Attosecond Photoelectron Diffraction Of H₂⁺ And Its Applications For Coulomb Potential Imaging

The development of attosecond science has provided light sources with extremely short pulse duration for photoelectron diffraction,solving the problem of insufficient resolution in time while retaining high resolution in space.Attosecond photoelectron diffraction has enabled the investigation of laser-matter interaction with unprecedented spatio-temporal resolution and allows direct access to the structure dynamics in atoms and molecules,and therefore has attracted great interest in the ultrafast community.Although the significance of the coulomb potential in describing the attosecond photoelectron diffraction has been extensively studied,how to extract physical information in a quantitative way remain a challenging task.In this thesis,we investigate the photoionization of hydrogen molecular ions by an attosecond pulse in different initial states.1)we study the case where the initial state of the molecule is a single state and use a two-centre interference model to extract the coulomb potential of the molecule.2)we carried out a theoretical analysis of attosecond photoelectron diffraction from an non-stationary electron wave-packet.Firstly,we have analysed the attosecond photoelectron diffraction spectrum of H2+ at different parameters when the initial state is the ground state and analyzed the formation of the diffraction structure.Then we modified the mathematical formula depicting the photoelectron angular distribution under the plane wave approximation by introducing the coulomb potential induced phase shift,and proposed a simple scheme to reconstruct the coulomb potential of molecules using a two-centre interference model,which provides an important basis for further realization of molecular structure dynamics detection at attosecond time resolution.In addition,we have systematically investigated the attosecond photoelectron diffraction of non-stationary electron wave packets of hydrogen molecular ions.We calculated the photoelectron diffraction spectrum with the electron density distribution localized to a single nucleus and explained the asymmetric diffraction structure caused by forward single scattering.Further,we "monitored" the photoelectron angular distribution during the evolution of the electron wave packet and qualitatively analyzed the effects of electron density,laser parameters and internuclear distances on the photoelectron diffraction structure,shedding light to the timeresolved detection of charge migration processes in molecules..