M. Martins and W. Wurth
SPECTROSCOPY WITH FLASH
IN THE ENERGY RANGE FROM 30 EV TO 600 EV
The SASE soft x-ray free electron laser FLASH will generate coherent radiation of several gigawatts peak power in an energy range of
about 20 eV to about 200 eV. In combination with the grating monochromator for
this energy range which has been designed by our group and was set in operation
in summer 2005 this device will provide an average photon flux at the
experiment which is about four orders of magnitude larger as compared to modern
third generation synchrotron sources and a photon flux per pulse (pulse width
150 fs) which is similar to the photon flux generated in 0.01 - 0.1 s at these
sources. In terms of flux density assuming a focus of 150 x 20 mm2 the
estimates show an average flux density of 1020 photons/cm2 and a flux density
per bunch of 1015 photons/cm2 for the monochromatized beam.
These unprecedented high values allow for a large variety of exceptional
experiments which are presently not possible at conventional third generation
synchrotron sources.
Quite generally one can distinguish two classes of experiments which can be
performed exploiting the extraordinary source parameters. Firstly, we will be
able to perform similar spectroscopic experiments (photoemission, resonant
absorption and resonant inelastic scattering, x-ray emission) as they are
performed at third generation synchrotron sources but with much higher spectral
and/or spatial and/or temporal resolution, respectively, sacrificing flux to
gain resolution. Alternatively, we can imagine to investigate samples which are
much more dilute than we are used to today also using the above mentioned
conventional spectroscopic techniques, Secondly, the source will enable us to
perform new kind of experiments in the XUV regime which so far have only been
possible with conventional lasers in the visible or the UV range of photon
energies. Among those are correlated two pulse pump-probe experiments which
will enable us to investigate ultrafast dynamical processes using
element-specific spectroscopic techniques as well as nonlinear spectroscopic
experiments like two photon absorption processes.
|
