On Block Surface Roughness Testing Device for Transparent Substrates.
DEPARTMENT OF THE NAVY WASHINGTON DC
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Method for measuring surface roughness of optical blocks is taught even if the block is a transparent substrate. The amount of false scattering observed is minimized with the use of a detection telescope using a moveable aperture and an image plane sufficient in size to pass the image of the illuminating spot. Incident angle of light is at least 45 degrees. A viewing angle greater than 20 degrees from the specular of the illuminating light is also recommended for peak efficiency. The transparent substrate could be mounted in black pitch to reduce the amount of bottom scatter present. Author
- Optical Detection and Detectors