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Bulk darkening of flux-grown KTiOPO4

A quantitative assessment of the bulk darkening phenomenon for flux-grown KTiOPO4 (KTP) is reported. Measurements were made for KTP use as a component for second harmonic generation of 1064 nm Nd:YAG operating in a pulsed mode. The results show that 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 indicates an improved reliability. The onset of slight bulk darkening revealed no adverse effects on conversion efficiency.