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    Air lasing: Phenomena and mechanisms
    Helong Li(李贺龙), Danwen Yao(姚丹雯), Siqi Wang(王思琪), Yao Fu(付尧), Huailiang Xu(徐淮良)
    Chin. Phys. B, 2019, 28 (11): 114204.   DOI: 10.1088/1674-1056/ab47f5
    Abstract223)   HTML    PDF (2054KB)(176)      
    Air lasing is a concept that refers to remote no-cavity (mirrorless) optical amplification in ambient air with the air constituents as the gain media. Due to the high potential of air lasing in view of applications in atmospheric sensing, a variety of pumping schemes have been proposed so far for building up population-inverted gain media in air and producing forward and/or backward directional lasing emissions. This review paper presents an overview of recent advances in the experimental observations and physical understanding of air lasing in various pumping schemes of air molecules by intense laser fields. Special emphasis is given to the strong-field-induced N2+ air lasing, the mechanism of which is currently still in a hot debate.
    Quantitative rescattering theory for nonsequential double ionization
    Zhangjin Chen(陈长进), Fang Liu(刘芳), Hua Wen(文华)
    Chin. Phys. B, 2019, 28 (12): 123401.   DOI: 10.1088/1674-1056/ab54b3
    Abstract230)   HTML    PDF (5364KB)(166)      
    We review the recently improved quantitative rescattering theory for nonsequential double ionization, in which the lowering of threshold due to the presence of electric field at the time of recollision has been taken into account. First, we present the basic theoretical tools which are used in the numerical simulations, especially the quantum theories for elastic scattering of electron as well as the processes of electron impact excitation and electron impact ionization. Then, after a brief discussion about the properties of the returning electron wave packet, we provide the numerical procedures for the simulations of the total double ionization yield, the double-to-single ionization ratio, and the correlated two-electron momentum distribution.
    Bohmian trajectory perspective on strong field atomic processes
    Xuan-Yang Lai(赖炫扬), Xiao-Jun Liu(柳晓军)
    Chin. Phys. B, 2020, 29 (1): 013205.   DOI: 10.1088/1674-1056/ab5c0f
    Abstract400)   HTML    PDF (1701KB)(352)      
    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 Schrödinger 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.
    Review on non-dipole effects in ionization and harmonic generation of atoms and molecules
    Mu-Xue Wang(王慕雪), Si-Ge Chen(陈思格), Hao Liang(梁昊), Liang-You Peng(彭良友)
    Chin. Phys. B, 2020, 29 (1): 013302.   DOI: 10.1088/1674-1056/ab5c10
    Abstract287)   HTML    PDF (2540KB)(433)      
    In this review, we will focus on recent progress on the investigations of nondipole effects in few-electron atoms and molecules interacting with light fields. We first briefly survey several popular theoretical methods and relevant concepts in strong field and attosecond physics beyond the dipole approximation. Physical phenomena stemming from the breakdown of the dipole approximation are then discussed in various topics, including the radiation pressure and photon-momentum transfer, the atomic stabilization, the dynamic interference, and the high-order harmonic generation. Whenever available, the corresponding experimental observations of these nondipole effects are also introduced respectively in each topics.
    Influence of intraband motion on the interband excitation and high harmonic generation
    Rui-Xin Zuo(左瑞欣), Xiao-Hong Song(宋晓红), Xi-Wang Liu(刘希望), Shi-Dong Yang(杨士栋), Wei-Feng Yang(杨玮枫)
    Chin. Phys. B, 2019, 28 (9): 094208.   DOI: 10.1088/1674-1056/ab3446
    Abstract419)   HTML    PDF (2800KB)(304)      

    Tunnelling, acceleration, and collision of electrons are the basic events in the process of high harmonic generation (HHG) in strong-field interaction with atoms. However, the periodic array of atoms in semiconductor structure makes three steps become interatomic coherent process which leads to complicated carrier dynamics and two sources of high harmonic emission:interband polarization and intraband current. The difference of features of high harmonic generation between semiconductors and atoms is strongly linked to the unique presence of intraband motion which manifests itself a nontrivial role in intertwined two dynamics. Here, we review recent experimental and theoretical advances of understanding coupled interband and intraband mechanisms of HHG in semiconductors. Particularly we focus on the influence of intraband motion on the interband excitation, and on the subsequent HHG emission and attosecond pulse generation.