We report efficient generation of tunable femtosecond pulses in the ultraviolet (UV) by intracavity doubling of a visible femtosecond optical parametric oscillator (OPO). The OPO, based on a 400m BiB3O6 crystal and pumped at 415 nm in the blue, can provide visible femtosecond signal pulses across 500–710 nm. Using a 500m crystal of -BaB2O4 internal to the OPO cavity, efficient frequency doubling of the signal pulses into the UV is achieved, providing tunable femtosecond pulses across 250–355 nm with up to 225mW of average power at 76 MHz. Cross-correlation measurements result in UV pulses with durations down to 132fs for 180 fs blue pump pulses
