The senior author’s interpolation formula for computing the dispersion of glass has been appropriately modified and applied to infrared materials. Indices of refraction for 14 optical materials that are suitable for practical refracting systems have been fitted by the modified formula and have been tabulated at increments of 0.5µ for the useful transmittance range of each material. The method of applying the dispersion formula is discussed and is illustrated by the design of two three-element superachromats corrected for the region of 2.0–5.0µ.
MAX HERZBERGER and CALVIN D. SALZBERG, "Refractive Indices of Infrared Optical Materials and Color Correction of Infrared Lenses," J. Opt. Soc. Am. 52, 420-424 (1962)