A Refractive-Index Interpolation Fit Criterion for Materials Used in Optical Design

Optical designers need to know the index of refraction of optical materials in order to design and accurately predict the performance of an optical system. The indices must' be known at wavelengths that are pertinent to the system being designed not the ones in the vendor's brochure or the technical publication where the data was found. For optical glasses, the vendors have been aiding the designer since the late 1960s by providing an interpolation formula and coefficients. This allows the designer to accurately determine the index of the glass at any wavelength in the visible and very near infrared. Infrared or ultraviolet transmitting materials usually do not have vendor supplied coefficients, and the raw index data available is often of uncertain accuracy. What does a designer do when he needs the information after the glass has passed the inflection point in its dispersion curve or needs to use an optical material other than glass?