Method and apparatus for counting or examining optical interference rings or lines

Abstract

Abstract 595,940. Interferometers utilising light sensitive cells. STULAND, T. July 10, 1945, No. 17580. [Class 40 (iii)] [Also in Group XX] Interference patterns are imaged on a mask constituted by an image (e.g. a photographic negative) of the pattern, so that any disturbance results in light passing through the mask to a photo-electric cell. In Fig. 1, the interference pattern is produced by light from a source S, reflected from fixed and movable reflectors M2, M3, and the cell PE actuates a counter C to count the production of bands as M3 is moved and thus indicating the extent of movement. To determine an unknown wavelength in terms of the light from S, a similar system is added using the other side of M3 as a reflector, so that a comparison of the two counters enables the wavelength to be compared, Fig. 3, not shown. By using equipment developing Newton rings, vibration can be detected, Fig. 3, not shown. The invention may also be applied to measure changes in refractive index.

Inventors

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