Simulation of X-ray transmission and spatial imaging of polycapillary lenses with square cross-sections

Conventional polycapillary X-ray lenses are fabricated using an arrangement of hollow cylindrical tubes (i.e., capillaries) in a hexagonal structure, which necessarily includes triangular-shaped non-functional spaces between the capillaries. These non-functional spaces reduce the transmission efficiency of the lens, and can also affect the utilization of the pixels of charge-coupled devices in imaging applications. These disadvantages can be overcome by adopting a polycapillary X-ray lens structure with a square cross-section fabricated from a square matrix array of capillaries, each with equivalent square cross-sections. We develop a mathematical model of a square poly-capillary X-ray lens, and also present a simulation-driven numerical method for calculating the X-ray transmission efficiency, intensity distribution of the exit plane and the focal spot based on a ray-tracing technique.