脉冲激光偏振方向对氧分子高次谐波的影响——基于含时密度泛函理论的模拟

采用含时密度泛函方法,结合赝势模型和电子交换相关作用的广义梯度近似,模拟了氧分子在超强飞秒激光脉冲作用下的高次谐波产生现象,并研究了激光脉冲偏振方向对氧分子高次谐波的影响.结果表明氧分子的高次谐波谱具有典型原子谐波谱的特征;当θ=45°(激光偏振方向与分子轴向夹角)时,谐波谱强度最大.这与文献报道的实验结果基本一致.     

脉冲激光偏振方向对氮分子高次谐波的影响——基于含时密度泛函理论的模拟

采用含时密度泛函方法,结合赝势模型和电子交换相关作用的广义梯度近似,模拟了氮分子在超强飞秒激光脉冲作用下的高次谐波产生现象,并研究了激光脉冲偏振方向对氮分子高次谐波的影响.结果表明氮分子的高次谐波谱具有典型原子谐波谱的特征;谐波谱强度随着θ(激光偏振方向与分子轴向夹角)的增大而减小.这与J.Itatanl在Nature上报道的实验结果基本一致.     

脉冲激光偏振方向对氮分子高次谐波的影响－－基于含时密度泛函理论的模拟

采用含时密度泛函方法，结合赝势模型和电子交换相关作用的广义梯度近似，模拟了氮分子在超强飞秒激光脉冲作用下的高次谐波产生现象，并研究了激光脉冲偏振方向对氮分子高次谐波的影响.结果表明氮分子的高次谐波谱具有典型原子谐波谱的特征；谐波谱强度随着θ(激光偏振方向与分子轴向夹角)的增大而减小.这与J.Itatanl在Nature上报道的实验结果基本一致. 关键词： 含时密度泛函理论 激光偏振方向 高次谐波 氮分子     

分子对飞秒激光场响应的含时密度泛函理论研究

采用含时密度泛函理论方法研究线性分子碳化锂（Li2C2）对飞秒激光场响应的电子-离子动力学行为。在典型的近共振和非共振的激光频率作用下,分别对比分析了分子的共振和非共振电离过程。研究发现：分子在共振频率激光场的作用下发生更强的电离过程,并倾向于发生库伦爆炸,键长的振荡断裂与电离相互促进影响,而分子在较弱的激光场作用下发生单光子电离过程;随着双脉冲时间间隔的增加,离化电子数在一定范围内呈振荡上升趋势,随后趋于常数。     

分子对飞秒激光场响应的含时密度泛函理论研究

采用含时密度泛函理论方法研究线性分子碳化锂(Li2C2)对飞秒激光场响应的电子-离子动力学行为.在典型的近共振和非共振的激光频率作用下,分别对比分析了分子的共振和非共振电离过程.研究发现:分子在共振频率激光场的作用下发生更强的电离过程,并倾向于发生库伦爆炸,键长的振荡断裂与电离相互促进影响,而分子在较弱的激光场作用下发生单光子电离过程;随着双脉冲时间间隔的增加,离化电子数在一定范围内呈振荡上升趋势,随后趋于常数.     

用TDMA法计算谐振子在强激光脉冲下的高次谐波

用含时薛定谔方程的多态展开(TDMA)方法求解含时薛定谔方程。该方法将含时波函数以基函数展开，通过求解展开系数的一阶微分方程组得到任意时刻的波函数。并将这一方法用于强激光场中谐振子的高次谐波的计算，以HCl分子为例，计算了在脉冲激光作用下高次谐波的产生和对应的激光强度、波长和脉冲宽度。     

相对论圆偏振激光与固体靶作用产生高次谐波

超短超强激光与固体靶表面等离子体相互作用可以通过高次谐波的方式产生从极紫外到软X射线波段的相干辐射,获得飞秒甚至阿秒量级的超短脉冲,可用于观测原子或分子中的电子运动等超快动力学过程.本文实验研究了相对论圆偏振飞秒激光与固体靶相互作用的高次谐波产生过程,实验结果表明,在较大入射角下,圆偏振激光也可以有效地产生高次谐波辐射.通过预脉冲控制靶表面的预等离子体密度标长,发现高次谐波的产生效率随密度标长的增加而单调下降.进一步通过二维粒子模拟程序,分析了激光的偏振以及预等离子体密度标长对高次谐波产生的影响,很好地解释了实验观测结果.     

飞秒激光脉冲在氮气中产生高次谐波的实验研究

报道了以氮气为介质产生高次谐波的实验结果。实验中主要研究了不同的气体密度、不同入射激光能量和不同偏振对高次谐波辐射强度及谐波级次的影响。并从理论上进行了定性分析。分析结果表明：要想得到较高次、较强的谐波辐射，必须反复进行实验，确定最佳的激光能量和气体密度，以减少由于自由电子密度的提高而导致的相位失配的影响。     

提高飞秒超强激光脉冲对比度的新方法

文章在简要描述飞秒超强激光脉冲对比度有关概念及其测量方法的基础上,介绍了空间滤波和时间滤波,以及提高注入脉冲种子对比度和强度的技术,环形腔放大技术,光参量啁啾脉冲放大技术（OPCPA）,双啁啾脉冲放大技术（DCPA）,采用高阶非线性晶体滤波等几种提高对比度的新方法和新技术.采用这些方法和技术,在最近一两年的时间里,人们成功地将多年来徘徊在106量级的飞秒超强激光脉冲对比度,提高到了1011的新水平,从而为强场物理的研究提供了更为理想的光源.     

提高飞秒超强激光脉冲对比度的新方法

文章在简要描述飞秒超强激光脉冲对比度有关概念及其测量方法的基础上,介绍了空间滤波和时间滤波,以及提高注入脉冲种子对比度和强度的技术,环形腔放大技术,光参量啁啾脉冲放大技术（OPCPA）,双啁啾脉冲放大技术（DCPA）,采用高阶非线性晶体滤波等几种提高对比度的新方法和新技术.采用这些方法和技术,在最近一两年的时间里,人们成功地将多年来徘徊在106量级的飞秒超强激光脉冲对比度,提高到了1011的新水平,从而为强场物理的研究提供了更为理想的光源.     

High-order harmonic generation of the cyclo[18]carbon molecule irradiated by circularly polarized laser pulse

High-order harmonic generation of the cyclo[18]carbon (C₁₈) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of the ring molecule C₆ H₆ having similar ionization potential, the C₁₈ molecule has higher efficiency and cutoff energy than C₆ H₆ with the same laser field parameters. Further researches indicate that the harmonic efficiency and cutoff energy of the C₁₈ molecule increase gradually with the increase of the laser intensity of the driving laser or decrease of the wavelength, both are larger than those of the C₆ H₆ molecule. Through the analysis of the time-dependent evolution of the electronic wave packets, it is also found that the higher efficiency of harmonic generation can be attributed to the larger spatial scale of the C₁₈ molecule, which leads to a greater chance for the ionized electrons from one atom to recombine with others of the parent molecule. Selecting the suitable driving laser pulse, it is demonstrated that high-order harmonic generation in the C₁₈ molecule has a wide range of applications in producing circularly polarized isolated attosecond pulse.     

联合双原子在组合脉冲辐照下的高次谐波发射

首先采用经典的“三步模型“理论,分析了一维普薛耳-特勒势(P-T势)模型原子在组合脉冲作用下的动力学行为,进而利用该组合脉冲辐照联合双原子模型,通过调节组合脉冲的场幅、相位以及设定原子的核间距,使原子有适当的电离和较大的复合效率,因而在截止位置远达Ip 8Up处获得了效率高达10-9的高次谐波发射.     

High-order harmonic generation of N2molecule in two-color circularly polarized laser fields

The generation of high-order harmonics and the attosecond pulse of the N_2 molecule in two-color circularly polarized laser fields are investigated by the strong-field Lewenstein model. We show that the plateau of spectra is dramatically extended and a continuous harmonic spectrum with the bandwidth of 113 e V is obtained. When a static field is added to the x direction, the quantum path control is realized and a supercontinuum spectrum can be obtained, which is beneficial to obtain a shorter attosecond pulse. The underlying physical mechanism is well explained by the time–frequency analysis and the semi-classical three-step model with a finite initial transverse velocity. By superposing several orders of harmonics in the combination of two-color circularly polarized laser fields and a static field, an isolated attosecond pulse with a duration of 30 as can be generated.     

High-order harmonic generation of the N2 molecule in two-color circularly polarized laser fields

The generation of high-order harmonics and the attosecond pulse of the N₂ molecule in two-color circularly polarized laser fields are investigated by the strong-field Lewenstein model. We show that the plateau of spectra is dramatically extended and a continuous harmonic spectrum with the bandwidth of 113 eV is obtained. When a static field is added to the x direction, the quantum path control is realized and a supercontinuum spectrum can be obtained, which is beneficial to obtain a shorter attosecond pulse. The underlying physical mechanism is well explained by the time-frequency analysis and the semi-classical three-step model with a finite initial transverse velocity. By superposing several orders of harmonics in the combination of two-color circularly polarized laser fields and a static field, an isolated attosecond pulse with a duration of 30 as can be generated.     

High-order harmonic generation by self-guided femtosecond laser pulses in argon

High-order harmonic generation (HHG) with 40 fs laser pulse in a quasistatic gas cell filled with argon gas was studied. Experiment results in several aspects were given and analyzed. As a result of balancing diffraction and plasma defocusing, and a large harmonic-generation cross-section, the spatial quality of the 23rd harmonic is successfully optimized with a divergence angle of 0.38 mrad. The modulation of spectral spatial divergence angle by the gas pressure was given, which was explained by the formation of plasma channel. The effect of initial laser pulse chirp on the harmonic generation and the harmonic spectral blueshift under different gas pressure were given and analyzed.     

High-order harmonic generation with a two-color laser pulse

We theoretically investigate the electron dynamics of the high-order harmonics generation process by combining a near-infrared 800 nm driving pulse with a mid-infrared 2000 nm control field. We also investigate the emission time of harmonics using time-frequency analysis to illustrate the physical mechanisms of high-order harmonic generation. We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variations in harmonic intensity for different control field strengths and delays. We find that the width of the harmonic plateau can be extended when the control electric field is added, and a supercontinuum from 198 to 435 eV is generated, from which an isolated 61-as pulse can be directly obtained.     

High-order harmonic generation with a two-color laser pulse

We theoretically investigate the electron dynamics of the high-order harmonics generation process by combining a near-infrared 800 nm driving pulse with a mid-infrared 2000 nm control field.We also investigate the emission time of harmonics using time-frequency analysis to illustrate the physical mechanisms of high-order harmonic generation.We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variations in harmonic intensity for different control field strengths and delays.We find that the width of the harmonic plateau can be extended when the control electric field is added,and a supercontinuum from 198 to 435 eV is generated,from which an isolated 61-as pulse can be directly obtained.     

利用相位啁啾单色中红外激光场产生高次谐波

本文通过求解薛定谔方程,理论探索了高次谐波及孤立阿秒脉冲在相位调制的单色中红外激光场中的产生.研究结果表明,通过加入含时相位啁啾小量,能够有效的提高高次谐波的产生效率,获得超宽平台谐波谱及超短孤立阿秒脉冲.特别是在相位为0.3π的基础上,同时加入啁啾小量βt,在β=0.3时,可得到带宽为822 e V的超连续高次谐波平台.最后通过叠加第二平台高次谐波,可得到带宽仅为2.7 as的孤立阿秒脉冲.且脉冲强度比没有加入啁啾小量的情况下显著增强.