Showing papers by "Stefano Marchesini published in 2003"

X-ray image reconstruction from a diffraction pattern alone

Abstract: A solution to the inversion problem of scattering would offer aberration-free diffraction-limited three-dimensional images without the resolution and depth-of-field limitations of lens-based tomographic systems. Powerful algorithms are increasingly being used to act as lenses to form such images. Current image reconstruction methods, however, require the knowledge of the shape of the object and the low spatial frequencies unavoidably lost in experiments. Diffractive imaging has thus previously been used to increase the resolution of images obtained by other means. Here we experimentally demonstrate an inversion method, which reconstructs the image of the object without the need for any such prior knowledge.

Coherent X-ray diffractive imaging: applications and limitations.

Abstract: The inversion of a diffraction pattern offers aberration-free diffraction-limited 3D images without the resolution and depth-of-field limitations of lens-based tomographic systems, the only limitation being radiation damage. We review our recent experimental results, in which X-ray images were reconstructed from the diffraction pattern alone. A preliminary analysis of the radiation dose needed for CXDI imaging and the dose tolerance of frozen-hydrated life-science samples suggests that 3D tomography at a resolution of about 10 nm may be possible. In material science, where samples are less sensitive to radiation damage, we expect CXDI to be able to achieve 1 to 2 nm resolution using modern x-ray synchrotron sources. For higher resolution imaging of biological material, strategies based on fast-pulse illumination from proposed x-ray free-electron laser sources, can be considered as described in Neutze et al. Nature 406, 752–757 (2000).

Experimental lensless soft-X-ray imaging using iterative algorithms: phasing diffuse scattering.

Abstract: Images of randomly placed two-dimensional arrays of gold balls have been reconstructed from their soft-X-ray transmission diffraction patterns. An iterative hybrid input-output (HiO) algorithm was used to solve the phase problem for the continuous distribution of diffuse X-ray scattering. Knowledge of the approximate size of the clusters was required. The images compare well with scanning electron microscope (SEM) images of the same sample. The use of micrometre-sized silicon nitride window supports is suggested, and absorption filters have been used to allow collection of low spatial frequencies often obscured by a beam stop. This method of phasing diffuse scattering may have application to scattering from individual inorganic nanostructures or single macromolecules.

Inversion of x-ray diffuse scattering to images using prepared objects

Abstract: The inversion of far-field scattered intensity to a near-field wave field (image) is demonstrated using soft-x-ray scattering from a random cluster of gold balls. The only a priori information assumed about the scatterer is compact support (an isolated object), a condition enforced by using an atomic force microscope to assist in the preparation of the object. The object support function is obtained from the autocorrelation function of the object. X-ray images of 50-nm-diam gold balls are obtained by this method with 10-nm resolution. The method may be applied to other radiations and to nanostructures and macromolecules which cannot be crystallized. Other favorable types of prepared objects are considered.

X-ray fluorescence holography: going beyond the diffraction limit

Abstract: X-ray fluorescence holography (XFH) is a method for obtaining diffraction-limited images of the local atomic structure around a given type of emitter. The reconstructed wave field represents a distorted image of the scatterer electron-density distribution, i.e., it is a convolution of the charge-density distribution with a point spread function characteristic of the measurement. We here consider several methods for the iterative deconvolution of such XFH holograms, and via theoretical simulations evaluate them from the point of view of going beyond the diffraction limit so as to image the electron charge density. Promising results for future applications are found for certain methods, and other possible image-enhancement techniques are also discussed.

X-ray microscopy by phase-retrieval methods at the advanced light source

Abstract: We report our experiments in soft x-ray coherent diffraction leading to reconstructed images via phase retrieval methods. We describe the history and principles of the method and the technical systems we have used to implement it. The main requirement is to have a sufficiently isolated sample.

X-ray holography

Abstract: In the last decade holographic methods using hard X-rays were developed. They are able to resolve atomic distances, and can give the 3D arrangement of atoms around a selected element. Therefore, hard X-ray holography has potential applications in chemistry, biology and physics. In this article we give a general description of these methods and discuss the developments in the experimental technique. The capabilities of hard X-ray holography are demonstrated by examples.