We study the time structure, the frequency composition, and the shot to shot fluctuations of the radiation emitted by a free-electron laser starting from shot noise in the electron beam longitudinal distribution, taking into account slippage and finite bunch length effects. We find a very difkrent behavior when the bunch length, Eg, is much longer than the cooperation length, E"or of the order of a few 8,. The field evolution is dominated by slippage eÃects in both cases, and shows the presence of superradiant spikes.

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The principle of the tomography technique and the different possible set‐ups, which can be used to obtain medium‐(10 μm) and high‐(1 μm) resolution, three‐dimensional, non‐destructive images, are shown in this paper. Illustrations are made of the applications of the technique in the field of materials science. Examples are given for medium‐resolution images of metallic foams and model metal matrix composites that are reinforced with spherical particles. High‐resolution examples are shown for aluminium alloys. For low‐absorbent materials we show that the phase contrast obtained using synchrotron radiation can provide a valuable solution. The quantitative use of these images, coupled with in‐situ tensile tests or used for the simple analysis of the initial microstructure of several structural materials, is also described.

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The aim of this paper is to report the very first in situ observations of the deformation behaviour of an Al-Cu alloy in the semisolid state by using ultrafast, high-resolution X-ray microtomography. It is shown that this deformation is non-homogeneous and involves an accumulation of liquid at an intergranular surface nearly perpendicular to the strain axis. Once the liquid is no longer able to feed such a region, micropores form and grow at this surface, finally leading to a crack.