Deep ultraviolet GHz femtosecond pulses generation from a high-power Kerr-lens mode-locked oscillator

This Letter reports an efficient second- and fourth-harmonic generation based on a stability-enhanced GHz Kerr-lens mode-locked Yb:CYA oscillator. It produces 104-fs pulses with an average power of 8.34 W at a repetition rate of 1.08 GHz, corresponding to a peak power of 65 kW. Benefitting from the automatically and fully integrated design, the oscillator exhibits an excellent long-term stability with root mean square of the power fluctuation of only 0.17% during 64-hours free running. It also has a low-noise property with a timing jitter of 6.4 ps in a span from 10 Hz to 1 MHz. By cascading LBO and BBO crystals, the near-infrared GHz femtosecond laser is extended to visible and deep ultraviolet regions. With the maximum conversion efficiencies of 56.8% and 5.1%, the maximum average powers are 4.57 W at 519 nm and 409 mW at 259 nm, respectively. To the best of our knowledge, this is the first experimental demonstration of the fourth-harmonic generation directly from a GHz femtosecond oscillator, which suggests a practical path to obtain a watt-level deep ultraviolet femtosecond laser at a GHz repetition rate.