Few-layer black phosphorus (BP) was successfully fabricated by liquid phase exfoliation (LPE) method. By using the BP saturable absorber (SA), a passively Q-switched solid-state laser at the central wavelength of 1988 nm was demonstrated. Under an absorbed diode-pumped power of 3.38 W, an average power of 151 mW was generated with a minimum pulse width of 1.78 µs and repetition rate of 19.25 kHz, corresponding to pulse energy of 7.84 μJ. Our experimental results showed that BP could be used as an excellent SA for achieving mid-infrared solid-state pulsed lasers. To the best of our knowledge, it was the first time to obtain a Q-switched solid-state laser of 2 μm based on BP-SA.

An efficient Er:SrF₂ crystal, lightly Er-doped to a concentration of 4at.%, was successfully grown by the traditional Bridgman method and displayed excellent spectral properties. A diode-end-pumped passively Q-switched dual-wavelength laser, operating at 2.79 μm wavelength, was demonstrated with this crystal by using black phosphorus as the saturable absorber (BP-SA). In the compact passively Q-switched Er:SrF₂ laser, the maximum average output power of 180 mW was achieved at an absorbed pump power of 2.47 W, with a pulse duration of 702 ns and a repetition rate of 77.03 kHz. To the best of our knowledge, this is the first reported application of BP-SA to dual-wavelength pulse laser operation in the mid-infrared region.

A molybdenum disulfide (${\mathrm{MoS}}_2$) saturable absorber was fabricated by thermally decomposing the ammonium thiomolybdate. By using the ${\mathrm{MoS}}_2$ absorber, a compact diode-pumped passively $Q$-switched $\mathrm{Tm}\text{:}{\mathrm{GdVO}}_4$ laser has been demonstrated. A stable $Q$-switched laser with repetition rates from 25.58 to 48.09 kHz was achieved. Maximum average output power was 100 mW with the shortest pulse duration of 0.8 μs. Maximum pulse energy is 2.08 μJ at center of 1902 nm.

Bismuth nanosheets (Bi-NSs) were successfully prepared and employed as saturable absorbers to generate a diode-pumped dual-wavelength ${\mathrm{Er}}^{3+}\text{:}{\mathrm{SrF}}_2$ laser in the mid-infrared region. $Q$-switched pulses with a maximum output power of 0.226 W were obtained at an absorbed pump power of 1.97 W. A repetition rate of 56.20 kHz and a minimum pulse duration of 980 ns were achieved. To the best of our knowledge, we present the first application of Bi-NSs in a mid-infrared all-solid-state laser. The results prove that Bi-NSs may be applied as an optical modulator in mid-infrared photonic devices or as a mode-locker and $Q$-switcher.