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Applied Optics

Applied Optics


  • Vol. 41, Iss. 22 — Aug. 1, 2002
  • pp: 4497–4502

Digital Hilbert transformation for separation measurement of thicknesses and refractive indices of layered objects by use of a wavelength-scanning heterodyne interference confocal microscope

Yuuki Watanabe and Ichirou Yamaguchi  »View Author Affiliations

Applied Optics, Vol. 41, Issue 22, pp. 4497-4502 (2002)

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A wavelength-scanning heterodyne interference confocal microscope quickly accomplishes the simultaneous measurement of the thickness and the refractive index of a sample by detection of the amplitude and the phase of the interference signal during a sample scan. However, the measurement range of the optical path difference (OPD) that is obtained from the phase changes is limited by the time response of the phase-locked loop circuit in the FM demodulator. To overcome this limitation and to improve the accuracy of the separation measurement, we propose an OPD detection using digital signal processing with a Hilbert transform. The measurement range is extended approximately five times, and the resolution of the OPD is improved to 5.5 from 9 µm without the electrical noise of the FM demodulator circuit. By applying this method for simultaneous measurement of thickness and the refractive index, we can measure samples 20–30-µm thick with refractive indices between 1 and 1.5.

© 2002 Optical Society of America

OCIS Codes
(040.2840) Detectors : Heterodyne
(110.6960) Imaging systems : Tomography
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(120.5050) Instrumentation, measurement, and metrology : Phase measurement
(180.1790) Microscopy : Confocal microscopy

Original Manuscript: December 27, 2001
Revised Manuscript: April 15, 2002
Published: August 1, 2002

Yuuki Watanabe and Ichirou Yamaguchi, "Digital Hilbert transformation for separation measurement of thicknesses and refractive indices of layered objects by use of a wavelength-scanning heterodyne interference confocal microscope," Appl. Opt. 41, 4497-4502 (2002)

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