Studies On The Photodetachment Of H~-Near The Surface By Laser Pulse And Time-dependent Ifeld

In recent years, laser technique and surface physics have a rapid development, muchattention has been paid to the dynamic properties of the photo-induced atoms or ions onsurfaces. From the experiment we know that the precision of the photodetachmentcross-section is related to the width of the laser pulse, for a laser pulse with a certain widthcan product the spectrum with a certain width. Recently, because the time-dependent externalfields in scientific experiments and practical application are common, the character of theabsorption spectroscopy of the time-dependent external fields has aroused wide concernamong the people. When the negative ion is in the oscillating electric field, being subject tothe unsteady field, the period and the action of the closed orbit will all change and this willincrease the complexity of the problem and produce the new modulation phenomenon. Thismakes the photodetachment of negative ion become more complex and interesting, this paperaccording to the above problems for the further research.The main works of this thesis are and listed as follows:Firstly, using the closed orbit theory and the formulas of laser pulse photodetachmentcross section of H-ion near a metal surface and in electric field near a metal surface, wecalculate the laser pulse photodetachment cross section of this system. The results suggestthat if the pulse width is much longer than the particular closed orbit period, the contributionof that closed orbit to the photodetachment cross section is very small, if the pulse width ismuch shorter than the particular closed orbit period，the influence on the photodetachmentcross section is nearly disappeared. For the double laser pulse cross section depends not onlyon the pulse width, but also on the time delay and the relative phase of the two pulses. Forcertain relative phase between the two pulses, the photodetachment cross section is increased;while for other relative phases, the photodetachment cross section is reduced.Secondly, we study the properties of the photo-induced electronic of the wave packetdynamics when the metal surface and electric field survive together and the impact exerted bythe ion-surface distance, laser pulse width and the electronic image state lifetime etc on theevolutions and revival structure of the detached electron is discussed. The results show thatwith the increase of the ion-surface distance, the influence of the mirror potential becomessmall and the interference effect is weakened, the evolution structure becomes more and more simple. But when the laser pulse is increased, the electron will be set to the higher electronicstate so the interference effect becomes strong and the evolution structure becomes morecomplex. We find when considering the electronic state lifetime，the amplitudes of thequantum probability density decreases gradually with time evolution，the whole wave packetstructure has a significant attenuation and the lifetime can weaken the interferencephenomenon in the process of wave packet evolution. But after a period of time, the wavepacket exhibits periodical collapse and expansion with the evolution of time，at last therevival structure disappears.Thirdly, using time-dependent closed orbit theory and the first order classicalperturbation theory, we study the photodetachment of H-in an electric field near a metalsurface plus a weak oscillating electric field. The calculated results suggest that the influenceof the oscillating electric field depends both on the oscillating electric field strength and theion-surface distance. For a given ion-surface distance, as we increase the strength of theoscillating electric field, the oscillating amplitude in the photodetachment cross section isreduced greatly. On the other hand, if we keep the strength of the oscillating electric fieldunchanged, with the increase of the ion-surface distance, the oscillating amplitude of thecross section is decreased while its frequency is increased. Furthermore, we also find thatwhen the ion-surface is large than100a.u., the influence of oscillating on thephotodetachment of H-in electric field near metal surface will be weakened periodically.This thesis is divided into five chapters. The first chapter is introduction, whichintroduces the research significance of the photodetachment of negative ions and reviews thedevelopment history of the closed orbit theory. The present research status of thephotodetachment of negative ions, the subject we choose and the main work what we havedone are also mentioned in this part. In chapter two, we investigate the influence of the laserpulse on the photodetachment of H-ion in electric field near a metal surface. In chapter three,we study the impact exerted by the ion-surface distance, laser pulse width and the electronicimage state lifetime etc on the evolutions and revival structure of the detached electron. Inchapter four, we study the impact exerted by a weak oscillating electric field on thephotodetachment of H-in an electric field and near a metal surface. In chapter five, we makea summary for this thesis and have a prospection for the study of other systems.