Enhancement of electric and magnetic dipole transition of rare-earth-doped thin films tailored by high-index dielectric nanostructures

Abstract

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...

Evolutionary Optimization of All‐Dielectric Magnetic Nanoantennas

“…A similar comparison can be performed between the genetically optimized antenna and other commonly used dielectric resonators for enhanced magnetic fields such as a single silicon disk or a dimer of Si disks (see Figure S5, Supporting Information). Importantly, the magnetic field intensity enhancements simulated here for a disk dimer and a hollow nanodisk are in good agreement with recently reported experimental values, validating the relevance of the comparison made here. These simulations indicate that the GA design offers a very significant enhancement of the magnetic field intensity above the antenna that is 10× and 8× larger than for a single disk or a dimer, respectively.…”

“…Along the same lines, some of these structures were theoretically shown to strongly increase the emission rates of magnetic dipoles . In fact, experimental evidence for the capacity of optical nanoantennas to manipulate the emission of such dipoles at visible or near‐infrared wavelengths has been brought about recently. In that context, based on Mie resonances, high index dielectric nanoparticles are of particular interest to efficiently enhance the magnetic optical field at visible wavelengths through strong displacement currents taking place inside these nanoantennas .…”

Light-emitting metasurfaces

“…In accordance with theoretical expectations, a moderate magnetic emission enhancement of about 3, as estimated by the authors, was observed. In another work [245], a homogeneous 10-nmthick film of Eu 3+ -doped nanoclusters was deposited on single silicon nanorods and dimers. The samples were raster-scanned under a tightly focused laser beam, and the PL maps were recorded.…”

Quantum theory of near-field optical imaging with rare-earth atomic clusters

“…A physical interpretation of the mechanism causing the imaging process, has been highlighting the role of the electric part of the photonic local density of states (e-LDOS) at the emitter position [16]. Recently, delicate experiments have addressed light emission from rare earth doped emitters, supporting both, strong electric and magnetic dipolar transitions [17][18][19][20].…”