KTP optical parametric oscillator pumped by laser with an SBS phase conjugate mirror

Potassium Titanium Oxide Phosphate (KTP) is a new nonlinear frequency-conversion crystal. It has high nonlinear coefficient, high damage threshold, easily-polished surface, and a broad transparency range. In this paper, the calculation method of angle phase-matching for parametric generation in KTP was presented. The angle phase-matching curve and their characteristics in KTP pumped by 532 nm, 694.3 nm radiation were calculated and analyzed. The propagating principal plane (x-y plane) and 56 degree(s) cut angle to z-axis were selected in our experiment, and the measured results agreed well with the calculated ones. The quality of laser beam is an important factor of affecting OPO threshold fluence and conversion efficiency, so the phase-conjugate technology of Stimulated Brillouin Scattering (SBS) for improving the pump laser beam quality was discussed and applied to the pump laser system. The tuning curves and output energy of KTP OPO pumped by Ruby laser (0.6943 micrometers ), the second harmonic of Nd:YAG (0.532 micrometers ) were measured and compared with the theoretical cases. An important result was obtained that the amplified back SBS light which was employed to pump KTP OPO could greatly reduce the OPO threshold.