超短脉冲高次谐波谱的截止频率分析

本文数值计算了超短脉冲(脉冲持续时间为两个光学周期)的高次谐波发射功率谱.研究结果表明,超短脉冲谐波谱的截止频率不再符合IP 3.17UP的截止规则(IP为原子电离势,UP为有质动力能).对此,本文采用"三步"模型给出了合理解释,并用小波变换验证了结果的正确性.     

Internal collision double ionization of molecules driven by co-rotating two-color circularly polarized laser pulses

The double ionization process of molecules driven by co-rotating two-color circularly polarized fields is investigated with a three-dimensional classical ensemble model. Numerical results indicate that a considerable part of the sequential double ionization(DI) events of molecules occur through internal collision double ionization(ICD), and the ICD recollision mechanism is significantly different from that in non-sequential double ionization(NSDI). By analyzing the results of internuclear distan...     

Probing dynamic interference in high-order harmonic generation from long-range molecular ion:Bohmian trajectory investigation

Using Bohmlan trajectory （151） method, we investigate the dynamic interference in nlgn-orcter narmonlc generauon from diatomic molecular ions. It is demonstrated that the main characteristics of the molecular harmonic spectrum can be well reproduced by only two BTs which are located at the two ions. This haiapens because these two localized trajectories can receive and store the whole collision information coming from all of the other re-collision trajectories. Therefore, the amplitudes and frequencies of these two trajectories represent the intensity and frequency distribution of the harmonic generation. Moreover, the interference between these two trajectories shows a dip in the harmonic spectrum, which reveals the molecular structure information.     

量子路径控制生成宽频软X射线连续辐射谱

数值研究了双色激光脉冲与一维氩原子相互作用的谐波发射功率谱.双色激光脉冲由800 nm和1600 nm的两束激光组成,脉冲持续时间为9.7 fs.计算结果表明,相对相位为π时,谐波截止频率从单色场情形的58 eV大幅度地展宽到316 eV,获得频宽为93 eV的软X射线连续辐射谱.此外,还采用短程的普薛耳－特勒势和长程的软化库仑势进行比对,数值结果表明该连续辐射谱的存在具有普适性.通过半经典的“三步”模型和时频分析小波变换方法对该连续辐射谱进行分析,发现其主要由单一的“短”量子路径生成,直接叠加频率从22 关键词： 红外双色激光脉冲 连续辐射谱 阿秒脉冲     

超高次谐波的共振增强

本文计算了一维模型单电子分子离子在强激光作用下的高次谐波发射功率谱,光强从9.83×1013 W/cm2到1.1×1014 W/cm2.研究发现,在这个光强范围,谐波谱的超高次部分(相应的单光子能量大于Ip+3.2Up,Ip是原子电离势,Up是有质动力能)的发射功率出现了增强现象.研究认为,这是由高能电子布居几率的共振增强造成的.     

Accurate prediction of interference minima in linear molecular harmonic spectra by a modified two-center model

We demonstrate that the interference minima in the linear molecular harmonic spectra can be accurately predicted by a modified two-center model. Based on systematically investigating the interference minima in the linear molecular harmonic spectra by the strong-field approximation(SFA), it is found that the locations of the harmonic minima are related not only to the nuclear distance between the two main atoms contributing to the harmonic generation, but also to the symmetry of the molecular orbital. Therefore, we modify the initial phase difference between the double wave sources in the two-center model, and predict the harmonic minimum positions consistent with those simulated by SFA.     

High-intensity molecular harmonic generation without ionization

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.     

Single X-Ray Attosecond Pulse Generation by Using Combined Pulses Irradiating on a United Two-Atom System

A scheme of a single x-ray attosecond pulse generation from a two-atom system exposed to the combined laser pulses is proposed. Our numerical results show that a single x-ray attosecond pulse rather than a train one can be produced by modulation of ionization. Furthermore, when we change the peak intensity Ih of the high-frequency pulse and keep the intensity of the low-frequency pulse constant, we can find that a range of Ih where the intensity of the attosecond pulse is optimal is available, and a explanation by the stimulated property of the recombination is also presented.     

利用正交偏振双色场产生孤立阿秒脉冲

利用强场近似理论开展了正交偏振双色场与氦原子相互作用产生高次谐波和阿秒脉冲的理论研究。正交偏振双色场由少周期的4 fs钛宝石驱动脉冲激光和与它偏振方向垂直的8 fs倍频控制脉冲构成。研究发现,通过合理选择两束脉冲之间的相对相位,能够控制高次谐波发射过程中长、短电子轨道的选择。当相对相位调整为1.2π时,平台谐波主要来自短轨道电子的贡献,由于其运动时间短、波包扩散少,且没有与长轨道电子谐波产生干涉,沿驱动脉冲电场方向的高次谐波谱具有较高强度和较小调制幅度的超连续平台区,通过对第120次到第180次超连续谐波进行傅里叶变换,可产生脉宽为54 as的高强度孤立阿秒脉冲。所提方案对组合脉冲相对相位的选取要求并不严苛,在0.3π的变化范围内皆可获得脉宽较短的孤立阿秒脉冲,同时控制脉冲电场强度的变化对上述数值模拟结果的影响也很小。     

晶体环境下高次谐波谱的截止频率分析

通过数值求解中红外飞秒光脉冲与一维单电子多阱势相互作用的含时薛定谔方程, 研究了晶体环境下的高次谐波发射光谱, 发现了晶体谐波谱的截止位置公式.研究发现, 不同于气体环境下的谐波谱截止频率规律, 晶体谐波谱的截止频率与激光电场的峰值振幅及晶格参数成线性关系. 鉴于准经典力学的三步模型对于气体谐波截止频率的解释, 进一步采用准经典力学方法验证了晶体谐波截止位置规律的正确性. 关键词： 中红外飞秒光脉冲 晶体 高次谐波 截止频率