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.

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.

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.

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.

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.

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

Generation of programmable temporal pulse shape and applications in micromachining

NASA Astrophysics Data System (ADS)

Peng, X.; Jordens, B.; Hooper, A.; Baird, B. W.; Ren, W.; Xu, L.; Sun, L.

2009-02-01

In this paper we presented a pulse shaping technique on regular solid-state lasers and the application in semiconductor micromachining. With a conventional Q-switched laser, all of the parameters can be adjusted over only limited ranges, especially the pulse width and pulse shape. However, some laser link processes using traditional laser pulses with pulse widths of a few nanoseconds to a few tens of nanoseconds tend to over-crater in thicker overlying passivation layers and thereby cause IC reliability problems. Use of a laser pulse with a special shape and a fast leading edge, such as tailored pulse, is one technique for controlling link processing. The pulse shaping technique is based on light-loop controlled optical modulation to shape conventional Q-switched solid-state lasers. One advantage of the pulse shaping technique is to provide a tailored pulse shape that can be programmed to have more than one amplitude value. Moreover, it has the capability of providing programmable tailored pulse shapes with discrete amplitude and time duration components. In addition, it provides fast rising and fall time of each pulse at fairly high repetition rate at 355nm with good beam quality. The regular-to-shaped efficiency is up to 50%. We conclude with a discussion of current results for laser processing of semiconductor memory link structures using programmable temporal pulse shapes. The processing experiments showed promising results with shaped pulse.

Generation of dark hollow femtosecond pulsed beam by phase-only liquid crystal spatial light modulator

NASA Astrophysics Data System (ADS)

Nie, Yongming; Ma, Haotong; Li, Xiujian; Hu, Wenhua; Yang, Jiankun

2011-07-01

Based on the refractive laser beam shaping system, the dark hollow femtosecond pulse beam shaping technique with a phase-only liquid crystal spatial light modulator (LC-SLM) is demonstrated. The phase distribution of the LC-SLM is derived by the energy conservation and constant optical path principle. The effects of the shaping system on the temporal properties, including spectral phase distribution and bandwidth of the femtosecond pulse, are analyzed in detail. Experimental results show that the hollow intensity distribution of the output pulsed beam can be maintained much at more than 1200mm. The spectral phase of the pulse is changed, and the pulse width is expanded from 199 to 230fs, which is caused by the spatial--temporal coupling effect. The coupling effect mainly depends on the phase-only LC-SLM itself, not on its loaded phase distribution. The experimental results indicate that the proposed shaping setup can generate a dark hollow femtosecond pulsed beam effectively, because the temporal Gaussian waveform is unchanged.

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

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

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.

Broadband optical frequency comb generator based on driving N-cascaded modulators by Gaussian-shaped waveform

NASA Astrophysics Data System (ADS)

Hmood, Jassim K.; Harun, Sulaiman W.

2018-05-01

A new approach for realizing a wideband optical frequency comb (OFC) generator based on driving cascaded modulators by a Gaussian-shaped waveform, is proposed and numerically demonstrated. The setup includes N-cascaded MZMs, a single Gaussian-shaped waveform generator, and N-1 electrical time delayer. The first MZM is driven directly by a Gaussian-shaped waveform, while delayed replicas of the Gaussian-shaped waveform drive the other MZMs. An analytical model that describes the proposed OFC generator is provided to study the effect of number and chirp factor of cascaded MZM as well as pulse width on output spectrum. Optical frequency combs at frequency spacing of 1 GHz are generated by applying Gaussian-shaped waveform at pulse widths ranging from 200 to 400 ps. Our results reveal that, the number of comb lines is inversely proportional to the pulse width and directly proportional to both number and chirp factor of cascaded MZMs. At pulse width of 200 ps and chirp factor of 4, 67 frequency lines can be measured at output spectrum of two-cascaded MZMs setup. Whereas, increasing the number of cascaded stages to 3, 4, and 5, the optical spectra counts 89, 109 and 123 frequency lines; respectively. When the delay time is optimized, 61 comb lines can be achieved with power fluctuations of less than 1 dB for five-cascaded MZMs setup.

Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses.

PubMed

Jukna, Vytautas; Jarnac, Amélie; Milián, Carles; Brelet, Yohann; Carbonnel, Jérôme; André, Yves-Bernard; Guillermin, Régine; Sessarego, Jean-Pierre; Fattaccioli, Dominique; Mysyrowicz, André; Couairon, Arnaud; Houard, Aurélien

2016-06-01

Acoustic signals generated by filamentation of ultrashort terawatt laser pulses in water are characterized experimentally. Measurements reveal a strong influence of input pulse duration on the shape and intensity of the acoustic wave. Numerical simulations of the laser pulse nonlinear propagation and the subsequent water hydrodynamics and acoustic wave generation show that the strong acoustic emission is related to the mechanism of superfilamention in water. The elongated shape of the plasma volume where energy is deposited drives the far-field profile of the acoustic signal, which takes the form of a radially directed pressure wave with a single oscillation and a very broad spectrum.

Generation of dark hollow femtosecond pulsed beam by phase-only liquid crystal spatial light modulator.

PubMed

Nie, Yongming; Ma, Haotong; Li, Xiujian; Hu, Wenhua; Yang, Jiankun

2011-07-20

Based on the refractive laser beam shaping system, the dark hollow femtosecond pulse beam shaping technique with a phase-only liquid crystal spatial light modulator (LC-SLM) is demonstrated. The phase distribution of the LC-SLM is derived by the energy conservation and constant optical path principle. The effects of the shaping system on the temporal properties, including spectral phase distribution and bandwidth of the femtosecond pulse, are analyzed in detail. Experimental results show that the hollow intensity distribution of the output pulsed beam can be maintained much at more than 1200 mm. The spectral phase of the pulse is changed, and the pulse width is expanded from 199 to 230 fs, which is caused by the spatial-temporal coupling effect. The coupling effect mainly depends on the phase-only LC-SLM itself, not on its loaded phase distribution. The experimental results indicate that the proposed shaping setup can generate a dark hollow femtosecond pulsed beam effectively, because the temporal Gaussian waveform is unchanged. © 2011 Optical Society of America

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.

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.

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.

Experiments of a 100 kV-level pulse generator based on metal-oxide varistor

NASA Astrophysics Data System (ADS)

Cui, Yan-cheng; Wu, Qi-lin; Yang, Han-wu; Gao, Jing-ming; Li, Song; Shi, Cheng-yu

2018-03-01

This paper introduces the development and experiments of a 100 kV-level pulse generator based on a metal-oxide varistor (MOV). MOV has a high energy handling capacity and nonlinear voltage-current (V-I) characteristics, which makes it useful for high voltage pulse shaping. Circuit simulations based on the measured voltage-current characteristics of MOV verified the shaping concept and showed that a circuit containing a two-section pulse forming network (PFN) will result in better defined square pulse than a simple L-C discharging circuit. A reduced-scale experiment was carried out and the result agreed well with simulation prediction. Then a 100 kV-level pulse generator with multiple MOVs in a stack and a two-section pulse forming network (PFN) was experimented. A pulse with a voltage amplitude of 90 kV, rise time of about 50 ns, pulse width of 500 ns, and flat top of about 400 ns was obtained with a water dummy load of 50 Ω. The results reveal that the combination of PFN and MOV is a practical way to generate high voltage pulses with better flat top waveforms, and the load voltage is stable even if the load's impedance varies. Such pulse generator can be applied in many fields such as surface treatment, corona plasma generation, industrial dedusting, and medical disinfection.

Pulse shaping of on-chip microresonator frequency combs: investigation of temporal coherence

NASA Astrophysics Data System (ADS)

Ferdous, F.; Miao, H.; Leaird, D. E.; Srinivasan, K.; Chen, L.; Aksyuk, V.; Weiner, A. M.

2013-03-01

We use pulse shaping to investigate the temporal coherence of frequency combs generated in microresonators pumped by a strong CW laser. We observe that different groups of comb lines have different mutual coherence.

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.

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.

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.

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.

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.

Kinetic study of terahertz generation based on the interaction of two-color ultra-short laser pulses with molecular hydrogen gas

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

Soltani Gishini, M. S.; Ganjovi, A., E-mail: Ganjovi@kgut.ac.ir; Saeed, M.

In this work, using a two dimensional particle in cell-Monte Carlo collision simulation scheme, interaction of two-color ultra-short laser pulses with the molecular hydrogen gas (H{sub 2}) is examined. The operational laser parameters, i.e., its pulse shape, duration, and waist, are changed and, their effects on the density and kinetic energy of generated electrons, THz electric field, intensity, and spectrum are studied. It is seen that the best pulse shape generating the THz signal radiation with the highest intensity is a trapezoidal pulse, and the intensity of generated THz radiation is increased at the higher pulse durations and waists. Formore » all the operational laser parameters, the maximum value of emitted THz signal frequency always remains lower than 5 THz. The intensity of applied laser pulses is taken about 10{sup 14} w/cm{sup 2}, and it is observed that while a small portion of the gaseous media gets ionized, the radiated THz signal is significant.« less

Pulse transmission receiver with higher-order time derivative pulse generator

DOEpatents

Dress, Jr., William B.; Smith, Stephen F.

2003-08-12

Systems and methods for pulse-transmission low-power communication modes are disclosed. A pulse transmission receiver includes: a front-end amplification/processing circuit; a synchronization circuit coupled to the front-end amplification/processing circuit; a clock coupled to the synchronization circuit; a trigger signal generator coupled to the clock; and at least one higher-order time derivative pulse generator coupled to the trigger signal generator. The systems and methods significantly reduce lower-frequency emissions from pulse transmission spread-spectrum communication modes, which reduces potentially harmful interference to existing radio frequency services and users and also simultaneously permit transmission of multiple data bits by utilizing specific pulse shapes.

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

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.

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.

Optically activated switches for the generation of complex electrical waveforms with multigigahertz bandwidth

NASA Astrophysics Data System (ADS)

Skeldon, Mark D.; Okishev, Andrey V.; Letzring, Samuel A.; Donaldson, William R.; Green, Kenton; Seka, Wolf D.; Fuller, Lynn F.

1995-01-01

An electrical pulse-generation system using two optically activated Si photoconductive switches can generate shaped electrical pulses with multigigahertz bandwidth. The Si switches are activated by an optical pulse whose leading edge is steepened by stimulated Brillouin scattering (SBS) in CCl4. With the bandwidth generated by the SBS process, a laser having a 1- to 3-ns pulse width is used to generate electrical pulses with approximately 80-ps rise times (approximately 4-GHz bandwidth). Variable impedance microstrip lines are used to generate complex electrical waveforms that can be transferred to a matched load with minimal loss of bandwidth.

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.

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.

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.

Pulse transmission transmitter including a higher order time derivate filter

DOEpatents

Dress, Jr., William B.; Smith, Stephen F.

2003-09-23

Systems and methods for pulse-transmission low-power communication modes are disclosed. A pulse transmission transmitter includes: a clock; a pseudorandom polynomial generator coupled to the clock, the pseudorandom polynomial generator having a polynomial load input; an exclusive-OR gate coupled to the pseudorandom polynomial generator, the exclusive-OR gate having a serial data input; a programmable delay circuit coupled to both the clock and the exclusive-OR gate; a pulse generator coupled to the programmable delay circuit; and a higher order time derivative filter coupled to the pulse generator. The systems and methods significantly reduce lower-frequency emissions from pulse transmission spread-spectrum communication modes, which reduces potentially harmful interference to existing radio frequency services and users and also simultaneously permit transmission of multiple data bits by utilizing specific pulse shapes.

A simple sub-nanosecond ultraviolet light pulse generator with high repetition rate and peak power.

PubMed

Binh, P H; Trong, V D; Renucci, P; Marie, X

2013-08-01

We present a simple ultraviolet sub-nanosecond pulse generator using commercial ultraviolet light-emitting diodes with peak emission wavelengths of 290 nm, 318 nm, 338 nm, and 405 nm. The generator is based on step recovery diode, short-circuited transmission line, and current-shaping circuit. The narrowest pulses achieved have 630 ps full width at half maximum at repetition rate of 80 MHz. Optical pulse power in the range of several hundreds of microwatts depends on the applied bias voltage. The bias voltage dependences of the output optical pulse width and peak power are analysed and discussed. Compared to commercial UV sub-nanosecond generators, the proposed generator can produce much higher pulse repetition rate and peak power.

Bibliography of Soviet Laser Developments. Number 43, September-October 1979.

DTIC Science & Technology

1980-06-01

Laser Materials, Ultrashort Pulse Generation, X-ray Lasers , Gamma Lasers , Laser Theory, Laser Biological Effects, Laser Communications, Laser ...chemical lasers ; components; nonlinear optics; spectroscopy of laser materials; ultrashort pulse generation; theoretical aspects of advanced lasers ; and...and A.L. Traynin (0). Study on single crystals of shaped germanium, irradiated by a pulsed CO 2 laser .

Versatile Stimulation Back-End With Programmable Exponential Current Pulse Shapes for a Retinal Visual Prosthesis.

PubMed

Maghami, Mohammad Hossein; Sodagar, Amir M; Sawan, Mohamad

2016-11-01

This paper reports on the design, implementation, and test of a stimulation back-end, for an implantable retinal prosthesis. In addition to traditional rectangular pulse shapes, the circuit features biphasic stimulation pulses with both rising and falling exponential shapes, whose time constants are digitally programmable. A class-B second generation current conveyor is used as a wide-swing, high-output-resistance stimulation current driver, delivering stimulation current pulses of up to ±96 μA to the target tissue. Duration of the generated current pulses is programmable within the range of 100 μs to 3 ms. Current-mode digital-to-analog converters (DACs) are used to program the amplitudes of the stimulation pulses. Fabricated using the IBM 130 nm process, the circuit consumes 1.5×1.5 mm 2 of silicon area. According to the measurements, the DACs exhibit DNL and INL of 0.23 LSB and 0.364 LSB, respectively. Experimental results indicate that the stimuli generator meets expected requirements when connected to electrode-tissue impedance of as high as 25 k Ω. Maximum power consumption of the proposed design is 3.4 mW when delivering biphasic rectangular pulses to the target load. A charge pump block is in charge of the upconversion of the standard 1.2-V supply voltage to ±3.3V.

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.

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.

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

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.

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).

Solid-state pulse modulator using Marx generator for a medical linac electron-gun

NASA Astrophysics Data System (ADS)

Lim, Heuijin; Hyeok Jeong, Dong; Lee, Manwoo; Lee, Mujin; Yi, Jungyu; Yang, Kwangmo; Ro, Sung Chae

2016-04-01

A medical linac is used for the cancer treatment and consists of an accelerating column, waveguide components, a magnetron, an electron-gun, a pulse modulator, and an irradiation system. The pulse modulator based on hydrogen thyratron-switched pulse-forming network is commonly used in linac. As the improvement of the high power semiconductors in switching speed, voltage rating, and current rating, an insulated gate bipolar transistor has become the more popular device used for pulsed power systems. We propose a solid-state pulse modulator to generator high voltage by multi-stacked storage-switch stages based on the Marx generator. The advantage of our modulator comes from the use of two semiconductors to control charging and discharging of the storage capacitor at each stage and it allows to generate the pulse with various amplitudes, widths, and shapes. In addition, a gate driver for two semiconductors is designed to reduce the control channels and to protect the circuits. It is developed for providing the pulsed power to a medical linac electron-gun that requires 25 kV and 1 A as the first application. In order to improve the power efficiency and achieve the compactness modulator, a capacitor charging power supply, a Marx pulse generator, and an electron-gun heater isolated transformer are constructed and integrated. This technology is also being developed to extend the high power pulsed system with > 1 MW and also other applications such as a plasma immersed ion implantation and a micro pulse electrostatic precipitator which especially require variable pulse shape and high repetition rate > 1 kHz. The paper describes the design features and the construction of this solid-state pulse modulator. Also shown are the performance results into the linac electron-gun.

Genetic algorithm driven spectral shaping of supercontinuum radiation in a photonic crystal fiber

NASA Astrophysics Data System (ADS)

Michaeli, Linor; Bahabad, Alon

2018-05-01

We employ a genetic algorithm to control a pulse-shaping system pumping a nonlinear photonic crystal with ultrashort pulses. With this system, we are able to modify the spectrum of the generated supercontinuum (SC) radiation to yield narrow Gaussian-like features around pre-selected wavelengths over the whole SC spectrum.

Optical reprogramming of human somatic cells using ultrashort Bessel-shaped near-infrared femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Uchugonova, Aisada; Breunig, Hans Georg; Batista, Ana; König, Karsten

2015-11-01

We report a virus-free optical approach to human cell reprogramming into induced pluripotent stem cells with low-power nanoporation using ultrashort Bessel-shaped laser pulses. Picojoule near-infrared sub-20 fs laser pulses at a high 85 MHz repetition frequency are employed to generate transient nanopores in the membrane of dermal fibroblasts for the introduction of four transcription factors to induce the reprogramming process. In contrast to conventional approaches which utilize retro- or lentiviruses to deliver genes or transcription factors into the host genome, the laser method is virus-free; hence, the risk of virus-induced cancer generation limiting clinical application is avoided.

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

Kelley, R.P., E-mail: rpkelley@ufl.edu; Ray, H.; Jordan, K.A.

An empirical investigation of the scintillation mechanism in a pressurized {sup 4}He gas fast neutron detector was conducted using pulse shape fitting. Scintillation signals from neutron interactions were measured and averaged to produce a single generic neutron pulse shape from both a {sup 252}Cf spontaneous fission source and a (d,d) neutron generator. An expression for light output over time was then developed by treating the decay of helium excited states in the same manner as the decay of radioactive isotopes. This pulse shape expression was fitted to the measured neutron pulse shape using a least-squares optimization algorithm, allowing an empiricalmore » analysis of the mechanism of scintillation inside the {sup 4}He detector. A further understanding of this mechanism in the {sup 4}He detector will advance the use of this system as a neutron spectrometer. For {sup 252}Cf neutrons, the triplet and singlet time constants were found to be 970 ns and 686 ns, respectively. For neutrons from the (d,d) generator, the time constants were found to be 884 ns and 636 ns. Differences were noted in the magnitude of these parameters compared to previously published data, however the general relationships were noted to be the same and checked with expected trends from theory. Of the excited helium states produced from a {sup 252}Cf neutron interaction, 76% were found to be born as triplet states, similar to the result from the neutron generator of 71%. The two sources yielded similar pulse shapes despite having very different neutron energy spectra, validating the robustness of the fits across various neutron energies.« less

Laser induced periodic surface structuring on Si by temporal shaped femtosecond pulses.

PubMed

Almeida, G F B; Martins, R J; Otuka, A J G; Siqueira, J P; Mendonca, C R

2015-10-19

We investigated the effect of temporal shaped femtosecond pulses on silicon laser micromachining. By using sinusoidal spectral phases, pulse trains composed of sub-pulses with distinct temporal separations were generated and applied to the silicon surface to produce Laser Induced Periodic Surface Structures (LIPSS). The LIPSS obtained with different sub-pulse separation were analyzed by comparing the intensity of the two-dimensional fast Fourier Transform (2D-FFT) of the AFM images of the ripples (LIPSS). It was observed that LIPSS amplitude is more emphasized for the pulse train with sub-pulses separation of 128 fs, even when compared with the Fourier transform limited pulse. By estimating the carrier density achieved at the end of each pulse train, we have been able to interpret our results with the Sipe-Drude model, that predicts that LIPSS efficacy is higher for a specific induced carrier density. Hence, our results indicate that temporal shaping of the excitation pulse, performed by spectral phase modulation, can be explored in fs-laser microstructuring.

Ultra-flat SPM-broadened spectra in a highly nonlinear fiber using parabolic pulses formed in a fiber Bragg grating

NASA Astrophysics Data System (ADS)

Parmigiani, Francesca; Finot, Christophe; Mukasa, Kazunori; Ibsen, Morten; Roelens, Michael A.; Petropoulos, Periklis; Richardson, David J.

2006-08-01

We propose a new method for generating flat self-phase modulation (SPM)-broadened spectra based on seeding a highly nonlinear fiber (HNLF) with chirp-free parabolic pulses generated using linear pulse shaping in a superstructured fiber Bragg grating (SSFBG). We show that the use of grating reshaped parabolic pulses allows substantially better performance in terms of the extent of SPM-based spectral broadening and flatness relative to conventional hyperbolic secant (sech) pulses. We demonstrate both numerically and experimentally the generation of SPM-broadened pulses centred at 1542 nm with 92% of the pulse energy remaining within the 29 nm 3 dB spectral bandwidth. Applications in spectra slicing and pulse compression are demonstrated.

DAC-board based X-band EPR spectrometer with arbitrary waveform control

NASA Astrophysics Data System (ADS)

Kaufmann, Thomas; Keller, Timothy J.; Franck, John M.; Barnes, Ryan P.; Glaser, Steffen J.; Martinis, John M.; Han, Songi

2013-10-01

We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8-10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles "seen" by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ⩽250 ps resolution. The implications and potential applications of these capabilities will be discussed.

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

Generation of high-intensity sub-30 as pulses by inhomogeneous polarization gating technology in bowtie-shaped nanostructure

NASA Astrophysics Data System (ADS)

Feng, Liqiang; Feng, A. Yuanzi

2018-04-01

The generation of high-order harmonics and single attosecond pulses (SAPs) from He atom driven by the inhomogeneous polarization gating technology in a bowtie-shaped nanostructure is theoretically investigated. The results show that by the proper addition of bowtie-shaped nanostructure along the driven laser polarization direction, the harmonic emission becomes sensitive to the position of the laser field, and the harmonics emitted at the maximum orders that generate SAPs occur only at one side of the region inside the nanostructure. As a result, not only the harmonic cutoff can be extended, but also the modulations of the harmonics can be decreased, showing a carrier envelope phase independent harmonic cutoff with a bandwidth of 310 eV. Further, with the proper introduction of an ultraviolet pulse, the harmonic yield can be enhanced by 2 orders of magnitude. Finally, by the Fourier transformation of the selected harmonics, some SAPs with a full width at half maximum of sub-30 as can be obtained.

A recoil-proton spectrometer based on a p-i-n diode implementing pulse-shape discrimination.

PubMed

Agosteo, S; D'Angelo, G; Fazzi, A; Foglio Para, A; Pola, A; Ventura, L; Zotto, P

2004-01-01

A recoil-proton spectrometer was created by coupling a p-i-n diode with a polyethylene converter. The maximum detectable energy, imposed by the thickness of the totally depleted layer, is approximately 6 MeV. The minimum detectable energy is limited by the contribution of secondary electrons generated by photons in the detector assembly. This limit is approximately 1.5 MeV at full-depletion voltage and was decreased using pulse-shape discrimination. The diode was set up in the 'reverse-injection' configuration (i.e. with the N+ layer adjacent to the converter). This configuration provides longer collection times for the electron-hole pairs generated by the recoil-protons. The pulse-shape discrimination was based on the zero-crossing time of bipolar signals from a (CR)2-(RC)2 filter. The detector was characterised using monoenergetic neutrons generated in the Van De Graaff CN accelerator at the INFN-Laboratori Nazionali di Legnaro. The energy limit for discrimination proved to be approximately 900 keV.

Femtosecond versus picosecond laser pulses for film-free laser bioprinting.

PubMed

Petit, Stephane; Kérourédan, Olivia; Devillard, Raphael; Cormier, Eric

2017-11-01

We investigate the properties of microjets in the context of film-free laser induced forward transfer in the femtosecond and picosecond regimes. The influence of the pulse duration (ranging from 0.4 to 12 ps) and the energy (ranging from 6 to 12 μJ) is systematically studied on the height, diameter, speed, volume, and shape of the jets. The 400 fs pulses generate thin and stable jets compatible with bioprinting, while 14 ps pulses generate more unstable jets. A pulse duration around 8 ps seems, therefore, to be an interesting trade-off to cover many bio-applications of microjets generated by lasers.

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.

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.

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

Cladding-pumped passively mode-locked fiber laser generating femtosecond and picosecond pulses

NASA Astrophysics Data System (ADS)

Fermann, M. E.; Harter, D.; Minelly, J. D.; Vienne, G. G.

1996-07-01

Passively mode-locked fiber lasers cladding pumped by broad-area diode-laser arrays are described. With a dispersion-compenstated erbium-ytterbium fiber oscillator, 200-fs pulses with pulse energies up to 100 pJ are generated at a wavelength of 1560 nm. In a highly dispersive cavity, pulse widths of 3 ps with pulse energies up to 1 nJ are obtained. A saturable absorber is used for pulse startup, whereas nonlinear polarization evolution is exploited for steady-state pulse shaping. An environmentally stable design is ensured by use of a compensation scheme for linear polarization drifts in the cavity.

Cladding-pumped passively mode-locked fiber laser generating femtosecond and picosecond pulses.

PubMed

Fermann, M E; Harter, D; Minelly, J D; Vienne, G G

1996-07-01

Passively mode-locked fiber lasers cladding pumped by broad-area diode-laser arrays are described. With a dispersion-compenstated erbium-ytterbium fiber oscillator, 200-fs pulses with pulse energies up to 100 pJ are generated at a wavelength of 1560 nm. In a highly dispersive cavity, pulse widths of 3 ps with pulse energies up to 1 nJ are obtained. A saturable absorber is used for pulse startup, whereas nonlinear polarization evolution is exploited for steady-state pulse shaping. An environmentally stable design is ensured by use of a compensation scheme for linear polarization drifts in the cavity.

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.

Narrowband supercontinuum control using phase shaping

NASA Astrophysics Data System (ADS)

Austin, Dane R.; Bolger, Jeremy A.; de Sterke, C. Martijn; Eggleton, Benjamin J.; Brown, Thomas G.

2006-12-01

We study theoretically, numerically and experimentally the effect of self-phase modulation of ultrashort pulses with spectrally narrow phase features. We show that spectral enhancement and depletion is caused by changing the relative phase between the initial field and the nonlinearly generated components. Our theoretical results explain observations of supercontinuum enhancement by fiber Bragg gratings, and predict similar enhancements for spectrally shaped pulses in uniform fiber. As proof of principle, we demonstrate this effect in the laboratory using a femtosecond pulse shaper.

Generating high-power short terahertz electromagnetic pulses with a multifoil radiator.

PubMed

Vinokurov, Nikolay A; Jeong, Young Uk

2013-02-08

We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the z axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the z axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the z axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device.

High-symmetry organic scintillator systems

DOEpatents

Feng, Patrick L.

2018-02-06

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based on the pulse shapes of the output signals.

High-symmetry organic scintillator systems

DOEpatents

Feng, Patrick L.

2017-07-18

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based on the pulse shapes of the output signals.

High-symmetry organic scintillator systems

DOEpatents

Feng, Patrick L.

2017-06-14

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based on the pulse shapes of the output signals.

High-symmetry organic scintillator systems

DOEpatents

Feng, Patrick L.

2017-09-05

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based on the pulse shapes of the output signals.

High-symmetry organic scintillator systems

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

Feng, Patrick L.

An ionizing radiation detector or scintillator system includes a scintillating material comprising an organic crystalline compound selected to generate photons in response to the passage of ionizing radiation. The organic compound has a crystalline symmetry of higher order than monoclinic, for example an orthorhombic, trigonal, tetragonal, hexagonal, or cubic symmetry. A photodetector is optically coupled to the scintillating material, and configured to generate electronic signals having pulse shapes based on the photons generated in the scintillating material. A discriminator is coupled to the photon detector, and configured to discriminate between neutrons and gamma rays in the ionizing radiation based onmore » the pulse shapes of the output signals.« less

Synthesizing genetic sequential logic circuit with clock pulse generator.

PubMed

Chuang, Chia-Hua; Lin, Chun-Liang

2014-05-28

Rhythmic clock widely occurs in biological systems which controls several aspects of cell physiology. For the different cell types, it is supplied with various rhythmic frequencies. How to synthesize a specific clock signal is a preliminary but a necessary step to further development of a biological computer in the future. This paper presents a genetic sequential logic circuit with a clock pulse generator based on a synthesized genetic oscillator, which generates a consecutive clock signal whose frequency is an inverse integer multiple to that of the genetic oscillator. An analogous electronic waveform-shaping circuit is constructed by a series of genetic buffers to shape logic high/low levels of an oscillation input in a basic sinusoidal cycle and generate a pulse-width-modulated (PWM) output with various duty cycles. By controlling the threshold level of the genetic buffer, a genetic clock pulse signal with its frequency consistent to the genetic oscillator is synthesized. A synchronous genetic counter circuit based on the topology of the digital sequential logic circuit is triggered by the clock pulse to synthesize the clock signal with an inverse multiple frequency to the genetic oscillator. The function acts like a frequency divider in electronic circuits which plays a key role in the sequential logic circuit with specific operational frequency. A cascaded genetic logic circuit generating clock pulse signals is proposed. Based on analogous implement of digital sequential logic circuits, genetic sequential logic circuits can be constructed by the proposed approach to generate various clock signals from an oscillation signal.

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.

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.

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

Random pulse generator

NASA Technical Reports Server (NTRS)

Lindsey, R. S., Jr. (Inventor)

1975-01-01

An exemplary embodiment of the present invention provides a source of random width and random spaced rectangular voltage pulses whose mean or average frequency of operation is controllable within prescribed limits of about 10 hertz to 1 megahertz. A pair of thin-film metal resistors are used to provide a differential white noise voltage pulse source. Pulse shaping and amplification circuitry provide relatively short duration pulses of constant amplitude which are applied to anti-bounce logic circuitry to prevent ringing effects. The pulse outputs from the anti-bounce circuits are then used to control two one-shot multivibrators whose output comprises the random length and random spaced rectangular pulses. Means are provided for monitoring, calibrating and evaluating the relative randomness of the generator.

Plasmon-shaped polarization gating for high-order-harmonic generation

NASA Astrophysics Data System (ADS)

Wang, Feng; He, Lixin; Chen, Jiawei; Wang, Baoning; Zhu, Xiaosong; Lan, Pengfei; Lu, Peixiang

2017-12-01

We present a plasmon-shaped polarization gating for high-order-harmonic generation by using a linearly polarized laser field to illuminate two orthogonal bow-tie nanostructures. The results show that when these two bow-tie nanostructures have nonidentical geometrical sizes, the transverse and longitudinal components of the incident laser field will experience different phase responses, thus leading to a time-dependent ellipticity of laser field. For the polarizing angle of incident laser field in the range from 45∘ to 60∘, the dominant harmonic emission is gated within the few optical cycles where the laser ellipticity is below 0.3. Then sub-50-as isolated attosecond pulses (IAPs) can be generated. Such a plasmon-shaped polarization gating is robust for IAP generation against the variations of the carrier-envelope phases of the laser pulse. Moreover, by changing the geometrical size of one of the bow-tie nanostructures, the electron dynamics can be effectively controlled and the more efficient supercontinuum as well as IAP can be generated.

Eye-Safe KGd(WO4)2:Nd Laser: Nano- and Subnanosecond Pulse Generation in Self-Frequency Raman Conversion Mode with Active Q-Switching

NASA Astrophysics Data System (ADS)

Dashkevich, V. I.; Orlovich, V. A.

2017-03-01

The shape of the multimode Stokes pulse generated by an eye-safe KGd(WO4)2:Nd laser with self-frequency Raman conversion and active Q-switching was shown to depend on the inhomogeneity of the active-medium pump. The laser generated a short and undistorted Stokes pulse of length 2.5 ns that increased with increasing laser cavity length for a moderately inhomogeneous pump characterized by a higher population inversion in the center of the active element. The energy of the Stokes pulse ( 11.5 mJ) varied little as the output-mirror reflectivity varied in the range 5-45%. The Raman pulse became distorted if the inhomogeneity of the pump was increased considerably. The degree of pump inhomogeneity was negligible with fundamental TEM00 mode selection. The laser generated subnanosecond Stokes pulses with peak power in the MW range.

Synthesizing genetic sequential logic circuit with clock pulse generator

PubMed Central

2014-01-01

Background Rhythmic clock widely occurs in biological systems which controls several aspects of cell physiology. For the different cell types, it is supplied with various rhythmic frequencies. How to synthesize a specific clock signal is a preliminary but a necessary step to further development of a biological computer in the future. Results This paper presents a genetic sequential logic circuit with a clock pulse generator based on a synthesized genetic oscillator, which generates a consecutive clock signal whose frequency is an inverse integer multiple to that of the genetic oscillator. An analogous electronic waveform-shaping circuit is constructed by a series of genetic buffers to shape logic high/low levels of an oscillation input in a basic sinusoidal cycle and generate a pulse-width-modulated (PWM) output with various duty cycles. By controlling the threshold level of the genetic buffer, a genetic clock pulse signal with its frequency consistent to the genetic oscillator is synthesized. A synchronous genetic counter circuit based on the topology of the digital sequential logic circuit is triggered by the clock pulse to synthesize the clock signal with an inverse multiple frequency to the genetic oscillator. The function acts like a frequency divider in electronic circuits which plays a key role in the sequential logic circuit with specific operational frequency. Conclusions A cascaded genetic logic circuit generating clock pulse signals is proposed. Based on analogous implement of digital sequential logic circuits, genetic sequential logic circuits can be constructed by the proposed approach to generate various clock signals from an oscillation signal. PMID:24884665

High-flux soft x-ray harmonic generation from ionization-shaped few-cycle laser pulses

PubMed Central

Brahms, Christian; Gregory, Andrew; Tisch, John W. G.; Marangos, Jon P.

2018-01-01

Laser-driven high-harmonic generation provides the only demonstrated route to generating stable, tabletop attosecond x-ray pulses but has low flux compared to other x-ray technologies. We show that high-harmonic generation can produce higher photon energies and flux by using higher laser intensities than are typical, strongly ionizing the medium and creating plasma that reshapes the driving laser field. We obtain high harmonics capable of supporting attosecond pulses up to photon energies of 600 eV and a photon flux inside the water window (284 to 540 eV) 10 times higher than previous attosecond sources. We demonstrate that operating in this regime is key for attosecond pulse generation in the x-ray range and will become increasingly important as harmonic generation moves to fields that drive even longer wavelengths. PMID:29756033

High-order UWB pulses scheme to generate multilevel modulation formats based on incoherent optical sources.

PubMed

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

2013-11-18

We present a high-order UWB pulses generator based on a microwave photonic filter which provides a set of positive and negative samples by using the slicing of an incoherent optical source and the phase inversion in a Mach-Zehnder modulator. The simple scalability and high reconfigurability of the system permit a better accomplishment of the FCC requirements. Moreover, the proposed scheme permits an easy adaptation to pulse amplitude modulation, bi phase modulation, pulse shape modulation and pulse position modulation. The flexibility of the scheme for being adaptable to multilevel modulation formats permits to increase the transmission bit rate by using hybrid modulation formats.

Noise characterization of a pulse train generated by actively mode-locked lasers

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

Eliyahu, D.; Salvatore, R.A.; Yariv, A.

1996-07-01

We analyze the entire power spectrum of pulse trains generated by a continuously operating actively mode-locked laser in the presence of noise. We consider the effect of amplitude, pulse-shape, and timing-jitter fluctuations that are characterized by stationary processes. Effects of correlations between different parameters of these fluctuations are studied also. The nonstationary timing-jitter fluctuations of passively mode-locked lasers and their influence on the power spectrum is discussed as well. {copyright} {ital 1996 Optical Society of America.}

Pulse transmission transceiver architecture for low power communications

DOEpatents

Dress, Jr., William B.; Smith, Stephen F.

2003-08-05

Systems and methods for pulse-transmission low-power communication modes are disclosed. A method of pulse transmission communications includes: generating a modulated pulse signal waveform; transforming said modulated pulse signal waveform into at least one higher-order derivative waveform; and transmitting said at least one higher-order derivative waveform as an emitted pulse. The systems and methods significantly reduce lower-frequency emissions from pulse transmission spread-spectrum communication modes, which reduces potentially harmful interference to existing radio frequency services and users and also simultaneously permit transmission of multiple data bits by utilizing specific pulse shapes.

Laser Shock Wave-Assisted Patterning on NiTi Shape Memory Alloy Surfaces

NASA Astrophysics Data System (ADS)

Ilhom, Saidjafarzoda; Seyitliyev, Dovletgeldi; Kholikov, Khomidkohodza; Thomas, Zachary; Er, Ali O.; Li, Peizhen; Karaca, Haluk E.; San, Omer

2018-01-01

Shape memory alloys (SMAs) are a unique class of smart materials and they were employed in various applications in engineering, biomedical, and aerospace technologies. Here, we report an advanced, efficient, and low-cost direct imprinting method with low environmental impact to create thermally controllable surface patterns. Patterned microindents were generated on Ni50Ti50 (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30% was observed. Recovery ratio decreased and stabilized when the number of pulses and thus the well depth were further increased. A numerical simulation of pressure evolution in shape memory alloys showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were found in our simulation.

Laser Shock Wave-Assisted Patterning on NiTi Shape Memory Alloy Surfaces

NASA Astrophysics Data System (ADS)

Ilhom, Saidjafarzoda; Seyitliyev, Dovletgeldi; Kholikov, Khomidkohodza; Thomas, Zachary; Er, Ali O.; Li, Peizhen; Karaca, Haluk E.; San, Omer

2018-03-01

Shape memory alloys (SMAs) are a unique class of smart materials and they were employed in various applications in engineering, biomedical, and aerospace technologies. Here, we report an advanced, efficient, and low-cost direct imprinting method with low environmental impact to create thermally controllable surface patterns. Patterned microindents were generated on Ni50Ti50 (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30% was observed. Recovery ratio decreased and stabilized when the number of pulses and thus the well depth were further increased. A numerical simulation of pressure evolution in shape memory alloys showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were found in our simulation.

Peculiarity of convergence of shock wave generated by underwater electrical explosion of ring-shaped wire

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

Shafer, D.; Toker, G. R.; Gurovich, V. Tz.

2013-05-15

Nanosecond timescale underwater electrical wire explosions of ring-shaped Cu wires were investigated using a pulsed generator with a current amplitude up to 50 kA. It was shown that this type of wire explosion results in the generation of a toroidal shock wave (SW). Time- and space-resolved optical diagnostics were used to determine azimuthal uniformity of the shock wave front and its velocity. It was found that the shock wave preserves its circular front shape in the range of radii 50μm

Coherent pump pulses in Double Electron Electron Resonance Spectroscopy

PubMed Central

Tait, Claudia E.; Stoll, Stefan

2016-01-01

The recent introduction of shaped pulses to Double Electron Electron Resonance (DEER) spectroscopy has led to significant enhancements in sensitivity through increased excitation bandwidths and improved control over spin dynamics. The application of DEER has so far relied on the presence of an incoherent pump channel to average out most undesired coherent effects of the pump pulse(s) on the observer spins. However, in fully coherent EPR spectrometers that are increasingly used to generate shaped pulses, the presence of coherent pump pulses means that these effects need to be explicitly considered. In this paper, we examine the effects of coherent rectangular and sech/tanh pump pulses in DEER experiments with up to three pump pulses. We show that, even in the absence of significant overlap of the observer and pump pulse excitation bandwidths, coherence transfer pathways involving both types of pulses generate spin echoes of considerable intensity. These echoes introduce artefacts, which, if not identified and removed, can easily lead to misinterpretation. We demonstrate that the observed echoes can be quantitatively modelled using a simple spin quantum dynamics approach that includes instrumental transfer functions. Based on an analysis of the echo crossing artefacts, we propose efficient phase cycling schemes for their suppression. This enables the use of advanced DEER experiments, characterized by high sensitivity and increased accuracy for long-distance measurements, on novel fully coherent EPR spectrometers. PMID:27339858

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.

Analysis of radial and longitudinal field of plasma wakefield generated by a Laguerre-Gauss laser pulse

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

Firouzjaei, Ali Shekari; Shokri, Babak

In the present paper, we study the wakes known as the donut wake which is generated by Laguerre-Gauss (LG) laser pulses. Effects of the special spatial profile of a LG pulse on the radial and longitudinal wakefields are presented via an analytical model in a weakly non-linear regime in two dimensions. Different aspects of the donut-shaped wakefields have been analyzed and compared with Gaussian-driven wakes. There is also some discussion about the accelerating-focusing phase of the donut wake. Variations of longitudinal and radial wakes with laser amplitude, pulse length, and pulse spot size have been presented and discussed. Finally, wemore » present the optimum pulse duration for such wakes.« less

Transmission and full-band coherent detection of polarization-multiplexed all-optical Nyquist signals generated by Sinc-shaped Nyquist pulses

PubMed Central

Zhang, Junwen; Yu, Jianjun; Chi, Nan

2015-01-01

All optical method is considered as a promising technique for high symbol rate Nyquist signal generation, which has attracted a lot of research interests for high spectral-efficiency and high-capacity optical communication system. In this paper, we extend our previous work and report the fully experimental demonstration of polarization-division multiplexed (PDM) all-optical Nyquist signal generation based on Sinc-shaped Nyquist pulse with advanced modulation formats, fiber-transmission and single-receiver full-band coherent detection. Using this scheme, we have successfully demonstrated the generation, fiber transmission and single-receiver full-band coherent detection of all-optical Nyquist PDM-QPSK and PDM-16QAM signals up to 125-GBaud. 1-Tb/s single-carrier PDM-16QAM signal generation and full-band coherent detection is realized, which shows the advantage and feasibility of the single-carrier all-optical Nyquist signals. PMID:26323238

Implementation of a SVWP-based laser beam shaping technique for generation of 100-mJ-level picosecond pulses.

PubMed

Adamonis, J; Aleknavičius, A; Michailovas, K; Balickas, S; Petrauskienė, V; Gertus, T; Michailovas, A

2016-10-01

We present implementation of the energy-efficient and flexible laser beam shaping technique in a high-power and high-energy laser amplifier system. The beam shaping is based on a spatially variable wave plate (SVWP) fabricated by femtosecond laser nanostructuring of glass. We reshaped the initially Gaussian beam into a super-Gaussian (SG) of the 12th order with efficiency of about 50%. The 12th order of the SG beam provided the best compromise between large fill factor, low diffraction on the edges of the active media, and moderate intensity distribution modification during free-space propagation. We obtained 150 mJ pulses of 532 nm radiation. High-energy, pulse duration of 85 ps and the nearly flat-top spatial profile of the beam make it ideal for pumping optical parametric chirped pulse amplification systems.

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.

Optical generation of millimeter-wave pulses using a fiber Bragg grating in a fiber-optics system.

PubMed

Ye, Qing; Qu, Ronghui; Fang, Zujie

2007-04-10

A scheme is proposed to transform an optical pulse into a millimeter-wave frequency modulation pulse by using a weak fiber Bragg grating (FBG) in a fiber-optics system. The Fourier transformation method is used to obtain the required spectrum response function of the FBG for the Gaussian pulse, soliton pulse, and Lorenz shape pulse. On the condition of the first-order Born approximation of the weak fiber grating, the relation of the refractive index distribution and the spectrum response function of the FBG satisfies the Fourier transformation, and the corresponding refractive index distribution forms are obtained for single-frequency modulation and linear-frequency modulation millimeter-wave pulse generation. The performances of the designed fiber gratings are also studied by a numerical simulation method for a supershort pulse transmission.

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.

Alpha/beta pulse shape discrimination in plastic scintillation using commercial scintillation detectors.

PubMed

Bagán, H; Tarancón, A; Rauret, G; García, J F

2010-06-18

Activity determination in different types of samples is a current need in many different fields. Simultaneously analysing alpha and beta emitters is now a routine option when using liquid scintillation (LS) and pulse shape discrimination. However, LS has an important drawback, the generation of mixed waste. Recently, several studies have shown the capability of plastic scintillation (PS) as an alternative to LS, but no research has been carried out to determine its capability for alpha/beta discrimination. The objective of this study was to evaluate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape analysis (PSA). The results obtained show that PS pulses had lower energy than LS pulses. As a consequence, a lower detection efficiency, a shift to lower energies and a better discrimination of beta and a worst discrimination of alpha disintegrations was observed for PS. Colour quenching also produced a decrease in the energy of the particles, as well as the effects described above. It is clear that in PS, the discrimination capability was correlated with the energy of the particles detected. Taking into account the discrimination capabilities of PS, a protocol for the measurement and the calculation of alpha and beta activities in mixtures using PS and commercial scintillation detectors has been proposed. The new protocol was applied to the quantification of spiked river water samples containing a pair of radionuclides ((3)H-(241)Am or (90)Sr/(90)Y-(241)Am) in different activity proportions. The relative errors in all determinations were lower than 7%. These results demonstrate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape and to quantify mixtures without generating mixed waste. 2010 Elsevier B.V. All rights reserved.

Note: A rectangular pulse generator for 50 kV voltage, 0.8 ns rise time, and 10 ns pulse width based on polymer-film switch.

PubMed

Wu, Hanyu; Zhang, Xinjun; Sun, Tieping; Zeng, Zhengzhong; Cong, Peitian; Zhang, Shaoguo

2015-10-01

In this article, we describe a rectangular pulse generator, consisting of a polymer-film switch, a tri-plate transmission line, and parallel post-shaped ceramic resistor load, for 50-kV voltage, 0.8-ns rise time, and 10-ns width. The switch and resistors are arranged in atmospheric air and the transmission line can work in atmospheric air or in transformer oil to change the pulse width from 6.7 ns to 10 ns. The fast switching and low-inductance characteristics of the polymer-film switch ensure the fast rising wavefront of <1 ns. This generator can be applied in the calibration of nanosecond voltage dividers and used for electromagnetic pulse tests as a fast-rising current injection source.

PULSE SYNTHESIZING GENERATOR

DOEpatents

Kerns, Q.A.

1963-08-01

>An electronlc circuit for synthesizing electrical current pulses having very fast rise times includes several sinewave generators tuned to progressively higher harmonic frequencies with signal amplitudes and phases selectable according to the Fourier series of the waveform that is to be synthesized. Phase control is provided by periodically triggering the generators at precisely controlled times. The outputs of the generators are combined in a coaxial transmission line. Any frequency-dependent delays that occur in the transmission line can be readily compensated for so that the desired signal wave shape is obtained at the output of the line. (AEC)

Record fifth-harmonic-generation efficiency producing 211 nm, joule-level pulses using cesium lithium borate

DOE PAGES

Begishev, I. A.; Bromage, J.; Yang, S. T.; ...

2018-05-16

The fifth harmonic of a pulsed Nd:YLF laser has been realized in a cascade of nonlinear crystals with a record efficiency of 30%. Cesium lithium borate is used in a Type-I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes optimize efficiency. Furthermore, energies of the fifth harmonic up to 335 mJ in 2.4 ns pulses were demonstrated.

Record fifth-harmonic-generation efficiency producing 211  nm, joule-level pulses using cesium lithium borate

DOE PAGES

Begishev, I. A.; Bromage, J.; Yang, S. T.; ...

2018-01-01

The fifth harmonic of a pulsed Nd:YLF laser has been realized in a cascade of nonlinear crystals with a record efficiency of 30%. Cesium lithium borate is used in a Type-I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes optimize efficiency. Energies of the fifth harmonic up to 335 mJ in 2.4 ns pulses were demonstrated.

Record fifth-harmonic-generation efficiency producing 211 nm, joule-level pulses using cesium lithium borate

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

Begishev, I. A.; Bromage, J.; Yang, S. T.

The fifth harmonic of a pulsed Nd:YLF laser has been realized in a cascade of nonlinear crystals with a record efficiency of 30%. Cesium lithium borate is used in a Type-I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes optimize efficiency. Furthermore, energies of the fifth harmonic up to 335 mJ in 2.4 ns pulses were demonstrated.

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

Photonic generation of FCC-compliant UWB pulses based on modified Gaussian quadruplet and incoherent wavelength-to-time conversion

NASA Astrophysics Data System (ADS)

Mu, Hongqian; Wang, Muguang; Tang, Yu; Zhang, Jing; Jian, Shuisheng

2018-03-01

A novel scheme for the generation of FCC-compliant UWB pulse is proposed based on modified Gaussian quadruplet and incoherent wavelength-to-time conversion. The modified Gaussian quadruplet is synthesized based on linear sum of a broad Gaussian pulse and two narrow Gaussian pulses with the same pulse-width and amplitude peak. Within specific parameter range, FCC-compliant UWB with spectral power efficiency of higher than 39.9% can be achieved. In order to realize the designed waveform, a UWB generator based on spectral shaping and incoherent wavelength-to-time mapping is proposed. The spectral shaper is composed of a Gaussian filter and a programmable filter. Single-mode fiber functions as both dispersion device and transmission medium. Balanced photodetection is employed to combine linearly the broad Gaussian pulse and two narrow Gaussian pulses, and at same time to suppress pulse pedestals that result in low-frequency components. The proposed UWB generator can be reconfigured for UWB doublet by operating the programmable filter as a single-band Gaussian filter. The feasibility of proposed UWB generator is demonstrated experimentally. Measured UWB pulses match well with simulation results. FCC-compliant quadruplet with 10-dB bandwidth of 6.88-GHz, fractional bandwidth of 106.8% and power efficiency of 51% is achieved.

Reflection and diffraction corrections for nonlinear materials characterization by quasi-static pulse measurement

NASA Astrophysics Data System (ADS)

Nagy, Peter B.; Qu, Jianmin; Jacobs, Laurence J.

2014-02-01

A harmonic acoustic tone burst propagating through an elastic solid with quadratic nonlinearity produces not only a parallel burst of second harmonic but also an often neglected quasi-static pulse associated with the acoustic radiation-induced eigenstrain. Although initial analytical and experimental studies by Yost and Cantrell suggested that the pulse might have a right-angled triangular shape with the peak displacement at the leading edge being proportional to the length of the tone burst, more recent theoretical, analytical, numerical, and experimental studies proved that the pulse has a flat-top shape and the peak displacement is proportional to the propagation length. In this paper, analytical and numerical simulation results are presented to illustrate two types of finite-size effects. First, the finite axial dimension of the specimen cannot be simply accounted for by a linear reflection coefficient that neglects the nonlinear interaction between the combined incident and reflected fields. Second, the quasistatic pulse generated by a transducer of finite aperture suffers more severe divergence than both the fundamental and second harmonic pulses generated by the same transducer. These finite-size effects can make the top of the quasi-static pulse sloped rather than flat and therefore must be taken into consideration in the interpretation of experimental data.

Reflection and diffraction corrections for nonlinear materials characterization by quasi-static pulse measurement

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

Nagy, Peter B.; Qu, Jianmin; Jacobs, Laurence J.

A harmonic acoustic tone burst propagating through an elastic solid with quadratic nonlinearity produces not only a parallel burst of second harmonic but also an often neglected quasi-static pulse associated with the acoustic radiation-induced eigenstrain. Although initial analytical and experimental studies by Yost and Cantrell suggested that the pulse might have a right-angled triangular shape with the peak displacement at the leading edge being proportional to the length of the tone burst, more recent theoretical, analytical, numerical, and experimental studies proved that the pulse has a flat-top shape and the peak displacement is proportional to the propagation length. In thismore » paper, analytical and numerical simulation results are presented to illustrate two types of finite-size effects. First, the finite axial dimension of the specimen cannot be simply accounted for by a linear reflection coefficient that neglects the nonlinear interaction between the combined incident and reflected fields. Second, the quasistatic pulse generated by a transducer of finite aperture suffers more severe divergence than both the fundamental and second harmonic pulses generated by the same transducer. These finite-size effects can make the top of the quasi-static pulse sloped rather than flat and therefore must be taken into consideration in the interpretation of experimental data.« less

Control of periodic surface structures on silicon by combined temporal and polarization shaping of femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Fraggelakis, F.; Stratakis, E.; Loukakos, P. A.

2018-06-01

We demonstrate the capability to exercise advanced control on the laser-induced periodic surface structures (LIPSS) on silicon by combining the effect of temporal shaping, via tuning the interpulse temporal delay between double femtosecond laser pulses, along with the independent manipulation of the polarization state of each of the individual pulses. For this, cross-polarized (CP) as well as counter-rotating (CR) double circularly polarized pulses have been utilized. The pulse duration was 40 fs and the central wavelength of 790 nm. The linearly polarized double pulses are generated by a modified Michelson interferometer allowing the temporal delay between the pulses to vary from Δτ = -80 ps to Δτ = +80 ps with an accuracy of 0.2 fs. We show the significance of fluence balance between the two pulse components and its interplay with the interpulse delay and with the order of arrival of the individually polarized pulse components of the double pulse sequence on the final surface morphology. For the case of CR pulses we found that when the pulses are temporally well separated the surface morphology attains no axial symmetry. But strikingly, when the two CP pulses temporally overlap, we demonstrate, for the first time in our knowledge, the detrimental effect that the phase delay has on the ripple orientation. Our results provide new insight showing that temporal pulse shaping in combination with polarization control gives a powerful tool for drastically controlling the surface nanostructure morphology.

Optical pulse response of a fibre ring resonator

NASA Astrophysics Data System (ADS)

Pandian, G. S.; Seraji, Faramarz E.

1991-06-01

This article presents the optical pulse response analysis of a fiber ring resonator. It is shown that several interesting functions, namely optical pulse generation, and equalization of fiber dispersion can be realized by using the resonator. The theory is presented in an easy to understand manner, by first considering the steady-state response. The results of the transient pulse response are explained in relation to the steady state results. The results related to optical pulse shaping will be of interest to the future when coherent optical pulse and switching circuits will become available.

Pulse evolution and mode selection characteristics in a TEA-CO2 laser perturbed by injection of external radiation

NASA Technical Reports Server (NTRS)

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

1983-01-01

A grating-tunable TEA-CO2 laser with an unstable resonator cavity, modified to allow injection of CW CO2 laser radiation at the resonant transition line by means of an intracavity NaCl window, has been used to study the coupling requirements for generation of single frequency pulses. The width and shape of the mode selection region, and the dependence of the gain-switched spike buildup time and the pulse shapes on the intensity and detuning frequency of the injected radiation are reported. Comparisons of the experimental results with previously reported mode selection behavior are discussed.

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

Lintereur, Azaree T.; Ely, James H.; Stave, Jean A.

The goal of this was research effort was to test the ability of two poly vinyltoluene research samples to produce recordable, distinguishable signals in response to gamma rays and neutrons. Pulse shape discrimination was performed to identify if the signal was generated by a gamma ray or a neutron. A standard figure of merit for pulse shape discrimination was used to quantify the gamma-neutron pulse separation. Measurements were made with gamma and neutron sources with and without shielding. The best figure of merit obtained was 1.77; this figure of merit was achieved with the first sample in response to anmore » un-moderated 252Cf source shielded with 5.08 cm of lead.« less

Experimental demonstration of wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) in LiNbO3 waveguides

NASA Astrophysics Data System (ADS)

Wang, Jian; Sun, Junqiang; Lou, Chuanhong; Sun, Qizhen

2005-09-01

All-optical wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) is proposed and experimentally demonstrated in periodically poled LiNbO3 (PPLN) waveguides. The signal pulse with 40-GHz repetition rate and 1.57- ps pulse width is adopted. The converted idler wavelength can be tuned from 1527.4 to 1540.5nm as the signal wavelength is varied from 1561.9 to 1548.4nm. No obvious changes of the pulse shape and width, also no chirp are observed in the converted idler pulse. The results imply that single-to-multiple channel wavelength conversions can be achieved by appropriately tuning the two pump wavelengths.

Experimental demonstration of wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) in LiNbO3 waveguides.

PubMed

Wang, Jian; Sun, Junqiang; Lou, Chuanhong; Sun, Qizhen

2005-09-19

All-optical wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) is proposed and experimentally demonstrated in periodically poled LiNbO3 (PPLN) waveguides. The signal pulse with 40-GHz repetition rate and 1.57- ps pulse width is adopted. The converted idler wavelength can be tuned from 1527.4 to 1540.5nm as the signal wavelength is varied from 1561.9 to 1548.4nm. No obvious changes of the pulse shape and width, also no chirp are observed in the converted idler pulse. The results imply that single-to-multiple channel wavelength conversions can be achieved by appropriately tuning the two pump wavelengths.

Broad-spectrum neodymium-doped laser glasses for high-energy chirped-pulse amplification.

PubMed

Hays, Greg R; Gaul, Erhard W; Martinez, Mikael D; Ditmire, Todd

2007-07-20

We have investigated two novel laser glasses in an effort to generate high-energy, broad-spectrum pulses from a chirped-pulse amplification Nd:glass laser. Both glasses have significantly broader spectra (>38 nm FWHM) than currently available Nd:phosphate and Nd:silicate glasses. We present calculations for small signal pulse amplification to simulate spectral gain narrowing. The technique of spectral shaping using mixed-glass architecture with an optical parametric chirped-pulse amplification front end is evaluated. Our modeling shows that amplified pulses with energies exceeding 10 kJ with sufficient bandwidth to achieve 120 fs pulsewidths are achievable with the use of the new laser glasses. With further development of current technologies, a laser system could be scaled to generate one exawatt in peak power.

Generation of single attosecond pulse within one atomic unit by using multi-cycle inhomogeneous polarization gating technology in bowtie-shaped nanostructure

NASA Astrophysics Data System (ADS)

Feng, Liqiang; Liu, Hang

2018-04-01

The generations of high-order harmonic spectra and single attosecond pulses (SAPs) driven by the multi-cycle inhomogeneous polarization gating (PG) technology in the bowtie-shaped nanostructure have been theoretically investigated. It is found that by setting the bowtie-shaped nanostructure along the driven laser polarization direction, not only the extension of the harmonic cutoff can be achieved, caused by the surface plasmon polaritons, but also the modulations of the harmonics can be decreased, caused by the PG technology and the inhomogeneous effect. As a result, the contribution of the harmonic plateau is only from one harmonic emission peak with the dominant short quantum path. Further, by properly adding a half-cycle pulse into the driven laser field, the harmonic emission process can be precisely controlled in the half-cycle duration and a supercontinuum with the bandwidth of 263 eV can be obtained. Finally, by directly superposing the harmonics from this supercontinuum, a SAP with the full width at half maximum of 23 as can be obtained, which is shorter than one atomic unit.

Generation of parabolic similaritons in tapered silicon photonic wires: comparison of pulse dynamics at telecom and mid-infrared wavelengths.

PubMed

Lavdas, Spyros; Driscoll, Jeffrey B; Jiang, Hongyi; Grote, Richard R; Osgood, Richard M; Panoiu, Nicolae C

2013-10-01

We study the generation of parabolic self-similar optical pulses in tapered Si photonic nanowires (Si-PhNWs) at both telecom (λ=1.55 μm) and mid-infrared (λ=2.2 μm) wavelengths. Our computational study is based on a rigorous theoretical model, which fully describes the influence of linear and nonlinear optical effects on pulse propagation in Si-PhNWs with arbitrarily varying width. Numerical simulations demonstrate that, in the normal dispersion regime, optical pulses evolve naturally into parabolic pulses upon propagation in millimeter-long tapered Si-PhNWs, with the efficiency of this pulse-reshaping process being strongly dependent on the spectral and pulse parameter regime in which the device operates, as well as the particular shape of the Si-PhNWs.

A Tesla-type repetitive nanosecond pulse generator for solid dielectric breakdown research.

PubMed

Zhao, Liang; Pan, Ya Feng; Su, Jian Cang; Zhang, Xi Bo; Wang, Li Min; Fang, Jin Peng; Sun, Xu; Lui, Rui

2013-10-01

A Tesla-type repetitive nanosecond pulse generator including a pair of electrode and a matched absorption resistor is established for the application of solid dielectric breakdown research. As major components, a built-in Tesla transformer and a gas-gap switch are designed to boost and shape the output pulse, respectively; the electrode is to form the anticipated electric field; the resistor is parallel to the electrode to absorb the reflected energy from the test sample. The parameters of the generator are a pulse width of 10 ns, a rise and fall time of 3 ns, and a maximum amplitude of 300 kV. By modifying the primary circuit of the Tesla transformer, the generator can produce both positive and negative pulses at a repetition rate of 1-50 Hz. In addition, a real-time measurement and control system is established based on the solid dielectric breakdown requirements for this generator. With this system, experiments on test samples made of common insulation materials in pulsed power systems are conducted. The preliminary experimental results show that the constructed generator is capable to research the solid dielectric breakdown phenomenon on a nanosecond time scale.

Optimally shaped narrowband picosecond pulses for femtosecond stimulated Raman spectroscopy.

PubMed

Hoffman, David P; Valley, David; Ellis, Scott R; Creelman, Mark; Mathies, Richard A

2013-09-09

A comparison between a Fabry-Pérot etalon filter and a conventional grating filter for producing the picosecond (ps) Raman pump pulses for femtosecond stimulated Raman spectroscopy (FSRS) is presented. It is shown that for pulses of equal energy the etalon filter produces Raman signals twice as large as that of the grating filter while suppressing the electronically resonant background signal. The time asymmetric profile of the etalon-generated pulse is shown to be responsible for both of these observations. A theoretical discussion is presented which quantitatively supports this hypothesis. It is concluded that etalons are the ideal method for the generation of narrowband ps pulses for FSRS because of the optical simplicity, efficiency, improved FSRS intensity and reduced backgrounds.

Pulse transmission receiver with higher-order time derivative pulse correlator

DOEpatents

Dress, Jr., William B.; Smith, Stephen F.

2003-09-16

Systems and methods for pulse-transmission low-power communication modes are disclosed. A pulse transmission receiver includes: a higher-order time derivative pulse correlator; a demodulation decoder coupled to the higher-order time derivative pulse correlator; a clock coupled to the demodulation decoder; and a pseudorandom polynomial generator coupled to both the higher-order time derivative pulse correlator and the clock. The systems and methods significantly reduce lower-frequency emissions from pulse transmission spread-spectrum communication modes, which reduces potentially harmful interference to existing radio frequency services and users and also simultaneously permit transmission of multiple data bits by utilizing specific pulse shapes.

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.

Theoretical extension and experimental demonstration of spectral compression in second-harmonic generation by Fresnel-inspired binary phase shaping

NASA Astrophysics Data System (ADS)

Li, Baihong; Dong, Ruifang; Zhou, Conghua; Xiang, Xiao; Li, Yongfang; Zhang, Shougang

2018-05-01

Selective two-photon microscopy and high-precision nonlinear spectroscopy rely on efficient spectral compression at the desired frequency. Previously, a Fresnel-inspired binary phase shaping (FIBPS) method was theoretically proposed for spectral compression of two-photon absorption and second-harmonic generation (SHG) with a square-chirped pulse. Here, we theoretically show that the FIBPS can introduce a negative quadratic frequency phase (negative chirp) by analogy with the spatial-domain phase function of Fresnel zone plate. Thus, the previous theoretical model can be extended to the case where the pulse can be transformed limited and in any symmetrical spectral shape. As an example, we experimentally demonstrate spectral compression in SHG by FIBPS for a Gaussian transform-limited pulse and show good agreement with the theory. Given the fundamental pulse bandwidth, a narrower SHG bandwidth with relatively high intensity can be obtained by simply increasing the number of binary phases. The experimental results also verify that our method is superior to that proposed in [Phys. Rev. A 46, 2749 (1992), 10.1103/PhysRevA.46.2749]. This method will significantly facilitate the applications of selective two-photon microscopy and spectroscopy. Moreover, as it can introduce negative dispersion, hence it can also be generalized to other applications in the field of dispersion compensation.

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.

Direct generation of 128-fs Gaussian pulses from a compensation-free fiber laser using dual mode-locking mechanisms

NASA Astrophysics Data System (ADS)

Peng, Junsong; Zhan, Li; Gu, Zhaochang; Qian, Kai; Luo, Shouyu; Shen, Qishun

2012-03-01

We have experimentally demonstrated the direct generation of 128-fs pulses in an all-anomalous-dispersion all-fiber mode-locked laser. The laser is free of dispersion compensation in the cavity based on standard single mode fiber (SMF). The time-bandwidth product is 0.536. The laser is achieved by using two mode-lockers, one is nonlinear polarization rotation (NPR), and the other is nonlinear amplifying loop mirror. The coexistence of dual mode-locking mechanisms can decrease the cavity length to 12-m, and also results in producing high-quality pulses with a Gaussian shape both on the pulse profile and spectrum, but without Kelly sidebands.

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.

Photonic generation of ultra-wideband signals by direct current modulation on SOA section of an SOA-integrated SGDBR laser.

PubMed

Lv, Hui; Yu, Yonglin; Shu, Tan; Huang, Dexiu; Jiang, Shan; Barry, Liam P

2010-03-29

Photonic ultra-wideband (UWB) pulses are generated by direct current modulation of a semiconductor optical amplifier (SOA) section of an SOA-integrated sampled grating distributed Bragg reflector (SGDBR) laser. Modulation responses of the SOA section of the laser are first simulated with a microwave equivalent circuit model. Simulated results show a resonance behavior indicating the possibility to generate UWB signals with complex shapes in the time domain. The UWB pulse generation is then experimentally demonstrated for different selected wavelength channels with an SOA-integrated SGDBR laser.

Efficient Z gates for quantum computing

NASA Astrophysics Data System (ADS)

McKay, David C.; Wood, Christopher J.; Sheldon, Sarah; Chow, Jerry M.; Gambetta, Jay M.

2017-08-01

For superconducting qubits, microwave pulses drive rotations around the Bloch sphere. The phase of these drives can be used to generate zero-duration arbitrary virtual Z gates, which, combined with two Xπ /2 gates, can generate any SU(2) gate. Here we show how to best utilize these virtual Z gates to both improve algorithms and correct pulse errors. We perform randomized benchmarking using a Clifford set of Hadamard and Z gates and show that the error per Clifford is reduced versus a set consisting of standard finite-duration X and Y gates. Z gates can correct unitary rotation errors for weakly anharmonic qubits as an alternative to pulse-shaping techniques such as derivative removal by adiabatic gate (DRAG). We investigate leakage and show that a combination of DRAG pulse shaping to minimize leakage and Z gates to correct rotation errors realizes a 13.3 ns Xπ /2 gate characterized by low error [1.95 (3 ) ×10-4] and low leakage [3.1 (6 ) ×10-6] . Ultimately leakage is limited by the finite temperature of the qubit, but this limit is two orders of magnitude smaller than pulse errors due to decoherence.

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.

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.

A Kolsky tension bar technique using a hollow incident tube

NASA Astrophysics Data System (ADS)

Guzman, O.; Frew, D. J.; Chen, W.

2011-04-01

Load control of the incident pulse profiles in compression Kolsky bar experiments has been widely used to subject the specimen to optimal testing conditions. Tension Kolsky bars have been used to determine dynamic material behavior since the 1960s with limited capability to shape the loading pulses due to the pulse-generating mechanisms. We developed a modified Kolsky tension bar where a hollow incident tube is used to carry the incident stress waves. The incident tube also acts as a gas gun barrel that houses the striker for impact. The main advantage of this new design is that the striker impacts on an impact cap of the incident tube. Compression pulse shapers can be attached to the impact cap, thus fully utilizing the predictive compression pulse-shaping capability in tension experiments. Using this new testing technique, the dynamic tensile material behavior for Al 6061-T6511 and TRIP 800 (transformation-induced plasticity) steel has been obtained.

Laser shock wave assisted patterning on NiTi shape memory alloy surfaces

NASA Astrophysics Data System (ADS)

Seyitliyev, Dovletgeldi; Li, Peizhen; Kholikov, Khomidkhodza; Grant, Byron; Karaca, Haluk E.; Er, Ali O.

2017-02-01

An advanced direct imprinting method with low cost, quick, and less environmental impact to create thermally controllable surface pattern using the laser pulses is reported. Patterned micro indents were generated on Ni50Ti50 shape memory alloys (SMA) using an Nd:YAG laser operating at 1064 nm combined with suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities which generates pressure pulses up to 10 GPa on the surface was focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the NiTi surface. Scanning electron microscope (SEM) and optical microscope images of square pattern with different sizes were studied. One dimensional profile analysis shows that the depth of the patterned sample initially increase linearly with the laser energy until 125 mJ/pulse where the plasma further absorbs and reflects the laser beam. In addition, light the microscope image show that the surface of NiTi alloy was damaged due to the high power laser energy which removes the graphite layer.

Coiled transmission line pulse generators

DOEpatents

McDonald, Kenneth Fox

2010-11-09

Methods and apparatus are provided for fabricating and constructing solid dielectric "Coiled Transmission Line" pulse generators in radial or axial coiled geometries. The pour and cure fabrication process enables a wide variety of geometries and form factors. The volume between the conductors is filled with liquid blends of monomers, polymers, oligomers, and/or cross-linkers and dielectric powders; and then cured to form high field strength and high dielectric constant solid dielectric transmission lines that intrinsically produce ideal rectangular high voltage pulses when charged and switched into matched impedance loads. Voltage levels may be increased by Marx and/or Blumlein principles incorporating spark gap or, preferentially, solid state switches (such as optically triggered thyristors) which produce reliable, high repetition rate operation. Moreover, these Marxed pulse generators can be DC charged and do not require additional pulse forming circuitry, pulse forming lines, transformers, or an a high voltage spark gap output switch. The apparatus accommodates a wide range of voltages, impedances, pulse durations, pulse repetition rates, and duty cycles. The resulting mobile or flight platform friendly cylindrical geometric configuration is much more compact, light-weight, and robust than conventional linear geometries, or pulse generators constructed from conventional components. Installing additional circuitry may accommodate optional pulse shape improvements. The Coiled Transmission Lines can also be connected in parallel to decrease the impedance, or in series to increase the pulse length.

Cost-effective WDM-PON Delivering Up/Down-stream Data on a Single Wavelength Using Soliton Pulse

NASA Astrophysics Data System (ADS)

Tawade, Laxman

2013-06-01

This paper presents wavelength division multiplexing passive optical network (WDM-PON) system delivering downstream 2.5 Gbit/s data and upstream 1 Gbit/s data on a single wavelength using pulse source is mode locked laser which generating a single pulse of "sech" shape with specified power and width i.e. soliton pulse. The optical source for downstream data and upstream data is sech pulse generator at central office and reflective semiconductor optical amplifier (RSOA) at each optical network unit. We also investigate analysis of backscattered optical signal for upstream data and downstream data simultaneously. Bit error rate, Q-Factor were measured to demonstrate the proposed scheme. In this paper Long reach aspects of an access network is investigated using single channel scenario.

The use of linear programming techniques to design optimal digital filters for pulse shaping and channel equalization

NASA Technical Reports Server (NTRS)

Houts, R. C.; Burlage, D. W.

1972-01-01

A time domain technique is developed to design finite-duration impulse response digital filters using linear programming. Two related applications of this technique in data transmission systems are considered. The first is the design of pulse shaping digital filters to generate or detect signaling waveforms transmitted over bandlimited channels that are assumed to have ideal low pass or bandpass characteristics. The second is the design of digital filters to be used as preset equalizers in cascade with channels that have known impulse response characteristics. Example designs are presented which illustrate that excellent waveforms can be generated with frequency-sampling filters and the ease with which digital transversal filters can be designed for preset equalization.

Doped luminescent materials and particle discrimination using same

DOEpatents

Doty, F. Patrick; Allendorf, Mark D; Feng, Patrick L

2014-10-07

Doped luminescent materials are provided for converting excited triplet states to radiative hybrid states. The doped materials may be used to conduct pulse shape discrimination (PSD) using luminescence generated by harvested excited triplet states. The doped materials may also be used to detect particles using spectral shape discrimination (SSD).

Laser Pulse Duration Is Critical For the Generation of Plasmonic Nanobubbles

PubMed Central

2015-01-01

Plasmonic nanobubbles (PNBs) are transient vapor nanobubbles generated in liquid around laser-overheated plasmonic nanoparticles. Unlike plasmonic nanoparticles, PNBs’ properties are still largely unknown due to their highly nonstationary nature. Here we show the influence of the duration of the optical excitation on the energy efficacy and threshold of PNB generation. The combination of picosecond pulsed excitation with the nanoparticle clustering provides the highest energy efficacy and the lowest threshold fluence, around 5 mJ cm–2, of PNB generation. In contrast, long excitation pulses reduce the energy efficacy of PNB generation by several orders of magnitude. Ultimately, the continuous excitation has the minimal energy efficacy, nine orders of magnitude lower than that for the picosecond excitation. Thus, the duration of the optical excitation of plasmonic nanoparticles can have a stronger effect on the PNB generation than the excitation wavelength, nanoparticle size, shape, or other “stationary” properties of plasmonic nanoparticles. PMID:24916057

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.

Design, characterization and experimental validation of a compact, flexible pulsed power architecture for ex vivo platelet activation

PubMed Central

Caiafa, Antonio; Jiang, Yan; Klopman, Steve; Morton, Christine; Torres, Andrew S.; Loveless, Amanda M.; Neculaes, V. Bogdan

2017-01-01

Electric pulses can induce various changes in cell dynamics and properties depending upon pulse parameters; however, pulsed power generators for in vitro and ex vivo applications may have little to no flexibility in changing the pulse duration, rise- and fall-times, or pulse shape. We outline a compact pulsed power architecture that operates from hundreds of nanoseconds (with the potential for modification to tens of nanoseconds) to tens of microseconds by modifying a Marx topology via controlling switch sequences and voltages into each capacitor stage. We demonstrate that this device can deliver pulses to both low conductivity buffers, like standard pulsed power supplies used for electroporation, and higher conductivity solutions, such as blood and platelet rich plasma. We further test the effectiveness of this pulse generator for biomedical applications by successfully activating platelets ex vivo with 400 ns and 600 ns electric pulses. This novel bioelectrics platform may provide researchers with unprecedented flexibility to explore a wide range of pulse parameters that may induce phenomena ranging from intracellular to plasma membrane manipulation. PMID:28746392

Fast pulsed excitation wiggler or undulator

DOEpatents

van Steenbergen, Arie

1990-01-01

A fast pulsed excitation, electromagnetic undulator or wiggler, employing geometrically alternating substacks of thin laminations of ferromagnetic material, together with a single turn current loop excitation of the composite assembly, of such shape and configuration that intense, spatially alternating, magnetic fields are generated; for use as a pulsed mode undulator or wiggler radiator, for use in a Free Electron Laser (FEL) type radiation source or, for use in an Inverse Free Electron Laser (IFEL) charged particle accelerator.

Fiber-laser frequency combs for the generation of tunable single-frequency laser lines, mm- and THz-waves and sinc-shaped Nyquist pulses

NASA Astrophysics Data System (ADS)

Schneider, Thomas

2015-03-01

High-quality frequency comb sources like femtosecond-lasers have revolutionized the metrology of fundamental physical constants. The generated comb consists of frequency lines with an equidistant separation over a bandwidth of several THz. This bandwidth can be broadened further to a super-continuum of more than an octave through propagation in nonlinear media. The frequency separation between the lines is defined by the repetition rate and the width of each comb line can be below 1 Hz, even without external stabilization. By extracting just one of these lines, an ultra-narrow linewidth, tunable laser line for applications in communications and spectroscopy can be generated. If two lines are extracted, the superposition of these lines in an appropriate photo-mixer produces high-quality millimeter- and THz-waves. The extraction of several lines can be used for the creation of almost-ideally sinc-shaped Nyquist pulses, which enable optical communications with the maximum-possible baud rate. Especially combs generated by low-cost, small-footprint fs-fiber lasers are very promising. However due to the resonator length, the comb frequencies have a typical separation of 80 - 100 MHz, far too narrow for the selection of single tones with standard optical filters. Here the extraction of single lines of an fs-fiber laser by polarization pulling assisted stimulated Brillouin scattering is presented. The application of these extracted lines as ultra-narrow, stable and tunable laser lines, for the generation of very high-quality mm and THz-waves with an ultra-narrow linewidth and phase noise and for the generation of sinc-shaped Nyquist pulses with arbitrary bandwidth and repetition rate is discussed.

Conceptual design of an intense positron source based on an LIA

NASA Astrophysics Data System (ADS)

Long, Ji-Dong; Yang, Zhen; Dong, Pan; Shi, Jin-Shui

2012-04-01

Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.

Photonic ultrawideband impulse radio generation and modulation over a fiber link using a phase modulator and a delay interferometer.

PubMed

Shao, Jing; Sun, Junqiang

2012-08-15

We propose and experimentally demonstrate a simple and flexible photonic scheme for generation and modulation of ultrawideband (UWB) using a phase modulator and a fiber delay interferometer (DI)-based multichannel frequency discrimination. By introducing a Gaussian signal to the phase modulator, the UWB polarity-switchable doublet pulses can be achieved by combining the pair of UWB monocycle pulses with inverted polarities at the DI outputs under proper time delay. Furthermore, the pulse shape modulation, pulse position modulation, and on-off keying can be performed by coding the electrical data patterns and adjusting the time delay between the two monocycle pulses. Only a laser source introduced in the architecture guarantees the excellent dispersion tolerance over 75 km optical fiber link for UWB pulse sequence, which has potential application in future high-speed UWB impulse radio over optical fiber access networks.

Extended range radiation dose-rate monitor

DOEpatents

Valentine, Kenneth H.

1988-01-01

An extended range dose-rate monitor is provided which utilizes the pulse pileup phenomenon that occurs in conventional counting systems to alter the dynamic response of the system to extend the dose-rate counting range. The current pulses from a solid-state detector generated by radiation events are amplified and shaped prior to applying the pulses to the input of a comparator. The comparator generates one logic pulse for each input pulse which exceeds the comparator reference threshold. These pulses are integrated and applied to a meter calibrated to indicate the measured dose-rate in response to the integrator output. A portion of the output signal from the integrator is fed back to vary the comparator reference threshold in proportion to the output count rate to extend the sensitive dynamic detection range by delaying the asymptotic approach of the integrator output toward full scale as measured by the meter.

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.

Spectral line-by-line pulse shaping of on-chip microresonator frequency combs

NASA Astrophysics Data System (ADS)

Ferdous, Fahmida; Miao, Houxun; Leaird, Daniel E.; Srinivasan, Kartik; Wang, Jian; Chen, Lei; Varghese, Leo Tom; Weiner, Andrew M.

2011-12-01

Recently, on-chip comb generation methods based on nonlinear optical modulation in ultrahigh-quality-factor monolithic microresonators have been demonstrated, where two pump photons are transformed into sideband photons in a four-wave-mixing process mediated by Kerr nonlinearity. Here, we investigate line-by-line pulse shaping of such combs generated in silicon nitride ring resonators. We observe two distinct paths to comb formation that exhibit strikingly different time-domain behaviours. For combs formed as a cascade of sidebands spaced by a single free spectral range that spread from the pump, we are able to compress stably to nearly bandwidth-limited pulses. This indicates high coherence across the spectra and provides new data on the high passive stability of the spectral phase. For combs where the initial sidebands are spaced by multiple free spectral ranges that then fill in to give combs with single free-spectral-range spacing, the time-domain data reveal partially coherent behaviour.

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.

Evolution of bubble clouds induced by pulsed cavitational ultrasound therapy - histotripsy.

PubMed

Xu, Zhen; Raghavan, M; Hall, T L; Mycek, M-A; Fowlkes, J B

2008-05-01

Mechanical tissue fractionation can be achieved using successive, high-intensity ultrasound pulses in a process termed histotripsy. Histotripsy has many potential clinical applications where noninvasive tissue removal is desired. The primary mechanism for histotripsy is believed to be cavitation. Using fast-gated imaging, this paper studies the evolution of a cavitating bubble cloud induced by a histotripsy pulse (10 and 14 cycles) at peak negative pressures exceeding 21MPa. Bubble clouds are generated inside a gelatin phantom and at a tissue-water interface, representing two situations encountered clinically. In both environments, the imaging results show that the bubble clouds share the same evolutionary trend. The bubble cloud and individual bubbles in the cloud were generated by the first cycle of the pulse, grew with each cycle during the pulse, and continued to grow and collapsed several hundred microseconds after the pulse. For example, the bubbles started under 10 microm, grew to 50 microm during the pulse, and continued to grow 100 microm after the pulse. The results also suggest that the bubble clouds generated in the two environments differ in growth and collapse duration, void fraction, shape, and size. This study furthers our understanding of the dynamics of bubble clouds induced by histotripsy.

A 1 MA, variable risetime pulse generator for high energy density plasma research

NASA Astrophysics Data System (ADS)

Greenly, J. B.; Douglas, J. D.; Hammer, D. A.; Kusse, B. R.; Glidden, S. C.; Sanders, H. D.

2008-07-01

COBRA is a 0.5Ω pulse generator driving loads of order 10nH inductance to >1MA current. The design is based on independently timed, laser-triggered switching of four water pulse-forming lines whose outputs are added in parallel to drive the load current pulse. The detailed design and operation of the switching to give a wide variety of current pulse shapes and rise times from 95to230ns is described. The design and operation of a simple inductive load voltage monitor are described which allows good accounting of load impedance and energy dissipation. A method of eliminating gas bubbles on the underside of nearly horizontal insulator surfaces in water was required for reliable operation of COBRA; a novel and effective solution to this problem is described.

The impact of photon flight path on S1 pulse shape analysis in liquid xenon two-phase detectors

NASA Astrophysics Data System (ADS)

Moongweluwan, M.

2016-02-01

The LUX dark matter search experiment is a 350 kg dual-phase xenon time projection chamber located at the 4850 ft level of the Sanford Underground Research Facility in Lead, SD. The success of two-phase xenon detectors for dark matter searches relies on their ability to distinguish electron recoil (ER) background events from nuclear recoil (NR) signal events. Typically, the NR-ER discrimination is obtained from the ratio of the electroluminescence light (S2) to the prompt scintillation light (S1). Analysis of the S1 pulse shape is an additional discrimination technique that can be used to distinguish NR from ER. Pulse-shape NR-ER discrimination can be achieved based on the ratio of the de-excitation processes from singlet and triplet states that generate the S1. The NR S1 is dominated by the de-excitation process from singlet states with a time constant of about 3 ns while the ER S1 is dominated by the de-excitation process from triplet states with a time constant of about 24 ns. As the size of the detectors increases, the variation in the S1 photon flight path can become comparable to these decay constants, reducing the utility of pulse-shape analysis to separate NR from ER. The effect of path length variations in the LUX detector has been studied using the results of simulations and the impact on the S1 pulse shape analysis is discussed.

Photonic-chip-based all-optical ultra-wideband pulse generation via XPM and birefringence in a chalcogenide waveguide.

PubMed

Tan, Kang; Marpaung, David; Pant, Ravi; Gao, Feng; Li, Enbang; Wang, Jian; Choi, Duk-Yong; Madden, Steve; Luther-Davies, Barry; Sun, Junqiang; Eggleton, Benjamin J

2013-01-28

We report a photonic-chip-based scheme for all-optical ultra-wideband (UWB) pulse generation using a novel all-optical differentiator that exploits cross-phase modulation and birefringence in an As₂S₃ chalcogenide rib waveguide. Polarity-switchable UWB monocycles and doublets were simultaneously obtained with single optical carrier operation. Moreover, transmission over 40-km fiber of the generated UWB doublets is demonstrated with good dispersion tolerance. These results indicate that the proposed approach has potential applications in multi-shape, multi-modulation and long-distance UWB-over-fiber communication systems.

Asymmetric W-shaped and M-shaped soliton pulse generated from a weak modulation in an exponential dispersion decreasing fiber

NASA Astrophysics Data System (ADS)

Liu, Xiang-Shu; Zhao, Li-Chen; Duan, Liang; Yang, Zhan-Ying; Yang, Wen-Li

2017-12-01

Not Available Project supported by the National Natural Science Foundation of China (Grant No. 11475135), the Fund from Shaanxi Province Science Association of Colleges and Universities (Grant No. 20160216), and Guangxi Provincial Education Department Research Project, China (Grant No. 2017KY0776).

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

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.

RF pulse shape control in the compact linear collider test facility

NASA Astrophysics Data System (ADS)

Kononenko, Oleksiy; Corsini, Roberto

2018-07-01

The Compact Linear Collider (CLIC) is a study for an electron-positron machine aiming at accelerating and colliding particles at the next energy frontier. The CLIC concept is based on the novel two-beam acceleration scheme, where a high-current low-energy drive beam generates RF in series of power extraction and transfer structures accelerating the low-current main beam. To compensate for the transient beam-loading and meet the energy spread specification requirements for the main linac, the RF pulse shape must be carefully optimized. This was recently modelled by varying the drive beam phase switch times in the sub-harmonic buncher so that, when combined, the drive beam modulation translates into the required voltage modulation of the accelerating pulse. In this paper, the control over the RF pulse shape with the phase switches, that is crucial for the success of the developed compensation model, is studied. The results on the experimental verification of this control method are presented and a good agreement with the numerical predictions is demonstrated. Implications for the CLIC beam-loading compensation model are also discussed.

Photonic microwave waveforms generation based on pulse carving and superposition in time-domain

NASA Astrophysics Data System (ADS)

Xia, Yi; Jiang, Yang; Zi, Yuejiao; He, Yutong; Tian, Jing; Zhang, Xiaoyu; Luo, Hao; Dong, Ruyang

2018-05-01

A novel photonic approach for various microwave waveforms generation based on time-domain synthesis is theoretically analyzed and experimentally investigated. In this scheme, two single-drive Mach-Zehnder modulators are used for pulses shaping. After shifting the phase and implementing envelopes superposition of the pulses, desired waveforms can be achieved in time-domain. The theoretic analysis and simulations are presented. In the experimental demonstrations, a triangular waveform, square waveform, and half duty cycle sawtooth (or reversed-sawtooth) waveform are generated successfully. By utilizing time multiplexing technique, a frequency-doubled sawtooth (or reversed-sawtooth) waveform with 100% duty cycle can be obtained. In addition, a fundamental frequency sawtooth (or reversed-sawtooth) waveform with 100% duty cycle can also be achieved by the superposition of square waveform and frequency-doubled sawtooth waveform.

Numerical investigation of a scalable setup for efficient terahertz generation using a segmented tilted-pulse-front excitation.

PubMed

Pálfalvi, László; Tóth, György; Tokodi, Levente; Márton, Zsuzsanna; Fülöp, József András; Almási, Gábor; Hebling, János

2017-11-27

A hybrid-type terahertz pulse source is proposed for high energy terahertz pulse generation. It is the combination of the conventional tilted-pulse-front setup and a transmission stair-step echelon-faced nonlinear crystal with a period falling in the hundred-micrometer range. The most important advantage of the setup is the possibility of using plane parallel nonlinear optical crystal for producing good-quality, symmetric terahertz beam. Another advantage of the proposed setup is the significant reduction of imaging errors, which is important in the case of wide pump beams that are used in high energy experiments. A one dimensional model was developed for determining the terahertz generation efficiency, and it was used for quantitative comparison between the proposed new hybrid setup and previously introduced terahertz sources. With lithium niobate nonlinear material, calculations predict an approximately ten-fold increase in the efficiency of the presently described hybrid terahertz pulse source with respect to that of the earlier proposed setup, which utilizes a reflective stair-step echelon and a prism shaped nonlinear optical crystal. By using pump pulses of 50 mJ pulse energy, 500 fs pulse length and 8 mm beam spot radius, approximately 1% conversion efficiency and 0.5 mJ terahertz pulse energy can be reached with the newly proposed setup.

Efficient graphene saturable absorbers on D-shaped optical fiber for ultrashort pulse generation

PubMed Central

Zapata, J. D.; Steinberg, D.; Saito, L. A. M.; de Oliveira, R. E. P.; Cárdenas, A. M.; de Souza, E. A. Thoroh

2016-01-01

We demonstrated a method to construct high efficiency saturable absorbers based on the evanescent light field interaction of CVD monolayer graphene deposited on side-polished D-shaped optical fiber. A set of samples was fabricated with two different core-graphene distances (0 and 1 μm), covered with graphene ranging between 10 and 25 mm length. The mode-locking was achieved and the best pulse duration was 256 fs, the shortest pulse reported in the literature with CVD monolayer graphene in EDFL. As result, we find a criterion between the polarization relative extinction ratio in the samples and the pulse duration, which relates the better mode-locking performance with the higher polarization extinction ratio of the samples. This criterion also provides a better understanding of the graphene distributed saturable absorbers and their reproducible performance as optoelectronic devices for optical applications. PMID:26856886

Etching of semiconductors and metals by the photonic jet with shaped optical fiber tips

NASA Astrophysics Data System (ADS)

Pierron, Robin; Lecler, Sylvain; Zelgowski, Julien; Pfeiffer, Pierre; Mermet, Frédéric; Fontaine, Joël

2017-10-01

The etching of semiconductors and metals by a photonic jet (PJ) generated with a shaped optical fiber tip is studied. Etched marks with a diameter of 1 μm have been realized on silicon, stainless steel and titanium with a 35 kHz pulsed laser, emitting 100 ns pulses at 1064 nm. The selection criteria of the fiber and its tip are discussed. We show that a 100/140 silica fiber is a good compromise which takes into account the injection, the working distance and the energy coupled in the higher-order modes. The energy balance is performed on the basis of the known ablation threshold of the material. Finally, the dependence between the etching depth and the number of pulses is studied. Saturation is observed probably due to a redeposition of the etched material, showing that a higher pulse energy is required for deeper etchings.

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.

Nonlinear effects during interaction of femtosecond doughnut-shaped laser pulses with glasses: overcoming intensity clamping

NASA Astrophysics Data System (ADS)

Bulgakova, Nadezhda M.; Zhukov, Vladimir P.; Fedoruk, Mikhail P.; Rubenchik, Alexander M.

2017-05-01

Interaction of femtosecond laser pulses with a bulk glass (fused silica as an example) has been studied numerically based on non-linear Maxwell's equations supplemented by the hydrodynamics-type equations for free electron plasma for the cases of Gaussian linearly-polarized and doughnut-shaped radially-polarized laser beams. For Gaussian pulses focused inside glass (800 nm wavelength, 45 fs duration, numerical aperture of 0.25), the free electron density in the laser-excited region remains subcritical while the locally absorbed energy density does not exceed 2000 J/cm3 in the range of pulse energies of 200 nJ - 2 μJ. For doughnut-shaped pulses, the initial high-intensity ring of light is shrinking upon focusing. Upon reaching a certain ionization level on its way, the light ring splits into two branches, one of which shrinks swiftly toward the beam axis well before the geometrical focus, leading to generation of supercritical free electron density. The second branch represents the laser light scattered by the electron plasma away from the beam axis. The final laserexcited volume represents a tube of 0.5-1 μm in radius and 10-15 μm long. The local maximum of absorbed energy can be more than 10 times higher compared to the case of Gaussian beams of the same energy. The corresponding pressure levels have been evaluated. It is anticipated that, in the case of doughnut-shaped pulses, the tube-like shape of the deposited energy should lead to implosion of material that can be used for improving the direct writing of high-refractive index optical structures inside glass or for achieving extreme thermodynamic states of matter.

Photonic generation of ultra-wide-band doublet pulse through monolithic integration of tapered directional coupler and quantum well waveguide.

PubMed

Kuo, Yu-Zheng; Wu, Jui-Pin; Wu, Tsu-Hsiu; Chiu, Yi-Jen

2012-10-22

We proposed and demonstrated a novel scheme of photonic ultra-wide-band (UWB) doublet pulse based on monolithic integration of tapered optical-direction coupler (TODC) and multiple-quantum-well (MQW) waveguide. TODC is formed by a top tapered MQW waveguide vertically integrating with an underneath passive waveguide. Through simultaneous field-driven optical index- and absorption- change in MQW, the partial optical coupling in TODC can be used to get a valley-shaped of optical transmission against voltage. Therefore, doublet-enveloped optical pulse can be realized by high-speed and high-efficient conversion of input electrical pulse. By just adjusting bias through MQW, 1530 nm photonic UWB doublet optical pulse with 75-ps pulse width, below -41.3 dBm power, 125% fractional bandwidth, and 7.5 GHz of -10 dB bandwidth has been demonstrated, fitted into FCC requirement (3.1 GHz~10.6 GHz). Doublet-pulse data transmission generated in optical fiber is also performed for further characterization, exhibiting a successful 1.25 Gb/s error-free transmission. It suggests such optoelectronic integration template can be applied for photonic UWB generation in fiber-based communications.

Demonstration of an 8 × 25-Gb/s optical time-division multiplexing system

NASA Astrophysics Data System (ADS)

Wang, Dong; Huo, Li; Li, Yunbo; Wang, Lei; Li, Han; Jiang, Xiangyu; Chen, Xin; Lou, Caiyun

2017-11-01

An 8 × 25-Gb/s optical time-division multiplexing (OTDM) system is demonstrated experimentally. The optical pulse source is based on optical frequency comb (OFC) generation and pulse shaping, which can generate nearly chirp-free 25-GHz 1.6-ps optical Gaussian pulse. The eightfold optical time-division demultiplexer consists of a single-driven dual-parallel Mach-Zehnder modulator (DPMZM) and a Mamyshev reshaper. Error-free demultiplexing of 8 × 25-Gb/s back-to-back (B2B) signal with a power penalty of 4.1 dB to 4.4 dB at a bit error rate (BER) of 10-9 is achieved to confirm the performance of the proposed system.

The Mathematical Modeling and Computer Simulation of Electrochemical Micromachining Using Ultrashort Pulses

NASA Astrophysics Data System (ADS)

Kozak, J.; Gulbinowicz, D.; Gulbinowicz, Z.

2009-05-01

The need for complex and accurate three dimensional (3-D) microcomponents is increasing rapidly for many industrial and consumer products. Electrochemical machining process (ECM) has the potential of generating desired crack-free and stress-free surfaces of microcomponents. This paper reports a study of pulse electrochemical micromachining (PECMM) using ultrashort (nanoseconds) pulses for generating complex 3-D microstructures of high accuracy. A mathematical model of the microshaping process with taking into consideration unsteady phenomena in electrical double layer has been developed. The software for computer simulation of PECM has been developed and the effects of machining parameters on anodic localization and final shape of machined surface are presented.

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

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.

Development of extreme ultraviolet and soft x-ray multilayer optics for scientific studies with femtosecond/attosecond sources

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

Aquila, Andrew Lee

The development of multilayer optics for extreme ultraviolet (EUV) radiation has led to advancements in many areas of science and technology, including materials studies, EUV lithography, water window microscopy, plasma imaging, and orbiting solar physics imaging. Recent developments in femtosecond and attosecond EUV pulse generation from sources such as high harmonic generation lasers, combined with the elemental and chemical specificity provided by EUV radiation, are opening new opportunities to study fundamental dynamic processes in materials. Critical to these efforts is the design and fabrication of multilayer optics to transport, focus, shape and image these ultra-fast pulses This thesis describes themore » design, fabrication, characterization, and application of multilayer optics for EUV femtosecond and attosecond scientific studies. Multilayer mirrors for bandwidth control, pulse shaping and compression, tri-material multilayers, and multilayers for polarization control are described. Characterization of multilayer optics, including measurement of material optical constants, reflectivity of multilayer mirrors, and metrology of reflected phases of the multilayer, which is critical to maintaining pulse size and shape, were performed. Two applications of these multilayer mirrors are detailed in the thesis. In the first application, broad bandwidth multilayers were used to characterize and measure sub-100 attosecond pulses from a high harmonic generation source and was performed in collaboration with the Max-Planck institute for Quantum Optics and Ludwig- Maximilians University in Garching, Germany, with Professors Krausz and Kleineberg. In the second application, multilayer mirrors with polarization control are useful to study femtosecond spin dynamics in an ongoing collaboration with the T-REX group of Professor Parmigiani at Elettra in Trieste, Italy. As new ultrafast x-ray sources become available, for example free electron lasers, the multilayer designs described in this thesis can be extended to higher photon energies, and such designs can be used with those sources to enable new scientific studies, such as molecular bonding, phonon, and spin dynamics.« less

Pulse generator with intermediate inductive storage as a lightning simulator

NASA Astrophysics Data System (ADS)

Kovalchuk, B. M.; Kharlov, A. V.; Zherlytsyn, A. A.; Kumpyak, E. V.; Tsoy, N. V.

2016-06-01

Compact transportable generators are required for simulating a lightning current pulse for electrical apparatus testing. A bi-exponential current pulse has to be formed by such a generator (with a current rise time of about two orders of magnitude faster than the damping time). The objective of this study was to develop and investigate a compact pulse generator with intermediate inductive storage and a fuse opening switch as a simulator of lightning discharge. A Marx generator (six stages) with a capacitance of 1 μF and an output voltage of 240 kV was employed as primary storage. In each of the stages, two IK-50/3 (50 kV, 3 μF) capacitors are connected in parallel. The generator inductance is 2 μH. A test bed for the investigations was assembled with this generator. The generator operates without SF6 and without oil in atmospheric air, which is very important in practice. Straight copper wires with adjustable lengths and diameters were used for the electro-explosive opening switch. Tests were made with active-inductive loads (up to 0.1 Ω and up to 6.3 μH). The current rise time is lower than 1200 ns, and the damping time can be varied from 35 to 125 μs, following the definition of standard lightning current pulse in the IEC standard. Moreover, 1D MHD calculations of the fuse explosion were carried out self-consistently with the electric circuit equations, in order to calculate more accurately the load pulse parameters. The calculations agree fairly well with the tests. On the basis of the obtained results, the design of a transportable generator was developed for a lightning simulator with current of 50 kA and a pulse shape corresponding to the IEEE standard.

Communication: Analytical optimal pulse shapes obtained with the aid of genetic algorithms: Controlling the photoisomerization yield of retinal

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

Guerrero, R. D., E-mail: rdguerrerom@unal.edu.co; Arango, C. A., E-mail: caarango@icesi.edu.co; Reyes, A., E-mail: areyesv@unal.edu.co

We recently proposed a Quantum Optimal Control (QOC) method constrained to build pulses from analytical pulse shapes [R. D. Guerrero et al., J. Chem. Phys. 143(12), 124108 (2015)]. This approach was applied to control the dissociation channel yields of the diatomic molecule KH, considering three potential energy curves and one degree of freedom. In this work, we utilized this methodology to study the strong field control of the cis-trans photoisomerization of 11-cis retinal. This more complex system was modeled with a Hamiltonian comprising two potential energy surfaces and two degrees of freedom. The resulting optimal pulse, made of 6 linearlymore » chirped pulses, was capable of controlling the population of the trans isomer on the ground electronic surface for nearly 200 fs. The simplicity of the pulse generated with our QOC approach offers two clear advantages: a direct analysis of the sequence of events occurring during the driven dynamics, and its reproducibility in the laboratory with current laser technologies.« less

Digital micromirror device-based ultrafast pulse shaping for femtosecond laser.

PubMed

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

2015-06-15

In this Letter, we present a new digital micromirror device (DMD)-based ultrafast pulse shaper, i.e., DUPS. To the best of our knowledge, the DUPS is the first binary pulse shaper that can modulate high repetition rate laser sources at up to a 32 kHz rate (limited by the DMD pattern rate). Since pulse modulation occurs in the frequency domain through reflective two-dimensional micromirror arrays, i.e., DMD, the DUPS is not only compact and low in cost, but also possesses a high damage threshold that is critical for high pulse energy laser applications. In this work, a grating pair was introduced in the DUPS to compensate the DMD induced dispersion. Double pulses were generated to validate the effectiveness of the DUPS and calibrate the system. Subsequently, we demonstrated arbitrary phase shaping capability by continuous tuning of group velocity dispersion (GVD) and modulation of half-spectrum shifted by π. The overall efficiency was measured to be 1.7%, while an efficiency of up to 5% can be expected when high efficiency gratings and properly coated DMDs are used.

Synthesis of arbitrary pulse waveforms in QCL-seeded ns-pulse CO₂ laser for optimization of an LPP EUV source.

PubMed

Nowak, Krzysztof M; Kurosawa, Yoshiaki; Suganuma, Takashi; Kawasuji, Yasufumi; Nakarai, Hiroaki; Saito, Takashi; Fujimoto, Junichi; Mizoguchi, Hakaru

2016-07-01

One of the unique features of the quantum-cascade-laser-seeded, nanosecond-pulse CO₂ laser, invented for the purpose of generation of extreme UV by laser-produced-plasma, is a robust synthesis of arbitrary pulse waveforms. In the present Letter we report on experimental results that are, to our best knowledge, the first demonstration of such functionality obtainable from nanosecond-pulse CO₂ laser technology. An online pulse duration adjustment within 10-40 ns was demonstrated, and a few exemplary pulse waveforms were synthesized, such as "tophat," "tailspike," and "leadspike" shapes. Such output characteristics may be useful to optimize the performance of LPP EUV source.

Anomalous domain inversion in LiNbO3 single crystals investigated by scanning probe microscopy

NASA Astrophysics Data System (ADS)

Lilienblum, M.; Soergel, E.

2011-09-01

Ferroelectric domains were written in lithium niobate (LiNbO3) single crystals by applying voltage pulses to the tip of a scanning force microscope. The generated domains are subsequently imaged by piezoresponse force microscopy. As it has been previously observed not only full domains but also doughnut-shaped ones arise from tip-based domain formation. In this contribution, we present our experiments which were carried out with 10-20 μm thin LiNbO3 single crystals. We show that by choosing appropriate writing parameters, domains of predetermined shape (full or doughnut) can be reliably generated. In addition to the duration and the amplitude of the voltage pulse the moment of the retraction of the tip from the sample surface was found to be a crucial parameter for reproducible domain formation.

Towards Terawatt Sub-Cycle Long-Wave Infrared Pulses via Chirped Optical Parametric Amplification and Indirect Pulse Shaping

PubMed Central

Yin, Yanchun; Chew, Andrew; Ren, Xiaoming; Li, Jie; Wang, Yang; Wu, Yi; Chang, Zenghu

2017-01-01

We present an approach for both efficient generation and amplification of 4–12 μm pulses by tailoring the phase matching of the nonlinear crystal Zinc Germanium Phosphide (ZGP) in a narrowband-pumped optical parametric chirped pulse amplifier (OPCPA) and a broadband-pumped dual-chirped optical parametric amplifier (DC-OPA), respectively. Preliminary experimental results are obtained for generating 1.8–4.2 μm super broadband spectra, which can be used to seed both the signal of the OPCPA and the pump of the DC-OPA. The theoretical pump-to-idler conversion efficiency reaches 27% in the DC-OPA pumped by a chirped broadband Cr2+:ZnSe/ZnS laser, enabling the generation of  Terawatt-level 4–12 μm pulses with an available large-aperture ZGP. Furthermore, the 4–12 μm idler pulses can be compressed to sub-cycle pulses by compensating the tailored positive chirp of the idler pulses using the bulk compressor NaCl, and by indirectly controlling the higher-order idler phase through tuning the signal (2.4–4.0 μm) phase with a commercially available acousto-optic programmable dispersive filter (AOPDF). A similar approach is also described for generating high-energy 4–12 μm sub-cycle pulses via OPCPA pumped by a 2 μm Ho:YLF laser. PMID:28367966

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

Method for generating a plasma wave to accelerate electrons

DOEpatents

Umstadter, D.; Esarey, E.; Kim, J.K.

1997-06-10

The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, with its pulse-shaping subsystem; the electron gun system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode triggering system; the electron diagnostics; and the feedback system between the electron diagnostics and the laser system. The system also includes plasma source including vacuum chamber, magnetic lens, and magnetic field means. The laser system produces a train of pulses that has been optimized to maximize the axial electric field amplitude of the plasma wave, and thus the electron acceleration, using the method of the invention. 21 figs.

Method for generating a plasma wave to accelerate electrons

DOEpatents

Umstadter, Donald; Esarey, Eric; Kim, Joon K.

1997-01-01

The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, with its pulse-shaping subsystem; the electron gun system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode triggering system; the electron diagnostics; and the feedback system between the electron diagnostics and the laser system. The system also includes plasma source including vacuum chamber, magnetic lens, and magnetic field means. The laser system produces a train of pulses that has been optimized to maximize the axial electric field amplitude of the plasma wave, and thus the electron acceleration, using the method of the invention.

Modeling and Numerical Simulation of Microwave Pulse Propagation in Air Breakdown Environment

NASA Technical Reports Server (NTRS)

Kuo, S. P.; Kim, J.

1991-01-01

Numerical simulation is used to investigate the extent of the electron density at a distant altitude location which can be generated by a high-power ground-transmitted microwave pulse. This is done by varying the power, width, shape, and carrier frequency of the pulse. The results show that once the breakdown threshold field is exceeded in the region below the desired altitude location, electron density starts to build up in that region through cascading breakdown. The generated plasma attenuates the pulse energy (tail erosion) and thus deteriorates the energy transmission to the destined altitude. The electron density saturates at a level limited by the pulse width and the tail erosion process. As the pulse continues to travel upward, though the breakdown threshold field of the background air decreases, the pulse energy (width) is reduced more severely by the tail erosion process. Thus, the electron density grows more quickly at the higher altitude, but saturates at a lower level. Consequently, the maximum electron density produced by a single pulse at 50 km altitude, for instance, is limited to a value below 10(exp 6) cm(exp -3). Three different approaches are examined to determine if the ionization at the destined location can be improved: a repetitive pulse approach, a focused pulse approach, and two intersecting beams. Only the intersecting beam approach is found to be practical for generating the desired density level.

Shaped cathodes for the production of ultra-short multi-electron pulses

PubMed Central

Petruk, Ariel Alcides; Pichugin, Kostyantyn; Sciaini, Germán

2017-01-01

An electrostatic electron source design capable of producing sub-20 femtoseconds (rms) multi-electron pulses is presented. The photoelectron gun concept builds upon geometrical electric field enhancement at the cathode surface. Particle tracer simulations indicate the generation of extremely short bunches even beyond 40 cm of propagation. Comparisons with compact electron sources commonly used for femtosecond electron diffraction are made. PMID:28191483

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

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.

Simulation results of Pulse Shape Discrimination (PSD) for background reduction in INTEGRAL Spectrometer (SPI) germanium detectors

NASA Technical Reports Server (NTRS)

Slassi-Sennou, S. A.; Boggs, S. E.; Feffer, P. T.; Lin, R. P.

1997-01-01

Pulse Shape Discrimination (PSD) for background reduction will be used in the INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL) imaging spectrometer (SPI) to improve the sensitivity from 200 keV to 2 MeV. The observation of significant astrophysical gamma ray lines in this energy range is expected, where the dominant component of the background is the beta(sup -) decay in the Ge detectors due to the activation of Ge nuclei by cosmic rays. The sensitivity of the SPI will be improved by rejecting beta(sup -) decay events while retaining photon events. The PSD technique will distinguish between single and multiple site events. Simulation results of PSD for INTEGRAL-type Ge detectors using a numerical model for pulse shape generation are presented. The model was shown to agree with the experimental results for a narrow inner bore closed end cylindrical detector. Using PSD, a sensitivity improvement factor of the order of 2.4 at 0.8 MeV is expected.

Nanoplasmonic generation of ultrashort EUV pulses

NASA Astrophysics Data System (ADS)

Choi, Joonhee; Lee, Dong-Hyub; Han, Seunghwoi; Park, In-Yong; Kim, Seungchul; Kim, Seung-Woo

2012-10-01

Ultrashort extreme-ultraviolet (EUV) light pulses are an important tool for time-resolved pump-probe spectroscopy to investigate the ultrafast dynamics of electrons in atoms and molecules. Among several methods available to generate ultrashort EUV light pulses, the nonlinear frequency upconversion process of high-harmonic generation (HHG) draws attention as it is capable of producing coherent EUV pulses with precise control of burst timing with respect to the driving near-infrared (NIR) femtosecond laser. In this report, we present and discuss our recent experimental data obtained by the plasmon-driven HHG method that generate EUV radiation by means of plasmonic nano-focusing of NIR femtosecond pulses. For experiment, metallic waveguides having a tapered hole of funnel shape inside were fabricated by adopting the focused-ion-beam process on a micro-cantilever substrate. The plasmonic field formed within the funnelwaveguides being coupled with the incident femtosecond pulse permitted intensity enhancement by a factor of ~350, which creates a hot spot of sub-wavelength size with intensities strong enough for HHG. Experimental results showed that with injection of noble gases into the funnel-waveguides, EUV radiation is generated up to wavelengths of 32 nm and 29.6 nm from Ar and Ne gas atoms, respectively. Further, it was observed that lower-order EUV harmonics are cut off in the HHG spectra by the tiny exit aperture of the funnel-waveguide.

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.

Theoretical and Experimental Investigations of Coincidences in Poisson Distributed Pulse Trains and Spectral Distortion Caused by Pulse Pileup.

NASA Astrophysics Data System (ADS)

Bristow, Quentin

1990-01-01

Part one of this two-part study is concerned with the multiple coincidences in pulse trains from X-ray and gamma radiation detectors which are the cause of pulse pileup. A sequence of pulses with inter-arrival times less than tau, the resolving time of the pulse-height analysis system used to acquire spectra, is called a multiple pulse string. Such strings can be classified on the basis of the number of pulses they contain, or the number of resolving times they cover. The occurrence rates of such strings are derived from theoretical considerations. Logic circuits were devised to make experimental measurements of multiple pulse string occurrence rates in the output from a NaI(Tl) scintillation detector over a wide range of count rates. Markov process theory was used to predict state transition rates in the logic circuits, enabling the experimental data to be checked rigorously for conformity with those predicted for a Poisson distribution. No fundamental discrepancies were observed. Part two of the study is concerned with a theoretical analysis of pulse pileup and the development of a discrete correction algorithm, based on the use of a function to simulate the coincidence spectrum produced by partial sums of pulses. Monte Carlo simulations, incorporating criteria for pulse pileup inherent in the operation of modern ADC's, were used to generate pileup spectra due to coincidences between two pulses, (1st order pileup) and three pulses (2nd order pileup), for different semi-Gaussian pulse shapes. Coincidences between pulses in a single channel produced a basic probability density function spectrum which can be regarded as an impulse response for a particular pulse shape. The use of a flat spectrum (identical count rates in all channels) in the simulations, and in a parallel theoretical analysis, showed the 1st order pileup distorted the spectrum to a linear ramp with a pileup tail. The correction algorithm was successfully applied to correct entire spectra for 1st and 2nd order pileup; both those generated by Monte Carlo simulations and in addition some real spectra acquired with a laboratory multichannel analysis system.

Entropy analysis of frequency and shape change in horseshoe bat biosonar

NASA Astrophysics Data System (ADS)

Gupta, Anupam K.; Webster, Dane; Müller, Rolf

2018-06-01

Echolocating bats use ultrasonic pulses to collect information about their environments. Some of this information is encoded at the baffle structures—noseleaves (emission) and pinnae (reception)—that act as interfaces between the bats' biosonar systems and the external world. The baffle beam patterns encode the direction-dependent sensory information as a function of frequency and hence represent a view of the environment. To generate diverse views of the environment, the bats can vary beam patterns by changes to (1) the wavelengths of the pulses or (2) the baffle geometries. Here we compare the variability in sensory information encoded by just the use of frequency or baffle shape dynamics in horseshoe bats. For this, we use digital and physical prototypes of both noseleaf and pinnae. The beam patterns for all prototypes were either measured or numerically predicted. Entropy was used as a measure to compare variability as a measure of sensory information encoding capacity. It was found that new information was acquired as a result of shape dynamics. Furthermore, the overall variability available for information encoding was similar in the case of frequency or shape dynamics. Thus, shape dynamics allows the horseshoe bats to generate diverse views of the environment in the absence of broadband biosonar signals.

Parallel-Processing CMOS Circuitry for M-QAM and 8PSK TCM

NASA Technical Reports Server (NTRS)

Gray, Andrew; Lee, Dennis; Hoy, Scott; Fisher, Dave; Fong, Wai; Ghuman, Parminder

2009-01-01

There has been some additional development of parts reported in "Multi-Modulator for Bandwidth-Efficient Communication" (NPO-40807), NASA Tech Briefs, Vol. 32, No. 6 (June 2009), page 34. The focus was on 1) The generation of M-order quadrature amplitude modulation (M-QAM) and octonary-phase-shift-keying, trellis-coded modulation (8PSK TCM), 2) The use of square-root raised-cosine pulse-shaping filters, 3) A parallel-processing architecture that enables low-speed [complementary metal oxide/semiconductor (CMOS)] circuitry to perform the coding, modulation, and pulse-shaping computations at a high rate; and 4) Implementation of the architecture in a CMOS field-programmable gate array.

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.

High-power femtosecond pulses without a modelocked laser

PubMed Central

Fu, Walter; Wright, Logan G.; Wise, Frank W.

2017-01-01

We demonstrate a fiber system which amplifies and compresses pulses from a gain-switched diode. A Mamyshev regenerator shortens the pulses and improves their coherence, enabling subsequent amplification by parabolic pre-shaping. As a result, we are able to control nonlinear effects and generate nearly transform-limited, 140-fs pulses with 13-MW peak power—an order-of-magnitude improvement over previous gain-switched diode sources. Seeding with a gain-switched diode results in random fluctuations of 2% in the pulse energy, which future work using known techniques may ameliorate. Further development may allow such systems to compete directly with sources based on modelocked oscillators in some applications while enjoying unparalleled robustness and repetition rate control. PMID:29214187

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.

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

Bičiūnas, A.; Arlauskas, A.; Adamonis, J.

We report on terahertz (THz) emission from tellurium crystal surfaces excited by femtosecond optical pulses. Measurements were performed on three differently cut Te samples and with different wavelength optical excitation pulses. THz pulse amplitude dependences on the azimuthal angle measured at various excitation wavelengths have evidenced that three different mechanisms are responsible for THz generation in tellurium: second order nonlinear optical rectification effect, dominating at lower excitation photon energies, as well as transverse and ordinary photo-Dember effects, which emerge at energies larger than 0.9 eV. The shapes of the azimuthal angle dependences were also explained by theoretical model.

Simulating the inception of pulsed discharges near positive electrodes

NASA Astrophysics Data System (ADS)

Teunissen, Jannis; Ebert, Ute

2013-09-01

With 3D particle simulations we study the inception of pulsed discharges near positive electrodes. In different geometries, we first determine the breakdown voltage. Then we study the probability of inception for a fast voltage pulse. This probability mostly depends on the availability of seed electrons to generate the initial electron avalanches. These results are compared with experimental observations. Then we investigate how the shape of a starting discharge affects its further development. In particular, we discuss the formation of so-called ``inception clouds.'' JT was supported by STW-project 10755.

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.

Electronic switching circuit uses complementary non-linear components

NASA Technical Reports Server (NTRS)

Zucker, O. S.

1972-01-01

Inherent switching properties of saturable inductors and storage diodes are combined to perform large variety of electronic functions, such as pulse shaping, gating, and multiplexing. Passive elements replace active switching devices in generation of complex waveforms.

Passive mode-locking of 3.25μm GaSb-based type-I quantum-well cascade diode lasers

NASA Astrophysics Data System (ADS)

Feng, Tao; Shterengas, Leon; Kipshidze, Gela; Hosoda, Takashi; Wang, Meng; Belenky, Gregory

2018-02-01

Passively mode-locked type-I quantum well cascade diode lasers emitting in the methane absorption band near 3.25 μm were designed, fabricated and characterized. The deep etched 5.5-μm-wide single spatial mode ridge waveguide design utilizing split-contact architecture was implemented. The devices with absorber to gain section length ratios of 11% and 5.5% were studied. Lasers with the longer absorber section ( 300 μm) generated smooth bell-shape-like emission spectrum with about 30 lasing modes at full-width-at-half-maximum level. Devices with reverse biased absorber section demonstrated stable radio frequency beat with nearly perfect Lorentzian shape over four orders of magnitude of intensity. The estimated pulse-to-pulse timing jitter was about 110 fs/cycle. Laser generated average power of more than 1 mW in mode-locked regime.

Latest results on solarization of optical glasses with pulsed laser radiation

NASA Astrophysics Data System (ADS)

Jedamzik, Ralf; Petzold, Uwe

2017-02-01

Femtosecond lasers are more and more used for material processing and lithography. Femtosecond laser help to generate three dimensional structures in photoresists without using masks in micro lithography. This technology is of growing importance for the field of backend lithography or advanced packaging. Optical glasses used for beam shaping and inspection tools need to withstand high laser pulse energies. Femtosecond laser radiation in the near UV wavelength range generates solarization effects in optical glasses. In this paper results are shown of femtosecond laser solarization experiments on a broad range of optical glasses from SCHOTT. The measurements have been performed by the Laser Zentrum Hannover in Germany. The results and their impact are discussed in comparison to traditional HOK-4 and UVA-B solarization measurements of the same materials. The target is to provide material selection guidance to the optical designer of beam shaping lens systems.

Strong terahertz emission by optical rectification of shaped laser pulse in transversely magnetized plasma

NASA Astrophysics Data System (ADS)

Singh, Ram Kishor; Singh, Monika; Rajouria, Satish Kumar; Sharma, R. P.

2017-07-01

This communication presents a theoretical model for efficient terahertz (THz) radiation generation by the optical rectification of shaped laser pulse in transversely magnetised ripple density plasma. The laser beam imparts a nonlinear ponderomotive force to the electron and this force exerts a nonlinear velocity component in both transverse and axial directions which have spectral components in the THz range. These velocity components couple with the pre-existing density ripple and give rise to a strong nonlinear current density which drives the THz wave in the plasma. The THz yield increases with the increasing strength of the background magnetic field and the sensitivity depends on the ripple wave number. The emitted power is directly proportional to the square of the amplitude of the density ripple. For exact phase matching condition, the normalised power of the generated THz wave can be achieved of the order of 10-4.

Near-infrared resonance-mediated chirp control of a coherently generated broadband deep-ultraviolet spectrum

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

Rybak, Leonid; Chuntonov, Lev; Gandman, Andrey

2011-09-15

We investigate the use of shaped near-infrared (NIR) femtosecond pulses to control the generation of coherent broadband deep-ultraviolet (DUV) radiation in an atomic resonance-mediated (2+1) three-photon excitation to a broad far-from-resonance continuum. Previously, we have shown control over the total emitted DUV yield. Here, we experimentally demonstrate phase control over the spectral characteristics (central frequency and bandwidth) of the emitted broadband DUV radiation. It is achieved by tuning the linear chirp applied to the exciting NIR femtosecond pulse. The study is conducted with Na vapor.

2 µm high-power dissipative soliton resonance in a compact σ-shaped Tm-doped double-clad fiber laser

NASA Astrophysics Data System (ADS)

Du, Tuanjie; Li, Weiwei; Ruan, Qiujun; Wang, Kaijie; Chen, Nan; Luo, Zhengqian

2018-05-01

We report direct generation of a high-power, large-energy dissipative soliton resonance (DSR) in a 2 µm Tm-doped double-clad fiber laser. A compact σ-shaped cavity is formed by a fiber Bragg grating and a 10/90 fiber loop mirror (FLM). The 10/90 FLM is not only used as an output mirror, but also acts as a nonlinear optical loop mirror for initiating mode locking. The mode-locked laser can deliver high-power, nanosecond DSR pulses at 2005.9 nm. We further perform a comparison study of the effect of the FLM’s loop length on the mode-locking threshold, peak power, pulse energy, and optical spectrum of the DSR pulses. We achieve a maximum average output power as high as 1.4 W, a maximum pulse energy of 353 nJ, and a maximum peak power of 84 W. This is, to the best of our knowledge, the highest power for 2 µm DSR pulses obtained in a mode-locked fiber laser.

Rise time analysis of pulsed klystron-modulator for efficiency improvement of linear colliders

NASA Astrophysics Data System (ADS)

Oh, J. S.; Cho, M. H.; Namkung, W.; Chung, K. H.; Shintake, T.; Matsumoto, H.

2000-04-01

In linear accelerators, the periods during the rise and fall of a klystron-modulator pulse cannot be used to generate RF power. Thus, these periods need to be minimized to get high efficiency, especially in large-scale machines. In this paper, we present a simplified and generalized voltage rise time function of a pulsed modulator with a high-power klystron load using the equivalent circuit analysis method. The optimum pulse waveform is generated when this pulsed power system is tuned with a damping factor of ˜0.85. The normalized rise time chart presented in this paper allows one to predict the rise time and pulse shape of the pulsed power system in general. The results can be summarized as follows: The large distributed capacitance in the pulse tank and operating parameters, Vs× Tp , where Vs is load voltage and Tp is the pulse width, are the main factors determining the pulse rise time in the high-power RF system. With an RF pulse compression scheme, up to ±3% ripple of the modulator voltage is allowed without serious loss of compressor efficiency, which allows the modulator efficiency to be improved as well. The wiring inductance should be minimized to get the fastest rise time.

Shape-retainment control using an antagonistic shape memory alloy system

NASA Astrophysics Data System (ADS)

Ikeda, T.; Sawamura, K.; Senba, A.; Tamayama, M.

2015-04-01

Since shape memory alloy (SMA) actuators can generate large force per unit weight, they are expected as one of the next generation actuators for aircraft. To keep a position of conventional control surfaces or morphing wings with SMA actuators, the SMA actuators must keep being heated, and the heating energy is not small. To save the energy, a new control method proposed for piezoelectric actuators utilizing hysteresis in deformation [Ikeda and Takahashi, Proc. SPIE 8689 (2013), 86890C] is applied to an antagonistic SMA system. By using the control method any position can be an equilibrium point within hysteresis of stress-strain diagrams. To confirm a feasibility of the control method, a fundamental experiment is performed. The SMA wires are heated by applying electric current to the wires. When a pulsed current is applied to the two SMA wires alternately, the equilibrium position changes between two positions alternately, and when a series of pulse whose amplitude increases gradually is applied to one SMA wire, the equilibrium position changes like a staircase. However, just after the pulse the position returns slightly, that is, overshoot takes place. To investigate such a behavior of the system, numerical simulation is also performed. The one-dimensional phase transformation model [Ikeda, Proc. SPIE 5757 (2005), 344-352] is used for a constitutive model of the SMA wires. The simulated result agrees with the experiment qualitatively, including the overshoot. By examining volume fraction of each phase, it is found that the overshoot is caused by that austenite phase transforms into stress-induced martensite phase during the cooling process after the pulse.

Calculation of craters resulting from impact rupture of rock mass using pulse hydrodynamic problem formulation

NASA Astrophysics Data System (ADS)

Gorodilov, LV; Rasputina, TB

2018-03-01

A liquid–solid hydrodynamic model is used to determine shapes and sizes of craters generated by impact rupture of rocks. Near the impact location, rock is modeled by an ideal incompressible liquid, in the distance—by an absolute solid. The calculated data are compared with the experimental results obtained under impact treatment of marble by a wedge-shaped tool.

Nanosecond pulsed laser generation of holographic structures on metals

NASA Astrophysics Data System (ADS)

Wlodarczyk, Krystian L.; Ardron, Marcus; Weston, Nick J.; Hand, Duncan P.

2016-03-01

A laser-based process for the generation of phase holographic structures directly onto the surface of metals is presented. This process uses 35ns long laser pulses of wavelength 355nm to generate optically-smooth surface deformations on a metal. The laser-induced surface deformations (LISDs) are produced by either localized laser melting or the combination of melting and evaporation. The geometry (shape and dimension) of the LISDs depends on the laser processing parameters, in particular the pulse energy, as well as on the chemical composition of a metal. In this paper, we explain the mechanism of the LISDs formation on various metals, such as stainless steel, pure nickel and nickel-chromium Inconel® alloys. In addition, we provide information about the design and fabrication process of the phase holographic structures and demonstrate their use as robust markings for the identification and traceability of high value metal goods.

Methods and apparatuses using filter banks for multi-carrier spread-spectrum signals

DOEpatents

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A

2014-10-14

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to the synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.

Methods and apparatuses using filter banks for multi-carrier spread-spectrum signals

DOEpatents

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A

2014-05-20

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to the synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.

Single-molecule photon emission statistics for systems with explicit time dependence: Generating function approach

NASA Astrophysics Data System (ADS)

Peng, Yonggang; Xie, Shijie; Zheng, Yujun; Brown, Frank L. H.

2009-12-01

Generating function calculations are extended to allow for laser pulse envelopes of arbitrary shape in numerical applications. We investigate photon emission statistics for two-level and V- and Λ-type three-level systems under time-dependent excitation. Applications relevant to electromagnetically induced transparency and photon emission from single quantum dots are presented.

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

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.

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.

Generation of High-Power High-Intensity Short X-Ray Free-Electron-Laser Pulses

DOE PAGES

Guetg, Marc W.; Lutman, Alberto A.; Ding, Yuantao; ...

2018-01-03

X-ray free-electron lasers combine a high pulse power, short pulse length, narrow bandwidth, and high degree of transverse coherence. Any increase in the photon pulse power, while shortening the pulse length, will further push the frontier on several key x-ray free-electron laser applications including single-molecule imaging and novel nonlinear x-ray methods. This Letter shows experimental results at the Linac Coherent Light Source raising its maximum power to more than 300% of the current limit while reducing the photon pulse length to 10 fs. As a result, this was achieved by minimizing residual transverse-longitudinal centroid beam offsets and beam yaw andmore » by correcting the dispersion when operating over 6 kA peak current with a longitudinally shaped beam.« less

Generation of High-Power High-Intensity Short X-Ray Free-Electron-Laser Pulses

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

Guetg, Marc W.; Lutman, Alberto A.; Ding, Yuantao

X-ray free-electron lasers combine a high pulse power, short pulse length, narrow bandwidth, and high degree of transverse coherence. Any increase in the photon pulse power, while shortening the pulse length, will further push the frontier on several key x-ray free-electron laser applications including single-molecule imaging and novel nonlinear x-ray methods. This Letter shows experimental results at the Linac Coherent Light Source raising its maximum power to more than 300% of the current limit while reducing the photon pulse length to 10 fs. As a result, this was achieved by minimizing residual transverse-longitudinal centroid beam offsets and beam yaw andmore » by correcting the dispersion when operating over 6 kA peak current with a longitudinally shaped beam.« less

Sodium inversion recovery MRI on the knee joint at 7 T with an optimal control pulse.

PubMed

Lee, Jae-Seung; Xia, Ding; Madelin, Guillaume; Regatte, Ravinder R

2016-01-01

In the field of sodium magnetic resonance imaging (MRI), inversion recovery (IR) is a convenient and popular method to select sodium in different environments. For the knee joint, IR has been used to suppress the signal from synovial fluids, which improves the correlation between the sodium signal and the concentration of glycosaminoglycans (GAGs) in cartilage tissues. For the better inversion of the magnetization vector under the spatial variations of the B0 and B1 fields, the IR sequence usually employ adiabatic pulses as the inversion pulse. On the other hand, it has been shown that RF shapes robust against the variations of the B0 and B1 fields can be generated by numerical optimization based on optimal control theory. In this work, we compare the performance of fluid-suppressed sodium MRI on the knee joint in vivo, between one implemented with an adiabatic pulse in the IR sequence and the other with the adiabatic pulse replaced by an optimal-control shaped pulse. While the optimal-control pulse reduces the RF power deposited to the body by 58%, the quality of fluid suppression and the signal level of sodium within cartilage are similar between two implementations. Copyright © 2015 Elsevier Inc. All rights reserved.

Method and apparatus for providing pulse pile-up correction in charge quantizing radiation detection systems

DOEpatents

Britton, Jr., Charles L.; Wintenberg, Alan L.

1993-01-01

A radiation detection method and system for continuously correcting the quantization of detected charge during pulse pile-up conditions. Charge pulses from a radiation detector responsive to the energy of detected radiation events are converted to voltage pulses of predetermined shape whose peak amplitudes are proportional to the quantity of charge of each corresponding detected event by means of a charge-sensitive preamplifier. These peak amplitudes are sampled and stored sequentially in accordance with their respective times of occurrence. Based on the stored peak amplitudes and times of occurrence, a correction factor is generated which represents the fraction of a previous pulses influence on a preceding pulse peak amplitude. This correction factor is subtracted from the following pulse amplitude in a summing amplifier whose output then represents the corrected charge quantity measurement.

Investigation of the morphology of the features generated via femtosecond lasers in the interior of a bovine cornea sections

NASA Astrophysics Data System (ADS)

Vukelic, Sinisa; Kongsuwan, Panjawat; Yao, Y. Lawrence

2013-02-01

Nonlinear absorption of femtosecond laser pulses enables the induction of bubble cavities in the interior of eye cornea without affecting other parts of an eye, a phenomena utilized for flap formation in laser assisted corneal surgery. In the present study laser pulses were focused in the interior of the sections of bovine cornea. Tight focus of the laser pulses results in the plasma formation followed by its explosive expansion, which drives cavity formation. The morphology of the generated features as well as the nature of the physical mechanisms of the phenomenon as a function of process parameters is discussed. Numerical model is proposed to develop predictive capabilities for the feature size and shape and the results are compared against the experimental findings.

Femtosecond noncollinear SFG dynamics in autocorrelator setup at low level of photons

NASA Astrophysics Data System (ADS)

Tenishev, Vladimir P.; Persson, A.; Larsson, J.

2004-06-01

We report here the characteristics of noncollinear sum frequency generation in nonlinear KDP crystals by ultrashort (80 fsec) IR pulses irradiated by the intense Ti:Sapphire laser and their behavior in single shot auto-crosscorrelator (ACC) configuration. In particular we study the case where one of the beams is very weak. Our aim is to develop a procedure to provide delay time signal between light pulses for time resolved pump probe experiments based on the extraction of the phase-matched SHG spatial distribution by means of pulse shape analysis technique. We intend to apply these results to synchronize a weak short-pulse source and an intense Ti:Sapphire laser and to measure the pulse time jitter between them.

Remote photoacoustic detection of liquid contamination of a surface.

PubMed

Perrett, Brian; Harris, Michael; Pearson, Guy N; Willetts, David V; Pitter, Mark C

2003-08-20

A method for the remote detection and identification of liquid chemicals at ranges of tens of meters is presented. The technique uses pulsed indirect photoacoustic spectroscopy in the 10-microm wavelength region. Enhanced sensitivity is brought about by three main system developments: (1) increased laser-pulse energy (150 microJ/pulse), leading to increased strength of the generated photoacoustic signal; (2) increased microphone sensitivity and improved directionality by the use of a 60-cm-diameter parabolic dish; and (3) signal processing that allows improved discrimination of the signal from noise levels through prior knowledge of the pulse shape and pulse-repetition frequency. The practical aspects of applying the technique in a field environment are briefly examined, and possible applications of this technique are discussed.

Arbitrary temporal shape pulsed fiber laser based on SPGD algorithm

NASA Astrophysics Data System (ADS)

Jiang, Min; Su, Rongtao; Zhang, Pengfei; Zhou, Pu

2018-06-01

A novel adaptive pulse shaping method for a pulsed master oscillator power amplifier fiber laser to deliver an arbitrary pulse shape is demonstrated. Numerical simulation has been performed to validate the feasibility of the scheme and provide meaningful guidance for the design of the algorithm control parameters. In the proof-of-concept experiment, information on the temporal property of the laser is exchanged and evaluated through a local area network, and the laser adjusted the parameters of the seed laser according to the monitored output of the system automatically. Various pulse shapes, including a rectangular shape, ‘M’ shape, and elliptical shape are achieved through experimental iterations.

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.

Giant pulses of the Crab Nebula pulsar as an indicator of a strong electromagnetic wave

NASA Astrophysics Data System (ADS)

Popov, M. V.; Rudnitskii, A. G.; Soglasnov, V. A.

2017-03-01

The spectra and visibility functions of giant pulses of the Crab Nebula pulsar derived from VLBI observations carried out through the "RadioAstron" project in 2015 are analyzed. Parameters of the scattering of the pulses in the interstellar medium are measured, namely, the scattering time and decorrelation bandwidth. A comparative analysis of the shapes of the spectra and visibility functions of giant pulses obtained in real observations and via modeling of their scattering is carried out. The results suggest the presence of short bursts ( dt < 30 ns) in the structure of the giant pulses at 1668 MHz, whose brightness temperatures exceed 1038 K. These pulses propagate in the pulsar magnetosphere in a strong electromagneticwave regime, leading to the generation of additional radiation perpendicular to the direction of propagation of the giant pulses. This radiation may be associated with anomalous components of the mean pulse profile observed at frequencies above 4 GHz.

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.

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.

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

Plasma x-ray radiation source.

PubMed

Popkov, N F; Kargin, V I; Ryaslov, E A; Pikar', A S

1995-01-01

This paper gives the results of studies on a plasma x-ray source, which enables one to obtain a 2.5-krad radiation dose per pulse over an area of 100 cm2 in the quantum energy range from 20 to 500 keV. Pulse duration is 100 ns. Spectral radiation distributions from a diode under various operation conditions of a plasma are obtained. A Marx generator served as an initial energy source of 120 kJ with a discharge time of T/4 = 10-6 s. A short electromagnetic pulse (10-7 s) was shaped using plasma erosion opening switches.

Improved sensitivity for W-band Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements with shaped pulses

NASA Astrophysics Data System (ADS)

Bahrenberg, Thorsten; Rosenski, Yael; Carmieli, Raanan; Zibzener, Koby; Qi, Mian; Frydman, Veronica; Godt, Adelheid; Goldfarb, Daniella; Feintuch, Akiva

2017-10-01

Chirp and shaped pulses have been recently shown to be highly advantageous for improving sensitivity in DEER (double electron-electron resonance, also called PELDOR) measurements due to their large excitation bandwidth. The implementation of such pulses for pulse EPR has become feasible due to the availability of arbitrary waveform generators (AWG) with high sampling rates to support pulse shaping for pulses with tens of nanoseconds duration. Here we present a setup for obtaining chirp pulses on our home-built W-band (95 GHz) spectrometer and demonstrate its performance on Gd(III)-Gd(III) and nitroxide-nitroxide DEER measurements. We carried out an extensive optimization procedure on two model systems, Gd(III)-PyMTA-spacer-Gd(III)-PyMTA (Gd-PyMTA ruler; zero-field splitting parameter (ZFS) D ∼ 1150 MHz) as well as nitroxide-spacer-nitroxide (nitroxide ruler) to evaluate the applicability of shaped pulses to Gd(III) complexes and nitroxides, which are two important classes of spin labels used in modern DEER/EPR experiments. We applied our findings to ubiquitin, doubly labeled with Gd-DOTA-monoamide (D ∼ 550 MHz) as a model for a system with a small ZFS. Our experiments were focused on the questions (i) what are the best conditions for positioning of the detection frequency, (ii) which pump pulse parameters (bandwidth, positioning in the spectrum, length) yield the best signal-to-noise ratio (SNR) improvements when compared to classical DEER, and (iii) how do the sample's spectral parameters influence the experiment. For the nitroxide ruler, we report an improvement of up to 1.9 in total SNR, while for the Gd-PyMTA ruler the improvement was 3.1-3.4 and for Gd-DOTA-monoamide labeled ubiquitin it was a factor of 1.8. Whereas for the Gd-PyMTA ruler the two setups pump on maximum and observe on maximum gave about the same improvement, for Gd-DOTA-monoamide a significant difference was found. In general the choice of the best set of parameters depends on the D parameter of the Gd(III) complex.

Reconfigurable optofluidic switch for generation of optical pulse width modulation based on tunable reflective interface.

PubMed

Mansuori, M; Zareei, G H; Hashemi, H

2015-10-01

We present a numerical method for generation of optical pulse width modulation (PWM) based on tunable reflective interface by using a microfluidic droplet. We demonstrate a single layer, planar, optofluidic PWM switch that is driven by excited alternating microbubbles. The main parameters of generation of this PWM such as frequency and speed of switching can be controlled by the mass flow rates of input fluids, and the shape of plug or droplet. Advantages of this design are the reconfigurability in design and the easy control of the switching parameters. The validation of the proposed design is carried out by employing the finite element method (FEM) for the mechanical simulation and the finite-difference time-domain (FDTD) for the optical simulation.

High performance mode locking characteristics of single section quantum dash lasers.

PubMed

Rosales, Ricardo; Murdoch, S G; Watts, R T; Merghem, K; Martinez, Anthony; Lelarge, Francois; Accard, Alain; Barry, L P; Ramdane, Abderrahim

2012-04-09

Mode locking features of single section quantum dash based lasers are investigated. Particular interest is given to the static spectral phase profile determining the shape of the mode locked pulses. The phase profile dependence on cavity length and injection current is experimentally evaluated, demonstrating the possibility of efficiently using the wide spectral bandwidth exhibited by these quantum dash structures for the generation of high peak power sub-picosecond pulses with low radio frequency linewidths.

A Novel Transcranial Magnetic Stimulator Inducing Near Rectangular Pulses with Controllable Pulse Width (cTMS)

PubMed Central

Jalinous, Reza; Lisanby, Sarah H.

2013-01-01

A novel transcranial magnetic stimulation (TMS) device with controllable pulse width (PW) and near rectangular pulse shape (cTMS) is described. The cTMS device uses an insulated gate bipolar transistor (IGBT) with appropriate snubbers to switch coil currents up to 7 kA, enabling PW control from 5 μs to over 100 μs. The near-rectangular induced electric field pulses use 22–34% less energy and generate 67–72% less coil heating compared to matched conventional cosine pulses. CTMS is used to stimulate rhesus monkey motor cortex in vivo with PWs of 20 to 100 μs, demonstrating the expected decrease of threshold pulse amplitude with increasing PW. The technological solutions used in the cTMS prototype can expand functionality, and reduce power consumption and coil heating in TMS, enhancing its research and therapeutic applications. PMID:18232369

Subpicosecond thin-disk laser oscillator with pulse energies of up to 25.9 microjoules by use of an active multipass geometry.

PubMed

Neuhaus, Joerg; Bauer, Dominik; Zhang, Jing; Killi, Alexander; Kleinbauer, Jochen; Kumkar, Malte; Weiler, Sascha; Guina, Mircea; Sutter, Dirk H; Dekorsy, Thomas

2008-12-08

The pulse shaping dynamics of a diode-pumped laser oscillator with active multipass cell was studied experimentally and numerically. We demonstrate the generation of high energy subpicosecond pulses with a pulse energy of up to 25.9 microJ at a pulse duration of 928 fs directly from a thin-disk laser oscillator. These results are achieved by employing a selfimaging active multipass geometry operated in ambient atmosphere. Stable single pulse operation has been obtained with an average output power in excess of 76 W and at a repetition rate of 2.93 MHz. Self starting passive mode locking was accomplished using a semiconductor saturable absorber mirror. The experimental results are compared with numerical simulations, showing good agreement including the appearance of Kelly sidebands. Furthermore, a modified soliton-area theorem for approximating the pulse duration is presented. (c) 2008 Optical Society of America

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.

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

Ramp compression of a metallic liner driven by a shaped 5 MA current on the SPHINX machine

NASA Astrophysics Data System (ADS)

D'Almeida, Thierry; Lassalle, Francis; Morell, Alain; Grunenwald, Julien; Zucchini, Frédéric; Loyen, Arnaud; Maysonnave, Thomas; Chuvatin, Alexandre

2013-06-01

SPHINX is a 6MA, 1- μs Linear Transformer Driver operated by the CEA Gramat (France) and primarily used for imploding Z-pinch loads for radiation effects studies. Among the options that are currently being considered for improving the generator performances, there is a compact Dynamic Load Current Amplifier (DLCM). A method for performing magnetic ramp compression experiments, without modifying the generator operation scheme, was developed using the DLCM to shape the initial current pulse. We present the overall experimental configuration chosen for these experiments, based on electrical and hydrodynamic simulations. Initial results obtained over a set of experiments on an aluminum cylindrical liner, ramp-compressed to a peak pressure of 23 GPa, are presented. Details of the electrical and Photonic Doppler Velocimetry (PDV) setups used to monitor and diagnose the ramp compression experiments are provided. Current profiles measured at various locations across the system, particularly the load current, agree with simulated current profile and demonstrate adequate pulse shaping by the DLCM. The liner inner free surface velocity measurements agree with the hydrocode results obtained using the measured load current as the input. Higher ramp pressure levels are foreseen in future experiments with an improved DLCM system.

Detection of pulsed neutrons with solid-state electronics

NASA Astrophysics Data System (ADS)

Chatzakis, J.; Rigakis, I.; Hassan, S. M.; Clark, E. L.; Lee, P.

2016-09-01

Measurements of the spatial and time-resolved characteristics of pulsed neutron sources require large area detection materials and fast circuitry that can process the electronic pulses readout from the active region of the detector. In this paper, we present a solid-state detector based on the nuclear activation of materials by neutrons, and the detection of the secondary particle emission of the generated radionuclides’ decay. The detector utilizes a microcontroller that communicates using a modified SPI protocol. A solid-state, pulse shaping filter follows a charge amplifier, and it is designed as an inexpensive, low-noise solution for measuring pulses measured by a digital counter. An imaging detector can also be made by using an array of these detectors. The system can communicate with an interface unit and pass an image to a personal computer.

Main drive optimization of a high-foot pulse shape in inertial confinement fusion implosions

NASA Astrophysics Data System (ADS)

Wang, L. F.; Ye, W. H.; Wu, J. F.; Liu, Jie; Zhang, W. Y.; He, X. T.

2016-12-01

While progress towards hot-spot ignition has been made achieving an alpha-heating dominated state in high-foot implosion experiments [Hurricane et al., Nat. Phys. 12, 800 (2016)] on the National Ignition Facility, improvements are needed to increase the fuel compression for the enhancement of the neutron yield. A strategy is proposed to improve the fuel compression through the recompression of a shock/compression wave generated by the end of the main drive portion of a high-foot pulse shape. Two methods for the peak pulse recompression, namely, the decompression-and-recompression (DR) and simple recompression schemes, are investigated and compared. Radiation hydrodynamic simulations confirm that the peak pulse recompression can clearly improve fuel compression without significantly compromising the implosion stability. In particular, when the convergent DR shock is tuned to encounter the divergent shock from the capsule center at a suitable position, not only the neutron yield but also the stability of stagnating hot-spot can be noticeably improved, compared to the conventional high-foot implosions [Hurricane et al., Phys. Plasmas 21, 056314 (2014)].

Design of compact piezoelectric transducers for shock wave applications

NASA Astrophysics Data System (ADS)

Dreyer, Thomas; Liebler, Marko; Riedlinger, Rainer E.; Ginter, Siegfried

2003-10-01

The application of focused intense sound pulses to treat several orthopedic diseases has gained in importance during the past years. Self-focusing piezoelectric transducers known from ESWL are not well suited for this purpose due to their size. Therefore compact transducers have to be designed. This implies an increase of the pressure pulse amplitude generated at the radiating surface. A stacked placement of two piezoelectric layers driven by two high-voltage pulses with an adjustable delay accomplishes this. Several designs are presented here representing transducers of different sizes. In principle piezoelectric transducers have the ability to vary the pressure pulse shape to a wider extent than other shock wave sources. Based on FEM simulations of the transducer the influence of some driving parameters, like a variation of the interpulse delay or shape of the driving voltage, on the resulting focal pressure signal is demonstrated. The results show the feasibility to control some parameters of the signal, for example the peak negative pressure amplitude. This possibility could provide new aspects in basic research as well as in clinical applications.

Endurance Enhancement and High Speed Set/Reset of 50 nm Generation HfO2 Based Resistive Random Access Memory Cell by Intelligent Set/Reset Pulse Shape Optimization and Verify Scheme

NASA Astrophysics Data System (ADS)

Higuchi, Kazuhide; Miyaji, Kousuke; Johguchi, Koh; Takeuchi, Ken

2012-02-01

This paper proposes a verify-programming method for the resistive random access memory (ReRAM) cell which achieves a 50-times higher endurance and a fast set and reset compared with the conventional method. The proposed verify-programming method uses the incremental pulse width with turnback (IPWWT) for the reset and the incremental voltage with turnback (IVWT) for the set. With the combination of IPWWT reset and IVWT set, the endurance-cycle increases from 48 ×103 to 2444 ×103 cycles. Furthermore, the measured data retention-time after 20 ×103 set/reset cycles is estimated to be 10 years. Additionally, the filamentary based physical model is proposed to explain the set/reset failure mechanism with various set/reset pulse shapes. The reset pulse width and set voltage correspond to the width and length of the conductive-filament, respectively. Consequently, since the proposed IPWWT and IVWT recover set and reset failures of ReRAM cells, the endurance-cycles are improved.

Numerical solution of Boltzmann tranport equation for TEA CO 2 laser having nitrogen-lean gas mixtures to predict laser characteristics and gas lifetime

NASA Astrophysics Data System (ADS)

Kumar, Manoj; Khare, Jai; Nath, A. K.

2007-02-01

Selective laser isotope separation by TEA CO 2 laser often needs short tail-free pulses. Using laser mixtures having very little nitrogen almost tail free laser pulses can be generated. The laser pulse characteristics and its gas lifetime is an important issue for long-term laser operation. Boltzmann transport equation is therefore solved numerically for TEA CO 2 laser gas mixtures having very little nitrogen to predict electron energy distribution function (EEDF). The distribution function is used to calculate various excitation and dissociation rate of CO 2 to predict laser pulse characteristics and laser gas lifetime, respectively. Laser rate equations have been solved with the calculated excitation rates for numerically evaluated discharge current and voltage profiles to calculate laser pulse shape. The calculated laser pulse shape and duration are in good agreement with the measured laser characteristics. The gas lifetime is estimated by integrating the equation governing the dissociation of CO 2. An experimental study of gas lifetime was carried out using quadrapole mass analyzer for such mixtures to estimate the O 2 being produced due to dissociation of CO 2 in the pulse discharge. The theoretically calculated O 2 concentration in the laser gas mixture matches with experimentally observed value. In the present TEA CO 2 laser system, for stable discharge the O 2 concentration should be below 0.2%.

Practical application of pulsed "eye-safe" microchip laser to laser rangefinders

NASA Astrophysics Data System (ADS)

Młyńczak, J.; Kopczyński, K.; Mierczyk, Z.; Zygmunt, M.; Natkański, S.; Muzal, M.; Wojtanowski, J.; Kirwil, P.; Jakubaszek, M.; Knysak, P.; Piotrowski, W.; Zarzycka, A.; Gawlikowski, A.

2013-09-01

The paper describes practical application of pulsed microchip laser generating at 1535-nm wavelength to a laser rangefinder. The complete prototype of a laser rangefinder was built and investigated in real environmental conditions. The measured performance of the device is discussed. To build the prototype of a laser rangefinder at a reasonable price and shape a number of basic considerations had to be done. These include the mechanical and optical design of a microchip laser and the opto-mechanical construction of the rangefinder.

Tunable Broadband Radiation Generated Via Ultrafast Laser Illumination of an Inductively Charged Superconducting Ring

PubMed Central

Bulmer, John; Bullard, Thomas; Dolasinski, Brian; Murphy, John; Sparkes, Martin; Pangovski, Krste; O’Neill, William; Powers, Peter; Haugan, Timothy

2015-01-01

An electromagnetic transmitter typically consists of individual components such as a waveguide, antenna, power supply, and an oscillator. In this communication we circumvent complications associated with connecting these individual components and instead combine them into a non-traditional, photonic enabled, compact transmitter device for tunable, ultrawide band (UWB) radiation. This device is a centimeter scale, continuous, thin film superconducting ring supporting a persistent super-current. An ultrafast laser pulse (required) illuminates the ring (either at a point or uniformly around the ring) and perturbs the super-current by the de-pairing and recombination of Cooper pairs. This generates a microwave pulse where both ring and laser pulse geometry dictates the radiated spectrum’s shape. The transmitting device is self contained and completely isolated from conductive components that are observed to interfere with the generated signal. A rich spectrum is observed that extends beyond 30 GHz (equipment limited) and illustrates the complex super-current dynamics bridging optical, THz, and microwave wavelengths. PMID:26659022

Methods and apparatuses using filter banks for multi-carrier spread spectrum signals

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

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A

2017-01-31

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to themore » synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.« less

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%).

Methods and apparatuses using filter banks for multi-carrier spread spectrum signals

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

Moradi, Hussein; Farhang, Behrouz; Kutsche, Carl A.

2016-06-14

A transmitter includes a synthesis filter bank to spread a data symbol to a plurality of frequencies by encoding the data symbol on each frequency, apply a common pulse-shaping filter, and apply gains to the frequencies such that a power level of each frequency is less than a noise level of other communication signals within the spectrum. Each frequency is modulated onto a different evenly spaced subcarrier. A demodulator in a receiver converts a radio frequency input to a spread-spectrum signal in a baseband. A matched filter filters the spread-spectrum signal with a common filter having characteristics matched to themore » synthesis filter bank in the transmitter by filtering each frequency to generate a sequence of narrow pulses. A carrier recovery unit generates control signals responsive to the sequence of narrow pulses suitable for generating a phase-locked loop between the demodulator, the matched filter, and the carrier recovery unit.« less

Scalable patterning using laser-induced shock waves

NASA Astrophysics Data System (ADS)

Ilhom, Saidjafarzoda; Kholikov, Khomidkhodza; Li, Peizhen; Ottman, Claire; Sanford, Dylan; Thomas, Zachary; San, Omer; Karaca, Haluk E.; Er, Ali O.

2018-04-01

An advanced direct imprinting method with low cost, quick, and minimal environmental impact to create a thermally controllable surface pattern using the laser pulses is reported. Patterned microindents were generated on Ni50Ti50 shape memory alloys and aluminum using an Nd: YAG laser operating at 1064 nm combined with a suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities, which generate pressure pulses up to a few GPa on the surface, were focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the surface. Scanning electron microscope and optical microscope images show that various patterns were obtained on the surface with high fidelity. One-dimensional profile analysis indicates that the depth of the patterned sample initially increases with the laser energy and later levels off. Our simulations of laser irradiation process also confirm that high temperature and high pressure could be generated when the laser energy density of 2 J/cm2 is used.

Generation of attosecond electron beams in relativistic ionization by short laser pulses

NASA Astrophysics Data System (ADS)

Cajiao Vélez, F.; Kamiński, J. Z.; Krajewska, K.

2018-03-01

Ionization by relativistically intense short laser pulses is studied in the framework of strong-field quantum electrodynamics. Distinctive patterns are found in the energy probability distributions of photoelectrons, which are sensitive to the properties of a driving laser field. It is demonstrated that these electrons are generated in the form of solitary attosecond wave packets. This is particularly important in light of various applications of attosecond electron beams such as in ultrafast electron diffraction and crystallography, or in time-resolved electron microscopy of physical, chemical, and biological processes. We also show that, for intense laser pulses, high-energy ionization takes place in narrow regions surrounding the momentum spiral, the exact form of which is determined by the shape of a driving pulse. The self-intersections of the spiral define the momenta for which the interference patterns in the energy distributions of photoelectrons are observed. Furthermore, these interference regions lead to the synthesis of single-electron wave packets characterized by coherent double-hump structures.

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).

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.

Manipulation of group-velocity-locked vector dissipative solitons and properties of the generated high-order vector soliton structure.

PubMed

Zhu, S N; Wu, Z C; Fu, S N; Zhao, L M

2018-03-20

Details of various composites of the projections originated from a fundamental group-velocity-locked vector dissipative soliton (GVLVDS) are both experimentally and numerically explored. By combining the projections from the orthogonal polarization components of the GVLVDS, a high-order vector soliton structure with a double-humped pulse profile along one polarization and a single-humped pulse profile along the orthogonal polarization can be observed. Moreover, by de-chirping the composite double-humped pulse, the time separation between the two humps is reduced from 15.36 ps to 1.28 ps, indicating that the frequency chirp of the GVLVDS contributes significantly to the shaping of the double-humped pulse profile.

Pulsed welding plasma source

NASA Astrophysics Data System (ADS)

Knyaz'kov, A.; Pustovykh, O.; Verevkin, A.; Terekhin, V.; Shachek, A.; Tyasto, A.

2016-04-01

It is shown that in order to form the current pulse of a near rectangular shape, which provides conversion of the welding arc into a dynamic mode, it is rational to connect a forming element made on the basis of an artificial forming line in series to the welding DC circuit. The paper presents a diagram of a pulsed device for welding with a non-consumable electrode in argon which was developed using the forming element. The conversion of the arc into the dynamic mode is illustrated by the current and voltage oscillograms of the arc gap and the dynamic characteristic of the arc within the interval of one pulse generation time in the arc gap. The background current travels in the interpulse interval.

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.

Ultrashort polarization-tailored bichromatic fields from a CEP-stable white light supercontinuum.

PubMed

Kerbstadt, Stefanie; Timmer, Daniel; Englert, Lars; Bayer, Tim; Wollenhaupt, Matthias

2017-05-29

We apply ultrafast polarization shaping to an ultrabroadband carrier envelope phase (CEP) stable white light supercontinuum to generate polarization-tailored bichromatic laser fields of low-order frequency ratio. The generation of orthogonal linearly and counter-rotating circularly polarized bichromatic fields is achieved by introducing a composite polarizer in the Fourier plane of a 4 f polarization shaper. The resulting Lissajous- and propeller-type polarization profiles are characterized experimentally by cross-correlation trajectories. The scheme provides full control over all bichromatic parameters and allows for individual spectral phase modulation of both colors. Shaper-based CEP control and the generation of tailored bichromatic fields is demonstrated. These bichromatic CEP-stable polarization-shaped ultrashort laser pulses provide a versatile class of waveforms for coherent control experiments.

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.

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.

Ultrashort polarization-tailored bichromatic fields

NASA Astrophysics Data System (ADS)

Kerbstadt, Stefanie; Englert, Lars; Bayer, Tim; Wollenhaupt, Matthias

2017-06-01

We present a novel concept for the generation of ultrashort polarization-shaped bichromatic laser fields. The scheme utilizes a 4f polarization pulse shaper based on a liquid crystal spatial light modulator for independent amplitude and phase modulation of femtosecond laser pulses. By choice of either a conventional (p) or a composite (p-s) polarizer in the Fourier plane, the shaper setup enables the generation of parallel linearly and orthogonal linearly polarized bichromatic fields. Additional use of a ? wave plate behind the setup yields co-rotating and counter-rotating circularly polarized bichromatic fields. The scheme allows to independently control the spectral amplitude, phase and polarization profile of the output fields, offering an enormous versatility of bichromatic waveforms.

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.

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.

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.

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.

Compact 1 mJ fiber MOPA for space-based laser-ablation resonant ionization mass spectrometry (LARIMS)

NASA Astrophysics Data System (ADS)

Mu, Xiaodong; Crain, William; Nguyen, Can; Ionov, Pavel; Steinvurzel, Paul; Dotan, Yaniv; Karuza, Petras; Lotshaw, William; Rose, Todd; Beck, Steven; Anderson, F. Scott

2018-02-01

A 1064 nm, 1 mJ pulsed fiber MOPA module, housed in 16"x14"x2.5" package for application in a lunar and planetary in-situ surface dating instrument is demonstrated. The module is based on a three-stage MOPA with a 60 μm core tapered fiber terminal amplifier. The master oscillator and first two preamplifier stages, which generate 20 μJ pulses, are all contained on a 13"x11"x1" board. Several improvements to the electronic signal control were instrumental to the laser development, including bipolar drive of the phase modulator for SBS suppression, shaping of the seed pulse to compensate pulse steepening, and pulsed operation of the power amplifier pump to reduce spontaneous emission at low pulse repetition frequency. The packaged laser runs at a repetition rate of 10 kHz and generates 10 ns pulses at 1 mJ with a 40 GHz linewidth, an M2 1.2 beam quality, and an 18 dB polarization extinction ratio. The modular design enables seven independent lasers to be stacked in a 20"x18"x16.25" enclosure, supporting a path towards a fiber laser based LARIMS for advanced materials characterization and chronological dating in harsh and remote environments.

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

Multi-Modulator for Bandwidth-Efficient Communication

NASA Technical Reports Server (NTRS)

Gray, Andrew; Lee, Dennis; Lay, Norman; Cheetham, Craig; Fong, Wai; Yeh, Pen-Shu; King, Robin; Ghuman, Parminder; Hoy, Scott; Fisher, Dave

2009-01-01

A modulator circuit board has recently been developed to be used in conjunction with a vector modulator to generate any of a large number of modulations for bandwidth-efficient radio transmission of digital data signals at rates than can exceed 100 Mb/s. The modulations include quadrature phaseshift keying (QPSK), offset quadrature phase-shift keying (OQPSK), Gaussian minimum-shift keying (GMSK), and octonary phase-shift keying (8PSK) with square-root raised-cosine pulse shaping. The figure is a greatly simplified block diagram showing the relationship between the modulator board and the rest of the transmitter. The role of the modulator board is to encode the incoming data stream and to shape the resulting pulses, which are fed as inputs to the vector modulator. The combination of encoding and pulse shaping in a given application is chosen to maximize the bandwidth efficiency. The modulator board includes gallium arsenide serial-to-parallel converters at its input end. A complementary metal oxide/semiconductor (CMOS) field-programmable gate array (FPGA) performs the coding and modulation computations and utilizes parallel processing in doing so. The results of the parallel computation are combined and converted to pulse waveforms by use of gallium arsenide parallel-to-serial converters integrated with digital-to-analog converters. Without changing the hardware, one can configure the modulator to produce any of the designed combinations of coding and modulation by loading the appropriate bit configuration file into the FPGA.

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.

Numerical investigation of the effect of driving voltage pulse shapes on the characteristics of low-pressure argon dielectric barrier discharge

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

Eslami, E., E-mail: eeslami@iust.ac.ir; Barjasteh, A.; Morshedian, N.

2015-06-15

In this work, we numerically compare the effect of a sinusoidal, triangular, and rectangular pulsed voltage profile on the calculated particle production, electric current, and gas voltage in a dielectric barrier discharge. The total argon gas pressure of 400 Pa, the distance between dielectrics of 5 mm, the dielectric thickness of 0.7 mm, and the temperature of T = 300 K were considered as input parameters. The different driving voltage pulse shapes (triangular, rectangular, and sinusoidal) are considered as applied voltage with a frequency of 7 kHz and an amplitude of 700 V peak to peak. It is shown thatmore » applying a rectangular voltage, as compared with a sinusoidal or triangle voltage, increases the current peak, while the peak width is decreased. Higher current density is related to high production of charged particles, which leads to the generation of some highly active species, such as Ar* (4s level), and Ar** (4p level) in the gap.« less

Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers

NASA Astrophysics Data System (ADS)

Liu, Junhai; Wang, Lisha; Han, Wenjuan; Xu, Honghao; Zhong, Degao; Teng, Bing

2016-10-01

It is demonstrated that plate-shaped crystals of Yb:LuPO4, which are grown from spontaneous nucleation by high-temperature solution method, can be utilized to make microchip lasers operating in continuous-wave (CW) or passively Q-switched mode. Efficient operation of such a microchip laser, which is built with a 0.3 mm thick crystal plate in a 2 mm long plane-parallel cavity, is realized at room temperature. With 2.37 W of pump power absorbed, 1.45 W of CW output power is generated with a slope efficiency of 73%. When passively Q-switched with a Cr4+:YAG crystal plate as saturable absorber, the laser produces a maximum pulsed output power of 0.53 W at 1013.3 nm, at a pulse repetition rate of 23.8 kHz, the resulting pulse energy, duration, and peak power are 22.3 μJ, 4.0 ns, and 5.6 kW, respectively.

Pulse-shape discrimination of the new plastic scintillators in neutron-gamma mixed field using fast digitizer card

NASA Astrophysics Data System (ADS)

Jančář, A.; Kopecký, Z.; Dressler, J.; Veškrna, M.; Matěj, Z.; Granja, C.; Solar, M.

2015-11-01

Recently invented plastic scintillator EJ-299-33 enables pulse-shape discrimination (PSD) and thus measurement of neutron and photon spectra in mixed fields. In this work we compare the PSD properties of EJ-299-33 plastic and the well-known NE-213 liquid scintillator in monoenergetic neutron fields generated by the Van de Graaff accelerator using the 3H(d, n)4He reaction. Pulses from the scintillators are processed by a newly developed digital measuring system employing the fast digitizer card. This card contains two AD converters connected to the measuring computer via 10 Gbps optical ethernet. The converters operate with a resolution of 12 bits and have two differential inputs with a sampling frequency 1 GHz. The resulting digital channels with different gains are merged into one composite channel with a higher digital resolution in a wide dynamic range of energies. Neutron signals are fully discriminated from gamma signals. Results are presented.

Dynamic optical arbitrary waveform shaping based on cascaded optical modulators of single FBG.

PubMed

Chen, Jingyuan; Li, Peili

2015-08-10

A dynamic optical arbitrary waveform generation (O-AWG) with amplitude and phase independently controlled in optical modulators of single fiber Bragg Grating (FBG) has been proposed. This novel scheme consists of several optical modulators. In the optical modulator (O-MOD), a uniform FBG is used to filter spectral component of the input signal. The amplitude is controlled by fiber stretcher (FS) in Mach-Zehnder interference (MZI) structure through interference of two MZI arms. The phase is manipulated via the second FS in the optical modulator. This scheme is investigated by simulation. Consequently, optical pulse trains with different waveforms as well as pulse trains with nonuniform pulse intensity, pulse spacing and pulse width within each period are obtained through FSs adjustment to alter the phase shifts of signal in each O-MOD.

GigaGauss solenoidal magnetic field inside bubbles excited in under-dense plasma

PubMed Central

Lécz, Zs.; Konoplev, I. V.; Seryi, A.; Andreev, A.

2016-01-01

This paper proposes a novel and effective method for generating GigaGauss level, solenoidal quasi-static magnetic fields in under-dense plasma using screw-shaped high intensity laser pulses. This method produces large solenoidal fields that move with the driving laser pulse and are collinear with the accelerated electrons. This is in contrast with already known techniques which rely on interactions with over-dense or solid targets and generates radial or toroidal magnetic field localized at the stationary target. The solenoidal field is quasi-stationary in the reference frame of the laser pulse and can be used for guiding electron beams. It can also provide synchrotron radiation beam emittance cooling for laser-plasma accelerated electron and positron beams, opening up novel opportunities for designs of the light sources, free electron lasers, and high energy colliders based on laser plasma acceleration. PMID:27796327

GigaGauss solenoidal magnetic field inside bubbles excited in under-dense plasma

NASA Astrophysics Data System (ADS)

Lécz, Zs.; Konoplev, I. V.; Seryi, A.; Andreev, A.

2016-10-01

This paper proposes a novel and effective method for generating GigaGauss level, solenoidal quasi-static magnetic fields in under-dense plasma using screw-shaped high intensity laser pulses. This method produces large solenoidal fields that move with the driving laser pulse and are collinear with the accelerated electrons. This is in contrast with already known techniques which rely on interactions with over-dense or solid targets and generates radial or toroidal magnetic field localized at the stationary target. The solenoidal field is quasi-stationary in the reference frame of the laser pulse and can be used for guiding electron beams. It can also provide synchrotron radiation beam emittance cooling for laser-plasma accelerated electron and positron beams, opening up novel opportunities for designs of the light sources, free electron lasers, and high energy colliders based on laser plasma acceleration.

Generation of 1.5-octave intense infrared pulses by nonlinear interactions in DAST crystal

NASA Astrophysics Data System (ADS)

Vicario, C.; Monoszlai, B.; Arisholm, G.; Hauri, C. P.

2015-09-01

Infrared pulses with large spectral width extending from 1.2 to 3.4 μm are generated in the organic crystal DAST (4-N, N-dimethylamino-4‧-N‧-methylstilbazolium tosylate). The input pulse has a central wavelength of 1.5 μm and 65 fs duration. With 2.8 mJ input energy we obtained up to 700 μJ in the broadened spectrum. The output can be easily scaled up in energy by increasing the crystal size together with the energy and the beam size of the pump. The ultra-broad spectrum is ascribed to cascaded second order processes mediated by the exceptionally large effective χ 2 nonlinearity of DAST, but the shape of the spectrum indicates that a delayed χ 3 process may also be involved. Numerical simulations reproduce the experimental results qualitatively and provide an insight in the mechanisms underlying the asymmetric spectral broadening.

Advanced injection seeder for various applications: form LIDARs to supercontinuum sources

NASA Astrophysics Data System (ADS)

Grzes, Pawel

2017-12-01

The paper describes an injection seeder driver (prototype) for a directly modulated semiconductor laser diode. The device provides adjustable pulse duration and repetition frequency to shape an output signal. A temperature controller stabilizes a laser diode spectrum. Additionally, to avoid a back oscillation, redundant power supply holds a generation until next stages shut down. Low EMI design and ESD protection guarantee stable operation even in a noisy environment. The controller is connected to the PC via USB and parameters of the pulse are digitally controlled through a graphical interface. The injection seeder controller can be used with a majority of commercially available laser diodes. In the experimental setup a telecommunication DFB laser with 4 GHz bandwidth was used. It allows achieving subnanosecond pulses generated at the repetition rate ranging from 1 kHz to 50 MHz. The developed injection seeder controller with a proper laser diode can be used in many scientific, industrial and medical applications.

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.

Neutron kinetics in moderators and SNM detection through epithermal-neutron-induced fissions

NASA Astrophysics Data System (ADS)

Gozani, Tsahi; King, Michael J.

2016-01-01

Extension of the well-established Differential Die Away Analysis (DDAA) into a faster time domain, where more penetrating epithermal neutrons induce fissions, is proposed and demonstrated via simulations and experiments. In the proposed method the fissions stimulated by thermal, epithermal and even higher-energy neutrons are measured after injection of a narrow pulse of high-energy 14 MeV (d,T) or 2.5 MeV (d,D) source neutrons, appropriately moderated. The ability to measure these fissions stems from the inherent correlation of neutron energy and time ("E-T" correlation) during the process of slowing down of high-energy source neutrons in common moderating materials such as hydrogenous compounds (e.g., polyethylene), heavy water, beryllium and graphite. The kinetic behavior following injection of a delta-function-shaped pulse (in time) of 14 MeV neutrons into such moderators is studied employing MCNPX simulations and, when applicable, some simple "one-group" models. These calculations served as a guide for the design of a source moderator which was used in experiments. Qualitative relationships between slowing-down time after the pulse and the prevailing neutron energy are discussed. A laboratory system consisting of a 14 MeV neutron generator, a polyethylene-reflected Be moderator, a liquid scintillator with pulse-shape discrimination (PSD) and a two-parameter E-T data acquisition system was set up to measure prompt neutron and delayed gamma-ray fission signatures in a 19.5% enriched LEU sample. The measured time behavior of thermal and epithermal neutron fission signals agreed well with the detailed simulations. The laboratory system can readily be redesigned and deployed as a mobile inspection system for SNM in, e.g., cars and vans. A strong pulsed neutron generator with narrow pulse (<75 ns) at a reasonably high pulse frequency could make the high-energy neutron induced fission modality a realizable SNM detection technique.

[INVITED] On the mechanisms of single-pulse laser-induced backside wet etching

NASA Astrophysics Data System (ADS)

Tsvetkov, M. Yu.; Yusupov, V. I.; Minaev, N. V.; Akovantseva, A. A.; Timashev, P. S.; Golant, K. M.; Chichkov, B. N.; Bagratashvili, V. N.

2017-02-01

Laser-induced backside wet etching (LIBWE) of a silicate glass surface at interface with a strongly absorbing aqueous dye solution is studied. The process of crater formation and the generated optoacoustic signals under the action of single 5 ns laser pulses at the wavelength of 527 nm are investigated. The single-pulse mode is used to avoid effects of incubation and saturation of the etched depth. Significant differences in the mechanisms of crater formation in the ;soft; mode of laser action (at laser fluencies smaller than 150-170 J/cm2) and in the ;hard; mode (at higher laser fluencies) are observed. In the ;soft; single-pulse mode, LIBWE produces accurate craters with the depth of several hundred nanometers, good shape reproducibility and smooth walls. Estimates of temperature and pressure of the dye solution heated by a single laser pulse indicate that these parameters can significantly exceed the corresponding critical values for water. We consider that chemical etching of glass surface (or molten glass) by supercritical water, produced by laser heating of the aqueous dye solution, is the dominant mechanism responsible for the formation of crater in the ;soft; mode. In the ;hard; mode, the produced craters have ragged shape and poor pulse-to-pulse reproducibility. Outside the laser exposed area, cracks and splits are formed, which provide evidence for the shock induced glass fracture. By measuring the amplitude and spectrum of the generated optoacoustic signals it is possible to conclude that in the ;hard; mode of laser action, intense hydrodynamic processes induced by the formation and cavitation collapse of vapor-gas bubbles at solid-liquid interface are leading to the mechanical fracture of glass. The LIBWE material processing in the ;soft; mode, based on chemical etching in supercritical fluids (in particular, supercritical water) is very promising for structuring of optical materials.

Diagnosis of warm dense conditions in foil targets heated by intense femtosecond laser pulses using Kα imaging spectroscopy

DOE PAGES

Bae, L. J.; Zastrau, U.; Chung, H. -K.; ...

2018-03-01

Warm dense conditions in titanium foils irradiated with intense femtosecond laser pulses are diagnosed using an x-ray imaging spectroscopy technique. The line shapes of radially resolved titanium Kα spectra are measured with a toroidally bent GaAs crystal and an x-ray charge-coupled device. Measured spectra are compared with the K-shell emissions modeled using an atomic kinetics – spectroscopy simulation code. Kα line shapes are strongly affected by warm (5-40 eV) bulk electron temperatures and imply multiple temperature distributions in the targets. Finally, the spatial distribution of temperature is dependent on the target thickness, and a thin target shows an advantage tomore » generate uniform warm dense conditions in a large area.« less

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.

Diagnosis of warm dense conditions in foil targets heated by intense femtosecond laser pulses using Kα imaging spectroscopy

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

Bae, L. J.; Zastrau, U.; Chung, H. -K.

Warm dense conditions in titanium foils irradiated with intense femtosecond laser pulses are diagnosed using an x-ray imaging spectroscopy technique. The line shapes of radially resolved titanium Kα spectra are measured with a toroidally bent GaAs crystal and an x-ray charge-coupled device. Measured spectra are compared with the K-shell emissions modeled using an atomic kinetics – spectroscopy simulation code. Kα line shapes are strongly affected by warm (5-40 eV) bulk electron temperatures and imply multiple temperature distributions in the targets. Finally, the spatial distribution of temperature is dependent on the target thickness, and a thin target shows an advantage tomore » generate uniform warm dense conditions in a large area.« less

A tripolar current-steering stimulator ASIC for field shaping in deep brain stimulation.

PubMed

Valente, Virgilio; Demosthenous, Andreas; Bayford, Richard

2012-06-01

A significant problem with clinical deep brain stimulation (DBS) is the high variability of its efficacy and the frequency of side effects, related to the spreading of current beyond the anatomical target area. This is the result of the lack of control that current DBS systems offer on the shaping of the electric potential distribution around the electrode. This paper presents a stimulator ASIC with a tripolar current-steering output stage, aiming at achieving more selectivity and field shaping than current DBS systems. The ASIC was fabricated in a 0.35-μ m CMOS technology occupying a core area of 0.71 mm(2). It consists of three current sourcing/sinking channels. It is capable of generating square and exponential-decay biphasic current pulses with five different time constants up to 28 ms and delivering up to 1.85 mA of cathodic current, in steps of 4 μA, from a 12 V power supply. Field shaping was validated by mapping the potential distribution when injecting current pulses through a multicontact DBS electrode in saline.

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.

Avoiding the side effects of electric current pulse application to electroporated cells in disposable small volume cuvettes assures good cell survival.

PubMed

Grys, Maciej; Madeja, Zbigniew; Korohoda, Włodzimierz

2017-01-01

The harmful side effects of electroporation to cells due to local changes in pH, the appearance of toxic electrode products, temperature increase, and the heterogeneity of the electric field acting on cells in the cuvettes used for electroporation were observed and discussed in several laboratories. If cells are subjected to weak electric fields for prolonged periods, for example in experiments on cell electrophoresis or galvanotaxis the same effects are seen. In these experiments investigators managed to reduce or eliminate the harmful side effects of electric current application. For the experiments, disposable 20 μl cuvettes with two walls made of dialysis membranes were constructed and placed in a locally focused electric field at a considerable distance from the electrodes. Cuvettes were mounted into an apparatus for horizontal electrophoresis and the cells were subjected to direct current electric field (dcEF) pulses from a commercial pulse generator of exponentially declining pulses and from a custom-made generator of double and single rectangular pulses. More than 80% of the electroporated cells survived the dcEF pulses in both systems. Side effects related to electrodes were eliminated in both the flow through the dcEF and in the disposable cuvettes placed in the focused dcEFs. With a disposable cuvette system, we also confirmed the sensitization of cells to a dcEF using procaine by observing the loading of AT2 cells with calceine and using a square pulse generator, applying 50 ms single rectangular pulses. We suggest that the same methods of avoiding the side effects of electric current pulse application as in cell electrophoresis and galvanotaxis should also be used for electroporation. This conclusion was confirmed in our electroporation experiments performed in conditions assuring survival of over 80% of the electroporated cells. If the amplitude, duration, and shape of the dcEF pulse are known, then electroporation does not depend on the type of pulse generator. This knowledge of the characteristics of the pulse assures reproducibility of electroporation experiments using different equipment.

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.

Photonuclear Contributions to SNS Pulse Shapes

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

McClanahan, Tucker C.; Iverson, Erik B.; Gallmeier, Franz X.

Short-pulsed sources like the Spallation Neutron Source (SNS) and ISIS produce bursts of neutron pulses at rates of 10-60 Hz, with sub-microsecond proton pulses impacting on high-Z target materials. Moderators are grouped around the target to receive the fast neutrons generated from spallation reactions to moderate them effciently to thermal and sub-thermal energies and to feed narrow neutron pulses to neutron scattering instruments. The scattering instruments use the neutrons as a probe for material investigations, and make use of time-of-flight (TOF) methods for resolving the neutron energy. The energy resolution of scattering instruments depends on the narrow time-structure of themore » neutron pulses, while neutrons in the long tail of the emission time distributions can degrade the instrument performance and add undesired background to measurements. The SNS neutronics team is investigating a possible source term impacting the background at short-pulsed spallation sources. The ISIS TS2 project claims to have significantly reduced neutron scattering instrument background levels by the elimination or reduction of iron shielding in the target-moderator-reflector assembly. An alternative hypothesis, also proposed by ISIS, suggests that this apparent reduction arises from moving beamline shielding away from the neutron guide channels, reducing albedo down the beamlines. In both hypotheses, the background neutrons in question are believed to be generated by photonuclear reactions. If the background neutrons are indeed generated via photonuclear channels, then they are generated in a time-dependent fashion, since most of the high-energy photons capable of inducing photonuclear production are gone within a few microseconds following the proton pulse. To evaluate this e ect, we have enabled photonuclear reactions in a series of studies for the SNS first target station (FTS) taking advantage of its Monte Carlo model. Using a mixture of ENDF/B VII.0 and TENDL-2014 photonuclear cross sections available and the CEM03 physics model within MCNPX 2.6.0 in the simulation, we are able to estimate the impact of photoneutron production on both overall neutron production and delayed neutron production. We find that a significant number of photon-induced neutrons are produced a few milliseconds after the proton pulse, following prompt gamma emission through the capture of neutrons in the slowing-down and thermalization processes. We name these "slowing-down delayed neutrons" to distinguish them from either "activation-delayed neutrons" or "beta-delayed neutrons." The beta-delayed and activation-delayed neutrons were not part of this study, and will be addressed elsewhere. While these other delayed neutron channels result in the time-independent (constant) production of fast neutrons outside of the prompt pulse, the slowing-down delayed neutrons also a ect the shape of the pulses. Although numerically insignificant in most cases, we describe a set of scenarios related to T0-chopper operation in which the slowing-down delayed neutrons may be important.« 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

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).

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.

Electron path control of high-order harmonic generation by a spatially inhomogeneous field

NASA Astrophysics Data System (ADS)

Mohebbi, Masoud; Nazarpoor Malaei, Sakineh

2016-04-01

We theoretically investigate the control of high-order harmonics cut-off and as-pulse generation by a chirped laser field using a metallic bow tie-shaped nanostructure. The numerical results show that the trajectories of the electron wave packet are strongly modified, the short quantum path is enhanced, the long quantum path is suppressed and the low modulated spectrum of the harmonics can be remarkably extended. Our calculated results also show that, by confining electron motion, a broadband supercontinuum with the width of 1670 eV can be produced which directly generates an isolated 34 as-pulse without phase compensation. To explore the underlying mechanism responsible for the cut-off extension and the quantum path selection, we perform time-frequency analysis and a classical simulation based on the three-step model.

Bimorphic polymeric photomechanical actuator

NASA Technical Reports Server (NTRS)

Sarkisov, Sergey S. (Inventor); Curley, Michael J. (Inventor); Adamovsky, Grigory (Inventor); Sarkisov, Jr., Sergey S. (Inventor); Fields, Aisha B. (Inventor)

2006-01-01

A bimorphic polymeric photomechanical actuator, in one embodiment using polyvinylidene fluoride (PVDF) as a photosensitive body, transmitting light over fiber optic cables, and controlling the shape and pulse duration of the light pulse to control movement of the actuator. Multiple light beams are utilized to generate different ranges of motion for the actuator from a single photomechanical body and alternative designs use multiple light beams and multiple photomechanical bodies to provide controlled movement. Actuator movement using one or more ranges of motion is utilized to control motion to position an actuating element in three dimensional space.

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.

High speed fabrication of absorbance-enhanced micro-nanostructures on nickel surface using hundred-nanosecond pulsed laser

NASA Astrophysics Data System (ADS)

Fu, Jinxiang; Zhang, Jingyuan; Liang, Hao; Wang, Yibo; Zhang, Zhiyan; Liu, Yannan; Lin, Xuechun

2017-01-01

We report the generation of micro-nanostructures on nickel surface using a pulsed laser with pulse duration of 100/200 ns. The blacken nickel, which is covered with dense broccoli-like clusters having strong light trapping capacity covering broad spectrum (200-2000 nm), can be produced at a high laser scanning speed up to 100 mm/s. The absorbance of the blacken nickel can be over 98% in the UV, more than 97% in the visible, and over 90% in the near IR. In addition, by treating the nickel surface with two crossing scans of the laser, highly organized and shape-controllable periodic arrays of hump-craters can be fabricated.

D-D neutron generator development at LBNL.

PubMed

Reijonen, J; Gicquel, F; Hahto, S K; King, M; Lou, T-P; Leung, K-N

2005-01-01

The plasma and ion source technology group in Lawrence Berkeley National Laboratory is developing advanced, next generation D-D neutron generators. There are three distinctive developments, which are discussed in this presentation, namely, multi-stage, accelerator-based axial neutron generator, high-output co-axial neutron generator and point source neutron generator. These generators employ RF-induction discharge to produce deuterium ions. The distinctive feature of RF-discharge is its capability to generate high atomic hydrogen species, high current densities and stable and long-life operation. The axial neutron generator is designed for applications that require fast pulsing together with medium to high D-D neutron output. The co-axial neutron generator is aimed for high neutron output with cw or pulsed operation, using either the D-D or D-T fusion reaction. The point source neutron generator is a new concept, utilizing a toroidal-shaped plasma generator. The beam is extracted from multiple apertures and focus to the target tube, which is located at the middle of the generator. This will generate a point source of D-D, T-T or D-T neutrons with high output flux. The latest development together with measured data will be discussed in this article.

Compact neutron generator

DOEpatents

Leung, Ka-Ngo; Lou, Tak Pui

2005-03-22

A compact neutron generator has at its outer circumference a toroidal shaped plasma chamber in which a tritium (or other) plasma is generated. A RF antenna is wrapped around the plasma chamber. A plurality of tritium ion beamlets are extracted through spaced extraction apertures of a plasma electrode on the inner surface of the toroidal plasma chamber and directed inwardly toward the center of neutron generator. The beamlets pass through spaced acceleration and focusing electrodes to a neutron generating target at the center of neutron generator. The target is typically made of titanium tubing. Water is flowed through the tubing for cooling. The beam can be pulsed rapidly to achieve ultrashort neutron bursts. The target may be moved rapidly up and down so that the average power deposited on the surface of the target may be kept at a reasonable level. The neutron generator can produce fast neutrons from a T-T reaction which can be used for luggage and cargo interrogation applications. A luggage or cargo inspection system has a pulsed T-T neutron generator or source at the center, surrounded by associated gamma detectors and other components for identifying explosives or other contraband.

Effect of pulse temporal shape on optical trapping and impulse transfer using ultrashort pulsed lasers.

PubMed

Shane, Janelle C; Mazilu, Michael; Lee, Woei Ming; Dholakia, Kishan

2010-03-29

We investigate the effects of pulse duration on optical trapping with high repetition rate ultrashort pulsed lasers, through Lorentz-Mie theory, numerical simulation, and experiment. Optical trapping experiments use a 12 femtosecond duration infrared pulsed laser, with the trapping microscope's temporal dispersive effects measured and corrected using the Multiphoton Intrapulse Interference Phase Scan method. We apply pulse shaping to reproducibly stretch pulse duration by 1.5 orders of magnitude and find no material-independent effects of pulse temporal profile on optical trapping of 780nm silica particles, in agreement with our theory and simulation. Using pulse shaping, we control two-photon fluorescence in trapped fluorescent particles, opening the door to other coherent control applications with trapped particles.

Triangular laser-induced submicron textures for functionalising stainless steel surfaces

NASA Astrophysics Data System (ADS)

Romano, Jean-Michel; Garcia-Giron, Antonio; Penchev, Pavel; Dimov, Stefan

2018-05-01

Processing technologies that engineer surfaces with sub-micron topographies are of a growing interest to a range of optical, hydrophobic and microbiological applications. One of the promising technologies for creating such topographies employs ultra-short laser pulses to produce laser-induced periodic surface structures (LIPSS) that often result in non-regular, quasi-periodic nanoripples and nanopillars. In this research near infrared ultra-short pulses of 310 fs with a circular polarisation was used to texture ferritic stainless steel workpieces. A single-step process was designed to generate low spatial frequency LIPSS (LSFL) over relatively large areas. Apart from highly regular and homogeneous parallel lines with approximately 900 nm periodicity, extraordinarily uniform triangular-LSFL in hexagonal arrangements was created. The generation of such LSFL was found to be highly repeatable but very sensitive to the used laser processing settings. Therefore, the sensitivity of triangular-LSFL formation to the used laser processing settings, i.e. pulse to pulse distance, pulse fluence and focal plane offsets, were investigated in regard to the resulting morphologies and functional properties, i.e. structural colors and super-hydrophobicity. Finally, the capability of this technology for producing uniform triangular-shaped LSFL on relatively large surface areas of stainless steel plates was studied.

Single-pulse and burst-mode ablation of gold films measured by quartz crystal microbalance

NASA Astrophysics Data System (ADS)

Andrusyak, Oleksiy G.; Bubelnik, Matthew; Mares, Jeremy; McGovern, Theresa; Siders, Craig W.

2005-02-01

Femtosecond ablation has several distinct advantages: the threshold energy fluence for the onset of damage and ablation is orders of magnitude less than for traditional nanosecond laser machining, and by virtue of the rapid material removal of approximately an optical penetration depth per pulse, femtosecond machined cuts can be cleaner and more precise than those made with traditional nanosecond or longer pulse lasers. However, in many materials of interest, especially metals, this limits ablation rates to 10-100 nm/pulse. We present the results of using multiple pulse bursts to significantly increase the per-burst ablation rate compared to a single pulse with the same integrated energy, while keeping the peak intensity of each individual pulse below the air ionization limit. Femtosecond ablation with pulses centered at 800-nm having integrated energy of up to 30 mJ per pulse incident upon thin gold films was measured via resonance frequency shifts in a gold-electrode-coated quartz-crystal oscillator. Measurements were performed using Michelson-interferometer-based burst generators, with up to 2 ns pulse separations, as well as pulse shaping by programmable acousto-optic dispersive filter (Dazzler from FastLite) with up to 2 ps pulse separations.

Passive, active, and hybrid mode-locking in a self-optimized ultrafast diode laser

NASA Astrophysics Data System (ADS)

Alloush, M. Ali; Pilny, Rouven H.; Brenner, Carsten; Klehr, Andreas; Knigge, Andrea; Tränkle, Günther; Hofmann, Martin R.

2018-02-01

Semiconductor lasers are promising sources for generating ultrashort pulses. They are directly electrically pumped, allow for a compact design, and therefore they are cost-effective alternatives to established solid-state systems. Additionally, their emission wavelength depends on the bandgap which can be tuned by changing the semiconductor materials. Theoretically, the obtained pulse width can be few tens of femtoseconds. However, the generated pulses are typically in the range of several hundred femtoseconds only. Recently, it was shown that by implementing a spatial light modulator (SLM) for phase and amplitude control inside the resonator the optical bandwidth can be optimized. Consequently, by using an external pulse compressor shorter pulses can be obtained. We present a Fourier-Transform-External-Cavity setup which utilizes an ultrafast edge-emitting diode laser. The used InGaAsP diode is 1 mm long and emits at a center wavelength of 850 nm. We investigate the best conditions for passive, active and hybrid mode-locking operation using the method of self-adaptive pulse shaping. For passive mode-locking, the bandwidth is increased from 2.34 nm to 7.2 nm and ultrashort pulses with a pulse width of 216 fs are achieved after external pulse compression. For active and hybrid mode-locking, we also increased the bandwidth. It is increased from 0.26 nm to 5.06 nm for active mode-locking and from 3.21 nm to 8.7 nm for hybrid mode-locking. As the pulse width is strongly correlated with the bandwidth of the laser, we expect further reduction in the pulse duration by increasing the bandwidth.

Method and apparatus for the formation of a spheromak plasma

DOEpatents

Yamada, Masaaki; Furth, Harold P.; Stix, Thomas H.; Todd, Alan M. M.

1982-01-01

A method and apparatus for forming a detached, compact toroidally shaped spheromak plasma by an inductive mechanism. A generally spheroidal vacuum vessel (1) houses a toroidally shaped flux ring or core (2) which contains poloidal and toroidal field generating coils. A plasma discharge occurs with the pulsing of the toroidal field coil, and the plasma is caused to expand away from the core (2) and toward the center of the vacuum vessel (1). When the plasma is in an expanded state, a portion of it is pinched off in order to form a separate, detached spheromak plasma configuration. The detached plasma is supported by a magnetic field generated by externally arranged equilibrium field coils (5).

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

Pulse-shape discrimination techniques for the COBRA double beta-decay experiment at LNGS

NASA Astrophysics Data System (ADS)

Zatschler, S.; COBRA Collaboration

2017-09-01

In modern elementary particle physics several questions arise from the fact that neutrino oscillation experiments have found neutrinos to be massive. Among them is the so far unknown nature of neutrinos: either they act as so-called Majorana particles, where one cannot distinguish between particle and antiparticle, or they are Dirac particles like all the other fermions in the Standard Model. The study of neutrinoless double beta-decay (0νββ-decay), where the lepton number conservation is violated by two units, could answer the question regarding the underlying nature of neutrinos and might also shed light on the mechanism responsible for the mass generation. So far there is no experimental evidence for the existence of 0νββ-decay, hence, existing experiments have to be improved and novel techniques should be explored. One of the next-generation experiments dedicated to the search for this ultra-rare decay is the COBRA experiment. This article gives an overview of techniques to identify and reject background based on pulse-shape discrimination.

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.

Improving the phase response of an atom interferometer by means of temporal pulse shaping

NASA Astrophysics Data System (ADS)

Fang, Bess; Mielec, Nicolas; Savoie, Denis; Altorio, Matteo; Landragin, Arnaud; Geiger, Remi

2018-02-01

We study theoretically and experimentally the influence of temporally shaping the light pulses in an atom interferometer, with a focus on the phase response of the interferometer. We show that smooth light pulse shapes allow rejecting high frequency phase fluctuations (above the Rabi frequency) and thus relax the requirements on the phase noise or frequency noise of the interrogation lasers driving the interferometer. The light pulse shape is also shown to modify the scale factor of the interferometer, which has to be taken into account in the evaluation of its accuracy budget. We discuss the trade-offs to operate when choosing a particular pulse shape, by taking into account phase noise rejection, velocity selectivity, and applicability to large momentum transfer atom interferometry.

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.

High-speed three-dimensional shape measurement for dynamic scenes using bi-frequency tripolar pulse-width-modulation fringe projection

NASA Astrophysics Data System (ADS)

Zuo, Chao; Chen, Qian; Gu, Guohua; Feng, Shijie; Feng, Fangxiaoyu; Li, Rubin; Shen, Guochen

2013-08-01

This paper introduces a high-speed three-dimensional (3-D) shape measurement technique for dynamic scenes by using bi-frequency tripolar pulse-width-modulation (TPWM) fringe projection. Two wrapped phase maps with different wavelengths can be obtained simultaneously by our bi-frequency phase-shifting algorithm. Then the two phase maps are unwrapped using a simple look-up-table based number-theoretical approach. To guarantee the robustness of phase unwrapping as well as the high sinusoidality of projected patterns, TPWM technique is employed to generate ideal fringe patterns with slight defocus. We detailed our technique, including its principle, pattern design, and system setup. Several experiments on dynamic scenes were performed, verifying that our method can achieve a speed of 1250 frames per second for fast, dense, and accurate 3-D measurements.

Theoretical and experimental investigations of coincidences in Poisson distributed pulse trains and spectral distortion caused by pulse pileup

NASA Astrophysics Data System (ADS)

Bristow, Quentin

1990-03-01

The occurrence rates of pulse strings, or sequences of pulses with interarrival times less than the resolving time of the pulse-height analysis system used to acquire spectra, are derived from theoretical considerations. Logic circuits were devised to make experimental measurements of multiple pulse string occurrence rates in the output from a scintillation detector over a wide range of count rates. Markov process theory was used to predict state transition rates in the logic circuits, enabling the experimental data to be checked rigorously for conformity with those predicted for a Poisson distribution. No fundamental discrepancies were observed. Monte Carlo simulations, incorporating criteria for pulse pileup inherent in the operation of modern analog to digital converters, were used to generate pileup spectra due to coincidences between two pulses (first order pileup) and three pulses (second order pileup) for different semi-Gaussian pulse shapes. Coincidences between pulses in a single channel produced a basic probability density function spectrum. The use of a flat spectrum showed the first order pileup distorted the spectrum to a linear ramp with a pileup tail. A correction algorithm was successfully applied to correct entire spectra (simulated and real) for first and second order pileups.

Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy β and nuclear recoils in liquid argon with DEAP-1

DOE PAGES

Amaudruz, P. -A.; Batygov, M.; Beltran, B.; ...

2016-09-17

The DEAP-1 low-background liquid argon detector has been used to measure scintillation pulse shapes of beta decays and nuclear recoil events and to demonstrate the feasibility of pulse-shape discrimination down to an electron-equivalent energy of 20 keV ee. The relative intensities of singlet/triplet states in liquid argon have been measured as a function of energy between 15 and 500 keVee for both beta and nuclear recoils. Using a triple-coincidence tag we find the fraction of beta events that are misidentified as nuclear recoils to be less than 6 x 10 -8 between 43-86 keV ee and that the discrimination parametermore » agrees with a simple analytic model. The discrimination measurement is currently limited by nuclear recoils induced by cosmic-ray generated neutrons, and is expected to improve by operating the detector underground at SNOLAB. The analytic model predicts a beta misidentification fraction of 10 -10 for an electron-equivalent energy threshold of 20 keV ee. This reduction allows for a sensitive search for spin-independent scattering of WIMPs from 1000 kg of liquid argon with a WIMP-nucleon cross-section sensitivity of 10 -46 cm 2.« less

Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy β and nuclear recoils in liquid argon with DEAP-1

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

Amaudruz, P. -A.; Batygov, M.; Beltran, B.

The DEAP-1 low-background liquid argon detector has been used to measure scintillation pulse shapes of beta decays and nuclear recoil events and to demonstrate the feasibility of pulse-shape discrimination down to an electron-equivalent energy of 20 keV ee. The relative intensities of singlet/triplet states in liquid argon have been measured as a function of energy between 15 and 500 keVee for both beta and nuclear recoils. Using a triple-coincidence tag we find the fraction of beta events that are misidentified as nuclear recoils to be less than 6 x 10 -8 between 43-86 keV ee and that the discrimination parametermore » agrees with a simple analytic model. The discrimination measurement is currently limited by nuclear recoils induced by cosmic-ray generated neutrons, and is expected to improve by operating the detector underground at SNOLAB. The analytic model predicts a beta misidentification fraction of 10 -10 for an electron-equivalent energy threshold of 20 keV ee. This reduction allows for a sensitive search for spin-independent scattering of WIMPs from 1000 kg of liquid argon with a WIMP-nucleon cross-section sensitivity of 10 -46 cm 2.« less

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.

Reducing Conservatism of Analytic Transient Response Bounds via Shaping Filters

NASA Technical Reports Server (NTRS)

Kwan, Aiyueh; Bedrossian, Nazareth; Jan, Jiann-Woei; Grigoriadis, Karolos; Hua, Tuyen (Technical Monitor)

1999-01-01

Recent results show that the peak transient response of a linear system to bounded energy inputs can be computed using the energy-to-peak gain of the system. However, analytically computed peak response bound can be conservative for a class of class bounded energy signals, specifically pulse trains generated from jet firings encountered in space vehicles. In this paper, shaping filters are proposed as a Methodology to reduce the conservatism of peak response analytic bounds. This Methodology was applied to a realistic Space Station assembly operation subject to jet firings. The results indicate that shaping filters indeed reduce the predicted peak response bounds.

Tuning characteristics of narrowband THz radiation generated via optical rectification in periodically poled lithium niobate.

PubMed

Weiss, C; Torosyan, G; Meyn, J P; Wallenstein, R; Beigang, R; Avetisyan, Y

2001-04-23

The tuning properties of pulsed narrowband THz radiation generated via optical rectification in periodically poled lithium niobate have been investigated. Using a disk-shaped periodically poled crystal tuning was easily accomplished by rotating the crystal around its axis and observing the generated THz radiation in forward direction. In this way no beam deflection during tuning was observed. The total tuning range extended from 180 GHz up to 830 GHz and was limited by the poling period of 127 microm which determines the maximum THz frequency in forward direction.

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

Rapid convergence of optimal control in NMR using numerically-constructed toggling frames

NASA Astrophysics Data System (ADS)

Coote, Paul; Anklin, Clemens; Massefski, Walter; Wagner, Gerhard; Arthanari, Haribabu

2017-08-01

We present a numerical method for rapidly solving the Bloch equation for an arbitrary time-varying spin-1/2 Hamiltonian. The method relies on fast, vectorized computations such as summation and quaternion multiplication, rather than slow computations such as matrix exponentiation. A toggling frame is constructed in which the Hamiltonian is time-invariant, and therefore has a simple analytical solution. The key insight is that constructing this frame is faster than solving the system dynamics in the original frame. Rapidly solving the Bloch equations for an arbitrary Hamiltonian is particularly useful in the context of NMR optimal control. Optimal control theory can be used to design pulse shapes for a range of tasks in NMR spectroscopy. However, it requires multiple simulations of the Bloch equations at each stage of the algorithm, and for each relevant set of parameters (e.g. chemical shift frequencies). This is typically time consuming. We demonstrate that by working in an appropriate toggling frame, optimal control pulses can be generated much faster. We present a new alternative to the well-known GRAPE algorithm to continuously update the toggling-frame as the optimal pulse is generated, and demonstrate that this approach is extremely fast. The use and benefit of rapid optimal pulse generation is demonstrated for 19F fragment screening experiments.

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

Neural-network-designed pulse sequences for robust control of singlet-triplet qubits

NASA Astrophysics Data System (ADS)

Yang, Xu-Chen; Yung, Man-Hong; Wang, Xin

2018-04-01

Composite pulses are essential for universal manipulation of singlet-triplet spin qubits. In the absence of noise, they are required to perform arbitrary single-qubit operations due to the special control constraint of a singlet-triplet qubit, while in a noisy environment, more complicated sequences have been developed to dynamically correct the error. Tailoring these sequences typically requires numerically solving a set of nonlinear equations. Here we demonstrate that these pulse sequences can be generated by a well-trained, double-layer neural network. For sequences designed for the noise-free case, the trained neural network is capable of producing almost exactly the same pulses known in the literature. For more complicated noise-correcting sequences, the neural network produces pulses with slightly different line shapes, but the robustness against noises remains comparable. These results indicate that the neural network can be a judicious and powerful alternative to existing techniques in developing pulse sequences for universal fault-tolerant quantum computation.

Fundamentals of Transcranial Electric and Magnetic Stimulation Dose: Definition, Selection, and Reporting Practices

PubMed Central

Peterchev, Angel V.; Wagner, Timothy A.; Miranda, Pedro C.; Nitsche, Michael A.; Paulus, Walter; Lisanby, Sarah H.; Pascual-Leone, Alvaro; Bikson, Marom

2011-01-01

The growing use of transcranial electric and magnetic (EM) brain stimulation in basic research and in clinical applications necessitates a clear understanding of what constitutes the dose of EM stimulation and how it should be reported. The biological effects of EM stimulation are mediated through an electromagnetic field injected (via electric stimulation) or induced (via magnetic stimulation) in the body. Therefore, transcranial EM stimulation dose ought to be defined by all parameters of the stimulation device that affect the electromagnetic field generated in the body, including the stimulation electrode or coil configuration parameters: shape, size, position, and electrical properties, as well as the electrode or coil current (or voltage) waveform parameters: pulse shape, amplitude, width, polarity, and repetition frequency; duration of and interval between bursts or trains of pulses; total number of pulses; and interval between stimulation sessions and total number of sessions. Knowledge of the electromagnetic field generated in the body may not be sufficient but is necessary to understand the biological effects of EM stimulation. We believe that reporting of EM stimulation dose should be guided by the principle of reproducibility: sufficient information about the stimulation parameters should be provided so that the dose can be replicated. This paper provides fundamental definition and principles for reporting of dose that encompass any transcranial EM brain stimulation protocol. PMID:22305345

Fundamentals of transcranial electric and magnetic stimulation dose: definition, selection, and reporting practices.

PubMed

Peterchev, Angel V; Wagner, Timothy A; Miranda, Pedro C; Nitsche, Michael A; Paulus, Walter; Lisanby, Sarah H; Pascual-Leone, Alvaro; Bikson, Marom

2012-10-01

The growing use of transcranial electric and magnetic (EM) brain stimulation in basic research and in clinical applications necessitates a clear understanding of what constitutes the dose of EM stimulation and how it should be reported. This paper provides fundamental definitions and principles for reporting of dose that encompass any transcranial EM brain stimulation protocol. The biologic effects of EM stimulation are mediated through an electromagnetic field injected (via electric stimulation) or induced (via magnetic stimulation) in the body. Therefore, transcranial EM stimulation dose ought to be defined by all parameters of the stimulation device that affect the electromagnetic field generated in the body, including the stimulation electrode or coil configuration parameters: shape, size, position, and electrical properties, as well as the electrode or coil current (or voltage) waveform parameters: pulse shape, amplitude, width, polarity, and repetition frequency; duration of and interval between bursts or trains of pulses; total number of pulses; and interval between stimulation sessions and total number of sessions. Knowledge of the electromagnetic field generated in the body may not be sufficient but is necessary to understand the biologic effects of EM stimulation. We believe that reporting of EM stimulation dose should be guided by the principle of reproducibility: sufficient information about the stimulation parameters should be provided so that the dose can be replicated. Copyright © 2012 Elsevier Inc. All rights reserved.

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.

Transient thermoelectric supercooling: Isosceles current pulses from a response surface perspective and the performance effects of pulse cooling a heat generating mass

NASA Astrophysics Data System (ADS)

Piggott, Alfred J., III

With increased public interest in protecting the environment, scientists and engineers aim to improve energy conversion efficiency. Thermoelectrics offer many advantages as thermal management technology. When compared to vapor compression refrigeration, above approximately 200 to 600 watts, cost in dollars per watt as well as COP are not advantageous for thermoelectrics. The goal of this work was to determine if optimized pulse supercooling operation could improve cooling capacity or efficiency of a thermoelectric device. The basis of this research is a thermal-electrical analogy based modeling study using SPICE. Two models were developed. The first model, a standalone thermocouple with no attached mass to be cooled. The second, a system that includes a module attached to a heat generating mass. With the thermocouple study, a new approach of generating response surfaces with characteristic parameters was applied. The current pulse height and pulse on-time was identified for maximizing Net Transient Advantage, a newly defined metric. The corresponding pulse height and pulse on-time was utilized for the system model. Along with the traditional steady state starting current of Imax, Iopt was employed. The pulse shape was an isosceles triangle. For the system model, metrics new to pulse cooling were Qc, power consumption and COP. The effects of optimized current pulses were studied by changing system variables. Further studies explored time spacing between pulses and temperature distribution in the thermoelement. It was found net Q c over an entire pulse event can be improved over Imax steady operation but not over steady I opt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced in transient pulse operation due to the different time constants of Qc and Pin. In some cases lower performance interface materials allow more Qc and better COP during transient operation than higher performance interface materials. Important future work might look at developing innovative ways of biasing Joule heat to Th..

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.

Skyrmion-based high-frequency signal generator

NASA Astrophysics Data System (ADS)

Luo, Shijiang; Zhang, Yue; Shen, Maokang; Ou-Yang, Jun; Yan, Baiqian; Yang, Xiaofei; Chen, Shi; Zhu, Benpeng; You, Long

2017-03-01

Many concepts for skyrmion-based devices have been proposed, and most of their possible applications are based on the motion of skyrmions driven by a dc current in an area with a constricted geometry. However, skyrmion motion driven by a pulsed current has not been investigated so far. In this work, we propose a skyrmion-based high-frequency signal generator based on the pulsed-current-driven circular motion of skyrmions in a square-shaped film by micromagnetic simulation. The results indicate that skyrmions can move in a closed curve with central symmetry. The trajectory and cycle period can be adjusted by tuning the size of the film, the current density, the Dzyaloshinskii-Moriya interaction constant, and the local in-plane magnetic anisotropy. The period can be tuned from several nanoseconds to tens of nanoseconds, which offers the possibility to prepare high-frequency signal generator based on skyrmions.

Multioctave infrared supercontinuum generation in large-core As₂S₃ fibers.

PubMed

Théberge, Francis; Thiré, Nicolas; Daigle, Jean-François; Mathieu, Pierre; Schmidt, Bruno E; Messaddeq, Younès; Vallée, Réal; Légaré, François

2014-11-15

We report on infrared supercontinuum (SC) generation through laser filamentation and subsequent nonlinear propagation in a step-index As2S3 fiber. The 100 μm core and high-purity As2S3 fiber used exhibit zero-dispersion wavelength around 4.5 μm, a mid-infrared background loss of 0.2  dB/m, and a maximum loss of only 0.55  dB/m at the S-H absorption peak around 4.05 μm. When pumping with ultrashort laser pulses slightly above the S-H absorption band, broadband infrared supercontinua were generated with a 20 dB spectral flatness spanning from 1.5 up to 7 μm. The efficiency and spectral shape of the SC produced by ultrashort pulses in large-core As2S3 fiber are mainly determined by its dispersion, the S-H contaminant absorption, and the mid-infrared nonlinear absorption.

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.

Generation, storage, and retrieval of nonclassical states of light using atomic ensembles

NASA Astrophysics Data System (ADS)

Eisaman, Matthew D.

This thesis presents the experimental demonstration of several novel methods for generating, storing, and retrieving nonclassical states of light using atomic ensembles, and describes applications of these methods to frequency-tunable single-photon generation, single-photon memory, quantum networks, and long-distance quantum communication. We first demonstrate emission of quantum-mechanically correlated pulses of light with a time delay between the pulses that is coherently controlled by utilizing 87Rb atoms. The experiment is based on Raman scattering, which produces correlated pairs of excited atoms and photons, followed by coherent conversion of the atomic states into a different photon field after a controllable delay. We then describe experiments demonstrating a novel approach for conditionally generating nonclassical pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. We observe nonclassical correlations in relative photon number between correlated pairs of photons, and create few-photon light pulses with sub-Poissonian photon-number statistics via conditional detection on one field of the pair. Spatio-temporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and electromagnetically induced transparency (EIT) in an optically dense atomic medium. Finally, we demonstrate the use of EIT for the controllable generation, transmission, and storage of single photons with tunable frequency, timing, and bandwidth. To this end, we study the interaction of single photons produced in a "source" ensemble of 87Rb atoms at room temperature with another "target" ensemble. This allows us to simultaneously probe the spectral and quantum statistical properties of narrow-bandwidth single-photon pulses, revealing that their quantum nature is preserved under EIT propagation and storage. We measure the time delay associated with the reduced group velocity of the single-photon pulses and report observations of their storage and retrieval. Together these experiments utilize atomic ensembles to realize a narrow-bandwidth single-photon source, single-photon memory that preserves the quantum nature of the single photons, and a primitive quantum network comprised of two atomic-ensemble quantum memories connected by a single photon in an optical fiber. Each of these experimental demonstrations represents an essential element for the realization of long-distance quantum communication.

A new time calibration method for switched-capacitor-array-based waveform samplers

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

Kim, H.; Chen, C. -T.; Eclov, N.

2014-08-24

Here we have developed a new time calibration method for the DRS4 waveform sampler that enables us to precisely measure the non-uniform sampling interval inherent in the switched-capacitor cells of the DRS4. The method uses the proportionality between the differential amplitude and sampling interval of adjacent switched-capacitor cells responding to a sawtooth-shape pulse. In the experiment, a sawtooth-shape pulse with a 40 ns period generated by a Tektronix AWG7102 is fed to a DRS4 evaluation board for calibrating the sampling intervals of all 1024 cells individually. The electronic time resolution of the DRS4 evaluation board with the new time calibrationmore » is measured to be ~2.4 ps RMS by using two simultaneous Gaussian pulses with 2.35 ns full-width at half-maximum and applying a Gaussian fit. The time resolution dependencies on the time difference with the new time calibration are measured and compared to results obtained by another method. Ultimately, the new method could be applicable for other switched-capacitor-array technology-based waveform samplers for precise time calibration.« less

A new time calibration method for switched-capacitor-array-based waveform samplers

NASA Astrophysics Data System (ADS)

Kim, H.; Chen, C.-T.; Eclov, N.; Ronzhin, A.; Murat, P.; Ramberg, E.; Los, S.; Moses, W.; Choong, W.-S.; Kao, C.-M.

2014-12-01

We have developed a new time calibration method for the DRS4 waveform sampler that enables us to precisely measure the non-uniform sampling interval inherent in the switched-capacitor cells of the DRS4. The method uses the proportionality between the differential amplitude and sampling interval of adjacent switched-capacitor cells responding to a sawtooth-shape pulse. In the experiment, a sawtooth-shape pulse with a 40 ns period generated by a Tektronix AWG7102 is fed to a DRS4 evaluation board for calibrating the sampling intervals of all 1024 cells individually. The electronic time resolution of the DRS4 evaluation board with the new time calibration is measured to be 2.4 ps RMS by using two simultaneous Gaussian pulses with 2.35 ns full-width at half-maximum and applying a Gaussian fit. The time resolution dependencies on the time difference with the new time calibration are measured and compared to results obtained by another method. The new method could be applicable for other switched-capacitor-array technology-based waveform samplers for precise time calibration.

A New Time Calibration Method for Switched-capacitor-array-based Waveform Samplers.

PubMed

Kim, H; Chen, C-T; Eclov, N; Ronzhin, A; Murat, P; Ramberg, E; Los, S; Moses, W; Choong, W-S; Kao, C-M

2014-12-11

We have developed a new time calibration method for the DRS4 waveform sampler that enables us to precisely measure the non-uniform sampling interval inherent in the switched-capacitor cells of the DRS4. The method uses the proportionality between the differential amplitude and sampling interval of adjacent switched-capacitor cells responding to a sawtooth-shape pulse. In the experiment, a sawtooth-shape pulse with a 40 ns period generated by a Tektronix AWG7102 is fed to a DRS4 evaluation board for calibrating the sampling intervals of all 1024 cells individually. The electronic time resolution of the DRS4 evaluation board with the new time calibration is measured to be ~2.4 ps RMS by using two simultaneous Gaussian pulses with 2.35 ns full-width at half-maximum and applying a Gaussian fit. The time resolution dependencies on the time difference with the new time calibration are measured and compared to results obtained by another method. The new method could be applicable for other switched-capacitor-array technology-based waveform samplers for precise time calibration.

A New Time Calibration Method for Switched-capacitor-array-based Waveform Samplers

PubMed Central

Kim, H.; Chen, C.-T.; Eclov, N.; Ronzhin, A.; Murat, P.; Ramberg, E.; Los, S.; Moses, W.; Choong, W.-S.; Kao, C.-M.

2014-01-01

We have developed a new time calibration method for the DRS4 waveform sampler that enables us to precisely measure the non-uniform sampling interval inherent in the switched-capacitor cells of the DRS4. The method uses the proportionality between the differential amplitude and sampling interval of adjacent switched-capacitor cells responding to a sawtooth-shape pulse. In the experiment, a sawtooth-shape pulse with a 40 ns period generated by a Tektronix AWG7102 is fed to a DRS4 evaluation board for calibrating the sampling intervals of all 1024 cells individually. The electronic time resolution of the DRS4 evaluation board with the new time calibration is measured to be ~2.4 ps RMS by using two simultaneous Gaussian pulses with 2.35 ns full-width at half-maximum and applying a Gaussian fit. The time resolution dependencies on the time difference with the new time calibration are measured and compared to results obtained by another method. The new method could be applicable for other switched-capacitor-array technology-based waveform samplers for precise time calibration. PMID:25506113

High-resolution line-shape spectroscopy during a laser pulse based on Dual-Broad-Band-CARS interferometry

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

Vereschagin, Konstantin A; Vereschagin, Alexey K; Smirnov, Valery V

2006-07-31

A high-resolution spectroscopic method is developed for recording Raman spectra of molecular transitions in transient objects during a laser pulse with a resolution of {approx}0.1 cm{sup -1}. The method is based on CARS spectroscopy using a Fabry-Perot interferometer for spectral analysis of the CARS signal and detecting a circular interferometric pattern on a two-dimensional multichannel photodetector. It is shown that the use of the Dual-Broad-Band-CARS configuration to obtain the CARS process provides the efficient averaging of the spectral-amplitude noise of the CARS signal generated by a laser pulse and, in combination with the angular integration of the two-dimensional interference pattern,more » considerably improves the quality of interferograms. The method was tested upon diagnostics of the transient oxygen-hydrogen flame where information on the shapes of spectral lines of the Q-branch of hydrogen molecules required for measuring temperature was simultaneously obtained and used. (special issue devoted to the 90th anniversary of a.m. prokhorov)« less

Coherent diffractive imaging of single helium nanodroplets with a high harmonic generation source.

PubMed

Rupp, Daniela; Monserud, Nils; Langbehn, Bruno; Sauppe, Mario; Zimmermann, Julian; Ovcharenko, Yevheniy; Möller, Thomas; Frassetto, Fabio; Poletto, Luca; Trabattoni, Andrea; Calegari, Francesca; Nisoli, Mauro; Sander, Katharina; Peltz, Christian; J Vrakking, Marc; Fennel, Thomas; Rouzée, Arnaud

2017-09-08

Coherent diffractive imaging of individual free nanoparticles has opened routes for the in situ analysis of their transient structural, optical, and electronic properties. So far, single-shot single-particle diffraction was assumed to be feasible only at extreme ultraviolet and X-ray free-electron lasers, restricting this research field to large-scale facilities. Here we demonstrate single-shot imaging of isolated helium nanodroplets using extreme ultraviolet pulses from a femtosecond-laser-driven high harmonic source. We obtain bright wide-angle scattering patterns, that allow us to uniquely identify hitherto unresolved prolate shapes of superfluid helium droplets. Our results mark the advent of single-shot gas-phase nanoscopy with lab-based short-wavelength pulses and pave the way to ultrafast coherent diffractive imaging with phase-controlled multicolor fields and attosecond pulses.Diffraction imaging studies of free individual nanoparticles have so far been restricted to XUV and X-ray free - electron laser facilities. Here the authors demonstrate the possibility of using table-top XUV laser sources to image prolate shapes of superfluid helium droplets.

Enhanced laser conditioning using temporally shaped pulses

DOE PAGES

Kafka, K. R. P.; Papernov, S.; Demos, S. G.

2018-03-06

Laser conditioning was investigated as a function of the temporal shape and duration of 351-nm, nanosecond pulses for fused-silica substrates polished via magnetorheological finishing. Here, the aim is to advance our understanding of the dynamics involved to enable improved control of the interaction of laser light with the material to optimize laser conditioning. Gaussian pulses that are temporally truncated at the intensity peak are observed to enhance laser conditioning, in comparison to a Gaussian pulse shape.

Enhanced laser conditioning using temporally shaped pulses.

PubMed

Kafka, K R P; Papernov, S; Demos, S G

2018-03-15

Laser conditioning was investigated as a function of the temporal shape and duration of 351 nm nanosecond pulses for fused-silica substrates polished via magnetorheological finishing. The aim is to advance our understanding of the dynamics involved to enable improved control of the interaction of laser light with the material to optimize laser conditioning. Gaussian pulses that are temporally truncated at the intensity peak are observed to enhance laser conditioning, in comparison to a Gaussian pulse shape.

Enhanced laser conditioning using temporally shaped pulses

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

Kafka, K. R. P.; Papernov, S.; Demos, S. G.

Laser conditioning was investigated as a function of the temporal shape and duration of 351-nm, nanosecond pulses for fused-silica substrates polished via magnetorheological finishing. Here, the aim is to advance our understanding of the dynamics involved to enable improved control of the interaction of laser light with the material to optimize laser conditioning. Gaussian pulses that are temporally truncated at the intensity peak are observed to enhance laser conditioning, in comparison to a Gaussian pulse shape.

Reconstructing surface wave profiles from reflected acoustic pulses using multiple receivers.

PubMed

Walstead, Sean P; Deane, Grant B

2014-08-01

Surface wave shapes are determined by analyzing underwater reflected acoustic signals collected at multiple receivers. The transmitted signals are of nominal frequency 300 kHz and are reflected off surface gravity waves that are paddle-generated in a wave tank. An inverse processing algorithm reconstructs 50 surface wave shapes over a length span of 2.10 m. The inverse scheme uses a broadband forward scattering model based on Kirchhoff's diffraction formula to determine wave shapes. The surface reconstruction algorithm is self-starting in that source and receiver geometry and initial estimates of wave shape are determined from the same acoustic signals used in the inverse processing. A high speed camera provides ground-truth measurements of the surface wave field for comparison with the acoustically derived surface waves. Within Fresnel zone regions the statistical confidence of the inversely optimized surface profile exceeds that of the camera profile. Reconstructed surfaces are accurate to a resolution of about a quarter-wavelength of the acoustic pulse only within Fresnel zones associated with each source and receiver pair. Multiple isolated Fresnel zones from multiple receivers extend the spatial extent of accurate surface reconstruction while overlapping Fresnel zones increase confidence in the optimized profiles there.

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.

Explosive shock damage potential in space structures

NASA Technical Reports Server (NTRS)

Mortimer, R. W.

1972-01-01

The effects of a pulse shape on the transient response of a cylindrical shell are presented. Uniaxial, membrane, and bending theories for isotropic shells were used in this study. In addition to the results of the analytical study, the preliminary results of an experimental study into the generation and measurement of shear waves in a cylindrical shell are included.

Using Social Media to Engage Youth: Education, Social Justice, & Humanitarianism

ERIC Educational Resources Information Center

Liang, Belle; Commins, Meghan; Duffy, Nicole

2010-01-01

While youth typically turn to social media for gossip, photo sharing, and friendship building, can it also be used to inspire them toward greater goals? The creators of GenerationPulse.com explore how two theories salient to adolescent social development (positive youth development and relational health) were used to shape a social media website…

Compact biomedical pulsed signal generator for bone tissue stimulation

DOEpatents

Kronberg, J.W.

1993-06-08

An apparatus for stimulating bone tissue for stimulating bone growth or treating osteoporosis by applying directly to the skin of the patient an alternating current electrical signal comprising wave forms known to simulate the piezoelectric constituents in bone. The apparatus may, by moving a switch, stimulate bone growth or treat osteoporosis, as desired. Based on low-power CMOS technology and enclosed in a moisture-resistant case shaped to fit comfortably, two astable multivibrators produce the desired waveforms. The amplitude, pulse width and pulse frequency, and the subpulse width and subpulse frequency of the waveforms are adjustable. The apparatus, preferably powered by a standard 9-volt battery, includes signal amplitude sensors and warning signals indicate an output is being produced and the battery needs to be replaced.

20 T portable bipolar magnetic pulser.

PubMed

Wolf Cruz, R R; Dias, A L B; Bonfim, M J C

2010-06-01

High magnetic fields are required for the study of hard magnetic materials and, in many cases, the reversal of these fields is essential. This paper describes a portable pulse generator capable of producing bipolar magnetic fields up to 20 T into a copper coil. The peak current around 7 kA is achieved by discharging two capacitor banks through a combination of thyristors and fast diodes. Each pulse polarity has a semisinusoidal shape with 18 mus base width. Pulse triggering is computer controlled and magnetic measurements are done by an induction coil or Kerr effect acquired by a sampling oscilloscope. The whole apparatus weighs less than 2 kg. Hysteresis loops of NdFeB magnets were done to demonstrate the viability of the system.

Compact biomedical pulsed signal generator for bone tissue stimulation

DOEpatents

Kronberg, James W.

1993-01-01

An apparatus for stimulating bone tissue for stimulating bone growth or treating osteoporosis by applying directly to the skin of the patient an alternating current electrical signal comprising wave forms known to simulate the piezoelectric constituents in bone. The apparatus may, by moving a switch, stimulate bone growth or treat osteoporosis, as desired. Based on low-power CMOS technology and enclosed in a moisture-resistant case shaped to fit comfortably, two astable multivibrators produce the desired waveforms. The amplitude, pulse width and pulse frequency, and the subpulse width and subpulse frequency of the waveforms are adjustable. The apparatus, preferably powered by a standard 9-volt battery, includes signal amplitude sensors and warning signals indicate an output is being produced and the battery needs to be replaced.

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

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.

Short infrared (IR) laser pulses can induce nanoporation

NASA Astrophysics Data System (ADS)

Roth, Caleb C.; Barnes, Ronald A.; Ibey, Bennett L.; Glickman, Randolph D.; Beier, Hope T.

2016-03-01

Short infrared (IR) laser pulses on the order of hundreds of microseconds to single milliseconds with typical wavelengths of 1800-2100 nm, have shown the capability to reversibly stimulate action potentials (AP) in neuronal cells. While the IR stimulation technique has proven successful for several applications, the exact mechanism(s) underlying the AP generation has remained elusive. To better understand how IR pulses cause AP stimulation, we determined the threshold for the formation of nanopores in the plasma membrane. Using a surrogate calcium ion, thallium, which is roughly the same shape and charge, but lacks the biological functionality of calcium, we recorded the flow of thallium ions into an exposed cell in the presence of a battery of channel antagonists. The entry of thallium into the cell indicated that the ions entered via nanopores. The data presented here demonstrate a basic understanding of the fundamental effects of IR stimulation and speculates that nanopores, formed in response to the IR exposure, play an upstream role in the generation of AP.

Spectral dynamics of THz pulses generated by two-color laser filaments in air: the role of Kerr nonlinearities and pump wavelength.

PubMed

Nguyen, A; González de Alaiza Martínez, P; Déchard, J; Thiele, I; Babushkin, I; Skupin, S; Bergé, L

2017-03-06

We theoretically and numerically study the influence of both instantaneous and Raman-delayed Kerr nonlinearities as well as a long-wavelength pump in the terahertz (THz) emissions produced by two-color femtosecond filaments in air. Although the Raman-delayed nonlinearity induced by air molecules weakens THz generation, four-wave mixing is found to impact the THz spectra accumulated upon propagation via self-, cross-phase modulations and self-steepening. Besides, using the local current theory, we show that the scaling of laser-to-THz conversion efficiency with the fundamental laser wavelength strongly depends on the relative phase between the two colors, the pulse duration and shape, rendering a universal scaling law impossible. Scaling laws in powers of the pump wavelength may only provide a rough estimate of the increase in the THz yield. We confront these results with comprehensive numerical simulations of strongly focused pulses and of filaments propagating over meter-range distances.

Muonic molecular ions p p μ and p d μ driven by superintense VUV laser pulses: Postexcitation muonic and nuclear oscillations and high-order harmonic generation

NASA Astrophysics Data System (ADS)

Paramonov, Guennaddi K.; Saalfrank, Peter

2018-05-01

The non-Born-Oppenheimer quantum dynamics of p p μ and p d μ molecular ions excited by ultrashort, superintense VUV laser pulses polarized along the molecular axis (z ) is studied by the numerical solution of the time-dependent Schrödinger equation within a three-dimensional (3D) model, including the internuclear distance R and muon coordinates z and ρ , a transversal degree of freedom. It is shown that in both p p μ and p d μ , muons approximately follow the applied laser field out of phase. After the end of the laser pulse, expectation values , <ρ > , and demonstrate "post-laser-pulse" oscillations in both p p μ and p d μ . In the case of p d μ , the post-laser-pulse oscillations of and appear as shaped "echo pulses." Power spectra, which are related to high-order harmonic generation (HHG), generated due to muonic and nuclear motion are calculated in the acceleration form. For p d μ it is found that there exists a unique characteristic frequency ωoscp d μ representing both frequencies of post-laser-pulse muonic oscillations and the frequency of nuclear vibrations, which manifest themselves by very sharp maxima in the corresponding power spectra of p d μ . The homonuclear p p μ ion does not possess such a unique characteristic frequency. The "exact" dynamics and power, and HHG spectra of the 3D model are compared with a Born-Oppenheimer, fixed-nuclei model featuring interesting differences: postpulse oscillations are absent and HHG spectra are affected indirectly or directly by nuclear motion.

Optical generation and detection of gigahertz-frequency longitudinal and shear acoustic waves in liquids: Theory and experiment

NASA Astrophysics Data System (ADS)

Klieber, Christoph; Pezeril, Thomas; Andrieu, Stéphane; Nelson, Keith A.

2012-07-01

We describe an adaptation of picosecond laser ultrasonics tailored for study of GHz-frequency longitudinal and shear acoustic waves in liquids. Time-domain coherent Brillouin scattering is used to detect multicycle acoustic waves after their propagation through variable thickness liquid layers into a solid substrate. A specialized optical pulse shaping method is used to generate sequences of pulses whose repetition rate determines the acoustic frequency. The measurements reveal the viscoelastic liquid properties and also include signatures of the optical and acoustic cavities formed by the multilayer sample assembly. Modeling of the signals allows their features to be distinguished so that liquid properties can be extracted reliably. Longitudinal and shear acoustic wave data from glycerol and from the silicon oil DC704 are presented.

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.

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.

Optical shaping of gas targets for laser–plasma ion sources

DOE PAGES

Dover, N. P.; Cook, N.; Tresca, O.; ...

2016-02-09

In this paper, we report on the experimental demonstration of a technique to generate steep density gradients in gas-jet targets of interest to laser–plasma ion acceleration. By using an intentional low-energy prepulse, we generated a hydrodynamic blast wave in the gas to shape the target prior to the arrival of an intense COmore » $$_{2}$$($${\\it\\lambda}\\approx 10~{\\rm\\mu}\\text{m}$$) drive pulse. This technique has been recently shown to facilitate the generation of ion beams by shockwave acceleration (Trescaet al.,Phys. Rev. Lett., vol. 115 (9), 2015, 094802). Here, we discuss and introduce a model to understand the generation of these blast waves and discuss in depth the experimental realisation of the technique, supported by hydrodynamics simulations. With appropriate prepulse energy and timing, this blast wave can generate steepened density gradients as short as$$l\\approx 20~{\\rm\\mu}\\text{m}$$($1/e$), opening up new possibilities for laser–plasma studies with near-critical gaseous targets.« less

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.

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

Spectral wings of the fiber supercontinuum and the dark-bright soliton interaction.

PubMed

Milián, C; Marest, T; Kudlinski, A; Skryabin, D V

2017-05-01

We present experimental and numerical data on the supercontinuum generation in an optical fiber pumped in the normal dispersion range where the seeded dark and the spontaneously generated bright solitons contribute to the spectral broadening. We report the dispersive radiation arising from the interaction of the bright and dark solitons. This radiation consists of the two weak dispersing pulses that continuously shift their frequencies and shape the short and long wavelength wings of the supercontinuum spectrum.

16.7 W 885 nm diode-side-pumped actively Q-switched Nd:YAG/YVO4 intracavity Raman laser at 1176 nm

NASA Astrophysics Data System (ADS)

Jiang, Pengbo; Zhang, Guizhong; Liu, Jian; Ding, Xin; Sheng, Quan; Yu, Xuanyi; Sun, Bing; Shi, Rui; Wu, Liang; Wang, Rui; Yao, Jianquan

2017-11-01

We proposed and experimentally demonstrated the generation of high-power 1176 nm Stokes wave by frequency shifting of a 885 nm diode-side-pumped Nd:YAG laser using a YVO4 crystal in a Z-shaped cavity configuration. Employing the 885 nm diode-side-pumped scheme and the Z-shaped cavity, for the first time to our knowledge, we realized the thermal management effectively, achieving excellent 1176 nm Stokes wave consequently. With an incident pump power of ~190.0 W, a maximum average output power of 16.7 W was obtained at the pulse repetition frequency of 10 kHz. The pulse duration and spectrum linewidth of the Stokes wave at the maximum output power were 20.3 ns and ~0.08 nm, respectively.

Duobinary pulse shaping for frequency chirp enabled complex modulation.

PubMed

Che, Di; Yuan, Feng; Khodakarami, Hamid; Shieh, William

2016-09-01

The frequency chirp of optical direct modulation (DM) used to be a performance barrier of optical transmission system, because it broadens the signal optical spectrum, which becomes more susceptible to chromatic dispersion induced inter-symbol interference (ISI). However, by considering the chirp as frequency modulation, the single DM simultaneously generates a 2-D signal containing the intensity and phase (namely, the time integral of frequency). This complex modulation concept significantly increases the optical signal to noise ratio (OSNR) sensitivity of DM systems. This Letter studies the duobinary pulse shaping (DB-PS) for chirp enabled DM and its impact on the optical bandwidth and system OSNR sensitivity. DB-PS relieves the bandwidth requirement, at the sacrifice of system OSNR sensitivity. As DB-PS induces a controlled ISI, the receiver requires one more tap for maximum likelihood sequence estimation (MLSE). We verify this modified MLSE with a 10-Gbaud duobinary PAM-4 transmission experiment.

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.

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

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.

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.

30-W Yb3+-pulsed fiber laser with wavelength tuning

NASA Astrophysics Data System (ADS)

Davydov, B. L.; Krylov, A. A.

2007-12-01

We have investigated various pulsed operation regimes of a diode-pumped Yb3+-doped fiber laser with both an acoustooptic filter and a shutter inside the resonator. To imbed the polarization-sensitive acoustooptic-tunable spectral filter into the polarization-nonmaintaining resonator, based on an “isotropic” single-mode fiber without “polarization’ losses, we have used a CaCO3 single-crystal nondispersive thermostable polarization splitter. Stable smooth bell-shaped laser pulses were obtained in the Q-switch generation regime across the entire wavelength tuning band. Their duration depended on the resonator travel time and their repetition rate was determined exclusively by the outer high-frequency generator controlling the acoustooptic shutter. A pulsed laser radiation tuning bandwidth of more than 20-nm at a repetition rate band of 10-100 kHz was observed in the amplification band of the Yb3+-doped fiber. A stable average power of 30 W of the pulsed 70-ns 100-kHz laser radiation in a near Gaussian beam was reached by means of the two-stage amplifier based on Yb3+-doped fibers with an enlarged mode field diameter (14 μm). The amplifier was pumped by λ = 975 nm CW multimode laser diodes with a maximum average power of 42 W.

10 Gb/s optical carrier distributed network with W-band (0.1 THz) short-reach wireless communication system

NASA Astrophysics Data System (ADS)

Chow, C. W.; Yang, L. G.; Yeh, C. H.; Huang, C. B.; Shi, J. W.; Pan, C. L.

2012-10-01

Millimeter-wave (mm-wave) operated in W-band (75 GHz-0.11 THz) is of particular interests, since this frequency band can carry signals at much higher data rates. We demonstrate a 10 Gb/s optical carrier-distributed network with the wireless communication system. The mm-wave signal at carrier frequency of 0.1 THz is generated by a high speed near-ballistic uni-traveling carrier photodiode (NBUTC-PD) based transmitter (Tx), which is optically excited by optical short pulses. The optical pulse source is produced from a self-developed photonic mm-wave waveform generator (PMWG), which allows spectral line-by-line pulse shaping. Hence these optical pulses have high tolerance to fiber chromatic dispersion. The W-band 10 Gb/s wireless data is transmitted and received via a pair of horn antennas. The received 10 Gb/s data is envelope-detected and then used to drive an optical modulator at the remote antenna unit (RAU) to produce the upstream signal sending back to the central office (CO). 20 km single mode fiber (SMF) error free transmission is achieved. Analysis about the optimum repetition rate of the optical pulse source and the transmission performance of the upstream signal are also performed and discussed.

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

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.

A Ku band pulsed electron paramagnetic resonance spectrometer using an arbitrary waveform generator for quantum control experiments at millikelvin temperatures

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

Yap, Yung Szen, E-mail: yungszen@utm.my; Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor; Tabuchi, Yutaka

2015-06-15

We present a 17 GHz (Ku band) arbitrary waveform pulsed electron paramagnetic resonance spectrometer for experiments down to millikelvin temperatures. The spectrometer is located at room temperature, while the resonator is placed either in a room temperature magnet or inside a cryogen-free dilution refrigerator; the operating temperature range of the dilution unit is from ca. 10 mK to 8 K. This combination provides the opportunity to perform quantum control experiments on electron spins in the pure-state regime. At 0.6 T, spin echo experiments were carried out using γ-irradiated quartz glass from 1 K to 12.3 mK. With decreasing temperatures, wemore » observed an increase in spin echo signal intensities due to increasing spin polarizations, in accordance with theoretical predictions. Through experimental data fitting, thermal spin polarization at 100 mK was estimated to be at least 99%, which was almost pure state. Next, to demonstrate the ability to create arbitrary waveform pulses, we generate a shaped pulse by superposing three Gaussian pulses of different frequencies. The resulting pulse was able to selectively and coherently excite three different spin packets simultaneously—a useful ability for analyzing multi-spin system and for controlling a multi-qubit quantum computer. By applying this pulse to the inhomogeneously broadened sample, we obtain three well-resolved excitations at 8 K, 1 K, and 14 mK.« less

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

Runaway breakdown and hydrometeors in lightning initiation.

PubMed

Gurevich, A V; Karashtin, A N

2013-05-03

The particular electric pulse discharges are observed in thunderclouds during the initiation stage of negative cloud-to-ground lightning. The discharges are quite different from conventional streamers or leaders. A detailed analysis reveals that the shape of the pulses is determined by the runaway breakdown of air in the thundercloud electric field initiated by extensive atmospheric showers (RB-EAS). The high amplitude of the pulse electric current is due to the multiple microdischarges at hydrometeors stimulated and synchronized by the low-energy electrons generated in the RB-EAS process. The series of specific pulse discharges leads to charge reset from hydrometeors to the free ions and creates numerous stretched ion clusters, both positive and negative. As a result, a wide region in the thundercloud with a sufficiently high fractal ion conductivity is formed. The charge transport by ions plays a decisive role in the lightning leader preconditioning.

Wrinkle-like slip pulse on a fault between different materials

USGS Publications Warehouse

Andrews, D.J.; Ben-Zion, Y.

1997-01-01

Pulses of slip velocity can propagate on a planar interface governed by a constant coefficient of friction, where the interface separates different elastic materials. Such pulses have been found in two-dimensional plane strain finite difference calculations of slip on a fault between elastic media with wave speeds differing by 20%. The self-sustaining propagation of the slip pulse arises from interaction between normal and tangential deformation that exists only with a material contrast. These calculations confirm the prediction of Weertman [1980] that a dislocation propagating steadily along a material interface has a tensile change of normal traction with the same pulse shape as slip velocity. The self-sustaining pulse is associated with a rapid transition from a head wave traveling along the interface with the S wave speed of the faster material, to an opposite polarity body wave traveling with the slower S speed. Slip occurs during the reversal of normal particle velocity. The pulse can propagate in a region with constant coefficient of friction and an initial stress state below the frictional criterion. Propagation occurs in only one direction, the direction of slip in the more compliant medium, with rupture velocity near the slower S wave speed. Displacement is larger in the softer medium, which is displaced away from the fault during the passage of the slip pulse. Motion is analogous to a propagating wrinkle in a carpet. The amplitude of slip remains approximately constant during propagation, but the pulse width decreases and the amplitudes of slip velocity and stress change increase. The tensile change of normal traction increases until absolute normal traction reaches zero. The pulse can be generated as a secondary effect of a drop of shear stress in an asperity. The pulse shape is unstable, and the initial slip pulse can change during propagation into a collection of sharper pulses. Such a pulse enables slip to occur with little loss of energy to friction, while at the same time increasing irregularity of stress and slip at the source. Copyright 1997 by the American Geophysical Union.

Effect of pulse duration on photomechanical response of soft tissue during Ho:YAG laser ablation

NASA Astrophysics Data System (ADS)

Jansen, E. Duco; Motamedi, Massoud; Pfefer, T. Joshua; Asshauer, Thomas; Frenz, Martin; Delacretaz, Guy P.; Abela, George S.; Welch, Ashley J.

1995-05-01

Mechanical injury during pulsed holmium laser ablation of tissue is caused by rapid bubble expansion and collapse or by laser-induced pressure waves. In this study the effect of pulse duration on the photomechanical response of soft tissue during holmium:YAG laser ablation has been investigated. The dynamics of laser-induced bubble formation was documented in water and in transparent polyacrylamide tissue phantoms with a water concentration of 84%. Holmium:YAG laser radiation ((lambda) equals 2.12 micrometers ) was delivered in water or tissue phantoms via an optical fiber (200 or 400 micrometers ). The laser was operated in either the Q- switched mode ((tau) p equals 500 ns, Qp equals 14 +/- 1 mJ, 200 micrometers fiber, Ho equals 446 mJ/mm2) or the free-running mode ((tau) p equals 100 - 1100 microsecond(s) , Qp equals 200 +/- 5 mJ, 400 micrometers fiber, Ho equals 1592 mJ/mm2). Bubble formation was documented using a fast flash photography setup while simultaneously a PVDP needle hydrophone (40 ns risetime), recorded pressures. The effect of the pulse duration on the photomechanical response of soft biological tissue was evaluated by delivering 5 pulses of 800 mJ to the intimal side of porcine aorta in vitro, followed by histologic evaluation. It was observed that, as the pulse duration was increased the bubble shape changed from almost spherical for Q-switched pulses to a more elongated, cylindrical shape for the longer pulse durations. The bubble expansion velocity was larger for shorter pulse durations. A thermo- elastic expansion wave was measured only during Q-switched pulse delivery. All pulses that induced bubble formation generated pressure waves upon collapse of the bubble in water as well as in the gel. The amplitude of the pressure wave depended strongly on the size and geometry of the laser-induced bubble. The important findings of this study were (1) the magnitude of collapse pressure wave decreased as laser pulse duration increased, and (2) mechanical tissue damage is reduced significantly by using longer pulse durations (> 460 microsecond(s) , for the pulse energy used).

Characteristics of nonlinear imaging of broadband laser stacked by chirped pulses

NASA Astrophysics Data System (ADS)

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

2014-11-01

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

Performance of a neutron spectrometer based on a PIN diode.

PubMed

Agosteo, S; D'Angelo, G; Fazzi, A; Para, A Foglio; Pola, A; Ventura, L; Zotto, P

2005-01-01

The neutron spectrometer discussed in this work consists of a PIN diode coupled with a polyethylene converter. Neutrons are detected through the energy deposited by recoil-protons in silicon. The maximum detectable energy is -6 MeV and is imposed by the thickness of the fully depleted layer (300 microm for the present device). The minimum detectable energy which can be assessed with pulse-shape discrimination (PSD) is -0.9 MeV. PSD is performed with a crossover method and setting the diode in the 'reverse-injection' configuration (i.e. with the N+ layer adjacent to the converter). This configuration provides longer collection times for the electron-hole pairs generated by the recoil-protons. The limited interval of detectable energies restricts the application of this spectrometer to low-energy neutron fields, such as the ones which can be produced at facilities hosting low-energy ion accelerators. The capacity to reproduce continuous neutron spectra was investigated by optimising the electronic chain for pulse-shape discrimination. In particular, the spectrometer was irradiated with neutrons that were generated by striking a thick beryllium target with protons of several energies and the measured spectra were compared with data taken from the literature.

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.

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.

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.

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.

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.

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.

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.

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.

Shaping the spectrum of random-phase radar waveforms

DOEpatents

Doerry, Armin W.; Marquette, Brandeis

2017-05-09

The various technologies presented herein relate to generation of a desired waveform profile in the form of a spectrum of apparently random noise (e.g., white noise or colored noise), but with precise spectral characteristics. Hence, a waveform profile that could be readily determined (e.g., by a spoofing system) is effectively obscured. Obscuration is achieved by dividing the waveform into a series of chips, each with an assigned frequency, wherein the sequence of chips are subsequently randomized. Randomization can be a function of the application of a key to the chip sequence. During processing of the echo pulse, a copy of the randomized transmitted pulse is recovered or regenerated against which the received echo is correlated. Hence, with the echo energy range-compressed in this manner, it is possible to generate a radar image with precise impulse response.

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

Robustness of high-fidelity Rydberg gates with single-site addressability

NASA Astrophysics Data System (ADS)

Goerz, Michael H.; Halperin, Eli J.; Aytac, Jon M.; Koch, Christiane P.; Whaley, K. Birgitta

2014-09-01

Controlled-phase (cphase) gates can be realized with trapped neutral atoms by making use of the Rydberg blockade. Achieving the ultrahigh fidelities required for quantum computation with such Rydberg gates, however, is compromised by experimental inaccuracies in pulse amplitudes and timings, as well as by stray fields that cause fluctuations of the Rydberg levels. We report here a comparative study of analytic and numerical pulse sequences for the Rydberg cphase gate that specifically examines the robustness of the gate fidelity with respect to such experimental perturbations. Analytical pulse sequences of both simultaneous and stimulated Raman adiabatic passage (STIRAP) are found to be at best moderately robust under these perturbations. In contrast, optimal control theory is seen to allow generation of numerical pulses that are inherently robust within a predefined tolerance window. The resulting numerical pulse shapes display simple modulation patterns and can be rationalized in terms of an interference between distinct two-photon Rydberg excitation pathways. Pulses of such low complexity should be experimentally feasible, allowing gate fidelities of order 99.90-99.99% to be achievable under realistic experimental conditions.

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)

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.

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.

Reconfigurable ultra-wideband waveform generation with simple photonic devices

NASA Astrophysics Data System (ADS)

Dastmalchi, Mansour; Abtahi, Mohammad; Lemus, David; Rusch, Leslie A.; LaRochelle, Sophie

2012-08-01

We propose and experimentally demonstrate a low cost, low power consumption technique for ultra-wideband pulse shaping. Our approach is based on thermal apodization of two identical linearly chirped fiber Bragg gratings (LCFBG) placed in both arms of a balanced photodetector. Resistive heating elements with low electrical power consumption are used to tune the LCFBG spectral responses. Using a standard gain switched distributed feedback laser as a pulsed optical source and a simple energy detector receiver, we measured a bit error rate of 1.5×10-4 at a data rate of 1 Gb/s after RF transmission over a 1-m link.

Characteristics of a Direct Current-driven plasma jet operated in open air

NASA Astrophysics Data System (ADS)

Li, Xuechen; Di, Cong; Jia, Pengying; Bao, Wenting

2013-09-01

A DC-driven plasma jet has been developed to generate a diffuse plasma plume by blowing argon into the ambient air. The plasma plume, showing a cup shape with a diameter of several centimeters at a higher voltage, is a pulsed discharge despite a DC voltage is applied. The pulse frequency is investigated as a function of the voltage under different gap widths and gas flow rates. Results show that plasma bullets propagate from the hollow needle to the plate electrode by spatially resolved measurement. A supposition about non-electroneutral trail of the streamer is proposed to interpret these experimental phenomena.

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.

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.

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.

Pulsed eddy current inspection of broach support plates in steam generators

NASA Astrophysics Data System (ADS)

Mokros, Sarah Gwendolyn

Steam Generators (SGs) are a critical component of nuclear reactors, employing thousands of SG tubes to convert heat generated in the reactor core into useable energy. SG tubes are supported at numerous locations by Broach Support Plates (BSPs) that have trefoil shaped holes, which prevent excessive tube vibrations, while allowing water to easily flow through the support structures. A number of degradation modes occur in SGs, such as SG tube fretting, cracking or denting, requiring periodic inspection. Currently, conventional Eddy Current Testing (ECT) is used to non-destructively assess the condition of SG tubes and components. However, as reactors age, new modes of degradation will likely appear that may be difficult to detect and characterize using conventional ECT, such as wall loss in BSPs and build-up of corrosion products, which typically form as a hard sludge called magnetite. Pulsed Eddy Current (PEC) technologies are an emerging technique that is presented in this work as a method to further advance inspection techniques used in CANDURTM nuclear reactors. A PEC probe was designed to inspect the unique shape of the trefoil shaped hole to detect and characterize wall loss and the presence of magnetite in A516 carbon steel BSPs with trefoil shaped holes from within 15.9 mm (5/8") Alloy-800 SG tubes. PEC was also used to observe how measurements of wall loss were affected by the presence of magnetite. This work presents Finite Element Method (FEM) simulations and experimental results collected to observe these degradation modes. The probe was demonstrated to be capable of detecting far side wall loss as low as 20%, locating and characterizing the relative permeability of magnetite, and of detecting wall loss when magnetite was present. FEM simulations and experimental results were found to be in good agreement, suggesting that additional investigations of the effects of BSP degradation on PEC signal response may also be performed using FEM models.

Handheld probe for portable high frame photoacoustic/ultrasound imaging system

NASA Astrophysics Data System (ADS)

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

2013-03-01

Photoacoustics is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophors. In current research, this technique uses large and costly photoacoustic systems with a low frame rate imaging. To open the door for widespread clinical use, a compact, cost effective and fast system is required. In this paper we report on the development of a small compact handset pulsed laser probe which will be connected to a portable ultrasound system for real-time photoacoustic imaging and ultrasound imaging. The probe integrates diode lasers driven by an electrical driver developed for very short high power pulses. It uses specifically developed highly efficient diode stacks with high frequency repetition rate up to 10 kHz, emitting at 800nm wavelength. The emitted beam is collimated and shaped with compact micro optics beam shaping system delivering a homogenized rectangular laser beam intensity distribution. The laser block is integrated with an ultrasound transducer in an ergonomically designed handset probe. This handset is a building block enabling for a low cost high frame rate photoacoustic and ultrasound imaging system. The probe was used with a modified ultrasound scanner and was tested by imaging a tissue mimicking phantom.

Watering the Tree of Science: Science Education, Local Knowledge, and Agency in Zambia's PSA Program

NASA Astrophysics Data System (ADS)

Lample, Emily

With increased public interest in protecting the environment, scientists and engineers aim to improve energy conversion efficiency. Thermoelectrics offer many advantages as thermal management technology. When compared to vapor compression refrigeration, above approximately 200 to 600 watts, cost in dollars per watt as well as COP are not advantageous for thermoelectrics. The goal of this work was to determine if optimized pulse supercooling operation could improve cooling capacity or efficiency of a thermoelectric device. The basis of this research is a thermal-electrical analogy based modeling study using SPICE. Two models were developed. The first model, a standalone thermocouple with no attached mass to be cooled. The second, a system that includes a module attached to a heat generating mass. With the thermocouple study, a new approach of generating response surfaces with characteristic parameters was applied. The current pulse height and pulse on-time was identified for maximizing Net Transient Advantage, a newly defined metric. The corresponding pulse height and pulse on-time was utilized for the system model. Along with the traditional steady state starting current of Imax, Iopt was employed. The pulse shape was an isosceles triangle. For the system model, metrics new to pulse cooling were Qc, power consumption and COP. The effects of optimized current pulses were studied by changing system variables. Further studies explored time spacing between pulses and temperature distribution in the thermoelement. It was found net Q c over an entire pulse event can be improved over Imax steady operation but not over steady I opt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced in transient pulse operation due to the different time constants of Qc and Pin. In some cases lower performance interface materials allow more Qc and better COP during transient operation than higher performance interface materials. Important future work might look at developing innovative ways of biasing Joule heat to Th..

Recent advances in chemical synthesis methodology of inorganic materials and theoretical computations of metal nanoparticles/carbon interfaces

NASA Astrophysics Data System (ADS)

Harris, Andrew G.

With increased public interest in protecting the environment, scientists and engineers aim to improve energy conversion efficiency. Thermoelectrics offer many advantages as thermal management technology. When compared to vapor compression refrigeration, above approximately 200 to 600 watts, cost in dollars per watt as well as COP are not advantageous for thermoelectrics. The goal of this work was to determine if optimized pulse supercooling operation could improve cooling capacity or efficiency of a thermoelectric device. The basis of this research is a thermal-electrical analogy based modeling study using SPICE. Two models were developed. The first model, a standalone thermocouple with no attached mass to be cooled. The second, a system that includes a module attached to a heat generating mass. With the thermocouple study, a new approach of generating response surfaces with characteristic parameters was applied. The current pulse height and pulse on-time was identified for maximizing Net Transient Advantage, a newly defined metric. The corresponding pulse height and pulse on-time was utilized for the system model. Along with the traditional steady state starting current of Imax, Iopt was employed. The pulse shape was an isosceles triangle. For the system model, metrics new to pulse cooling were Qc, power consumption and COP. The effects of optimized current pulses were studied by changing system variables. Further studies explored time spacing between pulses and temperature distribution in the thermoelement. It was found net Q c over an entire pulse event can be improved over Imax steady operation but not over steady I opt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced in transient pulse operation due to the different time constants of Qc and Pin. In some cases lower performance interface materials allow more Qc and better COP during transient operation than higher performance interface materials. Important future work might look at developing innovative ways of biasing Joule heat to Th..

Network performance analysis and management for cyber-physical systems and their applications

NASA Astrophysics Data System (ADS)

Emfinger, William A.

With increased public interest in protecting the environment, scientists and engineers aim to improve energy conversion efficiency. Thermoelectrics offer many advantages as thermal management technology. When compared to vapor compression refrigeration, above approximately 200 to 600 watts, cost in dollars per watt as well as COP are not advantageous for thermoelectrics. The goal of this work was to determine if optimized pulse supercooling operation could improve cooling capacity or efficiency of a thermoelectric device. The basis of this research is a thermal-electrical analogy based modeling study using SPICE. Two models were developed. The first model, a standalone thermocouple with no attached mass to be cooled. The second, a system that includes a module attached to a heat generating mass. With the thermocouple study, a new approach of generating response surfaces with characteristic parameters was applied. The current pulse height and pulse on-time was identified for maximizing Net Transient Advantage, a newly defined metric. The corresponding pulse height and pulse on-time was utilized for the system model. Along with the traditional steady state starting current of Imax, Iopt was employed. The pulse shape was an isosceles triangle. For the system model, metrics new to pulse cooling were Qc, power consumption and COP. The effects of optimized current pulses were studied by changing system variables. Further studies explored time spacing between pulses and temperature distribution in the thermoelement. It was found net Q c over an entire pulse event can be improved over Imax steady operation but not over steady I opt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced in transient pulse operation due to the different time constants of Qc and Pin. In some cases lower performance interface materials allow more Qc and better COP during transient operation than higher performance interface materials. Important future work might look at developing innovative ways of biasing Joule heat to Th..

Soft error aware physical synthesis

NASA Astrophysics Data System (ADS)

Assis, Thiago Rocha de

With increased public interest in protecting the environment, scientists and engineers aim to improve energy conversion efficiency. Thermoelectrics offer many advantages as thermal management technology. When compared to vapor compression refrigeration, above approximately 200 to 600 watts, cost in dollars per watt as well as COP are not advantageous for thermoelectrics. The goal of this work was to determine if optimized pulse supercooling operation could improve cooling capacity or efficiency of a thermoelectric device. The basis of this research is a thermal-electrical analogy based modeling study using SPICE. Two models were developed. The first model, a standalone thermocouple with no attached mass to be cooled. The second, a system that includes a module attached to a heat generating mass. With the thermocouple study, a new approach of generating response surfaces with characteristic parameters was applied. The current pulse height and pulse on-time was identified for maximizing Net Transient Advantage, a newly defined metric. The corresponding pulse height and pulse on-time was utilized for the system model. Along with the traditional steady state starting current of Imax, Iopt was employed. The pulse shape was an isosceles triangle. For the system model, metrics new to pulse cooling were Qc, power consumption and COP. The effects of optimized current pulses were studied by changing system variables. Further studies explored time spacing between pulses and temperature distribution in the thermoelement. It was found net Q c over an entire pulse event can be improved over Imax steady operation but not over steady I opt operation. Qc can be improved over Iopt operation but only during the early part of the pulse event. COP is reduced in transient pulse operation due to the different time constants of Qc and Pin. In some cases lower performance interface materials allow more Qc and better COP during transient operation than higher performance interface materials. Important future work might look at developing innovative ways of biasing Joule heat to Th..

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.

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.

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.

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

Development of models simulating operation of elements of radio devices, for solving problems of ensuring electromagnetic compatibility of radio electronic means

NASA Astrophysics Data System (ADS)

Glotov, V. V.; Ostroumov, I. V.; Romashchenko, M. A.

2018-05-01

To study the effect of phase-shift signals parameters on EMC of REM, a generalized signal generation model in a radio transmitter was developed which allows obtaining digital representations of phase-shift signals, which are a continuous pulse in the time domain and on the frequency axis with different signal element envelope shapes.

Recursive Algorithms for Real-Time Digital CR-RCn Pulse Shaping

NASA Astrophysics Data System (ADS)

Nakhostin, M.

2011-10-01

This paper reports on recursive algorithms for real-time implementation of CR-(RC)n filters in digital nuclear spectroscopy systems. The algorithms are derived by calculating the Z-transfer function of the filters for filter orders up to n=4 . The performances of the filters are compared with the performance of the conventional digital trapezoidal filter using a noise generator which separately generates pure series, 1/f and parallel noise. The results of our study enable one to select the optimum digital filter for different noise and rate conditions.

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.

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.

Rapid and slow: Varying magma ascent rates as a mechanism for Vulcanian explosions

NASA Astrophysics Data System (ADS)

Cassidy, Mike; Cole, Paul. D.; Hicks, Kelby E.; Varley, Nick R.; Peters, Nial; Lerner, Allan H.

2015-06-01

Vulcanian explosions are one of the most common types of volcanic activity observed at silicic volcanoes. Magma ascent rates are often invoked as being the fundamental control on their explosivity, yet this factor is poorly constrained for low magnitude end-member Vulcanian explosions, which are particularly poorly understood, partly due to the rarity of ash samples and low gas fluxes. We describe ash generated by small Vulcanian explosions at Volcán de Colima in 2013, where we document for the first time marked differences in the vesicularity, crystal characteristics (volume fraction, size and shape) and glass compositions in juvenile material from discrete events. We interpret these variations as representing differing ascent styles and speeds of magma pulses within the conduit. Heterogeneous degassing during ascent leads to fast ascending, gas-rich magma pulses together with slow ascending gas-poor magma pulses within the same conduit. This inferred heterogeneity is complemented by SO2 flux data, which show transient episodes of both open and closed system degassing, indicating efficient shallow fracture sealing mechanisms, which allows for gas overpressure to generate small Vulcanian explosions.

Effects of current on droplet generation and arc plasma in gas metal arc welding

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

Hu, J.; Tsai, H. L.

2006-09-01

In gas metal arc welding (GMAW), a technology using pulsed currents has been employed to achieve the one-droplet-per-pulse (ODPP) metal transfer mode with the advantages of low average currents, a stable and controllable droplet generation, and reduced spatter. In this paper, a comprehensive model was developed to study the effects of different current profiles on the droplet formation, plasma generation, metal transfer, and weld pool dynamics in GMAW. Five types of welding currents were studied, including two constant currents and three wave form currents. In each type, the transient temperature and velocity distributions of the arc plasma and the moltenmore » metal, and the shapes of the droplet and the weld pool were calculated. The results showed that a higher current generates smaller droplets, higher droplet frequency, and higher electromagnetic force that becomes the dominant factor detaching the droplet from the electrode tip. The model has demonstrated that a stable ODPP metal transfer mode can be achieved by choosing a current with proper wave form for given welding conditions.« less

Generation and transmission of multilevel quadrature amplitude modulation formats using only one optical modulator: MATLAB Simulink simulation models

NASA Astrophysics Data System (ADS)

Binh, Le Nguyen

2009-04-01

A geometrical and phasor representation technique is presented to illustrate the modulation of the lightwave carrier to generate quadrature amplitude modulated (QAM) signals. The modulation of the amplitude and phase of the lightwave carrier is implemented using only one dual-drive Mach-Zehnder interferometric modulator (MZIM) with the assistance of phasor techniques. Any multilevel modulation scheme can be generated, but we illustrate specifically, the multilevel amplitude and differential phase shift keying (MADPSK) signals. The driving voltage levels are estimated for driving the traveling wave electrodes of the modulator. Phasor diagrams are extensively used to demonstrate the effectiveness of modulation schemes. MATLAB Simulink models are formed to generate the multilevel modulation formats, transmission, and detection in optically amplified fiber communication systems. Transmission performance is obtained for the multilevel optical signals and proven to be equivalent or better than those of binary level with equivalent bit rate. Further, the resilience to nonlinear effects is much higher for MADPSK of 50% and 33% pulse width as compared to non-return-to-zero (NRZ) pulse shaping.

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

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.

Ultrafast excited-state dynamics in shape- and composition-controlled gold–silver bimetallic nanostructures

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

Zarick, Holly F.; Boulesbaa, Abdelaziz; Talbert, Eric M.

In this paper, we have examined the ultrafast dynamics of shape- and composition-controlled bimetallic Au/Ag core/shell nanostructures with transient absorption spectroscopy (TAS) as a function of Ag layer thickness (0–15 nm) and pump excitation fluence (50–500 nJ/pulse). Our synthesis approach generated both bimetallic nanocubes and nanopyramids with distinct dipolar plasmon resonances and plasmon dephasing behavior at the resonance. Lifetimes obtained from TAS at low powers (50 nJ/pulse) demonstrated minimal dependence on the Ag layer thickness, whereas at high power (500 nJ/pulse) a rise in electron–phonon coupling lifetime (τ 1) was observed with increasing Ag shell thickness for both nanocubes andmore » nanopyramids. This is attributable to the stronger absorption of the 400 nm pump pulse with higher Ag content, which induced higher electron temperatures. The phonon–phonon scattering lifetime (τ 2) also rises with increasing Ag layer, contributed both by the increasing size of the Au/Ag nanostructures as well as by surface chemistry effects. Further, we observed that even the thinnest, 2 nm, Ag shell strongly impacts both τ 1 and τ 2 at high power despite minimal change in overall size, indicating that the nanostructure composition also strongly impacts the thermalization temperature following absorption of 400 nm light. We also observed a shape-dependent trend at high power, where τ 2 increased for the nanopyramids with increasing Ag shell thickness and nanostructure size, but bimetallic nanocubes demonstrated an unexpected decrease in τ 2 for the thickest, 15 nm, Ag shell. This was attributed to the larger number of corners and edges in the nanocubes relative to the nanopyramids.« less

Wavelength stabilized high pulse power laser diodes for automotive LiDAR

NASA Astrophysics Data System (ADS)

Knigge, A.; Klehr, A.; Wenzel, H.; Zeghuzi, A.; Fricke, J.; Maaßdorf, A.; Liero, A.; Tränkle, G.

2018-03-01

Diode lasers generating optical pulses with high peak power and lengths in the nanosecond range are key components of systems for free-space communication, metrology, material processing, spectroscopy, and light detection and ranging (LiDAR) as needed for object detection and autonomous driving. Automotive LiDAR systems demand additionally a good beam quality and low wavelength shift with temperature due to the wide operating temperature span. We present here internally wavelength stabilized lasers emitting ns optical pulses from an emission aperture between 30 μm and 100 μm with peak powers of tens of Watts at wavelengths around 905 nm. The vertical structure based on AlGaAs (confinement and cladding layers) and InGaAs (active quantum well) is especially optimized for pulsed operation with respect to the implementation of a surface Bragg grating with a high reflectivity. The fabricated 6 mm long distributed Bragg reflector (DBR) broad area (BA) lasers are electrically driven by an in-house developed high-speed unit generating 3 to 10 ns long nearly rectangular shaped current pulses with amplitudes of up to 250 A. Such lasers emit optical pulses with a peak power of more than 30 W at 95 A pulse current up to a temperature of 85°C with a wavelength shift as low as 65 pm/K and a lateral beam propagation factor less than 10. The influence of the lateral aperture width and the pulse length on the beam quality will be shown. A monolithic integration of 3 DBR BA lasers on a single chip whose emission can be combined into a single beam raises the output power to more than 100 W.

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

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.

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.

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.

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.

Propagation of relativistic surface harmonics radiation in free space

NASA Astrophysics Data System (ADS)

an der Brügge, Daniel; Pukhov, Alexander

2007-09-01

Relativistic high-harmonics generation from overdense plasma surfaces is studied using three-dimensional particle-in-cell simulations. It is shown that the simple vacuum propagation in the real three-dimensional geometry strongly affects the harmonics spectrum on the optical axis. It may even lead to the formation of attosecond pulses without any special optical filters. To make good use of these effects it is necessary to shape either the laser pulse focal spot, or the surface material in such a way that the S-number of the interaction [see Gordienko and Pukhov, Phys. Plasmas 12, 043109 (2005)] is preserved over the largest possible area. The three-dimensional simulations are carefully compared with the one-dimensional ones. It is shown that the one-dimensional models work well even in cases where the laser is focused to a quite small spot on the harmonics generating surface (σ≈λ).

On second harmonic generation and multiphoton-absorption induced luminescence from laser-reshaped silver nanoparticles embedded in glass.

PubMed

Zolotovskaya, S A; Tyrk, M A; Stalmashonak, A; Gillespie, W A; Abdolvand, A

2016-10-28

Spherical silver nanoparticles (NPs) of 30 nm diameter embedded in soda-lime glass were uniformly reshaped (elongated) after irradiation by a linearly polarised 250 fs pulsed laser operating within the NPs' surface plasmon resonance band. We observed second harmonic generation (SHG) and multiphoton-absorption-induced luminescence (MAIL) in the embedded laser-reshaped NPs upon picosecond (10 ps) pulsed laser excitation at 1064 nm. A complementary study of SHG and MAIL was conducted in soda-lime glass containing embedded, mechanically-reshaped silver NPs of a similar elongation ratio (aspect ratio) to the laser-reshaped NPs. This supports the notion that the observed difference in SHG and MAIL in the studied nanocomposite systems is due to the shape modification mechanism. The discrete dipole approximation method was used to assess the absorption and scattering cross-sections of the reshaped NPs with different elongation ratios.

Ultraviolet and near-infrared femtosecond temporal pulse shaping with a new high-aspect-ratio one-dimensional micromirror array.

PubMed

Weber, Stefan M; Extermann, Jérôme; Bonacina, Luigi; Noell, Wilfried; Kiselev, Denis; Waldis, Severin; de Rooij, Nico F; Wolf, Jean-Pierre

2010-09-15

We demonstrate the capabilities of a new optical microelectromechanical systems device that we specifically developed for broadband femtosecond pulse shaping. It consists of a one-dimensional array of 100 independently addressable, high-aspect-ratio micromirrors with up to 3 μm stroke. We apply linear and quadratic phase modulations demonstrating the temporal compression of 800 and 400 nm pulses. Because of the device's surface flatness, stroke, and stroke resolution, phase shaping over an unprecedented bandwidth is attainable.

Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors

NASA Astrophysics Data System (ADS)

Luo, X. L.; Modamio, V.; Nyberg, J.; Valiente-Dobón, J. J.; Nishada, Q.; de Angelis, G.; Agramunt, J.; Egea, F. J.; Erduran, M. N.; Ertürk, S.; de France, G.; Gadea, A.; González, V.; Goasduff, A.; Hüyük, T.; Jaworski, G.; Moszyński, M.; Di Nitto, A.; Palacz, M.; Söderström, P.-A.; Sanchis, E.; Triossi, A.; Wadsworth, R.

2018-07-01

The issue of pulse pile-up is frequently encountered in nuclear experiments involving high counting rates, which will distort the pulse shapes and the energy spectra. A digital method of off-line processing of pile-up pulses is presented. The pile-up pulses were firstly identified by detecting the downward-going zero-crossings in the first-order derivative of the original signal, and then the constituent pulses were reconstructed based on comparing the pile-up pulse with four models that are generated by combining pairs of neutron and γ standard pulses together with a controllable time interval. The accuracy of this method in resolving the pile-up events was investigated as a function of the time interval between two pulses constituting a pile-up event. The obtained results show that the method is capable of disentangling two pulses with a time interval among them down to 20 ns, as well as classifying them as neutrons or γ rays. Furthermore, the error of reconstructing pile-up pulses could be kept below 6% when successive peaks were separated by more than 50 ns. By applying the method in a high counting rate of pile-up events measurement of the NEutron Detector Array (NEDA), it was empirically found that this method can reconstruct the pile-up pulses and perform neutron- γ discrimination quite accurately. It can also significantly correct the distorted pulse height spectrum due to pile-up events.

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.

Electric field induced needle-pulsed arc discharge carbon nanotube production apparatus: circuitry and mechanical design.

PubMed

Kia, Kaveh Kazemi; Bonabi, Fahimeh

2012-12-01

A simple and low cost apparatus is reported to produce multiwall carbon nanotubes and carbon nano-onions by a low power short pulsed arc discharge reactor. The electric circuitry and the mechanical design details and a micro-filtering assembly are described. The pulsed-plasma is generated and applied between two graphite electrodes. The pulse width is 0.3 μs. A strong dc electric field is established along side the electrodes. The repetitive discharges occur in less than 1 mm distance between a sharp tip graphite rod as anode, and a tubular graphite as cathode. A hydrocarbon vapor, as carbon source, is introduced through the graphite nozzle in the cathode assembly. The pressure of the chamber is controlled by a vacuum pump. A magnetic field, perpendicular to the plasma path, is provided. The results show that the synergetic use of a pulsed-current and a dc power supply enables us to synthesize carbon nanoparticles with short pulsed plasma. The simplicity and inexpensiveness of this plan is noticeable. Pulsed nature of plasma provides some extra degrees of freedom that make the production more controllable. Effects of some design parameters such as electric field, pulse frequency, and cathode shape are discussed. The products are examined using scanning probe microscopy techniques.

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.

Electric field induced needle-pulsed arc discharge carbon nanotube production apparatus: Circuitry and mechanical design

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

Kia, Kaveh Kazemi; Bonabi, Fahimeh

A simple and low cost apparatus is reported to produce multiwall carbon nanotubes and carbon nano-onions by a low power short pulsed arc discharge reactor. The electric circuitry and the mechanical design details and a micro-filtering assembly are described. The pulsed-plasma is generated and applied between two graphite electrodes. The pulse width is 0.3 {mu}s. A strong dc electric field is established along side the electrodes. The repetitive discharges occur in less than 1 mm distance between a sharp tip graphite rod as anode, and a tubular graphite as cathode. A hydrocarbon vapor, as carbon source, is introduced through themore » graphite nozzle in the cathode assembly. The pressure of the chamber is controlled by a vacuum pump. A magnetic field, perpendicular to the plasma path, is provided. The results show that the synergetic use of a pulsed-current and a dc power supply enables us to synthesize carbon nanoparticles with short pulsed plasma. The simplicity and inexpensiveness of this plan is noticeable. Pulsed nature of plasma provides some extra degrees of freedom that make the production more controllable. Effects of some design parameters such as electric field, pulse frequency, and cathode shape are discussed. The products are examined using scanning probe microscopy techniques.« less

Progress Towards Improved Analysis of TES X-ray Data Using Principal Component Analysis

NASA Technical Reports Server (NTRS)

Busch, S. E.; Adams, J. S.; Bandler, S. R.; Chervenak, J. A.; Eckart, M. E.; Finkbeiner, F. M.; Fixsen, D. J.; Kelley, R. L.; Kilbourne, C. A.; Lee, S.-J.;

Electric field induced needle-pulsed arc discharge carbon nanotube production apparatus: Circuitry and mechanical design

NASA Astrophysics Data System (ADS)

Kia, Kaveh Kazemi; Bonabi, Fahimeh

2012-12-01

A simple and low cost apparatus is reported to produce multiwall carbon nanotubes and carbon nano-onions by a low power short pulsed arc discharge reactor. The electric circuitry and the mechanical design details and a micro-filtering assembly are described. The pulsed-plasma is generated and applied between two graphite electrodes. The pulse width is 0.3 μs. A strong dc electric field is established along side the electrodes. The repetitive discharges occur in less than 1 mm distance between a sharp tip graphite rod as anode, and a tubular graphite as cathode. A hydrocarbon vapor, as carbon source, is introduced through the graphite nozzle in the cathode assembly. The pressure of the chamber is controlled by a vacuum pump. A magnetic field, perpendicular to the plasma path, is provided. The results show that the synergetic use of a pulsed-current and a dc power supply enables us to synthesize carbon nanoparticles with short pulsed plasma. The simplicity and inexpensiveness of this plan is noticeable. Pulsed nature of plasma provides some extra degrees of freedom that make the production more controllable. Effects of some design parameters such as electric field, pulse frequency, and cathode shape are discussed. The products are examined using scanning probe microscopy techniques.

Pulse-shape discrimination with Cs2HfCl6 crystal scintillator

NASA Astrophysics Data System (ADS)

Cardenas, C.; Burger, A.; Goodwin, B.; Groza, M.; Laubenstein, M.; Nagorny, S.; Rowe, E.

2017-10-01

The results of investigation into cesium hafnium chloride (Cs2HfCl6) scintillating crystals as a promising detector to search for rare nuclear processes occurring in Hf isotopes is reported. The light output, quenching factor, and pulse-shape characteristics have been investigated at room temperature. The scintillation response of the crystal induced by α-particles and γ-quanta were studied to determine possibility of particle discrimination. Using the optimal filter method we obtained clear separation between signals with a factor of merit (FOM) = 9.3. This indicates that we are able to fully separate signals originating from α-particles and γ-quanta. Similar fruitful discrimination power was obtained by applying the mean time method (FOM = 7) and charge integration method (FOM = 7.5). The quenching factor for collimated 4 MeV α-particles is found to be 0.36, showing that α-particles generate more than a third of the light compared to γ-quanta at the same energy.

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.

A single-board NMR spectrometer based on a software defined radio architecture

NASA Astrophysics Data System (ADS)

Tang, Weinan; Wang, Weimin

2011-01-01

A single-board software defined radio (SDR) spectrometer for nuclear magnetic resonance (NMR) is presented. The SDR-based architecture, realized by combining a single field programmable gate array (FPGA) and a digital signal processor (DSP) with peripheral radio frequency (RF) front-end circuits, makes the spectrometer compact and reconfigurable. The DSP, working as a pulse programmer, communicates with a personal computer via a USB interface and controls the FPGA through a parallel port. The FPGA accomplishes digital processing tasks such as a numerically controlled oscillator (NCO), digital down converter (DDC) and gradient waveform generator. The NCO, with agile control of phase, frequency and amplitude, is part of a direct digital synthesizer that is used to generate an RF pulse. The DDC performs quadrature demodulation, multistage low-pass filtering and gain adjustment to produce a bandpass signal (receiver bandwidth from 3.9 kHz to 10 MHz). The gradient waveform generator is capable of outputting shaped gradient pulse waveforms and supports eddy-current compensation. The spectrometer directly acquires an NMR signal up to 30 MHz in the case of baseband sampling and is suitable for low-field (<0.7 T) application. Due to the featured SDR architecture, this prototype has flexible add-on ability and is expected to be suitable for portable NMR systems.

Optically controlled laser-plasma electron accelerator for compact gamma-ray sources

NASA Astrophysics Data System (ADS)

Kalmykov, S. Y.; Davoine, X.; Ghebregziabher, I.; Shadwick, B. A.

2018-02-01

Generating quasi-monochromatic, femtosecond γ-ray pulses via Thomson scattering (TS) demands exceptional electron beam (e-beam) quality, such as percent-scale energy spread and five-dimensional brightness over 1016 A m-2. We show that near-GeV e-beams with these metrics can be accelerated in a cavity of electron density, driven with an incoherent stack of Joule-scale laser pulses through a mm-size, dense plasma (n 0 ˜ 1019 cm-3). Changing the time delay, frequency difference, and energy ratio of the stack components controls the e-beam phase space on the femtosecond scale, while the modest energy of the optical driver helps afford kHz-scale repetition rate at manageable average power. Blue-shifting one stack component by a considerable fraction of the carrier frequency makes the stack immune to self-compression. This, in turn, minimizes uncontrolled variation in the cavity shape, suppressing continuous injection of ambient plasma electrons, preserving a single, ultra-bright electron bunch. In addition, weak focusing of the trailing component of the stack induces periodic injection, generating, in a single shot, a train of bunches with controllable energy spacing and femtosecond synchronization. These designer e-beams, inaccessible to conventional acceleration methods, generate, via TS, gigawatt γ-ray pulses (or multi-color pulse trains) with the mean energy in the range of interest for nuclear photonics (4-16 MeV), containing over 106 photons within a microsteradian-scale observation cone.

History of shock wave lithotripsy

NASA Astrophysics Data System (ADS)

Delius, Michael

2000-07-01

The first reports on the fragmentation of human calculi with ultrasound appeared in the fifties. Initial positive results with an extracorporeal approach with continuous wave ultrasound could, however, not be reproduced. A more promising result was found by generating the acoustic energy either in pulsed or continuous form directly at the stone surface. The method was applied clinically with success. Extracorporeal shock-wave generators unite the principle of using single ultrasonic pulses with the principle of generating the acoustic energy outside the body and focusing it through the skin and body wall onto the stone. Häusler and Kiefer reported the first successful contact-free kidney stone destruction by shock waves. They had put the stone in a water filled cylinder and generated a shock wave with a high speed water drop which was fired onto the water surface. To apply the new principle in medicine, both Häusler and Hoff's group at Dornier company constructed different shock wave generators for the stone destruction; the former used a torus-shaped reflector around an explosion wire, the latter the electrode-ellipsoid system. The former required open surgery to access the kidney stone, the latter did not. It was introduced into clinical practice after a series of experiments in Munich.

Contour forming of metals by laser peening

DOEpatents

Hackel, Lloyd; Harris, Fritz

2002-01-01

A method and apparatus are provided for forming shapes and contours in metal sections by generating laser induced compressive stress on the surface of the metal workpiece. The laser process can generate deep compressive stresses to shape even thick components without inducing unwanted tensile stress at the metal surface. The precision of the laser-induced stress enables exact prediction and subsequent contouring of parts. A light beam of 10 to 100 J/pulse is imaged to create an energy fluence of 60 to 200 J/cm.sup.2 on an absorptive layer applied over a metal surface. A tamping layer of water is flowed over the absorptive layer. The absorption of laser light causes a plasma to form and consequently creates a shock wave that induces a deep residual compressive stress into the metal. The metal responds to this residual stress by bending.

Experimental application of pulsed Ho:YAG laser-induced liquid jet as a novel rigid neuroendoscopic dissection device.

PubMed

Ohki, Tomohiro; Nakagawa, Atsuhiro; Hirano, Takayuki; Hashimoto, Tokitada; Menezes, Viren; Jokura, Hidefumi; Uenohara, Hiroshi; Sato, Yasuhiko; Saito, Tsutomu; Shirane, Reizo; Tominaga, Teiji; Takayama, Kazuyoshi

2004-01-01

Although water jet technology has been considered as a feasible neuroendoscopic dissection methodology because of its ability to perform selective tissue dissection without thermal damage, problems associated with continuous use of water and the ensuing fountain-effect-with catapulting of the tissue-could make water jets unsuitable for endoscopic use, in terms of safety and ease of handling. Therefore, the authors experimented with minimization of water usage during the application of a pulsed holmium:yttrium-aluminum-garnet (Ho:YAG) laser-induced liquid jet (LILJ), while assuring the dissection quality and the controllability of a conventional water jet dissection device. We have developed the LILJ generator for use as a rigid neuroendoscope, discerned its mechanical behavior, and evaluated its dissection ability using the cadaveric rabbit ventricular wall. The LILJ generator is incorporated into the tip of a stainless steel tube (length: 22 cm; internal diameter: 1.0 mm; external diameter: 1.4 mm), so that the device can be inserted into a commercial, rigid neuroendoscope. Briefly, the LILJ is generated by irradiating an internally supplied water column within the stainless steel tube using the pulsed Ho:YAG laser (wave length: 2.1 microm, pulse duration time: 350 microseconds) and is then ejected through the metal nozzle (internal diameter: 100 microm). The Ho:YAG laser pulse energy is conveyed through optical quartz fiber (core diameter: 400 microm), while cold water (5 degrees C) is internally supplied at a rate of 40 ml/hour. The relationship between laser energy (range: 40-433 mJ/pulse), standoff distance (defined as the distance between the tip of the optical fiber and the nozzle end; range: 10-30 mm), and the velocity, shape, pressure, and average volume of the ejected jet were analyzed by means of high-speed camera, PVDF needle hydrophone, and digital scale. The quality of the dissection plane, the preservation of blood vessels, and the penetration depth were evaluated using five fresh cadaveric rabbit ventricular walls, under neuroendoscopic vision. Jet velocity (7.0-19.6 m/second) and pressure (0.07-0.28 MPa) could be controlled by varying the laser energy, which determined the penetration depth in the cadaveric rabbit ventricular wall (0.07-1.30 mm/shot). The latter could be cut into desirable shapes-without thermal effects-under clear neuroendoscopic vision. The average volume of a single ejected jet could be confined to 0.42-1.52 microl/shot, and there was no accompanying generation of shock waves. Histological specimens revealed a sharp dissection plane and demonstrated that blood vessels of diameter over 100 microm could be preserved, without thermal damage. The present pulsed LILJ system holds promise as a safe and reliable dissection device for deployment in a rigid neuroendoscope. Copyright 2004 Wiley-Liss, Inc.

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

Lesion Generation Through Ribs Using Histotripsy Therapy Without Aberration Correction

PubMed Central

Kim, Yohan; Wang, Tzu-Yin; Xu, Zhen; Cain, Charles A.

2012-01-01

This study investigates the feasibility of using high-intensity pulsed therapeutic ultrasound, or histotripsy, to non-invasively generate lesions through the ribs. Histotripsy therapy mechanically ablates tissue through the generation of a cavitation bubble cloud, which occurs when the focal pressure exceeds a certain threshold. We hypothesize that histotripsy can generate precise lesions through the ribs without aberration correction if the main lobe retains its shape and exceeds the cavitation initiation threshold and the secondary lobes remain below the threshold. To test this hypothesis, a 750-kHz focused transducer was used to generate lesions in tissue-mimicking phantoms with and without the presence of rib aberrators. In all cases, 8000 pulses with 16 to 18 MPa peak rarefactional pressure at a repetition frequency of 100 Hz were applied without aberration correction. Despite the high secondary lobes introduced by the aberrators, high-speed imaging showed that bubble clouds were generated exclusively at the focus, resulting in well-confined lesions with comparable dimensions. Collateral damage from secondary lobes was negligible, caused by single bubbles that failed to form a cloud. These results support our hypothesis, suggesting that histotripsy has a high tolerance for aberrated fields and can generate confined focal lesions through rib obstacles without aberration correction. PMID:22083767

Lesion generation through ribs using histotripsy therapy without aberration correction.

PubMed

Kim, Yohan; Wang, Tzu-Yin; Xu, Zhen; Cain, Charles A

2011-11-01

This study investigates the feasibility of using high-intensity pulsed therapeutic ultrasound, or histotripsy, to non-invasively generate lesions through the ribs. Histotripsy therapy mechanically ablates tissue through the generation of a cavitation bubble cloud, which occurs when the focal pressure exceeds a certain threshold. We hypothesize that histotripsy can generate precise lesions through the ribs without aberration correction if the main lobe retains its shape and exceeds the cavitation initiation threshold and the secondary lobes remain below the threshold. To test this hypothesis, a 750-kHz focused transducer was used to generate lesions in tissue-mimicking phantoms with and without the presence of rib aberrators. In all cases, 8000 pulses with 16 to 18 MPa peak rarefactional pressure at a repetition frequency of 100 Hz were applied without aberration correction. Despite the high secondary lobes introduced by the aberrators, high-speed imaging showed that bubble clouds were generated exclusively at the focus, resulting in well-confined lesions with comparable dimensions. Collateral damage from secondary lobes was negligible, caused by single bubbles that failed to form a cloud. These results support our hypothesis, suggesting that histotripsy has a high tolerance for aberrated fields and can generate confined focal lesions through rib obstacles without aberration correction.

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.

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.

Muscle contraction during electro-muscular incapacitation: A comparison between square-wave pulses and the TASER(®) X26 Electronic control device.

PubMed

Comeaux, James A; Jauchem, James R; Cox, D Duane; Crane, Carrie C; D'Andrea, John A

2011-01-01

Electronic control devices (including the Advanced TASER(®) X26 model produced by TASER International) incapacitate individuals by causing muscle contractions. To provide information relevant to development of future potential devices, effects of monophasic square waves with different parameters were compared with those of the X26 electronic control device, using two animal models (frogs and swine). Pulse power, electrical pulse charge, pulse duration, and pulse repetition frequency affected muscle contraction. There was no difference in the charge required, between the square waveform and the X26 waveform, to cause approximately the same muscle-contraction response (in terms of the strength-duration curve). Thus, on the basis of these initial studies, the detailed shape of a waveform may not be important in terms of generating electro-muscular incapacitation. More detailed studies, however, may be required to thoroughly test all potential waveforms to be considered for future use in ECDs. 2010 American Academy of Forensic Sciences. Published 2010. This article is a U.S. Government work and is in the public domain in the U.S.A.

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.

Simulation of gamma-ray spectra for a variety of user-specified detector designs

NASA Technical Reports Server (NTRS)

Rester, A. C., Jr.

1994-01-01

The gamma-ray spectrum simulation program BSIMUL was designed to allow the operator to follow the path of a gamma-ray through a detector, shield and collimator whose dimensions are entered by the operator. It can also be used to simulate spectra that would be generated by a detector. Several improvements have been made to the program within the last few months. The detector, shield and collimator dimensions can now be entered through an interactive menu whose options are discussed below. In addition, spectra containing more than one gamma-ray energy can now be generated with the menu - for isotopes listed in the program. Adding isotopes to the main routine is also quite easy. Subroutines have been added to enable the operator to specify the material and dimensions of a collimator. This report details the progress made in simulating gamma-ray spectra for a variety of user-specified detector designs. In addition, a short discussion of work done in the related areas of pulse shape analysis and the spectral analysis is included. The pulse shape analysis and spectral analysis work is being performed pursuant to the requirements of contract F-94-C-0006, for the Advanced Research Projects Agency and the U.S. Air Force.

Growth of surface structures correlated with structural and mechanical modifications of brass by laser-induced Si plasma ions implantation

NASA Astrophysics Data System (ADS)

Ahmad, Shahbaz; Bashir, Shazia; Rafique, M. Shahid; Yousaf, Daniel

2017-04-01

Laser-produced Si plasma is employed as an ion source for implantation on the brass substrate for its surface, structural, and mechanical modifications. Thomson parabola technique is employed for the measurement of energy and flux of Si ions using CR-39. In response to stepwise increase in number of laser pulses from 3000 to 12000, four brass substrates were implanted by laser-induced Si plasma ions of energy 290 keV at different fluxes ranging from 45 × 1012 to 75 × 1015 ions/cm2. SEM analysis reveals the formation of nano/micro-sized irregular shaped cavities and pores for the various ion fluxes for varying numbers of laser pulses from 3000 to 9000. At the maximum ion flux for 12,000 pulses, distinct and organized grains with hexagonal and irregular shaped morphology are revealed. X-ray diffractometer (XRD) analysis exhibits that a new phase of CuSi (311) is identified which confirms the implantation of Si ions in brass substrate. A significant decrease in mechanical properties of implanted brass, such as Yield Stress (YS), Ultimate Tensile Strength (UTS), and hardness, with increasing laser pulses from 3000 to 6000 is observed. However, with increasing laser pulses from 9000 to a maximum value of 12,000, an increase in mechanical properties like hardness, YS, and UTS is observed. The generation as well as annihilation of defects, recrystallization, and intermixing of Si precipitates with brass matrix is considered to be responsible for variations in surface, structural, and mechanical modifications of brass.

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.

Photonic arbitrary waveform generation applicable to multiband UWB communications.

PubMed

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

2010-12-06

A novel photonic structure for arbitrary waveform generation (AWG) is proposed based on the electrooptical intensity modulation of a broadband optical signal which is transmitted by a dispersive element and the optoelectrical processing is realized by combining an interferometric structure with balanced photodetection. The generated waveform can be fully reconfigured through the control of the optical source power spectrum and the interferometric structure. The use of balanced photodetection permits to remove the baseband component of the generated signal which is relevant in certain applications. We have theoretically described and experimentally demonstrated the feasibility of the system by means of the generation of different pulse shapes. Specifically, the proposed structure has been applicable to generate Multiband UWB signaling formats regarding to the FCC requirements in order to show the flexibility of the system.

Radially and azimuthally polarized laser induced shape transformation of embedded metallic nanoparticles in glass.

PubMed

Tyrk, Mateusz A; Zolotovskaya, Svetlana A; Gillespie, W Allan; Abdolvand, Amin

2015-09-07

Radially and azimuthally polarized picosecond (~10 ps) pulsed laser irradiation at 532 nm wavelength led to the permanent reshaping of spherical silver nanoparticles (~30 - 40 nm in diameter) embedded in a thin layer of soda-lime glass. The observed peculiar shape modifications consist of a number of different orientations of nano-ellipsoids in the cross-section of each written line by laser. A Second Harmonic Generation cross-sectional scan method from silver nanoparticles in transmission geometry was adopted for characterization of the samples after laser modification. The presented approach may lead to sophisticated marking of information in metal-glass nanocomposites.

Long-term hole spin memory in the resonantly amplified spin coherence of InGaAs/GaAs quantum well electrons.

PubMed

Yugova, I A; Sokolova, A A; Yakovlev, D R; Greilich, A; Reuter, D; Wieck, A D; Bayer, M

2009-04-24

Pulsed optical excitation of the negatively charged trion has been used to generate electron spin coherence in an n-doped (In,Ga)As/GaAs quantum well. The coherence is monitored by resonant spin amplification detected at times exceeding the trion lifetime by 2 orders of magnitude. Still, even then signatures of the hole spin dynamics in the trion complex are imprinted in the signal leading to an unusual batlike shape of the magnetic field dispersion of spin amplification. From this shape information about the spin relaxation of both electrons and holes can be derived.

Effect of the depolarization field on coherent optical properties in semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Mitsumori, Yasuyoshi; Watanabe, Shunta; Asakura, Kenta; Seki, Keisuke; Edamatsu, Keiichi; Akahane, Kouichi; Yamamoto, Naokatsu

2018-06-01

We study the photon echo spectrum of self-assembled semiconductor quantum dots using femtosecond light pulses. The spectrum shape changes from a single-peaked to a double-peaked structure as the time delay between the two excitation pulses is increased. The spectrum change is reproduced by numerical calculations, which include the depolarization field induced by the biexciton-exciton transition as well as the conventional local-field effect for the exciton-ground-state transition in a quantum dot. Our findings suggest that various optical transitions in tightly localized systems generate a depolarization field, which renormalizes the resonant frequency with a change in the polarization itself, leading to unique optical properties.

High speed micromachining with high power UV laser

NASA Astrophysics Data System (ADS)

Patel, Rajesh S.; Bovatsek, James M.

2013-03-01

Increasing demand for creating fine features with high accuracy in manufacturing of electronic mobile devices has fueled growth for lasers in manufacturing. High power, high repetition rate ultraviolet (UV) lasers provide an opportunity to implement a cost effective high quality, high throughput micromachining process in a 24/7 manufacturing environment. The energy available per pulse and the pulse repetition frequency (PRF) of diode pumped solid state (DPSS) nanosecond UV lasers have increased steadily over the years. Efficient use of the available energy from a laser is important to generate accurate fine features at a high speed with high quality. To achieve maximum material removal and minimal thermal damage for any laser micromachining application, use of the optimal process parameters including energy density or fluence (J/cm2), pulse width, and repetition rate is important. In this study we present a new high power, high PRF QuasarR 355-40 laser from Spectra-Physics with TimeShiftTM technology for unique software adjustable pulse width, pulse splitting, and pulse shaping capabilities. The benefits of these features for micromachining include improved throughput and quality. Specific example and results of silicon scribing are described to demonstrate the processing benefits of the Quasar's available power, PRF, and TimeShift technology.

[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.

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.

Manipulating femtosecond laser interactions in bulk glass and thin-film with spatial light modulation (Conference Presentation)

NASA Astrophysics Data System (ADS)

Alimohammadian, Ehsan; Ho, Stephen; Ertorer, Erden; Gherghe, Sebastian; Li, Jianzhao; Herman, Peter R.

2017-03-01

Spatial Light Modulators (SLM) are emerging as a power tool for laser beam shaping whereby digitally addressed phase shifts can impose computer-generated hologram patterns on incoming laser light. SLM provide several additional advantages with ultrashort-pulsed lasers in controlling the shape of both surface and internal interactions with materials. Inside transparent materials, nonlinear optical effects can confine strong absorption only to the focal volume, extend dissipation over long filament tracks, or reach below diffraction-limited spot sizes. Hence, SLM beam shaping has been widely adopted for laser material processing applications that include parallel structuring, filamentation, fiber Bragg grating formation and optical aberration correction. This paper reports on a range of SLM applications we have studied in femtosecond processing of transparent glasses and thin films. Laser phase-fronts were tailored by the SLM to compensate for spherical surface aberration, and to further address the nonlinear interactions that interplay between Kerr-lens self-focusing and plasma defocusing effects over shallow and deep focusing inside the glass. Limits of strong and weak focusing were examined around the respective formation of low-loss optical waveguides and long uniform filament tracks. Further, we have employed the SLM for beam patterning inside thin film, exploring the limits of phase noise, resolution and fringe contrast during interferometric intra-film structuring. Femtosecond laser pulses of 200 fs pulse duration and 515 nm wavelength were shaped by a phase-only LCOS-SLM (Hamamatsu X10468-04). By imposing radial phase profiles, axicon, grating and beam splitting gratings, volume shape control of filament diameter, length, and uniformity as well as simultaneous formation of multiple filaments has been demonstrated. Similarly, competing effects of spherical surface aberration, self-focusing, and plasma de-focusing were studied and delineated to enable formation of low-loss optical waveguides over shallow and deep focusing conditions. Lastly, SLM beam shaping has been successfully extended to interferometric processing inside thin transparent film, enabling the arbitrary formation of uniform or non-uniform, symmetric or asymmetric patterns of flexible shape on nano-scale dimensions without phase-noise degradation by the SLM patterning. We present quantized structuring of thin films by a single laser pulse, demonstrating λ/2nfilm layer ejection control, blister formation, nano-cavities, and film colouring. Closed intra-film nanochannels with high aspect ratio (20:1) have been formed inside 3.5 um thick silica, opening new prospects for sub-cellular studies and lab-in-film concepts that integrate on CMOS silicon technologies.

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.

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

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

Influence of ambient pressure on surface structures generated by ultrashort laser pulse irradiation

NASA Astrophysics Data System (ADS)

JJ Nivas, J.; Allahyari, E.; Gesuele, F.; Maddalena, P.; Fittipaldi, R.; Vecchione, A.; Bruzzese, R.; Amoruso, S.

2018-02-01

We report an experimental investigation on the surface structures induced by linearly polarized ≈ 900 fs laser pulses, at λ = 1055 nm, on silicon at different values of the ambient pressure, from 10-4 mbar to one atmosphere. Our experimental findings address interesting influences of the surrounding pressure on: (1) the spatial period of ripples; (2) the formation of micro-grooves; (3) the shape of the structured area. Moreover, the effects of various states of polarization in vacuum as well as of circularly polarized pulses in air vs vacuum are also addressed. We identify as one possible key element of such experimental observations: the fact that as the pressure raises the ablated nanoparticles produced during the femtosecond ablation process of the target get deposited more and more on the sample surface covering the irradiated spot area and influencing the structuring process.

Characteristics of 1.9 μm laser emission from hydrogen-filled hollow-core fiber by stimulated Raman scattering

NASA Astrophysics Data System (ADS)

Gu, Bo; Chen, Yubin; Wang, Zefeng

2016-11-01

We report here the detailed characteristics of 1.9 μm laser emission from hydrogen-filled hollow-core fiber by stimulated Raman scattering. A 6.5 m hydrogen-filled Ice-cream negative curvature hollow-core fiber is pumped with a high peak power, narrow linewidth, liner polarized subnanosecond pulsed 1064 nm microchip laser, generating pulsed 1908.5 nm vibrational Stokes wave. The linewidth of the pump laser and the vibrational Stokes wave is about 1 GHz and 2 GHz respectively. And the maximum Raman conversion quantum efficiency is about 48%. We also studied the pulse shapes of the pump laser and the vibrational Stokes wave. The polarization dependence of the vibrational and the rotational stimulated Raman scattering is also investigated. In addition, the beam profile of vibrational Stokes wave shows good quality, which may be taken advantage of in many applications.

Femtosecond laser polishing of optical materials

NASA Astrophysics Data System (ADS)

Taylor, Lauren L.; Qiao, Jun; Qiao, Jie

2015-10-01

Technologies including magnetorheological finishing and CNC polishing are commonly used to finish optical elements, but these methods are often expensive, generate waste through the use of fluids or abrasives, and may not be suited for specific freeform substrates due to the size and shape of finishing tools. Pulsed laser polishing has been demonstrated as a technique capable of achieving nanoscale roughness while offering waste-free fabrication, material-specific processing through direct tuning of laser radiation, and access to freeform shapes using refined beam delivery and focusing techniques. Nanosecond and microsecond pulse duration radiation has been used to perform successful melting-based polishing of a variety of different materials, but this approach leads to extensive heat accumulation resulting in subsurface damage. We have experimentally investigated the ability of femtosecond laser radiation to ablate silicon carbide and silicon. By substituting ultrafast laser radiation, polishing can be performed by direct evaporation of unwanted surface asperities with minimal heating and melting, potentially offering damage-free finishing of materials. Under unoptimized laser processing conditions, thermal effects can occur leading to material oxidation. To investigate these thermal effects, simulation of the heat accumulation mechanism in ultrafast laser ablation was performed. Simulations have been extended to investigate the optimum scanning speed and pulse energy required for processing various substrates. Modeling methodologies and simulation results will be presented.

Tunable femtosecond near-infrared source based on a Yb:LYSO-laser-pumped optical parametric oscillator

NASA Astrophysics Data System (ADS)

Wen-Long, Tian; Zhao-Hua, Wang; Jiang-Feng, Zhu; Zhi-Yi, Wei

2016-01-01

We demonstrate a widely tunable near-infrared source from 767 nm to 874 nm generated by the intracavity second harmonic generation (SHG) in an optical parametric oscillator pumped by a Yb:LYSO solid-state laser. The home-made Yb:LYSO oscillator centered at 1035 nm delivers an average power of 2 W and a pulse duration as short as 351 fs. Two MgO doped periodically poled lithium niobates (MgO:PPLN) with grating periods of 28.5-31.5 μm in steps of 0.5 μm and 19.5-21.3 μm in steps of 0.2 μm are used for the OPO and intracavity SHG, respectively. The maximum average output power of 180 mW at 798 nm was obtained and the output pulses have pulse duration of 313 fs at 792 nm if a sech2-pulse shape was assumed. In addition, tunable signal femtosecond pulses from 1428 nm to 1763 nm are also realized with the maximum average power of 355 mW at 1628 nm. Project supported by the National Key Basic Research Program of China (Grant No. 2013CB922402), the National Key Scientific Instruments Development Program of China (Grant No. 2012YQ120047), the National Natural Science Foundation of China (Grant Nos. 61205130 and 11174361), and the Key Deployment Project of Chinese Academy of Sciences (Grant No. KJZD-EW-L11-03).

Wear-reducing Surface Functionalization of Implant Materials Using Ultrashort Laser Pulses

NASA Astrophysics Data System (ADS)

Oldorf, P.; Peters, R.; Reichel, S.; Schulz, A.-P.; Wendlandt, R.

The aim of the project called "EndoLas" is the development of a reproducible and reliable method for a functionalization of articulating surfaces on hip joint endoprostheses due to a reduction of abrasion and wear by the generation of micro structures using ultrashort laser pulses. On the one hand, the microstructures shall ensure the capture of abraded particles, which cause third-body wear and thereby increase aseptic loosening. On the other hand, the structures shall improve or maintain the tribologically important lubricating film. Thereby, the cavities serve as a reservoir for the body's own synovial fluid. The dry friction, which promotes abrasion and is a part of the mixed friction in the joint, shall therefore be reduced. In experimental setups it was shown, that the abrasive wear can be reduced significantly due to micro-structuring the articulating implant surfaces. To shape the fine and deterministic cavities on the surfaces, an ultra-short pulsed laser, which is integrated in a high-precision, 5-axes micro-machining system, was used. The laser system, based on an Yb:YAG thin-disk regenerative amplifier, has an average output power of 50 W at the fundamental wavelength of 1030 nm, a maximum repetition rate of 400 kHz and a pulse duration of 6 ps. Due to this, a maximum pulse energy of 125 μJ is achievable. Furthermore external second and third harmonic generation enables the usage of wavelengths in the green and violet spectral range.

Petawatt pulsed-power accelerator

DOEpatents

Stygar, William A.; Cuneo, Michael E.; Headley, Daniel I.; Ives, Harry C.; Ives, legal representative; Berry Cottrell; Leeper, Ramon J.; Mazarakis, Michael G.; Olson, Craig L.; Porter, John L.; Wagoner; Tim C.

2010-03-16

A petawatt pulsed-power accelerator can be driven by various types of electrical-pulse generators, including conventional Marx generators and linear-transformer drivers. The pulsed-power accelerator can be configured to drive an electrical load from one- or two-sides. Various types of loads can be driven; for example, the accelerator can be used to drive a high-current z-pinch load. When driven by slow-pulse generators (e.g., conventional Marx generators), the accelerator comprises an oil section comprising at least one pulse-generator level having a plurality of pulse generators; a water section comprising a pulse-forming circuit for each pulse generator and a level of monolithic triplate radial-transmission-line impedance transformers, that have variable impedance profiles, for each pulse-generator level; and a vacuum section comprising triplate magnetically insulated transmission lines that feed an electrical load. When driven by LTD generators or other fast-pulse generators, the need for the pulse-forming circuits in the water section can be eliminated.

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.

DynPeak: An Algorithm for Pulse Detection and Frequency Analysis in Hormonal Time Series

PubMed Central

Vidal, Alexandre; Zhang, Qinghua; Médigue, Claire; Fabre, Stéphane; Clément, Frédérique

2012-01-01

The endocrine control of the reproductive function is often studied from the analysis of luteinizing hormone (LH) pulsatile secretion by the pituitary gland. Whereas measurements in the cavernous sinus cumulate anatomical and technical difficulties, LH levels can be easily assessed from jugular blood. However, plasma levels result from a convolution process due to clearance effects when LH enters the general circulation. Simultaneous measurements comparing LH levels in the cavernous sinus and jugular blood have revealed clear differences in the pulse shape, the amplitude and the baseline. Besides, experimental sampling occurs at a relatively low frequency (typically every 10 min) with respect to LH highest frequency release (one pulse per hour) and the resulting LH measurements are noised by both experimental and assay errors. As a result, the pattern of plasma LH may be not so clearly pulsatile. Yet, reliable information on the InterPulse Intervals (IPI) is a prerequisite to study precisely the steroid feedback exerted on the pituitary level. Hence, there is a real need for robust IPI detection algorithms. In this article, we present an algorithm for the monitoring of LH pulse frequency, basing ourselves both on the available endocrinological knowledge on LH pulse (shape and duration with respect to the frequency regime) and synthetic LH data generated by a simple model. We make use of synthetic data to make clear some basic notions underlying our algorithmic choices. We focus on explaining how the process of sampling affects drastically the original pattern of secretion, and especially the amplitude of the detectable pulses. We then describe the algorithm in details and perform it on different sets of both synthetic and experimental LH time series. We further comment on how to diagnose possible outliers from the series of IPIs which is the main output of the algorithm. PMID:22802933

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.

Applications of Optical Coherent Transient Technology to Pulse Shaping, Spectral Filtering, Arbitrary Waveform Generation and RF Beamforming

DTIC Science & Technology

2006-04-15

was amplified by injection locking of a high power diode laser and further amplified to -300 mW with a semiconductor optical amplifier. This light...amplifiers at 793nm, cascaded injection locked amplifiers at 793nm, and frequency chirped lasers at 793nm. 15. SUBJECT TERMS Optical Coherent Transients...injection- locking for broadband optical signal amplification ................. 34 2.10. Tapered semiconductor optical amplifier

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.

3D absolute shape measurement of live rabbit hearts with a superfast two-frequency phase-shifting technique

PubMed Central

Wang, Yajun; Laughner, Jacob I.; Efimov, Igor R.; Zhang, Song

2013-01-01

This paper presents a two-frequency binary phase-shifting technique to measure three-dimensional (3D) absolute shape of beating rabbit hearts. Due to the low contrast of the cardiac surface, the projector and the camera must remain focused, which poses challenges for any existing binary method where the measurement accuracy is low. To conquer this challenge, this paper proposes to utilize the optimal pulse width modulation (OPWM) technique to generate high-frequency fringe patterns, and the error-diffusion dithering technique to produce low-frequency fringe patterns. Furthermore, this paper will show that fringe patterns produced with blue light provide the best quality measurements compared to fringe patterns generated with red or green light; and the minimum data acquisition speed for high quality measurements is around 800 Hz for a rabbit heart beating at 180 beats per minute. PMID:23482151

The light ion pulsed power induction accelerator for ETF

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

Mazarakis, M.G.; Olson, R.E.; Olson, C.L.

1994-12-31

Our Engineering Test Facility (ETF) driver concept is based on HERMES III and RHEPP technologies. Actually, it is a scaled-down version of the LMF design incorporating repetition rate capabilities of up to 10 Hz CW. The preconceptual design presented here provides 200-TW peak power to the ETF target during 10 ns, equal to 2-MJ total ion beam energy. Linear inductive voltage addition driving a self-magnetically insulated transmission line (MITL) is utilized to generate the 36-MV peak voltage needed for lithium ion beams. The {approximately} 3-MA ion current is achieved by utilizing many accelerating modules in parallel. Since the current permore » module is relatively modest ({approximately}300 kA), two-stage or one-stage extraction diodes can be utilized for the generation of singly charged lithium ions. The accelerating modules are arranged symmetrically around the fusion chamber in order to provide uniform irradiation onto the ETF target. In addition, the modules are fired in a programmed sequence in order to generate the optimum power pulse shape onto the target. This design utilizes RHEPP accelerator modules as the principal power source.« less

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.

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.

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.

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.

Morphology and structure of TixOy nanoparticles generated by femtosecond laser ablation in water

NASA Astrophysics Data System (ADS)

Donėlienė, Jolanta; Rudzikas, Matas; Rades, Steffi; Dörfel, Ilona; Peplinski, Burkhard; Sahre, Mario; Pellegrino, Francesco; Maurino, Valter; Ulbikas, Juras; Galdikas, Algirdas; Hodoroaba, Vasile-Dan

2018-04-01

In this work femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD (two instruments operated in different geometries) and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.

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.