Thomas: Theoretical study of photoelectron angular distributions in single-photon ionization of aligned N2 and CO2

Phys. Rev. A 81, 033421 (2010)  http://pra.aps.org/abstract/PRA/v81/i3/e033421

Theoretical study of photoelectron angular distributions in single-photon ionization of aligned N2 and CO2

the angular distribution of the momenta of XUV ionised electrons is going to bare much relevance to the XUV initiated HHG experiment which is being constucted in the basement at the moment. i would like to take this journal club as an opportunity to involve both theoreticians and experimentalists in a discussion about the differing properties of XUV and tunnel ionised electrons and how we can use these properties to our advantage. i would also like to discuss the possibilities of writing a ral proposal for attempting to measure the ion state resolved angular distribution of the emitted electrons. for experimentalists all that theory has been prompted by J. Phys. Chem. A2008, 112, 9382–9386.

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.

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 "
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-14-12082


also read:
"Determining the phase-energy coupling coefficient in carrier-envelope phase measurements"
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-32-7-796

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
(1986).

Amelle: Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy

Conical Intersection Dynamics in NO₂ Probed by Homodyne High-Harmonic Spectroscopy

1. H. J. Wörner¹,²,*, 
2. J. B. Bertrand¹, 
3. B. Fabre³, 
4. J. Higuet³, 
5. H. Ruf³, 
6. A. Dubrouil³, 
7. S. Patchkovskii¹, 
8. M. Spanner¹,
9. Y. Mairesse³, 
10. V. Blanchet⁴, 
11. E. Mével³, 
12. E. Constant³, 
13. P. B. Corkum¹, 
14. D. M. Villeneuve¹

+Author Affiliations

1. ¹Joint Laboratory for Attosecond Science, National Research Council of Canada and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6.
2. ²Laboratorium für Physikalische Chemie, Eidgenössische Technische Hochschule Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
3. ³Centre Lasers Intenses et Applications, Université de Bordeaux, CEA, CNRS, UMR5107, 351 Cours de la Libération, 33405 Talence, France.
4. ⁴Laboratoire Collisions Agrégats Réactivité (IRSAMC), UPS, Université de Toulouse, F-31062 Toulouse, France and CNRS, UMR 5589, F-31062 Toulouse, France

1. ↵*To whom correspondence should be addressed. E-mail: woerner@phys.chem.ethz.ch

ABSTRACT

Conical intersections play a crucial role in the chemistry of most polyatomic molecules, ranging from the simplest bimolecular reactions to the photostability of DNA. The real-time study of the associated electronic dynamics poses a major challenge to the latest techniques of ultrafast measurement. We show that high-harmonic spectroscopy reveals oscillations in the electronic character that occur in nitrogen dioxide when a photoexcited wave packet crosses a conical intersection. At longer delays, we observe the onset of statistical dissociation dynamics. The present results demonstrate that high-harmonic spectroscopy could become a powerful tool to highlight electronic dynamics occurring along nonadiabatic chemical reaction pathways.

http://www.sciencemag.org/content/334/6053/208

Thomas Gaumnitz: Chirped Auger emission at FLASH reveals long-range electron correlation

The energy of Auger electrons, i.e. secondary electrons emitted after a non-radiative decay of a deeply bound electronic core-hole, is an intrinsic property of the electronic structure of the excited atom and does not directly rely on the energy of the exciting photon, electron or ion. The electron emission is not mono-energetic, though; the fast - attosecond to femtosecond - decay times imply corresponding spectral widths in a range of a few tens of meV to a few eV. This time-energy correspondence suggests a uniform distribution of all energy components over time. In this work, we demonstrate that under spectroscopically relevant conditions, this presumption is wrong. Instead, our time-resolved experiments show evidence of an energetic chirp, i.e. a pronounced time-dependent variation of the Auger-electrons´ kinetic energy. It appears as a consequence of the correlated motion of both photo- and Auger electrons in the Coulomb field of the remaining ion. While the underlying mechanism - also known as ‘post-collision interaction’ (PCI) - has extensively been discussed in the literature, no attention has so far been paid to the consequence of the effect for the temporal properties of the escaping electron wave packets. We visualize this temporal energy variation by superimposing 13.5nm XUV pulses from FLASH with the oscillating electric field of a strong terahertz (THz) wave from the FLASH THz undulator in a xenon gas-target. Significantly, modified widths of kinetic energy spectra for opposite field gradients clearly indicate a chirp (see Fig. 1).

Figure 1: Kinetic energy spectra of xenon Auger lines formed after absorption of XUV photons in the presence of a THz field. The modified widths of the Auger lines for opposite field gradients indicate an energy chirp.


The experiments have been confirmed in the laboratory where a high harmonics XUV source and a laser based THz source were employed. The observed spectral modulations are reproduced with semi-classical as well as  quantum simulations, and are explained by an analytical model, which includes PCI in the presence of a time-dependent streaking field.

Stefan: High-energy density laboratory astrophysics studies of accretion shocks in magnetic cataclysmic variables

In this paper we present the experimental simulation of the accretion column in magnetic cataclysmic variables using high-power lasers. With an appropriate target and adapted diagnostics, the dynamics and the main physical properties of laboratory accreting plasma have been characterised. The results obtained validate the experimental design and prove the formation of a reverse shock which compresses and heats the accreting plasma. The data are compared to 2D radiation hydrodynamic simulations, confirming the experimental scenario.

http://www.sciencedirect.com/science/article/pii/S1574181811000875