High-resolution optical design of the sub-meV ARPES beamline at the Ultrafast Transient Experimental Facility

The Ultrafast Transient Experimental Facility (UTEF) at Chongqing University is constructing a next-generation angle-resolved photoemission spectroscopy (ARPES) beamline designed to simultaneously achieve sub-meV energy resolution, continuous photon energy tunability (10-40 eV), high photon flux (>10¹² photons s^-1 at the sample position), full polarization control, and ultra-low-temperature sample environments (<1.5 K). Leveraging the unique advantages of UTEF's low-energy (0.5 GeV), high-beam-current (500-1000 mA) storage ring, the beamline is capable of generating high-flux EUV radiation, enabling detailed exploration of complex quantum materials. The beamline employs two high-groove-density gratings and one low-groove-density grating to achieve, respectively, an energy resolving power exceeding 100000 and photon fluxes greater than 5×10¹³ photons s^-1. A dual-endstation layout enables flexible operation for both ultra-high-resolution measurements at ultra-low temperatures and large-angle, high-flux spin-resolved experiments. Through comprehensive optical optimization-including mirror coatings, customized grating groove profiles and precision focusing geometry-the system can deliver photon flux exceeding 10¹⁴ photons s^-1 (0.1% bandwidth)^-1 with a spatial beam spot size of approximately 30 µm, while maintaining sub-0.4 meV energy resolution. This work presents the optical design and projected performance of the UTEF ARPES beamline.