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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Retrieval of target structure information from laser-induced photoelectrons by few-cycle bicircular laser fields

By analyzing theoretical results from a numerical solution of the time-dependent Schrödinger equation for atoms in few-cycle bicircular laser pulses, we show that high-energy photoelectron momentum spectra can be used to extract accurate elastic scattering differential cross sections of the target ion with free electrons. We find that the retrieval range for a scattering angle with bicircular pulses is wider than with linearly polarized pulses, although the retrieval method has to be modified to account for different returning directions of the electron in the continuum. Overall, this result can be used to extend the range of applicability of ultrafast imaging techniques such as laser-induced electron diffraction and for the accurate characterization of laser pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Helicity-Selective Enhancement and Polarization Control of Attosecond High Harmonic Waveforms Driven by Bichromatic Circularly Polarized Laser Fields

High harmonics driven by two-color counter-rotating circularly-polarized laser fields are a unique source of bright, circularly-polarized, extreme ultraviolet and soft x-ray beams, where the individual harmonics themselves are completely circularly polarized. Here, we demonstrate the ability to preferentially select either the right or left circularly polarized harmonics simply by adjusting the relative intensity ratio of the bichromatic circularly polarized driving laser field. In the frequency domain, this significantly enhances the harmonic orders that rotate in the same direction as the higher intensity driving laser. In the time domain, this helicity-dependent enhancement corresponds to control over the polarization of the resulting attosecond waveforms. Here, this helicity control enables the generation of circularly-polarized high harmonics with a user-defined polarization of the underlying attosecond bursts. In the future, this technique should allow for the production of bright highly elliptical harmonic supercontinua as well as the generation of isolated elliptically polarized attosecond pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Effects of Laser Bandwidth in Direct-Drive High-Performance DT-Layered Implosions on the OMEGA Laser

In direct-drive inertial confinement fusion, the laser bandwidth reduces the laser imprinting seed of hydrodynamic instabilities. The impact of varying bandwidth on the performance of direct-drive DT-layered implosions was studied in targets with different hydrodynamic stability properties. The stability was controlled by changing the shell adiabat from (α F ≃ 5) (more stable) to (α F ≃ 3.5) (less stable). Herein these experiments show that the performance of lower adiabat implosions improves considerably as the bandwidth is raised indicating that further bandwidth increases, beyond the current capabilities of OMEGA, would be greatly beneficial. These results suggest that the future generation of ultra-broadband lasers could enable achieving high convergence and possibly high gains in direct drive ICF.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Positronium Laser Cooling via the 1 3 S − 2 3 P Transition with a Broadband Laser Pulse

We report on laser cooling of a large fraction of positronium (Ps) in free flight by strongly saturating the 1 3 S − 2 3 P transition with a broadband, long-pulsed 243 nm alexandrite laser. The ground state Ps cloud is produced in a magnetic and electric field-free environment. We observe two different laser-induced effects. The first effect is an increase in the number of atoms in the ground state after the time Ps has spent in the long-lived 2 3 P states. The second effect is one-dimensional Doppler cooling of Ps, reducing the cloud’s temperature from 380(20) to 170(20) K. We demonstrate a 58(9)% increase in the fraction of Ps atoms with v 1 D < 3.7 × 10 4 m s − 1 . Published by the American Physical Society 2024

Glöggler, L. T. (ORCID:0000000301948680)↗
DOE OSTI2018

Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam

The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation reaction. When interacting with a high-energy electron beam, today’s lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We present evidence of radiation reaction in the collision of an ultrarelativistic electron beam generated by laser-wakefield acceleration ( ϵ > 500 MeV ) with an intense laser pulse (a 0 > 10). We measure an energy loss in the postcollision electron spectrum that is correlated with the detected signal of hard photons (γ rays), consistent with a quantum description of radiation reaction. The generated γ rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy ϵ crit > 30 MeV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Greater than 1000-fold Gain in a Free-Electron Laser Driven by a Laser-Plasma Accelerator with High Reliability

Compact free-electron lasers (FELs) based on plasma-based accelerators have been envisioned for many years. While recent milestone experiments have demonstrated feasibility, further progress is needed to establish laser-plasma-accelerator-driven FELs as reliable light sources. Demonstrating both full FEL saturation and reliable operation commensurate with conventional FEL facilities is critical. We report progress on both of these fronts. FEL gain exceeding 1000 at a wavelength of 420 nm in the self-amplified spontaneous emission regime has been measured. Lower and upper bounds for the characteristic exponential gain length were measured at 16.7-22.5 cm. Additionally, reliability of the laser-plasma-accelerator-driven FEL, defined here as the percentage of shots displaying FEL gain, reached an unprecedented level of greater than 90% over the course of an hour while operating at 1 Hz repetition rate.

Barber, S K↗
DOE OSTI2022

Towards performing high-resolution inelastic X-ray scattering measurements at hard X-ray free-electron lasers coupled with energetic laser drivers

High-resolution inelastic X-ray scattering is an established technique in the synchrotron community, used to investigate collective low-frequency responses of materials. When fielded at hard X-ray free-electron lasers (XFELs) and combined with high-intensity laser drivers, it becomes a promising technique for investigating matter at high temperatures and high pressures. This technique gives access to important thermodynamic properties of matter at extreme conditions, such as temperature, material sound speed, and viscosity. The successful realization of this method requires the acquisition of many identical laser-pump/X-ray-probe shots, allowing the collection of a sufficient number of photons necessary to perform quantitative analyses. Here, a 2.5-fold improvement in the energy resolution of the instrument relative to previous works at the Matter in Extreme Conditions (MEC) endstation, Linac Coherent Light Source (LCLS), and the High Energy Density (HED) instrument, European XFEL, is presented. Some aspects of the experimental design that are essential for improving the number of photons detected in each X-ray shot, making such measurements feasible, are discussed. A careful choice of the energy resolution, the X-ray beam mode provided by the XFEL, and the position of the analysers used in such experiments can provide a more than ten-fold improvement in the photometrics. The discussion is supported by experimental data on 10 µm-thick iron and 50 nm-thick gold samples collected at the MEC endstation at the LCLS, and by complementary ray-tracing simulations coupled with thermal diffuse scattering calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Batch crystallization of rhodopsin for structural dynamics using an X-ray free-electron laser

A new batch preparation method is presented for high-density micrometre-sized crystals of the G protein-coupled receptor rhodopsin for use in time-resolved serial femtosecond crystallography at an X-ray free-electron laser using a liquid jet. Rhodopsin is a membrane protein from the G protein-coupled receptor family. Together with its ligand retinal, it forms the visual pigment responsible for night vision. In order to perform ultrafast dynamics studies, a time-resolved serial femtosecond crystallography method is required owing to the nonreversible activation of rhodopsin. In such an approach, microcrystals in suspension are delivered into the X-ray pulses of an X-ray free-electron laser (XFEL) after a precise photoactivation delay. Here, a millilitre batch production of high-density microcrystals was developed by four methodical conversion steps starting from known vapour-diffusion crystallization protocols: (i) screening the low-salt crystallization conditions preferred for serial crystallography by vapour diffusion, (ii) optimization of batch crystallization, (iii) testing the crystal size and quality using second-harmonic generation (SHG) imaging and X-ray powder diffraction and (iv) production of millilitres of rhodopsin crystal suspension in batches for serial crystallography tests; these crystals diffracted at an XFEL at the Linac Coherent Light Source using a liquid-jet setup.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Residual stresses in Cu matrix composite surface deposits after laser melt injection

Abstract Tungsten carbide particles reinforced metal matrix composite (MMC) coatings can significantly improve surface wear resistance owing to their increased surface hardness. However, the presence of macro‐ and micro‐residual stresses in MMC coatings can have detrimental effects, such as reducing service life. In this study, neutron diffraction was used to determine the residual stresses in spherical fused tungsten carbide (sFTC) reinforced Cu matrix composite surface deposits after laser melt injection. We also developed a thermo‐mechanical coupled finite element model to predict residual stresses. Our findings reveal that sFTC/Cu composite deposits produced with a preheating temperature of 400°C have low residual stresses, with a maximum tensile residual stress of 98 MPa in the Cu matrix on the top surface. In contrast, the sFTC/bronze (CuAl10Ni5Fe4) composite deposit exhibits very high residual stresses, with a maximum tensile residual stress in the Cu matrix on the top surface reaching 651 MPa. These results provide a better understanding of the magnitudes and distributions of residual stresses in sFTC‐reinforced Cu matrix composite surface deposits manufactured via laser melt injection.

Zhang, Xingxing↗
DOE OSTI2016

Unit cell determination of coexisting post-perovskite and H-phase in (Mg,Fe)SiO3 using multigrain XRD: compositional variation across a laser heating spot at 119 GPa

Multigrain X-ray diffraction (XRD) can be used to accurately calculate the unit cell parameters of individual mineral phases in a mineral assemblage contained in a diamond anvil cell (DAC). Coexisting post-perovskite (ppv) and H-phase were synthesized at 119 GPa and 2500 K from (Mg 0.85 Fe 0.15 )SiO 3 in a laser-heated DAC. The unit cell parameters of the ppv and coexisting H-phase were determined using multigrain XRD with a 5 μm spatial resolution, close to the size of the X-ray beam, to understand compositional variations across the center area (20–30 μm) in a laser-heated sample. The ppv phase was Fe-depleted and the unit cell volume of ppv decreased by only 0.16 % (corresponding to ~3 % variation of FeSiO 3 ) from the heating center to 10 μm off the center, while the sample pressure remained at 119 GPa in a Ne quasi-hydrostatic environment. The unit cell volume of the H-phase decreased by 0.54 % (~10 % variation of FeSiO 3 content) over the same 10 μm distance. Both phases were more Fe-enriched in the slightly hotter center. This observation suggests that thermal diffusion may not be the major driver for the compositional variations of ppv and H-phase in the center portion of a laser-heated sample. Instead, these variations could be caused by a temperature effect on the partitioning between the ppv and H-phase over the small gradient.

58 GEOSCIENCES↗
DOE OSTI2024

Laser micro-machining and damage testing of rounded shadow cone blockers on silica glass for arresting laser damage growth by redirection of light

Structured conical blockers manufactured on optical input surfaces are being used to shadow, and thereby, arrest growth of exit surface damage on large optics for applications in high-energy laser systems to extend their lifetime usage. However, as the size of the Shadow Cone Blocker (SCB) is increased, the deflected light must be carefully managed to prevent consequential damage from downstream intensification. Here, we design and fabricate a distinct input SCB geometry to alleviate this problem, enabling larger damage site mitigation. The demonstrated ~1 mm diameter SCB was manufactured with a convergent approach using a CO 2 pulsed laser ablative scanning sequence on a fused silica window. The SCB design was refined to maximize resistance to both input and exit surface damage initiations on 1 cm thick fused silica windows when exposed to 351 nm irradiation and validated with laser damage testing. The design showed to prevent damage onset to the exit surface for incident fluences on the SCB of 10.7 ± 1.3 J·cm -2 and is resistant to damage on the input surface exceeding 30 J·cm -2 input fluence.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Detection limits for laser absorption spectroscopy of Li in laser ablation plumes

A high-sensitivity laser absorption spectroscopy (LAS) method is demonstrated for rapid and non-contact analysis of Li in solids. Glass samples with Li concentrations ranging from 1-500 ppm by mass are ablated in 5 Torr air, and time-resolved Li atomic absorption is measured using a tunable laser near 671 nm. Significant improvements in analytical performance over prior laser-induced breakdown techniques are demonstrated. Here, a single-shot limit of detection (LOD) of 180 ppb is shown for fixed wavelength operation, improving to 6 ppb with averaging over 1000 ablation shots (100 s acquisition time). Isotope-resolved Li absorption spectra are measured with a 17 ppb LOD in 40 s. Methods for optimizing LOD based on noise/averaging properties of LAS experiments in LA plumes are discussed.

(020.3260) Isotope shifts↗
NASA NTRS1975

Laser head for simultaneous optical pumping of several dye lasers

The invention is a laser head for simultaneous pumping several dye lasers with a single flash lamp. The laser head includes primarily a multi-elliptical cylinder cavity with a single flash lamp placed along the common focal axis of the cavity and with capillary tube dye cells placed along each of the other focal axes of the cavity. The inside surface of the cavity is polished. Hence, the single flash lamp supplies the energy to the several dye cells.

Mumola, P. B.↗
NASA NTRS1974

GaAs laser diode pumped Nd:YAG laser

A 1.5-mm by 3-cm neodymium-ion doped YAG laser rod has been side pumped using a GaAs laser diode array tuned to the 8680-A absorption line, achieving a multimode average output power of 120 mW for a total input power of 20 W to the final-stage laser diode drivers. The pumped arrangement was designed to take advantage of the high brightness of a conventional GaAs array as a linear source by introducing the pump light through a slit into a close-wrapped gold coated pump cavity. This cavity forms an integrating chamber for the pump light.

Conant, L. C.↗
NASA NTRS1982

Studies of single-mode injection lasers and of quaternary materials. Volume 1: Single-mode constricted double-heterojunction AlGaAs diode lasers

Constricted double-heterojunction (CDH) lasers are presented as the class of single-mode nonplanar-substrate devices for which the lasing cavity is on the least resistive electrical path between the contact and the substrate. Various types of CDH structures are considered under three general topics: liquid-phase epitaxy over channeled substrates, lateral mode control, and current control in nonplanar-substrate devices. Ridge-guide CDH lasers have positive-index lateral-mode confinement and provide: single-mode CW operation to 7 mW/facet at room temperature and to 3 mW/facet at 150 C; light-current characteristics with second-harmonic distortion as low as -57 dB below the fundamental level; threshold-current temperature coefficients, as high as 375 C (pulsed) and 310 C (CW); constant external differential quantum efficiency to 100 C; and lasing operation to 170 C CW and 280 C pulsed. Semileakyguide CDH lasers have an asymmetric leaky cavity for lateral-mode confinement and provide single-mode operation to 15 to 20 mW/facet CW and to 50 mW/facet at 50% duty cycle. Modulation characteristics and preliminary reliability data are discussed.

Botez, D.↗