High-beam-quality operation of a 2 μm passively Q-switched solid-state laser based on a boron nitride saturable absorber

Boron nitride (BN) nanosheets were used as the material sources which were coated on a calcium fluoride mirror to achieve a saturable absorber (SA). A passively Q-switched solid-state laser at 2000.5 nm was demonstrated with a Tm,Ho:YAlO3 (Tm,Ho:YAP) crystal and a SA based on BN. An average output power of 650 mW was obtained with a minimum pulse width of 6.3 μs at the pulsed repetition frequency of 41.7 kHz, corresponding to a per pulse energy of 13 μJ. The beam quality factor was measured to be Mx2=1.06 and My2=1.07 at the maximum output power.