Einstein coefficients

In atomic, molecular, and optical physics, the Einstein coefficients are quantities describing the probability of absorption or emission of a photon by an atom or molecule. The Einstein ''A'' coefficients are related to the rate of spontaneous emission of light, and the Einstein ''B'' coefficients are related to the absorption and stimulated emission of light. Throughout this article, "light" refers to any electromagnetic radiation, not necessarily in the visible spectrum.

These coefficients are named after Albert Einstein, who proposed them in 1916. Provided by Wikipedia