THz-driven dynamics probed by time-resolved ARPES – the high repetition rate opportunity

Terahertz radiation offers unique control of low-energy excitations in matter. Fundamental modes, such as molecular rotations, lattice vibrations, electron and ion motion or spin precession can be coherently controlled on an ultrafast timescale, while parasitic electronic excitations are suppressed, because of the low THz photon energy.
The THz-induced effects, e.g. phase transitions in solids or modifications of chemical reactions are intrinsically connected to changes in the electronic structure of the material. The natural way to directly probe these changes is time- and angle-resolved photoelectron spectroscopy (tr-ARPES).
The main challenges which have impeded the experimental realization are:
availability of high field and high repetition rate THz source
knowledge and control of interaction of photo- electrons with THz field (“streaking”)
Accelerator-based THz sources like FLASH and TELBE provide ideal conditions for establishing feasibility and dynamic range of THz-pump tr-ARPES.