Refractive indices and dispersion values of optical glass melts deviate from the catalog data. The difference must be considered during the optical design of precision optics to avoid significant performance losses. The melt data are supplied as tables with refractive index and dispersion values for a few wavelengths in the visible range of the spectrum. Several numerical methods for the inter- and extrapolation of melt data are examined. Good performance is achieved with procedures, that do not 'forget' the catalog behavior of the glass. They use the melt data only for corrections of the catalog values. Best results are obtained with a refractive index correction formula with only two free parameters. A modified version of this method calculates the melt coefficients for the Sellmeier dispersion formula which can be entered into the user glass catalog of commercial optical design programs and allow an ease access to the melt data.
"Melt-dependent refractive index interpolation for optical glasses", Proc. SPIE 3737, Design and Engineering of Optical Systems II, (27 August 1999); doi: 10.1117/12.360038; https://doi.org/10.1117/12.360038