Li, S.Driver, T.Al Haddad, A.Champenois, E. G.Agaker, M.Alexander, O.Barillot, T.Bostedt, C.Garratt, D.Kjellsson, L.Lutman, A. A.Rubensson, J-ESathe, C.Marinelli, A.Marangos, J. P.Cryan, J. P.2021-08-282021-08-282021-08-282021-07-1410.1088/1361-6455/abcdf1https://infoscience.epfl.ch/handle/20.500.14299/181028WOS:000684385400001X-ray photoelectron spectroscopy (XPS) measures the binding energy of core-level electrons, which are well-localised to specific atomic sites in a molecular system, providing valuable information on the local chemical environment. The technique relies on measuring the photoelectron spectrum upon x-ray photoionisation, and the resolution is often limited by the bandwidth of the ionising x-ray pulse. This is particularly problematic for time-resolved XPS, where the desired time resolution enforces a fundamental lower limit on the bandwidth of the x-ray source. In this work, we report a novel correlation analysis which exploits the correlation between the x-ray and photoelectron spectra to improve the resolution of XPS measurements. We show that with this correlation-based spectral-domain ghost imaging method we can achieve sub-bandwidth resolution in XPS measurements. This analysis method enables XPS for sources with large bandwidth or spectral jitter, previously considered unfeasible for XPS measurements.OpticsPhysics, Atomic, Molecular & ChemicalOpticsPhysicsx-ray photoelectron spectroscopyfree-electron laserghost imagingamo physicstext::journal::journal article::research article