PWO photo-elastic parameter calibration by laser-based polariscope

We systematically measured the photo-elastic parameter f σ of PbWO 4 (PWO) for crystals of different thicknesses. We observed a linear behaviour of f σ as a function of the thickness for low level applied stresses. This result was corroborated by numerical simulations. f σ allows the evaluation of the residual internal stress, useful for crystal quality control. In this work, we also propose a new polariscope based on laser light, which allows a fast measurement and mapping of the internal stress of crystals with high resolution owing to the reduced laser-beam dimension.