High power tungstate-crystal Raman laser operating in the strong thermal lensing regime

We report an investigation into a double metal tungstate Raman laser when pumped at elevated average powers. Potassium gadolinium tungstate (KGW) was placed in an external cavity configured for second-Stokes output and pumped at pulse repetition rate of 38 kHz with up to 46 W of average power. For output powers above 3 W, we observe preferential excitation of Hermite-Gaussian transverse modes whose order in the X-1' principal direction of the thermal expansion tensor scales linearly with Raman power. We deduce that strong astigmatic thermal lensing is induced in the Raman crystal with a negative component in the X-1' direction. At maximum pump power, 8.3 W of output power was obtained at a conversion efficiency of 18%. (C)2014 Optical Society of America