X-ray Dose Rate and Spectral Measurements during Ultrafast Laser Machining Using a Calibrated (High-Sensitivity) Novel X-ray Detector

Mosel, Philip; Sankar, Pranitha; Düsing, Jan Friedrich; Dittmar, Günter; Püster, Thomas; Jäschke, Peter; Vahlbruch, Jan-Willem; Morgner, Uwe; Kovačev, Milutin

doi:10.3390/ma14164397

Cited by 11 publications

(11 citation statements)

References 23 publications

(28 reference statements)

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“…During the surface process with a pulse energy of 1980 µJ, an ambient dose equivalent rate d H *(10)/d t of around 1 µSv/h was measured. These X-ray emission dose rates are much lower compared to the mSv/h reported recently in the literature for the same laser pulse duration and a lower laser pulse energy [ 11 , 12 , 18 , 19 ].…”

Section: Resultsmentioning

confidence: 51%

“…With the microSHAPE TM USP-laser machine employing a tungsten workpiece, the measured dose rates are much smaller than expected for a laser-induced plasma generated at peak intensities of 3.3 × 10 15 W/cm 2 with tungsten as a target material. In the literature, typically, dose rates in the range of mSv/h are measured for such high peak intensities [ 18 , 19 ]. As can be seen from Table 1 , the measured dose rate decreased with increasing pulse energy, which is unexpected.…”

Section: Discussionmentioning

confidence: 99%

“…The use of laser peak intensities above 10 13 W/cm 2 in combination with laser pulse repetition rates in the few 100 kHz range can already lead to X-ray dose rates clearly exceeding the permitted limits for members of the public. Tungsten and steel in particular show significant X-ray emission [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. In [ 11 ], it was demonstrated that other materials such as aluminum and glass show significantly lower X-ray emissions.…”

Section: Introductionmentioning

confidence: 99%

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X-ray Emission Hazards from Ultrashort Pulsed Laser Material Processing in an Industrial Setting

et al. 2021

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Interactions between ultrashort laser pulses with intensities larger than 1013 W/cm2 and solids during material processing can lead to the emission of X-rays with photon energies above 5 keV, causing radiation hazards to operators. A framework for inspecting X-ray emission hazards during laser material processing has yet to be developed. One requirement for conducting radiation protection inspections is using a reference scenario, i.e., laser settings and process parameters that will lead to an almost constant and high level of X-ray emissions. To study the feasibility of setting up a reference scenario in practice, ambient dose rates and photon energies were measured using traceable measurement equipment in an industrial setting at SCHOTT AG. Ultrashort pulsed (USP) lasers with a maximum average power of 220 W provided the opportunity to measure X-ray emissions at laser peak intensities of up to 3.3 × 1015 W/cm2 at pulse durations of ~1 ps. The results indicate that increasing the laser peak intensity is insufficient to generate high dose rates. The investigations were affected by various constraints which prevented measuring high ambient dose rates. In this work, a list of issues which may be encountered when performing measurements at USP-laser machines in industrial settings is identified.

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Section: Resultsmentioning

confidence: 51%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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X-ray Emission Hazards from Ultrashort Pulsed Laser Material Processing in an Industrial Setting

et al. 2021

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“…This X-ray emission might lead to possibly hazardous dose rates for an operator. Today, it is generally presumed to be a safety issue that resulted in new regulations and numerous investigations [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”

Section: Introductionmentioning

confidence: 99%

Influence of Pulse Duration on X-ray Emission during Industrial Ultrafast Laser Processing

et al. 2022

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Soft X-ray emissions during the processing of industrial materials with ultrafast lasers are of major interest, especially against the background of legal regulations. Potentially hazardous soft X-rays, with photon energies of >5 keV, originate from the fraction of hot electrons in plasma, the temperature of which depends on laser irradiance. The interaction of a laser with the plasma intensifies with growing plasma expansion during the laser pulse, and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, pulse duration is one of the dominant laser parameters that determines the soft X-ray emission. An existing analytical model, in which the fraction of hot electrons was treated as a constant, was therefore extended to include the influence of the duration of laser pulses on the fraction of hot electrons in the generated plasma. This extended model was validated with measurements of H (0.07) dose rates as a function of the pulse duration for a constant irradiance of about 3.5 × 1014 W/cm2, a laser wavelength of 800 nm, and a pulse repetition rate of 1 kHz, as well as for varying irradiance at the laser wavelength of 1030 nm and pulse repetition rates of 50 kHz and 200 kHz. The experimental data clearly verified the predictions of the model and confirmed that significantly decreased dose rates are generated with a decreasing pulse duration when the irradiance is kept constant.

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“…This is the result of the amazing progress in the development of modern USPL systems towards kilowatt average power that is delivered by ultrashort pulses at high pulse repetition frequencies (PRF) ranging between ten to hundreds of megahertz (MHz) [1]. In this case, millions of ultrashort pulses interact with the substrate surface in a short time, and the X-ray photons released by each single pulse accumulate to high X-ray dose levels, reaching up to 1 Sv/h [2,3]. In fact, such high X-ray emissions exceed innumerably the limit values for the general population and occupationally exposed persons in a calendar year, which are specified in the German Radiation Protection Act, and can cause serious health damage to the exposed parts of the human body.…”

Section: Introductionmentioning

confidence: 99%

Enhanced X-ray Emissions Arising from High Pulse Repetition Frequency Ultrashort Pulse Laser Materials Processing

et al. 2022

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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 × 1013 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.

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X-ray Dose Rate and Spectral Measurements during Ultrafast Laser Machining Using a Calibrated (High-Sensitivity) Novel X-ray Detector

Cited by 11 publications

References 23 publications

X-ray Emission Hazards from Ultrashort Pulsed Laser Material Processing in an Industrial Setting

X-ray Emission Hazards from Ultrashort Pulsed Laser Material Processing in an Industrial Setting

Influence of Pulse Duration on X-ray Emission during Industrial Ultrafast Laser Processing

Enhanced X-ray Emissions Arising from High Pulse Repetition Frequency Ultrashort Pulse Laser Materials Processing

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