Angle-tuned type II external-cavity frequency doubling without temperaturestabilization

We report frequency doubling of a low-power cw diode laser at 1064 nm in an external ring cavity by use of an angle-tuned KTP type II crystal. We demo nstrate a new setup that requires no temperature stabilization of the cryst al. An intracavity lambda/2 plate rotates the polarization of the fundament al after each cavity round trip by 90 degrees; this provides the two eigenp olarizations of the crystal required for a type II nonlinear process. As a result, it is possible to maintain the resonance condition by use of a stan dard locking circuit. (C) 1999 Optical Society of America.