Carrier fringes interferometry by superposing the first harmonic of two rulings with different period

•A spatial carrier interferometry method using two different gratings is presented.•A diffraction order of each rulings spectrum is filtering in the Fourier plane.•A controlled period difference is created by rotating azimuthally each grating.•The slope of the generated linear phase depends directly of period difference.

This paper presents a method for introducing carrier fringes in an interferogram based on the interference of first harmonic of two rulings with different periods. The setup is built on a 4f optical system consisting of two apertures in the input plane and a Ronchi ruling in the Fourier plane; in each aperture a Ronchi ruling of a different period is placed. This proposal is based on filtering in the Fourier plane the 1st-order of diffraction of each spectrum of the rulings in the object plane; we demonstrate that the slope of the generated linear phase depends directly on period difference. In this manuscript, we develop a theoretical model and show experimental results.