Table 1.

A summary of the dependence of the angular spectrum of two-photon radiation as a function of initial and final electronic states for a few selected initial electronic states

Transition	Angular spectrum
$s\to s$	${\sin }^4\left(\frac{\theta -\theta \prime }{2}\right)$
$d_{xy}\to s$	${\sin }^2(\theta +\theta \prime )$
$d_{xz}\to s$	${(\cos \theta +\cos \theta \prime )}^2$
$d_{yz}\to s$	${(\sin \theta +\sin \theta \prime )}^2$