Dr. Nektarios Koukourakis Profile

Dr. Nektarios Koukourakis

at TU Dresden

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Author

Publications (21)

Proceedings Article | 1 April 2020 Presentation

Fast measurement of mechanical properties with impulsive stimulated Brillouin microscopy (Conference Presentation)

Benedikt Krug, Nektarios Koukourakis, Jürgen Czarske

Proc. SPIE. 11359, Biomedical Spectroscopy, Microscopy, and Imaging

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In biomedicine, the mechanical properties of cells and tissues are increasingly recognized as indicator of pathological processes. Established measurement methods do not meet the requirements of biomedicine simultaneously: high spatial resolution, high throughput, non-contact, no markers and low measurement uncertainty. One particularly emerging technique, spontaneous Brillouin microscopy, enables optical three dimensional measurements with high spatial resolution. However, it suffers from low signal to noise ratio (SNR), which results in a long measurements duration. Impulsive stimulated Brillouin scattering (ISBS) is promising to overcome this shortcoming. In ISBS microscopy, an excitation takes place in the measurement volume through the superposition of two beams of an ultra-short pulsed laser. The resulting fringe pattern creates a standing acoustic wave in the sample. This standing wave can be probed with a continuous wave (cw) laser. The deflected part of the probe beam is amplitude modulated and can be measured by a photodiode. The determined center frequency is proportional to the sound velocity in the measurement volume and thus provides information on the local mechanical properties. For experiments, an ISBS microscope was built and characterized. Using this setup, measurements were carried out on the biological model material hydrogel. For the first time hydrogels of different stiffness could be discriminated. According to the requirements of biomedicine, the measurement volume has been reduced in size and thus a lateral resolution at cellular level was achieved. Based on an improved setup, investigations on the minimum measurement duration while satisfying the biomedical requirements mentioned above could be carried. The next steps are the transfer of the measurement technology to an application in biomedicine. A combination with other measurement techniques to a multimodal system might also be useful. In summary, Results obtained in our Research underline that ISBS microscopy offers an enormous potential for biomedical applications.

Proceedings Article | 30 March 2020 Presentation

Piezo-actuated adaptive elements in scanning microscopy (Conference Presentation)

Wenjie Wang, Nektarios Koukourakis, Jürgen Czarske

Proc. SPIE. 11351, Unconventional Optical Imaging II

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Proceedings Article | 4 March 2019 Presentation

Axial scanning and spherical aberration correction in confocal microscopy employing an adaptive lens (Conference Presentation)

Jürgen Czarske, Florian Lemke, Matthias Wapler, Ulricke Wallrabe, Nektarios Koukourakis, Katrin Philipp

Proc. SPIE. 10886, Adaptive Optics and Wavefront Control for Biological Systems V

KEYWORDS: Confocal microscopy, Microscopes, Monochromatic aberrations, Microfluidics, Imaging systems, Glasses, Composites, Optical microscopy, Microfluidic imaging, Phase measurement

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Proceedings Article | 24 May 2018 Presentation + Paper

Axial scanning and spherical aberration correction in confocal microscopy employing an adaptive lens

Katrin Philipp, Florian Lemke, Matthias Wapler, Nektarios Koukourakis, Ulrike Wallrabe, Jürgen Czarske

Proc. SPIE. 10679, Optics, Photonics, and Digital Technologies for Imaging Applications V

KEYWORDS: Actuators, Confocal microscopy, Microscopes, Monochromatic aberrations, Sensors, Wavefronts, Adaptive optics, Control systems, Objectives, Phase measurement

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Proceedings Article | 15 March 2018 Presentation

Holographic endoscope based on coherent fiber bundles and adaptive optics (Conference Presentation)

Robert Kuschmierz, Dirk Schubert, Nektarios Koukourakis, Jürgen Czarske

Proc. SPIE. 10502, Adaptive Optics and Wavefront Control for Biological Systems IV

KEYWORDS: Endoscopy, Phase conjugation, Holography, Biomedical optics, Digital holography, Calibration, Adaptive optics, Endoscopes, Spatial light modulators, Optical tweezers

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Proceedings Article | 26 June 2017 Paper

Structured illumination 3D microscopy using adaptive lenses and multimode fibers

Jürgen Czarske, Katrin Philipp, Nektarios Koukourakis

Proc. SPIE. 10335, Digital Optical Technologies 2017

KEYWORDS: Optical components, Microscopes, Luminescence, Adaptive optics, 3D metrology

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Proceedings Article | 13 June 2017 Paper

Application of adaptive optics for flexible laser induced ultrasound field generation and uncertainty reduction in measurements

Lars Büttner, Felix Schmieder, Martin Teich, Nektarios Koukourakis, Jürgen Czarske

Proc. SPIE. 10449, Fifth International Conference on Optical and Photonics Engineering

KEYWORDS: Refractive index, Inspection, Wavefronts, Adaptive optics, Optical testing, Velocity measurements, Wavefront distortions, Laser metrology

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The availability of spatial light modulators as standard turnkey components and their ongoing development makes them attractive for a huge variety of optical measurement systems in industry and research. Here, we outline two examples of how optical measurements can benefit from spatial light modulators. Ultrasound testing has become an indispensable tool for industrial inspection. Contact-free measurements can be achieved by laser-induced ultrasound. One disadvantage is that due to the highly divergent sound field of the generated shear waves for a point-wise thermoelastic excitation, only a poor spatial selectivity can be achieved. This problem can be solved by creating an ultrasound focus by means of a ring-like laser intensity distribution, but standard fixed-form optical components used for their generation are always optimised to a fixed set of parameters. Here, we demonstrate, how a predefined intensity pattern as e.g. a ring can be created from an arbitrary input laser beam using a phase-retrieval algorithm to shape an ultrasound focus in the sample. By displaying different patterns on the spatial light modulator, the focus can be traversed in all three directions through the object allowing a fast and highly spatially resolving scanning of the sample. Optical measurements take often place under difficult conditions. They are affected by variations of the refractive index, caused e.g. by phase boundaries between two media of different optical density. This will result in an increased measurement uncertainty or, in the worst case, will cause the measurement to fail. To overcome these limitations, we propose the application of adaptive optics. Optical flow velocity measurements based on image correlation in water that are performed through optical distortions are discussed. We demonstrate how the measurement error induced by refractive index variations can be reduced if a spatial light modulator is used in the measurement setup to compensate for the wavefront distortions.

Proceedings Article | 21 February 2017 Paper

Spherical aberration correction of adaptive lenses

Katrin Philipp, Florian Lemke, Matthias Wapler, Ulrike Wallrabe, Nektarios Koukourakis, Jürgen Czarske

Proc. SPIE. 10073, Adaptive Optics and Wavefront Control for Biological Systems III

KEYWORDS: Confocal microscopy, Microscopes, Monochromatic aberrations, Aberration correction, Beam splitters, Holography, Digital holography, Lenses, Wavefronts, Wavefront aberrations, Adaptive optics, Deformable mirrors, Zernike polynomials, Confocal laser scanning microscopy, Optical aberrations, Spherical lenses

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Proceedings Article | 21 February 2017 Presentation + Paper

Adaptive flow-field measurements using digital holography

Jürgen Czarske, Nektarios Koukourakis, Bob Fregin, Jörg König, Lars Büttner

Proc. SPIE. 10074, Quantitative Phase Imaging III

KEYWORDS: Stars, Digital holography, Particles, Wavefronts, Adaptive optics, Optical testing, Spatial light modulators, Image quality, Phase measurement, Wavefront distortions

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Proceedings Article | 26 April 2016 Paper

Wavefront shaping for flow-field measurements through varying phase boundaries

J. Czarske, N. Koukourakis, J. Koenig, B. Fregin, L. Büttner

Proc. SPIE. 9890, Optical Micro- and Nanometrology VI

KEYWORDS: Aberration correction, Holograms, Holography, Microfluidics, Biomedical optics, Digital holography, Scattering, Sensors, Particles, Wavefronts, Wavefronts, Adaptive optics, Optical testing, Spatial light modulators, Spatial light modulators, Image quality, Liquid crystal on silicon, Phase measurement, Particle image velocimetry

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Proceedings Article | 26 April 2016 Paper

Perspectives of multimode fibers and digital holography for optogenetics

Jürgen Czarske, Daniel Haufe, Nektarios Koukourakis, Lars Büttner

Proc. SPIE. 9890, Optical Micro- and Nanometrology VI

KEYWORDS: Multimode fibers, Optical fibers, Phase conjugation, Digital holography, Scattering media, Light scattering, Digital cameras, Single mode fibers, Spatial light modulators, Image transmission, Optogenetics, Tissue optics, Neurons, Neurophotonics, Brain

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Proceedings Article | 26 April 2016 Paper

High-contrast 3D image acquisition using HiLo microscopy with an electrically tunable lens

Katrin Philipp, André Smolarski, Andreas Fischer, Nektarios Koukourakis, Moritz Stürmer, Ulricke Wallrabe, Jürgen Czarske

Proc. SPIE. 9890, Optical Micro- and Nanometrology VI

KEYWORDS: Confocal microscopy, Microscopes, 3D acquisition, Speckle, Cameras, Microscopy, Microscopy, Image acquisition, 3D metrology, Objectives, 3D scanning, Electroluminescent displays, 3D image processing

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Proceedings Article | 15 March 2016 Presentation + Paper

Adaptive wavefront shaping for flow-field measurements

N. Koukourakis, B. Fregin, L. Büttner, J. Czarske

Proc. SPIE. 9717, Adaptive Optics and Wavefront Control for Biological Systems II

KEYWORDS: Optical imaging, Aberration correction, Biomedical optics, Digital holography, Tissues, Scattering, Sensors, Error analysis, Light scattering, Wavefronts, Adaptive optics, Control systems, Optical testing, Spatial light modulators, Image quality, Digital imaging, Digital image correlation, Wavefront distortions

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Proceedings Article | 24 September 2015 Paper

Compact low-cost lensless digital holographic microscope for topographic measurements of microstructures in reflection geometry

A. Adinda-Ougba, B. Kabir, N. Koukourakis, F. Mitschker, N. Gerhardt, M. Hofmann

Proc. SPIE. 9628, Optical Systems Design 2015: Optical Fabrication, Testing, and Metrology V

KEYWORDS: Microscopes, Beam splitters, Light sources, Holograms, Holography, Digital holography, Reflection, Reflectivity, Image resolution, Semiconductor lasers

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Proceedings Article | 17 July 2015 Paper

In-process deformation measurements of translucent high speed fibre-reinforced disc rotors

Katrin Philipp, Angelos Filippatos, Nektarios Koukourakis, Robert Kuschmierz, Christoph Leithold, Albert Langkamp, Andreas Fischer, Jürgen Czarske

Proc. SPIE. 9524, International Conference on Optical and Photonic Engineering (icOPEN 2015)

KEYWORDS: Doppler effect, Sensors, Calibration, Polymers, Glasses, Temporal resolution, Signal processing, Magnetic sensors, Translucency, Motion measurement

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Proceedings Article | 22 June 2015 Paper

Quantitative phase imaging by wide field lensless digital holographic microscope

A. Adinda-Ougba, N. Koukourakis, A. Essaidi, N. Gerhardt, M. Hofmann

Proc. SPIE. 9529, Optical Methods for Inspection, Characterization, and Imaging of Biomaterials II

KEYWORDS: Microscopes, Holograms, Holography, 3D image reconstruction, Digital holography, Sensors, Semiconductor lasers, Phase retrieval, Image retrieval, Reconstruction algorithms

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Proceedings Article | 1 May 2014 Paper

Effects of axial scanning in confocal microscopy employing adaptive lenses (CAL)

N. Koukourakis, M. Finkeldey, M. Stürmer, N. Gerhardt, U. Wallrabe, M. Hofmann, J. Czarske, A. Fischer

Proc. SPIE. 9132, Optical Micro- and Nanometrology V

KEYWORDS: Actuators, Confocal microscopy, Microsystems, Curium, Lenses, Sensors, Microactuators, Image quality, Objectives, Terahertz technology

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Proceedings Article | 22 February 2013 Paper

Quantitative phase analysis through scattering media by depth-filtered digital holography

Sebastian Goebel, Volker Jaedicke, Nektarios Koukourakis, Helge Wiethoff, Adamou Adinda-Ougba, Nils Gerhardt, Hubert Welp, Martin Hofmann

Proc. SPIE. 8589, Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XX

KEYWORDS: Holograms, Digital holography, Scattering, Scattering media, Optical coherence tomography, Spectroscopy, Light scattering, Reflectivity, Fourier transforms, Tomography

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Proceedings Article | 2 February 2012 Paper

Photoluminescence and optical gain of Ga(NAsP) heterostructures pseudomorphically grown on silicon (001) substrate

N. Koukourakis, M. Klimasch, D. Funke, N. Gerhardt, M. Hofmann, S. Liebich, M. Zimprich, B. Kunert, K. Volz, W. Stolz

Proc. SPIE. 8266, Silicon Photonics VII

KEYWORDS: Quantum wells, Luminescence, Silicon, Nitrogen, Optical testing, Semiconductor lasers, Integrated optics, Silicon photonics, Heterojunctions, Temperature metrology

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Proceedings Article | 26 July 2011 Paper

Colliding pulse mode-locked lasers as light sources for single-shot holography

Doris Grosse, Nektarios Koukourakis, Nils Gerhardt, Tobias Schlauch, Jan Balzer, Andreas Klehr, Götz Erbert, Günther Tränkle, Martin Hofmann

Proc. SPIE. 8001, International Conference on Applications of Optics and Photonics

KEYWORDS: Light sources, Holograms, Holography, Optical coherence tomography, Mode locking, Crystals, Semiconductor lasers, Diodes, Laser crystals, Pulsed laser operation

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Proceedings Article | 4 March 2011 Paper

High modal gain in Ga(NAsP)/(BGa)((As)P) heterostructures grown lattice matched on (001) silicon

N. Koukourakis, D. Funke, N. Gerhardt, M. Hofmann, S. Liebich, C. Bückers, S. Zinnkann, M. Zimprich, A. Beyer, S. Chatterjee, S. Koch, B. Kunert, K. Volz, W. Stolz

Proc. SPIE. 7939, Gallium Nitride Materials and Devices VI

KEYWORDS: Quantum wells, Statistical analysis, Gallium arsenide, Silicon, Optical testing, Semiconductor lasers, CMOS technology, Photonic integrated circuits, Heterojunctions, Temperature metrology

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Showing 5 of 21 publications

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