Optical Film Thickness Monitor.
DEPARTMENT OF THE NAVY WASHINGTON D C
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The patent describes an apparatus for measuring the optical thickness of a thin film on a substrate by using two light beams of different wavelengths. The beams are chopped into a series of time-alternating pulses, passed through the film and substrate and detected to provide an electrical pulse output. Alternate pulses are then subtracted from each other and the differences are averaged. A null occurs whenever the optical film thickness is at integral quarter-wavelengths of the average wavelength of the two light beams.
- Test Facilities, Equipment and Methods