Above Barrier Ionization Of Kramers-Henneberger Atoms

With the emergence of superintense and ultrashort pulsed lasers,a new subjectstrong field physics was born.In superintense lasers,perturbation theory is no longer valid to study interaction between atoms and lasers.New nonperturbative methods have to be used,such as High Frequency Floquet Theory(HFFT).Atoms and molecules exposed to superintense laser field exhibit an exotic phenomenon:ionization rate decreases as laser intensity increases.This new phenomenon is called“atomic stabilization”.According to HFFT,in high-frequency limit,a new Coulomb potential is formed between the oscillating electron and the nucleus,which is called the KramersHenneberger(KH)potential or“dressed”potential.The KH potential can support many bound states which are called the KH states.The corresponding atoms are called the KH atoms.KH atoms can only exist in superintense laser fields,and superintense lasers are usually focused laser beams.Therefore,in the focused laser field,KH state electrons will experience ponderomotive(PM)force,which comes from the nonuniform spatial distribution of the PM potential.In this paper,starting from the Time dependent Schrodinger Equation(TDSE),by using frame transformation(from laboratory to KH frame)and high-frequency approximation,we convert the time dependent Schrodinger equation into a time-independent one.Variational method is used to solve the Schrodinger equation and the variational parameters are coefficients of basis functions.Finally we obtain eigenfunctions,energy levels and PM forces of KH states hydrogen atoms.The work of this thesis consists of the following two parts:1.We study the KH eigenstates of a hydrogen atom in linearly polarized laser fields,including the ground state and some specific excited states.Here we use a set of new basis functions to solve the Schrodinger equation which are completely different from literature,but can obtain KH eigenstates of hydrogen atoms very accurately.We focus our study on energy levels and structures of eigenstates with symmetry of ?g and ?u.At large quiver amplitude,in addition to the famous“dichotomy”structure exhibited by ground and first excited states,we also find multi-lobe structures in higher excited states.2.We study the effects of PM force on atomic structure and stabilization of KH atoms in focused laser fields.According to theoretical calculation,PM force is proportional to square of electron's quiver amplitude,however,the critical force for above barrier ionization(ABI)of KH state decreases dramatically.Such that PM force-induced ABI occurs.We take some laser parameters as examples to study the relation between area of ABI and laser intensity in the focal plane.With increasing laser intensity,the area of ABI increases significantly.Our work will pave the way for experimental study of PM force-induced ABI.