Density Dependence in Thermal Rayleigh Scattering in Gases

Abstract

Additional measurements of critical absorption coefficients and anti-Stokes shifts have been made in stimulated thermal Rayleigh scattering in C0 2 and CH 4 . The threshold power for different absorption coefficients was determined as a function of density. The results are in qualitative agreement with the theoretical predictions of Gray and Herman.

A linearized theory of transient laser heating in fluids

“…One finds that %=(y -1), and that c, To%' = [(y -1)/y]vo. A third assumption that is often appropriate is that the population transfer has reached a steady state; often the population decay rate is on the order of nanoseconds, during which time the acoustic and dissipative processes in the medium have produced negligible effects [22]. With these assumptions, the more familiar equation [1,2,5] for the medium perturbation is recovered, but in this case dissipative efFects are properly treated:…”

“…In general, the decay rate I depends on both the population decay rate and the diffusion of stored internal energy [6,21,22]. Typically, however, the relaxation rate is dominated by the two-level population decay rate, equal to the inverse of the T2 decay time [22].…”

“…Typically, however, the relaxation rate is dominated by the two-level population decay rate, equal to the inverse of the T2 decay time [22]. This is especially true for forward scattering, for which the low spatial frequencies involved imply that diffusion occurs on a relatively long time scale.…”