Two excellent seminars on ultrafast science
Thursday August 25 in 1525-626
14:00-14:45: Attosecond probing of electron correlation in xenon by two-color driven high-order harmonic generation
Caterina Vozzi, Department of Physics, Politecnico Milano, Italy
14:45-15:00 Discussion
15:00-15:20: Coffee and cake
15:20-16:05:
Attosecond science with gases and liquids: From the extreme ultraviolet to soft X-rays
Hans Jakob Wörner,
Laboratory of Physical Chemistry, ETH Zürich, Switzerland
16:05-16:20: Discussion
Lars Bojer Madsen and Henrik Stapelfeldt
Attosecond probing of electron correlation in xenon
by two-color driven high-order harmonic generation
Caterina Vozzi
Department of Physics, Politecnico Milano, Italy
High-order harmonic generation (HHG) is a sensitive probe of atomic and molecular structures. Recently this research field greatly benefited from the exploitation of mid-IR driving pulses that allowed the extension of
the harmonic emission to higher photon energies, giving access to several phenomena previously unexplored with this technique, such as the giant resonance in xenon. This enhancement in the harmonic generation yield around 100 eV has been interpreted in terms
of the electronic structure of xenon, suggesting the key role of single and multi-electron contributions to the harmonic generation process. In our work, we exploited HHG by a two-color field, combining this powerful experimental approach with a mid-IR driving
source, providing the evidence of a deviation of the xenon response with respect to the expected atomic behavior which is interpreted as the fingerprint of electron correlation effects.
Attosecond science with gases and liquids:
from the extreme ultraviolet to soft X-rays
Hans Jakob Wörner
Laboratory of Physical Chemistry, ETH Zürich, Switzerland
The ultrafast motion of electrons and holes following light-matter interaction is fundamental to a broad range of chemical and biophysical processes. In this lecture, I will discuss two recent experiments carried out
in our group that measure the atomic-scale motion of charge with attosecond temporal resolution (1 as = 10-18s). The first experiment is carried out on isolated, spatially oriented molecules in the gas phase. We advance high-harmonic spectroscopy
to resolve spatially and temporally the migration of an electron hole immediately following ionization of iodoacetylene, while simultaneously demonstrating extensive control over the process. A multidimensional approach, based on the measurement of both even
and odd harmonic orders, enables us to reconstruct both quantum amplitudes and phases of the electronic states with a resolution of ~100 as. We separately reconstruct quasi-field-free and laser-controlled charge migration as a function of the spatial orientation
of the molecule and determine the shape of the hole created by ionization [1].
The second experiment is carried out on a free-flowing microjet of liquid water. We use an attosecond pulse train synchronized with a near-infrared laser pulse to temporally resolve the process of photoemission from liquid
water using the RABBIT technique. We measure a delay on the order of 50 as between electrons emitted from the HOMO of liquid water compared to that of gas-phase water and a substantially reduced modulation contrast of the corresponding sidebands. Since our
measurements on solvated water molecules are referenced to isolated ones, the measured delays reflect the delays caused by electron transport through the aqueous environment. The relative modulation contrast,
in turn, contains information on dephasing processes. These experiments make the liquid phase and its fascinating mechanisms accessible to attosecond time-resolved measurements [2].
[1] P. M. Kraus, B. Mignolet, D. Baykusheva, A. Rupenyan, L. Horny, E. F. Penka, G. Grassi, O. I. Tolstikhin, J. Schneider, F. Jensen, L. B. Madsen, A. D. Bandrauk, F. Remacle, and H. J.
Wörner, Science 350, 790 (2015).
[2] I. Jordan, M. Huppert, M. Peper, A. von Conta, L. Seiffert, Th.
Fennel and H.J. Wörner, to be published.