High average power Q-switched Ho³⁺:YAG laser with a single-line emission at 2122 nm

We present an efficient Q-switched dual-crystal Ho³⁺:YAG laser resonator achieving an output power of 56 W at an incident pump power of 100.7 W with a slope efficiency of 64.4%. The setup was pump power limited. Notably, by carefully tuning multiple etalons placed within the cavity, we achieved a single-line spectral emission at 2122 nm. This deviates from the typical emission wavelengths of 2090 nm or 2096 nm for Ho³⁺:YAG at comparable output powers in Q-switched operation. The laser exhibited very good beam quality, approaching diffraction-limited performance with an excellent M²- < 1.2. At the maximum output power, a pulse FWHM of 100 ns was measured.