Research On The Initial Distribution Of The Tunneling Electron Wave Packet Based On Strong-field Photoelectron Interference

In the process of strong-field laser interaction with atoms and molecules,electrons can get rid of the binding of the nucleus through the quantum tunneling effect,and tunneling ionization occurs.Since tunneling ionization can induce many interesting strong-field physical phenomena,such as high harmonic generation,non-sequential double ionization,and photoelectron interference,the research on tunneling ionization has been a hot research topic of strong field photophysics.Generally,tunneling ionization can be divided into two steps: tunneling and classical motion.The initial electronic wave packet distribution after tunneling has a decisive influence on subsequent processes(such as photoelectron interference structures,etc.),and provides an important basis for the study of the quantum tunneling process.The study of the initial distribution of tunneling electron wave packets can give a deeper understanding of many phenomena in strong-field physics.It can can also promote the research field of strong-field laser-matter interaction.In this paper,the initial distribution of the tunneling electron wave packet is studied,based on the photoelectron interference structure.The three-dimensional photoelectron momentum distribution was detected by a cold target recoil ion momentum spectrometer system(ie COLTRIMS device).The photoelectron interference structures and initial distribution of tunneling electrons were studied.The scaling law of the photoelectron holographic structure and the ellipticity of the elliptically polarized laser field is established.Furthermore,the initial longitudinal momentum of the tunneling electron wave packet is measured by photoelectron holography.It is confirmed that the tunneling electron wave packet has non-zero initial longitudinal momentum,revealing the non-adiabatic strong field tunneling ionization process.Our studies will have important guiding significance on the atom molecular structure imaging and the generation of the attosecond light source.The main research contents of the thesis are as follows:Firstly,the photoelectron holography and the initial distribution of tunneling electrons under mid-infrared laser field are studied.An interference structure called "inner-spider" structure exists in the low-energy region of the photoelectron momentum distribution.By using the quantum-trajectroy Monte Carlo model,the initial distribution of tunneling electrons of the "inner-spider" structure is studiedg.Comparing with the semi-classical model,which ignores the coulomb potential,the coulomb effect on the photoelectron holography structure is revealed.This study is of great significance for detecting the dynamic process of low-energy electrons and studying low-energy structures.Secondly,the initial distribution of the tunneling electrons in the photoelectron holography and the above-threshold ionization in the elliptically polarized laser field is studied.The tunneling ionization process of atoms and molecules in the elliptically polarized laser field is very different from that in the linearly polarized laser field.By measuring the photoelectron holographic interference structure under different laser ellipticities,the holographic fringe spacing decreases with the increase of the laser ellipticity,and the scaling law between the photoelectron holographic structure and the laser ellipticity is established.In addition,the above threshold ionization structure under the elliptically polarized laser field is also studied.It is found that the deflection angle of the photoelectron angular distribution maximum decreases with the increase of the laser ellipticity.It is found that this phenomenon is due to the attosecond ionization time difference of the electrons in the elliptically polarized laser field.Finally,the initial momentum of tunneling electrons is accurately measured by photoelectron holography.In this paper,a method for measuring the initial longitudinal momentum of tunneling electrons by using photoelectron holography is presented.The phtoelectron holographic structures are measured by using an orthogonal two-color laser field formed by a strongfundamental laser field(800nm)and a weak second-harmonic laser field(400nm)with perpendicular polarization directions.The intermediate canonical momentum is extracted by the photoelectron holographic interference fringes,which change with the perturbative second-harmonic laser field.Then,the initial longitudinal momentum is measured by the coupling relationship between the intermediate canonical momentum components.This study shows that the initial longitudinal momentum of electrons at the tunneling exit is not zero,which is inconsistent with the classical adiabatic approximation theory and reveals the non-adiabatic characteristics of the electron tunneling process.