should be determined by Boltzmann is Boltzmann's law
(5.15)
From these two equations (5.14) and (5.15) we get
(5.16)
If this has to agree with the Planck’s radiation law (5.10) we must have
(5.17)
We note:
If stimulated emission did not exist we should have got B21 = 0.
Instead we got B12 = B21. Thus, we see that Stimulated Emission is exactly the reverse process of absorption.
In Bohr’s model spontaneous emission was included although it appears contrary to the idea that all energy levels are stationary states.
Stimulated emission appears naturally in semi-classical treatment of radiation interaction with atoms i.e. when atom is treated quantum mechanically and radiation is treated classically.
Spontaneous emission cannot be explained unless electromagnetic fields are also quantized.
Later, we will show that population inversion leads to coherent amplification of an electromagnetic wave.
should be determined by Boltzmann is Boltzmann's law
