[en] At the CEA Laser 'Megajoule' facility, amorphous hydrogenated carbon (a-C:H or CH_x) is the nominal ablator used to achieve inertial confinement fusion experiments. These targets are filled with a fusible mixture of deuterium-tritium in order to perform ignition. Since the achievement of ignition greatly depends on the physical properties of the shell, there must be precise control of thicknesses, doping concentration, and roughness. Experimental devices associated with suitable characterizations are described in this paper. The tolerances and yields for each specification are also presented. Some specifications are largely reached; high-frequency surface roughness due to isolated surface defects appears to be the main yield-limiting factor. A microscopic approach of stress thin film measurement is described to examine oxygen uptake in CH_x film. (authors)

[en] Full text: Photoelectron imaging spectroscopy has recently emerged as a powerful tool capable of providing detailed information on the microscopic properties of matter. In a standard velocity map imaging (VMI) experiment eV kinetic energy electrons or ions are projected towards a 2D position sensitive detector. Therefore the obtained image corresponds to the classical projection of a Newton sphere that, in principle, allows a direct reconstruction of the initial 3D velocity distribution of the particles. Improvements on the standard VMI set-up, allowing the study of meV electrons, led to the recording of 2D patterns which are drastically modified with respect to those obtained with high kinetic energy electrons. The most striking effect is the observation of radial signal modulations due to quantum interferences. Moreover, ionic core gives rise to a re-scattering ionization channel. Simulations based on wavepacket propagation have been performed and we have shown that when ionization of hydrogenic atoms occurs via a Stark resonance above the saddle point energy, the measured image represents a direct projection of the bound component of the electronic wavefunction magnified to macroscopic dimensions by a factor 10⁶. Hence it is fully justified to consider the meV-VMI apparatus as a photoionization microscope, corresponding to the smallest Youngs slit experimental setup ever implemented. For a non-hydrogenic atom, on the other hand, the presence of the electronic core leads to mixing of the parabolic electronic states which modifies the wavefunction. As a consequence, a smooth evolution of the interferogram patterns with energy is expected. Experimental results on Xe and Li will be presented and discussed. (author)