Ionization Of Atoms And Molecules In The Two-color Strong Laser Fields

With the rapid development of laser technology,the interaction between laser and matter produces a series of high-order nonlinear physical processes,including above-threshold ionization,high-order harmonic,non-sequential double ionization and so on.These interesting physical phenomena have greatly aroused the interest of experimental physicists and theoretical physicists,thus further promoting the development and application of strong field physics,which has significant contributions to the detection of the internal structure of matter and ultra-fast dynamics processes,as well as the manipulation of chemical reactions.In this paper,the frequency domain theory is used,which is based on the non-perturbation quantum electrodynamics.In this theoretical framework,the laser field,the atoms and molecules are regarded as an isolated system,and the laser field is quantized,the initial state and final state of the transition are given,after the interaction between matter and light,the transition matrix elements of the corresponding physical process are obtained.In this paper,we mainly study the above-threshold ionization process.By combining with the appropriate laser field parameters,the angular resolved above-threshold ionization energy spectrum of atoms and molecules is obtained by numerical calculation,and the results are analyzed in detail.Finally,our conclusion is given.The main research work of this paper is as follows:?1?We study the total angular resolution ATI energy spectrum of hydrogen atoms under the two-color laser field,where the two-color laser field is composed of elliptically polarized IR laser and linearly polarized XUV laser.We found that the total ATI energy spectrum presents a multi-platform and asymmetric interference structure,and the energy spectrum continuously shifts to the right with the increase of elliptically polarization degree.In order to analyze the reasons of interference fringes,we divided the total ATI process into two parts:direct ATI and rescattered ATI.For direct ATI,the reason for the interference fringes is that under the elliptically polarized IR laser,the emission direction of the ionized electrons is perpendicular to the polarization direction of the XUV laser,so the ionization probability is minimal.For the rescattering ATI,the dip structure in the rescattering ATI energy spectrum mainly comes from the interference superposition of waist structure of the sub-channel by means of channel separation and saddle point approximation,while the waist structure of the sub-channel is caused by violation of energy conservation before and after the collision in the recollision process of electrons.?2?We give two different geometric configurations of H₃²⁺,which are linear and triangular,and obtain the direct ATI angular resolution energy spectrum of H₃²⁺molecules in the monochromatic laser field,and compare the energy spectrum characteristics of the two configurations.Later,we add a beam of linear polarization laser on the basis of the monochromatic laser,the direct ATI spectrum of H₃²⁺in the two-color laser field has been studied.We found ATI spectrum in the two-color laser field is more sensitive to the molecular structure than that of monochromatic laser field,and molecular different configurations of ATI spectrum in the two-color laser fields shows different interference fringes,we analysis the reason of the formation of the interference fringes in the detail.In addition,by changing the laser intensity and molecular internuclear distance,we compared angular resolution ATI energy spectrum of the triangular configuration of H₃²⁺molecules with linear configuration.Finally,we concluded that the direct ATI energy spectrum in the two-color laser field has the ability to identify two different molecular configurations of H₃²⁺.?3?We study the angular resolution ATI spectra of polyatomic molecules in the linearly polarized IR+XUV two-color laser field.Here,the polyatomic molecules we studied are SF₆ and CH₄ molecules.The purpose of using two-color laser field is to get a wider and higher energy spectrum,where IR laser can broaden the energy spectrum,and XUV laser can increase the ionization probability of electrons in the molecule.This is beneficial for extracting the structure information of complex polyatomic molecules.We find that molecular orbitals in the momentum space can be simplified in the high energy region,and with these simplified molecular orbitals we can obtain many interference fringe formulas which carry information about the molecular bond length.Therefore,the interference fringe of ATI spectrum can be used to predict the molecular bond length by the corresponding interference formula.Here,we propose a new imaging method from the perspective of frequency domain,which will have important applications for complex polyatomic molecular imaging in the future.