Photodetachment Of Negative Ion Research Articles

Wall Induced-oscillations in Photo detachment of Homo Nuclear Diatomic Molecular Negative ion

The Pd (Photodetachment) of a hydrogen molecular negative ions near a soft reflecting wall is being investigated theoretically, focusing on the differential and total Pd.CS (Photodetachment Cross Section) when the laser polarisation is along the molecular axis of the ion. Quantum interference becomes evident on the observable plane when the two components of the electron wave superimpose at a considerable distance and propagate outward. The investigation of these interferences contributes to improving our understanding of the structure of diatomic molecular negative ions. Wall-induced fluctuations are observed in the detached electron spectra. As the distance between the ion and wall (R) increases, the wall effect diminishes, and the results approach those of the Ions in free space, the oscillation amplitude in the Pd.CS decreases, and their frequency increases as both Walls (R) and the distance between the two opposing ion centers (d) increase. The oscillations eventually cease to exist, and the CS (cross-section) exhibits uniform behavior at tremendous values of R and (R→∞,d→∞ ) resulting in the match to the Ions in free space.

Semiclassical study on photodetachment of hydrogen negative ion in a harmonic potential confined by a quantum well

Abstract We have studied the photodetachment dynamics of the H− ion in a harmonic potential confined in a quantum well for the first time. The closed orbits of the detached electron in a confined harmonic potential are found and the photodetachment spectra of this system are calculated. It is interesting to find that the photodetachment spectra depend sensitively on the size of the quantum well and the harmonic frequency. For smaller size of the quantum well, the harmonic potential can be considered as a perturbation, the interference effect between the returning electron wave bounced back by the quantum well and the initial outgoing wave is very strong, which makes the photodetachment spectra exhibits an irregular saw-tooth structure. With the increase of the size of the quantum well, the photodetachment spectra oscillates complicatedly in the higher energy region. For very large size of the quantum well, the photodetachment spectra approach to the case in a free harmonic potential, which is a regular saw-tooth structure. In addition, the harmonic frequency can also affect the photodetachment spectra of this system greatly. Our work provides a new method for the study of spatially confined low-dimensional systems and may guide the future experimental research for the photodetachment dynamics in the ion trap.

Interferences driven by the few-cycle laser field in the photodetachment of Cl− ion

The time-dependent semiclassical theory is extended to study the photodetachment of negative ions with outer p-state electrons. The photodetachment cross section of Cl− ion is specially studied exposed to a few-cycle laser field. Considering the influence of laser field effects, the photodetachment cross section is found to oscillate complicatedly with increasing laser intensity and frequency. We demonstrate that different types of closed orbit have different impacts on the interference structures in the photodetachment cross section. Detailed analysis of the t-ti map of the detached electron reveals a remarkably correlation with the initial phase in the laser field. Additionally, the profiles of photodetachment cross section show strong dependence on the optical cycle number N in the laser field, indicating that it is an important parameter for controlling the photodetachment of negative ion. The method adopted in this work is universal, and can be applied to study the photodetachment of other halide negative ions in the laser field, such as F− ion, Br− ion, etc This work provides a new method for the experimentalists to coherent control of the photodetachment process of negative ion using a few-cycle laser field.

Photodetachment dynamics of negative ion confined in a time-dependent quantum well

We investigate the photodetachment dynamics of negative ion confined in a time-dependent trap created by a quantum well with an oscillating wall for the first time. Compared with the photodetachment of negative ion in a quantum well with static walls, the movement of the detached electron becomes substantially complicated and interesting as one wall in the quantum well oscillates with time. The position–time plot of the detached electron in the quantum well shows a fractal structure of asymptotic self-similarity due to the influence of the oscillating wall. The returning kinetic energy of the detached electron may have been accelerated to high energy by colliding with the oscillating wall. By calculating the photodetachment cross section of this system, we find that the oscillating wall in the quantum well functions as an external driving potential for the photodetachment of negative ion. The photodetachment cross section becomes increasingly complicated due to the influence of the oscillating wall. In addition, the amplitude, initial phase, and the initial position of the oscillating wall all affect the photodetachment cross section of this system. Our study may guide future experimental investigations on the photodetachment dynamics in the ion trap.

Quantum photodetachment of hydrogen negative ion in a harmonic potential subjected to static electric field

Photodetachment of negative ions has attracted immense interest owing to its fundamental nature and practical implications with regard to technology. In this study, we explore the quantum dynamics of the photodetachment cross section of negative ion of hydrogen H− in the perturbed one dimensional linear harmonic potential via static electric field. To this end, the quantum formula for total photodetachment cross section of the H− ion is derived by calculating the dipole matrix element in spherical coordinates. In order to obtain the detached electron wave function, we have solved the time-independent Schrödinger wave equation for the perturbed Hamiltonian of the harmonic oscillator in momentum representation. To acquire the corresponding normalized final state detached electron wave function in momentum space, we have employed an approach analogous to the WKB (Wenzel–Kramers–Brillouin) approximation. The resulting analytical formula of total photodetachment cross section depicts interesting oscillator structure that varies considerably with incident-photon energy, oscillator potential frequency, and electric field strength as elucidated by the numerical results. The current problem having close analogy with the Stark effect in charged harmonic oscillator may have potential implications in atomic and molecular physics and quantum optics.

Photodetachment dynamics of negative ions near a moving surface

Photodetachment dynamics of negative ions near a moving surface is investigated for the first time. An analytical formula for the photodetachment cross section of negative ions induced by the moving surface has been put forward. This formula is universal and appropriate to any negative ion no matter the photodetachment is dominated by an s-wave source or a p-wave source. In contrast to the photodetachment of negative ion near a static surface, the returning kinetic energy of the detached electron is different from its initial value after it is bounced back by the moving surface; therefore, an additional modulation function related to the electron’s initial and returning momentum is multiplied in the oscillating cross section. As a demonstration, we calculate the photodetachment cross section of H− and Cl− ions near a moving surface. It is shown that the photodetachment cross section depends on the electron’s energy and the speed of the moving surface sensitively. Therefore, we can control the photodetachment dynamics of negative ion by a moving surface. Our work provides some insights into the behavior of photodetachment dynamics of negative ion near a moving surface and may guide the future experiments toward this field.

Photodetachment of the H− ion in a quantum well with one expanding wall

The standard closed orbit theory is extended to investigate the photodetachment of a negative ion near a moving wall. The photodetachment cross section of the ${\mathrm{H}}^{\ensuremath{-}}$ ion in a quantum well with one expanding wall is specifically put forward. In contrast to the photodetachment of the negative ion in a static quantum well, the returning kinetic energy of the detached electron is different from its initial value after collision with the moving wall, therefore an additional modulation factor appears in the oscillating cross section, which depends on the electron's initial outgoing and returning momentum. Four different types of closed orbits are found for the detached electron in a quantum well with one expanding wall, and their connections with the oscillating cross section are analyzed quantitatively. The calculation results suggest that the photodetachment cross section of this system depends on the speed of the moving wall and the initial distances from the ion to the walls sensitively. The method used in this paper is universal and can be extended to study the photodetachment of the nonhydrogenic negative ion near a moving wall, whether the wall is moving with constant velocity or oscillatory. The results provide insight into the behavior of photodetachment dynamics of the negative ion in the presence of a moving boundary and may have potential interest for future experimental researches.

Photodetachment cross section of a negative molecular ion near a nanospherical surface

The photodetachment of a diatomic negative molecular ion (H) near a nanospherical surface is investigated. Analytical results for the flux of detached electron waves and photodetachment cross section are derived. It is demonstrated that the flux of the detached electron waves and photodetachment cross section of H near a nanospherical surface are directly related to the radius of curvature, inter-ion–surface distance, and bond length or separation of the atomic centers. These parameters strongly influence the oscillating structure of the detached electron spectra of the molecular ions. Fine control over these parameters can be used to determine structural information of negative ions, curvature and roughness in the surface at the nanoscale, and dissociation of molecules near surfaces and fields.

Production Ratio for Para- and Ortho-Ps in Photodetachment of Ps $$^-$$ -

Para- and ortho-Ps atoms are formed in the photodetachment of positronium negative ion. Since the lifetime against the pair annihilation is much shorter for para-Ps(ns) than for ortho-Ps(ns), the production ratio of para- and ortho-Ps atoms is important for the photodetachment experiments. We have derived the ratio explicitly.

Development of an energy-tunable positronium beam apparatus using the photodetachment of the positronium negative ion

SynopsisWe report on the development of an energy-tunable positronium beam apparatus at Tokyo University of Science. The positronium beam is generated using the photodetachment of the positronium negative ion, a bound state of one positron and two electrons. Positronium negative ions are efficiently emitted from a Na- coated tungsten surface by bombardment with a slow positron beam. The intermediate-energy positronium beam produced in this fashion can be used for fundamental studies of antimatter-matter interactions with solid surfaces.

Photodetachment of hydrogen negative ion near inelastic surfaces: Arbitrary laser polarization direction

The photodetachment of hydrogen negative ion near different inelastic surfaces is investigated by the semiclassical closed orbit theory for arbitrary laser polarization direction . A two‐term formula of photodetachment cross section consisting of a smooth background term and an oscillatory term is derived. The oscillatory term contains an extra angular factor that describes the dependence of oscillations in total cross section on the laser polarization direction. It is observed that the amplitude of oscillations in cross section reaches maximum at when laser polarization is parallel to the z‐axis and it approaches zero as the laser polarization direction becomes perpendicular to the z‐axis. It is also observed that as the reflection coefficient , which accounts for the inelastic behavior of the surfaces, increases the amplitude of oscillation also increases. © 2015 Wiley Periodicals, Inc.

Photodetachment of negative hydrogen ion in circularly polarized monochromatic and bichromatic laser fields

We theoretically have investigated the detachment of negative hydrogen ion in circularly polarized monochromatic and bichromatic laser fields by calculating the photoelectron momentum distributions (PMDs). We find that the PMDs are controlled by the electric field of laser pulse. For circularly polarized monochromatic laser fields, the PMDs are perfect and isotropic rings, and the photodetachment rates in random direction are same. For this case, the photoelectron momentum spectra directly reflect the electronic distributions of negative hydrogen ion. For circularly polarized bichromatic laser field, the PMDs are inversion asymmetric, but symmetric about a certain axis. The emission directions of the photoelectrons vary with the electric field shape, that is to say that the emission directions of the photoelectrons vary with the carrier-envelope (CE) phases, which decide the electric field of laser pulse. The maximal photodetachment rates and the spectra shape, however, are same for the different CE phases.

Interference in the Photodetachment of a Negative Ion near Two Perpendicular Elastic Surfaces

The interference in the photodetachment of a negative hydrogen ion near two perpendicular elastic surfaces has been studied using the theoretical imaging method. Firstly, we analyze the images of the detached electron caused by the surfaces. Then we put forward an analytic formula for calculating the detached electron probability density and electron flux distribution at a given observation plane. Due to the influence of the two perpendicular elastic surfaces, four detached electron waves which propagate from the ion source to the same point on the detector plane will interfere and lead to an interference pattern in the electron's probability density and flux distribution. Our calculation results suggest that the electron flux distributions on the detector plane are not only related to the electron energy, but also are related to the position of the ion relative to the surfaces. Compared to the photodetachment of a H^- ion near one elastic surface, the oscillatory structure in the flux distribution of our system becomes much more complicated. This study provides a new understanding of the photodetachment process of negative ions in the vicinity of surfaces and may guide future research in photodetachment microscopy experiments.

Threshold behaviour in photodetachment into a final state with large negative polarizability

In a recent experiment, Lindahl et al. (Lindahl A. O. et al., Phys. Rev. Lett., 108 (2012) 033004) observed a new threshold behavior in the photodetachment of the potassium negative ion when the residual atom is left in the state. Unfortunately the resonance close to threshold made it more difficult to apply the semi-classical model that was developed to describe the threshold behavior. In this paper we present a study of the threshold behavior of the partial cross-section in the photodetachment of the sodium negative ion. The experiment was conducted using a collinear beams apparatus where the detection was performed using a resonance ionization scheme. We observe the same threshold behavior as in the previous experiment, but without any obfuscating resonance. The model derived in the previous paper is found to fit the observed cross-section up to 35 meV above threshold. The present experiment clearly demonstrates the threshold behaviour for the fundamental process of a free electron moving in the field of an atom with a large negative polarizability.

Photodetachment of a Hydrogen Negative Ion inside an Annular Nano-Microcavity

The photodetachment of a hydrogen negative ion inside an annular nano-microcavity is studied based on the semiclassical closed orbit theory. The closed orbit of the photo-detached electron in an annular nano-microcavity is investigated and the total photodetachment cross section of this system is calculated. The calculation results suggest that the oscillatory structure in the photodetachment cross section depends on the shape of the microcavity sensitively. If the outer radius R of the annular microcavity is given, with an increase of the inner radius Rin, the number of the closed orbits increased correspondingly and the oscillating amplitude in the photodetachment cross section becomes larger. In order to show the correspondence between the cross section and the detached electron's closed orbits clearly, we calculate the Fourier transformation of the cross section and find that each peak corresponds to the length of one closed orbit. We hope that our results will be useful in understanding the photodetachment or the transport and escape process of negative ions in a microcavity.

Study on the photodetachment of H- ion near a dielectric sphere

Photodetachment of hydrogen negative ion near a dielectric sphere has been studied by using the image method combined with the semiclassical closed orbit theory. Firstly, we analyze the image charge distribution of the detached electron near the dielectric sphere; then we put forward the Hamiltonian for this system. By solving the Hamiltonian canonical equations, we can find the closed orbits of the detached electrons moving near the dielectric sphere. With the help of the semiclassical closed orbit theory, we derive the formula for calculating the photodetachment cross section of this system. Then we can calculate and analyze the photodetachment cross section. Calculated results suggest that the photodetachment cross section of the hydrogen negative ion near a dielectric sphere is not only related to the photon energy, but also the dielectric constant of the sphere. For a given dielectric sphere, with the increase of photon energy, the oscillating amplitude in the photodetachment cross section decreases while the oscillation frequency increases. When the photon energy is increased to a critical value, the oscillating structures in the cross section disappear. In addition, with the increase in the dielectric constant of the dielectric sphere, the oscillating structure in the photodetachment cross section becomes much more complicated. When the dielectric constant is increased to infinity, the photodetachment cross section of this system is consistent with the photodetachment cross section of the hydrogen negative ion near a metal sphere. Therefore, we can control the photodetachment cross section of the hydrogen negative ion near a dielectric sphere by changing the photon energy and the dielectric constant. Our study may provide some theoretical guidance and reference values for the experimental research of photodetachment of negative ion near the dielectric sphere.

Photodetachment of H− ion near two repulsive centers

Based on a theoretical model for the photodetachment of negative ion near a repulsive center, we study the photodetachment of H− ion near two repulsive centers. Using the semiclassical closed orbit theory, we study the classical motion of the detached electron and calculate the photodetachment cross section of H− ion near two repulsive centers. It is found that the repulsive centers have significant effects on the photodetachment of H− ion. The photodetachment cross section of our system is strongly oscillatory compared to the photodetachment near one repulsive center. The calculation results suggest: if one repulsive center is kept fixed, with the decrease of the distance between two repulsive centers, the oscillating amplitude in the cross section becomes enlarged and the photodetachment cross section exhibits a multi-periodic oscillatory structure. In order to show the correspondence between the oscillation in the photodetachment cross section and the detached electron's classical closed orbits clearly, we make a Fourier transformation for the scaled photodetachment cross section of this system. Each peak in the Fourier transformed cross section corresponds to the scaled action of one closed orbit. We hope that our study will be useful in directing the future experimental research of the photodetachment processes of multiply charged anions.

Orbital alignment in atoms generated by photodetachment in a strong laser field

A pump-probe laser scheme is employed to investigate orbital alignment and its dynamics in the ground state of laser-generated neutral atoms. The alignment is initiated by electron photodetachment of an atomic negative ion in a strong laser pulse. The electron density distribution in the ground state of the residual atom is probed by means of strong-field ionization in a second laser pulse at a delayed time. The principle of the probe method relies on the fact that the portion of the electron density distribution oriented along the laser polarization axis constitutes the ionization yield in the high-energy jets of emitted electrons. A systematic study is carried out on C, Si, and Ge atoms, which possess two electrons in an open $p$ shell. A pronounced temporal modulation in the yield of high-energy electrons is observed for C and Si, revealing a periodic spatial rearrangement of the electron density distribution in these atoms. Its period is defined by the beat between the $J=1$ and $J=2$ spin-orbit components of the ground state.

Photodetachment of hydrogen negative ion inside a circular microcavity

The photodetachment of a hydrogen negative ion inside a circular microcavity is studied based on the semiclassical closed orbit theory. The closed orbit of the photo-detached electron in a circular microcavity is investigated and the photodetachment cross section of this system is calculated. The calculation result suggests that oscillating structure appears in the photodetachment cross section, which is caused by the interference effects of the returning electron waves with the outgoing waves traveling along the closed orbits. Besides, our study suggests that the photodetachment cross section of the negative ions depends on the laser polarization sensitively. In order to show the correspondence between the cross section and the closed orbits of the detached electron clearly, we calculate the Fourier transformation of the cross section and find that each peak corresponds to the length of one closed orbit. We hope that our results will be useful for understanding the photodetachment process of negative ions or the electron transport in a microcavity.

Photodetachment of H- near a deform sphere

On the basis of the theoretical imaging method, we study the photodetachment of H- near a deform sphere. We deduce the formula of the detached electron flux. Then we calculate the detached electron flux distribution and the photodetachment cross-section. The calculation results suggest that the influence of the plane on the photodetachment of negative hydrogen ion is only within a certain range. In the region close to the z axis, the spherical effect dominates and the electron flux and photodetachment cross section are the same as those that exist only on the sphere surface. While in the region far from the z axis, both the plane and sphere surface have significant effect and the electron flux and photodetachment cross section become much complicated. If we fix the radius of sphere and the distance between the deform sphere and the negative hydrogen ion, the oscillating amplitude in the electron flux fist increases and then decreases with the increase of the photon energy. Finally it increases slowly. But the oscillating frequency becomes complicated at all times. If we fix the distance between the deform sphere and the negative hydrogen ion, the detached electron flux distribution becomes more like that in the sphere case as the radius of the sphere increases. Hence, we can control the photodetachment of H- near the deform sphere by changing the incident photon energy or the radius of the sphere. Our results will provide some reference values for the photodetachment of H- near the curved surface and the experimental research of microscopy photodetachment.