Polarization time

The Poincare vector, combined with the optical intensity, provides a geometric representation of the polarization state of a beam-like electromagnetic field. For fluctuating beam fields this vector normalized by the instantaneous intensity traces, as a function of time, a path on the Poincare sphere. We introduce a measure for the average time period over which the Poincare vector in a stationary beam remains substantially unchanged. This time interval defines the 'polarization time' and from it one deduces the polarization length of the beam. Our analysis is based on an intensity-normalized correlation function associated with the Poincare vector. For fields obeying Gaussian statistics this correlation function takes on a simple form in terms of previously defined quantities that characterize the polarization and temporal coherence properties of the beam. We discuss beams of blackbody radiation as an illustrative example.