Time-resolved two-photon momentum microscopy—A new approach to study hot carrier lifetimes in momentum space

The dynamics of optically excited charge and spin carriers in condensed matter systems play a crucial role for many fundamental as well as device relevant processes in solids. Here, we describe the novel approach of time-resolved two-photon momentum microscopy to investigate the quasiparticle lifetime of optically excited electrons throughout the entire accessible energy and momentum space in a fixed experimental geometry. This method combines the established optical tools of time-resolved two-photon photoemission spectroscopy with a photoemission electron microscope operated in the k-space mode. We will discuss the experimental details and the data analysis procedure of this novel method and demonstrate its capability to reveal the hot electron dynamics in energy and momentum space for the prototypical Cu(111) surface. This example clearly shows the huge potential of this method to gain new insights into the momentum-dependent quasiparticle lifetime and the corresponding complex momentum- and energy-dependent scattering phenomena in condensed matter.