Study On The Electron Tunneling Dynamics With Attosecond Resolution

In a strong laser field,atoms and molecules can undergo quantum tunneling ionization,and whether electron tunneling takes time is a basic quantum mechanics problem.The development of ultrafast physics technology with femtosecond or even attosecond resolution provides a new solution for the study of tunneling time.The current research on tunneling ionization time is still very controversial: one viewpoint is that there is a nonzero tunneling ionization time,and the other is that tunneling ionization is instantaneous.In this thesis,the energy-resolved attosecond scheme is used to carry out an experimental study on the electron tunneling time.This thesis is based on the measurement by using Cold Target Recoil Ion Momentum Imaging Spectrometer(COLTRIMS)and a 40 fs elliptically polarized laser pulse for ionizing simultaneously two different target atoms in two groups of mixed noble gases(Xe/Kr,Ar/Kr).The photoelectron momentum distribution(PMD)of different atoms was obtained by coincidence measurement.At the same time,each experiment was conducted in various laser intensity conditions,and energy-resolved attosecond angle measurement was performed,in which a series of experimental phenomena were observed.The PMD measured in the experiment presents a series of Above Threshold Ionization(ATI)rings separated by single-photon energy,and these rings exhibit different angular offsets.Under the same laser intensity,the deflection of peak angles for different atoms are completely different and this difference also depends on the ATI order.For the first-order ATI,the peak angle difference between Xe and Kr ranges from3.8° to 4.2°,which is greater than the angle between Ar and Kr,whose difference is 0.3°～1.2°.As the ATI order increases,the angle difference between the two atoms increases at first,and then decreases.The angle difference between Xe and Kr increases up to about 19.2°,and the angle difference between Ar and Kr increases up to about 13.3°.The angle difference between Ar and Kr decreases more,and the difference in high-order ATI becomes smaller.This trend is consistent with the ionization time.In addition,the dependence of the ATI peak deflection angle of all atoms on the energy change is consistent,and it decreases approximately at the second-order ATI,that is around 1.5-3 e V and reaches the maximum.In the ATI peak change curve of each group of experiments,we observed that the ATI angular distribution gradually splits from a single-peak to a double-peak structure as the ATI order increases.This feature exists in different laser intensities for different atoms.We speculate this phenomenon may be caused by intracycle interference in laser fiels.The energy-resolved measurement results are confirmed by the three-dimensional TDSE calculations.Our method has good accuracy and universality,and is insensitive to laser carrier envelope phase,pulse width and other conditions.These works have laid the foundation for further in-depth research on the accurate understanding of the dynamics of atoms and molecules on the attosecond scale.