Interaction of Rydberg atoms with two contrapropagating ultrashort laser pulses

Abstract

In this paper we investigate how Rydberg atoms respond to perturbation by two contrapropagating ultrashort laser pulses. We consider the case where the durations of both pulses ${\ensuremath{\tau}}_{1}$ and ${\ensuremath{\tau}}_{2}$ are shorter than the inverse of the initial-state energy ${\ensuremath{\epsilon}}_{i}^{\ensuremath{-}1}$. When acting alone such a pulse passes through the atom without noticeable alteration in the atomic state. The situation is different if two such pulses interfere in the region of atom localization. In this case the atomic response is significantly enhanced. This is due to the nonzero momentum transferred to the electron by the interplay of the electric field of one pulse and the magnetic field of the other. The sudden perturbation approximation is used to evaluate the transition probabilities. They are shown to depend on the atom position with respect to the pulse interference region. This dependence is determined by the relationship between the atomic diameter ${d}_{i}$ and the interference-region size $l=c({\ensuremath{\tau}}_{1}+{\ensuremath{\tau}}_{2})$ ($c$ is the speed of light). If ${d}_{i}\ensuremath{\ll}l$ this dependence is sensitive to the function form of the pulses. For sufficiently strong fields the atoms can be ionized completely. In the opposite case of ${d}_{i}\ensuremath{\gg}l$ the transition probabilities are sensitive to the electron density distribution along the propagation direction. The probabilities of the initial-state destruction and atom ionization drop as $l∕{d}_{i}$ irrespective of the characteristics of the pulses.