Attosecond streaking of photoelectron emission from disordered solids

Attosecond streaking of photoelectrons emitted by extreme ultraviolet light has begun to reveal how electrons behave during their transport within simple crystalline solids. Many sample types within nanoplasmonics, thin-film physics, and semiconductor physics, however, do not have a simple single crystal structure. The electron dynamics which underpin the optical response of plasmonic nanostructures and wide-bandgap semiconductors happen on an attosecond timescale. Measuring these dynamics using attosecond streaking will enable such systems to be specially tailored for applications in areas such as ultrafast opto-electronics. We show that streaking can be extended to this very general type of sample by presenting streaking measurements on an amorphous film of the wide-bandgap semiconductor tungsten trioxide, and on polycrystalline gold, a material that forms the basis of many nanoplasmonic devices. Our measurements reveal the near-field temporal structure at the sample surface, and photoelectron wavepacket temporal broadening consistent with a spread of electron transport times to the surface

Time-Resolved Ion Spectrometry on Xenon with Jitter-Compensated Soft X-Ray Pulses of a Free-Electron Laser

Atomic inner-shell relaxation dynamics were measured at the free-electron laser in Hamburg, FLASH, delivering 92 eV pulses. The decay of 4d core holes created in xenon was followed by detection of ion charge states after illumination with delayed 400 nm laser pulses. A timing jitter of the order of several hundred femtoseconds between laser- and accelerator-pulses was compensated for by a simultaneous delay measurement in a single-shot x-ray/laser cross-correlator. After sorting of the tagged spectra according to the measured delays, a temporal resolution equivalent to the pulse duration of the optical laser could be established. While results on ion charge states up to Xe4+ are compatible with a previous study using a high-harmonic soft x-ray source, a new relaxation pathway is opened by the nonlinear excitation of xenon atoms in the intense free-electron laser light field, leading to the formation of Xe$^{5+}$

Ion-charge-state chronoscopy of cascaded atomic Auger decay

Uphues T, Schultze M, Kling MF, et al. Ion-charge-state chronoscopy of cascaded atomic Auger decay. New Journal of Physics. 2008;10(2): 025009.It has recently been demonstrated that apart from the electron detection realized in the attosecond streak camera, also ion detection can be used for establishing extreme-ultraviolet pump) visible probe experiments, temporally resolving the dynamics of atomic inner-shell relaxation processes. We utilize this method for studying the Auger decay of krypton atoms following the creation of vacancy states in the 3d shell. It is shown that the electronic relaxation occurs through different pathways, each involving cascades of sequential steps which are followed in their native temporal succession

Attosecond real-time observation of electron tunnelling in atoms

Uiberacker M, Uphues T, Schultze M, et al. Attosecond real-time observation of electron tunnelling in atoms. Nature. 2007;446(7136):627-632.Atoms exposed to intense light lose one or more electrons and become ions. In strong fields, the process is predicted to occur via tunnelling through the binding potential that is suppressed by the light field near the peaks of its oscillations. Here we report the real-time observation of this most elementary step in strong-field interactions: light-induced electron tunnelling. The process is found to deplete atomic bound states in sharp steps lasting several hundred attoseconds. This suggests a new technique, attosecond tunnelling, for probing short-lived, transient states of atoms or molecules with high temporal resolution. The utility of attosecond tunnelling is demonstrated by capturing multi-electron excitation (shake-up) and relaxation ( cascaded Auger decay) processes with subfemtosecond resolution