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We present an efficient Q-switched dual-crystal Ho 3+ :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 Ho 3+ :YAG at comparable output powers in Q-switched operation. The laser exhibited very good beam quality, approaching diffraction-limited performance with an excellent M 2 - < 1.2. At the maximum output power, a pulse FWHM of 100 ns was measured.

A continuous-wave crossed-Porro prism Ho 3+ :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 M 2  < 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.

A Tm 3+ :Ho 3+ -codoped free-space single-oscillator fiber laser is under investigation with special focus on the power scalability of emission wavelengths from 2.1 µm to 2.2 µm. Using a tunable diffraction grating, a 200-nm tunable laser source is built. Laser output powers above 10 W are delivered from 1990 nm up to 2190 nm, demonstrating the range for stable high-power laser operation. By replacing the diffraction grating by a highly reflective, narrow linewidth volume Bragg grating, power scaling is performed at 2.1 µm and is even enabled at a wavelength of 2.2 µm. Using a volume Bragg grating (VBG) at 2.1 µm, a slope efficiency of 49% is measured with an output power of 262 W. Using another VBG with a center wavelength of 2.2 µm, the fiber laser delivers a record power of 77 W with a slope efficiency of 29%.

A mid-infrared ${{\rm ZnGeP}&#95;2}$ optical parametric oscillator pumped by a ${{\rm Tm}^{3 +}}$-doped fiber laser is reported, providing pulse energies of $230 \;\unicode{x00B5}{\rm J}$, pulse widths of 40 ns, and peak powers of ${\sim}6\;{\rm kW} $ with excellent efficiency and beam quality. The pump source is an actively $Q$-switched single oscillator optimized to generate high pulse energies.

The beam quality of a high-energy mid-infrared ZnGeP 2 (ZGP) optical parametric oscillator has been improved by use of a negative lens inside the nonplanar fractional-image-rotation enhancement (FIRE) resonator compensating for the thermal lensing and gain guiding effects. With an f=-0.9  m CaF 2 lens, the beam quality is 1.5 and ∼2 for the resonant signal beam and the non-resonant idler beam, respectively. Up to 33 mJ of mid-infrared pulse energy in the 3-5 μm wavelength range is obtained with 94 mJ of pump energy on the crystal. This is an improvement of the beam quality by a factor of 3 for the signal beam and ∼2 for the idler beam compared without using a lens inside the FIRE resonator.

A single-oscillator actively Q-switched mode-locked (QML) thulium-doped silica fiber laser is presented and used to pump a ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF (ZBLAN) fiber for mid-infrared (mid-IR) supercontinuum (SC) generation. The fiber laser provided high-peak-power levels directly from the oscillator delivering single mode-locked pulse energies up to 48 μJ, being 2-4 orders of magnitude higher than conventional continuous wave mode-locked lasers. By pumping a ZBLAN fiber specially designed for high-output-power SC generation, 7.8 W have been achieved in all spectral bands with a spectrum extending to 4.2 μm.

A high-energy mid-infrared ZnGeP 2 (ZGP) optical parametric oscillator (OPO) based on the nonplanar fractional-image-rotation enhancement resonator pumped by a 2.05 μm Ho 3+ :YLF laser is presented. Up to 120 mJ pulse energy in a rotationally symmetric beam is generated in the 3-5 μm wavelength range at 1 Hz repetition rate. Slope efficiencies of up to 78% are achieved with respect to the pump pulse energy incident onto the ZGP crystal. The OPO pulses have a duration close to 15 ns, corresponding to a maximum peak power of 8 MW. A measurement of M 2 dependence on pump beam diameter is presented.

First results on a diode-pumped multikilowatt-class Er(3+):YAG solid-state heat-capacity laser (SSHCL) are reported. The laser achieves an output power of 4650 W and output energies in excess of 440 J. A moderate crystal temperature increase due to crystal heating of 56.7 K/s is measured at 11.3 kW of pump power and the temperature-related power drop is determined to 8.8 W/K. The presented work is believed to be the first multi-kilowatt-class resonantly diode-pumped Er(3+):YAG laser.

A diode-pumped Q-switched Tm(3+),Ho(3+)-codoped double-clad silica fiber laser is reported providing average powers of up to 12.3 W at 2072.7 nm and stable pulse widths of only 45 ns and repetition rates in the range 10-100 kHz. Instabilities in pulse shape occur at nonoptimum cavity alignment and were found to be linked to the mechanism responsible for self mode locking.

A diode-pumped Q-switched Tm(3+)-doped double-clad silica fiber laser is reported providing average powers of up to 30 W at pulse widths of only 41 ns and repetition rates in the range of 10-125 kHz. Up to 270 microJ pulse energy was produced. Amplified spontaneous emission (ASE) buildup limits the maximum peak power, and the pump power and average output power at the point of ASE induced clamping were found to depend linearly on the repetition rate.