A Fully Quantized Study Of Atomic Double Ionization In Strong Laser Fields

Strong-field double ionization refers to the phenomenon of ionization of two electrons driven by a strong laser field.This process provides a simple and effective way to study the electron correlation effect that exists widely in the microscopic world.In this thesis,the non-perturbative scattering theory is used to quantize both the laser field and the atoms,and the physical process of the non-sequential double ionization of the atoms in the strong laser field is systematically studied.In this thesis,the eigenstate of electron pair moving in strong laser field is used to deduce the transition matrix element and the analytical expression of double ionization rate for double ionization.The main research results of this paper are as follows:(1)The eigenstates of electron pairs moving in a strong laser field are derived.Using the unitary transformation,the motion state of the two electrons in the strong laser field is divided into two degrees of freedom: inner and outer.The inner degree of freedom describes the relative motion of the system of two electrons around its center of mass,which can be described by the eigenstate of the Coulomb repulsion potential,independent of the external laser field;the outer degree of freedom describes the system of two electrons as a whole in the laser field,Which can be described by a quantized Volkov state.Two eigenstates of motion together describe the eigenstates of electron pairs moving in a strong laser field.(2)The analytical expressions of the transition matrix elements and the double ionization rate of the double ionization are deduced.Using the fully quantized Coulomb-Volkov state and the non-perturbative scattering theory,the transition element are deduced.It is found that the matrix element under the first-order approximation represents the direct ionization of two electrons under the action of the laser field,which includes the energy distribution process caused by the Coulomb interaction between the electrons and the multiphoton ionization process of the quasiparticle.This corresponds to the shake off mechanism of double ionization;the matrix element under the second-order approximation includes the multiphoton ionization of a single electron,the interaction between the ionized electron and the bound electron,and the exit process.This corresponds to the re-collision mechanism.Using the obtained transition matrix elements,the analytical expressions of the double ionization rate in the shake off mechanism and the recollision mechanism are deduced respectively.(3)Using the analytical expression of the ionization rate of the shake off mechanism,the double ionization process of helium-like atoms in a strong laser field is studied,and the effect of Coulomb repulsion between two electrons is shown.The study found that the Coulomb force between the two electrons effectively increases the ionization rate of high-energy electrons by two to three orders of magnitude,but the ionization rate of low-energy photoelectrons is suppressed.(4)The effects of the photoelectron exit process on the double ionization rate and the photoelectron angular distribution in different double ionization mechanisms are studied.By comparing the double ionization rate without the appearance and the double ionization rate with the appearance process,it is found that the appearance process of the photoelectrons has a certain degree of inhibition on the double ionization rate,and the inhibition degree is about two orders of magnitude;The photoelectron exit process significantly modulates the angular distribution of the photoelectron pairs and changes the spatial distribution of the outgoing photoelectron pairs.