Reshaping the Second-Order Polar Response of Hybrid Metal–Dielectric Nanodimers

Abstract

We combine the field confinement of plasmonics with the flexibility of multiple Mie resonances by bottom-up assembly of hybrid metal-dielectric nanodimers. We investigate the electromagnetic coupling between nanoparticles in heterodimers consisting of gold and barium titanate (BaTiO3 or BTO) nanoparticles through nonlinear second-harmonic spectroscopy and polarimetry. The overlap of the localized surface plasmon resonant dipole mode of the gold nanoparticle with the dipole and higher-order Mie resonant modes in the BTO nanoparticle lead to the formation of hybridized modes in the visible spectral range. We employ the pick-and-place technique to construct the hybrid nanodimers with controlled diameters by positioning the nanoparticles of different types next to each other under a scanning electron microscope. Through linear scattering spectroscopy, we observe the formation of hybrid modes in the nanodimers. We show that the modes can be directly accessed by measuring the dependence of the second-harmonic generation (SHG) signal on the polarization and wavelength of the pump. We reveal both experimentally and theoretically that the hybridization of plasmonic and Mie-resonant modes leads to a strong reshaping of the SHG polarization dependence in the nanodimers, which depends on the pump wavelength. We compare the SHG signal of each hybrid nanodimer with the SHG signal of single BTO nanoparticles to estimate the enhancement factor due to the resonant mode coupling within the nanodimers. We report up to 2 orders of magnitude for the SHG signal enhancement compared with isolated BTO nanoparticles.

High-harmonic generation at the nanoscale boosted by bound states in the continuum

“…However, the efficiency of nonlinear effects in such structures remains extremely low due to high losses and heating limiting the maximum powers. Optical nonlinear effects could be enhanced further in hybrid structures and novel materials [7][8][9][10], but different approaches are required.…”

Engineering of the Second‐Harmonic Emission Directionality with III–V Semiconductor Rod Nanoantennas

“…We performed the SHG polar measurements in the spectral range of 800-1400 nm (Figure 3). As we already showed in our previous works [39,62] in the regions where the contribution of the ED (and MD as well) resonances to the emitted SHG is low, the shape of the SHG polar signal is defined by the crystal structure of the nanoantenna.…”

“…Far-Field Linear Spectroscopy: Characterization of linear scattering cross-sections was performed in a dark-field spectroscopy setup, described in detail in the previous works. [39,58,65] The nanoantenna sample was irradiated with a halogen lamp source. The scattered light was collected in a transmission geometry using a 50x objective with an NA = 0.55.…”

“…Nonlinear Optical Characterization: Nonlinear optical measurements of the SHG spectra were performed with a nonscanning transmission optical microscope described in detail in the previous works. [39,58,59] For the excitation of the samples, a tunable Ti:Sapphire laser (from 700 to 1080 nm with steps of 10 nm) was used. For the region from 1080 to 1400 nm, structures were excited with the optical parametric oscillator (OPO) system attached to the Ti:Sapphire laser.…”

“…Some of these effects were recently demonstrated in single semiconductor nanodisks with low-radiative resonances, in nanoparticle dimers through excitation of anapole states and also in hybrid metal-dielectric nanostructures. [38][39][40][41][42][43][44] One way to engineer the directionality of scattered light with all-dielectric antennas is based on the interplay between the electric and magnetic modes. In the case of lower-order multipoles such as electric (ED) and magnetic (MD) dipole modes, their interference may lead to a strong forward or backward light scattering also known as Kerker effect [45] and such structures resemble artificial Huygens elements.…”