There has been great interest in high-repetition, high-power ultraviolet (UV) source for various applications in semiconductor processing, micro machining, and other fields. Discovery of CsLiB6O10(CLBO) crystals have enabled the production of such practical high-power all solid-state UV lasers. In 2001, UV output power up to 23.0 W by fourth harmonic generation of Nd:YAG laser was achieved.
In general, one of the limiting factors for the development of high-power solid-state UV lasers is laser-induce damage of NLO crystal due to some kinds of defects inside the materials. Recently, we have succeeded to grow the high crystallinity CLBO with an enhanced bulk laser damage resistance. On these samples, an increase in the surface damage resistance could be expected. Measurement of the surface laser-induced damage threshold (LIDT) on CLBO crystals with various crystallinity was performed by using a 266 nm laser. For the crystal with high damage resistance (15-18 GW/cm2), LIDT of as-polished surface was 1.3 times higher than that of crystal with conventional damage resistance (9-12 GW/cm2). In addition, polishing compound embedded inside the crystal surface was removed by using an ion-beam etching process. We have observed 1.5 times improved surface LIDT by ion beam etching for both high damage resistance and conventional damage resistance samples. The relationships between vickers hardness and crystal quality will be presented.