Atoms in an excited state n
changes its state from n
to n
spontaneously.
The number of transitions is proportional to the number of atoms
in the n
state
as
![\begin{displaymath}
A_{n_u\rightarrow n}N_{n_u},
\end{displaymath}](img724.png) |
(2.133) |
where
represents the probability of transition
from n
to n in unit time.
This coefficient is called Einstein's
coefficient.
The lifetime of n
level is related to this coefficient
as
![\begin{displaymath}
\tau_{\rm life}(n_u)=\frac{1}{A_{n_u\rightarrow n}+A_{n_u\rightarrow n_d}},
\end{displaymath}](img726.png) |
(2.134) |
for this three-level atom.
Kohji Tomisaka
2009-12-10