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Abstract:
This thesis deals with the coherent control of the multiphoton ionization (MPI) of 6Li initially in the ground state by an ultrafast bichromatic laser field consisting of 780/390 nm radiation.
We demonstrate a left-right asymmetry control of the photoelectron angular distributions (PADs) of the main photoline with respect to a plane orthogonal to the laser polarization direction by varying the relative phase between the fundamental and secondharmonic (SH) pulses with subwavelength accuracy. Good agreement is found between the measurements and calculations at the appropriate absolute intensities of the two harmonics.
We also study the photoelectron spectra of the main photoline and the first Above- Threshold Ionization (ATI) photoline resulting from the ionization with temporally overlapping and non-overlapping two-color pulses. For this, we perform a delay scan between the two harmonics, which extends between the SH pulse advancing the fundamental pulse and vice versa with a delay step size of 3.36 times the optical period of the fundamental light of 2.6 fs. This reveals delay-dependent features of the photoelectron spectra. To several of them, we can attribute a dominant partial-wave character contributing to the interference pattern of the photoelectron spectrum. Since several MPI pathways exhibit intermediate resonances with long-living Rydberg states, we are also interested in whether the interaction order of the two harmonics has an effect on the photoelectron spectra in the case of both temporally overlapping and non-overlapping pulses. Here, we generally do not find overall agreement with our expectations according to the ionization pathways or the theoretical predictions, except for a few selected features.
All the experimental results are compared with calculations based on the solution of the time-dependent Schrödinger equation in the single-active electron approximation. These calculations were performed by Prof. Klaus Bartschat (Drake University, Des Moines, Iowa, USA).
