Derivation Analytically, the Sellmeier equation models the refractive index as due to a series of optical resonances within the bulk material. Its derivation from the Kramers-Kronig relations requires a few assumptions about the material, from which any deviations will affect the model's accuracy: There exists a number of resonances, and the final refractive index can be calculated from the sum over the contributions from all resonances. All optical resonances are at wavelengths far away from the wavelengths of interest, where the model is applied. At these resonant frequencies, the imaginary component of the susceptibility () can be modeled as a delta function.
derivation analytically the sellmeier equation models the refractive index as due to a series of optical resonances within the bulk material its derivation from the kramers-kronig relations requires a few assumptions about the material from which any deviations will affect the model's accuracy there exists a number of resonances and the final refractive index can be calculated from the sum over the contributions from all resonances all optical resonances are at wavelengths far away from the wavelengths of interest where the model is applied at these resonant frequencies the imaginary component of the susceptibility () can be modeled as a delta function