Three-photon photoemission on metallic transition metal dichalcogenide NiTe$_{2}$
Three-photon photoemission (3PPE) signals on NiTe$_{2}$ are observed for the first time upon ultraviolet excitations. In the energy range beyond two-photon excitations, an energy-momentum dispersive feature is clearly identified with characteristic light polarization dependence. Based on its dispersion, spectral width, as well as intensity as a function of the parallel momentum, this dispersive 3PPE feature could be ascribed to an image potential resonance overlapping with an unoccupied Ni $4s$ -Te $4d$/$5p$ bulk band in accordance with the electronic band structure. Our results underlie higher-order non-linear photoemission on metallic transition metal dichalcogenides and facilitate future ultrafast studies of coherent electron dynamics in anisotropic, two-dimensional systems.