Experimental and numerical study of stimulated Raman scattering in an astigmatic focus

An astigmatic focus has been used to increase the conversion efficiency of a Raman cell at high pump energy. Experimental and numerical results show that the increased conversion is due to the reduction of cascade second order Stokes. It is shown that other effects, namely Brillouin scattering, anti-Stokes generation, and ground-state depletion, are negligible for the present experimental setup. The experimental and numerical calculations are in agreement. In particular, good agreement was obtained for the cross-over energy, i.e., the pump energy where the ordinary and the astigmatic focus give the same Stokes energy. Below this energy an ordinary focus gives a higher conversion than an astigmatic focus, while above this energy this is reversed