We study the resonant sequential two-photon ionization of neutral atoms by a combination of twisted- and plane-wave light within a fully relativistic framework. In particular, the ionization of an isotropic ensemble of neutral sodium atoms ($Z = 11$) from their ground $3^{2}S_{1/2}$ state via the $3^{2}P_{3/2}$ level is considered. We investigate in details the influence of the kinematic parameters of incoming twisted radiation on the photoelectron angular distribution and the circular dichroism. Moreover we study the influence of the geometry of the process on these quantities. This is performed by changing the propagation directions of the incoming twisted and plane-wave light. It is found that the dependence on the kinematic parameters of the twisted photon is the strongest if the plane-wave and twisted light beams are perpendicular to each other.
Ionization collisions have important consequences in many physical phenomena, and the mechanism that leads to ionization is not universal. Double differential cross sections (DDCSs) are often used to identify ionization mechanisms because they exhibit features that distinguish close collisions from grazing collisions. In the angular DDCS, a sharp peak indicates ionization through a close binary collision, while a broad angular distribution points to a grazing collision. In the DDCS energy spectrum, electrons ejected through a binary encounter collision result in peak at an energy predicted fro…
Electron vortex beams (EVB, also known as twisted electron beams) possess an intrinsic orbital angular momentum (OAM) with respect to their propagation direction. This intrinsic OAM represents a new degree of freedom that provides new insights into investigating the dynamics of electron impact ionization. In this communication, we present, in the first-Born approximation (FBA), the angular profiles of the triple differential cross-section (TDCS) for the (e, 2e) process on CH4 and NH3 molecular targets in the coplanar asymmetric geometry. We compare the TDCS of the EVB for different values of O…
Double ionization of an atom by single-photon absorption in the presence of a neighbouring atom is studied. The latter is, first, resonantly photoexcited and, afterwards, transfers the excitation energy radiationlessly to the other atom, leading to its double ionization. The process relies on the combined effect of interatomic and intraatomic electron correlations. It can dominate over the direct double photoionization by several orders of magnitude at interatomic distances up to few nanometers. The relative position of the neighbouring atom is shown to exert a characteristic influence on the …
Interplay between relativistic energy corrections and resonant excitations in x-ray multiphoton ionization dynamics of Xe atoms
本文从理论上研究了重原子的X射线多光子电离动力学。当原子暴露于由X射线自由电子激光（XFEL）产生的强X射线脉冲时，它通过一系列单光子电离和伴随的弛豫过程电离成高电荷离子，并且其最终电荷状态受到可以通过单光子电离电离的最后离子状态的限制。如果X射线多光子电离涉及重原子中的深内壳层电子，则相对论效应引起的能量移动在电离动力学中起重要作用，如[Phys.\修订版本\ Lett. \textbf{110}，173005（2013）]。另一方面，如果X射线束具有宽的能量带宽，则高强度X射线脉冲可以驱动宽范围的离子状态的共振光激发，并且甚至超过直接单光子电离极限，如在[Nature\ Photon.]中首次提出的。\textbf{6}，858（2012）]。为了研究相对论和共振效应，我们扩展了\textsc{xatom}工具包，将相对论能量校正和共振激发在X射线多光子电离动力学计算。计算了光子能量分别为1.5keV和5.5keV的强流XFEL脉冲与双原子相互作用系统的电荷态分布。对于这两种光子能量，我们证明了共振激发的电离动力学的作用是改变由于轨道能级的相对论效应的显着移位。因此，要准确模拟高X射线强度下的多光子多重电离动力学，必须考虑这两种效应。
We present the angular profiles of the triple differential cross-section (TDCS) for the (e,2e) process on the noble gas atoms, namely He (1s), Ne (2s and 2p), and Ar (3p) for the plane wave and the twisted electron impact. We develop the theoretical formalism in the first-born approximation. The present study compares the TDCS for different values of orbital angular momentum number $m$ and opening angles $θ_p$ of the twisted electron beam with that of the plane wave beam. In addition, we also investigate the TDCS for macroscopic atomic targets to explore the influence of opening angle $θ_p$ of…
In this communication, we present the results of the Five-fold Differential Cross Section (5DCS) and Triple Differential Cross Section (TDCS) for the (e,2e) process on molecular hydrogen ($H_2$) by the plane wave and the twisted electron beam impact. The formalism is developed within the first Born approximation using the plane wave and the twisted wave for the incident electron beam. We describe the plane wave, Heitler-London type wave function and Coulomb wave for the scattered electron, $H_2$ molecular state, and the ejected electron respectively. We compare the angular profiles of the 5DCS…
We study resonant two-photon ionization of helium atoms via the $1s3p$, $1s4p$ and $1s5p^1$P$_1$ states using the 15$^\mathrm{th}$ harmonic of a titanium-sapphire laser for the excitation and a weak fraction of the laser field for the ionization. The phase of the photoelectron wavepackets is measured by an attosecond interferometric technique, using the 17$^\mathrm{th}$ harmonic. We perform experiments with angular resolution using a velocity map imaging spectrometer and with high energy resolution using a magnetic bottle electron spectrometer. Our results are compared to calculations using th…
The ionization of atoms with sequences of attosecond pulses gives rise to excited ionic states that are entangled with the emitted photoelectron. Still, the ionic ensemble preserves some coherence that can be controlled through the laser parameters. In helium, control of the $2s/2p$ He$^+$ coherence is mediated by the autoionizing states below the $N=2$ threshold [Phys. Rev. Res. {\bf 3}, 023233 (2021)]. In the present work we study the role of the resonances both below and above the $N=3$ threshold on the coherence of the $N=3$ He$^+$ ion, in the attosecond pump-probe ionization of the helium…
It is shown that it is feasible to use ultrashort time delay between two XUV femtosecond pulses in order to control two photon resonant ionization. The proposal is demonstrated on the spectrum of Helium, in terms of nonperturbative solutions of the time dependent Schroedinger equation. Comparison with results from second order time dependent perturbation theory provides additional insight.
Modulation of attosecond beating in resonant two-photon ionization
本文在RABBIT（Reconstruction of Attosecond Beating By Interference of Two-photon transitions）的基础上，对存在自电离态时的光电子阿秒拍频进行了理论研究。我们表明，作为一个谐波穿越共振，其边带表现出峰值相移以及拍频本身的调制。此外，即使当泵浦脉冲和探测脉冲不重叠时，两个谐振路径之间的拍频也持续存在，从而提供灵敏的非全息干涉测量装置来重构相干亚稳波包。我们定量描述这些现象与一般的有限脉冲分析模型，占中间和最终的共振双光子过程的影响，在一个可以忽略不计的计算成本。在N=2的双激发态区域，模型预测与精确的从头计算结果非常吻合。
In this communication, we present the results of the triple differential cross-section (TDCS) for the (e,2e) process on H2O molecule for the plane wave and the twisted electron beam impact. The formalism is developed in the first Born approximation. We describe the plane/twisted wave, plane wave, the linear combination of atomic orbitals (LCAO) (self-consistent field LCAO method) and Coulomb wave for the incident electron, scattered electron, the molecular state of H2O, and the ejected electron, respectively. We investigate the angular profiles of the TDCS for the outer orbitals 1B1, 3A1, 1B2,…
Anomalous Autler-Townes Splitting in Resonant Multiphoton Ionization Driven by Bright Squeezed Vacuum
Huazhong University of Science and Technology（华中科技大学）；Shanghai Jiao Tong University（上海交通大学）；Technion–Israel Institute of Technology（以色列理工学院）；Guangdong Technion–Israel Institute of Technology（广东以色列理工学院）
We investigate the discrete orbital angular momentum (OAM) of photoelectrons freed in strongfield ionization. We use these `twisted' electrons to provide an alternative interpretation on existing experimental work of vortex interferences caused by strong field ionization mediated by two counterrotating circularly polarized pulses separated by a delay. Using the strong field approximation, we derive an interference condition for the vortices. In computations for a neon target we find very good agreement of the vortex condition with photoelectron momentum distributions computed with the strong f…
We present an experimental study on the photoionization dynamics of non-resonant one-color two-photon single valence ionization of neutral argon atoms. Using 9.3 eV photons produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and ions produced from non-resonant two-photon ionization in coincidence. Photoionization from the $3p$ orbital produces a photoelectron scattering wave function with $p$ and $f$ partial wave components, which interfere and result in a photoelectron angular distribution with peak amplitude perpendicular to the VUV pol…
We present a theoretical investigation of the resonant elastic scattering of laser photons by ultra-relativistic partially stripped ions, that is the core process of the Gamma Factory project. Special emphasis in our study is placed on the angular distribution and polarization of scattered photons as observed in the collider and ion-rest reference frames. In order to describe these (angular and polarization) properties for arbitrary relativistic many-electron ion, the general approach, based on the application of irreducible polarization tensors, is laid down. By making use of the polarization…
Measurements of the phase of two-photon matrix elements are presented for resonant and antiresonant two-color ionization of helium. A tunable, narrow-bandwidth, near-infrared (NIR) laser source is used for extreme ultra-violet (XUV) high-harmonic generation (HHG). The 15th harmonic of the laser is used within (1+1') XUV+NIR two-photon ionization, and tuned in and out of resonance with members of the 1s$n$p $^1$P$_1$ ($n=3,4,5$) Rydberg series, covering a broad spectral range with high spectral resolution. The technique allows to observe characteristic rapid changes in the phase of the two-phot…
We present a theoretical investigation of the resonant elastic scattering of twisted light, carrying angular momentum, by partially stripped ions. Special emphasis is placed on a question of whether the scattered radiation is also twisted. In order to investigate such an "angular momentum transfer", we develop an approach that allows us to find a quantum state of the final photon without projecting it onto a detector state. A general expression for this so--called \textit{evolved} state of outgoing radiation is derived and it can be used to analyze the resonant scattering by any ion, independe…
Photoionization of an atom in the presence of a neighboring atom of different species is studied. The latter first undergoes resonant photoexcitation, leading to an autoionizing state of the diatomic system. Afterwards, the excitation energy is transferred radiationlessly via a two-center Auger process to the other atom, causing its ionization. Assuming a fixed internuclear distance, it has been predicted theoretically that this indirect ionization pathway can strongly dominate over the direct photoionization. Here, we extend the theory of resonant two-center photoionization by including the n…
We present an experimental and theoretical energy- and angle-resolved study on the photoionization dynamics of non-resonant one-color two-photon single valence ionization of neutral N$_2$ molecules. Using 9.3 eV photons produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and ions produced from one-color two-photon ionization in coincidence. Photoionization of N$_2$ populates the X $^2Σ^+_g$, A $^2Π_u$, and B $^2Σ^+_u$ ionic states of N$_2^+$, where the photoelectron angular distributions associated with the X $^2Σ^+_g$ and A $^2Π_u$ state…
We theoretically explore a variant of RABBITT spectroscopy in which the attosecond-pulse train comprises isolated pairs of consecutive harmonics of the fundamental infrared probe frequency. In this scheme, one-photon and two-photon amplitudes interfere resulting in an asymmetric photoelectron emission. This interferometric principle has the potential of giving access to the time-resolved ionization of systems that exhibit autoionizing states, since it imprints the group delay of both one-photon and two-photon resonant transitions in the energy-resolved photoelectron anisotropy as a function of…
We present a multichannel photoelectron interferometry technique based on trichromatic pulse shaping for unambiguous determination of quantum phases in multiphoton ionization (MPI) of potassium atoms. The colors of the laser field are chosen to produce three energetically separated photoelectron interferograms in the continuum. While the red pulse is two-photon resonant with the $3d$-state resulting in a (2+1) resonance-enhanced MPI (REMPI), a (1+2) REMPI occurs via the non-resonant intermediate $4p$-state with an initial green or blue pulse. We show that ionization via a non-resonant intermed…
This work reports on the application of a novel electric field-ionization setup for high-resolution laser spectroscopy measurements on bunched fast atomic beams in a collinear geometry. In combination with multi-step resonant excitation to Rydberg states using pulsed lasers, the field ionization technique demonstrates increased sensitivity for isotope separation and measurement of atomic parameters over non-resonant laser ionization methods. The setup was tested at the Collinear Resonance Ionization Spectroscopy experiment at ISOLDE-CERN to perform high-resolution measurements of transitions i…
We present a new and efficient method of generating twisted gamma rays utilizing highly accelerated helium-like ions; they are excited to a chosen state by irradiating two optical lasers and emit a photon with orbital angular momentum in the deexcitation process. We study its emission rate together with other properties such as background and photo-ionization processes.
