Vortex Electron Momenta In Atomic Ionization By Polarized Attosecond Pulses And Stark Effect

Over the past decade,investigation and the successful generation of attosecond laser pulses in the laboratory have witnessed the progress in strong field physics,and attosecond sciences have burgeoned.Recently,researchers have discovered that vortex-like electron momentum spectra can be generated by ionization of atoms using oppositely circularly polarized and time-delayed attosecond pulses.The complex interference patterns can be effectively used to characterize the dynamic processes of atoms and molecules exposed to intense light fields.In the present thesis work,the vortex electron momenta induced by attosecond pulses are extensively investigated through numerical simulation and theoretical calculation.The research work can be summarized as follows:Firstly,an approximate analytical method based on strong field approximation(SFA)theory and an accurate theoretical method based on wave-packet theory are deployed,and the vortex electron momenta generated by ionization of the hydrogen atom are numerically studied,counting the dynamic Stark effect.We define the ac Stark coefficient by two different methods and interrogate the distortion,decomposition and fusion of the vortex electron momentum patterns under the influence of the ac Stark effect.The results show that the vortex electron momenta can be utilized as a novel tool for studying the dynamic Stark effect.Secondly,the vortex electron momenta generated by ionization of the hydrogen atom in an elliptical polarized field are simulated,and a novel type of orthogonally elliptically polarized and time-delayed pulse combination is proposed to study the ionization characteristics for elliptically polarized laser field.We have suggested a theoretical approach,termed as ‘the irregularity of overlapped fields',to explain the morphology of the vortex electron momenta induced by the pulse combination,and found that the symmetry,the location,the direction and the number of the vortex arms are very sensitive to the ellipticity and the time delay.These observations are of great significance for investigating complex-polarized ultrashort pulses and their intrinsic properties in atomic ionization.Finally,the vortex electron momenta generated by ionization of the hydrogen atom by the combined pulses of isolated attosecond pulse-infrared radiation(IAP-IR)are interrogated.Based on this scheme,a method for isolated attosecond pulse-carrier envelope phase(IAP-CEP)characterization exploiting the vortex momentum spectra is proposed.According to the theory of Ramsey interference,we construct an IAP-IR time-delayed pulse pair and simulate the vortex-like momentum distributions induced by this pulse combination.The numerical results have unveiled that some parameters of the vortex patterns show a good linear relationship with the IAP-CEP,therefore,the proposed method can be employed as an ideal tool for characterizing the IAP-CEP.