Theoretical Study Of Orientation And Ionization Of Diatomic Molecules Controlled By Laser Pulses

The research object of molecular reaction dynamics is atomic and molecular dynamics processes at micro-level,which covers a wide range of disciplines.The new energy development,atmospheric and environmental pollution,catalytic reaction in chemistry,the design of functional molecules,bioluminescence and its mechanisms are closely related to molecular reaction dynamics.The molecular orientation and photoionization dynamics controlled by laser pulses have been research hotspots in molecular reaction dynamics.As the laser technology develops,researchers have put forward many theoretical and experimental schemes to realize molecular orientation and photoionization.Among them,the application of shaped laser pulse in molecular orientation and photoionization has also attracted much attention.The following describes the main research works of this paper:(1)Using density matrix theory,we propose four laser field schemes,numerically simulate the orientation of LiH molecules induced by laser pulses with two different envelope shapes.The results show that the envelope shape of the terahertz single-cycle laser pulse(SCP)has significant effects on molecular orientation degree and duration.When a SCP with adjusted laser field amplitude and carrier envelope phase is used to steer the molecular orientation,a larger orientation degree can be obtained by the Gaussian-shaped SCP,while a longer orientation duration can be realized by the sin~2-shaped SCP.When combined with the two-color femtosecond laser pulse,the sin~2-shaped SCP is better than Gaussian-shaped SCP,either in improving orientation degree and duration or in stability and controllability shown with increasing temperature.The optimal molecular orientation can be realized under the combination of the two-color femtosecond laser pulse and sin~2-shaped SCP which has the appropriate delay time:the maximal orientation degrees are 0.801 at T=0 K and 0.450 at T=20 K;the maximal orientation duration is 31.3%of the rotational period at T=0 K.(2)Basing on pump-probe technology,we propose a theoretical scheme of using the pump pulse and shaped probe pulse(its envelope has plateau time)to control the photoionization process of NaK molecules.For convenience,we call this shaped probe pulse as the probe pulse with plateau time.The effects of plateau time,duration and laser amplitude of probe pulse on ionization probability and photoelectron spectrum are discussed respectively.In addition,the delay time between pump and probe pulses also has a certain effect on the ionization probability and photoelectron spectrum.The scheme can effectively increase the ionization probability with the maximum ionization probability of 0.889,and enhance the intensity of photoelectron spectrum.