Stokes-parameter photopolarimeter using an optically or mechanically rotatable two-detector assembly

A two-detector photopolarimeter for measuring the four Stokes parameters of a monochromatic or quasi-monochromatic light beam in an arbitrary state of partial elliptical polarization is described. Each detector is partially specularly reflecting at oblique incidence, and the plane of incidence is rotated (by other than 90°) between the two successive reflections. The two-detector assembly is itself rotated manually or with a stepping motor solidly as one unit around the axis of the incident beam. Mechanical rotation may be eliminated by using a Faraday rotator in front of a stationary arrangement of two detectors. Conditions under which singularities may occur (which lead to an incomplete measurement of polarization) are discussed. Optimum geometry and detector-surface characteristics are identified