T2: Strong field theory
The goals of our research are: to explore the opportunities offered by the ubiquitous nature of sub-laser cycle response to strong IR fields for shaping, controlling and imaging quantum matter, to understand the link between topological and chiral dynamical phenomena and to create new concepts for shaping, controlling, and imaging of “oriented” media: media with orbital momentum, spin, and handedness, including efficient chiral discrimination in molecules with optical fields.
See viewpoint by Olga Smirnova in Nature Reviews Physics
An object is called chiral if it cannot be superimposed on its mirror image by any rotation. One example is our left and right hands. Just like our hands, molecules can also be chiral; left handed and right handed molecules are called enantiomers. Distinguishing left and right enantiomers is both vital and hard.
In this research topic we focus on using nonlinear interaction of light with chiral molecules. We design and apply tailored light pulses to induce, control, and time-resolve ultrafast electronic and vibronic dynamics in chiral molecules. Our goals are to developing new methods to separate left-handed and right-handed molecules with light, to understand and to manipulate chiral interactions.
High Harmonic Spectroscopy
The interaction of light with atoms, molecules, semiconductors and dielectrics can lead to strong polarization of charges in these systems, generating harmonics of the incident light field. At sufficiently high intensities, e.g. 1013-1014 W/cm2, the number of emitted harmonics can be very large, ranging from tens to several hundreds and even more. The availability of such extremely broad coherent spectrum, spanning across several tens to hundreds of electronvolts, implies extraordinary temporal resolution of the underlying charge dynamics, down to tens of attoseconds in typical experiments. High harmonic spectroscopy uses high harmonic emission to reconstruct attosecond electronic response in atoms, molecules, and transparent solids to intense light.
One recent example of our work is the application of high harmonic spectroscopy to detect attosecond laser-driven chiral hole dynamics in the two enantiomers of a chiral molecule, with a temporal resolution of about a tenth of a femtosecond. Another recent example is the use of high harmonic spectroscopy to follow a light-induced phase transition (insulator to metal) in a strongly correlated quantum material, a Mott insulator, with a temporal resolution of one femtosecond.
Spin-polarization and spin-resolved processes in strong fields
Ionization of atoms or molecules in strong laser fields is often viewed as optical tunnelling of the departing electron through the potential barrier created by the combined action of the binding potential and the voltage applied by the laser electric field. Optical tunnelling launches a variety of strong-field processes triggered and controlled by the laser field, such as high harmonic generation, laser-induced electron diffraction and holography.
In this topic, we focus on the roles of the orbital momentum and spin of the departing electron, both in optical tunnelling and in the processes that follow. The spin and the orbital momentum of the tunneling electron are correlated to the spin and the orbital momentum of the hole it leaves behind, and the latter are coupled by spin-orbit interaction in the core. As a result, the strong sensitivity of optical tunnelling to the electron’s orbital angular momentum, together with the spin-orbit interaction, can lead to the generation of highly spin-polarized electrons during optical tunnelling. Controlling the motion of attosecond spin-polarized electron bunches with the laser field after tunnelling opens an exciting opportunity to study spin-resolved processes, such as spin-orbit hole dynamics, elastic and inelastic spin-resolved scattering, and strong-field induced holography with spin-polarized electrons, with attosecond temporal resolution.
Strong field response of quantum materials
The new generation of light sources brings a remarkable flexibility in sculpting light at the scale of individual electric field oscillations, opening unique opportunities for attosecond and strong field physics.
In this research topic, we explore these new opportunities in controlling strong field response of quantum materials on the sub-cycle time scale. We are looking at controlling and shaping light-induced phase transitions in strongly correlated solids, detecting topological phase transitions in two-dimensional materials, using tailored multi-color mid-infrared laser fields to generate spin-selected excitations in a desired valley of the Brillouin zones of quantum materials.