High-order Harmonic Radiation And Tunneling Ionization Of Atoms And Molecules In A Two-dimensional Strong Laser Field

As an effective means of exploring the micro world,it is of great significance to study the interaction between light and matter.In this paper,the high-order harmonic generation(HHG)and tunneling ionization processes(TI)of model atoms and molecules in a strong two-dimensional laser field are studied numerically and analytically by using the time-dependent Schrodinger equation(TDSE)and the strong-field approximation(SFA).Several factors affecting the emission of HHG of linear molecules and some characteristics of two-dimensional tunneling of electrons are summarized,which reveal the micro structure and dynamics of atoms and molecules under the strong field.The first chapter start with the emergence and development of laser,introduces some physical phenomena of atoms and molecules in the strong field,and expounds the concepts and theoretical issues involved.The second chapter briefly introduced and deduced the two theory methods used in this paper to study the strong-field physics,solving TDSE and the SFA.In chapter three,we study the spectral and temporal properties of HHG from aligned molecules in orthogonal two-color laser fields(OTC)consisting of a strong fundamental field and its second harmonic.Numerical simulations show that the HHG depends strongly on the relative phase between these two colors and the molecular alignment.In particular,for some cases,HHG differs remarkably in consecutive half cycles of the fundamental field.As the emission of harmonics is very strong in a half laser cycle,it is weak in the following half.A simple model related to the molecular structure is proposed to explain these phenomena.Our results suggest a potential approach for generating trains of attosecond pulses with only one pulse per cycle over a wide energy region.In chapter four,we study tunneling ionization of atoms in strong two-dimensional laser fields numerically and analytically,with focusing on OTC and circularly polarized fields.We pay attention to the tunneling route,along which the electron exits the barrier formed by the two-dimensional laser field and the Coulomb potential,for the maximal tunneling probability(i.e.,the most probable route for tunneling).This route corresponds to the maximal amplitude in two-dimensional photoelectron momentum distributions in the laser polarization plane.We compare the most probable route of two-dimensional tunneling with the classical predictions and the predictions of single-color-field approximations where it is assumed that the tunneling is dominated by the main component of the two-dimensional laser field with larger laser amplitudes.With these comparisons,some basic properties of two-dimensional tunneling are discussed.Our work sheds light on complex dynamics of atomic tunneling ionization in two-dimensional laser fields.