Retracing Behaviors of Phase-matching Angle in Non-collinear Phase-matched BBO Optical Parametric Oscillators

The retracing behaviors of phase-matching angle, which are the key phenomena for realizing multiple-wavelength optical parametric oscillators (MWOPO), have been observed in a LBO crystal [1] and also studied in other crystals in the collinear phase-matching configurations. However, based on collinear phase-matching the implementation of MWOPO is limited by the specific ranges of pump wavelength, particularly for the widely used BBO crystal. In this paper, we, on the one hand, present the results of theoretical study on the retracing behaviors of a BBO crystal based on non-collinear phase-matching configurations. On the other hand, we demonstrate our experimental results of the retracing behavior of a BBO optical parametric oscillator (OPO) pumped by the second-harmonic of a Q-switched Nd:YAG laser. Particularly, we discovered that near the turning point of the retracing curve, there was an angle around which a broad wavelength range could be simultaneously phase-matched. Based on this observation, we have implemented an OPO with an extremely broad signal and idler spectra.