Coefficients used in the quantum theory of radiation,
related to the possibility of a transition occurring
between the ground state and an excited state in the
processes of induced emission and spontaneous emission.
For an atom exposed to electromagnetic radiation,
the rate of absorption Ra is give by Ra
= Bp, where p is the density of electromagnetic
radiation and B is Einstein B coefficient associated
The rate of induced emission is also given by Bp
with the coefficient B of induced emission being equal
to the coefficient of absorption.
These coefficients were put forward by Albert Einstein in 1916 -17 in his
analysis of the quantum theory of radiation.