This post describes how to get material data from the Material database or from a material fit.
The following plots show the raw sampled data (green dots) of the complex refractive indices of Silicon as well as their fitted curves (blue lines) that are actually used in the FDTD simulation.
You might have noticed that the plots of the retrieved sampled data using the getindex look slightly different from those visualized in the material explorer. This is because the sampling frequency (wavelength) points used in the above script file is different from those in the material database. The refractive index at the specified frequency is then linearly interpolated from the neighboring frequencies where the data is available.