Method and apparatus for measuring the absolute thickness of dust defocus layers
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United States of America Patent
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Mar 28, 1989
Grant Date -
N/A
app pub date -
Jun 5, 1986
filing date -
Jun 5, 1986
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A method and apparatus for measuring the absolute thickness of dust defocus layers upon spinning optical disks utilizes a collimated, expanded beam of light from a helium-neon laser which is focused into a converging beam and directed towards the layer at a predetermined angle of incidence defined by an angular spread centered about the angle of incidence. A pair of divergent beams reflecting from the upper and lower surfaces of the layer are received by a collecting mirror and are recollimated by a collimating lens to be incident upon a self-scanning photodiode array. The divergent beams form a monotonic interference pattern having a fringe density which is proportional to the distance between the upper and lower surfaces, and which is determined by the photodiode array.
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