Parametric polarization pulse shaping methods and control of excitation dynamics in ultracold rubidium
Fabian Weise
This work focuses on the developments of ultrafast laser pulse shaping techniques and their application to diatomic molecular systems in order to reveal fundamental effects in light matter interaction. It describes the development of a new pulse shaper consisting of a sequence of four liquid crystal arrays and a polarizer. This pulse shaper is the first non- interferometric setup for unrestricted phase, amplitude, and polarization shaping. Moreover, a parametric encoding of the electrical field was developed which allowed for generating pulse sequences consisting of several sub-pulses. Each sub-pulse can be controlled in its physically apparent parameters: energy, position in time, phase, and chirps as well as state of polarization with ellipticity, orientation, and helicity. The feasibility of the setup is illustrated by systematic variations of single and double pulses, which are experimentally generated and measured. In these series of pulses, one of the pulses parameters is varied while the other parameters are kept constant. This proves the precise control of the pulse shape. Further, more complex pulses are shown to give an impression of the capabilities of this setup in combination with the parameterization. For some fields of application, it could be desirable to guide the phase, amplitude and polarization shaped pulses through an optical fiber. For example, life science could benefit from shaped pulses in the area of imaging and photodynamic therapy. In order to make the shaped pulses available at the distal end of an optical fiber, the effects of the fiber have to be compensated. In this work, the generation of phase, amplitude, and polarization shaped pulses after transmission trough an optical fiber is presented. This is demonstrated for two types of optical fibers – a standard single-mode fiber and a microstructured hollow core photonic crystal fiber. The procedure for the determined generation of parametrically shaped pulses differs for both types of optical fibers. The capabilities of parametrically shaped pulse sequences are – again – illustrated by a series of example pulses. The parametrically shaped pulses transmitted through the hollow core fiber are implemented in a coherent control experiment. For this purpose, the potassium dimer produced in a molecular beam serves as a test system. The multi-photon ionization is studied by a closed feedback loop optimization and shaper-assisted pump-probe spectroscopy. These experiments revealed the excitation path including the vibrational dynamics in the first and second excited state. Further, the relevance of the polarization control in the excitation process is highlighted. Moreover, coherent control techniques are applied to investigate the interaction of shaped femtosecond laser pulses with ultracold atoms and molecules. The focus of these experiments is the control of the photoassociation of a colliding atom pair to a bound molecule. This process is investigated using two-color pump-probe spectroscopy. The molecular transients are compared to theoretical calculations. The analysis of this data reveals the interaction process which is discussed in the time and frequency domain. In a second experiment, the multi-photon ionization of ultracold rubidium dimers is optimized in a closed feedback loop. In this optimization, a parameterization in the frequency domain is employed which extracts the relevant transition frequencies. In combination with a complementary experiment the excitation pathway was revealed.
•Jan 1, 2010•0 citations