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SUMMARY:Time-resolved molecular electron dynamics
DTSTART:20140410T163000
DTEND:20140410T173000
DTSTAMP:20260407T043232Z
UID:e3c40d1a835ccbac8dd9159e343666f689c5e107554f593ea5029e06
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. M.J.J. Vrakking\nDirector of the Max Born Institut für 
 Nichtlineare Optik und Kurzzeit- Spektroskopie im Forschungsverbund Berlin
 \nAttosecond time-resolved molecular dynamics\nThe intrinsic timescale of 
 dynamical processes that occur at molecular length-scales is ultrafast. It
  ranges from femtosecond (1 fs = 10-15 s) to picosecond\n(1 ps = 10-12 s) 
 timescales when considering structural changes in small molecules\, and ca
 n involve attosecond (1 as = 10-18 s) timescales in the case of electronic
  processes. Correspondingly\, the emergence of attosecond science in the l
 ast decade has had a major impact on our understanding of light-induced pr
 ocesses.  Attosecond science aims at probing electronic motion on the ato
 mic length-scale\, and – more generally - is concerned with the ultrafas
 t motion of charges (including electrons\, holes and – in some cases - p
 rotons)\, as well as the interactions between them. Electrons play a cruci
 al role in nature\, as they link atoms together in the process of forming 
 molecular bonds and define the optical properties of macroscopic materials
 .\nIn the last few years our group has taken first steps towards the imple
 mentation of attosecond pump-probe techniques in molecular systems. In doi
 ng so\, we have up to now followed the existing paradigm of using two-colo
 r XUV+IR experimental protocols\, where an attosecond pulse (or an attosec
 ond 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 t
 echniques are in progress.\nIn our first application of attosecond pump-pr
 obe 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 e
 ither of the two protons was measured as a function of XUV-IR time delay a
 nd revealed the importance of both coupling of the electronic degrees of f
 reedom and electron entanglement on the attosecond to few-femtosecond time
 scale. These experiments have been followed by similar experiments on H2\,
  O2 and N2 involving the use of an APT.\nProbing of attosecond dynamics us
 ing an attosecond pulse is relevant to attempts to observe charge migratio
 n processes on attosecond to few-femtosecond timescales\, which have been 
 predicted in the literature. An essential aspect of such schemes is the ab
 ility to perform experiments where attosecond pulses are able to make obse
 rvations of time-dependent electron densities. In recent experiments\, we 
 have shown that variations in molecular charge densities associated with p
 olarization of the molecules in an electric field can be reflected in phot
 oionization yield measurements. Together with recent results showing that 
 ionic hole wavepackets can be formed by strong-field ionization this sugge
 sts a possible way to study charge migration.
LOCATION:CH G1 495 https://plan.epfl.ch/?room==CH%20G1%20495
STATUS:CONFIRMED
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