Time-resolved photoelectron emission from atoms and surfaces: the photoeffect revisited*

Streaking spectroscopy experiments enable the resolution in time of photo-ionization processes at the natural time scale (tens of attoseconds, 1 as = 10$^{-18}$ seconds) of the motion of valence electrons in atoms and solids. This ultrahigh time resolution allows the observation of an apparent ``delay-time'' \textit{difference} between the release and detection of photoelectrons from different initial states of atoms and solids. These delays are typically of the order of tens of attoseconds and are a measure of the net quantum phase that is accumulated during the \textit{entire} photoemission process, including the release, propagation, and detection of the photoelectron. I will discuss different interpretations of and contributions to photoemission delay times based on the comparison of calculated time-resolved photo-electron spectra with recent experiments [1,2]. In particular, for time-resolved photo-emission from metal surfaces [3,4], we find our calculated electron spectra to be very sensitive to details in the modeling of dielectric-response and electron-propagation effects during the laser-assisted XUV excitation and emission process [5]. The sensitivity of photoemission time delays to the plasmonic response of solid surfaces suggests the time-resolved observation of collective (plasmonic, excitonic, etc.) excitations in atoms, nano-particles, and solids. \\[4pt] [1] C.-H. Zhang and U. Thumm,\textit{ Phys. Rev}. A \textbf{82}, 043405 (2010);\\[0pt] [2] \textit{Phys. Rev}. A \textbf{84}, 033401 (2011);\\[0pt] [3] \textit{Phys. Rev. Lett}. \textbf{102}, 123601 (2009);\\[0pt] [4] \textit{Phys. Rev}. A \textbf{84}, 065403 (2011);\\[0pt] [5] \textit{Phys. Rev}. A \textbf{84}, 063403 (2011).