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°, Ф= 134.4 °) was compared with the crystal cut in the direction of (θ= 90 °, Ф = 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 11.3mW of green light has been obtained with an incident power of 520mW. 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.