Attoseconds & Picometer: Atomic-Scale Dynamics in Matter
Atomic-scale rearrangements are essential for understanding the behavior
and function of molecules and advanced materials.
All macroscopic changes involve local rearrangement of the atoms and
electron density, which define the fundamental mechanisms of the change. The
length and time scales of nuclear motions are picometer and femtoseconds;
electrons can move as fast as within attoseconds. A combined,
four-dimensional approach with both temporal and spatial resolution is therefore essential for
capturing the action all at once.
Ultrafast Electron Diffraction and Imaging
The techniques of ultrafast electron diffraction and microscopy allow to "make
a movie" of atomic-scale movements, by simultaneously providing picometer resolution
and femtosecond timing. A laser pulse is used to initiate the dynamics, and
ultrashort electron pulses are diffracted to visualize the atomic-scale structures as they
evolve. Ultrafast diffraction results in four-dimensional information
including space and time. The approach is therefore ideal for visualizing
the many complicated ultrafast transitions
that do not proceed directly from the initial to the
final conformation, but rather follow complex non-equilibrium reaction pathways. The materials that we investigate include molecular crystals, surface
adsorbates, nanostructures, charge-transfer compounds, photonic devices, eventually biomolecules,
and many more.
Down to Attoseconds: Observation of Electrons Dynamics
Femtosecond resolution is perfect for observing atoms, but the motion of electrons is expected to involve times as short as attoseconds.
In principle, ultrafast
electron diffraction is capable of accessing this time scale, because the
de Broglie wavelength of our electrons supports pulse durations of one attosecond
and less. Our route into this regime is based on
the compression of single-electron
packets in synthesized electrical and optical fields. In contrast to spectroscopic
approaches with optical pulses, attosecond electron pulses, once realized, may offer direct
four-dimensional visualization of charge density dynamics with combined
spatial and temporal resolution. Attosecond electron diffraction will be a
free space approach with very monochromatic beams, which will allow us to investigate
the motions of electron density in a large variety of complex systems, such as nonlinear optical materials, photonic devices,
molecular crystals, superconductors, and many others.
For further information, please have a look at some relevant publications.