TY - JOUR A1 - Gerhard, Christoph A1 - Letien, Emilie A1 - Cressent, Thomas A1 - Hofmann, Mandy T1 - Inline monitoring of hydrogenous plasma-induced defect formation within fused silica via plasma emission spectroscopy JF - Applied Physics A: Materials Science and Processing N2 - In this paper, the indirect monitoring of plasma-induced defect formation within fused silica via plasma emission spectroscopy is presented. It is shown that low-pressure plasma treatment with hydrogen as process gas leads to a decrease in UV transmission of fused silica. This decrease can be directly attributed to oxygen vacancy-related defects and the presence of hydrogen within the silicon dioxide glass network. By the analysis of the plasma composition, it was observed that the amount of oxygen within the plasma increases with increasing treatment duration. Hence, oxygen was continuously released from glass network in the course of the plasma treatment. It was further observed that this release is strongly dependent on the applied plasma power where the lowest process efficiency occurs at the highest plasma power. It is shown that an increase in plasma power leads to a remarkable increase in light emission from the working gas, hydrogen. This observation indicates that the higher the degree of excitation and ionisation of the plasma, the lower the efficiency of plasma-induced formation of oxygen deficiency-related defects. This finding is of mentionable relevance for a better understanding of plasma-induced surface modification and coating processes. Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-13118 SN - 1432-0630 VL - 126 ER - TY - JOUR A1 - Bauer, Joachim A1 - Gutke, Marko A1 - Heinrich, Friedhelm A1 - Edling, Matthias A1 - Stoycheva, Vesela A1 - Kaltenbach, Alexander A1 - Burkhardt, Martin A1 - Gruenefeld, Martin A1 - Gamp, Matthias A1 - Gerhard, Christoph A1 - Steglich, Patrick A1 - Steffen, Sebastian A1 - Herzog, Michael A1 - Dreyer, Christian A1 - Schrader, Sigurd T1 - Novel UV-transparent 2-component polyurethane resin for chip-on-board LED micro lenses JF - Optical Materials Express N2 - 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. Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-13472 SN - 2159-3930 VL - 10 IS - 9 SP - 2085 EP - 2099 ER - TY - JOUR A1 - Gerhard, Christoph A1 - Dobis, Alexander T1 - Manufacturing-induced surface contaminations JF - Vakuum in Forschung und Praxis N2 - Summary In the course of classical optics manufacturing glass components are in permanent direct contact with aqueous operating materials. Such contact leads to a certain absorption of water and hydrogenous compounds that may induce severe glass defects. In this contribution, absorption of hydrogen and other contaminants during grinding of glass was observed and qualitatively detected via laser-induced breakdown spectroscopy. It is shown that hydrogen, calcium, magnesium, and carbon are implanted into the glass surface where the contaminant concentration increases over grinding time or contact time of the glass surface with water and the grinding tool, respectively. The contaminants hydrogen, calcium, and magnesium can be attributed to the water used as lubricant. In contrast, carbon most likely originates from wear debris of the used silicon carbide grinding pads. Several possible mechanisms that lead to such surface contamination of glasses during grinding – diffusion, accumulation in micro cracks as well as the formation of hydrated silica – are finally introduced. Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-15656 VL - 33 IS - 1 SP - 33 EP - 37 PB - Wiley ER - TY - JOUR A1 - Hermann, Jörg A1 - Grojo, David A1 - Axente, Emanuel A1 - Gerhard, Christoph A1 - Burger, Miloš A1 - Craciun, Valentin T1 - Ideal radiation source for plasma spectroscopy generated by laser ablation JF - Physical Review E N2 - Laboratory plasmas inherently exhibit temperature and density gradients leading to complex investigations. We show that plasmas generated by laser ablation can constitute a robust exception to this. Supported by emission features not observed with other sources, we achieve plasmas of various compositions which are both uniform and in local thermodynamic equilibrium. These properties characterize an ideal radiation source opening multiple perspectives in plasma spectroscopy. The finding also constitutes a breakthrough in the analytical field as fast analyses of complex materials become possible. Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-16132 VL - 96 IS - 5 PB - American Physical Society (APS) ER - TY - GEN A1 - Gerhard, Christoph A1 - Letien, Emilie A1 - Cressent, Thomas A1 - Hofmann, Mandy T1 - Impact of the plasma power on plasma-induced increase in absorption of fused silica T2 - Wissenschaftliche Beiträge 2019 N2 - In the last decades, laser machining of fused silica has gained in importance where the main challenge is to overcome the high transmission of this medium in order to achieve surface absorption. One approach is plasma treatment using hydrogenous process gases. In doing so, a near-surface glass layer is chemically modified by a removal of oxygen and an implantation of hydrogen, resulting in the formation of optically active defects and an increase in absorption. Against this background, the impact of the plasma power on plasma-induced increase in absorption of fused silica was investigated in the present work. Here, the highest efficiency of the plasma treatment process was found at the lowest applied plasma power whereas for higher plasma powers, a notably lower increase in absorption was observed. This effect is attributed to the decomposition of plasma species required for initiating the formation of optically active defects within the glass. Such decomposition increases with rising power due to the corresponding increase in electric field strength within the plasma. This finding is of substantial interest for an extensive understanding of plasma-glass interactions. N2 - Die Laserbearbeitung von Quarzglas hat in den letzten Jahrzehnten an Bedeutung gewonnen. Dabei besteht die Herausforderung darin, die hohe Transmission dieses Mediums zu überwinden. Hierzu stellt eine Plasmabehandlung mittels wasserstoffhaltigen Prozessgasen einen Ansatz dar. Dabei wird eine oberflächennahe Glasschicht durch Entfernung von Sauerstoff und Implantation von Wasserstoff chemisch modifiziert, woraus die Ausbildung optisch aktiver Defekte und ein Anstieg der Absorption resultieren. Vor diesem Hintergrund wurde in dieser Arbeit der Einfluss der Plasmaleistung auf die plasmainduzierte Absorptionssteigerung untersucht. Die höchste Effizienz der Plasmabehandlung wurde bei der geringsten applizierten Leistung erzielt, wohingegen bei höheren Plasmaleistungen nennenswert geringere Absorptionssteigerungen beobachtet wurden. Dieser Effekt wird auf den Zerfall von Plasmaspezies, die für eine Ausbildung optisch aktiver Defekte benötigt werden, zurückgeführt, welcher mit ansteigender Leistung und dem damit einhergehenden Anstieg der elektrischen Feldstärke im Plasma anwächst. Diese Erkenntnis ist von hohem Interesse für ein umfassendes Verständnis von Plasma-Glas-Wechselwirkungen. N2 - Ces dernières décennies, les applications laser en usine composées de silice fondue ont gagné en importance, l'enjeu consistant à surmonter le problème de la transmission élevée de ce milieu dans le but d’obtenir l’absorption de surface. Une façon d’aborder le problème est d’appliquer le traitement au plasma en utilisant des procédés au gaz de dihydrogène. En agissant ainsi, une couche de verre proche de la surface est modifiée chimiquement par l’ablation d’oxygène et l’implantation d’hydrogène, ce qui provoque la formation de défauts optiquement actifs et l’augmentation de l’absorption. Dans ce contexte, l’impact de la puissance du plasma sur l’augmentation de l’absorption de silice fondue induite par le plasma a été étudié dans cet article. Ici, la meilleure efficacité du traitement au plasma a été constatée à la puissance de plasma la plus faible tandis que pour de plus fortes puissances, une augmentation bien plus faible en absorption a été observée. Cet effet est attribué à la décomposition des espèces de plasma requises dans la formation des défauts optiquement actifs à l’intérieur du verre. Une telle décomposition augmente avec la montée de puissance due à l'augmentation de force du champ électrique dans le plasma. Cette découverte est d’un intérêt considérable pour une compréhension plus poussée des interactions plasma-verre. Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-10802 SN - 0949-8214 VL - 23 SP - 33 EP - 37 ER - TY - JOUR A1 - Gerhard, Christoph A1 - Gimpel, Thomas A1 - Tasche, Daniel A1 - Koch, Jennifer A1 - Brückner, Stephan A1 - Flachenecker, Günter A1 - Wieneke, Stephan A1 - Schade, Wolfgang A1 - Viöl, Wolfgang T1 - Atmospheric pressure plasma-assisted femtosecond laser engraving of aluminium JF - Journal of Physics D: Applied Physics N2 - In this contribution, we report on the impact of direct dielectric barrier discharge argon plasma at atmospheric pressure on femtosecond laser engraving of aluminium. It is shown that the assisting plasma strongly affects the surface geometry and formation of spikes of both laser-engraved single lines and patterns of adjacent lines with an appropriate overlap. Further, it was observed that the overall ablation depth is significantly increased in case of large-scale patterning whereas no notable differences in ablation depth are found for single lines. Several possible mechanisms and underlying effects of this behaviour are suggested. The increase in ablation depth is supposed to be due to a plasma-induced removal of debris particles from the cutting point via charging and oxidation as supported by EDX analysis of the re-solidified debris. Furthermore, the impact of a higher degree of surface wrinkling as well as direct interactions of plasma species with the aluminium surface on the ablation process are discussed. Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-10521 SN - 1361-6463 VL - 51 SP - 1 EP - 7 ER - TY - JOUR A1 - Gerhard, Christoph A1 - Stappenbeck, Marco T1 - Impact of the Polishing Suspension Concentration on Laser Damage of Classically Manufactured and Plasma Post-Processed Zinc Crown Glass Surfaces JF - Applied Sciences N2 - The laser-induced damage threshold of optics is an issue of essential importance in high-power laser applications. However, the complex and partially interacting mechanisms as well as the underlying reasons for laser damage of glass surfaces are not yet fully understood. The aim of the present work is to contribute to a better understanding of such damage mechanisms by providing original results on the impact of classical glass surface machining on the laser-induced damage threshold. For this purpose, glass samples were prepared with well-defined process conditions in terms of the used lapping and polishing agents and suspensions. Further, the samples were post-processed by atmospheric pressure plasma for precision cleaning. The laser-induced damage threshold and surface contamination by residues from the manufacturing process were determined before and after plasma post-processing. It is shown that the polishing suspension concentration has a certain impact on the laser-induced damage threshold and surface contamination by residues from used working materials. The highest damage threshold of 15.2 J/cm² is found for the lowest surface contamination by carbon which occurs in the case of the highest polishing suspension concentration. After plasma treatment for merely 60 s, this value was increased to 20.3 J/cm² due to the removal of surface-adherent carbon. The results thus imply that the laser-induced damage threshold can notably be increased by first choosing appropriate process parameters during classical manufacturing and second plasma post-processing for surface finishing. Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-10556 SN - 2076-3417 VL - 8 IS - 9 SP - 1 EP - 15 PB - MDPI ER -