Small-angle x-ray scattering tensor tomography provides three-dimensional information on the unre-solved material anisotropic microarchitecture, which can be hundreds of times smaller than an image... Show moreSmall-angle x-ray scattering tensor tomography provides three-dimensional information on the unre-solved material anisotropic microarchitecture, which can be hundreds of times smaller than an image pixel. We develop a direct filtered back-projection method based on algebraic filters that enables rapid tensor-tomographic reconstructions and is a few orders of magnitude faster compared to established techniques, given the same computational resources. We demonstrate the accuracy of the method on exper-imental data for a fiber-reinforced material sample. The achieved acceleration may pave the way toward the investigation of multiple large samples as well as rapid control and feedback during in situ tensor-tomographic experiments, opening perspectives for the understanding of the fundamental link between functional material properties and microarchitecture. Show less
The ability to control the electromagnetic near field with metasurfaces offers potential applications over the frequency range from radio frequency to optical domains. In this work, we show an... Show moreThe ability to control the electromagnetic near field with metasurfaces offers potential applications over the frequency range from radio frequency to optical domains. In this work, we show an essential feature of metasurfaces, subwavelength field confinement via excitation of a large number of eigenstates in a narrow frequency range, and demonstrate an innovative way of visualizing profiles of metasurface eigenmodes with the aid of a magnetic resonance imaging (MRI) system. We show that by tuning different eigenmodes of the metasurface to the Larmor frequency, we can passively tailor the near-field distribution to adjust the desired pattern of radio-frequency excitation in a MRI experiment. Our work demonstrates a practical nonperturbed rapid way of imaging metasurface eigenmodes. Show less
Marchand, R.; Sachl, R.; Kalbac, M.; Hof, M.; Tromp, R.M.; Amaro, M.; ... ; Juffmann, T. 2021
The electric double layer (EDL) formed around charged nanostructures at the liquid-solid interface determines their electrochemical activity and influences their electrical and optical... Show moreThe electric double layer (EDL) formed around charged nanostructures at the liquid-solid interface determines their electrochemical activity and influences their electrical and optical polarizability. We experimentally demonstrate that restructuring of the EDL at the nanoscale can be detected by dark-field scattering microscopy. Temporal and spatial characterization of the scattering signal demonstrates that the potentiodynamic optical contrast is proportional to the accumulated charge of polarizable ions at the interface and that its time derivative represents the nanoscale ionic current. The material specificity of the EDL formation is used in our work as a label-free contrast mechanism to image nanostructures and perform spatially resolved cyclic voltammetry on an ion-current density of a few attoamperes, corresponding to the exchange of only a few hundred ions. Show less
Metasurfaces represent a new paradigm in artificial subwavelength structures due to their potential to overcome many challenges typically associated with bulk metamaterials. The ability to make... Show moreMetasurfaces represent a new paradigm in artificial subwavelength structures due to their potential to overcome many challenges typically associated with bulk metamaterials. The ability to make very thin structures and change their properties dynamically makes metasurfaces an exceptional meta-optics platform for engineering advanced electromagnetic and photonic metadevices. Here, we suggest and demonstrate experimentally a tunable metasurface capable of enhancing significantly the local image quality in magnetic resonance imaging. We present a design of the hybrid metasurface based on electromagnetically coupled dielectric and metallic elements. We demonstrate how to tailor the spectral characteristics of the metasurface eigenmodes by changing dynamically the effective permittivity of the structure. By maximizing a coupling between metasurface eigenmodes and transmitted and received fields in the magnetic resonance imaging (MRI) system, we enhance the device sensitivity that results in a substantial improvement of the image quality. Show less
Snijders, H.J.; Frey, J.A.; Norman, J.; Post, V.P.; Gossard, A.C.; Bowers, J.E.; ... ; Bouwmeester, D. 2018
