@article{BauerGutkeHeinrichetal.2020, author = {Bauer, Joachim and Gutke, Marko and Heinrich, Friedhelm and Edling, Matthias and Stoycheva, Vesela and Kaltenbach, Alexander and Burkhardt, Martin and Gruenefeld, Martin and Gamp, Matthias and Gerhard, Christoph and Steglich, Patrick and Steffen, Sebastian and Herzog, Michael and Dreyer, Christian and Schrader, Sigurd}, title = {Novel UV-transparent 2-component polyurethane resin for chip-on-board LED micro lenses}, series = {Optical Materials Express}, volume = {10}, journal = {Optical Materials Express}, number = {9}, issn = {2159-3930}, doi = {10.1364/OME.393844}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-13472}, pages = {2085 -- 2099}, year = {2020}, abstract = {In this work we present a novel optical polymer system based on polyurethane elastomer components, which combines excellent UV transparency with high thermal stability, good hardness, high surface tension and long pot life. The material looks very promising for encapsulation and microlensing applications for chip-on-board (CoB) light-emitting diodes (LED). The extinction coefficient k, refractive index n, and bandgap parameters were derived from transmission and reflection measurements in a wavelength range of 200-890 nm. Thermogravimetry and differential scanning calorimetry were used to provide glass transition and degradation temperatures. The surface tension was determined by means of contact angle measurements. As proof of concept, a commercial InGaN-CoB-LED is used to demonstrate the suitability of the new material for the production of microlenses.}, language = {en} } @inproceedings{KirchnerVillringerGutkeetal.2023, author = {Kirchner, Thomas and Villringer, Claus and Gutke, Marko and Laufer, Jan}, title = {Plano-concave optical sensor for transcranial photoacoustic measurements}, series = {Opto-Acoustic Methods and Applications in Biophotonics VI}, booktitle = {Opto-Acoustic Methods and Applications in Biophotonics VI}, publisher = {Society of Photo-Optical Instrumentation Engineers (SPIE)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-17840}, year = {2023}, abstract = {Biomedical photoacoustics is usually used to image absorption-based contrast in soft tissues up to depths of several centimeters and with sub-millimeter resolution. By contrast, measuring Photoacoustic (PA) signals through hard bone tissue shows severe signal degradation due to aberration and high attenuation of high frequency acoustic signal components. This is particularly noticeable when measuring through thicker, human, skull bone. Which is the main reason why transcranial PA imaging in humans has so far proved challenging to implement. To tackle this challenge, we developed an optical resonator sensor based on a previous planar-concave design. This sensor was found to be highly suitable for measuring the low-pressure amplitude and low acoustic frequency signals that are transmitted through human cranial bone. A plano-concave optical resonator sensor was fabricated to provide high sensitivity in the acoustic frequency range of DC to around 2 MHz, a low noise equivalent pressure and a small active element size enabling it to significantly outperform conventional piezoelectric transducers when measuring PA waves transmitted through ex vivo human cranial bones.}, language = {en} } @article{BauerFursenkoHeinrichetal.2022, author = {Bauer, Joachim and Fursenko, Oksana and Heinrich, Friedhelm and Gutke, Marko and Kornejew, Eckhart and Br{\"o}del, Oliver and Dietzel, Birgit and Kaltenbach, Alexander and Burkhardt, Martin and Edling, Matthias and Steglich, Patrick and Herzog, Michael and Schrader, Sigurd}, title = {Determination of optical constants and scattering properties of transparent polymers for use in optoelectronics}, series = {Optical Materials Express}, volume = {12}, journal = {Optical Materials Express}, number = {1}, publisher = {Optica Publishing Group}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15666}, pages = {204 -- 224}, year = {2022}, abstract = {Knowledge of optical constants, i.e. refractive index n and extinction coefficient k, and light scattering properties of optical polymers are required to optimize micro-optics for light-emitting diodes in terms of efficiency, color properties and light distribution. We present here a model-based diagnostic approach to determine the optical properties of polymers, which should be particularly useful in the development of plastics for optical applications. Optical constants and scattering coefficients were obtained from transmission and reflection measurements in a wavelength range from UV to NIR taking into account scattering effects due to rough surfaces and volume inhomogeneity. Based on the models for the dielectric function, the molecular optical transition energies Eg, critical point energies, Urbach energies and exciton transition energies were determined. Rayleigh and Mie scattering model and van de Hulst\&\#x0027;s anomalous diffraction theory were applied to characterize scattering due to volume inhomogeneities. Scalar diffraction theory was applied to account for surface roughness scattering. Atomic force microscopy with nanomechanical characterization was used to characterize domains in size and shape and to assign optical scattering to a suitable morphological model. The combined optical and mechanical characterization help to improve the qualification of new polymer materials for optical applications.}, language = {en} }