Helmholtz-Keteller formula

Helmholtz-Keteller formula

[′helm‚hōlts ′ked·əl·ər ‚fȯr·myə·lə]
(optics)
A dispersion formula in which the difference between the square of the index of refraction and unity is set equal to a sum of terms each of which is associated with a resonant wavelength of the medium.