Improvement of stability and efficiency in diode-pumped passively Q-switched intracavity optical parametric oscillator with a monolithic cavity

We improve the performance of intracavity optical parametric oscillator (IOPO) pumped by a diode-pumped Q-switched Nd:YVO₄/Cr⁴⁺:YAG laser. The IOPO cavity is formed independently by a monolithic KTP crystal that the mirrors are directly deposited on top of the nonlinear crystal. We study the performances of this IOPO cavity with different reflectivity of the output coupler at 1.5 μm (R_s) of 80 and 50%. The average power of 1.5 μm is up to 3.3 W at the maximum pump power of 16.8 W for both cases. The diode-to-signal conversion efficiency is up to 20%, which is the highest one for IOPOs to our best knowledge. At the maximum pump power, the pulse energies are 41 μJ with the pulse width of 3 ns at a pulse repetition rate (PRR) of 80 kHz for R_s = 80% and 51 μJ with the pulse width of 1.2 ns at a PRR of 65 kHz for R_s = 50%, respectively. The pulse amplitude fluctuations in standard deviation are 2.6% for R_s = 80% and 4% for R_s = 50%, respectively.