Optical method for measuring uniform thickness of the order of 10 μm–1 mm of transparent solid and liquid films

An optical-interference method is proposed for measuring the thickness of ‘‘fairly thick’’ films of transparent (or weakly absorbing) solid materials or liquids. It uses a laser beam with an incident angle, on the subject film, changing with time, causing an alternation of constructive and destructive interferences of beams reflected, respectively, at upper and lower surfaces of the film. The total irradiance of the beams interfering with each other is continuously detected and recorded. From the number of periodical changes of the irradiance during the change of the incident angle over a specified range we can readily calculate the thickness of the film. A simple apparatus has been designed and constructed to realize this method. It has been shown that the method is applicable to measurements of thicknesses of both solid and liquid films, provided the films are kept stationary enough.