Signal-to-noise ratio analysis of one- and two-channel halfwave plate polarimeters

The theoretical shot-noise-limited signal-to-noise ratio (SNR) is compared for one- and two-channel halfwave plate polarimeters, where rotation of the halfwave plate within the system causes a corresponding rotation in the incident linear polarization. This analysis estimates the smallest possible waveplate rotation that may be resolved by each polarimeter. It is shown that, at least theoretically, the differentially amplified two-channel polarimeter provides a superior SNR and thus correspondingly greater angular resolution. The degradation of the SNR as a result of polarization imperfections that might be introduced by less than ideal optical components is also considered.