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Abstract

This thesis explores the photoionization dynamics in atoms using phase-locked two-color pulses, a high-frequency extreme ultraviolet (XUV) and a low-frequency infrared (IR) pulse, with the focus on extending the understanding of the interaction between the IR field and the outgoing electrons. To achieve this, a multi-sideband RABBITT (reconstruction of attosecond beating by two-photon transitions) technique was developed. An attosecond-beamline is constructed which includes a femtosecond IR laser, a highorder harmonic generation module for producing XUV pulses, an interferometer, and a reaction microscope. The setup enables angle-differential and coincidence measurements of photoionization and photodissociation processes with attosecond precision in a pumpprobe configuration. The XUV pulse initiates the photoionization process, and the resulting photoelectron interacts with the IR field, exchanging several photons as it escapes the ionic potential. Depending on the combination of XUV and IR photon exchanges, and/or the angularmomentum channels involved, the photoelectrons can reach the same state via different quantum paths. The resulting signal in the photoelectron spectrum is the coherent superposition of all these distinct quantum paths, which oscillates as the temporal delay between the XUV and IR pulses varies, creating an interferogram. The recorded angle-differential photoelectron interferograms in helium and argon enable the extraction of information on the relative amplitudes and phases of the dipole transition matrix elements associated with the many-order continuum-continuum transitions. We compare the experimental results with ab initio theoretical calculations based on solving the time-dependent Schrodinger equation and use a few-level-model simulation to ¨ understand the impact of different parameters on the photoelectron interferogram and the extracted information.