Nanostep height measurement via spatial mode projection

We demonstrate an optical scheme for measuring the thickness of thin nanolayers with the use of light beam ’ s spa- tial modes. The novelty in our scheme is the projection of the beam reflected by the sample onto a properly tailored spatial mode. In the experiment described below, we are able to measure a step height smaller than 10 nm, i.e., one- eightieth ( 1 ∕ 80 ) of the wavelength with a standard error in the picometer scale. Since our scheme enhances the signal-to-noise ratio, which effectively increases the sensitivity of detection, the extension of this technique to the detection of subnanometric layer thicknesses is feasible