Theoretical Study On Controlling The Orientation Of NaI Molecules Using Ultrashort Laser Pulse

The orientation and alignment of molecules are one of important researches in the study of molecular reaction dynamics.With the development of modern laser technology,Researchers can use various laser technologies to control the alignment and orientation of molecules.This thesis mainly uses the time-dependent quantum wave packet theory to theoretically study the use of ultrashort laser pulse to induce the orientation dynamics of NaI molecules.Taking the NaI molecule as an example,the theoretical scheme of using few-cycle terahertz pulse and half-cycle terahertz pulse to induce the orientation of NaI molecules are studied.The major achievements are as follows:(1)A method of using few-cycle terahertz pulse to control the orientation of the NaI molecule has been proposed.The time-dependent quantum wave packet theory is used to accurately solve the time-dependent Schrodinger equation including vibrational and rotational degrees of freedom.By optimizing the parameters of the few-cycle terahertz pulse,the maximum orientation value of 0.824 can be reached at E0=2.4×108W/cm2,?=0.1THz,?=0.Changing the carrier envelope phase(CEP)of the few-cycle terahertz pulse can effectively enhance the molecular orientation.When the center frequency is in the low frequency region,more rotational dynamics are excited.Choosing a proper center frequency can get a better orientation effect.In addition,the electric field amplitude of the few-cycle terahertz pulse also has a greater influence on the molecular orientation.When E0=2.4×108W/cm2,the orientation takes the maximum value,and the effective duration of the maximum orientation is 6.14 ps.Numerical calculation results show that our proposed scheme can effectively control the orientation of the NaI molecule.(2)The usage of half-cycle terahertz pulse to induce the orientation of the NaI molecule is studied.We discuss the influence of the CEP of the half-cycle terahertz pulse on the field-free orientation of the NaI molecule.When the CEP of half-cycle terahertz pulse?=0.53?,the laser pulse presents asymmetry structure,and a larger orientation value of 0.819 is obtained.We also investigated the influence of electric field amplitude on the orientation of the Nal molecule when CEP is 0 and 0.55? respectively.At E0=3.9×108V/cm,the maximum orientation value is obtained for both CEPs.The maximum effective orientation duration of the NaI molecule can reach 24.71 ps at E0=3.9×108V/cm and ?=0.557?.Therefore,using half-cycle terahertz pulse to induce the orientation of NaI molecules is an effective theoretical solution.