Study On The Ionization Property Of Atoms And Molecules In The Intense Laser Field

Strong field ionization has been the hot topic on atomic and molecular physics in recentyears. In this paper, we bring a major focus on the ionization property of atoms and moleculesin the intense laser field, and some calculations are presented, which are about the ionizationquantities in the multiphoton and tunneling ionization regimes. The main contents are listed asfollows:The first part is the overview of strong field ionization, which is the topic of this paper.We simply introduce a development trend of the laser output that the pulse duration isbecoming shorter and the laser focused intensity is becoming higher. We discuss the threemost common types of strong field ionization, namely, multiphoton ionization, tunnelingionization and over-the-barrier ionization. We also propose three quantities, namely,ionization rate, ionization probability and ionization signal, all of which can give a descriptionof ionization property. We point out the key meaning of strong field physics and strong fieldionization.The second part is the introduction of the theories of strong field physics and strong fieldionization. We state three fundermental theories of strong field physics, namely, classicaltheory, semiclassical theory and quantum theory. We write down the time-dependentSchr dinger equation (TDSE) of atoms exposed to an intense laser field in the velocity gaugeand length gauge. And we list two kinds of methods for solving TDSE, namely,approximation model method and numerical solution method. We lay out the theoretical basesand the concrete steps of split-operator method and generalized pseudospectral method. Wealso deduce the ionization rate in a static and electric field for the ground state of thehydrogen atom. We present the extended expressions of Perelomov-Popov-Terent’ev(PPT)theory, Ammosov-Delone-Krainov(ADK)theory and MO-ADK theory.The third part is the calculation of the ionization probability of atoms in a linearlypolarized laser field. With three different methods, i.e. the PPT theory, the ADK theory andthe numerical solution of the TDSE, we work out the ionization probabilities of H, He and Neatoms versus peak intensity, and find that the ionization probabilities from the PPT accordquite well with those from the TDSE in a wider range from multiphoton to tunnelingionization, while the ADK results are reliable only in the tunneling ionization regime. Inaddition, we also work out the ionization probabilities of hydrogen atom versus laser intensity at three different laser wavelengths (λ=600nm,800nm and1200nm), and demonstrate that thePPT theory can well predict the wavelength dependence of ionization probability as well asthe TDSE. Only when the laser wavelength is long enough, will the result of ADK be close tothose of TDSE.The fourth part is the summary of this paper and the outlook of future work.