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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 51, Iss. 12 — Dec. 1, 1961
  • pp: 1340–1341

An Alignment Interferometer for Precision Straightness-Measurements and Control Even of Rapidly Moving Carriages

GEORGE W. STROKE  »View Author Affiliations

JOSA, Vol. 51, Issue 12, pp. 1340-1341 (1961)

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A new, easily adjusted and very stable interferometer, defining a semistatic fringe field by reflection on two mirrors, has permitted a simple solution to the problem of rapid and accurate alignment of moving carriages, of fixed reference beams, and of carriage-ways in the interferometric domain. Precisions in the 0.1-sec-of-arc range are easily obtained in visual work in rotations up to minutes of arc, without the usual limitations of slow fringe counting and of loss of fringe-contrast at large path differences in particular. In fact, the fringe-contrast is independent of the distance from the reference-support to the moving mirrors in this interferometer, and permits measurements and alignments over traverses and distances of many feet if required. Precisions in the 0.01-sec-of-arc range and better can be obtained with the help of electronic location of interference fringes. Experiments with carriages moving at rates up to 1-foot/sec and over distances of the order of 1½ ft have demonstrated the versatility of the alignment interferometer in various applications, in particular in the alignment of ways on a velocity-of-light apparatus and on ruling engines.

GEORGE W. STROKE, "An Alignment Interferometer for Precision Straightness-Measurements and Control Even of Rapidly Moving Carriages," J. Opt. Soc. Am. 51, 1340-1341 (1961)

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  1. G. W. Stroke, J. Opt. Soc. Am. 47, 1097 (1957); 48, 276 (1958).
  2. One inch equals approximately 100 000 fringes at 5461 A (green mercury line) and 1 sec of arc equals approximately 5/106 radians. Thus 0.1 fringe in a 10-in. lever arm corresponds to about 1/107 radians (or 1/50 sec of arc).
  3. J. Peters and G. W. Stroke, J. Opt. Soc. Am. 43, 668 (1953); 43, 1231 (1953).
  4. It is clear that very large rotations up to minutes of arc can be measured with this interferometer by using somewhat shorter lever arms (with a 4-in. lever arm, a passage of 120 fringes through the field can be easily read and gives a total angle of about 1 min of arc): for this purpose, it may also sometimes be of advantage to restrict the aperture-widths of the mirrors (5) and (6) in the x direction and use apertures in the form of "slits" with their length parallel to the z axis.1
  5. P. Jacquinot, Repts. on Progr. in Phys. 23, 267 (1960).
  6. The "equal-inclination" ring fringe system formed by this interferometer, as a result of the path-difference deliberately introduced between the two beams, gives it an essential advantage in fringe-position reading accuracy over a "zero-path" difference interferometer using a wedge between the beams and producing an "equal-thickness" line-fringe system, such as the alignment interferometer described in U. S. Patent No. 2,880,644 (April 7, 1959) by E. M. Brockway and D. R. Herriott: that interferometer applies a Kösters double image prism assembly for both beam splitting and the attainment of the necessary "lever arm" and angular rotation sensitivity, and is thus generally also further limited by the available prism dimensions to only much smaller sensitivity values than the ones considered in the alignment interferometers using mirrors and an equal-inclination ring system discussed in the present work.
  7. G. R. Harrison and G. W. Stroke, J. Opt. Soc. Am. 45, 112 (1955); 50, 1153 (1960).
  8. G. R. Harrison, N. Sturgis, S. C. Baker, and G. W. Stroke, J. Opt. Soc. Am. 47, 15 (1957).
  9. A straightness of better than 0.02 fringes across the interferometer arm is obtained in this engine with the help of the "two-interferometer" servocontrol system which operates from the difference between the two fringe signals produced by the motion of two portions of a long mirror, moving at the rate of about 2.5 fringes/sec. A fringe rate of about 40 fringes/sec, usable for measuring purposes, would require about 23 hr for a single straightness reading over a 10-in. traverse with the "two-interferometer" system, while this reading can now be obtained in only a few minutes with the new alignment interferometer described here.
  10. J. R. Zacharias, G. R. Harrison, G. W. Stroke, S. J. Mason, and C. L. Searle, Mass. Inst. Technol., Research Lab. Electronics, Quart. Progr. Rept., (January 15, 1956), p. 68.
  11. G. W. Stroke and J. R. Zacharias, Mass. Inst. Technol. Research Lab. Electronics, Quart. Progr. Rept. (October 15, 1958), p. 69.

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