Resolving and weighing the quantum orbits in strong-field tunneling ionization

Jia Tan,Wei Cao,Xu Han,Qingbin Zhang,Min Li,Shengliang Xu,Peixiang Lu,Yueming Zhou

doi:10.1117/1.ap.3.3.035001

Jia Tan, Wei Cao + Show 6 more

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https://doi.org/10.1117/1.ap.3.3.035001

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Abstract

Tunneling ionization of atoms and molecules induced by intense laser pulses contains the contributions of numerous quantum orbits. Identifying the contributions of these orbits is crucial for exploring the application of tunneling and for understanding various tunneling-triggered strong-field phenomena. We perform a combined experimental and theoretical study to identify the relative contributions of the quantum orbits corresponding to the electrons tunneling ionized during the adjacent rising and falling quarter cycles of the electric field of the laser pulse. In our scheme, a perturbative second-harmonic field is added to the fundamental driving field. By analyzing the relative phase dependence of the signal in the photoelectron momentum distribution, the relative contributions of these two orbits are unambiguously determined. Our results show that their relative contributions sensitively depend on the longitudinal momentum and modulate with the transverse momentum of the photoelectron, which is attributed to the interference of the electron wave packets of the long orbit. The relative contributions of these orbits resolved here are important for the application of strong-field tunneling ionization as a photoelectron spectroscopy for attosecond time-resolved measurements.

Highlights

Laser-induced tunneling ionization of atoms and molecules is a fundamental process in strong-field physics
Numerous quantum orbits contribute to the photoelectron momentum distribution (PEMD), giving rise to the interference structures such as the above-threshold ionization rings[35] and the spider-like holographic pattern.[18,36]
The ionization time of the photoelectron is usually determined based on the assumption that the long orbit dominates the photoelectron yields

Summary

Introduction

Laser-induced tunneling ionization of atoms and molecules is a fundamental process in strong-field physics. It is the first step for various intriguing phenomena in attosecond science, such as high-order above-threshold ionization,[1] high-order harmonic generation,[2] and enhanced double/multiple ionization.[3,4,5] detailed understanding of the tunneling step is of fundamental importance for attosecond science. Great efforts have been made to reveal the dynamics of strong-field tunneling. The questions of how long it takes the electron to tunnel through the potential barrier[6,7,8] and when the tunneling electron appears at the outside of the barrier have been surveyed in depth.[9,10,11] The features of the tunneling electron wave packet have been widely studied.[12,13,14,15,16]

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