Flatness Measurements with Optical Flats

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An optical flat is a glass, fused silica, Zerodur or sapphire disk polished to a high degree of flatness, typically within a few millionths of an inch, and is used as a reference to evaluate the accuracy of flat surfaces.

Measuring flatness using an optical flat entails direct contact between the specimen to be measured and the optical flat itself. Holding the surface of a high precision optical flat against the test specimen under monochromatic light creates visible light bands, which are formed by the air gaps where the two surfaces are not in perfect contact. These interference fringes show the contour of the surface under test. The light and dark patterns visually represent the flatness of the surface being tested, and it is the curve and spacing between these fringes which indicate the surface accuracy.

Disadvantages of Surface Flatness Measurements with Optical Flats:

Introducing a New Flatness Measuring Instrument from Valley Design

Patent pending, our new non-contact interferometer, the Indars Interferometer, is designed to alleviate the problems inherent with using optical flats or Fizeau interferometers as discussed above. The Indars Interferometer has been specifically optimized for the flatness characterization of thin, transparent wafers, substrates and windows. Its unique design allows wafers to be positioned vertically, eliminating most bending forces applied by gravity and without necessitating the application of flatness distorting films.

For additional information on Optical flat interferometer see:

Optical Flat Interferometer

Indars Interferometer

Please call or e-mail for further details.

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Updated: 23 August 2010

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