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Using an Optical Flat to Determine Surface Accuracy
As a reference piece, a single-sided optical flat is placed in contact with a test surface under a monochromatic light. When this is done, an interference pattern of dark and light bands can be seen. The shape of this interference pattern provides an accurate visual representation of the flatness of the test surface. If the interference pattern is curved, the flatness of the test piece is less than that of the reference. However, if the interference bands are straight and evenly spaced, the flatness of the test piece is equal to or higher than that of the reference flat. An optical flat of greater accuracy than the test piece is required to display a change in the interference pattern. Advanced Optics offers ¼ wave, 1/10 wave and 1/20 wave optical flats to meet various application requirements.
Flatness Error of One Fringe
(1/2 wave)
(top view of optical flat) |
Test Piece
Perfectly Flat
(top view of optical flat) |
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