Theoretical study of the tunable second-harmonic generation (SHG) enhancement factor of gold nanotubes

A theoretical calculation is performed to investigate the second-harmonic generation enhancement factor in gold nanotubes. The SHG at both inner and outer interfaces is greatly enhanced by the surface plasmon resonance (SPR) which induces a local field effect and fluctuations of the density of oscillatory electrons in the gold wall. The outer interface mode resulting from both basic and double frequency is more sensitive to the gold wall thickness. The coupling of the inner interface with outer interface makes the SHG enhancement factor increase greatly. Furthermore, the SPR frequency and local field intensity can be modulated by varying the dielectric constant, and consequently the position and intensity of the SHG peaks can be tuned. This work shows the potential of gold nanotubes for nonlinear optics at the nanoscale.