Wedge-shaped slice-selective adiabatic inversion pulse for controlling temporal width of bolus in pulsed arterial spin labeling

PubMed Central

Guo, Jia; Buxton, Richard B.; Wong, Eric C.

2015-01-01

Purpose In pulsed arterial spin labeling (PASL) methods, arterial blood is labeled via inverting a slab with uniform thickness, resulting in different temporal widths of boluses in vessels with different flow velocities. This limits the temporal resolution and signal-to-noise ratio (SNR) efficiency gains in PASL-based methods intended for high temporal resolution and SNR efficiency, such as Turbo-ASL and Turbo-QUASAR. Theory and Methods A novel wedge-shaped (WS) adiabatic inversion pulse is developed by adding in-plane gradient pulses to a slice-selective (SS) adiabatic inversion pulse to linearly modulate the inversion thicknesses at different locations while maintaining the adiabatic properties of the original pulse. A hyperbolic secant (HS) based WS inversion pulse was implemented. Its performance was tested in simulations, phantom and human experiments, and compared to an SS HS inversion pulse. Results Compared to the SS inversion pulse, the WS inversion pulse is capable of inducing different inversion thicknesses at different locations. It can be adjusted to generate a uniform temporal width of boluses in arteries at locations with different flow velocities. Conclusion The WS inversion pulse can be used to control the temporal widths of labeled boluses in PASL experiments. This should benefit PASL experiments by maximizing labeling duty cycle, and improving temporal resolution and SNR efficiency. PMID:26451521

Time-to-space mapping of femtosecond pulses.

PubMed

Nuss, M C; Li, M; Chiu, T H; Weiner, A M; Partovi, A

1994-05-01

We report time-to-space mapping of femtosecond light pulses in a temporal holography setup. By reading out a temporal hologram of a short optical pulse with a continuous-wave diode laser, we accurately convert temporal pulse-shape information into a spatial pattern that can be viewed with a camera. We demonstrate real-time acquisition of electric-field autocorrelation and cross correlation of femtosecond pulses with this technique.

THE TEMPORAL AND SPECTRAL CHARACTERISTICS OF 'FAST RISE AND EXPONENTIAL DECAY' GAMMA-RAY BURST PULSES

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

Peng, Z. Y.; Ma, L.; Yin, Y.

2010-08-01

In this paper, we have analyzed the temporal and spectral behavior of 52 fast rise and exponential decay (FRED) pulses in 48 long-duration gamma-ray bursts (GRBs) observed by the CGRO/BATSE, using a pulse model with two shape parameters and the Band model with three shape parameters, respectively. It is found that these FRED pulses are distinguished both temporally and spectrally from those in the long-lag pulses. In contrast to the long-lag pulses, only one parameter pair indicates an evident correlation among the five parameters, which suggests that at least four parameters are needed to model burst temporal and spectral behavior.more » In addition, our studies reveal that these FRED pulses have the following correlated properties: (1) long-duration pulses have harder spectra and are less luminous than short-duration pulses and (2) the more asymmetric the pulses are, the steeper are the evolutionary curves of the peak energy (E{sub p}) in the {nu}f{sub {nu}} spectrum within the pulse decay phase. Our statistical results give some constraints on the current GRB models.« less

Simple and robust generation of ultrafast laser pulse trains using polarization-independent parallel-aligned thin films

NASA Astrophysics Data System (ADS)

Wang, Andong; Jiang, Lan; Li, Xiaowei; Wang, Zhi; Du, Kun; Lu, Yongfeng

2018-05-01

Ultrafast laser pulse temporal shaping has been widely applied in various important applications such as laser materials processing, coherent control of chemical reactions, and ultrafast imaging. However, temporal pulse shaping has been limited to only-in-lab technique due to the high cost, low damage threshold, and polarization dependence. Herein we propose a novel design of ultrafast laser pulse train generation device, which consists of multiple polarization-independent parallel-aligned thin films. Various pulse trains with controllable temporal profile can be generated flexibly by multi-reflections within the splitting films. Compared with other pulse train generation techniques, this method has advantages of compact structure, low cost, high damage threshold and polarization independence. These advantages endow it with high potential for broad utilization in ultrafast applications.

Spike Train Similarity Space (SSIMS) Method Detects Effects of Obstacle Proximity and Experience on Temporal Patterning of Bat Biosonar

PubMed Central

Accomando, Alyssa W.; Vargas-Irwin, Carlos E.; Simmons, James A.

2018-01-01

Bats emit biosonar pulses in complex temporal patterns that change to accommodate dynamic surroundings. Efforts to quantify these patterns have included analyses of inter-pulse intervals, sonar sound groups, and changes in individual signal parameters such as duration or frequency. Here, the similarity in temporal structure between trains of biosonar pulses is assessed. The spike train similarity space (SSIMS) algorithm, originally designed for neural activity pattern analysis, was applied to determine which features of the environment influence temporal patterning of pulses emitted by flying big brown bats, Eptesicus fuscus. In these laboratory experiments, bats flew down a flight corridor through an obstacle array. The corridor varied in width (100, 70, or 40 cm) and shape (straight or curved). Using a relational point-process framework, SSIMS was able to discriminate between echolocation call sequences recorded from flights in each of the corridor widths. SSIMS was also able to tell the difference between pulse trains recorded during flights where corridor shape through the obstacle array matched the previous trials (fixed, or expected) as opposed to those recorded from flights with randomized corridor shape (variable, or unexpected), but only for the flight path shape in which the bats had previous training. The results show that experience influences the temporal patterns with which bats emit their echolocation calls. It is demonstrated that obstacle proximity to the bat affects call patterns more dramatically than flight path shape. PMID:29472848

Spike Train Similarity Space (SSIMS) Method Detects Effects of Obstacle Proximity and Experience on Temporal Patterning of Bat Biosonar.

PubMed

Accomando, Alyssa W; Vargas-Irwin, Carlos E; Simmons, James A

2018-01-01

Bats emit biosonar pulses in complex temporal patterns that change to accommodate dynamic surroundings. Efforts to quantify these patterns have included analyses of inter-pulse intervals, sonar sound groups, and changes in individual signal parameters such as duration or frequency. Here, the similarity in temporal structure between trains of biosonar pulses is assessed. The spike train similarity space (SSIMS) algorithm, originally designed for neural activity pattern analysis, was applied to determine which features of the environment influence temporal patterning of pulses emitted by flying big brown bats, Eptesicus fuscus . In these laboratory experiments, bats flew down a flight corridor through an obstacle array. The corridor varied in width (100, 70, or 40 cm) and shape (straight or curved). Using a relational point-process framework, SSIMS was able to discriminate between echolocation call sequences recorded from flights in each of the corridor widths. SSIMS was also able to tell the difference between pulse trains recorded during flights where corridor shape through the obstacle array matched the previous trials (fixed, or expected) as opposed to those recorded from flights with randomized corridor shape (variable, or unexpected), but only for the flight path shape in which the bats had previous training. The results show that experience influences the temporal patterns with which bats emit their echolocation calls. It is demonstrated that obstacle proximity to the bat affects call patterns more dramatically than flight path shape.

Spatio-temporal shaping of photocathode laser pulses for linear electron accelerators

NASA Astrophysics Data System (ADS)

Mironov, S. Yu; Andrianov, A. V.; Gacheva, E. I.; Zelenogorskii, V. V.; Potemkin, A. K.; Khazanov, E. A.; Boonpornprasert, P.; Gross, M.; Good, J.; Isaev, I.; Kalantaryan, D.; Kozak, T.; Krasilnikov, M.; Qian, H.; Li, X.; Lishilin, O.; Melkumyan, D.; Oppelt, A.; Renier, Y.; Rublack, T.; Felber, M.; Huck, H.; Chen, Y.; Stephan, F.

2017-10-01

Methods for the spatio-temporal shaping of photocathode laser pulses for generating high brightness electron beams in modern linear accelerators are discussed. The possibility of forming triangular laser pulses and quasi-ellipsoidal structures is analyzed. The proposed setup for generating shaped laser pulses was realised at the Institute of Applied Physics (IAP) of the Russian Academy of Sciences (RAS). Currently, a prototype of the pulse-shaping laser system is installed at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). Preliminary experiments on electron beam generation using ultraviolet laser pulses from this system were carried out at PITZ, in which electron bunches with a 0.5-nC charge and a transverse normalized emittance of 1.1 mm mrad were obtained. A new scheme for the three-dimensional shaping of laser beams using a volume Bragg profiled grating is proposed at IAP RAS and is currently being tested for further electron beam generation experiments at the PITZ photoinjector.

Gaussian temporal modulation for the behavior of multi-sinc Schell-model pulses in dispersive media

NASA Astrophysics Data System (ADS)

Liu, Xiayin; Zhao, Daomu; Tian, Kehan; Pan, Weiqing; Zhang, Kouwen

2018-06-01

A new class of pulse source with correlation being modeled by the convolution operation of two legitimate temporal correlation function is proposed. Particularly, analytical formulas for the Gaussian temporally modulated multi-sinc Schell-model (MSSM) pulses generated by such pulse source propagating in dispersive media are derived. It is demonstrated that the average intensity of MSSM pulses on propagation are reshaped from flat profile or a train to a distribution with a Gaussian temporal envelope by adjusting the initial correlation width of the Gaussian pulse. The effects of the Gaussian temporal modulation on the temporal degree of coherence of the MSSM pulse are also analyzed. The results presented here show the potential of coherence modulation for pulse shaping and pulsed laser material processing.

Advanced Laser Technologies for High-brightness Photocathode Electron Gun

NASA Astrophysics Data System (ADS)

Tomizawa, Hiromitsu

A laser-excited photocathode RF gun is one of the most reliable high-brightness electron beam sources for XFELs. Several 3D laser shaping methods have been developed as ideal photocathode illumination sources at SPring-8 since 2001. To suppress the emittance growth caused by nonlinear space-charge forces, the 3D cylindrical UV-pulse was optimized spatially as a flattop and temporally as squarely stacked chirped pulses. This shaping system is a serial combination of a deformable mirror that adaptively shapes the spatial profile with a genetic algorithm and a UV-pulse stacker that consists of four birefringent α-BBO crystal rods for temporal shaping. Using this 3D-shaped pulse, a normalized emittance of 1.4 π mm mrad was obtained in 2006. Utilizing laser's Z-polarization, Schottky-effect-gated photocathode gun was proposed in 2006. The cathode work functions are reduced by a laser-induced Schottky effect. As a result of focusing a radially polarized laser pulse with a hollow lens in vacuum, the Z-field (Z-polarization) is generated at the cathode.

Temporal femtosecond pulse shaping dependence of laser-induced periodic surface structures in fused silica

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

Shi, Xuesong; Jiang, Lan; Li, Xin, E-mail: lixin02@bit.edu.cn

2014-07-21

The dependence of periodic structures and ablated areas on temporal pulse shaping is studied upon irradiation of fused silica by femtosecond laser triple-pulse trains. Three types of periodic structures can be obtained by using pulse trains with designed pulse delays, in which the three-dimensional nanopillar arrays with ∼100–150 nm diameters and ∼200 nm heights are first fabricated in one step. These nanopillars arise from the break of the ridges of ripples in the upper portion, which is caused by the split of orthogonal ripples in the bottom part. The localized transient electron dynamics and corresponding material properties are considered for the morphologicalmore » observations.« less

High aspect ratio nanoholes in glass generated by femtosecond laser pulses with picosecond intervals

NASA Astrophysics Data System (ADS)

Ahn, Sanghoon; Choi, Jiyeon; Noh, Jiwhan; Cho, Sung-Hak

2018-02-01

Because of its potential uses, high aspect ratio nanostructures have been interested for last few decades. In order to generate nanostructures, various techniques have been attempted. Femtosecond laser ablation is one of techniques for generating nanostructures inside a transparent material. For generating nanostructures by femtosecond laser ablation, previous studies have been attempted beam shaping such as Bessel beam and temporal tailored beam. Both methods suppress electron excitation at near surface and initiate interference of photons at certain depth. Recent researches indicate that shape of nanostructures is related with temporal change of electron density and number of self-trapped excitons. In this study, we try to use the temporal change of electron density induced by femtosecond laser pulse for generating high aspect ratio nanoholes. In order to reveal the effect of temporal change of electron density, secondary pulses are irradiated from 100 to 1000 ps after the irradiation of first pulse. Our result shows that diameter of nanoholes is increasing and depth of nanoholes is decreasing as pulse to pulse interval is getting longer. With manipulating of pulse to pulse interval, we could generate high aspect ratio nanoholes with diameter of 250-350 nm and depth of 4∼6 μm inside a glass.

Deconvolving the temporal response of photoelectric x-ray detectors for the diagnosis of pulsed radiations

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

Zou, Shiyang; Song, Peng; Pei, Wenbing

2013-09-15

Based on the conjugate gradient method, a simple algorithm is presented for deconvolving the temporal response of photoelectric x-ray detectors (XRDs) to reconstruct the resolved time-dependent x-ray fluxes. With this algorithm, we have studied the impact of temporal response of XRD on the radiation diagnosis of hohlraum heated by a short intense laser pulse. It is found that the limiting temporal response of XRD not only postpones the rising edge and peak position of x-ray pulses but also smoothes the possible fluctuations of radiation fluxes. Without a proper consideration of the temporal response of XRD, the measured radiation flux canmore » be largely misinterpreted for radiation pulses of a hohlraum heated by short or shaped laser pulses.« less

Maximizing energy deposition by shaping few-cycle laser pulses

NASA Astrophysics Data System (ADS)

Gateau, Julien; Patas, Alexander; Matthews, Mary; Hermelin, Sylvain; Lindinger, Albrecht; Kasparian, Jérôme; Wolf, Jean-Pierre

2018-07-01

We experimentally investigate the impact of pulse shape on the dynamics of laser-generated plasma in rare gases. Fast-rising triangular pulses with a slower decay lead to early ionization of the gas and depose energy more efficiently than their temporally reversed counterparts. As a result, in both argon and krypton, the induced shockwave as well as the plasma luminescence are stronger. This is due to an earlier availability of free electrons to undergo inverse Bremsstrahlung on the pulse trailing edge. Our results illustrate the ability of adequately tailored pulse shapes to optimize the energy deposition in gas plasmas.

Impact of initial pulse shape on the nonlinear spectral compression in optical fibre

NASA Astrophysics Data System (ADS)

Boscolo, Sonia; Chaussard, Frederic; Andresen, Esben; Rigneault, Hervé; Finot, Christophe

2018-02-01

We theoretically study the effects of the temporal intensity profile of the initial pulse on the nonlinear propagation spectral compression process arising from nonlinear propagation in an optical fibre. Various linearly chirped input pulse profiles are considered, and their dynamics is explained with the aid of time-frequency representations. While initially parabolic-shaped pulses show enhanced spectral compression compared to Gaussian pulses, no significant spectral narrowing occurs when initially super-Gaussian pulses are used. Triangular pulses lead to a spectral interference phenomenon similar to the Fresnel bi-prism experiment.

Airy pulse shaping using time-dependent power-law potentials

NASA Astrophysics Data System (ADS)

Han, Tianwen; Chen, Hao; Qin, Chengzhi; Li, Wenwan; Wang, Bing; Lu, Peixiang

2018-06-01

We investigate the temporal and spectral evolutions of finite-energy Airy pulses in the presence of power-law optical potentials. The potentials are generated by the time-dependent pumped light, which propagates together with the Airy pulses in a highly nonlinear optical fiber. We show that the intrinsic acceleration of Airy pulses can be modified by an external force that stems from a linear potential, and hence unidirectional frequency shift can be realized. When a triangle potential is employed, the pulse will exhibit self-splitting both in temporal and spectral domains. Additionally, as a parabolic potential is utilized, both the temporal waveform and frequency spectrum of the Airy pulse will exchange alternately between the Airy and Gaussian profiles. By using higher-order power-law potentials, we also realize both revival and antirevival effects for the Airy pulses. The study may find wide applications in pulse reshaping and spectral-temporal imaging for both optical communication and signal processing.

The shaped pulses control and operation on the SG-III prototype facility

NASA Astrophysics Data System (ADS)

Ping, Li; Wei, Wang; Sai, Jin; Wanqing, Huang; Wenyi, Wang; Jingqin, Su; Runchang, Zhao

2018-04-01

The laser driven inertial confined fusion experiments require careful temporal shape control of the laser pulse. Two approaches are introduced to improve the accuracy and efficiency of the close loop feedback system for long term operation in TIL; the first one is a statistical model to analyze the variation of the parameters obtained from previous shots, the other is a matrix algorithm proposed to relate the electrical signal and the impulse amplitudes. With the model and algorithm applied in the pulse shaping in TIL, a variety of shaped pulses were produced with a 10% precision in half an hour for almost three years under different circumstance.

Femtosecond direct space-to-time pulse shaping in an integrated-optic configuration.

PubMed

Leaird, D E; Weiner, A M

2004-07-01

We demonstrate femtosecond operation of an integrated-optic direct space-to-time pulse shaper for which there is a direct mapping (no Fourier transform) between the spatial position of the masking function and the temporal position in the output waveform. The apparatus is used to generate trains of more than 30 pulses as an ultrafast optical data packet over approximately an 80-ps temporal window.

Pulse shaping in mode-locked fiber lasers by in-cavity spectral filter.

PubMed

Boscolo, Sonia; Finot, Christophe; Karakuzu, Huseyin; Petropoulos, Periklis

2014-02-01

We numerically show the possibility of pulse shaping in a passively mode-locked fiber laser by inclusion of a spectral filter into the laser cavity. Depending on the amplitude transfer function of the filter, we are able to achieve various regimes of advanced temporal waveform generation, including ones featuring bright and dark parabolic-, flat-top-, triangular- and saw-tooth-profiled pulses. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for controlling the dynamics of mode-locked fiber lasers.

Pulse generation and preamplification for long pulse beamlines of Orion laser facility.

PubMed

Hillier, David I; Winter, David N; Hopps, Nicholas W

2010-06-01

We describe the pulse generation, shaping, and preamplification system for the nanosecond beamlines of the Orion laser facility. The system generates shaped laser pulses of up to approximately 1 J of 100 ps-5 ns duration with a programmable temporal profile. The laser has a 30th-power supergaussian spatial profile and is diffraction limited. The system is capable of imposing 2D smoothing by spectral dispersion upon the beam, which will produce a nonuniformity of 10% rms at the target.

Effect of the temporal laser pulse asymmetry on pair production processes during intense laser-electron scattering

NASA Astrophysics Data System (ADS)

Hojbota, C. I.; Kim, Hyung Taek; Kim, Chul Min; Pathak, V. B.; Nam, Chang Hee

2018-06-01

We investigate the effects of laser pulse shape on strong-field quantum electrodynamics (QED) processes during the collision between a relativistic electron beam and an intense laser pulse. The interplay between high-energy photon emission and two pair production processes, i.e. nonlinear Breit–Wheeler (BW) and Trident, was investigated using particle-in-cell simulations. We found that the temporal evolution of these two processes could be controlled by using laser pulses with different degrees of asymmetry. The temporal envelope of the laser pulse can significantly affect the number of pairs coming from the Trident process, while the nonlinear BW process is less sensitive to it. This study shows that the two QED processes can be examined with state-of-the-art petawatt lasers and the discrimination of the two pair creation processes is feasible by adjusting the temporal asymmetry of the colliding laser pulse.

Pair Production Induced by Ultrashort and Ultraintense Laser Pulses in Plasmas

NASA Astrophysics Data System (ADS)

Luo, Yue-E.; Wang, Xue-Wen; Wang, Yuan-Sheng; Ji, Shen-Tong; Yu, Hong

2018-06-01

The probability of Schwinger pair production is calculated, which is induced by an ultraintense and ultrashort laser pulse propagating in a plasma. The dependence of the probability on the amplitude of the laser pulse and the frequency of plasmas is analyzed. Particularly, the effect of the pulse duration on the probability is discussed, by introducing a pulse-shape function to describe the temporal shape of the laser pulse. The results show that a laser with shorter pulse is more efficient in pair production. The probability of pair production increases when the order of the duration is comparable to the period of a laser.

Picosecond temporal contrast of Ti:Sapphire lasers (Conference Presentation)

NASA Astrophysics Data System (ADS)

Kalashnikov, Mikhail P.; Khodakovskiy, Nikita

2017-05-01

The temporal shape of recompressed Ti:sapphire CPA pulses typically contains relatively long pre- and post- pedestals appearing on a picosecond time scale. Despite playing a key role in laser-matter interactions, these artifacts - especially the shape of the leading front of the recompressed pulses - are poorly investigated and understood. The related publications consider picosecond pedestals appearing at both fronts of the main pulse to be related to scattering of the stretched pulse off diffraction gratings inside the stretcher or due to clipping of the pulse spectrum at dielectric coatings. In our experiments we analyzed different types of stretcher-compressor combinations used in Ti:Sapphire laser systems. These include a prism-based stretcher and a bulk compressor, transmission and reflection diffraction gratings - based combinations. We identified pedestals that are typical for the particular stretcher-compressor combination. Especially investigated are those which are coherent with the major recompressed pulse, since with self-phase modulation in power amplifiers they will grow nonlinearly and finally appear symmetric around the major pulse, generating the pre-pedestal from the post-pedestal. Thus, a previously unreported influence of the trailing pedestal has been identified. It is commonly known that recompressed pulses from Ti:sapphire chirped-pulse amplifier systems are accompanied by a slowly decaying ragged post-pedestal. The detailed investigation shows that it consists of numerous pulses with temporal separation in the picosecond range. These are coherent with the main pulse. Moreover, the temporal structure of the trailing pedestal is independent of the particular realization of the Ti:sapphire system and it is present in radiation of any Ti:Sapphire CPA system including Kerr- mode locked master oscillators. Our investigations show that the coherent ragged post-pedestal is the post-radiation of inverted Ti:sapphire medium resulting from phonon-photon interactions.

Improved safety of retinal photocoagulation with a shaped beam and modulated pulse

NASA Astrophysics Data System (ADS)

Sramek, Christopher; Brown, Jefferson; Paulus, Yannis M.; Nomoto, Hiroyuki; Palanker, Daniel

2010-02-01

Shorter pulse durations help confine thermal damage during retinal photocoagulation, decrease treatment time and minimize pain. However, safe therapeutic window (the ratio of threshold powers for rupture and mild coagulation) decreases with shorter exposures. A ring-shaped beam enables safer photocoagulation than conventional beams by reducing the maximum temperature in the center of the spot. Similarly, a temporal pulse modulation decreasing its power over time improves safety by maintaining constant temperature for a significant portion of the pulse. Optimization of the beam and pulse shapes was performed using a computational model. In vivo experiments were performed to verify the predicted improvement. With each of these approaches, the pulse duration can be decreased by a factor of two, from 20 ms down to 10 ms while maintaining the same therapeutic window.

Optical emission and nanoparticle generation in Al plasmas using ultrashort laser pulses temporally optimized by real-time spectroscopic feedback

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

Guillermin, M.; Colombier, J. P.; Audouard, E.

2010-07-15

With an interest in pulsed laser deposition and remote spectroscopy techniques, we explore here the potential of laser pulses temporally tailored on ultrafast time scales to control the expansion and the excitation degree of various ablation products including atomic species and nanoparticulates. Taking advantage of automated pulse-shaping techniques, an adaptive procedure based on spectroscopic feedback is applied to regulate the irradiance and enhance the optical emission of monocharged aluminum ions with respect to the neutral signal. This leads to optimized pulses usually consisting in a series of femtosecond peaks distributed on a longer picosecond sequence. The ablation features induced bymore » the optimized pulse are compared with those determined by picosecond pulses generated by imposed second-order dispersion or by double pulse sequences with adjustable picosecond separation. This allows to analyze the influence of fast- and slow-varying envelope features on the material heating and the resulting plasma excitation degree. Using various optimal pulse forms including designed asymmetric shapes, we analyze the establishment of surface pre-excitation that enables conditions of enhanced radiation coupling. Thin films elaborated by unshaped femtosecond laser pulses and by optimized, stretched, or double pulse sequences are compared, indicating that the nanoparticles generation efficiency is strongly influenced by the temporal shaping of the laser irradiation. A thermodynamic scenario involving supercritical heating is proposed to explain enhanced ionization rates and lower particulates density for optimal pulses. Numerical one-dimensional hydrodynamic simulations for the excited matter support the interpretation of the experimental results in terms of relative efficiency of various relaxation paths for excited matter above or below the thermodynamic stability limits. The calculation results underline the role of the temperature and density gradients along the ablated plasma plume which lead to the spatial distinct locations of excited species. Moreover, the nanoparticles sizes are computed based on liquid layer ejection followed by a Rayleigh and Taylor instability decomposition, in good agreement with the experimental findings.« less

Generation of 360 ps laser pulse with 3 J energy by stimulated Brillouin scattering with a nonfocusing scheme.

PubMed

Zhu, Xuehua; Wang, Yulei; Lu, Zhiwei; Zhang, Hengkang

2015-09-07

A new technique for generating high energy sub-400 picosecond laser pulses is presented in this paper. The temporally super-Gaussian-shaped laser pulses are used as light source. When the forward pump is reflected by the rear window of SBS cell, the frequency component that fulfills Brillouin frequency shift in its sideband spectrum works as a seed and excites SBS, which results in efficient compression of the incident pump pulse. First the pulse compression characteristics of 20th-order super-Gaussian temporally shaped pulses with 5 ns duration are analyzed theoretically. Then experiment is carried out with a narrow-band high power Nd:glass laser system at the double-frequency and wavelength of 527 nm which delivers 5 ns super-Gaussian temporally shaped pulses with single pulse energy over 10 J. FC-40 is used as the active SBS medium for its brief phonon lifetime and high power capacity. In the experiment, the results agree well with the numerical calculations. With pump energy of 5.36J, the compression of pulse duration from 5 ns to 360 ps is obtained. The output energy is 3.02 J and the peak-power is magnified 8.3 times. Moreover, the compressed pulse shows a high stability because it is initiated by the feedback of rear window rather than the thermal noise distributing inside the medium. This technique of generating high energy hundred picosecond laser pulses has simple structure and is easy to operate, and it also can be scaled to higher energy pulse compression in the future. Meanwhile, it should also be taken into consideration that in such a nonfocusing scheme, the noise-initiated SBS would increase the distortion on the wavefront of Stokes beam to some extent, and the pump energy should be controlled below the threshold of noise-initiated SBS.

Mid-infrared beam splitter for ultrashort pulses.

PubMed

Somma, Carmine; Reimann, Klaus; Woerner, Michael; Kiel, Thomas; Busch, Kurt; Braun, Andreas; Matalla, Mathias; Ickert, Karina; Krüger, Olaf

2017-08-01

A design is presented for a beam splitter suitable for ultrashort pulses in the mid-infrared and terahertz spectral range consisting of a structured metal layer on a diamond substrate. Both the theory and experiment show that this beam splitter does not distort the temporal pulse shape.

Optimal pulse design for communication-oriented slow-light pulse detection.

PubMed

Stenner, Michael D; Neifeld, Mark A

2008-01-21

We present techniques for designing pulses for linear slow-light delay systems which are optimal in the sense that they maximize the signal-to-noise ratio (SNR) and signal-to-noise-plus-interference ratio (SNIR) of the detected pulse energy. Given a communication model in which input pulses are created in a finite temporal window and output pulse energy in measured in a temporally-offset output window, the SNIR-optimal pulses achieve typical improvements of 10 dB compared to traditional pulse shapes for a given output window offset. Alternatively, for fixed SNR or SNIR, window offset (detection delay) can be increased by 0.3 times the window width. This approach also invites a communication-based model for delay and signal fidelity.

Femtosecond profiling of shaped x-ray pulses

NASA Astrophysics Data System (ADS)

Hoffmann, M. C.; Grguraš, I.; Behrens, C.; Bostedt, C.; Bozek, J.; Bromberger, H.; Coffee, R.; Costello, J. T.; DiMauro, L. F.; Ding, Y.; Doumy, G.; Helml, W.; Ilchen, M.; Kienberger, R.; Lee, S.; Maier, A. R.; Mazza, T.; Meyer, M.; Messerschmidt, M.; Schorb, S.; Schweinberger, W.; Zhang, K.; Cavalieri, A. L.

2018-03-01

Arbitrary manipulation of the temporal and spectral properties of x-ray pulses at free-electron lasers would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the free-electron laser driving electron bunch can be tuned to emit a pair of x-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the x-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fully suppressed. Therefore, the ability to directly characterize the x-rays is essential to ensure precise and consistent control. In this work, we have generated x-ray pulse pairs via electron bunch shaping and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. This achievement completes an important step toward future x-ray pulse shaping techniques.

Applications of Space-Time Duality

NASA Astrophysics Data System (ADS)

Plansinis, Brent W.

The concept of space-time duality is based on a mathematical analogy between paraxial diffraction and narrowband dispersion, and has led to the development of temporal imaging systems. The first part of this thesis focuses on the development of a temporal imaging system for the Laboratory for Laser Energetics. Using an electro-optic phase modulator as a time lens, a time-to-frequency converter is constructed capable of imaging pulses between 3 and 12 ps. Numerical simulations show how this system can be improved to image the 1-30 ps range used in OMEGA-EP. By adjusting the timing between the pulse and the sinusoidal clock of the phase modulator, the pulse spectrum can be selectively narrowed, broadened, or shifted. An experimental demonstration of this effect achieved spectral narrowing and broadening by a factor of 2. Numerical simulations show narrowing by a factor of 8 is possible with modern phase modulators. The second part of this thesis explores the space-time analog of reflection and refraction from a moving refractive index boundary. From a physics perspective, a temporal boundary breaks translational symmetry in time, requiring the momentum of the photon to remain unchanged while its energy may change. This leads to a shifting and splitting of the pulse spectrum as the boundary is crossed. Equations for the reflected and transmitted frequencies and a condition for total internal reflection are found. Two of these boundaries form a temporal waveguide, which confines the pulse to a narrow temporal window. These waveguides have a finite number of modes, which do not change during propagation. A single-mode waveguide can be created, allowing only a single pulse shape to form within the waveguide. Temporal reflection and refraction produce a frequency dependent phase shift on the incident pulse, leading to interference fringes between the incident light and the reflected light. In a waveguide, this leads to self-imaging, where the pulse shape reforms periodically at finite propagation lengths. Numerical simulations are performed for the specific case where the moving boundary is produced through cross-phase modulation. In this case, the Kerr nonlinearity causes the boundary to change during propagation, leading to unique temporal and spectral behavior.

Experimental research on time-resolved evolution of cathode plasma expansion velocity in a long pulsed magnetically insulated coaxial diode

NASA Astrophysics Data System (ADS)

Zhu, Danni; Zhang, Jun; Zhong, Huihuang; Ge, Xingjun; Gao, Jingming

2018-02-01

Unlike planar diodes, separate research of the axial and radial plasma expansion velocities is difficult for magnetically insulated coaxial diodes. Time-resolved electrical diagnostic which is based on the voltage-ampere characteristics has been employed to study the temporal evolution of the axial and radial cathode plasma expansion velocities in a long pulsed magnetically insulated coaxial diode. Different from a planar diode with a "U" shaped profile of temporal velocity evolution, the temporal evolution trend of the axial expansion velocity is proved to be a "V" shaped profile. Apart from the suppression on the radial expansion velocity, the strong magnetic field is also conducive to slowing down the axial expansion velocity. Compared with the ordinary graphite cathode, the carbon velvet and graphite composite cathode showed superior characteristics as judged by the low plasma expansion velocity and long-term electrical stability as a promising result for applications where long-pulsed and reliable operation at high power is required.

Long-Lag, Wide-pulse Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Norris, J. P.; Bonnell, J. T.; Kazanas, D.; Scargle, . D.; Hakkila, J.; Giblin, T. W.

2004-01-01

Currently, the best available probe of the early phase of gamma-ray burst (GRB) jet attributes is the prompt gamma-ray emission, in which several intrinsic and extrinsic variables determine GRB pulse evolution. Bright, usually complex bursts have many narrow pulses that are difficult to model due to overlap. However, the relatively simple, long spectral lag, wide-pulse bursts may have simpler physics and are easier to model. In this work we analyze the temporal and spectral behavior of wide pulses in 24 long-lag bursts, using a pulse model with two shape parameters - width and asymmetry - and the Band spectral model with three shape parameters. We find that pulses in long-lag bursts are distinguished both temporally and spectrally from those in bright bursts: the pulses in long spectral lag bursts are few in number, and approximately 100 times wider (10s of seconds), have systematically lower peaks in vF(v), harder low-energy spectra and softer high-energy spectra. We find that these five pulse descriptors are essentially uncorrelated for our long-lag sample, suggesting that at least approximately 5 parameters are needed to model burst temporal and spectral behavior. However, pulse width is strongly correlated with spectral lag; hence these two parameters may be viewed as mutual surrogates. We infer that accurate formulations for estimating GRB luminosity and total energy will depend on several gamma-ray attributes, at least for long-lag bursts. The prevalence of long-lag bursts near the BATSE trigger threshold, their predominantly low vF(v) spectral peaks, and relatively steep upper power-law spectral indices indicate that Swift will detect many such bursts.

Temporal Electron-bunch Shaping from a Photoinjector for Advanced Accelerator Applications

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

Lemery, Francois; Piot, Philippe

2014-07-01

Advanced-accelerator applications often require the production of bunches with shaped temporal distributions. An example of sought-after shape is a linearly-ramped current profile that can be improve the transformer ratio in beam-driven acceleration, or produce energy-modulated pulse for, e.g., the subsequent generation of THz radiation. Typically,  such a shaping is achieved by manipulating ultra-relativistic electron bunches. In this contribution we discuss the possibility of shaping the bunch via photoemission and demonstrate using particle-in-cell simulations the production of MeV electron bunches with quasi-ramped current profile.

Femtosecond profiling of shaped x-ray pulses

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

Hoffmann, M. C.; Grguras, I.; Behrens, C.

Arbitrary manipulation of the temporal and spectral properties of x-ray pulses at free-electron lasers would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the free-electron laser driving electron bunch can be tuned to emit a pair of x-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the x-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fullymore » suppressed. Therefore, the ability to directly characterize the x-rays is essential to ensure precise and consistent control. In this work, we have generated x-ray pulse pairs via electron bunch shaping and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. Furthermore, this achievement completes an important step toward future x-ray pulse shaping techniques.« less

Femtosecond profiling of shaped x-ray pulses

DOE PAGES

Hoffmann, M. C.; Grguras, I.; Behrens, C.; ...

2018-03-26

Arbitrary manipulation of the temporal and spectral properties of x-ray pulses at free-electron lasers would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the free-electron laser driving electron bunch can be tuned to emit a pair of x-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the x-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fullymore » suppressed. Therefore, the ability to directly characterize the x-rays is essential to ensure precise and consistent control. In this work, we have generated x-ray pulse pairs via electron bunch shaping and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. Furthermore, this achievement completes an important step toward future x-ray pulse shaping techniques.« less

High field terahertz pulse generation from plasma wakefield driven by tailored laser pulses

NASA Astrophysics Data System (ADS)

Chen, Zi-Yu

2013-06-01

A scheme to generate high field terahertz (THz) pulses by using tailored laser pulses interaction with a gas target is proposed. The laser wakefield based THz source is emitted from the asymmetric laser shape induced plasma transverse transient net currents. Particle-in-cell simulations show that THz emission with electric filed strength over 1 GV/cm can be obtained with incident laser at 1×1019 W/cm2 level, and the corresponding energy conversion efficiency is more than 10-4. The intensity scaling holds up to high field strengths. Such a source also has a broad tunability range in amplitude, frequency spectra, and temporal shape.

Long-Lag, Wide-pulse Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Norris, J. P.; Bonnell, J. T.; Kazanas, D.; Scargie, J. D.; Hakkila, J.; Giblin, T. W.

2005-01-01

The best available probe of the early phase of gamma-ray burst (GRB) jet attributes is the prompt gamma-ray emission, in which several intrinsic and extrinsic variables determine observed GRB pulse evolution, including at least: jet opening angle, profiles of Lorentz factor and matter/field density, distance of emission region from central source, and viewing angle. Bright, usually complex bursts have many narrow pulses that are difficult to model due to overlap. However, the relatively simple, long spectral lag, wide-pulse bursts may have simpler physics and are easier to model. We have analyzed the temporal and spectral behavior of wide pulses in 24 long-lag bursts from the BATSE sample, using a pulse model with two shape parameters - width and asymmetry - and the Band spectral model with three shape parameters. We find that pulses in long-lag bursts are distinguished both temporally and spectrally from those in bright bursts: the pulses in long spectral lag bursts are few in number, and approximately 100 times wider (10s of seconds), have systemtically lower peaks in nu*F(nu), harder low-energy spectra and softer high-energy spectra. These five pulse descriptors are essentially uncorrelated for our long-lag sample, suggesting that at least approximately 5 parameters are needed to model burst temporal and spectral behavior, roughly commensurate with the theoretical phase space. However, we do find that pulse width is strongly correlated with spectral lag; hence these two parameters may be viewed as mutual surrogates. The prevalence of long-lag bursts near the BATSE trigger threshold, their predominantly low nu*F(nu) spectral peaks, and relatively steep upper power-law spectral indices indicate that Swiift will detect many such bursts.

Quantum phase amplification for temporal pulse shaping and super-resolution in remote sensing

NASA Astrophysics Data System (ADS)

Yin, Yanchun

The use of nonlinear optical interactions to perform nonclassical transformations of electromagnetic field is an area of considerable interest. Quantum phase amplification (QPA) has been previously proposed as a method to perform nonclassical manipulation of coherent light, which can be experimentally realized by use of nonlinear optical mixing processes, of which phase-sensitive three-wave mixing (PSTWM) is one convenient choice. QPA occurs when PSTWM is operated in the photon number deamplification mode, i.e., when the energy is coherently transferred among the low-frequency signal and idler waves and the high-frequency pump wave. The final state is nonclassical, with the field amplitude squeezed and the phase anti-squeezed. In the temporal domain, the use of QPA has been studied to facilitate nonlinear pulse shaping. This novel method directly shapes the temporal electric field amplitude and phase using the PSTWM in a degenerate and collinear configuration, which has been analyzed using a numerical model. Several representative pulse shaping capabilities of this technique have been identified, which can augment the performance of common passive pulse shaping methods operating in the Fourier domain. The analysis indicates that a simple quadratic variation of temporal phase facilitates pulse compression and self-steepening, with features significantly shorter than the original transform-limited pulse. Thus, PSTWM can act as a direct pulse compressor based on the combined effects of phase amplification and group velocity mismatch, even without the subsequent linear phase compensation. Furthermore, it is shown numerically that pulse doublets and pulse trains can be produced at the pump frequency by utilizing the residual linear phase of the signal. Such pulse shaping capabilities are found to be within reach of this technique in common nonlinear optical crystals pumped by pulses available from compact femtosecond chirped-pulse amplification laser systems. The use of QPA in the spatial domain has also been studied as a method to enhance the spatial resolution of imaging systems. A detailed model has been developed for achieving both super-resolution and detection of phase-amplified light. The imaging resolution problem considered here is treated as a binary hypotheses testing problem. Resolution enhancement is achieved by magnification of the angular separation of two targets in the sub-Rayleigh regime. The detection model includes optimization of detector segmentation, detector noise, and detection in both the spatial and the spatial frequency domain, which provide strategies for the optimization of the signal-to-noise ratio that take advantage of both the change of the field distribution and the change of energy of the signal in the QPA process. Proof-of-principle experiments have been conducted in the spatial domain. For the first time, beam angular amplification has been demonstrated, and the experimental result is in good agreement with simulations. The experimental demonstration has been achieved by observing the correlation of amplitude and angular phase in the phase-sensitive three-wave mixing process using ultrashort laser pulses and utilizing a type I three-wave mixing process. Several diagnostics have been developed and employed in the experimental measurements, including the near-field diagnostic, the far-field diagnostic, and the interferometry diagnostic. They have all been used to confirm the existence and study the properties of the QPA process on a shot-to-shot basis. Specifically, amplitude was measured in the near-field diagnostic, while the angular phase was indirectly measured in the far-field diagnostic by determining the position of the beam centroid. Interferometric measurements have been found to be of insufficient accuracy for this measurement in the way they were implemented. The demonstration of beam angular amplification by use of QPA lays the foundation for future integrated demonstration of imaging resolution enhancement, while the results of the modeling in the time domain open opportunities for development of flexible pulse shaping benefitting a variety of ultrafast applications.

Continuous and lurching traveling pulses in neuronal networks with delay and spatially decaying connectivity

PubMed Central

Golomb, David; Ermentrout, G. Bard

1999-01-01

Propagation of discharges in cortical and thalamic systems, which is used as a probe for examining network circuitry, is studied by constructing a one-dimensional model of integrate-and-fire neurons that are coupled by excitatory synapses with delay. Each neuron fires only one spike. The velocity and stability of propagating continuous pulses are calculated analytically. Above a certain critical value of the constant delay, these pulses lose stability. Instead, lurching pulses propagate with discontinuous and periodic spatio-temporal characteristics. The parameter regime for which lurching occurs is strongly affected by the footprint (connectivity) shape; bistability may occur with a square footprint shape but not with an exponential footprint shape. For strong synaptic coupling, the velocity of both continuous and lurching pulses increases logarithmically with the synaptic coupling strength gsyn for an exponential footprint shape, and it is bounded for a step footprint shape. We conclude that the differences in velocity and shape between the front of thalamic spindle waves in vitro and cortical paroxysmal discharges stem from their different effective delay; in thalamic networks, large effective delay between inhibitory neurons arises from their effective interaction via the excitatory cells which display postinhibitory rebound. PMID:10557346

All-Fiber, Directly Chirped Laser Source for Chirped-Pulse-Amplification

NASA Astrophysics Data System (ADS)

Xin, Ran

Chirped-pulse-amplification (CPA) technology is widely used to produce ultra-short optical pulses (sub picosecond to femtoseconds) with high pulse energy. A chirped pulse laser source with flexible dispersion control is highly desirable as a CPA seed. This thesis presents an all-fiber, directly chirped laser source (DCLS) that produces nanosecond, linearly-chirped laser pulses at 1053 nm for seeding high energy CPA systems. DCLS produces a frequency chirp on an optical pulse through direct temporal phase modulation. DCLS provides programmable control for the temporal phase of the pulse, high pulse energy and diffraction-limited beam performance, which are beneficial for CPA systems. The DCLS concept is first described. Its key enabling technologies are identified and their experimental demonstration is presented. These include high-precision temporal phase control using an arbitrary waveform generator, multi-pass phase modulation to achieve high modulation depth, regenerative amplification in a fiber ring cavity and a negative feedback system that controls the amplifier cavity dynamics. A few technical challenges that arise from the multi-pass architecture are described and their solutions are presented, such as polarization management and gain-spectrum engineering in the DCLS fiber cavity. A DCLS has been built and its integration into a high energy OPCPA system is demonstrated. DCLS produces a 1-ns chirped pulse with a 3-nm bandwidth. The temporal phase and group delay dispersion on the DCLS output pulse is measured using temporal interferometry. The measured temporal phase has an ˜1000 rad amplitude and is close to a quadratic shape. The chirped pulse is amplified from 0.9 nJ to 76 mJ in an OPCPA system. The amplified pulse is compressed to close to its Fourier transform limit, producing an intensity autocorrelation trace with a 1.5-ps width. Direct compressed-pulse duration control by adjusting the phase modulation drive amplitude is demonstrated. Limitation to pulse compression is investigated using numerical simulation.

Electron beam dynamics in an ultrafast transmission electron microscope with Wehnelt electrode.

PubMed

Bücker, K; Picher, M; Crégut, O; LaGrange, T; Reed, B W; Park, S T; Masiel, D J; Banhart, F

2016-12-01

High temporal resolution transmission electron microscopy techniques have shown significant progress in recent years. Using photoelectron pulses induced by ultrashort laser pulses on the cathode, these methods can probe ultrafast materials processes and have revealed numerous dynamic phenomena at the nanoscale. Most recently, the technique has been implemented in standard thermionic electron microscopes that provide a flexible platform for studying material's dynamics over a wide range of spatial and temporal scales. In this study, the electron pulses in such an ultrafast transmission electron microscope are characterized in detail. The microscope is based on a thermionic gun with a Wehnelt electrode and is operated in a stroboscopic photoelectron mode. It is shown that the Wehnelt bias has a decisive influence on the temporal and energy spread of the picosecond electron pulses. Depending on the shape of the cathode and the cathode-Wehnelt distance, different emission patterns with different pulse parameters are obtained. The energy spread of the pulses is determined by space charge and Boersch effects, given by the number of electrons in a pulse. However, filtering effects due to the chromatic aberrations of the Wehnelt electrode allow the extraction of pulses with narrow energy spreads. The temporal spread is governed by electron trajectories of different length and in different electrostatic potentials. High temporal resolution is obtained by excluding shank emission from the cathode and aberration-induced halos in the emission pattern. By varying the cathode-Wehnelt gap, the Wehnelt bias, and the number of photoelectrons in a pulse, tradeoffs between energy and temporal resolution as well as beam intensity can be made as needed for experiments. Based on the characterization of the electron pulses, the optimal conditions for the operation of ultrafast TEMs with thermionic gun assembly are elaborated. Copyright © 2016 Elsevier B.V. All rights reserved.

Tomography and Purification of the Temporal-Mode Structure of Quantum Light

NASA Astrophysics Data System (ADS)

Ansari, Vahid; Donohue, John M.; Allgaier, Markus; Sansoni, Linda; Brecht, Benjamin; Roslund, Jonathan; Treps, Nicolas; Harder, Georg; Silberhorn, Christine

2018-05-01

High-dimensional quantum information processing promises capabilities beyond the current state of the art, but addressing individual information-carrying modes presents a significant experimental challenge. Here we demonstrate effective high-dimensional operations in the time-frequency domain of nonclassical light. We generate heralded photons with tailored temporal-mode structures through the pulse shaping of a broadband parametric down-conversion pump. We then implement a quantum pulse gate, enabled by dispersion-engineered sum-frequency generation, to project onto programmable temporal modes, reconstructing the quantum state in seven dimensions. We also manipulate the time-frequency structure by selectively removing temporal modes, explicitly demonstrating the effectiveness of engineered nonlinear processes for the mode-selective manipulation of quantum states.

Exploiting temporal gradients of antibiotic concentration against the emergence of resistance

NASA Astrophysics Data System (ADS)

Bauer, Marianne; Ngampruetikorn, Vudtiwat; Frey, Erwin; Stephens, Greg

A very simple model for antibiotic resistance - involving one normal and one more resistant species interacting indirectly through a carrying capacity - shows that the temporal variation of the antibiotic can affect the effect of the antibiotic. For a single antibiotic pulse, we find that for different minimal inhibitory concentrations of the two species an optimal pulse shape may exist, which increases the likelihood of bacterial extinction. For a long series of pulses, efficiency does not vary monotonically with the length of the gap between two individual pulses, but instead, the gap length can be optimised by exploiting the competition between the two species. Finally, a series of pulses is not always more efficient than a single pulse. Shorter pulses may be more efficient in an initial time window without risking population level resistance. We elucidate this behaviour with a phase diagram, and discuss the meaning of this work for current experiments. (equally contributing author).

Shape-Controllable Gold Nanoparticle-MoS2 Hybrids Prepared by Tuning Edge-Active Sites and Surface Structures of MoS2 via Temporally Shaped Femtosecond Pulses.

PubMed

Zuo, Pei; Jiang, Lan; Li, Xin; Li, Bo; Xu, Yongda; Shi, Xuesong; Ran, Peng; Ma, Tianbao; Li, Dawei; Qu, Liangti; Lu, Yongfeng; Grigoropoulos, Costas P

2017-03-01

Edge-active site control of MoS 2 is crucial for applications such as chemical catalysis, synthesis of functional composites, and biochemical sensing. This work presents a novel nonthermal method to simultaneously tune surface chemical (edge-active sites) and physical (surface periodic micro/nano structures) properties of MoS 2 using temporally shaped femtosecond pulses, through which shape-controlled gold nanoparticles are in situ and self-assembly grown on MoS 2 surfaces to form Au-MoS 2 hybrids. The edge-active sites with unbound sulfurs of laser-treated MoS 2 drive the reduction of gold nanoparticles, while the surface periodic structures of laser-treated MoS 2 assist the shape-controllable growth of gold nanoparticles. The proposed novel method highlights the broad application potential of MoS 2 ; for example, these Au-MoS 2 hybrids exhibit tunable and highly sensitive SERS activity with an enhancement factor up to 1.2 × 10 7 , indicating the marked potential of MoS 2 in future chemical and biological sensing applications.

Diffusion pore imaging with generalized temporal gradient profiles.

PubMed

Laun, Frederik B; Kuder, Tristan A

2013-09-01

In porous material research, one main interest of nuclear magnetic resonance diffusion (NMR) experiments is the determination of the shape of pores. While it has been a longstanding question if this is in principle achievable, it has been shown recently that it is indeed possible to perform NMR-based diffusion pore imaging. In this work we present a generalization of these previous results. We show that the specific temporal gradient profiles that were used so far are not unique as more general temporal diffusion gradient profiles may be used. These temporal gradient profiles may consist of any number of "short" gradient pulses, which fulfil the short-gradient approximation. Additionally, "long" gradient pulses of small amplitude may be present, which can be used to fulfil the rephasing condition for the complete profile. Some exceptions exist. For example, classical q-space gradients consisting of two short gradient pulses of opposite sign cannot be used as the phase information is lost due to the temporal antisymmetry of this profile. Copyright © 2013 Elsevier Inc. All rights reserved.

Thermally controlled femtosecond pulse shaping using metasurface based optical filters

NASA Astrophysics Data System (ADS)

Rahimi, Eesa; Şendur, Kürşat

2018-02-01

Shaping of the temporal distribution of the ultrashort pulses, compensation of pulse deformations due to phase shift in transmission and amplification are of interest in various optical applications. To address these problems, in this study, we have demonstrated an ultra-thin reconfigurable localized surface plasmon (LSP) band-stop optical filter driven by insulator-metal phase transition of vanadium dioxide. A Joule heating mechanism is proposed to control the thermal phase transition of the material. The resulting permittivity variation of vanadium dioxide tailors spectral response of the transmitted pulse from the stack. Depending on how the pulse's spectrum is located with respect to the resonance of the band-stop filter, the thin film stack can dynamically compress/expand the output pulse span up to 20% or shift its phase up to 360°. Multi-stacked filters have shown the ability to dynamically compensate input carrier frequency shifts and pulse span variations besides their higher span expansion rates.

Novel applications of photonic signal processing: Temporal cloaking and biphoton pulse shaping

NASA Astrophysics Data System (ADS)

Lukens, Joseph M.

We experimentally demonstrate two innovative applications of photonic technologies previously solidified in the field of classical optical communications. In the first application, we exploit electro-optic modulator technology to develop a novel "time cloak,'' a device which hides events in time by manipulating the flow of a probing light beam. Our temporal cloak is capable of masking high-speed optical data from a receiver, greatly improving the feasibility of time cloaking and bringing such exotic concepts to the verge of practical application. In the second specialization, high-resolution Fourier-transform pulse shaping---perfected for multi-wavelength telecom networks---is applied to shape the correlations of entangled photon pairs, states which have received considerable attention in nonlocal tests of quantum theory and in quantum key distribution. Using nonlinear waveguides fabricated out of periodically poled lithium niobate, we are able to demonstrate ultrafast coincidence detection with record-high efficiency, which coupled with our pulse shaper allows us to realize for the first time several capabilities in biphoton control, including high-order dispersion cancellation, orthogonal spectral coding, correlation train generation, and tunable delay control. Each of these experiments represents an important advance in quantum state manipulation, with the potential to impact developments in quantum information. And more generally, our work introducing telecommunication technology into both temporal cloaking and biphoton control highlights the potential of such tools in more nascent outgrowths of classical and quantum optics.

First-principles electron dynamics control simulation of diamond under femtosecond laser pulse train irradiation.

PubMed

Wang, Cong; Jiang, Lan; Wang, Feng; Li, Xin; Yuan, Yanping; Xiao, Hai; Tsai, Hai-Lung; Lu, Yongfeng

2012-07-11

A real-time and real-space time-dependent density functional is applied to simulate the nonlinear electron-photon interactions during shaped femtosecond laser pulse train ablation of diamond. Effects of the key pulse train parameters such as the pulse separation, spatial/temporal pulse energy distribution and pulse number per train on the electron excitation and energy absorption are discussed. The calculations show that photon-electron interactions and transient localized electron dynamics can be controlled including photon absorption, electron excitation, electron density, and free electron distribution by the ultrafast laser pulse train.

Temporal Order in Periodically Driven Spins in Star-Shaped Clusters

NASA Astrophysics Data System (ADS)

Pal, Soham; Nishad, Naveen; Mahesh, T. S.; Sreejith, G. J.

2018-05-01

We experimentally study the response of star-shaped clusters of initially unentangled N =4 , 10, and 37 nuclear spin-1 /2 moments to an inexact π -pulse sequence and show that an Ising coupling between the center and the satellite spins results in robust period-2 magnetization oscillations. The period is stable against bath effects, but the amplitude decays with a timescale that depends on the inexactness of the pulse. Simulations reveal a semiclassical picture in which the rigidity of the period is due to a randomizing effect of the Larmor precession under the magnetization of surrounding spins. The timescales with stable periodicity increase with net initial magnetization, even in the presence of perturbations, indicating a robust temporal ordered phase for large systems with finite magnetization per spin.

Observation of strong continuous-variable Einstein-Podolsky-Rosen entanglement using shaped local oscillators

NASA Astrophysics Data System (ADS)

Shinjo, Ami; Hashiyama, Naoyuki; Koshio, Akane; Eto, Yujiro; Hirano, Takuya

2016-10-01

The continuous-variable (CV) Einstein-Podolsky-Rosen (EPR) paradox and steering are demonstrated using a pulsed light source and waveguides. We shorten the duration of the local oscillator (LO) pulse by using parametric amplification to improve the temporal mode-matching between the entangled pulse and the LO pulse. After correcting for the amplifier noise, the product of the measured conditional variance of the quadrature-phase amplitudes is 0.74 < 1, which satisfies the EPR-Reid criterion.

Effect of temporal pulse shaping on the reduction of laser weld defects in a Pd-Ag-Sn dental alloy.

PubMed

Bertrand, C; Poulon-Quintin, A

2011-03-01

To describe the influence of pulse shaping on the behavior of a palladium-based dental alloy during laser welding and to show how its choice is effective to promote good weld quality. Single spots, weld beads and welds with 80% overlapping were performed on Pd-Ag-Sn cast plates. A pulsed Nd:Yag laser was used with a specific welding procedure using all the possibilities for pulse-shaping: (1) the square pulse shape as the default setting, (2) a rising edge slope for gradual heating, (3) a falling edge slope to slow the cooling and (4) a combination of a rising and falling edges called bridge shape. The optimization of the pulse shape is supposed to enhance weldability and produce defect-free welds (cracks, pores…) Vickers microhardness measurements were made on cross sections of the welds. A correlation between laser welding parameters and microstructure evolution was found. Hot cracking and internal porosities were systematically detected when using rapid cooling. The presence of these types of defects was significantly reduced with the slow cooling of the molten pool. The best weld quality was obtained with the use of the bridge shape. The use of a slow cooling ramp is the only way to significantly reduce the presence of typical defects within the welds for this Pd-based alloy studied. Copyright © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Amplitude Modulator Chassis

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

Erbert, G

2009-09-01

The Amplitude Modulator Chassis (AMC) is the final component in the MOR system and connects directly to the PAM input through a 100-meter fiber. The 48 AMCs temporally shape the 48 outputs of the MOR using an arbitrary waveform generator coupled to an amplitude modulator. The amplitude modulation element is a two stage, Lithium Niobate waveguide device, where the intensity of the light passing through the device is a function of the electrical drive applied. The first stage of the modulator is connected to a programmable high performance Arbitrary Waveform Generator (AWG) consisting of 140 impulse generators space 250 psmore » apart. An arbitrary waveform is generated by independently varying the amplitude of each impulse generator and then summing the impulses together. In addition to the AWG a short pulse generator is also connected to the first stage of the modulator to provide a sub 100-ps pulse used for timing experiments. The second stage of the modulator is connect to a square pulse generator used to further attenuate any pre or post pulse light passing through the first stage of the modulator. The fast rise and fall time of the square pulse generator is also used to produce fast rise and fall times of the AWG by clipping the AWG pulse. For maximum extinction, a pulse bias voltage is applied to each stage of the modulator. A pulse voltage is applied as opposed to a DC voltage to prevent charge buildup on the modulator. Each bias voltage is adjustable to provide a minimum of 50-dB extinction. The AMC is controlled through ICCS to generate the desired temporal pulse shape. This process involves a closed-loop control algorithm, which compares the desired temporal waveform to the produced optical pulse, and iterates the programming of the AWG until the two waveforms agree within an allowable tolerance.« less

Pulse Duration of Seeded Free-Electron Lasers

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

Finetti, Paola; Hoppner, Hauke; Allaria, Enrico

The pulse duration, and, more generally, the temporal intensity profile of free-electron laser (FEL) pulses, is of utmost importance for exploring the new perspectives offered by FELs; it is a nontrivial experimental parameter that needs to be characterized. We measured the pulse shape of an extreme ultraviolet externally seeded FEL operating in high-gain harmonic generation mode. Two different methods based on the cross-correlation of the FEL pulses with an external optical laser were used. The two methods, one capable of single-shot performance, may both be implemented as online diagnostics in FEL facilities. The measurements were carried out at the seededmore » FEL facility FERMI. The FEL temporal pulse characteristics were measured and studied in a range of FEL wavelengths and machine settings, and they were compared to the predictions of a theoretical model. Finally, the measurements allowed a direct observation of the pulse lengthening and splitting at saturation, in agreement with the proposed theory.« less

Pulse Duration of Seeded Free-Electron Lasers

DOE PAGES

Finetti, Paola; Hoppner, Hauke; Allaria, Enrico; ...

2017-06-16

The pulse duration, and, more generally, the temporal intensity profile of free-electron laser (FEL) pulses, is of utmost importance for exploring the new perspectives offered by FELs; it is a nontrivial experimental parameter that needs to be characterized. We measured the pulse shape of an extreme ultraviolet externally seeded FEL operating in high-gain harmonic generation mode. Two different methods based on the cross-correlation of the FEL pulses with an external optical laser were used. The two methods, one capable of single-shot performance, may both be implemented as online diagnostics in FEL facilities. The measurements were carried out at the seededmore » FEL facility FERMI. The FEL temporal pulse characteristics were measured and studied in a range of FEL wavelengths and machine settings, and they were compared to the predictions of a theoretical model. Finally, the measurements allowed a direct observation of the pulse lengthening and splitting at saturation, in agreement with the proposed theory.« less

Computationally efficient optimization of radiation drives

NASA Astrophysics Data System (ADS)

Zimmerman, George; Swift, Damian

2017-06-01

For many applications of pulsed radiation, the temporal pulse shape is designed to induce a desired time-history of conditions. This optimization is normally performed using multi-physics simulations of the system, adjusting the shape until the desired response is induced. These simulations may be computationally intensive, and iterative forward optimization is then expensive and slow. In principle, a simulation program could be modified to adjust the radiation drive automatically until the desired instantaneous response is achieved, but this may be impracticable in a complicated multi-physics program. However, the computational time increment is typically much shorter than the time scale of changes in the desired response, so the radiation intensity can be adjusted so that the response tends toward the desired value. This relaxed in-situ optimization method can give an adequate design for a pulse shape in a single forward simulation, giving a typical gain in computational efficiency of tens to thousands. This approach was demonstrated for the design of laser pulse shapes to induce ramp loading to high pressure in target assemblies where different components had significantly different mechanical impedance, requiring careful pulse shaping. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Analytical treatment of self-phase-modulation beyond the slowly varying envelope approximation

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

Syrchin, M.S.; Zheltikov, A.M.; International Laser Center, M.V. Lomonosov Moscow State University, 119899 Moscow

Analytical treatment of the self-phase-modulation of an ultrashort light pulse is extended beyond the slowly varying envelope approximation. The resulting wave equation is modified to include corrections to self-phase-modulation due to higher-order spatial and temporal derivatives. Analytical solutions are found in the limiting regimes of high nonlinearities and very short pulses. Our results reveal features that can significantly impact both pulse shape and the evolution of the phase.

A direct temporal domain approach for ultrafast optical signal processing and its implementation using planar lightwave circuits

NASA Astrophysics Data System (ADS)

Xia, Bing

Ultrafast optical signal processing, which shares the same fundamental principles of electrical signal processing, can realize numerous important functionalities required in both academic research and industry. Due to the extremely fast processing speed, all-optical signal processing and pulse shaping have been widely used in ultrafast telecommunication networks, photonically-assisted RFlmicro-meter waveform generation, microscopy, biophotonics, and studies on transient and nonlinear properties of atoms and molecules. In this thesis, we investigate two types of optical spectrally-periodic (SP) filters that can be fabricated on planar lightwave circuits (PLC) to perform pulse repetition rate multiplication (PRRM) and arbitrary optical waveform generation (AOWG). First, we present a direct temporal domain approach for PRRM using SP filters. We show that the repetition rate of an input pulse train can be multiplied by a factor N using an optical filter with a free spectral range that does not need to be constrained to an integer multiple of N. Furthermore, the amplitude of each individual output pulse can be manipulated separately to form an arbitrary envelope at the output by optimizing the impulse response of the filter. Next, we use lattice-form Mach-Zehnder interferometers (LF-MZI) to implement the temporal domain approach for PRRM. The simulation results show that PRRM with uniform profiles, binary-code profiles and triangular profiles can be achieved. Three silica based LF-MZIs are designed and fabricated, which incorporate multi-mode interference (MMI) couplers and phase shifters. The experimental results show that 40 GHz pulse trains with a uniform envelope pattern, a binary code pattern "1011" and a binary code pattern "1101" are generated from a 10 GHz input pulse train. Finally, we investigate 2D ring resonator arrays (RRA) for ultraf ast optical signal processing. We design 2D RRAs to generate a pair of pulse trains with different binary-code patterns simultaneously from a single pulse train at a low repetition rate. We also design 2D RRAs for AOWG using the modified direct temporal domain approach. To demonstrate the approach, we provide numerical examples to illustrate the generation of two very different waveforms (square waveform and triangular waveform) from the same hyperbolic secant input pulse train. This powerful technique based on SP filters can be very useful for ultrafast optical signal processing and pulse shaping.

Femtosecond laser pulse shaping at megahertz rate via a digital micromirror device.

PubMed

Gu, Chenglin; Chang, Yina; Zhang, Dapeng; Cheng, Jiyi; Chen, Shih-Chi

2015-09-01

In this Letter, we present a scanner and digital micromirror device (DMD)-based ultrafast pulse shaper, i.e., S-DUPS, for programmable ultrafast pulse modulation, achieving a shaping rate of 2 MHz. To our knowledge, the S-DUPS is the fastest programmable pulse shaper reported to date. In the S-DUPS, the frequency spectrum of the input pulsed laser is first spread horizontally, and then mapped to a thin stripe on the DMD programmed with phase modulation patterns. A galvanometric scanner, synchronized with the DMD, subsequently scans the spectrum vertically on the DMD to achieve a shaping rate up to 10 s MHz. A grating pair and a cylindrical lens in front of the DMD compensate for the temporal and spatial dispersion of the system. To verify the concept, experiments were conducted with the DMD and the galvanometric scanner operated at 2 kHz and 1 kHz, respectively, achieving a 2 MHz speed for continuous group velocity dispersion tuning, as well as 2% efficiency. Up to 5% efficiency of S-DUPS can be expected with high efficiency gratings and optical components of proper coatings.

Single-shot temporal characterization of kilojoule-level, picosecond pulses on OMEGA EP

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

Waxer, Leon; Dorrer, Christophe; Kalb, Adam

To achieve a variety of experimental conditions, the OMEGA EP laser provides kilojoule-level pulses over a pulse-width range of 0.6 to 100 ps. Precise knowledge of the pulse width is important for laser system safety and the interpretation of experimental results. This paper describes the development and implementation of a single-shot, ultrashort-pulse measurement diagnostic, which provides an accurate characterization of the output pulse shape. We also present a brief overview of the measurement algorithm; discuss design considerations necessary for implementation in a complex, user-facility environment; and review the results of the diagnostic commissioning shots, which demonstrated excellent agreement with predictions.

Single-shot temporal characterization of kilojoule-level, picosecond pulses on OMEGA EP

DOE PAGES

Waxer, Leon; Dorrer, Christophe; Kalb, Adam; ...

2018-02-19

To achieve a variety of experimental conditions, the OMEGA EP laser provides kilojoule-level pulses over a pulse-width range of 0.6 to 100 ps. Precise knowledge of the pulse width is important for laser system safety and the interpretation of experimental results. This paper describes the development and implementation of a single-shot, ultrashort-pulse measurement diagnostic, which provides an accurate characterization of the output pulse shape. We also present a brief overview of the measurement algorithm; discuss design considerations necessary for implementation in a complex, user-facility environment; and review the results of the diagnostic commissioning shots, which demonstrated excellent agreement with predictions.

Optimal control of photoelectron emission by realistic waveforms

NASA Astrophysics Data System (ADS)

Solanpää, J.; Ciappina, M. F.; Räsänen, E.

2017-09-01

Recent experimental techniques in multicolor waveform synthesis allow the temporal shaping of strong femtosecond laser pulses with applications in the control of quantum mechanical processes in atoms, molecules, and nanostructures. Prediction of the shapes of the optimal waveforms can be done computationally using quantum optimal control theory. In this work we demonstrate the control of above-threshold photoemission of one-dimensional hydrogen model with pulses feasible for experimental waveform synthesis. By mixing different spectral channels and thus lowering the intensity requirements for individual channels, the resulting optimal pulses can extend the cutoff energies by at least up to 50% and bring up the electron yield by several orders of magnitude. Insights into the electron dynamics for optimized photoelectron emission are obtained with a semiclassical two-step model.

Carbon nanotube mode lockers with enhanced nonlinearity via evanescent field interaction in D-shaped fibers

NASA Astrophysics Data System (ADS)

Song, Yong-Won; Yamashita, Shinji; Goh, Chee S.; Set, Sze Y.

2007-01-01

We demonstrate a novel passive mode-locking scheme for pulsed lasers enhanced by the interaction of carbon nanotubes (CNTs) with the evanescent field of propagating light in a D-shaped optical fiber. The scheme features all-fiber operation as well as a long lateral interaction length, which guarantees a strong nonlinear effect from the nanotubes. Mode locking is achieved with less than 30% of the CNTs compared with the amount of nanotubes used for conventional schemes. Our method also ensures the preservation of the original morphology of the individual CNTs. The demonstrated pulsed laser with our CNT mode locker has a repetition rate of 5.88 MHz and a temporal pulse width of 470 fs.

Carbon nanotube mode lockers with enhanced nonlinearity via evanescent field interaction in D-shaped fibers.

PubMed

Song, Yong-Won; Yamashita, Shinji; Goh, Chee S; Set, Sze Y

2007-01-15

We demonstrate a novel passive mode-locking scheme for pulsed lasers enhanced by the interaction of carbon nanotubes (CNTs) with the evanescent field of propagating light in a D-shaped optical fiber. The scheme features all-fiber operation as well as a long lateral interaction length, which guarantees a strong nonlinear effect from the nanotubes. Mode locking is achieved with less than 30% of the CNTs compared with the amount of nanotubes used for conventional schemes. Our method also ensures the preservation of the original morphology of the individual CNTs. The demonstrated pulsed laser with our CNT mode locker has a repetition rate of 5.88 MHz and a temporal pulse width of 470 fs.

Creating Extended and Dense Plasma Channels in Air by Using Spatially and Temporally Shaped Ultra-Intense Laser Pulses

DTIC Science & Technology

2011-08-16

Wolf, Phys. Rev. Lett. 104, 103903 (2010). 6. M. Aközbek, M. Scalora , C. Bowden, and S. L. Chin, Opt. Commun. 191, 353 (2001). 7. A. Couairon, Phys...Aközbek, M. Scalora , C. Bowden, and S. L. Chin, “White-light continuum generation and filamentation during the propagation of ultra-short laser pulses in

Characteristic measurement for femtosecond laser pulses using a GaAs PIN photodiode as a two-photon photovoltaic receiver

NASA Astrophysics Data System (ADS)

Chen, Junbao; Xia, Wei; Wang, Ming

2017-06-01

Photodiodes that exhibit a two-photon absorption effect within the spectral communication band region can be useful for building an ultra-compact autocorrelator for the characteristic inspection of optical pulses. In this work, we develop an autocorrelator for measuring the temporal profile of pulses at 1550 nm from an erbium-doped fiber laser based on the two-photon photovoltaic (TPP) effect in a GaAs PIN photodiode. The temporal envelope of the autocorrelation function contains two symmetrical temporal side lobes due to the third order dispersion of the laser pulses. Moreover, the joint time-frequency distribution of the dispersive pulses and the dissimilar two-photon response spectrum of GaAs and Si result in different delays for the appearance of the temporal side lobes. Compared with Si, GaAs displays a greater sensitivity for pulse shape reconstruction at 1550 nm, benefiting from the higher signal-to-noise ratio of the side lobes and the more centralized waveform of the autocorrelation trace. We also measure the pulse width using the GaAs PIN photodiode, and the resolution of the measured full width at half maximum of the TPP autocorrelation trace is 0.89 fs, which is consistent with a conventional second-harmonic generation crystal autocorrelator. The GaAs PIN photodiode is shown to be highly suitable for real-time second-order autocorrelation measurements of femtosecond optical pulses. It is used both for the generation and detection of the autocorrelation signal, allowing the construction of a compact and inexpensive intensity autocorrelator.

Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon.

PubMed

Derrien, Thibault J-Y; Krüger, Jörg; Itina, Tatiana E; Höhm, Sandra; Rosenfeld, Arkadi; Bonse, Jörn

2013-12-02

The formation of near-wavelength laser-induced periodic surface structures (LIPSS) on silicon upon irradiation with sequences of Ti:sapphire femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied theoretically. For this purpose, the nonlinear generation of conduction band electrons in silicon and their relaxation is numerically calculated using a two-temperature model approach including intrapulse changes of optical properties, transport, diffusion and recombination effects. Following the idea that surface plasmon polaritons (SPP) can be excited when the material turns from semiconducting to metallic state, the "SPP active area" is calculated as function of fluence and double-pulse delay up to several picoseconds and compared to the experimentally observed rippled surface areas. Evidence is presented that multi-photon absorption explains the large increase of the rippled area for temporally overlapping pulses. For longer double-pulse delays, relevant relaxation processes are identified. The results demonstrate that femtosecond LIPSS on silicon are caused by the excitation of SPP and can be controlled by temporal pulse shaping.

Pulse-Shaping-Based Nonlinear Microscopy: Development and Applications

NASA Astrophysics Data System (ADS)

Flynn, Daniel Christopher

The combination of optical microscopy and ultrafast spectroscopy make the spatial characterization of chemical kinetics on the femtosecond time scale possible. Commercially available octave-spanning Ti:Sapphire oscillators with sub-8 fs pulse durations can drive a multitude of nonlinear transitions across a significant portion of the visible spectrum with minimal average power. Unfortunately, dispersion from microscope objectives broadens pulse durations, decreases temporal resolution and lowers the peak intensities required for driving nonlinear transitions. In this dissertation, pulse shaping is used to compress laser pulses after the microscope objective. By using a binary genetic algorithm, pulse-shapes are designed to enable selective two-photon excitation. The pulse-shapes are demonstrated in two-photon fluorescence of live COS-7 cells expressing GFP-variants mAmetrine and tdTomato. The pulse-shaping approach is applied to a new multiphoton fluorescence resonance energy transfer (FRET) stoichiometry method that quantifies donor and acceptor molecules in complex, as well as the ratio of total donor to acceptor molecules. Compared to conventional multi-photon imaging techniques that require laser tuning or multiple laser systems to selectively excite individual fluorophores, the pulse-shaping approach offers rapid selective multifluorphore imaging at biologically relevant time scales. By splitting the laser beam into two beams and building a second pulse shaper, a pulse-shaping-based pump-probe microscope is developed. The technique offers multiple imaging modalities, such as excited state absorption (ESA), ground state bleach (GSB), and stimulated emission (SE), enhancing contrast of structures via their unique quantum pathways without the addition of contrast agents. Pulse-shaping based pump-probe microscopy is demonstrated for endogenous chemical-contrast imaging of red blood cells. In the second section of this dissertation, ultrafast spectroscopic techniques are used to characterize structure-function relationships of two-photon absorbing GFP-type probes and optical limiting materials. Fluorescence lifetimes of GFP-type probes are shown to depend on functional group substitution position, therefore, enabling the synthesis of designer probes for the possible study of conformation changes and aggregation in biological systems. Similarly, it is determined that small differences in the structure and dimensionality of organometallic macrocycles result in a diverse set of optical properties, which serves as a basis for the molecular level design of nonlinear optical materials.

Adjustable repetition-rate multiplication of optical pulses using fractional temporal Talbot effect with preceded binary intensity modulation

NASA Astrophysics Data System (ADS)

Xie, Qijie; Zheng, Bofang; Shu, Chester

2017-05-01

We demonstrate a simple approach for adjustable multiplication of optical pulses in a fiber using the temporal Talbot effect. Binary electrical patterns are used to control the multiplication factor in our approach. The input 10 GHz picosecond pulses are pedestal-free and are shaped directly from a CW laser. The pulses are then intensity modulated by different sets of binary patterns prior to entering a fiber of fixed dispersion. Tunable repetition-rate multiplication by different factors of 2, 4, and 8 have been achieved and up to 80 GHz pulse train has been experimentally generated. We also evaluate numerically the influence of the extinction ratio of the intensity modulator on the performance of the multiplied pulse train. In addition, the impact of the modulator bias on the uniformity of the output pulses has also been analyzed through simulation and experiment and a good agreement is reached. Last, we perform numerical simulation on the RF spectral characteristics of the output pulses. The insensitivity of the signal-to-subharmonic noise ratio (SSNR) to the laser linewidth shows that our multiplication scheme is highly tolerant to the incoherence of the input optical pulses.

From few-cycle femtosecond pulse to single attosecond pulse-controlling and tracking electron dynamics with attosecond precision

NASA Astrophysics Data System (ADS)

Wang, He

The few-cycle femtosecond laser pulse has proved itself to be a powerful tool for controlling the electron dynamics inside atoms and molecules. By applying such few-cycle pulses as a driving field, single isolated attosecond pulses can be produced through the high-order harmonic generation process, which provide a novel tool for capturing the real time electron motion. The first part of the thesis is devoted to the state of the art few-cycle near infrared (NIR) laser pulse development, which includes absolute phase control (carrier-envelope phase stabilization), amplitude control (power stabilization), and relative phase control (pulse compression and shaping). Then the double optical gating (DOG) method for generating single attosecond pulses and the attosecond streaking experiment for characterizing such pulses are presented. Various experimental limitations in the attosecond streaking measurement are illustrated through simulation. Finally by using the single attosecond pulses generated by DOG, an attosecond transient absorption experiment is performed to study the autoionization process of argon. When the delay between a few-cycle NIR pulse and a single attosecond XUV pulse is scanned, the Fano resonance shapes of the argon autoionizing states are modified by the NIR pulse, which shows the direct observation and control of electron-electron correlation in the temporal domain.

Three-dimensional spatiotemporal focusing of holographic patterns

PubMed Central

Hernandez, Oscar; Papagiakoumou, Eirini; Tanese, Dimitrii; Fidelin, Kevin; Wyart, Claire; Emiliani, Valentina

2016-01-01

Two-photon excitation with temporally focused pulses can be combined with phase-modulation approaches, such as computer-generated holography and generalized phase contrast, to efficiently distribute light into two-dimensional, axially confined, user-defined shapes. Adding lens-phase modulations to 2D-phase holograms enables remote axial pattern displacement as well as simultaneous pattern generation in multiple distinct planes. However, the axial confinement linearly degrades with lateral shape area in previous reports where axially shifted holographic shapes were not temporally focused. Here we report an optical system using two spatial light modulators to independently control transverse- and axial-target light distribution. This approach enables simultaneous axial translation of single or multiple spatiotemporally focused patterns across the sample volume while achieving the axial confinement of temporal focusing. We use the system's capability to photoconvert tens of Kaede-expressing neurons with single-cell resolution in live zebrafish larvae. PMID:27306044

Accreting, highly magnetized neutron stars at the Eddington limit: a study of the 2016 outburst of SMC X-3

NASA Astrophysics Data System (ADS)

Koliopanos, Filippos; Vasilopoulos, Georgios

2018-06-01

Aims: We study the temporal and spectral characteristics of SMC X-3 during its recent (2016) outburst to probe accretion onto highly magnetized neutron stars (NSs) at the Eddington limit. Methods: We obtained XMM-Newton observations of SMC X-3 and combined them with long-term observations by Swift. We performed a detailed analysis of the temporal and spectral behavior of the source, as well as its short- and long-term evolution. We have also constructed a simple toy-model (based on robust theoretical predictions) in order to gain insight into the complex emission pattern of SMC X-3. Results: We confirm the pulse period of the system that has been derived by previous works and note that the pulse has a complex three-peak shape. We find that the pulsed emission is dominated by hard photons, while at energies below 1 keV, the emission does not pulsate. We furthermore find that the shape of the pulse profile and the short- and long-term evolution of the source light-curve can be explained by invoking a combination of a "fan" and a "polar" beam. The results of our temporal study are supported by our spectroscopic analysis, which reveals a two-component emission, comprised of a hard power law and a soft thermal component. We find that the latter produces the bulk of the non-pulsating emission and is most likely the result of reprocessing the primary hard emission by optically thick material that partly obscures the central source. We also detect strong emission lines from highly ionized metals. The strength of the emission lines strongly depends on the phase. Conclusions: Our findings are in agreement with previous works. The energy and temporal evolution as well as the shape of the pulse profile and the long-term spectra evolution of the source are consistent with the expected emission pattern of the accretion column in the super-critical regime, while the large reprocessing region is consistent with the analysis of previously studied X-ray pulsars observed at high accretion rates. This reprocessing region is consistent with recently proposed theoretical and observational works that suggested that highly magnetized NSs occupy a considerable fraction of ultraluminous X-ray sources.

Single-shot, high-resolution, fiber-based phase-diversity photodetection of optical pulses

NASA Astrophysics Data System (ADS)

Dorrer, C.; Waxer, L. J.; Kalb, A.; Hill, E. M.; Bromage, J.

2016-03-01

Temporally characterizing optical pulses is an important task when building, optimizing, and using optical sources. Direct photodetection with high-bandwidth photodiodes and real-time oscilloscopes is only adequate for optical pulses longer than ~10 ps; diagnostics based on indirect strategies are required to characterize femtosecond and sub-10-ps coherent sources. Most of these diagnostics are based on nonlinear optics and can be difficult to implement for the single-shot characterization of nonrepetitive events. A temporal diagnostic based on phase diversity is demonstrated in the context of picosecond high-energy laser systems, where single-shot pulse measurements are required for system safety and interpretation of experimental results. A plurality of ancillary optical pulses obtained by adding known amounts of chromatic dispersion to the pulse under test are directly measured by photodetection and processed to reconstruct the input pulse shape. This high-sensitivity (~50-pJ) diagnostic is based on a pulse replicator composed of fiber splitters and delay fibers, making it possible to operate with fiber sources and free-space sources after fiber coupling. Experimental data obtained with a high-bandwidth real-time oscilloscope demonstrate accurate characterization of pulses from a high-energy chirped-pulse amplification system, even for pulses shorter than the photodetection impulse response.

Linear ultrafast dynamics of plasmon and magnetic resonances in nanoparticles

NASA Astrophysics Data System (ADS)

Lazzarini, Carlo Maria; Tadzio, Levato; Fitzgerald, Jamie M.; Sánchez-Gil, José A.; Giannini, Vincenzo

2017-12-01

In this study we present an analytical description of the ultrafast localized surface plasmon and magnetic resonance dynamics in a single nanoparticle (Ag or Si), driven by an ultrashort (fs time scale) Gaussian pulse. Three possible scenarios have been found depending on the incident field, i.e., pulse duration much shorter than, similar to, and much longer than the localized surface plasmon resonance (LSPR) lifetime. A rich physics arises for τpulse<τLSPR , even in the linear regime. The surface plasmon dynamics is manifested as (i) a temporal delay of the surface plasmon excitation with regard to the freely propagating pulse and as (ii) a negative exponential tail after the exciting pulse is over. In addition, for sub-fs pulses clear oscillations in the near-field decay have been observed. A similar scenario has been observed considering a nonabsorbing Si sphere. Nanoparticle resonance dynamics may lead to a wealth of new phenomena and applications in nanophotonics such as multipole order resonance interference, pulse-induced delay or temporal shaping on the fs scale, high harmonic generation, attosecond near-field pulse sources, and electron acceleration from metasurface or 3D engineered nanostructures.

The effects of focusing power on TEA CO2 laser-induced gas breakdown and the consequent pulse shaping effects

NASA Astrophysics Data System (ADS)

Beheshtipour, Saleheh; Safari, Ebrahim; Majdabadi, Abbas; Silakhori, Kaveh

2018-02-01

Transversely Excited Atmospheric (TEA) CO2 laser pulses were used in order to generate an optical breakdown in a variety of mono- and polyatomic molecules using different focusing powers. The dependence of the spark kernel geometry and the transmitted pulse shapes on the focusing power as well as the pressure, molecular weight, and ionization energy of the gases was investigated in detail. Partial removal of the transmitted pulse tail in the 0.05-2.6 μs range together with shortened spikes in the 10-60 ns range has been observed by applying a 2.5 cm focal length lens for all the gases. At higher focal lengths, this effect is only incompletely observed for He gas. Spatial-temporal analyses of the laser beams and the relevant plasma plumes indicate that this behavior is due to the drop in the plasma density below the critical level, before the laser pulse tail is completed.

Temporally Shaped Current Pulses on a Two-Cavity Linear Transformer Driver System

DTIC Science & Technology

2011-06-01

essentially at a fraction of the total switch voltage. Non-uniform corona current characteristics of the different corona needles could cause imperfect...withstand twice the capacitor voltage. A pulse applied to the switch trigger electrodes initiate closure of each switch. We have arranged triggering in...internal cavity potential to ground, allows the trigger electrode of the spark gaps to be at ground potential during charging, and eliminates a

Compact pulsed high-energy Er:glass laser

NASA Astrophysics Data System (ADS)

Wan, Peng; Liu, Jian

2012-03-01

Bulk Erbium-doped lasers are widely used for long-distance telemetry and ranging. In some applications such as coherent Doppler radars, laser outputs with a relatively long pulse width, good beam profile and pulse shape are required. High energy Q-switched Er:glass lasers were demonstrated by use of electro-optic (E/O) Q-switching or frustrated total internal reflection (FTIR) Q-switching. However, the output pulse durations in these lasers were fixed to relatively small values and extremely hard to tune. We report here on developing a novel and compact Q-switched Er:Yb co-doped phosphate glass laser at an eye-safe wavelength of 1.5 μm. A rotating mirror was used as a Q-switch. Co-linear pump scheme was used to maintain a good output beam profile. Near-perfect Gaussian temporal shape was obtained in our experiment. By changing motor rotation speed, pulse duration was tunable and up to 240 ns was achieved. In our preliminary experiment, output pulse energies of 44 mJ and 4.5 mJ were obtained in free-running and Q-switched operation modes respectively.

Compensation of Gradient-Induced Magnetic Field Perturbations

PubMed Central

Nixon, Terence W.; McIntyre, Scott; Rothman, Douglas L.; de Graaf, Robin A.

2008-01-01

Pulsed magnetic field gradients are essential for MR imaging and localized spectroscopy applications. However, besides the desired linear field gradients, pulsed currents in a strong external magnetic field also generate unwanted effects like eddy currents, gradient coil vibrations and acoustic noise. While the temporal magnetic field perturbations associated with eddy currents lead to spectral line shape distortions and signal loss, the vibration-related modulations lead to anti-symmetrical sidebands of any large signal (i.e. water), thereby obliterating the signals from smaller signals (i.e. metabolites). Here the measurement, characterization and compensation of vibrations-related magnetic field perturbations is presented. Following a quantitative evaluation of the various temporal components of the main magnetic field, a digital B0 magnetic field waveform is generated which reduces all temporal variations of the main magnetic field to within the spectral noise level. PMID:18329304

Improving the therapeutic window of retinal photocoagulation by spatial and temporal modulation of the laser beam

NASA Astrophysics Data System (ADS)

Sramek, Christopher; Leung, Loh-Shan; Leng, Theodore; Brown, Jefferson; Paulus, Yannis M.; Schuele, Georg; Palanker, Daniel

2011-02-01

Decreasing the pulse duration helps confine damage, shorten treatment time, and minimize pain during retinal photocoagulation. However, the safe therapeutic window (TW), the ratio of threshold powers for thermomechanical rupture of Bruch's membrane and mild coagulation, also decreases with shorter exposures. Two potential approaches toward increasing TW are investigated: (a) decreasing the central irradiance of the laser beam and (b) temporally modulating the pulse. An annular beam with adjustable central irradiance was created by coupling a 532-nm laser into a 200-μm core multimode optical fiber at a 4-7 deg angle to normal incidence. Pulse shapes were optimized using a computational model, and a waveform generator was used to drive a PASCAL photocoagulator (532 nm), producing modulated laser pulses. Acute thresholds for mild coagulation and rupture were measured in Dutch-Belted rabbit in vivo with an annular beam (154-163 μm retinal diameter) and modulated pulse (132 μm, uniform irradiance ``flat-top'' beam) with 2-50 ms pulse durations. Thresholds with conventional constant-power pulse and a flat-top beam were also determined. Both annular beam and modulated pulse provided a 28% increase in TW at 10-ms duration, affording the same TW as 20-ms pulses with conventional parameters.

Laser-launched flyer plate and confined laser ablation for shock wave loading: validation and applications.

PubMed

Paisley, Dennis L; Luo, Sheng-Nian; Greenfield, Scott R; Koskelo, Aaron C

2008-02-01

We present validation and some applications of two laser-driven shock wave loading techniques: laser-launched flyer plate and confined laser ablation. We characterize the flyer plate during flight and the dynamically loaded target with temporally and spatially resolved diagnostics. With transient imaging displacement interferometry, we demonstrate that the planarity (bow and tilt) of the loading induced by a spatially shaped laser pulse is within 2-7 mrad (with an average of 4+/-1 mrad), similar to that in conventional techniques including gas gun loading. Plasma heating of target is negligible, in particular, when a plasma shield is adopted. For flyer plate loading, supported shock waves can be achieved. Temporal shaping of the drive pulse in confined laser ablation allows for flexible loading, e.g., quasi-isentropic, Taylor-wave, and off-Hugoniot loading. These techniques can be utilized to investigate such dynamic responses of materials as Hugoniot elastic limit, plasticity, spall, shock roughness, equation of state, phase transition, and metallurgical characteristics of shock-recovered samples.

Bi-Annual Report 2010-2011: Shaping pulse flows to meet environmental and energy objectives

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

Jager, Yetta

2010-10-01

This report describes a bioenergetic model developed to allocate seasonal pulse flows to benefit salmon growth. The model links flow with floodplain inundation and production of invertebrate prey eaten by juvenile Chinook salmon. A unique quantile modeling approach is used to describe temporal variation among juvenile salmon spawned at different times. Preliminary model outputs are presented and future plans to optimize flows both to maximize salmon growth and hydropower production are outlined.

Advertisement-call preferences in diploid-tetraploid treefrogs (Hyla chrysoscelis and Hyla versicolor): implications for mate choice and the evolution of communication systems.

PubMed

Gerhardt, H Carl

2005-02-01

Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. Two-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor.

Simultaneous multislice refocusing via time optimal control.

PubMed

Rund, Armin; Aigner, Christoph Stefan; Kunisch, Karl; Stollberger, Rudolf

2018-02-09

Joint design of minimum duration RF pulses and slice-selective gradient shapes for MRI via time optimal control with strict physical constraints, and its application to simultaneous multislice imaging. The minimization of the pulse duration is cast as a time optimal control problem with inequality constraints describing the refocusing quality and physical constraints. It is solved with a bilevel method, where the pulse length is minimized in the upper level, and the constraints are satisfied in the lower level. To address the inherent nonconvexity of the optimization problem, the upper level is enhanced with new heuristics for finding a near global optimizer based on a second optimization problem. A large set of optimized examples shows an average temporal reduction of 87.1% for double diffusion and 74% for turbo spin echo pulses compared to power independent number of slices pulses. The optimized results are validated on a 3T scanner with phantom measurements. The presented design method computes minimum duration RF pulse and slice-selective gradient shapes subject to physical constraints. The shorter pulse duration can be used to decrease the effective echo time in existing echo-planar imaging or echo spacing in turbo spin echo sequences. © 2018 International Society for Magnetic Resonance in Medicine.

Two-photon equivalent weighting of spatial excimer laser beam profiles

NASA Astrophysics Data System (ADS)

Eva, Eric; Bauer, Harry H.; Metzger, K.; Pfeiffer, A.

2001-04-01

Damage in optical materials for semiconductor lithography applications caused by exposure to 248 or 193 nm light is usually two-photon driven, hence it is a nonlinear function of incident intensity. Materials should be tested with flat- topped temporal and spatial laser beam profiles to facilitate interpretation of data, but in reality this is hard to achieve. Sandstrom provided a formula that approximates any given temporal pulse shape with a two- photon equivalent rectangular pulse (Second Symposium on 193 nm Lithography, Colorado Springs 1997). Known as the integral-square pulse duration, this definition has been embraced as an industry standard. Originally faced with the problem of comparing results obtained with pseudo-Gaussian spatial profiles to literature data, we found that a general solution for arbitrarily inhomogeneous spatial beam profiles exists which results in a definition much similar to Sandstrom's. In addition, we proved the validity of our approach in experiments with intentionally altered beam profiles.

Enhanced attosecond pulse generation in the vacuum ultraviolet using a two-colour driving field for high harmonic generation

NASA Astrophysics Data System (ADS)

Matía-Hernando, P.; Witting, T.; Walke, D. J.; Marangos, J. P.; Tisch, J. W. G.

2018-03-01

High-harmonic radiation in the extreme ultraviolet and soft X-ray spectral regions can be used to generate attosecond pulses and to obtain structural and dynamic information in atoms and molecules. However, these sources typically suffer from a limited photon flux. An additional issue at lower photon energies is the appearance of satellites in the time domain, stemming from insufficient temporal gating and the spectral filtering required for the isolation of attosecond pulses. Such satellites limit the temporal resolution. The use of multi-colour driving fields has been proven to enhance the harmonic yield and provide additional control, using the relative delays between the different spectral components for waveform shaping. We describe here a two-colour high-harmonic source that combines a few-cycle near-infrared pulse with a multi-cycle second harmonic pulse, with both relative phase and carrier-envelope phase stabilization. We observe strong modulations in the harmonic flux, and present simulations and experimental results supporting the suppression of satellites in sub-femtosecond pulses at 20 eV compared to the single colour field case, an important requirement for attosecond pump-probe measurements.

Terahertz spin current pulses controlled by magnetic heterostructures

NASA Astrophysics Data System (ADS)

Kampfrath, T.; Battiato, M.; Maldonado, P.; Eilers, G.; Nötzold, J.; Mährlein, S.; Zbarsky, V.; Freimuth, F.; Mokrousov, Y.; Blügel, S.; Wolf, M.; Radu, I.; Oppeneer, P. M.; Münzenberg, M.

2013-04-01

In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime. Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states. Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters.

Wide-band profile domain pulsar timing analysis

NASA Astrophysics Data System (ADS)

Lentati, L.; Kerr, M.; Dai, S.; Hobson, M. P.; Shannon, R. M.; Hobbs, G.; Bailes, M.; Bhat, N. D. Ramesh; Burke-Spolaor, S.; Coles, W.; Dempsey, J.; Lasky, P. D.; Levin, Y.; Manchester, R. N.; Osłowski, S.; Ravi, V.; Reardon, D. J.; Rosado, P. A.; Spiewak, R.; van Straten, W.; Toomey, L.; Wang, J.; Wen, L.; You, X.; Zhu, X.

2017-04-01

We extend profile domain pulsar timing to incorporate wide-band effects such as frequency-dependent profile evolution and broad-band shape variation in the pulse profile. We also incorporate models for temporal variations in both pulse width and in the separation in phase of the main pulse and interpulse. We perform the analysis with both nested sampling and Hamiltonian Monte Carlo methods. In the latter case, we introduce a new parametrization of the posterior that is extremely efficient in the low signal-to-noise regime and can be readily applied to a wide range of scientific problems. We apply this methodology to a series of simulations, and to between seven and nine years of observations for PSRs J1713+0747, J1744-1134 and J1909-3744 with frequency coverage that spans 700-3600 Mhz. We use a smooth model for profile evolution across the full frequency range, and compare smooth and piecewise models for the temporal variations in dispersion measure (DM). We find that the profile domain framework consistently results in improved timing precision compared to the standard analysis paradigm by as much as 40 per cent for timing parameters. Incorporating smoothness in the DM variations into the model further improves timing precision by as much as 30 per cent. For PSR J1713+0747, we also detect pulse shape variation uncorrelated between epochs, which we attribute to variation intrinsic to the pulsar at a level consistent with previously published analyses. Not accounting for this shape variation biases the measured arrival times at the level of ˜30 ns, the same order of magnitude as the expected shift due to gravitational waves in the pulsar timing band.

Raman Amplification and Tunable Pulse Delays in Silicon Waveguides

NASA Astrophysics Data System (ADS)

Rukhlenko, Ivan D.; Garanovich, Ivan L.; Premaratne, Malin; Sukhorukov, Andrey A.; Agrawal, Govind P.

2010-10-01

The nonlinear process of stimulated Raman scattering is important for silicon photonics as it enables optical amplification and lasing. However, generally employed numerical approaches provide very little insight into the contribution of different silicon Raman amplifier (SRA) parameters. In this paper, we solve the coupled pump-signal equations analytically and derive an exact formula for the envelope of a signal pulse when picosecond optical pulses are amplified inside a SRA pumped by a continuous-wave laser beam. Our solution is valid for an arbitrary pulse shape and fully accounts for the Raman gain-dispersion effects, including temporal broadening and group-velocity reduction. Our results are useful for optimizing the performance of SRAs and for engineering controllable signal delays.

Laser pulse sampler

DOEpatents

Vann, C.

1998-03-24

The Laser Pulse Sampler (LPS) measures temporal pulse shape without the problems of a streak camera. Unlike the streak camera, the laser pulse directly illuminates a camera in the LPS, i.e., no additional equipment or energy conversions are required. The LPS has several advantages over streak cameras. The dynamic range of the LPS is limited only by the range of its camera, which for a cooled camera can be as high as 16 bits, i.e., 65,536. The LPS costs less because there are fewer components, and those components can be mass produced. The LPS is easier to calibrate and maintain because there is only one energy conversion, i.e., photons to electrons, in the camera. 5 figs.

Hotspot activity and plume pulses recorded by geometry of spreading axes

NASA Astrophysics Data System (ADS)

Abelson, Meir; Agnon, Amotz

2001-06-01

Anomalous plan view geometry (planform) of spreading axes is shown to be a faithful indicator of hotspot influence, possibly capable of detecting pulses of hotspot discharge. A planform anomaly (PA) occurs when the orientation of second-order ridge segments is prominently oblique to the spreading direction. PA is found in the vicinity of hotspots at shallow ridges (<1.5 km), suggesting hotspot influence. In places the PA and shallow bathymetry are accompanied by geochemical anomalies, corroborating hotspot influence. This linkage is best expressed in the western Gulf of Aden, where the extent of the PA from the Afar hotspot coincides with the extent of La/Sm and Sr isotopic anomalies. Using fracture mechanics we predict PA to reflect overpressurized melt that dominates the stresses in the crust, consistent with hotspot regime. Accordingly, the temporal variations of the planform previously inferred from magnetic anomalies around the Kolbeinsey Ridge (KR), north of Iceland, record episodes of interaction with the hotspot and major pulses of the plume. This suggestion is corroborated by temporal correlation of episodes showing PA north of Iceland with plume pulses previously inferred by the V-shaped ridges around the Reykjanes Ridge (RR), south of Iceland. In contrast to the RR, the temporal correlation suggests simultaneous incidence of the plume pulses at Iceland and KR, hundreds of kilometers to the north. A deep northward branch of the Iceland plume active during pulse-periods may explain these observations.

Spectrally tunable, temporally shaped parametric front end to seed high-energy Nd:glass laser systems

DOE PAGES

Dorrer, C.; Consentino, A.; Cuffney, R.; ...

2017-10-18

Here, we describe a parametric-amplification–based front end for seeding high-energy Nd:glass laser systems. The front end delivers up to 200 mJ by parametric amplification in 2.5-ns flat-in-time pulses tunable over more than 15 nm. Spectral tunability over a range larger than what is typically achieved by laser media at similar energy levels is implemented to investigate cross-beam energy transfer in multibeam target experiments. The front-end operation is simulated to explain the amplified signal’s sensitivity to the input pump and signal. A large variety of amplified waveforms are generated by closed-loop pulse shaping. Various properties and limitations of this front endmore » are discussed.« less

Spectrally tunable, temporally shaped parametric front end to seed high-energy Nd:glass laser systems

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

Dorrer, C.; Consentino, A.; Cuffney, R.

Here, we describe a parametric-amplification–based front end for seeding high-energy Nd:glass laser systems. The front end delivers up to 200 mJ by parametric amplification in 2.5-ns flat-in-time pulses tunable over more than 15 nm. Spectral tunability over a range larger than what is typically achieved by laser media at similar energy levels is implemented to investigate cross-beam energy transfer in multibeam target experiments. The front-end operation is simulated to explain the amplified signal’s sensitivity to the input pump and signal. A large variety of amplified waveforms are generated by closed-loop pulse shaping. Various properties and limitations of this front endmore » are discussed.« less

Ultrafast Beam Filamentation: Spatio-Temporal Characterization and Control

DTIC Science & Technology

2013-11-01

measurement of spectral phase[7]. The output of the laser passes through a BK7 plate set at a Brewster angle to clean up the polarization of the beam...at the focus of a lens . In this configuration, the pulse focuses temporally and spatially at the same time. We developed a theory for understanding...focus by shaping only the spatial phase of the starting beam. Finally, we showed for the first time that Kerr- lens modelocking can be achieved in a Ti

Method and apparatus for measuring the intensity and phase of an ultrashort light pulse

DOEpatents

Kane, Daniel J.; Trebino, Rick P.

1998-01-01

The pulse shape I(t) and phase evolution x(t) of ultrashort light pulses are obtained using an instantaneously responding nonlinear optical medium to form a signal pulse. A light pulse, such a laser pulse, is split into a gate pulse and a probe pulse, where the gate pulse is delayed relative to the probe pulse. The gate pulse and the probe pulse are combined within an instantaneously responding optical medium to form a signal pulse functionally related to a temporal slice of the gate pulse corresponding to the time delay of the probe pulse. The signal pulse is then input to a wavelength-selective device to output pulse field information comprising intensity vs. frequency for a first value of the time delay. The time delay is varied over a range of values effective to yield an intensity plot of signal intensity vs. wavelength and delay. In one embodiment, the beams are overlapped at an angle so that a selected range of delay times is within the intersection to produce a simultaneous output over the time delays of interest.

Evolution of energy deposition during glass cutting with pulsed femtosecond laser radiation

NASA Astrophysics Data System (ADS)

Kalupka, C.; Großmann, D.; Reininghaus, M.

2017-05-01

We report on investigations of the energy deposition in the volume of thin glass during an ablation cutting process with pulsed femtosecond laser radiation by time-resolved pump-probe shadowgraphy. For a single laser pulse, the temporal evolution of the transient electronic excitation of the glass volume is imaged up to 10 ps after initial excitation. For an increasing number of laser pulses, the spatial excitation of the glass volume significantly changes compared to single pulse irradiation. Sharp spikes are observed, which reduce the transmission of the illuminating probe pulse. This indicates local maxima of the absorption and, therefore, energy deposition of the pump pulse energy in the glass volume. Furthermore, for an increasing number of pulses, different shapes of the surface ablation crater are observed. To study the correlation between the shape of the surface ablation crater and the energy deposition in the glass volume, simulations of the spatial intensity distribution of the pump pulse are executed by means of linear beam propagation method. We show that the transient excitation spikes observed by pump-probe shadowgraphy can be explained by refraction and diffraction of the laser radiation at the surface ablation crater. Our results provide an experimental validation for the physical reason of an ablation stop for an ablation cutting process. Moreover, the simulations allow for the prediction of damage inside the glass volume.

Supercontinuum optimization for dual-soliton based light sources using genetic algorithms in a grid platform.

PubMed

Arteaga-Sierra, F R; Milián, C; Torres-Gómez, I; Torres-Cisneros, M; Moltó, G; Ferrando, A

2014-09-22

We present a numerical strategy to design fiber based dual pulse light sources exhibiting two predefined spectral peaks in the anomalous group velocity dispersion regime. The frequency conversion is based on the soliton fission and soliton self-frequency shift occurring during supercontinuum generation. The optimization process is carried out by a genetic algorithm that provides the optimum input pulse parameters: wavelength, temporal width and peak power. This algorithm is implemented in a Grid platform in order to take advantage of distributed computing. These results are useful for optical coherence tomography applications where bell-shaped pulses located in the second near-infrared window are needed.

High-speed multi-frame dynamic transmission electron microscope image acquisition system with arbitrary timing

DOEpatents

Reed, Bryan W.; DeHope, William J.; Huete, Glenn; LaGrange, Thomas B.; Shuttlesworth, Richard M.

2016-02-23

An electron microscope is disclosed which has a laser-driven photocathode and an arbitrary waveform generator (AWG) laser system ("laser"). The laser produces a train of temporally-shaped laser pulses each being of a programmable pulse duration, and directs the laser pulses to the laser-driven photocathode to produce a train of electron pulses. An image sensor is used along with a deflector subsystem. The deflector subsystem is arranged downstream of the target but upstream of the image sensor, and has a plurality of plates. A control system having a digital sequencer controls the laser and a plurality of switching components, synchronized with the laser, to independently control excitation of each one of the deflector plates. This allows each electron pulse to be directed to a different portion of the image sensor, as well as to enable programmable pulse durations and programmable inter-pulse spacings.

New Light Sources and Concepts for Electro-Optic Sampling

DTIC Science & Technology

1994-03-01

Research to improve electro - optic sampling led to the development of several high performance optical phase modulators. These phase modulators serve...method of optical pulse shape measurement was demonstrated with 3 ps time resolution, excellent power sensitivity and relative system simplicity. These experiments have opened up the field of temporal optics. Electro - optic sampling.

Generation of individually modulated femtosecond pulse string by multilayer volume holographic gratings.

PubMed

Yan, Xiaona; Gao, Lirun; Yang, Xihua; Dai, Ye; Chen, Yuanyuan; Ma, Guohong

2014-10-20

A scheme to generate individually modulated femtosecond pulse string by multilayer volume holographic grating (MVHG) is proposed. Based on Kogelnik's coupled-wave theory and matrix optics, temporal and spectral expressions of diffracted field are given when a femtosecond pulse is diffracted by a MVHG. It is shown that the number of diffracted sub-pulses in the pulse string equals to the number of grating layers of the MVHG, peak intensity and duration of each diffracted sub-pulse depend on thickness of the corresponding grating layer, whereas pulse interval between adjacent sub-pulses is related to thickness of the corresponding buffer layer. Thus by modulating parameters of the MVHG, individually modulated femtosecond pulse string can be acquired. Based on Bragg selectivity of the volume grating and phase shift provided by the buffer layers, we give an explanation on these phenomena. The result is useful to design MVHG-based devices employed in optical communications, pulse shaping and processing.

Design and calibration of zero-additional-phase SPIDER

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

Baum, Peter; Riedle, Eberhard

2005-09-01

Zero-additional-phase spectral phase interferometry for direct electric field reconstruction (ZAP-SPIDER) is a novel technique for measuring the temporal shape and phase of ultrashort optical pulses directly at the interaction point of a spectroscopic experiment. The scheme is suitable for an extremely wide wavelength region from the ultraviolet to the near infrared. We present a comprehensive description of the experimental setup and design guidelines to effectively apply the technique to various wavelengths and pulse durations. The calibration of the setup and procedures to check the consistency of the measurement are discussed in detail. We show experimental data for various center wavelengthsmore » and pulse durations down to 7 fs to verify the applicability to a wide range of pulse parameters.« less

Nonlinear scattering of ultrashort laser pulses on two-level system

NASA Astrophysics Data System (ADS)

Astapenko, Valery A.; Sakhno, Sergey V.

2015-05-01

The presentation is devoted to the theoretical investigation of nonlinear scattering of ultrashort electromagnetic pulses (USP) on two-level quantum system. We consider the scattering of several types of USP, namely, so called corrected Gaussian pulse (CGP) and cosine wavelet pulse. Such pulses have no constant component in their spectrum in contrast with traditional Gaussian pulse. It should be noted that the presence of constant component in the limit of ultrashort pulse durations leads to unphysical results. The main purpose of the present work is the investigation of the change of pulse temporal shape after scattering as a function of initial phase at different distances from the target. Numerical calculations are based on the solution of Bloch equations and expression for scattering field strength via dipole moment of two-level system exposed by the action of incident USP. In our calculation we also account for the influence of refracting index of the air on electric field strength in the pulse after scattering.

Soliton propagation in tapered silicon core fibers.

PubMed

Peacock, Anna C

2010-11-01

Numerical simulations are used to investigate soliton-like propagation in tapered silicon core optical fibers. The simulations are based on a realistic tapered structure with nanoscale core dimensions and a decreasing anomalous dispersion profile to compensate for the effects of linear and nonlinear loss. An intensity misfit parameter is used to establish the optimum taper dimensions that preserve the pulse shape while reducing temporal broadening. Soliton formation from Gaussian input pulses is also observed--further evidence of the potential for tapered silicon fibers to find use in a range of signal processing applications.

Preparation of an exponentially rising optical pulse for efficient excitation of single atoms in free space.

PubMed

Dao, Hoang Lan; Aljunid, Syed Abdullah; Maslennikov, Gleb; Kurtsiefer, Christian

2012-08-01

We report on a simple method to prepare optical pulses with exponentially rising envelope on the time scale of a few ns. The scheme is based on the exponential transfer function of a fast transistor, which generates an exponentially rising envelope that is transferred first on a radio frequency carrier, and then on a coherent cw laser beam with an electro-optical phase modulator. The temporally shaped sideband is then extracted with an optical resonator and can be used to efficiently excite a single (87)Rb atom.

Temporal evolution of atmosphere pressure plasma jets driven by microsecond pulses with positive and negative polarities

NASA Astrophysics Data System (ADS)

Shao, Tao; Yang, Wenjin; Zhang, Cheng; Fang, Zhi; Zhou, Yixiao; Schamiloglu, Edl

2014-09-01

Current-voltage characteristics, discharge images, and optical spectra of atmospheric pressure plasma jets (APPJs) are studied using a microsecond pulse length generator producing repetitive output pulses with different polarities. The experimental results show that the APPJs excited by the pulses with positive polarity have longer plume, faster propagation speed, higher power, and more excited species, such as \\text{N}2 , O, He, \\text{N}2+ , than that with the negatively excited APPJs. The images taken using an intensified charge-coupled device show that the APPJs excited by pulses with positive polarity are characterized by a bullet-like structure, while the APPJs excited by pulses with negative polarity are continuous. The propagation speed of the APPJs driven by a microsecond pulse length generator is about tens of km/s, which is similar to the APPJs driven by a kHz frequency sinusoidal voltage source. The analysis shows that the space charge accumulation effect plays an important role during the discharge. The transient enhanced electric field induced by the accumulated ions between the needle-like electrode and the nozzle in the APPJs excited by pulses with negative polarity enhances electron field emission from the cathode, which is illustrated by the bright line on the time-integrated images. This makes the shape of the APPJ excited using pulses with negative polarity different from the bullet-like shape of the APPJs excited by pulses with positive polarity.

Free-time and fixed end-point optimal control theory in dissipative media: application to entanglement generation and maintenance.

PubMed

Mishima, K; Yamashita, K

2009-07-07

We develop monotonically convergent free-time and fixed end-point optimal control theory (OCT) in the density-matrix representation to deal with quantum systems showing dissipation. Our theory is more general and flexible for tailoring optimal laser pulses in order to control quantum dynamics with dissipation than the conventional fixed-time and fixed end-point OCT in that the optimal temporal duration of laser pulses can also be optimized exactly. To show the usefulness of our theory, it is applied to the generation and maintenance of the vibrational entanglement of carbon monoxide adsorbed on the copper (100) surface, CO/Cu(100). We demonstrate the numerical results and clarify how to combat vibrational decoherence as much as possible by the tailored shapes of the optimal laser pulses. It is expected that our theory will be general enough to be applied to a variety of dissipative quantum dynamics systems because the decoherence is one of the quantum phenomena sensitive to the temporal duration of the quantum dynamics.

High-speed multiframe dynamic transmission electron microscope image acquisition system with arbitrary timing

DOEpatents

Reed, Bryan W.; DeHope, William J.; Huete, Glenn; LaGrange, Thomas B.; Shuttlesworth, Richard M.

2015-10-20

An electron microscope is disclosed which has a laser-driven photocathode and an arbitrary waveform generator (AWG) laser system ("laser"). The laser produces a train of temporally-shaped laser pulses of a predefined pulse duration and waveform, and directs the laser pulses to the laser-driven photocathode to produce a train of electron pulses. An image sensor is used along with a deflector subsystem. The deflector subsystem is arranged downstream of the target but upstream of the image sensor, and has two pairs of plates arranged perpendicular to one another. A control system controls the laser and a plurality of switching components synchronized with the laser, to independently control excitation of each one of the deflector plates. This allows each electron pulse to be directed to a different portion of the image sensor, as well as to be provided with an independently set duration and independently set inter-pulse spacings.

High-speed multiframe dynamic transmission electron microscope image acquisition system with arbitrary timing

DOEpatents

Reed, Bryan W.; Dehope, William J; Huete, Glenn; LaGrange, Thomas B.; Shuttlesworth, Richard M

2016-06-21

An electron microscope is disclosed which has a laser-driven photocathode and an arbitrary waveform generator (AWG) laser system ("laser"). The laser produces a train of temporally-shaped laser pulses of a predefined pulse duration and waveform, and directs the laser pulses to the laser-driven photocathode to produce a train of electron pulses. An image sensor is used along with a deflector subsystem. The deflector subsystem is arranged downstream of the target but upstream of the image sensor, and has two pairs of plates arranged perpendicular to one another. A control system controls the laser and a plurality of switching components synchronized with the laser, to independently control excitation of each one of the deflector plates. This allows each electron pulse to be directed to a different portion of the image sensor, as well as to be provided with an independently set duration and independently set inter-pulse spacings.

Improving Depth, Energy and Timing Estimation in PET Detectors with Deconvolution and Maximum Likelihood Pulse Shape Discrimination

PubMed Central

Berg, Eric; Roncali, Emilie; Hutchcroft, Will; Qi, Jinyi; Cherry, Simon R.

2016-01-01

In a scintillation detector, the light generated in the scintillator by a gamma interaction is converted to photoelectrons by a photodetector and produces a time-dependent waveform, the shape of which depends on the scintillator properties and the photodetector response. Several depth-of-interaction (DOI) encoding strategies have been developed that manipulate the scintillator’s temporal response along the crystal length and therefore require pulse shape discrimination techniques to differentiate waveform shapes. In this work, we demonstrate how maximum likelihood (ML) estimation methods can be applied to pulse shape discrimination to better estimate deposited energy, DOI and interaction time (for time-of-flight (TOF) PET) of a gamma ray in a scintillation detector. We developed likelihood models based on either the estimated detection times of individual photoelectrons or the number of photoelectrons in discrete time bins, and applied to two phosphor-coated crystals (LFS and LYSO) used in a previously developed TOF-DOI detector concept. Compared with conventional analytical methods, ML pulse shape discrimination improved DOI encoding by 27% for both crystals. Using the ML DOI estimate, we were able to counter depth-dependent changes in light collection inherent to long scintillator crystals and recover the energy resolution measured with fixed depth irradiation (~11.5% for both crystals). Lastly, we demonstrated how the Richardson-Lucy algorithm, an iterative, ML-based deconvolution technique, can be applied to the digitized waveforms to deconvolve the photodetector’s single photoelectron response and produce waveforms with a faster rising edge. After deconvolution and applying DOI and time-walk corrections, we demonstrated a 13% improvement in coincidence timing resolution (from 290 to 254 ps) with the LFS crystal and an 8% improvement (323 to 297 ps) with the LYSO crystal. PMID:27295658

Improving Depth, Energy and Timing Estimation in PET Detectors with Deconvolution and Maximum Likelihood Pulse Shape Discrimination.

PubMed

Berg, Eric; Roncali, Emilie; Hutchcroft, Will; Qi, Jinyi; Cherry, Simon R

2016-11-01

In a scintillation detector, the light generated in the scintillator by a gamma interaction is converted to photoelectrons by a photodetector and produces a time-dependent waveform, the shape of which depends on the scintillator properties and the photodetector response. Several depth-of-interaction (DOI) encoding strategies have been developed that manipulate the scintillator's temporal response along the crystal length and therefore require pulse shape discrimination techniques to differentiate waveform shapes. In this work, we demonstrate how maximum likelihood (ML) estimation methods can be applied to pulse shape discrimination to better estimate deposited energy, DOI and interaction time (for time-of-flight (TOF) PET) of a gamma ray in a scintillation detector. We developed likelihood models based on either the estimated detection times of individual photoelectrons or the number of photoelectrons in discrete time bins, and applied to two phosphor-coated crystals (LFS and LYSO) used in a previously developed TOF-DOI detector concept. Compared with conventional analytical methods, ML pulse shape discrimination improved DOI encoding by 27% for both crystals. Using the ML DOI estimate, we were able to counter depth-dependent changes in light collection inherent to long scintillator crystals and recover the energy resolution measured with fixed depth irradiation (~11.5% for both crystals). Lastly, we demonstrated how the Richardson-Lucy algorithm, an iterative, ML-based deconvolution technique, can be applied to the digitized waveforms to deconvolve the photodetector's single photoelectron response and produce waveforms with a faster rising edge. After deconvolution and applying DOI and time-walk corrections, we demonstrated a 13% improvement in coincidence timing resolution (from 290 to 254 ps) with the LFS crystal and an 8% improvement (323 to 297 ps) with the LYSO crystal.

Diffractive optics for quasi-direct space-to-time pulse shaping.

PubMed

Mínguez-Vega, Gladys; Mendoza-Yero, Omel; Lancis, Jesús; Gisbert, Rafael; Andrés, Pedro

2008-10-13

The strong chromatic behavior associated with a conventional diffractive lens is fully exploited to propose a novel optical device for pulse shaping in the femtosecond regime. This device consists of two optical elements: a spatially patterned circularly symmetric mask and a kinoform diffractive lens, which are facing each other. The system performs a mapping between the spatial position of the masking function expressed in the squared radial coordinate and the temporal position in the output waveform. This space-to-time conversion occurs at the chromatic focus of the diffractive lens, and makes it possible to tailor the output central wavelength along the axial location of the output point. Inspection of the validity of our device is performed by means of computer simulations involving the generation of femtosecond optical packets.

Amplifying modeling for broad bandwidth pulse in Nd:glass based on hybrid-broaden mechanism

NASA Astrophysics Data System (ADS)

Su, J.; Liu, L.; Luo, B.; Wang, W.; Jing, F.; Wei, X.; Zhang, X.

2008-05-01

In this paper, the cross relaxation time is proposed to combine the homogeneous and inhomogeneous broaden mechanism for broad bandwidth pulse amplification model. The corresponding velocity equation, which can describe the response of inverse population on upper and low energy level of gain media to different frequency of pulse, is also put forward. The gain saturation and energy relaxation effect are also included in the velocity equation. Code named CPAP has been developed to simulate the amplifying process of broad bandwidth pulse in multi-pass laser system. The amplifying capability of multi-pass laser system is evaluated and gain narrowing and temporal shape distortion are also investigated when bandwidth of pulse and cross relaxation time of gain media are different. Results can benefit the design of high-energy PW laser system in LFRC, CAEP.

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

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

Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

Here, we discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. Furthermore, we show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. Finally, the combination of narrow absorption peaks in the sample with ultrafast broadbandmore » excitation pulses is especially prone to this effect.« less

Generation of Ramped Current Profiles in Relativistic Electron Beams Using Wakefields in Dielectric Structures

DOE PAGES

Andonian, G.; Barber, S.; O’Shea, F. H.; ...

2017-02-03

We show that temporal pulse tailoring of charged-particle beams is essential to optimize efficiency in collinear wakefield acceleration schemes. In this Letter, we demonstrate a novel phase space manipulation method that employs a beam wakefield interaction in a dielectric structure, followed by bunch compression in a permanent magnet chicane, to longitudinally tailor the pulse shape of an electron beam. This compact, passive, approach was used to generate a nearly linearly ramped current profile in a relativistic electron beam experiment carried out at the Brookhaven National Laboratory Accelerator Test Facility. Here, we report on these experimental results including beam and wakefieldmore » diagnostics and pulse profile reconstruction techniques.« less

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

DOE PAGES

Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

2017-03-06

Here, we discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. Furthermore, we show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. Finally, the combination of narrow absorption peaks in the sample with ultrafast broadbandmore » excitation pulses is especially prone to this effect.« less

Optimal control of multiphoton ionization dynamics of small alkali aggregates

NASA Astrophysics Data System (ADS)

Lindinger, A.; Bartelt, A.; Lupulescu, C.; Vajda, S.; Woste, Ludger

2003-11-01

We have performed transient multi-photon ionization experiments on small alkali clusters of different size in order to probe their wave packet dynamics, structural reorientations, charge transfers and dissociative events in different vibrationally excited electronic states including their ground state. The observed processes were highly dependent on the irradiated pulse parameters like wavelength range or its phase and amplitude; an emphasis to employ a feedback control system for generating the optimum pulse shapes. Their spectral and temporal behavior reflects interesting properties about the investigated system and the irradiated photo-chemical process. First, we present the vibrational dynamics of bound electronically excited states of alkali dimers and trimers. The scheme for observing the wave packet dynamics in the electronic ground state using stimulated Raman-pumping is shown. Since the employed pulse parameters significantly influence the efficiency of the irradiated dynamic pathways photo-induced ioniziation experiments were carried out. The controllability of 3-photon ionization pathways is investigated on the model-like systems NaK and K2. A closed learning loop for adaptive feedback control is used to find the optimal fs pulse shape. Sinusoidal parameterizations of the spectral phase modulation are investigated in regard to the obtained optimal field. By reducing the number of parameters and thereby the complexity of the phase moduation, optimal pulse shapes can be generated that carry fingerprints of the molecule's dynamical properties. This enables to find "understandable" optimal pulse forms and offers the possiblity to gain insight into the photo-induced control process. Characteristic motions of the involved wave packets are proposed to explain the optimized dynamic dissociation pathways.

Single-shot high-resolution characterization of optical pulses by spectral phase diversity

DOE PAGES

Dorrer, C.; Waxer, L. J.; Kalb, A.; ...

2015-12-15

The concept of spectral phase diversity is proposed and applied to the temporal characterization of optical pulses. The experimental trace is composed of the measured power of a plurality of ancillary optical pulses derived from the pulse under test by adding known amounts of chromatic dispersion. The spectral phase of the pulse under test is retrieved by minimizing the error between the experimental trace and a trace calculated from the optical spectrum using the known diagnostic parameters. An assembly composed of splitters and dispersive delay fibers has been used to generate 64 ancillary pulses whose instantaneous power can be detectedmore » in a single shot with a high-bandwidth photodiode and oscilloscope. Pulse-shape reconstruction for pulses shorter than the photodetection impulse response has been demonstrated.The diagnostic is experimentally shown to accurately characterize pulses from a chirped-pulse–amplification system when its stretcher is detuned from the position for optimal recompression. As a result, various investigations of the performance with respect to the number of ancillary pulses and the range of chromatic dispersion generated in the diagnostic are presented.« less

Single-shot high-resolution characterization of optical pulses by spectral phase diversity

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

Dorrer, C.; Waxer, L. J.; Kalb, A.

The concept of spectral phase diversity is proposed and applied to the temporal characterization of optical pulses. The experimental trace is composed of the measured power of a plurality of ancillary optical pulses derived from the pulse under test by adding known amounts of chromatic dispersion. The spectral phase of the pulse under test is retrieved by minimizing the error between the experimental trace and a trace calculated from the optical spectrum using the known diagnostic parameters. An assembly composed of splitters and dispersive delay fibers has been used to generate 64 ancillary pulses whose instantaneous power can be detectedmore » in a single shot with a high-bandwidth photodiode and oscilloscope. Pulse-shape reconstruction for pulses shorter than the photodetection impulse response has been demonstrated.The diagnostic is experimentally shown to accurately characterize pulses from a chirped-pulse–amplification system when its stretcher is detuned from the position for optimal recompression. As a result, various investigations of the performance with respect to the number of ancillary pulses and the range of chromatic dispersion generated in the diagnostic are presented.« less

Spatio-temporal variation of fish taxonomic composition in a South-East Asian flood-pulse system.

PubMed

Kong, Heng; Chevalier, Mathieu; Laffaille, Pascal; Lek, Sovan

2017-01-01

The Tonle Sap Lake (TSL) is a flood-pulse system. It is the largest natural lake in South-East Asia and constitutes one of the largest fisheries over the world, supporting the livelihood of million peoples. Nonetheless, the Mekong River Basin is changing rapidly due to accelerating water infrastructure development (hydropower, irrigation, flood control, and water supply) and climate change, bringing considerable modifications to the annual flood-pulse of the TSL. Such modifications are expected to have strong impacts on fish biodiversity and abundance. This paper aims to characterize the spatio-temporal variations of fish taxonomic composition and to highlights the underlying determinants of these variations. For this purpose, we used data collected from a community catch monitoring program conducted at six sites during 141 weeks, covering two full hydrological cycles. For each week, we estimated beta diversity as the total variance of the site-by-species community matrix and partitioned it into Local Contribution to Beta Diversity (LCBD) and Species Contribution to Beta Diversity (SCBD). We then performed multiple linear regressions to determine whether species richness, species abundances and water level explained the temporal variation in the contribution of site and species to beta diversity. Our results indicate strong temporal variation of beta diversity due to differential contributions of sites and species to the spatial variation of fish taxonomic composition. We further found that the direction, the shape and the relative effect of species richness, abundances and water level on temporal variation in LCBD and SCBD values greatly varied among sites, thus suggesting spatial variation in the processes leading to temporal variation in community composition. Overall, our results suggest that fish taxonomic composition is not homogeneously distributed over space and time and is likely to be impacted in the future if the flood-pulse dynamic of the system is altered by human activities.

Interaction dynamics of temporal and spatial separated cavitation bubbles in water

NASA Astrophysics Data System (ADS)

Tinne, N.; Ripken, T.; Lubatschowski, H.

2010-02-01

The LASIK procedure is a well established laser based treatment in ophthalmology. Nowadays it includes a cutting of the corneal tissue bases on ultra short pulses which are focused below the tissue surface to create an optical breakdown and hence a dissection of the tissue. The energy of the laser pulse is absorbed by non-linear processes that result in an expansion of a cavitation bubble and rupturing of the tissue. Due to a reduction of the duration of treatment the current development of ultra short laser systems points to higher repetition rates. This in turn results in a probable interaction between different cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. We present a high-speed photography analysis of cavitation bubble interaction for two spatial separated laser-induced optical breakdowns varying the laser pulse energy as well as the spatial distance. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape, asymmetric water streams and jet formation were observed. The results of this research can be used to comprehend and optimize the cutting effect of ultra short pulse laser systems with high repetition rates (> 1 MHz).

Analysis and Optimization of Pulse Dynamics for Magnetic Stimulation

PubMed Central

Goetz, Stefan M.; Truong, Cong Nam; Gerhofer, Manuel G.; Peterchev, Angel V.; Herzog, Hans-Georg; Weyh, Thomas

2013-01-01

Magnetic stimulation is a standard tool in brain research and has found important clinical applications in neurology, psychiatry, and rehabilitation. Whereas coil designs and the spatial field properties have been intensively studied in the literature, the temporal dynamics of the field has received less attention. Typically, the magnetic field waveform is determined by available device circuit topologies rather than by consideration of what is optimal for neural stimulation. This paper analyzes and optimizes the waveform dynamics using a nonlinear model of a mammalian axon. The optimization objective was to minimize the pulse energy loss. The energy loss drives power consumption and heating, which are the dominating limitations of magnetic stimulation. The optimization approach is based on a hybrid global-local method. Different coordinate systems for describing the continuous waveforms in a limited parameter space are defined for numerical stability. The optimization results suggest that there are waveforms with substantially higher efficiency than that of traditional pulse shapes. One class of optimal pulses is analyzed further. Although the coil voltage profile of these waveforms is almost rectangular, the corresponding current shape presents distinctive characteristics, such as a slow low-amplitude first phase which precedes the main pulse and reduces the losses. Representatives of this class of waveforms corresponding to different maximum voltages are linked by a nonlinear transformation. The main phase, however, scales with time only. As with conventional magnetic stimulation pulses, briefer pulses result in lower energy loss but require higher coil voltage than longer pulses. PMID:23469168

Spectral splitting of optical pulses inside a dispersive medium at a temporal boundary

DOE PAGES

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

2016-11-07

We show numerically that the spectrum of an optical pulse splits into multiple, widely separated, spectral bands when it arrives at a temporal boundary across which refractive index changes suddenly. At the same time, the pulse breaks into several temporally separated pulses traveling at different speeds. The number of such pulses depends on the dispersive properties of the medium. We study the effect of second- and third-order dispersion in detail but also consider briefly the impact of other higher-order terms. As a result, a temporal waveguide formed with two temporal boundaries can reflect the temporally separated pulses again and again,more » increasing the number of pulses trapped within the temporal waveguide.« less

Storage of RF photons in minimal conditions

NASA Astrophysics Data System (ADS)

Cromières, J.-P.; Chanelière, T.

2018-02-01

We investigate the minimal conditions to store coherently a RF pulse in a material medium. We choose a commercial quartz as a memory support because it is a widely available component with a high Q-factor. Pulse storage is obtained by varying dynamically the light-matter coupling with an analog switch. This parametric driving of the quartz dynamics can be alternatively interpreted as a stopped-light experiment. We obtain an efficiency of 26%, a storage time of 209 μs and a time-to-bandwidth product of 98 by optimizing the pulse temporal shape. The coherent character of the storage is demonstrated. Our goal is to connect different types of memories in the RF and optical domain for quantum information processing. Our motivation is essentially fundamental.

Resistance and resilience of microbial communities--temporal and spatial insurance against perturbations.

PubMed

Baho, Didier L; Peter, Hannes; Tranvik, Lars J

2012-09-01

Bacteria play fundamental roles for many ecosystem processes; however, little empirical evidence is available on how environmental perturbations affect their composition and function. We investigated how spatial and temporal refuges affect the resistance and resilience of a freshwater bacterioplankton community upon a salinity pulse perturbation in continuous cultures. Attachment to a surface avoided the flushing out of cells and enabled re-colonization of the liquid phase after the perturbation, hence serving as a temporal refuge. A spatial refuge was established by introduction of bacteria from an undisturbed reservoir upstream of the continuous culture vessel, acting analogous to a regional species pool in a metacommunity. The salinity pulse affected bacterial community composition and the rates of respiration and the pattern of potential substrate utilization as well as the correlation between composition and function. Compared with the no-refuge treatment, the temporal refuge shortened return to pre-perturbation conditions, indicating enhanced community resilience. Composition and function were less disturbed in the treatment providing a spatial refuge, suggesting higher resistance. Our results highlight that spatial and temporal dynamics in general and refuges in particular need to be considered for conceptual progress in how microbial metacommunities are shaped by perturbations. © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd.

Coherent control of alkali cluster fragmentation dynamics

NASA Astrophysics Data System (ADS)

Lindinger, Albrecht; Lupulescu, Cosmin; Bartelt, Andreas; Vajda, Štefan; Wöste, Ludger

2003-06-01

Metal clusters exhibit extraordinary chemical and catalytic properties, which sensitively depend upon their size. This behavior makes them interesting candidates for the real-time analysis of ultrafast photo-induced processes—ultimately leading to coherent control scenarii. We have performed transient multi-photon ionization experiments on small alkali clusters of different size in order to probe their wave packet dynamics, structural reorientations, charge transfers and dissociative events in different vibrationally excited electronic states including their ground state. The observed processes were highly dependent on the irradiated pulse parameters, like its phase, amplitude and duration; an emphasis to employ a feedback control system for generating the optimum pulse shapes. Their spectral and temporal behavior reflects interesting properties about the investigated system and the irradiated photochemical process. We present first the vibrational dynamics of bound, dissociated, and pre-dissociated electronically excited states of alkali dimers and trimers. The scheme for observing the wave packet dynamics in the electronic ground state using stimulated Raman-pumping is shown. Since the employed pulse parameters significantly influence the efficiency of the irradiated dynamic pathways photo-induced fragmentation experiments on bifurcating reaction channels were carried out. In these experiments different branching ionization and fragmentation pathways of electronically excited Na 2K were investigated. By employing an evolutionary algorithm for optimizing the phase and amplitude of the applied laser field, the yield of the resulting parent or fragment ions could significantly be influenced and interesting features could be concluded from the obtained optimum pulse shapes revealing the characteristic molecular oscillation period. Moreover, the influence on the optimal pulse shape due to fragmentation from larger clusters into NaK is obtained. The substructure of the optimal pulse shape thereby offers new insight into the fragmentation channel during the control process. Characteristic motions of the involved wave packets are proposed, in order to explain the optimized dynamic dissociation pathways.

80GHz waveform generator by optical Fourier synthesis of four spectral sidebands (Conference Presentation)

NASA Astrophysics Data System (ADS)

Fatome, Julien; Hammani, Kamal; Kibler, Bertrand; Finot, Christophe

2016-04-01

Versatile and easy to implement methods to generate arbitrary optical waveforms at high repetition rates are of considerable interest with applications in optical communications, all-optical signal processing, instrumentation systems and microwave signal manipulation. While shaping sinusoidal, Gaussian or hyperbolic secant intensity profiles is commonly achieved by means of modulators or mode-locked lasers, other pulse profiles such as parabolic, triangular or flat-top shapes still remain challenging to synthesize. In this context, several strategies were already explored. First, the linear pulse shaping is a common method to carve an initial ultrashort pulse train into the desired shape. The line-by-line shaping of a coherent frequency comb made of tens of spectral components was also investigated to generate more complex structures whereas Fourier synthesis of a few discrete frequencies spectrum was exploited to efficiently generate high-fidelity ultrafast periodic intensity profiles. Besides linear shaping techniques, several nonlinear methods were implemented to benefit from the adiabatic evolution of the intensity pulse profile upon propagation in optical fibers. Other examples of efficient methods are based on the photonic generation involving specific Mach-Zehnder modulators, microwave photonic filters as well as frequency-to-time conversion. In this contribution, we theoretically and experimentally demonstrate a new approach enabling the synthesis of periodic high-repetition rate pulses with various intensity profiles ranging from parabola to triangular and flat-top pulses. More precisely by linear phase and amplitude shaping of only four spectral lines is it possible to reach the targeted temporal profile. Indeed, tailoring the input symmetric spectrum only requires the determination of two physical parameters: the phase difference between the inner and outer spectral sidebands and the ratio between the amplitude of these sidebands. Therefore, a systematic bidimensional analysis provides the optimum parameters and also highlights that switching between the different waveforms is achieved by simply changing the spectral phase between the inner and outer sidebands. We successfully validate this concept with the generation of high-fidelity ultrafast periodic waveforms at 40 GHz by shaping with a liquid cristal on insulator a four sideband comb resulting from a phase-modulated continuous wave. In order to reach higher repetition rates, we also describe a new scenario to obtain the required initial spectrum by taking advantage of the four-wave mixing process occurring in a highly nonlinear fiber. This approach is experimentally implemented at a repetition rate of 80-GHz by use of intensity and phase measurements that stress that full-duty cycle, high-quality, triangular, parabolic or flat-top profiles are obtained in full agreement with numerical simulations. The reconfigurable property of this photonic waveform generator is confirmed. Finally, the generation of bunch of shaped pulses is investigated, as well as the impact of Brillouin backscattering.

Characterization and compression of dissipative-soliton-resonance pulses in fiber lasers

PubMed Central

Li, Daojing; Li, Lei; Zhou, Junyu; Zhao, Luming; Tang, Dingyuan; Shen, Deyuan

2016-01-01

We report numerical and experimental studies of dissipative-soliton-resonance (DSR) in a fiber laser with a nonlinear optical loop mirror. The DSR pulse presents temporally a flat-top profile and a clamped peak power. Its spectrum has a rectangle profile with characteristic steep edges. It shows a unique behavior as pulse energy increases: The rectangle part of the spectrum is unchanged while the newly emerging spectrum sits on the center part and forms a peak. Experimental observations match well with the numerical results. Moreover, the detailed evolution of the DSR pulse compression is both numerically and experimentally demonstrated for the first time. An experimentally obtained DSR pulse of 63 ps duration is compressed down to 760 fs, with low-intensity pedestals using a grating pair. Before being compressed to its narrowest width, the pulse firstly evolves into a cat-ear profile, and the corresponding autocorrelation trace shows a crown shape, which distinguishes itself from properties of other solitons formed in fiber lasers. PMID:27025189

A single-shot spatial chirp method for measuring initial AC conductivity evolution of femtosecond laser pulse excited warm dense matter

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

Chen, Z.; Hering, P.; Brown, S. B.

To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), a spatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Here, temporal evolution of AC conductivity in laser excited warm dense gold was also measured.

A single-shot spatial chirp method for measuring initial AC conductivity evolution of femtosecond laser pulse excited warm dense matter

DOE PAGES

Chen, Z.; Hering, P.; Brown, S. B.; ...

2016-09-19

To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), a spatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Here, temporal evolution of AC conductivity in laser excited warm dense gold was also measured.

Excitation of H+2 with one-cycle laser pulses: shaped post-laser-field electronic oscillations, generation of higher- and lower-order harmonics

NASA Astrophysics Data System (ADS)

Paramonov, Guennaddi K.; Kühn, Oliver; Bandrauk, André D.

2017-08-01

Non-Born-Oppenheimer quantum dynamics of H+2 excited by shaped one-cycle laser pulses linearly polarised along the molecular axis have been studied by the numerical solution of the time-dependent Schrödinger equation within a three-dimensional model, including the internuclear separation, R, and the electron coordinates z and ρ. Laser carrier frequencies corresponding to the wavelengths λl = 25 nm through λl = 400 nm were used and the amplitudes of the pulses were chosen such that the energy of H+2 was close to its dissociation threshold at the end of any laser pulse applied. It is shown that there exists a characteristic oscillation frequency ωosc ≃ 0.2265 au (corresponding to the period of τosc ≃ 0.671 fs and the wavelength of λosc ≃ 201 nm) that manifests itself as a 'carrier' frequency of temporally shaped oscillations of the time-dependent expectation values ⟨z ⟩ and ⟨∂V/∂z ⟩ that emerge at the ends of the laser pulses and exist on a timescale of at least 50 fs. Time-dependent expectation values ⟨ρ⟩ and ⟨∂V /∂ρ⟩ of the optically passive degree of freedom, ρ, demonstrate post-laser-field oscillations at two basic frequencies ωρ1 ≈ ωosc and ωρ2 ≈ 2ωosc. Power spectra associated with the electronic motion show higher- and lower-order harmonics with respect to the driving field.

High-accuracy reference standards for two-photon absorption in the 680–1050 nm wavelength range

PubMed Central

de Reguardati, Sophie; Pahapill, Juri; Mikhailov, Alexander; Stepanenko, Yuriy; Rebane, Aleksander

2016-01-01

Degenerate two-photon absorption (2PA) of a series of organic fluorophores is measured using femtosecond fluorescence excitation method in the wavelength range, λ2PA = 680–1050 nm, and ~100 MHz pulse repetition rate. The function of relative 2PA spectral shape is obtained with estimated accuracy 5%, and the absolute 2PA cross section is measured at selected wavelengths with the accuracy 8%. Significant improvement of the accuracy is achieved by means of rigorous evaluation of the quadratic dependence of the fluorescence signal on the incident photon flux in the whole wavelength range, by comparing results obtained from two independent experiments, as well as due to meticulous evaluation of critical experimental parameters, including the excitation spatial- and temporal pulse shape, laser power and sample geometry. Application of the reference standards in nonlinear transmittance measurements is discussed. PMID:27137334

Effects of laser source parameters on the generation of narrow band and directed laser ultrasound

NASA Technical Reports Server (NTRS)

Spicer, James B.; Deaton, John B., Jr.; Wagner, James W.

1992-01-01

Predictive and prescriptive modeling of laser arrays is performed to demonstrate the effects of the extension of array elements on laser array performance. For a repetitively pulsed laser source (the temporal laser array), efficient frequency compression is best achieved by detecting longitudinal waves off-epicenter in plates where the source size and shape directly influence the longitudinal wave shape and duration; the longitudinal array may be tailored for a given repetition frequency to yield efficient overtone energy compression into the fundamental frequency band. For phased arrays, apparent array directivity is heavily influenced by array element size.

Interactions between butterfly-shaped pulses in the inhomogeneous media

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

Liu, Wen-Jun; Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190; Huang, Long-Gang

2014-10-15

Pulse interactions affect pulse qualities during the propagation. Interactions between butterfly-shaped pulses are investigated to improve pulse qualities in the inhomogeneous media. In order to describe the interactions between butterfly-shaped pulses, analytic two-soliton solutions are derived. Based on those solutions, influences of corresponding parameters on pulse interactions are discussed. Methods to control the pulse interactions are suggested. - Highlights: • Interactions between butterfly-shaped pulses are investigated. • Methods to control the pulse interactions are suggested. • Analytic two-soliton solutions for butterfly-shaped pulses are derived.

Quantum simulation of ultrafast dynamics using trapped ultracold atoms.

PubMed

Senaratne, Ruwan; Rajagopal, Shankari V; Shimasaki, Toshihiko; Dotti, Peter E; Fujiwara, Kurt M; Singh, Kevin; Geiger, Zachary A; Weld, David M

2018-05-25

Ultrafast electronic dynamics are typically studied using pulsed lasers. Here we demonstrate a complementary experimental approach: quantum simulation of ultrafast dynamics using trapped ultracold atoms. Counter-intuitively, this technique emulates some of the fastest processes in atomic physics with some of the slowest, leading to a temporal magnification factor of up to 12 orders of magnitude. In these experiments, time-varying forces on neutral atoms in the ground state of a tunable optical trap emulate the electric fields of a pulsed laser acting on bound charged particles. We demonstrate the correspondence with ultrafast science by a sequence of experiments: nonlinear spectroscopy of a many-body bound state, control of the excitation spectrum by potential shaping, observation of sub-cycle unbinding dynamics during strong few-cycle pulses, and direct measurement of carrier-envelope phase dependence of the response to an ultrafast-equivalent pulse. These results establish cold-atom quantum simulation as a complementary tool for studying ultrafast dynamics.

Picosecond supercontinuum laser with consistent emission parameters over variable repetition rates from 1 to 40 MHz

NASA Astrophysics Data System (ADS)

Schönau, Thomas; Siebert, Torsten; Härtel, Romano; Klemme, Dietmar; Lauritsen, Kristian; Erdmann, Rainer

2013-02-01

An freely triggerable picosecond visible supercontinuum laser source is presented that allows for a uniform spectral profile and equivalent pulse characteristics over variable repetition rates from 1 to 40MHz. The system features PM Yb3+-doped fiber amplification of a picosecond gain-switched seed diode at 1062 nm. The pump power in the multi-stage amplifier is actively adjusted by a microcontroller for a consistent peak power of the amplified signal in the full range of repetition rates. The length of the PCF is scaled to deliver a homogeneous spectrum and minimized distortion of the temporal pulse shape.

All-optical UWB generation and modulation using SOA-XPM effect and DWDM-based multi-channel frequency discrimination.

PubMed

Wang, Fei; Dong, Jianji; Xu, Enming; Zhang, Xinliang

2010-11-22

An all-optical UWB pulses generation and modulation scheme using cross phase modulation (XPM) effect of semiconductor optical amplifier (SOA) and DWDM-based multi-channel frequency discrimination is proposed and demonstrated, which has potential application in multiuser UWB-Over-Fiber communication systems. When a Gaussian pulse light and a wavelength-tunable CW probe light are together injected into the SOA, the probe light out from the SOA will have a temporal chirp due to SOA-XPM effect. When the chirped probe light is tuned to the slopes of single DWDM channel transmittance curve, the optical phase modulation to intensity modulation conversion is achieved at DWDM that serves as a multi-channel frequency discriminator, the inverted polarity Gaussian monocycle and doublet pulse is detected by a photodetector, respectively. If the probe lights are simultaneously aimed to different slopes of several DWDM channels, multi-channel or binary-phase-coded UWB signal generation can be acquired. Using proposed scheme, pulse amplitude modulation (PAM), pulse polarity modulation (PPM) and pulse shape modulation (PSM) to UWB pulses also can be conveniently realized.

The calculation of weakly non-spherical cavitation bubble impact on a solid

NASA Astrophysics Data System (ADS)

Aganin, A. A.; Guseva, T. S.; Kosolapova, L. A.; Khismatullina, N. A.

2016-11-01

The effect of small spheroidal non-sphericity of a cavitation bubble touching a solid at the beginning of its collapse on its impact on the solid of a copper-nickel alloy is investigated. The impact on the solid is realized by means of a high-speed liquid jet arising at collapse on the bubble surface. The shape of the jet, its velocity and pressure are calculated by the boundary element method. The spatial and temporal characteristics of the pressure pulses on the solid surface are determined by the CIP-CUP method on dynamically adaptive grids without explicitly separating the gas-liquid interface. The solid surface layer dynamics is evaluated by the Godunov method. The results are analyzed in dimensionless variables obtained with using the water hammer pressure, the time moment and the jet-solid contact area radius at which the jet begins to spread on the solid surface. It is shown that in those dimensionless variables, the dependence of the spatial and temporal characteristics of the solid surface pressure pulses on the initial bubble shape non-sphericity is relatively small. The nonsphericity also slightly influences the main qualitative features of the dynamic processes inside the solid, whereas its effect on their quantitative characteristics can be significant.

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

Aalseth, Craig E.; Day, Anthony R.; Fuller, Erin S.

Abstract A new ultra-low-background proportional counter (ULBPC) design was recently developed at Pacific Northwest National Laboratory (PNNL). This design, along with an ultra-low-background counting system (ULBCS) which provides passive and active shielding with radon exclusion, has been developed to complement a new shallow underground laboratory (~30 meters water-equivalent) constructed at PNNL. After these steps to mitigate dominant backgrounds (cosmic rays, external gamma-rays, radioactivity in materials), remaining background events do not exclusively arise from ionization of the proportional counter gas. Digital pulse-shape discrimination (PSD) is thus employed to further improve measurement sensitivity. In this work, a template shape is generated formore » each individual sample measurement of interest, a "self-calibrating" template. Differences in event topology can also cause differences in pulse shape. In this work, the temporal region analyzed for each event is refined to maximize background discrimination while avoiding unwanted sensitivity to event topology. This digital PSD method is applied to sample and background data, and initial measurement results from a biofuel methane sample are presented in the context of low-background measurements currently being developed.« less

High-harmonic and single attosecond pulse generation using plasmonic field enhancement in ordered arrays of gold nanoparticles with chirped laser pulses.

PubMed

Yang, Ying-Ying; Scrinzi, Armin; Husakou, Anton; Li, Qian-Guang; Stebbings, Sarah L; Süßmann, Frederik; Yu, Hai-Juan; Kim, Seungchul; Rühl, Eckart; Herrmann, Joachim; Lin, Xue-Chun; Kling, Matthias F

2013-01-28

Coherent XUV sources, which may operate at MHz repetition rate, could find applications in high-precision spectroscopy and for spatio-time-resolved measurements of collective electron dynamics on nanostructured surfaces. We theoretically investigate utilizing the enhanced plasmonic fields in an ordered array of gold nanoparticles for the generation of high-harmonic, extreme-ultraviolet (XUV) radiation. By optimization of the chirp of ultrashort laser pulses incident on the array, our simulations indicate a potential route towards the temporal shaping of the plasmonic near-field and, in turn, the generation of single attosecond pulses. The inherent effects of inhomogeneity of the local fields on the high-harmonic generation are analyzed and discussed. While taking the inhomogeneity into account does not affect the optimal chirp for the generation of a single attosecond pulse, the cut-off energy of the high-harmonic spectrum is enhanced by about a factor of two.

100J Pulsed Laser Shock Driver for Dynamic Compression Research

NASA Astrophysics Data System (ADS)

Wang, X.; Sethian, J.; Bromage, J.; Fochs, S.; Broege, D.; Zuegel, J.; Roides, R.; Cuffney, R.; Brent, G.; Zweiback, J.; Currier, Z.; D'Amico, K.; Hawreliak, J.; Zhang, J.; Rigg, P. A.; Gupta, Y. M.

2017-06-01

Logos Technologies and the Laboratory for Laser Energetics (LLE, University of Rochester) - in partnership with Washington State University - have designed, built and deployed a one of a kind 100J pulsed UV (351 nm) laser system to perform real-time, x-ray diffraction and imaging experiments in laser-driven compression experiments at the Dynamic Compression Sector (DCS) at the Advanced Photon Source, Argonne National Laboratory. The laser complements the other dynamic compression drivers at DCS. The laser system features beam smoothing for 2-d spatially uniform loading of samples and four, highly reproducible, temporal profiles (total pulse duration: 5-15 ns) to accommodate a wide variety of scientific needs. Other pulse shapes can be achieved as the experimental needs evolve. Timing of the laser pulse is highly precise (<200 ps) to allow accurate synchronization of the x-rays with the dynamic compression event. Details of the laser system, its operating parameters, and representative results will be presented. Work supported by DOE/NNSA.

Pulse Shaped 8-PSK Bandwidth Efficiency and Spectral Spike Elimination

NASA Technical Reports Server (NTRS)

Tao, Jian-Ping

1998-01-01

The most bandwidth-efficient communication methods are imperative to cope with the congested frequency bands. Pulse shaping methods have excellent effects on narrowing bandwidth and increasing band utilization. The position of the baseband filters for the pulse shaping is crucial. Post-modulation pulse shaping (a low pass filter is located after the modulator) can change signals from constant envelope to non-constant envelope, and non-constant envelope signals through non-linear device (a SSPA or TWT) can further spread the power spectra. Pre-modulation pulse shaping (a filter is located before the modulator) will have constant envelope. These two pulse shaping methods have different effects on narrowing the bandwidth and producing bit errors. This report studied the effect of various pre-modulation pulse shaping filters with respect to bandwidth, spectral spikes and bit error rate. A pre-modulation pulse shaped 8-ary Phase Shift Keying (8PSK) modulation was used throughout the simulations. In addition to traditional pulse shaping filters, such as Bessel, Butterworth and Square Root Raised Cosine (SRRC), other kinds of filters or pulse waveforms were also studied in the pre-modulation pulse shaping method. Simulations were conducted by using the Signal Processing Worksystem (SPW) software package on HP workstations which simulated the power spectral density of pulse shaped 8-PSK signals, end to end system performance and bit error rates (BERS) as a function of Eb/No using pulse shaping in an AWGN channel. These results are compared with the post-modulation pulse shaped 8-PSK results. The simulations indicate traditional pulse shaping filters used in pre-modulation pulse shaping may produce narrower bandwidth, but with worse BER than those in post-modulation pulse shaping. Theory and simulations show pre- modulation pulse shaping could also produce discrete line power spectra (spikes) at regular frequency intervals. These spikes may cause interference with adjacent channel and reduce power efficiency. Some particular pulses (filters), such as trapezoid and pulses with different transits (such as weighted raised cosine transit) were found to reduce bandwidth and not generate spectral spikes. Although a solid state power amplifier (SSPA) was simulated in the non-linear (saturation) region, output power spectra did not spread due to the constant envelope 8-PSK signals.

Diagnostics, Control and Performance Parameters for the BELLA High Repetition Rate Petawatt Class Laser

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

Nakamura, Kei; Mao, Hann-Shin; Gonsalves, Anthony J.

A laser system producing controllable and stable pulses with high power and ultrashort duration at high repetition rate is a key component of a high energy laser-plasma accelerator (LPA). Precise characterization and control of laser properties are essential to understanding laser-plasma interactions required to build a 10-GeV class LPA. This study discusses the diagnostics, control and performance parameters of a 1 Hz, 1 petawatt (PW) class laser at the Berkeley Lab Laser Accelerator (BELLA) facility. The BELLA PW laser provided up to 46 J on target with a 1% level energy fluctuation and 1.3-μrad pointing stability. The spatial profile wasmore » measured and optimized by using a camera, wavefront sensor, and deformable mirror (ILAO system). The focus waist was measured to be r 0 = 53 μm and the fraction of energy within the circular area defined by the first minimum of the diffraction pattern (r = 67 μm) was 0.75. The temporal profile was controlled via the angle of incidence on a stretcher and a compressor, as well as an acousto-optic programmable dispersive. The temporal pulse shape was measured to be about 33 fs in full width at half maximum (WIZZLER and GRENOUILLE diagnostics). In order to accurately evaluate peak intensity, the energy-normalized peak fluence, and energy-normalized peak power were analyzed for the measured spatial and temporal mode profiles, and were found to be 15 kJ/(cm 2 J) with 6% fluctuation (standard deviation) and 25 TW/J with 5% fluctuation for 46-J on-target energy, respectively. This yielded a peak power of 1.2 PW and a peak intensity of 17×10 18 W/cm 2 with 8% fluctuation. A method to model the pulse shape for arbitrary compressor grating distance with high accuracy was developed. The pulse contrast above the amplified spontaneous emission pedestal was measured by SEQUOIA and found to be better than 10 9. The first order spatiotemporal couplings (STCs) were measured with GRENOUILLE, and a simulation of the pulse's evolution at the vicinity of the target was presented. A maximum pulse front tilt angle of less than 7 mrad was achieved. The reduction of the peak power caused by the first order STCs was estimated to be less than 1%. Finally, the capabilities described in this paper are essential for generation of high quality electron beams.« less

Diagnostics, Control and Performance Parameters for the BELLA High Repetition Rate Petawatt Class Laser

DOE PAGES

Nakamura, Kei; Mao, Hann-Shin; Gonsalves, Anthony J.; ...

2017-05-25

A laser system producing controllable and stable pulses with high power and ultrashort duration at high repetition rate is a key component of a high energy laser-plasma accelerator (LPA). Precise characterization and control of laser properties are essential to understanding laser-plasma interactions required to build a 10-GeV class LPA. This study discusses the diagnostics, control and performance parameters of a 1 Hz, 1 petawatt (PW) class laser at the Berkeley Lab Laser Accelerator (BELLA) facility. The BELLA PW laser provided up to 46 J on target with a 1% level energy fluctuation and 1.3-μrad pointing stability. The spatial profile wasmore » measured and optimized by using a camera, wavefront sensor, and deformable mirror (ILAO system). The focus waist was measured to be r 0 = 53 μm and the fraction of energy within the circular area defined by the first minimum of the diffraction pattern (r = 67 μm) was 0.75. The temporal profile was controlled via the angle of incidence on a stretcher and a compressor, as well as an acousto-optic programmable dispersive. The temporal pulse shape was measured to be about 33 fs in full width at half maximum (WIZZLER and GRENOUILLE diagnostics). In order to accurately evaluate peak intensity, the energy-normalized peak fluence, and energy-normalized peak power were analyzed for the measured spatial and temporal mode profiles, and were found to be 15 kJ/(cm 2 J) with 6% fluctuation (standard deviation) and 25 TW/J with 5% fluctuation for 46-J on-target energy, respectively. This yielded a peak power of 1.2 PW and a peak intensity of 17×10 18 W/cm 2 with 8% fluctuation. A method to model the pulse shape for arbitrary compressor grating distance with high accuracy was developed. The pulse contrast above the amplified spontaneous emission pedestal was measured by SEQUOIA and found to be better than 10 9. The first order spatiotemporal couplings (STCs) were measured with GRENOUILLE, and a simulation of the pulse's evolution at the vicinity of the target was presented. A maximum pulse front tilt angle of less than 7 mrad was achieved. The reduction of the peak power caused by the first order STCs was estimated to be less than 1%. Finally, the capabilities described in this paper are essential for generation of high quality electron beams.« less

Diagnostics, Control and Performance Parameters for the BELLA High Repetition Rate Petawatt Class Laser

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

Nakamura, K; Mao, HS; Gonsalves, AJ

2017-08-01

© 2017 IEEE. A laser system producing controllable and stable pulses with high power and ultrashort duration at high repetition rate is a key component of a high energy laser-plasma accelerator (LPA). Precise characterization and control of laser properties are essential to understanding laser-plasma interactions required to build a 10-GeV class LPA. This paper discusses the diagnostics, control and performance parameters of a 1 Hz, 1 petawatt (PW) class laser at the Berkeley Lab Laser Accelerator (BELLA) facility. The BELLA PW laser provided up to 46 J on target with a 1% level energy fluctuation and 1.3-μrad pointing stability. Themore » spatial profile was measured and optimized by using a camera, wavefront sensor, and deformable mirror (ILAO system). The focus waist was measured to be r 0 = 53 μm and the fraction of energy within the circular area defined by the first minimum of the diffraction pattern (r = 67 μm) was 0.75. The temporal profile was controlled via the angle of incidence on a stretcher and a compressor, as well as an acousto-optic programmable dispersive. The temporal pulse shape was measured to be about 33 fs in full width at half maximum (WIZZLER and GRENOUILLE diagnostics). In order to accurately evaluate peak intensity, the energy-normalized peak fluence, and energy-normalized peak power were analyzed for the measured spatial and temporal mode profiles, and were found to be 15 kJ/(cm 2 J) with 6% fluctuation (standard deviation) and 25 TW/J with 5% fluctuation for 46-J on-target energy, respectively. This yielded a peak power of 1.2 PW and a peak intensity of 17×10 18 W/cm 2 with 8% fluctuation. A method to model the pulse shape for arbitrary compressor grating distance with high accuracy was developed. The pulse contrast above the amplified spontaneous emission pedestal was measured by SEQUOIA and found to be better than 10 9 . The first order spatiotemporal couplings (STCs) were measured with GRENOUILLE, and a simulation of the pulse's evolution at the vicinity of the target was presented. A maximum pulse front tilt angle of less than 7 mrad was achieved. The reduction of the peak power caused by the first order STCs was estimated to be less than 1%. The capabilities described in thispaper are essential for generation of high quality electron beams.« less

1D and 2D diffusion pore imaging on a preclinical MR system using adaptive rephasing: Feasibility and pulse sequence comparison

NASA Astrophysics Data System (ADS)

Bertleff, Marco; Domsch, Sebastian; Laun, Frederik B.; Kuder, Tristan A.; Schad, Lothar R.

2017-05-01

Diffusion pore imaging (DPI) has recently been proposed as a means to acquire images of the average pore shape in an image voxel or region of interest. The highly asymmetric gradient scheme of its sequence makes it substantially demanding in terms of the hardware of the NMR system. The aim of this work is to show the feasibility of DPI on a preclinical 9.4 T animal scanner. Using water-filled capillaries with an inner radius of 10 μm, four different variants of the DPI sequence were compared in 1D and 2D measurements. The pulse sequences applied cover the basic implementation using one long and one temporally narrow gradient pulse, a CPMG-like variant with multiple refocusing RF pulses as well as two variants splitting up the long gradient and distributing it on either side of the refocusing pulse. Substantial differences between the methods were found in terms of signal-to-noise ratio, contrast, blurring, deviations from the expected results and sensitivity to gradient imperfections. Each of the tested sequences was found to produce characteristic gradient mismatches dependent on the absolute value, direction and sign of the applied q-value. Read gradients were applied to compensate these mismatches translating them into time shifts, which enabled 1D DPI yielding capillary radius estimations within the tolerances specified by the manufacturer. For a successful DPI application in 2D, a novel gradient amplitude adaption scheme was implemented to correct for the occurring time shifts. Using this adaption, higher conformity to the expected pore shape, reduced blurring and enhanced contrast were achieved. Images of the phantom's pore shape could be acquired with a nominal resolution of 2.2 μm.

Temporal self-splitting of optical pulses

NASA Astrophysics Data System (ADS)

Ding, Chaoliang; Koivurova, Matias; Turunen, Jari; Pan, Liuzhan

2018-05-01

We present mathematical models for temporally and spectrally partially coherent pulse trains with Laguerre-Gaussian and Hermite-Gaussian Schell-model statistics as extensions of the standard Gaussian Schell model for pulse trains. We derive propagation formulas of both classes of pulsed fields in linearly dispersive media and in temporal optical systems. It is found that, in general, both types of fields exhibit time-domain self-splitting upon propagation. The Laguerre-Gaussian model leads to multiply peaked pulses, while the Hermite-Gaussian model leads to doubly peaked pulses, in the temporal far field (in dispersive media) or at the Fourier plane of a temporal system. In both model fields the character of the self-splitting phenomenon depends both on the degree of temporal and spectral coherence and on the power spectrum of the field.

Dynamics of focused femtosecond laser pulse during photodisruption of crystalline lens

NASA Astrophysics Data System (ADS)

Gupta, Pradeep Kumar; Singh, Ram Kishor; Sharma, R. P.

2018-04-01

Propagation of laser pulses of femtosecond time duration (focused through a focusing lens inside the crystalline lens) has been investigated in this paper. Transverse beam diffraction, group velocity dispersion, graded refractive index structure of the crystalline lens, self-focusing, and photodisruption in which plasma is formed due to the high intensity of laser pulses through multiphoton ionization have been taken into account. The model equations are the modified nonlinear Schrödinger equation along with a rate equation that takes care of plasma generation. A close analysis of model equations suggests that the femtosecond laser pulse duration is critical to the breakdown in the lens. Our numerical simulations reveal that the combined effect of self-focusing and multiphoton ionization provides the breakdown threshold. During the focusing of femtosecond laser pulses, additional spatial pulse splitting arises along with temporal splitting. This splitting of laser pulses arises on account of self-focusing, laser induced breakdown, and group velocity distribution, which modifies the shape of laser pulses. The importance of the present study in cavitation bubble generation to improve the elasticity of the eye lens has also been discussed in this paper.

A full time-domain approach to spatio-temporal dynamics of semiconductor lasers. II. Spatio-temporal dynamics

NASA Astrophysics Data System (ADS)

Böhringer, Klaus; Hess, Ortwin

The spatio-temporal dynamics of novel semiconductor lasers is discussed on the basis of a space- and momentum-dependent full time-domain approach. To this means the space-, time-, and momentum-dependent Full-Time Domain Maxwell Semiconductor Bloch equations, derived and discussed in our preceding paper I [K. Böhringer, O. Hess, A full time-domain approach to spatio-temporal dynamics of semiconductor lasers. I. Theoretical formulation], are solved by direct numerical integration. Focussing on the device physics of novel semiconductor lasers that profit, in particular, from recent advances in nanoscience and nanotechnology, we discuss the examples of photonic band edge surface emitting lasers (PBE-SEL) and semiconductor disc lasers (SDLs). It is demonstrated that photonic crystal effects can be obtained for finite crystal structures, and leading to a significant improvement in laser performance such as reduced lasing thresholds. In SDLs, a modern device concept designed to increase the power output of surface-emitters in combination with near-diffraction-limited beam quality, we explore the complex interplay between the intracavity optical fields and the quantum well gain material in SDL structures. Our simulations reveal the dynamical balance between carrier generation due to pumping into high energy states, momentum relaxation of carriers, and stimulated recombination from states near the band edge. Our full time-domain approach is shown to also be an excellent framework for the modelling of the interaction of high-intensity femtosecond and picosecond pulses with semiconductor nanostructures. It is demonstrated that group velocity dispersion, dynamical gain saturation and fast self-phase modulation (SPM) are the main causes for the induced changes and asymmetries in the amplified pulse shape and spectrum of an ultrashort high-intensity pulse. We attest that the time constants of the intraband scattering processes are critical to gain recovery. Moreover, we present new insight into the physics of nonlinear coherent pulse propagation phenomena in active (semiconductor) gain media. Our numerical full time-domain simulations are shown to generally agree well with analytical predictions, while in the case of optical pulses with large pulse areas or few-cycle pulses they reveal the limits of analytic approaches. Finally, it is demonstrated that coherent ultrafast nonlinear propagation effects become less distinctive if we apply a realistic model of the quantum well semiconductor gain material, consider characteristic loss channels and take into account de-phasing processes and homogeneous broadening.

Pulse shaping with transmission lines

DOEpatents

Wilcox, Russell B.

1987-01-01

A method and apparatus for forming shaped voltage pulses uses passive reflection from a transmission line with nonuniform impedance. The impedance of the reflecting line varies with length in accordance with the desired pulse shape. A high voltage input pulse is transmitted to the reflecting line. A reflected pulse is produced having the desired shape and is transmitted by pulse removal means to a load. Light activated photoconductive switches made of silicon can be utilized. The pulse shaper can be used to drive a Pockels cell to produce shaped optical pulses.

Pulse shaping with transmission lines

DOEpatents

Wilcox, R.B.

1985-08-15

A method and apparatus for forming shaped voltage pulses uses passive reflection from a transmission line with nonuniform impedance. The impedance of the reflecting line varies with length in accordance with the desired pulse shape. A high voltage input pulse is transmitted to the reflecting line. A reflected pulse is produced having the desired shape and is transmitted by pulse removal means to a load. Light activated photoconductive switches made of silicon can be utilized. The pulse shaper can be used to drive a Pockels cell to produce shaped optical pulses.

Effect of quench on alpha/beta pulse shape discrimination of liquid scintillation cocktails.

PubMed

DeVol, Timothy A; Theisen, Christopher D; DiPrete, David P

2007-05-01

The objectives of this paper are (1) to illustrate that knowledge of the external quench parameter is insufficient to properly setup a pulse shape discriminating liquid scintillation counter (LSC) for quantitative measurement, (2) to illustrate dependence on pulse shape discrimination on the radionuclide (more than just radiation and energy), and (3) to compare the pulse shape discrimination (PSD) of two commercial instruments. The effects various quenching agents, liquid scintillation cocktails, radionuclides, and LSCs have on alpha/beta pulse shape discriminating liquid scintillation counting were quantified. Alpha emitting radionuclides (239)Pu and (241)Am and beta emitter (90)Sr/(90)Y were investigated to quantify the nuclide dependence on alpha/beta pulse shape discrimination. Also, chemical and color quenching agents, nitromethane, nitric acid, and yellow dye impact on alpha/beta pulse shape discrimination using PerkinElmer Optiphase "HiSafe" 2 and 3, and Ultima Gold AB liquid scintillation cocktails were determined. The prepared samples were counted on the PerkinElmer Wallac WinSpectral 1414 alpha/beta pulse shape discriminating LSC. It was found that for the same level of quench, as measured by the external quench parameter, different quench agents influenced the pulse shape discrimination and the pulse shape discrimination parameters differently. The radionuclide also affects alpha/beta pulse shape discrimination. By comparison with the PerkinElmer Tri-carb 3150 TR/AB, the Wallac 1414 exhibited better pulse shape discrimination capability under the same experimental conditions.

Laser fusion pulse shape controller

DOEpatents

Siebert, Larry D.

1977-01-01

An apparatus for controlling the pulse shape, i.e., the pulse duration and intensity pattern, of a pulsed laser system, and which is particularly well adapted for controlling the pellet ignition pulse in a laser-driven fusion reaction system. The apparatus comprises a laser generator for providing an optical control pulse of the shape desired, a pulsed laser triggered by the control pulse, and a plurality of optical Kerr-effect gates serially disposed at the output of the pulsed laser and selectively triggered by the control pulse to pass only a portion of the pulsed laser output generally corresponding in shape to the control pulse.

A low power radiofrequency pulse for simultaneous multislice excitation and refocusing.

PubMed

Eichner, Cornelius; Wald, Lawrence L; Setsompop, Kawin

2014-10-01

Simultaneous multislice (SMS) acquisition enables increased temporal efficiency of MRI. Nonetheless, MultiBand (MB) radiofrequency (RF) pulses used for SMS can cause large energy deposition. Power independent of number of slices (PINS) pulses reduce RF power at cost of reduced bandwidth and increased off-resonance dependency. This work improves PINS design to further reduce energy deposition, off-resonance dependency and peak power. Modifying the shape of MB RF-pulses allows for mixing with PINS excitation, creating a new pulse type with reduced energy deposition and SMS excitation characteristics. Bloch Simulations were used to evaluate excitation and off-resonance behavior of this "MultiPINS" pulse. In this work, MultiPINS was used for whole-brain MB = 3 acquisition of high angular and spatial resolution diffusion MRI at 7 Tesla in 3 min. By using MultiPINS, energy transmission and peak power for SMS imaging can be significantly reduced compared with PINS and MB pulses. For MB = 3 acquisition in this work, MultiPINS reduces energy transmission by up to ∼50% compared with PINS pulses. The energy reduction was traded off to shorten the MultiPINS pulse, yielding higher signal at off-resonances for spin-echo acquisitions. MB and PINS pulses can be combined to enable low energy and peak power SMS acquisition. Copyright © 2014 Wiley Periodicals, Inc.

Spatial and temporal control of thermal waves by using DMDs for interference based crack detection

NASA Astrophysics Data System (ADS)

Thiel, Erik; Kreutzbruck, Marc; Ziegler, Mathias

2016-02-01

Active Thermography is a well-established non-destructive testing method and used to detect cracks, voids or material inhomogeneities. It is based on applying thermal energy to a samples' surface whereas inner defects alter the nonstationary heat flow. Conventional excitation of a sample is hereby done spatially, either planar (e.g. using a lamp) or local (e.g. using a focused laser) and temporally, either pulsed or periodical. In this work we combine a high power laser with a Digital Micromirror Device (DMD) allowing us to merge all degrees of freedom to a spatially and temporally controlled heat source. This enables us to exploit the possibilities of coherent thermal wave shaping. Exciting periodically while controlling at the same time phase and amplitude of the illumination source induces - via absorption at the sample's surface - a defined thermal wave propagation through a sample. That means thermal waves can be controlled almost like acoustical or optical waves. However, in contrast to optical or acoustical waves, thermal waves are highly damped due to the diffusive character of the thermal heat flow and therefore limited in penetration depth in relation to the achievable resolution. Nevertheless, the coherence length of thermal waves can be chosen in the mmrange for modulation frequencies below 10 Hz which is perfectly met by DMD technology. This approach gives us the opportunity to transfer known technologies from wave shaping techniques to thermography methods. We will present experiments on spatial and temporal wave shaping, demonstrating interference based crack detection.

Selective two-photon excitation of a vibronic state by correlated photons.

PubMed

Oka, Hisaki

2011-03-28

We theoretically investigate the two-photon excitation of a molecular vibronic state by correlated photons with energy anticorrelation. A Morse oscillator having three sets of vibronic states is used, as an example, to evaluate the selectivity and efficiency of two-photon excitation. We show that a vibrational mode can be selectively excited with high efficiency by the correlated photons, without phase manipulation or pulse-shaping techniques. This can be achieved by controlling the quantum correlation so that the photon pair concurrently has two pulse widths, namely, a temporally narrow width and a spectrally narrow width. Though this concurrence is seemingly contradictory, we can create such a photon pair by tailoring the quantum correlation between two photons.

Waveform synthesizer

DOEpatents

Franks, L.A.; Nelson, M.A.

1979-12-07

The invention is a method by which an optical pulse of an arbitrary but defined shape may be transformed into a virtual multitude of optical or electrical output pulse shapes. Since the method is not limited to any particular input pulse shape, the output pulse shapes that can be generated thereby are virtually unlimited. Moreover, output pulse widths as narrow as about 0.1 nsec can be readily obtained since optical pulses of less than a few picoseconds are available for use as driving pulses. The range of output pulse widths obtainable is very large, the limiting factors being the driving source energy and the particular shape of the desired output pulse.

Symmetry-controlled time structure of high-harmonic carrier fields from a solid

PubMed Central

Langer, F.; Hohenleutner, M.; Huttner, U.; Koch, S. W.; Kira, M.; Huber, R.

2017-01-01

High-harmonic (HH) generation in crystalline solids1–6 marks an exciting development, with potential applications in high-efficiency attosecond sources7, all-optical bandstructure reconstruction8,9, and quasiparticle collisions10,11. Although the spectral1–4 and temporal shape5 of the HH intensity has been described microscopically1–6,12, the properties of the underlying HH carrier wave have remained elusive. Here we analyse the train of HH waveforms generated in a crystalline solid by consecutive half cycles of the same driving pulse. Extending the concept of frequency combs13–15 to optical clock rates, we show how the polarization and carrier-envelope phase (CEP) of HH pulses can be controlled by crystal symmetry. For some crystal directions, we can separate two orthogonally polarized HH combs mutually offset by the driving frequency to form a comb of even and odd harmonic orders. The corresponding CEP of successive pulses is constant or offset by π, depending on the polarization. In the context of a quantum description of solids, we identify novel capabilities for polarization- and phase-shaping of HH waveforms that cannot be accessed with gaseous sources. PMID:28572835

Single-shot spectro-temporal characterization of XUV pulses from a seeded free-electron laser

PubMed Central

De Ninno, Giovanni; Gauthier, David; Mahieu, Benoît; Ribič, Primož Rebernik; Allaria, Enrico; Cinquegrana, Paolo; Danailov, Miltcho Bojanov; Demidovich, Alexander; Ferrari, Eugenio; Giannessi, Luca; Penco, Giuseppe; Sigalotti, Paolo; Stupar, Matija

2015-01-01

Intense ultrashort X-ray pulses produced by modern free-electron lasers (FELs) allow one to probe biological systems, inorganic materials and molecular reaction dynamics with nanoscale spatial and femtoscale temporal resolution. These experiments require the knowledge, and possibly the control, of the spectro-temporal content of individual pulses. FELs relying on seeding have the potential to produce spatially and temporally fully coherent pulses. Here we propose and implement an interferometric method, which allows us to carry out the first complete single-shot spectro-temporal characterization of the pulses, generated by an FEL in the extreme ultraviolet spectral range. Moreover, we provide the first direct evidence of the temporal coherence of a seeded FEL working in the extreme ultraviolet spectral range and show the way to control the light generation process to produce Fourier-limited pulses. Experiments are carried out at the FERMI FEL in Trieste. PMID:26290320

Streak camera based SLR receiver for two color atmospheric measurements

NASA Technical Reports Server (NTRS)

Varghese, Thomas K.; Clarke, Christopher; Oldham, Thomas; Selden, Michael

1993-01-01

To realize accurate two-color differential measurements, an image digitizing system with variable spatial resolution was designed, built, and integrated to a photon-counting picosecond streak camera, yielding a temporal scan resolution better than 300 femtosecond/pixel. The streak camera is configured to operate with 3 spatial channels; two of these support green (532 nm) and uv (355 nm) while the third accommodates reference pulses (764 nm) for real-time calibration. Critical parameters affecting differential timing accuracy such as pulse width and shape, number of received photons, streak camera/imaging system nonlinearities, dynamic range, and noise characteristics were investigated to optimize the system for accurate differential delay measurements. The streak camera output image consists of three image fields, each field is 1024 pixels along the time axis and 16 pixels across the spatial axis. Each of the image fields may be independently positioned across the spatial axis. Two of the image fields are used for the two wavelengths used in the experiment; the third window measures the temporal separation of a pair of diode laser pulses which verify the streak camera sweep speed for each data frame. The sum of the 16 pixel intensities across each of the 1024 temporal positions for the three data windows is used to extract the three waveforms. The waveform data is processed using an iterative three-point running average filter (10 to 30 iterations are used) to remove high-frequency structure. The pulse pair separations are determined using the half-max and centroid type analysis. Rigorous experimental verification has demonstrated that this simplified process provides the best measurement accuracy. To calibrate the receiver system sweep, two laser pulses with precisely known temporal separation are scanned along the full length of the sweep axis. The experimental measurements are then modeled using polynomial regression to obtain a best fit to the data. Data aggregation using normal point approach has provided accurate data fitting techniques and is found to be much more convenient than using the full rate single shot data. The systematic errors from this model have been found to be less than 3 ps for normal points.

Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for gas-phase temperature measurements

NASA Astrophysics Data System (ADS)

Miller, Joseph Daniel

Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) is employed for quantitative gas-phase temperature measurements in combustion processes and heated flows. In this approach, ultrafast 100-fs laser pulses are used to induce vibrational and rotational transitions in N2 and O2, while a third spectrally narrowed picosecond pulse is used to probe the molecular response. Temporal suppression of the nonresonant contribution and elimination of collisional effects are achieved by delay of the probe pulse, while sufficient spectral resolution is maintained for frequency-domain detection and thermometry. A theoretical framework is developed to model experimental spectra by phenomenologically describing the temporal evolution of the vibrational and rotational wavepackets as a function of temperature and pressure. Interference-free, single-shot vibrational fs/ps CARS thermometry is demonstrated at 1-kHz from 1400-2400 K in a H2-air flame, with accuracy better than 3%. A time-asymmetric exponential pulse shape is introduced to optimize nonresonant suppression with a 103 reduction at a probe delay of 0.31 ps. Low-temperature single-shot thermometry (300-700 K) with better than 1.5% accuracy is demonstrated using a fully degenerate rotational fs/ps CARS scheme, and the influence of collision energy transfer on thermometry error is quantified at atmospheric pressure. Interference-free thermometry, without nonresonant contributions and collision-induced error, is demonstrated for the first time using rotational fs/ps CARS at room temperature and pressures from 1-15 atm. Finally, the temporal and spectral resolution of fs/ps CARS is exploited for transition-resolved time-domain measurements of N2 and O2 self-broadened S-branch Raman linewidths at pressures of 1-20 atm.

Single-shot pulse duration and intensity diagnostic for 10-ps MeV gamma pulses based on interferometry

NASA Astrophysics Data System (ADS)

Peng, Bo-dong; Hei, Dong-wei; Song, Yan; Liu, Jun; Zhao, Jun

2018-04-01

To measure the temporal width and the intensity evolution versus time of a MeV gamma pulse generated by a Compton Scatter Source, a time-space conversion method is proposed. This design is based on the consideration that the temporal length of the MeV pulse is proportional to the spatial length of the pulse in a certain semiconductor. The spatial length and the intensity evolution versus time of the MeV pulse can be obtained by recording the region of the refractive index change that is induced by the MeV pulse. The simulation suggests that the equivalent temporal spread of a mono-energy MeV δ pulse in a bulk semiconductor is on the order of picoseconds and does not vary significantly with photon energy and material type. According to our analysis, the excess carrier generation time, excess carrier diffusion and recombination do not significantly influence the temporal resolution of this method. The temporal response of the refractive index change to a MeV pulse is also fast enough to meet the measurement requirements. The signal generation process for measuring a 10-ps MeV pulse with a 200-fs probe beam is analyzed, revealing that the transverse size of the MeV pulse does not influence the temporal resolution of this method.

Information entropy method and the description of echo hologram formation in gaseous media

NASA Astrophysics Data System (ADS)

Garnaeva, G. I.; Nefediev, L. A.; Akhmedshina, E. N.

2018-02-01

The effect of collisions with a change in velocity of gas particles, on the value of information entropy, is associated with the spectral structure of the echo hologram’s response, where its temporal form is considered. It is shown that collisions with a change in gas particle velocity increase the ‘parasitical’ information, on the background of which the information contained in the temporary shape of the object laser pulse is lost.

Narrow linewidth picosecond UV pulsed laser with mega-watt peak power.

PubMed

Huang, Chunning; Deibele, Craig; Liu, Yun

2013-04-08

We demonstrate a master oscillator power amplifier (MOPA) burst mode laser system that generates 66 ps/402.5 MHz pulses with mega-watt peak power at 355 nm. The seed laser consists of a single frequency fiber laser (linewidth < 5 KHz), a high bandwidth electro-optic modulator (EOM), a picosecond pulse generator, and a fiber based preamplifier. A very high extinction ratio (45 dB) has been achieved by using an adaptive bias control of the EOM. The multi-stage Nd:YAG amplifier system allows a uniformly temporal shaping of the macropulse with a tunable pulse duration. The light output from the amplifier is converted to 355 nm, and over 1 MW peak power is obtained when the laser is operating in a 5-μs/10-Hz macropulse mode. The laser output has a transform-limited spectrum with a very narrow linewidth of individual longitudinal modes. The immediate application of the laser system is the laser-assisted hydrogen ion beam stripping for the Spallation Neutron Source (SNS).

Temporal and frequency characteristics of a narrow light beam in sea water.

PubMed

Luchinin, Alexander G; Kirillin, Mikhail Yu

2016-09-20

The structure of a light field in sea water excited by a unidirectional point-sized pulsed source is studied by Monte Carlo technique. The pulse shape registered at the distances up to 120 m from the source on the beam axis and in its axial region is calculated with a time resolution of 1 ps. It is shown that with the increase of the distance from the source the pulse splits into two parts formed by components of various scattering orders. Frequency and phase responses of the beam are calculated by means of the fast Fourier transform. It is also shown that for higher frequencies, the attenuation of harmonic components of the field is larger. In the range of parameters corresponding to pulse splitting on the beam axis, the attenuation of harmonic components in particular spectral ranges exceeds the attenuation predicted by Bouguer law. In this case, the transverse distribution of the amplitudes of these harmonics is minimal on the beam axis.

Thickness determination of polymeric multilayer surface protection systems for concrete by means of pulse thermography

NASA Astrophysics Data System (ADS)

Altenburg, S. J.; Krankenhagen, R.; Bavendiek, F.

2017-02-01

For thickness determination of polymer based surface protection systems for concrete surfaces, so far only destructive measurement techniques are available. Pulse thermography appears to be well suited for non-destructive thickness evaluation in these systems. Here, we present first results of the development of a respective measurement and analysis procedure. Since surface protection systems consist of a number of layers, a model for the calculation of the surface temperature of a multi-layer structure on a semi-infinite (concrete) substrate in pulse thermography setup was developed. It considers semitransparency of the upmost layer and thermal losses at the surface. It also supports the use of an arbitrary temporal shape of the heating pulse to properly describe the measurement conditions for different heat sources. Simulations for one and three layers on the substrate are presented and first results from fitting the model to experimental data for thickness determination and verification of the model are presented.

A spatio-temporal index for aerial full waveform laser scanning data

NASA Astrophysics Data System (ADS)

Laefer, Debra F.; Vo, Anh-Vu; Bertolotto, Michela

2018-04-01

Aerial laser scanning is increasingly available in the full waveform version of the raw signal, which can provide greater insight into and control over the data and, thus, richer information about the scanned scenes. However, when compared to conventional discrete point storage, preserving raw waveforms leads to vastly larger and more complex data volumes. To begin addressing these challenges, this paper introduces a novel bi-level approach for storing and indexing full waveform (FWF) laser scanning data in a relational database environment, while considering both the spatial and the temporal dimensions of that data. In the storage scheme's upper level, the full waveform datasets are partitioned into spatial and temporal coherent groups that are indexed by a two-dimensional R∗-tree. To further accelerate intra-block data retrieval, at the lower level a three-dimensional local octree is created for each pulse block. The local octrees are implemented in-memory and can be efficiently written to a database for reuse. The indexing solution enables scalable and efficient three-dimensional (3D) spatial and spatio-temporal queries on the actual pulse data - functionalities not available in other systems. The proposed FWF laser scanning data solution is capable of managing multiple FWF datasets derived from large flight missions. The flight structure is embedded into the data storage model and can be used for querying predicates. Such functionality is important to FWF data exploration since aircraft locations and orientations are frequently required for FWF data analyses. Empirical tests on real datasets of up to 1 billion pulses from Dublin, Ireland prove the almost perfect scalability of the system. The use of the local 3D octree in the indexing structure accelerated pulse clipping by 1.2-3.5 times for non-axis-aligned (NAA) polyhedron shaped clipping windows, while axis-aligned (AA) polyhedron clipping was better served using only the top indexing layer. The distinct behaviours of the hybrid indexing for AA and NAA clipping windows are attributable to the different proportion of the local-index-related overheads with respect to the total querying costs. When temporal constraints were added, generally the number of costly spatial checks were reduced, thereby shortening the querying times.

Ballistic Deficits for Ionization Chamber Pulses in Pulse Shaping Amplifiers

NASA Astrophysics Data System (ADS)

Kumar, G. Anil; Sharma, S. L.; Choudhury, R. K.

2007-04-01

In order to understand the dependence of the ballistic deficit on the shape of rising portion of the voltage pulse at the input of a pulse shaping amplifier, we have estimated the ballistic deficits for the pulses from a two-electrode parallel plate ionization chamber as well as for the pulses from a gridded parallel plate ionization chamber. These estimations have been made using numerical integration method when the pulses are processed through the CR-RCn (n=1-6) shaping network as well as when the pulses are processed through the complex shaping network of the ORTEC Model 472 spectroscopic amplifier. Further, we have made simulations to see the effect of ballistic deficit on the pulse-height spectra under different conditions. We have also carried out measurements of the ballistic deficits for the pulses from a two-electrode parallel plate ionization chamber as well as for the pulses from a gridded parallel plate ionization chamber when these pulses are processed through the ORTEC 572 linear amplifier having a simple CR-RC shaping network. The reasonable matching of the simulated ballistic deficits with the experimental ballistic deficits for the CR-RC shaping network clearly establishes the validity of the simulation technique

Electrothermal Action of the Pulse of the Current of a Short Artificial-Lightning Stroke on Test Specimens of Wires and Cables of Electric Power Objects

NASA Astrophysics Data System (ADS)

Baranov, M. I.; Rudakov, S. V.

2018-03-01

The authors have given results of investigations of the electrothermal action of aperiodic pulses of temporal shape 10/350 μs of the current of a short artificial-lightning stroke on test specimens of electric wires and cables with copper and aluminum cores and sheaths with polyvinylchloride and polyethylene insulations of power circuits of industrial electric power objects. It has been shown that the thermal stability of such wires and cables is determined by the action integral of the indicated current pulse. The authors have found the maximum permissible and critical densities of this pulse in copper and aluminum current-carrying parts of the wires and cables. High-current experiments conducted under high-voltage laboratory conditions on a unique generator of 10/350 μs pulses of an artificial-lightning current with amplitude-time parameters normalized according to the existing requirements of international and national standards and with tolerances on them have confirmed the reliability of the proposed calculated estimate for thermal lightning resistance of cabling and wiring products.

Electrothermal Action of the Pulse of the Current of a Short Artificial-Lightning Stroke on Test Specimens of Wires and Cables of Electric Power Objects

NASA Astrophysics Data System (ADS)

Baranov, M. I.; Rudakov, S. V.

2018-05-01

The authors have given results of investigations of the electrothermal action of aperiodic pulses of temporal shape 10/350 μs of the current of a short artificial-lightning stroke on test specimens of electric wires and cables with copper and aluminum cores and sheaths with polyvinylchloride and polyethylene insulations of power circuits of industrial electric power objects. It has been shown that the thermal stability of such wires and cables is determined by the action integral of the indicated current pulse. The authors have found the maximum permissible and critical densities of this pulse in copper and aluminum current-carrying parts of the wires and cables. High-current experiments conducted under high-voltage laboratory conditions on a unique generator of 10/350 μs pulses of an artificial-lightning current with amplitude-time parameters normalized according to the existing requirements of international and national standards and with tolerances on them have confirmed the reliability of the proposed calculated estimate for thermal lightning resistance of cabling and wiring products.

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

Robey, H. F.; MacGowan, B. J.; Landen, O. L.

Indirectly driven capsule implosions on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] are being performed with the goal of compressing a layer of cryogenic deuterium-tritium (DT) fuel to a sufficiently high areal density (ρR) to sustain the self-propagating burn wave that is required for fusion power gain greater than unity. These implosions are driven with a temporally shaped laser pulse that is carefully tailored to keep the DT fuel on a low adiabat (ratio of fuel pressure to the Fermi degenerate pressure). In this report, the impact of variations in the laser pulse shapemore » (both intentionally and unintentionally imposed) on the in-flight implosion adiabat is examined by comparing the measured shot-to-shot variations in ρR from a large ensemble of DT-layered ignition target implosions on NIF spanning a two-year period. A strong sensitivity to variations in the early-time, low-power foot of the laser pulse is observed. It is shown that very small deviations (∼0.1% of the total pulse energy) in the first 2 ns of the laser pulse can decrease the measured ρR by 50%.« less

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

DOE PAGES

Cao, D.; Boehly, T. R.; Gregor, M. C.; ...

2018-05-16

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the VISAR diagnostic on OMEGA. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (α ~ 3) implosions, but agreement degrades for lower-adiabat (α ~ 1) designs. Several possibilities for this difference are studied: errors in placing the target at the center of irradiation (target offset),more » variations in energy between the different incident beams (power imbalance), and errors in modeling the laser energy coupled into the capsule. Simulation results indicate that shock timing is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to target offset and beam power imbalance. A new technique under development to infer coronal profiles using x-ray self-emission imaging can be applied to the pulse shapes used in shock-timing experiments. In conclusion, this will help identify improved physics models to implement in codes and consequently enhance shock-timing predictive capability for low-adiabat pulses.« less

Optimizing coherent anti-Stokes Raman scattering by genetic algorithm controlled pulse shaping

NASA Astrophysics Data System (ADS)

Yang, Wenlong; Sokolov, Alexei

2010-10-01

The hybrid coherent anti-Stokes Raman scattering (CARS) has been successful applied to fast chemical sensitive detections. As the development of femto-second pulse shaping techniques, it is of great interest to find the optimum pulse shapes for CARS. The optimum pulse shapes should minimize the non-resonant four wave mixing (NRFWM) background and maximize the CARS signal. A genetic algorithm (GA) is developed to make a heuristic searching for optimized pulse shapes, which give the best signal the background ratio. The GA is shown to be able to rediscover the hybrid CARS scheme and find optimized pulse shapes for customized applications by itself.

Plasma ignition for laser propulsion

NASA Technical Reports Server (NTRS)

Askew, R. F.

1982-01-01

For a specific optical system a pulsed carbon dioxide laser having an energy output of up to 15 joules was used to initiate a plasma in air at one atmosphere pressure. The spatial and temporal development of the plasma were measured using a multiframe image converter camera. In addition the time dependent velocity of the laser supported plasma front which moves opposite to the direction of the laser pulse was measured in order to characterize the type of wavefront developed. Reliable and reproducible spark initiation was achieved. The lifetime of the highly dense plasma at the initial focal spot was determined to be less than 100 nanoseconds. The plasma front propagates toward the laser at a variable speed ranging from zero to 1.6 x 1,000,000 m/sec. The plasma front propagates for a total distance of approximately five centimeters for the energy and laser pulse shape employed.

Nearly fully compressed 1053 nm pulses directly obtained from 800 nm laser-seeded photonic crystal fiber below zero dispersion point

NASA Astrophysics Data System (ADS)

Refaeli, Zaharit; Shamir, Yariv; Ofir, Atara; Marcus, Gilad

2018-02-01

We report a simple robust and broadly spectral-adjustable source generating near fully compressed 1053 nm 62 fs pulses directly out of a highly-nonlinear photonic crystal fiber. A dispersion-nonlinearity balance of 800 nm Ti:Sa 20 fs pulses was obtained initially by negative pre-chirping and then launching the pulses into the fibers' normal dispersion regime. Following a self-phase modulation spectral broadening, some energy that leaked below the zero dispersion point formed a soliton whose central wavelength could be tuned by Self-Frequency-Raman-Shift effect. Contrary to a common approach of power, or, fiber-length control over the shift, here we continuously varied the state of polarization, exploiting the Raman and Kerr nonlinearities responsivity for state of polarization. We obtained soliton pulses with central wavelength tuned over 150 nm, spanning from well below 1000 to over 1150 nm, of which we could select stable pulses around the 1 μm vicinity. With linewidth of > 20 nm FWHM Gaussian-like temporal-shape pulses with 62 fs duration and near flat phase structure we confirmed high quality pulse source. We believe such scheme can be used for high energy or high power glass lasers systems, such as Nd or Yb ion-doped amplifiers and systems.

Comparison of implosion core metrics: A 10 ps dilation X-ray imager vs a 100 ps gated microchannel plate [Comparison of implosion core shape observations, 10 ps dilation X-ray imager vs 100 ps gated microchannel plate

DOE PAGES

Nagel, S. R.; Benedetti, L. R.; Bradley, D. K.; ...

2016-08-05

The dilation x-ray imager (DIXI) is a high-speed x-ray framing camera that uses the pulse-dilation technique to achieve a temporal resolution of less than 10 ps. This is a 10× improvement over conventional framing cameras currently employed on the National Ignition Facility (NIF) (100 ps resolution), and otherwise only achievable with 1D streaked imaging. A side effect of the dramatically reduced gate width is the comparatively lower detected signal level. Therefore we implement a Poisson noise reduction with non-local principal component analysis method to improve the robustness of the DIXI data analysis. Furthermore, we present results on ignition-relevant experiments atmore » the NIF using DIXI. In particular we focus on establishing that/when DIXI gives reliable shape metrics (P 0, P 2 and P 4 Legendre modes, and their temporal evolution/swings).« less

Comparison of implosion core metrics: A 10 ps dilation X-ray imager vs a 100 ps gated microchannel plate [Comparison of implosion core shape observations, 10 ps dilation X-ray imager vs 100 ps gated microchannel plate

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

Nagel, S. R.; Benedetti, L. R.; Bradley, D. K.

The dilation x-ray imager (DIXI) is a high-speed x-ray framing camera that uses the pulse-dilation technique to achieve a temporal resolution of less than 10 ps. This is a 10× improvement over conventional framing cameras currently employed on the National Ignition Facility (NIF) (100 ps resolution), and otherwise only achievable with 1D streaked imaging. A side effect of the dramatically reduced gate width is the comparatively lower detected signal level. Therefore we implement a Poisson noise reduction with non-local principal component analysis method to improve the robustness of the DIXI data analysis. Furthermore, we present results on ignition-relevant experiments atmore » the NIF using DIXI. In particular we focus on establishing that/when DIXI gives reliable shape metrics (P 0, P 2 and P 4 Legendre modes, and their temporal evolution/swings).« less

Spatial and temporal pulse propagation for dispersive paraxial optical systems.

PubMed

Marcus, G

2016-04-04

The formalism for pulse propagation through dispersive paraxial optical systems first presented by Kostenbauder (IEEE J. Quant. Elec.261148-1157 (1990)) using 4 × 4 ray-pulse matrices is extended to 6 × 6 matrices and includes non-separable spatial-temporal couplings in both transverse dimensions as well as temporal dispersive effects up to a quadratic phase. The eikonal in a modified Huygens integral in the Fresnell approximation is derived and can be used to propagate pulses through complicated dispersive optical systems within the paraxial approximation. In addition, a simple formula for the propagation of ultrashort pulses having a Gaussian profile both spatially and temporally is presented.

Ultra-narrow band diode lasers with arbitrary pulse shape modulation (Conference Presentation)

NASA Astrophysics Data System (ADS)

Ryasnyanskiy, Aleksandr I.; Smirnov, Vadim; Mokhun, Oleksiy; Glebov, Alexei L.; Glebov, Leon B.

2017-03-01

Wideband emission spectra of laser diode bars (several nanometers) can be largely narrowed by the usage of thick volume Bragg gratings (VBGs) recorded in photo-thermo-refractive glass. Such narrowband systems, with GHz-wide emission spectra, found broad applications for Diode Pumped Alkali vapor Lasers, optically pumped rare gas metastable lasers, Spin Exchange Optical Pumping, atom cooling, etc. Although the majority of current applications of narrow line diode lasers require CW operation, there are a variety of fields where operation in a different pulse mode regime is necessary. Commercial electric pulse generators can provide arbitrary current pulse profiles (sinusoidal, rectangular, triangular and their combinations). The pulse duration and repetition rate however, have an influence on the laser diode temperature, and therefore, the emitting wavelength. Thus, a detailed analysis is needed to understand the correspondence between the optical pulse profiles from a diode laser and the current pulse profiles; how the pulse profile and duty cycle affects the laser performance (e.g. the wavelength stability, signal to noise ratio, power stability etc.). We present the results of detailed studies of the narrowband laser diode performance operating in different temporal regimes with arbitrary pulse profiles. The developed narrowband (16 pm) tunable laser systems at 795 nm are capable of operating in different pulse regimes while keeping the linewidth, wavelength, and signal-to-noise ratio (>20 dB) similar to the corresponding CW modules.

ON THE LACK OF TIME DILATION SIGNATURES IN GAMMA-RAY BURST LIGHT CURVES

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

Kocevski, Daniel; Petrosian, Vahe

2013-03-10

We examine the effects of time dilation on the temporal profiles of gamma-ray burst (GRB) pulses. By using prescriptions for the shape and evolution of prompt gamma-ray spectra, we can generate a simulated population of single-pulsed GRBs at a variety of redshifts and observe how their light curves would appear to a gamma-ray detector here on Earth. We find that the observer frame duration of individual pulses does not increase with redshift as 1 + z, which one would expect from cosmological expansion. This time dilation is masked by an opposite and often stronger effect: with increasing redshift and decreasingmore » signal-to-noise ratio only the brightest portion of the light curve can be detected. The results of our simulation are consistent with the fact that the simple time dilation of GRB light curves has not materialized in either the Swift or Fermi detected GRBs with known redshift. We show that the measured durations and associated E{sub iso} estimates for GRBs detected near the instrument's detection threshold should be considered lower limits to the true values. Furthermore, we conclude that attempts at distinguishing between long and short GRBs, at even moderate redshifts, cannot be done based on a burst's temporal properties alone.« less

Acousto-Optic Spectrum Analyzer: Temporal Response and Detection of Pulsed Signals.

DTIC Science & Technology

1986-12-01

ACOUSTO - OPTIC SPECTRUM ANALYZER: TEMPORAL RESPONSE AND I/i DETECTION OF PULSED SIGUALS(U) DEFENCE RESEARCH ESTABLISHMENT OTTANA (ONTARIO) J...8217:. -.....:.-...............--.. - ---:-..--.-..,. ,: i’,.. IJT~c FILE C P National Defe’ se + Deence nationale 0 0 ACOUSTO - OPTIC SPECTRUM ANALYZER: TEMPORAL RESPONSE AND DETECTION 0 OF PULSED...Ottawa |S, .±~ |-----------------------..,---.-- -- - - - rNatiorna! Defen~se Deterice r dornale ACOUSTO - OPTIC SPECTRUM ANALYZER: TEMPORAL RESPONSE

Optical Arbitrary Waveform Generators Based on Temporal and Spectral Shaping of Optical Pulses in Nonlinear Metamaterials

DTIC Science & Technology

2011-06-01

of a flat-top (thin lines) and a kink (thick lines) soliton . Here = 0.25,Q = 1.786 553 604 650 208 for the dark soliton (Q = 1.786 553 7 for the flat...localization and transport in different physical settings, ranging from metal-dielectric (i.e. plasmonic) to photonic crystal waveguides. The solitons ...settings, ranging from metal--dielectric (i.e. plasmonic) to photonic crystal waveguides. The solitons exist for focusing, defocusing and even for

Investigation of FPGA-Based Real-Time Adaptive Digital Pulse Shaping for High-Count-Rate Applications

NASA Astrophysics Data System (ADS)

Saxena, Shefali; Hawari, Ayman I.

2017-07-01

Digital signal processing techniques have been widely used in radiation spectrometry to provide improved stability and performance with compact physical size over the traditional analog signal processing. In this paper, field-programmable gate array (FPGA)-based adaptive digital pulse shaping techniques are investigated for real-time signal processing. National Instruments (NI) NI 5761 14-bit, 250-MS/s adaptor module is used for digitizing high-purity germanium (HPGe) detector's preamplifier pulses. Digital pulse processing algorithms are implemented on the NI PXIe-7975R reconfigurable FPGA (Kintex-7) using the LabVIEW FPGA module. Based on the time separation between successive input pulses, the adaptive shaping algorithm selects the optimum shaping parameters (rise time and flattop time of trapezoid-shaping filter) for each incoming signal. A digital Sallen-Key low-pass filter is implemented to enhance signal-to-noise ratio and reduce baseline drifting in trapezoid shaping. A recursive trapezoid-shaping filter algorithm is employed for pole-zero compensation of exponentially decayed (with two-decay constants) preamplifier pulses of an HPGe detector. It allows extraction of pulse height information at the beginning of each pulse, thereby reducing the pulse pileup and increasing throughput. The algorithms for RC-CR2 timing filter, baseline restoration, pile-up rejection, and pulse height determination are digitally implemented for radiation spectroscopy. Traditionally, at high-count-rate conditions, a shorter shaping time is preferred to achieve high throughput, which deteriorates energy resolution. In this paper, experimental results are presented for varying count-rate and pulse shaping conditions. Using adaptive shaping, increased throughput is accepted while preserving the energy resolution observed using the longer shaping times.

Effects of temporal laser profile on the emission spectra for underwater laser-induced breakdown spectroscopy: Study by short-interval double pulses with different pulse durations

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

Tamura, Ayaka, E-mail: tamura.ayaka.88m@st.kyoto-u.ac.jp; Matsumoto, Ayumu; Nishi, Naoya

We investigate the effects of temporal laser profile on the emission spectra of laser ablation plasma in water. We use short-interval (76 ns) double pulses with different pulse durations of the composing two pulses for the irradiation of underwater target. Narrow atomic spectral lines in emission spectra are obtained by the irradiation, where the two pulses are wide enough to be merged into a single-pulse-like temporal profile, while deformed spectra are obtained when the two pulses are fully separated. The behavior of the atomic spectral lines for the different pulse durations is consistent with that of the temporal profiles of themore » optical emission intensities of the plasma. All these results suggest that continuous excitation of the plasma during the laser irradiation for ∼100 ns is a key to obtain narrow emission spectral lines.« less

Community temporal variability increases with fluctuating resource availability

PubMed Central

Li, Wei; Stevens, M. Henry H.

2017-01-01

An increase in the quantity of available resources is known to affect temporal variability of aggregate community properties. However, it is unclear how might fluctuations in resource availability alter community-level temporal variability. Here we conduct a microcosm experiment with laboratory protist community subjected to manipulated resource pulses that vary in intensity, duration and time of supply, and examine the impact of fluctuating resource availability on temporal variability of the recipient community. The results showed that the temporal variation of total protist abundance increased with the magnitude of resource pulses, as protist community receiving infrequent resource pulses (i.e., high-magnitude nutrients per pulse) was relatively more unstable than community receiving multiple resource pulses (i.e., low-magnitude nutrients per pulse), although the same total amounts of nutrients were added to each community. Meanwhile, the timing effect of fluctuating resources did not significantly alter community temporal variability. Further analysis showed that fluctuating resource availability increased community temporal variability by increasing the degree of community-wide species synchrony and decreasing the stabilizing effects of dominant species. Hence, the importance of fluctuating resource availability in influencing community stability and the regulatory mechanisms merit more attention, especially when global ecosystems are experiencing high rates of anthropogenic nutrient inputs. PMID:28345592

Community temporal variability increases with fluctuating resource availability

NASA Astrophysics Data System (ADS)

Li, Wei; Stevens, M. Henry H.

2017-03-01

An increase in the quantity of available resources is known to affect temporal variability of aggregate community properties. However, it is unclear how might fluctuations in resource availability alter community-level temporal variability. Here we conduct a microcosm experiment with laboratory protist community subjected to manipulated resource pulses that vary in intensity, duration and time of supply, and examine the impact of fluctuating resource availability on temporal variability of the recipient community. The results showed that the temporal variation of total protist abundance increased with the magnitude of resource pulses, as protist community receiving infrequent resource pulses (i.e., high-magnitude nutrients per pulse) was relatively more unstable than community receiving multiple resource pulses (i.e., low-magnitude nutrients per pulse), although the same total amounts of nutrients were added to each community. Meanwhile, the timing effect of fluctuating resources did not significantly alter community temporal variability. Further analysis showed that fluctuating resource availability increased community temporal variability by increasing the degree of community-wide species synchrony and decreasing the stabilizing effects of dominant species. Hence, the importance of fluctuating resource availability in influencing community stability and the regulatory mechanisms merit more attention, especially when global ecosystems are experiencing high rates of anthropogenic nutrient inputs.

Invited Review Article: Pump-probe microscopy.

PubMed

Fischer, Martin C; Wilson, Jesse W; Robles, Francisco E; Warren, Warren S

2016-03-01

Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.

Generation of broadband laser by high-frequency bulk phase modulator with multipass configuration.

PubMed

Zhang, Peng; Jiang, Youen; Zhou, Shenlei; Fan, Wei; Li, Xuechun

2014-12-10

A new technique is presented for obtaining a large broadband nanosecond-laser pulse. This technique is based on multipass phase modulation of a single-frequency nanosecond-laser pulse from the integrated front-end source, and it is able to shape the temporal profile of the pulse arbitrarily, making this approach attractive for high-energy-density physical experiments in current laser fusion facilities. Two kinds of cavity configuration for multipass modulation are proposed, and the performances of both of them are discussed theoretically in detail for the first time to our knowledge. Simulation results show that the bandwidth of the generated laser pulse by this approach can achieve more than 100 nm in principle if adjustment accuracy of the time interval between contiguous passes is controlled within 0.1% of a microwave period. In our preliminary experiment, a 2 ns laser pulse with 1.35-nm bandwidth in 1053 nm is produced via this technique, which agrees well with the theoretical result. Owing to an all-solid-state structure, the energy of the pulse achieves 25 μJ. In the future, with energy compensation and spectrum filtering, this technique is expected to generate a nanosecond-laser pulse of 3 nm or above bandwidth with energy of about 100 μJ.

Invited Review Article: Pump-probe microscopy

PubMed Central

Wilson, Jesse W.; Robles, Francisco E.; Warren, Warren S.

2016-01-01

Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications. PMID:27036751

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

NASA Astrophysics Data System (ADS)

Cao, D.; Boehly, T. R.; Gregor, M. C.; Polsin, D. N.; Davis, A. K.; Radha, P. B.; Regan, S. P.; Goncharov, V. N.

2018-05-01

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the velocity interferometry system for any reflector diagnostic [T. R. Boehly et al., Phys. Plasmas 18, 092706 (2011)] on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (α ˜ 3) implosions, but agreement degrades for lower-adiabat (α ˜ 1) designs. Simulation results indicate that the shock timing discrepancy is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to the target offset and beam power imbalance. To aid in verifying the coronal profile's influence, a new technique under development to infer coronal profiles using x-ray self-emission imaging [A. K. Davis et al., Bull. Am. Phys. Soc. 61, BAPS.2016.DPP.NO8.7 (2016)] can be applied to the pulse shapes used in shock-timing experiments.

High contrast research in the Nd:glass laser system based on optical parametric amplification temporal cleaning device

NASA Astrophysics Data System (ADS)

Lu, Xiaoming; Leng, Yuxin; Sui, Zhan; Li, Yanyan; Zhang, Zongxin; Xu, Yi; Guo, Xiaoyang; Liu, Yanqi; Li, Ruxin; Xu, Zhizhan

2014-02-01

We demonstrate high amplified spontaneous emission (ASE) contrast pulses in a Nd:glass laser system based on the hybrid double chirped pulse amplification (double CPA) scheme. By an OPA temporal cleaning device, ~100 uJ/46 fs/ 1011 clean pulses are generated and amplified in the next Nd:glass laser. After compressor, >150 mJ/~0.5 ps/1 Hz pulses can be obtained. The ASE temporal contrast of amplified pulses is ~1011 with energy gain ~2.5×104 in the Nd:glass amplifiers.

A pulse-shape discrimination method for improving Gamma-ray spectrometry based on a new digital shaping filter

NASA Astrophysics Data System (ADS)

Qin, Zhang-jian; Chen, Chuan; Luo, Jun-song; Xie, Xing-hong; Ge, Liang-quan; Wu, Qi-fan

2018-04-01

It is a usual practice for improving spectrum quality by the mean of designing a good shaping filter to improve signal-noise ratio in development of nuclear spectroscopy. Another method is proposed in the paper based on discriminating pulse-shape and discarding the bad pulse whose shape is distorted as a result of abnormal noise, unusual ballistic deficit or bad pulse pile-up. An Exponentially Decaying Pulse (EDP) generated in nuclear particle detectors can be transformed into a Mexican Hat Wavelet Pulse (MHWP) and the derivation process of the transform is given. After the transform is performed, the baseline drift is removed in the new MHWP. Moreover, the MHWP-shape can be discriminated with the three parameters: the time difference between the two minima of the MHWP, and the two ratios which are from the amplitude of the two minima respectively divided by the amplitude of the maximum in the MHWP. A new type of nuclear spectroscopy was implemented based on the new digital shaping filter and the Gamma-ray spectra were acquired with a variety of pulse-shape discrimination levels. It had manifested that the energy resolution and the peak-Compton ratio were both improved after the pulse-shape discrimination method was used.

Application of nonlinear pulse shaping of femtosecond pulse generation in a fiber amplifier at 500 MHz repetition rate

NASA Astrophysics Data System (ADS)

Liu, Yang; Luo, Daping; Wang, Chao; Zhu, Zhiwei; Li, Wenxue

2018-03-01

We numerically and experimentally demonstrate that a nonlinear pulse shaping technique based on pre-chirping management in a short gain fiber can be exploited to improve the quality of a compressed pulse. With prior tuning of the pulse chirp, the amplified pulse express different nonlinear propagating processes. A spectrum with s flat top and more smooth wings, showing a similariton feature, generates with the optimal initial pulse chirp, and the shortest pulses with minimal pulse pedestals are obtained. Experimental results show the ability of nonlinear pulse shaping to enhance the quality of compressed pulses, as theoretically expected.

Generation of arbitrarily shaped picosecond optical pulses using an integrated electrooptic waveguide modulator.

PubMed

Haner, M; Warren, W S

1987-09-01

We have produced complex software adjustable laser pulse shapes with ~10-ps resolution, and pulse energies up to 100 microJ for spectroscopic applications. The key devices are a high damage threshold electrooptic directional coupler and a GaAs circuit for synthesizing arbitrarily shaped microwave pulses.

Probing coherence in microcavity frequency combs via optical pulse shaping

NASA Astrophysics Data System (ADS)

Ferdous, Fahmida; Miao, Houxun; Wang, Pei-Hsun; Leaird, Daniel E.; Srinivasan, Kartik; Chen, Lei; Aksyuk, Vladimir; Weiner, Andrew M.

2012-09-01

Recent investigations of microcavity frequency combs based on cascaded four-wave mixing have revealed a link between the evolution of the optical spectrum and the observed temporal coherence. Here we study a silicon nitride microresonator for which the initial four-wave mixing sidebands are spaced by multiple free spectral ranges (FSRs) from the pump, then fill in to yield a comb with single FSR spacing, resulting in partial coherence. By using a pulse shaper to select and manipulate the phase of various subsets of spectral lines, we are able to probe the structure of the coherence within the partially coherent comb. Our data demonstrate strong variation in the degree of mutual coherence between different groups of lines and provide support for a simple model of partially coherent comb formation.

Numerical investigation of trichel pulse of negative corona discharge in N2-O2 mixture

NASA Astrophysics Data System (ADS)

Xia, Qing; Zhang, Yu; Jiang, Zhaorui; Wang, Ronggang; Ouyang, Jiting

2017-12-01

Trichel pulse of negative corona discharge in atmospheric air is investigated numerically using a 2D fluid model. The model consists of a hyperbolic cathode tip and a plane anode, and considers 11 kinds of particles and the most important interactions among them. The spatio-temporal evolution of charged species and the electric field are evaluated during the pulse process. During the pulse rising edge, the positive ions accumulate ahead of the tip forming the temporal cathode sheath, significantly enhancing the local field. In the pulse decay edge, the temporal sheath collapses and the discharge falls back to a low-current mode. In the pulse interval, the discharge does not cease but sustains weakly until the next pulse. The location of the temporal sheath is independent of the averaged value during the Trichel pulse regime and also the same with that in a normal glow regime, which determines a nearly constant pulse rising time at given configurations. However, a smaller tip radius will lead to their decrease. The effect of negative ions on the pulse process is studied by adjusting the attachment rates. It indicates that the negative ions are actually not necessary in the Trichel pulse process, but will influence the pulse waveform significantly.

Demonstration of Flying Mirror with Improved Efficiency

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

Pirozhkov, Alexander S.; Kando, Masaki; Fukuda, Yuji

2009-07-25

A strongly nonlinear wake wave driven by an intense laser pulse can act as a partially reflecting relativistic mirror (the flying mirror)[S. V. Bulanov, et al., Bulletin of the Lebedev Physics Institute, No. 6, 9 (1991); S. V. Bulanov, et al., Phys. Rev. Lett. 91, 085001 (2003)]. Upon reflection from such mirror, a counter-propagating optical-frequency laser pulse is directly converted into high-frequency radiation, with a frequency multiplication factor approx4gamma{sup 2}(the double Doppler effect). We present the results of recent experiment in which the photon number in the reflected radiation was at least several thousand times larger than in our proof-of-principlemore » experiment [M. Kando, et al., Phys. Rev. Lett. 99, 135001 (2007); A. S. Pirozhkov, et al., Phys. Plasmas 14, 123106 (2007)]. The flying mirror holds promise of generating intense coherent ultrashort XUV and x-ray pulses that inherit their temporal shape and polarization from the original optical-frequency (laser) pulses. Furthermore, the reflected radiation bears important information about the reflecting wake wave itself, which can be used for its diagnostics.« less

Femtosecond optical injection of intact plant cells using a reconfigurable platform

NASA Astrophysics Data System (ADS)

Mitchell, Claire A.; Kalies, Stefan; Cizmar, Tomas; Bellini, Nicola; Kubasik-Thayil, Anisha; Heisterkamp, Alexander; Torrance, Lesley; Roberts, Alison G.; Gunn-Moore, Frank J.; Dholakia, Kishan

2014-03-01

The use of ultrashort-pulsed lasers for molecule delivery and transfection has proved to be a non-invasive and highly efficient technique for a wide range of mammalian cells. This present study investigates the effectiveness of femtosecond photoporation in plant cells, a hard-to-manipulate yet agriculturally relevant cell type, specifically suspension tobacco BY-2 cells. Both spatial and temporal shaping of the light field is employed to optimise the delivery of membrane impermeable molecules into plant cells using a reconfigurable optical system designed to be able to switch easily between different spatial modes and pulse durations. The use of a propagation invariant Bessel beam was found to increase the number of cells that could be viably optoinjected, when compared to the use of a Gaussian beam. Photoporation with a laser producing sub-12 fs pulses, coupled with a dispersion compensation system to retain the pulse duration at focus, reduced the power required for efficient optical injection by 1.5-1.8 times when compared to a photoporation with a 140 fs laser output.

A 100J-level nanosecond pulsed DPSSL for pumping high-efficiency, high-repetition rate PW-class lasers

NASA Astrophysics Data System (ADS)

De Vido, M.; Ertel, K.; Mason, P. D.; Banerjee, S.; Phillips, P. J.; Smith, J. M.; Butcher, T. J.; Chekhlov, O.; Divoky, M.; Pilar, J.; Hooker, C.; Shaikh, W.; Lucianetti, A.; Hernandez-Gomez, C.; Mocek, T.; Edwards, C.; Collier, J. L.

2017-02-01

In this paper, we review the development, at the STFC's Central Laser Facility (CLF), of high energy, high repetition rate diode-pumped solid-state laser (DPSSL) systems based on cryogenically-cooled multi-slab ceramic Yb:YAG. Up to date, two systems have been completed, namely the DiPOLE prototype and the DiPOLE100 system. The DiPOLE prototype has demonstrated amplification of nanosecond pulses in excess of 10 J at 10 Hz repetition rate with an opticalto- optical efficiency of 22%. The larger scale DiPOLE100 system, designed to deliver 100J temporally-shaped nanosecond pulses at 10 Hz repetition rate, has been developed at the CLF for the HiLASE project in the Czech Republic. Recent experiments conducted on the DiPOLE100 system demonstrated the energy scalability of the DiPOLE concept to the 100 J pulse energy level. Furthermore, second harmonic generation experiments carried out on the DiPOLE prototype confirmed the suitability of DiPOLE-based systems for pumping high repetition rate PW-class laser systems based on Ti:sapphire or optical parametric chirped pulse amplification (OPCPA) technology.

Hadronic vs. electromagnetic pulse shape discrimination in CsI(Tl) for high energy physics experiments

NASA Astrophysics Data System (ADS)

Longo, S.; Roney, J. M.

2018-03-01

Pulse shape discrimination using CsI(Tl) scintillators to perform neutral hadron particle identification is explored with emphasis towards application at high energy electron-positron collider experiments. Through the analysis of the pulse shape differences between scintillation pulses from photon and hadronic energy deposits using neutron and proton data collected at TRIUMF, it is shown that the pulse shape variations observed for hadrons can be modelled using a third scintillation component for CsI(Tl), in addition to the standard fast and slow components. Techniques for computing the hadronic pulse amplitudes and shape variations are developed and it is shown that the intensity of the additional scintillation component can be computed from the ionization energy loss of the interacting particles. These pulse modelling and simulation methods are integrated with GEANT4 simulation libraries and the predicted pulse shape for CsI(Tl) crystals in a 5 × 5 array of 5 × 5 × 30 cm3 crystals is studied for hadronic showers from 0.5 and 1 GeV/c KL0 and neutron particles. Using a crystal level and cluster level approach for photon vs. hadron cluster separation we demonstrate proof-of-concept for neutral hadron detection using CsI(Tl) pulse shape discrimination in high energy electron-positron collider experiments.

Temporal cross-correlation of x-ray free electron and optical lasers using soft x-ray pulse induced transient reflectivity.

PubMed

Krupin, O; Trigo, M; Schlotter, W F; Beye, M; Sorgenfrei, F; Turner, J J; Reis, D A; Gerken, N; Lee, S; Lee, W S; Hays, G; Acremann, Y; Abbey, B; Coffee, R; Messerschmidt, M; Hau-Riege, S P; Lapertot, G; Lüning, J; Heimann, P; Soufli, R; Fernández-Perea, M; Rowen, M; Holmes, M; Molodtsov, S L; Föhlisch, A; Wurth, W

2012-05-07

The recent development of x-ray free electron lasers providing coherent, femtosecond-long pulses of high brilliance and variable energy opens new areas of scientific research in a variety of disciplines such as physics, chemistry, and biology. Pump-probe experimental techniques which observe the temporal evolution of systems after optical or x-ray pulse excitation are one of the main experimental schemes currently in use for ultrafast studies. The key challenge in these experiments is to reliably achieve temporal and spatial overlap of the x-ray and optical pulses. Here we present measurements of the x-ray pulse induced transient change of optical reflectivity from a variety of materials covering the soft x-ray photon energy range from 500eV to 2000eV and outline the use of this technique to establish and characterize temporal synchronization of the optical-laser and FEL x-ray pulses.

Temporal overlap estimation based on interference spectrum in CARS microscopy

NASA Astrophysics Data System (ADS)

Zhang, Yongning; Jiang, Junfeng; Liu, Kun; Huang, Can; Wang, Shuang; Zhang, Xuezhi; Liu, Tiegen

2018-01-01

Coherent Anti-Stokes Raman Scattering (CARS) microscopy has attracted lots of attention because of the advantages, such as noninvasive, label-free, chemical specificity, intrinsic three-dimension spatial resolution and so on. However, the temporal overlap of pump and Stokes has not been solved owing to the ultrafast optical pulse used in CARS microscopy. We combine interference spectrum of residual pump in Stokes path and nonlinear Schrodinger equation (NLSE) to realize the temporal overlap of pump pulse and Stokes pulse. At first, based on the interference spectrum of pump pulse and residual pump in Stokes path, the optical delay is defined when optical path difference between pump path and Stokes path is zero. Then the relative optical delay between Stokes pulse and residual pump in PCF can be calculated by NLSE. According to the spectrum interference and NLSE, temporal overlap of pump pulse and Stokes pulse will be realized easily and the imaging speed will be improved in CARS microscopy.

Effect of the combination of different welding parameters on melting characteristics of grade 1 titanium with a pulsed Nd-Yag laser.

PubMed

Bertrand, C; Laplanche, O; Rocca, J P; Le Petitcorps, Y; Nammour, S

2007-11-01

The laser is a very attractive tool for joining dental metallic alloys. However, the choice of the setting parameters can hardly influence the welding performances. The aim of this research was to evaluate the impact of several parameters (pulse shaping, pulse frequency, focal spot size...) on the quality of the microstructure. Grade 1 titanium plates have been welded with a pulsed Nd-Yag laser. Suitable power, pulse duration, focal spot size, and flow of argon gas were fixed by the operator. Five different pulse shapes and three pulse frequencies were investigated. Two pulse shapes available on this laser unit were eliminated because they considerably hardened the metal. As the pulse frequency rose, the metal was more and more ejected, and a plasma on the surface of the metal increased the oxygen contamination in the welded area. Frequencies of 1 or 2 Hz are optimum for a dental use. Three pulse shapes can be used for titanium but the rectangular shape gives better results.

High-speed pulse-shape generator, pulse multiplexer

DOEpatents

Burkhart, Scott C.

2002-01-01

The invention combines arbitrary amplitude high-speed pulses for precision pulse shaping for the National Ignition Facility (NIF). The circuitry combines arbitrary height pulses which are generated by replicating scaled versions of a trigger pulse and summing them delayed in time on a pulse line. The combined electrical pulses are connected to an electro-optic modulator which modulates a laser beam. The circuit can also be adapted to combine multiple channels of high speed data into a single train of electrical pulses which generates the optical pulses for very high speed optical communication. The invention has application in laser pulse shaping for inertial confinement fusion, in optical data links for computers, telecommunications, and in laser pulse shaping for atomic excitation studies. The invention can be used to effect at least a 10.times. increase in all fiber communication lines. It allows a greatly increased data transfer rate between high-performance computers. The invention is inexpensive enough to bring high-speed video and data services to homes through a super modem.

Waveform synthesizer

DOEpatents

Franks, Larry A.; Nelson, Melvin A.

1981-01-01

A method of producing optical and electrical pulses of desired shape. An optical pulse of arbitrary but defined shape illuminates one end of an array of optical fiber waveguides of differing lengths to time differentiate the input pulse. The optical outputs at the other end of the array are combined to form a synthesized pulse of desired shape.

Nanoscale magnetic ratchets based on shape anisotropy

NASA Astrophysics Data System (ADS)

Cui, Jizhai; Keller, Scott M.; Liang, Cheng-Yen; Carman, Gregory P.; Lynch, Christopher S.

2017-02-01

Controlling magnetization using piezoelectric strain through the magnetoelectric effect offers several orders of magnitude reduction in energy consumption for spintronic applications. However strain is a uniaxial effect and, unlike directional magnetic field or spin-polarized current, cannot induce a full 180° reorientation of the magnetization vector when acting alone. We have engineered novel ‘peanut’ and ‘cat-eye’ shaped nanomagnets on piezoelectric substrates that undergo repeated deterministic 180° magnetization rotations in response to individual electric-field-induced strain pulses by breaking the uniaxial symmetry using shape anisotropy. This behavior can be likened to a magnetic ratchet, advancing magnetization clockwise with each piezostrain trigger. The results were validated using micromagnetics implemented in a multiphysics finite elements code to simulate the engineered spatial and temporal magnetic behavior. The engineering principles start from a target device function and proceed to the identification of shapes that produce the desired function. This approach opens a broad design space for next generation magnetoelectric spintronic devices.

A Hybrid Fiber/Solid-State Regenerative Amplifier with Tunable Pulse Widths for Satellite Laser Ranging

NASA Technical Reports Server (NTRS)

Coyle, Barry; Poulios, Demetrios

2013-01-01

A fiber/solid-state hybrid seeded regenerative amplifier, capable of achieving high output energy with tunable pulse widths, has been developed for satellite laser ranging applications. The regenerative amplifier cavity uses a pair of Nd:YAG zigzag slabs oriented orthogonally to one another in order to make thermal lensing effects symmetrical and simplify optical correction schemes. The seed laser used is a fiber-coupled 1,064-nm narrowband (<0.02 nm) diode laser that is discretely driven in a new short-pulsed mode, enabling continuously tunable seed pulse widths in the 0.2-to-0.4-ns range. The amplifier gain unit consists of a pair of Brewster-cut 6-bounce zigzag Nd:YAG laser slabs, oriented 90deg relative to each other in the amplifier head. This arrangement creates a net-symmetrical thermal lens effect (an opposing singleaxis effect in each slab), and makes thermo-optical corrections simple by optimizing the curvature of the nearest cavity mirror. Each slab is pumped by a single 120-W, pulsed 808-nm laser diode array. In this configuration, the average pump beam distribution in the slabs had a 1-D Gaussian shape, which matches the estimated cavity mode size. A half-wave plate between the slabs reduces losses from Fresnel reflections due to the orthogonal slabs Brewster-cut end faces. Successful "temporal" seeding of the regenerative amplifier cavity results in a cavity Q-switch pulse envelope segmenting into shorter pulses, each having the width of the input seed, and having a uniform temporal separation corresponding to the cavity round-trip time of approx. =10 ns. The pulse energy is allowed to build on successive passes in the regenerative amplifier cavity until a maximum is reached, (when cavity gains and losses are equal), after which the pulse is electro- optically switched out on the next round trip The overall gain of the amplifier is approx. =82 dB (or a factor of 1.26 million). After directing the amplified output through a LBO frequency doubling crystal, approx. = 2.1 W of 532-nm output (>1 mJ) was measured. This corresponds to a nonlinear conversion efficiency of >60%. Furthermore, by pulse pumping this system, a single pulse per laser shot can be created for the SLR (satellite laser ranging) measurement, and this can be ejected into the instrument. This is operated at the precise frequency needed by the measurement, as opposed to commercial short-pulsed, mode-locked systems that need to operate in a continuous fashion, or CW (continuous wave), and create pulses at many MHz. Therefore, this design does not need to throw away or dump 99% of the laser energy to produce what is required; this system can be far smaller, more efficient, cheaper, and readily deployed in the field when packaged efficiently. Finally, by producing custom diode seed pulses electronically, two major advantages over commercial systems are realized: First, this pulse shape is customizable and not affected by the cavity length or gain of the amplifier cavity, and second, it can produce adjustable (selectable) pulse widths by simply adding multiple seed diodes and coupling each into commercial, low-cost fiber-optic combiners.

X-Ray Pulse Selector With 2 ns Lock-in Phase Setting And Stability

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

Lindenau, B.; Raebiger, J.; Polachowski, S.

2004-05-12

Selector devices, which are based on magnetically suspended, high speed triangular shutter rotors, have been designed and built in cooperation with ESRF, APS, and recently Spring-8 for time resolved studies with isolated x-ray pulses at white beam lines. The x-ray pulse selection is accomplished by means of a beam channel along one of the edges of the triangular rotor, which opens once per revolution. Entrance and exit apertures of the channel can be designed wedge shaped for variable tuning of the channel height between 0.1 mm to 0.9 mm. At the 1 kHz maximum operation frequency of a 220 mmmore » diameter disk with 190 mm channel length, the practicable open times of the channel are demonstrated to range down to 200 ns. The selector drive electronics is directly coupled to the storage ring RF clock for rotational phase control. It allows for continuous selector operation in phase locked mode to the temporal pulse structure of the synchrotron at 2 ns RMS stability. The phase angle between the pulse transmission period and the synchrotron bunch sequence can be adjusted with similar precision for X-ray pulse selection according to the experimental needs. ID09, Michael Wulff ; BioCARS 14-BM, Reinhard Pahl; BL40-XU, Shin-ichi Adachi.« less

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

Fischer, Martin C., E-mail: Martin.Fischer@duke.edu; Wilson, Jesse W.; Robles, Francisco E.

Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulsesmore » offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.« less

Temporal waveguides for optical pulses

DOE PAGES

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

2016-05-12

Here we discuss, temporal total internal reflection (TIR), in analogy to the conventional TIR of an optical beam at a dielectric interface, is the total reflection of an optical pulse inside a dispersive medium at a temporal boundary across which the refractive index changes. A pair of such boundaries separated in time acts as the temporal analog of planar dielectric waveguides. We study the propagation of optical pulses inside such temporal waveguides, both analytically and numerically, and show that the waveguide supports a finite number of temporal modes. We also discuss how a single-mode temporal waveguide can be created inmore » practice. In contrast with the spatial case, the confinement can occur even when the central region has a lower refractive index.« less

The effect of the pulse repetition rate on the fast ionization wave discharge

NASA Astrophysics Data System (ADS)

Huang, Bang-Dou; Carbone, Emile; Takashima, Keisuke; Zhu, Xi-Ming; Czarnetzki, Uwe; Pu, Yi-Kang

2018-06-01

The effect of the pulse repetition rate (PRR) on the generation of high energy electrons in a fast ionization wave (FIW) discharge is investigated by both experiment and modelling. The FIW discharge is driven by nanosecond high voltage pulses and is generated in helium with a pressure of 30 mbar. The axial electric field (E z ), as the driven force of high energy electron generation, is strongly influenced by PRR. Both the measurement and the model show that, during the breakdown, the peak value of E z decreases with the PRR, while after the breakdown, the value of E z increases with the PRR. The electron energy distribution function (EEDF) is calculated with a model similar to Boeuf and Pitchford (1995 Phys. Rev. E 51 1376). It is found that, with a low value of PRR, the EEDF during the breakdown is strongly non-Maxwellian with an elevated high energy tail, while the EEDF after the breakdown is also non-Maxwellian but with a much depleted population of high energy electrons. However, with a high value of PRR, the EEDF is Maxwellian-like without much temporal variation both during and after the breakdown. With the calculated EEDF, the temporal evolution of the population of helium excited species given by the model is in good agreement with the measured optical emission, which also depends critically on the shape of the EEDF.

Characteristics of the inductive nitrogen laser generation

NASA Astrophysics Data System (ADS)

Razhev, A. M.; Churkin, D. S.; Kargapoltsev, E. S.

2016-05-01

The results of the experimental study of energy, temporal, spectral and spatial characteristics of UV inductive laser generation are presented. The study has identified a number of characteristics which demonstrate the differences between electron parameters of inductively coupled plasma and the plasma of longitudinal and transverse electrical discharges. The mechanism of simultaneous occurrence of Lewis-Rayleigh afterglow representing transitions between higher vibrational substates of B3Πg and A3∑u+ states; laser generation at C3Πu→B3Πg transition as well as the absence of IR radiation at 1st positive system typical for electrical discharge nitrogen lasers has been thoroughly researched. The major characteristic is ring shaped laser beam which size and width depend on excitation conditions. Inductive UV nitrogen laser is found to operate in ASE regime, but has a low divergence of 0.4±0.1 mrad and high pulse-to-pulse stability (laser pulse deviation amplitude did not exceed 1%).

PULSE BROADENING MEASUREMENTS FROM THE GALACTIC CENTER PULSAR J1745-2900

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

Spitler, L. G.; Lee, K. J.; Eatough, R. P.

2014-01-01

We present temporal scattering measurements of single pulses and average profiles of PSR J1745-2900, a magnetar recently discovered only 3 arcsec away from Sagittarius A* (Sgr A*), from 1.2 to 18.95 GHz using the Effelsberg 100 m Radio Telescope, the Nançay Decimetric Radio Telescope, and the Jodrell Bank Lovell Telescope. Single pulse analysis shows that the integrated pulse profile above 2 GHz is dominated by pulse jitter, while below 2 GHz the pulse profile shape is dominated by scattering. This is the first object in the Galactic center (GC) with both pulse broadening and angular broadening measurements. We measure a pulse broadening time scale at 1 GHzmore » of τ{sub 1GHz} = 1.3 ± 0.2 and pulse broadening spectral index of α = –3.8 ± 0.2, which is several orders of magnitude lower than predicted by the NE2001 model (Cordes and Lazio 2002). If this scattering time scale is representative of the GC as a whole, then previous surveys should have detected many pulsars. The lack of detections implies either our understanding of scattering in the GC is incomplete or there are fewer pulsars in the GC than previously predicted. Given that magnetars are a rare class of radio pulsar, there are likely many canonical and millisecond pulsars in the GC, and not surprisingly, scattering in the GC is spatially complex.« less

Design and implementation of an optimal laser pulse front tilting scheme for ultrafast electron diffraction in reflection geometry with high temporal resolution.

PubMed

Pennacchio, Francesco; Vanacore, Giovanni M; Mancini, Giulia F; Oppermann, Malte; Jayaraman, Rajeswari; Musumeci, Pietro; Baum, Peter; Carbone, Fabrizio

2017-07-01

Ultrafast electron diffraction is a powerful technique to investigate out-of-equilibrium atomic dynamics in solids with high temporal resolution. When diffraction is performed in reflection geometry, the main limitation is the mismatch in group velocity between the overlapping pump light and the electron probe pulses, which affects the overall temporal resolution of the experiment. A solution already available in the literature involved pulse front tilt of the pump beam at the sample, providing a sub-picosecond time resolution. However, in the reported optical scheme, the tilted pulse is characterized by a temporal chirp of about 1 ps at 1 mm away from the centre of the beam, which limits the investigation of surface dynamics in large crystals. In this paper, we propose an optimal tilting scheme designed for a radio-frequency-compressed ultrafast electron diffraction setup working in reflection geometry with 30 keV electron pulses containing up to 10 5 electrons/pulse. To characterize our scheme, we performed optical cross-correlation measurements, obtaining an average temporal width of the tilted pulse lower than 250 fs. The calibration of the electron-laser temporal overlap was obtained by monitoring the spatial profile of the electron beam when interacting with the plasma optically induced at the apex of a copper needle (plasma lensing effect). Finally, we report the first time-resolved results obtained on graphite, where the electron-phonon coupling dynamics is observed, showing an overall temporal resolution in the sub-500 fs regime. The successful implementation of this configuration opens the way to directly probe structural dynamics of low-dimensional systems in the sub-picosecond regime, with pulsed electrons.

Design and implementation of an optimal laser pulse front tilting scheme for ultrafast electron diffraction in reflection geometry with high temporal resolution

PubMed Central

Pennacchio, Francesco; Vanacore, Giovanni M.; Mancini, Giulia F.; Oppermann, Malte; Jayaraman, Rajeswari; Musumeci, Pietro; Baum, Peter; Carbone, Fabrizio

2017-01-01

Ultrafast electron diffraction is a powerful technique to investigate out-of-equilibrium atomic dynamics in solids with high temporal resolution. When diffraction is performed in reflection geometry, the main limitation is the mismatch in group velocity between the overlapping pump light and the electron probe pulses, which affects the overall temporal resolution of the experiment. A solution already available in the literature involved pulse front tilt of the pump beam at the sample, providing a sub-picosecond time resolution. However, in the reported optical scheme, the tilted pulse is characterized by a temporal chirp of about 1 ps at 1 mm away from the centre of the beam, which limits the investigation of surface dynamics in large crystals. In this paper, we propose an optimal tilting scheme designed for a radio-frequency-compressed ultrafast electron diffraction setup working in reflection geometry with 30 keV electron pulses containing up to 105 electrons/pulse. To characterize our scheme, we performed optical cross-correlation measurements, obtaining an average temporal width of the tilted pulse lower than 250 fs. The calibration of the electron-laser temporal overlap was obtained by monitoring the spatial profile of the electron beam when interacting with the plasma optically induced at the apex of a copper needle (plasma lensing effect). Finally, we report the first time-resolved results obtained on graphite, where the electron-phonon coupling dynamics is observed, showing an overall temporal resolution in the sub-500 fs regime. The successful implementation of this configuration opens the way to directly probe structural dynamics of low-dimensional systems in the sub-picosecond regime, with pulsed electrons. PMID:28713841

100J-level nanosecond pulsed Yb:YAG cryo-cooled DPSSL amplifier

NASA Astrophysics Data System (ADS)

Smith, J. M.; Butcher, T. J.; Mason, P. D.; Ertel, K.; Phillips, P. J.; Banerjee, S.; De Vido, M.; Chekhlov, O.; Divoky, M.; Pilar, J.; Shaikh, W.; Hooker, C.; Lucianetti, A.; Hernandez Gomez, C.; Mocek, T.; Edwards, C.; Collier, J. L.

2018-02-01

We report on the successful demonstration of the world's first kW average power, 100 Joule-class, high-energy, nanosecond pulsed diode-pumped solid-state laser (DPSSL), DiPOLE100. Results from the first long-term test for amplification will be presented; the system was operated for 1 hour with 10 ns duration pulses at 10 Hz pulse repetition rate and an average output energy of 105 J and RMS energy stability of approximately 1%. The laser system is based on scalable cryogenic gas-cooled multi-slab ceramic Yb:YAG amplifier technology. The DiPOLE100 system comprises three major sub-systems, a spatially and temporally shaped front end, a 10 J cryo-amplifier and a 100 J cryo-amplifier. The 10 J cryo-amplifier contain four Yb:YAG ceramic gain media slabs, which are diode pumped from both sides, while a multi-pass architecture configured for seven passes enables 10 J of energy to be extracted at 10 Hz. This seeds the 100 J cryo-amplifier, which contains six Yb:YAG ceramic gain media slabs with the multi-pass configured for four passes. Our future development plans for this architecture will be introduced including closed-loop pulse shaping, increased energy, higher repetition rates and picosecond operation. This laser architecture unlocks the potential for practical applications including new sources for industrial materials processing and high intensity laser matter studies as envisioned for ELI [1], HiLASE [2], and the European XFEL [3]. Alternatively, it can be used as a pump source for higher repetition rate PW-class amplifiers, which can themselves generate high-brightness secondary radiation and ion sources leading to new remote imaging and medical applications.

Resolving the shape of a sonoluminescence pulse in sulfuric acid by the use of streak camera.

PubMed

Huang, Wei; Chen, Weizhong; Cui, Weicheng

2009-06-01

A streak camera is used to measure the shape of sonoluminescence pulses from a cavitation bubble levitated stably in a sulfuric acid solution. The shape and response to an acoustic pressure field of the sonoluminescence pulse in 85% by weight sulfuric acid are qualitatively similar to those in water. However, the pulse width in sulfuric acid is wider than that in water by over one order of magnitude. The width of the sonoluminescence pulse is strongly dependent on the concentration of the sulfuric acid solution, while the skewed distribution of the shape remains unchanged.

Laser pulse stacking method

DOEpatents

Moses, Edward I.

1992-01-01

A laser pulse stacking method is disclosed. A problem with the prior art has been the generation of a series of laser beam pulses where the outer and inner regions of the beams are generated so as to form radially non-synchronous pulses. Such pulses thus have a non-uniform cross-sectional area with respect to the outer and inner edges of the pulses. The present invention provides a solution by combining the temporally non-uniform pulses in a stacking effect to thus provide a more uniform temporal synchronism over the beam diameter.

Laser pulse stacking method

DOEpatents

Moses, E.I.

1992-12-01

A laser pulse stacking method is disclosed. A problem with the prior art has been the generation of a series of laser beam pulses where the outer and inner regions of the beams are generated so as to form radially non-synchronous pulses. Such pulses thus have a non-uniform cross-sectional area with respect to the outer and inner edges of the pulses. The present invention provides a solution by combining the temporally non-uniform pulses in a stacking effect to thus provide a more uniform temporal synchronism over the beam diameter. 2 figs.

Pulse Shaped Constant Envelope 8-PSK Modulation Study

NASA Technical Reports Server (NTRS)

Tao, Jianping; Horan, Sheila

1997-01-01

This report provides simulation results for constant envelope pulse shaped 8 Level Phase Shift Keying (8 PSK) modulation for end to end system performance. In order to increase bandwidth utilization, pulse shaping is applied to signals before they are modulated. This report provides simulation results of power spectra and measurement of bit errors produced by pulse shaping in a non-linear channel with Additive White Gaussian Noise (AWGN). The pulse shaping filters can placed before (Type B) or after (Type A) signals are modulated. Three kinds of baseband filters, 5th order Butterworth, 3rd order Bessel and Square-Root Raised Cosine with different BTs or roll off factors, are utilized in the simulations. The simulations were performed on a Signal Processing Worksystem (SPW).

Controlling multiple plasma channels created by a high-power femtosecond laser pulse

NASA Astrophysics Data System (ADS)

Kosareva, O. G.; Luo, Q.

2005-10-01

Femtosecond light filaments are comparatively long regions of the spatially and temporally localized radiation zones, which generate free electrons in the medium. At high pulse peak power multiple filaments are produced leading to stochastic plasma channels (Mlejnek et al.: PRL 83, 2938 (1999)). In both atmospheric long-distance propagation (Sprangle et al., PRE 66, 046418 (2002), Kasparian et al, Science 301, 61 (2003)) and focusing the radiation into condensed matter important issues are production of elongated plasma channels, as well as high conversion efficiency to the white light. We control stochastic plasma channels by changing the initial beam size or shape. The result is the increase in the plasma density and white light signal. Control by regular small-scale perturbations allows us to suppress atmospheric turbulence in air and create an array of well-arranged filaments in fused silica.

Fast spatial beam shaping by acousto-optic diffraction for 3D non-linear microscopy.

PubMed

Akemann, Walther; Léger, Jean-François; Ventalon, Cathie; Mathieu, Benjamin; Dieudonné, Stéphane; Bourdieu, Laurent

2015-11-02

Acousto-optic deflection (AOD) devices offer unprecedented fast control of the entire spatial structure of light beams, most notably their phase. AOD light modulation of ultra-short laser pulses, however, is not straightforward to implement because of intrinsic chromatic dispersion and non-stationarity of acousto-optic diffraction. While schemes exist to compensate chromatic dispersion, non-stationarity remains an obstacle. In this work we demonstrate an efficient AOD light modulator for stable phase modulation using time-locked generation of frequency-modulated acoustic waves at the full repetition rate of a high power laser pulse amplifier of 80 kHz. We establish the non-local relationship between the optical phase and the generating acoustic frequency function and verify the system for temporal stability, phase accuracy and generation of non-linear two-dimensional phase functions.

Spatial control of recollision wave packets with attosecond precision.

PubMed

Kitzler, Markus; Lezius, Matthias

2005-12-16

We propose orthogonally polarized two-color laser pulses to steer tunneling electrons with attosecond precision around the ion core. We numerically demonstrate that the angles of birth and recollision, the recollision energy, and the temporal structure of the recolliding wave packet can be controlled without stabilization of the carrier-envelope phase of the laser, and that the wave packet's properties can be described by classical relations for a point charge. This establishes unique mapping between parameters of the laser field and attributes of the recolliding wave packet. The method is capable of probing ionic wave packet dynamics with attosecond resolution from an adjustable direction and might be used as an alternative to aligning molecules. Shaping the properties of the recollision wave packet by controlling the laser field may also provide new routes for improvement of attosecond pulse generation via high harmonic radiation.

Optimization methods of pulse-to-pulse alignment using femtosecond pulse laser based on temporal coherence function for practical distance measurement

NASA Astrophysics Data System (ADS)

Liu, Yang; Yang, Linghui; Guo, Yin; Lin, Jiarui; Cui, Pengfei; Zhu, Jigui

2018-02-01

An interferometer technique based on temporal coherence function of femtosecond pulses is demonstrated for practical distance measurement. Here, the pulse-to-pulse alignment is analyzed for large delay distance measurement. Firstly, a temporal coherence function model between two femtosecond pulses is developed in the time domain for the dispersive unbalanced Michelson interferometer. Then, according to this model, the fringes analysis and the envelope extraction process are discussed. Meanwhile, optimization methods of pulse-to-pulse alignment for practical long distance measurement are presented. The order of the curve fitting and the selection of points for envelope extraction are analyzed. Furthermore, an averaging method based on the symmetry of the coherence function is demonstrated. Finally, the performance of the proposed methods is evaluated in the absolute distance measurement of 20 μ m with path length difference of 9 m. The improvement of standard deviation in experimental results shows that these approaches have the potential for practical distance measurement.

Spatial and temporal pulse propagation for dispersive paraxial optical systems

DOE PAGES

Marcus, G.

2016-04-01

The formalism for pulse propagation through dispersive paraxial optical systems first presented by Kostenbauder (IEEE J. Quant. Elec. 261148–1157 (1990)) using 4 × 4 ray-pulse matrices is extended to 6 × 6 matrices and includes non-separable spatial-temporal couplings in both transverse dimensions as well as temporal dispersive effects up to a quadratic phase. The eikonal in a modified Huygens integral in the Fresnell approximation is derived and can be used to propagate pulses through complicated dispersive optical systems within the paraxial approximation. Additionally, a simple formula for the propagation of ultrashort pulses having a Gaussian profile both spatially and temporallymore » is presented.« less

Spatial and temporal pulse propagation for dispersive paraxial optical systems

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

Marcus, G.

The formalism for pulse propagation through dispersive paraxial optical systems first presented by Kostenbauder (IEEE J. Quant. Elec. 261148–1157 (1990)) using 4 × 4 ray-pulse matrices is extended to 6 × 6 matrices and includes non-separable spatial-temporal couplings in both transverse dimensions as well as temporal dispersive effects up to a quadratic phase. The eikonal in a modified Huygens integral in the Fresnell approximation is derived and can be used to propagate pulses through complicated dispersive optical systems within the paraxial approximation. Additionally, a simple formula for the propagation of ultrashort pulses having a Gaussian profile both spatially and temporallymore » is presented.« less

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

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

Cao, D.; Boehly, T. R.; Gregor, M. C.

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the VISAR diagnostic [T. R. Boehly et al., Phys. Plasmas 18, 092706 (2011)] on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (alpha ~ 3) implosions, but agreement degrades for lower-adiabat (alpha ~ 1)more » designs. Several possibilities for this difference are studied: (1) errors in placing the target at the center of irradiation (target offset), (2) variations in energy between the different incident beams (power imbalance), and (3) errors in modeling the laser energy coupled into the capsule. Simulation results indicate that shock timing is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to target offset and beam power imbalance. A new technique under development to infer coronal profiles using x-ray self-emission imaging [A. K. Davis et al., Bull. Am. Phys. Soc. 61, BAPS.2016.DPP.NO8.7 (2016)] can be applied to the pulse shapes used in shock-timing experiments. This will help identify improved physics models to implement in codes and consequently enhance shock-timing predictive capability for low-adiabat pulses.« less

Increase in the neutron yield from a dense plasma-focus experiment performed with a conical tip placed in the centre of the anode end

NASA Astrophysics Data System (ADS)

Kubes, P.; Paduch, M.; Cikhardt, J.; Cikhardtova, B.; Klir, D.; Kravarik, J.; Rezac, K.; Zielinska, E.; Sadowski, M. J.; Szymaszek, A.; Tomaszewski, K.; Zaloga, D.

2017-09-01

The paper describes the evolution of self-organized structures inside a pinched plasma column during the phase of the effective production of fusion neutrons, as observed in the mega-ampere plasma focus experiment performed with a conical tip placed in the centre of the anode face. In a comparison with the plane anode face configuration, the described anode shape facilitated transformations in the pinch column during the neutron production and increased the neutron yield several times. Simultaneously, it decreased the minimal diameter and the length of the pinched column, and it depressed the first neutron pulse. It also induced shorter pulses of X-rays and neutrons, which enabled the determination of a temporal difference between the emission of electron and deuteron beams. The fast electrons were produced mainly during a disruption of the pinch constriction, while the fast deuterons - during the formation and explosion of plasmoids. The paper also presents the temporal evolution of a current distribution in the plasmoid during the neutron production, as well as the appearance and stable positions of current filaments traces upon the surface of the conical anode tip.

Temporal lenses for attosecond and femtosecond electron pulses

PubMed Central

Hilbert, Shawn A.; Uiterwaal, Cornelis; Barwick, Brett; Batelaan, Herman; Zewail, Ahmed H.

2009-01-01

Here, we describe the “temporal lens” concept that can be used for the focus and magnification of ultrashort electron packets in the time domain. The temporal lenses are created by appropriately synthesizing optical pulses that interact with electrons through the ponderomotive force. With such an arrangement, a temporal lens equation with a form identical to that of conventional light optics is derived. The analog of ray diagrams, but for electrons, are constructed to help the visualization of the process of compressing electron packets. It is shown that such temporal lenses not only compensate for electron pulse broadening due to velocity dispersion but also allow compression of the packets to durations much shorter than their initial widths. With these capabilities, ultrafast electron diffraction and microscopy can be extended to new domains,and, just as importantly, electron pulses can be delivered directly on an ultrafast techniques target specimen. PMID:19541639

A low-cost programmable pulse generator for physiology and behavior

PubMed Central

Sanders, Joshua I.; Kepecs, Adam

2014-01-01

Precisely timed experimental manipulations of the brain and its sensory environment are often employed to reveal principles of brain function. While complex and reliable pulse trains for temporal stimulus control can be generated with commercial instruments, contemporary options remain expensive and proprietary. We have developed Pulse Pal, an open source device that allows users to create and trigger software-defined trains of voltage pulses with high temporal precision. Here we describe Pulse Pal’s circuitry and firmware, and characterize its precision and reliability. In addition, we supply online documentation with instructions for assembling, testing and installing Pulse Pal. While the device can be operated as a stand-alone instrument, we also provide application programming interfaces in several programming languages. As an inexpensive, flexible and open solution for temporal control, we anticipate that Pulse Pal will be used to address a wide range of instrumentation timing challenges in neuroscience research. PMID:25566051

Pulse shaping circuit for active counting of superheated emulsion

NASA Astrophysics Data System (ADS)

Murai, Ikuo; Sawamura, Teruko

2005-08-01

A pulse shaping circuit for active counting of superheated emulsions is described. A piezoelectric transducer is used for sensing bubble formation acoustically and the acoustic signal is transformed to a shaping pulse for counting. The circuit has a short signal processing time in the order of 10 ms.

Effect of laser pulse shaping parameters on the fidelity of quantum logic gates.

PubMed

Zaari, Ryan R; Brown, Alex

2012-09-14

The effect of varying parameters specific to laser pulse shaping instruments on resulting fidelities for the ACNOT(1), NOT(2), and Hadamard(2) quantum logic gates are studied for the diatomic molecule (12)C(16)O. These parameters include varying the frequency resolution, adjusting the number of frequency components and also varying the amplitude and phase at each frequency component. A time domain analytic form of the original discretized frequency domain laser pulse function is derived, providing a useful means to infer the resulting pulse shape through variations to the aforementioned parameters. We show that amplitude variation at each frequency component is a crucial requirement for optimal laser pulse shaping, whereas phase variation provides minimal contribution. We also show that high fidelity laser pulses are dependent upon the frequency resolution and increasing the number of frequency components provides only a small incremental improvement to quantum gate fidelity. Analysis through use of the pulse area theorem confirms the resulting population dynamics for one or two frequency high fidelity laser pulses and implies similar dynamics for more complex laser pulse shapes. The ability to produce high fidelity laser pulses that provide both population control and global phase alignment is attributed greatly to the natural evolution phase alignment of the qubits involved within the quantum logic gate operation.

The Tölz Temporal Topography Study: mapping the visual field across the life span. Part II: cognitive factors shaping visual field maps.

PubMed

Poggel, Dorothe A; Treutwein, Bernhard; Calmanti, Claudia; Strasburger, Hans

2012-08-01

Part I described the topography of visual performance over the life span. Performance decline was explained only partly by deterioration of the optical apparatus. Part II therefore examines the influence of higher visual and cognitive functions. Visual field maps for 95 healthy observers of static perimetry, double-pulse resolution (DPR), reaction times, and contrast thresholds, were correlated with measures of visual attention (alertness, divided attention, spatial cueing), visual search, and the size of the attention focus. Correlations with the attentional variables were substantial, particularly for variables of temporal processing. DPR thresholds depended on the size of the attention focus. The extraction of cognitive variables from the correlations between topographical variables and participant age substantially reduced those correlations. There is a systematic top-down influence on the aging of visual functions, particularly of temporal variables, that largely explains performance decline and the change of the topography over the life span.

Efficient optical pulse stacker system

DOEpatents

Seppala, Lynn G.; Haas, Roger A.

1982-01-01

Method and apparatus for spreading and angle-encoding each pulse of a multiplicity of small area, short pulses into several temporally staggered pulses by use of appropriate beam splitters, with the optical elements being arranged so that each staggered pulse is contiguous with one or two other such pulses, and the entire sequence of stacked pulses comprising a single, continuous long pulse. The single long pulse is expanded in area, and then doubly passed through a nonstorage laser amplifier such as KrF. After amplification, the physically separated, angle-encoded and temporally staggered pulses are recombined into a single pulse of short duration. This high intensity output beam is well collimated and may be propagated over long distance, or used for irradiating inertial confinement fusion targets.

Laser-to-hot-electron conversion limitations in relativistic laser matter interactions due to multi-picosecond dynamics

NASA Astrophysics Data System (ADS)

Schollmeier, M.; Sefkow, A. B.; Geissel, M.; Arefiev, A. V.; Flippo, K. A.; Gaillard, S. A.; Johnson, R. P.; Kimmel, M. W.; Offermann, D. T.; Rambo, P. K.; Schwarz, J.; Shimada, T.

2015-04-01

High-energy short-pulse lasers are pushing the limits of plasma-based particle acceleration, x-ray generation, and high-harmonic generation by creating strong electromagnetic fields at the laser focus where electrons are being accelerated to relativistic velocities. Understanding the relativistic electron dynamics is key for an accurate interpretation of measurements. We present a unified and self-consistent modeling approach in quantitative agreement with measurements and differing trends across multiple target types acquired from two separate laser systems, which differ only in their nanosecond to picosecond-scale rising edge. Insights from high-fidelity modeling of laser-plasma interaction demonstrate that the ps-scale, orders of magnitude weaker rising edge of the main pulse measurably alters target evolution and relativistic electron generation compared to idealized pulse shapes. This can lead for instance to the experimentally observed difference between 45 MeV and 75 MeV maximum energy protons for two nominally identical laser shots, due to ps-scale prepulse variations. Our results show that the realistic inclusion of temporal laser pulse profiles in modeling efforts is required if predictive capability and extrapolation are sought for future target and laser designs or for other relativistic laser ion acceleration schemes.

On the use of a chirped Bragg grating as a cavity mirror of a picosecond Nd : YAG laser

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

Zubko, A E; Shashkov, E V; Smirnov, A V

2016-02-28

The first experimental evidence is presented that the use of a chirped volume Bragg grating (CVBG) as a cavity mirror of a Q-switched picosecond Nd : YAG laser with self-mode-locking leads to significant changes in the temporal parameters of the laser output. Measurements have been performed at two positions of the CVBG: with the grating placed so that shorter wavelengths reflected from its front part lead longer wavelengths or with the grating rotated through 180°, so that longer wavelengths are reflected first. In the former case, the duration of individual pulses in a train increased from ∼35 to ∼300 ps,more » whereas the pulse train shape and duration remained the same as in the case of a conventional laser with a mirror cavity. In the latter case, the full width at half maximum of pulse trains increased from ∼70 ns (Nd : YAG laser with a mirror cavity) to ∼1 ms, and the duration of individual pulses increased from 35 ps to ∼1.2 ns, respectively, which is more typical of free-running laser operation. (laser crystals and braggg ratings)« less

Handheld probe integrating laser diode and ultrasound transducer array for ultrasound/photoacoustic dual modality imaging.

PubMed

Daoudi, K; van den Berg, P J; Rabot, O; Kohl, A; Tisserand, S; Brands, P; Steenbergen, W

2014-10-20

Ultrasound and photoacoustics can be utilized as complementary imaging techniques to improve clinical diagnoses. Photoacoustics provides optical contrast and functional information while ultrasound provides structural and anatomical information. As of yet, photoacoustic imaging uses large and expensive systems, which limits their clinical application and makes the combination costly and impracticable. In this work we present and evaluate a compact and ergonomically designed handheld probe, connected to a portable ultrasound system for inexpensive, real-time dual-modality ultrasound/photoacoustic imaging. The probe integrates an ultrasound transducer array and a highly efficient diode stack laser emitting 130 ns pulses at 805 nm wavelength and a pulse energy of 0.56 mJ, with a high pulse repetition frequency of up to 10 kHz. The diodes are driven by a customized laser driver, which can be triggered externally with a high temporal stability necessary to synchronize the ultrasound detection and laser pulsing. The emitted beam is collimated with cylindrical micro-lenses and shaped using a diffractive optical element, delivering a homogenized rectangular light intensity distribution. The system performance was tested in vitro and in vivo by imaging a human finger joint.

Pulse shape measurements using single shot-frequency resolved optical gating for high energy (80 J) short pulse (600 fs) laser

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

Palaniyappan, S.; Johnson, R.; Shimada, T.

2010-10-15

Relevant to laser based electron/ion accelerations, a single shot second harmonic generation frequency resolved optical gating (FROG) system has been developed to characterize laser pulses (80 J, {approx}600 fs) incident on and transmitted through nanofoil targets, employing relay imaging, spatial filter, and partially coated glass substrates to reduce spatial nonuniformity and B-integral. The device can be completely aligned without using a pulsed laser source. Variations of incident pulse shape were measured from durations of 613 fs (nearly symmetric shape) to 571 fs (asymmetric shape with pre- or postpulse). The FROG measurements are consistent with independent spectral and autocorrelation measurements.

General purpose pulse shape analysis for fast scintillators implemented in digital readout electronics

NASA Astrophysics Data System (ADS)

Asztalos, Stephen J.; Hennig, Wolfgang; Warburton, William K.

2016-01-01

Pulse shape discrimination applied to certain fast scintillators is usually performed offline. In sufficiently high-event rate environments data transfer and storage become problematic, which suggests a different analysis approach. In response, we have implemented a general purpose pulse shape analysis algorithm in the XIA Pixie-500 and Pixie-500 Express digital spectrometers. In this implementation waveforms are processed in real time, reducing the pulse characteristics to a few pulse shape analysis parameters and eliminating time-consuming waveform transfer and storage. We discuss implementation of these features, their advantages, necessary trade-offs and performance. Measurements from bench top and experimental setups using fast scintillators and XIA processors are presented.

Interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser

NASA Astrophysics Data System (ADS)

Wang, Da-Shuai; Wu, Ge; Gao, Bo; Tian, Xiao-Jian

2013-01-01

We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the inter-cavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, a stronger gain saturation energy will result in a higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compared to conventional solitons.

Subharmonic emissions from microbubbles: effect of the driving pulse shape.

PubMed

Biagi, Elena; Breschi, Luca; Vannacci, Enrico; Masotti, Leonardo

2006-11-01

The aims of this work are to investigate the response of the ultrasonic contrast agents (UCA) insonified by different arbitrary-shaped pulses at different acoustic pressures and concentration of the contrast agent focusing on subharmonic emission. A transmission setup was developed in order to insonify the contrast agent contained in a measurement chamber. The transmitted ultrasonic signals were generated by an arbitrary wave generator connected to a linear power amplifier able to drive a single-element transducer. The transmitted ultrasonic pulses that passed through the contrast agent-filled chamber were received by a second transducer or a hydrophone aligned with the first one. The radio frequency (RF) signals were acquired by fast echographic multiparameters multi-image novel apparatus (FEMMINA), which is an echographic platform able to acquire ultrasonic signals in a real-time modality. Three sets of ultrasonic signals were devised in order to evaluate subharmonic response of the contrast agent respect with sinusoidal burst signals used as reference pulses. A decreasing up to 30 dB in subharmonic response was detected for a Gaussian-shaped pulse; differences in subharmonic emission up to 21 dB were detected for a composite pulse (two-tone burst) for different acoustic pressures and concentrations. Results from this experimentation demonstrated that the transmitted pulse shape strongly affects subharmonic emission in spite of a second harmonic one. In particular, the smoothness of the initial portion of the shaped pulses can inhibit subharmonic generation from the contrast agents respect with a reference sinusoidal burst signal. It also was shown that subharmonic generation is influenced by the amplitude and the concentration of the contrast agent for each set of the shaped pulses. Subharmonic emissions that derive from a nonlinear mechanism involving nonlinear coupling among different oscillation modes are strongly affected by the shape of the ultrasonic driving pulse.

Self-calibrating d-scan: measuring ultrashort laser pulses on-target using an arbitrary pulse compressor.

PubMed

Alonso, Benjamín; Sola, Íñigo J; Crespo, Helder

2018-02-19

In most applications of ultrashort pulse lasers, temporal compressors are used to achieve a desired pulse duration in a target or sample, and precise temporal characterization is important. The dispersion-scan (d-scan) pulse characterization technique usually involves using glass wedges to impart variable, well-defined amounts of dispersion to the pulses, while measuring the spectrum of a nonlinear signal produced by those pulses. This works very well for broadband few-cycle pulses, but longer, narrower bandwidth pulses are much more difficult to measure this way. Here we demonstrate the concept of self-calibrating d-scan, which extends the applicability of the d-scan technique to pulses of arbitrary duration, enabling their complete measurement without prior knowledge of the introduced dispersion. In particular, we show that the pulse compressors already employed in chirped pulse amplification (CPA) systems can be used to simultaneously compress and measure the temporal profile of the output pulses on-target in a simple way, without the need of additional diagnostics or calibrations, while at the same time calibrating the often-unknown differential dispersion of the compressor itself. We demonstrate the technique through simulations and experiments under known conditions. Finally, we apply it to the measurement and compression of 27.5 fs pulses from a CPA laser.

Identification of the formation phases of filamentary damage induced by nanosecond laser pulses in bulk fused silica

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

Shen, Chao; Xu, Zhongjie; Chambonneau, Maxime, E-mail: chambonneau@lp3.univ-mrs.fr, E-mail: jiangtian198611@163.com

2015-09-14

Employing a pump-probe polarization-based two-frame shadowgraphy setup, the formation of filamentary damage induced in bulk fused silica by a nanosecond pulse at 1064 nm is investigated with a picosecond probe. Three different phases are exhibited in the damage experiments. The first phase is the formation of a micrometric plasma channel along the laser direction during the beginning of the pulse likely caused by multi-photon ionization. This channel exhibits growth during ∼400 ps, and the newly grown plasma is discrete. Then, during the end of the pulse, this channel evolves into a tadpole-like morphology showing an elliptical head upstream the laser fluxmore » followed by a thin tail. This observed asymmetry is attributed to shielding effects caused by both the plasma and hot modified silica. Once the damage shows its almost final morphology, a last phase consists in the launch of a pressure wave enlarging it after the laser pulse. The physical mechanisms that might be involved in the formation of plasma channels are discussed. The experimental data are first confronted to the moving breakdown model which overestimates the filamentary damage length. Finally, taking into account the temporal shape of the laser pulses, the coupling between Kerr-induced self-focusing and stimulated Brillouin scattering is discussed to interpret the observations.« less

Spatial release from masking improves sound pattern discrimination along a biologically relevant pulse-rate continuum in gray treefrogs

PubMed Central

Ward, Jessica L.; Buerkle, Nathan P.; Bee, Mark A.

2013-01-01

Frogs form large choruses during the mating season in which males produce loud advertisement calls to attract females and repel rival males. High background noise levels in these social aggregations can impair vocal perception. In humans, spatial release from masking contributes to our ability to understand speech in noisy social groups. Here, we tested the hypothesis that spatial separation between target signals and ‘chorus-shaped noise’ improves the ability of female gray treefrogs (Hyla chrysoscelis) to perform a behavioral discrimination task based on perceiving differences in the pulsatile structure of advertisement calls. We used two-stimulus choice tests to measure phonotaxis (approach toward sound) in response to calls differing in pulse rate along a biologically relevant continuum between conspecific (50 pulses s−1) and heterospecific (20 pulses s−1) calls. Signals were presented in quiet, in colocated noise, and in spatially separated noise. In quiet conditions, females exhibited robust preferences for calls with relatively faster pulse rates more typical of conspecific calls. Behavioral discrimination between calls differing in pulse rate was impaired in the presence of colocated noise but similar between quiet and spatially separated noise conditions. Our results indicate that spatial release from energetic masking facilitates a biologically important temporal discrimination task in frogs. We discuss these results in light of previous work on spatial release from masking in frogs and other animals. PMID:24055623

Effect of polarization and focusing on laser pulse driven auto-resonant particle acceleration

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

Sagar, Vikram; Sengupta, Sudip; Kaw, Predhiman

2014-04-15

The effect of laser polarization and focusing is theoretically studied on the final energy gain of a particle in the Auto-resonant acceleration scheme using a finite duration laser pulse with Gaussian shaped temporal envelope. The exact expressions for dynamical variables viz. position, momentum, and energy are obtained by analytically solving the relativistic equation of motion describing particle dynamics in the combined field of an elliptically polarized finite duration pulse and homogeneous static axial magnetic field. From the solutions, it is shown that for a given set of laser parameters viz. intensity and pulse length along with static magnetic field, themore » energy gain by a positively charged particle is maximum for a right circularly polarized laser pulse. Further, a new scheme is proposed for particle acceleration by subjecting it to the combined field of a focused finite duration laser pulse and static axial magnetic field. In this scheme, the particle is initially accelerated by the focused laser field, which drives the non-resonant particle to second stage of acceleration by cyclotron Auto-resonance. The new scheme is found to be efficient over two individual schemes, i.e., auto-resonant acceleration and direct acceleration by focused laser field, as significant particle acceleration can be achieved at one order lesser values of static axial magnetic field and laser intensity.« less

Pulse Shape Correlation for Laser Detection and Ranging (LADAR)

DTIC Science & Technology

2010-03-01

with the incoming measured laser pulse [3]. All of these shapes are symmetric. Siegman and Liu’s findings indicate that the pulse is seldom symmetric...of Engineering, Air Force Institute of Technology (AETC), Wright Pat- terson AFB, OH, March 2007. 10. Siegman , Anthony E. Lasers . University Science...Pulse Shape Correlation for Laser Detection and Ranging (LADAR) THESIS Brian T. Deas, Major, USAF AFIT/GE/ENG/10-07 DEPARTMENT OF THE AIR FORCE AIR

Virtual active touch using randomly patterned intracortical microstimulation.

PubMed

O'Doherty, Joseph E; Lebedev, Mikhail A; Li, Zheng; Nicolelis, Miguel A L

2012-01-01

Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices.

Linear optical pulse compression based on temporal zone plates.

PubMed

Li, Bo; Li, Ming; Lou, Shuqin; Azaña, José

2013-07-15

We propose and demonstrate time-domain equivalents of spatial zone plates, namely temporal zone plates, as alternatives to conventional time lenses. Both temporal intensity zone plates, based on intensity-only temporal modulation, and temporal phase zone plates, based on phase-only temporal modulation, are introduced and studied. Temporal zone plates do not exhibit the limiting tradeoff between temporal aperture and frequency bandwidth (temporal resolution) of conventional linear time lenses. As a result, these zone plates can be ideally designed to offer a time-bandwidth product (TBP) as large as desired, practically limited by the achievable temporal modulation bandwidth (limiting the temporal resolution) and the amount of dispersion needed in the target processing systems (limiting the temporal aperture). We numerically and experimentally demonstrate linear optical pulse compression by using temporal zone plates based on linear electro-optic temporal modulation followed by fiber-optics dispersion. In the pulse-compression experiment based on temporal phase zone plates, we achieve a resolution of ~25.5 ps over a temporal aperture of ~5.77 ns, representing an experimental TBP larger than 226 using a phase-modulation amplitude of only ~0.8π rad. We also numerically study the potential of these devices to achieve temporal imaging of optical waveforms and present a comparative analysis on the performance of different temporal intensity and phase zone plates.

Effect of crash pulse shape on seat stroke requirements for limiting loads on occupants of aircraft

NASA Technical Reports Server (NTRS)

Carden, Huey D.

1992-01-01

An analytical study was made to provide comparative information on various crash pulse shapes that potentially could be used to test seats under conditions included in Federal Regulations Part 23 Paragraph 23.562(b)(1) for dynamic testing of general aviation seats, show the effects that crash pulse shape can have on the seat stroke requirements necessary to maintain a specified limit loading on the seat/occupant during crash pulse loadings, compare results from certain analytical model pulses with approximations of actual crash pulses, and compare analytical seat results with experimental airplace crash data. Structural and seat/occupant displacement equations in terms of the maximum deceleration, velocity change, limit seat pan load, and pulse time for five potentially useful pulse shapes were derived; from these, analytical seat stroke data were obtained for conditions as specified in Federal Regulations Part 23 Paragraph 23.562(b)(1) for dynamic testing of general aviation seats.

Quantitative ESD Guidelines for Charged Spacecraft Derived from the Physics of Discharges

NASA Technical Reports Server (NTRS)

Frederickson, A. R.

1992-01-01

Quantitative guidelines are proposed for Electrostatic Discharge (ESD) pulse shape on charged spacecraft. The guidelines are based on existing ground test data, and on a physical description of the pulsed discharge process. The guidelines are designed to predict pulse shape for surface charging and internal charging on a wide variety of spacecraft structures. The pulses depend on the area of the sample, its capacitance to ground, and the strength of the electric field in the vacuum adjacent to the charged surface. By knowing the pulse shape, current vs. time, one can determine if nearby circuits are threatened by the pulse. The quantitative guidelines might be used to estimate the level of threat to an existing spacecraft, or to redesign a spacecraft to reduce its pulses to a known safe level. The experiments which provide the data and the physics that allow one to interpret the data will be discussed, culminating in examples of how to predict pulse shape/size. This method has been used, but not confirmed, on several spacecraft.

Realizing Ultrafast Electron Pulse Self-Compression by Femtosecond Pulse Shaping Technique.

PubMed

Qi, Yingpeng; Pei, Minjie; Qi, Dalong; Yang, Yan; Jia, Tianqing; Zhang, Shian; Sun, Zhenrong

2015-10-01

Uncorrelated position and velocity distribution of the electron bunch at the photocathode from the residual energy greatly limit the transverse coherent length and the recompression ability. Here we first propose a femtosecond pulse-shaping method to realize the electron pulse self-compression in ultrafast electron diffraction system based on a point-to-point space-charge model. The positively chirped femtosecond laser pulse can correspondingly create the positively chirped electron bunch at the photocathode (such as metal-insulator heterojunction), and such a shaped electron pulse can realize the self-compression in the subsequent propagation process. The greatest advantage for our proposed scheme is that no additional components are introduced into the ultrafast electron diffraction system, which therefore does not affect the electron bunch shape. More importantly, this scheme can break the limitation that the electron pulse via postphotocathode static compression schemes is not shorter than the excitation laser pulse due to the uncorrelated position and velocity distribution of the initial electron bunch.

flexTMS--a novel repetitive transcranial magnetic stimulation device with freely programmable stimulus currents.

PubMed

Gattinger, Norbert; Moessnang, Georg; Gleich, Bernhard

2012-07-01

Transcranial magnetic stimulation (TMS) is able to noninvasively excite neuronal populations due to brief magnetic field pulses. The efficiency and the characteristics of stimulation pulse shapes influence the physiological effect of TMS. However, commercial devices allow only a minimum of control of different pulse shapes. Basically, just sinusoidal and monophasic pulse shapes with fixed pulse widths are available. Only few research groups work on TMS devices with controllable pulse parameters such as pulse shape or pulse width. We describe a novel TMS device with a full-bridge circuit topology incorporating four insulated-gate bipolar transistor (IGBT) modules and one energy storage capacitor to generate arbitrary waveforms. This flexible TMS (flexTMS ) device can generate magnetic pulses which can be adjusted with respect to pulse width, polarity, and intensity. Furthermore, the equipment allows us to set paired pulses with a variable interstimulus interval (ISI) from 0 to 20 ms with a step size of 10  μs. All user-defined pulses can be applied continually with repetition rates up to 30 pulses per second (pps) or, respectively, up to 100 pps in theta burst mode. Offering this variety of flexibility, flexTMS will allow the enhancement of existing TMS paradigms and novel research applications.

Counting-loss correction for X-ray spectroscopy using unit impulse pulse shaping.

PubMed

Hong, Xu; Zhou, Jianbin; Ni, Shijun; Ma, Yingjie; Yao, Jianfeng; Zhou, Wei; Liu, Yi; Wang, Min

2018-03-01

High-precision measurement of X-ray spectra is affected by the statistical fluctuation of the X-ray beam under low-counting-rate conditions. It is also limited by counting loss resulting from the dead-time of the system and pile-up pulse effects, especially in a high-counting-rate environment. In this paper a detection system based on a FAST-SDD detector and a new kind of unit impulse pulse-shaping method is presented, for counting-loss correction in X-ray spectroscopy. The unit impulse pulse-shaping method is evolved by inverse deviation of the pulse from a reset-type preamplifier and a C-R shaper. It is applied to obtain the true incoming rate of the system based on a general fast-slow channel processing model. The pulses in the fast channel are shaped to unit impulse pulse shape which possesses small width and no undershoot. The counting rate in the fast channel is corrected by evaluating the dead-time of the fast channel before it is used to correct the counting loss in the slow channel.

Compton suppression in BEGe detectors by digital pulse shape analysis.

PubMed

Mi, Yu-Hao; Ma, Hao; Zeng, Zhi; Cheng, Jian-Ping; Li, Jun-Li; Zhang, Hui

2017-03-01

A new method of pulse shape discrimination (PSD) for BEGe detectors is developed to suppress Compton-continuum by digital pulse shape analysis (PSA), which helps reduce the Compton background level in gamma ray spectrometry. A decision parameter related to the rise time of a pulse shape was presented. The method was verified by experiments using 60 Co and 137 Cs sources. The result indicated that the 60 Co Peak to Compton ratio and the Cs-Peak to Co-Compton ratio could be improved by more than two and three times, respectively. Copyright © 2016 Elsevier Ltd. All rights reserved.

Components for monolithic fiber chirped pulse amplification laser systems

NASA Astrophysics Data System (ADS)

Swan, Michael Craig

The first portion of this work develops techniques for generating femtosecond-pulses from conventional fabry-perot laser diodes using nonlinear-spectral-broadening techniques in Yb-doped positive dispersion fiber ampliers. The approach employed an injection-locked fabry-perot laser diode followed by two stages of nonlinear-spectral-broadening to generate sub-200fs pulses. This thesis demonstrated that a 60ps gain-switched fabry-perot laser-diode can be injection-locked to generate a single-longitudinal-mode pulse and compressed by nonlinear spectral broadening to 4ps. Two problems have been identified that must be resolved before moving forward with this approach. First, gain-switched pulses from a standard diode-laser have a number of characteristics not well suited for producing clean self-phase-modulation-broadened pulses, such as an asymmetric temporal shape, which has a long pulse tail. Second, though parabolic pulse formation occurs for any arbitrary temporal input pulse profile, deviation from the optimum parabolic input results in extensively spectrally modulated self-phase-modulation-broadened pulses. In conclusion, the approach of generating self-phase-modulation-broadened pulses from pulsed laser diodes has to be modified from the initial approach explored in this thesis. The first Yb-doped chirally-coupled-core ber based systems are demonstrated and characterized in the second portion of this work. Robust single-mode performance independent of excitation or any other external mode management techniques have been demonstrated in Yb-doped chirally-coupled-core fibers. Gain and power efficiency characteristics are not compromised in any way in this novel fiber structure up to the 87W maximum power achieved. Both the small signal gain at 1064nm of 30.3dB, and the wavelength dependence of the small signal gain were comparable to currently deployed large-mode-area-fiber technology. The efficiencies of the laser and amplifier were measured to be 75% and 54% respectively. With the inherent design tradeoff between the fundamental mode loss and higher order mode suppression, loss effects on system efficiency in different configurations were investigated. From these investigations it was seen that the slope-efficiency depends only on the total loss of the active fiber, and that when loss is present, the counter-propagating configuration has substantial advantages over the co-propagating case. In this thesis chirally-coupled-core fiber as the technological basis for the next generation of monolithic high power fiber laser systems has been established.

Synchronization scenarios in the Winfree model of coupled oscillators

NASA Astrophysics Data System (ADS)

Gallego, Rafael; Montbrió, Ernest; Pazó, Diego

2017-10-01

Fifty years ago Arthur Winfree proposed a deeply influential mean-field model for the collective synchronization of large populations of phase oscillators. Here we provide a detailed analysis of the model for some special, analytically tractable cases. Adopting the thermodynamic limit, we derive an ordinary differential equation that exactly describes the temporal evolution of the macroscopic variables in the Ott-Antonsen invariant manifold. The low-dimensional model is then thoroughly investigated for a variety of pulse types and sinusoidal phase response curves (PRCs). Two structurally different synchronization scenarios are found, which are linked via the mutation of a Bogdanov-Takens point. From our results, we infer a general rule of thumb relating pulse shape and PRC offset with each scenario. Finally, we compare the exact synchronization threshold with the prediction of the averaging approximation given by the Kuramoto-Sakaguchi model. At the leading order, the discrepancy appears to behave as an odd function of the PRC offset.

Pulsed Thermal Emission from the Accreting Pulsar XMMU J054134.7-682550

NASA Astrophysics Data System (ADS)

Manousakis, Antonis; Walter, Roland; Audard, Marc; Lanz, Thierry

2009-05-01

XMMU J054134.7-682550, located in the LMC, featured a type II outburst in August 2007. We analyzed XMM-Newton (EPIC-MOS) and RXTE (PCA) data in order to derive the spectral and temporal characteristics of the system throughout the outburst. Spectral variability, spin period evolution, energy dependent pulse shape are discussed. The outburst (LX~3×1038 erg/s~LEDD) spectrum can be modeled using, cutoff power law, soft X-ray blackbody, disk emission, and cyclotron absorption line. The blackbody component shows a sinusoidal behavior, expected from hard X-ray reprocessing on the inner edge of the accretion disk. The thickness of the inner accretion disk (width of ~75 km) can be constrained. The spin-up of the pulsar during the outburst is the signature of a (huge) accretion rate. Simbol-X will provide similar capabilities as XMM-Newton and RXTE together, for such bright events.

Modeling of a UV laser beam—silicon nitride interaction

NASA Astrophysics Data System (ADS)

Dgheim, J. A.

2016-11-01

A numerical model is developed to study heat and radiation transfers during the interaction between a UV laser beam and silicon nitride. The laser beam has temporal Gaussian or Gate shapes of a wavelength of 247 nm, with pulse duration of 27 ns. The mathematical model is based on the heat equation coupled to Lambert-Beer relationship by taking into account the conduction, convection and radiation phenomena. The resulting equations are schemed by the finite element method. Comparison with the literature shows qualitative and quantitative agreements. The investigated parameters are the temperature, the timing of the melting process and the melting phase thickness. The effects of the laser fluences, ranging from 500 to 16 000 J.m-2, the Gaussian and Gate shapes on the heat transfer, and the melting phenomenon are studied.

Femtosecond dynamics of energetic electrons in high intensity laser-matter interactions

NASA Astrophysics Data System (ADS)

Pompili, R.; Anania, M. P.; Bisesto, F.; Botton, M.; Castellano, M.; Chiadroni, E.; Cianchi, A.; Curcio, A.; Ferrario, M.; Galletti, M.; Henis, Z.; Petrarca, M.; Schleifer, E.; Zigler, A.

2016-10-01

Highly energetic electrons are generated at the early phases of the interaction of short-pulse high-intensity lasers with solid targets. These escaping particles are identified as the essential core of picosecond-scale phenomena such as laser-based acceleration, surface manipulation, generation of intense magnetic fields and electromagnetic pulses. Increasing the number of the escaping electrons facilitate the late time processes in all cases. Up to now only indirect evidences of these important forerunners have been recorded, thus no detailed study of the governing mechanisms was possible. Here we report, for the first time, direct time-dependent measurements of energetic electrons ejected from solid targets by the interaction with a short-pulse high-intensity laser. We measured electron bunches up to 7 nanocoulombs charge, picosecond duration and 12 megaelectronvolts energy. Our ’snapshots’ capture their evolution with an unprecedented temporal resolution, demonstrat- ing a significant boost in charge and energy of escaping electrons when increasing the geometrical target curvature. These results pave the way toward significant improvement in laser acceleration of ions using shaped targets allowing the future development of small scale laser-ion accelerators.

Hong-Ou-Mandel Interference Between Triggered And Heralded Single Photons From Separate Atomic Systems

NASA Astrophysics Data System (ADS)

Cere, Alessandro; Leong, Victor; Kaur Gulati, Gurpreet; Srivathsan, Bharath; Kosen, Sandoko; Kurtsiefer, Christian

2015-05-01

The realization of quantum networks and long distance quantum communication rely on the capability of generating entanglement between separated nodes. We demonstrate the compatibility of two different sources of single photons: a single atom and four-wave mixing in a cold cloud of atoms. The four-wave mixing process in a cloud of cold 87Rb generates photon pairs. The cascade level scheme used ensures the generation of heralded single photons with exponentially decaying temporal envelope. The temporal shape of the heralding photons matches the shape of photons emitted by spontaneous decay but for the shorter coherence time A single 87Rb atom is trapped in an far-off-resonance optical dipole trap and can be excited with high probability using a short (~3 ns) intense pulse of resonant light, emitting a single photon by spontaneous decay. A large numerical aperture lens collects ~4% of the total fluorescence. The heralded and the triggered photons are launched into a Houng-Ou-Mandel interferometer: a symmetrical beam-splitter with outputs connected to single photon detectors. Scanning the relative delay between the two sources we observe the HOM dip with a maximum visibility of 70 +/-4%.

Second-order shaped pulsed for solid-state quantum computation

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

Sengupta, Pinaki

2008-01-01

We present the construction and detailed analysis of highly optimized self-refocusing pulse shapes for several rotation angles. We characterize the constructed pulses by the coefficients appearing in the Magnus expansion up to second order. This allows a semianalytical analysis of the performance of the constructed shapes in sequences and composite pulses by computing the corresponding leading-order error operators. Higher orders can be analyzed with the numerical technique suggested by us previously. We illustrate the technique by analyzing several composite pulses designed to protect against pulse amplitude errors, and on decoupling sequences for potentially long chains of qubits with on-site andmore » nearest-neighbor couplings.« less

Beam engineering for zero conicity cutting and drilling with ultra fast laser (Conference Presentation)

NASA Astrophysics Data System (ADS)

Letan, Amelie; Mishchik, Konstantin; Audouard, Eric; Hoenninger, Clemens; Mottay, Eric P.

2017-03-01

With the development of high average power, high repetition rate, industrial ultrafast lasers, it is now possible to achieve a high throughput with femtosecond laser processing, providing that the operating parameters are finely tuned to the application. Femtosecond lasers play a key role in these processes, due to their ability to high quality micro processing. They are able to drill high thickness holes (up to 1 mm) with arbitrary shapes, such as zero-conicity or even inversed taper, but can also perform zero-taper cutting. A clear understanding of all the processing steps necessary to optimize the processing speed is a main challenge for industrial developments. Indeed, the laser parameters are not independent of the beam steering devices. Pulses energy and repetition rate have to be precisely adjusted to the beam angle with the sample, and to the temporal and spatial sequences of pulses superposition. The purpose of the present work is to identify the role of these parameters for high aspect ratio drilling and cutting not only with experimental trials, but also with numerical estimations, using a simple engineering model based on the two temperature description of ultra-fast ablation. Assuming a nonlinear logarithmic response of the materials to ultrafast pulses, each material can be described by only two adjustable parameters. Simple assumptions allow to predict the effect of beam velocity and non-normal incident beams to estimate profile shapes and processing time.

Driving qubit phase gates with sech shaped pulses

NASA Astrophysics Data System (ADS)

Long, Junling; Ku, Hsiang-Sheng; Wu, Xian; Lake, Russell; Barnes, Edwin; Economou, Sophia; Pappas, David

As shown in 1932 by Rozen and Zener, the Rabi model has a unique solution whereby, for a given pulse length or amplitude, a sech(t/sigma) shaped pulse can be used to drive complete oscillations around the Bloch sphere that are independent of detuning with only a resultant detuning-dependent phase accumulation. Using this property, single qubit phase gates and two-qubit CZ gates have been proposed. In this work we explore the effect of different drive pulse shapes, i.e. square, Gaussian, and sech, as a function of detuning for Rabi oscillations of a superconducting transmon qubit. An arbitrary, single-qubit phase gate is demonstrated with the sech(t/sigma) pulse, and full tomography is performed to extract the fidelity. This is the first step towards high fidelity, low leakage two qubit CZ gates, and illustrates the efficacy of using analytic solutions of the qubit drive prior to optimal pulse shaping.

Wilcoxon signed-rank-based technique for the pulse-shape analysis of HPGe detectors

NASA Astrophysics Data System (ADS)

Martín, S.; Quintana, B.; Barrientos, D.

2016-07-01

The characterization of the electric response of segmented-contact high-purity germanium detectors requires scanning systems capable of accurately associating each pulse with the position of the interaction that generated it. This process requires an algorithm sensitive to changes above the electronic noise in the pulse shapes produced at different positions, depending on the resolution of the Ge crystal. In this work, a pulse-shape comparison technique based on the Wilcoxon signed-rank test has been developed. It provides a method to distinguish pulses coming from different interaction points in the germanium crystal. Therefore, this technique is a necessary step for building a reliable pulse-shape database that can be used later for the determination of the position of interaction for γ-ray tracking spectrometry devices such as AGATA, GRETA or GERDA. The method was validated by comparison with a χ2 test using simulated and experimental pulses corresponding to a Broad Energy germanium detector (BEGe).

Optimal Dynamic Detection of Explosives (ODD-EX)

DTIC Science & Technology

2011-12-29

2. Control of nitromethane photoionization efficiency with shaped femtosecond pulses, J. Roslund, O. Shir, A. Dogariu, R. Miles, H. Rabitz, J. Chem...feedback loop. 2. Control of nitromethane photoionization efficiency with shaped femtosecond pulses, J. Roslund, O. Shir, A. Dogariu, R. Miles, H. Rabitz...resonances that allow a significant increase in the photoionization efficiency of nitromethane with shaped near-infrared femtosecond pulses. The

A survey of pulse shape options for a revised plastic ablator ignition design

NASA Astrophysics Data System (ADS)

Clark, Daniel; Eder, David; Haan, Steven; Hinkel, Denise; Jones, Ogden; Marinak, Michael; Milovich, Jose; Peterson, Jayson; Robey, Harold; Salmonson, Jay; Smalyuk, Vladimir; Weber, Christopher

2014-10-01

Recent experimental results using the ``high foot'' pulse shape on the National Ignition Facility (NIF) have shown encouraging progress compared to earlier ``low foot'' experiments. These results strongly suggest that controlling ablation front instability growth can dramatically improve implosion performance, even in the presence of persistent, large, low-mode distortions. In parallel, Hydro. Growth Radiography experiments have so far validated the techniques used for modeling ablation front growth in NIF experiments. It is timely then to combine these two results and ask how current ignition pulse shapes could be modified so as to improve implosion performance, namely fuel compressibility, while maintaining the stability properties demonstrated with the high foot. This talk presents a survey of pulse shapes intermediate between the low and high foot extremes in search of a more optimal design. From the database of pulse shapes surveyed, a higher picket version of the original low foot pulse shape shows the most promise for improved compression without loss of stability. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Virtual Active Touch Using Randomly Patterned Intracortical Microstimulation

PubMed Central

O’Doherty, Joseph E.; Lebedev, Mikhail A.; Li, Zheng; Nicolelis, Miguel A.L.

2012-01-01

Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices. PMID:22207642

Kisspeptin and LH pulsatile temporal coupling in PCOS patients.

PubMed

Katulski, Krzysztof; Podfigurna, Agnieszka; Czyzyk, Adam; Meczekalski, Blazej; Genazzani, Alessandro D

2018-05-04

To evaluate the temporal coupling between spontaneous kisspeptin and luteinizing hormone (LH) pulsatile releases in polycystic ovary syndrome (PCOS) patients. We examined 71 patients diagnosed with PCOS. A 2 h pulsatility study was performed to evaluate serum kisspeptin and LH pulse frequency and concentration, sampled every 10 min; baseline follicle-stimulating hormone (FSH), estradiol (E2), prolactin (PRL), cortisol, 17-hydroksy-progesterone (17OHP), testosterone (T), free testosterone index (FTI, and insulin levels were also measured. Detect and Specific Concordance (SC) algorithms were used to evaluate the temporal coupling associations between spontaneous episodic secretion of kisspeptin and LH. All PCOS patients demonstrated LH and kisspeptin pulsatile secretions. When the SC index was calculated across the sample of PCOS patients (n = 71), no temporal coupling was observed between kisspeptin and LH pulses. When PCOS patients were subdivided according to their menstrual cyclicity, oligomenorrheic patients demonstrated elevated kisspeptin pulse frequency. Additionally, the SC index reveled a temporal coupling between kisspeptin and LH secretory peaks only in eumenorrheic patients (n = 30, intermenstrual interval < 45 days). Oligomenorrheic PCOS patients (intermenstrual interval > 45 days) did not demonstrate temporal coupling between kisspeptin and LH secretory peaks. The study of the endogenous kisspeptin and LH pulsatile release revealed the temporal coupling of kisspeptin with LH secretory pulses only in eumenorrheic. This data supports the hypothesis that neuroendocrine impairments in PCOS affect the coupling of kisspeptin with LH pulses and potentially worsen as the disease progresses, becoming unequivocally evident in oligomenorrheic PCOS patients.

What is the Temporal Analog of Reflection and Refraction of Optical Beams?

PubMed

Plansinis, B W; Donaldson, W R; Agrawal, G P

2015-10-30

It is shown numerically and analytically that when an optical pulse approaches a moving temporal boundary across which the refractive index changes, it undergoes a temporal equivalent of reflection and refraction of optical beams at a spatial boundary. The main difference is that the role of angles is played by changes in the frequency. The frequency dependence of the dispersion of the material in which the pulse is propagating plays a fundamental role in determining the frequency shifts experienced by the reflected and refracted pulses. Our analytic expressions for these frequency shifts allow us to find the condition under which an analog of total internal reflection may occur at the temporal boundary.

Laser-pulse shape effects on magnetic field generation in underdense plasmas

NASA Astrophysics Data System (ADS)

Gopal, Krishna; Raja, Md. Ali; Gupta, Devki Nandan; Avinash, K.; Sharma, Suresh C.

2018-07-01

Laser pulse shape effect has been considered to estimate the self-generated magnetic field in laser-plasma interaction. A ponderomotive force based physical mechanism has been proposed to investigate the self-generated magnetic field for different spatial profiles of the laser pulse in inhomogeneous plasmas. The spatially inhomogeneous electric field of a laser pulse imparts a stronger ponderomotive force on plasma electrons. Thus, the stronger ponderomotive force associated with the asymmetric laser pulse generates a stronger magnetic field in comparison to the case of a symmetric laser pulse. Scaling laws for magnetic field strength with the laser and plasma parameters for different shape of the pulse have been suggested. Present study might be helpful to understand the plasma dynamics relevant to the particle trapping and injection in laser-plasma accelerators.

The time resolved measurement of ultrashort terahertz-band electric fields without an ultrashort probe

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

Walsh, D. A., E-mail: david.walsh@stfc.ac.uk; Snedden, E. W.; Jamison, S. P.

The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG (frequency resolved optical gating) measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe, and self-referenced FROG makes the technique inherently immunemore » to timing jitter between the optical probe and THz pulse and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators.« less

TW-class hollow-fiber compressor with tunable pulse duration (Conference Presentation)

NASA Astrophysics Data System (ADS)

Boehle, Frederik; Vernier, Aline; Kretschmar, Martin; Jullien, Aurélie; Kovacs, Mate; Romero, Rosa M.; Crespo, Helder M.; Simon, Peter; Nagy, Tamas; Lopez-Martens, Rodrigo

2017-05-01

CEP-stable few-cycle light pulses find numerous applications in attosecond science, most notably the production of isolated attosecond pulses for studying ultrafast electronic processes in matter [1]. Scaling up the pulse energy of few-cycle pulses could extend the scope of applications to even higher intensity processes, such as attosecond dynamics of relativistic plasma mirrors [2]. Hollow fiber compressors are widely used to produce few-cycle pulses with excellent spatiotemporal quality [3], where octave-spanning broadened spectra can be temporally compressed to sub-2-cycle duration [4,5]. Several tricks help increase the output energy: using circularly polarized light [6], applying a pressure gradient along the fiber [7] or even temporal multiplexing [8]. The highest pulse energy of 5 mJ at 5 fs pulse duration was achieved by using a hollow fiber in pressure gradient mode [9] but in this case no CEP stabilization was achieved, which is crucial for most applications of few-cycle pulses. Nevertheless, it did show that in order to scale up the peak power, the effective length and area mode of the fiber had to be increased proportionally, thereby requiring the use of longer waveguides with larger apertures. Thanks to an innovative design utilizing stretched flexible capillaries [10], we recently demonstrated the generation CEP-stable sub-4fs pulses with 3mJ energy using a 2m length 450mm bore hollow fiber in pressure gradient mode [11]. Here, we show that a stretched hollow-fiber compressor operated in pressure gradient mode can generate relativistic intensity pulses with continuously tunable waveform down to almost a single cycle (3.5fs at 750nm central wavelength). The pulses are characterized online using an integrated d-scan device directly under vacuum [12]. While the pulse shape is tuned, all other pulse characteristics, such as energy, pointing stability and focal distribution remain the same on target, making it possible to explore the dynamics of plasma mirrors using controllable relativistic-intensity light waveforms at 1kHz. [1] Krausz and Ivanov, Rev. Mod. Phys. 81, 163 (2009). [2] Borot et al., Nature Phys. 8, 417-421 (2012). [3] Nisoli et al., Appl. Phys. Lett. 68, 2793-2795 (1996). [4] Park et al., Opt. Lett. 34, 2342-2344 (2009). [5] Schweinberger et al., Opt. Lett. 37, 3573-5 (2012). [6] Chen et al., Opt. Lett. 34, 1588-1590 (2009). [7] Suda et al., Appl. Phys. Lett. 86, 111116 (2005). [8] Jacqmin et al., Opt. Lett. 40, 709-712 (2015) [9] Bohman et al., Opt. Lett. 35, 1887-9 (2010). [10] Nagy et al., Appl. Opt. 47, 3264-3268 (2008). [11] Boehle et al., Las. Phys. Lett. 11, 095401 (2014). [12] Miranda et al., Opt. Express 20, 18732-43 (2012)

Method for distance determination using range-gated imaging suitable for an arbitrary pulse shape

NASA Astrophysics Data System (ADS)

Kabashnikov, Vitaly; Kuntsevich, Boris

2017-10-01

A method for distance determination with the help of range-gated viewing systems suitable for the arbitrary shape of the illumination pulse is proposed. The method is based on finding the delay time at which maximum of the return pulse energy takes place. The maximum position depends on the pulse and gate durations and, generally speaking, on the pulse shape. If the pulse length is less than or equal to the gate duration, the delay time appropriate to the maximum does not depend on the pulse shape. At equal pulse and gate durations, there is a strict local maximum, which turns into a plateau when pulse is shorter than gate duration. A delay time appropriate to the strict local maximum or the far boundary of the plateau (where non-strict maximum is) is directly related to the distance to the object. These findings are confirmed by analytical relationships for trapezoid pulses and numerical results for the real pulse shape. To verify the proposed method we used a vertical wall located at different distances from 15 to 120m as an observed object. Delay time was changing discretely in increments of 5 ns. Maximum of the signal was determined by visual observation of the object on the monitor screen. The distance defined by the proposed method coincided with the direct measurement with accuracy 1- 2m, which is comparable with the delay time step multiplied by half of the light velocity. The results can be useful in the development of 3-D vision systems.

Flying mirror model for interaction of a super-intense laser pulse with a thin plasma layer: Transparency and shaping of linearly polarized laser pulses

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

Kulagin, Victor V.; Cherepenin, Vladimir A.; Hur, Min Sup

2007-11-15

A self-consistent one-dimensional (1D) flying mirror model is developed for description of an interaction of an ultra-intense laser pulse with a thin plasma layer (foil). In this model, electrons of the foil can have large longitudinal displacements and relativistic longitudinal momenta. An approximate analytical solution for a transmitted field is derived. Transmittance of the foil shows not only a nonlinear dependence on the amplitude of the incident laser pulse, but also time dependence and shape dependence in the high-transparency regime. The results are compared with particle-in-cell (PIC) simulations and a good agreement is ascertained. Shaping of incident laser pulses usingmore » the flying mirror model is also considered. It can be used either for removing a prepulse or for reducing the length of a short laser pulse. The parameters of the system for effective shaping are specified. Predictions of the flying mirror model for shaping are compared with the 1D PIC simulations, showing good agreement.« less

Attosecond-resolved photoionization of chiral molecules.

PubMed

Beaulieu, S; Comby, A; Clergerie, A; Caillat, J; Descamps, D; Dudovich, N; Fabre, B; Géneaux, R; Légaré, F; Petit, S; Pons, B; Porat, G; Ruchon, T; Taïeb, R; Blanchet, V; Mairesse, Y

2017-12-08

Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light-propagation axis. We implemented self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wave packets emitted upon photoionization of camphor by circularly polarized laser pulses. We measured a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wave packets emitted through an autoionizing state further reveals the chiral character of strongly correlated electronic dynamics. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Nanosecond pulse shaping at 780 nm with fiber-based electro-optical modulators and a double-pass tapered amplifier

DOE PAGES

Rogers, III, C. E.; Gould, P. L.

2016-02-01

Here, we describe a system for generating frequency-chirped and amplitude-shaped pulses on time scales from sub-nanosecond to ten nanoseconds. The system starts with cw diode-laser light at 780 nm and utilizes fiber-based electro-optical phase and intensity modulators, driven by an arbitrary waveform generator, to generate the shaped pulses. These pulses are subsequently amplified to several hundred mW with a tapered amplifier in a delayed double-pass configuration. Frequency chirps up to 5 GHz in 2 ns and pulse widths as short as 0.15 ns have been realized.

Nanosecond pulse shaping at 780 nm with fiber-based electro-optical modulators and a double-pass tapered amplifier.

PubMed

Rogers, C E; Gould, P L

2016-02-08

We describe a system for generating frequency-chirped and amplitude-shaped pulses on time scales from sub-nanosecond to ten nanoseconds. The system starts with cw diode-laser light at 780 nm and utilizes fiber-based electro-optical phase and intensity modulators, driven by an arbitrary waveform generator, to generate the shaped pulses. These pulses are subsequently amplified to several hundred mW with a tapered amplifier in a delayed double-pass configuration. Frequency chirps up to 5 GHz in 2 ns and pulse widths as short as 0.15 ns have been realized.

Cavity length dependence of mode beating in passively Q-switched Nd-solid state lasers

NASA Astrophysics Data System (ADS)

Zameroski, Nathan D.; Wanke, Michael; Bossert, David

2013-03-01

The temporal intensity profile of pulse(s) from passively Q-switched and passively Q-switched mode locked (QSML) solid-state lasers is known to be dependent on cavity length. In this work, the pulse width, modulation depth, and beat frequencies of a Nd:Cr:GSGG laser using a Cr+4:YAG passive Q-switch are investigated as function cavity length. Measured temporal widths are linearly correlated with cavity length but generally 3-5 ns larger than theoretical predictions. Some cavity lengths exhibit pulse profiles with no modulation while other lengths exhibit complete amplitude modulation. The observed beat frequencies at certain cavity lengths cannot be accounted for with passively QSML models in which the pulse train repetition rate is τRT-1, τRT= round-trip time. They can be explained, however, by including coupled cavity mode-locking effects. A theoretical model developed for a two section coupled cavity semiconductor laser is adapted to a solid-state laser to interpret measured beat frequencies. We also numerically evaluate the temporal criterion required to achieve temporally smooth Q-switched pulses, versus cavity length and pump rate. We show that in flash lamp pumped systems, the difference in buildup time between longitudinal modes is largely dependent on the pump rate. In applications where short pulse delay is important, the pumping rate may limit the ability to achieve temporally smooth pulses in passively Q-switched lasers. Simulations support trends in experimental data. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Evidence for speckle effects on pulsed CO2 lidar signal returns from remote targets

NASA Technical Reports Server (NTRS)

Menzies, R. T.; Kavaya, M. J.; Flamant, P. H.

1984-01-01

A pulsed CO2 lidar was used to study statistical properties of signal returns from various rough surfaces at distances near 2 km. These included natural in situ topographic materials as well as man-made hard targets. Three lidar configurations were used: heterodyne detection with single temporal mode transmitter pulses, and direct detection with single and multiple temporal mode pulses. The significant differences in signal return statistics, due largely to speckle effects, are discussed.

Analytical optimal pulse shapes obtained with the aid of genetic algorithms

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

Guerrero, Rubén D., E-mail: rdguerrerom@unal.edu.co; Arango, Carlos A.; Reyes, Andrés

2015-09-28

We propose a methodology to design optimal pulses for achieving quantum optimal control on molecular systems. Our approach constrains pulse shapes to linear combinations of a fixed number of experimentally relevant pulse functions. Quantum optimal control is obtained by maximizing a multi-target fitness function using genetic algorithms. As a first application of the methodology, we generated an optimal pulse that successfully maximized the yield on a selected dissociation channel of a diatomic molecule. Our pulse is obtained as a linear combination of linearly chirped pulse functions. Data recorded along the evolution of the genetic algorithm contained important information regarding themore » interplay between radiative and diabatic processes. We performed a principal component analysis on these data to retrieve the most relevant processes along the optimal path. Our proposed methodology could be useful for performing quantum optimal control on more complex systems by employing a wider variety of pulse shape functions.« less

Ultrafast and Doppler-free femtosecondoptical ranging based on dispersivefrequency-modulated interferometry.

PubMed

Xia, Haiyun; Zhang, Chunxi

2010-03-01

An ultrafast and Doppler-free optical ranging system based on dispersive frequency-modulated interferometry is demonstrated. The principle is similar to the conventional frequency-modulated continuous-wave interferometry where the range information is derived from the beat frequency between the object signal and the reference signal. However, a passive and static frequency scanning is performed based on the chromatic dispersion of a transform-limited femtosecond pulse in the time domain. We point out that the unbalanced dispersion introduced in the Mach-Zehnder interferometer can be optimized to eliminate the frequency chirp in the temporal interferograms pertaining to the third order dispersion of the all-fiber system, if the dynamic range being considered is small. Some negative factors, such as the polarization instability of the femtosecond pulse, the power fluctuation of the optical signal and the nonuniform gain spectrum of the erbium-doped fiber amplifier lead to an obvious envelope deformation of the temporal interferograms from the Gaussian shape. Thus a new data processing method is proposed to guarantee the range resolution. In the experiment, the vibration of a speaker is measured. A range resolution of 1.59 microm is achieved with an exposure time of 394 fs at a sampling rate of 48.6 MHz.

Pulse shaping system research of CdZnTe radiation detector for high energy x-ray diagnostic

NASA Astrophysics Data System (ADS)

Li, Miao; Zhao, Mingkun; Ding, Keyu; Zhou, Shousen; Zhou, Benjie

2018-02-01

As one of the typical wide band-gap semiconductor materials, the CdZnTe material has high detection efficiency and excellent energy resolution for the hard X-ray and the Gamma ray. The generated signal of the CdZnTe detector needs to be transformed to the pseudo-Gaussian pulse with a small impulse-width to remove noise and improve the energy resolution by the following nuclear spectrometry data acquisition system. In this paper, the multi-stage pseudo-Gaussian shaping-filter has been investigated based on the nuclear electronic principle. The optimized circuit parameters were also obtained based on the analysis of the characteristics of the pseudo-Gaussian shaping-filter in our following simulations. Based on the simulation results, the falling-time of the output pulse was decreased and faster response time can be obtained with decreasing shaping-time τs-k. And the undershoot was also removed when the ratio of input resistors was set to 1 to 2.5. Moreover, a two stage sallen-key Gaussian shaping-filter was designed and fabricated by using a low-noise voltage feedback operation amplifier LMH6628. A detection experiment platform had been built by using the precise pulse generator CAKE831 as the imitated radiation pulse which was equivalent signal of the semiconductor CdZnTe detector. Experiment results show that the output pulse of the two stage pseudo-Gaussian shaping filter has minimum 200ns pulse width (FWHM), and the output pulse of each stage was well consistent with the simulation results. Based on the performance in our experiment, this multi-stage pseudo-Gaussian shaping-filter can reduce the event-lost caused by pile-up in the CdZnTe semiconductor detector and improve the energy resolution effectively.

Multi-pulse frequency shifted (MPFS) multiple access modulation for ultra wideband

DOEpatents

Nekoogar, Faranak [San Ramon, CA; Dowla, Farid U [Castro Valley, CA

2012-01-24

The multi-pulse frequency shifted technique uses mutually orthogonal short duration pulses o transmit and receive information in a UWB multiuser communication system. The multiuser system uses the same pulse shape with different frequencies for the reference and data for each user. Different users have a different pulse shape (mutually orthogonal to each other) and different transmit and reference frequencies. At the receiver, the reference pulse is frequency shifted to match the data pulse and a correlation scheme followed by a hard decision block detects the data.

Method of and apparatus for measuring vapor density

DOEpatents

Nelson, Loren D.; Cerni, Todd A.

1989-01-01

Apparatus and method determine the concentration of an individual component, such as water vapor, of a multi-component mixture, such as a gaseous mixture for cooling a nuclear reactor. A hygrometer apparatus includes an infrared source for producing a broadband infrared energy beam that includes a strong water vapor absorption band and a weak water vapor absorption region. The beam is chopped to select infrared pulses. A temporally first pulse has a wavelength in the weakly absorbing region, a temporally second pulse has a wavelength in the strong band and a temporally third pulse has a wavlength in the weakly absorbing region. A fourth reference pulse representing background radiation is interposed in such chopped pulses. An indium arsenide infrared sensor is responsive to the pulses for generating an output signal in proportion to: ##EQU1## where N1 is proportional to the transmission through the sample of the first signal, N4 is related to the background radiation, and [K2 (N2-N4)+K3 (N3-N4)] is the time-weighted average of the transmission through the sample of the second and third pulses applicable at the time of the second pulse, with the reference pulse N4 being subtracted in each case to render the ratio independent of variations in the background radiation.

Femtosecond laser pulse distortion in Ti:sapphire multipass amplifier by atomic phase shifts

NASA Astrophysics Data System (ADS)

Hwang, Seungjin; Jeong, Jihoon; Cho, Seryeyohan; Lee, Jongmin; Yu, Tae Jun

2017-11-01

We have derived modified Frantz-Nodvik equations that simultaneously account for atomic phase shift (APS) and gain depletion as the chirped laser pulse passes through a gain medium, and have analyzed the effect of temporal pulse distortion in a Ti:sapphire multipass amplifier chain. The combination of APS and gain depletion distorted a temporal pulse and decreased the peak power. The pulse width increased from 21.3 fs to 22.8 fs and the peak power reduced to 89% for the PW class Ti:sapphire CPA laser system in the particular conditions.

Perspectives of shaped pulses for EPR spectroscopy

NASA Astrophysics Data System (ADS)

Spindler, Philipp E.; Schöps, Philipp; Kallies, Wolfgang; Glaser, Steffen J.; Prisner, Thomas F.

2017-07-01

This article describes current uses of shaped pulses, generated by an arbitrary waveform generator, in the field of EPR spectroscopy. We show applications of sech/tanh and WURST pulses to dipolar spectroscopy, including new pulse schemes and procedures, and discuss the more general concept of optimum-control-based pulses for applications in EPR spectroscopy. The article also describes a procedure to correct for experimental imperfections, mostly introduced by the microwave resonator, and discusses further potential applications and limitations of such pulses.

Phase stabilization of multidimensional amplification architectures for ultrashort pulses

NASA Astrophysics Data System (ADS)

Müller, M.; Kienel, M.; Klenke, A.; Eidam, T.; Limpert, J.; Tünnermann, A.

2015-03-01

The active phase stabilization of spatially and temporally combined ultrashort pulses is investigated theoretically and experimentally. Particularly, considering a combining scheme applying 2 amplifier channels and 4 divided-pulse replicas a bistable behavior is observed. The reason is mutual influence of the optical error signals that is intrinsic to temporal polarization beam combining. A successful mitigation strategy is proposed and is analyzed theoretically and experimentally.

Femtosecond optical packet generation by a direct space-to-time pulse shaper.

PubMed

Leaird, D E; Weiner, A M

1999-06-15

We demonstrate femtosecond operation of a direct space-to-time pulse shaper in which there is direct mapping (no Fourier transform) between the spatial position of the masking function and the temporal position in the output waveform. We use this apparatus to generate trains of 20 pulses as an ultrafast optical data packet over an approximately 40-ps temporal window.

Dye laser traveling wave amplifier

NASA Technical Reports Server (NTRS)

Davidson, F.; Hohman, J.

1984-01-01

A flashlamp pumped dye laser suitable for use as a single stage amplifier is described. Particular emphasis is placed on the efforts to increase output pulse energy and improve the temporal profile of the injected pulse. By using high power thin film polarizers, output energies reach from 4 to 45 mJ. Various dispersive elements are used to develop an amplified pulse with an extremely clean temporal profile.

Generation and multi-octave shaping of mid-infrared intense single-cycle pulses

NASA Astrophysics Data System (ADS)

Krogen, Peter; Suchowski, Haim; Liang, Houkun; Flemens, Noah; Hong, Kyung-Han; Kärtner, Franz X.; Moses, Jeffrey

2017-03-01

The generation of intense mid-infrared (mid-IR) optical pulses with customizable shape and spectra spanning a multiple-octave range of vibrational frequencies is an elusive technological capability. While some recent approaches to mid-IR supercontinuum generation—such as filamentation, multicolour four-wave-mixing and optical rectification—have successfully generated broad spectra, no process has been identified for achieving complex pulse shaping at the generation step. The adiabatic frequency converter allows for a one-to-one transfer of spectral phase through nonlinear frequency conversion over a larger-than-octave-spanning range and with an overall linear phase transfer function. Here, we show that we can convert shaped near-infrared (near-IR) pulses to shaped, energetic, multi-octave-spanning mid-IR pulses lasting only 1.2 optical cycles, and extendable to the sub-cycle regime. We expect this capability to enable a new class of precisely controlled nonlinear interactions in the mid-IR spectral range, from nonlinear vibrational spectroscopy to strong light-matter interactions and single-shot remote sensing.

Pulse analysis of acoustic emission signals. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Houghton, J. R.

1976-01-01

A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio are examined in the frequency domain analysis, and pulse shape deconvolution is developed for use in the time domain analysis. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameters values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emissions associated with: (1) crack propagation, (2) ball dropping on a plate, (3) spark discharge and (4) defective and good ball bearings.

Interaction between pulsed discharge and radio frequency discharge burst at atmospheric pressure

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

Zhang, Jie; College of Science, Donghua University, Shanghai 201620; Guo, Ying

The atmospheric pressure glow discharges (APGD) with dual excitations in terms of pulsed voltage and pulse-modulation radio frequency (rf) power are studied experimentally between two parallel plates electrodes. Pulse-modulation applied in rf APGD temporally separates the discharge into repetitive discharge bursts, between which the high voltage pulses are introduced to ignite sub-microsecond pulsed discharge. The discharge characteristics and spatio-temporal evolution are investigated by means of current voltage characteristics and time resolved imaging, which suggests that the introduced pulsed discharge assists the ignition of rf discharge burst and reduces the maintain voltage of rf discharge burst. Furtherly, the time instant ofmore » pulsed discharge between rf discharge bursts is manipulated to study the ignition dynamics of rf discharge burst.« less

Smoothed spectra for enhanced dispersion-free pulse duration reduction of passively Q-switched microchip lasers.

PubMed

Lehneis, R; Jauregui, C; Steinmetz, A; Limpert, J; Tünnermann, A

2014-02-01

We present an enhanced technique for dispersion-free pulse shortening, which exploits the interplay of different third-order nonlinear effects in a waveguide structure. When exceeding a certain value of the pulse energy coupled into the waveguide, the typical oscillations of self-phase modulation (SPM)-broadened spectra vanish during pulse propagation. Such smoothed spectra ensure a high pulse quality of the spectrally filtered and, therefore, temporally shortened pulses independently of the filtering position. A reduction of the pulse duration from 138 to 24 ps has been achieved while preserving a high temporal quality. To the best of our knowledge, the nonlinear smoothing of SPM-broadened spectra is used in the context of dispersion-free pulse duration reduction for the first time.

Effect of nonlinear absorption on self focusing of short laser pulse in a plasma

NASA Astrophysics Data System (ADS)

Kumar, Ashok

2012-06-01

Paraxial theory of self focusing of short pulse laser in a plasma under transient and saturating effects of nonlinearity and nonlinear absorption is developed. The absorption is averaged over the cross-section of the beam and is different for different time segments of the pulse. The electron temperature includes cumulative effect of previous history of temporal profile of pulse intensity, however, the ambipolar diffusion is taken to be faster than the heating time. The relaxation effect causes self-distortion of the pulse temporal profile where as the nonlinear absorption weakens self focusing. For the pulses of duration comparable to the electron ion collision time, the front part of the pulse gets defocused where as the latter part undergoes periodic self focusing.

Use of biphase-coded pulses for wideband data storage in time-domain optical memories.

PubMed

Shen, X A; Kachru, R

1993-06-10

We demonstrate that temporally long laser pulses with appropriate phase modulation can replace either temporally brief or frequency-chirped pulses in a time-domain optical memory to store and retrieve information. A 1.65-µs-long write pulse was biphase modulated according to the 13-bit Barker code for storing multiple bits of optical data into a Pr(3+):YAlO(3) crystal, and the stored information was later recalled faithfully by using a read pulse that was identical to the write pulse. Our results further show that the stored data cannot be retrieved faithfully if mismatched write and read pulses are used. This finding opens up the possibility of designing encrypted optical memories for secure data storage.

Construction and temporal behaviour study of multi RLC intense light pulses for dermatological applications.

PubMed

Hamoudi, Walid K; Ismail, Raid A; Shakir, Hussein A

2017-10-01

Driving a flash lamp in an intense pulsed light system requires a high-voltage DC power supply, capacitive energy storage and a flash lamp triggering unit. Single, double, triple and quadruple-mesh discharge and triggering circuits were constructed to provide intense light pulses of variable energy and time durations. The system was treated as [Formula: see text] circuit in some cases and [Formula: see text] circuit in others with a light pulse profile following the temporal behaviour of the exciting current pulse. Distributing the energy delivered to one lamp onto a number of LC meshes permitted longer current pulses, and consequently increased the light pulse length. Positive results were obtained when using the system to treat skin wrinkles.

Systems and methods for selective detection and imaging in coherent Raman microscopy by spectral excitation shaping

DOEpatents

Xie, Xiaoliang Sunney; Freudiger, Christian; Min, Wei

2016-03-15

A microscopy imaging system is disclosed that includes a light source system, a spectral shaper, a modulator system, an optics system, an optical detector and a processor. The light source system is for providing a first train of pulses and a second train of pulses. The spectral shaper is for spectrally modifying an optical property of at least some frequency components of the broadband range of frequency components such that the broadband range of frequency components is shaped producing a shaped first train of pulses to specifically probe a spectral feature of interest from a sample, and to reduce information from features that are not of interest from the sample. The modulator system is for modulating a property of at least one of the shaped first train of pulses and the second train of pulses at a modulation frequency. The optical detector is for detecting an integrated intensity of substantially all optical frequency components of a train of pulses of interest transmitted or reflected through the common focal volume. The processor is for detecting a modulation at the modulation frequency of the integrated intensity of substantially all of the optical frequency components of the train of pulses of interest due to the non-linear interaction of the shaped first train of pulses with the second train of pulses as modulated in the common focal volume, and for providing an output signal for a pixel of an image for the microscopy imaging system.

What is the temporal analog of reflection and refraction of optical beams?

DOE PAGES

Plansinis, B. W.; Donaldson, W. R.; Agrawal, G. P.

2015-10-28

It is shown numerically and analytically that when an optical pulse approaches a moving temporal boundary across which the refractive index changes, it undergoes a temporal equivalent of reflection and refraction of optical beams at a spatial boundary. The main difference is that the role of angles is played by changes in the frequency. The frequency dependence of the dispersion of the material in which the pulse is propagating plays a fundamental role in determining the frequency shifts experienced by the reflected and refracted pulses. As a result, our analytic expressions for these frequency shifts allow us to find themore » condition under which an analog of total internal reflection may occur at the temporal boundary.« less

Electrical pulse generator

DOEpatents

Norris, Neil J.

1979-01-01

A technique for generating high-voltage, wide dynamic range, shaped electrical pulses in the nanosecond range. Two transmission lines are coupled together by resistive elements distributed along the length of the lines. The conductance of each coupling resistive element as a function of its position along the line is selected to produce the desired pulse shape in the output line when an easily produced pulse, such as a step function pulse, is applied to the input line.

Pulse shaping and energy storage capabilities of angularly multiplexed KrF laser fusion drivers

NASA Astrophysics Data System (ADS)

Lehmberg, R. H.; Giuliani, J. L.; Schmitt, A. J.

2009-07-01

This paper describes a rep-rated multibeam KrF laser driver design for the 500kJ Inertial Fusion test Facility (FTF) recently proposed by NRL, then models its optical pulse shaping capabilities using the ORESTES laser kinetics code. It describes a stable and reliable iteration technique for calculating the required precompensated input pulse shape that will achieve the desired output shape, even when the amplifiers are heavily saturated. It also describes how this precompensation technique could be experimentally implemented in real time on a reprated laser system. The simulations show that this multibeam system can achieve a high fidelity pulse shaping capability, even for a high gain shock ignition pulse whose final spike requires output intensities much higher than the ˜4MW/cm2 saturation levels associated with quasi-cw operation; i.e., they show that KrF can act as a storage medium even for pulsewidths of ˜1ns. For the chosen pulse, which gives a predicted fusion energy gain of ˜120, the simulations predict the FTF can deliver a total on-target energy of 428kJ, a peak spike power of 385TW, and amplified spontaneous emission prepulse contrast ratios IASE/I<3×10-7 in intensity and FASE/F<1.5×10-5 in fluence. Finally, the paper proposes a front-end pulse shaping technique that combines an optical Kerr gate with cw 248nm light and a 1μm control beam shaped by advanced fiber optic technology, such as the one used in the National Ignition Facility (NIF) laser.

Laser-to-hot-electron conversion limitations in relativistic laser matter interactions due to multi-picosecond dynamics

DOE PAGES

Schollmeier, Marius; Sefkow, Adam B.; Geissel, Matthias; ...

2015-04-20

High-energy short-pulse lasers are pushing the limits of plasma-based particle acceleration, x-ray generation, and high-harmonic generation by creating strong electromagnetic fields at the laser focus where electrons are being accelerated to relativistic velocities. Understanding the relativistic electron dynamics is key for an accurate interpretation of measurements. We present a unified and self-consistent modeling approach in quantitative agreement with measurements and differing trends across multiple target types acquired from two separate laser systems, which differ only in their nanosecond to picosecond-scale rising edge. Insights from high-fidelity modeling of laser-plasma interaction demonstrate that the ps-scale, orders of magnitude weaker rising edge ofmore » the main pulse measurably alters target evolution and relativistic electron generation compared to idealized pulse shapes. This can lead for instance to the experimentally observed difference between 45 MeV and 75 MeV maximum energy protons for two nominally identical laser shots, due to ps-scale prepulse variations. Our results indicate that the realistic inclusion of temporal laser pulse profiles in modeling efforts is required if predictive capability and extrapolation are sought for future target and laser designs or for other relativistic laser ion acceleration schemes.« less

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

Kolbasin, V. A.; Ivanov, A. I.; Pedash, V. Y.

The two pulse shape discrimination methods were implemented in real-time. The pulse gradient analysis method was implemented programmatically on PC. The method based on artificial neural network was programmatically implemented using CUDA platform. It is shown that both implementations can provide up to 10{sup 6} pulses per second processing performance. The results for pulse shape discrimination using polycrystalline stilbene and LiF detectors were shown. (authors)

Temporal selectivity by single neurons in the torus semicircularis of Batrachyla antartandica (Amphibia: Leptodactylidae).

PubMed

Penna, M; Lin, W Y; Feng, A S

2001-12-01

We investigated the response selectivities of single auditory neurons in the torus semicircularis of Batrachyla antartandica (a leptodactylid from southern Chile) to synthetic stimuli having diverse temporal structures. The advertisement call for this species is characterized by a long sequence of brief sound pulses having a dominant frequency of about 2000 Hz. We constructed five different series of synthetic stimuli in which the following acoustic parameters were systematically modified, one at a time: pulse rate, pulse duration, pulse rise time, pulse fall time, and train duration. The carrier frequency of these stimuli was fixed at the characteristic frequency of the units under study (n=44). Response patterns of TS units to these synthetic call variants revealed different degrees of selectivity for each of the temporal variables. A substantial number of neurons showed preference for pulse rates below 2 pulses s(-1), approximating the values found in natural advertisement calls. Tonic neurons generally showed preferences for long pulse durations, long rise and fall times, and long train durations. In contrast, phasic and phasic-burst neurons preferred stimuli with short duration, short rise and fall times and short train durations.

Pulses of movement across the sea ice: population connectivity and temporal genetic structure in the arctic fox.

PubMed

Norén, Karin; Carmichael, Lindsey; Fuglei, Eva; Eide, Nina E; Hersteinsson, Pall; Angerbjörn, Anders

2011-08-01

Lemmings are involved in several important functions in the Arctic ecosystem. The Arctic fox (Vulpes lagopus) can be divided into two discrete ecotypes: "lemming foxes" and "coastal foxes". Crashes in lemming abundance can result in pulses of "lemming fox" movement across the Arctic sea ice and immigration into coastal habitats in search for food. These pulses can influence the genetic structure of the receiving population. We have tested the impact of immigration on the genetic structure of the "coastal fox" population in Svalbard by recording microsatellite variation in seven loci for 162 Arctic foxes sampled during the summer and winter over a 5-year period. Genetic heterogeneity and temporal genetic shifts, as inferred by STRUCTURE simulations and deviations from Hardy-Weinberg proportions, respectively, were recorded. Maximum likelihood estimates of movement as well as STRUCTURE simulations suggested that both immigration and genetic mixture are higher in Svalbard than in the neighbouring "lemming fox" populations. The STRUCTURE simulations and AMOVA revealed there are differences in genetic composition of the population between summer and winter seasons, indicating that immigrants are not present in the reproductive portion of the Svalbard population. Based on these results, we conclude that Arctic fox population structure varies with time and is influenced by immigration from neighbouring populations. The lemming cycle is likely an important factor shaping Arctic fox movement across sea ice and the subsequent population genetic structure, but is also likely to influence local adaptation to the coastal habitat and the prevalence of diseases.

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

Ginsz, M.; Duchene, G.; Didierjean, F.

The state-of-the art gamma-ray spectrometers such as AGATA and GRETA are using position sensitive multi-segmented HPGe crystals. Pulse-shape analysis (PSA) allows to retrieve the localisation of the gamma interactions and to perform gamma-ray tracking within germanium. The precision of the localisation depends on the quality of the pulse-shape database used for comparison. The IPHC laboratory developed a new fast scanning table allowing to measure experimental pulse shapes in the whole volume of any crystal. The results of the scan of an AGATA 36-fold segmented tapered coaxial detector are shown here, 48580 experimental pulse shapes are extracted within 2 weeks ofmore » scanning. These data will contribute to AGATA PSA performances, but have also applications for gamma cameras or Compton-suppressed detectors. (authors)« less

Control of nitromethane photoionization efficiency with shaped femtosecond pulses.

PubMed

Roslund, Jonathan; Shir, Ofer M; Dogariu, Arthur; Miles, Richard; Rabitz, Herschel

2011-04-21

The applicability of adaptive femtosecond pulse shaping is studied for achieving selectivity in the photoionization of low-density polyatomic targets. In particular, optimal dynamic discrimination (ODD) techniques exploit intermediate molecular electronic resonances that allow a significant increase in the photoionization efficiency of nitromethane with shaped near-infrared femtosecond pulses. The intensity bias typical of high-photon number, nonresonant ionization is accounted for by reference to a strictly intensity-dependent process. Closed-loop adaptive learning is then able to discover a pulse form that increases the ionization efficiency of nitromethane by ∼150%. The optimally induced molecular dynamics result from entry into a region of parameter space inaccessible with intensity-only control. Finally, the discovered pulse shape is demonstrated to interact with the molecular system in a coherent fashion as assessed from the asymmetry between the response to the optimal field and its time-reversed counterpart.

Uni-directional optical pulses, temporal propagation, and spatial and temporal dispersion

NASA Astrophysics Data System (ADS)

Kinsler, P.

2018-02-01

I derive a temporally propagated uni-directional optical pulse equation valid in the few cycle limit. Temporal propagation is advantageous because it naturally preserves causality, unlike the competing spatially propagated models. The exact coupled bi-directional equations that this approach generates can be efficiently approximated down to a uni-directional form in cases where an optical pulse changes little over one optical cycle. They also permit a direct term-to-term comparison of the exact bi-directional theory with its corresponding approximate uni-directional theory. Notably, temporal propagation handles dispersion in a different way, and this difference serves to highlight existing approximations inherent in spatially propagated treatments of dispersion. Accordingly, I emphasise the need for future work in clarifying the limitations of the dispersion conversion required by these types of approaches; since the only alternative in the few cycle limit may be to resort to the much more computationally intensive full Maxwell equation solvers.

Spatio-temporal modeling and optimization of a deformable-grating compressor for short high-energy laser pulses

DOE PAGES

Qiao, Jie; Papa, J.; Liu, X.

2015-09-24

Monolithic large-scale diffraction gratings are desired to improve the performance of high-energy laser systems and scale them to higher energy, but the surface deformation of these diffraction gratings induce spatio-temporal coupling that is detrimental to the focusability and compressibility of the output pulse. A new deformable-grating-based pulse compressor architecture with optimized actuator positions has been designed to correct the spatial and temporal aberrations induced by grating wavefront errors. An integrated optical model has been built to analyze the effect of grating wavefront errors on the spatio-temporal performance of a compressor based on four deformable gratings. Moreover, a 1.5-meter deformable gratingmore » has been optimized using an integrated finite-element-analysis and genetic-optimization model, leading to spatio-temporal performance similar to the baseline design with ideal gratings.« less

Measurement of the Shock Velocity and Symmetry History in Decaying Shock Pulses

NASA Astrophysics Data System (ADS)

Baker, Kevin; Milovich, Jose; Jones, Oggie; Robey, Harry; Smalyuk, Vladimir; Casey, Daniel; Celliers, Peter; Clark, Dan; Giraldez, Emilio; Haan, Steve; Hamza, Alex; Berzak-Hopkins, Laura; Jancaitis, Ken; Kroll, Jeremy; Lafortune, Kai; MacGowan, Brian; Macphee, Andrew; Moody, John; Nikroo, Abbas; Peterson, Luc; Raman, Kumar; Weber, Chris; Widmayer, Clay

2014-10-01

Decaying first shock pulses are predicted in simulations to provide more stable implosions and still achieve a low adiabat in the fuel, enabling a higher fuel compression similar to ``low foot'' laser pulses. The first step in testing these predictions was to measure the shock velocity for both a three shock and a four shock adiabat-shaped pulse in a keyhole experimental platform. We present measurements of the shock velocity history, including the decaying shock velocity inside the ablator, and compare it with simulations, as well as with previous low and high foot pulses. Using the measured pulse shape, the predicted adiabat from simulations is presented and compared with the calculated adiabat from low and high foot laser pulse shapes. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

Photonic ultra-wideband pulse generation, hybrid modulation and dispersion-compensation-free transmission in multi-access communication systems.

PubMed

Tan, Kang; Shao, Jing; Sun, Junqiang; Wang, Jian

2012-01-16

We propose and demonstrate a scheme for optical ultrawideband (UWB) pulse generation by exploiting a half-carrier-suppressed Mach-Zehnder modulator (MZM) and a delay-interferometer- and wavelength-division-multiplexer-based, reconfigurable and multi-channel differentiator (DWRMD). Multi-wavelength, polarity- and shape-switchable UWB pulses of monocycle, doublet, triplet, and quadruplet are experimentally generated simply by tuning two bias voltages to modify the carrier-suppression ratio of MZM and the differential order of DWRMD respectively. The pulse position modulation, pulse shape modulation, pulse amplitude modulation and binary phase-shift keying modulation of UWB pulses can also be conveniently realized with the same scheme structure, which indicates that the hybrid modulation of those four formats can be achieved. Consequently, the proposed approach has potential applications in multi-shape, multi-modulation and multi-access UWB-over-fiber communication systems.

Femtosecond pulse shaping using the geometric phase.

PubMed

Gökce, Bilal; Li, Yanming; Escuti, Michael J; Gundogdu, Kenan

2014-03-15

We demonstrate a femtosecond pulse shaper that utilizes polarization gratings to manipulate the geometric phase of an optical pulse. This unique approach enables circular polarization-dependent shaping of femtosecond pulses. As a result, it is possible to create coherent pulse pairs with orthogonal polarizations in a 4f pulse shaper setup, something until now that, to our knowledge, was only achieved via much more complex configurations. This approach could be used to greatly simplify and enhance the functionality of multidimensional spectroscopy and coherent control experiments, in which multiple coherent pulses are used to manipulate quantum states in materials of interest.

Spatiotemporal light-beam compression from nonlinear mode coupling

NASA Astrophysics Data System (ADS)

Krupa, Katarzyna; Tonello, Alessandro; Couderc, Vincent; Barthélémy, Alain; Millot, Guy; Modotto, Daniele; Wabnitz, Stefan

2018-04-01

We experimentally demonstrate simultaneous spatial and temporal compression in the propagation of light pulses in multimode nonlinear optical fibers. We reveal that the spatial beam self-cleaning recently discovered in graded-index multimode fibers is accompanied by significant temporal reshaping and up to fourfold shortening of the injected subnanosecond laser pulses. Since the nonlinear coupling among the modes strongly depends on the instantaneous power, we explore the entire range of the nonlinear dynamics with a single optical pulse, where the optical power is continuously varied across the pulse profile.

Transmitter Pulse Estimation and Measurements for Airborne TDEM Systems

NASA Astrophysics Data System (ADS)

Vetrov, A.; Mejzr, I.

2013-12-01

The processing and interpretation of Airborne Time Domain EM data requires precise description of the transmitter parameters, including shape, amplitude and length of the transmitted pulse. There are several ways to measure pulse shape of the transmitter loop. Transmitted pulse can be recorded by a current monitor installed on the loop. The current monitor readings do not give exact image due to own time-domain physical characteristics of the current monitor. Another way is to restore the primary pulse shape from the receiver data recorded on-time, if such is possible. The receiver gives exact image of the primary field projection combined with the ground response, which can be minimized at high altitude pass, usually with a transmitter elevation higher than 1500 ft from the ground. The readings on the receiver are depending on receiver position and orientation. Modeling of airborne TDEM transmitter pulse allows us to compare estimated and measured shape of the pulse and apply required corrections. Airborne TDEM system transmitter pulse shape has been studied by authors while developing P-THEM system. The data has been gathered during in-doors and out-doors ground tests in Canada, as well as during flight tests in Canada and in India. The P-THEM system has three-axes receiver that is suspended on a tow-cable in the midpoint between the transmitter and the helicopter. The P-THEM receiver geometry does not require backing coils to dump the primary field. The system records full-wave data from the receiver and current monitor installed on the transmitter loop, including on-time and off-time data. The modeling of the transmitter pulse allowed us to define the difference between estimated and measured values. The higher accuracy pulse shape can be used for better data processing and interpretation. A developed model can be applied to similar systems and configurations.

Method of and apparatus for measuring vapor density

DOEpatents

Nelson, L.D.; Cerni, T.A.

1989-10-17

Apparatus and method are disclosed which determine the concentration of an individual component, such as water vapor, of a multi-component mixture, such as a gaseous mixture for cooling a nuclear reactor. A hygrometer apparatus includes an infrared source for producing a broadband infrared energy beam that includes a strong water vapor absorption band and a weak water vapor absorption region. The beam is chopped to select infrared pulses. A temporally first pulse has a wavelength in the weakly absorbing region, a temporally second pulse has a wavelength in the strong band and a temporally third pulse has a wavelength in the weakly absorbing region. A fourth reference pulse representing background radiation is interposed in such chopped pulses. An indium arsenide infrared sensor is responsive to the pulses for generating an output signal in proportion to an equation given in the patent where N1 is proportional to the transmission through the sample of the first signal, N4 is related to the background radiation, and [K2 (N2-N4) + K3 (N3-N4)] is the time-weighted average of the transmission through the sample of the second and third pulses applicable at the time of the second pulse, with the reference pulse N4 being subtracted in each case to render the ratio independent of variations in the background radiation. 11 figs.

Digital pulse processing and electronic noise analysis for improving energy resolutions in planar TlBr detectors

NASA Astrophysics Data System (ADS)

Tada, Tsutomu; Hitomi, Keitaro; Tanaka, Tomonobu; Wu, Yan; Kim, Seong-Yun; Yamazaki, Hiromichi; Ishii, Keizo

2011-05-01

Digital pulse processing and electronic noise analysis are proposed for improving energy resolution in planar thallium bromide (TlBr) detectors. An energy resolution of 5.8% FWHM at 662 keV was obtained from a 0.5 mm thick planar TlBr detector at room temperature using a digitizer with a sampling rate of 100 MS/s and 8 bit resolution. The electronic noise in the detector-preamplifier system was measured as a function of pulse shaping time in order to investigate the optimum shaping time for the detector. The depth of interaction (DOI) in TlBr detectors for incident gamma-rays was determined by taking the ratio of pulse heights for fast-shaped to slow-shaped signals. FWHM energy resolution of the detector was improved from 5.8% to 4.2% by implementing depth correction and by using the obtained optimum shaping time.

Characterization of pulsed flow attenuation on a regulated montane river

NASA Astrophysics Data System (ADS)

Fong, C. S.; Yarnell, S. M.; Fleenor, W. E.; Viers, J. H.

2013-12-01

A major benefit of hydropower is its ability to respond quickly to fluctuating electrical loads. However, the sharp changes in discharge caused by this practice have detrimental environmental effects downstream. This study investigated the effects of hydrograph shape on attenuation of regulated pulsed flow events by first categorizing, then modeling the downstream movement of representative pulses on the upper Tuolumne River below Holm Powerhouse in the Sierra Nevada mountains of California. This system was managed by a public utility and produced flow pulses primarily for hydroelectricity generation and/or whitewater recreation. Operations were highly influenced by a system-wide "Water First" policy, which prioritized drinking water supply and quality over other beneficial uses. Pulses were therefore associated with a spectrum of time scales, from predetermined schedules decided far in advance to hydropeaking operations responding to real-time demands. We extracted underlying hydrograph shape patterns using principal component analysis on individual pulsed flow events released from 1988-2012 (n=4439). From principal component loadings, six shape categories were determined: rectangular, front-step, back-step, goalpost, centered tower, and other. The rectangular and stepped shapes were the most frequent, composing 62% and 24% of total events, respectively. The rectangular shape was often produced by 'standard' hydropeaking or recreational releases, while the stepped shapes were often used for water conservation or were recreational flows bordered by periods of electricity generation. The stepped shape increased in occurrence after the "Water First" policy took effect in 1993 and dominated two drier years (2007 and 2009). After categorization by shape, magnitude and durational indices were used to fabricate representative pulsed flow events. Attenuation of these representative pulses was then modeled using a 1D hydraulic model of 42 river km prepared in HEC-RAS. As no operational measures or physical structures existed within the system to counter the adverse effects of pulsed flow events, natural attenuation was the only potential major mitigation agent. However, model results demonstrated a clear durational threshold for representative pulses (~ 3-5 hrs) over which the degree of attenuation of ramping rates and peak discharge approached a limit. These thresholds were unique to the study reach and were dependent upon river morphology, bed characteristics, and flow rates. Increasing baseflows did not necessarily increase attenuation of pulses, most likely due to minimal increases in bed friction forces in this fairly steep and confined channel. Simulations of front and back-step representative pulses showed trade-offs between attenuation of peak magnitudes and steepness of ramping rates. Finally, a range of rising ramping rates were shown to steepen downstream above initial rates due to the study reach's channel morphology. Reshaping pulses to be more ecologically benign at all points downstream was infeasible if the system was required to maintain current electricity production and recreational service levels.

Band-selective shaped pulse for high fidelity quantum control in diamond

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

Chang, Yan-Chun; Xing, Jian; Liu, Gang-Qin

High fidelity quantum control of qubits is crucially important for realistic quantum computing, and it becomes more challenging when there are inevitable interactions between qubits. We introduce a band-selective shaped pulse, refocusing BURP (REBURP) pulse, to cope with the problems. The electron spin of nitrogen-vacancy centers in diamond is flipped with high fidelity by the REBURP pulse. In contrast with traditional rectangular pulses, the shaped pulse has almost equal excitation effect in a sharply edged region (in frequency domain). So the three sublevels of host {sup 14}N nuclear spin can be flipped accurately simultaneously, while unwanted excitations of other sublevelsmore » (e.g., of a nearby {sup 13}C nuclear spin) is well suppressed. Our scheme can be used for various applications such as quantum metrology, quantum sensing, and quantum information process.« less

Single-pulse interference caused by temporal reflection at moving refractive-index boundaries

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

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

Here, we show numerically and analytically that temporal reflections from a moving refractive-index boundary act as an analog of Lloyd’s mirror, allowing a single pulse to produce interference fringes in time as it propagates inside a dispersive medium. This interference can be viewed as the pulse interfering with a virtual pulse that is identical to the first, except for a π-phase shift. Furthermore, if a second moving refractive-index boundary is added to create the analog of an optical waveguide, a single pulse can be self-imaged or made to produce two or more pulses by adjusting the propagation length in amore » process similar to the Talbot effect.« less

Single-pulse interference caused by temporal reflection at moving refractive-index boundaries

DOE PAGES

Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

2017-09-29

Here, we show numerically and analytically that temporal reflections from a moving refractive-index boundary act as an analog of Lloyd’s mirror, allowing a single pulse to produce interference fringes in time as it propagates inside a dispersive medium. This interference can be viewed as the pulse interfering with a virtual pulse that is identical to the first, except for a π-phase shift. Furthermore, if a second moving refractive-index boundary is added to create the analog of an optical waveguide, a single pulse can be self-imaged or made to produce two or more pulses by adjusting the propagation length in amore » process similar to the Talbot effect.« less

Elemental analysis using temporal gating of a pulsed neutron generator

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

Mitra, Sudeep

Technologies related to determining elemental composition of a sample that comprises fissile material are described herein. In a general embodiment, a pulsed neutron generator periodically emits bursts of neutrons, and is synchronized with an analyzer circuit. The bursts of neutrons are used to interrogate the sample, and the sample outputs gamma rays based upon the neutrons impacting the sample. A detector outputs pulses based upon the gamma rays impinging upon the material of the detector, and the analyzer circuit assigns the pulses to temporally-based bins based upon the analyzer circuit being synchronized with the pulsed neutron generator. A computing devicemore » outputs data that is indicative of elemental composition of the sample based upon the binned pulses.« less

Alpha-gamma pulse-shape discrimination in Gd3Al2Ga3O12 (GAGG):Ce3+ crystal scintillator using shape indicator

NASA Astrophysics Data System (ADS)

Tamagawa, Yoichi; Inukai, Yuji; Ogawa, Izumi; Kobayashi, Masaaki

2015-09-01

The pulse-shape discrimination (PSD) in a GAGG single-crystal scintillator was studied by using a shape indicator (SI) parameter of the optimal digital filter method. SI is one of the most useful PSD methods that use typical pulse shapes. Excellent discrimination between 0.662 MeV γ-rays and 5.48 MeV α-rays was achieved. For a cut at SI=0.0056, 99.95% of the γ-rays and only 0.22% of the α-rays were retained. Selection of background events (γ and α) in the GAGG scintillator was achieved by using the PSD method.

Rod-like bacterial shape is maintained by feedback between cell curvature and cytoskeletal localization

PubMed Central

Ursell, Tristan S.; Nguyen, Jeffrey; Monds, Russell D.; Colavin, Alexandre; Billings, Gabriel; Ouzounov, Nikolay; Gitai, Zemer; Shaevitz, Joshua W.; Huang, Kerwyn Casey

2014-01-01

Cells typically maintain characteristic shapes, but the mechanisms of self-organization for robust morphological maintenance remain unclear in most systems. Precise regulation of rod-like shape in Escherichia coli cells requires the MreB actin-like cytoskeleton, but the mechanism by which MreB maintains rod-like shape is unknown. Here, we use time-lapse and 3D imaging coupled with computational analysis to map the growth, geometry, and cytoskeletal organization of single bacterial cells at subcellular resolution. Our results demonstrate that feedback between cell geometry and MreB localization maintains rod-like cell shape by targeting cell wall growth to regions of negative cell wall curvature. Pulse-chase labeling indicates that growth is heterogeneous and correlates spatially and temporally with MreB localization, whereas MreB inhibition results in more homogeneous growth, including growth in polar regions previously thought to be inert. Biophysical simulations establish that curvature feedback on the localization of cell wall growth is an effective mechanism for cell straightening and suggest that surface deformations caused by cell wall insertion could direct circumferential motion of MreB. Our work shows that MreB orchestrates persistent, heterogeneous growth at the subcellular scale, enabling robust, uniform growth at the cellular scale without requiring global organization. PMID:24550515

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

Mabe, Andrew N.; Glenn, Andrew M.; Carman, M. Leslie

Transparent plastic scintillators with pulse shape discrimination containing 6Li salicylate have been synthesized by bulk polymerization with a maximum 6Li loading of 0.40 wt%. Photoluminescence and scintillation responses to gamma-rays and neutrons are reported in this paper. Plastics containing 6Li salicylate exhibit higher light yields and permit a higher loading of 6Li as compared to previously reported plastics based on lithium 3-phenylsalicylate. However, pulse shape discrimination performance is reduced in lithium salicylate plastics due to the requirement of adding more nonaromatic monomers to the polymer matrix as compared to those based on lithium 3-phenylsalicylate. Finally, reduction in light yield andmore » pulse shape discrimination performance in lithium-loaded plastics as compared to pulse shape discrimination plastics without lithium is interpreted in terms of energy transfer interference by the aromatic lithium salts.« less

Enhancement of temporal contrast of high-power laser pulses in an anisotropic medium with cubic nonlinearity

NASA Astrophysics Data System (ADS)

Kuz'mina, M. S.; Khazanov, E. A.

2015-05-01

We consider the methods for enhancing the temporal contrast of super-high-power laser pulses, based on the conversion of radiation polarisation in a medium with cubic nonlinearity. For a medium with weak birefringence and isotropic nonlinearity, we propose a new scheme to enhance the temporal contrast. For a medium with anisotropic nonlinearity, the efficiency of the temporal contrast optimisation is shown to depend not only on the spatial orientation of the crystal and B-integral, but also on the type of the crystal lattice symmetry.

Temporal VUV Emission Characteristics Related to Generations and Losses of Metastable Atoms in Xenon Pulsed Barrier Discharge

NASA Astrophysics Data System (ADS)

Motomura, Hideki; Loo, Ka Hong; Ikeda, Yoshihisa; Jinno, Masafumi; Aono, Masaharu

Although xenon pulsed dielectric barrier discharge is one of the most promising substitutes for mercury low-pressure discharge for fluorescent lamps, the efficacy of xenon fluorescent lamp is not enough for practical use for general lighting. To improve the efficacy it is indispensable to clarify mechanisms of vacuum ultraviolet (VUV) emissions, which excite phosphor, from xenon discharge related to plasma characteristics. In this paper emission waveforms and temporal change of metastable atom density are measured and temporal VUV emission characteristics related to generations and losses of metastable atoms in xenon pulsed barrier discharge is investigated. It is shown that the lamp efficacy is improved by about 10% with shorter pulse in which the two VUV emission peaks in a pulse are overlapped. It is also shown that at the lower pressure of 1.3 kPa metastable atoms generated during on-period of the voltage pulse are not efficiently consumed for VUV emissions in the off-period of the voltage pulse because of lower rate of three-body collision and quenching. This fact is thought to be one of the reasons why the lamp efficacy is low at lower pressure.

Spatial hearing benefits demonstrated with presentation of acoustic temporal fine structure cues in bilateral cochlear implant listeners.

PubMed

Churchill, Tyler H; Kan, Alan; Goupell, Matthew J; Litovsky, Ruth Y

2014-09-01

Most contemporary cochlear implant (CI) processing strategies discard acoustic temporal fine structure (TFS) information, and this may contribute to the observed deficits in bilateral CI listeners' ability to localize sounds when compared to normal hearing listeners. Additionally, for best speech envelope representation, most contemporary speech processing strategies use high-rate carriers (≥900 Hz) that exceed the limit for interaural pulse timing to provide useful binaural information. Many bilateral CI listeners are sensitive to interaural time differences (ITDs) in low-rate (<300 Hz) constant-amplitude pulse trains. This study explored the trade-off between superior speech temporal envelope representation with high-rate carriers and binaural pulse timing sensitivity with low-rate carriers. The effects of carrier pulse rate and pulse timing on ITD discrimination, ITD lateralization, and speech recognition in quiet were examined in eight bilateral CI listeners. Stimuli consisted of speech tokens processed at different electrical stimulation rates, and pulse timings that either preserved or did not preserve acoustic TFS cues. Results showed that CI listeners were able to use low-rate pulse timing cues derived from acoustic TFS when presented redundantly on multiple electrodes for ITD discrimination and lateralization of speech stimuli.

Pulse analysis of acoustic emission signals

NASA Technical Reports Server (NTRS)

Houghton, J. R.; Packman, P. F.

1977-01-01

A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio were examined in the frequency domain analysis and pulse shape deconvolution was developed for use in the time domain analysis. Comparisons of the relative performance of each analysis technique are made for the characterization of acoustic emission pulses recorded by a measuring system. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameter values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emission associated with (a) crack propagation, (b) ball dropping on a plate, (c) spark discharge, and (d) defective and good ball bearings. Deconvolution of the first few micro-seconds of the pulse train is shown to be the region in which the significant signatures of the acoustic emission event are to be found.

Distance Determination by Gated Viewing Systems Taking into Account the Illuminating Pulse Shape

NASA Astrophysics Data System (ADS)

Gorobets, V. A.; Kuntsevich, B. F.; Shabrov, D. V.

2017-11-01

For gated viewing systems with triangular and trapezoidal illuminating pulses, we have obtained the range-intensity profiles (RIPs) of the signal as the time delay was varied between the leading edges of the gate pulse and the illuminating pulse. We have established that if the duration of the illuminating pulse Δtlas is less than or equal to the duration of the gate pulse ΔtIC, then the expressions for the characteristic distances are the same as for rectangular pulses and they can be used to determine the distance to objects. When Δtlas > ΔtIC, in the case of triangular illuminating pulses the RIP is bell-shaped. For trapezoidal pulses, the RIP is bell-shaped with or without a plateau section. We propose an empirical method for determining the characteristic distances to the RIP maximum and the boundary points for the plateau section, which we then use to calculate the distance to the object. Using calibration constants, we propose a method for determining the distance to an object and we have experimentally confirmed the feasibility of this method.

Pulse analysis of acoustic emission signals

NASA Technical Reports Server (NTRS)

Houghton, J. R.; Packman, P. F.

1977-01-01

A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio were examined in the frequency domain analysis, and pulse shape deconvolution was developed for use in the time domain analysis. Comparisons of the relative performance of each analysis technique are made for the characterization of acoustic emission pulses recorded by a measuring system. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameters values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emissions associated with: (1) crack propagation, (2) ball dropping on a plate, (3) spark discharge and (4) defective and good ball bearings. Deconvolution of the first few micro-seconds of the pulse train are shown to be the region in which the significant signatures of the acoustic emission event are to be found.

Spatiotemporal analysis of turbulent jets enabled by 100-kHz, 100-ms burst-mode particle image velocimetry

NASA Astrophysics Data System (ADS)

Miller, Joseph D.; Jiang, Naibo; Slipchenko, Mikhail N.; Mance, Jason G.; Meyer, Terrence R.; Roy, Sukesh; Gord, James R.

2016-12-01

100-kHz particle image velocimetry (PIV) is demonstrated using a double-pulsed, burst-mode laser with a burst duration up to 100 ms. This enables up to 10,000 time-sequential vector fields for capturing a temporal dynamic range spanning over three orders of magnitude in high-speed turbulent flows. Pulse doublets with inter-pulse spacing of 2 µs and repetition rate of 100 kHz are generated using a fiber-based oscillator and amplified through an all-diode-pumped, burst-mode amplifier. A physics-based model of pulse doublet amplification in the burst-mode amplifier is developed and used to accurately predict oscillator pulse width and pulse intensity inputs required to generate equal-energy pulse doublets at 532 nm for velocity measurements. The effect of PIV particle response and high-speed-detector limitations on the spatial and temporal resolution are estimated in subsonic turbulent jets. An effective spatial resolution of 266-275 µm and temporal resolution of 10 µs are estimated from the 8 × 8 pixel correlation window and inter-doublet time spacing, respectively. This spatiotemporal resolution is sufficient for quantitative assessment of integral time and length scales in highly turbulent jets with Reynolds numbers in the range 15,000-50,000. The temporal dynamic range of the burst-mode PIV measurement is 1200, limited by the 85-ms high-energy portion of the burst and 30-kHz high-frequency noise limit.

Experimental determination of pore shapes using phase retrieval from q -space NMR diffraction

NASA Astrophysics Data System (ADS)

Demberg, Kerstin; Laun, Frederik Bernd; Bertleff, Marco; Bachert, Peter; Kuder, Tristan Anselm

2018-05-01

This paper presents an approach to solving the phase problem in nuclear magnetic resonance (NMR) diffusion pore imaging, a method that allows imaging the shape of arbitrary closed pores filled with an NMR-detectable medium for investigation of the microstructure of biological tissue and porous materials. Classical q -space imaging composed of two short diffusion-encoding gradient pulses yields, analogously to diffraction experiments, the modulus squared of the Fourier transform of the pore image which entails an inversion problem: An unambiguous reconstruction of the pore image requires both magnitude and phase. Here the phase information is recovered from the Fourier modulus by applying a phase retrieval algorithm. This allows omitting experimentally challenging phase measurements using specialized temporal gradient profiles. A combination of the hybrid input-output algorithm and the error reduction algorithm was used with dynamically adapting support (shrinkwrap extension). No a priori knowledge on the pore shape was fed to the algorithm except for a finite pore extent. The phase retrieval approach proved successful for simulated data with and without noise and was validated in phantom experiments with well-defined pores using hyperpolarized xenon gas.

Experimental determination of pore shapes using phase retrieval from q-space NMR diffraction.

PubMed

Demberg, Kerstin; Laun, Frederik Bernd; Bertleff, Marco; Bachert, Peter; Kuder, Tristan Anselm

2018-05-01

This paper presents an approach to solving the phase problem in nuclear magnetic resonance (NMR) diffusion pore imaging, a method that allows imaging the shape of arbitrary closed pores filled with an NMR-detectable medium for investigation of the microstructure of biological tissue and porous materials. Classical q-space imaging composed of two short diffusion-encoding gradient pulses yields, analogously to diffraction experiments, the modulus squared of the Fourier transform of the pore image which entails an inversion problem: An unambiguous reconstruction of the pore image requires both magnitude and phase. Here the phase information is recovered from the Fourier modulus by applying a phase retrieval algorithm. This allows omitting experimentally challenging phase measurements using specialized temporal gradient profiles. A combination of the hybrid input-output algorithm and the error reduction algorithm was used with dynamically adapting support (shrinkwrap extension). No a priori knowledge on the pore shape was fed to the algorithm except for a finite pore extent. The phase retrieval approach proved successful for simulated data with and without noise and was validated in phantom experiments with well-defined pores using hyperpolarized xenon gas.

Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism.

PubMed

Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J; Mancuso, Christopher A; Hogle, Craig W; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L; Dorney, Kevin M; Chen, Cong; Shpyrko, Oleg G; Fullerton, Eric E; Cohen, Oren; Oppeneer, Peter M; Milošević, Dejan B; Becker, Andreas; Jaroń-Becker, Agnieszka A; Popmintchev, Tenio; Murnane, Margaret M; Kapteyn, Henry C

2015-11-17

We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.

Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism

PubMed Central

Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D.; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J.; Mancuso, Christopher A.; Hogle, Craig W.; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L.; Dorney, Kevin M.; Chen, Cong; Shpyrko, Oleg G.; Fullerton, Eric E.; Cohen, Oren; Oppeneer, Peter M.; Milošević, Dejan B.; Becker, Andreas; Jaroń-Becker, Agnieszka A.; Popmintchev, Tenio; Murnane, Margaret M.; Kapteyn, Henry C.

2015-01-01

We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform. PMID:26534992

Receiver design, performance analysis, and evaluation for space-borne laser altimeters and space-to-space laser ranging systems

NASA Technical Reports Server (NTRS)

Davidson, Frederic M.; Sun, Xiaoli; Field, Christopher T.

1995-01-01

Laser altimeters measure the time of flight of the laser pulses to determine the range of the target. The simplest altimeter receiver consists of a photodetector followed by a leading edge detector. A time interval unit (TIU) measures the time from the transmitted laser pulse to the leading edge of the received pulse as it crosses a preset threshold. However, the ranging error of this simple detection scheme depends on the received, pulse amplitude, pulse shape, and the threshold. In practice, the pulse shape and the amplitude are determined by the target target characteristics which has to be assumed unknown prior to the measurement. The ranging error can be improved if one also measures the pulse width and use the average of the leading and trailing edges (half pulse width) as the pulse arrival time. The ranging error becomes independent of the received pulse amplitude and the pulse width as long as the pulse shape is symmetric. The pulse width also gives the slope of the target. The ultimate detection scheme is to digitize the received waveform and calculate the centroid as the pulse arrival time. The centroid detection always gives unbiased measurement even for asymmetric pulses. In this report, we analyze the laser altimeter ranging errors for these three detection schemes using the Mars Orbital Laser Altimeter (MOLA) as an example.

Antimatched Electromagnetic Metasurfaces for Broadband Arbitrary Phase Manipulation in Reflection

DOE PAGES

Tsilipakos, Odysseas; Koschny, Thomas; Soukoulis, Costas M.

2018-03-21

Metasurfaces impart phase discontinuities on impinging electromagnetic waves that are typically limited to 0-2π. Here, we demonstrate that multiresonant metasurfaces can break free from this limitation and supply arbitrarily large, tunable time delays over ultrawide bandwidths. As such, ultrathin metasurfaces can act as the equivalent of thick bulk structures by emulating the multiple geometric resonances of three-dimensional systems that originate from phase accumulation with effective material resonances implemented on the surface itself via suitable subwavelength meta-atoms. We describe a constructive procedure for defining the required sheet admittivities of such metasurfaces. Importantly, the proposed approach provides an exactly linear phase responsemore » so that broadband pulses can experience the desired group delay without any distortion of the pulse shape. We focus on operation in reflection by exploiting an antimatching condition, satisfied by interleaved electric and magnetic Lorentzian resonances in the surface admittivities, which completely zeroes out transmission through the metasurface. As a result, the proposed metasurfaces can perfectly reflect a broadband pulse imparting a prescribed group delay. The group delay can be tuned by modifying the implemented resonances, thus opening up diverse possibilities in the temporal applications of metasurfaces.« less

Antimatched Electromagnetic Metasurfaces for Broadband Arbitrary Phase Manipulation in Reflection

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

Tsilipakos, Odysseas; Koschny, Thomas; Soukoulis, Costas M.

Metasurfaces impart phase discontinuities on impinging electromagnetic waves that are typically limited to 0-2π. Here, we demonstrate that multiresonant metasurfaces can break free from this limitation and supply arbitrarily large, tunable time delays over ultrawide bandwidths. As such, ultrathin metasurfaces can act as the equivalent of thick bulk structures by emulating the multiple geometric resonances of three-dimensional systems that originate from phase accumulation with effective material resonances implemented on the surface itself via suitable subwavelength meta-atoms. We describe a constructive procedure for defining the required sheet admittivities of such metasurfaces. Importantly, the proposed approach provides an exactly linear phase responsemore » so that broadband pulses can experience the desired group delay without any distortion of the pulse shape. We focus on operation in reflection by exploiting an antimatching condition, satisfied by interleaved electric and magnetic Lorentzian resonances in the surface admittivities, which completely zeroes out transmission through the metasurface. As a result, the proposed metasurfaces can perfectly reflect a broadband pulse imparting a prescribed group delay. The group delay can be tuned by modifying the implemented resonances, thus opening up diverse possibilities in the temporal applications of metasurfaces.« less

Short-Term Depression, Temporal Summation, and Onset Inhibition Shape Interval Tuning in Midbrain Neurons

PubMed Central

Baker, Christa A.

2014-01-01

A variety of synaptic mechanisms can contribute to single-neuron selectivity for temporal intervals in sensory stimuli. However, it remains unknown how these mechanisms interact to establish single-neuron sensitivity to temporal patterns of sensory stimulation in vivo. Here we address this question in a circuit that allows us to control the precise temporal patterns of synaptic input to interval-tuned neurons in behaviorally relevant ways. We obtained in vivo intracellular recordings under multiple levels of current clamp from midbrain neurons in the mormyrid weakly electric fish Brienomyrus brachyistius during stimulation with electrosensory pulse trains. To reveal the excitatory and inhibitory inputs onto interval-tuned neurons, we then estimated the synaptic conductances underlying responses. We found short-term depression in excitatory and inhibitory pathways onto all interval-tuned neurons. Short-interval selectivity was associated with excitation that depressed less than inhibition at short intervals, as well as temporally summating excitation. Long-interval selectivity was associated with long-lasting onset inhibition. We investigated tuning after separately nullifying the contributions of temporal summation and depression, and found the greatest diversity of interval selectivity among neurons when both mechanisms were at play. Furthermore, eliminating the effects of depression decreased sensitivity to directional changes in interval. These findings demonstrate that variation in depression and summation of excitation and inhibition helps to establish tuning to behaviorally relevant intervals in communication signals, and that depression contributes to neural coding of interval sequences. This work reveals for the first time how the interplay between short-term plasticity and temporal summation mediates the decoding of temporal sequences in awake, behaving animals. PMID:25339741

Demonstration of radiation pulse shaping with nested-tungsten-wire-array pinches for high-yield inertial confinement fusion.

PubMed

Cuneo, M E; Vesey, R A; Sinars, D B; Chittenden, J P; Waisman, E M; Lemke, R W; Lebedev, S V; Bliss, D E; Stygar, W A; Porter, J L; Schroen, D G; Mazarakis, M G; Chandler, G A; Mehlhorn, T A

2005-10-28

Nested wire-array pinches are shown to generate soft x-ray radiation pulse shapes required for three-shock isentropic compression and hot-spot ignition of high-yield inertial confinement fusion capsules. We demonstrate a reproducible and tunable foot pulse (first shock) produced by interaction of the outer and inner arrays. A first-step pulse (second shock) is produced by inner array collision with a central CH2 foam target. Stagnation of the inner array at the axis produces the third shock. Capsules optimized for several of these shapes produce 290-900 MJ fusion yields in 1D simulations.

Broadband spectral shaping in regenerative amplifier based on modified polarization-encoded chirped pulse amplification

NASA Astrophysics Data System (ADS)

Wang, Xinliang; Lu, Xiaoming; Liu, Yanqi; Xu, Yi; Wang, Cheng; Li, Shuai; Yu, Linpeng; Liu, Xingyan; Liu, Keyang; Xu, Rongjie; Leng, Yuxin

2018-06-01

We present an intra-cavity spectral shaping method to suppress the spectral narrowing in a Ti:sapphire (Ti:Sa) regenerative amplifier. The spectral shaping is realized by manipulating the stored energies of two Ti:Sa crystals with orthogonal c-axes, changing the length of a quartz plate, and rotating a broadband achromatic half-wave plate. Using this method, in our proof-of-concept experiment, an 84-nm-(FWHM)-broadband amplified pulse with an energy gain larger than 106 is obtained, which supports a 17.8 fs Fourier-transform-limited pulse duration. The pulse is compressed to 18.9 fs.

Comparison between Trichel pulse in negative corona and self-pulsing in other configurations

NASA Astrophysics Data System (ADS)

Xia, Qing; Zhang, Yu; He, Feng; Qin, Yu; Jiang, Zhaorui; Ouyang, Jiting

2018-02-01

We present here a comparison study on self-pulsing phenomena in negative corona, hollow cathode discharges (HCD) and parallel-plate discharge in air. The voltage-current (V-I) curve, the waveforms of self-pulsed currents, and the time-resolved images of the pulsed discharge are measured under various operating conditions. It is experimentally evidenced that the Trichel pulse in a negative corona and the self-pulsing in HCD and/or parallel-plate discharge have similar features as well as spatial-temporal developing process. It is suggested that they should have a similar mechanism that the pulsing reflects the mode transition of discharge between the low-current Townsend and the high-current normal glow. The pulse rising corresponds to the breakdown and formation of temporal glow discharge in a background of low-current Townsend discharge, while the decay edge relates to the transition back to Townsend discharge. The pulse interval is the re-building process of the space charge layer of high density to ensure the glow breakdown.

Fresh-slice multicolour X-ray free-electron lasers

DOE PAGES

Lutman, Alberto A.; Maxwell, Timothy J.; MacArthur, James P.; ...

2016-10-24

X-ray free-electron lasers (XFELs) provide femtosecond X-ray pulses with a narrow energy bandwidth and unprecedented brightness. Ultrafast physical and chemical dynamics, initiated with a site-specific X-ray pulse, can be explored using XFELs with a second ultrashort X-ray probe pulse. However, existing double-pulse schemes are complicated, difficult to customize or provide only low-intensity pulses. Here we present the novel fresh-slice technique for multicolour pulse production, wherein different temporal slices of an electron bunch lase to saturation in separate undulator sections. This method combines electron bunch tailoring from a passive wakefield device with trajectory control to provide multicolour pulses. The fresh-slice schememore » outperforms existing techniques at soft X-ray wavelengths. It produces femtosecond pulses with a power of tens of gigawatts and flexible colour separation. The pulse delay can be varied from temporal overlap to almost one picosecond. As a result, we also demonstrate the first three-colour XFEL and variably polarized two-colour pulses.« less

Pulse compressor with aberration correction

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

Mankos, Marian

In this SBIR project, Electron Optica, Inc. (EOI) is developing an electron mirror-based pulse compressor attachment to new and retrofitted dynamic transmission electron microscopes (DTEMs) and ultrafast electron diffraction (UED) cameras for improving the temporal resolution of these instruments from the characteristic range of a few picoseconds to a few nanoseconds and beyond, into the sub-100 femtosecond range. The improvement will enable electron microscopes and diffraction cameras to better resolve the dynamics of reactions in the areas of solid state physics, chemistry, and biology. EOI’s pulse compressor technology utilizes the combination of electron mirror optics and a magnetic beam separatormore » to compress the electron pulse. The design exploits the symmetry inherent in reversing the electron trajectory in the mirror in order to compress the temporally broadened beam. This system also simultaneously corrects the chromatic and spherical aberration of the objective lens for improved spatial resolution. This correction will be found valuable as the source size is reduced with laser-triggered point source emitters. With such emitters, it might be possible to significantly reduce the illuminated area and carry out ultrafast diffraction experiments from small regions of the sample, e.g. from individual grains or nanoparticles. During phase I, EOI drafted a set of candidate pulse compressor architectures and evaluated the trade-offs between temporal resolution and electron bunch size to achieve the optimum design for two particular applications with market potential: increasing the temporal and spatial resolution of UEDs, and increasing the temporal and spatial resolution of DTEMs. Specialized software packages that have been developed by MEBS, Ltd. were used to calculate the electron optical properties of the key pulse compressor components: namely, the magnetic prism, the electron mirror, and the electron lenses. In the final step, these results were folded into a model describing the key electron-optical parameters of the complete pulse compressor. The simulations reveal that the mirror pulse compressor can reduce the temporal spread of UEDs and DTEMs to the sub-100 femtosecond level for practical electron bunch sizes. EOI’s pulse compressors can be designed and built to attach to different types of UEDs and DTEMs, thus making them suitable for enhancing the study of the structure, composition, and bonding states of new materials at ultrafast time scales to advance material science research in the field of nanotechnology as well as biomedical research.« less

Construction and characterization of ultraviolet acousto-optic based femtosecond pulse shapers

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

Mcgrane, Shawn D; Moore, David S; Greenfield, Margo T

2008-01-01

We present all the information necessary for construction and characterization of acousto optic pulse shapers, with a focus on ultraviolet wavelengths, Various radio-frequency drive configurations are presented to allow optimization via knowledgeable trade-off of design features. Detailed performance characteristics of a 267 nm acousto-optic modulator (AOM) based pulse shaper are presented, Practical considerations for AOM based pulse shaping of ultra-broad bandwidth (sub-10 fs) amplified femtosecond pulse shaping are described, with particular attention paid to the effects of the RF frequency bandwidth and optical frequency bandwidth on the spatial dispersion of the output laser pulses.

Study on the Depth, Rate, Shape, and Strength of Pulse with Cardiovascular Simulator.

PubMed

Lee, Ju-Yeon; Jang, Min; Shin, Sang-Hoon

2017-01-01

Pulse diagnosis is important in oriental medicine. The purpose of this study is explaining the mechanisms of pulse with a cardiovascular simulator. The simulator is comprised of the pulse generating part, the vessel part, and the measurement part. The pulse generating part was composed of motor, slider-crank mechanism, and piston pump. The vessel part, which was composed with the aorta and a radial artery, was fabricated with silicon to implement pulse wave propagation. The pulse parameters, such as the depth, rate, shape, and strength, were simulated. With changing the mean pressure, the floating pulse and the sunken pulse were generated. The change of heart rate generated the slow pulse and the rapid pulse. The control of the superposition time of the reflected wave generated the string-like pulse and the slippery pulse. With changing the pulse pressure, the vacuous pulse and the replete pulse were generated. The generated pulses showed good agreements with the typical pulses.

Optical sampling by laser cavity tuning.

PubMed

Hochrein, Thomas; Wilk, Rafal; Mei, Michael; Holzwarth, Ronald; Krumbholz, Norman; Koch, Martin

2010-01-18

Most time-resolved optical experiments rely either on external mechanical delay lines or on two synchronized femtosecond lasers to achieve a defined temporal delay between two optical pulses. Here, we present a new method which does not require any external delay lines and uses only a single femtosecond laser. It is based on the cross-correlation of an optical pulse with a subsequent pulse from the same laser. Temporal delay between these two pulses is achieved by varying the repetition rate of the laser. We validate the new scheme by a comparison with a cross-correlation measurement carried out with a conventional mechanical delay line.

Laser beam temporal and spatial tailoring for laser shock processing

DOEpatents

Hackel, Lloyd; Dane, C. Brent

2001-01-01

Techniques are provided for formatting laser pulse spatial shape and for effectively and efficiently delivering the laser energy to a work surface in the laser shock process. An appropriately formatted pulse helps to eliminate breakdown and generate uniform shocks. The invention uses a high power laser technology capable of meeting the laser requirements for a high throughput process, that is, a laser which can treat many square centimeters of surface area per second. The shock process has a broad range of applications, especially in the aerospace industry, where treating parts to reduce or eliminate corrosion failure is very important. The invention may be used for treating metal components to improve strength and corrosion resistance. The invention has a broad range of applications for parts that are currently shot peened and/or require peening by means other than shot peening. Major applications for the invention are in the automotive and aerospace industries for components such as turbine blades, compressor components, gears, etc.

Temporally and Spatially Resolved Plasma Spectroscopy in Pulsed Laser Deposition of Ultra-Thin Boron Nitride Films (Postprint)

DTIC Science & Technology

2015-04-24

AFRL-RX-WP-JA-2016-0196 TEMPORALLY AND SPATIALLY RESOLVED PLASMA SPECTROSCOPY IN PULSED LASER DEPOSITION OF ULTRA-THIN BORON NITRIDE...AND SPATIALLY RESOLVED PLASMA SPECTROSCOPY IN PULSED LASER DEPOSITION OF ULTRA-THIN BORON NITRIDE FILMS (POSTPRINT) 5a. CONTRACT NUMBER FA8650...distributions within a PVD plasma plume ablated from a boron nitride (BN) target by a KrF laser at different pressures of nitrogen gas were investigated

Auditory Temporal Acuity Probed With Cochlear Implant Stimulation and Cortical Recording

PubMed Central

Kirby, Alana E.

2010-01-01

Cochlear implants stimulate the auditory nerve with amplitude-modulated (AM) electric pulse trains. Pulse rates >2,000 pulses per second (pps) have been hypothesized to enhance transmission of temporal information. Recent studies, however, have shown that higher pulse rates impair phase locking to sinusoidal AM in the auditory cortex and impair perceptual modulation detection. Here, we investigated the effects of high pulse rates on the temporal acuity of transmission of pulse trains to the auditory cortex. In anesthetized guinea pigs, signal-detection analysis was used to measure the thresholds for detection of gaps in pulse trains at rates of 254, 1,017, and 4,069 pps and in acoustic noise. Gap-detection thresholds decreased by an order of magnitude with increases in pulse rate from 254 to 4,069 pps. Such a pulse-rate dependence would likely influence speech reception through clinical speech processors. To elucidate the neural mechanisms of gap detection, we measured recovery from forward masking after a 196.6-ms pulse train. Recovery from masking was faster at higher carrier pulse rates and masking increased linearly with current level. We fit the data with a dual-exponential recovery function, consistent with a peripheral and a more central process. High-rate pulse trains evoked less central masking, possibly due to adaptation of the response in the auditory nerve. Neither gap detection nor forward masking varied with cortical depth, indicating that these processes are likely subcortical. These results indicate that gap detection and modulation detection are mediated by two separate neural mechanisms. PMID:19923242

Experimental demonstration of novel cascaded SFG+DFG wavelength conversion of picosecond pulses in LiNbO 3 waveguides

NASA Astrophysics Data System (ADS)

Wang, Jian; Sun, Junqiang; Luo, Chuanhong

2006-06-01

A novel cascaded χ (2) wavelength conversion of picosecond pulses based on sum frequency generation and difference frequency generation (SFG+DFG) is proposed and experimentally demonstrated in LiNbO 3 waveguides. The signal pulse with 40-GHz repetition rate and 1.57-ps pulse width is adopted. First of all, high conversion efficiency about -18.93dB can be achieved with low power level required for both two pump lights, which is greatly enhanced approximately 8dB compared with the conventional cascaded second-order nonlinear interactions (SHG+DFG) with a single and much higher power pump. Secondly, the wavelength of the converted idler wave can be tuned from 1527.4 to 1540.5nm when the signal wavelength is changed from 1561.9 to 1548.4nm, and about 13.1nm converted idler bandwidth is achieved with the conversion efficiency higher than -31dB. Thirdly, two pump wavelengths can be separated as large as 17.3nm. Meanwhile, when one pump wavelength is fixed at 1549.1nm, the other can be tuned within a wide wavelength range about 7.6nm with the conversion efficiency higher than -34dB, which is much larger than that in the SHG+DFG situation. Finally, the temporal waveform of the converted idler pulse is observed with rather clear appearance achieved, and no obvious changes of the pulse shape and width are found compared with its corresponding original injected signal, showing that our proposed scheme exhibits a very good conversion performance.

Pulse shape discrimination and classification methods for continuous depth of interaction encoding PET detectors.

PubMed

Roncali, Emilie; Phipps, Jennifer E; Marcu, Laura; Cherry, Simon R

2012-10-21

In previous work we demonstrated the potential of positron emission tomography (PET) detectors with depth-of-interaction (DOI) encoding capability based on phosphor-coated crystals. A DOI resolution of 8 mm full-width at half-maximum was obtained for 20 mm long scintillator crystals using a delayed charge integration linear regression method (DCI-LR). Phosphor-coated crystals modify the pulse shape to allow continuous DOI information determination, but the relationship between pulse shape and DOI is complex. We are therefore interested in developing a sensitive and robust method to estimate the DOI. Here, linear discriminant analysis (LDA) was implemented to classify the events based on information extracted from the pulse shape. Pulses were acquired with 2×2×20 mm(3) phosphor-coated crystals at five irradiation depths and characterized by their DCI values or Laguerre coefficients. These coefficients were obtained by expanding the pulses on a Laguerre basis set and constituted a unique signature for each pulse. The DOI of individual events was predicted using LDA based on Laguerre coefficients (Laguerre-LDA) or DCI values (DCI-LDA) as discriminant features. Predicted DOIs were compared to true irradiation depths. Laguerre-LDA showed higher sensitivity and accuracy than DCI-LDA and DCI-LR and was also more robust to predict the DOI of pulses with higher statistical noise due to low light levels (interaction depths further from the photodetector face). This indicates that Laguerre-LDA may be more suitable to DOI estimation in smaller crystals where lower collected light levels are expected. This novel approach is promising for calculating DOI using pulse shape discrimination in single-ended readout depth-encoding PET detectors.

Pulse Shape Discrimination and Classification Methods for Continuous Depth of Interaction Encoding PET Detectors

PubMed Central

Roncali, Emilie; Phipps, Jennifer E.; Marcu, Laura; Cherry, Simon R.

2012-01-01

In previous work we demonstrated the potential of positron emission tomography (PET) detectors with depth-of-interaction (DOI) encoding capability based on phosphor-coated crystals. A DOI resolution of 8 mm full-width at half-maximum was obtained for 20 mm long scintillator crystals using a delayed charge integration linear regression method (DCI-LR). Phosphor-coated crystals modify the pulse shape to allow continuous DOI information determination, but the relationship between pulse shape and DOI is complex. We are therefore interested in developing a sensitive and robust method to estimate the DOI. Here, linear discriminant analysis (LDA) was implemented to classify the events based on information extracted from the pulse shape. Pulses were acquired with 2 × 2 × 20 mm3 phosphor-coated crystals at five irradiation depths and characterized by their DCI values or Laguerre coefficients. These coefficients were obtained by expanding the pulses on a Laguerre basis set and constituted a unique signature for each pulse. The DOI of individual events was predicted using LDA based on Laguerre coefficients (Laguerre-LDA) or DCI values (DCI-LDA) as discriminant features. Predicted DOIs were compared to true irradiation depths. Laguerre-LDA showed higher sensitivity and accuracy than DCI-LDA and DCI-LR and was also more robust to predict the DOI of pulses with higher statistical noise due to low light levels (interaction depths further from the photodetector face). This indicates that Laguerre-LDA may be more suitable to DOI estimation in smaller crystals where lower collected light levels are expected. This novel approach is promising for calculating DOI using pulse shape discrimination in single-ended readout depth-encoding PET detectors. PMID:23010690

Optical integrator for optical dark-soliton detection and pulse shaping.

PubMed

Ngo, Nam Quoc

2006-09-10

The design and analysis of an Nth-order optical integrator using the digital filter technique is presented. The optical integrator is synthesized using planar-waveguide technology. It is shown that a first-order optical integrator can be used as an optical dark-soliton detector by converting an optical dark-soliton pulse into an optical bell-shaped pulse for ease of detection. The optical integrators can generate an optical step function, staircase function, and paraboliclike functions from input optical Gaussian pulses. The optical integrators may be potentially used as basic building blocks of all-optical signal processing systems because the time integrals of signals may sometimes be required for further use or analysis. Furthermore, an optical integrator may be used for the shaping of optical pulses or in an optical feedback control system.

Laser pulse shape design for laser-indirect-driven quasi-isentropic compression experiments

NASA Astrophysics Data System (ADS)

Xue, Quanxi; Jiang, Shaoen; Wang, Zhebin; Wang, Feng; Zhao, Xueqing; Ding, Yongkun

2018-02-01

Laser pulse shape design is a key work in the design of indirect-laser-driven experiments, especially for long pulse laser driven quasi-isentropic compression experiments. A method for designing such a laser pulse shape is given here. What's more, application experiments were performed, and the results of a typical shot are presented. At last of this article, the details of the application of the method are discussed, such as the equation parameter choice, radiation ablation pressure expression, and approximations in the method. The application shows that the method can provide reliable descriptions of the energy distribution in a hohlraum target; thus, it can be used in the design of long-pulse laser driven quasi-isentropic compression experiments and even other indirect-laser-driven experiments.

Neutron/ γ-ray digital pulse shape discrimination with organic scintillators

NASA Astrophysics Data System (ADS)

Kaschuck, Y.; Esposito, B.

2005-10-01

Neutrons and γ-rays produce light pulses with different shapes when interacting with organic scintillators. This property is commonly used to distinguish between neutrons (n) and γ-rays ( γ) in mixed n/ γ fields as those encountered in radiation physics experiments. Although analog electronic pulse shape discrimination (PSD) modules have been successfully used for many years, they do not allow data reprocessing and are limited in count rate capability (typically up to 200 kHz). The performance of a n/ γ digital pulse shape discrimination (DPSD) system by means of a commercial 12-bit 200 MSamples/s transient recorder card is investigated here. Three organic scintillators have been studied: stilbene, NE213 and anthracene. The charge comparison method has been used to obtain simultaneous n/ γ discrimination and pulse height analysis. The importance of DPSD for high-intensity radiation field measurements and its advantages with respect to analog PSD are discussed. Based on post-experiment simulations with acquired data, the requirements for fast digitizers to provide DPSD with organic scintillators are also analyzed.

Pulsed plane wave analytic solutions for generic shapes and the validation of Maxwell's equations solvers

NASA Technical Reports Server (NTRS)

Yarrow, Maurice; Vastano, John A.; Lomax, Harvard

1992-01-01

Generic shapes are subjected to pulsed plane waves of arbitrary shape. The resulting scattered electromagnetic fields are determined analytically. These fields are then computed efficiently at field locations for which numerically determined EM fields are required. Of particular interest are the pulsed waveform shapes typically utilized by radar systems. The results can be used to validate the accuracy of finite difference time domain Maxwell's equations solvers. A two-dimensional solver which is second- and fourth-order accurate in space and fourth-order accurate in time is examined. Dielectric media properties are modeled by a ramping technique which simplifies the associated gridding of body shapes. The attributes of the ramping technique are evaluated by comparison with the analytic solutions.

Dynamic and interaction of fs-laser induced cavitation bubbles for analyzing the cutting effect

NASA Astrophysics Data System (ADS)

Tinne, N.; Schumacher, S.; Nuzzo, V.; Ripken, T.; Lubatschowski, H.

2009-07-01

A prominent laser based treatment in ophthalmology is the LASIK procedure which nowadays includes a cutting of the corneal tissue based on ultra short pulses. Focusing an ultra short laser pulse below the surface of biological tissue an optical breakdown is caused and hence a dissection is obtained. The laser energy of the laser pulses is absorbed by nonlinear processes. As a result a cavitation bubble expands and ruptures the tissue. Hence positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the duration of the treatment the current development of ultra short laser systems points to higher repetition rates in the range of hundreds of KHz or even MHz instead of tens of kHz. This in turn results in a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra short pulse laser systems with high (> 1 MHz) repetition rates.

Temporally resolved diagnosis of an atmospheric-pressure pulse-modulated argon surface wave plasma by optical emission spectroscopy

NASA Astrophysics Data System (ADS)

Chen, Chuan-Jie; Li, Shou-Zhe; Zhang, Jialiang; Liu, Dongping

2018-01-01

A pulse-modulated argon surface wave plasma generated at atmospheric pressure is characterized by means of temporally resolved optical emission spectroscopy (OES). The temporal evolution of the gas temperature, the electron temperature and density, the radiative species of atomic Ar, and the molecular band of OH(A) and N2(C) are investigated experimentally by altering the instantaneous power, pulse repetitive frequency, and duty ratio. We focused on the physical phenomena occurring at the onset of the time-on period and after the power interruption at the start of the time-off period. Meanwhile, the results are discussed qualitatively for an in-depth insight of its dynamic evolution.

Terahertz wavefront assessment based on 2D electro-optic imaging

NASA Astrophysics Data System (ADS)

Cahyadi, Harsono; Ichikawa, Ryuji; Degert, Jérôme; Freysz, Eric; Yasui, Takeshi; Abraham, Emmanuel

2015-03-01

Complete characterization of terahertz (THz) radiation becomes an interesting yet challenging study for many years. In visible optical region, the wavefront assessment has been proved as a powerful tool for the beam profiling and characterization, which consequently requires 2-dimension (2D) single-shot acquisition of the beam cross-section to provide the spatial profile in time- and frequency-domain. In THz region, the main problem is the lack of effective THz cameras to satisfy this need. In this communication, we propose a simple setup based on free-space collinear 2D electrooptic sampling in a ZnTe crystal for the characterization of THz wavefronts. In principle, we map the optically converted, time-resolved data of the THz pulse by changing the time delay between the probe pulse and the generated THz pulse. The temporal waveforms from different lens-ZnTe distances can clearly indicate the evolution of THz beam as it is converged, focused, or diverged. From the Fourier transform of the temporal waveforms, we can obtain the spectral profile of a broadband THz wave, which in this case within the 0.1-2 THz range. The spectral profile also provides the frequency dependency of the THz pulse amplitude. The comparison between experimental and theoretical results at certain frequencies (here we choose 0.285 and 1.035 THz) is in a good agreement suggesting that our system is capable of THz wavefront characterization. Furthermore, the implementation of Hartmann/Shack-Hartmann sensor principle enables the reconstruction of THz wavefront. We demonstrate the reconstruction of THz wavefronts which are changed from planar wave to spherical one due to the insertion of convex THz lens in the THz beam path. We apply and compare two different reconstruction methods: linear integration and Zernike polynomial. Roughly we conclude that the Zernike method provide smoother wavefront shape that can be elaborated later into quantitative-qualitative analysis about the wavefront distortion.

Nonlinear pulse shaping and polarization dynamics in mode-locked fiber lasers

NASA Astrophysics Data System (ADS)

Boscolo, Sonia; Sergeyev, Sergey V.; Mou, Chengbo; Tsatourian, Veronika; Turitsyn, Sergei; Finot, Christophe; Mikhailov, Vitaly; Rabin, Bryan; Westbrook, Paul S.

2014-03-01

We review our recent progress on the study of new nonlinear mechanisms of pulse shaping in passively mode-locked fiber lasers. These include a mode-locking regime featuring pulses with a triangular distribution of the intensity, and spectral compression arising from nonlinear pulse propagation. We also report on our recent experimental studies unveiling new types of vector solitons with processing states of polarization for multi-pulse and tightly bound-state soliton (soliton molecule) operations in a carbon nanotube (CNT) mode-locked fiber laser with anomalous dispersion cavity.

Control of wavepacket dynamics in mixed alkali metal clusters by optimally shaped fs pulses

NASA Astrophysics Data System (ADS)

Bartelt, A.; Minemoto, S.; Lupulescu, C.; Vajda, Š.; Wöste, L.

We have performed adaptive feedback optimization of phase-shaped femtosecond laser pulses to control the wavepacket dynamics of small mixed alkali-metal clusters. An optimization algorithm based on Evolutionary Strategies was used to maximize the ion intensities. The optimized pulses for NaK and Na2K converged to pulse trains consisting of numerous peaks. The timing of the elements of the pulse trains corresponds to integer and half integer numbers of the vibrational periods of the molecules, reflecting the wavepacket dynamics in their excited states.

The optimal input optical pulse shape for the self-phase modulation based chirp generator

NASA Astrophysics Data System (ADS)

Zachinyaev, Yuriy; Rumyantsev, Konstantin

2018-04-01

The work is aimed to obtain the optimal shape of the input optical pulse for the proper functioning of the self-phase modulation based chirp generator allowing to achieve high values of chirp frequency deviation. During the research, the structure of the device based on self-phase modulation effect using has been analyzed. The influence of the input optical pulse shape of the transmitting optical module on the chirp frequency deviation has been studied. The relationship between the frequency deviation of the generated chirp and frequency linearity for the three options for implementation of the pulse shape has been also estimated. The results of research are related to the development of the theory of radio processors based on fiber-optic structures and can be used in radars, secure communications, geolocation and tomography.

Acousto-optic replication of ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Yushkov, Konstantin B.; Molchanov, Vladimir Ya.; Ovchinnikov, Andrey V.; Chefonov, Oleg V.

2017-10-01

Precisely controlled sequences of ultrashort laser pulses are required in various scientific and engineering applications. We developed a phase-only acousto-optic pulse shaping method for replication of ultrashort laser pulses in a TW laser system. A sequence of several Fourier-transform-limited pulses is generated from a single femtosecond laser pulse by means of applying a piecewise linear phase modulation over the whole emission spectrum. Analysis demonstrates that the main factor which limits maximum delay between the pulse replicas is spectral resolution of the acousto-optic dispersive delay line used for pulse shaping. In experiments with a Cr:forsterite laser system, we obtained delays from 0.3 to 3.5 ps between two replicas of 190 fs transform-limited pulses at the central wavelength of laser emission, 1230 nm.

A 100 J-level nanosecond DPSSL for high energy density experiments

NASA Astrophysics Data System (ADS)

Butcher, Thomas; Mason, Paul; Banerjee, Saumyabrata; Ertel, Klaus; Phillips, P. Jonathan; Smith, Jodie; De Vido, Mariastefania; Chekhlov, Oleg; Divoky, Martin; Pilat, Jan; Priebe, Gerd; Toncian, Toma; Shaikh, Waseem; Hooker, Chris; Lucianetti, Antonio; Hernandez-Gomez, Cristina; Mocek, Tomas; Edwards, Chris; Collier, John

2017-05-01

We present an overview of the cryo-amplifier concept and design utilized in the DiPOLE100 laser system built for use at the HiLASE Center, which has been successfully tested operating at an average power of 1kW. Following this we describe the alterations made to the design in the second generation system being constructed for high energy density (HED) experiments in the HED beamline at the European XFEL. These changes are predominantly geometric in nature, however also include improved mount design and improved control over the temporal shape of the output pulse. Finally, we comment on future plans for development of the DiPOLE laser amplifier architecture.

A fast BK-type KCa current acts as a postsynaptic modulator of temporal selectivity for communication signals.

PubMed

Kohashi, Tsunehiko; Carlson, Bruce A

2014-01-01

Temporal patterns of spiking often convey behaviorally relevant information. Various synaptic mechanisms and intrinsic membrane properties can influence neuronal selectivity to temporal patterns of input. However, little is known about how synaptic mechanisms and intrinsic properties together determine the temporal selectivity of neuronal output. We tackled this question by recording from midbrain electrosensory neurons in mormyrid fish, in which the processing of temporal intervals between communication signals can be studied in a reduced in vitro preparation. Mormyrids communicate by varying interpulse intervals (IPIs) between electric pulses. Within the midbrain posterior exterolateral nucleus (ELp), the temporal patterns of afferent spike trains are filtered to establish single-neuron IPI tuning. We performed whole-cell recording from ELp neurons in a whole-brain preparation and examined the relationship between intrinsic excitability and IPI tuning. We found that spike frequency adaptation of ELp neurons was highly variable. Postsynaptic potentials (PSPs) of strongly adapting (phasic) neurons were more sharply tuned to IPIs than weakly adapting (tonic) neurons. Further, the synaptic filtering of IPIs by tonic neurons was more faithfully converted into variation in spiking output, particularly at short IPIs. Pharmacological manipulation under current- and voltage-clamp revealed that tonic firing is mediated by a fast, large-conductance Ca(2+)-activated K(+) (KCa) current (BK) that speeds up action potential repolarization. These results suggest that BK currents can shape the temporal filtering of sensory inputs by modifying both synaptic responses and PSP-to-spike conversion. Slow SK-type KCa currents have previously been implicated in temporal processing. Thus, both fast and slow KCa currents can fine-tune temporal selectivity.

Amorphization dynamics of Ge{sub 2}Sb{sub 2}Te{sub 5} films upon nano- and femtosecond laser pulse irradiation

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

Siegel, J.; Gawelda, W.; Puerto, D.

2008-01-15

Phase transformations of crystalline Ge{sub 2}Sb{sub 2}Te{sub 5} films upon pulsed laser irradiation have been studied using in situ reflectivity measurements with temporal resolution. Two different configurations allowed point probing with nanosecond temporal resolution and imaging with subpicosecond temporal and micrometer spatial resolution. The role of the pulse duration and laser fluence on the dynamics of the phase change and the degree of amorphization is discussed. Several advantageous features of femtosecond compared to nanosecond laser-induced amorphization are identified. Moreover, a high-resolution study of the amorphization dynamics reveals the onset of amorphization at moderate fluences to occur within {approx}100 ps aftermore » arrival of the laser pulse. At high fluences, amorphization occurs after {approx}430 ps and the molten phase is characterized by an anomalously low reflectivity value, indicative of a state of extreme supercooling.« less

Dynamics of femtosecond laser-induced periodic surface structures on silicon by high spatial and temporal resolution imaging

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

Jia, X., E-mail: jiaxin@sdju.edu.cn; Department of Mathematics and Physics, Shanghai Dianji University, Shanghai 201306; Jia, T. Q., E-mail: tqjia@phy.ecnu.edu.cn

2014-04-14

The formation dynamics of periodic ripples induced by femtosecond laser pulses (pulse duration τ = 50 fs and central wavelength λ = 800 nm) are studied by a collinear pump-probe imaging technique with a temporal resolution of 1 ps and a spatial resolution of 440 nm. The ripples with periods close to the laser wavelength begin to appear upon irradiation of two pump pulses at surface defects produced by the prior one. The rudiments of periodic ripples emerge in the initial tens of picoseconds after fs laser irradiation, and the ripple positions keep unmoved until the formation processes complete mainly in a temporal span of 1500 ps. Themore » results suggest that the periodic deposition of laser energy during the interaction between femtosecond laser pulses and sample surface plays a dominant role in the formation of periodic ripples.« less

[Low level alpha activity measurements with pulse shape discrimination--the analytical system and its characteristics].

PubMed

Noguchi, M; Satoh, K; Higuchi, H

1984-12-01

Pulse shape discrimination of alpha and beta rays with liquid scintillation counting was investigated for the purpose of low level alpha activity measurements. Various liquid scintillators for pulse shape discrimination were examined by means of pulse rise time analysis. A new scintillator of low cost and of superior characteristics was found. The figure of merits better than 3.5 in rise time spectrum and the energy resolution better than 9% were obtained for carefully prepared samples. The background counting rate for a sample of 10 ml was reduced to 0.013 cpm/MeV in the range of alpha ray energy 5 to 7 MeV.

Temporal Behavior of the Pump Pulses, Residual Pump Pulses, and THz Pulses for D2O Gas Pumped by a TEA CO2 Laser

NASA Astrophysics Data System (ADS)

Geng, Lijie; Zhang, Zhifeng; Zhai, Yusheng; Su, Yuling; Zhou, Fanghua; Qu, Yanchen; Zhao, Weijiang

2016-08-01

Temporal behavior of the pump pulses, residual pump pulses, and THz pulses for optically pumped D2O gas molecules was investigated by using a tunable TEA CO2 laser as the pumping source. The pulse profiles of pump laser pulses, residual pump pulses, and the THz output pulses were measured, simultaneously, at several different gas pressures. For THz pulse, the pulse delay between the THz pulse and the pump pulse was observed and the delay time was observed to increase from 40 to 70 ns with an increase in gas pressure from 500 to 1700 Pa. Both THz pulse broadening and compression were observed, and the pulse broadening effect transformed to the compression effect with increasing the gas pressure. For the residual pump pulse, the full width at half maximum (FWHM) of the main pulse decreased with increasing gas pressure, and the main pulse disappeared at high gas pressures. The secondary pulses were observed at high gas pressure, and the time intervals of about 518 and 435 ns were observed between the THz output pulse and the secondary residual pump pulse at the pressure of 1400 Pa and 1700 Pa, from which the vibrational relaxation time constants of about 5.45 and 5.55 μs Torr were obtained.

Spiking suppression of high power QCW pulse 1319 nm Nd:YAG laser with different intracavity doublers

NASA Astrophysics Data System (ADS)

Bian, Qi; Zuo, Jun-Wei; Guo, Chuan; Xu, Chang; Shen, Yu; Zong, Nan; Bo, Yong; Peng, Qin-Jun; Chen, Hong-Bin; Cui, Da-Fu; Xu, Zu-Yan

2016-09-01

We describe the results of our efforts in suppressing spiking of a high power, high beam quality 1319 nm Nd:YAG microsecond-pulse laser with three different intracavity frequency doublers. The 1319 nm laser is generated by a quasi-continuous-wave diode-pumped Nd:YAG ring laser system. One potassium titanyl phosphate (KTP), two KTPs and one lithium triborate (LBO) as frequency doublers are installed in the ring resonator and tested, respectively. At 800 Hz repetition rate, with a pulse width of 100 µs, performances of spiking suppression for each case are observed. The average output power are 23.6 W, 22.7 W and 23.4 W with beam quality factors of M 2  =  2.21, 1.28 and 1.25 for one KTP, two KTPs and one LBO, respectively. The corresponding brightness are 270 MW/(cm2·sr), 780 MW/(cm2·sr) and 860 MW/(cm2·sr). With better beam quality, higher brightness, and easier maintainability, the LBO is the best option of the three. A laser rate equation model including the insertion loss of the doubler is applied for theoretical analysis of the output temporal pulse shape and power, and the simulated results agree well with the experimental data.

Terahertz pulse generation by the tilted pulse front technique using an M-shaped optical system

NASA Astrophysics Data System (ADS)

Morita, Ken; Shiozawa, Kento; Suizu, Koji; Ishitani, Yoshihiro

2018-05-01

To achieve the phase matching condition in terahertz (THz) pulse generation by the tilted pulse front technique, it is necessary to rebuild the entire optical setup if the optical conditions, such as excitation wavelength, temperature of nonlinear crystal, and output THz frequency, are changed. We propose THz pulse generation by the tilted pulse front technique using an M-shaped configuration. This system allows us to change the optical conditions only by tuning a few optics and without rebuilding the entire setup. We change the excitation wavelength at a fixed radiation frequency and assess the performance of the proposed system.

Radioanalytical Chemistry for Automated Nuclear Waste Process Monitoring

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

Devol, Timothy A.

2005-06-01

Comparison of different pulse shape discrimination methods was performed under two different experimental conditions and the best method was identified. Beta/gamma discrimination of 90Sr/90Y and 137Cs was performed using a phoswich detector made of BC400 (2.5 cm OD x 1.2 cm) and BGO (2.5 cm O.D. x 2.5 cm ) scintillators. Alpha/gamma discrimination of 210Po and 137Cs was performed using a CsI:Tl (2.8 x 1.4 x 1.4 cm3) scintillation crystal. The pulse waveforms were digitized with a DGF-4c (X-Ray Instrumentation Associates) and analyzed offline with IGOR Pro software (Wavemetrics, Inc.). The four pulse shape discrimination methods that were compared include:more » rise time discrimination, digital constant fraction discrimination, charge ratio, and constant time discrimination (CTD) methods. The CTD method is the ratio of the pulse height at a particular time after the beginning of the pulse to the time at the maximum pulse height. The charge comparison method resulted in a Figure of Merit (FoM) of 3.3 (9.9 % spillover) and 3.7 (0.033 % spillover) for the phoswich and the CsI:Tl scintillator setups, respectively. The CTD method resulted in a FoM of 3.9 (9.2 % spillover) and 3.2 (0.25 % spillover), respectively. Inverting the pulse shape data typically resulted in a significantly higher FoM than conventional methods, but there was no reduction in % spillover values. This outcome illustrates that the FoM may not be a good scheme for the quantification of a system to perform pulse shape discrimination. Comparison of several pulse shape discrimination (PSD) methods was performed as a means to compare traditional analog and digital PSD methods on the same scintillation pulses. The X-ray Instrumentation Associates DGF-4C (40 Msps, 14-bit) was used to digitize waveforms from a CsI:Tl crystal and BC400/BGO phoswich detector.« less

OPCPA front end and contrast optimization for the OMEGA EP kilojoule, picosecond laser

DOE PAGES

Dorrer, C.; Consentino, A.; Irwin, D.; ...

2015-09-01

OMEGA EP is a large-scale laser system that combines optical parametric amplification and solid-state laser amplification on two beamlines to deliver high-intensity, high-energy optical pulses. The temporal contrast of the output pulse is limited by the front-end parametric fluorescence and other features that are specific to parametric amplification. The impact of the two-crystal parametric preamplifier, pump-intensity noise, and pump-signal timing is experimentally studied. The implementation of a parametric amplifier pumped by a short pump pulse before stretching, further amplification, and recompression to enhance the temporal contrast of the high-energy short pulse is described.

Strong and Long Makes Short: Strong-Pump Strong-Probe Spectroscopy.

PubMed

Gelin, Maxim F; Egorova, Dassia; Domcke, Wolfgang

2011-01-20

We propose a new time-domain spectroscopic technique that is based on strong pump and probe pulses. The strong-pump strong-probe (SPSP) technique provides temporal resolution that is not limited by the durations of the pump and probe pulses. By numerically exact simulations of SPSP signals for a multilevel vibronic model, we show that the SPSP signals exhibit electronic and vibrational beatings on time scales which are significantly shorter than the pulse durations. This suggests the possible application of SPSP spectroscopy for the real-time investigation of molecular processes that cannot be temporally resolved by pump-probe spectroscopy with weak pump and probe pulses.

System for generating pluralities of optical pulses with predetermined frequencies in a temporally and spatially overlapped relationship

DOEpatents

Meyerhofer, David D.; Schmid, Ansgar W.; Chuang, Yung-ho

1992-01-01

Ultra short (pico second and shorter) laser pulses having components of different frequency which are overlapped coherently in space and with a predetermined constant relationship in time, are generated and may be used in applications where plural spectrally separate, time-synchronized pulses are needed as in wave-length resolved spectroscopy and spectral pump probe measurements for characterization of materials. A Chirped Pulse Amplifier (CPA), such as a regenerative amplifier, which provides amplified, high intensity pulses at the output thereof which have the same spatial intensity profile, is used to process a series of chirped pulses, each with a different central frequency (the desired frequencies contained in the output pulses). Each series of chirped pulses is obtained from a single chirped pulse by spectral windowing with a mask in a dispersive expansion stage ahead of the laser amplifier. The laser amplifier amplifies the pulses and provides output pulses with like spatial and temporal profiles. A compression stage then compresses the amplified pulses. All the individual pulses of different frequency, which originated in each single chirped pulse, are compressed and thereby coherently overlapped in space and time. The compressed pulses may be used for the foregoing purposes and other purposes wherien pulses having a plurality of discrete frequency components are required.

System for generating pluralities of optical pulses with predetermined frequencies in a temporally and spatially overlapped relationship

DOEpatents

Meyerhofer, D.D.; Schmid, A.W.; Chuang, Y.

1992-03-10

Ultrashort (pico second and shorter) laser pulses having components of different frequency which are overlapped coherently in space and with a predetermined constant relationship in time, are generated and may be used in applications where plural spectrally separate, time-synchronized pulses are needed as in wave-length resolved spectroscopy and spectral pump probe measurements for characterization of materials. A Chirped Pulse Amplifier (CPA), such as a regenerative amplifier, which provides amplified, high intensity pulses at the output thereof which have the same spatial intensity profile, is used to process a series of chirped pulses, each with a different central frequency (the desired frequencies contained in the output pulses). Each series of chirped pulses is obtained from a single chirped pulse by spectral windowing with a mask in a dispersive expansion stage ahead of the laser amplifier. The laser amplifier amplifies the pulses and provides output pulses with like spatial and temporal profiles. A compression stage then compresses the amplified pulses. All the individual pulses of different frequency, which originated in each single chirped pulse, are compressed and thereby coherently overlapped in space and time. The compressed pulses may be used for the foregoing purposes and other purposes wherien pulses having a plurality of discrete frequency components are required. 4 figs.

Single-Shot Measurement of Temporally-Dependent Polarization State of Femtosecond Pulses by Angle-Multiplexed Spectral-Spatial Interferometry

NASA Astrophysics Data System (ADS)

Lin, Ming-Wei; Jovanovic, Igor

2016-09-01

We demonstrate that temporally-dependent polarization states of ultrashort laser pulses can be reconstructed in a single shot by use of an angle-multiplexed spatial-spectral interferometry. This is achieved by introducing two orthogonally polarized reference pulses and interfering them with an arbitrarily polarized ultrafast pulse under measurement. A unique calibration procedure is developed for this technique which facilitates the subsequent polarization state measurements. The accuracy of several reconstructed polarization states is verified by comparison with that obtained from an analytic model that predicts the polarization state on the basis of its method of production. Laser pulses with mJ-level energies were characterized via this technique, including a time-dependent polarization state that can be used for polarization-gating of high-harmonic generation for production of attosecond pulses.

LASER APPLICATIONS IN MEDICINE: Effect of glucose concentration in a model light-scattering suspension on propagation of ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Popov, A. P.; Priezzhev, A. V.; Myllylä, Risto

2005-11-01

The propagation of laser pulses in the 2% aqueous solution of intralipid — a suspension of lipid particles with optical properties close to those of the human skin, is numerically simulated at different glucose concentrations. The temporal profiles of 820-nm laser pulses diffusely backscattered from a flat, 2-mm thick solution layer are simulated. The laser pulse profiles are detected by fibreoptic detectors of diameter 0.3 mm with the numerical apertures 0.19, 0.29, and 0.39. It is shown that this method can be used to detect changes in the glucose level in the physiological concentration range (100-500 mg dL-1) by monitoring variations in the peak intensity and area of the laser pulse temporal profile (pulse energy).

Realizing up-conversion fluorescence tuning in lanthanide-doped nanocrystals by femtosecond pulse shaping method

PubMed Central

Zhang, Shian; Yao, Yunhua; Shuwu, Xu; Liu, Pei; Ding, Jingxin; Jia, Tianqing; Qiu, Jianrong; Sun, Zhenrong

2015-01-01

The ability to tune color output of nanomaterials is very important for their applications in laser, optoelectronic device, color display and multiplexed biolabeling. Here we first propose a femtosecond pulse shaping technique to realize the up-conversion fluorescence tuning in lanthanide-doped nanocrystals dispersed in the glass. The multiple subpulse formation by a square phase modulation can create different excitation pathways for various up-conversion fluorescence generations. By properly controlling these excitation pathways, the multicolor up-conversion fluorescence can be finely tuned. This color tuning by the femtosecond pulse shaping technique is realized in single material by single-color laser field, which is highly desirable for further applications of the lanthanide-doped nanocrystals. This femtosecond pulse shaping technique opens an opportunity to tune the color output in the lanthanide-doped nanocrystals, which may bring a new revolution in the control of luminescence properties of nanomaterials. PMID:26290391

Transparent plastic scintillators for neutron detection based on lithium salicylate

DOE PAGES

Mabe, Andrew N.; Glenn, Andrew M.; Carman, M. Leslie; ...

2015-10-14

Transparent plastic scintillators with pulse shape discrimination containing 6Li salicylate have been synthesized by bulk polymerization with a maximum 6Li loading of 0.40 wt%. Photoluminescence and scintillation responses to gamma-rays and neutrons are reported in this paper. Plastics containing 6Li salicylate exhibit higher light yields and permit a higher loading of 6Li as compared to previously reported plastics based on lithium 3-phenylsalicylate. However, pulse shape discrimination performance is reduced in lithium salicylate plastics due to the requirement of adding more nonaromatic monomers to the polymer matrix as compared to those based on lithium 3-phenylsalicylate. Finally, reduction in light yield andmore » pulse shape discrimination performance in lithium-loaded plastics as compared to pulse shape discrimination plastics without lithium is interpreted in terms of energy transfer interference by the aromatic lithium salts.« less

Imaging feedback for histotripsy by characterizing dynamics of acoustic radiation force impulse (ARFI)-induced shear waves excited in a treated volume.

PubMed

Wang, Tzu-Yin; Hall, Timothy L; Xu, Zhen; Fowlkes, J Brian; Cain, Charles A

2014-07-01

Our previous study indicated that shear waves decay and propagate at a lower speed as they propagate into a tissue volume mechanically fractionated by histotripsy. In this paper, we hypothesize that the change in the shear dynamics is related to the degree of tissue fractionation, and can be used to predict histotripsy treatment outcomes. To test this hypothesis, lesions with different degrees of tissue fractionation were created in agar-graphite tissue phantoms and ex vivo kidneys with increasing numbers of therapy pulses, from 0 to 2000 pulses per treatment location. The therapy pulses were 3-cycle 750-kHz focused ultrasound delivered at a peak negative/positive pressure of 17/108 MPa and a repetition rate of 50 Hz. The shear waves were excited by acoustic radiation force impulse (ARFI) focused at the center of the lesion. The spatial and temporal behavior of the propagating shear waves was measured with ultrasound plane wave imaging. The temporal displacement profile at a lateral location 10 mm offset to the shear excitation region was detected with M-mode imaging. The decay and delay of the shear waves were quantitatively characterized on the temporal displacement profile. Results showed significant changes in two characteristics on the temporal displacement profile: the peak-to-peak displacement decayed exponentially with increasing numbers of therapy pulses; the relative time-to-peak displacement increased with increasing numbers of therapy pulses, and appeared to saturate at higher numbers of pulses. Correspondingly, the degree of tissues fractionation, as indicated by the percentage of structurally intact cell nuclei, decreased exponentially with increasing numbers of therapy pulses. Strong linear correlations were found between the two characteristics and the degree of tissue fractionation. These results suggest that the characteristics of the shear temporal displacement profile may provide useful feedback information regarding the treatment outcomes.

Interaction dynamics of fs-laser induced cavitation bubbles and their impact on the laser-tissue-interaction of modern ophthalmic laser systems

NASA Astrophysics Data System (ADS)

Tinne, N.; Ripken, T.; Lubatschowski, H.; Heisterkamp, A.

2011-07-01

A today well-known laser based treatment in ophthalmology is the LASIK procedure which nowadays includes cutting of the corneal tissue with ultra-short laser pulses. Instead of disposing a microkeratome for cutting a corneal flap, a focused ultra-short laser pulse is scanned below the surface of biological tissue causing the effect of an optical breakdown and hence obtaining a dissection. Inside the tissue, the energy of the laser pulses is absorbed by non-linear processes; as a result a cavitation bubble expands and ruptures the tissue. Hence, positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the amount of laser energy, with a moderate duration of treatment at the same time, the current development of ultra-short pulse laser systems points to higher repetition rates in the range of even Megahertz instead of tens or hundreds of Kilohertz. In turn, this results in a pulse overlap and therefor a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus, the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. The effects will be discussed regarding the medical ophthalmic application of fs-lasers. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra-short pulse laser systems with high (> 500 kHz) repetition rates.

The Dripping Handrail Model: Transient Chaos in Accretion Systems

NASA Technical Reports Server (NTRS)

Young, Karl; Scargle, Jeffrey D.; Cuzzi, Jeffrey (Technical Monitor)

1995-01-01

We define and study a simple dynamical model for accretion systems, the "dripping handrail" (DHR). The time evolution of this spatially extended system is a mixture of periodic and apparently random (but actually deterministic) behavior. The nature of this mixture depends on the values of its physical parameters - the accretion rate, diffusion coefficient, and density threshold. The aperiodic component is a special kind of deterministic chaos called transient chaos. The model can simultaneously exhibit both the quasiperiodic oscillations (QPO) and very low frequency noise (VLFN) that characterize the power spectra of fluctuations of several classes of accretion systems in astronomy. For this reason, our model may be relevant to many such astrophysical systems, including binary stars with accretion onto a compact object - white dwarf, neutron star, or black hole - as well as active galactic nuclei. We describe the systematics of the DHR's temporal behavior, by exploring its physical parameter space using several diagnostics: power spectra, wavelet "scalegrams," and Lyapunov exponents. In addition, we note that for large accretion rates the DHR has periodic modes; the effective pulse shapes for these modes - evaluated by folding the time series at the known period - bear a resemblance to the similarly- determined shapes for some x-ray pulsars. The pulsing observed in some of these systems may be such periodic-mode accretion, and not due to pure rotation as in the standard pulsar model.

Effect of pulsed discharge on the ignition of pulse modulated radio frequency glow discharge at atmospheric pressure

NASA Astrophysics Data System (ADS)

Qiu, Shenjie; Guo, Ying; Han, Qianhan; Bao, Yun; Zhang, Jing; Shi, J. J.

2018-01-01

A pulsed discharge is introduced between two sequential pulse-modulated radio frequency glow discharges in atmospheric helium. The dependence of radio frequency discharge ignition on pulsed discharge intensity is investigated experimentally with the pulse voltage amplitudes of 650, 850, and 1250 V. The discharge characteristics and dynamics are studied in terms of voltage and current waveforms, and spatial-temporal evolution of optical emission. With the elevated pulsed discharge intensity of two orders of magnitude, the ignition of radio frequency discharge is enhanced by reducing the ignition time and achieving the stable operation with a double-hump spatial profile. The ignition time of radio frequency discharge is estimated to be 2.0 μs, 1.5 μs, and 1.0 μs with the pulse voltage amplitudes of 650, 850, and 1250 V, respectively, which is also demonstrated by the spatial-temporal evolution of optical emission at 706 and 777 nm.

Cognitive-Behavioral Therapy versus Temporal Pulse Amplitude Biofeedback Training for Recurrent Headache

ERIC Educational Resources Information Center

Martin, Paul R.; Forsyth, Michael R.; Reece, John

2007-01-01

Sixty-four headache sufferers were allocated randomly to cognitive-behavioral therapy (CBT), temporal pulse amplitude (TPA) biofeedback training, or waiting-list control. Fifty-one participants (14M/37F) completed the study, 30 with migraine and 21 with tension-type headache. Treatment consisted of 8, 1-hour sessions. CBT was highly effective,…

Signal recognition efficiencies of artificial neural-network pulse-shape discrimination in HPGe -decay searches

NASA Astrophysics Data System (ADS)

Caldwell, A.; Cossavella, F.; Majorovits, B.; Palioselitis, D.; Volynets, O.

2015-07-01

A pulse-shape discrimination method based on artificial neural networks was applied to pulses simulated for different background, signal and signal-like interactions inside a germanium detector. The simulated pulses were used to investigate variations of efficiencies as a function of used training set. It is verified that neural networks are well-suited to identify background pulses in true-coaxial high-purity germanium detectors. The systematic uncertainty on the signal recognition efficiency derived using signal-like evaluation samples from calibration measurements is estimated to be 5 %. This uncertainty is due to differences between signal and calibration samples.

Modulation rate transfer functions from four species of stranded odontocete (Stenella longirostris, Feresa attenuata, Globicephala melas, and Mesoplodon densirostris).

PubMed

Smith, Adam B; Pacini, Aude F; Nachtigall, Paul E

2018-04-01

Odontocete marine mammals explore the environment by rapidly producing echolocation signals and receiving the corresponding echoes, which likewise return at very rapid rates. Thus, it is important that the auditory system has a high temporal resolution to effectively process and extract relevant information from click echoes. This study used auditory evoked potential methods to investigate auditory temporal resolution of individuals from four different odontocete species, including a spinner dolphin (Stenella longirostris), pygmy killer whale (Feresa attenuata), long-finned pilot whale (Globicephala melas), and Blainville's beaked whale (Mesoplodon densirostris). Each individual had previously stranded and was undergoing rehabilitation. Auditory Brainstem Responses (ABRs) were elicited via acoustic stimuli consisting of a train of broadband tone pulses presented at rates between 300 and 2000 Hz. Similar to other studied species, modulation rate transfer functions (MRTFs) of the studied individuals followed the shape of a low-pass filter, with the ability to process acoustic stimuli at presentation rates up to and exceeding 1250 Hz. Auditory integration times estimated from the bandwidths of the MRTFs ranged between 250 and 333 µs. The results support the hypothesis that high temporal resolution is conserved throughout the diverse range of odontocete species.

Femtosecond parabolic pulse shaping in normally dispersive optical fibers.

PubMed

Sukhoivanov, Igor A; Iakushev, Sergii O; Shulika, Oleksiy V; Díez, Antonio; Andrés, Miguel

2013-07-29

Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initial pulse duration, chirp and energy. Applicability of different fibers for femtosecond pulse shaping is analyzed. Recommendation for shortest parabolic pulse formation is made based on the analysis presented.

Strong Field Optical and Quantum Control

NASA Astrophysics Data System (ADS)

Schumacher, Douglass William

1995-01-01

This work presents the results of an effort to use unique forms of optical radiation to better probe and control matter. Results are presented of a study of intense field photo-ionization of krypton and xenon in a two-color field. The use of a two-color field provides a valuable probe, the relative optical phase, into the dynamics of the ionization process. It is found that phase dependent tunneling character is preserved even though the photoelectron spectra indicate that the experiments performed were well into the multi-photon regime of ionization. Evidence for core scattering of the departing electrons is seen in the changes to the phase dependent spectra as the polarization of the exciting light is varied from linear to slightly elliptical. To further control the optical field, a pulse shaper was constructed using liquid crystal modulators that allowed either spectral phase or spectral amplitude shaping of a short pulse. The results were characterized using cross-correlations. The shaped light was then subsequently amplified in a chirped pulse amplifier. This light was characterized using Frequency Resolved Optical Gating, a newly developed technique for the complete determination of the optical field in a short pulse. The shaped pulses were then used to tailor atomic radial wavepackets in cesium. The evolution of the wavepackets was monitored by measuring atomic auto-interferograms for the case of amplitude shaping, which was used to control the atomic states excited. Cross -interferograms were used for phase shaping, which was used to select the initial phase of the atomic states. The cross-interferograms required the simultaneous amplification of a shaped and an unshaped pulse in our amplifier.

Control of Chemical Dynamics Using Arbitrary Shaped Optical Pulses and Laser-Enhanced NMR Spectroscopy.

NASA Astrophysics Data System (ADS)

Goswami, Debabrata

A key feature of this thesis is the application of novel laser techniques to various fields of spectroscopy. The overall effort has been towards achieving either chemical control or enhanced spectroscopic resolution. The issue of chemical control forms the major bulk. Over the past decade, theoretical and technological developments have made it possible for a modern day chemist to be a more active participant in nature's chemical processes. Consequently, although the idea of manipulating chemical reactions has been a long term dream, it is only now that realization of such dreams has become realistic. One of the major contributions that is leading towards this realization is the development of pulse shaping techniques. Here, we concentrate on the important developments in this area that has come by recently, particularly emphasizing new results from our laboratory. We discuss in detail the current state-of-the-art, and present some experimental and theoretical demonstrations of chemical control by using arbitrarily shaped pulses. The major strength of our approach to pulse shaping has been in considering "robustness in the laboratory" as a primary constraint. Most of the shapes, addressed here, work under adiabatic conditions where the exact shape of the pulse is not critical as long as the basic criteria dictated by the adiabatic theorem are satisfied. A novel approach of "molecular pulse shaping"--using the molecule itself to generate its own pulse shape--is presented as an example of the ultimate form of robustness. Finally, we get into the issue of resolution enhancement by coupling laser radiation into a Nuclear Magnetic Resonance (NMR) spectrometer. Spectroscopic resolution enhancement is an everlasting effort in the field of NMR--even more for biological NMR. We present some of the recent experimental findings in our laboratory that show selective dispersion in the NMR spectrum when it is acquired under a non-resonant laser irradiation of the sample. Albeit promising, the observed effects are weak and the theoretical understanding of these experiments is not profound enough for implementing any immediate applications.

Influence of angular acceleration-deceleration pulse shapes on regional brain strains.

PubMed

Yoganandan, Narayan; Li, Jianrong; Zhang, Jiangyue; Pintar, Frank A; Gennarelli, Thomas A

2008-07-19

Recognizing the association of angular loading with brain injuries and inconsistency in previous studies in the application of the biphasic loads to animal, physical, and experimental models, the present study examined the role of the acceleration-deceleration pulse shapes on region-specific strains. An experimentally validated two-dimensional finite element model representing the adult male human head was used. The model simulated the skull and falx as a linear elastic material, cerebrospinal fluid as a hydrodynamic material, and cerebrum as a linear viscoelastic material. The angular loading matrix consisted coronal plane rotation about a center of rotation that was acceleration-only (4.5 ms duration, 7.8 krad/s/s peak), deceleration-only (20 ms, 1.4 krad/s/s peak), acceleration-deceleration, and deceleration-acceleration pulses. Both biphasic pulses had peaks separated by intervals ranging from 0 to 25 ms. Principal strains were determined at the corpus callosum, base of the postcentral sulcus, and cerebral cortex of the parietal lobe. The cerebrum was divided into 17 regions and peak values of average maximum principal strains were determined. In all simulations, the corpus callosum responded with the highest strains. Strains were the least under all simulations in the lower parietal lobes. In all regions peak strains were the same for both monophase pulses suggesting that the angular velocity may be a better metric than peak acceleration or deceleration. In contrast, for the biphasic pulse, peak strains were region- and pulse-shape specific. Peak values were lower in both biphasic pulses when there was no time separation between the pulses than the corresponding monophase pulse. Increasing separation time intervals increased strains, albeit non-uniformly. Acceleration followed by deceleration pulse produced greater strains in all regions than the other form of biphasic pulse. Thus, pulse shape appears to have an effect on regional strains in the brain.

Variable-pulse-shape pulsed-power accelerator

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

Stoltzfus, Brian S.; Austin, Kevin; Hutsel, Brian Thomas

A variable-pulse-shape pulsed-power accelerator is driven by a large number of independent LC drive circuits. Each LC circuit drives one or more coaxial transmission lines that deliver the circuit's output power to several water-insulated radial transmission lines that are connected in parallel at small radius by a water-insulated post-hole convolute. The accelerator can be impedance matched throughout. The coaxial transmission lines are sufficiently long to transit-time isolate the LC drive circuits from the water-insulated transmission lines, which allows each LC drive circuit to be operated without being affected by the other circuits. This enables the creation of any power pulsemore » that can be mathematically described as a time-shifted linear combination of the pulses of the individual LC drive circuits. Therefore, the output power of the convolute can provide a variable pulse shape to a load that can be used for magnetically driven, quasi-isentropic compression experiments and other applications.« less

Pulse shape optimization for electron-positron production in rotating fields

NASA Astrophysics Data System (ADS)

Fillion-Gourdeau, François; Hebenstreit, Florian; Gagnon, Denis; MacLean, Steve

2017-07-01

We optimize the pulse shape and polarization of time-dependent electric fields to maximize the production of electron-positron pairs via strong field quantum electrodynamics processes. The pulse is parametrized in Fourier space by a B -spline polynomial basis, which results in a relatively low-dimensional parameter space while still allowing for a large number of electric field modes. The optimization is performed by using a parallel implementation of the differential evolution, one of the most efficient metaheuristic algorithms. The computational performance of the numerical method and the results on pair production are compared with a local multistart optimization algorithm. These techniques allow us to determine the pulse shape and field polarization that maximize the number of produced pairs in computationally accessible regimes.

Optical ultra-wide-band pulse bipolar and shape modulation based on a symmetric PM-IM conversion architecture.

PubMed

Wang, Shiguang; Chen, Hongwei; Xin, Ming; Chen, Minghua; Xie, Shizhong

2009-10-15

A simple and feasible technique for ultra-wide-band (UWB) pulse bipolar modulation (PBM) and pulse shape modulation (PSM) in the optical domain is proposed and demonstrated. The PBM and PSM are performed using a symmetric phase modulation to intensity modulation conversion architecture, including a couple of phase modulators and an optical bandpass filter (OBPF). Two optical carriers, which are separately phase modulated by two appropriate electrical pulse patterns, are at the long- and short-wavelength linear slopes of the OBPF spectrum, respectively. The high-speed PBM and PSM without limit of chip length, polarity, and shape are implemented in simulation and are also verified by experiment. (c) 2009 Optical Society of America.

Testing low-mode symmetry control with low-adiabat, extended pulse-lengths in BigFoot implosions on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hohenberger, Matthias; Casey, D. T.; Thomas, C. A.; Baker, K. L.; Spears, B. K.; Khan, S. F.; Hurricane, O. A.; Callahan, D.

2017-10-01

The Bigfoot approach to indirect-drive inertial confinement fusion (ICF) has been developed as a compromise trading high-convergence and areal densities for high implosion velocities, large adiabats and hydrodynamic stability. Shape control and predictability are maintained by using relatively short laser pulses and merging the shocks within the DT-ice layer. These design choices ultimately limit the theoretically achievable performance, and one strategy to increase the 1-D performance is to reduce the shell adiabat by extending the pulse shape. However, this can result in loss of low-mode symmetry control, as the hohlraum ``bubble,'' the high-Z material launched by the outer-cone beams during the early part of the laser pulse, has more time to expand and will eventually intercept inner-cone beams preventing them from reaching the hohlraum waist, thus losing equatorial capsule drive. We report on experimental results exploring shape control and predictability with extended pulse shapes in BigFoot implosions. Prepared by LLNL under Contract DE-AC52-07NA27344.

Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

NASA Astrophysics Data System (ADS)

Peterchev, Angel V.; DʼOstilio, Kevin; Rothwell, John C.; Murphy, David L.

2014-10-01

Objective. This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach. We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with a lower voltage rating than prior cTMS devices. Main results. cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences (\\lt 10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in ten healthy volunteers. Significance. The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool.

ENDOR with band-selective shaped inversion pulses

NASA Astrophysics Data System (ADS)

Tait, Claudia E.; Stoll, Stefan

2017-04-01

Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity. Band-selective inversion pulses are characterized by almost rectangular inversion profiles, leading to full inversion for spin packets with resonance offsets within the pulse excitation bandwidth and leaving spin packets outside the excitation bandwidth largely unaffected. Here, we explore the consequences of using different band-selective amplitude-modulated pulses designed for NMR as the inversion pulse in ENDOR. We find an increased sensitivity for small hyperfine couplings compared to rectangular pulses of the same bandwidth. In echo-detected Davies-type ENDOR, finite Fourier series inversion pulses combine the advantages of increased absolute ENDOR sensitivity of short rectangular inversion pulses and increased sensitivity for small hyperfine couplings of long rectangular inversion pulses. The use of pulses with an almost rectangular frequency-domain profile also allows for increased control of the hyperfine contrast selectivity. At X-band, acquisition of echo transients as a function of radiofrequency and appropriate selection of integration windows during data processing allows efficient separation of contributions from weakly and strongly coupled nuclei in overlapping ENDOR spectra within a single experiment.

Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

PubMed Central

D’Ostilio, Kevin; Rothwell, John C; Murphy, David L

2014-01-01

Objective This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with lower voltage rating than prior cTMS devices. Main results cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences (<10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in 10 healthy volunteers. Significance The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool. PMID:25242286

Unitary scintillation detector and system

DOEpatents

McElhaney, Stephanie A.; Chiles, Marion M.

1994-01-01

The invention is a unitary alpha, beta, and gamma scintillation detector and system for sensing the presence of alpha, beta, and gamma radiations selectively or simultaneously. The scintillators are mounted in a light-tight housing provided with an entrance window for admitting alpha, beta, and gamma radiation and excluding ambient light from the housing. Light pulses from each scintillator have different decay constants that are converted by a photosensitive device into corresponding differently shaped electrical pulses. A pulse discrimination system identifies the electrical pulses by their respective pulse shapes which are determined by decay time. The identified electrical pulses are counted in separate channel analyzers to indicate the respective levels of sensed alpha, beta, and gamma radiations.

Extension of FRI for modeling of electrocardiogram signals.

PubMed

Quick, R Frank; Crochiere, Ronald E; Hong, John H; Hormati, Ali; Baechler, Gilles

2012-01-01

Recent work has developed a modeling method applicable to certain types of signals having a "finite rate of innovation" (FRI). Such signals contain a sparse collection of time- or frequency-limited pulses having a restricted set of allowable pulse shapes. A limitation of past work on FRI is that all of the pulses must have the same shape. Many real signals, including electrocardiograms, consist of pulses with varying widths and asymmetry, and therefore are not well fit by the past FRI methods. We present an extension of FRI allowing pulses having variable pulse width (VPW) and asymmetry. We show example results for electrocardiograms and discuss the possibility of application to signal compression and diagnostics.

A Fiber-Optic System Generating Pulses of High Spectral Density

NASA Astrophysics Data System (ADS)

Abramov, A. S.; Zolotovskii, I. O.; Korobko, D. A.; Fotiadi, A. A.

2018-03-01

A cascade fiber-optic system that generates pulses of high spectral density by using the effect of nonlinear spectral compression is proposed. It is demonstrated that the shape of the pulse envelope substantially influences the degree of compression of its spectrum. In so doing, maximum compression is achieved for parabolic pulses. The cascade system includes an optical fiber exhibiting normal dispersion that decreases along the fiber length, thereby ensuring that the pulse envelope evolves toward a parabolic shape, along with diffraction gratings and a fiber spectral compressor. Based on computer simulation, we determined parameters of cascade elements leading to maximum spectral density of radiation originating from a subpicosecond laser pulse of medium energy.

Unitary scintillation detector and system

DOEpatents

McElhaney, S.A.; Chiles, M.M.

1994-05-31

The invention is a unitary alpha, beta, and gamma scintillation detector and system for sensing the presence of alpha, beta, and gamma radiations selectively or simultaneously. The scintillators are mounted in a light-tight housing provided with an entrance window for admitting alpha, beta, and gamma radiation and excluding ambient light from the housing. Light pulses from each scintillator have different decay constants that are converted by a photosensitive device into corresponding differently shaped electrical pulses. A pulse discrimination system identifies the electrical pulses by their respective pulse shapes which are determined by decay time. The identified electrical pulses are counted in separate channel analyzers to indicate the respective levels of sensed alpha, beta, and gamma radiations. 10 figs.

Shaping and timing gradient pulses to reduce MRI acoustic noise.

PubMed

Segbers, Marcel; Rizzo Sierra, Carlos V; Duifhuis, Hendrikus; Hoogduin, Johannes M

2010-08-01

A method to reduce the acoustic noise generated by gradient systems in MRI has been recently proposed; such a method is based on the linear response theory. Since the physical cause of MRI acoustic noise is the time derivative of the gradient current, a common trapezoid current shape produces an acoustic gradient coil response mainly during the rising and falling edge. In the falling edge, the coil acoustic response presents a 180 degrees phase difference compared to the rising edge. Therefore, by varying the width of the trapezoid and keeping the ramps constant, it is possible to suppress one selected frequency and its higher harmonics. This value is matched to one of the prominent resonance frequencies of the gradient coil system. The idea of cancelling a single frequency is extended to a second frequency, using two successive trapezoid-shaped pulses presented at a selected interval. Overall sound pressure level reduction of 6 and 10 dB is found for the two trapezoid shapes and a single pulse shape, respectively. The acoustically optimized pulse shape proposed is additionally tested in a simulated echo planar imaging readout train, obtaining a sound pressure level reduction of 12 dB for the best case.

Adding a dimension to the infrared spectra of interfaces: 2D SFG spectroscopy via mid-IR pulse shaping

NASA Astrophysics Data System (ADS)

Zanni, Martin

2012-02-01

Sum-frequency generation spectroscopy provides an infrared spectrum of interfaces and thus has widespread use in the materials and chemical sciences. In this presentation, I will present our recent work in developing a 2D pulse sequence to generate 2D SFG spectra of interfaces, in analogy to 2D infrared spectra used to measure bulk species. To develop this spectroscopy, we have utilized many of the tricks-of-the-trade developed in the 2D IR and 2D Vis communities in the last decade, including mid-IR pulse shaping. With mid-IR pulse shaping, the 2D pulse sequence is manipulated by computer programming in the desired frequency resolution, rotating frame, and signal pathway. We believe that 2D SFG will become an important tool in the interfacial sciences in an analogous way that 2D IR is now being used in many disciplines.

Paired Pulse Basis Functions for the Method of Moments EFIE Solution of Electromagnetic Problems Involving Arbitrarily-shaped, Three-dimensional Dielectric Scatterers

NASA Technical Reports Server (NTRS)

MacKenzie, Anne I.; Rao, Sadasiva M.; Baginski, Michael E.

2007-01-01

A pair of basis functions is presented for the surface integral, method of moment solution of scattering by arbitrarily-shaped, three-dimensional dielectric bodies. Equivalent surface currents are represented by orthogonal unit pulse vectors in conjunction with triangular patch modeling. The electric field integral equation is employed with closed geometries for dielectric bodies; the method may also be applied to conductors. Radar cross section results are shown for dielectric bodies having canonical spherical, cylindrical, and cubic shapes. Pulse basis function results are compared to results by other methods.

Time-domain SFG spectroscopy using mid-IR pulse shaping: practical and intrinsic advantages.

PubMed

Laaser, Jennifer E; Xiong, Wei; Zanni, Martin T

2011-03-24

Sum-frequency generation (SFG) spectroscopy is a ubiquitous tool in the surface sciences. It provides infrared transition frequencies and line shapes that probe the structure and environment of molecules at interfaces. In this article, we apply techniques learned from the multidimensional spectroscopy community to SFG spectroscopy. We implement balanced heterodyne detection to remove scatter and the local oscillator background. Heterodyning also separates the resonant and nonresonant signals by acquiring both the real and imaginary parts of the spectrum. We utilize mid-IR pulse shaping to control the phase and delay of the mid-IR pump pulse. Pulse shaping allows phase cycling for data collection in the rotating frame and additional background subtraction. We also demonstrate time-domain data collection, which is a Fourier transform technique, and has many advantages in signal throughput, frequency resolution, and line shape accuracy over existing frequency domain methods. To demonstrate time-domain SFG spectroscopy, we study an aryl isocyanide on gold, and find that the system has an inhomogeneous structural distribution, in agreement with computational results, but which was not resolved by previous frequency-domain SFG studies. The ability to rapidly and actively manipulate the mid-IR pulse in an SFG pules sequence makes possible new experiments and more accurate spectra. © 2011 American Chemical Society

Direct measurement of the pulse duration and frequency chirp of seeded XUV free electron laser pulses

NASA Astrophysics Data System (ADS)

Azima, Armin; Bödewadt, Jörn; Becker, Oliver; Düsterer, Stefan; Ekanayake, Nagitha; Ivanov, Rosen; Kazemi, Mehdi M.; Lamberto Lazzarino, Leslie; Lechner, Christoph; Maltezopoulos, Theophilos; Manschwetus, Bastian; Miltchev, Velizar; Müller, Jost; Plath, Tim; Przystawik, Andreas; Wieland, Marek; Assmann, Ralph; Hartl, Ingmar; Laarmann, Tim; Rossbach, Jörg; Wurth, Wilfried; Drescher, Markus

2018-01-01

We report on a direct time-domain measurement of the temporal properties of a seeded free-electron laser pulse in the extreme ultraviolet spectral range. Utilizing the oscillating electromagnetic field of terahertz radiation, a single-shot THz streak-camera was applied for measuring the duration as well as spectral phase of the generated intense XUV pulses. The experiment was conducted at FLASH, the free electron laser user facility at DESY in Hamburg, Germany. In contrast to indirect methods, this approach directly resolves and visualizes the frequency chirp of a seeded free-electron laser (FEL) pulse. The reported diagnostic capability is a prerequisite to tailor amplitude, phase and frequency distributions of FEL beams on demand. In particular, it opens up a new window of opportunities for advanced coherent spectroscopic studies making use of the high degree of temporal coherence expected from a seeded FEL pulse.

Heating of solid targets with laser pulses

NASA Technical Reports Server (NTRS)

Bechtel, J. H.

1975-01-01

Analytical and numerical solutions to the heat-conduction equation are obtained for the heating of absorbing media with pulsed lasers. The spatial and temporal form of the temperature is determined using several different models of the laser irradiance. Both surface and volume generation of heat are discussed. It is found that if the depth of thermal diffusion for the laser-pulse duration is large compared to the optical-attenuation depth, the surface- and volume-generation models give nearly identical results. However, if the thermal-diffusion depth for the laser-pulse duration is comparable to or less than the optical-attenuation depth, the surface-generation model can give significantly different results compared to the volume-generation model. Specific numerical results are given for a tungsten target irradiated by pulses of different temporal durations and the implications of the results are discussed with respect to the heating of metals by picosecond laser pulses.

High precision and high aspect ratio laser drilling: challenges and solutions

NASA Astrophysics Data System (ADS)

Uchtmann, Hermann; He, Chao; Gillner, Arnold

2016-03-01

Laser drilling is a very versatile tool to produce high accuracy bores in small and large geometries using different technologies. In large and deep hole drilling laser drilling can be found in drilling cooling holes into turbomachinery components such as turbine blades. In micro drilling, the technology is used for the generation of nozzles and filters. However, especially in macro drilling, the process often causes microstructure changes and induces defects such as recast layers and cracks. The defects are caused by the melt dominated drilling process by using pulse durations in the range of some 100 μm up to a few ms. A solution of this problem is the use of ultrashort pulsed laser radiation with pulse durations in the range of some 100 fs up to a few ps, however with the disadvantage of long drilling times. Thus, the aim of this work is to combine the productive process by using ms pulsed fiber laser radiation with subsequent ablation of existing recast layers at the hole wall by using ultrashort pulsed laser radiation. By using fast scanning techniques the recast layer can be avoided almost completely. With a similar technology also very small hole can be produced. Using a rotating dove prism a circular oscillation of the laser spots is performed and holes are drilled at intervals in 1 mm thick stainless steel (1.4301) by ultra-short laser pulses of 7 ps at 515 nm. The formation of hole and the behavior of energy deposition differ from other drilling strategies due to the helical revolution. The temporal evolution of the hole shape is analyzed by means of SEM techniques from which three drilling phases can be distinguished.

Impact of temporal, spatial and cascaded effects on the pulse formation in ultra-broadband parametric amplifiers.

PubMed

Lang, T; Harth, A; Matyschok, J; Binhammer, T; Schultze, M; Morgner, U

2013-01-14

A 2 + 1 dimensional nonlinear pulse propagation model is presented, illustrating the weighting of different effects for the parametric amplification of ultra-broadband spectra in different regimes of energy scaling. Typical features in the distribution of intensity and phase of state-of-the-art OPA-systems can be understood by cascaded spatial and temporal effects.

rf design of a pulse compressor with correction cavity chain for klystron-based compact linear collider

NASA Astrophysics Data System (ADS)

Wang, Ping; Zha, Hao; Syratchev, Igor; Shi, Jiaru; Chen, Huaibi

2017-11-01

We present an X-band high-power pulse compression system for a klystron-based compact linear collider. In this system design, one rf power unit comprises two klystrons, a correction cavity chain, and two SLAC Energy Doubler (SLED)-type X-band pulse compressors (SLEDX). An rf pulse passes the correction cavity chain, by which the pulse shape is modified. The rf pulse is then equally split into two ways, each deploying a SLEDX to compress the rf power. Each SLEDX produces a short pulse with a length of 244 ns and a peak power of 217 MW to power four accelerating structures. With the help of phase-to-amplitude modulation, the pulse has a dedicated shape to compensate for the beam loading effect in accelerating structures. The layout of this system and the rf design and parameters of the new pulse compressor are described in this work.

FIBRE AND INTEGRATED OPTICS. OPTICAL PROCESSING OF INFORMATION: Method for optical data processing based on a two-pulse photon echo

NASA Astrophysics Data System (ADS)

Zakharov, S. M.; Manykin, Eduard A.

1995-02-01

The principles of optical processing based on dynamic spatial—temporal properties of two-pulse photon echo signals are considered. The properties of a resonant medium as an on-line filter of temporal and spatial frequencies are discussed. These properties are due to the sensitivity of such a medium to the Fourier spectrum of the second exiting pulse. Degeneracy of quantum resonant systems, demonstrated by the coherent response dependence on the square of the amplitude of the second pulse, can be used for 'simultaneous' correlation processing of optical 'signals'. Various methods for the processing of the Fourier optical image are discussed.

Assessing mental stress from the photoplethysmogram: a numerical study

PubMed Central

Charlton, Peter H; Celka, Patrick; Farukh, Bushra; Chowienczyk, Phil; Alastruey, Jordi

2018-01-01

Abstract Objective: Mental stress is detrimental to cardiovascular health, being a risk factor for coronary heart disease and a trigger for cardiac events. However, it is not currently routinely assessed. The aim of this study was to identify features of the photoplethysmogram (PPG) pulse wave which are indicative of mental stress. Approach: A numerical model of pulse wave propagation was used to simulate blood pressure signals, from which simulated PPG pulse waves were estimated using a transfer function. Pulse waves were simulated at six levels of stress by changing the model input parameters both simultaneously and individually, in accordance with haemodynamic changes associated with stress. Thirty-two feature measurements were extracted from pulse waves at three measurement sites: the brachial, radial and temporal arteries. Features which changed significantly with stress were identified using the Mann–Kendall monotonic trend test. Main results: Seventeen features exhibited significant trends with stress in measurements from at least one site. Three features showed significant trends at all three sites: the time from pulse onset to peak, the time from the dicrotic notch to pulse end, and the pulse rate. More features showed significant trends at the radial artery (15) than the brachial (8) or temporal (7) arteries. Most features were influenced by multiple input parameters. Significance: The features identified in this study could be used to monitor stress in healthcare and consumer devices. Measurements at the radial artery may provide superior performance than the brachial or temporal arteries. In vivo studies are required to confirm these observations. PMID:29658894

Logic circuit detects both present and missing negative pulses in superimposed wave trains

NASA Technical Reports Server (NTRS)

Rice, R. E.

1967-01-01

Pulse divide and determination network provides a logical determination of pulse presence within a data train. The network uses digital logic circuitry to divide positive and negative pulses, to shape the separated pulses, and to determine, by means of coincidence logic, if negative pulses are missing from the pulse train.

Selective RF pulses in NMR and their effect on coupled and uncoupled spin systems

NASA Astrophysics Data System (ADS)

Slotboom, J.

1993-10-01

This thesis describes various aspects of the usage of shaped RF-pulses for volume selection and spectral editing. Contents: Introduction--The History of Magnetic Resonance in a Nutshell, and The Usage of RF Pulses in Contemporary MRS and MRI; Theoretical and Practical Aspects of Localized NMR Spectroscopy; The Effects of RF Pulse Shape Discretization on the Spatially Selective Performance; Design of Frequency-Selective RF Pulses by Optimizing a Small Number of Pulse Parameters; A Single-Shot Localization Pulse Sequence Suited for Coils with Inhomogeneous RF Fields Using Adiabatic Slice-Selective RF Pulses; The Bloch Equations for an AB System and the Design of Spin State Selective RF Pulses for Coupled Spin Systems; The Effects of Frequency Selective RF Pulses on J Coupled Spin-1/2 Systems; A Quantitative (1)H MRS in vivo Study of the Effects of L-Ornithine-L-Aspartate on the Development of Mild Encephalopathy Using a Single Shot Localization Technique Based on SAR Reduced Adiabatic 2(pi) Pulses.

Study and Characterization of Subharmonic Emissions by Using Shaped Ultrasonic Driving Pulse

NASA Astrophysics Data System (ADS)

Masotti, L.; Biagi, E.; Breschi, L.; Vannacci, E.

Subharmonic emissions from Ultrasound Contrast Agents (UCAs) were studied by a Pulse Inversion method in order to assess the feasibility of implementation of this technique to subharmonic imaging. Interesting results concerning the dependence of the subharmonic emission with respect to initial pulse shape are presented. The experimentation was performed also by varying the acoustic pressure and concentration of the contrast agent (SonoVue®)

Multi-pulse multi-delay (MPMD) multiple access modulation for UWB

DOEpatents

Dowla, Farid U.; Nekoogar, Faranak

2007-03-20

A new modulation scheme in UWB communications is introduced. This modulation technique utilizes multiple orthogonal transmitted-reference pulses for UWB channelization. The proposed UWB receiver samples the second order statistical function at both zero and non-zero lags and matches the samples to stored second order statistical functions, thus sampling and matching the shape of second order statistical functions rather than just the shape of the received pulses.

Effect of Pulse Shape on Spall Strength

NASA Astrophysics Data System (ADS)

Smirnov, V. I.; Petrov, Yu. V.

2018-03-01

This paper analyzes the effect of the time-dependent shape of a load pulse on the spall strength of materials. Within the framework of a classical one-dimensional scheme, triangular pulses with signal rise and decay portions and with no signal rise portions considered. Calculation results for the threshold characteristics of fracture for rail steel are given. The possibility of optimization of fracture by selecting a loading time with the use of an introduced characteristic of dynamic strength (pulse fracture capacity) is demonstrated. The study is carried out using a structure-time fracture criterion.

Co Laser.

DTIC Science & Technology

1976-01-01

Experimental and Pre- 9 dieted Temporal Behavior of the Laser Output Pulse for a 20% CO and 80% N2 Mixture 3 Comparison of the Normalized Experimental...and Pre- 10 dieted Temporal Behavior of the Laser Output Pulse for a 20% CO and 80% A~ Mixture 4 Predictions of the Temporal Variation of Small...Z o < z CD o o ÜJ 10 -7 .1 D4862 II i i r~rT"T pco (Torr) ♦ 700 O 350 A 200 O 100 + i & i J I \\ I I I 1.0 AVERAUü

Spatio-temporal characterisation of a 100 kHz 24 W sub-3-cycle NOPCPA laser system

NASA Astrophysics Data System (ADS)

Witting, Tobias; Furch, Federico J.; Vrakking, Marc J. J.

2018-04-01

In recent years, OPCPA and NOPCPA laser systems have shown the potential to supersede Ti:sapphire plus post-compression based laser systems to drive next generation attosecond light sources via direct amplification of few-cycle pulses to high pulse energies at high repetition rates. In this paper, we present a sub 3-cycle, 100 kHz, 24 W NOPA laser system and characterise its spatio-temporal properties using the SEA-F-SPIDER technique. Our results underline the importance of spatio-temporal diagnostics for these emerging laser systems.

Investigating membrane nanoporation induced by bipolar pulsed electric fields via second harmonic generation

NASA Astrophysics Data System (ADS)

Moen, E. K.; Ibey, B. L.; Beier, H. T.; Armani, A. M.

2016-09-01

Electric pulses have become an effective tool for transporting cargo (DNA, drugs, etc.) across cell membranes. This enhanced transport is believed to occur through temporary pores formed in the plasma membrane. Traditionally, millisecond duration, monopolar (MP) pulses are used for electroporation, but bipolar (BP) pulses have proven equally effective as MP pulses with the added advantage of less cytotoxicity. With the goal of further reducing cytotoxic effects and inducing non-thermal, intra-cellular effects, researchers began investigating reduced pulse durations, pushing into the nanosecond regime. Cells exposed to these MP, nanosecond pulsed electric fields (nsPEFs) have shown increased repairable membrane permeability and selective channel activation. However, attempts to improve this further by moving to the BP pulse regime has proven unsuccessful. In the present work, we use second harmonic generation imaging to explore the structural effects of bipolar nsPEFs on the plasma membrane. By varying the temporal spacing between the pulse phases over several orders of magnitude and comparing the response to a single MP case, we systematically examine the disparity in cellular response. Our circuit-based model predicts that, as the temporal spacing increases several orders of magnitude, nanoporation increases and eventually exceeds the MP case. On the whole, our experimental data agree with this assertion; however, a detailed analysis of the data sets demonstrates that biological processes may play a larger role in the observed response than previously thought, dominating the effect for temporal spacing up to 5 μs. These findings could ultimately lead to understanding the biophysical mechanism underlying all electroporation.

Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism

DOE PAGES

Fan, Tingting; Grychtol, Patrik; Knut, Ronny; ...

2015-11-03

Here, we demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantummore » trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N 4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.« less

Numerical simulations of self-focusing of ultrafast laser pulses

NASA Astrophysics Data System (ADS)

Fibich, Gadi; Ren, Weiqing; Wang, Xiao-Ping

2003-05-01

Simulation of nonlinear propagation of intense ultrafast laser pulses is a hard problem, because of the steep spatial gradients and the temporal shocks that form during the propagation. In this study we adapt the iterative grid distribution method of Ren and Wang [J. Comput. Phys. 159, 246 (2000)] to solve the two-dimensional nonlinear Schrödinger equation with normal time dispersion, space-time focusing, and self-steepening. Our simulations show that, after the asymmetric temporal pulse splitting, the rear peak self-focuses faster than the front one. As a result, the collapse of the rear peak is arrested before that of the front peak. Unlike what has sometimes been conjectured, however, collapse of the two peaks is not arrested through multiple splittings, but rather through temporal dispersion.

Means and method for characterizing high power, ultra short laser pulses in a real time, on line manner

DOEpatents

Veligdan, J.T.

1994-03-08

An ultra short (<10 ps), high power laser pulse is temporally characterized by a system that uses a physical measurement of a wavefront that has been altered in a known manner. The system includes a first reflection switch to remove a portion of a pulse from a beam of pulses, then includes a second reflection switch, operating in a mode that is opposite to the first reflection switch, to slice off a portion of that removed portion. The sliced portion is then directed to a measuring device for physical measurement. The two reflection switches are arranged with respect to each other and with respect to the beam of ultra short pulses such that physical measurement of the sliced portion is related to the temporal measurement of the ultra short pulse by a geometric or trigonometric relationship. The reflection switches are operated by a control pulse that is directed to impinge on each of the reflection switches at a 90[degree] angle of incidence. 8 figures.

Means and method for characterizing high power, ultra short laser pulses in a real time, on line manner

DOEpatents

Veligdan, James T.

1994-01-01

An ultra short (<10 ps), high power laser pulse is temporally characterized by a system that uses a physical measurement of a wavefront that has been altered in a known manner. The system includes a first reflection switch to remove a portion of a pulse from a beam of pulses, then includes a second reflection switch, operating in a mode that is opposite to the first reflection switch, to slice off a portion of that removed portion. The sliced portion is then directed to a measuring device for physical measurement. The two reflection switches are arranged with respect to each other and with respect to the beam of ultra short pulses such that physical measurement of the sliced portion is related to the temporal measurement of the ultra short pulse by a geometric or trigonometric relationship. The reflection switches are operated by a control pulse that is directed to impinge on each of the reflection switches at a 90.degree. angle of incidence.

Dynamics of a gain-switched distributed feedback ridge waveguide laser in nanoseconds time scale under very high current injection conditions.

PubMed

Klehr, A; Wenzel, H; Brox, O; Schwertfeger, S; Staske, R; Erbert, G

2013-02-11

We present detailed experimental investigations of the temporal, spectral and spatial behavior of a gain-switched distributed feedback (DFB) laser emitting at a wavelength of 1064 nm. Gain-switching is achieved by injecting nearly rectangular shaped current pulses having a length of 50 ns and a very high amplitude up to 2.5 A. The repetition frequency is 200 kHz. The laser has a ridge waveguide (RW) for lateral waveguiding with a ridge width of 3 µm and a cavity length of 1.5 mm. Time resolved investigations show, depending on the amplitude of the current pulses, that the optical power exhibits different types of oscillatory behavior during the pulses, accompanied by changes in the lateral near field intensity profiles and optical spectra. Three different types of instabilities can be distinguished: mode beating with frequencies between 25 GHz and 30 GHz, switching between different lateral intensity profiles with a frequency of 0.4 GHz and self-sustained oscillations with a frequency of 4 GHz. The investigations are of great relevance for the utilization of gain-switched DFB-RW lasers as seed lasers for fiber laser systems and in other applications, which require a high optical power.

Optimisation of cascaded Yb fiber amplifier chains using numerical-modelling

NASA Astrophysics Data System (ADS)

He, F.; Price, J. H.; Vu, K. T.; Malinowski, A.; Sahu, J. K.; Richardson, D. J.

2006-12-01

We show that it is possible to adapt existing software packages developed originally for modeling telecommunication devices and systems to reliably predict and optimize the performance of high-power Ytterbium-doped fiber amplifier and laser systems. The ready availability of a flexible, user-friendly design tool should be of considerable practical interest to scientists and engineers working with this important new laser technology since Ytterbium amplifier and amplifier cascades are often difficult to optimize experimentally due to the three-level nature of the Ytterbium laser transition. As examples of the utility and accuracy of the software, as well as the complexity of the systems and amplifier properties that can be successfully modeled, we present a comparison of experimental and theoretical results for individual core and cladding pumped amplifiers, and also for an ultra-short pulse four-stage amplifier system optimized both to provide a broad gain bandwidth and to minimize nonlinear effects. We also show how high energy 100 ns pulses with complex user definable temporal profiles can be created in a gain-saturated amplifier by suitable pre-shaping of the low-energy input pulses. Furthermore, with appropriate modifications the same software package can be applied to fiber amplifiers based on other rare-earth elements and glass hosts.

Latest developments on fibered MOPA in mJ range with hollow-core fiber beam delivery and fiber beam shaping used as seeder for large scale laser facilities (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gleyze, Jean-François; Scol, Florent; Perrin, Arnaud; Gouriou, Pierre; Valentin, Constance; Bouwmans, Géraud; Hugonnot, Emmanuel

2017-05-01

The Laser Megajoule (LMJ) is a French large scale laser facility dedicated to inertial fusion and plasma physics research. LMJ front-ends are based on fiber laser technology at nanojoule range [1]. Scaling the energy of those fiber seeders to the millijoule range is a way to upgrade LMJ's front ends architecture and could also be used as seeder for lasers for ELI project for example. However, required performances are so restrictive (optical-signal-to-noise ratio higher than 50 dB, temporally-shaped nanosecond pulses and spatial single-mode top-hat beam output) that such fiber systems are very tricky to build. High-energy fiber amplifiers In 2015, we have demonstrated, an all-fiber MOPA prototype able to produce a millijoule seeder, but unfortunately not 100% conform for all LMJ's performances. A major difficulty was to manage the frequency modulation used to avoid stimulated Brillouin scattering, to amplitude modulation (FM-AM) conversion, this limits the energy at 170µJ. For upgrading the energy to the millijoule range, it's necessary to use an amplifier with a larger core fiber. However, this fiber must still be flexible; polarization maintaining and exhibit a strictly single-mode behaviour. We are thus developing a new amplifier architecture based on an Yb-doped tapered fiber: its core diameter is from a narrow input to a wide output (MFD 8 to 26 µm). A S² measurement on a 2,5m long tapered fiber rolled-up on 22 cm diameter confirmed that this original geometry allows obtaining strictly single-mode behaviour. In a 1 kHz repetition rate regime, we already obtain 750 µJ pulses, and we are on the way to mJ, respecting LMJ performances. Beam delivery In LMJ architecture the distance between the nanojoule fiber seeder and the amplifier stages is about 16 m. Beam delivery is achieved with a standard PM fiber, such a solution is no longer achievable with hundreds of kilowatt peak powers. An efficient way to minimize nonlinear effects is to use hollow-core (HC) fibers. The comparison between the different fibers will be presented in the conference. Fiber spatial beam shaping Spatial beam shaping (top-hat profile) is mandatory to optimize the energy extraction in free-space amplifier. It would be very interesting to obtain a flat-top beam in an all-fiber way. Accordingly, we have design and realize a large mode area single-mode top-hat fiber able to deliver a coherent top-hat beam. This fiber, with larger MFD adapted to mJ pulse, will be implemented to perform the spatial beam shaping from coherent Gaussian profile to coherent top-hat intensity profile in the mJ range. In conclusion, we will present an all-fiber MOPA built to fulfil stringent requirements for large scale laser facility seeding. We have already achieved 750 µJ with 10 ns square pulses. Transport of high peak power pulses over 17 m in a hollow-core fiber has been achieved and points out FM to AM conversion management issues. Moreover, spatial beam shaping is obtained by using specifically designed single-mode fibers. Various optimizations are currently under progress and will be presented.

Full Spectrum Conversion Using Traveling Pulse Wave Quantization

DTIC Science & Technology

2017-03-01

Full Spectrum Conversion Using Traveling Pulse Wave Quantization Michael S. Kappes Mikko E. Waltari IQ-Analog Corporation San Diego, California...temporal-domain quantization technique called Traveling Pulse Wave Quantization (TPWQ). Full spectrum conversion is defined as the complete...pulse width measurements that are continuously generated hence the name “traveling” pulse wave quantization. Our TPWQ-based ADC is composed of a

Femtosecond gas phase electron diffraction with MeV electrons.

PubMed

Yang, Jie; Guehr, Markus; Vecchione, Theodore; Robinson, Matthew S; Li, Renkai; Hartmann, Nick; Shen, Xiaozhe; Coffee, Ryan; Corbett, Jeff; Fry, Alan; Gaffney, Kelly; Gorkhover, Tais; Hast, Carsten; Jobe, Keith; Makasyuk, Igor; Reid, Alexander; Robinson, Joseph; Vetter, Sharon; Wang, Fenglin; Weathersby, Stephen; Yoneda, Charles; Wang, Xijie; Centurion, Martin

2016-12-16

We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.

Ring-shaped pulse oximeter and its application: measurement of SpO2 and blood pressure during sleep and during flight.

PubMed

Kishimoto, Aya; Tochikubo, Osamu; Ohshige, Kenji; Yanaga, Akihiko

2005-01-01

Respiratory and cardiovascular functions show circadian and day-to-day changes. We have developed a wireless ring-shaped pulse oximeter in collaboration with MC Medical Inc. and Advanced Medical Inc. We investigated the accuracy of this pulse oximeter and its application in daily life. Percutaneous arterial oxygen saturation (SpO2) of 47 volunteers was measured simultaneously with the ring-shaped pulse oximeter and a standard pulse oximeter. A total of 103 volunteers underwent measurement of SpO2 for 24 hr, and 11 healthy volunteers underwent measurement of SpO2 and blood pressure (BP) during flight. SpO2 and heart rate (HR) were measured and recorded every 20 sec, cabin barometric pressure and cabin oxygen concentration equivalent to sea level were measured minute-to-minute, and BP was measured every 3 min with a portable BP recorder during each flight. The SpO2 values measured with the ring-shaped pulse oximeter were similar to those measured with the standard method. The mean SpO2 during sleep was significantly lower in the group with high-normal BP or mild hypertension than in the group with normal BP. During flight, the mean change in SpO2 was -2.4 +/- 1.7% during nose-up flight, and 2.1 +/- 2.6% during nose-down flight. There was a significant correlation between change in SpO2 and change in systolic BP during nose-up flight. The wireless ring-shaped pulse oximeter was useful for investigating changes in SpO2 and its effect on BP in daily life during sleep and during air travel.

Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers

PubMed Central

Yao, B. C.; Rao, Y. J.; Wang, Z. N.; Wu, Y.; Zhou, J. H.; Wu, H.; Fan, M. Q.; Cao, X. L.; Zhang, W. L.; Chen, Y. F.; Li, Y. R.; Churkin, D.; Turitsyn, S.; Wong, C. W.

2015-01-01

Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and wide-wavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses. PMID:26687730

Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers.

PubMed

Yao, B C; Rao, Y J; Wang, Z N; Wu, Y; Zhou, J H; Wu, H; Fan, M Q; Cao, X L; Zhang, W L; Chen, Y F; Li, Y R; Churkin, D; Turitsyn, S; Wong, C W

2015-12-21

Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and wide-wavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses.

A precedence effect underlies preferences for calls with leading pulses in the grey treefrog, Hyla versicolor

PubMed Central

Marshall, Vincent T.; Gerhardt, H. Carl

2010-01-01

The temporal relationship between signals often has strong and repeatable influences on receiver behaviour. While several studies have shown that receivers prefer temporally leading signals, we show that the relative timing of signal elements within overlapping signals can also have repeatable influences on receiver responses. Female grey treefrogs, Hyla versicolor, preferred overlapping conspecific advertisement call alternatives in which pulses were in the leading position relative to pulses in an alternative. The preference was maintained even when the first pulse of the stimulus with leading pulses began after that of the call with following pulses. To rule out the possibility of masking interference of the pulse pattern, we used a split-pulse design in which the playback of two nonoverlapping pulse elements were synchronized from spatially separated speakers. Females were attracted to the source of the short (6 ms) leading pulse element, which did not attract females in isolation even though its amplitude was 24 dB lower than the long (24 ms) following element, which did attract females in isolation. Taken together, our results fall within a range of phenomena that have been classified as precedence effects. However, to our knowledge, showing localization based on successive leading pulses rather than the very first-arriving pulse is a novel discovery for nonhuman animals. PMID:20625471

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

Clark, D. S.; Milovich, J. L.; Hinkel, D. E.

Recent experimental results using the “high foot” pulse shape for inertial confinement fusion ignition experiments on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] have shown encouraging progress compared to earlier “low foot” experiments. These results strongly suggest that controlling ablation front instability growth can significantly improve implosion performance even in the presence of persistent, large, low-mode distortions. Simultaneously, hydrodynamic growth radiography experiments have confirmed that ablation front instability growth is being modeled fairly well in NIF experiments. It is timely then to combine these two results and ask how current ignition pulse shapes couldmore » be modified to improve one-dimensional implosion performance while maintaining the stability properties demonstrated with the high foot. This paper presents such a survey of pulse shapes intermediate between the low and high foot extremes in search of an intermediate foot optimum. Of the design space surveyed, it is found that a higher picket version of the low foot pulse shape shows the most promise for improved compression without loss of stability.« less

Axially adjustable magnetic properties in arrays of multilayered Ni/Cu nanowires with variable segment sizes

NASA Astrophysics Data System (ADS)

Shirazi Tehrani, A.; Almasi Kashi, M.; Ramazani, A.; Montazer, A. H.

2016-07-01

Arrays of multilayered Ni/Cu nanowires (NWs) with variable segment sizes were fabricated into anodic aluminum oxide templates using a pulsed electrodeposition method in a single bath for designated potential pulse times. Increasing the pulse time between 0.125 and 2 s in the electrodeposition of Ni enabled the formation of segments with thicknesses ranging from 25 to 280 nm and 10-110 nm in 42 and 65 nm diameter NWs, respectively, leading to disk-shaped, rod-shaped and/or near wire-shaped geometries. Using hysteresis loop measurements at room temperature, the axial and perpendicular magnetic properties were investigated. Regardless of the segment geometry, the axial coercivity and squareness significantly increased with increasing Ni segment thickness, in agreement with a decrease in calculated demagnetizing factors along the NW length. On the contrary, the perpendicular magnetic properties were found to be independent of the pulse times, indicating a competition between the intrawire interactions and the shape demagnetizing field.

Dynamics of contextual modulation of perceived shape in human vision

PubMed Central

Gheorghiu, Elena; Kingdom, Frederick A. A.

2017-01-01

In biological vision, contextual modulation refers to the influence of a surround pattern on either the perception of, or the neural responses to, a target pattern. One studied form of contextual modulation deals with the effect of a surround texture on the perceived shape of a contour, in the context of the phenomenon known as the shape aftereffect. In the shape aftereffect, prolonged viewing, or adaptation to a particular contour’s shape causes a shift in the perceived shape of a subsequently viewed contour. Shape aftereffects are suppressed when the adaptor contour is surrounded by a texture of similarly-shaped contours, a surprising result given that the surround contours are all potential adaptors. Here we determine the motion and temporal properties of this form of contextual modulation. We varied the relative motion directions, speeds and temporal phases between the central adaptor contour and the surround texture and measured for each manipulation the degree to which the shape aftereffect was suppressed. Results indicate that contextual modulation of shape processing is selective to motion direction, temporal frequency and temporal phase. These selectivities are consistent with one aim of vision being to segregate contours that define objects from those that form textured surfaces. PMID:28230085

Temporal narrowing of neutrons produced by high-intensity short-pulse lasers

DOE PAGES

Higginson, D. P.; Vassura, L.; Gugiu, M. M.; ...

2015-07-28

The production of neutron beams having short temporal duration is studied using ultraintense laser pulses. Laser-accelerated protons are spectrally filtered using a laser-triggered microlens to produce a short duration neutron pulse via nuclear reactions induced in a converter material (LiF). This produces a ~3 ns duration neutron pulse with 10 4 n/MeV/sr/shot at 0.56 m from the laser-irradiated proton source. The large spatial separation between the neutron production and the proton source allows for shielding from the copious and undesirable radiation resulting from the laser-plasma interaction. Finally, this neutron pulse compares favorably to the duration of conventional accelerator sources andmore » should scale up with, present and future, higher energy laser facilities to produce brighter and shorter neutron beams for ultrafast probing of dense materials.« less

All-optical framing photography based on hyperspectral imaging method

NASA Astrophysics Data System (ADS)

Liu, Shouxian; Li, Yu; Li, Zeren; Chen, Guanghua; Peng, Qixian; Lei, Jiangbo; Liu, Jun; Yuan, Shuyun

2017-02-01

We propose and experimentally demonstrate a new all optical-framing photography that uses hyperspectral imaging methods to record a chirped pulse's temporal-spatial information. This proposed method consists of three parts: (1) a chirped laser pulse encodes temporal phenomena onto wavelengths; (2) a lenslet array generates a series of integral pupil images;(3) a dispersive device disperses the integral images at void space of image sensor. Compared with Ultrafast All-Optical Framing Technology(Daniel Frayer,2013,2014) and Sequentially Time All-Optical Mapping Photography( Nakagawa 2014, 2015), our method is convenient to adjust the temporal resolution and to flexibly increase the numbers of frames. Theoretically, the temporal resolution of our scheme is limited by the amount of dispersion that is added to a Fourier transform limited femtosecond laser pulse. Correspondingly, the optimal number of frames is decided by the ratio of the observational time window to the temporal resolution, and the effective pixels of each frame are mostly limited by the dimensions M×N of the lenslet array. For example, if a 40fs Fourier transform limited femtosecond pulse is stretched to 10ps, a CCD camera with 2048×3072 pixels can record 15 framing images with temporal resolution of 650fs and image size of 100×100 pixels. As spectrometer structure, our recording part has another advantage that not only amplitude images but also frequency domain interferograms can be imaged. Therefore, it is comparatively easy to capture fast dynamics in the refractive index change of materials. A further dynamic experiment is being conducted.

Lidar Luminance Quantizer

NASA Technical Reports Server (NTRS)

Quilligan, Gerard; DeMonthier, Jeffrey; Suarez, George

2011-01-01

This innovation addresses challenges in lidar imaging, particularly with the detection scheme and the shapes of the detected signals. Ideally, the echoed pulse widths should be extremely narrow to resolve fine detail at high event rates. However, narrow pulses require wideband detection circuitry with increased power dissipation to minimize thermal noise. Filtering is also required to shape each received signal into a form suitable for processing by a constant fraction discriminator (CFD) followed by a time-to-digital converter (TDC). As the intervals between the echoes decrease, the finite bandwidth of the shaping circuits blends the pulses into an analog signal (luminance) with multiple modes, reducing the ability of the CFD to discriminate individual events

An analytical model for the calculation of the change in transmembrane potential produced by an ultrawideband electromagnetic pulse.

PubMed

Hart, Francis X; Easterly, Clay E

2004-05-01

The electric field pulse shape and change in transmembrane potential produced at various points within a sphere by an intense, ultrawideband pulse are calculated in a four stage, analytical procedure. Spheres of two sizes are used to represent the head of a human and the head of a rat. In the first stage, the pulse is decomposed into its Fourier components. In the second stage, Mie scattering analysis (MSA) is performed for a particular point in the sphere on each of the Fourier components, and the resulting electric field pulse shape is obtained for that point. In the third stage, the long wavelength approximation (LWA) is used to obtain the change in transmembrane potential in a cell at that point. In the final stage, an energy analysis is performed. These calculations are performed at 45 points within each sphere. Large electric fields and transmembrane potential changes on the order of a millivolt are produced within the brain, but on a time scale on the order of nanoseconds. The pulse shape within the brain differs considerably from that of the incident pulse. Comparison of the results for spheres of different sizes indicates that scaling of such pulses across species is complicated. Published 2004 Wiley-Liss, Inc.

Temporal correlation measurements of pulsed dual CO2 lidar returns. [for atmospheric pollution detection

NASA Technical Reports Server (NTRS)

Menyuk, N.; Killinger, D. K.

1981-01-01

A pulsed dual-laser direct-detection differential-absorption lidar DIAL system, operating near 10.6 microns, is used to measure the temporal correlation and statistical properties of backscattered returns from specular and diffuse topographic targets. Results show that atmospheric-turbulence fluctuations can effectively be frozen for pulse separation times on the order of 1-3 msec or less. The diffuse target returns, however, yielded a much lower correlation than that obtained with the specular targets; this being due to uncorrelated system noise effects and different statistics for the two types of target returns.

Atmospheric correlation time measurements using coherent CO2 lidar

NASA Technical Reports Server (NTRS)

Ancellet, G. M.; Menzies, R. T.

1986-01-01

A pulsed TEA-CO2 lidar with coherent detection was used to measure the correlation time of backscatter from an ensemble of atmospheric aerosol particles which are illuminated by the pulsed radiation. The correlation time of the backscatter return signal is important in studies of atmospheric turbulence and its effects on optical propagation and backscatter. If the temporal coherence of the pulse is large enough, then the temporal coherence of the return signal is dominated by the turbulence and shear for a variety of interesting atmospheric conditions. Various techniques for correlation time measurement are discussed and evaluated.

New bioacoustic and distributional data on Bokermannohyla sapiranga Brandão et al., 2012 (Anura: Hylidae): revisiting its diagnosis in comparison with B. pseudopseudis (Miranda-Ribeiro, 1937).

PubMed

De Carvalho, Thiago Ribeiro; Giaretta, Ariovaldo Antonio; Teixeira, Bernardo Franco Da Veiga; Martins, Lucas Borges

2013-12-11

In this paper, we provide new bioacoustic and distributional data on Bokermannohyla sapiranga, as well as additional comparative bioacoustic data on topotypes of B. pseudopseudis, and re-evaluate the differential diagnosis of the former species with respect to the latter. Head shapes (dorsal and lateral views) presented such variation that should not be used to differentially diagnose them as originally proposed. On the other hand, the presence of a dermal ridge along outer tarsi, and color patterns of the eyes and dorsal surface of hand/toe disks still represent diagnostic characters between both species. We also found differences in temporal (call duration; notes per call), spectral (dominant frequency; harmonics), and structural (pulsed/non-pulsed note structure) traits of their calls. Distribution of B. sapiranga is extended eastward (Paracatu), which corresponds to the first record for the State of Minas Gerais, whereas B. pseudopseudis distribution seems to be restricted to rocky montane field environments of northern Goiás State.

Characterization and optimization of an eight-channel time-multiplexed pulse-shaping system

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

Dorrer, Christophe; Bittle, Wade A.; Cuffney, Robert

High-performance optical pulse shaping is paramount to photonics and lasers applications for which high-resolution optical waveforms must be generated. We investigate the design and performance of a time-multiplexed pulse shaping (TMPS) system in which optical waveforms from a single pulse-shaping unit are demultiplexed and retimed before being sent to different optical systems. This architecture has the advantages of low cost and low relative jitter between optical waveforms because a single pulse-shaping system, e.g., a high-performance arbitrary waveform generator driving a Mach-Zehnder modulator, generates all the waveforms. We demonstrate an eight-channel TMPS system based on a 1 × 8 LiNbO 3more » demultiplexer composed of four stages of 1 × 2 Δβ phase-reversal switches that allow for demultiplexing and extinction enhancement via application of a control voltage modifying the propagation constant difference between adjacent waveguides. It is shown that optimal demultiplexing, i.e. low insertion loss and high extinction ratio between channels, requires optimization in dynamic operation because of the slow component of the switches’ response. Lastly, we demonstrate losses lower than 5 dB, extinction ratios of the order of 70 dB for a four-channel system and 50 dB for an eight-channel system, and jitter added by the demultiplexer smaller than 0.1 ps.« less

Characterization and optimization of an eight-channel time-multiplexed pulse-shaping system

DOE PAGES

Dorrer, Christophe; Bittle, Wade A.; Cuffney, Robert; ...

2016-12-06

High-performance optical pulse shaping is paramount to photonics and lasers applications for which high-resolution optical waveforms must be generated. We investigate the design and performance of a time-multiplexed pulse shaping (TMPS) system in which optical waveforms from a single pulse-shaping unit are demultiplexed and retimed before being sent to different optical systems. This architecture has the advantages of low cost and low relative jitter between optical waveforms because a single pulse-shaping system, e.g., a high-performance arbitrary waveform generator driving a Mach-Zehnder modulator, generates all the waveforms. We demonstrate an eight-channel TMPS system based on a 1 × 8 LiNbO 3more » demultiplexer composed of four stages of 1 × 2 Δβ phase-reversal switches that allow for demultiplexing and extinction enhancement via application of a control voltage modifying the propagation constant difference between adjacent waveguides. It is shown that optimal demultiplexing, i.e. low insertion loss and high extinction ratio between channels, requires optimization in dynamic operation because of the slow component of the switches’ response. Lastly, we demonstrate losses lower than 5 dB, extinction ratios of the order of 70 dB for a four-channel system and 50 dB for an eight-channel system, and jitter added by the demultiplexer smaller than 0.1 ps.« less

Pure-phase selective excitation in fast-relaxing systems.

PubMed

Zangger, K; Oberer, M; Sterk, H

2001-09-01

Selective pulses have been used frequently for small molecules. However, their application to proteins and other macromolecules has been limited. The long duration of shaped-selective pulses and the short T(2) relaxation times in proteins often prohibited the use of highly selective pulses especially on larger biomolecules. A very selective excitation can be obtained within a short time by using the selective excitation sequence presented in this paper. Instead of using a shaped low-intensity radiofrequency pulse, a cluster of hard 90 degrees pulses, delays of free precession, and pulsed field gradients can be used to selectively excite a narrow chemical shift range within a relatively short time. Thereby, off-resonance magnetization, which is allowed to evolve freely during the free precession intervals, is destroyed by the gradient pulses. Off-resonance excitation artifacts can be removed by random variation of the interpulse delays. This leads to an excitation profile with selectivity as well as phase and relaxation behavior superior to that of commonly used shaped-selective pulses. Since the evolution of scalar coupling is inherently suppressed during the double-selective excitation of two different scalar-coupled nuclei, the presented pulse cluster is especially suited for simultaneous highly selective excitation of N-H and C-H fragments. Experimental examples are demonstrated on hen egg white lysozyme (14 kD) and the bacterial antidote ParD (19 kD). Copyright 2001 Academic Press.

Delayed photo-emission model for beam optics codes

DOE PAGES

Jensen, Kevin L.; Petillo, John J.; Panagos, Dimitrios N.; ...

2016-11-22

Future advanced light sources and x-ray Free Electron Lasers require fast response from the photocathode to enable short electron pulse durations as well as pulse shaping, and so the ability to model delays in emission is needed for beam optics codes. The development of a time-dependent emission model accounting for delayed photoemission due to transport and scattering is given, and its inclusion in the Particle-in-Cell code MICHELLE results in changes to the pulse shape that are described. Furthermore, the model is applied to pulse elongation of a bunch traversing an rf injector, and to the smoothing of laser jitter onmore » a short pulse.« less

Picosecond and sub-picosecond flat-top pulse generation using uniform long-period fiber gratings

NASA Astrophysics Data System (ADS)

Park, Y.; Kulishov, M.; Slavík, R.; Azaña, J.

2006-12-01

We propose a novel linear filtering scheme based on ultrafast all-optical differentiation for re-shaping of ultrashort pulses generated from a mode-locked laser into flat-top pulses. The technique is demonstrated using simple all-fiber optical filters, more specifically uniform long period fiber gratings (LPGs) operated in transmission. The large bandwidth typical for these fiber filters allows scaling the technique to the sub-picosecond regime. In the experiments reported here, 600-fs and 1.8-ps Gaussian-like optical pulses (@ 1535 nm) have been re-shaped into 1-ps and 3.2-ps flat-top pulses, respectively, using a single 9-cm long uniform LPG.

A comparative study of optimum and suboptimum direct-detection laser ranging receivers

NASA Technical Reports Server (NTRS)

Abshire, J. B.

1978-01-01

A summary of previously proposed receiver strategies for direct-detection laser ranging receivers is presented. Computer simulations are used to compare performance of candidate implementation strategies in the 1- to 100-photoelectron region. Under the condition of no background radiation, the maximum-likelihood and minimum mean-square error estimators were found to give the same performance for both bell-shaped and rectangular optical-pulse shapes. For signal energies greater than 100 photoelectrons, the root-mean-square range error is shown to decrease as Q to the -1/2 power for bell-shaped pulses and Q to the -1 power for rectangular pulses, where Q represents the average pulse energy. Of several receiver implementations presented, the matched-filter peak detector was found to be preferable. A similar configuration, using a constant-fraction discriminator, exhibited a signal-level dependent time bias.

A compact pulse shape discriminator module for large neutron detector arrays

NASA Astrophysics Data System (ADS)

Venkataramanan, S.; Gupta, Arti; Golda, K. S.; Singh, Hardev; Kumar, Rakesh; Singh, R. P.; Bhowmik, R. K.

2008-11-01

A cost-effective high-performance pulse shape discriminator module has been developed to process signals from organic liquid scintillator-based neutron detectors. This module is especially designed for the large neutron detector array used for studies of nuclear reaction dynamics at the Inter University Accelerator Center (IUAC). It incorporates all the necessary pulse processing circuits required for neutron spectroscopy in a novel fashion by adopting the zero crossover technique for neutron-gamma (n- γ) pulse shape discrimination. The detailed layout of the circuit and different features of the module are described in the present paper. The quality of n- γ separation obtained with this electronics is much better than that of commercial modules especially in the low-energy region. The results obtained with our module are compared with similar setups available in other laboratories.

Pulse-shaping based two-photon FRET stoichiometry

PubMed Central

Flynn, Daniel C.; Bhagwat, Amar R.; Brenner, Meredith H.; Núñez, Marcos F.; Mork, Briana E.; Cai, Dawen; Swanson, Joel A.; Ogilvie, Jennifer P.

2015-01-01

Förster Resonance Energy Transfer (FRET) based measurements that calculate the stoichiometry of intermolecular interactions in living cells have recently been demonstrated, where the technique utilizes selective one-photon excitation of donor and acceptor fluorophores to isolate the pure FRET signal. Here, we present work towards extending this FRET stoichiometry method to employ two-photon excitation using a pulse-shaping methodology. In pulse-shaping, frequency-dependent phases are applied to a broadband femtosecond laser pulse to tailor the two-photon excitation conditions to preferentially excite donor and acceptor fluorophores. We have also generalized the existing stoichiometry theory to account for additional cross-talk terms that are non-vanishing under two-photon excitation conditions. Using the generalized theory we demonstrate two-photon FRET stoichiometry in live COS-7 cells expressing fluorescent proteins mAmetrine as the donor and tdTomato as the acceptor. PMID:25836193

Exploring the Pulse Structure of the Gamma-Ray Bursts from the Swift Burst Alert Telescop

NASA Astrophysics Data System (ADS)

Martinez, Juan-Carlos; Team 1: Jon Hakkila, Amy Lien, Judith, Racusin, Team 2: Antonino Cucchiara, David Morris

2018-01-01

Gamma-ray bursts (GRBs) are one of the brightest and most intense explosions in our universe. For this project, we studied the shape of 400 single pulse GRBs using data gathered from Swift's Burst Alert Telescope (BAT). Hakkila et al. (2015) have discovered a mathematical Model that describes the GRB’s pulse shapes. Following the method in Hakkila et al. (2015), we fit GRB pulses with the Norris function and examined the residual in the fitting, to see whether the results are consistent with the one reported in Hakkila et al. (2015).

Focus characterization at an X-ray free-electron laser by coherent scattering and speckle analysis

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

Sikorski, Marcin; Song, Sanghoon; Schropp, Andreas

2015-04-14

X-ray focus optimization and characterization based on coherent scattering and quantitative speckle size measurements was demonstrated at the Linac Coherent Light Source. Its performance as a single-pulse free-electron laser beam diagnostic was tested for two typical focusing configurations. The results derived from the speckle size/shape analysis show the effectiveness of this technique in finding the focus' location, size and shape. In addition, its single-pulse compatibility enables users to capture pulse-to-pulse fluctuations in focus properties compared with other techniques that require scanning and averaging.

Modeling the Pulse Signal by Wave-Shape Function and Analyzing by Synchrosqueezing Transform

PubMed Central

Wang, Chun-Li; Yang, Yueh-Lung; Wu, Wen-Hsiang; Tsai, Tung-Hu; Chang, Hen-Hong

2016-01-01

We apply the recently developed adaptive non-harmonic model based on the wave-shape function, as well as the time-frequency analysis tool called synchrosqueezing transform (SST) to model and analyze oscillatory physiological signals. To demonstrate how the model and algorithm work, we apply them to study the pulse wave signal. By extracting features called the spectral pulse signature, and based on functional regression, we characterize the hemodynamics from the radial pulse wave signals recorded by the sphygmomanometer. Analysis results suggest the potential of the proposed signal processing approach to extract health-related hemodynamics features. PMID:27304979

Modeling the Pulse Signal by Wave-Shape Function and Analyzing by Synchrosqueezing Transform.

PubMed

Wu, Hau-Tieng; Wu, Han-Kuei; Wang, Chun-Li; Yang, Yueh-Lung; Wu, Wen-Hsiang; Tsai, Tung-Hu; Chang, Hen-Hong

2016-01-01

We apply the recently developed adaptive non-harmonic model based on the wave-shape function, as well as the time-frequency analysis tool called synchrosqueezing transform (SST) to model and analyze oscillatory physiological signals. To demonstrate how the model and algorithm work, we apply them to study the pulse wave signal. By extracting features called the spectral pulse signature, and based on functional regression, we characterize the hemodynamics from the radial pulse wave signals recorded by the sphygmomanometer. Analysis results suggest the potential of the proposed signal processing approach to extract health-related hemodynamics features.

Flexible approach to vibrational sum-frequency generation using shaped near-infrared light

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

Chowdhury, Azhad U.; Liu, Fangjie; Watson, Brianna R.

We describe a new approach that expands the utility of vibrational sum-frequency generation (vSFG) spectroscopy using shaped near-infrared (NIR) laser pulses. Here, we demonstrate that arbitrary pulse shapes can be specified to match experimental requirements without the need for changes to the optical alignment. In this way, narrowband NIR pulses as long as 5.75 ps are readily generated, with a spectral resolution of about 2.5 cm -1, an improvement of approximately a factor of 3 compared to a typical vSFG system. Moreover, the utility of having complete control over the NIR pulse characteristics is demonstrated through nonresonant background suppression frommore » a metallic substrate by generating an etalon waveform in the pulse shaper. The flexibility afforded by switching between arbitrary NIR waveforms at the sample position with the same instrument geometry expands the type of samples that can be studied without extensive modifications to existing apparatuses or large investments in specialty optics.« less

Time history prediction of direct-drive implosions on the Omega facility

DOE PAGES

Laffite, S.; Bourgade, J. L.; Caillaud, T.; ...

2016-01-14

We present in this article direct-drive experiments that were carried out on the Omega facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Two different pulse shapes were tested in order to vary the implosion stability of the same target whose parameters, dimensions and composition, remained the same. The direct-drive configuration on the Omega facility allows the accurate time-resolvedmeasurement of the scattered light. We show that, provided the laser coupling is well controlled, the implosion time history, assessed by the “bang-time” and the shell trajectory measurements, can be predicted. This conclusion is independent on the pulse shape. Inmore » contrast, we show that the pulse shape affects the implosion stability, assessed by comparing the target performances between prediction and measurement. For the 1-ns square pulse, the measuredneutron number is about 80% of the prediction. Lastly, for the 2-step 2-ns pulse, we test here that this ratio falls to about 20%.« less

Time history prediction of direct-drive implosions on the Omega facility

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

Laffite, S.; Bourgade, J. L.; Caillaud, T.

We present in this article direct-drive experiments that were carried out on the Omega facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Two different pulse shapes were tested in order to vary the implosion stability of the same target whose parameters, dimensions and composition, remained the same. The direct-drive configuration on the Omega facility allows the accurate time-resolvedmeasurement of the scattered light. We show that, provided the laser coupling is well controlled, the implosion time history, assessed by the “bang-time” and the shell trajectory measurements, can be predicted. This conclusion is independent on the pulse shape. Inmore » contrast, we show that the pulse shape affects the implosion stability, assessed by comparing the target performances between prediction and measurement. For the 1-ns square pulse, the measuredneutron number is about 80% of the prediction. Lastly, for the 2-step 2-ns pulse, we test here that this ratio falls to about 20%.« less

Time history prediction of direct-drive implosions on the Omega facility

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

Laffite, S.; Bourgade, J. L.; Caillaud, T.

We present in this article direct-drive experiments that were carried out on the Omega facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Two different pulse shapes were tested in order to vary the implosion stability of the same target whose parameters, dimensions and composition, remained the same. The direct-drive configuration on the Omega facility allows the accurate time-resolved measurement of the scattered light. We show that, provided the laser coupling is well controlled, the implosion time history, assessed by the “bang-time” and the shell trajectory measurements, can be predicted. This conclusion is independent on the pulse shape.more » In contrast, we show that the pulse shape affects the implosion stability, assessed by comparing the target performances between prediction and measurement. For the 1-ns square pulse, the measured neutron number is about 80% of the prediction. For the 2-step 2-ns pulse, we test here that this ratio falls to about 20%.« less

Flexible approach to vibrational sum-frequency generation using shaped near-infrared light

DOE PAGES

Chowdhury, Azhad U.; Liu, Fangjie; Watson, Brianna R.; ...

2018-04-23

We describe a new approach that expands the utility of vibrational sum-frequency generation (vSFG) spectroscopy using shaped near-infrared (NIR) laser pulses. Here, we demonstrate that arbitrary pulse shapes can be specified to match experimental requirements without the need for changes to the optical alignment. In this way, narrowband NIR pulses as long as 5.75 ps are readily generated, with a spectral resolution of about 2.5 cm -1, an improvement of approximately a factor of 3 compared to a typical vSFG system. Moreover, the utility of having complete control over the NIR pulse characteristics is demonstrated through nonresonant background suppression frommore » a metallic substrate by generating an etalon waveform in the pulse shaper. The flexibility afforded by switching between arbitrary NIR waveforms at the sample position with the same instrument geometry expands the type of samples that can be studied without extensive modifications to existing apparatuses or large investments in specialty optics.« less

Acoustic Rectification in Dispersive Media

NASA Technical Reports Server (NTRS)

Cantrell, John H.

2008-01-01

It is shown that the shapes of acoustic radiation-induced static strain and displacement pulses (rectified acoustic pulses) are defined locally by the energy density of the generating waveform. Dispersive properties are introduced analytically by assuming that the rectified pulses are functionally dependent on a phase factor that includes both dispersive and nonlinear terms. The dispersion causes an evolutionary change in the shape of the energy density profile that leads to the generation of solitons experimentally observed in fused silica.

Neurophysiological correlates of abnormal somatosensory temporal discrimination in dystonia.

PubMed

Antelmi, Elena; Erro, Roberto; Rocchi, Lorenzo; Liguori, Rocco; Tinazzi, Michele; Di Stasio, Flavio; Berardelli, Alfredo; Rothwell, John C; Bhatia, Kailash P

2017-01-01

Somatosensory temporal discrimination threshold is often prolonged in patients with dystonia. Previous evidence suggested that this might be caused by impaired somatosensory processing in the time domain. Here, we tested if other markers of reduced inhibition in the somatosensory system might also contribute to abnormal somatosensory temporal discrimination in dystonia. Somatosensory temporal discrimination threshold was measured in 19 patients with isolated cervical dystonia and 19 age-matched healthy controls. We evaluated temporal somatosensory inhibition using paired-pulse somatosensory evoked potentials, spatial somatosensory inhibition by measuring the somatosensory evoked potentials interaction between simultaneous stimulation of the digital nerves in thumb and index finger, and Gamma-aminobutyric acid-ergic (GABAergic) sensory inhibition using the early and late components of high-frequency oscillations in digital nerves somatosensory evoked potentials. When compared with healthy controls, dystonic patients had longer somatosensory temporal discrimination thresholds, reduced suppression of cortical and subcortical paired-pulse somatosensory evoked potentials, less spatial inhibition of simultaneous somatosensory evoked potentials, and a smaller area of the early component of the high-frequency oscillations. A logistic regression analysis found that paired pulse suppression of the N20 component at an interstimulus interval of 5 milliseconds and the late component of the high-frequency oscillations were independently related to somatosensory temporal discrimination thresholds. "Dystonia group" was also a predictor of enhanced somatosensory temporal discrimination threshold, indicating a dystonia-specific effect that independently influences this threshold. Increased somatosensory temporal discrimination threshold in dystonia is related to reduced activity of inhibitory circuits within the primary somatosensory cortex. © 2016 International Parkinson and Movement Disorder Society. © 2016 International Parkinson and Movement Disorder Society.

Gauss-Legendre quadrature method used to evaluate the spatio-temporal intensity of ultrashort pulses in the focal region of lenses.

PubMed

García-Martínez, L; Rosete-Aguilar, M; Garduño-Mejia, J

2012-01-20

We analyze the spatio-temporal intensity of sub-20 femtosecond pulses with a carrier wavelength of 810 nm along the optical axis of low numerical aperture achromatic and apochromatic doublets designed in the IR region by using the scalar diffraction theory. The diffraction integral is solved by expanding the wave number around the carrier frequency of the pulse in a Taylor series up to third order, and then the integral over the frequencies is solved by using the Gauss-Legendre quadrature method. The numerical errors in this method are negligible by taking 96 nodes and the computational time is reduced by 95% compared to the integration method by rectangles. We will show that the third-order group velocity dispersion (GVD) is not negligible for 10 fs pulses at 810 nm propagating through the low numerical aperture doublets, and its effect is more important than the propagation time difference (PTD). This last effect, however, is also significant. For sub-20 femtosecond pulses, these two effects make the use of a pulse shaper necessary to correct for second and higher-order GVD terms and also the use of apochromatic optics to correct the PTD effect. The design of an apochromatic doublet is presented in this paper and the spatio-temporal intensity of the pulse at the focal region of this doublet is compared to that given by the achromatic doublet. © 2012 Optical Society of America

Frequency-domain nonlinear optics in two-dimensionally patterned quasi-phase-matching media.

PubMed

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

2016-07-11

Advances in the amplification and manipulation of ultrashort laser pulses have led to revolutions in several areas. Examples include chirped pulse amplification for generating high peak-power lasers, power-scalable amplification techniques, pulse shaping via modulation of spatially-dispersed laser pulses, and efficient frequency-mixing in quasi-phase-matched nonlinear crystals to access new spectral regions. In this work, we introduce and demonstrate a new platform for nonlinear optics which has the potential to combine these separate functionalities (pulse amplification, frequency transfer, and pulse shaping) into a single monolithic device that is bandwidth- and power-scalable. The approach is based on two-dimensional (2D) patterning of quasi-phase-matching (QPM) gratings combined with optical parametric interactions involving spatially dispersed laser pulses. Our proof of principle experiment demonstrates this technique via mid-infrared optical parametric chirped pulse amplification of few-cycle pulses. Additionally, we present a detailed theoretical and numerical analysis of such 2D-QPM devices and how they can be designed.

Sputter crater formation in the case of microsecond pulsed glow discharge in a Grimm-type source. Comparison of direct current and radio frequency modes

NASA Astrophysics Data System (ADS)

Efimova, Varvara; Hoffmann, Volker; Eckert, Jürgen

2012-10-01

Depth profiling with pulsed glow discharge is a promising technique. The application of pulsed voltage for sputtering reduces the sputtering rate and thermal stress and hereby improves the analysis of thin layered and thermally fragile samples. However pulsed glow discharge is not well studied and this limits its practical use. The current work deals with the questions which usually arise when the pulsed mode is applied: Which duty cycle, frequency and pulse length must be chosen to get the optimal sputtering rate and crater shape? Are the well-known sputtering effects of the continuous mode valid also for the pulsed regime? Is there any difference between dc and rf pulsing in terms of sputtering? It is found that the pulse length is a crucial parameter for the crater shape and thermal effects. Sputtering with pulsed dc and rf modes is found to be similar. The observed sputtering effects at various pulsing parameters helped to interpret and optimize the depth resolution of GD OES depth profiles.

Efficient photoassociation of ultracold cesium atoms with picosecond pulse laser

NASA Astrophysics Data System (ADS)

Hai, Yang; Hu, Xue-Jin; Li, Jing-Lun; Cong, Shu-Lin

2017-08-01

We investigate theoretically the formation of ultracold Cs2 molecules via photoassociation (PA) with three kinds of pulses (the Gaussian pulse, the asymmetric shaped laser pulse SL1 with a large rising time and a small falling time and the asymmetric shaped laser pulse SL2 with a small rising time and a large falling time). For the three kinds of pulses, the final population on vibrational levels from v‧ = 120 to 175 of the excited state displays a regular oscillation change with pulse width and interaction strength, and a high PA efficiency can be achieved with optimised parameters. The PA efficiency in the excited state steered by the SL1-pulse (SL2-pulse) train with optimised parameters which is composed of four SL1 (SL2) pulses is 1.74 times as much as that by the single SL1 (SL2) pulse due to the population accumulation effect. Moreover, a dump laser is employed to transfer the excited molecules from the excited state to the vibrational level v″ = 12 of the ground state to obtain stable molecules.

Passive and active pulse stacking scheme for pulse shaping

DOEpatents

Harney, Robert C.; Schipper, John F.

1977-01-01

Apparatus and method for producing a sequence of radiation pulses with a pulse envelope of time variation which is controllable by an external electromagnetic signal applied to an active medium or by a sectored reflector, through which the radiation passes.

White light for the fast lane: supercontinuum generation in all-normal dispersion fibers for ultrafast photonics

NASA Astrophysics Data System (ADS)

Heidt, Alexander M.

2014-03-01

This talk will give an overview of the unique properties of supercontinuum generation (SCG) in all-normal dispersion (ANDi) fibers pumped by ultrashort pulses and the possibilities they offer for ultrafast photonics applications. In contrast to their anomalously pumped counterparts, the SCG process in ANDi fibers conserves a single ultrashort pulse in the time domain, completely suppresses soliton formation and decay, and avoids noise-amplifying nonlinear dynamics. The resulting spectra combine the best of both worlds - the broad, more than octave-spanning bandwidths usually associated with anomalous dispersion pumping with the high temporal coherence, pulse-to-pulse stability and well-defined temporal pulse characteristics known from the normal dispersion regime. These characteristics are ideally suited for ultrafast photonics, and I will present application examples including the generation of high quality single-cycle pulses and their amplification, as well as ultrafast spectroscopy. This talk will also explore the exciting new possibilities enabled by extending this approach into the mid-IR spectral region using novel soft glass fiber designs.

Time-diagnostics for improved dynamics experiments at XUV FELs

NASA Astrophysics Data System (ADS)

Drescher, Markus; Frühling, Ulrike; Krikunova, Maria; Maltezopoulos, Theophilos; Wieland, Marek

2010-10-01

Significantly structured and fluctuating temporal profiles of pulses from self-amplified spontaneous emission free electron lasers as well as their unstable timing require time diagnostics on a single-shot basis. The duration and structure of extreme-ultraviolet (XUV) pulses from the Free Electron Laser (FEL) in Hamburg (FLASH) are becoming accessible using a variation of the streak camera principle, where photoemitted electrons are energetically streaked in the electric field component of a terahertz electromagnetic wave. The timing with respect to an independently generated laser pulse can be measured in an XUV/laser cross-correlator, based on a non-collinear superposition of both pulses on a solid state surface and detection of XUV-induced modulations of its reflectivity for visible light. Sorting of data according to the measured timing dramatically improves the temporal resolution of an experiment sampling the relaxation of transient electronic states in xenon after linear- as well as nonlinear excitation with intense XUV pulses from FLASH.

Power balance on a multibeam laser

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

Sampat, Sid; Kelly, John H.; Kosc, Tanya Z.

Inertial confinement fusion (ICF) cryogenic experiments on the 60-beam OMEGA laser have strict requirements for the laser energy delivered on target to be power balanced in order to maximize target-irradiation uniformity. For OMEGA, this quantity (power balance) is inferred from measurements of the time-integrated energy and time-resolved, spatially integrated temporal profile of each of the 60 beams at the output of the laser. The work presented here proposes a general definition of power balance as measured at the laser output and discusses the conditions that are fundamental to achieving laser power balance. Power balance necessitates equal gain across all stagesmore » of amplification, equal net losses across each amplifier stage, equal frequency conversion (from 1053 nm to 351 nm) of all 60 beams, and equal beam path lengths (beam timing). Typical OMEGA ICF laser pulse shapes consist of one or more short (100-ps) “pickets” followed by a shaped “drive” pulse of 1 to 2 ns. For these experiments, power balance is assessed for the pickets and the drive independently, with the ultimate goal of achieving root-mean-square (rms) imbalance across all 60 beams of less than 2% rms on both. Our work presents a comprehensive summary of laser shot campaigns conducted to significantly improve laser power balance from typical rms values of 4.7% and 5.2%, respectively, to the 3% level for both features along with a discussion of future work required to further reduce the rms power imbalance of the laser system.« less

Adaptive Quantum Control of Charge Motion in Semiconductor Heterostructures

NASA Astrophysics Data System (ADS)

Reitze, David

1998-05-01

Quantum control of electronic wavepacket motion and interactions using ultrafast lasers has moved from the conceptual stage to reality, in large part driven by advances in quantum control theory (R. J. Gordon and S. A. Rice, Ann. Rev. Phys. Chem. (1997), in press.) (M. Shapiro and P. Brumer, J. Chem. Soc. Faraday Trans. V93, 1263 (1997).) (D. Neuhauser and H. Rabitz, Acc. Chem. Res. V26, 496 (1993).) and experimental pulse shaping methods (A. M. Weiner, D. E. Leaird, G. P. Wiederrecht, and K. A. Nelson, Science V247, 412 (1990).) (A. Efimov, C. Schaffer, and D. H. Reitze, J. Opt. Soc. Am VB12, 1968 (1995).). Here, we apply these methods to controlling charge motion in semiconductor heterostructures. Control of coherent charge dynamics in heterostructures enjoys an advantage in that spatial potential profiles can be adjusted almost arbitrarily. Thus, control of charge motion can be exerted by tailoring both the temporal and spatial interactions of the charges with the controlling optical and static fields. In this talk, we demonstrate an experimental feedback loop which adaptively shapes fs pulses in a quantum contol pump-probe experiment, apply it to the control of coherent wavepacket motion in DC-biased asymmetric double quantum well(ADQW) structures, and compare to theoretical predictions of quantum control in ADQWs (N. M. Beach, D. H. Reitze, and J. L. Krause, submitted to Opt. Exp.) (J. L. Krause, D. H. Reitze, G. D. Sanders, A. Kuznetsov, and C. J. Stanton, to appear in Phys. Rev. B).

Analytical one-dimensional model for laser-induced ultrasound in planar optically absorbing layer.

PubMed

Svanström, Erika; Linder, Tomas; Löfqvist, Torbjörn

2014-03-01

Ultrasound generated by means of laser-based photoacoustic principles are in common use today and applications can be found both in biomedical diagnostics, non-destructive testing and materials characterisation. For certain measurement applications it could be beneficial to shape the generated ultrasound regarding spectral properties and temporal profile. To address this, we studied the generation and propagation of laser-induced ultrasound in a planar, layered structure. We derived an analytical expression for the induced pressure wave, including different physical and optical properties of each layer. A Laplace transform approach was employed in analytically solving the resulting set of photoacoustic wave equations. The results correspond to simulations and were compared to experimental results. To enable the comparison between recorded voltage from the experiments and the calculated pressure we employed a system identification procedure based on physical properties of the ultrasonic transducer to convert the calculated acoustic pressure to voltages. We found reasonable agreement between experimentally obtained voltages and the voltages determined from the calculated acoustic pressure, for the samples studied. The system identification procedure was found to be unstable, however, possibly from violations of material isotropy assumptions by film adhesives and coatings in the experiment. The presented analytical model can serve as a basis when addressing the inverse problem of shaping an acoustic pulse from absorption of a laser pulse in a planar layered structure of elastic materials. Copyright © 2013 Elsevier B.V. All rights reserved.

Power balance on a multibeam laser

NASA Astrophysics Data System (ADS)

Sampat, S.; Kelly, J. H.; Kosc, T. Z.; Rigatti, A. L.; Kwiatkowski, J.; Donaldson, W. R.; Romanofsky, M. H.; Waxer, L. J.; Dean, R.; Moshier, R.

2018-02-01

Inertial confinement fusion (ICF) cryogenic experiments on the 60-beam OMEGA laser have strict requirements for the laser energy delivered on target to be power balanced in order to maximize target-irradiation uniformity. For OMEGA, this quantity (power balance) is inferred from measurements of the time-integrated energy and time-resolved, spatially integrated temporal profile of each of the 60 beams at the output of the laser. The work presented here proposes a general definition of power balance as measured at the laser output and discusses the conditions that are fundamental to achieving laser power balance. Power balance necessitates equal gain across all stages of amplification, equal net losses across each amplifier stage, equal frequency conversion (from 1053 nm to 351 nm) of all 60 beams, and equal beam path lengths (beam timing). Typical OMEGA ICF laser pulse shapes consist of one or more short (100-ps) "pickets" followed by a shaped "drive" pulse of 1 to 2 ns. For these experiments, power balance is assessed for the pickets and the drive independently, with the ultimate goal of achieving root-mean-square (rms) imbalance across all 60 beams of less than 2% rms on both. This work presents a comprehensive summary of laser shot campaigns conducted to significantly improve laser power balance from typical rms values of 4.7% and 5.2%, respectively, to the 3% level for both features along with a discussion of future work required to further reduce the rms power imbalance of the laser system.

Power balance on a multibeam laser

DOE PAGES

Sampat, Sid; Kelly, John H.; Kosc, Tanya Z.; ...

2018-02-15

Inertial confinement fusion (ICF) cryogenic experiments on the 60-beam OMEGA laser have strict requirements for the laser energy delivered on target to be power balanced in order to maximize target-irradiation uniformity. For OMEGA, this quantity (power balance) is inferred from measurements of the time-integrated energy and time-resolved, spatially integrated temporal profile of each of the 60 beams at the output of the laser. The work presented here proposes a general definition of power balance as measured at the laser output and discusses the conditions that are fundamental to achieving laser power balance. Power balance necessitates equal gain across all stagesmore » of amplification, equal net losses across each amplifier stage, equal frequency conversion (from 1053 nm to 351 nm) of all 60 beams, and equal beam path lengths (beam timing). Typical OMEGA ICF laser pulse shapes consist of one or more short (100-ps) “pickets” followed by a shaped “drive” pulse of 1 to 2 ns. For these experiments, power balance is assessed for the pickets and the drive independently, with the ultimate goal of achieving root-mean-square (rms) imbalance across all 60 beams of less than 2% rms on both. Our work presents a comprehensive summary of laser shot campaigns conducted to significantly improve laser power balance from typical rms values of 4.7% and 5.2%, respectively, to the 3% level for both features along with a discussion of future work required to further reduce the rms power imbalance of the laser system.« less

In vivo Proton Electron Double Resonance Imaging of Mice with Fast Spin Echo Pulse Sequence

PubMed Central

Sun, Ziqi; Li, Haihong; Petryakov, Sergey; Samouilov, Alex; Zweier, Jay L.

2011-01-01

Purpose To develop and evaluate a 2D fast spin echo (FSE) pulse sequence for enhancing temporal resolution and reducing tissue heating for in vivo proton electron double resonance imaging (PEDRI) of mice. Materials and Methods A four-compartment phantom containing 2 mM TEMPONE was imaged at 20.1 mT using 2D FSE-PEDRI and regular gradient echo (GRE)-PEDRI pulse sequences. Control mice were infused with TEMPONE over ∼1 min followed by time-course imaging using the 2D FSE-PEDRI sequence at intervals of 10 – 30 s between image acquisitions. The average signal intensity from the time-course images was analyzed using a first-order kinetics model. Results Phantom experiments demonstrated that EPR power deposition can be greatly reduced using the FSE-PEDRI pulse sequence compared to the conventional gradient echo pulse sequence. High temporal resolution was achieved at ∼4 s per image acquisition using the FSE-PEDRI sequence with a good image SNR in the range of 233-266 in the phantom study. The TEMPONE half-life measured in vivo was ∼72 s. Conclusion Thus, the FSE-PEDRI pulse sequence enables fast in vivo functional imaging of free radical probes in small animals greatly reducing EPR irradiation time with decreased power deposition and provides increased temporal resolution. PMID:22147559

Multi-Chromatic Ultrashort Pulse Filamentation and Bulk Modification in Dielectrics

DTIC Science & Technology

2016-05-05

multi -pulse fields 7 6 Filamentation and bulk modification by spatio-temporally chirped pulses 8 7 Quantum modeling of photoionization and nonlinear...pulses. (b) two co-propagating pulses of di↵erent frequencies. 4) Develop non-time-averaged multi -chromatic quantum -mechanical models of photoion- ization...very well with those of the extended multi -rate equation using the relaxation approximation, which is much faster. A continued collaboration to also

Ultrafast scanning probe microscopy

DOEpatents

Weiss, S.; Chemla, D.S.; Ogletree, D.F.; Botkin, D.

1995-05-16

An ultrafast scanning probe microscopy method is described for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample. 6 Figs.

Ultrafast scanning probe microscopy

DOEpatents

Weiss, Shimon; Chemla, Daniel S.; Ogletree, D. Frank; Botkin, David

1995-01-01

An ultrafast scanning probe microscopy method for achieving subpicosecond-temporal resolution and submicron-spatial resolution of an observation sample. In one embodiment of the present claimed invention, a single short optical pulse is generated and is split into first and second pulses. One of the pulses is delayed using variable time delay means. The first pulse is then directed at an observation sample located proximate to the probe of a scanning probe microscope. The scanning probe microscope produces probe-sample signals indicative of the response of the probe to characteristics of the sample. The second pulse is used to modulate the probe of the scanning probe microscope. The time delay between the first and second pulses is then varied. The probe-sample response signal is recorded at each of the various time delays created between the first and second pulses. The probe-sample response signal is then plotted as a function of time delay to produce a cross-correlation of the probe sample response. In so doing, the present invention provides simultaneous subpicosecond-temporal resolution and submicron-spatial resolution of the sample.

Postnatal temporal bone ontogeny in Pan, Gorilla, and Homo, and the implications for temporal bone ontogeny in Australopithecus afarensis.

PubMed

Terhune, Claire E; Kimbel, William H; Lockwood, Charles A

2013-08-01

Assessments of temporal bone morphology have played an important role in taxonomic and phylogenetic evaluations of fossil taxa, and recent three-dimensional analyses of this region have supported the utility of the temporal bone for testing taxonomic and phylogenetic hypotheses. But while clinical analyses have examined aspects of temporal bone ontogeny in humans, the ontogeny of the temporal bone in non-human taxa is less well documented. This study examines ontogenetic allometry of the temporal bone in order to address several research questions related to the pattern and trajectory of temporal bone shape change during ontogeny in the African apes and humans. We further apply these data to a preliminary analysis of temporal bone ontogeny in Australopithecus afarensis. Three-dimensional landmarks were digitized on an ontogenetic series of specimens of Homo sapiens, Pan troglodytes, Pan paniscus, and Gorilla gorilla. Data were analyzed using geometric morphometric methods, and shape changes throughout ontogeny in relation to size were compared. Results of these analyses indicate that, despite broadly similar patterns, African apes and humans show marked differences in development of the mandibular fossa and tympanic portions of the temporal bone. These findings indicate divergent, rather than parallel, postnatal ontogenetic allometric trajectories for temporal bone shape in these taxa. The pattern of temporal bone shape change with size exhibited by A. afarensis showed some affinities to that of humans, but was most similar to extant African apes, particularly Gorilla. Copyright © 2013 Wiley Periodicals, Inc.

Pulse shape discrimination for background rejection in germanium gamma-ray detectors

NASA Technical Reports Server (NTRS)

Feffer, P. T.; Smith, D. M.; Campbell, R. D.; Primbsch, J. H.; Lin, R. P.

1989-01-01

A pulse-shape discrimination (PSD) technique is developed to reject the beta-decay background resulting from activation of Ge gamma-ray detectors by cosmic-ray secondaries. These beta decays are a major source of background at 0.2-2 MeV energies in well shielded Ge detector systems. The technique exploits the difference between the detected current pulse shapes of single- and multiple-site energy depositions within the detector: beta decays are primarily single-site events, while photons at these energies typically Compton scatter before being photoelectrically absorbed to produce multiple-site events. Depending upon the amount of background due to sources other than beta decay, PSD can more than double the detector sensitivity.

Studies of neutron-γ pulse shape discrimination in EJ-309 liquid scintillator using charge integration method

NASA Astrophysics Data System (ADS)

Pawełczak, I. A.; Ouedraogo, S. A.; Glenn, A. M.; Wurtz, R. E.; Nakae, L. F.

2013-05-01

Pulse shape discrimination capability based on the charge integration has been investigated for liquid scintillator EJ-309. The effectiveness of neutron-γ discrimination in 4-in. diameter and 3-in. thick EJ-309 cells coupled with 3-in. photomultiplier tubes has been carefully studied in the laboratory environment and compared to the commonly used EJ-301 liquid scintillator formulation. Influences of distortions in pulse shape caused by 13.7-m long cables necessary for some remote operations have been examined. The parameter space for an effective neutron-γ discrimination for these assays, such as position and width of a gate used for integration of the delayed light, has been explored.

Beyond the single-atom response in absorption line shapes: probing a dense, laser-dressed helium gas with attosecond pulse trains.

PubMed

Liao, Chen-Ting; Sandhu, Arvinder; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B

2015-04-10

We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently, to the appearance of new, narrow features in the absorption line.

Versatile analog pulse height computer performs real-time arithmetic operations

NASA Technical Reports Server (NTRS)

Brenner, R.; Strauss, M. G.

1967-01-01

Multipurpose analog pulse height computer performs real-time arithmetic operations on relatively fast pulses. This computer can be used for identification of charged particles, pulse shape discrimination, division of signals from position sensitive detectors, and other on-line data reduction techniques.