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

摘要: 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 energy range of 20–2000 eV. The beam spot size at the ARPES endstation is H:60μm×V:30μm, while the vertical size is a crucial factor in determining the energy resolution of the beam, which is influenced by the exit slit. Notably, the energy resolution at the ARPES sample positions has been measured to be an 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.