Micro-polishing of 4H-SiC surfaces using femtosecond laser vector beams and wobble-based scanning
Chung-Wei Cheng, Che Tseng, Jia-Fan Kuo
The production of 4H-SiC wafers typically involves laser slicing followed by multiple polishing steps to achieve the desired surface flatness. This study investigates the feasibility of micro-polishing 4H-SiC surfaces using femtosecond laser vector beams. In the first stage, high-fluence processing at 1.39 J/cm² was performed using femtosecond laser vector beams combined with wobble scanning to simulate the rough surface morphology produced by laser slicing, resulting in a surface roughness (Sz) of 32.3 μm. In the subsequent stage, a lower fluence of 1.25 J/cm² was employed along with a defocused beam (Z = -50 μm) for micro-polishing, which reduced the surface roughness to 9.0 μm. These results demonstrate the potential of femtosecond laser vector beams for precision micro-ablation and polishing of 4H-SiC surfaces.
Keywords: femtosecond laser; vector beam; 4H-SiC; micro-polishing
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Thickness of over-coated SiO2 and the Femtosecond laser induced damage
Jing Meng, Jonathan Watson, Pete Kupinski
In ultrafast laser application, the top layer of thin film not only serve the spectrum purpose, but also protects the stacks from the application environment, such as plasma, UV light and so on. It is found the thickness of the over-coated silica can affect the laser induced damage even though it is wide bandgap material and sitting in very low electric field intensity.
Keywords: Thin film; Overcoat; Ultrafast laser damage, Blister; Mechanical robustness
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The effect of laser emission mode on the cutting of lithium metal as a solid-state battery anode
Pourya Heidari Orojloo, Pantaleone Barbieri, Daniela Fontana, Ali Gökhan Demir
Lithium metal as an anode in the solid-state battery is a promising alternative to the intercalation type of anode in the lithium-ion battery. However, cutting of this component mechanically is challenging due to its high surface adhesion, chemical reactivity, and low rigidity. On the other hand, the melting temperature of this material is very low (180 °C) compared to conventional metals, rendering it problematic a stable thermal cutting operation. While the laser is an appealing solution for scaling up the cutting process of lithium metal, the ideal laser type to be used for this operation still requires further attention. Accordingly, this work investigates impact of continuous wave and ns-pulsed laser sources on the cut quality and productivity of 50 µm-thick pure Li sheets. Processing conditions are discussed to address the environmental control issues for reactivity along with the different processing regimes observed.
Keywords: Laser cutting; Lithium metal; Solid-state battery; Anode
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From Macro to Micro: Multimode Fiber Lasers in Direct Laser Interference Patterning
Bogdan Voisiat, Wei Wang, Dominik Britz, Andrés Fabian Lasagni
This study introduces a pioneering advancement in Direct Laser Interference Patterning (DLIP) through the integration of a high-power multimode pulsed nanosecond fiber laser, for high-precision microfabrication processes. By employing an innovative beam-shaping approach using the Extended Laser Interference Patterning System (ELIPSYS®) from SurFunction GmbH, the inherent limitations of low coherence and beam quality in multimode lasers are effectively addressed. This novel configuration enabled the generation of precise, well-defined periodic line-like microstructures with a periodicity of 24 µm and aspect ratios up to 0.8, while maintaining a significant deep focus range of approximately 0.6 mm, which is crucial for large-area applications. The impact of critical laser parameters, specifically pulse energy and pulse-to-pulse overlap, on the resulting structure depth and uniformity of the structures is comprehensively investigated. Confocal microscopy characterization confirmed an optimal processing window, balancing structure depth and uniformity across patterned surfaces. These findings demonstrate the feasibility and significant potential of coupling high-power multimode fiber lasers with DLIP technology, enhancing process efficiency and scalability while opening new opportunities for integrating these versatile and high-power lasers into industrial-scale microfabrication that demands high precision and throughput over large areas.
Keywords: Direct laser interference patterning, ELIPSYS system, high-power multimode fiber laser, surface micro processing, periodic line-like structures
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Impact of polarization angle on ablation efficiency and structure formation in DLIP processing
Francisco Udo Marins Almeida, Bogdan Voisiat, Ignacio Tabares, Fabian Ränke, Andrés Fabian Lasagni
Direct Laser Interference Pattering (DLIP) has evolved as an efficient method for surface functionalization by producing periodic structures. When using femtosecond or picosecond laser sources, the produced topographies are also covered by Laser Induced Periodic Surface Structures (LIPSS), being its orientation controlled by the polarization direction of the laser beam. On the other hand, their orientation has an effect not only on the geometry of the produced patterns, but also in the ablation efficiency during the structuring process. In this work, stainless steel 304 and aluminum 2024 plates are treated with 12 ps and 70 ps laser pulses (1064 nm) using DLIP, producing line-like structures with 6.0 µm and 5.4 µm periods. The polarization direction and thus the LIPSS orientation is controlled during the process. It was found that the ablation efficiency can be improved significantly when the LIPSS are perpendicular to the DLIP features, and that the line-like geometry of the DLIP features affects the expected orientation of the LIPSS.
Keywords: Direct Laser Interference Pattering; Laser Induced Periodic Surface Structures; Polarization control; Ablation efficiency
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FT-Based Device for Characterization of Laser-textured Periodic Surface Topographies
Bogdan Voisiat, Agustin Esteban Götte, Marcelo Daniel Sallese, Marcos Soldera, Andrés Fabian Lasagni
Laser-induced periodic surface structures (LIPSS) and direct laser interference patterning (DLIP) offer scalable approaches for functionalizing surfaces with sub-micron precision. Ensuring process reliability and reproducibility in such applications requires robust, real-time monitoring solutions. In this study, a compact diffraction-based optical system is employed to characterize surface topographies indirectly by analyzing the intensity distribution of the resulting diffraction patterns. LIPSS, as well as dot-like periodic structures generated by DLIP, are fabricated on stainless steel using picosecond pulsed lasers at wavelengths of 1064 nm and 532 nm, respectively. By correlating the intensities of the 0th and ±1st diffraction orders with structure depth, the system enables accurate estimation of the average depth and spatial period of the surface features, with mean errors below 15% and 2%, respectively. This method provides a rapid, non-destructive, and industrially compatible monitoring solution for quality assurance in laser surface texturing processes.
Keywords: Laser-induced periodic surface structures (LIPSS); Direct laser interference patterning (DLIP); Scatterometry; Process monitoring
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Martin Shulevski, Siwar Darawshe, Adam El-Sarout, Samuel Fink
Integrated sensors are becoming increasingly important for structural health monitoring (SHM) of components. Additively manufactured strain gauges can be used to evaluate the mechanical stress of materials with sensitivity comparable to that of manually applied strain gauges. We propose an approach that involves the application of strain gauges to metal components using an inkjet printing process with a nanoparticle silver ink. In a post-processing step, the strain gauges are laser-sintered to functionalize the material and adjust the resistivity of the thin film. The strain gauges presented exhibit resistance values from 320 Ω to 520 Ω. We report on the results of tensile tests with the contacted sensors and characterizing their electrical properties, as well as the proportionality factor of the strain gauges in dependence of the laser process parameters. The electromechanical characterization of the 200 nm thick strain gauges for different sintering parameters yields strain gauge factors ranging from 0.35–0.68, which remain stable throughout strain measurements. With a hysteresis error smaller than 1% and an electrical drift not surpassing 10%, the strain gauges show high sensitivity, reliability and flexibility.
Keywords: printed electronics; strain gauges; inkjet printing; laser-sintering; tensile strain measurement; sensor integration; structural health monitoring
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Indentation technique based on laser-induced shockwaves for material testing with moving specimen
Laurin Schaper, Tim Radel
A method for determining material hardness of metals is based on laser-induced shockwaves generated with a pulsed TEA-CO2 nanosecond laser. The laser creates a plasma, which interacts further with the laser beam and subsequently generates a shockwave. The shockwave is ignited above a spherical indenter, made of Al2O3, which is pushed thereby into the metal surface. The indentation geometry can be analyzed to draw conclusions about material properties. The process duration depends mainly on two factors: Generating and analyzing the indentations. To speed up the indentation process an approach with a constant movement of the specimen during indentation was tested. The results show a constant reduction of indentation diameter and depth with moving specimen compared to non-moving specimen until 900 mm/min. At higher speeds the deviation increases. Therefore, positioning times with acceleration and deceleration can be avoided and thus up to 900 indentations per minute with 1 mm distance between each indentation could be realized.
Keywords: indentation; hardness; laser-induced shockwave; constant movement; material testing
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Laser-generated reflection gratings on shape memory actuators
Damian L. Haske, Jan Marx, Marvin Schuleit, Evgeny L. Gurevich, Cemal Esen, Andreas Ostendorf
The employment of ultrashort laser pulses has enabled the fabrication of grating structures on a shape memory material, suitable for strain measurement by recording the interference pattern in the reflected light. This development signifies a novel application of laser-generated microstructures and facilitates direct strain measurement on the object without the necessity of an additional layer, as often required by conventional methods. The grating period was varied between 5 µm and 10 µm. Furthermore, Laser Induced Periodic Surface Structures (LIPSS) have been demonstrated to function as a grating structure for the purpose of producing lower grating periods. The application of LIPSS has been demonstrated to result in a grating period reduction down to approximately 620 nm. Moreover, the employment of LIPSS eliminates the requirement for monochromatic light in strain measurement applications. Illumination with a white light source leads to a color shift in the reflected light, which depends on the degree of stretching.
Keywords: LIPSS; NiTi; USP; tensile test; Bessel beam; shape memory effect
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Scaling effects of fast laser drying processes in battery production
Delil Idris Demir, Mariam Saad, Samuel Moritz Fink
This study investigates the effects of laser drying on the quality of graphite-based lithium-ion battery anodes, using a water-based slurry of graphite, conductive carbon, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). The slurry was coated onto copper foil using a roll-to-roll slot-die process and dried by either a convection oven or a laser module for comparison. Process parameters such as wet coating thickness (130 μm and 200 μm), web speed (1 m/min and 2 m/min), and drying temperature (70–110 °C) were systematically varied. Residual humidity and adhesion were evaluated using thermogravimetric analysis and adhesion testing, respectively. Results show that laser drying achieves up to 90% of the adhesion values obtained with conventional oven drying for thin coatings (130 μm) in less than half the drying time. Laser-dried electrodes also exhibit lower residual humidity compared to oven-dried benchmarks. However, higher evaporation rates and greater coating thicknesses promote binder migration and reduce adhesion, highlighting the need for precise control of drying parameters. Overall, laser drying demonstrates significant potential for efficient, high-quality electrode manufacturing, particularly for thinner coatings.
Keywords: Laser drying; Electrode manufacturing; Binder migration; Lithium-ion battery; Residual humidity; Adhesion; Scaling effects
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Laser-Based Drying of PEMFC Catalyst Layers
Manuella Guirgues, Samuel Fink, Sathishkumar Natarajan
With the production speed being a major obstacle in the economic production of polymer exchange membrane fuel cells (PEMFCs), introducing laser based drying of the coated catalyst layers could bring drying times from minutes down to just a few seconds. Laser-based drying is also a more efficient alternative to oven drying and has a much smaller footprint. In this paper we present the effects of the laser irradiation on the catalyst layer, demonstrating the degree of drying and the microstructure of the laser-based dried catalyst layers at different drying temperatures and interaction times. For this purpose, a 980nm diode laser with a closed temperature control loop is used to dry screen printed catalyst layers in a semi-continuous process.
Keywords: PEMFC production; Laser-based drying; Membrane Electrode Assembly (MEA) production
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