Dependence of stimulated Brillouin scattering on target material and f number

Journal Article · Tue Dec 01 04:00:00 EST 1981 · Phys. Fluids; (United States)

DOI:https://doi.org/10.1063/1.863312· OSTI ID:5925899

Clayton, C E; Joshi, C; Yasuda, A; Chen, F F

Stimulated Brillouin scattering of CO/sub 2/ laser radiation from a pre-ionized gas target is observed and studied with the following parameter changes: (1) f/7.5 focusing versus f/2 focusing, (2) nitrogen plasma versus hydrogen plasma, (3) pure nitrogen versus nitrogen with a hydrogen impurity, and (4) single line operation of the laser versus multiline operation. The f-number dependence is found to be weak because the increased intensity with the smaller f number is offset by the shorter interaction length for the Brillouin instability. The instability growth in nitrogen is found to be more severe than in hydrogen because the nitrogen plasma has a higher ZT/sub e//T/sub i/ resulting in a lower damping rate for the ion-acoustic wave. In all the above cases the Brillouin reflectivity reaches saturation and the inferred saturation amplitudes of the ion-acoustic waves are consistent with ion trapping being the saturation mechanism. Addition of a small amount (approx. =6%) of a light ion impurity (hydrogen) to a heavy ion plasma (nitrogen) virtually extinguishes the Brillouin instability. Finally, multiline operation of the CO/sub 2/ laser pump, with the line separation ..delta omega.. and the instability growth rate ..gamma.. such that ..delta omega../..gamma..>>1, is seen to reduce the Brillouin reflectivity as if each line were acting independently, as expected.

• Research Organization: Department of Electrical Sciences and Engineering, University of California, Los Angeles, California 90024
• OSTI ID: 5925899
• Journal Information: Phys. Fluids; (United States), Journal Name: Phys. Fluids; (United States) Vol. 24:12; ISSN PFLDA
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700108* -- Fusion Energy-- Plasma Research-- Wave Phenomena
BRILLOUIN EFFECT
CARBON DIOXIDE LASERS
COHERENT SCATTERING
DAMPING
ELECTROMAGNETIC RADIATION
ELEMENTS
FLUIDS
FOCUSING
GAS LASERS
GASES
HYDROGEN
ION ACOUSTIC WAVES
ION WAVES
IONIZED GASES
LASER RADIATION
LASERS
NITROGEN
NONMETALS
PLASMA
PLASMA WAVES
RADIATIONS
SCATTERING
TARGETS