This PDF file contains the front matter associated with SPIE Proceedings Volume 11989, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Nanoscale structuring of hard, brittle, and high-quality cm-scale optical crystals has remained a two-dimensional surface process until the recent report that 3D architectures can be sculpted inside laser crystals (YAG and sapphire) with feature sizes on the 100 nm level and nanoscale precision. The mechanism by which these phenomena can occur is a giant wetchemical etching selectivity of around a million (~106 ) between photomodified and unmodified crystal volumes, which enables nanopores (~200 nm) to reach mm-scale lengths, discovered and recently reported by A. Ródenas et al. [1]. We report here recent results that expand the state-of-the-art on this new 3D nanolithographic technique for undoped YAG

Diffraction-free Bessel beams have been of great interest for laser processing of transparent materials. Compared to traditional Gaussian beams, the Bessel-Gauss beams has thin focus profile which remains invariant over much longer propagation distances. Achieved in such a way extended depth of focusing in combination with precise energy deposition has opened diverse promising applications in display industry. Here we have analyzed the effect of conical angle on the interaction of Bessel beam with a display panel having multiple organic and inorganic layers on a glass. First, we have shown that experimentally observed thermal damages in display emission area are caused by long Bessel beam tails in contrast to Gaussian beams, where the damages are driven by heat diffusion. Second, we study the role of Kerr effect and arising instabilities in non-linear propagation through the glass substrate. Using numerical simulations and in-situ pump-probe microscopy methods we gain the knowledge of primary steps of energy deposition with high temporal and spatial resolution. At high laser intensities and low numerical aperture, the original Bessel beam profile can be de-stabilized leading to the longitudinal fluctuation of intensity. The laser processing with high conical angle Bessel beams is much more resistant to undesirable beam self-focusing and phase self-modulation effects, which enables us to achieve the regime of optimal laser energy deposition for high-quality glass cutting.

We analyze the concept of using customized spatially variable waveplates for beam tailoring towards enhanced various glass microwelding process. These elements work as precise flat optical elements that have very high diffraction efficiency (<90%), high optical damage threshold, and can be freely customized for specific needs that transform the spatial intensity profile into tailored beam shape. In this work, we investigate custom made flat-top beam and "C" shaped beams for deep microwelding purposes. By using numerical simulations and experimental research we compare the performance of such beams and demonstrate thin glass deep microwelding capabilities using custom beam shaping elements.

Diffraction limited high NA focusing at depth up to 4 mm in transparent media is an important optical task in variety of micromachining applications, nanostructuring, selective laser etching (SLE), optical data storage, and microscopy. By high NA focusing inside glass or another medium, the workpiece becomes a part of the optical system and its flat surface induces significant spherical aberration that reduces the concentration of light energy and physical resolution. The deeper the focusing and the higher the NA, the stronger the aberration and light scattering. The solution to compensate for spherical aberration by deep high NA focusing, for example up to 4 mm in sapphire with NA0.8, is suggested in the form of an aplanatic objective of the patented optical design aplanoXX, supplied with a protective window. The function of spherical aberration of this objective matches the aberration function of the flat optical surface of this medium; therefore, exact compensation of spherical aberration is realized simultaneously with focusing in the medium at a given depth for an arbitrary NA with providing a single spherical wavefront inside the medium. Due to flexibility of adjustable optical system, the aplanoXX objective can be adapted to operate with fused silica, sapphire, silicon carbide, silicon, glasses, media of eye in applications based on ultra-short pulse lasers in spectra around 1030 nm, 800 nm (Ti:Sapphire), second harmonic (green). The replaceable window protects the optics from damages by particles ejected during material processing. The paper presents an analysis of high NA focusing inside a transparent medium at different depths on the examples of fused silica and sapphire, as well as the experimental application results, confirming performance of the optics.

When glass sheets are cut to shape, ultra short laser pulses with an elongated, usually straight, focal volume (line focus) can be used to modify the workpiece throughout its entire depth with one single laser shot. At the same time, processed glass is often required to have a seamed or round edge, which usually requires an extra grinding step. Alternatively, curved line foci can be used to combine cutting and edge shaping of glass sheets in one laser process. We reconsider the Airy-Gauss beam for this purpose. Plasma ignition in the side lobes of the Airy beam and surface damage provoke unwanted effects, in particular an asymmetric laser modification of the glass sheet. We provide numerical results on the origins of the asymmetry of the volume modification and show that with rather simple optical adjustments a symmetric convex edge can be created in a 920 μm thick glass sheet.

Utilization of parts made by combining dissimilar materials, such as different polymers, metals, or semiconductor to polymers, are nowadays highly demanded for the fabrication of electronic, electromechanical, medical micro-devices, and analytical systems (e.g., lab-on-chip). Techniques for joining such hybrid micro-devices, generally based on gluing or thermal processes, remain a challenging task presenting some drawbacks, such as deterioration and contamination of the substrates. Ultrashort laser welding is a non-contact and flexible technique to precisely weld similar and dissimilar materials. In this case, the only constrain is that the upper substrate is transparent to the laser wavelength. This technique has been demonstrated both for welding polymers and polymers to metallic substrates, but never for joining polymers to silicon. In this work, we report on direct femtosecond laser welding of Poly(methyl methacrylate) (PMMA) and silicon. The laser welding was performed in ambient air by focusing ultrashort laser pulses at high repetition rate at the interface between the two, being PMMA transparent to the laser wavelength. A mechanical homogenous pressure was applied on the sandwiched substrates during all the laser process. The Si-PMMA weld strength was evaluated as a function of the laser and processing parameters, e.g., repetition rate, scan speed, and the overlap between adjacent scan lines.

However the phenomena of titanium and Ti alloys laser processing seems to be well studied, there are still numerous cases of application, as functionalization of medical devices surface, being undiscovered. The task of antibacterial properties of the surface on account of TiO₂ covering for medical applications is both demanded and not well studied, while the solution itself is complicated and fundamentally beguiling. Here we demonstrate a novel approach of fast and cheap laser-based technique to obtain TiO₂ covering on the titanium mesh for controlled bone augmentation in oral implantology.

In the field of micro and nano structuring ultrashort pulsed (USP) laser processing attracts increasing attention due to its ability to generate high-precision structures. A simulation of the USP process can lead to a reduced process development time and help to achieve a better geometrical quality of the manufactured microstructures. To predict the ablation shape, temperature distribution and distortion in a USP ablation process, a detailed simulation of the physical processes during and after the laser ablation is required. Different simulation tools such as multiscale simulations are already established but still need different and accurate input parameters regarding the material properties of the workpiece to be machined 1. A material characterization procedure that can be used in a standardized way for different materials and processing stations needs to be developed. The procedure determines the absorption coefficient, penetration depth and ablation threshold precisely matched to a USP machine and the material used. Based on the material characterization procedure a calibration of the used simulation has to be carried out as precisely as possible. The simulation can then be applied for a digital process development and subsequently validated with specific experiments1.

The texturing of copper surfaces with ultrashort laser pulses leads to microscopic groove formation but results also in nanostructure development at the surface. Both structure types, micro- and nanostructures, are influenced by the laser processing parameters such as the laser power, the scanning speed, the repetition rate, and the line spacing. The generated nanostructures determine mainly the macroscopic properties of the laser-modified copper surface such as the optical reflectivity as well as the secondary electron yield (SEY). To study these effects, polycrystalline copper surfaces were irradiated with infrared picosecond laser radiation (wavelength of 1064 nm, pulse duration of 12 ps, repetition rate of 100 kHz and 1 MHz, respectively) and the secondary electron yield, as well as morphology and shape of the formed nanostructures were analyzed by scanning electron microscopy. The impact of the laser processing parameters on morphology and SEY show the effect of the nanostructures. From these correlations, the reduction of the SEY with increasing accumulated laser fluence and decreasing scanning speed has been identified as a general trend. Especially at high laser power (< 1.9 W) and low scanning speed (< 20 mm/s), the irradiation leads to the formation of compact nanostructures that results in surfaces with a SEY maximum as low as 0.7. SEY values lower than unity are interesting for practical applications of SEY reduction in particle accelerators. Fast processing is necessary to fulfil the technical and technological demands of the deployment and the fabrication of advanced accelerator components. Based on the results, a productivity of ~ 110 s/cm² for SEY ≤ 1 can be estimated at a laser power of 15 W.

Thin-film solar technologies are very attractive due to their potential for low production costs. As in all thin-film technologies, high efficiency of small cells might be maintained with the transition to larger areas when for this purpose the areas are segmented and electrically connected in series with each other. This reduces the current load on the thin-films and the related ohmic losses. For CuIn_1-xGa_xSe₂ (CIGS) thin film solar cells the industrial segmentation and interconnection is mostly based on mechanical scratching. Here the individual layers – front contact, absorber and back contact - are locally and slightly offset to each other removed right after their deposition. In order to meet architects’ (for e.g. BIPV applications) requirements for the shape of the module, it is beneficial to allow for a geometry adaption of the modules after the layer stack deposition. This is supported by a so-called back-end interconnection, i.e. to perform the segmentation and interconnection after the deposition of the whole layer stack. The back-end interconnection is enabled by the combination of laser-based segmentation processes and printing techniques. Furthermore, compared to mechanical scratching, laser-based interconnection promises a possible reduction of segmentation related dead area losses. In this paper we present a laser-based selective structuring of patterns for a back-end interconnection on CIGS thin film solar cells. We apply an ultrashort pulsed laser with a wavelength of 1030 nm and investigate the impact of various process parameters. Before laser processing samples were stabilized under AM1.5 at 55°C for 40 minutes to reduce metastabilities within CIGS thin film solar cells.

Further efforts are needed to increase the power and energy density of lithium-ion batteries. This increase can be achieved by developing new electrode architectures and new active materials. As a new active material for anodes, silicon is in the focus of current research, as it has an order of magnitude higher specific energy density compared to the commonly used graphite. In terms of new architecture, printing anodes with the "laser induced forward transfer" (LIFT) process offers a variety of possibilities. For this work, printing with LIFT adapted anode paste was realized and corresponding laser parameters were optimized. The anodes were printed with graphite for subsequent analyses in a coin cell and compared with state-of-the-art coated electrodes made with the same paste. The conventional coated electrodes were either calendered or uncalendered. It was shown that the electrochemical behavior of the printed anodes is comparable to that of the conventional coated anodes. Finally, preliminary studies were made to print an anode with a multilayer architecture. Within the anode layer, which consists of three individual printed layers, silicon layers are incorporated in order to significantly increase the specific capacity.

Graphite anode material is commonly used in lithium-ion batteries. Due to the demand for a significantly increased energy density for xEVs (electromotive vehicles), there is worldwide a strong effort to add nano-sized silicon particles to composite graphite electrodes. Silicon has the benefit to provide one order of magnitude higher gravimetrical energy density than graphite. However, a bottleneck of silicon is its huge volume expansion of about 300 % during electrochemical cycling which induces high compressive stress and subsequent film delamination, crack formation, and finally degradation of electrochemical cells. In this study, thick film graphite, silicon, and silicon–graphite composite electrodes were developed and subsequently ultrafast laser structured in order to reduce compressive stress during electrochemical cycling and diffusion overpotential. The latter one is a critical issue at elevated power densities and for high film thicknesses, i.e., mass loading. By laser ablation, grid structures were introduced into the electrodes and 3D elemental mapping could demonstrate that new lithium-ion diffusion pathways arise along the structure's sidewalls and are activated with increasing power densities. It was successfully shown that laser structured electrodes benefit from a homogenous lithiation, reduced compressive stress, and an overall improved electrochemical performance in comparison to unstructured electrodes. A reduced mechanical and chemical cell degradation was achieved with structured electrodes in comparison to unstructured ones and design rules for silicon–graphite electrode architectures were derived. Laser structuring of electrodes offers a new manufacturing tool for next-generation battery production to overcome current limitations in electrode design and cell performance.

Solid-state batteries (SSBs) are a promising technology for high travelling ranges and safety in future electromobility. In SSBs, separator and liquid electrolyte materials are combined in a solid-state electrolyte layer. Possible materials for SSBs are ceramic oxides, for example LiCoO2 (LCO) as cathode material and Li7La3Zr2O12 (LLZO) as electrolyte material. By means of screen printing, a mixed cathode material (mixture of cathode and electrolyte material to have higher ionic conductivity in the cathode) is applied on a stainless steel current collector foil and after thermal processing, the electrolyte material is printed on top of the sintered mixed cathode to create a half-cell. Both layers are thermally post treated (dried and sintered) in consecutive steps to produce functional layers for SSBs. Conventional heat treatment is done in an oven process. A main disadvantage is the diffusion of materials into adjacent layers due to long process times (range of minutes) at high temperatures. Furthermore, the battery half-cell cannot be treated at high temperatures due to incompatibilities in decomposition temperatures of LLZO and LCO. Preservation of the crystal structure and a suitable temperature management during the sintering process are of enormous importance. By means of laser processing, short interaction times (range of seconds and below) are realized. High heating rates show potential for reducing diffusion processes and preserving the crystal structure of the materials. In this work, the influence of different interaction times on crystal structure and adhesion are investigated for laser sintering of LLZO and LCO micro particle layers.

Lithium-ion batteries have dominated the field of electrochemical energy storage for years due to their high energy density. Recently, with the rapid development of E-mobility, the quest for high power and high energy batteries with reduced production costs has aroused great interest and is still a huge challenge. The energy density at battery level can be increased by using electrodes with thicknesses > 150 μm. However, capacity fade of thick-film electrodes at C-rates > C/2 is observed. To compensate the capacity loss, 3D architectures with a high aspect ratio are produced using ultrafast laser ablation. In addition, aqueous processing of cathodes using water-based binders can achieve environmentally friendly production and cost reduction by replacing the conventional organic PVDF binder and the toxic and volatile NMP solvent. However, the pH value of aqueous processed cathode slurries increases to 12 due to the reaction between active material and water, which decreases the specific capacity of the cells and on the other side results in chemical corrosion of the current collector during casting. In order to determine the optimal pH range and avoid the damage of the current collector, slurries with pH values ranging from 8 to 12 are manufactured.

In this work, thick-film Li(Ni_0.6Mn_0.2Co_0.2)O₂ electrodes are manufactured with aqueous binders and acid adjustment, and are subsequently structured using ultrafast laser ablation. This combination is beneficial to achieve green production, low cost, high power, and high energy application of lithium-ion batteries.

Laser structuring is introduced to homogenize the wetting of electrodes with liquid electrolyte, to avoid or significantly shorten the process time of warm ageing, and to reduce the lithium-ion diffusion overpotential that occurs during highperformance operation or when thick-film electrodes are applied. For the integration of the laser structuring process into the cell production line, the process speed must be adapted to the electrode coating speed. Various strategies, including increasing the repetition rate and laser power, beam shaping, where the Gaussian beam is formed into a rectangular intensity profile (1D top-hat), and multibeam processing by beam splitting, are pursued here. In the presented study, a laser system providing an average pulse duration of 600 fs, repetition rates in the MHz range, and a maximum power of 300 W, was applied. The ablation results are compared to those of a ps laser system that operates at lower repetition rates. The ablation depth and width as well as the appearance of the structures depending on the applied maximum energy density, repetition rate, and structuring speed, were evaluated, while the pulse overlap was kept constant. It was shown that the use of very high repetition rates leads to a decrease in ablation depth as well as a widening of the manufactured grooves, as the developing of material vapor plasma and ejected particles modify the absorption of subsequent laser pulses. A maximal scanning speed of 1.7 m/s could be achieved for the laser structuring applying a Gaussian beam.

We report on an experimental and theoretical investigation on the laser ablation of silicon with THz bursts of fs pulses. Craters were generated by varying the burst features, i.e., the number of pulses and the intra-burst repetition rate, and compared to those obtained in Normal Pulse Mode (NPM). A general reduction of the thermal load was observed using bursts, though with a lower ablation rate. In fact, shallower craters were obtained when increasing the number of pulses and reducing the intra-burst repetition rates at fixed processing time and burst energy. However, for bursts at 2 THz, some combinations of process parameters allowed a higher specific ablation rate compared to NPM. Simulations based on the numerical solution of the density-dependent two temperature model showed that bursts with more pulses or with lower intra-burst repetition rates lead to a lower final temperature, thus supporting the experimental findings. This is ascribed to changes of the reflectivity dependent on the number of pulses. Accordingly, different amounts of energy are transferred from the laser pulse to the sample, which also leads to changes in specific ablation rates. The origin of such a behavior was found to be the non-linear absorption processes, especially the two-photon absorption.

MicroLED displays are among the most promising technologies for very small and large displays soon. The market adoption strongly depends on costs of the display. Shrinking MicroLED sizes with additional throughput and yield improvements are the key to a wider spread usage of the technology. Laser Lift-Off, a release of III-V based MicroLED´s from the growth wafer, and laser-based mass transfer are two mandatory process steps within the MicroLED display process chain. A UV laser masked based high precision imaging system will be presented which is capable to process GaN based MicroLED´s down to a few microns. The flexible maskbased system can process single die´s, large fields, and selective patterns of LED dies. Process results are depending on the precision and alignment of the dedicated laser beam. The influence of beam-to-die alignment, energy densities, material combination, and contact versus non-contact transfer will be shown and discussed. Both LLO and transfer can be scaled to large field sizes to enable a high throughput processing that pushes the technology into reasonable production time scales. Beam shapes, process speed assumptions, and capable substrate sizes will be discussed. Finally, a flexible system concept will be presented that can cover both LLO and selective mass transfer with corresponding different energy densities. This system concept has a capability to process MicroLED displays for AR/VR but also larger formats e.g. tiles which can be combined to large MicroLED TV´s or commercial signage applications.

UV line beam optics are nowadays an integral part of manufacturing chains in semiconductor and display technology. Amongst others the most prominent applications are the large area annealing of semiconductor materials and the laser lift off process used e.g. for debonding of flexible displays. Here we report on a very flexible platform based on our DPSSL technology and a wavelength of 343 nm. This laser technology provides superior reliability combined with very high pulse energy stabilities. Within our optical design the beam shape along the scan direction can be either gaussian or tophat. We show which fluences can be achieved depending on beam shape and beam width and refer to the relevant applications.

Pulsed laser deposition has evolved into a production technology for growing thin film materials with properties which are challenging to obtain by classical deposition methods such as sputtering or sol-gel deposition. Novel wafer based PLD system technology based on powerful excimer lasers allows universities, institutes and foundries to add 30+ new materials and material systems to their deposition portfolio enabling fabrication e.g. of electro-optical materials, transparent conductive oxides and perovskites. Dielectric, ferroelectric and piezoelectric material depositions can also be performed in any desirable sequence and can run with a single wafer load-lock, cassette handler or integrated with pre-clean station as part of the Solmates cluster platform. Deposition results obtained with the latest 300 mm wafer platform will be discussed.

Pulsed laser ablation is steadily gaining popularity in micromachining to keep pace with the increasing demand for precision manufacturing and functional surfaces. However, efficient laser processing under atmospheric conditions primarily suffers from particle redeposition and therefore requires additional cleaning steps to obtain high surface quality. To reduce additional cleanings steps after manufacturing, laser ablation in liquid allows for a significant reduction in particle redeposition as particles rapidly cool down and penetrate into the liquid without stitching to the surface. However, laser ablation in liquid is accompanied by the complex interaction between the hot molten material, the generated plasma and the over-critical liquid in the ablation zone. During this interaction, chemical reactions at the surface can take place and cause a persistent change of surface chemistry. Since the surface chemistry is a key aspect for micromachining, the interaction has to be studied to determine whether laser processing in liquids can be a feasible alternative to laser processing under ambient atmospheric conditions while reducing the problem of redeposition. Here, we present the results on the change of surface chemistry by laser ablation in liquid of a pristine silicon substrate. The micromachining process is either performed in an aqueous or gaseous environment and studied in dependence of laser intensity. The changes in surface chemistry are evaluated by micro-Raman spectroscopy and EDX.

Shape Memory Alloys (SMA) have unique characteristics to memorize their original structure and retain them when activated by heat or stress, however, there still much to be done in terms of fatigue life and phase modifiability. In this project, we propose a tunable treatment method using shockwaves created by nanosecond and picosecond pulsed lasers assisted with magnetic field to create 3-D structures on NiTi SMA. When the laser pulse hits the surface, its energy is partially absorbed, which ablates the surface resulting a plasma plume. By confining the plasma using dielectric medium and magnetic field, the shockwave is tuned for vertical transfer of the pressure gradient on the surface. Optical profilometer and SEM results confirm that the shockwave pressure became uniform when magnetic field was used. The less heat affected zones on the crater, and equal depth across the crater indicates a stable surface morphology due to magnetic field. Moreover, Shape-memory properties were also investigated with differential scanning calorimetry (DSC) measurements of NiTi samples, and the results indicate significant phase broadening, reaching up to 33% from the initial, and shifts in austenitic and martensitic phases of 5 °C. The tunability of the shockwave using magnetic field and water confinement expands the usage in treatment and imprinting of SMAs for biomedical and industrial applications.

Ultrashort pulse (USP) laser machining is characterized by a large spatial precision in the micrometer range and very high processing speeds: Laser pulses with durations of only a few hundred femtoseconds are deflected over the workpiece at speeds of up to 10 m/s. Due to the tradeoff between the precision and productivity, machining processes already last up to multiple days, as is the case for example for structuring complete mold tools of dashboards. It is therefore essential to implement online defect detection and their elimination in order to increase the stability of the established processing as well as accelerate the process development. Because of the rapid changes during the machining, cost-intensive sensor integration, as well as the high requirements on spatial accuracy, online monitoring of USP laser micromachining represents a great challenge, we solve by spatially resolving optical process emissions at different wavelength ranges collected laterally. The monitoring system, that had previously been developed and had undergone initial testing, was further evaluated in this work. Analyses were carried out to investigate the potential of detecting the surface roughness prior to processing as well as its change induced by the USP laser machining. Their success is however dependent on many factors described in this work. Furthermore, successful localization of defects that emerge during processing was shown. Additionally, the possibility of online process control was demonstrated by transferring the analysis algorithms to FPGA, therefore implementing real-time defect detection and feedback.

Suitable topography of structured surfaces may allow attaining innovative surface properties including friction reduction, superhydrophobicity, self-cleaning, anti-icing and many more. Despite a list of attractive applications of functional surfaces and demonstrated capability of lasers to produce them, the speed of laser micro and nanostructuring is still low with respect to many industry standards. In this work, we introduce a unique combination of high-energy pulsed ultrashort laser system HiLASE PERLA with up-to-date most promising multi-beam micro and nanostructuring technologies able to produce for example more than 40,000 beamlets with productivity over 1900 cm²/min.

Amongst the technologies enabling surface structuring at the nanoscale, Ultra-Short Pulse laser (USP) plays a key role when targeting high process robustness, high throughput, and large area processing. In the frame of “Tres Clean” project, texturing of ≈1 m² surfaces has been recently shown, with the possibility to effectively replicate the nanostructures by injection moulding. Nevertheless, extend USP nanotexturing over several m2 through continuous production represents still an issue due to the need of high-power P, and difficult process control. The “New Skin” project could represent a turning point pushing the readiness of USP-nanotexturing with a significant up-scale of the production volume. Here we show the results obtained with a demonstrative pilot production line based on a roll-to-roll approach and including a 350 W, fs laser and a polygon scanner delivering the beam at scan speed v_s < 350 m/s. Line speed values vl are comprised between 3 and 20 mm/s. By systematic variation of some key process parameters (pulse energy and repetition rate) we optimised the nano-structures morphology which has been characterised through FFT and SEM analysis. A throughput of 5 minutes/m² with an acceptable structure’s quality is reported over several m² surfaces. Possible applications and values propositions are introduced and discussed.

Medical implants, such as dental screws or hip stems, are made of biocompatible materials so that they can be well integrated into living organisms. For instance, titanium and its alloys offer high biocompatibility and osseointegration, making these materials very common in such applications. Furthermore, the new advancements in additive manufacturing allow to customize the fabrication of implants which are tailored to the patients’ individual needs. Furthermore, it is known that the structural elements with feature sizes in the micrometer range on the implants’ surface play a significant role in the attachment and proliferation of cells. These elements can be fabricated through laser-based texturing methods that offer high flexibility and high throughput. In this work, we explore the potential of fabricating surface microstructures on additive manufactured near-beta titanium alloy parts (Ti-13Nb-13Zr), using the Direct Laser Interference Patterning (DLIP) technique. Hereby, a single laser beam is split into two sub-beams that are subsequently recombined on the substrate surface where they form a line-like interference pattern with a defined spatial period. We combine DLIP with a picosecond-pulsed laser source and investigate the morphologies and surface features that can be created. Thereby, different laser wavelengths were employed, including 355 nm, 532 nm and 1064 nm. The resulting surface textures are analyzed using scanning electron microscopy (SEM) and confocal microscopy (CM), showing different types of laserinduced periodic surface structures (LIPSS), of which the geometry and size depended on the used process parameters.

Direct Laser Interference Patterning (DLIP) and Laser Induced Period Surface Structures (LIPSS) are two distinct technologies for periodic surface texturing. Based on different physics phenomena, they enable structures often showing dissimilar morphology and pitch. It has been reported the possibility of superposing LIPSS over DLIP with a final multiscale, hierarchical morphology where the two structures coexist. Here, we report a novel approach in DLIP structuring based on the use of a galvo scanner with large aperture (30 mm) and an F-theta lens combining large entrance pupil (< 20 mm) and relatively small focal length (30 mm). We show that by using a 10 ps laser source emitting at λ=1064 nm, this set-up makes possible a DLIP pitch value Λ as low as 1.4 μm which become comparable with the LIPSS period ≈ 800 – 900 nm. Interestingly, in these experimental conditions, we identified a process window (fluence, number of passes, polarization) where LIPSS formation on stainless-steel surface is strongly affected by the presence of DLIP. Two highly homogeneous, uninterrupted, regular LIPSS arise between two successive DLIP crests with a period reduced to 470 nm, which is sensibly lower than expected. As a result, highly regular ripples with a narrow angular distribution and having a period < λ/2 are observed. Finally, all the generated structures have been characterised by SEM and FFT. We believe that our results represent a promising approach for the high throughput generation over large surface of highly regular structures in the range of few hundreds of nm.

Nature provides many examples of surface structures with multiple functionalities. Some of those, such as light management and self-cleaning, are of interest for increasing the efficiency of optoelectronic devices, such as OLEDs, and for adding new surface functions. However, mimicking and transferring these textures to polymers over large areas often requires complex processes at high costs. Here, we demonstrate a low-cost strategy to fabricate hierarchically textured polyethylene terephthalate (PET) films by plate-to-plate hot embossing. Laser-machined stainless-steel plates with doublescaled hole-like textures were used as master for hot embossing. The larger structure with a period between 30 µm and 70 µm and depths up to 8 µm was produced by direct laser writing (DLW), whereas the smaller structure featuring a period of 3 µm at a depth up to 2 µm was fabricated by direct laser interference patterning (DLIP). The textured surfaces of stainless steel were then molded onto PET films at a pressure of 42 MPa and a temperature of 85°C using a hydraulic press. Topographical characterization was performed by confocal microscopy and scanning electron microscopy. Experiments have shown an increased static water contact angle up to 105°. Furthermore, the hierarchically microtextured foils were studied as out-coupling layers in OLEDs, showing a potential increase in device efficiency of up to 57%. The results thus indicate a good suitability of the developed surfaces for use in highly efficient OLEDs with easy-to-clean properties.

Micro-scale removal of Cu from a dielectric substrate has applications in microelectronics, patch antenna fabrication and frequency selective surface (FSS) manufacturing. Pulsed laser-based micro-scribing of Copper (Cu) from a dielectric is a preferred technique to avoid the adverse effects of chemical etching, such as toxicity and corrosive nature of the etchant, difficulty in fabrication of mask etc. However, pulsed laser-assisted removal of Cu from a dielectric in the air will produce recast layer/ redeposit, oxide layer near the ablation zone and thermal damage to the dielectric is another challenge. In this study, a hybrid technique with nanosecond laser-activated electrochemical micro-scribing of Cu is demonstrated. The technique was extended to remove 35 μm Cu from Rogers-RO4003 dielectric with a thickness ≈0.75 mm to fabricate FSS samples in X-band. The Cu-deposited dielectric substrate was immersed in Sodium Chloride (NaCl) solution, the laser beam was directed through a negatively biased tool electrode and the sample was biased positively. In this hybrid technique, along with laser-assisted material removal, laser-activated electrochemical etching also removed Cu selectively. The laser irradiation coupled with the NaCl solution induced preferential micro-etching, resulting in improved surface morphology without re-deposition and recast layer and thermal protection to the dielectric substrate. The FSS sample produced with the laser-hybrid micro-scribing was working at 10.3 GHz.

Two-photon-absorption (2PA) techniques enables the possibility to create extremely fine structures in photosensitive materials. For direct laser writing as micro- or nanofabrication a laser system can be combined with highly precise positioning systems. These are mostly limited by a few hundreds micrometer positioning range with applications based on piezoelectric stages or even just relatively few tens micrometer positioning range with applications based on galvanometer scanners. Although these techniques are precise, but stitching methods are required for larger fabrication areas. Therefore, a setup consisting of a femtosecond laser for 2PA and a nanopositioning and nanomeasuring machine (NMM-1) was developed for high precision laser writing on lager surfaces. Further developments of the system should enable a significant improvement in high-precision and stitching free direct laser writing. In order to combine the the femtosecond laser and the NMM-1 into a functional unit, to write complex structures with highest accuracy and homogeneity, further improvements like a beam expansion for a better use of the numerical aperture of the objective and a new femtosecond laser with a integrated power measurement are realized. This showed improvements in line width for nano strucuring. Advantages and disadvantages as well as further developments of the NMM-1 system will be discussed related to current developments in the laser beam and nanopositioning system optimization.

Modern two-photon-polymerization 3D printing technology allows for the creation of almost arbitrary threedimensional structures for the production of complex freeform optical surfaces. While being highly controllable and accurate to below 100 nm some systematic deviation by volumetric changes during the polymerization and development process remains. This can however be corrected for when the surface deviation is known. We present a method to include repeatable measurements and the consequent shape correction during the production process of monolithically created complex freeform lens systems. Measurement concepts as well as consequences to shape improvements are shown. An example for the application of such corrections for the creation of low profile multi-aperture large field of view objectives is presented.

Additive Manufacturing methods enable the fabrication of complex 3D components for a wide range of applications, ranging from prototyping up to part manufacturing in industrial several sectors including aerospace and medical industries. In particular, the surface quality of these parts have to be improve in order to reach standard qualities or to obtain specific surface functions. In this frame, this research work reports on laser-based surface finishing treatments of additive manufactured specimens consisting on a new innovative aluminum-alloy (Scancromal®). The experiments are performed with a picosecond pulsed-laser system operating at a fundamental wavelength of 1064 nm, aiming the fabrication of functionalized surfaces with improved properties through topographical features in the micrometer range. To characterize the surface topography, the specimens are analyzed using Confocal Microscopy (CM) and Scanning Electron Microscopy (SEM). Contact Angle measurements are used for the determination of wetting and icing-repellent characteristics of lasertreated AM substrates. Additionally, surface free energy (SFE) is determined and compared with the reference samples. The results show a significant influence of the laser treatment on the surface quality of the treated samples and its resulting wettability behavior. For instance, the water contact angle (WCA) could be increased from 62° to 134°, while the freezing time is also increased from 11 to 25 s after laser treatment, which can be an advantage for some applications and extend the feasibility of AM components beyond the current state of the art.

Additive Manufacturing (AM) processes enable the fabrication of complex three dimensional lightweight parts in a simple way, making these technologies attractive and viable for a wide range of applications in industrial sectors such as aerospace and medical industry. However, it is well known that surfaces of AM components have a relative high roughness level, which can limit their applicability in industrial fields. This study describes the surface modification of AM parts by Direct Laser Writing (DLW) and Direct Laser Interference Patterning (DLIP) to improve the surface quality of additive manufactured specimens made of Titanium 6Al 4V (Ti64) and an Al-Mg-Sc based alloy (Scalmalloy®). The experiments are carried out with an Ytterbium fiber laser and a Nd:YVO4 solid-state laser for DLW and DLIP process, respectively. The DLW laser process enabled the reduction of the initial surface roughness as well as facilitating the fabrication of defined periodical textures with feature sizes in the micrometer range, implemented by DLIP. These textures permitted to control the wettability of the surfaces. The laser treated and non-processed parts are characterized using White Light Interferometry (WLI), Confocal Microscopy (CM) and Scanning Electron Microscopy (SEM). Additionally, the wettability behavior was analyzed through long-term water contact angle measurements over a period of 50 days.