Low Threshold and High Conversion Efficiency Nanosecond Mid-Infrared KTA OPO

Based on a Type II non-critically phase-matched KTA crystal, a low-threshold and high conversion efficiency mid-infrared optical parametric oscillator (OPO) pumped by a diode-end-pumped Nd:YVO₄ laser is demonstrated. The OPO threshold is only 0.825W. The maximum output power of 435mW at 3.47μm is achieved with the repetition rate of 30kHz, corresponding to an optical-to-optical conversion efficiency of 4.4%. The photon conversion efficiency is as high as about 64%. The pulse width is 3.5ns with a peak power of 4kW for the maximum output power.