Coherent optical 2D photoelectron spectroscopy

Coherent multidimensional spectroscopy (CMDS) and photoelectron spectroscopy have become invaluable tools to elucidate the quantum properties and ultrafast dynamics of matter. Here, we report the combination of both complementary methods in a single experiment. This becomes technically feasible with the implementation of efficient single-counting detection and multichannel software-based lock-in amplification. The approach offers high temporal, spectral, and kinetic energy resolution, enables differential CMDS experiments with unprecedented selectivity, and enhances the dynamic range of CMDS by two orders of magnitude. The demonstrated principle opens up a perspective for atomically resolved CMDS experiments using X-ray photoelectron spectroscopy.