The optical linear birefringence measurement using a Zeeman laser

In the paper we present a new optical system that uses a transverse Zeeman dual-frequency laser in conjunction with plane polariscope for simultaneously measuring both the principal axis angle and the retardance of the optical linearly birefringent materials. The Zeeman laser produces a standard heterodyne signal as a polarizer is set in front of a photodetector. Owing to the use of a Zeeman laser and design of optical configuration, the measurement system has the advantages of compact structure, low non-linearity, high stability, and good portability. By using the amplitudes of a reference signal and of two measuring signals, a simply derived algorithm can obtain the principal axis angle and the retardance directly and easily. The dynamic range of the principal axis angle measurement is limited in the range from 0° to 90° and that of the retardance measurement is extended to be 180° successfully. According to the measurement results, the average absolute errors of the principal axis angle and the retardance measurements for a quarter-wave plate with its principal axis angle set at 90° are determined to be 1.47° and 2.85%, respectively. The absolute error of the retardance measurement is within the uncertainty range of 5% or more for commercial quarter-wave plates.