An interferometric microimaging system for probing laser plasmas with an X-ray laser

The probing of dense (1021-1022 electrons/cm3) laser plasmas produced by high energy pulsed lasers usually makes use of X-ray emission imaging, or, more recently, of microradiography, i.e. of absorption imaging. However, it is well known that probing the index of refraction would bring much valuable informations. As far as index is concerned, interferometry is the choice method. However, the plasma context makes necessary to use for probing a very large brilliance, single pulse source, delivering energetic radiation, such as a soft X-ray laser. We report the design of a dedicated interferometric microimaging system, based on a Fresnel bimirror interferometer, associated with an off-axis spherical mirror, aspherized for diffraction limited (DL) imaging. In the first realization, the ideal mirror shape was approximated by a torus, making the system not diffraction limited. In a second step (currently in progress), a nearly perfect system will be realized, for diffraction limited resolution. The design and the realization techniques will be discussed and the first tests of the toroidal system will be presented