Low-threshold widely-tunable intracavity Q-switched Nd:YVO₄/PPLN optical parametric generator

A quasi-phase-matched intracavity optical parametric generator (QPM-IOPG) is demonstrated based on multi-grating periodically poled lithium niobate (PPLN) internal to an acousto-optically Q-switched Nd:YVO₄ laser. The PPLN crystal is 20 mm long and periodically poled along the z-axis by using external electric poling technique. While the Q-switch repetition rate is set at 19 kHz, the signal wavelength can be continuously tuned from 1384 nm to 1541 nm by combining temperature tuning and grating tuning. The measured signal pulse width is approximately 80 ns. While the PPLN crystal temperature is 140°C, the QPM-IOPG threshold is just 0.93 W with the 29 μm grating period and 3 W of laser diode (LD) pump power produces 140 mW signal output. With the 26.5 μm grating period, the QPM-IOPG threshold is increased to 1.36 W and at an incident LD pump of 3 W, 105 mW signal is obtained. The reason of the different thresholds and conversion efficiencies for various grating periods is analyzed and the theoretical calculation of the QPM-IOPG threshold is also presented.