Forward stimulated thermal Rayleigh scattering*

This investigation has examined the forward-scattered spectrum of the light from a giant-pulse ruby laser, which was focused into liquids to which absorbers were added. Anti-Stokes shifts of about one-half of the incident linewidth were observed, the same shift as that for back-scattered light. The shift has a small dependence upon the liquid used but does not depend upon the kind of absorber, or the amount of absorption above a critical value, and, except for the lowest powers used, is independent of incident laser power. It is found that almost all of the non-absorbed light is transmitted, but at the shifted frequency. The intense, shifted, forward-scattered light is explained as an interaction of the stimulated back-scattered light with the incident light which preferentially amplifies certain frequencies of the incident laser profile at the expense of the back-scattered light. It is concluded that forward scattering is an important technique for additional observations of stimulated thermal scattering.