Analysis of dark-field imaging mechanism in LPDI system based on coherence length control and point spread function approximation

This paper investigates the dark-field imaging mechanism of the Line-scan Phase Differential Imaging (LPDI) system based on coherence length control and point spread function (PSF) approximation. By establishing quantitative relationships between line-source geometric parameters and coherence length, and combining them with a sinc-function discretization model of PSF, the amplification mechanism of phase gradient signals is revealed. Experiments demonstrate that the LPDI system can image and detect phase gradients at the 100 nm level in large-aperture optics (over 400mm) with a resolution of 50 μm, thereby validating the accuracy of the theoretical model and the high sensitivity of the system.