Optimization of stimulated Raman scattering with astigmatic lenses

The conversion efficiency of a Raman cell at high pump energies has been increased with an astigmatic focus. Experimental and numerical results show that the increased conversion is due to the reduction of cascade second order Stokes. For our experimental setup, it is shown that other effects, namely Brillouin scattering, anti-Stokes generation, and ground-state depletion, are negligible. Another important advantage of an astigmatic focus is the reduced risk of optical breakdown due to the lower intensity at the focus with only a small gain reduction. Good agreement was found between experimental and numerical results. In particular, the pump energy where the conversion for an ordinary focus is identical to an astigmatic focus is reproduced by the calculations.