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.     

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 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.     

Photodetachment dynamics of H~- ion in a harmonic potential plus a time-dependent oscillating electric field

The photodetachment dynamics of H~- ion in a harmonic potential plus an oscillating electric field is studied using the time-dependent closed orbit theory. An analytical formula for calculating the photodetachment cross section of this system is put forward. It is found that the photodetachment cross section of this system is nearly unaffected for the weak oscillating electric field strength, but oscillates complicatedly when the oscillating electric field strength turns strong. In addition, the frequency of the harmonic potential and the oscillating electric field(the frequency of the harmonic potential and the frequency of the oscillating electric field are the same in the paper, unless otherwise stated.) can also affect the photodetachment dynamics of this system. With the increase of the frequency in the harmonic potential and the oscillating electric field, the number of the closed orbits for the detached electrons increased, which makes the oscillatory structure in the photodetachment cross section much more complex. Our study presents an intuitive understanding of the photodetachment dynamics driven by a harmonic potential plus an oscillating electric field from a space and time dependent viewpoint.This study is very useful in guiding the future experimental research for the photodetachment dynamics in the electric field both changing with space and time.     

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.     

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.     

Photodetachment microscopy of a hydrogen negative ion in an electric field near a metal surface

According to the semi-classical theory, we study the photodetachment microscopy of H- in the electric field near a metal surface. During the photodetachment, the electron is photo-detached by a laser and the electron is drawn toward a position-sensitive detector. The electron flux distribution is measured as a function of position. Two classical paths lead the ion to any point in the classically allowed region on the detector, and waves traveling along these paths produce an interference pattern. If the metal surface perpendicular to the electric field is added, we find that the interference pattern is related not only to the electron energy and the electric-field strength, but also to the ion-surface distance. In addition, the laser polarization also has a great influence on the electron flux distribution. We present calculations predicting the interference pattern that may be seen in experiment. We hope that our study can provide a new understanding of the electron flux distribution of negative ions in an external field and surface, and can guide future experimental research on negative ion photo-detachment microscopy.     

Photodetachment microscopy of the hydrogen negative ion in electric field near a metal surface

According to the semi-classical theory, we study the photodetachment microscopy of H^- in the electric field near a metal surface. During the photodetachment, the electron is photo-detached by a laser and the electron is drawn toward a position-sensitive detector. The electron flux distribution is measured as a function of position. Two classical paths lead the ion to any point in the classically allowed region on the detector, and waves traveling along these paths produce an interference pattern. If the metal surface perpendicular to the electric field is added, we find that the interference pattern is related not only to the electron energy and the electric-field strength, but also to the ion--surface distance. Besides, the laser polarization also has a great influence on the electron flux distribution. We present calculations predicting the interference pattern that may be seen in experiment. We hope that our study can provide a new understanding of the electron flux distribution of negative ions in external field and surface, and can guide the future experimental research on the negative ion photo-detachment microscopy.     

Photodetachment of H- in a static electric field

We derive a formula using closed-orbit theory for the photodetachment cross-section of H^- in the presence of a static electric field when there is an arbitrary angle θ_L between the laser polarization direction and the static electric field. This formula generalizes the previous result for laser polarization parallel to the static electric field, the effect of laser polarization direction appears as a factor cos²(θ_L) in the amplitude of the oscillation. A photodetachment cross-section formula valid above and below detachment threshold is proposed.     

Temporal interference driven by an oscillating electric field in photodetachment of H~- ion

The real time domain interferometry for the photodetachment dynamics driven by the oscillating electric field has been studied for the first time. Both the geometry of the detached electron trajectories and the electron probability density are shown to be different from those in the photodetachment dynamics in a static electric field. The influence of the oscillating electric field on the detached electron leads to a surprisingly intricate shape of the electron waves, and multiple interfering trajectories generate complex interference patterns in the electron probability density. Using the semiclassical open-orbit theory, we calculate the interference patterns in the time-dependent electron probability density for different electric field strengths, different frequencies and phases in the oscillating electric field. This method is universal, and can be extended to study the photoionization dynamics of the atoms in the time-dependent electric field. Our study can guide the future experimental researches in the photodetachment or photoionization microscopy of negative ions and atoms in the oscillating electric field.     

电场不均匀性对外场中负离子光剥离的影响

用蒙特卡罗方法研究了不均匀外场中氢负离子的光剥离.模拟结果显示出电场的不均匀抑制了光剥离截面和相应调制函数的振荡.光剥离截面的高能部分比阅值附近部分对电场的不均匀性更为敏感.结後果对纯电场和平行电场与磁场两种情形均适用.     

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.     

Photodetachment of H<Superscript>−</Superscript> ion in crossed gradient electric and magnetic fields

We study the photodetachment of H ^? ion in crossed gradient electric and magnetic fields and put forward an analytical formula for calculating the photodetachment cross-section. Compared to the photodetachment of H ^? ion in a gradient electric field, the Hamiltonian of the detached electron has three degrees of freedom, which makes the dynamical behaviour of the detached electron complex. Photodetachment cross-section for various external fields and the laser polarization are calculated and displayed. A comparison with the photodetachment cross-section in crossed uniform electric and magnetic fields or in a single gradient electric field has been made. The agreement of our results with the above two special cases suggests the correctness of our calculation. Our study may have some potential applications in the photodetachment microscopy experiment or in ion detection.     

Photo-Detached Electron Flux Distribution in a Gradient Electric Field

This paper investigates the flux distributions of the electron photo-detached from H-ion localized in a gradient electric field. In contrast with the photodetachment in the uniform electric field [Phys. Rev. A 40(1989) 4983],where only two electron trajectories interfere at each given point on a detector, for the photodetachment in a gradient electric field, the electrons waves can travel along multiple paths from the negative ion to a given point on the detector plane, which makes the electron flux distributions on the detector plane become much complex. Using the semi-classical theory, we put forward a formula for calculating the electron flux. Our calculation results suggest that the electron flux distributions on a given detector plane is not only related to the propagation time of the detached electron, but also related to the detached electron's energy. With the increase of the detached electron's energy, the oscillating region in the electron flux distributions becomes enlarged and the oscillating structure in the flux distributions becomes much more complicated. This study will guide future experiment research on the photodetachment microscopy of the negative ions in the presence of non-uniform external fields.     

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.     

Composition of a non-self-sustained discharge plasma in an N2: O2: H2O mixture at atmospheric pressure

The plasma composition of a discharge sustained by a pulsed ionization source of μs duration is computed. It is shown that, within a time interval of ∼10⁻⁶ s after the ionization pulse, the dependences of the ion densities on the electric field and ionization source power show features that should be taken into account when developing laser systems for controlling electric discharges in long air gaps. The effect of the plasma composition on the efficiency of electron photodetachment from negative O ₂ ⁻ ions is investigated by the example of a discharge initiation system consisting of two lasers with different pulse durations and wavelengths. Plasmochemical processes under conditions of enhanced electron photodetachment from negative O ₂ ⁻ ions are simulated. It is shown that photodetachment can increase the electron density for a time of <10⁻⁵ s.     

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 H-near a metal surface

By using the closed orbit theory, the photodetachment cross section of H^- near a metal surface is derived and calculated. The results show that the metal surface has great influence on the photodetachment process. As the ion-surface distance is very large, the influence of the electrostatic image potential caused by the metal surface becomes small and can be neglected. The period, action, and length of the detached electron＇s closed orbit are nearly the same as the case of the photodetachment of H^- near an elastic interface. However, with the decrease of the ion-surface distance, the influence of the metal surface becomes significant. The amplitude of the oscillation in the photodetachment cross section becomes complicated. Each resonance peak in the Fourier transformed cross section is associated with one electron＇s closed orbit. Unlike the case of the photodetachment of H^- near an elastic interface, the length of the closed orbit does not equal the twice distance between the ion and the surface. But with the increase of the ion-surface distance, the length of the closed orbit approaches the case of the closed orbit near an elastic interface, which suggests the correctness of our method. This study provides a new understanding on the photodetachment process of H^- in the presence of a metal surface.