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Quantum Dots Detect Surface Damage

Photonics.com
May 2009
ROCHESTER, NY, May 13, 2009 -- 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



GLOSSARY
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.  
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