Two-Dimensional X-Ray Beam Phase Sensing

We present a new method to analyze quantitatively the wave front of a partially coherent x-ray beam. The technique is based on the use of two-dimensional speckle patterns combined with digital image correlation algorithms and offers a pixel size resolution, a high accuracy, and a reduced sensitivity to mechanical vibrations thanks to a very simple setup. The requirements on transverse and longitudinal coherence are also low. Finally, we show how the method can be used for phase contrast imaging applications by a single sample exposure process.

Figure 1

DIC principle. The position of a speckle subset of few pixels is tracked from one image to the next using a cross-correlation criterion.

Figure 2

Two possible configurations. In configuration (a), the sample is removed to obtain a reference beam and work differentially, while in configuration (b) two shots are taken at different distances from the membrane to act as a Hartmann sensor, the sample remaining in the beam.

Figure 3

(a) Reconstruction of the ESRF BM05 wave front after double reflection on Si(111) monochromator. (b) Wave front departure from a perfect spherical wave front.

Figure 4

Displacement vector field at center (a) and phase-map reconstruction of the cone sample (b). The blurs in the phase map correspond to phase accidents that are due to the presence of micro air bubbles in the glue of the sample holder.