1 January 1988 New Correlation For On-Line Film Thickness Measurement
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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.
Roger F. Edgar, Roger F. Edgar, Peter H. Hindle, Peter H. Hindle, "New Correlation For On-Line Film Thickness Measurement," Optical Engineering 27(1), 270150 (1 January 1988). https://doi.org/10.1117/12.7976641 . Submission:

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