Einstein Coefficients were developed by Einstein in 1916 to describe how atoms absorb and re-emit photons. We introduce these coefficients and derive the Einstein Relations between them using Bolzmann and Planck statistics. More material at: https://casper.astro.berkeley.edu/astrobaki/index.php/Einstein_Coefficients
Also, check out my novel!
https://www.aaronrparsons.com/books-portfolio/coherence