Probing Resonant Photoionization Delay Time By Molecular Attoclock

The application of laser technology in probing structure of matter and its motion has greatly improved the accuracy in theoretical and experimental research.Ultra-short intense pulses acting on atoms and molecules can detect physical phenomena that have not been discovered by traditional techniques,which also makes ultra-fast process physics a hot topic in the forefront.With the maturity of ultra-fast and ultra-short laser technology with less period,the internal structure of atoms and molecules can be measured with more accurate results.Attosecond spectrum energy spectrum based on atom can obtain the electron tunneling dynamic process in attosecond time resolution,but the complex spatial structure of molecules makes this problem difficult.In order to solve this problem,a molecular atomic clock with electron tunneling position resolution is constructed in the experiment of Ar-Kr dimer ionization,and a transient resonant ionization process is found.Two different ionization channels corresponding to direct and resonance deflection angles are observed in the photoelectron angle distribution within the molecular framework.We confirm the existence of a quasi-bound state in Ar-Kr system,and these excited electrons are temporarily trapped in negative energy ～-0.41 a.u.In the coulomb well of and then released into the continuum.Using direct tunneling ionization as a reference frame,it is found that the resonance delay of the electron in the resonant quasi-bound state is 3.5 ± 0.037 fs,if the different molecular axis is considered,and the maximum deviation is 0.2 fs.In the experiment of Ar-Kr dimer ionization,we also found that there are a certain amount of excited electrons after the laser field ends.Frustrated tunneling ionization mechanism and tightly bound mechanism are also observed in the excited electrons,and the analysis shows that the wavelength has an obvious regulation effect on the electrons of the two mechanisms.It is calculated that with the 60 TW and 1600 nm laser,the excited electron had a 5-photon transition.Finally,the trajectory similar to Lissajous is found in the trajectory of bound electrons,which verifies again that the resonance-like excitation occurs in Ar-Kr system,and there is a quasibound state related to Ar-Kr intrinsic energy.Our work provides not only impetus for the exploration of ultrafast electron dynamics in complex systems,but also provide a semi-classical representation of electron trapping dynamics in quantum resonance states.