Christian Buth, Kenneth J. Schafer
Using attoscience, we study the electron correlations responsible for Auger decay in krypton atoms. The Auger decay is induced by a pulse train or a twin pulse composed of subpulses of attosecond duration. During the Auger decay an optical dressing laser may be present. Interference effects between the ejected Auger electron wave packets are predicted.
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We examine the archetype of an interference experiment for Auger electrons: two electron wave packets are launched by inner-shell ionizing a krypton atom using two attosecond light pulses with a variable time delay. This setting is an attosecond realization of the Ramsey method of separated oscillatory fields. Interference of the two ejected Auger-electron wave packets is predicted, indicating that the coherence between the two pulses is passed to the Auger electrons. For the detection of the interference pattern an accurate coincidence measurement of photo- and Auger electrons is necessary. T…
The low-energy electron spectra emitted in the radioactive decay of the $^{83}$Rb and $^{83}$Sr isotopes were measured with a combined electrostatic electron spectrometer. Radioactive sources used were prepared by ion implantation of $^{83}$Sr into a high purity polycrystalline platinum foil at 30 keV and by vacuum-evaporation deposition of $^{83}$ Rb on the same type of foil. From the measured conversion electron spectra, the electron binding energies (referenced to the Fermi level) for the K, L$_1$ , L$_2$ , L$_3$ , M$_1$ , M$_2$, and M$_3$ shell/subshells of krypton in the platinum host wer…
We predict that attosecond spectroscopy could be used to observe time delay for electron emission {in the C$^{1+}$ ion} from a few step processes {that include electron impact excitation}. The results reveal that the photon energy corresponding to the excitation to the $1s 2s^{2} 2p^{2} \, ^{2}D_{1.5}$ level from the ground one has to be used to study the emission of the electrons produced with the largest probability from a few step processes. Double and triple Auger processes are investigated in the C$^{1+}$ ion as a sequence of single Auger transition with subsequent ionization by the Auger…
Probing coherent electronic superpositions of singly- and doubly-excited states of krypton with attosecond four-wave mixing spectroscopy
利用阿秒四波混频光谱探测氪原子单激发态和双激发态的相干电子叠加，揭示双激发态与单激发态的相互作用，并建立可处理的理论模型用于电子态的计量与控制。
We present the first fully ab initio calculations for attosecond transient absorption spectroscopy of atomic krypton with overlapping pump and probe pulses. Within the time-dependent configuration interaction singles (TDCIS) approach, we describe the pump step (strong-field ionization using a near-infrared pulse) as well as the probe step (resonant electron excitation using an extreme- ultraviolet pulse) from first principles. We extent our TDCIS model and account for the spin-orbit splitting of the occupied orbitals. We discuss the spectral features seen in a recent attosecond transient absor…
Comment on "Brilliant source of 19.2 attosecond soft X-ray pulses below the atomic unit of time"
本文评论Ardana-Lamas等人对19.2阿秒软X射线脉冲的重新表征，指出其忽略俄歇电子、低能谐波及脉冲啁啾等关键因素，结论有效性存疑。
Light-induced states are commonly observed in the photoionization spectra of laser-dressed atoms. The properties of autoionizing polaritons, entangled states of light and Auger resonances, however, are largely unexplored. We employ attosecond transient-absorption spectroscopy to study the evolution of autoionizing states in argon, dressed by a tunable femtosecond laser pulse. The avoided crossings between the $3s^{-1}4p$ and several light-induced states indicates the formation of polariton multiplets. We measure a controllable stabilization of the polaritons against ionization, in excellent ag…
The KLM+KLN Auger electron spectrum of rubidium (Z=37) emitted in the electron capture decay of radioactive $^{83}$Sr in a polycrystalline platinum matrix and also $^{85}$Sr in polycrystalline platinum and carbon matrices as well as in an evaporated layer onto a carbon backing was experimentally studied in detail for the first time using a combined electrostatic electron spectrometer. Energies, relative intensities, and natural widths of fifteen basic spectrum components were determined and compared with both theoretical predictions and experimental data for krypton (Z=36). Relative spectrum l…
The KLL Auger spectrum of rubidium following the electron capture decay of $^{83}$Sr and $^{85}$Sr isotopes was experimentally studied in detail for the first time using one $^{83}$Sr source and three $^{85}$Sr sources in different host matrices. Energies, relative intensities, and natural widths of all the nine well-resolved basic spectrum components were determined and compared with both predictions and experimental data for krypton. Results of our multiconfiguration Dirac-Fock calculations demonstrated an influence of the "atomic structure effect" on absolute energies of the KLL transitions…
Intense X-ray free-electron lasers (XFELs) can rapidly excite matter, leaving it in inherently unstable states that decay on femtosecond timescales. As the relaxation occurs primarily via Auger emission, excited state observations are constrained by Auger decay. In situ measurement of this process is therefore crucial, yet it has thus far remained elusive at XFELs due to inherent timing and phase jitter, which can be orders of magnitude larger than the timescale of Auger decay. Here, we develop a new approach termed self-referenced attosecond streaking, based upon simultaneous measurements of …
We present a study of high-order-harmonic generation (HHG) assisted by extreme ultraviolet (XUV) attosecond pulses, which can lead to the excitation of inner-shell electrons and the generation of a second HHG plateau. With the treatment of a one-dimensional model of krypton, based on time-dependent configuration interaction singles (TDCIS) of an effective two-electron system, we show that the XUV-assisted HHG spectrum reveals the duration of the semiclassical electron trajectories. The results are interpreted by the strong-field approximation (SFA) and the importance of the hole transfer durin…
We study photoionization of various noble gas atoms by attosecond pulses produced in High Harmonic Generation (HHG). We use a pump-probe experiment to measure the time delays of electrons photoionized from Neon, Argon, and Krypton relative to those photoionized from Helium atoms. The Attosecond Pulse Train (APT) is characterized and the relative delay in photoionization of various noble gases is measured. The photoionization delay of Ne, Ar, and Kr is determined using previously calculated values for the He atomic delay and the delay associated with the probe process.
We devise an ab initio formalism for the quantum dynamics of Auger decay by laser-dressed atoms which are inner-shell ionized by extreme ultraviolet (XUV) light. The optical dressing laser is assumed to be sufficiently weak such that ground-state electrons are neither excited nor ionized by it. However, the laser has a strong effect on continuum electrons which we describe in strong-field approximation with Volkov waves. The XUV light pulse has a low peak intensity and its interaction is treated as a one-photon process. The quantum dynamics of the inner-shell hole creation with subsequent Auge…
We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a high-intensity free-electron laser pulse in a cell filled with Xe or Kr gas, the medium is quasi instantaneously population-inverted by inner-shell ionization on the giant resonance followed by Auger decay. On the timescale of 100 ps a macroscopic polarization builds up in the medium, resulting in superfluorescent emission of several Xe and Kr lines in the forward direction. As the number of emitters in the system is increased by either raising the pressur…
We investigate the interaction of Xe with isolated attosecond XUV pulses. Specifically, we calculate the ion yields and determine the pathways leading to the formation of ionic charged states up to Xe$^{5+}$. To do so, in our formulation we account for single-photon absorption, sequential multi-photon absorption, direct two-photon absorption, single and double Auger decays, and shake-off. We compare our results for the ion yields and for ion yield ratios with recent experimental results obtained for 93 eV and 115 eV attosecond XUV pulses. In particular, we investigate the role that a sequence …
Time-domain measurement of Auger electron dynamics in xenon atoms after giant resonant photoionization
本研究通过时域测量揭示了氙原子在巨共振光电离后的Auger电子动力学，发现氙的N₄,5OO Auger电子表现出异常的时间偏移和产量最小值，挑战了现有理论。
The photoionization of xenon atoms in the 70-100 eV range reveals several fascinating physical phenomena such as a giant resonance induced by the dynamic rearrangement of the electron cloud after photon absorption, an anomalous branching ratio between intermediate Xe$^+$ states separated by the spin-orbit interaction and multiple Auger decay processes. These phenomena have been studied in the past, using in particular synchrotron radiation, but without access to real-time dynamics. Here, we study the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometr…
We present the experimental observation of two-center interference in the ionization time delays of Kr2. Using attosecond electron-ion-coincidence spectroscopy, we simultaneously measure the photoionization delays of krypton monomer and dimer. The relative time delay is found to oscillate as a function of the electron kinetic energy, an effect that is traced back to constructive and destructive interference of the photoelectron wave packets that are emitted or scattered from the two atomic centers. Our interpretation of the experimental results is supported by solving the time-independent Schr…
Attosecond x-ray pulses offer unprecedented opportunities for probing and triggering new types of ultrafast motion. At the same time, pulse characterization of x-rays presents new challenges that do not exist in the UV regime. Inner-shell ionization is the dominant ionization mechanism for x-rays and it is followed by secondary processes like fluorescence, Auger decay, and shake-up.In general, we find that inner-shell ionization and secondary processes can create additional delay-dependent modulations that will affect pulse reconstruction schemes. Our recently proposed pulse characterization m…
Attosecond Delays in X-ray Molecular Ionization
本研究利用XFEL产生的阿秒软X射线脉冲，首次测量了NO分子氧K壳层阈值附近核心电子的X射线光发射延迟，发现高达700阿秒的意外大延迟，并通过理论建模揭示了形状共振、Auger-Meitner电子碰撞和多电子散射等复杂关联动力学机制。
The Auger decay is a relevant recombination channel during the first few femtoseconds of molecular targets impinged by attosecond XUV or soft X-ray pulses. Including this mechanism in time--dependent simulations of charge--migration processes is a difficult task, and Auger scatterings are often ignored altogether. In this work we present an advance of the current state-of-the-art by putting forward a real--time approach based on nonequilibrium Green's functions suitable for first-principles calculations of molecules with tens of active electrons. To demonstrate the accuracy of the method we re…
The attosecond ultrafast ionization dynamics of correlated two- or many-electron systems have, so far, been mainly addressed investigating atomic systems. In the case of single ionization, it is well known that electron-electron correlation modifies the ionization dynamics and observables beyond the single active electron picture, resulting in effects such as the Auger effect or shake-up/down and knock-up/down processes. Here, we extend these works by investigating the attosecond ionization of a molecular system involving correlated two-electron dynamics, as well as non-adiabatic nuclear dynam…
The Auger-Meitner Radioisotope Microscope: an instrument for characterization of Auger electron multiplicities and energy distributions
本研究研发了阿贡俄歇放射性同位素显微镜（ARM），通过离子-电子符合等技术表征俄歇电子的多重性与能量分布，结合低温缓冲气体束和多击探测器扩展至放射源表征，可为原子模型基准测试及肿瘤剂量学提供关键低能区数据。
Quantum Interference in Two-Atom Resonant X-ray Scattering of an Intense Attosecond Pulse
研究两非相互作用Ne+离子在强极紫外脉冲驱动下的共振X射线散射，分析脉冲强度、原子配置和初始电子态对总散射信号的影响，发现共振散射产率高于非共振，信号角依赖性类似双原子结构因子，干涉条纹可见度受脉冲面积和初始电子态影响。
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