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

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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.