Photopolarimeter using two modulated optical rotators

The basic compensator-analyzer-polarimeter is automated by inserting two modulated optical rotators, one in front of the compensator and the other between the compensator and the analyzer. The modulated optical rotators (e.g., two series-connected Faraday cells) are excited by the same ac source to produce sinusoidal optical rotations of the same frequency, generally of different amplitudes, that are mutally in or 180 degrees out of phase. We show that, when the radiation leaving this generalized polarimeter (which is of constant polarization) is linearly detected, limited Fourier analysis of the resulting signal yields the four Stokes parameters of the incident radiation.