Collective Effects in Second-Harmonic Generation from Plasmonic Oligomers

Abstract

We investigate collective effects in plasmonic oligomers of different symmetries using second-harmonic generation (SHG) microscopy with cylindrical vector beams (CVBs). The oligomers consist of gold nanorods that have a longitudinal plasmon resonance close to the fundamental wavelength that is used for SHG excitation and whose long axes are arranged locally such that they follow the distribution of the transverse component of the electric field of radially or azimuthally polarized CVBs in the focal plane. We observe that SHG from such rotationally symmetric oligomers is strongly modified by the interplay between the polarization properties of the CVB and interparticle coupling. We find that the oligomers with radially oriented nanorods exhibit small coupling effects. In contrast, we find that the oligomers with azimuthally oriented nanorods exhibit large coupling effects that lead to silencing of SHG from the whole structure. Our experimental results are in very good agreement with numerical calculations based on the boundary element method. The work describes a new route for studying coupling effects in complex arrangements of nano-objects and thereby for tailoring the efficiency of nonlinear optical effects in such structures.

Strong second-harmonic generation from Au–Al heterodimers

“…This phenomenon has been reported as the 'silencing' of the second order nonlinear response. 8,20,43,44 Although a strong near-field enhancement is present, the nonlinear polarization vectors at each side of the gap are out of phase and their contributions to the far-field SH wave tend to cancel each other out. 43,44 The destructive interference finally results in a limited far-field SH signal, despite the amplitude of the nonlinear surface polarization.…”

“…8 LSPRs have indeed attracted particular attention as they allow enhancing and concentrating electromagnetic fields in sub-wavelength volumes. 14,15 Their influences on the nonlinear optical properties of plasmonic nanoantennas such as SHG, 8,[16][17][18][19][20] twophoton photoluminescence (TPL), 9,21,22 third and higher harmonics generation, 23 as well as multi-photon photoluminescence 9 have been thoroughly investigated. Nonlinear plasmonics, as a new branch of nano optics, has emerged recently.…”

Demonstration of longitudinally polarized optical needles

“…The excitation beam originated from a mode-locked laser (excitation wavelength of 1060 nm, pulse length of 140 fs, repetition rate of 80 MHz). First, we modified the excitation path of our custom-built cylindrical-vectorbeam-equipped point-scanning nonlinear optical microscope [36][37][38][39]41,42] to incorporate the generation of the RPBG and related vector beams. This is done by converting the linearlypolarized Gaussian output of the laser into an RP or AP doughnut-shaped beam using a commercial polarization mode converter (MC, Arcoptix, S.A.).…”

Selective excitation of localized surface plasmons by structured light

“…Conversely, nanooligomers and metasurfaces were used to create structured light at the nanoscale [12,13]. The complex phase-polarization pattern of structured light was implemented in materials science to control the chirality of twisted metal nanostructures [14], in nonlinear optics to increase the efficiency of second harmonic generation [15], and in nanoscale low-power optical trapping to increase the trap stiffness [16]. A number of new effects were also observed, such as dichroism of a plasmonic nanostructure interacting with OAM beams [17], and a spin-Hall effect in the scattering of structured light from a plasmonic nanowire [18].…”