We report our study of the magneto-optical effect in a strictly linear regime on spin-polarized cold cesium atoms. Due to the low intensity and the short illumination period of the probe beam, less than 7.5% of the sample atoms change their states by absorbing probe photons. We produce a medium of atoms at rest in either the
6S1∕2,F=3,mF=0 or
6S1∕2,F=3,mF=3 state by optically pumping atoms trapped in a magneto-optical trap. We use the
D1 resonance with large lower and upper state hyperfine splittings as a probe transition to avoid hyperfine mixing from the Zeeman interaction. Under this idealized situation we measure the Stokes parameters in order to find the polarization rotation and circular dichroism experienced by the probe light. We find that there are qualitative differences between the results for the
mF=0 and
mF=3 cases. While dispersion and consequent Faraday rotation play a dominant role when the atoms are in the
mF=0 state, it is dissipation and circular dichroism that are important when they are in the
mF=3 state. Similarly, while the size of the Faraday rotation and the circular dichroism for the
mF=0 case scales linearly with the applied magnetic field, for the
mF=3 case it is the shift of the probe polarization change versus frequency that is linearly proportional to the magnetic field strength.
We report on the observation of nonlinear Faraday rotation with cold atoms at a temperature of
100 $\ensuremath{\mu}$K. The observed nonlinear rotation of the light polarization plane is up to
0.1 rad over the
1-mm-size atomic cloud in approximately
10-mG magnetic field. The nonlinearity of rotation results from long-lived coherence of ground-state Zeeman sublevels created by a near-resonant light. The method allows for creation, detection, and control of atomic superposition states. It also allows applications for precision magnetometry with high spatial and temporal resolution.
We present a modified scheme for detection of the magneto-optical rotation (MOR) effect, where a linearly polarized laser field is interacting with cold
87Rb atoms in an integrating sphere. The rotation angle of the probe beam's polarization plane is detected in the experiment. The results indicate that the biased magnetic field, the probe light intensity and detuning, and the cold atoms' temperature are key parameters for the MOR effect. This scheme may improve the contrast of the rotation signal and provide an useful approach for high contrast cold atom clocks and magnetometers.