A. K. Samusev

Magnetic and electric hotspots with silicon nanodimers

The study of the resonant behavior of silicon nanostructures provides a new route for achieving efficient control of both electric and magnetic components of light. We demonstrate experimentally and numerically that enhancement of localized electric and magnetic fields can be achieved in a silicon nanodimer. For the first time, we experimentally observe hotspots of the magnetic field at visible wavelengths for light polarized across the nanodimers primary axis, using near-field scanning optical microscopy.

Probing magnetic and electric optical responses of silicon nanoparticles

We study experimentally both magnetic and electric optically induced resonances of silicon nanoparticles by combining polarization-resolved dark-field spectroscopy and near-field scanning optical microscopy measurements. We reveal that the scattering spectra exhibit strong sensitivity of electric dipole response to the probing beam polarization and attribute the characteristic asymmetry of measured near-field patterns to the excitation of a magnetic dipole mode. The proposed experimental approach can serve as a powerful tool for the study of photonic nanostructures possessing both electric and magnetic optical responses.

Magnetic dipole radiation tailored by substrates: numerical investigation

Nanoparticles of high refractive index materials can possess strong magnetic polarizabilities and give rise to artificial magnetism in the optical spectral range. While the response of individual dielectric or metal spherical particles can be described analytically via multipole decomposition in the Mie series, the influence of substrates, in many cases present in experimental observations, requires different approaches. Here, the comprehensive numerical studies of the influence of a substrate on the spectral response of high-index dielectric nanoparticles were performed. In particular, glass, perfect electric conductor, gold, and hyperbolic metamaterial substrates were investigated. Optical properties of nanoparticles were characterized via scattering cross-section spectra, electric field profiles, and induced electric and magnetic moments. The presence of substrates was shown to have significant impact on particles magnetic resonances and resonant scattering cross-sections. Variation of substrate material provides an additional degree of freedom in tailoring optical properties of magnetic multipoles, important in many applications.

Enhancement of artificial magnetism via resonant bianisotropy.

All-dielectric “magnetic light” nanophotonics based on high refractive index nanoparticles allows controlling magnetic component of light at nanoscale without having high dissipative losses. The artificial magnetic optical response of such nanoparticles originates from circular displacement currents excited inside those structures and strongly depends on geometry and dispersion of optical materials. Here an approach for enhancing of magnetic response via resonant bianisotropy effect is proposed and analyzed. The key mechanism of enhancement is based on electric-magnetic interaction between two electrically and magnetically resonant nanoparticles of all-dielectric dimer. It was shown that proper geometrical arrangement of the dimer in respect to the incident illumination direction allows flexible control over all vectorial components of the magnetic moment, tailoring the latter in the dynamical range of 100% and delivering enhancement up to 36% relative to performances of standalone spherical particles. The proposed approach provides pathways for designs of all-dielectric metamaterials and metasurfaces with strong magnetic responses.

Nanoscale patterning of metal nanoparticle distribution in glasses

We show that electric field imprinting technique allows for patterning of metal nanoparticles in the glass matrix at the subwavelength scale. The formation of glass-metal nanocomposite strips with a width down to 150 nm is demonstrated. The results of near-field microscopy of imprinted patterns are in good agreement with the performed numerical modeling. Atomic force microscopy reveals that imprinting also results in the formation of nanoscale surface profile with the height going down with the decrease of the strip width. The experiments prove the applicability of this technique for the fabrication of nanoscale plasmonic components.

Two-dimensional light diffraction from thin opal films

This paper reports on experimental and theoretical investigations of light diffraction from thin films of synthetic opal. The diffraction patterns have been studied visually and recorded in different scattering geometries with the films illuminated with white unpolarized light. The diffraction pattern obtained with the film illuminated with a light beam along the [111] axis, which is normal to the film surface, has C6 symmetry and consists of six strong reflections arranged symmetrically with respect to the incident beam. This pattern becomes substantially more complicated when the film is illuminated by white light at an arbitrary angle to the [111] axis. An experimental study of the spectral response and angular relations of the diffraction patterns has established a fairly full pattern of transformation of diffraction reflections obtained under variation of the angle of light incidence on an opal film. The remarkably good matching of experimental and calculated data provides compelling evidence for light diffraction from thin opal films being two-dimensional.

Chirality Driven by Magnetic Dipole Response for Demultiplexing of Surface Waves

waves Ivan S. Sinev,1 Andrey A. Bogdanov,1 Filipp E. Komissarenko,1, 2 Kristina S. Frizyuk,1 Mihail I. Petrov,1 Ivan S. Mukhin,1, 2 Sergey V. Makarov,1 Anton K. Samusev,1 Andrei V. Lavrinenko,1, 3 and Ivan V. Iorsh1 1)Department of Nanophotonics and Metamaterials, ITMO University 197101 St. Petersburg, Russiaa) 2)St. Petersburg Academic University, 194021 St. Petersburg, Russia 3)Department of Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark

Mapping electromagnetic fields near a subwavelength hole

We study, both experimentally and theoretically, the scattering of electromagnetic waves by a subwavelength hole fabricated in a thin metallic film. We employ the scanning near-field optical microscopy in order to reconstruct experimentally the full three-dimensional structure of the electromagnetic fields in the vicinity of the hole. We observe an interference of all excited waves with an incident laser beam which allows us to gain the information about the wave phases. Along with the well-known surface plasmon polaritons propagating primarily in the direction of the incident beam polarization, we observe the free-space radiation diffracted by the hole. We compare the experimental results with the fields of pure electric and pure magnetic dipoles as well as with direct numerical simulations. We confirm that a single hole in a thin metallic film excited at the normal incidence manifests itself as an effective magnetic dipole in the visible spectral range.

Nanoscale Generation of White Light for Ultrabroadband Nanospectroscopy

Achieving efficient localization of white light at the nanoscale is a major challenge due to the diffraction limit, and nanoscale emitters generating light with a broadband spectrum require complicated engineering. Here we suggest a simple, yet highly efficient, nanoscale white-light source based on a hybrid Si/Au nanoparticle with ultrabroadband (1.3-3.4 eV) spectral characteristics. We incorporate this novel source into a scanning-probe microscope and observe broadband spectrum of photoluminescence that allows fast mapping of local optical response of advanced nanophotonic structures with submicron resolution, thus realizing ultrabroadband near-field nanospectroscopy.

Microwave platform as a valuable tool for characterization of nanophotonic devices

The rich potential of the microwave experiments for characterization and optimization of optical devices is discussed. While the control of the light fields together with their spatial mapping at the nanoscale is still laborious and not always clear, the microwave setup allows to measure both amplitude and phase of initially determined magnetic and electric field components without significant perturbation of the near-field. As an example, the electromagnetic properties of an add-drop filter, which became a well-known workhorse of the photonics, is experimentally studied with the aid of transmission spectroscopy measurements in optical and microwave ranges and through direct mapping of the near fields at microwave frequencies. We demonstrate that the microwave experiments provide a unique platform for the comprehensive studies of electromagnetic properties of micro- and nanophotonic devices, and allow to obtain data which are hardly acquirable by conventional optical methods.