Varied line spacing plane gratings have the features of self-focusing , aberration-reduced and easy manufacturing ,which are widely applied in synchrotron radiation, plasma physics and space astronomy, and other fields. In the study of diffracting imaging , the optical path function is expanded into maclaurin series, aberrations are expressed by the coefficient of series, most of the aberration coefficients are similar and the category is more, can't directly reflects image quality in whole. The paper will study on diffraction imaging of the varied line spacing plane gratings by using computer simulation technology, for a method judging the image quality visibly. In this paper, light beam from some object points on the same object plane are analyzed and simulated by ray trace method , the evaluation function is set up, which can fully scale the image quality. In addition, based on the evaluation function, the best image plane is found by search algorithm .
Recently, ZWP grating diffraction imaging instrument has been applied in the research and teaching of bi-grating imaging effects by some universities. However, there are problems exposed in the use. The main problem is position location of bi-grating operation which hardly achieves the “Z” shape that is fit for imaging path, especially the diagonal direction deviation of the second grating when it is moving in the platform, which leads to measurement errors for the bi-grating diffraction imaging, and the experiment results are inaccurate. To the grating imaging instrument, the electronic control method has been studied, which is to control moving and rotation of gratings more easily and with high measurement accuracy. The new reform plan of the grating imaging instrument is done and tested, and the experiment results are compared with before reform undone.