High efficiency nanosecond passively Q-switched 23 µm Tm:YLF laser using a ReSe₂-based saturable output coupler

A 785 nm diode-pumped nanosecond passively Q-switched (PQS) 2.3 µm Tm:YLF laser using a ReSe2-based saturable output coupler (SOC) was reported for the first time. The SOC combined the function of a passive Q-switch and output coupler, greatly reducing the additional insertion loss compared with a conventional separate structure. The modulation depth, saturation intensity, and nonsaturable loss for this ReSe2-based SOC were determined to be 1.3%, 1.7 GW/cm2, and 0.2%, respectively. A maximum average output power of 486 mw, a shortest pulse width of 716 ns, and a repetition rate of 5.0 kHz were obtained under the absorbed pump power of 7.21 W. The nanosecond pulses make the diode-pumped compact 2.3 µm thulium solid-state lasers more attractive for practical applications.