arXiv subjects

Stefano Marchesini

Publications and source records attributed to Stefano Marchesini.

23 records · Page 2Linked to original sources

arXiv2016

Rank-1 accelerated illumination recovery in scanning diffractive imaging by transparency estimation

We consider the problem of blind ptychography, that is the joint estimation of an unknown object and an illumination function from diffraction intensity measurements. In ptychography, diffraction measurements from neighboring regions of the same object are related to each other by a pairwise relationship between overlapping frames. When the illumination is well known, the relationship among frames is given by a linear projection operator. We propose a power iteration-projection algorithm that minimizes the global pairwise discrepancy among frames. We accelerate the convergence of power method by subtracting the estimated localized average transparency of the unknown object. The method is effective for weakly scattering and low contrast objects or piecewise smooth specimens.

math.OC↗

arXiv2015

Alternating Projection, Ptychographic Imaging and Phase Synchronization

We demonstrate necessary and sufficient conditions of the local convergence of the alternating projection algorithm to a unique solution up to a global phase factor. Additionally, for the ptychography imaging problem, we discuss phase synchronization and graph connection Laplacian, and show how to construct an accurate initial guess to accelerate convergence speed to handle the big imaging data in the coming new light source era.

math.OC↗

arXiv2013

Augmented projections for ptychographic imaging

Ptychography is a popular technique to achieve diffraction limited resolution images of a two or three dimensional sample using high frame rate detectors. We introduce a relaxation of common projection algorithms to account for instabilities given by intensity and background fluctuations, position errors, or poor calibration using multiplexing illumination. This relaxation introduces an additional phasing optimization at every step that enhances the convergence rate of common projection algorithms. Numerical tests exhibit the exact recovery of the object and the noise when there is high redundancy in the data.

physics.optics↗

arXiv2012

Phase retrieval by power iterations

I show that the power iteration method applied to the phase retrieval problem converges under special conditions. One is given the relative phases between small non-overlapping groups of pixels of a recorded intensity pattern, but no information on the phase between the groups of pixels. Numerical tests show that the inverse block iteration recovers the solution in 1 iteration.

physics.optics↗

arXiv2006

Femtosecond Diffractive Imaging with a Soft-X-ray Free-Electron Laser

Theory predicts that with an ultrashort and extremely bright coherent X-ray pulse, a single diffraction pattern may be recorded from a large macromolecule, a virus, or a cell before the sample explodes and turns into a plasma. Here we report the first experimental demonstration of this principle using the FLASH soft X-ray free-electron laser. An intense 25 fs, 4 10^13 W/cm^2 pulse, containing 10^12 photons at 32 nm wavelength, produced a coherent diffraction pattern from a nano-structured non-periodic object, before destroying it at 60,000 K. A novel X-ray camera assured single photon detection sensitivity by filtering out parasitic scattering and plasma radiation. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling, shows no measurable damage, and extends to diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one.

physics.optics↗