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Author: Chigrin, Dmitry N. × DDC: 530 × WGL Institute: DWI ×

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Now showing 1 - 4 of 4
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    Optimizing the Geometry of Photoacoustically Active Gold Nanoparticles for Biomedical Imaging
    (Washington, DC : ACS, 2020) García-Álvarez, Rafaela; Chen, Lisa; Nedilko, Alexander; Sánchez-Iglesias, Ana; Rix, Anne; Lederle, Wiltrud; Pathak, Vertika; Lammers, Twan; von Plessen, Gero; Kostarelos, Kostas; Liz-Marzán, Luis M.; Kuehne, Alexander J.C.; Chigrin, Dmitry N.
    Photoacoustics is an upcoming modality for biomedical imaging, which promises minimal invasiveness at high penetration depths of several centimeters. For superior photoacoustic contrast, imaging probes with high photothermal conversion efficiency are required. Gold nanoparticles are among the best performing photoacoustic imaging probes. However, the geometry and size of the nanoparticles determine their photothermal efficiency. We present a systematic theoretical analysis to determine the optimum nanoparticle geometry with respect to photoacoustic efficiency in the near-infrared spectral range, for superior photoacoustic contrast. Theoretical predictions are illustrated by experimental results for two of the most promising nanoparticle geometries, namely, high aspect ratio gold nanorods and gold nanostars. Copyright © 2020 American Chemical Society.
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    Phonon-Polaritonic Bowtie Nanoantennas: Controlling Infrared Thermal Radiation at the Nanoscale
    (Washington, DC : ACS Publications, 2017) Wang, Tao; Li, Peining; Chigrin, Dmitry N.; Giles, Alexander J.; Bezares, Francisco J.; Glembocki, Orest J.; Caldwell, Joshua D.; Taubner, Thomas
    A conventional thermal emitter exhibits a broad emission spectrum with a peak wavelength depending upon the operation temperature. Recently, narrowband thermal emission was realized with periodic gratings or single microstructures of polar crystals supporting distinct optical modes. Here, we exploit the coupling of adjacent phonon-polaritonic nanostructures, demonstrating experimentally that the nanometer-scale gaps can control the thermal emission frequency while retaining emission line widths as narrow as 10 cm-1. This was achieved by using deeply subdiffractional bowtie-shaped silicon carbide nanoantennas. Infrared far-field reflectance spectroscopy, near-field optical nanoimaging, and full-wave electromagnetic simulations were employed to prove that the thermal emission originates from strongly localized surface phonon-polariton resonances of nanoantenna structures. The observed narrow emission line widths and exceptionally small modal volumes provide new opportunities for the user-design of near- and far-field radiation patterns for advancements in infrared spectroscopy, sensing, signaling, communications, coherent thermal emission, and infrared photodetection. © 2017 American Chemical Society.
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    The Potential of Combining Thermal Scanning Probes and Phase-Change Materials for Tunable Metasurfaces
    (Weinheim : Wiley-VCH, 2020) Michel, Ann-Katrin U.; Meyer, Sebastian; Essing, Nicolas; Lassaline, Nolan; Lightner, Carin R.; Bisig, Samuel; Norris, David J.; Chigrin, Dmitry N.
    Metasurfaces allow for the spatiotemporal variation of amplitude, phase, and polarization of optical wavefronts. Implementation of active tunability of metasurfaces promises compact flat optics capable of reconfigurable wavefront shaping. Phase-change materials (PCMs) are a prominent material class enabling reconfigurable metasurfaces due to their large refractive index change upon structural transition. However, commonly employed laser-induced switching of PCMs limits the achievable feature sizes and restricts device miniaturization. Thermal scanning-probe-induced local switching of the PCM germanium telluride is proposed to realize near-infrared metasurfaces with feature sizes far below what is achievable with diffraction-limited optical switching. The design is based on a planar multilayer and does not require fabrication of protruding resonators as commonly applied in the literature. Instead, it is numerically demonstrated that a broad-band tuning of perfect absorption can be realized by the localized tip-induced crystallization of the PCM. The spectral response of the metasurface is explained using resonance mode analysis and numerical simulations. To facilitate experimental realization, a theoretical description of the tip-induced crystallization employing multiphysics simulations is provided to demonstrate the great potential for fabricating compact reconfigurable metasurfaces. The concept can be applied not only for plasmonic sensing and spatial frequency filtering, but also be transferred to all-dielectric metasurfaces. © 2020 Wiley-VCH GmbH
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    Multiphysics simulations of adaptive metasurfaces at the meta-atom length scale
    (Berlin : de Gruyter, 2020) Meyer, Sebastian; Tan, Zhi Yang; Chigrin, Dmitry N.
    Adaptive metasurfaces (MSs) provide immense control over the phase, amplitude and propagation direction of electromagnetic waves. Adopting phase-change materials (PCMs) as an adaptive medium allows us to tune functionality of MSs at the meta-atom length scale providing full control over MS (re-)programmability. Recent experimental progress in the local switching of PCM-based MSs promises to revolutionize adaptive photonics. Novel possibilities open new challenges, one of which is a necessity to understand and be able to predict the phase transition behavior at the sub-micrometer scale. A meta-atom can be switched by a local deposition of heat using optical or electrical pulses. The deposited energy is strongly inhomogeneous and the resulting phase transition is spatially non-uniform. The drastic change of the material properties during the phase transition leads to time-dependent changes in the absorption rate and heat conduction near the meta-atom. These necessitate a self-consistent treatment of electromagnetic, thermal and phase transition processes. Here, a self-consistent multiphysics description of an optically induced phase transition in MSs is reported. The developed model is used to analyze local tuning of a perfect absorber. A detailed understanding of the phase transition at the meta-atom length scale will enable a purposeful design of programmable adaptive MSs. © 2020 Sebastian Meyer, Dmitry N. Chigrin et al., published by De Gruyter, Berlin/Boston 2020.