Measurement Technology

Optical measurement of thin layers

At the Chair of Applied Laser Technology optical methods for the inline quality control of thin films and their integration in a roll-to-roll system for the production of organic photovoltaic cells are investigated in a cooperation project funded by the EFRE NRW.

The quality control, which is carried out by means of ellipsometry, includes the determination of the layer thickness and the drying quality. With an image width of 100mm, this allows a lateral resolution of 0.1mm at a repetition rate of 10Hz. The technology is non-destructive and enables the examination of multi-layer systems during the coating process.

Frederik Kiel, M.Sc., Room ID 05/645, Tel. +49 (0)234 / 32 23896, E-Mail:

Prof. Dr.-Ing. Cemal Esen, Room ID 05/643, Tel. +49 (0)234 / 32 25697, E-Mail:

Intelligent optical sensor system

The monitoring of biochemical substances is of great relevance for medical care, for example in the context of drug development or patient monitoring. Compact, robust and highly sensitive sensor technology is required for efficient implementation. Due to their high sensitivity, miniaturizability and cost efficiency, the demand for optical measurement methods increased significantly in this area. Due to the high sensitivity of the measurement principle based on an optical ring resonator, a large number of different substances such as proteins, antibodies, DNA or RNA strands or small molecules can be detected and analyzed.
Within the framework of the VIP+ project IntellOSS, funded by the German Federal Ministry of Education and Research, an intelligent platform using an optical measurement method based on whispering gallery mode resonators (WGM) is being developed.

  • A. Saetchnikov, E. A. Tcherniavskaia, V. Saetchnikov, und A. Ostendorf, „Intelligent optical microresonator imaging sensor for early stage classification of dynamical variations“, Advanced photonics research, Bd. 2021, Art. Nr. 2100242, Okt. 2021, doi: 10.1002/adpr.202100242.
  • A. Saetchnikov, E. Tcherniavskaia, V. Saetchnikov, und A. Ostendorf, „Deep-learning powered whispering gallery mode sensor based on multiplexed imaging at fixed frequency“, Opto-electronic advances, Bd. 3, Nr. 11, Art. Nr. 200048, Nov. 2020, doi: 10.29026/oea.2020.200048.
  • A. Saetchnikov, E. A. Tcherniavskaia, V. Saetchnikov, und A. Ostendorf, „A laser written 4D optical microcavity for advanced biochemical sensing in aqueous environment“, Journal of lightwave technology, Bd. 38, Nr. 8, S. 2530–2538, Feb. 2020, doi: 10.1109/jlt.2020.2973933.
  • A. Saetchnikov, E. A. Tcherniavskaia, V. V. Skakun, V. Saetchnikov, und A. Ostendorf, „Reusable dispersed resonators-based biochemical sensor for parallel probing“, IEEE sensors journal / Institute of Electrical and Electronics Engineers, Bd. 19, Nr. 17, S. 7644–7651, Mai 2019, doi: 10.1109/jsen.2019.2916861.

Anton Saetchnikov, M.Sc., Room ID 05/631, Tel. +49 (0)234 / 32 28485, E-Mail:

Prof. Dr.-Ing. habil. Andreas Ostendorf, Room ID 05/621, Tel. +49 (0)234 / 32 25233, Mail:

Microparticle array

A large number of different optical measurement techniques have become established in metrology, not least because of their high sensitivity. Resonance effects in particular play a special role. Due to their high symmetry, spherical microparticles represent resonators of special quality. The resonance properties are significantly influenced by changes in the ambient conditions (e.g. refractive index, temperature, etc.). Thus, even the smallest accumulations on the particle surface cause a measurable shift of the resonance frequencies, which usually must be determined with the help of tunable laser systems. However, if one illuminates a collective of different particles, any change in the ambient conditions will cause a change in the intensity distribution. The resonance spectrum of each particle is unique, thus conclusions about the ambient conditions can be drawn by simply observing the intensity distribution. 

  • T. Weigel, C. Esen, G. Schweiger, und A. Ostendorf, „Whispering gallery mode pressure sensing“, in Optical sensing and detection II, 2012, Bd. 8439, S. 1–6. doi: 10.1117/12.921759.
  • T. Weigel, R. Nett, G. Schweiger, und A. Ostendorf, „High resolution spectroscopy with a microparticle array sensor“, in Optical sensing and detection, 2010, Bd. 7726, S. 1–5. doi: 10.1117/12.854360.

Dr.-Ing. Dipl.-Phys. Thomas Weigel, Room ID 05/635, Tel. +49 (0)234 / 32 23455, E-Mail:
Prof. Dr.-Ing. habil. Andreas Ostendorf, Room ID 05/621, Tel. +49 (0)234 / 32 25233, Mail:

Geometrical Optics Application Tool

The power of today's computer systems makes a simulation of more and more complex optical systems possible. Opensource packages are available for some scientific problems, but they are mostly isolated solutions. Commercially available program packages are usually very complex and costly, moreover they are mostly tailored to the field of optical design. At the Chair of Laser Application Technology, geometrical optics, i.e. beam optics taking phase information into account, has been used for many years to handle a wide variety of optical tasks. The underlying computation is always very similar, therefore an abstract platform was developed within this project, which can be adapted to a variety of problems. Due to the modular structure, not only the light sources and objects but also the calculation methods can be easily modified. This library has already been successfully used for the calculation of the beam path, elastic scattering and force calculation in optical tweezers. 

  • R. Münster, O. Mierka, S. Turek, T. Weigel, und A. Ostendorf, „Benchmarking and validation of a combined CFD-optics solver for micro-scale problems“, OSA continuum, Bd. 3, Nr. 11, S. 3070–3081, 2020, doi: 10.1364/osac.399876.
  • T. Weigel, R. Ghadiri, C. Esen, G. Schweiger, und A. Ostendorf, „Influence of multiple particles in optical tweezers on the trapping efficiency“, in Complex light and optical forces VIII, 2014, Bd. 8999, S. 1–5. doi: 10.1117/12.2037322.

Dr.-Ing. Dipl.-Phys. Thomas Weigel, Room ID 05/635, Tel. +49 (0)234 / 32 23455, E-Mail:
Prof. Dr.-Ing. habil. Andreas Ostendorf, Room ID 05/621, Tel. +49 (0)234 / 32 25233, Mail:


Hydrogen-fueled vehicles for passenger and freight transport require a reliable infrastructure that provides hydrogen to most accessible places. The HyQ²Ra project is addressing the high sensitivity of fuel cells to impurities in hydrogen. Some chemical compounds can cause damage to the fuel cell even at challenging concentrations as low as a few ppb (parts per billion). This is to be prevented with the aid of a novel analysis method based on the inelastic scattering of laser light by molecules (Raman scattering): The chemical composition of the hydrogen is continuously monitored during the refueling process, while at the same time the amount of hydrogen consumed can be determined.

  • still to follow

Christian Günther, M.Sc., Room ID 05/651, Tel. +49 (0)234 / 32 23392, E-Mail:
Philipp Maack, Room ID 05/645, Tel. +49 (0)234 / 32 23643, E-Mail:
Prof. Dr.-Ing. Cemal Esen, Room ID 05/643, Tel. +49 (0)234 / 32 25697, E-Mail: