Method for acquiring the characteristic parameter of the dual-spiral moiré fringes.

Based on moiré phenomena and the Talbot self-imaging effect, dual-spiral moiré fringes could be acquired with two spiral gratings. This kind of special moiré fringes could be used to test the collimation of the light beam, which was significant in many correlative applications. The characteristic parameter of the dual-spiral moiré fringes reflected the collimation condition directly. A method with two algorithms, which were respectively based on Fourier transform and the phase-shifting algorithm, was proposed and simulated to extract the characteristic parameter. The influence of the random noise on the extraction was also analyzed and discussed.