  Results of a fairly straightforward experiment on resonant magneto-optical
rotation by rubidium-87 atoms revealed strong time-dependence of the
polarization plane of light emerging from atomic vapors following a sudden
irradiation with a laser beam. The rotation of the plane appears as a not
direct consequence of the influence of the magnetic field on atoms. Reported
measurements conducted using a vapor cell without any buffer gas or an
anti-relaxation wall coating show that transmitted light has initially the same
(linear) polarization as the incident one. Rotation of the polarization plane
caused by an axial magnetic field develops in time scales similar to the pace
of establishing the optical pumping/relaxation equilibrium in the atomic
ensemble. The traditional passive Faraday rotation picture providing working
description for the resonant magneto-optical effects in steady-state conditions
does not explain the observed sequence of evolution of the polarization. The
picture has to be augmented with analysis of time dependence in the spatial
distribution of relevant quantum states within the atomic ensemble as well as
longitudinal and transversal intensity profiles of the light beam. Isolation of
external effects caused by the optical pumping and relaxation processes from
consequences of internal atomic coherences should uncover more details of
mechanisms of the latter in the presence of magnetic field. Plentitude of data
available from time-dependent polarization measurements provides strong
incentives for further development and tests of comprehensive models of
coherent interactions of atomic ensembles with radiation and possibly a base
for additional advance in understanding and applications of these phenomena.
