Spectrometer for hard X-ray free-electron laser based on diffraction focusing

X-ray free-electron lasers (XFELs) generate sequences of ultra-short spatiallycoherent pulses of X-ray radiation. A diffraction focusing spectrometer (DFS),which is able to measure the whole energy spectrum of the radiation of a singleXFEL pulse with an energy resolution of E/E ’ 2 106, is proposed. This ismuch better than for most modern X-ray spectrometers. Such resolution allowsone to resolve the fine spectral structure of the XFEL pulse. The effect ofdiffraction focusing occurs in a single-crystal plate due to dynamical scattering,and is similar to focusing in a Pendry lens made from a metamaterial with anegative refraction index. Such a spectrometer is easier to operate than thosebased on bent crystals. It is shown that the DFS can be used in a wide energyrange from 5 keV to 20 keV