“…The spectrum clearly displays two EUV transmission drops assigned to the spin-orbit split resonances of the 2p levels at 99.76 eV (L 3 edge) and 100.45 eV (L 2 edge), corresponding, respectively, to emission features C and E. The present data are compared with (i) a spectrum from a nominally identical sample obtained by a synchrotron measurement (at the BEAR beamline of the Elettra synchrotron [61], yellow line) with comparable energy resolution and acquisition time; (ii) a measurement performed at FERMI by using narrow-band (seeded-mode) FEL emission and scanning the photon energy (gray line). It is worth noticing the lower-energy resolution of about 75 meV due to the reduced number of experimental points collected in the same acquisition time (2 h); and (iii) a measurement performed at FERMI (in SASE-like mode) obtained by exploiting the ghost spectroscopy method (green line) [18]: The energy and temporal resolution, as well as the acquisition time, are comparable.…”