A3

3 types of interactions between matter and radiation

Stimulated absorption
Spontaneous emission
Stimulated emission

Stimulated absorption

radiation excites a molecule

Spontaneous emission

excited molecule emits radiation spontaneously

stimulated emission

radiation of the correct frequency results in the excited molecule emitting radiation and lowering in energy

rate of stimulated absorption

dNi/dt = -B_ij p(v) n_i

rate of stimulated emission

dn_j/dt = -B_ji p(v) n_j

when b_ij = b_ji

g = 0

B_ij = (g=0)

[8π³ / (4πε₀)3h² ] * R_ij²

R_ij =

∫psi*_j µ psi_i , the transition moment

R_ij = 0

forbidden transition

rate of spontaneous emission

dn_j/dt = -A_ij n_j

A_ij - Einstein A coefficient