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 [cid:image005.jpg@01D1F95E.D282BB00] [http://www.nccr-must.ch/libraries.bilder/woerner1.jpg] 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.
