STSM by Eva Lindroth, Stockholm University (SE)  with Fernando Martín, Universidad Autonoma de Madrid (ES)
On December 13th, 2015 (6 days)

Fully-correlated transition matrix elements for the description of atomic attosecond experiments

During the last decades laser source  technology  has seen substantial  progress.  In the spectral range from  extreme ultraviolet to soft X-rays
highly coherent, short pulsed, radiation, can now give access to  time resolved information  of elementary charge-transfer processes in atomic and molecular systems.  An accurate theoretical description, using either ab-initio methods or models, is seminal for the understanding of   the features appearing on the attosecond time scale, and for the interpretation of the sometimes cumbersome results obtained in experiments.

Angularly-resolved experiments on rare gases with the RABBITT -technique  (reconstruction of attosecond beating by interference of two-photon transitions)  have recently been performed by the group of Ursula Keller at ETH, in Zürich,   demonstrating an angular anisotropy
of the photoionization delay.  This anisotropy  is clearly seen even in  helium where both the initial atomic state and the final ionic state are isotropic, and is there solely due to the second photon being exchanged in the RABBITT process, allowing for final quantum states with two
different symmetries.  The groups in Madrid and Stockholm have used different approaches, both ab initio and models, to account for the anisotropy.
In the next step also the results in neon and argon have to be explained and here we want to combine the approaches and use transition matrix elements calculated in Stockholm in the model that has been developed in Madrid

The helium results are submitted as a joint experimental and theory paper, and the calculations  on argon and neon  started during the STSM.  The results will be published later this year.
allsidebands_delayFigure caption:
Calculated angular dependence of the photoemission delay in neon for different photoelectron energies. The angle is measured relative the linear polarization axis of the laser field, and the  delay is given relative that in the forward direction. The calculation is done using lowest order perturbation theory for the light-matter interaction and with many-electron effects included at the level of RPAE (random-phase approximation with exchange).

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