X-ray phase-contrast imaging (XPCI) provides superior sensitivity for the diagnosis of low-Z materials compared to absorption-based techniques. Betatron radiation generated by laser-wakefield accelerators, which offers high photon flux, ultra-short duration and relatively high spatial coherence, is a promising compact source for XPCI. So far, knowledge about how to control wakefield accelerator and realize high quality XPCI is still lacking. This study investigated the influence of gas pressure (plasma density) on betatron source characteristics and on the performance of propagation-based XPCI. Through particle-in-cell (PIC) and wave-optics simulations, we explore the relationship between gas pressure and imaging characteristics such as spatial resolution and brightness and find an optimal operation window. Experimental results confirm this optimal operation window at 40~45  psi (plasma density ~ 3-4×1018 cm^-3 ), with which a peak photon flux of  8 ×10^12   phs/sr  and a contrast of 20.32%  at the spatial resolution of 5 μm  are realized. This study demonstrates a pathway for the optimization of betatron-based XPCI, enabling synchrotron-comparable spatial resolution in a laboratory-scale setup and shows the potential of XPCI in ultrafast microscopic imaging applications.
 

Phase-Contrast Imaging,Betatron radiation source,Spatial Resolution,Wave-optic Simulation