Decomposition of a magneto-optical signal into a superposition of signals from different velocity groups and at different magnetic fields
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Figure 6. Decomposition of a magneto-optical signal into a superposition of signals from different velocity groups and at different magnetic fields. Left panel: the solid black line shows the magneto-optical signal as it would be observed in a vapour cell at room temperature. The dashed and dotted lines show the signals for the different velocity groups that make up the room temperature velocity distribution. Right panel: distribution of the atomic angular momentum at different values of the magnetic field B for the velocity groups in resonance at a (Doppler) detuning of 0, 5 and −5 MHz.
We present the results of an investigation of the different physical processes that influence the shape of nonlinear magneto-optical signals both at small magnetic field values (~100 mG) and at large magnetic field values (several tens of Gauss). We used a theoretical model that provided an accurate description of experimental signals for a wide range of experimental parameters. By turning various effects 'on' or 'off' inside this model, we investigated the origin of different features of the measured signals. We confirmed that the narrowest structures, with widths of the order of 100 mG, are related mostly to coherences among ground-state magnetic sublevels. The shape of the curves at other scales could be explained by taking into account the different velocity groups of atoms that come into and out of resonance with the exciting laser field. Coherent effects in the excited state can also play a role, although they mostly affect the polarization components of the fluorescence. The results of theoretical calculations are compared with experimental measurements of laser-induced fluorescence from the D2 line of atomic rubidium as a function of the magnetic field.