Subcycle-and Orbital-resolved Ultrafast Dynamics Of Atoms And Molecules In Strong Laser Fields

The structure and energy of the atoms and molecules are governed by the interaction and motion of the electrons and nuclei,which occur on the ultrafast time scales of femtosecond or attosecond.The rapidly developed ultrafast laser technique provides an effective tool for precisely probing and controlling the involved ultrafast dynamics.The dynamics of atoms and molecules in strong laser fields are very rich and meanwhile complex.Probing and understanding of these ultrafast dynamics in the simple system on the atomic scale are significant for us to reveal the complex dynamics in larger molecules or liquid phase,and promote applications in other related fields.The investigation of the ultrafast behavior of atoms and molecules by using well-controlled ultrashort laser pulses,in particular the temporal evolution and multi-orbital effects,is crucial for us to understand the structure change and interaction of molecules.This thesis focuses on the subcycle and orbital-resolved dynamics of atoms and molecules in strong laser fields by measuring the photo-ionization created electrons and ions in coincidence.The main contents and results are summarized below.?I?Subcycle characterization of the photoelectron emission in the single ionization of ArBy partially overlapping two time-delayed orthogonally polarized multicycle laser pulses of the same carrier frequency,a polarization-skewed laser field is constructed with the polarization rotating continuously inside the overlapping region.As the polarization direction of the laser field is uniquely related to its temporal evolution,the photoelectrons emitted at different instants will be emitted to different directions and thus leading to different momenta.By measuring the 3-dimensional momentum distribution of photoelectrons and ions coincidently,subcycle dynamics of the photoelectron emission is resolved in the single ionization of Ar atom.The effects of the Coulomb focusing on the electron trajectories and final momenta distribution is revealed.?II?Timing different pathways of the dissociative single ionization of H₂Driven by a polarization-skewed laser field,the ionization instants of H₂ and photon-coupled dipole-transition instants of the stretching H₂⁺ is encoded in the emission directions of the photoelectrons and nuclear fragments.By coincidently measuring the momenta of photoelectrons and ions produced in the dissociative ionization of H₂,it's found that the one-photon and net-two-photon dissociation pathways undergoes the same stretching time to reach the one-photon transition point.Depending on the mass of the nuclei,the stretching time of D₂ is?2 times more than that of H₂ for the same dissociation pathway.?III?Multi-orbital effect in the single ionization of C₂H₂By ionizing the pre-align C₂H₂ molecule at alignment or anti-alignment times using an ultrashort probe pulse,multi-orbital effect in the single ionization of C₂H₂molecule are recognized by examining the corresponding photoelectron momenta.Depending on whether the released electron comes from the HOMO or HOMO-1orbital,the C₂H₂ molecule will mostly populate the bounded cation state or dissociate into a neutral and a charged nuclear fragments correspondingly.