TIME-RESOLVED 2-PHOTON PHOTOEMISSION FROM CU(100) - ENERGY-DEPENDENCEOF ELECTRON RELAXATION

A time-domain measurement of the relaxation time of photoexcited elect rons as a function of excitation energy at a single-crystal Cu(100) su rface has been made with time-resolved two-photon photoemission. The r elaxation lifetime of the excited electrons is found to decrease rapid ly with the amount of excitation energy above the Fermi level, and we compare the measured lifetimes with a calculation based on Fermi-liqui d theory. The results reveal a qualitative agreement with the theory, and indicate that effects due to transport of the electrons away from the surface and into the bulk are important.