Steering Population Transfer Of Diatomic Molecules By An Ultrashort Pulse Train

In recent years,simulating the dynamic processes of atoms and molecules by ultrashort pulses has become a hot research filed,as the realization of ultrashort pulses,and the population transfer is an important research topic in this field.In the paper,the wave functions are obtained by solving the time-dependent quantum wave packet,and the Na₂ molecule is numerically simulated via the adiabatic passage by light-induced potentials,and we finally investigate the population transfer of Na₂ molecules in two-level systems and three-level systems with ultrashort pulse trains.In the two-level system,we steer the population transfer of the Na₂ molecules by an ultrashort pulse train,and study the influences of the pulse sequence and pulse widths on the population transfer.In the three-level system,the population transfer of the Na₂ molecules is controlled by two time-delayed ultrashort pulse trains,and we investigate the impact of the pulse pairs,the pulse widths,the time delay,the repetition period of probe pulse train,and the relative phase on the population transfer efficiency.In addition,we study the population transfer efficiency with different pulse widths of the two pulse trains.T he corresponding calculations and theoretical analysis are given.The results show that the ultrashort pulse train is an efficient and feasible solution for controlling population transfer,and the population transfer can be steered by laser parameters.In a large range of laser parameters,the pulse pairs and the pulse widths of the pulse trains have great influences on the population transfer efficiency.And with the increase of the pulse pairs and the pulse widths,the population transfer can be efficiently achieved at lower intensities.By optimizing the time delay between the two pulse trains,the population transfer efficiency is increased,when the time delayt?28?3.25T,the population transfer efficiency reaches a maximum.The process of the population transfer depends crucially on the repetition periods of probe pulse train,the larger the repetition periods are,the lager intensities are needed to achieve the complete population transfer because of the weaker coupling between the adjacent pulses.The relative phase and the unequal pulse widths will also affect the population transfer efficiency.If the relative phase ??? or the pulse widths of the two pulse trains are not equal,the population cannot be effectively transferred to the target state.Therefore,in the simulation calculations,we always choose the relative phase ???=0 and the same pulse widths of the two pulse trains for an efficient population transfer.The efficient population transfer at lower intensities can be realized by an ultrashort pulse train.Compared with a single laser pulse,this is a scheme that can be used for a lager laser parameter range and is more conducive to experimental applications.