Experimental observation of higher-order anapoles in individual silicon disks under in-plane illumination

[EN] Anapole states¿characterized by a strong suppression of far-field scattering¿naturally arise in high-index nanoparticles as a result of the interference between certain multipolar moments. Recently, the first-order electric anapole, resulting from the interference between the electric and toroidal dipoles, was characterized under in-plane illumination as required in on-chip photonics. Here, we go a step further and report on the observation of higher-order (magnetic and second-order electric) anapole states in individual silicon disks under in-plane illumination. To do so, we increase the disk dimensions (radius and thickness) so that such anapoles occur at telecom wavelengths. Experiments show dips in the far-field scattering perpendicular to the disk plane at the expected wavelengths and the selected polarizations, which we interpret as a signature of high-order anapoles. Some differences between normal and in-plane excitation are discussed, in particular, the non-cancelation of the sum of the Cartesian electric and toroidal moments for in-plane incidence. Our results pave the way toward the use of different anapole states in photonic integrated circuits either on silicon or other high-index dielectric materials.This work was supported by Generalitat Valenciana under Grant No. GRISOLIAP/2018/164, the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the International Research Training Group (IRTG) 2675 "Meta-ACTIVE," Project No. 437527638, and Generalitat Valenciana (Grant Nos. PROMETEO/2019/123, IDIFEDER/2020/041, and IDIFEDER/2021/061).Díaz-Escobar, E.; Barreda-Gómez, ÁI.; Griol Barres, A.; Martínez, A. (2022). Experimental observation of higher-order anapoles in individual silicon disks under in-plane illumination. Applied Physics Letters. 121(20):1-8. https://doi.org/10.1063/5.0108438181212

Spectral response of dielectric nano-antennas in the far- and near-field regimes

Recent studies show that the spectral behaviour of localized surface plasmon resonances (LPSRs) in metallic nanoparticles su er from both a redshift and a broadening in the transition from the far- to the near-field regimes. An interpretation of this efect was given in terms of the evanescent and propagating components of the angular spectrum representation of the radiated eld. Due to the increasing interest awakened by magnetodielectric materials as a both low-loss material option for nanotechnology applications, and also for their particular scattering properties, here we study the spectral response of a magnetodielectric nanoparticle as a basic element of a dielectric nano-antenna. This study is made by analyzing the changes su ered by the scattered electromagnetic field when propagating from the surface of this dielectric nanostructure to the far-zone in terms of propagating and evanescent plane wave components of the radiated fields.This research was supported by MICINN (Spanish Ministry of Science and Innovation) with project FIS2013- 45854-P

Comportamiento electromagnético de sustratos nanoestructurados contaminados con objetos micrométricos

En este trabajo se estudia el comportamiento electromagnético de objetos dieléctricos micrométricos, situados sobre sustratos metálicos estructurados mediante nanoagujeros distribuidos periódicamente. Atendiendo a la resonancia (1,0) de Transmisión Óptica Extraordinaria, se ha investigado numéricamente la influencia de la geometría del objeto en los espectros de transmisión. Concretamente, el estudio se ha basado en el desplazamiento espectral del máximo de transmisión a medida que la superficie de contacto entre el objeto y el sustrato nanoestructurado cambia

Analysis of directionality effects in magnetodielectric core-shell nanoparticles by means of polarimetric techniques

The influence of increasing the core size of a Ag-Si core-shell nanoparticle has been investigated by using the values of the linear polarization degree at right angle scattering configuration, PL(90º). Changes in dipolar resonances and Scattering Directionality Conditions as a function of the core radius (Rint) for a fixed shell size (Rext = 230 nm) have been analyzed. An empirical formula to obtain the ratio Rint/Rext by monitoring the influence of the magnetic dipolar resonance in PL(90º) has been found.This research was supported by MICINN (FIS2013-45854-P). Ángela I. Barreda and Y. Gutiérrez want to express their gratitude to the University of Cantabria for their FPU grant

Electromagnetic polarization-controlled perfect switching effect with high-refractive-index dimers and the beam-splitter configuration

Sub-wavelength particles made from high-index dielectrics, either individual or as ensembles, are ideal candidates for multifunctional elements in optical devices. Their directionality effects are traditionally analysed through forward and backward measurements, even if these directions are not convenient for in-plane scattering practical purposes. Here we present unambiguous experimental evidence in the microwave range that for a dimer of HRI spherical particles, a perfect switching effect is observed out of those directions as a consequence of the mutual particle electric/magnetic interaction. The binary state depends on the excitation polarization. Its analysis is performed through the linear polarization degree of scattered radiation at a detection direction perpendicular to the incident direction: the beam-splitter configuration. The scaling property of Maxwell's equations allows the generalization of our results to other frequency ranges and dimension scales, for instance, the visible and the nanometric scale.This research has been supported by MINECO (Secretaría de Estado de Investigación, Desarrollo e Innovación) through project FIS2013-45854-P and Fundación IBERDROLA-ESPAÑA through its Research on Energy and the Environment Program. A.I.B. wants to thank the University of Cantabria for her FPU grant. We also acknowledge the opportunity provided by the Centre Commun de Ressources en Microonde to use its fully equipped anechoic chamber and for financing H.S. PhD grant

Polarimetric techniques for determining morphology and optical features of High Refractive Index dielectric nanoparticles size

The spectral evolution of the degree of linear polarization (PL) at a scattering angle of 90º is studied numerically for high refractive index (HRI) dielectric spherical nanoparticles. The behaviour of PL(90º) is analyzed as a function of the refractive index of the surrounding medium and the particle radius. We focus on the spectral region where both electric and magnetic resonances of order not higher than two are located for various semiconductor materials with low absorption. The spectral behavior of PL(90º) has only a small, linear dependence on nanoparticle size R. This weak dependence makes it experimentally feasible to perform real-time retrievals of both the refractive index of the external medium and the NP size R. From an industrial point of view, pure materials are nonrealistic, since they can only be provided under certain conditions. For this reason, we also study the effect of contaminants on the resonances of silicon NPs by considering the spectral evolution of PL(90º).This research was supported by MICINN (Spanish Ministry of Science and Innovation, project FIS2013-45854-P)

Electromagnetic behavior of dielectric objects on metallic periodically nanostructured substrates

In this research, we investigate the electromagnetic behavior of a metallic thin-film with a periodic array of subwavelength apertures when dielectric objects are located on it. The influence of size, geometry and optical properties of the objects on the transmission spectra is numerically analyzed. We study the sensitivity of this system to changes in the refractive index of the illuminated volume induced by the presence of objects with sizes from hundreds of nanometers (submicron-sized objects) to a few microns (micron-sized objects). Parameters such as the object volume within the penetration depth of the surface plasmon in the buffer medium or the contact surface between the object and the nanostructured substrate strongly affect the sensitivity. The proposed system models the presence of objects and their detection through the spectral shifts undergone by the transmission spectra. Also, we demonstrate that these can be used for obtaining information about the refractive index of a micron-sized object immersed in a buffer and located on the nanostructured sensitive surface. We believe that results found in this study can help biomedical researchers and experimentalists in the process of detecting and monitoring biological organisms of large sizes (notably, cells).Ministerio de Economía y Competitividad (MINECO) (Secretaría de Estado de Investigación, Desarrollo e Innovación) (FIS2013-45854-P); Fundación IBERDROLA-ESPAÑA Research on Energy and the Environment Program. A.I.B. wants to thank the University of Cantabria for her FPU grant

Using linear polarization for sensing and monitoring nanoparticle purity

We analyze the effect of contaminants on the quadrupolar magnetic, dipolar electric and dipolar magnetic resonances of silicon nanoparticles (NPs) by considering the spectral evolution of the linear polarization degree at right angle scattering configuration, PL(90º). From an optical point of view, a decrease in the purity of silicon nanoparticles due to the presence of contaminants impacts the NP effective refractive index. We study this effect for a silicon nanosphere of radius 200 nm embedded in different media. The weakness of the resonances induced on the PL(90º) spectrum because of the lack of purity can be used to quantify the contamination of the material. In addition, it is shown that Kerker conditions also suffer from a spectral shift, which is quantified as a function of material purity.This research was supported by MICINN (Spanish Ministry of Science and Innovation, project FIS2013-45854-P)

Comportamiento electromagnético de dímeros de nanopartículas

ABSTRACT:Nanophotonics is the part of nanoscience that is dedicated to the study of the interaction between electromagnetic radiation and matter. Specifically, the electromagnetic behavior of dielectric and/or metallic nanoparticles is currently a topic of great interest, because of their applications in such different fields as: biomedicine, communications, food industry, cosmetics, etc. In the case of metallic nanoparticles, electronic plasma in confined to nanometric scale. When they are excited with electromagnetic radiation, localized surface plasmons can be produced (LSP). Due to this phenomena, an enhancement of the electric field in the vicinity of nanoparticles is produced and the energy of incident radiation is confined to nanometric dimensions. The spectral properties of LSP depend on geometric properties (size and shape) of the nanoparticles and of the optical properties of nanoparticles and surrounding medium. In the case of dielectric nanoparticles, free electrons are not found. For this reason, resonances that are observed in spectrum are not plasmonics. In these particles magnetic effects appear as a consequence of displacement currents. The main objective of this work is to analyze the electromagnetic behavior of spherical nanoparticles dimers: metallic and dielectric with high refractive index. The study has been carried out paying attention to: spectral properties, near field maps and the spectral polarimetric parameter: “linear polarization degree measured at 90º”. We have simulated different sizes, configurations and gaps, for silver and silicon particles. Due to dimer problem cannot be result in an analytical way, in order to obtain the results we have to use a numerical method: COMSOL. With the objective of interpreting the obtained plots we have reviewed different aspects: Mie theory, Drude-Lorentz model and coupled-dipole method. The found results have allowed us understanding the interaction electromagnetic mechanisms, the possibility of generating hot-spots, and determine in which spectral ranges the dipolar electric effect dominate over the magnetic ones and vice-versa for the case of silicon particles.RESUMEN:La nanofotónica es la parte de la nanociencia dedicada al estudio de la interacción de la radiación electromagnética con la materia a escala nanométrica. En concreto, el interés por conocer el comportamiento electromagnético de nanopartículas dieléctricas y/o metálicas es muy frecuente en la actualidad, por sus aplicaciones en campos tan diversos como la biomedicina, las comunicaciones, la industria alimentaria, la cosmética, etc. En el caso de las nanopartículas metálicas, el plasma electrónico confinado en dimensiones nanométricas, adecuadamente excitado mediante radiación electromagnética, puede producir resonancias plasmónicas localizadas (LSP). Por ello, se produce un fuerte aumento del campo electromagnético en la proximidad de la nanoestructura y la energía de la radiación incidente queda confinada en dimensiones nanometricas. Las propiedades espectrales de las LSP dependen de las propiedades geométricas (tamaño y forma) de las nanopartículas y de sus propiedades ópticas, así como de las de su entorno. En el caso de las nanopartículas dieléctricas no hay electrones libres presentes, por este motivo las resonancias que se observan en el espectro no tienen origen plasmónico. En ellas aparecen efectos magnéticos debidos a corrientes de desplazamiento. El principal objetivo del trabajo es analizar el comportamiento electromagnético de dímeros de nanopartículas esféricas: metálicas y dieléctricas con alto índice de refracción. El estudio se ha llevado a cabo prestando atención a propiedades espectrales, mapas de campo cercano y al parámetro polarimétrico espectral “grado de polarización lineal medido a 90º”. Se han estudiado diferentes configuraciones geométricas para nano-partículas de plata y silicio. Dado que el problema del dímero no tiene solución analítica, para conseguir los resultados se ha utilizado como método numérico COMSOL. Los resultados encontrados nos han permitido comprender los mecanismos electromagnéticos de interacción, la posibilidad de generar “hot-spots” y determinar en qué regiones espectrales dominan los efectos dipolares eléctricos sobre los magnéticos y vice-versa para el caso de partículas de silicio.Grado en Físic

Comportamiento electromagnético de dispositivos plasmónicos con nanoagujeros. Aplicaciones en biosensores

ABSTRACT: Development of nanotechnology in the last decades has allowed the knowledge and experimental exploration of new physical phenomena to nanometric scale. Concretely, in nanophotonics field, the interaction of light with matter to such small scale has provided interesting applications in medicine, physics, biology, materials… Paying attention to the development of biosensors, it is found as their sensitivity can increase by using nanohole arrays perforated in metallic thin films. This fact is based on Extraordinary Optical Transmission (EOT). Since its discovery by Ebbesen et al. in 1998 much effort has been realized with the objective of reaching high values of the sensitivity. When nanoholes, which are distributed periodically, are illuminated by wavelengths greater than the nanohole aperture and than the distance between them, in the transmission spectrum, different resonances are observed for some concrete wavelengths. These take place due to the interaction between surface plasmons at both dielectric-metal interfaces of the nanohole array. In this project, using as numerical method: Finite Element Method (FEM) implemented in the commercial software COMSOL, we have simulated different geometries. All of them are constituted by a thin metallic film where nanoholes are perforated, located on a dielectric substrate, in order to design a biosensor easy to manufacture and with a high sensitivity (high variation of the peaks in the transmission spectrum due to changes in the buffer optics constants). In all the simulated biosensors, nanohole array was perforated in a gold thin film, the diameter of nanoapertures was 180nm and the period (distance between two consecutive nanoholes) was 500nm. The thickness of the thin film was changed along the project. During the project we paid special attention to a concrete configuration, which consists of a Fabry-Perot nanocavity set under the nanohole array, due to the high sensitivity to changes in the buffer refractive index that this nanostructure presents, when buffer is introduced inside the nanocavity. The sensitivity for the different nanostructures considered was obtained through the peaks spectral shift observed in the ransmission/reflection spectra as a function of the changes in the buffer refractive index, Δλ/Δn.RESUMEN: El desarrollo de la nanotecnología en las últimas décadas ha permitido el conocimiento y la exploración experimental de nuevos fenómenos físicos a escala nanométrica. Concretamente, en el campo de la nanofotónica, la interacción de la luz con la materia a tan pequeña escala, ha proporcionado interesantes aplicaciones en medicina, física, biología, materiales… Prestando atención al desarrollo de los biosensores, se encuentra como su sensibilidad aumenta cuando se utilizan arrays de nanoagujeros perforados en finas películas metálicas. Este hecho está basado en la Transmisión Óptica Extraordinaria (EOT). Desde su descubrimiento por Ebbesen et al. en 1998 se ha realizado mucho esfuerzo con el fin de alcanzar altos valores de la sensibilidad. Cuando los nanoagujeros, los cuales se encuentran distribuidos periódicamente, son iluminados por longitudes de onda mayores que la apertura del nanoagujero y la distancia entre ellos, en el espectro de trasmisión se observan diferentes resonancias, para algunas longitudes de onda concretas. Éstas son debidas a la interacción entre los plasmones superficiales formados en ambas superficies dieléctrico-metal del array de nanoagujeros. En este proyecto, utilizando como método numérico, Método de Elementos Finitos (FEM), implementado en el software comercial, COMSOL, hemos trabajado con diferentes geometrías en las que están presentes una lámina metálica con una distribución periódica de nanoagujeros colocada sobre un medio dieléctrico, con el fin de ser empleadas como biosensores. Se han buscado geometrías fáciles de fabricar y que presenten una elevada sensibilidad (alta variación del espectro de trasmisión frente a las propiedades ópticas del medio colocado sobre la lámina con nanoagujeros). En todos los biosensores simulados, el array de nanoagujeros fue perforado en una fina película de oro, el diámetro de las nanoaperturas fue 180nm y el periodo (distancia entre dos nanoagujeros consecutivos) fue 500nm. El espesor de la fina lámina fue variado a lo largo del proyecto. La sensibilidad para las diferentes nanoestructuras consideradas, fue obtenida a partir del corrimiento espectral de los picos observados en los espectros de transmisión/reflexión, en función del índice de refracción del buffer, Δλ/Δn.Máster en Física, Instrumentación y Medio Ambient