Automatic correction of propagation distance in ptychographic image reconstruction.

Accurate propagation-distance determination is critical in ptychographic imaging because axial uncertainty degrades reconstruction fidelity and introduces defocus artifacts. We propose a joint auto-focusing ptychographic iterative engine (jPIE) that treats the sample-to-detector distance as an adjustable parameter and updates it jointly with the object and probe during iterative reconstruction. Using a residual-controlled adaptive strategy, jPIE performs distance correction within the reconstruction loop without slice-by-slice searches. Simulations and optical experiments show that jPIE recovers the propagation distance at the 0.01 mm level under the tested conditions, suppresses distance-induced artifacts, and reduces the computational burden compared with conventional slice-based autofocus and zPIE.