共查询到20条相似文献,搜索用时 62 毫秒
1.
2.
研究人员正在寻求突破飞秒界限的途径.文章简单评述了高次谐波产生阿秒脉冲的可能性、现实性、面临的障碍以及新的科学挑战. 相似文献
3.
4.
拉伸分子高次谐波产生的阿秒控制 总被引:1,自引:1,他引:0
通过数值求解一维含时薛定谔方程,本文研究了高频阿秒脉冲对拉伸双原子分子模型与低频飞秒激光脉冲相互作用产生高次谐波谱的影响.研究表明,若阿秒脉冲在低频脉冲的第二个光学周期截止处注入时,只第二个平台截止位置IP 5.6UP(IP为电离势,UP为有质动力能)附近谐波的效率得到显著提高;若阿秒脉冲的包络峰值处于低频脉冲第三个光学周期T/4(为飞秒激光脉冲的光学周期)附近时,则谐波谱出现了明显的整体抬高现象.对此,本文根据拉伸分子谐波谱的四种产生机制及阿秒脉冲在飞秒激光不同相位注入时的电子电离曲线,对这些谐波谱的结构给出了合理解释. 相似文献
5.
当红外强激光和极紫外(XUV)阿秒脉冲共同作用于原子分子时,电离出去的电子通常会吸收和辐射激光光子而发生能量扩展.讨论了由于XUV阿秒脉冲的短波长与扩展后的电子波包尺度可相比拟时在高次谐波产生过程中引起的非偶极效应.采用H+2作为模型分子,并把分子轴置于激光场的传播方向,通过解二维含时薛定谔方程并比较考虑非偶极效应和采用偶极近似两种方法计算得到的结果,两者相比,前者的谐波强度降低,谐波频率向低级次稍有移动,电子能谱的能带内出现了更多的光电子峰.在相同的光电子能量处,两种方法计算得到的信号强度相差2—5倍.并且这种非偶极效应随着红外基频光光强的增大而增强,随阿秒脉冲波长的增大而减弱.
关键词:
非偶极效应
光场空间不均匀性
阿秒脉冲
高次谐波产生 相似文献
6.
7.
本文通过数值求解二维含时薛定谔方程,研究了圆偏振激光和太赫兹组合场作用下,H+2的高次谐波发射和孤立阿秒(1 as=10-18s)脉冲的产生.研究发现,无论在圆偏振激光场的x或y方向附加一个太赫兹场,都可以产生一个比较平滑的连续谐波谱.通过时频分析我们发现,高次谐波的贡献主要来自于短轨道.适当选取一些级次的连续谐波进行叠加,可以得到129 as或83 as的孤立阿秒脉冲. 相似文献
8.
李娜娜 《原子与分子物理学报》2015,32(6)
本文通过数值求解二维含时薛定谔方程,研究了圆偏振激光和太赫兹组合场作用下,H2+的高次谐波发射和孤立阿秒脉冲的产生。研究发现,无论在圆偏振激光场的 或 方向附加一个太赫兹场,都可以产生一个比较平滑的连续谐波谱。通过时频分析我们发现,高次谐波的贡献主要来自于短轨道。适当选取一些级次的连续谐波进行叠加,可以得到129 as或83 as的孤立阿秒脉冲。 相似文献
9.
10.
本文理论上研究了初态为基态与第一激发态等权叠加的一维氦离子在空间非均匀啁啾双色场驱动下氦离子的高次谐波发射及孤立阿秒脉冲的产生. 研究表明, 一维氦离子在空间非均匀啁啾双色场驱动下发射的高次谐波相对于均匀场情况截止位置得到明显扩展, 得到了光滑的超连续谱,并应用半经典三步模型解释了高次谐波发射的物理机理. 通过小波变换的方法对连续谱进行了时频分析, 并且与电子的经典运动轨迹进行了对比分析, 结果显示在空间非均匀场中长量子轨道消失, 短量子轨道加强. 讨论了空间非均匀啁啾双色场中时间延迟对谐波和孤立阿秒脉冲产生的影响, 发现适当调整时间延迟值可以得到较大延展的光滑的超连续谐波谱, 本方案中时间延迟为t0=1.6πup/ω1时得到了最大延展, 通过对谐波中600次到680次(80次)谐波合成得到32 as的孤立脉冲. 相似文献
11.
冯立强 《原子与分子物理学报》2015,32(2):269-274
数值研究了不对称分子He H2+在两束激光场形成的组合驱动场下发射高次谐波以及阿秒脉冲的特点.为了有效的展宽谐波的截止能量,基频场选择为5fs/800nm的啁啾激光场.计算结果表明,当啁啾参数和分子核间距分别选择为β=0.4和R=8.0a.u.时,不仅谐波波谱变得非常平滑而且其截止能量得到了有效的展宽.随后通过加入并且优化第二束控制激光场,谐波截止能量得到了进一步的展宽,形成了一个600e V的超平滑连续区.最后分别叠加280次到330次和330次到380次谐波可获得脉宽为78as的两个孤立阿秒X射线光源. 相似文献
12.
13.
我们提出利用频率为ω,3ω和强度较弱的2ω组成的三色圆偏振激光组合脉冲驱动氦原子能够得到椭偏率较大的阿秒脉冲链的一种方法.通过强场近似方法,计算了氦原子在两色和三色圆偏振激光组合脉冲驱动下发射高次谐波谱及其合成阿秒脉冲链,比较了氦原子(初态为s态)在这两种情况下发射高次谐波谱的特点及其合成阿秒脉冲链椭偏率的大小,结果发现,在反旋的两色ω,3ω激光脉冲基础上加入了频率为2ω的第三色激光脉冲联合作用到氦原子上,所得到的阿秒脉冲链的椭偏率相对于双圆场情况下有所增加,通过调整ω,3ω激光的强度比,并且选择适当的第三色激光的强度,对初态为s态的原子,仍能够得到具有较大椭偏率的阿秒脉冲链. 相似文献
14.
In order to observe the high-field effect, the external laser field must reach its peak intensity before the electron ionization. To this end, it is important to reduce pulse duration to typical attosecond timescale. In this paper, the interaction electron dynamics between attosecond pulses and dielectric is investigated within the time-dependent density functional theory. Taking the CaF2 crystal as an example, we give a comparison of electron dynamics response between single and double pulses. Moreover, the nonlinear energy absorption and electron excitation processes are simulated by adjusting the polarization direction of the sub-pulse. Present results demonstrate that the double pulses show lower electron excitation and energy absorption than the single pulse, which is in accordance with experimental higher ablation threshold and smaller heat-affected zones of the double pulses. In addition, the curves of final excited electron number and energy absorption exhibit the quasi-symmetry about the axis of 180°, which has not been reported yet. 相似文献
15.
H. Wabnitz Y. Mairesse L. J. Frasinski M. Stankiewicz W. Boutu P. Breger P. Johnsson H. Merdji P. Monchicourt P. Salières K. Varjú M. Vitteau B. Carré 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):305-311
We investigate the carrier-envelope phase dependence of the total ionization yield for single and double ionization of xenon.
We compare our results to theoretical calculations and to the phase dependent asymmetry in photoelectron emission. We observe
that the phase dependence of the photoion yields, regardless if single or double ionization, is at least 2-3 orders of magnitude
below the photoelectron emission signal. We conclude that total photoionization yields are only very weakly dependent on the
carrier envelope phase, and that they are not a useful means for measurement of the phase. It seems possible that the broad
bandwidth of few-cycle pulses facilitates multiphoton ionization, which leads to a randomization of strong field ionization
phase dependencies. Besides, we observe that the spatial asymmetry in photoelectron emission appears to be useful as an indicator
for the laser pulse duration in the few cycle regime. 相似文献
16.
André D. Bandrauk 《Molecular physics》2016,114(3-4):344-355
ABSTRACTMolecular high-order harmonic generation(MHOHG) is simulated for H+2 in the nonlinear nonperturbative regime of laser-molecule interactions with ultrashort intense circularly polarised laser pulses. It is shown that combinations of co-rotating or counter-rotating pulses produce laser-induced Coriolis forces with electron-parent ion recollisions, thus enhancing circularly polarised MHOHG, the source of circularly polarised attosecond pulses. Such pulses can be used to induce electron attosecond currents for the generation of attosecond magnetic field pulses, new tools for molecular attomagnetism. 相似文献
17.
采用组合激光脉冲(800 nm/9.4 fs 24 nm/1 fs)辐照联合两原子体系产生高次谐波,获得了单一的X-射线阿秒脉冲.我们发现,当固定钛宝石激光的峰值强度并改变高频谐波脉冲的峰值强度Ih时,存在一个优选的Ih范围,在该范围内相应的阿秒脉冲最优化,即强度达到最强,对此,本文从受激复合的角度给出了合理解释. 相似文献
18.
Production of subfemtosecond optical pulses or pulses with predetermined sub-cycle shape of electric field demands a broadband coherent light source of few octaves of bandwidth. Previous work has shown that such a broadband light source can be obtained by the molecular modulation technique. In this article, we review theoretical and experimental improvements in this area: from increasing the efficiency of the generation process by use of hollow waveguides to increasing the number of sidebands generated by the Raman additive technique, or by combined vibrational and rotational Raman generation. We find that stimulated rotational Raman scattering can be either enhanced or suppressed at proper detunings from vibrational Raman resonance in the same molecular ensemble. 相似文献
19.
The generations of the high-order harmonics and the attosecond pulses from helium atom driven by the mid-infrared symmetric and asymmetric nonhomogeneous field have been theoretically investigated. It is found that (i) due to the surface plasmon polaritons in the metallic nanostructure, the extensions of the harmonics from the positive and the negative laser amplitudes, or only from the positive laser amplitude can be found for the cases of symmetric and asymmetric nonhomogeneous fields, respectively. (ii) The wavelength scalings of the harmonic cutoff and the harmonic yield show that the harmonic cutoff and the harmonic yield can be extended and decreased with the increase in laser wavelength, respectively. However, due to the limit of the gap size of the nanostructure, the threshold value of the harmonic cutoff can be achieved for a given gap size of the nanostructure. (iii) By adding a weak terahertz field to the mid-infrared fundamental field with the asymmetric nonhomogeneous effect, the intensity of the harmonic plateau can be enhanced by one order of magnitude, showing a 1280?eV supercontinuum with the single quantum trajectory contribution. Finally, by properly superposing the harmonics, some attosecond X-ray pulses shorter than 35 as can be produced. 相似文献
20.
In this paper, we theoretically investigate the asymmetric molecular high-order harmonic emission and the attosecond X-ray pulse generation when the asymmetric molecular HeH2+ ion is exposed to an intense chirped pulse. It is found that the molecular harmonics are strongly dependent on the internuclear distance R as well as the chirp parameter, showing a smooth and intense harmonic plateau at R = 8.0 a.u. and β = 0.4. Further, by adding a subharmonic controlling pulse with the optimised conditions, a supercontinuum with a bandwidth of 602 eV can be obtained. Finally, by properly superposing the selected harmonics in the supercontinuum region, a series of isolated X-ray pulses with durations of sub-80 as are directly generated. 相似文献