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.