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arXiv:2305.00732

Spin-orientation-resolved attosecond chronoscopy in strong field ionization

Minqqing Liu, Wei‐Chao Jiang

Published May 1, 2023• 0 citations
arXivHTMLPDF

Abstract

Attosecond chronoscopy represents a major breakthrough in the study of ultrafast phenomena and has the potential to revolutionize our understanding of the fundamental physics of matter. We theoretically investigate the spin-orientation-resolved attosecond chronoscopy for the first time by the circular RABBIT technique for Kr atoms. Due to the spin-orbit interaction and the sensitivity of ionization in circularly polarized fields to the sense of electron rotation in the initial state, the spin-resolved ionization rates of photoelectrons emitted from $^2P_{1/2}$ and $^2P_{3/2}$ channels can be expressed via $m$-resolved ionization rates of initial state, where $m$ is the orbital magnetic quantum number. We demonstrate that the yields difference between spin-up and spin-down photoelectrons from each channel are closely associated with the different behaviors of corresponding Wigner time delay. We find that the Wigner time delay between spin-up and spin-down photoelectrons in the polarization plane can reach several tens of attoseconds in the co-rotating geometry, but a few attoseconds in the counter-rotating geometry. Our approach opens up a new avenue for probing the spin-dependent behavior of Wigner time delay, and lays the foundation for spin-orientation-resolved attosecond chronoscopy, which can be verified by the current experimental techniques.

DOI
10.48550/arxiv.2305.00732

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Attosecond chronoscopy represents a major breakthrough in the study of ultrafast phenomena and has the potential to revolutionize our understanding of the fundamental physics of matter. We theoretically investigate the spin-orientation-resolved attosecond chronoscopy for the first time by the circular RABBIT technique for Kr atoms. Due to the spin-orbit interaction and the sensitivity of ionization in circularly polarized fields to the sense of electron rotation in the initial state, the spin-resolved ionization rates of photoelectrons emitted from 2P1/2^2P_{1/2}2P1/2​ and 2P3/2^2P_{3/2}2P3/2​ channels can be expressed via mmm-resolved ionization rates of initial state, where mmm is the orbital magnetic quantum number. We demonstrate that the yields difference between spin-up and spin-down photoelectrons from each channel are closely associated with the different behaviors of corresponding Wigner time delay. We find that the Wigner time delay between spin-up and spin-down photoelectrons in the polarization plane can reach several tens of attoseconds in the co-rotating geometry, but a few attoseconds in the counter-rotating geometry. Our approach opens up a new avenue for probing the spin-dependent behavior of Wigner time delay, and lays the foundation for spin-orientation-resolved attosecond chronoscopy, which can be verified by the current experimental techniques.
We demonstrate that strong-field ionization of atoms in circularly polarized laser fields generates a photoelectron spin texture with toroidal topology in momentum space. Using time-dependent Schrödinger equation simulations, spin-resolved classical-trajectory Monte Carlo calculations, and an extended spin-resolved strong-field approximation including intermediate excitation pathways, we show that the rotation angle of this spin torus provides access to attosecond relative time delays associated with photoelectron wave packets released by tunneling from the counter-rotating and co-rotating ppp-orbital channels. When intermediate-state dynamics become significant, the torus develops a clear splitting. These results establish photoelectron spin textures as a complementary source of dynamical information beyond conventional momentum spectroscopy, and identify spin polarization as a robust internal degree of freedom for self-referenced attosecond metrology.
Abstract Attosecond chronoscopy is central to the understanding of ultrafast electron dynamics from gas to condensed phase with attosecond temporal resolution. It has, however, not yet been able to determine the timing of individual partial waves, and steering their contribution has been a substantial challenge. Here, we develop a polarization-skewed attosecond chronoscopy to reveal their roles from the angle-resolved photoionization phase shifts in rare gas atoms. By scanning the relative polarization angle between an extreme-ultraviolet attosecond pulse train and a phase-locked near-infrared laser field serving as a partial wave meter, we break the cylindrical symmetry and observe an emission direction dependent phase shift in the photoionized electron momenta. The experimental observations are well supported by numerical simulations using the R-matrix with time-dependence method, and by analytical analysis using the soft-photon approximation. Our symmetry-resolved, partial-wave analysis identifies the transition rate and phase shifts of each individual ionization pathway in the attosecond photoelectron emission dynamics. Our findings provide critical insights into the ubiquitous attosecond optical timer and the underlying attosecond photoionization dynamics, thereby offer new perspectives for the control, manipulation, and exploration of ultrafast electron dynamics in complex systems.
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Attosecond chronoscopy enables the exploration of correlated electron dynamics in real time. One key observable of attosecond physics is the determination of "time zero" of photoionization, the time delay with which the wave packet of the ionized electron departs from the ionic core. This observable has become accessible by experimental advances in attosecond streaking and reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) techniques. In this Letter, we explore photoionization time delays by strong extreme ultraviolet fields beyond the linear-response limit. We identify novel signatures in time delays signifying strong coupling between atoms and light fields and the light-field dressing of the ion. As a prototypical case, we study the interelectronic coherence and entanglement in helium driven by a strong extreme ultraviolet field. By the numerical solution of the time-dependent Schrödinger equation in its full dimensionality, we show that the time delay of the photoionized electron allows one to monitor the ultrafast variations of coherence dynamics and entanglement in real time.
The past thirty years witnessed rapid developing of strong field physics that leads to the first generation of attosecond (10−18 s) pulses. The duration of available pulses has recently been reduced to less than 100 as, approaching the Kepler period of a classical electron revolving around the nucleus. For the first time, electron motions inside atoms, molecules and solids can be traced, probed and even steered in real time. It pushed the study on ultrafast dynamic processes into a new frontier, giving birth to attosecond physics. The development of attosecond pulses provides unprecedented coherent ultrashort XUV (extreme ultra-violet) of soft X-ray sources that enable imaging the atomic structure and resolving the related quantum dynamics for matter science. In particular, it allows the probing and monitoring of electron dynamics in the natural time scale of attoseconds with atomic spatial resolution. The generation and applications of attosecond pulses are directly related to the control and manipulation of the sub-cycle electron dynamics. Recent studies on the correlated multielectron dynamics have provided insight into the optical and dynamical properties of matter in the perspectives of time, phase and entanglement. It deepens our understanding on some of the fundamental questions, e.g., how the single or multiple photons are absorbed and how short are the quantum processes such as photoionization, tunneling ionization and charge migration. Although currently attosecond pulses are limited by the flux and pulse duration, the combination of attosecond pulses with intense infrared laser pulses paves new ways of controlling and probing electron dynamics in the domains of energy, time and space that lays the foundation for petahertz optoelectronics and attosecond pulse based transient spectroscopy. In this review, we will first briefly summarize the advancement of strong field and ultrafast physics including the relevant experimental findings, the theoretical explorations, the related technologies and the possible applications. Then we focus on the sub-cycle electron or multielectron dynamics and their manifestation on the ionization and coherent radiation properties. We start with the time behavior of Fano resonance and how it can be probed in time domain. In section 2, the correlated electron dynamics is discussed in term of anti-screening effect and Pauli effect that influence strong field ionization and high harmonic generation processes. In section 3, the coherent emission with frequency from terahertz to soft XUV and their joint measurement are discussed by emphasizing the generation mechanism of terahertz wave in two-color laser pulses. The developed high-harmonic and terahertz wave spectroscopy (HATS) is shown capable of imaging the molecular structure and dynamics. In section 4, the time-resolving of electron and hole dynamics and their coherence is proposed based on attosecond transient absorption technique. The coherence of ionization and the correlated electron dynamics is hinted crucial for electron-hole interaction. The topics are very limited and mainly selected from the perspectives of our group.