Johannes Gutenberg-Universität, Institut für Physik, D-55099 Mainz, Germany
With the advent of femtosecond lasers a novel application of PEEM as "detector" in all-optical pump-probe experiments has become became possible. This contribution summarizes the present state of the technique and presents several examples. The pioneering experiments of fs-laser PEEM have been performed by O. Schmidt et al. [1,2]. A frequency-doubled Ti:sapphire laser oscillator was used whose photon energy (typically 3.1 eV) lies below the work function threshold of most metals (e. g. ≥4.2 eV for Ag). Thus, the observed electron signal in the microscope results from two-photon photoemission (2PPE). Time-resolved 2PPE has been extensively investigated in order to understand electron dynamics at metal and semiconductor surfaces. However, in previous spatially integrating experiments it was not possible to systematically investigate, for example, local variations of the electron dynamics or the effect of surface inhomogeneities on the 2PPE process. A striking example is the nonlinear enhancement of the integral photoemission yield due to so-called hot spots at surfaces. This effect is the result of the interaction between the exciting intense laser field and surface defects . Of particular interest is the specific hot-electron dynamics (for metals described by Fermi liquid theory) of spatially heterogeneous systems or the spatiotemporal behaviour of localized surface plasmon excitations as has been studied using interferometric time-resolved PEEM by Kubo et al.  with a temporal precision in the attosecond range. Finally, the PEEM is capable to detect the optical near field in the vicinity of resonantly excited "nano-antenna" (in our case tailored Ag crescents lithographically produced on Si) . Examples of all approaches are presented and discussed.
 O. Schmidt et al., Surf. Sci. 482-485 (2001) 687
 O. Schmidt et al., Appl Phys. B 74 (2002) 223
 M. Cinchetti et al., Appl. Phys. Lett. 83 (2003) 1503-5
 A. Kubo et al., Nano Letters 5 (2005) 1123
 M. Cinchetti et al., Phys. Rev. Lett. 95 (2005) 047601
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