The rapid and precise determination of the optical thickness of thin coatings in a vacuum

The classical interference experiment with a double slit is adapted for measuring the optical thickness (n - 1)d of transparent and slightly absorbing thin films on transparent or reflecting substrates and for measuring the geometrical thickness d of metal films on reflecting substrates. Also, a method is described for measuring in vacuum the optical thickness of transparent or slightly absorbing thin films on transparent substrates. Results are given of measurements on magnesium fluoride, silicon monoxide, and zinc sulfide films. The influence of admitting air into the vacuum chamber has been investigated. With the available arrangements, a precision of lambda/1000 in the determination of the optical or geometrical thickness is easily obtainable for all film thicknesses. A thickness determination can he completed in about 1 min.