Probing Electron Correlation on the Attosecond Timescale

Abstract: This thesis describes how photoemission stimulated by an attosecond pulse train (APT) can be used to extract information on electron correlation in simple quantum systems such as atoms. The emission of the electron by an APT induces a reorganization of the electrons remaining in the ion core. This reorganization causes a change in the trajectory of the emitted electron. An infrared (IR) field is used to probe the delay induced by the ion's potential and the electron's reorganization via an interferometric technique. This thesis focuses on how the delay can be measured in various atomic systems and on how physical information about the electron correlations may be extracted. The first chapter of the thesis presents a brief overview of the attosecond techniques which have been used. It describes how the APTs are generated via a non-linear process called High Order Harmonic Generation (HHG), and how these pulses are characterized temporally using the so-called RABITT technique (reconstruction of attosecond beating by interference in a two-photon transitions). Finally, the different parts of the experimental set-up are described: the laser system, the APT generation chamber and the different detectors. The second part focuses on a theoretical description of the photo-ionization process. The delays measured in the RABITT technique are derived and interpreted using perturbation theory. The influence of electron correlation on the delay is then investigated in the case of a Fano resonance and in double photoionization. The third chapter describes experimental results obtained in various atomic systems. A comparison is made between the photoemission delays from the outer valence shells of argon, neon, and helium; between the inner and outer valence shells of argon; between the on-resonance and off-resonance delays for argon levels interacting in a Fano resonance; and between the delay induced by single and double photoionization in xenon. The experimental results are compared with calculations using several different atomic codes.