Molecular Nonadiabatic Alignment And Orientation, And Dissociation/Lonization In Femtosecond Laser

In this thesis, using methyl halide molecules as an example, we perform acombined experimental and theoretical study on static electric field orientation andfemtosecond laser nonadiabatic alignment and orientation of molecules. Theinfluences of orientation and alignment from different rotational states of moleculeshave been discussed. A clear and systematic recognition on molecular rotationaldynamics and its physical mechanism is obtained. We also perform a study onmolecular ionization, dissociation and Coulomb explosion by using aligned molecules.The angular dependent tunneling ionization from precision measurement of differentmolecules in strong laser field (1013-1014W/cm2) provides a direct proof and test fordeveloping theoretical approaches of strong field molecular processes.Polyatomic molecules have complex structure and energy levels, the ionizationand dissociation of polyatomic molecules in intense femtosecond laser field containsthe complexity of quantum states and many-particle correlation, the underlyingmechanisms for strong field phenomena need to be uncovered. New experimentaltechniques are need to develop and more effects are need to consider in theory forperforming a deep research. We develop a molecular orientation manipulation methodbasing on the combination of rotational state selection and femtosecond lasernonadiabatic rotational state excitation. The orientation of rotational state selectedmolecules in static field has been studied, the relation of rotational state on molecularorientation is clarified by comparing the orientation of different molecules. We findthat the orientation of molecules in static electric field is related on the rotational stateat moderate electric field strength. Based on the rotational state selection, thenonresonant rotational state excitation after fs laser excitation is studied, and theinfuence of different rotational states on the non-adiabatic orientation and alignmentof molecules is studied. It is found that the degree of orientation and alignment can be increased by using rotational state selection method. The study of mechanisms ofthese ultrafast laser induced processes provides an elaborate method to precisionmanipulate the orientation and alignment of CH3I and CH3Br molecules, and themaximum degree of orientation...