A description is given of an extremely simple interferometer which is easy to construct and adjust. It is admirably suited to the measurement of small displacements. It can be adjusted and used with either monochromatic or white light. Each of the small, light mirrors used needs have only one optical surface. The sensitivity can be increased by using multiple reflections without unnecessary loss of intensity, since the surfaces are all fully aluminized. Tests on the interferometer have shown that it is capable of detecting displacements of λ/2n where λ is the average wave-length of the light used and n is the number of reflections from the moving mirror (nearly normal incidence). When n=1, 2, ⋯, 7, one fringe corresponds to λ/2, λ/4, ⋯, λ/14, respectively. Under best (easily attainable) conditions 14 reflections can be obtained, whence a shift of 1 fringe would correspond to λ/28. Extreme care in the preparation of optical parts might yield 20 reflections and a displacement sensitivity of λ/40 for each fringe shift. A compound multiple reflection interferometer is also described which gives twice the sensitivity mentioned above, i.e., roughly λ/4n for each fringe shift. Selected plate glass can be used for a single reflection since only a very small mirror surface is required.
© 1936 Optical Society of AmericaFull Article | PDF Article
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