High-harmonic generation in solids directly driven by a MHz high-power commercial fiber laser

Solid high-harmonic generation (sHHG) is a compact method for producing deep-ultraviolet and vacuum-ultraviolet (VUV) radiation at wavelengths near or below 200 nm. Generally, sHHG relies on ultrashort laser pulses (10-50 fs) at modest repetition rates (kHz) for sub-10 W average power. Here, we demonstrate VUV generation driven by a 50 W, turnkey, MHz-repetition-rate Yb-fiber laser with a pulse duration of ∼0.5 ps. We investigate the optimum material based on the detected 5th harmonic (H5 = 206 nm) flux with a 1.25 MHz driver, and find the following order: α-SiO₂ > MgO > α-Al₂O₃ > ZnO > CaF₂. However, at an average power of 50 W, MgO performs best, yielding an H5 photon flux of ∼10¹⁰ photons/s. The most stable high-power operation was at 20 W, with an H5 and H7 flux of 7.1 × 10⁹ and 5.2 × 10⁸ photons/s, and RMS fluctuations of 0.80% and 1.14%, respectively.