J. Synchrotron Rad. (2000). 7, 196±201 Phase imaging using highly coherent X-rays: radiography, tomography, diffraction topography Jose  Baruchel, a * Peter Cloetens, a Ju È rgen Ha È rtwig, a Wolfgang Ludwig, a Lucia Mancini, a ² Petra Pernot a and Michel Schlenker b a ESRF, BP 220, 38043 Grenoble, France, and b Laboratoire Louis Ne  el, CNRS, BP 166, 38042 Grenoble, France. E-mail: baruchel@esrf.fr (Received 31 January 2000; accepted 23 February 2000 ) Several hard X-rays imaging techniques greatly bene®t from the coherence of the beams delivered by the modern synchrotron radiation sources. This is illustrated with examples recorded on the `long' (145 m) ID19 `imaging' beamline of the ESRF. Phase imaging is directly related to the small angular size of the source as seen from one point of the sample (`effective divergence' ' microradians). When using the `propagation' technique, phase radiography and tomography are instrumentally very simple. They are often used in the `edge detection' regime, where the jumps of density are clearly observed. The in situ damage assessment of micro-heterogeneous materials is one example of the many applications. Recently a more quantitative approach has been developed, which provides a three-dimensional density mapping of the sample (`holotomography'). The combination of diffraction topography and phase-contrast imaging constitutes a powerful tool. The observation of holes of discrete sizes in quasicrystals, and the investigation of poled ferroelectric materials, result from this combination Keywords: X-ray coherence; phase-sensitive imaging; tomography; holotomography; diffraction topography. 1. Introduction The advent of synchrotron radiation facilities with small `effective divergence'  (small angular size of the source as seen from one point of the sample) made it possible to observe phase images by simple `propagation' of the beam. This can be performed, for instance, at station 7.6 of the SRS, Daresbury Laboratory, where the effective divergence  is less than 3 mrad (Lang et al., 1987; Tanner et al., 1998). However, the availability of third-generation synchrotron radiation sources has turned this propagation-based form of radiography into a standard experimental technique, in which contrast arises from phase variations across the transmitted beam through Fresnel diffraction (Snigirev et al., 1995; Cloetens et al. , 1996). Two forms of this technique are now operational: either the edges of the inhomogene- ities are directly imaged, or it is possible to reconstruct quantitatively the phase shift introduced by the object, from images recorded at different distances (Cloetens, Ludwig, Baruchel, Van Dyck et al., 1999). Phase radio- graphy and its three-dimensional companion, phase tomography, are providing new information on the mechanics of composites and polymers (Cloetens, Pateyron-Salome  et al. , 1997; Buf®e Áre et al. , 1999) as well as on biological materials (Spanne et al. , 1999). Various works on coherent X-ray optics have been recently carried out. For instance, the Talbot effect which applies to periodic objects, a classical and spectacular example of Fresnel diffraction (self-imaging, periodic as a function of defo- cusing distance), was investigated in the hard X-ray range (Cloetens, Guigay et al. , 1997), and a Fresnel biprism was built up from two diamond crystals and the corresponding interference patterns were recorded and used to char- acterize the source (Lang & Makepeace, 1999). About 40 years ago, Bragg-diffraction imaging (X-ray topography) developed into practical use. It directly reveals crystal defects in the bulk of large single crystals, and helped to produce large practically perfect crystals for the microelectronics industry. An exciting recent development is the combination of phase radiography with X-ray topo- graphy. When applied to quasicrystals, information about local strain ®elds and inhomogeneities such as holes with discrete sizes, or precipitates, is simultaneously obtained (Mancini, Reinier et al., 1998). The phase effects can also be observed in the diffracted beam image itself. Faint defects can be visualized using the associated phase modulation of the diffracted beam (Baruchel, 1996; Kuznetsov et al. , 1999). Spectacular effects also result from the phase contribution to Bragg-diffraction imaging in periodically poled ferroelectric crystals (Hu et al., 1998; Rejma Ânkova  -Pernot et al., 1998). The contrast mechanism is now understood to be related to the Talbot 196 # 2000 International Union of Crystallography Journal of Synchrotron Radiation Printed in Great Britain ± all rights reserved ISSN 0909-0495 # 2000 ² Present address: Instituto LAMEL, CNR, Via Gobetti 101, 40129 Bologna, Italy.