Abstract
The emission of laser induced X-rays from materials processing ultra-short pulsed laser systems was measured. The absolute spectral photon fluence was determined using a thermoluminescence detector based few-channel spectrometer. The spectra at 10 cm from the laser focus were in the energy region between 2 and 25 keV with mean energies of ~4–6 keV (when weighted by fluence or directional dose equivalent) and up to 13 keV (when weighted by ambient dose equivalent). The operational quantities, ′(0.07), ′(3) and *(10), were determined to be in the order of 1600–7300, 16–71 and 1–4 mSv per hour processing time, respectively, depending on the material and condition of the workpiece. The dose contribution due to photons above 30 keV was for all quantities negligible, i.e. below 10−3.
Highlights
Ultra-short pulsed lasers have been developed in the last decades for both research and various applications[1]
The electrons from the plasma produce bremsstrahlung and characteristic X-rays. These photons are expected to be in the energy region of a few tens of keV, as the laser reaches intensities in the order of 1014 W/cm2(5)
To reduce the photon fluence, and the pile-up effects, an active spectrometer could be positioned at larger distances, but this would result in an unwanted attenuation especially for low energy photons
Summary
Ultra-short pulsed lasers have been developed in the last decades for both research and various applications[1]. In the last few years, larger intensities of up to the order of 1014 W/cm are in use for materials processing resulting in an unwanted production of ionizing radiation[3, 4]. Advantages of such systems are, for example, extremely small holes (a few tens of μm in diameter) with nearly perfect edges due to the evaporation of the material, as opposed to holes produced by melting the material. The electrons from the plasma produce bremsstrahlung and characteristic X-rays These photons are expected to be in the energy region of a few tens of keV, as the laser reaches intensities in the order of 1014 W/cm2(5). To reduce the photon fluence, and the pile-up effects, an active spectrometer could be positioned at larger distances, but this would result in an unwanted attenuation especially for low energy photons
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