BULK-DARKENING THRESHOLD OF FLUX-GROWN KTIOPO4

A quantitative assessment of the bulk-darkening phenomenon for flux-grown KTiOPO4 is reported. Measurements were made for KTiOPO4 use as a component for second-harmonic generation of 1064-nm Nd:YAG radiation operating in a pulsed mode. The results show that the bulk-darkening severity increases with fluence and exposure time. Irreversible bulk darkening has been observed at laser energies ranging from 8.8 to 18 J/cm2 depending on the shot count. Fluences exceeding 15 J/cm2 can cause catastrophic damage. Data taken at elevated temperatures indicate an improved reliability. The onset of slight bulk darkening revealed no adverse effects on conversion efficiency.