false alarms (Rfa or Nfa). In this paper, the authors' previous research in performance measurement of compression transforms is extended to include (a) benchmarking algorithms and software tools, (b) a suite of error exemplars that are designed to elicit compression transform behavior in an operationally relevant context, and (c) a posteriori analysis of performance data. The following transforms are applied to a suite of 64 error exemplars: Visual Pattern Image Coding (VPIC [1]), Vector Quantization with a fast codebook search algorithm (VQ [2,3]), JPEG and a preliminary implementation of JPEG 2000 [4,5], and EBLAST [6-8]. Compression ratios range from 2:1 to 200:1, and various noise levels and types are added to the error exemplars to produce a database of 7,680 synthetic test images. Several global and local (e.g., featural) distortion measures are applied to the decompressed test imagery to provide a basis for rate-distortion and rate-performance analysis as a function of noise and compression transform type.

Schmalz, Mark S.

2004-10-01

345

Coherent Control of Lithium Atom by Adiabatic Rapid Passage with Chirped Microwave Pulses  

NASA Astrophysics Data System (ADS)

Using the time-dependent multilevel approach and the B-spline technique, populations of Rydberg lithium atoms in chirped microwave pulses are demonstrated. Firstly the populations of two energy levels are controlled by the microwave pulse parameters. Secondly the atoms experience the consequence 70s-71p-72s-73p-74s in a microwave field using optimized microwave field parameters. It is shown that the coherent control of the population transfer in the microwave field from the initial to the target states can be accomplished by optimizing the microwave field parameters.

Jiang, Li-Juan; Zhang, Xian-Zhou; Ma, Huan-Qiang; Xia, Li-Hua; Jia, Guang-Rui

2012-07-01

346

Heterodyne architecture for tunable laser chirped dispersion spectroscopy using optical processing.  

PubMed

Dispersion-based spectroscopic techniques present many desirable features when compared with classical absorption spectroscopy implementations, such as the normalization-free operation and the extended dynamic range. In this Letter, we present a new sensor design based on direct optical processing for heterodyne conversion in tunable laser chirped dispersion spectroscopy that allows sensor implementations using low-speed photodetectors and low-cost FM demodulators. The performance of the new setup has been validated using as a target the ro-vibrational transition of methane at approximately 1650.96 nm. PMID:24784058

Martín-Mateos, Pedro; Jerez, Borja; Acedo, Pablo

2014-05-01

347

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

PubMed

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

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

2014-07-01

348

Quasi-transform-limited pulse transmission in dispersion managed soliton system  

Microsoft Academic Search

A Gaussian pulse with frequency chirping is transmitted in a dispersion management (DM) soliton system. The existence of an initial chirping makes the pulsewidth and amplitude fluctuate over distance around their initial values, and increases the energy enhancement factor. The quasi-transform-limited pulse generated with spectral windowing is also propagated in the DM soliton system. With proper energy enhancement, the quasi-transform-limited

Yang Jing Wen; Xiang Lin Yang

1999-01-01

349

The Laplace Transform Galerkin Technique: A time-continuous finite element theory and application to mass transport in groundwater  

NASA Astrophysics Data System (ADS)

A time-continuous numerical technique, referred to as the Laplace Transform Galerkin (LTG) method, is developed and applied to the problem of solute transport in porous media. After application of Galerkin's procedure and subdivision of the domain into finite elements, the method involves a simple application of the Laplace transformation to eliminate the temporal derivatives appearing in the space-discretized set of ordinary differential equations. Then, by solving the resulting transformed system of algebraic equations in Laplace p space, numerical inversion of the Laplace-transformed nodal concentration is performed using the robust and accurate Crump (1976) algorithm. The Crump algorithm permits the concentration to be evaluated from a range of time values from a single set of Laplace p space solutions. Because each of the needed p space solutions are independent, the algorithm is well suited for execution on multiprocessor parallel computers. It is demonstrated by means of a series of examples that the LTG scheme is capable of providing highly accurate solutions essentially devoid of numerical dispersion for grid Peclet numbers in excess of 30. Examination of the complex-valued, Laplace-domain concentration profiles reveal that they are generally smooth, well-behaved oscillatory functions compared to the profiles in the time domain, thus permitting the use of a coarse finite element grid. Because of the nature of the Laplace transformation, the LTG method is particularly well suited to the problem of transient groundwater flow and solute transport in fractured porous media or multiple aquifer-aquitard systems based on the dual-porosity integrodifferential equation approach.

Sudicky, E. A.

1989-08-01

350

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

NASA Astrophysics Data System (ADS)

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.

Kong, Weiwei

2014-03-01

351

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

SciTech Connect

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

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

2009-04-15

352

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

PubMed

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

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

1998-04-01

353

Investigation of noise suppression, pulse intensity and chirp of an actively mode-locked semiconductor fiber ring laser  

NASA Astrophysics Data System (ADS)

An actively mode-locked fiber ring laser that utilizes an EDFA and semiconductor optical amplifier (SOA) is presented. The SOA enhances noise suppression. Active mode-locking was demonstrated at repetition rates up to 20 GHz. The effects of intra-cavity power and SOA current on noise suppression are studied for two types of commercially available SOA. The frequency resolved optical gating technique is used to characterize the output pulse stream intensity and frequency chirp.

Evans, Ivan; O'Riordan, Colm; Connelly, Michael J.; Barry, Liam P.; Clarke, Aisling M.; Anandarajah, Prince M.

2007-12-01

354

Anti-ship missile tracking with a chirped AM ladar - Update: design, model predictions, and experimental results  

Microsoft Academic Search

Shipboard infrared search and track (IRST) systems can detect sea-skimming, anti-ship missiles at long ranges. Since IRST systems cannot measure range and line-of-sight (LOS) velocity, they have difficulty distinguishing missiles from false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a ladar based on the chirped amplitude modulation (AM) technique to provide range

Brian Redman; William Ruff; Barry Stann; Mark Giza; William Lawler; John Dammann; William Potter

2005-01-01

355

A broadband Fourier-transform microwave spectrometer with laser ablation source: The rotational spectrum of nicotinic acid  

NASA Astrophysics Data System (ADS)

A chirped pulse Fourier transform microwave spectrometer (CP-FTMW) has been combined with a laser ablation source to investigate the broadband rotational spectra of solid biomolecules in the 6.0-18 GHz region. This technique has been successfully applied to the conformational study of nicotinic acid for which two conformers have been characterized for the first time in the gas phase. The quadrupole hyperfine structure originated by a 14N nucleus has been completely resolved for both rotamers using a LA-MB-FTMW spectrometer.

Mata, S.; Peña, I.; Cabezas, C.; López, J. C.; Alonso, J. L.

2012-10-01

356

Optical generation of linearly chirped microwave pulses using fiber Bragg gratings  

Microsoft Academic Search

We demonstrate a new method to generate broad spectrum chirped microwave pulses using an electrooptical system. Two fiber Bragg gratings and a mode-locked fiber laser were used to generate pulses with a linear frequency chirp. The bandwidth of the microwave pulses can be significantly broader than the bandwidth that can be obtained using electronic systems. The parameters of the chirp

Avi Zeitouny; Sander Stepanov; Oren Levinson; Moshe Horowitz

2005-01-01

357

Application of chirped fiber Bragg grating sensors for identification of crack locations in composites  

Microsoft Academic Search

Chirped fiber Bragg grating (FBG) sensors were applied for the identification of crack locations in carbon fiber reinforced plastic (CFRP) laminates since the reflection spectrum from a chirped FBG was expressed as a function of the position along the grating. For the crack identification in the 90° ply of a cross-ply laminate, a chirped FBG sensor, whose grating length and

Yoji Okabe; Ryohei Tsuji; Nobuo Takeda

2004-01-01

358

Chirped soliton interaction in strongly dispersion-managed wavelength-division-multiplexing systems.  

PubMed

We theoretically analyze nonlinear interactions between chirped solitons in dispersion-managed wavelength-division-multiplexing (WDM) systems. We employ the perturbation method to evaluate frequency and chirp shifts caused by collisions among different WDM channels. It is shown that a chirped soliton suffers less frequency shift and time displacement than an ideal soliton, indicating its potential applicability for WDM systems. PMID:18087336

Hirooka, T; Hasegawa, A

1998-05-15

359

Simulation and experimental characterization of dual chirped long period fiber gratings  

NASA Astrophysics Data System (ADS)

We demonstrate a novel device consisting of two concatenated chirped long period fiber gratings (LPG) that exhibit multiple pass bands. Transmission spectra of single and dual chirped LPG were simulated theoretically and investigated experimentally show a qualitatively good match. The dual chirped LPGs with multiple pass bands in the transmission spectrum could find applications as WDM channel isolation filter.

Tiwari, Umesh; Singla, Nidhi; Mishra, Vandana; Shenoy, M. R.; Thyagarajan, K.; Jain, Subhash C.; Singh, Nahar; Kapur, Pawan

2010-12-01

360

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

PubMed

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

Levy, Yoav; Azhari, Haim

2007-05-01

361

Rainbow trapping using chirped all-dielectric periodic structures  

NASA Astrophysics Data System (ADS)

We report a numerical investigation of rainbow trapping (light of different wavelengths) at different spatial locations in a newly designed two-dimensional photonic structure that is formed using chirping parameters in two-dimensional photonic crystals. Chirped parameters ensure trapping of certain light wavelengths inside these structures. To achieve broadband electromagnetic wave trapping, we properly adjust and chirp the position and dielectric filling factor of each unit cell within a photonic crystal structure. The low group velocity regions of the dielectric continuum bands at the Brillouin zone edge enable different wavelengths to be slowed and stopped along the propagation direction. The all-dielectric transparent material nature of the proposed structure realizes light trapping in different electromagnetic regions by spatially varying the effective refractive index of the structure.

Kurt, H.; Yilmaz, D.

2013-03-01

362

Chirped pulse inverse free-electron laser vacuum accelerator  

DOEpatents

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.

Hartemann, Frederic V. (Dublin, CA); Baldis, Hector A. (Pleasanton, CA); Landahl, Eric C. (Walnut Creek, CA)

2002-01-01

363

Phase-locking transition in a chirped superconducting Josephson resonator.  

PubMed

We observe a sharp threshold for dynamic phase locking in a high-Q transmission line resonator embedded with a Josephson tunnel junction, and driven with a purely ac, chirped microwave signal. When the drive amplitude is below a critical value, which depends on the chirp rate and is sensitive to the junction critical current I0, the resonator is only excited near its linear resonance frequency. For a larger amplitude, the resonator phase locks to the chirped drive and its amplitude grows until a deterministic maximum is reached. Near threshold, the oscillator evolves smoothly in one of two diverging trajectories, providing a way to discriminate small changes in I0 with a nonswitching detector, with potential applications in quantum state measurement. PMID:18851320

Naaman, O; Aumentado, J; Friedland, L; Wurtele, J S; Siddiqi, I

2008-09-12

364

40-MHz Ultrasound Imaging with Chirps and Annular Arrays  

PubMed Central

High-frequency ultrasound (HFU) shows promise for fine-resolution imaging. However, the depth of field (DOF) and penetration depth of HFU waves limit clinical significance. In a previous study using a 17-MHz annular array, we established that chirp coded excitation and synthetic focusing can improve penetration depth and DOF simultaneously. In this study, we evaluated the same approach using two five-element annular arrays with focal lengths of 12 mm, total apertures of 6 mm. The annular arrays had center frequencies of ?35 MHz and were excited by a 4-?s chirp signal spanning the frequency range 15–65 MHz. Results demonstrated that DOF could be increased by a factor of about 3, SNR could be increased by more than 10 dB, and penetration depth into an attenuating phantom could be increased by 1.8 mm. The chirp imaging method was then evaluated on low-contrast phantoms and mouse embryos.

Mamou, Jonathan; Aristizabal, Orlando; Silverman, Ronald H.; Ketterling, Jeffrey A.

2011-01-01

365

Optical parametric chirped pulse amplification based on photonic crystal fibre  

NASA Astrophysics Data System (ADS)

A compact two-stage optical parametric chirped pulse amplifier based on photonic crystal fibre is demonstrated. A 1064-nm soliton pulse is obtained in a home-made photonic crystal fibre (PCF) with femtosecond pulse pumping and then amplified to 2 mJ in an Nd:YAG regenerative amplifier. After the amplified pulses pass through the LBO crystal, the 532-nm double-frequency light with an energy of 0.8 mJ and a duration of over 100 ps at 10-Hz repetition rate is generated as a pump source in the following two-stage optical parametric amplification (OPA). The 850-nm chirped signal light gain from the stretcher is 1.5×104 in the first-stage OPA while it is 120 in the second-stage OPA. The total signal gain of optical parametric chirped pulse amplification (OPCPA) can reach 1.8×106.

Wang, He-Lin; Yang, Ai-Jun; Leng, Yu-Xin; Wang, Cheng; Xu, Zhi-Zhan; Hou, Lan-Tian

2011-08-01

366

Schwinger vacuum pair production in chirped laser pulses  

SciTech Connect

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

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

2010-08-15

367

Phase-sensitive amplification of chirped optical pulses in fibers.  

PubMed

In this paper a detailed analysis is made of the phase-sensitive amplification (PSA) of optical pulses by degenerate four-wave mixing (phase-conjugation) in fibers. Formulas are derived, which show that the amplification level and phase sensitivity depend strongly on the phase of the signal pulse, but weakly on its chirp, and the difference between its carrier frequency and the average pump frequency. Solitons, which are unchirped, and dispersion-managed solitons, which are weakly chirped, are suitable for in-line and post-transmission PSA. Pseudo-linear pulses, which are strongly chirped, are unsuitable for in-line PSA, but post-transmission dispersion compensation makes them suitable for PSA prior to detection. PMID:19532620

McKinstrie, C J; Moore, R O; Radic, S; Jiang, R

2007-04-01

368

Beam energy chirp effects in seeded free-electron lasers  

NASA Astrophysics Data System (ADS)

Seeded free-electron lasers (FELs) hold great promise for generating high brilliance radiation pulses with a narrow bandwidth, which typically requires an electron bunch with relatively uniform energy distribution. However, it has been pointed out that the beam energy curvature generated in the acceleration process may degrade the output radiation pulse quality of seeded FELs. In this paper, we studied the beam energy chirp effects in various seeded FEL configurations. The theoretical and simulation results show that the performance degradation of high gain harmonic generation scheme is proportional to the beam energy chirp, while the advanced seeding schemes, e.g. echo-enabled harmonic generation and phase merging enhanced harmonic generation, are capable of eliminating the effect of the electron beam energy chirp.

Wang, Guanglei; Feng, Chao; Deng, Haixiao; Zhang, Tong; Wang, Dong

2014-07-01

369

Effects of collisions on energetic particle-driven chirping bursts  

SciTech Connect

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.

Lesur, M. [Itoh Research Center for Plasma Turbulence, Kyushu University, Kasuga, Kasuga Koen 6-1, Fukuoka 816-8580 (Japan)] [Itoh Research Center for Plasma Turbulence, Kyushu University, Kasuga, Kasuga Koen 6-1, Fukuoka 816-8580 (Japan)

2013-05-15

370

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

371

Dense Monoenergetic Proton Beams from Chirped Laser-Plasma Interaction  

NASA Astrophysics Data System (ADS)

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.

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

2011-10-01

372

Effects of frequency chirp on magnetron injection locking  

SciTech Connect

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

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

2008-07-15

373

Effects of frequency chirp on magnetron injection locking  

NASA Astrophysics Data System (ADS)

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

Pengvanich, P.; Lau, Y. Y.; Luginsland, J. W.; Gilgenbach, R. M.; Cruz, E.; Schamiloglu, E.

2008-07-01

374

Monolithic optical parametric oscillator using chirped quasi-phase matching  

NASA Astrophysics Data System (ADS)

We describe a highly efficient monolithic, Q-switched, nanosecond optical parametric oscillator based on a magnesium-oxide-doped periodically poled lithium niobate crystal and containing multiple quasi-phase-matched gratings. The crystal consisted of a single unchirped grating and five gratings containing progressively increasing amounts of longitudinal chirp. The monolithic design makes the device highly compact, stable, and robust, and it demonstrated a pump-to-signal conversion efficiency of around 50%, generating 50 ?J pulses at 1.55 ?m with a spectral bandwidth of 20 nm. Sonogram traces are presented showing the effect of crystal chirp on the temporal and spectral performance.

Tillman, Karl A.; Reid, Derryck T.

2007-06-01

375

Temperature insensitive accelerometer based on a strain-chirped FBG  

NASA Astrophysics Data System (ADS)

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.

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

2009-10-01

376

A robust digital image watermarking using transformation domain and evolutionary computation techniques  

Microsoft Academic Search

With the rapid expansion ofInternet and distributed technology, multimedia security and digital rights man­ agement have been received much attention in the lit­ erature. As a major method for intellectual property right protecting, digital watermarking techniques have been widely studied and used. Extensive algorithms have been proposed for digital images. In this paper , a robust digital image watermarking scheme

Chih-Chin Lail; Hsin-Chih Chenl; Geng-Ming Yehl; Chen-Sen Ouyang

2011-01-01

377

Elucidation of structure and nature of the PdO-Pd transformation using in situ PDF and XAS techniques.  

PubMed

The PdO-Pd phase transformation in a 4 wt% Pd/Al2O3 catalyst has been investigated using in situ X-ray absorption spectroscopy (XAS) and in situ X-ray total scattering (also known as high-energy X-ray diffraction) techniques. Both the partial and total pair distribution functions (PDF) from these respective techniques have been analysed in depth. New information from PDF analysis of total scattering data has been garnered using the differential PDF (d-PDF) approach where only correlations orginating from PdO and metallic Pd are extracted. This method circumvents problems encountered in characerising the catalytically active components due to the diffuse scattering from the disordered ?-Al2O3 support phase. Quantitative analysis of the palladium components within the catalyst allowed for the phase composition to be established at various temperatures. Above 850 °C it was found that PdO had converted to metallic Pd, however, the extent of reduction was of the order ca. 70% Pd metal and 30% PdO. Complementary in situ XANES and EXAFS were performed, with heating to high temperature and subsequent cooling in air, and the results of the analyses support the observations, that residual PdO is detected at elevated temperatures. Hysteresis in the transformation upon cooling is confirmed from XAS studies where reoxidation occurs below 680 °C. PMID:23657756

Keating, Jonathan; Sankar, Gopinathan; Hyde, Timothy I; Kohara, Shinji; Ohara, Koji

2013-06-14

378

Measurement and control of the frequency chirp rate of high-order harmonic pulses  

SciTech Connect

We measure the chirp rate of harmonics 13 to 23 in argon by cross correlation with a 12 femtosecond probe pulse. Under low ionization conditions, we directly measure the negative chirp due to the atomic dipole phase, and show that an additional chirp on the pump pulse is transferred to the qth harmonic as q times the fundamental chirp. Our results are in accord with simulations using the experimentally measured 815 nm pump and probe pulses. The ability to measure and manipulate the harmonic chirp rate is essential for the characterization and optimization of attosecond pulse trains.

Mauritsson, J.; Johnsson, P.; Lopez-Martens, R.; Varju, K.; L'Huillier, A. [Department of Physics, Lund Institute of Technology, P. O. Box 118, SE-221 00 Lund (Sweden); Kornelis, W.; Biegert, J.; Keller, U. [Physics Department, Swiss Federal Institute of Technology (ETH Zuerich), CH-8093 Zurich (Switzerland); Gaarde, M.B.; Schafer, K.J. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States)

2004-08-01

379

Analysis in the instantaneous frequency forms of a chirped laser pulse  

SciTech Connect

We analyze two forms of the instantaneous frequency of a linearly chirped laser pulse. Using a 3D test particle simulation, numerical results are presented for electrons accelerated by a chirped laser pulse with these two linearly chirped forms of the instantaneous frequency. We summarize that the linearly chirped frequency, {omega}(t)={omega}{sub 0}[1-{alpha}(t-z/c)] is reasonable, {omega}{sub 0} is laser frequency at z=0 and t=0, and {alpha} is the frequency chirp parameter.

Yuan, C. J.; Wu, X. Y.; Wang, P. X. [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education, China and Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai 200433 (China); Wang, J. X. [State Key Laboratory of Precision Spectroscopy and Department of Physics, East China Normal University, Shanghai 200062 (China)

2011-10-15

380

An efficient watermarking technique for satellite images using discrete cosine transform  

NASA Astrophysics Data System (ADS)

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.

AL-Mansoori, Saeed

2012-10-01

381

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

NASA Astrophysics Data System (ADS)

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

Li, Yanhong; Zhang, Li; Li, Zhuo

2013-09-01

382

Broadband absorption bleaching in chirped InGaAs quantum dot semiconductor optical amplifier operating at 1211-1285 nm  

NASA Astrophysics Data System (ADS)

We report on photoinduced absorption bleaching of InAs/InGaAs chirped quantum dot semiconductor optical amplifier (QD SOA) waveguide devices investigated by the traditional femtosecond pump-probe technique applied for a waveguide configuration. To gain broader spectra for the device a chirped QD structure including three groups of quantum dots each dedicated to a ground state transition at wavelength 1285, 1243 and 1211 nm was designed. Photoinduced transmission spectra consisting of ground state transition for the groups of QD's involved showed coincidence with the electroluminescence spectra and even more exceeded to longer wavelength. From photoinduced transmission kinetics absorption recovery in the range of picoseconds was considered. For comparison a device with typical high photoinduced absorption demonstrating large suppression of absorption bleaching was shown and interpreted.

Jelmakas, E.; Tomaši?nas, R.; Vengris, M.; Rafailov, E.; Krestnikov, I.

2013-10-01

383

All-optical electrical chirped pulse generation based on nonlinear wavelength-to-time conversion in a chirped fiber Bragg grating  

Microsoft Academic Search

In this paper, we propose and demonstrate a novel approach to optically generating chirped microwave pulse with tunable chirp rate based on spectral shaping and nonlinear wavelength-to-time conversion using a tunable nonlinearly chirped fiber Bragg grating (NL-CFBG). In our approach, the optical power spectrum of a ultrashort pulse from a femtosecond pulsed laser (FSPL) is shaped by a two-tap Sagnac

Chao Wang; Jianping Yao

2007-01-01

384

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

National Technical Information Service (NTIS)

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; a...

W. G. Fateley R. M. Hammaker

1992-01-01

385

Chirp and Click Evoked Auditory Steady State Responses.  

National Technical Information Service (NTIS)

In this study, Auditory Steady State Responses (ASSR) to 100 microsec clicks and 4 msec cochlear chirps are recorded in adult subjects at repetition rates of 20 to 100Hz in 10 Hz increments, Response characteristics of ASSRs are compared in the frequency ...

Y. Hekimoglu O. Ozdamar R. E. Delgado

2001-01-01

386

Chirped microwave photonic filter with high frequency tuning capability  

Microsoft Academic Search

A chirped single-bandpass photonic filter is proposed improving the delay performance achieved by microstrip structures. Frequency range is extended up to tens of GHz since carrier- suppression-effect is avoided although double-side-band is employed. OCIS codes: (000.0000) General;

Mario Bolea; Jose Mora; Beatriz Ortega; Jose Capmany

2011-01-01

387

Reconfigurability and tunability of a chirped microwave photonic pulse generator  

Microsoft Academic Search

We propose and demonstrate a microwave chirped pulse generator which is based on the effects of the dispersion slope over the propagation of an optical broadband signal. A complete reconfigurability of the generated signal waveform is easily achieved by a suitable adjustment of the optical source power distribution profile. Moreover, large frequency tuning range and TBWP control of the pulse

M. Bolea; J. Mora; B. Ortega; J. Capmany

2010-01-01

388

Amplification of optical pulse signal using chirped fiber grating  

Microsoft Academic Search

These chirped fiber Bragg gratin is an attractive and practical element in particular context of dense wavelength- division multiplexing. We introduce a structure to realize working mode of the optical pulse's high power amplification. Also we analyze the variation of pulse signal after broaden or compression together with the variation in frequency domain and the peak intensity of pulse signal

Weihai Ni; Li Zhan; YuXing Xia

2002-01-01

389

Coherent control of stimulated Raman scattering using chirped laser pulses  

Microsoft Academic Search

A novel method for the control of stimulated Raman scattering and hot electron production in short-pulse laser-plasma interactions is proposed. It relies on the use of a linear frequency chirp in nonbandwidth limited pulses. Theoretical calculations show that a 12% bandwidth will eliminate Raman forward scattering for a plasma density that is 1% of the critical density. The predicted changes

Evan S. Dodd; Donald Umstadter

2001-01-01

390

Habituation analysis of chirp vs. tone evoked auditory late responses  

Microsoft Academic Search

We have recently shown that tone evoked auditory late responses are able to proof that habituation is occurring. The sweep to sweep analysis using time scale coherence method from is used. Where clear results using tone evoked ALRs were obtained. Now it is of interest how does the results behave using chirp evoked ALRs compared to tone evoked ALRs so

Kevin Kern; Vladislav Royter; Farah I. Corona-Strauss; Mai Mariam; Daniel J. Strauss

2010-01-01

391

Optimization of apodized linearly chirped fiber gratings for optical communications  

Microsoft Academic Search

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

Karin Ennser; N. Zervas; Richard I. Laming

1998-01-01

392

Coded multiple chirp spread spectrum system and overlay service  

NASA Technical Reports Server (NTRS)

An asynchronous spread-spectrum system called coded multiple chirp is proposed, and the possible spread-spectrum overlay over an analog FM-TV signal is investigated by computer simulation. Multiple single-sloped up and down chirps are encoded by a pseudonoise code and decoded by dechirpers (pulse-compression filters) followed by a digital code correlator. The performance of the proposed system, expressed in terms of in probability of bit error and code miss probability, is similar to that of FSK (frequency shift keying) using codewords if sufficient compression gain is used. When chirp is used to overlay an FM-TV channel, two chirp signals with data rate up to 25 kb/s could be overlaid in a 36-MHz satellite transponder without significant mutual interference. Performance estimates for a VSAT (very small aperture terminal) earth station operating at C-band show that a 2.4-m antenna and 300-mW transmitter could send a 2.4-kb/s signal to a large central earth station over an occupied channel.

Kim, Junghwan; Pratt, Timothy; Ha, Tri T.

1988-01-01

393

On the Utility of Chirp Modulation for Digital Signaling  

Microsoft Academic Search

The issue of signal selection in binary data transmission is presented. The question of the relative utility of linear frequency sweeping (LFS or chirp), compared to PSK and FSK, in terms of error probability and spectrum usage, is discussed. The transmission media considered are the coherent, partially coherent, Rayleigh, and Rician channel models. Theoretically, LFS has unconditionally superior characteristics in

A. Berni; W. Gregg

1973-01-01

394

Influence of nonideal chirped fiber grating characteristics on dispersion cancellation  

Microsoft Academic Search

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

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

1998-01-01

395

Design of apodized linearly chirped fiber gratings for dispersion compensation  

Microsoft Academic Search

We investigate and compare the equalization performance of various apodization functions in linearly chirped fiber gratings, with a view of determining an optimum profile for the design and fabrication of chromatic dispersion compensators. A discussion concerning the relation of these apodization functions with the group delay characteristic of the equalizer is presented yielding important results connected with the grating design.

Daniel Pastor; J. Capmany; D. Ortega; V. Tatay; J. Marti

1996-01-01

396

Effects of frequency chirp on magnetron injection locking  

Microsoft Academic Search

In this paper, effects of time-varying frequencies on the injection locking behavior are explored. Of interest is when the driver frequency is linearly swept (chirp) in time, e.g., for frequency search when the oscillator frequency is not known. It is found that complete locking similar to the constant frequency case can no longer occur. Instead, frequency of the oscillator \\

P. Pengvanich; Yue Ying Lau; J. W. Luginsland; R. M. Gilgenbach; E. Cruz; E. Schamiloglu

2008-01-01

397

Effects of frequency chirp on magnetron injection locking  

Microsoft Academic Search

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

P. Pengvanich; Y. Y. Lau; J. W. Luginsland; R. M. Gilgenbach; E. Cruz; E. Schamiloglu

2008-01-01

398

Generating nonlinear FM chirp radar signals by multiple integrations  

DOEpatents

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.

Doerry, Armin W. (Albuquerque, NM) [Albuquerque, NM

2011-02-01

399

Chirped fiber Bragg gratings for electrically tunable time delay lines  

Microsoft Academic Search

In this paper, a continuously variable delay line for phased array antennas is presented. The proposed delay line operates at a single wavelength and is based on properly designed linearly chirped fiber Bragg gratings. Continuous true time delay can be achieved by changing the temperature or strain along the grating region. Numerical results show that the delay line can be

Vincenzo Italia; Marco Pisco; Stefania Campopiano; Andrea Cusano; Antonello Cutolo

2005-01-01

400

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

PubMed

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

Raupach, Sebastian; Grosche, Gesine

2014-06-01

401

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

DOEpatents

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.

Bennett, Corey Vincent (Livermore, CA)

2011-11-22

402

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

PubMed

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

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

2010-01-01

403

Laser beam transformation technique for high-power laser diode linear arrays  

NASA Astrophysics Data System (ADS)

This paper reports on a novel pair of microlens arrays (MLA's) for efficient coupling of the high aspect ratio optical beam emitted by high-power laser diode linear arrays (also referred to as laser diode bars) into the core of multimode optical fibers. These novel MLA's overcome the limitations observed when using high fill factors laser diode bars. The MLA designs are described. Results from modelling work show good coupling performances for laser diode bars with fill factors up to 75%. The technique for fabricating the complex surface profiles of the MLA's is discussed. Masters are first fabricated and MLA's are then replicated, so that volume production at low cost can be envisioned. The fabricated MLA's have been used for reshaping and fiber coupling the output of a 10-mm laser diode bar. An efficiency of 74% has been obtained when coupling into an optical fiber having a core diameter of 400 ?m and a numerical aperture of 0.22.

Grenier, Paul; Taillon, Yves; Wang, Min; Topart, Patrice; Asselin, Daniel; Parent, André

2006-03-01

404

Dispersion tuning of a linearly chirped fiber Bragg grating without a center wavelength shift by applying a strain gradient  

Microsoft Academic Search

We propose a new method for controlling the chirp of a linearly chirped fiber Bragg grating (FBG) without a center wavelength shift by using beam bending. The beam consists of a plastic sleeve enclosing a 10-cm-long chirped FBG and a metal rod. The grating pitch could be varied to give positive or negative chirp as well as zero chirp (i.e.

T. Imai; T. Komukai; M. Nakazawa

1998-01-01

405

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

NASA Astrophysics Data System (ADS)

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 ? 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.

Demeter, Gabor

2014-06-01

406

Multifractal detrended fluctuation analysis of human EEG: preliminary investigation and comparison with the wavelet transform modulus maxima technique.  

PubMed

Recently, many lines of investigation in neuroscience and statistical physics have converged to raise the hypothesis that the underlying pattern of neuronal activation which results in electroencephalography (EEG) signals is nonlinear, with self-affine dynamics, while scalp-recorded EEG signals themselves are nonstationary. Therefore, traditional methods of EEG analysis may miss many properties inherent in such signals. Similarly, fractal analysis of EEG signals has shown scaling behaviors that may not be consistent with pure monofractal processes. In this study, we hypothesized that scalp-recorded human EEG signals may be better modeled as an underlying multifractal process. We utilized the Physionet online database, a publicly available database of human EEG signals as a standardized reference database for this study. Herein, we report the use of multifractal detrended fluctuation analysis on human EEG signals derived from waking and different sleep stages, and show evidence that supports the use of multifractal methods. Next, we compare multifractal detrended fluctuation analysis to a previously published multifractal technique, wavelet transform modulus maxima, using EEG signals from waking and sleep, and demonstrate that multifractal detrended fluctuation analysis has lower indices of variability. Finally, we report a preliminary investigation into the use of multifractal detrended fluctuation analysis as a pattern classification technique on human EEG signals from waking and different sleep stages, and demonstrate its potential utility for automatic classification of different states of consciousness. Therefore, multifractal detrended fluctuation analysis may be a useful pattern classification technique to distinguish among different states of brain function. PMID:23844189

Zorick, Todd; Mandelkern, Mark A

2013-01-01

407

A fuzzy information optimization processing technique for monitoring the transformer in neural-network on-line  

Microsoft Academic Search

In the electricity utilities around the world, a large number of power transformers are operating beyond their design life. The reliability and quality of power transformers is vital to system operation. In order to determine the condition of the insulation in transformers, many methods are developed. The most interesting methods for identifying fault conditions of the insulation for oil-filled transformer

Denghua Mei; Huaqing Min

2005-01-01

408

Two-dimensional cell parameters measurement of nematic liquid crystal using optical interferometry and Fourier transform fringe analysis technique  

NASA Astrophysics Data System (ADS)

We report a method for the measurement of nematic liquid crystal (NLC) cell parameters i.e., switching voltage, birefringence, retardation, dielectric anisotropy, average tilt angle and change in refractive index with applied DC voltage to LC material. The proposed method is based on optical interferometry and Fourier transform fringe analysis technique, in which we obtain 2-dimensional (2D) phase map of the interferograms as a function of applied voltage. Mach-Zehnder interferometer (MZI) was used for the study of cell parameters and interferograms were recorded at different applied DC voltages to NLC cell using CCD camera. From the phase map, 2D-refractive index distribution of the LC cell with applied voltage was reconstructed. Analytical equations are derived based on optical interferometry and then solved to obtain cell parameters. The present method is fast and can give 2D-cell parameters from only two quick interferograms.

Inam, M.; Singh, G.; Srivastava, V.; Prakash, J.; Joshi, T.; Biradar, A. M.; Mehta, D. S.

2011-11-01

409

A kurtosis-guided adaptive demodulation technique for bearing fault detection based on tunable-Q wavelet transform  

NASA Astrophysics Data System (ADS)

This paper presents an adaptive demodulation technique for bearing fault detection. It is implemented via the tunable-Q wavelet transform (TQWT). With the TQWT, the bearing vibration signal is decomposed into sub-signals corresponding to different band-pass filters of the TQWT. Kurtosis as an effective indicator of signal impulsiveness is adopted to guide the merging of the sub-signals leading to a signal component which contains information most relevant to the bearing fault. The purpose of the proposed approach is to adaptively search for the best filter for envelope demodulation analysis. In fact, the implementation of the proposed method can be interpreted as the process to obtain the optimal filter for the Hilbert demodulation analysis by two steps of merging of the band-pass filters of the TQWT. The effectiveness of the proposed method has been demonstrated by both simulation and experimental analyses.

Luo, Jiesi; Yu, Dejie; Liang, Ming

2013-05-01

410

Anti-ship missile tracking with a chirped amplitude modulation ladar  

NASA Astrophysics Data System (ADS)

Shipboard infrared search and track (IRST) systems can detect sea-skimming anti-ship missiles at long ranges. Since IRST systems cannot measure range and velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. ARL is developing a ladar based on its patented chirped amplitude modulation (AM) technique to provide unambiguous range and velocity measurements of targets handed over to it by the IRST. Using the ladar's range and velocity data, false alarms and clutter objects will be distinguished from valid targets. If the target is valid, it's angular location, range, and velocity, will be used to update the target track until remediation has been effected. By using an array receiver, ARL's ladar can also provide 3D imagery of potential threats in support of force protection. The ladar development program will be accomplished in two phases. In Phase I, currently in progress, ARL is designing and building a breadboard ladar test system for proof-of-principle static platform field tests. In Phase II, ARL will build a brassboard ladar test system that will meet operational goals in shipboard testing against realistic targets. The principles of operation for the chirped AM ladar for range and velocity measurements, the ladar performance model, and the top-level design for the Phase I breadboard are presented in this paper.

Redman, Brian C.; Stann, Barry L.; Ruff, William C.; Giza, Mark M.; Aliberti, Keith; Lawler, William B.

2004-09-01

411

Imaging of human tooth using ultrasound based chirp-coded nonlinear time reversal acoustics.  

PubMed

Human tooth imaging sonography is investigated experimentally with an acousto-optic noncoupling set-up based on the chirp-coded nonlinear time reversal acoustic concept. The complexity of the tooth internal structure (enamel-dentine interface, cracks between internal tubules) is analyzed by adapting the nonlinear elastic wave spectroscopy (NEWS) with the objective of the tomography of damage. Optimization of excitations using intrinsic symmetries, such as time reversal (TR) invariance, reciprocity, correlation properties are then proposed and implemented experimentally. The proposed medical application of this TR-NEWS approach is implemented on a third molar human tooth and constitutes an alternative of noncoupling echodentography techniques. A 10 MHz bandwidth ultrasonic instrumentation has been developed including a laser vibrometer and a 20 MHz contact piezoelectric transducer. The calibrated chirp-coded TR-NEWS imaging of the tooth is obtained using symmetrized excitations, pre- and post-signal processing, and the highly sensitive 14 bit resolution TR-NEWS instrumentation previously calibrated. Nonlinear signature coming from the symmetry properties is observed experimentally in the tooth using this bi-modal TR-NEWS imaging after and before the focusing induced by the time-compression process. The TR-NEWS polar B-scan of the tooth is described and suggested as a potential application for modern echodentography. It constitutes the basis of the self-consistent harmonic imaging sonography for monitoring cracks propagation in the dentine, responsible of human tooth structural health. PMID:21371732

Dos Santos, Serge; Prevorovsky, Zdenek

2011-08-01

412

Measurement of non-instantaneous contribution to the ?(3) in different liquids using femtosecond chirped pulses  

NASA Astrophysics Data System (ADS)

In the Born-Oppenheimer approximation and considering a Debye nuclear motion, a theoretical computation of pump-probe two-beam coupling in liquids using femtosecond chirped pulses is proposed. This technique makes it possible to specifically evidence the non-instantaneous contribution to the third-order susceptibility ?(3). Our model, which is an extension at the femtosecond scale of the one proposed by Dogariu et al., describes the temporal evolution of the probe signal as a function of different parameters such as the linear laser chirp, the ratio between the pulse duration and the nuclear response time. Experimentally, this method is applied to characterize the non-instantaneous ?(3) contribution in transparent liquids such as CS 2, benzene and toluene. Time resolved pump-probe coupling data using parallel and perpendicular linear polarizations fit well with the model developed. The experimental ratio R between both fast and slow non-instantaneous ?(3)XXXX and ?(3)XYYX elements of the tensor is equal to 1.33±0.01 in all the liquids studied, and is in good agreement with the expected liquid nuclear symmetry.

Langot, P.; Montant, S.; Freysz, E.

2000-04-01

413

Calculation and manipulation of the chirp rates of high-order harmonics  

SciTech Connect

We calculate the linear chirp rates of high-order harmonics in argon, generated by intense, 810 nm laser pulses, and explore the dependence of the chirp rate on harmonic order, driving laser intensity, and pulse duration. By using a time-frequency representation of the harmonic fields we can identify several different linear chirp contributions to the plateau harmonics. Our results, which are based on numerical integration of the time-dependent Schroedinger equation, are in good agreement with the adiabatic predictions of the strong field approximation for the chirp rates. Extending the theoretical analysis in the recent paper by Mauritsson et al. [Phys. Rev. A 70, 021801(R) (2004)], we also manipulate the chirp rates of the harmonics by adding a chirp to the driving pulse. We show that the chirp rate for harmonic q is given by the sum of the intrinsic chirp rate, which is determined by the new duration and peak intensity of the chirped driving pulse, and q times the external chirp rate.

Murakami, M.; Mauritsson, J.; Schafer, K.J.; Gaarde, M.B. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States); L'Huillier, A. [Department of Physics, Lund Institute of Technology, P. O. Box 118, S-22100 Lund (Sweden)

2005-01-01

414

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

PubMed

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

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

2006-04-01

415

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

416

Study of the Q branch structure of the 14N and 15N isotopologues of the ?4 band of ammonia using frequency chirped quantum cascade lasers.  

PubMed

Intrapulse quantum cascade (QC) laser spectrometers are able to produce both saturation and molecular alignment of a gas sample owing to the rapid sweep of the radiation through the absorption features. In the QC lasers used to study the (14)N and (15)N isotopologues of the ?4 band of ammonia centered near 1625 cm(-1), the variation of the chirp rate during the scan is very large, from ca. 85 to ca. 15 MHz ns(-1). In the rapid chirp zone the collisional interaction time of the laser radiation with the gas molecules is short, and large rapid passage effects are seen, whereas at the slow chirp end the line shape resembles that of a Doppler broadened line. The total scan range of the QC laser of ca. 10 cm(-1) is sufficient to allow the spectra of both isotopologues to be recorded and the rapid and slow interactions with the laser radiation to be seen. The rapid passage effects are enhanced by the use of an off axis Herriott cell with an effective path length of 62 m, which allows a buildup of polarization to occur. The effective resolution of the chirped QC laser is ca. 0.012 cm(-1) full width at half-maximum in the 1625 cm(-1) region. The results of these experiments are compared with those of other studies of the ?4 band of ammonia carried out using Fourier transform and Laser Stark spectroscopy. They also demonstrate the versatility of the down chirped QC laser for investigating collisional effects in low pressure gases using long absorbing path lengths. PMID:23581971

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

2013-10-01

417

Tunable narrowband optical parametric oscillator using a transversely chirped Bragg grating.  

PubMed

We demonstrate a novel technique for locking and tuning of a near-degenerate nanosecond optical parametric oscillator (OPO) using a transversely chirped volume Bragg grating. When the grating was translated, the OPO signal wavelength could be tuned from 1011 to 1023 nm (3.5 THz). The OPO was based on a periodically poled KTiOPO(4) as a nonlinear crystal and was pumped at 532 nm with up to 1.9 mJ of energy. The generated signal at an energy of 0.37 mJ had a bandwidth of 0.50 nm and a suppression of broadband background of >30 dB. The demonstrated technique is widely applicable for the construction of narrowband tunable sources. PMID:19373337

Jacobsson, Björn; Pasiskevicius, Valdas; Laurell, Fredrik; Rotari, Eugeniu; Smirnov, Vadim; Glebov, Leonid

2009-02-15

418

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

PubMed

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

Mohanan, Sharika; Srivastava, Atul

2014-04-10

419

Detection of linear features using a localized radon transform with a wavelet filter  

SciTech Connect

One problem of interest to the oceanic engineering community is the detection and enhancement of internal wakes in open water synthetic aperture radar (SAR) images. Internal wakes, which occur when a ship travels in a stratified medium, have a V shape extending from the ship, and a chirp-like feature across each arm. The Radon transform has been applied to the detection and the enhancement problems in internal wake images to account for the linear features while the wavelet transform has been applied to the enhancement problem in internal wake images to account for the chirp-like features. In this paper, a new transform, a localized Radon transform with a wavelet filter (LRTWF), is developed which accounts for both the linear and the chirp-like features of the internal wake. This transform is then incorporated into optimal and sub-optimal detection schemes for images (with these features) which are contaminated by additive Gaussian noise.

Warrick, A L; Delaney, P A

1999-12-13

420

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

Microsoft Academic Search

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(s) crystals for Hadamard masking material. 13 figs, refs.

W. G. Fateley; R. M. Hammaker

1992-01-01

421

A novel inductance-based technique for discrimination of internal faults from magnetizing inrush currents in power transformers  

Microsoft Academic Search

This paper presents a new methodology for discrimination between inrush currents and internal faults for a three-phase power transformer. This algorithm is based on instantaneous inductance. First, this method calculates differential inductance of transformer phases from primary side view of transformer by using voltage and current signals. Then, the algorithm compares differential inductance with a threshold value. If the calculated

H. Abniki; H. Monsef; P. Khajavi; H. Dashti

2010-01-01

422

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

SciTech Connect

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.

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

1992-11-15

423

Short-pulse chirped adiabatic population transfer in diatomic molecules  

NASA Astrophysics Data System (ADS)

Using the concept of light-induced potentials introduced by Garraway and Suominen [Phys. Rev. Lett. 80, 932 (1998)], we study alternative schemes of adiabatic population transfer in a diatomic molecule from the lowest vibrational level of the ground electronic state to the lowest vibrational level of a third electronic state via allowed optical transitions from the ground and third electronic states to a second electronic state. Our chirped-pulse rapid adiabatic passage scheme is implemented with short-duration optical pulses, and can be understood in terms of ``road design engineering'' of the light-induced time-dependent adiabatic potential upon which the dynamics occurs. We explicitly show that complete adiabatic vibronic population transfer occurs using chirped picosecond-duration pulses in the sodium dimer example.

Kallush, S.; Band, Y. B.

2000-04-01

424

Excitation of the Morse oscillator by an ultrashort chirped pulse  

SciTech Connect

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

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

2010-03-15

425

Interaction of strongly chirped pulses with two-level atoms  

SciTech Connect

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

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

2011-07-15

426

Measuring spatial chirp in ultrashort pulses using single-shot Frequency-Resolved Optical Gating.  

PubMed

We show that the spatio-temporal distortion, spatial chirp, is naturally and easily measured by single-shot versions of second-harmonic generation frequency-resolved optical gating (SHG FROG) (including the extremely simple version, GRENOUILLE);. While SHG FROG traces are ordinarily symmetrical, a pulse with spatial chirp yields a trace with a shear that is approximately twice the pulse spatial chirp. As a result, the trace shear unambiguously reveals both the magnitude and sign of the pulse spatial chirp. The effects of spatial chirp can then be removed from the trace and the intensity and phase vs. time also retrieved, yielding a full description of the spatially chirped pulse in space and time. PMID:19461707

Akturk, Selcuk; Kimmel, Mark; O'Shea, Patrick; Trebino, Rick

2003-01-13

427

Frequency-chirp rates of harmonics driven by a few-cycle pulse  

SciTech Connect

We present numerical calculations of the time-frequency characteristics of cutoff harmonics generated by few-cycle laser pulses. We find that for driving pulses as short as three optical cycles, the adiabatic prediction for the harmonic chirp rate is very accurate. This negative chirp is so large that the resulting bandwidth causes substantial overlap between neighboring harmonics, and the harmonic phase therefore appears to not vary in time or frequency. By adding a compensating positive chirp to the driving pulse, which reduces the harmonic bandwidth and allows for the appearance of the negative chirp, we can measure the harmonic chirp rates. We also find that the positive chirp on the driving pulse causes the harmonics to shift down in frequency. We show that this counterintuitive result is caused by the change in the strong field continuum dynamics introduced by the variation of the driving frequency with time.

Murakami, M.; Mauritsson, J.; Gaarde, M.B. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States)

2005-08-15

428

Pulsing dynamics in Ytterbium based chirped-pulse oscillators.  

PubMed

The properties of passively mode-locked laser oscillators based on Ytterbium doped gain media are studied theoretically along with experimental data. Based on the chirped-pulse approach limitations due to excessive non-linearities are avoided, opening up new routes for energy scaling of mode-locked solid-state oscillators. Predictions about potential future pulse energies are made and possible experimental problems are discussed. PMID:18794966

Siegel, Martin; Palmer, Guido; Emons, Moritz; Schultze, Marcel; Ruehl, Axel; Morgner, Uwe

2008-09-15

429

Tilted Fiber Bragg Grating for Chirped Microwave Waveform Generation  

Microsoft Academic Search

At iltedfiber Bragg grating (TFBG) as an optical spectral shaper to generate a chirped microwave waveform in a spectral-shaping and wavelength-to-time (SS-WTT) mapping system is proposed and demonstrated. The key component in the system is the TFBG, which has multiple resonant peaks with linearly increasing spacing in its transmission spectrum. By incor- porating aT FBG into an SS-WTT system, ac

Ming Li; Li-Yang Shao; Jacques Albert; Jianping Yao

2011-01-01

430

Chirped nonlinear cavity for digital quantum state readout without switching  

Microsoft Academic Search

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

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

2009-01-01

431

Excitation and control of chirped nonlinear ion-acoustic waves  

NASA Astrophysics Data System (ADS)

Large-amplitude ion acoustic waves are excited and controlled by a chirped frequency driving perturbation. The process involves capturing into autoresonance (a continuous nonlinear synchronization) with the drive by passage through the linear resonance in the problem. The transition to autoresonance has a sharp threshold on the driving amplitude. The theory of this transition is developed beyond the Korteweg-de Vries limit by using the Whitham's averaged variational principle within the water bag model and compared with Vlasov-Poisson simulations.

Friedland, L.; Shagalov, A. G.

2014-05-01

432

Compact multi-pass amplifier for chirped-pulse amplification  

NASA Astrophysics Data System (ADS)

A compact and simple multi-pass amplifier configuration suited for chirped-pulse amplification that can fit about 16 passes is presented. This configuration uses a pair of spherical mirrors with a diameter of two inches, and a sapphire window to shift the path of the seed beam and allow easy extraction from the amplifier. We present experimental results obtained using eight passes with this configuration, together with calculations for the gain achievable with the presented configuration.

Ruiz-de-La-Cruz, A.; Rangel-Rojo, R.

2006-03-01

433

Generalized chirp-like polyphase sequences with optimum correlation properties  

Microsoft Academic Search

A new general class of polyphase sequences with ideal periodic autocorrelation function is presented. The new class of sequences is based on the application of Zadoff-Chu polyphase sequences of length N=sm2, where s and m are any positive integers. It is shown that the generalized chirp-like sequences of odd length have the optimum crosscorrelation function under certain conditions. Finally, recently

Branislav M. Popovic

1992-01-01

434

Advanced sounding. II - First results from an advanced chirp ionosonde  

NASA Astrophysics Data System (ADS)

A BR Communications 'chirp' ionosonde has been modified to allow the measurement of the phase of ionospherically reflected echoes. The use of a dual-channel receiver and microprocessor-based control allows phase comparisons of temporally and spatially diverse echoes from which Doppler velocity, angle of arrival, and polarization mode can be evaluated, in addition to group range and amplitude. A test study of the ionosphere at Grahamstown is described.

Poole, A. W. V.; Evans, G. P.

1985-12-01

435

Frequency range extension of actively mode-locked lasers integrated with electroabsorption modulators using chirped gratings  

Microsoft Academic Search

We have fabricated actively mode-locked lasers integrated with electroabsorption modulators and chirped gratings. A chirped grating with a large chirp rate of 1.45 Å\\/?m can be realized by using multiphase-shifted patterns. Short pulses of 4-6 ps were generated over a wide frequency range from 18.9-19.8 GHz. We observed jumps in the wavelength during detuning. These jumps arise from multiple lobes

Kenji Sato; Hiroyuki Ishii; Isamu Kotaka; Yasuhiro Kondo; Mitsuo Yamamoto

1997-01-01

436

All-fiber devices for chromatic dispersion compensation based on chirped distributed resonant coupling  

Microsoft Academic Search

We review the principle of operation and characteristics of all-fiber devices for dispersion compensation based on chirped distributed resonant coupling. These devices are the chirped Bragg grating, the chirped intermodal coupler, and the tapered two-dissimilar-core fiber. We discuss the use of a figure of merit to characterize equalizing filters. Based on a specific example, filter responses are computed and their

Francois Ouellette; Jean-Francois Cliche; Stephane Gagnon

1994-01-01

437

A Novel Real-Time Chirp Measurement Method for Ultrashort Optical Pulses  

NASA Astrophysics Data System (ADS)

Rapid measurements of ultrashort optical pulse chirping were realized with a newly developed real-time chirp monitor. The application of a moving coil translator and electrical filters enabled the rapid measurement and decoding of fringe-resolved second-harmonic-generation (FRSHG) autocorrelation. The prototype system displayed chirping characteristics at a repetition rate higher than a few hertz, which demonstrates the usefulness of this monitor for dye laser system alignment.

Mogi, Kazuo; Naganuma, Kazunori; Yamada, Hajime

1988-11-01

438

Measuring spatial chirp in ultrashort pulses using single-shot Frequency-Resolved Optical Gating  

Microsoft Academic Search

We show that the spatio-temporal distortion, spatial chirp, is naturally and easily measured by single-shot versions of second-harmonic generation frequency-resolved optical gating (SHG FROG) (including the extremely simple version, GRENOUILLE)`. While SHG FROG traces are ordinarily symmetrical, a pulse with spatial chirp yields a trace with a shear that is approximately twice the pulse spatial chirp. As a result, the

Selcuk Akturk; Mark Kimmel; Patrick O'Shea; Rick Trebino

2003-01-01

439

Auditory brainstem responses to chirps delivered by different insert earphones  

PubMed Central

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.

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

2012-01-01

440

Selective excitation of LI2 by chirped laser pulses with all possible interstate radiative couplings  

NASA Astrophysics Data System (ADS)

We have numerically explored the feasibility and the mechanism of population transfer to the excited E 1?g electronic state of Li2 from the v=0 level of the ground electronic state X 1?g using the A 1?u state as an intermediate. In this system, the use of transform limited pulses with a frequency difference greater than the maximum Rabi frequency does not produce population transfer when all possible radiative couplings are taken into account. We have employed two synchronous pulses far detuned from the allowed transition frequencies, mainly with the lower frequency pulse positively chirped, and both pulses coupling the successive pair of states, X-A and A-E. The adiabaticity of the process has been investigated by a generalized Floquet calculation in the basis of 12 field dressed molecular states, and the results have been compared with those obtained from the full solution of time dependent Schrödinger equation. The conventional representation of the process in terms of three (or four) adiabatic potentials is not valid. It has been found that for cases of almost complete population transfer in full calculations with the conservation of the vibrational quantum number, adiabatic passage is attained with the 12 state Floquet model but not with the six state model. The agreement between the full calculations and the 12 state Floquet calculations is generally good when the transfer is adiabatic. Another characteristic feature of this work is the gaining of control over the vibrational state preparation in the final electronic state by careful tuning of the laser parameters as well as the chirp rate sign. This causes time dependent changes in the adiabatic potentials and nonadiabatic transfers can be made to occur between them.

Chatterjee, Souvik; Bhattacharyya, S. S.

2010-10-01

441

Chirped femtosecond solitons and double-kink solitons in the cubic-quintic nonlinear Schroedinger equation with self-steepening and self-frequency shift  

SciTech Connect

We demonstrate that the competing cubic-quintic nonlinearity induces propagating solitonlike dark(bright) solitons and double-kink solitons in the nonlinear Schroedinger equation with self-steepening and self-frequency shift. Parameter domains are delineated in which these optical solitons exist. Also, fractional-transform solitons are explored for this model. It is shown that the nonlinear chirp associated with each of these optical pulses is directly proportional to the intensity of the wave and saturates at some finite value as the retarded time approaches its asymptotic value. We further show that the amplitude of the chirping can be controlled by varying the self-steepening term and self-frequency shift.

Alka,; Goyal, Amit; Gupta, Rama; Kumar, C. N.; Raju, Thokala Soloman [Department of Physics, Panjab University, Chandigarh 160 014 (India); Department of Physics, Karunya University, Coimbatore 641 114 (India)

2011-12-15

442

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

443

Chirped holographic grating used as the dispersive element in an optical spectrometer  

SciTech Connect

We have developed a new design of optical spectrometer based on the use of a chirped holographic grating inscribed on a flat substrate. This type of grating has a surface modulation with a spatially varying period. The ability of the chirped grating to focus a beam is exploited to reduce significantly the physical dimensions of the instrument. Wavelength selection is achieved by a pure translation of the chirped grating. The properties of the chirped grating spectrometer have been characterized with different lasers and arc lamps and compared with those of two commercial spectrometers. A performance parameter has been defined, enabling the various instruments to be compared.

Fortin, Gilles; McCarthy, Nathalie

2005-08-10

444

Detonation discrimination techniques using a Fourier transform infrared spectrometer system and a near-infrared focal plane array  

NASA Astrophysics Data System (ADS)

To investigate the possibility of battlespace characterization, including the ability to classify munitions type and size, experimental data has been collected remotely from ground-based sensors, processed, and analyzed for several conventional munitions. The spectral, temporal and spatial infrared signatures from bomb detonations were simultaneously recorded using a Bomem MR157 Fourier Transform Infrared Spectrometer and an Indigo Systems Alpha Near-Infrared camera. Three different high explosive materials at three different quantities each were examined in one series of field studies. The FTIR spectra were recorded at 4 cm-1 spectral resolution and 123-ms temporal resolution using both HgCdTd (500-6000 cm-1) and InSb (1800-6000 cm-1) detectors. Novel key features have been identified that will aid in discriminating various types and sizes of flashes. These features include spectral dependent projections of one event's temporal data onto another event's temporal data, time dependence of the fireball size, ratios of specific integrated bands, and spectral dependence of temporal fit constants. Using Fisher discrimination and principal component techniques these features are projected onto a line that maximizes the differences in the classes of flashes and then identify the Bayesian decision boundaries for classification.

Dills, Anthony N.; Gross, Kevin; Perram, Glen P.

2003-09-01

445

Transverse spectral filtering and Mellin transform techniques applied to the effect of outer scale on tilt and tilt anisoplanatism  

SciTech Connect

The process of setting up problems of wave propagation through turbulence and reducing the expressions to integrals is typically lengthy. Furthermore, to yield useful results the integrals must be evaluated numerically, except for the simplest problems. Here procedures are given for quickly writing an integral expression and easily evaluating it analytically, yielding a series solution that requires only a few terms to yield accurate results. The solution can also be expressed as a finite sum of generalized hypergeometric functions. The approach uses the Rytov approximation and filter functions in the spatial domain to express quantities of interest such as Zernike modes and effects of anisoplanatism for single or counterpropagating or copropagating plane or spherical waves in integral form. The integrals are readily evaluated with Mellin transforms. The authors illustrate the technique by deriving the tilt jitter of a single wave and the jitter between two waves with outer-scale effects present. It is shown that outer scale has a significant effect on tilt even for large outer-scale sizes. The effect of outer scale on tilt anisoplanatism is less pronounced. 36 refs., 7 figs.

Sasiela, R.J.; Shelton, J.D. (Massachsetts Inst. of Technology, Lexington (United States))

1993-04-01

446

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)

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%.

Vasilyev, Arseny

447

Image restoration in chirp-pulse microwave CT (CP-MCT).  

PubMed

Chirp-pulse microwave computed tomography (CP-MCT) is a technique for imaging the distribution of temperature variations inside biological tissues. Even if resolution and contrast are adequate to this purpose, a further improvement of image quality is desirable. In this paper, we discuss the blur of CP-MCT images and we propose a method for estimating the corresponding point spread function (PSF). To this purpose we use both a measured and a computed projection of a cylindrical phantom. We find a good agreement between the two cases. Finally the estimated PSF is used for deconvolving data corresponding to various kinds of cylindrical phantoms. We use an iterative nonlinear deconvolution method which assures nonnegative solutions and we demonstrate the improvement of image quality which can be obtained in such a way. PMID:10851813

Bertero, M; Miyakawa, M; Boccacci, P; Conte, F; Orikasa, K; Furutani, M

2000-05-01

448

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

PubMed Central

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

Nikodem, Michal; Wysocki, Gerard

2012-01-01

449

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

PubMed

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

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

2000-09-01

450

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

451

Generating nonlinear FM chirp waveforms for radar.  

SciTech Connect

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.

Doerry, Armin Walter

2006-09-01

452

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

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.

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

2010-05-15

453

Utilizing a Chirp Sonar to Accurately Characterize Newly Deposited Material at the Calcasieu Ocean Dredged Material Disposal Site, Louisiana.  

National Technical Information Service (NTIS)

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. Subbottom reflection data, generated by a chirp sonar transmitting a 4 to ...

S. G. Schock D. J. Keith D. L. Debruin E. Dettmann G. Tracey

1992-01-01

454

0.1 V 13 GHz Transformer-Based Quadrature Voltage-Controlled Oscillator with a Capacitor Coupling Technique in 90 nm Complementary Metal Oxide Semiconductor  

NASA Astrophysics Data System (ADS)

A low power-supply voltage and high-frequency quadrature voltage-controlled oscillator (QVCO) using a combination of capacitor coupling and transformer feedback techniques is presented. The capacitor coupling technique can boost the transconductance of the LC-VCO core and coupling transconductance of QVCO at high frequency. Also, this technique can improve the quality factor of the QVCO at high frequency with low power-supply voltage, compared with the conventional QVCO. In addition, the capacitor coupling QVCO with transformer feedback can improve the quality factor of QVCO. Using this topology, the QVCO is able to operate at over 10 GHz with lower power-supply voltage. Implemented in the 90 nm complementary metal oxide semiconductor (CMOS) process, the proposed QVCO measures 1-MHz-offset phase noise of -94 dBc/Hz at 13 GHz while consuming 0.68 mW from a 0.1 V power-supply.

Kamimura, Tatsuya; Lee, Sang-yeop; Tanoi, Satoru; Ito, Hiroyuki; Ishihara, Noboru; Masu, Kazuya

2012-04-01

455

Simulation of optical pulse compression using parabolic pulse with linear chirp  

NASA Astrophysics Data System (ADS)

It is the key of realizing high speed, large capacity fiber information transmission that achieve ultrashort optical pulse by optical pulse compression. At present, the compression method that is achieving parabolic pulse with linear chirp and compensating the linear chirp is paid more attention. Based on the two schemes for the parabolic pulse with linear chirp by the normal dispersion decreasing fiber or the fiber amplifier with a normal dispersion, more study on the characteristics of the parabolic pulse with linear chirp in the different dispersion decreasing profiles (such as cosine, Gaussian, linear, exponential and hyperbolic) is showed; the results show that, for different dispersion decreasing profiles, the good linear chirp and parabolic shapes that are good for pulse compression can be generated. Moreover, a novel scheme for the parabolic pulse, which is achieved by a dispersion decreasing fiber amplifier with a normal dispersion, is presented. Numerical simulations show that, compared with the parabolic pulses generated in the normal dispersion decreasing fiber or the fiber amplifier, the parabolic pulse generated by the novel scheme has the better linear chirp and the more pulse energy; the gain has an obviously effect on the intensity and quality of the linear chirp, which is that the output pulse has a smaller pulse width and higher pulse power after the chirp is compensated.

Wang, Zun-zhi

2013-08-01

456

Reconfigurable optical fiber-based microwave dispersive line for single-shot chirped microwave pulse compression  

Microsoft Academic Search

A fiber-based approach for reconfigurable and single-shot chirped microwave pulse compression is proposed and demonstrated based on a time-spectrum convolution system. Different nanosecond-long, GHz-bandwidth linearly chirped microwave pulses are successfully compressed using the same platform.

Ming Li; Antonio Malacarne; Nezih Belhadj; Sophie LaRochelle; Jianping Yao; Jose Azana

2012-01-01

457

Chirped Microwave Pulse Compression Using a Photonic Microwave Filter With a Nonlinear Phase Response  

Microsoft Academic Search

Chirped microwave pulse compression using a photonic microwave filter with nonlinear phase response to implement matched filtering is proposed and investigated. The photonic microwave filter with the required phase response is realized based on optical phase to microwave phase conversion through single-sideband modulation and heterodyne detection. A detailed theoretical analysis on the photonic microwave filter design and the linearly chirped

Chao Wang; Jianping Yao

2009-01-01

458

Photonic generation of linearly chirped millimeter wave based on comb-spacing tunable optical frequency comb  

NASA Astrophysics Data System (ADS)

We demonstrated a photonic approach to generate a phase-continuous frequency-linear-chirped millimeter-wave (mm-wave) signal with high linearity based on continuous-wave phase modulated optical frequency comb and cascaded interleavers. Through linearly sweeping the frequency of the radio frequency (RF) driving signal, high-order frequency-linear-chirped optical comb lines are generated and then extracted by the cascaded interleavers. By beating the filtered high-order comb lines, center frequency and chirp range multiplied linear-chirp microwave signals are generated. Frequency doubled and quadrupled linear-chirp mm-wave signals of range 48.6 to 52.6 GHz and 97.2 to 105.2 GHz at chirp rates of 133.33 and 266.67 GHz/s are demonstrated with the ±1st and ±2nd optical comb lines, respectively, while the RF driving signal is of chirp range 24.3 to 26.3 GHz and chirp time 30 ms.

Xia, Zongyang; Xie, Weilin; Sun, Dongning; Shi, Hongxiao; Dong, Yi; Hu, Weisheng

2013-12-01

459

An attempt of high-speed imaging of the chirp radar-type microwave computed tomography  

Microsoft Academic Search

Methods for high speed imaging of the chirp radar-type microwave computed tomography have been investigated to show the feasibility of biological imaging. Electronic scan of the array antennas is a major scheme to reduce the data acquisition time. However, quick sweep of the chirp pulse microwave signal and data acquisition in time domain are also useful for the purpose. By

Michio Miyakawa; Toyohiko Hayashi

1997-01-01

460

Temperature-insensitive displacement sensing using the chirp effect of fiber Bragg grating  

Microsoft Academic Search

A new approach for displacement sensing based on chirp effect of fiber Bragg under strain-gradient is proposed and demonstrated in this paper. Strain gradient chirp of fiber Brag grating is realized by attaching the grating slant ways on a side face of a simple cantilever beam. The strain gradient, which is formed along the gratin when the free of the

Zhengrong Tong; Yonglin Huang; Hongyun Meng; Xinyong Dong; Guiyun Kai; Xiaoyi Dong

2002-01-01

461

High channel-count comb filter based on chirped sampled fiber Bragg grating and phase shift  

Microsoft Academic Search

Based on strongly chirped sampled fiber Bragg grating and phase shifts, a novel approach to obtain high channel-count comb filters is proposed in this letter. Various channel spacing can be achieved by a single strongly chirped phase mask where the required phase shifts can be gained by a precise translation stage. Comb filters with channel spacing of 50, 100, and

Yitang Dai; Xiangfei Chen; Ximing Xu; Chongcheng Fan; Shizhong Xie

2005-01-01

462

Effect of pulse profile and chirp on a laser wakefield generation  

SciTech Connect

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.

Zhang Xiaomei; Shen Baifei; Ji Liangliang; Wang Wenpeng; Xu Jiancai; Yu Yahong; Yi Longqing; Wang Xiaofeng [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Hafz, Nasr A. M. [Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Kulagin, V. [Sternberg Astronomical Institute of Moscow State University, Moscow 119992 (Russian Federation); Moscow Institute of Physics and Technology, Dolgoprudny, Moscow region, 141700 (Russian Federation)

2012-05-15

463

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

Microsoft Academic Search

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

A. Moreira; Yonghong Huang

1994-01-01

464

Simple measurement of fiber dispersion and of chirp parameter of intensity modulated light emitter  

Microsoft Academic Search

We report a novel method to measure two important parameters for optical fiber intensity modulated transmission systems: dispersion of optical fibers and chirp parameter of modulated light emitters. The method is easy, quick, and accurate for chirp parameter in the -10-to-10 range

F. Devaux; Y. Sorel; J. F. Kerdiles

1993-01-01

465

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

SciTech Connect

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

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

2009-02-23

466

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

PubMed

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

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

2012-11-01

467

Effects of auditory selective attention on chirp evoked auditory steady state responses  

Microsoft Academic Search

Auditory steady state responses (ASSRs) are frequently used to assess auditory function. Recently, the interest in effects of attention on ASSRs has increased. In this paper, we investigated for the first time possible effects of attention on AS-SRs evoked by amplitude modulated and frequency modulated chirps paradigms. Different paradigms were designed using chirps with low and high frequency content, and

Andreas Bohr; Corinna Bernarding; Daniel J. Strauss; Farah I. Corona-Strauss

2011-01-01