Ho:KY(WO4)2 thin-disk laser passively Q-switched by a GaSb-based SESAM.

A Holmium thin-disk laser based on a 3 at.% Ho:KY(WO4)2 / KY(WO4)2 epitaxy and single-bounce pumping by a 1960 nm Tm-fiber laser is passively Q-switched with a GaSb-based quantum-well semiconductor saturable absorber mirror. It generates an average output power of 551 mW at 2056 nm with a slope efficiency of 44% (with respect to the absorbed pump power). The best pulse characteristics (energy and duration) are 4.1 µJ / 201 ns at a repetition rate of 135 kHz and the conversion efficiency with respect to the continuous-wave regime is as high as 93%.

Holmium thin-disk laser based on Ho:KY(WO4)2/KY(WO4)2 epitaxy with 60% slope efficiency and simplified pump geometry.

We report on the first holmium (Ho3+) monoclinic double tungstate thin-disk laser. It is based on a 250 µm thick 3 at. % Ho:KY(WO4)2 active layer grown on a (010)-oriented KY(WO4)2 substrate. When pumped by a Tm-fiber laser at 1960 nm with a single-bounce (single double-pass) pump geometry, the CW Ho:KY(WO4)2 thin-disk laser generated 1.01 W at 2057 nm, corresponding to a slope efficiency η of 60% and a laser threshold of only 0.15 W. Implementing a double-bounce (second double-pass) for the pump, the output of this laser was scaled to 1.57 W with η=55%. The maximum stimulated emission cross section σSE of the Ho3+ ions in the epitaxial layer reaches 2.5×10-20 cm2 at 2056.5 nm for E‖Nm. The Ho:KY(WO4)2 epitaxial structures are promising for multi-watt mode-locked thin-disk lasers at ∼2.06 µm.

Mid-infrared supercontinuum generation to 12.5µm in large NA chalcogenide step-index fibres pumped at 4.5µm.

We present numerical modeling of mid-infrared (MIR) supercontinuum generation (SCG) in dispersion-optimized chalcogenide (CHALC) step-index fibres (SIFs) with exceptionally high numerical aperture (NA) around one, pumped with mode-locked praseodymium-doped (Pr(3+)) chalcogenide fibre lasers. The 4.5um laser is assumed to have a repetition rate of 4MHz with 50ps long pulses having a peak power of 4.7kW. A thorough fibre design optimisation was conducted using measured material dispersion (As-Se/Ge-As-Se) and measured fibre loss obtained in fabricated fibre of the same materials. The loss was below 2.5dB/m in the 3.3-9.4µm region. Fibres with 8 and 10µm core diameters generated an SC out to 12.5 and 10.7µm in less than 2m of fibre when pumped with 0.75 and 1kW, respectively. Larger core fibres with 20µm core diameters for potential higher power handling generated an SC out to 10.6µm for the highest NA considered but required pumping at 4.7kW as well as up to 3m of fibre to compensate for the lower nonlinearities. The amount of power converted into the 8-10µm band was 7.5 and 8.8mW for the 8 and 10µm fibres, respectively. For the 20µm core fibres up to 46mW was converted.

Q-switched Ho:Lu2O3 laser at 2.12 µm.

We report on a Q-switched Ho:Lu2O3 laser resonantly pumped by a GaSb-based laser diode stack at 1.9 µm. The maximum output energy extracted from the compact plano-plano acousto-optically Q-switched resonator was 8 mJ at a 100 Hz pulse repetition rate, while the peak power was 40 kW. The laser wavelength was 2.124 µm.

Holmium-doped Lu2O3, Y2O3, and Sc2O3 for lasers above 2.1 µm.

Efficient room-temperature laser operation was obtained in the wavelength range from 2117 nm to 2134 nm with Ho:Lu(2)O(3) and Ho:Y(2)O(3) as the active materials. With an FBG-stabilized Tm-doped fiber laser as the pump source, the maximum slope efficiency and output power of the Ho:Y(2)O(3) laser were 63% and 18.8 W, respectively. With Ho:Lu(2)O(3) the respective values were 76% and 25.2 W. With Ho:Sc(2)O(3) as the active material the accessible wavelength range could be expanded to 2158 nm in a diode-pumped setup.

Directly diode-pumped high-energy Ho:YAG oscillator.

We report on the high-energy laser operation of an Ho:YAG oscillator resonantly pumped by a GaSb-based laser diode stack at 1.9 µm. The output energy was extracted from a compact plano-concave acousto-optically Q-switched resonator optimized for low repetition rates. Operating at 100 Hz, pulse energies exceeding 30 mJ at a wavelength of 2.09 µm were obtained. The corresponding pulse duration at the highest pump power was 100 ns, leading to a maximum peak power above 300 kW. Different pulse repetition rates and output coupling transmissions of the Ho:YAG resonator were studied. In addition, intracavity laser-induced damage threshold measurements are discussed.

Efficient diode-pumped laser operation of Tm:Lu2O3 around 2 µm.

We report on the first diode-pumped laser operation of thulium-doped Lu2O3. With a very compact setup an output power of 75 W and slope efficiencies of around 40% with respect to the incident pump power were achieved at room temperature. Free running laser operation was observed at wavelengths of 2065 nm and 1965 nm. With a birefringent filter the wavelength could continuously be tuned from 1922 nm to 2134 nm. The thermal conductivity of Tm:Lu2O3 was measured for different dopant concentrations and is compared to the one of thulium-doped YAG.