Stable and tunable single frequency mid-infrared optical parametric oscillator

We have demonstrated a single frequency mid-infrared optical parametric oscillator pumped by a high power continuous wave single frequency fiber amplifier. The pump power was 15W and the corresponding extraction efficiency was 56%, which is close to the theoretical calculated maximum efficiency of 70% under Gaussian beam assumption. In the experiments the volume Bragg grating was 14.9 mm long with the diffractive efficiency of 99.5% at 1550.5 nm. The diffractive spectral linewidth was 0.27 nm. When the working temperature of the PPLN crystal was 51.5°C and the poling period was 30.5μm a stable idler radiation at 3400 nm was generated. To obtain single frequency operation, an uncoated YAG inter-cavity etalon with 5 mm thickness was inserted into the folded cavity. Stable single frequency operation was obtained with the spectral linewidth of 37.5 MHz and the output power of 2.2 W. The central wavelength stability was better than 520 MHz over 1 hour, which was limited by the resolution of the spectrometer. By changing the angle of the YAG etalon the central wavelength of the idler was varied in the range of 0.24 nm.