Abstract
Gd1-XYXCa4O(BO3)3 (GdYCOB) crystal has considerable potential as a noncritically phase-matched third-harmonic generator of Nd:YAG lasers. However, during high-power third-harmonic generation (THG), THG performance was limited by photoinduced damages. We observed two kinds of photoinduced damages. One was a "gray-track" that was formed during high-peak-power THG. Another was photorefractive damage that was induced by high-repetitive THG. Electron paramagnetic resonance (EPR) measurement suggested that the gray-tracking was related to Y2+ ions that converted from Y3+ by exposure to UV light.