Generalized hybrid anapole modes in all-dielectric ellipsoid particles[Invited]
2021
Numerous exciting optical effects in all-dielectric
high-refractive-index structures are associated with so-called toroidal
electrodynamics. Among these effects are anapoles, nonradiated states
caused by interference phenomena, e.g. between electric dipole and
toroidal dipole modes. For a spherical particle it is possible to reach
simultaneous destructive interference for electric, magnetic, and
corresponding toroidal dipole modes (so-called hybrid anapole mode), by
varying the refractive index and/or particle size. However, there are no
sufficient degrees of freedom within spherical geometry to extend the
hybrid anapole mode effect to higher multipoles. Due to the optical
theorem, it is also impossible to create the ideal anapole with
destructive interference for all multipoles under plane wave illumination.
In principle, it is possible to suppress radiation losses for the finite
number of multipoles only by constructing the nanoantenna with complex
geometry. Our approach of the hybrid anapole state excitation, we
demonstrate in ellipsoidal all-dielectric particle providing cancellation
of both electric and magnetic scattering up to quadrupole modes. This
effect is achieved due to the optimised geometry of the ellipsoidal
particle. Moreover, we provide classification of novel anapoles arising
due to interference between moments and their mean- square radii (MSR) of
electric, magnetic and toroidal family and introduce generalized anapoles
for high order interaction between moments. Our concept is useful for the
design of light controlling devices, reflectionless metasurfaces, high
Q-factor opened resonators and nonscattering particle
development.
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