From,
\(E_p=\hbar\left\{1-\sqrt{tan(\theta_v)}\right\}\cfrac{c}{x_c}\)
for \(0\lt\theta\lt45^o\),
\(E_p\gt0\)
emission is followed by absorption.
For \(45^o\lt\theta\lt90^o\),
\(E_p\lt0\)
absorption is followed by emission, as a result there is a small delay before emission.
At \(\theta=45^o\),
\(E_p=0\)
there is no emission, absorption occurs once of the initial excitation photon.
At \(\theta=90^o\),
\(E_p\to\infty\)
Not probable, but \(\small{\theta}\) can come close to ninety degrees.
