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Author: Schmidt, Markus A. × End date: 2019 × Start date: 2010 × Type: Text × search.filters.applied.f.series: Scientific reports 5 (2015) × WGL Institute: IPHT ×

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    Ultrathin niobium nanofilms on fiber optical tapers--a new route towards low-loss hybrid plasmonic modes
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Wieduwilt, Torsten; Tuniz, Alessandro; Linzen, Sven; Goerke, Sebastian; Dellith, Jan; Hübner, Uwe; Schmidt, Markus A.
    Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices.
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    Faraday rotation and photoluminescence in heavily Tb(3+)-doped GeO2-B2O3-Al2O3-Ga2O3 glasses for fiber-integrated magneto-optics
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Gao, Guojun; Winterstein-Beckmann, Anja; Surzhenko, Oleksii; Dubs, Carsten; Dellith, Jan; Schmidt, Markus A.; Wondraczek, Lothar
    We report on the magneto-optical (MO) properties of heavily Tb3+-doped GeO2-B2O3-Al2O3-Ga2O3 glasses towards fiber-integrated paramagnetic MO devices. For a Tb3+ ion concentration of up to 9.7 × 1021 cm−3, the reported glass exhibits an absolute negative Faraday rotation of ~120 rad/T/m at 632.8 nm. The optimum spectral ratio between Verdet constant and light transmittance over the spectral window of 400–1500 nm is found for a Tb3+ concentration of ~6.5 × 1021 cm−3. For this glass, the crystallization stability, expressed as the difference between glass transition temperature and onset temperature of melt crystallization exceeds 100 K, which is a prerequisite for fiber drawing. In addition, a high activation energy of crystallization is achieved at this composition. Optical absorption occurs in the NUV and blue spectral region, accompanied by Tb3+ photoluminescence. In the heavily doped materials, a UV/blue-to-green photo-conversion gain of ~43% is achieved. The lifetime of photoluminescence is ~2.2 ms at a stimulated emission cross-section σem of ~1.1 × 10−21 cm2 for ~ 5.0 × 1021 cm−3 Tb3+. This results in an optical gain parameter σem*τ of ~2.5 × 10−24 cm2s, what could be of interest for implementation of a Tb3+ fiber laser.