This PDF file contains the front matter associated with SPIE Proceedings Volume 12873, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Laser technology has become an essential tool for material processing and offers significant advantages for overcoming limitations of different material processes. For example, the use of femtosecond lasers with ultrashort pulses and high maximum intensities enables the processing of transparent materials such as glass by non-linear process mechanism. This provides a more accurate and controlled energy delivery, which has the advantage of reducing heat-affected areas and thermal damage, as well as achieving accuracy up to the submicron range. It is ideal for processing sustainable materials such as glass for use in integrated sensors for lab-on-a-Chip or photonic devices. However, there are major differences in the fabrication and quality of waveguides based on different glass types and the laser parameters used. This work focuses on the study of volume processing in different glass materials, particularly comparing the direct writing of waveguides between BK7 borosilicate and fused silica glass. The inscribed micro-optical structures, including waveguides and beam splitters within the volume, were fabricated using a femtosecond NIR laser with 350 fs pulse duration in combination with a galvanometer scanner and a long focal length of 100 mm. We investigated the process stability and formation process for the inscription of waveguides in both glass types. By systematically changing laser parameters such as pulse energy, repetition rate and scan velocity the waveguide quality, continuity and properties of the refractive index change are shown comparing the processing regimes for borosilicate and fused silica glass in order to optimize the laser process parameters further.

In this work, we evaluate the advantages and limitations of the Selective Laser-induced Etching (SLE) process for the fabrication of novel three-dimensional microresonator structures. Microresonators are resonant optical structures with the ability to store light of a specific wavelength. They are used as non-linear optical components, in sensors or even in integrated photonic devices. These structures are characterized by the optical quality factor Q as a measure of the optical storage capabilities. Q is significantly influenced by a high-quality optical surface with low surface roughness. In addition to surface quality and small dimensions, from tens of microns to millimeters, high optical nonlinearity is a key requirement in these fields. The fabrication of 3D fused silica parts fulfilling these requirements is an ongoing challenge in the field of microfabrication in quantum technology. The SLE process is used to fabricate three-dimensional parts of transparent materials such as fused silica with a high degree of geometric freedom in a two-step process. In the first step, a model of the part is written into the material using Ultrashort Pulse (USP) laser radiation. In the second step, the laser-written shape is wet-chemically etched in aqueous KOH to expose the part. The fabrication of 2D disk microresonators with high Q-factors is evaluated by studying the surface roughness of the SLE process followed by polishing. The polished samples are characterized and Q-factors >107 are achieved. In addition, the extent to which dimensions and geometry differ between design and real SLE components is analyzed. The SLE process will thus be investigated as a possible process for the future fabrication of three-dimensional microresonators.

Modification of glass with Ultrashort Pulsed (USP) laser radiation with subsequent wet chemical etching is a well-known process, especially for fused silica, and is referred to as Selective Laser induced Etching (SLE). The main advantage of the SLE process is that almost any 3D geometry can be produced, but currently this is mainly limited to the use of fused silica samples with flat surfaces. To extend the SLE process, we have now processed 400 µm thick upward curved borosilicate glass. In the initial studies on planar borosilicate glass, the first process parameters are found and partially transferred to the curved samples. However, it is found that etching of simple structures occurs at different rates when comparing planar and curved material. This presents a challenge for processing curved surfaces, where optical aberrations like spherical aberrations, astigmatism, and coma distort the spot geometry. We are able to spiral cut the curved 400 μm thick borosilicate glass sample as well as drill through it using the SLE process. Difficulties are observed in the structuring of the area with high incident angles at greater radii, since here the influence of optical aberrations becomes dominant. Thus, sufficient modification by the laser radiation is no longer possible. This prevents the subsequent etching process. This allows the limits of the SLE process to be evaluated for thin upward curved borosilicate glass. The spiral created from the curved glass shows high flexibility and therefore the high durability of the material after processing.

We introduce ultrafast laser machining concepts where microscopic modifications can be produced at macroscopic levels. The efficient use of the source’s energy and power performance is enabled by optical tools that distribute the radiation onto large surfaces or into large volumes. Here, holographic beam splitters are used to create focus copies at arbitrary positions in the working volume of a focusing unit. This allows, for example, to cut transparent materials with customized edges in a single laser pass or to high-speed texture articles with curved surfaces without adjusting the focus position.

Laser-Induced Periodic Surface Structures (LIPSS) are normally created to induce peculiar surface properties but, despite their interesting properties, LIPSS generation has a main drawback which is its low throughput rate. This limits applications on large surfaces. In this work, adaptive optics is used to increase productivity, and processing tests are conducted on stainless steel and nickel-titanium alloy as examples of surfaces for biomedical and luxury applications. The use of a deformable mirror to dynamically control the wavefront and the spatial energy distribution at the focal point of a picosecond laser is introduced and discussed. The shape of the focused beam is theoretically predicted and experimentally investigated with a sub-micron, high-resolution beam profiler. The shape obtained in the focus can be dynamically controlled at the level of the single vector to be scanned. Results confirm that this method can overcome the aforementioned limitations and significantly increase the throughput rate in LIPSS generation.

In this work, the use of an innovative, compact femtosecond laser operating in the GHz regime for laser ablation and micro-texturing is investigated and discussed. The processing performances of burst mode for pulses shot in the GHz regime are numerically simulated. The proposed ablation model is based on the two-temperature model and considers, in a simplified way, the effect of plasma. The numerical results are compared in terms of ablation depth with experimental investigations on stainless steels. The numerical outputs allow an understanding of the influence of different process parameters and support the selection of the operating window where GHz laser became competitive with traditional ultrashort laser sources in the MHz regime.

Laser material micro-processing with high repetition frequencies of laser pulses is able to initiate heat accumulation effects that can decrease processing rate and quality. In order to gain deeper insights into these effects, a temperature measurement system with nanosecond time resolution was developed using infrared detector and a set of parabolic mirrors. For measurement in more industrially relevant processes on larger areas, alternative configurations were developed: measurement through the scan head and multifocus ellipsoidal mirror. This work is initially focused on comparison of advantages and limitations of the developed measurement configurations by signal to noise ratio, field of view and measurable temperature range. The measurement systems were then used for the analysis of polygon scanner based high-speed laser surface texturing of steel and ceramics substrates as a preparation method for thermal spraying of coatings. GHz burst femtosecond laser ablation was analyzed and long-time process monitoring using FPGA hardware analysis was developed and performed for the laser texturing process.

The comprehension of microhole formation during percussion drilling of metals using ultrashort laser pulses is still limited. The shape of a microhole can be impacted by factors like heat accumulation, the emergence of side channels, bending, and bulging. Understanding these defects is challenging due to constraints in conventional diagnostics. To address this issue, high-speed synchrotron x-ray imaging was employed to capture the spatial and temporal evolution of the microhole shape during laser percussion drilling of stainless steel. The recorded images reveal that heat accumulation leads to the creation of a melt film on the microhole walls, exhibiting dynamic fluctuations throughout the drilling process. Furthermore, a transversal widening or bulging of the microhole can be seen later in the process. Additionally, the emergence of side channels was observed in the region of maximum drilling depth, where the overall fluence on the microhole walls falls below the threshold fluence.

Selective Laser-induced Etching (SLE) is a laser-based process which enables the fabrication of three-dimensional parts from transparent materials with an enormous freedom of geometry and micrometer precision. A current research focus for the SLE process is the development and fabrication of ion traps made of fused silica for the ion-based approach of quantum computing. With the help of micrometer-sized electrically controllable components, ions are trapped inside an electrical field and their state is manipulated by means of laser radiation in the context of complex computing operations. Another research focus is the fabrication of fiber-chip couplers which are necessary components of smallest laser sources with the purpose to minimize and simplify the current complex experimental setup of a quantum computer. This work presents the current development of laser / SLE-based processes for the fabrication of microelectronic devices and quantum computing applications.

Three dimensionally (3D) engineered scaffolds are a viable alternative to investigate cells in physiologically relevant configurations. Two photon polymerization (TPP) is a 3D maskless laser direct writing technology that employs a focused femtosecond (fs) laser beam to produce a localized chemical reaction with high precision that ultimately leads to polymerization of a photosensitive material inside the focal volume. TPP has the capability of creating synthetic polymer constructs with 3D complex architectures and high resolution far beyond the diffraction limit. TPP was demonstrated to fulfill technical requirements necessary for fabricating personalized 3D scaffolds for tissue engineering and regenerative medicine applications. Herein, we propose the use of polymeric scaffolds fabricated by TPP for cancer research, specifically as model structures for cancer cell invasion assessment in 3D environments. In particular, the aim is to evaluate cancer cell interaction with confined spaces developed in a woodpile-like polymeric scaffold with pore dimensions less than 1 μm in microchannel cross-section. TPP of negative photoresist SU-8 was conducted using a 3D Lithography platform produced by Nanoscribe GmbH. Scaffolds with uniform networks of pores with sizes down to 0.66 μm were successfully produced, which were then used for melanoma cancer cell invasion assays. The scaffolds demonstrated potential for use in testing the invasion potential of melanoma cancer cells in comparison to normal melanocytes. Time-lapse microscopy observations were carried out to assess the optimal intervals for cell analysis in interaction with scaffolds. Preliminary in vitro tests suggested that melanoma-melanocytes co-culture may exhibit a more invasive potential in narrower spaces as compared to normal melanocytes alone, while an inhibitory effect on melanocyte invasion may be attributed to melanoma cells present in co-culture.

Direct laser writing based on two-photon polymerization offers the capability of sub-micron accuracy and printing of curves in three-dimensional space. Maintaining the amplitude of the writing speed constant, the profile accuracy can be improved, which makes the fabrication of structures with complex exterior shapes feasible. Moreover, the filling pattern of the interior space of a structure can enhance significantly its mechanical response. These observations are applied to the case of Phloeodes diabolicus since its toughness is a result of the existence of special hinges and the orientation of the fibers in the interior space of its shell. In addition, an iteration feedback simulation procedure using LS-Dyna is proposed, and its usage is demonstrated in the case of complex geometries inspired by Phloeodes diabolicus.

Laser processing is flexible with many parameters such as wavelength, pulse duration, and pulse energy. Today, these parameters are optimized by human experience and intuition. To meet the mass customization need in the coming super smart society or Society 5.0, we want to replace them with approaches driven by data, Artificial Intelligence (AI), and science and theory that highly integrate Cyberspace and Physical Space (CPS). To promote smart production, we develop CPS laser manufacturing capable of proposing the optimal processing parameters the optimal processing parameters based on simulation in cyberspace. Understanding laser processing belongs to multiscale and multidisciplinary cutting-edge science. For example, how atoms, molecules, and materials behave under intense laser irradiation is at the forefront of atomic, molecular, optical, condensed matter, and high energy density physics, involving highly nonlinear, dynamical processes. One of our focuses is to understand and simulate such strong laser matter interaction by combining different techniques, including AI and even starting from the first principles of quantum mechanics. We build a nationwide STELLA network of about 100 researchers including both theoreticians and experimentalists, the latter who develop cutting-edge data collection and operando measurement techniques.

We demonstrate the ability to create functionalized microfluidic channels using Femtosecond Laser Surface Processing (FLSP). FLSP is an emerging advanced manufacturing technology used to modify the surface properties of materials directly and permanently by producing self-organized quasi-periodic micro- and nano-scale surface features along with surface and subsurface chemical and grain structure changes. We demonstrate on Hastelloy X that by controlling the laser fluence and pulse count, the depth of the microchannels and height of the FLSP microstructures within the microchannels can be controlled independently.

The demand for optimized and affordable lithium-ion battery systems increases with the growing number of electrified vehicles. To this aim, 3D electrode architectures and new high energy density materials like silicon are in the focus of research. To implement silicon in the LIFT-process for fast prototype development, a silicon-rich paste was developed and optimized for the printing. The electrodes containing the silicon-rich paste showed a rather high specific capacity of 3029 mAh⋅g ^-1. To achieve an enhanced cyclability, a new electrode architecture was developed by using subtractive and additive laser processing in a process chain. For this purpose, a state-of-the-art coated graphite electrode was structured, and the cavities were subsequently partially filled with the silicon-rich paste. After reaching end-of-life, the coin cells were disassembled and analyzed using SEM and LIBS measurements regarding the failure mechanisms.

A novel rapid and green manufacturing technology of metallic and Transparent Conducting Oxide (TCO) patterns on flexible substrate at normal environment is presented. Functional materials are synthesized, deposited, and thermally treated using an economic continuous wave laser digital manufacturing system integrated with a multiphase reactive precursor fluid delivering device. The deposited patterns show excellent electrical conductivity, mechanical and optical properties. Comprehensive analyses on the physics of the microscale transport phenomena were carried out to investigate the coupled photo-thermal-fluid-mass transfer and their effects on the process. The developed model was able to effectively and efficiently optimizing the process parameters that affect the surface morphology, properties and deposition rate of the microstructures. The developed physical model was also integrated with in-situ measurements and intelligent data-driven analysis to monitor, control and optimize the process proactively. This low-carbon processing techniques demonstrated the laser-based micro- and nanoscale green, digital-twin manufacturing for advanced semiconductor devices and electronics.

This study investigates the relationship between a material’s ablation threshold and the quality of metal-to-glass weld. Our analysis demonstrates that materials with lower ablation thresholds demand less radiation energy for achieving maximum shear stress, indicating a potential link to the quality of metal-to-glass welds. The findings suggest that Alloy 36, due to its high ablation threshold and relatively low melting temperature, holds promise for enabling stronger and more enduring metal-to-glass connections. In the present work, a weld resistant to shear stress up to 5MPa was achieved with Alloy 36 and both fused silica and borosilicate glass. The latter holds promise for industrial exploitation due to the very similar coefficient of thermal expansion between the glass and the metal.

Structuring electrodes of lithium-ion batteries with liquid electrolyte leads to an increase in the performance of the battery cell, as shown in several studies. The effective diffusion of the lithium ions can be significantly increased by introducing microchannels. This leads on the one hand to higher charge and discharge rates, and on the other hand to an increase in the number of charge cycles and thus to a longer lifetime. Even though there are already many publications on the laser structuring of electrodes, the fundamental interaction mechanisms have not yet been fully developed without doubt. Also, the lack of progress productivity is currently preventing industrial application. For this reason, the influence of pulse-bursts on the laser structuring process of the active material of electrodes was investigated within the scope of this work. The influence of the variation of the number of pulse bursts, the repetition rate as well as the peak fluence on the ablation rate and the ablation efficiency was investigated. The results were evaluated by an automated analysis procedure to allow a systematic and statistical assessment of 110 induced features per parameter set in a time-saving manner. It was shown that the efficiency of the individual pulses could be increased by up to 75% when machining NMC. Due to the pulse bursts, a five times greater increase in the ablation rate could be achieved on the anode side. In addition, cross-sections of the introduced pores were examined by scanning electron microscopy combined with EDS analysis to identify a possible thermal influence of the laser material processing.

Lithium-ion batteries are widely used today due to their high energy density, long life cycles, and low self-discharge rates. It commonly uses graphite as an anode material with a high theoretical capacity of 372mAh/g. At the same time, several research groups explore ways to further increase the energy storage capacity of lithium-ion batteries by, for example, adding silicon to the graphite anode material. Silicon is naturally abundant and inexpensive, with low environmental impact and a significantly higher theoretical specific capacity of approximately 4200mAh/g. A drawback is that graphite-silicon composite anode materials tend to degrade during the charge/discharge cycles, leading to decreased storage capacity over time. This degradation is associated with the size of the silicon particles, where large, micrometer-sized silicon particles are more susceptible to instability than smaller, nanometre-sized particles. To address this issue, we present an investigation using laser-assisted processing of nano-graphite-silicon composites. This process uses low-cost micrometer-sized silicon particles mixed with nano-graphite powder and a 1064 nm continuous wave laser to process the nano-graphite-silicon-coated anode material under various conditions and atmospheres (ambient and nitrogen). The performance of the lithium-ion battery is affected by different processing conditions. Specifically, the intensity of the 0.25V and 0.5V anodic peaks, which indicate the delithiation of silicon, is particularly affected, with the inclusion of an additional broader shoulder peak at around 0.3-0.35V. Our investigation suggests that laser-assisted processing of nano-graphite-silicon-composite materials is a scalable concept with the potential to improve the performance of nano-graphite-silicon anodes for lithium-ion batteries.

A rather new approach for simultaneously achieving high energy and high-power density of a battery electrode is the use of a high-voltage cathode material in conjunction with a three-dimensional (3D) electrode architecture created through ultrafast laser structuring. In the presented work, LiNi_0.5Mn_1.5O₄ (LNMO) cathodes were laser structured using a high-power ultrashort pulsed laser source with an average laser power up to 300 W. An investigation of the ablation behavior of LNMO cathodes was performed by a variation of laser and process parameters. The impact of the laser pulse peak fluence and the repetition rate on the ablation depth and width of the generated grooves was analyzed, while keeping the pulse-to-pulse distance constant. An electrochemical analysis of unstructured and selected laser structured LNMO cathodes was conducted to study the influence of the laser structuring on the electrochemical performance. It could be shown that the combination of LNMO with the advantages of a 3D electrode design is leading to outstanding electrochemical properties.

Microstructural adaptation of surfaces for the production of highly specialized functionalities is becoming more and more important in many industrial fields due to significantly enhanced product properties. One of these areas is the microstructure adaptation of lithium-ion battery electrodes, which can be improved in many different ways through the modification. However, in order to be able to scale up processes such as selective surface ablation or geometric structure adaptation, fundamental knowledge of process mechanisms as well as beam-matter interactions is necessary. In the present study, geometric structuring for microstructure adaptation of lithium-ion battery electrodes, were investigated using a fast IR measurement technique. With the help of these investigations, it could be shown how a potential ablation mechanism is taking place. This knowledge can support the transformation of such processes from the laboratory scale to a larger production scale. Composite electrodes were used as material, which consist of a large proportion of graphite and a small proportion of polymer binder.

Graphite anodes with high areal loading of 3.6 mAh cm^-2 were laser structured with various design patterns using an ultrashort pulsed laser system of high average power (⪆300 W). The upscaling potential of the most common pattern types in literature, namely the line, grid, and hexagonal hole pattern were evaluated and the influence of process parameters like laser fluence and repetition rate on the ablation characteristics were examined. The fast-charging capability of full-cells containing structured graphite anodes were studied with NMC622 cathodes. For each structure pattern the onset of lithium plating during fast-charging was determined by differential voltage analysis of the voltage relaxation.

In recent years, there has been a notable surge in efforts to advance hydrogen electrolysers and fuel cell technology, pinpointing green hydrogen as a viable avenue toward the decarbonization of pivotal industries. Laser drilling emerges as a fundamental technology, enabling the creation of porous structures and micro-holes in critical components essential for constructing contemporary hydrogen electrolysers. To effectively bring micro-hole drilling into commercial use within this domain, it is imperative to develop processing capabilities that facilitate high-speed operations and increased throughput rates across diverse materials. This study investigates the potential of generating micro-holes through 1 mm thick C263 Nickel alloy, a prevalent material utilized in hydrogen electrolysers, using a single-mode fibre laser. Employing a single-mode fibre laser in conjunction with a nozzle-based coaxial processing gas, the research investigates the process of creating these holes. Experimental trials were conducted to comprehend how peak power and pulse duration influence the size and quality of micro-holes drilled by a single pulse of laser energy. The results showcased the production of micro-holes with an average diameter of less than 80 μm at a rate of around 680 holes per second, maintaining a high level of consistency.

Copper substrates were functionalized using ultrashort pulsed laser surface processing to create micro- and nano-scale features to enhance the electrocatalytic nature of the surfaces for the electrochemical reduction of carbon dioxide. Post-processing of the laser-functionalized copper surfaces was carried out to increase the efficiency and stability of the electrocatalyst. A maximum current density of 55 mA/cm² was achieved during carbon dioxide reduction reaction (CO2RR) over the laser processed copper, and the stability of the surface was enhanced by modifying the chemical and physical nature of the surfaces. The surfaces were chemically and physically analyzed before and after the reduction reaction.

It is becoming increasingly clear that there is more than just a gradual change in the automotive industry, especially when it comes to future drive systems. There are different designs and degrees of electrification - from hybrid to pure battery vehicles - with different electrical outputs, ranges and driving shares. New components significantly change the share of value added in the vehicle. The focus of value creation is shifting further from mechanics to electrics/electronics. Whether e-mobility or hydrogen propulsion, the laser and photonics industry has seized the opportunity to change manufacturing processes and convince decision-makers of the undisputed benefits of photonic tools in the relevant production chains. And since most applications, e.g., in battery manufacturing and their use for e-mobility, started from scratch, the most profitable manufacturing tools could and can be used directly. It turns out that it makes sense not to transform an existing process from the "pre-laser age" into the modern age. The laser has undoubted advantages over other tools in these production chains. When you talk about processing speed, low energy input, automation, which is very easy to implement with lasers, energy efficiency and freedom from contact, then there is no getting around the laser as a tool. This paper gives an overview of some applications in battery production and e-mobility from the perspective of a supplier of sensors and processing tools. The focus is on laser welding, as process monitoring, and control play an important role here and describes the intersection between industrial requirements and photonics when it comes to efficient production tools for tomorrow's mobility. It is about sensor technology, it is about beam shaping, it is about material processing, and it is about AI.

High quality poly(methyl methacrylate) (PMMA) thin nanocomposite films doped with different concentration of silver (Ag) nanoparticles are demonstrated. SEM and TEM confirmed the presence of Ag-PMMA nanocomposites with excellent dispersion of Ag nanoparticles into the PMMA matrix and nanoparticles with an average size of 9 nm. By using a direct Laser writing system with a continuous wave 405 nm diode Laser source the films were exposed, allowing the formation of hole-like or linear patterns in the sub 200nm regime, using a 280nm FWHM sized laser spot, demonstrating, for the first time, the potential for sub-diffraction limit laser processing in such 2-material composite systems.

This study investigates the ablation process of stainless steels using ultrashort pulsed laser bursts with a MHz intra-burst repetition rate. Multiple laser parameters, including pulse fluence, pulse number per burst, inter-burst repetition rate and scan speed, are varied to study their influences on the ablation process. Laser ablation in single-pulse and burst modes are compared in terms of ablation efficiency and surface quality. It is found that burst-mode ablation can generate much better surface quality than single-pulse ablation, despite slightly reduced ablation efficiency. Different types of surface structures can be generated by the ablation process and their formation mechanisms are analyzed. This work highlights the advantage of burst-mode ablation in achieving ultra-smooth surfaces on stainless steel and unveils the optimization strategy for machining high-quality microstructures while maintaining high ablation efficiency.

This study introduces an innovative liquid atomization method that utilizes an optical approach. The technique involves the precise deposition of a metal film at the end of a hollow optical fiber, using the photothermal effect to achieve highly efficient liquid atomization. In contrast to previous studies on optical atomizers, our research demonstrates substantial advancements, particularly in precision control and the extension of ejection distances. Furthermore, this study explores the potential applications of this technology in scenarios involving high-laser power. While atomization techniques are commonly observed in everyday life through spray mechanisms, our research significantly enhances precision control, making it particularly relevant to the biomedical field. In summary, our study contributes significantly to the evolution of atomization techniques, holding great promise for practical utilization in the future, especially in fields such as nanoprinting and biomedical applications. Our innovative approach opens up new possibilities for precise liquid atomization, expanding the horizons of applications across various domains.

Tangential laser turning is applied to generate rotationally symmetric parts on a micrometer scale. Due to the non-contact material ablation, this process is especially advantageous for machining brittle materials such as stellite, which tends to easily break during conventional lathe. Furthermore, the use of focused ultrashort laser pulses enables the process to machine a large variety of materials because of the low heat input into the work piece. By impinging a cylindrical work piece laterally, a distortion of the projected circular, focused laser beam on the material surface occurs. In order to predict the actual fluence and intensity distribution on the rotating work piece, fundamental calculations and experimental results are necessary. Against this background, we report on laser turning of cylindrical components using ultrashort laser pulses with attention to the geometrical conditions and the resulting intensity distribution on the work piece. Particularly, the laser spot formation on a cylindrical surface at an oblique angle is discussed. In addition, the use of a trepanning optic in the laser turning process and the resulting beam path on the surface will be issued. The superimposed motion of the work piece rotation, trepanning rotation and linear laser feed rate is subject to fundamental calculations and experimental results.

We report on process sensing using a membrane-free optical microphone to monitor the acoustic emission during ultrashort pulsed laser ablation of multilayer materials. The acoustic emission during ablation is used to detect material transitions, with the specific signatures allowing to create a reliable process control for identifying individual layers. The outstanding properties of membrane-free optical microphones in terms of high bandwidth and high temporal resolution are ideally qualified for characterizing an ultrashort pulsed laser process, with its properties and capabilities being presented in this contribution. In particular, for layer- and material-selective ablation of multilayer printed circuit board components, copper and polyimide layers are ablated and the material transition is detected by analyzing the acoustic signal at different frequency levels, which is a novelty in the field of ultrashort pulsed laser process sensing. The investigations show that the optical microphone can be used to resolve both the scanning paths and ablated layers by means of interruptions in a time-resolved acoustic spectrogram. Furthermore, as a result of a higher ablation rate of polyimide compared to copper and thus the increase of the emitted acoustic energy, the material transition between copper and polyimide layers can clearly be detected. The detection of this process event can be used for process control.

Direct Laser Interference Patterning (DLIP) is an established technology for producing textured and functional surfaces using beam-shaped laser radiation. It consists of producing high-intensity interference patterns by overlapping two or more laser beams at the material surface. In this work, new possibilities for producing textured surfaces on metals and polymers using high-throughput concepts for DLIP are presented. The first concept describes the development of a new DLIP optical head (called xDLIP) with an outstanding depth of focus of approximately 10 mm, which can be equipped with fs, ps or ns pulsed laser systems. This approach makes this device ideal to treat large areas as well as three-dimensional parts. In particular, a setup using an industrial robot system is shown. The second approach includes the combination of a new DLIP optical system with a polygon scanner, showing the possibility to treat metallic and polymer surfaces. This includes configurations for reaching 7.0 and 21.0 μm spatial periods at throughputs beyond 1 m²/min. Finally, DLIP is implemented into a roll-to-roll process using a high-power picosecond pulsed laser source, in which the main laser beam is shaped into two elongated beams which go through a scanner system. Using this setup, aluminum and copper foils with thicknesses of 20 μm and 9 μm, respectively, are processed.

Zirconia is known to be a hard-to-machine in the sintered state. In this study, the zirconia samples were patterned and then sintered. A nanosecond Nd:YAG laser operating at 1064 and was used to pattern the zirconia surface. A confined plasma was formed through the interaction between the laser beam and a copper grid template. The template was covered by a sacrificial aluminum layer, and the plasma was confined using a glass slide. The size and depth of the pattern were shown to be dependent on the shape of the grid, fluence, exposure time, confinement medium, wavelength, and beam spot size. We successfully achieved patterns ranging in size from 7 μm to 40 μm with depths of up to 3 μm. The resulting patterned surfaces were characterized using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The findings on the nature of the patterning will help in controlling functionality of zirconia, such as hardness, biofilm formation, and osteointegration.

Freeform Laser cutting for glass sheets, based on the Corning® nanoPerforation process, is a well-established process in multiple industrial applications, in the consumer electronics, automotive and semiconductor industry. Ultrashort pulsed lasers offer the possibility for a very confined energy deposition using non-diffractive beams, resulting in laser cuts with exceptional performance at high process speeds. Further benefits include an optimized material utilization for this clean, energy efficient and waste free technology. The fundamental understanding of the interdependencies of various laser process parameter and glass composition by relying on accessible glass properties, like CTE (coefficient of thermal expansion) or hardness, is the key to optimize the laser cutting results. This Knowledge enables fast process development, resulting in highest quality in sub-surface damage, edge strength and chipping distribution. Design of Experiments (DOE) is an efficient method to reveal the underlying correlation for this very specific non-linear laser material interaction. As the CTQ’s are not independent from each other, a DOE based approach systematically describes the interaction. The resulting advantage is a high process stability and yield which consequently facilitates a robust solution for industrial implementation. The machine- and laser configuration based on this know-how allows to cut a wide range of glass compositions and thickness by manipulating software-based recipes rather than by time- and cost-intensive reconfiguration of the optical setup.

Microresonator-based Kerr soliton microcombs are coherent light sources consisting of equally spaced and phase locked discrete optical frequency components, which are essential tools for practical applications in precision spectroscopy and data processing. While anomalous microresonator dispersion is mandatory for Kerr soliton microcomb formation, so far almost all dispersions are susceptible to manufacturing error and cannot be tuned once the microstructure is made. Moreover, microcomb formation in strongly Raman-active mediums like Lithium Niobate (LN) is challenging in the suppression of stimulated Raman scattering and mode crossing due to the existence of densely distributed multiple Whispering Galley Mode (WGM) families. Here, Kerr soliton microcombs were formed in a normal dispersion LN microdisk resonator by mode trimming. Despite that the fundamental WGM family is of normal dispersion and there are densely distributed high-order WGM families within the LN microdisk, high-Q square modes of anomalous dispersion and small mode volume are coherently formed by introducing weak perturbation for mode trimming. Under the optical pump of the square mode of 35-mW power, densely distributed WGM families are avoided to be excited, leading to the suppression of Raman scattering effects and mode crossing, and the formation of soliton microcomb with a spectrum spanning from 1450 nm to 1620 nm.

Femtosecond lasers can induce Laser-Induced Periodic Surface Structures (LIPSS) on the surfaces of diverse materials. However, the relatively high roughness of these structures is a major challenge. This research, centered on SiC materials and utilizing linear polarization, aimed to address this issue. The study successfully produced uniform structure and minimal roughness by controlling fluence and scanning speed. This structure was characterized by High-Quality Low Spatial Frequency LIPSS (HQ-LSFL).

Surface topography modifications are well-established strategies to improve the biological response of biomaterials and their performance and reliability when used as implants. Studies have shown for instance that surface roughening creates a physical anchorage between the implant and bone and improves its primary and long-term stabilization. This study reports on the fabrication of repetitive periodic structures on CoCrMo and AZ91D magnesium alloys using direct laser interference patterning. An infrared ultra-short, pulsed laser, with a wavelength of 1064 nm and 10 ps laser pulses was combined with a two-beam interference optics to produce line-like patterns. Both, the surface topography and chemical modifications are analyzed using confocal microscopy, scanning electron microscopy and Energy Dispersive Spectroscopy (EDS). By varying the applied laser fluence and pulse overlap different patterns were produced. In particular, homogeneous structures could be achieved for many used process conditions. The used spatial period was 5 μm, and the structure depth was varied up to 0.85 μm and 2.5 μm, for CoCrMo and AZ91D, respectively. For high energy, sub-micrometric secondary structures, so-called LIPSS, could also be observed. In addition, oxidation effects were confirmed by EDS analysis.

Alumina Toughened Zirconia (ATZ) materials are characterized by high strength and high wear resistance, making them ideal for medical applications. On the other hand, several applications require the treatment of the product surface in order to obtain additional functionalities based on micro and nano structures, for instance using laser-based treatments. In this frame, the processability of these materials is strongly affected by different process parameters, such as pulse duration, burst of pulses and laser wavelength. Thus, the aim of this study is to determine the ablation characteristics of sintered alumina toughened zirconia by varying different process parameters such as laser wavelength, laser fluence and number of pulses per burst. In addition, the different features that are produced are reported. The laser treated samples are characterized using confocal microscopy, scanning electron microscopy, and changes in the coloration are investigated using optical spectroscopy. Finally, color changes that are induced during the laser treatment could be reverted using a heat treatment in drying oven.

We report on laser drilling of borehole arrays using a high-power ultrashort pulse laser with particular focus on reducing heat accumulation in the workpiece by optimizing the drilling sequence, particularly for highly efficient multi-spot drilling. Different optimization approaches are chosen to improve the drilling sequence, also comparing a simplex algorithm and an evolutionary algorithm. From a laser application point of view, we also compare drilling sequences using a single spot and up to 16-fold multi-spots generated by a spatial light modulator, as to accelerate the drilling process in terms of the number of drilled holes per second. To evaluate the temperatures generated during drilling of up to 40,000 holes in less than 76 seconds in stainless steel foil, temperatures are measured by a thermal imaging camera and subsequently compared to a COMSOL-based simulation for all optimized drilling sequences. With respect to an average temperature of 706 °C without optimization, a reduction by 252 °C, i.e., a reduction by nearly 36 % based on the Celsius scale, is achieved using a 4 × 4 beam splitter and an optimized drilling sequence with a drilling rate of 526 holes per second. In addition, using a 2 × 2 beam splitter, a temperature reduction of up to 40.5 % is achieved for a drilling process with a rate of 129 holes per second using an optimized drilling sequence.

Due to their special beam profile, Bessel beams offer advantageous properties for micro-drilling and internal volume processing, especially for transparent materials. In addition, the laser power of industrial ultrashort pulsed lasers has increased significantly in recent years, offering the possibility of highly efficient processes using multispot profiles. We report on optical simulations and an experimental optical setup for generating multiBessel beams by combining a refractive axicon and a spatial light modulator. This setup offers a new possibility of multiBessel beam generation by functional division of the Bessel beam generation by the axicon and the possibility of separation flexible beam splitting by a spatial light modulator. The beam profiles generated with this setup are analyzed and compared in this study using optical simulations and experiments. In addition to the analysis of the Bessel beams in the machining plane, they are also analyzed in the propagation direction by means of intensity distributions measured by a camera in small-step z positions. Furthermore, the experimental applicability of the module-based beam shaping system is demonstrated by integrating into an existing laser system.

Tangential laser ablation as carried out in the ultrashort pulse laser turning process is an approach to generate rotationally symmetric workpieces of high precision on a microscopic scale. The lateral laser impingement on the cylindrical workpiece ensures both process stability and control, while the use of ultrashort pulsed lasers greatly reduces machining forces and heat input into the material. The flexibility in design makes this process a cost-efficient solution for prototype manufacturing as well as volume production and the feasible dimensions of the ultrashort pulsed laser ablation surpasses the capabilities of conventional injection molding. Due to its wide variety of applications in the automotive industry, medical technologies, healthcare supplies or in the lighting technology and optics, the machining of polymethyl methacrylate (PMMA) with focused ultrashort laser pulses represents an auspicious research subject. Against this background, we report on laser turning of polymer PMMA using ultrashort laser pulses for generating rotationally symmetric workpieces. By comparing two different wavelengths for the process, namely 1030 nm and 343 nm, the difference in ablation rate as well as the suitability for geometry generation is evaluated. Particularly, the effect of the Rayleigh range for generating steep and large muff shaped features and the laser spot formation on the cylindrical surface is being discussed. Supplementary, the pulse to pulse overlaps and its effects on the process result on a curved surface is subject to the presented studies.

Piercing and cutting of polyimide film were investigated by our He-free CO₂ laser excited by longitudinal pulsed discharge without pre-ionization. The samples were polyimide film with a thickness of 50 μm, 100 μm, 150 μm and 200 μm. The laser pulse was a short pulse with a tail and had a laser energy of 39.6 mJ, a spike pulse width of 384 ns, a tail length of 108 μs, and an energy ratio of the spike pulse to the pulse tail of 1:128 at a repetition rate of 200 Hz. The laser beam was circular flat-top shape. The laser beam was focused to a diameter of 508 μm, with a fluence per pulse of 19.4 J/cm². The minimum total irradiation fluence required for piercing in the film with a thickness of 200 μm was 389 J/cm². The minimum scanning speed required for cutting in the film with a thickness of 200 μm was 15 mm/s.

We have developed a longitudinally excited CO₂ laser (wavelength: 10.6 μm) with controllable laser parameters such as a laser pulse shape. A CO2 laser is absorbed at a glass surface due to the high absorption of glass materials. CO₂ laser processing is a thermal process, and thermal effects such as cracks and HAZ occur on the glass surface. Thermal effects depend on not only the laser irradiation conditions but also glass materials. There are various types of glass having different physical constants related to heat, such as the thermal expansion coefficient and the softening point. Six types of glass, namely, crown glass, soda-lime glass, borosilicate glass, low-expansion borosilicate glass, alkali-free glass and synthetic quartz glass were irradiated with various types of short CO₂ laser pulses. In the conditions of this experiment, no cracks occurred in any material. The size of the HAZ depended on the glass material, while the cutting depth was independent of the glass material.

Additive manufacturing is rapidly growing, where selective laser sintering technology dominates for industrial use. In the case of polymer selective laser sintering, polyamide is the standard material. However, polyamide is an electrical insulator, and for specific applications, it would be desirable to be able to manufacture polymer-based electrically conductive parts. Electromagnetic compatibility is one of the most significant targeted applications, where the introduction of electric vehicles raises new electromagnetic compatibility demands. The goal is, therefore, to develop an electrically conductive composite material for selective laser sintering using graphene as the additive. Composites are prepared by mixing polyamide, graphene, and additives with varying graphene/polyamide ratios. The aim of this investigation is the laser-assisted processing of the resulting graphene/polyamide composites with various parameters to sinter the material, forming a solid conductive structure. The structure is characterized using SEM and resistance measurements. Results show sheet resistance values of about 700Ω/sq after laser-assisted processing with good powder flowability.

The fabrication of flexible hybrid electronics involves depositing ink onto a substrate using micro-dispensing techniques, including direct ink write processes. In most cases, the ink comprises solvents, binders, and nanoparticle material. To achieve the desired printed film characteristics, the deposited ink must be treated to evaporate the solvents and binders and melt, or sinter, the nanoparticles to form a continuous film. Laser sintering is a method for achieving this process for flexible hybrid electronic production. An incident laser beam is directed onto the printed film’s surface to sinter the particles rather than alternative thermal processes. The laser sintering parameters vary with the ink film composition, substrate, and film thickness. This study uses different laser systems, film compositions, and substrates to achieve the optimal laser sintering parameters for the desired application. The inks studied include silver, doped barium titanate, and silver-palladium on glass, polyimide, and alumina substrates. This work aims to develop sintering parameters for flexible hybrid electronics fabrication on the International Space Station.

Machining micro-holes with high-power pulsed laser is very common, but due to the mechanism of laser processing, micro-cracks, recast layer and heat-affected zones in hole walls are difficult to avoid. Hybrid processing of laser beam machining with Electrochemical Machining (ECM) can effectively eliminate these defects and improve processing efficiency. This paper proposes to use a synchronized laser and electrochemical machining method. A metal tube electrode is used to guide and transmit the laser to the machining area to achieve high coaxial coupling of laser and electrochemical energy. An experimental system of laser beam machining with ECM is developed, and the surface quality of hole walls are studied on aluminum alloy and stainless-steel workpiece. The effects of ECM voltage and current on the rate of laser beam machining with ECM and the surface quality of hole walls (recast layer, micro-cracks, surface roughness, etc.) are analyzed. The experimental results show that the machining current increases with the increase of pulse voltage, the material removal rate increases, the micropore clearance increases, and the machining precision decreases. By adopting appropriate ECM parameters, the fast processing of micro-holes is realized, with smooth side wall, small taper, good entrance roundness, and the recast layer of the hole wall is fully removed.