Improved Electronic Half‐Shadow Method for the Measurement of Birefringence and Dichroism

Two methods for measuring optical anisotropy are described. The first one is based on an earlier suggestion by Kent and Lawson [J. Opt. Soc. Am. 27, 117 (1937)] and allows the simultaneous independent measurement of birefringent phase shift and dichroism. The second one, which is restricted to phase shift measurements, uses essentially a rotating birefringent plate and is capable of eliminating systematic errors due to spurious rotation in the compensator and polarization dependence of the detector. Preliminary experiments carried out with interference‐filtered visible light yielded a sensitivity of one minute of arc in the phase shift, and 2×10−3 in the ratio of transmittance for the two polarizations (in the vicinity of transmittance ratio 1) at a signal‐to‐noise ratio of the order of 10.