The mitigation of secondary electron yield (SEY) is critical for high-vacuum and high-power applications, notably in high-energy particle accelerators such as the Large Hadron Collider (LHC). This study investigates the influence of ultrashort pulsed laser irradiation on the surface nano-structuring of polycrystalline copper and its subsequent impact on SEY reduction. Samples were processed across a broad parameter space, including wavelengths from 343 nm to 1064 nm, pulse durations from 150 fs to 12 ps, repetition rates from 1 kHz up to 1 MHz, and line spacing from 10 to 50 µm. Results demonstrate that the maximum SEY δmax is primarily governed by the accumulated laser fluence Фacc. Specifically, δmax decreases with increasing Фacc, driven by reduced scan speeds and higher pulse energies, until reaching a saturation threshold at approximately Фacc = 1000 J/cm². Beyond this threshold, δmax stabilizes between 0.7 and 0.9, a behavior found to be almost independent of wavelength, frequency, line spacing, or pulse duration within the investigated ranges. Morphological analyses reveal that at Фacc ≥ 300 J/cm², a dense layer of "cauliflower-like" nanostructures forms. The layer forms via a redeposition process from the ablated material. The reduction of SEY directly correlates with an increasing thickness of this nanostructured layer, providing a scalable and wavelength-independent method.

Atmospheric pressure plasma jet (APPJ) etching is a precise method for optical surface fabrication, yet processing multi-component glasses like N-BK7 leads to the formation of non-volatile metal fluoride residual layers. These porous layers degrade surface quality and necessitate effective post-processing. This study investigates the removal of these residual layers using ultrashort pulse laser radiation at a wavelength of 343 nm. Pulse durations of 260 fs, 500 fs, and 1000 fs were systematically tested. Surface characterization was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and white light interferometry (WLI). Four distinct processing regimes were identified, ranging from substrate damage to selective removal and layer modification. The investigation revealed a significant dependence of the process window on pulse duration. While no parameter window at 260 fs could be found in which the residue layer could be removed without damaging the substrate, a stable process window was successfully identified at 500 fs and 1000 fs. This behavior is attributed to different removal mechanisms. Shorter pulses lead to converging ablation thresholds for the layer and substrate, whereas longer pulses promote thermomechanical spallation. Furthermore, EDX analysis confirmed the formation of Sodium Fluoride (NaF) crystallites in modified areas, indicating recrystallization processes within the residual layer at lower fluences. These results confirm the feasibility of ultrashort pulse laser cleaning for optical surfaces, highlighting the necessity of optimizing pulse duration to ensure selective removal. That coupled laser-plasma process paves the way for high-precision surface structuring of technical glass.

The functionality of surfaces is dependent on two characteristic properties: surface topography and chemical composition. For instance, the secondary electron yield (SEY) of metal surfaces can be adjusted by surface nanostructures or by altering the surface composition. In this study, the two concepts are combined in a one-step process. Reactive Laser ablation based nanostructuring of copper surfaces in a carbon-containing atmosphere was performed, which results in the formation of a metal-particle carbon composite layer. Copper was irradiated with IR ps laser radiation (lambda = 1030 nm, Delta tp = 10 ps, frep = 100 kHz, Phi acc = 2300 J/cm2) in an acetylene atmosphere. The process results in the production of a nanostructured surface with a significant carbon content. The resultant maximum SEY (delta max) depends on the treatment parameters and on the storage time of the copper surface in air after the laser treatment process. The delta max of the laser treated copper surface was 1.2 after two weeks storage and increased to 1.4 after one year storage, while an electron conditioning (electron energy: 250 eV, electron dose: 3 & sdot;10-2C/mm2) after the one year allows delta max reduction down to 0.61. The results show that besides the topography the chemical composition plays an important role for the resulting SEY. In particular, the modification induced by electron conditioning results in a chemical reduction of the carbon-oxide bonds.

Masking of thin films and bulk materials is traditionally applied for the transfer of micron patterns into the functional material according to the requirements of the application. For optical purposes, lithographically produced micron patterns are transferred by plasma/ion etching, which is a traditional technology in microelectronics and other micron technologies. However, pattern transfer by atmospheric pressure plasma etching can help to save time and cost for a future sustainable production. Therefore, the pattern transfer of lithographic resist masks into fused silica using atmospheric pressure reactive plasma jets (APPJ) was studied as a new approach of micropatterning. First the etch rates of the potential masking materials, e.g. photoresists, as well as of fused silica as substrate are studied in dependence on the APPJ etching parameters, in particular on the gas composition (O-2/CF4) and the dwell time of the APPJ tool's footprint. Typical etch rates of the masking materials are in the range of 140 to 370 nms(-1) whereas the fused silica has a rate of 25 to 80 nms(-1). The surface morphology of masking materials changes during etching and features additional nanoscale roughness and waviness. The surface roughness of the etched masking materials and the fused silica are 2 to 5 nm rms and 1.5 nm rms for etch depths of similar to 3000 nm and similar to 600 nm, respectively. Finally, the pattern transfer by APPJ of a diffraction grating with a period of 15 mu m, depth of 230 nm and a roughness below 2 nm rms into fused silica was demonstrated.

Ultraviolet nanoimprint lithography（UV-NIL） is a versatile and cost-effective technique for the fabrication of micro-and nanostructures by copying master patterns in a planar or a roll-to-roll process through curing of a liquid UV-sensitive precursor. For applications with a high pattern complexity, new UV-NIL process chains must be specified. Master fabrication is a challenging part of the development and often cannot be accomplished using a single master fabrication technique. Therefore, an approach combining different patterning fabrication techniques is developed here for polymer masters using laser direct writing and photolithography. The polymer masters produced in this way are molded into inverse silicone stamps that are used for roll-to-roll replication into an acrylate formulation. To fit the required roller size for large-area UV-NIL, several submasters with micrometer-sized dot and line gratings and prism arrays, which have been patterned by these different techniques, are assembled to final size of ～200 × 600 mm 2 with an absolute precision of better than 50 μm. The size of the submasters allows the use of standard laboratory equipment for patterning and direct writing, thus enabling the fabrication of micro-and even nanostructures when electron-beam writing is utilized. In this way, the effort, time, and costs for the fabrication of masters for UV-NIL processes are reduced, enabling further development for particular structures and applications. Using this approach, patterns fabricated with different laboratory tools are finally replicated by UV-NIL in an acrylate formulation, demonstrating the high quality of the whole process chain.

The generation of periodic surface structures (LIPSS) using Laser is a well-known and extensively researched effect. The majority of known und studied LIPSS are generated by multi-pulse irradiation, with single-pulse LIPSS being currently under-researched. This study investigated the single-pulse generation of LIPSS on a silicon Si(100) surface covered with a SiO2 layer. The layer system was irradiated by single IR fs laser pulse (260 fs, 1030 nm, 2 mu J). Single pulse irradiation allows the production of LIPSS on the Si surface below the SiO2 layer without disturbing the SiO2 layer. These subsurface LIPSS have a period of approximately 1 mu m. In addition, multiple, laterally separated single pulses were applied to the SiO2/Si and the effect of the formed structures as a function of the spacing and geometry of the single pulses was systematically analyzed. When employing multiple single pulses, it is evident that when the distance between irradiation points is below 20 mu m, LIPSS areas are formed that are significantly larger than the area of the separated single points especially in polarization direction.

Pattern transfer of lithographically produced patterns is a key technology in microelectronics and other micro- and nanotechnologies. This approach has been perfected continuously to meet the requirements for size and quality, but vacuum processes are required for pattern transfer into microelectronic materials. Here an atmospheric pressure approach of pattern transfer by laser ablation is proposed and demonstrated. Similar plasma-based pattern transfer laser beams provide a directed energy impact to the exposed material, but the resulting material reactions are different as distinct primary processes govern the material removal mechanism by ablation. The laser ablation-based pattern transfer mechanism comprises (i) optical effects such as laser photon absorption and scattering processes, (ii) thermal processes such as material heating and melting, and (iii) laser ablation processes of the masking and the substrate materials. These characteristics cause topographical effects of laser-based pattern transfer (LiPT) process that results in a specific sidewall angle of the transferred pattern due to cone formation effects, trench formation related to diffraction and reflection at the patterns and surrounding wavy pattern due to laser beam diffraction. The ablation rate ratio determines the selectivity for laser-based pattern transfer and therewith the limit in depth. The pattern transfer can be achieved locally with varying parameters including different inclination angles. The results pave the way to a new approach for sustainable economic fabrication processes that do not need vacuum and reactive gases.

Atmospheric pressure plasma jet (APPJ) machining of optical materials, e.g. fused silica and silicon carbide is capable of generating free-form optical surfaces with excellent precision and low surface roughness. However, APPJ etching of the commonly used optical glass N-BK7 (R), which contains various metal oxides, with fluorine-containing gases results in the formation of surface residues consisting of metal fluorides. The accumulated residues form a layer on the glass substrate that deteriorates the etching process in terms of etching rate and surface roughness but can be ablated by pulsed laser irradiation. The aim of this study is to reduce the residual layer thickness required for its laser removal as a prerequisite to increased shape accuracy and reduced process-induced roughness. N-BK7 (R) samples were etched with APPJ while varying the surface temperature. Subsequently the APPJ-etched area was irradiated by excimer laser at different wavelengths (2 = 193; 248; 308 nm; tPulse = 20 ns). The etched and laser-exposed sample surfaces were thereafter analyzed by WLI and SEM. It can be shown that residual layers resulting from etching at different temperatures can be removed at wavelengths of 193 nm and 248 nm. The thinnest layer for complete removal demonstrated is 95 nm at a wavelength of 193 nm. The minimum layer thicknesses for 2 = 248 nm are in the range of 190-320 nm. At a wavelength of 308 nm, neither removal of the residual layer nor damage to the glass could be detected for the selected fluence range.

Laser-induced plasma etching (LIPE) offers a promising technique for high-quality surface processing under atmospheric pressure. This study investigates the surface modification of polytetrafluoroethylene (PTFE) in air using a high-repetition-rate ultrashort pulsed laser. Key process and laser parameters, including repetition rate, pulse energy, plasma-to-surface distance, and etching time, were analyzed for their impact on etching rates and surface morphology. The etching rate of PTFE under stationary conditions was measured in the picometer-per-pulse range, enabling precise vertical control. Results show that etching rates increase with increasing pulse energy and repetition rate but decrease with greater plasma-to-surface distances. The generated etch grooves are circular and significantly larger than the laser spot size, with etched surfaces exhibiting reduced surface roughness compared to unetched surfaces. Line pattern etching was demonstrated by moving the sample at a constant speed in front of the laser-induced plasma. Unlike laser ablation, LIPE achieves superior vertical depth precision and significantly smoother surface morphology, making it a valuable tool for ultra-precise surface machining applications.

Laser-induced periodic surface structures (LIPSS) attract considerable attention due to the manifold applications enabled by these self-organised structures ranging from optical colouring to bio-mimicking or wetting effects. The mechanism of LIPSS-formation at metal surfaces includes laser-ablation processes that results in phase transitions, explosive material removal and partial redeposition of the ablation products in the form of nanoscopic debris or even sub-micrometre-sized spherical particles in case of melt ejection. For some applications, these particulates, debris, and microscopic features on top of the periodic surface structures are disadvantageous. We studied wet-chemical cleaning approaches to remove redeposited material from LIPSS to enhance their applicability. LIPSS on copper with a lateral periodicity of similar to 365 nm, that were fabricated by ultrashort pulse laser exposure (lambda: 515 nm, t(p): 260 fs), were cleaned with different liquids ranging from solvents to microemulsions. The surface morphologies were characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) to study the surface topography, the size and density of surface particulates as well as other surface contaminations before and after wet cleaning. The LIPSS surface composition was analysed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Energy-dispersive x-ray spectroscopy (EDX) at the FIB-cross sections. The different cleaning approaches are classified with respect to their capability to remove particles and contaminations as well as to their influence on the morphology and shape of LIPSS pattern, whereby substantial differences are found. At least two wet-chemical solutions enable the removal of nanoparticles with only minor modification of the LIPSS topography. The main effect of wet cleaning is the detachment of particulates including sub-micrometre-sized spheres due to a gentle and selective etching of the interface region between the LIPSS and the redeposited material that comprise of modified copper and copper oxides.

The use of beam-based technologies to process optical elements with nanoscale precision enables the fabrication of freeform surfaces. In particular, atmospheric pressure plasma jets (APPJs) have desirable properties, e.g., depth precision < 5 nm, low surface roughness and processing at atmospheric conditions. However, the composition of optical glasses and glass ceramics, containing metal oxides, leads to the formation of non-volatile reaction products that remain on the substrate surface. These residues reduce the etching rate and cause severe roughening of the surface. Laser irradiation has already been demonstrated as a promising option for removing the residual layer and the aim of the current work is to integrate it into the APPJ system for simultaneous processing. Therefore, an excimer laser (λ = 248 nm; tPulse = 20 ns) with a maximum pulse frequency of 100 Hz was added to a plasma jet setup and experiments with varying laser fluences as well as laser frequencies were performed on N-BK7 substrates. White light interferometry was used to analyse the samples. The experiments showed an improved etching result with higher removal rates for the combined process at high laser pulse frequency (100 Hz) and fluences in the range of 0.1-0.45 J·cm-2.

The fabrication of plasmonic 3D microstructures is still a challenge. In this study, the fabrication of gold‐nanoparticle (Au‐NP)‐filled acrylate‐based micron‐scale cuboids forming plasmonic 3D particles is investigated. UV curable acrylate is mixed with HAuCl 4 and spin‐coated onto a fused silica wafer. UV light and heat treatment of the layer result in polymerization of the acrylate and formation of Au‐NPs with a plasmonic resonance ranging from 535 to 550 nm. The plasmonic resonance wavelength decreases slightly with increasing UV dose. The resonance wavelength can be shifted by a subsequent annealing process. The decreasing resonance wavelength with increasing annealing temperature is discussed as a result of the increasing Au‐NPs. The size and the distribution of the resulting gold particles in the acrylate matrix is investigated by transmission electron microscopy. The Au‐NPs‐filled acrylate layer is laser structured using a UV‐femtosecond laser, which allows the fabrication of adjustable micro‐cuboids with edge lengths down to 15 μm. The laser‐cut micro‐cuboids are transferred into isopropanol and the plasmonic properties of the structures in the liquid are successfully demonstrated. The presented concept allows easy and large‐scale fabrication of plasmonic microstructures with independently adjustable plasmonic properties and microstructural size and shape.

Stainless steel (SST) is an important material for a variety of applications including construction, food, and medical. Highly hydrophobic wetting properties enhance the surface properties of SST to support processes such as self‐cleaning . However, applications also require long‐term stability of such properties against chemical and mechanical influences from the environment or technical processes. Therefore, the reduction of highly hydrophobicity of chemically modified, laser‐textured SST surfaces is investigated in relation to abrasive wear using hierarchical structures, micro‐/nanotextured surface, and support structures that shield the highly hydrophobic pattern. Surface textures comprising ridges, grooves (size: 50–500 μm; depth: up to 100 μm), and a nanostructured grooves bottom are machined by infrared ultrashort pulse laser ablation into SST and are subsequently chemically modified by a self‐assembled monolayer of a fluorinated, phosphonic acid‐modified alkane. Abrasive wear tests of these surfaces show decreasing water contact angles with increasing wear of the modified surface of the support structures. However, there is good stability of the highly hydrophobic properties due to the protection of modified areas at the groove bottom. The proposed wetting model for such designed functionalized laser textures shows possibilities for further optimization of such robust highly hydrophobic surfaces and adaptation to specific applications.

Pattern transfer by plasma etching is a traditional standard technology in microelectronics and other micron technologies. These technologies require vacuum conditions, which limit throughput, size, and low-cost fabrication. Recent developments in low cost atmospheric plasma technologies may be suitable to realize pattern transfer without vacuum conditions. Reactive atmospheric plasma jet etching has been used to transfer aluminum mask patterns to fused silica. Aluminum line patterns of 2.5 to 50 µm width on fused silica wafer are exposed to a static as well as a scanning CF4/O2 reactive atmospheric plasma jet with a footprint diameter of 0.85 mm (full width at half maximum), resulting in etching only the SiO2 and causing a nearly isotropic etch with an etch rate of about 200 nm/s. As a result, line narrowing, trapezoidal line cross-sections, and under-etching were observed. The successfully transferred line patterns with the demonstrated widths and depths are of technological interest in various fields of application. Therefore, this approach enables low-cost patterning of fused silica through the use of reactive atmospheric plasma jet etching for micron-scale pattern transfer. This advancement addresses the limitations of both traditional vacuum-based and wet etching methods.

The use of beam‐based technologies to process optical elements with nanoscale precision enables the fabrication of freeform surfaces. Especially, atmospheric pressure plasma jets (APPJ) have desirable properties such as atmospheric pressure machining, dry processing, and direct writing capabilities. However, the presence of metal oxides in optical glasses leads to the formation of nonvolatile reaction products during APPJ etching with fluorine‐containing gas mixtures, forming a residual layer that increases surface roughness and alters etching behavior. To prevent the formation of the residual layer, the APPJ process is combined with laser cleaning. For a possible future in situ cleaning of the residual layer during the plasma process, laser parameter ranges need to be found to remove the residual layer without damaging the glass surface. Therefore, planar etchings are performed by APPJ on N‐BK7 and Zerodur and the etched planes are subsequently laser irradiated with varying pulse numbers and fluences. The processed samples are then examined by scanning electron microscopy. For both N‐BK7 and Zerodur, a parameter range is identified that results in clean surfaces. The best machining results are achieved with 2–16 pulses and laser fluences of 0.6–1.2 J cm −2 for N‐BK7 and 0.56–0.7 J cm −2 for Zerodur.

Atmospheric pressure plasma jet (APPJ) etching of Zerodur (R) with fluorine containing process gases leads to the generation of non-volatile metal fluorides which remain on the surface and form a residual layer. This results in masking effects and therefore an increasing roughness and altered etching behavior. The removal of the residual layer by laser irradiation has already been demonstrated and the aim of the present work is to further develop this process combination by reducing the residual layer thickness. For this purpose, etchings were performed with APPJ and the resulting residues were subsequently irradiated with an excimer laser (lambda = 248 nm) with varying fluence. The samples were analyzed by white light interferometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. In the fluence range of 0.3-0.6 J.cm(-2) the residual layer can be removed without damaging the glass ceramic surface. EDX measurements show similar results for the laser-cleaned regions and an untreated Zerodur reference indicating that the residual layer can completely be removed.

Droplet-induced self-folding processes enable the easy and cost-effective fabrication of millimeter to submillimeter 3D structures from planar templates. These templates were fabricated by laser cutting of polymer foils that offer a high flexibility in design. The interaction of water droplets with template surfaces induces a surface tension force that causes the deformation of the laser-cut templates needed to form the 3D structures. In this study, laser patterning of 25 mu m thick polyimide (PI) foils by UV ultrashort pulse laser ablation was used to systematically investigate the effect of hinge geometry on the bending and self-folding process of cubes. The deposition of water droplets on the laser-structured samples leads to forces that move the side faces of the cube template causing a defined deformation of the hinges of the PI template and resulting in a bending angle between hinged template regions. The bending angle was determined as a function of hinge geometry and water droplet volume. The bending angle is increased with increasing droplet volume below a certain maximum but decreased with increasing hinge thickness and width. Finally, 2D laser cut templates with optimized v-shaped hinge structures was sucessful formed into a cube by laser droplet induced self folding.

Ultrashort-pulse laser processing of copper is performed in air to reduce the secondary electron yield (SEY). By UV (355 nm), green (532 nm), and IR (1064 nm) laser-light induced surface modification, this study investigates the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence) on the ablation depth, surface oxidation, topography, and ultimately on the SEY. Increasing the accumulated laser fluence results in a gradual change from a Cu2O to a CuO-dominated surface with deeper micrometer trenches, higher density of redeposited surface particles from the plasma phase, and a reduced SEY. While the surface modifications are less pronounced for IR radiation at low accumulated fluence (<1000 J/cm2), analogous results are obtained for all wavelengths when reaching the nonlinear absorption regime, for which the SEY maximum converges to 0.7. Furthermore, independent of the extent of the structural transformations, an electron-induced surface conditioning at 250 eV allows a reduction of the SEY maximum below unity at doses of 5×10-4 C/mm2. Consequently, optimization of processing parameters for application in particle accelerators can be obtained for a sufficiently low SEY at controlled ablation depth and surface particle density, which are factors that limit the surface impedance and the applicability of the material processing for ultrahigh vacuum systems. The relations between processing parameters and surface features will provide guidance in treating the surface of vacuum components, especially beam screens of selected magnets of the Large Hadron Collider or of future colliders.

Focusing of femtosecond laser pulses in gases can produce different gas breakdown phenomena depending on the focusing conditions: from simple optical breakdown like laser “sparks” to a nonlinear optical breakdown like filamentation. The dynamics of such plasmas after the pulse exposure is dependent on the energy deposited by the laser in the breakdown volume. Using a time- and position-dependent breakdown model, we estimate the breakdown volume and show that the energy deposited by the laser in this breakdown volume determines the characteristics of laser-induced plasma in the post-pulse exposure regime. Experimentally we find that for different focal lengths there exists a threshold value of the energy density beyond which a transition from an ellipsoidal shape to a spherical shape can be observed, followed by a toroidal expansion of the produced plasma. When electron density and electron temperature are expressed as a function of the energy density, deviations from the parabolic dependence on irradiance are observed. They imply additional ionization by multiphoton ionization in the plasma volume that occurs when the peak power of the laser pulse is above the critical power for self-focusing in air. The relevance of this experimental and theoretical study is to prevent undesired self-focusing conditions during material processing, a step toward well-controlled laser-plasma etching without laser ablation.

The irradiation of metals with ultrashort laser pulses enables the rapid and cost-effective production of nanostructured surfaces with a wide range of industrial applications. The laser-induced surface roughening modifies the interaction processes upon electron impact, leading to a modification of the secondary electron emission. In this study, the nanostructuring as well as the secondary electron yield (SEY) variation of polycrystalline copper surfaces was investigated by irradiation with 1030 nm infrared ultrashort laser pulses at a constant repetition rate of 100 kHz. The influence of varying the pulse duration between 238 fs and 10 ps, the laser power and the number of laser pulses per unit area (induced by varying the scanning speed) on the surface topography and the SEY was investigated. Irrespective of the pulse duration, irradiation with low scan speed (v <= 20 mm/s) and high laser power (P >= 2.6 W) results in the formation of a surface with compact nanostructures and a very low maximum SEY delta max < 0.7. The delta max increased slightly with increasing pulse duration at similar laser parameters. Increasing the pulse duration also resulted in a slight decrease in the ablation threshold and volume. The observed SEY dependence is probably explained by the pulse duration dependence of the ablation. The results suggest that nanostructured copper surfaces with very low SEY can be produced with ultrashort laser pulses over a wide range of pulse durations.