Appearances can be deceiving, so they say. And a polished surface that appears defect-free can hide a layer of defects. This subsurface damage can be difficult to detect, but can degrade performance in optical components. That’s why finding it is important for manufacturers. Existing methods for finding subsurface damage in polished glass require extensive sample preparation or are even destructive to components. But quantum dots could change all that. A team made up of researchers from the University of North Carolina at Charlotte and Northrup Grumman Synoptics reported that fluorescent quantum dots could be used to "tag" subsurface damage as it is formed. In a talk at Optifab 2009 in Rochester, NY, Brigid A. Mullany of UNC said she and the research team added fluorescent quantum dots to the abrasive slurries used in lapping and polishing glass samples. Confocal microscope imaging revealed increased retention of quantum dots near the surface in samples lapped and polished with quantum dots, compared to samples simply exposed to quantum dots. Mullany worked with Wesley B. Williams, Patrick J. Moyer and Wesley C. Parker of UNC and Mark H. Randles of Northrop Grumman Synoptics on the project. They concluded that the presence of quantum dots after lapping/polishing with tagged slurries indicates the presence of subsurface damage and that wide-field fluorescence is a quick way to detect such damage. It does not, however, reveal the depth of the damage, Mullany said. But she added that polishing can both correct the damage and remove the remaining quantum dots. Laura S. Marshall laura.marshall@laurin.com