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.