Polarization effects in intracavity type II three-wave mixing

Optical parametric oscillator is studied by inserting a type II KTP crystal in a linear double cavity where the infrared cavity is different from the green cavity in order to ensure triple resonance conditions and low threshold operation. The device is pumped by the infrared beam produced by a cw Nd:YAG laser. We observed vectorial second harmonic generation, and, above thresholds of the order of 100 mW, degenerate and non degenerate self pumped OPO oscillation. Phase properties of the degenerate oscillation and the related dynamics as pitchfork bifurcation at the oscillation threshold are also considered. The insertion of a birefringent element inside the OPO cavity modifies the polarization eigenmodes of the OPO and can be used to attenuate the critical role of the crystal's temperature for vectorial second harmonic generation and OPO oscillation.