I have just begun setting up an interferometer to take some measurements. I am trying to reproduce one paper I found in literature for 3 DoF homodyne interferometry. The detector is merly a CMOS sensor. Here is a picture of the paper I am trying to reproduce: from the spatial interference pattern, these guys managed to extract information about relative tilts and displacements between the mirrors applying FFT algorithms to each pixel line.
Applying FFT to their picture, I got something similar like that (for only one [pixel line), and it seems to agree fairly well apart from the scale. However, when I try to do the same to a fringe pattern I got from my setup I obtain this:
The intensity is not sinusoidal adn there are plateaus where the maximum intensity is detected: is there a way to get more spacing, or smoother fringes?