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Applied Optics

Applied Optics


  • Vol. 39, Iss. 25 — Sep. 1, 2000
  • pp: 4607–4615

Dispersion-insensitive measurement of thickness and group refractive index by low-coherence interferometry

Dominic F. Murphy and Dónal A. Flavin  »View Author Affiliations

Applied Optics, Vol. 39, Issue 25, pp. 4607-4615 (2000)

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We describe a low-coherence interferometric technique for simultaneous measurement of geometric thickness and group refractive index of highly dispersive samples. The technique is immune to the dispersion-induced asymmetry of the interferograms, thus overcoming limitations associated with some other low-coherence approaches to this simultaneous measurement. We use the experimental configuration of a tandem interferometer, with the samples to be characterized placed in an air gap in one arm of the measurement interferometer. Unambiguous, dispersion-insensitive measurements of critical group-delay imbalances in the measurement interferometer are determined from the optical frequency dependence of interferogram phases, by means of dispersive Fourier transform spectrometry. Sample thickness and group refractive index are calculated from these group delays. A thickness measurement precision of 0.2 µm and group index measurement accuracy of 5 parts in 105 across a wavelength range of 150 nm have been achieved for BK7 and fused-silica glass samples in the thickness range 2000 to 6000 µm.

© 2000 Optical Society of America

OCIS Codes
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(260.2030) Physical optics : Dispersion

Original Manuscript: February 4, 2000
Revised Manuscript: May 30, 2000
Published: September 1, 2000

Dominic F. Murphy and Dónal A. Flavin, "Dispersion-insensitive measurement of thickness and group refractive index by low-coherence interferometry," Appl. Opt. 39, 4607-4615 (2000)

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