Wolfgang Sellmeier

Wolfgang Sellmeier was a German theoretical physicist who worked on how light interacts with ordinary matter. In 1872 he published a long paper on the resonances that ether vibrations excite in the particles of a body and on the reaction of those particles on the vibrations, written chiefly to explain dispersion and its anomalies. His central idea was that the particles in matter oscillate harmonically when a light wave passes through, which he used to account for the anomalous dispersion reported by Christian Christiansen and August Kundt. The resulting relation between a material's refractive index and the wavelength of the light is the Sellmeier equation, still used to describe dispersion in transparent materials away from their absorption peaks. The physics community took up his approach quickly, and it became the basis for dispersion theories by Hermann von Helmholtz, Woldemar Voigt and Paul Drude.