Factors of influencing the value of w in the bi-grating diffraction imaging equation

The bi-grating diffraction imaging effect is the effect that a clear object image can be seen after the polychromatic beam coming from object is diffracted twice by two gratings. And the bi-grating diffraction imaging equation reflects the relationship between the spatial frequencies, diffraction orders, and positions of the two gratings, it plays an important role during the use of the bi-grating imaging. This paper reported on factors of influencing the value of w in the bi-grating diffraction imaging equation. The coefficient W is approximately equal to 1 when the bi-grating system under the ideal conditions, but in fact, it is not strictly equal to 1. This paper researched factors of influencing the value of W and studied the law of these values deviate from 1 for the bi-grating system when the two gratings are parallel to each other by experiments. The experiment results show that: when the center of the second one grating G2 is set in the side of wavelength shorter than centre wavelength of the diffraction beam of the first grating G1, the value of W decreases, otherwise, it increases.