Continuous-wave coherent ultraviolet source at 326 nm based on frequency trippling of fiber amplifiers.

We have demonstrated a tunable single frequency source of continuous-wave (CW) coherent ultraviolet (UV) radiation at lambda (3omega) = 326 nm. Laser light of a tunable diode laser at lambda(omega) = 977 nm was split and injected into two independent fiber amplifiers yielding 1 W and 0.4 W, respectively. The 1 W branch was resonantly frequency doubled, resulting in 120 mW of useful power at lambda(2omega) = 488 nm. The third harmonic was generated by summation of the second branch of lambda(omega) and lambda(2omega) which were enhanced by a doubly resonant cavity. This light source has TEM(00) character and can be continuously tuned over more than 18 GHz. It is of interest for efficient laser cooling of In and potentially other applications.