We describe a power scaling strategy for longitudinally diode-pumped Tm:YLF lasers based on optimisation of the thulium doping level and the gain geometry. Carefully designed laser experiments at lower powers are shown to allow a simple means for accurately predicting the thermal loading and hence the power scaling properties of this system, including the effects of ground-state depletion, cross-relaxation and energy transfer upconversion. An optimised doping level of 2at.% and a slab geometry are shown experimentally to allow scaling of a single gain unit to output powers of ~70W, limited by the available pump power, and a strategy for scaling well beyond 100W output is discussed.

We describe a power scaling strategy for longitudinally diode-pumped Tm:YLF lasers based on optimisation of the thulium doping level and the gain geometry. Carefully designed laser experiments at lower powers are shown to allow a simple means for accurately predicting the thermal loading and hence the power scaling properties of this system, including the effects of ground-state depletion, cross-relaxation and energy transfer upconversion. An optimised doping level of 2at.% and a slab geometry are shown experimentally to allow scaling of a single gain unit to output powers of ~70W, limited by the available pump power, and a strategy for scaling well beyond 100W output is discussed.

We present a novel, compact and power scalable Ho:YAG laser based on intracavity side-pumping by a high-power Tm:YLF slab laser. 14W of continuous wave output power is obtained at 2.09µm in the current experiments, with the clear prospect of reaching the 100W regime in a power scaled version.

Several remote sensing applications require pulsed sources in the mid-infrared spectral regime with high average powers and good beam quality. Ho:YAG lasers have a number of attractive features for high power generation at 2.1microns, either for direct applications or as a pump source for parametric conversion to longer infra-red wavelengths. Unfortunately, direct diode pumping of Ho:YAG is not practical, so a two-step process is generally employed in which one or more diode-pumped thulium-doped lasers are used to directly pump (in-band) the Ho:YAG laser. In response, we have investigated a slab-based architecture for scaling the output power of a Tm:YLF laser to the 100W power regime at 1.91microns, corresponding to a strong Ho:YAG absorption line. Multiple slab lasers with moderate beam quality in the plane of the slab can be combined to efficiently end-pump a low-doping concentration Ho:YAG rod in a pump-guided configuration. In a preliminary demonstration, two 2at.% doped Tm:YLF slab lasers with a spatially multiplexed output of 74W were employed to end-pump a 1.5mm diameter, 80mm long, 0.25at.% Ho:YAG barrel-polished rod. A twomirror plano-concave cavity, with 11% output coupling transmission, produced a CW output of 38W with a slope efficiency of 60% with respect to the incident power. Q-switched operation at a repetition rate of 20Hz with two intracavity Brewster plate polarizers and a 60% transmitting output coupler produced 14mJ pulses with a pulse duration (FWHM) of 18ns. This architecture offers an attractive route for future high-power 2micron lasers.

Single-end-pumped laser performance of 2, 4, and 6at.% Tm-doped YLF rods is reported. For the pumping configuration employed, crystal fracture was observed to occur for a thermal load per unit absorption length of ~13W/cm. The 2at.% Tm-doped crystal was found to have a quantum yield of ~90% of that of 4at.% Tm. However, due to a lower thermal loading density, the maximum possible incident pump power is predicted to be >60% higher, hence offering a greater output power per rod for the lower doping concentration. Power scaling considerations are discussed with reference to crossrelaxation, upconversion, and thermal loading of the host crystal.