Low-threshold, high-efficiency, widely tunable infrared source from a KTP-based optical parametric oscillator

We demonstrate a widely tunable infrared optical parametric oscillator with a low pump threshold and high efficiency, which is based on the nonlinear material KTP and pumped by Q-switched nanosecond lasers operating at 1.047 mu m. For a KTP crystal cut at theta = 63.4 degrees, phi = 0 degrees, the achieved signal wavelength tuning of the optical parametric oscillator was 1.58-1.64 mu m. By nonresonantly reflecting the pump wave back through the nonlinear medium, more than a factor of 3 reduction in pump threshold was observed. The external conversion efficiency (from pump to signal) was as high as similar to 40%. Theoretical models developed for predicting phase-matching parameters and pump threshold are also described and shown to be in good agreement with experimental observations. (C) 1997 Optical Society of America [S0740-3224(97)00312-3].