  We report on investigations of nonlinear magneto-optical rotation (NMOR) in
rubidium vapor subjected to a modulated magnetic field and continuous-wave (CW)
laser-light illumination. By superimposing modulation and a static (DC)
magnetic field, we demonstrate the appearance of resonances at both small and
large (compared to the ground-state relaxation rate) values of the static
field. Since in conventional NMOR, there is no rotation at high fields, this
suggests an existence of a novel mechanism generating anisotropy in the
considered case, which we identify as parametric resonance. The experiments are
performed using light of small ellipticity and rotation signals are
significantly enhanced by combining atom-induced polarization rotation with a
passive rotation induced with a wave plate. All the observations are supported
with theoretical simulations. The density-matrix formalism and angular-momentum
probability surfaces are used to provide intuitive explanation of the observed
signals.
