Attosecond Electron Wave Packet Interferences

Abstract: Attosecond pulses offer a new route to produce temporally localized electron wave packets (EWPs) that can easily be tailored by altering the properties of the attosecond pulses. In this thesis we will present different experiments, supported by theory, where attosecond EWPs are created in presence of a strong infrared (IR) field. By tuning the central frequency of the attosecond pulses and/or changing the target gas, the initial energy of the wave packets is set to be either above, or below the ionization potential. In a first set of experiments, trains of free attosecond EWPs separated by half a laser period are created by single photon ionization. Depending on the timing of ionization compared to the external IR field, a shear and/or a phase difference between the consecutive EWPs is induced. Because the EWPs are created coherently, interferences depending on their phase difference will occur. The analysis of the interferograms enables to retrieve information about the phase of the EWPs. In a second set of experiments, bound electron wave packets are created below the ionization potential of a target gas. In the case of a train of bound EWPs, we find that the ionization is greatly enhanced by the presence of the infrared laser field and that this enhancement strongly depends on the timing between the attosecond pulses and the laser field. We show that this effect can be attributed to interference between consecutive wave packets. In the case of a single bound EWP, we are able to probe its time evolution with a short IR pulse.