We propose a simple experimental technique to separately map the emission from electric and magnetic dipole transitions close to single dielectric nanostructures, using a few nanometer thin film of rare-earth ion doped clusters. Rare-earth ions provide electric and magnetic dipole transitions of similar magnitude. By recording the photoluminescence from the deposited layer excited by a focused laser beam, we are able to simultaneously map the electric and magnetic emission enhancement on individual nanostructures. In spite of being a diffraction-limited far-field method with a spatial resolution of a few hundred nanometers, our approach appeals by its simplicity and high signal-to-noise ratio. We demonstrate our technique at the example of single silicon nanorods and dimers, in which we find a significant separation of electric and magnetic near-field contributions. Our method paves the way towards the efficient and rapid characterization of the electric and magnetic optical response of complex photonic nanostructures.In the last decades, photonic nanostructures emerged as powerful instruments to control light at the subwavelength scale. 1 The interest in nano-optics lies usually in the control of the optical electric field, since the response of materials to rapidly oscillating magnetic fields is extremely weak. Actually, materials with a substantial magnetic response to electromagnetic radiation (i.e. µ = 1) are not known in nature. However, properly designed nanostructures allow to significantly boost the magnetic response. For instance metallic (split-)ring resonators support a magnetic moment which is proportional to the area covered by the ring's aperture. For frequencies in the visible range this area is usually about 10 6 times larger than the equivalent area in atoms, defined by the Bohr radius, which explains the emergence of observable effects related to the optical magnetic field. 2 In consequence, it is possible to overcome the natural limitation to µ = 1 by designing so-called meta-materials, which are ordered arrangements of meta-units like splitring resonators. 3 Using metals requires nanostructures of complex shape to obtain a significant magnetic response. On the other hand, in dielectrics of high refractive index, a magnetic response arises naturally from the curl of the electric field. 4,5 Very simple geometries like spheres 6 or cylinders 7 are actually sufficient to induce a strong magnetic field enhancement. 8 An additional advantage of high-index dielectric nanostructures is their low dissipation. Silicon (Si) for example has a very low absorption through the entire visible range compared to noble metals. 9 This weak absorption associated to the indirect gap in the near infrared becomes cumbersome only for applica- * tions involving propagation of visible light across distances of tens to hundreds of microns. Thus, in submicron dielectric nano-structures the absorption can usually be neglected. 10 In summary, high-index nanostructures seem to provide an appropriate platform to study the co...
When the sizes of photonic nanoparticles are much smaller than the excitation wavelength, their optical response can be efficiently described with a series of polarizability tensors. Here, we propose a universal method to extract the different components of the response tensors associated with small plasmonic or dielectric particles. We demonstrate that the optical response can be faithfully approximated, as long as the effective dipole is not induced by retardation effects, hence do not depend on the phase of the illumination. We show that the conventional approximation breaks down for a phase-driven dipolar response, such as optical magnetic resonances in dielectric nanostructures. To describe such retardation induced dipole resonances in intermediate-size dielectric nanostructures, we introduce "pseudo-polarizabilities" including first-order phase effects, which we demonstrate at the example of magnetic dipole resonances in dielectric spheres and ellipsoids. Our method paves the way for fast simulations of large and inhomogeneous meta-surfaces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.