TIME-RESOLVED COHERENT PHOTOELECTRON-SPECTROSCOPY OF QUANTIZED ELECTRONIC STATES ON METAL-SURFACES

Time-resolved two-photon photoemission in combination with the coheren t excitation of several quantum states was used to study the ultrafast electron dynamics of image-potential states on metal surfaces, For a (100) surface oi copper, the spectroscopy of quantum beats made previo usly unresolved high-order states (quantum number n greater than or eq ual to 4) experimentally accessible, By exciting electrons close to th e vacuum level, electron wave packets could be created and detected th at described the quasi-classical periodic motion of weakly bound elect rons, They traveled more than 200 Angstrom away from the surface and o scillated back and forth with a period of 800 femtoseconds.