A Theoretical Study On The Photoionization In The Ultrashort Laser Pulse

The rapid developments of modern laser technologies have significantly increased the pulse intensity and reduced the pulse duration.An ultrastrong laser pulse could accelerate an electron at rest to have a relativistic speed,which offers an opportunity to explore the fundamental physical law under extreme conditions.Meanwhile,an ultrashort laser pulse could resolve the electron motion in a short time scale,which serves as an ultrafast camera to capture the motion of the microscopic world.In this thesis,we study the laser interaction with simple atoms,molecules,and free electrons.First,we investigate the photoelectron momentum distribution in the presence of a mid-infrared pulse.A numerical simulation technique is developed utilizing the Lippmann-Schwinger equation for the Green function.Based on the technique,we carry out systematical ab initio simulations to study the photoelectron momentum distribution of atoms and molecules in the infrared laser pulse and connect the non-monotonic change of the distribution tilt angle with the fluctuation of the ionization instants.Noticing the tunneling ionization probability depends exponentially on the electric field,we propose a strategy to characterize the carrier-envelope phase of an isolated attosecond pulse.The proposal has the advantages of being robust against the focal volume intensity average effect and the uncertainty of mid-infrared pulse's carrier-envelope phase.With the semiclassical Monte Carlo trajectories simulations,we unravel the classical origin of the ionization probability enhancement of the high energy direct ionization electron and identify the relationship between the Coulomb effect and the topology structure of the electrons' initial phase space.Second,we investigate the ionization due to intense high-frequency pulses.Based on the dynamics of the Kramers-Henneberger states,we explore the mechanism of the adiabatic ionization stabilization,the ionization due to the nonadiabatic change of the laser intensity,and the dynamic interference.We point out that an adiabatically rotating laser axis could produce the non-Abelian geometric phase and result in the spin-flipping.Based on the ab initio simulations,we demonstrate the possibility of realizing Young's double-slit interference using a single atom and observe the charge resonance enhanced ionization.These results show that an atom in the intense high-frequency pulse has similar properties as molecules,which implies the possibility of studying the molecule physics with an atom.In return,the photoelectron momentum distribution carrying the double-slit interference structure provides unambiguous evidence on the existence of KramersHenneberger states,and thus the adiabatic stabilization.Third,we investigate the transfer of the photon linear momentum and angular momentum to the atoms and molecules.We find the photon momentum partition law between the photoelectron and the ion presents Young's double-slit interference.To study the photon momentum partition law in a general situation,we construct the exact nondipole Volkov wave function in the nonrelativistic regime and build the nondipole strong-field approximation.Based on the nondipole strong-field approximation,we explore the general photon partition law,the effect of Coulomb potential,and the initial conditions for the nondipole nonadiabatic tunneling ionization.Combined with the experiment,we investigate the nuclei rotation due to the absorption of the photon angular momentum and unravel the mechanism of photon angular momentum transfer.Fourth,we investigate the strong-field quantum electrodynamics.Based on the local constant field approximation,we transform the radiation problem in a general laser field as effective synchrotron radiation.We develop a spin-resolved semiclassical radiation reaction model to study the bichromatic strong-field quantum electrodynamics cascades.The numerical simulations demonstrate the possibility of producing the highly spinpolarized positron beam with the present laser facility.At last,we developed the spinor-helicity formalism for the strong field quantum electrodynamics.Combined with the Britto-Cachazo-Feng-Witten recursion relation,the spinor-helicity formalism could significantly simplify the calculations of the strong-field quantum electrodynamics.