共查询到19条相似文献,搜索用时 93 毫秒
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理论研究了多周期激光相位角对H2+谐波频移的影响。结果表明,在多周期激光驱动下H2+谐波光谱在零相位时呈现蓝移现象。随着激光相位增大,谐波光谱由蓝移转向红移。随着激光相位进一步增大,谐波红移减弱。理论分析表明谐波频移是由激光上升和下降区域谐波辐射强度变化引起的。并且谐波辐射强度变化对激光相位比较敏感。 相似文献
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通过数值求解激光驱动下电子在一维周期势场中运动的薛定谔方程,研究了晶体在激光场中发射的低阶谐波强度随激光波长的变化规律,结果表明,晶体发射低阶谐波强度随激光波长的变化规律与晶体发射高次谐波第一平台区域的变化规律不同.已有的研究表明晶体发射高次谐波第一平台区域的强度会随激光波长的增加而衰减,而我们发现晶体发射低阶谐波的强度会随激光波长的增加而增加.通过对晶体发射低阶谐波的时频分析、晶体价带能量变化与激光光子能量的关系,解释了晶体发射低阶谐波强度随激光波长增加而增加的原因. 相似文献
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理论研究了在激光相位和啁啾调控共同影响下高次谐波光谱的变化。结果表明:当激光相位为0时,一阶啁啾调控使谐波能量延伸。二阶啁啾调控会呈现高强度谐波平台区。当激光相位为0.5π时,一阶啁啾调控可以获得连续平台区,但是强度较弱。在二阶啁啾调控下,谐波能量得到明显增大。通过谐波时频分析给出了不同激光波形下产生高次谐波光谱的原因。 相似文献
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数值研究了激光脉宽对H_2~+和T_2~+谐波辐射的影响.计算结果表明:(i)对于谐波频移现象:在少周期激光场下,H_2~+和T_2~+谐波辐射呈现红移.随着激光脉宽增大,H_2~+谐波辐射呈现蓝移; T_2~+谐波辐射红移减弱.(ii)对于谐波振幅强度:H_2~+和T_2~+谐波辐射强度会随着激光脉宽增大而增强.但是,在少周期激光场下,H_2~+谐波截至能量附近的强度要大于T_2~+.在多周期激光场下,T_2~+谐波截至能量附近的强度要大于H_2~+. 相似文献
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理论研究了长脉宽激光驱动下啁啾引入时刻对H_2~+高次谐波光谱的影响.结果表明,在长脉宽激光驱动下,H_2~+在激光前半程区域具有较高的谐波辐射效率.因此,在激光前半程引入啁啾调控可获得高强度光谱连续区.此外,在啁啾调控区域引入单极激光场可以进一步获得高能谐波连续区.最后,叠加谐波连续区的谐波,可获得39 as的孤立脉冲. 相似文献
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研究发现,在超强激光作用下电子运动的相对论效应可导致高次谐波辐射,采用单电子模型计算分析了不同偏振微光作用下的高次谐波发射,表明圆偏振激光较线偏振激光更有利于高次谐波产生。 相似文献
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通过数值求解二维含时薛定谔方程,理论研究了正交偏振双色激光场作用下H2+分子高次谐波发射和孤立阿秒脉冲的产生. 数值结果显示,改变激光场的强度比,可以调控高次谐波强度以及谐波椭偏率. 结果表明随着场强比的增加,y方向的谐波强度不断提高. 当场强比为1:2.5时,x方向和y方向分别仅有奇次谐波和偶次谐波产生,并且偶次谐波的强度比奇次谐波强度高2-3个数量级. 此时,奇次谐波的椭偏率最大可以达到0.3,偶次谐波的椭偏率接近于0. 此外,通过改变分子的准直角可以控制谐波的椭偏率,基于这一现象,利用椭圆偏振高次谐波的平台区合成了椭偏率为0.05的椭圆偏振阿秒脉冲链. 相似文献
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It is shown that the irradiation of atomic clusters by a superintense femtosecond laser pulse gives rise to various harmonics of the laser field. They arise as a result of elastic collisions of free electrons with atomic ions inside the clusters in the presence of the laser filed. The yield of even harmonics whose electromagnetic field is transverse is attributed to the relativism of the motion of electrons and the consideration of their drift velocity associated with the internal ionization of atoms and atomic ions of a cluster. These harmonics are emitted in the same direction as odd harmonics. The conductivities and electromagnetic fields of the harmonics are calculated. The generation efficiency of the harmonics slowly decreases as the harmonic number increases. The generation of even harmonics ceases when the drift velocity of electrons becomes equal to zero and only the oscillation velocity of electrons is nonzero. The results can also be applied to the irradiation of solid-state targets inside a skin layer. 相似文献
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Generation of even and odd harmonics in the skin layer formed during the interaction of a short relativistic laser pulse with solid targets is considered. The complex motion of free electrons in the skin layer along the electric field vector and along the direction of propagation of a laser wave is analyzed. The Fourier expansion of the trajectory of this motion is used to obtain the components of the conductivity tensor and of the amplitude of the transverse electromagnetic field of harmonics propagating along the electric field. Even harmonics appear due to relativistic effects. The efficiency of generation of even and odd harmonics at the leading front of a laser pulse is calculated. 相似文献
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We present a velocity-gauge model for the generation of even-order high harmonics, and reveal that the even-order harmonics originate from the multiple-step transitions among the energy bands in momentum space, while the odd-order harmonics are mainly from direct transitions. The lower valence band is found vital for the generation of even harmonics. Relative intensity of even-order harmonics versus the odd orders is calculated and shows a growing trend as the laser field amplitude increases. 相似文献
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We present experimental results in which a second-order effect, namely two-photon ionization of atomic He induced by a superposition of harmonics, is observed. The harmonics are generated in a Xe gas-jet using a 790-nm 10-Hz femtosecond Ti:sapphire laser and are subsequently focused into a He gas-jet with a Kirkpatrick–Baez arrangement. The superposition is formed by using a thin In filter and it comprises the 7th to 13th harmonics. Solving the time-dependent Schrödinger equation for He in a polychromatic laser field, the He + ion yield is calculated as a function of the total XUV intensity. Using the calculated yield and taking into account the focusing and transmission properties of the arrangement, the number of He + ions produced per laser pulse is estimated and is found to be in reasonable agreement with its measured value. The total number of ions produced non-resonantly follows a nearly quadratic dependence on the harmonic intensity, thus establishing the feasibility of a second-order auto-correlation measurement of the superposition of harmonics, i.e., of a direct temporal characterization of attosecond pulse trains. 相似文献
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用隧道电离模型,研究了激光和气体相互作用中,不同气体密度及激光强度下,气体电离及激光能量损耗物过程,并研究了这种效应引起的高次谐波。 相似文献
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Zhang GP 《Physical review letters》2005,95(4):047401
High harmonic generation (HHG) requires a strong laser field, but in C60 a relatively weak laser field is sufficient. Numerical results presented here show that, while its low order harmonics result from the laser field, its high order ones are mainly from the multiple excitations. Since high order harmonics directly correlate with electronic transitions, the HHG spectrum accurately measures transition energies. Therefore, C60 is not only a promising material for HHG, but may also present an opportunity to develop HHG into an electronic structure probing tool. 相似文献