Phase-matched second-harmonic generation at 789.5 nm in a GaSe crystal

Phase-matched second-harmonic generation in the highly χ(2)-active layered semiconductor GaSe is demonstrated in the near-infrared frequency region. Due to the high indices of refraction, the internal phase-matching angle of about 30° is beyond the critical angle of total reflection for a z-cut crystal. This problem is overcome by sandwiching the crystal between two half-cylindrical glass rods, which leads to a shift of the critical angle to larger values.