Influence of the illumination coherency and illumination aperture on the ptychographic iterative microscopy

While ptychography is an algorithm based on coherent illumination, satisfactory reconstructions can still be generated in most experiments, even though the radiation sources that are used are not ideally coherent. The underlying physics of this phenomenon is that the diffraction patterns of partially coherent illumination can be treated as those of purely coherent illumination by altering the intensities of the diffracted beams relative to their real values. On the other hand, due to the inconsistency in the altering interference among all the diffraction beams, noise/distortion is always involved in the reconstructed images. Furthermore, for a weak object, the noise/distortion in the reconstruction can be mostly reduced by using a highly curved beam for illumination in the data recording and forcing the dark field diffraction to be zero in the reconstruction.