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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Effect of collisions on amplification of laser beams by Brillouin scattering in plasmas

We report on particle in cell simulations of energy transfer between a laser pump beam and a counter-propagating seed beam using the Brillouin scattering process in uniform plasma including collisions. The results presented show that the ion acoustic waves excited through naturally occurring Brillouin scattering of the pump field are preferentially damped without affecting the driven Brillouin scattering process resulting from the beating of the pump and seed fields together. We find that collisions, including the effects of Landau damping, allow for a more efficient transfer of energy between the laser beams, and a significant reduction in the amount of seed pre-pulse produced.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Amplification of interference color by using liquid crystal for protein detection

Micrometer-sized, periodic protein lines printed on a solid surface cause interference color which is invisible to the naked eye. However, the interference color can be amplified by using a thin layer of liquid crystal (LC) covered on the surface to form a phase diffraction grating. Strong interference color can thus be observed under ambient light. By using the LC-amplified interference color, we demonstrate naked-eye detection of a model protein—immunoglobulin G (IgG). Limit of detection can reach 20 μg/ml of IgG without using any instrumentation. This detection method is potentially useful for the development of low-cost and portable biosensors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Non-filamentated ultra-intense and ultra-short pulse fronts in three-dimensional Raman seed amplification

Ultra-intense and ultra-short laser pulses may be generated up to the exawatt-zetawatt regime due to parametric processes in plasmas. The minimization of unwanted plasma processes leads to operational limits which are discussed here with respect to filamentation. Transverse filamentation, which originally was derived for plane waves, is being investigated for seed pulse propagation in the so called π-pulse limit. A three-dimensional (3D) three-wave-interaction model is the basis of the present investigation. To demonstrate the applicability of the three-wave-interaction model, the 1D pulse forms are compared with those obtained from 1D particle in cell and Vlasov simulations. Although wave-breaking may occur, the kinetic simulations show that the leading pumped pulse develops a form similar to that obtained from the three-wave-interaction model. In the main part, 2D and 3D filamentation processes of (localized) pulses are investigated with the three-wave-interaction model. It is shown that the leading pulse front can stay filamentation-free, whereas the rear parts show transverse modulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Terahertz electromagnetic wave generation and amplification by an electron beam in the elliptical plasma waveguides with dielectric rod

The propagation of electromagnetic waves in an elliptical plasma waveguide including strongly magnetized plasma column and a dielectric rod is investigated. The dispersion relation of guided hybrid electromagnetic waves is obtained. Excitation of the waves by a thin annular relativistic elliptical electron beam will be studied. The time growth rate of electromagnetic waves is obtained. The effects of relative permittivity constant of dielectric rod, radius of dielectric rod, accelerating voltage, and current density of the annular elliptical beam on the growth rate and the frequency spectra are numerically presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Pressure-driven amplification and penetration of resonant magnetic perturbations

We show that a resonant magnetic perturbation applied to the boundary of an ideal plasma screw-pinch equilibrium with nested surfaces can penetrate inside the resonant surface and into the core. The response is significantly amplified with increasing plasma pressure. We present a rigorous verification of nonlinear equilibrium codes against linear theory, showing excellent agreement.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Parametric amplification of broadband radiation of a cw superluminescent diode under picosecond pumping

It is proposed to use cw superluminescent diodes with a spectral width of about 300 cm{sup −1} and high spatial coherence as seed radiation sources in parametric amplifiers with picosecond pumping in order to form broadband picosecond pulses. A two-cascade parametric amplifier based on BaB{sub 2}O{sub 4} (BBO) crystals is pumped by 20-ps pulses of the second harmonic of an Nd : YAG laser. For a superluminescent diode spectral width of 275 cm{sup −1} (centre wavelength 790 nm), the spectral width of picosecond pulses at the parametric amplifier output is 203 cm{sup −1}. At a total pump energy of 7.2 mJ for BBO crystals, the energy of the enhanced emission of the superluminescent diode is found to be 0.6 mJ.

42 ENGINEERING↗
DOE OSTI2017

Formation and amplification of 50-ps pulses in a THL-100 hybrid laser system

Results of investigations of a THL-100 visible hybrid laser system consisting of a Ti : sapphire front end and a photodissociation XeF(C – A) amplifier are reported. The front end generates linearly chirped second harmonic pulses with a duration of 50 ps, an energy up to 5 mJ, and a high beam quality. Saturation of the XeF(C – A) amplifier at an input energy exceeding 2 mJ is demonstrated, and the output energy of 3.2 J is obtained, which makes it possible to achieve a peak power of about 50 TW in a 50-fs pulse. (paper)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Numerical analysis of amplification of picosecond pulses in a THL-100 laser system with an increase in the pump energy of the XeF(C – A) amplifier

Energy characteristics of laser radiation with a pulse width of 50 ps at an elevated pump energy of the XeF(C – A) amplifier of a hybrid THL-100 laser system are analysed numerically. The dynamics of the change in the energy and maximum intensity of laser radiation with an increase in the pump energy of the XeF(C – A) amplifier from 270 to 400 J is investigated. The results of studying the influence of the input beam divergence on the energy characteristics of the output beam are presented. It is shown that, for the existing system of mirrors, an increase in the pump energy to 400 J leads to an increase in the output energy from 3.2 to 5.5 J at a maximum radiation intensity of 57 GW cm{sup −2}. A system of amplifier mirrors with 27 laser beam passes and enlarged divergence angle of the amplified beam is considered. Theoretically, the proposed system of mirrors allows one to increase the laser pulse energy to 7.5 J at a maximum intensity of no more than 14.8 GW cm{sup −2}. The calculated efficiency of the conversion of the pump energy absorbed in the amplifier gas chamber into the lasing energy exceeds 3 % in this regime. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Fibre-optic 100 fs pulse amplification and transmission system in the telecom range

We have fabricated and investigated an efficient all-fibre source of ultrashort pulses of 100 fs duration with an energy of up to 5 nJ in the telecom range (near λ = 1.56 μm). Pulses from an erbium-doped fibre master oscillator with a minimum duration of 127 fs and repetition rate of 38.1 MHz were amplified in an erbium-doped active fibre to a maximum average power of 194.3 mW with a 30 % efficiency under pumping by 640-mW single-mode laser diodes at a wavelength λ{sub pump} = 976 nm and then compressed to an ∼100 fs duration in a silica fibre with reduced nonlinearity (LMA fibre). The compressed pulses were launched with an efficiency over 80 % into a hollow-core microstructured revolver fibre (HCRF) with a cladding formed by noncontacting cylindrical silica glass capillary tubes and a 61-μm-diameter hollow core. The measured loss for the fundamental mode of this fibre was under 30 dB km{sup −1} at λ = 1.56 μm. Owing to the weak nonlinearity and low dispersion of the HCRF, output pulses were similar in characteristics (duration and spectrum) to input pulses even at HCRF lengths above 10 m. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Amplification of dissipative solitons with a polarisation-maintaining tapered fibre amplifier

The generation of strongly chirped dissipative solitons offers great opportunities for generating high-power laser pulses of short duration. We demonstrate the possibility of amplifying such pulses in a polarisation-maintaining tapered fibre having 32 μm mode diameter at the output end. Highly chirped pulses with a repetition rate of 14.3 MHz and a duration of 10 ps at 1055 nm centre wavelength are amplified in an all-fibre circuit to 2.11 μJ energy and compressed by diffraction gratings to a duration of ∼297 fs. Reducing the pulse repetition rate to 1 MHz allows a 16.5 μJ output pulse energy to be achieved without manifestations of SRS and self-phase modulation in the spectrum. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

PARTICLE ACCELERATION AND MAGNETIC FIELD AMPLIFICATION IN THE JETS OF 4C74.26

We model the multi-wavelength emission in the southern hotspot of the radio quasar 4C74.26. The synchrotron radio emission is resolved near the shock with the MERLIN radio-interferometer, and the rapid decay of this emission behind the shock is interpreted as the decay of the amplified downstream magnetic field as expected for small scale turbulence. Electrons are accelerated to only 0.3 TeV, consistent with a diffusion coefficient many orders of magnitude greater than in the Bohm regime. If the same diffusion coefficient applies to the protons, their maximum energy is only ∼100 TeV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Cosmic bubble and domain wall instabilities I: parametric amplification of linear fluctuations

This is the first paper in a series where we study collisions of nucleated bubbles taking into account the effects of small initial (quantum) fluctuations in a fully 3+1-dimensional setting. In this paper, we consider the evolution of linear fluctuations around highly symmetric though inhomogeneous backgrounds. In particular, we demonstrate that a large degree of asymmetry develops over time from tiny initial fluctuations superposed upon planar and SO(2,1) symmetric backgrounds. These fluctuations are inevitable consequences of zero-point vacuum oscillations, so excluding them by enforcing a high degree of spatial symmetry is inconsistent in a quantum treatment. To simplify the analysis we consider the limit of two colliding planar walls, with mode functions for the fluctuations characterized by the wavenumber transverse to the collision direction and a longitudinal shape along the collision direction x, which we solve for. In the linear regime, the fluctuations obey a linear wave equation with a time- and space-dependent mass m{sub eff}(x,t). In situations where the walls collide multiple times, m{sub eff} oscillates in time. We use Floquet theory to study the evolution of the fluctuations and generalize the calculations familiar from the preheating literature to the case with many coupled degrees of freedom. The inhomogeneous case has bands of unstable transverse wavenumbers k{sub ⊥} whose corresponding mode functions grow exponentially. By examining the detailed spatial structure of the mode functions in x, we identify both broad and narrow parametric resonance generalizations of the homogeneous m{sub eff}(t) case of preheating. The unstable k{sub ⊥} modes are longitudinally localized, yet can be described as quasiparticles in the Bogoliubov sense. We define an effective occupation number and show they are created in bursts for the case of well-defined collisions in the background. The transverse-longitudinal coupling accompanying nonlinearity radically breaks this localized particle description, with nonseparable 3D modes arising that will be studied in subsequent papers.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Leaky unstable modes and electromagnetic radiation amplification by an anisotropic plasma slab

The interaction between electromagnetic radiation and a photoionized plasma slab with an anisotropic electron velocity distribution is studied. It is shown that the fields of leaky modes are amplified due to the development of aperiodic instability in the slab, which leads to an increase in both the reflected and transmitted fields. The transmitted field can significantly increase only if the slab thickness does not exceed the ratio of the speed of light to the electron plasma frequency, whereas there is no upper bound on the slab thickness for the reflected signal to be amplified.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Nonthermal plasmas around black holes, relevant collective modes, new configurations, and magnetic field amplification

The radiation emission from Shining Black Holes is most frequently observed to have nonthermal features. It is therefore appropriate to consider relevant collective processes in plasmas surrounding black holes that contain high energy particles with nonthermal distributions in momentum space. A fluid description with significant temperature anisotropies is the simplest relevant approach. These anisotropies are shown to have a critical influence on: (a) the existence and characteristics of stationary plasma and field ring configurations, (b) the excitation of “thermo-gravitational modes” driven by temperature anisotropies and gradients that involve gravity and rotation, (c) the generation of magnetic fields over macroscopic scale distances, and (d) the transport of angular momentum.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Amplification of Nonpotential Waves in a Magnetized Beam–Plasma System Taking into Account the Evolution of the Plasma

We have analyzed the beam instability taking into account nonpotential effects in a completely magnetized plasma with a density varying slowly with time. It is shown that a frequency shift appears in the amplified signal (during the propagation in such an electrodynamic system); analytic relations determining this shift have been obtained.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

On the Diffusivity of Moist Static Energy and Implications for the Polar Amplification Response to Climate Warming

Energy balance models (EBMs) have been widely used in a range of climate problems, but the assumption of constant diffusivity in the parameterization of the moist static energy (MSE) flux can be hardly justified. We demonstrate in this study that the diffusive MSE flux can be derived from the basic energy balance equation with a few tolerable assumptions. The estimated diffusivity is both spatially and seasonally dependent, and its midlatitude average is then tested against several scaling theories for the midlatitude eddy diffusivity. The result supports the diffusivity theory of Held and Larichev (1996) modified for the moist atmosphere, affording a dynamics-based parameterization of MSE diffusivity. The implementation of the parameterization in an EBM leads to an interactive MSE diffusivity that accounts for the midlatitude eddy response to climate forcing perturbations. Under a uniform radiative forcing, the EBM with a diffusivity so parameterized produces a weakening of the midlatitude diffusivity and a modestly polar-amplified surface temperature response as an inevitable outcome under the dual constraints of the nonlinear Clausius-Clapeyron relation and the temperature gradient-dependent diffusivity, even in the absence of any poleward amplifying radiative feedbacks. As the consequence of more isothermal temperature and reduced diffusivity, the variance of the midlatitude surface temperature also decreases with warming.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

EXor OUTBURSTS FROM DISK AMPLIFICATION OF STELLAR MAGNETIC CYCLES

EXor outbursts—moderate-amplitude disk accretion events observed in Class I and Class II protostellar sources—have timescales and amplitudes that are consistent with the viscous accumulation and release of gas in the inner disk near the dead zone boundary. We suggest that outbursts are indirectly triggered by stellar dynamo cycles, via poloidal magnetic flux that diffuses radially outward through the disk. Interior to the dead zone the strength of the net field modulates the efficiency of angular momentum transport by the magnetorotational instability. In the dead zone changes in the polarity of the net field may lead to stronger outbursts because of the dominant role of the Hall effect in this region of the disk. At the level of simple estimates we show that changes to kG-strength stellar fields could stimulate disk outbursts on 0.1 au scales, though this optimistic conclusion depends upon the uncertain efficiency of net flux transport through the inner disk. The model predicts a close association between observational tracers of stellar magnetic activity and EXor events.

79 ASTRONOMY AND ASTROPHYSICS↗