Molecular Orientation In Electrostatic/Laser Field And Stark Deceleration Assisted By Orientation

Molecular orientation is the behavior that the molecular permanent dipole moment points to a specific direction in a laboratory frame when the molecules interact with external fields. With the development of molecular cooling, more and more researchers engaged in the study of the molecular orientation and proposed various methods, such as hexapole field state selector, brute force method, combined fields molecular orientation, and laser field techniques. Compared with isotropic molecules, oriented molecules are more important for the studies of the chemical reaction dynamics, pendular spectroscopy, photoelectron imaging and other relations.This thesis firstly proposes a method by switching an electrostatic field to orient molecules with small rotational constant. The nonadiabatic molecular orientation can be realized when the switching time of the electrostatic field is similar to the molecular rotational period, and the field-free molecular orientation can provide more opportunities for further applications. Secondly, the method of combined fields to orient molecules with small permanent dipole moment is proposed. This method is based on the coupling of the electrostatic and laser fields because the molecular alignment induced by the laser field can be converted to the molecular orientation, and even in a weak electrostatic field condition, a large degree of the molecular orientation can be obtained. Thirdly, the thesis studies the enhancement of two non-Gaussian laser fields to the molecular orientation combined with an electrostatic field. As to a slow turn-on and rapid turn-off laser field, the molecular orientation can obtain the maximal degree at the peak intensity of the laser pulse and reappeared periodically after the laser field turns off. The molecular orientation can also be enhanced by the cubic phase shaped femtosecond laser pulse in the combined fields, which is mainly due to the special rising edge of the shaped pulse. Finally, the molecular orientation of combined fields is applied in the molecular Stark deceleration. The preliminary analysis indicates that the linearly polarized laser field can enhance the efficiency of molecular deceleration obviously.A summary and an outlook of this work are stated at the end of this thesis.