N.-I. Toto-Arellano, G. Rodríguez-Zurita, A. Martínez García, J. Vázquez-Castillo, J. Ra, and as Álvarez., Analysis of the $\pi$ phase-shifts obtained in the Fourier spectra of phase gratings and grids by using two-window grating interferometry, Rev. Mex. Fís. 56, (2010).