Confocal Detection Of Rayleigh Scattering For Residual Stress Measurement In Chemically Tempered Glass

A new optical method is presented for evaluation of the stress profile in chemically tempered (chemically strengthened) glass based on confocal detection of scattered laser beam. Theoretically, a lateral resolution of 0.2 mu m and a depth resolution of 0.6 mu m could be achieved by using a confocal microscope with high-NA immersion objective. The stress profile in the 250 mu m thick surface layer of chemically tempered lithium aluminosilicate glass was measured with a high spatial resolution to illustrate the capability of the method. The confocal method is validated using transmission photoelastic and Na+ ion concentration profile measurement. Compositional influence on the stress-optic coefficient is calculated and discussed. Our method opens up new possibilities for three-dimensional scattered light tomography of mechanical imaging in birefringent materials. (C) 2015 AIP Publishing LLC.