Abstract

We have measured the spatial coherence of an initially fully spatially coherent pump laser beam following stimulated Brillouin scattering (SBS) in SF₆ gas at 15 atm. Using a simple interferometric technique, we find that the fraction of the diameter of the scattered beam which is spatially coherent decreases with increasing f/No. of the incident 308-nm pump beam. Surprisingly, we also find that the spatial coherence of the scattered beam increases with decreasing pump energy. To our knowledge, these measurements are the first to address the issue of spatial coherence in SBS and point toward an important measure of the fidelity of phase conjugation produced by SBS. The influence of a weak seed beam on the coherence of the phase conjugate beam is also discussed.

© 1986 Optical Society of America