Olga Smirnova Talks About Attosecond Science
Fast Breaking Commentary, October 2010
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Article: High harmonic interferometry of multi-electron dynamics in molecules
Authors: Smirnova, O;Mairesse,
Y;Patchkovskii, S;Dudovich, N;Villeneuve, D;Corkum,
P;Ivanov, MY |
Olga Smirnova talks with ScienceWatch.com and answers a few questions about this month's Fast Breaking Paper paper in the field of Physcis.
Why do you think your paper is highly cited? Does
it describe a new discovery, methodology, or synthesis of knowledge?
Would you summarize the significance of your paper in layman's
terms?
Imaging structures and dynamics is a major direction of modern science which encompasses physics, chemistry, and biology. Femtosecond science focuses on following the movements of atoms within a molecule. However, much faster motion—that of electrons—underlies and controls the life of atoms and their motion in molecules. This electronic motion occurs on the attosecond time-scale (1 asec=10-18 sec). The dream of attosecond science is to find ways to follow this motion.
Our paper has made a new step towards realizing this dream by starting a new direction in attosecond science—the high harmonic spectroscopy of attosecond multi-electron dynamics. High harmonic emission occurs when an electron, liberated from a molecule by an incident intense laser field, gains energy from the field and recombines with the hole (the lack of electron) left in the molecule [1].
"...we have introduced the ideas of tracking multiple orbitals using harmonic phase measurement. The basis for this measurement was the ingenious experimental approach developed largely by Yann Mairesse and also described in our paper."
In our Nature paper [2] and in the sequence of following papers [3,4] we have shown that high harmonic emission encodes the information about hole shape and its dynamics in the amplitudes, phases, and polarization of the harmonic light. The sequence of high harmonics can be viewed as a movie, with different harmonics corresponding to successive frames of this movie [5].
In our paper we have shown how to develop this movie for the CO2 molecule. We have used the exquisite temporal resolution offered by harmonic emission to track the attosecond motion of a hole created in a molecule by ionization.
How did you become involved in this research, and
how would you describe the particular challenges, setbacks, and
successes that you've encountered along the way? Where do you see your
research leading in the future? Do you foresee any
social or political implications for your research?
My involvement in this research was stimulated by a sequence of beautiful
and very puzzling experiments performed by Dr. Yann Mairesse and Dr. Nirit
Dudovich in the laboratory of Prof. Paul Corkum and Dr. David Villeneuve at
the National Research Council (NRC) of Canada, where I had also been
working at the time. The experimental puzzles discovered by Yann and Nirit
added to the already-existing controversies in interpreting earlier
experimental data on CO2 obtained in Tokyo [6], Milano [7], and Boulder
[8].
Prof. Paul Corkum and Dr. David Villeneuve at the NRC Canada have created
an extraordinarily stimulating and inspiring atmosphere. The discovered
experimental puzzles were discussed and debated by everyone. It was during
these brainstorming meetings that we started to find the first clues that
developed into the series of new concepts and ideas.
A lot of the ideas directly challenged the common wisdom of those days. For example, it has been always assumed that during strong-field ionization the electron is removed from the highest occupied molecular orbital (HOMO) and nobody expected that deeper lying orbitals could have an important contribution.
However, not only did we realize that this had to be the case, we also realized that participation of multiple orbitals (multiple channels) in harmonic generation is the key to encoding attosecond multi-electron dynamics in high harmonic spectra. We also had to introduce a new concept—the relative phase of strong-field ionization from different orbitals.
Simultaneously, we introduced the ideas of tracking multiple orbitals using harmonic phase measurement. The basis for this measurement was the ingenious experimental approach developed largely by Yann Mairesse and also described in our paper. Finally, we had to understand the implications for polarization properties of high harmonic generation [4].
It took a couple of months to develop the concepts and pilot models. Once it became clear that we were on the right track, it took me a year to develop better theoretical approaches in collaboration with Dr. Serguei Patchkovskii and Prof. Misha Ivanov, and the work has only begun. The range of challenges to theory is enormous and there is a long road ahead.
Regarding the paper itself, it had a dramatic fate. After we had presented our first results, it took over two years for the full range of our ideas to become accepted by the community. Some of our first ideas, reported at the conferences, turned out to be sufficiently clear and simple to be quickly adopted. While we were proud of this impact, we still wanted our full story to be heard, and we had quite a bit more to say.
"The dream of attosecond science is to find ways to follow electron motion."
Our paper had been rejected several times, first from Nature and then from Nature Physics, where it was also accidentally shelved and lost for half a year. However, as we continued to work, the full range of our ideas gradually won the recognition of the community. One could say that our work was finally been accepted into Nature after a nine-round bout. But all is well that ends well.
We continue to develop high harmonic spectroscopy of multi-electron dynamics with the team of friends now scattered across France, UK, Israel, Germany, and Canada [9]. The Junior theory group at Max-Born Institute (Berlin, Germany) is currently developing theoretical tools and new imaging schemes to investigate ultrafast electron-nuclear dynamics in larger molecules (than CO2 and N2 that we have originally studied) and in liquids.
The focus is on characterization of attosecond-scale preparation of
electronic coherence, and its subsequent evolution over tens of
femtoseconds. With charge transfer playing a vital role in many biological
and chemical systems, such study opens a route to discovering and
characterizing new mechanisms of chemical reactivity.
1. Corkum P.B., Plasma perspective on strong field multiphoton ionization.
Phys. Rev. Lett. 71, 1994–1997 (1993).
2. Smirnova O. et al., High harmonic interferometry of
multi-electron dynamics in molecules. Nature 460 (2009).
3. Smirnova O. et al., Strong-field control and spectroscopy of
attosecond electron-hole dynamics in molecules, PNAS 106, 16556
(2009).
4. Smirnova O. et al., Attosecond circular dichroism spectroscopy,
Phys. Rev. Lett. 102, 063601 (2009)
5. Baker S. et al., Probing proton dynamics in molecules on an
attosecond time scale. Science 312, 424–427 (2006).
6. Kanai T., Minemoto S., & Sakai H., Quantum interference during
high-order
harmonic generation from aligned molecules. Nature 435,
470–474 (2005).
7. Vozzi C. et al., Controlling two-center interference in
molecular high harmonic
generation. Phys. Rev. Lett. 95, 153902 (2005).
8. Zhou X. et al., Molecular recollision interferometry in high
harmonic generation.
Phys. Rev. Lett. 100, 073902 (2008).
9. Mairesse Y. et al., Interferometry of multichannel dynamics in
strong field ionization.
Phys. Rev. Lett. 104, 213601 (2010).
Dr. Olga Smirnova
Junior theory group leader
Max-Born-Institut fuer Nichtlineare Optik und
Kurzzeitspektroskopie
Berlin, Germany
KEYWORDS: ALIGNED MOLECULES; LASER FIELDS; GENERATION; IONIZATION; INTERFERENCE; ELECTRONS; PULSES.