Measurement And Manipulation Of Quantum Orbit-resolved Strong-field Photoelectron

Strong field photoionization is the most basic process of the laser and matter interaction,which comes from the transition of electrons from the bound orbit to the continuous state in the strong laser field.Therefore,distinguishing the ionization characteristics of different bound quantum orbits will not only deepen the understanding of the ionization process,but also provide new degrees of freedom to control the ionization process.Atoms and molecules are the basic units of matter.Hence,an insight into the strong field photoionization properties of atoms and molecules can be used to explore the internal structure of atoms and molecules,and manipulate ultra-fast dynamics.In this paper,electrons from two degenerate orbitals are completely separated via orbit helicity-dependent Freeman resonance ionization in a single-color circularly polarized laser field.This orbital resolution ability can be used to generate energy-resolved highly spin-polarized electrons in the photoelectron energy spectrum.By replacing the single-color circularly polarized laser field with the counter-rotating two-color circularly polarized laser field,we can completely separate the electrons from two degenerate orbits in the photoelectron angular distributions,and obtain angle-resolved spin-polarized electrons.By adjusting the intensity ratio of the two beams,we study the competitive relationship between different channels and the asymmetry in the photoelectron angular distribution.Using the near-circularly polarized laser field to select specific intermediate states for resonance ionization,we measure the self-reference ionization delay between resonance channels.The main work and innovation of this paper are as follows:(1)We propose a new scheme to control the resonance ionization characteristics of the P₊and P_-orbits of the Xe atom ground state by changing the intensity of the circularly polarized laser with a center wavelength of 410 nm.According to the transition selection rule,the Rydberg state obtained after four-photon excitation from the P_-orbit has lower energy than the Rydberg state reached after excitation from the P₊orbit,so the P_-orbit needs a higher laser intensity for four-photon Freeman resonance ioniztaion,but at this time P₊orbit would undergo non-resonant ionization.With the increase of laser intensity,the P_-orbital emission electron peak via resonance ionization is unchanged in the energy spectrum,while the P₊orbital emission electron peak via non-resonant ionization moves toward lower energy,so we can clearly resolve the contribution of P₊and P_-orbits in the ionization energy spectrum,and thereby further separate electrons with high spin polarization from the photoelectron energy spectrum,which is expected to be applied to detect the ring currents state of single-atom.Our scheme has been proved to be suitable for laser pulses with wavelengths ranging from 400 nm to 410 nm and intensity ranging from 6×10¹³ W/cm² to 1×10¹⁴ W/cm².(2)A scheme is proposed to separate the P₊and P_-orbital contributions of Ar atoms in the angle-resolved photoelectron momentum spectrum by the counter-rotating two-color(400 nm+800 nm)circularly polarized laser field.For the P₊and P_-orbits containing ring currents with opposite helicities,the excitation ionization process is sensitive to the helicity of the driving laser.Therefore,changing the intensity ratio of the two lasers with opposite helicities can effectively control the ionization channels.By manipulating the ionization rates of the ionization channel that absorbs six-photons of 400 nm but releases one-photon of 800 nm and ionization channel that absorbs five-photons of 400 nm and one-photon of 800 nm,the two ionization channels with a phase difference of 1.07?can respectively present a three-lobed and six-lobed structure in the photoelectron angular distribution.According to the law of spin-orbit coupling,this angle-resolved orbit selection and ionization channel regulation abilities can be further applied to generate angle-resolved spin-polarized electrons.(3)Using the near-circularly polarized laser field to select a specific intermediate state to achieve resonance ionization,the experimental measured results show that the ionization delay between the 4f and 5f resonance channels is 45.6 as.Since the selected intermediate states only differ in the principal quantum number,but have the same angular quantum number and magnetic quantum number,our research reveals the influence of the radial part of the electron orbit on the photoionization time.