IMPROVED INTERFEROMETER FOR MEASURING UNSTEADY FILM THICKNESS

An interferometer previously developed for measuring instantaneous fil m thickness of the order of 10 mu m-1 mm [T. Ohyama, K. Endoh, A. Mika mi, and Y. H. Mori, Rev. Sci. Instrum. 59, 2018 (1988)] has been impro ved with respect to both facility of handling and accuracy of thicknes s determination. The improved version of the interferometer uses an ex panded laser beam focused aslant on the subject film. The rays reflect ed from the front and rear surfaces of the film form interference frin ges on a screen, which are then recorded in the form of a single snaps hot interferogram or as a set of serial interferograms to be geometric ally analyzed. Experiments with thin glass plates as sample films veri fied the expected advantages of the new version over the original one. The improved version of the interferometer was also tested on a liqui d film asymptotically thinning as it drained down a vertical plate. Th e test indicated that the accuracy and precision of the new improved v ersion far exceed those of other transient film-thickness measuring te chniques. (C) 1996 American Institute of Physics.