Strong field and attosecond physics in solids

Probing Excitation Dynamics with Time-Resolved Spectroscopy

The possibility to probe systems with light not only statically but with time-resolution in pump and probe configurations gives experimental access to excitation dynamics in materials. The description of such non-equilibrium systems poses both conceptual and technical challenges for theoretical spectroscopy. Our approach to this problem uses time-dependent density functional theory (TDDFT), which provides a direct way of both creating excitations in materials and probing them with (classical) electromagnetic fields. Since this method is a first-principles approach and our implementation in the OCTOPUS code does not require basis functions, we can tackle a wide range of spectroscopies and time-scales.

Among them are ultrafast, attosecond processes in solids that can be observed with transient optical absorption spectroscopy, where TDDFT gives insight into the dynamics of excited electrons in the conduction band manifold. At longer time-scales, time-resolved angular resolved photoelectron spectroscopy (ARPES) allows the observation of electronic bands under pump-probe conditions. We simulate this spectroscopy by computing the electronic structure, its excitation and probe, the evolution of photoelectrons, and their detection all within one TDDFT framework. Combining these techniques and utilizing the large parameter space of different pump-probe and multiphoton regimes, we describe a variety of cutting-edge experiments and propose novel spectroscopic setups.

This research line opens exciting avenues for understanding and manipulating the ultrafast electronic dynamics in both molecules and solids, bridging the gap between fundamental science and practical applications.