共查询到19条相似文献,搜索用时 93 毫秒
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在强场近似下,利用Lewenstein模型研究了N2分子在强激光场中发射高次谐波的干涉效应,通过对N2分子产生的高次谐波和分子中单个原子产生高次谐波的比较,表明了干涉效应的存在. 得出随着高次谐波阶数的增加,干涉极小值会随着分子轴与激光偏振方向间夹角的增加而减小,在角度接近900附近时干涉效应消失,与两中心干涉模型预测的趋势一致. 通过分析高次谐波产生的机制和相位随取向角的变化,给出了干涉产生的原因. 相似文献
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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。 相似文献
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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
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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. 相似文献
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理论研究了H2+、D2+、T2+辐射高次谐波的特点.结果表明,在核运动影响下,不仅奇次谐波呈现红移现象,而且谐波光谱呈现非奇次谐波.随着核质量增大,奇次谐波频移和非几次谐波强度都减弱.但是随着激脉宽增大,非奇次谐波的产生明显被增强.理论分析表明,谐波频移是由谐波辐射在激光上升和下降区间的非对称性导致的;非奇次谐波是由于分子对称性在较大核间距离处遭破坏产生的. 相似文献
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High-order harmonic generation spectrum of an excited one-dimensional Coulomb atom in an intense laser field 下载免费PDF全文
Response of the wave packet of a one-dimensional Coulomb atom
to an intense laser field is calculated using the symmetrized
split operator fast Fourier method. The high-order harmonic
generation (HHG) of the initial state separately being the ground and excited states
is presented. When the hardness parameter \alpha in the soft
Coulomb potential V(x)=-1/\sqrt{x^2+\alpha} is chosen to be small
enough, the so-called hard Coulomb potential
V(x)=-1/|x| can be obtained. It is well known that the hard one-dimensional Coulomb atom
has an unstable ground
state with an energy eigenvalue of $\sim0.5$ and it
has no states corresponding to physical states in the true atoms, and
has the first and second excited states being degenerate. The parity effects on the HHG
can be seen from the first and second excited states of the hard
one-dimensional Coulomb atom. The HHG spectra of the excited states
from both the soft and hard Coulomb atom models are shown to have more
complex structures and to be much stronger than the corresponding
HHG spectrum of the ground state of the soft Coulomb model with
$\alpha=2$ in the same laser field. Laser-induced non-resonant
one-photon emission is also observed. 相似文献
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Nonsequential double ionization (NSDI) processes of nonaligned diatomic molecules N2 and O2 are studied using the S-matrix theory. Our results show that the NSDI process significantly depends on the molecular symmetry and structure. The ratio of NSDI rate to single ionization rate as a function of the field intensity is obtained. It is found that N2 behaves closely with its companion atom Ar in the ratios over the entire intensity range, while O2 exhibits an obvious suppression effect, which is qualitatively consistent with the experiment. 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
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Second harmonic generation (SHG) was observed in PbO-B2O3 glasses after heat treatment at elevated temperature followed by rapid quenching in water at room temperature (about 25 °C). According to the results of thermally stimulated depolarization current (TSDC) measurement and XRD patterns, no depletion layer or crystals was found in the rapidly quenched glass samples. The thermally induced nonlinear layer is located in the regions extended from the surface and 8 μm into the bulk. The possible mechanism responsible for the SHG is that the bond deformation of glass structure induced by stress gradient breaks the inversion symmetry of glass. The influencing factors of the SH intensity are also discussed. 相似文献
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High-order harmonic generation of CO_2 with different vibrational modes in an intense laser field 下载免费PDF全文
We apply the strong-field Lewenstein model to demonstrate the high-order harmonic generation of CO_2 with three vibrational modes(balance vibration,bending vibration,and stretching vibration) driven by an intense laser field.The results show that the intensity of harmonic spectra is sensitive to molecular vibrational modes,and the high harmonic efficiency with stretching vibrational mode is the strongest.The underlying physical mechanism of the harmonic emission can be well explained by the corresponding ionization yield and the time-frequency analysis.Finally,we demonstrate the attosecond pulse generation with different vibrational modes and an isolated attosecond pulse with a duration of about 112 as is generated. 相似文献
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N. Hay R. de Nalda T. Halfmann K.J. Mendham M.B. Mason M. Castillejo J.P. Marangos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):231-240
We have studied high-order harmonic generation (HHG) from organic molecules irradiated with near-infrared high intensity laser
pulses of 70 fs and 240 fs duration. The molecular systems studied were the aromatics benzene and naphthalene and the alkanes
cyclopropane and cyclohexane (cyclic) and n-hexane (linear). Harmonic intensities were measured both as a function of laser intensity (in the range 5×1013-5×1015 W cm-2) and as a function of ellipticity of the laser field polarisation. The results were compared with those from the xenon atom.
For 70 fs pulses, harmonic generation from the organic systems was similar to that of xenon, revealing an atom-like behaviour
for molecules when the laser pulse duration is shorter than the fragmentation timescale of the molecule. We note significant
differences between molecules with respect to HHG efficiencies and the suppression of HHG in larger species. We discuss these
differences in the context of the molecular properties, electronic structure and behaviour of ionisation and fragmentation
that result in enhancement of field ionisation in larger systems. Study of the polarisation ellipticity dependence of HHG
shows that the harmonic yield in molecules is less sensitive to the polarisation than for atoms (xenon). This is consistent
with the expected behaviour given the larger recollision cross-section presented by the core in the molecular system compared
to the atom. Our results suggest that study of HHG from molecules exposed to ultra-short pulses is potentially a powerful
tool for understanding the electron dynamics of molecules exposed to an intense field.
Received 14 September 2000 and Received in final form 6 December 2000 相似文献
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A fibre laser at 1111.6 nm is frequency doubled by two inhomogeneous MgO:LiNbO3 waveguides and the output powers of 85 mW and 49 mW at 555.8 nm have been generated with the conversion efficiencies of 47% and 27% respectively. By analysing the second harmonic generation temperature tuning curves, we investigate the influence of the optical inhomogeneities upon the conversion efficiency. The final result shows that the efficiency difference is mainly affected by the optical inhomogeneities in our case. 相似文献
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D. H. Shi J. F. Sun Z. L. Zhu H. Ma Y. F. Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):253-259
To quantify the changes in the geometric shielding effect in a molecule as the incident electron energy varies, an empirical
fraction, which represents the total cross section contributions of shielded atoms in a molecule at different energies, is
presented. Using this empirical
fraction, the total cross sections for electron scattering by
CH4, C2H6, C2H3F3, C2H4,
C2F4, C2Cl4 and C2Cl2F2 are
calculated over a wide energy range from 30 to 5000 eV by the
additivity rule model at the Hartree-Fock level. The quantitative
total cross sections are compared with those obtained by
experiment and other theories where available. Good agreement is
attained above 100 eV. 相似文献