Laser Active Materials for High-Intensity Lasers

Many laser materials have been discovered or rediscovered in the last 30 years but only a few of them have been really considered or could be envisaged in the development of the present and future high-intensity laser chains. It is the case of Ti:Sapphire, because of its exceptional spectroscopic and thermo-mechanical properties, and a number of Yb³⁺ doped crystals, because of their relatively broad absorption and emission bands allowing for diode pumping and the generation and the amplification of short pulses, but also because of reduced thermal loads resulting from a low quantum defect. It could be the case of other promising laser materials based on Pr³⁺ - or Cr²⁺-doped crystals and ceramics which have not been considered yet for this type of applications because of more exotic pump and laser wavelengths. Therefore, without entering into the details of the optical properties and the laser performance of these systems, which can be found in many other articles, a review is made and data presented here on the three important following aspects: our ability of developing ultrahigh quality and large size laser elements of the considered materials, the impact of the thermal loads on their spectral properties, and the multiphoton and nonlinear processes which can be the origin of the degradation or the perturbation of their optical properties at high pump and laser intensities. For that description, the considered laser materials have been divided into three categories: Ti³⁺:Sapphire, the most important Yb³⁺-doped laser crystals and ceramics, and some more prospective materials among which Pr³⁺:LiYF₄, Cr ²⁺ZnSe and Cr²⁺:ZnS.