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Advanced Pulse Laser Machining Technology

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Manufacturing Processes and Systems".

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 48063

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Jörg Krüger

E-Mail Website
Guest Editor
Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany
Interests: pulse laser material processing; laser surface functionalization; laser applications for the preservation of the cultural heritage; laser safety and secondary hazards
Dr. Jörn Bonse

E-Mail Website
Guest Editor
Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
Interests: laser–matter interaction; femtosecond laser technology; laser ablation; ultrashort laser pulses and applications; micro- and nano-structured surfaces; surface functionalization by of laser-textured surfaces; biomimetics; ultrafast microscopy; time-resolved spectroscopy; plasmonics; laser processes in photovoltaics; laser safety
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Advanced Pulse Laser Machining Technology is a rapidly growing field to tailor special industrial and scientific applications. This is significantly driven by the availability of high-repetition rate laser sources and novel beam delivery concepts.

This Special Issue focuses on developments in areas of surface and volume laser material processing, including spatial and temporal beam shaping, Bessel-beam dicing, direct laser interference patterning (DLIP), laser-induced forward transfer (LIFT), pulse burst machining, waveguide writing, and two-photon polymerization. Additionally, limitations of modern laser processing caused by failure of laser optics or unwanted secondary hazards like X-ray emission are addressed.

Here, we would like to attract contributors from industry and academics. This Special Issue shall bundle original research and review articles of the latest achievements.

Dr. Jörg Krüger
Dr. Jörn Bonse
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Advanced ultrashort-laser technology
  • Bessel-beam laser dicing
  • Direct laser interference patterning (DLIP)
  • High-repetition rate ultrafast laser processing
  • Laser-induced forward transfer (LIFT)
  • Limitations of laser optics
  • Pulse burst machining
  • Spatial beam shaping for precision machining
  • Temporal beam shaping for precision machining
  • Two-photon polymerization
  • Volume processing, waveguide writing
  • X-ray hazards during ultrafast laser processing

Published Papers (17 papers)

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Editorial

Jump to: Research, Review, Other

4 pages, 523 KiB  
Editorial
Special Issue “Advanced Pulse Laser Machining Technology”
by Jörg Krüger and Jörn Bonse
Materials 2023, 16(2), 819; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16020819 - 14 Jan 2023
Cited by 1 | Viewed by 1599
Abstract
“Advanced Pulse Laser Machining Technology” is a rapidly growing field that can be tailored to special industrial and scientific applications [...] Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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Research

Jump to: Editorial, Review, Other

17 pages, 11826 KiB  
Article
Worst-Case X-ray Photon Energies in Ultrashort Pulse Laser Processing
by Katrin Böttcher, Mayka Schmitt Rahner, Ulf Stolzenberg, Sebastian Kraft, Jörn Bonse, Carsten Feist, Daniel Albrecht, Björn Pullner and Jörg Krüger
Materials 2022, 15(24), 8996; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15248996 - 16 Dec 2022
Cited by 4 | Viewed by 1310
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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13 pages, 3580 KiB  
Article
Enhanced X-ray Emissions Arising from High Pulse Repetition Frequency Ultrashort Pulse Laser Materials Processing
by Jörg Schille, Sebastian Kraft, Dany Kattan and Udo Löschner
Materials 2022, 15(8), 2748; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15082748 - 08 Apr 2022
Cited by 7 | Viewed by 1420
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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13 pages, 4071 KiB  
Article
A Practical Comparison of Beam Shuttering Technologies for Pulsed Laser Micromachining Applications
by Damon G. K. Aboud, Michael J. Wood, Gianluca Zeppetelli, Nithin Joy and Anne-Marie Kietzig
Materials 2022, 15(3), 897; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15030897 - 25 Jan 2022
Cited by 3 | Viewed by 2400
Abstract
In this report we investigate the performance of various beam shutter technologies when applied to femtosecond laser micromachining. Three different shutter options are considered: a mechanical blade shutter, a bistable rotary solenoid shutter, and an electro-optic modulator (EOM) shutter. We analyzed the behavior [...] Read more.
In this report we investigate the performance of various beam shutter technologies when applied to femtosecond laser micromachining. Three different shutter options are considered: a mechanical blade shutter, a bistable rotary solenoid shutter, and an electro-optic modulator (EOM) shutter. We analyzed the behavior of each shutter type during repeated open/close commands (period of 10 ≤ T ≤ 200 ms) using both high-speed videography and practical micromachining experiments. To quantify the performance at varying cycle periods, we introduce a new variable called the compliance that characterizes the average state of the shutter with respect to its intended position. We found that the solenoid shutter responds poorly to sequential commands. The mechanical shutter provides reliable performance for cycled commands as short as T = 40 ms, but begins to lag significantly behind the control signal for T ≤ 20 ms. The EOM shutter provides the most precise and reliable performance, with an opening time of only 0.6 ms and a high compliance with the signal commands, even when cycled very quickly (T = 10 ms). Overall, this study acts as an extensive practical guide for other laser users when considering different shutter options for their laser system and desired application. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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17 pages, 3548 KiB  
Article
X-ray Emission Hazards from Ultrashort Pulsed Laser Material Processing in an Industrial Setting
by Ulf Stolzenberg, Mayka Schmitt Rahner, Björn Pullner, Herbert Legall, Jörn Bonse, Michael Kluge, Andreas Ortner, Bernd Hoppe and Jörg Krüger
Materials 2021, 14(23), 7163; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14237163 - 24 Nov 2021
Cited by 7 | Viewed by 2439
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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9 pages, 6464 KiB  
Article
High Aspect Ratio Structuring of Glass with Ultrafast Bessel Beams
by Christian Vetter, Remo Giust, Luca Furfaro, Cyril Billet, Luc Froehly and Francois Courvoisier
Materials 2021, 14(22), 6749; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14226749 - 09 Nov 2021
Cited by 10 | Viewed by 2080
Abstract
Controlling the formation of high aspect ratio void channels inside glass is important for applications like the high-speed dicing of glass. Here, we investigate void formation using ultrafast Bessel beams in the single shot illumination regime. We characterize the morphology of the damages [...] Read more.
Controlling the formation of high aspect ratio void channels inside glass is important for applications like the high-speed dicing of glass. Here, we investigate void formation using ultrafast Bessel beams in the single shot illumination regime. We characterize the morphology of the damages as a function of pulse energy, pulse duration, and position of the beam inside fused silica, Corning Eagle XG, and Corning Gorilla glass. While a large set of parameters allow for void formation inside fused silica, the operating window is much more restricted for Eagle XG and Gorilla glass. The transient formation of a molten layer around voids enables us interpreting the evolution of the morphology with pulse energy and duration. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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12 pages, 32014 KiB  
Article
Squared Focal Intensity Distributions for Applications in Laser Material Processing
by Henrike Schlutow, Ulrike Fuchs, Frank A. Müller and Stephan Gräf
Materials 2021, 14(17), 4981; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14174981 - 31 Aug 2021
Cited by 4 | Viewed by 2425
Abstract
Tailored intensity profiles within the focal spot of the laser beam offer great potential for a well-defined control of the interaction process between laser radiation and material, and thus for improving the processing results. The present paper discusses a novel refractive beam-shaping element [...] Read more.
Tailored intensity profiles within the focal spot of the laser beam offer great potential for a well-defined control of the interaction process between laser radiation and material, and thus for improving the processing results. The present paper discusses a novel refractive beam-shaping element that provides different squared intensity distributions converted from the Gaussian output beam of the utilized femtosecond (fs) laser. Using the examples of surface structuring of stainless-steel on the micro- and nano-scale, the suitability of the beam-shaping element for fs-laser material processing with a conventional f-Theta lens is demonstrated. In this context, it was shown that the experimental structuring results are in good agreement with beam profile measurements and numerical simulations of the beam-shaping unit. In addition, the experimental results reveal the improvement of laser processing in terms of a significantly reduced processing time during surface nano-structuring and the possibility to control the ablation geometry during the fabrication of micro-channels. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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18 pages, 5492 KiB  
Article
Study on X-ray Emission Using Ultrashort Pulsed Lasers in Materials Processing
by Joerg Schille, Sebastian Kraft, Theo Pflug, Christian Scholz, Maurice Clair, Alexander Horn and Udo Loeschner
Materials 2021, 14(16), 4537; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14164537 - 12 Aug 2021
Cited by 15 | Viewed by 2045
Abstract
The interaction of ultrashort pulsed laser radiation with intensities of 1013 W cm−2 and above with materials often results in an unexpected high X-ray photon flux. It has been shown so far, on the one hand, that X-ray photon emissions increase [...] Read more.
The interaction of ultrashort pulsed laser radiation with intensities of 1013 W cm−2 and above with materials often results in an unexpected high X-ray photon flux. It has been shown so far, on the one hand, that X-ray photon emissions increase proportionally with higher laser power and the accumulated X-ray dose rates can cause serious health risks for the laser operators. On the other hand, there is clear evidence that little variations of the operational conditions can considerably affect the spectral X-ray photon flux and X-ray emissions dose. In order to enhance the knowledge in this field, four ultrashort pulse laser systems for providing different complementary beam characteristics were employed in this study on laser-induced X-ray emissions, including peak intensities between 8 × 1012 W∙cm−2 < I0 < 5.2 × 1016 W∙cm−2, up to 72.2 W average laser power as well as burst/bi-burst processing mode. By the example of AISI 304 stainless steel, it was verified that X-ray emission dose rates as high as H˙′ (0.07) > 45 mSv h−1 can be produced when low-intensity ultrashort pulses irradiate at a small 1 µm intra-line pulse distance during laser beam scanning and megahertz pulse repetition frequencies. For burst and bi-burst pulses, the second intra-burst pulse was found to significantly enhance the X-ray emission potentially induced by laser pulse and plasma interaction. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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13 pages, 4603 KiB  
Article
X-ray Dose Rate and Spectral Measurements during Ultrafast Laser Machining Using a Calibrated (High-Sensitivity) Novel X-ray Detector
by Philip Mosel, Pranitha Sankar, Jan Friedrich Düsing, Günter Dittmar, Thomas Püster, Peter Jäschke, Jan-Willem Vahlbruch, Uwe Morgner and Milutin Kovacev
Materials 2021, 14(16), 4397; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14164397 - 05 Aug 2021
Cited by 11 | Viewed by 2166
Abstract
Ultrashort pulse laser machining is subject to increase the processing speeds by scaling average power and pulse repetition rate, accompanied with higher dose rates of X-ray emission generated during laser–matter interaction. In particular, the X-ray energy range below 10 keV is rarely studied [...] Read more.
Ultrashort pulse laser machining is subject to increase the processing speeds by scaling average power and pulse repetition rate, accompanied with higher dose rates of X-ray emission generated during laser–matter interaction. In particular, the X-ray energy range below 10 keV is rarely studied in a quantitative approach. We present measurements with a novel calibrated X-ray detector in the detection range of 2–20 keV and show the dependence of X-ray radiation dose rates and the spectral emissions for different laser parameters from frequently used metals, alloys, and ceramics for ultrafast laser machining. Our investigations include the dose rate dependence on various laser parameters available in ultrafast laser laboratories as well as on industrial laser systems. The measured X-ray dose rates for high repetition rate lasers with different materials definitely exceed the legal limitations in the absence of radiation shielding. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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15 pages, 1735 KiB  
Article
Competition Effects during Femtosecond Laser Induced Element Redistribution in Ba- and La-Migration Based Laser Written Waveguides
by Manuel Macias-Montero, Pedro Moreno-Zárate, Francisco Muñoz, Belén Sotillo, Marina Garcia-Pardo, Rosalía Serna, Paloma Fernandez and Javier Solis
Materials 2021, 14(12), 3185; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14123185 - 09 Jun 2021
Cited by 3 | Viewed by 2034
Abstract
Fs-laser induced element redistribution (FLIER) has been a subject of intensive research in recent years. Its application to various types of glasses has already resulted in the production of efficient optical waveguides, tappers, amplifiers and lasers. Most of the work reported on FLIER-based [...] Read more.
Fs-laser induced element redistribution (FLIER) has been a subject of intensive research in recent years. Its application to various types of glasses has already resulted in the production of efficient optical waveguides, tappers, amplifiers and lasers. Most of the work reported on FLIER-based waveguides refers to structures produced by the cross-migration of alkali (Na, K) and lanthanides (mostly La). The latter elements act as refractive index carrying elements. Herein, we report the production of Ba-based, FLIER-waveguides in phosphate glass with an index contrast > 10−2. Phosphate glasses modified with the same amount of Na2O and K2O, and variable amounts of BaO and/or La2O3 were used to produce the FLIER-waveguides with Ba and or La acting as index carriers. Ba-only modified glasses show a waveguide writing threshold and light guiding performance comparable to that of La-based structures. However, mixed Ba-La glasses show a much higher element migration threshold, and much smaller compositionally modified regions. This behavior is consistent with a competition effect in the cross-migration of both elements (Ba and La) against the alkalis. Such an effect can be applied to inhibit undesired element redistribution effects in fs-laser processing applications in multicomponent glasses. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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19 pages, 8331 KiB  
Article
Backward Flux Re-Deposition Patterns during Multi-Spot Laser Ablation of Stainless Steel with Picosecond and Femtosecond Pulses in Air
by Tong Zhou, Sebastian Kraft, Walter Perrie, Jörg Schille, Udo Löschner, Stuart Edwardson and Geoff Dearden
Materials 2021, 14(9), 2243; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14092243 - 27 Apr 2021
Cited by 4 | Viewed by 2128
Abstract
We report on novel observations of directed re-deposition of ablation debris during the ultrafast laser micro-structuring of stainless steel in the air with multi-beams in close proximity on the surface. This interesting phenomenon is observed with both 10 ps and 600 fs NIR [...] Read more.
We report on novel observations of directed re-deposition of ablation debris during the ultrafast laser micro-structuring of stainless steel in the air with multi-beams in close proximity on the surface. This interesting phenomenon is observed with both 10 ps and 600 fs NIR laser pulses at 5 kHz repetition rate. Ablation spot geometries could be altered with the use of beam splitting optics or a phase-only Spatial Light modulator. At low fluence (F ~ 1.0 J cm−2) and pulse exposure of a few hundred pulses, the debris appears as concentrated narrow “filaments” connecting the ablation spots, while at higher fluence, (F ~ 5.0 J cm−2) energetic jets of material emanated symmetrically along the axes of symmetry, depositing debris well beyond the typical re-deposition radius with a single spot. Patterns of backward re-deposition of debris to the surface are likely connected with the colliding shock waves and plasma plumes with the ambient air causing stagnation when the spots are in close proximity. The 2D surface debris patterns are indicative of the complex 3D interactions involved over wide timescales during ablation from picoseconds to microseconds. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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21 pages, 19601 KiB  
Article
Single Femtosecond Laser-Pulse-Induced Superficial Amorphization and Re-Crystallization of Silicon
by Camilo Florian, Daniel Fischer, Katharina Freiberg, Matthias Duwe, Mario Sahre, Stefan Schneider, Andreas Hertwig, Jörg Krüger, Markus Rettenmayr, Uwe Beck, Andreas Undisz and Jörn Bonse
Materials 2021, 14(7), 1651; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14071651 - 27 Mar 2021
Cited by 22 | Viewed by 4484
Abstract
Superficial amorphization and re-crystallization of silicon in <111> and <100> orientation after irradiation by femtosecond laser pulses (790 nm, 30 fs) are studied using optical imaging and transmission electron microscopy. Spectroscopic imaging ellipsometry (SIE) allows fast data acquisition at multiple wavelengths and provides [...] Read more.
Superficial amorphization and re-crystallization of silicon in <111> and <100> orientation after irradiation by femtosecond laser pulses (790 nm, 30 fs) are studied using optical imaging and transmission electron microscopy. Spectroscopic imaging ellipsometry (SIE) allows fast data acquisition at multiple wavelengths and provides experimental data for calculating nanometric amorphous layer thickness profiles with micrometric lateral resolution based on a thin-film layer model. For a radially Gaussian laser beam and at moderate peak fluences above the melting and below the ablation thresholds, laterally parabolic amorphous layer profiles with maximum thicknesses of several tens of nanometers were quantitatively attained. The accuracy of the calculations is verified experimentally by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (STEM-EDX). Along with topographic information obtained by atomic force microscopy (AFM), a comprehensive picture of the superficial re-solidification of silicon after local melting by femtosecond laser pulses is drawn. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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13 pages, 5247 KiB  
Article
Dual Laser Beam Processing of Semiconducting Thin Films by Excited State Absorption
by Christoph Wenisch, Sebastian Engel, Stephan Gräf and Frank A. Müller
Materials 2021, 14(5), 1256; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14051256 - 06 Mar 2021
Cited by 2 | Viewed by 2045
Abstract
We present a unique dual laser beam processing approach based on excited state absorption by structuring 200 nm thin zinc oxide films sputtered on fused silica substrates. The combination of two pulsed nanosecond-laser beams with different photon energies—one below and one above the [...] Read more.
We present a unique dual laser beam processing approach based on excited state absorption by structuring 200 nm thin zinc oxide films sputtered on fused silica substrates. The combination of two pulsed nanosecond-laser beams with different photon energies—one below and one above the zinc oxide band gap energy—allows for a precise, efficient, and homogeneous ablation of the films without substrate damage. Based on structuring experiments in dependence on laser wavelength, pulse fluence, and pulse delay of both laser beams, a detailed concept of energy transfer and excitation processes during irradiation was developed. It provides a comprehensive understanding of the thermal and electronic processes during ablation. To quantify the efficiency improvements of the dual-beam process compared to single-beam ablation, a simple efficiency model was developed. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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20 pages, 3523 KiB  
Article
Prediction of Optimum Process Parameters Fabricated by Direct Laser Interference Patterning Based on Central Composite Design
by Mikhael El-Khoury, Bogdan Voisiat, Tim Kunze and Andrés Fabián Lasagni
Materials 2020, 13(18), 4101; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13184101 - 15 Sep 2020
Cited by 6 | Viewed by 2407
Abstract
In this study, we report on the optimization of the direct laser interference patterning process by applying the design of experiments approach. The periodic line-like microstructures of a 8.50 µm spatial period were fabricated by a two-beam interference setup with nanosecond laser pulses, [...] Read more.
In this study, we report on the optimization of the direct laser interference patterning process by applying the design of experiments approach. The periodic line-like microstructures of a 8.50 µm spatial period were fabricated by a two-beam interference setup with nanosecond laser pulses, varying laser fluence, pulse overlap, and hatch distance. Central composite design with three factors and five levels was implemented to optimize the required number of experiments. The experimental and numerical results show the impact of various structuring process parameters on surface uniformity. The responses measured are the structure height, height error, and waviness of the pattern. An analysis of the microstructures on the patterned surface was conducted by confocal microscopy and scanning electron microscopy. A 3D-characterization method based on morphological filtering, which allows a holistic view of the surface properties, was applied, and a new qualification scheme for surface microstructures was introduced. Empirical models were also developed and validated for establishing relationships between process parameters and performance criteria. Multi-objective optimization was performed to achieve a minimal value of structure height errors and waviness. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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9 pages, 4849 KiB  
Communication
Micromachining of Invar with 784 Beams Using 1.3 ps Laser Source at 515 nm
by Petr Hauschwitz, Bohumil Stoklasa, Jiří Kuchařík, Hana Turčičová, Michael Písařík, Jan Brajer, Danijela Rostohar, Tomáš Mocek, Martin Duda and Antonio Lucianetti
Materials 2020, 13(13), 2962; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13132962 - 02 Jul 2020
Cited by 15 | Viewed by 3455
Abstract
To fulfil the requirements for high-resolution organic light-emitting diode (OLED) displays, precise and high-quality micrometer-scale patterns have to be fabricated inside metal shadow masks. Invar has been selected for this application due to its unique properties, especially a low coefficient of thermal expansion. [...] Read more.
To fulfil the requirements for high-resolution organic light-emitting diode (OLED) displays, precise and high-quality micrometer-scale patterns have to be fabricated inside metal shadow masks. Invar has been selected for this application due to its unique properties, especially a low coefficient of thermal expansion. In this study, a novel cost-efficient method of multi-beam micromachining of invar will be introduced. The combination of a Meopta beam splitting, focusing and monitoring module with a galvanometer scanner and HiLASE high-energy pulse laser system emitting ultrashort pulses at 515 nm allows drilling and cutting of invar foil with 784 beams at once with high precision and almost no thermal effects and heat-affected zone, thus significantly improving the throughput and efficiency. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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Review

Jump to: Editorial, Research, Other

40 pages, 15141 KiB  
Review
Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses
by Daniel J. Förster, Beat Jäggi, Andreas Michalowski and Beat Neuenschwander
Materials 2021, 14(12), 3331; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14123331 - 16 Jun 2021
Cited by 57 | Viewed by 7974
Abstract
Laser processing with ultra-short double pulses has gained attraction since the beginning of the 2000s. In the last decade, pulse bursts consisting of multiple pulses with a delay of several 10 ns and less found their way into the area of micromachining of [...] Read more.
Laser processing with ultra-short double pulses has gained attraction since the beginning of the 2000s. In the last decade, pulse bursts consisting of multiple pulses with a delay of several 10 ns and less found their way into the area of micromachining of metals, opening up completely new process regimes and allowing an increase in the structuring rates and surface quality of machined samples. Several physical effects such as shielding or re-deposition of material have led to a new understanding of the related machining strategies and processing regimes. Results of both experimental and numerical investigations are placed into context for different time scales during laser processing. This review is dedicated to the fundamental physical phenomena taking place during burst processing and their respective effects on machining results of metals in the ultra-short pulse regime for delays ranging from several 100 fs to several microseconds. Furthermore, technical applications based on these effects are reviewed. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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Other

12 pages, 3528 KiB  
Perspective
Printing via Laser-Induced Forward Transfer and the Future of Digital Manufacturing
by Camilo Florian and Pere Serra
Materials 2023, 16(2), 698; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16020698 - 11 Jan 2023
Cited by 4 | Viewed by 2079
Abstract
In the last decades, digital manufacturing has constituted the headline of what is starting to be known as the ‘fourth industrial revolution’, where the fabrication processes comprise a hybrid of technologies that blur the lines between fundamental sciences, engineering, and even medicine as [...] Read more.
In the last decades, digital manufacturing has constituted the headline of what is starting to be known as the ‘fourth industrial revolution’, where the fabrication processes comprise a hybrid of technologies that blur the lines between fundamental sciences, engineering, and even medicine as never seen before. One of the reasons why this mixture is inevitable has to do with the fact that we live in an era that incorporates technology in every single aspect of our daily lives. In the industry, this has translated into fabrication versatility, as follows: design changes on a final product are just one click away, fabrication chains have evolved towards continuous roll-to roll processes, and, most importantly, the overall costs and fabrication speeds are matching and overcoming most of the traditional fabrication methods. Laser-induced forward transfer (LIFT) stands out as a versatile set of fabrication techniques, being the closest approach to an all-in-one additive manufacturing method compatible with virtually any material. In this technique, laser radiation is used to propel the material of interest and deposit it at user-defined locations with high spatial resolution. By selecting the proper laser parameters and considering the interaction of the laser light with the material, it is possible to transfer this technique from robust inorganic materials to fragile biological samples. In this work, we first present a brief introduction on the current developments of the LIFT technique by surveying recent scientific review publications. Then, we provide a general research overview by making an account of the publication and citation numbers of scientific papers on the LIFT technique considering the last three decades. At the same time, we highlight the geographical distribution and main research institutions that contribute to this scientific output. Finally, we present the patent status and commercial forecasts to outline future trends for LIFT in different scientific fields. Full article
(This article belongs to the Special Issue Advanced Pulse Laser Machining Technology)
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