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Spheroidal-wave analysis of time delay in molecular reconstruction of attosecond beating by interference of two-photon transitions around a Cooper-like minimum

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Physical Review A 2023年第1期108卷 013112-013112页

作者： Qinghua Ke Yueming Zhou Yijie Liao Min Li Kunlong Liu Peixiang Lu School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

By numerically solving the three-dimensional time-dependent Schrödinger equation, we have studied the energy- and angle-resolved time delay in H2+ photoionization using the reconstruction of attosecond beating by the interference of two-photon transition (RABITT) technique. Around the electron energy of Ec∼1.4 a.u., the RABITT time delay varies significantly with the energy and emission angle. The time delay changes from positive values to negative values as the increasing energy and emission angle. We have applied the spheroidal wave analysis to reveal this interesting time delay. By analyzing the time-delay dependent modulation of the anisotropic parameters, the energy and angle dependence of the time delay is well interpreted from the perspective of spheroidal wave interference. It shows that the Cooper-like minimum of a p spheroidal wave is responsible for this sign change of the RABITT time delay.

关键词： Atomic & molecular processes in external fields Atomic & molecular structure Photoemission

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Interference effect in high-order harmonic generation from degenerate current-carrying orbitals of polyatomic molecules

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Physical Review A 2020年第2期101卷 023406-023406页

作者： Dian Wang Xiaosong Zhu Hua Yuan Pengfei Lan Peixiang Lu School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

When the molecules with degenerate current-carrying orbitals are exposed to the bichromatic counterrotating circularly polarized (BCCP) laser fields, the destructive interference between high harmonics from these orbitals results in a strong suppression of harmonic emission with the selected helicity. As a result, there are large intensity differences between the high harmonics with opposite helicities in a wide spectral range. This interference effect is related to the noncylindrical symmetry of the molecular current-carrying orbitals and therefore depends on the relative orientation between the molecule and the driving laser fields. Furthermore, our results show that this interference can be controlled by adjusting the relative intensity ratio of the BCCP field. Finally, we show that highly elliptically polarized attosecond pulses can be generated by using this interference and their ellipticities can be tuned by controlling the molecular orientation.

关键词： Atomic & molecular processes in external fields High-order harmonic generation Ultrafast optics Ultrafast phenomena

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Orientation dependence of high-order harmonic generation in nanowire

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Physical Review A 2019年第3期99卷 033421-033421页

作者： Jiapeng Li Qingbin Zhang Liang Li Xiaosong Zhu Tengfei Huang Pengfei Lan Peixiang Lu School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

We investigate the orientation dependence of high-order harmonic generation (HHG) in nanowires by solving the time-dependent Schrödinger equation. It is found that the harmonic spectrum exhibits a two-plateau structure and the two plateaus have different orientation dependences. The harmonic yield of the first plateau reaches a maximum when the laser field is parallel to the nanowire and gets a strong suppression when the laser field is perpendicular to the nanowire. The harmonic yield of the second plateau increases first and reduces eventually with the change of the nanowire orientation. These phenomena can be explained by the time-dependent population imaging and the analysis of the transition probability between different energy bands. Our analysis shows a strong band-sensitive orientation dependence in low-dimensional material.

关键词： High-order harmonic generation Nonlinear optics Ultrafast optics

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Scattering singularities of optical waveguides under complex modulation

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Physical Review A 2020年第3期101卷 033818-033818页

作者： Qingjie Liu Chengzhi Qin Bing Wang Peixiang Lu School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

We employ complex index modulation to manipulate light scattering in a waveguide and achieve different kinds of singularities in the system. The singularities refer to poles or zeros in the scattering and transfer matrices. By using spatially complex index modulation, we realize unidirectional zero-reflection singularities, which can be manipulated by adjusting the modulation phase difference between the real and imaginary parts. Laser-coherent perfect absorber singularities with both diverging reflectance and transmittance are also achieved by cascading two waveguides with different modulation phases. Meanwhile, bidirectional zero-reflection singularities with reflectionless light transporting on both sides of the waveguides are also demonstrated. In addition, we utilize temporally complex modulation to obtain transfer matrix singularities and achieve nonreciprocal light transmission. The study may find great applications in light amplification, attenuation, and absorption, as well as constructing nonreciprocal optical devices.

关键词： Lasers Photonics Waveguides

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Valley-resolved interband excitation and emission in gapped graphene

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Physical Review A 2022年第4期106卷 043505-043505页

作者： Hubin Cui Liang Li Tengfei Huang Jiapeng Li Pengfei Lan Peixiang Lu School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

We theoretically investigate the electronic dynamics in gapped graphene driven by a bicircular field. The results indicate that the residual population on the conduction band is obviously asymmetric in the K and K′ valleys. Through analyzing the electron trajectory, we find that the interband transitions are determined by the compensation of two phases: the dynamic phase and the full dipole phase (including the transition dipole phase and the Berry phase). When the rates of change of the dynamic phase and the full dipole phase nearby the ionization time have the inverse signs, the unidirectional interband transition from the valence band (VB) to the conduction band (CB) results in the constructive interference of the population. In contrast, when they have the same signs, the bidirectional transition (CB→VB and VB→CB) results in the destructive interference. The constructive interference and the destructive interference lead to the asymmetric distribution of the CB population. Moreover, we also investigate the harmonic emission and find that only the 3n+2 harmonics are generated in the cutoff region. This phenomenon can be attributed to the asymmetric distribution of the CB population and the trefoil vector potential of the electric field. Due to the dependence on population distribution, the harmonics can be a promising optical way to detect the valley excitation of the gapped graphene.

关键词： Light-matter interaction Nonlinear optics Strong electromagnetic field effects Ultrafast optics Ultrafast phenomena

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Resolving the time evolution of the dissociative nuclear wave packet in the repulsive state of H2+ via wave-packet interference

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Physical Review A 2022年第4期105卷 043116-043116页

作者： Pengkun Cao Qingbin Zhang Kunlong Liu Peixiang Lu School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

The temporal evolution of the dissociative nuclear wave packet (NWP) is intuitive for studying and understanding the dissociation mechanisms of molecules driven by laser fields. Yet, the time-domain information is encoded in the phase term of the wave function and is vanishing when the wave packet is being detected. Here, we demonstrate that the dynamic information for the dissociative NWP in the repulsive state of H2+ can be reconstructed using the wave-packet interference approach. In this approach, a reference pulse following the driving pulse is applied and creates a secondary dissociative NWP for coherent interference with the target NWP. By analyzing the modulation of the observed kinetic energy release distribution, we obtain the time-dependent yield of the target NWP and find a delay of its peak with respect to the field maximum. The delay is reduced when shorter or weaker driving pulses are applied. We attribute the delay to the competition between the three-photon and net-two-photon dissociation channels of H2+.

关键词： Atomic & molecular processes in external fields Photodissociation Ions Schroedinger equation

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Determination of the Ionization Time Using Attosecond Photoelectron Interferometry

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Physical Review Letters 2018年第25期121卷 253203-253203页

作者： Jia Tan Yueming Zhou Mingrui He Yinbo Chen Qinghua Ke Jintai Liang Xiaosong Zhu Min Li Peixiang Lu School of Physics and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

Laser-induced electron tunneling ionization from atoms and molecules plays as the trigger for a broad class of interesting strong-field phenomena in attosecond community. Understanding the time of electron tunneling ionization is vital to achieving the ultimate accuracy in attosecond metrology. We propose a novel attosecond photoelectron interferometer, which is based on the interference of the direct and near-forward rescattering electron wave packets, to determine the time information characterizing the tunneling process. Adding a weak perturbation in orthogonal to the strong fundamental field, the phases of the direct and the near-forward rescattering electron wave packets are modified, leading to the shift of the interferogram in the photoelectron momentum distributions. By analyzing the response of the interferogram to the perturbation, the real part of the ionization time, which denotes the instant when the electron exits the potential barrier, and the associated rescattering time are precisely retrieved. Moreover, the imaginary part of the ionization time, which has been interpreted as a quantity related to electron motion under the potential barrier, is also unambiguously determined.

关键词： Atomic & molecular processes in external fields

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Asymmetric Switching of Edge Modes by Dynamically Encircling Multiple Exceptional Points

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Physical Review Applied 2023年第6期19卷 064050-064050页

作者： Yicong Zhang Weiwei Liu Shuaifei Ren Tianyan Chai Yanan Wang Hua Long Kai Wang Bing Wang Peixiang Lu Wuhan National Laboratory for Optoelectronics and School of Physics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

Dynamically encircling exceptional points (EPs) in the parameter space of a non-Hermitian system has drawn widespread attention for realizing asymmetric mode switching and related applications. While previous works have been restricted to two-level systems, the switching between edge states in a multistate system that contains more complex dynamics remains to be explored. Herein, asymmetric switching of edge modes in multistate systems is demonstrated by encircling multiple EPs. A multistate non-Hermitian system containing multiple EPs is constructed based on a one-dimensional lattice, which can support four edge-localized modes. Dynamically encircling the EPs in parameter space leads to a specific edge mode surviving to the end, determined by the encircling direction. Correspondingly, optical waveguide arrays are designed to investigate mode evolution through refractive index modulation. Simulated results show that clockwise (counterclockwise) encirclement leads to an output mode localized at the left (right) side of the waveguide array with a phase difference of 0 (π), regardless of the input modes; this excellently illustrates the asymmetric switching of edge modes in a multistate system. Moreover, such an effect can be extended to the multistate system with an arbitrary number of EPs. This work enables investigation of interesting effects in non-Hermitian physics by engineering the EPs and topological properties, especially for complex multistate systems, which will be useful for developing functional nanophotonic devices.

关键词： Nanophotonics Symmetry protected topological states Topological effects in photonic systems Non-Hermitean systems Waveguide arrays PT-symmetry Adiabatic approximation Schroedinger equation

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Elliptically polarized attosecond pulse generation by corotating bicircular laser fields

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Physical Review A 2022年第4期106卷 043115-043115页

作者： Wenqing Li Xiaosong Zhu Pengfei Lan Peixiang Lu Wuhan National Laboratory for Optoelectronics and School of Physics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

We revisit high-order-harmonic generation (HHG) in corotating bicircular fields, which possess high optical chirality, and extend the study to a frequency ratio higher than 1:2. By analyzing the classical trajectories in the corotating bicircular fields in the rotating frame, we show that the Coriolis-force effect that hinders HHG decreases with the frequency ratio. Given these features, we propose a method for producing highly elliptically polarized attosecond pulses (with ellipticity up to ε=0.88) using the corotating bicircular field with a frequency ratio of 1:3. A comparison is also made with the extensively studied counter-rotating configurations with a frequency ratio of 1:2 considering various laser parameters. The results affirm the validity and superiority of the corotating configurations, from which both the ellipticity and yield of generated attosecond pulses are higher than those from the counter-rotating configurations.

关键词： Electron & positron scattering Light-matter interaction Atoms

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Direct imaging of molecular rotation with high-order-harmonic generation

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Physical Review A 2019年第5期99卷 053419-053419页

作者： Yanqing He Lixin He Pengfei Lan Baoning Wang Liang Li Xiaosong Zhu Wei Cao Peixiang Lu Wuhan National Laboratory for Optoelectronics and School of Physics Huazhong University of Science and Technology Wuhan 430074 China Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan Institute of Technology Wuhan 430205 China

Direct imaging of molecular dynamics is a long-standing goal in physics and chemistry. As an emerging tool, high-order-harmonic spectroscopy (HHS) enables accessing molecular dynamics on femtosecond to attosecond time scales. However, decoding information from the harmonic signals is usually painstaking due to the coherent nature of high-order-harmonic generation (HHG). Here we show that this obstacle can be effectively overcome by exploiting machine learning in HHS. Combining the machine learning with an angle-resolved HHS method, the molecular movie with femtosecond resolution is reconstructed from the angular distributions of HHG measured at various time delays of the probe pulse. Such a movie distinctly shows the full information of the coherent rotational dynamics of molecules, which is unattained in previous studies. The experimental retrievals are in good agreement with the numerical simulations. Our findings provide a comprehensive picture of molecular rotation in space and time, which will facilitate the development of related research on molecular dynamics imaging.

关键词： Atomic & molecular processes in external fields

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