【作者】 束传存；

【导师】 丛书林；

【作者基本信息】 大连理工大学 ， 原子与分子物理， 2010， 博士

【摘要】 本学位论文发展了超短激光脉冲控制双原子分子的理论模型,主要在量子态的相干控制和控制分子的定向两个方面进行了深入的研究。论文的理论方法是基于精确求解包含了振转自由度的薛定谔方程的含时量子波包方法。在量子态的调控方面,本论文提出了一个包含了Stark效应和邻近电子态影响的布居转移模型。利用Stark能级移动调节跃迁频率并选择合适的激光脉冲参数,初始电子态布居可以被绝热地转移到目标电子态。通过完整的含时量子波包计算结合三能级近似的定性分析,本论文也研究了采用受激拉曼绝热通道(STIRAP)方法实现对分子振转量子态的控制。研究发现利用超短皮秒激光脉冲可以刘分子体系实现振转量子态的绝热控制,初始转动温度对受激拉曼绝热通道过程有一定的影响。在控制分子的定向研究中,提出了两种实现场后分子定向的理论控制方案。首先以LiH分子为例研究了利用一束红外激光脉冲和一束时间延迟的太赫兹半周期脉冲实现场后分子定向的方案。在这个方案中,一束首先打开的红外激光脉冲被用来选择控制分子到一个高的振转态,紧随其后的太赫兹半周期脉冲通过非共振转动激发生分子定向。数值计算表明,这个方法即使在室温下也可以获得比较好的场后分子定向。另一个方案是利用载波包络相位稳定的太赫兹周期量级激光脉冲实现载波包络相位敏感的场后分子定向。数值计算表明,在当前分子束技术允许的条件下,这个方法可以实现有效的场后分子定向。产生的场后分子定向对周期量级脉冲的载波包络相位非常敏感,这可能为研究载波包络相位控制分子定向提供一个新的思路。值得一提的是,在这个方案中扮演重要角色的周期量级激光脉冲在目前实验上已经可以实现。本文以LiH和LiCl分子为例,利用精确求解含时薛定谔方程、刚体近似模型和冲量近似模型详细地研究了太赫兹周期量级激光脉冲产生场后分子定向的动力学机理。一个瞬间的“踢”模型可以用来很好地理解太赫兹周期量级激光脉冲产生场后分子定向的动力学。在场后分子定向的应用方面,本论文提出了一种利用场后分子定向探测太赫兹周期量级激光脉冲载波包络相位的方法。利用场后分子定向可以恢复的特性,因场后分子定向退相引起的载波包络相位漂移的影响可以很自然地被消除。更多还原

【Abstract】 This thesis develops theoretical model for quantum control of diatomic molecules with ultrashort laser pulses, which mainly involves the coherent control of quantum state and spatial degrees of freedom. The theoretical method is based on the nu-merical solution of the time-dependent Schrodinger equation including the vibrational and rotational degrees of freedom. The effect of rotational temperature on the quan-tum control is considered by statistically averaging over the solutions of Schrodinger equation for all possible initially rovibrational states weighed by a Boltzmann factor. For the quantum state manipulation, a model for controlling the population trans-fer between the electronic states is discussed, and the effects of the Stark shift and neighboring electronic states on the population transfer are considered. By utilizing the Stark shift to modulate the transition frequency and choosing the suitable laser frequency, the population can be adiabatically transferred from the initial electronic state to the target electronic state. By combining exactly wave packet calculations and the qualitative analysis of simple three-level approximation the coherent population transfer between molecular rovibrational states by a stimulated Raman adiabatic pas-sage (STIRAP) mechanism is also investigated to control the rovibrational quantum state in the molecular electronic states. The calculated results have shown that the population can be adiabatically transferred from one rovibrational state to another rovibrational state, and the initial rotational temperatures have evident influence on transfer process.For the control of spatial degrees of freedom, two strategies for generating an efficient field-free molecular orientation are proposed. Firstly, with LiH molecules as an example, a scenario used for controlling molecular orientation was suggested with an infrared laser pulse and a delayed half-cycle pulse. The infrared laser pulse ex-cites the molecules in a thermally initial state to a specific rovibrational state, and then the half-cycle pulse orients the molecules by rotational excitation. Numerical calculation shows that an efficient field-free time-dependent orientation can be real-ized even at room temperature. Secondly, a strategy for generating carrier-envelope phase-dependent field-free molecular orientation was proposed with the use of carrier- envelope phase (CEP) stabilization and asymmetric terahertz (THz) few-cycle laser pulses. An efficient field-free molecular orientation can be obtained even at higher temperatures. Moreover, a simple dependence of the field-free orientation on the CEP was demonstrated, which implies that the CEP becomes an important parameter for control of molecular orientation. More importantly, the realization of this scenario is appealing based on the fact that the intense few-cycle THz pulse with duration as short as a few optical cycles is available as a measrue tool. This thesis also investigates in detail the dynamics of field-free orientation driven by THz few-cycle pulses. Exact results by numerically solving the time-dependent Schrodinger equation including the vibrational and rotational degrees of freedom are compared to the rigid-rotor approx-imation as well as to the impulsive approximation. Two different molecules, LiH and LiCl, are considered. A delta-kicked rotor model is well demonstrated for understand-ing the dynamics of field-free molecular orientation with THz few-cycle pulses.For application of the field-free molecular orientation, an experimentally feasible approach was proposed to determine the CEP of a few-cycle pulse by observing the field-free molecular orientation. The degree of orientation sensitively depends on the CEP, providing a new route for measurement of the CEP without phase ambiguity. By taking advantage of revivals of the field-free molecular orientation, an important effect of the CEP drift caused by the dephasing of the generating medium on the accurate measurement of the CEP value is naturally eliminated.更多还原