Fringe visibility in X-ray interferometer using dual triangular phase gratings

Abstract

In recent years, the X-ray interferometer using dual phase gratings has been extensively studied. The large periodic fringes produced by the X-ray interferometer using dual phase gratings can be directly detected by ordinary detectors. At the same time, the X-ray interferometer using dual phase gratings can reduce the radiation dose of the sample without using absorption gratings. Meanwhile, a high fringe visibility is always preferred to achieve a high signal-to-noise ratio for X-ray grating interferometry. However, recent studies have reported that experimental fringe visibility in X-ray interferometer using dual rectangular phase gratings is relatively low. Therefore, it is necessary to further increase the fringe visibility in X-ray interferometry using dual phase gratings. This work focuses on the analysis of fringe visibility in X-ray interferometer using dual triangular phase gratings. Based on the fringe intensity distribution formula of X-ray dual phase grating interferometer, the fringe visibility of the dual triangular phase grating interferometer is investigated as a function of the grating spacing under monochromatic and polychromatic illumination, respectively. For comparison, the fringe visibility of the dual rectangular phase grating interferometer is also studied under the same condition. The results show that the maximum fringe visibility of the dual triangular phase grating interferometer increases with the phase shift increasing regardless of monochromatic or polychromatic illumination. Under monochromatic illumination, the maximum fringe visibility of dual 5π/2 triangular phase gratings is about 21% higher than that of dual rectangular phase gratings. Under polychromatic illumination, the fringe visibility of dual 5π/2 triangular phase gratings is at least 23% higher than that of dual rectangular phase gratings. Under polychromatic illumination, the greater the deviation of X-ray average energy from the grating design energy, the greater the decrease of maximum fringe visibility of the dual phase grating interferometer is. In addition, with the increase of the focal size of X-ray source, the maximum fringe visibility of the dual phase grating interferometer decreases, under polychromatic illumination. We hope that those results can be used as guidelines for designing and optimizing X-ray interferometer using dual triangular phase gratings.