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

In 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 mu m resolution within a field having a radius about 100 mu m; 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 held (typically, the resolution can be better than in mu m 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-ray sources, either a cw one or a series of laser plasmas from the Octal-Heliotrope 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-ray diagnostics on the future powerful laser facilities. (C) 1997 American Institute of Physics.