"The goal of my dissertation work was to study nonlinear laser-matter interactions and to obtain a better understanding of the various processes occurring during these interactions. Advances in femtosecond laser technology have become widely adopted in a nonlinear laser spectroscopy and photochemistry. With the extreme temporal and spatial confinements it becomes possible to induce nonlinear responses of the material and to study them with high temporal resolution. The complexity of the medium response to the excitation field necessitates control the excitation process in order to figure out its origin, for example, inter-or intra-molecular dynamics. Therefore, over the last two decades, femtosecond pulse-shaping methods have been developed to reach an unprecedented level of control over the ultrafast laser waveforms where spectral amplitude and phase can be specified in accordance to expected response. The characterization and tailoring of femtosecond pulses was central for my research projects. Experimental results are presented in three chapters. Chapter 2 focuses on two topics: (1) generation of flat top temporal shape pulses with sharp on and off fronts and no loss of spectral bandwidth for particular spectroscopic applications; (2) characterization of noisy ultrafast laser sources, namely, pulse-to-pulse stability, caused by spectral phase or amplitude noise. Chapter 3 presents the fundamentals of Raman spectroscopy and development of a non-contact no-reagents system operating in the eye-safe 1600-1800 nm wavelength range for standoff trace detection of explosives and high-speed imaging, 0.06 ms per pixel. The system used in this project is based on the latest ideas in coherent Raman spectroscopy and technologies to perform selective coherent vibrational excitation of a particular chemical compound with sensitivity of sub-mg/cm2 . Chapter 4 describes time-resolved transition-state spectroscopy of sodium iodide (NaI) by taking advantage of modern lasers and pulse shaping to better map the low-lying electronic states. High-level ab initio multi-reference configuration interaction and density matrix calculations were used to simulate time dependent wave packet dynamics of NaI pumped to the A 0 + state. The results in this dissertation demonstrate the utility of tailored ultrafast laser pulses. Using advanced laser technology and photonic control methods we gain a better understanding of time-resolved dynamics of a chemical reaction and nonlinear spectroscopy. During my work I got to develop new approaches for characterization of the laser source itself and how to tailor it using pulse shaping. The work presented here should serve future studies on nonlinear laser-matter interactions with a novel photonic control schemes."--Pages ii-iii.
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