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Applied Optics

Applied Optics


  • Vol. 36, Iss. 6 — Feb. 20, 1997
  • pp: 1223–1234

Real-time precision refractometry: new approaches

Mark L. Eickhoff and J. L. Hall  »View Author Affiliations

Applied Optics, Vol. 36, Issue 6, pp. 1223-1234 (1997)

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We introduce two new approaches for near-real-time, high-precision tracking of the refractive index of the ambient atmosphere. The methods can be realized at low cost and are expected to have important practical application in those accurate dimensional metrology applications employing interferometry in air. A valuable potential application is the control of step-and-repeat mask positioning for integrated circuit production in which temporal stability time scales over days can be crucial. Extension of the methods to absolute index measurement is discussed.

© 1997 Optical Society of America

Original Manuscript: September 11, 1995
Revised Manuscript: March 25, 1996
Published: February 20, 1997

Mark L. Eickhoff and J. L. Hall, "Real-time precision refractometry: new approaches," Appl. Opt. 36, 1223-1234 (1997)

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  1. P. Schellekens, G. Wilkening, F. Reinboth, M. J. Downs, K. P. Birch, J. Spronck, “Measurements of the refractive index of air using interference refractometers,” Metrologia 22, 279–287 (1986). Our quoted formula contains the 103 correction for the misprint of their D term, as noted by C. Rischel, P. S. Ramanujam, “Refractive index of air: errata,” Metrologia 26, 263 (1989).
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  10. Mention of specific products and manufacturers is for the purpose of technical communication only and does not constitute an endorsement nor does it imply that products from other manufacturers would be less suitable.
  11. Ruska Instrument Corp., Houston, Texas (personal communication, 13July1993).
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  17. ©Microsoft Corp.
  18. This refractometer approach is described by J. L. Hall, P. J. Martin, M. L. Eickhoff, M. P. Winters, “Highly accurate in-situ determination of the refractivity of an ambient atmosphere,” U.S. patent5,218,426 (8June1993).
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  28. However, because of the curved mirrors, there is a substantial diffractive phase shift. This can be determined to high precision by measurement of off-axis modes. However, it often turns out to be difficult to determine the diffraction correction with sufficient accuracy, so one usually uses these high-finesse interferometers to determine differences between nearby optical frequencies. Some precise measurements with ultrastable cavities with high finesse will be reported separately.
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  31. J. J. Snyder, “Algorithm for fast digital analysis of interference fringes,” Appl. Opt. 19, 1223–1225 (1980). [CrossRef] [PubMed]
  32. M. P. Winters (personal communication, 1988).

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