Selective Induction of Optical Magnetism

Abstract

An extension of the Maxwell-Faraday law of electromagnetic induction to optical frequencies requires spatially appropriate materials and optical beams to create resonances and excitations with curl. Here we employ cylindrical vector beams with azimuthal polarization to create electric fields that selectively drive magnetic responses in dielectric core-metal nanoparticle "satellite" nanostructures. These optical frequency magnetic resonances are induced in materials that do not possess spin or orbital angular momentum. Multipole expansion analysis of the scattered fields obtained from electrodynamics simulations show that the excitation with azimuthally polarized beams selectively enhances magnetic vs electric dipole resonances by nearly 100-fold in experiments. Multipolar resonances (e.g., quadrupole and octupole) are enhanced 5-fold by focused azimuthally versus linearly polarized beams. We also selectively excite electric multipolar resonances in the same identical nanostructures with radially polarized light. This work opens new opportunities for spectroscopic investigation and control of "dark modes", Fano resonances, and magnetic modes in nanomaterials and engineered metamaterials.

Designing “Metamolecules” for Photonic Function: Reduced Backscattering

“…By contrast, single particle (scattering) measurements of individual metamolecules give sharper spectra, but with significant variation from metamolecule to metamolecule. [ 20 ] Structural characterization by scanning or transmission electron microscopy (SEM or TEM) reveals only partial information about the metamolecule structures. [ 12,15,20 ] Therefore, detailed understanding of the optical properties of core–satellite metamolecules has not been possible to date for three main reasons.…”

“…In our previous work, [ 20 ] single particle scattering spectroscopy measurements were performed using optical vector beams to illuminate individual SiO 2 –Ag nanoparticle core–satellite nanoclusters (metamolecules). We showed that focused vector beams allow selective excitation of collective optical magnetic modes.…”

“…In addition, we also found the simulated spectra varied considerably with different structural permutations of the Ag nanoparticle arrangements. [ 20,26 ] A strong scattering peak at ≈900 nm was observed in some experimental spectra, but not in FDTD simulations. We attributed it to the formation of short “chains” of Ag nanoparticles with sub‐nanometer gaps (nearly touching).…”

Assembling 1D and Janus Nanobelts into 2D Aeolotropic Conductive Janus Membranes and 3D Double‐Walled Janus Tubes

“…At present, multi-functional nanomaterials [13,14] have attracted extensive attention from researchers. Nanomaterials [15][16][17][18][19][20][21][22][23] with a single function such as magnetic, [24] conductive [25] or fluorescent characteristics [26,27] are developing towards multifunctional nanomaterids such as with magnetismfluorescence, [28][29][30] fluorescence-conduction, [31,32] conduction-magnetism [33,34] dual-functionality and fluorescence-conductionmagnetism [35,36] tri-functionality. In this way, it is possible to realize double or triple functions in a nanostructured material, which is of great significance for the development of nanoscience and technology.…”

Self-assembled microrings of Au nanoparticle and Au nanorod clusters formed at the equators of Janus particles

“…[5][6][7] Manna and co-workers studied optical magnetism in silver (Ag) NP clusters prepared by assembling the NPs on thiol-terminated silica particles. 8 Formation of Au NP cluster shells on coreshell particles with amino-terminated polybutadiene shells and polystyrene cores has also been reported; strong plasmonic coupling and near infrared (NIR) absorption was observed. 9 Thus, three-dimensionally symmetric metal NP clusters have been successfully prepared on spherical particles.…”