Physical Investigation of Self-Induced Laser Focus Displacement during Photodisruption with Ultrashort Laser Pulses

在飞秒激光对光学透明材料的应用过程中，探测到了一种迄今未知和未被研究的轴向激光焦移。激光扰动区从几何上预期的焦点区域移向激光。因此，在焦斑范围内激光切割的理论上可能的精度是不可能达到的。测量到了高达几十分之一微米的意外轴向位移。在常见的激光应用中，通过选择适当的激光重复频率和扫描参数来抑制这种影响。据我们所知，在文献中没有对这种由超短激光脉冲引起的现象进行解释。在下面的资金申请中，应解释出现这种现象的原因，从而确定避免这种影响的方法。因此，在切割过程中，将分析所考虑的材料的光学密度和光学击穿阈值等参数与先前脉冲的关系。此外，还将进行计算机模拟以验证实验结果。根据各种材料的不同，影响将被分类，并参考基本的物理材料属性。展望未来，可以有目的地抑制这种不满意的切割质量。

A so far unknown and uninvestigated axial laser focus displacement was detected during fs-laser application of optically transparent materials. The laser disruption zone moves towards the laser out of the geometrically expected focus region. Hence, the theoretically possible precision of laser cuts in the range of the focal spot cannot be achieved. Unintended axial displacements of up to several tenth of micrometer were measured. In common laser applications, this effect is suppressed by choosing appropriate laser repetition and scanning parameters. To our best knowledge, there exists no explanation of this phenomenon caused by ultrashort laser pulses within the literature. In the following request for funding, the reason of the phenomenon shall be explained and hence methods to avoid this effect will be determined. Therefore, parameters as optical density of the regarded materials and optical breakdown threshold in dependence of previous pulses will be analyzed during the cutting procedure. Furthermore, computer simulations will be performed to confirm the experimental results. Based on a variety of materials, the effect will be categorized and referred to basic physical material properties. Prospectively, a suppression of this unsatisfied cutting quality can be performed on purpose.