Einstein’s Theory of Atom-Radiation Interaction

Abstract

In 1917, Einstein formulated a theory of spontaneous stimulated emission and absorption, based on purely phenomenological considerations [1.1]. His results paved the way for an understanding, in a qualitative way, of the basic ingredients of the atom-radiation interaction, and could be useful for describing the processes of absorption, light scattering by atoms, stimulated emission in a variety of laser and maser systems, etc. This happened after Planck found that the spectral distribution of blackbody radiation could be explained by quantizing the energy [1.2], and Einstein had explained the photoelectric effect [1.3] by postulating the existence of energy packets that were later called photons.