Development of Multi-Resolution Electron Spectrometer Array at LCLS-II

A newly deployed angle resolving electron time-of-flight spectrometer array at the LCLS-II user facility has been developed to advance the capabilities of gas-phase electron spectroscopy experiments at MHz repetition rate. Multi-resolution COokiebox (MRCO) integrates 16 electron time-of-flight (TOF) spectrometers in an equiangular array at a plane perpendicular to the X-ray propagation direction, with 4 additional TOFs at 54.7 degrees relative to the X-ray polarization axis. This configuration allows for the simultaneous capture of electron spectra based on both energy and angle, with individual energy resolution control for each TOF unit. The spectrometers feature electrostatic lensing composed of 25 electrodes and retardation mechanisms optimized for high-energy resolution angle-resolved photoelectron and Auger electron spectroscopy, alongside attosecond angular streaking experiments. Engineered for an energy resolution of 0.25 eV across a 100 eV spectrum, the system's adjustable retardation facilitates the accommodation of electron kinetic energies ranging from 0 to 2 keV. The array's performance has been experimentally validated through preliminary experiments focusing on Neon, Argon, and N₂O resonant core photoexcitation. This work outlines the results from the initial commissioning phase, demonstrating the array's capabilities for Free-electron Laser X-ray photoelectron based experiments and photon diagnostics, and provides potential users with an overview of the expected performance metrics of this high data rate capable electron spectrometer array at LCLS-II.