“Femtosecond diffractive imaging with a free electron laser : Iterative Image Reconstruction”
Felipe MAIA - Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University, Sweden
Mercredi 08/11/2006, 11:00
NIMBE Bât 522, p 138, CEA-Saclay
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. We report the first experimental demonstration of this principle using the FLASH soft X-ray free-electron laser. An intense 25 fs, 4 × 1013 W/cm2 pulse, containing 1012 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. How to approach image reconstruction from a mathematical point of view and it's numerous problems. Practical solutions to the image reconstruction that works (most of the times). Current algorithms in use and their advantages. Common problems of image reconstruction in the real world and some possible solutions.