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X-ray imaging of biological materials has, in the past, relied on the difference in absorption between the two of the main constituents of living matter (water and carbon) at certain energies. In recent years, phase techniques relying on the X-ray refractive index difference of materials have been developed that have allowed biological and other low-contrast materials to be imaged. In this primer, we aim to cover some of the terminology and methods involved in X-ray phase imaging and provide a framework for understanding phase-imaging and phase-retrieval methods. We conclude with a discussion on some of the most recent advances in this field where far-field diffraction patterns of samples can be inverted to provide very high-resolution structure leading, possibly, to the prospect of single-molecule imaging. [ABSTRACT FROM AUTHOR]

We develop an analytical model for three dimensional phase contrast tomography for a pure phase object. The model incorporates an extended source, which is suitable for a laboratory based microfocus x-ray source. From the modeled intensities for the tomographic data set we obtain a model reconstruction and define a reconstruction quality factor that allows us to optimize the tomographic reconstruction for given feature sizes in an object. [ABSTRACT FROM AUTHOR]

The rapid development of new sources of coherent X-rays, such as third-generation synchrotrons, high-harmonic-generation lasers and X-ray free-electron lasers, has led to the emergence of the new field of X-ray coherent science. The extension of coherent methods to the X-ray regime makes possible methods such as coherent diffraction, X-ray photon-correlation spectroscopy, speckle interferometry and ultrafast probing at atomic resolution and femtosecond timescales. Despite rapid improvements in the resolution that conventional X-ray optics can achieve, new methods for manipulating X-rays are required to push this to the atomic scale. Here we demonstrate a coherent imaging technique that enables us to image the complex field at the focus of an X-ray zone plate without the need for conventional X-ray lenses. There are no fundamental limits on the resolution of this lensless imaging technique other than the wavelength of the X-rays themselves. The ability to characterize the beam with one measurement makes the method ideally suited to characterizing the fields generated by pulsed coherent X-ray sources. [ABSTRACT FROM AUTHOR]

X-ray radiography and x-ray tomography are important tools for noninvasive characterization of materials. Historically, the contrast mechanism used with these techniques has been absorption. However, for any given sample there are x-ray energies for which absorption contrast is poor. Alternatively, when good contrast can be obtained, radiation damage from an excessive dose may become an issue. Consequently, phase-contrast methods have in recent years been implemented at both synchrotron and laboratory facilities. A range of radiographic and tomographic demonstrations have now been made, typically utilizing the coherent flux from an insertion device at a synchrotron or a microfocus laboratory source. In this paper we demonstrate that useful results may be obtained using a bending magnet source at a synchrotron. In particular we show that the same beamline can be used to make and characterize a sample made by x-ray lithographic methods. [ABSTRACT FROM AUTHOR]

This article reviews the developing field of x-ray phase contrast radiography. The underlying principles are outlined and some experimental results are reviewed. The paper then uses simulations to explore the potential application of this method to the imaging of very low Z elements within a very high Z envelope. We predict that it should be possible to image very light elements such as hydrogen within a gold envelope using small laboratory-based sources. [ABSTRACT FROM AUTHOR]

A class of imaging, condensing, and collimating devices for x rays is investigated which is based on the use of an array of small channels of square cross section. The focusing and collimating effect arises from external reflection of near-grazing-incidence rays at the interior channel surfaces. Rays are redirected by being singly reflected from two orthogonal channel surfaces and are imaged from a source point to a square region with a side length M[sub T] + 1 times that of the channel side length, where M[sub T] is the transverse magnification. The image and source locations are related by a thin-lens formula. The point spread function and the efficiency of these focusing devices are calculated. Two energy regimes with different channel reflectivity characteristics are examined in detail: the hard x-ray regime (E > 8 keV) and the soft x-ray regime (E < 200 eV). For these cases the efficiency of focusing x rays depends only on the channel aspect ratio and reflectivity parameters. A discussion is made of channel plates of other configurations, such as arrays of rectangular channels. The results are supported by Monte Carlo simulations. [ABSTRACT FROM AUTHOR]