an-analog-macroscopic-technique-for-studying-molecular-hydrodynamic

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a ...

University of North Carolina at Charlotte

Grinding, lapping, and polishing are finishing processes used to achieve critical surface parameters in a variety of precision optical and electronic components. As these processes remove material from the surface through mechanical and chemical interactions, they may induce a damaged layer of cracks, voids, and stressed material below the surface. This subsurface damage (SSD) can degrade the performance of a final product by creating optical aberrations due to diffraction, premature failure in oscillating components, and a reduction in the laser induced damage threshold of high energy optics. As these defects lie beneath the surface, they are difficult to detect, and while many methods are available to detect SSD, they can have notable limitations regarding sample size and type, preparation time, or can be destructive in nature. The authors tested a nondestructive method for assessing SSD that consisted of tagging the abrasive slurries used in lapping and polishing with quantum dots (nano-sized fluorescent particles). Subsequent detection of fluorescence on the processed surface is hypothesized to indicate SSD. Quantum dots that were introduced to glass surfaces during the lapping process were retained through subsequent polishing and cleaning processes. The quantum dots were successfully imaged by both wide field and confocal fluorescence microscopy techniques. The detected fluorescence highlighted features that were not observable with optical or interferometric microscopy. Atomic force microscopy and additional confocal microscope analysis indicate that the dots are firmly embedded in the surface but do not appear to travel deep into fractures beneath the surface. Etching of the samples exhibiting fluorescence confirmed that SSD existed. SSD-free samples exposed to quantum dots did not retain the dots in their surfaces, even when polished in the presence of quantum dots.

Using quantum dots to tag subsurface damage in lapped and polished glass samples.

The short-term dynamic properties of a wide range of commercially available optical polishing pitches were determined with an impact frequency response test. A simple dynamic model is presented to evaluate the relevance of the measurement variations across the range of pitches tested. Test results show that harder pitches have higher natural frequencies and lower damping ratios. Strong correlations between pitch hardness (as measured by the indent test) and the natural frequency only existed among pitches from the same series, i.e., the Gugolz or Acculap series. This implies that pitches with similar hardness values from different manufacturers have different dynamic properties.

Article	Year
Using quantum dots to tag subsurface damage in lapped and polished glass samples. Applied optics\| PubMed ID: 19767933	2009
Optical polishing pitches: impact frequency responses and indentation depths. Applied optics\| PubMed ID: 20090809	2010

Brigid Mullany

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