Ptychographic coherent diffractive imaging with orthogonal probe relaxation

Abstract

Ptychography is a scanning coherent diffractive imaging (CDI) technique that relies upon a high level of stability of the illumination during the course of an experiment. This is particularly an issue for coherent short wavelength sources, where the beam intensity is usually tightly focused on the sample in order to maximize the photon flux density on the illuminated region of the sample and thus a small change in the beam position results in a significant change in illumination of the sample. We present an improved ptychographic method that allows for limited stability of the illumination wavefront and thus significantly improve the reconstruction quality without additional prior knowledge. We have tested our reconstruction method in a proof of concept experiment, where the beam instability of a visible light source was emulated using a piezo driven mirror, and also in a short wavelength microscopy CDI setup using a high harmonic generation source in the extreme ultraviolet range. Our work shows a natural extension of the ptychography method that paves the way to use ptychographic imaging with any limited pointing stability coherent source such as free electron or soft X-ray lasers and improve reconstruction quality of long duration synchrotron experiments.

EUV reticle inspection using phase retrieval algorithms: a performance comparison

“…Further DM iterations could improve this reconstruction, as well as additional modifications of the algorithm to account for illumination wavefront instabilities or sample drift. [14][15][16][17] From Fig. 6B one can see that rPIE failed to reconstruct the object.…”

Beam drift and partial probe coherence effects in EUV reflective-mode coherent diffractive imaging

“…While the mentioned enhancements to ptychographic reconstruction allow superior resolution for partially coherent systems, they do not take into account the slowly varying incident illumination. Recently, an advanced reconstruction algorithm has been proposed that can reconstruct a different probe for every scan position [31]. All probes are mutually orthogonal and are linked together by a projection into a lower dimensional space using a singular value decomposition (SVD).…”

Arbitrary-path fly-scan ptychography

“…The illumination modesP r, j depend on the shift per operator S i j . Since the standard ptychographic reconstruction methods assume that the illumination modes are constant during the scan, with exception of the orthogonal probe relaxation ptychography [15], the operator S i j has to be constant for all scan positions as well.…”