Relaxation mechanisms affecting magneto-optical resonances in an extremely thin cell: Experiment and theory for the cesiumD1line

Abstract

We have measured magneto-optical signals obtained by exciting the D1 line of cesium atoms confined to an extremely thin cell (ETC), whose walls are separated by less than one micrometer, and developed an improved theoretical model to describe these signals with experimental precision. The theoretical model was based on the optical Bloch equations and included all neighboring hyperfine transitions, the mixing of the magnetic sublevels in an external magnetic field, and the Doppler effect, as in previous studies. However, in order to model the extreme conditions in the ETC more realistically, the model was extended to include a unified treatment of transit relaxation and wall collisions with relaxation rates that were obtained directly from the thermal velocities of the atoms and the length scales involved. Furthermore, the interaction of the atoms with different regions of the laser beam were modeled separately to account for the varying laser beam intensity over the beam profile as well as saturation effects that become important near the center of the beam at the relatively high laser intensities used during the experiments in order to obtain measurable signals. The model described the experimentally measured signals for laser intensities for magnetic fields up to 55 G and laser intensities up to 1 W/cm 2 with excellent agreement.

Angular momentum alignment-to-orientation conversion in the ground state of Rb atoms at room temperature

“…The full Hamiltonian can be written as Ĥ = Ĥ0 + ĤB + V , where Ĥ0 is unperturbed system Hamiltonian, ĤB describes the interaction with the external magnetic field, and V = − d • E(t) is the operator which describes atom -laser field interaction in the electric dipole approximation. The operator includes electric field of excitation light E(t) and an electric dipole operator d. The general OBEs (1) can be transformed into explicit rate equations for the Zeeman coherences within the ground (ρ gigj ) and excited (ρ eiej ) states by applying the rotating-wave approximation, averaging over and decorrelating from the stochastic phases of laser radiation, and adiabatically eliminating the optical coherences [27][28][29][30]:…”

“…The theoretical model uses a constant value for power density instead of actual power distribution. As the power density is increased, Ω R cannot be related to the square root of the power density I by the same constant k R as for the lower power densities [30,32], if one merely assumes that the laser power density distribution within the beam is Gaussian. This leads to the more complex relationship between I and Ω R which has a simple explanation.…”

Spatial dynamics of laser-induced fluorescence in an intense laser beam: An experimental and theoretical study with alkali-metal atoms

“…The theoretical model used here is a further development of previous efforts [22], which has been subjected to some initial testing in the specialized context of an extremely thin cell [23]. The description of coherent processes starts with the optical Bloch equation (OBE):…”

Alignment-to-orientation conversion in a magnetic field at nonlinear excitation of theD2line of rubidium: Experiment and theory

“…In practice, the estimation is not straightforward as the power density I is not constant across the laser beam, but in the theoretical model only a constant average value is used in place of the actual power distribution. Theoretical and experimental evidence suggests [26,27] that Ω R cannot be related to the square root of the laser power density I by a simple constant k R for all values of the laser power density if one merely assumes that the power density distribution within the beam is Gaussian. This fact has a simple explanation.…”