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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Ionization of helium by an ultrashort extreme-ultraviolet laser pulse

We theoretically study photoelectron angular distributions and related anisotropy parameters for the competition of one- and two-photon ionization of He in an ultrashort extreme-ultraviolet laser pulse, using numerical results from the time-dependent Schrödinger equation. We explore the transition between the two processes for variation of the pulse duration, peak intensity, and central frequency or photoelectron energy. In the results obtained for fixed pulse parameters the transition and interference between the processes can be observed in the even (β 2 , β 4 ) and odd (β 1 , β 3 ) parameters, respectively, while the onset of the impact of three-photon ionization is observed via β5 at high peak intensities. Lastly, we show that the transition can be observed via the even anisotropy parameters in pulses without carrier-to-envelope stabilization as well as in free-electron laser pulses with fluctuating pulse shape.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Absorption of relativistic multi-picosecond laser pulses in wire arrays

We study the interaction of intense multi-picosecond laser pulses with arrays of carbon wires attached to solid substrates. Here, we find that laser absorption in wire arrays resembles that in flat targets with very large uniform plasma density gradients. Performing two-dimensional particle-in-cell simulations, we optimize target parameters like wire thickness and -distance for energy absorption of a 2picosecond laser pulse with a large focal spot; this has implications for x-ray- and charged particle source development.

43 PARTICLE ACCELERATORS↗
NASA NTRS1984

Fizeau wavemeter for pulsed laser wavelength measurement

A Fizeau wavelength meter optimized for use with pulsed laser sources has been developed and characterized which demonstrates a CW resolution better than 2 parts in 10 to the 7th and a pulsed resolution better than 1 part in 10 to the 6th. The static optical design is based on a Fizeau wedge interferometer, which together with spatial filtering and collimating optics is used to produce a pattern of parallel fringes which is imaged on a linear photodiode array and analyzed by a minicomputer. A series of CW and pulsed measurements of various narrowband laser sources are described, and particular difficulties involved in pulsed laser measurements with the wavemeter are examined.

Morris, M. B.↗
DOE OSTI2025

Enhanced quantum radiation with flying-focus laser pulses

The emission of a photon by an electron in an intense laser field is one of the most fundamental processes in electrodynamics and underlies the many applications that utilize high-energy photon beams. This process is typically studied for electrons colliding head-on with a stationary-focus laser pulse. Here, we show that the energy lost by electrons in the quantum regime and the yield of emitted photons can be substantially increased by replacing a stationary-focus pulse with an equal-energy flying-focus pulse whose focus co-propagates with the electrons. Furthermore, these advantages of the flying focus result from the energy loss and the photon yield scaling more favorably with the interaction time than the laser intensity in the quantum regime, with the latter also holding in the classical regime. Monte Carlo simulations of electrons colliding with equal-energy stationary and flying-focus laser pulses demonstrate these advantages.

Compton scattering↗
DOE OSTI2021

High-power non-perturbative laser delivery diagnostics at the final focus of 100-TW-class laser pulses

Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus, both in position and angle, is critical to many laser applications such as optical guiding, laser–plasma acceleration, and laser-produced secondary radiation. We present an online, non-destructive laser diagnostic, capable of measuring the transverse position and pointing angle at focus. The diagnostic is based on a unique double-surface-coated wedged-mirror design for the final steering optic in the laser line, producing a witness beam highly correlated with the main beam. By propagating low-power kilohertz pulses to focus, we observed spectra of focus position and pointing angle fluctuations dominated by frequencies below 70 Hz. The setup was also used to characterize the excellent position and pointing angle correlation of the 1 Hz high-power laser pulses to this low-power kilohertz pulse train, opening a promising path to fast non-perturbative feedback concepts even on few-hertz-class high-power laser systems.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Using double pulse laser ablation in air to enhance the strength of laser-driven shocks

In the process of multi-pulse laser ablation, inter-pulse delay time, Δ t , is known to be an important parameter for maximizing ablation efficiency as well as impulse imparted to the target. In this work, using photon Doppler velocimetry, we show that for single pairs of colinear pulses (1064 nm, 8 ns, ∼ 60 J cm -2 per pulse) in air, the peak free surface velocity of the back surface of an aluminum target (125 µm thick) is increased, by a factor of nearly 3, when Δ t = 10 microseconds, compared with both pulses arriving simultaneously (Δ t = 0). Fast imaging of the ablation process suggests this enhancement is due to rarefaction of the contiguous air in the passage of the leading shock produced by ablation, which then in turn allows a larger fraction of the energy of the second pulse to reach the target surface. This interpretation is strengthened by additional experiments in which the two pulses do not overlap on the target surface, but the shock strength is nevertheless enhanced. Given a fixed energy budget this work suggests a prescription for maximizing laser-driven shock strength by judicious choice of inter-pulse delay.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

Abstract Progress in ultrafast science allows for probing quantum superposition states with ultrashort laser pulses in the new regime where several linear and nonlinear ionization pathways compete. Interferences of pathways can be observed in the photoelectron angular distribution and in the past they have been analyzed for atoms and molecules in a single quantum state via anisotropy and asymmetry parameters. Those conventional parameters, however, do not provide comprehensive tools for probing superposition states in the emerging research area of bright and ultrashort light sources, such as free-electron lasers and high-order harmonic generation. We propose a new set of generalized asymmetry parameters which are sensitive to interference effects in the photoionization and the interplay of competing pathways as the laser pulse duration is shortened and the laser intensity is increased. The relevance of the parameters is demonstrated using results of state-of-the-art numerical solutions of the time-dependent Schrödinger equation for ionization of helium atom and neon atom.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2004

Synchronization of video recording and laser pulses including background light suppression

An apparatus for and a method of triggering a pulsed light source, in particular a laser light source, for predictable capture of the source by video equipment. A frame synchronization signal is derived from the video signal of a camera to trigger the laser and position the resulting laser light pulse in the appropriate field of the video frame and during the opening of the electronic shutter, if such shutter is included in the camera. Positioning of the laser pulse in the proper video field allows, after recording, for the viewing of the laser light image with a video monitor using the pause mode on a standard cassette-type VCR. This invention also allows for fine positioning of the laser pulse to fall within the electronic shutter opening. For cameras with externally controllable electronic shutters, the invention provides for background light suppression by increasing shutter speed during the frame in which the laser light image is captured. This results in the laser light appearing in one frame in which the background scene is suppressed with the laser light being uneffected, while in all other frames, the shutter speed is slower, allowing for the normal recording of the background scene. This invention also allows for arbitrary (manual or external) triggering of the laser with full video synchronization and background light suppression.

Kalshoven, Jr., James E.↗
DOE OSTI2020

Pathways to excitation of atoms with bicircular laser pulses

We study the excitation of the hydrogen atom by bichromatic circularly polarized laser pulses using numerical solutions of the time-dependent Schrödinger equation. The results are in agreement with the selection rules for multiphoton processes in such fields, namely, excited states are populated in which orbital angular momentum and magnetic quantum numbers are either both odd or both even, independent of the relative helicity, peak intensity, and pulse duration of the pulses. For co-rotating pulses the results show that excitation predominantly proceeds to states with magnetic quantum number of the same helicity as the laser pulses. Besides pathways via direct photon absorption from the ground state our results indicate that a transfer of population among the Rydberg states occurs via Λ-type transitions. In the case of counter-rotating pulses the largest excitation probability is found for Rydberg states that differ in magnetic quantum number by Δm=±3. This pattern allows us to estimate how many photons from each of the two bichromatic fields have been absorbed. Finally, we confirm that a population in Rydberg states beyond a maximum orbital angular quantum number is unlikely.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1970

Pulsed laser holography

High speed pulsed ruby laser holography, discussing transmission-reflection holocameras and applications

Heflinger, L. O.↗
DOE OSTI2020

Self-compression of laser pulses in a discrete medium

Using the discrete nonlinear Schrödinger equation, we study the laser radiation self-action dynamics in a nanostructured waveguide system. It is shown that for a laser pulse energy exceeding the critical value, the nonlinear evolution of the wave field markedly differs from the corresponding process in a continuous medium. While the pulse propagates in a discrete medium, its length decreases to values comparable to the scale of the structure and the velocity decreases to zero. The system parameters are determined at which the wave field after the laser pulse termination begins to propagate in the opposite direction in a compressed form. The process of slowing down and stopping the pulse is accompanied by strong radiation losses, so that about a third of the energy of the initial field distribution remains in the final compressed state. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Microstructure and defect engineering of graphite anodes by pulsed laser annealing for enhanced performance of lithium-ion batteries

We report nanosecond pulsed laser annealing significantly improves cyclability and current carrying capacity of lithium-ion batteries (LIBs). This improvement is achieved by engineering of microstructure and defect contents present in graphite in a controlled way by using pulsed laser annealing (PLA) to increase the number density of Li + ion trapping sites. The PLA treatment causes the following changes: (1) creates surface steps and grooves between the grains to improve Li + ion charging and intercalation rates; (2) removes inactive polyvinylidene difluoride (PVDF) binder from the top of graphite grains and between the grains which otherwise tends to block the Li + migration; and (3) produces carbon vacancies in (0001) planes which can provide Li + charging sites. From X-ray diffraction data, we find upshift in diffraction peak or reduction in planar spacing, from which vacancy concentration was estimated to be about 1.0%, which is higher than the thermodynamic equilibrium concentration of vacancies. The laser treatment creates single and multiple C vacancies which provide sites for Li + ions, and it also produces steps and grooves for Li + ions to enter the intercalating sites. It is envisaged that the formation of these sites enhances Li+ ion absorption during charge and discharge cycles. The current capacity increases from an average 360 mAh/g to 430 mAh/g, and C–V shows significant reduction in SEI layer formation after the laser treatment. If the vacancy concentration is too high and charge-discharge cycles are long, then trapping of electrons by Li + may occur, which can lead to Li 0 formation and Li plating causing reduction in current capacity.

25 ENERGY STORAGE↗
DOE OSTI2020

Laser pulse driven control of charge and spin order in the two-dimensional Kondo lattice

Fast and dynamical control of quantum phases is highly desired in the application of quantum phenomena in devices. On the experimental side, ultrafast laser pulses provide an ideal platform to induce femtosecond dynamics in a variety of materials. Here we show that a laser pulse driven heavy fermion system can be tuned to dynamically evolve into a phase, which is not present in equilibrium. Using the state-of-the-art time-dependent variational Monte Carlo method, we perform numerical simulations of realistic laser pulses applied to the Kondo lattice model. By tracking spin and charge degrees of freedom we identify a dynamical phase transition, within the partially Kondo screened phase, from a charge ordered into a metallic state, while preserving the spin order of the system. Furthermore, we propose using high-harmonic generation and nonequilibrium optical conductivity to identify the dynamical phase transition in an ultrafast experiment.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interference microscopy study of the preplasma formed on an iron target surface exposed to high-power femtosecond laser pulses

The characteristic scale of spread of the plasma formed on the surface of a bulk iron target irradiated by a femtosecond laser pulse with an intensity of 10{sup 16} W cm{sup −2} is measured by time-resolved interference microscopy using femtosecond pulses emitted by a Cr : forsterite laser system with an intensity contrast of 10{sup 7}. The chosen technique is demonstrated to be efficient in such measurements. It is shown experimentally that, as a result of laser pulse impact, the displacement of a plasma layer with a density exceeding critical does not exceed 30 nm. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Polarization Dependent Excitation and High Harmonic Generation from Intense Mid-IR Laser Pulses in ZnO

The generation of high order harmonics from femtosecond mid-IR laser pulses in ZnO has shown great potential to reveal new insight into the ultrafast electron dynamics on a few femtosecond timescale. In this work we report on the experimental investigation of photoluminescence and high-order harmonic generation (HHG) in a ZnO single crystal and polycrystalline thin film irradiated with intense femtosecond mid-IR laser pulses. The ellipticity dependence of the HHG process is experimentally studied up to the 17th harmonic order for various driving laser wavelengths in the spectral range 3–4 µm. Interband Zener tunneling is found to exhibit a significant excitation efficiency drop for circularly polarized strong-field pump pulses. For higher harmonics with energies larger than the bandgap, the measured ellipticity dependence can be quantitatively described by numerical simulations based on the density matrix equations. The ellipticity dependence of the below and above ZnO band gap harmonics as a function of the laser wavelength provides an efficient method for distinguishing the dominant HHG mechanism for different harmonic orders.

tunneling excitation↗
NASA NTRS1993

Test results from LAGEOS-2 optical characterization using pulsed lasers

The Laser Geodynamic Satellite-2 (LAGEOS-2) has undergone extensive optical testing at NASA Goddard Space Flight Center during 1989. The techniques included measuring the far field diffraction pattern using cw and pulsed lasers. In the pulsed measurement technique, response of the satellite was studied by measuring the far-field diffraction pattern (FFDP) as a function of pulsewidth, wavelength, polarization, position in the FFDP, detector/processing techniques, and satellite orientation. The purpose of the pulsed laser testing was two-fold: (1) to characterize the satellite optical response with the detector and signal processing electronics currently used in most SLR stations using the portable laser ranging standard, and (2) to characterize the satellite response for various conditions using the highest bandwidth optical detector (streak camera) available for the next generation of satellite laser ranging (SLR) technology. The portable ranging standard employed multiple measurement devices and an optical calibration scheme to eliminate range-dependent and amplitude-dependent systematics. These precautions were taken to eliminate/minimize instrumental errors and provide maximum accuracy. For LAGEOS orbit (6000 Km), ground stations are located 34 to 38 Mu radians off the axis of the return signal from the satellite; therefore, an optical mask was used to restrict the field of view (FOV) of detection to this annular region of the FFDP. The two measurement techniques were implemented using an aperture sharing scheme and complemented each other by providing mutual verification.

Varghese, Thomas K.↗
DOE OSTI2024

Spatiotemporal control of high-intensity laser pulses with a plasma lens

Spatiotemporal control encompasses a variety of techniques for producing laser pulses with dynamic intensity peaks that move independently of the group velocity. This controlled motion of the intensity peak offers a new approach to optimizing laser-based applications and enhancing signatures of fundamental phenomena. Here, we demonstrate spatiotemporal control with a plasma optic. A chirped laser pulse focused by a plasma lens exhibits a moving focal point, or “flying focus,” that can travel at an arbitrary, predetermined velocity. Unlike currently used conventional or adaptive optics, a plasma lens can be located close to the interaction region and can operate at an orders of magnitude higher, near-relativistic intensity. Published by the American Physical Society 2024

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Enabling elliptically polarized high harmonic generation with short cross polarized laser pulses

Abstract Enabling elliptically polarized high-order harmonics overcomes a historical limitation in the generation of this highly nonlinear process in atomic, molecular and optical physics with applications in other branches. Here, we shed new light on a controversy between experimental observations and theoretical predictions on the possibility to generate harmonics with large ellipticity using two bichromatic laser pulses which are linearly polarized in orthogonal directions. Results of numerical calculations confirm the previous experimental data that in short laser pulses even harmonics with large ellipticity can be obtained for the interaction of such cross-polarized laser pulses with atoms initially in a s - or p -state, while odd harmonics have low ellipticity. The amount of the ellipticity can be controlled via the relative carrier-envelope phase of the pulses, their intensity ratio and the duration of the pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗