Stress measurement of transparent elements based on polarized camera

The stress measurement is of great significance for the manufacture and use of optical elements. Based on the principle of stress birefringence, a method to measure the stress distribution by polarized camera was proposed. The stress value and calculation formulas of stress direction were derived from Stokes matrix and Mueller matrix, and the main errors affecting the measurement accuracy of the system were analyzed theoretically. In order to verify the feasibility of the method, a device for measuring the stress distribution was constructed. A quarter wave plate of 633 nm was measured by this device, and the error was 0.86 nm. The full-field stress phase retardation and stress direction diagrams of headlight lens were obtained by further measurement. The measured phase retardation was used to calculate the stress birefringence value of central region of the lens of 9.21 nm/mm and the principal stress difference of 2.45 MPa. The symbolic rules were used to adjust the stress direction of the lens, and the results accorded with the principle of stress continuity. This method measures the stress distribution without rotating the optical elements, which can realize the real-time measurement of stress retardation and stress direction.