Anapoles in Free-Standing III–V Nanodisks Enhancing Second-Harmonic Generation

Abstract

Nonradiating electromagnetic configurations in nanostructures open new horizons for applications due to two essential features: a lack of energy losses and invisibility to the propagating electromagnetic field. Such radiationless configurations form a basis for new types of nanophotonic devices, in which a strong electromagnetic field confinement can be achieved together with lossless interactions between nearby components. In our work, we present a new design of free-standing disk nanoantennas with nonradiating current distributions for the optical near-infrared range. We show a novel approach to creating nanoantennas by slicing III-V nanowires into standing disks using focused ion-beam milling. We experimentally demonstrate the suppression of the far-field radiation and the associated strong enhancement of the second-harmonic generation from the disk nanoantennas. With a theoretical analysis of the electromagnetic field distribution using multipole expansions in both spherical and Cartesian coordinates, we confirm that the demonstrated nonradiating configurations are anapoles. We expect that the presented procedure of designing and producing disk nanoantennas from nanowires becomes one of the standard approaches to fabricating controlled chains of standing nanodisks with different designs and configurations. These chains can be essential building blocks for new types of lasers and sensors with low power consumption.

Nonradiating photonics with resonant dielectric nanostructures

“…Other than THG, enhanced second-harmonic generation (SHG) was also recently reported by using nonradiating anapoles by Timofeeva and co-workers in Ref. [125]. This work proposed an interesting fabrication process relying on ion-beam billing to slice nanowires, resulting in nanodisks in a vertical free standing configuration.…”

Optical Anapoles: Concepts and Applications

“…In ref. SHG intensity at the anapole state in the geometry of vertically standing GaAs/AlGaAs pillars on a substrate was demonstrated to exceed that in the bare layer up to 5 times (see Figure d). Rocco et al studied the effective coupling of electric and toroidal modes in AlGaAs nanodimers to enhance the SHG efficiency with respect to the case of a single isolated nanodisk.…”

“…d) Wavelength dependence of the SHG spectra from the GaAs/AlGaAs disk (blue lines) and epitaxial layer (red lines, signal is multiplied by 10 3 ), the dashed gray lines are the SHG spectra envelopes; recorded by sweeping the excitation laser wavelength from 690 to 900 nm with 10 nm step. Adapted with permission . Copyright 2015, 2016, 2017, 2018, American Chemical Society.…”

Nonradiating anapole states in nanophotonics: from fundamentals to applications

“…Inspired by the advances in Ge or Si disks, researchers also explored the anapole states supported by nanostructures made of III-V materials such as GaAs, AlGaAs, or InAs, which have noncentrosymmetric structures and thus become an ideal platform for second harmonic generation (SHG) [109][110][111]. In particular, we mention the recent study by Timofeeva et al [110], in which they developed a novel FIB slicing technique to fabricate free-standing nanodisks and investigated their nonlinear response enhanced by anapole states. This special configuration is able to realize toroidal response and anapole states with different orientations and polarization selectivity.…”