High power lasers with up to 16 kilowatts of continuous power are used today in industry for cutting and welding metal plates in materials processing. These laser systems are based partly on the thin disk laser concept. Typically, in multi-mode operation these lasers emit with a beam quality factor M² > 20 and require a short distance from the emission aperture to the work piece. However, for the application of laser radiation over large distances of several kilometres or more, a virtually diffraction limited beam quality (M² → 1) is required.
At the Institute of Technical Physics, work focuses on research into extending the power scalability of thin disk lasers with virtually diffraction limited beam quality in the multi-kilowatt range. The advantages of thin disk lasers are based on their power scalability, high efficiency, low thermal lensing and negligible birefringence in the laser medium. The laser-active medium consists of a very thin crystal disk (a few hundred microns thick), which is cooled on the back surface. This enables very high pump power densities to be obtained. Power scaling can be achieved by increasing the active surface at a constant pump power density. In this case, both the temperatures in the disk and the required brightness of the pump diodes remain constant. Another possibility for the power scaling is the optical coupling of several disks within one resonator, with the advantage of scaling the overall gain coefficient. Furthermore, modular power scaling based on the oscillator-amplifier concept is the subject of the activities in this area.