An iterative approach to remove the influence of light ray bending from micron-scale scattered light tomography

We present numerical experiments to test an iterative approach which can remove refraction-induced errors form scattered light tomography. Gradient scattered light tomography is the first method capable of direct non-destructive residual stress measurement in chemically strengthened glass. The method is based on an oblique incidence scattered light photoelasticity combined with an iterative approach to remove the influence of light ray bending from the scattered light method. In this article further numerical experiments are performed which demonstrated that the iterative approach grants the removal of the influence of light ray bending from stress profiles that have complicated shapes. Two classical examples of stress profiles in chemically strengthened glass were studied: (1) unusual stress profile, where the outermost layers of the surface are in tension (tensile surface stresses being 300 MPa), rather than compression; (2) relaxed compressive stresses in the outermost surface layer with a depth of 20 µm. We found that the nature and rate of convergence of the iterative process were notably different for compressive and tensile stresses. The analyzed stress profiles were taken from literature and hence are realistic representations of the ones that researchers might come across in glass science. Refraction induced reconstruction error Δσ as a function of surface stress and incidence angle were simulated.