Yb-fiber-laser-pumped, high-repetition-rate picosecond optical parametric oscillator tunable in the ultraviolet

We report a compact tunable 240-MHz picosecond source for the ultraviolet based on intra-cavity frequency doubling of a signal-resonant MgO:sPPLT optical parametric oscillator (OPO), synchronously pumped at 532 nm in the green by the second harmonic of a mode-locked Yb-fiber laser at 80-MHz repetition rate. By deploying a 30-mm-long multi-grating MgO:sPPLT crystal for the OPO and a 5-mm-long BiB(3)O(6) crystal for internal doubling, we have generated tunable UV radiation across 317-340.5 nm, with up to 30 mW at 334.5 nm. The OPO also provides tunable visible signal in the red, across 634-681 nm, and mid-infrared idler radiation over 2429-3298 nm, with as maximum signal power of 800 mW at 642 nm. The signal pulses have a temporal duration of 12 ps at 665 nm and exhibit high spatial beam quality with Gaussian profile. The signal power is recorded to be naturally stable with a fluctuation of 1.4% rms over 14 hours, while UV power degradation has been observed and studied.