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

在以激光为基础的制造业中，许多应用都受益于发射可见光辐射的激光。与通常使用的波长为1.03微米的近红外辐射相比，可见激光辐射导致吸收率增加，从而改善了工艺稳定性。目前，尚无已知的激光活性材料可直接产生平均功率在千瓦范围内的可见光辐射。然而，在波长为1.03µm的腔内倍频薄片激光器中，这种连续波运转的功率可以在绿光光谱范围内实现。在腔内倍频的情况下，输出耦合程度、腔内功率以及晶体内部红外和绿光之间的相位匹配之间是非线性耦合的。这使得这类激光器非常容易受到功率波动的影响，这可能会破坏光学元件。此外，非线性晶体内的最佳光束半径强烈依赖于输出功率。在这个项目中，将研究腔内自适应光学的使用，以实现输出功率高达1kW且光束质量受限的稳定激光运行，同时保持与输出功率无关的持续高的光学效率(&gt；45%)。此外，自适应光学应该允许在激光运行期间在M2=1和M2=10之间准静态调节光束质量。可变形反射镜的技术局限性、相关激光参数的获取具有挑战性以及激光特性之间的非线性耦合导致了一个复杂的控制问题，这就需要对已有的控制方法进行扩展和修改。只有通过激光技术与系统和控制工程之间的跨学科合作才能实现上述目标。

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.