超短脉冲强激光与固体靶作用产生的高次谐波红移

用一维粒子模拟程序研究了超短脉冲强激光与超临界密度等离子体平板作用产生的高次谐波。分析了振荡镜面模型所不能解释的伴随高次谐波出现的频率红移现象。通常激光与固体靶作用中的高次谐波是由于激光从振荡靶面的反射产生的.除此之外，相对论光强的激光与固体靶作用还应考虑光压对靶的烧蚀推进作用，这时激光相当于从一个移动的振荡靶面反射，所以产生了带有红移的高次谐波. 关键词： 红移 超短脉冲强激光 高次谐波 粒子模拟     

THE MAGNETIC POTENTIAL FOR THE ELLIPSOIDAL MEG PROBLEM

In magnetoencephalography （MEG） a primary current is activated within a bounded conductive medium, i.e., the head. The primary current excites an induction current and the total （primary plus induction） current generates a magnetic field which, outside the conductor, is irrotational and solenoidal. Consequently, the exterior magnetic field can be expressed as the gradient of a harmonic function, known as the magnetic potential. We show that for the case of a triaxial ellipsoidal conductor this potential is obtained by using integration along a specific path which is dictated by the geometrical characteristics of the ellipsoidal system as well as by utilizing special properties of ellipsoidal harmonics. The vector potential representation of the magnetic field is also obtained.     

弱谐波情况下透射光栅衍射效率标定方法

同步辐射光源中的高次谐波会使透射光栅衍射效率标定精度变差。为了校正光源中的高次谐波对透射光栅衍射效率标定的影响,提出了一种光源存在弱谐波情况下的透射光栅衍射效率标定方法,通过使用谐波X射线的衍射效率修正基波衍射效率标定中谐波的影响,从而得到更为准确的透射光栅衍射效率。使用该标定方法在北京同步辐射光源上开展了透射光栅相对衍射效率标定工作。实验结果表明：在100~800 eV存在高次谐波能段,修正后透射光栅一级与零级的相对衍射效率与理论模拟结果吻合较好,修正后光栅二级与一级的相对衍射效率更接近理论模拟结果,但与理论模拟结果仍有较大偏差,该偏差主要来源光栅较弱的二级衍射。     

圆柱腔低频声场的球谐函数分解及声场再现

针对圆柱腔低频声场的球谐函数分解,提出了基于移动式球形传声器阵列(简称球阵)测量的空间域直接求解法。利用空间域测量数据,在压缩感知(Compressive Sensing,CS)理论框架下通过一次线性方程组求解,获得整体坐标系下的声场展开系数。首先讨论了感知矩阵的列相关性,比较不同球阵形式及球面采样点数目,不同球谐函数截断阶数以及空间测量位置等的影响。随后在飞机舱室模型内利用文中提出的方法求解声场展开系数,再现腔内水平面的声压分布,并与传统球坐标变换方法做比较。实验结果表明,利用空间域直接求解法,通过球面随机挑选10个采样点的刚性球阵在声腔3个位置进行声场测量,不仅能够有效求解声场展开系数,而且声场再现精度更高,同时计算效率也显著提高。     

阿秒光脉冲技术的发展和应用

阿秒光脉冲的产生方法获得2023年诺贝尔物理学奖,引起了人们的广泛兴趣。阿秒脉冲是通过周期量级的飞秒脉冲产生高次谐波得到的,其中需要许多关键技术,包括飞秒脉冲压缩技术、脉冲载波相位的稳定控制以及脉冲强度的提高。文章简要介绍阿秒脉冲的产生方法,及其发展趋势和应用。     

Orientation dependence in high harmonics of ZnO with polarization corrections to counteract the birefringent effect

We investigate the influence of the birefringence on the high-order harmonics in an a-cut Zn O crystal with midinfrared laser pulses. The high harmonics exhibit strong dependence on the alignment of the crystal with respect to the laser polarization. We introduce the Jones calculus to counteract the birefringent effect and obtain the harmonics with polarization corrections in Zn O. We show that the birefringent effect plays an important role in the orientation dependence of HHG.     

H2+分子双H核对高次谐波辐射的贡献

理论研究了H2+分子双H核对高次谐波辐射的贡献。结果表明：在少周期激光场下，由于激光场的反对称性，负向H核辐射谐波强度高于正向H核。随着激光脉宽增大，激光波形趋于对称，因此导致双H核辐射谐波的反对称结构减小。谐波辐射的时频分析图显示，当激光场为正向时(E(t) > 0.0)，负向H核辐射谐波强度高于正向H核；当激光场反向时(E(t) < 0.0)，正向H核辐射谐波强度高于负向H核。最后，通过分析含时电子波包及H2+的缀饰态给出了电子在双H核之间转移的原因。     

Calculation of the branch points of the eigenfunctions corresponding to wave spheroidal functions

A method for calculating eigenvalues λ_mn(c) corresponding to the wave spheroidal functions in the case of a complex parameter c is proposed, and a comprehensive numerical analysis is performed. It is shown that some points c _s are the branch points of the functions λ_mn(c) with different indexes n ₁ and n ₂ so that the value λ_{mn 1} (c _s ) is a double one: λ_{mn 1} (c _s ) = λ_{mn 2} (c _s ). The numerical analysis suggests that, for each fixed m, all the branches of the eigenvalues λ_mn(c) corresponding to the even spheroidal functions form a complete analytic function of the complex argument c. Similarly, all the branches of the eigenvalues λ_mn(c) corresponding to the odd spheroidal functions form a complete analytic function of c. To perform highly accurate calculations of the branch points c _s of the double eigenvalues λ_mn(c _s), the Padé approximants, the Hermite-Padé quadratic approximants, and the generalized Newton iterative method are used. A large number of branch points are calculated.     

Highly accurate calculation of angular spheroidal functions

A new method for calculating the angular spheroidal functions of the first kind is proposed. The method is partly based on the known representations of these functions; however, some additional structures proposed in this work ensure efficient highly accurate calculation function values at a given point for a wide range of parameters.