The polarization dependence of two-photon absorption rates for randomly oriented molecules

The method and results are presented for the analysis of the two-photon absorption experiment for randomly oriented molecules (in a single-beam regime) that can be easily extended to higher-order processes without any assumption regarding the nature of the initial state. Some known results were recovered and some new ones presented. The ratio of the averaged transition rate for circularly polarized light to the one for linearly polarized light, Ω, can be obtained from the following rules: (a) for any transition involving two states of the same symmetry (on any point group), Ω < 1: (b) exceptions to rule (a) are found in T, T_h, T_d, O and O_h groups for which A ? A transitions give Ω = 0 and E ? E gives Ω = $\text{24}\text{31}$: and (c) for any transition involving two states of different symmetry, Ω = $\text{3}\text{2}$. The results of these predictions are in excellent agreement with the available experimental data.