Moiré methods in interferometry

Diffraction grating three-beam interferometry without self-imaging regime contrast modulations

“…When the illuminating beam wave front is deformed by an optical system or phase object, the self-image lines depart from straightness proportionally to the first-order derivative (gradient) of the phase distribution [3,4,8]. In the case of more significant wave front changes and/or larger lateral shear values, the phase second-order derivative of tested phase distribution degrades the contrast in the self-image planes [3,8,10,11].…”

“…(2), i.e., when the second-order derivative of the lens aberration has influence on the fringe pattern. Figure 2(a) shows one of the three-beam Ronchigrams with characteristic elliptical form bands of the zero contrast value modulating the gradient fringes [3,8,10,11]. They are characteristic to considerable spherical aberration present in the system under test and exemplify the grating three or more diffraction order interference (selfimaging) limitations of Ronchi/Talbot interferometry.…”