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- ItemNumerical and Experimental Demonstration of Intermodal Dispersive Wave Generation(Weinheim : Wiley VCH, 2021) Lüpken, Niklas M.; Timmerkamp, Maximilian; Scheibinger, Ramona; Schaarschmidt, Kay; Schmidt, Markus A.; Boller, Klaus‐J.; Fallnich, CarstenEvidence of intermodal dispersive wave generation mediated by intermodal cross-phase modulation (iXPM) between different transverse modes during supercontinuum generation in silicon nitride waveguides is presented. The formation of a higher-order soliton in one strong transverse mode leads to phase modulation of a second, weak transverse mode by iXPM. The phase modulation enables not only supercontinuum generation but also dispersive wave generation within the weak mode, that otherwise has insufficient power to facilitate dispersive wave formation. The nonlinear frequency conversion scheme presented here suggests phase-matching conditions beyond what is currently known, which can be exploited for extending the spectral bandwidth within supercontinuum generation.
- ItemCharged domains in ferroelectric, polycrystalline yttrium manganite thin films resolved with scanning electron microscopy(Bristol : IOP Publ., 2020) Rayapati, Venkata Rao; Bürger, Danilo; Du, Nan; Kowol, Cornelia; Blaschke, Daniel; Stöcker, Hartmut; Matthes, Patrick; Patra, Rajkumar; Skorupa, Ilona; Schulz, Stefan E.; Schmidt, HeidemarieWe have investigated ferroelectric charged domains in polycrystalline hexagonal yttrium manganite thin films (Y1Mn1O3, Y0.95Mn1.05O3, Y1Mn0.99Ti0.01O3, and Y0.94Mn1.05Ti0.01O3) by scanning electron microscopy (SEM) in secondary electron emission mode with a small acceleration voltage. Using SEM at an acceleration voltage of 1.0 kV otherwise homogenous surface charging effects are reduced, polarization charges can be observed and polarization directions (±Pz) of the ferroelectric domains in the polycrystalline thin films can be identified. Thin films of different chemical composition have been deposited by pulsed laser deposition on Pt/SiO2/Si structures under otherwise same growth conditions. Using SEM it has been shown that different charged domain density networks are existing in polycrystalline yttrium manganite thin films. © 2020 IOP Publishing Ltd.
- ItemCorrelations between the structure and superconducting properties of MT-YBaCuO(Bristol : IOP Publ., 2020) Prikhna, T.A.; Moshchill, V.E.; Rabier, J.; Chaud, X.; Joulain, A.; Pan, A.V.; Litskendorf, D.; Habisreuther, T.Comprehensive experimental results of fully oxidized (up to YBa2Cu3O6,9-7) melt-Textured YBaCuO materials with different microstructures are presented. These microstructures are built respectively: (1) with a high dislocations density but almost without twins (after high temperature treatment at 2 GPa) and (2) with a high twin density, but practically free from dislocations and stacking faults (after high temperature oxygenation at 10-16 MPa). It is shown that for attaining high critical current densities and fields of irreversibility (jc(H-c, 0 T)=9•104 A/cm2, H irr=9.7 T at 77 K), a high twin density in YBa2Cu3O6.9-7 matrix of MT-YBCO is required. The density of twins in fully oxidized materials depends on the distances between Y2BaCuO5 inclusions, larger twin densities are related to shorter distances between inclusions. The influence of phase composition of the initial powder mixtures on the distances between Y2BaCuO5 inclusions have been characterized and discussed. © Published under licence by IOP Publishing Ltd.
- ItemObservation of Ultrafast Solid-Density Plasma Dynamics Using Femtosecond X-Ray Pulses from a Free-Electron Laser(College Park, Md. : APS, 2018) Kluge, Thomas; Rödel, Melanie; Metzkes-Ng, Josefine; Pelka, Alexander; Laso Garcia, Alejandro; Prencipe, Irene; Rehwald, Martin; Nakatsutsumi, Motoaki; McBride, Emma E.; Schönherr, Tommy; Garten, Marco; Hartley, Nicholas J.; Zacharias, Malte; Grenzer, Jörg; Erbe, Artur; Georgiev, Yordan M.; Galtier, Eric; Nam, Inhyuk; Lee, Hae Ja; Glenzer, Siegfried; Bussmann, Michael; Gutt, Christian; Zeil, Karl; Rödel, Christian; Hübner, Uwe; Schramm, Ulrich; Cowan, Thomas E.The complex physics of the interaction between short-pulse ultrahigh-intensity lasers and solids is so far difficult to access experimentally, and the development of compact laser-based next-generation secondary radiation sources, e.g., for tumor therapy, laboratory astrophysics, and fusion, is hindered by the lack of diagnostic capabilities to probe the complex electron dynamics and competing instabilities. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small-angle x-ray scattering of femtosecond x-ray free-electron laser pulses facilitates new capabilities for direct in situ characterization of intense short-pulse laser-plasma interactions at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short-pulse high-intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the preinscribed grating, due to plasma expansion. The density maxima are interleaved, forming a double frequency grating in x-ray free-electron laser projection for a short time, which is a hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets.
- ItemNanograting-Enhanced Optical Fibers for Visible and Infrared Light Collection at Large Input Angles(Basel : MDPI, 2021) Wang, Ning; Zeisberger, Matthias; Hübner, Uwe; Schmidt, Markus A.The efficient incoupling of light into particular fibers at large angles is essential for a multitude of applications; however, this is difficult to achieve with commonly used fibers due to low numerical aperture. Here, we demonstrate that commonly used optical fibers functionalized with arrays of metallic nanodots show substantially improved large-angle light-collection performances at multiple wavelengths. In particular, we show that at visible wavelengths, higher diffraction orders contribute significantly to the light-coupling efficiency, independent of the incident polarization, with a dominant excitation of the fundamental mode. The experimental observation is confirmed by an analytical model, which directly suggests further improvement in incoupling efficiency through the use of powerful nanostructures such as metasurface or dielectric gratings. Therefore, our concept paves the way for high-performance fiber-based optical devices and is particularly relevant within the context of endoscopic-type applications in life science and light collection within quantum technology.
- ItemWafer-level uniformity of atomic-layer-deposited niobium nitride thin films for quantum devices(New York, NY : Inst., 2021) Knehr, Emanuel; Ziegler, Mario; Linzen, Sven; Ilin, Konstantin; Schanz, Patrick; Plentz, Jonathan; Diegel, Marco; Schmidt, Heidemarie; Il’iche, Evgeni; Siegel, MichaelSuperconducting niobium nitride thin films are used for a variety of photon detectors, quantum devices, and superconducting electronics. Most of these applications require highly uniform films, for instance, when moving from single-pixel detectors to arrays with a large active area. Plasma-enhanced atomic layer deposition (ALD) of superconducting niobium nitride is a feasible option to produce high-quality, conformal thin films and has been demonstrated as a film deposition method to fabricate superconducting nanowire single-photon detectors before. Here, we explore the property spread of ALD-NbN across a 6-in. wafer area. Over the equivalent area of a 2-in. wafer, we measure a maximum deviation of 1% in critical temperature and 12% in switching current. Toward larger areas, structural characterizations indicate that changes in the crystal structure seem to be the limiting factor rather than film composition or impurities. The results show that ALD is suited to fabricate NbN thin films as a material for large-area detector arrays and for new detector designs and devices requiring uniform superconducting thin films with precise thickness control.
- ItemCoherent interaction of atoms with a beam of light confined in a light cage(London : Nature Publishing Group, 2021) Davidson-Marquis, Flavie; Gargiulo, Julian; Gómez-López, Esteban; Jang, Bumjoon; Kroh, Tim; Müller, Chris; Ziegler, Mario; Maier, Stefan A.; Kübler, Harald; Schmidt, Markus A.; Benson, OliverControlling coherent interaction between optical fields and quantum systems in scalable, integrated platforms is essential for quantum technologies. Miniaturised, warm alkali-vapour cells integrated with on-chip photonic devices represent an attractive system, in particular for delay or storage of a single-photon quantum state. Hollow-core fibres or planar waveguides are widely used to confine light over long distances enhancing light-matter interaction in atomic-vapour cells. However, they suffer from inefficient filling times, enhanced dephasing for atoms near the surfaces, and limited light-matter overlap. We report here on the observation of modified electromagnetically induced transparency for a non-diffractive beam of light in an on-chip, laterally-accessible hollow-core light cage. Atomic layer deposition of an alumina nanofilm onto the light-cage structure was utilised to precisely tune the high-transmission spectral region of the light-cage mode to the operation wavelength of the atomic transition, while additionally protecting the polymer against the corrosive alkali vapour. The experiments show strong, coherent light-matter coupling over lengths substantially exceeding the Rayleigh range. Additionally, the stable non-degrading performance and extreme versatility of the light cage provide an excellent basis for a manifold of quantum-storage and quantum-nonlinear applications, highlighting it as a compelling candidate for all-on-chip, integrable, low-cost, vapour-based photon delay.
- ItemPinning and trapped field in MgB2- and MT-YBaCuO bulk superconductors manufactured under pressure(Bristol : IOP Publ., 2016) Prikhna, T.; Eisterer, M.; Chaud, X.; Weber, H.W.; Habisreuther, T.; Moshchil, V.; Kozyrev, A.; Shapovalov, A.; Gawalek, W.; Wu, M.; Litzkendorf, D.; Goldacker, W.; Sokolovsky, V.; Shaternik, V.; Rabier, J.; Joulain, A.; Grechnev, G.; Boutko, V.; Gusev, A.; Shaternik, A.; Barvitskiy, P.The relevant pinning centers of Abrikosov vortices in MgB2-based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgBx (x>4) phases. The high critical current densities, jc, of 106 and 103A/cm2 at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB2 structure in small amounts (MgB1.5O0.5), which is supported by Auger studies and calculations of the DOS and the binding energy. The jc of melt textured YBa2Cu3O7-δ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the Y123 structure, but also on the density of twins and micro-cracks formed during the oxygenation (due to shrinking of the c-lattice parameter). The density of twins and microcracks increases with the reduction of the distance between Y2BaCuO5 (Y211) inclusions in Y123. At 77 K jc=8·104 A/cm2 in self-field and jc=103 A/cm2 at 10 T were found in materials oxygenated at 16 MPa for 3 days with a density of twins of 22–35 per µm (thickness of the lamellae: 45-30 nm) and a density of micro-cracks of 200–280 per mm. Pinning can occur at the points of intersection between the Y123 twin planes and the Y211 inclusions. MTYBaCuO at 77 K can trap 1.4 T (38×38×17 mm, oxygenated at 0.1 MPa for 20 days) and 0.8 T (16 mm in diameter and 10 mm thick with 0.45 mm holes oxygenated at 10 MPa for 53 h). The sensitivity of MgB2 to magnetic field variations (flux jumps) complicates estimates of the trapped field. At 20 K 1.8 T was found for a block of 30 mm in diameter and a thickness of 7.5 mm and 1.5 T (if the magnetic field was increased at a rate of 0.1 T) for a ring with dimensions 24×18 mm and a thickness of 8 mm.
- ItemAdvances in bioimaging - Challenges and potentials(Bristol : IOP Publ., 2018) Eggeling, Christian[No abstract available]
- ItemFiber Fabry-Perot interferometer for curvature sensing(Berlin ; Heidelberg : Springer, 2016) Monteiro, Catarina S.; Ferreira, Marta S.; Silva, Susana O.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, OrlandoA curvature sensor based on an Fabry-Perot (FP) interferometer was proposed. A capillary silica tube was fusion spliced between two single mode fibers, producing an FP cavity. Two FP sensors with different cavity lengths were developed and subjected to curvature and temperature. The FP sensor with longer cavity showed three distinct operating regions for the curvature measurement. Namely, a linear response was shown for an intermediate curvature radius range, presenting a maximum sensitivity of 68.52 pm/m-1. When subjected to temperature, the sensing head produced a similar response for different curvature radii, with a sensitivity varying from 0.84 pm/°C to 0.89 pm/°C, which resulted in a small cross-sensitivity to temperature when the FP sensor was subjected to curvature. The FP cavity with shorter length presented low sensitivity to curvature.