| In this thesis, we present work on coherent control of multilevel quantum systems in the strong field limit using shaped ultrafast laser pulses. In recent years there have been numerous multiphoton absorption experiments in two, three, and four-level atomic/molecular systems and many are performed in the limit of weak fields where perturbation theory is valid. Here, we describe a series of experiments aimed at exploring and understanding multiphoton transitions when the exciting field is strong and perturbation theory breaks down. Our approach to strong field control utilizes both parameterized scans of various pulse shapes and closed-loop learning control to identify a pulse shape that is optimal for populating a target quantum state. With this we will highlight the difference between sequential population transfer and adiabatic rapid passage in multilevel systems with multiphoton coupling between levels. Additionally, we examine strong field control of a four-level atomic interferometer and show how interference in a target state changes from resonant pathways in the frequency domain to time-domain interference via a singe path.;Further, we use shaped femtosecond pulses to demonstrate a phenomenon in which a three-level atom becomes a modulator of an ultrafast pulse. The results are based on a pump-probe scheme that is very similar to Electromagnetically Induced Transparency (EIT). Important dynamics associated with a time-dependent coupling field are examined. Lastly, we extend previous work on two-photon driven superfluorescence from a shaped ultrafast drive laser and show how stimulated emission near threshold can turn modest coherent control yields into essentially perfect discrimination between systems where a control factor of about 104 is achieved between atomic and molecular species. |
