Attosecond photoelectron interferometry: from wavepackets to density matrices

Sammanfattning: Through the advent of high-order harmonic generation and attosecond light pulses, photoionization dynamics has been studied on the attosecond time-scale, the intrinsic time-scale of such dynamics. When the electron leaves the atomic potential a phase shift is imprinted on the electron wavefunction. The measurement of this phase, together with amplitude allows us to determine the dynamics that of the photoionization.In this thesis, attosecond (10−18 s) and femtosecond (10−15 s) photoionization dynamics are studied using the photoelectron interferometry technique, Reconstruction of Attosecond Beating By Interference of two-photon Transitions (RABBIT). In RABBIT, the electron wave-packet is interfered with itself, and through this spectral interference, the spectral amplitude and phase can be retrieved.Attosecond time-delay measurements, are performed in argon and xenon where different aspects of electron correlation are investigated. In argon photoionization is studied in the region of the Cooper minumum, where the ionization cross section rapidly decrease. In xenon photoionization is studied across the 4d giant dipole resonance. Resonant dynamics is stud- ied using energy-resolved RABBIT. The studied resonances are the 1s3p, 1s4p, 1s5p (below threshold) and 2s2p (above threshold) in He and 3s−14p (above threshold) in Ar. Most of the measurements in the thesis are angular-integrated.If the photoelectron is prepared as a mixed state, RABBIT is unsuccessful in characterizing the quantum state of the electron, since it cannot be represented as a wavefunction. Therefore a quantum state tomography protocol for photoelectrons (KRAKEN) was developed and tested experimentally in non-resonant ionization of helium, neon and argon. In the case of neon and argon, due to spin-orbit splitting, the entanglement between the photoelectron and ion leads to decoherence induced by incomplete measurements where the state of the ion is not measured.