Delamination testing of polyurethane pads adhered to polishing tool using a digital holographic nondestructive testing method

Abstract

We demonstrate an application of digital holography for detection of a new type of defect, i.e., delamination of polyurethane pads on a polishing tool used on a high-speed computerized numerical control machine for production of precision optics. The method enabled us to acquire both qualitative and quantitative information about the delaminated region in the polishing pad. A delaminated region of 13.6 mm × 10.8 mm is detected and measured on the surface of the polishing pad. An increase in the delaminated region by 30% is noticed after completion of the polishing process with the delaminated polishing pad. The effect of delamination of the polishing pad on an optical surface is experimentally demonstrated using it for polishing a BK-7 glass substrate. These investigations may enable production of improved quality precision optics at the commercial level.