Coherent control and its applications in molecular recognition

The fundamental design of this dissertation involves the use of the laser as a tool to recognize molecules. The work presented here has relevance to a variety of fields, including nonlinear optics and spectroscopy, coherent control of laser-matter interactions, biomedical imaging and analytical chemistry. My work involves a series of experiments utilizing a femtosecond laser system and an instrument known as a pulse shaper. It entails new applications of coherent laser control, where tailoring the shape of laser pulses by phase modulation causes changes in the impact of the excitation field on different processes such as multiphoton excitation and photoionization.; The application of coherent control methods to biomedical imaging hinges on the possibility that phase-modulated femtosecond laser pulses can propagate through biological tissue. The approach used in this dissertation corrects spectral phase distortions introduced by imaging optics, maintains laser pulse optimization throughout the experiment and initiates phase manipulation in order to gain selectivity that is analogous to that which can be achieved by tuning a longer laser pulse. This capability is used to demonstrate functional imaging by selective two-photon excitation. Furthermore, phase modulation is exploited as a means to curtail the damaging effects of multiphoton excitation in biomedical applications, thus increasing the prospect for cellular and molecular identification, including cancer detection.; The use of phase modulation of femtosecond laser pulses is also shown here as a means to recognize isomeric molecules based on their ionization and fragmentation patterns. The selectivity that is attainable with shaped pulse technology is coupled with the inherent sensitivity of mass spectrometry to not only distinguish between isomers, but to quantify them in isomeric mixtures. Although chemical identification is carried out quite efficiently with standard mass spectrometry, the dilemma involving the identification of isomeric compounds is addressed here by laser control. The environmental, pharmaceutical and analytical chemistry fields could stand to benefit from this "customized" mass spectrometry approach. Additionally, the concept of utilizing chiral femtosecond pulses as a tool for enantiomeric resolution is introduced.