60 mJ Q-switched Ho:YLF laser end-pumped by QCW thulium fiber laser

In this paper, an efficient electro-optical Q-switched performance of a 0.5% Ho:YLF laser pumped by a Tm: fiber laser at single-pass and double-pass configurations was studied. Efficient performance was achieved with double-pass pumping; therefore, in a continuous-wave operation, a maximum output power of 19.5 W at 2056.85 nm was extracted, corresponding to optical-to-optical efficiency of 27%. The measured output characteristics for the U-shape concave–concave resonator confirm LASCAD simulation results. In the Q-switched performance, the output energy of 60 mJ was achieved at a 10 Hz repetition rate. The pulse duration of 24.5 ns corresponding to 2.45 MW peak power was recorded. Optical-to-optical efficiency was 5.16%, and 26.6% Q-switched-to-free running modes conversion efficiency was obtained. A slope of 0.2 mJ/°C was recorded for change in the cooling temperature. The energy instability during 5 min was 1.08%. The average M2 factor for x and y directions was measured at 1.56.