Nonlinear laser--matter interaction processes in long-scale-length plasmas

Journal Article · Wed Jul 01 00:00:00 EDT 1992 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860191· OSTI ID:7285127

Seka, W; Bahr, R E; Short, R W; Simon, A; Craxton, R S ^[1]; Montgomery, D S ^[2]; Rubenchik, A E ^[3]

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1. Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States)
2. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
3. USSR Academy of Science, Siberian Branch, Institute for Automation and Electrometry, Novosibirsk (Russia)

This paper reports on nonlinear laser--plasma interaction experiments using long-scale-length plasmas produced by the 24-beam OMEGA laser system operating at 351 nm. The experiments were carried out with distributed phase plates (DPP's) in all beams and with and without smoothing by spectral dispersion (SSD). Most of the beams were used to create a large preformed plasma, which had gradient scale lengths of {le}800 {mu}m at electron densities below a quarter of the critical density {ital n}{sub {ital c}} and temperatures in excess of 1 keV. One of the beams, the interaction beam,'' was timed independently and tightly focused to intensities {similar to}10{sup 15} W/cm{sup 2}. All beams had pulse durations of {similar to}0.6 nsec. The interaction processes studied were mainly Raman scattering and the two-plasmon decay (TPD) instability as evidenced by its characteristic 3/2-harmonic emission. Details of the Raman and 3/2-harmonic spectra are presented. Evidence was found for the TPD instability close to its Landau cutoff density at {similar to} 0.2{ital n}{sub {ital c}}. Raman emission was narrow-band and observed only from densities {lt} 0.2{ital n}{sub {ital c}}. For late timings of the interaction beam, the Raman emission appeared to originate from near the peak of the density profile, but for earlier timings it appeared to come from densities a factor of 2 below the calculated peak. Application of SSD affected the 3/2-harmonic emission only slightly, but it strongly reduced the Raman emission. A discussion is given of some models that attempt to explain these observations.

• DOE Contract Number: FC03-85DP40200
• OSTI ID: 7285127
• Journal Information: Physics of Fluids B; (United States), Vol. 4:7; ISSN 0899-8221
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
LASER-PRODUCED PLASMA
PLASMA INSTABILITY
BEAM-PLASMA SYSTEMS
NONLINEAR PROBLEMS
PLASMONS
RAMAN SPECTRA
TURBULENCE
ULTRAVIOLET SPECTRA
VISIBLE SPECTRA
INSTABILITY
PLASMA
QUASI PARTICLES
SPECTRA
700350* - Plasma Production
Heating
Current Drive
& Interactions- (1992-)
700340 - Plasma Waves
Oscillations
& Instabilities- (1992-)