Diffraction of light beams from the phase steps due to abrupt/sharp changes in the boundary of the steps leads to Fresnel fringes whose visibility and intensity profile depend on the change of the step height or light incident angle. The visibility has been utilized in measurements of different physical quantities. In this paper, for the first time to our knowledge, by introducing the fitting method as a fast method, we show that by fitting the theoretical intensity distributions on the experimental intensity profiles of the light diffracted from a step at different incident angles, one can specify the step height with precision of a few nanometers. In addition, we show that this approach provides accurate film thickness in a broad range of thicknesses using modest instrumentation. Furthermore, based on Fresnel diffraction from the phase step, we have manufactured and trademarked an optical device for measuring the thickness of thin films.
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