Passively Q-switched 1.57-mu m intracavity optical parametric oscillator

We demonstrate an eye-safe KTP-based optical parametric oscillator (OPO) dr iven intracavity by a diode-pumped 1064-nm Nd:YAG laser, passively Q-switch ed by a Cr4+ :YAG crystal. The characteristics of this system, which operat es at 1570 nm with a repetition rate as high as 50 Hz, are studied as a fun ction of Cr4+:YAG optical density. Under optimum conditions the OPO generat es 1.5-mJ, 3.4 +/- 0.1-ns pulses in a single transverse mode. For a Cr4+:YA G Q-switch element with an optical density of 0.5 the conversion efficiency of the intracavity energy is similar to 45% with the ratio of OPO to Nd:YA G peak-pulse intensity exceeding unity. These and other OPO characteristics compare favorably with a simple rate equation model of the OPO dynamics. ( C) 1999 Optical Society of America.