CC BY
11LM-I-30
Undesired X-ray emission during ultrashort pulse laser material
processing
H. Legall1, J. Bonse1, J. Krüger1
1- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
joerg. krueger@bam. de
The use of ultrashort laser pulses for material processing in air has many advantages. Due to the progressive development in the laser sector, average powers in the kW range with pulse repetition rates exceeding the MHz-level are available [1]. The machining with high-intensity laser pulses can be accompanied by the generation of a near-surface electron plasma due to absorption and ionization of the material, a subsequent plasma heating by the laser pulse, and finally an interaction of "hot" plasma electrons with the workpiece leading to continuous and characteristic X-ray radiation (Fig. 1).
Fig. 1. Scheme of X-ray generation during ultrashort pulse laser material processing in air.
The amount of this unwanted X-ray radiation is determined by the laser parameters (pulse duration, intensity, wavelength, polarization), the workpiece (atomic number, surface preparation), and the laser process management (scanning or stationary regime, laser turning). The use of laser intensities above 1013 W/cm2 in combination with laser pulse repetition rates in the few 100 kHz-range can lead to X-ray dose rates exceeding the permitted X-ray limits for members of the public. Especially the materials tungsten and steel show significant X-ray emission [2-7].
Recently, the current state of the art in the field of undesired generation of X-ray radiation during ultrashort pulse laser processing in air was reviewed [8]. In this presentation, important aspects of the measured X-ray doses, X-ray spectra, and practical issues of radiation protection are discussed.
[1] C.J. Saraceno, D. Sutter, Th. Metzger, M.A. Ahmed, The amazing progress of high-power ultrafast thin-disk lasers, Journal of the European Optical Society - Rapid Publications, 15, 15 (2019). https://doi.org/10.1186/s41476-019-0108-1
[2] H. Legall, C. Schwanke, S. Pentzien, G. Dittmar, J. Bonse, J. Krüger, X-ray emission as a potential hazard during ultrashort pulse laser material processing, Applied Physics A 124, 407 (2018). https://doi.org/10.1007/s00339-018-1828-6
[3] R. Behrens, B. Pullner, M. Reginatto, X-ray emission from materials processing lasers, Radiation Protection Dosimetry 183, 361 (2019) https://doi .org/10.1093/rpd/ncy126
[4] H. Legall, C. Schwanke, J. Bonse, J. Krüger, The influence of processing parameters on X-ray emission during ultra-short pulse laser machining, Applied Physics A 125, 570 (2019). https://doi.org/10.1007/s00339-019-2827-y
[4] R. Weber, R. Giedl-Wagner, D.J. Förster, A. Pauli, T. Graf, J.E. Balmer, Expected X-ray dose rates resulting from industrial ultrafasl laser applications, Applied Physics A 125, 635 (2019). https://doi.org/10.1007/s00339-019-2885-1
[6] H. Legall, C. Schwanke, J. Bonse, J. Krüger, X-ray radiation protection aspects during ultrashort laser processing, Journal of Laser Applications 32, 022004 (2020). https://doi.org/10.2351/1.5134778
[7] C. Freitag, R. Giedl-Wagner, X-ray protection in an industrial production environment, PhotonicsViews 17, 37 (2020). https://doi.org/10.1002/phvs.202000020
[8] H. Legall, J. Bonse, J. Krüger, Review of X-ray exposure and safety issues arising from ultra-short pulse laser material processing, Journal of Radiological Protection 41, R28 (2021). https://doi.org/10.1088/1361-6498/abcb16
