Rydberg Excitation And Ionization Dynamics Of Atoms In Femtosecond Intense Laser Field

The development of laser technology has greatly promoted the progress of modern physics,especially the emergence of Femtosecond Intense Laser pulses,which enable people to study the microstructures of matter and the dynamic properties of atoms and their internal electrons under extreme conditions.In recent years,a series of novel non-linear physical phenomena have been observed experimentally,such as above threshold/higher-order above threshold ionization,non-sequential double ionization and high-order harmonic generation.As a new strong-field phenomenon,the strong-field Rydberg excitation is not only considered as an important supplement to the tunneling-rescattering process,but also has important application prospects in photo-controlled chemical reactions,acceleration of neutral particles and quantum information.In this paper,the excitation and ionization dynamics of atoms driven by Femtosecond Intense Laser field are systematically studied by using quantum theory.Electron dynamics in different kinds of atomic systems are studied by using different optical field parameters.The effects of excitation and excited states of strong field neutral Rydberg atoms on ionization behavior are discussed in depth.On this basis,we further develop the Kramers-Henneberger quantum method for the behavior of excited states of atoms in low-frequency laser fields,which explains the relevant physical phenomena well.The main research work of this paper is as follows:(1)The strong field Rydberg excitation of rare gas atoms and the ionization regulation of the atomic excited state are studied.By theoretical calculation,the changes of neutral excited atoms and ionized electrons with the intensity of laser field are studied,and the reverse oscillation structures in the two yields are observed.This phenomenon is reasonably explained by combining the shift of excitation level and ionization threshold boundary under the action of light field and the selection rule of dipole transition.By adjusting the parameters of light field such as time delay and laser frequency,the time and position of Rydberg electrons are changed,a scheme of atomic excited state ionization modulated by two-color laser pulses is proposed.(2)The applications of angular momentum state neutrally Rydberg atoms in quantum information and quantum computation are studied.The special quantum states of atoms are fabricated by using two time-delayed bicolor unipolar laser pulses,the preparation and evolution of electron wave packets,and the modulation and shaping of wave packets.Based on the dependence of photoelectron low energy momentum distribution and angular distribution on the initial state of ionization,an effective method for distinguishing degenerate angular momentum states of energy levels is proposed.(3)The influence of atomic resonance excited states on the above threshold ionization process is studied.Above threshold ionization processes of different atomic systems in tunneling and multiphoton regions were studied by using ultrashort laser pulses of different wavelengths.It is found that the low-energy structure of electron momentum spectrum is insensitive to the internal electronic structure of atoms during the tunneling process driven by long-wavelength light field,and the direct ionization process dominates the tunneling process.Therefore,the above threshold ionization process does not depend on the resonance effect of the excited state level.For the multi-photon region with short wavelength laser pulses,the low energy part of the electron momentum distribution and the angular distribution of energy strongly depend on the bound state energy level of the target atom,and the multi-photon process dominates.The difference of resonance states in the process of multi-photon excitation results in the difference of final suprathreshold ionization momentum distribution and angular distribution.(4)The application of Kramers-Henneberger transformation in the interpretation of Rydberg excitation in atomic strong field is studied.In mathematical processing,the static nuclear coordinate system is transformed into oscillating electronic coordinate system by coordinate transformation,and the effective potential under the combined action of light field and atomic nucleus in the new coordinate system is obtained.By analyzing the influence of light field parameters such as wavelength on the effective atomic potential,the physical processes of the generation and population of the excited states of atoms with different effective potentials are studied.We also extend the method developed in the high frequency field to the low frequency field,and give the application scope of the theory in the low frequency field.A new physical image of intense field excitation of atoms independent of traditional multi-photon and tunneling mechanism is presented by using the low-frequency field KH method.