@misc{13495, abstract = {{The use of additive manufacturing for rapid prototyping of near-infrared and terahertz components provides seamless and error-free production. This article discusses the additive manufacturing and post-processing of axicons and their performance evaluation using attenuation and near-field-measurements based fundamental techniques. The axicons are manufactured using the materials cyclic olefin copolymer (TOPAS) and polymethyl methacrylate (PMMA), for their respective use in terahertz and near-infrared applications. The optical and terahertz components manufactured using traditional 3D-printing processes, e.g., fused filament fabrication or stereolithography apparatus exhibit high surface roughness in the range of 15 ± 2.5 µm, resulting in undesired propagation and scattering in the near infrared wavelengths. This research work proposes an economical post-processing technique for additively manufactured terahertz and near-infrared axicons for applications in multispectral characterization, e.g., bio-sensing. The authors used an enhanced method of dip-coating, which involves interval dipping and intermittent hardening to achieve better surface finish. An emphasis is placed on interval dipping and intermittent hardening, which lead to excellent transparency in case of additively-manufactured near-infrared axicons. The dip-coated samples exhibit surface roughness below 10 nm. With the use of heated resin material as the coating layer, due to reduced viscosity, the resin material distributes uniformly over the surface of the 3D-printed terahertz and near-infrared axicons. The authors also observed that the DOF length deviation between unprocessed and enhanced dip-coated axicons remains within the measurement error estimation from analytical calculations. In addition to the improved surface finish and transparency, the coatings are also closely matched in refractive index to the axicon material. Such post-processed axicons pave the way for producing a wide array of systems in the fields of communication, imaging, and bio-sensing.}}, author = {{Shrotri, Abhijeet Narendra and Starsaja, Annamarija and Joshi, Suraj and Preu, Sascha and Stübbe, Oliver}}, booktitle = {{Photonics}}, issn = {{2304-6732}}, keywords = {{additive manufacturing, stereolithography, dip-coating, post-processing}}, number = {{3}}, publisher = {{MDPI AG}}, title = {{{Multispectral Characterization of Additively Manufactured and Dip-Coated Axicons}}}, doi = {{10.3390/photonics13030264}}, volume = {{13}}, year = {{2026}}, } @unpublished{13346, abstract = {{This article discusses the additive manufacturing and post-processing of axicons, and their performance evaluation using attenuation and near-field-measurements based fundamental techniques. The axicons are manufactured using the materials cyclic olefin copolymer (TOPAS) and polymethyl methacrylate (PMMA), for their respective use in terahertz and near-infrared applications. An emphasis is placed on the dip-coating-based post-processing. Interval dipping and intermittent hardening lead to excellent surface finish and transparency in case of additively-manufactured near-infrared axicons. The dip-coated samples exhibit surface roughness of sub 10nm, and a uniformly distributed thin layer coating over the axicon surface. In addition to the improved surface finish and transparency, the coatings are also closely matched in refractive index to the axicon material. Such post-processed axicons pave the way for rapid-prototyping and production.}}, author = {{Shrotri, Abhijeet Narendra and Starsaja, Annamarija and Joshi, Suraj and Preu, Sascha and Stübbe, Oliver}}, booktitle = {{Optica Open}}, issn = {{2334-2536 }}, keywords = {{additive manufacturing, stereolithography, dip-coating, post-processing}}, pages = {{5}}, publisher = {{Optica Publishing Group}}, title = {{{Multispectral characterization of additively manufactured and dip-coated axicons}}}, doi = {{https://doi.org/10.1364/opticaopen.31149016}}, year = {{2026}}, } @unpublished{13363, abstract = {{This article discusses the additive manufacturing and post-processing of axicons, and their performance evaluation using attenuation and near-field-measurements based fundamental techniques. The axicons are manufactured using the materials cyclic olefin copolymer (TOPAS) and polymethyl methacrylate (PMMA), for their respective use in terahertz and near-infrared applications. An emphasis is placed on the dip-coating-based post-processing. Interval dipping and intermittent hardening lead to excellent surface finish and transparency in case of additively-manufactured near-infrared axicons. The dip-coated samples exhibit surface roughness of sub 10 nm, and a uniformly distributed thin layer coating over the axicon surface. In addition to the improved surface finish and transparency, the coatings are also closely matched in refractive index to the axicon material. Such post-processed axicons pave the way for rapid-prototyping and production.}}, author = {{Shrotri, Abhijeet Narendra and Starsaja, Annamarija and Joshi, Suraj and Preu, Sascha and Stübbe, Oliver}}, booktitle = {{Photonics: Open Access Journal}}, issn = {{2304-6732 }}, keywords = {{additive manufacturing, stereolithography, dip-coating, post-processing}}, pages = {{15}}, publisher = {{MDPI }}, title = {{{Multispectral Characterization of Additively Manufactured and Dip-Coated Axicons}}}, doi = {{https://doi.org/10.20944/preprints202602.0389.v1}}, year = {{2026}}, } @misc{12424, abstract = {{Additive manufacturing of optical, electrical, and mechanical components is a beneficial approach for the rapid prototyping of components and error elimination, with short turnaround times. However, additively manufactured components usually have rough surfaces that need post-processing, particularly for optical components, where the surface roughness must be a small fraction of the wavelength. We demonstrate an innovative and economical approach by dip-coating with the same resin used for printing in a simple post-processing step, providing high transparency to the 3D-printed optical components and reducing surface roughness while achieving perfect index matching of the coating layer. The surface roughness of the 3D-printed optical components drops to 5 nm (arithmetic average) after the dip-coating process. We observed significant performance enhancements after comparing the unprocessed optical components and the dip-coated optical components, including optical transparency and a shiny surface finish for previously rough surfaces.}}, author = {{Shrotri, Abhijeet Narendra and Preu, Sascha and Stübbe, Oliver}}, booktitle = {{Coatings : open access journal}}, issn = {{2079-6412}}, keywords = {{additive manufacturing, post-processing, optics, dip-coating}}, number = {{2}}, publisher = {{MDPI AG}}, title = {{{Achieving Transparency and Minimizing Losses of Rough Additively Manufactured Optical Components by a Dip-Coating Surface Finish}}}, doi = {{10.3390/coatings15020210}}, volume = {{15}}, year = {{2025}}, } @unpublished{13029, abstract = {{Additive manufacturing of optical, electrical and mechanical components is a beneficial approach for rapid prototyping of components and error elimination with short turn around times. However, additively manufactured components usually have rough surfaces which need post-processing, in particular for optical components where the surface roughness must be a small fraction of the wavelength. We demonstrate an innovative and economical approach by dip-coating with the same resin as used for printing, providing high transparency of the 3D-printed optical components and reduced surface roughness with perfect index matching of the coating layer in a simple post processing step. The surface roughness of the 3D-printed optical components drops to 5 nm (arithmetic average) after the dip-coating process. We observed significant performance enhancement after comparing the unprocessed optical components and dip-coated optical components, including achieving optical transparency and shiny surface finish of previously rough surfaces.}}, author = {{Shrotri, Abhijeet Narendra and Preu, Sascha and Stübbe, Oliver}}, booktitle = {{Coatings : open access journal}}, keywords = {{additive manufacturing, post-processing, optics, dip-coating}}, pages = {{10}}, publisher = {{MDPI}}, title = {{{Achieving Transparency and Minimizing Loss of Rough Additively Manufactured Optical Components by a Dip-Coating Surface Finish}}}, doi = {{10.20944/preprints202501.1899.v1}}, year = {{2025}}, } @misc{11359, abstract = {{The reliability and lifetime of electrical contacts is an important aspect in system reliability and is influenced by numerous factors. Micro motions as well as vibrations lead to fretting wear, which can result in wear through of the protective coating. If this layer is worn through, the non-noble layer underneath is exposed, resulting in the occurrence of fretting corrosion with further relative motion. This leads to an increased electrical contact resistance (ECR) and can cause the contact to fail. Increasing the hardness of the coating material can reduce the wear and in turn increase contacts’ lifetime. The micro hardness, wear and lifetime of contacts with modified hard silver coatings are investigated in fretting wear and corrosion tests and the results compared to a conventional silver coating. Since one of the modifications shows a significant reduction in wear and hence improvement in lifetime, further analysis with SEM and FIB is conducted in order to identify the key mechanisms leading to this improvement. With a further increase in lifetime however, fatigue as well as delamination of the coating are revealed to be of high relevance. Both can be main causes of electrical contact failure under fretting load. In general, at lower number of cycles, increased micro hardness has the greatest effect on lifetime and wear while at the higher number of cycles, fatigue is observed to be the dominant failure mechanism.}}, author = {{Probst, Roman and Song, Jian}}, booktitle = {{2023 IEEE 68th Holm Conference on Electrical Contacts (HOLM)}}, isbn = {{979‐8‐3503‐4244‐4}}, issn = {{2158‐9992}}, keywords = {{electrical contacts, lifetime, silver coating, fretting corrosion, fatigue, wear through}}, location = {{Seattle }}, pages = {{88 -- 94}}, publisher = {{IEEE}}, title = {{{Influence of Hardness and Fatigue on the Lifetime of a Modified Silver Coating in Fretting Wear and Corrosion Tests}}}, doi = {{10.1109/holm56075.2023.10352299}}, year = {{2023}}, }