Mapping residual stresses in PbWO4 crystals using photo-elastic analysis

PWO photo-elastic parameter calibration by laser-based polariscope

“…In previous works [1,5] we experimentally verified in PWO samples that f s is a constant for a sample with z ¼ d, as C ell scales with s y , in the range from 0.2 to 4 MPa which falls in our field of interest. In fact, in a material with very low failure stress, the residual stress necessarily cannot reach high values, as experimentally verified.…”

“…1). The use of a laser source instead of a non-coherent diffused light source implies some changes to the image-acquisition configuration compared with classical polariscope based on a non-coherent diffuse light source [1,5,6,10]. Firstly, owing to the laser-source intrinsic polarisation, the polariser is not required.…”

“…In previous works [1,5,6] we observed interference fringe patterns and collected them directly on a CMOS camera sensor with objective lenses focused to infinite. In this case, dealing with a laser source, we cannot do this because the laser spot intensity saturates the CMOS sensor and masks the fringe pattern.…”

“…The main task in image analysis was to identify the shape of the first-order dark fringe (phase difference D ¼ pÞ [1,5,6]. Calculation of the curve that best fitted the firstorder interference fringe was based on the finding of a large number of minimum-intensity points in the region between the centre (called melatope, see Ref.…”

“…The laser beam dimension allows mapping [5,6] of the internal stress distribution with sufficient spatial resolution even in small crystals.…”