Conversion of bright magneto-optical resonances into dark resonances at fixed laser frequency forD2excitation of atomic rubidium

Abstract

Nonlinear magneto-optical resonances on the hyperfine transitions belonging to the D2 line of rubidium were changed from bright to dark resonances by changing the laser power density of the single exciting laser field or by changing the vapor temperature in the cell. In one set of experiments atoms were excited by linearly polarized light from an extended cavity diode laser with polarization vector perpendicular to the light's propagation direction and magnetic field, and laser induced fluorescence (LIF) was observed along the direction of the magnetic field, which was scanned. A low-contrast bright resonance was observed at low laser power densities when the laser was tuned to the Fg = 2 −→ Fe = 3 transition of 87 Rb and near to the Fg = 3 −→ Fe = 4 transition of 85 Rb. The bright resonance became dark as the laser power density was increased above 0.6mW/cm 2 or 0.8 mW/cm 2 , respectively. When the Fg = 2 −→ Fe = 3 transition of 87 Rb was excited with circularly polarized light in a second set of experiments, a bright resonance was observed, which became dark when the temperature was increased to around 50 o C. The experimental observations at room temperature could be reproduced with good agreement by calculations based on a theoretical model, although the theoretical model was not able to describe measurements at elevated temperatures, where reabsorption was thought to play a decisive role. The model was derived from the optical Bloch equations and included all nearby hyperfine components, averaging over the Doppler profile, mixing of magnetic sublevels in the external magnetic field, and a treatment of the coherence properties of the exciting radiation field.

Dependence of the shapes of nonzero-field level-crossing signals in rubidium atoms on the laser frequency and power density

“…However, in order to describe accurately real systems, it is necessary to take into account all neighboring hyperfine transitions, the magnetic-field-induced mixing of magnetic sublevels of identical m that belong to different hyperfine levels, the Doppler profile, and the coherence properties of the radiation. Models with these characteristics have been developed over the years to describe zero-field resonances in the ground and excited states with great precision [5]. In this work, we show that nonzero level-crossing signals in magnetic fields can be described by a theoretical model over a wide range of magnetic fields to nearly experimental accuracy.…”

“…Our model takes into account possible contributions to the transition probabilities from all neighboring hyperfine transitions, the effects of Doppler broadening, the splitting of the hyperfine levels in the magnetic field, and the coherence properties of the exciting laser radiation [15]. This model had been widely applied to zero-field resonances in the ground state [5] and achieved good agreement between experimentally measured and calculated curves. The experimental parameters, in particular the laser frequency, were carefully controlled during the measurements in order to allow precise comparison with theory.…”

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

“…By comparing the results of the theoretical models, one can see that the theoretical curve of the single region model agrees well with experimental measurements for cases were the laser power is low, but starts to deviate significantly in cases where the laser power is higher. This behavior has already been observed experimentally numerous times in ordinary cells ( [13,14,26,28]) where theoretical calculations start to deviate from experimental data at laser powers where absorption at the center of the laser beam has reached saturation. In the case of the ETC even the lowest laser power used is noticeably higher than laser powers used in ordinary cell experiments, but, because of the strong relaxation by collisions with cell walls, noticeable deviations from experimental results start at only very high laser power densities.…”

“…Indeed, using the resonant cross-section of the D 1 line for π-polarized radiation and the density of cesium at 165 • C [25] one obtains an optical pathlength of 1.5 µm, which becomes comparable to the cell thickness and corresponds to an optical depth (OD) of 0.6. At similar optical depths (OD ∼ 0.66), reabsorption effects have been observed to start to play a role in an ordinary cell [26,27]. To study ETC effects without the added complication of reabsorption, we chose to conduct experiments at a temperature in the cesium reservoir of 90 • C, at which the optical absorption length is greater than 80 µm.…”

Magnetic Field Gradiometer with Sub-Micron Spatial Resolution Based on Caesium Vapour in an Extremely Thin Cell

“…For instance, nonlinear MORs have been studied experimentally and theoretically for D 1 excitation of atomic caesium, and the theoretical model [9] is successful for describing the resonances in detail [10]. Moreover, the theoretical model has proved itself by describing more complex systems with partially resolved hyperfine levels, such as the Rb D 1 and D 2 lines [11], [12], and it was in good agreement with experiments carried out in the ETC as well [13].…”