Optical design of the U7 undulator beamline at the Pohang Light Source

The first insertion-device beamline at the Pohang Light Source is designed for high-resolution spectroscopy and spectromicroscopy. The beamline will contain a variable-included-angle plane-grating monochromator (VIA-PGM) using a grating substrate which has seven different grooves with different depths. The advantages of this scheme will be the fixed exit-slit position and the mechanical stability of the grating scan mechanism while changing the photon energy range. The beamline is designed to cover the photon energy range 20-2000 eV. The estimated spectral resolution, E/Delta E, is above 8000 in the photon energy range below 500 eV, and above 4000 for the remaining photon energy range. The estimated Bur at the end-station is of the order of 10(12) photons s(-1) (0.1% bandwidth)(-1).