Principles of an intracavity polarimeter for measuring small optical anisotropies with an application to diffractive dichroism

An intracavity polarimeter is described that is capable of measuring both weak birefringence and dichroism simultaneously. It uses, for the first time to our knowledge, polarization flips in a quasi-isotropic He-Ne laser. The laser operates at 3.39 micrometers. Calibration of the polarimeter is carried out by using the anisotropic properties of a tilted plate. As an illustration of the sensitivity, the diffractive anisotropy of an intracavity slit is measured.