Patent ID: 7202950

Claim:
An apparatus for measuring retardance in a sample, comprising: a sample chamber for receiving the sample; an illuminator for providing an illumination light; optics for directing the illumination light toward the sample; a detector for measuring an intensity of light incident on the detector; optics for directing light that has interacted with the sample toward the detector; a first polarizer for selectively transmitting light that is substantially circularly polarized; a second polarizer for selectively transmitting light that has a selected elliptical polarization state; a controller for varying a selected elliptical polarization state of the second polarizer to correspond to a plural number of states χ i with a chosen Poincare latitude and longitude within a distance ε of a chosen pole of a Poincare sphere; and a processor connected to the detector for determining the sample retardance from the measured incident light intensity obtained when the second polarizer is set to each of the states χ i ; wherein none of the states χ i corresponds to circular polarization.