Noninvasive Inspection of Anisotropic Crystals: Innovative Photoelasticity-Based Methods

The mass production of new generations of high quality and very performant scintillating crystals requires sophisticated measurement systems and inspection tools in order to have reliable and precise data from such anisotropic materials. These measurement systems must be compatible with the industrial requirements and must be able to provide effective feedbacks aimed to the control of the crystals' production quality. In this paper, a set of photoelasticity-based methods, solving the main limits of the presently available inspection systems, is presented. The main characteristics of such methods are the noninvasiveness, precision, and speed, which are well suited for their use in the industrial environment. This paper describes a set of measurement techniques and reports on real experimental data obtained on crystals having different cutting geometries with respect to the optic axes. The use of the proposed measurement methods, from laser conoscopy to laser sphenoscopy, along the optic axis and orthogonal to it, therefore provides a portfolio of noninvasive measurement techniques, and therefore, it is opening valuable space for the quality control of crystals in a production environment, optimizing important aspects such as the time duration of the inspection and its spatial resolution.