Theoretical Study Of Ionization Properties For Diatomic Molecules In An Intense Laser Field

Many interesting nonlinear strong-field phenomena, such as high-energy above-threshold ionization（HATI） 、 non-sequential double ionization（NSDI） 、 and high-order harmonic generation（HHG）, will happen when a molecule is exposed to an intense laser field. Tunneling ionization of molecules is the first step of these strong-field rescattering processes. The angular dependence of ionization rate（or probability） P（θ）（θ is the angle between the molecular axis and the laser ’s polarization direction） and ionization suppression of molecule in comparison to its companion atom are two important topics have been paid much attention。Theoretically, P（θ） can be obtained by using Schr?dinger equation（SAE- TDSE） based on single-active-electron approximation、time-dependent density functional theory（TDDFT） or time-dependent Hatree-Fock（TDHF）. However, these methods are very time-consuming. Fortunately, Some simple physical models like molecular Ammosov-Delone-Krainov（MO-ADK） 、 the molecular Perelomov-Popov-Terent’ev（MO-PPT） 、 the molecular strong-field approximation（MO-SFA） and the weak- field asymptotic theory（WFAT）. The advantages of these models are much less computing time and can predict quanlitatively experimental measurements. In addition, Ionization suppression of molecules have been attracted much attention since discrepancies between theoretical calculations and experimental observations in some molecules.In this dissertation, we mainly study ionization rate and ionization suppression of molecules using MO-ADK、MO-PPT models. We determine structure parameters Clm in the MO-ADK model for the HOMO of 27 selected dimers, where wave functions with the correct asymptotic behavior are obtained by solving time independent Schr?dinger equation of linear molecules with B-spline functions and one-electron potentials which is numerically created with LBa model. Using the MO-ADK model, we study the alignment-dependent ionization probabilities of several selected dimers and compare them with the MO-SFA calculations. We show the MO-PPT can successfully give the laser wavelength dependence of ionization rates（or probabilities）. Based on the MO-PPT model, two diatomic molecules having valence orbital with anti-bonding systems（i.e.Cl₂,Ne₂）show strong ionization suppression while comparing with their corresponding closest companion atoms.