Theoretical background
Refractometry and interferometry in chemical analysis

The electromagnetic radiation wave incident on the molecules exerts forces on the electrons of the constituent atoms, setting them in motion. These forces accelerate the electrons, so that the molecules are in a position to emit radiation. In this way, as they pass through a material medium, a whole host of secondary waves are superimposed on the incident wave. The result is the complex phenomena of absorption, scattering, refraction, fluorescence...

In an attempt to explain these light-matter interaction phenomena, a theory has been established, based on the simplifying assumption that the moving electron is subject only to the electric field produced by the exciting wave, neglecting the fields produced by the surrounding molecules, themselves illuminated by the incident wave. This theory leads to the establishment of a fundamental relationship, known as the Lorentz-Lorenz...