Fachbereich
Physik
|
Fachbereich Physik |
|
M. Martins and W. WurthSPECTROSCOPY WITH FLASHIN THE ENERGY RANGE FROM 30 EV TO 600 EVThe 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.
|
