Large-field high-resolution X-ray microscope for studying laser plasmas

International audienceIn 1948, P. Kirkpatrick and A. V. Baez developed an x-ray microscope (energy range about 100 eV-10 keV) composed of two concave spherical mirrors working at grazing incidence. That device, named KB microscope, presents a 3-5 μm resolution within a field having a radius about 100 μm; outside that field, its resolution lowers rapidly when the object point recedes from the center. The adjunction of two similar mirrors can notably increase the useful field (typically, the resolution can be better than 10 μm within a 2-mm-diam field of view), which is necessary for studying laser plasmas. Its main advantage with respect to more simple optics, as the pinhole, is that it can be located far enough from the plasma to avoid any destruction during the shot. We describe such a microscope that we call KBA microscope and present some images of fine metallic grids. Those grids were backlighted by x-raysources, either a cw one or a series of laser plasmas from the Octal-Héliotrope facility. Examining the films in detail shows that the experimental results are very close to the theoretical characteristics; hence the interest of this device for the x-raydiagnostics on the future powerful laser facilities

Fragile links, frozen identities: the governance of telecommunication networks and Europe (1944–53)

International audienceDuring 1944-1953 the governance of international telecommunication networks within the International Telecommunication Union framework became much more permeable to politics than before. The foundation of the United Nations system, East-West tensions, and the early dynamics of European integration were three forces that taken together questioned the traditional vision of technical cooperation among experts. The negotiations among the actors, experts, diplomats and politicians resulted in both the survival of the ITU and a freeze of European contemporary projects building a new European identity upon telecommunication networks