Third harmonic generation of a short pulse laser in a plasma density ripple created by a machining beam

Journal Article · Fri Feb 15 04:00:00 EST 2008 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2836618· OSTI ID:21103835

Liu, C S; Tripathi, V K ^[1]

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1. Center of Mathematical and Theoretical Sciences, National Central University, Chung Li, Taiwan 3200 (China)

An intense machining laser beam, impinged on a gas jet target, causes space periodic ionization of the gas and heats the electrons. The nonuniform plasma pressure leads to atomic density redistribution. When, after a suitable time delay, a second more intense laser pulse is launched along the periodicity wave vector q-vector, a plasma density ripple n{sub q} is instantly created, leading to resonant third harmonic generation when q=4{omega}{sub p}{sup 2}/(3{omega}c{gamma}{sub 0}), where {omega}{sub p} is the plasma frequency, {omega} is the laser frequency, and {gamma}{sub 0} is the electron Lorentz factor. The third harmonic is produced through the beating of ponderomotive force induced second harmonic density oscillations and the quiver velocity of electrons at the fundamental. The relativistic mass nonlinearity plays no role in resonant coupling. The energy conversion efficiency scales as the square of plasma density and square of depth of density ripple, and is {approx}0.2% for normalized laser amplitude a{sub o}{approx}1 in a plasma of 1% critical density with 20% density ripple. The theory explains several features of a recent experiment.

• OSTI ID: 21103835
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 2 Vol. 15; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BEAMS
ELECTRONS
HARMONIC GENERATION
LANGMUIR FREQUENCY
LASER BEAM MACHINING
LASERS
NONLINEAR PROBLEMS
PLASMA DENSITY
PLASMA JETS
PLASMA PRESSURE
PONDEROMOTIVE FORCE
RELATIVISTIC RANGE