Carrier fringes by axial translation of the first lens in a double aperture common-path interferometer

•A method for introducing carrier fringes by axial displacement of a lens.•This lens is the first of a double-aperture common-path interferometer.•The axial displacement of the lens is within the range (0, 90) mm, and is linearly proportional to the generated carrier frequency.•The axial displacement is made manually, however the carrier frequency is obtained with good accuracy.

This paper presents a method for introducing carrier fringes in a double-aperture common-path interferometer. By using the Fresnel diffraction theory, we demonstrated that the axial displacement of the first lens of the 4f optical system involved is linearly proportional to the carrier frequency introduced in the interferogram (both for positive or negative values) in a wide range. Because this displacement is of the order of centimetres, its experimental generation is very simple, practical, and with acceptable accuracy, being carried out by means of a non-sophisticated system. A theoretical model and experimental results are shown.