Probing Photoemission Time Delay And Molecular Structure With Attosecond Photoelectron Interferometry

Photoionization of atoms and molecules is a fundamental laser-matter interaction process.When the atom or molecule interacts with the strong laser field,the electron can be ionized by different mechanisms.Due to the coherence of the electron wavepacket,there are rich interference phenomena in the photoelectron momentum distributions(PEMD),which contains information about photoemission,molecular spatial structure and ultrafast electron dynamics.In this paper,we have carried out interference studies of photoelectron wave packets through different ionization mechanisms such as two-photon ionization,multi-photon ionization and tunneling ionization.With these interferences,we have revealed the time delay in atomic and molecular photoionization,the time delay of continuum-continuum transition and have probed the molecule structure and electron dynamics.The main contents and innovations of this dissertation follow(1)We have investigated the time delay around the Cooper minimum in diatomic molecule photoionization.With the reconstruction of attosecond beating by interference of two-photon transition(RABITT),the energy-and angle-resolved photoemission time delay change from positive to negative values around the Cooper minimum.To explain the angle and energy dependence of the time delay,we have developed the spheroidal wave method in diatomic molecule photoionization.By analyzing the anisotropic parameters,it turns out that the Cooper minimum is responsible for the sign change in the RABITT time delay.Moreover,with the spheroidal wave method,the angular distributions in single-photon ionization are accurately described.In this paper,we have provided a quantitative theoretical analysis method for the diatomic molecule photoionization problem.(2)We have proposed the two-color circularly polarized(TCCP)laser fields to investigate the time delay of the continuum-continuum transition in two-photon and multiphoton ionization.In the co-and counter-rotating TCCP laser fields,different time delays have been extracted from the sideband modulation in the PEMDs.By comparing the interference channels in the co-and counter-rotating TCCP laser pulses and fitting the phase shifts of the anisotropic parameters,the electron angular-momentum dependent time delay has been retrieved.In two-photon ionization,the photoemission time delay difference between the co-and counter-rotating TCCP laser fields is less than 10 attosecond.While in multiphoton ionization,the photoemission time delay difference reaches 150 attosecond since the angular momentum is larger.In this paper,the relation between the continuumcontinuum time delay and the electron angular momentum is revealed.(3)We have probed molecular structure and electron dynamics with two-dimensional photoelectron holography in the counter-rotating TCCP laser pulses.By changing the intensity ratio of the TCCP laser fields,the interference structures in the PEMDs have been separated.With the strong field approximation,the holographic interference and other intracycle interference are determined.By changing the relative phase,the collision angle of the rescattering electron can be controlled to probe the molecular structure.Moreover,the TCCP laser field provide a multicycle time window to visualize the supposition state evolution.In this paper,two-dimensional holographic interference is applied to probe the molecular structure of hydrogen molecule ion and the dynamic process of supposition state.