FDTD calculations were performed using the Ansys-Lumerical FDTD Solutions package. Palik's parameters were used for the thin gold film in the lower layer of the MIM structure. Calculations were performed using the experimentally obtained permittivity for the upper nanodisk structure. The nanodisc diameter was swept from 500 nm to 2000 nm in 100 nm increments and recalculated in 10 nm increments, especially in regions of lower reflectivity. The permittivity of Palik was used for SiO 2 , and calculations were performed for the film thicknesses of 50, 100, 150, 200, 300, and 400 nm. The thickness of the Au nanostructures was set to 50 nm under the same conditions as those used in the experiment.