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Broadband tunable femtosecond laser pulses are of great interest in numerous fields, such as spectroscopy or imaging. Here, we report on the generation of rapidly tunable radiation in the near UV by using intracavity non-collinear sum-frequency mixing between the visible pulses of a non-collinear optical parametric oscillator (NOPO) and a near-infrared beam. The NOPO is pumped by the third harmonic of an Yb-based master oscillator fiber amplifier (MOFA). For sum-frequency mixing, remaining fundamental pulses at 1030 nm are used. With this approach, near-UV pulses in a range of 333-413 nm with average output powers up to 90mW and pulse durations from 158-240 fs are achieved. Fast tunability is demonstrated over the whole tuning range by varying just the cavity length. The system also allows for the generation of two simultaneous synchronized output pulse trains in the visible and the near-UV spectral range.

A large range of laser-matter applications employ ultrashort pulses and high laser intensity. Such processes can lead to unrequired X-ray generation, which represents a hazardous radiation factor even for common laboratory research-grade laser systems. We present here an analysis of the radiation dose rate and X-ray spectrum emitted during ablation of a rotating copper cylinder with respect to several laser parameters. The results show that focused sub-picosecond pulses with intensity above 1013 W/cm2 can exceed the annual irradiation limit even in one hour, requiring appropriate shielding for the safety of the researchers.