Probe And Control Ultrafast Ionization Dynamics Of Atoms And Molecules In Strong Laser Fields

Ultrafast electron dynamics in atom or molecule,being the conestone in the science of light matter interaction,is on the attosecond time scale.The research of ultrafast electron dynamics opens a new chapter for the study of matter structure and the manipulation of chemical reaction,and will hopefully spur more interest on the exploration of life science.The recently developed advance techniques of ultrashort and intense laser technique and electron-ion coincidence measurement pave the way of accurately probing and controling the attosecond electron motion in atoms or molecules.By coincidently measuring the three-dimensional momentum of photoionization and dissociation induced electrons and ions in Cold target recoil ion momentum spectroscopy,this thesis focuses on the study of probing and controlling the ultrafast electron dynamics in strong-field ionization of atoms and molecules.The main content and inovation are summarized below:? Image the molecular internuclear distance and orientation with electron wavepackets interferenceBased on the electron-ion coincidence measurement,a dissociation pathway resolved photoelectron angular distributions(PAD)of H2 is measured in linear polarized ultraviolet laser fields.We uncover the roles of the molecular orientation and internuclear distance in the dissociative ionization of H2.The PAD of stretched-bound dissociation pathway demonstrates that the initial phase of ionized electron and its subsenquent action in the Coulomb field is very sensitive to the molecular alignment.The interference electron wave packets released from different internuclear distance and molecule alignment give rise to distinct mode structure in the PAD.? Attosecond multiphoton resonance photoelectron emission time delayAn attosecond phase-controlled orthogonal two-color(OTC)femtosecond laser pulse is employed to probe the time delay of photoelectron emission in strong-field ionization of atoms.Driven by the OTC fields,the intermediate excited states of 4f and 5p are coherently populated by absorping multiple photons from the ground state.Additional one SH or FW photon can release these excited electrons.We observed a multiphoton resonance absorption time delay of 140±40 attoseconds between photoelectrons emitted via the 4f and 5p Rydberg states of Argon.? Two-dimensional electron localization and its attosecond manipulationThe localization of remaining delocalized bound electron after photoionization can lead to directional bound breaking.An intense phase-controlled orthogonally polarized two-color ultrashort laser pulse is used to steer a two-dimensional electron localization in the polarization plane of the driven laser field.Emission-direction and kinetic-energy dependent asymmetric dissociation of H2 is observed as a function of the relative phase of the orthogonally polarized two-color pulse.Significant asymmetric proton emission is measured in the direction between two polarization axes? Probe the tunneling site of localized electron in polyatomic molecules and verify the intermediate state in molecular isomerization via above threshold double ionization electron spectra through the developed two electrons and two ions four-body coincidence measurement technique in strong laser fieldIn the prototype system of polyatomic molecule of C2H2,considering the significant reseach topic of electron tunneling site,we experimentally investigated the dissociative double ionization of acetylene in strong laser fields by measuring two fragment ions and two electrons in coincidence.Firstly,by distinguished the sysmmetry of ionized electrons,the significant role of ?-sysmmetry(HOMO-1,or HOMO-2)in dissociation channel is experimentally verified.With the help of molecular angular streaking,I firstly measured the localized electron tunneling site in the deprotonation dissociation channel of polyatomic molecules,realzing the breakthrough from diatomic to small organic molecules.In multiphoton ionization regine,we experimentally investigate the channel-resolved above-threshold double ionization(ATDI)of acetylene by using an ultraviolet femtosecond laser pulse.As compared to the sequential process,diagonal lines in the electron-electron joint energy spectrum are observed for the nonsequential ATDI owing to the correlative sharing of the absorbed multiphoton energies.We demonstrate that the distinct channel-resolved sequential and nonsequential ATDI spectra can clearly reveal the proton migration intermediate state in photon-induced acetylene-vinylidene isomerization.