Second harmonic generation in metasurfaces with multipole resonant coupling

Abstract

<jats:title>Abstract</jats:title><jats:p>We report on the numerical demonstration of enhanced second harmonic generation (SHG) originating from collective resonances in plasmonic nanoparticle arrays. The nonlinear optical response of the metal nanoparticles is modeled by employing a hydrodynamic nonlinear Drude model implemented into Finite-Difference Time-Domain (FDTD) simulations, and effective polarizabilities of nanoparticle multipoles in the lattice are analytically calculated at the fundamental wavelength by using a coupled dipole–quadrupole approximation. Excitation of narrow collective resonances in nanoparticle arrays with electric quadrupole (EQ) and magnetic dipole (MD) resonant coupling leads to strong linear resonance enhancement. In this work, we analyze SHG in the vicinity of the lattice resonance corresponding to different nanoparticle multipoles and explore SHG efficiency by varying the lattice periods. Coupling of electric quadrupole and magnetic dipole in the nanoparticle lattice indicates symmetry breaking and the possibility of enhanced SHG under these conditions. By varying the structure parameters, we can change the strength of electric dipole (ED), EQ, and MD polarizabilities, which can be used to control the linewidth and magnitude of SHG emission in plasmonic lattices. Engineering of lattice resonances and associated magnetic dipole resonant excitations can be used for spectrally narrow nonlinear response as the SHG can be enhanced and controlled by higher multipole excitations and their lattice resonances. We show that both ED and EQ–MD lattice coupling contribute to SHG, but the presence of strong EQ–MD coupling is important for spectrally narrow SHG and, in our structure, excitation of narrow higher-order multipole lattice resonances results in five times enhancement.</jats:p>

Second harmonic generation under doubly resonant lattice plasmon excitation

“…6a. The center wavelength of the SHG (516.6 nm) is slightly red-shifted with respect to the half excitation wavelength, probably due to the asymmetry between forward and backward scattered light [38]. The angular dependence of the SHG spectrum is shown in Fig.…”

Optical Harmonic Generation in 2D Materials

“…On the other hand, as spacing in the perpendicular direction p y increases (from p y = 250 nm to 405 nm), the SHG intensity at the Rayleigh anomaly wavelength increases consistently, whereas it decreases as p y further increases which is attributed to the strengthening and weakening of multipole resonances. [ 321 ] Here, a hybrid structure is designed which combines a chirped surface plasmon metasurface with a 1L TMD to achieve a coherent SHG covering the entire visible light spectrum.…”

Diffraction-induced quadrupolar lattice plasmon modes of high-quality factors for silver nanoparticle arrays

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