Two-Intensity Measurement Method for Determining the Fast Axis and Phase Retardation of a Wave Plate

A simple method for determining phase retardation and fast axis of a wave plate by using two-intensity measuring method is presented. In order to eliminate the influence of light source, double optical path method is adopted. In the first optical path, the wave plate is sandwiched between a polarizer and an analyzer, and the wave plate can be placed at any initial fast axis direction. A detector behind the analyzer is used to measure the output light intensity. In the second optical path, another detector is used to monitor the light intensity fluctuation. With rotation of the wave plate, the two-point intensity, maximum and minimum output light intensity, and the rotation angle at the first extreme point are measured in the first optical path. At the same time, in the second optical path the corresponding light intensity are detected. Base on the two-intensity and the rotation angle in the first optical path and the light intensity in the second optical path, the phase retardation and fast axis of the wave plate can be determined simultaneously. The advantage of this method is its simplicity of implementation, low cost, better accuracy and easier operation. We believe that the method reported in this paper should be a useful approach for measurement of a wave plate without the need to use complex and expensive apparatus.