Probing Ultrafast Dynamics Of Atom Strongfield Tunneling Ionization With Photoelectron Interferometry

Tunneling is a fundamental process in quantum mechanics and it has been used in many areas of science and technology,such as scanning tunneling microscopy,tunneling junction,tunneling diode,tunneling field-effect transistors,etc.Laser-induced tunneling ionization is one of the most fundamental and ubiquitous quantum processes,which initiates a broad range of important phenomena in the ultrafast science community.Accurately measuring atomic/molecular ultrafast dynamics in strong-field tunneling ionization is of great significance for understanding these phenomena and exploring their application.Recently,rapidly developing attosecond technology provides the opportunity for probing ultrafast dynamics of atom in strong-field tunneling ionization.Up to now,based on attosecond detection techniques such as high-order harmonics and attoclock,many important problems of strong-field tunneling ionization,such as how long it takes for the electron to tunnel through the potential barrier,the initial position and velocity of the tunneling electron wave packets(EWPs)have been solved.Specifically,more information about atomic or molecular ultrafast dynamics in strong-field tunneling ionization are contained in the phase of EWPs.These EWPs undergoing different paths and reaching to the detector with the same final momenta can interfere with each other.Recently,much attention has been paid to the strongfield photoelectron interference.These interference structures serve as another important tool to probe the ultrafast dynamics of atom in strong-field tunneling ionization.Therefore,this thesis based on the strong-field photoelectron interference explores the ultrafast dynamics of atom in strong-field tunneling ionization.The main contents and innovations are as follows:1)With the strong-field photoelectron holography(SFPH),the correspondence between the tunneling ionization time of electron and the final momenta is measured.This SFPH is derived from the interference of the near forward rescattering EWP and the direct EWP.By adding a perturbative second harmonic(SH)to the strong fundamental(FM)field,the motion paths of the rescattering and the direct EWPs are disturbed,and thus the SFPH is shifted.Analyzing the response of SFPH to the SH field,the tunneling ionization time of EWP can be accurately measured.In this scheme,the complex influence of Coulomb correlation can be safely canceled,and thus the time retrieval processes are greatly simplified.Our results show that tunneling ionization time of electron is a complex number.The relationship between the tunneling ionization time of electron and the final momenta is consistent with that from quantum orbit model.In experiment,the attosecond photoelectron interferometer has also been implemented.2)Based on the SFPH,we also propose a novel scheme to measure the laser intensity.In this scheme,the SFPH fringes change periodically with the relative phase of orthogonally polarized two-color field,and the amplitude of changes has a minimum.Our results show that the longitudinal momentum of the minimum equals to 0.6 times the amplitude of FM vector potential.By measuring the longitudinal momentum of the minimum,the laser intensity can be accurately calibrated.3)Employing the temporal double-slit interference,we measure the time information of direct EWP.The temporal double-slit interference comes from the interference of two direct EWPs,which are ionized at the adjacent quarter cycles of laser pulse.In our scheme,adding a weak SH to a strong FM field with parallel polarization,the relative phase of these two direct EWPs is changed,and thus the temporal double-slit interference is disturbed.By analyzing the response of the temporal double-slit interference to the weak SH field,the imaginary part of the ionization time of the direct EWP can be accurately determined.Similar to the SFPH scheme mentioned above,in this scheme,the influence of long range Coulomb potential can be ignored.Therefore,this scheme is stable and feasible,and it can be extended to probing the time characteristics of more complex molecules in strong-field tunneling ionization.4)With the phase of the phase spectroscopy(PP)in parallel two-color field,we identify the relative contributions of the quantum orbits corresponding to the electrons tunneling ionized at the adjacent falling(long orbit)and rising(short orbit)quarter periods of the electric field of the laser pulse.In previous studies,it is generally believed that in the low-energy region(below 2Up),the contribution of the long orbits is dominant,and that of short is very small and can be ignored.Our results show that their relative contribution is sensitively dependent on the longitudinal momentum and modulated with the lateral momentum of the photoelectron.At the holographic interference minima,the contribution of the short orbit is even greater than that of the long orbit.This is due to that the direct EWP of the long orbit destructively interferes with that of near forward rescattering EWP,reducing the contribution of long orbits.Our study quantifies the relative contribution of long and short orbits.This information is necessary to establish an exact correspondence between the ionization time and final photoelectron momentum in photoelectron momentum distributions(PEMDs),and it is of great significance to probe the atom dynamics in attosecond scale.5)With the two-color PP spectroscopy,we also study the relative contribution of the multiple-returning recollision orbits to the high-energy PEMD.By analyzing the high-energy PP spectroscopy,a characteristic phase jump is observed.With semi-classical model,we demonstrate that the phase jump origins from the competition of orbits where the recollision occurs at different returning.Moreover,our results demonstrate the relative contribution of multiple-retuning recollision orbits depends on the ellipticity and wavelength of FM laser pulse.In elliptically polarized laser field,the high-energy photoelectron yield favors the contribution of the second-returning recollision orbits.In the mid-infrared laser field,the relative contribution of multiple-returning recollision orbits to the PEMD is very complex and it depends on the electron final momentum.