Second Harmonic Generation from Ultrathin Gold Nanotubes

Abstract

We numerically study second harmonic generation from plasmonic nanotubes of air-core and ultrathin gold shell using classical nonlocal hydrodynamic model of free electron. We demonstrate that the nonlocal effect of gold significantly affects the linear optical response and second harmonic generation in such ultrathin nanotubes with shell down to a few nanometers or subnanometer scale, comparing with the conventional local Drude model of gold. We specially emphasize second harmonic generation from the nanotube structures of dipole plasmon resonance at fundamental wavelength and dipole/quadrupole resonance at second harmonic wavelength. Our results indicate that, the output of second harmonic generation is dominantly enhanced by the dipole plasmon resonance at fundamental wavelength via the strong local electric field and also can be significantly enhanced by dipole- and quadrupole-resonant scattering at second harmonic wavelength. The nonlinear sources of second harmonic generation in ultrathin gold nanotubes, including nonlinear Coulomb interaction, convective term, Lorentz force, and nonlinear pressure are studied separately, and the dominant contributions from convective term and nonlinear Coulomb term are reported.