Schille Jörg, Kraft Sebastian, Kattan Dany, Löschner Udo
Laserinstitut Hochschule Mittweida, University of Applied Sciences Mittweida, Technikumplatz 17, 09648 Mittweida, Germany.
Institut für Laser-und Plasmaphysik, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany.
Materials (Basel). 2022 Apr 8;15(8):2748. doi: 10.3390/ma15082748.
The ongoing trend in the development of powerful ultrashort pulse lasers has attracted increasing attention for this technology to be applied in large-scale surface engineering and modern microfabrication. However, the emission of undesired X-ray photon radiation was recently reported even for industrially relevant laser irradiation regimes, causing serious health risks for laser operators. In the meantime, more than twenty influencing factors have been identified with substantial effects on X-ray photon emission released by ultrashort pulse laser processes. The presented study on enhanced X-ray emission arising from high pulse repetition frequency ultrashort pulse laser processing provides new insights into the interrelation of the highest-contributing parameters. It is verified by the example of AISI 304 substrates that X-ray photon emission can considerably exceed the legal dose rate limit when ultrashort laser pulses with peak intensities below 1 × 10 W/cm² irradiate at a 0.5 MHz pulse repetition frequency. The peak intensity threshold value for X-ray emissions decreases with larger laser spot sizes and longer pulse durations. Another key finding of this study is that the suction flow conditions in the laser processing area can affect the released X-ray emission dose rate. The presented results support the development of effective X-ray protection strategies for safe and risk-free ultrashort pulse laser operation in industrial and academic research applications.
高功率超短脉冲激光器不断发展的趋势，已引起人们对该技术在大规模表面工程和现代微加工中应用的日益关注。然而，最近有报道称，即使在与工业相关的激光辐照条件下，也会产生不希望的X射线光子辐射，这对激光操作人员构成了严重的健康风险。与此同时，已确定有二十多个影响因素对超短脉冲激光加工产生的X射线光子发射有重大影响。本文对高脉冲重复频率超短脉冲激光加工产生的增强X射线发射进行了研究，为影响最大的参数之间的相互关系提供了新的见解。以AISI 304基板为例验证了，当峰值强度低于1×10 W/cm²的超短激光脉冲以0.5 MHz的脉冲重复频率辐照时，X射线光子发射可能会大大超过法定剂量率限值。X射线发射的峰值强度阈值会随着激光光斑尺寸增大和脉冲持续时间延长而降低。本研究的另一个关键发现是，激光加工区域的抽吸流动条件会影响释放的X射线发射剂量率。本文结果有助于制定有效的X射线防护策略，以便在工业和学术研究应用中实现安全无风险的超短脉冲激光操作。
