High-power ultraviolet 278-nm laser from fourth-harmonic generation of an Nd:YAG amplifier in CsB3O5 crystal

We report on the experimental investigation and theoretical analysis of a nanosecond pulse high power ultraviolet (UV) 278 nm laser by fourth-harmonic generation (FHG) of a 1112-nm Nd:YAG amplifier in LiB3O5 (LBO) and CsB3O5 (CBO) crystals. The UV laser delivers a maximum average power of 10.3 W at 278 nm with peak power of 36.8 kW under input pump power of 41 W at 556 nm. This is, to the best of our knowledge, the highest output power at the specific UV wavelength of 278 nm. We also performed the theoretical investigation on the FHG with a model in the Gaussian approximation of both spatial and temporal profiles, especially accounting for the two-photon absorption effect in CBO crystal for the first time. The average output power, pulse width, and beam spatial distribution of the UV laser were simulated. The theoretical calculations are in close agreement with the experimental results.