Dependence of the Refractive Index for Flint Glass to an Energy Background*

We study the dependence of the refractive index for flint glass with the change of energy background. An increase in the energy background increases the vibration of the electric dipole constituents. When the background energy is small, the vibration of dipoles can be considered linear, and the interaction between light and matter is described by the Lorentz model, where the refractive index is dependent on the Cauchy parameter, C. We assess the changes in the refractive index by measuring changes of C values when a V voltage is set up across the glass. The assisting voltage changes the frequency of vibratory dipoles according to the energy conservation hf' = hf + eV, for voltages less than 10volts, which corresponds to an energy below the first opacity threshold for flint glass.

When we measure the change in the index of refraction using the reflection of a 650 nm laser beam near the Brewster angle assisted by a lower voltage set across the glass surface (from 0 to 2.4volts) for preserving the linear response of the surface dipoles, we observe that the Cauchy parameter for the surface dipoles remains practically the same, of 11254 ± 2 (within 0.02%). Adding more background energy from a voltage set up across the glass is therefore necessary. But in this case, the surface dipoles will be stressed into a strong non-linear vibrational regime. Therefore, the study should be done on bulk dipoles with light passing through glass, instead of surface dipoles. Using the minimum deviation method, we observe that a measurable change in C is only possible for voltages higher than 5volts. Thus, for light transmitted through flint glass, we find that the parameter C changes from 11180 at no voltage, to 11220 at 5 volts, and to 11280 at 10volts, which is about 0.9% larger than at 0V, while the error bar for C is only 0.5% in all cases. This result proves that an additional energy background can induce inside flint glass a measurable change of its refractive index.