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 ph ase-matching direction (theta = 66.3 degrees, phi = 134.4 degrees) was comp ared with the crystal cut in the direction of (theta = 90 degrees, phi = 46 degrees). Results show that the former has a higher second-harmonic conver sion efficiency than the latter. Using Ti:sapphire laser as pumping source, a maximum of 11.3 mW of green light has been obtained with an incident pow er 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.