Stimulated Light Scattering in Binary Gas Mixtures
Quarterly technical rept. for period ending 27 Jun 1971
HARVARD UNIV CAMBRIDGE MA DIV OF ENGINEERING AND APPLIED PHYSICS
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The theory of stimulated light scattering from a binary gas mixture was developed. It considers the coupling of a laser wave and a scattered light wave with the collective modes of the mixture. It was found that in a binary gas mixture in which the different types of molecules have a large difference in mass and polarizability, it is possible to generate stimulated scattering from local fluctuations in the concentration. The shift in frequency between the laser and backward scattered wave was observed systematically as a function of helium concentration from 0 to 90 in mixtures of He and SF6 in which the partial pressure of SF6 was 5 atm., and in mixtures of He and Xe in which the partial pressure of Xe was 8 atm. In both cases, for helium concentration less than 60 the frequency shift of the backscattered light is characteristic of stimulated Brillouin scattering in the mixture. As the helium concentration increases above 60, the frequency shift decreases and rapidly approaches the small values which are characteristic of stimulated concentration scattering. The experimental observations are in good agreement with theoretical predictions.