A system and method for measuring coating thickness upon a substrate is
disclosed. A near infrared light is directed upon the coating and
reflected near infrated light is collected to determine the coating
thickness. A diffuser is placed between the coating and the reflected
near infrared light collector to improve the accuracy of the measurement,
especially for coating thickness of less than about 2 mils and for
coatings with shiny surfaces. The diffuser is formed of a low density
polytetrafluoroethylene fluoropolymer film.