Iterative autofocusing strategy for axial distance error correction in ptychography

The axial distance error can degrade the quality and resolution of the image reconstructed by ptychography. An iterative autofocusing method is proposed to correct the axial distance error. Based on the Fresnel integral theory, an axial distance error model is established to present the effect of the axial distance error on the recovered image. The information of the retrieved image is chosen to calculate the axial distance by autofocusing algorithm. The calculated distance is used to replace the axial distance and applied for the image reconstruction. When the calculated axial distance reaches the convergence, the distance can be accurately obtained that can be used to enhance the quality and resolution of the reconstructed image. Simulations and experiments have been conducted to verify the performance of the proposed method.