Abstract
For the European x-ray free electron laser (XFEL) a split-and-delay unit based on geometrical wavefront beam splitting and multilayer mirrors is built which covers the range of photon energies from 5 keV up to 20 keV. Maximum delays between $\mathrm{\ensuremath{\Delta}}\ensuremath{\tau}=\ifmmode\pm\else\textpm\fi{}2.5\text{ }\text{ }\mathrm{ps}$ at $h\ensuremath{\nu}=20\text{ }\mathrm{keV}$ and up to $\mathrm{\ensuremath{\Delta}}\ensuremath{\tau}=\ifmmode\pm\else\textpm\fi{}23\text{ }\text{ }\mathrm{ps}$ at $h\ensuremath{\nu}=5\text{ }\text{ }\mathrm{keV}$ will be possible. Time-dependent wave-optics simulations have been performed by means of Synchrotron Radiation Workshop software for XFEL pulses at $h\ensuremath{\nu}=5\text{ }\text{ }\mathrm{keV}$. The XFEL radiation was simulated using results of time-dependent simulations applying the self-amplified spontaneous emission code FAST. Main features of the optical layout, including diffraction on the beam splitter edge and optics imperfections measured with a nanometer optic component measuring machine slope measuring profiler, were taken into account. The impact of these effects on the characterization of the temporal properties of XFEL pulses is analyzed. An approach based on fast Fourier transformation allows for the evaluation of the temporal coherence despite large wavefront distortions caused by the optics imperfections. In this way, the fringes resulting from time-dependent two-beam interference can be filtered and evaluated yielding a coherence time of ${\ensuremath{\tau}}_{c}=0.187\text{ }\text{ }\mathrm{fs}$ (HWHM) for real, nonperfect mirrors, while for ideal mirrors a coherence time of ${\ensuremath{\tau}}_{c}=0.191\text{ }\text{ }\mathrm{fs}$ (HWHM) is expected.
Highlights
Among the light sources available in the hard x-ray regime free-electron laser (FEL) radiation generated by self-amplified spontaneous emission (SASE) provides widely tunable ultrashort light pulses with unprecedented pulse energies, coherence properties and a well-defined wavefront
Data acquired with the nanometer optic component measuring machine (NOM) provides an essential input for subsequent optimization technologies such as ion beam figuring and for the simulations presented in this paper
In this paper a detailed simulation of the influence of nonperfect mirrors on a measurement of the temporal coherence properties of hard x-ray pulses at hν 1⁄4 5 keV generated by the European x-ray free electron laser (XFEL) is presented
Summary
Among the light sources available in the hard x-ray regime free-electron laser (FEL) radiation generated by self-amplified spontaneous emission (SASE) provides widely tunable ultrashort light pulses with unprecedented pulse energies, coherence properties and a well-defined wavefront. SLAC National Accelerator Laboratory (USA) [1] and SACLA in Japan [2] the European x-ray free electron laser (XFEL) is under construction in Hamburg (Germany). With electron bunches accelerated to energies of up to 17.5 GeV the machine will provide photon energies between hν 1⁄4 3 keV and hν 1⁄4 24 keV at the undulator sources SASE1 and SASE2. In the burst mode very high repetition rates of 2700 pulses at 4.5 MHz per burst at a repetition rate of 10 Hz will be possible, due to superconducting accelerators
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have