  We present the results of an investigation of the different physical
processes that influence the shape of the 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 on 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 magnetic field.
