Spatial mode structure of stimulated Stokes emission from a Raman generator

The spatial mode structure of the stimulated Stokes emission from a H2 Raman generator has been accurately determined by using a linear photodiode array and imaging techniques. The diffraction-limited pump beam was obtained by spatially clipping the output of an injection-locked XeCl laser. The spatial profiles of the stimulated Stokes beam are compared with the predictions of Yariv’s theory of propagation in a quadratic gain medium applied to Raman scattering [ A. Yariv , Quantum Electronics ( Wiley, New York, 1975)]. While the theory compares well with the experimental data at low intensities, the spatial profile develops features at higher intensities that are not predicted by the simple theory.