利用整形激光脉冲控制原子光缔合动力学及碰撞过程中电荷转移
发布时间：2018-12-27 18:50
【摘要】：利用激光脉冲控制原子的光缔合和碰撞过程中的电荷转移是当前原子与分子物理研究领域的两个热点研究方向。本论文在理论上研究了利用整形脉冲激光调控碰撞原子光缔合及电荷转移过程。主要工作概括如下： (1)提出了利用整形脉冲提高超冷原子光缔合几率的理论方案。通过求解两态薛定谔方程,我们发现：具有缓慢打开、迅速关闭特性的激光脉冲在达到峰值强度之后,能够减少激光与分子的能量交换,进而阻止激发电子态的光缔合分子解离回到基电子态的散射态上,达到提高光缔合效率的效果。光缔合几率随着脉冲关闭时间的缩短而增大。在此基础上,还利用整形脉冲链的布居累积效应提高光缔合几率。 (2)从理论上研究了利用调制脉冲来控制超冷原子的光缔合动力学过程。研究结果表明,含时电场的形状和频谱分布对包络相位很敏感。当包络周期大于脉冲的半高全宽时,光谱强度分布可以通过改变包络相位修正。相关振动态的富兰克-康登(Frank-Condon)因子、激光脉冲的频谱强度分布以及激光场的时域不对称性均影响光缔合分子的振动态布居分布和光缔合效率。 (3)从理论上研究了采用三阶相位皮秒脉冲控制超冷原子的光缔合动力学过程。三阶相位脉冲由于延长了时域上的延续时间而增加了脉冲面积,因而增加了光缔合效率。尽管当脉冲面积一定时,三阶相位脉冲的能量较低,但当脉冲面积大于某个值时,却能明显提高光缔合效率。与高斯脉冲相比,三阶相位脉冲无法改变布居的振动态分布范围,因为它们与高斯脉冲的光谱分布相同。 (4)采取优化控制理论,利用基电子态的一个较高振动态,把光缔合形成的外势阱中的分子转移到内势阱的一个振动态上。这要求优化脉冲的频谱足够宽,能够覆盖初始态和目标态的能级差。由优化脉冲产生的激发态内势阱中布居可以用一束高斯脉冲完全转移到基电子态的较低振动能级上。 (5)基于两态绝热表象,从理论上研究了优化激光控制慢碰撞H++D中的电荷转移过程。在没有外场情况下,通过非绝热耦合得到的电荷转移几率较低,而在优化控制方案中,利用自由态与多个振动态之间的跃迁,几乎100%控制电荷转移。我们采用了两种不同的目标态来获取优化激光场：能够进行自我调节的目标态(自适应目标态)更加高效,但得到的电荷转移后的波包结构很复杂；固定目标态收敛得更慢些,但可以得到与设定目标完全匹配的波包。
[Abstract]:Controlling the photoassociation of atoms and the charge transfer during collisions by using laser pulses are two hot research directions in the field of atomic and molecular physics. In this paper, the photoassociation and charge transfer processes of collisional atoms controlled by plastic pulse laser are studied theoretically. The main works are summarized as follows: (1) A theoretical scheme to improve the photoassociation probability of ultracold atoms by shaping pulses is proposed. By solving the two-state Schrodinger equation, we find that the laser pulse with the characteristics of slow opening and quick closing can reduce the energy exchange between the laser and the molecule after the peak intensity is reached. Furthermore, the dissociation of the photoassociating molecules excited by the electron state is prevented from returning to the scattering state of the base electronic state, so that the photoassociation efficiency can be improved. The photoassociation probability increases with the shortening of pulse closing time. On this basis, the population accumulation effect of plastic pulse chain is used to improve the probability of photoassociation. (2) the photoassociation kinetics of ultracold atoms controlled by modulated pulses is studied theoretically. The results show that the shape and spectrum distribution of the time-dependent electric field are sensitive to the envelope phase. When the envelope period is larger than the full width of the pulse, the spectral intensity distribution can be corrected by changing the envelope phase. The Frank-Condon factor, the spectral intensity distribution of the laser pulse and the time-domain asymmetry of the laser field all affect the dynamic population distribution and the photoassociation efficiency of the photoassociated molecules. (3) the photoassociation kinetics of ultracold atoms controlled by third-order picosecond pulses is studied theoretically. The third order phase pulse increases the pulse area by prolonging the duration of time domain, thus increasing the photoassociation efficiency. Although the energy of the third order phase pulse is low when the pulse area is constant, the photoassociation efficiency can be improved obviously when the pulse area is larger than a certain value. Compared with Gao Si pulse, the third-order phase pulse can not change the dynamic distribution range of population, because they are the same spectral distribution as Gao Si pulse. (4) by using the optimal control theory, the molecules in the external potential well formed by photoassociation are transferred to a vibration state of the inner potential well by using a higher vibration state of the base electronic state. This requires that the spectrum of the optimized pulse be wide enough to cover the energy difference between the initial state and the target state. The population in the excited state generated by the optimized pulse can be completely transferred to the lower vibrational energy level of the base electronic state by a beam of Gao Si pulses. (5) based on the two-state adiabatic representation, the charge transfer process in the optimized laser controlled slow collision H D is studied theoretically. In the case of no external field, the probability of charge transfer obtained by non-adiabatic coupling is lower. In the optimal control scheme, almost 100% of the transition between free state and multiple vibration dynamics is used to control the charge transfer. We adopt two different target states to obtain the optimized laser field: the self-adjusting target state (adaptive target state) is more efficient, but the wavepacket structure after charge transfer is very complex; The fixed target state converges more slowly, but a wave packet that exactly matches the target setting can be obtained.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O562
本文编号：2393465
[Abstract]:Controlling the photoassociation of atoms and the charge transfer during collisions by using laser pulses are two hot research directions in the field of atomic and molecular physics. In this paper, the photoassociation and charge transfer processes of collisional atoms controlled by plastic pulse laser are studied theoretically. The main works are summarized as follows: (1) A theoretical scheme to improve the photoassociation probability of ultracold atoms by shaping pulses is proposed. By solving the two-state Schrodinger equation, we find that the laser pulse with the characteristics of slow opening and quick closing can reduce the energy exchange between the laser and the molecule after the peak intensity is reached. Furthermore, the dissociation of the photoassociating molecules excited by the electron state is prevented from returning to the scattering state of the base electronic state, so that the photoassociation efficiency can be improved. The photoassociation probability increases with the shortening of pulse closing time. On this basis, the population accumulation effect of plastic pulse chain is used to improve the probability of photoassociation. (2) the photoassociation kinetics of ultracold atoms controlled by modulated pulses is studied theoretically. The results show that the shape and spectrum distribution of the time-dependent electric field are sensitive to the envelope phase. When the envelope period is larger than the full width of the pulse, the spectral intensity distribution can be corrected by changing the envelope phase. The Frank-Condon factor, the spectral intensity distribution of the laser pulse and the time-domain asymmetry of the laser field all affect the dynamic population distribution and the photoassociation efficiency of the photoassociated molecules. (3) the photoassociation kinetics of ultracold atoms controlled by third-order picosecond pulses is studied theoretically. The third order phase pulse increases the pulse area by prolonging the duration of time domain, thus increasing the photoassociation efficiency. Although the energy of the third order phase pulse is low when the pulse area is constant, the photoassociation efficiency can be improved obviously when the pulse area is larger than a certain value. Compared with Gao Si pulse, the third-order phase pulse can not change the dynamic distribution range of population, because they are the same spectral distribution as Gao Si pulse. (4) by using the optimal control theory, the molecules in the external potential well formed by photoassociation are transferred to a vibration state of the inner potential well by using a higher vibration state of the base electronic state. This requires that the spectrum of the optimized pulse be wide enough to cover the energy difference between the initial state and the target state. The population in the excited state generated by the optimized pulse can be completely transferred to the lower vibrational energy level of the base electronic state by a beam of Gao Si pulses. (5) based on the two-state adiabatic representation, the charge transfer process in the optimized laser controlled slow collision H D is studied theoretically. In the case of no external field, the probability of charge transfer obtained by non-adiabatic coupling is lower. In the optimal control scheme, almost 100% of the transition between free state and multiple vibration dynamics is used to control the charge transfer. We adopt two different target states to obtain the optimized laser field: the self-adjusting target state (adaptive target state) is more efficient, but the wavepacket structure after charge transfer is very complex; The fixed target state converges more slowly, but a wave packet that exactly matches the target setting can be obtained.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O562
【参考文献】
相关期刊论文 前2条
1 冉玲苓;曲士良;郭忠义;;Surface mico-structures on amorphous alloys induced by vortex femtosecond laser pulses[J];Chinese Physics B;2010年03期
2 周勇;苗泉;王传奎;;Effect of Lorentz local field correction on propagation of ultrashort laser pulse in one-dimensional para-nitroaniline (PNA) molecules[J];Chinese Physics B;2011年04期
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