X-ray radiation protection is necessary for ultrashort laser processing

Ultrashort pulse laser processing allows for unprecedented precision but comes with the potential problem of hazardous X-ray radiation at high laser pulse repetition rates. To aid with radiation protection considerations, Legall et al. present updated results on the mechanism of X-ray generation, its scalability to higher peak intensities and the effectiveness of using various shielding materials for lowering X-ray doses.

“Our work points to a hazard being potentially present in all industrial laser micromachining applications with high repetition rate ultrashort laser pulses,” said author Herbert Legall. “In this context, the X-ray emission is an unwanted side effect dangerous for machine operators.”

X-ray generation can be caused by a laser-plasma interaction process known as resonance absorption. The researchers found the X-ray dose from this mechanism does not directly scale with the atomic number of the processed material. This is in contradiction to many predictions, implying the radiation danger may require more precautions than previously thought.

As expected, their spectral dose rate measurement results showed that the ideal shielding for X-ray protection is lead. However, to compromise for weight and cost, steel is an appropriate alternative. On the other hand, materials widely used for laser safety, like aluminum and glass, are unsuitable for X-ray shielding and would require a thickness about 30-40 times that of steel to achieve an equivalent protection level.

“Our work shows that apart from normal laser safety issues regarding optical radiation, X-ray protection must also be considered to ensure that the laser-generated X-ray doses stay below the safety limits,” Legall said. “Investigations must be extended to a wider range of real-world laser and processing parameters.”

Source: “X-ray radiation protection aspects during ultrashort laser processing,” by Herbert Legall, Christoph Schwanke, Jörn Bonse, and Jörg Krüger, Journal of Laser Applications (2020). The article can be accessed at https://lia.scitation.org/doi/10.2351/1.5134778 .