Photodetachment of H-- in an electric field between two parallel interfaces

By using the closed orbit theory, the photodetachment cross section of H- in a static electric field between two parallel elastic interfaces is derived and calculated. It is found that the photodetachment cross section depends on the electric field and the distance between the ion and the elastic interface. The oscillation of the cross section becomes more complicated than in the case of H- near one elastic interface. The results show that near the detachment threshold, the influence of the additional interface can be neglected. But with the increase of the energy, its influence becomes great. At some energies, the cross sections display sharp peaks, contrasting with the staircase structure when only one interface exists. This study provides a new understanding of the photodetachment process of H- in the presence of external field and interfaces.     

氢负离子在微腔中的光剥离研究

利用闭合轨道理论,研究了氢负离子在金属面和弹性界面组成的微腔中的光剥离截面.结果表明,微腔的上下表面对氢负离子的光剥离截面产生很大影响.若固定金属面与氢负离子之间的距离不变,当弹性界面与氢负离子之间的距离很大时,弹性界面对氢负离子光剥离截面的影响很小,光剥离截面的振荡幅度和振荡频率与只有金属面时的情况类似.随着弹性界面和氢负离子之间距离的不断减小,光剥离截面的振荡幅度增大,振荡频率减小.若保持氢负离子和弹性界面之间的距离不变,随着金属面和氢负离子之间距离d₀的不断增大, 关键词： 光剥离截面 闭合轨道理论 微腔     

Magnetic field effect in photodetachment from negative ion in electric field near metal surface

Based on the closed-orbit theory, the magnetic field effect in the photodetachment of negative ion in the electric field near a metal surface is studied for the first time. The results show that the magnetic field can produce a significant effect on the photodetachment of negative ion near a metal surface. Besides the closed orbits previously found by Du et al. for the H in the electric field near a metal surface (J. Phys. B 43 035002 (2010)), some additional closed orbits are produced due to the effect of magnetic field. For a given ion-surface distance and an electric field strength, the cross section depends sensitively on the magnetic field strength. As the magnetic field strength is very small, its influence can be neglected. With the increase of the magnetic field strength, the number of the closed orbits increases greatly and the oscillation in the cross section becomes much more complex. Therefore we can control the photodetachment cross section of the negative ion by changing the magnetic field strength. We hope that our results may guide future experimental studies for the photodetachment process of negative ion in the presence of external fields and surfaces.     

激光脉冲对氢负离子在金属面附近光剥离的影响

利用闭合轨道理论和金属面附近氢负离子的双脉冲光剥离截面的计算公式,计算了氢负离子在金属面附近激光脉冲作用下的光剥离截面.计算结果表明:如果脉冲宽度远大于闭合轨道的回归周期时,它对光剥离截面的影响很小;当脉冲宽度小于闭合轨道的周期或者可以和闭合轨道的周期相比较时,光剥离截面的振荡幅度大大地减弱.光剥离截面除了与脉冲宽度有关外,还与双脉冲之间的时间延迟、相位差有关.对于某些相位差, 双脉冲光剥离截面的取值增大; 而对于另外一些相位差, 光剥离截面的取值减小.因此,可以利用脉冲激光来控制氢负离子在表面附近光剥离 关键词： 激光脉冲 光剥离截面 金属面 闭合轨道理论     

The influence of electric field on the photodetachment of H- near a metal surface

The influence of electric field on the photodetachment of H-near a metal surface is investigated based on the closed-orbit theory.It is found that the photodetachment of H-near a metal surface is not only related to the electric field strength but also to the electric field direction.If the electric field is along the +z axis,it can strengthen the oscillation in the photodetachment cross section.However,if the electric field is along the -z axis,since the direction of electric field force is opposite to that of static-image force caused by the metal surface,the situation becomes much more complicated.When the electric field is very weak,its influence can be neglected.The photodetachment cross section is nearly the same as that when a single metal surface exists.When the electric field strength is strong enough,the electric field force is able to counteract the metallic attraction,therefore no closed orbit is formed.If the electric field continues to increase until its influence becomes dominant,the photodetachment cross section approaches the case of the photodetachment of H- in an electric field.Our results may be useful for guiding future experimental studies on the photodetachment of negative ions near surfaces.     

氢负离子在均匀电场和金属面附近的光剥离研究

利用闭合轨道理论,计算了氢负离子在均匀电场和金属面附近的光剥离截面.结果表明,在均匀电场的基础上加上金属面之后,在电离阈附近氢负离子的光剥离截面发生了很大的变化,和仅有均匀电场存在时的光剥离截面相比,截面的振荡幅度增大,振荡频率减小.并且在电场强度相同时,随着金属面与氢负离子距离的不断增大,光剥离截面振荡的幅度不断减小,振荡的频率不断增大,当金属面和氢负离子的距离增大到一定值时,金属面的影响消失,氢负离子的光剥离截面趋近于只有电场存在时的情况.这一结果对于研究负离子体系在界面附近的光剥离问题具有一定的参考价值.     

The influence of interface modifier on photodetachment of negative ions in an electric field near a metal surface

Based on closed-orbit theory,the influence of an interface modifier on the photodetachment of H- in an electric field near a metal surface is studied.It is demonstrated that the interface strengthens the oscillations in the photodetachment cross section.However,when the electric field environments are different,the strengthening oscillations are caused by different sources.When the electric field direction is upward,the interface enhances the oscillations by shortening the period and the action of the closed orbit.When the electric field direction is downward,the interface strengthens the oscillations either by extending the coherent energy range or by increasing the total number of the closed orbits.We hope that our results will be conducive to the understanding of the photodetachment process of negative ions near interfaces,cavities and ion traps.     

Photodetachment of H^- in a Static Electric Field near a Surface

The photodetachment of H^- in a static electric field near a surface is investigated based on the closed orbit theory. It is found the distance between the ion and the surface modulates the cross section of photodetachment. For an elastic surface perpendicular to electric field, the detachment spectrum displays a staircase structure, in contrast with the smooth oscillation when only the electric field exists.     

Photodetachment of H- near Elastic Surface in Parallel Electric and Magnetic Fields

The photodetachment cross section of H^- in parallel electric and magnetic fields near an elastic surface is derived and calculated by using the closed orbit theory. It is found that the elastic surface can produce some interesting effects. Besides the closed orbits previously found by Peters et al. for the H^- in parallel electric and magnetic fields, some additional closed orbits are produced due to the effect of the elastic surface. The results show that the cross section oscillation is much more complicated in comparison with the cross section of H^- in parallel external fields without surface. Each peak in the Fourier transformed cross section corresponds to the period of one detached electron closed orbit. This study provides a new understanding of the photodetachment of negative ions in the presence of external fields and surface.     

Photodetachment of a Negative Hydrogen Molecular Ion near an Interface

Photodetachment of a negative hydrogen molecular ion near an interface is studied by using the two-centre model and the closed orbit theory. The calculation results show that the photodetachment cross section is related to the distance between the two centres in the H₂^- and different molecular ion-interface distances. The comparison between the cross section of H₂^- near an interface with the section of Hˉ shows that at the equilibrium distance of two centres and at low photon energy, the photodetachment cross section of H₂^- is about twice the cross section of Hˉ, which shows that the interference of the two nuclei is very strong; when the distance between the two centres is large, the section of H₂^- is almost the same as the cross section of Hˉ near one interface, which indicates that the interference effect of the two centres anishes.     

氢负离子在电介质球面附近的光剥离研究

利用镜像法结合半经典闭合轨道理论,对氢负离子在电介质球面附近的光剥离进行了研究.首先利用镜像法分析了剥离电子在电介质球内的镜像电荷分布情况,然后给出了体系的哈密顿量.通过求解哈密顿正则方程,找到了剥离电子在电介质球面附近运动时的闭合轨道.借助于半经典闭合轨道理论,推导出了体系的光剥离截面,并且对光剥离截面进行了计算和分析.计算结果表明,氢负离子在电介质球面附近的光剥离截面不仅与入射光子的能量有关,而且还与电介质球面的介电常数有关.对于给定的电介质球面,随着入射光子的能量增加,光剥离截面的振荡振幅减小、振荡频率增加.当入射光子的能量增加到某一临界值时,光剥离截面的振荡结构消失.除此之外,随着电介质球面介电常数的增大,光剥离截面的振荡结构变得更加复杂.当电介质常数增大到无穷大时,体系的光剥离截面和氢负离子在金属球面附近的光剥离截面一致.因此,可以通过改变入射光子的能量及电介质球面的介电常数对氢负离子在电介质球面附近的光剥离截面进行调控研究.研究结果对负离子体系在电介质球面附近的光剥离的实验研究可以提供一定的理论指导和参考价值.     

氢负离子在磁场和电介质表面附近光剥离的研究

利用闭合轨道理论, 研究了变化的磁场和不同电介质表面对氢负离子光剥离截面的影响, 并推导出了该体系下的光剥离截面公式. 结果发现, 氢负离子的光剥离截面不仅与磁场的强度有关, 而且还与电介质常数有关. 当氢负离子到电介质表面的距离和电介质常数一定时, 体系的光剥离截面中的振荡随磁场的变化而明显变化. 随着磁场强度的 增大, 体系的闭合轨道数目增多, 光剥离截面的振荡越来越复杂. 当氢负离子到电介质表面的距离和磁场强度一定时, 电介质常数的变化对光剥离截面的影响也很重要, 随着电介质常数的增大, 体系的闭合轨道数目增多, 光剥离截面的振荡也变得越来越复杂. 因此, 可以通过改变磁场强度和电解质常数来调整负离子的光剥离截面. 此结果 对于研究负离子体系在表面附近和外场中的光剥离问题具有一定的参考价值.     

Photo-detachment cross section of H- near two parallel interfaces

The photo-detachment cross section of H^- near two parallel elastic interfaces is derived and calculated by using the closed orbit theory. The photo-detachment cross section of H^- near two interfaces is shown to exhibit multi-periodic oscillations when the distance between the H^- and the interface is varied. Each peak in the Fourier transformed photo-detachment cross section corresponds to the length of a closed orbit, which is quite similar to the case of atomic spontaneous emissions in a dielectric slab. This study provides a new understanding of the photo=detachment process of H^- in the presence of interfaces.     

Photodetachment of negative ion in a gradient electric field near a metal surface

Based on closed-orbit theory, the photodetachment of H in a gradient electric field near a metal surface is studied. It is demonstrated that the gradient electric field has a significant influence on the photodetachment of negative ions near a metal surface. With the increase of the gradient of the electric field, the oscillation in the photodetachment cross section becomes strengthened. Besides, in contrast to the photodetachment of H near a metal surface in a uniform electric field, the oscillating amplitude and the oscillating region in the cross section of a gradient electric field also become enlarged. Therefore, we can use the gradient electric field to control the photodetachment of negative ions near a metal surface. We hope that our results will be useful for understanding the photodetachment of negative ions in the vicinity of surfaces, cavities, and ion traps.     

Coherent control of photodetachment of H− in an electric field near a metal surface

We show that the photodetachment of H^? in an electric field near a metal surface can be controlled by using a single or double laser pulse. The method of theoretical analysis used is semi-classical closed orbit theory. The results show that if the period of a certain closed orbit is longer than the pulse width of the single-pulse laser, the contribution of that closed orbit to the photodetachment cross-section will be greatly reduced. As for the double-pulse laser, the pulse width, phase difference and the time delay between the two pulses all play an important role in the photodetachment cross-section. With the decrease of the time delay, the oscillating amplitude of the cross-section increases while the oscillating frequency decreases. Therefore, laser pulses can be used to control the photodetachment process of negative ions or atoms in an external field near metal surfaces.     

氢负离子在变形球面附近的光剥离

利用理论模型成像方法, 对氢负离子在变形球面附近的光剥离进行了研究. 首先, 推导出了光剥离电子通量的计算公式, 然后对电子通量分布和光剥离截面进行了计算.结果表明: 平面效应只在一定范围内对氢负离子的光剥离过程产生影响. 在距离z轴比较近的区域, 球面效应起主要作用, 电子通量分布和光剥离截面与只有球面存在的情况一致, 此时平面效应可以忽略; 距离z轴较远的区域, 平面效应和球面效应共同起作用, 此时变形球面对光剥离过程会产生比较大的影响. 当球面半径和氢负离子到球面之间的距离给定, 随着入射光子的能量增大, 光剥离电子通量的振幅先增大后减小, 然后又慢慢增大, 振荡频率增大.当固定球面与氢负离子之间的距离, 随着球面半径的增大, 光剥离电子的通量趋向于只存在球面的情况.因此, 可以通过改变入射光子能量和球面的半径对氢负离子的光剥离进行调控. 本文的结果对于研究负离子体系在曲面附近的光剥离及光剥离 显微问题的实验研究具有一定的参考价值. 关键词： 理论模型成像方法 光剥离电子通量 光剥离截面 变形球面     

界面附近光剥离过程中的量子经典对应

研究了氢负离子在弹性墙附近的光剥离过程，导出了剥离截面的解析公式。此截面为光滑背景项与一正弦振荡项之和，后者与离子与弹性墙的距离有关。分析了光剥离电离的经典动力学及其量子对应。在本模型中，半经典光剥离截面与量子结果一致。