Linear birefringence measurement with a differential-phase optical heterodyne polarimeter

To measure the linear birefringence of a quartz crystal, an optical heterodyne ring interferometer associated with a differential phase detection technique is proposed. The differential phase detection performs a common noise rejection similar to a balanced detector for noise reduction. The differential phase detection also plays the role of a phase modulation to amplitude modulation (AM) converter to decode the phase difference between two equal amplitude input heterodyne signals with the same carrier frequency. In this study, a quartz Babinet compensator is used as a test sample and the linear birefringence of the quartz can be measured in terms of the magnitude of an AM signal from a differential amplifier. In comparison with conventional methods, a wider dynamic range and better accuracy of the linear birefringence measurement of a crystal in Babinet compensator geometry are realized. From the experimental results, the linear birefringence of quartz with accuracy of 10^-5 order is obtained. The error analysis is also presented.