Use of X-ray radiation from UKP laser material processing for time-resolved determination of the irradiance acting on the workpiece (X4irrad)

在用超短激光脉冲加工材料的过程中，即使在工业生产条件下，也能发射出可测量量的光子能量为bbbb3kev的x射线辐射。由于空气对光子能量超过3kev的x射线是透明的，因此即使在正常大气压下，这种辐射也能以低损失传播。虽然x射线代表了一个潜在的安全问题，但从物理角度来看，它们包含了关于激光过程的重要信息，这些信息可用于诊断和获取新知识，因为发射光谱强烈依赖于加工参数，尤其是辐照度。由于单个激光脉冲的峰值强度高，以及现代超快激光器的平均功率越来越高，热焦点移位（由于平均功率）和空气中等离子体形成的散焦（由于峰值强度高）等效应在实践中变得越来越令人不安。然而，当使用具有高平均功率的超快激光器时，影响作用在工件上的辐照度的焦点位置的确定仍然没有令人满意地解决-特别是在时间分辨率方面。因此，本项目的目的是利用超短脉冲对材料加工过程中的x射线发射进行时间和光谱分辨测量和分析，以获得有关直接作用在工件上和加工过程中的辐照度的可靠信息，从而能够得出有关焦点移位或散焦的结论。同时，所获得的结果可用于显著扩展迄今为止相对稀疏的关于x射线发射与处理参数依赖关系的数据。

During material processing with ultrashort laser pulses, a measurable amount of x-ray radiation with photon energies of >3 keV is emitted even under industrial production conditions. Since air is transparent to x-rays with photon energies exceeding about 3 keV, this radiation can propagate with low losses even at normal atmospheric pressure. Although x-rays represent a potential safety issue, from a physical point of view they contain important information about the laser process, which can be used for diagnostics and the acquisition of new knowledge, since the emission spectra are strongly dependent on the processing parameters - among other things, especially the irradiance. Due to the high peak intensities of the individual laser pulses, as well as the increasingly high average power of modern ultrafast lasers, effects such as thermal focus shift (due to the average power) and defocusing by plasma formation in the air (due to the high peak intensity) are becoming increasingly disturbing in practice. However, the determination of the focus position, which influences the irradiance acting on the workpiece is still not satisfactorily solved today - especially not with time resolution - when using ultrafast lasers with high average power. The aim of the present project is therefore to use the temporally and spectrally resolved measurement and analysis of the X-ray emission during material processing with ultrashort pulses to obtain reliable information about the irradiance acting on the workpiece directly and during the process and thus to be able to draw conclusions about focus shift or defocusing. At the same time, the results obtained can be used to significantly expand the comparably sparse data available to date on the dependence of the x-ray emission on the processing parameters.