Does someone can explain that?
The transition frequency v of atoms exposed to the
lattice electric field of E is described as,
hv = hv^(0)-(1/4) alpha(e,w)E^2-(1/64) gama(e,w)E^4
where v^(0) is the transition frequency between the unperturbed atomic states, alpha(e,w) and gama(e,w) are...