Diffraction-limited superresolution ptychography in the Rayleigh-Sommerfeld regime.

Superresolution in lensless near-field ptychography is demonstrated via the application of a strongly curved illumination function. The reconstruction is performed using the Rayleigh-Sommerfeld diffraction integral, which is implemented via a pixel-size adjustable angular spectrum method. In this manner, the reconstructed object details, which are not only smaller than the pixel size of the sensor but even smaller than the smallest resolvable object detail defined by the effective NA of the 2D sensor, are enabled. The expected resolution, as predicted by the angles of scatter present in the optical configuration, is experimentally validated using a US air force resolution test target. The approach discussed here is not limited to ptychography; it can be extended to other coherent diffractive imaging modalities such as object scanning holography or optical diffraction tomography, so as to enable high-resolution near-field quantitative phase imaging.