An improved quantum trajectory Monte Carlo method involving the Stark shift of the initial state, Coulomb potential, and multielectron polarization-induced dipole potential is used to revisit the origin of the low-energy interference structure in the photoelectron momentum distribution of the xenon atom subjected to an intense laser field, and resolve the different contributions of these three effects. In addition to the well-studied radial finger-like interference structure, a ring-like interference structure induced by interference among electron wave packets emitted from multi-cycle time windows of the laser field is found in the low energy part of the photoelectron momentum spectrum. It is attributed to the combined effect of the Coulomb potential and Stark shift. Our finding provides new insight into the imaging of electron dynamics of atoms and molecules with intense laser fields.
In this paper we study the ionization rate and the Stark shift of a one-dimensional model of the H$_{2}^{+}$ ion. The finding of these two quantities is reduced to the solutions of a complex eigenvalue problem. We solve this problem both numerically and analytically. In the latter case we consider the regime of small external electrostatic fields and small internuclear distances. We find an excellent agreement between the ionization rate computed with the two approaches, even when the approximate result is pushed beyond its expected validity. The ionization rate is very sensitive to small chan…
We report on the appearance of a structure at low energies in the photo-electron momentum distribution of the hydrogen atom exposed to two-color counter-rotating bi-circular laser fields. These structures, which arise due to AC-Stark shifted resonances, break the three-fold symmetry, typical for the $ω-2ω$ bi-circular fields. We discuss the physical origin of this structure in terms of partial-wave interference between direct ionization channels and a resonant pathway, that passes through the AC-Stark shifted state and show how the underlying Rydberg state population depend on the field streng…
Holographic interferences in strong-field ionization beyond the dipole approximation: The influence of the peak and focal volume averaged laser intensity
We study single-photon ionization of aligned H$_2^+$ in a high-frequency low-intensity laser field. We focus on the case where the laser frequency is not far larger than the ionization potential of the target. The calculated photoelectron momentum distribution through numerical solution of time-dependent Schrödinger equation shows clear interference patterns. By developing a theory model applicable for high-frequency laser field, we show that the interference patterns can not be explained by the interference of the electronic wave with the observed momentum between these two atomic centers of …
Attosecond dynamics in strong-field tunnel ionization are encoded in intricate holographic patterns in the photoelectron momentum distributions (PMDs). These patterns show the interference between two or more superposed quantum electron trajectories, which are defined by their ionization times and subsequent evolution in the laser field. We determine the ionization time separation between interfering pairs of electron orbits by performing a differential Fourier analysis on the measured momentum spectrum. We identify electron holograms formed by trajectory pairs whose ionization times are separ…
Multielectron polarization effects in strong-field ionization: Narrowing of momentum distributions and imprints in interference structures
我们扩展了半经典两步模型[Phys. Rev. A 94，013415（2016）]，以包括多电子极化诱导的偶极势。利用这个模型，我们研究了多电子效应在线偏振激光脉冲电离光电子动量分布中的印记。我们预测缩小的纵向动量分布，由于电子聚焦的诱导偶极电位。我们发现，核心的极化也修改光电子动量分布的干涉结构。具体地，可以改变电子动量分布的低能量部分中的扇形干涉结构的数量。我们分析了这种干扰效应的机制。对多电子偶极势的解释似乎改善了理论与实验的一致性。
We investigate the resonance-enhanced few-photon ionization of atomic lithium by linearly polarized light whose frequency is tuned near the 2s-2p transition. Considering the direction of light polarization orthogonal to the quantization axis, the process can be viewed as an atomic "double-slit experiment" where the 2p states with magnetic quantum numbers m_l=+-1 act as the slits. In our experiment, we can virtually close one of the two slits by preparing lithium in one of the two circularly polarized 2p states before subjecting it to the ionizing radiation. This allows us to extract the interf…
Quantum calculations of tunneling in strong-field ionization (SFI) predict intricate momentum distributions due to sub-laser-cycle attosecond electron dynamics. These are obscured in most experiments by the dominance of inter-cycle interference patterns which are the hallmark of above-threshold ionization (ATI). Highly controlled 1- to 2-cycle laser pulses produce less inter-cycle interference but cannot accurately recreate the sub-cycle features produced by uniform cycle calculations due to the effect of the carrier envelope of the pulse. We present a simple and effective technique to recover…
The double-slit interference in single-photon ionization of the diatomic molecular ion $\mathrm{H}_2^+$ is theoretically studied beyond the dipole approximation. Via simulating and comparing the interactions of the prealigned $\mathrm{H}_2^+$ and the hydrogen atom with the xuv pulses propagating in different directions, we illustrate two kinds of effects that are encoded in the interference patterns of the photoelectrons from $\mathrm{H}_2^+$: (i) the photon-momentum transfer and (ii) the finite speed of light. While both effects could modify the maxima of the interference fringes, we show tha…
Multipath holographic interference in strong-field quantum tunnel ionization is key to revealing sub-Angstrom attosecond dynamics for molecular movies. This critical sub-cycle motion is often obscured by longer time-scale effects such as ring-shaped patterns that appear in above-threshold ionization (ATI). In the present work, we overcome this problem by combining two novel techniques in theory and experimental analysis: unit-cell averaging and time-filtering data and simulations. Together these suppress ATI rings and enable an unprecedented highly-detailed quantitative match between strong-fi…
Intra- and intercycle interference of angle-resolved electron emission in laser assisted XUV atomic ionization
本文对红外激光作用下超紫外脉冲电离氢原子进行了理论研究。激光辅助光电子效应问题通常采用成熟的理论来描述。然而，由Maquet等人在Journal of Modern Optics 54，1847（2007）中首次提出的公知的软光子近似和Kazansky在Phys.Rev.A 82，033420（2010）中的理论完全不能预测与偏振方向优先的电子发射。利用一个简单的半经典模型，研究了两个光场均为同向线偏振时光电子的角分辨能量分布。我们彻底分析和表征两个不同的发射区域中的角能域：（i）平行状区域的贡献的两个经典的轨迹每个光学周期和（ii）的类椭圆形区域的贡献的四个经典的轨迹每个光学周期。我们表明，我们的半经典模型是能够评估的角度分辨光电子谱的干涉图案在两个不同的上述区域。来自不同光学激光周期的电子轨迹引起称为边带的与角度无关的周期间干涉。这些边带被来自同一光周期中产生的电子轨道的干涉的角度依赖性粗粒结构调制。我们显示我们的半经典模型的准确性作为IR和XUV脉冲之间的时间延迟的函数，也作为激光强度的函数，通过比较半经典预测的角度分辨光电子光谱与连续扭曲波强场近似和从头算解的时间依赖的薛定谔方程。
We analyze interference processes in atomic ionization induced by a two-color laser with fundamental frequency $ω$ and its second harmonic $2ω$. The interplay between inter- and intracycle interference processes give rise to multiphoton peaks which can be named as main or ATI peaks and sidebands, in analogy to the well-known RABBIT (reconstruction of attosecond harmonic beating by interference of two-photon transitions). We use the saddle point approximation (SPA) to extract the complex ionization times of the interfering electron trajectories. Changing the relative phase between the two color…
We review the semiclassical two-step model for strong-field ionization. The semiclassical two-step model describes quantum interference and accounts for the ionic potential beyond the semiclassical perturbation theory. We discuss formulation and implementation of this model, its further developments, as well as some of the applications. The reviewed applications of the model include strong-field holography with photoelectrons, multielectron polarization effects in ionization by an intense laser pulse, and strong-field ionization of the hydrogen molecule.
