Improving the accuracy of visual interferometric angular measurements.
Uniform tint in multiple beam interferometry is a most sensitive method for detecting angular displacement between two flat surfaces. But as the sample size decreases, results become less accurate. To achieve a uniform dark tint, which is more sensitive than is a light tint, one must align the mirror axially. The accuracy of the instrument is increased by incorporating a stepped mirror. The steps are approximately lambda/20 high and preferably of concentric geometry. The stepped surface provides at least one part of the total surface having the uniform dark tint condition. Setting accuracy of 0.01 see of arc is easily achieved.
Langenbeck
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