Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution Delta E/E = 1.1 x10(-4) and wave-number resolution of Delta k/k = 3 x 10(-3), allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to 5.2/angstrom in 100 separate bins, with only 0.34% wavenumber blurring. The dispersion of 0.418 eV/13.5 mu m agrees with predictions within 1.3%. The reflection homogeneity over the entire wavenumber range was measured and used to normalize the amplitude of scattering spectra. The proposed spectrometer is superior to a mosaic highly annealed pyrolytic graphite spectrometer when the energy resolution needs to be comparable to the LCLS seeded bandwidth of 1 eV and a significant range of wavenumbers must be covered in one exposure. (c) 2014 AIP Publishing LLC.