Inter-Relation between Optical Constants for Lead Telluride and Silicon

There exists a general principle that in any oscillatory or frequency responsive system the real and imaginary components of the impedance are inter-dependent. Applied to the optical properties of materials this principle means that the real and imaginary parts of the dielectric constant are inter-dependent. Sufficient information is now available on lead telluride (in a companion paper by D G Avery) and silicon for this principle to be used to calculate the refractive indices from the absorption data. The values obtained show good agreement with the experimental values. Estimates of the effect of temperature show that for PbTe the refractive index should increase on cooling, while for silicon it should decrease.