Investigation on repetition-rate division dynamics in a high-power high-repetition-rate 2-μm Q-switched Ho:YLF laser.

We demonstrated a high-power, high-efficiency 2-μm Ho:YLF laser and investigated the repetition-rate division phenomenon in high-repetition-rate Q-switched mode of operation. The Ho:YLF laser produced 135 W of output power with an optical conversion efficiency of 68.3% in CW regime and over 55 W of average power in Q-switched regime, which, to the best of our knowledge, represent the highest power values achieved for both CW and Q-switched regimes of Ho:YLF lasers. Notably, a regular repetition-rate division phenomenon was observed when operating at high repetition rate of 10-30 kHz, i.e., the pulse repetition frequency shows an integer division of the set frequency, which is attributed to the insufficient energy storage during individual Q-switched cycles. To elucidate the underlying dynamics, we proposed a Q-switched laser model based on quasi-three-level rate equations, specifically tailored to the Ho:YLF gain medium. Theoretical analysis demonstrates that increasing the pump intensity is an effective approach to overcome the frequency division phenomenon. This study could provide practical design guidelines for achieving stable pulsed outputs in high-repetition-rate quasi-three-level Q-switched lasers.