Methods for resonator internal frequency doubling in efficiency maximized adaptive disk lasers in variable operation

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In laser-based manufacturing, many applications benefit from lasers emitting visible radiation. The visible laser radiation leads to an increased absorptivity and hence to an improved process stability when compared to the commonly used near-infrared radiation with a wavelength of 1.03 µm. Currently, no laser-active materials are known that allow the direct generation of visible radiation with high average power in the kW range. However, such powers in continuous-wave operation can be achieved in the green spectral range with intra-cavity frequency doubled thin-disk lasers emitting at a wavelength of 1.03 µm.In the case of intra-cavity frequency doubling, the degree of output coupling, the intra-cavity power and the phase matching between the infrared and green waves inside the crystal are non-linearly coupled with each other. This makes such lasers very susceptible to power fluctuations, which can destroy optical components. In addition, the optimum beam radius within the non-linear crystal strongly depends on the output power. Within this project, the use of intra-cavity adaptive optics will be investigated in order to achieve stable laser operation with an output power of up to 1 kW with diffraction-limited beam quality and, at the same time, constantly high optical efficiency (> 45 %) independent of the output power. In addition, the adaptive optics should allow quasi-static adjustment of the beam quality between M2 = 1 and M2 = 10 during laser operation. The technical limitations of the deformable mirrors, the challenging aquisition of the relevant laser quantities and the non-linear coupling between the laser properties lead to a complex control problem, which requires the extension and modification of known control methods. The aforementioned goals can only be achieved through interdisciplinary cooperation between laser technology and systems and control engineering.