TRANSVERSE BEAM PROFILES ON TRAVELING-WAVE OPTICAL PARAMETRIC GENERATION IN KTIOPO4 CRYSTALS

Transverse beam profiles on traveling-wave optical parametric generation in KTiOPO4 crystals pumped by short optical pulses are investigated. The transverse beam profile deformation and splitting due to the back-conversion in the traveling-wave parametric propagation process is clarified for the first time from experimental observations and calculations. The transverse beam profile becomes ring shaped when there is no walk-off and deforms by expanding to the walk-off direction when walk-off exists. The deformation of the profile can be reduced by using a short crystal or decreasing the pump intensity due to the subsequent reduction in back-conversion. However, in these cases, the conversion efficiency becomes very low (3%-4%). We can improve the conversion efficiency while keeping good transverse beam profiles by using the two-crystal beam overlapping technique. The optimum conditions for this technique are clarified through calculations and it is shown that conversion efficiency of more than 18% can be achieved when they are used. (C) 1995 American Institute of Physics.