Emission and Absorption of Light

Abstract

It was from the study of the emission and absorption of light that such subjects as spectrochemical analysis, atomic physics and quantum mechanics grew and led further to the inventions of the maser and the laser. It was eventually found that the emission and absorption of light by matter took place discretely with an energy quantum or a photon as a unit, and it was this fact which became the foundation of the development of quantum physics during this century. Before deriving Planck’s law of thermal radiation which first showed the necessity of using the quantized energy of light, we shall calculate the mode density of electromagnetic waves.