Nobel Lecture: Manipulating atoms with photons

Abstract

Consider first a light beam with frequency L propagating through a medium consisting of atoms with resonance frequency A . The index of refraction describing this propagation has an imaginary part and a real part which are associated with two types of physical processes. The incident photons can be absorbed, more precisely scattered in all directions. The corresponding attenuation of the light beam is maximum at resonance. It is described by the imaginary part of the index of refraction which varies with L A as a Lorentz absorption curve. We will call such an effect a dissipative (or absorptive) effect. The speed of propagation of light is also modified. The corresponding dispersion is described by the real part n of the index of refraction whose difference from 1, n1, varies with L A as a Lorentz dispersion curve. We will call such an effect a reactive (or dispersive) effect.