Time-resolved molecular electron dynamics
Event details
| Date | 10.04.2014 |
| Hour | 16:30 › 17:30 |
| Speaker |
Prof. M.J.J. Vrakking Director of the Max Born Institut für Nichtlineare Optik und Kurzzeit- Spektroskopie im Forschungsverbund Berlin |
| Location | |
| Category | Conferences - Seminars |
Attosecond time-resolved molecular dynamics
The intrinsic timescale of dynamical processes that occur at molecular length-scales is ultrafast. It ranges from femtosecond (1 fs = 10-15 s) to picosecond
(1 ps = 10-12 s) timescales when considering structural changes in small molecules, and can involve attosecond (1 as = 10-18 s) timescales in the case of electronic processes. Correspondingly, the emergence of attosecond science in the last decade has had a major impact on our understanding of light-induced processes. Attosecond science aims at probing electronic motion on the atomic length-scale, and – more generally - is concerned with the ultrafast motion of charges (including electrons, holes and – in some cases - protons), as well as the interactions between them. Electrons play a crucial role in nature, as they link atoms together in the process of forming molecular bonds and define the optical properties of macroscopic materials.
In the last few years our group has taken first steps towards the implementation of attosecond pump-probe techniques in molecular systems. In doing so, we have up to now followed the existing paradigm of using two-color XUV+IR experimental protocols, where an attosecond pulse (or an attosecond pulse train, APT) is used to initiate or probe the ultrafast dynamics of interest, and where the optical cycle of an IR laser field is used as a clock that allows to take measurements on attosecond timescales. At the same time, efforts to develop attosecond XUV pump-attosecond XUV probe techniques are in progress.
In our first application of attosecond pump-probe spectroscopy to a molecular system, we have investigated dissociative ionization of H2 under the influence of an isolated attosecond pulse that was followed – at a variable time delay - by a few-cycle infrared laser pulse. Selective localization of the single remaining bound electron on either of the two protons was measured as a function of XUV-IR time delay and revealed the importance of both coupling of the electronic degrees of freedom and electron entanglement on the attosecond to few-femtosecond timescale. These experiments have been followed by similar experiments on H2, O2 and N2 involving the use of an APT.
Probing of attosecond dynamics using an attosecond pulse is relevant to attempts to observe charge migration processes on attosecond to few-femtosecond timescales, which have been predicted in the literature. An essential aspect of such schemes is the ability to perform experiments where attosecond pulses are able to make observations of time-dependent electron densities. In recent experiments, we have shown that variations in molecular charge densities associated with polarization of the molecules in an electric field can be reflected in photoionization yield measurements. Together with recent results showing that ionic hole wavepackets can be formed by strong-field ionization this suggests a possible way to study charge migration.
The intrinsic timescale of dynamical processes that occur at molecular length-scales is ultrafast. It ranges from femtosecond (1 fs = 10-15 s) to picosecond
(1 ps = 10-12 s) timescales when considering structural changes in small molecules, and can involve attosecond (1 as = 10-18 s) timescales in the case of electronic processes. Correspondingly, the emergence of attosecond science in the last decade has had a major impact on our understanding of light-induced processes. Attosecond science aims at probing electronic motion on the atomic length-scale, and – more generally - is concerned with the ultrafast motion of charges (including electrons, holes and – in some cases - protons), as well as the interactions between them. Electrons play a crucial role in nature, as they link atoms together in the process of forming molecular bonds and define the optical properties of macroscopic materials.
In the last few years our group has taken first steps towards the implementation of attosecond pump-probe techniques in molecular systems. In doing so, we have up to now followed the existing paradigm of using two-color XUV+IR experimental protocols, where an attosecond pulse (or an attosecond pulse train, APT) is used to initiate or probe the ultrafast dynamics of interest, and where the optical cycle of an IR laser field is used as a clock that allows to take measurements on attosecond timescales. At the same time, efforts to develop attosecond XUV pump-attosecond XUV probe techniques are in progress.
In our first application of attosecond pump-probe spectroscopy to a molecular system, we have investigated dissociative ionization of H2 under the influence of an isolated attosecond pulse that was followed – at a variable time delay - by a few-cycle infrared laser pulse. Selective localization of the single remaining bound electron on either of the two protons was measured as a function of XUV-IR time delay and revealed the importance of both coupling of the electronic degrees of freedom and electron entanglement on the attosecond to few-femtosecond timescale. These experiments have been followed by similar experiments on H2, O2 and N2 involving the use of an APT.
Probing of attosecond dynamics using an attosecond pulse is relevant to attempts to observe charge migration processes on attosecond to few-femtosecond timescales, which have been predicted in the literature. An essential aspect of such schemes is the ability to perform experiments where attosecond pulses are able to make observations of time-dependent electron densities. In recent experiments, we have shown that variations in molecular charge densities associated with polarization of the molecules in an electric field can be reflected in photoionization yield measurements. Together with recent results showing that ionic hole wavepackets can be formed by strong-field ionization this suggests a possible way to study charge migration.
Practical information
- General public
- Free
Organizer
- Dr Frank van Mourik