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Optical Engineering

New Correlation For On-Line Film Thickness Measurement
Author(s): Roger F. Edgar; Peter H. Hindle
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Paper Abstract

A new optical method for determining film thickness is described in which a set of measured transmittance values for a sample of unknown thickness is correlated with sets of transmittance values predicted for different known thicknesses. A reiterative calculation is used to determine the thickness for which the predicted and measured values yield an optimum correlation. The method is particularly suited to on-line use in a film production process, where the sample is moving and cannot be contacted. The predicted transmittance values may be based on a model involving either absorption or interference. A simple, robust optical system can be used, even when using an interference-based model capable of X/100 accuracy. Criteria for selection of measurement wavelengths and bandwidths are outlined, and strategies for the reiterative calculation sequence are explained.

Paper Details

Date Published: 1 January 1988
PDF: 5 pages
Opt. Eng. 27(1) 270150 doi: 10.1117/12.7976641
Published in: Optical Engineering Volume 27, Issue 1
Show Author Affiliations
Roger F. Edgar, Infrared Engineering Limited (England)
Peter H. Hindle, Infrared Engineering Limited (England)

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