Interferometric Ronchi test by using substructured gratings

In order to increase the sharpness of the fringes in the Ronchi test we consider their interferometric interpretation. The advantage of this approach is that we can obtain the irradiance profile directly. In this work we propose to use different kinds of substructured gratings in order to obtain sharp fringes. Each grating period is divided in a number equal width strips which can be transparent or opaque; the transmission coefficients for the strips across the grating period is not periodic but is a chosen binary sequence. We develop the equations to obtain the corresponding irradiance profiles and perform an analysis of these profiles and of the sharpness of the fringes for different sequences and positions of the gratings. Numerical results for a 3000 mm radius of curvature parabolic mirror are shown. We found that the fringes are sharper at the Rayleigh distance and on other planes in and out of focus of the mirror.