Publications Search Results

Now showing 1 - 10 of 122
  • Publication
    Properties of new transparent polymers for optical applications
    ( 2021)
    Schulz, U.
    ;
    Gratzke, N.
    ;
    Seifert, T.
    ;
    Hahmann, C.
    ;
    Rickelt, F.
    ;
    Schröder, S.
    Transparent thermoplastic polymers are widely used as materials for precision optical lenses as well as for sensing and lighting. The advantages of transparent polymers for optical parts are significant weight reduction, high impact strength, molding options and cost saving mass-production. Antireflection (AR) coatings are essential to improve transmission and contrast of lenses, windows and display covers. Polymer-capable coating conditions must be investigated for each type of polymer because of the varying chemical and physical properties of optical polymers. A presently well-established coating technology for plastics is plasma ion-assisted deposition (Plasma-IAD). It enables the coating deposition at low temperature as well as low-energy plasma conditions and ion bombardment to tailor the optical and mechanical properties of oxide layers. A good understanding of complex interactions of polymer surfaces with plasma and high-energetic radiation is a key factor to achieve polymer optics with high-end AR-properties and long-time durability. The Aim of this study is to evaluate and to understand the surface properties of polymers which are relevant for the deposition of optical coatings and for its later application. The investigation is focused primarily on the new polymer types APEL, Iupizita EP and OKP. They are compared with the long-established materials such as polycarbonate (Makrolon) and ZeonexE48R. The optical properties of the polymers are systematically studied including the influence of aging caused by UV-irradiation, humidity and heat. In addition, properties like surface hardness, water absorption and thermal stability are compared and discussed. Different pre-treatments and designs are considered to bond multilayer AR systems to surfaces with high adhesive strength. In addition, plasma-etching technology AR-plas is applied to achieve AR properties for the visible spectral range (VIS).
  • Publication
    Tunable exciton-polaritons emerging from WS2 monolayer excitons in a photonic lattice at room temperature
    ( 2021)
    Lackner, L.
    ;
    Dusel, M.
    ;
    Egorov, O.A.
    ;
    Han, B.
    ;
    Knopf, H.
    ;
    Eilenberger, F.
    ;
    Schröder, S.
    ;
    Watanabe, K.
    ;
    Taniguchi, T.
    ;
    Tongay, S.
    ;
    Anton-Solanas, C.
    ;
    Höfling, S.
    ;
    Schneider, C.
    Engineering non-linear hybrid light-matter states in tailored lattices is a central research strategy for the simulation of complex Hamiltonians. Excitons in atomically thin crystals are an ideal active medium for such purposes, since they couple strongly with light and bear the potential to harness giant non-linearities and interactions while presenting a simple sample-processing and room temperature operability. We demonstrate lattice polaritons, based on an open, high-quality optical cavity, with an imprinted photonic lattice strongly coupled to excitons in a WS2 monolayer. We experimentally observe the emergence of the canonical band-structure of particles in a one-dimensional lattice at room temperature, and demonstrate frequency reconfigurability over a spectral window exceeding 85 meV, as well as the systematic variation of the nearest-neighbour coupling, reflected by a tunability in the bandwidth of the p-band polaritons by 7 meV. The technology presented in this work is a critical demonstration towards reconfigurable photonic emulators operated with non-linear photonic fluids, offering a simple experimental implementation and working at ambient conditions.
  • Publication
    Coatings with barrier layers for extreme-short wavelengths
    ( 2021)
    Yulin, S.
    ;
    Trost, M.
    ;
    Schwinde, S.
    ;
    Schröder, S.
    Over the last few decades, remarkable progress has been made in the field of multilayer coatings for the EUV spectral region, mainly due to the demands of EUV lithography for the semiconductor industry. The progress is associated with a deep understanding of the multilayer film growth, application of advanced smoothing technologies for multilayer interfaces, as well as the development of modern deposition and characterization techniques. The projection optics precisely coated by Mo/Si mirrors with 70 % reflectivity is the heart of the performance of industrial EUVL steppers recently developed by ASML for high-volume chip production. While the EUVL at 13.5 nm has just launched into the market, the first high-performance LaN/B multilayer mirrors with reflectivity up to 61 % were developed for the next emerging lithography generation with a reduced wavelength of 6.6 nm. Recent technological progress in EUVL optics and radiation sources triggered the development of compact microscopes in the water window spectral range (2.4 - 4.4 nm). The optimization of the multilayer design and deposition process of Cr/V, Cr/Sc and Cr/C mirrors resulted in reflectivity of 14.5% at 2.42 nm, 27.0 % at 3.16 nm, and 15,6% at a wavelength of 4.42 nm, respectively. These promising and still not limiting results indicate a large potential for future application of multilayer coated optics in various application fields such as microscopy in the water window, plasma diagnostics, spectroscopy, and astrophysics.
  • Publication
    Second Harmonic Generation in monolayer WS2 with double resonant Bragg-Cavities
    ( 2021)
    Knopf, H.
    ;
    Zilk, M.
    ;
    Bernet, S.
    ;
    Ngo, G.Q.
    ;
    Abtahi, F.A.
    ;
    George, A.
    ;
    Najafidehaghani, E.
    ;
    Gan, Z.
    ;
    Weissflog, M.
    ;
    Vogl, T.
    ;
    Turchanin, A.
    ;
    Schulz, U.
    ;
    Schröder, S.
    ;
    Eilenberger, F.
    Transition metal dichalcogenides (TMDCs) are semiconducting 2D-materials with a direct bandgap in a range of 1.0 to 2.5 eV [1]. They exhibit strong second-order nonlinearity per unit thickness, making them interesting for nonlinear light-conversion devices [2]. Due to their small thickness, an interaction enhancement is paramount for efficient operation [3]. We have previously demonstrated that such enhancement can be acchieved by embedding TMDCs into monolithic resonators [4] if a gentle coating process compliant with the sensitive nature of the monolayer TMDC flakes is utilized.
  • Publication
    Fully tuneable bloch-band polaritons emerging from WS2 monolayer excitons in an optical lattice at room temperature
    ( 2021)
    Lackner, L.
    ;
    Dusel, M.
    ;
    Anton-Solanas, C.
    ;
    Knopf, H.
    ;
    Eilenberger, F.
    ;
    Egorov, O.
    ;
    Schröder, S.
    ;
    Höfling, S.
    ;
    Schneider, C.
    The engineering of non-linear light-matter states in optical lattices has emerged as a key research strategy for the exploration of Hamiltonians in the spirit of ultrafast- and possibly quantum-simulation. It furthermore has revealed its potential to probe non-trivial topology phenomena. Excitons in atomically thin crystals have emerged as an ideal active medium for such purposes, since they couple strongly with light, and bear the potential to harness giant non-linearities and interactions. In this work, we present a pioneering experiment conducted at room temperature in an open optical cavity of high quality, with an implemented one-dimensional photonic lattice (see Fig. 1a ). Such optical microstructure has been utilized recently in experiments addressing Bloch-mode condensates using fluorescent proteins [1] . In our present work, however, we integrate an atomically thin layer of WS 2 in such a device [2] . We discuss the strong-to-weak coupling crossover, and highlight the emergence of a lattice-band-structure in the tight-binding configuration at room temperature, fuelled by the emission from monolayer excitons ( Fig. 1b ).
  • Publication
    Demonstration of a polariton step potential by local variation of light-matter coupling in a van-der-Waals heterostructure
    ( 2020)
    Rupprecht, C.
    ;
    Klaas, M.
    ;
    Knopf, H.
    ;
    Taniguchi, T.
    ;
    Watanabe, K.
    ;
    Qin, Y.
    ;
    Tongay, S.
    ;
    Schröder, S.
    ;
    Eilenberger, F.
    ;
    Höfling, S.
    ;
    Schneider, C.
    The large oscillator strength of excitons in transition metal dichalcogenide layers facilitates the formation of exciton-polariton resonances for monolayers and van-der-Waals heterostructures embedded in optical microcavities. Here, we show, that locally changing the number of layers in a WSe2/hBN/WSe2 van-der-Waals heterostructure embedded in a monolithic, high-quality-factor cavity gives rise to a local variation of the coupling strength. This effect yields a polaritonic stair case potential, which we demonstrate at room temperature. Our result paves the way towards engineering local polaritonic potentials at length scales down to atomically sharp interfaces, based on purely modifying its real part contribution via the coherent light-matter coupling strength g.
  • Publication
    Optical interference coatings measurement problem 2019
    ( 2020)
    Trost, M.
    ;
    Duparré, A.
    ;
    Ristau, D.
    ;
    Schröder, S.
    The 2019 Optical Interference Coatings measurement problem comprised the determination of the total backscattering, forward scattering, reflectance, and transmittance spectra of a multilayer system.
  • Publication
    Light scattering characterization of single-layer nanoporous SiO2 antireflection coating in visible light
    ( 2020)
    Sekman, Y.
    ;
    Felde, N.
    ;
    Ghazaryan, L.
    ;
    Szeghalmi, A.
    ;
    Schröder, S.
    Antireflective coatings are widely applied on transparent optical components to reduce reflections at surfaces. Nanoporous silica (NP SiO2) thin films with tailored refractive index properties are used as single-layer antireflective coatings providing nearly zero reflectivity. In this work, light scattering properties of nanoporous silica single-layer antireflective coatings are investigated in order to determine their optical quality by means of total scattering and detailed roughness analysis. Scattering and roughness characterization of the samples coated with different film thicknesses were realized to distinguish the influences of nanopores and surface roughness on scattering losses in the visible (VIS) spectral range. No significant correlation of scattering losses with the film thickness is found, showing negligible influence of the nanopores to the overall scattering properties compared with the dominating effect of interface roughness. Moreover, the scattering losses from coated fused silica glass were observed as low as 20 ppm (0.002%). It is confirmed that NP SiO2 single-layer antireflective coatings are suitable to be used in optics demanding extremely low scattering characteristics.
  • Publication
    Black and white fused silica: Modified sol-gel process combined with moth-eye structuring for highly absorbing and diffuse reflecting SiO2 glass
    ( 2020)
    Brunner, R.
    ;
    Kraus, M.
    ;
    Hirte, J.
    ;
    Diao, Z.
    ;
    Weishaupt, K.
    ;
    Spatz, J.P.
    ;
    Harzendorf, T.
    ;
    Trost, M.
    ;
    Munser, A.S.
    ;
    Schröder, S.
    ;
    Bär, M.
    Diffuse reflecting (white) and highly absorbing (black) fused silica based materials are presented, which combine volume modified substrates and surfaces equipped with antireflective moth-eye-structures. For diffuse reflection, micrometer sized cavities are created in bulk fused silica during a sol-gel process. In contrast, carbon black particles are added to get the highly absorbing material. The moth-eye-structures are prepared by block copolymer micelle nanolithography (BCML), followed by a reactive-ion-etching (RIE) step. The moth-eye-structures drastically reduce the specular reflectance on both diffuse reflecting and highly absorbing samples across a wide spectral range from 250 nm to 2500 nm and for varying incidence angles. The adjustment of the height of the moth-eye-structures allows us to select the spectral position of the specular reflectance minimum, which measures less than 0.1%. Diffuse Lambertian-like scattering and absorbance appear nearly uniform across the selected spectral range, showing a slight decrease with increasing wavelength.
  • Publication
    Linear and nonlinear absorption of titanium dioxide films produced by plasma ion-assisted electron beam evaporation: Modeling and experiments
    ( 2020)
    Stenzel, O.
    ;
    Wilbrandt, S.
    ;
    Mühlig, C.
    ;
    Schröder, S.
    Titanium dioxide films were prepared by plasma ion-assisted electron beam evaporation. Linear optical properties were investigated in terms of spectrophotometry using the beta-distributed oscillator (ß_do) model as a parametrized dispersion law. The nonlinear two-photon absorption coefficient of titanium dioxide was determined by means of the laser-induced deflection technique at a wavelength of 800 nm. The obtained values of (2-5) × 10−11 cm/W were consistent with published experimental values for rutile as well as for simulations performed in the frames of the ß_do and Sheik-Bahae models.