Characterization of bare substrates for non-standard materials can be carried out from photometric and ellipsometric spectra.

Several ellipsometric and spectrophotometric data files can be fitted simultaneously.

The errors in the measurement (imprecision of spectral data) are always taken into account in the fitting algorithms.

Many models have been included for describing the spectral behavior of complex refractive index (for transparent materials, semiconductors, metals...), covering a wide range of applications:

• Cauchy
• Sellmeier
• Lorenz Oscillators
• Tauc-Lorentz
• Forouhi-Bloomer
• Drude

Effective Medium Approximation (EMA) models for the description of layers with mixtures of materials are also available. The optical constants of the materials are read from a file. This model is used to implement interface layers and surface roughness.

In-depth inhomogeneity (of the refractive index n) within the layer can be modeled according to different shapes (linear profile, 2-line profile, segmented profile...).

The fittings can be restricted to regions of the spectra, named "targets". This allows to exclude inaccurate data that could prevent a meaningful characterization.

The fitting procedure can also include an estimation of the error on the parameters, thus providing an assessment on the quality of the result. This estimation is done by evaluating the covariance matrix of the χ² at its minimum.