Einstein coefficients

Einstein coefficients describe spontaneous emission, stimulated emission and absorption between atomic levels. With $B$ multiplying radiation energy density per frequency, thermal detailed balance gives $g_i{B}_{ij}=g_j{B}_{ji}$ and $A_{ji}/B_{ji}=8\pi h{\nu }^3/c^3$. Coefficients defined using mean specific intensity instead have a different normalization; specify the radiation convention.

Einstein coefficients are a set of quantifiable parameters that describe the interaction of atoms or molecules with electromagnetic radiation. They are critical in the field of quantum mechanics and spectroscopy and were introduced by Albert Einstein in his seminal works on the theory of radiation in the early 20th century.