We developed a tunable ultraviolet continuous-wave light source by fre
quency tripling of a Ti:sapphire laser. The third harmonic was generat
ed in a BBO crystal by sum-frequency mixing between the fundamental wa
ve and the second harmonic which was generated in a LBO crystal placed
in an external built-up cavity. The third harmonic power of 8 nW was
obtained at 252 nm wavelength with an input fundamental power of 500 m
W. The tuning range of the third harmonic was from 252 nm to 267 nm.