Giant enhancement of second harmonic generation by engineering double plasmonic resonances at nanoscale

Abstract

We have investigated second harmonic generation (SHG) from Ag-coated LiNbO 3 (LN) core-shell nanocuboids and found that giant SHG can occur via deliberately designed double plasmonic resonances. By controlling the aspect ratio, we can tune fundamental wave (FW) and SHG signal to match the longitudinal and transverse plasmonic modes simultaneously, and achieve giant enhancement of SHG by 3×10 5 in comparison to a bare LN nanocuboid and by about one order of magnitude to the case adopting only single plasmonic resonance. The underlying key physics is that the double-resonance nanoparticle enables greatly enhanced trapping and harvesting of incident FW energy, efficient internal transfer of optical energy from FW to SHW, and much improved power to transport the SHG energy from the nanoparticle to the far-field region. In this work we will address this problem by insightful design. The most important thing is to look for a nanoparticle with double SPR modes. For this purpose, we turn to nanoparticles of anisotropic geometry, among which nanorods have attracted great attention due to their dimension induced wavelength tunability and polarization sensitivity [11][12][13]. One can control the aspect ratio of nanorods easily and obtain double SPR modes simultaneously, which are associated with the longitudinal and transverse SPR modes [14,15]. Moreover, the optical cross-sections of nanorods are much higher than those of nanospheres, and this has attributed nanorods promising features in wide applications like low-threshold surface plasmon amplification [16,17] and ultrafast optical devices [18]. The two SPR modes can be designed to enable their wavelengths matched to the absorption bands and emission bands of fluorescent molecules absorbed in gold nanorods [19] for enhancing their fluorescence intensity. It would be expected that this double-resonance mechanism should also play a very good role in enhancing SHG intensity of nanostructured materials.To illustrate and confirm this hypothesis, we propose and design an anisotropic nanoparticle, an Ag-coated LiNbO 3 (LN) core-shell nanocuboid [Ag-LN in Fig. 1(a) [23,24]. This approach is efficient equally for nonlinear optical problem solutions.Assume a plane wave FW at the frequency of ω 1 is incident upon a nonlinear particle. The FW electric field 1

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

“…The strategy of getting a qualitative increase of SHG from centrosymmetric metals by designing nanostructures of asymmetric geometrical shapes was identified . It was found that in order to make it efficient, the SHG engineering should rely on a certain selection rule, expressed in a semi‐empirical criterion as where E 2 is the SHG field, is the surface nonlinear susceptibility tensor component, considered to be the dominant SHG source, and are the components of the fields perpendicular to the metal‐dielectric boundary for the modes at the fundamental and SH frequencies, respectively, and the integration is performed over the nanostructure surface. Particularly, this approach was used to optimise SHG from multiresonant coupled nanoantennas (Figure c) .…”

Spatially-Controllable Hot Spots for Plasmon-Enhanced Second-Harmonic Generation in AgNP-ZnO Nanocavity Arrays

“…Usually, the excitation of LSPRs results in hot spots featuring locally enhanced electromagnetic field in close vicinity to photon-excited nanostructures [21]. Engineering hybrid nanostructures that combine plasmonic nanostructures with materials with large second-order susceptibility gives an opportunity to realize the effective integration of strongly enhanced and independently tunable resonances and intense sources of SH polarization [18,22,23,24]. Particular interest lies in the fact that PESHG can be achieved due to the stimulated excitation of hot spots depending on the excitation and emission energies.…”

Enhanced Second Harmonic Generation by Mode Matching in Gain-assisted Double-plasmonic Resonance Nanostructure

“…Employing Fano or magnetic plasmon resonances to avoid scattering and nonradiative losses at fundamental frequency has been proved as an efficient way to enhance SHG 20 – 23 . Moreover, when two plasmonic resonance modes are properly matched to both the fundamental and SH frequencies, the SH emission can be further enhanced 16 , 24 , 25 .…”