Ultrafast Quantum Coherent Control Of Molecular Dynamics

The ultra-short pulse duration and the ultra-high laser intensity are the main feature of the femtosecond laser pulse. The former allows one to observe the molecular dynamics behavior in femtosecond time scale and reveals the nature of the photophysical and photochemical processes, while the latter can greatly change the molecular structure behavior, such as arrangement and orientation, isomerizaiton, ionization, dissociation, coulomb explosion and so on. Therefore, employing the femtosecond laser pulse as a tool to measure and control the molecular photophysical and photochemical processes has become a hot topic in recent years. With the advent of femtosecond pulse shaping technique, it provided a new experimental method to study the molecular-laser interaction, and has been proved to be an ideal tool to manipulate the molecular dynamics behavior induced by the femtosecond laser pulse. In this thesis, we focused on studying the control of molecular multi-photon absorption, molecular arrangement and orientation, terahertz radiation generation and coherent anti-Stokes Raman scattering, and the details are presented as follow:1) The development of the femtosecond laser technology and the main physical phenomena of the interfaction of molecule and femtosecond laser were briefly reviewed, and the principle of coherent control strategy and the physical basis of femtosecond pulse shaping technique were simply introduced.2) In the control of the molecular multi-photon absorption, we showed that the two-photon fluorescence intensity in coumarin480can be effectively suppressed by varying the laser polarization and phase; we studied the control of the resonance-mediated two-photon absorption in the glass sample doped with Er3+by a π phase modulation, and showed that the laser repetition rate will affect the control efficiency; we also showed that the single-and two-photon fluorescence intensity in Er3+can be effectively suppressed and enhanced by a π or square phase modulation.3) In the control of the molecular arrangement and orientation, we proposed a scheme to achieve the field-free molecular orientation around the half rotational periods with the combination of single-and dual-color laser pulses, and discussed the effect of laser intensity and pulse duration of the single-color laser pulse on the molecular orientation degree induced by the dual-color laser pulse; we also showed that the field-free molecular orientation induced by a single dual-color laser pulse can be significantly enhanced by separating it into two time-delayed dual-color sub-pulses, and found that the maximum enhancement of the molecular orientation is achieved with their intensity ratio of1:2.4) In the control of the terahertz radiation generation, we established the transient photoncurrent model to study terahertz radiation generation in molecular-laser interaction, and discussed the effect of the relative phase, the central frequency and the total intensity of the dual-color laser pulse on the terahertz radiation generation; we also analyzed the dependence of optimal intensity ratio of the dual-color laser pulse on the maximal terahertz radiation generation for different laser intensites, and explained the physical mechanism based on our transition photocurrent model. Furthermore, we obtained the terahertz pulse train via optical rectification in ZnTe crystal by the shaped femtosecond laser pulses with a square phase modulation.5) In the control of the coherent anti-Stokes Raman scatting (CARS), we proposed a feasible scheme to achieve a high-resolution coherent anti-Stokes Raman scatting spctra by shaping the femtosecond laser pulse with a rectangular amplitude modulation, and showed that the fine energy-level diagram of the molecule can be obtained by observing these holes in the CARS spectrum induced by the shaped femtosecond laser pulse.