THz wave emission from argon in two-color laser field

Terahertz(THz) wave emission from argon atom in a two-color laser pulses is studied numerically by solving the one-dimensional(1D) time-dependent Schr ¨odinger equation. The THz spectra we obtained include both discontinuous and continuum ones. By using the special basis functions that we previously proposed, our analysis points out that the discontinuous and continuum parts are contributed by bound–bound and continuum–continuum transition of atomic energy levels. Although the atomic wave function is strongly dressed during the interaction with laser fields, our identification for the discontinuous part of the THz wave shows that the transition between highly excited bound states can still be well described by the field-free basis function in the tunneling ionization regime.     

基于多组态含时Hartree-Fock方法研究电子关联对于H_2分子强场电离的影响

发展了三维的处理双原子分子非微扰电子动力学的多组态含时Hartree-Fock方法,并利用该方法研究了电子关联对于H_2分子强场电离概率的影响.该方法采用能够精确处理双中心库仑势的椭球坐标系,以及减小双电子积分计算量的有限元-离散变量基函数方法.利用多组态含时Hartree-Fock方法计算了H_2分子随分子取向角度变化的XUV光电离结果,并通过与单组态结果的对比研究了电子关联对于单电离和双电离概率的不同影响.研究表明,电子关联对于单电离过程影响很小,而在双电离过程中则发挥了重要作用,导致了电离概率的减小.该方法为进一步研究强场物理过程中的电子关联效应奠定了基础.     

基于阿秒XUV-飞秒IR泵浦-探测的冷靶反冲离子动量成像谱仪

利用多道可见光谱探测系统测量了Hα、CⅢ(464.7nm)和OⅡ(441.5nnm)谱线的时间行为,得出了碳、氢和氧元素的入射通量。在简化模型下算出了氧碳间的化学溅射率,结果表明HT-6M托卡马克边界杂质产生机制主要是氢氧间的化学溅射和氧碳间的化学溅射,因此控制氧杂质尤其重要。     

电子动力学及相干辐射的强场调控与阿秒探测——强场与阿秒物理领域中的重大课题研究进展

电子动力学及相干辐射的强场调控与阿秒探测是强场物理与阿秒物理领域中的重大课题。通过同步探测阿秒辐射和太赫兹辐射,文章作者首次实现了阿秒精度的太赫兹产生动力学的探测与控制,表明阿秒物理与太赫兹技术的结合有助于深入理解强场驱动下太赫兹产生机制和电子再散射动力学,展示了利用双色场控制电子波包相干相位,实现超快物理过程强场调控的可能。文章作者所提出的精确刻画太赫兹时域瞬时电场方案,有助于推动极化敏感的太赫兹谱学研究。可以预期,阿秒脉冲与太赫兹源技术不会局限于原子分子物理领域。实现阿秒物理与太赫兹技术之间的互为抽运与探测,将会极大地推动化学、材料科学、凝聚态物理等领域的高时空分辨的超快动力学探测。     

Theory of Tunnel Ionization in Complex Systems

We present a detailed derivation of the Ammosov-Delone-Krainov theory of tunnel ionization in complex systems （CS-ADK）. A few mistakes in the previous works have been found and corrected. The theory is then applied to CO2, showing that CS-ADK yields better agreement with experiment than the molecular ADK theory.     

Multi-Electron Effects in Attosecond Transient Absorption of CO Molecules

Using the fully propagated time-dependent Hartree–Fock method, we identify that both the dynamic core polarization and multiorbital contributions are important in the attosecond transient absorption of CO molecules.The dynamics of core electrons effectively modifies the behaviors of electrons in the highest occupied molecular orbital, resulting in the modulation of intensity and position of the absorption peaks. Depending on the alignment angles, different inner orbitals are identified to contribute, and even dominate the total absorption spectra. As a result, multi-electron fingerprints are encoded in the absorption spectra, which shed light on future applications of attosecond transient absorption in complex systems.     

Phase dependence of third-order harmonic generation in gases induced by two-color laser field

We experimentally demonstrate third-harmonic generation(THG) in gases ionized by a femtosecond laser pulse superimposed on its second-harmonic(SH). The mechanism of THG has been investigated, and it demonstrates that a third-order nonlinear process dominates at low pump intensity. Asymmetric third-harmonic(TH) spectra are observed at different time delays in two color fields, which are attributed to the process of the four-wave mixing(FWM) of the broad spectrum of pump pulses. A joint measuremen...     

Generation of 88 as Isolated Attosecond Pulses with Double Optical Gating

Isolated attosecond pulses with a duration of 88 as are generated in the spectral range of 29-72 eV using double optical gating technique.The gate width is set to be shorter than half the optical cycle to avoid carrier envelop phase stabilization of the 4.2 fs driving laser pulses centered at 800 nm.The attosecond pulse duration is measured with the technique of frequency resolved optical gating for complete reconstruction of attosecond bursts.     

Laser-Chirp Controlled Terahertz Wave Generation from Air Plasma

We report the laser-chirp controlled terahertz(THz) wave generation from two-color-laser-induced air plasma.Our experimental results reveal that the THz wave is affected by both the laser energy and chirp,leading to radiation minima that can be quantitatively reconstructed using the linear-dipole-array model.The phase difference between the two colors,determined by the chirp and intensity of the laser,can account for the radiation minima.Furthermore,we observe an asynchronous variation in the ge...