Coherent control of resonant nonlinear interactions in ultrafast solution-phase photochemistry

Coherent control extends the study of photochemical reactions from observation to active control of molecular dynamics and reaction yield. The goal of this dissertation is to identify ultrafast laser pulses that exploit coherent light-molecule interactions in solution-phase photochemical systems to drive targeted chemical behavior. Adaptive feedback control is used to find optimal electric fields. Optical control parameters are derived by analyzing both the form of the optimal pulse and trends in the optimization search.; This dissertation identifies ultrafast pulses that control the photoisomerization of 1,3-cyclohexadiene (CHD) in solution. CHD undergoes an electrocyclic ring-opening reaction to form 1,3,5-cis-hexatriene (Z-HT) following the absorption of ultraviolet light. The reaction is mediated by conical intersections connecting an optically dark intermediate excited state with the ground electronic state. Adaptive feedback control is used to find an optimal electric field for multiphoton excitation of CHD with phase-shaped 800 nm pulses. The optimal negatively chirped pulses produced twice as much Z-HT as the transform-limited pulse, despite the intensity dependence intrinsic to multiphoton absorption. A mechanism is proposed through which impulsive excitation of ground state vibrational modes assists wave packet localization on the optically dark excited state. Challenges to coherent control in the condensed phase are discussed, including ultrafast dissipation, ultrafast dephasing, and competing nonlinear interactions with solvent molecules.; Adaptive feedback control is also used to control vibrational coherences and population dynamics in laser dyes in solution. Ultrafast visible pulses are shaped so that the spectral phase follows wave packet motion on the excited-state potential energy surface of the dye. Earlier studies on the laser dye LD690 are extended to investigate the molecular response under blue-detuned pulses and nonlinearly chirped pulses. With the aid of adaptive feedback control experiments, it is shown that detuned pulses with positive linear chirp preferentially generate excited-state vibrational coherences through resonant two-photon absorption. These results suggest new experimental schemes for the coherent control of excited-state wave packets in chemically reactive systems.