attosecond spectroscopy

With the waveform-controlled few-cycle/single-cycle VIS/NIR pulses and the synchronized sub-femtosecond and attosecond UV/VUV/XUV/SXR pulses the toolbox of attosecond spectroscopy is well equipped, allowing a range of different pump-probe techniques to be applied to a range of different physical systems. At LAP we are developing six attosecond spectroscopy beamlines, AS-1 to AS-6 for interrogating hyperfast electronic and concomitant processes of the microcosm. Here, we outline a few fundamental questions and possible ways of answering them.

multi-electron dynamics and electron-electron interactions in atoms
electron wavepacket and coupled electron-nuclear dynamics in molecules
electron excitation/relaxation/correlation/transport in condensed matter
collective electron motion in nano-particles and nano-assemblies

Electrons in atoms: How does an electron transfer energy to another one inside atoms and molecules? How does optical field ionization happen in time and how does the atom’s electronic system respond to the sudden loss of one or more electrons? Can more than one electron escape from atoms within a half wave cycle of a strong ionizing optical field and if yes, how are they correlated? We seek answers to these and other fundamental questions about the way electrons respond to excitations, by triggering motion with an asec pulse and sample outgoing (positive-energy) electrons or probe excited valence states with few-cycle light via attosecond streaking and tunneling, respectively. Alternatively, electronic excitation and rearrangement will be induced by optical-field ionization excitation and probed with an attosecond pulse by transient absorption and photoelectron spectroscopy.
contact: E. Goulielmakis, M. Kling, M. Schultze

Electrons in molecules: Can electron wavepacket motion be realized in controlled fashion in molecular orbitals and watched in real time? Can electron motion and subsequent structural changes in molecules be controlled with the field of synthesized light? To address these questions of far-reaching importance, we plan to launch an electron wavepacket via single-photon transition induced from the ground state into several excited electronic states of molecules with a broadband near-1-fs/sub-fs UV/VUV pulse and probe the subsequent motion with a time-delayed attosecond XUV/SXR pulse via attosecond absorption or photoelectron spectroscopy. Later, we wish to affect/steer this motion with synthesized, several-octave-bandwidth UV/VIS/NIR fields.
contact: M. Fieß, R. Kienberger

Electrons in solids: Is photoemission from solids delayed or modified by interaction of the outgoing electron with the delocalized and/or localized electron of the system, i.e. does the first moment of photoemission from solids carry information about multi-electron effects? How does charge screening (e.g. mirror charge) build up in metals? How do hot electrons relax and lose their coherence in semiconductors? How does charge transfer happen in host-guest systems, can it be optimized for more efficient solar cells? Can electric current in solid-state structures be driven and controlled with light fields? In the pursuit of seeking answers to these questions, we shall trigger and probe dynamics with an XUV/SXR attosecond pulse and by attosecond streaking of outgoing electrons, respectively. Dynamics excited with an intense, near-1-fs/sub-fs UV/VUV pulse will be probed with an asec XUV/SXR pulse.
contact: R. Ernstorfer, R. Kienberger

Collective electron motion: How does collective electron motion unfold in nanoparticles and nanostructured solids on a sub-femtosecond time scale and nanometer spatial scale? Resonant excitation with a few-cycle/single-cycle UV/VIS/NIR pulse will start this collective motion, synthesized UV/VIS/NIR waveforms will be used for its control and an attosecond pulse will probe the unfolding collective dynamics via photoelectron spectroscopy.
contact: U. Kleineberg, M. Kling

references:

Atomic transient recorder, R. Kienberger et al. Nature 427, 817 (2004)

Attosecond real-time observation of electron tunneling in atoms, M. Uiberacker et al. Nature 446, 627 (2007)

Attosecond science, Tp. B. Corkum, F. Krausz Nature Phys. 3, 381 (2007)

Attosecond physics, MF. Krausz, M. Y. Ivanov Rev. Mod. Phys. 81, 163 (2009)

On the feasibility of an ultrafast purely electronic reorganization in lithium hydride, F. Remacle et al. Chem. Phys. 338, 342 (2007)

Attosecond spectroscopy in condensed matter, A. L. Cavalieri et al. Nature 449, 1029 (2007)

basics:

tools:

the attosecond beamlines

Fig. 1. LAP tools for time-resolved spectroscopy with sub-100-asec resolution. Nanojoule-energy, isolated 80-attosecond XUV pulses (shown in violet) generated with near-single-cycle, 3.3-fs laser pulses (electric field shown in red) from FP-1 of LAP generates permit precision attosecond measurements (in this case the recollision time of electrons in ionizing atoms) with a resolution comparable to the atomic unit of time (∼24 asec).

Fig. 2. The cover photo shows the laser (red) and XUV (violet) beam impinging a target under study, along with a two-component mirror introducing the attosecond delay between the attosecond XUV pulse and the single-cycle laser wave.

Fig. 3. Attosecond spectroscopy in condensed matter. Real-time observation of angstrom-scale electron transport in solids: photoelectrons released by an attosecond XUV-pulse from localized (core) states reach the surface some 110 asec later than those librated from delocalized states at the Fermi edge of the conduction band.