Illustrate the A and B coefficients of Einstein in shortly.

Einstein’s A and B coefficients:

Einstein suggested a mathematical expression for the existence of stimulated emission of light that is termed as Einstein’s expression.

Into atomic system, each three transition processes as stimulated absorption, spontaneous emission and stimulated emission happen simultaneously. While photons interact along with atoms, both upward i.e., absorption and downward i.e., emission transitions happen. At equilibrium such transition rates should be equal.