added to the classical attenuation contrast. A spatial redistribution of the photons occurs due to wm 
deflections (more generally due to Fresnel diffraction). This is normally considered as a nuisance in : 
attenuation imaging. However, it can also make possible a ‘phase imaging’ technique. This imaging 
mode is based on simple propagation (3). The occurrence of contrast can be understood as due to.» = 
interference between parts of the wavefront that have suffered slightly different angular deviations. mn 
The overlap between parts of the wavefront is only possible after propagation over a certain yich hä 
distance. The spatial coherence of the x-ray beams delivered at ESRF ensures good contrast in the yur 
interference patterns. (see the 3D 
Phase imaging is in general much more sensitive than absorption imaging. It is crucial when the fp «i: 
attenuation contrast is too small for instance to observe light materials such as polymers, but also to analyze 5 
distinguish absorbing constituents with similar x-ray attenuation. can give DI 
The setup is the same as for attenuation tomography. Phase sensitivity is obtained by increasing the allovs. Fig 
sample detector distance. Phase imaging can be used straightforwardly in a qualitative way mainly process (6 
useful for edge detection. It has also been shown (4) to be an excellent way of improving the one wilh 
detection of cracks even in their early development stage (i.e. when they are not widely opened). were com! 
The detection of such isolated features smaller than the spatial resolution is possible thanks to the fact that db 
interference pattern they produce. A more quantitative approach, holotomography, has been specimen 
implemented to extract the quantitative distribution of the phase in two dimensional projection solidificat 
images, then to turn it into 3D reconstructions. The phase retrieval procedure is based on a few such al) 
radiographs recorded at different distances with respect to the specimen and can be combined with in spite of 
tomography. It allows then to reconstruct in each point of the sample the decrement with respect to yey oe 
unity of the refractive index. This decrement is essentially proportional to the electron or mass fig: 
density of the material. imaging a 
this saz. 
of the sam 
. wall. The 
„Distance D___ ; ES eee vps 
A (7 Sample le pi 
Te IW $s 
TCT, Monochromatic Sou Synchrotron radiation tomobook 
2D detector 7 beam I Rd mr Slits 
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Rotation stage Wiggler ID 19 
. Double crystal 
J monochromator Microstri 
ro) 3D imag 
A common 
— the ini 
like the ı 
ming 
Figure 2 : Tomographic setup at ESRF on the ID19 beam line. Kam 
ames 
Qualitative results wa: 
mers; 
Microtomography with a medium resolution gives excellent results in the field of the analysis of the Tir 
internal structure and the deformation modes of metallic foams. Foams exhibit very low density 
(70-90 % of the material is composed of void) so the dimensions of the studied samples can be very 
large. The desired resolution is of the order of 40 um for this kind of application. What is imaged in 
that case is not the internal microstructure of the walls but the architecture and the meso 
150m 
97