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Tuesday, 31 July 2012

Malte: Strong field quantum control in CO2 in (1+2+3) steps

The polarisation dependence of double ionisation in CO2 and dissociative excitation of the parent ion
has been investigated experimentally via laser induced impulsive alignment. For the ?first time, the
recollision contribution to these channels is identifi?ed unambiguously and resolved angularly. This
is achieved by employing an elliptically polarised probe pulse, which maintains a main polarisation
direction while switching of? recollision. It was found that tunnel-ionisation from lower lying orbitals
in the neutral and thus higher lying excited states in the parent ion are involved in all of the investigated
processes, even at relatively low intensities. While CO+ is formed almost exclusively via tunnel ionisation from HOMO-2 followed by strong ?field excitation, recollision was found to be a signi?cant channel for O+ production. A strong polarisation dependence in both channels enables varying the associated branching ratios and demonstrates the possibility of strong fi?eld quantum control via the laser polarisation.

Tuesday, 10 July 2012

Zara: Coupling between energy and phase in hollow-core fiber based f-to-2f interferometers

Journal club about the paper:

"Coupling between energy and phase in hollow-core fiber based f-to-2f interferometers "

also read:
"Determining the phase-energy coupling coefficient in carrier-envelope phase measurements"

Tuesday, 3 July 2012

Bridgette: Laser Enabled Auger Decay in Atoms and Molecules: Probing Electron Correlation in Inner-valence ionised States

Auger type decay processes play a fundamental role in atomic/molecular spectroscopy, sur-
face analysis, radiation damage, etc. These transitions can be viewed as consisting of two steps.
Firstly, a high energy photon produces a hole in an inner electronic shell, emitting a photoelec-
tron with kinetic energy dependent on the incident photon. Then the hole is lled by a valence
electron and a second valence electron is emitted with energy dependent on the energy levels of
the singly and doubly charged ions and not the incident photon energy. Auger decay processes
are considered to be an important manifestation of electron correlation as they are only possible
because of electron-electron interactions.

Recently, Murnane and Kapteyn [1] have investigated Laser-Enabled Auger Decay (LEAD)
in the multi-photon regime for vacancies that are not energetic enough to undergo the normal
Auger decay. Here we show that if considered in the single-photon regime, the LEAD process
provides a valuable insight into electron correlation in the inner valence ionised states. Firstly,
we analyse the single photon LEAD for the 2s-ionised state in Ne . A detailed investigation of
the mechanism of this single-photon LEAD process reveals that it is only possible because the
initial 2s-1 one-hole state contains con gurations of the type two holes and an electron excited
to a high-energy orbital. The cross-section of the single-photon LEAD process becomes a direct
measure of this con guration mixing. We use the rst-principles algebraic diagrammatic con-
struction (ADC) scheme and the Stieltjes imaging technique[2] to evaluate the single-photon
LEAD cross-sections in ns-ionised states of Ne and Ar. The correlation in the inner valence
ionised states of trans-1,3 Butadiene are investigated as they are an example of a molecule with
strong con guration mixing resulting in the breakdown of the molecular orbital (MO) picture
of ionisation[3]. We show that the breakdown of the MO picture leads to a dramatic increase
of the single-photon LEAD cross-section relative to the atomic case. Finally, we propose that
single photon LEAD can be a sensitive experimental probe for the attosecond hole migration
triggered by the MO breakdown.

1 P. Ranitovic, X. M. Tong, C. W. Hogle, X. Zhou, Y. Liu, N. Toshima, M. M. Murnane,
H. C. Kapteyn, Phys. Rev. Lett. 106, 053002 (2011).
2 See e.g. K. Gokhberg, V. Vysotskiy, L. S. Cederbaum, L. Storchi, F. Tarantelli, V. Averbukh,
J. Chem. Phys. 130, 064104 (2009).
3 L. S. Cederbaum, W. Domcke, J. Schirmer, W. Von Niessen, Adv. Chem. Phys. 65, 115