Impact of repetitive, ultra-short soft X-ray pulses from processing of steel with ultrafast lasers on human cell cultures

Ultrafast lasers, with pulse durations below a few picoseconds, are of significant interest to the industry, offering a cutting-edge approach to enhancing manufacturing processes and enabling the fabrication of intricate components with unparalleled accuracy. When processing metals at irradiances exceeding the evaporation threshold of about 10^10 W/cm2 these processes can generate ultra-short, soft X-ray pulses with photon energies above 5 keV. This has prompted extensive discussions and regulatory measures on radiation safety. However, the impact of these ultra-short X-ray pulses on molecular pathways in the context of living cells, has not been investigated so far. Using laser pulses of 250 fs and 6.7 ps, along with pulse repetition rates exceeding 10 kHz, we conducted the first molecular characterization of epithelial cell responses to ultra-short soft X-ray pulses generated during processing of steel with ultrafast lasers. Ambient exposure of vitro human cell cultures, followed by imaging of the DNA damage response and fitting of the data to an experimentally calibrated model of dose rate estimation, revealed a linear increase in the DNA damage response relative to the exposure dose. This is in line with findings from work using continuous wave soft X-ray sources and suggests that the ultra-short X-ray pulses do not generate additional hazard. This research contributes valuable insights into the biological effects of ultrafast laser processes and their potential implications for user safety.