Abstract

We have made measurements of the Raman amplification of a Stokes seed for various ratios of input Stokes intensity to input pump laser intensity. The Raman medium was vibrational hydrogen with the pump and Stokes undergoing a shallow focus through the cell to stay well below the Stokes-anti-Stokes phase matching angle. With small injection ratios, independent of whether the Stokes and pump were correlated, the Stokes was amplified and the pump deleted, as normally expected. However, if the Stokes and pump were initially uncorrelated, as the injection ratio approached unity the Raman gain significantly diminished and the pump and Stokes were observed to copropagate without interaction. This effective gain suppression is predicted by the solution of the Raman gain equations for a broadband pump with negligible dispersion.¹ Also predicted, and observed experimentally, is that the effect should disappear when the pump and Stokes become correlated. Measurements of the beam quality and spectral width of the input and output pump were also made. We believe that these results point to a potentially useful technique for suppressing SRS for laser propagation through various media.

© 1988 Optical Society of America