I am simulating a gold nanorod pair to obtain scattering spectrum and more properties such as refractive index. This rod pair geometry is known to behave as negative-index material in NIR (Drachev, V. P. et al. Laser Physics … (2006). doi:10.1002/lapl.200510062), so I use this geometry as a practice to simulate metamaterials.
However the results are different between plane source and TFSF source. The scattering spectrum obtained with plane source has many steep peaks, while the spectrum with TFSF source is smooth. This aspect affects all other calculations such as refractive index with S parameters (I have already turned “grating analysis” of S parameter on to get rid of diffractions).
I would like to know the meaning of this difference and this kind of steep peaks. Here I attach the files.