A high-pulse-energy mid-infrared light source is presented, based on a zinc–germanium–phosphide optical parametric oscillator (ZGP OPO) pumped by an actively Q -switched high-pulse-energy H o 3 + : Y A G laser. The H o 3 + : Y A G pump laser source is capable of generating a pulse energy of 15 mJ from a single H o 3 + : Y A G rod at room temperature at a pulse repetition frequency (PRF) of 700 Hz. A maximum power of 20.1 W at a central wavelength of 2090 nm can be obtained in continuous operation, with a slope efficiency of 45.1%. A good beam quality with an M 2 better than 1.3 was achieved in Q -switched operation. The presented laser architecture was used as a suitable pump source for a ZGP-based OPO. Operated at a PRF of 2 kHz and pumped with a pulse energy of 8 mJ, a low conversion threshold of 1.5 W and a maximum total output power of 6.3 W could be obtained in a linear ZGP-based OPO. At maximum power, the peak power of the generated mid-infrared radiation exceeded 120 kW, while the beam quality was affected by the strong gain lens building inside the nonlinear material as a consequence of the high-energy pump pulses.

A continuous-wave crossed-Porro prism Ho3+:YAG laser is presented and compared with a corresponding mirror resonator. A maximum output power of 30.7 W is reached with a slope efficiency of 67.4 % with respect to the absorbed pump power. The laser output beam shows a very good beam quality of better than M2 < 1.2 which clearly surpasses that of the mirror resonator. In terms of alignment sensitivity, the crossed-Porro prism resonator is superior to the mirror resonator due to the retro-reflective nature of the prisms in the axis around the apex.

We present investigations on output power limitations of near-diffraction-limited compact $$\hbox {Ho}^{3+}$$ Ho 3 + :YAG laser resonators employing a homogeneous or segmented laser crystal. An approach for designing a segmented crystal is presented. Maximum output powers of $${57.6}\,\hbox {W}$$ 57.6 W and $${51.9}\,\hbox {W}$$ 51.9 W are reached with the homogeneous and segmented crystal, respectively, resulting in pulse energies of $${1.14}\,\hbox {mJ}$$ 1.14 mJ and $${1.04}\,\hbox {mJ}$$ 1.04 mJ at a repetition rate of $${50}\,\hbox {kHz}$$ 50 kHz in Q-switched operation. Interferometric experiments are conducted to derive the radial temperature profile for both crystals. Simulations based on a split-step beam propagation method are used to model the longitudinal temperature gradient in both crystals.

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