Second-harmonic generation from a KBe_2BO_3F_2 crystal in the deep ultraviolet

By use of KBe(2)BO(3)F(2) (KBBF) crystal with a size of 10 mmx10 mm x1.2 mm and a special prism-coupling technique (PCT), fourth-harmonic generation of Ti:sapphire laser systems from 200 to 179.4 nm has been achieved. Moreover, with a Ti:sapphire laser with a 50-fs pulse duration and a 1-kHz repetition rate, conversion efficiency as high as 13% from 400 to 200 nm without any surface-loss correction has also been obtained. The data show that with the PCT a KBBF crystal can produce deep-UV coherent light with measurable power output.