Development and Performance of Ultra-High Energy Resolution Dreamline Beamline at SSRF

Abstract: The ultrahigh-energy-resolution soft X-ray beamline, "Dreamline," at the Shanghai Synchrotron Radiation Facility (SSRF), has been successfully constructed and is now fully operational for conducting angle-resolved photoemission spectroscopy (ARPES) and photoelectron emission microscopy (PEEM) experiments. Both branches of the beamline utilize a sophisticated plane-grating monochromator equipped with four variable-line-spacing gratings, enabling it to span an impressive energy range of 20–2000 eV. To achieve optimal performance in photon flux, energy-resolving power, and focus spot size, extensive optical optimization has been carried out. Notably, the energy resolution at the ARPES sample positions has been measured to be an impressive 17.2 meV at 867.1 eV, setting a new benchmark for the highest resolution capability within this energy range among similar international facilities. Furthermore, under the 4σ opening of the white light slit, the full energy range flux of double undulator exceeds 10¹² photons per second per 0.01% bandwidth (phs/s/0.01%BW) below 800 eV when selecting the appropriate grating, while the flux across the full energy range remains above 10¹¹ phs/s/0.01%BW. The "Dreamline" beamline boasts a wide energy range support coupled with ultra-high energy resolution, making it an invaluable tool for advancing research in quantum materials.