Passively Q-switched Tm:YLF laser based on Ho:YAG crystal as a saturable absorber

A millijoule-level passively Q-switched Tm:YLF solid-state laser, utilizing a Ho:YAG as a saturable absorber, is presented. A volume Bragg grating (VBG) is implemented as the output coupler to stabilize the laser wavelength to the holmium absorption peak of 1879.3 nm, thereby overcoming the challenges of using holmium-doped crystals as saturable absorbers and enabling high-energy pulse generation. Pulse energies up to 2.7 mJ at repetition rates up to 100 Hz were achieved, with beam quality measured to be M² < 1.1. This work addresses the limitations of holmium-doped crystals as saturable absorbers for thulium lasers, demonstrating their potential for high-energy pulse production in the 2 μm range.