The relationship between extraordinary optical transmission and surface-enhanced Raman scattering in subwavelength metallic nanohole arrays.

Nanohole arrays in an Ag film were used as a substrate for surface-enhanced Raman scattering in the optical range. Extraordinary optical transmission and local field enhancement in Ag nanohole arrays were theoretically simulated using three-dimensional finite difference time domain method. The periodicity of the holes was adjusted to control the transmission intensity and electric field intensity. The calculation results show that the peak position of transmission red-shifts as the periodicity increases, while the peak intensity decreases linearly. The electric field is localized in a very small region at the edges of the holes, which means the surface-enhanced Raman scattering originates only from a small number of molecules located in the edge regions. The electric field intensity changes with the excitation wavelength in a similar trend to the transmission intensity. Both the electric field intensity and transmission intensity reach their maximum value at the frequency of surface plasmon resonance. The structure that gives resonant transmission provides the maximum surface-enhanced Raman scattering signal. Controllable and predictable surface-enhanced Raman scattering can be produced by using this novel nanostructure. The structure can be optimized to get the maximum surface-enhanced Raman scattering signal at a certain excitation wavelength through numerical simulations.