Laser-excited PEEM using a fully tunable fs-laser system

摘要

The ferroelectric domain structure on a (001) surface of a $BaTiO_{3}$ single crystal prepared under ultrahigh vacuum conditions is imaged by laser-excited photoemission electron microscopy (PEEM). The PEEM images allow for discrimination of three domain types by their different photoemission yields. To characterize the contrast between the different ferroelectric domains of $BaTiO_{3}$(001) in the region of 4.0–4.6 eV close to the photoemission threshold, the broad wavelength tunability of the femtosecond laser system is used. The femtosecond time resolution within two-photon PEEM experiments, using two fully independently tunable laser beams, is demonstrated for the first image potential state of Ag(001). In a pump-probe setup with a cross-correlation full-width at half-maximum of 70 fs, an angle-integrated apparent lifetime of 40 fs is derived from the PEEM intensities. In contrast with energy-resolved two-photon photoemission measurements, PEEM data reveal a 17-fs shorter lifetime. This difference is discussed by considering the co-excitation of bulk states, which leads to an additional time-dependent photoelectron contribution in PEEM.