Stimulated Brillouin scattering in gaseous nitrogen, methane, and carbon dioxide has been observed using a giant pulse laser and employing gas densities from 19 to 385 amagat. Stimulated Brillouin scattering was also observed in carbon-dioxide liquid at 26°C and through the transition temperature. The density threshold below which no Brillouin scattering was observed was 56 amagat for nitrogen, 19 amagat for methane, 350 amagat for gaseous carbon dioxide, and 385 amagat for liquid carbon dioxide. The velocity of sound in each case increases markedly with increasing pressure. The velocity of sound extrapolated to 1 amagat density for nitrogen and methane agrees closely with the isothermal velocity. There is some evidence to indicate an amplitude dependence on the measured velocities.
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