The orientation-dependence of the diffraction patterns of the 1D-grating experiments have been systematically studied by utilizing the 3-axis-rotation apparatus. It is shown that the spacings between adjacent diffraction orders are non-uniform. Namely, from “one end” of the pattern to “other end”, the spacings between adjacent diffraction orders gradually increase. In this article, we systematically study the orientation-dependence of the diffraction patterns of the 2D-cross-grating. The experiments show that the diffraction patterns are non-uniform as that of the 1D-grating experiments.

This extraordinary phenomenon challenges the existing theoretical description of the grating experiments. The above observed phenomena provide the comprehensive phenomena to theoretical study of the grating experiments. We suggest that the complete mathematical model should contain three rotation angles as parameters and should be able to describe the phenomena of the non-uniform-spacing, curved, expanded, inclined and mirror-symmetric diffraction patterns consistently.