This PDF file contains the front matter associated with SPIE Proceedings Volume 7921, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

A new method to fabricate microstructures built by polymer microparticles using a bottom-up technique is presented. The microstructures find broad application in micro-fluidics technology, photonics and tissue-engineering. The handling of the particles is realized by a holographic optical tweezers setup, ensuring the precise allocation of the particles to the desired structure. A biochemical technique ensures that the structure remains stable independent of the laser source. We show that with this method complex two-dimensional durable structures can be assembled and cannot be separated by optical forces. The structures are extendable during the entire fabrication process and can be linked to further particles and structures as desired.

Digital microfabrication processes are non-lithographic techniques ideally capable of directly generating patterns and structures of functional materials for the rapid prototyping of electronic, optical and sensor devices. Laser Direct-Write is an example of digital microfabrication that offers unique advantages and capabilities. A key advantage of laser directwrite techniques is their compatibility with a wide range of materials, surface chemistries and surface morphologies. These processes have been demonstrated in the fabrication of a wide variety of microelectronic elements such as interconnects, passives, antennas, sensors, power sources and embedded circuits. Recently, a novel laser direct-write technique able to digitally microfabricate thin film-like structures has been developed at the Naval Research Laboratory. This technique, known as Laser Decal Transfer, is capable of generating patterns with excellent lateral resolution and thickness uniformity using high viscosity metallic nano-inks. The high degree of control in size and shape achievable has been applied to the digital microfabrication of 3-dimensional stacked assemblies, MEMS-like structures and freestanding interconnects. Overall, laser forward transfer is perhaps the most flexible digital microfabrication process available in terms of materials versatility, substrate compatibility and range of speed, scale and resolution. This paper will describe the unique advantages and capabilities of laser decal transfer, discuss its applications and explore its role in the future of digital microfabrication.

The studies toward the formation of Si and Ge films and micropatterns by wet process using laser direct writing method are reported. First is the the formation of Si film by laser scanning irradiation to Si nano- or micro-particle dispersed films. By using organogermanium nanocluster (OrGe) as a dispersion medium of Si particles, a homogeneous Si film was formed by laser scanning irradiation on a Si particle/OrGe composite film. The micro-Raman spectra showed the formation of the polycrystalline Ge and SiGe alloy during the fusion of the Si particles by laser irradiation. The second is the formation of the Si and Ge micropatterns by LLDW (liquid phase laser direct writing) method. Micro-Raman spectra showed the formation of polycrystalline Si and Ge micropatterns by laser irradiation on the interfaces of SiCl₄/substrate and GeCl₄/substrate, respectively.

Plastics play an important role in almost every facet of our lives and constitute a wide variety of products, from everyday products such as food and beverage packaging, over furniture and building materials to high tech products in the automotive, electronics, aerospace, white goods, medical and other sectors [1]. The objective of PolyBright, the European Research project on laser polymer welding, is to provide high speed and flexible laser manufacturing technology and expand the limits of current plastic part assembly. New laser polymer joining processes for optimized thermal management in combination with adapted wavelengths will provide higher quality, high processing speed up to 1 m/s and robust manufacturing processes at lower costs. Key innovations of the PolyBright project are fibre lasers with high powers up to 500 W, high speed scanning and flexible beam manipulation systems for simultaneous welding and high-resolution welding, such as dynamic masks and multi kHz scanning heads. With this initial step, PolyBright will break new paths in processing of advanced plastic products overcoming the quality and speed limitations of conventional plastic part assembly. Completely new concepts for high speed processing, flexibility and quality need to be established in combination with high brilliance lasers and related equipment. PolyBright will thus open new markets for laser systems with a short term potential of over several 100 laser installations per year and a future much larger market share in the still growing plastic market. PolyBright will hence establish a comprehensive and sustainable development activity on new high brilliance lasers that will strengthen the laser system industry.

Oxide and non oxide ceramics (Al₂O₃, SiC) were brazed to commercial steel with active filler alloys using a CO2-laser (l = 10.64 μm). Two different laser intensity profiles were used for heating up the compound: A laser output beam presenting a Gaussian profile and a homogenized, nearly top head profile were applied for joining the compounds in an Argon stream. The temperature distribution with and without the homogenizing optic was measured during the process and compared to the results of a finite element model simulating the brazing process with the different laser intensity profiles. Polished microsections were prepared for characterization of the different joints by scanning electron micrographs and EDXanalysis. In order to evaluate the effects of the different laser intensity profiles on the compound, the shear strengths of the braze-joints were determined. Additionally residual stresses which were caused by the gradient of thermal expansion between ceramic and metal were determined by finite element modeling. The microsections did not exhibit differences between the joints, which were brazed with different laser profiles. However the shear tests proved, that an explicit increase of compound strength up to 34 MPa of the ceramic/metal joints can be achieved with the top head profile, whereas the joints brazed with the Gaussian profile achieved only shear strength values of 24 MPa. Finally tribological pin-on-disc tests proved the capability of the laser brazed joints with regard to the application conditions.

Joining of similar or dissimilar materials with a thickness in the range of micrometers and sub micrometers is of great interest for a number of applications in, e.g., micro technology, photovoltaic and thin-film technology. A laser micro joining process using 25 ns long KrF excimer laser pulses for joining thin films and foils is demonstrated. Metal films of silver, aluminium, copper, molybdenum and titanium with thicknesses down to 500 nm deposited on polyimide substrates were used for bonding to a 12.5 μm thick silver foil. The laser fluencies used for joining of the foil to the metal films are in the range of 3.5 J/cm². The laser-induced joints were investigated by SEM (scanning electron microscope), optical microscopy, and a tensile strength tester. The shear stress calculated from the tensile force measurements and considering the laser-exposed area to be the bonding area is 0.5 N/mm² for silver/aluminium bonds. The tensile strength is not only determined by the bond between the metal films but also by the adhesion of the thin film to the substrate. Synergetic effects lead to bond formation comprising of thermal, mechanical, and chemical processes.

Laser welding is a commonly used process to assemble medical devices. The heat produced during the laser welding process may have an adverse effect on the mechanical integrity of the case assembly and the functionality of heat sensitive electronic components. In order to maintain the mechanical integrity of the case assembly and to protect the subcomponents, it is important to control the temperature in the assembling process, the investigation of the temperature distribution in the assembly during laser welding is thus necessary. In this paper, we report an experimental method and a numerical simulation for the investigation of the temperature field in the process of laser welding the eyelet to the case subassembly of the Functional Electrical Battery Powered Microstimulator (FEBPM). A pulsed 1064nm Nd:YAG laser is used as an example in this paper.

To up-grade selective laser melting (SLM) process for manufacturing real components, high mechanical properties of final product must be achieved. The properties of a part produced by SLM technology depend strongly on the properties of each single track and each single layer. In this study, effects of the processing parameters such as laser power, scanning speed and powder layer thickness on the single tracks formation are analyzed. It is shown that, by choosing an optimal technological window and appropriate strategy of SLM, it is possible to manufacture highly complex parts with mechanical properties comparable to those of wrought material.

Temperature monitoring in the laser impact zone is carried out by an originally developed bi-colour pyrometer which is integrated with the optical scanning system of the PHENIX PM-100 machine. Experiments are performed with variation of basic process parameters such as powder layer thickness (0-120μm), hatch distance (60μm-1000μm), and fabrication strategy (the so-called "one-zone" and "two-zone").

Fast growth of diamond crystals in open air was achieved by laser-assisted combustion synthesis through vibrational excitation of precursor molecules. A wavelength-tunable CO₂ laser (spectrum range from 9.2 to 10.9 μm) was used for the vibrational excitation in synthesis of diamond crystals. A pre-mixed C₂H₄/C₂H₂/O₂ gas mixture was used as precursors. Through resonant excitation of the CH2-wagging mode of ethylene (C2H4) molecules using the CO2 laser tuned at 10.532 Μm, high-quality diamond crystals were grown on silicon substrates with a high growth rate of ~139 μm/hr. Diamond crystals with a length up to 5 mm and a diameter of 1 mm were grown in 36 hours. Sharp Raman peaks at 1332 cm^-1 with full width at half maximum (FWHM) values around 4.5 cm^-1 and distinct X-ray diffraction spectra demonstrated the high quality of the diamond crystals. The effects of the resonant excitation of precursor molecules by the CO2 laser were investigated using optical emission spectroscopy.

Periodic diameter modulation of carbon nanotubes (CNTs) by quick temperature variation was successfully achieved in laser-assisted chemical vapor deposition process. Tapered and diameter-alternating CNTs were grown by periodic modulation of the temperature due to inverse relationship between the temperature and the diameter of the CNTs. The diameter-modulated single-walled carbon nanotubes (SWNTs) were integrated into field-effect transistors (FETs) structure to investigate their electronic transport properties. The tapered SWNTs showed electronic properties similar to Schottky diodes indicating clear evidence of different bandgaps at two ends of the tubes. However, the electronic transport of the diameter-modulated SWNTs showed a very small current magnitude which is attributed to the large number of defects and the electron confinement in the periodic quantum well arrays. Transmission electron microscopy and Raman spectroscopy were also studied to investigate the structural and electronic properties of the structures.

The nonlinear absorption character determines a high potential of ultrafast laser pulses for 3D processing of transparent materials, particularly for optical functions. This is based on refractive index engineering involving thermo-mechanical, and structural rearrangements of the dielectric matrix. Challenges are related to the time-effectiveness of irradiation, correct beam delivery, and the influence of material properties on the exposure results. Particularly for light-guiding applications it is suitable to master positive refractive index changes in a time-efficient manner, considering that the result depends on the deposited energy and its relaxation paths. To address these challenges several irradiation concepts based on adaptive optics in spatial and temporal domains were developed. We review here some of the applications from various perspectives. A physical aspect is related to temporal pulse shaping and time-synchronized energy delivery tuned to material transient reactions, enabling thus a synergetic interaction between light and matter and, therefore, optimal results. Examples will be given concerning refractive index flip in thermally expansive glasses by thermo-mechanical regulation and energy confinement by nonlinear control. A second engineering aspect is related to processing efficiency. We give insights into beam-delivery corrections and 3D parallel complex photoinscription techniques utilizing dynamic wavefront engineering. Additionally, in energetic regimes, ultrafast laser radiation can generate an intriguing nanoscale spontaneous arrangement, leading to form birefringence and modulated index patterns. Using the birefringence properties and the deriving anisotropic optical character, polarization sensitive devices were designed and fabricated. The polarization sensitivity allows particular light propagation and confinement properties in 3D structures.

Flexible organic photovoltaics have gained increasing interests during the last decades. Toward increasing the efficiency and decreasing the cost per Watt, they are on their way to the market. The approach of laser patterning technology has been expected to motivate the industrialization of organic photovoltaics. In this paper high repetition picosecond laser radiation fabricated trenches of ITO on flexible PET (Polyethylene terephthalate) substrate are presented. In order to obtain clean removal ITO layer without damaging PET substrate, 1064nm, 532nm and 355nm wavelengths with different laser fluencies and scanning strategies are applied and optimized. The results reveal the different principles for ablation of ITO layer with different wavelengths. The ITO layer is successfully and selectively removed by 1064nm laser radiation with 0.63J/cm² fluence and 4m/s scanning speed.

In this contribution, we report on a laser-chemical removal method for precise machining of micro forming tools. Thereby, a focused machining laser beam is guided coaxially to an etchant jet stream. Since the material removal is caused by laser-induced chemical reactions using this method, machining is achieved at low laser powers. Hence, material stressing involving micro cracks and further parasitic effects can be avoided. Due to these advantages, this method offers a suitable technique for the finishing of precision micro tools. Several experiments have been performed at rotary swaging jaws made of Stellite 21 in order to chamfer the edged transition section between the operating sphere and the tool flank. The influence of both different laser powers and work piece traverse speeds has been investigated. For this purpose, several parallel laser paths were applied along the edged transition section when varying the process parameters. Here, the incident laser beam is subjected to different angles of incidence. Due to reflection effects, the process parameters have to be matched with respect to the particular angle of incidence during the machining. In this vein, the edged transition section of rotary swaging jaws was chamfered at radii in the range of 120 μm.

Ultrafast laser pulses are a powerful tool to process dielectrics. Here, we review our recent work concerning high aspect ratio micro and nanochannel processing in glass. We show how femtosecond Bessel beams overcome many of the difficulties associated with Gaussian beams. We report on single shot processing of nanochannels with aspect ratio up to 100. Underlying physical phenomena are discussed.

A near infrared sub-15 femtosecond laser scanning microscope was employed for structuring of bulk colored glass and polymethylmethacrylate (PMMA). The 400-mW Ti-Sapphire laser operates at 85 MHz with an M-shaped emission spectrum with maxima at 770 nm and 827 nm. Using a high numerical aperture objective light intensity of about 7 TW/cm² at the focal plane can be reached. For PMMA a mean power of less than 17 mW, which corresponds to a pulse energy of 0.2 nJ, was sufficient for ablating material. Holes of a diameter of less than 170 nm were produced. Two-photon fluorescence measurements, which can be performed with the same microscope, reveal an extension of the focus length in the specimen, which is most likely caused by self-focusing effects. By applying the same power, the refractive index of the glass could be changed. Islands at the glass surface of a size of less than 100 nm have been produced.

Recent year, they require the high performances of laser as a light source in variety application area. For instance, those are a shorter wavelength, a shorter pulse width. In order to serve those needs, an improvement of the laser damage threshold value of optical element used in the laser applications is required. And they reported that a surface-roughness of glass substrate as used coated optical element exert also influence that. Currently, the chemical mechanical polishing method (CMP method) is general used as the polishing method of optical element. This method is a friction method. Therefore, the reduction of the surface-roughness is prevented by generation of scratches and digs that keep happening by contamination in slurry. In order to solve this problem, we propose the optical near-field etching method (ONE). The ONE is operated by irradiation of a SHG light (λ=532nm) of Nd:YAG laser on glass substrate in chlorine gas atmosphere that have a optical absorption band edge of 400nm. The radical formation of the chlorine molecular is created by non-adiabatic photochemical reaction due to optical near-field occurred in glass surface. And the etching is progressed in the projection of glass surface. With this processing, we can achieve the reduction of R_a value of surfaceroughness from 0.2nm to 0.13nm. In addition, we gave the mirror coating to the glass substrate to which the surfaceroughness was improved by ONE and measured the laser damage threshold value. Accordingly, we obtained 14.0J/cm²as the laser damage threshold value. The laser damage threshold value of the glass substrate without ONE is 8.2J/cm². It is shown that the laser damage threshold increase by 1.7 times by ONE.

Highly efficient diffractive beam splitters surface-structured on submicron scale are presented. Submicron relief structures formed on the surfaces of a splitter work as an anti-reflective layer to improve the beam-splitting efficiency. Surface structuring is conducted using deep-UV, liquid-immersion interference lithography and dry etching. Rigorously designed structures with a period of 140 nm and a depth of 55 nm are lithographed onto fused-silica splitters. Splitting efficiencies at 266 nm are increased by 8% to agree favorably with a theoretical value, while Fresnel reflections are substantially reduced. Surface-structured beam splitters reported here are of great use in industrial machining applications using high-power pulsed lasers.

Laser induced forward transfer (LIFT) is used to print Li-ion battery electrodes. We show a preferred orientation of LiCoO2 particles in the (003) direction relative to non-laser transferred materials. While the laser energy does not alter the degree of orientation, the number of passes and transfer distance both have a significant influence on the observed texturing. We use a geometric argument based on the arrangement of plate-like particles on the substrate to explain the observations. When the plate-like particles encounter a perfectly flat substrate, they are able to align flat, causing (003) domains parallel to the substrate to be over 30 times more predominant than either (101) and (104) domains. From this maximum degree of orientation subsequent passes decrease the overall texturing of the samples as transferred particles encounter increasingly rough surfaces. At larger transfer distances, the areal density of particles reaching the substrate decreases, resulting in increased available substrate surface area and therefore more predominant particle orienting.

The material development for advanced lithium-ion batteries plays an important role in future mobile applications and energy storage systems. It is assumed that electrode materials made of nano-composited materials will improve battery lifetime and will lead to an enhancement of lithium diffusion and thus improve battery capacity and cyclability. A major problem concerning thin film electrodes is, that increasing film thickness leads to an increase in lithium diffusion path lengths and thereby a decrease in power density. To overcome this problem, the investigation of a 3D-battery system with an increased surface area is necessary. UV-laser micromachining was applied to create defined line or grating structures via mask imaging. SnO₂ is a highly investigated anode material for lithium-ion batteries. Yet, the enormous volume changes occurring during electrochemical cycling lead to immense loss of capacity. The formation of micropatterns via laser ablation to create structures which enable the compensation of the volume expansion was investigated in detail. Thin films of SnO₂ were deposited in Ar:O₂ atmosphere via r.f. magnetron sputtering on silicon and stainless steel substrates. The thin films were studied with X-ray diffraction to determine their crystallinity. The electrochemical properties of the manufactured films were investigated via electrochemical cycling against a lithium anode.

The development of future battery systems is mainly focused on powerful rechargeable lithium-ion batteries. To satisfy this demand, current studies are focused on cathodes based on nano-composite materials which lead to an increase in power density of the LIB primarily due to large electrochemically active surface areas. Electrode materials made of lithium manganese oxides (Li-Mn-O) are assumed to replace commonly used cathode materials like LiCoO2 due to less toxicity and lower costs. Thin films in the Li-Mn-O system were synthesized by non-reactive r.f. magnetron sputtering of a LiMn₂O₄ target on silicon and stainless steel substrates. In order to enhance power density and cycle stability of the cathode material, direct laser structuring methods were investigated using a laser system operating at a wavelength of 248 nm. Therefore, high aspect ratio micro-structures were formed on the thin films. Laser annealing processes were investigated in order to achieve an appropriate crystalline phase for unstructured and structured thin films as well as for an increase in energy density and control of grain size. Laser annealing was realized via a high power diode laser system. The effects of post-thermal treatment on the thin films were studied with Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The formation of electrochemically active and inactive phases was discussed. Surface chemistry was investigated via X-ray photoelectron spectroscopy. Interaction between UV-laser radiation and the thin film material was analyzed through ablation experiments. Finally, to investigate the electrochemical properties, the manufactured thin film cathodes were cycled against a lithium anode. The formation of a solid electrolyte interphase on the cathode side was discussed.

Selective thin film structuring with laser beams was already being deployed in industries such as the display industry and the photovoltaic industry. However developments in tailored performances of laser beams, such as spatial profile, temporal behaviour and wavelength will improve the resource efficiency and reduce the production cost and this in turn will make more applications accessible. For optimizing selective thin film structuring different wavelengths were used. In this paper the results will be presented and discussed.

The ALPINE project is developing innovative fiber lasers for the scribing of new thin film photovoltaic modules with the aims to push forward the European research and development of fiber laser systems and solar energy exploitation. The fiber lasers will be based on photonic crystal fibers, which are characterized by unusual and interesting light guiding properties exploited to deliver high power with excellent beam quality and high resonator stability and efficiency, and will be applied to substitute mechanical scribing steps in the photovoltaic module production. In addition, new photovoltaic thin film technologies is applied, which is based on cadmium telluride and copper indium diselenide materials. With a potential conversion efficiency just below that of crystalline silicon, these new material approaches are ready to enter the market with low manufacturing costs for immediate economic or environment impact.

Low-damage laser scribing of thin films to perform series interconnection (external and integrated) of thin-film CIGS solar cells for module fabrication is still a challenge. In consequence, the influence of laser scribing parameters on the electrical characteristics of thin-film CIGS solar cells must be studied in addition to standard analytical techniques for imaging and spectroscopy. Hence, CIGS solar cells were scribed with ultrashort Ti:Sapphire laser pulses with a wavelength of 775 nm and a pulse length of 150 fs. The I-V curves with the open circuit voltage, parallel, and series resistance were measured directly after the laser-scribing process and were compared with initial cell parameters. Apart from studying the influence of laser fluence etc. also various laser-scribing geometries were examined. The most significant effect of the laser-scribing procedure can be found for the parallel resistance. Laser ablation and laser-induced material modifications during scribing results in (i) alterations of the material properties of the films, e.g. the CIGS, and (ii) material modifications outside of the laser scribe, where the interfaces, e.g. p-n junction, primarily are effected; both effects are leading to the sudden decrease in parallel resistance. Morphology, topography, geometry and material modifications of the laser-scribed areas were analyzed by scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDX) and focused ion beam (FIB) cross sectioning. The results of the laserscribing induced alterations are discussed in relation to the applied scribing parameters. A model is introduced to improve the understanding of the physical reasons of the measured solar cell degradation while scribing.

Flexible large area organic photovoltaic (OPV) is currently one of the fastest developing areas of organic electronics. New light absorbing polymer blends combined with new transparent conductive materials provide higher power conversion efficiencies while new and improved production methods are developed to achieve higher throughput at reduced cost. A typical OPV is formed by TCO layers as the transparent front contact and polymers as active layer as well as interface layer between active layer and front contact. The several materials have to be patterned in order to allow for a row connection of the solar cell. 3D-Micromac used ultra-short pulsed lasers to evaluate the applicability of various wavelengths for the selective ablation of the indium tin oxide (ITO) layer and the selective ablation of the bulk hetero junction (BHJ) consisting of poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) on top of a Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) without damaging the ITO. These lasers in combination with high performance galvanometer scanning systems achieve superior scribing quality without damaging the substrate. With scribing speeds of 10 m/s and up it is possible to integrate this technology into a roll-to-roll manufacturing tool. The functionality of an OPV usually also requires an annealing step, especially when using a BHJ for the active layer consisting of P3HT:PCBM, to optimize the layers structure and therewith the efficiency of the solar cell (typically by thermal treatment, e.g. oven). The process of laser annealing was investigated using a short-pulsed laser with a wavelength close to the absorption maximum of the BHJ.

We report on fast and flexible laser processing technology for crystalline solar cells by using ultra-short laser pulses and a combination of Diffractive Optical Elements (DOE´s) for beam splitting with conventional scanner technology. The focus is laid on damage reduction, decreasing processing times, and efficient processing strategies. We demonstrate the process conversion from single-spot to multi-spot ablation of thin-films and bulk material, e.g. nitride ablation and edge isolation. We will point out an increase in ablation efficiency by a factor of 3 and an additional increase in processing speed by a factor of > 50 for surface ablation processes. The DOE in combination with scanner technology provides a fast and flexible system where only an industrial proven DOE has to be implemented in front of the scanner. Due to this modification the technology can be easily adapted. Using multi-spot technology for processing of crystalline solar cells, heat accumulation has to be analyzed. Limitations in spot distance and geometrical arrangements are discussed and described mathematically. Results and process windows will be shown for a thin-film ablation (surface) and a laser edge isolation (bulk) process on crystalline solar cells. An estimation of cycle times and area throughput will show the potential for using DOE´s especially combined with ultra-short pulse lasers.