Measuring Ultra-Thin Air Films
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Air films in the 100 nm range are measured with an accuracy of 1 nm in a white light interferometric set-up, using sheared beams having a constant path difference of some 1000 nm. Interferometric thickness measurements in the sub-wavelength range do not yield periodic interference signals but require an absolute determination of the intensities, which is very difficult to realize in practice because of the great number of parameters involved. A periodic interference pattern can however be artificially generated by introducing a fixed path difference between the beams of a two-beam interferometric set-up. Figs. 1 and 2 are lateral elevational and top views of a shearing interferometric set-up for measuring the air film 16 between a glass disk 14 and a reflecting sample 15.