摘要:
利用含时微扰论和闭合轨道理论相结合的方法，给出了氢负离子在梯度电场中自关联函数的计算公式，并且对体系的自关联函数进行了计算和分析。重点探讨了激光脉冲的宽度、梯度电场中背景电场强度及电场梯度对氢负离子体系的自关联函数的影响。研究结果表明，当激光脉冲的脉冲宽度较短，远小于剥离电子的闭合轨道的周期时，量子波包的回归现象显著，自关联函数中会出现一系列比较明显的回归峰，这是由于沿闭合轨道返回的电子波包和出射的电子波包之间产生干涉形成的。但是随着激光脉冲宽度的增加，量子波包的回归现象减弱。当脉冲宽度和闭合轨道的周期相差不是很大时，自关联函数中的回归峰逐渐变宽，振荡渐趋平缓，相邻的峰之间发生相互干涉，从而导致对应关系消失。除此之外，我们还发现梯度电场中背景电场强度和电场梯度对体系的自关联函数也会发生显著的影响。随着背景电场强度和电场梯度的增加，剥离电子的闭合轨道的周期变短，自关联函数中回归峰的个数逐渐增加，量子回归现象增强。因此，我们可以通过改变脉冲的宽度、外加电场强度的大小对氢负离子发生光剥离的自关联函数进行调控。我们的结果对于实验研究原子或离子体系在外场中的波包动力学性质可以提供一定的参考价值。
Abstract:
Using the combination of the time-dependent perturbation theory and the closed-orbit theory, we put forward a calculation formula for the autocorrelation function of H ion in a gradient electric field, and then calculate and analyze the autocorrelation function of the system. Especially, we discuss the effect of laser pulse width, electric field strength and the electric field gradient on the autocorrelation function of H ion in a gradient electric field. It is demonstrated that when the laser pulse width is very narrow, far less than the period of the detached electron, the quantum wave packet revival phenomenon is significant. A series of sharp reviving peaks appear in the autocorrelation function, which are caused by the interference between the returning electron wave packets travelling along the closed orbit and the outgoing electron wave packets. However, with the increase of laser pulse width, the quantum wave packet revival phenomenon becomes weakened. When the difference between the pulse width and the period of the closed orbit is not very large, the reviving peaks in the autocorrelation function become widely spread gradually and the oscillatory structures get flattened. This correspondence will vanish finally due to the interference between the adjacent peaks. In addition, our study also suggests that the background electric field strength and the electric field gradient in the gradient electric field can also have significant effects on the autocorrelation function. With the increase of background electric field strength and electric field gradient, the period of the detached electron’s closed orbit gets shorter, the number of the revival peaks in the autocorrelation function is increased gradually, and the quantum wave packet revival phenomenon will be enhanced. Therefore, we can control the autocorrelation function of the hydrogen negative ion by changing the laser pulse width and the external electric field strength. Our results will provide some reference values for the experimental research on the wave packet dynamic property of atoms or ions in external fields.
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