Investigations On Atomic Single Ionization In An Intense Laser Field

With the development of laser technology,ultra-intense and ultra-short laser pulses can be obtained in the laboratory.So many nonlinear phenomena,such as above-threshold ioniza-tion,hiah-order above threshold ionization,high-order harmonic generation,and nonsequential ionization,have been observed in the experiment when atoms or molecules are exposed to the intense laser field.The study of these phenomena helps us understand the ultra-fast motion of electrons at the microscopic scale and realize the atomic and molecular structure imaging and the real-time detection of charge transfer,chemical reaction and so on.In recent decades,great efforts have been done on experimental observations and theoretical research in order to study the underlying mechanisms.Based on the so-called three-step model,many phenomena have been successfully explained.However,the underlying mechanisms of many phenomena still remain controversial.By numerically solving the time-dependent Schrodinger equation and KFR theory,we have investigated single ionization phenomena in atoms interact with the intense laser field.The main works are listed as follows:1.We have investigated the dynamics of electrons from the multiphoton to tunneling regimes.By numerically solving the time-dependent Schrodinger equation,we obtain the time-dependent ground state population.Then,applying the Fourier transform on the ground state population,we get the frequency information carried by the ground state population.By an-alyzing the dynamics of ground state evolution,we discuss the motion behavior of electrons from the multiphoton to tunneling regimes.2.We have proposed a scheme to reconstruct the populations of bound states via pho-toelectron momentum spectra.Adding two laser pulses with time delay and tuning the time delay,we can obtain the photoelectron momentum spectra for different time delays.Next,by performing the Fourier transform on the time delay,we can obtain frequency-resolved photon-electron spectroscopy.According to the theoretical derivation,we know that the spectroscopy can separate ionization from different bound states to different positions on the spectrum.Based on this feature,we propose a scheme to reconstruct the populations of bound states and verify it by numerically solving the time-dependent Schrodinger equation.3.We have established a quantum model without excited states from the Schrodinger equation and applied this model to investigate the resonance-like enhancement phenomenon in the high-order threshold ionization.In our calculated system,the model can basically reproduce the enhanced structures obtained by the Schrodinger equation.This indicates that the excited states are not a key factor in the resonance-like enhancement.Besides,based on the model,we divide the motion process into three processes:direct ionization from the ground state to the continuum state,re-scattering between the continuum states,and the recombination process from the continuum state to the ground state.We find that the interference between different momentum transfer channels leads to the resonance-like enhancement,while direct ionization and recombination processes can affect the details of the enhanced structures.Finally,we also discuss the dependence of the enhancement structure on the laser intensity and the ATI peak.