Nonlinear optical conversion of Nd:glass laser multimode radiation into the second harmonic in KDP crystal

The second-harmonic generation (SHG) of Nd:glass multimode laser radiation in a 3?cm long KDP crystal has been studied both experimentally and theoretically for type I doubling at power densities of up to 2.5 GW cm?2, radiation divergence of 0.5?3.5 mrad and between 100?1000 transverse modes. The theoretical calculations of SHG were performed in the fixed-field approximation, fixed-intensity approximation and in the nonlinear regime. The maximum experimental conversion efficiency of 52% was obtained for the case of partially polarized radiation with divergence of 0.5 mrad and 100 transverse modes.