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Title: Nonlinear evolution of the plasma beat wave: Compressing the laser beat notes via electromagnetic cascading

Abstract

The near-resonant beat wave excitation of an electron plasma wave (EPW) can be employed for generating the trains of few-femtosecond electromagnetic (EM) pulses in rarefied plasmas. The EPW produces a comoving index grating that induces a laser phase modulation at the difference frequency. As a result, the cascade of sidebands red and blue shifted by integer multiples of the beat frequency is generated in the laser spectrum. The bandwidth of the phase-modulated laser is proportional to the product of the plasma length, laser wavelength, and amplitude of the electron density perturbation. When the beat frequency is lower than the electron plasma frequency, the redshifted spectral components are advanced in time with respect to the blueshifted ones near the center of each laser beat note. The group velocity dispersion of plasma compresses so chirped beat notes to a few-laser-cycle duration thus creating a train of sharp EM spikes with the beat periodicity. Depending on the plasma and laser parameters, chirping and compression can be implemented either concurrently in the same, or sequentially in different plasmas. Evolution of the laser beat wave and electron density perturbations is described in time and one spatial dimension in a weakly relativistic approximation. Using the compressionmore » effect, we demonstrate that the relativistic bistability regime of the EPW excitation [G. Shvets, Phys. Rev. Lett. 93, 195004 (2004)] can be achieved with the initially subthreshold beat wave pulse.« less

Authors:
;  [1]
  1. Department of Physics and Institute for Fusion Studies, University of Texas at Austin, One University Station C1500, Austin, Texas 78712 (United States)
Publication Date:
OSTI Identifier:
20779247
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics; Journal Volume: 73; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevE.73.046403; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; APPROXIMATIONS; COMPRESSION; ELECTROMAGNETIC RADIATION; ELECTRON DENSITY; ELECTRON PLASMA WAVES; EVOLUTION; EXCITATION; LANGMUIR FREQUENCY; LASERS; MODULATION; NONLINEAR PROBLEMS; PERIODICITY; PULSES; RELATIVISTIC PLASMA; RELATIVISTIC RANGE; SPECTRAL SHIFT; WAVELENGTHS

Citation Formats

Kalmykov, Serguei, and Shvets, Gennady. Nonlinear evolution of the plasma beat wave: Compressing the laser beat notes via electromagnetic cascading. United States: N. p., 2006. Web. doi:10.1103/PHYSREVE.73.0.
Kalmykov, Serguei, & Shvets, Gennady. Nonlinear evolution of the plasma beat wave: Compressing the laser beat notes via electromagnetic cascading. United States. doi:10.1103/PHYSREVE.73.0.
Kalmykov, Serguei, and Shvets, Gennady. Sat . "Nonlinear evolution of the plasma beat wave: Compressing the laser beat notes via electromagnetic cascading". United States. doi:10.1103/PHYSREVE.73.0.
@article{osti_20779247,
title = {Nonlinear evolution of the plasma beat wave: Compressing the laser beat notes via electromagnetic cascading},
author = {Kalmykov, Serguei and Shvets, Gennady},
abstractNote = {The near-resonant beat wave excitation of an electron plasma wave (EPW) can be employed for generating the trains of few-femtosecond electromagnetic (EM) pulses in rarefied plasmas. The EPW produces a comoving index grating that induces a laser phase modulation at the difference frequency. As a result, the cascade of sidebands red and blue shifted by integer multiples of the beat frequency is generated in the laser spectrum. The bandwidth of the phase-modulated laser is proportional to the product of the plasma length, laser wavelength, and amplitude of the electron density perturbation. When the beat frequency is lower than the electron plasma frequency, the redshifted spectral components are advanced in time with respect to the blueshifted ones near the center of each laser beat note. The group velocity dispersion of plasma compresses so chirped beat notes to a few-laser-cycle duration thus creating a train of sharp EM spikes with the beat periodicity. Depending on the plasma and laser parameters, chirping and compression can be implemented either concurrently in the same, or sequentially in different plasmas. Evolution of the laser beat wave and electron density perturbations is described in time and one spatial dimension in a weakly relativistic approximation. Using the compression effect, we demonstrate that the relativistic bistability regime of the EPW excitation [G. Shvets, Phys. Rev. Lett. 93, 195004 (2004)] can be achieved with the initially subthreshold beat wave pulse.},
doi = {10.1103/PHYSREVE.73.0},
journal = {Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics},
number = 4,
volume = 73,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2006},
month = {Sat Apr 15 00:00:00 EDT 2006}
}
  • A general analytical solution for the temporal (or spatial) evolution of electromagnetic cascading in the context of beat-wave generation of intense plasma waves is given. The amplitude of the nonlinear beat plasmon can be solved separately, after which the solution of the whole electromagnetic cascade can be constructed in terms of Bessel functions. Implications of the analytical model for the beat-wave acceleration, plasma heating, and laser fusion are discussed.
  • The electrostatic oscillating two-stream instability of laser-driven plasma beat-wave was studied recently by Gupta et al. [Phys. Plasmas 11, 5250 (2004)], who applied their theory to limit the amplitude level of a plasma wave in the beat-wave accelerator. As a self-generated magnetic field is observed in laser-produced plasma, hence, the electromagnetic oscillating two-stream instability may be another possible mechanism for the saturation of laser-driven plasma beat-wave. The efficiency of this scheme is higher than the former.
  • Through particle-in-cell simulations, the evolution of nonlinear plasma waves is examined in one-dimensional collisionless plasma undergoing mechanical compression. Unlike linear waves, whose wavelength decreases proportionally to the system length L(t), nonlinear waves, such as solitary electron holes, conserve their characteristic size {Delta} during slow compression. This leads to a substantially stronger adiabatic amplification as well as rapid collisionless damping when L approaches {Delta}. On the other hand, cessation of compression halts the wave evolution, yielding a stable mode.
  • A train of few-laser-cycle relativistically intense radiation spikes with a terahertz repetition rate can be organized self-consistently in plasma from two frequency detuned co-propagating laser beams of low intensity. Large frequency bandwidth for the compression of spikes is produced via laser-induced periodic modulation of the plasma refractive index. The beat-wave-driven electron plasma wave downshifted from the plasma frequency creates a moving index grating thus inducing a periodic phase modulation of the driving laser (in spectral terms, electromagnetic cascading). The group velocity dispersion compresses the chirped laser beat notes to a few-cycle duration and relativistic intensity either concurrently in the same,more » or sequentially in different plasmas. Particle-in-cell simulations indicate that the effect persists in a realistic three-dimensional axisymmetric geometry.« less
  • Acceleration and heating of a relativistic electron beam by cascading nonlinear Landau damping involving three or four intense electromagnetic waves in a plasma are studied theoretically based on kinetic wave equations and transport equations derived from relativistic Vlasov{endash}Maxwell equations. Three or four electromagnetic waves excite successively two or three nonresonant beat-wave-driven relativistic electron plasma waves with a phase velocity near the speed of light [{ital v}{sub {ital p}}={ital c}(1{minus}{gamma}{sup {minus}2}{sub {ital p}}){sup 1/2}, {gamma}{sub {ital p}}={omega}/{omega}{sub {ital pe}}]. Three beat waves interact nonlinearly with the electron beam and accelerate it to a highly relativistic energy {gamma}{sub {ital p}}{ital m}{sub {italmore » e}}{ital c}{sup 2} more effectively than by the usual nonlinear Landau damping of two electromagnetic waves. It is proved that the electron beam can be accelerated to more highly relativistic energy in the plasma whose electron density decreases temporally with an appropriate rate because of the temporal increase of {gamma}{sub {ital p}}. {copyright} {ital 1996 American Institute of Physics.}« less