Self-frequency doubling laser performance of Nd:GdCOB crystal with a phase-matching angle out of the principal plane

The self-frequency doubling laser performance of Nd:GdCOB crystal cut in phase-matching direction (θ = 66.3°, φ = 134.4°) was compared with the crystal cut in the direction of (θ = 90°, φ = 46°). Results show that the former has a higher second-harmonic conversion efficiency than the latter. Using Ti:sapphire laser as pumping source, a maximum of 11.3m W of green light has been obtained with an incident power of 520 mW. This corresponds to an optical-optical conversion efficiency of 2.2%. Laser threshold for self-frequency doubling operation is measured to be 1 mW. To our knowledge, this is the lowest threshold achieved so far.