PHASE-MATCHED 2ND-HARMONIC GENERATION AT 789.5-NM IN A GASE CRYSTAL

Phase-matched second-harmonic generation in the highly chi((2))-active layered semiconductor GaSe is demonstrated in the near-infrared frequ ency region. Due to the high indices of refraction, the internal phase -matching angle of about 30 degrees is beyond the critical angle of to tal reflection for a z-cut crystal. This problem is overcome by sandwi ching the crystal between two half-cylindrical glass rods, which leads to a shift of the critical angle to larger values. (C) 1996 American Institute of Physics.