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In this paper, we illustrate the latest advancement on the eye-safe Solid State Heat-Capacity Laser (SSHCL) investigated for the development of medium and high energy laser sources. Nearly all the solid-state lasers considered for defence applications in the range of 10 kW up to over 100 kW emit at a wavelength of 1.03 μm– 1.06 μm. Therefore, we perform research on an alternative emitting around 1.6 μm, which unites many advantages in use (robustness, a simple technology, flexibility in volume and weight). The heat-capacity principle, in which the laser material is cooled only after the laser action has ended, results in low temperature gradients in the laser medium, leading to a good beam quality and a high performance. Previous investigations on Er3+:YAG SSHCL demonstrated the scalability of the heat-capacity laser principle and up to 4.65 kW and 440 J in less than 800 ms have been achieved, representing the current world record in eye-safe diode-pumped solid-state laser technology. Optical-to-optical efficiencies of over 41% and slope efficiencies of over 51% are obtained with respect to the incident pump power. In this report we further investigate the possibility of compensating any parasitic residual heating. Indeed, it has been shown that the optimal laser operation is directly coupled with the intensity distribution of the laser mode inside the laser medium. The ideal resonator configurations are those which allow an extraction of the laser energy as homogeneous as possible. Using an intra-cavity adaptive optics system beams with phase fronts as flat as possible, on the order of less that 1/10 of the wavelength for each of the considered Zernike polynomials have been generated, and the shot duration has been lengthened by 50%. The influence of the crystal geometry on the pump distribution homogeneity and the possible ways for maximizing the extraction efficiency are investigated.
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