Brewster-oriented passive Q-switch intracavity optical parametric oscillator

The behaviour of passively Q-switched solid-state lasers containing intracavity optical parametric oscillators (OPOs) is described, and a model to optimize this system's performance is developed. Meanwhile, an Nd:YAG laser-pumped KTiOPO₄ (KTP) intracavity OPO for eye safe laser output is studied experimentally. A Brewster-oriented bis-(4-dimethylaminodithiobenzil)-nickel (BDN) dye film is employed in laser cavity, which plays the double role of a passive Q-switch and a Brewster plate, to Q-switch the light to increase its intensity and polarize the light so that the polarization plane of fundamental irradiation is perpendicular to the $Z$-axis of KTP serving as the OPO nonlinear crystal, thereby providing type II phase matching conditions to generate 1.572$\mu$m eye-safe signal laser. Eye-safe signal radiations of 6.6mJ per pulse at 1.572$\mu$m wavelength and pulse width as narrow as 6.0ns (FWHM) were obtained. Peak power was up to 1.1MW.