Experimental Investigations on Power Scaling of High-Brightness cw Ytterbium-Doped Thin-Disk Lasers

Abstract

The core topic of the present thesis is the improvement of the brightness of thin-disk lasers at a targeted output power of one kilowatt and beyond. For an output power of several kilowatts the intention was to approach a beam quality factor of M2≈ 8, whereas for the thin-disk lasers with an optical output power up to one kilowatt a near diffraction limited beam quality was aimed. Multi-kilowatt beams with high brightness offer advantages for fast and precise material processing applications such as remote cutting, where the beam must propagate over large distances. In the second case a thin-disk laser generating ultrashort pulses can be developed in a further stage. In order to improve the beam quality of a thin-disk laser it is essential to know very precisely how the thin disk deforms in laser operation whereby special attention has to be paid on the aspherical part of this deformation which can be in the order of a few tens of Nanometers. For this reason, an interferometric setup was developed which was optimized to measure the disk deformation during laser operation with high precision. Thus, interferometric measurements in real-time could be carried out when operating the different thin-disk lasers up to an optical output power of approximately four kilowatt. The obtained results were directly used to optimize the beam quality of each thin-disk laser individually.