Method for measuring retardation of a quarter-wave plate based on normalized secondary harmonic component

A method for measuring retardation of a quarter-wave plate based on normalized secondary harmonic component is proposed, and the measuring principle is analyzed. The optical measuring system is composed of a laser, a polarizer, a phase modulator, the quarter-wave plate to be measured, an analyzer and a detector. The azimuths of the transmission axes of the polarizer and the analyzer with respect to the modulating axis of the phase modulator are +45°, 0°, respectively. The retardation of the quarter-wave plate is calculated precisely using the normalized secondary harmonic components prior to and after 22.5° rotation of the quarter-wave plate. In this method, the major axis position of the quarter-wave plate is not required to be known in advance, and the measured retardation is independent of the intensity fluctuation of the light source. The feasibility of the method is verified by the experiments.