This PDF file contains the front matter associated with SPIE Proceedings Volume 8244, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The realization of stable bonds between different glasses has attracted a lot interest in recent years. However, conventional bonding techniques are often problematic due to required thermal annealing steps which may lead to induced stress, whereas glue and other adhesives tend to degrade over time. These problems can be overcome by using ultrashort laser pulses. When focussed at the interface, the laser energy is deposited locally in the focal volume due to nonlinear absorption processes. While even single pulses can lead to the formation of bonds between transparent glass substrates, the application of high repetition rates offers an additional degree of freedom. If the time between two pulses is shorter than the time required for heat diffusion out of the focal volume, heat accumulation of successive pulses leads to localized melting at the interface. The subsequent resolidification finally yields strong and robust bonds. Using optimized processing parameters, we achieved a breaking strength up 95% of the pristine bulk material. In this paper, we will detail the experimental background and the influence of the laser parameters on the achievable breaking strength.

Development of techniques for joining and welding materials on a micrometer scale is of great importance in a number of applications, including life science, sensing, optoelectronics and MEMS packaging. In this paper, methods of welding and sealing optically transparent materials using a femtosecond fiber laser (1 MHz & 1030 nm) were demonstrated which overcome the limit of small area welding of optical materials from previous work. When fs laser pulses are tightly focused at the interface of the materials, localized heat accumulation based on nonlinear absorption and quenching occur around the focal volume, which melts and resolidifies, thus welds the materials without inserting an intermediate layer. The welding process does not need any preprocessing before the welding. At first, single line welding results with different laser parameters was studied. Then successful bonding between fused silica with multi line scanning method was introduced. Finally, complete sealing of transparent materials with fs laser was demonstrated. Scanning electron microscopy (SEM) images of the sample prove successful welding without voids or cracks. This laser micro-welding technique can be extended to welding of semiconductor materials and has potential for various applications, such as optoelectronic devices and MEMS system.

In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock resistant mounting technique by soldering of optical components. Based on this technique a new generation of laser sources for aerospace applications is designed. In these laser systems solder technique replaces the glued and bolted connections between optical component, mount and base plate. Alignment precision in the arc second range and realization of long term stability of every single part in the laser system is the main challenge. At the Fraunhofer Institute for Laser Technology ILT a soldering and mounting technique has been developed for high precision packaging. The specified environmental boundary conditions (e.g. a temperature range of -40 °C to +50 °C) and the required degrees of freedom for the alignment of the components have been taken into account for this technique. In general the advantage of soldering compared to gluing is that there is no outgassing. In addition no flux is needed in our special process. The joining process allows multiple alignments by remelting the solder. The alignment is done in the liquid phase of the solder by a 6 axis manipulator with a step width in the nm range and a tilt in the arc second range. In a next step the optical components have to pass the environmental tests. The total misalignment of the component to its adapter after the thermal cycle tests is less than 10 arc seconds. The mechanical stability tests regarding shear, vibration and shock behavior are well within the requirements.

The application of photonic crystal fibers (PCF), especially in high power fiber laser systems, requires special preparation technologies with some significant differences compared to standard fibers. Features, like air-clad structures, highly rare-earth doped cores with low NA and stress applying parts of the PCFs, require additional steps in fiber preparation and innovative splicing technologies to gain optical properties. Here we discuss a contamination- free carbon dioxide laser splicing device, which is used for defined air-clad collapsing and end cap splicing to get a stable and sealed fiber end face with preserved high beam quality and additional functionality. The special design of the computer-controlled laser splicing process provides a versatile tool with high reproducibility for joining different geometries with an adjustable well-balanced heat distribution. A wide range of PCFs with different diameters, air-clad structures and doped materials up to ~2 mm have been spliced. For selected PCF-end cap splices cleave or polishing requirements as well as results on beam quality, tensile strength and further splicing features are presented.

A 405 nm LDs crystallization method of a-Si has been applied to the processing of bottom gate (BG) type microcystalline (μc-) Si TFT for the first time. We have successfully demonstrated superior I-V characteristics of BG μc- Si TFTs. In order to verify the validity of our process, we performed a heat flow simulation and compared commercially available lasers having wavelengths of 405, 445 and 532 nm. The simulation explained well the experimental results and showed that the wavelength is a crucial factor on uniformity, energy efficiency, and process margin and the 405 nm gave the best results among the three wavelengths.

Ultrashort pulsed lasers are increasingly used in micromachining applications. Their short pulse lengths lead to well defined thresholds for the onset of material ablation and to the formation of only very small heat affected zones, which can be practically neglected in the majority of cases. Structure sizes down to the sub-micron range are possible in almost all materials - including heat sensitive materials. Ultrashort pulse laser ablation - even though called "cold ablation" - in fact is a heat driven process. Ablation takes place after a strong and fast temperature increase carrying away most of the heat with the ablated particles. This type of heat convection is not possible when reducing the laser fluence slightly below the ablation threshold. In this case temperature decreases slower giving rise to heat-induced material deformations and melt dynamics. After cooling down protruding structures can remain - ablation-free laser surface structuring is possible. Structure formation is boosted on thin metal films and offers best reproducibility and broadest processing windows for metals with high ductility and weak electron phonon coupling strength. All approaches to understand the process formation are currently based only on images of the final structures. The pump-probe imaging investigations presented here lead to a better process understanding.

OLED lighting is expected to be one of the fastest growing markets in the area of organic electronics. The state of the art production is mainly based on vacuum deposition processes, which, in order to simplify the material handling, will most probably be embedded in a roll-to-roll environment. While reducing the handling costs also implies challenges to the patterning of the several OLED layers. Laser micromachining applying ultra-short pulsed laser sources has the potential to fully satisfy the requirements. Within this paper the latest findings on the separate scribing steps P1, P2 and P3 will be presented.

We have studied the kinetics of a congruent, pixilated laser forward transfer process known as laser decal transfer (LDT). This process allows the transfer and patterning of silver nanoparticle inks such that the transferred pixels or "voxels" maintain the shape of the laser illumination. This process is capable of creating freestanding and bridging structures with near thin-film like properties.

The ability to manufacture and assemble complex three-dimensional (3D) systems via traditional photolithographic techniques has attracted increasing attention. However, most of the work to date still utilizes the traditional patterning and etching processes designed for the semiconductor industry where 2D structures are first fabricated, followed by some alternative technique for releasing these structures out-of-plane. Here we present a novel technique called Laser Origami, which has demonstrated the ability to generate 3D microstructures through the controlled out-of-plane folding of 2D patterns. This non-lithographic, and non silicon-based process is capable of microfabricating 3D structures of arbitrary shape and geometric complexity on a variety of substrates. The Laser Origami technique allows for the design and fabrication of arrays of 3D microstructures, where each microstructure can be made to fold independently of the others. Application of these folded micro-assemblies might make possible the development of highly complex and interconnected electrical, optical and mechanical 3D systems. This article will describe the unique advantages and capabilities of Laser Origami, discuss its applications and explore its role for the assembly and generation of 3D microstructures.

Nano-structured surfaces were generated by laser interference lithography and femtosecond-laser direct writing of photo resists that subsequently were metallized by electroless plating or sputter deposition of silver. Laser lithography was performed with a 405 nm coherent diode laser in AZ9260, using two-beam interference with double illumination by 90° rotating of the substrate, leading to 2D periodic surface patterns with smallest features of the order of 200 nm. With fs-laser direct writing using a Ti-sapphire oscillator of 800 nm and 15 fs pulse length, feature sizes down to 100 nm were realized in SU8, even with aspect ratios much larger than 1. Metallization with electroless plating delivered either grainy silver coatings with a grain size around 100 nm or needle-like silver coatings with a needle length around 100 nm and a width of around 10 nm. The metallized substrates were exposed to aqueous solutions of Rhodamine 6G (Rh6G) of different concentrations and the corresponding Raman signals were recorded with a Raman micro-probe spectrometer. The nano-structured surfaces lead to formation of Raman bands attributable to Rh6G. In case of the grainy silver coatings, surfaces without nano-structures did not show Raman activity, indicating that grating-coupled surface plasmons play the dominant role for Raman enhancement. In case of substrates coated with the needle-shaped silver crystallites, Raman activity was also seen in regions without laser-generated nano-structures, indicating that localized particle plasmons play the dominant role for Raman enhancement. A comparison with Raman spectra measured with conventional Raman spectrometer showed that the enhancement factor achieved by the laser-generated nano-structures themself, is of the order of 6×10⁴. Raman intensity as a function of Rh6G concentration revealed a regular behaviour, as expected from a Langmuir isotherm.

In-situ observation of the in-volume modification of glasses by focused ultra-short pulsed laser radiation with an interferometer microscope allows for the spatially resolved measurement of the transient optical path difference (OPD) in the surrounding of the laser-induced modification. By the relation of refractive index and temperature an estimation of temperature during modification process is possible. The absorption of the laser radiation is measured and is, together with the estimation of processing temperature during modification, a first step towards a process model for the induced modifications of the transparent material.

Periodic patterned surfaces do not merely provide unique properties, but act as intelligent surfaces capable of selectively influencing multiple functionalities. One of the most recent technologies allowing fabrication of periodic arrays within the micro- and submicrometer scales is Direct Laser Interference Patterning (DLIP). The method permits the direct treatment of the material's surface based on locally induced photothermal or photochemical processes. Furthermore, DLIP is particularly suited to fabricate periodic patterns on planar and non-planar surfaces offering a route to large-scale production. In this paper, the fabrication of spatially ordered structures on different materials such as polymers, metals and diamond like carbon films is discussed. Several application examples as function of the processed material are introduced, including bio functional surfaces for cell guidance on polymers, wear resistant properties for structured diamond carbon like coatings and metals, as well as micro-patterned flexible polymers with controlled optical properties.

We report on the integration of a size-based three-dimensional filter, with micrometer-sized pores, in a commercial microfluidic chip. The filter is fabricated inside an already sealed microfluidic channel using the unique capabilities of two-photon polymerization. This direct-write technique enables integration of the filter by post-processing in a chip that has been fabricated by standard technologies. The filter is located at the intersection of two channels in order to control the amount of flow passing through the filter. Tests with a suspension of 3-ìm polystyrene spheres in a Rhodamine 6G solution show that 100% of the spheres are stopped, while the fluorescent molecules are transmitted through the filter. We demonstrate operation up to a period of 25 minutes without any evidence of clogging. Moreover, the filter can be cleaned and reused by reversing the flow.

Improved spectral resolutions were achieved in laser-induced breakdown spectroscopy (LIBS) through generation of high-temperature and low-density plasmas. A first pulse from a KrF excimer laser was used to produce particles by perpendicularly irradiating targets in air. A second pulse from a 532 nm Nd:YAG laser was introduced parallel to the sample surface to reablate the particles. Optical scattering from the first-pulse plasmas was imaged to elucidate particle formation in the plasmas. Narrower line widths (full width at half maximums: FWHMs) and weaker self-absorption were observed from time-integrated LIBS spectra. Estimation of plasma temperatures and densities indicates that high temperature and low density can be achieved simultaneously in plasmas to improve LIBS resolutions.

A pair of permanent magnets and an aluminum hemispherical cavity (diameter: 11.1 mm) were both used to confine plasmas produced by chromium targets in air using a KrF excimer laser in laser-induced breakdown spectroscopy. A significant enhancement factor of about 24 in the emission intensity of Cr lines was acquired at a laser fluence of 6.2 J/cm² using the hybrid confinement. In comparison, an enhancement factor of only about 12 was obtained with just a cavity. The Si plasmas, however, were not influenced by the presence of magnets as Si is hard to ionize and, hence, has less free electrons and positive ions. The hybrid confinement mechanism is discussed using shock wave theory in the presence of a magnetic field.

Bio-inspired surfaces targeting functional characteristics such as anti-reflectivity, self-cleaning effects or a drag reduction are of significant interest to industry. In this feasibility study, process chains for the mass production of so-called shark skin structured surfaces are investigated. Due to their drag reduction properties, such bio-inspired surfaces are of relevance to a number of applications in which particular aqua- and aerodynamic characteristics are required. The design of the shark skin structure relies on a bio-mimetic analytical model to generate the 3D surface model necessary to achieve the targeted surface functionality. The process chains presented combine laser ablation as a method for micro structuring masters for high throughput replication employing injection molding. In particular, three different process chains that rely on micro second (μs), nano second (ns) and pico second (ps) laser ablation systems to pattern mold inserts were investigated. Then, these inserts were integrated into a tool for micro injection molding and replication trials were carried out. The results show that all three laser sources can be utilized to create this kind of micro cavities. This research indicates that these micro structures can be replicated successfully, but further work is required to optimize the replication and laser structuring process.

Micro forming tools require high surface quality as well as contour accuracy, i.e. close tolerances at small dimensions. However, their structuring with necessary accuracy is limited to a small number of applicable technologies due to the mechanical properties of the tool material on micro scale. This contribution reports on an approach for machining techniques for precise tool finishing, developed at Bremer Institut für angewandte Strahltechnik GmbH (BIAS) called Laser-Jet-Process (LJP). This approach is based on a laser-chemical etching method where a focused laser beam is guided coaxially to an etchant jet-stream onto the material surface. The material removal is a result of laser-induced chemical reactions between etchant and surface at low laser powers. The evaluation of data shows a strong correlation of material removal and several process variables. In particular, high laser powers combined with high feed rates of the work piece and low flow rates of the etchant result in a break-off in material removal. In order to overcome this issue, the process boundaries have been experimentally determined and implemented in a quality control system. The quality control system consists of an automated path planning model and an inverse process model. The automated path planning model computes position and Gaussian intensity profile for a sequence of overlapping laser removal paths to achieve the desired tool shape. The inverse process model renders specific process variables for every single removal path from a pre-assembled data pool within experimentally defined boundary conditions.

Microassembling with holographic optical tweezers (HOT) is a flexible manufacturing technology for the precise fabrication of complex microstructures. In contrast to classical direct writing techniques, here, microparticles are transported within a fluid to appropriate positions, where they are finally bound. Therefore, optical forces act against the inner friction of the fluid. This effect limits the microassembling process in the meaning of process speed. In this work we investigate these limitations depending on the applied laser power and particle size. Additionally, different to conventional optical tweezers, HOTs use spatial light modulators (SLM) to control the laser beam and the object's position. This is performed at discrete step sizes caused by successively imaging respective kinoforms on the SLM at specific refresh rates. An optimization of the step size and the applied update rate are crucial to reach maximum velocities in particle movement. Therefore, the performance of dynamic particle manipulation is investigated in individual experiments. Stable manipulation velocities of up to 114 μm/s have been reported in our work using 6 μm polystyrene particles and an applied laser power of 445 mW.

We have fabricated entirely by femtosecond micromachining a plastic optofluidic chip with integrated microfluidics and optical excitation/detection. First a microfluidic channel and two fiber grooves were ablated on one surface of the PMMA substrate. In order to collect and focus the fluorescence signal onto a detector, two binary Fresnel lenses were micromachined on the back surface of the substrate. The operatio of the integrated optofluidic chip was demonstrated by filling the channel with different Rhodamine 6G solution, and a limit of detection of 50 nM was achieved.

Element migration in multicomponent glass is a phenomenon induced by high-repetition femtosecond laser irradiation and enables spatially selective modification of glass composition. Since the composition of a glass affects its material properties such as refractive index, luminescence, etching rate, viscosity, crystallization temperature, and phase-separation property, element migration is of great interest for practical applications. However, the mechanisms underlying migration have not been elucidated. In this study, we succeeded in identifying its driving force. In an experimental study, we simultaneously focused two beams of femtosecond laser pulses into two spatially-separated spots inside silicate glass. We observed the formation of characteristically shaped element distributions by electron probe microanalysis. In addition, we performed numerical simulations in which we considered concentration- and temperature-gradient-driven diffusions. The simulation results were in excellent qualitative agreement with the experimental results, indicating that element migration can be explained by thermodiffusion and that the driving force is the temperature gradient. These results constitute an important advance for three-dimensional control of glass properties.

Laser processing is generally known for low thermal influence, precise energy processing and the possibility to ablate every type of material independent on hardness and vaporisation temperature. The use of ultra-short pulsed lasers offers new possibilities in the manufacturing of high end products with extra high processing qualities. For achieving a sufficient and economical processing speed, high average power is needed. To scale the power for industrial uses the picosecond laser system has been developed, which consists of a seeder, a preamplifier and an end amplifier. With the oscillator/amplifier system more than 400W average power and maximum pulse energy 1mJ was obtained. For study of high speed processing of large embossing metal roller two different ps laser systems have been integrated into a cylinder engraving machine. One of the ps lasers has an average power of 80W while the other has 300W. With this high power ps laser fluencies of up to 30 J/cm² at pulse repetition rates in the multi MHz range have been achieved. Different materials (Cu, Ni, Al, steel) have been explored for parameters like ablation rate per pulse, ablation geometry, surface roughness, influence of pulse overlap and number of loops. An enhanced ablation quality and an effective ablation rate of 4mm³/min have been achieved by using different scanning systems and an optimized processing strategy. The max. achieved volume rate is 20mm³/min.

Drilling of micro through-holes in defined geometry, i.e. entrance diameter and taper, is gaining in importance in different fields of application and production. To exploit the advantages of laser technology for micro machining, versatile trepanning systems based on rotating optics have been designed and implemented. The advanced trepanning systems enable the controlled adjustment of beam displacement and inclination during operation. With a patented measuring device, the angular position of the rotating optics is determined online. The presented compact and lowweight trepanning systems can drill differently tapered through-holes with a diameter in a range of 50 to 1500 μm. Various solid-state laser sources have been used in combination with the presented laser trepanning system for material ablation. The wavelength und pulse width range from 355 to 1550 nm and sub-ps to 100 ns. The novel trepanning systems have been customized for different applications, ranging from basic research quest to industrial production. This presentation outlines the development steps and application results, accenting laser micro drilling of up to 1 mm thick metal and dielectric samples.

To serve the high need of lithium-ion secondary batteries of the automobile industry in the next ten years it is necessary to establish highly reliable, fast and non abrasive machining processes. In previous works [1] it was shown that high cutting speeds with several meters per second are achievable. For this, mainly high power single mode fibre lasers with up to several kilo watts were used. Since lithium-ion batteries are very fragile electro chemical systems, the cutting speed is not the only thing important. To guarantee a high cycling stability and a long calendrical life time the edge quality and the heat affected zone (HAZ) are equally important. Therefore, this paper tries to establish an analytical model for the geometry of the cutting edge based on the ablation thresholds of the different materials. It also deals with the composition of the HAZ in dependence of the pulse length, generated by laser remote cutting with pulsed fibre laser. The characterisation of the HAZ was done by optical microscopy, SEM, EDX and Raman microscopy.

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.

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.

In this work, a laser welding process for attaching conducting ribbons to a miniaturized feedthru is introduced. A pulsed 1064nm Nd:YAG laser was used as an example in this study. A numerical simulation by means of finite element method (FEM) for the prediction of temperatures in the feedthru assembly is presented. The approach used was intended to solve the energy balance equation with appropriate initial and boundary conditions. A laser weld joint strength test was conducted using a Mechanical Strength Tester. The influence of processing parameters, such as laser power and pulse duration, on the temperature distribution and the weld joint strength are investigated and discussed.

The laser sintering of Si particle films was studied toward a wet process manufacturing of a Si solar cell. Si particle films were formed by spin-coating from the dispersion solutions of Si nano- and microparticles in an organic solvent. The I-V characteristics of a schottky diode solar cell consisting of a Si particle film and an Au-coated PET film showed rectifying behavior and photovoltaic effect. With the aim of improving the physical and electrical properties of the Si particle films, the laser sintering of the Si particle films was investigated by changing the wavelength of laser beam using CW DPSS lasers (457, 1064 nm). In the preparation of the Si particle film, organosilicon nanocluster (OrSi) and organogermanium nanocluster (OrGe) were used as a binder polymer. The structural changes of the Si particle by laser irradiation were studied by micro-Raman spectroscopy. The peak position of the Raman band remarkably depended on the laser wavelength. The IR laser (1064 nm) sintering with a large penetration depth gave the higher quality crystal Si film than that prepared by visible laser (457 nm) sintering judging from the shift of the LO and TO phonon band from 520 cm^-1 of single crystal Si.

The laser is an extremely suitable non-contact tool for fast and automated in-line processes for example used to improve the efficiency of solar cells. With ultra-short pulsed laser radiation it is possible to decrease the reflectivity by modifying the surface topology of silicon. For the proposed modification, the optimum process window for altering the silicon surface topology on a micrometer scale is found at small laser fluencies at finite repetition rates. A promising up scaling method is process parallelization using in parallel a multiple set of interaction zones with the optimized process characteristics for single process interaction. Based on the single process, required laser process parameters and optical parameters for parallel processing are derived theoretically in order to enable a wafer processing in standard cycle times. Exemplarily 5-inch mc-silicon solar wafers are machined using a linear 7-times diffractive optical element (DOE), and in a second step solar cells are built up to determine the efficiency gain by the laser surface modification. A preliminary absolute efficiency gain of Δη > 0.2 % is achieved.