Dr. H.J. Wörner
Joint Laboratory for Attosecond Science
National Research Council of
100,
Monday, February 8, 2010
4:30 p.m.
Cardwell 102
Following Chemical Reactions Using High-Harmonic Interferometry
One of
the main goals of modern ultrafast science is to image a chemical reaction as it
occurs.
Recently, laser-induced recollision has demonstrated that imaging of both the
nuclear and electronic structure of a static molecule
is simultaneously possible [1,2]. In this talk, we apply
these new methods to the time-resolved observation of chemical reactions [3].
The coherence of high-harmonic generation turns the unavoidably low fraction of
excited molecules into an advantage as the unexcited molecules act as a local
oscillator. The application of the transient grating technique allows us to
measure both amplitude and phase of the excited state emission and its evolution
on the femtosecond time scale [4]. Using the photodissociation of Br2
as an example, we show that the high-harmonic
amplitude encodes the internuclear separation by quantum interference at short
times and scattering of the photoelectrons at longer times. The high-harmonic
phase records the attosecond dynamics of the electron. We will discuss how
high-harmonic spectroscopy can be used in the future to investigate
non-adiabatic molecular dynamics, image electronic ring currents and attosecond
charge transport along molecular chains.
[1]
J. Itatani et al.
Nature
432,
867–871 (2004).
[2] M. Meckel et al., Science 320, 1478–1482 (2008).
[3]
V. H. Le, A.-T. Le, R. H. Xie and C. D. Lin,
Phys. Rev. A
76, 013414 (2007)
[4] H. J. Wörner, J. B. Bertrand, D. V. Kartashov, P. B. Corkum and D. M.
Villeneuve, Nature (submitted)