A new four-step phase-shifting method for birefringence measurement based on the plane polariscope is proposed. The plane polariscope to carry this phase-shifting method is characterized by triple polarizers. One fixed polarizer is used as a linearly polarized state generator; the other two rotatable linear polarizers act as phase shifters. The measurement ranges are (0, π ) for phase retardation and (−π/4 , +π/4 ) for azimuth angle. Numerical simulation is carried out, and two mica wave plates are tested and evaluated. Compared with other commonly used methods on Senarmont or circular polariscopes, this method has the simplest optical setup and also is free from the errors of quarter wave plates. It has less wavelength dependence and temperature dependence and is expected to be more cost-effective and environmentally robust.
The theoretical and experimental analysis on the effects of extinction ratios of linear polarizer and analyzer in the measurement of birefringent retardance by a five-step phase-shifting method based on the plane polariscope is presented. Stokes vector and Mueller matrix are the tools used to perform this theoretical analysis. The theoretical analysis show that the coefficients of extinction ratios of linear polarizer and analyzer in plane polariscopic configuration can be eliminated by phase shifting and will not introduce errors with our proposed five-step method. A mica quarter waveplate with previously given phase retardation is tested and evaluated. The experimental comparison has been made between the calcite Glan-Thompson based system with extremely high extinction ratios and plastic Polaroid film based system with relatively lower extinction ratios. The experimental results show that there is no significant difference between the measured values from these two systems, which agrees well with the conclusion of theoretical analysis. Also, good experimental accuracy and repeatability are achieved as well by the proposed five-step phase-shifting method.
In this paper, one approach of angle measurement of optical wedge used dual-frequency laser interferometer
is referred. The asymmetry of the optical corner cubes in reflector housing is analyzed which has a notable effect on the
uncertainty of the measurement result. The asymmetry is constituted by two components: ▵h, the height difference
between optical corner cubes, and ▵α, the non-parallelism between two front surfaces of optical corner cubes. At last the
influence of this error is obtained, and a precision compensation model for angle measurement is established.
Keywords: dual-frequency laser interference, sinusoidal measurement angle, optical corner cube, asymmetry