XCIV. The drude dispersion formula shown to be applicable to any medium irrespective of the polarization field

Abstract

It is shown that the well known dispersion formula of Drude is applicable to a dense medium even when the polarization fields 'associated with the different types of oscillators may all be different. The parameters involved in the formula are naturally the frequencies and the oscillator strengths of the oscillators in the medium, both of them as influenced by the mutual interactions between the oscillators, i.e. as influenced by the polarization fields. The observed data on dispersion will enable us to determine these parameters. In the Lorentz type of dispersion formula, on the other hand, the frequencies and the oscillator strengths involved are those of the isolated oscillators, which naturally are independent of the polarization field, and hence the effect of the polarization field on dispersion has to be taken into account explicitly. Because of this, the Lorentz type of formula needs for its formulation explicit information regarding the polarization field, which cannot be supplied by the observed dispersion data alone. The reduction of the Drude formula to one of the Lorentz type, and the appropriate information regarding the polarization field that is needed for this purpose, are also discussed in the paper.