Measurement System for Very Small Photoelastic Constant of Polymer Films

We produced a new system for measuring the small photoelastic constant of a polymer thin film with a small birefringence. Using our mesurement system, we evaluated the photoelastic constant of a polymer film in real time by quantitative analysis. Photoelastic constants of 11.30 × 10 −12 Pa −1 for a cellulose triacetate film and 78.38 × 10 −12 Pa −1 for a polycarbonate film were obtained. Furthermore, we obtained a small photoelastic constant of 0.12 × 10 −12 Pa −1 for a cycloolefin film for liquid crystal displays, using our new measurement system. This value is very small. We emphasize that, if a small change in retardation and stress cannot be detected simultaneously using our system, then we cannot obtain such a small photoelastic constant.