Hi,
I’m having trouble getting a good model fit for Si in the 713 um wavelength band.
As can be seen in the following picture:
The FDTD model tracks the experimental data acceptably for the real part of the refractive index, but not at all for the imaginary part. As can be seen, the fit chosen by FDTD has only two coefficients whereas I would prefer a large number of coefficients to get a tighter fit.
I also tried changing the weighting of the imaginary part over a range of values (1e1  1e5). This resulted in either a poor compromise where the fit was unacceptable for both parts, or a good fit for the imaginary component and a poor fit for the real one.

Why are the two functions coupled in the fitting process? Seems like fitting each function separately (or at least having the option to) would have been a better approach here.

Is it possible for me to input a functional model myself? i.e. find the fit I would like to work with in a separate program (e.g. Matlab) and input the model directly?
Would appreciate any input on this subject,
Cheers