PWO photo-elastic parameter calibration by laser-based polariscope

We systematically measured the photo-elastic parameter fσ of PbWO4 (PWO) for crystals of different thicknesses. We observed a linear behaviour of fσ as a function of the thickness for low level applied stresses. This result was corroborated by numerical simulations. fσ 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.