Előadó: Sándor Péter (SZFI)
Az előadás témája: Molecular Strong-Field Ionization viewed with Photoelectron Velocity Map Imaging
Az előadás időpontja: 2020. október 27. kedd, 10.00
Helyszín: videokonferencia, https://letsmeet.wigner.hu/szeminarium
Strong-field ionization is the key first step of the 3-step model which explains phenomena such as high-harmonic generation and attosecond pulse generation, which are currently at the forefront of ultrafast science. By understanding the changes that ionization brings about in the atomic/molecular system, one hopes to make the latter two processes more efficient. In my talk I will highlight experiments of molecular strong-field ionization that show that in contrast to earlier assumptions, even at the lowest intensities required for multi-photon ionization, not just the lowest energy, but higher-lying ionic states are also populated. For halogenated methane molecules (systems that can be regarded as essentially triatomic), different ionization-dissociation pathways are identified with the help of a coincidence Velocity Map Imaging apparatus that maps photoelectrons according to their vector momentum in coincidence with the accompanying ion. Furthermore, we follow nonadiabatic temporal dynamics of the electronic structure of the ion on a few tens of femtoseconds scale with using ultrashort pulses of ~9 fs in duration and interpret the results with ab-initio electronic structure calculations. We find that the dynamics on the neutral and ionic state potentials are not solely driven by the color content of the exciting laser pulses, but instead it is really their shortness in time—relative to nuclear motion—that determines the outcome of the experiment. This result has the implication that one can indeed 'freeze' the effects of molecular vibrations on photoionization if the interaction time is kept sufficiently short.