Absorção de luz por um átomo em um meio e o momento da luz na matéria

Abstract

In this dissertation we study a simple interaction model of a light pulse with a resonant atom immerse in a linear, nondispersive dielectric medium. The model consists in a classic treatment for the atom, considering a xed nucleus and the electron cloud as a harmonic oscillator (Lorentz model), being forced by the electromagnetic radiation of the incident pulse and absorbing energy and momentum in the process. The electric dipole oscilation generates a second electromagnetic wave that overlaps with the incident pulse. We will make energy and momentum calculations for the electromagnetic wave, as well as transmitted to the resonant atom and to the surroundings, in order to nd conservation of energy and momentum in the process. We use these calculations to investigate the Abraham-Minkowski controversy, that debates the correct expression for electromagnetic momentum within a material medium. In 1908 Minkowski predicted that the momentum of a light wave in a medium would be proportional to the refractive index, while in 1909 Abraham predicted that the momentum would be proportional to the inverse of the refractive index, what initiated a century long debate. Today we understand that both formulations are correct, with Abraham's momentum associated with kinetic momentum and Minkowski's associated with the canonical momentum of the electromagnetic wave. The main objective of this paper is to investigate the role of Abraham's and Minkowski's momentum in the presented system.