Noncollinear optical parametric oscillator design for walk-off reduction in GaSe crystals

We grow and fabricate GaSe crystals for nonlinear optical applications. One possible application for this material is an optical parametric oscillator (OPO), which could be pumped with a Nd:YAG laser, but due to the large walk-off, is generally impractical. We present a noncollinear OPO design that significantly reduces the effect of walk-off, which could make an OPO possible with GaSe. The pump, signal, and idler propagation directions are arranged to form nearly collinear rays of power flow. The design minimizes the overlap angle between the rays, and as much as an order of magnitude improvement is obtained compared to the walk-off angle of a collinear OPO. With a 1.06-μm pump, an overlap angle as small as 0.35 deg can be achieved, which is half that of a conventional OPO using ZnGeP 2 .