Summary of Part I

Often, photon scattering is considered as a particular case of the spectroscopic theory of absorption and emission of photons during the transition of an atom between its states. This theory assumes that the transitions are caused by the incident field. In the first order of the perturbation theory, according to Fermi’s golden rule, the probability of the transition between initial and final states, which is caused by the dipole interaction \( \hat{V}=-\mathbf{d}\cdot \mathbf{E} \) , is proportional to \( {\left|\left\langle i\right|\hat{V}\left|f\right\rangle \right|}^2 \) [1].