Refractometry

Creating accurate refractive index profiles has been very important in dealing with modern photonic equipment.
In a dispersive media, the refractive index is a function of the wavelength.
This is usually chromatic dispersion where blue light travels slower through the material than a red material. This explains how colors seperate in a prism.
This wavelength will be characterized by an ABBE number which is a combination of three already defined wavelengths.