The X-ray Free Electron Lasers: a great opportunity for science,
        a challenge for detectors!

    X-ray Free Electron Lasers are in the process of revolutionizing
    photon science ; not only will they improve by several orders of
    magnitude the available peak brilliance and pulse intensities, but
    they will also provide pulses of much shorter period than existing
    light sources (shorter than 100fs), and the light produced will also
    be almost completely coherent. This opens the road to a whole range
    of new experiments, such as ultra fast coherent diffraction
    imaging, high energy density matter experiments, or femto-second
    time resolved experiments.

    These new experiments will also set the detectors requirements at an
    unprecedented level: the position sensitive detectors will have to
    register at very high speed (up to 5MHz for the European XFEL) up to
    10^4 photons per pixel (up to 12keV) while maintaining single photon
    sensitivity. In addition they may have to face integrated doses of
    the order of 1GGy, within a few years of operation. Those
    requirements have triggered the development of innovative technical
    solutions such as /dynamically gain switching/ or /non
    linear-response DEPFET/ based amplifiers,/ in-pixel digital or
    analogue storage pipelines/, and large and flexible DAQ systems.

    During this talk some examples of scientific applications of XFEL
    facilities and their attached requirements for detectors will be
    presented. Then emphasis will be put on the specific difficulties
    attached to detectors development for XFEL applications, and finally
    a presentation of the innovative technical solutions adopted for the
    three European-XFEL large pixel detectors projects, will be given.