Decreasing feature size of surface texturing structures created by laser dispersing of ceramic particles
B.R. Ettema, G.R.B.E. Römer, D.T.A. Matthews

Wear resistance of the surface of steel rolls, used to transfer desired roughness profiles onto steel strip in steel production, can be improved by embedding micrometer sized ceramic particles from a preplaced layer into a tool steel surface utilizing locally derived laser-induced melt pools, in a process termed laser implantation. Dome shaped surface structures with significantly increased hardness can be achieved. Reported experiments in literate focus on implantations with 150-400 μm diameter and 10-30μm in height. However, features with smaller diameter and height are desired for technology adoption. This paper presents and discusses first experimental results of implantations with a diameter below 150 μm, with heights between 1-15 μm and significantly increased hardness. For that purpose, a Nd:YAG laser source (focal diameter 54 μm, pulse times tp= 3-15 ms, pulse power 20-50 W average) was used to induce a melt pool driving the embedding.

Keywords: laser implantation; laser dispersion; ceramic particles; surface texturing

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Black marking of titanium containing commercial glass
Lukas Janos Richter, Clemens M. Beckmann, Jürgen Ihlemann

Laser marking of glass products can be used to enhance the visual appearance, for product identification, traceability and fraud prevention. We demonstrate that high-contrast black markings can be produced on commercial TiO2-containing glasses by pulsed excimer laser irradiation without any special treatment of the surface. The black markings can be partly attributed to a scattering effect due to the formation of a microstructure on the surface. It is enhanced by laser-induced oxygen reduction of the TiO2 and an associated increase in light absorption. Measurements show a phase separation in titanium and silicon-rich material in an area of the microstructure close to the surface. An inclination of the sample during irradiation allows the fabrication of microstructures with a preferred direction. Our results show a simple method for creating high-contrast surface markings on commercial glass.

Keywords: TiO2-containing glass; Black marking; Surface microstructure; Excimer laser

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High resolution ultrashort UV pulsed laser processing with parallel Bessel beams for cylinder tooling
Stephan Buening, Martin Osbild, Keming Du, Arnold Gillner

Micro structuring with ultrashort laser pulses in the UV wavelength range makes it possible to create surface structures in the sub micrometer range on rotating tools that lead to specific functional properties. To transfer these functionalities from the tool to large surfaces (e.g. foils), a roll-to-roll nanoimprint application is the most efficient method, as processing speeds of up to 20 m² per min are possible.
This paper presents the optical setup of a laser structuring machine that uses four parallel Bessel beams. Each beamlet can be modulated individually to allow flexible generation of arbitrary surface structures. Ablation results with structure sizes of 1 μm are presented. A strategy for estimating the position-dependent peak fluence based on CMOS images of the Bessel beam along the propagation has been developed. In addition, a novel approach for lateral Bessel beam scanning for efficient machining of cylinders based on RF shifting in AODs is presented in this paper.

Keywords: Bessel beam; ultrafast laser; ultra-short pulse laser; micro structuring; nano structuring

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Generation and characterisation of different colors on 304 stainless steel using femtosecond laser pulses in GHz burst mode
Arnas Vyšniauskas, Evaldas Kažukauskas, Valdemar Stankevič

Our study presents an approach for color generation on 304 Stainless Steel surfaces using femtosecond laser pulses in GHz burst mode and the analysis of processing parameters influence to the generated colors. The colors on a metal surface are usually generated by few mechanisms: 1) color generation due to the surface heating and oxide layer growth and 2) color generation due to femtosecond laser-induced nano-structures. We demonstrate the processing window sensitivity to obtain a constant color using a spectrometer color characterization method. The CIE color difference parameter ΔEab* was used and allowed to compare the obtained colors. The wide range of colors on stainless steel surface was demonstrated. The problems with color homogeneity occur when processing larger surfaces and this was analyzed using a hyperspectral camera. This approach has potential applications for decorative coatings and surface engineering and provide valuable insights into the mechanisms of color generation on stainless steel.

Keywords: Stainless steel; Femtosecond; Burst pulses; Color difference

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The effect of temporal pulse overlaps to the morphology on stainless steel 304 at ps laser micro structuring
Munehiro Chijiiwa, Niklas Berger, Mareike Schäfer, Peter Mitschang, and Johannes A. L’huillier

In this study, for creating a bumpy structure on the thin metal films with low heat accumulation, morphologies at different heat accumulation conditions were examined by changing the time interval between laser pulses (1 μs, 2.5 μs, and 25 μs), applying these with the same spatial pulse overlap. The comparison of morphologies and calculated saturation temperature showed that there are conditions where a bumpy structure is formed, even below the critical saturation temperature for bumpy structures. To discuss the boundary of the growth mechanism of a bumpy structure, which incubation mechanism is dominant at the different time intervals is studied. The analysis from the incubation model showed that for a time interval between pulses of 25 μs, the absorption and no longer the heat accumulation is the dominant factor. The results promote the idea that the boundary of mechanism for forming bumpy structures might be predictable by the incubation model.

Keywords: USP laser; heat accumulation; morphology; incubation effect

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3D laser structuring of thick composite cathodes to improve solid-state battery performance
Oihane Beldarrain, Aldara Pan, Ainara Rodríguez, Isabel Ayerdi, Leire Fernández, María Carmen Morant-Miñana

3D electrode structuring is of growing interest in the battery field. In recent years, different strategies for such structuring have been addressed and, among them, USP laser technology has emerged as a very attractive approach. Anodes and cathodes have been laser structured, and 3D structures have been found to favor ionic transport in the faradaic electrodes of batteries, thus improving the performance of these energy storage devices. However, the reported works correspond mainly to lithium-ion batteries with liquid electrolyte, while the application of this technology in solid-state batteries has not been explored yet. In the present work, femtosecond laser structuring of solid-state battery cathodes is addressed for the first time. A methodical study of laser process parameters is performed. SEM and optical profilometry are used to analyze the profiles of the generated structures, while XRD analysis is used to evaluate the chemical changes produced in the material by laser processing.

Keywords: Solid-state cells; thick composite cathode; femtosecond laser; 3D structuring.

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Improving the absorption of copper for near-infrared laser beams to optimize laser spot welding quality of copper to aluminum
Mahdi Amne Elahi, Mohammadhossein Norouzian, Peter Plapper

Laser spot welding of copper-aluminum has gained significant attention thanks to the unique properties of these metals in addition to the capabilities of laser welding. Applying the laser on the aluminum side in an overlap configuration is well-studied in the literature however, directing the beam from the copper may bring some advantages to better control the final microstructure of the weld and minimize the formation of intermetallic compounds. The issue to be addressed is the considerable reflectivity of copper surfaces for well-established near-infrared laser sources. In this paper, the absorption of copper is improved by implementing laser-based surface structuring. The absorption of copper is tracked with online temperature measurement and offline microscopic observation. In addition, the shear load of welded copper-aluminum samples with different copper surface conditions and laser powers was considered to explain the absorption of the laser beam and optimize the microstructure of the weld zone regarding the formation of intermetallic compounds.

Keywords: laser welding of Cu-Al; laser beam absorption; intermetallic compounds; laser-based surface structuring

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Industrial scale riblets manufacturing with a high energy femtosecond laser and a Multi-Plane Light Conversion beam-shaper
Ivan Gusachenko, Martin Delaigue, Dmitry Nuzhdin, Mahmoud Ziat, Adrien Douard, Gwenn Pallier, Eric Audouard, Clemens Honninger, Eric Mottay, Guillaume Labroille

Riblets manufacturing lead to the reduction of flight fuel consumption by 2-3%. However, achieving the necessary high precision in texturing and high processing speed to engrave large surfaces is challenging. To overcome this challenge, an innovative combination of high repetition rate (40MHz) and high-energy (3 mJ) femtosecond laser with an optimal beam management has been developed. The beam-shaper based on Multi-Plane Light Conversion (MPLC) technology enables beam division and square top-hat generation, resulting in a high level of homogeneity of spots. The change from Gaussian to square top-hat improves the process speed by 10. Combined with beam-splitting a 90 times speed increase is demonstrated.
In this study, we present texturing tests that demonstrate the efficacy of this new technique. This breakthrough combination of laser and beam-shaping has the potential to revolutionize the aerospace industry by enabling the production of high-quality riblets at a faster rate and with greater precision.

Keywords: Laser; Additive Manufacturing; powder; Nickel; 3D-Printing; beam shaping; MPLC; cracking; porosity

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Laser-based crystallization of oxide ceramic thin films for solid oxide fuel cells
Jonas Frühling, Sarah Schreyer, Samuel Fink, Christian Vedder

Solid Oxide Fuel Cells show the highest efficiency of all available fuel cell types. However, this technology is still subject to limitations, such as insufficient cycling stability and long start-up times. With the use of a thin proton-conducting electrolyte and a metallic support it is expected to overcome these limitations.
To manufacture such a cell, the membrane electrode assembly is wet-chemically deposited onto the metallic support and then thermally crystallized. Conventional methods (Rapid Thermal Annealing or oven) lead to unwanted interactions with the substrate material. The use of a laser beam for thermal crystallization of the thin films allows very short processing times and therefore offers the potential to completely crystallize the thin films without the formation of minor phases. In this work electrolyte material is crystallized using a laser beam, and the influence of different process parameters is investigated using X-ray diffraction and transmission electron microscopy.

Keywords: solid oxide fuel cells; laser processing; crystallization; thin films

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High efficient laser method of powder production
Y. Chivel

A process is presented for obtaining a spherical powder in a wide range of sizes 50 nm - 50 μm, in which a continuous near-surface optical discharge with a temperature of 20 kK is formed using conical laser beams in an inert gas flow, into which material is introduced in the form of a wire or irregular raw powder. The condensation of particles is strongly and rapidly quenched by an inert gas flow, producing high supersaturation. The process capacity is 0.5 kg/kWh with a laser power of 10 kW.

Keywords: atomization; melting; optical discharge; laser evaporation; gas-phase condensation; particles

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Shorter period Laser Induced Periodic Surface Structure generation with a Multi-Plane Light Conversion Beam Shaper and a femtosecond laser at 515nm.
Dmitry Nuzhdin, Kathrin Placzek, Mahmoud Ziat, Ivan Gusachenko, Adrien Douard, Gwenn Pallier, Daniel Holder, Guillaume Labroille

Processing at 515nm presents advantages compared to 1030nm: the depth of field is four times longer and the achievable sharpness is twice smaller. Moreover, it has been demonstrated that processing at 515nm is more efficient in terms of ablation efficiency for some materials despite the 50% conversion loss in terms of energy.
We describe how a beam shaper based on Multi-Plane Light Conversion (MPLC) combined with a 300fs 515nm laser improves Laser Induced Periodic Surface Structure (LIPSS) generation on stainless steel. The beam-shaper provides a sharper square top-hat with an extended depth of field up to 10 times higher compared to other beam-shaping technologies.
LIPSS has been generated with 130μm and 50μm squares enabling a smaller period compared to IR processing, down to 0,5μm. The transition from the textured to non-textured area is reduced to 2μm thanks to the sharp edges of the top-hat profile.

Keywords: Laser ; LIPSS ; ultra-short pulses ; green laser ; laser induced periodic surface ; surface texturation ; dynamic tailored beam shaping; transtion

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Hybrid gold-silver nanoparticles synthesis using a nanosecond laser treatment and their use in Raman spectroscopy
Evaldas Stankevičius, Vita Petrikaitė, Ilja Ignatjev, Romualdas Trusovas, Sonata Adomavičiūtė-Grabusovė, Valdas Šablinskas, Martynas Talaikis, Justinas Čeponkus, Lina Mikoliūnaitė, Algirdas Selskis, Gediminas Niaura

Surface-enhanced Raman spectroscopy (SERS) has led to a large number of Raman enhancement studies due to its ability to analyze biomolecules and chemical compounds with remarkable sensitivity. It should be noted that a common problem with SERS substrates prepared chemically is the contamination of surfaces with molecules used to reduce or stabilize nanoparticles. Thus, although SERS substrates can be produced by a variety of methods, there is still a need for the development of SERS substrates with high enhancement factor, excellent reliability, no adsorbed impurities, and good scalability at low cost.
Here, we demonstrate a simple method for the production of SERS substrates using a laser treatment of hybrid gold-silver films. The presented approach does not use complicated procedures such as etching and template creation. The manufacturing process is primarily based on a spinodal wetting process of the molten gold/silver film.

Keywords: Hybrid gold-silver nanoparticles; thin films; SERS;

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Tool mastering by ultrashort pulsed laser for roll-to-roll processes
Stephan Bruening

Ultra-short pulsed lasers are becoming increasingly popular in industrial applications for tool mastering in high-precision mass-manufacturing. In order to be able to produce large surfaces in the shortest possible time, cylinder tools structured with USP lasers are often used in roll-to-roll (R2R) processes. Surface features / functions in R2R processes can be created by ink transfer in flexographic, gravure or screen printing processes or applied by embossing or nanoimprint processes. Printed electronics, optical films, light-conducting structures, antibacterial and biomedical properties and the adjustment of friction properties are further examples of functional topographies. UV lasers up to IR lasers are used for the surface functionalisation of cylinder tools. With Bessel beam configurations, ablation diameters of up to one μm are possible here. Multi-laser, -scan and -beam configurations are possible to accelerate the process.

Keywords: Ultrashort pulsed lasers, functional surfaces, mass production

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Direct writing of copper-based electrodes using femtosecond laser reductive sintering of copper (II) oxide nanoparticles
Mizue Mizoshiri, Kyohei Yoshidomi, Hirokazu Komatsu, Evgenia M. Khairullina, Ilya I. Tumkin

Specific surface area of the electrodes is an important feature for electrochemical detection. We investigated the porous nature with specific surface area of the copper-based electrodes fabricated by femtosecond laser reductive sintering using two copper (II) oxide nanoparticle inks with different grain size distributions, Gaussian and bimodal distributions. Although the electrode fabricated using the ink with bimodal distribution exhibited high density, the higher current was obtained by using the electrode fabricated using the ink with Gaussian distribution for electrolysis reaction. These results suggest the advantage of the large surface area of the electrodes by comparing to the resistance of the electrodes. In the presentation, we will introduce the cobalt-added copper-based electrodes for nonenzymatic glucose detection.

Keywords: femtosecond laser reductive sintering; coppe (II) oxide nanoparticle; electrode; nonenzymatic glucose; nanoparticle distribution;

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Process temperature measurement in the production of metal oxide layers by fast IR-detector
Alexander Nikolai Kaiser, Max-Jonathan Kleefoot, Eliene Olivera , Harald Riegel

A variety of temperature-critical processes can be realized with laser material processing. For example, material surfaces can be functionalized by micro structuring with suitable parameter selection and processing strategies. Especially in the field of functional surfaces for tribological, optical, or biological applications micro structuring is versatile.
Further functionalization of the surface is the targeted heating to produce temper colors. The surface is heated locally, creating an oxide layer that develops a specific color when exposed to light. This process is known as laser coloring. In the latest literature, mainly the color and material changes related to the laser parameters were analyzed.
In this work, we want to analyze the process of laser coloring with a fast infrared detector. With the help of the detector, it should be possible to establish a correlation between the used laser parameters, the material, the produced color, and the measured infrared signal.

Keywords: Laser; micro structuring; surface functionalized; laser coloring; temperature measurement

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Laser interference-treatment tunes surface states and corrosion behavior of additively manufactured near-beta
Ti alloy
Frederic Schell, Phil Goldberg, Avinash Hariharan, Martin Hantusch, Magdalena Ola Cichocka, Nicolás Pérez, Andrea Voß, Lars Giebeler, Volker Hoffmann, Christoph Zwahr, Andrés Fabián Lasagni, Annett Gebert

Near-beta titanium alloys are promising bone implant materials due to their low elastic modulus and good corrosion resistance. To optimize their surface properties, we apply direct laser interference patterning (DLIP) microtextures using nano (ns)- and picosecond (ps) pulses to an additively manufactured Ti-13Nb-13Zr alloy. It was observed that both the surface topography and chemistry as well as the microstructure are affected by the laser treatment. Single- and multiscale topographies were obtained by ns- and ps-DLIP, respectively. The nanosecond texturing led to an increased cubic β-phase fraction and the formation of a 25 nm thick passive layer, resulting in improved corrosion resistance. The ps-DLIP exhibited a defective surface oxide layer and a larger surface area due to the multi-scale topography, but nonetheless achieved improved corrosion resistance related to a partial wetting state.

Keywords: laser powder bed fusion; direct laser interference patterning; beta titanium alloy; corrosion

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High power femtosecond laser to improve aerodynamic performance
Eric Audouard, Martin Delaigue, Julien Pouysegur, Eric Mottay

Femtosecond laser now reaching 1 kW of mean power can be used in laser solutions for aeronautic, allowing consumption reduction. It is indeed known that the drag can be reduced by suited texturation on plane wings. Hybrid Laminar Flow Control (HLFC) uses multiple micro holes drilling. In the frame of the European Project MULTIPOINT, using a kW femtosecond laser, drilling of holes on Titanium with 0.8 mm thickness can be achieved at a drilling speed of 150 holes per second. Riblets are micro grooves engraved in the direction of flow. In the frame of the French Project CHASSEUR, the surfacing speed today near 1 cm2/min is expected to reach 25 cm2/min by combining a 300 W fs laser with a spatial shaping of multiple square spots.

Keywords: Femtosecond laser texturing, Riblets, Drilling