Step height measurement using lateral shearing cyclic path optical configuration setup and polarization phase-shifting interferometry

Abstract

We present a step height measurement technique using a lateral shearing cyclic path optical configuration (CPOC) setup and polarization phase shifting interferometry (PPSI). In the technique, the CPOC setup generates two orthogonally polarized, laterally sheared, converging beams that get focused at the back focal plane of a positive lens placed at the input beam of the CPOC setup. These focusing beams are reflected back into the CPOC setup by the step optics, positioned in such a way that one of the surfaces of the step optics coincides exactly with the focus point of one of the laterally sheared focusing beams. The CPOC recombines the beams reflected from the step surfaces and the beams re-pass through the lens, which produces collimated and spherical interfering wave fronts for the respective beams. Using PPSI, the radius of the spherical wavefront emerging from the lens, which is related to the focal shift introduced between the reflected beams due to the step height, is determined. The novelty of the technique is the introduction of the CPOC setup and the use of a single wavelength light source to determine the large step height. Results obtained for a step height of 1.340 mm are presented.