Probing Molecular Structure And Valence Electron Ultrafast Process With Strong-field Photoelectron Holography

The emergence of the femtosecond and attosecond laser sources boosts the rapid development of the ultrafast detection techniques,which open wide perspectives for the detection with unprecedented temporal and spatical resolution in physics,chemistry,material science and biology.It opens up the way for detecting the atomic/molecular structure on its intrinsic space scale,and to trace the strong-field physical process,chemical reaction and bioprocess with attosecond temporal resolution,heralding the advent of attosecond physics and attosecond chemistry.At present,attosecond detection techniques based on high-order harmonics spectroscopy,attosecond transient absorbtion spectrum and strong-field photoelectron spectrum have been developed and experimentally implemented to image the molecular orbital,trace the nuclear motion and monitor the valence electron dynamics.Recently,electron rescattering based strong-field photoelectron holography(SFPH)has drawn considerable attention.Since its discovery,SFPH has been considered as a promising attosecond detection technique,because the structural and dynamical information of the targets have been stored in the ionization and rescattering processes of the valence electron.However,controlling the SFPH process and developing methods to retrieve the structural/dynamical information from it still need detailed investigations as they are the keys for its applications.This thesis focuses on detailed study of the SFPH-based ultrafast detection scheme and its further developments.We analyse the formation and the manipulation of the SFPH pattern,and propose schemes to extract atomic/molecular structural information and monitor the ultrafast valence electron motion in the molecules.Our study is of great importance for both the investigation of the attosecond detection techniques and the application of the SFPH technique.The main research contents of this thesis are as follows:First,we investigate the control of the SFPH pattern.Utilizing the orthogonally polarized two-color(OTC)laser field,the spatial and temporal control of the recollision process of the rescattering electron can be realized.By varying the relative phase of the OTC field,the recollision time of the returning eletron can be accurately controlled,and thus the holographic pattern can be selectively switched on and off.The recollision angle of the returning electron can be adjusted by varying the relative intensity of the OTC field,enabling SFPH to record the structural information of the targets from different angles.Effective control over the SFPH pattern is of great importance for imaging molecular structure and ultrafast dynamics with SFPH-based scheme.Secondly,we propose a SFPH-based scheme to reveal the structural information of the atoms and molecules.Adopting the adiabatic theory,we explain that the inherent structural information,the phase of the scattering amplitude,is encoded in the phase of the SFPH pattern.The holographic fringes shift with the targets,indicating the difference of the phase of the scattering amplitude between various targets.Because the phase of the scattering amplitude has a one-to-one mapping with the internuclear distance of the molecule,the internuclear distance can be deduced from the shift of the holographic fringes.Moreover,we find that the information of the ultrafast process of the valence electron is also encoded in the phase of the SFPH pattern.Based on this,we propose a SFPH-based scheme,combing attosecond temporal and picometer spatial resolutions,to visualize the ultrafast charge migration in the molecules.With this scheme,the real-time observation of the charge migration in the hydrogen molecule ion is achieved.In a further step,we investigate the charge migration in more complicated molecule with this scheme.By employing the holographic fringes of the ground state as a reference,the ultrafast charge migration in the asymmetric molecule is directly visualized,which indicates that the usage of this SFPH-based scheme can be effectively broadened.Finally,we propose a scheme to snapshot the moving valence electron wavepacket in molecules using SFPH.By investigating the bifurcation structure in the SFPH pattern of the superposition state of the hydrogen molecule ion,we find that the longitudinal location of this bifurcation structure reveals the transient relative phase of the superposition state,and its transverse location reveals the relative phase of the superposition state.With this bifurcation structure,the transient electron wavepacket of the superposition state can be directly visualized.