Cylindrical vector beams reveal radiationless anapole condition in a resonant state

TL;DR

This paper demonstrates how cylindrical vector beams can excite radiationless anapole states in resonant nanostructures, enabling control over light-matter interactions with potential applications in meta-optics.

Contribution

It introduces a novel method to excite optical anapoles in nanoparticles using tightly focused radially and azimuthally polarized beams, bypassing complex multipolar superpositions.

Findings

Successful excitation of anapole states in Si nanoparticles.

High contrast switching between anapole and magnetic resonant scattering.

Generalizable approach applicable to various nanostructures.

Abstract

Nonscattering optical anapole condition is corresponding to the excitation of radiationless field distributions in open resonators, which offers new degrees of freedom for tailoring light-matter interaction. Conventional mechanisms for achieving such a condition relies on sophisticated manipulation of electromagnetic multipolar moments of all orders to guarantee superpositions of vanished moment strengths at the same wavelength. In contrast, here we report on the excitation of optical radiationless anapole hidden in a resonant state of a Si nanoparticle utilizing tightly focused radially polarized (RP) beam. The coexistence of magnetic resonant state and anapole condition at the same wavelength further enables the triggering of resonant state by tightly focused azimuthally polarized (AP) beam whose corresponding electric multipole coefficient could be zero. As a result, high contrast inter-transition between radiationless anapole condition and ideal magnetic resonant scattering can be achieved experimentally in visible spectrum. The proposed mechanism is general which can be realized in different types of nanostructures. Our results showcase that the unique combination of structured light and structured Mie resonances could provide new degrees of freedom for tailoring light-matter interaction, which might shed new light on functional meta-optics.