Dynamics of photon-photon scattering in Rb vapor

Processes such as self-focusing and four-wave mixing, which classically can be described in terms of an intensity-dependent refractive index (the optical Kerr effect), appear at the microscopic level to involve momentum exchange among photons, as if there were a photon-photon interaction potential. A simple example of this is self-focusing of a collimated beam by a medium with a positive Kerr coefficient. Outside of the medium, the photons propagate freely, without interactions. Within the medium, the photons of the beam are drawn together as if there were an attractive potential between the photons. The goal of this research is to determine the domain of validity of a description in terms of a photon-photon interaction potential