利用x射线激光干涉诊断等离子体电子密度

x射线激光探针干涉方法是诊断高温高密度激光等离子体电子密度等信息的重要工具.利用神光Ⅱ装置输出激光驱动的类镍-银x射线激光作为探针，成功地进行了马赫-曾德尔干涉法诊断实验，获得了清晰的包含等离子体信息的动态干涉条纹图像，并据此给出了待测C8H8等离子体临界面附近电子密度的空间分布. 关键词： 等离子体电子密度诊断 x射线激光 马赫-曾德尔干涉仪     

x射线激光传输过程中的折射和饱和效应

以类镍银139nm(4d→4p，J=0→1)的x射线激光为例，采用二维光线追踪的方法，研究了x射线激光在等离子体介质中的折射及增益饱和效应，计算了x射线激光输出强度随焦线长度的变化和饱和输出光强.计算结果表明折射对光线在等离子体中的传输和放大有重要影响.利用实验参数对类镍银x射线激光的输出强度和增益系数进行了模拟，得到与实验相符的结果. 关键词： x射线激光 光线追踪 折射和饱和效应 激光等离子体     

等离子体中X射线激光传输与电子密度诊断的理论及数值比较

通过数值模拟描述X射线激光在等离子体介质中传输的傍轴偏微分方程,分析了等离子体电子密度诊断中折射率测量法(如Abel变换方法)的成立条件及适用范围.同时分析了由Schrdinger形式理论得到的电子密度诊断的修正项的效果,并给出了修正后的电子密度诊断算法. 关键词： 等离子体 电子密度 X射线激光 Abel变换     

用高速示波器观察不同原子序数Z靶材料激光等离子体X射线瞬时波形

高强度短脉冲激光打靶产生瞬时激光等离子体的电子温度,电子密度及其分布等参数随靶材料原子序数Z的改变而不同,以致激光等离子体辐射的x射线的光子能量和脉冲宽度等均有差别,因而,对这一差别的探讨,对于研究激光等离子体的时间演化及x射线的辐射强度变化的物理过程、激光—x射线的转换情况等提供了线索。而软x射线各种参数的确定,均以对超快软x射线的时间分辩的探测结果为基础的。     

激光诱导环氧玻璃钢等离子体电子密度测量（英）

利用马赫曾德尔干涉测量系统采集到等离子体的激光干涉图像。为了提高数据处理的精度,应用了改进的数字式二次曝光傅里叶法从干涉图中获取了初始的缠绕相位,并采用改进的基于掩膜与枝切法的相位解缠算法对缠绕相位进行相位解缠。在对解缠相位做Abel逆变换后,得到了不同延时时刻下激光诱导环氧玻璃钢等离子体电子密度的空间分布。结果显示：测量得到的电子密度主要为1018 cm-3数量级。实验表明,在记录的时间范围内激光等离子体的电子总数变化不大,且电子密度的变化与等离子体体积的变化大致成反比。     

激光诱导环氧玻璃钢等离子体电子密度测量（英文）

利用马赫曾德尔干涉测量系统采集到等离子体的激光干涉图像。为了提高数据处理的精度,应用了改进的数字式二次曝光傅里叶法从干涉图中获取了初始的缠绕相位,并采用改进的基于掩膜与枝切法的相位解缠算法对缠绕相位进行相位解缠。在对解缠相位做Abel逆变换后,得到了不同延时时刻下激光诱导环氧玻璃钢等离子体电子密度的空间分布。结果显示:测量得到的电子密度主要为1018 cm~(-3)数量级。实验表明,在记录的时间范围内激光等离子体的电子总数变化不大,且电子密度的变化与等离子体体积的变化大致成反比。     

激光诱导环氧玻璃钢等离子体电子密度测量（英文）北大核心CSCD

利用马赫曾德尔干涉测量系统采集到等离子体的激光干涉图像。为了提高数据处理的精度,应用了改进的数字式二次曝光傅里叶法从干涉图中获取了初始的缠绕相位,并采用改进的基于掩膜与枝切法的相位解缠算法对缠绕相位进行相位解缠。在对解缠相位做Abel逆变换后,得到了不同延时时刻下激光诱导环氧玻璃钢等离子体电子密度的空间分布。结果显示:测量得到的电子密度主要为1018 cm~(-3)数量级。实验表明,在记录的时间范围内激光等离子体的电子总数变化不大,且电子密度的变化与等离子体体积的变化大致成反比。     

激光脉冲放大器传输波的计算

研究了一个非线性激光脉冲放大器传输系统，利用广义泛函-变分迭代理论和方法，得到了相应系统的近似解.从而为设计激光脉冲放大器提供了便利. 关键词： 激光 放大器 非线性     

利用人工神经网络进行激光等离子体诊断

利用前馈神经网络对激光等离子体打靶实验中所得的Ｘ光光谱数据进行处理，可以方便地球出等离子体的电子温度和电子密度等参数。在对网络的训练时采用误差信号反向传输算法，训练后的神经网络能够有效地对Ｘ光光谱数据进行处理，文中给出了用此法算出的Ｍｇ等离子体电子温度和电子密度的空间分布轮廓，与用传统方法所得的结果完全吻合。     

基于自相似模型的二维X射线激光等离子体流体力学

从自相似方法出发,建立了简化的二维X射线激光等离子体流体动力学模型. 利用该模型研究了平板靶X射线激光的二维流体力学行为. 研究表明,当激光作用结束后,经过一段时间的演化电子密度和温度沿线聚焦方向逐渐达到平衡,该结果对X射线激光的优化设计具有重要意义. 关键词： X射线激光 二维流体力学计算 自相似方法     

Nonlinear Airy Light Bullets in a 3D Self‐Defocusing Medium

The (3+1)‐dimensional [(3+1)D] nonlinear Schrödinger (NLS) equation is investigated, describing the propagation of nonlinear spatiotemporal wave packets in a self‐defocusing medium, and a new type of Airy spatiotemporal solutions is presented. By using the reductive perturbation method, the (3+1)D NLS equation is reduced to the spherical Kortewegde Vries (SKdV) equation. Based on the Hirota's bilinear method, the bilinear form of the SKdV equation is constructed and Airy light bullet (LB) solutions of different orders are obtained, which depend on the sets of two free constants associated with the amplitude and initial phase. The results show that these Airy LBs can exist in the self‐defocusing medium and their intensities can be controlled by selecting the suitable free parameters along the propagation distance. As examples, three types of low‐order approximate LB solutions are presented and their intensity profiles numerically discussed. The obtained results are helpful in exploring nonlinear phenomena in a self‐defocusing medium and providing a new approach for possible experimental verification of LBs.     

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利用数值方法研究了双温离子、磁场、非均匀性和波的斜向传播对三维非线性尘埃声孤波振幅和宽度的影响。运用约化摄动法得到描述三维非线性尘埃声孤波的非标准变系数Korteweg-de Vries(KdV)方程。然后把非标准变系数KdV方程变为标准变系数KdV方程,并且得到了此标准变系数KdV方程的近似解析解。研究结果表明,此系统中存在着两种形式的孤波,即压缩型孤波和稀疏型孤波,外部磁场对三维非线性尘埃声孤波的宽度有影响,而对其振幅没有影响。此外,波的相速度与波的斜向传播和非均匀性有着非常紧密的联系。     

非热离子对非均匀碰撞热尘埃等离子体中三维孤波的影响

从理论上研究了非热离子、外部磁场、碰撞对非均匀热尘埃等离子体中三维非线性尘埃声孤波的影响。运用约化摄动法得到描述三维非线性尘埃声孤波的非标准的变系数Korteweg-de Vries(KdV)方程。然后把非标准KdV方程变为标准的变系数KdV方程,并且得到了标准的变系数KdV方程的近似解析解。由此解析解可以看出,非热离子的数目、碰撞、非均匀性、波的斜向传播、尘埃颗粒和非热离子的温度对三维非线性尘埃声孤波的振幅和宽度有很大的影响。外部磁场对三维非线性尘埃声孤波的宽度有影响,而对其振幅没有影响。此外,波的相速度与非热离子、波的斜向传播、尘埃颗粒的温度和非均匀性有关。     

Transport equations of amplitudes in the eikonal approximation of dynamical diffraction equations

An approach of the eikonal approximation of the dynamical diffraction equations of X-rays in deformed crystals, based on the second-order differential equations for the transmitted and diffracted waves, is presented. By analogy with usual optics, this approach allows one not only to obtain the eikonal equation and to study the behavior of the amplitude in zero-order approximation, which usually is performed in the eikonal dynamical diffraction theory, but also to establish for all orders of the amplitude asymptotic expansion the corresponding transport equations and to present their solutions as integrals over the amplitude propagation trajectory. Summarizing the transport equations, an equation for the total amplitude, analogous with the parabolic diffraction equation in optics, is obtained.     

非均匀光纤中暗孤子传输特性研究

由于变系数非线性Schrödinger方程的增益、色散和非线性项都是变化的, 根据方程这一特点可以研究光脉冲在非均匀光纤中的传输特性. 本文利用Hirota方法, 得到非线性Schrödinger方程的解析暗孤子解. 然后根据暗孤子解对暗孤子的传输特性进行讨论, 并且分析各个物理参量对暗孤子传输的影响. 经研究发现, 通过调节光纤的损耗、色散和非线性效应都能有效的控制暗孤子的传输, 从而提高非均匀光纤中的光脉冲传输质量. 此外, 本文还得到了所求解方程的解析双暗孤子解, 最后对两个暗孤子相互作用进行了探讨. 本文得到的结论有利于研究非均匀光纤中的孤子控制技术.     

Modulational instability in the cubic-quintic nonlinear Schrödinger equation through the variational approach

The dynamics of nonlinear pulse propagation in an average dispersion-managed soliton system is governed by a constant coefficient nonlinear Schrödinger (NLS) equation. For a special set of parameters the constant coefficient NLS equation is completely integrable. The same constant coefficient NLS equation is also applicable to optical fiber systems with phase modulation or pulse compression. We also investigate MI arising in the cubic-quintic nonlinear Schrödinger equation for ultrashort pulse propagation. Within this framework, we derive ordinary differential equations (ODE’s) for the time evolution of the amplitude and phase of modulation perturbations. Analyzing the ensuing ODE’s, we derive the classical modulational instability criterion and identify it numerically. We show that the quintic nonlinearity can be essential for the stability of solutions. The evolutions of modulational instability are numerically investigated and the effects of the quintic nonlinearity on the evolutions are examined. Numerical simulations demonstrate the validity of the analytical predictions.     

Localization in the model of contacting media with specific nonlinearity and interface interaction

In this paper, we consider the new model of nonlinear contacting media based on nonlinear Schrodinger equation with point potential and term, which is depended stepwise on field amplitude. Such a model theoretically describes a change in properties of the boundary regions along the interface between a Kerr-type crystal with cubic nonlinearity and a nonlinear medium characterized by abruptly change in dielectric constant depending on field amplitude. The short-range local interaction between wave and interface is taken into account by point potential in nonlinear Schrodinger equation. We obtain two new types of localized states characterized by composite structure consisting of three parts of the field distributions. We find exact and approximate solutions of dispersion equations. We described new properties of the spectrum of localized states arising as a result of the interaction of the wave with the interface and the presence of threshold field of the switching between the medium constants. All results are obtained in an analytical form. The proposed theory can be used to describe the propagation features of intense light beams localized along media interfaces in nonlinear optics, and to describe Bose-Einstein condensates with cubic nonlinearity.     

Structure of the axial intensity minima in the Fresnel diffraction on a circular opening and superluminous effects

The “classical” problem of plane-wave diffraction by a circular opening is inspected with one particular interest to check the existence of axial zeroes of amplitude, which can produce a specific type of phase singularities. We investigate the problem using paraxial and nonparaxial solutions of scalar wave equation based on Hankel transform. The main result of investigation is the detection of the absence of any exact amplitude zeroes in the Fresnel diffraction field. Instead, sharp phase variations localized at the regions of axial amplitude minima with longitudinal and transversal dimensions of the order of one wavelength are revealed. These phase variations influence on the phase velocity, which drops up to c/2 in the point of axial amplitude minimum. Also, superluminous effects of wavefront propagation are discussed.     

Stable Soliton Propagation in a System with Spectral Filtering and Nonlinear Gain

Stable soliton propagation in a system with linear and nonlinear gain and spectral filtering is investigated. Different types of exact analytical solutions of the cubic and the quintic complex Ginzburg-Landau equation (CGLE) are reviewed. The conditions to achieve stable soliton propagation are analyzed within the domain of validity of soliton perturbation theory. We derive an analytical expression defining the region in the parameter space where stable pulselike solutions exist, which agrees with the numerical results obtained by other authors. An analytical expression for the soliton amplitude corresponding to the quintic CGLE is also obtained. We show that the minimum value of this amplitude depends only on the ratio between the linear gain and the quintic gain saturating term.     

Stable Soliton Propagation in a System with Spectral Filtering and Nonlinear Gain

Stable soliton propagation in a system with linear and nonlinear gain and spectral filtering is investigated. Different types of exact analytical solutions of the cubic and the quintic complex Ginzburg-Landau equation (CGLE) are reviewed. The conditions to achieve stable soliton propagation are analyzed within the domain of validity of soliton perturbation theory. We derive an analytical expression defining the region in the parameter space where stable pulselike solutions exist, which agrees with the numerical results obtained by other authors. An analytical expression for the soliton amplitude corresponding to the quintic CGLE is also obtained. We show that the minimum value of this amplitude depends only on the ratio between the linear gain and the quintic gain saturating term.