Analysis of the stimulated Raman effects in an anisotropic crystal KDP

The semiclassical model of Shen and Bloembergen is applied to discuss the stimulated Raman effects in an anisotropic medium. In crystal KDP when the linear electrooptic effects are suppressed by proper orientation of the laser polarization with respect to the crystal axes, the coupled-wave analysis for Stokes generation give rise to solutions of ten composite Stokes-vibrational waves in the (anisotropic) Raman active medium. These composite waves may be identified as two ordinary forward-traveling waves, two ordinary backward-traveling waves, three extraordinary forward-traveling waves, and three extraordinary backward-traveling waves. When the phonons are nonpropagating, the solutions reduce to only one ordinary and one extraordinary wave in each direction. The thresholds and Stokes generations in this situation are discussed. Owing to the anisotropy of the crystal, it is found that the dispersion of KDP in general allows the momentum-matching condition for the coupling between Stokes and anti-Stokes waves to be nearly satisfied in five different situations.