Less Is More: Enhancement of Second-Harmonic Generation from Metasurfaces by Reduced Nanoparticle Density

Abstract

We investigate optical second-harmonic generation (SHG) from metasurfaces where noncentrosymmetric V-shaped gold nanoparticles are ordered into regular array configurations. In contrast to expectations, a substantial enhancement of the SHG signal is observed when the number density of the particles in the array is reduced. More specifically, by halving the number density, we obtain over 5-fold enhancement in SHG intensity. This striking result is attributed to favorable interparticle interactions mediated by the lattice, where surface-lattice resonances lead to spectral narrowing of the plasmon resonances. Importantly, however, the results cannot be explained by the improved quality of the plasmon resonance alone. Instead, the lattice interactions also lead to further enhancement of the local fields at the particles. The experimental observations agree very well with results obtained from numerical simulations including lattice interactions.

Efficient nonlinear metasurfaces by using multiresonant high-Q plasmonic arrays

“…We then performed linear and SHG simulations by using the above-mentioned NDDA method [27,28]. The simulated metasurface consisted of 600 × 600 particles corresponding to a physical size of around 250 × 500 μm 2 , and was illuminated by a normally incident x-polarized plane wave.…”

“…We use the NDDA approach to understand how multiresonant metasurfaces can be realized by arranging nanoparticles into periodic arrays supporting SLRs. The treatment follows earlier work on utilizing SLRs in nonlinear optics [26][27][28].…”

“…The SHG response of a metasurface can now be predicted with the aid of the above equations [27,28]. Specifically, the form of Eq.…”

“…However, relatively high-Q-factor resonances (Q > 100) can be achieved by arranging metal nanoparticles into periodic arrays, where particles become optically coupled and give rise to very narrow resonances, known as surface lattice resonances (SLRs) [15][16][17][18]. In fact, SLRs have already been utilized in many applications [19][20][21][22], where several works have also investigated their potential for nonlinear optics [23][24][25][26][27][28][29]. However, the nonlinear responses of multiresonant and high-Q-factor SLR arrays have not yet been investigated.…”

Nonlinear Spectral‐Imaging Study of Second‐ and Third‐Harmonic Enhancements by Surface‐Lattice Resonances

“…Therefore, in addition to the shape and size of the nanoparticles, the shape and periodic parameters of the lattice inevitably influence the resonance mass and intensity. Highly narrow resonances can be achieved by tuning the lattice constant within manufacturing technology, which has been studied extensively 15–17. However, the surface nonlinearity of two‐photon excited fluorescence (2PEF), three‐photon excited fluorescence (3PEF), SHG, and THG, which is affected by the lattice resonance, and has been revealed by reflected spectral and inverted microscopic methods, particularly with high sensitivity and high resolution, remains insufficiently understood.…”