Theoretical and experimental evaluation of piezo-optic parameters and photoelastic constant in Tetragonal PWO

The tetragonal PbWO4 (PWO) is one of the most important scintillating crystals, being used both into CMS at CERN and in the PANDA project at FAIR. Light yield and other relevant scintillation properties depend, among many factors, also on the crystal mechanical quality. Accordingly, a detailed knowledge of crystal piezo-optic properties is a mandatory step towards understanding its the elasto-optic behaviour and to perform crystal quality control. In this paper we evaluatefor the first time, by means of both from photoelastic and X-ray measurements, some components of the piezo-optic tensor; moreover, when the crystal is acted upon by an uniaxial stress, we obtain an evaluation for angle of rotation angle of the optic plane under stress as well as the photoelastic constant. These parameters are necessary in order to detect the residual stresses within the crystal, if any, and to give an overall quality measure. Such a methodology is in general suitable for any tetragonal crystals.