Dr. Nektarios Koukourakis Profile

Dr. Nektarios Koukourakis

at TU Dresden

SPIE Involvement:

Author

Publications (37)

Proceedings Article | 13 March 2024 Presentation

Investigation on impulsive stimulated Brillouin microscopy for high-speed elastography in hydrogel

David Krause, John Böhm, Leon Liebig, Nektarios Koukourakis, Jürgen Czarske

Proceedings Volume PC12844, PC128440E (2024) https://doi.org/10.1117/12.3004808

KEYWORDS: Signal to noise ratio, Microscopy, Hydrogels, Elastography, Signal processing, Pulse signals, Image acquisition, Tissues, Scattering, Mirrors

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Proceedings Article | 5 October 2023 Presentation

3D cell rotation in multicore fiber-based optical diffraction tomography with isotropic resolution using deep learning

Jiawei Sun, Nektarios Koukourakis, Juergen Czarske

Proceedings Volume PC12649, PC126490R (2023) https://doi.org/10.1117/12.2676123

KEYWORDS: Phased array optics, Multicore fiber, Optical tomography, Diffraction, Deep learning, Computer generated holography, Spatial light modulators, Digital holography, Single mode fibers, Refractive index

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Proceedings Article | 5 October 2023 Presentation

Reference-less phase retrieval of multimode fibers using a deep neural network

Qian Zhang, Yuan Sui, Dennis Pohle, Nektarios Koukourakis, Jürgen Walter Czarske, Stefan Rothe

Proceedings Volume PC12655, PC126550Q (2023) https://doi.org/10.1117/12.2674072

KEYWORDS: Phase retrieval, Neural networks, Multimode fibers, Education and training, Spatial light modulators, Phase measurement, Holography, Wavefronts, Wavefront distortions, Photonics

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Proceedings Article | 28 September 2023 Presentation

Optical diffraction tomography based on AI-driven adaptive optical cell-rotation

Nektarios Koukourakis, Jiawei Sun, Jürgen Czarske

Proceedings Volume PC12655, PC126550B (2023) https://doi.org/10.1117/12.2678217

KEYWORDS: Phased array optics, Adaptive optics, Optical tomography, Diffraction, Spatial light modulators, Tomography, Optical manipulation, Machine learning, Imaging systems, Artificial intelligence

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Proceedings Article | 28 September 2023 Presentation + Paper

Chromatic aberration correction using reinforcement learning

Katharina Schmidt, Ning Guo, Wenjie Wang, Jürgen Czarske, Nektarios Koukourakis

Proceedings Volume 12655, 126550A (2023) https://doi.org/10.1117/12.2675887

KEYWORDS: Chromatic aberrations, Machine learning, Aberration correction, Holography, Manufacturing, Imaging systems, Holograms

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Proceedings Article | 12 August 2023 Presentation

Multicore fiber endoscopy for 3D rotation of cancer cells

Juergen Czarske, Nektarios Koukourakis, Jiawei Sun

Proceedings Volume PC12622, PC1262205 (2023) https://doi.org/10.1117/12.2678494

KEYWORDS: Multicore fiber, Phased array optics, Cancer, Endoscopy, Optical tomography, Digital holography, Diffraction, Control systems, Computer generated holography, Spatial resolution

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Proceedings Article | 16 March 2023 Presentation

Investigation of neurodegeneration in the human organoid retina with transmission matrix measurements (Conference Presentation)

Jürgen Czarske, Nektarios Koukourakis, Stefan Rothe, Felix Wagner, Mike Karl

Proceedings Volume PC12388, PC123880E (2023) https://doi.org/10.1117/12.2661936

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Proceedings Article | 16 March 2023 Presentation + Paper

Image quality enhancement for ultra-thin lensless multi-core fiber phase endoscopes

Jiawei Sun, Nektarios Koukourakis, Juergen Czarske

Proceedings Volume 12389, 1238904 (2023) https://doi.org/10.1117/12.2651444

KEYWORDS: Multicore fiber, Endoscopes, Denoising, Phase reconstruction, Image restoration, Phase imaging, Speckle, Image enhancement, Biological imaging

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Proceedings Article | 15 March 2023 Presentation

Impulsive stimulated Brillouin microscopy for high-speed biomedical diagnostics (Conference Presentation)

Nektarios Koukourakis, Leon Liebig, Jürgen Czarske

Proceedings Volume PC12381, PC1238109 (2023) https://doi.org/10.1117/12.2651776

KEYWORDS: Microscopy, Biomedical optics, Diagnostics, Signal to noise ratio, Signal generators, Signal analyzers, Blood, Biological research

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Proceedings Article | 20 December 2022 Presentation

Real-time quantitative phase imaging through a multicore fiber using deep learning

Jiawei Sun, Nektarios Koukourakis, Jürgen Czarske

Proceedings Volume 12318, 123180F (2022) https://doi.org/10.1117/12.2642514

KEYWORDS: Phase imaging, Speckle pattern, In vivo imaging, Ultrafast phenomena, Tissues, Refractive index, Neural networks, Image restoration, Endoscopy, Cancer

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Proceedings Article | 3 October 2022 Presentation

3D cell-rotation using multi-core fiber-based lab-on-a-chip for optical tomography

Jiawei Sun, Nektarios Koukourakis, Jürgen Czarske

Proceedings Volume PC12198, PC1219808 (2022) https://doi.org/10.1117/12.2633783

KEYWORDS: Optical tomography, Lab on a chip, Tomography, Optical manipulation, Computer generated holography, Spatial light modulators, Surgery, Single mode fibers, Phased arrays, Phased array optics

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Proceedings Article | 30 May 2022 Presentation

Understanding neurodegeneration in human organoid retina with optical microscopy

Jürgen Czarske, Nektarios Koukourakis, Stefan Rothe, Felix Wagner, Mike Karl

Proceedings Volume PC12144, PC121440M (2022) https://doi.org/10.1117/12.2622155

KEYWORDS: Tissues, Retina, Optical microscopy, Neurodegeneration, Light scattering, Scattering, Cell death, Pathology, Optical properties, Imaging systems

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Proceedings Article | 20 May 2022 Presentation

Confidential optical data transmission through multimode fibres based on holographic transmission matrix measurements

Stefan Rothe, Karl-Ludwig Besser, Nektarios Koukourakis, Eduard Jorswieck, Jürgen Czarske

Proceedings Volume PC12136, PC1213608 (2022) https://doi.org/10.1117/12.2620317

KEYWORDS: Data transmission, Multimode fibers, Holography, Space division multiplexing, Quantum efficiency, Transmitters, Time metrology, Spatial light modulators, Signal to noise ratio, Receivers

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SPIE Journal Paper | 10 April 2021 Open Access

3D-scanning microscopy with adaptive lenses and prisms for zebrafish studies

Wenjie Wang, Florian Lemke, Matthias Wapler, Ulrike Wallrabe, Jürgen Czarske, Nektarios Koukourakis

JOM, Vol. 1, Issue 02, 024501, (April 2021) https://doi.org/10.1117/12.10.1117/1.JOM.1.2.024501

KEYWORDS: Prisms, Microscopy, 3D scanning, Lenses, Microscopes, Digital holography, Objectives, Optical microsystems, Luminescence, Monochromatic aberrations

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Proceedings Article | 5 March 2021 Presentation

Multi-dimensional cell-rotation using multi-core fibers and wavefront shaping

Jiawei Sun, Nils Dunkelberg, Nektarios Koukourakis, Robert Kuschmierz, Juergen Czarske, Jochen Guck

Proceedings Volume 11653, 116530J (2021) https://doi.org/10.1117/12.2576224

KEYWORDS: Optical fibers, Wavefronts, Spatial light modulators, Calibration, Tomography, Stars, Spatial frequencies, Single mode fibers, Phase retrieval, Holography

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Proceedings Article | 5 March 2021 Presentation

Advancing impulsive stimulated Brillouin microscopy using a femtosecond laser for biomechanics

Benedikt Krug, Nektarios Koukourakis, Jürgen Czarske

Proceedings Volume 11645, 116450R (2021) https://doi.org/10.1117/12.2577497

KEYWORDS: Microscopy, Femtosecond phenomena, Spatial resolution, Signal to noise ratio, Continuous wave operation, Tissues, Superposition, Scattering, Pulsed laser operation, Photodiodes

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Proceedings Article | 1 April 2020 Presentation

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

Benedikt Krug, Nektarios Koukourakis, Jürgen Czarske

Proceedings Volume 11359, 1135905 (2020) https://doi.org/10.1117/12.2555358

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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

Proceedings Volume 11351, 113511D (2020) https://doi.org/10.1117/12.2555383

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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

Proceedings Volume 10886, 108860E (2019) https://doi.org/10.1117/12.2507440

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

Proceedings Volume 10679, 106790E (2018) https://doi.org/10.1117/12.2307377

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

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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

Proceedings Volume 10502, 1050217 (2018) https://doi.org/10.1117/12.2286934

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

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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

Proceedings Volume 10335, 1033519 (2017) https://doi.org/10.1117/12.2270301

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

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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

Proceedings Volume 10449, 104490R (2017) https://doi.org/10.1117/12.2269963

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

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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 Presentation + Paper

Adaptive flow-field measurements using digital holography

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

Proceedings Volume 10074, 100740F (2017) https://doi.org/10.1117/12.2252084

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

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Proceedings Article | 21 February 2017 Paper

Spherical aberration correction of adaptive lenses

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

Proceedings Volume 10073, 1007303 (2017) https://doi.org/10.1117/12.2250891

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

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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

Proceedings Volume 9890, 98900L (2016) https://doi.org/10.1117/12.2227052

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

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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

Proceedings Volume 9890, 989005 (2016) https://doi.org/10.1117/12.2231583

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

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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

Proceedings Volume 9890, 98900A (2016) https://doi.org/10.1117/12.2225596

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

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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

Proceedings Volume 9717, 97170Z (2016) https://doi.org/10.1117/12.2212408

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

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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

Proceedings Volume 9628, 962818 (2015) https://doi.org/10.1117/12.2191073

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

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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

Proceedings Volume 9524, 952407 (2015) https://doi.org/10.1117/12.2185090

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

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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

Proceedings Volume 9529, 952903 (2015) https://doi.org/10.1117/12.2184471

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

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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

Proceedings Volume 9132, 91320P (2014) https://doi.org/10.1117/12.2052152

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

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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

Proceedings Volume 8589, 85891J (2013) https://doi.org/10.1117/12.2001159

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

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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

Proceedings Volume 8266, 82660R (2012) https://doi.org/10.1117/12.907677

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

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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

Proceedings Volume 8001, 80010O (2011) https://doi.org/10.1117/12.892185

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

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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

Proceedings Volume 7939, 793927 (2011) https://doi.org/10.1117/12.873170

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

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Showing 5 of 37 publications

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