@misc{DoehringProbullaKomziketal.2018, author = {D{\"o}hring, Thorsten and Probulla, Theodor and Komzik, Richard and Mann, Michael and Sivanic, Peter and Stollenwerk, Manfred}, title = {Slovak-Bavarian collaboration on the development of telescope instrumentation}, editor = {Hambalek, Lubomir}, organization = {Hochschule Aschaffenburg}, pages = {1}, year = {2018}, abstract = {Within the project SLOBATCO (Slovak-Bavarian Telescope Collaboration) the Astronomical Institute of the Slovak Academy of Sciences and Aschaffenburg University of Applied Sciences collaborate in the development and commissioning of the new {\O}1.3 m astronomical telescope and the corresponding scientific instrumentation. The project is funded by the Bavarian Academic Center for Central, Eastern and Southeastern Europe (BAYHOST). Technical work packages are targeting filter wheel software for the VIS camera, additional IR filters, and an upgrade of the mirror coating facility by additional sputtering equipment.}, subject = {Spiegelteleskop}, language = {en} } @article{ProbstBegouDoehringetal.2018, author = {Probst, Anne-Catherine and Begou, Thomas and D{\"o}hring, Thorsten and Zeising, Sebastian and Stollenwerk, Manfred and Stadtm{\"u}ller, Johannes and Emmerich, Florian and Lumeau, Julien}, title = {Coating stress analysis and compensation for iridium-based x-ray mirrors}, series = {Applied Optics}, volume = {2018}, journal = {Applied Optics}, number = {57 (29)}, editor = {Publishing OSA,}, pages = {8775 -- 8779}, year = {2018}, abstract = {Iridium-based coatings for mirrors of x-ray telescopes are studied. In particular, stress-induced deformation is characterized and shown to be compressive and equal to -1786  MPa. Two methods for stress compensation are then studied. One relies on the deposition of silica on the back surface of the substrate and a second one relies on the deposition of a chromium sublayer. Advantages and drawbacks of each of these techniques are presented.}, subject = {R{\"o}ntgenteleskop}, language = {en} } @inproceedings{DoehringStollenwerkSchmittetal.2022, author = {D{\"o}hring, Thorsten and Stollenwerk, Manfred and Schmitt, Paul and Szeghalmi, Andrea}, title = {Umweltbest{\"a}ndige Spiegelbeschichtungen aus Iridium f{\"u}r den infraroten Spektralbereich}, series = {DGaO Proceedings}, volume = {2022}, booktitle = {DGaO Proceedings}, number = {123}, publisher = {DGaO}, organization = {TH Aschaffenburg}, issn = {1614-8436}, pages = {1 -- 2}, year = {2022}, abstract = {Das Edelmetall Iridium ist hart; extrem dicht; thermisch, mechanisch und chemisch stabil; weist eine hohe Reflektivit{\"a}t im mittleren und fernen Infrarot auf und hat eine hohe Best{\"a}ndigkeit gegen{\"u}ber Umwelteinfl{\"u}ssen - auch ohne weitere Schutzschichten. Es wurden die komplexen Brechungsindizes f{\"u}r Iridium-Spiegelbeschichtungen bestimmt, welche vorhandene Literaturwerte erg{\"a}nzen.}, subject = {Iridium}, language = {de} } @article{SchmittFeldeDoehringetal.2022, author = {Schmitt, Paul and Felde, Nadja and D{\"o}hring, Thorsten and Stollenwerk, Manfred and Uschmann, Ingo and Hanemann, Kevin and Siegler, Marie and Klemm, Georg and Gratzke, Nancy and T{\"u}nnermann, Andreas and Schwinde, Stefan and Schr{\"o}der, Sven and Szeghalmi, Adriana}, title = {Optical, structural, and functional properties of highly reflective and stable iridium mirror coatings for infrared applications}, series = {Optical Materials Express}, volume = {2022}, journal = {Optical Materials Express}, number = {12 / 2}, doi = {10.1364/OME.447306}, pages = {545 -- 559}, year = {2022}, abstract = {Metallic coatings are essential for numerous optical systems due to their high and broadband refl ectivity in the infrared spectral range. In contrast to well-established (protected)silver and gold mirror coatings, iridium is environmentally durable, referring to ISO 9211-3 and thermally stable up to 600 °C even without protective layers, as demonstrated. Additionally,the optical and related structural properties of atomic layer deposited (ALD) and magnetron sputtered (MS) Ir coatings were investigated using spectrophotometry, FTIR, ellipsometry, WLI,AFM, XRR, XRD, SEM, and electrical resistivity measurements. The properties of Ir ALD and Ir MS coatings diff er due to their topography and microstructure.}, subject = {Iridium}, language = {en} } @article{SchmittFeldeDoehringetal.2022, author = {Schmitt, Paul and Felde, Nadja and D{\"o}hring, Thorsten and Stollenwerk, Manfred and Uschmann, Ingo and Hanemann, Kevin and Siegler, Marie and Klemm, Georg and Gratzke, Nancy and T{\"u}nnermann, Andreas and Schwinde, Stefan and Schr{\"o}der, Sven and Szeghalmi, Adriana}, title = {Optical, structural, and functional properties of highly reflective and stable iridium mirrorcoatings for infrared applications: supplement}, series = {Optical Materials Express}, volume = {2022}, journal = {Optical Materials Express}, number = {12/2}, doi = {10.6084/m9.figshare.17121509}, pages = {545 -- 559}, year = {2022}, abstract = {Metallic coatings are essential for numerous optical systems due to their high and broadband refl ectivity in the infrared spectral range. In contrast to well-established (protected)silver and gold mirror coatings, iridium is environmentally durable, referring to ISO 9211-3 and thermally stable up to 600 °C even without protective layers, as demonstrated. Additionally,the optical and related structural properties of atomic layer deposited (ALD) and magnetron sputtered (MS) Ir coatings were investigated using spectrophotometry, FTIR, ellipsometry, WLI, AFM, XRR, XRD, SEM, and electrical resistivity measurements. The properties of Ir ALD and Ir MS coatings diff er due to their topography and microstructure.}, subject = {Iridium}, language = {en} } @misc{DoehringStollenwerkSchmittetal.2022, author = {D{\"o}hring, Thorsten and Stollenwerk, Manfred and Schmitt, Paul and Szeghalmi, Adriana}, title = {Umweltbest{\"a}ndige Spiegelbeschichtungen aus Iridium f{\"u}r den infraroten Spektralbereich}, publisher = {DGaO}, organization = {TH Aschaffenburg}, pages = {1 -- 1}, year = {2022}, abstract = {Hochreflektierende Metallbeschichtungen sind essenziell f{\"u}r zahlreiche optische Elemente. Bew{\"a}hrte Spiegelbeschichtungen aus Silber und Gold bieten eine hohe und breitbandige Eigenreflexion im infraroten Spektralbereich, sind ohne geeignete Schutzschichten jedoch anf{\"a}llig gegen{\"u}ber Umwelteinfl{\"u}ssen und mechanischer Beanspruchung. Insbesondere im langwelligen Spektralbereich verringern die Absorptionsbanden dieser Schutzschichten teilweise die hohe Spiegelreflektivit{\"a}t wieder. Das Edelmetall Iridium (Ir) ist hart; extrem dicht; thermisch, mechanisch und chemisch stabil; weist eine {\"a}hnlich hohe Reflektivit{\"a}t im mittleren und fernen Infrarot, wie Silber und Gold, auf und hat zus{\"a}tzlich eine hohe Best{\"a}ndigkeit gegen{\"u}ber Umwelteinfl{\"u}ssen - auch ohne Schutzschichten. In diesem Beitrag werden die optischen und strukturellen Eigenschaften von Iridium-Spiegelbeschichtungen, welche mittels Atomlagenabscheidung (ALD) und DC-Magnetron-Sputtern hergestellt wurden, vorgestellt und miteinander verglichen. Die komplexen Brechungsindizes f{\"u}r ALD-erzeugte und gesputterte Iridium-Spiegelbeschichtungen wurden f{\"u}r Wellenl{\"a}ngen von 200 nm bis 20 μm bestimmt, welche nun bereits vorhandene Literaturwerte erg{\"a}nzen.}, subject = {Iridium}, language = {de} } @inproceedings{DoehringStollenwerkSchmittetal.2022, author = {D{\"o}hring, Thorsten and Stollenwerk, Manfred and Schmitt, Paul and Szeghalmi, Adriana}, title = {Environmentally stable iridium mirror coatings for the infrared spectral range}, series = {Proceedings of SPIE}, volume = {2022}, booktitle = {Proceedings of SPIE}, number = {12298}, publisher = {SPIE}, organization = {TH Aschaffenburg}, doi = {https://doi.org/10.1117/12.2632057}, pages = {122980A-1 -- 122980A-08}, year = {2022}, abstract = {Highly reflective metal coatings are essential for numerous optical elements. Established mirror coatings made of silver (Ag) and gold (Au) offer high and broadband self-reflection in the infrared (IR) spectral range but are susceptible to environmental influences and mechanical stress without suitable protective layers. In the long-wavelength spectral range, in particular, the absorption bands of these protective layers partially reduce the high mirror reflectivity again. However, the noble metal iridium (Ir) is hard, extremely dense, and thermally, mechanically, and chemically stable. Iridium provides a similarly high reflectivity in the mid (MIR) and far-infrared (FIR) spectral range, as silver and gold, and high resistance to environmental influences - even without protective layers. In this paper, the different deposition processes, as well as the optical and structural properties of iridium mirror coatings fabricated by atomic layer deposition (ALD) and by magnetron sputtering (MS), are presented and compared with each other. The complex refractive indices for ALD and MS deposited iridium mirror coatings were determined for wavelengths from 200 nm to 20 μm, complementing the existing literature values. We demonstrate that iridium mirror coatings offer a high and broadband reflectivity from the mid to far-infrared spectral range. In contrast to established - protected - silver and gold mirror coatings, the iridium coatings are environmentally durable and thermally stable up to 600 °C, even without protective layers. Therefore, as an interesting mirror coating material, iridium has the potential for special applications in infrared astronomy and probably also for industrial instruments.}, subject = {Iridium}, language = {en} } @misc{DoehringRoedlingKimmeletal.2021, author = {D{\"o}hring, Thorsten and R{\"o}dling, Claudius and Kimmel, Kevin and Zeising, Sebastian and Stadtm{\"u}ller, Johannes and Stollenwerk, Manfred and Verma, Shruti and Rees, Paul}, title = {Optical characterization of reflective coatings for astronomical telescope mirrors}, series = {DGaO Jahrestagung}, volume = {2021}, journal = {DGaO Jahrestagung}, organization = {TH Aschaffenburg}, pages = {1 -- 1}, year = {2021}, abstract = {With ground based optical telescopes astronomers observe celestial objects over a wide spectral range. As usually three or even more reflections at telescope mirrors are involved, good reflection properties of the mirror coatings are important. The aluminum evaporation technique has been - and is still - the standard solution for the reflective coatings of large astronomical mirrors. Such coatings have excellent reflectivity in the ultraviolet and in the visible, but perform poorly in the infrared. Silver is the metal having highest reflectivity for wavelengths longward of 400 nm, but isn´t the best choice for reflectivity in the ultraviolet and for blue light. To avoid degradation by oxidation, durable silver coatings need to be protected by transmitting overcoating layers. In the presented study, different metallic coatings - including unusual ones like sputtered iridium - are characterized to identify a coating that is most suitable for the spectral range from ultraviolet to infrared. Experimental results are compared to simulations based on the complex refractive indices of these materials. Thereby dependence of incidence angle and polarization is also considered.}, subject = {Spiegelteleskop}, language = {en} } @inproceedings{FreudenmannStollenwerkDoehringetal.2021, author = {Freudenmann, Dominic and Stollenwerk, Manfred and D{\"o}hring, Thorsten and Stadtm{\"u}ller, Johannes and Negri, Michele and Lauck, Felix}, title = {Combustion efficiency of iridium coated pellets for environmentally friendly space propulsion}, series = {14th Pico- and Nanosatellite Workshop, W{\"u}rzburg, Germany}, booktitle = {14th Pico- and Nanosatellite Workshop, W{\"u}rzburg, Germany}, year = {2021}, abstract = {Most of the satellite engines still uses critical fuels such as hydrazine, which is chemically aggressive, toxic and carcinogenic. New developments for satellite engines try to avoid such critical propellants. One promising approach is the usage of rocket-grade hydrogen peroxide [H2O2] in mono- and bipropellant driven rocket engines. Catalysts in the rocket engines convert the hydrogen peroxide by an exothermic catalytic reaction; the resulting hot gases oxygen and water vapor provide the thrust. Currently used catalysts are, for example, Al2O3 pellets impregnated with platinum. Within a joint research project of Aschaffenburg University and the German Aerospace Center new catalysts are developed. They consist of ceramic pellets coated with iridium using the magnetron sputtering process. Thereby the surface structure of the iridium layers strongly depends on the used sputtering process conditions [1]. After optimization of the sputtering parameters, it was demonstrated in laboratory experiments that the catalytic effect (measured by the volume of released gas) can be increased by a factor of four compared to platinum impregnated pellets [2]. In first hot firing tests at the test bench complex M11 at the DLR- Institute of Space Propulsion, these new, iridium-based catalysts have been used in a model combustion chamber for hydrogen peroxide decomposition. For this purpose, the reaction chamber was filled with iridium pellets in the high-altitude simulation chamber of the M11.2 test bench. The model chamber was equipped with numerous measuring devices like temperature and pressure sensors (e.g. Tcat, pcat). With the help of the mass flow and the herein obtained data, performance characteristics of the propellant system were accessible. High-concentrated hydrogen peroxide was used in the experiments as monopropellant (~ 87-wt.\% H2O2). During the experiments, the combustion chamber was operated in pulse mode and in continuous mode. Aim of this campaign called MoCa ("Monopropellant Catalytic Demonstrator") is the demonstration of functionality and the performance evaluation of this iridium-based monopropellant system. Recent experimental results will be presented. References: [1] A. B{\"u}ttner et al., Thin Solid Films 2018, 662: 41-46 [2] M. Stollenwerk et al., Journal of Materials Science 2021, 56(16), 9974-9984}, subject = {Satellitentechnik}, language = {de} } @inproceedings{DoehringStadtmuellerStollenwerketal.2021, author = {D{\"o}hring, Thorsten and Stadtm{\"u}ller, Johannes and Stollenwerk, Manfred and Cotroneo, Vincenzo and Pareschi, Giovanni and Gibertini, Eugenio and Magagnin, Luca}, title = {Low-density coatings for enhanced X-ray reflectivity of astronomical telescope mirrors}, series = {DGaO Proceedings}, volume = {2021}, booktitle = {DGaO Proceedings}, number = {122}, publisher = {DGaO}, organization = {TH Aschaffenburg}, issn = {1614-8436}, pages = {1 -- 2}, year = {2021}, abstract = {High reflectivity grazing incidence mirrors of astronomical X-ray telescopes are usually coated with thin layers of iridium, gold, or platinum. Due to a series of absorption edges, these noble metals have low reflectivity in the 2 - 4 keV band. We present the development of innovative material combinations using chromium and an additional layer of polydopamine for enhanced reflectivity X-ray coatings.}, subject = {R{\"o}ntgenteleskop}, language = {en} }