This PDF file contains the front matter associated with SPIE Proceedings Volume 9351, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

It has been known that wavelength, power density, interaction time and material properties have great influence on processing characteristics in laser material processing, in which materials with higher reflectivity classify into difficultto- weld materials. In electronic industry, aluminum alloy is widely used as structural components due to its high specific strength, and copper became an important material because of its excellent electrical conductivity. These materials have high reflectivity and high thermal conductivity, which results in instability of energy absorption and processing results. Therefore, welding defects might be noticed in the micro-joining of aluminum alloy and copper. In this paper, the smart laser micro-welding of difficult-to-weld materials such as aluminum alloy and copper were discussed. The combination of a pulsed Nd:YAG laser and a continuous diode laser could perform high-performance micro-welding of aluminum alloy. A pulsed Nd:YAG laser was absorbed effectively from the beginning of laser scanning by pre-heating Nd:YAG laser pulse with the superposition of continuous diode laser, and wide and deep weld bead could be obtained with better surface integrity. As for micro-welding of copper material, stable absorption state could be achieved using a pulsed green Nd:YAG laser, since its absorptivity showed almost constant values with change of power density. A longer pulse duration was effective to achieve not only high absorptivity but also low deviation of absorptivity. The pulse waveform with maximum peak at the early period and a long pulse duration led to stabilizing the penetration depth with less porosity.

The generation of microsized components found in LEDs, watches, molds as well as other types of micromechanics and microelectronics require a corresponding micro cutting tool in order to be manufactured, typically by milling or turning. Micro cutting tools are made of cemented tungsten carbide and are conventionally fabricated either by electrical discharge machining (EDM) or by grinding. An alternative method is proposed through a laser-based solution operating in the picosecond pulse duration whereby the beam is deflected using a modified galvanometer-driven micro scanning system exhibiting a high numerical aperture. A micro cutting tool material which cannot be easily processed using conventional methods is investigated, which is a fine grain polycrystalline diamond composite (PCD). The generation of various micro cutting tool relevant geometries, such as chip breakers and cutting edges, are demonstrated. The generated geometries are subsequently evaluated using scanning electron microscopy (SEM) and quality is measured in terms of surface roughness and cutting edge sharpness. Additionally, two processing strategies in which the laser beam processes tangentially and orthogonally are compared in terms of quality.

Ablation threshold experiments on various materials are carried out using a picosecond laser generating second harmonic radiation in air at atmospheric pressure. Various materials are investigated which vary according to their different electronic band gap structure and include: silicon, fine grain polycrystalline diamond, copper, steel and tungsten carbide. Through the use of scanning electron microscopy and 3D confocal microscopy, the crater depth and diameter are determined and a correlation is found. The ablation thresholds are given for the aforementioned materials and compared with recent literature results. Picosecond laser-material interactions are modelled using the two-temperature model, simulated and compared with experimental results for metallic materials. An extension of the two-temperature model to semiconducting and insulating materials is discussed. This alternative model uses multiple rate equations to describe the transient free electron density. Additionally, a set of coupled ordinary differential equations describes the processes of multiphoton excitation, inverse bremsstrahlung, and collisional excitation. The resulting electron density distribution can be used as an input for an electron density dependent twotemperature model. This multiple rate equation model is a generic and fast model, which provides important information like ablation threshold, ablation depth and optical properties.

Femtosecond-pulsed laser welding of transparent materials on a micrometer scale is a versatile tool for the fabrication and assembly of electronic, electromechanical, and especially biomedical micro-devices. In this paper, we report on microwelding of two transparent layers of polymethyl methacrylate (PMMA) with femtosecond laser pulses at 1030 nm in the MHz regime. We aim at exploiting localized heat accumulation to weld the two layers without any preprocessing of the sample and any intermediate absorbing media, by focusing fs-laser pulses at the interface.

The modifications produced by the focused laser beam into the bulk material have been firstly investigated depending on the laser process parameters aiming to produce continuous melting. Results have been evaluated based on heat accumulation models. Finally, fs-laser welding of PMMA samples have been successfully demonstrated and tested by leakage tests for application in direct laser assembly of microfluidic devices.

The main objective of this work is to adapt Laser Induced Forward Transfer (LIFT), a well-known laser direct writing technique for material transfer, to define metallic contacts (fingers and busbars) onto c-Si cells. A layer of a commercial silver paste (viscosity around 30-50 kcPs), with thickness in the order of tens of microns, is applied over a glass substrate using a coater.. The glass with the silver paste is set at a controlled gap over the c-Si cell. A solid state pulsed laser (532 nm) is focused on the glass/silver interface producing a droplet of silver that it is transferred to the acceptor substrate. The process parameters (silver paste thickness, gap and laser parameters -spot size, pulse energy and overlapping of pulses) are modified and the morphology of the voxels is studied using confocal microscopy. Long lines are printed with a scanner and their uniformity, width, and height are studied. Examples of metallization of large areas (up to 10 cm x 10 cm) over c-Si cells are presented.

An integrated technology chain for laser-microstructuring and bonding of polymer foils for fast, flexible and low-cost manufacturing of multilayer lab-on-a-chip devices especially for complex cell and tissue culture applications, which provides pulsatile fluid flow within physiological ranges at low media-to-cells ratio, was developed and established. Initially the microfluidic system is constructively divided into individual layers which are formed by separate foils or plates. Based on the functional boundary conditions and the necessary properties of each layer the corresponding foils and plates are chosen. In the third step the foils and plates are laser microstructured and functionalized from both sides. In the fourth and last manufacturing step the multiple plates and foils are joined using thermal diffusion bonding. Membranes for pneumatically driven valves and micropumps where bonded via chemical surface modification. Based on the established lab-on-a-chip platform for perfused cell-based assays, a multilayer microfluidic system with two parallel connected cell culture chambers was successfully implemented.

Femtosecond Laser Surface Processing (FLSP) is a versatile technique for the fabrication of a wide variety of micro/nanostructured surfaces with tailored physical and chemical properties. Through control over processing conditions such as laser fluence, incident pulse count, polarization, and incident angle, the size and density of both micrometer and nanometer-scale surface features can be tailored. Furthermore, the composition and pressure of the environment both during and after laser processing have a substantial impact on the final surface chemistry of the target material. FLSP is therefore a powerful tool for optimizing interfacial phenomena such as wetting, wicking, and phasetransitions associated with a vapor/liquid/solid interface. In the present study, we utilize a series of multiscale FLSPgenerated surfaces to improve the efficiency of vapor generation on a structured surface. Specifically, we demonstrate that FLSP of stainless steel 316 electrode surfaces in an alkaline electrolysis cell results in increased efficiency of the water-splitting reaction used to generate hydrogen. The electrodes are fabricated to be superhydrophilic (the contact angle of a water droplet on the surface is less than 5 degrees). The overpotential of the hydrogen evolution reaction (HER) is measured using a 3-electrode configuration with a structured electrode as the working electrode. The enhancement is attributed to several factors including increased surface area, increased wettability, and the impact of micro/nanostructures on the bubble formation and release. Special emphasis is placed on identifying and isolating the relative impacts of the various contributions.

In this study, ps-laser micromachining of different types of metals like copper, aluminum, titanium, tungsten and zinc have been investigated. Their single-pulse damage thresholds for the laser wavelengths of 355 nm, 532 nm and 1064 nm were experimentally determined. The laser-induced surface morphology both in the low and high fluence regime, as well as in the transition area, were examined for all investigated metals by scanning electron microscopy. Single pulse experiments and multi-pulse ablation experiments for up to 6 pulses using time-delays between successive pulses of 1 s and 20 ns were carried out. Our observations show that the surface morphologies significantly change from single-pulse ablation to the application of a second pulse. By comparing different separation times in the multi-pulse experiments we show that the burst-mode in ps-laser processing accumulates heat. This results in strong arising melting films, smoothing of the ablation craters and melt splashes outside of the crater. We found out, that copper and aluminum as well as titanium and zinc show similar ablation behavior by using the burst mode.

Femtosecond laser irradiation applied to Fused Silica (the amorphous form of SiO₂) defines a novel technology platform for highly integrated all-optical microsystems and beyond. In contrast with common approaches that rely on combining materials to achieve particular functions, femtosecond-laser fabricated microsystems rely on single material monolith, whose properties are locally and in the three-dimension functionalized by selective exposure. The combination of laserfunctionalized zones with different physical properties allows us to direct-write integrated systems without the need for further assembly of packaging steps or without the need for multiple processing steps, like for instance sequences of layers deposition, exposure and etching steps.

We measured the dielectric constant of optically excited silicon and tungsten using a dual-angle femtosecond reflectivity pump-probe technique. The energy deposition in the formation of laser-induced periodic surface structures (LIPSS) is then investigated by simulating the laser pulse interaction with an initially random distributed rough surface using 3D-Finite Difference Time Domain (FDTD) method, with the measured dielectric constant as a material input. We found in the FDTD simulation periodic energy deposition patterns both perpendicular and parallel to the laser polarization. The origin of them are discussed for originally plasmonic and non-plasmonic material.

Femtosecond laser surface processing (FLSP) is a powerful technique used to create self-organized microstructures with nanoscale features on metallic surfaces. By combining FLSP surface texturing with surface chemistry changes, either induced by the femtosecond laser during processing or introduced through post processing techniques, the wetting properties of metals can be altered. In this work, FLSP is demonstrated as a technique to create superhydrophobic surfaces on grade 2 titanium and 304 stainless steel that can retain an air film (plastron) between the surface and a surrounding liquid when completely submerged. It is shown that the plastron lifetime when submerged in distilled water or synthetic stomach acid is critically dependent on the specific degree of surface micro- and nano-roughness, which can be tuned by controlling various FLSP parameters. The longest plastron lifetime was on a 304 stainless steel sample that was submerged in distilled water and maintained a plastron for 41 days, the length of time of the study, with no signs of degradation. Also demonstrated for the first time is the precise control of pulse fluence and pulse count to produce three unique classes of surface micron/nano-structuring on titanium.

Due to a growing demand of cost-efficient lithium-ion batteries with an increased energy and power density as well as an increased life-time, the focus is set on intercalation cathode materials like LiFePO₄. It has a high practical capacity, is environmentally friendly and has low material costs. However, its low electrical conductivity and low ionic diffusivity are major drawbacks for its use in electrochemical storage devices or electric vehicles. By adding conductive agents, the electrical conductivity can be enhanced. By increasing the surface of the cathode material which is in direct contact with the liquid electrolyte the lithium-ion diffusion kinetics can be improved. A new approach to increase the surface of the active material without changing the active particle packing density or the weight proportion of carbon black is the laser-assisted generation of 3D surface structures in electrode materials. In this work, ultrafast laser radiation was used to create a defined surface structure in LiFePO₄ electrodes. It was shown that by using ultrashort laser pulses instead of nanosecond laser pulses, the ablation efficiency could be significantly increased. Furthermore, melting and debris formation were reduced. To investigate the diffusion kinetics, electrochemical methods such as cyclic voltammetry and galvanostatic intermittent titration technique were applied. It could be shown that due to a laser generated 3D structure, the lithium-ion diffusion kinetic, the capacity retention and cell life-time can be significantly improved.

Evenly spaced conductive grids of copper and aluminum thin films on polyamide substrate are used for parabolic reflector-antennas, aboard telecommunications satellite. In the present paper, laser micro scribing of thin films using a flat-top and Gaussian laser beam profile are analyzed with 95% overlapping of the diameter of the laser spot. Laser scribing is performed using the Q-switched Nd³⁺: YAG (355, 532 nm) laser. The influence of laser irradiation and beam shape are experimentally analyzed using non-contact optical profilometer and scanning electron microscope (SEM). Laser scribing using flat-top profile produced near rectangular micro channels in copper thin films. Using Gaussian profile the probability of melting is greater than vaporization as observed using SEM images; this melt pool plays a prominent role in re-solidification at the edges. Depth of the scribe channel is observed to be 20% high for 532 nm wavelength compared to 355 nm wavelength. Effect of different environments such as air, water and vacuum on the channel depth and quality is reported. The response of aluminum and copper for high fluences is also studied. Theoretical modeling of the laser-material interaction using Comsol mulitphysics 4.4 is discussed.

We investigated the effect of burstmode with nanosecond (ns) time delay between subpulses on sodalime glass volume machining. We observed in tight focusing configuration that the use of burstmode with ns time delay between subpulses does not increase the absorption efficiency and does not bring a significant effect on the heat affected zone diameter with respect to single pulse mode. On the contrary in loose focusing configuration the use of burst mode allows increasing the aspect ratio of the heat affected zone without extra energy absorption. This effect is highly interesting for filamentation glass cutting applications.

In this paper, laser processing of fiber reinforced thermoplastics is investigated with different laser sources. Aim of the study is to determine the process windows in which selective ablation of polymer matrix and homogenous ablation of matrix and fiber occurs. To reach this, laser sources with different wavelengths (10600 nm, 1064 nm and 532 nm) and pulse durations in μs, ns and ps regime are compared on their ablation behavior of natural and black colored glass fiber reinforced polypropylene. Best results were achieved with ns lasers with IR wavelength at black colored material. At this parameter combination a wide process window can be shown where no damage of the reinforcing fibers happens.

Deep engraving of 3D textures is a very demanding process for the creation of master tool e. g molds, forming tools or coining dies. As these masters are uses for reproduction of 3D patterns the materials for the tools are typically hard and brittle and thus difficult to machine. The new generation of industrial femtosecond lasers provides both high accuracy engraving results and high ablation rates at the same time. Operation at pulse energies of typically 40 μJ and repetition rates in the Mhz range the detrimental effect of heat accumulation has to be avoided. Therefore high scanning speeds are required to reduce the pulse overlap below 90%. As a consequence scan speeds in the range of 25-50 m/s a needed, which is beyond the capability of galvo scanners. In this paper we present results using a combination of a polygon scanner with a high average power femtosecond laser and compare this to results with conventional scanners. The effects of pulse energy and scan speed of the head on geometrical accuracy are discussed. The quality of the obtained structures is analyzed by means of 3D surface metrology microscope as well as SEM images.

Metal mirrors are an attractive solution for scan mirrors working with ultra-short pulse lasers. Small mechanical inertia and a small mirror mass are required. Therefore, the mirrors have to be very stiff and a high quality optical surface has to be provided. This can be achieved with lightweight AlSi based mirrors with diamond-turned NiP polishable plating.

Different coating options were evaluated in order to provide the necessary high reflectivity and a satisfactory laser damage threshold for ultrashort laser pulses in the few ps to fs regime at λ = 1030 nm. High-reflective metal layers enhanced by dielectric HfO₂/SiO₂ stacks were found to be the most advantageous coating option due to their comparatively small thickness and measured damage thresholds above 1 J/cm²@8ps.

Many research teams have begun pursuing optical micromachining technology in recent years due to its associated noncontact and fast speed characteristics. However, the focal spot sizes and the depth of focus (DOF) strongly influenced the design requirements of the micromachining system. The focal spot size determines the minimum features can be fabricated, which is inversely proportional to the DOF. That is, smaller focal spot size led to shorter DOF. However, the DOF of the emitted visible or near-infrared light beam is typically limited to tens of nanometers for traditional optic system. The disadvantages of using nanosecond laser for micromachining such as burrs formation and surface roughness were found to further influence the accuracy of machined surfaces. To alleviate all of the above-mentioned problems, sub-wavelength annular aperture (SAA) illuminated with 780 nm femtosecond laser were integrated to develop the new laser micromachining system presented in this paper. We first optimized the parameters for high transmittance associated with the SAA structure for the 780 nm femtosecond laser used by adopting the finite difference time domain simulations method. A lateral microscope was modified from a traditional microscope to facilitate the measurement of the emitted light beam optical energy distribution. To verify the newly developed system performance the femtosecond laser was used to illuminate the SAA fabricated on the metallic film to produce the Bessel light beam so as to perform micromachining and process on silicon, PCB board and glass. Experimental results were found to match the original system design goals reasonably well.

Interferential irradiation of high power laser pulses can produce arrays of periodic nanostructures on surfaces. Patterning Si wafers directly by high power laser pulses indicates that the trench depth is limited to the laser pulse intensity. We present our recent studies on direct laser patterning of polystyrene coated Si wafers, which are irradiated interferentially by high power laser pulses. Polystyrene films were formed on silicon wafers with thickness controlled based on a previously developed method. Interferential irradiations of laser pulses are applied on the polystyrene coated Si wafer. The laser pulse intensities are varied along with other interferential parameters such as interference angle and laser wavelengths of 532, 355, and 266nm. The polystyrene film is dissolved to expose the patterned Si surfaces. Atomic force microscopy (AFM) images from the patterned Si surfaces indicate that the area covered with the films has trenches deeper than those on bare Si wafers patterned at the same laser intensity. Furthermore, studies of AFM images indicate that the thicker the polystyrene coating, the deeper the trenches that are produced by direct laser patterning Si surfaces. The enhancement and modification due to polymer films may enhance the security features by improving the quality of holograms.

Recently an alternative to conventional methods based on vacuum processes such as evaporation or sputtering is desired to reduce the energy consumption and the environmental impact. Printed electronics has been developed as a one of the candidates, which is based on wet processes using soluble functional materials such as organic semiconductors, inorganic nanomaterials, organic-inorganic hybrids, and so on. Although inkjet printing has been studied widely as a core technology of printed electronics, the limitation of resolution is around 20 micrometer. The combination of the inkjet printing with other selective metallization process is necessary because the resolution of several micrometers is required in some optical and electrical devices. The laser processing has emerged as an attractive technique in microelectronics because of the fascinating features such as high resolution, high degree of flexibility to control the resolution and size of the micro-patterns, high speed, and a little environmental pollution. In this paper, the present status and future outlook of selective metallization for interconnection and the formation of transparent conductive film based on the laser processing using metal nanoparticles were reported. The laser beam irradiation to metal nanoparticles causes the fast and efficient sintering by plasmon resonance of metal nanoparticle, where the absorbed energy is confined in a nanoparticle and the nanoparticle acts as a nano-heater. The laser irradiation to metal nanoparticles was applied to the laser direct writing of metal wiring and micropatterns using silver and copper nanoparticles.

The progressive miniaturization of electronic devices requires an ever-increasing density of interconnects attached via solder joints. As a consequence, the overall size and spacing (or pitch) of these solder joint interconnects keeps shrinking. When the pitch between interconnects decreases below 200 μm, current technologies, such as stencil printing, find themselves reaching their resolution limit. Laser direct-write (LDW) techniques based on laser-induced forward transfer (LIFT) of functional materials offer unique advantages and capabilities for the printing of solder pastes. At NRL, we have demonstrated the successful transfer, patterning, and subsequent reflow of commercial Pb-free solder pastes using LIFT. Transfers were achieved both with the donor substrate in contact with the receiving substrate and across a 25 μm gap, such that the donor substrate does not make contact with the receiving substrate. We demonstrate the transfer of solder paste features down to 25 μm in diameter and as large as a few hundred microns, although neither represents the ultimate limit of the LIFT process in terms of spatial dimensions. Solder paste was transferred onto circular copper pads as small as 30 μm and subsequently reflowed, in order to demonstrate that the solder and flux were not adversely affected by the LIFT process.

Laser welding of polymers increasingly finds application in a large number of industries such as medical technology, automotive, consumer electronics, textiles or packaging. More and more, it replaces other welding technologies for polymers, e. g. hot-plate, vibration or ultrasonic welding. At the same rate, demands on the quality of the weld, the flexibility of the production system and on processing speed have increased.

Traditionally, diode lasers were employed for plastic welding with flat-top beam profiles. With the advent of fiber lasers with excellent beam quality, the possibility to modify and optimize the beam profile by beam-shaping elements has opened.

Diffractive optical elements (DOE) can play a crucial role in optimizing the laser intensity profile towards the optimal M-shape beam for enhanced weld seam quality. We present results on significantly improved weld seam width constancy and enlarged process windows compared to Gaussian or flat-top beam profiles. Configurations in which the laser beam diameter and shape can be adapted and optimized without changing or aligning the laser, fiber-optic cable or optical head are shown.

In this work we have investigated the use of laser sintering of different ink-jet printed nano-particle links (NPIs) on paper substrates. Laser sintering is shown to offer a fast and non-destructive way to produce paper based printed electronics. A continuous wave fiber laser source at 1064 nm is used and evaluated in combination with a galvo-scanning mirror system. A conductivity in order of 2.16 _* 10⁷ S/m is reached for the silver NPI structures corresponding to nearly 35 % conductivity compared to that of bulk silver and this is achieved without any observable damage to the paper substrate.

With roll-to-roll processes, millions of reproductions (e.g. RFID-antennas or Fresnel-lenses) can be produced in a fast and economical way. The processing of replica tools for such printing and embossing applications requires in many cases sub-μm and μm-structures. Ultra-short pulse lasers with ps- and fs-pulse durations and in single pulse or burst mode operation are appropriate tools to generate this micro- or nanostructures. In recent years the ongoing development of these laser sources and of fast beam delivery optics allows higher ablation rates combined with a superior quality for several materials like copper and brass as well as glass and dielectrics.

Different ps-laser systems at 10 ps with up to 80 W at 1064 nm with a pulse repetition rate up to 8 MHz and energies up to 50 μJ (at lower repetition rate) have been used in a micro-engraving system for large cylindrical workpieces. This setup allows the micro structuring of cylinder surfaces as well as the processing of thin film substrate sheets up to a thickness of approximately 300 μm. Dimensions up to 7 m face length and circumferences up to 1,3 m can be processed with an accuracy of about 1μm. A variety of metals have been investigated by structuring 2D and 3D elements. The process is nearly melt-free, but the resulting surface structure of the ablated zone depends on the sort of metal. The high fluencies also enable the engraving of transparent materials which allow a much faster micro processing speed compared to metals. This work shows examples of micro-structuring melamine-resin coated cylinder surfaces and hybrid materials.

Progress towards 3-D subsurface structuring of polymers using femtosecond lasers is presented. Highly localised refractive index changes can be generated deep in transparent optical polymers without pre doping for photosensitisation or post processing by annealing. Understanding the writing conditions surpasses the limitations of materials, dimensions and chemistry, to facilitate unique structures entirely formed by laser-polymeric interactions to overcome materials, dimensional, refractive index and wavelength constraints.. Numerical aperture, fluence, temporal pulselength, wavelength and incident polarisation are important parameters to be considered, in achieving the desired inscription. Non-linear aspects of multiphoton absorption, plasma generation, filamentation and effects of incident polarisation on the writing conditions will be presented.

Direct Laser Interference Patterning (DLIP) technique were employed in the development of optical biosensors based on Biophotonic Sensing Cells (BICELLs). Fabrication was carried out by laser patterning of cross-linked SU-8 thin films deposited both on silicon (Si) and glass substrates. Different photonic structures were developed in order to prove their biosensing suitability by mean of and indirect immunoassay of Bovine Serum Albumin (BSA)/anti-BSA, demonstrating that patterned areas improve the sensitivity in comparison with non-patterned sensing surfaces.

Direct Laser Interference Patterning (DLIP) has shown to be a fabrication technology capable of producing large area periodic surface patterns on almost any kind of material. The produced structures have been used in the past to provide surfaces with new enhanced properties. On the other hand, the industrial use of this technology is still at the beginning due to the lack of appropriate and affordable systems, especially for small and medium enterprises. In this paper, the use of DLIP for the fabrication of periodic structures using different structuring strategies and optical concepts is discussed. Different technological challenges are addressed.

The demand of highly efficient transparent electrodes without the use of rare earth materials such as indium requires a new generation of thin metallic films with both high transparency and electrical conductivity. For this purpose, Direct Laser interference Patterning was used to fabricate periodic hole-like surface patterns on thin metallic films in order to improve their optical transparency by selective laser ablation of the material and at the same time keeping the electrical properties at an acceptable level. Metallic films consisting of aluminum and copper with film thicknesses ranging between 5 and 40 nm were deposited on glass substrates and treated with nanosecond and picosecond pulse laser system. In order to analyze the processability of the films, the laser ablation threshold for each material as function of the layer thickness and pulse duration was firstly determined. After analyzing these initial experiments, the samples were structured with a 1.7 μm spatial period hole-like-pattern using three beam direct laser interference patterning. The structural quality of the fabricated structures was analyzed as function laser energy density (laser fluence) using scanning electron microscopy (SEM), atom force microscopy (AFM). Finally, optical and electrical properties of the films were characterized using optical spectroscopy, as well as surface impedance measurements.

Recently a parametric decay model was proposed in order to foresee LIPSS interspaces, and experimental results are in reasonable agreement. To confirm the possibility assumed by the model of pre-formed plasma generation, Ti surface was irradiated by a femtosecond (fs) laser beam composed by double fs pulses, with a fixed delay of 160 fs. The fluence of the first pulse (FPP), responsible for surface plasma formation, was varied in the range 10-50 mJ cm^-2 and always kept below the LIPSS formation threshold fluence (FLIPSS) of Ti for 50-single-shots exposure. The fluence of the delayed pulse (FLP), responsible for LIPSS formation, was varied in the range 60-150 mJ cm^-2 and always kept above FLIPSS. Regardless the specific fluence FLP of the delayed pulse, the interspace of the grating structures increases with the increase of FPP, that is the increase of the surface plasma density. This tendency suggests that a variation of the surface plasma density, due to a variation of FPP, actually leads to a modification of the grating features, highlighting the driving role of the first pulse in LIPSS formation. Moreover, we observed that the LIPSS periodicities after double pulse exposures are in quite good agreement with data on LIPSS periodicities after single 160 fs pulse irradiations on Ti surface and with the curve predicted by the parametric decay model. This experimental result suggests that the preformed plasma might be produced in the rising edge of the temporal profile of the laser pulse.

High-intensity, blue LEDs have attracted interest because of their wide applications. Dicing method using tightly focused ultra-fast laser beam inside the sapphire substrate is one of the remarkable processing method in terms of high yield and LED performance. In this paper, we would like to introduce the polarization controlled laser processing technique in which laser beam is focused tightly inside the sapphire substrate. The morphology of a cut line can be controlled by changing the direction of laser polarization to an orientation at of the substrate. We, moreover, found that the crack inside the sapphire substrate can be elongated by using the double pulse train for 20 % larger than the single pulse when the pulse interval was 20 nsec. The crack was fabricated effectively by shorter pulse interval.

Micro- and nanostructures exhibit a growing commercial interest where a fast, cost-effective, and large-area production is attainable. Laser methods have a great potential for the easy fabrication of surface structures into flexible polymer foils like polyimide (PI). In this study two different concepts for the structuring of polymer foils using a KrF excimer laser were tested and compared: the laser-induced ablation and the laser-induced shock wave structuring. The direct front side laser irradiation of these polymers allows the fabrication of different surface structures. For example: The low laser fluence treatment of PI results in nano-sized cone structures where the cone density can be controlled by the laser parameters. This allows inter alia the laser fabrication of microscopic QR code and high-resolution grey-tone images. Furthermore, the laser treatment of the front side of the polymer foil allows the rear side structuring due to a laserinduced shock wave. The resultant surface structures were analysed by optical and scanning electron microscopy (SEM) as well as white light interferometry (WLI).

A novel method of direct growth of patterned graphene on SiC(0001) surfaces using KrF excimer-laser irradiation is proposed. It relies on the local sublimation of Si atoms within the irradiated area to induce graphene growth through a rearrangement of surplus carbon. A laser with a wavelength of 248 nm was pulsed with a duration of 55 ns and a repetition rate of 100 Hz that was used to graphene forming. Following laser irradiation of 1.2 J/cm² (5000 shots) under an Ar atmosphere (500 Pa), characteristic graphene peaks were observed in the Raman spectra of the irradiated area, thereby confirming the formation of graphene. The ratio between the graphene bands in the Raman spectra was used to estimate the grain size at 61.3 nm. Through high-resolution transmission electron microscopy, it was confirmed that two layers of graphene were indeed formed in the laser irradiated region. Using this knowledge, we also demonstrate that line-and-space (LandS) graphene patterns with a pitch of 8 μm can be directly formed using our method.

In Lithium-Ion battery production many different active material coatings are used to serve the individual needs of the final product. Furthermore laser processing becomes the method of choice in the production to allow a maximum degree of freedom and reduce tooling costs. The used electrode coatings and its different components highly influence the laser process and its results in terms of quality and efficiency. To achieve a better understanding of the ablation mechanism high speed video recording was used to allow a more detailed observation of the cutting and ablation mechanism, respectively. Based on these insights an analytical model was created and verified by time resolved shadowgraph imaging and experimental determined laser ablation thresholds.

Lithium-ion batteries require an increase in cell life-time as well as an improvement in cycle stability in order to be used as energy storage systems, e.g. for stationary devices or electric vehicles. Nowadays, several cathode materials such as Li(NiMnCo)O₂ (NMC) are under intense investigation to enhanced cell cycling behavior by simultaneously providing reasonable costs. Previous studies have shown that processing of three-dimensional (3D) micro-features in electrodes using nanosecond laser radiation further increases the active surface area and therefore, the lithium-ion diffusion cell kinetics. Within this study, NMC cathodes were prepared by tape-casting and laser-structured using nanosecond laser radiation. Furthermore, laser-induced breakdown spectroscopy (LIBS) was used in a first experimental attempt to analyze the lithium distribution in unstructured NMC cathodes at different state-of-charges (SOC). LIBS will be applied to laser-structured cathodes in order to investigate the lithium distribution at different SOC. The results will be compared to those obtained for unstructured electrodes to examine advantages of 3D micro-structures with respect to lithium-ion diffusion kinetics.

Strong efforts are currently undertaken in order to further improve the electrochemical performance of high energy lithium-ion batteries containing thick composite electrode materials. The properties of these electrode materials such as active surface area, film thickness, and film porosity strongly impact the cell life-time and cycling stability. A rather new approach is to generate hierarchical architectures into cathode materials by laser direct ablation as well as by laserassisted formation of self-organized structures. It could be shown that appropriate surface structures can lead to a significant improvement of lithium-ion diffusion kinetics leading to higher specific capacities at high charging and discharging currents.

In this paper, the formation of self-organized conical structures in intercalation materials such as LiCoO₂ and LiNi_1/3Mn_1/3Co_1/3O₂ is investigated in detail. For this purpose, the cathode materials are exposed to excimer laser radiation with wavelengths of 248 nm and 193 nm leading to cone structures with outer dimensions in the micrometer range. The process of cone formation is investigated using laser ablation inductively coupled plasma mass spectrometry and laser-induced breakdown spectroscopy (LIBS). Cone formation can be initiated for laser fluences up to 3 J/cm² while selective removal of lithium was observed to be one of the key issues for starting the cone formation process. It could be shown that material re-deposition supports the cone-growth process leading to a low loss of active material. Besides the cone formation process, laser-induced chemical surface modification will be analysed by LIBS.

High capacity Li-ion batteries are composed of alternating stacked cathode and anode layers with thin separator membranes in between for preventing internal shorting. Such batteries can suffer from insufficient cell reliability, safety and electrochemical performance due to poor liquid electrolyte wetting properties. Within the electrolyte filling process, homogeneous wetting of cathode, separator and anode layers is strongly requested due to the fact that insufficient electrolyte wetting of battery components can cause limited capacity under challenging operation or even battery failure. The capacity of the battery is known to be limited by the quantity of wetting of the electrode and separator layers. Therefore, laser structuring processes have recently been developed for forming capillary micro-structures into cathode and anode layers leading to improved wetting properties. Additionally, many efforts have been undertaken to enhance the wettability and safety issues of separator layers, e.g. by applying thin coatings to polymeric base materials. In this paper, we present a rather new approach for ultrafast femtosecond laser patterning of surface coated separator layers. Laser patterning allows the formation of micro-vias and micro-channel structures into thin separator membranes. Liquid electrolyte wetting properties were investigated before and after laser treatment. The electrochemical cyclability of batteries with unstructured and laser-structured separators was tested in order to determine an optimal combination with respect to separator material, functional coating and laser-induced surface topography.

In this work, a detailed study on the effect of ambient and beam profile in the crystallization of a-Si thin films is presented. A Q switched Nd³⁺: YAG laser, with the wavelength 532 nm and pulse duration 6 ns FWHM is considered. Laser annealing is performed with a Gaussian beam and flat-top beam profile on 400 nm and 1000 nm thick a-Si films deposited on c-Si substrate. In order to induce annealing along with texturing of surface, laser beam overlap technique with a 90% spot overlapping is used. Experiments are perfomed in air and in water ambience. XRD peaks corresponding to poly-silicon thin film are observed with the Nd³⁺:YAG laser treatment. Raman spectroscopy analysis confirms the formation of poly crystalline films. Changes in surface morphology is observed using Scanning Electron Microscope. In theoretical simulation, thermal modeling is used and nanosecond laser induced annealing at a longer wavelength has been found to be suitable for crystallization of thick amorphous silicon films but results in heating the substrate.

A groove-shaped array with average 25 μm interval, 25 μm wall thickness, 75 μm depth and a columnar array with average 30 μm side length, 25 μm interval, 43 μm depth are processed by 1064 nm picosecond laser on polytetrafluoroethylene (PTFE) surface at room temperature. The water contact angle of modified PTFE surface can reach 167^°, which show super hydrophobic surface of PTFE is prepared. It is observed super hydrophobic surface reflects metal luster underwater through the glassware when super hydrophobic PTFE entirely immerses in pure water. The experiment conducts super hydrophobic surface will enhance intensity of reflection of visible light underwater, which is due to total internal reflection of super hydrophobic surface und erwater.

Laser processing of thin glass has proven problematic due to the inefficient coupling of optical energy into glass and the difficulty achieving an economical processing speed while maintaining cut quality. Laser glass processing is pertinent to touch screen display, microfluidic, microoptic and photovoltaic applications. The results of the laser scribing of 110 μm thick alkali free glass with various laser sources are presented. The laser sources include a CO_₂ laser, nanosecond UV laser and femtosecond IR laser. The contrasting absorption mechanisms are discussed. Cut quality and processing speed are characterised using SEM and optical microscopy techniques. Alternative laser techniques for thin glass processing are also considered.

Direct-write laser processing has been demonstrated to be capable of both surface patterning of micro- and nanoscale structures on polymer surfaces without significant modification of the surface chemistry or optical transmission of the laser processed area. In this work, the creation of microchannels via direct-write laser processing of 188 μm thickness cyclic olefin polymers is demonstrated, along with a route towards channel functionalization. Cyclic olefin polymers (COP) are an emerging class of polymers noted for their high chemical resistance, biocompatibility and higher optical transparency when compared to other common polymers. These properties make them excellent substrates for the fabrication of microfluidic devices. This paper presents the first investigation into infrared laser processing of COP using a 1064 nm Nd:YAG laser. Scanning electron microscopy and Raman spectroscopy were utilized to investigate the morphology and composition of these laser textured surfaces.

A route for functionalization of these substrates for chemical and biological speciation and separation was examined using carbon nanoparticles. The nanoparticles were produced using pulsed laser ablation in liquid (PLAL) which has been reported as a fast and adaptable method for nanoparticle production. The nanoparticles produced were using transmission electron microscopy while the coating of substrates with these CNPs was examined using SEM. These results are discussed in the context of development of a new route for achieving surfaces optimized for microfluidicbased separations and speciation.

Indium-tin-oxide (ITO) is a widely used electrode material for liquid crystal cell applications because of its transparency in the visible spectral range and its high electrical conductivity. Important examples of applications are displays and optical phase modulators. We report on subwavelength periodic structuring and precise laser cutting of 150 nm thick indium-tin-oxide films on glass substrates, which were deposited by magnetron reactive DC-sputtering from an indiumtin target in a low-pressure oxygen atmosphere. In order to obtain nanostructured electrodes laser-induced periodic surface structures with a period of approximately 100 nm were generated using tightly focused high-repetition rate sub-15 femtosecond pulsed Ti:sapphire laser light, which was scanned across the sample by galvanometric mirrors. Three-dimensional spacers were produced by multiphoton photopolymerization in ma-N 2410 negative-tone photoresist spin-coated on top of the ITO layers. The nanostructured electrodes were aligned in parallel to set up an electrically switchable nematic liquid crystal cell.

The emission properties of double-pulse (DP) over single-pulse (SP) femtosecond laser breakdown spectroscopy (fs- LIBS) of polymethyl methacrylate (PMMA) were investigated. The signal enhancements in the DP fs-LIBS strongly depended on the DP delay and were influenced by the type of emission particles. Intensity enhancement of emission lines increased in the sequence of molecules, neutral atoms, and ions. Electron density and temperature were reported to characterize the plasmas. Both the electron density and plasma temperature exhibit similar variation trajectories with respect to the DP delay and feature a distinct increase at an optimal DP delay of ~80 ps, indicating reheating of preproduced plume is responsible for the emission enhancement. The dependence of the signal emission on laser energy was also studied, showing the emission intensity was linear to the pulse energy. However, the signal enhancement was nonlinear to the pulse energy, suggesting that the signal enhancement was related to the energy coupling efficiency of second pulse to the first pulse generated plume.

We propose the fabrication of two types high performance texturized antireflective structures on crystalline (100) silicon (c-Si) surface by hybrid picosecond laser scanning irradiation followed by chemical corrosion. The design and the fabrication with high controllable performance were studied. The hybrid method includes 1064 nm picosecond (ps) laser scanning to form micro-hole array and subsequently short-time alkaline corrosion. After ps laser processing, there is little reconsolidation and heat affect zone on the silicon surface, which is beneficial to achieve the precise chemical corrosion effect. Depending on the laser scanning intervals, scanning times and chemical corrosion time, a variety of surface texture morphologies, even a special micro-nano hierarchical structure in which finer nano-structures formed in the micro units of the texture, were achieved. Observing with SEM, the average diameter of the micro-holes in the micro-nano hierarchica is 25~30 μm, while the average size of the nano-level ladder-like structures on the micro-hole wall is from dozens to hundreds of nanometers. Comparing to the traditional laser texturing techniques for c-Si solar cell, the whole laser processing was carried out in an open air ambient without using etch mask and SF₆/O₂ plasma. The results show the reflectance value of the fabricated c-Si surfaces can reach as low as 6% (400 nm~1000 nm). This is a potential method for economical antireflective structures fabrication which is ideal for using in the high-efficiency silicon-based photoelectronic devices.

Nanostructuring of dielectric surfaces has a widespread field of applications. In this work the recently introduced laser method validates this novel concept for complex nanostructuring of dielectric surfaces. This concept combines the mechanism of self-assembly of metal films due to laser irradiation with the concept of laser-assisted transfer of these patterns into the underlying material. The present work focuses on pattern formation in fused silica near the border of the laser spot, where distorted nested ring-like patterns were found in contrast to concentric ring patterns at homogeneous laser irradiation. For the experiments a lateral homogeneous spot of a KrF excimer laser (λ = 248 nm) and a Gaussian beam Yb fiber laser (λ = 1064 nm) was used for irradiation of a thin chromium layer onto fused silica resulting in the formation of different ring structures into the fused silica surface. The obtained structures were analysed by AFM and SEM. It is found that the mechanism comprises laser-induced metal film melting, contraction of the molten metal, and successive transfer of the metal hole geometry to the fused silica. Simulations taking into account the heat and the Navier-Stokes equations were compared with the experimental results. A good agreement of simulation results with experimental data was found. These first results demonstrate that the variation of the laser beam profile allows the local control of the melt dynamics which causes changes of the shape and the size of the ring patterns. Hence, a light-controlled self-assembly is feasible.

Microstructuring of Polymer Optical Fibers-POF through surface modification with UV excimer laser radiation has been performed and studied. The laser modified surface cavities on fibers act as material receptors of exact volume allowing highly controllable and repeatable structures. The effect of Laser writing conditions on different etching characteristics of cladding and core materials of the fibres are presented. Ablated structures on the fibres are examined for optimised sensors' response characteristics. As a case study humidity and ammonia sensors are demonstrated by employing sensitive block copolymer materials on suitably micromachined segments of fibres.