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Self Levelling Reference Plane for Interferometric Flatness Testing

IP.com Disclosure Number: IPCOM000089274D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Jaerisch, W: AUTHOR [+3]

Abstract

The flatness of optical surfaces is generally determined by interferometrically comparing the surface with an optical flat. For this purpose the optical flat is placed on or, without contact, above the test surface, and is illuminated by means of monochromatic light.

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Self Levelling Reference Plane for Interferometric Flatness Testing

The flatness of optical surfaces is generally determined by interferometrically comparing the surface with an optical flat. For this purpose the optical flat is placed on or, without contact, above the test surface, and is illuminated by means of monochromatic light.

To obtain a minimum number of fringes in reflected light, the contactless test plate is manually levelled by a set of screws. Deformations of the test surface are determined by counting the number of fringes and by evaluating their shape. The reproducibility of the measurement depends, to a considerable degree, on how the optical flat is levelled. As this operation is operator dependent, it is time consuming and scarcely reproducible.

The levelling procedure of the reference plate can be made operator independent by implementing the optical flat in an air gauge which is placed above the test surface.

Circular optical flat 1 in the figure is rigidly mounted in a frame 2 which may be provided, for example, at the top and bottom, with an air bearing segment 3a and 3b consisting of several circularly arranged jet bores 4.

When the number of jets in bearing 3a and 3b is identical and supply pressure P is constant, an air gap 1(a) = 1(b) = 1 is obtained.

1(a) = 1(b) is dependent on the number and the shape of bores 4, and can be varied via supply pressure P. If optical flat 1 is inserted in frame 2 in such a manner that its bottom side coi...