A fourth-generation light source (Korea-4GLS) with 4-GeV electron energy, 58-pm-rad electron emittance, and 400-mA electron current is under construction at Ochang, Korea. Here, we describe the advantages of the Korea-4GLS compared with the light source at Pohang (Pohang Light Source: PLS-II) in terms of the geometry of its probing techniques and application materials. In the case of probing laterally homogeneous specimens where an X-ray size from 10 µm to 1 mm is permissible and the sample is generally larger, then techniques such as X-ray scattering, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy benefit from flux increase. In this case, the Korea-4GLS is better than the PLS-II in the energy range of approximately 1–2.5 keV (higher energy spectrum for soft X-ray-based techniques), 2–4 keV (medium energy-based techniques), and 10–100 keV (higher energy spectrum for hard X-ray-based techniques). When probing laterally inhomogeneous specimens, the X-ray size must be below 1 µm. Here, nano-probe and spectro-nanoscopy techniques, such as coherent diffraction imaging, ptychography, scanning type transmission X-ray microscopy, or photoelectron microscopy leverage the increase in brilliance. These techniques can leverage all photon energy ranges, especially soft X-ray spectro-nanoscopes (>100-fold gain at the focused area) that require an exit slit as a virtual light source.

Keywords: Fourth-generation light source, Korea-4GLS, Nanoprobe, Spectro-nanoscopy, Brilliance