A diode-end-pumped self-$Q$-switched mid-infrared laser was demonstrated with ${\mathrm{Er}}^{3+}$, ${\mathrm{Pr}}^{3+}$ co-doped ${\mathrm{CaF}}_2$ crystal for, to the best of our knowledge, the first time. Maximum average output power of 262 mW was achieved and the corresponding slope efficiency was 14.9%. Stable self-$Q$-switched laser pulses as short as 718 ns were obtained with a repetition rate of 52.63 kHz at the center wavelength of 2803.7 nm. This highly compact nanosecond laser using a 3 at. % ${\mathrm{Er}}^{3+}$ and 0.03 at. % ${\mathrm{Pr}}^{3+}$ co-doped ${\mathrm{CaF}}_2$ crystal is free from any active or passive modulators in cavity, potentially promising for a micro and integrated diode-pumped mid-infrared laser system.

We reported an intra-cavity pumped Q-switched laser with dual-wavelength synchronous output at 2066.7 nm and 1940nm. Ho:YLF crystal was pumped by a self-Q-switched Tm:YAP laser, which was served as both a gain medium and a saturable absorber simultaneously. For Ho:YLF laser, under 11.4-W incident pump power, a stable pulse laser was achieved at 2066.7 nm with the highest peak power of 69.65 W and the pulse repetition rate of 42.14 kHz. Under the same incident pump power, the highest peak power and pulse repetition rate of Tm:YAP laser were 17.85 W and 50.82 kHz, corresponding to the central wavelength of 1940nm. These results suggested that Q-switching without additional absorber element were effective way to obtain high-efficiency and compact 2.1 µm pulsed laser.

A 3 at.% Er³⁺:Ca_0.8Sr_0.2F₂ mixed crystal was grown successfully with a Ca:Sr molar ratio of about 4:1. This was applied as a laser gain medium and pumped by diode laser, obtaining a continuous-wave output power of 1.41 W with a slope efficiency of 39.2%, thus exceeding the Stokes limit by about 5%. Furthermore, with MXene as a saturable absorber, passive Q-switched mode-locking operation was experimentally demonstrated for the first time, to the best of our knowledge. The mode-locked pulses under the Q-switched pulse envelope had a high repetition rate of 103.2 MHz at a center wavelength of 2,796.7 nm.