A critical review on the thickness effect of birefringent coatings

In this paper, a reconsideration of the thickness effect of birefringent coating on the accuracy of the results obtained by this powerful experimental method was attempted. It was proved that thickness correction factorF, introduced by Duffy,1 is sensitive to higher harmonic terms of the functions in which the given displacement-distribution function is expanded. Correction of experimental results obtained with thick coatings and based on Duffy's correction method may lead to significant errors. However, this method remains very useful in predicting the proper thickness of the coating for a given strain distribution.