Optical material processing is a rapidly growing technology promising high flexibility and product diversity, productivity, quality and competitiveness for virtually every segment of science and industry. The uniqueness of optical material processing lies in its suitability for multiple applications spanning from macro to nano technologies. For example, the automotive industry already strongly benefits from laser beam welding which has become a standard joining process within the last decade. On the other hand, ultrafast lasers are applied to create sub-diffraction limited structures, opening up new possibilities such as production of functional surfaces or metamaterials. Additionally, ongoing development of lasers strongly promotes further application of advanced optical technologies for material processing. Development and optimization of those technologies requires not only deep knowledge in optics, but also a large degree of interdisciplinary thinking and team-orientated working since various aspects of physics, materials engineering, chemistry, electrodynamics, fluid/gas dynamics and numerical simulation and optimization, as well as economic and manufacturing aspects, have to be considered. In both, industry and academia there is a great need for highly qualified staff in this field. Thus the objective of the graduate school in the field of optical material processing is to do both – to perform fundamental research and technology development, as well as to provide students with a strong theoretical and educational background in the modules described below.

The key component in the following modules will be a close link between (academic) research and industrial applications, which will be extremely beneficial for students’ future careers.

Laser Micro and Nano Processing. The module “Laser Micro and Nano Processing” deals with application of short and ultrashort pulsed lasers for micro joining, structuring, adjusting and annealing purposes. High laser intensities achievable by modern ultrafast lasers allow performing material processing in nonlinear regimes resulting in significantly improved quality, with much higher degree of spatial resolution and with drastically reduced undesirable heat effects. The research will include basic theoretical and experimental investigations of ultrafast laser mater interaction mechanisms in order to fully exploit their full potentials as well as development of efficient and reliable micro/nano processing technologies. As an example, an important research direction is the combination of near field and ultrafast effects for direct 2D and 3D material structuring with characteristic sizes below 100 nm and for direct nano assembly. Further research is also needed in the field of laser beam micro joining, such as nonlinear ultrafast laser glass welding which has a vast potential for micro optoelectronics. Laser micro welding, soldering, and brazing of electronic parts and components, especially for heat sensitive applications, is another active research field. Additionally, efficient and reliable ultrafast laser system integration is still a challenging engineering task that has to be addressed in order to make the technologies commercially viable.

The number of possible applications of lasers in micro and nano technology is large and still growing. The purpose of this module is to develop laser technologies in the field further and to impart related knowledge to the graduates. A strong interdisciplinary approach is necessary to fulfill this task.

Optical Processing in Nanoelectronics. The module “Optical Processing in Nanoelectronics” focuses on the application of optical methods for generation and measurement of micro- and nanostructures for applications in microelectronics and optics. The research topics deal with optical simulation and on optical processing and measurement for semiconductor technology.

One major activity includes the development and application of models for simulation of optical lithography and optical measurement techniques. These models are used to describe the diffraction of light from micro- and nanostructures by rigorous methods, to simulate the image formation in advanced optical imaging systems such as projection steppers for semiconductor lithography, and to characterize the interaction of light with photosensitive materials such as photoresists. The ongoing miniaturization in microelectronics, sensors, flat panel displays, photovoltaics, and other technologies requires a selection of the most promising lithographic techniques for the economic fabrication of new components and systems. This includes non-destructive optical methods for measurement and inspection of nano-patterns. Combination of predictive models with advanced optimization techniques such as single- and multi-objective genetic algorithms, particle swarm optimizers , memetic algorithms etc. will be used to devise new design methods,  which consider both device and fabrication aspects in the early development phase. The realization of the described goals requires a high level of multidisciplinary research which combines theoretical optics with advanced mathematical algorithms, modern computational engineering, and device technology.

Optical metrology and processing is an essential approach in semiconductor technology.  Current activities focus on in-line and in situ optical inspection like full wafer defect analysis by large area scatterometry. High k dielectrics as one of the most prominent materials introduced into semiconductor technologies require optical models with proper material parameters in order to measure nanometer layer thickness and to control  chemical composition, e.g. by ellipsometry. Within a new approach, optical analysis was extended into the VUV regime to gain bang gap information on advanced dielectrics.  We will further investigate this approach for nanostructured layer systems, like nanocrystaline substrate layers or particle based semiconductor devices.

One of the first step & repeat UV –Imprint systems for large wafers was brought in to operation. Structures down to minimum sizes of 20nm were successfully printed by this method. In ongoing research activities, suitable templates and UV-resist are developed. Recently, we have demonstrated for the first time a full wafer UV based SCIL (Substrate Conformal Imprint Lithography) process using acrylate based  resist which allowed for very fast  processing times, exceeding state of the art process speed by more than an order of magnitude.  This advanced approach will be extended to direct printing of functionalized UV curable resist layers. Applications are large scale nano-optical surface structuring for LED and solar cell devices or directly printed nanoparticle filled magnetic or conductive structures.

Laser Macro Processing. The module “Laser Macro Processing” concentrates on the use of high power lasers for joining, cutting and forming purposes with a focus on automotive applications. The potential of these technologies that have already been successfully introduced into industrial production is by far not yet fully exploited.

Challenges lie in the opening of new application fields as well as in the extension of known processes, for example in the welding of dissimilar materials, as required for the production of high power electronics in automotive industry. Current research is focused on alternative welding techniques as well as the integration of new beam sources. Furthermore, laser brazing may offer an interesting alternative approach as a wide variety of dissimilar materials can be bonded. Another important trend, and not only in the automotive industry, is lightweight design, where precipitation hardened aluminium alloys are of great interest as they show excellent strength. Unfortunately they suffer from poor formability. Combining local laser heat treatment with intelligent irradiation strategies, the formability of these alloys can be temporarily enhanced, enabling the forming of so called Tailor Heat Treated Blanks.

In order to improve existent processes and to open up ways for innovations, a deeper understanding of the process dynamics and underlying mechanisms is necessary. Therefore numerical simulation models are currently developed that already permit new insights in melt flow dynamics and the formation of process errors. In addition to numerical simulations, information can be gained from online process monitoring. From an industrial point of view, the steadily growing degree of automation in series production and the increasing demand on the quality of products requires the development of novel fast process monitoring and control systems and advanced signal processing methods.

Another focus within this module is the exploitation of the new possibilities that come up with the development of high brightness solid state lasers (fibre lasers, disk lasers). These lasers provide excellent beam quality enabling remote processing with scanner optics. Thus new welding and cutting strategies are possible e.g. to minimize distortion due to the heat input. Another possibility is to shape the heat source to directly influence the melt pool dynamics. It has already been shown that this could be an appropriate method to avoid weld failures (cracks, blow outs …).

Training for the graduate students in this field of work is vital as they must earn knowledge both on a variety of physical phenomena (including e.g. coupling phenomena, melt pool dynamics, plasma physics, beam propagation etc.) as well as on engineering problems (quality, reliability, costs etc.). Thus a close collaboration of the participating scientists, as experts in all these fields, is necessary to manage these scientific challenges.

Laser Based Rapid Manufacturing. Totally new approaches to production engineering are launched by the further development of progressive new laser techniques. Rapid manufacturing and tooling as well as direct production techniques have tremendous potential to be essential features of the agile and flexible factory of the future; they are already emerging as a new paradigm for reducing production time and cost by eliminating many steps between design and manufacture. The module “Laser Based Rapid Manufacturing” imparts knowledge on the several variants for laser assisted additive generation of prototypes, tools and products. The focus is on the development of novel powder systems and their qualification for selective laser melting of high-strength and super-high-strength aluminium alloys with functionally gradient material properties. Powder systems with different particle size and distribution of elementary components are investigated to produce alloys during laser melting with different microstructural conditions, allowing the realisation of functionally graded parts with an optimized profile of properties.

In order to extend the diversity of parts manufacturable by rapid manufacturing technologies, future research will address polymer-based multimaterial components. For the realization of such components a new system technology will be developed, including versatile powder feed designs, novel irradiation strategies such as simultaneous irradiation and beam shaping techniques using microlens arrays.