Research Priority and Multidisciplinary Approach
The research activities of the principal investigators form the basis of the broad thematic structure of SAOT. Due to these different disciplines involved, based on a joint sound knowledge in the
The area of “Fundamentals of Optical Technologies” covers basic fundamentals of optics and of the different application fields mentioned in the six other topics. Research in this area will be carried out for the optical part by the Institute of Optics, Information and Photonics (IOIP) of the Faculty of Sciences and the Max Planck Institute for the Science of Light (MPL) and for the other parts within the SAOT.
Optics is a field where progress in applications is still closely related to advances in fundamental research. This development started with the invention of the laser, which along with the transistor is regarded as the most important innovation of the 20th century. Even the impressive advances achieved in microelectronics are mainly driven by a rapid development of optics, mainly of optical lithography. Advances in technologies originally developed to structure and process semiconductors have often enabled vice-versa the creation of new photonic materials and components.
While research in fundamental questions of optics is part of the topics covered in the International Max Planck Research School for Optics and Imaging (IMPRS) and is of essential interest to the MPL and the University IOIP, fundamentals of optics differ from the other six topics as a certain knowledge of the basics is an essential prerequisite for the curriculum. Students with very different backgrounds are brought together and to provide them with a common understanding an entrance academy covering the basics is run at the beginning. Courses are tailored to the needs of physicists or engineers, respectively, these two being the main addressees of SAOT. The goal is to establish a common basic understanding of the fundamentals of optics among the doctoral candidates.
As students applying are expected to have a degree – Master or diploma – in Physics, Engineering or a related field, a sound knowledge in geometrical and wave optics are a prerequisite. Thus these two topics are not treated explicitly, but be part of the introductory lectures on classical optics recapitulating the basic ideas of geometrical and wave optics and their link to electrodynamics. In this way a common point of departure and a joint notation for further lectures is established. Afterwards the following topics are taught in some detail. However, it should be clear that the goal is not to become an expert in any of these fields, but to get an idea and deepen the knowledge if necessary in one of the other six topics.
Atom and Quantum Optics – For quantum physics light is an interesting object for two reasons: light in itself is quantized and its quantum properties can be studied more easily than in many other systems. In addition light is an excellent tool to investigate the quantum properties of matter. Having discussed the quantum nature of light, a quantum mechanical description of the laser is given. Furthermore the lectures introduce the basic issues of quantum optics such as parametric down-conversion, parametric oscillation, squeezing and entanglement. Finally some current developments are discussed e.g. quantum information processing and the formation of Bose-Einstein condensates.
Spectroscopy – Optical spectroscopy as a non-invasive technique is widely used to study materials in all phases. Starting from the basic processes leading to absorption, fluorescence or Raman scattering, to name just the most common spectroscopic techniques, more advanced techniques like CARS (coherent anti-Stokes Raman scattering) are to be discussed. The different atomic, molecular or condensed matter processes leading to the observed scattering spectra will be analyzed. Different types of spectrometers will be introduced and discussed with respect to possible applications.
Nanophotonics – With the progress in micro- and nanostructuring techniques a new field of optics and photonics has emerged. Novel effective materials have been formed by patterning conventional substances with sub-micron resolution. A new understanding of light propagation far from any geometrical optical approaches is required to correctly predict the field evolution in sub-wavelength structures. Lectures will start with an introduction into the physics of photonic crystals. Then the course will move on while discussing the optical response of composites of resonant scatterers as dielectric spheres or metallic sub-wavelength structures. An overview over recent works on the creation of a magnetic response at optical frequencies and on the creation of so-called negatively refracting metamaterials will conclude this section.
Laser Technology – Since the invention of the laser a multitude of laser systems for various applications has been developed. After a short review on the basic principles of laser technology such as stimulated emission, cavity design and mode-locking, different types of lasers and their respective applications will be presented. Thus a wide range of common laser technologies will be introduced, e.g. laser assisted manufacturing, various medical applications or high-precision metrology.
Interferometry – Another widely used non-invasive optical method is interferometry. In astronomy interferometry is one of the major experimental techniques to gather information from objects which are too far away to be resolved by conventional imaging. Interferometry is also used to measure the surface topography of a given object, e.g. an aspheric lens, with nanometre precision or to study the flow characteristics of fluids by laser Doppler anemometry. Different types of interferometers will be introduced. Finally the design and application of diffractive and refractive micro-optical elements in interferometric testing or wavefront sensing will be discussed.
Link to other main topics – The course fundamentals of optical applications will form the basis for the more advanced lectures of the SAOT curriculum. Its optical part will provide a common understanding of optics as well as a jointly used vocabulary and notation, thus enabling an ongoing discussion among the students of the graduate school. Its success will be essential to achieve the level of excellence required for the graduate school. In addition the course provides important links between fundamentals of optics and various applications in a second major section of this Entrance Academy of SAOT where these fundamentals will be manifested. This second part will also deal with the fundamentals of the application fields as far as optics can be considered to contribute to the solution of particular problems, e.g., in mechanical and chemical engineering, in electrical engineering and electronics, in computer science, and in medicine as being covered in the main topics of SAOT. It will therefore perfectly fit to the general aim of the graduate school.
Lecture Program – As a sound knowledge in fundamental optical technologies is key to all further studies this course will be given in the beginning of the Entrance Academy including lectures and exercises. Depending on prior knowledge different emphases will be given in the courses. Peer-to-peer teaching by the advanced students will be part of the teaching concept, having manifold advantages. With their own experience of the first year still fresh the advanced students will be able to identify the specific problems that are usually encountered quite easily. Teaching will be another useful element in their own education program and finally teaching consolidates their own knowledge.
Optics Fundamentals is covered in more detail in a lecture course on this subject the examination of which has to be passed successfully during the educational phase at SAOT.
the research and education program and the particular research subjects are clustered into the six main topics covered by SAOT
Metrology is of increasing importance in all areas of our daily life, starting in the exchange and trade of goods and covering all aspects of product development, medicine and life sciences, environmental detection, process engineering, and the experimental determination of data in all disciplines of the natural sciences, but also in many other areas. Metrology represents the only possibility to acquire objective quantitative information about technical and physical quantities and their interrelations in order to draw reliable conclusions for the intended purposes.
Particularly optical measuring technologies are rapidly increasing in importance due to their excellent attributes regarding precision, measurement rate and absence of disturbance. Light is an excellent tool for gaining remote information and without any contact to the object. Optical metrology is applied for realizing basic units (SI units) and derived units, for fundamental research in natural sciences, for the development of technical processes and technical equipment, for transport and traffic control, for the measurement of characteristics of elements and materials, for diagnostics and treatment in medicine, about environmental pollution and for safety in air traffic and in space missions.
Based on a broad spectrum of theoretical research work and different applications of metrology the doctoral candidates can either choose advanced modules which focus on one of a large variety of topics or just enhance their knowledge. The courses comprise lectures, exercises, seminar talks, working groups for conducting experiments in the laboratory and excursions to companies developing or applying optical measurement technology. The offered range of courses and topics is based on
the specific features and characteristics of electromagnetic radiation with emphasis on frequencies in the optical range (and particularly of laser light) and the description on the basis of corpuscular phenomena
the different generation methods of coherent and non-coherent light and the interactions between matter and light,
a selection of the wide bandwidth of different applications with specific accentuation on sensors, signal analysis, signal transmission, processing and evaluation and complete measurement systems.
The courses are strongly related to the research activities of the participating institutes and cover several central points which are briefly described in the following modules.
Ultra-precise measurements of optical quantities like light power, optical spectra or the exact wavelength are key tasks for the design and analysis of optical systems. Also high precision measurements of the field of gravity are investigated. Modern light wave measurement methods realized in excellent instruments like wavemeters, optical spectrum analysers or optical time-domain reflectometers for the scientific development of new laser sources or components and subassemblies for high-speed optical communication systems are highlights in this field. Furthermore, definition and measurement of laser beam quality is a focus of courses and research work as a crucial parameter for the application of a specific laser in material processing or in laser-based precision metrology.
Laser techniques for process diagnostics and thermophysical properties determination. Advanced laser techniques are necessary for the investigation of reactive and non-reactive multiphase flows and in particular of technical processes, e.g., in combustion processes for the detection and monitoring of pollutants. Temperature, pressure, density, concentration, state of aggregation, flow velocity, particle size and properties of state have to be determined using, e.g., linear and nonlinear light scattering methods based on Mie, Rayleigh or Raman scattering, laser-induced fluorescence and laser-induced incandescence. In process engineering, e.g., nanoparticles can be characterized in-situ regarding size, size distribution and mass fraction using laser-based techniques. Laser Doppler and Phase Doppler Anemometry for single, two-phase and multiphase fluid flows and the application of techniques with two- and three-dimensional local resolution, e.g., Particle Image Velocimetry (PIV) and stereo PIV are highly developed techniques for flow field characterization. And especially for the high-precision determination of thermophysical properties of fluids such as viscosity, surface tension, thermal diffusivity, sound speed, sound attenuation and the specific heats, modern optical techniques and in particular dynamic light scattering are indispensable.
Sensorics, measurement principles and methods for different physical and chemical applications like gas analysis are considered and further developed within this module, e.g., with tuneable diode lasers. The measurement of ultra sound shock waves, of ultra short time intervals (down to femto second range) and of optical properties of materials, compounds and components are covered, and optical spectrum analysis is one of the useful tools. Fibre-optic sensors for pressure, strain and temperature based on the modal field distribution in optical fibres, on stimulated Brillouin scattering or on fibre-Bragg gratings should also be mentioned.
Optical technologies for vibration measurement (for amplitudes down to picometer and frequencies up to 1 GHz) based on laser interferometers, laser Doppler equipment and laser scanning vibrometers, e.g., for development of micro-electromechanical systems like micro-sensors (like 2D ultra sound antenna arrays for medical applications) and micro-actuators (e.g., for loudspeakers on a chip in hearing aids) form another group of sensors to be applied for the detection of physical properties.
Application of optical high precision measurement procedures for geometrical quantities of workpieces, machine tools and assembly equipment. From nanometer range up to meter range, measurements of roughness, waviness, surface topography, size, dimension, form and position deviations of workpieces can be single point based, line based or area based; static and dynamic behaviour of machine tools and assembly equipment. An important area of research in which the doctoral candidates will be involved is the development of measurement strategies for multisensor coordinate measurement techniques for 3D measurement based on optical sensors in combination with additional sensors (e.g. computer tomography and tactile sensor systems) especially for the inspection and testing of micro-electromechanical devices. This research topic is strongly connected with the challenge of multisensor data-fusion techniques and algorithms as well as the expression of uncertainty in multisensoric-measurement environments. Furthermore new optical sensors and probe systems for nano-positioning and nano-measuring technologies will be investigated and tested in industrial applications. Triangulation method, moiré and structured light methods, homodyne, polarization and heterodyne interferometry (e.g. Twyman-Green, Michelson-, Mach-Zehnder, Shearing-, grazing incidence interferometers), Shack-Hartmann wavefront sensor, speckle methods, holographic methods, microscopy, confocal microscopy, conoscopy, white light interferometry, near field scanning optical microscopy, fringe projection methods, and others will be introduced to the students. Research activities that can be carried out in the above mentioned topics are e.g. absolute calibration of the surface deviations of cylindrical specimens by means of grazing incidence interferometry or absolute calibration of the surface deviations of rotationally symmetric aspheric surfaces with perpendicular incidence interferometry.
Application of optical methods in medicine (diagnostics and monitoring) for detection and monitoring of soft tissue changes, characteristics of blood circulation, respiration gas analysis, features, test and application of complex innovative measuring systems like laser scanning tomography, optical coherence tomography and Doppler laser flowmetry, wave front and ray tracing analysis etc are in the focus of this module. The functionality and application of the “Light-spot Hydrophone”, developed for precise characterization of ultrasound shock-waves, which is used for the medical therapy of kidney and bladder stones with ultrasound lithotripters will be covered. Application of optical methods (phase shift based triangulation methods) in oral and maxillofacial surgery for modelling, prediction, intra operative monitoring and comparison of nominal and real state as well as for post operative analysis of operation caused alterations of the face surface will be discussed. Other tasks are e.g. the prediction of changes of facial surface after surgical intervention are based on data of optical measurements. Spectroscopic measurements on the eye’s retina provide information on the health status. Based on a numerical model, detailed knowledge will be gained about opto-mechanical properties of the eye. New surgical techniques as well as optical and technical devices can be developed thereby improving quality and function of vision.
Environmental pollution analysis and protection. Far-infrared electromagnetic radiation (with frequencies in Tera-Hertz region) can be used for observing biomedical malfunctions of living organisms or to detect hazardous substances or objects in safety-critical areas. LIDAR systems are based on the techniques of laser-induced fluorescence and laser Raman scattering for pollutant trace detection and concentration measurements to detect particulate matter and fine dust in the atmosphere. Design and development of components like lenses, mirrors or polarizing wire-grids and dielectric wave guides are the prerequisites to build up advanced measurement systems.
Altogether courses selected from the large variety of topics shown above are composed according to the ongoing research work and interests of the students. Small groups will be formed in order to meet the interests of the students and to achieve an efficient knowledge transfer as well as an effective joint knowledge acquisition.
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.
Optics in Medicine is a highly interdisciplinary topic: Implications come from the technical side concerning set-ups and applications for diagnostics and therapy as well as from a bio-medical side concerning anatomy, physiology and pathology of biological structures from the sub-cellular level to the complete human body. Due to the diversity and heterogeneity of biological tissue in all its facets and the goal of adapting optical technologies to these challenges, Optics in Medicine is a demanding field of research. To cover the whole variety of theoretical knowledge and practical skills for reaching competency and to succeed in this fast developing field, it is a necessity for young researchers to receive a focused and specialized training in all aspects of medical optics.
The SAOT program ”Optics in Medicine” focuses on the comprehensive development of all abilities necessary for the independent realization of bio-optical research projects at the top of the scale. For this process SAOT has built up a unique infrastructure representing an interdisciplinary fusion point for technicians, engineers, physicists and clinicians of all expertise.
The Clinical Photonics Laboratory (CPL) was established as a central area for bio-optical experiments where both needs are satisfied – the purity of high-tech optical equipment and the safety and hygiene necessary for bio-tissue treatment. A special hands-on course concerning safety and hygiene as well as bio-tissue treatment is established for all students choosing the Optics in Medicine topic to allow for a practical and deeper understanding of the characteristics and special needs concerning bio-material treatment.
Supported by the outstanding infrastructure of SAOT, several interdisciplinary projects arose in the topic “Optics in Medicine” which were externally reviewed and receive highly-ranked funding. Exploration of new concepts for sensor based tissue specific laser surgery, Development of basic methods applied on time-of-flight camera-technology in open and lapraroscopic surgery, Pilot study on the three-dimensional prediction of morphological surface structures of the human face, Fusion of fluorescence based and micro-CT imaging for diagnostic purposes. SAOT-PhD-students with a focus on the topic “Optics in Medicine” are integrated in these projects as integral part of research activities providing a high level training “on the job” from planning and conducting experimental work, followed by analyzing and assessing the data, to presenting the results on international congresses and in high quality journals in the field.
All the mentioned projects inherit a major translational aspect, combining medical and technical aspects at its best to enhance future diagnostics and treatment. The straight forward goal of these projects is to evolve the knowledge in both fields – optics and medicine – and in a further step promote the transfer of the achievements to bring new ideas to daily life clinical applications and improve the patients’ health and quality of life.
Modular Education, Training and Research in Optics in Medicine
According to the goal of SAOT several synergistic tracks of education, training and research sounding the wide field of medicine and optics were combined providing a comprehensive and elite curriculum to qualify high-end professionals in biomedical optics.
These tracks are given in 4 consecutive Modules: “Basics of Optics in Medicine” (Module 1) covers fundamental knowledge of human biology (physiology and biochemistry) and pathology at the beginning of the curriculum. Possibilities and boundaries of the combination of optical technologies and medicine are discussed in detail.
A clear understanding of human anatomy is essential for any further bio-optical training and research. Module 2 “Basics of Anatomy” builds up on the first introductory module and provides an even deeper understanding of the micro and macro structure of the human body. A special focus is laid on the optical system of the eye as it is a unique biological model for the transformation of light into chemical and electrical energy and further on into meaningful information.
Combining the sound understanding of human biology with opto-technical know-how is the essence of bio-optics and one major goal of the interdisciplinary SAOT topic “Optics in Medicine”. Only the artful combination of both domains enables the valuable development of optical applications in medicine.
One broad field of optical application in medicine is diagnostics. Module 3 “Application of Optics in Medical Diagnosis” imparts knowledge about the use of optical diagnostic systems on a cellular level (biophotonics) as well as on a tissue/organ level (endoscopy, spectroscopy, ophthalmology) or on the level of surface structures (optical face/skull scan, 3D-reconstruction). Non-invasive optical diagnostics has to come with an intensified understanding of optical bio-tissue properties and the optical change by pathological alteration of the tissues. Hence, a focus of this module is laid on optical tissue identification for early diagnosis and therapy planning, especially in terms of malignancy.
Therapy is another important application of optical technologies. Module 4 “Optics in Therapy” deepens the knowledge about light-tissue interaction, established in Module 3, and allows for an intensive experience concerning the use of light for therapy. Two widely used clinical applications of optics, laser surgery and photodynamic therapy, are discussed and reviewed in detail concerning the different reactions of various tissues towards the source of light and the applied parameters.
Basics of Optics in Medicine
The multiple activities and main topics, forming the basis of the thematic structure of SAOT, may have important implications for future applications in medicine. The graduate school offers a unique opportunity to explore the frontiers of optical technologies as applied to health and disease by networking science and technology with medical and clinical optical programs. Graduate students will learn about optical technologies in medicine, how new technologies could be forged into prototype diagnostic and therapeutic tools and what must be known about ethical, legal and ergonomic aspects of medical optics. Accompanying the multidisciplinary fundamentals of optics and their application in the technical field the medical institutes (anatomy) and departments (ophthalmology, oral and maxillofacial surgery, internal medicine) present to the graduates the transfer of this knowledge to biological systems. A special focus will be laid on the comprehensive understanding of the interaction between light and living tissue, complementing the knowledge about the interaction between light and technical matter. The deep understanding and technological specification sheet for developing and producing new optical equipment will be achieved by an interdisciplinary approach, an appropriate learning background, including hospital based training and research, by special-topic-academies, inter-professional seminars and the interdisciplinary mentoring program consisting of technicians and specialists from the medical field.
Basics of Anatomy
A sound understanding of the functional morphology of the human body is a basic need for an interdisciplinary approach to bio-optics in medicine. Knowledge of the biological building plan and the functional processes – from the sub-cellular level, over the organ level, to the whole body system – allows for the development of opto-technical solutions for medical problems and vice versa. Hence, providing competence in the field of anatomy and physiology of the human body is an essential and integral part of the education and training curriculum in “Optics in Medicine”. On base of normal anatomy and function the PhD-students get a deeper understanding of pathological alterations of the different systems in the human body – an understanding which is crucial for any further training and research concerning clinical applications of optics in diagnostics and therapy.
A central focus is laid on the eye being the optical apparatus of humans. From several points of view this “bio-optical system” seems to represent the interdisciplinarity of optics in medicine: The eye is unique among all other sensory organs because it can transform light into chemical and electrical energy, which then is translated into information. The functional knowledge of this anatomical unit allows for direct detection of the interactions between light and living cells. Following the stream of light the young researchers learn about the biological ocular systems of cornea and lens, followed by the temporal and spatial conversion of the electromagnetic waves into a high number of synchronized streams of data which are conducted via the optic nerve and its more than 1,000,000 fibres to the optic cortex where they are translated into the visible picture. Hence, studying the biological optical system provides a new vision on technical optical systems initiating cross-linking the experiences from both fields of knowledge.
On base of that, research as part of the “Basics in Anatomy” module concentrates on factors and circumstances causing severe vision defects on morphological, physiological and molecular levels: The structures of the eye are closely analyzed, in order to develop eye simulations for therapeutic purposes. Loss of accommodation during human life (presbyopia) as well as the opacification of the human lens in the context of cataract drives the development of intraocular lenses. Multifocal as well as accommodative lenses are currently under investigation to restore far as well as near sight following cataract surgery. Additionally, the eye contains a variety of different tissues in close proximity to each other (retina = brain derived, uvea = vascular tissue, cornea = avascular tissue) which can easily and uniquely in the body be investigated under direct vision through the optical apparatus of the eye enabling to develop optical scanning and early detection methods for a huge variety of diseases.
Application of Optics in Medical Diagnostics
Laser optical, photonic and biophotonic principles revolutionize diagnostic investigational and clinical medicine. Light-based technologies are often contact-free, have little impact on the integrity of living matter and can therefore easily be applied in situ. Advanced optical technologies in medicine are applied to detect and monitor cellular biochemistry and function, tissue characteristics, structure and function of organs and interchange between functional body units. Several optical specialties are closely related to this issue – building the interdisciplinary background of optical technologies in medical diagnostics: Optical Materials and Systems develop and optimize laser systems for opto-medical diagnostic applications; Optical Metrology is an integral issue for any diagnostic application of diagnostics in medicine including the huge field of Imaging, an ever growing domain in medical science and detection of diseases. Tissue, cells, proteins and DNA can be labelled with optical tags and their fluorescence or incandescence is measured and modifications interpreted according to the physiological or pathological situation. Native, untagged methods have been in the focus of biophotonics and represent an important medical diagnostic technique of the future: Confocal laser microscopy and optical coherent tomography are most often applied, recently combined with endoscopes and indwelling catheters. These modalities can be combined with other imaging modalities (ultrasound, CT, MRT, PET, nuclear medicine) to evolve as molecular imaging tools for functional analysis and navigation. Fluorescence spectroscopy, light absorption and scattering analysis, angle-resolved low coherence interferometry and spontaneous biophotonic activity will also offer opportunities for non-invasive tissue or blood/body fluid analysis. Technological challenges will be miniaturization, integration of optical technologies into chip and sensor development and new biooptic materials including new laser sources like ultrashort laser pulses, organic diodes and ultrasensitive metrological methods.
Recent research projects concerning Optics in Diagnosis were implemented and performed in the interdisciplinary setting of SAOT. Clinicians work together with engineers in a wide range from fundamental research on optical identification and imaging of normal and pathological conditions of biological matter to precise and innovative prototype-tools for diagnostic applications:
The correct function of all the components of the human optical system is dependent on a sufficient nutrition. Sophisticated laser technology has allowed the visualisation of vasculature and other structures of the retina and the optic nerve head to diagnose ocular diseases precisely. Visualization of changes in ocular capillaries also allows the diagnosis of general vascular disorders. Examples for such diagnostic tools are laser scanning systems, laser polarimetry, optical coherence tomography, all of which allow for optaining precise information about the retinal vessels, the retina, the retinal pigment epithelium and the choroid. Furthermore metabolic products like lipofuscin can be used to judge disease processes in the retina and help to determine the dignity of tumors of the choroid. Further improvement of the resolution of imaging techniques might allow progress into the cellular or molecular level.
The intra-operative application of optical 3D sensors and metrology will dramatically meliorate the control of reconstruction procedures and enhance the outcome of surgical interventions. Starting from the assessment of facial symmetry a model is established which allow for the creation of surface target data of the face in cases of congenital or acquired facial defects caused by trauma or cancer. Based on that, optical scanning of the face deformity enables the surgeon to evaluate the necessary surgical steps and the pre-fabrication of alloplastic implants for a correct and precise construction or reconstruction of the patients face according to the optical established surface model. A focus is put on a high-speed and reliable diagnostic and modelling system for an intra-operative real-time evaluation of the intended surgical outcome.
Differentiation between malignant and physiological tissue is successfully performed by existing fluorescence imaging systems. Several systems for this “optical biopsy” are already used in the clinical setting. However, the histological evaluation after invasive surgical tissue resection is still the “gold standard due to its higher accuracy. Hence, the accuracy of optical diagnostic systems in tumor diagnostic need further technical enhancement, followed by clinical evaluation to enable a highly reliable diagnostic alternative to the invasive standard of surgical and pathological tumor verification. Additionally, any surgical manipulation by a scalpel, electric cutting or coagulation, ultrasound based surgery and laser surgery cause an alteration of the tissue which may be followed by an alteration of the optical properties of tissue. An interdisciplinary research group investigates the fundamentals and possibilities of optical tumor tissue identification after alteration by surgical procedures. Solving this problem would allow for an intraoperative optical tumor detection in terms of a guidance for exact and complete cancer removal with an tremendous impact on the survival rate and the life quality of patients.
Application of Optics in Medical Therapy
Laser tissue processing has many advantages. The possibility to work remotely leads to high precision and little trauma. Furthermore, a high level of sterility can be guaranteed. Spreading of germs by mechanical procedures is avoided. The same applies to malignant cells, a risk in tumor resection not to be underestimated. The cutting geometry can be selected unrestrictedly as this procedure does not depend on the dimensions of classical surgical instruments. The laser can thus also be used for endoscopic surgery in areas that are difficult to reach and may be combined with robotic and automated surgery.
Several types of lasers are currently used in surgery. The effects of the laser beam on biological tissue depend on the wavelength of the monochromatic light that can be reflected, scattered or absorbed. Different components of biological tissue absorb light in different wavelength regions, followed by a deposition of energy in the tissue. Factors influencing the interaction of biological tissue and laser light are – from a technical point of view – the mode of application, e.g., contious or pulsed mode, pulse duration, all over application time and diameter of the application field and from a biomedical point of view the type of tissue, the amount of blood circulation, pathological alterations of the tissue, the proportion of tissue types in organs or compound tissues, to name just some of them. Hence, one focus of research is concentrated on the investigation of the interaction of different laser wave length with the variety of different biological tissues. New developments and technical optimizations for laser surgical instruments are an interdisciplinary challenge, approached by a close cooperation of Optics in Medicine with other SAOT topics and Medical Departments: Optical Material Processing, Optical Material and Systems, Department of Oral and Maxillofacial Surgery and Department of Ophthalmology.
However, in spite of all advantages of laser assisted surgery, there is one major drawback which limits the surgical application of lasers: the lack of haptic feedback during the laser surgery. Due to that fact the use of laser surgery is restricted to the treatment of superficial tissue layers in clinical practice so far which allows a direct control of the ablation by the surgeon. Performing laser surgery with a deeper penetration of the tissue, the surgeon gets neither information about the actual ablation depth nor information about the ablated tissue at the bottom of the cut. Therefore, in cases where the anatomy of the operation area is complex, the use of lasers involves the risk of iatrogenic damage or destruction of structures that should be preserved, e.g., blood vessels and nerves. Their damage may affect immensely both function and aesthetics with a huge impact on life quality of the patients. Hence, one major goal is the development of a tissue-specific laser surgery. Different topics of SAOT contribute to this field of research, combining optical diagnostics with therapeutic applications of optics – optical metrology provides the possibility of remote tissue identification and differentiation. Additionally, the interaction of laser and tissue causes itself optical and acoustic emissions such as burn- or pyrolysis lights, thermal radiation, air- and structure-borne sounds which can be detected by photodiodes, pyrometers, microphones and piezoelectric accelerometers to identify the actually processed biological material. On base of that, closed loop control systems are developed for the control of a laser surgery which ablates tissue specific, e.g., removes fat tissue and muscle but does not harm nerve tissue or major blood vessels. An expansion of this promising field of research is the transfer of optical detection of tumor tissue to an optical guidance for laser tumor resection. In terms of translational aspects of optical technologies towards therapy systems this would allow for a very precise surgical resection of only the carcinoma sparing the surrounding tissue with tremendous advancements for the functional restoration of patients after tumor resection.
Another important and evolving therapeutic field of Optics in Medicine is vision. On the one hand optical technologies can dramatically enhance the possibilities to treat diseases of the eye or – in severe cases – may technically replace the sense of vision in humans: Refractive corneal surgery uses advanced wave-front analysis techniques to provide algorithms, which are used for treatment of refractive errors with excimer and femtosecond lasers. The further development of laser techniques will enable the reliable treatment of myopia as well as hyperopia and astigmatism. Such laser equipment can also be used for curative surgery to treat corneal diseases and to provide for sophisticated cutting techniques for corneal transplantation.
One of the great dreams of mankind is artificial vision, which through opto-mechanical stimulation allows the provision of sight for ocular blindness. The implantation of chips in the subretinal or epiretinal space could allow for supplementation of the visual pathway with useful information in diseases which normally would cause blindness. In the future, direct stimulation of the visual cortex with electrical signals from video systems might even bypass the eye and allow for a new era of artificial vision.
On the other hand optical vision technology can influence and meliorate endoscopic, minimal invasive and robotic surgery. High precision time of flight camera systems and 3-dimensinal imaging systems are developed to be combined with high-end surgical technology to enhance the quality of view during the operation via a minimal invasive approach and the surgical accuracy, hence reducing the operation time and patients’ morbidity.
Optical technologies are the enabling technologies for our communication networks. The ever increasing demand of bandwidth boosts new developments in a wide range of optical components, optical transmission systems and optical networks. This also leads to short innovation cycles and therefore a high demand in research work in the fields mentioned above. During the last few years the integration of electronic and optical signal processing and conditioning can be observed. For example forward error correction methods, digital signal processing for equalization are important actual topics of this field. But also e.g. the implementation of advanced multilevel modulation formats optical decoding devices and research in the field of flexible dynamic network issues are important aspects at the field of optics.
Future ultra high capacity systems and networks also will have to focus on technologies for optical signal regeneration, optical processing of multilevel phase and amplitude encoded signals, optimized concepts for mixed optical and electronic signal equalization techniques, new concepts for capacity increase in optical networks and of course energy efficient communication system designs.
In addition to these backbone network related topics, optical transmission technologies are also important in short distance systems like in house applications and automotive applications or at even shorter distance in data centres and in inter and intra circuit data transfer.
Besides the classical optical communication applications, optical quantum communication is investigated in basic research and also evokes some interest in different areas of application.
The research activities in SAOT so far concentrated on the topics related to next generation optical communication systems. Here optical regeneration concepts for phase encoded signals were investigated, concepts for signal power transient suppression in dynamically switched optical communication networks were developed, signal noise interaction during fiber propagation was studied, concepts for compensation of signal distortions by digital backward propagation and electronic equalization were studied, and finally work on few mode and multi mode fibber propagation has been started. In the field of quantum communication the activities range from quantum information theory and optical quantum information theory to quantum information processing.
Ongoing and new future research work and education is planned in the fields given in the following paragraphs.
High capacity transmission systems
The research program for the next future in high capacity transmission systems will concentrate on the demands of actual and next generation optical transmission systems. Here we plan to further develop the various schemes of optical signal regeneration. The concepts to be investigated will also include e.g. phase sensitive amplification and new concepts for the still open question for regeneration of wavelength division multiplexing signals. A special emphasis will also be put on the regeneration of multilevel phase and amplitude encoded signals like quadrature amplitude modulation (QAM)
Due to the fact that new system concepts include a significant amount of electronic equalization these concepts have to be included in the next period of research. The equalization of linear fiber propagation effects has developed quite well during the last few years but mitigation of nonlinear propagation effects is still a topic of research. The research started in this field of digital backward propagation will be continued in order to explore the potential of various methods and also to take complexity restrictions in future hardware implementations into account.
The development of a setup behaving like a material with negative Kerr nonlinearity opens the door for future investigation of new concepts of link designs including this new type of devices. Here also the interaction with receiver side electronic compensation techniques has to be considered. This is important e.g. for optimum phase noise compensation.
In order to raise the transmission capacity, multiple input multiple output (MIMO) system concepts based on few mode fibers are discussed. Based on some first theoretical investigations, this topic has to be treated in more detail for example in the context of launching conditions, launching devices, propagation effects, channel separation and suitable signal processing.
Short range systems
Besides the quite well established concepts for multimode transmission using polymer optical fibers optical transmission concepts for short range transmission are attractive candidates to overcome the challenges of ultra high data rate transport within e.g. data centers, systems or even chips. Integrated microphotonics and optical interconnect will gain in importance over the next years. Within the SAOT the potential to launch research activities in this field have to be considered as also here highly interdisciplinary aspects characterize this field.
Advanced optical components
The planned activities in the context of few mode fiber transmission raise the question for optical components with a sufficient amount of modal selectivity. For example the inscription of fiber Bragg gratings in few mode fibers and the study of their usability for modal selection or modal filtering would clearly support the modal selective concepts in future. This devices are at the time being investigated in terms of their fabrication concepts, their usage in fiber sensors and fiber lasers. The broadening of the field of application will produce a lot of benefit in the scientific field but also for the overall goals of SAOT.
In addition to the classical optical communication and signal processing, the use of the quantum nature of light especially for ultra short soliton pulses has potential for future applications. Thus the behaviour of devices and subsystems for non-classical light has to be studied to explore the capability of usage in these new types of systems. Especially research on quantum information processing, quantum key distribution, quantum cryptography and quantum protocols is of high importance in this context.
New optical materials as well as efficient light sources are the basis for optical systems design. The term “Optical Materials and Systems” is meant to include systems for the generation of light like lasers, LEDs or OLEDs, for the conversion of light as photonic crystal fibers and classical optical systems and micro- and nano-optical materials and systems, in which light is controlled and transported. The advancing possibilities to create tailor-made materials with structures on the wavelength and sub-wavelength scale has promoted the development of optical materials and elements with desired optical functionality. The topics within this thematic priority span a wide range from more physics-driven basic research, i.e. understanding and designing new materials, to the engineering sciences with applications of these new materials and systems.
The different participating institutes cover a large range of these topics from basic developments to applications. This thematic priority are divided into several modules, both in research and in teaching
Advanced Laser Design. Fiber lasers and disk lasers have recently attracted much attention due to their high output power and excellent beam quality. Especially non-linear optical effects in such lasers will be investigated. For example, Raman fiber lasers can generate light at wavelengths which cannot easily be obtained by conventional solid-state lasers but are very promising for medical applications. Careful numerical analysis and design of such lasers as well as experimental investigations with new types of fibers will be performed in order to optimize e.g. spectral properties of generated light. Fiber-Bragg Gratings (FBGs) acting as micro-mirrors machined directly into optical fibers are key components in fiber lasers. Sophisticated FBGs with special and tunable spectral properties will also be studied closely. Different types of photonic crystal fibres (PCF) will be further optimize for light conversion and super continuum generation. Gas-filled hollow core will be used as new light sources in using the hollow core as a very small laser tube for e.g. a HeNe or HeCd laser, but also by higher harmonic generation PCF filled with noble gases. For use in high precision metrology, ultra-stable lasers, i.e. with a stabilization on the sub-Hz level will be developed.
New optical materials. Classical optics was always limited to the use of a few transparent materials. New optical materials are conventional substances with subwavelength-structures, designed in a way to induce new optical properties, e.g. extreme refractive indices, extremely low velocity of light, high birefringence. Two groups of structures are being focused on, both having received considerable attention in recent years. The first group includes photonic crystal fibers, in short PCF, i.e. optical fibers with a lateral structure. These two-dimensional crystals offer possibilities to fabricate fibers for specific purposes with tailor-made characteristics, but also serve as a model system to observe chemical reactions or light-matter interactions in confined space, but with a sufficiently long interaction length. While the basic principles have been clarified in the past years, a wide variety of applications of PCF in e.g. telecommunications, metrology, chemical and biochemical sensing, are being currently explored. PCF from other materials, e.g. soft glasses, that guide light in the infrared and are thus potential candidates for the use in optical material processing, are currently under investigation and will be further optimized towards applications. The voids of PCFs will be filled with metals to create new types of plasmonic filters.
The second group of optical materials includes 3-dimensional effective materials with structures in the subwavelength and nanometer-regime, as photonic crystals and so-called metamaterials. Some progress has already been obtained with respect to the self-assembly of colloidal particles in regular lattices thus forming resonant structures. In the next funding period those opals will be combined with metallic structures to generate mixed states of plasmons and Bloch modes and to extend the capability of photonic crystals towards sensing and light harvesting in solar cells. With the availability of advanced structuring techniques the field of metamaterials has received increasing interest. Fundamental effects as negative refraction and super resolution imaging could be demonstrated in the microwave domain and now those results are about to be transferred to the optical region. Using lithographic methods effective optical materials will be generated from metallic films and investigated optically. An alternative approach is to tailor and assemble organic macromolecules as carbon nanotubes to obtain a suitable magnetic or dielectric response in the optical domain. Research and teaching has already profited from the installation of microstructuring and fibre drawing equipment in Erlangen. An even deeper involvement of students into these new technologies is planned for the next funding period.
Micro-optical elements and their applications. Diffractive as well as refractive elements have numerous applications, e.g. in beam shaping, interferometry or as a wave front sensor. Especially absolute interferometric tests of large surfaces, e.g. aspherics or cylinders, can be performed. While binary structures are quite commonly used, grey tone lithography is a sophisticated technique. However, there is quite some experience in Erlangen using it, e.g. for the production of microlens arrays that can be used as highly sensitive wave front sensors. The design of the micro-optical element needed for a specific application often requires simulation techniques, as described in the computational optics module. In addition we will apply new analytical techniques as so-called transformation optics to generate new optical designs by transforming already known systems. The technology of producing all kinds of elements is available in Erlangen. Thus the whole range from design to application can be covered.
Polarization-optimized systems. Up to now polarization as an optimizing factor in optical systems has been rather neglected. However, experiments with systems with a high numerical aperture have shown quite early that a TEM00 laser mode does not exhibit the theoretical minimum focal spot and is also distorted in shape. Recently it has been shown that certain polarization patterns, which seem at first sight complicated, offer superior optical performance, e.g. a smaller focal spot. These results have potential applications in optical data storage, microscopy and lithography. Another interesting feature of radial polarization, being one example for a specific polarization pattern, is the existence of a considerable longitudinal component of the electrical field at the focus. This component can be used to couple to small structures like quantum wells or quantum dots. In particular the application of polarization tailored beams in combination with advanced recording schemes and with a clever numerical evaluation allows for a detailed investigation and characterization of optical nanostructures with sub-wavelength resolution. Those schemes will be extended towards a polarization sensitive scanning microscopy with subwavelength resolution.
THz Photonics. The Terahertz (THz) or far-infrared spectral region is attractive for possible applications in biomedical studies, as “fingerprints” for bio-molecules or for remote sensing and imaging. During the last funding period considerable progress has been obtained in the development of a room temperature CW-THz source using a photo-mixing technique. Now stable and reliable continuous wave THz sources are available and will be used to characterize materials also for that spectral range. Metamaterials originally developed for microwave applications will be optimized for the THz domain to create artificial dielectrics and micro-structured surfaces with novel spectral properties, for example as anti-reflection coatings and frequency-selective surfaces. Furthermore, advanced systems for metrology, sensing and imaging will be scrutinized.
Computational optics is a basic discipline for research in optics and for the development and optimization of applications in optics, like lasers, lenses, optical nanostructures or imaging. Therefore, there are several connections of the main topic “computational optics” to the other main topics. The research and training activities in computational optics can be divided into the following research directions (modules):
- Imaging lab and pattern recognition
- Simulation and optimization of optical systems
- Simulation of optical waves
- Laser simulation
Imaging lab and pattern recognition – Image processing, computer vision and pattern recognition research is tackling the hard problem of designing efficient algorithms for the analysis of image data acquired by a wide range of optical systems. Nowadays the used sensor technology ranges form standard CCD cameras over X-ray systems to optical coherence tomography devices. For the development of cognitive visual systems it is mandatory to provide core technologies of computational optics. For the quantitative analysis of image data, the mathematical modelling of the transfer function of the optical system and the calibration of the optical system are crucial. This includes, for instance, the projection mapping from 3-D to 2-D, lens distortion or the attenuation of x-ray quanta while being propagated through material. For the reconstruction of higher dimensional image information, numerical algorithms have to be developed that solve the ill-conditioned inverse problems robustly and efficiently. Examples are the 3-D reconstruction of volumes from 2-D x-ray projections, the computation of 3-D surface data using optical sensors like stereo cameras or the computation of in-vivo data based on phase modulated light as it is done in time of flight imaging. The major focus of current research is on the development of the technologies for the mathematical modelling and algorithmic description of optical systems used for image analysis. A huge potential for innovation in this emerging field is seen in the close interdisciplinary collaboration of experts in physics, engineering, computer science and medicine and the resulting synergies.
Simulation and optimization of optical systems – There are a variety of optical simulation methods which are adapted to a specific problem. But, in many cases several simulation methods can be combined if a proper interface between the different physical models describing the light distribution can be found.
One example is the combination of a rigorous diffraction theory for periodic structures and ray tracing. By doing this, also diffractive optical elements with very short period sizes (of only some wavelengths) can be simulated together with a complete optical system consisting of lenses, mirrors and so on. Of course, such a combination of different methods is only valid approximately. For the combination of a rigorous diffraction theory and ray tracing it is for example assumed that there is a strictly periodic and infinitely extended grating, whereas in practice a diffractive optical element has a locally varying period size and a finite size of the element. This approximation is valid with good accuracy in most practical cases
Simulation of optical waves – Research work is done exemplarily in thin film solar cells. Thin film solar cells are an innovative low cost technology in renewable energies. To increase absorbing of light in solar cells, light trapping is a very importing research topic in photovoltaics. The main concepts to improve light trapping are suitable nanostructures, rough interfaces between the different layers and use of plasmonic effects to increase the intensity of light in thin film solar cells. The aim of research is to perform simulations on high performance computers to improve light trapping in thin film solar cells and to improve simulation techniques for analyzing optical waves in thin film solar cells.
Laser simulation – Solid state lasers are widely used lasers for industrial and medical applications. In particular diode-pumped solid state lasers with amplifiers are used to obtain Q-switch lasers with very high pulse energy. The aim of research is to improve the simulation techniques for such kind of lasers by using Finite Element discretizations for Maxwell’s equations. By this approach an accurate simulation of the optical wave inside and outside the resonator is possible. This includes losses caused by apertures and thermal induced stress birefringence.
Each doctoral candidate (DC) chooses three of these major topics which will be deepened in the course of the SAOT program. One topic builds the frame of the research project the DC works on during his/her doctoral studies and two additional ones form the areas for further specialization. Details can be found in the Credit Point System (CPS).