Abstract

Hydrogen molecular gas is a favorite system for Raman scattering studies.^1-3 One interesting aspect of this system is that a ring pattern is observed in the spatial distribution of the Stokes emission.¹ We report in this paper theoretical and experimental studies of such a ring pattern as a function of sample pressure, beam waist, laser intensity and emission frequency. Our experiment was carried out by passing a tightly-focused frequency-doubled Nd: YAG laser through a 25 cm sample cell containing hydrogen molecules. When the pressure was varied we observed changes in the pattern of the transverse profile of the forward scattered Stokes wave. At a pressure of 50 psi a ring structure was observed. As the pressure was increased from 100 psi to 800 psi via 150 and 300 a central peak appeared and the ring pattern gradually faded away. In our experimental setup the anti-Stokes scattering was measured and determined to be not important. Other experimental results, not closely related to the spatial pattern discussed here, will be presented somewhere else.

© 1988 Optical Society of America