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.

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

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.

Progress of long pulse operation with high performance plasma in KSTAR

NASA Astrophysics Data System (ADS)

Bae, Young; Kstar Team

2015-11-01

Recent KSTAR experiments showed the sustained H-mode operation up to the pulse duration of 46 s at the plasma current of 600 kA. The long-pulse H-mode operation has been supported by long-pulse capable neutral beam injection (NBI) system with high NB current drive efficiency attributed by highly tangential injections of three beam sources. In next phase, aiming to demonstrate the long pulse stationary high performance plasma operation, we are attempting the long pulse inductive operation at the higher performance (MA plasma current, high normalized beta, and low q95) for the final goal of demonstration of ITER-like baseline scenario in KSTAR with progressive improvement of the plasma shape control and higher neutral beam injection power. This paper presents the progress of long pulse operation and the analysis of energy confinement time and non-inductive current drive in KSTAR.

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.

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.

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.

REX, a 5-MV pulsed-power source for driving high-brightness electron beam diodes

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

Carlson, R.L.; Kauppila, T.J.; Ridlon, R.N.

1991-01-01

The Relativistic Electron-beam Experiment, or REX accelerator, is a pulsed-power source capable of driving a 100-ohm load at 5 MV, 50 kA, 45 ns (FWHM) with less than a 10-ns rise and 15-ns fall time. This paper describes the pulsed-power modifications, modelling, and extensive measurements on REX to allow it to drive high impedance (100s of ohms) diode loads with a shaped voltage pulse. A major component of REX is the 1.83-m-diam {times} 25.4-cm-thick Lucite insulator with embedded grading rings that separates the output oil transmission line from the vacuum vessel that contains the re-entrant anode and cathode assemblies. Amore » radially tailored, liquid-based resistor provides a stiff voltage source that is insensitive to small variations of the diode current and, in addition, optimizes the electric field stress across the vacuum side of the insulator. The high-current operation of REX employs both multichannel peaking and point-plane diverter switches. This mode reduces the prepulse to less than 2 kV and the postpulse to less than 5% of the energy delivered to the load. Pulse shaping for the present diode load is done through two L-C transmission line filters and a tapered, glycol-based line adjacent to the water PFL and output switch. This has allowed REX to drive a diode producing a 4-MV, 4.5-kA, 55-ns flat-top electron beam with a normalized Lapostolle emittance of 0.96 mm-rad corresponding to a beam brightness in excess of 4.4 {times} 10{sup 8} A/m{sup 2} {minus}rad{sup 2}. 6 refs., 13 figs.« less

Absorption spectrum of a two-level system subjected to a periodic pulse sequence

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

Fotso, H. F.; Dobrovitski, V. V.

We investigate how the quantum control of a two-level system (TLS) coupled to photons can modify and tune the TLS’s photon absorption spectrum. Tuning and controlling the emission and the absorption is of much interest e.g. for the development of efficient interfaces between stationary and flying qubits in modern architectures for quantum computation and quantum communication. We consider the periodic pulse control, where the TLS is subjected to a periodic sequence of the near-resonant Rabi driving pulses, each pulse implementing a 180° rotation. For small inter-pulse delays, the absorption spectrum features a pronounced peak of stimulated emission at the pulsemore » frequency, as well as equidistant satellite peaks with smaller spectral weights. As long as the detuning between the carrier frequency of the driving and the TLS transition frequency remains moderate, this spectral shape shows little change. Therefore, the quantum control allows shifting the absorption peak to a desired position, and locks the absorption peak to the carrier frequency of the driving pulses. Detailed description of the spectrum, and its evolution as a function time, the inter-pulse spacing and the detuning, is presented.« less

Absorption spectrum of a two-level system subjected to a periodic pulse sequence

DOE PAGES

Fotso, H. F.; Dobrovitski, V. V.

2017-06-01

We investigate how the quantum control of a two-level system (TLS) coupled to photons can modify and tune the TLS’s photon absorption spectrum. Tuning and controlling the emission and the absorption is of much interest e.g. for the development of efficient interfaces between stationary and flying qubits in modern architectures for quantum computation and quantum communication. We consider the periodic pulse control, where the TLS is subjected to a periodic sequence of the near-resonant Rabi driving pulses, each pulse implementing a 180° rotation. For small inter-pulse delays, the absorption spectrum features a pronounced peak of stimulated emission at the pulsemore » frequency, as well as equidistant satellite peaks with smaller spectral weights. As long as the detuning between the carrier frequency of the driving and the TLS transition frequency remains moderate, this spectral shape shows little change. Therefore, the quantum control allows shifting the absorption peak to a desired position, and locks the absorption peak to the carrier frequency of the driving pulses. Detailed description of the spectrum, and its evolution as a function time, the inter-pulse spacing and the detuning, is presented.« less

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

Plasma Gradient Piston: a new approach to precision pulse shaping

NASA Astrophysics Data System (ADS)

Prisbrey, Shon T.

2011-10-01

We have successfully developed a method to create shaped pressure drives from large shocks that can be applied to a wide variety of experimental platforms. The method consists of transforming a large shock or blast wave into a ramped pressured drive by utilizing a graded density reservoir that unloads across a gap and stagnates against the sample being studied. The utilization of a graded density reservoir, different materials, and a gap transforms the energy in the initial large shock into a quasi-isentropic ramped compression. Control of the ramp history is via the size of the initial shock, the chosen reservoir materials, their densities, the thickness of each density layer, and the gap size. There are two keys to utilizing this approach to create ramped drives: the ability to produce a large shock, and making the layered density reservoir. A number of facilities can produce the strong initial shock (Z, Omega, NIF, Phoenix, high explosives, NIKE, LMJ, pulsed power,...). We have demonstrated ramped drives from 0.5 to 1.5 Mbar utilizing a large shock created at the Omega laser facility. We recently concluded a pair of NIF drive shots where we successfully converted a hohlraum-generated shock into a stepped, ramped pressure drive with a peak pressure of ~4 - 5 Mbar in a Ta sample. We will explain the basic concepts needed for producing a ramped pressure drive, compare experimental data with simulations from Omega (Pmax ~ 1 Mbar) and NIF (Pmax ~ 5-10 Mbar), and present designs for ramped, staged-shock designs up to Pmax ~ 30 Mbar. The approach that we have developed enables precision pulse shaping of the drive (applied pressure vs. time) via target characteristics, as opposed to tailoring laser power vs time or Z-pinch facility current vs time. This enables ramped, quasi-isentropic materials studies to be performed on a wide variety of HED facilities. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-490532.

Design of Interactively Time-Pulsed Microfluidic Mixers in Microchips using Numerical Simulation

NASA Astrophysics Data System (ADS)

Fu, Lung-Ming; Tsai, Chien-Hsiung

2007-01-01

In this paper, we propose a novel technique in which driving voltages are applied interactively to the respective inlet fluid flows of three configurations of a microfluidic device, namely T-shaped, double-T-shaped, and double-cross-shaped configurations, to induce electroosmotic flow (EOF) velocity variations in such a way as to develop a rapid mixing effect in the microchannel. In these configurations a microfluidic mixer apply only one electrokinetic driving force, which drives the sample fluids and simultaneously produces a periodic switching frequency. It requires no other external driving force to induce perturbations to the flow field. The effects of the main applied electric field, the interactive frequency, and the pullback electric field on the mixing performance are thoroughly examined numerically. The optimal interactive frequency range for a given set of micromixer parameters is identified for each type of control mode. The numerical results confirm that micromixers operating at an optimal interactive frequency are capable of delivering a significantly enhanced mixing performance. Furthermore, it is shown that the optimal interactive frequency depends upon the magnitude of the main applied electric field. The interactively pulsed mixers developed in this study have a strong potential for use in lab-on-a-chip systems. They involve a simpler fabrication process than either passive or active on-chip mixers and require less human intervention in operation than their bulky external counterparts.

Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance

DOE PAGES

Li, S.; Alverson, S.; Bohler, D.; ...

2017-08-17

The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ultraviolet, a wavelength where direct laser manipulation becomes challenging. In this paper, we present a novel application of a digital micromirror device (DMD) for the 253 nm drive laser at the Linear Coherent Light Source. Laser profile shaping is accomplished through an iterative algorithm that takes into account shaping error and efficiency.more » Next, we use laser shaping to control the X-ray laser output via an online optimizer, which shows improvement in FEL pulse energy. Lastly, as a preparation for electron beam shaping, we use the DMD to measure the photocathode quantum efficiency across cathode surface with an averaged laser rms spot size of 59 μm. In conclusion, our experiments demonstrate promising outlook of using DMD to shape ultraviolet lasers for photocathode rf guns with various applications.« less

Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance

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

Li, S.; Alverson, S.; Bohler, D.

The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ultraviolet, a wavelength where direct laser manipulation becomes challenging. In this paper, we present a novel application of a digital micromirror device (DMD) for the 253 nm drive laser at the Linear Coherent Light Source. Laser profile shaping is accomplished through an iterative algorithm that takes into account shaping error and efficiency.more » Next, we use laser shaping to control the X-ray laser output via an online optimizer, which shows improvement in FEL pulse energy. Lastly, as a preparation for electron beam shaping, we use the DMD to measure the photocathode quantum efficiency across cathode surface with an averaged laser rms spot size of 59 μm. In conclusion, our experiments demonstrate promising outlook of using DMD to shape ultraviolet lasers for photocathode rf guns with various applications.« less

Ultraviolet laser transverse profile shaping for improving x-ray free electron laser performance

NASA Astrophysics Data System (ADS)

Li, S.; Alverson, S.; Bohler, D.; Egger, A.; Fry, A.; Gilevich, S.; Huang, Z.; Miahnahri, A.; Ratner, D.; Robinson, J.; Zhou, F.

2017-08-01

The photocathode rf gun is one of the most critical components in x-ray free electron lasers. The drive laser strikes the photocathode surface, which emits electrons with properties that depend on the shape of the drive laser. Most free electron lasers use photocathodes with work function in the ultraviolet, a wavelength where direct laser manipulation becomes challenging. In this paper, we present a novel application of a digital micromirror device (DMD) for the 253 nm drive laser at the Linear Coherent Light Source. Laser profile shaping is accomplished through an iterative algorithm that takes into account shaping error and efficiency. Next, we use laser shaping to control the X-ray laser output via an online optimizer, which shows improvement in FEL pulse energy. Lastly, as a preparation for electron beam shaping, we use the DMD to measure the photocathode quantum efficiency across cathode surface with an averaged laser rms spot size of 59 μ m . Our experiments demonstrate promising outlook of using DMD to shape ultraviolet lasers for photocathode rf guns with various applications.

Determining the Carrier-Envelope Phase of Intense Few-Cycle Laser Pulses

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

Mackenroth, F.; Di Piazza, A.; Keitel, C. H.

2010-08-06

The electromagnetic radiation emitted by an ultrarelativistic accelerated electron is extremely sensitive to the precise shape of the field driving the electron. We show that the angular distribution of the photons emitted by an electron via multiphoton Compton scattering off an intense (I>10{sup 20} W/cm{sup 2}), few-cycle laser pulse provides a direct way of determining the carrier-envelope phase of the driving laser field. Our calculations take into account exactly the laser field, include relativistic and quantum effects and are in principle applicable to presently available and future foreseen ultrastrong laser facilities.

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

Modeling texture transitions in cholesteric liquid crystal droplets

NASA Astrophysics Data System (ADS)

Selinger, Robin; Gimenez-Pinto, Vianney; Lu, Shin-Ying; Selinger, Jonathan; Konya, Andrew

2012-02-01

Cholesteric liquid crystals can be switched reversibly between planar and focal-conic textures, a property enabling their application in bistable displays, liquid crystal writing tablets, e-books, and color switching ``e-skins.'' To explore voltage-pulse induced switching in cholesteric droplets, we perform simulation studies of director dynamics in three dimensions. Electrostatics calculations are solved at each time step using an iterative relaxation method. We demonstrate that as expected, a low amplitude pulse drives the transition from planar to focal conic, while a high amplitude pulse drives the transition from focal conic back to the planar state. We use the model to explore the effects of droplet shape, aspect ratio, and anchoring conditions, with the goal of minimizing both response time and energy consumption.

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

Goncharov, V.N.; Knauer, J.P.; McKenty, P.W.

(B204)Hydrodynamic instabilities seeded by laser imprint and surface roughness limit the compression ratio and neutron yield in the direct-drive inertial confinement fusion target designs. New improved-performance designs use adiabat shaping to increase the entropy of only the outer portion of the shell, reducing the instability growth. The inner portion of the shell is kept on a lower entropy to maximize shell compressibility. The adiabat shaping is implemented using a high-intensity picket in front of the main-drive pulse. The picket launches a strong shock that decays as it propagates through the shell. This increases the ablation velocity and reduces the Rayleigh-Taylormore » growth rates. In addition, as shown earlier [T.J.B. Collis and S. Skupsky, Phys. Plasmas 9 275 (2002)], the picket reduces the instability seed due to the laser imprint. To test the results of calculations, a series of the picket pulse implosions of CH capsules were performed on the OMEGA laser system [T.R. Boehly, D .L. Brown, R.S. Craxton, et al., Opt. Commun. 133, 495 (1997)]. The experiments demonstrated a significant improvement in target yields for the pulses with the picket compared to the pulses without the picket. Results of the theory and experiments with adiabat shaping are being extended to future OMEGA and the National Ignition Facility's [J.A. Paisner, J.D. Boyes, S.A. Kumpan, W.H. Lowdermilk, and M.S. Sorem, Laser Focus World 30, 75 (1994)] cryogenic target designs.« less

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

An in-flight radiography platform to measure hydrodynamic instability growth in inertial confinement fusion capsules at the National Ignition Facility

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

Raman, K. S.; Smalyuk, V. A.; Casey, D. T.

2014-07-15

A new in-flight radiography platform has been established at the National Ignition Facility (NIF) to measure Rayleigh–Taylor and Richtmyer–Meshkov instability growth in inertial confinement fusion capsules. The platform has been tested up to a convergence ratio of 4. An experimental campaign is underway to measure the growth of pre-imposed sinusoidal modulations of the capsule surface, as a function of wavelength, for a pair of ignition-relevant laser drives: a “low-foot” drive representative of what was fielded during the National Ignition Campaign (NIC) [Edwards et al., Phys. Plasmas 20, 070501 (2013)] and the new high-foot [Dittrich et al., Phys. Rev. Lett. 112,more » 055002 (2014); Park et al., Phys. Rev. Lett. 112, 055001 (2014)] pulse shape, for which the predicted instability growth is much lower. We present measurements of Legendre modes 30, 60, and 90 for the NIC-type, low-foot, drive, and modes 60 and 90 for the high-foot drive. The measured growth is consistent with model predictions, including much less growth for the high-foot drive, demonstrating the instability mitigation aspect of this new pulse shape. We present the design of the platform in detail and discuss the implications of the data it generates for the on-going ignition effort at NIF.« less

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.

Relationship between symmetry and laser pulse shape in low-fill hohlraums at the National Ignition Facility

NASA Astrophysics Data System (ADS)

MacLaren, Steve; Zylstra, A. B.; Yi, A.; Kline, J. L.; Kyrala, G. A.; Kot, L. B.; Loomis, E. N.; Perry, T. S.; Shah, R. C.; Masse, L. P.; Ralph, J. E.; Khan, S. F.

2017-10-01

Typically in indirect-drive inertial confinement fusion (ICF) hohlraums cryogenic helium gas fill is used to impede the motion of the hohlraum wall plasma as it is driven by the laser pulse. A fill of 1 mg/cc He has been used to significantly suppress wall motion in ICF hohlraums at the National Ignition Facility (NIF); however, this level of fill also causes laser-plasma instabilities (LPI) which result in hot electrons, time-dependent symmetry swings and reduction in drive due to increased backscatter. There are currently no adequate models for these phenomena in codes used to simulate integrated ICF experiments. A better compromise is a fill in the range of 0.3 0.6 mg/cc, which has been shown to provide some reduction in wall motion without incurring significant LPI effects. The wall motion in these low-fill hohlraums and the resulting effect on symmetry due to absorption of the inner cone beams by the outer cone plasma can be simulated with some degree of accuracy with the hydrodynamics and inverse Bremsstrahlung models in ICF codes. We describe a series of beryllium capsule implosions in 0.3 mg/cc He fill hohlraums that illustrate the effect of pulse shape on implosion symmetry in the ``low-fill'' regime. In particular, we find the shape of the beginning or ``foot'' of the pulse has significant leverage over the final symmetry of the stagnated implosion. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

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

Ignition at NIF: Where we have been, and where we are going

NASA Astrophysics Data System (ADS)

Rosen, Mordecai

2014-10-01

This talk reviews results from the past several years in the pursuit of indirect-drive ignition on the National Ignition Facility (NIF), and summarizes ideas and plans for moving forward. We describe the challenging issues encountered by the low-adiabat (``low foot''), ``ignition point design'' approach, such as: hydrodynamic instability growth and ensuing mix of the CH ablator into the DT hot spot; very high convergence implosions with resultant imperfect symmetry; possible other issues such as hot electron preheat. The complex interplay among these issues is a key theme. We describe the progress that has been made in the understanding and diagnosis of these issues. We present the results from the high-adiabat (``high foot'') approach, with its property of relative hydrodynamic stability when compared to the low foot approach, its somewhat reduced convergence ratio, and its achievement of entering the alpha heating regime, an important milestone on the road to ignition. Paths forward towards ignition include excursions from the present approaches in pulse shape, hohlraum, and choice of ablator. Further pulse shaping can lower the adiabat of the high foot approach and lead to higher performance if it continues to retain its hydrodynamic stability properties. Conversely, pulse shaping can provide for ``adiabat-shaping'' for the low foot approach for it to try to attain better stability. A plethora of hohlraum approaches (size, shape, materials, gas fills) can improve the zero-order drive, as well as the low-mode shape of the implosion. Diagnosing, and then correcting, the time dependence of the symmetry is also a key issue. A variety of ablator materials, along with carefully engineering the drive spectrum, can increase implosion velocity. The high-density carbon ablator has shown promising results in this regard. Some combinations of these developments may allow for an operating space that has a relatively short pulse, in a near vacuum hohlraum. That combination has shown, to date, much better coupling efficiency, and a much lower level of laser plasma instabilities (thus, less electron preheat), than the longer pulse, full gas-fill, ignition hohlraums. Advances in modeling, experimental platforms, and diagnostic techniques developed over the past several years have been key enabling technologies in moving towards ignition, and we anticipate further advances as well. We gratefully acknowledge the dedicated efforts of many hundreds of personnel across the globe who have participated in the laser construction, operation, target fabrication, and all aspects of the target physics program, that have taken us this far towards ignition. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

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.

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

DOE PAGES

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

2018-05-16

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

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

Terahertz spin current pulses controlled by magnetic heterostructures

NASA Astrophysics Data System (ADS)

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

2013-04-01

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

Acceleration and evolution of a hollow electron beam in wakefields driven by a Laguerre-Gaussian laser pulse

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

Zhang, Guo-Bo; College of Science, National University of Defense Technology, Changsha 410073; Chen, Min, E-mail: minchen@sjtu.edu.cn, E-mail: yanyunma@126.com

2016-03-15

We show that a ring-shaped hollow electron beam can be injected and accelerated by using a Laguerre-Gaussian laser pulse and ionization-induced injection in a laser wakefield accelerator. The acceleration and evolution of such a hollow, relativistic electron beam are investigated through three-dimensional particle-in-cell simulations. We find that both the ring size and the beam thickness oscillate during the acceleration. The beam azimuthal shape is angularly dependent and evolves during the acceleration. The beam ellipticity changes resulting from the electron angular momenta obtained from the drive laser pulse and the focusing forces from the wakefield. The dependence of beam ring radiusmore » on the laser-plasma parameters (e.g., laser intensity, focal size, and plasma density) is studied. Such a hollow electron beam may have potential applications for accelerating and collimating positively charged particles.« less

Scalable entanglement in trapped ions using optimal control of multimode couplings

NASA Astrophysics Data System (ADS)

Debnath, Shantanu; Choi, Taeyoung; Manning, T. Andrew; Figgatt, Caroline; Monroe, Chris

2014-05-01

We perform high fidelity multipartite entanglement of ion subsets in a chain of five Yb+ qubits using optimal pulse shaping. A focused mode-locked laser beam individually addresses qubits to couple them to multiple collective transverse modes of motion to perform entangling phase gates on pairs of adjacent qubits. Pulse shaping by modulating the amplitude and phase of the laser can drive high fidelity gates for certain pulse solutions that are relatively insensitive to detuning errors. We create entangled states in the GHZ class and witness genuine tripartite entanglement using individual state detection. This method of engineering the evolution of multiple modes scales well for large qubit registers by keeping gate times short. This work is supported by grants from the U.S. Army Research Office with funding from the DARPA OLE program, IARPA, and the MURI program; and the NSF Physics Frontier Center at JQI.

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

NASA Astrophysics Data System (ADS)

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

2018-05-01

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

New tuning method of the low-mode asymmetry for ignition capsule implosions

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

Gu, Jianfa, E-mail: gu-jianfa@iapcm.ac.cn; Dai, Zhensheng; Zou, Shiyang

2015-12-15

In the deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility, the hot spot and the surrounding main fuel layer show obvious P2 asymmetries. This may be caused by the large positive P2 radiation flux asymmetry during the peak pulse resulting form the poor propagation of the inner laser beam in the gas-filled hohlraum. The symmetry evolution of ignition capsule implosions is investigated by applying P2 radiation flux asymmetries during different time intervals. A series of two-dimensional simulation results show that a positive P2 flux asymmetry during the peak pulse results in a positive P2 shell ρR asymmetry;more » while an early time positive P2 flux asymmetry causes a negative P2 in the fuel ρR shape. The opposite evolution behavior of shell ρR asymmetry is used to develop a new tuning method to correct the radiation flux asymmetry during the peak pulse by adding a compensating same-phased P2 drive asymmetry during the early time. The significant improvements of the shell ρR symmetry, hot spot shape, hot spot internal energy, and neutron yield indicate that the tuning method is quite effective. The similar tuning method can also be used to control the early time drive asymmetries.« less

Unraveling shock-induced chemistry using ultrafast lasers

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

Moore, David Steven

The exquisite time synchronicity between shock and diagnostics needed to unravel chemical events occurring in picoseconds has been achieved using a shaped ultrafast laser pulse to both drive the shocks and interrogate the sample via a multiplicity of optical diagnostics. The shaped laser drive pulse can produce well-controlled shock states of sub-ns duration with sub-10 ps risetimes, sufficient for investigation offast reactions or phase transformations in a thin layer with picosecond time resolution. The shock state is characterized using ultrafast dynamic ellipsometry (UDE) in either planar or Gaussian spatial geometries, the latter allowing measurements of the equation of state ofmore » materials at a range of stresses in a single laser pulse. Time-resolved processes in materials are being interrogated using UDE, ultrafast infrared absorption, ultrafast UV/visible absorption, and femtosecond stimulated Raman spectroscopy. Using these tools we showed that chemistry in an energetic thin film starts only after an induction time of a few tens of ps, an observation that allows differentiation between proposed shock-induced reaction mechanisms. These tools are presently being applied to a variety of energetic and reactive sample systems, from nitromethane and carbon disulfide, to microengineered interfaces in tunable energetic mixtures. Recent results will be presented, and future trends outlined.« less

A multiscale, hierarchical model of pulse dynamics in arid-land ecosystems

USGS Publications Warehouse

Collins, Scott L.; Belnap, Jayne; Grimm, N. B.; Rudgers, J. A.; Dahm, Clifford N.; D'Odorico, P.; Litvak, M.; Natvig, D. O.; Peters, Douglas C.; Pockman, W. T.; Sinsabaugh, R. L.; Wolf, B. O.

2014-01-01

Ecological processes in arid lands are often described by the pulse-reserve paradigm, in which rain events drive biological activity until moisture is depleted, leaving a reserve. This paradigm is frequently applied to processes stimulated by one or a few precipitation events within a growing season. Here we expand the original framework in time and space and include other pulses that interact with rainfall. This new hierarchical pulse-dynamics framework integrates space and time through pulse-driven exchanges, interactions, transitions, and transfers that occur across individual to multiple pulses extending from micro to watershed scales. Climate change will likely alter the size, frequency, and intensity of precipitation pulses in the future, and arid-land ecosystems are known to be highly sensitive to climate variability. Thus, a more comprehensive understanding of arid-land pulse dynamics is needed to determine how these ecosystems will respond to, and be shaped by, increased climate variability.

Ultrahigh-resolution spectroscopy with atomic or molecular dark resonances: Exact steady-state line shapes and asymptotic profiles in the adiabatic pulsed regime

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

Zanon-Willette, Thomas; Clercq, Emeric de; Arimondo, Ennio

2011-12-15

Exact and asymptotic line shape expressions are derived from the semiclassical density matrix representation describing a set of closed three-level {Lambda} atomic or molecular states including decoherences, relaxation rates, and light shifts. An accurate analysis of the exact steady-state dark-resonance profile describing the Autler-Townes doublet, the electromagnetically induced transparency or coherent population trapping resonance, and the Fano-Feshbach line shape leads to the linewidth expression of the two-photon Raman transition and frequency shifts associated to the clock transition. From an adiabatic analysis of the dynamical optical Bloch equations in the weak field limit, a pumping time required to efficiently trap amore » large number of atoms into a coherent superposition of long-lived states is established. For a highly asymmetrical configuration with different decay channels, a strong two-photon resonance based on a lower states population inversion is established when the driving continuous-wave laser fields are greatly unbalanced. When time separated resonant two-photon pulses are applied in the adiabatic pulsed regime for atomic or molecular clock engineering, where the first pulse is long enough to reach a coherent steady-state preparation and the second pulse is very short to avoid repumping into a new dark state, dark-resonance fringes mixing continuous-wave line shape properties and coherent Ramsey oscillations are created. Those fringes allow interrogation schemes bypassing the power broadening effect. Frequency shifts affecting the central clock fringe computed from asymptotic profiles and related to the Raman decoherence process exhibit nonlinear shapes with the three-level observable used for quantum measurement. We point out that different observables experience different shifts on the lower-state clock transition.« less

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

PubMed

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

2017-03-01

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

Suppression of laser nonuniformity imprinting using a thin high-z coating.

PubMed

Karasik, Max; Weaver, J L; Aglitskiy, Y; Oh, J; Obenschain, S P

2015-02-27

Imprinting of laser nonuniformity is a limiting factor in direct-drive inertial confinement fusion experiments, particularly when available laser smoothing is limited. A thin (∼400  Å) high-Z metal coating is found to substantially suppress laser imprint for planar targets driven by pulse shapes and intensities relevant to implosions on the National Ignition Facility while retaining low adiabat target acceleration. A hybrid of indirect and direct drive, this configuration results in initial ablation by x rays from the heated high-Z layer, creating a large standoff for perturbation smoothing.

Ultrasonic unipolar pulse/echo instrument

DOEpatents

Hughes, M.J.; Hsu, D.K.; Thompson, D.O.; Wormley, S.J.

1993-04-06

An ultrasonic unipolar pulse/echo instrument uses active switches and a timing and drive circuitry to control electrical energy to a transducer, the discharging of the transducer, and the opening of an electrical pathway to the receiving circuitry for the returning echoes. The active switches utilize MOSFET devices along with decoupling circuitry to insure the preservation of the unipolar nature of the pulses, insure fast transition times, and maintain broad band width and time resolution. A housing contains the various circuitry and switches and allows connection to a power supply and a movable ultrasonic transducer. The circuitry maintains low impedance input to the transducer during transmitting cycles, and high impedance between the transducer and the receiving circuit during receive cycles to maintain the unipolar pulse shape. A unipolar pulse is valuable for nondestructive evaluation, a prime use for the present instrument.

Ultrasonic unipolar pulse/echo instrument

DOEpatents

Hughes, Michael S.; Hsu, David K.; Thompson, Donald O.; Wormley, Samuel J.

1993-01-01

An ultrasonic unipolar pulse/echo instrument uses active switches and a timing and drive circuitry to control electrical energy to a transducer, the discharging of the transducer, and the opening of an electrical pathway to the receiving circuitry for the returning echoes. The active switches utilize MOSFET devices along with decoupling circuitry to insure the preservation of the unipolar nature of the pulses, insure fast transition times, and maintain broad band width and time resolution. A housing contains the various circuitry and switches and allows connection to a power supply and a movable ultrasonic transducer. The circuitry maintains low impedance input to the transducer during transmitting cycles, and high impedance between the transducer and the receiving circuit during receive cycles to maintain the unipolar pulse shape. A unipolar pulse is valuable for nondestructive evaluation, a prime use for the present instrument.

Performance of beryllium targets with full-scale capsules in low-fill 6.72-mm hohlraums on the National Ignition Facility

DOE PAGES

Simakov, A. N.; Wilson, D. C.; Yi, S. A.; ...

2017-05-10

When used with 1.06-mm beryllium (Be) capsules on the National Ignition Facility, gold hohlraums with the inner diameter of 5.75 mm and helium gas fill density of 1.6 mg/cm 3 exhibit significant drive degradation due to laser energy backscatter (of order 14%–17%) and “missing” X-ray drive energy (about 32% during the main pulse). Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Larger, 6.72-mm hohlraums with fill densities ≤0.6 mg/cm 3 generally offer improved drive efficiency, reduced hot-electron preheat, and better control of the implosion symmetry without CBET. Recently, we carried out anmore » exploratory campaign to evaluate performance of 1.06-mm Be capsules in such hohlraums and determine optimal hohlraum parameters. Specifically, we performed in this paper a hohlraum fill-density scan with a three-shock, 9.5-ns laser pulse and found that an appropriate axial laser repointing and azimuthal outer-quad splitting resulted in significantly improved hohlraum energetics at fill densities ≤0.3 mg/cm 3 (with backscattered and “missing” energies being of about 5% and 23% of the total laser energy, respectively). The capsule shape at stagnation was slightly oblate and improved with lowering the fill density. We also performed an implosion with a lower-picket, 12.6-ns pulse at the hohlraum fill density of 0.15 mg/cm 3 to observe comparable hohlraum energetics (about 3% of backscattered and 27% of “missing” energy) but an even more oblate implosion shape. Finally, achieving symmetric implosions of 1.06-mm Be capsules in low-fill, 6.72-mm gold hohlraums with reasonably low-adiabat pulses may not be feasible. However, symmetric implosions have recently been successfully demonstrated in such hohlraums with 0.8-mm Be capsules.« less

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

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

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

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

Optimizing pulse shaping and zooming for acceleration to high velocities and fusion neutron production on the Nike laser

NASA Astrophysics Data System (ADS)

Karasik, Max; Weaver, J. L.; Aglitskiy, Y.; Zalesak, S. T.; Velikovich, A. L.; Oh, J.; Obenschain, S. P.; Arikawa, Y.; Watari, T.

2010-11-01

We will present results from follow-on experiments to the record-high velocities of 1000 km/s achieved on Nike [Karasik et al., Phys. Plasmas 17, 056317 (2010) ], in which highly accelerated planar foils of deuterated polystyrene were made to collide with a witness foil to produce extreme shock pressures and result in heating of matter to thermonuclear temperatures. Still higher velocities and higher target densities are required for impact fast ignition. The aim of these experiments is shaping the driving pulse to minimize shock heating of the accelerated target and using the focal zoom capability of Nike to achieve higher densities and velocities. Spectroscopic measurements of electron temperature achieved upon impact will complement the neutron time-of-flight ion temperature measurement. Work is supported by US DOE and Office of Naval Research.

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

Weilacher, F.; Radha, P. B., E-mail: rbah@lle.rochester.edu; Collins, T. J. B.

Ongoing polar-direct-drive (PDD) implosions on the National Ignition Facility (NIF) [J. D. Lindl and E. I. Moses, Phys. Plasmas 18, 050901 (2011)] use existing NIF hardware, including indirect-drive phase plates. This limits the performance achievable in these implosions. Spot shapes are identified that significantly improve the uniformity of PDD NIF implosions; outer surface deviation is reduced by a factor of 7 at the end of the laser pulse and hot-spot distortion is reduced by a factor of 2 when the shell has converged by a factor of ∼10. As a result, the neutron yield increases by approximately a factor ofmore » 2. This set of laser spot shapes is a combination of circular and elliptical spots, along with elliptical spot shapes modulated by an additional higher-intensity ellipse offset from the center of the beam. This combination is motivated in this paper. It is also found that this improved implosion uniformity is obtained independent of the heat conduction model. This work indicates that significant improvement in performance can be obtained robustly with the proposed spot shapes.« less

Analysis and Optimization of Pulse Dynamics for Magnetic Stimulation

PubMed Central

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

2013-01-01

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

Storage of RF photons in minimal conditions

NASA Astrophysics Data System (ADS)

Cromières, J.-P.; Chanelière, T.

2018-02-01

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

Effect of the carrier-envelope phase of the driving laser field on the high-order harmonic attosecond pulse

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

Zeng Zhinan; Li Ruxin; Yu Wei

2003-01-01

The effect of the carrier-envelope phase of a few-cycle driving laser field on the generation and measurement of high-order harmonic attosecond pulses is investigated theoretically. We find that the position of the generated attosecond soft-x-ray pulse in the cutoff region is locked to the oscillation of the driving laser field, but not to the envelope of the laser pulse. This property ensures the success of the width measurement of an attosecond soft-x-ray pulse based on the cross correlation between the attosecond pulse and its driving laser pulse [M. Hentschel et al., Nature (London) 414, 509 (2001)]. However, there still existsmore » a timing jitter of the order of tens of attoseconds between the attosecond pulse and its driving laser field. We also propose a method to detect the carrier-envelope phase of the driving laser field by measuring the spatial distribution of the photoelectrons induced by the attosecond soft-x-ray pulse and its driving laser pulse.« 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.

Contribution For Arc Temperature Affected By Current Increment Ratio At Peak Current In Pulsed Arc

NASA Astrophysics Data System (ADS)

Kano, Ryota; Mitubori, Hironori; Iwao, Toru

2015-11-01

Tungsten Inert Gas (TIG) Welding is one of the high quality welding. However, parameters of the pulsed arc welding are many and complicated. if the welding parameters are not appropriate, the welding pool shape becomes wide and shallow.the convection of driving force contributes to the welding pool shape. However, in the case of changing current waveform as the pulse high frequency TIG welding, the arc temperature does not follow the change of the current. Other result of the calculation, in particular, the arc temperature at the reaching time of peak current is based on these considerations. Thus, the accurate measurement of the temperature at the time is required. Therefore, the objective of this research is the elucidation of contribution for arc temperature affected by current increment ratio at peak current in pulsed arc. It should obtain a detail knowledge of the welding model in pulsed arc. The temperature in the case of increment of the peak current from the base current is measured by using spectroscopy. As a result, when the arc current increases from 100 A to 150 A at 120 ms, the transient response of the temperature didn't occur during increasing current. Thus, during the current rise, it has been verified by measuring. Therefore, the contribution for arc temperature affected by current increment ratio at peak current in pulsed arc was elucidated in order to obtain more knowledge of welding model of pulsed arc.

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.

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.

Design of piezoelectric probe for measurement of longitudinal and shear components of elastic wave

NASA Astrophysics Data System (ADS)

Aoyanagi, Masafumi; Wakatsuki, Naoto; Mizutani, Koichi; Ebihara, Tadashi

2017-07-01

We focus on ultrasonic probes for nondestructive tests and evaluation. Transient characteristics of probes are important for nondestructive tests such as the pulse echo method. We previously reported the principle of measurement using a piezoelectric probe with triaxial sensitivities. In the results, it was calculated that the probe could transmit and receive particle displacement which contains normal and tangential components. It was confirmed that the probe had sensitivities in triaxial directions. However, its performance in terms of frequency and transient characteristics has not been evaluated. The purpose of this study is to design a probe by changing its shape to obtain better performance. The transient characteristics of probes in longitudinal and shear driving were evaluated by the inverse Fourier transformation of frequency responses of longitudinal and shear components, using the two-dimensional finite element method. As a result, the sensitivities at the dips of frequency characteristics increased when using our probe compared with those measured using conventional probes in longitudinal and shear driving. Hence, the performance in terms of the frequency response was improved by more than 3 dB under the conditions in this simulation. Also, the pulse width of impulse response was decreased by half compared with that of probes with conventional shapes.

Symmetry control in subscale near-vacuum hohlraums

NASA Astrophysics Data System (ADS)

Turnbull, D.; Berzak Hopkins, L. F.; Le Pape, S.; Divol, L.; Meezan, N.; Landen, O. L.; Ho, D. D.; Mackinnon, A.; Zylstra, A. B.; Rinderknecht, H. G.; Sio, H.; Petrasso, R. D.; Ross, J. S.; Khan, S.; Pak, A.; Dewald, E. L.; Callahan, D. A.; Hurricane, O.; Hsing, W. W.; Edwards, M. J.

2016-05-01

Controlling the symmetry of indirect-drive inertial confinement fusion implosions remains a key challenge. Increasing the ratio of the hohlraum diameter to the capsule diameter (case-to-capsule ratio, or CCR) facilitates symmetry tuning. By varying the balance of energy between the inner and outer cones as well as the incident laser pulse length, we demonstrate the ability to tune from oblate, through round, to prolate at a CCR of 3.2 in near-vacuum hohlraums at the National Ignition Facility, developing empirical playbooks along the way for cone fraction sensitivity of various laser pulse epochs. Radiation-hydrodynamic simulations with enhanced inner beam propagation reproduce most experimental observables, including hot spot shape, for a majority of implosions. Specular reflections are used to diagnose the limits of inner beam propagation as a function of pulse length.

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.

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.

Gas-filled Rugby hohlraum energetics and implosions experiments on OMEGA

NASA Astrophysics Data System (ADS)

Casner, Alexis; Philippe, F.; Tassin, V.; Seytor, P.; Monteil, M. C.; Villette, B.; Reverdin, C.

2010-11-01

Recent experiments [1,2] have validated the x-ray drive enhancement provided by rugby-shaped hohlraums over cylinders in the indirect drive (ID) approach to inertial confinement fusion (ICF). This class of hohlraum is the baseline design for the Laser Mégajoule program, is also applicable to the National Ignition Facility and could therefore benefit ID Inertial Fusion Energy studies. We have carried out a serie of energetics and implosions experiments with OMEGA ``scale 1'' rugby hohlraums [1,2]. For empty hohlraums these experiments provide complementary measurements of backscattered light along 42 cone, as well as detailed drive history. In the case of gas-filled rugby hohlraums we have also study implosion performance (symmetry, yield, bangtime, hotspot spectra...) using a high contrast shaped pulse leading to a different implosion regime and for a range of capsule convergence ratios. These results will be compared with FCI2 hydrocodes calculations and future experimental campaigns will be suggested. [4pt] [1] F. Philippe et al., Phys. Rev. Lett. 104, 035004 (2010). [0pt] [2] H. Robey et al., Phys. Plasnas 17, 056313 (2010).

Stabilization of high-compression, indirect-drive inertial confinement fusion implosions using a 4-shock adiabat-shaped drive

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

MacPhee, A. G.; Peterson, J. L.; Casey, D. T.

Hydrodynamic instabilities and poor fuel compression are major factors for capsule performance degradation in ignition experiments on the National Ignition Facility. Using a recently developed laser drive profile with a decaying first shock to tune the ablative Richtmyer-Meshkov (ARM) instability and subsequent in-flight Rayleigh-Taylor growth, we have demonstrated reduced growth compared to the standard ignition pulse whilst maintaining conditions for a low fuel adiabat needed for increased compression. Using in-flight x-ray radiography of pre-machined modulations, the first growth measurements using this new ARM-tuned drive have demonstrated instability growth reduction of ∼4× compared to the original design at a convergence ratiomore » of ∼2. Corresponding simulations give a fuel adiabat of ∼1.6, similar to the original goal and consistent with ignition requirements.« less

Stabilization of high-compression, indirect-drive inertial confinement fusion implosions using a 4-shock adiabat-shaped drive

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

MacPhee, A. G.; Peterson, J. L.; Casey, D. T.

Hydrodynamic instabilities and poor fuel compression are major factors for capsule performance degradation in ignition experiments on the National Ignition Facility. Using a recently developed laser drive profile with a decaying first shock to tune the ablative Richtmyer-Meshkov (ARM) instability and subsequent in-flight Rayleigh-Taylor growth, we have demonstrated reduced growth compared to the standard ignition pulse whilst maintaining conditions for a low fuel adiabat needed for increased compression. Here, using in-flight x-ray radiography of pre-machined modulations, the first growth measurements using this new ARM-tuned drive have demonstrated instability growth reduction of ~4× compared to the original design at a convergencemore » ratio of ~2. Corresponding simulations give a fuel adiabat of ~1.6, similar to the original goal and consistent with ignition requirements.« less

Stabilization of high-compression, indirect-drive inertial confinement fusion implosions using a 4-shock adiabat-shaped drive

DOE PAGES

MacPhee, A. G.; Peterson, J. L.; Casey, D. T.; ...

2015-08-01

Hydrodynamic instabilities and poor fuel compression are major factors for capsule performance degradation in ignition experiments on the National Ignition Facility. Using a recently developed laser drive profile with a decaying first shock to tune the ablative Richtmyer-Meshkov (ARM) instability and subsequent in-flight Rayleigh-Taylor growth, we have demonstrated reduced growth compared to the standard ignition pulse whilst maintaining conditions for a low fuel adiabat needed for increased compression. Here, using in-flight x-ray radiography of pre-machined modulations, the first growth measurements using this new ARM-tuned drive have demonstrated instability growth reduction of ~4× compared to the original design at a convergencemore » ratio of ~2. Corresponding simulations give a fuel adiabat of ~1.6, similar to the original goal and consistent with ignition requirements.« less

Experimental demonstration of an efficient hybrid equalizer for short-reach optical SSB systems

NASA Astrophysics Data System (ADS)

Zhu, Mingyue; Ying, Hao; Zhang, Jing; Yi, Xingwen; Qiu, Kun

2018-02-01

We propose an efficient enhanced hybrid equalizer combining the feed forward equalization (FFE) with a modified Volterra filter to mitigate the linear and nonlinear interference for the short-reach optical single side-band (SSB) system. The optical SSB signal is generated by a relatively low-cost dual-drive Mach-Zehnder modulator (DDMZM). The two driving signals are a pair of Hilbert signals with Nyquist pulse-shaped four-level pulse amplitude modulation (NPAM-4). After the fiber transmission, the neighboring received symbols are strongly correlated due to the pulse spreading in time domain caused by the chromatic dispersion (CD). At the receiver equalization stage, the FFE followed by higher order terms of modified Volterra filter, which utilizes the forward and backward neighboring symbols to construct the kernels with strong correlation, are used as an enhanced hybrid equalizer to mitigate the inter symbol interference (ISI) and nonlinear distortion due to the interaction of the CD and the square-law detection. We experimentally demonstrate that the optical SSB NPAM-4 signal of 40 Gb/s transmitting over 80 km standard single mode fiber (SSMF) with a bit-error-rate (BER) of 7 . 59 × 10-4.

Nonspherical dynamics and shape mode stability of ultrasound contrast agent microbubbles

NASA Astrophysics Data System (ADS)

Calvisi, Michael

2016-11-01

Ultrasound contrast agents (UCAs) are shell encapsulated microbubbles developed originally for ultrasound imaging enhancement. UCAs are more recently being exploited for therapeutic applications, such as for drug delivery, gene therapy, and tissue ablation. Ultrasound transducer pulses can induce spherical (radial) UCA oscillations, translation, and nonspherical shape oscillations, the dynamics of which are highly coupled. If driven sufficiently strongly, the ultrasound can induce breakup of UCAs, which can facilitate drug or gene delivery but should be minimized for imaging purposes to increase residence time and maximize diagnostic effect. Therefore, an understanding of the interplay between the acoustic driving and nonspherical shape mode stability of UCAs is essential for both diagnostic and therapeutic applications. In this work, we use both analytical and numerical methods to analyze shape mode stability for cases of small and large nonspherical oscillations, respectively. To analyze shape mode stability in the limit of small nonspherical perturbations, we couple a radial model of a lipid-coated microbubble with a model for bubble translation and nonspherical shape oscillation. This hybrid model is used to predict shape mode stability for ultrasound driving frequencies and pressure amplitudes of clinical interest. In addition, calculations of the stability of individual shape modes, residence time, maximum radius, and translation are provided with respect to acoustic driving parameters and compared to an unshelled bubble. The effects of shell elasticity, shell viscosity, and initial radius on stability are investigated. Furthermore, the well-established boundary element method (BEM) is used to investigate the dynamics and shape stability of large amplitude nonspherical oscillations of an ultrasonically-forced, polymer-coated microbubble near a rigid boundary. Different instability modes are identified based on the degree of jetting and proximity to the boundary. This insight is used to develop diagrams that delineate regions of stability from instability based on the breakup mechanism, in parameter ranges of ultrasound frequency and amplitude relevant to medical applications.

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.

Phase matching of high order harmonic generation using dynamic phase modulation caused by a non-collinear modulation pulse

DOEpatents

Cohen, Oren; Kapteyn, Henry C.; Mumane, Margaret M.

2010-02-16

Phase matching high harmonic generation (HHG) uses a single, long duration non-collinear modulating pulse intersecting the driving pulse. A femtosecond driving pulse is focused into an HHG medium (such as a noble gas) to cause high-harmonic generation (HHG), for example in the X-ray region of the spectrum, via electrons separating from and recombining with gas atoms. A non-collinear pulse intersects the driving pulse within the gas, and modulates the field seen by the electrons while separated from their atoms. The modulating pulse is low power and long duration, and its frequency and amplitude is chosen to improve HHG phase matching by increasing the areas of constructive interference between the driving pulse and the HHG, relative to the areas of destructive interference.

How to Drive CARS in Reverse

DTIC Science & Technology

2013-11-07

pulse . This pulse is then used to drive a coherent anti-Stokes Raman scattering scheme, resulting in a strong chemically specific signal propagating...generation of a backward propagating stimulated Raman pulse . This pulse is then used to drive a coherent anti-Stokes Raman scattering scheme, resulting in a...proposed to re- motely generate a spatially coherent backward propagating pulse . The first uses the impurities in air as a lasing medium [2]. Two photon

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.

Symmetry control in subscale near-vacuum hohlraums

DOE PAGES

Turnbull, D.; Berzak Hopkins, L. F.; Le Pape, S.; ...

2016-05-18

Controlling the symmetry of indirect-drive inertial confinement fusion implosions remains a key challenge. Increasing the ratio of the hohlraum diameter to the capsule diameter (case-to-capsule ratio, or CCR) facilitates symmetry tuning. By varying the balance of energy between the inner and outer cones as well as the incident laser pulse length, we demonstrate the ability to tune from oblate, through round, to prolate at a CCR of 3.2 in near-vacuum hohlraums at the National Ignition Facility, developing empirical playbooks along the way for cone fraction sensitivity of various laser pulse epochs. Radiation-hydrodynamic simulations with enhanced inner beam propagation reproduce mostmore » experimental observables, including hot spot shape, for a majority of implosions. In conclusion, specular reflections are used to diagnose the limits of inner beam propagation as a function of pulse length.« less

Bunch modulation in LWFA blowout regime

NASA Astrophysics Data System (ADS)

Vyskočil, Jiří; Klimo, Ondřej; Vieira, Jorge; Korn, Georg

2015-05-01

Laser wakefield acceleration (LWFA) is able to produce high quality electron bunches interesting for many applications ranging from coherent light sources to high energy physics. The blow-out regime of LWFA provides excellent accelerating structure able to maintain small transverse emittance and energy spread of the accelerating electron beam if combined with localised injection. A modulation of the back of a self-injected electron bunch in the blowout regime of Laser Wakefield Acceleration appears 3D Particle-in-Cell simulations with the code OSIRIS. The shape of the modulation is connected to the polarization of the driving laser pulse, although the wavelength of the modulation is longer than that of the pulse. Nevertheless a circularly polarized laser pulse leads to a corkscrew-like modulation, while in the case of linear polarization, the modulation lies in the polarization plane.

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.

Composite and shaped pulses for efficient and robust pumping of disconnected eigenstates in magnetic resonance

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

Theis, T.; Feng, Y.; Wu, T.

2014-01-07

Hyperpolarization methods, which can enhance nuclear spin signals by orders of magnitude, open up important new opportunities in magnetic resonance. However, many of these applications are limited by spin lattice relaxation, which typically destroys the hyperpolarization in seconds. Significant lifetime enhancements have been found with “disconnected eigenstates” such as the singlet state between a pair of nearly equivalent spins, or the “singlet-singlet” state involving two pairs of chemically equivalent spins; the challenge is to populate these states (for example, from thermal equilibrium magnetization or hyperpolarization) and to later recall the population into observable signal. Existing methods for populating these statesmore » are limited by either excess energy dissipation or high sensitivity to inhomogeneities. Here we overcome the limitations by extending recent work using continuous-wave irradiation to include composite and adiabatic pulse excitations. Traditional composite and adiabatic pulses fail completely in this problem because the interactions driving the transitions are fundamentally different, but the new shapes we introduce can move population between accessible and disconnected eigenstates over a wide range of radio-frequency (RF) amplitudes and offsets while depositing insignificant amounts of power.« less

Higher Velocity High-Foot Implosions on the National Ignition Facility Laser

NASA Astrophysics Data System (ADS)

Callahan, Debra

2014-10-01

After the end of the National Ignition Campaign on the National Ignition Facility (NIF) laser, we began a campaign to test capsule performance using a modified laser pulse-shape that delivers higher power early in the pulse (``high foot''). This pulse-shape trades one-dimensional performance (peak compression) for increased hydrodynamic stability. The focus of the experiments this year have been to improve performance by increasing the implosion velocity using higher laser power/energy, depleted uranium hohlraums, and thinner capsules. While the mix of ablator material into the hotspot has been low for all of these implosions, the challenge has been to keep the implosion shape under control. As the peak laser power is increased, the plasma density in the hohlraum is increased - making it more and more challenging for the inner cone beams to reach the midplane of the hohlraum and resulting in an oblate implosion. Depleted uranium hohlraums have higher albedo than Au hohlraums, which leads to additional drive and improved implosion shape. Thinner ablators increase the velocity by reducing the amount of payload; thinner ablators also put less mass into the hohlraum which results in improved inner beam propagation. These techniques have allowed us to push the capsule to higher and higher velocity. In parallel with this effort, we are exploring other hohlraums such as the rugby shaped hohlraum to allow us to push these implosions further. This talk will summarize the progress of the high foot campaign in terms of both capsule and hohlraum performance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Spatial control of photoemitted electron beams using a microlens-array transverse-shaping technique

DOE PAGES

Halavanau, A.; Qiang, G.; Ha, G.; ...

2017-10-26

A transversely inhomogeneous laser distribution on the photocathode surface generally produces electron beams with degraded beam quality. In this paper, we explore the use of microlens arrays to dramatically improve the transverse uniformity of an ultraviolet drive-laser pulse used in a photoinjector. Here, we also demonstrate a capability of microlens arrays to generate transversely modulated electron beams and present an application of such a feature to diagnose the properties of a magnetized beam.

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

PubMed

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

2008-02-01

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

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.

Dense plasma formation on the surface of a ferroelectric induced by a driving pulse with a fast fall time

NASA Astrophysics Data System (ADS)

Chirko, K.; Krasik, Ya. E.; Sayapin, A.; Felsteiner, J.; Bernshtam, V.

2003-08-01

Experimental results are presented of dense plasma formation on the surface of a BaTi-based ferroelectric sample during the fall time of a driving pulse. A negative or positive driving pulse (⩽14 kV), with a slow rise time (˜450 ns) and a fast fall time (40-200 ns), was applied to the rear electrode of the ferroelectric. It was found by different electrical, optical, and spectroscopic diagnostics that this method allows one to form a plasma with a larger density (˜3×1013 cm-3) as compared with that formed by a driving pulse with a fast rise time (⩽4×1012 cm-3). It was shown that the shorter the fall time of the driving pulse the more intense plasma formation occurs. The most uniform and dense plasma formation occurs with a positive driving pulse. In addition, it was found that the shorter the fall time of the positive driving pulse the larger are the current amplitude, the energy, and the divergence of the emitted electrons. The obtained results are discussed in terms of the surface plasma formation and the compensation process of the polarization surface charge of the ferroelectric sample.

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

The High-Foot Implosion Campaign on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hurricane, Omar

2013-10-01

The `High-Foot' platform manipulates the laser pulse-shape coming from the National Ignition Facility (NIF) laser to create an indirect drive 3-shock implosion that is significantly more robust against instability growth involving the ablator and also modestly reduces implosion convergence ratio. This tactic gives up on theoretical high-gain in an inertial confinement fusion implosion in order to obtain better control of the implosion and bring experimental performance in-line with calculated performance, yet keeps the absolute capsule performance relatively high. This approach is generally consistent with the philosophy laid out in a recent international workshop on the topic of ignition science on NIF [``Workshop on the Science of Fusion Ignition on NIF,'' Lawrence Livermore National Laboratory Report, LLNL-TR-570412 (2012). Op cit. V. Gocharov and O.A. Hurricane, ``Panel 3 Report: Implosion Hydrodynamics,'' LLNL-TR-562104 (2012)]. Side benefits our the High-Foot pulse-shape modification appear to be improvements in hohlraum behavior--less wall motion achieved through higher pressure He gas fill and improved inner cone laser beam propagation. Another consequence of the `High-Foot' is a higher fuel adiabat, so there is some relation to direct-drive experiments performed at the Laboratory for Laser Energetics (LLE). In this talk, we will cover the various experimental and theoretical motivations for the High-Foot drive as well as cover the experimental results that have come out of the High-Foot experimental campaign. Most notably, at the time of this writing record DT layer implosion performance with record low levels of inferred mix and excellent agreement with one-dimensional implosion models without the aid of mix models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

RhoA GTPase inhibition organizes contraction during epithelial morphogenesis

PubMed Central

Mason, Frank M.; Xie, Shicong; Vasquez, Claudia G.; Tworoger, Michael

2016-01-01

During morphogenesis, contraction of the actomyosin cytoskeleton within individual cells drives cell shape changes that fold tissues. Coordination of cytoskeletal contractility is mediated by regulating RhoA GTPase activity. Guanine nucleotide exchange factors (GEFs) activate and GTPase-activating proteins (GAPs) inhibit RhoA activity. Most studies of tissue folding, including apical constriction, have focused on how RhoA is activated by GEFs to promote cell contractility, with little investigation as to how GAPs may be important. Here, we identify a critical role for a RhoA GAP, Cumberland GAP (C-GAP), which coordinates with a RhoA GEF, RhoGEF2, to organize spatiotemporal contractility during Drosophila melanogaster apical constriction. C-GAP spatially restricts RhoA pathway activity to a central position in the apical cortex. RhoGEF2 pulses precede myosin, and C-GAP is required for pulsation, suggesting that contractile pulses result from RhoA activity cycling. Finally, C-GAP expression level influences the transition from reversible to irreversible cell shape change, which defines the onset of tissue shape change. Our data demonstrate that RhoA activity cycling and modulating the ratio of RhoGEF2 to C-GAP are required for tissue folding. PMID:27551058

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

PubMed

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

2007-05-01

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

Laser fusion pulse shape controller

DOEpatents

Siebert, Larry D.

1977-01-01

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

Production of low-Z ions in the Dresden superconducting electron ion beam source for medical particle therapy.

PubMed

Zschornack, G; Schwan, A; Ullmann, F; Grossmann, F; Ovsyannikov, V P; Ritter, E

2012-02-01

We report on experiments with a new superconducting electron beam ion source (EBIS-SC), the Dresden EBIS-SC, with the objective to meet the main requirements for their application in particle-therapy facilities. Synchrotrons as well as innovative accelerator concepts, such as high-gradient linacs which are driven by a large-current cyclotron (CYCLINACS) and direct drive RF linear accelerators may benefit from the advantages of EBISs in regard to their functional principle. First experimental studies of the production of low-Z ions such as H(+), H(2)(+), H(3)(+), C(4+), and C(6+) are presented. Particular attention is paid to the ion output, i.e., the number of ions per pulse and per second, respectively. Important beam parameters in this context are, among others, ion pulse shaping, pulse repetition rates, beam emittance, and ion energy spread.

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.

Tailored electron bunches with smooth current profiles for enhanced transformer ratios in beam-driven acceleration

DOE PAGES

Lemery, F.; Piot, P.

2015-08-03

Collinear high-gradient O(GV/m) beam-driven wakefield methods for charged-particle acceleration could be critical to the realization of compact, cost-efficient, accelerators, e.g., in support of TeV-scale lepton colliders or multiple-user free-electron laser facilities. To make these options viable, the high accelerating fields need to be complemented with large transformer ratios >2, a parameter characterizing the efficiency of the energy transfer between a wakefield-exciting “drive” bunch to an accelerated “witness” bunch. While several potential current distributions have been discussed, their practical realization appears challenging due to their often discontinuous nature. In this paper we propose several alternative continuously differentiable (smooth) current profiles whichmore » support enhanced transformer ratios. We especially demonstrate that one of the devised shapes can be implemented in a photo-emission electron source by properly shaping the photocathode-laser pulse. We finally discuss a possible superconducting linear-accelerator concept that could produce shaped drive bunches at high-repetition rates to drive a dielectric-wakefield accelerator with accelerating fields on the order of ~60 MV/m and a transformer ratio ~5 consistent with a recently proposed multiuser free-electron laser facility.« less

Tailored electron bunches with smooth current profiles for enhanced transformer ratios in beam-driven acceleration

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

Lemery, F.; Piot, P.

Collinear high-gradient O(GV/m) beam-driven wakefield methods for charged-particle acceleration could be critical to the realization of compact, cost-efficient, accelerators, e.g., in support of TeV-scale lepton colliders or multiple-user free-electron laser facilities. To make these options viable, the high accelerating fields need to be complemented with large transformer ratios >2, a parameter characterizing the efficiency of the energy transfer between a wakefield-exciting “drive” bunch to an accelerated “witness” bunch. While several potential current distributions have been discussed, their practical realization appears challenging due to their often discontinuous nature. In this paper we propose several alternative continuously differentiable (smooth) current profiles whichmore » support enhanced transformer ratios. We especially demonstrate that one of the devised shapes can be implemented in a photo-emission electron source by properly shaping the photocathode-laser pulse. We finally discuss a possible superconducting linear-accelerator concept that could produce shaped drive bunches at high-repetition rates to drive a dielectric-wakefield accelerator with accelerating fields on the order of ~60 MV/m and a transformer ratio ~5 consistent with a recently proposed multiuser free-electron laser facility.« less

Two-qubit gates and coupling with low-impedance flux qubits

NASA Astrophysics Data System (ADS)

Chow, Jerry; Corcoles, Antonio; Rigetti, Chad; Rozen, Jim; Keefe, George; Rothwell, Mary-Beth; Rohrs, John; Borstelmann, Mark; Divincenzo, David; Ketchen, Mark; Steffen, Matthias

2011-03-01

We experimentally demonstrate the coupling of two low-impedance flux qubits mediated via a transmission line resonator. We explore the viability of experimental coupling protocols which involve selective microwave driving on the qubits independently as well as fast frequency tuning through on-chip flux-bias. Pulse-shaping techniques for single-qubit and two-qubit gates are employed for reducing unwanted leakage and phase errors. A joint readout through the transmission line resonator is used for characterizing single-qubit and two-qubit states.

Developing a bright 17 keV x-ray source for probing high-energy-density states of matter at high spatial resolution

NASA Astrophysics Data System (ADS)

Huntington, C. M.; Park, H.-S.; Maddox, B. R.; Barrios, M. A.; Benedetti, R.; Braun, D. G.; Hohenberger, M.; Landen, O. L.; Regan, S. P.; Wehrenberg, C. E.; Remington, B. A.

2015-04-01

A set of experiments were performed on the National Ignition Facility (NIF) to develop and optimize a bright, 17 keV x-ray backlighter probe using laser-irradiated Nb foils. High-resolution one-dimensional imaging was achieved using a 15 μm wide slit in a Ta substrate to aperture the Nb Heα x-rays onto an open-aperture, time integrated camera. To optimize the x-ray source for imaging applications, the effect of laser pulse shape and spatial profile on the target was investigated. Two laser pulse shapes were used—a "prepulse" shape that included a 3 ns, low-intensity laser foot preceding the high-energy 2 ns square main laser drive, and a pulse without the laser foot. The laser spatial profile was varied by the use of continuous phase plates (CPPs) on a pair of shots compared to beams at best focus, without CPPs. A comprehensive set of common diagnostics allowed for a direct comparison of imaging resolution, total x-ray conversion efficiency, and x-ray spectrum between shots. The use of CPPs was seen to reduce the high-energy tail of the x-ray spectrum, whereas the laser pulse shape had little effect on the high-energy tail. The measured imaging resolution was comparably high for all combinations of laser parameters, but a higher x-ray flux was achieved without phase plates. This increased flux was the result of smaller laser spot sizes, which allowed us to arrange the laser focal spots from multiple beams and produce an x-ray source which was more localized behind the slit aperture. Our experiments are a first demonstration of point-projection geometry imaging at NIF at the energies (>10 keV) necessary for imaging denser, higher-Z targets than have previously been investigated.

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

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.

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.

Power balance on a multibeam laser

NASA Astrophysics Data System (ADS)

Sampat, S.; Kelly, J. H.; Kosc, T. Z.; Rigatti, A. L.; Kwiatkowski, J.; Donaldson, W. R.; Romanofsky, M. H.; Waxer, L. J.; Dean, R.; Moshier, R.

2018-02-01

Inertial confinement fusion (ICF) cryogenic experiments on the 60-beam OMEGA laser have strict requirements for the laser energy delivered on target to be power balanced in order to maximize target-irradiation uniformity. For OMEGA, this quantity (power balance) is inferred from measurements of the time-integrated energy and time-resolved, spatially integrated temporal profile of each of the 60 beams at the output of the laser. The work presented here proposes a general definition of power balance as measured at the laser output and discusses the conditions that are fundamental to achieving laser power balance. Power balance necessitates equal gain across all stages of amplification, equal net losses across each amplifier stage, equal frequency conversion (from 1053 nm to 351 nm) of all 60 beams, and equal beam path lengths (beam timing). Typical OMEGA ICF laser pulse shapes consist of one or more short (100-ps) "pickets" followed by a shaped "drive" pulse of 1 to 2 ns. For these experiments, power balance is assessed for the pickets and the drive independently, with the ultimate goal of achieving root-mean-square (rms) imbalance across all 60 beams of less than 2% rms on both. This work presents a comprehensive summary of laser shot campaigns conducted to significantly improve laser power balance from typical rms values of 4.7% and 5.2%, respectively, to the 3% level for both features along with a discussion of future work required to further reduce the rms power imbalance of the laser system.

Apparatus for and method of operating a cylindrical pulsed induction mass launcher

DOEpatents

Cowan, M. Jr.; Duggin, B.W.; Widner, M.M.

1992-06-30

An electromagnetic cylindrical projectile mass launcher and a method of operation is provided which includes a cylindrical projectile having a conducting armature, a cylindrical barrel in which the armature is received, a plurality of electromagnetic drive coil stages, a plurality of pulse energy sources, and a pulsed power arrangement for generating magnetic pulses forming a pulsed magnetic wave along the length of the launcher barrel. The pulsed magnetic wave provides a propelling force on the projectile along the drive coil. The pulsed magnetic wave of the drive coil stages is advanced along the armature faster than the projectile to thereby generate an induced current wave in the armature. The pulsed generation of the magnetic wave minimizes electromagnetic heating of the projectile and provides for smooth acceleration of the projectile through the barrel of the launcher. 2 figs.

Apparatus for and method of operating a cylindrical pulsed induction mass launcher

DOEpatents

Cowan, Jr., Maynard; Duggin, Billy W.; Widner, Melvin M.

1992-01-01

An electromagnetic cylindrical projectile mass launcher and a method of operation is provided which includes a cylindrical projectile having a conducting armature, a cylindrical barrel in which the armature is received, a plurality of electromagnetic drive coil stages, a plurality of pulse energy sources, and a pulsed power arrangement for generating magnetic pulses forming a pulsed magnetic wave along the length of the launcher barrel. The pulsed magnetic wave provides a propelling force on the projectile along the drive coil. The pulsed magnetic wave of the drive coil stages is advanced along the armature faster than the projectile to thereby generate an induced current wave in the armature. The pulsed generation of the magnetic wave minimizes electromagnetic heating of the projectile and provides for smooth acceleration of the projectile through the barrel of the launcher.

Natural Divertor Spherical Tokamak Plasmas with bean shape and ergodic limiter

NASA Astrophysics Data System (ADS)

Ribeiro, Celso; Herrera, Julio; Chavez, Esteban; Tritz, Kevin

2013-10-01

The former spherical tokamak (ST) MEDUSA (Madison EDUcation Small Aspect.ratio tokamak, R < 0.14 m, a < 0.10 m, BT < 0.5T, Ip < 40 kA, 3 ms pulse) is being recommissioned in Costa Rica Institute of Technology. The main objectives of the MEDUSA-CR project are training and to clarify several issues in relevant physics for conventional and mainly STs, including beta studies in bean-shaped ST plasmas, transport, heating and current drive via Alfvén wave, and natural divertor STs with ergodic magnetic limiter. We report here improvements in the self-consistency of these equilibrium comparisons and a preliminary study of their MHD stability beta limits. VIE-ITCR, IAEA-CRP contract 17592, National Instruments of Costa Rica.

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.

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.

Performance and Mix Measurements of Indirect Drive Cu-Doped Be Implosions

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

Casey, D.  T.; Woods, D. T.; Smalyuk, V. A.

2015-05-19

The ablator couples energy between the driver and fusion fuel in inertial confinement fusion (ICF). Because of its low opacity, high solid density, and material properties, beryllium has long been considered an ideal ablator for ICF ignition experiments at the National Ignition Facility. We report here the first indirect drive Be implosions driven with shaped laser pulses and diagnosed with fusion yield at the OMEGA laser. The results show good performance with an average DD neutron yield of ~2 × 10⁹ at a convergence ratio of R₀/R ~ 10 and little impact due to the growth of hydrodynamic instabilities andmore » mix. In addition, the effect of adding an inner liner of W between the Be and DD is demonstrated.« less

The Hohlraum Drive Campaign on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Moody, John D.

2013-10-01

The Hohlraum drive effort on the National Ignition Facility (NIF) laser has three primary goals: 1) improve hohlraum performance by improving laser beam propagation, reducing backscatter from laser plasma interactions (LPI), controlling x-ray and electron preheat, and modifying the x-ray drive spectrum; 2) improve understanding of crossbeam energy transfer physics to better evaluate this as a symmetry tuning method; and 3) improve modeling in order to find optimum designs. Our experimental strategy for improving performance explores the impact of significant changes to the hohlraum shape, wall material, gasfill composition, and gasfill density on integrated implosion experiments. We are investigating the performance of a rugby-shaped design that has a significantly larger diameter (7 mm) at the waist than our standard 5.75 mm diameter cylindrical-shaped hohlraum but maintains approximately the same wall area. We are also exploring changes to the gasfill composition in cylindrical hohlraums by using neopentane at room temperature to compare with our standard helium gasfill. In addition, we are also investigating higher He gasfill density (1.6 mg/cc vs nominal 0.96 mg/cc) and increased x-ray drive very early in the pulse. Besides these integrated experiments, our strategy includes experiments testing separate aspects of the hohlraum physics. These include time-resolved and time-integrated measurements of cross-beam transfer rates and laser-beam spatial power distribution at early and late times using modified targets. Non-local thermal equilibrium modeling and heat transport relevant to ignition experiments are being studied using sphere targets on the Omega laser system. These simpler targets provide benchmarks for improving our modeling tools. This talk will summarize the results of the Hohlraum Drive campaign and discuss future directions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA2-344.

Charge and spin dynamics driven by ultrashort extreme broadband pulses: A theory perspective

NASA Astrophysics Data System (ADS)

Moskalenko, Andrey S.; Zhu, Zhen-Gang; Berakdar, Jamal

2017-02-01

This article gives an overview on recent theoretical progress in controlling the charge and spin dynamics in low-dimensional electronic systems by means of ultrashort and ultrabroadband electromagnetic pulses. A particular focus is put on sub-cycle and single-cycle pulses and their utilization for coherent control. The discussion is mostly limited to cases where the pulse duration is shorter than the characteristic time scales associated with the involved spectral features of the excitations. The relevant current theoretical knowledge is presented in a coherent, pedagogic manner. We work out that the pulse action amounts in essence to a quantum map between the quantum states of the system at an appropriately chosen time moment during the pulse. The influence of a particular pulse shape on the post-pulse dynamics is reduced to several integral parameters entering the expression for the quantum map. The validity range of this reduction scheme for different strengths of the driving fields is established and discussed for particular nanostructures. Acting with a periodic pulse sequence, it is shown how the system can be steered to and largely maintained in predefined states. The conditions for this nonequilibrium sustainability are worked out by means of geometric phases, which are identified as the appropriate quantities to indicate quasistationarity of periodically driven quantum systems. Demonstrations are presented for the control of the charge, spin, and valley degrees of freedom in nanostructures on picosecond and subpicosecond time scales. The theory is illustrated with several applications to one-dimensional semiconductor quantum wires and superlattices, double quantum dots, semiconductor and graphene quantum rings. In the case of a periodic pulsed driving the influence of the relaxation and decoherence processes is included by utilizing the density matrix approach. The integrated and time-dependent spectra of the light emitted from the driven system deliver information on its spin-dependent dynamics. We review examples of such spectra of photons emitted from pulse-driven nanostructures as well as a possibility to characterize and control the light polarization on an ultrafast time scale. Furthermore, we consider the response of strongly correlated systems to short broadband pulses and show that this case bears a great potential to unveil high order correlations while they build up upon excitations.

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

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

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

2004-05-12

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

High speed, high current pulsed driver circuit

DOEpatents

Carlen, Christopher R.

2017-03-21

Various technologies presented herein relate to driving a LED such that the LED emits short duration pulses of light. This is accomplished by driving the LED with short duration, high amplitude current pulses. When the LED is driven by short duration, high amplitude current pulses, the LED emits light at a greater amplitude compared to when the LED is driven by continuous wave current.

Isolated Attosecond Pulse Generation without the Need to Stabilize the Carrier-Envelope Phase of Driving Lasers

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

Gilbertson, Steve; Khan, Sabih D.; Wu Yi

2010-08-27

Single isolated attosecond pulses can be extracted from a pulse train with an ultrafast gate in the generation target. By setting the gate width sufficiently narrow with the generalized double optical gating, we demonstrate that single isolated attosecond pulses can be generated with any arbitrary carrier-envelope phase value of the driving laser. The carrier-envelope phase only affects the photon flux, not the pulse duration or contrast. Our results show that isolated attosecond pulses can be generated using carrier-envelope phase unstabilized 23 fs pulses directly from chirped pulse amplifiers.

Novel pulsed switched power supply for a fast field cycling NMR spectrometer.

PubMed

Sousa, D M; Fernandes, P A L; Marques, G D; Ribeiro, A C; Sebastião, P J

2004-01-01

In this paper, we outline the operating principles of a pulsed switched power supply for a fast field-cycling nuclear magnetic resonance spectrometer. The power supply uses a variant of a four-quadrant chopper with a duty cycle that defines the average output current. With this topology only two semiconductors are necessary to drive hundreds of amperes with an output power of several kilowatts. The output current ripple has a well-defined shape that can be reduced to acceptable values by a careful design of the semiconductors' controlling circuits and drivers. A power supply prototype was tested with a home build air-core magnet operating with fields between 0 and 0.21 T. The system is computer controlled using pulse generator and data acquisition PC cards, and specific user-friendly home-developed software. A comparative proton relaxometry study in two well-known liquid crystal compounds 5CB and MBBA was performed to check the reproducibility of the T1 measurements.

Optimized pulse shaping for trapped ion quantum computing

NASA Astrophysics Data System (ADS)

Manning, T.; Debnath, Shantanu; Choi, Taeyoung; Figgatt, Caroline; Monroe, Chris

2013-05-01

We perform entangling phase gates between pairs of qubits in a chain of trapped atomic ytterbium ions. Beat notes between frequency comb lines of a pulsed laser coherently drive Raman transitions that couple the hyperfine qubits to multiple collective transverse modes of motion. By optimizing the phase and amplitude of segmented laser pulses, we demonstrate a five-segment scheme to entangle two qubits with high fidelity over a range of detunings. We compare this special case of full control of spin-motion entanglement to a traditional single-segment gate. We extend this scheme to selectively entangle pairs of qubits in larger chains using individual optical addressing, where we couple to all the motional modes. We show how these robust gates can achieve high fidelities for practical gate times in an approach that scales realistically to much larger numbers of qubits. This work is supported by grants from the U.S. Army Research Office with funding from the DARPA OLE program, IARPA, and the MURI program; and the NSF Physics Frontier Center at JQI.

[INVITED] Control of femtosecond pulsed laser ablation and deposition by temporal pulse shaping

NASA Astrophysics Data System (ADS)

Garrelie, Florence; Bourquard, Florent; Loir, Anne--Sophie; Donnet, Christophe; Colombier, Jean-Philippe

2016-04-01

This study explores the effects of temporal laser pulse shaping on femtosecond pulsed laser deposition (PLD). The potential of laser pulses temporally tailored on ultrafast time scales is used to control the expansion and the excitation degree of ablation products including atomic species and nanoparticles. The ablation plume generated by temporally shaped femtosecond pulsed laser ablation of aluminum and graphite targets is studied by in situ optical diagnostic methods. Taking advantage of automated pulse shaping techniques, an adaptive procedure based on spectroscopic feedback regulates the irradiance for the enhancement of typical plasma features. Thin films elaborated by unshaped femtosecond laser pulses and by optimized sequence indicate that the nanoparticles generation efficiency is strongly influenced by the temporal shaping of the laser irradiation. The ablation processes leading either to the generation of the nanoparticles either to the formation of plasma can be favored by using a temporal shaping of the laser pulse. Insights are given on the possibility to control the quantity of the nanoparticles. The temporal laser pulse shaping is shown also to strongly modify the laser-induced plasma contents and kinetics for graphite ablation. Temporal pulse shaping proves its capability to reduce the number of slow radicals while increasing the proportion of monomers, with the addition of ionized species in front of the plume. This modification of the composition and kinetics of plumes in graphite ablation using temporal laser pulse shaping is discussed in terms of modification of the structural properties of deposited Diamond-Like Carbon films (DLC). This gives rise to a better understanding of the growth processes involved in femtosecond-PLD and picosecond-PLD of DLC suggesting the importance of neutral C atoms, which are responsible for the subplantation process.

Active lamp pulse driver circuit. [optical pumping of laser media

NASA Technical Reports Server (NTRS)

Logan, K. E. (Inventor)

1983-01-01

A flashlamp drive circuit is described which uses an unsaturated transistor as a current mode switch to periodically subject a partially ionized gaseous laser excitation flashlamp to a stable, rectangular pulse of current from an incomplete discharge of an energy storage capacitor. A monostable multivibrator sets the pulse interval, initiating the pulse in response to a flash command by providing a reference voltage to a non-inverting terminal of a base drive amplifier; a tap on an emitter resistor provides a feedback signal sensitive to the current amplitude to an inverting terminal of amplifier, thereby controlling the pulse amplitude. The circuit drives the flashlamp to provide a squarewave current flashlamp discharge.

Frequency-chirp rates of harmonics driven by a few-cycle pulse

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

Murakami, M.; Mauritsson, J.; Gaarde, M.B.

2005-08-15

We present numerical calculations of the time-frequency characteristics of cutoff harmonics generated by few-cycle laser pulses. We find that for driving pulses as short as three optical cycles, the adiabatic prediction for the harmonic chirp rate is very accurate. This negative chirp is so large that the resulting bandwidth causes substantial overlap between neighboring harmonics, and the harmonic phase therefore appears to not vary in time or frequency. By adding a compensating positive chirp to the driving pulse, which reduces the harmonic bandwidth and allows for the appearance of the negative chirp, we can measure the harmonic chirp rates. Wemore » also find that the positive chirp on the driving pulse causes the harmonics to shift down in frequency. We show that this counterintuitive result is caused by the change in the strong field continuum dynamics introduced by the variation of the driving frequency with time.« less

System for generating shaped optical pulses and measuring optical pulses using spectral beam deflection (SBD)

DOEpatents

Skupsky, Stanley; Kessler, Terrance J.; Letzring, Samuel A.

1993-01-01

A temporally shaped or modified optical output pulse is generated from a bandwidth-encoded optical input pulse in a system in which the input pulse is in the form of a beam which is spectrally spread into components contained within the bandwidth, followed by deflection of the spectrally spread beam (SBD) thereby spatially mapping the components in correspondence with the temporal input pulse profile in the focal plane of a lens, and by spatially selective attenuation of selected components in that focal plane. The shaped or modified optical output pulse is then reconstructed from the attenuated spectral components. The pulse-shaping system is particularly useful for generating optical pulses of selected temporal shape over a wide range of pulse duration, such pulses finding application in the fields of optical communication, optical recording and data storage, atomic and molecular spectroscopy and laser fusion. An optical streak camera is also provided which uses SBD to display the beam intensity in the focal plane as a function of time during the input pulse.

System for generating shaped optical pulses and measuring optical pulses using spectral beam deflection (SBD)

DOEpatents

Skupsky, S.; Kessler, T.J.; Letzring, S.A.

1993-11-16

A temporally shaped or modified optical output pulse is generated from a bandwidth-encoded optical input pulse in a system in which the input pulse is in the form of a beam which is spectrally spread into components contained within the bandwidth, followed by deflection of the spectrally spread beam (SBD) thereby spatially mapping the components in correspondence with the temporal input pulse profile in the focal plane of a lens, and by spatially selective attenuation of selected components in that focal plane. The shaped or modified optical output pulse is then reconstructed from the attenuated spectral components. The pulse-shaping system is particularly useful for generating optical pulses of selected temporal shape over a wide range of pulse duration, such pulses finding application in the fields of optical communication, optical recording and data storage, atomic and molecular spectroscopy and laser fusion. An optical streak camera is also provided which uses SBD to display the beam intensity in the focal plane as a function of time during the input pulse. 10 figures.

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

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

PubMed

Haner, M; Warren, W S

1987-09-01

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

Oceanographic drivers and mistiming processes shape breeding success in a seabird

PubMed Central

2016-01-01

Understanding the processes driving seabirds' reproductive performance through trophic interactions requires the identification of seasonal pulses in marine productivity. We investigated the sequence of environmental and biological processes driving the reproductive phenology and performance of the storm petrel (Hydrobates pelagicus) in the Western Mediterranean. The enhanced light and nutrient availability at the onset of water stratification (late winter/early spring) resulted in annual consecutive peaks in relative abundance of phytoplankton, zooplankton and ichthyoplankton. The high energy-demanding period of egg production and chick rearing coincided with these successive pulses in food availability, pointing to a phenological adjustment to such seasonal patterns with important fitness consequences. Indeed, delayed reproduction with respect to the onset of water stratification resulted in both hatching and breeding failure. This pattern was observed at the population level, but also when confounding factors such as individuals' age or experience were also accounted for. We provide the first evidence of oceanographic drivers leading to the optimal time-window for reproduction in an inshore seabird at southern European latitudes, along with a suitable framework for assessing the impact of environmentally driven changes in marine productivity patterns in seabird performance. PMID:26962134

Oceanographic drivers and mistiming processes shape breeding success in a seabird.

PubMed

Ramírez, Francisco; Afán, Isabel; Tavecchia, Giacomo; Catalán, Ignacio A; Oro, Daniel; Sanz-Aguilar, Ana

2016-03-16

Understanding the processes driving seabirds' reproductive performance through trophic interactions requires the identification of seasonal pulses in marine productivity. We investigated the sequence of environmental and biological processes driving the reproductive phenology and performance of the storm petrel (Hydrobates pelagicus) in the Western Mediterranean. The enhanced light and nutrient availability at the onset of water stratification (late winter/early spring) resulted in annual consecutive peaks in relative abundance of phytoplankton, zooplankton and ichthyoplankton. The high energy-demanding period of egg production and chick rearing coincided with these successive pulses in food availability, pointing to a phenological adjustment to such seasonal patterns with important fitness consequences. Indeed, delayed reproduction with respect to the onset of water stratification resulted in both hatching and breeding failure. This pattern was observed at the population level, but also when confounding factors such as individuals' age or experience were also accounted for. We provide the first evidence of oceanographic drivers leading to the optimal time-window for reproduction in an inshore seabird at southern European latitudes, along with a suitable framework for assessing the impact of environmentally driven changes in marine productivity patterns in seabird performance. © 2016 The Author(s).

Ellipticity dependence of high harmonics generated using 400 nm driving lasers

NASA Astrophysics Data System (ADS)

Cheng, Yan; Khan, Sabih; Zhao, Kun; Zhao, Baozhen; Chini, Michael; Chang, Zenghu

2011-05-01

High order harmonics generated from 400 nm driving pulses hold promise of scaling photon flux of single attosecond pulses by one to two orders of magnitude. We report ellipticity dependence and phase matching of high order harmonics generated from such pulses in Neon gas target and compared them with similar measurements using 800 nm driving pulses. Based on measured ellipticity dependence, we predict that double optical gating (DOG) and generalized double optical gating (GDOG) can be employed to extract intense single attosecond pulses from pulse train, while polarization gating (PG) may not work for this purpose. This material is supported by the U.S. Army Research Office under grant number W911NF-07-1-0475, and by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

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.

Multi-Kilovolt Solid-State Picosecond Switch Studies

DTIC Science & Technology

2013-06-01

waveforms for the SiC device. Figure 7 shows the nanosecond driving pulse and the delayed avalanche breakdown of the SiC device. The driving...of the sharpened pulse RS VS VOLTAGE SOURCE TEST DEVICE VOLTAGE MONITOR R1 R2 TO SCOPE Figure 6. Simplified SiC avalanche diode test setup 0 2 4...Measured waveforms showing nanosecond driving pulse and subnanosecond delayed avalanche dreakdown of SiC device 50 µm 75 µm 10 µm p+ n+n Anode Cathode

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

PubMed

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

2007-11-01

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

High-speed pulse-shape generator, pulse multiplexer

DOEpatents

Burkhart, Scott C.

2002-01-01

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

Waveform synthesizer

DOEpatents

Franks, Larry A.; Nelson, Melvin A.

1981-01-01

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

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.

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.

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

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

Sagar, Vikram; Sengupta, Sudip; Kaw, Predhiman

2014-04-15

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

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.

UWB dual burst transmit driver

DOEpatents

Dallum, Gregory E [Livermore, CA; Pratt, Garth C [Discovery Bay, CA; Haugen, Peter C [Livermore, CA; Zumstein, James M [Livermore, CA; Vigars, Mark L [Livermore, CA; Romero, Carlos E [Livermore, CA

2012-04-17

A dual burst transmitter for ultra-wideband (UWB) communication systems generates a pair of precisely spaced RF bursts from a single trigger event. An input trigger pulse produces two oscillator trigger pulses, an initial pulse and a delayed pulse, in a dual trigger generator. The two oscillator trigger pulses drive a gated RF burst (power output) oscillator. A bias driver circuit gates the RF output oscillator on and off and sets the RF burst packet width. The bias driver also level shifts the drive signal to the level that is required for the RF output device.

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).

Pulse-Width-Modulating Driver for Brushless dc Motor

NASA Technical Reports Server (NTRS)

Salomon, Phil M.

1991-01-01

High-current pulse-width-modulating driver for brushless dc motor features optical coupling of timing signals from low-current control circuitry to high-current motor-driving circuitry. Provides high electrical isolation of motor-power supply, helping to prevent fast, high-current motor-driving pulses from being coupled through power supplies into control circuitry, where they interfere with low-current control signals.

The effects of aniline impurities on monopropellant hydrazine thruster performance

NASA Technical Reports Server (NTRS)

Holcomb, L.; Mattson, L.; Oshiro, R.

1976-01-01

Both a 0.45-N and a 0.9-N thruster representative of the designs being flown on 3-axis stabilized spacecraft were used in testing various grades of hydrazine for the phenomenon of monopropellant hydrazine thruster catalyst bed poisoning. Both designs employed Shell 405 ABSG spontaneous catalyst. It is found that pulse shape distortion can be minimized, if not eliminated, by using aniline-free hydrazine. The mechanisms for both steady-state and pulse-mode performance loss are associated with the formation of a catalyst coke similar to the polycyclic aromatic poisons encountered in the petroleum industry. These poisoning mechanisms are reversible, with high-temperature operation being required to drive off the aniline coke deposits. It is recommended that a purified-grade hydrazine be considered for any mission that imposes operational conditions on a thruster which can result in aniline-induced poisoning of the catalyst bed.

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.

Metal liner-driven quasi-isentropic compression of deuterium

NASA Astrophysics Data System (ADS)

Weinwurm, Marcus; Bland, Simon N.; Chittenden, Jeremy P.

2013-09-01

Properties of degenerate hydrogen and deuterium (D) at pressures of the order of terapascals are of key interest to Planetary Science and Inertial Confinement Fusion. In order to recreate these conditions in the laboratory, we present a scheme, where a metal liner drives a cylindrically convergent quasi-isentropic compression in a D fill. We first determined an external pressure history for driving a self-similar implosion of a D shell from a fictitious flow simulation [D. S. Clark and M. Tabak, Nucl. Fusion 47, 1147 (2007)]. Then, it is shown that this D implosion can be recreated inside a beryllium liner by shaping the current pulse. For a peak current of 10.8 MA cold and nearly isochoric D is assembled at around 12 500 kg/m3. Finally, our two-dimensional Gorgon simulations show the robustness of the implosion method to the magneto-Rayleigh-Taylor instability when using a sufficiently thick liner.

X-ray frequency combs from optically controlled resonance fluorescence

NASA Astrophysics Data System (ADS)

Cavaletto, Stefano M.; Harman, Zoltán; Buth, Christian; Keitel, Christoph H.

2013-12-01

An x-ray pulse-shaping scheme is put forward for imprinting an optical frequency comb onto the radiation emitted on a driven x-ray transition, thus producing an x-ray frequency comb. A four-level system is used to describe the level structure of N ions driven by narrow-bandwidth x rays, an optical auxiliary laser, and an optical frequency comb. By including many-particle enhancement of the emitted resonance fluorescence, a spectrum is predicted consisting of equally spaced narrow lines which are centered on an x-ray transition energy and separated by the same tooth spacing as the driving optical frequency comb. Given an x-ray reference frequency, our comb could be employed to determine an unknown x-ray frequency. While relying on the quality of the light fields used to drive the ensemble of ions, the model has validity at energies from the 100 eV to the keV range.

Pulse shaping circuit for active counting of superheated emulsion

NASA Astrophysics Data System (ADS)

Murai, Ikuo; Sawamura, Teruko

2005-08-01

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

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

PubMed

Zaari, Ryan R; Brown, Alex

2012-09-14

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

Magnetic compression laser driving circuit

DOEpatents

Ball, D.G.; Birx, D.; Cook, E.G.

1993-01-05

A magnetic compression laser driving circuit is disclosed. The magnetic compression laser driving circuit compresses voltage pulses in the range of 1.5 microseconds at 20 kilovolts of amplitude to pulses in the range of 40 nanoseconds and 60 kilovolts of amplitude. The magnetic compression laser driving circuit includes a multi-stage magnetic switch where the last stage includes a switch having at least two turns which has larger saturated inductance with less core material so that the efficiency of the circuit and hence the laser is increased.

Magnetic compression laser driving circuit

DOEpatents

Ball, Don G.; Birx, Dan; Cook, Edward G.

1993-01-01

A magnetic compression laser driving circuit is disclosed. The magnetic compression laser driving circuit compresses voltage pulses in the range of 1.5 microseconds at 20 Kilovolts of amplitude to pulses in the range of 40 nanoseconds and 60 Kilovolts of amplitude. The magnetic compression laser driving circuit includes a multi-stage magnetic switch where the last stage includes a switch having at least two turns which has larger saturated inductance with less core material so that the efficiency of the circuit and hence the laser is increased.

A compact, low jitter, nanosecond rise time, high voltage pulse generator with variable amplitude.

PubMed

Mao, Jiubing; Wang, Xin; Tang, Dan; Lv, Huayi; Li, Chengxin; Shao, Yanhua; Qin, Lan

2012-07-01

In this paper, a compact, low jitter, nanosecond rise time, command triggered, high peak power, gas-switch pulse generator system is developed for high energy physics experiment. The main components of the system are a high voltage capacitor, the spark gap switch and R = 50 Ω load resistance built into a structure to obtain a fast high power pulse. The pulse drive unit, comprised of a vacuum planar triode and a stack of avalanche transistors, is command triggered by a single or multiple TTL (transistor-transistor logic) level pulses generated by a trigger pulse control unit implemented using the 555 timer circuit. The control unit also accepts user input TTL trigger signal. The vacuum planar triode in the pulse driving unit that close the first stage switches is applied to drive the spark gap reducing jitter. By adjusting the charge voltage of a high voltage capacitor charging power supply, the pulse amplitude varies from 5 kV to 10 kV, with a rise time of <3 ns and the maximum peak current up to 200 A (into 50 Ω). The jitter of the pulse generator system is less than 1 ns. The maximum pulse repetition rate is set at 10 Hz that limited only by the gas-switch and available capacitor recovery time.

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Milovich, J. L.; Dewald, E. L.; Pak, A.; Michel, P.; Town, R. P. J.; Bradley, D. K.; Landen, O.; Edwards, M. J.

2016-03-01

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or "picket") period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time. However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P2), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the "Rev5" CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using different hohlraum geometries and picket powers show good agreement with experimental data.

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

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

Milovich, J. L., E-mail: milovich1@llnl.gov; Dewald, E. L.; Pak, A.

2016-03-15

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or “picket”) period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time.more » However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P{sub 2}), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the “Rev5” CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using different hohlraum geometries and picket powers show good agreement with experimental data.« less

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

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

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

2010-10-15

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

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

NASA Astrophysics Data System (ADS)

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

2016-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2013-01-01

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

Small Patch Antennas for UWB Wireless Body Area Network

NASA Astrophysics Data System (ADS)

Klemm, M.; Tröster, G.

This paper presents the transient characteristics of an aperture-stacked patch antenna (ASPA) and its miniaturized version. These antennas were designed for ultra-wideband (UWB) body area network (BAN) applications, to operate within the 3 to 6 GHz frequency band. The APSA with large ground plane size has a planar dimensions 70 × 70 mm2, the smaller version has dimensions 32 × 26 mm2. The latest yields 85% reduction of the antenna surface. Time- and frequency-domain characteristics of these antennas were calculated in a transmission mode (Tx) and also in a complete, two-antenna (Tx-Rx) system. We have used 3 different waveforms to drive the antenna: gaussian pulse (duration-250 ps), monocycle pulse (duration-300 ps) and defined wavelet (duration-650 ps). The received pulses have very similar shapes (fidelity >90%), but they differ in the voltage amplitudes. Results show that the highest received voltage (best transmission efficiency) is achieved for the pulse with the closest spectrum to the antenna's transfer function characteristic. In order to disclose the effects of the human body proximity, two body models were built and full-wave FDTD method was employed to carry out the simulations. Significant changes of the UWB antenna performance when close to the body were identified. The most important effects are the seriously decreased radiation efficiency (16 to 34%) and different (from that in a free space) shape of the antenna transfer function. The first one can have the impact on low power implementations of UWB wearable radios; the second one discloses possible influence on the UWB systems design (especially for template receivers). The impact of the human body on antenna characteristics was identified to be a key factor in UWB body-worn antenna design.

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

NASA Astrophysics Data System (ADS)

Xin, Ran

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

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

Demonstration of High Performance in Layered Deuterium-Tritium Capsule Implosions in Uranium Hohlraums at the National Ignition Facility.

PubMed

Döppner, T; Callahan, D A; Hurricane, O A; Hinkel, D E; Ma, T; Park, H-S; Berzak Hopkins, L F; Casey, D T; Celliers, P; Dewald, E L; Dittrich, T R; Haan, S W; Kritcher, A L; MacPhee, A; Le Pape, S; Pak, A; Patel, P K; Springer, P T; Salmonson, J D; Tommasini, R; Benedetti, L R; Bond, E; Bradley, D K; Caggiano, J; Church, J; Dixit, S; Edgell, D; Edwards, M J; Fittinghoff, D N; Frenje, J; Gatu Johnson, M; Grim, G; Hatarik, R; Havre, M; Herrmann, H; Izumi, N; Khan, S F; Kline, J L; Knauer, J; Kyrala, G A; Landen, O L; Merrill, F E; Moody, J; Moore, A S; Nikroo, A; Ralph, J E; Remington, B A; Robey, H F; Sayre, D; Schneider, M; Streckert, H; Town, R; Turnbull, D; Volegov, P L; Wan, A; Widmann, K; Wilde, C H; Yeamans, C

2015-07-31

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a "high-foot" laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shape closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10^{16} neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel.

Hydrodynamic instabilities and mix studies on NIF: predictions, observations, and a path forward

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

Remington, B. A.; Atherton, L. J.; Benedetti, L. R.

The goals of the Mix Campaign are to determine how mix affects performance, locate the "mix cliff", locate the source of the mix, and develop mitigation methods that allow performance to be increased. We have used several different drive pulse shapes and capsule designs in the Mix Campaign, to understand sensitivity to drive peak power, level of coast, rise time to peak power, adiabat, and dopant level in the capsule. Ablator material mixing into the hot spot has been shown conclusively with x-ray spectroscopy. The observed neutron yield drops steeply when the hot spot mix mass becomes too large. Themore » mix appears to be driven by ablation- front Rayleigh-Taylor instabilities. A high foot, higher adiabat drive has a more stable ablation front and has allowed the mix mass in the hot spot to be reduced significantly. We found two recent high foot shots achieved neutron yields > 10 15 and measured neutron yield over clean 1D simulation (YOC) > 50%, which was one of the central goals of the Mix Campaign.« less

Hydrodynamic instabilities and mix studies on NIF: predictions, observations, and a path forward

DOE PAGES

Remington, B. A.; Atherton, L. J.; Benedetti, L. R.; ...

2016-04-01

The goals of the Mix Campaign are to determine how mix affects performance, locate the "mix cliff", locate the source of the mix, and develop mitigation methods that allow performance to be increased. We have used several different drive pulse shapes and capsule designs in the Mix Campaign, to understand sensitivity to drive peak power, level of coast, rise time to peak power, adiabat, and dopant level in the capsule. Ablator material mixing into the hot spot has been shown conclusively with x-ray spectroscopy. The observed neutron yield drops steeply when the hot spot mix mass becomes too large. Themore » mix appears to be driven by ablation- front Rayleigh-Taylor instabilities. A high foot, higher adiabat drive has a more stable ablation front and has allowed the mix mass in the hot spot to be reduced significantly. We found two recent high foot shots achieved neutron yields > 10 15 and measured neutron yield over clean 1D simulation (YOC) > 50%, which was one of the central goals of the Mix Campaign.« less

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

NASA Technical Reports Server (NTRS)

Carden, Huey D.

1992-01-01

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

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

NASA Technical Reports Server (NTRS)

Frederickson, A. R.

1992-01-01

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

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

PubMed

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

2015-10-01

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

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

PubMed

Gattinger, Norbert; Moessnang, Georg; Gleich, Bernhard

2012-07-01

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

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

PubMed

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

2018-03-01

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

Compton suppression in BEGe detectors by digital pulse shape analysis.

PubMed

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

2017-03-01

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

Experimental Demonstration of X-Ray Drive Enhancement with Rugby-Shaped Hohlraums

NASA Astrophysics Data System (ADS)

Philippe, F.; Casner, A.; Caillaud, T.; Landoas, O.; Monteil, M. C.; Liberatore, S.; Park, H. S.; Amendt, P.; Robey, H.; Sorce, C.; Li, C. K.; Seguin, F.; Rosenberg, M.; Petrasso, R.; Glebov, V.; Stoeckl, C.

2010-01-01

Rugby-shaped hohlraums have been suggested as a way to enhance x-ray drive in the indirect drive approach to inertial confinement fusion. This Letter presents an experimental comparison of rugby-shaped and cylinder hohlraums used for D2 and DHe3-filled capsules implosions on the Omega laser facility, demonstrating an increase of x-ray flux by 18% in rugby-shaped hohlraums. The highest yields to date for deuterium gas implosions in indirect drive on Omega (1.5×1010 neutrons) were obtained, allowing for the first time the measurement of a DD burn history. Proton spectra measurements provide additional validation of the higher drive in rugby-shaped hohlraums.

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

The relationship between gas fill density and hohlraum drive performance at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hall, G. N.; Jones, O. S.; Strozzi, D. J.; Moody, J. D.; Turnbull, D.; Ralph, J.; Michel, P. A.; Hohenberger, M.; Moore, A. S.; Landen, O. L.; Divol, L.; Bradley, D. K.; Hinkel, D. E.; Mackinnon, A. J.; Town, R. P. J.; Meezan, N. B.; Berzak Hopkins, L.; Izumi, N.

2017-05-01

Indirect drive inertial confinement fusion experiments were conducted at the National Ignition Facility to investigate the performance of the hohlraum drive as a function of hohlraum gas fill density by imploding high-density-carbon capsules using a 2-shock laser pulse. Measurements characterized the backscatter behavior, the production of hot electrons, the motion and brightness of the laser spots on the hohlraum wall, and the efficiency of the hohlraum x-ray drive as a function of gas fill density ρgf between 0.03 mg/cc ("near vacuum") and 1.6 mg/cc. For hohlraums with ρgf up to 0.85 mg/cc, very little stimulated Raman backscatter (SRS) was observed. For higher ρgf, significant SRS was produced and was observed to occur during the rise to peak laser power and throughout the main pulse. The efficiency with which laser energy absorbed by the hohlraum is converted into drive energy was measured to be the same for ρgf ≥ 0.6 mg/cc once the laser reached peak power. However, for the near vacuum case, the absorbed energy was converted to drive energy more efficiently throughout the pulse and maintained an efficiency ˜10% higher than the gas filled hohlraums throughout the main pulse.

The relationship between gas fill density and hohlraum drive performance at the National Ignition Facility

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

Hall, G. N.; Jones, O. S.; Strozzi, D. J.

Indirect drive inertial confinement fusion experiments were conducted at the National Ignition Facility to investigate the performance of the hohlraum drive as a function of hohlraum gas fill density by imploding high-density-carbon capsules using a 2-shock laser pulse. Our ,easurements characterize the backscatter behavior, the production of hot electrons, the motion and brightness of the laser spots on the hohlraum wall, and the efficiency of the hohlraum x-ray drive as a function of gas fill density ρ gf between 0.03 mg/cc (“near vacuum”) and 1.6 mg/cc. For hohlraums with ρ gf up to 0.85 mg/cc, very little stimulated Raman backscattermore » (SRS) was observed. Furthermore, for higher ρ gf, significant SRS was produced and was observed to occur during the rise to peak laser power and throughout the main pulse. The efficiency with which laser energy absorbed by the hohlraum is converted into drive energy was measured to be the same for ρ gf ≥ 0.6 mg/cc once the laser reached peak power. But, for the near vacuum case, the absorbed energy was converted to drive energy more efficiently throughout the pulse and maintained an efficiency ~10% higher than the gas filled hohlraums throughout the main pulse.« less

The relationship between gas fill density and hohlraum drive performance at the National Ignition Facility

DOE PAGES

Hall, G. N.; Jones, O. S.; Strozzi, D. J.; ...

2017-05-11

Indirect drive inertial confinement fusion experiments were conducted at the National Ignition Facility to investigate the performance of the hohlraum drive as a function of hohlraum gas fill density by imploding high-density-carbon capsules using a 2-shock laser pulse. Our ,easurements characterize the backscatter behavior, the production of hot electrons, the motion and brightness of the laser spots on the hohlraum wall, and the efficiency of the hohlraum x-ray drive as a function of gas fill density ρ gf between 0.03 mg/cc (“near vacuum”) and 1.6 mg/cc. For hohlraums with ρ gf up to 0.85 mg/cc, very little stimulated Raman backscattermore » (SRS) was observed. Furthermore, for higher ρ gf, significant SRS was produced and was observed to occur during the rise to peak laser power and throughout the main pulse. The efficiency with which laser energy absorbed by the hohlraum is converted into drive energy was measured to be the same for ρ gf ≥ 0.6 mg/cc once the laser reached peak power. But, for the near vacuum case, the absorbed energy was converted to drive energy more efficiently throughout the pulse and maintained an efficiency ~10% higher than the gas filled hohlraums throughout the main pulse.« less

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.

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.

Pulse-burst laser systems for fast Thomson scattering (invited)

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

Den Hartog, D. J.; Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin-Madison, Madison, Wisconsin 53706; Ambuel, J. R.

2010-10-15

Two standard commercial flashlamp-pumped Nd:YAG (YAG denotes yttrium aluminum garnet) lasers have been upgraded to ''pulse-burst'' capability. Each laser produces a burst of up to 15 2 J Q-switched pulses (1064 nm) at repetition rates of 1-12.5 kHz. Variable pulse-width drive (0.15-0.39 ms) of the flashlamps is accomplished by insulated gate bipolar transistor (IGBT) switching of electrolytic capacitor banks. Direct control of the laser Pockels cell drive enables optimal pulse energy extraction, and up to four 2 J laser pulses during one flashlamp pulse. These lasers are used in the Thomson scattering plasma diagnostic system on the MST reversed-field pinchmore » to record the dynamic evolution of the electron temperature profile and temperature fluctuations. To further these investigations, a custom pulse-burst laser system with a maximum pulse repetition rate of 250 kHz is now being commissioned.« less

Electromagnetic or other directed energy pulse launcher

DOEpatents

Ziolkowski, Richard W.

1990-01-01

The physical realization of new solutions of wave propagation equations, such as Maxwell's equations and the scaler wave equation, produces localized pulses of wave energy such as electromagnetic or acoustic energy which propagate over long distances without divergence. The pulses are produced by driving each element of an array of radiating sources with a particular drive function so that the resultant localized packet of energy closely approximates the exact solutions and behaves the same.

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.

Simultaneous gates in frequency-crowded multilevel systems using fast, robust, analytic control shapes

NASA Astrophysics Data System (ADS)

Theis, L. S.; Motzoi, F.; Wilhelm, F. K.

2016-01-01

We present a few-parameter ansatz for pulses to implement a broad set of simultaneous single-qubit rotations in frequency-crowded multilevel systems. Specifically, we consider a system of two qutrits whose working and leakage transitions suffer from spectral crowding (detuned by δ ). In order to achieve precise controllability, we make use of two driving fields (each having two quadratures) at two different tones to simultaneously apply arbitrary combinations of rotations about axes in the X -Y plane to both qubits. Expanding the waveforms in terms of Hanning windows, we show how analytic pulses containing smooth and composite-pulse features can easily achieve gate errors less than 10-4 and considerably outperform known adiabatic techniques. Moreover, we find a generalization of the WAHWAH (Weak AnHarmonicity With Average Hamiltonian) method by Schutjens et al. [R. Schutjens, F. A. Dagga, D. J. Egger, and F. K. Wilhelm, Phys. Rev. A 88, 052330 (2013)], 10.1103/PhysRevA.88.052330 that allows precise separate single-qubit rotations for all gate times beyond a quantum speed limit. We find in all cases a quantum speed limit slightly below 2 π /δ for the gate time and show that our pulses are robust against variations in system parameters and filtering due to transfer functions, making them suitable for experimental implementations.

Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers

PubMed Central

Chen, Ming-Chang; Mancuso, Christopher; Hernández-García, Carlos; Dollar, Franklin; Galloway, Ben; Popmintchev, Dimitar; Huang, Pei-Chi; Walker, Barry; Plaja, Luis; Jaroń-Becker, Agnieszka A.; Becker, Andreas; Murnane, Margaret M.; Kapteyn, Henry C.; Popmintchev, Tenio

2014-01-01

High harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, to date the shortest subfemtosecond (attosecond, 10−18 s) pulses have been produced only in the extreme UV region of the spectrum below 100 eV, which limits the range of materials and molecular systems that can be explored. Here we experimentally demonstrate a remarkable convergence of physics: when midinfrared lasers are used to drive high harmonic generation, the conditions for optimal bright, soft X-ray generation naturally coincide with the generation of isolated attosecond pulses. The temporal window over which phase matching occurs shrinks rapidly with increasing driving laser wavelength, to the extent that bright isolated attosecond pulses are the norm for 2-µm driving lasers. Harnessing this realization, we experimentally demonstrate the generation of isolated soft X-ray attosecond pulses at photon energies up to 180 eV for the first time, to our knowledge, with a transform limit of 35 attoseconds (as), and a predicted linear chirp of 300 as. Most surprisingly, advanced theory shows that in contrast with as pulse generation in the extreme UV, long-duration, 10-cycle, driving laser pulses are required to generate isolated soft X-ray bursts efficiently, to mitigate group velocity walk-off between the laser and the X-ray fields that otherwise limit the conversion efficiency. Our work demonstrates a clear and straightforward approach for robustly generating bright isolated attosecond pulses of electromagnetic radiation throughout the soft X-ray region of the spectrum. PMID:24850866

Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers.

PubMed

Chen, Ming-Chang; Mancuso, Christopher; Hernández-García, Carlos; Dollar, Franklin; Galloway, Ben; Popmintchev, Dimitar; Huang, Pei-Chi; Walker, Barry; Plaja, Luis; Jaroń-Becker, Agnieszka A; Becker, Andreas; Murnane, Margaret M; Kapteyn, Henry C; Popmintchev, Tenio

2014-06-10

High harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, to date the shortest subfemtosecond (attosecond, 10(-18) s) pulses have been produced only in the extreme UV region of the spectrum below 100 eV, which limits the range of materials and molecular systems that can be explored. Here we experimentally demonstrate a remarkable convergence of physics: when midinfrared lasers are used to drive high harmonic generation, the conditions for optimal bright, soft X-ray generation naturally coincide with the generation of isolated attosecond pulses. The temporal window over which phase matching occurs shrinks rapidly with increasing driving laser wavelength, to the extent that bright isolated attosecond pulses are the norm for 2-µm driving lasers. Harnessing this realization, we experimentally demonstrate the generation of isolated soft X-ray attosecond pulses at photon energies up to 180 eV for the first time, to our knowledge, with a transform limit of 35 attoseconds (as), and a predicted linear chirp of 300 as. Most surprisingly, advanced theory shows that in contrast with as pulse generation in the extreme UV, long-duration, 10-cycle, driving laser pulses are required to generate isolated soft X-ray bursts efficiently, to mitigate group velocity walk-off between the laser and the X-ray fields that otherwise limit the conversion efficiency. Our work demonstrates a clear and straightforward approach for robustly generating bright isolated attosecond pulses of electromagnetic radiation throughout the soft X-ray region of the spectrum.

PULSE RATE DIVIDER

DOEpatents

McDonald, H.C. Jr.

1962-12-18

A compact pulse-rate divider circuit affording low impedance output and high input pulse repetition rates is described. The circuit features a single secondary emission tube having a capacitor interposed between its dynode and its control grid. An output pulse is produced at the anode of the tube each time an incoming pulse at the control grid drives the tube above cutoff and the duration of each output pulse corresponds to the charging time of the capacitor. Pulses incoming during the time the grid bias established by the discharging capacitor is sufficiently negative that the pulses are unable to drive the tube above cutoff do not produce output pulses at the anode; these pulses are lost and a dividing action is thus produced by the circuit. The time constant of the discharge path may be vanied to vary in turn the division ratio of the circuit; the time constant of the charging circuit may be varied to vary the width of the output pulses. (AEC)

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

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.

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

NASA Astrophysics Data System (ADS)

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

2016-07-01

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

Optimal Dynamic Detection of Explosives (ODD-EX)

DTIC Science & Technology

2011-12-29

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

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.

LLE Review Quarterly Report (January-March 1999). Volume 78

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

Regan, Sean P.

1999-03-01

This volume of the LLE Review, covering the period January-March 1999, features two articles concerning issues relevant to 2-D SSD laser-beam smoothing on OMEGA. In the first article J. D. Zuegel and J. A. Marozas present the design of an efficient, bulk phase modulator operating at approximately 10.5 GHz, which can produce substantial phase-modulated bandwidth with modest microwave drive power. This modulator is the cornerstone of the 1-THz UV bandwidth operation planned for OMEGA this year. In the second article J. A. Marozas and J. H. Kelly describe a recently developed code -- Waasese -- that simulates the collective behaviormore » of the optical components in the SSD driver line. The measurable signatures predicted by the code greatly enhance the diagnostic capability of the SSD driver line. Other articles in this volume are titled: Hollow-Shell Implosion Studies on the 60-Beam, UC OMEGA Laser System; Simultaneous Measurements of Fuel Areal Density, Shell Areal Density, and Fuel Temperature in D 3He-Filled Imploding Capsules; The Design of Optical Pulse Shapes with an Aperture-Coupled-Stripline Pulse-Shaping System; Measurement Technique for Characterization of Rapidly Time- and Frequency-Varying Electronic Devices; and, Damage to Fused-Silica, Spatial-Filter Lenses on the OMEGA Laser System.« less

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

NASA Astrophysics Data System (ADS)

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

2018-07-01

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

Influence of wave-packet dynamics on the medium gain of an atomic system

NASA Astrophysics Data System (ADS)

Delagnes, J. C.; Bouchene, M. A.

2007-10-01

A sequence of two femtosecond pulses—a strong driving π -polarized pulse and a weak propagating σ -polarized pulse—excites resonantly the S1/2→P1/2 transition of an atomic system. Strong interference effects take place in the system between absorption and emission paths leading to a substantial amplification of the σ pulse. We study the influence of the fine structure on the medium gain when the contribution of the off-resonant P3/2 level is taken into account. A drastic reduction of the medium gain is obtained. This effect is explained within the bright-state dark-state formalism where the strong driving pulse creates a wave packet that can be trapped in a state—the bright state—leading to a significant reduction of the gain for the σ pulse. Finally, we also show that periodical gain dependence with the driving pulse energy exhibits a significant change in its period value (compared with expected Rabi oscillations).

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

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

Xu Junjie; Zeng Bin; Yu Yongli

2010-11-15

We demonstrate high-order harmonic generation in a wave form synthesized by a multicycle 800-nm chirped laser pulse and a chirp-free laser pulse. Compared with the case of using only a chirped pulse, both the harmonic cutoff and the extreme ultraviolet supercontinuum can be extended when a weak chirp-free pulse is combined with the chirped pulse. When chirp-free pulse intensity grows, the cutoff energy and bandwidth of the supercontinuum grow as well. It is found that the broad supercontinuum can be achieved for a driving pulse with long duration even though the driving pulse reaches 10 optical cycles. An isolated attosecondmore » pulse with duration of about 59 as is obtained, and after appropriate phase compensation with a duration of about 11 as. In addition, by performing time-frequency analyses and the classical trajectory simulation, the difference in supercontinuum generation between the preceding wave form and a similar wave form synthesized by an 800-nm fundamental pulse and a 1600-nm subharmonic pulse is investigated.« less

Design of a Radiographic Integrated Test Stand (RITS) Based on a Voltage Adder, To Drive a Diode Immersed in a High Magnetic Field

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

Bailey, V.L.; Corcoran, P.; Droemer, D.

Recent experiments (1) have adapted existing magne-tically insulated induction voltage adders (Sabre, Hermes III) to drive a 10 MV diode immersed in magnetic fields as high as 50 T. In such a diode, an electron beam of tens of kA can be confined by the magnetic field to a diameter of about 1 mm, and when it strikes a high-Z anode it can create a bremsstrahlung x-ray source intense enough to radiograph massive objects with high resolution. RITS is an adder system designed specially to drive such diodes, and it will be used to develop and exploit them. As inmore » other adder-based pulsers such as Sabre, Hermes III, and Kalif-Heliq the induction cells have amorphous- iron cores, and the pulse-forming system consists of water dielectric pulse lines and self-closing water switches that are pulse-charged from Marx-charged intermediate water capacitors through laser-triggered Rimfire switches. An oil prepulse switch in series with each pulse line is designed to reduce cathode prepulse to less than ± 5 kV, and a means is provided to bias the cathode and avoid negative prepulse entirely. The RITS pulse-forming system consists of two modules. Each module has one Marx that charges two 3 MV intermediate stores, each of which charges three 7.8 ohm pulselines, making six pulselines per module. The two modules in concert can supply 1.35 MV, 50 ns pulses to a twelve-cell adder and thus drive a 16 MV diode with a single pulse. The 1.35 MV induction cells each have a single-point feed, from which a single, slotted azimuthal oil transmission line distributes energy uniformly around the cell. The modules can also be pulsed separately at different times, either to power two 8 MV adders that each drive one of two closely-spaced cathodes immersed in a common magnetic field, or to provide two separate pulses to a common six- cell adder and a single 8 NIV diode; in these two-pulse modes, the spacing of the two 50 ns pulses may be chosen to be anything from a few hundred ns upward. The use of only one pulse line per cell has been shown to increase the extent to which the cell voltages can vary with the timing of closure of the water switches. This and all other functions of RITS have been simulated in detail, and a conservative electrical design has been developed. This will be illustrated, along with the conceptual design of a pulse-sorting network that can couple two pulselines efilciently to one cell when the two RITS modules drive a common adder in two-pulse mode.« less

Robust generation of isolated attosecond pulse against the variation of carrier envelope phase of driving laser pulses

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

Zou Pu; Zeng Zhinan; Zheng Yinghui

2010-11-15

We propose a scheme for generating isolated attosecond pulse (IAP) via high-order harmonic generation in gases using a chirped two-color laser field of multicycle duration. In contrast to previous techniques where the stable carrier-envelope phase (CEP) of the driving laser pulses is a prerequisite for IAP generation, the proposed scheme is robust against the large variation of CEP. We show the generation of IAP with an intensity fluctuation less than 50% and an intensity contrast ratio higher than 5:1 when the CEP shift is as large as 1.35{pi}.

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

Wavelength-dependence of double optical gating for attosecond pulse generation

NASA Astrophysics Data System (ADS)

Tian, Jia; Li, Min; Yu, Ji-Zhou; Deng, Yong-Kai; Liu, Yun-Quan

2014-10-01

Both polarization gating (PG) and double optical gating (DOG) are productive methods to generate single attosecond (as) pulses. In this paper, considering the ground-state depletion effect, we investigate the wavelength-dependence of the DOG method in order to optimize the generation of single attosecond pulses for the future application. By calculating the ionization probabilities of the leading edge of the pulse at different driving laser wavelengths, we obtain the upper limit of duration for the driving laser pulse for the DOG setup. We find that the upper limit duration increases with the increase of laser wavelength. We further describe the technical method of choosing and calculating the thickness values of optical components for the DOG setup.

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.

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.

Plasma boundary shape control and real-time equilibrium reconstruction on NSTX-U

DOE PAGES

Boyer, M. D.; Battaglia, D. J.; Mueller, D.; ...

2018-01-25

Here, the upgrade to the National Spherical Torus eXperiment (NSTX-U) included two main improvements: a larger center-stack, enabling higher toroidal field and longer pulse duration, and the addition of three new tangentially aimed neutral beam sources, which increase available heating and current drive, and allow for flexibility in shaping power, torque, current, and particle deposition profiles. To best use these new capabilities and meet the high-performance operational goals of NSTX-U, major upgrades to the NSTX-U control system (NCS) hardware and software have been made. Several control algorithms, including those used for real-time equilibrium reconstruction and shape control, have been upgradedmore » to improve and extend plasma control capabilities. As part of the commissioning phase of first plasma operations, the shape control system was tuned to control the boundary in both inner-wall limited and diverted discharges. It has been used to accurately track the requested evolution of the boundary (including the size of the inner gap between the plasma and central solenoid, which is a challenge for the ST configuration), X-point locations, and strike point locations, enabling repeatable discharge evolutions for scenario development and diagnostic commissioning.« less

Plasma boundary shape control and real-time equilibrium reconstruction on NSTX-U

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

Boyer, M. D.; Battaglia, D. J.; Mueller, D.

Here, the upgrade to the National Spherical Torus eXperiment (NSTX-U) included two main improvements: a larger center-stack, enabling higher toroidal field and longer pulse duration, and the addition of three new tangentially aimed neutral beam sources, which increase available heating and current drive, and allow for flexibility in shaping power, torque, current, and particle deposition profiles. To best use these new capabilities and meet the high-performance operational goals of NSTX-U, major upgrades to the NSTX-U control system (NCS) hardware and software have been made. Several control algorithms, including those used for real-time equilibrium reconstruction and shape control, have been upgradedmore » to improve and extend plasma control capabilities. As part of the commissioning phase of first plasma operations, the shape control system was tuned to control the boundary in both inner-wall limited and diverted discharges. It has been used to accurately track the requested evolution of the boundary (including the size of the inner gap between the plasma and central solenoid, which is a challenge for the ST configuration), X-point locations, and strike point locations, enabling repeatable discharge evolutions for scenario development and diagnostic commissioning.« less

Plasma boundary shape control and real-time equilibrium reconstruction on NSTX-U

NASA Astrophysics Data System (ADS)

Boyer, M. D.; Battaglia, D. J.; Mueller, D.; Eidietis, N.; Erickson, K.; Ferron, J.; Gates, D. A.; Gerhardt, S.; Johnson, R.; Kolemen, E.; Menard, J.; Myers, C. E.; Sabbagh, S. A.; Scotti, F.; Vail, P.

2018-03-01

The upgrade to the National Spherical Torus eXperiment (NSTX-U) included two main improvements: a larger center-stack, enabling higher toroidal field and longer pulse duration, and the addition of three new tangentially aimed neutral beam sources, which increase available heating and current drive, and allow for flexibility in shaping power, torque, current, and particle deposition profiles. To best use these new capabilities and meet the high-performance operational goals of NSTX-U, major upgrades to the NSTX-U control system (NCS) hardware and software have been made. Several control algorithms, including those used for real-time equilibrium reconstruction and shape control, have been upgraded to improve and extend plasma control capabilities. As part of the commissioning phase of first plasma operations, the shape control system was tuned to control the boundary in both inner-wall limited and diverted discharges. It has been used to accurately track the requested evolution of the boundary (including the size of the inner gap between the plasma and central solenoid, which is a challenge for the ST configuration), X-point locations, and strike point locations, enabling repeatable discharge evolutions for scenario development and diagnostic commissioning.

Robust spherical direct-drive design for NI

NASA Astrophysics Data System (ADS)

Masse, Laurent; Hurricane, O.; Michel, P.; Nora, R.; Tabak, M.; Lawrence Livermore Natl Lab Team

2016-10-01

Achieving ignition in a direct-drive or indirect-drive cryogenic implosion is a tremendous challenge. Both approaches need to deal with physic and technologic issues. During the past years, the indirect drive effort on the National Ignition Facility (NIF) has revealed unpredicted lost of performances that force to think to more robust designs and to dig into detailed physics aspects. Encouraging results have been obtained using a strong first shock during the implosion of CH ablator ignition capsules. These ``high-foot'' implosion results in a significantly lower ablation Rayleigh-Taylor instability growth than that of the NIC point design capsule. The trade-off with this design is a higher fuel adiabat that limits both fuel compression and theoretical capsule yield. The purpose of designing this capsule is to recover a more ideal one-dimensional implosion that is in closer agreement to simulation predictions. In the same spirit of spending energy on margin, at the coast of decreased performance, we are presenting here a study on ``robust'' spherical direct drive design for NIF. This 2-Shock direct drive pulse shape results in a high adiabat (>3) and low convergence (<17) implosion designed to produce a near 1D-like implosion. We take a particular attention to design a robust implosion with respect to long-wavelength non uniformity seeded by power imbalance and target offset. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

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

DOE PAGES

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

2016-02-01

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

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

PubMed

Rogers, C E; Gould, P L

2016-02-08

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

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

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.

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.

Perspectives of shaped pulses for EPR spectroscopy

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Low-jitter high-power thyristor array pulse driver and generator

DOEpatents

Hanks, Roy L.

2002-01-01

A method and apparatus for generating low-jitter, high-voltage and high-current pulses for driving low impedance loads such as detonator fuses uses a MOSFET driver which, when triggered, discharges a high-voltage pre-charged capacitor into the primary of a toroidal current-multiplying transformer with multiple isolated secondary windings. The secondary outputs are suitable for driving an array of thyristors that discharge a precharged high-voltage capacitor and thus generating the required high-voltage and high-current pulse.

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

NASA Astrophysics Data System (ADS)

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

2017-03-01

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

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

NASA Technical Reports Server (NTRS)

Houghton, J. R.

1976-01-01

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

VCSELs in short-pulse operation for time-of-flight applications

NASA Astrophysics Data System (ADS)

Moench, Holger; Gronenborn, Stephan; Gu, Xi; Gudde, Ralph; Herper, Markus; Kolb, Johanna; Miller, Michael; Smeets, Michael; Weigl, Alexander

2018-02-01

VCSEL arrays are the ideal light source for 3D imaging applications. The narrow emission spectrum and the ability for short pulses make them superior to LEDs. Combined with fast photodiodes or special camera chips spatial information can be obtained which is needed in diverse applications like camera autofocus, indoor navigation, 3D-object recognition, augmented reality or autonomously driving vehicles. Pulse operation at the ns scale and at low duty cycle can work with significantly higher current than traditionally used for VCSELs in continuous wave operation. With reduced thermal limitations at low average heat dissipation very high currents become feasible and tens of Watts output power have been realized with small VCSEL chips. The optical emission pattern of VCSELs can be tailored to the desired field of view using beam shaping elements. Such optical elements also enable laser safe class 1 products. A detailed analysis of the complete system and the operation mode is required to calculate the maximum permitted power for a safe system. The good VCSEL properties like robustness, stability over temperature and the potential for integrated solutions open a huge potential for VCSELs in new mass applications in the consumer and automotive markets.

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.

Effect of driving voltage polarity on dynamic response characteristics of electrowetting liquid lens

NASA Astrophysics Data System (ADS)

Na, Xie; Ning, Zhang; Rong-Qing, Xu

2018-05-01

A test device is developed for studying the dynamic process of an electrowetting liquid lens. By analyzing the light signals through the liquid lens, the dynamical properties of the lens are investigated. In our experiment, three types of pulse, i.e., sine, bipolar pulse, and single pulse signals, are employed to drive the liquid lens, and the dynamic characteristics of the lens are subsequently analyzed. The results show that the positive and negative polarities of the driving voltage can cause a significant difference in the response of the liquid lens; meanwhile, the lens’s response to the negative polarity of the driving voltage is clearer. We use the theory of charge restraint to explain this phenomenon, and it is concluded that the negative ions are more easily restrained by a dielectric layer. This work gives direct guidance for practical applications based on an electrowetting liquid lens.

Electrical pulse generator

DOEpatents

Norris, Neil J.

1979-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2009-07-01

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

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

The first target experiments on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Landen, O. L.; Glenzer, S. H.; Froula, D. H.; Dewald, E. L.; Suter, L. J.; Schneider, M. B.; Hinkel, D. E.; Fernandez, J. C.; Kline, J. L.; Goldman, S. R.; Braun, D. G.; Celliers, P. M.; Moon, S. J.; Robey, H. S.; Lanier, N. E.; Glendinning, S. G.; Blue, B. E.; Wilde, B. H.; Jones, O. S.; Schein, J.; Divol, L.; Kalantar, D. H.; Campbell, K. M.; Holder, J. P.; McDonald, J. W.; Niemann, C.; MacKinnon, A. J.; Collins, G. W.; Bradley, D. K.; Eggert, J. H.; Hicks, D. G.; Gregori, G.; Kirkwood, R. K.; Young, B. K.; Foster, J. M.; Hansen, J. F.; Perry, T. S.; Munro, D. H.; Baldis, H. A.; Grim, G. P.; Heeter, R. F.; Hegelich, M. B.; Montgomery, D. S.; Rochau, G. A.; Olson, R. E.; Turner, R. E.; Workman, J. B.; Berger, R. L.; Cohen, B. I.; Kruer, W. L.; Langdon, A. B.; Langer, S. H.; Meezan, N. B.; Rose, H. A.; Still, C. H.; Williams, E. A.; Dodd, E. S.; Edwards, M. J.; Monteil, M.-C.; Stevenson, R. M.; Thomas, B. R.; Coker, R. F.; Magelssen, G. R.; Rosen, P. A.; Stry, P. E.; Woods, D.; Weber, S. V.; Young, P. E.; Alvarez, S.; Armstrong, G.; Bahr, R.; Bourgade, J.-L.; Bower, D.; Celeste, J.; Chrisp, M.; Compton, S.; Cox, J.; Constantin, C.; Costa, R.; Duncan, J.; Ellis, A.; Emig, J.; Gautier, C.; Greenwood, A.; Griffith, R.; Holdner, F.; Holtmeier, G.; Hargrove, D.; James, T.; Kamperschroer, J.; Kimbrough, J.; Landon, M.; Lee, F. D.; Malone, R.; May, M.; Montelongo, S.; Moody, J.; Ng, E.; Nikitin, A.; Pellinen, D.; Piston, K.; Poole, M.; Rekow, V.; Rhodes, M.; Shepherd, R.; Shiromizu, S.; Voloshin, D.; Warrick, A.; Watts, P.; Weber, F.; Young, P.; Arnold, P.; Atherton, L.; Bardsley, G.; Bonanno, R.; Borger, T.; Bowers, M.; Bryant, R.; Buckman, S.; Burkhart, S.; Cooper, F.; Dixit, S. N.; Erbert, G.; Eder, D. C.; Ehrlich, R. E.; Felker, B.; Fornes, J.; Frieders, G.; Gardner, S.; Gates, C.; Gonzalez, M.; Grace, S.; Hall, T.; Haynam, C. A.; Heestand, G.; Henesian, M. A.; Hermann, M.; Hermes, G.; Huber, S.; Jancaitis, K.; Johnson, S.; Kauffman, B.; Kelleher, T.; Kohut, T.; Koniges, A. E.; Labiak, T.; Latray, D.; Lee, A.; Lund, D.; Mahavandi, S.; Manes, K. R.; Marshall, C.; McBride, J.; McCarville, T.; McGrew, L.; Menapace, J.; Mertens, E.; Murray, J.; Neumann, J.; Newton, M.; Opsahl, P.; Padilla, E.; Parham, T.; Parrish, G.; Petty, C.; Polk, M.; Powell, C.; Reinbachs, I.; Rinnert, R.; Riordan, B.; Ross, G.; Robert, V.; Tobin, M.; Sailors, S.; Saunders, R.; Schmitt, M.; Shaw, M.; Singh, M.; Spaeth, M.; Stephens, A.; Tietbohl, G.; Tuck, J.; van Wonterghem, B. M.; Vidal, R.; Wegner, P. J.; Whitman, P.; Williams, K.; Winward, K.; Work, K.; Wallace, R.; Nobile, A.; Bono, M.; Day, B.; Elliott, J.; Hatch, D.; Louis, H.; Manzenares, R.; O'Brien, D.; Papin, P.; Pierce, T.; Rivera, G.; Ruppe, J.; Sandoval, D.; Schmidt, D.; Valdez, L.; Zapata, K.; MacGowan, B. J.; Eckart, M. J.; Hsing, W. W.; Springer, P. T.; Hammel, B. A.; Moses, E. I.; Miller, G. H.

2007-08-01

A first set of shock timing, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4 beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics (HEDP). In parallel, a robust set of optical and X-ray spectrometers, interferometer, calorimeters and imagers have been activated. The experiments have been undertaken with laser powers and energies of up to 8 TW and 17 kJ in flattop and shaped 1 9 ns pulses focused with various beam smoothing options. The experiments have demonstrated excellent agreement between measured and predicted laser-target coupling in foils and hohlraums, even when extended to a longer pulse regime unattainable at previous laser facilities, validated the predicted effects of beam smoothing on intense laser beam propagation in long scale-length plasmas and begun to test 3D codes by extending the study of laser driven hydrodynamic jets to 3D geometries.

Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams.

PubMed

Liu, Lie; Li, Limin; Wen, Jianchun; Wan, Hong

2009-02-01

This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a approximately 450 kV, approximately 400 ns pulse. It was found that 300-400 MW, approximately 250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.

Four dimensional imaging of E. coli nucleoid organization and dynamics in living cells

PubMed Central

Fisher, J. K.; Bourniquel, A.; Witz, G.; Weiner, B.; Prentiss, M.; Kleckner, N.

2013-01-01

Visualization of living E. coli nucleoids, defined by HupA-mCherry, reveals a discrete, dynamic helical ellipsoid. Three basic features emerge. (i) Nucleoid density efficiently coalesces into longitudinal bundles, giving a stiff, low DNA density ellipsoid. (ii) This ellipsoid is radially confined within the cell cylinder. Radial confinement gives helical shape and drives and directs global nucleoid dynamics, including sister segregation. (iii) Longitudinal density waves flux back and forth along the nucleoid, with 5–10% of density shifting within 5s, enhancing internal nucleoid mobility. Furthermore, sisters separate end-to-end in sequential discontinuous pulses, each elongating the nucleoid by 5–15%. Pulses occur at 20min intervals, at defined cell cycle times. This progression is mediated by sequential installation and release of programmed tethers, implying cyclic accumulation and relief of intra-nucleoid mechanical stress. These effects could comprise a chromosome-based cell cycle engine. Overall, the presented results suggest a general conceptual framework for bacterial nucleoid morphogenesis and dynamics. PMID:23623305

Soft x-ray tomography for real-time applications: present status at Tore Supra and possible future developments.

PubMed

Mazon, D; Vezinet, D; Pacella, D; Moreau, D; Gabelieri, L; Romano, A; Malard, P; Mlynar, J; Masset, R; Lotte, P

2012-06-01

This paper is focused on the soft x-ray (SXR) tomography system setup at Tore Supra (DTOMOX) and the recent developments made to automatically get precise information about plasma features from inverted data. The first part describes the main aspects of the tomographic inversion optimization process. Several observations are made using this new tool and a set of shape factors is defined to help characterizing the emissivity field in a real-time perspective. The second part presents a detailed off-line analysis comparing the positions of the magnetic axis obtained from a magnetic equilibrium solver, and the maximum of the reconstructed emissivity field for ohmic and heated pulses. A systematic discrepancy of about 5 cm is found in both cases and it is shown that this discrepancy increases during sawtooth crashes. Finally, evidence of radially localized tungsten accumulation with an in-out asymmetry during a lower hybrid current drive pulse is provided to illustrate the DTOMOX capabilities for a precise observation of local phenomena.

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)

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.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, C.E.; Boothe, R.W.

1994-02-15

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figures.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, C.E.; Boothe, R.W.

1996-01-23

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figs.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, Charles E.; Boothe, Richard W.

1996-01-01

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, Charles E.; Boothe, Richard W.

1994-01-01

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

Prototype Solid State Induction Modulator for SLAC NLC

NASA Astrophysics Data System (ADS)

Cassel, R. L.; DeLamare, J. E.; Nguyen, M. N.; Pappas, G. C.; Cook, E.

2002-08-01

The Next Linear Collider accelerator proposal at SLAC requires a high efficiency, highly reliable, and low cost pulsed power modulator to drive the X band klystrons. The present NLC envisions a solid-state induction modulator design to drive up to 8 klystrons to 500kV for 3muS at 120 PPS with one modulator (>1,000 megawatt pulse, 500kW average). A prototype modulator is presently under construction, which well power 4 each 5045 SLAC klystron to greater than 380 kV for 3muS (>600 megawatt pulse, >300 kW Ave.). The modulator will be capable of driving the 8 each X band klystrons when they become available. The paper covers the design, construction, fabrication and preliminary testing of the prototype modulator.

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

Spatial Control of Photoemitted Electron Beams using a Micro-Lens-Array Transverse-Shaping Technique

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

Halavanau, A.; Qiang, G.; Ha, G.

2017-07-24

A common issue encountered in photoemission electron sources used in electron accelerators is the transverse inhomogeneity of the laser distribution resulting from the laser-amplification process and often use of frequency up conversion in nonlinear crystals. A inhomogeneous laser distribution on the photocathode produces charged beams with lower beam quality. In this paper, we explore the possible use of microlens arrays (fly-eye light condensers) to dramatically improve the transverse uniformity of the drive laser pulse on UV photocathodes. We also demonstrate the use of such microlens arrays to generate transversely-modulated electron beams and present a possible application to diagnose the propertiesmore » of a magnetized beam.« less

Pulsed power accelerator for material physics experiments

DOE PAGES

Reisman, D.  B.; Stoltzfus, B.  S.; Stygar, W.  A.; ...

2015-09-01

We have developed the design of Thor: a pulsed power accelerator that delivers a precisely shaped current pulse with a peak value as high as 7 MA to a strip-line load. The peak magnetic pressure achieved within a 1-cm-wide load is as high as 100 GPa. Thor is powered by as many as 288 decoupled and transit-time isolated bricks. Each brick consists of a single switch and two capacitors connected electrically in series. The bricks can be individually triggered to achieve a high degree of current pulse tailoring. Because the accelerator is impedance matched throughout, capacitor energy is delivered tomore » the strip-line load with an efficiency as high as 50%. We used an iterative finite element method (FEM), circuit, and magnetohydrodynamic simulations to develop an optimized accelerator design. When powered by 96 bricks, Thor delivers as much as 4.1 MA to a load, and achieves peak magnetic pressures as high as 65 GPa. When powered by 288 bricks, Thor delivers as much as 6.9 MA to a load, and achieves magnetic pressures as high as 170 GPa. We have developed an algebraic calculational procedure that uses the single brick basis function to determine the brick-triggering sequence necessary to generate a highly tailored current pulse time history for shockless loading of samples. Thor will drive a wide variety of magnetically driven shockless ramp compression, shockless flyer plate, shock-ramp, equation of state, material strength, phase transition, and other advanced material physics experiments.« 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.

Techniques for Enhancing Implosion Performance on High-Foot Ignition Capsules on NIF

NASA Astrophysics Data System (ADS)

Dittrich, T. R.; Hurricane, O.; Berzak Hopkins, L. F.; Callahan, D. A.; Clark, D.; Haan, S. W.; Hinkel, D. E.; Ma, T.; Nikroo, A.; Pak, A. E.; Park, H. S.; Salmonson, J. D.; Weber, C. R.

2016-10-01

Two options that have the potential to improve implosion performance in the High-Foot series of ignition capsules on NIF will be presented. The first option explores changing the shape of the x-ray drive to include a 4th and even a 5th shock in the implosion. According to simulations, these extra shocks improve the configuration of the assembled fuel and lead to improved confinement and performance. A ``ramp compression'' between the foot of the drive and the main pulse is also investigated. The second option studies the effect of increasing the Si dopant in a thin-shell capsule. NIF shot N150211 produced relatively high fusion yield (7.6E15 neutrons) but may have suffered from shell burn through. Increasing the Si dopant may delay this burn through yet preserve high implosion velocity. This work was performed under the auspices of the Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

Symmetry tuning for DIME Campaign

NASA Astrophysics Data System (ADS)

Krasheninnikova, Natalia; Schmitt, Mark; Tregillis, Ian; Bradley, P.; Cobble, J.; Kyrala, G.; Murphy, T.; Obrey, K.; Hsu, S.; Shah, R.; Batha, S.; Craxton, S.; McKenty, P.

2012-10-01

Defect Induced Mix Experiment (DIME) investigates the effects of 4 pi as well as surface feature-driven mix on the directly driven ICF capsule implosion. To minimize the effects of the laser-drive asymmetry, beam pointings, pulse shape, and the energy distribution between the lasers need to be optimized for a particular capsule and shot energy. In support of the DIME experimental campaigns on OMEGA and NIF, symmetry tuning was performed with the rad-hydro code HYDRA. To assess the impact on the symmetry, synthetic radiographs and self-emission images were examined and compared with the experimental results from OMEGA and NIF shots. The dynamics of the capsules imploded under polar direct drive conditions were compared with symmetrically driven ones and the effects of cross-beam transfer and the laser imprinting on the symmetry were also investigated. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy.

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

Hurricane, O. A., E-mail: hurricane1@llnl.gov; Callahan, D. A.; Casey, D. T.

The “High-Foot” platform manipulates the laser pulse-shape coming from the National Ignition Facility laser to create an indirect drive 3-shock implosion that is significantly more robust against instability growth involving the ablator and also modestly reduces implosion convergence ratio. This strategy gives up on theoretical high-gain in an inertial confinement fusion implosion in order to obtain better control of the implosion and bring experimental performance in-line with calculated performance, yet keeps the absolute capsule performance relatively high. In this paper, we will cover the various experimental and theoretical motivations for the high-foot drive as well as cover the experimental resultsmore » that have come out of the high-foot experimental campaign. At the time of this writing, the high-foot implosion has demonstrated record total deuterium-tritium yields (9.3×10{sup 15}) with low levels of inferred mix, excellent agreement with implosion simulations, fuel energy gains exceeding unity, and evidence for the “bootstrapping” associated with alpha-particle self-heating.« less

Myosin-dependent remodeling of adherens junctions protects junctions from Snail-dependent disassembly

PubMed Central

Weng, Mo

2016-01-01

Although Snail is essential for disassembly of adherens junctions during epithelial–mesenchymal transitions (EMTs), loss of adherens junctions in Drosophila melanogaster gastrula is delayed until mesoderm is internalized, despite the early expression of Snail in that primordium. By combining live imaging and quantitative image analysis, we track the behavior of E-cadherin–rich junction clusters, demonstrating that in the early stages of gastrulation most subapical clusters in mesoderm not only persist, but move apically and enhance in density and total intensity. All three phenomena depend on myosin II and are temporally correlated with the pulses of actomyosin accumulation that drive initial cell shape changes during gastrulation. When contractile myosin is absent, the normal Snail expression in mesoderm, or ectopic Snail expression in ectoderm, is sufficient to drive early disassembly of junctions. In both cases, junctional disassembly can be blocked by simultaneous induction of myosin contractility. Our findings provide in vivo evidence for mechanosensitivity of cell–cell junctions and imply that myosin-mediated tension can prevent Snail-driven EMT. PMID:26754645

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

NASA Astrophysics Data System (ADS)

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

2014-10-01

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

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

PubMed

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

2012-01-16

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

Femtosecond pulse shaping using the geometric phase.

PubMed

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

2014-03-15

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

The shock/shear platform for planar radiation-hydrodynamics experiments on the National Ignition Facility

DOE PAGES

Doss, F. W.; Kline, J. L.; Flippo, K. A.; ...

2015-04-17

An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130 μm/ns shocks into a CH foam-filled shock tube (~ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for >10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment tomore » the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.« less

Acceleration of planar foils by the indirect-direct drive scheme

NASA Astrophysics Data System (ADS)

Honrubia, J. J.; Martínez-Val, J. M.; Bocher, J. L.; Faucheux, G.

1996-05-01

We have investigated the hydrodynamic response of plastic and aluminum foils accelerated by a pulse formed by an x-ray prepulse followed by the main laser pulse. This illumination scheme, so-called indirect-direct drive scheme, has been proposed as an alternative to the direct and indirect drive. The advantages of such a scheme are that it can contribute to solve the problem of uniformity of the direct drive and, at the same time, it can be much more efficient and use simpler targets than the indirect-drive. Experiments about this hybrid drive scheme have been performed at Limeil with the PHEBUS facility and the standard experimental set-up and diagnostics. The agreement between experiments and simulations is good for quantities such as the energy of the laser converted into x-rays and the burnthrough time of the converter foil. To simulate the full hydrodynamic evolution of the converter and target foils separated a distance of 1 mm, 2-D effects should be taken into account. The basic goals have been to check the simulation codes developed by the Institute of Nuclear Fusion and to determine the hydrodynamic response of the target foil to the hybrid pulse. These goals have been fulfilled.

Research on long pulse ECRH system of EAST in support of ITER

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

Wang, Xiaojie, E-mail: xjiew@ipp.ac.cn; Liu, Fukun; Shan, Jiafang

2015-12-10

Experimental Advanced Superconducting Tokamak (EAST), as a fully superconducting tokamak in China, aims to achieve high performance plasma under steady-state operation. To fulfill the physical objectives of EAST, a program of 4-MW long pulse electron cyclotron resonance heating and current drive (EC H&CD) system, which would offer greater flexibility for plasma shape and plasma stabilization has been launched on EAST since 2011. The system, composed of 4 gyrotrons with nominal 1MW output power and 1000s pulse length each, is designed with the feature of steerable power handling capabilities at 140 GHz, using second harmonic of the extraordinary mode(X2). The missions ofmore » the ECRH system are to provide plasma heating, current drive, plasma profile tailoring and control of magneto-hydrodynamic (MHD) instabilities. Presently, the first two 140-GHz 1-MW gyrotrons, provided by GYCOM and CPI, respectively, have been tested at long pulse operation. The tubes, the associated power supplies, cooling system, cryogenic plant, 2 transmission lines and an equatorial launcher are now installed at EAST. The power generated from each tube will be transmitted by an evacuated corrugated waveguide transmission line and injected into plasma from the low field side (radial port) through a front steering equatorial launcher. Considering the diverse applications of the EC system, the beam’s launch angles can be continuously varied with the optimized scanning range of over 30° in poloidal direction and ±25° in toroidal, as well as the polarization could be adjusted during the discharge by the orientations of a pair of polarizers in the transmission line to maintain the highest absorption for different operational scenarios. The commissioning of the first 2MW ECRH plant for EAST is under way. The design, R&D activities and recent progress of the long pulse 140-GHz ECRH system are presented in this paper. As the technological requirements for EAST ECRH have many similarities with ITER devices, the installation and experience of EAST ECRH system may provide valuable data for the ITER.« less

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.

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

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.

Combination spindle-drive system for high precision machining

DOEpatents

Gerth, Howard L.

1977-07-26

A combination spindle-drive is provided for fabrication of optical quality surface finishes. Both the spindle-and-drive utilize the spindle bearings for support, thereby removing the conventional drive-means bearings as a source of vibration. An airbearing spindle is modified to carry at the drive end a highly conductive cup-shaped rotor which is aligned with a stationary stator to produce torque in the cup-shaped rotor through the reaction of eddy currents induced in the rotor. This arrangement eliminates magnetic attraction forces and all force is in the form of torque on the cup-shaped rotor.

Alternative Shapes and Shaping Techniques for Enhanced Transformer Ratios in Beam Driven Techniques

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

Lemery, F.; Piot, P.

The transformer ration of collinear beam-driven techniques can be significantly improved by shaping the current profile of the drive bunch. To date, several current shapes have been proposed to increase the transformer ratio and produce quasi-uniform energy loss within the drive bunch. Some of these tailoring techniques are possible as a results of recent beam-dynamics advances, e.g., transverse-to-longitudinal emittance exchanger. In ths paper, we propose an alternative class of longitudinal shapes that enable high transformer ratio and uniform energy loss across the drive bunch. We also suggest a simple method based on photocathode-laser shaping and passive shaping in wakefield structuremore » to realize shape close to the theoretically optimized current profiles.« less

Characterization of pulsed flow attenuation on a regulated montane river

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

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

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

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

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

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.

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 Quantum Efficiency and Robustness of Cesium-Based Photocathodes

DTIC Science & Technology

2010-01-01

photocathodes produce picosecond-pulsed, high- current electron beams for photoinjection applications like free electron lasers . In photoinjectors, a...pulsed drive laser incident on the photocathode causes photoemission of short, dense bunches of electrons, which are then accelerated into a...relativistic, high quality beam. Future free electron lasers demand reliable photocathodes with long-lived quantum efficiency at suitable drive laser

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.

Instrument for the measurement and determination of chemical pulse column parameters

DOEpatents

Marchant, Norman J.; Morgan, John P.

1990-01-01

An instrument for monitoring and measuring pneumatic driving force pulse parameters applied to chemical separation pulse columns obtains real time pulse frequency and root mean square amplitude values, calculates column inch values and compares these values against preset limits to alert column operators to the variations of pulse column operational parameters beyond desired limits.

Demonstration of radiation pulse shaping with nested-tungsten-wire-array pinches for high-yield inertial confinement fusion.

PubMed

Cuneo, M E; Vesey, R A; Sinars, D B; Chittenden, J P; Waisman, E M; Lemke, R W; Lebedev, S V; Bliss, D E; Stygar, W A; Porter, J L; Schroen, D G; Mazarakis, M G; Chandler, G A; Mehlhorn, T A

2005-10-28

Nested wire-array pinches are shown to generate soft x-ray radiation pulse shapes required for three-shock isentropic compression and hot-spot ignition of high-yield inertial confinement fusion capsules. We demonstrate a reproducible and tunable foot pulse (first shock) produced by interaction of the outer and inner arrays. A first-step pulse (second shock) is produced by inner array collision with a central CH2 foam target. Stagnation of the inner array at the axis produces the third shock. Capsules optimized for several of these shapes produce 290-900 MJ fusion yields in 1D simulations.

Broadband spectral shaping in regenerative amplifier based on modified polarization-encoded chirped pulse amplification

NASA Astrophysics Data System (ADS)

Wang, Xinliang; Lu, Xiaoming; Liu, Yanqi; Xu, Yi; Wang, Cheng; Li, Shuai; Yu, Linpeng; Liu, Xingyan; Liu, Keyang; Xu, Rongjie; Leng, Yuxin

2018-06-01

We present an intra-cavity spectral shaping method to suppress the spectral narrowing in a Ti:sapphire (Ti:Sa) regenerative amplifier. The spectral shaping is realized by manipulating the stored energies of two Ti:Sa crystals with orthogonal c-axes, changing the length of a quartz plate, and rotating a broadband achromatic half-wave plate. Using this method, in our proof-of-concept experiment, an 84-nm-(FWHM)-broadband amplified pulse with an energy gain larger than 106 is obtained, which supports a 17.8 fs Fourier-transform-limited pulse duration. The pulse is compressed to 18.9 fs.

780nm-range VCSEL array for laser printer system and other applications at Ricoh

NASA Astrophysics Data System (ADS)

Jikutani, Naoto; Itoh, Akihiro; Harasaka, Kazuhiro; Sasaki, Toshihide; Sato, Shunichi

2016-03-01

A 780 nm-range 40 channels vertical-cavity surface-emitting laser (VCSEL) array was developed as a writing light source for printers. A 15° off missoriented GaAs substrate, an aluminum-free GaInAsP/GaInP compressively-strained multiple quantum well and an anisotropic-shape transverse-mode filter were employed to control polarization characteristics. The anisotropic-shape transverse-mode filter also suppressed higher transverse-mode and enabled high-power single-mode operation. Thus, orthogonal-polarization suppression-ratio (OPSR) of over 22 dB and side-mode suppression-ratio (SMSR) of 30 dB were obtained at operation power of 3mW at same time for wide oxide-aperture range below 50 μm2. Moreover, a thermal resistance was reduced for 38% by increasing a thickness of high thermal conductivity layer (3λ/4-AlAs layer) near a cavity. By this structure, a peak-power increased to 1.3 times. Moreover, a power-fall caused by self-heating at pulse-rise was decreased to 10% and the one caused by a thermal-crosstalk between channels was decreased to 46%. The VCSEL array was mounted in a ceramic package with a tilted seal glass to prevent optical-crosstalk caused by other channels. Thus, we achieved stable-output and high-quality beam characteristics for long-duration pulse drive.

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.

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

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

Murakami, M.; Mauritsson, J.; Schafer, K.J.

2005-01-01

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

Influence of driving frequency on discharge modes in the dielectric barrier discharge excited by a triangle voltage

NASA Astrophysics Data System (ADS)

Li, Xuechen; Liu, Rui; Jia, Pengying; Wu, Kaiyue; Ren, Chenhua; Yin, Zengqian

2018-01-01

A one-dimensional fluid model in atmospheric pressure argon is employed to investigate the influence of the driving frequency on dielectric barrier discharge modes excited by a triangle voltage. Results indicate that a stepped discharge mode is obtained with a low driving frequency of 35 kHz. The current amplitude increases, while its plateau duration decreases with increasing the frequency. The stepped discharge transits into a multi-pulsed mode when the frequency is increased to 80 kHz. With its further increment, the pulse number decreases, and a double-pulsed discharge is realized at 90 kHz, which finally transits to a single-pulsed discharge. Through analyzing spatial distributions of electron density, ion density, and electric field, it can be concluded that the discharge regime transits from a Townsend-like discharge to a glow discharge with increasing the frequency. The regime transition is further verified by analyzing voltage-current curves. These simulated results are consistent with the experimental phenomena.

The new RLA test status

NASA Astrophysics Data System (ADS)

Smith, D. L.; Mazarakis, M. G.; Skogmo, P.; Bennett, L. F.; Olson, W. R.; George, M.; Harden, M. J.; Turman, B. N.; Moya, S. A.; Henderson, J. L.

The Recirculating Linear Accelerator (RLA) is returning to operation with a new relativistic electron beam (REB) injector and a modified accelerating cavity. Upon completion of our pulsed-power test program, we will capture the injected beam on an Ion Focussed Regime (IFR) guiding channel in either a spiral or a closed racetrack drift tube. The relativistic beam will recirculate for four passes through two accelerating cavities, in phase with the ringing cavity voltage, and increase to 8--12 MeV before being extracted. We designed the METGLAS ribbon-wound core, inductively isolated, four-stage injector to produce beam parameters of 4 MeV, 10--20 kA, and 40--55 ns FWHM. The three-line radial cavity is being modified to improve the 1-MV accelerating pulse shape while an advanced cavity design study is in progress. This is a continuation of the Sandia National Laboratory program to develop compact, high-voltage gradient, linear induction accelerators. The RLA concept is based on guiding an injected REB with an IFR channel. This channel is formed from a plasma created with a low energy electron beam inside a beam line containing about 2 x 10(exp -4) Torr of argon. The REB is injected onto the IFR channel and is transported down the beamline through a water dielectric accelerating cavity based on the ET-2 design. If the round-tip path of the beam matches the period of the cavity, the REB can be further accelerated by the ringing waveform on every subsequent pass. We have installed the new REB injector because we need a higher amplitude, longer duration, flat-topped pulse shape with a colder beam than that produced by the previous injector. We made extensive use of computer simulations in the form of network solver and electrostatic field stress analysis codes to aid in the design and modifications for the new RLA. The pulsed-power performance of the RLA injector and cavity and the associated driving hardware are discussed.

Study on the Depth, Rate, Shape, and Strength of Pulse with Cardiovascular Simulator.

PubMed

Lee, Ju-Yeon; Jang, Min; Shin, Sang-Hoon

2017-01-01

Pulse diagnosis is important in oriental medicine. The purpose of this study is explaining the mechanisms of pulse with a cardiovascular simulator. The simulator is comprised of the pulse generating part, the vessel part, and the measurement part. The pulse generating part was composed of motor, slider-crank mechanism, and piston pump. The vessel part, which was composed with the aorta and a radial artery, was fabricated with silicon to implement pulse wave propagation. The pulse parameters, such as the depth, rate, shape, and strength, were simulated. With changing the mean pressure, the floating pulse and the sunken pulse were generated. The change of heart rate generated the slow pulse and the rapid pulse. The control of the superposition time of the reflected wave generated the string-like pulse and the slippery pulse. With changing the pulse pressure, the vacuous pulse and the replete pulse were generated. The generated pulses showed good agreements with the typical pulses.

Observation of hohlraum-wall motion with spectrally selective x-ray imaging at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Izumi, N.; Meezan, N. B.; Divol, L.; Hall, G. N.; Barrios, M. A.; Jones, O.; Landen, O. L.; Kroll, J. J.; Vonhof, S. A.; Nikroo, A.; Jaquez, J.; Bailey, C. G.; Hardy, C. M.; Ehrlich, R. B.; Town, R. P. J.; Bradley, D. K.; Hinkel, D. E.; Moody, J. D.

2016-11-01

The high fuel capsule compression required for indirect drive inertial confinement fusion requires careful control of the X-ray drive symmetry throughout the laser pulse. When the outer cone beams strike the hohlraum wall, the plasma ablated off the hohlraum wall expands into the hohlraum and can alter both the outer and inner cone beam propagations and hence the X-ray drive symmetry especially at the final stage of the drive pulse. To quantitatively understand the wall motion, we developed a new experimental technique which visualizes the expansion and stagnation of the hohlraum wall plasma. Details of the experiment and the technique of spectrally selective x-ray imaging are discussed.

Observation of hohlraum-wall motion with spectrally selective x-ray imaging at the National Ignition Facility.

PubMed

Izumi, N; Meezan, N B; Divol, L; Hall, G N; Barrios, M A; Jones, O; Landen, O L; Kroll, J J; Vonhof, S A; Nikroo, A; Jaquez, J; Bailey, C G; Hardy, C M; Ehrlich, R B; Town, R P J; Bradley, D K; Hinkel, D E; Moody, J D

2016-11-01

The high fuel capsule compression required for indirect drive inertial confinement fusion requires careful control of the X-ray drive symmetry throughout the laser pulse. When the outer cone beams strike the hohlraum wall, the plasma ablated off the hohlraum wall expands into the hohlraum and can alter both the outer and inner cone beam propagations and hence the X-ray drive symmetry especially at the final stage of the drive pulse. To quantitatively understand the wall motion, we developed a new experimental technique which visualizes the expansion and stagnation of the hohlraum wall plasma. Details of the experiment and the technique of spectrally selective x-ray imaging are discussed.

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

Adjustable, High Voltage Pulse Generator with Isolated Output for Plasma Processing

NASA Astrophysics Data System (ADS)

Ziemba, Timothy; Miller, Kenneth E.; Prager, James; Slobodov, Ilia

2015-09-01

Eagle Harbor Technologies (EHT), Inc. has developed a high voltage pulse generator with isolated output for etch, sputtering, and ion implantation applications within the materials science and semiconductor processing communities. The output parameters are independently user adjustable: output voltage (0 - 2.5 kV), pulse repetition frequency (0 - 100 kHz), and duty cycle (0 - 100%). The pulser can drive loads down to 200 Ω. Higher voltage pulsers have also been tested. The isolated output allows the pulse generator to be connected to loads that need to be biased. These pulser generators take advantage modern silicon carbide (SiC) MOSFETs. These new solid-state switches decrease the switching and conduction losses while allowing for higher switching frequency capabilities. This pulse generator has applications for RF plasma heating; inductive and arc plasma sources; magnetron driving; and generation of arbitrary pulses at high voltage, high current, and high pulse repetition frequency. This work was supported in part by a DOE SBIR.

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

Optical integrator for optical dark-soliton detection and pulse shaping.

PubMed

Ngo, Nam Quoc

2006-09-10

The design and analysis of an Nth-order optical integrator using the digital filter technique is presented. The optical integrator is synthesized using planar-waveguide technology. It is shown that a first-order optical integrator can be used as an optical dark-soliton detector by converting an optical dark-soliton pulse into an optical bell-shaped pulse for ease of detection. The optical integrators can generate an optical step function, staircase function, and paraboliclike functions from input optical Gaussian pulses. The optical integrators may be potentially used as basic building blocks of all-optical signal processing systems because the time integrals of signals may sometimes be required for further use or analysis. Furthermore, an optical integrator may be used for the shaping of optical pulses or in an optical feedback control system.

Laser pulse shape design for laser-indirect-driven quasi-isentropic compression experiments

NASA Astrophysics Data System (ADS)

Xue, Quanxi; Jiang, Shaoen; Wang, Zhebin; Wang, Feng; Zhao, Xueqing; Ding, Yongkun

2018-02-01

Laser pulse shape design is a key work in the design of indirect-laser-driven experiments, especially for long pulse laser driven quasi-isentropic compression experiments. A method for designing such a laser pulse shape is given here. What's more, application experiments were performed, and the results of a typical shot are presented. At last of this article, the details of the application of the method are discussed, such as the equation parameter choice, radiation ablation pressure expression, and approximations in the method. The application shows that the method can provide reliable descriptions of the energy distribution in a hohlraum target; thus, it can be used in the design of long-pulse laser driven quasi-isentropic compression experiments and even other indirect-laser-driven experiments.

Neutron/ γ-ray digital pulse shape discrimination with organic scintillators

NASA Astrophysics Data System (ADS)

Kaschuck, Y.; Esposito, B.

2005-10-01

Neutrons and γ-rays produce light pulses with different shapes when interacting with organic scintillators. This property is commonly used to distinguish between neutrons (n) and γ-rays ( γ) in mixed n/ γ fields as those encountered in radiation physics experiments. Although analog electronic pulse shape discrimination (PSD) modules have been successfully used for many years, they do not allow data reprocessing and are limited in count rate capability (typically up to 200 kHz). The performance of a n/ γ digital pulse shape discrimination (DPSD) system by means of a commercial 12-bit 200 MSamples/s transient recorder card is investigated here. Three organic scintillators have been studied: stilbene, NE213 and anthracene. The charge comparison method has been used to obtain simultaneous n/ γ discrimination and pulse height analysis. The importance of DPSD for high-intensity radiation field measurements and its advantages with respect to analog PSD are discussed. Based on post-experiment simulations with acquired data, the requirements for fast digitizers to provide DPSD with organic scintillators are also analyzed.

Pulsed plane wave analytic solutions for generic shapes and the validation of Maxwell's equations solvers

NASA Technical Reports Server (NTRS)

Yarrow, Maurice; Vastano, John A.; Lomax, Harvard

1992-01-01

Generic shapes are subjected to pulsed plane waves of arbitrary shape. The resulting scattered electromagnetic fields are determined analytically. These fields are then computed efficiently at field locations for which numerically determined EM fields are required. Of particular interest are the pulsed waveform shapes typically utilized by radar systems. The results can be used to validate the accuracy of finite difference time domain Maxwell's equations solvers. A two-dimensional solver which is second- and fourth-order accurate in space and fourth-order accurate in time is examined. Dielectric media properties are modeled by a ramping technique which simplifies the associated gridding of body shapes. The attributes of the ramping technique are evaluated by comparison with the analytic solutions.

Nonlinear pulse shaping and polarization dynamics in mode-locked fiber lasers

NASA Astrophysics Data System (ADS)

Boscolo, Sonia; Sergeyev, Sergey V.; Mou, Chengbo; Tsatourian, Veronika; Turitsyn, Sergei; Finot, Christophe; Mikhailov, Vitaly; Rabin, Bryan; Westbrook, Paul S.

2014-03-01

We review our recent progress on the study of new nonlinear mechanisms of pulse shaping in passively mode-locked fiber lasers. These include a mode-locking regime featuring pulses with a triangular distribution of the intensity, and spectral compression arising from nonlinear pulse propagation. We also report on our recent experimental studies unveiling new types of vector solitons with processing states of polarization for multi-pulse and tightly bound-state soliton (soliton molecule) operations in a carbon nanotube (CNT) mode-locked fiber laser with anomalous dispersion cavity.

Control of wavepacket dynamics in mixed alkali metal clusters by optimally shaped fs pulses

NASA Astrophysics Data System (ADS)

Bartelt, A.; Minemoto, S.; Lupulescu, C.; Vajda, Š.; Wöste, L.

We have performed adaptive feedback optimization of phase-shaped femtosecond laser pulses to control the wavepacket dynamics of small mixed alkali-metal clusters. An optimization algorithm based on Evolutionary Strategies was used to maximize the ion intensities. The optimized pulses for NaK and Na2K converged to pulse trains consisting of numerous peaks. The timing of the elements of the pulse trains corresponds to integer and half integer numbers of the vibrational periods of the molecules, reflecting the wavepacket dynamics in their excited states.

The optimal input optical pulse shape for the self-phase modulation based chirp generator

NASA Astrophysics Data System (ADS)

Zachinyaev, Yuriy; Rumyantsev, Konstantin

2018-04-01

The work is aimed to obtain the optimal shape of the input optical pulse for the proper functioning of the self-phase modulation based chirp generator allowing to achieve high values of chirp frequency deviation. During the research, the structure of the device based on self-phase modulation effect using has been analyzed. The influence of the input optical pulse shape of the transmitting optical module on the chirp frequency deviation has been studied. The relationship between the frequency deviation of the generated chirp and frequency linearity for the three options for implementation of the pulse shape has been also estimated. The results of research are related to the development of the theory of radio processors based on fiber-optic structures and can be used in radars, secure communications, geolocation and tomography.

DC drive system for cine/pulse cameras

NASA Technical Reports Server (NTRS)

Gerlach, R. H.; Sharpsteen, J. T.; Solheim, C. D.; Stoap, L. J.

1977-01-01

Camera-drive functions are separated mechanically into two groups which are driven by two separate dc brushless motors. First motor, a 90 deg stepper, drives rotating shutter; second electronically commutated motor drives claw and film transport. Shutter is made of one piece but has two openings for slow and fast exposures.

Full characterization of an attosecond pulse generated using an infrared driver

PubMed Central

Zhang, Chunmei; Brown, Graham G.; Kim, Kyung Taec; Villeneuve, D. M.; Corkum, P. B.

2016-01-01

The physics of attosecond pulse generation requires using infrared driving wavelength to reach the soft X-rays. However, with longer driving wavelength, the harmonic conversion efficiency drops significantly. It makes the conventional attosecond pulse measurement using streaking very difficult due to the low photoionization cross section in the soft X-rays region. In-situ measurement was developed for precisely this purpose. We use in-situ measurement to characterize, in both space and time, an attosecond pulse produced by ultrafast wavefront rotation of a 1.8 μm fundamental beam. We confirm what models suggest – that each beamlet is an isolated attosecond pulse in the time domain. We get almost constant flat wavefront curvature through the whole photon energy range. The measurement method is scalable to the soft X-ray spectral region. PMID:27230961

Energy sweep compensation of induction accelerators

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

Sampayan, S.E.; Caporaso, G.J.; Chen, Y-J

1990-09-12

The ETA-II linear induction accelerator (LIA) is designed to drive a microwave free electron laser (FEL). Beam energy sweep must be limited to {plus minus}1% for 50 ns to limit beam corkscrew motion and ensure high power FEL output over the full duration of the beam flattop. To achieve this energy sweep requirement, we have implemented a pulse distribution system and are planning implementation of a tapered pulse forming line (PFL) in the pulse generators driving acceleration gaps. The pulse distribution system assures proper phasing of the high voltage pulse to the electron beam. Additionally, cell-to-cell coupling of beam inducedmore » transients is reduced. The tapered PFL compensates for accelerator cell and loading nonlinearities. Circuit simulations show good agreement with preliminary data and predict the required energy sweep requirement can be met.« less

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.

[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.

Uniform laser-driven relativistic electron layer for coherent Thomson scattering.

PubMed

Wu, H-C; Meyer-ter-Vehn, J; Fernández, J; Hegelich, B M

2010-06-11

A novel scheme is proposed to generate uniform relativistic electron layers for coherent Thomson backscattering. A few-cycle laser pulse is used to produce the electron layer from an ultrathin solid foil. The key element of the new scheme is an additional foil that reflects the drive-laser pulse, but lets the electrons pass almost unperturbed. Making use of two-dimensional particle-in-cell simulations and well-known basic theory, it is shown that the electrons, after interacting with both the drive and reflected laser pulses, form a very uniform flyer freely cruising with a high relativistic γ factor exactly in the drive-laser direction (no transverse momentum). It backscatters the probe light with a full Doppler shift factor of 4γ(2). The reflectivity and its decay due to layer expansion are discussed.

Far-infrared-light shadowgraphy for high extraction efficiency of extreme ultraviolet light from a CO2-laser-generated tin plasma

NASA Astrophysics Data System (ADS)

Matsukuma, Hiraku; Hosoda, Tatsuya; Suzuki, Yosuke; Yogo, Akifumi; Yanagida, Tatsuya; Kodama, Takeshi; Nishimura, Hiroaki

2016-08-01

The two-color, double-pulse method is an efficient scheme to generate extreme ultraviolet light for fabricating the next generation semiconductor microchips. In this method, a Nd:YAG laser pulse is used to expand a several-tens-of-micrometers-scale tin droplet, and a CO2 laser pulse is subsequently directed at the expanded tin vapor after an appropriate delay time. We propose the use of shadowgraphy with a CO2 laser probe-pulse scheme to optimize the CO2 main-drive laser. The distribution of absorption coefficients is derived from the experiment, and the results are converted to a practical absorption rate for the CO2 main-drive laser.

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 use of lasers for achieving extreme conditions of matter, and fusion

NASA Astrophysics Data System (ADS)

Roberts, P. D.

2012-05-01

Since the early'70s AWE has focussed on indirect drive as a means of accessing high energy density regimes. We give a brief historical perspective of this work and the rationale for the construction of the ORION laser. This laser is currently in commissioning and is scheduled to commence experiments in 2012. The ORION laser is configured to provide long pulses (~ 1ns) with a high degree of pulse shape flexibility, together with synchronised short pulse (~1ps) irradiation. The paper describes how this combination should enable pressures in excess of 1 Gb and temperatures of greater than 500 eV to be achieved. The ability to access and diagnose such conditions has applications in many fields; examples are given in planetary science, astrophysics and inertial fusion energy. For these applications we first describe the approach to measuring equation of state and opacity properties in the high energy density regime. Such properties are then incorporated into integrated computer simulation codes and validated against laser experiments, some of which have been conducted recently at the OMEGA laser at the University of Rochester. The paper concludes with a discussion of inertial fusion energy and the new high energy density regimes that this would access, if successful.

Development of a drive system for a sequential space camera

NASA Technical Reports Server (NTRS)

Sharpsteen, J. T.; Solheim, C. D.; Stoap, L. J.

1976-01-01

Breadboard models of single and dual motor drives for the shutter, claw and magazine of a space camera system were designed and tested. The single motor technique utilizes a single electronically commutated motor to drive the claw and shutter without resorting to a solenoid actuated clutch for pulse operation. Shutter speed is established by a combination of the cinemode speed and the opening of the conventional DAC two piece shutter. Pulse mode operation is obtained by applying power at a fixed clock rate and removing power at an appropriate point in the mechanical cycle such that the motor comes to rest by system friction. The dual motor approach utilizes a stepper motor to drive the shutter and an electronically commutated dc motor to drive the claw and magazine functions. The motors are synchronized electronically.

Plasma heating and current drive using intense, pulsed microwaves

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

Cohen, B.I.; Cohen, R.H.; Nevins, W.M.

1988-01-01

The use of powerful new microwave sources, e.g., free-electron lasers and relativistic gyrotrons, provide unique opportunities for novel heating and current-drive schemes in the electron-cyclotron and lower-hybrid ranges of frequencies. These high-power, pulsed sources have a number of technical advantages over conventional, low-intensity sources; and their use can lead to improved current-drive efficiencies and better penetration into a reactor-grade plasma in specific cases. The Microwave Tokamak Experiment at Lawrence Livermore National Laboratory will provide a test for some of these new heating and current-drive schemes. This paper reports theoretical progress both in modeling absorption and current drive for intense pulsesmore » and in analyzing some of the possible complications that may arise, e.g., parametric instabilities and nonlinear self-focusing. 22 refs., 9 figs., 1 tab.« less

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

Observation of hohlraum-wall motion with spectrally selective x-ray imaging at the National Ignition Facility

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

Izumi, N., E-mail: izumi2@llnl.gov; Meezan, N. B.; Divol, L.

The high fuel capsule compression required for indirect drive inertial confinement fusion requires careful control of the X-ray drive symmetry throughout the laser pulse. When the outer cone beams strike the hohlraum wall, the plasma ablated off the hohlraum wall expands into the hohlraum and can alter both the outer and inner cone beam propagations and hence the X-ray drive symmetry especially at the final stage of the drive pulse. To quantitatively understand the wall motion, we developed a new experimental technique which visualizes the expansion and stagnation of the hohlraum wall plasma. Details of the experiment and the techniquemore » of spectrally selective x-ray imaging are discussed.« 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.

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.

Realizing up-conversion fluorescence tuning in lanthanide-doped nanocrystals by femtosecond pulse shaping method

PubMed Central

Zhang, Shian; Yao, Yunhua; Shuwu, Xu; Liu, Pei; Ding, Jingxin; Jia, Tianqing; Qiu, Jianrong; Sun, Zhenrong

2015-01-01

The ability to tune color output of nanomaterials is very important for their applications in laser, optoelectronic device, color display and multiplexed biolabeling. Here we first propose a femtosecond pulse shaping technique to realize the up-conversion fluorescence tuning in lanthanide-doped nanocrystals dispersed in the glass. The multiple subpulse formation by a square phase modulation can create different excitation pathways for various up-conversion fluorescence generations. By properly controlling these excitation pathways, the multicolor up-conversion fluorescence can be finely tuned. This color tuning by the femtosecond pulse shaping technique is realized in single material by single-color laser field, which is highly desirable for further applications of the lanthanide-doped nanocrystals. This femtosecond pulse shaping technique opens an opportunity to tune the color output in the lanthanide-doped nanocrystals, which may bring a new revolution in the control of luminescence properties of nanomaterials. PMID:26290391

Transparent plastic scintillators for neutron detection based on lithium salicylate

DOE PAGES

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

2015-10-14

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

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

PubMed

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

2014-02-01

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

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

PubMed

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

2010-06-01

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

Scaling single-wavelength optical interconnects to 180 Gb/s with PAM-M and pulse shaping

NASA Astrophysics Data System (ADS)

Dris, Stefanos; Bakopoulos, Paraskevas; Argyris, Nikolaos; Spatharakis, Christos; Avramopoulos, Hercules

2016-03-01

Faced with surging datacenter traffic demand, system designers are turning to multi-level optical modulation with direct detection as the means of reaching 100 Gb/s in a single optical lane; a further upgrade to 400 Gb/s is envisaged through wavelength-multiplexing of multiple 100 Gb/s strands. In terms of modulation formats, PAM-4 and PAM-8 are considered the front-runners, striking a good balance between bandwidth-efficiency and implementation complexity. In addition, the emergence of energy-efficient, high-speed CMOS digital-to-analog converters (DACs) opens up new possibilities: Spectral shaping through digital filtering will allow squeezing even more data through low-cost, low-bandwidth electro-optic components. In this work we demonstrate an optical interconnect based on an EAM that is driven directly with sub-volt electrical swing by a 65 GSa/s arbitrary waveform generator (AWG). Low-voltage drive is particularly attractive since it allows direct interfacing with the switch/server ASIC, eliminating the need for dedicated, power-hungry and expensive electrical drivers. Single-wavelength throughputs of 180 and 120 Gb/s are experimentally demonstrated with 60 Gbaud optical PAM-8 and PAM-4 respectively. Successful transmission over 1250 m SMF is achieved with direct-detection, using linear equalization via offline digital signal processing in order to overcome the strong bandwidth limitation of the overall link (~20 GHz). The suitability of Nyquist pulse shaping for optical interconnects is also investigated experimentally with PAM-4 and PAM-8, at a lower symbol rate of 40 Gbaud (limited by the sampling rate of the AWG). To the best of our knowledge, the rates achieved are the highest ever using optical PAM-M formats.

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.

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

Barnard, J. J.; Hay, M. J.; Logan, B. G.

The simulations provided in this milestone have solidified the theoretical underpinning of direct drive targets and also the ability to design experiments on NDCX II that will enhance our understanding of ion-beam hydrodynamic coupling, and thus be relevant to IFE. For the case of the IFE targets, we have studied hydro and implosion efficiency using HYDRA in ID, a starting point towards the goal of polar direct drive in geometry compatible with liquid wall chambers. Recent analysis of direct drive fusion energy targets using heavy ion beams has found high coupling efficiency of ion beam energy into implosion energy. However,more » to obtain optimal coupling, the ion energy must increase during the pulse in order to penetrate the outflowing ablated material, and deposit the energy close enough to the fuel so that the fuel achieves sufficient implosion velocity. We have computationally explored ID (radial) time dependent models of ion driven direct drive capsule implosions using the Arbitrary Lagrangian-Eulerian (ALE) code HYDRA, to help validate the theoretical analysis done so far, particularly exploring the effects of varying the ion energy and ion current over the course of the pulse. On NDCX II, experiments have been proposed to explore issues of ion penetration of the outflowing plasma over the course of the ion pulse. One possibility is to create a first pulse of ions that heats a planar target, and produces an outflow of material. A second pulse, {approx}10 ns after the first, of higher ion energy (and hence larger projected range) will interact with this outflow before reaching and further heating the target. We have investigated whether the change in range can be tailored to match the evolution of the ablation front. We have carried out simulations using the one-dimensional hydrodynamic code DISH and HYDRA to set parameters for this class of experiments. DISH was upgraded with an ion deposition algorithm, and we have carried out ID (planar) simulations. HYDRA was also used for ID (planar) and 2D (r,z) simulations of potential experiments. We have also explored whether similar physics could be studied using an energy ramp (i.e., a velocity tilt) rather than two separate pulses. We have shown that an optimum occurs in the macropulse duration (with fixed velocity tilt) that maximizes the shock strength. In the area of IFE target design we have continued to explore direct drive targets composed of deuterium-tritium fuel and ablator layers. We have extended our previous target designs at 0.44 MJ drive energy, gain 50, (50 MeV foot, 500 MeV main pulse, Rb ion, which requires a large number of beams due to a high beam space charge constraint) to a power plant scale 3.7 MJ drive energy, gain {approx}150 (220 MeV foot, 2.2 GeV main pulse, Hg ion) that eases requirements on the accelerator. We have studied the effects of two important design choices on ICF target performance. We have shown that increasing the number of foot pulses may reduce the target's in-flight adiabat and consequently improve its compressibility and fusion yield. As in the case of laser drive, the first three shocks are the most important to the target's performance, with additional shocks contributing only marginally to compression and burn. We have also demonstrated that ion range lengthening during the main pulse can further reduce the target adiabat and improve the efficiency with which beam energy is coupled into the target. (Ion range lengthening using two different kinetic energies for the foot and main pulse has previously proven effective in the design of high gain targets).« less

Femtosecond parabolic pulse shaping in normally dispersive optical fibers.

PubMed

Sukhoivanov, Igor A; Iakushev, Sergii O; Shulika, Oleksiy V; Díez, Antonio; Andrés, Miguel

2013-07-29

Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initial pulse duration, chirp and energy. Applicability of different fibers for femtosecond pulse shaping is analyzed. Recommendation for shortest parabolic pulse formation is made based on the analysis presented.

Strong Field Optical and Quantum Control

NASA Astrophysics Data System (ADS)

Schumacher, Douglass William

1995-01-01

This work presents the results of an effort to use unique forms of optical radiation to better probe and control matter. Results are presented of a study of intense field photo-ionization of krypton and xenon in a two-color field. The use of a two-color field provides a valuable probe, the relative optical phase, into the dynamics of the ionization process. It is found that phase dependent tunneling character is preserved even though the photoelectron spectra indicate that the experiments performed were well into the multi-photon regime of ionization. Evidence for core scattering of the departing electrons is seen in the changes to the phase dependent spectra as the polarization of the exciting light is varied from linear to slightly elliptical. To further control the optical field, a pulse shaper was constructed using liquid crystal modulators that allowed either spectral phase or spectral amplitude shaping of a short pulse. The results were characterized using cross-correlations. The shaped light was then subsequently amplified in a chirped pulse amplifier. This light was characterized using Frequency Resolved Optical Gating, a newly developed technique for the complete determination of the optical field in a short pulse. The shaped pulses were then used to tailor atomic radial wavepackets in cesium. The evolution of the wavepackets was monitored by measuring atomic auto-interferograms for the case of amplitude shaping, which was used to control the atomic states excited. Cross -interferograms were used for phase shaping, which was used to select the initial phase of the atomic states. The cross-interferograms required the simultaneous amplification of a shaped and an unshaped pulse in our amplifier.

Control of Chemical Dynamics Using Arbitrary Shaped Optical Pulses and Laser-Enhanced NMR Spectroscopy.

NASA Astrophysics Data System (ADS)

Goswami, Debabrata

A key feature of this thesis is the application of novel laser techniques to various fields of spectroscopy. The overall effort has been towards achieving either chemical control or enhanced spectroscopic resolution. The issue of chemical control forms the major bulk. Over the past decade, theoretical and technological developments have made it possible for a modern day chemist to be a more active participant in nature's chemical processes. Consequently, although the idea of manipulating chemical reactions has been a long term dream, it is only now that realization of such dreams has become realistic. One of the major contributions that is leading towards this realization is the development of pulse shaping techniques. Here, we concentrate on the important developments in this area that has come by recently, particularly emphasizing new results from our laboratory. We discuss in detail the current state-of-the-art, and present some experimental and theoretical demonstrations of chemical control by using arbitrarily shaped pulses. The major strength of our approach to pulse shaping has been in considering "robustness in the laboratory" as a primary constraint. Most of the shapes, addressed here, work under adiabatic conditions where the exact shape of the pulse is not critical as long as the basic criteria dictated by the adiabatic theorem are satisfied. A novel approach of "molecular pulse shaping"--using the molecule itself to generate its own pulse shape--is presented as an example of the ultimate form of robustness. Finally, we get into the issue of resolution enhancement by coupling laser radiation into a Nuclear Magnetic Resonance (NMR) spectrometer. Spectroscopic resolution enhancement is an everlasting effort in the field of NMR--even more for biological NMR. We present some of the recent experimental findings in our laboratory that show selective dispersion in the NMR spectrum when it is acquired under a non-resonant laser irradiation of the sample. Albeit promising, the observed effects are weak and the theoretical understanding of these experiments is not profound enough for implementing any immediate applications.

Influence of angular acceleration-deceleration pulse shapes on regional brain strains.

PubMed

Yoganandan, Narayan; Li, Jianrong; Zhang, Jiangyue; Pintar, Frank A; Gennarelli, Thomas A

2008-07-19

Recognizing the association of angular loading with brain injuries and inconsistency in previous studies in the application of the biphasic loads to animal, physical, and experimental models, the present study examined the role of the acceleration-deceleration pulse shapes on region-specific strains. An experimentally validated two-dimensional finite element model representing the adult male human head was used. The model simulated the skull and falx as a linear elastic material, cerebrospinal fluid as a hydrodynamic material, and cerebrum as a linear viscoelastic material. The angular loading matrix consisted coronal plane rotation about a center of rotation that was acceleration-only (4.5 ms duration, 7.8 krad/s/s peak), deceleration-only (20 ms, 1.4 krad/s/s peak), acceleration-deceleration, and deceleration-acceleration pulses. Both biphasic pulses had peaks separated by intervals ranging from 0 to 25 ms. Principal strains were determined at the corpus callosum, base of the postcentral sulcus, and cerebral cortex of the parietal lobe. The cerebrum was divided into 17 regions and peak values of average maximum principal strains were determined. In all simulations, the corpus callosum responded with the highest strains. Strains were the least under all simulations in the lower parietal lobes. In all regions peak strains were the same for both monophase pulses suggesting that the angular velocity may be a better metric than peak acceleration or deceleration. In contrast, for the biphasic pulse, peak strains were region- and pulse-shape specific. Peak values were lower in both biphasic pulses when there was no time separation between the pulses than the corresponding monophase pulse. Increasing separation time intervals increased strains, albeit non-uniformly. Acceleration followed by deceleration pulse produced greater strains in all regions than the other form of biphasic pulse. Thus, pulse shape appears to have an effect on regional strains in the brain.

Multiplication and Presence of Shielding Material from Time-Correlated Pulse-Height Measurements of Subcritical Plutonium Assemblies

DOE PAGES

Monterial, Mateusz; Marleau, Peter; Paff, Marc; ...

2017-01-20

Here, we present the results from the first measurements of the Time-Correlated Pulse-Height (TCPH) distributions from 4.5 kg sphere of α-phase weapons-grade plutonium metal in five configurations: bare, reflected by 1.27 cm and 2.54 cm of tungsten, and 2.54 cm and 7.62 cm of polyethylene. A new method for characterizing source multiplication and shielding configuration is also demonstrated. The method relies on solving for the underlying fission chain timing distribution that drives the spreading of the measured TCPH distribution. We found that a gamma distribution fits the fission chain timing distribution well and that the fit parameters correlate with bothmore » multiplication (rate parameter) and shielding material types (shape parameter). The source-to-detector distance was another free parameter that we were able to optimize, and proved to be the most well constrained parameter. MCNPX-PoliMi simulations were used to complement the measurements and help illustrate trends in these parameters and their relation to multiplication and the amount and type of material coupled to the subcritical assembly.« less

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

Multiplication and Presence of Shielding Material from Time-Correlated Pulse-Height Measurements of Subcritical Plutonium Assemblies

NASA Astrophysics Data System (ADS)

Monterial, Mateusz; Marleau, Peter; Paff, Marc; Clarke, Shaun; Pozzi, Sara

2017-04-01

We present the results from the first measurements of the Time-Correlated Pulse-Height (TCPH) distributions from 4.5 kg sphere of α-phase weapons-grade plutonium metal in five configurations: bare, reflected by 1.27 cm and 2.54 cm of tungsten, and 2.54 cm and 7.62 cm of polyethylene. A new method for characterizing source multiplication and shielding configuration is also demonstrated. The method relies on solving for the underlying fission chain timing distribution that drives the spreading of the measured TCPH distribution. We found that a gamma distribution fits the fission chain timing distribution well and that the fit parameters correlate with both multiplication (rate parameter) and shielding material types (shape parameter). The source-to-detector distance was another free parameter that we were able to optimize, and proved to be the most well constrained parameter. MCNPX-PoliMi simulations were used to complement the measurements and help illustrate trends in these parameters and their relation to multiplication and the amount and type of material coupled to the subcritical assembly.

Exploring symmetry in near-vacuum hohlraums

NASA Astrophysics Data System (ADS)

Berzak Hopkins, L.; Le Pape, S.; Divol, L.; Meezan, N.; MacKinnon, A.; Ho, D. D.; Jones, O.; Khan, S.; Ma, T.; Milovich, J.; Pak, A.; Ross, J. S.; Thomas, C.; Turnbull, D.; Amendt, P.; Wilks, S.; Zylstra, A.; Rinderknecht, H.; Sio, H.; Petrasso, R.

2015-11-01

Recent experiments with near-vacuum hohlraums, which utilize a minimal but non-zero helium fill, have demonstrated performance improvements relative to conventional gas-filled (0.96 - 1.6 mg/cc helium) hohlraums: minimal backscatter, reduced capsule drive degradation, and minimal suprathermal electron generation. Because this is a low laser-plasma interaction platform, implosion symmetry is controlled via pulse-shaping adjustments to laser power balance. Extending this platform to high-yield designs with high-density carbon capsules requires achieving adequate symmetry control throughout the pulse. In simulations, laser propagation is degraded suddenly by hohlraum wall expansion interacting with ablated capsule material. Nominal radiation-hydrodynamics simulations have not yet proven predictive on symmetry of the final hotspot, and experiments show more prolate symmetry than preshot calculations. Recent efforts have focused on understanding the discrepancy between simulated and measured symmetry and on alternate designs for symmetry control through varying cone fraction, trade-offs between laser power and energy, and modifications to case-to-capsule ratio. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

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.

STREAK CAMERA MEASUREMENTS OF THE APS PC GUN DRIVE LASER

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

Dooling, J. C.; Lumpkin, A. H.

We report recent pulse-duration measurements of the APS PC Gun drive laser at both second harmonic and fourth harmonic wavelengths. The drive laser is a Nd:Glass-based chirped pulsed amplifier (CPA) operating at an IR wavelength of 1053 nm, twice frequency-doubled to obtain UV output for the gun. A Hamamatsu C5680 streak camera and an M5675 synchroscan unit are used for these measurements; the synchroscan unit is tuned to 119 MHz, the 24th subharmonic of the linac s-band operating frequency. Calibration is accomplished both electronically and optically. Electronic calibration utilizes a programmable delay line in the 119 MHz rf path. Themore » optical delay uses an etalon with known spacing between reflecting surfaces and is coated for the visible, SH wavelength. IR pulse duration is monitored with an autocorrelator. Fitting the streak camera image projected profiles with Gaussians, UV rms pulse durations are found to vary from 2.1 ps to 3.5 ps as the IR varies from 2.2 ps to 5.2 ps.« less

Laser drive development for the APS Dynamic Compression Sector

NASA Astrophysics Data System (ADS)

Lagrange, Thomas; Swift, Damian; Reed, Bryan; Bernier, Joel; Kumar, Mukul; Hawreliak, James; Eggert, Jon; Dixit, Sham; Collins, Gilbert

2013-06-01

The Dynamic Compression Sector (DCS) at the APS synchrotron offers unprecedented possibilities for x-ray diffraction and scattering measurements in-situ during dynamic loading, including single-shot data collection with x-ray energies high enough (tens of kV) to study high-Z samples in transmission as well as reflection. Dynamic loading induced by laser ablation is an important component of load generation, as the duration, strain rate, and pressure can be controlled via the energy, spot size, and pulse shape. Using radiation hydrodynamics simulations, validated by experiments at several laser facilities, we have investigated the relationship between irradiance history and pressure for ablative loads designed to induce shock and ramp loading in the nanosecond to microsecond range, and including free ablation and also ablation confined by a transparent substrate. We have investigated the effects of lateral release, which constrains the minimum diameter of the focal spot for a given drive duration. In this way, we are able to relate the desired drive conditions to the total laser energy needed, which dictates the laser technologies suitable for a given type of experiment. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

NASA Astrophysics Data System (ADS)

Peterchev, Angel V.; DʼOstilio, Kevin; Rothwell, John C.; Murphy, David L.

2014-10-01

Objective. This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach. We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with a lower voltage rating than prior cTMS devices. Main results. cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences (\\lt 10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in ten healthy volunteers. Significance. The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool.

ENDOR with band-selective shaped inversion pulses

NASA Astrophysics Data System (ADS)

Tait, Claudia E.; Stoll, Stefan

2017-04-01

Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity. Band-selective inversion pulses are characterized by almost rectangular inversion profiles, leading to full inversion for spin packets with resonance offsets within the pulse excitation bandwidth and leaving spin packets outside the excitation bandwidth largely unaffected. Here, we explore the consequences of using different band-selective amplitude-modulated pulses designed for NMR as the inversion pulse in ENDOR. We find an increased sensitivity for small hyperfine couplings compared to rectangular pulses of the same bandwidth. In echo-detected Davies-type ENDOR, finite Fourier series inversion pulses combine the advantages of increased absolute ENDOR sensitivity of short rectangular inversion pulses and increased sensitivity for small hyperfine couplings of long rectangular inversion pulses. The use of pulses with an almost rectangular frequency-domain profile also allows for increased control of the hyperfine contrast selectivity. At X-band, acquisition of echo transients as a function of radiofrequency and appropriate selection of integration windows during data processing allows efficient separation of contributions from weakly and strongly coupled nuclei in overlapping ENDOR spectra within a single experiment.

Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

PubMed Central

D’Ostilio, Kevin; Rothwell, John C; Murphy, David L

2014-01-01

Objective This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with lower voltage rating than prior cTMS devices. Main results cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences (<10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in 10 healthy volunteers. Significance The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool. PMID:25242286

Two-dimensional fluid droplet arrays generated using a single nozzle

DOEpatents

Lee, Eric R.; Perl, Martin L.

1999-11-02

Amplitudes of drive pulses received by a horizontally-placed dropper determine the horizontal displacements of droplets relative to an ejection aperture of the dropper. The drive pulses are varied such that the dropper generates a two-dimensional array of vertically-falling droplets. Vertical and horizontal interdroplet spacings may be varied in real time. Applications include droplet analysis experiments such as Millikan fractional charge searches and aerosol characterization, as well as material deposition applications.

Unitary scintillation detector and system

DOEpatents

McElhaney, Stephanie A.; Chiles, Marion M.

1994-01-01

The invention is a unitary alpha, beta, and gamma scintillation detector and system for sensing the presence of alpha, beta, and gamma radiations selectively or simultaneously. The scintillators are mounted in a light-tight housing provided with an entrance window for admitting alpha, beta, and gamma radiation and excluding ambient light from the housing. Light pulses from each scintillator have different decay constants that are converted by a photosensitive device into corresponding differently shaped electrical pulses. A pulse discrimination system identifies the electrical pulses by their respective pulse shapes which are determined by decay time. The identified electrical pulses are counted in separate channel analyzers to indicate the respective levels of sensed alpha, beta, and gamma radiations.

Extension of FRI for modeling of electrocardiogram signals.

PubMed

Quick, R Frank; Crochiere, Ronald E; Hong, John H; Hormati, Ali; Baechler, Gilles

2012-01-01

Recent work has developed a modeling method applicable to certain types of signals having a "finite rate of innovation" (FRI). Such signals contain a sparse collection of time- or frequency-limited pulses having a restricted set of allowable pulse shapes. A limitation of past work on FRI is that all of the pulses must have the same shape. Many real signals, including electrocardiograms, consist of pulses with varying widths and asymmetry, and therefore are not well fit by the past FRI methods. We present an extension of FRI allowing pulses having variable pulse width (VPW) and asymmetry. We show example results for electrocardiograms and discuss the possibility of application to signal compression and diagnostics.

A Fiber-Optic System Generating Pulses of High Spectral Density

NASA Astrophysics Data System (ADS)

Abramov, A. S.; Zolotovskii, I. O.; Korobko, D. A.; Fotiadi, A. A.

2018-03-01

A cascade fiber-optic system that generates pulses of high spectral density by using the effect of nonlinear spectral compression is proposed. It is demonstrated that the shape of the pulse envelope substantially influences the degree of compression of its spectrum. In so doing, maximum compression is achieved for parabolic pulses. The cascade system includes an optical fiber exhibiting normal dispersion that decreases along the fiber length, thereby ensuring that the pulse envelope evolves toward a parabolic shape, along with diffraction gratings and a fiber spectral compressor. Based on computer simulation, we determined parameters of cascade elements leading to maximum spectral density of radiation originating from a subpicosecond laser pulse of medium energy.

Unitary scintillation detector and system

DOEpatents

McElhaney, S.A.; Chiles, M.M.

1994-05-31

The invention is a unitary alpha, beta, and gamma scintillation detector and system for sensing the presence of alpha, beta, and gamma radiations selectively or simultaneously. The scintillators are mounted in a light-tight housing provided with an entrance window for admitting alpha, beta, and gamma radiation and excluding ambient light from the housing. Light pulses from each scintillator have different decay constants that are converted by a photosensitive device into corresponding differently shaped electrical pulses. A pulse discrimination system identifies the electrical pulses by their respective pulse shapes which are determined by decay time. The identified electrical pulses are counted in separate channel analyzers to indicate the respective levels of sensed alpha, beta, and gamma radiations. 10 figs.

Shaping and timing gradient pulses to reduce MRI acoustic noise.

PubMed

Segbers, Marcel; Rizzo Sierra, Carlos V; Duifhuis, Hendrikus; Hoogduin, Johannes M

2010-08-01

A method to reduce the acoustic noise generated by gradient systems in MRI has been recently proposed; such a method is based on the linear response theory. Since the physical cause of MRI acoustic noise is the time derivative of the gradient current, a common trapezoid current shape produces an acoustic gradient coil response mainly during the rising and falling edge. In the falling edge, the coil acoustic response presents a 180 degrees phase difference compared to the rising edge. Therefore, by varying the width of the trapezoid and keeping the ramps constant, it is possible to suppress one selected frequency and its higher harmonics. This value is matched to one of the prominent resonance frequencies of the gradient coil system. The idea of cancelling a single frequency is extended to a second frequency, using two successive trapezoid-shaped pulses presented at a selected interval. Overall sound pressure level reduction of 6 and 10 dB is found for the two trapezoid shapes and a single pulse shape, respectively. The acoustically optimized pulse shape proposed is additionally tested in a simulated echo planar imaging readout train, obtaining a sound pressure level reduction of 12 dB for the best case.

Sensing mode atomic force microscope

DOEpatents

Hough, Paul V. C.; Wang, Chengpu

2003-01-01

An atomic force microscope utilizes a pulse release system and improved method of operation to minimize contact forces between a probe tip affixed to a flexible cantilever and a specimen being measured. The pulse release system includes a magnetic particle affixed proximate the probe tip and an electromagnetic coil. When energized, the electromagnetic coil generates a magnetic field which applies a driving force on the magnetic particle sufficient to overcome adhesive forces exhibited between the probe tip and specimen. The atomic force microscope includes two independently displaceable piezo elements operable along a Z-axis. A controller drives the first Z-axis piezo element to provide a controlled approach between the probe tip and specimen up to a point of contact between the probe tip and specimen. The controller then drives the first Z-axis piezo element to withdraw the cantilever from the specimen. The controller also activates the pulse release system which drives the probe tip away from the specimen during withdrawal. Following withdrawal, the controller adjusts the height of the second Z-axis piezo element to maintain a substantially constant approach distance between successive samples.

Pulsed Eddy Current Probe Design Based on Transient Circuit Analysis

NASA Astrophysics Data System (ADS)

Cadeau, Trevor J.; Krause, Thomas W.

2009-03-01

Probe design parameters affecting depth of penetration of pulsed eddy currents in multi-layer aluminum 2024-T3 were examined. Several probe designs were evaluated for their ability to detect a discontinuity at the bottom of a stack of aluminum plates. The reflection type probes, consisting of pick-up coil and encircling drive coil, were characterized based on their transient response to a square pulse excitation. Probes with longer fundamental time constants, equivalent to a lower driving frequency, generated greater depth of penetration. However, additional factors such as inductive and resistive load, and excessive coil heating were also factors that limited signal-to-noise response with increasing layer thickness.

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.

Generation of multicolor vacuum ultraviolet pulses through four-wave sum-frequency mixing in argon

NASA Astrophysics Data System (ADS)

Shi, Liping; Li, Wenxue; Zhou, Hui; Wang, Di; Ding, Liang'en; Zeng, Heping

2013-11-01

We demonstrate efficient generation of multicolor vacuum ultraviolet pulses with excellent mode quality through χ(3)-based four-wave sum-frequency mixing and third-order harmonic generation of 400- and 267-nm femtosecond laser pulses in argon gas. The χ(3)-based nonlinear optical processes were optimized with appropriate control of gas pressure and group velocity delay between the driving pulses. Furthermore, the pulse breakup effects were observed for tightly focused ultraviolet pulses.

Paired Pulse Basis Functions for the Method of Moments EFIE Solution of Electromagnetic Problems Involving Arbitrarily-shaped, Three-dimensional Dielectric Scatterers

NASA Technical Reports Server (NTRS)

MacKenzie, Anne I.; Rao, Sadasiva M.; Baginski, Michael E.

2007-01-01

A pair of basis functions is presented for the surface integral, method of moment solution of scattering by arbitrarily-shaped, three-dimensional dielectric bodies. Equivalent surface currents are represented by orthogonal unit pulse vectors in conjunction with triangular patch modeling. The electric field integral equation is employed with closed geometries for dielectric bodies; the method may also be applied to conductors. Radar cross section results are shown for dielectric bodies having canonical spherical, cylindrical, and cubic shapes. Pulse basis function results are compared to results by other methods.

Time-domain SFG spectroscopy using mid-IR pulse shaping: practical and intrinsic advantages.

PubMed

Laaser, Jennifer E; Xiong, Wei; Zanni, Martin T

2011-03-24

Sum-frequency generation (SFG) spectroscopy is a ubiquitous tool in the surface sciences. It provides infrared transition frequencies and line shapes that probe the structure and environment of molecules at interfaces. In this article, we apply techniques learned from the multidimensional spectroscopy community to SFG spectroscopy. We implement balanced heterodyne detection to remove scatter and the local oscillator background. Heterodyning also separates the resonant and nonresonant signals by acquiring both the real and imaginary parts of the spectrum. We utilize mid-IR pulse shaping to control the phase and delay of the mid-IR pump pulse. Pulse shaping allows phase cycling for data collection in the rotating frame and additional background subtraction. We also demonstrate time-domain data collection, which is a Fourier transform technique, and has many advantages in signal throughput, frequency resolution, and line shape accuracy over existing frequency domain methods. To demonstrate time-domain SFG spectroscopy, we study an aryl isocyanide on gold, and find that the system has an inhomogeneous structural distribution, in agreement with computational results, but which was not resolved by previous frequency-domain SFG studies. The ability to rapidly and actively manipulate the mid-IR pulse in an SFG pules sequence makes possible new experiments and more accurate spectra. © 2011 American Chemical Society

LMJ Target design with the A1040 CH-ignition capsule in a cocktail holraum

NASA Astrophysics Data System (ADS)

Malinie, G.; Boniface, C.

2008-11-01

The A1040 indirect-drive ignition capsule was originally designed for the ``Full LMJ'' 240-beam configuration. An ``Ignition milestone'' has been scheduled, when the LMJ will be only partly completed, with a 160-beam, 2-cone configuration. A first approach to meet this milestone is to scale down the capsule and hohlraum of the full LMJ design. Here we use a different approach and show the A1040 ``as is'' can still meet the milestone, provided that a suitable cocktail-walled rugby hohlraum is used to drive the capsule. This is because this kind of hohlraum has a better energetic efficiency than the gold-walled cylinder originally used. From 1D and 2D integrated simulations, we investigate the influence of various parameters of the design, such as the shape of the four steps of the laser pulse, the density of the H/He gas filling of the hohlraum, and the effect of a thin gold coating on the outer surface of the polyimid window used to contain the gas.

The structure of the Laser Entrance Hole in NIF Ignition gas-filled hohlraums

NASA Astrophysics Data System (ADS)

Schneider, M. B.; Doeppner, T.; Thomas, C. A.; Widmann, K.; MacLaren, S. A.; Meezan, N. B.; Bell, P. M.; Benedetti, L. R.; Bradley, D. K.; Callahan, D. A.; Eder, D.; Hammer, J. H.; Hinkel, D. E.; Jones, O. S.; Michel, P.; Milovich, J. L.; Moody, J. D.; Moore, A. J.; Park, H. S.; Ralph, J. E.; Regan, S. E.; Strozzi, D. J.; Town, R. P.

2014-10-01

At the National Ignition Facility (NIF), the energy from 192 laser beams is converted to an x-ray drive in a gas-filled hohlraum. The drive heats and implodes a fuel capsule. The laser beams enter the hohlraum via laser entrance holes (LEHs) at each end. The LEH size decreases as heated plasma from the LEH material blows radially inward but this is largely balanced by hot plasma in the laser deposition region pushing radially outward. Compared to models, the LEH size is larger than predicted. In addition, the plasma in the LEH region is hotter than predicted. Instead of being at the radiation temperature of about 300 eV, it is at an electron temperature of 1 to a few keV. The experimental measurements for this conclusion are discussed. Data on the LEH as a function of laser pulse shape, gas fill, and energy transfer are presented. This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

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.

Logic circuit detects both present and missing negative pulses in superimposed wave trains

NASA Technical Reports Server (NTRS)

Rice, R. E.

1967-01-01

Pulse divide and determination network provides a logical determination of pulse presence within a data train. The network uses digital logic circuitry to divide positive and negative pulses, to shape the separated pulses, and to determine, by means of coincidence logic, if negative pulses are missing from the pulse train.

Selective RF pulses in NMR and their effect on coupled and uncoupled spin systems

NASA Astrophysics Data System (ADS)

Slotboom, J.

1993-10-01

This thesis describes various aspects of the usage of shaped RF-pulses for volume selection and spectral editing. Contents: Introduction--The History of Magnetic Resonance in a Nutshell, and The Usage of RF Pulses in Contemporary MRS and MRI; Theoretical and Practical Aspects of Localized NMR Spectroscopy; The Effects of RF Pulse Shape Discretization on the Spatially Selective Performance; Design of Frequency-Selective RF Pulses by Optimizing a Small Number of Pulse Parameters; A Single-Shot Localization Pulse Sequence Suited for Coils with Inhomogeneous RF Fields Using Adiabatic Slice-Selective RF Pulses; The Bloch Equations for an AB System and the Design of Spin State Selective RF Pulses for Coupled Spin Systems; The Effects of Frequency Selective RF Pulses on J Coupled Spin-1/2 Systems; A Quantitative (1)H MRS in vivo Study of the Effects of L-Ornithine-L-Aspartate on the Development of Mild Encephalopathy Using a Single Shot Localization Technique Based on SAR Reduced Adiabatic 2(pi) Pulses.

Interspecific variation of calls in clownfishes: degree of similarity in closely related species.

PubMed

Colleye, Orphal; Vandewalle, Pierre; Lanterbecq, Déborah; Lecchini, David; Parmentier, Eric

2011-12-19

Clownfishes are colorful coral reef fishes living in groups in association with sea anemones throughout the Indo-Pacific Ocean. Within their small societies, size hierarchy determines which fish have access to reproduction. These fishes are also prolific callers whose aggressive sounds seem to play an important role in the social hierarchy. Agonistic interactions being involved in daily behaviour suggest how acoustic communication might play an important role in clownfish group. Sounds were recorded and compared in fourteen clownfish species (some of which have never been recorded before) to evaluate the potential role of acoustic communication as an evolutionary driving force. Surprisingly, the relationship between fish size and both dominant frequency and pulse duration is not only species-specific; all the specimens of the 14 species are situated on exactly the same slope, which means the size of any Amphiprion can be predicted by both acoustic features. The number of pulses broadly overlaps among species, whereas the pulse period displays the most variation even if it shows overlap among sympatric species. Sound comparisons between three species (A. akallopisos, A. ocellaris and A. frenatus) having different types of teeth and body shape do not show differences neither in the acoustic waveform nor in the power spectrum. Significant overlap in acoustic features demonstrates that the sound-producing mechanism is highly conservative among species. Differences in the calls of some species are due to size dimorphism and the sound variation might be in this case a by-product. This morphological constraint does not permit a consideration of acoustic communication as the main driving force in the diversification of clownfishes. Moreover, calls are not produced to find mate and consequently are less subject to variations due to partner preference, which restricts the constraints of diversification. Calls are produced to reach and defend the competition to mate access. However, differences in the pulse period between cohabiting species show that, in some case, sounds can help to differentiate the species, to prevent competition between cohabiting species and to promote the diversification of taxa.

Interspecific variation of calls in clownfishes: degree of similarity in closely related species

PubMed Central

2011-01-01

Background Clownfishes are colorful coral reef fishes living in groups in association with sea anemones throughout the Indo-Pacific Ocean. Within their small societies, size hierarchy determines which fish have access to reproduction. These fishes are also prolific callers whose aggressive sounds seem to play an important role in the social hierarchy. Agonistic interactions being involved in daily behaviour suggest how acoustic communication might play an important role in clownfish group. Sounds were recorded and compared in fourteen clownfish species (some of which have never been recorded before) to evaluate the potential role of acoustic communication as an evolutionary driving force. Results Surprisingly, the relationship between fish size and both dominant frequency and pulse duration is not only species-specific; all the specimens of the 14 species are situated on exactly the same slope, which means the size of any Amphiprion can be predicted by both acoustic features. The number of pulses broadly overlaps among species, whereas the pulse period displays the most variation even if it shows overlap among sympatric species. Sound comparisons between three species (A. akallopisos, A. ocellaris and A. frenatus) having different types of teeth and body shape do not show differences neither in the acoustic waveform nor in the power spectrum. Conclusion Significant overlap in acoustic features demonstrates that the sound-producing mechanism is highly conservative among species. Differences in the calls of some species are due to size dimorphism and the sound variation might be in this case a by-product. This morphological constraint does not permit a consideration of acoustic communication as the main driving force in the diversification of clownfishes. Moreover, calls are not produced to find mate and consequently are less subject to variations due to partner preference, which restricts the constraints of diversification. Calls are produced to reach and defend the competition to mate access. However, differences in the pulse period between cohabiting species show that, in some case, sounds can help to differentiate the species, to prevent competition between cohabiting species and to promote the diversification of taxa. PMID:22182416

Multi-pulse multi-delay (MPMD) multiple access modulation for UWB

DOEpatents

Dowla, Farid U.; Nekoogar, Faranak

2007-03-20

A new modulation scheme in UWB communications is introduced. This modulation technique utilizes multiple orthogonal transmitted-reference pulses for UWB channelization. The proposed UWB receiver samples the second order statistical function at both zero and non-zero lags and matches the samples to stored second order statistical functions, thus sampling and matching the shape of second order statistical functions rather than just the shape of the received pulses.

Effect of Pulse Shape on Spall Strength

NASA Astrophysics Data System (ADS)

Smirnov, V. I.; Petrov, Yu. V.

2018-03-01

This paper analyzes the effect of the time-dependent shape of a load pulse on the spall strength of materials. Within the framework of a classical one-dimensional scheme, triangular pulses with signal rise and decay portions and with no signal rise portions considered. Calculation results for the threshold characteristics of fracture for rail steel are given. The possibility of optimization of fracture by selecting a loading time with the use of an introduced characteristic of dynamic strength (pulse fracture capacity) is demonstrated. The study is carried out using a structure-time fracture criterion.

Isolated attosecond pulses in the water window

NASA Astrophysics Data System (ADS)

Chang, Zenghu

Millijoule level, few-cycle, carrier-envelope phase (CEP) stable Ti:Sapphire lasers have been the workhorse for the first generation attosecond light sources in the last decade. The spectral range of isolated attosecond pulses with sufficient photon flux for time-resolved pump-probe experiments has been limited to extreme ultraviolet (10 to 150 eV). The shortest pulses achieved are 67 as. The center wavelength of Ti:Sapphire lasers is 800 nm. It was demonstrated in 2001 that the cutoff photon energy of the high harmonic spectrum can be extended by increasing the center wavelength of the driving lasers. In recent years, mJ level, two-cycle, carrier-envelope phase stabilized lasers at 1.6 to 2.1 micron have been developed by compressing pulses from Optical Parametric Amplifiers with gas-filled hollow-core fibers or by implementing Optical Parametric Chirped Pulse Amplification (OPCPA) techniques. Recently, when long wavelength driving was combined with polarization gating, isolated soft x-rays in the water window (280-530 eV) were generated in our laboratory. The number of x-ray photons in the 120-400 eV range is comparable to that generated with Ti:Sapphire lasers in the 50 to 150 eV range. The yield of harmonic generation depends strongly on the ellipticity of the driving fields, which is the foundation of polarization gating. When the width of the gate was set to less than one half of the laser cycle, a soft x-ray supercontinuum was generated. The intensity of the gated x-ray spectrum is sensitive to the carrier-envelope phase of the driving laser, which indicates that single isolated attosecond pulses were generated. The ultrabroadband isolated x-ray pulses with 53 as duration were characterized by attosecond streaking measurements. This work has been supported by the DARPA PULSE program (W31P4Q1310017); the Army Research Office (W911NF-14-1-0383, W911NF-15-1- 0336); the Air Force Office of Scientific Research (FA9550-15-1-0037, FA9550-16-1-0149), and NSF 1506345.

Power balance on a multibeam laser

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

Sampat, Sid; Kelly, John H.; Kosc, Tanya Z.

Inertial confinement fusion (ICF) cryogenic experiments on the 60-beam OMEGA laser have strict requirements for the laser energy delivered on target to be power balanced in order to maximize target-irradiation uniformity. For OMEGA, this quantity (power balance) is inferred from measurements of the time-integrated energy and time-resolved, spatially integrated temporal profile of each of the 60 beams at the output of the laser. The work presented here proposes a general definition of power balance as measured at the laser output and discusses the conditions that are fundamental to achieving laser power balance. Power balance necessitates equal gain across all stagesmore » of amplification, equal net losses across each amplifier stage, equal frequency conversion (from 1053 nm to 351 nm) of all 60 beams, and equal beam path lengths (beam timing). Typical OMEGA ICF laser pulse shapes consist of one or more short (100-ps) “pickets” followed by a shaped “drive” pulse of 1 to 2 ns. For these experiments, power balance is assessed for the pickets and the drive independently, with the ultimate goal of achieving root-mean-square (rms) imbalance across all 60 beams of less than 2% rms on both. Our work presents a comprehensive summary of laser shot campaigns conducted to significantly improve laser power balance from typical rms values of 4.7% and 5.2%, respectively, to the 3% level for both features along with a discussion of future work required to further reduce the rms power imbalance of the laser system.« less

Power balance on a multibeam laser

DOE PAGES

Sampat, Sid; Kelly, John H.; Kosc, Tanya Z.; ...

2018-02-15

Inertial confinement fusion (ICF) cryogenic experiments on the 60-beam OMEGA laser have strict requirements for the laser energy delivered on target to be power balanced in order to maximize target-irradiation uniformity. For OMEGA, this quantity (power balance) is inferred from measurements of the time-integrated energy and time-resolved, spatially integrated temporal profile of each of the 60 beams at the output of the laser. The work presented here proposes a general definition of power balance as measured at the laser output and discusses the conditions that are fundamental to achieving laser power balance. Power balance necessitates equal gain across all stagesmore » of amplification, equal net losses across each amplifier stage, equal frequency conversion (from 1053 nm to 351 nm) of all 60 beams, and equal beam path lengths (beam timing). Typical OMEGA ICF laser pulse shapes consist of one or more short (100-ps) “pickets” followed by a shaped “drive” pulse of 1 to 2 ns. For these experiments, power balance is assessed for the pickets and the drive independently, with the ultimate goal of achieving root-mean-square (rms) imbalance across all 60 beams of less than 2% rms on both. Our work presents a comprehensive summary of laser shot campaigns conducted to significantly improve laser power balance from typical rms values of 4.7% and 5.2%, respectively, to the 3% level for both features along with a discussion of future work required to further reduce the rms power imbalance of the laser system.« less

Study of Conical Pulsed Inductive Thruster with Multiple Modes of Operation

NASA Technical Reports Server (NTRS)

Miller, Robert; Eskridge, Richard; Martin, Adam; Rose, Frank

2008-01-01

An electrodeless, pulsed, inductively coupled thruster has several advantages over current electric propulsion designs. The efficiency of a pulsed inductive thruster is dependent upon the pulse characteristics of the device. Therefore, these thrusters are throttleable over a wide range of thrust levels by varying the pulse rate without affecting the thruster efficiency. In addition, by controlling the pulse energy and the mass bit together, the ISP of the thruster can also be varied with minimal efficiency loss over a wide range of ISP levels. Pulsed inductive thrusters will work with a multitude of propellants, including ammonia. Thus, a single pulsed inductive thruster could be used to handle a multitude of mission needs from high thrust to high ISP with one propulsion solution that would be variable in flight. A conical pulsed inductive lab thruster has been built to study this form of electric propulsion in detail. This thruster incorporates many advantages that are meant to enable this technology as a viable space propulsion technology. These advantages include incorporation of solid state switch technology for all switching needs of the thruster and pre-ionization of the propellant gas prior to acceleration. Pre-ionizing will significantly improve coupling efficiency between drive and bias fields and the plasma. This enables lower pulse energy levels without efficiency reduction. Pre-ionization can be accomplished at a small fraction of the drive pulse energy.

Analytic solution and pulse area theorem for three-level atoms

NASA Astrophysics Data System (ADS)

Shchedrin, Gavriil; O'Brien, Chris; Rostovtsev, Yuri; Scully, Marlan O.

2015-12-01

We report an analytic solution for a three-level atom driven by arbitrary time-dependent electromagnetic pulses. In particular, we consider far-detuned driving pulses and show an excellent match between our analytic result and the numerical simulations. We use our solution to derive a pulse area theorem for three-level V and Λ systems without making the rotating wave approximation. Formulated as an energy conservation law, this pulse area theorem can be used to understand pulse propagation through three-level media.

Ring-shaped pulse oximeter and its application: measurement of SpO2 and blood pressure during sleep and during flight.

PubMed

Kishimoto, Aya; Tochikubo, Osamu; Ohshige, Kenji; Yanaga, Akihiko

2005-01-01

Respiratory and cardiovascular functions show circadian and day-to-day changes. We have developed a wireless ring-shaped pulse oximeter in collaboration with MC Medical Inc. and Advanced Medical Inc. We investigated the accuracy of this pulse oximeter and its application in daily life. Percutaneous arterial oxygen saturation (SpO2) of 47 volunteers was measured simultaneously with the ring-shaped pulse oximeter and a standard pulse oximeter. A total of 103 volunteers underwent measurement of SpO2 for 24 hr, and 11 healthy volunteers underwent measurement of SpO2 and blood pressure (BP) during flight. SpO2 and heart rate (HR) were measured and recorded every 20 sec, cabin barometric pressure and cabin oxygen concentration equivalent to sea level were measured minute-to-minute, and BP was measured every 3 min with a portable BP recorder during each flight. The SpO2 values measured with the ring-shaped pulse oximeter were similar to those measured with the standard method. The mean SpO2 during sleep was significantly lower in the group with high-normal BP or mild hypertension than in the group with normal BP. During flight, the mean change in SpO2 was -2.4 +/- 1.7% during nose-up flight, and 2.1 +/- 2.6% during nose-down flight. There was a significant correlation between change in SpO2 and change in systolic BP during nose-up flight. The wireless ring-shaped pulse oximeter was useful for investigating changes in SpO2 and its effect on BP in daily life during sleep and during air travel.

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

Clark, D. S.; Milovich, J. L.; Hinkel, D. E.

Recent experimental results using the “high foot” pulse shape for inertial confinement fusion ignition experiments on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] have shown encouraging progress compared to earlier “low foot” experiments. These results strongly suggest that controlling ablation front instability growth can significantly improve implosion performance even in the presence of persistent, large, low-mode distortions. Simultaneously, hydrodynamic growth radiography experiments have confirmed that ablation front instability growth is being modeled fairly well in NIF experiments. It is timely then to combine these two results and ask how current ignition pulse shapes couldmore » be modified to improve one-dimensional implosion performance while maintaining the stability properties demonstrated with the high foot. This paper presents such a survey of pulse shapes intermediate between the low and high foot extremes in search of an intermediate foot optimum. Of the design space surveyed, it is found that a higher picket version of the low foot pulse shape shows the most promise for improved compression without loss of stability.« less

Axially adjustable magnetic properties in arrays of multilayered Ni/Cu nanowires with variable segment sizes

NASA Astrophysics Data System (ADS)

Shirazi Tehrani, A.; Almasi Kashi, M.; Ramazani, A.; Montazer, A. H.

2016-07-01

Arrays of multilayered Ni/Cu nanowires (NWs) with variable segment sizes were fabricated into anodic aluminum oxide templates using a pulsed electrodeposition method in a single bath for designated potential pulse times. Increasing the pulse time between 0.125 and 2 s in the electrodeposition of Ni enabled the formation of segments with thicknesses ranging from 25 to 280 nm and 10-110 nm in 42 and 65 nm diameter NWs, respectively, leading to disk-shaped, rod-shaped and/or near wire-shaped geometries. Using hysteresis loop measurements at room temperature, the axial and perpendicular magnetic properties were investigated. Regardless of the segment geometry, the axial coercivity and squareness significantly increased with increasing Ni segment thickness, in agreement with a decrease in calculated demagnetizing factors along the NW length. On the contrary, the perpendicular magnetic properties were found to be independent of the pulse times, indicating a competition between the intrawire interactions and the shape demagnetizing field.

Radially polarized, half-cycle, attosecond pulses from laser wakefields through coherent synchrotronlike radiation.

PubMed

Li, F Y; Sheng, Z M; Chen, M; Yu, L L; Meyer-ter-Vehn, J; Mori, W B; Zhang, J

2014-10-01

Attosecond bursts of coherent synchrotronlike radiation are found when driving ultrathin relativistic electron disks in a quasi-one-dimensional regime of wakefield acceleration, in which the laser waist is larger than the wake wavelength. The disks of overcritical density shrink radially due to focusing wakefields, thus providing the transverse currents for the emission of an intense, radially polarized, half-cycle pulse of about 100 attoseconds in duration. The electromagnetic pulse first focuses to a peak intensity (7×10(20)W/cm(2)) 10 times larger than the driving pulse and then emerges as a conical beam. Basic dynamics of the radiative process are derived analytically and in agreement with particle-in-cell simulations. By making use of gas targets instead of solids to form the ultrathin disks, this method allows for high repetition rates required for applications.

Enhanced hole boring with two-color relativistic laser pulses in the fast ignition scheme

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

Yu, Changhai; Tian, Ye; Li, Wentao

A scheme of using two-color laser pulses for hole boring into overdense plasma as well as energy transfer into electron and ion beams has been studied using particle-in-cell simulations. Following an ultra-short ultra-intense hole-boring laser pulse with a short central wavelength in extreme ultra-violet range, the main infrared driving laser pulse can be guided in the hollow channel preformed by the former laser and propagate much deeper into an overdense plasma, as compared to the case using the infrared laser only. In addition to efficiently transferring the main driving laser energy into energetic electrons and ions generation deep inside themore » overdense plasma, the ion beam divergence can be greatly reduced. The results might be beneficial for the fast ignition concept of inertial confinement fusion.« less

Time-resolved microscopy reveals the driving mechanism of particle formation during ultrashort pulse laser ablation of dentin-like ivory

NASA Astrophysics Data System (ADS)

Domke, Matthias; Gavrilova, Anna; Rapp, Stephan; Frentzen, Matthias; Meister, Joerg; Huber, Heinz P.

2015-07-01

In dental health care, the application of ultrashort laser pulses enables dental tissue ablation free from thermal side effects, such as melting and cracking. However, these laser types create undesired micro- and nanoparticles, which might cause a health risk for the patient or surgeon. The aim of this study was to investigate the driving mechanisms of micro- and nanoparticle formation during ultrashort pulse laser ablation of dental tissue. Time-resolved microscopy was chosen to observe the ablation dynamics of mammoth ivory after irradiation with 660 fs laser pulses. The results suggest that nanoparticles might arise in the excited region. The thermal expansion of the excited material induces high pressure in the surrounding bulk tissue, generating a pressure wave. The rarefaction wave behind this pressure wave causes spallation, leading to ejection of microparticles.

Lidar Luminance Quantizer

NASA Technical Reports Server (NTRS)

Quilligan, Gerard; DeMonthier, Jeffrey; Suarez, George

2011-01-01

This innovation addresses challenges in lidar imaging, particularly with the detection scheme and the shapes of the detected signals. Ideally, the echoed pulse widths should be extremely narrow to resolve fine detail at high event rates. However, narrow pulses require wideband detection circuitry with increased power dissipation to minimize thermal noise. Filtering is also required to shape each received signal into a form suitable for processing by a constant fraction discriminator (CFD) followed by a time-to-digital converter (TDC). As the intervals between the echoes decrease, the finite bandwidth of the shaping circuits blends the pulses into an analog signal (luminance) with multiple modes, reducing the ability of the CFD to discriminate individual events

An analytical model for the calculation of the change in transmembrane potential produced by an ultrawideband electromagnetic pulse.

PubMed

Hart, Francis X; Easterly, Clay E

2004-05-01

The electric field pulse shape and change in transmembrane potential produced at various points within a sphere by an intense, ultrawideband pulse are calculated in a four stage, analytical procedure. Spheres of two sizes are used to represent the head of a human and the head of a rat. In the first stage, the pulse is decomposed into its Fourier components. In the second stage, Mie scattering analysis (MSA) is performed for a particular point in the sphere on each of the Fourier components, and the resulting electric field pulse shape is obtained for that point. In the third stage, the long wavelength approximation (LWA) is used to obtain the change in transmembrane potential in a cell at that point. In the final stage, an energy analysis is performed. These calculations are performed at 45 points within each sphere. Large electric fields and transmembrane potential changes on the order of a millivolt are produced within the brain, but on a time scale on the order of nanoseconds. The pulse shape within the brain differs considerably from that of the incident pulse. Comparison of the results for spheres of different sizes indicates that scaling of such pulses across species is complicated. Published 2004 Wiley-Liss, Inc.

Interacting dynamic Wannier-Stark ladder driven by a periodic pulse train

NASA Astrophysics Data System (ADS)

Hino, Ken-Ichi; Tong, Xiao Min; Toshima, Nobuyuki

2008-01-01

The electronic structures of the Floquet states of the dynamic Wannier-Stark ladder (DWSL) are examined, where the DWSL is formed by driving the biased superlattices (SLs) by the periodic pulse train (PPT) with the electric field F(t) —with time t —and the temporal period 2π/ω . For a strong F(t) , interminiband interactions, namely, the ac-Zener tunneling (ac-ZT), are predominantly caused in the DWSL. Such a system is termed the interacting DWSL. In order to understand the details of the Floquet states and the modulation patterns by alteration of a couple of the PPT laser parameters, the linear absorption spectra, αabs(ωp;ω) , of optical interband transitions invoked by the monochromatic probe laser fp(t) with the frequency ωp are calculated, where the spectra are not only linear in fp(t) but also nonlinear in F(t) . The exciton effect is not included for the sake of simplicity. For the PPT driving with unit-pulse shapes largely deviated from the square and saw-toothed profiles, the spectra show unexpected dent structures, differing a great deal from the corresponding ac-ZT-free spectra basically similar to those of the original SLs just showing the ascending steplike structure. To deepen the understanding of this anomaly, the spectra of αabs0(ωp;ω)∝∂αabs(ωp;ω)/∂ωp are also calculated, whereby the dent structures become spectral dips showing the negative absorption. It is found that such anomalous behavior is attributed to the ac-ZT between different minibands that accompanies emission/absorption of the nonzero net number of photons with Jω (with J a nonzero integer). This anomaly also shows the unusual time dependence in the dual-time optical susceptibility associated with αabs0(ωp;ω) . Moreover, the possibility of existence of the negative absorption in the more realistic excitonic spectra is speculated.

The Rocket Equation Improvement under ICF Implosion Experiment

NASA Astrophysics Data System (ADS)

Wang, Yanbin; Zheng, Zhijian

2013-10-01

The ICF explosion process has been studied in details. The rocket equation has been improved in explosive process by introducing the pressure parameter of fuel. Some methods could be drawn by the improved rocket equation. And the methods could be used to improve ICF target design, driving pulse design and experimental design. The First is to increase ablation pressure. The second is to decrease pressure of fuel. The third is to use larger diameter of target sphere. And the forth is to a shorten driving pulse.

Consolidation of materials by pulse-discharge processes

NASA Astrophysics Data System (ADS)

Strizhakov, E. L.; Nescoromniy, S. V.

2017-07-01

The article presents the research and the analysis of the pulse-discharge processes of capacitor discharge sintering: CD Stud Welding, capacitor discharge percussion welding (CDPW), high-voltage capacitor welding with an inductive-dynamic drive (HVCW with IDD), pulse electric current sintering (PECS) of powders. The comparative analysis of the impact parameter is presented.

Broadband tunable integrated CMOS pulser with 80-ps minimum pulse width for gain-switched semiconductor lasers.

PubMed

Chen, Shaoqiang; Diao, Shengxi; Li, Pengtao; Nakamura, Takahiro; Yoshita, Masahiro; Weng, Guoen; Hu, Xiaobo; Shi, Yanling; Liu, Yiqing; Akiyama, Hidefumi

2017-07-31

High power pulsed lasers with tunable pulse widths are highly favored in many applications. When combined with power amplification, gain-switched semiconductor lasers driven by broadband tunable electric pulsers can meet such requirements. For this reason, we designed and produced a low-cost integrated CMOS pulse generator with a minimum pulse width of 80 ps and a wide tuning range of up to 270 ns using a 40-nm microelectronic process technique. We used this pulser to drive a 1.3-µm semiconductor laser diode directly, and thereafter investigated the gain-switching properties of the laser system. The optical pulses consist of a spike followed by a steady state region. Tuning the width of the electrical pulse down to approximately 1.5 ns produces optical pulses consisting only of the spike, which has a minimum pulse-width of 100 ps. Moreover, the duration of the steady state can be tuned continuously by tuning the electrical pulse width, with a peak power of approximately 5 mW. The output voltage of the electric pulser has a tuning range of 0.8-1.5 V that can be used to directly drive semiconductor laser diodes with wavelengths in the near-infrared spectrum, which are suitable for power amplification with rare-earth doped fiber amplifiers.

Pure-phase selective excitation in fast-relaxing systems.

PubMed

Zangger, K; Oberer, M; Sterk, H

2001-09-01

Selective pulses have been used frequently for small molecules. However, their application to proteins and other macromolecules has been limited. The long duration of shaped-selective pulses and the short T(2) relaxation times in proteins often prohibited the use of highly selective pulses especially on larger biomolecules. A very selective excitation can be obtained within a short time by using the selective excitation sequence presented in this paper. Instead of using a shaped low-intensity radiofrequency pulse, a cluster of hard 90 degrees pulses, delays of free precession, and pulsed field gradients can be used to selectively excite a narrow chemical shift range within a relatively short time. Thereby, off-resonance magnetization, which is allowed to evolve freely during the free precession intervals, is destroyed by the gradient pulses. Off-resonance excitation artifacts can be removed by random variation of the interpulse delays. This leads to an excitation profile with selectivity as well as phase and relaxation behavior superior to that of commonly used shaped-selective pulses. Since the evolution of scalar coupling is inherently suppressed during the double-selective excitation of two different scalar-coupled nuclei, the presented pulse cluster is especially suited for simultaneous highly selective excitation of N-H and C-H fragments. Experimental examples are demonstrated on hen egg white lysozyme (14 kD) and the bacterial antidote ParD (19 kD). Copyright 2001 Academic Press.

Delayed photo-emission model for beam optics codes

DOE PAGES

Jensen, Kevin L.; Petillo, John J.; Panagos, Dimitrios N.; ...

2016-11-22

Future advanced light sources and x-ray Free Electron Lasers require fast response from the photocathode to enable short electron pulse durations as well as pulse shaping, and so the ability to model delays in emission is needed for beam optics codes. The development of a time-dependent emission model accounting for delayed photoemission due to transport and scattering is given, and its inclusion in the Particle-in-Cell code MICHELLE results in changes to the pulse shape that are described. Furthermore, the model is applied to pulse elongation of a bunch traversing an rf injector, and to the smoothing of laser jitter onmore » a short pulse.« less

Picosecond and sub-picosecond flat-top pulse generation using uniform long-period fiber gratings

NASA Astrophysics Data System (ADS)

Park, Y.; Kulishov, M.; Slavík, R.; Azaña, J.

2006-12-01

We propose a novel linear filtering scheme based on ultrafast all-optical differentiation for re-shaping of ultrashort pulses generated from a mode-locked laser into flat-top pulses. The technique is demonstrated using simple all-fiber optical filters, more specifically uniform long period fiber gratings (LPGs) operated in transmission. The large bandwidth typical for these fiber filters allows scaling the technique to the sub-picosecond regime. In the experiments reported here, 600-fs and 1.8-ps Gaussian-like optical pulses (@ 1535 nm) have been re-shaped into 1-ps and 3.2-ps flat-top pulses, respectively, using a single 9-cm long uniform LPG.

Conceptual design of a pulsed-power accelerator optimized for megajoule-class 1-TPa dynamic-material-physics experiments

DOE PAGES

Stygar, William A.; Reisman, David B.; Stoltzfus, Brian S.; ...

2016-07-07

In this study, we have developed a conceptual design of a next-generation pulsed-power accelerator that is optmized for driving megajoule-class dynamic-material-physics experiments at pressures as high as 1 TPa. The design is based on an accelerator architecture that is founded on three concepts: single-stage electrical-pulse compression, impedance matching, and transit-time-isolated drive circuits. Since much of the accelerator is water insulated, we refer to this machine as Neptune. The prime power source of Neptune consists of 600 independent impedance-matched Marx generators. As much as 0.8 MJ and 20 MA can be delivered in a 300-ns pulse to a 16-mΩ physics load;more » hence Neptune is a megajoule-class 20-MA arbitrary waveform generator. Neptune will allow the international scientific community to conduct dynamic equation-of-state, phase-transition, mechanical-property, and other material-physics experiments with a wide variety of well-defined drive-pressure time histories. Because Neptune can deliver on the order of a megajoule to a load, such experiments can be conducted on centimeter-scale samples at terapascal pressures with time histories as long as 1 μs.« less

Ultimate waveform reproducibility of extreme-ultraviolet pulses by high-harmonic generation in quartz

NASA Astrophysics Data System (ADS)

Garg, M.; Kim, H. Y.; Goulielmakis, E.

2018-05-01

Optical waveforms of light reproducible with subcycle precision underlie applications of lasers in ultrafast spectroscopies, quantum control of matter and light-based signal processing. Nonlinear upconversion of optical pulses via high-harmonic generation in gas media extends these capabilities to the extreme ultraviolet (EUV). However, the waveform reproducibility of the generated EUV pulses in gases is inherently sensitive to intensity and phase fluctuations of the driving field. We used photoelectron interferometry to study the effects of intensity and carrier-envelope phase of an intense single-cycle optical pulse on the field waveform of EUV pulses generated in quartz nanofilms, and contrasted the results with those obtained in gas argon. The EUV waveforms generated in quartz were found to be virtually immune to the intensity and phase of the driving field, implying a non-recollisional character of the underlying emission mechanism. Waveform-sensitive photonic applications and precision measurements of fundamental processes in optics will benefit from these findings.

A comparative study of optimum and suboptimum direct-detection laser ranging receivers

NASA Technical Reports Server (NTRS)

Abshire, J. B.

1978-01-01

A summary of previously proposed receiver strategies for direct-detection laser ranging receivers is presented. Computer simulations are used to compare performance of candidate implementation strategies in the 1- to 100-photoelectron region. Under the condition of no background radiation, the maximum-likelihood and minimum mean-square error estimators were found to give the same performance for both bell-shaped and rectangular optical-pulse shapes. For signal energies greater than 100 photoelectrons, the root-mean-square range error is shown to decrease as Q to the -1/2 power for bell-shaped pulses and Q to the -1 power for rectangular pulses, where Q represents the average pulse energy. Of several receiver implementations presented, the matched-filter peak detector was found to be preferable. A similar configuration, using a constant-fraction discriminator, exhibited a signal-level dependent time bias.

A compact pulse shape discriminator module for large neutron detector arrays

NASA Astrophysics Data System (ADS)

Venkataramanan, S.; Gupta, Arti; Golda, K. S.; Singh, Hardev; Kumar, Rakesh; Singh, R. P.; Bhowmik, R. K.

2008-11-01

A cost-effective high-performance pulse shape discriminator module has been developed to process signals from organic liquid scintillator-based neutron detectors. This module is especially designed for the large neutron detector array used for studies of nuclear reaction dynamics at the Inter University Accelerator Center (IUAC). It incorporates all the necessary pulse processing circuits required for neutron spectroscopy in a novel fashion by adopting the zero crossover technique for neutron-gamma (n- γ) pulse shape discrimination. The detailed layout of the circuit and different features of the module are described in the present paper. The quality of n- γ separation obtained with this electronics is much better than that of commercial modules especially in the low-energy region. The results obtained with our module are compared with similar setups available in other laboratories.

Pulse-shaping based two-photon FRET stoichiometry

PubMed Central

Flynn, Daniel C.; Bhagwat, Amar R.; Brenner, Meredith H.; Núñez, Marcos F.; Mork, Briana E.; Cai, Dawen; Swanson, Joel A.; Ogilvie, Jennifer P.

2015-01-01

Förster Resonance Energy Transfer (FRET) based measurements that calculate the stoichiometry of intermolecular interactions in living cells have recently been demonstrated, where the technique utilizes selective one-photon excitation of donor and acceptor fluorophores to isolate the pure FRET signal. Here, we present work towards extending this FRET stoichiometry method to employ two-photon excitation using a pulse-shaping methodology. In pulse-shaping, frequency-dependent phases are applied to a broadband femtosecond laser pulse to tailor the two-photon excitation conditions to preferentially excite donor and acceptor fluorophores. We have also generalized the existing stoichiometry theory to account for additional cross-talk terms that are non-vanishing under two-photon excitation conditions. Using the generalized theory we demonstrate two-photon FRET stoichiometry in live COS-7 cells expressing fluorescent proteins mAmetrine as the donor and tdTomato as the acceptor. PMID:25836193

Exploring the Pulse Structure of the Gamma-Ray Bursts from the Swift Burst Alert Telescop

NASA Astrophysics Data System (ADS)

Martinez, Juan-Carlos; Team 1: Jon Hakkila, Amy Lien, Judith, Racusin, Team 2: Antonino Cucchiara, David Morris

2018-01-01

Gamma-ray bursts (GRBs) are one of the brightest and most intense explosions in our universe. For this project, we studied the shape of 400 single pulse GRBs using data gathered from Swift's Burst Alert Telescope (BAT). Hakkila et al. (2015) have discovered a mathematical Model that describes the GRB’s pulse shapes. Following the method in Hakkila et al. (2015), we fit GRB pulses with the Norris function and examined the residual in the fitting, to see whether the results are consistent with the one reported in Hakkila et al. (2015).

Focus characterization at an X-ray free-electron laser by coherent scattering and speckle analysis

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

Sikorski, Marcin; Song, Sanghoon; Schropp, Andreas

2015-04-14

X-ray focus optimization and characterization based on coherent scattering and quantitative speckle size measurements was demonstrated at the Linac Coherent Light Source. Its performance as a single-pulse free-electron laser beam diagnostic was tested for two typical focusing configurations. The results derived from the speckle size/shape analysis show the effectiveness of this technique in finding the focus' location, size and shape. In addition, its single-pulse compatibility enables users to capture pulse-to-pulse fluctuations in focus properties compared with other techniques that require scanning and averaging.

Modeling the Pulse Signal by Wave-Shape Function and Analyzing by Synchrosqueezing Transform

PubMed Central

Wang, Chun-Li; Yang, Yueh-Lung; Wu, Wen-Hsiang; Tsai, Tung-Hu; Chang, Hen-Hong

2016-01-01

We apply the recently developed adaptive non-harmonic model based on the wave-shape function, as well as the time-frequency analysis tool called synchrosqueezing transform (SST) to model and analyze oscillatory physiological signals. To demonstrate how the model and algorithm work, we apply them to study the pulse wave signal. By extracting features called the spectral pulse signature, and based on functional regression, we characterize the hemodynamics from the radial pulse wave signals recorded by the sphygmomanometer. Analysis results suggest the potential of the proposed signal processing approach to extract health-related hemodynamics features. PMID:27304979

Modeling the Pulse Signal by Wave-Shape Function and Analyzing by Synchrosqueezing Transform.

PubMed

Wu, Hau-Tieng; Wu, Han-Kuei; Wang, Chun-Li; Yang, Yueh-Lung; Wu, Wen-Hsiang; Tsai, Tung-Hu; Chang, Hen-Hong

2016-01-01

We apply the recently developed adaptive non-harmonic model based on the wave-shape function, as well as the time-frequency analysis tool called synchrosqueezing transform (SST) to model and analyze oscillatory physiological signals. To demonstrate how the model and algorithm work, we apply them to study the pulse wave signal. By extracting features called the spectral pulse signature, and based on functional regression, we characterize the hemodynamics from the radial pulse wave signals recorded by the sphygmomanometer. Analysis results suggest the potential of the proposed signal processing approach to extract health-related hemodynamics features.

Flexible approach to vibrational sum-frequency generation using shaped near-infrared light

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

Chowdhury, Azhad U.; Liu, Fangjie; Watson, Brianna R.

We describe a new approach that expands the utility of vibrational sum-frequency generation (vSFG) spectroscopy using shaped near-infrared (NIR) laser pulses. Here, we demonstrate that arbitrary pulse shapes can be specified to match experimental requirements without the need for changes to the optical alignment. In this way, narrowband NIR pulses as long as 5.75 ps are readily generated, with a spectral resolution of about 2.5 cm -1, an improvement of approximately a factor of 3 compared to a typical vSFG system. Moreover, the utility of having complete control over the NIR pulse characteristics is demonstrated through nonresonant background suppression frommore » a metallic substrate by generating an etalon waveform in the pulse shaper. The flexibility afforded by switching between arbitrary NIR waveforms at the sample position with the same instrument geometry expands the type of samples that can be studied without extensive modifications to existing apparatuses or large investments in specialty optics.« less

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

A compact 7-cell Si-drift detector module for high-count rate X-ray spectroscopy.

PubMed

Hansen, K; Reckleben, C; Diehl, I; Klär, H

2008-05-01

A new Si-drift detector module for fast X-ray spectroscopy experiments was developed and realized. The Peltier-cooled module comprises a sensor with 7 × 7-mm 2 active area, an integrated circuit for amplification, shaping and detection, storage, and derandomized readout of signal pulses in parallel, and amplifiers for line driving. The compactness and hexagonal shape of the module with a wrench size of 16mm allow very short distances to the specimen and multi-module arrangements. The power dissipation is 186mW. At a shaper peaking time of 190 ns and an integration time of 450 ns an electronic rms noise of ~11 electrons was achieved. When operated at 7 °C, FWHM line widths around 260 and 460 eV (Cu-K α ) were obtained at low rates and at sum-count rates of 1.7 MHz, respectively. The peak shift is below 1% for a broad range of count rates. At 1.7-MHz sum-count rate the throughput loss amounts to 30%.

Spectral modification of shock accelerated ions using a hydrodynamically shaped gas target

DOE PAGES

Tresca, O.; Polyanskiy, M. N.; Dover, N. P.; ...

2015-08-28

We report on reproducible shock acceleration from irradiation of a λ=10 μm CO2 laser on optically shaped H2 and He gas targets. A low energy laser prepulse (I≲10 14 W cm –2) is used to drive a blast wave inside the gas target, creating a steepened, variable density gradient. This is followed, after 25 ns, by a high intensity laser pulse (I>10 16 W cm –2) that produces an electrostatic collisionless shock. Upstream ions are accelerated for a narrow range of prepulse energies. For long density gradients (≳40 μm), broadband beams of He + and H + were routinely produced,more » whilst for shorter gradients (≲20 μm), quasimonoenergetic acceleration of protons is observed. These measurements indicate that the properties of the accelerating shock and the resultant ion energy distribution, in particular the production of narrow energy spread beams, is highly dependent on the plasma density profile. These findings are corroborated by 2D particle-in-cell simulations.« less

The non-canonical Wnt-PCP pathway shapes the mouse caudal neural plate.

PubMed

López-Escobar, Beatriz; Caro-Vega, José Manuel; Vijayraghavan, Deepthi S; Plageman, Timothy F; Sanchez-Alcazar, José A; Moreno, Roberto Carlos; Savery, Dawn; Márquez-Rivas, Javier; Davidson, Lance A; Ybot-González, Patricia

2018-05-08

The last stage of neural tube (NT) formation involves closure of the caudal neural plate (NP), an embryonic structure formed by neuromesodermal progenitors and newly differentiated cells that becomes incorporated into the NT. Here, we show in mouse that, as cell specification progresses, neuromesodermal progenitors and their progeny undergo significant changes in shape prior to their incorporation into the NT. The caudo-rostral progression towards differentiation is coupled to a gradual reliance on a unique combination of complex mechanisms that drive tissue folding, involving pulses of apical actomyosin contraction and planar polarised cell rearrangements, all of which are regulated by the Wnt-PCP pathway. Indeed, when this pathway is disrupted, either chemically or genetically, the polarisation and morphology of cells within the entire caudal NP is disturbed, producing delays in NT closure. The most severe disruptions of this pathway prevent caudal NT closure and result in spina bifida. In addition, a decrease in Vangl2 gene dosage also appears to promote more rapid progression towards a neural fate, but not the specification of more neural cells. © 2018. Published by The Company of Biologists Ltd.

Magnetically Suspended Linear Pulse Motor for Semiconductor Wafer Transfer in Vacuum Chamber

NASA Technical Reports Server (NTRS)

Moriyama, Shin-Ichi; Hiraki, Naoji; Watanabe, Katsuhide; Kanemitsu, Yoichi

1996-01-01

This paper describes a magnetically suspended linear pulse motor for a semiconductor wafer transfer robot in a vacuum chamber. The motor can drive a wafer transfer arm horizontally without mechanical contact. In the construction of the magnetic suspension system, four pairs of linear magnetic bearings for the lift control are used for the guidance control as well. This approach allows us to make the whole motor compact in size and light in weight. The tested motor consists of a double-sided stator and a transfer arm with a width of 50 mm and a total length of 700 mm. The arm, like a ladder in shape, is designed as the floating element with a tooth width of 4 mm (a tooth pitch of 8 mm). The mover mass is limited to about 1.6 kg by adopting such an arm structure, and the ratio of thrust to mover mass reaches to 3.2 N/kg under a broad air gap (1 mm) between the stator teeth and the mover teeth. The performance testing was carried out with a transfer distance less than 450 mm and a transfer speed less than 560 mm/s. The attitude of the arm was well controlled by the linear magnetic bearings with a combined use, and consequently the repeatability on the positioning of the arm reached to about 2 micron. In addition, the positioning accuracy was improved up to about 30 micron through a compensation of the 128-step wave current which was used for the micro-step drive with a step increment of 62.5 micron.

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.

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.

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.

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

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

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

2010-08-01

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

Sputter crater formation in the case of microsecond pulsed glow discharge in a Grimm-type source. Comparison of direct current and radio frequency modes

NASA Astrophysics Data System (ADS)

Efimova, Varvara; Hoffmann, Volker; Eckert, Jürgen

2012-10-01

Depth profiling with pulsed glow discharge is a promising technique. The application of pulsed voltage for sputtering reduces the sputtering rate and thermal stress and hereby improves the analysis of thin layered and thermally fragile samples. However pulsed glow discharge is not well studied and this limits its practical use. The current work deals with the questions which usually arise when the pulsed mode is applied: Which duty cycle, frequency and pulse length must be chosen to get the optimal sputtering rate and crater shape? Are the well-known sputtering effects of the continuous mode valid also for the pulsed regime? Is there any difference between dc and rf pulsing in terms of sputtering? It is found that the pulse length is a crucial parameter for the crater shape and thermal effects. Sputtering with pulsed dc and rf modes is found to be similar. The observed sputtering effects at various pulsing parameters helped to interpret and optimize the depth resolution of GD OES depth profiles.

Efficient photoassociation of ultracold cesium atoms with picosecond pulse laser

NASA Astrophysics Data System (ADS)

Hai, Yang; Hu, Xue-Jin; Li, Jing-Lun; Cong, Shu-Lin

2017-08-01

We investigate theoretically the formation of ultracold Cs2 molecules via photoassociation (PA) with three kinds of pulses (the Gaussian pulse, the asymmetric shaped laser pulse SL1 with a large rising time and a small falling time and the asymmetric shaped laser pulse SL2 with a small rising time and a large falling time). For the three kinds of pulses, the final population on vibrational levels from v‧ = 120 to 175 of the excited state displays a regular oscillation change with pulse width and interaction strength, and a high PA efficiency can be achieved with optimised parameters. The PA efficiency in the excited state steered by the SL1-pulse (SL2-pulse) train with optimised parameters which is composed of four SL1 (SL2) pulses is 1.74 times as much as that by the single SL1 (SL2) pulse due to the population accumulation effect. Moreover, a dump laser is employed to transfer the excited molecules from the excited state to the vibrational level v″ = 12 of the ground state to obtain stable molecules.

Capacitor charging FET switcher with controller to adjust pulse width

DOEpatents

Mihalka, Alex M.

1986-01-01

A switching power supply includes an FET full bridge, a controller to drive the FETs, a programmable controller to dynamically control final output current by adjusting pulse width, and a variety of protective systems, including an overcurrent latch for current control. Power MOSFETS are switched at a variable frequency from 20-50 kHz to charge a capacitor load from 0 to 6 kV. A ferrite transformer steps up the DC input. The transformer primary is a full bridge configuration with the FET switches and the secondary is fed into a high voltage full wave rectifier whose output is connected directly to the energy storage capacitor. The peak current is held constant by varying the pulse width using predetermined timing resistors and counting pulses. The pulse width is increased as the capacitor charges to maintain peak current. A digital ripple counter counts pulses, and after the desired number is reached, an up-counter is clocked. The up-counter output is decoded to choose among different resistors used to discharge a timing capacitor, thereby determining the pulse width. A current latch shuts down the supply on overcurrent due to either excessive pulse width causing transformer saturation or a major bridge fault, i.e., FET or transformer failure, or failure of the drive circuitry.

Passive and active pulse stacking scheme for pulse shaping

DOEpatents

Harney, Robert C.; Schipper, John F.

1977-01-01

Apparatus and method for producing a sequence of radiation pulses with a pulse envelope of time variation which is controllable by an external electromagnetic signal applied to an active medium or by a sectored reflector, through which the radiation passes.

Pulsed Artificial Electrojet Generation

NASA Astrophysics Data System (ADS)

Papadopoulos, K.

2008-12-01

Traditional techniques for generating low frequency signals in the ULF/ELF range (.1-100 Hz) and rely on ground based Horizontal Electric Dipole (HED) antennas. It is, furthermore, well known that a Vertical Electric Dipole (VED) is by more than 50 dB more efficient than a HED with the same dipole current moment. However, the prohibitively long length of VED antennas in the ELF/ULF range coupled with voltage limitations due to corona discharge in the atmosphere make them totally impracticable. In this paper we discuss a novel concept, inspired by the physics of the equatorial electrojet, that allows for the conversion of a ground based HED to a VED in the E-region of the equatorial ionosphere with current moment comparable to the driving HED. The paper focuses in locations near the dip-equator, where the earth's magnetic is in predominantly in the horizontal direction. The horizontal electric field associated with a pulsed HED drives a large Hall current in the ionospheric E-region, resulting in a vertical current. It is shown that the pulsed vertical current in the altitude range 80-130 km, driven by a horizontal electric field of, approximately, .1 mV/m at 100 km altitude, is of the order of kA. This results in a pulsed VED larger than 106 A-m. Such a pulsed VED will drive ELF/ULF pulses with amplitude in excess of .1 nT at a lateral range larger than few hundred kilometers. This is by three orders of magnitude larger than the one expected by a HED with comparable current moment. The paper will conclude with the description of a sneak-through technique that allows for creating pulsed electric fields in the ionosphere much larger than expected from steady state oscillatory HED antennas.

A 1-D Study of the Ignition Space for Magnetic Indirect (X-ray) Drive Targets

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

Cobble, James Allen; Sinars, Daniel Brian

The ICF program today is investigating three approaches to achieving multi-MJ fusion yields and ignition: (1) laser indirect (x-ray) drive on the National Ignition Facility (NIF), (2) laser direct drive (primarily on the Omega laser facility at the University of Rochester), and (3) magnetic direct drive on the Z pulsed power facility. In this white paper we briefly consider a fourth approach, magnetic indirect drive, in which pulsedpower- driven x-ray sources are used in place of laser driven sources. We first look at some of the x-ray sources studied on Z prior to 2007 before the pulsed power ICF programmore » shifted to magnetic direct drive. We then show results from a series of 1D Helios calculations of double-shell capsules that suggest that these sources, scaled to higher temperatures, could be a promising path to achieving multi-MJ fusion yields and ignition. We advocate here that more detailed design calculations with widely accepted 2D/3D ICF codes should be conducted for a better assessment of the prospects.« less

Optimized Ion Energy Profiles for Heavy Ion Direct Drive Targets

NASA Astrophysics Data System (ADS)

Hay, Michael J.; Barnard, John J.; Perkins, L. John; Logan, B. Grant

2009-11-01

Recent 1-D implosion calculations [1] have characterized pure-DT targets delivering gains of 50-90 with less than 0.5 MJ of heavy ion direct drive. With a payload fraction of 1/3, these low-aspect ratio targets operate near the peak of rocket efficiency and achieve ˜10% overall coupling efficiencies (vs. the 15-20% efficiencies analytically predicted for less stable, higher-aspect ratio targets). In Ref. 1, the ion energy is ramped directly from a 50 MeV foot pulse to a 500 MeV main pulse. In this paper, we instead tune the ion energy throughout the drive to closely match the beam deposition with the inward progress of the ablation front. We will present the ion energy and intensity time histories that maximize drive efficiency and gain for a single target at constant integrated drive energy. [1] L. J. Perkins, B. G. Logan, J. J. Barnard, and M. J. Hay. ``High Efficiency High Gain Heavy Ion Direct Drive Targets,'' Bulletin of the American Physical Society, vol. 54: DPP, Nov. 2009.

A polar-drive-ignition design for the National Ignition Facility

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

Collins, T. J. B.; Marozas, J. A.; Anderson, K. S.

2012-05-15

Polar drive [Skupsky et al., Phys. Plasmas 11, 2763 (2004)] will enable direct-drive experiments to be conducted on the National Ignition Facility (NIF) [Miller et al., Opt. Eng. 43, 2841 (2004)], while the facility is configured for x-ray drive. A polar-drive ignition design for the NIF has been developed that achieves a gain of 32 in two-dimensional (2-D) simulations, which include single- and multiple-beam nonuniformities and ice and outer-surface roughness. This design requires both single-beam UV polarization smoothing and one-dimensional (1-D) multi-frequency modulator (MFM) single-beam smoothing to achieve the required laser uniformity. The multi-FM smoothing is employed only during themore » low-intensity portion of the laser pulse, allowing for the use of sufficient smoothing-by-spectral-dispersion bandwidth while maintaining safe laser operations during the high-intensity part of the pulse. This target is robust to all expected sources of perturbations.« less

Shock drive capabilities of a 30-Joule laser at the matter in extreme conditions hutch of the Linac Coherent Light Source

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

Brown, Shaughnessy Brennan; Hashim, Akel; Gleason, Arianna

In this paper, we measure the shock drive capabilities of a 30 J, nanosecond, 527 nm laser system at the matter in extreme conditions hutch of the Linac Coherent Light Source. Using a velocity interferometer system for any reflector, we ascertain the maximum instantaneous ablation pressure and characterize its dependence on a drive laser spot size, spatial profile, and temporal profile. We also examine the effects of these parameters on shock spatial and temporal uniformity. Our analysis shows the drive laser capable of generating instantaneous ablation pressures exceeding 160 GPa while maintaining a 1D shock profile. We find that slopemore » pulses provide higher instantaneous ablation pressures than plateau pulses. Our results show instantaneous ablation pressures comparable to those measured at the Omega Laser Facility in Rochester, NY under similar optical drive parameters. In conclusion, we analyze how optical laser ablation pressures are compare with known scaling relations, accounting for variable laser wavelengths.« less

Shock drive capabilities of a 30-Joule laser at the matter in extreme conditions hutch of the Linac Coherent Light Source

DOE PAGES

Brown, Shaughnessy Brennan; Hashim, Akel; Gleason, Arianna; ...

2017-10-23

In this paper, we measure the shock drive capabilities of a 30 J, nanosecond, 527 nm laser system at the matter in extreme conditions hutch of the Linac Coherent Light Source. Using a velocity interferometer system for any reflector, we ascertain the maximum instantaneous ablation pressure and characterize its dependence on a drive laser spot size, spatial profile, and temporal profile. We also examine the effects of these parameters on shock spatial and temporal uniformity. Our analysis shows the drive laser capable of generating instantaneous ablation pressures exceeding 160 GPa while maintaining a 1D shock profile. We find that slopemore » pulses provide higher instantaneous ablation pressures than plateau pulses. Our results show instantaneous ablation pressures comparable to those measured at the Omega Laser Facility in Rochester, NY under similar optical drive parameters. In conclusion, we analyze how optical laser ablation pressures are compare with known scaling relations, accounting for variable laser wavelengths.« less

A Compact 700-KV Erected Pulse Forming Network for HPM Applications (Postprint)

DTIC Science & Technology

2011-04-28

previously investigated for driving rail guns , electric launchers, or other nonlinear loads albeit for much longer pulse lengths [8]. In this version...The output of the generator was connected to a coaxial CuS04 resistor through 100-ft of coaxial high-voltage cable. The current pulse on the cable was...shown in Figure 6. This pulse was delivered to a 50-ohm cable and measured by a coaxial inline CVR at the generator output. Typical pulse

X-ray lasers and methods utilizing two component driving illumination provided by optical laser means of relatively low energy and small physical size

DOEpatents

Rosen, Mordecai D.; Matthews, Dennis L.

1991-01-01

An X-ray laser (10), and related methodology, are disclosed wherein an X-ray laser target (12) is illuminated with a first pulse of optical laser radiation (14) of relatively long duration having scarcely enough energy to produce a narrow and linear cool plasma of uniform composition (38). A second, relatively short pulse of optical laser radiation (18) is uniformly swept across the length, from end to end, of the plasma (38), at about the speed of light, to consecutively illuminate continuously succeeding portions of the plasma (38) with optical laser radiation having scarcely enough energy to heat, ionize, and invert them into the continuously succeeding portions of an X-ray gain medium. This inventive double pulse technique results in a saving of more than two orders of magnitude in driving optical laser energy, when compared to the conventional single pulse approach.

Thermally controlled femtosecond pulse shaping using metasurface based optical filters

NASA Astrophysics Data System (ADS)

Rahimi, Eesa; Şendur, Kürşat

2018-02-01

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

Pulse shape discrimination for background rejection in germanium gamma-ray detectors

NASA Technical Reports Server (NTRS)

Feffer, P. T.; Smith, D. M.; Campbell, R. D.; Primbsch, J. H.; Lin, R. P.

1989-01-01

A pulse-shape discrimination (PSD) technique is developed to reject the beta-decay background resulting from activation of Ge gamma-ray detectors by cosmic-ray secondaries. These beta decays are a major source of background at 0.2-2 MeV energies in well shielded Ge detector systems. The technique exploits the difference between the detected current pulse shapes of single- and multiple-site energy depositions within the detector: beta decays are primarily single-site events, while photons at these energies typically Compton scatter before being photoelectrically absorbed to produce multiple-site events. Depending upon the amount of background due to sources other than beta decay, PSD can more than double the detector sensitivity.

Studies of neutron-γ pulse shape discrimination in EJ-309 liquid scintillator using charge integration method

NASA Astrophysics Data System (ADS)

Pawełczak, I. A.; Ouedraogo, S. A.; Glenn, A. M.; Wurtz, R. E.; Nakae, L. F.

2013-05-01

Pulse shape discrimination capability based on the charge integration has been investigated for liquid scintillator EJ-309. The effectiveness of neutron-γ discrimination in 4-in. diameter and 3-in. thick EJ-309 cells coupled with 3-in. photomultiplier tubes has been carefully studied in the laboratory environment and compared to the commonly used EJ-301 liquid scintillator formulation. Influences of distortions in pulse shape caused by 13.7-m long cables necessary for some remote operations have been examined. The parameter space for an effective neutron-γ discrimination for these assays, such as position and width of a gate used for integration of the delayed light, has been explored.

Beyond the single-atom response in absorption line shapes: probing a dense, laser-dressed helium gas with attosecond pulse trains.

PubMed

Liao, Chen-Ting; Sandhu, Arvinder; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B

2015-04-10

We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently, to the appearance of new, narrow features in the absorption line.

Versatile analog pulse height computer performs real-time arithmetic operations

NASA Technical Reports Server (NTRS)

Brenner, R.; Strauss, M. G.

1967-01-01

Multipurpose analog pulse height computer performs real-time arithmetic operations on relatively fast pulses. This computer can be used for identification of charged particles, pulse shape discrimination, division of signals from position sensitive detectors, and other on-line data reduction techniques.

Microwave detector

DOEpatents

Meldner, H.W.; Cusson, R.Y.; Johnson, R.M.

1985-02-08

A microwave detector is provided for measuring the envelope shape of a microwave pulse comprised of high-frequency oscillations. A biased ferrite produces a magnetization field flux that links a B-dot loop. The magnetic field of the microwave pulse participates in the formation of the magnetization field flux. High-frequency insensitive means are provided for measuring electric voltage or current induced in the B-dot loop. The recorded output of the detector is proportional to the time derivative of the square of the envelope shape of the microwave pulse.

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.

Measurement of (222)Rn by absorption in plastic scintillators and alpha/beta pulse shape discrimination.

PubMed

Mitev, Krasimir K

2016-04-01

This work demonstrates that common plastic scintillators like BC-400, EJ-200 and SCSF-81 absorb radon and their scintillation pulse decay times are different for alpha- and beta-particles. This allows the application of pulse shape analysis for separation of the pulses of alpha- and beta-particles emitted by the absorbed radon and its progeny. It is shown that after pulse shape discrimination of beta-particles' pulses, the energy resolution of BC-400 and EJ-200 alpha spectra is sufficient to separate the peaks of (222)Rn, (218)Po and (214)Po and allows (222)Rn measurements that are unaffected by the presence of thoron ((220)Rn) in the environment. The alpha energy resolution of SCSF-81 in the experiments degrades due to imperfect collection of the light emitted inside the scintillating fibers. The experiments with plastic scintillation microspheres (PSM) confirm previous findings of other researchers that PSM have alpha-/beta-discrimination properties and show suitability for radon measurements. The diffusion length of radon in BC-400 and EJ-200 is determined. The pilot experiments show that the plastic scintillators are suitable for radon-in-soil-gas measurements. Overall, the results of this work suggest that it is possible to develop a new type of radon measurement instruments which employ absorption in plastic scintillators, pulse-shape discrimination and analysis of the alpha spectra. Such instruments can be very compact and can perform continuous, real-time radon measurements and thoron detection. They can find applications in various fields from radiation protection to earth sciences. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

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

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

2014-07-21

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

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.

Multiplex CARS imaging with spectral notch shaped laser pulses delivered by optical fibers.

PubMed

Oh, Seung Ryeol; Park, Joo Hyun; Kim, Kyung-Soo; Lee, Jae Yong; Kim, Soohyun

2017-12-11

We present an experimental demonstration of single-pulse coherent anti-Stokes Raman spectroscopy (CARS) using a spectrally shaped broadband laser that is delivered by an optical fiber to a sample at its distal end. The optical fiber consists of a fiber Bragg grating component to serve as a narrowband notch filter and a combined large-mode-area fiber to transmit such shaped ultrashort laser pulses without spectral distortion in a long distance. Experimentally, our implementation showed a capability to measure CARS spectra of various samples with molecular vibrations in the fingerprint region. Furthermore, CARS imaging of poly(methyl methacrylate) bead samples was carried out successfully under epi-CARS geometry in which backward-scattered CARS signals were collected into a multimode optical fiber. A compatibility of single-pulse CARS scheme with fiber optics, verified in this study, implies a potential for future realization of compact all-fiber CARS spectroscopic imaging systems.

Recoverable stress induced two-way shape memory effect on NiTi surface using laser-produced shock wave

NASA Astrophysics Data System (ADS)

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

2017-02-01

The surfaces of Ni50Ti50 shape memory alloys (SMAs) were patterned by laser scribing. This method is more simplistic and efficient than traditional indentation techniques, and has also shown to be an effective method in patterning these materials. Different laser energy densities ranging from 5 mJ/pulse to 56 mJ/pulse were used to observe recovery on SMA surface. The temperature dependent heat profiles of the NiTi surfaces after laser scribing at 56 mJ/pulse show the partially-recovered indents, which indicate a "shape memory effect (SME)" Experimental data is in good agreement with theoretical simulation of laser induced shock wave propagation inside NiTi SMAs. Stress wave closely followed the rise time of the laser pulse to its peak values and initial decay. Further investigations are underway to improve the SME such that the indents are recovered to a greater extent.

Neutron Spectroscopy for pulsed beams with frame overlap using a double time-of-flight technique

NASA Astrophysics Data System (ADS)

Harrig, K. P.; Goldblum, B. L.; Brown, J. A.; Bleuel, D. L.; Bernstein, L. A.; Bevins, J.; Harasty, M.; Laplace, T. A.; Matthews, E. F.

2018-01-01

A new double time-of-flight (dTOF) neutron spectroscopy technique has been developed for pulsed broad spectrum sources with a duty cycle that results in frame overlap, where fast neutrons from a given pulse overtake slower neutrons from previous pulses. Using a tunable beam at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory, neutrons were produced via thick-target breakup of 16 MeV deuterons on a beryllium target in the cyclotron vault. The breakup spectral shape was deduced from a dTOF measurement using an array of EJ-309 organic liquid scintillators. Simulation of the neutron detection efficiency of the scintillator array was performed using both GEANT4 and MCNP6. The efficiency-corrected spectral shape was normalized using a foil activation technique to obtain the energy-dependent flux of the neutron beam at zero degrees with respect to the incoming deuteron beam. The dTOF neutron spectrum was compared to spectra obtained using HEPROW and GRAVEL pulse height spectrum unfolding techniques. While the unfolding and dTOF results exhibit some discrepancies in shape, the integrated flux values agree within two standard deviations. This method obviates neutron time-of-flight spectroscopy challenges posed by pulsed beams with frame overlap and opens new opportunities for pulsed white neutron source facilities.

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.

2D IR Spectroscopy using Four-Wave Mixing, Pulse Shaping, and IR Upconversion: A Quantitative Comparison

PubMed Central

Rock, William; Li, Yun-Liang; Pagano, Philip; Cheatum, Christopher M.

2013-01-01

Recent technological advances have led to major changes in the apparatuses used to collect 2D IR spectra. Pulse shaping offers several advantages including rapid data collection, inherent phase stability, and phase cycling capabilities. Visible array detection via upconversion allows the use of visible detectors that are cheaper, faster, more sensitive, and less noisy than IR detectors. However, despite these advantages, many researchers are reluctant to implement these technologies. Here we present a quantitative study of the S/N of 2D IR spectra collected with a traditional four-wave mixing (FWM) apparatus, with a pulse shaping apparatus, and with visible detection via upconversion to address the question of whether or not weak chromophores at low concentrations are still accessible with such an apparatus. We find that the enhanced averaging capability of the pulse shaping apparatus enables the detection of small signals that would be challenging to measure even with the traditional FWM apparatus, and we demonstrate this ability on a sample of cyanylated dihydrofolate reductase (DHFR). PMID:23687988

An algorithm for charge-integration, pulse-shape discrimination and estimation of neutron/photon misclassification in organic scintillators

NASA Astrophysics Data System (ADS)

Polack, J. K.; Flaska, M.; Enqvist, A.; Sosa, C. S.; Lawrence, C. C.; Pozzi, S. A.

2015-09-01

Organic scintillators are frequently used for measurements that require sensitivity to both photons and fast neutrons because of their pulse shape discrimination capabilities. In these measurement scenarios, particle identification is commonly handled using the charge-integration pulse shape discrimination method. This method works particularly well for high-energy depositions, but is prone to misclassification for relatively low-energy depositions. A novel algorithm has been developed for automatically performing charge-integration pulse shape discrimination in a consistent and repeatable manner. The algorithm is able to estimate the photon and neutron misclassification corresponding to the calculated discrimination parameters, and is capable of doing so using only the information measured by a single organic scintillator. This paper describes the algorithm and assesses its performance by comparing algorithm-estimated misclassification to values computed via a more traditional time-of-flight estimation. A single data set was processed using four different low-energy thresholds: 40, 60, 90, and 120 keVee. Overall, the results compared well between the two methods; in most cases, the algorithm-estimated values fell within the uncertainties of the TOF-estimated values.

2-Shock layered tuning campaign

NASA Astrophysics Data System (ADS)

Masse, Laurent; Dittrich, T.; Khan, S.; Kyrala, G.; Ma, T.; MacLaren, S.; Ralph, J.; Salmonson, J.; Tipton, R.; Los Alamos Natl Lab Team; Lawrence Livermore Natl Lab Team

2016-10-01

The 2-Shock platform has been developed to maintain shell sphericity throughout the compression phase of an indirect-drive target implosion and produce a stagnating hot spot in a quasi 1D-like manner. A sub-scale, 1700 _m outer diameter, and thick, 200 _m, uniformly Silicon doped, gas-filled plastic capsule is driven inside a nominal size 5750 _m diameter ignition hohlraum. The hohlraum fill is near vacuum to reduce back-scatter and improve laser/drive coupling. A two-shock pulse of about 1 MJ of laser energy drives the capsule. The thick capsule prevents ablation front feed-through to the imploded core. This platform has demonstrated its efficiency to tune a predictable and reproducible 1-D implosion with a nearly round shape. It has been shown that the high foot performance was dominated by the local defect growth due to the ablation front instability and by the hohlraum radiation asymmetries. The idea here is to take advantage of this 2-Shock platform to design a 1D-like layered implosion and eliminates the deleterious effects of radiation asymmetries and ablation front instability growth. We present the design work and our first experimental results of this near one-dimensional 2-Shock layered design. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

Laser system using ultra-short laser pulses

DOEpatents

Dantus, Marcos [Okemos, MI; Lozovoy, Vadim V [Okemos, MI; Comstock, Matthew [Milford, MI

2009-10-27

A laser system using ultrashort laser pulses is provided. In another aspect of the present invention, the system includes a laser, pulse shaper and detection device. A further aspect of the present invention employs a femtosecond laser and binary pulse shaping (BPS). Still another aspect of the present invention uses a laser beam pulse, a pulse shaper and a SHG crystal.

Electron acceleration by laser produced wake field: Pulse shape effect

NASA Astrophysics Data System (ADS)

Malik, Hitendra K.; Kumar, Sandeep; Nishida, Yasushi

2007-12-01

Analytical expressions are obtained for the longitudinal field (wake field: Ex), density perturbations ( ne') and the potential ( ϕ) behind a laser pulse propagating in a plasma with the pulse duration of the electron plasma period. A feasibility study on the wake field is carried out with Gaussian-like (GL) pulse, rectangular-triangular (RT) pulse and rectangular-Gaussian (RG) pulse considering one-dimensional weakly nonlinear theory ( ne'/n0≪1), and the maximum energy gain acquired by an electron is calculated for all these three types of the laser pulse shapes. A comparative study infers that the RT pulse yields the best results: In its case maximum electron energy gain is 33.5 MeV for a 30 fs pulse duration whereas in case of GL (RG) pulse of the same duration the gain is 28.6 (28.8)MeV at the laser frequency of 1.6 PHz and the intensity of 3.0 × 10 18 W/m 2. The field of the wake and hence the energy gain get enhanced for the higher laser frequency, larger pulse duration and higher laser intensity for all types of the pulses.

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

PubMed Central

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

2018-01-01

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

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

PubMed

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

2018-01-01

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

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.

Anisotropy modulations of femtosecond laser pulse induced periodic surface structures on silicon by adjusting double pulse delay.

PubMed

Han, Weina; Jiang, Lan; Li, Xiaowei; Wang, Qingsong; Li, Hao; Lu, YongFeng

2014-06-30

We demonstrate that the polarization-dependent anisotropy of the laser-induced periodic surface structure (LIPSS) on silicon can be adjusted by designing a femtosecond laser pulse train (800 nm, 50 fs, 1 kHz). By varying the pulse delay from 100 to 1600 fs within a double pulse train to reduce the deposited pulse energy, which weakens the directional surface plasmon polarition (SPP)-laser energy coupling based on the initial formed ripple structure, the polarization-dependent geometrical morphology of the LIPSS evolves from a nearly isotropic circular shape to a somewhat elongated elliptical shape. Meanwhile, the controllable anisotropy of the two-dimensional scanned-line widths with different directions is achieved based on a certain pulse delay combined with the scanning speed. This can effectively realize better control over large-area uniform LIPSS formation. As an example, we further show that the large-area LIPSS can be formed with different scanning times under different pulse delays.

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.

Analysis of hybrid mode-locking of two-section quantum dot lasers operating at 1.5 microm.

PubMed

Heck, Martijn J R; Salumbides, Edcel J; Renault, Amandine; Bente, Erwin A J M; Oei, Yok-Siang; Smit, Meint K; van Veldhoven, René; Nötzel, Richard; Eikema, Kjeld S E; Ubachs, Wim

2009-09-28

For the first time a detailed study of hybrid mode-locking in two-section InAs/InP quantum dot Fabry-Pérot-type lasers is presented. The output pulses have a typical upchirp of approximately 8 ps/nm, leading to very elongated pulses. The mechanism leading to this typical pulse shape and the phase noise is investigated by detailed radio-frequency and optical spectral studies as well as time-domain studies. The pulse shaping mechanism in these lasers is found to be fundamentally different than the mechanism observed in conventional mode-locked laser diodes, based on quantum well gain or bulk material.

The Effects of Low Dose-Rate Ionizing Radiation on the Shapes of Transients in the LM124 Operational Amplifier

NASA Technical Reports Server (NTRS)

Buchner, Stephen; McMorrow, Dale; Roche, Nicholas; Dusseau, Laurent; Pease, Ron L.

2008-01-01

Shapes of single event transients (SETs) in a linear bipolar circuit (LM124) change with exposure to total ionizing dose (TID) radiation. SETs shape changes are a direct consequence of TID-induced degradation of bipolar transistor gain. A reduction in transistor gain causes a reduction in the drive current of the current sources in the circuit, and it is the lower drive current that most affects the shapes of large amplitude SETs.

Dynamics of shaping ultrashort optical dissipative solitary pulses in the actively mode-locked semiconductor laser with an external long-haul single-mode fiber cavity

NASA Astrophysics Data System (ADS)

Shcherbakov, Alexandre S.; Moreno Zarate, Pedro

2010-02-01

We describe the conditions of shaping regular trains of optical dissipative solitary pulses, excited by multi-pulse sequences of periodic modulating signals, in the actively mode-locked semiconductor laser heterostructure with an external long-haul single-mode silicon fiber exhibiting square-law dispersion, cubic Kerr nonlinearity, and linear optical losses. The presented model for the analysis includes three principal contributions associated with the modulated gain, optical losses, as well as linear and nonlinear phase shifts. In fact, the trains of optical dissipative solitary pulses appear within simultaneous presenting and a balance of mutually compensating interactions between the second-order dispersion and cubic-law Kerr nonlinearity as well as between active medium gain and linear optical losses in the combined cavity. Within such a model, a contribution of the nonlinear Ginzburg-Landau operator to shaping the parameters of optical dissipative solitary pulses is described via exploiting an approximate variational procedure involving the technique of trial functions. Finally, the results of the illustrating proof-of-principle experiments are briefly presented and discussed in terms of optical dissipative solitary pulses.

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.

Fast quantum logic gates with trapped-ion qubits

NASA Astrophysics Data System (ADS)

Schäfer, V. M.; Ballance, C. J.; Thirumalai, K.; Stephenson, L. J.; Ballance, T. G.; Steane, A. M.; Lucas, D. M.

2018-03-01

Quantum bits (qubits) based on individual trapped atomic ions are a promising technology for building a quantum computer. The elementary operations necessary to do so have been achieved with the required precision for some error-correction schemes. However, the essential two-qubit logic gate that is used to generate quantum entanglement has hitherto always been performed in an adiabatic regime (in which the gate is slow compared with the characteristic motional frequencies of the ions in the trap), resulting in logic speeds of the order of 10 kilohertz. There have been numerous proposals of methods for performing gates faster than this natural ‘speed limit’ of the trap. Here we implement one such method, which uses amplitude-shaped laser pulses to drive the motion of the ions along trajectories designed so that the gate operation is insensitive to the optical phase of the pulses. This enables fast (megahertz-rate) quantum logic that is robust to fluctuations in the optical phase, which would otherwise be an important source of experimental error. We demonstrate entanglement generation for gate times as short as 480 nanoseconds—less than a single oscillation period of an ion in the trap and eight orders of magnitude shorter than the memory coherence time measured in similar calcium-43 hyperfine qubits. The power of the method is most evident at intermediate timescales, at which it yields a gate error more than ten times lower than can be attained using conventional techniques; for example, we achieve a 1.6-microsecond-duration gate with a fidelity of 99.8 per cent. Faster and higher-fidelity gates are possible at the cost of greater laser intensity. The method requires only a single amplitude-shaped pulse and one pair of beams derived from a continuous-wave laser. It offers the prospect of combining the unrivalled coherence properties, operation fidelities and optical connectivity of trapped-ion qubits with the submicrosecond logic speeds that are usually associated with solid-state devices.

Fast quantum logic gates with trapped-ion qubits.

PubMed

Schäfer, V M; Ballance, C J; Thirumalai, K; Stephenson, L J; Ballance, T G; Steane, A M; Lucas, D M

2018-02-28

Quantum bits (qubits) based on individual trapped atomic ions are a promising technology for building a quantum computer. The elementary operations necessary to do so have been achieved with the required precision for some error-correction schemes. However, the essential two-qubit logic gate that is used to generate quantum entanglement has hitherto always been performed in an adiabatic regime (in which the gate is slow compared with the characteristic motional frequencies of the ions in the trap), resulting in logic speeds of the order of 10 kilohertz. There have been numerous proposals of methods for performing gates faster than this natural 'speed limit' of the trap. Here we implement one such method, which uses amplitude-shaped laser pulses to drive the motion of the ions along trajectories designed so that the gate operation is insensitive to the optical phase of the pulses. This enables fast (megahertz-rate) quantum logic that is robust to fluctuations in the optical phase, which would otherwise be an important source of experimental error. We demonstrate entanglement generation for gate times as short as 480 nanoseconds-less than a single oscillation period of an ion in the trap and eight orders of magnitude shorter than the memory coherence time measured in similar calcium-43 hyperfine qubits. The power of the method is most evident at intermediate timescales, at which it yields a gate error more than ten times lower than can be attained using conventional techniques; for example, we achieve a 1.6-microsecond-duration gate with a fidelity of 99.8 per cent. Faster and higher-fidelity gates are possible at the cost of greater laser intensity. The method requires only a single amplitude-shaped pulse and one pair of beams derived from a continuous-wave laser. It offers the prospect of combining the unrivalled coherence properties, operation fidelities and optical connectivity of trapped-ion qubits with the submicrosecond logic speeds that are usually associated with solid-state devices.

Performance of a Miniature Pulse Tube Cryocooler

NASA Astrophysics Data System (ADS)

Matsumoto, N.; Yasukawa, Y.; Ohshima, K.; Minematsu, S.; Takeuchi, T.; Yoshizawa, K.; Matsushita, T.; Mizoguchi, Y.

2006-04-01

Fuji Electric Group has developed a miniature pulse tube cryocooler (PTC) of U-shaped configuration with a specific cooling capacity of 2W at 70K and requiring 100W of electrical input power. The emphasis has been on compactness, light weight, high performance, high reliability and low cost. This PTC is for commercial applications: for example, semiconductivity and high temperature superconductivity (HTS) devices used in wireless telecommunication systems and imaging sensors. The dimensions of the PTC have been reduced to 246mm wide by 232mm high and a weight of 8.5kg as integral configurations. The linear compressor motor uses two sets of moving coils to drive twin pistons supported by flexure bearings in a dual opposed configuration. The phase shifter, consisting of an inertance tube and reservoir tank, has been optimized. We produced and tested a prototype reduced-cost PTC. The prototype has a cooling capacity greater than 2.5W at 70K with 100W of electrical input power. The vibration of the cold head is less than 2 micrometers (peak to peak) when the hot-end side flange of the expander is fixed. This paper describes in detail its performance including inclination and vibration.

Pulsed field probe of real time magnetization dynamics in magnetic nanoparticle systems

NASA Astrophysics Data System (ADS)

Foulkes, T.; Syed, M.; Taplin, T.

2015-05-01

Magnetic nanoparticles (MNPs) are extensively used in biotechnology. These applications rely on magnetic properties that are a keen function of MNP size, distribution, and shape. Various magneto-optical techniques, including Faraday Rotation (FR), Cotton-Mouton Effect, etc., have been employed to characterize magnetic properties of MNPs. Generally, these measurements employ AC or DC fields. In this work, we describe the results from a FR setup that uses pulsed magnetic fields and an analysis technique that makes use of the entire pulse shape to investigate size distribution and shape anisotropy. The setup employs a light source, polarizing components, and a detector that are used to measure the rotation of light from a sample that is subjected to a pulsed magnetic field. This magnetic field "snapshot" is recorded alongside the intensity pulse of the sample's response. This side by side comparison yields useful information about the real time magnetization dynamics of the system being probed. The setup is highly flexible with variable control of pulse length and peak magnitude. Examining the raw data for the response of bare Fe3O4 and hybrid Au and Fe3O4 nanorods reveals interesting information about Brownian relaxation and the hydrodynamic size of these nanorods. This analysis exploits the self-referencing nature of this measurement to highlight the impact of an applied field on creating a field induced transparency for a longitudinal measurement. Possible sources for this behavior include shape anisotropy and field assisted aggregate formation.

Lithotripsy Performance of Specially Designed Laser Fiber Tips.

PubMed

Kronenberg, Peter; Traxer, Olivier

2016-05-01

We evaluated and compared a standard laser lithotripsy fiber to laser fibers claimed to have lithotripsy performance enhancing features. A special AccuMax™ 200 polished tip fiber and an AccuTrac™ ball-shaped tip fiber, each with an approximately 240 μm core, were compared to a standard 272 μm core fiber (Rocamed™). The polished and ball-shaped tip fibers were used and reused without preparation. The standard fiber was stripped and cleaved according to manufacturer instructions after each experiment. An automated laser fragmentation testing system was used to perform multiple 30-second laser lithotripsy experiments. To mimic most typical lithotripsy conditions soft and hard stone materials were used with high frequency, low pulse energy (20 Hz and 0.5 J) or with low frequency, high pulse energy (5 Hz and 2.0 J) lithotripter settings. Ablation volumes and laser fiber tip photographs before and after lithotripsy were compared. The standard and ball-shaped tip fibers did not differ in ablation volume (p = 0.72) but they ablated 174% and 188% more stone, respectively, than the polished tip fiber (p <0.0001). The ball-shaped tip showed remarkable fiber tip degradation after short-term use at low frequency, high pulse energy settings. When high pulse energy settings were applied first even for short-term use, the ablation volume achieved by the polished and ball-shaped tip fibers at high frequency, low pulse energy settings decreased more than 20%. The standard laser fiber was as good as and sometimes better than the specially designed fibers. Rapid degradation of the specially designed laser fiber tips strongly limits their general usefulness but ball-shaped tip fibers may be useful in specific situations. Copyright © 2016 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Green synthesis of gold nanoparticles of different sizes and shapes using agar-agar water solution and femtosecond pulse laser irradiation

NASA Astrophysics Data System (ADS)

Almeida de Matos, Ricardo; da Silva Cordeiro, Thiago; Elgul Samad, Ricardo; Dias Vieira, Nilson; Coronato Courrol, Lilia

2012-11-01

We report a method to create gold nanoparticles of different sizes and shapes using agar-agar water solution and irradiation with light from a xenon lamp, followed by ultrashort laser pulses. No additives, such as solvents, surfactants or reducing agents, were used in the procedure. Laser irradiation (laser ablation) was important to the reduction of the nanoparticles diameter and formation of another shapes. Distilled water was used as solvent and agar-agar (hydrophilic colloid extracted from certain seaweeds) was important for the stabilization of gold nanoparticles, avoiding their agglomeration. The formation of gold nanoparticles was confirmed with ultraviolet-visible absorption and TEM microscopy. The gold nanoparticles acquired spherical, prism, and rod shapes depending on the laser parameters. Variation of laser irradiation parameters as pulse energy, irradiation time and repetition rate was assessed. The relevant mechanisms contributing for the gold nanoparticles production are discussed.

Electron beam switched discharge for rapidly pulsed lasers

DOEpatents

Pleasance, Lyn D.; Murray, John R.; Goldhar, Julius; Bradley, Laird P.

1981-01-01

Method and apparatus for electrical excitation of a laser gas by application of a pulsed voltage across the gas, followed by passage of a pulsed, high energy electron beam through the gas to initiate a discharge suitable for laser excitation. This method improves upon current power conditioning techniques and is especially useful for driving rare gas halide lasers at high repetition rates.

MeV electron acceleration at 1kHz with <10 mJ laser pulses

NASA Astrophysics Data System (ADS)

Salehi, Fatholah; Goers, Andy; Hine, George; Feder, Linus; Kuk, Donghoon; Kim, Ki-Yong; Milchberg, Howard

2016-10-01

We demonstrate laser driven acceleration of electrons at 1 kHz repetition rate with pC charge above 1MeV per shot using < 10 mJ pulse energies focused on a near-critical density He or H2 gas jet. Using the H2 gas jet, electron acceleration to 0.5 MeV in 10 fC bunches was observed with laser pulse energy as low as 1.3mJ . Using a near-critical density gas jet sets the critical power required for relativistic self-focusing low enough for mJ scale laser pulses to self- focus and drive strong wakefields. Experiments and particle-in-cell simulations show that optimal drive pulse duration and chirp for maximum electron bunch charge and energy depends on the target gas species. High repetition rate, high charge, and short duration electron bunches driven by very modest pulse energies constitutes an ideal portable electron source for applications such as ultrafast electron diffraction experiments and high rep. rate γ-ray production. This work is supported by the US Department of Energy, the National Science Foundation, and the Air Force Office of Scientific Research.

Overview of Initial NSTX-U Experimental Operations

NASA Astrophysics Data System (ADS)

Battaglia, Devon; the NSTX-U Team

2016-10-01

Initial operation of the National Spherical Torus Experiment Upgrade (NSTX-U) has satisfied a number of commissioning milestones, including demonstration of discharges that exceed the field and pulse length of NSTX. ELMy H-mode operation at the no-wall βN limit is obtained with Boronized wall conditioning. Peak H-mode parameters include: Ip = 1 MA, BT0 = 0.63 T, WMHD = 330 kJ, βN = 4, βN/li = 6, κ = 2.3, τE , tot >50 ms. Access to high-performance H-mode scenarios with long MHD-quiescent periods is enabled by the resilient timing of the L-H transition via feedback control of the diverting time and shape, and correction of the dominant n =1 error fields during the Ip ramp. Stationary L-mode discharges have been realized up to 1 MA with 2 s discharges achieved at Ip = 650 kA. The long-pulse L-mode discharges enabled by the new central solenoid supported initial experiments on error field measurements and correction, plasma shape control, controlled discharge ramp-down, L-mode transport and fast ion physics. Increased off-axis current drive and reduction of fast ion instabilities has been observed with the new, more tangential neutral beamline. The initial results support that access to increased field, current and heating at low-aspect-ratio expands the regimes available to develop scenarios, diagnostics and predictive models that inform the design and optimization of future burning plasma tokamak devices, including ITER. Work Supported by U.S. DOE Contract No. DE-AC02-09CH11466.

Mode-locked thin-disk lasers and their potential application for high-power terahertz generation

NASA Astrophysics Data System (ADS)

Saraceno, Clara J.

2018-04-01

The progress achieved in the last few decades in the performance of ultrafast laser systems with high average power has been tremendous, and continues to provide momentum to new exciting applications, both in scientific research and technology. Among the various technological advances that have shaped this progress, mode-locked thin-disk oscillators have attracted significant attention as a unique technology capable of providing ultrashort pulses with high energy (tens to hundreds of microjoules) and at very high repetition rates (in the megahertz regime) from a single table-top oscillator. This technology opens the door to compact high repetition rate ultrafast sources spanning the entire electromagnetic spectrum from the XUV to the terahertz regime, opening various new application fields. In this article, we focus on their unexplored potential as compact driving sources for high average power terahertz generation.

Design and performance evaluation of a dispersion compensation unit using several chirping functions in a tanh apodized FBG and comparison with dispersion compensation fiber.

PubMed

Mohammed, Nazmi A; Solaiman, Mohammad; Aly, Moustafa H

2014-10-10

In this work, various dispersion compensation methods are designed and evaluated to search for a cost-effective technique with remarkable dispersion compensation and a good pulse shape. The techniques consist of different chirp functions applied to a tanh fiber Bragg grating (FBG), a dispersion compensation fiber (DCF), and a DCF merged with an optimized linearly chirped tanh FBG (joint technique). The techniques are evaluated using a standard 10 Gb/s optical link over a 100 km long haul. The linear chirp function is the most appropriate choice of chirping function, with a pulse width reduction percentage (PWRP) of 75.15%, lower price, and poor pulse shape. The DCF yields an enhanced PWRP of 93.34% with a better pulse quality; however, it is the most costly of the evaluated techniques. Finally, the joint technique achieved the optimum PWRP (96.36%) among all the evaluated techniques and exhibited a remarkable pulse shape; it is less costly than the DCF, but more expensive than the chirped tanh FBG.

Excitation of atoms and ions in plasmas by ultra-short electromagnetic pulses

NASA Astrophysics Data System (ADS)

Astapenko, V. A.; Sakhno, S. V.; Svita, S. Yu; Lisitsa, V. S.

2017-02-01

The problem of atoms and ions diagnostics in rarefied and dense plasmas by ultrashort laser pulses (USP) is under consideration. The application of USP provides: 1) excitation from ground states due to their carrier frequency high enough, 2) penetration into optically dense media due to short pulses duration. The excitation from ground atomic states increases sharply populations of excited atomic states in contrast with standard laser induced fluorescence spectroscopy based on radiative transitions between excited atomic states. New broadening parameter in radiation absorption, namely inverse pulse duration time 1/τ appears in addition to standard line-shape width in the profile G(ω). The Lyman-beta absorption spectra for USP are calculated for Holtsmark static broadening mechanism. Excitation of highly charged H-like ions in hot plasmas is described by both Gaussian shapes for Doppler broadening and pulse spectrum resulting in analytical absorption line-shape. USP penetration into optically thick media and corresponding excitation probability are calculated. It is shown a great effect of USP duration on excitation probabilities in optically thick media. The typical situations for plasma diagnostics by USP are discussed in details.

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

PubMed

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

2015-09-01

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

Carrier-envelope phase-stabilized attosecond pulses from asymmetric molecules

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

Lan Pengfei; Lu Peixiang; Cao Wei

2007-08-15

High-order harmonic generation from asymmetric molecules is investigated, and the concept of phase-stabilized infrared ultrashort laser pulses is extended to the extreme ultraviolet regime. It is shown that the ionization symmetry in consecutive half optical cycles is broken for asymmetric molecules, and both even and odd harmonics with comparable intensity are produced. In the time domain, only one attosecond pulse is generated in each cycle of the driving field, and the carrier-envelope phases of the attosecond pulses are equal. Consequently, a clean attosecond pulse train with the same carrier-envelope phase from pulse to pulse is obtained in the extreme ultravioletmore » regime.« less

Spatiotemporal optical pulse transformation by a resonant diffraction grating

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

Golovastikov, N. V.; Bykov, D. A., E-mail: bykovd@gmail.com; Doskolovich, L. L., E-mail: leonid@smr.ru

The diffraction of a spatiotemporal optical pulse by a resonant diffraction grating is considered. The pulse diffraction is described in terms of the signal (the spatiotemporal incident pulse envelope) passage through a linear system. An analytic approximation in the form of a rational function of two variables corresponding to the angular and spatial frequencies has been obtained for the transfer function of the system. A hyperbolic partial differential equation describing the general form of the incident pulse envelope transformation upon diffraction by a resonant diffraction grating has been derived from the transfer function. A solution of this equation has beenmore » obtained for the case of normal incidence of a pulse with a central frequency lying near the guided-mode resonance of a diffraction structure. The presented results of numerical simulations of pulse diffraction by a resonant grating show profound changes in the pulse envelope shape that closely correspond to the proposed theoretical description. The results of the paper can be applied in creating new devices for optical pulse shape transformation, in optical information processing problems, and analog optical computations.« less

Principal Component Analysis for pulse-shape discrimination of scintillation radiation detectors

NASA Astrophysics Data System (ADS)

Alharbi, T.

2016-01-01

In this paper, we report on the application of Principal Component analysis (PCA) for pulse-shape discrimination (PSD) of scintillation radiation detectors. The details of the method are described and the performance of the method is experimentally examined by discriminating between neutrons and gamma-rays with a liquid scintillation detector in a mixed radiation field. The performance of the method is also compared against that of the conventional charge-comparison method, demonstrating the superior performance of the method particularly at low light output range. PCA analysis has the important advantage of automatic extraction of the pulse-shape characteristics which makes the PSD method directly applicable to various scintillation detectors without the need for the adjustment of a PSD parameter.

Laser imprint reduction for the critical-density foam buffered target driven by a relatively strong foot pulse at early stage of laser implosions

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

Li, J. W., E-mail: li-jiwei@iapcm.ac.cn; He, X. T.; Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100094

In order to reduce the effect of laser imprint in direct-drive ignition scheme a low-density foam buffered target has been proposed. This target is driven by a laser pulse with a low-intensity foot at the early stage of implosion, which heats the foam and elongates the thermal conduction zone between the laser absorption region and ablation front, increasing the thermal smoothing effect. In this paper, a relatively strong foot pulse is adopted to irradiate the critical-density foam buffered target. The stronger foot, near 1 × 10{sup 14 }W/cm{sup 2}, is able to drive a radiative shock in the low-density foam, which helps smoothmore » the shock and further reduce the effect of laser imprint. The radiative shock also forms a double ablation front structure between the two ablation fronts to further stabilize the hydrodynamics, achieving the similar results to a target with a high-Z dopant in the ablator. 2D analysis shows that for the critical-density foam buffered target irradiated by the strong foot pulse, the laser imprint can be reduced due to the radiative shock in the foam and an increased thermal smoothing effect. It seems viable for the critical-density foam buffered target to be driven by a relatively strong foot pulse with the goal of reducing the laser imprint and achieving better implosion symmetry in the direct-drive laser fusion.« less

High-rep-rate Thomson scattering for LHD

NASA Astrophysics Data System (ADS)

den Hartog, D. J.; Borchardt, M. T.; Holly, D. J.; Schmitz, O.; Yasuhara, R.; Yamada, I.; Funaba, H.; Osakabe, M.; Morisaki, T.

2017-10-01

A high-rep-rate pulse-burst laser system is being built for the LHD Thomson scattering (TS) diagnostic. This laser will have two operating scenarios, a fast-burst sequence of 15 kHz rep rate for at least 15 ms, and a slow-burst sequence of 1 kHz for at least 50 ms. There will be substantial flexibility in burst sequences for tailoring to experimental requirements. This new laser system will operate alongside the existing lasers in the LHD TS diagnostic, and will use the same beamline. This increase in temporal resolution capability complements the high spatial resolution (144 points) of the LHD TS diagnostic, providing unique measurement capability unmatched on any other fusion experiment. The new pulse-burst laser is a straightforward application of technology developed at UW-Madison, consisting of a Nd:YAG laser head with modular flashlamp drive units and a customized control system. Variable pulse-width drive of the flashlamps is accomplished by IGBT (insulated gate bipolar transistor) switching of electrolytic capacitor banks. Direct control of the laser Pockels cell drive enables optimal pulse energy extraction, producing >1.5 J q-switched pulses with 20 ns FWHM. Burst operation of this laser system will be used to capture fast time evolution of the electron temperature and density profiles during events such as ELMs, RMP perturbations, and various MHD modes. This work is supported by the U. S. Department of Energy and the National Institute for Fusion Science (Japan).

Coherent control of the formation of cold heteronuclear molecules by photoassociation

NASA Astrophysics Data System (ADS)

de Lima, Emanuel F.

2017-01-01

We consider the formation of cold diatomic molecules in the electronic ground state by photoassociation of atoms of dissimilar species. A combination of two transition pathways from the free colliding pair of atoms to a bound vibrational level of the electronic molecular ground state is envisioned. The first pathway consists of a pump-dump scheme with two time-delayed laser pulses in the near-infrared frequency domain. The pump pulse drives the transition to a bound vibrational level of an excited electronic state, while the dump pulse transfers the population to a bound vibrational level of the electronic ground state. The second pathway takes advantage of the existing permanent dipole moment and employs a single pulse in the far-infrared domain to drive the transition from the unbound atoms directly to a bound vibrational level in the electronic ground state. We show that this scheme offers the possibility to coherently control the photoassociation yield by manipulating the relative phase and timing of the pulses. The photoassociation mechanism is illustrated for the formation of cold LiCs molecules.

Signatures of asymmetry in neutron spectra and images predicted by three-dimensional radiation hydrodynamics simulations of indirect drive implosions

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

Chittenden, J. P., E-mail: j.chittenden@imperial.ac.uk; Appelbe, B. D.; Manke, F.

2016-05-15

We present the results of 3D simulations of indirect drive inertial confinement fusion capsules driven by the “high-foot” radiation pulse on the National Ignition Facility. The results are post-processed using a semi-deterministic ray tracing model to generate synthetic deuterium-tritium (DT) and deuterium-deuterium (DD) neutron spectra as well as primary and down scattered neutron images. Results with low-mode asymmetries are used to estimate the magnitude of anisotropy in the neutron spectra shift, width, and shape. Comparisons of primary and down scattered images highlight the lack of alignment between the neutron sources, scatter sites, and detector plane, which limits the ability tomore » infer the ρr of the fuel from a down scattered ratio. Further calculations use high bandwidth multi-mode perturbations to induce multiple short scale length flows in the hotspot. The results indicate that the effect of fluid velocity is to produce a DT neutron spectrum with an apparently higher temperature than that inferred from the DD spectrum and which is also higher than the temperature implied by the DT to DD yield ratio.« less

Quantum coherence in photo-ionisation with tailored XUV pulses

NASA Astrophysics Data System (ADS)

Carlström, Stefanos; Mauritsson, Johan; Schafer, Kenneth J.; L'Huillier, Anne; Gisselbrecht, Mathieu

2018-01-01

Ionisation with ultrashort pulses in the extreme ultraviolet (XUV) regime can be used to prepare an ion in a superposition of spin-orbit substates. In this work, we study the coherence properties of such a superposition, created by ionising xenon atoms using two phase-locked XUV pulses at different frequencies. In general, if the duration of the driving pulse exceeds the quantum beat period, dephasing will occur. If however, the frequency difference of the two pulses matches the spin-orbit splitting, the coherence can be efficiently increased and dephasing does not occur.

Low-noise pulse conditioner

DOEpatents

Bird, David A.

1983-01-01

A low-noise pulse conditioner is provided for driving electronic digital processing circuitry directly from differentially induced input pulses. The circuit uses a unique differential-to-peak detector circuit to generate a dynamic reference signal proportional to the input peak voltage. The input pulses are compared with the reference signal in an input network which operates in full differential mode with only a passive input filter. This reduces the introduction of circuit-induced noise, or jitter, generated in ground referenced input elements normally used in pulse conditioning circuits, especially speed transducer processing circuits.

Pulse-height defect due to electron interaction in dead layers of Ge/Li/ gamma-ray detectors

NASA Technical Reports Server (NTRS)

Larsen, R. N.; Strauss, M. G.

1969-01-01

Study shows the pulse-height degradation of gamma ray spectra in germanium/lithium detectors to be due to electron interaction in the dead layers that exist in all semiconductor detectors. A pulse shape discrimination technique identifies and eliminates these defective pulses.

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.

LASER BIOLOGY AND MEDICINE: Arterial pulse shape measurement using self-mixing effect in a diode laser

NASA Astrophysics Data System (ADS)

Hast, J.; Myllylä, Risto; Sorvoja, H.; Miettinen, J.

2002-11-01

The self-mixing effect in a diode laser and the Doppler technique are used for quantitative measurements of the cardiovascular pulses from radial arteries of human individuals. 738 cardiovascular pulses from 10 healthy volunteers were studied. The Doppler spectrograms reconstructed from the Doppler signal, which is measured from the radial displacement of the radial artery, are compared to the first derivative of the blood pressure signals measured from the middle finger by the Penaz technique. The mean correlation coefficient between the Doppler spectrograms and the first derivative of the blood pressure signals was 0.84, with a standard deviation of 0.05. Pulses with the correlation coefficient less than 0.7 were neglected in the study. Percentage of successfully detected pulses was 95.7%. It is shown that cardiovascular pulse shape from the radial artery can be measured noninvasively by using the self-mixing interferometry.

Control of retinal isomerization in bacteriorhodopsin in the high-intensity regime

PubMed Central

Florean, Andrei C.; Cardoza, David; White, James L.; Lanyi, J. K.; Sension, Roseanne J.; Bucksbaum, Philip H.

2009-01-01

A learning algorithm was used to manipulate optical pulse shapes and optimize retinal isomerization in bacteriorhodopsin, for excitation levels up to 1.8 × 1016 photons per square centimeter. Below 1/3 the maximum excitation level, the yield was not sensitive to pulse shape. Above this level the learning algorithm found that a Fourier-transform-limited (TL) pulse maximized the 13-cis population. For this optimal pulse the yield increases linearly with intensity well beyond the saturation of the first excited state. To understand these results we performed systematic searches varying the chirp and energy of the pump pulses while monitoring the isomerization yield. The results are interpreted including the influence of 1-photon and multiphoton transitions. The population dynamics in each intermediate conformation and the final branching ratio between the all-trans and 13-cis isomers are modified by changes in the pulse energy and duration. PMID:19564608

Optimal control of the strong-field ionization of silver clusters in helium droplets

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

Truong, N. X.; Goede, S.; Przystawik, A.

Optimal control techniques combined with femtosecond laser pulse shaping are applied to steer and enhance the strong-field induced emission of highly charged atomic ions from silver clusters embedded in helium nanodroplets. With light fields shaped in amplitude and phase we observe a substantial increase of the Ag{sup q+} yield for q>10 when compared to bandwidth-limited and optimally stretched pulses. A remarkably simple double-pulse structure, containing a low-intensity prepulse and a stronger main pulse, turns out to produce the highest atomic charge states up to Ag{sup 20+}. A negative chirp during the main pulse hints at dynamic frequency locking to themore » cluster plasmon. A numerical optimal control study on pure silver clusters with a nanoplasma model converges to a similar pulse structure and corroborates that the optimal light field adapts to the resonant excitation of cluster surface plasmons for efficient ionization.« less

Tapered pulse tube for pulse tube refrigerators

DOEpatents

Swift, Gregory W.; Olson, Jeffrey R.

1999-01-01

Thermal insulation of the pulse tube in a pulse-tube refrigerator is maintained by optimally varying the radius of the pulse tube to suppress convective heat loss from mass flux streaming in the pulse tube. A simple cone with an optimum taper angle will often provide sufficient improvement. Alternatively, the pulse tube radius r as a function of axial position x can be shaped with r(x) such that streaming is optimally suppressed at each x.

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.

Effect of a target on the stimulated emission of microsecond CO2-laser pulses

NASA Astrophysics Data System (ADS)

Baranov, V. Iu.; Dolgov, V. A.; Maliuta, D. D.; Mezhevov, V. S.; Semak, V. V.

1987-12-01

The paper reports a change in the pulse shape of a TEA CO2 laser with an unstable cavity under the interaction between the laser radiation and a metal surface in the presence of a breakdown plasma. It is shown that a continuous change in the phase difference between the wave reflected in the cavity and the principal cavity wave gives rise to changes in the pulse shape and the appearance of power fluctuations. The possible effect of these phenomena on the laser treatment of materials is considered.

High-energy 100-ns single-frequency all-fiber laser at 1064 nm

NASA Astrophysics Data System (ADS)

Fu, Shijie; Shi, Wei; Tang, Zhao; Shi, Chaodu; Bai, Xiaolei; Sheng, Quan; Chavez-Pirson, Arturo; Peyghambarian, N.; Yao, Jianquan

2018-02-01

A high-energy, single-frequency fiber laser with long pulse duration of 100 ns has been experimentally investigated in an all-fiber architecture. Only 34-cm long heavily Yb-doped phosphate fiber was employed in power scaling stage to efficiently suppress the Stimulated Brillouin effect (SBS). In the experiment, 0.47 mJ single pulse energy was achieved in power scaling stage at the pump power of 16 W. The pre-shaped pulse was gradually broadened from 103 to 140 ns during the amplification without shape distortion.

Hunting the Dark Matter with DEAP/CLEAN

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

Giuliani, F.

2010-02-10

The potential of the DEAP/CLEAN program for direct Dark Matter detection to test various dark matter models is illustrated. The scintillation pulse of a noble liquid like Argon or Neon has two well distinguished time constants allowing a very reliable correlation between pulse shape and type of event. This pulse shape discrimination already provides the power of rejecting a background10{sup 8}-10{sup 9} times larger than the signal. MiniCLEAN, a 500 kg LAr detector, is currently under construction, and a 3.6 ton detector, DEAP-3600, under development.

Microwave detector

DOEpatents

Meldner, Heiner W.; Cusson, Ronald Y.; Johnson, Ray M.

1986-01-01

A microwave detector (10) is provided for measuring the envelope shape of a microwave pulse comprised of high-frequency oscillations. A biased ferrite (26, 28) produces a magnetization field flux that links a B-dot loop (16, 20). The magnetic field of the microwave pulse participates in the formation of the magnetization field flux. High-frequency insensitive means (18, 22) are provided for measuring electric voltage or current induced in the B-dot loop. The recorded output of the detector is proportional to the time derivative of the square of the envelope shape of the microwave pulse.

Experimental study on Response Parameters of Ni-rich NiTi Shape Memory Alloy during Wire Electric Discharge Machining

NASA Astrophysics Data System (ADS)

Bisaria, Himanshu; Shandilya, Pragya

2018-03-01

Nowadays NiTi SMAs are gaining more prominence due to their unique properties such as superelasticity, shape memory effect, high fatigue strength and many other enriched physical and mechanical properties. The current studies explore the effect of machining parameters namely, peak current (Ip), pulse off time (TOFF), and pulse on time (TON) on wire wear ratio (WWR), and dimensional deviation (DD) in WEDM. It was found that high discharge energy was mainly ascribed to high WWR and DD. The WWR and DD increased with the increase in pulse on time and peak current whereas high pulse off time was favourable for low WWR and DD.

Time-resolved gamma spectroscopy of single events

NASA Astrophysics Data System (ADS)

Wolszczak, W.; Dorenbos, P.

2018-04-01

In this article we present a method of characterizing scintillating materials by digitization of each individual scintillation pulse followed by digital signal processing. With this technique it is possible to measure the pulse shape and the energy of an absorbed gamma photon on an event-by-event basis. In contrast to time-correlated single photon counting technique, the digital approach provides a faster measurement, an active noise suppression, and enables characterization of scintillation pulses simultaneously in two domains: time and energy. We applied this method to study the pulse shape change of a CsI(Tl) scintillator with energy of gamma excitation. We confirmed previously published results and revealed new details of the phenomenon.

Pulse Shape Analysis and Discrimination for Silicon-Photomultipliers in Helium-4 Gas Scintillation Neutron Detector

NASA Astrophysics Data System (ADS)

Barker, Cathleen; Zhu, Ting; Rolison, Lucas; Kiff, Scott; Jordan, Kelly; Enqvist, Andreas

2018-01-01

Using natural helium (helium-4), the Arktis 180-bar pressurized gas scintillator is capable of detecting and distinguishing fast neutrons and gammas. The detector has a unique design of three optically separated segments in which 12 silicon-photomultiplier (SiPM) pairs are positioned equilaterally across the detector to allow for them to be fully immersed in the helium-4 gas volume; consequently, no additional optical interfaces are necessary. The SiPM signals were amplified, shaped, and readout by an analog board; a 250 MHz, 14-bit digitizer was used to examine the output pulses from each SiPMpair channel. The SiPM over-voltage had to be adjusted in order to reduce pulse clipping and negative overshoot, which was observed for events with high scintillation production. Pulse shaped discrimination (PSD) was conducted by evaluating three different parameters: time over threshold (TOT), pulse amplitude, and pulse integral. In order to differentiate high and low energy events, a 30ns gate window was implemented to group pulses from two SiPM channels or more for the calculation of TOT. It was demonstrated that pulses from a single SiPM channel within the 30ns window corresponded to low-energy gamma events while groups of pulses from two-channels or more were most likely neutron events. Due to gamma pulses having lower pulse amplitude, the percentage of measured gamma also depends on the threshold value in TOT calculations. Similarly, the threshold values were varied for the optimal PSD methods of using pulse amplitude and pulse area parameters. Helium-4 detectors equipped with SiPMs are excellent for in-the-field radiation measurement of nuclear spent fuel casks. With optimized PSD methods, the goal of developing a fuel cask content monitoring and inspection system based on these helium-4 detectors will be achieved.

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.

Waveform agile high-power fiber laser illuminators for directed-energy weapon systems

NASA Astrophysics Data System (ADS)

Engin, Doruk; Lu, Wei; Kimpel, Frank; Gupta, Shantanu

2012-06-01

A kW-class fiber-amplifier based laser illuminator system at 1030nm is demonstrated. At 125 kHz pulse repetition rate, 1.9mJ energy per pulse (235W average power) is achieved for 100nsec pulses with >72% optical conversion efficiency, and at 250kHz repetition, >350W average power is demonstrated, limited by the available pumps. Excellent agreement is established between the experimental results and dynamic fiber amplifier simulation, for predicting the pulse shape, spectrum and ASE accumulation throughout the fiber-amplifier chain. High pulse-energy, high power fiber-amplifier operation requires careful engineering - minimize ASE content throughout the pre-amplifier stages, use of large mode area gain fiber in the final power stage for effective pulse energy extraction, and pulse pre-shaping to compensate for the laser gain-saturation induced intra-pulse and pulse-pattern dependent distortion. Such optimization using commercially available (VLMA) fibers with core size in the 30-40μm range is estimated to lead to >4mJ pulse energy for 100nsec pulse at 50kHz repetition rate. Such waveform agile high-power, high-energy pulsed fiber laser illuminators at λ=1030nm satisfies requirements for active-tracking/ranging in high-energy laser (HEL) weapon systems, and in uplink laser beacon for deep space communication.

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

Wavelength Dependence of Nanosecond IR Laser-Induced Breakdown in Water: Evidence for Multiphoton Initiation via an Intermediate State

DTIC Science & Technology

2015-04-29

bubble generation and shock wave emission in water for femtosecond to nanosecond laser pulses . ...breakdown threshold in water for nanosecond (ns) IR laser pulses . Avalanche ionization (AI) is the most powerful mechanism driving IR ns laser-induced...acknowledged that femtosecond (fs) and picosecond (ps) IR breakdown is initiated by photoionization because ultrashort pulses are sufficiently

Electron beam-switched discharge for rapidly pulsed lasers

DOEpatents

Pleasance, L.D.; Murray, J.R.; Goldhar, J.; Bradley, L.P.

1979-12-11

A method and apparatus are designed for electrical excitation of a laser gas by application of a pulsed voltage across the gas, followed by passage of a pulsed, high energy electron beam through the gas to initiate a discharge suitable for laser excitation. This method improves upon current power conditioning techniques and is especially useful for driving rare gas halide lasers at high repetition rates.

Efficient and precise calculation of the b-matrix elements in diffusion-weighted imaging pulse sequences.

PubMed

Zubkov, Mikhail; Stait-Gardner, Timothy; Price, William S

2014-06-01

Precise NMR diffusion measurements require detailed knowledge of the cumulative dephasing effect caused by the numerous gradient pulses present in most NMR pulse sequences. This effect, which ultimately manifests itself as the diffusion-related NMR signal attenuation, is usually described by the b-value or the b-matrix in the case of multidirectional diffusion weighting, the latter being common in diffusion-weighted NMR imaging. Neglecting some of the gradient pulses introduces an error in the calculated diffusion coefficient reaching in some cases 100% of the expected value. Therefore, ensuring the b-matrix calculation includes all the known gradient pulses leads to significant error reduction. Calculation of the b-matrix for simple gradient waveforms is rather straightforward, yet it grows cumbersome when complexly shaped and/or numerous gradient pulses are introduced. Making three broad assumptions about the gradient pulse arrangement in a sequence results in an efficient framework for calculation of b-matrices as well providing some insight into optimal gradient pulse placement. The framework allows accounting for the diffusion-sensitising effect of complexly shaped gradient waveforms with modest computational time and power. This is achieved by using the b-matrix elements of the simple unmodified pulse sequence and minimising the integration of the complexly shaped gradient waveform in the modified sequence. Such re-evaluation of the b-matrix elements retains all the analytical relevance of the straightforward approach, yet at least halves the amount of symbolic integration required. The application of the framework is demonstrated with the evaluation of the expression describing the diffusion-sensitizing effect, caused by different bipolar gradient pulse modules. Copyright © 2014 Elsevier Inc. All rights reserved.

A triple-crystal phoswich detector with digital pulse shape discrimination for alpha/beta/gamma spectroscopy

NASA Astrophysics Data System (ADS)

White, Travis L.; Miller, William H.

1999-02-01

Researchers at the University of Missouri - Columbia have developed a three-crystal phoswich detector coupled to a digital pulse shape discrimination system for use in alpha/beta/gamma spectroscopy. Phoswich detectors use a sandwich of scintillators viewed by a single photomultiplier tube to simultaneously detect multiple types of radiation. Separation of radiation types is based upon pulse shape difference among the phosphors, which has historically been performed with analog circuitry. The system uses a GaGe CompuScope 1012, 12 bit, 10 MHz computer-based oscilloscope that digitally captures the pulses from a phoswich detector and subsequently performs pulse shape discrimination with cross-correlation analysis. The detector, based partially on previous phoswich designs by Usuda et al., uses a 10 mg/cm 2 thick layer of ZnS(Ag) for alpha detection, followed by a 0.254 cm CaF 2(Eu) crystal for beta detection, all backed by a 2.54 cm NaI(Tl) crystal for gamma detection. Individual energy spectra and count rate information for all three radiation types are displayed and updated periodically. The system shows excellent charged particle discrimination with an accuracy of greater than 99%. Future development will include a large area beta probe with gamma-ray discrimination, systems for low-energy photon detection (e.g. Bremsstrahlung or keV-range photon emissions), and other health physics instrumentation.

Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus.

PubMed

Giacomelli, L; Conroy, S; Gorini, G; Horton, L; Murari, A; Popovichev, S; Syme, D B

2014-02-01

The Joint European Torus (JET, Culham, UK) is the largest tokamak in the world devoted to nuclear fusion experiments of magnetic confined Deuterium (D)/Deuterium-Tritium (DT) plasmas. Neutrons produced in these plasmas are measured using various types of neutron detectors and spectrometers. Two of these instruments on JET make use of organic liquid scintillator detectors. The neutron emission profile monitor implements 19 liquid scintillation counters to detect the 2.45 MeV neutron emission from D plasmas. A new compact neutron spectrometer is operational at JET since 2010 to measure the neutron energy spectra from both D and DT plasmas. Liquid scintillation detectors are sensitive to both neutron and gamma radiation but give light responses of different decay time such that pulse shape discrimination techniques can be applied to identify the neutron contribution of interest from the data. The most common technique consists of integrating the radiation pulse shapes within different ranges of their rising and/or trailing edges. In this article, a step forward in this type of analysis is presented. The method applies a tomographic analysis of the 3-dimensional neutron and gamma pulse shape and pulse height distribution data obtained from liquid scintillation detectors such that n/γ discrimination can be improved to lower energies and additional information can be gained on neutron contributions to the gamma events and vice versa.

Group velocity of the light pulse in an open V-type system

NASA Astrophysics Data System (ADS)

Li, Jingjuan; Fan, Xijun; Tian, Shufen; Liu, Chengpu; Gong, Shangqing; Xu, Zhizhan

2007-04-01

We investigate the group velocity of the probe light pulse in an open V-type system with spontaneously generated coherence. We find that, not only varying the relative phase between the probe and driving pulses can but varying the atomic exit rate or incoherent pumping rate also can manipulate dramatically the group velocity, even make the pulse propagation switching from subluminal to superluminal; the subliminal propagation can be companied with gain or absorption, but the superluminal propagation is always companied with absorption.

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

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

Zheng Yinghui; Zeng Zhinan; Zou Pu

2009-07-24

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

Influence of driving frequency on discharge modes in a dielectric-barrier discharge with multiple current pulses

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

Jiang, Weiman; Tang, Jie; Wang, Yishan

2013-07-15

A one-dimensional self-consistent fluid model was employed to investigate the effect of the driving frequency on the discharge modes in atmospheric-pressure argon discharge with multiple current pulses. The discharge mode was discussed in detail not only at current peaks but also between two adjacent peaks. The simulation results show that different transitions between the Townsend and glow modes during the discharge take place with the driving frequency increased. A complicated transition from the Townsend mode, through glow, Townsend, and glow, and finally back to the Townsend one is found in the discharge with the driving frequency of 8 kHz. Theremore » is a tendency of transition from the Townsend to glow mode for the discharge both at the current peaks and troughs with the increasing frequency. The discharge in the half period can all along operate in the glow mode with the driving frequency high enough. This is resulted from the preservation of more electrons in the gas gap and acquisition of more electron energy from the swiftly varying electric field with the increase in driving frequency. Comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increment of the driving frequency allows the plasma chemistry to be enhanced. This electrical characteristic is important for the applications, such as surface treatment and biomedical sterilization.« less

The National Ignition Facility: Transition to a User Facility

NASA Astrophysics Data System (ADS)

Moses, E. I.; Atherton, J.; Lagin, L.; Larson, D.; Keane, C.; MacGowan, B.; Patterson, R.; Spaeth, M.; Van Wonterghem, B.; Wegner, P.; Kauffman, R.

2016-03-01

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) has been operational since March 2009 and has been transitioning to a user facility supporting ignition science, high energy density science (HEDS), national security applications, and fundamental science. The facility has achieved its design goal of 1.8 MJ and 500 TW of 3ω light on target, and has performed target experiments with 1.9 MJ at peak powers of 410 TW. The facility is on track to perform over 200 target shots this year in support of all of its user communities. The facility has nearly 60 diagnostic systems operational and has shown flexibility in laser pulse shape and performance to meet the requirements of its multiple users. Progress continues on its goal of demonstrating thermonuclear burn in the laboratory. It has performed over 40 indirect-drive experiments with cryogenic-layered capsules. New platforms are being developed for HEDS and fundamental science. Equation-of-state and material strength experiments have been done on a number of materials with pressures of over 50 MBars obtained in diamond, conditions never previously encountered in the laboratory and similar to those found in planetary interiors. Experiments are also in progress investigating radiation transport, hydrodynamic instabilities, and direct drive implosions. NIF continues to develop as an experimental facility. Advanced Radiographic Capability (ARC) is now being installed on NIF for producing high-energy radiographs of the imploded cores of ignition targets and for short pulse laser-plasma interaction experiments. One NIF beam is planned for conversion to two picosecond beams in 2014. Other new diagnostics such as x-ray Thomson scattering, low energy neutron spectrometer, and multi-layer reflecting x-ray optics are also planned. Incremental improvements in laser performance such as improved optics damage performance, beam balance, and back reflection control are being pursued.

Neutron spectroscopy for pulsed beams with frame overlap using a double time-of-flight technique

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

Harrig, K. P.; Goldblum, B. L.; Brown, J. A.

A new double time-of- ight (dTOF) neutron spectroscopy technique has been developed for pulsed broad spectrum sources with a duty cycle that results in frame overlap, where fast neutrons from a given pulse overtake slower neutrons from previous pulses. Using a tunable beam at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory, neutrons were produced via thick-target breakup of 16 MeV deuterons on a beryllium target in the cyclotron vault. The breakup spectral shape was deduced from a dTOF measurement using an array of EJ-309 organic liquid scintillators. Simulation of the neutron detection efficiency of the scintillator array was performedmore » using both GEANT4 and MCNP6. The efficiency- corrected spectral shape was normalized using a foil activation technique to obtain the energy-dependent flux of the neutron beam at zero degrees with respect to the incoming deuteron beam. The dTOF neutron spectrum was compared to spectra obtained using HEPROW and GRAVEL pulse height spectrum unfolding techniques. While the unfolding and dTOF results exhibit some discrepancies in shape, the integrated flux values agree within two standard deviations. As a result, this method obviates neutron time-of-flight spectroscopy challenges posed by pulsed beams« less

Application of a deconvolution method for identifying burst amplitudes and arrival times in Alcator C-Mod far SOL plasma fluctuations

NASA Astrophysics Data System (ADS)

Theodorsen, Audun; Garcia, Odd Erik; Kube, Ralph; Labombard, Brian; Terry, Jim

2017-10-01

In the far scrape-off layer (SOL), radial motion of filamentary structures leads to excess transport of particles and heat. Amplitudes and arrival times of these filaments have previously been studied by conditional averaging in single-point measurements from Langmuir Probes and Gas Puff Imaging (GPI). Conditional averaging can be problematic: the cutoff for large amplitudes is mostly chosen by convention; the conditional windows used may influence the arrival time distribution; and the amplitudes cannot be separated from a background. Previous work has shown that SOL fluctuations are well described by a stochastic model consisting of a super-position of pulses with fixed shape and randomly distributed amplitudes and arrival times. The model can be formulated as a pulse shape convolved with a train of delta pulses. By choosing a pulse shape consistent with the power spectrum of the fluctuation time series, Richardson-Lucy deconvolution can be used to recover the underlying amplitudes and arrival times of the delta pulses. We apply this technique to both L and H-mode GPI data from the Alcator C-Mod tokamak. The pulse arrival times are shown to be uncorrelated and uniformly distributed, consistent with a Poisson process, and the amplitude distribution has an exponential tail.

Pulse shape discrimination of Cs2LiYCl6:Ce3+ detectors at high count rate based on triangular and trapezoidal filters

NASA Astrophysics Data System (ADS)

Wen, Xianfei; Enqvist, Andreas

2017-09-01

Cs2LiYCl6:Ce3+ (CLYC) detectors have demonstrated the capability to simultaneously detect γ-rays and thermal and fast neutrons with medium energy resolution, reasonable detection efficiency, and substantially high pulse shape discrimination performance. A disadvantage of CLYC detectors is the long scintillation decay times, which causes pulse pile-up at moderate input count rate. Pulse processing algorithms were developed based on triangular and trapezoidal filters to discriminate between neutrons and γ-rays at high count rate. The algorithms were first tested using low-rate data. They exhibit a pulse-shape discrimination performance comparable to that of the charge comparison method, at low rate. Then, they were evaluated at high count rate. Neutrons and γ-rays were adequately identified with high throughput at rates of up to 375 kcps. The algorithm developed using the triangular filter exhibits discrimination capability marginally higher than that of the trapezoidal filter based algorithm irrespective of low or high rate. The algorithms exhibit low computational complexity and are executable on an FPGA in real-time. They are also suitable for application to other radiation detectors whose pulses are piled-up at high rate owing to long scintillation decay times.

Neutron spectroscopy for pulsed beams with frame overlap using a double time-of-flight technique

DOE PAGES

Harrig, K. P.; Goldblum, B. L.; Brown, J. A.; ...

2017-10-16

A new double time-of- ight (dTOF) neutron spectroscopy technique has been developed for pulsed broad spectrum sources with a duty cycle that results in frame overlap, where fast neutrons from a given pulse overtake slower neutrons from previous pulses. Using a tunable beam at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory, neutrons were produced via thick-target breakup of 16 MeV deuterons on a beryllium target in the cyclotron vault. The breakup spectral shape was deduced from a dTOF measurement using an array of EJ-309 organic liquid scintillators. Simulation of the neutron detection efficiency of the scintillator array was performedmore » using both GEANT4 and MCNP6. The efficiency- corrected spectral shape was normalized using a foil activation technique to obtain the energy-dependent flux of the neutron beam at zero degrees with respect to the incoming deuteron beam. The dTOF neutron spectrum was compared to spectra obtained using HEPROW and GRAVEL pulse height spectrum unfolding techniques. While the unfolding and dTOF results exhibit some discrepancies in shape, the integrated flux values agree within two standard deviations. As a result, this method obviates neutron time-of-flight spectroscopy challenges posed by pulsed beams« less

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

Shaw, B. H.; Applied Science and Technology, University of California, Berkeley, California 94720; Tilborg, J. van

Solid-based surface high-harmonic generation from a tape is experimentally studied. By operating at mildly relativistic normalized laser strengths a{sub 0}≲0.2, harmonics up to the 17th order are efficiently produced in the coherent wake emission (CWE) regime. CWE pulse properties, such as divergence, energy, conversion efficiency, and spectrum, are investigated for various tape materials and drive laser conditions. A clear correlation between surface roughness and harmonic beam divergence is found. At the measured pulse properties for the 15th harmonic (conversion efficiency ∼6.5×10{sup −7}, divergence ∼7−15 mrad), the 100-mJ-level drive laser produces several MWs of extreme ultra-violet pulses. The spooling tape configurationmore » enables multi-Hz operation over thousands of shots, making this source attractive as a seed to the few-Hz laser-plasma-accelerator-driven free-electron laser (FEL). Models indicate that these CWE pulses with MW level powers are sufficient for seed-induced bunching and FEL gain.« less

Nike Experiment to Observe Strong Areal Mass Oscillations in a Rippled Target Hit by a Short Laser Pulse

NASA Astrophysics Data System (ADS)

Aglitskiy, Y.; Karasik, M.; Velikovich, A. L.; Serlin, V.; Weaver, J. L.; Kessler, T. J.; Schmitt, A. J.; Obenschain, S. P.; Metzler, N.; Oh, J.

2010-11-01

When a short (sub-ns) laser pulse deposits finite energy in a target, the shock wave launched into it is immediately followed by a rarefaction wave. If the irradiated surface is rippled, theory and simulations predict strong oscillations of the areal mass perturbation amplitude in the target [A. L. Velikovich et al., Phys. Plasmas 10, 3270 (2003).] The first experiment designed to observe this effect has become possible by adding short-driving-pulse capability to the Nike laser, and has been scheduled for the fall of 2010. Simulations show that while the driving pulse of 0.3 ns is on, the areal mass perturbation amplitude grows by a factor ˜2 due to ablative Richtmyer-Meshkov instability. It then decreases, reverses phase, and reaches another maximum, also about twice its initial value, shortly after the shock breakout at the rear target surface. This signature behavior is observable with the monochromatic x-ray imaging diagnostics fielded on Nike.

Optimization of vehicle deceleration to reduce occupant injury risks in frontal impact.

PubMed

Mizuno, Koji; Itakura, Takuya; Hirabayashi, Satoko; Tanaka, Eiichi; Ito, Daisuke

2014-01-01

In vehicle frontal impacts, vehicle acceleration has a large effect on occupant loadings and injury risks. In this research, an optimal vehicle crash pulse was determined systematically to reduce injury measures of rear seat occupants by using mathematical simulations. The vehicle crash pulse was optimized based on a vehicle deceleration-deformation diagram under the conditions that the initial velocity and the maximum vehicle deformation were constant. Initially, a spring-mass model was used to understand the fundamental parameters for optimization. In order to investigate the optimization under a more realistic situation, the vehicle crash pulse was also optimized using a multibody model of a Hybrid III dummy seated in the rear seat for the objective functions of chest acceleration and chest deflection. A sled test using a Hybrid III dummy was carried out to confirm the simulation results. Finally, the optimal crash pulses determined from the multibody simulation were applied to a human finite element (FE) model. The optimized crash pulse to minimize the occupant deceleration had a concave shape: a high deceleration in the initial phase, low in the middle phase, and high again in the final phase. This crash pulse shape depended on the occupant restraint stiffness. The optimized crash pulse determined from the multibody simulation was comparable to that from the spring-mass model. From the sled test, it was demonstrated that the optimized crash pulse was effective for the reduction of chest acceleration. The crash pulse was also optimized for the objective function of chest deflection. The optimized crash pulse in the final phase was lower than that obtained for the minimization of chest acceleration. In the FE analysis of the human FE model, the optimized pulse for the objective function of the Hybrid III chest deflection was effective in reducing rib fracture risks. The optimized crash pulse has a concave shape and is dependent on the occupant restraint stiffness and maximum vehicle deformation. The shapes of the optimized crash pulse in the final phase were different for the objective functions of chest acceleration and chest deflection due to the inertial forces of the head and upper extremities. From the human FE model analysis it was found that the optimized crash pulse for the Hybrid III chest deflection can substantially reduce the risk of rib cage fractures. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Electrical motor/generator drive apparatus and method

DOEpatents

Su, Gui Jia

2013-02-12

The present disclosure includes electrical motor/generator drive systems and methods that significantly reduce inverter direct-current (DC) bus ripple currents and thus the volume and cost of a capacitor. The drive methodology is based on a segmented drive system that does not add switches or passive components but involves reconfiguring inverter switches and motor stator winding connections in a way that allows the formation of multiple, independent drive units and the use of simple alternated switching and optimized Pulse Width Modulation (PWM) schemes to eliminate or significantly reduce the capacitor ripple current.

Alternating absorption features during attosecond-pulse propagation in a laser-controlled gaseous medium

NASA Astrophysics Data System (ADS)

Pfeiffer, Adrian N.; Bell, M. Justine; Beck, Annelise R.; Mashiko, Hiroki; Neumark, Daniel M.; Leone, Stephen R.

2013-11-01

Recording the transmitted spectrum of a weak attosecond pulse through a medium, while a strong femtosecond pulse copropagates at variable delay, probes the strong-field dynamics of atoms, molecules, and solids. Usually, the interpretation of these measurements is based on the assumption of a thin medium. Here, the propagation through a macroscopic medium of helium atoms in the region of fully allowed resonances is investigated both theoretically and experimentally. The propagation has dramatic effects on the transient spectrum even at relatively low pressures (50 mbar) and short propagation lengths (1 mm). The absorption does not evolve monotonically with the product of propagation distance and pressure, but regions with characteristics of Lorentz line shapes and characteristics of Fano line shapes alternate. Criteria are deduced to estimate whether macroscopic effects can be neglected or not in a transient absorption experiment. Furthermore, the theory in the limit of single-atom response yields a general equation for Lorentz- and Fano-type line shapes at variable pulse delay.

Laser Spot Welding of Copper-aluminum Joints Using a Pulsed Dual Wavelength Laser at 532 and 1064 nm

NASA Astrophysics Data System (ADS)

Stritt, Peter; Hagenlocher, Christian; Kizler, Christine; Weber, Rudolf; Rüttimann, Christoph; Graf, Thomas

A modulated pulsed laser source emitting green and infrared laser light is used to join the dissimilar metals copper and aluminum. The resultant dynamic welding process is analyzed using the back reflected laser light and high speed video observations of the interaction zone. Different pulse shapes are applied to influence the melt pool dynamics and thereby the forming grain structure and intermetallic phases. The results of high-speed images and back-reflections prove that a modulation of the pulse shape is transferred to oscillations of the melt pool at the applied frequency. The outcome of the melt pool oscillation is shown by the metallurgically prepared cross-section, which indicates different solidification lines and grain shapes. An energy-dispersivex-ray analysis shows the mixture and the resultant distribution of the two metals, copper and aluminum, within the spot weld. It can be seen that the mixture is homogenized the observed melt pool oscillations.

Improved pulse shape discrimination in EJ-301 liquid scintillators

NASA Astrophysics Data System (ADS)

Lang, R. F.; Masson, D.; Pienaar, J.; Röttger, S.

2017-06-01

Digital pulse shape discrimination has become readily available to distinguish nuclear recoil and electronic recoil events in scintillation detectors. We evaluate digital implementations of pulse shape discrimination algorithms discussed in the literature, namely the Charge Comparison Method, Pulse-Gradient Analysis, Fourier Series and Standard Event Fitting. In addition, we present a novel algorithm based on a Laplace Transform. Instead of comparing the performance of these algorithms based on a single Figure of Merit, we evaluate them as a function of recoil energy. Specifically, using commercial EJ-301 liquid scintillators, we examined both the resulting acceptance of nuclear recoils at a given rejection level of electronic recoils, as well as the purity of the selected nuclear recoil event samples. We find that both a Standard Event fit and a Laplace Transform can be used to significantly improve the discrimination capabilities over the whole considered energy range of 0 - 800keVee . Furthermore, we show that the Charge Comparison Method performs poorly in accurately identifying nuclear recoils.

High-order harmonic generation in a capillary discharge

DOEpatents

Rocca, Jorge J.; Kapteyn, Henry C.; Mumane, Margaret M.; Gaudiosi, David; Grisham, Michael E.; Popmintchev, Tenio V.; Reagan, Brendan A.

2010-06-01

A pre-ionized medium created by a capillary discharge results in more efficient use of laser energy in high-order harmonic generation (HHG) from ions. It extends the cutoff photon energy, and reduces the distortion of the laser pulse as it propagates down the waveguide. The observed enhancements result from a combination of reduced ionization energy loss and reduced ionization-induced defocusing of the driving laser as well as waveguiding of the driving laser pulse. The discharge plasma also provides a means to spectrally tune the harmonics by tailoring the initial level of ionization of the medium.

Impaired color naming of food and body shape words: weight phobia or distinct affective state?

PubMed

Green, M W; Elliman, N A; Rogers, P J; Welch, D A

1997-01-01

The current study investigated whether a concern with body shape and weight represents a distinct affective state, or whether it is better conceptualized as a highly specific form of anxiety. The color-naming performance of women with a high Drive for Thinness score was examined under three experimental conditions: when a photograph of chocolate was present, when actual chocolate was present, and a control condition. High Drive for Thinness subjects demonstrated relatively impaired color naming of body shape words in the picture condition, but not in the food or control conditions. Although there was a significant impairment in the color naming of food words, this was unaffected by condition or degree of Drive for Thinness. The results are interpreted as supporting an analogy between weight/body shape concerns and subclinical phobic anxiety.

Effects of chirp on two-dimensional Fourier transform electronic spectra.

PubMed

Tekavec, Patrick F; Myers, Jeffrey A; Lewis, Kristin L M; Fuller, Franklin D; Ogilvie, Jennifer P

2010-05-24

We examine the effect that pulse chirp has on the shape of two- dimensional electronic spectra through calculations and experiments. For the calculations we use a model two electronic level system with a solvent interaction represented by a simple Gaussian correlation function and compare the resulting spectra to experiments carried out on an organic dye molecule (Rhodamine 800). Both calculations and experiments show that distortions due to chirp are most significant when the pulses used in the experiment have different amounts of chirp, introducing peak shape asymmetry that could be interpreted as spectrally dependent relaxation. When all pulses have similar chirp the distortions are reduced but still affect the anti-diagonal symmetry of the peak shapes and introduce negative features that could be interpreted as excited state absorption.

Coherent control of photoelectron wavepacket angular interferograms

NASA Astrophysics Data System (ADS)

Hockett, P.; Wollenhaupt, M.; Baumert, T.

2015-11-01

Coherent control over photoelectron wavepackets, via the use of polarization-shaped laser pulses, can be understood as a time and polarization-multiplexed process, where the final (time-integrated) observable coherently samples all instantaneous states of the light-matter interaction. In this work, we investigate this multiplexing via computation of the observable photoelectron angular interferograms resulting from multi-photon atomic ionization with polarization-shaped laser pulses. We consider the polarization sensitivity of both the instantaneous and cumulative continuum wavefunction; the nature of the coherent control over the resultant photoelectron interferogram is thus explored in detail. Based on this understanding, the use of coherent control with polarization-shaped pulses as a methodology for a highly multiplexed coherent quantum metrology is also investigated, and defined in terms of the information content of the observable.

[Low level alpha activity measurements with pulse shape discrimination--application to the determination of alpha-nuclides in environmental samples].

PubMed

Satoh, K; Noguchi, M; Higuchi, H; Kitamura, K

1984-12-01

Liquid scintillation counting of alpha rays with pulse shape discrimination was applied to the analysis of 226Ra and 239+240Pu in environmental samples and of alpha-emitters in/on a filter paper. The instrument used in this study was either a specially designed detector or a commercial liquid scintillation counter with an automatic sample changer, both of which were connected to the pulse shape discrimination circuit. The background counting rate in alpha energy region of 5-7 MeV was 0.01 or 0.04 cpm/MeV, respectively. The figure of merit indicating the resolving power for alpha- and beta-particles in time spectrum was found to be 5.7 for the commercial liquid scintillation counter.

Significantly different pulse shapes for γ- and α-rays in Gd3Al2Ga3O12:Ce3+ scintillating crystals

NASA Astrophysics Data System (ADS)

Kobayashi, Masaaki; Tamagawa, Yoichi; Tomita, Shougo; Yamamoto, Akihiro; Ogawa, Izumi; Usuki, Yoshiyuki

2012-12-01

We have found that scintillation in Gd3Al2Ga3O12 (GAGG):Ce3+ garnet single crystals has significantly different pulse shapes for 0.662 MeV γ- and 5.47 MeV α-rays. The decay and rise times for γ-rays are smaller by 50% and threefold, respectively, than those for α-rays. Because the GAGG:Ce is a dense, efficient and fast-response scintillator and because it can be grown in large-size single crystals, it should be a promising unified target and a detector material in the study of neutrinoless double beta decay of 160Gd through the use of pulse shape discrimination between the β-ray signals and the α-ray-induced backgrounds.

DriveWise: An Interdisciplinary Hospital-Based Driving Assessment Program

ERIC Educational Resources Information Center

O'Connor, Margaret G.; Kapust, Lissa R.; Hollis, Ann M.

2008-01-01

Health care professionals working with the elderly have opportunities through research and clinical practice to shape public policy affecting the older driver. This article describes DriveWise, an interdisciplinary hospital-based driving assessment program developed in response to clinical concerns about the driving safety of individuals with…

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.

Reconfigurable Drive Current System

NASA Technical Reports Server (NTRS)

Alhorn, Dean C. (Inventor); Dutton, Kenneth R. (Inventor); Howard, David E. (Inventor); Smith, Dennis A. (Inventor)

2017-01-01

A reconfigurable drive current system includes drive stages, each of which includes a high-side transistor and a low-side transistor in a totem pole configuration. A current monitor is coupled to an output of each drive stage. Input channels are provided to receive input signals. A processor is coupled to the input channels and to each current monitor for generating at least one drive signal using at least one of the input signals and current measured by at least one of the current monitors. A pulse width modulation generator is coupled to the processor and each drive stage for varying the drive signals as a function of time prior to being supplied to at least one of the drive stages.

A Compton scattering setup for pulse shape discrimination studies in germanium detectors.

PubMed

von Sturm, K; Belogurov, S; Brugnera, R; Garfagnini, A; Lippi, I; Modenese, L; Rosso, D; Turcato, M

2017-07-01

Pulse shape discrimination is an important handle to improve sensitivity in low background experiments. A dedicated setup was built to investigate the response of high-purity germanium detectors to single Compton scattered events. Using properly collimated γ-ray sources, it is possible to select events with known interaction location. The aim is to correlate the position dependent signal shape with geometrical and electrical properties of the detector. We report on design and performance of the setup with a first look on data. Copyright © 2017 Elsevier Ltd. All rights reserved.