The Investigation Of Controlling Of Atomic Non-sequential Double Ionization Under Strong Laser Pulse

With the development of science technology,the research on the interaction between light and matter has attracted much attention.During the past decades,with the rapid development of the laser technology,the pulse width of laser fields was shortened gradually while the laser intensity was increased greatly.This great achievement has made the research of light-mater interaction extend into the domain of strong-field physics.Subsequently,a series of novel strong-field phenomena have been observed,such as multi-photo ionization,above-threshold ionization,high order harmonic generation,and non-sequential double ionization(NSDI).Among all,NSDI has attracted much attention,because it contained the electron correlation phenomenon,which can play a key role in the light-matter interaction.The discovery greatly challenged the traditional photo-physics theory which is based on the single electron approximation and excited a great upsurge of studying electron correlation in strong laser field.Transient state in chemical reaction,transient evolution,structural changing in reaction and other curious quantum effects always happen in the extreme temporal and spatial scale.Using strong ultrafast laser pulse,we can understand the microstructure information in atomic and molecular scale,and also understand the transient state in attosecond time scale.Those investigations have profound research significance and wide application prospect.For example,we can infer the energy level structure of a target particle through studying the photoelectron momentum distribution.Investigation of tomographic imaging of molecular orbitals by high-harmonic generation.Obtaining high-harmonic supercontinuum spectrum by tuning parameters of laser pulse,which then generates a single attosecond pulse.In strong field double ionization,we can control sub-cycle dynamics of ionizing electrons.In earlier studies,the shapes of laser field are simple due to the limitation of experimental technology.In recent years,the development of the ultra-short laser technology and the experimental measurement methods enables us to control the electron dynamics by laser pulses with a significant amount of control parameters.For example,using of circularly and elliptically polarized laser pulse enables us to investigate in the two dimensional polarized plane,which broaden the research freedom of micro-mechanism.Composite laser pulses,e.g.two-color laser pulse,offer us numerous research approaches.We can explore the dynamics of ionizing electrons by a few-cycle laser pulse with the effect of carrier-envelope-phase.Using few-cycle laser,we can also analyze symmetrical problems in strong field phenomena.As the above,increasing research means are discovered in understanding the interaction between light and matter.Therefore,researchers endlessly uncover the physical details in the fundamental strong field phenomena,and reveal abundant complicated physical mechanisms,such as,in strong field ionization,nonadiabatic effects in ionization process,core-electron polarization effect,influence on NSDI by recollision with many times return,different excitation pathways in recollision-induced excitation ionization,thermalization process in recollision,Long-range Coulomb effect and low-energy structures,doubly excited state below the recollision threshold,shielding effect by inner electrons,and recollision under the Coulomb barrier.Those complicated investigations on strong field phenomena are exactly frontier issue in this field.Part of understanding of the underlying physical mechanisms is imperfect,especially in exploring influence on those strong filed physical mechanisms by laser parameters when the field conditions are changed.In addition,how to directionally control them by laser pulses is also a key point in research after partly understanding some of those phenomena.In this thesis,we discus some details problems of ionization channels that have not been fully understood in NSDI.Using classical model,we investigate the influence of different type laser pulses on excitation pathways in NSDI,double excited state and recollision channels with different return times,and then reveal the controlling of atomic double ionization by laser pulses.The novelty of the thesis are summarized as follows:The carrier-envelop-phase dependence of NSDI of atomic Ar with few-cycle elliptically polarized laser pulse is investigated using 2D classical ensemble method.We distinguish two particular recollision channels in NSDI,which are recollision-impact ionization and recollision-induced excitation with subsequent ionization.We separate the two channels according to the delay time between recollision and final double ionization.By tracing the history of the trajectories,we find the electron correlation spectra as well as the competitions between the two channels are sensitively dependent on the carrier-envelop-phase.Finally,control can be achieved between the two channels by varying the carrier-envelop-phase.NSDI of Ar by a counter-rotating two-color circularly polarized laser field is investigated.At the combined intensity in the‘‘knee”structure range,the double ionization occurs mainly through recollision induced excitation followed by subsequent ionization of Ar~-.By tracing the history of the recollision trajectories,we explain how the relative intensity ratio of the two colors controls the correlated electron dynamics and optimizes the ionization yields.The major channels contributing to enhancing the double ionization are through the elliptical trajectories with smaller travel time but not through the triangle shape or the other long cycle trajectories.Furthermore,the correlated electron dynamics could be limited to the attosecond time scale by adjusting the relative intensity ratio.Furthermore,we investigate the correlated-electron dynamics of Mg atom from a doubly excited,transition state in few-cycle circularly polarized laser field at low laser intensity using the classical ensemble method.The low energy transfer during the recollision process indicates that the two electrons cannot release directly,but it can pass through a doubly excited state,and then escape with the ionization time difference.The numerical results show that the feature of the sequential double ionization can be observed in the NSDI process.The results demonstrate that the intermediate state has lost any memory of its formation dynamics.The distribution of the angle between the two release directions of the two electrons also depends on the ionization time difference.Furthermore,the influence of e-e Coulomb repulsion is discussed.Finally,the double ionization from doubly excited state in counter-rotating two-color circularly polarized laser field is briefly discussed.At last,by partially overlapping time-delayed linearly polarized laser pulses and circularly polarized laser pulses,we construct an optical waveform with time dependent ellipticity.The first electron is ionized by the linearly polarized laser pulses and then is affected by the subsequent circularly polarized laser pulses.This delayed effect disturbs the ionizing electron at the transverse direction,which influences the number of returns before recollision.The number of returns in the recollision orbit can be controlled by changing the delay time between the two laser pulses.By tracing the history of the recollision trajectories,we explain how the time dependent ellipticity controls the different double ionization channels.In the last chapter,we close this thesis by drawing a conclusion on the major results and giving a perspective on the promising directions in strong field ionization.