Studies On The Oscillating Characteristics Of The Photodetachment Cross Section Of H~- Near A Metal Surface

Photodetachment of negative ions is a typical example of fundamental processes where light and matter interact and an important way for cognizing the structure of negative ions. It is well known that the process of photodetachment is easily affected by the external environment. Initially people mainly study the photodetachment of negative ions in electric and magnetic field. In recent years, along with the fast development of laser and vacuum techniques, much attention has been paid to the photo-induced electronic excitations of adsorbates on surfaces, so the study of photodetachment is extended to the vicinity of surface. Closed orbit theory is broadly used to explain the question of atomic absorption and anionic photodetachment in strong external fields due to its clear physical picture and wide availability. In this paper, we exactly use this theory to study the modulation of an electric field and an elastic interface on the photodetachment of H_ near a metal surface and the influence of a metallic microcavity on the photodetachment cross section of H_. The results provide a reference value for experimentally studying the photodetachment of negative ions near surfaces and have a great significance for understanding electron scattering at surfaces and for further developing optical instruments such as photodetachment microscopes.The main works of this thesis are and listed as follows:Firstly,the influence of electric field direction and magnitude on the photodetachment of H_ in an electric field near a metal surface is investigated. Using the closed orbit theory, we analyze the trajectories of the detached-electron and derive the photodetachment cross section formula step by step when the angle between the field and the positive z-axis is 0, 180 and an arbitrary value in turn. The results show that when the direction of the electric field is along the positive z-axis, with the increasing of the electric field, the oscillating amplitude of the photodetachment cross section increases while the oscillating frequency decreases. When the direction of the electric field is along the negative z-axis, since the direction of the electric field force and the image Coulomb force is opposite, the oscillating structure of the photodetachment cross section becomes very complicated. As the electric field is very weak, the photodetachment cross section approaches to the case when only a metal surface exists. When the electric field grows to such a value that the electric field force and the image Coulomb force are equal to each other, the photodetachment cross section is the same as the case in a free space. As the electric field is very strong, the photodetachment cross section approaches to the case when only the electric field exists. If the magnitude of the electric field is kept constant and the field direction changes, the closer angleαmoves to 90 degrees, the smaller the oscillations in the photodetachment cross section are.Secondly, the effect exerted by an elastic interface on the photodetachment of H_ in an electric field near a metal surface is studied. It is found that the oscillations in the photodetachment cross section become stronger after the interface is added. And the causes of those strengthened oscillations depend on the size and direction of the external electric field. When the electric field 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 augments the oscillations by increasing the total number of the closed orbits or by extending the coherent incident energy range.Thirdly, the photodetachment of H_ in a metallic microcavity is researched. Since the metallic microcavity is made up of two parallel metal surfaces, infinite number of image charges can be produced theoretically, as a result the image potential acting on the detached electron is very complicated. So in this part we firstly make an approximate disposal for the image potential and then analyze the photodetachment cross section semi-classically. It is demonstrated that the oscillating structure in the photodetachment cross section can be modulated by changing the distance between the wall of the microcavity and the H_. Meanwhile, to show the relation between the oscillations in the photodetachment cross section and the classical closed orbits of detached electron clearly, we make a Fourier transformation for the scaled photodetachment cross section of this system and find that each peak in the Fourier transformed cross section corresponds to the scaled action of a closed orbit. This demonstrates that the oscillations in the cross section are caused by the interferences of the electronic wave travelling along the closed orbit and the outgoing wave.This thesis is divided into five chapters. The first chapter is introduction, which introduces the research significance of the photodetachment of negative ions and reviews the development history of the closed orbit theory. The present research status of the photodetachment of negative ions, the subject we have chosen and the main work we have done are also mentioned in this part. In chapter two, we investigate the photodetachment of H_ in an electric field near a metal surface, and the studies are focused on the influence of the electric field and magnitude on the photodetachment cross section. In chapter three, we study the effect exerted by an elastic interface on the photodetachment of H_ in an electric field near a metal surface, and the reasons of the enhanced oscillations caused by the interface are given a detailed analysis. In chapter four, we research the photodetachment of H_ in a metallic microcavity, and the relationship between the oscillation structure in the photodetachment cross section and the closed orbit is revealed. In chapter five, we make a summary for this thesis and have a prospection for the future study.