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Taking snapshots of a moving electron wave packet in molecules using photoelectron holography in strong-field tunneling ionization

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Chinese Physics B 2021年第12期30卷 348-353页

作者：何明睿樊洋周月明陆培祥 Department of Basic Courses Naval University of EngineeringWuhan 430033China School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and TechnologyWuhan 430074China

Coherent superposition of electronic states induces attosecond electron motion in molecules.We theoretically investigate the strong-field ionization of this superposition state by numerically solving the time-dependent Schrodinger equation.In the obtained photoelectron momentum distribution,an intriguing bifurcation structure appears in the strong-field holographic interference pattern.We demonstrate that this bifurcation structure directly provides complete information about the status of the transient wave function of the superposition state:the horizontal location of the bifurcation in the momentum distribution reveals the relative phase of the involved components of the superposition state and the vertical position indicates the relative coefficient.Thus,this bifurcation structure takes a snapshot of the transient electron wave packet of the superposition state and provides an intuitive way to monitor electron motion in molecules.

关键词： strong-field ionization photoelectron holography charge migration

Attosecond ionization time delays in strong-field physics

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Chinese Physics B 2024年第1期33卷 102-121页

作者：马永哲倪宏程吴健 State Key Laboratory of Precision Spectroscopy East China Normal UniversityShanghai 200241China

Electronic processes within atoms and molecules reside on the timescale of attoseconds. Recent advances in the laserbased pump-probe interrogation techniques have made possible the temporal resolution of ultrafast electronic processes on the attosecond timescale, including photoionization and tunneling ionization. These interrogation techniques include the attosecond streak camera, the reconstruction of attosecond beating by interference of two-photon transitions, and the attoclock. While the former two are usually employed to study photoionization processes, the latter is typically used to investigate tunneling ionization. In this review, we briefly overview these timing techniques towards an attosecond temporal resolution of ionization processes in atoms and molecules under intense laser fields. In particular, we review the backpropagation method, which is a novel hybrid quantum-classical approach towards the full characterization of tunneling ionization dynamics. Continued advances in the interrogation techniques promise to pave the pathway towards the exploration of ever faster dynamical processes on an ever shorter timescale.

关键词： strong-field ionization attosecond time delay photoionization time delay tunneling time delay attosecond streak camera reconstruction of attosecond beating by interference of two-photon transitions(RABBITT) attoclock backpropagation

Comparative study of photoionization of atomic hydrogen by solving the one-and three-dimensional time-dependent Schrödinger equations

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Chinese Physics B 2021年第8期30卷 327-336页

作者：王顺 Shahab Ullah Khan 田晓庆孙慧斌姜维超 College of Physics and Optoelectronic Engineering Shenzhen UniversityShenzhen 518060China

We develop a numerical scheme for solving the one-dimensional(1D)time-dependent Schrödinger equation(TDSE),and use it to study the strong-field photoionization of the atomic hydrogen.The photoelectron energy spectra obtained for pulses ranging from XUV to near infrared are compared in detail to the spectra calculated with our well-developed code for accurately solving the three-dimensional(3D)TDSE.For XUV pulses,our discussions cover intensities at which the ionization is in the perturbative and nonperturbative regimes.For pulses of 400 nm or longer wavelengths,we distinguish the multiphoton and tunneling regimes.Similarities and discrepancies between the 1D and 3D calculations in each regime are discussed.The observed discrepancies mainly originate from the differences in the transition matrix elements and the energy level structures created in the 1D and 3D calculations.

关键词： time-dependent Schrodinger equation(TDSE) strong-field ionization photoelectron spectra dynamic interference

strong-field photoionization of intense laser fields by controlling optical singularities

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Science China(Physics,Mechanics & Astronomy) 2021年第7期64卷 91-97页

作者： Yiqi Fang Zhenning Guo Peipei Ge Xueyan Ma Meng Han Xiaoyang Yu Yongkai Deng Qihuang Gong Yunquan Liu State Key Laboratory for Mesoscopic Physics and Frontiers Science Center for Nano-optoelectronics School of PhysicsPeking UniversityBeijing100871China Collaborative Innovation Center of Quantum Matter Peking UniversityBeijing100871China Collaborative Innovation Center of Extreme Optics Shanxi UniversityTaiyuan030006China Peking University Yangtze Delta Institute of Optoelectronics Nantong226001China

The spatial features of a light field, such as in the form of the optical singularities, provide a new degree of freedom for the application of light fields in different areas of science and technology. However, although the exploration of structured light is growing rapidly, the investigation of strong-field photoionization using such light fields is noticeably lagging behind. Here, we present an experimental study that reveals the signatures of intense, structured light fields with controlled optical singularities in strong-field photoionization. The different types of optical singularities can be identified through photoionization observables,i.e., photoelectron momentum distributions(PMDs). By concurrently shifting the locations of the phase and polarization singularities, the focal electric field features can be designated, and subsequently, the photoionization appearances can be manipulated. In this process, the behaviors of the different intense optical singularities are clearly visualized by the PMDs. This work will advance both the strong-field science and singularity optics.

关键词： strong-field ionization optical singularity spin-orbit interaction

strong-field response time and its implications on attosecond measurement

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Chinese Physics B 2022年第3期31卷 16-23页

作者：陈超车佳殷谢雪娇王赏辛国国陈彦军 College of Physics and Information Technology Shaan'xi Normal UniversityXi'an 710119China College of Physics and Hebei Key Laboratory of Photophysics Research and Application Hebei Normal UniversityShijiazhuang 050024China School of Physics Northwest UniversityXi'an 710127China

To measure and control the electron motion in atoms and molecules by the strong laser field on the attosecond time scale is one of the research frontiers of atomic and molecular photophysics. It involves many new phenomena and processes and raises a series of questions of concepts, theories, and methods. Recent studies show that the Coulomb potential can cause the ionization time lag(about 100 attoseconds) between instants of the field maximum and the ionization-rate maximum. This lag can be understood as the response time of the electronic wave function to the strong-field-induced ionization event. It has a profound influence on the subsequent ultrafast dynamics of the ionized electron and can significantly change the time–frequency properties of electron trajectory(an important theoretical tool for attosecond measurement). Here, the research progress of response time and its implications on attosecond measurement are briefly introduced.

关键词： response time strong-field ionization Coulomb effect attosecond measurement

Imprint of transient electron localization in H2+ using circularly-polarized laser pulse

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Chinese Physics B 2020年第12期29卷 221-226页

作者：罗江华李军张华峰 School of Physics and Optoelectronic Engineering Yangtze UniversityJingzhou 434023China National Mobile Communications Research Laboratory Southeast UniversityNanjing 210096China

Photoelectron momentum distribution of hydrogen molecular ion in a circularly polarized laser pulse is calculated by solving the three-dimensional time-dependent Schrodinger equation(3D-TDSE).At the intermediate internuclear distance,an unusual multi-peak structure is observed in the angular distribution,which is proved to be a signature of the transient localization of the electron upon alternating nucleus.By tracing the time-dependent ionization rate and bound state populations,we provide a clear evidence that the transient electron localization still exists in circularly polarized pulse and the corresponding multiple ionization bursts are directly mapped onto observable angular distributions.In addition,we introduce an intuitive strong-field approximation model which incorporates laser-induced subcycle internal electron dynamics to isolate the effect of the Coulomb potential of the parent ions.In this way,the timing of each ionization burst can be directly read out from the angular distributions.Our results suggest that the ionization time serves as a sensitive tool encoding intramolecular electron dynamics and can be measured using attoclock technique.

关键词： strong-field ionization ultrafast phenomena photoelectron spectrum

Bohmian trajectory perspective on strong field atomic processes

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Chinese Physics B 2020年第1期29卷 1-8页

作者：赖炫扬柳晓军 State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and MathematicsInnovation Academy for Precision Measurement Science and TechnologyChinese Academy of Sciences

The interaction of an atom with an intense laser field provides an important approach to explore the ultrafast electron dynamics and extract the information of the atomic and molecular structures with unprecedented attosecond temporal and angstrom spatial resolution.To well understand the strong field atomic processes,numerous theoretical methods have been developed,including solving the time-dependent Schrodinger equation(TDSE),classical and semiclassical trajectory method,quantum S-matrix theory within the strong-field approximation,etc.Recently,an alternative and complementary quantum approach,called Bohmian trajectory theory,has been successfully used in the strong-field atomic physics and an exciting progress has been achieved in the study of strong-field phenomena.In this paper,we provide an overview of the Bohmian trajectory method and its perspective on two strong field atomic processes,i.e.,atomic and molecular ionization and high-order harmonic generation,respectively.

关键词： Bohmian trajectory strong-field ionization high-order harmonic generation