Free‐electron Optical Nonlinearities in Plasmonic Nanostructures: A Review of the Hydrodynamic Description

Abstract

Requirements of integrated photonics and miniaturisation of optical devices demand efficient nonlinear components not constrained by conventional macroscopic nonlinear crystals. Intrinsic nonlinear response of free carriers in plasmonic materials provides opportunities to design both second-and third-order nonlinear optical properties of plasmonic nanostructures and control light with light using Kerr-type nonlinearities as well as achieve harmonic generation. This review summarises principles of free-carrier nonlinearities in the hydrodynamic description in both perturbative and non-perturbative regimes, considering also contribution of nonlocal effects. Engineering of harmonic generation, solitons, nonlinear refraction and ultrafast all-optical switching in plasmonic nanostructures and metamaterials are discussed. The full hydrodynamic consideration of nonlinear dynamics of free carriers reveals key contributions to the nonlinear effects defined by the interplay between a topology of the nanostructure and nonlinear response of the fermionic gas at the nanoscale, allowing design of high effective nonlinearities in a desired spectral range. Flexibility and unique features of free-electron nonlinearities are important for nonlinear plasmonic applications in free-space as well as integrated and quantum nanophotonic technologies.

Structural Second Order Nonlinearity in Metamaterials

“…The spectral and polarization dependences of the SHG are in a good agreement with the full-wave numerical simulations ( Fig. 2 b) which implement the hydrodynamic model of the SHG generation in plasmonic media [35,40,41] (see SI [36] for the details of the numerical simulations). In this model the nonlinear polarization of gold is given by…”

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

“…[1][2][3][4] Nonlinear generation in photonic nanostructures constantly attracts the interest of researchers seeking to enhance the efficiency of higher order effects and to control the emission of the generated light 5 . Recently, the focus in nonlinear generation switched from fully metallic nanostructures [6][7][8][9] to dielectric and semiconductor resonant systems due to rapidly developing all-dielectric Mie-resonant nanophotonics. 10,11 The intrinsic advantage of non-plasmonic resonant systems [12][13][14] is the low losses and the enhanced second-order nonlinear response due to a bulk nonlinearity of materials.…”

Magnetic moment generation in small gold nanoparticles via the plasmonic inverse Faraday effect

“…Such models were recently used to model the electron dynamics in thin films [35], metallic nanostructures [36][37][38][39], semiconductor quantum wells [40] and molecular systems [41]. Many recent studies have emphasized the importance of spatial nonlocal effects in the optical response of plasmonic systems [36,38,[42][43][44]. The latter are suitably incorporated in the QHD model through the self-consistent fields and lead to spatial variations of the electron density.…”