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Applied Optics

Applied Optics


  • Vol. 1, Iss. 4 — Jul. 1, 1962
  • pp: 415–420

Control of a Ruling Engine by a Modulated Interferometer

Horace W. Babcock  »View Author Affiliations

Applied Optics, Vol. 1, Issue 4, pp. 415-420 (1962)

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This paper describes a system of interferometric control as applied to the smaller ruling engine of the Mount Wilson Observatory. The usual mechanism intermittently advances the grating carriage with a spacing closely approximating an integral number of fringes of green Hg198 light. A Michelson interferometer monitors this motion. The interferometer is modulated by deflecting the compensating plate electromagnetically, thus correcting for barometric pressure changes and also causing the fringe pattern to oscillate with a small amplitude at 60 cps. The oscillating fringe pattern is scanned by a phototube and is reproduced on a monitoring cathode-ray tube; any decentering of the nth fringe is detected by synchronous demodulation and is converted to a stored electrical charge. During each spacing operation, a differential correction proportional to the stored error signal is introduced into the mechanism. Corrections average about 1 centifringe (2.5 × 10−7 cm). The system is relatively simple and ensures a very high order of precision in spacing, with extremely straight grooves.

© 1962 Optical Society of America

Original Manuscript: November 7, 1961
Published: July 1, 1962

Horace W. Babcock, "Control of a Ruling Engine by a Modulated Interferometer," Appl. Opt. 1, 415-420 (1962)

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