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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

Optical chirp z-transform processor with a simplified architecture.  

PubMed

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

Ngo, Nam Quoc

2014-12-29

3

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

4

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

5

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

6

Estimation of multiple accelerated motions using chirp-Fourier transform and clustering.  

PubMed

Motion estimation in the spatiotemporal domain has been extensively studied and many methodologies have been proposed, which, however, cannot handle both time-varying and multiple motions. Extending previously published ideas, we present an efficient method for estimating multiple, linearly time-varying motions. It is shown that the estimation of accelerated motions is equivalent to the parameter estimation of superpositioned chirp signals. From this viewpoint, one can exploit established signal processing tools such as the chirp-Fourier transform. It is shown that accelerated motion results in energy concentration along planes in the 4-D space: spatial frequencies-temporal frequency-chirp rate. Using fuzzy c-planes clustering, we estimate the plane/motion parameters. The effectiveness of our method is verified on both synthetic as well as real sequences and its advantages are highlighted. PMID:17283773

Alexiadis, Dimitrios S; Sergiadis, George D

2007-01-01

7

Characterization of the dispersion of chirped fiber Bragg grating through Fourier transform spectrometry method  

Microsoft Academic Search

Introduces a Fourier transform spectrometric method for the precise characterization of dispersion of chirped FBGs(fiber Bragg grating). The measurement system is a fiber Michelson interferometer composed of a broadband EDFA (Erium doped fiber amplifier) light source, a 3db 2×2 fiber coupler, a pair of polarization controllers, a optical attenuator, a fiber filter, an O\\/E converter, A\\/D converter, computer and a

Qingshan Chen; Naiguang Lu; Feng Jiang

2008-01-01

8

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

PubMed

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

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

2014-12-01

9

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

10

Characterization of the dispersion of chirped fiber Bragg grating through Fourier transform spectrometry method  

NASA Astrophysics Data System (ADS)

Introduces a Fourier transform spectrometric method for the precise characterization of dispersion of chirped FBGs(fiber Bragg grating). The measurement system is a fiber Michelson interferometer composed of a broadband EDFA (Erium doped fiber amplifier) light source, a 3db 2×2 fiber coupler, a pair of polarization controllers, a optical attenuator, a fiber filter, an O/E converter, A/D converter, computer and a optical path difference (OPD) scanning system. The digital interferogram of the system is acquired by recording the electric signal produced by the O/E converter through the A/D converter and by computer during the scanning of OPD. The recorded interferogram is then manipulated through a process involving low-pass filtering, fast Fourier transformation, phase unwrapping and computation of the numerical differentials of the unwrapped phase to the wavelength so as to obtain the relative group delay of the chirped FBG under test. It is proved by practical experiments that the repeatability of the system is up to Ps(picosecond) magnitude order.

Chen, Qingshan; Lu, Naiguang; Jiang, Feng

2008-03-01

11

Fourier-transform electron spin resonance with bandwidth-compensated chirp pulses  

NASA Astrophysics Data System (ADS)

Electron spin echo experiments using chirp pulses at X-band around 9 GHz have been performed with a home-built spectrometer based on an arbitrary waveform generator. Primary echoes without phase dispersion were obtained by employing the Böhlen-Bodenhausen scheme with the refocusing pulse being half as long as the coherence-generating pulse. To account for physical bandwidth limitation by the resonator, the instantaneous sweep rate of the chirps was adapted to the spectrometer’s frequency response function, which can be recorded from the sample under study within a few minutes. Such bandwidth-compensated chirp pulses are experimentally shown to achieve an almost uniform excitation bandwidth that exceeds the resonator bandwidth. This uniform excitation allows for computing frequency-domain spectra by Fourier-transformation (FT) of the echo signal. For a nitroxide in dilute solid solution with a spectral width of 200 MHz, the FT EPR spectrum agrees remarkably well with a field-swept echo-detected EPR spectrum. The overall spectral perturbation for operation far beyond the resonator bandwidth was characterized by acquiring a 700 MHz wide spectral range of a copper (II) EPR spectrum with nearly uniform amplitude with excitation and refocusing pulses of 200 and 100 ns, respectively. Furthermore, peculiarities were observed in solid-state FT EPR spectra of disordered systems. To understand these peculiarities two-dimensional data sets were acquired that correlate the FT EPR spectrum to inversion recovery or nuclear modulation. The echo envelope modulation experiments reveal echo decay rates increased by enhanced instantaneous diffusion and passage-specific effects in the nuclear modulations. The latter effect can be suppressed by nuclear modulation averaging. Apparent longitudinal relaxation times for a given subset of orientations are influenced by nuclear modulation effects. Proper extraction of orientation-dependent relaxation times thus requires an experimental setup that minimizes the modulations.

Doll, Andrin; Jeschke, Gunnar

2014-09-01

12

Fourier-transform electron spin resonance with bandwidth-compensated chirp pulses.  

PubMed

Electron spin echo experiments using chirp pulses at X-band around 9GHz have been performed with a home-built spectrometer based on an arbitrary waveform generator. Primary echoes without phase dispersion were obtained by employing the Böhlen-Bodenhausen scheme with the refocusing pulse being half as long as the coherence-generating pulse. To account for physical bandwidth limitation by the resonator, the instantaneous sweep rate of the chirps was adapted to the spectrometer's frequency response function, which can be recorded from the sample under study within a few minutes. Such bandwidth-compensated chirp pulses are experimentally shown to achieve an almost uniform excitation bandwidth that exceeds the resonator bandwidth. This uniform excitation allows for computing frequency-domain spectra by Fourier-transformation (FT) of the echo signal. For a nitroxide in dilute solid solution with a spectral width of 200MHz, the FT EPR spectrum agrees remarkably well with a field-swept echo-detected EPR spectrum. The overall spectral perturbation for operation far beyond the resonator bandwidth was characterized by acquiring a 700MHz wide spectral range of a copper (II) EPR spectrum with nearly uniform amplitude with excitation and refocusing pulses of 200 and 100ns, respectively. Furthermore, peculiarities were observed in solid-state FT EPR spectra of disordered systems. To understand these peculiarities two-dimensional data sets were acquired that correlate the FT EPR spectrum to inversion recovery or nuclear modulation. The echo envelope modulation experiments reveal echo decay rates increased by enhanced instantaneous diffusion and passage-specific effects in the nuclear modulations. The latter effect can be suppressed by nuclear modulation averaging. Apparent longitudinal relaxation times for a given subset of orientations are influenced by nuclear modulation effects. Proper extraction of orientation-dependent relaxation times thus requires an experimental setup that minimizes the modulations. PMID:25063952

Doll, Andrin; Jeschke, Gunnar

2014-09-01

13

High-spectral-resolution multiplex CARS spectroscopy using chirped pulses  

Microsoft Academic Search

A novel technique for achieving high spectral resolution with a femtosecond laser system is presented. Transform-limited 800 nm, 90 femtosecond (fs) pulses pass off two gratings, stretching the pulse in time to a pulse width of several picoseconds due to an induced linear temporal chirp directly proportional to the grating separation. This chirped pulse is the degenerate pump (omegaP) and

Kelly P. Knutsen; Justin C. Johnson; Abigail E. Miller; Poul B. Petersen; Richard J. Saykally

2004-01-01

14

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

15

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

NASA Astrophysics Data System (ADS)

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" microwave-microwave double resonance (MW-MW DR) measurements, in which we pump all transitions within a relatively broad frequency range (> 50 MHz) simultaneously. Transitions connected to peaks within the bandwidth of the coarse pulse are intensity modulated, revealing approximate connectivities that can be refined by performing ``fine" MW-MW DR measurements. Prospects for using this method to perform automated, time-efficient MW-MW DR on samples with dense spectra and unknown assignments will be discussed. Susskind, J., J. Chem. Phys. 53, 2492 (1970). Jacobsen, S., Andresen, U., and Mäder, H., Struct. Chem. 14, 217 (2003).

Finneran, Ian A.; Shipman, Steven T.

2011-06-01

16

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

17

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

18

Digital chirp modulation  

NASA Astrophysics Data System (ADS)

A technique for digital chirp synthesis is described. The method involves storing the in-phase and quadrature components of a sampled chirp waveform in a high-speed memory element. The baseband chirp is directly applied to an IF carrier using digital-to-analog converters which in turn drive a linearized quadriphase modulator. Out-of-band alias and harmonic products are removable via a output bandpass filter, and PN chopping of both the data and carrier is performed in order to spread the carrier leakage through the quadriphase modulator hybrid. It is shown that digital chirp modulation is comparatively insensitive to the large insertion losses which are found in most analog SWD modulators. A 1-bit quantized version of the digital waveform for a 2 Delta-wide chirp from -Delta F to +Delta F is illustrated in graphic form.

Komara, M. A.; Andren, C. F.

19

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

20

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

PubMed

We report the development of a new instrument that combines chirped-pulse microwave spectroscopy with a pulsed uniform supersonic flow. This combination promises a nearly universal detection method that can deliver isomer and conformer specific, quantitative detection and spectroscopic characterization of unstable reaction products and intermediates, product vibrational distributions, and molecular excited states. This first paper in a series of two presents a new pulsed-flow design, at the heart of which is a fast, high-throughput pulsed valve driven by a piezoelectric stack actuator. Uniform flows at temperatures as low as 20 K were readily achieved with only modest pumping requirements, as demonstrated by impact pressure measurements and pure rotational spectroscopy. The proposed technique will be suitable for application in diverse fields including fundamental studies in spectroscopy, kinetics, and reaction dynamics. PMID:25338889

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

2014-10-21

21

High-spectral-resolution multiplex CARS spectroscopy using chirped pulses  

NASA Astrophysics Data System (ADS)

A novel technique for achieving high spectral resolution with a femtosecond laser system is presented. Transform-limited 800 nm, 90 femtosecond (fs) pulses pass off two gratings, stretching the pulse in time to a pulse width of several picoseconds due to an induced linear temporal chirp directly proportional to the grating separation. This chirped pulse is the degenerate pump (?P) and probe (?p) pulse for the CARS experiment. When overlapped in time with the 1050 nm, 90 fs transform-limited Stokes (?S) pulse, only a fraction of the chirped ?p pulse generates the CARS signal, thereby creating a temporal slit that defines the spectral resolution of the technique. Spectra for liquid methanol and liquid isooctane are presented, with ~6 cm-1 spectral resolution achieved for isooctane. Resonance enhancement and the mechanism of achieving high spectral resolution are shown by adjusting the ?S wavelength and ?p delay relative to the ?S pulse.

Knutsen, Kelly P.; Johnson, Justin C.; Miller, Abigail E.; Petersen, Poul B.; Saykally, Richard J.

2004-06-01

22

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

23

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

24

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

PubMed

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. PMID:22183443

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

2012-02-01

25

Intravascular ultrasound chirp imaging  

NASA Astrophysics Data System (ADS)

We demonstrate the feasibility of intravascular ultrasound (IVUS) chirp imaging as well as chirp reversal ultrasound contrast imaging at intravascular ultrasound frequency. Chirp excitations were emitted with a 34 MHz single crystal intravascular transducer and compared to conventional Gaussian-shaped pulses of equal acoustic pressure. The signal to noise ratio of the chirp images was increased by up to 9 dB relative to the conventional images. Imaging of contrast microbubbles was implemented by chirp reversal, achieving a contrast to tissue ratio of 12 dB. The method shows potential for intravascular imaging of structures in and beyond coronary atherosclerotic plaques including vasa vasorum.

Maresca, D.; Jansen, K.; Renaud, G.; van Soest, G.; Li, X.; Zhou, Q.; de Jong, N.; Shung, K. K.; van der Steen, A. F. W.

2012-01-01

26

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

27

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

28

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

29

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

PubMed

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

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

2014-11-01

30

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

2014-12-01

31

A Transformed Lagged Ensemble Forecasting Technique for Increasing Ensemble Size  

E-print Network

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

Hansens, Jim

32

A FILTER DESIGN TECHNIQUE FOR STEERABLE PYRAMID IMAGE TRANSFORMS  

E-print Network

, and L1(~!) is a narrowband low­pass filter. The system diagram for a single stage of the steerableA FILTER DESIGN TECHNIQUE FOR STEERABLE PYRAMID IMAGE TRANSFORMS Anestis Karasaridis Eero a novel recursive filter design technique for multi­scale ``pyramid'' transforms. The recursion in the de

Simoncelli, Eero

33

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

E-print Network

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 ...

Park, Barratt

34

Amplitude-modulation chirp imaging for contrast detection.  

PubMed

We propose an amplitude-modulation chirp imaging method for contrast detection with high-frequency ultrasound. Our proposed method detects microbubbles by extracting and then selectively compressing the component of the backscattered chirp signal modulated by changes in the radii of microbubbles at their resonance frequency. Microbubbles are sonicated simultaneously with a narrowband, low-frequency pumping signal at their resonance frequency and a wideband, high-frequency imaging chirp signal. Changes in the radii of the resonant microbubbles result in periodic changes in their acoustic cross section that modulate the amplitude of the backscattered imaging chirp signal, forming pumping and imaging frequency sum-and-difference chirp terms. The frequency-sum or -difference chirp component is then extracted by a bandpass filter (BPF). Because a long imaging pulse duration is required to obtain a sufficient modulation depth on the chirp for contrast detection and to facilitate frequency-sum-and-difference signal extraction with the BPF, a chirp with a longer-than-usual waveform is used so pulse compression of the extracted chirp signal can then be performed to maintain the axial resolution, and even further improve the signal-to-noise ratio and contrast-to-tissue ratio. Experiments performed on flow phantoms with and without a speckle-generating background were performed to demonstrate the efficacy of the proposed technique. These results indicate that our proposed method can potentially provide high-resolution contrast detection in the microvasculature. PMID:20800180

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

2010-09-01

35

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

36

Image watermarking technique based on the steerable pyramid transform  

E-print Network

Image watermarking technique based on the steerable pyramid transform Fadoua DRIRA, Florence DENIS@liris.cnrs.fr fdenis@liris.cnrs.fr atilla.baskurt@liris.cnrs.fr ABSTRACT The application of the steerable pyramid properties of steerable pyramid transform that are relevant for use in image watermarking; these properties

Baskurt, Atilla

37

Technique for the metrology calibration of a Fourier transform spectrometer  

SciTech Connect

A method is presented for using a Fourier transform spectrometer (FTS) to calibrate the metrology of a second FTS. This technique is particularly useful when the second FTS is inside a cryostat or otherwise inaccessible.

Spencer, Locke D.; Naylor, David A

2008-11-10

38

Fourier transform techniques for the inference of cloud motion  

NASA Technical Reports Server (NTRS)

The development and evaluation are reported of phase shift techniques based on the Fourier transform for the estimation of cloud motion from geosynchronous meteorological satellite photographs. An alternative approach to cloud motion estimation, involving thresholding, was proposed and studied.

Lo, R. C.; Rosenfeld, A.

1974-01-01

39

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

PubMed

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

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

2008-07-01

40

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

PubMed

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

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

2006-06-01

41

Chirp and polarization control of femtosecond molecular fragmentation  

PubMed Central

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

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

2013-01-01

42

A FILTER DESIGN TECHNIQUE FOR STEERABLE PYRAMID IMAGE TRANSFORMS  

E-print Network

A FILTER DESIGN TECHNIQUE FOR STEERABLE PYRAMID IMAGE TRANSFORMS Anestis Karasaridis Eero orientation bandwidths. 2. FILTER CONSTRAINTS The decomposition is best de ned in the Fourier domain, where-oriented high- pass lter, and L1~! is a narrowband low-pass lter. The system diagram for a single stage

Simoncelli, Eero

43

Chirped-pulse four-wave Raman mixing in molecular hydrogen  

NASA Astrophysics Data System (ADS)

Four-wave Raman mixing (FWRM) in molecular hydrogen was studied using chirped pump and Stokes pulses emitting at 802 and 1,203 nm, respectively. The group delay dispersion (GDD) of the anti-Stokes pulse was examined employing a frequency-resolved optical gating system at different GDDs of the pump and Stokes pulses (0 or ±1,000 fs2). As a result, the energy and the sign of GDD for the anti-Stokes pulse remained unchanged, when the pump and Stokes pulses had the GDD with the same sign. When the sign was not the same, the energy decreased and only the portion useful for resonant FWRM was converted into a Raman emission. This technique has a potential for use in compensation of dispersion by passing the negatively chirped high-order Raman sidebands through the optics with positive chirps in the spectral region from the deep-ultraviolet to the near-infrared, to generate multiple transform-limited Raman pulses and then to produce an ultrashort optical pulse by a Fourier synthesis of these Raman emissions.

Shitamichi, Osamu; Kida, Yuichiro; Imasaka, Totaro

2014-07-01

44

High spectral resolution multiplex CARS spectroscopy using chirped pulses  

NASA Astrophysics Data System (ADS)

A simple technique for achieving high spectral resolution coherent anti-Stokes Raman scattering (CARS) spectra with a femtosecond laser system is presented. A linearly chirped and stretched (˜10 ps) pump pulse generates CARS signal only when overlapped in time with the Stokes pulse (90 fs), creating a `temporal slit' that defines the spectral resolution of the technique. Multiplex CARS spectra for liquid methanol and liquid isooctane are presented, demonstrating a spectral resolution of better than 5 cm -1. This new chirped (c-CARS) technique should prove useful for chemically-selective imaging applications, as it significantly reduces the non-resonant background contribution.

Knutsen, K. P.; Johnson, J. C.; Miller, A. E.; Petersen, P. B.; Saykally, R. J.

2004-04-01

45

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

SciTech Connect

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

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

2005-07-15

46

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

47

High spectral resolution multiplex CARS spectroscopy using chirped pulses  

Microsoft Academic Search

A simple technique for achieving high spectral resolution coherent anti-Stokes Raman scattering (CARS) spectra with a femtosecond laser system is presented. A linearly chirped and stretched (?10 ps) pump pulse generates CARS signal only when overlapped in time with the Stokes pulse (90 fs), creating a `temporal slit' that defines the spectral resolution of the technique. Multiplex CARS spectra for

K. P. Knutsen; J. C. Johnson; A. E. Miller; P. B. Petersen; R. J. Saykally

2004-01-01

48

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

49

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

50

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

51

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

52

The use of chirped pulse millimeter-wave spectroscopy in chemical dynamics and kinetics  

E-print Network

.Chirped-pulse millimeter wave (CPmmW) spectroscopy is a revolutionary technique that has taken advantage of advances in electronics to give high signal to noise broadband rotational spectra in a very short period of time ...

Shaver, Rachel Glyn

2013-01-01

53

Feature-level image fusion technique based on wavelet transform  

Microsoft Academic Search

The character of MRA (Multi-resolution Analysis) of wavelet transform can make the image be divided into different frequency spaces, so the image information in different frequency spaces can be processed and the features of the original image can be controlled. Wavelet transform is used widely in image compressing, edge detecting, noise filtering, image fusing etc. Based on Mallat fast algorithm

Zhigang Fan; Songling Fu; Runshun Li; Baojun Zuo

2002-01-01

54

SAW device provides hyperbolic chirp  

Microsoft Academic Search

The 'echo' location system employed by bats utilizes pulses whose frequency varies with time. This system is hyperbolically, rather than linearly weighted. It is pointed out that this concept of hyperbolic weighting, implemented with relatively inexpensive surface accoustic wave (SAW) devices, can be applied to torpedo guidance and satellite interception. The use of hyperbolic weighting allows the use of chirp

R. H. Johnson

1983-01-01

55

Embedded wavelet packet transform technique for texture compression  

NASA Astrophysics Data System (ADS)

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

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

1995-09-01

56

A VSP transformation technique for the determination of subsurface structure  

E-print Network

of downgoing energy. Page 31 32 33 34 21 Semblance section for the fault VSP. Contours from 0. 0 to . 576 by 0. 115. . . . . . . . . . . . . ~ . . ~ 36 22 Transformed VSP showing the faulted reflector. 23 Pinchout model. 24 YSP generated from... the pinchout model. 25 Pinchout VSP after removal of downgoing energy. 39 26 Semblance section for the pinchout VSP. Contours from 0. 0 to . 911 by 0. 0911. . . . . . . . . . . . . . , . . . . . . 44 27 Transformed VSP showing pinchout. 28 Unconformity...

Malloy, Jeffrey Edward

1985-01-01

57

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

58

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

59

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

60

Integrated PWM and transformer switching technique for AC voltage regulation  

Microsoft Academic Search

This paper presents a novel approach for precise and fast AC voltage regulation. The proposed method integrates switching transformer taps and AC PWM control to achieve smooth voltage control. This paper presents the computer simulations and mathematical analysis made with the proposed voltage regulation concept implemented in a typical distribution system. The electromagnetic transient program (EMTP) was used for computer

G. G. Karady; P. Parihar

1994-01-01

61

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

62

SAW device provides hyperbolic chirp  

NASA Astrophysics Data System (ADS)

The 'echo' location system employed by bats utilizes pulses whose frequency varies with time. This system is hyperbolically, rather than linearly weighted. It is pointed out that this concept of hyperbolic weighting, implemented with relatively inexpensive surface accoustic wave (SAW) devices, can be applied to torpedo guidance and satellite interception. The use of hyperbolic weighting allows the use of chirp by reducing the nonlinearity of the Doppler shift. The use of a hyperbolically weighted chirp (HWC) provides an approach for substantially overcoming a problem caused by the Doppler effect. The block diagram of a typical spread spectrum detection, tracking, and homing system is presented. This system uses a nonlinearly weighted SAW device as a spectrum spreader and compressor.

Johnson, R. H.

1983-11-01

63

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

64

Quadratic polar coordinate transform technique for the demodulation of circular carrier interferogram  

NASA Astrophysics Data System (ADS)

A quadratic polar coordinate transform technique is proposed to improve the demodulation accuracy of the circular carrier interferogram. Through the quadratic coordinate transform, the circular carrier interferogram is converted to the linear carrier interferogram with uniform spatial frequency, whose signal spectrum is significantly separated from the unwanted ones. Thus, the phase under test can be accurately retrieved by the conventional Fourier transform technique. Both the simulant and experimental results demonstrate that the proposed technique can be used for precise demodulation of the phase distribution of a circular carrier interferogram.

Li, Jin-Peng; Song, Le; Chen, Lei; Li, Bo; Han, Zhi-Gang; Gu, Chen-Feng

2015-02-01

65

Novel combinatorial probabilistic Hough transform technique for detection of underwater bubbles  

Microsoft Academic Search

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

John Y. Goulermas; Panos Liatsis

1997-01-01

66

Variational formulation of hyperbolic heat conduction problems applying Laplace transform technique  

E-print Network

Variational formulation of hyperbolic heat conduction problems applying Laplace transform technique In this paper, a non-Fourier heat conduction problem is analyzed by employing newly developed theory-transformed hyperbolic heat conduction equation is developed. The results were used for evaluation of parameters used

67

Novel Technique to Improve the Fault Detection Sensitivity in Transformer Impulse Test  

Microsoft Academic Search

Insulation is identified as one of the most important constructional rudiments of a transformer, and any weakness of insulation would lead to a transformer failure. To check the insulation integrity, a sensitive technique like the standard impulse test is used. Testing of winding insulation is performed by comparing the voltage and current waveforms of reduced and full test voltages, previously.

Essam Al-Ammar; George G. Karady; H. Jin Sim

2008-01-01

68

Application of electro-optic modulation technique for PD monitoring of power transformers  

Microsoft Academic Search

Partial discharge (PD) detection is an important technique for assessing the health of high voltage power transformers. A partial discharge signal within an oil-filled power transformer may reach a winding first, then travel along the winding to the bushing core bar. The bushing, acting like a capacitor, can transfer the high frequency components of the partial discharge signal to its

L. Hao; P. L. Lewin; Y. Tian; J. S. Wilkinson; S. J. Sutton; S. G. Swingler

2006-01-01

69

Dynamic wavelength switching of a remote nitrogen or air laser with chirped femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

We experimentally investigate the influence of the chirp of 800?nm Ti:sapphire pump laser pulses on the lasing behaviors of N2+ ions for the transitions between the excited electronic B2?u+ state (v? = 0) and the ground X2?g+ state (v = 0,1) at wavelengths of 391 and 428?nm. We found that as the chirp of the pump laser pulses varies from negative to positive, the intensities of the lasing signals at 391 and 428?nm show different chirp-dependent behaviors. Namely, the coherent emission at 391?nm reaches the maximum when the chirp of the pump pulse is transform-limited; whereas the 428?nm emission becomes strongest when the pump pulse is negatively chirped. This observation is ascribed to different self-generated seed sources produced in the plasma channel, which is verified by introducing an external seed for a pump–probe measurement. Our finding enables switching of wavelengths of remote lasing emissions of N2+ by manipulating the chirp of the pump laser pulses.

Jing, Chenrui; Xie, Hongqiang; Li, Guihua; Zeng, Bin; Chu, Wei; Zhang, Haisu; Ni, Jielei; Yao, Jinping; Xu, Huailiang; Cheng, Ya; Xu, Zhizhan

2015-01-01

70

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

71

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

72

A Hough Transform based Technique for Text Segmentation  

Microsoft Academic Search

Text segmentation is an inherent part of an OCR system irrespective of the\\u000adomain of application of it. The OCR system contains a segmentation module\\u000awhere the text lines, words and ultimately the characters must be segmented\\u000aproperly for its successful recognition. The present work implements a Hough\\u000atransform based technique for line and word segmentation from digitized images.\\u000aThe

Satadal Saha; Subhadip Basu; Mita Nasipuri; Dipak Kr. Basu

2010-01-01

73

Redox transformations in peroxidases studied by pulse radiolysis technique  

NASA Astrophysics Data System (ADS)

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

G?bicka, L.; G?bicki, J. L.

74

Chirped Incoherent Scatter Radar Plasma Line Measurements.  

NASA Astrophysics Data System (ADS)

The detectability of the plasma line in incoherent scatter radar experiments on the ionospheric plasma can be increased by factors in the range of 10 - 50 by chirping the transmitter frequency and the receiver local oscillator at a rate matching the linear change of plasma line frequency with height. The method of observation is explained in detail and experiments carried out at the Arecibo Observatory are described. The design of special equipment that had to be constructed is also discussed. Plasma line frequency versus height profiles with a frequency accuracy better than one part in 1000 were obtained with 0.4 s integration per point. The strength of the plasma line return and the point where the linear change of plasma line frequency, determined by the chirp rate, is tangent to the locally parabolic plasma line frequency profile were also determined with high accuracy. Using a nonlinear least squares fit it is possible to also determine the quadratic coefficient of a locally parabolic plasma line frequency versus height profile. In measurements of the daytime ionosphere the plasma line was found to be enhanced by about 70 times over that of thermal equilibrium. Observations during ionospheric modification experiments show that on the time scale of the 1 second integration period used the high frequency heater wave creates plasma depletions instantly. For a scale height of 51 km, a plasma line frequency of 5.1 MHz, a plasma line frequency gradient of 50 kHz/km and a HF-heater power density input of 800 kW/m('2) the heated region is depleted by 3 to 5% of its electrons. This provides the first direct evidence that the heater-induced modifications involve Langmuir waves trapped in cavities, cavitons. A number of future applications of this observation technique are discussed.

Birkmayer, Wolfram Siegfried

1987-09-01

75

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

Microsoft Academic Search

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

Jian-Da Wu; Jien-Chen Chen

2006-01-01

76

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

77

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

78

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

79

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

SciTech Connect

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, E-mail: chuckcklee@yahoo.com [Department of Photonics, National Sun-Yat-Sen University, Kaohsiung 80400, Taiwan (China); Lin, Yuan-Yao [Department of Electrical Engineering, Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 30010, Taiwan (China); Lin, Sung-Hui [Department of Photonics, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Lin, Gong-Ru [Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National Taiwan University, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan (China); Pan, Ci-Ling [Department of Photonics, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Department of Physics, National Tsing Hwa University, Hsinchu 30010, Taiwan (China)

2014-04-28

80

Chirp Characterization of External Modulators With Finite Extinction Ratio Using Linear Optical Sampling  

Microsoft Academic Search

We demonstrate a network monitoring technique for the frequency chirping of external modulators based on linear optical sampling. We present ??-parameter waveforms of digital data modulation from simultaneously measured amplitude and phase. Digital data modulation was compared to sinusoidal modulation to demonstrate the measurement capabilities. The high sensitivity of our technique was used to resolve the detailed impact of a

Tasshi Dennis; Paul A. Williams

2010-01-01

81

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

E-print Network

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.

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

2011-01-01

82

Chapter 55: Video-as-Data and Digital Video Manipulation Techniques for Transforming  

E-print Network

Chapter 55: Video-as-Data and Digital Video Manipulation Techniques for Transforming Learning and current progress of the Digital Interactive Video Exploration and Reflection (DIVER) Project at Stanford University. The DIVER Project aspires to accelerate cul- tural appropriation of video as a fluid expressive

Paris-Sud XI, Université de

83

A Robust Transform Domain Narrowband Interference Suppression Technique in Wireless Communications  

Microsoft Academic Search

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

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

2008-01-01

84

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

85

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

86

Spatial filtering of light by chirped photonic crystals  

SciTech Connect

We propose an efficient method for spatial filtering of light beams by propagating them through two-dimensional (also three dimensional) chirped photonic crystals, i.e., through the photonic structures with fixed transverse lattice period and with the longitudinal lattice period varying along the direction of the beam propagation. We prove the proposed idea by numerically solving the paraxial propagation equation in refraction-index-modulated media and we evaluate the efficiency of the process by harmonic-expansion analysis. The technique can be also applied for filtering (for cleaning) of the packages of atomic waves (Bose condensates), also to improve the directionality of acoustic and mechanical waves.

Staliunas, Kestutis [ICREA, Departament de Fisica i Enginyeria Nuclear, Universitat Politecnica de Catalunya, Colom 11, E-08222 Terrassa, Barcelona (Spain); Sanchez-Morcillo, Victor J. [Instituto de Investigacion para la Gestion Integrada de Zonas Costeras, Universidad Politecnica de Valencia, Ctra. Natzaret-Oliva S/N, 46730 Grao de Gandia (Spain)

2009-05-15

87

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

SciTech Connect

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

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

2010-03-15

88

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

89

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

90

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

91

An effective coding technique for the compression of one-dimensional signals using wavelet transforms  

Microsoft Academic Search

This paper introduces an effective technique for the compression of one-dimensional signals using wavelet transforms. It is based on generating a binary stream of 1s and 0s that encodes the wavelet coefficients structure (i.e., encodes the locations of zero and nonzero coefficients). A new coding algorithm, similar to the run length encoding, has been developed for the compression of the

Mohammed Abo-Zahhad; Bashar A. Rajoub

2002-01-01

92

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

93

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

94

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

95

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

96

Unambiguous evaluation of a chirp measurement standard  

NASA Astrophysics Data System (ADS)

This article describes an automated evaluation method for the chirp standard. Chirp calibration standards provide a way to describe the transfer behavior of different spatial frequencies as they contain sinusoidal functions of varying wavelengths (Krüger-Sehm et al 2007 chirp calibration standards for surface measuring instruments Tech. Mess. tm 74 572–76 Pehnelt et al 2011 Comparative analysis of optical surface measuring systems with a chip calibration standard Tech. Mess. tm 78 457–62). By introducing a new, automated evaluation method, an improvement for the application of the chirp standard can be achieved. The data-preprocessing for topography and profile measurement data and the fit of the geometric elements are described. Automated evaluation can reduce the labor required to evaluate measured data and make it easier to compare different evaluations in the course of standardization. The algorithm can be used to characterize the so-called ‘small scale fidelity’ of an optical instrument. The term ‘small scale fidelity’ is currently discussed in the optical group of working group no. 16 of the ISO technical committee 213.

Seewig, Jörg; Eifler, Matthias; Wiora, Georg

2014-10-01

97

A fast Fourier transform accelerated Ewald summation technique for the vector electromagnetic rectangular cavity Green's function  

NASA Astrophysics Data System (ADS)

A fast Fourier transform accelerated Ewald method for the computation of the vector electromagnetic rectangular cavity Green's function in terms of the electric field due to electric currents is presented and used in a boundary integral formulation. The Ewald summation technique suffers from the high-frequency breakdown when it is applied to Green's functions of wave problems. In the case of the rectangular cavity Green's function, the number of necessary terms in the spectral series grows, therefore, cubically with frequency for a given accuracy. To counteract the high-frequency breakdown, the evaluation of the spectral series is accelerated with an inverse fast Fourier transform in this work. At high frequencies, a speed-up of up to four orders of magnitude is achieved. As an application example, a reverberation chamber containing a metallic enclosure and a mode-stirrer is modeled.

Gruber, M. E.; Koenen, C.; Eibert, T. F.

2015-01-01

98

Transformer  

NSDL National Science Digital Library

This applet is about transformers. The number of turns on the primary and secondary winding, load resistance, frequency and amplitude of the voltage can be set by the user. The voltage and current waveforms are shown. A detailed mathematical analysis along with snap shots of voltage and current waveforms of a real transformer is also provided. This simulation is part of a simulation library.

Ng, Chiu-King

2007-10-16

99

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

100

A Parallel Mixed Integer Programming-Finite Element Method Technique for Global Design Optimization of Power Transformers  

Microsoft Academic Search

Transformer design optimization is determined by minimizing the transformer cost taking into consideration constraints imposed both by international specifications and customer needs. The main purpose of this work is the development and validation of an optimization technique based on a parallel mixed integer nonlinear programming methodology in conjunction with the finite element method, in order to reach a global optimum

Eleftherios I. Amoiralis; Marina A. Tsili; Pavlos S. Georgilakis; Antonios G. Kladas; Athanassios T. Souflaris

2008-01-01

101

Transformation  

NSDL National Science Digital Library

This video clip demonstrates the process of transformation. When a bacterial cell dies, the DNA in the cell breaks into fragments. This free DNA can be taken up by certain bacteria and integrated into their DNA.

American Society For Microbiology

2002-01-01

102

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

103

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

104

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

NASA Astrophysics Data System (ADS)

This paper presents a recursive Hilbert transform method for the time-varying property identification of large-scale shear-type buildings with limited sensor deployments. An observer technique is introduced to estimate the building responses from limited available measurements. For an n-story shear-type building with l measurements (l ? n), the responses of other stories without measurements can be estimated based on the first r mode shapes (r ? l) as-built conditions and l measurements. Both the measured responses and evaluated responses and their Hilbert transforms are then used to track any variation of structural parameters of a multi-story building over time. Given floor masses, both the stiffness and damping coefficients of the building are identified one-by-one from the top to the bottom story. When variations of parameters are detected, a new developed branch-and-bound technique can be used to update the first r mode shapes with the identified parameters. A 60-story shear building with abruptly varying stiffness at different floors is simulated as an example. The numerical results indicate that the proposed method can detect variations of the parameters of large-scale shear-type buildings with limited sensor deployments at appropriate locations.

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

2012-10-01

105

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

106

Chirped incoherent scatter radar plasma line measurements  

NASA Astrophysics Data System (ADS)

The detectability of the plasma line in incoherent scatter radar experiments on the ionospheric plasma can be increased by factors in the range of 10 to 50 by chirping the transmitter frequency and the receiver local oscillator at a rate matching the linear change of plasma line frequency with height. The method of observation is explained in detail and experiments carried out at the Arecibo Observatory are described.

Birkmayer, Wolfram Siegfried

107

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

108

A Novel Semi-Fragile Image Watermarking, Authentication and Self-restoration Technique Using the Slant Transform  

E-print Network

A Novel Semi-Fragile Image Watermarking, Authentication and Self-restoration Technique Using.ho@surrey.ac.uk Abstract A novel semi-fragile digital watermarking method based on the Slant transform (SLT) for image. Semi-fragile watermarking techniques for image content authentication have recently attracted much

Doran, Simon J.

109

SAR processing with stepped chirps and phased array antennas.  

SciTech Connect

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

Doerry, Armin Walter

2006-09-01

110

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

111

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

112

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

113

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

PubMed

A 'powder-poling' technique was developed to study electric field induced structural transformations in ferroelectrics exhibiting a morphotropic phase boundary (MPB). The technique was employed on soft PZT exhibiting a large longitudinal piezoelectric response (d33 ? 650 pC N(-1)). It was found that electric poling brings about a considerable degree of irreversible tetragonal to monoclinic transformation. The same transformation was achieved after subjecting the specimen to mechanical stress, which suggests an equivalence of stress and electric field with regard to the structural mechanism in MPB compositions. The electric field induced structural transformation was also found to be accompanied by a decrease in the spatial coherence of polarization. PMID:25629264

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

2015-02-25

114

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

PubMed

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

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

2015-02-01

115

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

NASA Astrophysics Data System (ADS)

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

Kohler, Bern; Yakovlev, Vladislav V.; Wilson, Kent R.; Squier, Jeff; Delong, Kenneth W.; Trebino, Rick

1995-03-01

116

Generation of Arbitrary Frequency Chirps with a Fiber-Based Phase Modulator and Self-Injection-Locked Diode Laser  

E-print Network

We present a novel technique for producing pulses of laser light whose frequency is arbitrarily chirped. The output from a diode laser is sent through a fiber-optical delay line containing a fiber-based electro-optical phase modulator. Upon emerging from the fiber, the phase-modulated pulse is used to injection-lock the laser and the process is repeated. Large phase modulations are realized by multiple passes through the loop while the high optical power is maintained by self-injection-locking after each pass. Arbitrary chirps are produced by driving the modulator with an arbitrary waveform generator.

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

2006-01-01

117

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

118

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

119

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

120

chirp, 7/8/1996 BAYESIAN SPECTRUM AND CHIRP ANALYSIS y  

E-print Network

spectrum and chirp (frequency change) rate for the case that one has incomplete noisy data on values y). In that problem we estimate the spectrum of a time series (y 1 \\Delta \\Delta \\Delta y N ), from incomplete data consisting of a few autocovariances (R 0 \\Delta \\Delta \\Delta Rm ); m ! N , measured from the entire time

Rodriguez, Carlos

121

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

SciTech Connect

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

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

2009-11-12

122

The Theta Laser A Low Noise Chirped Pulse Laser  

E-print Network

The Theta Laser A Low Noise Chirped Pulse Laser Dimitrios Mandridis dmandrid@creol.ucf.edu April 29 Applications of Uniform-Intensity Chirped-Pulse Lasers [1] Y. Han, and B. Jalali, J. Lightwave Technol., 21 Coherence Tomography ( Medical ) Laser Ranging ( Millitary ) #12;6 Outline · Applications of frequency swept

Van Stryland, Eric

123

Frequency-chirped readout of spatial-spectral absorption features  

SciTech Connect

This paper examines the physical mechanisms of reading out spatial-spectral absorption features in an inhomogeneously broadened medium using linear frequency-chirped electric fields. A Maxwell-Bloch model using numerical calculation for angled beams with arbitrary phase modulation is used to simulate the chirped field readout process. The simulation results indicate that any spatial-spectral absorption feature can be read out with a chirped field with the appropriate bandwidth, duration, and intensity. Mapping spectral absorption features into temporal intensity modulations depends on the chirp rate of the field. However, when probing a spatial-spectral grating with a chirped field, a beat signal representing the grating period can be created by interfering the emitted photon echo chirped field with a reference chirped field, regardless of the chirp rate. Comparisons are made between collinear and angled readout configurations. Readout signal strength and spurious signal distortions are investigated as functions of the grating strength and the Rabi frequency of the readout pulse. Using a collinear readout geometry, distortions from optical nutation on the transmitted field and higher-order harmonics are observed, both of which are avoided in an angled beam geometry.

Chang, Tiejun; Mohan, R. Krishna; Harris, Todd L.; Merkel, Kristian D. [Spectrum Laboratory, Montana State University, Bozeman, Montana 59717 (United States); Tian Mingzhen [Physics Department, Montana State University, Bozeman, Montana 59717 (United States); Babbitt, Wm. Randall [Spectrum Laboratory, Montana State University, Bozeman, Montana 59717 (United States); Physics Department, Montana State University, Bozeman, Montana 59717 (United States)

2004-12-01

124

Chirped optical solitons in single-mode birefringent fibers  

NASA Astrophysics Data System (ADS)

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

Mahmood, M. F.

1996-12-01

125

A New Hybrid DCT and Contourlet Transform Based JPEG Image Steganalysis Technique  

Microsoft Academic Search

In this paper, a universal steganalysis scheme for JPEG images based upon hybrid transform features is presented. We first\\u000a analyzed two different transform domains (Discrete Cosine Transform and Discrete Contourlet Transform) separately, to extract\\u000a features for steganalysis. Then a combination of these two feature sets is constructed and employed for steganalysis. A Fisher\\u000a Linear Discriminant classifier is trained on features

Zohaib Khan; Atif Bin Mansoor

2009-01-01

126

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

127

Frequency chirping during a fishbone burst  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

128

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

129

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

130

Experimental investigation of superfocusing of plasmonic lens with chirped circular nanoslits.  

PubMed

A plasmonic lens with metallic chirped circular nanoslits corrugated on Au film supported on quartz substrate for the purpose of superfocusing was put forth and fabricated by means of focused ion beam direct milling technique. Topography of the lens was imaged using an atomic force microscope. After that a near-field scanning optical microscope was employed for optical characterization of focusing performance of the lens. Our experimental results verify the focusing performance and further demonstrate that they are in agreement with the theoretical calculation results. Focusing performance is significantly improved in comparison to that of the non-chirped lens. The lenses are possible to be used for the applications of bioimaging, detection, and inspection in submicron scale resolution. PMID:20389353

Fu, Yongqi; Liu, Yu; Zhou, Xiuli; Xu, Zongwei; Fang, Fengzhou

2010-02-15

131

Method for tuning chirp ratio of fiber gratings without central wavelength shift  

NASA Astrophysics Data System (ADS)

A method for tuning the chirp ratio of a fiber grating without the central wavelength shift is proposed by using a two-fixed-end compressive beam, which induces a linear strain distribution along the grating. This technique allows dynamic control of the grating's chirp ratio by changing the displacement of the translation stage. The 3-dB bandwidth tuning range is from 6.52 to 13.5 nm when the grating is tuned in the broadening way, while the bandwidth tuning range is from 6.52 to 0.95 nm in the compressing way. The proposed method has potential applications for the dynamic dispersion compensation and the sensors of pressure and displacement, etc., by detecting the change of bandwidth information.

Liu, Guanxiu; Feng, Dejun; Zhang, Maosen; Jia, Dongfang

2014-12-01

132

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

Microsoft Academic Search

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

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

2010-01-01

133

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

Microsoft Academic Search

Errors in discrete Abel inversion methods using Fourier transform techniques have been analyzed. The Fourier expansion method is very accurate but sensitive to noise. The Fourier-Hankel method has a significant systematic negative deviation, which increases with the radius; inversion error of the method can be reduced by adjusting the value of a factor. With a decrease of the factor both

Shuiliang Ma; Hongming Gao; Lin Wu

2008-01-01

134

In situ examination of tin oxide atomic layer deposition using quartz crystal microbalance and Fourier transform infrared techniques  

E-print Network

. Additional ex situ surface analysis using x-ray photoelectron spectroscopy XPS and Auger electron and Fourier transform infrared techniques X. Du Department of Chemical and Biological Engineering, University, Boulder, Colorado 80309 S. M. Georgea Department of Chemical and Biological Engineering, and Department

George, Steven M.

135

Nonlinear frequency chirping of toroidal Alfvén eigenmodes in tokamak plasmas  

NASA Astrophysics Data System (ADS)

Nonlinear frequency chirping of toroidal Alfén eigenmodes (TAE) driven by energetic particles is investigated by kinetic simulations in toroidal plasmas. It is found that the up–down symmetry of the frequency chirping of a TAE is broken due to an anisotropic pitch-angle distribution with dominant co-passing energetic particles. The nonuniform distribution of the free energy associated with the initial energetic particle distribution causes biased driving forces that result in a strongly asymmetric frequency chirping. The evolution of the perturbed distribution function in the phase space shows that a hole–clump pair moves together towards the magnetic axis for the small pitch-angle parameter cases. The downward chirping of the mode frequency is associated with the negative drift of the phase island in the KAM surfaces or the resonance ?f structures in the radial direction. On the other hand, the energetic particle distribution with larger pitch-angle parameters leads to upward chirping of the TAE frequency. The upward chirping is due to the drifting of the resonance structure towards the boundary of the simulation region and overlapping of different poloidal resonances in the (?, E) phase space at the late stage. The phase space dynamics provides a key mechanism for understanding the wave chirping direction and particle transport process.

Zhu, J.; Ma, Z. W.; Fu, G. Y.

2014-12-01

136

Analysis of chirped-pulse-amplification system based on Offner triplet stretcher and transmission grating compressor  

NASA Astrophysics Data System (ADS)

Analytical phase expressions are presented for an Offner stretcher and transmission grating compressor based on ray tracing and apply them to analyze a chirped-pulse-amplification (CPA) system. Besides, an optimization method to extract high-fidelity amplified pulse is proposed by controlling the phase of the entire system. Through theoretical analysis and numerical simulation, one can adjust the incident angle and perpendicular distance between gratings to completely compensate dispersion of Offner stretcher over entire wavelength. Finally, the optimized CPA system provides Fourier-transform-limit pulse which is identical with seed pulse.

Li, Lin; Li, Chaoming; Chen, Xinrong; Liu, Linyue; Wu, Jianhong

2014-11-01

137

Classification of Pecorino cheeses produced in Italy according to their ripening time and manufacturing technique using Fourier transform infrared spectroscopy.  

PubMed

Fourier-transform infrared spectroscopy, followed by linear discriminant analysis of the spectral data, was used to classify Italian Pecorino cheeses according to their ripening time and manufacturing technique. The Fourier transform infrared spectra of the cheeses were divided into 18 regions and the normalized absorbance peak areas within these regions were used as predictors. Linear discriminant analysis models were constructed to classify Pecorino cheeses according to different ripening stages (hard and semi-hard) or according to their manufacturing technique (fossa and nonfossa cheeses). An excellent resolution was achieved according to both ripening time and manufacturing technique. Also, a final linear discriminant analysis model considering the 3 categories (hard nonfossa, hard fossa, and semi-hard nonfossa) was constructed. A good resolution among the 3 categories was obtained. PMID:20854982

Lerma-García, M J; Gori, A; Cerretani, L; Simó-Alfonso, E F; Caboni, M F

2010-10-01

138

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

139

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

140

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

Microsoft Academic Search

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

Tapan K. Saha

2003-01-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

142

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

143

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

144

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

145

Dispersion compensation in chirped pulse amplification systems  

DOEpatents

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

Bayramian, Andrew James; Molander, William A.

2014-07-15

146

Quantum Fluctuations in the Chirped Pendulum  

E-print Network

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

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

2010-08-26

147

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

148

A High Precision Ranging Scheme for IEEE802.15.4a Chirp Spread Spectrum System  

NASA Astrophysics Data System (ADS)

This letter proposes a high precision ranging scheme based on the time of arrival estimation technique for the IEEE 802.15.4a chirp spread spectrum system. The proposed scheme consists of a linear channel impulse response estimation process with the zero forcing or minimum mean square error technique and the multipath delay estimation process with matrix pencil algorithm. The performance of the proposed scheme is compared with that of a well known MUSIC algorithm in terms of computational complexity and ranging precision. Simulation results demonstrate that the proposed scheme outperforms the MUSIC algorithm even though it has comparatively lower computational complexity.

Kim, Na Young; Kim, Sujin; Kim, Youngok; Kang, Joonhyuk

149

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

SciTech Connect

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

Stanford University; Department of Energy Resources Engineering Green Earth Sciences

2007-09-30

150

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

151

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. PMID:19079529

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

2011-01-01

152

Surface solitons in chirped photonic lattices Mario I. Molina,1,  

E-print Network

. [12] demon- strated that the soliton formation can be dramati- cally modified at the surface the surface and the critical power as a function of the lattice chirp, and also demon- strate how the lattice

153

A co-ordinate transformation technique for studying ux perturbations induced by strong  

E-print Network

Research Centre, Bombay-400085, India b Department of Reactor Physics, Chalmers University of Technology 5 manner and the solution is transformed back to the original parameter space. The method is equally

Pázsit, Imre

154

Narrowband pulse-enhanced upconversion of chirped broadband pulses  

Microsoft Academic Search

We propose and demonstrate an efficient sum-frequency mixing scheme based on narrowband and chirped broadband pulses. It combines the advantages of wider spectral acceptance bandwidth and of alleviating the temporal walk-off, which are both beneficial to higher conversion efficiency. Chirped sum-frequency pulses at 455 nm with energy up to 360 µJ, corresponding to a conversion efficiency of ~ 40%, are

Kun Zhao; Peng Yuan; Haizhe Zhong; Dongfang Zhang; Heyuan Zhu; Liezun Chen; Shuangchun Wen; Liejia Qian

2010-01-01

155

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

PubMed

An effort was made to synthesize nanostructured TiO(2) via sol-gel technique to obtain a 100% rutile polymorph of nanostructured TiO(2). The sol-gel synthesis technique was suitably modified by incorporating ultrasound to study the effect of cavitation on the phase transformation, crystallite size, crystallinity and morphological (scanning electron microscopy) properties of the obtained nano-TiO(2). It was observed that using ultrasound, yield of the nano-TiO(2) was improved from 86.35% to 95.078%. The phase transformation of anatase-to-rutile of TiO(2) was studied for both (ultrasound assisted and conventional) the processes. Complete phase transformation of the TiO(2) was observed as expected with and without the use of ultrasound but the marked reduction in the required calcination temperature for obtaining 100% phase transformation with ultrasound was the major achievement in the present study, leading to 70% energy savings during calcination. PMID:19850506

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

2010-02-01

156

Interaction of onboard transform-based lossy compression algorithms with EO/IR focal plane nonuniformity correction techniques  

NASA Astrophysics Data System (ADS)

This paper describes the effect of using lossy transform- based compression on IR framing sensor data with and without sensor anomaly pre-processing. Significant image degradation persists when ground-based non-uniformity correction processing is implemented after the sensor imagery has been compressed and reconstructed. Various techniques for non- uniformity correction, from low to high processing complexity, are applied before and after lossy compression at varying compression ratios. Results using both DCT and wavelet transform-based compression techniques indicate that on-board real-time compression algorithms and nonuniformity correction must be jointly optimized and that direct application of lossy compression without preprocessing for sensor anomalies reduces not only the compression efficiency and image fidelity, but also the performance of subsequent ground-based nonuniformity correction.

Linne von Berg, Dale C.

1998-07-01

157

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

PubMed

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

Bettini, Paolo; Guerreschi, Erika; Sala, Giuseppe

2014-01-01

158

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

159

A coupled-mode technique for the transformation of ship-generated waves over variable bathymetry regions  

Microsoft Academic Search

In the present work, a coupled-mode technique is applied to the transformation of ship's waves over variable bathymetry regions, characterised by parallel depth-contours, without any mild-slope assumption. This method can be used, in conjunction with ship's near-field wave data in deep water or in constant-depth, as obtained by the application of modern (linearised or non-linear) ship computational fluid dynamic (CFD)

K. A Belibassakis

2003-01-01

160

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

SciTech Connect

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

Du Hongchuan; Hu Bitao [School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000 (China)

2011-08-15

161

Color image hiding based on the phase retrieval technique and Arnold transform.  

PubMed

A new (to our knowledge) method is proposed in this paper for color image hiding and extracting using the phase retrieval algorithm in the fractional Fourier transform (FRFT) domain and Arnold transform (ART). Based on a cascaded phase iterative FRFT algorithm, the three channels (R, G, and B) of the secret color image permuted by ART are encrypted. Then the encoded information is embedded in the blue channel (B channel) of the enlarged color host image. Using the security enhanced encryption method, not only the random phase mask and the wavelength but also the transform parameters of ART and FRFT are provided as additional keys for decryption. It is shown that the security of information hiding will be enhanced. Computer simulations are performed to show the hiding capacity of the proposed system. Numerical results are presented to verify the validity and efficiency of the proposed method. PMID:21556114

Shi, Xiaoyan; Zhao, Daomu

2011-05-10

162

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

163

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

164

Direct generation of intense extreme ultraviolet supercontinuum with chirped 11-mJ pulses from a femtosecond laser amplifier  

E-print Network

We report on the generation of intense extreme ultraviolet (EUV) supercontinuum with photon energies spanning from 35 eV to 50 eV (i. e., supporting an isolated attosecond pulse with a duration of ~271 as) by loosely focusing 11-mJ chirped pulses from a femtosecond laser amplifier into a 10-mm long gas cell filled with krypton gas. We observe that when high-order harmonics are generated with transformed-limited ~35 fs pulses, only discrete harmonics can be produced; whereas for negatively chirped 188 fs pulses, EUV supercontinuum can be observed in single-shot harmonic spectrum. The dramatic change of spectral and temporal properties of the driver pulses after passing through the gas cell indicates that propagation effects play a significant role in promoting the generation of the EUV supercontinuum.

Zeng, Bin; Li, Guihua; Yao, Jinping; Ni, Jielei; Zhang, Haisu; Cheng, Ya; Xu, Zhizhan

2011-01-01

165

Implementation of a 1GHZ frontend using transform domain charge sampling techniques  

E-print Network

) . . . . . . . . . . . . . . . . 6 B. Transform Domain (TD) Sampling . . . . . . . . . . . . . 7 III CHARGE SAMPLING : : : : : : : : : : : : : : : : : : : : : : : 9 IV FRONT END ARCHITECTURE : : : : : : : : : : : : : : : : : 13 A. System Simulations in MATLAB... : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 25 14 Step by step topology operation : : : : : : : : : : : : : : : : : : : : : 26 15 Triangular approximation of the integration window for the over- lap topology : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 27 16 MATLAB comparison...

Kulkarni, Mandar Shashikant

2009-05-15

166

Dynamic analysis of impact induced phase transformation in Shape Memory Alloys using numerical techniques  

E-print Network

by the numerical solution of initial boundary value problems of a semi- infinite, one-dimensional SMA rod subjected to impact loading. Special focus was placed on the initiation and propagation of material phase transformation due to the presence of stress waves...

Jimenez-Victory, Juan Carlos

2012-06-07

167

Safe|A Semantic Technique for Transforming Programs in the Presence of Errors  

E-print Network

that produce errors. This is apparentlybecause being forced to preserve error behavior severely limits, and transformations to improve performance could change the behavior of error-producing programs. This approach the scope of programoptimization,even for correct programs. However, preserving error behavior is desirable

Aiken, Alex

168

Safe---A Semantic Technique for Transforming Programs in the Presence of Errors  

E-print Network

that produce errors. This is apparently because being forced to preserve error behavior severely limits as the implementor saw fit, and transformations to improve performance could change the behavior of error­producing the scope of program optimization, even for correct programs. However, preserving error behavior

Aiken, Alex

169

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

170

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

171

Phase transformations in methanol at high pressure measured by dielectric spectroscopy technique  

NASA Astrophysics Data System (ADS)

The dielectric response in methanol measured in wide pressure and temperature ranges (P < 6.0 GPa; 100 K < T < 360 K) reveals a series of anomalies which can be interpreted as a transformation between several solid phases of methanol including a hitherto unknown high-pressure low-temperature phase with the stability range P > 1.2 GPa and T < 270 K. In the intermediate P-T region P ? 3.4-3.7 GPa, T ? 260-280 K, a set of complicated structural transformations occurs involving four methanol crystalline structures. At higher pressures within the narrow range P ? 4.3-4.5 GPa methanol can be obtained in the form of fragile glass (Tg ? 200 K, mp ? 80 at P = 4.5 GPa) by relatively slow cooling.

Kondrin, M. V.; Pronin, A. A.; Lebed, Y. B.; Brazhkin, V. V.

2013-08-01

172

The forward and backward projection of acoustic fields from axisymmetric ultrasonic radiators using impulse response and Hankel transform techniques.  

PubMed

A generalized impulse response formulation to evaluate the harmonic pressure field of ultrasonic planar vibrators having axisymmetric nonuniform surface velocity distributions is presented. The harmonic pressure is expressed as a Fourier transform of a generalized impulse response which is a function of the spatially nonuniform velocity of the vibrator. A backward projection method is then developed to reconstruct the normal surface velocity of axisymmetric vibrators from harmonic field pressures using an angular spectrum or Hankel transform formulation. The numerical accuracy of the backward projection technique is evaluated using the impulse response formulation to evaluate the pressure fields for several velocity distributions on disk vibrators. Experiments were performed to reconstruct the velocity distributions over the surface of a uniformly driven piezoelectric ceramic disk and ceramic ring using farfield measurements of the complex pressure. The experimental results were in good agreement with theoretical results based on the electrode patterns of the transducers. PMID:6747093

Medeiros, A F; Stepanishen, P R

1984-06-01

173

A hybridized snapshot proper orthogonal decomposition-discrete wavelet transform technique for the analysis of flow structures and their time evolution  

Microsoft Academic Search

A novel hybrid technique has been proposed in order to reveal in a greater detail the turbulent flow structures and their time evolution, and to address the issues and limitations related to the application of snapshot proper orthogonal decomposition (POD) and wavelet transform technique. The proposed hybrid technique combines the inherent abilities of the snapshot proper orthogonal decomposition and the

Mandar V. Tabib; Mayur J. Sathe; Sagar S. Deshpande; Jyeshtharaj B. Joshi

2009-01-01

174

Enhancement of sound by soft reflections in exponentially chirped crystals  

NASA Astrophysics Data System (ADS)

The enhancement of sound inside a two dimensional exponentially chirped crystal during the soft reflections of waves is experimentally and theoretically explored in this work. The control of this enhancement is achieved by a gradual variation of the dispersion in the system by means of a chirp of the lattice constant. The sound enhancement is produced at some planes of the crystal in which the wave is softly reflected due to a progressive slowing down of the sound wave. We find that the character of the sound enhancement depends on the function of the variation of dispersion, i.e., on the function of the chirp. A simple coupled mode theory is proposed to find the analytical solutions of the sound wave enhancement in the exponentially chirped crystal. Harmonic and time domain numerical simulations are performed to interpret the concept of the soft reflections, and to check the analytically calculated field distributions both in good agreement with experiments. Specially we obtain stronger sound enhancement than in linearly chirped crystals. This sound enhancement could motivate applications in energy harvesting, e.g., to increase the efficiency of detectors and absorbers.

Cebrecos, A.; Picó, R.; Sánchez-Morcillo, V. J.; Staliunas, K.; Romero-García, V.; Garcia-Raffi, L. M.

2014-12-01

175

Comparative study of face recognition techniques that use joint transform correlation and principal component analysis  

NASA Astrophysics Data System (ADS)

Face recognition based on principal component analysis (PCA) that uses eigenfaces is popular in face recognition markets. We present a comparison between various optoelectronic face recognition techniques and a PCA-based technique for face recognition. Computer simulations are used to study the effectiveness of the PCA-based technique, especially for facial images with a high level of distortion. Results are then compared with various distortion-invariant optoelectronic face recognition algorithms such as synthetic discriminant functions (SDF), projection-slice SDF, optical-correlator-based neural networks, and pose-estimation-based correlation.

Alsamman, A.; Alam, Mohammad S.

2005-02-01

176

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

177

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

NASA Astrophysics Data System (ADS)

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

Ma, Shuiliang; Gao, Hongming; Wu, Lin

2008-03-01

178

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

PubMed

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

Ma, Shuiliang; Gao, Hongming; Wu, Lin

2008-03-20

179

Measurements of solar magnetic fields by Fourier transform techniques. I - Unsaturated lines  

NASA Technical Reports Server (NTRS)

If the basic profile shapes of the normal Zeeman triplet do not have zeros in their Fourier transform, the magnetic field splitting can be determined independent of the profile shape. When the ratio of the splitting of the components is greater than the intrinsic FWHM of the component profiles, the magnetic splitting can be determined with significantly greater accuracy than the measurement accuracy of the original profile. For Gaussian shaped components and a ratio of magnetic splitting to FWHM of 1.5, the noise reduction factor is 25.

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

1975-01-01

180

Chirped-cavity dispersion-compensation filter design.  

PubMed

A new basic structure of a dispersive-compensation filter, called a chirped-cavity dispersion-compensator (CCDC) filter, was designed to offer the advantages of small ripples in both reflectance and group-delay dispersion (GDD). This filter provides a high dispersion compensation, like the Gires-Tournois interferometer (GTI) filter, and a wide working bandwidth, like the chirped mirror (CM). The structure of the CCDC is a cavity-type Fabry-Perot filter with a spacer layer (2 mH or 2 mL) and a chirped high reflector. The CCDC filter can provide a negative GDD of -50 fs2 over a bandwidth of 56 THz with half the optical thickness of the CM or the GTI. PMID:16539259

Li, Ya-Ping; Chen, Sheng-Hui; Lee, Cheng-Chung

2006-03-01

181

Chirped-cavity dispersion-compensation filter design  

NASA Astrophysics Data System (ADS)

A new basic structure of a dispersive-compensation filter, called a chirped-cavity dispersion-compensator (CCDC) filter, was designed to offer the advantages of small ripples in both reflectance and group-delay dispersion (GDD). This filter provides a high dispersion compensation, like the Gires-Tournois interferometer (GTI) filter, and a wide working bandwidth, like the chirped mirror (CM). The structure of the CCDC is a cavity-type Fabry-Perot filter with a spacer layer (2 mH or 2 mL) and a chirped high reflector. The CCDC filter can provide a negative GDD of -50 fs2 over a bandwidth of 56 THz with half the optical thickness of the CM or the GTI.

Li, Ya-Ping; Chen, Sheng-Hui; Lee, Cheng-Chung

2006-03-01

182

Cognitive Implementation of Chirp Waveform in UWB System  

NASA Astrophysics Data System (ADS)

Cognitive Radios (CR) can recognize the communication environment and switch its communication scheme to more efficiently and flexibly utilize the radio spectrum. The performance of ultra wideband (UWB) degrades if interference is not suppressed properly. We propose here a series of adaptive chirp waveforms in UWB systems. By designing waveform shaping of both linear chirp and non-linear cases, we avoid the estimated spectrum of the on-going applications without the necessity of notch filters, and thus reduce the system complexity. We evaluate system performance of the proposed scheme by simulations and verify that the proposed scheme is a candidate for cognitive UWB systems.

Shen, Hanbing; Zhang, Weihua; Kwak, Kyung Sup

183

Narrowband pulse-enhanced upconversion of chirped broadband pulses  

NASA Astrophysics Data System (ADS)

We propose and demonstrate an efficient sum-frequency mixing scheme based on narrowband and chirped broadband pulses. It combines the advantages of wider spectral acceptance bandwidth and of alleviating the temporal walk-off, which are both beneficial to higher conversion efficiency. Chirped sum-frequency pulses at 455 nm with energy up to 360 µJ, corresponding to a conversion efficiency of ~ 40%, are obtained and the pulses can be compressed to ~ 110 fs. The sum-frequency mixing scheme may provide a promising route to the efficient generation of deep-ultraviolet femtosecond pulses.

Zhao, Kun; Yuan, Peng; Zhong, Haizhe; Zhang, Dongfang; Zhu, Heyuan; Chen, Liezun; Wen, Shuangchun; Qian, Liejia

2010-03-01

184

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

185

Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses.  

PubMed

The nuclear spins in nanostructured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resource while suppressing the noise. NMR techniques are challenging: the group III and V isotopes have large spins with widely different gyromagnetic ratios; in strained material there are large atom-dependent quadrupole shifts; and nanoscale NMR is hard to detect. We report NMR on 100,000 nuclear spins of a quantum dot using chirped radiofrequency pulses. Following polarization, we demonstrate a reversal of the nuclear spin. We can flip the nuclear spin back and forth a hundred times. We demonstrate that chirped NMR is a powerful way of determining the chemical composition, the initial nuclear spin temperatures and quadrupole frequency distributions for all the main isotopes. The key observation is a plateau in the NMR signal as a function of sweep rate: we achieve inversion at the first quantum transition for all isotopes simultaneously. These experiments represent a generic technique for manipulating nanoscale inhomogeneous nuclear spin ensembles and open the way to probe the coherence of such mesoscopic systems. PMID:25150719

Munsch, Mathieu; Wüst, Gunter; Kuhlmann, Andreas V; Xue, Fei; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D; Poggio, Martino; Warburton, Richard J

2014-09-01

186

Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses  

NASA Astrophysics Data System (ADS)

The nuclear spins in nanostructured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resource while suppressing the noise. NMR techniques are challenging: the group III and V isotopes have large spins with widely different gyromagnetic ratios; in strained material there are large atom-dependent quadrupole shifts; and nanoscale NMR is hard to detect. We report NMR on 100,000 nuclear spins of a quantum dot using chirped radiofrequency pulses. Following polarization, we demonstrate a reversal of the nuclear spin. We can flip the nuclear spin back and forth a hundred times. We demonstrate that chirped NMR is a powerful way of determining the chemical composition, the initial nuclear spin temperatures and quadrupole frequency distributions for all the main isotopes. The key observation is a plateau in the NMR signal as a function of sweep rate: we achieve inversion at the first quantum transition for all isotopes simultaneously. These experiments represent a generic technique for manipulating nanoscale inhomogeneous nuclear spin ensembles and open the way to probe the coherence of such mesoscopic systems.

Munsch, Mathieu; Wüst, Gunter; Kuhlmann, Andreas V.; Xue, Fei; Ludwig, Arne; Reuter, Dirk; Wieck, Andreas D.; Poggio, Martino; Warburton, Richard J.

2014-09-01

187

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

188

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

189

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

SciTech Connect

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

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

2014-06-15

190

Electron heating enhancement by frequency-chirped laser pulses  

SciTech Connect

Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2. Furthermore, it is noticed that for a chirped laser pulse with a{sub 0}?=?5, because of increasing the plasma transparency length, the laser pulse can penetrate up to about n{sub e}???6n{sub c}, where n{sub c} is plasma critical density. It shows 63% increase in the effective critical density compared to the relativistic induced transparency regime for an unchirped condition.

Yazdani, E.; Afarideh, H., E-mail: hafarideh@aut.ac.ir [Department of Energy Engineering and Physics, Amirkabir University of Technology, P.O. Box 15875-4413, Tehran (Iran, Islamic Republic of); Sadighi-Bonabi, R., E-mail: Sadighi@sharif.ir [Department of Physics, Sharif University of Technology, P.O. Box 11365-9567, Tehran (Iran, Islamic Republic of); Riazi, Z. [Physics and Accelerator School, Tehran (Iran, Islamic Republic of); Hora, H. [Department of Theoretical Physics, University of New South Wales, Sydney 2052 (Australia)

2014-09-14

191

Indoor Pseudo-ranging of Mobile Devices using Ultrasonic Chirps  

E-print Network

Introduction Location tracking on mobile devices like smart phones has already begun to revolutionize personal: building navigation (malls, factories, airports), augmented reality, location-aware pervasive computingIndoor Pseudo-ranging of Mobile Devices using Ultrasonic Chirps Patrick Lazik Anthony Rowe

Rowe, Anthony

192

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 M F; Grosche, Gesine

2014-06-01

193

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)

2011-02-01

194

Pulse compression on the Mark III FEL using energy chirping  

Microsoft Academic Search

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

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

1990-01-01

195

Indoor Pseudo-ranging of Mobile Devices using Ultrasonic Chirps  

E-print Network

Indoor Pseudo-ranging of Mobile Devices using Ultrasonic Chirps Patrick Lazik Anthony Rowe In this paper, we present an indoor ultrasonic location tracking system that can utilize off-the-shelf audio the human hearing frequency range where mobile devices are still sensitive. Typically transmitting data

Rowe, Anthony

196

Mechanism of inverted-chirp infrasonic radiation from sprites  

Microsoft Academic Search

Farges and Blanc (2010) reported inverted-chirp infrasonic signals with high frequencies arriving before low frequencies, possibly emitted by sprite discharges and observed on the ground at close range (<100 km) from the source. In the present work a parallel version of a 2-D FDTD model of infrasound propagation in a realistic atmosphere is applied to demonstrate that the observed morphology

Sebastien de Larquier; Victor P. Pasko

2010-01-01

197

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

E-print Network

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 $\\Lambda$-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 wavevectors. 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.

Gabor Demeter

2014-03-19

198

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

199

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

PubMed

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

Ortolan, Rodrigo Lício; Mori, Ricardo Naoki; Pereira, Roberto R Júnior; Cabral, Cristina M N; Pereira, José Carlos; Cliquet, Alberto Júnior

2003-03-01

200

A NEW TECHNIQUE FOR OBSERVING THE AMORPHOUS TO CRYSTALLINE TRANSFORMATION IN THIN SURFACE LAYERS ON SILICON WAFERS  

SciTech Connect

Thin amorphous ({alpha}) films of silicon created by ion-implantation have been studied in-situ while undergoing the amorphous to crystalline transformation in the electron microscope. The specimens were prepared in such a manner that the amorphous/crystalline interface was viewed edge-on and its advance during annealing was easily observed over distances of several microns. Growth rates and activation energies were measured. The active role that defects play during the regrowth process was also studied. An additional advantage of the technique was that in a single specimen different segments of the recrystallization front advanced along several different growth directions simultaneously, hence the effect of regrowth direction on the interface migration rate and defect formation was graphically displayed in a single specimen.

Drosd, B.; Washburn, J.

1980-02-01

201

Super-resolution technique for CW lidar using Fourier transform reordering and Richardson-Lucy deconvolution.  

PubMed

An interpolation method is described for range measurements of high precision altimetry with repeating intensity modulated continuous wave (IM-CW) lidar waveforms using binary phase shift keying (BPSK), where the range profile is determined by means of a cross-correlation between the digital form of the transmitted signal and the digitized return signal collected by the lidar receiver. This method uses reordering of the array elements in the frequency domain to convert a repeating synthetic pulse signal to single highly interpolated pulse. This is then enhanced further using Richardson-Lucy deconvolution to greatly enhance the resolution of the pulse. We show the sampling resolution and pulse width can be enhanced by about two orders of magnitude using the signal processing algorithms presented, thus breaking the fundamental resolution limit for BPSK modulation of a particular bandwidth and bit rate. We demonstrate the usefulness of this technique for determining cloud and tree canopy thicknesses far beyond this fundamental limit in a lidar not designed for this purpose. PMID:25503046

Campbell, Joel F; Lin, Bing; Nehrir, Amin R; Harrison, F Wallace; Obland, Michael D

2014-12-15

202

Reduction of group delay ripple of multi-channel chirped fiber gratings using adiabatic UV correction.  

PubMed

We demonstrate reduction of group delay ripple (GDR) from 24 ps to 9 ps peak to peak in a four channel 43 Gb/s dispersion compensating chirped fiber grating by adiabatic UV post processing. The eye opening penalty due to the grating GDR was improved from ~2dB to <1dB for all of the channels over a range of carrier frequencies of 15GHz. Our results demonstrate that at 43 Gb/s, the adiabatic UV correction technique is sufficient to substantially improve multi-channel fiber grating performance. We also discuss three limitations of the correction technique which cause GDR to vary from channel to channel: Noise in the sampling function, cladding mode loss, and varying channel reflectivity. While these limitations are visible in our results they do not reduce the effectiveness of the adiabatic correction for our gratings. PMID:19475109

Reyes, P; Sumetsky, M; Litchinitser, N; Westbrook, P

2004-06-14

203

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

204

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

205

Controlling the femtosecond laser-driven transformation of dicyclopentadiene into cyclopentadiene  

PubMed Central

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

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

2013-01-01

206

Transformations and availability of phosphorus in three contrasting soil types from native and farming systems: A study using fractionation and isotopic labeling techniques  

Microsoft Academic Search

Background, aim, and scope  Despite the contribution of many sequential P fractionation schemes to the study of P transformations in agricultural soils,\\u000a the nature of P in each fraction remains qualitative rather than mechanistic. This study used the sequential extraction and\\u000a isotopic dilution techniques to assess the recovery of a tracer (32P) in soil P fractions and to elucidate the transformation

D. T. Vu; C. Tang; R. D. Armstrong

2010-01-01

207

A laboratory technique for investigation of diffusion and transformation of volatile organic compounds in low permeability media  

NASA Astrophysics Data System (ADS)

A laboratory diffusion cell technique that permits spatial and temporal estimates of porewater concentrations over short intervals suitable for estimation of effective diffusion coefficients ( De) and degradation rate constants ( k) of volatile organic compounds (VOCs) in saturated low permeability media is presented. The diffusion cell is a sealed cylinder containing vapour reservoirs for sampling, including a vapour reservoir source and an array of vapour-filled "mini-boreholes", which are maintained water- and sediment-free by slightly negative porewater pressures. The vapour reservoirs were sampled by Solid Phase Micro-Extraction (SPME), resulting in minimal disturbance to the experimental system. Porewater concentrations are estimated from the measured vapour concentrations. Experiments were conducted using a non-reactive medium and five VOCs with a range in partitioning properties. Calibration experiments showed that equilibrium partition coefficients could be used for calculating concentrations in the vapour reservoir source from concentrations in the SPME coating after a 1-min microextraction and that the reservoir concentration was insignificantly affected by sampling. However, equilibrium was not reached during the one-min extraction of the boreholes; the microextraction reduced the borehole vapour concentrations, leading to diffusion of VOCs from porewater into the vapour-filled borehole. Thus, empirical partitioning coefficients were required for the determination of porewater VOC concentrations. The experimental data and numerical modelling indicate masses extracted by SPME extraction are relatively small, with minimal perturbation on processes studied in diffusion experiments. This technique shows promise for laboratory investigation of diffusion and transformation processes in low permeability media.

Gordon, Sue; Mackay, Doug; Górecki, Tadeusz; Cherry, John A.; Pawliszyn, Janusz

2002-08-01

208

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

209

Pulse compression on the Mark III FEL using energy chirping  

NASA Astrophysics Data System (ADS)

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

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

1990-10-01

210

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

211

Dense monoenergetic proton beams from chirped laser-plasma interaction  

E-print Network

Interaction of a frequency-chirped laser pulse with single protons and a hydrogen plasma cell is studied analytically and by means of particle-in-cell simulations, respectively. Feasibility of generating ultra-intense (10^7 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 10^21 W/cm^2.

Galow, Benjamin J; Liseykina, Tatyana V; Harman, Zoltan; Keitel, Christoph H

2011-01-01

212

Hyper dispersion pulse compressor for chirped pulse amplification systems  

DOEpatents

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

Barty, Christopher P. J. (Hayward, CA)

2011-11-29

213

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

214

A Novel Real-Time Chirp Measurement Method for Ultrashort Optical Pulses  

Microsoft Academic Search

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

Kazuo Mogi; Kazunori Naganuma; Hajime Yamada

1988-01-01

215

Research on Cascaded Chirp Fiber Bragg Grating in Quasi-linear Optical Transmission System  

NASA Astrophysics Data System (ADS)

A Cascaded chirp fiber Bragg grating has been theoretical analyzed by using coupled mode equations and transfer matrix method. As a dispersion compensator, a wide bandwidth, big dispersion value, and low delay ripple cascaded chirp fiber Bragg grating is designed for a 200 km 8 × 160 Gbit/s high speed quasi-linear optical transmission system. The system Q value of 7.15˜8.74 demonstrates the success of the design of the cascaded chirp fiber Bragg grating.

Cai, Ju; Bai, Qiujian; Su, Xin

2013-09-01

216

Shear wave speed and dispersion measurements using crawling wave chirps.  

PubMed

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

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

2014-10-01

217

Harmonic chirp imaging method for ultrasound contrast agent.  

PubMed

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

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

2005-02-01

218

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

219

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

220

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

221

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

NASA Technical Reports Server (NTRS)

A set of co-aligned high resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling quantitative description of sub visual coronal motions with low signal-to-noise ratios of the order of 0.1. The technique operates with a set of one-dimensional surfing signals extracted from position-timeplots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency - velocity space which exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square root dependence predicted for the slow mode magneto-acoustic wave which seems to be the dominating wave mode in the studied loop structures. This result extends recent observations by Kiddie et al. (2012) to a more general class of fan loop systems not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

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

2013-01-01

222

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

SciTech Connect

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

Zhu, Yimin; Uchida, Hiroyuki; Watanabe, Masahiro

1999-12-07

223

Chirped InGaAs quantum dot molecules for broadband applications  

PubMed Central

Lateral InGaAs quantum dot molecules (QDMs) formed by partial-cap and regrowth technique exhibit two ground-state (GS) peaks controllable via the thicknesses of InAs seed quantum dots (x), GaAs cap (y), and InAs regrowth (z). By adjusting x/y/z in a stacked QDM bilayer, the GS peaks from the two layers can be offset to straddle, stagger, or join up with each other, resulting in multi-GS or broadband spectra. A non-optimized QDM bilayer with a 170-meV full-width at half-maximum is demonstrated. The temperature dependencies of the emission peak energies and intensities from the chirped QDM bilayers are well explained by Varshni's equation and thermal activation of carriers out of constituent quantum dots. PMID:22480323

2012-01-01

224

A Novel Technique to Transform a Fractal LPF to BPF Using a Simple Combination of Defected Ground Structure (DGS) and a Narrow Gap Capacitive  

Microsoft Academic Search

In this paper we present a novel compact band pass microstrip filter employing metal-loaded slots etched in the ground plane (DGS) and a simple capacitive gap on the top. With the proposed technique, a simple transformation from LPF to a corresponding BPF was realized. We also presented, the equivalent circuit of the proposed BPF based on the equivalent circuit model

A. Boutejdar; A. Elsherbini; A. S. Omar

2007-01-01

225

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

226

Passive coherent beam combining of two femtosecond fiber chirped-pulse amplifiers  

E-print Network

Passive coherent beam combining of two femtosecond fiber chirped-pulse amplifiers Louis Daniault,1 femtosecond chirped- pulse amplifiers. The setup consists in the use of a well-balanced amplifying Sagnac amplifiers have great advantages to amplify ultrashort femtosecond pulses. Indeed, their geometry offers

Boyer, Edmond

227

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

SciTech Connect

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

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

1986-12-01

228

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

Microsoft Academic Search

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

S. Piazzolla; P. Spano; M. Tamburrini

1986-01-01

229

Analytical solutions for a two-level system driven by a class of chirped pulses  

SciTech Connect

We present analytical solutions for the problem of a two-level atom driven by a class of chirped pulses. The solutions are given in terms of Heun functions. By use of the appropriate chirping parameters, an enhancement of four orders of magnitude in the population transfer is obtained.

Jha, Pankaj K. [Institute for Quantum Science and Engineering and Department of Physics, Texas A and M University, College Station, Texas 77843 (United States); Rostovtsev, Yuri V. [Institute for Quantum Science and Engineering and Department of Physics, Texas A and M University, College Station, Texas 77843 (United States); Department of Physics, University of North Texas, 1155 Union Circle 311427, Denton, Texas 76203 (United States)

2010-07-15

230

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

231

Low Complexity Chirp Pulsed Ultra-Wideband System with Near-Optimum Multipath Performance  

Microsoft Academic Search

This paper describes the Impulse Radio Ultra- Wideband (IR-UWB) system using linear chirp UWB pulses as symbols. The novel method of coherent or differentially coherent detection of chirp pulses in multipath channels is introduced. The method divides detection in the receiver between its analog and digital part; in the analog part of the receiver, received signal is compressed in frequency

Igor Dotlic; Ryuji Kohno

2011-01-01

232

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

233

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

234

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

235

Observation of a giant-chirp dissipative soliton and near chirp-free pulse in a slight-normal-dispersion fiber laser  

NASA Astrophysics Data System (ADS)

We reported a switchable giant-chirp (GC) dissipative soliton and near-chirp-free (NCF) pulse in a slight-normal-dispersion fiber laser by tuning the pump power. The GC dissipative soliton exhibits a quasi-rectangular spectrum with bandwidth of 9?nm and duration of 8?ps. The time bandwidth product (TBP) is calculated as 8.8, indicating that the dissipative soliton is highly chirped. The NCF pulse has a bandwidth of 2.5?nm and a duration of 1.8?ps, which gives a TBP of 0.55, suggesting that the pulse almost is chirp free. Our numerical simulations confirm the experimental observations, and demonstrate that the operation state of dissipative system is very sensitive to the pump strength.

Mao, D.; Jiang, B. Q.; Zhang, W. D.; Zhao, J. L.

2014-10-01

236

Hadamard transform image coding  

Microsoft Academic Search

The introduction of the fast Fourier transform algorithm has led to the development of the Fourier transform image coding technique whereby the two-dimensional Fourier transform of an image is transmitted over a channel rather than the image itself. This devlopement has further led to a related image coding technique in which an image is transformed by a Hadamard matrix operator.

W. K. Pratt; J. Kane; H. C. Andrews

1969-01-01

237

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

SciTech Connect

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

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

2014-08-15

238

Chirp of the single attosecond pulse generated by a polarization gating  

SciTech Connect

The chirp of the xuv supercontinuum generated by a polarization gating is investigated by comparing three-dimensional nonadiabatic numerical simulations with classical calculations. The origin of the chirp is the dependence of the energy gain by an electron on the return time. The chirp is positive and its value is almost the same as that when a linearly polarized laser is used. Although the 250-eV-wide supercontinuum corresponds to a single attosecond pulse, the shortest duration of the pulse is limited by the chirp. By compensating the positive chirp with the negative group velocity dispersion of a Sn filter, it is predicted that a single 58-as pulse can be generated.

Chang Zenghu [Department of Physics, Kansas State University, Manhattan, Kansas 66506 (United States)

2005-02-01

239

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

SciTech Connect

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

Xu Junjie [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)

2011-03-15

240

Hough Transform from the Radon Transform  

Microsoft Academic Search

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

Stanley R. Deans

1981-01-01

241

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

SciTech Connect

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

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

2012-07-08

242

Nonlinear-optical vacuum ultraviolet generation at maximum atomic coherence controlled by a laser-induced Stark chirp of two-photon resonance  

NASA Astrophysics Data System (ADS)

A novel scheme is analyzed for efficient generation of vacuum ultraviolet radiation through four-wave mixing processes assisted by the Stark chirp of two photon resonance. In this three-laser technique, a delayed-pulse of strong off-resonant infrared radiation sweeps the laser-induced Stark shift of a two-photon transition and facilitates maximum two-photon coherence induced by the second ultraviolet laser. A judiciously delayed third pulse beats with this coherence and generates short-wavelength radiation. A numerical simulation of transient processes, which ensure maximum coherence, including those leading to Stark-chirped rapid adiabatic passage, is presented. Potential high power and energy conversion efficiency of the weak long-wavelength radiation to the VUV range is shown for a difference-frequency scheme based on parametric amplification of this signal and strong four-wave coupling at maximum atomic coherence.

Myslivets, S. A.; Popov, A. K.; Halfmann, T.; Marangos, J. P.; George, Thomas F.

2002-08-01

243

Chirped CPMG for well-logging NMR applications  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

244

Phase-Locked Control of Tiled-Grating Assemblies for Chirped-Pulse-Amplified Lasers Using a Mach-Zehnder Interferometer  

SciTech Connect

Multikilojoule petawatt lasers using chirped-pulse amplification are being constructed worldwide. Several systems have adopted a tiled-grating approach to meet the size requirements for the compression gratings. Grating tiles need to be precisely phased to ensure a transform-limited focal spot when focusing high-energy laser pulses in the target plane. A computer-control test system that uses a Mach-Zehnder interferometer capable of monitoring and correcting drift in the tiled-grating assemblies within the compressor is described.

Bunkenburg, J.; Kessler, T.J.; Skulski, W.; Huang, H.

2006-04-27

245

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

246

Application of Multivariate Calibration Techniques to Quantitative Analysis of Bandpass-Filtered Fourier Transform Infrared Interferogram Data  

Microsoft Academic Search

Multivariate calibration models are developed that allow quantita- tive analysis of short segments of Fourier transform infrared (FT- IR) interferogram data. Before the interferogram segments are sub- mitted to partial least-squares (PLS) regression analysis,a bandpass digital ® lter is applied to isolate a narrow range of frequencies that correspond to an absorption band of the target analyte. This adds frequency

Mutua J. Mattu; Gary W. Small; Mark A. Arnold

1997-01-01

247

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

SciTech Connect

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

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

2014-05-15

248

A 300 mV sub-threshold region 2.4 GHz voltage-controlled oscillator and frequency divider with transformer technique for ultralow power RF applications  

NASA Astrophysics Data System (ADS)

A new ultralow voltage 2.4 GHz voltage-controlled oscillator (VCO) and a divide-by-2 frequency divider circuits operating in a CMOS sub-threshold region using a transformer technique have been developed. In the sub-threshold region, the CMOS transistor high frequency performances are decreased to the point where oscillation and frequency division are challenging to achieve. The new proposed VCO uses the transformer feedback complementary VCO technique to improves VCO negative feedback gain. The circuits have been fabricated in a 65 nm standard CMOS process. The oscillation frequency is designed at 2.4 GHz under a 300 mV supply voltage. The total power consumption is 202 µW with noise performance of -96 dBc/Hz at 1 MHz offset. The new proposed frequency divider circuit consists of two stages master-slave D-type flip-flop (DFF). The DFF differential input is coupled to a transformer circuit instead of transistors to reduce the number of stacks. The minimum operating supply voltage is 300 mV with power consumption of 34 µW with a free-run frequency of 1.085 GHz.

Miyahara, Yasunori; Ishikawa, Keisuke; Kuroda, Tadahiro

2014-01-01

249

DNA Transformation  

NSDL National Science Digital Library

Stanley Cohen and Herbert Boyer's historic experiment used techniques to cut and paste DNA to create the first custom-made organism containing recombined or 'recombinant' DNA. Cohen and Boyer inserted the recombinant DNA molecule they created into E. coli bacteria by means of a plasmid, thereby inducing the uptake and expression of a foreign DNA sequence known as 'transformation.' This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents DNA transformation through a series of illustrations of the processes involved.

2012-04-06

250

Experimental demonstration of fiber optical parametric chirped-pulse amplification  

NASA Astrophysics Data System (ADS)

A fiber optical parametric chirped-pulse amplifier (FOPCPA) is experimentally demonstrated. A 1.76 ps signal at 1542 nm with a peak power of 20 mW is broadened to 40 ps, and then amplified by a 100-ps pulsed pump at 1560 nm. The corresponding idler at 1578 nm is generated as the FOPCPA output. The same medium used to stretch the signal is deployed to compress the idler to 3.8 ps, and another spool of fiber is deployed to further compress the idler to 1.87 ps. The peak power of the compressed idler is 2 W, which corresponds to a gain of 20 dB.

Zhou, Yue; Cheung, Kim K. Y.; Chui, P. C.; Wong, Kenneth K. Y.

2010-02-01

251

Femtosecond Chirp-Free Transient Absorption Method And Apparatus  

DOEpatents

A method and apparatus for femtosecond transient absorption comprising phase-sensitive detection, spectral scanning and simultaneous controlling of a translation stage to obtain TA spectra information having at least a sensitivity two orders of magnitude higher than that for single-shot methods, with direct, simultaneous compensation for chirp as the data is acquired. The present invention includes a amplified delay translation stage which generates a splittable frequency-doubled laser signal at a predetermined frequency f, a controllable means for synchronously modulating one of the laser signals at a repetition rate of f/2, applying the laser signals to a material to be sample, and acquiring data from the excited sample while simultaneously controlling the controllable means for synchronously modulating.

McBranch, Duncan W. (Santa Fe, NM); Klimov, Victor I. (White Rock, NM)

2001-02-20

252

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

NASA Astrophysics Data System (ADS)

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 simulations, a 10 Gb/s NRZ transmission system is compensated by this grating. The result demonstrates a significant improvement can be achieved in the eye pattern of the received signal.

Liu, Yumin; Yu, Zhongyuan; Zhang, Xiaoguang

2005-01-01

253

Photoinjector-driven chirped-pulsed free electron maser  

NASA Astrophysics Data System (ADS)

An ultra-short pulse, millimeter-wave free electron maser experiment is currently underway at UC Davis and Lawrence Livermore National Laboratory. A 8.5 kG, 30 mm period helical wiggler is used to transversally accelerate a train of one hundred 5 MeV, 0.25 nC, 1 ps duration micro bunches synchronously energized by a 20 MW, X-band photocathode RF linac. The photocathode is irradiated by a burst-mode, UV laser system which produces up to 100 pulses at 207 nm, with an energy of 10 mJ/pulse, and a pulse duration of 200 fs, at a repetition rate of 2.142 GHz. This system includes a 400 fs jitter synchronously modelocked AlGaAs semiconductor laser oscillator which is amplified by an eight-pass Ti:Al2O3 chirped pulse laser amplifier. The output of this amplifier is subsequently frequency quadrupled into the UV. Because the electron micro bunches are shorter than the radiation wavelength, the system coherently synchrotron radiates and behaves essentially as a prebunched FEM. In addition, by operating in a waveguide structure at grazing, where the bunch axial velocity in the wiggler matches the group velocity of the electromagnetic waves, one obtains output radiation pulses which are extremely short, and have greatly enhanced peak power. The device operates in the TE(sub 12) mode of a cylindrical waveguide, and will produce up to 2 MW of coherent synchrotron radiation power at 140 GHz, in a 15 ps FWHM pulse. The -3 dB instantaneous interaction bandwidth extends from 125 GHz to 225 GHz. The output pulse is chirped over the full interaction bandwidth. One of the major potential applications of such a device is an ultra-wideband millimeter-wave radar.

Lesage, G. P.; Hartemann, F. V.; Feng, H. X. C.; Fochs, S. N.; Heritage, J. P.; Luhmann, N. C., Jr.; Perry, M. D.; Westenskow, G. A.

1995-03-01

254

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

PubMed Central

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young’s modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200, and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size. PMID:17306697

Erpelding, Todd N.; Hollman, Kyle W.; O’Donnell, Matthew

2007-01-01

255

Multi-stage optimization of ultrabroadband high-energy optical parametric chirped pulse amplification  

E-print Network

We present a procedure for simultaneous optimization of efficiency-bandwidth product and superfluorescence noise suppression in ultrabroadband high-energy optical parametric chirped pulse amplification. Gain dependence of ...

Manzoni, Cristian

256

Effect of frequency chirp on supercontinuum generation in silicon waveguides with two zero-dispersion wavelengths  

NASA Astrophysics Data System (ADS)

The influence of initial chirp on supercontinuum generation in SOI rib waveguide with two zero-dispersion wavelengths was studied numerically, based on the generalized nonlinear Schrödinger equation (GNSE). The full-width at half-maximum (FWHM) and the peak power of the pre-chirped hyperbolic secant in the simulation are 50 fs and 50 W, respectively. The simulation results indicate that a positive initial chirp makes the energy transfer to the normal dispersion zone by affecting self-phase modulation (SPM) and four-wave mixing (FWM) processes, and therefore enhances the supercontinuum bandwidth as well as improves the spectral flatness. In particular, at the optimal initial chirp parameter of C=3, the bandwidth at -10 dB level increases to about 1620 nm (from 1140 to 2760 nm), exceeding an octave-spanning.

Cao, Yanmei; Zhang, Libin; Fei, Yonghao; Lei, Xun; Chen, Shaowu

2015-01-01

257

Variable-chirped microwave waveform generator based on reconfigurable microwave photonic filter  

NASA Astrophysics Data System (ADS)

An optical approach to generating chirped microwave signal using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response is proposed and demonstrated. In this scheme, a narrow band Gaussian pulse is used as the original signal. In order to eliminate the need for a wideband original microwave chirped-free signal, a mixer and a radio frequency signal are used to up-convert the spectrum of the original signal and the dispersion curve is tuned to minimize the attenuation caused by the fiber dispersion. Then the required frequency response can be reconstructed by a nonuniformly spaced PMDLF. Since the majority of the power of the original signal can bypass the filter, the power of the generated chirped microwave signal will be increased. A reconstruction example of a desired frequency response with a central frequency of 10 GHz is provided, and the generation of the corresponding chirped microwave signal is demonstrated by numerical simulations.

Chen, Dalei; Wang, Rong; Pu, Tao; Fang, Tao; Xiang, Peng; Zheng, Jiling; Wei, Zhihu; Xiong, Jintian

2014-09-01

258

A Multiterawatt Laser Using a High-Contrast, Optical Parametric Chirped-Pulse Presamplifier  

SciTech Connect

A laser has been built that uses optical parametric chirped-pulse preamplification and a glass booster amplifier. We review the performance of the 5-Hz, multijoule OPCPA pump laser, the 370-mJ OPCPA, and the overall laser.

Bagnoud, V.; Puth, J.; Begishev, I.; Guardalben, M.; Zuegel, J.D.; Forget, N.; LeBlanc, C.

2005-09-30

259

Spectral transmission characteristics of weakly tilted and tilted chirped fiber gratings: comparative studies  

NASA Astrophysics Data System (ADS)

In this paper the comparative study of spectral transmission characteristics of tilted Bragg gratings made using uniform phase mask and chirped phase mask are presented. Results are focused on low tilt angles with special interest on cladding modes behavior. The spectral characteristic shape for simultaneously tilted and chirped Bragg gratings point out its potential applications as amplitude discriminator in fiber sensing applications and gain flattening element for EDFA.

Osuch, Tomasz; Jurek, Tomasz; Jedrzejewski, Kazimierz

2013-10-01

260

Holocene sedimentation in the Skagerrak interpreted from chirp sonar and core data  

Microsoft Academic Search

High-resolution chirp sonar profiling in the northeastern Skagerrak shows acoustically stratified sediments draping a rough-surfaced substratum. A 32 metre long sediment core retrieved from the survey area encompasses the entire Holocene and latest Pleistocene. The uppermost seismo-acoustic units in the chirp profiles represent Holocene marine sediments. The lowermost unit is interpreted as ice-proximal glacial-marine sediments rapidly deposited during the last

Richard Gyllencreutz; Martin Jakobsson; Jan Backman

2005-01-01

261

Practical design of optical diagnostics for chirped-pulse free-electron lasers  

Microsoft Academic Search

In recent years there have been several proposals to operate rf-linac-driven FELs with chirped electron and optical micropulses for use in fast time-resolved experiments. We have been actively pursuing this application on the Mark-III infrared FEL at Duke University, and have designed and procured an apparatus to achieve broad-band compression of chirped optical pulses between roughly 2.5 mum and 4.1

Eric B. Szarmes; John M. J. Madey

1992-01-01

262

Recovering strain readings from chirping fiber Bragg gratings in composite overwrapped pressure vessels  

NASA Astrophysics Data System (ADS)

This study reports on signal recovery of optical fiber Bragg gratings embedded in a carbon fiber composite overwrapped pressure vessel's (COPV) structure which have become chirped due to microcracks. COPVs are commonly used for the storage of high pressure liquids and gases. They utilize a thin metal liner to seal in contents, with a composite overwrap to strengthen the vessel with minimal additional mass. A COPV was instrumented with an array of surface mounted and embedded fiber Bragg gratings (FBGs) for structural health monitoring (SHM) via strain sensing of the material. FBGs have been studied as strain sensors for the last couple decades. Many of the embedded FBGs reflected a multi-peak, chirped response which was not able to be interpreted well by the current monitoring algorithm. Literature and this study found that the chirping correlated with microcracks. As loading increases, so does the number of chirped FBGs and microcracks. This study uses optical frequency domain reflectometry (OFDR) to demultiplex the array of FBGs, and then sub- divide individual FBGs. When a FBG is sub-divided using OFDR, the gratings' strain along its length is recovered. The sub-divided chirped FBGs have strain gradients along their length from microcracks. Applying this to all chirped gratings, nearly the entirety of the embedded sensors' readings can be recovered into a series of single peak responses, which show very large local strains throughout the structure. This study reports on this success in recovering embedded FBGs signal, and the strain gradient from microcracks.

Strutner, Scott M.; Pena, Frank; Piazza, Anthony; Parker, Allen R.; Richards, W. Lance; Carman, Gregory P.

2014-04-01

263

Group velocity dispersion and relativistic effects on the wakefield induced by chirped laser pulse in parabolic plasma channel  

SciTech Connect

The excitation of wake field plasma waves by a short laser pulse propagating through a parabolic plasma channel is studied. The laser pulse is assumed to be initially chirped. In this regard, the effects of initial and induced chirp on the plasma wake field as well as the laser pulse parameters are investigated. The group velocity dispersion and nonlinear relativistic effects were taken into account to evaluate the excited wake field in two dimension using source dependent expansion method. Positive, negative, and un-chirped laser pulses were employed in numerical code to evaluate the effectiveness of the initial chirp on 2-D wake field excitation. Numerical results showed that for laser irradiances exceeding 10{sup 18}W/cm{sup 2}, an intense laser pulse with initial positive chirp generates larger wake field compared to negatively and un-chirped pulses.

Sohbatzadeh, F. [Department of Atomic and Molecular Physics, Science Faculty, University of Mazandaran, Babolsar (Iran, Islamic Republic of); Akou, H. [Department of Physics, Faculty of Basic Science, Babol University of Technology, Babol 47148-71167 (Iran, Islamic Republic of)

2013-04-15

264

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems  

NASA Astrophysics Data System (ADS)

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10-3, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.

Mangone, Fall; He, Jing; Tang, Jin; Xiao, Jiangnan; Chen, Ming; Li, Fan; Chen, Lin

2014-08-01

265

Modelling of a high resolution digital radiographic system and development of a filtering technique based on wavelet transforms  

Microsoft Academic Search

The first part of this paper describes a geometrical model of an iron cast object with a number of simple defects included in the volume. This model, together with a model of a specific digital X-ray system and procedure, is used to generate a simulated radiograph of the volume. This is then employed in the development of a filtering technique

Håkan Wirdelius; Lars Hammar

2004-01-01

266

Fourier transform-infrared spectroscopy and Gas chromatography-mass spectroscopy: reliable techniques for analysis of Parthenium mediated vermicompost.  

PubMed

Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography-mass spectroscopy have been carried out to investigate the chemical composition of Parthenium mediated vermicompost. Four different concentrations of Parthenium and cow dung mixtures were vermicomposted using the earthworms (Eudrilus eugeniae). FT-IR spectra reveal the absence of Parthenin toxin (sesquiterpene lactone) and phenols in vermicompost which was obtained from high concentration of cow dung mixed treatments. GC-MS analysis shows no phenolic compounds and predominant level of intermediate metabolites such as 4,8,12,16-Tetramethylheptadecan-4-olide (7.61%), 2-Pentadecanone, 6,10,14-trimethyl- (5.29%) and Methyl 16-methyl-heptadecanoate (4.69%) during the vermicomposting process. Spectral results indicated that Parthenin toxin and phenols can be eradicated via vermicomposting if mixed with appropriate quantity of cow dung. PMID:23998948

Rajiv, P; Rajeshwari, Sivaraj; Venckatesh, Rajendran

2013-12-01

267

High precision elimination of angular chirp in CPA laser systems with large stretching factors or high bandwidth  

NASA Astrophysics Data System (ADS)

We present a novel and highly sensitive method to determine the residual angular dispersion of high-power laser pulses after stretching, amplification, and re-compression of the pulses in a chirped-pulse amplification laser system. This method is based on the intentional deflection of a part of the the spectrum within the compressor and aligning the centers of gravity of the two resulting and separated foci with largest possible spectral separation in the far field. Using this technique, we were able to reduce the residual angular dispersion on pulses to less than 0.05 ?rad/nm in the vertical plane and less than 0.03 ?rad/nm in the horizontal plane, respectively. With this method, it is possible to minimize the deviation of the actual peak intensity for the focused laser pulses to less than 2 % of its theoretical limit.

Bödefeld, R.; Hornung, M.; Hein, J.; Kaluza, M. C.

2014-06-01

268

Blood Vessels Segmentation in Retina: Preliminary Assessment of the Mathematical Morphology and of the Wavelet Transform Techniques  

Microsoft Academic Search

http:\\/\\/www.ime.usp.br\\/~cesar\\/ Abstract. This work reports the development of a system for automatic analysis of retinal angiographic images. Particularly, we focus on the segmentation o f the blood vessels in these images. We started by implementing a previously k nown technique based on mathematical morphology. Due to some short comings of this method to ou r data, we have developed a

Jorge J. G. Leandro; Roberto Marcondes Cesar Junior; Herbert F. Jelinek

2001-01-01

269

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

PubMed

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

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

2014-11-01

270

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

SciTech Connect

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

Marcus, G.; Rosenzweig, J. B. [Particle Beam Physics Laboratory, Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095 (United States); Artioli, M.; Ciocci, F.; Del Franco, M.; Giannessi, L.; Petralia, A.; Quattromini, M. [ENEA C.R. Frascati, Via E. Fermi, 45 00044 Frascati, RM (Italy); Bacci, A.; Bellaveglia, M.; Chiadroni, E.; Di Pirro, G.; Ferrario, M.; Filippetto, D.; Gatti, G.; Rossi, A. R. [INFN-LNF, Via E. Fermi, 40 00044 Frascati, RM (Italy); Cianchi, A. [INFN-Roma Tor Vergata and University of Rome Tor Vergata, Via della Ricerca Scientifica, 1-00133 Rome (Italy); Labat, M. [ENEA C.R. Frascati, Via E. Fermi, 45 00044 Frascati, RM (Italy); SOLEIL, L'Orme des Merisiers Saint-Aubin, BP 48 91192 GIF-sur-Yvette Cedex (France); Mostacci, A. [Universita degli Studi di Roma La Sapienza, P.le Aldo Moro 5, 00185 Roma (Italy); Petrillo, V. [Universita degli Studi di Milano and INFN-MI, Via Celoria, 16 20133 Milano (Italy); and others

2012-09-24

271

Large-scale symmetry-adapted perturbation theory computations via density fitting and Laplace transformation techniques: Investigating the fundamental forces of DNA-intercalator interactions  

NASA Astrophysics Data System (ADS)

Symmetry-adapted perturbation theory (SAPT) provides a means of probing the fundamental nature of intermolecular interactions. Low-orders of SAPT (here, SAPT0) are especially attractive since they provide qualitative (sometimes quantitative) results while remaining tractable for large systems. The application of density fitting and Laplace transformation techniques to SAPT0 can significantly reduce the expense associated with these computations and make even larger systems accessible. We present new factorizations of the SAPT0 equations with density-fitted two-electron integrals and the first application of Laplace transformations of energy denominators to SAPT. The improved scalability of the DF-SAPT0 implementation allows it to be applied to systems with more than 200 atoms and 2800 basis functions. The Laplace-transformed energy denominators are compared to analogous partial Cholesky decompositions of the energy denominator tensor. Application of our new DF-SAPT0 program to the intercalation of DNA by proflavine has allowed us to determine the nature of the proflavine-DNA interaction. Overall, the proflavine-DNA interaction contains important contributions from both electrostatics and dispersion. The energetics of the intercalator interaction are are dominated by the stacking interactions (two-thirds of the total), but contain important contributions from the intercalator-backbone interactions. It is hypothesized that the geometry of the complex will be determined by the interactions of the intercalator with the backbone, because by shifting toward one side of the backbone, the intercalator can form two long hydrogen-bonding type interactions. The long-range interactions between the intercalator and the next-nearest base pairs appear to be negligible, justifying the use of truncated DNA models in computational studies of intercalation interaction energies.

Hohenstein, Edward G.; Parrish, Robert M.; Sherrill, C. David; Turney, Justin M.; Schaefer, Henry F.

2011-11-01

272

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

273

A chirp spread spectrum DPSK modulator and demodulator for a time shift multiple access communication system by using SAW devices  

Microsoft Academic Search

We have developed a modulator and a demodulator for DPSK modulated chirp signals using a SAW dispersive delay line and a SAW matched filter. The SAW chirp modulator spreads the 100 MHz spectrum between every 1 bit data interval of 1.5 ?sec and provides DPSK modulation, depending upon data. The SAW demodulator demodulates data using exclusive output pulses from two

Yoshihiko Takeuchi; K. Yamanouchi

1998-01-01

274

Extended chirp scaling algorithm for air- and spaceborne SAR data processing in stripmap and ScanSAR imaging modes  

Microsoft Academic Search

Presents a generalized formulation of the extended chirp scaling (ECS) approach for high precision processing of air- and spaceborne SAR data. Based on the original chirp scaling function, the ECS algorithm incorporates a new azimuth scaling function and a subaperture approach, which allow an effective phase-preserving processing of ScanSAR data without interpolation for azimuth geometric correction. The azimuth scaling can

A. Moreira; J. Mittermayer; R. Scheiber

1996-01-01

275

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

EPA Science Inventory

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

276

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

E-print Network

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...

Carrera, Juan J.; Chu, Shih-I

2007-03-16

277

First results of a deep tow CHIRP sonar seafloor imaging system  

USGS Publications Warehouse

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

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

1993-01-01

278

Control of Landau-Zener transition in NaI predissociation with chirped femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

We explore the control of the Landau-Zener (LZ) transition in NaI predissociation with low-intensity linearly and quadratically chirped femtosecond far-infrared laser pulses by solving the coupled time-dependent Schrödinger equations. We find that the LZ transition between the excited state and the ground state can be enhanced or be suppressed using a well-delayed control pulse with a proper linear or quadratic chirp. With instantaneously controlling the energy gap, the resonant population inversion induced by Rabi oscillation can facilitate or prohibit the molecular population transfer in the avoided-crossing region. This work provides a deep understanding of coherent control of LZ transition in molecular reaction with chirped femtosecond laser pulses.

Liu, Yuanxing; Liu, Yunquan; Gong, Qihuang

2013-03-01

279

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

SciTech Connect

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

Kopyciuk, T.; Parzynski, R. [Faculty of Physics, A. Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland)

2007-05-15

280

Transformational Learners: Transformational Teachers  

ERIC Educational Resources Information Center

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

Jones, Marguerite

2009-01-01

281

The Transformations of Transformations.  

ERIC Educational Resources Information Center

Harris's original idea of transformations has been changed several times in Chomsky's work. This article explicates these transformations, arguing that though their motivations are highly understandable, these transformations are not necessary for understanding the workings of natural languages. (Author/VWL)

Lin, Francis Y.

2000-01-01

282

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

SciTech Connect

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

Feng, Liqiang [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Chu, Tianshu [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023 (China); Institute for Computational Sciences and Engineering, Laboratory of New Fiber Materials and Modern Textile, the Growing Base for State Key Laboratory, Qingdao University, Qingdao, 266071 (China)

2011-11-15

283

Evaluation of chirp reversal power modulation sequence for contrast agent imaging  

NASA Astrophysics Data System (ADS)

Over the last decade, significant research effort has been focused on the use of chirp for contrast agent imaging because chirps are known to significantly increase imaging contrast-to-noise ratio (CNR). New imaging schemes, such as chirp reversal (CR), have been developed to improve contrast detection by increasing non-linear microbubble responses. In this study we evaluated the contrast enhancement efficiency of various chirped imaging sequences in combination with well-established imaging schemes such as power modulation (PM) and pulse inversion (PI). The imaging schemes tested were implemented on a fully programmable open scanner and evaluated by ultrasonically scanning (excitation frequency of 2.5?MHz amplitude of 350?kPa) a tissue-mimicking flow phantom comprising a 4?mm diameter tube through which aqueous dispersions (dilution fraction of 1/2000) of the commercial ultrasound contrast agent, SonoVue® were continuously circulated. The recovery of non-linear microbubble responses after chirp compression requires the development and the optimization of a specific filter. A compression filter was therefore designed and used to compress and extract several non-linear components from the received microbubble responses. The results showed that using chirps increased the image CNR by approximately 10?dB, as compared to conventional Gaussian apodized sine burst excitation but degraded the axial resolution by a factor of 1.4, at -3?dB. We demonstrated that the highest CNR and contrast-to-noise ratio (CTR) were achievable when CR was combined with PM as compared to other imaging schemes such as PI.

Novell, A.; Sennoga, CA; Escoffre, JM; Chaline, J.; Bouakaz, A.

2014-09-01

284

Evaluation of chirp reversal power modulation sequence for contrast agent imaging.  

PubMed

Over the last decade, significant research effort has been focused on the use of chirp for contrast agent imaging because chirps are known to significantly increase imaging contrast-to-noise ratio (CNR). New imaging schemes, such as chirp reversal (CR), have been developed to improve contrast detection by increasing non-linear microbubble responses. In this study we evaluated the contrast enhancement efficiency of various chirped imaging sequences in combination with well-established imaging schemes such as power modulation (PM) and pulse inversion (PI). The imaging schemes tested were implemented on a fully programmable open scanner and evaluated by ultrasonically scanning (excitation frequency of 2.5?MHz; amplitude of 350?kPa) a tissue-mimicking flow phantom comprising a 4?mm diameter tube through which aqueous dispersions (dilution fraction of 1/2000) of the commercial ultrasound contrast agent, SonoVue(®) were continuously circulated. The recovery of non-linear microbubble responses after chirp compression requires the development and the optimization of a specific filter. A compression filter was therefore designed and used to compress and extract several non-linear components from the received microbubble responses. The results showed that using chirps increased the image CNR by approximately 10?dB, as compared to conventional Gaussian apodized sine burst excitation but degraded the axial resolution by a factor of 1.4, at -3?dB. We demonstrated that the highest CNR and contrast-to-noise ratio (CTR) were achievable when CR was combined with PM as compared to other imaging schemes such as PI. PMID:25122547

Novell, A; Sennoga, C A; Escoffre, J M; Chaline, J; Bouakaz, A

2014-09-01

285

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

286

Noise filtering in parametric amplification by dressing the seed beam with spatial chirp.  

PubMed

We report a method for filtering out the noises produced in optical parametric chirped-pulse amplifiers by dressing the seed beam with spatial chirp. After dechirping the amplified signal with a compressor, the noises experience a spatiotemporal coupling, making themselves highly distinguishable from the compressed signal in space, and hence supporting noise filtering effectively and expediently in the spatial domain, which would otherwise not be possible. Numerical simulations performed for the proposed method show the capabilities of an order of magnitude reduction in the noise energy and several orders of magnitude enhancement in the temporal contrast. PMID:24979013

Wang, Jing; Ma, Jingui; Wang, Yongzhi; Yuan, Peng; Xie, Guoqiang; Qian, Liejia

2014-04-15

287

Chirped pulse formation dynamics in ultra-long mode-locked fiber lasers.  

PubMed

By modeling giant chirped pulse formation in ultra-long, normally dispersive, mode-locked fiber lasers, we verify convergence to a steady-state consisting of highly chirped and coherent, nanosecond-scale pulses, which is in good agreement with recent experimental results. Numerical investigation of the transient dynamics reveals the existence of dark soliton-like structures within the envelope of the initial noisy pulse structure. Quasi-stationary dark solitons can persist throughout a large part of the evolution from noise to a stable dissipative soliton solution of the mode-locked laser cavity. PMID:24690797

Kelleher, E J R; Travers, J C

2014-03-15

288

Modelling chirp as a function of reflectivity in electroabsorption modulated lasers (EML)  

NASA Astrophysics Data System (ADS)

We present a theoretical analysis of the chirp caused by the reflection of light from the Electro-Absorption Modulator (EAM) facet back into the laser. The work is modelled on our Essex Distributed Time Domain Model (eDTDM) (S. P. Higgins and A. J. Vickers, Proc SPIE Phys. and Simulations of Opto-Electron. Devices X11, 5349, 435 (2004) [1]; A. J. Vickers and S. P. Higgins, A new model for complex dynamic laser modelling, IEEE J Quantum Electron., 2005, awaiting publication [2]). A novel method of determining the chirp within the simulation is presented.

Higgins, S. P.; Vickers, A. J.

2006-03-01

289

Chirped pulse Raman amplification in Ba(NO3)2 crystals  

NASA Astrophysics Data System (ADS)

In this study, 35.5% conversion efficiency is obtained at the first Stokes component frequency (873 nm) upon two-stage chirped pulse Raman amplification in a Ba(NO3)2 crystal by an 8 mJ, 620 ps, 800 nm pump laser. A maximum energy of 4.22 mJ with 3.82% rms stability at the first Stokes pulse can be obtained under 35 mJ pump energy. Moreover, the chirped first Stokes pulse can be compressed to 143 fs.

Guo, Xiaoyang; Lu, Jun; Li, Wenkai; Xu, Yi; Lu, Xiaoming; Leng, Yuxin; Li, Ruxin

2015-04-01

290

Coherent XUV pulse generation using a chirped pulse combined with a unipolar pulse  

NASA Astrophysics Data System (ADS)

High-order harmonic emission and attosecond XUV source generation have been theoretically investigated using a chirped pulse combined with a unipolar pulse. It shows that the harmonic plateau is very sensitive to the chirp parameter and the intensity, pulse duration and relative position of the unipolar pulse. Further, by optimizing the laser parameters, a 714?eV supercontinuum bandwidth with a single short quantum path contribution has been obtained. Finally, by superposing the selected harmonic spectrum from the 70th to the 470th orders, an isolated attosecond pulse with a duration of 36 as can be obtained.

Feng, Liqiang; Liu, Hang

2015-01-01

291

Femtosecond laser pulse compression using angle of incidence optimization of chirped mirrors  

NASA Astrophysics Data System (ADS)

Optimal pulse compression following spectral broadening in a noble gas-filled hollow core fiber is a critical step towards producing isolated attosecond pulses. Here we present a systematic pulse shaping method based on the optimal selection of chirped mirrors and on the optimization of their angle of incidence. Feedback from second harmonic frequency resolved optical gating measurements is used to compute the optimal chirped mirror configuration of the next iteration in a genetic algorithm. Sub-5 fs pulses were achieved after a few iterations.

Marceau, C.; Gingras, G.; Toubou Bah, S.; Vallée, R.; Witzel, B.

2014-06-01

292

Practical design of optical diagnostics for chirped-pulse free-electron lasers  

NASA Astrophysics Data System (ADS)

In recent years there have been several proposals to operate rf-linac-driven FELs with chirped electron and optical micropulses for use in fast time-resolved experiments. We have been actively pursuing this application on the Mark-III infrared FEL at Duke University, and have designed and procured an apparatus to achieve broad-band compression of chirped optical pulses between roughly 2.5 ?m and 4.1 ?m, with subsequent measurement of pulse widths as short as 200 fs. The principles of design for this experiment will be reviewed, and extensions of the design to other wavelengths will be considered.

Szarmes, Eric B.; Madey, John M. J.

1992-07-01

293

Nonlinear energy deposition in water from fs-laser pulses: effect of the input chirp  

NASA Astrophysics Data System (ADS)

We present numerical and experimental investigation of the effect that the input pulse chirp has on the energy transfer from 5 ?J fs-pulses at 800 nm to water. The chirp is seen to control efficiently the energy transfer and the geometrical properties of the excited plasma volumes. Agreement between simulations and experiments is obtained via a parametric study, the details of which are presented here. These results may find applications in the control of underwater bubble and sound wave formation, and also in laser surgery involving aqueous media.

Milián, C.; Jarnac, Amelie; Brelet, Y.; Jukna, V.; Houard, A.; Mysyrowicz, A.; Couairon, A.

2014-05-01

294

Discriminating animal fats and their origins: assessing the potentials of Fourier transform infrared spectroscopy, gas chromatography, immunoassay and polymerase chain reaction techniques.  

PubMed

The objective of the reported study was to assess the abilities of various methods to differentiate the sources of fats used in feedstuff formulations. The main target was the identification of tallow (ruminant fat) and its differentiation from non-ruminant fats. Four different techniques were compared in terms of their suitability for enforcing existing and upcoming legislation on animal by-products: (1) Fourier transform infrared spectroscopy (FT-IR) applied to fat samples, (2) gas chromatography coupled with mass spectrometry (GC-MS) to determine fatty acid profiles, (3) immunoassays focusing on the protein fraction included in the fat, and (4) polymerase chain reaction (PCR) for the detection of bovine-specific DNA. Samples of the different fats and oils as well as mixtures of these fats were probed using these analytical methods. FT-IR and GC-MS differentiated pure fat samples quite well but showed limited ability to identify the animal species or even the animal class the fat(s) belonged to; no single compound or spectral signal that could permit species identification could be found. However, immunoassays and PCR were both able to identify the species or groups of species that the fats originated from, and they were the only techniques able to identify low concentrations of tallow in a mixture of fats prepared by the rendering industry, even when the samples had been sterilised at temperatures >133 degrees C. Fats used in animal nutrition come mainly from the rendering industry, thereby confirming the suitability of PCR and immunoassays for their identification. However, neither of these latter techniques was able to detect "premier jus" tallow, representing the highest quality standard of fat with extremely low protein concentration. PMID:15933852

Bellorini, Stefano; Strathmann, Stefan; Baeten, Vincent; Fumière, Olivier; Berben, Gilbert; Tirendi, Salvatore; von Holst, Christoph

2005-06-01

295

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

NASA Astrophysics Data System (ADS)

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

Asdornwised, Widhyakorn; Jitapunkul, Somchai

2004-07-01

296

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

NASA Astrophysics Data System (ADS)

We demonstrate significant enhancement of four-wave mixing in coherently driven mercury isotopes to generate vacuum-ultraviolet radiation at 125 nm. 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 313 nm excites the two-photon transition between the ground state 6s 21S 0 and the target state 7s 1S 0 in mercury. A strong, off-resonant radiation field at 1064 nm generates dynamic Stark shifts. These Stark shifts serve to induce a rapid adiabatic passage process on the two-photon transition. During the process a coherent superposition of the two states is established, which enhances the nonlinear-optical polarization in the medium to the maximum possible value. The maximum coherence permits efficient four-wave mixing of a pump laser and an additional probe laser at 626 nm. The efficiency is further enhanced, as the SCRAP process allows to stimulate the complete set of different mercury isotopes to participate in the frequency conversion process. This enlarges the effective atomic density of the medium. Thus, we observe the generation of vacuum-ultraviolet radiation at 125 nm enhanced by more than one order of magnitude with respect to conventional frequency conversion. Parallel to the frequency conversion process, we monitored the evolution of the population in the medium by laser-induced fluorescence. These data demonstrate efficient coherent population transfer by SCRAP.

Oberst, Martin; Klein, Jens; Halfmann, Thomas

2006-08-01

297

Single-channel broadband and multichannel narrowband filtering characteristics of linear chirped long-period fiber gratings  

NASA Astrophysics Data System (ADS)

Band-stop optical fiber filters based on linear chirped long-period fiber gratings (LPFGs) were investigated. The transmission characteristics of the linear chirped LPFGs were analyzed in detail with transfer matrix method. Linear chirp coefficient had a remarkable influence on the bandwidth of the transmission spectra. When the linear chirp coefficient was 10-9 and the transmission spectra corresponding to multiple cladding modes were superposed, the bandwidth of the transmission spectra could be expanded to >1000 nm. So the linear chirped LPFGs can be used for single-channel broadband band-stop filters, and the relationships between the grating parameters and the bandwidth of the transmission spectra were given. When the linear chirp coefficient is 10, several narrow and separated loss peaks appeared in the transmission spectra, which indicated that the linear chirped LPFGs can be used for multichannel narrowband filters. The variations of the grating parameters caused the shifts of the transmission spectra and the changes of the intervals between separated loss peaks. The conclusions that are significant in optimizing the fiber grating filters' design were obtained.

Yang, Ying; Gu, Zhengtian

2013-11-01

298

Broadband excitation by chirped pulses: application to single electron spins in diamond  

E-print Network

.4. Multi-line broadband spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4. Conclusions 13Broadband excitation by chirped pulses: application to single electron spins in diamond I Niemeyer1 are used. If the corresponding high power is not available or not desirable, the pulses can be replaced

Suter, Dieter

299

Phase control for production of high-fidelity optical pulses for chirped-pulse amplification  

NASA Astrophysics Data System (ADS)

We demonstrate continuous tuning of the cubic and quartic phases of the pulse stretcher in a chirped-pulse amplification laser system. We obtain near-bandwidth-limited recompression of 100-fs pulses by minimizing the total phase through fourth order.

Sullivan, A.; White, W. E.

1995-01-01

300

Quasi-Distributed Strain Sensor Incorporating a Chirped MoirÉ Fiber Bragg Grating  

Microsoft Academic Search

A quasi-distributed strain sensor with an average spatial resolution of 164 ?m over a length of 25 mm and a strain sensitivity of 0.8±0.01 pm\\/?? has been experimentally demonstrated. The sensor was formed by a chirped Moire´ fiber Bragg grating written into the core of single-mode optical fiber with a 244-nm continuous-wave laser.

A. M. Gillooly; L. Zhang; I. Bennion

2005-01-01

301

Comparison of binaural auditory brainstem responses and the binaural dierence potential evoked by chirps and clicks  

E-print Network

Comparison of binaural auditory brainstem responses and the binaural di¡erence potential evoked that compensate for the dispersion of the travelling wave on the basilar membrane evoke larger monaural brainstem auditory brainstem responses were recorded for clicks and chirps for levels from 10 to 60 dB nHL in steps

Oldenburg, Carl von Ossietzky, Universität

302

Characterization of a fiber-optic direct modulation analog link with chirp radar signals  

Microsoft Academic Search

This paper describes the experimental investigations carried out to evaluate the behaviour of a fiber-optic direct modulation analog link as a substitute of traditional transmission means, like coaxial cables or waveguides, for X-band chirp modulated radar signals. First of all, the link has been completely characterized, and the spurious frequency modulation has been measured in presence of pulsed signals. Afterwards,

Rossano Pardini; Umberto Bruno; Roberto Izzo

2009-01-01

303

The use of chirp overlapping properties for improved target resolution in an ultrasonic ranging system  

Microsoft Academic Search

The ability of many bat species to navigate, identify and capture prey has interested scientists for many years. It is known that bats possess extremely sophisticated echo location capabilities utilising chirp sequencing allied with an adaptive antenna system that enables extremely high resolution in 3D space. One particularly interesting aspect is that bats appear to resolve and locate targets with

F. Devaud; G. Hayward; J. J. Soraghan

2004-01-01

304

Multi-kilohertz repetition rate Ti:sapphire amplifier based on down-chirped pulse  

E-print Network

Multi-kilohertz repetition rate Ti:sapphire amplifier based on down-chirped pulse amplification energy and capable of being operated at repetition rates exceeding 40 kHz. This ti:sapphire based system makes use of a grism based stretcher, a cryogenically cooled ti:sapphire crystal and an astigmatically

305

Evaluation and application of the linear variable differential transformer technique for the assessment of human dorsal hand vein alpha-receptor activity.  

PubMed

Diurnal, day-to-day, intrasubject, and intersubject variability of responsiveness of dorsal hand veins to norepinephrine has been investigated in healthy young subjects through the use of a novel technique in which a linear variable differential transformer (LVDT) is placed directly over the vein. Under constant operating conditions, control vein diameter remained consistent. There is a log dose responsiveness to norepinephrine infused directly into the hand vein. There was little diurnal, day-to-day, or intrasubject variability in the dose of norepinephrine required to induce 50% constriction of hand vein diameter. The responsiveness to norepinephrine of different veins in either hand was also consistent. However, there was wide intersubject variability, apparently unrelated to age, gender, or other subject characteristics. We conclude that the LVDT method is reproducible and reliable and offers a relatively noninvasive means of assessing the effects of disease and drugs on the human dorsal hand vein in vivo. The LVDT technique has been applied to study the rate of onset, magnitude of effect, dose responsiveness, and duration of action of intravenous dihydroergotamine, 0.1, 0.2, and 0.4 mg, on human dorsal hand veins. Despite systemic intravenous administration, there was an average delay in maximum response of 30 minutes to 1 hour. Venoconstriction was incomplete, with a maximum reduction of approximately 50% of vein diameter after each of the larger doses. There was no significant difference between the effects produced by 0.2 or 0.4 mg, which persisted for 6 hours after dosing. PMID:2996818

Alradi, A O; Carruthers, S G

1985-11-01

306

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

PubMed

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

Karunakaran, Chandra P; Oelze, Michael L

2013-09-01

307

Direct DPSK modulation of chirp-managed laser as cost-effective downstream transmitter for symmetrical 10-Gbit/s WDM PONs.  

PubMed

This paper proposes the use of chirp-managed lasers (CML) as cost-effective downstream (DS) transmitters for next generation access networks. As the laser bandwidth is as high as 10 GHz, the CML could be directly modulated at 10 Gbit/s for downstream transmission in future wavelength division multiplexing passive optical networks (WDM PON). The laser adiabatic chirp, which is the main drawback limiting the transmission performance of directly modulated lasers, is now utilized to generate phase-shift keying (PSK) modulation format by direct modulation. At the user premise, the wavelength reuse technique based on reflective colorless upstream transmitter is applied. The optical network unit (ONU) reflects and orthogonally remodulates the received light with upstream data. A full-duplex transmission with symmetrical 10-Gbit/s bandwidth is demonstrated. Bit-error-rate measurement showed that optical power budgets of 29 dB at BER of 10(-9) or of 36 dB at BER of 10(-3) could be obtained with direct phase-shift-keying modulation of CML which proves that the proposed solution is a viable candidate for future WDM-PONs. PMID:23262890

Le, Quang Trung; Emsia, Ali; Briggmann, Dieter; Küppers, Franko

2012-12-10

308

An AWG-based 10 Gbit/s colorless WDM-PON system using a chirp-managed directly modulated laser  

NASA Astrophysics Data System (ADS)

We propose an arrayed waveguide grating (AWG)-based 10 Gbit/s per channel full duplex wavelength division multiplexing passive optical network (WDM-PON). A chirp managed directly modulated laser with return-to-zero (RZ) differential phase shift keying (DPSK) modulation technique is utilized for downlink (DL) direction, and then the downlink signal is re-modulated for the uplink (UL) direction using intensity modulation technique with the data rate of 10 Gbit/s per channel. A successful WDM-PON transmission operation with the data rate of 10 Gbit/s per channel over a distance of 25 km without any optical amplification or dispersion compensation is demonstrated with low power penalty.

Latif, Abdul; Yu, Chong-xiu; Xin, Xiang-jun; Husain, Aftab; Hussain, Ashiq; Munir, Abid; Khan, Yousaf

2012-09-01

309

Corn transformed  

SciTech Connect

Researchers have produced fertile corn transformed with a foreign gene that makes the plants resistant to the herbicide bialaphos. This achievement, is the first report of fertile transgenic corn in the reviewed literature, and it is the capstone of almost a decade's efforts to genetically engineer this country's most important crop. The only other major crop to be so manipulated is rice. The ability produce transgenic corn gives biologists a valuable tool to probe the whys and hows of gene expression and regulation. It may also give plant breeders a way to develop new corn varieties with a speed and predictability that would be impossible with classical breeding techniques.

Moffat, A.S.

1990-08-10

310

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

E-print Network

- ducting XFELs. In response, RadiaBeam Systems presents its work, building upon the theoretical work a compact, low-cost corrugated plate system with an ad- justable gap for tunable beam dechirping. Its

Brookhaven National Laboratory

311

Chirped-beam two-stage free-electron laser for high-power femtosecond x-ray pulse generation  

NASA Astrophysics Data System (ADS)

A method for generating femtosecond-duration x-ray pulses with a free-electron laser is presented. This method uses an energy-chirped electron beam propagating through an undulator to produce a frequency-chirped x-ray pulse by self-amplified spontaneous emission. A short temporal pulse is created by use of a monochromator to select a narrow radiation bandwidth. A second undulator is used to amplify the short-duration radiation. The radiation characteristics produced by a chirped-beam two-stage free-electron laser are calculated, and the performance of the chirped-beam two-stage option for the Linac Coherent Light Source is considered. 2002 Optical Society of America

Schroeder, Carl B.; Pellegrini, Claudio; Reiche, Sven; Arthur, John; Emma, Paul

2002-08-01

312

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

PubMed

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

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

2011-06-01

313

Technique for simultaneously multiplying the repetition rate of multiwavelength optical pulse trains  

Microsoft Academic Search

In this letter, we propose and numerically demonstrate a technique for synchronized multiplication of the repetition rate in multiwavelength optical pulse trains launched over a single fiber. The technique only requires linear reflection of the original signal in a single structure of superimposed chirped in-fiber Bragg gratings, which are specifically designed to provide a suitable group delay dispersion within each

José Azaña; Miguel A. Muriel

2001-01-01

314

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

PubMed Central

The current excitation strategy for harmonic and subharmonic imaging (HI and SHI) uses short sine-bursts. However, alternate pulsing strategies may be useful for enhancing nonlinear emissions from ultrasound contrast agents. The goal of this study was to corroborate the hypothesis that chirp-coded excitation can improve the performance of high-frequency HI and SHI. A secondary goal was to understand the mechanisms that govern the response of ultrasound contrast agents to chirp-coded and sine-burst excitation schemes. Numerical simulations and acoustic measurements were conducted to evaluate the response of a commercial contrast agent (Targestar-P®) to chirp-coded and sine-burst excitation (10?MHz frequency, peak pressures 290 kPa). The results of the acoustic measurements revealed an improvement in signal-to-noise ratio by 4 to 14?dB, and a two- to threefold reduction in the subharmonic threshold with chirp-coded excitation. Simulations conducted with the Marmottant model suggest that an increase in expansion-dominated radial excursion of microbubbles was the mechanism responsible for the stronger nonlinear response. Additionally, chirp-coded excitation detected the nonlinear response for a wider range of agent concentrations than sine-bursts. Therefore, chirp-coded excitation could be a viable approach for enhancing the performance of HI and SHI. PMID:23654417

Shekhar, Himanshu; Doyley, Marvin M.

2013-01-01

315

Single sub-50-attosecond pulse generation from chirp-compensated harmonic radiation using material dispersion  

SciTech Connect

A method for obtaining a single sub-50-attosecond pulse using harmonic radiation is proposed. For the generation of broad harmonic radiation during a single half-optical cycle, atoms are driven by a femtosecond laser pulse with intensity above the saturation intensity for optical field ionization and hence experience a large nonadiabatic increase of the laser electric field between optical cycles. Although the chirped structure of the harmonic radiation imposes a limit on the minimum achievable pulse duration, we demonstrate that its positive chirp can be compensated by the negative group delay dispersion of an appropriately selected x-ray filter material, used also for the spectral selection, resulting in a single attosecond pulse with a duration less than 50 as.

Kim, Kyung Taec; Kim, Chul Min; Umesh, G.; Nam, Chang Hee [Department of Physics and Coherent X-ray Research Center, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of); Baik, Moon-Gu [Department of Physics, Kyungwon University, Seongnam, Gyeonggi-do 461-701 (Korea, Republic of)

2004-05-01

316

Chirped-pulse oscillators: a route to high-power femtosecond pulses without external amplification.  

PubMed

We demonstrate a Kerr-lens mode-locked Ti:sapphire oscillator that generates 130-nJ, 26-fs and 220-nJ, 30-fs pulses at a repetition rate of 11 MHz. The generation of stable broadband, high-energy pulses from an extended-cavity oscillator is achieved by the use of chirped multilayer mirrors to produce a small net positive dispersion over a broad spectral range. The resultant chirped picosecond pulses are compressed by a dispersive delay line that is external to the laser cavity. The demonstrated peak powers, in excess of 5 MW, are to our knowledge the highest ever achieved from a cw-pumped laser and are expected to be scalable to tens of megawatts by an increase in the pump power and (or) a decrease in the repetition rate. The demonstrated source permits micromachining of any materials under relaxed focusing conditions. PMID:15233437

Fernandez, A; Fuji, T; Poppe, A; Fürbach, A; Krausz, F; Apolonski, A

2004-06-15

317

Ultrashort electron bunch generation by an energy chirping cell attached rf gun  

NASA Astrophysics Data System (ADS)

We present a new design for a rf electron gun to be used in ultrashort (˜1 ps) electron bunch generation. Using both simulation and measurement we evaluated the principle of this new type rf gun and were able to confirm an ultrashort bunch generation. During simulation, a bunch length of less than 100 fs(rms) with a 100 pC/bunch charge was confirmed at the optimum operating condition. The principle is to produce a linearly distributed longitudinal phase space by using an attached output cell specially designed for energy chirping. Such phase space distribution can be rotated by the velocity difference in the bunch. We already fabricated an energy chirping cell attached rf gun and successfully observed 0.2 THz coherent synchrotron radiation, which corresponds to less than 500 fs bunch. Such an electron gun can be used as a compact THz light source and a new electron injector with an ultrashort bunch.

Sakaue, K.; Koshiba, Y.; Mizugaki, M.; Washio, M.; Takatomi, T.; Urakawa, J.; Kuroda, R.

2014-02-01

318

Analysis of Pump-Induced Temporal Contrast Degradation in Optical Parametric Chirped-Pulse Amplification  

SciTech Connect

The pump-induced degradation of the temporal contrast of laser pulses amplified by optical parametric chirped-pulse amplification (OPCPA) is studied analytically. In OPCPA systems, the temporal fluctuations of the pump pulse are coupled to the spectrum of the chirped signal by the instantaneous parametric gain and lead to a reduction in the temporal contrast of the recompressed amplified signal. The intensity and shape of the induced temporal pedestal depend on the pump fluctuations and the parametric amplifier operating regime. General equations describing the contrast degradation are derived and applied to the case of sinusoidal pump-intensity modulation and pump amplified spontaneous emission. The reduction of the contrast in the amplified pulse is quantified analytically and via simulations for an OPCPA system.

Dorrer, C,

2007-12-12

319

Resonant nonlinearity in high-energy Er3+-fiber chirped-pulse-amplifiers  

NASA Astrophysics Data System (ADS)

We present experimental results, which show that the up-chirp of dispersively stretched femtosecond pulses decreases linearly with increasing pulse energy after amplification in Erbium-doped fibers. For 6 ?J output pulses a nonlinear dispersion of -4?106 fs? was measured. This nonlinear dispersive effect is attributable to the resonant dispersion of the Erbium-ions and the decrease of the inversion during pulse amplification and was about one order of magnitude larger than predicted by the literature. Most likely this deviation is attributable to the complex population dynamics of the Er3+-ions during pulse amplification, since in the literature the relation between the refractive index and Er3+-inversion was described for a quasi-static population distribution. Due to the high resonant dispersion the required compressor dispersion for minimum output pulse duration depends strongly on the output pulse energy in Erbium-doped fiber-based chirped-pulse-amplifier set-ups.

Adel, P.; Engelbrecht, M.; Wandt, D.; Fallnich, C.

2005-12-01

320

All optical quantum storage based on spatial chirp of the control field  

E-print Network

We suggest an all-optical quantum memory scheme which is based on the off-resonant Raman interaction of a signal quantum field and a strong control field in a three-level atomic medium in the case, when the control field has a spatially varying frequency across the beam, called a spatial chirp. We show that the effect of such a spatial chirp is analogous to the effect of a controllable reversible inhomogeneous broadening (CRIB) of the atomic transition used in the gradient echo memory (GEM) scheme. However, the proposed scheme does not require temporal modulation of the control field or the atomic levels, and can be realized without additional electric or magnetic fields. It means that materials demonstrating neither linear Stark nor Zeeman effects can be used and/or materials which are placed in specific external fields remain undisturbed.

Xiwen Zhang; Alexey Kalachev; Olga Kocharovskaya

2014-07-10

321

All-optical quantum storage based on spatial chirp of the control field  

NASA Astrophysics Data System (ADS)

We suggest an all-optical quantum memory scheme which is based on the off-resonant Raman interaction of a signal quantum field and a strong control field in a three-level atomic medium in the case where the control field has a spatially varying frequency across the beam, called a spatial chirp. We show that the effect of such a spatial chirp is analogous to the effect of a controllable reversible inhomogeneous broadening of the atomic transition used in the gradient echo memory scheme. The proposed scheme does not require temporal modulation of the control field or the atomic levels and can be realized without additional electric or magnetic fields. This means that materials demonstrating neither linear Stark nor Zeeman effects can be used and/or materials which are placed in specific external fields remain undisturbed.

Zhang, Xiwen; Kalachev, Alexey; Kocharovskaya, Olga

2014-11-01

322

Frequency chirp and pulse shape effects in self-modulated laser wakefield accelerators  

SciTech Connect

The effect of asymmetric laser pulses on plasma wave excitation in a self-modulated laser wakefield accelerator is examined. Laser pulse shape and frequency chirp asymmetries, controlled experimentally in the laser system through a grating pair compressor, are shown to strongly enhance measured electron yields for certain asymmetries. It is shown analytically that a positive (negative) frequency chirp enhances (suppresses) the growth rate of the Raman forward scattering and near-forward Raman sidescatter instabilities, but is of minimal importance for the experimental parameters. Temporal laser pulse shapes with fast rise times (< plasma period) are shown to generate larger wakes (compared to slow rise time pulses) which seed the growth of the plasma wave, resulting in enhanced electron yield.

Schroeder, C.B.; Esarey, E.; Geddes, C.G.R.; Toth, Cs.; Shadwick, B.A.; van Tilborg, J.; Faure, J.; Leemans, W.P.

2002-11-07

323

Transformation inverse design  

E-print Network

We present a new technique for the design of transformation-optics devices based on large-scale optimization to achieve the optimal effective isotropic dielectric materials within prescribed index bounds, which is ...

Liu, David

324

Investigation of the high-temporal contrast seed pulse amplification in optical parametric chirped pulse amplifier  

NASA Astrophysics Data System (ADS)

We theoretically and experimentally investigate the amplification of a high-temporal contrast seed pulse in an optical parametric chirped pulse amplifier. The amplified and compressed signal pulse contrast can be improved by using large seed pulse energies. And the theory model is modified for considering the seed pulse contrast and compressed pulse duration. From the modified model the calculated results agree with the experimental results better.

Guo, Xiaoyang; Zou, Xiao; Xu, Yi; Lu, Xiaoming; Li, Yanyan; Wang, Cheng; Leng, Yuxin; Li, Ruxin

2015-01-01

325

New stretcher scheme for a parametric amplifier of chirped pulses with frequency conversion  

SciTech Connect

The properties of hybrid prism-grating dispersion systems are studied. The scheme of a prism-grating stretcher matched to a standard compressor in the phase dispersion up to the fourth order inclusive is developed for a petawatt laser complex based on the optical parametric chirped-pulse amplification. The stretcher was used to obtain the {approx}200-TW peak power of laser radiation. (control of laser radiation parameters)

Freidman, Gennadii I; Yakovlev, I V [Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation)

2007-02-28

326

Chirp (2–7 kHz) echo characters in the Ulleung Basin  

Microsoft Academic Search

High-resolution (Chirp, 2–7 kHz) reflection profiles in the Ulleung Basin (35–37°N) made it possible to classify the uppermost\\u000a (ca. 50–70 m thick) sedimentary sequence into eleven discrete echo types. They are either (1) distinct (Echo Types IA, IB,\\u000a IC, ID, IE, and IF), (2) indistinct (Echo Types IIA, IIB, and IIC), (3) hyperbolic (Echo Type III), or (4) combined (Echo

S. K. Chough; S. H. Lee; J. W. Kim; S. C. Park; D. G. Yoo; H. S. Han; S. H. Yoon; S. B. Oh; Y. B. Kim; G. G. Back

1997-01-01

327

Diode-pumped chirped pulse amplification to the TW level using Yb:CaF2  

NASA Astrophysics Data System (ADS)

We present a terawatt diode-pumped chirped pulse amplifier using single-crystalline Yb:CaF2 as the gain medium. A maximum pulse energy of 420 mJ and a repetition rate of 1 Hz was obtained. After recompression, a pulse energy of 197 mJ and a pulse duration of 192 fs were achieved, corresponding to a peak power of 1 TW.

Siebold, M.; Hornung, M.; Hein, J.; Uecker, R.; Debus, A.; Kaluza, M. C.

2010-02-01

328

Application of SPICE simulation to study WDM and SCM systems using EDFAs with chirping  

Microsoft Academic Search

The authors have proposed an equivalent electrical circuit model of erbium-doped fiber amplifiers (EDFAs), including the chirping effect for teaching or studying the distortions and performance of lightwave transmission systems. Through the aid of a SPICE circuit simulator, its validity is demonstrated by analyzing the cross modulations of an eight-channel wavelength division multiplexing system. The intermodulations in an amplitude modulation-subcarrier

Jau-Ji Jou; Cheng-Kuang Liu

2002-01-01

329

Open-path sensor for atmospheric methane based on chirped laser dispersion spectroscopy  

NASA Astrophysics Data System (ADS)

The design and characterization of a near-IR Chirped Laser Dispersion Spectroscopy (CLaDS) sensor for atmospheric methane detection are reported. The near-IR CLaDS system exhibits the benefits of the prior mid-IR CLaDS systems implemented for open-path sensing while taking advantage of the robust fiber-optic components available in the near-IR. System noise, long-term stability, and comparison with existing technology for methane detection are presented.

Nikodem, Michal; Plant, Genevieve; Sonnenfroh, David; Wysocki, Gerard

2014-10-01

330

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

Microsoft Academic Search

The goal of this LDRD ER was to develop a robust and reliable technology to seed high-energy laser systems with chirped pulses that can be amplified to kilo-Joule energies and recompressed to sub-picosecond pulse widths creating extremely high peak powers suitable for petawatt class physics experiments. This LDRD project focused on the development of optical fiber laser technologies compatible with

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

2009-01-01

331

Long-term carrier-envelope phase stability from a grating-based, chirped pulse amplifier.  

PubMed

We demonstrate a carrier-envelope phase (CEP) stabilized, chirped pulse laser amplifier that exhibits greatly improved intrinsic long-term CEP stability compared with that of other amplifiers. This system employs a grating-based stretcher and compressor and a cryogenically cooled laser amplifier. Single-shot carrier envelope phase noise measurements are also presented that avoid underestimation of this parameter caused by fringe averaging and represent a rigorously accurate upper limit on CEP noise. PMID:16729097

Gagnon, Etienne; Thomann, Isabell; Paul, Ariel; Lytle, Amy L; Backus, Sterling; Murnane, Margaret M; Kapteyn, Henry C; Sandhu, Arvinder S

2006-06-15

332

Tunable optical delay line in SOI implemented with step chirped Bragg gratings and serial grating arrays  

NASA Astrophysics Data System (ADS)

Tunable optical delay devices have numerous applications in optical communications [1] and have been successfully implemented using slow light elements and fiber or waveguide gratings. There has been considerable interest in siliconon- insulator (SOI) as a technology platform for compact integration of optical signal processing systems. SOI-based delay lines have been realized using coupled ring resonators [2], photonic crystals [3], and various Bragg grating-based configurations including single or coupled chirped sidewall gratings [4,5] as well as tapered rib waveguide gratings [6]. By linearly chirping the period in sidewall gratings, relatively small delays (a few ps) over a bandwidth of tens of nm were demonstrated [4]; with tapered waveguides, significantly larger delays (300-500 ps) were obtained, albeit over a narrower bandwidth (< 2 nm) [6]. On the other hand, some signal processing applications may require large delays (e.g., tens to hundreds of ps) over large bandwidths (several to tens of nm). Several designs have been proposed to meet these requirements, e.g., a step-chirped rib waveguide grating providing 50 ps delay over 15 nm [7] or complementary apodized sidewall gratings providing up to 275 ps over 3 nm [8], however, they have not been realized experimentally. In this paper, we demonstrate discretely tunable optical delay lines that provide tens of ps delay (up to 65 ps) in steps of 15-32 ps over bandwidths of several tens of nm (35-70 nm). The devices are fabricated on SOI using electron beam lithography and implemented through two different approaches: serial sidewall Bragg grating arrays and the step-chirped sidewall Bragg gratings.

Spasojevic, Mina; Chen, Lawrence R.

2013-10-01

333

Chirped pulses sum frequency generation for deep-­UV picosecond pulse shaping  

NASA Astrophysics Data System (ADS)

We show by experiments and simulations that properly chirped laser pulses enable efficient and broadband sum frequency generation in nonlinear crystals. We achieved high energy, picosecond deep-UV pulses with spectral width one order of magnitude greater than the acceptance bandwidth of the nonlinear interaction. The broad spectrum supports shaping of ps flat-top deep-UV pulses with short rise- and fall-time, which are optimal for driving high brightness photocathode electron guns.

Vicario, Carlo; Trisorio, Alexandre; Arisholm, Gunnar; Hauri, Christoph P.

2012-03-01

334

Electro-optic measurement of THz field pulses with a chirped optical beam  

Microsoft Academic Search

Using a linearly chirped optical probe pulse in free-space electro-optic measurements, a temporal wave form of a co-propagating THz field is linearly encoded onto the frequency spectrum of the optical probe pulse, and then decoded by dispersing the probe beam from a grating to a detector array. We achieve acquisition of picosecond THz field pulses without using mechanical time-delay device.

Zhiping Jiang; X.-C. Zhang

1998-01-01

335

Non-collinear phase-matching geometries in optical parametric chirped-pulse amplification  

NASA Astrophysics Data System (ADS)

This study presents a full three-dimensional nonlinear pulse propagation and amplification model that includes considerations for phase-matching, diffraction, and walk-off effects. By using this model, two types of type I non-collinear phase-matching geometries in BBO based optical parametric chirped-pulse amplification are investigated theoretically and experimentally. The simulation results agree well with the experimental findings.

Guo, Xiaoyang; Xu, Yi; Zou, Xiao; Lu, Xiaoming; Li, Yanyan; Wang, Cheng; Leng, Yuxin; Li, Ruxin

2014-11-01

336

Chirped AM ladar for anti-ship missile tracking and force protection 3D imaging: update  

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 velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a chirped amplitude modulation ladar to provide range and velocity measurements for

Brian C. Redman; Barry Stann; William Lawler; Mark Giza; John Dammann; William Ruff; William Potter; Ronald G. Driggers; Jose Garcia; John Wilson; Keith Krapels

2006-01-01

337

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

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 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 and velocity measurements of potential targets handed-over by the distributed aperture system - IRST (DAS-IRST) being developed by the Naval Research Laboratory (NRL) and sponsored by the Office of Naval Research (ONR). Using the ladar's range and velocity data, false alarms and clutter will be eliminated, and valid missile targets' tracks will be updated. By using an array receiver, ARL's ladar will also provide 3D imagery of potential threats for force protection/situational awareness. The concept of operation, the Phase I breadboard ladar design and performance model results, and the Phase I breadboard ladar development program were presented in paper 5413-16 at last year's symposium. This paper will present updated design and performance model results, as well as recent laboratory and field test results for the Phase I breadboard ladar. Implications of the Phase I program results on the design, development, and testing of the Phase II brassboard ladar will also be discussed.

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

2005-05-01

338

Multiple slow waves and relevant transverse transmission and confinement in chirped photonic crystals.  

PubMed

The dispersion properties of rod-type chirped photonic crystals (PhCs) and non-channeled transmission in the direction of the variation of structural parameters from one cell of such a PhC to another are studied. Two types of configurations that enable multiple slow waves but differ in the utilized chirping scheme are compared. It is demonstrated that the multiple, nearly flat bands with a group index of refraction exceeding 180 can be obtained. For these bands, transmission is characterized by multiple narrow peaks of perfect transmission, strong field enhancement inside the slab, and large values of the Q-factor. Among the bands, there are some that show negative phase velocity. Symmetry with respect to the slab mid-plane must be kept in order to obtain constructive interferences that are necessary for reflection-free transmission. It is shown that 15 and more slow wave bands can be obtained in one configuration. The corresponding transmission peaks are well separated from each other, being the only significant feature of the transmission spectrum, while the Q-factor can exceed 10?. The observed features are preserved in a wide range of the incidence angle variation. They can be used for tuning the locations and spectral widths of the transmission peaks. Some comparisons with the chirped multilayer structures have been carried out. PMID:25321556

Serebryannikov, Andriy E; Cakmak, A Ozgur; Colak, Evrim; Caglayan, Humeyra; Kurt, Hamza; Ozbay, Ekmel

2014-09-01

339

Temporal and spectral characterization of femtosecond deep-UV chirped pulses  

NASA Astrophysics Data System (ADS)

In contrast to the case of pulses in the infrared (IR) and visible range, the temporal characterization of deep-UV femtosecond pulses in combination with their spectral features is still a challenge, essentially due to the lack of suitable nonlinear crystals for second harmonic autocorrelation. Here we report on the characterization of 260?nm, nearly 200?fs pulses, based on two photon absorption in fused silica. 260?nm pulses are obtained as the fourth harmonic component of a near-IR fundamental which is frequency up-converted into a double beta barium borate-based harmonic generator stage. By comparing the obtained pulse duration with its Fourier limit, estimated by measuring pulse spectra, a consistent pulse chirp is retrieved. This chirp is mostly attributed to the considerable group-velocity dispersion occurring in the last doubling stage which converts the green into UV radiation. Additionally, the spectral width of the probe pulse through the fused silica window turns out to be modulated as a function of the time delay between pump and probe in the two-photon absorption setup. The observed modulation is attributed to the interplay between spectrally selective absorption, due to the chirp of the pulses, and moderate self-phase modulation just occurring at the top of the temporal autocorrelation between pump and probe.

Valadan, Mohammadhassan; D’Ambrosio, Davide; Gesuele, Felice; Velotta, Raffaele; Altucci, Carlo

2015-02-01

340

Trends in ultrashort and ultrahigh power laser pulses based on optical parametric chirped pulse amplification  

NASA Astrophysics Data System (ADS)

Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992, optical parametric chirped pulse amplification (OPCPA) became the most promising method for the amplification of broadband optical pulses. In the meantime, we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers. The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level. Meanwhile, the output pulse duration based on optical parametric amplification has entered the range of few-optical-cycle field. In this paper, we overview the basic principles, trends in development, and current state of the ultrashort and laser systems based on OPCPA, respectively. Project supported by the National Natural Science Foundation of China (Grant Nos. 61378030 and 11127901), the National Basic Research Program of China(Grant No. 2011CB808101), and the International S&T Cooperation Program of China (Grant No. 2011DFA11300).

Xu, Lu; Yu, Liang-Hong; Chu, Yu-Xi; Gan, Ze-Biao; Liang, Xiao-Yan; Li, Ru-Xin; Xu, Zhi-Zhan

2015-01-01

341

Wideband-adjustable reflection-suppressed rejection filters using chirped and tilted fiber gratings.  

PubMed

Wideband-adjustable band-rejection filters based on chirped and tilted fiber Bragg gratings (CTFBG) are proposed and experimentally demonstrated. The flexible chirp-rate and wide tilt-angle provide the gratings with broadband filtering functions over a large range of bandwidths (from 10 nm to 150 nm), together with a low insertion loss (less than 1 dB) and a negligible back-reflection (lower than -20 dB). The slope profile of CTFBG in transmission can be easily tailored by adjusting the tilt angle, grating irradiation time and chirp rate-grating factor, and it is insensitive to the polarization state of the input light, as well as to temperature, axial strain and surrounding refractive index. Furthermore, by coating the CTFBG with a suitable polymer (whose refractive index is close to that of the cladding glass), the cladding modes no longer form weakly discrete resonances and leave a smoothly varying attenuation spectrum for high-quality band-rejection filters, edge filters and gain equalizers. PMID:25322019

Liu, Fu; Guo, Tuan; Wu, Chuang; Guan, Bai-Ou; Lu, Chao; Tam, Hwa-Yaw; Albert, Jacques

2014-10-01

342

A novel symmetric 10 Gbit/s architecture with a single feeder fiber for WDM-PON based on chirp-managed laser  

NASA Astrophysics Data System (ADS)

We propose the single feeder fiber architecture for wavelength division multiplexing passive optical network (WDM-PON) based on directly modulated chirp managed laser (CML). The downlink (DL) signal output from the laser is converted to return-to-zero (RZ) differential phase shift signal using a pulse carver. The downstream signal is reused as a carrier for the upstream using intensity modulation technique. Simulation results show the error-free performance at symmetric data rate of 10 Gbit/s per channel with negligible power penalty and improved receiver sensitivity for the uplink (UL), over 25 km standard single-mode fiber (SSMF). A low-cost and reduced circuitry network design is implemented on a single feeder fiber with the elimination of differential encoder and one external modulator.

Hussain, Aftab; Xin, Xiang-jun; Latif, Abdul; Hussain, Ashiq; Yu, Chong-xiu; Munir, Abid; Khan, Yousaf; Afridi, Muhammad Idrees

2012-11-01

343

Chloroplast transformation.  

PubMed

In this chapter we briefly review the developmental history and current research status of chloroplast transformation and introduce the merits of chloroplast transformation as compared with the nuclear genome transformation. Furthermore, according to the chloroplast transformation achieved in oilseed rape (Brassica napus), we introduce the preparation of explants, transformation methods, system selection, identification methods of the transplastomic plants, and experimental results. The technical points, the bottleneck, and the further research directions of the chloroplast transformation are discussed in the notes. PMID:16673924

Lu, Xiao-Mei; Yin, Wei-Bo; Hu, Zan-Min

2006-01-01

344

Best network chirplet chain: Near-optimal coherent detection of unmodeled gravitational wave chirps with a network of detectors  

SciTech Connect

The searches of impulsive gravitational waves (GW) in the data of the ground-based interferometers focus essentially on two types of waveforms: short unmodeled bursts from supernova core collapses and frequency modulated signals (or chirps) from inspiralling compact binaries. There is room for other types of searches based on different models. Our objective is to fill this gap. More specifically, we are interested in GW chirps ''in general,'' i.e., with an arbitrary phase/frequency vs time evolution. These unmodeled GW chirps may be considered as the generic signature of orbiting or spinning sources. We expect the quasiperiodic nature of the waveform to be preserved independently of the physics which governs the source motion. Several methods have been introduced to address the detection of unmodeled chirps using the data of a single detector. Those include the best chirplet chain (BCC) algorithm introduced by the authors. In the next years, several detectors will be in operation. Improvements can be expected from the joint observation of a GW by multiple detectors and the coherent analysis of their data, namely, a larger sight horizon and the more accurate estimation of the source location and the wave polarization angles. Here, we present an extension of the BCC search to the multiple detector case. This work is based on the coherent analysis scheme proposed in the detection of inspiralling binary chirps. We revisit the derivation of the optimal statistic with a new formalism which allows the adaptation to the detection of unmodeled chirps. The method amounts to searching for salient paths in the combined time-frequency representation of two synthetic streams. The latter are time series which combine the data from each detector linearly in such a way that all the GW signatures received are added constructively. We give a proof of principle for the full-sky blind search in a simplified situation which shows that the joint estimation of the source sky location and chirp frequency is possible.

Pai, Archana; Chassande-Mottin, Eric; Rabaste, Olivier [Max-Planck Institut fuer Gravitationsphysik, Am Muehlenberg 1, 14476 Potsdam (Germany); CNRS, AstroParticule et Cosmologie, 10, rue Alice Domon et Leonie Duquet, 75205 Paris Cedex 13, France and Observatoire de la Cote d'Azur, Bd de l'Observatoire, BP 4229, 06304 Nice (France); CNRS, AstroParticule et Cosmologie, 10, rue Alice Domon et Leonie Duquet, 75205 Paris Cedex 13 (France)

2008-03-15

345

Deriving Criteria-supporting Benchmark Values from Empirical Response Relationships: Comparison of Statistical Techniques and Effect of Log-transforming the Nutrient Variable  

EPA Science Inventory

In analyses supporting the development of numeric nutrient criteria, multiple statistical techniques can be used to extract critical values from stressor response relationships. However there is little guidance for choosing among techniques, and the extent to which log-transfor...

346

Transformations Preserving the Hankel Transform  

NASA Astrophysics Data System (ADS)

We classify all polynomial transformations of integer sequences which preserve the Hankel transform, thus generalizing examples due to Layman and Spivey & Steil. We also show that such transformations form a group under composition.

French, Christopher

2007-07-01

347

Clinical evaluation of chirp-coded excitation in medical ultrasound  

Microsoft Academic Search

Despite the enormous development in medical ultrasound (US) imaging over the last decades, penetration depth with satisfying image quality is often a problem in clinical practice. Coded excitation, used for years in radar techniques to increase signal-to-noise ratio (SNR), has recently been introduced in medical US scanning. In the present study, coded excitation using frequency-modulated US signals is implemented and

Morten H. Pedersen; Thanassis X. Misaridis; Jørgen A. Jensen

2003-01-01

348

Full-Field Spectroscopy at Megahertz-frame-rates: Application of Coherent Time-Stretch Transform  

NASA Astrophysics Data System (ADS)

Outliers or rogue events are found extensively in our world and have incredible effects. Also called rare events, they arise in the distribution of wealth (e.g., Pareto index), finance, network traffic, ocean waves, and e-commerce (selling less of more). Interest in rare optical events exploded after the sighting of optical rogue waves in laboratory experiments at UCLA. Detecting such tail events in fast streams of information necessitates real-time measurements. The Coherent Time-Stretch Transform chirps a pulsed source of radiation so that its temporal envelope matches its spectral profile (analogous to the far field regime of spatial diffraction), and the mapped spectral electric field is slow enough to be captured by a real-time digitizer. Combining this technique with spectral encoding, the time stretch technique has enabled a new class of ultra-high performance spectrometers and cameras (30+ MHz), and analog-to-digital converters that have led to the discovery of optical rogue waves and detection of cancer cells in blood with one in a million sensitivity. Conventionally, the Coherent Time-Stretch Transform maps the spectrum into the temporal electric field, but the time-dilation process along with inherent fiber losses results in reduction of peak power and loss of sensitivity, a problem exacerbated by extremely narrow molecular linewidths. The loss issue notwithstanding, in many cases the requisite dispersive optical device is not available. By extending the Coherent Time-Stretch Transform to the temporal near field, I have demonstrated, for the first time, phase-sensitive absorption spectroscopy of a gaseous sample at millions of frames per second. As the Coherent Time-Stretch Transform may capture both near and far field optical waves, it is a complete spectro-temporal optical characterization tool. This is manifested as an amplitude-dependent chirp, which implies the ability to measure the complex refractive index dispersion at megahertz frame rates. This technique is not only four orders of magnitude faster than even the fastest (kHz) spectrometers, but will also enable capture of real-time complex dielectric function dynamics of plasmas and chemical reactions (e.g. combustion). It also has applications in high-energy physics, biology, and monitoring fast high-throughput industrial processes. Adding an electro-optic modulator to the Time-Stretch Transform yields time-to-time mapping of electrical waveforms. Known as TiSER, it is an analog slow-motion processor that uses light to reduce the bandwidth of broadband RF signals for capture by high-sensitivity analog-to-digital converters (ADC). However, the electro-optic modulator limits the electrical bandwidth of TiSER. To solve this, I introduced Optical Sideband-only Amplification, wherein electro-optically generated modulation (containing the RF information) is amplified at the expense of the carrier, addressing the two most important problems plaguing electro-optic modulators: (1) low RF bandwidth and (2) high required RF drive voltages. I demonstrated drive voltage reductions of 5x at 10 GHz and 10x at 50 GHz, while simultaneously increasing the RF bandwidth.

DeVore, Peter Thomas Setsuda

349

UMLX : A graphical transformation language for MDA  

Microsoft Academic Search

With the increased use of modelling techniques has come the desire to use models as a programming language as part of a Model Driven Architecture. This desire can now be satisfied by exploiting XMI for model interchange and XSLT for model transformation. However the current transformation techniques are far removed from modelling techniques. We therefore describe a graphical transformation language,

Edward D. Willink

2003-01-01

350

Generalized Transforms and Special Functions  

E-print Network

We study the properties of different type of transforms by means of operational methods and discuss the relevant interplay with many families of special functions. We consider in particular the binomial transform and its generalizations. A general method, based on the use of the Fourier transform technique, is proposed for the study of the properties of functions of operators.

G. Dattoli; E. Sabia

2010-10-08

351

Effects of chirping on the dissociation dynamics of H2 in a two-frequency laser field Avijit Datta,1,2  

E-print Network

of frequency chirping of laser pulses on (1 1)-photon resonance-enhanced disso- ciation dynamics of H2-photon resonance or near resonance with the initial level. Predissociating levels embedded into continua the effect of frequency detuning and chirp width on the dissociation probability. Widths of the two peaks

Kim, Bongsoo

352

Adaptive transformer thermal overload protection  

Microsoft Academic Search

This paper is based on a report of the same title, prepared by Working Group K3 of the Substation Protection Subcommittee of the Power System Relaying Committee of the Power Engineering Society of the IEEE. The paper begins with background information on the causes, measurement techniques, and consequences of overheating in mineral-oil-immersed power transformers. Then techniques for adaptive transformer thermal

G. W. Swift; E. S. Zocholl; M. Bajpai; J. F. Burger; C. H. Castro; S. R. Chano; F. Cobelo; P. de Sa; E. C. Fennell; J. G. Gilbert; S. E. Grier; R. W. Haas; W. G. Hartmann; R. A. Hedding; P. Kerrigan; S. Mazumdar; D. H. Miller; P. G. Mysore; M. Nagpal; R. V. Rebbapragada; M. V. Thaden; J. T. Uchiyama; S. M. Usman; J. D. Wardlow; M. Yalla

2001-01-01

353

Ultrafast single-electron transfer in coupled quantum dots driven by a few-cycle chirped pulse  

SciTech Connect

We theoretically study the ultrafast transfer of a single electron between the ground states of a coupled double quantum dot (QD) structure driven by a nonlinear chirped few-cycle laser pulse. A time-dependent Schrödinger equation without the rotating wave approximation is solved numerically. We demonstrate numerically the possibility to have a complete transfer of a single electron by choosing appropriate values of chirped rate parameters and the intensity of the pulse. Even in the presence of the spontaneous emission and dephasing processes of the QD system, high-efficiency coherent transfer of a single electron can be obtained in a wide range of the pulse parameters. Our results illustrate the potential to utilize few-cycle pulses for the excitation in coupled quantum dot systems through the nonlinear chirp parameter control, as well as a guidance in the design of experimental implementation.

Yang, Wen-Xing, E-mail: wenxingyang2@126.com [Department of Physics, Southeast University, Nanjing 210096 (China); Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China); Chen, Ai-Xi [Department of Applied Physics, School of Basic Science, East China Jiaotong University, Nanchang 330013 (China); Bai, Yanfeng [Department of Physics, Southeast University, Nanjing 210096 (China); Lee, Ray-Kuang [Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China)

2014-04-14

354

Numerical analysis of the optimal length and profile of a linearly chirped fiber Bragg grating for dispersion compensation.  

PubMed

We propose a theoretical investigation of the length and coupling profile of a linearly chirped fiber Bragg grating for maximum dispersion compensation in a repeaterless optical communication system. The system consists of 100 km of standard optical fiber in which a 1550-nm signal, directly modulated at 2.5 Gbits/s, is launched. We discuss the results obtained with 6-, 4.33-, and 1-cm-long linearly chirped fiber Bragg gratings having Gaussian and uniform coupling profiles. We numerically show that a 4.33-cm-long chirped fiber Bragg grating having a uniform coupling profile is capable of compensating efficiently for the dispersion of our optical communication system. PMID:19859284

Thibault, S; Lauzon, J; Cliche, J F; Martin, J; Duguay, M A; Têtu, M

1995-03-15

355

Generation of green frequency comb from chirped ?(2) nonlinear photonic crystals  

NASA Astrophysics Data System (ADS)

Spectrally broad frequency comb generation over 510-555 nm range was reported on chirped quasi-phase-matching (QPM) ?(2) nonlinear photonic crystals of 12 mm length with periodicity stepwise increased from 5.9 ?m to 7.1 ?m. When pumped with nanosecond infrared (IR) frequency comb derived from a QPM optical parametric oscillator (OPO) and spanned over 1040 nm to 1090 nm wavelength range, the 520 nm to 545 nm up-converted green spectra were shown to consist of contributions from (a) second-harmonic generation among the signal or the idler modes, and (b) sum-frequency generation (SFG) from the neighboring pairs of the signal or the idler modes. These mechanisms led the up-converted green frequency comb to have the same mode spacing of 450 GHz as that in the IR-OPO pump comb. As the pump was further detuned from the aforementioned near-degeneracy point and moved toward the signal (1020-1040 nm) and the idler (1090-1110 nm) spectral range, the above QPM parametric processes were preserved in the chirped QPM devices to support up-converted green generation in the 510-520 nm and the 545-555 nm spectral regime. Additional 530-535 nm green spectral generation was also observed due to concurrence of multi-wavelength SFG processes between the (signal, idler) mode pairs. These mechanisms facilitate the chirped QPM device to support a single-pass up-conversion efficiency ˜10% when subject to an IR-OPO pump comb with 200 mW average power operated near- or off- the degeneracy point.

Lai, C.-M.; Chang, K.-H.; Yang, Z.-Y.; Fu, S.-H.; Tsai, S.-T.; Hsu, C.-W.; Yu, N. E.; Boudrioua, A.; Kung, A. H.; Peng, L.-H.

2014-12-01

356

Using a surface-sensitive chemical probe and a bulk structure technique to monitor the ?- to ?-Al2O3 phase transformation  

SciTech Connect

In this work, we investigated the phase transformation of ? Al2O3 to ? Al2O3 by ethanol TPD and XRD. Ethanol TPD showed remarkable sensitivity toward the surface structures of the aluminas studied. Maximum desorption rates for the primary product of ethanol adsorption, ethylene, were observed at 225°C, 245°C and 320°C over ?-, ?-, and ?-Al2O3, respectively. Ethanol TPD over a ? Al2O3 sample calcined at 800 °C clearly show that the surface of the resulting material possesses ?-alumina characteristics, even though only the ?-alumina phase was detected by XRD. These results strongly suggest that the ?-to-? phase transformation of alumina initiates at oxide particle surfaces. The results obtained are also consistent with our previous finding that the presence of penta-coordinated Al3+ sites, formed on the (100) facets of the alumina surface, are strongly correlated with the thermal stability of ?-alumina.

Kwak, Ja Hun; Peden, Charles HF; Szanyi, Janos

2011-06-30

357

10-MHz, Yb-fiber chirped-pulse amplifier system with large-scale transmission gratings.  

PubMed

Large-scale transmission gratings were produced for a stretcher and a compressor in the Yb-fiber chirped-pulse amplification system. A 23-W, 200-fs laser system with a 10-MHz repetition rate was demonstrated. Focused intensity as high as 10(14) W/cm(2) was achieved, which is high enough for multi-photon processes such as high-order harmonics generation and multi-photon ionization of neutral atoms. High-order harmonics up to 7th order were observed using Xe gas as a nonlinear medium. PMID:23736505

Kobayashi, Yohei; Hirayama, Nozomi; Ozawa, Akira; Sukegawa, Takashi; Seki, Takashi; Kuramoto, Yoshiyuki; Watanabe, Shuntaro

2013-05-20

358

Design of a monolithic tunable laser based on equivalent-chirp grating reflectors.  

PubMed

A Vernier-tuned distributed Bragg reflector (DBR) semiconductor laser is an effective monolithic approach for wide wavelength tunability, at the expense, however, of costly electron-beam lithography during fabrication. In this Letter, a tunable laser design with equivalent-chirp based, flat-top envelope grating reflectors is proposed that can be implemented easily by conventional two-beam interference lithography. The principle is described, and a detailed design shows uniform output power (0.08 dB variation) and excellent side-mode suppression ratio (47 dB minimum) within a wide tuning range (>32 nm) through numerical simulation. PMID:21124552

Dai, Yitang; Xu, Kun; Wu, Jian; Li, Yan; Hong, Xiaobin; Guo, Hongxiang; Lin, Jintong

2010-12-01

359

High-energy noncollinear optical parametric-chirped pulse amplification in LBO at 800 nm.  

PubMed

The optical parametric-chirped pulse amplification (OPCPA) based on large-aperture nonlinear optical crystals is promising for implementation of an ultrahigh peak-power laser system of 10 PW and beyond. We demonstrated the highest energy broadband OPCPA at 800 nm, to the best of our knowledge, by using an 80 mm in diameter LiB(3)O(5)(LBO) amplifier, with an output energy of 28.68 J, a bandwidth of 80 nm (FWHM), and conversion efficiency of 25.38%. After compression, a peak power of 0.61 PW with 33.8 fs pulse duration is produced. PMID:24322145

Xu, Lu; Yu, Lianghong; Liang, Xiaoyan; Chu, Yuxi; Hu, Zhanggui; Ma, Lin; Xu, Yi; Wang, Cheng; Lu, Xiaoming; Lu, Haihe; Yue, Yinchao; Zhao, Ying; Fan, Feidi; Tu, Heng; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan

2013-11-15

360

Maximum-channel-number Investigation of Limiting-Amplified Multiwavelength Dispersion Compensator Incorporating Chirped Fiber Gratings  

NASA Astrophysics Data System (ADS)

We theoretically investigate the design of an optical limiting-amplified multiwavelength dispersion compensator (LDC) incorporating multiple chirped fiber gratings (CFGs) and a common bidirectional erbium-doped fiber (EDF) amplifier. The LDC provides simultaneous dispersion compensation and limiting amplification of multiple dense wavelength division multiplexing (DWDM) signals. The design criteria for multiwavelength LDC are to provide high constant channel output power and low interchannel differential power by optimization of the EDF length. The influence of the CFG’s rejection ratio on the LDC is addressed. The dynamic range and maximum channel number of the LDC are studied. The multiwavelength LDC may facilitate easier DWDM system design flexibility and network implementation.

Chen, Yung-Kuang; Liang, Tsair-Chun; Su, Jing-Hong; Tzeng, Sohn-Ling

2000-12-01

361

Power scaling of supercontinuum seeded megahertz-repetition rate optical parametric chirped pulse amplifiers.  

PubMed

Optical parametric chirped-pulse amplifiers with high average power are possible with novel high-power Yb:YAG amplifiers with kW-level output powers. We demonstrate a compact wavelength-tunable sub-30-fs amplifier with 11.4 W average power with 20.7% pump-to-signal conversion efficiency. For parametric amplification, a beta-barium borate crystal is pumped by a 140 W, 1 ps Yb:YAG InnoSlab amplifier at 3.25 MHz repetition rate. The broadband seed is generated via supercontinuum generation in a YAG crystal. PMID:24690803

Riedel, R; Stephanides, A; Prandolini, M J; Gronloh, B; Jungbluth, B; Mans, T; Tavella, F

2014-03-15

362

Degenerated optical parametric chirped-pulse amplification with cesium lithium borate  

NASA Astrophysics Data System (ADS)

A gain amplifier for degenerated optical parametric chirped-pulse amplification (OPCPA) with lithium triborate and cesium lithium borate (CLBO) crystals was demonstrated in a near-collinear configuration. The signal gain of the final energy amplifier with CLBO was ˜6. After compression, the 123 fs pulse duration was obtained. Compared with potassium dihydrogen phosphate, it is confirmed that CLBO is more effective as a nonlinear crystal in a final power amplifier for terawatt or petawatt OPCPA systems. To our knowledge, this is the first demonstration of OPCPA with CLBO.

Zhao, Baozhen; Liang, Xiaoyan; Leng, Yuxin; Jiang, Yongliang; Wang, Cheng; Lu, Haihe; Du, Juan; Xu, Zhizhan; Shen, Dezhong

2006-01-01

363

Degenerated optical parametric chirped-pulse amplification with cesium lithium borate.  

PubMed

A gain amplifier for degenerated optical parametric chirped-pulse amplification (OPCPA) with lithium triborate and cesium lithium borate (CLBO) crystals was demonstrated in a near-collinear configuration. The signal gain of the final energy amplifier with CLBO was approximately 6. After compression, the 123 fs pulse duration was obtained. Compared with potassium dihydrogen phosphate, it is confirmed that CLBO is more effective as a nonlinear crystal in a final power amplifier for terawatt or petawatt OPCPA systems. To our knowledge, this is the first demonstration of OPCPA with CLBO. PMID:16463743

Zhao, Baozhen; Liang, Xiaoyan; Leng, Yuxin; Jiang, Yongliang; Wang, Cheng; Lu, Haihe; Du, Juan; Xu, Zhizhan; Shen, Dezhong

2006-01-20

364

High-fidelity biexciton generation in quantum dots by chirped laser pulses  

NASA Astrophysics Data System (ADS)

We present a detailed theoretical analysis of biexciton state generation in InAs-GaAs quantum dots by strong, chirped laser pulses. Specifically, we derive an accurate analytical expression, which not only provides a clear physical picture of the process, but also allows identifications of laser parameter regimes where efficient biexciton generation should be possible, even at temperatures up to 80 K. The results are confirmed by numerical simulations, in very good agreement with the model proposed. A clear choice of parameters is proposed, which might pave the way towards the optimal design of high-fidelity sources of entangled photon pairs based on individual quantum dots.

Debnath, A.; Meier, C.; Chatel, B.; Amand, T.

2013-11-01

365

22??GW peak-power fiber chirped-pulse-amplification system.  

PubMed

In this Letter, we report on a femtosecond fiber chirped-pulse-amplification system based on the coherent combination of the output of four ytterbium-doped large-pitch fibers. Each single channel delivers a peak power of about 6.2 GW after compression. The combined system emits 200 fs long pulses with a pulse energy of 5.7 mJ at 230 W of average power together with an excellent beam quality. The resulting peak power is 22 GW, which to the best of our knowledge is the highest value directly emitted from any fiber-based laser system. PMID:25503019

Klenke, Arno; Hädrich, Steffen; Eidam, Tino; Rothhardt, Jan; Kienel, Marco; Demmler, Stefan; Gottschall, Thomas; Limpert, Jens; Tünnermann, Andreas

2014-12-15

366

Chirped laser dispersion spectroscopy using a directly modulated quantum cascade laser  

SciTech Connect

Chirped laser dispersion spectroscopy (CLaDS) utilizing direct modulation of a quantum cascade laser (QCL) is presented. By controlling the laser bias nearly single- and dual-sideband CLaDS operation can be realized in an extremely simplified optical setup with no external optical modulators. Capability of direct single-sideband modulation is a unique feature of QCLs that exhibit a low linewidth enhancement factor. The developed analytical model shows excellent agreement with the experimental, directly modulated CLaDS spectra. This method overcomes major technical limitations of mid-infrared CLaDS systems by allowing significantly higher modulation frequencies and eliminating optical fringes introduced by external modulators.

Hangauer, Andreas, E-mail: hangauer@princeton.edu; Nikodem, Michal; Wysocki, Gerard, E-mail: gwysocki@princeton.edu [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States)] [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States); Spinner, Georg [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States) [Electrical Engineering Department, Princeton University, Princeton, New Jersey 08544 (United States); Institute for Quantum Electronics, ETH Zurich, 8093 Zurich (Switzerland)

2013-11-04

367

Effects of Detuning on Control of Intersubband Quantum Well Transitions with Chirped Electromagnetic Pulses  

SciTech Connect

We study the interaction of a chirped electromagnetic pulse with intersubband transitions of a double semiconductor quantum well. We specifically consider the interaction of the ground and first excited subbands with the electromagnetic field and use the nonlinear density matrix equations for the description of the system dynamics. These equations are solved numerically for various values of the electron sheet density for a realistic double GaAs/AlGaAs quantum well, and the efficiency of population transfer is discussed with emphasis given to the effects of the detuning of the central frequency of the electromagnetic field from resonance.

Blekos, Konstantinos; Terzis, Andreas F. [Physics Department, School of Natural Sciences, University of Patras, Patras 265 04 (Greece); Simserides, Constantinos [Institute of Materials Science, National Center of Scientific Research Demokritos, 153 10 Athens (Greece); Paspalakis, Emmanuel [Materials Science Department, School of Natural Sciences, University of Patras, Patras 265 04 (Greece)

2010-11-10

368

Optical Parametric Chirped-Pulse-Amplification Contrast Enhancement by Regenerative Pump Spectral Filtering  

SciTech Connect

We demonstrate an approach to fundamentally improve the contrast of optical parametric chirped-pulse amplifiers (OPCPA). The instantaneous parametric gain couples the temporal variations of the pump-pulse intensity to spectral variations of the intensity of the stretched signal pulse being amplified, which significantly degrade the temporal contrast of the amplified pulse after recompression. Simple and efficient pump-intensity noise reduction in an OPCPA system using a volume Bragg grating in a regenerative amplifier demonstrates contrast improvements up to 30 dB.

Dorrer, C.; Okishev, A.V.; Begishev, I.A.; Zuegel, J.D.; Smirnov, V.I.; Glebov, L.B.

2007-08-17

369

Three pulse UV photon echo studies of molecules in solution: effect of the chirp.  

PubMed

We report on the electronic dephasing times of the nonpolar chromophore diphenylacetylene (DPA) in ethanol and in cyclohexane (polar and nonpolar solvents respectively) by photon echo measurements in the ultraviolet. Contrary to previous reports, we observed sub-100-fs electronic dephasing times for DPA in both solvents. We identify fast dynamics of tau=40+/-10 fs on the photon echo peak shift (PEPS) traces of DPA in ethanol. In addition, we observed a dependence of the PEPS asymptotic value on the temporal chirp of the pulses. We propose a model to describe it in terms of phase-matching condition and beam geometry. PMID:20707574

Oskouei, A Ajdarzadeh; Tortschanoff, A; Bräm, O; van Mourik, F; Cannizzo, A; Chergui, M

2010-08-14

370

Propagation of the chirped microwave pulse in the longdistance sliding-mode plasma waveguide in air  

NASA Astrophysics Data System (ADS)

Propagation of the phase-modulated microwave pulse in the sliding-mode plasma waveguide in air is considered. It is shown that with the proper choice of the chirp parameter the peak intensity of the microwave pulse can be significantly enhanced with respect to the non-phase-modulated pulse thus compensating the attenuation by the pulse compression. Calculations show that the microwave pulse peak intensity at the end of plasma waveguide can be made larger than the initial peak intensity, even for the plasma waveguides of a few kilometres length.

Bogatskaya, A. V.; Smetanin, I. V.; Zvorykin, V. D.; Levchenko, A. O.; Ustinovskii, N. N.

2014-12-01

371

Spatial Characterization of Strong Fiber Bragg Gratings Using Thermal Chirp and Optical-Frequency-Domain Reflectometry  

NASA Astrophysics Data System (ADS)

A method that can spatially characterize gratings with grating strength |k|L up to 10 is presented. The grating is thermally chirped, which increases the transmissivity through the grating. The complex reflectivity spectrum is measured using optical-frequency-domain reflectometry, and the spatial profile is reconstructed using the time-domain layer-peeling algorithm. The spatial profiles of a uniform grating with grating strength |k|L = 8.25 (-66-dB minimum transmissivity) and a distributed-feedback fiber laser grating with grating strength |k|L = 7.5 are accurately reconstructed from the measured complex reflection spectrum.

Waagaard, Ole Henrik

2005-02-01

372

Spectrum bandwidth narrowing of Thomson scattering X-rays with energy chirped electron beams from laser wakefield acceleration  

SciTech Connect

We study incoherent Thomson scattering between an ultrashort laser pulse and an electron beam accelerated from a laser wakefield. The energy chirp effects of the accelerated electron beam on the final radiation spectrum bandwidth are investigated. It is found that the scattered X-ray radiation has the minimum spectrum width and highest intensity as electrons are accelerated up to around the dephasing point. Furthermore, it is proposed that the electron acceleration process inside the wakefield can be studied by use of 90° Thomson scattering. The dephasing position and beam energy chirp can be deduced from the intensity and bandwidth of the scattered radiation.

Xu, Tong; Chen, Min, E-mail: minchen@sjtu.edu.cn; Li, Fei-Yu; Yu, Lu-Le [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China)] [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Sheng, Zheng-Ming, E-mail: zmsheng@sjtu.edu.cn [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China) [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Zhang, Jie [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China) [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190 (China)

2014-01-06

373

2-?m wavelength, high-energy Ho:YLF chirped-pulse amplifier for mid-infrared OPCPA.  

PubMed

A 2-?m wavelength laser delivering up to 39-mJ energy, ?10??ps duration pulses at 100-Hz repetition rate is reported. The system relies on chirped pulse amplification (CPA): a modelocked Er:Tm:Ho fiber-seeder is followed by a Ho:YLF-based regenerative amplifier and a cryogenically cooled Ho:YLF single pass amplifier. Stretching and compressing are performed with large aperture chirped volume Bragg gratings (CVBG). At a peak power of 3.3 GW, the stability was <1%??rms over 1 h, confirming high suitability for OPCPA and extreme nonlinear optics applications. PMID:25680122

Hemmer, M; Sánchez, D; Jelínek, M; Smirnov, Vadim; Jelinkova, H; Kube?ek, V; Biegert, J

2015-02-15

374

transformations: representations  

E-print Network

Overview 1. Number transformations: from one base to another 2. Integer representations 3. Real rate, caches... #12; ECS 50, Discussion on 4/25 2 Integer Transformation: From Decimal to Binary Let, Discussion on 4/25 3 Integer Transformation: From Binary to Decimal Compute the weight of each digit position

Nguyen, Dat H.

375

Transformation Composition  

E-print Network

Proc. AGTIVE'99, to appear in LNCS Graph Transformation Modules and their Composition ? Frank,knirsch,kreo,kuskeg@informatik.uni-bremen.de Abstract. In this paper, we investigate the notion of transformation modules as a structuring principle. Based on the notion of transformation units, a concept that allows to specify binary relations on graphs

Drewes, Frank

376

Multiple-order adaptive dispersion compensation using polynomially-chirped grating devices  

NASA Astrophysics Data System (ADS)

Devices such as the planar arrayed-waveguide grating or the distributed Bragg reflector (AWG and DBR, respectively) are assuming increasing importance in the areas of fibre point-to-point communication and networking. In the particular context of dense wavelength-division multiplexing (DWDM), these devices play a well-established role as wavelength-selective elements. More recently, chirped variants have found use as dispersion compensators, offering wideband reduction of both basic and higher-order departures from constant group delay. However, up to the present time, the existence of a systematic approach to higher-order dispersion compensation has not been recognised. Additionally, we have identified a comprehensive isomorphism between AWG and DBR devices that allows the design characteristics of the former transverse geometry to be mapped on to the latter longitudinal structure. Here, we present a systematic study of these important passive optical grating-based devices which considers, firstly, analytic solutions for 2nd-order dispersion compensation (DC), and then 3rd- and 4th-order dispersion compensators with 100 GHz bandwidth. We then review optimisation strategies for DC, 3 dB bandwidth, and passband dispersion ripple, as determined by device chirp, apodisation, coupling strength and polyphase transfer function superposition. We conclude with a preliminary discussion of grating parametric sensitivity as evidenced by Monte Carlo analysis.

Parker, M. C.; Walker, S. D.

2001-10-01

377

Investigation of Thermal Effects in High Average Power Chirped Pulse Amplifiers  

NASA Astrophysics Data System (ADS)

High average power ultrafast chirped pulse amplifiers [1] have important applications for high brightness extreme ultraviolet sources and x-ray sources and for applications in materials processing. We have developed a Ti:sapphire regenerative chirped pulse amplifier system capable of producing 5W of amplified output power at repetition rates that can be varied from 5-10 kHz. High pump powers (in excess of 50 W) are required to achieve amplification factors of 10^6 and higher, resulting in significant heating of the crystal and concomitant thermal effects, such as thermal lensing, and thermal birefringence. A detailed characterization of these detrimental thermal effects on the mode profile, optical spectrum, and will be discussed along with measures undertaken to improve the amplifier's overall performance, including cryogenic cooling of the Ti-sapphire crystal, finite element analysis of the heating, thermal compensation based on negative temperature derivatives of the index of refraction, and cavity stability analysis.[1] S. Backus, et.al., Opt. Lett. 26, 465 (2001).

Ramanathan, Vidya

2005-11-01

378

Power limitations and pulse distortions in an Yb : KGW chirped-pulse amplification laser system  

SciTech Connect

We have studied self-action effects (self-focusing and self-phase modulation) and stimulated Raman scattering in an Yb : KGW chirped-pulse amplification laser system. The results demonstrate that self-focusing in combination with thermal lensing may significantly limit the chirped pulse energy in this system (down to 200 ?J) even at a relatively long pulse duration (50 ps). Nonlinear lenses in the laser crystals in combination with thermal lenses bring the regenerative amplifier cavity in the laser system to the instability zone and limit the average output power at pulse repetition rates under 50 kHz. Self-phase modulation, a manifestation of self-action, may significantly distort a recompressed femtosecond pulse at energies near the self-focusing threshold. Stimulated Raman scattering in such a laser has a weaker effect on output parameters than do self-focusing and thermal lensing, and Raman spectra are only observed in the case of pulse energy instability. (nonlinear optical phenomena)

Kim, G H; Yang, J; Kulik, A V; Sall, E G; Chizhov, S A; Kang, U [KERI, Russia Science Seuol, 612, DMC, Hi-Tech Industry Center, 1580 Sangam-dong, Mapo-gu, 121-835 Seoul (Korea, Republic of); Yashin, V E [Federal State Unitary Enterprise ' Scientific and Industrial Corporation 'Vavilov State Optical Institute', St. Petersburg (Russian Federation)

2013-08-31

379

Transformation Station  

NSDL National Science Digital Library

Shapes are all over the place in geometry. One way we can move these shapes is with transformations. Use these games to help you practice and identify the three types of transformations: reflections, translations, and rotations. Just as a refresher, watch this video about transformational geometry: Gingerbread Transformer! When you are ready...start playing the games!! Take it to the court for Basketball Geometry! Once you type in your name and choose a player, pay attention to the coach for a review on the three types of transformations. While you play, ...

Mrs. Stroud

2010-09-01

380

Semi-analytic technique for analyzing mode-locked lasers  

SciTech Connect

A semi-analytic tool is developed for investigating pulse dynamics in mode-locked lasers. It provides a set of rate equations for pulse energy, width, and chirp, whose solutions predict how these pulse parameters evolve from one round trip to the next and how they approach their final steady-state values. An actively mode-locked laser is investigated using this technique and the results are in excellent agreement with numerical simulations and previous analytical studies.

Usechak, N.G.; Agrawal, G.P.

2005-03-21

381

On a Chirplet Transform Based Method for Co-channel Voice Separation  

NASA Astrophysics Data System (ADS)

We use signal and image theory based algorithms to produce estimations of the number of wolves emitting howls or barks in a given field recording as an individuals counting alternative to the traditional trace collecting methodologies. We proceed in two steps. Firstly, we clean and enhance the signal by using PDE based image processing algorithms applied to the signal spectrogram. Secondly, assuming that the wolves chorus may be modelled as an addition of nonlinear chirps, we use the quadratic energy distribution corresponding to the Chirplet Transform of the signal to produce estimates of the corresponding instantaneous frequencies, chirp-rates and amplitudes at each instant of the recording. We finally establish suitable criteria to decide how such estimates are connected in time.

Dugnol, B.; Fernández, C.; Galiano, G.; Velasco, J.

382

High-resolution X-ray diffractometry and X-ray reflectometry techniques for structural studies of complicated thin-layered heterostructures: Complementarity between Fourier Transform-based procedures and simulation softwares  

NASA Astrophysics Data System (ADS)

Both x-ray reflectometry and high-resolution x-ray diffractometry techniques are used for the assessment of individual layer thicknesses and interfacial profiles inside complicated heterostructures, such as semi-conductor multilayers. In particular, the use of Fourier transform-based numerical treatments applied to both the reflectivity curves and the high-resolution diffraction profiles allows a fast and precise determination of the individual layer thicknesses. Moreover, we show the potentiality of this method by reporting x-ray reflectometry and diffractometry studies on waveguides structures and superlattices. Typical layer thicknesses from 0.5 nm to more than 1 ?m are accessible with these methods. We show the complementarity of both x-ray reflectometry and high-resolution diffraction techniques. Finally, the reliability of using a simulation software for the assessment of complicated interfacial roughness, such as segregation profiles, is reported. Key wordx-ray reflectometry, high-resolution x-ray diffractometry, semi-conductor heterostructures, thickness determination, Fourier Transform, interfacial segregation profiles.

Durand, O.; de Rossi, A.; Bouchier, A.

2004-11-01

383

Application of the newly constructed Chirp raw data recording system for shallow gas in the Korea Strait shelf mud off SE Korea  

NASA Astrophysics Data System (ADS)

Chirp is a marine high-resolution sub-bottom profiling system applied in a variety of marine geological and geophysical fields. Chirp source systems generate the sweep pulse with a frequency modulation of 2 - 7 kHz bandwidth. Commercial Chirp data acquisition systems provide the seismic data of the envelope type without polarity and phase information after real-time processing. To record the raw data preserving the polarity and phase information, we constructed the new data acquisition system and acquired the field data in the southeastern coast of Korea using the newly constructed system and the conventional Chirp system simultaneously. The survey data contains the acoustic blanking caused by shallow gas and the feature of rough seafloor in KSSM(Korea Strait shelf mud) off SE Korea. We performed the correlation of raw seismic data with the estimated sweep signature, deconvolution, swell effect correction and migration to compare the resolution of Chirp SBP sections and to enhance the features associated with shallow gas. When we compare Chirp SBP section preserving polarity and phase information with the conventional envelope section, the new section shows better continuity of the sedimentary layers and higher resolution than conventional section. Through the thorough examination of the Chirp sections after the data processing, a possible gas related acoustic anomaly was found at the rough seafloor and underlying sediments. The low P-wave velocity was identified among the physical properties measured from a piston core recovered at the survey area.

Kim, Young-Jun; Koo, Nam-Hyung; Chun, Jong-Hwa; Shin, Sung-Ryul; Cheong, Snons; Kim, Jeong-Ki; Lee, Ho-Young

2014-05-01

384

PUBLISHED ONLINE: 19 DECEMBER 2010 | DOI: 10.1038/NPHYS1867 Quantum fluctuations in the chirped pendulum  

E-print Network

in the chirped pendulum K. W. Murch1 *, R. Vijay1 , I. Barth2 , O. Naaman1 , J. Aumentado3 , L. Friedland2 and I. Siddiqi1 Anharmonic oscillators, such as the pendulum, are widely used for precision measurement1 is the electron charge. This system is analogous to a mechanical pendulum with angular coordinate = (Fig. 1a

Loss, Daniel

385

Characterization of integrated polarization-diversity DPSK demodulator with two-dimensional chirped grating couplers and ring resonators  

Microsoft Academic Search

We describe the design and experimental results of an integrated polarization-diversity DPSK demodulator. The integration of 2-D chirped grating couplers enabled polarization-diversity operation with two micro-ring resonators which converted the phase modulation to intensity modulation.

Xia Chen; Chao Li; Ying Gao; Lin Xu; Hon Ki Tsang; Chester Shu

2010-01-01

386

Coherent Control of Population Transfer in Rydberg Atoms via Chirped Microwave Pulses Juan J. Carrera, and Shih-I Chu*,,  

E-print Network

Coherent Control of Population Transfer in Rydberg Atoms via Chirped Microwave Pulses Juan J. It is shown that the coherent control of the population transfer from the high n to the low n states can nonperturbative investigation of the coherent population transfer among the 3D high-lying Rydberg hydrogen

Chu, Shih-I

387

Chirping a two-photon transition in a multistate ladder RID C-2713-2008 RID A-7617-2010  

E-print Network

Chirping a two-photon transition in a multistate ladder Wolfgang Merkel, Holger Mack, and Wolfgang P. Schleich* Institut f?r Quantenphysik, Universit?t Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany Eric Lutz Department of Physics...

Merkel, Wolfgang; Mack, Holger; Schleich, Wolfgang P.; Lutz, Eric; Paulus, Gerhard G.; Girard, Bertrand

2007-01-01

388

Isolated sub-30-attosecond pulse generation using a multicycle two-color chirped laser and a static electric field  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of high-order harmonic generation in a chirped two-color laser field, which is synthesized by a 10-fs/800-nm fundamental chirped pulse and a 10-fs/1760-nm subharmonic pulse. It is shown that a supercontinuum can be produced using the multicycle two-color chirped field. However, the supercontinuum reveals a strong modulation structure, which is not good for the generation of an isolated attosecond pulse. By adding a static electric field to the multicycle two-color chirped field, not only the harmonic cutoff is extended remarkably, but also the quantum paths of the high-order harmonic generation (HHG) are modified significantly. As a result, both the extension of the supercontinuum and the selection of a single quantum path are achieved, producing an isolated 23-as pulse with a bandwidth of about 170.6 eV. Furthermore, the influences of the laser intensities on the supercontinuum and isolated attosecond pulse generation are investigated.

Zhang, Gang-Tai

2014-04-01

389

Electronic tuning of delay lines based on chirped fiber gratings for phased arrays powered by a single optical carrier  

NASA Astrophysics Data System (ADS)

We propose a variable delay line for phased arrays antennas based on a chirped fiber grating. The line operates with an optical carrier at constant wavelength and the time delay of the radiofrequency modulating signal is modified stretching the grating with a piezoelectric translator, the grating response can be tuned at a speed of 0.68 nm/ms.

Pérez-Millán, P.; Torres-Peiró, S.; Mora, J.; Díez, A.; Cruz, Jose Luis; Andrés, M. V.

2004-08-01

390

High-contrast 1.16 PW Ti:sapphire laser system combined with a doubled chirped-pulse amplification  

E-print Network

High-contrast 1.16 PW Ti:sapphire laser system combined with a doubled chirped-pulse amplification]. The first peta- watt (PW) laser was based on a hybrid Ti:sapphire­ Nd:glass laser system [3]. Since then have been devel- oped, with Ti:sapphire as the gain medium, to offer the benefits of compact size

Wang, Wei Hua

391

High-Beam-Quality Optical Parametric Chirped-Pulse Amplification in Periodically-Poled KTiOPO4  

SciTech Connect

We have demonstrated a high-gain optical parametric chirped-pulse amplifier for Nd:glass-based short-pulse laser systems based on periodically poled potassium-titanyl-phosphate. Our amplifier produced high single-pass gain, broad bandwidth, excellent beam quality and stability.

Ebbers, C A; Schmidt, J R; Jovanovic, I

2003-09-25

392

Novel Applications of Chirp Managed Laser in Optical Fiber Communication Systems  

NASA Astrophysics Data System (ADS)

Nowadays, with the dramatically growing bandwidth requirement of Internet, the number of wavelength division multiplexing (WDM) channels of the optical fiber communication systems is increasing rapidly. Hence, optical transmitters with cost effectiveness, high power efficiency, and excellent transmission performance are necessary. Especially, for access and metropolitan applications, simple configuration is the essential factor. The conventional optical transmitter is composed of a laser as continuous-wave (CW) source and one or more external modulators for modulation. However, the high insertion loss, large driving voltage, and extra cost of external modulator make it relatively bulky and power-hungry. Chirp managed laser (CML), comprising a directly modulated semiconductor laser (DML) and a passive optical filter, is an alternative promising transmitter candidate. It has the merits of smaller device size, lower cost, less power consumption, and higher fiber chromatic dispersion (CD) tolerance, compared with that based on external modulator. In this thesis, we have investigated several novel applications of CML in optical fiber communication systems, taking advantage of its unique phase modulating and spectral reshaping properties. These topics include optical return-to-zero (RZ) pulses generation using CML, M-ary RZ differential phase-shift-keying (RZ-DPSK) signals generation using CML, and enhanced CD tolerance of CML with pre-emphasis. These CML-based designs consume low power for less electrical pre-coding, require reduced or no external modulator, and show notable transmission performances. Optical RZ pulses generation using CML: RZ pulses have been widely used in optical fiber communication systems together with on-off-keying (OOK) and DPSK modulation formats, for its high robustness towards inter symbol interference (ISI) and nonlinear distortions. In this thesis, we propose and experimentally demonstrate the technique of 10-Gb/s optical RZ pulses generation using CML. No external modulator is used for pulse carving. The frequency of the sinusoidal driving signal is half the output RZ pulse rate. 70-km and 50-km error-free SSMF transmissions have been achieved for the 10-Gb/s 33%-duty-cycle and 67%-duty-cycle CML-RZ- pulses based RZ-DPSK signals, respectively. Later, we extend to demonstrate the scheme of 20-Gb/s RZ pulses generation using CML driven at one-fourth the output pulse rate and investigate the transmission performance of the 20-Gb/s CML-RZ-pulses based RZ-OOK signal. M-ary RZ-DPSK signals generation using CML: M-ary RZ-DPSK is an attractive modulation format in optical fiber long-haul transmission systems, due to the advantages of high receiver sensitivity, increased spectral efficiency, and strong robustness against fiber nonlinearities. In this thesis, we propose and experimentally demonstrate the techniques of RZ-DPSK, ¾-RZ-DQPSK, and RZ-DQPSK signals generation using CML. First, we generate the 10-Gb/s RZ-DPSK signal using CML and pulse carver. It does not require any differential encoder or phase modulator (PM). The CML-based RZ-DPSK signal shows 3-dB higher receiver sensitivity after 70-km SSMF transmission without dispersion compensation and comparable nonlinear tolerance performance, compared with that generated by PM. Next, this proposal is generalized to generate the 10-Gbaud RZ-DQPSK signal using CML and pulse carver. Compared with the complex pre-coding required for the MZM-based RZ-DQPSK transmitter, only a simple exclusive-or (XOR) encoder is needed for that based on CML. Later, we demonstrate the scheme of 10-Gbaud ¾-RZ-DQPSK signal generation using single CML, without the need for external pulse carver. In this new signal format, the symbols with a differential phase shift of 0 remain non-return-to-zero (NRZ), while those with differential phase shifts of 0.5pi, pi, and 1.5pi are RZ. Error-free transmission is realized over 60-km SSMF without optical signal-noise-ratio (OSNR) penalty. Finally, we demonstrate the technique of 10.709-Gbaud RZ-DQPSK signal generation using single CML, w

Jia, Wei

393

Noncollinear Second-Harmonic Generation with Compensation of Phase Mismatch by Controlling Frequency Chirp and Tilted Pulse Fronts of Femtosecond Laser Pulses  

NASA Astrophysics Data System (ADS)

In order to achieve the efficient second-harmonic generation with femtosecond laser pulses, we studied a noncollinear second-harmonic generation with tilted pulse fronts and a suitableproper frequency chirp of fundamental pulses. We discussed the compensation of a phase-mismatch by controlling thea frequency chirp of fundamental pulses and an improvement of thea energy conversion efficiency usingwith our method. When the energy conversion efficiency was less than 0.4% under a phase-mismatch condition, we experimentally obtained a 30% energy conversion efficiency with a proper frequency chirp of fundamental pulses.

Aoyama, Makoto; Zhang, Tiejun; Tsukakoshi, Motowo; Yamakawa, Koichi

2000-06-01

394

Animating Transformations  

NSDL National Science Digital Library

In most introductory linear algebra courses, prominent applications of transformations or mappings are moving (rotating, reflecting, translating), resizing (contracting, expanding), changing the shape (shearing, projecting) objects in the plane. A typical problem in such courses is to write the matrix of a transformation that changes points in such prescribed ways. The goal of this demo is to help students more easily visualize such transformations on a wide class of plane objects.

Roberts, Lila F.

2003-01-24

395

Acceleration of proton bunches by petawatt chirped radially-polarized laser pulses  

NASA Astrophysics Data System (ADS)

Results from theoretical investigations will be presented which show that protons can be accelerated from rest to a few hundred MeV by a 1 PW chirped radially-polarized laser pulse of several hundred femtosecond duration and focused to a waist radius comparable to the radiation wavelength. Single-particle calculations are supported by many-particle and particle-in-cell simulations. Compared with laser acceleration by a similar linearly-polarized pulse, the gained energies are less, but have better beam quality. For a suitable initial phase, a particle bunch gets accelerated by the axial component Ez of the laser pulse and, initially focused by the transverse electric field component Er. Beam diffraction finally sets in due to the particle-particle Coulomb repulsion, after interaction with the pulse ceases to exist.

Salamin, Yousef; Galow, Benjamin; Li, Jian-Xing; Keitel, Christoph

2012-06-01

396

Acceleration of proton bunches by petawatt chirped radially polarized laser pulses  

NASA Astrophysics Data System (ADS)

Results from theoretical investigations are presented which show that protons can be accelerated from rest to a few hundred MeV by a 1-PW chirped radially polarized laser pulse of several hundred femtosecond duration and focused to a waist radius comparable to the radiation wavelength. Single-particle calculations are supported by many-particle and particle-in-cell simulations. Compared with laser acceleration by a similar linearly polarized pulse, the gained energies are less, but have better beam quality. For a suitable initial phase, a particle bunch gets accelerated by the axial component Ez of the laser pulse and, initially focused by the transverse electric field component Er. Beam diffraction finally sets in due to the particle-particle Coulomb repulsion, after interaction with the pulse ceases to exist.

Li, Jian-Xing; Salamin, Yousef I.; Galow, Benjamin J.; Keitel, Christoph H.

2012-06-01

397

The Effective CSR Forces on an Energy-Chirped Bunch under Magnetic Compression  

SciTech Connect

Following our earlier formulation of the coherent synchrotron radiation (CSR) effect on bunch dynamics in magnetic bends, here we investigate the behavior of the effective CSR forces for an energy-chirped Gaussian bunch in the bending plane around full compression, with special care being taken in the incorporation of the retardation relation. Our results show clearly a delayed response of the CSR forces to the compression or lengthening of the bunch length. In addition, around full compression, our results reveal sensitivity of the effective CSR forces on the particles' transverse position, as a consequence of the geometry of particle interaction and retardation in this regime. These results can serve as benchmarks to the numerical simulation of the CSR effects.

Rui Li

2007-06-25

398

Effects of Chirped Laser Pulses on Nonclassical Correlation and Entanglement of Photon Pairs from Single Atom  

E-print Network

We study the effects of arbitrary laser pulse excitations on quantum correlation, entanglement and the role of quantum noise. The transient quantities are computed exactly using a method that provides exact solutions of the Langevin field operators for photon pairs produced by a double Raman atom driven by laser pulses. Short pulses with appropriate chirping, delay and/or detuning can generate broadband photon pairs and yield results that provide insights on how to generate very large nonclassical correlation. We find that short pulses are not favorable for entanglement. The quantity was previously found to be phase-sensitive and this is used with the pulse area concept to explain the rapid variations of entanglement with pulse width and strength. Photon correlation and entanglement are favored by exclusively two different initial conditions. Analysis reinforces our understanding of the two nonclassical concepts.

C. H. Raymond Ooi

2008-03-15

399

All-fiber chirped pulse amplification using highly-dispersive air-core photonic bandgap fiber.  

PubMed

We show, for the first time to our knowledge, all-fiber chirped pulse amplification using an air-core photonic bandgap fiber. Pulses from a wavelength- and duration-tunable femtosecond/picosecond source at 10 GHz were dispersed in 100 m of dispersion compensating fiber before being amplified in an erbium-doped fiber amplifier and subsequently recompressed in 10 m of the anomalously dispersive photonic bandgap fiber. Pulses as short as 1.1 ps were obtained. As air-core fibers present negligible nonlinearity, the presented configuration can potentially be used to obtain ultra-high pulse peak powers. A study of the air-core fiber dispersion and dispersion slope is also presented. PMID:19471402

de Matos, C; Taylor, J; Hansen, T; Hansen, K; Broeng, J

2003-11-01

400

Chirp-free optical return-to-zero modulation based on a single microring resonator.  

PubMed

This paper proposes a chirp-free optical return-to-zero (RZ) modulator using a double coupled microring resonator. Optical RZ modulation is achieved by applying a clock (CLK) driving signal to the input coupling region and a non-return-to-zero (NRZ) driving signal to the output coupling region. Static and time-domain coupled-mode theory (CMT) based dynamic analyse are performed to theoretically investigate its performance in RZ modulation. The criteria to realize RZ modulation are deduced. Various RZ modulation formats, including RZ phase-shift-keying (RZ-PSK), carrier-suppressed RZ (CSRZ), and RZ intensity modulation formats, can be implemented by using CLK and NRZ signals with different combinations of polarities. Numerical simulations are performed and the feasibility of our modulator at 10 Gbit/s for the multiple RZ modulation formats is verified. PMID:22453445

Sun, Lili; Ye, Tong; Wang, Xiaowen; Zhou, Linjie; Chen, Jianping

2012-03-26

401

Deep-ultraviolet picosecond flat-top pulses by chirp-matched sum frequency generation.  

PubMed

Picosecond, flat-top, deep-UV pulses are needed to generate high-brightness electron beams to efficiently drive x-ray free electron lasers. Current metal photocathodes have low efficiency and therefore require high-energy pulses, and the generation of high-energy, flat-top pulses in the deep UV is still challenging. The low efficiencies of both the harmonic generation and deep-UV pulse shapers restrict the accessible pulse energy. Moreover, the acceptance bandwidth of the harmonic generation limits the minimum rise time of the flat-top profile. We present the generation of few-hundred microjoule, picosecond, deep-UV pulses using chirp-matched sum frequency generation. This scheme combined with IR spectral manipulation is a novel approach for deep-UV pulse shaping. It permits flat-top pulses with high energy and fast rise time, highly suited for high-brightness photoelectron beam production. PMID:22627515

Vicario, C; Trisorio, A; Arisholm, G; Hauri, C P

2012-05-15

402

Thermal properties of borate crystals for high power optical parametric chirped-pulse amplification.  

PubMed

The potential of borate crystals, BBO, LBO and BiBO, for high average power scaling of optical parametric chirped-pulse amplifiers is investigated. Up-to-date measurements of the absorption coefficients at 515 nm and the thermal conductivities are presented. The measured absorption coefficients are a factor of 10-100 lower than reported by the literature for BBO and LBO. For BBO, a large variation of the absorption coefficients was found between crystals from different manufacturers. The linear and nonlinear absorption coefficients at 515 nm as well as thermal conductivities were determined for the first time for BiBO. Further, different crystal cooling methods are presented. In addition, the limits to power scaling of OPCPAs are discussed. PMID:25089381

Riedel, R; Rothhardt, J; Beil, K; Gronloh, B; Klenke, A; Höppner, H; Schulz, M; Teubner, U; Kränkel, C; Limpert, J; Tünnermann, A; Prandolini, M J; Tavella, F

2014-07-28

403

Second Stokes component generation in the SRS of chirped laser pulses  

SciTech Connect

An experimental investigation was made of optical schemes for the generation of the second Stokes component in the SRS of broadband chirped laser pulses in high-pressure gases. Measurements were made of the energy conversion efficiency and the spatial characteristics of the light beam of the second Stokes component for one- and two-fold focusing of the pump radiation into the gas-filled cell as well as in schemes involving a quartz capillary and two gas-filled cells. The highest energy efficiency of conversion to the second Stokes component was attained in the case of cascade generation in the optical scheme with two pressurised-gas cells. In the SRS in hydrogen in this scheme, the Ti:sapphire laser radiation with a wavelength of 0.79 {mu}m was converted to the 2.3-{mu}m second Stokes component with an efficiency of 8.5%. (nonlinear-optics phenomena)

Konyashchenko, Aleksandr V; Losev, Leonid L; Tenyakov, S Yu

2011-05-31

404

Millijoule pulse energy high repetition rate femtosecond fiber chirped-pulse amplification system.  

PubMed

We report on an ytterbium-doped fiber chirped-pulse amplification (CPA) system delivering millijoule level pulse energy at repetition rates above 100 kHz corresponding to an average power of more than 100 W. The compressed pulses are as short as 800 fs. As the main amplifier, an 80 microm core diameter short length photonic crystal fiber is employed, which allows the generation of pulse energies up to 1.45 mJ with a B-integral as low as 7 at a stretched pulse duration of 2 ns. A stretcher-compressor unit consisting of dielectric diffraction gratings is capable of handling the average power without beam and pulse quality distortions. To our knowledge, we present the highest pulse energy ever extracted from fiber based femtosecond laser systems, and a nearly 2 orders of magnitude higher repetition rate than in previously published millijoule-level fiber CPA systems. PMID:18087520

Röser, F; Eidam, T; Rothhardt, J; Schmidt, O; Schimpf, D N; Limpert, J; Tünnermann, A

2007-12-15

405

Thermally switchable and discretely tunable comb filter with a linearly chirped fiber Bragg grating  

NASA Astrophysics Data System (ADS)

We propose and experimentally demonstrate a novel switchable and discretely tunable comb filter based on a thermally induced linearly chirped fiber Bragg grating. Experimentally we achieved a thermally induced optical bandpass filter that has eight switchable passband peaks with peak separations of 1.6 and 3.2 nm, a very narrow bandwidth (as small as 10 pm) of each peak, a tunable range of 16.5 nm, and a greater than 25 dB rejection ratio. Two spectral peaks separated by only 0.8 nm were also obtained with this comb filter. This filter provides the unique advantages of an all-fiber structure, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, low polarization sensitivity, simple structure, ease of fabrication, and low cost.

Ngo, N. Q.; Liu, D.; Tjin, S. C.; Dong, Xinyong; Shum, Ping

2005-11-01

406

All-fiber format compression of frequency chirped pulses in air-guiding photonic crystal fibers.  

PubMed

Air-cored, photonic band-gap crystal fibers exhibiting low nonlinearity and anomalous chromatic dispersion in spectral ranges inaccessible to conventional fibers can be used in the realization of all-fiber-format pulse compressors with unprecedented peak powers and wavelength diversity. Linear compression of inherently chirped and prestretched pulses by factors ranging from 20 to 80 around 1.0 and 1.5 microm have allowed generation of pulses as short as 163 fs. The results show that totally integrated femtosecond fiber laser sources can be realized throughout the visible and near-infrared and point to the possibility of megawatt peak and tens of watt average in-fiber power levels. PMID:15447403

de Matos, C J S; Popov, S V; Rulkov, A B; Taylor, J R; Broeng, J; Hansen, T P; Gapontsev, V P

2004-09-01

407

Transformation Telepresence  

E-print Network

of enterprise video collaboration necessary to support business goals. By showing the key business pain points and most effective strategies for integrating video, this report will show end users how telepresence can be used to transform organizations. Why Does Your Business Need to Transform? Traditionally, organizations

Fisher, Kathleen

408

Chirped AM ladar for anti-ship missile tracking and force protection 3D imaging: update  

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 line-of-sight velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a chirped amplitude modulation ladar to provide range and velocity measurements for tracking of targets handed over to it by the distributed aperture system IRST (DAS-IRST) under development at the Naval Research Laboratory (NRL) under Office of Naval Research (ONR) sponsorship. By using an array receiver based on Intevac Inc.'s Electron Bombarded Active Pixel Sensor (EBAPS) operating near 1.5 ?m wavelength, ARL's ladar also provides 3D imagery of potential threats in support of the force protection mission. In Phase I, ARL designed and built a breadboard ladar system for proof-of-principle static platform field tests. In Phase II, ARL is improving the ladar system to process and display 3D imagery and range-Doppler plots in near real-time, to re-register frames in near real-time to compensate for platform and target lateral motions during data acquisition, and to operate with better quality EBAPS tubes with higher quantum efficiency and better response spatial uniformity. The chirped AM ladar theory, breadboard design, performance model results, and initial breadboard preliminary test results were presented last year at this conference. This paper presents the results of tests at the Navy's Chesapeake Bay Detachment facility. The improvements to the ladar breadboard since last year are also presented.

Redman, Brian C.; Stann, Barry; Lawler, William; Giza, Mark; Dammann, John; Ruff, William; Potter, William; Driggers, Ronald G.; Garcia, Jose; Wilson, John; Krapels, Keith

2006-05-01

409

Transformation 1 - Plant Tissue Culture  

NSDL National Science Digital Library

This lesson explains the technique of tissue culture as used in plant transformation. It discusses important issues, such as the use of selectable markers, genotype specificity, and tissue culture alternatives.

410

The Fast Lifting Wavelet Transform  

NSDL National Science Digital Library

A tutorial on wavelet filters aimed at engineers. Focusses on "lifting," a technique for creating a general framework to design filters for every possible wavelet transform. May be read online or downloaded in PostScript format.

Valens, C.

411

Target Image Enhancement in Radar Imaging Using Fractional Fourier Transform  

NASA Astrophysics Data System (ADS)

This paper presents a new Range-Doppler Algorithm based on Fractional Fourier Transform (RDA-FrFT) to obtain High-Resolution (HR) images for targets in radar imaging. The performance of the proposed RDA-FrFT is compared with the classical RDA algorithm, which is based on the Fast Fourier Transform (FFT). A closed-form expression for the range and azimuth compression of the proposed RDA-FrFT is mathematically derived and analyzed from the HR Synthetic Aperture Radar (SAR) imaging point of view. The proposed RDA-FrFT takes its advantage of the property of the FrFT to resolve chirp signals with high precision. Results show that the proposed RDA-FrFT gives low Peak Side-Lobe (PSL) and Integrated Side-Lobe (ISL) levels in range and azimuth directions for detected targets. HR images are obtained using the proposed RDA-FrFT algorithm.

El-Mashed, M. G.; Dessouky, M. I.; El-Kordy, M.; Zahran, O.; Abd El-Samie, F. E.

2012-03-01

412

A Comparison of FTNMR and FTIR Techniques.  

ERIC Educational Resources Information Center

Nuclear magnetic resonance and infrared are two spectroscopic methods that commonly use the Fourier transform technique. Discussed are the similarities and differences in the use of the Fourier transform in these two spectroscopic techniques. (CW)

Ahn, Myong-Ku

1989-01-01

413

Application of the newly constructed Chirp SBP recording system for raw data with phase information for the study of shallow gas in Korea Strait shelf mud  

NASA Astrophysics Data System (ADS)

Chirp SBP(Sub-Bottom Profiler) is a marine high-resolution seismic system applied in a variety of marine geological and geophysical fields. The conventional Chirp SBP system records the positive envelope signal after real-time processing. To record the raw data preserving the polarity and phase information, we constructed the new data acquisition system, and acquired the field data in the southeastern coast of Korea using the new constructed system and the conventional Chirp SBP system simultaneously. Acoustic anomalies associated with shallow gas have been reported in KSSM(Korea Strait shelf mud) off SE Korea. We performed the correlation of raw seismic data with the estimated sweep signature, swell effect correction and deconvolution to compare the resolution of Chirp SBP sections and to enhance the features associated with shallow gas. When we compare Chirp SBP section preserving polarity and phase information with the conventional envelope section, the new section shows better continuity of the sedimentary layers and higher resolution than conventional section. A possible gas related acoustic anomaly was found on the Chirp SBP section and the piston core and KISOS(KIGAM Seafloor Observation System) data were acquired for the detailed analysis.

Kim, Y.; Koo, N.; Chun, J.; Shin, S.; Cheong, S.; Kim, J.

2013-12-01

414

Transformative copy  

E-print Network

The ability to create an unlimited number of identical copies is a privilege of digital documents. What if that would not be the case, if each copy of a digital file would go along with some sort of transformation? This ...

Offenhuber, Dietmar

2008-01-01

415

Transformation Golf  

NSDL National Science Digital Library

In this game students use the isometric transformations (sliding, flipping and turning) to sink a golf ball into a cup. There are nine holes in the course and learners are challenged to meet or break a par score.

2011-01-01

416

Covariant Transform  

NASA Astrophysics Data System (ADS)

Dedicated to the memory of Cora Sadosky The paper develops theory of covariant transform, which is inspired by the wavelet construction. It was observed that many interesting types of wavelets (or coherent states) arise from group representations which are not square integrable or vacuum vectors which are not admissible. Covariant transform extends an applicability of the popular wavelets construction to classic examples like the Hardy space H2, Banach spaces, covariant functional calculus and many others.

Kisil, Vladimir V.

2011-03-01

417

Maize Transformation  

Microsoft Academic Search

Plant genetic transformation technologies have brought fundamental changes to both plant biology laboratory research as well\\u000a as to modern agricultural field practices. Once a recalcitrant plant for tissue culture and gene delivery, maize is becoming\\u000a one of the most targeted cereal crops using genetic transformation for both basic and applied purposes. This chapter provides\\u000a a brief review of the history

Kan Wang; Bronwyn Frame; Yuji Ishida; Toshihiko Komari

418

New Waveform Analysis Method: the Chirplet Transform. Characterisation of the Induced-Seismicity From the Lacq gas Field (Western Pyrenees, France).  

NASA Astrophysics Data System (ADS)

Whole waveform records of waves radiated by induced-seismic events contain considerable information on event location, propagation medium, failure type, source size, and state of stress. Modern seismological studies of induced-seismicity related with hydrocarbons exploitation or storage benefit from time-frequency (TF) analysis techniques such as the windowed Fourier transform or the wavelet transform. These TF representations with fixed windows or kernels perform well only for limited classes of seismograms. Representations with signal-dependent kernels can overcome this limitation. A new five-parameter atomic decomposition of chirplets is developed for compact and precise representation of seismograms with chirp components. The five-parameter chirplet atom is obtained from the unit Gaussian function by successive applications of scaling, fractional Fourier transform, time-shift and frequency-shift operators of various duration. So, the chirplet transform unifies many of the disparate signal representation methods. In particular, the wide-range of TF methods such as the Fourier transform, spectrogram, Wigner distribution, and wavelet transform may each be shown to be a special case of the chirplet transform. We developed a methodology that recognizes the attributes of the waveforms of each seismic events. We first present and illustrate on synthetic examples this new formalism. Next, we illustrate its potentialities on seismograms recorded by 17 seismometers (Mark-Product L-4C - 12 bits) during the monitoring period (1974-1997) of the Lacq gas field (Western Pyrenees, France). Using the chirplet transform, each wave packet of the seismogram (mostly single component, sampling frequency = 150 Hz, duration = 15 s) is decomposed in terms of energy, arrival time, frequency, duration, shape (time-shear) and frequency modulation (frequency-shear). Thus, selected seismograms (N ˜ 5500 for 592 well-localized events) are described by a set of sextuplets which provide compact and precise representation of its inner structure, and form the basis for a classification of the seismic traces in the TF plane. Results obtained in terms of trace characterization and event parameter (date, location, magnitude, focal mechanism) are compared with the documented history of the reservoir (exploitation, fluid-injection, pressure, permeabilities and porosities maps, ...). Together, they allow to investigate earthquake induction and geomechanics processes at this site.

Bardainne, T.; Gaillot, P.; Senechal, G.

2004-12-01

419

High-power quantum-dot tapered tunable external-cavity lasers based on chirped and unchirped structures.  

PubMed

A high-power tunable external cavity laser configuration with a tapered quantum-dot semiconductor optical amplifier at its core is presented, enabling a record output power for a broadly tunable semiconductor laser source in the 1.2 - 1.3 µm spectral region. Two distinct optical amplifiers are investigated, using either chirped or unchirped quantum-dot structures, and their merits are compared, considering the combination of tunability and high output power generation. At 1230 nm, the chirped quantum-dot laser achieved a maximum power of 0.62 W and demonstrated nearly 100-nm tunability. The unchirped laser enabled a tunability range of 32 nm and at 1254 nm generated a maximum power of 0.97 W, representing a 22-fold increase in output power compared with similar narrow-ridge external-cavity lasers at the same current density. PMID:25321756

Haggett, Stephanie; Krakowski, Michel; Montrosset, Ivo; Cataluna, Maria Ana

2014-09-22

420

Ultraviolet-enhanced supercontinuum generation in uniform photonic crystal fiber pumped by a giant-chirped fiber laser.  

PubMed

We report on an ultraviolet-enhanced supercontinuum generation in a uniform photonic crystal fiber pumped by a giant-chirped mode-locked Yb-doped fiber laser. We find theoretically and experimentally that the initial pluses with giant chirp leads more initial energy transferred to the dispersive waves in visible and ultraviolet wavelength. An extremely wide optical spectrum spanning from 370 nm to beyond 2400 nm with a broad 3 dB spectral bandwidth of 367 nm (from 431 nm to 798 nm) is obtained. Over 36% (350 mW) of the total output power locates in the visible and ultraviolet regime between 370 nm and 850 nm with a maximum spectral power density of 1.6 mW/nm at 550 nm. PMID:25322044

Gao, Shoufei; Wang, Yingying; Sun, Ruoyu; Li, Huihui; Tian, Cuiping; Jin, Dongchen; Wang, Pu

2014-10-01

421

Narrow-bandwidth tunable picosecond pulses in the visible produced by noncollinear optical parametric amplification with a chirped blue pump.  

PubMed

Narrow-bandwidth (approximately 27 cm(-1)) tunable picosecond pulses from 480 nm-780 nm were generated from the output of a 1 kHz femtosecond titanium:sapphire laser system using a type I noncollinear optical parametric amplifier (NOPA) with chirped second-harmonic generation (SHG) pumping. Unlike a femtosecond NOPA, this system utilizes a broadband pump beam, the chirped 400 nm SHG of the Ti:sapphire fundamental, to amplify a monochromatic signal beam (spectrally-filtered output of a type II collinear OPA). Optimum geometric conditions for simultaneous phase- and group-velocity matching were calculated in the visible spectrum. This design is an efficient and simple method for generating tunable visible picosecond pulses that are synchronized to the femtosecond pulses. PMID:20357874

Co, Dick T; Lockard, Jenny V; McCamant, David W; Wasielewski, Michael R

2010-04-01

422

Wavelength-encoding/temporal-spreading optical code division multiple-access system with in-fiber chirped moiré gratings.  

PubMed

We propose an optical code division multiple-access (OCDMA) system that uses in-fiber chirped moiré gratings (CMG's) for encoding and decoding of broadband pulses. In reflection the wavelength-selective and dispersive nature of CMG's can be used to implement wavelength-encoding/temporal-spreading OCDMA. We give examples of codes designed around the constraints imposed by the encoding devices and present numerical simulations that demonstrate the proposed concept. PMID:18323934

Chen, L R; Smith, P W; de Sterke, C M

1999-07-20

423

A comparison of results derived from scaling VS chirp-ionosonde ionograms with the international reference ionosphere (IRI)  

Microsoft Academic Search

The results derived from processing vertical-incidence ionograms obtained with the chirp-ionosonde at Irkutsk for different winter time intervals (February) and at equinox are presented. The peak height hmF2 was determined by Dudeney's formula based on ionogram parameters, including the coefficient M(3000). The algorithm is suggested for determining the coefficient M(3000) in the automatic mode using the conventional form of the

V. P. Grozov; G. V. Kotovich

2003-01-01

424

High-order harmonic generation by chirped and self-guided femtosecond laser pulses. I. Spatial and spectral analysis  

SciTech Connect

For the analysis of high-order harmonics generated in a long gas jet by intense chirped femtosecond laser pulses, calculations of the laser propagation and harmonic generation were performed in terms of a nonadiabatic three-dimensional model. The self-guided propagation, observed at the conditions of bright harmonic generation, was confirmed by the model calculations. When using negatively chirped pulses, the calculated distribution of the harmonic field is spatially and spectrally confined, being generated on axis with a narrow spectral profile. The positively chirped pulses generate broad spectral distribution on axis, and narrow off axis, but in the latter case with a large emission angle. The estimation of harmonic beam divergence agreed well with experimentally measured data, showing the lowest divergence at the conditions of the brightest harmonic generation. Spectral, temporal, and spatial modifications of the propagated laser pulse are found to influence decisively the single-atom response and ultimately the harmonic field, providing a coherent picture of harmonic generation.

Tosa, V.; Kim, H.T.; Kim, I.J.; Nam, C.H. [Department of Physics, KAIST, Yuseong-gu, Daejeon, 305-701 (Korea, Republic of)

2005-06-15

425

Chirped pulse multiphoton ionization of nitrogen: control of selective rotational excitation in N(2)(+)(B 2Sigma(u)(+)).  

PubMed

We report on fluorescence spectra of N(2)(+)(B (2)Sigma(u)(+)) --> N(2)(+)(X (2)Sigma(g)(+)) obtained from multiphoton ionization of molecular nitrogen by 804 nm femtosecond laser pulses. The analysis of the fluorescence spectra reveals that the vibrational levels v = 0 and v = 4 in the B (2)Sigma(u)(+)-state of N(2)(+) are primarily populated. The rotational state distribution of N(2)(+)(B (2)Sigma(u)(+), v = 0) is determined from the rotationally resolved fluorescence spectra. It is demonstrated that the linear chirp of the 804 nm femtosecond laser pulse has a strong influence on the rotational state distribution of the vibrational ground state of the molecular cation N(2)(+)(B (2)Sigma(u)(+), v = 0). Possible mechanisms leading to the experimental results are discussed. The particular population of the vibrational levels as well as the linear chirp dependence of the fluorescence signal gives evidence for the importance of a resonant intermediate state. The N(2) a (1)Pi-state is likely involved in a resonant multiphoton excitation process. This permits to selectively control the rotational population of the cation that is formed via chirped pulse multiphoton ionization. PMID:19566159

Plenge, J; Wirsing, A; Raschpichler, C; Meyer, M; Rühl, E

2009-06-28

426

Transformation based endorsement systems  

NASA Technical Reports Server (NTRS)

Evidential reasoning techniques classically represent support for a hypothesis by a numeric value or an evidential interval. The combination of support is performed by an arithmetic rule which often requires restrictions to be placed on the set of possibilities. These assumptions usually require the hypotheses to be exhausitive and mutually exclusive. Endorsement based classification systems represent support for the alternatives symbolically rather than numerically. A framework for constructing endorsement systems is presented in which transformations are defined to generate and update the knowledge base. The interaction of the knowledge base and transformations produces a non-monotonic reasoning system. Two endorsement based reasoning systems are presented to demonstrate the flexibility of the transformational approach for reasoning with ambiguous and inconsistent information.

Sudkamp, Thomas

1988-01-01

427

SPATIAL TRANSFORMATIONS 1 Running head: Spatial transformations  

E-print Network

SPATIAL TRANSFORMATIONS 1 Running head: Spatial transformations Multiple Systems for Spatial Imagery: Transformations of Objects and Bodies Jeffrey M. Zacks* and Barbara Tversky * Washington COGNITION & COMPUTATION #12;SPATIAL TRANSFORMATIONS 2 Abstract Problem-solving often requires imagining

Zacks, Jeffrey M.

428

Fourier Transform Pairs The Fourier transform transforms a function of  

E-print Network

Fourier Transform Pairs The Fourier transform transforms a function of time, f(t), into a function of frequency, F(s): F {f(t)}(s) = F(s) = Z - f(t)e- j2st dt. The inverse Fourier transform transforms a func. The inverse Fourier transform of the Fourier trans- form is the identity transform: f(t) = Z - Z - f()e- j2s

Masci, Frank

429

Electrical and thermal performance of PWB transformers  

Microsoft Academic Search

The authors use analytical tools developed to predict the high-frequency characteristics of conventionally wound transformers and apply them to the planar printed wiring board (PWB) transformer case. The authors present a simple modeling technique that is useful in calculating the temperature rise for a PWB transformer assuming conduction through the base of the device as the only thermal path. These

Mahmoud P. Sayani; G. R. Skutt; P. S. Venkatraman

1991-01-01

430

Compiler transformations for high-performance computing  

Microsoft Academic Search

In the last three decades a large number of compiler transformations for optimizing programs have been implemented. Most optimizations for uniprocessors reduce the number of instructions executed by the program using transformations based on the analysis of scalar quantities and data-flow techniques. In contrast, optimizations for high-performance superscalar, vector, and parallel processors maximize parallelism and memory locality with transformations that

David F. Bacon; Susan L. Graham; Oliver J. Sharp

1994-01-01

431

The Laplace Transform 1 Laplace transform and inverse transform  

E-print Network

The Laplace Transform Name: 1 Laplace transform and inverse transform Definition. Let f(t) be a function defined for t 0. Then the integral L {f(t)} = 0 e-st f(t)dt is said to be the Laplace transform of f provided the integral converges. Fill in the following Laplace transforms. L {tn } = L {eat } = L

Yengulalp, Lynne

432

The Anna's hummingbird chirps with its tail: a new mechanism of sonation in birds.  

PubMed

A diverse array of birds apparently make mechanical sounds (called sonations) with their feathers. Few studies have established that these sounds are non-vocal, and the mechanics of how these sounds are produced remains poorly studied. The loud, high-frequency chirp emitted by a male Anna's hummingbird (Calypte anna) during his display dive is a debated example. Production of the sound was originally attributed to the tail, but a more recent study argued that the sound is vocal. Here, we use high-speed video of diving birds, experimental manipulations on wild birds and laboratory experiments on individual feathers to show that the dive sound is made by tail feathers. High-speed video shows that fluttering of the trailing vane of the outermost tail feathers produces the sound. The mechanism is not a whistle, and we propose a flag model to explain the feather's fluttering and accompanying sound. The flag hypothesis predicts that subtle changes in feather shape will tune the frequency of sound produced by feathers. Many kinds of birds are reported to create aerodynamic sounds with their wings or tail, and this model may explain a wide diversity of non-vocal sounds produced by birds. PMID:18230592

Clark, Christopher James; Feo, Teresa J

2008-04-22

433

Bathymetry, Chirp and Deep Crustal Structure of the Santos Basin SÃO Paulo Ridge Complex (sbspr)  

NASA Astrophysics Data System (ADS)

The SanBa (Santos Basin- Seismic Research experiment) research experiment is a joint project of the Department of Marine Geosciences (IFREMER: Institut Français de Recherche pour l'Exploitation de la MER, France), the Laboratory of "Oceanic Domain" (Institut Universitaire et Européen de la Mer, France), the Faculdade de Ciências da Universidade de Lisboa (Lattex and CGUL, Portugal), the Universidade de Brasilia (Brazil) and PETROBRAS. Its aim is to test hypotheses that have been proposed such as the existence of failed rift and a micro-block (Moulin et al., GSL submitted) or the presence of exhumed mantle on its south-eastern part (Zalan et al., AAPG 2009). Six wide-angle seismic data were acquired together with coincident deep frequency reflection seismic data during the SanBa cruise in Dec 2010 - Jan. 2011 (total > 850 Nm). Chirp and Bathymetry were also acquired during the cruise. The preliminary results suggest a very thin crust (< 5km) in the center and in the south-eastern part of the SBSPR. Both refraction and reflection data present a clear signal of the Moho in the distalmost part of the study area, which seems to preclude the exhumed mantle hypothesis."

Aslanian, D.; Klingelhoefer, F.; Moulin, M.; Schnurle, P.; Rabineau, M.; Afilhado, A.; Roest, W. R.; Feld, A.; Evain, M.; Rochat, A.; Rousic, D.; Rigoti, C. A.; Capechi, E.; Bochenek, G.; Viana, A. R.; Magnavita, L. P.; Szatmari, P.; Neto, M.; Soares, J. P.; Fuck, R. A.; Paula Ribas, M.; De Lima, M.; Corela, C.; Duarte, J.; Matias, L. M.; OBS Team of Sanba Cruise

2011-12-01

434

Hadamard transform imaging  

SciTech Connect

We have constructed a Hadamard transform Raman microscopic imaging system, and have developed it to a high definition (64K pixel) technique. We have demonstrated multispectral Raman imaging and developed the first three-dimensional (digital confocal) Raman imaging. We have explored the systematic errors in Hadamard multiplexing techniques and developed corrections. We have used our Raman microscope techniques to explore defect distributions on graphite electrodes and damage effects on SERS-activated silver electrodes. We have used the microprobe capabilities of our instrument to investigate the kinetics of polyacrylamide formation in electrolysis capabilities. We have worked closely with a manufacture of holographic displays to develop and incorporate holographic filters and holographic beam splitters into Raman spectrographs and microscopes. Finally, we have developed Hadamard multiplexing techniques for densitometric measurements of protein or nucleic acid blots.

Morris, M.D.

1992-01-01

435

Transforming IMAGINATION  

E-print Network

and translational research and help drive medical breakthroughs that will transform the health and well by rapid advances and breakthroughs on such fronts as genetics, genomics, immunology, informatics and stem and financial rewards of being the first to achieve major scientific breakthroughs. To compete effectively

Weber, David J.

436

Exploring Transformations  

NSDL National Science Digital Library

In this activity, students will explore transformations of an absolute value function. Step by step instructions guide students in using graphing calculators to examine the effect that stretching and translating has on the coordinates of the graph. Teacher notes and a worksheet are also included to aid in teaching this lesson.

2011-11-25

437

Transforming Schools.  

ERIC Educational Resources Information Center

The authors in this book address the issues that relate to the crisis in American education and review some of the proposed solutions. To transform education, schools must be examined as social systems that are interrelated with families, communities, and the world of work. Following the introduction, section 1, "Conditions for Educational…

Cookson, Peter W., Jr., Ed.; Schneider, Barbara, Ed.

438

Humanitarianism Transformed  

Microsoft Academic Search

The scale, scope, and significance of humanitarian action have expanded significantly since the late 1980s. This article reflects on two ways in which humanitarianism has been transformed. First, its purpose has been politicized. Whereas once humanitarian actors attempted to insulate themselves from the world of politics, they now work closely with states and attempt to eliminate the root causes of

Michael Barnett

2005-01-01

439

Transformation Time  

ERIC Educational Resources Information Center

The program for the march by librarians on America's capital for the American Library Association (ALA) conference is predictably loaded with lobbying, legislation, and DC tours. It also abounds with professional opportunity and reflects the impact of Leslie Burger, one of the most activist ALA presidents in recent history. Her "Transformation"…

Berry, John N., III

2007-01-01

440

Transformation & Metamorphosis  

ERIC Educational Resources Information Center

The sculptures of Canadian artist Brian Jungen are a great inspiration for a lesson on creating new forms. Jungen transforms found objects into unique creations without fully concealing their original form or purpose. Frank Stella's sculpture series, including "K.132,2007" made of stainless steel and spray paint, is another great example of…

Lott, Debra

2009-01-01

441

Stabilization of asphaltenes in aliphatic solvents using alkylbenzene-derived amphiphiles. 2. Study of the asphaltene-amphiphile interactions and structures using Fourier transform infrared spectroscopy and small-angle X-ray scattering techniques  

SciTech Connect

In the preceding paper in this issue, the influence of the chemical structure of a series of alkylbenzene-derived amphiphiles on the stabilization of asphaltenes was described. In this paper, we present the results of using Fourier transform infrared (FTIR) spectroscopy and small-angle X-ray scattering (SAXS) techniques to study the interaction between asphaltenes and two alkylbenzene-derived amphiphiles, p-alkylphenol and p-alkylbenzenesulfonic acid. FTIR spectroscopy was used to characterize and quantify the acid-base interactions between asphaltenes and amphiphiles. It was found that asphaltenes could hydrogen-bond to p-dodecylphenol amphiphiles. The hydrogen-bonding capacity of asphaltenes was estimated to be 1.6-2.0 mmol/g of asphaltene. On the other hand, the FTIR spectroscopic study indicated that asphaltenes had a complicated acid-base interaction with p-dodecylbenzenesulfonic acid (DBSA) amphiphiles with a stoichiometry of about 1.8 mmol of DBSA/g of asphaltene. The UV/vis spectroscopic study suggested that asphaltenes and DBSA could associate into large electronic conjugated complexes. Physical evidence of the association between asphaltenes and amphiphiles was obtained by SAXS measurements. 27 refs., 10 figs.

Chang, C.L.; Fogler, H.S. (Univ. of Michigan, Ann Arbor, MI (United States))

1994-06-01

442

Rainbow Fourier Transform  

NASA Technical Reports Server (NTRS)

We present a novel technique for remote sensing of cloud droplet size distributions. Polarized reflectances in the scattering angle range between 135deg and 165deg exhibit a sharply defined rainbow structure, the shape of which is determined mostly by single scattering properties of cloud particles, and therefore, can be modeled using the Mie theory. Fitting the observed rainbow with such a model (computed for a parameterized family of particle size distributions) has been used for cloud droplet size retrievals. We discovered that the relationship between the rainbow structures and the corresponding particle size distributions is deeper than it had been commonly understood. In fact, the Mie theory-derived polarized reflectance as a function of reduced scattering angle (in the rainbow angular range) and the (monodisperse) particle radius appears to be a proxy to a kernel of an integral transform (similar to the sine Fourier transform on the positive semi-axis). This approach, called the rainbow Fourier transform (RFT), allows us to accurately retrieve the shape of the droplet size distribution by the application of the corresponding inverse transform to the observed polarized rainbow. While the basis functions of the proxy-transform are not exactly orthogonal in the finite angular range, this procedure needs to be complemented by a simple regression technique, which removes the retrieval artifacts. This non-parametric approach does not require any a priori knowledge of the droplet size distribution functional shape and is computationally fast (no look-up tables, no fitting, computations are the same as for the forward modeling).

Alexandrov, Mikhail D.; Cairns, Brian; Mishchenko, Michael I.

2012-01-01

443

Rainbow Fourier transform  

NASA Astrophysics Data System (ADS)

We present a novel technique for remote sensing of cloud droplet size distributions. Polarized reflectances in the scattering angle range between 135° and 165° exhibit a sharply defined rainbow structure, the shape of which is determined mostly by single scattering properties of cloud particles, and therefore, can be modeled using the Mie theory. Fitting the observed rainbow with such a model (computed for a parameterized family of particle size distributions) has been used for cloud droplet size retrievals. We discovered that the relationship between the rainbow structures and the corresponding particle size distributions is deeper than it had been commonly understood. In fact, the Mie theory-derived polarized reflectance as a function of reduced scattering angle (in the rainbow angular range) and the (monodisperse) particle radius appears to be a proxy to a kernel of an integral transform (similar to the sine Fourier transform on the positive semi-axis). This approach, called the rainbow Fourier transform (RFT), allows us to accurately retrieve the shape of the droplet size distribution by the application of the corresponding inverse transform to the observed polarized rainbow. While the basis functions of the proxy-transform are not exactly orthogonal in the finite angular range, this procedure needs to be complemented by a simple regression technique, which removes the retrieval artifacts. This non-parametric approach does not require any a priori knowledge of the droplet size distribution functional shape and is computationally fast (no look-up tables, no fitting, computations are the same as for the forward modeling).

Alexandrov, Mikhail D.; Cairns, Brian; Mishchenko, Michael I.

2012-12-01

444

Transformations Journal  

NSDL National Science Digital Library

Different forms of communication have always had a tendency to transform interactions and everyday life in ways that have surprised people from many different backgrounds. Academics have long been interested in such dynamic transformations, and this electronic journal represents one of the responses to such processes. As their site notes, this journal is "dedicated to the exploration of ideas, issues and debates emerging out of contemporary global culture." Visitors to the site can read the complete version of every issue on the site, and they will be pleased to find such intriguing titles as "Rethinking Regionality", "Accidental Environments", and "Fleeing the City". Interested parties can also consult the site to learn about the journal's editorial board, their calls for papers, submission guidelines, and related links.

445

Investigation of a pulse compression technique for medical ultrasound: a simulation study  

Microsoft Academic Search

Pulse compression techniques that are capable of producing a large signal-to-noise (SNR) enhancement, have been used successfully\\u000a in many different fields. For medical applications, frequency-dependent attenuation in soft tissue can limit the usefulness\\u000a of this method. In the paper, this issue is examined through model-simulation studies. Frequency-modulation (FM) chirp, considered\\u000a in the study, is just one form of pulse coding

N. A. H. K. Rao

1994-01-01

446

Control of the high-order harmonics cutoff and attosecond pulse generation through the combination of a chirped fundamental laser and a subharmonic laser field  

SciTech Connect

We propose a method to generate an isolated attosecond (as) pulse in combination with a chirped fundamental laser field (5 fs, 800 nm) and a subharmonic laser field (12 fs, 1600 nm). It is shown that, for the case of the chirped parameter {beta}=0.25, not only is the efficiency of the extended harmonics enhanced, but also an ultrabroad supercontinuum is formed in the second plateau. For the case of {beta}=0.65, an ultrabroad supercontinuum spectrum with the width of about 1670 eV can be observed. Furthermore, due to the introduction of chirped pulse, the short quantum trajectory is enhanced, and the long one is suppressed. By superposing a properly selected range of the harmonic spectrum in the continuum region, an intense isolated 38-as pulse is generated.

Wu Jie; Zhang Gangtai; Xia Changlong; Liu Xueshen [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China)

2010-07-15

447

Chirped-Pulse Ftmw Spectroscopy of the Lactic ACID-H_2O System  

NASA Astrophysics Data System (ADS)

The previous study of the rotational spectrum of lactic acid in supersonic expansion revealed rather temperamental behaviour of signal intensity suggestive of considerable clusterization. Lactic acid samples contain an appreciable amount of water so that the presence of clusters with water, as well as lactic dimers is suspected. Several, mainly computational, studies of such species have already been published. Investigation of the chirped-pulse rotational spectrum of a heated lactic acid (LA) sample diluted in Ne carrier gas allowed unambiguous assignment of the LA-H_2O, LA-(H_2O)_2, and LA-(H_2O)_3 species. In addition, the rotational spectrum of the AaT conformer of lactic acid has been assigned. This conformer involves an intramolecular hydrogen bond to the hydroxyl of the carboxylic group and it has been estimated to be less stable by ca 10 kJ/mol than the most stable SsC conformer. The evidence for the assignment and a discussion of the derived properties for the new species are presented. L.Pszczó?kowski, E.Bia?kowska-Jaworska, Z.Kisiel, J. Mol. Spectrosc. 234, 106 (2005). J.Sadlej, J.Cz.Dobrowolski, J.E.Rode, M.H.Jamróz, PCCP 8, 101 (2006) M.Losada, H.Tran, Y.Xu, J. Chem. Phys. 128, 014508 (2008) A.Smaga, J.Sadlej, J. Phys. Chem. A 114, 4427 (2010). A.Borba, A.Gomez-Zavaglia, L.?apinski, R.Fausto, PCCP 6, 2101 (2004).

Kisiel, Zbigniew; Bia?kowska-Jaworska, Ewa; Zaleski, Daniel P.; Neill, Justin L.; Steber, Amanda L.; Pate, Brooks H.

2011-06-01

448

Bone-demineralization diagnosis in a bone-tissue-skin matrix using the pulsed-chirped photothermal radar  

NASA Astrophysics Data System (ADS)

A chirped pulsed photothermal radiometric radar 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, MPE) 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 (approx. 1 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 ca. 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. Compared to radar peak delay and amplitude, the long-delayed radar output amplitude is found to be more sensitive to subsurface conditions. Two-dimensional spatial plots of this parameter depicting the back surface conditions of bones with and without fat-tissue overlayers are presented.

Kaiplavil, Sreekumar; Mandelis, Andreas

2012-02-01

449

High peak-power monolithic femtosecond ytterbium fiber chirped pulse amplifier with a spliced-on hollow core fiber compressor.  

PubMed

We demonstrate a monolithic Yb-fiber chirped pulse amplifier that uses a dispersion matched fiber stretcher and a spliced-on hollow core photonic bandgap fiber compressor. For an output energy of 77 nJ, 220 fs pulses with 92% of the energy contained in the main pulse, can be obtained with minimal nonlinearities in the system. 135 nJ pulses are obtained with 226 fs duration and 82 percent of the energy in the main pulse. Due to the good dispersion match of the stretcher to the hollow core photonic bandgap fiber compressor, the duration of the output pulses is within 10% of the Fourier limited duration. PMID:25090494

Verhoef, A J; Jespersen, K; Andersen, T V; Grüner-Nielsen, L; Flöry, T; Zhu, L; Baltuška, A; Fernández, A

2014-07-14

450

Design of PETAL multipetawatt high-energy laser front end based on optical parametric chirped pulse amplification.  

PubMed

We report on a single shot optical parametric chirped pulse amplifier designed to seed the Petawatt Aquitaine Laser on the Laser Integration Line facility multipetawatt high-energy laser. The scheme is based on a stretched signal pulse at 1053 nm amplified with 20% conversion efficiency by a monomode pump pulse at 527 nm. The homemade pump laser is able to deliver a single shot beam with a square flat top spatial profile and programmable temporal shape. A high-stability 150 mJ, 8 nm, and 4.5 ns stretched pulse is then obtained with an excellent quality spatially shaped beam. PMID:18026557

Hugonnot, Emmanuel; Deschaseaux, Gérard; Hartmann, Olivier; Coïc, Hervé

2007-11-20

451

Single-shot high aspect ratio bulk nanostructuring of fused silica using chirp-controlled ultrafast laser Bessel beams  

SciTech Connect

We report single-shot, high aspect ratio nanovoid fabrication in bulk fused silica using zeroth order chirp-controlled ultrafast laser Bessel beams. We identify a unique laser pulse length and energy dependence of the physical characteristics of machined structures over which nanovoids of diameter in the range 200–400?nm and aspect ratios exceeding 1000 can be fabricated. A mechanism based on the axial energy deposition of nonlinear ultrashort Bessel beams and subsequent material densification or rarefaction in fused silica is proposed, intricating the non-diffractive nature with the diffusing character of laser-generated free carriers. Fluid flow through nanochannel is also demonstrated.

Bhuyan, M. K.; Velpula, P. K.; Colombier, J. P.; Olivier, T.; Faure, N.; Stoian, R., E-mail: razvan.stoian@univ-st-etienne.fr [Laboratoire Hubert Curien, UMR 5516 CNRS, Université de Lyon, Université Jean Monnet, 42000 Saint Etienne (France)

2014-01-13

452

Comparison of photoacoustic imaging systems using continuous-wave lasers with a chirped intensity modulation frequency to pulsed lasers  

NASA Astrophysics Data System (ADS)

We compare imaging systems using continuous-wave (CW) lasers with a chirped intensity modulation frequency to pulsed lasers. We show that the resolution is the same in both cases. We also compare the signal-to-noise ratio (SNR) of the two systems assuming the fluence is set by the American National Standards Institute (ANSI) limits. Although the SNR depends on several parameters, we find that it is about 20 dB to 30 dB larger for pulsed lasers for reasonable values of the parameters. However, CW diode lasers have the advantage of being compact and relatively inexpensive, which may outweigh the slightly lower SNR in many applications.

Petschke, Adam; La Rivière, Patrick J.

2011-03-01

453

Fiber-optic chirped FBG for distributed thermal monitoring of ex-vivo radiofrequency ablation of liver  

PubMed Central

A linearly chirped fiber Bragg grating (LCFBG) has been used as a temperature sensor for online monitoring of radiofrequency thermal ablation (RFTA). The LCFBG acts as a distributed sensor, with spatial resolution of 75 ?m. A white-light setup that records the LCFBG spectrum estimates the temperature profile in real time. Three RFTA experiments have been performed ex-vivo on porcine liver measuring the radial temperature distribution during the heating process. The analysis of thermal maps quantifies the spatial heat distribution along the measurement axis and determines the ablation efficiency. PMID:24940541

Tosi, Daniele; Macchi, Edoardo Gino; Gallati, Mario; Braschi, Giovanni; Cigada, Alfredo; Rossi, Sandro; Leen, Gabriel; Lewis, Elfed

2014-01-01

454

Low-chirp and high-power 1.55-?m strained-quantum-well complex-coupled DFB laser  

Microsoft Academic Search

High-power, low-chirp, and low-threshold current characteristics of 1.55 ?m complex-coupled compressively strained InGaAsP quantum-well DFB laser with a loss grating are presented. Kink-free light-current characteristics with single-mode power over 40 mW are demonstrated for uncoated devices. A relatively low threshold current of 10 mA and a high slope efficiency of 0.23 W\\/A have been obtained even with the loss grating

Chi-Yu Wang; Zuon-Min Chuang; Wei Lin; Yuan-Kuang Tu; Ching-Ting Lee

1996-01-01

455

Amplification of ultra-short optical pulses in a two-pump fiber optical parametric chirped pulse amplifier.  

PubMed

We demonstrate with realistic numerical simulations that fiber optical parametric chirped pulse amplification is able to amplify ultra-short optical pulses. Such amplifiers driven by two-pump waves can amplify pulse bandwidth twice as large as the one of a single pump configuration. We show that pulses as short as 50 fs can be directly amplified. In addition, we take benefit from the saturation regime to achieve spectral broadening which makes possible to reduce pulse duration down to 15 fs. PMID:23736440

Mussot, Arnaud; Kudlinski, Alexandre; d'Augères, Patrick Beaure; Hugonnot, Emmanuel

2013-05-20

456

Hamlet's Transformation.  

NASA Astrophysics Data System (ADS)

William Shakespeare's Hamlet has much evidence to suggest that the Bard was aware of the cosmological models of his time, specifically the geocentric bounded Ptolemaic and Tychonic models, and the infinite Diggesian. Moreover, Shakespeare describes how the Ptolemaic model is to be transformed to the Diggesian. Hamlet's "transformation" is the reason that Claudius, who personifies the Ptolemaic model, summons Rosencrantz and Guildenstern, who personify the Tychonic. Pantometria, written by Leonard Digges and his son Thomas in 1571, contains the first technical use of the word "transformation." At age thirty, Thomas Digges went on to propose his Perfit Description, as alluded to in Act Five where Hamlet's age is given as thirty. In Act Five as well, the words "bore" and "arms" refer to Thomas' vocation as muster-master and his scientific interest in ballistics. England's leading astronomer was also the father of the poet whose encomium introduced the First Folio of 1623. His oldest child Dudley became a member of the Virginia Company and facilitated the writing of The Tempest. Taken as a whole, such manifold connections to Thomas Digges support Hotson's contention that Shakespeare knew the Digges family. Rosencrantz and Guildenstern in Hamlet bear Danish names because they personify the Danish model, while the king's name is latinized like that of Claudius Ptolemaeus. The reason Shakespeare anglicized "Amleth" to "Hamlet" was because he saw a parallel between Book Three of Saxo Grammaticus and the eventual triumph of the Diggesian model. But Shakespeare eschewed Book Four, creating this particular ending from an infinity of other possibilities because it "suited his purpose," viz. to celebrate the concept of a boundless universe of stars like the Sun.

Usher, P. D.

1997-12-01

457

Rotary Transformer  

NASA Technical Reports Server (NTRS)

None given. From first Par: Many spacecraft (S/C) and surface rovers require the transfer of signals and power across rotating interfaces. Science instruments, antennas and solar arrays are elements needing rotary power transfer for certain (S/C) configurations. Delivery of signal and power has mainly been done by using the simplest means, the slip ring approach. This approach, although simple, leaves debris generating noise over a period of time...The rotary transformer is a good alternative to slip rings for signal and power transfer.

McLyman, Colonel Wm. T.

1996-01-01

458

Efficient terahertz wave generation from GaP crystals pumped by chirp-controlled pulses from femtosecond photonic crystal fiber amplifier  

SciTech Connect

A chirp-tunable femtosecond 10?W, 42?MHz photonic-crystal-fiber oscillator-amplifier system that is capable of delivering sub-60 fs light pulses at 1040?nm is used to demonstrate high-efficiency terahertz radiation generation via optical rectification in GaP crystals only a few millimeters in length. The optimization of the chirp of the fiber-laser pulses is shown to radically enhance the terahertz output, indicating one possible way to more efficiently use these extended nonlinear crystals in compact fiber-pumped terahertz radiation sources.

Li, Jiang; Shi, Junkai; Xu, Baozhong; Xing, Qirong; Wang, Chingyue [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); Chai, Lu, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn; Liu, Bowen; Hu, Minglie; Li, Yanfeng, E-mail: lu-chai@tju.edu.cn, E-mail: yanfengli@tju.edu.cn [Ultrafast Laser Laboratory, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education), Tianjin University, Tianjin 300072 (China); MOEMS Key Laboratory (Ministry of Education), Tianjin University, Tianjin 300072 (China); Fedotov, Andrey B. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Zheltikov, Aleksei M. [Physics Department, Russian Quantum Center, International Laser Center, M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843 (United States)

2014-01-20

459

160-Gb/s all-optical phase-transparent wavelength conversion through cascaded SFG-DFG in a broadband linear-chirped PPLN waveguide.  

PubMed

We experimentally demonstrated ultra-fast phase-transparent wavelength conversion using cascaded sum- and difference-frequency generation (cSFG-DFG) in linear-chirped periodically poled lithium niobate (PPLN). Error-free wavelength conversion of a 160-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) signal was successfully achieved. Thanks to the enhanced conversion bandwidth in the PPLN with linear-chirped periods, no optical equalizer was required to compensate the spectrum distortion after conversion, unlike a previous demonstration of 160-Gb/s RZ on-off keying (OOK) using fixed-period PPLN. PMID:20389627

Lu, Guo-Wei; Shinada, Satoshi; Furukawa, Hideaki; Wada, Naoya; Miyazaki, Tetsuya; Ito, Hiromasa

2010-03-15

460

nBn and pBp infrared detectors with graded barrier layer, graded absorption layer, or chirped strained layer super lattice absorption layer  

NASA Technical Reports Server (NTRS)

An nBn detector is described where for some embodiments the barrier layer has a concentration gradient, for some embodiments the absorption layer has a concentration gradient, and for some embodiments the absorption layer is a chirped strained layer super lattice. The use of a graded barrier or absorption layer, or the use of a chirped strained layer super lattice for the absorption layer, allows for design of the energy bands so that the valence band may be aligned across the device. Other embodiments are described and claimed.

Gunapala, Sarath D. (Inventor); Ting, David Z. (Inventor); Hill, Cory J. (Inventor); Bandara, Sumith V. (Inventor)

2010-01-01

461

Theoretical model calculations of long-haul edge-emitting communication lasers: comparison of fractally mixed, fine-pitched and continuously chirped DFB gratings  

NASA Astrophysics Data System (ADS)

We have studied index-coupled semiconductor distributed feedback (DFB) lasers and compared three types including continuously chirped gratings, fractally mixed gratings and fine-pitched gratings. Using transfer matrix model calculations self-consistently combined with the set of rate equations, important static and dynamic laser properties are compared and it is found that they can be designed to be nearly identical above laser threshold for the three types of lasers. Therefore, the grating configuration involving the lowest effort and production cost can be selected: continuously chirped DFB lasers implemented by bent waveguides. These gratings are very attractive since they show high performance and have the potential of production at lower cost.

Hillmer, H.; Prott, C.; Römer, F.; Hansmann, S.

2004-07-01

462

SIGNAL APPROXIMATION VIA THE GOPHER FAST FOURIER TRANSFORM  

E-print Network

SIGNAL APPROXIMATION VIA THE GOPHER FAST FOURIER TRANSFORM By I. Ben Segal and M.A. Iwen IMA-626-7370 URL: http://www.ima.umn.edu #12;Signal Approximation via the Gopher Fast Fourier Transform I. Ben the Gopher Fast Fourier Transform (GFFT), of the more recently developed sparse Fourier transform techniques

463

Intelligent Transformer Monitoring System Utilizing Neuro-Fuzzy  

E-print Network

Intelligent Transformer Monitoring System Utilizing Neuro-Fuzzy Technique Approach Intelligent Center Intelligent Transformer Monitoring System Utilizing Neuro-Fuzzy Technique Approach Final Project transformers and circuit breakers off-line, in order to assess whether the equipment is operating normally

464

Utilization of chirped laser pulses to measure stimulated Raman scattering of organic liquids in the terahertz regime  

NASA Astrophysics Data System (ADS)

With the present paper, we demonstrate an experimental setup connecting two highly innovative fields of research: stimulated Raman scattering (SRS) spectroscopy and terahertz (THz) spectroscopy of liquids. For this purpose, we use the spectral focusing method allowing us to excite and measure molecular vibrations by chirped laser pulses. With our experimental setup, we apply this method to the THz regime in order to detect the frequency dependence of SRS processes in organic liquids. More specifically, we focus two chirped laser pulses onto the sample to drive molecular vibrations at THz frequencies. Thereby, the time delay between the laser pulses is directly related to the driving frequency. Due to SRS process, an energy transfer between the two laser pulses is established. By detecting the corresponding energy change of only one of the two laser pulses, we are able to observe inverse Raman scattering and stimulated Raman gain scattering as well as the transition between both processes at zero delay time. The peak positions and the line shapes of the measured spectra agree well with literature data obtained by spontaneous Raman scattering spectroscopy and optical heterodyne detection optical Kerr effect spectroscopy. With the present setup, we are able to excite and detect molecular vibrations ranging over two orders of magnitude from 10 THz to ultra-low frequencies at 100 GHz.

Funkner, Stefan; Saito, Katsuya; Niehues, Gudrun; Yazawa, Yoshiki; Furuya, Takashi; Yamamoto, Kohji; Tani, Masahiko

2014-07-01

465

Dynamics and structure of the vertical ionospheric disturbances caused by Tohoku earthquake according to Irkutsk bistatic CHIRP-sounding  

NASA Astrophysics Data System (ADS)

In the work we present results of observation of the mid-scale vertical ionospheric irregularities caused by Tohoku earthquake with 1 minute temporary resolution. Their spatial and temporary dynamics is also investigated. The main instrument used in the analysis is bistatic CHIRP-sounder of own development of ISTP SB RAS. The CHIRP-sounder provides frequency change speed up to 1000 kHz/sec, and provides 1 minute temporal resolution, comparable with SuperDARN radars and GPS receivers network. The receiver and the transmitter of the sounder are located close to Irkutsk (52N,104E) at distance 120 km between each other. Synchronization of time and frequency is provided by GPS. As showed the analysis of the experimental data, the main response of the ionosphere was observed at Irkutsk from 06:10 to 07:00UT. Short-term variations of the electron density profile were also observed from 06:00UT. This corresponds to the main horizontal speed of disturbances about 2500 m/s and below. The vertical scale of the irregularities was 10-20 km. Irregularities practically weren't observed at heights above 200km. The obtained data don't contradict the data obtained by other researchers. Work was done under financial support of IV.12.2 OFN Russian Academy of Sciences program.

Berngardt, Oleg; Kotovich, Galina; Podlesnyi, Alexey

466

Single chirped pulse control of hyperfine states population in Rb atom in the framework of the four-level system  

NASA Astrophysics Data System (ADS)

Electron population dynamics within the hyperfine structure in the Rb atom induced by a single ns pulse is theoretically investigated. The aim is to develop a methodology of the implementation of linearly chirped laser pulses for the desired excitations in the Rb atoms resulting in the creation of predetermined non-equilibrium states. A semi-classical model of laser pulse interaction with a four-level system representing the hyperfine energy levels of the Rb atom involved into dynamics has been developed. The equations for the probability amplitudes were obtained from the Schrodinger equation with the Hamiltonian that described the time evolution of the population of the four states in the field interaction representation. A code was written in Fortran for a numerical analysis of the time evolution of probability amplitudes as a function of the field parameters. The dependence of the quantum yield on the pulse duration, the linear chirp parameter and the Rabi frequency was studied to reveal the conditions for the entire population transfer to the upper hyperfine state of the 5S1/2 electronic level. The results may provide a robust tool for quantum operations in the alkali atoms.

Zakharov, Vladislav; Malinovskaya, Svetlana

2012-06-01

467

Chirp-managed lasers as cost-efficient transmitters for 10-Gbit/s WDM-PONs  

NASA Astrophysics Data System (ADS)

Chirp-managed lasers (CML) are demonstrated as simple low-cost transmitter with high tolerance to chromatic dispersion. This manuscript proposes the use of CML as cost-effective downstream (DS) transmitters for next generation access networks. The laser chirp, which is the main drawback limiting the transmission performance of directly modulated lasers, is now used to generate differential phase-shift keying (DPSK) modulation format by direct modulation. The network architecture using CML as downstream DPSK transmitter is proposed. Bit­ error-rate measurement showed that an optical power budget of 36 dB could be obtained with direct phase-shift­ keying modulation ofCML which proves that the proposed solution is a strong candidate for future WDM-PONs. Budget-extended WDM-PON configuration is also demonstrated using Saturated Collision Amplifier, which is an amplification scheme that uses SOA saturation in order to maximize the output power and minimize the ASE noise and the polarization sensitivity. The extension scheme is demonstrated for four-wavelength 10 Gbit/s unidirectional downstream configuration with 60-dB maximum total optical budget for each wavelength.

Le, Quang Trung; Emsia, Ali; Briggmann, Dieter; Küppers, Franko

2013-01-01

468

Fourier-transform lidar.  

PubMed

We propose a new method based on the differential absorption lidar technique for multipollutant detection. A broadband laser is sent into the atmosphere in a wavelength range in which several pollutants absorb. The backscattered light is analyzed by a Fourier-transform spectrometer with time resolution. This mode of detection provides both spatial and high spectral resolution down to 0.01 cm(-1), allowing range-resolved measurements of several pollutants simultaneously. To demonstrate the feasibility of this method, we have measured water vapor concentration by using more than 10 individual lines in the 720-nm absorption band. The potential and the limitations are discussed critically. PMID:19862277

Douard, M; Bacis, R; Rambaldi, P; Ross, A; Wolf, J P; Fabre, G; Stringat, R

1995-10-15

469

Radar Range Sidelobe Reduction Using Adaptive Pulse Compression Technique  

NASA Technical Reports Server (NTRS)

Pulse compression has been widely used in radars so that low-power, long RF pulses can be transmitted, rather than a highpower short pulse. Pulse compression radars offer a number of advantages over high-power short pulsed radars, such as no need of high-power RF circuitry, no need of high-voltage electronics, compact size and light weight, better range resolution, and better reliability. However, range sidelobe associated with pulse compression has prevented the use of this technique on spaceborne radars since surface returns detected by range sidelobes may mask the returns from a nearby weak cloud or precipitation particles. Research on adaptive pulse compression was carried out utilizing a field-programmable gate array (FPGA) waveform generation board and a radar transceiver simulator. The results have shown significant improvements in pulse compression sidelobe performance. Microwave and millimeter-wave radars present many technological challenges for Earth and planetary science applications. The traditional tube-based radars use high-voltage power supply/modulators and high-power RF transmitters; therefore, these radars usually have large size, heavy weight, and reliability issues for space and airborne platforms. Pulse compression technology has provided a path toward meeting many of these radar challenges. Recent advances in digital waveform generation, digital receivers, and solid-state power amplifiers have opened a new era for applying pulse compression to the development of compact and high-performance airborne and spaceborne remote sensing radars. The primary objective of this innovative effort is to develop and test a new pulse compression technique to achieve ultrarange sidelobes so that this technique can be applied to spaceborne, airborne, and ground-based remote sensing radars to meet future science requirements. By using digital waveform generation, digital receiver, and solid-state power amplifier technologies, this improved pulse compression technique could bring significant impact on future radar development. The novel feature of this innovation is the non-linear FM (NLFM) waveform design. The traditional linear FM has the limit (-20 log BT -3 dB) for achieving ultra-low-range sidelobe in pulse compression. For this study, a different combination of 20- or 40-microsecond chirp pulse width and 2- or 4-MHz chirp bandwidth was used. These are typical operational parameters for airborne or spaceborne weather radars. The NLFM waveform design was then implemented on a FPGA board to generate a real chirp signal, which was then sent to the radar transceiver simulator. The final results have shown significant improvement on sidelobe performance compared to that obtained using a traditional linear FM chirp.

Li, Lihua; Coon, Michael; McLinden, Matthew

2013-01-01

470

Testability Transformation --Program Transformation to Improve Testability  

E-print Network

Testability Transformation -- Program Transformation to Improve Testability Mark Harman1 , Andr, 26 Richmond Street, Glasgow G1 1XH, UK. Corresponding Author. Abstract. Testability transformation. The goal is to improve the testing process by transforming a program to one that is more amenable

Binkley, David W.

471

Testability Transformation: Program Transformation to Improve Testability  

E-print Network

Testability Transformation: Program Transformation to Improve Testability An Overview of Recent Author. Abstract. Testability transformation is a new form of program transfor- mation in which the goal to some chosen test adequacy criterion. The goal is to improve the testing process by transforming

Singer, Jeremy

472

Single-harmonic enhancement by controlling the chirp of the driving laser pulse during high-order harmonic generation from GaAs plasma  

SciTech Connect

We report a study of the enhancement of the intensity of the 27th-harmonic radiation produced during the high-order harmonic generation from the GaAs plasma by controlling the chirp of the fundamental Ti:sapphire laser radiation. The influence of Ga and As ions on the enhancement of the 27th-harmonic radiation is also studied.

Ganeev, Rashid A.; Singhal, Himanshu; Naik, Prasad Anant; Arora, Vipul; Chakravarty, Uday; Chakera, Juzer Ali; Khan, Riyaz Ahmed; Redkin, Pavel V.; Raghuramaiah, Manchi; Gupta, Parshotam Dass [Akadempribor Scientific Association, Academy of Sciences of Uzbekistan, Tashkent 700125 (Uzbekistan); Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Samarqand State University, Samarqand 703004 (Uzbekistan); Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

2006-12-15

473

Efficient All-Diode-Pumped Double Stage Femtosecond Optical Parametric Chirped Pulse Amplification at 1-kHz with Periodically Poled KTiOPO4  

NASA Astrophysics Data System (ADS)

A practical efficient optical parametric chirped pulse amplification is demonstrated with periodically poled KTiOPO4. It provides a compact solution to amplify stretched pulses to the 100 ?J level (signal + idler) at 1 kHz. The amplified signal pulses near 1.57 ?m are recompressed to 270 fs.

Petrov, Valentin; Noack, Frank; Rotermund, Fabian; Pasiskevicius, Valdas; Fragemann, Anna; Laurell, Fredrik; Hundertmark, Holger; Adel, Peter; Fallnich, Carsten

2003-11-01

474

High Transformer ratios in collinear wakefield accelerators.  

SciTech Connect

Based on our previous experiment that successfully demonstrated wakefield transformer ratio enhancement in a 13.625 GHz dielectric-loaded collinear wakefield accelerator using the ramped bunch train technique, we present here a redesigned experimental scheme for even higher enhancement of the efficiency of this accelerator. Design of a collinear wakefield device with a transformer ratio R2, is presented. Using a ramped bunch train (RBT) rather than a single drive bunch, the enhanced transformer ratio (ETR) technique is able to increase the transformer ratio R above the ordinary limit of 2. To match the wavelength of the fundamental mode of the wakefield with the bunch length (sigmaz=2 mm) of the new Argonne wakefield accelerator (AWA) drive gun (where the experiment will be performed), a 26.625 GHz dielectric based accelerating structure is required. This transformer ratio enhancement technique based on our dielectric-loaded waveguide design will result in a compact, high efficiency accelerating structures for future wakefield accelerators.

Power, J. G.; Conde, M.; Yusof, Z.; Gai, W.; Jing, C.; Kanreykin, A.; Schoessow, P.; High Energy Physics; Euclid Techlabs, LLC

2008-01-01

475

A Posteriori Restoration of Block Transform-Compressed Data  

NASA Technical Reports Server (NTRS)

The Galileo spacecraft will use lossy data compression for the transmission of its science imagery over the low-bandwidth communication system. The technique chosen for image compression is a block transform technique based on the Integer Cosine Transform, a derivative of the JPEG image compression standard. Considered here are two known a posteriori enhancement techniques, which are adapted.

Brown, R.; Boden, A. F.

1995-01-01

476

Likelihood transform: making optimization and parameter estimation easier  

E-print Network

Parameterized optimization and parameter estimation is of great importance in almost every branch of modern science, technology and engineering. A practical issue in the problem is that when the parameter space is large and the available data is noisy, the geometry of the likelihood surface in the parameter space will be complicated. This makes searching and optimization algorithms computationally expensive, sometimes even beyond reach. In this paper, we define a likelihood transform which can make the structure of the likelihood surface much simpler, hence reducing the intrinsic complexity and easing optimization significantly. We demonstrate the properties of likelihood transform by apply it to a simplified gravitational wave chirp signal search. For the signal with an signal-to-noise ratio 20, likelihood transform has made a deterministic template-based search possible for the first time, which turns out to be 1000 times more efficient than an exhaustive grid- based search. The method in principle can be applied to other problems in other fields as the spirit of parameterized optimization and parameter estimation problem is the same.

Yan Wang