Low-threshold midinfrared optical parametric oscillation in periodically poled KTiOPO4

In this work we demonstrate low-threshold oscillation in the mid-IR spectral region with periodically poled KTiOPO4 (PPKTP) pumped at 1064 nm by a single-frequency Nd:YAG laser. THe compact pump laser had a diode-pumped passively Q-switched monolithic ring cavity configuration and could generate up to 70 (mu) J, 2 ns pulses. With two PPKTP crystals having ferroelectric domain inversion periods of 37.8 micrometers , the temperature tuning bands for the signal of 1720-1750 nm and 1850-1920 nm have been obtained. The lowest oscillation threshold of 8.3 (mu) J was obtained in a cavity using two mirrors reflecting 99 percent at the signal and the idler wavelengths. The maximum OPO output power of 6 mW and the pump depletion of 39 percent was achieved by driving cavity close to stability limit for the idler field. The output power was substantially increases to 36 mW by using output mirror with 90 percent reflectivity only in the signal band and optimizing pump focusing conditions. The external OPO efficiency in this case reached 21 percent.