American Journal Of Physics
The process of two‐photon excitation of atoms is explained by a simple conceptual model which takes into account virtual states of the atom as well as photon statistics. In addition to predicting the correct dependence of the two‐photon excitation probability on the intensity of incident light, the model also provides an explanation for a number of experimentally observed effects.
"A Simple Conceptual-Model For 2-Photon Absorption".
American Journal Of Physics.