Brewster Angle Apparatus for Thin Film Index Measurements

For refractive index measurements of solid thin films when film absorption is negligible, the Brewster angle method described by Abeles [ Compt. rend.228, 553 ( 1949)] is extremely convenient. An apparatus is described which facilitates routine index measurements using this method. A corner mirror system elimates the need for manually tracking the reflected beam as the angle of incidence is varied. Settings are reproducible to within about 0.1% of the index value under optimun conditions, the results agreeing with those of other observers.A method is described whereby the apparatus may be used for the routine measurement of the indexes of nonabsorbing liquid films.