17 research outputs found
SMUTHI: A python package for the simulation of light scattering by multiple particles near or between planar interfaces
SMUTHI is a python package for the efficient and accurate simulation of electromagnetic scattering by one or multiple wavelength-scale objects in a planarly layered medium. The software combines the T-matrix method for individual particle scattering with the scattering matrix formalism for the propagation of the electromagnetic field through the planar interfaces. In this article, we briefly introduce the relevant theoretical concepts and present the main features of SMUTHI. Simulation results obtained for several benchmark configurations are validated against commercial software solutions. Owing to the generality of planarly layered geometries and the availability of different particle shapes and light sources, possible applications of SMUTHI include the study of discrete random media, meta-surfaces, photonic crystals and glasses, perforated membranes and plasmonic systems, to name a few relevant examples at visible and near-visible wavelengths
Experimental demonstration of superdirective spherical dielectric antenna
An experimental demonstration of directivities exceeding the fundamental
Kildal limit, a phenomenon called superdirectivity, is provided for spherical
high-index dielectric antennas with an electric dipole excitation. A
directivity factor of about 10 with a total efficiency of more than 80\% for an
antenna having a size of a third of the wavelength was measured. High
directivities are shown to be associated with constructive interference of
particular electric and magnetic modes of an open spherical resonator. Both
analytic solution for a point dipole and a full-wave rigorous simulation for a
realistic dipole antenna were employed for optimization and analysis, yielding
an excellent agreement between experimentally measured and numerically
predicted directivities. The use of high-index low-loss ceramics can
significantly reduce the physical size of such antennas while maintaining their
overall high radiation efficiency. Such antennas can be attractive for various
high-frequency applications, such as antennas for the Internet of things, smart
city systems, 5G network systems, and others. The demonstrated concept can be
scaled in frequency
Hollow Gold Nanoparticles Produced by Femtosecond Laser Irradiation
[EN] Metallic hollow nanoparticles exhibit interesting optical properties that can be controlled by geometrical parameters. Irradiation with femtosecond laser pulses has emerged recently as a valuable tool for reshaping and size modification of plasmonic metal nanoparticles, thereby enabling the synthesis of nanostructures with unique morphologies. In this Letter, we use classical molecular dynamics simulations to investigate the solid-to-hollow conversion of gold nanoparticles upon femtosecond laser irradiation. Here, we suggest an efficient method for producing hollow nanoparticles under certain specific conditions, namely that the particles should be heated to a maximum temperature between 2500 and 3500 K, followed by a fast quenching to room temperature, with cooling rates lower than 120 ps. Therefore, we describe the experimental conditions for efficiently producing hollow nanoparticles, opening a broad range of possibilities for applications in key areas, such as energy storage and catalysis.This work has been funded by the Spanish Ministry of Science, Innovation and Universities (MICIU) (Grants RTI2018-095844-B-I00, PGC2018-096444-B-I00, and MAT2017-86659-R), the EUROfusion Consortium through Project ENR-IFE19.CCFE-01, and the Madrid Regional Government (Grants P2018/NMT-4389 and P2018/EMT-4437). A.P. is thankful for the support of FONDECYT under Grants 3190123 and 11180557, as well as from Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia FB-0807. K.L. acknowledges the support of the Russian Science Foundation (Project 19-19-00683). The authors acknowledge the computer resources and technical assistance provided by the Centro de Supercomputacion y Visualizacion de Madrid (CeSViMa) and the supercomputing infrastructure of the NLHPC (ECM-02). This Letter is based upon work from COST Action TUMIEE (CA17126)Castro-Palacio, JC.; Ladutenko, K.; Prada, A.; Gonzalez-Rubio, G.; Diaz-Nunez, P.; Guerrero-Martinez, A.; Fernández De Córdoba, P.... (2020). Hollow Gold Nanoparticles Produced by Femtosecond Laser Irradiation. The Journal of Physical Chemistry Letters. 11(13):5108-5114. https://doi.org/10.1021/acs.jpclett.0c01233S51085114111
Symmetry Breaking in Nanoparticles: Photogenerated Free Carrier-Induced Symmetry Breaking in Spherical Silicon Nanoparticle (Advanced Optical Materials 7/2018)
International audienc
Bound States in the Continuum in Multipolar Lattices
We develop a theory of bound states in the continuum (BICs) in multipolar
lattices -- periodic arrays of resonant multipoles. We predict that BICs are
completely robust to changes in lattice parameters remaining pinned to specific
directions in the -space. The lack of radiation for BICs in such structures
is protected by the symmetry of multipoles forming the lattice. We also show
that some multipolar lattices can host BICs forming a continuous line in the
-space and such BICs carry zero topological charge. The developed approach
sets a direct fundamental relation between the topological charge of BIC and
the asymptotic behavior of the Q-factor in its vicinity. We believe that our
theory is a significant step towards gaining deeper insight into the physics of
BICs and the engineering of high-Q states in all-dielectric metasurfaces.Comment: 7 pages, 4 figures, Supplemental materia