= Emission cross section
{title2=$W_{21}=\sigma_{21}I/(\hbar\omega)$}
The effective area converting incident photon flux into a <stimulated emission> rate for a specified transition, <frequency>, <polarization> and sublevel distribution. For statistically populated <energy levels> of <statistical weights> $g_1,g_2$, the <Einstein coefficients> imply $g_1\sigma_{12}=g_2\sigma_{21}$. The related <absorption cross section> therefore differs when the <statistical weights> differ.
Back to article page
