We observe enhanced third-harmonic generation from silicon nanodisks exhibiting both electric and magnetic dipolar resonances. Experimental characterization of the nonlinear optical response through third-harmonic microscopy and spectroscopy reveals that the third-harmonic generation is significantly enhanced in the vicinity of the magnetic dipole resonances. The field localization at the magnetic resonance results in two orders of magnitude enhancement of the harmonic intensity with respect to unstructured bulk silicon with the conversion efficiency limited only by the two-photon absorption in the substrate.
We demonstrate experimentally ultrafast all-optical switching in subwavelength nonlinear dielectric nanostructures exhibiting localized magnetic Mie resonances. We employ amorphous silicon nanodisks to achieve strong self-modulation of femtosecond pulses with a depth of 60% at picojoule-per-disk pump energies. In the pump-probe measurements, we reveal that switching in the nanodisks can be governed by pulse-limited 65 fs-long two-photon absorption being enhanced by a factor of 80 with respect to the unstructured silicon film. We also show that undesirable free-carrier effects can be suppressed by a proper spectral positioning of the magnetic resonance, making such a structure the fastest all-optical switch operating at the nanoscale.
Strong Mie-type magnetic dipole resonances in all-dielectric nanostructures provide novel opportunities for enhancing nonlinear effects at the nanoscale due to the intense electric and magnetic fields trapped within the individual nanoparticles. Here we study third-harmonic generation from quadrumers of silicon nanodisks supporting high-quality collective modes associated with the magnetic Fano resonance. We observe nontrivial wavelength and angular dependencies of the generated harmonic signal featuring a multifold enhancement of the nonlinear response in oligomeric systems.
It is known that the nonlinear optical properties of photonic nanostructures can be modified substantially due to strong field confinement and optical resonances. In this contribution, we study third-harmonic generation from lowloss subwavelength silicon nanodisks arranged in the form of trimer oligomers with varying distance between the nanoparticles. Each of the nanodisks exhibits both electric and magnetic Mie-type resonances that are shown to affect significantly the nonlinear response. We observe the thirdharmonic radiation intensity that is comparable to that of a bulk silicon slab and demonstrate a pronounced reshaping of the third-harmonic spectra due to interference of the nonlinearly generated waves augmented by an interplay between the electric and the magnetic dipolar resonances.
Control of light by an external magnetic field is one of the important methods for modulation of its intensity and polarisation [1]. Magneto-optical effects at the nanoscale are usually observed in magnetophotonic crystals [2,3], nanostructured hybrid materials [4][5][6] or magnetoplasmonic crystals [7][8][9][10][11]. An indirect action of an external magnetic field (e.g. through the Faraday effect) is explained by the fact that natural materials exhibit negligible magnetism at optical frequencies. However, the concept of metamaterials overcome this limitation imposed by nature by designing artificial subwavelength meta-atoms that support a strong magnetic response, usually termed as optical magnetism, even when they are made of nonmagnetic materials [12]. The fundamental question is what would be the effect of the interaction between an external magnetic field and an optically-induced magnetic response of metamaterial structures. Here we make the first step toward answering this fundamental question and demonstrate the multifold enhancement of the magneto-optical response of nanoantenna lattices due to the optical magnetism.Nanophotonics is often associated with plasmonic structures made of metals such as gold or silver. However, it is known that plasmonic structures suffer from high losses of metals, heating, and incompatibility with CMOS fabrication processes. Recent developments in the nanoscale optical physics gave birth to a new branch of nanophotonics aiming at the manipulation of opticallyinduced Mie-type resonances in dielectric nanoparticles made of materials with high refractive indices [12][13][14][15]. It has been shown recently that resonant dielectric structures offer unique opportunities for reduced dissipative losses and large resonant enhancement of both electric and magnetic fields. High-index dielectric structures can be employed as new building blocks to obtain unique functionalities such as magnetic Fano resonances [16,17], highly transmittable metasurfaces [18,19], and novel metadevices [20,21]. Here we extend the concept of high-index resonant nanophotonics to the case of magnetically active materials and study the magneto-optical (MO) response of a dielectric metasurface covered with a thin magnetic film, as shown schematically in Fig. 1. * Corresponding author: fedyanin@nanolab.phys.msu.ruWe emphasize that at the microscopic level the optical Figure 1. Schematic illustration of the enhancement of magneto-optical effects in a nanoscale structure. Linearly polarized light is focused on a dielectric metasurface composed of silicon nanoparticles supporting magnetic Mietype resonances, the metasurface is covered by a thin nickel film. The sample is subjected to the action of an external magnetic field oriented perpendicular to the wave vector of the incident light. Inset shows an SEM image of the sample.response is driven by electric dipoles, but high-index dielectric nanoparticles with this microscopic response generate effectively magnetic multipoles. Despite its geometrical simplicity, a ...
A novel type of nonlinear symmetry breaking in symmetric plasmonic oligomers is reported. By monitoring the strength of the second-harmonic signal while changing the polarization angle of the pump, we observe nonlinear symmetry breaking as a large variation in the generated nonlinear signal. Importantly, the strongly anisotropic nonlinear response is produced by a symmetric structure with isotropic linear response when rotating polarization. We provide theoretical analysis to describe and characterize this effect. Our finding opens new avenues to reveal and characterize the symmetry of nanoscale structures and molecules and also to remotely monitor variations of nearfield patterns produced by symmetric nanostructures.
Subwavelength silicon nanoparticles are known to support strongly localized Mie-type modes, including those with resonant electric and magnetic dipolar polarizabilities. Here we compare experimentally the efficiency of the third-harmonic generation from isolated silicon nanodiscs for resonant excitation at the two types of dipolar resonances. Using nonlinear spectroscopy, we observe that the magnetic dipolar mode yields more efficient third-harmonic radiation in contrast to the electric dipolar (ED) mode. This is further supported by full-wave numerical simulations, where the volume-integrated local fields and the directly simulated nonlinear response are shown to be negligible at the ED resonance compared with the magnetic one.This article is part of the themed issue 'New horizons for nanophotonics'.
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