共查询到19条相似文献,搜索用时 265 毫秒
1.
2.
3.
极紫外光和软X射线由于其波长和脉冲持续时间极短,可用于超快物理过程和物质微观结构的探测.最近几年,研究人员发现激光和等离子体相互作用可以产生持续时间极短(阿秒)且相干性较好的高次谐波辐射,其波长可接近甚至达到水窗波段.然而,实验研究指出,理论上应出现的一些谐波在实验中并没有出现.本文针对超短超强激光与非理想条件下的等离子体光栅靶相互作用产生高次谐波的物理过程进行了理论分析和粒子模拟.研究结果表明,等离子体光栅的周期性结构对于高次谐波的频谱和辐射角分布存在显著调制效果.光栅靶表面粗糙度直接影响光栅的光学调制效果,改变高次谐波的频谱分布和辐射角分布.理想光栅条件下,满足光栅匹配条件的特定阶数谐波明显获得增强,且辐射张角集中在平行靶面的方向.靶表面粗糙度的出现,导致光栅匹配条件失效,高次谐波能量向各阶分散且辐射张角逐渐偏离靶表面方向.研究结果较好地解释了实验中观测到的谐波频谱分布,为进一步的研究提供了一定参考. 相似文献
4.
5.
6.
对超短超强激光脉冲 (45fs,6× 10 17W /cm2 )与光致电离氦气形成的欠稠密等离子体相互作用中的二次谐波辐射进行了实验研究。测量了多种打靶强度的飞秒激光脉冲与不同气体密度氦气相互作用的二次谐波光谱 ,得到在欠稠密等离子体中二次谐波辐射与打靶激光能量的关系 ,分析了产生二次谐波辐射产生的物理机制 ,在考虑了强短脉冲激光电离气体产生的等离子体径向电子密度梯度因素 ,基于非线性作用过程的理论预期曲线与实验结果较好地吻合 相似文献
7.
8.
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 相似文献
9.
10.
11.
R. H?rlein S. G. Rykovanov B. Dromey Y. Nomura D. Adams M. Geissler M. Zepf F. Krausz G. D. Tsakiris 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):475-481
Harmonic generation from relativistically oscillating plasma surfaces formed during the interaction of high contrast lasers
with solid-density
targets has been shown to be an efficient source of extreme ultraviolet (XUV) and X-ray radiation. Recent work has demonstrated
that the exceptional
coherence properties of the driving laser can be mirrored in the emitted radiation, permitting diffraction limited performance
and attosecond phase
locking of the harmonic radiation. These unique properties may allow the coherent harmonic focusing (CHF) of high harmonics
generated from solid
density targets to intensities on the order of the Schwinger limit of 1029 W cm-2 with laser systems available in the near future [Phys. Rev. Lett. 93, 115002 (2004)] and thus pave the way for unique experiments exploring the nonlinear
properties of vacuum on ultra-fast timescales. In this paper we investigate experimentally as well as numerically the prospect
of focusing high
harmonics under realistic experimental conditions and demonstrate, using particle in cell (PIC) simulations, that precise
control of the wavefronts
and thus the focusability of the generated harmonics is possible with pre-shaped targets. 相似文献
12.
Analytical expressions for the density of magnetoactive plasma perturbed by circularly polarized relativistically strong laser radiation are obtained. 相似文献
13.
高次谐波椭偏率的调控为人们研究磁性材料和手性介质中的超快动力学过程提供了有效途径.本文理论研究了线偏振激光脉冲驱动下,H2~+和H32+分子高次谐波的偏振特性及阿秒脉冲产生.结果表明当取向角为0~o时,H2~+分子谐波的椭偏率几乎为0,而H32+分子谐波具有较大椭偏率,这是由于分子轨道对称性决定的.通过改变取向角的大小,可以调控高次谐波强度以及谐波椭偏率大小,为产生椭偏XUV脉冲提供了手段.同时,发现椭偏率较大的谐波阶次对应的谐波强度较小,分析表明分子的双中心干涉效应对椭偏率有很大的影响.对于H2~+和H32+分子,分别合成了椭偏率为0.75和0.55的椭圆偏振阿秒脉冲.这种大椭偏XUV脉冲的产生为高次谐波在材料与生物科学领域提供了重要应用. 相似文献
14.
The time-energy properties of high-order harmonic generation (HHG) are calculated for a linearly polarized 7-fs laser pulse with different carrier-envelope phases (CEPs). The quantum trajectory paths that contribute to an as (1 as=10-18 s) pulse in HHG are identified. The laser-duration dependence and the CEP dependence of HHG energy property are investigated. The study shows that an as extreme ultra-violet (XUV) pulse can be selected from HHG spectrum near cut-off energy with a bandpass optical filter. The theoretical prediction of the pulse duration is proportional to bandwidth. Analysis suggests that a measured narrowband as XUV pulse may consist of instantaneous shorter pulses each dependent on laser pulse duration, intensity, and CEP. These information can be used as references for producing, selecting, improving and manipulating (timing) as pulses. 相似文献
15.
S. M. Teichmann N. Bisht M. Hidalgo A. Honarfar M. G. Mingolla M. Turconi M. Clerici P. Di Trapani J. Biegert 《The European physical journal. Special topics》2011,199(1):89-100
Despite the fact that high order harmonic generation (HHG) aims at serving as a table-top light source for imaging applications
with extremely high spatial resolution, a general lack of accurate conversion efficiency measurements exists in the field.
Here, we present such a measurement for a HHG setup with a semi-infinite gas cell. By combining measurements with a calibrated
photodiode sensitive in the extreme ultra-violet (XUV) and spatially resolved spectral measurements of HHG spectra, we are
able to determine conversion efficiencies of the HHG process as well as brilliance values for individual harmonics. The method
is explained in detail and applicable to any target geometry. 相似文献
16.
通过数值求解一维原子的含时薛定谔方程, 研究了具有共振结构的原子在双色场(红外激光(IR)+极紫外光(XUV)) 驱动下发射高次谐波的特征. 研究结果表明, 具有共振结构的原子所发射的高次谐波与无共振结构原子(简称为一般原子)发射的高次谐波有明显不同, 共振结构的原子除了在某一能量附近(原子的共振能量+电离能)高次谐波的强度有很大提高外, 它还对XUV光的响应较一般原子表现得更为敏感, 即使XUV光的强度较弱, 也能够明显提高XUV光脉冲中心频率附近的谐波强度, 更重要的是通过调节双色场的时间延迟, 能使输入的XUV光的脉宽得到明显的压缩, 通过时间-频率分析给出了发生这种现象的原因. 由此提出了通过滤波-连续反馈的方式可使XUV光的脉冲从200 as压缩至120 as左右. 相似文献
17.
Exploration of High-Harmonic Generation from the CS_2 Molecule by the Lewenstein Method in Two-Color Circularly Polarized Laser Field 下载免费PDF全文
《中国物理快报》2017,(1)
The high harmonic generation(HHG) from the CS_2 molecule in intense laser fields is investigated using the extended Lewenstein method. The initial state is the highest-occupied molecular orbital of the CS_2 molecule,which can be well described by Gaussian wave packet using GAMESS-UK package. Compared with the case of the elliptical laser, the HHG can be extended in two-color circularly polarized laser field. The time-frequency analysis and classical electron trajectory as well as the ionization yield curve are also presented to further explain the underlying mechanism. After adding a static electric field on the z-direction, the single quantum path control is realized and the supercontinuum spectra are obtained. Moreover,an isolated 110 as pulse can be obtained by superposing the harmonics from 130 th to 180 th order. 相似文献
18.
葛鑫磊 《原子与分子物理学报》2022,39(4):044001
本文通过数值求解二维含时薛定谔方程理论的研究了圆偏振激光脉冲(circularly polarized laser pulse, CPLP)作用下H2+的高次谐波产生(high-order harmonic generation, HHG)。通过对比CPLP附加静电场和CPLP附加太赫兹场(terahertz, THz)时的高次谐波发射谱发现,当在CPLP的方向附加静电场时,谐波谱出现双平台结构,且布满调制,通过电子波包概率分布图像发现,电子三次与母核复合,量子轨道之间产生了较严重的干涉。当附加相同强度的THz场时,电子仅两次与母核复合,量子轨道之间的干涉减少,最终得到了86eV到208eV带宽为122eV的连续谱,相比于附加静电场,谐波谱变得连续且平滑,实现了量子轨道调控。最后,利用半经典三步模型、时频分析和电离几率等对谐波发射物理机制进行了深入研究。 相似文献
19.
利用原子的塞曼光谱对半导体激光器进行稳频 总被引:4,自引:1,他引:3
中性原子的超精细能级在磁场中产生塞曼分裂 ,另外 ,左旋和右旋圆偏振光激发下原子的跃迁选择定则不同 ,因此 ,原子在超精细塞曼能级间的吸收谱峰相对无磁场条件下的吸收谱峰有一定的移动。利用这一点 ,验证了一种简单、灵活的方法对半导体激光器进行稳频 ,使激光器的线宽稳到小于 1MHz。通过对实验结果的分析 ,发现由左旋和右旋圆偏振光激发引起的原子吸收谱峰移动之和与饱和吸收峰半高宽相等时 ,稳频效果最好 相似文献