NO分子形状共振阿秒动力学精密测量

Precise measurement of attosecond dynamics of NO molecular shape resonance

形状共振是分子电离散射过程中的一种重要现象,其阿秒量级的光电离延时的精密测量,是深入认识形状共振过程及成因的重要基础.本文使用基于近红外飞秒激光与极紫外阿秒脉冲串的阿秒符合干涉仪,利用双光子干涉的阿秒拍频重构的探测方法,对一氧化氮(NO)分子4σ电子的形状共振过程进行研究,实验测量了分子内有效电离延时对光子能量的依赖关系,通过对比双光子跃迁延时与单光子跃迁延时,发现单光子过程的Wigner延时是双光子跃迁延时随能量变化的主要原因.基于单中心展开的量子散射理论计算表明,在分子形状共振位置的电子电离延时,主要由连续态中高角动量离心势囚禁的电子决定.

Shape resonance is an important and ubiquitous phenomenon in the process of molecular scattering and photoionization.The study of the attosecond photoemission time delay in the vicinity of the shape resonance is of great significance for understanding its intrinsic origin on a nature time scale of electron motion.In this paper,an advanced attosecond coincidence interferometer consisting of a near-infrared femtosecond light source and an extreme ultraviolet attosecond pulse train is used to study the shape resonance process of the 4σelectron of nitric oxide molecules via reconstructing attosecond harmonic beating by measuring the interference of two-photon transitions(RABBIT).The energy dependent effective ionization time delay in the vicinity of the resonance energy region is reported.By comparing the relationship between the two-photon transition delay and the one-photon transition delay,it is found that the Wigner delay of the single-photon process is the main reason for the two-photon transition delay changing with energy.The effect of continuum-continuum delay is further explored.Theoretical calculations of the initial state(bound state)and final state(resonance state)electron wave function orbits of the resonance show that the shape resonance assisted time delay is dominated by the electrons trapped in the centrifugal potential barrier.