Development of a photoelectron spectrometer for hard x-ray photon diagnostics.

The development and characterization of an angle-resolved photoelectron spectrometer, based on the electron time-of-flight concept, for hard x-ray photon diagnostics at the European Free-Electron Laser, are described. The instrument is meant to provide users and operators with pulse-resolved, non-invasive spectral distribution diagnostics, which in the hard x-ray regime is a challenge due to the poor cross-section and high kinetic energy of photoelectrons for the available target gases. We report on the performances of this instrument as obtained using hard x-rays at the PETRA III synchrotron at DESY in multibunch mode. Results are compared with electron trajectory simulations. We demonstrate a resolving power of 10 eV at incident photon energies up to at least 20 keV.