Watt-Level Continuous-Wave and Black Phosphorus Passive Q-Switching Operation of Ho3+,Pr 3+:LiLuF4 Bulk Laser at 2.95 μm
Efficient continuous wave (CW) and passively Q-switched Ho<sup>3+</sup>,Pr<sup>3+</sup>:LiLuF <sub>4</sub> (Ho,Pr:LLF) laser operating at 2.95 <italic>μ</italic>m were realized using a 1150-nm Raman fiber laser as the pump source. A CW output power as high as 1.15 W, which we believe to be the highest one ever achieved from Ho <sup>3+</sup>-doped bulk laser emission around 3 <italic>μ</italic>m, corresponds to an optical-to-optical conversion efficiency of 14.5% and a slope efficiency of 15.5%, respectively. A high-quality saturable absorber (SA) based on multilayered black phosphorus (BP) nanosheet film deposited on a CaF<sub>2</sub> substrate was successfully fabricated and employed. Under the absorbed pump power of 7.36 W, the shortest pulse width of 194.3 ns was obtained, which is the shortest among the two-dimensional materials as SA around 3 <italic>μ</italic>m. The results not only indicated that Ho,Pr:LLF crystal would be a promising mid-infrared (MIR) gain medium for obtaining high power output, but verified that the multilayered BP is a promising optical modulator for generating short pulses in MIR spectral range.