Features of the high-power (up to 1 MW, 100 mJ) 3-$\mu$m nanosecond laser pulse generation in erbium-doped crystals in the repetitively pulsed regime

The amplification and generation properties of erbium-doped laser crystals (Er:YAG, Er:YSGG, Cr:Er:YSGG) with a high (up to 50%) concentration of an activator ion for obtaining high-power 3-$\mu$;m nanosecond laser pulses on a self-terminating transition have been studied. The measured gain in them under high-power nonselective lamp (up to 260 J) and selective diode (up to 3 J) pumping ranges from 1.2 to 2.1 and ensures the possibility of development of efficient amplifiers. It has been shown that the excitation of high-lying energy levels ($^{4}I_{9/2}$ and $^{4}I_{11/2}$) is decisive for the population inversion in Er:YAG, whereas this is less important for other erbium-doped media. Pulses with an energy of 62 mJ at 10 Hz have been obtained in the TEM$_{00}$ mode in the developed electro-optically $Q$-switched Er:YAG oscillator and two single-pass amplifiers. The optomechanical $Q$-switching based on a rotating mirror opens access to a higher output energy due to the absence of losses in optical elements and depolarization. Single pulses with an energy of 75 mJ and a duration of 123 ns at a repletion rate of 10 Hz have been obtained in the Er:YAG laser, whereas a high gain of Cr:ErYSGG limits obtaining single nanosecond pulses with this $Q$-switching method. The development of such sources with high peak and average powers is of interest for terawatt chirped-pulse amplification laser systems based on iron-ion-doped chalcogenides in the mid-infrared range (3–5 $\mu$m).