A method for measuring optical thickness changes in a thin film using a single laser beam is proposed and demonstrated. Theory suggests that when a half plane phase shift is applied to a Gaussian laser beam, interference fringes appear in the far field which position varies with the amount of phase shift. By measuring fringe pattern displacements, we demonstrate detection of optical changes in microns-thick chitosan films induced by temperature rises of a few degrees centigrade. Potential use for surface temperature measurements and other applications are discussed.

© 2013 Optical Society of America

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