Widely tunable fourth harmonic generation of a Ti:sapphire laser based on RBBF crystal

Fourth harmonic generation of a tunable Ti:sapphire laser with a repetition rate of 80 MHz and pulse duration similar to 150 fs has been realized in a single pass with an RbBe2BO3F2 crystal for the first time. A high average power was obtained which was tunable throughout a wide range from 180 to 232.5 nm. The output power over the whole range exceeded 2 mW, the highest being 43.3 mW at 202.5 nm. Moreover, deep-ultraviolet output with powers above 75 mW was obtained at 193.5 and 200 nm under a stronger focusing condition. This is the first attempt at the generation of tunable deep-ultraviolet light without using a KBBF crystal, which is very difficult to grow due to its strong layering tendency, and our attempt may provide new opportunities for the development of all-solid-state deep-ultraviolet coherent light sources.