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

Stolzenberg, U.; Rahner, Mayka Schmitt; Pullner, Björn; Legall, Herbert; Kluge, Michael; Ortner, A.; Hoppe, B.; Krüger, Jörg

doi:10.3390/ma14237163

Cited by 8 publications

(9 citation statements)

References 25 publications

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“…Several investigations were performed to analyze the X-ray emission for different laser and process parameters during ultrashort pulse laser machining of various technical materials [5][6][7][8][9][10][11][12][13][14][15][16][17]. Recently, possibly harmful X-ray emission was observed already at laser irradiances below 10 13 W cm −2 [18,19].…”

Section: Introductionmentioning

confidence: 99%

Worst-Case X-ray Photon Energies in Ultrashort Pulse Laser Processing

et al. 2022

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Ultrashort pulse laser processing can result in the secondary generation of unwanted X-rays if a critical laser irradiance of about 1013 W cm−2 is exceeded. Spectral X-ray emissions were investigated during the processing of tungsten and steel using three complementary spectrometers (based on CdTe and silicon drift detectors) simultaneously for the identification of a worst-case spectral scenario. Therefore, maximum X-ray photon energies were determined, and corresponding dose equivalent rates were calculated. An ultrashort pulse laser workstation with a pulse duration of 274 fs, a center wavelength of 1030 nm, pulse repetition rates between 50 kHz and 200 kHz, and a Gaussian laser beam focused to a spot diameter of 33 μm was employed in a single pulse and burst laser operation mode. Different combinations of laser pulse energy and repetition rate were utilized, keeping the average laser power constant close to the maximum power of 20 W. Peak irradiances I0 ranging from 7.3 × 1013 W cm−2 up to 3.0 × 1014 W cm−2 were used. The X-ray dose equivalent rate increases for lower repetition rates and higher pulse energy if a constant average power is used. Laser processing with burst mode significantly increases the dose rates and the X-ray photon energies. A maximum X-ray photon energy of about 40 keV was observed for burst mode processing of tungsten with a repetition rate of 50 kHz and a peak irradiance of 3 × 1014 W cm−2.

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Section: Introductionmentioning

confidence: 99%

Worst-Case X-ray Photon Energies in Ultrashort Pulse Laser Processing

et al. 2022

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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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“…Due to the interaction of such laser pulses with matter, plasmas are produced with electron temperatures of up to several MeV [5,6]. On the other hand, more and more short-pulsed lasers with rather low or medium intensities in the order of 10 11 W cm −2 up to 10 14 W cm −2 are used for materials processing [7][8][9][10][11][12][13][14][15][16][17]. In all cases, the so-called hot electron temperature is used to characterize the electron emissions.…”

Section: Introductionmentioning

confidence: 99%

On the distribution function of electron spectra from hot laser plasmas

Behrens

2024

Laser Phys.

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The emission of electrons from hot plasmas generated in the interaction of ultra-short (and ultra-high intensity) laser pulses with matter is often characterized by the so-called ‘hot electron temperature’. In this article it is shown that this number is not unambiguous. The reason is the following: to assign a temperature to an electron spectrum, it is necessary to describe the spectrum with a distribution function. However, different types of distribution functions are in use, e.g. the Boltzmann or Maxwell distribution, leading to different electron temperatures in spite of providing nearly the same form of the electron spectrum. For this reason, the main characteristics of all these distribution functions are presented in this article and compared. Depending on the distribution function used, the value of the hot electron temperature varies by up to 30% and in extreme cases by more than a factor of four. This fact should always be kept in mind when comparing values of hot electron temperatures. In addition, the reasons for using equilibrium distributions to describe the characteristics of laser-produced electrons—although probably no thermodynamic equilibrium is prevailing—are discussed.

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

Cited by 8 publications

References 25 publications

Worst-Case X-ray Photon Energies in Ultrashort Pulse Laser Processing

Worst-Case X-ray Photon Energies in Ultrashort Pulse Laser Processing

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

On the distribution function of electron spectra from hot laser plasmas

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