Auswahl der wissenschaftlichen Literatur zum Thema „Magnetic dipole nanoantenna“

A nanoantenna is a nanodevice that manipulates light propagation and enhances light-matter interaction at the nanoscale. Integration of an emitter into a nanoantenna capable of increasing local density of photonic states at the emission wavelength results in the enhanced spontaneous emission rate (Purcell effect). The most widely studied nanoantennas for the Purcell enhancement are plasmonic nanoantennas made from gold or silver nanostructures supporting surface plasmon resonances. In most cases, nanoantennas have been used for the enhancement of electric dipole-allowed transition of a molecule. In addition, recently, nanoantennas capable of enhancing magnetic dipole transition of a molecule are attracting attention. For the magnetic Purcell enhancement, nanoantennas have to have magnetic resonances at the optical frequency. Although it is possible to achieve magnetic resonances at the optical frequency by plasmonic nanostructures, the inherent absorption loss of noble metals limits the magnetic Purcell enhancement. On the other hand, nanoparticles of high refractive index dielectrics inherently have low-loss magnetic-type Mie resonances at the optical frequency, and thus are potentially more attractive as a material to realize large magnetic Purcell enhancement. We have developed spherical nanoparticles of crystalline silicon (Si) having the magnetic dipole (MD) and quadrupole (MQ) Mie resonances at the optical frequency [1]. In this work, to demonstrate the potential of a Si nanoparticle as a nanoantenna for the magnetic Purcell enhancement, we develop a composite nanoparticle, that is, a Si nanosphere decorated with europium ion (Eu3+) complexes, in which magnetic dipole emission of Eu3+ is efficiently coupled to the magnetic Mie modes of the nanosphere [2]. We systematically investigate the light scattering and photoluminescence spectra of the coupled system by means of single particle spectroscopy. The results are shown in Figure 1. By tuning the MQ Mie resonance of a Si nanosphere to the 5D0-7F1 magnetic dipole transition of Eu3+, the branching ratio between the magnetic and electric dipole (5D0-7F2) transitions is enhanced up to 7 times. The observed large magnetic Purcell enhancement offers an opportunity to develop novel fluorophores with enhanced magnetic dipole emission. Furthermore, the enhanced magnetic field of dielectric Mie resonators enhances otherwise very weak absorption due to magnetic dipole transition, and makes direct excitation of triplet states of a molecule possible [3]. Direct excitation of triplet states reduces photon energy necessary for energy conversion and chemical reactions utilizing a triplet state compared to a conventional process involving singlet-singlet excitation and singlet-triplet intersystem crossing. [1] H. Sugimoto, et. al., "Mie Resonator Color Inks of Monodispersed and Perfectly Spherical Crystalline Silicon Nanoparticles" Advanced Optical Materials, 8 (2020) 2000033. [2] H. Sugimoto, and Minoru Fujii, "Magnetic Purcell Enhancement by Magnetic Quadrupole Resonance of Dielectric Nanosphere Antenna", ACS Photonics, 8 (2021) 1794. [3] H. Sugimoto, et. al., "Direct Excitation of Triplet State of Molecule by Enhanced Magnetic Field of Dielectric Metasurfaces", Small, 2021, DOI: 10.1002/smll.202104458. Figure 1: Photoluminescence (red curves) and scattering (black curves) spectra of single Si naosphere-Eu3+ complex composite nanoparticles with different Si nanosphere diameters. The diameters are shown at the right end of the figure. Figure 1

Abstract A highly directive dielectric nanoantenna in an integrated chip may enable faster communication as their low losses and small size overcome the limitation of temperature enhancement and low data transfer rate. We optimize nanoantenna consist of Si-nanoblock in the near-infrared region to efficiently transfer a point dipole light to a highly directive light in the far-field region. We engineer the intrinsic electric and magnetic resonances of a Si-block nanoantenna by modifying and reducing its geometrical symmetry. We realize a pronounced enhancement of directivity by systematically inducing perturbation in the Silicon block so that both its reflection and rotational symmetries are broken. Finally, we retain the traditional method to increase resonance’s coupling to outer space by introducing substrate with an increasing refractive index. We find that the directivity has boosted rapidly.

The response of dipole nanoantennas (DNAs) studied widely in optical frequency range is sensitive to polarization of incident field. In this paper, we report the implementation of a cross nanoantenna (CNA) consisting of two orthogonal DNAs with a common feedgap and investigate its directional and polarization properties and compare them with those of the DNA. Interestingly the response of CNA is independent of polarization. We can operate the CNA in turnstile mode by using two identical light sources with cross polarization in phase quadrature. In such a case the radiation from the CNA is found omnidirectional like radio frequency turnstile antenna. We believe CNA could open new possibilities to study the novel phenomenon of light matter interaction. To the best of our knowledge, this is the first report on a turnstile antenna in optical frequencies.

We design an asymmetric nonlinear optical nanoantenna composed of a dielectric nanodisc and an adjacent nanobar. The proposed composite structure made of AlGaAs exhibits resonant response at both the fundamental and doubled frequencies. Being driven by the strong magnetic dipole resonance at the pump wavelength and a high-quality mode at the harmonic wavelength, the efficient second-harmonic radiation is generated predominantly along the vertical directions under the normally incident plane-wave excitation.

We compute generalized absorption and extinction cross-sections of an optical dipole nanoantenna in a structured environment. The expressions explicitly show the influence of radiation reaction and the local density of states on the intrinsic absorption properties of the antenna. Engineering the environment could allow to modify the overall absorption as well as the frequency and the linewidth of a resonant antenna. Conversely, a dipole antenna can be used to probe the photonic environment, in a similar way as a quantum emitter.

Rabi waves for the excitation of quantum nanoantennas with electrically controlled radiation and frequency characteristics were studied. The operational frequency of the visible range was based on the high frequency component of the current. The low frequency component and its operational frequency was in the terahertz range. The feature of the Rabi wave antenna depends on the carrier frequency on the electromagnetic field intensity. The contribution of high order magnetic multipoles became essential. The radiation properties of an antenna were the same as the ideal magnetic dipole. The antenna frequency spectrum corresponded to the amplitude modulated Rabi oscillations. The high frequency current was in the optical range in the vicinity of the quantum transition frequency. The radiation field of the nano antenna was considered equivalent to the field of magnetic dipole placed in the centre of current ring and oriented orthogonal to the ring plane. The equivalence was consequence of the electrical smallness of the antenna over the working range of frequency. The results obtained were in good agreement with previous results.

We study resonant photonic–plasmonic coupling between a gold dipole nanoantenna and a silicon nanodisc supporting electric and magnetic dipolar Mie-type resonances. Specifically, we consider two different cases for the mode structure of the silicon nanodisc, namely spectrally separate and spectrally matching electric and magnetic dipolar Mie-type resonances. In the latter case, the dielectric nanoparticle scatters the far fields of a unidirectional Huygens’ source. Our results reveal an anticrossing of the plasmonic dipole resonance and the magnetic Mie-type dipole resonance of the silicon nanodisc, accompanied by a clear signature of photonic–plasmonic mode hybridization in the corresponding mode profiles. These characteristics show that strong coupling is established between the two different resonant systems in the hybrid nanostructure. Furthermore, our results demonstrate that in comparison with purely metallic or dielectric nanostructures, hybrid metal–dielectric nanoresonators offer higher flexibility in tailoring the fractions of light which are transmitted, absorbed and reflected by the nanostructure over a broad range of parameters without changing its material composition. As a special case, highly asymmetric reflection and absorption properties can be achieved. This article is part of the themed issue ‘New horizons for nanophotonics’.

We have designed and realized all-dielectric lossless nanoantennas, in which a thin SiO2 layer doped with erbium ions is placed inside slotted silicon nanopillars arranged in a square array. The modal analysis has evi-denced that the slotted nanopillar array supports optical quasi-BIC resonances with ultra-high Q-factors (up to Q∼109), able to boost the electromagnetic local density of optical states in the optically active layer. Up to 3 orders of magnitude photoluminescence intensity increment and 2 orders of magnitude decay rate enhancement have been measured at room temperature when the Er3+ emission at about λ=1540 nm couples with the quasi-BIC resonances. Furthermore, by tailoring the nanopillar aspect ratio, the slot geometry has been exploited to obtain selective enhancements of the electric or magnetic dipole contribution to Er3+ radiative transitions in the NIR, keeping the emitter quantum efficiency almost unitary. Finally, by computing the angularly resolved elec-tromagnetic field enhancement inside the nanoslot, the nanoantenna directivity has been designed, proving that strong beaming effects can be obtained. Our findings have a direct impact on the development of bright and effi-cient photon sources operating at telecom wavelength that are of primary importance for quantum nanophotonic applications.

Single photon sources based on semiconductor quantum dots are one of the most prospective elements for optical quantum computing and cryptography. Such systems are often based on Bragg resonators, which provide several ways to control the emission of quantum dots. However, the fabrication of periodic structures with many thin layers is difficult. On the other hand, the coupling of single-photon sources with resonant nanoclusters made of high-index dielectric materials is known as a promising way for emission control. Our experiments and calculations show that the excitation of magnetic Mie-type resonance by linearly polarized light in a GaAs nanopillar oligomer with embedded InAs quantum dots leads to quantum emitters absorption efficiency enhancement. Moreover, the nanoresonator at the wavelength of magnetic dipole resonance also acts as a nanoantenna for a generated signal, allowing control over its radiation spatial profile. We experimentally demonstrated an order of magnitude emission enhancement and numerically reached forty times gain in comparison with unstructured film. These findings highlight the potential of quantum dots coupling with Mie-resonant oligomers collective modes for nanoscale single-photon sources development.

La détection de molécules chirales à l'aide de résonateurs plasmoniques est un domaine de recherche prometteur pour améliorer la sensibilité et la flexibilité de la détection. Cette approche vise à surmonter les limitations des méthodes conventionnelles, telles que la méthode chiroptique, qui présente des limitations en termes de sensibilité. Les résonateurs plasmoniques sont capables d'interagir de manière résonante avec la lumière, ce qui permet d'augmenter le couplage entre les molécules chirales et la lumière, tout en offrant un contrôle sur les propriétés de polarisation de la lumière. Les avancées récentes dans ce domaine ont porté sur la création de surfaces nanostructurées chirales avec des résonateurs spécifiques, mais le mécanisme sous-jacent à la réponse différentielle des biomolécules à la lumière polarisée circulairement reste mal compris. Dans le cadre de ce projet de doctorat, l'approche novatrice consiste à utiliser des nanostructures achirales anisotropes, telles que des nanoslits, pour interagir avec des molécules chirales. Ces nanostructures achirales offrent l'avantage de pouvoir inverser le signe du dichroïsme circulaire en contrôlant la polarisation incidente ou le sens de propagation de la lumière. En manipulant les symétries du champ électromagnétique à proximité des résonateurs, il devient possible d'étudier plus en détail le couplage électromagnétique entre les biomolécules chirales et les nanorésonateurs. Le projet vise à développer des nanorésonateurs plasmoniques innovants, basés sur des nanoslits, qui seront fonctionnalisés pour détecter des biomolécules chirales. Contrairement aux résonateurs chiraux, les résonateurs achiraux peuvent générer des signes de champs chiraux, offrant ainsi une grande flexibilité dans la détection. Le travail comprend la caractérisation et la compréhension de l'origine des champs chiraux, ainsi que des méthodes pour les rendre homogènes. Une partie de la recherche se concentre sur la conception d'une source de lumière superchirale pure à l'aide de nanoslits, qui peut être accordée en longueur d'onde et en polarisation. Dans cette perspective, des méthodes expérimentales sont présentées, notamment l'utilisation de la fluorescence détectée par dichroïsme circulaire (FDCD) pour les molécules sensibles aux énantiomères. Pour la réalisation de ces expériences, des résonateurs plasmoniques avec une résonance à 680 nm ont été choisis, correspondant à la bande d'absorption chirale de LHCII. Une idée intéressante consiste à bloquer le faisceau d'excitation pour ne recueillir que l'émission des molécules chirales, en étudiant les résonances des ouvertures dans une couche d'or opaque. En résumé, ce projet de doctorat vise à exploiter les avantages des nanostructures plasmoniques achirales pour améliorer la détection des molécules chirales en offrant une plus grande flexibilité dans la manipulation de la polarisation de la lumière et en explorant de nouvelles méthodes expérimentales pour cette détection
The detection of molecules based on fluorescence or Raman scattering has been widely studied and is currently used in industry and laboratories. However, many organic molecules of interest are chiral, and their chemical and biological properties depend on their enantiomer as well as on the chirality of their secondary structure. The quantity and chirality of biomolecules are classically determined by measuring the differential absorption between the two opposite circular polarizations (chiroptic method). However, this method is limited by the low differential absorption of chiral molecules, which is of the order of 10-3 in the UV part of the spectrum. Plasmonic resonators have the ability to resonantly interact with light and are characterized by a moderate quality factor and a low effective volume. This resonant interaction allows (i) to increase the coupling between molecules and light and (ii) to control the polarization properties of light. So far, the latest advances concern the implementation of nanostructured chiral surfaces with gammadion-type resonators or stacked twisted resonators that interact preferentially with a given helicity of light. However, the mechanism behind the differential response of biomolecules coupled to chiral resonators to circularly polarized light is still unclear, preventing the optimization of such detection. Moreover, in the research published so far, two different chiral sensors are needed to interact with right- and left-handed circularly polarized light, which requires complex calibration procedures. During the course of my PhD, I have studied the use of anisotropic achiral nanostructures to interact with chiral molecules. Indeed, they have the significant advantage over chiral nanostructures of changing the sign of the circular dichroism by controlling the incident polarization or the direction of propagation. Indeed, the symmetries of the electromagnetic field in close proximity to the resonators can be manipulated at will by changing illumination conditions hence providing a unique tool for studying the origin of the electromagnetic coupling between chiral biomolecule and nanoresonators. Consequently, in my PhD project I propose to use plasmonic nanoresonators to increase the light - “chiral matter” interactions in order to detect and study chiral molecules. I will use the concept of achiral plasmonic nanostructures (nanoslits) to develop innovative nanoresonators that will be used, once functionalized, to detect chiral biomolecules with enantiomer sensitivity. Indeed, achiral resonators can generate both signs of chiral fields as opposed to chiral resonators which would make their use very flexible. This work implies characterizing, describing and understanding the origins of chiral fields and how to make them homogeneous. Through the study of nanoslits, I demonstrate numerically and theoretically how to design a nanosource of pure superchiral light, free of any background and for which the sign of the chirality is tunable on-demand in wavelength and polarization. In the perspective, I will present experimental methods that could monitor the CD via fluorescence emission (FDCD for Fluorescence Detected Circular Dichroism) in the case of light harvesting molecules for molecules that need to be excited in the UV, autofluorescence may be used in conjunction with aluminum resonators. Without loss of generality, these considerations lead to the decision of investigating plasmonic resonators with resonance at 680 nm which correspond to the chiral absorption band of LHCII. The idea of blocking the excitation beam to collect only the emission of the chiral molecules leaded to the idea of investigating the resonances of openings in an opaque layer of gold

We study second-harmonic generation in plasmonic nanoantennas with multi-pole Mie lattice resonances, exploring excitation conditions and periods. The symmetry is broken because of the coupling between the magnetic dipole and electric quadrupole in the lattice.