The fundamental contributions made by Albert Einstein toward our present-day understanding of the nature of light are reviewed. In order to place this work into proper perspective, the theories of Hooke, Huygens, Newton, Fresnel, and Maxwell are first summarized, and a brief account is given of the researches of Kirchhoff, Wien, Rayleigh, Jeans, and Planck on equilibrium radiation laws. The main publications of Einstein that led to the formulation of the quantum theory of radiation are then discussed. These include his investigations on the particle aspects of radiation, on the wave-particle duality, on the elementary processes of energy exchange between gas molecules and a radiation field, and on photon statistics.
by Emil Wolf