We discuss the formation of self-images of a 2-D grating composed by two rulings of equal period, but in-plane rotated. We describe the in-register condition for setting the lensless Lau effect, with this type of gratings; and we propose to use the above configuration for interferometrically visualizing, in noncoherent light, phase structures, in two nonorthogonal directions.
J. C. Barreiro,
"Bidirectional Nonorthogonal Schardin-Lau Interferometer", Proc. SPIE 1121, Interferometry '89, (3 April 1989); doi: 10.1117/12.961330; https://doi.org/10.1117/12.961330