Development of a facility for probing the structural dynamics of materials with femtosecond X-ray pulses

We propose to use Thomson backscattering of far-infrared (FIR) pulses (100-300 mum wavelength range) by a 500 MeV electron beam to generate femtosecond X-rays at the TESLA Test Facility (TTF) at DESY. Using the parameters of the photocathode rf gun and the magnetic bunch compressors of the TESLA Test Facility (TTF), it is shown that electron pulses of 100-fs (FWHM) duration can be generated. Passing the short electron bunches through an undulator (after the conversion point) can provide a FIR high-power source with laser-like characteristics. On the basis of the TTF parameters we expect to produce X-ray pulses with 100-fs duration, an average brilliance of nearly 10(13) photons s(-1) mrad(-2) mm(-2) per 0.1% BW at a photon energy 50 keV. The total number of Thomson backscattered photons, produced by a single passage of the electron bunch through the mirror focus, can exceed 10(7) photons/pulse. We also describe the basic ideas for an upgrade to shorter X-ray pulse duration. It is demonstrated that the TTF has the capability of reaching the 10(12) photons s(-1) mrad(-2) mm(-2) per 0.1% BW brilliance at a ten femtosecond scale pulse duration.