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Holland J, Hagenlocher C, Weber R, Graf T. Self-Shielding of X-ray Emission from Ultrafast Laser Processing Due to Geometrical Changes of the Interaction Zone. MATERIALS (BASEL, SWITZERLAND) 2024; 17:1109. [PMID: 38473580 DOI: 10.3390/ma17051109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Revised: 02/23/2024] [Accepted: 02/26/2024] [Indexed: 03/14/2024]
Abstract
Materials processing with ultrashort laser pulses is one of the most important approaches when it comes to machining with very high accuracy. High pulse repetition rates and high average laser power can be used to attain high productivity. By tightly focusing the laser beam, the irradiances on the workpiece can exceed 1013 W/cm2, and thus cause usually unwanted X-ray emission. Pulsed laser processing of micro holes exhibits two typical features: a gradual increase in the irradiated surface within the hole and, with this, a decrease in the local irradiance. This and the shielding by the surrounding material diminishes the amount of ionizing radiation emitted from the process; therefore, both effects lead to a reduction in the potential X-ray exposure of an operator or any nearby person. The present study was performed to quantify this self-shielding of the X-ray emission from laser-drilled micro holes. Percussion drilling in standard air atmosphere was investigated using a laser with a wavelength of 800 nm a pulse duration of 1 ps, a repetition rate of 1 kHz, and with irradiances of up to 1.1·1014 W/cm. The X-ray emission was measured by means of a spectrometer. In addition to the experimental results, we present a model to predict the expected X-ray emission at different angles to the surface. These calculations are based on raytracing simulations to obtain the local irradiance, from which the local X-ray emission inside the holes can be calculated. It was found that the X-ray exposure measured in the surroundings strongly depends on the geometry of the hole and the measuring direction, as predicted by the theoretical model.
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Affiliation(s)
- Julian Holland
- Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany
| | - Christian Hagenlocher
- Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany
| | - Rudolf Weber
- Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany
| | - Thomas Graf
- Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany
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Garmatina A, Mareev E, Minaev N, Asharchuk N, Semenov T, Mozhaeva M, Korshunov A, Krivonosov Y, Dyachkova I, Buzmakov A, Koldaev V, Zolotov D, Dymshits Y, Gordienko V, Asadchikov V. Vacuum-free femtosecond fiber laser microplasma X-ray source for radiography. OPTICS EXPRESS 2023; 31:44259-44272. [PMID: 38178501 DOI: 10.1364/oe.502200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 11/23/2023] [Indexed: 01/06/2024]
Abstract
Radiographic imaging using X-rays is a tool for basic research and applications in industry, materials science, and medical diagnostics. In this article, we present a novel approach for the generation of X-rays using a vacuum-free microplasma by femtosecond fiber laser. By tightly focusing a laser pulse onto a micrometer-sized solid density near-surface plasma from a rotating copper target, we demonstrate the generation of Cu K-photons (8-9 keV) with high yield ∼ 1.6 × 109 phot/s/2π, and with a source size diameter of approximately 10 microns. Femtosecond fiber laser allows working with a high repetition rate (∼2 MHz) and moderate energy levels (10-40 µJ), ensuring the effective quasi-continuous generation of X-ray photons. Furthermore, we introduce a hybrid scheme that combines the tightly focusing laser-plasma X-ray generator with an online control unit for microplasma size source based on the back-reflected second harmonic generated in the laser-induced microplasma. The compactness and high performance of this vacuum-free femtosecond fiber laser microplasma X-ray source makes it a promising solution for advanced radiographic applications. Our preliminary results on the creation of a microfocus X-ray source provide insights into the feasibility and potential of this innovative approach.
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Krüger J, Bonse J. Special Issue "Advanced Pulse Laser Machining Technology". MATERIALS (BASEL, SWITZERLAND) 2023; 16:819. [PMID: 36676556 PMCID: PMC9861651 DOI: 10.3390/ma16020819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 01/13/2023] [Indexed: 06/17/2023]
Abstract
"Advanced Pulse Laser Machining Technology" is a rapidly growing field that can be tailored to special industrial and scientific applications [...].
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Böttcher K, Schmitt Rahner M, Stolzenberg U, Kraft S, Bonse J, Feist C, Albrecht D, Pullner B, Krüger J. Worst-Case X-ray Photon Energies in Ultrashort Pulse Laser Processing. MATERIALS (BASEL, SWITZERLAND) 2022; 15:8996. [PMID: 36556801 PMCID: PMC9783067 DOI: 10.3390/ma15248996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 12/12/2022] [Accepted: 12/14/2022] [Indexed: 06/17/2023]
Abstract
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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Affiliation(s)
- Katrin Böttcher
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
| | - Mayka Schmitt Rahner
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany
| | - Ulf Stolzenberg
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany
| | - Sebastian Kraft
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
| | - Jörn Bonse
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
| | - Carsten Feist
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany
| | - Daniel Albrecht
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany
| | - Björn Pullner
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany
| | - Jörg Krüger
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
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Garmatina AA, Asadchikov VE, Buzmakov AV, Dyachkova IG, Dymshits YM, Baranov AI, Myasnikov DV, Minaev NV, Gordienko VM. Microfocus Source of Characteristic X-Rays for Phase-Contrast Imaging Based on a Femtosecond Fiber Laser. CRYSTALLOGR REP+ 2022. [DOI: 10.1134/s1063774522060074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Mosel P, Sankar P, Appi E, Jusko C, Zuber D, Kleinert S, Düsing J, Mapa J, Dittmar G, Püster T, Böhmer-Brinks P, Vahlbruch JW, Morgner U, Kovacev M. Potential hazards and mitigation of X-ray radiation generated by laser-induced plasma from research-grade laser systems. OPTICS EXPRESS 2022; 30:37038-37050. [PMID: 36258622 DOI: 10.1364/oe.468135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Accepted: 08/18/2022] [Indexed: 06/16/2023]
Abstract
A large range of laser-matter applications employ ultrashort pulses and high laser intensity. Such processes can lead to unrequired X-ray generation, which represents a hazardous radiation factor even for common laboratory research-grade laser systems. We present here an analysis of the radiation dose rate and X-ray spectrum emitted during ablation of a rotating copper cylinder with respect to several laser parameters. The results show that focused sub-picosecond pulses with intensity above 1013 W/cm2 can exceed the annual irradiation limit even in one hour, requiring appropriate shielding for the safety of the researchers.
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Enhanced X-ray Emissions Arising from High Pulse Repetition Frequency Ultrashort Pulse Laser Materials Processing. MATERIALS 2022; 15:ma15082748. [PMID: 35454442 PMCID: PMC9032387 DOI: 10.3390/ma15082748] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/30/2022] [Accepted: 04/06/2022] [Indexed: 02/04/2023]
Abstract
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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Holland J, Weber R, Sailer M, Graf T. Influence of Pulse Duration on X-ray Emission during Industrial Ultrafast Laser Processing. MATERIALS 2022; 15:ma15062257. [PMID: 35329706 PMCID: PMC8950077 DOI: 10.3390/ma15062257] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/04/2022] [Accepted: 03/09/2022] [Indexed: 11/16/2022]
Abstract
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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Affiliation(s)
- Julian Holland
- Institut für Strahlwerkzeuge, Universität Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany; (R.W.); (T.G.)
- Correspondence: ; Tel.: +49-(0)711-685-64146
| | - Rudolf Weber
- Institut für Strahlwerkzeuge, Universität Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany; (R.W.); (T.G.)
| | - Marc Sailer
- TRUMPF Laser GmbH, Aichhalder Straße 39, 78713 Schramberg, Germany;
| | - Thomas Graf
- Institut für Strahlwerkzeuge, Universität Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany; (R.W.); (T.G.)
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Guo K, Yu Q, Liu F, Deng H, Yi T, Ren B, Su W, Zhu S, Wang Z, Wu J, Zhou P. Synthesis of Hexagonal Structured GaS Nanosheets for Robust Femtosecond Pulse Generation. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:378. [PMID: 35159722 PMCID: PMC8839219 DOI: 10.3390/nano12030378] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 01/04/2022] [Accepted: 01/21/2022] [Indexed: 02/04/2023]
Abstract
Gallium sulfide (GaS), with a hexagonal structure, has received extensive attention due to its graphene-like structure and derived optical properties. Here, high-quality GaS was obtained via chemical vapor synthesis and then prepared as a saturable absorber by the stamp-assisted localization-transfer technique onto fiber end face. The stability of the material and the laser damage threshold are maintained due to the optimized thickness and the cavity integration form. The potential of the GaS for nonlinear optics is explored by constructing a GaS-based Erbium-doped mode-locked fiber laser. Stable femtosecond (~448 fs) mode-locking operation of the single pulse train is achieved, and the robust mode-locked operation (>30 days) was recorded. Experimental results show the potential of GaS for multi-functional ultrafast high-power lasers and promote continuous research on graphene-like materials in nonlinear optics and photonics.
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Affiliation(s)
- Kun Guo
- College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China; (K.G.); (Q.Y.); (H.D.); (B.R.); (P.Z.)
| | - Qiang Yu
- College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China; (K.G.); (Q.Y.); (H.D.); (B.R.); (P.Z.)
| | - Fangqi Liu
- Hubei Province Key Laboratory of Systems Science in Metallurgical Process, College of Science, The State Key Laboratory for Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China; (F.L.); (S.Z.)
| | - Haiqin Deng
- College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China; (K.G.); (Q.Y.); (H.D.); (B.R.); (P.Z.)
| | - Tianan Yi
- College of Mechanical and Electrical Engineering, Hohai University, Changzhou 213022, China; (T.Y.); (W.S.)
| | - Bo Ren
- College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China; (K.G.); (Q.Y.); (H.D.); (B.R.); (P.Z.)
| | - Wei Su
- College of Mechanical and Electrical Engineering, Hohai University, Changzhou 213022, China; (T.Y.); (W.S.)
| | - Sicong Zhu
- Hubei Province Key Laboratory of Systems Science in Metallurgical Process, College of Science, The State Key Laboratory for Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China; (F.L.); (S.Z.)
| | - Zhiqiang Wang
- Aston Institute of Photonic Technologies, Aston University, Birmingham B4 7ET, UK
- Advanced Photonic Technology Lab, College of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
| | - Jian Wu
- College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China; (K.G.); (Q.Y.); (H.D.); (B.R.); (P.Z.)
| | - Pu Zhou
- College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China; (K.G.); (Q.Y.); (H.D.); (B.R.); (P.Z.)
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Stolzenberg U, Schmitt Rahner M, Pullner B, Legall H, Bonse J, Kluge M, Ortner A, Hoppe B, Krüger J. X-ray Emission Hazards from Ultrashort Pulsed Laser Material Processing in an Industrial Setting. MATERIALS 2021; 14:ma14237163. [PMID: 34885319 PMCID: PMC8658201 DOI: 10.3390/ma14237163] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 11/19/2021] [Accepted: 11/22/2021] [Indexed: 11/16/2022]
Abstract
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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Affiliation(s)
- Ulf Stolzenberg
- Physikalisch-Technische Bundesanstalt (PTB), Department of Radiation Protection Dosimetry, Bundesallee 100, 38116 Braunschweig, Germany; (M.S.R.); (B.P.)
- Correspondence:
| | - Mayka Schmitt Rahner
- Physikalisch-Technische Bundesanstalt (PTB), Department of Radiation Protection Dosimetry, Bundesallee 100, 38116 Braunschweig, Germany; (M.S.R.); (B.P.)
| | - Björn Pullner
- Physikalisch-Technische Bundesanstalt (PTB), Department of Radiation Protection Dosimetry, Bundesallee 100, 38116 Braunschweig, Germany; (M.S.R.); (B.P.)
| | - Herbert Legall
- Bundesanstalt für Materialforschung und -prüfung (BAM), Materials Chemistry Department, Unter den Eichen 87, 12205 Berlin, Germany; (H.L.); (J.B.); (J.K.)
| | - Jörn Bonse
- Bundesanstalt für Materialforschung und -prüfung (BAM), Materials Chemistry Department, Unter den Eichen 87, 12205 Berlin, Germany; (H.L.); (J.B.); (J.K.)
| | - Michael Kluge
- SCHOTT AG, Hattenbergstrasse 10, 55122 Mainz, Germany; (M.K.); (A.O.); (B.H.)
| | - Andreas Ortner
- SCHOTT AG, Hattenbergstrasse 10, 55122 Mainz, Germany; (M.K.); (A.O.); (B.H.)
| | - Bernd Hoppe
- SCHOTT AG, Hattenbergstrasse 10, 55122 Mainz, Germany; (M.K.); (A.O.); (B.H.)
| | - Jörg Krüger
- Bundesanstalt für Materialforschung und -prüfung (BAM), Materials Chemistry Department, Unter den Eichen 87, 12205 Berlin, Germany; (H.L.); (J.B.); (J.K.)
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