Extremely high quality soft X-ray beam line BL25SU of SPring-8:: instrumentation and research activities

Very high resolution and bright soft X-ray light is supplied with high stability and enough photon flux by the twin-helical undulator beam line BL25SU of SPring-8. Either helicity light with very high circular polarization is emitted on the same optical axis. The fundamental radiation can cover the hν region from 0.22 to 3 keV, among which the hν region below 2 keV is covered by a constant deviation angle monochromator with varied line spacing plane gratings (VLSPGM). The content of the higher order light is less than 1%. Accurate evaluation of the energy resolution of the VLSPGM is done by photoemission of the Fermi edge of Au. By using a grating with a central groove density of 600/mm, a resolution of better than 15,000 is realized at 870 eV, whereas a resolution of better than 20,000 is realized by using a grating with 1000/mm central groove density. experimental stations for solid state spectroscopy are permanently set up in tandem on BL25SU: (1) high resolution photoemission (2) magnetic circular dichroism of core absorption (3) two dimensional photoelectron diffraction. Behind (3) can be installed another instrument such as a spin polarized photoemission or a photoelectron emission microscope. High resolution bulk sensitive photoemission has become a reality above several hundred eV. The photoemission resolution near 1 keV is better than 100 meV. The status of the beam line and typical research activities are reported.