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This question was the focus of a recently completed one-year research project at the Laser Institute of Mittweida University of Applied Sciences. In close cooperation with the Federal Institute for Materials Research and Testing (BAM) in Berlin, initial investigations were carried out to shed light on the typical areas of application for ultrashort-pulse lasers in medicine. The published results made it onto the March cover of *Applied Physics A*.
Following the amendment of the Radiation Protection Act (StrlSchG) and the associated Radiation Protection Ordinance (StrlSchV), X-rays have been the subject of heated debate within the laser community in recent years, alongside laser radiation. X-rays, first described by Wilhelm Conrad Röntgen some 130 years ago, can be generated during certain laser processes and pose a genuine health risk to plant operators. Such secondary hazards have long been recognised from fundamental research involving high-intensity laser radiation, mostly using ultrashort-pulse (USP) lasers. As a result of the rapid development of Laser Technology towards high-power laser sources, significant doses of X-rays can now also be released during industrial laser processing. Research into this has also been carried out at the Laser Institute at Mittweida University of Applied Sciences (LHM) and at the Federal Institute for Materials Research and Testing (BAM) [Link to: BAM – Home page], and has shown measurable X-rays even below the previously known threshold intensity of laser radiation.
An important area of application for UKP laser radiation is medicine. Here, laser processes are used, for example, to correct vision defects (‘laser eye surgery’) or can be applied in dentistry or for skin treatments. Encouraged by these potential medical applications and the available findings on laser-induced X-rays in solid-state materials, the Federal Office for Radiation Protection (BfS) initiated a research project to ensure the principles of radiation protection (justification, dose limitation and optimisation). The BAM, as the institution commissioned to carry out the project tasks, benefited from the LHM’s extensive expertise and outstanding technical equipment. The working group based at the LHM, led by Professor Udo Löschner, was able to draw not only on UKP laser research systems designed for flexible processing tasks, but also on experience in handling biological materials and the necessary measurement technology.
At the start of the research project, a literature review was first carried out to identify the areas of application for UKP lasers with the greatest potential for risk, with ophthalmology and dentistry emerging as the key areas. In ophthalmology, UKP lasers are used for the targeted, micrometre-precise perforation of the cornea in the human eye. In dentistry, laser processes are used for the ablation and structuring of hard dental materials for the purpose of tooth preservation. These applications were modelled at the LHM using model experiments and demonstrated that, under certain conditions, laser-induced X-rays can also be generated in biological materials. Taking into account naturally occurring radioactivity (link to: BfS – Radioactivity in the Environment), limit values and processing scenarios were estimated in which the dose of laser-induced X-rays exceeds the statutory limit. Overall, it can be concluded that the risk posed by the laser irradiation regimens investigated is relatively low. A precise assessment of the risk potential during actual medical use is to be carried out following the project, particularly with regard to the use of higher average laser powers. However, questions remain regarding laser-induced X-ray emissions in medical applications, for example: What happens when UKP laser radiation interacts with bone tissue or strikes implants?
The findings from the research project were recently published in a joint paper by BAM and LHM in the renowned journal *Applied Physics A*. Link to: X-ray emission during the ablative processing of biological materials by ultrashort laser pulses | SpringerLink To the authors’ delight, the article was not only selected as Editor’s Choice but also features on the cover page of the journal’s March 2023 issue. These results are set to be made available to a broad specialist audience in the future as well. Presentations have already been scheduled for this year at the EMRS Conference in Strasbourg (FRA), the LIM Conference at World of Photonics in Munich, and the Mittweida Laser Conference.
This project was funded by the Federal Office for Radiation Protection (BfS) under administrative agreement 3621S42451.
Text: Sebastian Kraft
Photo: Applied Physics, Volume 129, (2023) March cover page