Boosting phase contrast with a grating Bonse–Hart interferometer of 200 nanometre grating period

Abstract

We report on a grating Bonse–Hart interferometer for phase-contrast imaging with hard X-rays. The method overcomes limitations in the level of sensitivity that can be achieved with the well-known Talbot grating interferometer, and without the stringent spectral filtering at any given incident angle imposed by the classic Bonse–Hart interferometer. The device operates in the far-field regime, where an incident beam is split by a diffraction grating into two widely separated beams, which are redirected by a second diffraction grating to merge at a third grating, where they coherently interfere. The wide separation of the interfering beams results in large phase contrast, and in some cases absolute phase images are obtained. Imaging experiments were performed using diffraction gratings of 200 nm period, at 22.5 keV and 1.5% spectral bandwidth on a bending-magnetic beamline. Novel design and fabrication process were used to achieve the small grating period. Using a slitted incident beam, we acquired absolute and differential phase images of lightly absorbing samples. An advantage of this method is that it uses only phase modulating gratings, which are easier to fabricate than absorption gratings of the same periods.

Dark-field tomography of an attenuating object using intrinsic x-ray speckle tracking

“…Equation (18) was used to calculate the effective DF signal, shown in Fig. 2, which was derived under the assumption that the SAXS fans emanating from the exit-surface of the sample are rotationally symmetric.…”

“…This "intrinsic noise" is closely related to the evident numerical division-by-zero instability in Eqn. (18). To deal with this instability, we propose two alternative approaches to numerically stabilise this expression.…”

“…From there, the attenuating-object approximation of the DF image was calculated using, once again, a Tikhonov-regularised weighted-determinant form of Eqn. (18). As we had SBXI data for six different well-resolved reference speckle-fields, N = 6 in Eqn.…”

“…Paganin et al 7 demonstrated a simple phase-retrieval algorithm for a single-material object using PB-PCI, which is based on the transport-of-intensity equation. 8 Some methods achieve phase-contrast by introducing additional optical elements, for example, grating interferometry, [9][10][11][12][13][14] single-grid PCI, 15 Bonse-Hart interferometry, [16][17][18] edge-illumination PCI, 19,20 and analyser-based PCI. [21][22][23][24][25] Speckle-based X-ray imaging (SBXI), first introduced in 2012 by Berujon et al 26 and Morgan et al, 27 uses a spatially random mask placed between the X-ray source and detector (see Fig.…”

‘Taking X-ray phase contrast imaging into mainstream applications’ and its satellite workshop ‘Real and reciprocal space X-ray imaging’

“…Another interesting aspect that emerged is that the field is continuing to evolve, with new examples of implementation already being presented at this same meeting (e.g. Wen et al [26] realized gratings with nanometric pitch which led to a hybrid between Talbot and Bonse-Hart interferometry), new implementation schemes (e.g. [27]), use of materials as common as paper to replace gratings or analysers [28] and much more.…”