X-ray coherent diffractive imaging is attracting interest within the x-ray community because it promises wavelength-limited
resolution for imaging nonperiodic objects. It is well known that a wave diffracted or scattered by an object can
be described simply by the Fourier transform of the object's electron density distribution. However, this result is general
only in the so-called far-field regime, where most practical work is done. In the near-field regime, evaluations of wave
field amplitudes become more complicated, and Fresnel diffraction and imaging effects have to be taken into account. In
this paper, we present an algorithm that can be used to reconstruct an object from a near-field diffraction pattern. The
algorithm uses the concept of a 'phase-chirped' distorted object, where a Fresnel-zone construction is embedded on an
original object. This algorithm can eliminate the twin image ambiguity in phase retrieval and will therefore improve the
convergence of retrieval. Our algorithm is a unified algorithm, consistent with those used in far-field experiments. Our
algorithm extends the applicability of Fourier-based iterative phasing algorithms that are already established for far-field
diffraction into the near-field holographic regime where phase retrieval has traditionally been difficult.
We apply the x-ray extended-range technique (XERT) to measure mass attenuation coefficients over one order of magnitude more accurately than previously reported in the literature. We describe the application of the XERT to the investigation of systematic effects due to harmonic energy components in the x-ray beam, scattering and fluorescence from the absorbing sample, the bandwidth of the x-ray beam, and thickness variations across the absorber. The high-accuracy measurements are used for comparison with different calculations of mass attenuation coefficients, and to identify particular regions where these calculations fail.
We have applied the x-ray extended-range technique (XERT) to measure mass attenuation coefficients over one order of magnitude more accurately than previously reported in the literature. We describe here the application of the XERT to the investigation of a number of systematic effects which has enabled us to ensure that these recent measurements are free from systematic error. In particular we describe our techniques for quantifying the effects of harmonic components in the x-ray beam, scattering and fluorescence from the absorbing sample, the bandwidth of the x-ray beam, and thickness variations across the absorber.
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