  The polarization plane rotation angle of probe signal in plasma is
calculated. The estimates of the residual gas average density and the average
magnitude of the magnetic field in a cesium plasma based on the effects of
Faraday and Cotton-Mouton in probe laser field has been found. It is shown,
that polarization plane rotation angle depends on resonance detuning of
incident laser wave and transition frequency of medium atoms, magnetic field
strength, and matrix element.
