High-average-power intracavity second-harmonic generation using KTiOPO(4) in an acousto-optically Q-switched Nd:YAG laser oscillator at 5 kHz.

We have demonstrated high-average-power second-harmonic generation with an output power of 5.6 W at 532 nm by intracavity frequency doubling using Type II KTiOPO(4) in a Nd:YAG laser oscillator acousto-optically Q switched at 5 kHz.(1) The average power achieved, limited only by the power-supply current available in these experiments, was about three times higher than what has been obtained in a state-of-the-art device using LiIO(3) as the doubler. More significantly, since no intrinsic limitations, such as saturation and material damage, have yet been observed, further improvement in the power output should be achievable. It is pointed out that previous studies on intracavity second-harmonic generation have been limited to the small-signal case; the present result shows the feasibility of operating an internally doubled oscillator for efficiently converting the fundamental to its harmonic in a high-power device.