Sum-frequency generation of cw ultraviolet radiation in periodically poled LiTaO3

We present cw sum-frequency generation of UV radiation at 355 nm based on a high-power laser at 1064 nm and a two-stage quasi-phase-matching nonlinear interaction in periodically poled LiTaO3 crystals. In a first stage, second harmonic at 532 nm is generated. Then, the outcoming IR and green light interact in a second nonlinear crystal to generate about 7 mW of ultraviolet radiation at the sum frequency.