Linear dichroism signals due to the alignment in the ground state of hydrogenlike atoms and their inversion in a single-beam optical pumping scheme

We present the results of theoretical and experimental investigation of optical linear dichroism signals caused by alignment, and arising under the action of pumping with linearly polarized light in a magnetic field transverse to the pumping in an ensemble of hydrogenlike (including alkali) atoms. Several simple models implying mixing of Zeeman sublevels of the excited state are considered, and common patterns among them are identified. It is shown that in the general case the properties of the medium causing dichroism can be characterized by only two parameters of the longitudinal and transverse linear polarizability, while in the case of complete mixing, by a single linear polarizability parameter. Expressions that relate these parameters to the transition probabilities are provided, as is an extension of the theory for the case of incomplete mixing of sublevels of the excited state. The single-beam scheme for recording linear dichroism signals, which is of greatest interest from a practical point of view, is investigated. It is shown that incomplete mixing can lead to inversion of dichroism signals in systems including more than one optical transition. A comparison with the results of an experimental study of dichroism in alkali-metal (cesium) vapors is made.