Unwanted x-ray emission during ultra-short pulse laser material processing and the influence of processing parameters

During laser material processing with ultrashort laser pulses an unwanted emission of X-rays in the regime of keV can occur, when a critical intensity is exceeded. The resulting emission per pulse is negligible but can rapidly accumulate to a significant value for the occupational safety, when high repetition rates (kHz) are used. In the present work, the characteristics of the resulting X-ray emission by means of the radiation dose, is investigated for various irradiation and process parameters. The varied parameters are inter alia material (steel and bismuth), intensity (max. 3*1014 W/cm²), polarization, surface roughness (0.1 µm < Ra < 13 µm) and pulse duration (0.95 ps – 10 ps). The results show a significant dependence of the tested parameters, are mostly in good agreement with present publications and complement them for various influencing factors. Furthermore, they confirm the potential health risk by laser induced X-ray emission during laser material processing with high intensities.