Abstract:

Femtosecond technology has enabled great advances in the field of observing and manipulating molecular processes on ultrafast time scales. There are now countless examples of successful quantum control applications in the laboratory, and the field is continuing to spread out into new applications in chemistry and biology.

This thesis introduces an application of quantum control to the experimental detection and identification of molecules, based on the theoretical work on the concept of optimal dynamic detection (ODD). In ODD the time dependent molecular Hamiltonian is used as the distinguishing factor between quantum systems. This approach offers a new way to distinguish very similar molecules, since even small dynamic differences can be optimally exploited to result in a distinguishable dynamic system response. The concept was implemented with the two very similar molecules riboflavin (RBF) and flavin-mononucleotide (FMN) in solution. The control field is produced by a combination of a shaped UV pulse and overlapping unshaped IR pulse centered at 400 and 800 nm respectively. The system response is the depleted fluorescence centered at 530 nm. The depleted fluorescence signal can be selectively manipulated by different optimized control pulse shapes. The pulse shapes are found by a closed-loop search strategy employing a genetic algorithm (GA).

With discriminating control pulses and the variable time-delay of the IR pulse it was possible to observe the time dependence of differential coherent control on the two flavin molecules produced by the optimized control fields. Furthermore, the discriminating pulses were used to determine the concentration of both flavin molecules in a mixture, which would be impossible with conventional optical spectroscopy, due to the high similarity of the absorption and emission spectra. The experiments represent a proof-of-principle that is challenging, but at the same time promising for the future of this approach.

Other aspects of the thesis include the development of an acousto-optical based pulse shaper in the UV, and a technique to monitor the spectral phase stability of the laser system, which is essential for highly phase-sensitive quantum control applications. Furthermore, the algorithms used in some applications have been compared in terms of performance, the possibility of normalizing multi-photon processes was explored and finally, robustness was explicitly incorporated into the closed-loop search criteria, leading to more stable control solutions in the laboratory.