  Diffraction of light beams from the phase steps due to the abrupt changes in
the boundary of step leads to Fresnel fringes that their 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 few nano meters precision. 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 an optical device is
manufactured to measurement of thickness of thin films.
