We report on continuous-wave (CW) and rhenium diselenide (${\mathrm{ReSe}}_2$) $Q$-switched dual-wavelength mid-infrared (MIR) laser performances of Er:YAP crystal in this Letter. Under an absorbed pump power of 5.5 W, a maximum CW Er:YAP laser output power of 1.02 W is obtained, corresponding to a slope efficiency of 25.3%. With multilayer ${\mathrm{ReSe}}_2$ material as a saturable absorber, a stable $Q$-switched Er:YAP crystal laser with dual-wavelength output of 2.73 and 2.80 μm is realized for the first time, to the best of our knowledge. The nonlinear optical measurements of the multilayer ${\mathrm{ReSe}}_2$ reveal efficient saturable absorption properties around 3 μm showing a modulation depth of 7.5% and a saturation intensity of $14.5\mathrm{\mu J}/{\mathrm{cm}}^2$. The maximum $Q$-switching output power reaches 526 mW, and the corresponding laser power jitter is around 3% in 1 h. The shortest pulse duration and the highest pulse repetition rate are 202.8 ns and 244.6 kHz, respectively. These results prove that Er:YAP crystal could be a reliable laser crystal for MIR solid-state lasers.

We propose a dynamically tunable broadband linear-to-circular cross polarization converter based on Dirac semimetals. The proposed converter unit cell consists of a center-cut cross-shaped metallic patterned structure with a sandwiched Dirac semimetal ribbon on a polyimide substrate bottomed with gold. The proposed system converts linear waves to right-hand circular polarized waves in the frequency ranges of 1.5–2.8 THz or to left-hand circular polarized waves in two narrow frequency ranges of 1.20–1.25 and 3.04–3.07 THz. The polarization conversion is dynamically tunable by varying the Fermi energy without re-optimizing the microstructures, which may further tunable polarizers and polarization switchers developments.

Pulses as short as 44 fs (6 optical cycles) with a spectral width of 120 nm are generated from a mode-locked solid-state laser near 2 µm employing an orthorhombic Tm:GdScO₃ perovskite crystal. The average power amounts to 188 mW at a repetition rate of ∼77.6 MHz. The strong inhomogeneous line broadening in GdScO₃ suggests optimum conditions for few-optical-cycle pulse generation of rare-earth ion doped GdScO₃ bulk lasers.

1T-titanium selenide (1T-TiSe₂), a representative of 1T phase transition metal dichalcogenides (TMDs), exhibits semimetallic behaviour with a nearly zero bandgap structure, which makes it a promising photoelectric material.

Platinum diselenide (PtSe ₂ ), a type-II Dirac semi-metal material, is a potential saturable absorber (SA) to generate visible pulsed lasers due to its prominent optoelectronic properties.

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.