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1.
Double-Exponentially Decayed Photoionization in CREI Effect: Numerical Experiment on 3D H2^+
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On the platform of the 3D H2^+ system, we perform a numerical simulation of its photoionization rate under excitation of weak to intense laser intensities with varying pulse durations and wavelengths. A novel method is proposed for calculating the photoionization rate: a double exponential decay of ionization probability is best suited for fitting this rate. Confirmation of the well-documented charge-resonance-enhanced ionization (CREI) effect at medium laser intensity and finding of ionization saturation at high light intensity corroborate the robustness of the suggested double-exponential decay process. Surveying the spatial and temporal variations of electron wavefunctions uncovers a mechanism for the double-exponentially decayed photoionization probability as onset of electron ionization along extra degree of freedom. Henceforth, the new method makes clear the origins of peak features in photoionization rate versus internuclear separation. It is believed that this multi-exponentially decayed ionization mechanism is applicable to systems with more degrees of motion. 相似文献
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Influence of the initial electronic state on minima of high-order harmonic spectrum radiated from hydrogen molecular ion
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We theoretically investigate the high-order harmonic generation of the one-dimensional hydrogen molecular ion at fixed intermediate internuclear distance, driven by a multicycle laser field. Our results show that the initial electronic state of the hydrogen molecular ion affects the modulation of the high-order harmonic spectrum, especially the positions of the minima. Based on the two-state model, the underlying physical mechanism of the minimum is analyzed and discussed.Further analysis shows that the different positions of the minima in the different initial electronic states can be understood via the different interferences of the two phase-adiabatic states at the ionization times. 相似文献
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通过数值求解含时薛定谔方程, 研究了原子在高频激光作用下的电离概率、光电子谱和谐波发射谱. 研究发现, 随着入射激光强度的增加, 原子的电离概率逐渐增加, 达到最大后下降, 其光电子发射谱和高次谐波发射谱均由单峰结构变成多峰. 而通过对谐波发射谱的时间-频率分析发现, 在电离抑制区域, 脉冲的峰值附近谐波受到抑制, 谐波发射主要发生在上升沿和下降沿, 二者的干涉效应产生了谐波的多峰值结构. 利用光电子发射谱和谐波发射谱随入射激光强度的改变规律, 可以实现对引起原子电离抑制的激光强度进行诊断. 相似文献
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C. Figueira de Morisson Faria 《Laser Physics》2009,19(4):797-804
We analyze the influence of different recombination scenarios, involving one or two centers, on high-order harmonic generation (HHG) in diatomic molecules, for different values of the internuclear separation. We work within the strong-field approximation, and employ modified saddle-point equations, in which the structure of the molecule is incorporated. We find that the two-center interference patterns, attributed to high-order harmonic emission at spatially separated centers, are formed by the quantum interference of the orbits starting at a center C j and finishing at a different center C ν in the molecule with those starting and ending at a same center C j . Within our framework, we also show that contributions starting at different centers exhibit different orders of magnitude, due to the influence of additional potential-energy shifts. This holds even for small internuclear distances. Similar results can also be obtained by considering single-atom saddle-point equations and an adequate choice of molecular prefactors. 相似文献
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考虑核间相互作用,利用修正的库仑玻恩模型(MCB-PT)计算了入射能量为16 MeV 的O7+碰撞氦单电离的全微分截面,并将计算结果与最近的实验数据和三体库仑波(3C)模型及含核间相互作用的连续扭曲波程函初态 (CDW-EIS-PT)模型所得结果进行了比较,发现MCB-PT理论结果在中间动量转移条件下binary峰的位置与实验结果符合得很好,且位于动量转移的方向上。此外,分析了扭曲效应对全微分截面的影响,表明随着动量转移的增加,扭曲效应更加明显。 相似文献
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考虑核间相互作用,利用修正的库仑玻恩模型(MCB-PT)计算了入射能量为16 MeV 的O7+碰撞氦单电离的全微分截面,并将计算结果与最近的实验数据和三体库仑波(3C)模型及含核间相互作用的连续扭曲波程函初态 (CDW-EIS-PT)模型所得结果进行了比较,发现MCB-PT理论结果在中间动量转移条件下binary峰的位置与实验结果符合得很好,且位于动量转移的方向上。此外,分析了扭曲效应对全微分截面的影响,表明随着动量转移的增加,扭曲效应更加明显。 相似文献
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The strong-field process of high-order harmonic generation in laser-irradiated light homonuclear diatomics (H 2 + , N2, and O2) is studied compared to atomic counterparts (of nearly identical ionization potential) within the velocity gauge version of conventional strong-field approximation. The applied strong-field approach (we alternatively developed earlier to incorporate rescattering effects beyond the quasiclassical saddle-point approximation) is currently extended to molecular case by means of supplementing the standard linear combination of atomic orbitals and molecular orbitals method. The associated model proved to adequately reproduce a general shape and detailed structure of molecular harmonic spectra, which demonstrate a number of remarkable distinctive differences from respective atomic spectra calculated under the same laser pulses. These revealed differences as well as other generic features (such as the extent of the high-frequency plateau and harmonic emission rates) are found to be strongly dependent on internuclear separation and also very sensitive to the orbital and bonding symmetry of the contributing molecular valence shell. In particular, for some group of harmonics, the emission rates were ascertained to dominate by contribution from inner molecular shells of higher binding energy and different orbital symmetry compared to the outermost molecular orbital normally predominantly contributing. Finally, due to a high suppression in ionization of O2 relative to counterpart atomic Xe, the harmonic spectrum calculated for O2 proved to demonstrate a noticeably longer plateau extending far beyond the harmonic cutoff in the Xe spectrum, in a fairly good accordance with relevant experiments. 相似文献
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冯立强 《原子与分子物理学报》2019,36(6)
理论研究了HeH2+分子发射高次谐波的空间分布情况。结果表明:分子谐波发射主要集中在He核和H核附近。当核间距离较小时,He核辐射谐波强度要比H核辐射谐波强度高2~3个数量级。当核间距离较大时,He核辐射谐波强度要比H核辐射谐波强度高4~5个数量级。当空间非均匀激光场引入后,谐波截止能量得到延伸,并且,随着空间非均匀激光场位置由负向到正向移动(-100 a.u.到100 a.u.),谐波截止得到进一步延伸。但是He核辐射谐波强度依然大于H核。最后,通过叠加谐波可获得脉宽在60 as的超短脉冲。 相似文献
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冯立强 《原子与分子物理学报》2018,35(6)
理论研究了HeH2+分子发射高次谐波的空间分布情况。结果表明:分子谐波发射主要集中在He核和H核附近。当核间距离较小时,He核辐射谐波强度要比H核辐射谐波强度高2~3个数量级。当核间距离较大时,He核辐射谐波强度要比H核辐射谐波强度高4~5个数量级。当空间非均匀激光场引入后,谐波截止能量得到延伸,并且,随着空间非均匀激光场位置由负向到正向移动(-100 a.u.到100 a.u.),谐波截止得到进一步延伸。但是He核辐射谐波强度依然大于H核。最后,通过叠加谐波可获得脉宽在60 as的超短脉冲。 相似文献
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冯立强 《原子与分子物理学报》2017,34(6):1103-1110
理论研究了HeH~(2+)分子发射高次谐波的空间分布情况.结果表明:分子谐波发射主要集中在He核和H核附近.当核间距离较小时,He核辐射谐波强度要比H核辐射谐波强度高2~3个数量级.当核间距离较大时,He核辐射谐波强度要比H核辐射谐波强度高4~5个数量级.当空间非均匀激光场引入后,谐波截止能量得到延伸,并且,随着空间非均匀激光场位置由负向到正向移动(-100 a.u.到100a.u.),谐波截止得到进一步延伸.但是He核辐射谐波强度依然大于H核.最后,通过叠加谐波可获得脉宽在60 as的超短脉冲. 相似文献
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High-order harmonic generation (HHG) of a helium model atom in an intense laser field has been numerically investigated. The influence of electron correlation on HHG is analysed by changing the strength between the electrons. The numerical results show that as the electron interaction strength becomes small, the first ionization energy increases rapidly, which results in the decrease in ionization. So the conversion efficiency of the high harmonic lying in the plateau decreases greatly, while the cutoff harmonic order in the harmonic spectrum increases. 相似文献
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We theoretically investigate high-order harmonic generation from H + 2 in an infrared laser field.Our numerical simulations show that a highly efficient plateau structure exists in the molecular harmonic spectrum.Under the action of the infrared laser pulse,the bound electronic wave packet in a potential well has enough time to tunnel through the effective potential barrier,which is formed by the molecular potential and the infrared laser field,and then recombine with the neighboring nucleus emitting a harmonic photon.During the entire dynamic process,because the wave packet is mainly located in the effective potential,the diffusion effect is of no significance,and thus a highly efficient harmonic plateau can be achieved.Specifically,the cut-off frequency of the plateau is linearly scaled with the peak amplitude of the infrared laser electric field,which may open another route to examine the internuclear distance of the molecule.Furthermore,one may detect the molecular bond lengths using the harmonic plateau. 相似文献
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Farrell JP Petretti S Förster J McFarland BK Spector LS Vanne YV Decleva P Bucksbaum PH Saenz A Gühr M 《Physical review letters》2011,107(8):083001
High harmonic spectra show that laser-induced strong field ionization of water has a significant contribution from an inner-valence orbital. Our experiment uses the ratio of H(2)O and D(2)O high harmonic yields to isolate the characteristic nuclear motion of the molecular ionic states. The nuclear motion initiated via ionization of the highest occupied molecular orbital (HOMO) is small and is expected to lead to similar harmonic yields for the two isotopes. In contrast, ionization of the second least bound orbital (HOMO-1) exhibits itself via a strong bending motion which creates a significant isotope effect. We elaborate on this interpretation by solving the time-dependent Schr?dinger equation to simulate strong field ionization and high harmonic generation from the water isotopes. We expect that this isotope marking scheme for probing excited ionic states in strong field processes can be generalized to other molecules. 相似文献
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利用广义伪谱方法精确数值求解了氢原子在强激光场中的三维含时薛定谔方程,获得了强激光中氢原子的含时波函数,利用时间依赖的偶极矩的傅里叶变换得到了高次谐波谱,研究了氢原子在强激光场中发射低于电离阈值的谐波谱对激光强度的依赖性.研究发现,激光强度在低于电离阈值的谐波产生的通道选择的过程中扮演着重要角色,主要有两种量子通道对阈下谐波的产生有贡献,即广义的短轨道和长轨道,其中长轨道对激光场强度比较敏感.结合小波时频变换、经典轨道分析、以及强度依赖的量子通道选择分析,本文阐明了其背后的物理机制. 相似文献
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利用全量子方法改进且加入核核作用(PT)的修正库仑玻恩近似(MCBPT)和前人基于半经典的方法且不考虑核核作用的修正库仑玻恩近似(MCB)计算了散射平面和垂直平面内100 Me V/amu C6+单电离氦原子的全微分截面,研究了核核作用对截面的影响.其结果与实验数据和3DW理论进行了比较.发现,对于小动量转移,MCBPT计算结果与实验符合的很好;对于大动量转移,MCB结果很好的反映了实验数据.而且,我们详细的分析了扭曲势效应对截面的影响,结果表明随着动量转移的增加扭曲势效应迅速增强. 相似文献
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An experimental study of high-order harmonic generation in nitrogen molecules (N2) has been made using intense visible (616 nm) dye-laser pulses, where the harmonic radiation up to the 21st order is observed. The harmonic distribution represents a plateau that is preceded by an intensity minimum at the 7th order. The harmonic generation characteristics were atomic-like. It has been found that there are some similarities in the high-order harmonic generation characteristics for N2 and Ar, including the highest-order harmonics, harmonic distributions, and the influence of the multiphoton ionization on the high-order harmonic generation. These similarities are reasonably attributed to the energetic correspondence of excited levels and ionization potentials. It is pointed out that the ac Stark shift of excited levels and ionization potentials plays an important role also in the high-order harmonic generation in N2. 相似文献
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In this paper high-order harmonic generation (HHG) spectra and the ionization probabilities of various charge states of small cluster Na2 in the multiphoton regimes are calculated by using time-dependent local density approximation (TDLDA) for one-colour (1064 nm) and two-colour (1064 nm and 532 nm) ultrashort (25 fs) laser pulses. HHG spectra of Na2 have not the large extent of plateaus due to pronounced collective effects of electron dynamics. In addition, the two-colour laser field can result in the breaking of the symmetry and generation of the even order harmonic such as the second order harmonic. The results of ionization probabilities show that a two-colour laser field can increase the ionization probability of higher charge state. 相似文献