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Rapid manufacturing of functionalized polymers enable a cost-efficient method for many applications in the biological, and medical sector. Laser structuring techniques differ for fast fabrication processes of thermoplastics. Here we report on direct UV laser ablation of polystyrene and polydimethylsiloxane to control wettability and bio-compatibility. For this purpose contact angle measurements and L929 cell growth experiments were performed as function of laser and process parameters. This work also describes the potential of laser-assisted hot embossing which has been introduced to replicate pre-fabricated micro- and nano-sized structures onto polymers proving it to be a cost-efficient and flexible method for surface functionalization. Therefore, pre-fabricated laser-induced periodic surface structures have been manufactured as mould inserts using ultrafast laser radiation near the ablation threshold. These mould inserts can also be made of nickel, silicon or glass proving laser-assisted hot embossing to be a versatile tool for the functionalization of thermoplastics and meet the requirements for modern manufacturing with regard to quality and production flexibility.

In this study, the effect of laser induced periodic patterning of α-β titanium alloy (Ti-6Al-4V) developed by excimer laser (ArF, with a laser fluence of 2.4 J/cm2, a laser pulse repetition rate of 200 Hz and 50 laser pulses) and Fiber laser (using a power of 5 W, frequency of 80 kHz, scan speed of 800 mm/s and 2 times scanning) on its microstructure and corrosion behaviour have been investigated. The microstructure of the patterned surface shows a significant refinement of grains with the presence of α and β. A very low mass fraction of TiO2 was noticed when patterning was performed using ArF laser. A significant improvement in total surface energy (from 37 mN/m for Ti-6Al-4V to 41 mN/m for ArF laser patterned surface and 40 mN/m for Fiber laser patterned surface) and polar energy (from 11 mN/m for Ti-6Al-4V to 26 mN/m for ArF laser patterned surface and 24 mN/m for Fiber laser patterned surface) have been observed. Corrosion rate was reduced due to laser patterning (from 6.12 mm/year for as-received Ti-6Al-4V to 2.17 × 10−2 mm/year for ArF laser patterned and 1.68 × 10−2 mm/year for Fiber laser patterned Ti-6Al-4V surfaces). Laser surface patterning improved apatite deposition from 15% area coverage for Ti-6Al-4V to 34% and 33% area coverage for ArF and Fiber laser patterned surfaces, respectively.

Although there have been numerous attempts to define how different laser polishing parameters affect the generated surface roughness, there has been no detailed investigation of how their effects can be combined to optimize the process. This paper applies statistical analysis to model and predict the resulting surface roughness for laser post-processing of components made of Ti-6Al-4V and produced by laser powder bed fusion. This model is based on analysis of a wide ranging experimental programme investigating how the interaction of the governing parameters, i.e., laser power, number of repetitions, axial feed rate, scanning speed, and focal position, affected surface roughness. The experimental programme was the result of a robust Design of Experiments analysis and experimental analysis using ANOVA. It is expected that the outcomes will contribute towards the understanding of how the governing parameters influence the laser polishing process and final surface roughness, and would be a tool for optimizing their selection. The results of the ANOVA (analysis of variance) revealed that the most significant parameters are scanning speed followed by laser power and then axial feed rate. In addition, a clear tendency for the estimated Ra to decrease with the increase in laser power at lower values of axial feed rate and of scanning speed, and a focal position in the region of 2 mm. It is noted that the process parameters were varied over wide ranges, including extreme values, which made it difficult to accurately model the dependent variable over the full range of experimental trials.

Laser polishing of metals consists of irradiating the part’s surface with a laser beam, thus generating a molten layer that is redistributed and resolidified to create a surface with reduced roughness. However, the process is also characterized by an instantaneously formation of heat-affected zones with consequent microstructural changes that influences the mechanical properties. In order to understand the microstructural evolution during laser polishing of Ti-6Al-4V laser-based powder bed fusion samples, a thermal model is applied in the current study to predict the dimensions of the melted zones and the heat-affected areas. Furthermore, the results obtained through the simulations are discussed and compared to the experimental data, thereby establishing the validity of the process models. Finally, the experimental studies also include the evaluation of the material hardness and residual stresses after laser polishing.

Laser processing technologies for micro-/nanostructuring of electrode materials have a great potential in improving the electrochemical performance and operational lifetime of lithium-ion cells. Different types of laser structuring were used on different surfaces such as metallic current collectors and thin or thick film electrodes. For thin metallic current collector foils, at anode and cathode sides, the self-organized structuring by laser-induced periodical surface structures and laser interference methods were successfully applied for improving electrode film adhesion and cell impedance. For thin and thick film electrode layers direct laser ablation with structure sizes down to the micrometer range and high aspect ratios were found most powerful in order to create three-dimensional (3D) cell architectures with benefits regarding cell performance and a homogenous wetting of composite electrodes with liquid electrolyte. A huge impact of laser formed 3D batteries regarding capacity retention and cell lifetime at high charging and discharging rates was detected. The impact on diffusion kinetics of laser structured 3D electrodes was studied using classical methods such galvanostatic intermittent titration technique and cyclic voltammetry. A further improvement of 3D battery performance due to an operation in high potential regime and for advanced high energy silicon anode material was achieved by joining of laser structuring and thin-film passivation either of active particles before laser patterning or by passivating of complete 3D electrodes after laser processing. Finally, laser-induced breakdown spectroscopy will be presented as a powerful tool for elemental mapping of entire 2D and 3D electrodes. The impact of 3D architectures on lithium distribution and chemical degradation processes in 2D batteries was investigated and analyzed.

Highlights • A prototype device combining a focused ion beam and a femtosecond laser is presented. • A case study of fabricating cantilevers for micro-mechanical tests into cold rolled tungsten foils was performed. • No coarsening of the ultra-fine grained microstructure was found after femtosecond laser ablation. • A sample array consisting of 100 cantilevers with a dimension of 420 ×60 ×25 μm3 was processed in only half an hour. The focused ion beam technique has become a standard tool for micro-mechanical sample preparation in the last decade due to its high precision and general applicability in material removal. Besides disadvantages such as possible ion damage and high operation costs especially the characteristically small removal rates represent a bottleneck for this application. In contrast, femtosecond lasers provide material removal rates orders of magnitude higher, with small or ideally without thermal impact on the surrounding material. Hence, a combination of these two methods offers an ideal tool for time-efficient, micrometer-sized sample preparation. A prototype implementing this idea is presented here in combination with a case study. Cantilevers with a length of several hundred micrometers were machined into 25 μm, 50 μm and 100 μm thick, cold rolled tungsten foils. Scanning electron microscopy analyses reveal the influence of laser parameters and different scanning routines on the resulting sample quality and the effect of the laser pulse length (femtoseconds versus nanoseconds) on the ultra-fine grained microstructure. Finally, the performance for unprecedented rapid sample preparation is demonstrated with a sample array consisting of 100 cantilevers with a dimension of 420 ×60 ×25 μm3 processed in only half an hour, opening completely new testing possibilities.

The present study concerns a detailed understanding of wear, corrosion and bio-activity behaviors of laser surface textured titanium alloy (Ti–6Al–4V) with line and dimple geometry developed by ArF excimer laser at a wavelength of 193 nm with a pulse length of 5 ns. The mechanical properties of the surface have been evaluated by measuring nano-hardness and wear resistance. The corrosion resistance property has also been evaluated in Hank's solution. The effect of laser surface texturing on bioactivity and cell attachment has also been studied. Laser surface texturing led to an increase in nano-hardness to a value of 4–6 GPa as compared to 2 GPa of the as-received Ti–6Al–4V. Furthermore, laser modified surfaces showed a significant increase in wear resistance and a marginal change in corrosion resistance. Textured surface shows a significant improvement in bioactivity in terms of calcium phosphate deposition rate in Hank's solution. XTT result shows, comparable cell viability of laser textured Ti–6Al–4V as that of as received Ti-alloy. Cell attachment study shows a reduced cell density in textured surface with a maximum reduction in dimple textured surface. Cells aligned themselves along the direction of texturing in linear textured surface.

Laser structuring of battery materials such as electrodes, current collectors, and separator materials becomes more and more a versatile tool for a flexible designing of battery performance with regard to high rate capability, reduced impedance and diffusion over-potential, enhanced battery lifetime, and a tremendous improvement of electrode wetting with liquid electrolyte. Especially structuring of thick film composite electrodes with film thickness up to 300 µm is of great interest for combining high energy and high power applications. Laser ablation by using ultrafast laser radiation ensures a high aspect ratio structuring without damaging or modifying the material properties of the active material, inactive compounds, and current collector. Thermal induced material modification and laser-induced material splatter on top of the electrode surfaces have been so far a major problem by using conventional nanosecond lasers. However, in recent years high power OEM-type ultrafast laser beam sources became available for industrial production. Those lasers provide powers of several 100 W up to the kW-regime with repetition rates of several tenfold MHz, which makes high-speed parallel material processing feasible. Finally, after introducing high-speed nanosecond laser cutting of electrodes almost one decade ago, we forecast that with regard to recent technical approaches quite soon high-speed electrode ultrafast laser structuring will entering the pilot line level. For this purpose, at KIT, parallel processing of cathode and anode materials with large foot print area is being developed in a roll-to-roll (R2R) environment in order to meet the process speed requirements of cell production. Furthermore, we are developing thick film electrode concepts for anodes made of graphite and silicon-graphite and cathodes based on Lithium-Nickel-Manganese-Cobalt-Oxide (NMC) with varying nickel content and water-based slurries. Electrode thicknesses in the range of 100-300 µm were synthesized for subsequent laser processing, cell assembly, and electrochemical characterization such as galvanostatic measurements, galvanostatic intermittent titration technique, cyclic voltammetry, and electrochemical impedance spectroscopy. Large area laser structuring in R2R environment for generation of three-dimensional (3D) electrode architectures with increased active surface area, enhanced mechanical integrity for high energy materials such as Si-graphite anodes and an overall boost in electrochemical performances on pouch cell level will be presented. Laser-induced breakdown spectroscopy (LIBS) was applied for elemental mapping of entire electrodes in order to characterize binder migration in ultra-thick film electrodes, and in post-mortem studies to evaluate degradation processes in unstructured, damaged, and structured thick film electrodes with large footprint (pouch cell level). Post-mortem studies show that significant chemical modifications across from electrodes with macroscopic surface defects could be detected while laser structured electrodes provide less inhomogeneity in lithium distribution in comparison to cells with unstructured electrodes. Furthermore, an inhomogeneity in mechanical load on cells could be identified as a main reason for cell degradation. LIBS is presented as a perfect tool to rapidly characterize and identify starting points for cell degradation on coin cell and pouch cell level. In summary, ultrafast laser structuring of electrodes provides a new manufacturing tool for next generation battery production to overcome current limitations in electrode design and cell performances.

This chapter reviews the use of laser-based material processing techniques, such as pulsed laser deposition (PLD), laser-induced forward transfer (LIFT), and material processing via three-dimentional laser structuring (LS) and laser annealing (LA) techniques for energy storage applications. It also reviews the recent work using these laser processing techniques for the fabrication of micropower sources and lessons learned from the characterization of their electrochemical properties. The chapter shows that laser processing techniques are ideally suited to prototype and fabricate these types of electrochemical energy storage components for hybrid micropower systems. It discusses PLD techniques for thin-film microbatteries, LIFT techniques for ultracapacitors and thick-film microbatteries, LA for controlling the grain size and crystalline phase of thin-film electrodes, and LS processes for modifying active electrode materials for Lithium ion microbatteries. The chapter concludes with a discussion of challenges and future directions offered by the use of lasers to develop the next generation of microbatteries.

The combination of additive manufacturing (AM) and subsequent laser polishing is a technical approach with high flexibility in comparison to conventional processes. AM parts often present the need of post-processing due to surfaces with roughness higher than the admissible for most applications. The laser polishing consists in ablation and melting of a small amount of material, through laser irradiation, which is redistributed to create a surface with low roughness and probably new functionalities. Besides the flexibility, laser polishing presents high processing speed and capability for localized surface treatment. In this study, the resulting characteristics of AM parts irradiated by laser sources with different technical features are investigated and discussed. The parameters applied were the pulse duration, scan speed, repetition rate and average laser power. To evaluate the impact of laser processing on the material the microstructure and surface roughness were analysed and correlated to the process parameters.

Organic semiconductor distributed feedback (DFB) lasers are of interest as external or chip-integrated excitation sources in the visible spectral range for miniaturized Raman-on-chip biomolecular detection systems. However, the inherently limited excitation power of such lasers as well as oftentimes low analyte concentrations requires efficient Raman detection schemes. We present an approach using surface-enhanced Raman scattering (SERS) substrates, which has the potential to significantly improve the sensitivity of on-chip Raman detection systems. Instead of lithographically fabricated Au/Ag-coated periodic nanostructures on Si/SiO2 wafers, which can provide large SERS enhancements but are expensive and time-consuming to fabricate, we use low-cost and large-area SERS substrates made via laser-assisted nanoreplication. These substrates comprise gold-coated cyclic olefin copolymer (COC) nanopillar arrays, which show an estimated SERS enhancement factor of up to ∼ 10(7). The effect of the nanopillar diameter (60-260 nm) and interpillar spacing (10-190 nm) on the local electromagnetic field enhancement is studied by finite-difference-time-domain (FDTD) modeling. The favorable SERS detection capability of this setup is verified by using rhodamine 6G and adenosine as analytes and an organic semiconductor DFB laser with an emission wavelength of 631.4 nm as the external fiber-coupled excitation source.

Lithium nickel manganese cobalt oxide (Li(Ni1/3Mn1/3Co1/3)O2, NMC) thick film electrodes were manufactured by using the doctor-blade technique (tape-casting). Ultrafast laser-structuring was performed in order to improve the electrochemical performance. For this purpose, three-dimensional (3D) micro-structures such as free standing micropillars were generated in NMC cathodes by using femtosecond laser ablation. Laser-induced breakdown spectroscopy (LIBS) was used for post-mortem investigation of the lithium distribution of unstructured and femtosecond laser-structured NMC electrodes. For achieving a variable State-of-Health (SoH), both types of electrodes were electrochemically cycled. LIBS calibration was performed based on NMC electrodes with defined lithium amount. Those samples were produced by titration technique in a voltage window of 3.0 V - 5.0 V. Elemental mapping and elemental depth-profiling of lithium with a lateral resolution of 100 μm were applied in order to characterize the whole electrode surface. The main goal is to develop an optimized 3D cell design with improved electrochemical properties which can be correlated to a characteristic lithium distribution along 3D micro-structures at different SoH.

Laser moulding is a new polymer moulding process developed and enhanced for the fabrication of micro- and nanostructured components at the Karlsruhe Institute of Technology. This report describes the potential offering by laser moulding. Besides known polymer moulding techniques like injection moulding or hot embossing, laser moulding can also achieve significant advantages compared to the existing technologies. Assisted by a high power diode laser radiation (wavelength 940 nm) a micro- or nanostructure of a mould will be transferred to a thermoplastic polymer product. With regard to the efficiency of production, micro- and nanostructures should be fast, competitive and flexibly transferred to a thermoplastic polymer surface. For this purpose the moulding by laser radiation provides ideal conditions, advantages and a variety of applications. These conditions, advantages and applications were tested by using different micro- or nanostructured mould inserts made of silicon, glass or nickel as well as different thermoplastic polymers which were used for replication such as, polymethylmethacrylate, polystyrene, cyclo-olefin copolymers and polyether ketones. The new technical approach and his first results will be described in this report.

Porous LiMn 2 O 4 thick-film cathodes for Li-ion microbatteries are realized by laser-printing. The porous structure of the printed composite cathode consisting of active powder, binder, carbon black and graphite enables ionic and electronic transport through 50–60 μm thick electrodes due to its high intrinsic active surface area. In order to further improve the cycle stability and capacity retention of the laser-printed thick-film cathodes for discharging rates up to 1 C, laser-printed thick films are first calendered in a press and then structured using ultrafast femtosecond-laser radiation in order to form three-dimensional (3D) cathode architectures. It is shown that calendered/laser structured cathodes in the form of rectangular 3D grids exhibit discharge capacity retention of 68% at a 1 C rate, while calendered but unstructured cathodes retain only about 45% of their initial capacity at the same discharge rate. Overall, the improved discharge capacity retention and reduced degradation during later cycles can be attributed to the combination of increased electrical contact with shortened Li-ion pathways.

The integration of organic semiconductor distributed feedback (DFB) laser sources into all-polymer chips is promising for biomedical or chemical analysis. However{,} the fabrication of DFB corrugations is often expensive and time-consuming. Here{,} we apply the method of laser-assisted replication using a near-infrared diode laser beam to efficiently fabricate inexpensive poly(methyl methacrylate) (PMMA) chips with spatially localized organic DFB laser pixels. This time-saving fabrication process enables a pre-defined positioning of nanoscale corrugations on the chip and a simultaneous generation of nanoscale gratings for organic edge-emitting laser pixels next to microscale waveguide structures. A single chip of size 30 mm [times] 30 mm can be processed within 5 min. Laser-assisted replication allows for the subsequent addition of further nanostructures without a negative impact on the existing photonic components. The minimum replication area can be defined as being as small as the diode laser beam focus spot size. To complete the fabrication process{,} we encapsulate the chip in PMMA using laser transmission welding.

Quantitative experiments of lithiation/delithiation rates were considered for a better understanding of electrochemical intercalation/deintercalation processes in laser structured thick film cathodes. Besides galvanostatic cycling for evaluation of specific discharge capacities, a suitable quantitative approach for determining the rate of Li-ion insertion in the active material and the rate of Li-ion transport in the electrolyte is expressed by chemical diffusion coefficient values. For this purpose, the galvanostatic intermittent titration technique has been involved. It could be shown that laser structured electrodes provide an enhanced chemical diffusion coefficient and an improved capacity retention at high charging and discharging rates.

NMC thick films were prepared by tape-casting and subsequent ultrafast laser-structuring. The lithium distribution in electrochemically cycled and unstructured or fs laser-structured NMC cathodes was investigated by using Laser-Induced Breakdown Spectroscopy (LIBS). The main goal is to develop an optimized three dimensional cell architecture with improved electrochemical properties based on studies of the homogeneity of the local State-of-Charge. LIBS experiments were carried out using a LIBS workstation equipped with a mode-locked diode pumped solid state Nd:YAG laser operating at a wavelength of 1063 nm. The element distribution was investigated using two different techniques: element mapping and element depth-profiling of the unstructured / fs laser-structured electrode surface. Results achieved from post-mortem studies using LIBS will be presented.

Industrial ultrafast lasers are a key component of many new industrial manufacturing processes. The virtually athermal nature of the laser–matter interaction process enables high-quality material processing for many different materials with feature size reaching into the nanometer scale. Advances in laser average power and beam-delivery technology have significantly improved the throughput and productivity of real-life industrial and medical applications. In this article, we present key examples of laser processing, including drilling, cutting, and surface processing. In particular, we describe how ultrafast lasers can improve vision in patients, extend battery lifetime, improve the efficiency of solar cells and infrared detectors, or be applied in the printing or microelectronics industries. These examples demonstrate how further developments rely on a combination of laser technology, beam handling and delivery, and laser–matter interaction processes.

Laser processes for cutting, modification and structuring of energy storage materials such as electrodes, separator materials and current collectors have a great potential in order to minimize the fabrication costs and to increase the performance and operational lifetime of high power lithium-ion-batteries applicable for stand-alone electric energy storage devices and electric vehicles. Laser direct patterning of battery materials enable a rather new technical approach in order to adjust 3D surface architectures and porosity of composite electrode materials such as LiCoO2, LiMn2O4, LiFePO4, Li(NiMnCo)O2, and Silicon. The architecture design, the increase of active surface area, and the porosity of electrodes or separator layers can be controlled by laser processes and it was shown that a huge impact on electrolyte wetting, lithium-ion diffusion kinetics, cell life-time and cycling stability can be achieved. In general, the ultrafast laser processing can be used for precise surface texturing of battery materials. Nevertheless, regarding cost-efficient production also nanosecond laser material processing can be successfully applied for selected types of energy storage materials. A new concept for an advanced battery manufacturing including laser materials processing is presented. For developing an optimized 3D architecture for high power composite thick film electrodes electrochemical analytics and post mortem analytics using laser-induced breakdown spectroscopy were performed. Based on mapping of lithium in composite electrodes, an analytical approach for studying chemical degradation in structured and unstructured lithium-ion batteries will be presented.

Thick-film electrodes (LiCoO2 cathode and carbon anode) are laser-printed onto metallic current collectors for fabricating Li-ion microbatteries. Microbatteries fabricated with these laser-printed thick-film electrodes demonstrate a significantly higher discharge capacity and power density than those made by sputter-deposited thin-film techniques. This increased performance is attributed to the porous structure of the laser-printed electrodes that allows improved ionic and electronic transport through the thick electrodes (up to ~100 µm) without a significant increase in internal resistance. Laser structuring process is applied to increase active surface area of the laser-printed LiCoO2 cathode films for improving cycle stability of microbatteries at high charging/discharging currents. Laser structuring parameters, including laser pulse number and laser fluence, are optimized for improving surface morphology of the films.

Recently microfluidic devices have emerged as a viable technology for the miniaturization of high throughput tools for analytical tasks related to structural biology such as screening of crystallization conditions and structural analysis. This work reports the manufacture of microfluidic chips in transparent thermoplastic polymers [poly(methylmethacrylate) (PMMA), and cyclic olefin copolymer (COC)] using two complementary technologies, injection moulding for the fabrication of the fluidic level and laser transmission welding for the sealing of the cover. A steel mould insert was produced by laser micro caving using a solid state laser radiation source (Nd:YAG, wavelength 1,064 nm). Fluidic chips of ~670 μm thickness comprising channels of 50 μm depth and width down to 50 μm were injection moulded in PMMA and COC. Joining of transparent thin cover film to the micro-injected fluidic level was performed by laser transmission welding using high power diode laser radiation (wavelength 940 nm) and an intermediate thin absorbing layer with a thickness of about several nanometers.

The crystallization of lithium manganese oxide thin films prepared by radio frequency magnetron sputtering on stainless steel substrates under 10 Pa argon pressure is demonstrated by a laser annealing technique. Laser annealing processes were developed as a function of annealing time and temperature with the objective to form an electrochemically active lithium manganese oxide cathode. It is demonstrated, that laser annealing with 940 nm diode laser radiation and an annealing time of 2000 s at 600 °C delivers appropriate parameters for formation of a crystalline spinel-like phase. Characteristic features of this phase could be detected via Raman spectroscopy, showing the characteristic main Raman band at 627 cm−1. Within cyclic voltammetric measurements, the two characteristic redox pairs for spinel lithium manganese oxide in the 4 V region could be detected, indicating that the film was well-crystallized and de-/intercalation processes were reversible. Raman post-analysis of a cycled cathode showed that the spinel-like structure was preserved within the cycling process but mechanical degradation effects such as film cracking were observed via scanning electron microscopy. Typical features for the formation of an additional surface reaction layer could be detected using X-ray photoelectron spectroscopy.

Experimental and numerical studies were conducted on the effects of the laser beam pulse shaping in the time domain on the quality of the welding seam in laser micro-welded AlMg3 with a thickness of 0.2 mm and 1 mm thick AlMg4.5 Mg foils, respectively. The pulse shaping was realized by a time sequence of three different rectangular pulses with different duration and power level. The first pulse was used to pre-heat the sample, welding occurred with the second pulse and the third pulse controlled the melt pool behavior. The power level and the duration of the single pulses were varied systematically and the resulting microstructure was analyzed by scanning electron microscope. The experiments were accompanied by numerical simulations based on a finite volume model which considers the transient heat flow, melt convection and the evolution of a gas capillary during the deep penetration welding process.

The rapid manufacturing of functional capillary electrophoresis (CE) chips made of polymethylmethacrylate (PMMA) based on laser processing technologies including structuring, surface functionalization and packaging was investigated. CO2 laser-assisted micro-patterning was demonstrated to have a great potential for the fabrication of micro-channel devices and the production capability of CO2 laser processes has been extended to micro-channels less than 30 μm width. A high reproducibility of micro-channel geometry was attained. The average deviation between the fabricated cross-section areas and the desired cross-section areas of micro-channels was better than 3%. The packaging of these micro-structured transparent polymers was successfully established with a laser transmission welding technique using high-power diode laser radiation. CE-chips with channel widths of 150, 100 and 50μm were fabricated and electro-analytically characterized. For this purpose high frequency contactless conductivity detection (CCD) was established. Detection of small ions (Li+, Na+, and K+) with concentrations down to 0.1 × 10−3 mol/l was performed. Analytical results compare well to those obtained by conventional hot embossing and thermal welding. Furthermore, UV-assisted surface modification can be used to influence the micro-analytical performance. The pattern qualities and analytical results show that laser-based technologies have a great potential for application in flexible and cost-efficient production of polymeric microfluidic devices.

An appropriate choice of laser and process parameters enables new approaches for the fabrication of polymeric lab-on-chip devices with integrated functionalities. We will present our current research results in laser-assisted modification of polystyrene (PS) with respect to the fabrication of polymer devices for cell culture applications. For this purpose laser micro-patterning of PS and subsequent surface functionalization was investigated as function of laser and process parameters. A high power ArF-excimer laser radiation source with a pulse length of 19 ns as well as a high repetition ArF-excimer laser source with a pulse length of 5 ns were used in order to study the influence of laser pulse length on laser-induced surface oxidation. The change in surface chemistry was characterized by X-ray photoelectron spectroscopy and contact angle measurements. The difference between laser-assisted modification versus UV-lamp assisted modification was investigated. A photolytic activation of specific areas of the polymer surface and subsequent oxidization in oxygen or ambient air leads to a chemically modified polymer surface bearing carboxylic acid groups well-suited for controlled competitive protein adsorption or protein immobilization. Finally, distinct areas for cell growth and adhesion are obtained.

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.

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 LiCoO 2 and LiNi 1/3 Mn 1/3 Co 1/3 O 2 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/cm 2 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.

The formation of laser-induced periodic surface structures (LIPSS) on metallic surfaces by femtosecond laser radiation was investigated. Various types of LIPSS could be formed on metallic surfaces such as copper and stainless steel. Nano-ripple formation was investigated as function of laser scanning speed, laser pulse number, and laser fluence. Hierarchical structures were generated on stainless steel surfaces and hydrophobic properties with water contact angles of about 145° could be achieved. It could be shown that direct femtosecond laser surface processing is a perfect tool for designing surface properties on micro- and nanometer scale which can be used for optical, biomedical, and tribological applications.

The local surface modification as well as the direct micro-ablation of polymethylmethacrylate (PMMA) with UV-laser radiation was studied with respect to the fabrication of optical monomode waveguides. Different UV sources were applied with a focus on excimer lasers and frequency-multiplied Nd:YAG lasers to investigate several concepts of integrated waveguides. One type of waveguides is realized by localized physical modification, which leads in one step to an integrated polymer waveguide with higher refractive index. A complementary type of waveguides includes the formation of small grooves, which are filled with index matched materials introducing a micro-scaled increase or decrease of the refractive index into the original PMMA substrate. The different laser-assisted fabrication techniques for polymer waveguide formation as well as the characterization of their local optical properties are discussed in detail. Lasergestutzte Fertigung von monomodigen Wellenleitern in Polymeren und ihre optische Charakterisierung Grundlegende Untersuchungen mittels UV-Laserstrahlquellen zur Fertigung von monomodigen optischen Wellenleiterstrukturen in Polymethylmetacrylat (PMMA) wurden durchgefuhrt. Hierzu wurden Prozesse zur lokalen Materialmodifizierung sowie ein Verfahren unter Einsatz von Mikroformabtrag studiert und weiterentwickelt. Fur die Arbeiten wurden Excimer-Laser (Wellenlangen: 193 nm, 248 nm), frequenzvervierfachte Nd:YAG-Laser (266 nm) und erganzend eine breitbandige UV-Lampe verwendet. Eine Sorte wellenleitender Strukturen basiert auf einer lokalen Brechungzahlerhohung mittels physikalischer Modifizierung, hier ermoglicht Laserstrahlung im Vergleich zur Maskenbelichtung mit UV-Lampen zusatzlich eine direkt schreibende Prozessfuhrung. Die zweite Fertigungsmethode setzt sich aus einer Abfolge von lasergestutztem Mikroformabtrag, mit dem Kanalstrukturen in PMMA erzeugt wurden, und einer Befullung mit brechzahlangpasstem Material zusammen, wodurch auf Mikrometerskalen der Brechungsindex lokal auf dem PMMA Substrat erhoht oder abgesenkt werden konnte. Die Diskussion der unterschiedlichen lasergestutzten Fertigungstechniken zur Herstellung polymerer Wellenleiterstrukturen wird in diesem Beitrag gefuhrt in Verbindung mit der Charakterisierung der lokalen optischen Eigenschaften.

The rapid fabrication of microcomponents made from polymers or composites will be presented. The whole fabrication process is divided into three main steps: first, direct patterning of polymers with excimer laser radiation enables the fabrication of first prototypes. Second, laser assisted micromachining using Nd:YAG or KrF-Excimer laser radiation allows a rapid manufacturing of microstructured mold inserts made of steel or polymer. Third, the application of UV-light-induced reaction injection molding (UV-RIM, photomolding) process using reactive monomer/polymer resins gives the access to the replication of the previously fabricated mold insert. For mold insert fabrication, the development of different process strategies is in progress in order to meet the best fit for three dimensional shapes (e.g., steep walls or slowly inclined walls). The development of mold inserts made of polymers is performed via UV laser ablation. This is a new promising method for the rapid manufacturing of microcomponents.

Lithium manganese oxide composite cathodes are realized by laser-printing. The printed cathode is a composite and consists of active powder, binder and conductive agents. Laser-printed cathodes are first calendered and then laser structured using femtosecond-laser radiation in order to form three-dimensional (3D) micro-grids in the cathode material. Three-dimensional micro-grids in calendered/laser structured cathodes exhibit improved discharge capacity retention at a 1 C discharging rate. Calendered but unstructured cathodes indicate the poorest cycling behavior at 1 C discharge. The improved capacity retention and the reduced degradation of calendered/structured cathodes can be attributed to both the increased electrical contact through calendering as well as shortened Li-ion pathways due to laser-induced 3D microgrids.

LiFePO 4 is a very promising material to be used as positive electrode for future lithium-ion batteries. Nevertheless, a reduced rate capability at high discharging and charging currents is the main drawback. In this work, a 3D structure was made in LiFePO 4 composite electrodes by applying ultrafast laser ablation. The change of the electrochemical properties in a lithium-ion half-cell due to laser structuring was studied in detail and will be discussed. The main challenging goal is to correlate cell properties such as capacity retention with laser parameters and laser generated microstructure. For microstructuring electrode materials an ultrafast as well as a ns fiber laser were used. The pulse duration was varied in the range from 350 fs to 200 ns. With ultrashort laser radiation, the ablation efficiency was increased. Electrochemical characterisations were performed. For this purpose, Swagelok® test cells with lithium metal as counter electrode were assembled. Main electrochemical parameters such as specific capacity and cycle stability were determined for the cells with structured and unstructured cathodes. It was shown that the rate capability for the cells with structured cathodes in comparison to cells with unstructured cathodes was significantly enhanced, especially for high charging and discharging rates.

Three-dimensional (3D) battery architectures are under current scientific investigation since they can achieve large areal energy capacities while maintaining high power densities. A main objective of surface patterning is the enhancement of lithium-ion diffusion which is often a limiting factor in lithium-ion cells. By using a rather new approach, laser material processing of thick-film electrodes has been investigated for the precise adjustment of 3D surface topography. Besides lithium-ion diffusion in electrode materials as an electrochemically limited process, a critical step in lithium-ion pouch cell manufacturing is the homogeneous electrolyte wetting of stacked electrodes and separators. This process requires cost expensive and time-consuming vacuum and storage processes at elevated temperatures. A new and cost efficient laser process has been successfully applied in order to significantly improve the electrode wetting and the battery operation. Preliminary investigations for testing the process on pouch cell geometry revealed higher capacities and increased cell life-time compared to standard cells without storage processes at elevated temperatures. The laser structuring process can be applied to commercial electrode materials and integrated into existing production lines.

Laser induced forward transfer (LIFT) process was used to print thick-film electrodes (LiCoO2 cathode and carbon anode) and solid-state polymer membranes for Li-ion microbatteries. Their electrochemical behaviors were characterized by cyclic voltammograms, capacity measurement and cycling performance. Microbatteries based on these laser-printed thick-film electrodes showed significantly higher discharge capacities than those made by sputter-deposited thin film techniques. This enhanced performance is attributed to the high surface area porous structure of the laser-printed electrodes that allows improved diffusion of the Li-ions across the 100 μm-thick electrodes without a significant internal resistance. In addition, a laser structuring process was used to prepare three-dimensional microstructures on the laserprinted thick-film electrodes to further improve battery performance by increasing the active surface area. These results indicate that the laser processing techniques are a viable approach for developing Li-ion microbatteries in microelectronic devices. This paper will show examples of Li-ion microbatteries fabricated with various polymer separators and structured electrodes using a combination of LIFT and excimer laser structuring processes.

Laser processing of electrode materials is a new technical approach in manufacturing of 3D batteries with improved electrochemical performance. Furthermore, laser-generated capillary structures transform electrodes to superwicking for liquid electrolytes leading to cost-efficient production. Abstract (35 Word Limit): above

The patterning of thin and thick films (100 nm-2 μm) is performed with excimer laser radiation (A = 248 nm, τ = 20 ns, e max = 5 J/cm 2 ). The laser ablation is investigated for the film systems: Fe 0.6 Co 0.4 /SiO 2 -multilayers, Tb 0.4 Fe 0.6 /Fe 0.5 Co 0.5 multilayers and SiN y -layers. The ablation process strongly depends on the film material, film thickness, as well as on the laser parameters such as laser fluence and number of pulses. The influence of using a beam homogenizer on the ablation process is discussed. For applications in microsystem technology, the minimal attainable structure sizes and an appropriate choice of laser parameters are determined. The patterning of SiN y -layers for application in solar cells is investigated.

In laparoscopic surgery the endoscopic camera is mounted to the end of an integrated rod lens system and, therefore, the whole endoscopic camera system is rigid. To obtain a better overview of the operation area, different lens systems with certain angles of view (0, 32, 45 and 70°) are used. To avoid changing the camera system during an operation, a flexible distal end for a single chip camera was built. Therefore an exchange of cameras during an operation is no longer necessary. The flexible tip is made of a superelastic Nitinol (NiTi) tube and can be angled up to 90° inside the human body. The outer diameter of the superelastic tube is 10.5 mm and, as there are no tubes of that size commercially available on the market, it was manufactured using NiTi sheet material. To enable angles of up to 90°, new structures were cut into the NiTi tube with a Nd-YAG laser. To reduce the induced tension at the bending zones, shape optimization was performed using the ABAQUS FEM software. This allowed a reduction in tension of about 40% for the optimized structure. Consequently, bending cycles of up to 105 are now possible. The angles are adjusted with the thumb on the proximal end of the endoscope and a locking device at this end enables the angle to be kept at any position for any time.

Chemical and morphological changes resulting from pretreatment with excimer-laser radiation were investigated for poly(butylene terephthalate) (PBT) surfaces. The irradiated surfaces were coated with aluminum or copper films of thickness 10 nm, enabling the effects of irradiation on the metal/polymer interface to be studied. In addition, adhesion was tested for electroplated nickel films on irradiated surfaces. Irradiation was carried out in air with KrF-excimer laser radiation (λ = 248 nm) at fluences per pulse in the range e = 3-600 mJ/cm2. The threshold fluence for material removal, et = 38 ± 12 mJ/cm2, was determined by profilometry measurements; the morphology of the irradiated surfaces was determined by optical and scanning electron microscopy; and the chemical properties of the polymer and the metal/polymer interface were studied with X-ray photoelectron spectroscopy (XPS). Depending on the irradiation conditions (fluence, number of laser pulses), various surface morphologies were found, including ...

Pulsed laser deposition as a method of physical vapour deposition suitable for the deposition of thin films with complex structures and compositions is briefly reviewed. Excimer, Nd:YAG and CO 2 laser radiation are comparatively investigated as a function of laser parameters and processing variables in order to deposit thin ceramic (Al 2 O 3 , ZrO 2 , SiC, BN, BaTiO 3 , Y 1 Ba 2 Cu 3 O 7- ) films on various substrates (stainless steel, hard metal, Si, ZrO 2 , SrTiO 3 ). The methods of generating multicomponent and multilayer thin films, including the advantages of pulsed laser deposition, are described, indicating the great future application potential of pulsed laser deposition as a versatile and flexible method for the generation of films with complex compositions and structures. The laser parameters and processing variables achieve different vapour and/or plasma states, represented in the number, momentum and energy of the ensemble of species generated, which are used to deposit thin films with defined properties according to the application, in view of the mechanical-technical properties, tribological properties, fatigue and thermal barrier, illustrated by examples.

The tailoring of chemical, morphological, and mechanical surface properties with laser radiation is described on the basis of the understanding and control of photon-matter interaction. The removal of matter by thermal and non-thermal processes including etching, the deposition of multilayer thin films, and the photoresistless patterning by direct and indirect processing techniques are illustrated by examples.

Laser -based material processing is well investigated for structuring , modification , and bonding of metals , ceramics , glasses, and polymers . Especially for material processing on micrometer, and nanometer scale laser-assisted processes will very likely become more prevalent as lasers offer more cost-effective solutions for advanced material research, and application. Laser ablation , and surface modification are suitable for direct patterning of materials and their surface properties. Lasers allow rapid prototyping and small-batch manufacturing . They can also be used to pattern moving substrates, permitting fly-processing of large areas at reasonable speed. Different types of laser processes such as ablation, modification, and welding can be successfully combined in order to enable a high grade of bulk and surface functionality. Ultraviolet lasers favored for precise and debris-free patterns can be generated without the need for masks, resist materials, or chemicals. Machining of materials, for faster operation, thermally driven laser processes using NIR and IR laser radiation, could be increasingly attractive for a real rapid manufacturing .

The further development of energy storage devices especially of lithium-ion batteries plays an important role in the ongoing miniaturization process towards lightweight, flexible mobile devices. To improve mechanical stability and to increase the power density of electrode materials while maintaining the same footprint area, a three-dimensional battery design is necessary. In this study different designs of three-dimensional cathode materials are investigated with respect to the electrochemical performance. Lithium cobalt oxide is considered as a standard cathode material, since it has been in use since the first commercialization of lithium-ion batteries. Various electrode designs were manufactured in lithium cobalt oxide electrodes via laser micro-structuring. Laser ablation experiments in ambient air were performed to obtain hierarchical and high aspect surface structures. Laser structuring using mask techniques as well as the formation of self-organized conical surface structures were studied in detail. In the latter case a density of larger than twenty million microstructures per square centimeter was obtained with a significant increase of active surface area. Laser annealing was applied for the control of the average grain size and the adjustment of a crystalline phase which exhibits electrochemical capacities in the range of the practical capacity known for lithium cobalt oxide. An investigation of cycling stability with respect to annealing parameters such as annealing time and temperature was performed using a diode laser operating at 940 nm. Information on the phase and crystalline structure were obtained using Raman spectroscopy and X-ray diffraction analysis. The electrochemical performance of the laser modified cathodes was studied via cyclic voltammetry and galvanostatic testing using a lithium anode and a standard liquid electrolyte.

Three-dimensional cathode architectures for rechargeable lithium-ion cells can provide better Li-ion diffusion due to larger electrochemical active surface area and therefore, may stabilize the cycling behaviour of an electrochemical cell. This features show great importance when aiming for long-life batteries, e.g. in stationary or portable power devices. In this study, lithium manganese oxide thin films were used as cathode material with the goal to stabilize their cycling behavior and to counter degradation effects which come up within the lithium manganese oxide system. Firstly, appropriate laser ablation parameters were selected in order to achieve defined three-dimensional structures with features sizes down to micro- and sub-micrometer scale by using mask imaging technique. Laser annealing was also applied onto the laser structured material in a second step in order to form an electrochemically active phase. Process development led to a laser annealing strategy for a flexible adjustment of crystallinity and grain size. Laser annealing was realized using a high power diode laser system operating at a wavelength of 940 nm. Information on the surface composition, chemistry and topography as well as studies on the crystalline phase of the material were obtained by using Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction analysis. The electrochemical activity of the laser modified lithium manganese oxide cathodes was explored by cyclic voltammetry measurements and galvanostatic testing by using a lithium anode and standard liquid electrolyte.

Electrode thin films made of LiCoO2, Li-Mn-O and SnO2 were synthesized by rf magnetron sputtering on silicon and stainless steel substrates. In order to increase the active surface direct laser structuring methods using ns- and ps-laser sources were applied. A laser system operating at a wavelength of 248 nm with a pulse length of 4-6 ns and repetition rates up to 500 Hz enabled the formation of high aspect ratio micro- and sub-micron structures with feature sizes down to less than 400 nm. Subsequent to the laser structuring process, laser annealing of LiCoO2 and Li-Mn-O was performed in order to achieve an appropriate crystalline phase which shows improved electrochemical cycling performance. Laser annealing was applied via a high power diode laser system operating at a wavelength of 940 nm. In case of LiCoO2 the high temperature phase was obtained through laser-annealing while for Li-Mn-O the spinel phase was formed. For both LiCoO2 and Li-Mn-O thin films appropriate annealing parameters were temperatures of up to 680 °C and an annealing time of 100 s.

Two types of laser patterning are of interest for application in microsystem technology: direct ablation of polymer material for the generation of two or three dimensional shapes such as microfluidic channels, curved shapes or micro-holes and alternatively photo-induced change of chemical or physical properties. An appropriate choice of laser and process parameters enables new approaches for the fabrication of lab-on-chip devices with integrated functionalities. We will present our current research results in laser-assisted ablation and modification of polystyrene (PS) with respect to the fabrication of polymer devices for high throughput planar patch clamping. Patch clamping is a highly sensitive technique used to measure the electrical activity of a cell. It is used in applications which include drug screening where there is demand for high throughput systems (HTS). While there are a few commercially available HTS patch clamping systems on the market using traditional patch clamping materials, there are no systems on the market using novel materials, or for dealing with cell networks - a physiologically important consideration for the developing fields of tissue engineering and understanding cell to cell interactions. This paper presents potential design approaches and processes for producing a polymer based automated patch clamping system. For this purpose laser micro-drilling of PS and subsequent surface functionalization was investigated as function of laser and process parameters. A high power ArF-excimer laser radiation source with pulse length of 20 ns (repetition rate up to 40 Hz) as well as high repetition ArF- and KrF-excimer laser sources with pulse lengths of 4-6 ns (repetition rates up to 500 Hz) were used in order to study the influence of laser pulse length on laser drilling and laser-induced surface modification. Micro-drilling of PS with diameters down to 1.5 μm were demonstrated. Furthermore the localized formation of chemical structures suitable for improved adhesion of single cells and cell networks was achieved on PS surfaces. A photolytic activation of specific areas of the polymer surface and subsequent oxidization in oxygen or ambient air leads to a chemically modified polymer surface bearing carboxylic acid groups well-suited for controlled competitive protein adsorption or protein immobilization. Finally, distinct areas for cell growth and adhesion are obtained. The combination of laser ablation and modification will be discussed for the laser-assisted fabrication of polymer devices for patch clamping.

Selective Laser Melting (SLM) is a generative manufacturing procedure mainly known for the application with metal powders. From these, metallic structures are produced in a layer-by-layer way. This layer-related procedure is comparable to the stereolithographic manufacturing of polymer devices. On a base plate, a thin layer of metal powder is spread. The powder is locally completely melted by the application of a focused laser beam. The base plate is then lowered by a value defined by the thickness of the metal layer, metal powder is spread again, and the local melting process is re-initiated. The complete procedure is continued as described, until the device is manufactured in the defined way. Commercially available metal powder can be used as base material. In principle, the SLM process should be suitable for the generation of metallic microstructures. The main precondition for the generation of microstructures by SLM is that the spatial resolution of the laser focus is small and precise enough to generate microstructure walls of around 100μm thickness in a reproducible way by melting metal powder. The walls should be gas- and leak-tight. In this publication, experimental results of the generation of metallic microstructure devices by SLM will be given. The process will be described in details. Process parameters for the generation of stainless steel devices having wall thicknesses in the range of about 100μm will be given. Examples for microstructure devices made by SLM will be shown. The devices can be manufactured in a reproducible way. Moreover, very first preliminary results on the use of ceramic powder as base material will be presented.

Laser-assisted patterning of polymers is investigated for the direct fabrication of polymeric lab-on-a-chip devices in microsystem technology for capillary electrophoresis chips in bio-analytical applications. In many cases the laser process induces a chemical, physical and topographical change in the laser treated surface. This material modification significantly influences the lab-on-a-chip-functionalities. We will present our current research results in laser-assisted modification of polystyrene (PS) and polymethylmethacrylate (PMMA) with respect to applications in micro-optics, micro-fluidics and cell culture applications. For this purpose the refractive index change, the wettability and the adsorption of proteins and the adhesion of animal cells were investigated as function of laser- and processing parameters. The possible change of surface chemistry was characterized by X-ray photoelectron spectroscopy. The local UV-laser-assisted formation of chemical structures suitable for improved cell adhesion was realized on two- and three-dimensional PS and polycarbonate (PC) surfaces. Above and below the laser ablation threshold two different mechanisms were detected. In one case the produced debris was responsible for improved cell adhesion, while in the other case a photolytical activation of the polymer surface including a subsequent oxidization in oxygen or ambient air leads to a highly localized alteration of protein adsorption from cell culture media and increased cell adhesion. The highly localized control of wettability on polymeric surfaces was investigated for PS and PMMA. In the case of PS the dynamic advancing contact angle could be adjusted between 2° and 150°. This was possible for a suitable exposure dose and an appropriate choice of processing gas (helium or oxygen). A similar but not so significant effect was observed for PMMA below the laser ablation threshold. For PMMA the dynamic advancing contact angle could be adjusted between nearly 50° and 80°. The adjustment of wettability for microfluidic application will be discussed. For the integration of integrated optical waveguides in micro-fluidic devices new approaches for a rapid manufacturing of optical singlemode waveguides made of PMMA were investigated. For this purpose a high repetition excimer laser radiation source was used in combination with a flexible mask technology. The waveguides were characterized for the visible optical range and for 1559 nm. The obtained structures reveal absorption losses of 0.7 dB/cm in the visible range.

CO2-laser-assisted micro-patterning of polymethylmethacrylate (PMMA) or cyclo-olefin copolymer (COC) has a great potential for the rapid manufacturing of polymeric devices including cutting and structuring. Channel widths of about 50 μm as well as large area patterning of reservoir structures or drilling of vias are established. For this purpose a high quality laser beam is necessary as well as an appropriate beam forming system. In combination with laser transmission welding a fast fabrication of two- and three-dimensional micro-fluidic devices was possible. Welding as well as multilayer welding of transparent polymers was investigated for different polymers such as PMMA, polyvinylidene fluoride (PVDF), COC, and polystyrene (PS). The laser transmission welding process is performed with a high-power diode laser (wavelength 940 nm). An absorption layer with a thickness of several nanometers is deposited onto the polymer surfaces. The welding process has been established for the welding of polymeric parts containing microchannels, if the width of the channels is equal or larger than 100μm. For smaller feature sizes the absorption layer is structured by UV-laser radiation in order to get a highly localized welding seam, e.g., for the limitation of thermal penetration and thermal damaging of functional features such as channels, thin walls or temperature-sensitive substances often contained in micro-fluidic devices. This process strategy was investigated for the welding of capillary electrophoresis chips and capillary blood separation chips, including channel widths of 100 μm and 30 μm. Analysis of the thickness of the absorption layer was carried out with optical transmission spectroscopy.

In this contribution experimental studies on the laser-assisted welding of transparent polymers with diode laser (wavelength 940 nm) are presented to discuss their potential for the fabrication of micro-devices for micro-chemical engineering and life science. Micro-channel devices such as capillary electrophoresis chips, heat exchangers or static mixers for liquids and gases consist of different micro-patterned sheets with structural details in the range of a few μm. In micro-chemical engineering, in general the sheets of micro-devices are made of metals. In our approaches the use of transparent and micro-patterned polymers such as polyvinylidene fluoride (PVDF) is investigated. For the development of micro-devices in life science the use of sheets made of transparent polymers such as polymethylmethacrylate (PMMA) is presented, e.g., in capillary electrophoresis chips. Devices are built up by stacks of micro-patterned sheets which have to be joined. These sheets are patterned by micro-milling, CO 2 -laser cutting or hot embossing. Laser-assisted polymer welding of transparent and opaque materials is well established. But the welding of only transparent components is still a challenge in micro-system technology, especially if micro-structures are included. For this purpose very thin absorbing layers with a thickness of about 5nm to 20nm are used in order to establish a welding process between transparent and micro-patterned polymers. The strength of the bonding is characterized by tensile tests as function of absorbing layer thickness, temperature, laser scan velocity and laser scan overlap. The topography is investigated with atomic force microscopy and low voltage scanning electron microscopy.

In this work the fabrication of integrated polymer waveguide components (waveguides, S-bends, splitters) by means of several approaches is reported. Fabrication of one type of waveguide involves laser-assisted micro-patterning of small grooves in (Polymethylmethacrylat) PMMA substrates which are subsequently filled with index-matched materials. Another type of waveguide is realized by local physical modification of PMMA in a laser direct writing process. The transmission characteristics of the waveguide were studied at the optical communication wavelengths of 1520-1620 nm. Fabrication of filled waveguides with oil as waveguide medium yielded low loss of 2.6 dB/cm and single-mode behavior for 10 μm wide grooves. Filling of 20 μm grooves with PMMA/MMA/dye mixture and subsequent polymerization yielded multi-mode waveguides with higher loss of 5.9 dB/cm. The laser direct writing (Nd:YAG, 266 nm) of waveguides showed loss of 6.3 dB/cm and multi-mode behavior indicating a need for further process optimization. Two Y-splitters fabricated by laser patterning and filling with branch radii of 10 mm and 25 mm showed device loss of 16 dB and 19 dB for a 25 mm device length. These results are compared to the performance of reference Y-splitters fabricated by UV-lithography, where parametric studies of the device geometry revealed the best branch radius of 20 mm.