Study On Above-Threshold Ionization Of Atoms In Intense Laser Fields

With the development of laser technology,the study of laser-matter interaction has attracted the closer attention of scientists.The above-threshold ionization of atoms and molecules in laser field has become one of the hot topics in the field of strong field physics.In recent years,a series of interesting nonlinear physical processes have been investigated and observed experimentally,such as above-threshold ionization(ATI),non-sequential double ionization(NSDI),high-order harmonic generation(HHG),etc.In this paper,the above-threshold ionization of atoms in a strong laser field is studied theoretically by solving the time-dependent Schr?dinger equation(TDSE).The main contents are as follows:(1)We theoretically study the above-threshold ionization of neon atom in chirped laser field by solving the three-dimensional time-dependent Schr?dinger equation.By comparing the energy spectrum,angular distribution and two-dimensional momentum spectrum of photoelectron from laser pulse with different chirp rate reveals that there is almost no chirp dependence in the single-photon ionization,while chirp dependence exists in the multiphoton ionization,and it is found that the dependence on chirp in the multiphoton ionization ATI can be attributed to the role of excited bound states.Next,by changing the wavelength of the laser in the multiphoton ionization process of neon atom,it is found that the dependence of the ATI spectrum on chirp becomes weaker as the wavelength decreases.(2)By solving the three-dimensional time-dependent Schr?dinger equation of hydrogen atom in the combined field of infrared and extreme ultraviolet laser pulses,the influence of XUV pulse on the photoelectron energy spectra and two-dimensional photoelectron momentum distribution(PMD)was studied theoretically.Our results show that,compared with the infrared laser only case,photoelectron energy spectra and two-dimensional photoelectron momentum distribution driven by the combined field presents an obvious interference enhanced structure,which is intensively depended on the intensity,photon energy and time delay of XUV pulse.The present method can be used to selectively enhance the high energy above-threshold ionization spectra.