Evidence of stimulated Raman scattering occurring in laser filaments in long-scale-length plasmas

Journal Article · Fri May 01 04:00:00 EDT 1992 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860086· OSTI ID:7113233

Afshar-rad, T; Coe, S E; Willi, O; Desselberger, M ^[1]

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1. Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BZ (United Kingdom)

A time-resolved study is presented of stimulated Raman backscatter (B-SRS) produced in a large-scale-length preformed plasma in an intense laser pulse. The first direct experimental results are presented to (i) show that the B-SRS is generated predominantly in laser filaments and (ii) provide a direct correlation between the spectral and spatial emission profiles of the B-SRS as a function of interaction irradiance. The anomalous'' B-SRS spectral features so commonly reported in time-resolved studies are shown to be the characteristic emission of B-SRS from filaments. The B-SRS fraction was also measured as a function of interaction irradiance. The B-SRS intensity threshold'' and saturating'' behavior recorded can be well described for the present interaction conditions. The onset of B-SRS is shown to be strongly correlated with the intensity threshold of the filamentation instability. The effect of laser beam smoothing'' techniques on the B-SRS emission have also been investigated, using either a random phase plate (RPP) or induced spatial incoherence (ISI). The results suggest that their effectiveness in suppressing B-SRS is strongly associated with their ability to reduce the level of filamentation while still producing a high level of plasma perturbation which can effectively destroy the phase-matching conditions necessary for B-SRS.

• OSTI ID: 7113233
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 4:5; ISSN 0899-8221; ISSN PFBPE
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700350* -- Plasma Production
Heating
Current Drive
& Interactions-- (1992-)
BACKSCATTERING
DAMPING
ELECTROMAGNETIC RADIATION
EMISSION
ENERGY-LEVEL TRANSITIONS
FILAMENTS
INSTABILITY
LANDAU DAMPING
LASER FUSION REACTORS
PARAMETRIC INSTABILITIES
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
RADIATIONS
RAMAN EFFECT
SCATTERING
STIMULATED EMISSION
THERMONUCLEAR REACTORS