A way to find precise dispersive curves and optical characterization of transparent dielectric.

  The index of refraction is the optical response of a material.  We study dielectrics transparent to visible and near-visible light. We use the minimum deviation method of light passing through triangularly shaped dielectrics in order to measure precisely their indices of refraction. This method is spectacular for students because they can discover that when they look through a rotating prism mounted on a spectrometer table, the emission spectrum lines from a discharge tube placed in front of the prism rotate in one direction, let’s say clockwise, till they reach a turning point from where the spectrum rotates exactly counterclockwise. This turning point corresponds to the minimum deviation angle.  The method is precise and allows to observe small differences between materials of same chemical composition. Using the Cauchy-Lorentz model for light propagating through transparent dielectrics, which considers the oscillations of the dipole constituents, we can find the density of electrons participating to light propagation, the speed of various lights released by the discharge source dispersed through the dielectric and its opacity wavelength. The students can recognize that light is emitted and detected as photons, but propagates and disperses as a wave through the dielectric.