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Orientation dependence of high-order harmonic generation in nanowire

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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Photoelectron Holographic Interferometry to Probe the Longitudinal Momentum Offset at the Tunnel Exit

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Physical Review Letters 2019年第18期122卷 183202-183202页

作者： Min Li Hui Xie Wei Cao Siqiang Luo Jia Tan Yudi Feng Baojie Du Weiyu Zhang Yang Li Qingbin Zhang Pengfei Lan Yueming Zhou 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

Laser-induced electron tunneling underlies numerous emerging spectroscopic techniques to probe attosecond electron dynamics in atoms and molecules. The improvement of those techniques requires an accurate knowledge of the exit momentum for the tunneling wave packet. Here we demonstrate a photoelectron interferometric scheme to probe the electron momentum longitudinal to the tunnel direction at the tunnel exit by measuring the photoelectron holographic pattern in an orthogonally polarized two-color laser pulse. In this scheme, we use a perturbative 400-nm laser field to modulate the photoelectron holographic fringes generated by a strong 800-nm pulse. The fringe shift offers direct experimental access to the intermediate canonical momentum of the rescattering electron, allowing us to reconstruct the momentum offset at the tunnel exit with high accuracy. Our result unambiguously proves the existence of nonzero initial longitudinal momentum at the tunnel exit and provides fundamental insights into the nonquasistatic nature of the strong-field tunneling.

关键词： Atomic & molecular processes in external fields Multiphoton or tunneling ionization & excitation Ultrafast phenomena

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Bounding Box Repairing Algorithm for Underwater Object Detection Based on IoU Optimization

Bounding Box Repairing Algorithm for Underwater Object Detec...

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International Conference on information Science and Control Engineering (ICISCE)

作者： Bingchuan Chen Lei Ma Jinmeng Wu Hubei Key Laboratory of Optical Information and Pattern Recognition Wuhan China School of Electrical and Information Engineering Wuhan Institute of Technology Wuhan China

In recent years, deep learning based methods have achieved excellent performance in standard object detection. However, these methods lack sufficient capabilities to handle underwater object detection due to these challenges: (1) underwater images have color shift and low contrast, and (2) various noises (sediments, bubbles, etc.) would cause blurring in underwater images. To address these problems, our work investigates optimization policies to detect low-contrast and blurred mine. We propose a bounding box repairing algorithm based on Intersection over Union (IoU) optimization. The algorithm mainly optimizes Mask Scoring R-CNN network. Firstly, we use the Mask Scoring R-CNN model to generate the coarse-grained detection results of mines. Secondly, we perform IoU between the coarse-grained boxes and the annotated boxes in the dataset to obtain the best matching area. Finally, we use the best matching area to repair the coarse-grained boxes. Experimental results show that our method achieves promising object detection and localization performance in underwater environment.

关键词： Location awareness Deep learning information science Image color analysis Object detection Maintenance engineering Sediments

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Interpreting attoclock experiments from the perspective of Bohmian trajectories

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Physical Review A 2022年第1期105卷 013119-013119页

作者： Wenhai Xie Min Li Yueming Zhou 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 theoretically study the attoclock using the Bohmian trajectory. The Bohmian trajectory includes a nonlocal quantum potential and the Coulomb potential, allowing us to separately study their effects on the attoclock. We show that the quantum potential has a significant effect on the photoelectron momentum spread while it only slightly affects the offset angle in the attoclock. We further show how the Coulomb potential affects the offset angle, revealing that the Coulomb force before the electron reaches the position of the classical tunnel exit has a significant contribution to the offset angle. Thus taking the full Coulomb effect into account during the tunneling ionization is a prerequisite for our understanding of the origin of the offset angle in the attoclock experiment. Our study also implies that there might be an inertia time for the initial wave function in response to the change of the laser electric field.

关键词： Atomic & molecular processes in external fields Multiphoton or tunneling ionization & excitation Photoemission

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Nonadiabaticity-induced ionization time shift in strong-field tunneling ionization

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Physical Review A 2019年第2期100卷 023414-023414页

作者： Wenhai Xie Min Li Siqiang Luo Mingrui He Kun Liu Qingbin Zhang Yueming Zhou 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

Laser-induced electron tunneling is one of the most fundamental strong-field phenomena. In laser-induced electron tunneling, it is usually assumed that the highest tunneling rate appears at the peak of the laser electric field corresponding to the shortest tunneling barrier. Here we show that this fundamental assumption is broken in an orthogonally polarized two-color laser field. We find that a rapid change of the instantaneous initial momentum at the tunnel exit can lead to a distinct ionization time shift between the instant of the maximum ionization rate and the peak of the electric-field strength. This ionization time shift can be either positive or negative depending on the degree of nonadiabaticity of the electron-tunneling process, and it is mapped to a measurable momentum shift in the photoelectron momentum distribution. These findings have significant implications for resolving attosecond electron dynamics and are essential to quantify possible tunneling delay time during strong-field ionization.

关键词： Atomic & molecular processes in external fields Multiphoton or tunneling ionization & excitation Ultrafast phenomena

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Tunable supermode converters based on Jx graphene waveguide arrays with transversely linear modulation

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Physical Review A 2024年第4期109卷 043507-043507页

作者： Shuaifei Ren Bing Wang Chengzhi Qin Weiwei Liu Lingzhi Zheng Zhuoxiong 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

Conventional mode converters are usually based on wave-number matching in the propagation direction. This often requires applying the periodic modulation in the longitudinal orientation. Here, we propose to construct an efficient supermode converter with only transverse modulation. By linearly changing the surface conductivity of Jx graphene waveguide arrays, we build a synthetic Jx lattice with linearly varying on-site potential in the modal dimension. It turns out that each supermode can fully transfer to its corresponding symmetric partner. The conversion distance of supermodes is inversely proportional to the ramp of linear modulation. In this way, tunable supermode converters can be readily implemented by modulating the surface conductivity of graphene sheets. This study may find promising applications in developing mode converters and mode-division multiplexers utilizing plasmonic waveguide arrays.

关键词： Photonics Graphene Waveguide arrays Mode coupling theory

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Acoustic Weyl semimetals in synthetic dimensions

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Physical Review Applied 2024年第5期21卷 054048-054048页

作者： Lingzhi Zheng Chengzhi Qin Xue-Feng Zhu Shuyue Chen Lange Zhao Zhuoxiong Liu Weiwei Liu 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

Here, we propose the construction of acoustic Weyl semimetals in synthetic dimensions based on a 2D coupling waveguide array under external dynamic modulations. The type-I, type-II, and line node acoustic Weyl semimetals can be realized in one lattice array and the associated transitions between different phases can be implemented by flexibly adjusting the dynamic modulations. The correspondence between different phases and symmetries is analyzed. The results clearly show that the spectra of topological surface states undergo bidirectional or unidirectional shifts in the frequency domain according to the type of Weyl points. Our work opens the door for studying acoustic Weyl physics in the synthetic dimensions and may have impacts on acoustic wave manipulation in both spatial and frequency domains.

关键词： Acoustic metamaterials Acoustic wave phenomena Acoustics Surface & interfacial phenomena Surface states Symmetry protected topological states Topological materials Weyl semimetal

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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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Asymmetry of the photoelectron momentum distribution from molecular ionization in elliptically polarized laser pulses

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Physical Review A 2019年第1期99卷 013431-013431页

作者： Ya-Nan Qin Min Li Yang Li Mingrui He Siqiang Luo Yali Liu Yueming Zhou 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 theoretically study the photoelectron momentum distributions (PMDs) of H2+ in elliptically polarized laser fields by numerically solving the time-dependent Schrödinger equation. Depending on the internuclear distance of H2+, the PMDs reveal different asymmetries with respect to the major and minor axes of the laser ellipse. At an internuclear distance corresponding to the enhanced ionization region, the asymmetry of the PMDs is opposite to that of the companion atom. We attribute this phenomenon to the effect of the internal scattered electrons, which are mainly released at an earlier ionization moment with respect to the field maximum within each half cycle. We further show that the asymmetry of the PMDs in the elliptical laser fields can be used to identify the instant when the electron wave packet is released from the molecule.

关键词： Atomic & molecular processes in external fields Multiphoton or tunneling ionization & excitation Molecules Schroedinger equation Semiclassical methods

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Double-blind decoupling of molecular rotation and high-order harmonic generation with a neural network

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Physical Review A 2024年第3期109卷 033105-033105页

作者： Siqi Sun Lixin He Chengqing Xu Yu Deng 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

High-order harmonic generation (HHG) through laser-molecule interaction provides a powerful means for detecting molecular structure and dynamics with subangström spatial and attosecond temporal resolution. However, accurately extracting molecular information from experimental harmonic spectra requires deconvolution of the angular average over the molecular rotational distribution, which is a challenging task due to the coherent nature of harmonic radiation. In this study we propose a deep-learning approach to disentangle the internal coupling between molecular alignment and single-molecule high-order harmonic radiation in experiments. With our method, the complex single-molecule dipole moments of high-order harmonics in both parallel and perpendicular directions, as well as the time-dependent molecular rotational distribution, can be simultaneously retrieved from the polarization-resolved angular distributions of HHG. From the retrieved harmonic dipole moments we can obtain comprehensive knowledge of the polarization states of the harmonics, including their ellipticity and helicity, without complicated experimental measurements. We demonstrate our method with two prototype molecules, N2 and CO2, in the experiment. Our approach provides an efficient way to disentangle single-molecule information from HHG experiments and will facilitate the study of molecular structure and dynamics imaging in complex polyatomic molecules.

关键词： High-order harmonic generation Strong-field-induced spectra Molecules High-harmonic generation High-order harmonic spectroscopy Molecular orbital theory Strong-field approximation

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