Dynamic Tuning and Swapping of Electric and Magnetic Dipolar Mie Resonances in High Index Dielectric Particles Dispersed in an Anisotropic Medium

Abstract

High refractive index (n > 2.5) dielectric particles support strong electric and magnetic Mie resonances in the visible region enabling optical properties such as directional scattering, anapole modes, and Fano resonances with applications in nanophotonics. Selenium particles, which possess a high refractive index at optical frequencies, have been synthesized using a controlled approach involving a moderate reduction of selenious acid to obtain particles of the desired size. The extinction spectra from UV–vis spectroscopy in conjunction with theoretical simulations confirm the presence of highly size‐dependent dipole and quadrupole Mie resonances in the visible region. Dynamic tuning of magnetic and electric Mie resonances and swapping of electric and magnetic dipoles are observed in a colloidal dispersion of 250 nm‐sized selenium particles in a nematic liquid crystal due to the anisotropic nature of the latter. Theoretical simulations reveal the presence of unidirectional scattering and photonic‐nanojet formation, attributed to generalized Kerker's effects in nanophotonics and meta‐optics, due to the swapping phenomena leading to the superposition of dipole and quadrupole resonances. The manipulation of Mie resonances in the liquid crystal based colloidal metamaterial has the potential for large‐scale and cost‐effective nanophotonic device applications.

Ultralow-Loss Substrate for Nanophotonic Dark-Field Microscopy

“…In contrast to Au NSs, it is possible to induce both the electric and magnetic resonances (i.e., all-dielectric Mie resonances) merely within the individual Se NSs. ,, As shown in Figure a (i.e., multipole expansion analyses), free-standing 360 nm Se NS can exhibit higher-order EQ and MQ modes together with fundamental ED and MD modes under the illumination of TM mode. Also, these modes can be spectrally overlapped with each other.…”

“…13,20,31−33 Meanwhile, Se NSs themselves can excite MD as well as ED without clustering. 37,38,47 More importantly, higher-order electric quadrupole (EQ) and MQ can be excited within individual Se NSs. Coupling between fundamental and higher-order modes enables a directional far-field scattering, 12,37,38 which can further elucidate the importance of low optical loss in both transmissive and reflective dark-field microscopic studies.…”

“…To induce unnatural magnetic dipole (MD) or quadrupole (MQ) resonances, more than three Au NSs need to be closely clustered with a nanometer gap. ,− ,− Herein, as a representative example, we self-assembled a close-packed heptamer, as this cluster can induce strong MD and its interference with ED. ,,− Especially, the bright ED mode can be partially used to induce MQ mode (i.e., Fano resonance); thus, this Fano resonance can be evidenced by scattering spectral dip (i.e., Fano minima). ,,− Meanwhile, Se NSs themselves can excite MD as well as ED without clustering. ,, More importantly, higher-order electric quadrupole (EQ) and MQ can be excited within individual Se NSs. Coupling between fundamental and higher-order modes enables a directional far-field scattering, ,, which can further elucidate the importance of low optical loss in both transmissive and reflective dark-field microscopic studies.…”