Review of research on ultraviolet and deep-UV nonlinear optical crystals in the last decade

Investigations on ultraviolet (UV) and deep-UV nonlinear optical (NLO) crystals over the last decade in our research group, including successes and failure, are discussed. Successes include the discovery of KBBF (KBe/sub 2/BO/sub 3/F/sub 2/) and KABO (K/sub 2/Al/sub 2/B/sub 2/O/sub 7/) crystals. By using a special prism coupling technique for KBBF, our group and Watanabe's group at the University of Tokyo have jointly shown that this crystal is suitable for fourth harmonic generation of the Ti:sapphire laser. On the other hand, we are surprised that SBBO (Sr/sub 2/Be/sub 2/B/sub 2/O/sub 7/) crystal, which has good linear and nonlinear optical properties, lacks structural completeness. As a result, the crystal has very poor optical homogeneity, and can not be used to produce deep-UV harmonic generation yet.