Imaging polarimetry for the determination of stress constraint in transparent solids

¹ ONERA, the Theoretical and Applied Optics Department (DOTA), 31055 Toulouse Cedex 4, France
² LPICM, UMR 7647, Ecole polytechnique, 91128 Palaiseau

Abstract

Using a Mueller matrix polarimeter based on liquid crystal cells [1] and the forward polar decomposition [2], we study the evolution of the birefringence property induced by an increasing compression of a Plexiglas sample. We measure the 2D distribution of the relative retardation δ, the azimuth angle α and the ellipticity angle ε of the sample. A noticeable advantage of such method is the possibility to map the stressinduced birefringence even if the material used for the reflexion implies partial depolarization of the scattered field. More generally, this method will be particularly useful in experimental situations where the light beam undergoes depolarization and/or dichroïsm in addition to birefringence effects because classical birefringence measurement methods are not able to perform an efficient discrimination between these 3 effects. Our experiment shows that the Plexiglas sample under investigation exhibits some weak stress-induced elliptic birefringence. According to simple numerical simulations, this observation is explained by the use of a bi-static illumination/detection configuration.