Development of an Angular Displacement Measurement by Birefringence Heterodyne Interferometry

The birefringence heterodyne interferometry for the angular measurement is presented. The advantage of the instrument is the large measurement range and high resolution. When p-and s-polarized beams pass through a birefringence crystal, the phase difference between these two polarized beams is sensitive to the incident angle. We can determine the angular variation with the heterodyne interferometer which can precisely detect the phase difference between these two polarized beams. Moreover, a new optical path is designed to enhance the sensitivity by means of a prism which combines the light to the birefringence crystal. There are two measurement modes in our system, a linear and a circular polarized mode. The experimental results show that the resolution of the linear polarized mode is 1.2°×10^-4 and the resolution of the circular polarized mode is 3°×10^-5.