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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

A New Laser Beam Pointing Method Using Laser Arrays

A new method is described for optical data transmissions from satellites using laser arrays for laser beam pointing. It combines a lens system and a vertical-cavity surface-emitting laser (VCSEL)/Photodetector Array, both mature technologies, in a novel way. This system is applied to satellites in low-Earth orbit, (LEO). It can replace current architectures which use dynamical systems, (i.e., moving parts) to point the laser, and which may use vibration isolation platforms. Results of computer simulations show diffraction limited beam propagation. Possible additional applications are to planetary distances (deep space optical communications, (DSOC)), to optical multiple access, (OMA), to communication between a constellation of close satellites, and to satellites that use modulating retro-reflectors. Keywords: laser beam pointing, free-space optical communication, low-Earth orbit (LEO) data communications, integrated VCSEL/ photodetector arrays, deep space optical communications (DSOC), optical multiple access (OMA), constellation of close satellites, modulating retro-reflectors.

Goorjian, P. M.↗
DOE OSTI2018

Influence of Laser Radiation Power Density on the Intensity of Spectral Lines for Main Components in a Clay Laser-Induced Plasma

We have studied the intensity of the spectral lines for the main components in clay: Al I 309.4 nm, Al II 358.7 nm, Mg II 279.6 nm, Ti II 323.6 nm vs. the position of the object relative to the focus of the optical system when the samples are exposed to single laser pulses from a YAG:Nd{sup 3+} laser. We have determined the permissible ranges for positioning the object relative to the focus of the optical system (positive and negative defocusing) for which there is practically no change in the reproducibility of the intensity for the spectral lines for red and white clay samples. We show that the position of the object relative to the focus of the optical system should be within the range ΔZ ~ ±1.5 mm for optimal laser pulse energies for the analyte spectral lines. We have calculated the radiation flux density for different laser pulse energies and different distances from the focus to the object. We have shown experimentally that reducing the radiation flux density leads to a decrease in the intensity of the analyte spectral lines.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The use of a digital micromirror array as a temporal gate and spatial-filtering device for laser-induced breakdown spectroscopy and laser ablation molecular isotopic spectrometry

A digital micromirror array (DMMA) is used in a simple and inexpensive approach for spatially resolved temporal gating of atomic emission detection in laser-induced breakdown spectroscopy (LIBS). Selected mirrors in the array are actuated at a time delayed from the primary laser pulse, permitting optical gating with a response time of 160 ns while using a conventional CCD detector. Detector gating is shown to decrease noise from short-lived spectroscopic background (both continuum and N II from air), improving signal-to-background ratios by 22-times for selected samples and emission lines. The utility of rapid temporal gating is also demonstrated for the optical detection of isotopes using the laser-ablation molecular isotope spectrometry (LAMIS) experiment. Additionally, optical temporal gating and spatial filtering are used to isolate regions of the laser-induced plasma, enhancing signal from molecular emission. The potential of the simple technique for use in field-portable LIBS and LAMIS experiments is explored.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Time-resolved soft x-ray spectra from laser-produced Cu plasma

The volumetric heating of a thin copper target has been studied with time resolved x-ray spectroscopy. The copper target was heated by a plasma produced using the Lawrence Livermore National Laboratory's Compact Multipulse Terawatt (COMET) laser. A variable spaced grating spectrometer coupled to an x-ray streak camera measured soft x-ray emission (800-1550 eV) from the back of the copper target to characterize the bulk heating of the target. Radiation hydrodynamic simulations were modeled in two-dimensions using the HYDRA code. The target conditions calculated by HYDRA were post-processed with the atomic kinetics code CRETIN to generate synthetic emission spectra. A comparison between the experimental and simulated spectra indicates the presence of specific ionization states of copper and the corresponding electron temperatures and ion densities throughout the laser-heated copper target.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Hot-electron generation from laser–pre-plasma interactions in cone-guided fast ignition

Two-dimensional particle-in-cell (PIC) simulations were performed for the cone-in-shell integrated fast-ignition experiments at the Omega Laser Facility [W. Theobald et al., Phys. Plasmas 18, 056305 (2011)]. The initial plasma density profile in the PIC simulations was taken from hydrodynamic simulations of the prepulse interaction with the gold cone. Hot-electron generation from laser–pre-plasma interactions and transport up to 100× the critical density (n c ) was studied. The simulation showed a mean divergence half-angle of 68° and 50% absorption for the hot electrons. The simulation results show that the generated hot electrons were dominated in number by low-energy electrons but in energy by multi-MeV electrons. Electron transport between 5 and 100 n c was ballistic. In the late stage of the simulation, all the results were largely independent of polarization, indicating a stochastic hot-electron–generation mechanism.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

High-quality electron beam from laser wake-field acceleration in laser produced plasma plumes

Generation of highly collimated ({theta}{sub div}{approx}10 mrad), quasi-monoenergetic electron beam with peak energy 12 MeV and charge {approx}50 pC has been experimentally demonstrated from self-guided laser wake-field acceleration (LWFA) in a plasma plume produced by laser ablation of solid nylon (C{sub 12}H{sub 22}N{sub 2}O{sub 2}){sub n} target. A 7 TW, 45 fs Ti:sapphire laser system was used for LWFA, and the plasma plume forming pulse was derived from the Nd:YAG pump laser of the same system. The results show that a reproducible, high quality electron beam could be produced from this scheme which is simple, low cost and has the capability for high repetition rate operation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Study of Rayleigh–Taylor growth in laser irradiated planar SiO{sub 2} targets at ignition-relevant conditions

Rayleigh–Taylor (RT) growth experiments were performed on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using planar SiO{sub 2} targets seeded with a single mode 60-μm wavelength perturbation driven at peak laser intensities up to 9 × 10{sup 14} W/cm{sup 2}. These are the first RT measurements in SiO{sub 2} at conditions relevant to direct-drive inertial confinement fusion ignition. The measured average modulation growth rates agree with the 2-D hydrodynamics code DRACO, providing an important step in the development of target ablators that are robust to RT growth and hot- electron preheat considerations when driven at the intensities required to achieve thermonuclear ignition.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Impact of laser power density on tribological properties of Pulsed Laser Deposited DLC films

Fabrication of wear resistant and low friction carbon films on the engineered substrates is considered as a challenging task for expanding the applications of diamond-like carbon (DLC) films. In this paper, pulsed laser deposition (PLD) technique is used to deposit DLC films on two different types of technologically important class of substrates such as silicon and AISI 304 stainless steel. Laser power density is one of the important parameter used to tailor the fraction of sp{sup 2} bonded amorphous carbon (a-C) and tetrahedral amorphous carbon (ta-C) made by sp{sup 3} domain in the DLC film. The I(D)/I(G) ratio decreases with the increasing laser power density which is associated with decrease in fraction of a-C/ta-C ratio. The fraction of these chemical components is quantitatively analyzed by EELS which is well supported to the data obtained from the Raman spectroscopy. Tribological properties of the DLC are associated with chemical structure of the film. However, the super low value of friction coefficient 0.003 is obtained when the film is predominantly constituted by a-C and sp{sup 2} fraction which is embedded within the clusters of ta-C. Such a particular film with super low friction coefficient is measured while it was deposited on steel at low laser power density of 2 GW/cm{sup 2}. The super low friction mechanism is explained by low sliding resistance of a-C/sp{sup 2} and ta-C clusters. Combination of excellent physical and mechanical properties of wear resistance and super low friction coefficient of DLC films is desirable for engineering applications. Moreover, the high friction coefficient of DLC films deposited at 9GW/cm{sup 2} is related to widening of the intergrain distance caused by transformation from sp{sup 2} to sp{sup 3} hybridized structure.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Novel signal inversion of laser beam induced current for femtosecond-laser-drilling-induced junction on vacancy-doped p-type HgCdTe

In this paper, experimental results of temperature-dependent signal inversion of laser beam induced current (LBIC) for femtosecond-laser-drilling-induced junction on vacancy-doped p-type HgCdTe are reported. LBIC characterization shows that the traps induced by femtosecond laser drilling are sensitive to temperature. Theoretical models for trap-related p-n junction transformation are proposed and demonstrated using numerical simulations. The simulations are in good agreement with the experimental results. The effects of traps and mixed conduction are possibly the main reasons that result in the novel signal inversion of LBIC microscope at room temperature. The research results provide a theoretical guide for practical applications of large-scale array HgCdTe infrared photovoltaic detectors formed by femtosecond laser drilling, which may act as a potential new method for fabricating HgCdTe photodiodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Measurement of the target current by inductive probe during laser interaction on terawatt laser system PALS

Measurements of the return-current flowing through a solid target irradiated with the sub-nanosecond kJ-class Prague Asterix Laser System is reported. A new inductive target probe was developed which allows us measuring the target current derivative in a kA/ns range. The dependences of the target current on the laser pulse energy for cooper, graphite, and polyethylene targets are reported. The experiment shows that the target current is proportional to the deposited laser energy and is strongly affected by the shot-to-shot fluctuations. The corresponding maximum target charge exceeded a value of 10 μC. A return-current dependence of the electromagnetic pulse produced by the laser-target interaction is presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Ordered horizontal Sb 2 Te 3 nanowires induced by femtosecond lasers

Nanowires are of intense interest on account of their ability to confine electronic and phononic excitations in narrow channels, leading to unique vibronic and optoelectronic properties. Most systems reported to date exhibit nanowire axes perpendicular to the substrate surface, while for many applications (e.g., photodetectors and sensors), a parallel orientation may be advantageous. Here in this paper, we report the formation of in-plane Sb 2 Te 3 nanowires using femtosecond laser irradiation. High-resolution scanning transmission electron microscopy imaging and element mapping reveal that an interesting laser-driven anion exchange mechanism is responsible for the nanowire formation. This development points the way to the scalable production of a distinct class of nanowire materials with in-plane geometry.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Laser Spectroscopic and Theoretical Studies of the Structures and Encapsulation Motifs of Functional Molecules

Extensive laser spectroscopic and theoretical studies have been recently carried out with the aim to reveal the structure and dynamics of encapsulation complexes in the gas phase. The characteristics of the encapsulation complexes are governed by the fact that (i) most of the host molecules are flexible and (ii) the complexes form high dimensional structures by using weak non-covalent interactions. These characteristics result in the possibility of the coexistence of many conformers in close energetic proximity. The combination of supersonic jet/laser spectroscopy and high level quantum chemical calculations is essential in tackling these challenging problems. In this report we describe our recent studies on the structures and dynamics of the encapsulation complexes formed by calix[4]arene (C4A), dibenzo-18-crown-6-ether (DB18C6), and benzo-18-crown-6-ether (B18C6) "hosts" interacting with N2, acetylene, water, and ammonia "guest" molecules. The gaseous host-guest complexes are generated under jet-cooled conditions. We apply various laser spectroscopic methods to obtain the conformer- and isomer-specified electronic and IR spectra. The experimental results are complemented with quantum chemical calculations ranging from density functional theory to high level first principles calculations at the MP2 and CCSD(T) levels of theory. We discuss the possible conformations of the bare host molecules, the structural changes they undergo upon complexation, and the key interactions that are responsible in stabilizing the specific complexes

electronic structure calculations↗
DOE OSTI2015

The effect of laser spot shapes on polar-direct-drive implosions on the National Ignition Facility

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 of 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.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Positron generation using laser-wakefield electron sources

Positron generation, using wakefield-accelerated electrons driven into a converter target, was investigated experimentally and through Monte Carlo simulations. Using experimentally measured initial electron distributions from a 60 fs laser system, modeling shows that a collimated wakefield electron beam of moderate energy (50–200 MeV) produces a large number of positrons (~10 7 ), which are emitted from the rear of a mm-scale, high-Z target with divergence angles between 50 and 150 mrad. The large perpendicular momentum of the positrons was found to be dominated by contributions from multiple small angle Coulomb scattering. Positrons were not observed above background noise for a range of targets where simulations indicate a 5–30× increase in the beam charge was necessary to exceed threshold detection. These results provide new understanding to the fundamental limitations of creating narrow-divergence, high-density positron beams from laser-wakefield platforms for use in future laboratory pair plasma experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Laser pulse driven terahertz generation via resonant transition radiation in inhomogeneous plasmas

An intense, short laser pulse propagating across a plasma boundary ponderomotively drives THz radiation. Full format PIC simulations and theoretical analysis are conducted to investigate the properties of this radiation. Simulation results which show the THz emission originates in regions of varying density and covers a broad spectrum with maximum frequency close to the maximum plasma frequency. In the case of a sharp vacuum-plasma boundary, the radiation is generated symmetrically at the plasma entrance and exit, and its properties are independent of plasma density when the density exceeds a characteristic value determined by the product of the plasma frequency and the laser pulse duration. For a diffuse vacuum-plasma boundary, the emission from the plasma entrance and exit is asymmetric: increasing and decreasing density ramps enhance and diminish the radiated energy, respectively. Enhancements by a factor of 50 are found and simulations show that a 1.66 J, 50 fs driver pulse can generate ∼400 μJ of THz radiation in a 1.2 mm increasing density ramp. We present a model that attributes this effect to a plasma resonance process in the density ramp. The results from the model match those of the simulations for ramp lengths less than 600 μm. For longer ramps for which simulations are too time consuming, the model shows that the amount of radiation reaches a maximum at a ramp length determined by collisional absorption.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Photonic circuits for laser stabilization with integrated ultra-high Q and Brillouin laser resonators

The integration of stabilized lasers, sources that generate spectrally pure light, will provide compact, low-cost solutions for applications including quantum information sciences, precision navigation and timing, metrology, and high-capacity fiber communications. We report a significant advancement in this field, demonstrating stabilization of an integrated waveguide Brillouin laser to an integrated waveguide reference cavity, where both resonators are fabricated using the same CMOS-compatible integration platform. We demonstrate reduction of the free running Brillouin laser linewidth to a 292 Hz integral linewidth and carrier stabilization to a 4.9 × 10 –13 fractional frequency at 8 ms reaching the cavity-intrinsic thermorefractive noise limit for frequencies down to 80 Hz. We achieve this level of performance using a pair of 56.4 x 10 6 quality factor Si 3 N 4 waveguide ring-resonators that reduce the high-frequency noise by the nonlinear Brillouin process and the low-frequency noise by Pound–Drever–Hall locking to the ultra-low loss resonator. These results represent an important step toward integrated stabilized lasers with reduced sensitivity to environmental disturbances for atomic, molecular, and optical physics (AMO), quantum information processing and sensing, and other precision scientific, sensing, and communications applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗