Model-Material Refractive-Index Fitting

Introduction

Model-material fitting uses parameterized optical models (such as Cauchy, Sellmeier, or other selectable model forms) to fit refractive-index behavior. It is used when a physically meaningful model is preferred over pointwise fitting.

Procedure

1. Select a material model that matches expected optical behavior.
2. Load measured spectra and set initial model parameters.
3. Configure parameter bounds, constraints, and optimization stop criteria.
4. Run fitting and inspect model parameter convergence.
5. Verify model validity in the target wavelength range and save parameters.

Example

A transparent dielectric layer is fitted with a Cauchy-type model. Starting from empirical initial parameters, optimization converges and outputs model coefficients that reproduce measured spectra within process tolerance.

Notes

• Choose the simplest valid model first, then increase complexity only when needed.
• Over-parameterized models may fit noise and reduce transferability.
• Always check both spectral residuals and parameter physical plausibility.