A 49.9 mJ High-Energy, 30 pm Narrow-Linewidth All-Solid-State 308 nm Laser Based on Grating-Selected OPO–OPA 2nd –SFG

We report a high-energy, narrow-linewidth all-solid-state 308 nm ultraviolet laser based on diffraction-grating-selected OPO-OPA 2nd -SFG.In this scheme, 308 nm was generated via SFG between the 730 nm OPO signal and the 532 nm pump in LBO crystal.To satisfy the stringent ultraviolet phase-matching requirements, an intracavity diffraction grating was introduced to compress the KTP-OPO linewidth to the picometer level and reduce divergence.After two-stage OPA amplification, the 730 nm output reached 99.8 mJ with a linewidth of 116 pm and a divergence of 0.61 mrad.By optimizing the linewidth, beam divergence, and LBO crystal length, and by suppressing back-conversion, 49.9 mJ at 308 nm was obtained, with a pulse width of 6.7 ns, a peak power of 6.2 MW, a linewidth below 30 pm, and a maximum energy utilization efficiency of 26.2%.Compared with free-running OPO pumping, the maximum SFG efficiency increased from 2.7% to 17.7% under identical SFG conditions.