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应用电子和多光子集团非弹性碰撞模型和冷等离子体模型，研究了飞秒强激光与线性等离子体发生多光子非线性Compton散射时，散射激光与入射激光形成的飞秒耦合激光场对线性等离子体层中光场和电子密度分布的影响。研究发现，在耦合激光的有质动力作用下，电子密度分布和离子密度分布比Compton散射前的偏离更加严重，电子密度的变化比离子密度的变化更快，产生的静电场更强。即使耦合激光场非常弱，电子的运动仍表现出相对论效应，仍有静电场存在。     

用同步光学探针诊断激光等离子体的温度分布和辐射的有质动力效应

探针光被高温高密度激光等离子体散射后,散射光谱中的电子成分和离子成分容易分离,由此可以测定等离子体的温度分布.同时,我们用干涉法测量等离子体电子密度分布,证明了辐射的有质动力的重要作用.     

激光尾波场横向波破的粒子模拟

用粒子模拟方法，研究激光脉冲的横向宽度有限时对产生激光尾波场和电子加热的影响. 在 纵向和横向有质动力的作用下，电子密度的空间分布形成“马蹄型”的低密度区，这些低密 度区好像运动的透镜，使长脉冲激光自聚焦，而且随着激光的传播，“马蹄型”的曲率越来 越大，直到产生横向波破. 横向波破一方面使得波破时静电场极值远小于波破极限，另一方 面将更多的电子推入加速相位，静电场“俘获”的电子数目大大增加，但最大电子动能明显 减小. 关键词： 尾波场 有质动力 电子俘获 横向波破     

对飞秒激光等离子体相互作用中横向箍缩的观察

用飞秒激光的Normaski偏振干涉法,对超短激光脉冲产生的等离子体膨胀过程进行了光学诊断,得到了有时间分辨的等离子体干涉图.发现飞秒激光等离子体在靶面平行的方向上出现了箍缩,使等离子体膨胀呈jet结构,这种箍缩现象是由自生磁场对等离子体的约束所造成. 关键词： 飞秒激光等离子体 光学诊断 电子密度分布     

紧聚焦的超短超强激光脉冲在真空中加速斜入射的相对论电子

研究了紧聚焦的线偏振飞秒超强高斯激光脉冲俘获并剧烈加速斜入射低能相对论电子的效应 ，发现被俘获的电子在激光脉冲纵向有质动力的强大加速作用下，可以获得GeV量级的能量 ，并详细研究了入射电子的初能量、斜入射角、电子与激光脉冲的相对延迟时间和激光脉冲 宽度等条件对电子能量增益的影响，发现当激光脉宽超过10λ时，脉宽对电子能量增益影响 不大. 关键词： 电子加速 有质动力 能量增益 束腰     

利用单飞秒激光脉冲驱动类氖钛X射线激光的研究

提出了一种利用单飞秒激光脉冲驱动类氖钛X射线激光的物理方案.利用自相似方法研究了不同脉冲前沿的单飞秒激光辐照钛平板靶产生的类氖钛X射线激光等离子体的特性,得到了电子温度、电子密度和定标长度三者的定标律,讨论了给定输入参数下各定标律曲线的特性.研究表明,利用单个飞秒激光能够实现X射线激光的产生,而且脉冲前沿强度随时间增长平缓的飞秒激光有利于驱动X射线激光.本研究为实验上实现单飞秒激光脉冲驱动X射线激光提供了一种新的方案.     

超短电子脉冲在聚焦强激光场中的三维有质动力散射

采用三维测试粒子模拟(test-padicle simulation)的方法，研究了聚焦的飞秒脉冲强激光与超短电子束进行有质动力的散射过程.详细讨论了超短电子束经过不同激光延迟下有质动力散射的空间分布特征和能谱特征.提出了通过测量电子束的空间分布和能谱分布实现对超短脉冲电子束的脉冲宽度测量的方法. 关键词： 有质动力散射 聚焦的飞激光 飞秒电子束     

飞秒激光等离子体中电子热传导现象的数值模拟

采用相对论电磁粒子模拟程序研究了飞秒激光等离子体相互作用中产生的电流密度、电场和自生磁场的发展演化过程。介绍了电子的非局域热输运的基本特性以及激光加热过程中温度烧蚀前沿稠密等离子体子区的预热效应、临界面附近的限流效应,以及冕区的反扩散与限流效应,得到了经典Spitzer-Harm理论描述的电子热传导随自生磁场的演化情形。数值模拟表明:在线性强激光作用下,由于电子初始时刻的无规则热运动,在等离子体上激发电磁不稳定性,而不稳定性激发的强电磁场使电子束在非常短的距离内沉积能量,同时对在激光有质动力推开电子时形成的超热电子能量输运产生抑制作用。     

有质动力和静电分离场对激光等离子体流体力学状态的影响

利用建立在欧拉坐标系上的一维电子_离子双流双温流体力学程序, 模拟了超短脉冲强激光 (1×1015W/cm2, 150fs)与线性密度梯度等离子体相互作用的流体力学过程. 模拟结果显示，入射激光与临界密度面的反射光叠加，在临界密度以下区域形成局域驻波， 产生的强有质动力在低密区驱动电子形成周期性密度结构——Bragg光栅，激光的反射被增 强. 临界密度处有质动力将等离子体分成向内和向外运动的两部分. 由于离子所受的有质动 力和热压强的梯度力远小于电子，体系产生了强静电分离场，离子的运动主要由该静电分离 场决定. 对双流双温模型和单流双温模型的模拟结果进行了比较. 当有质动力和热压强梯度 力较大时，两种模型对等离子体流体力学状态的描述有明显差异，单流双温模型无法描述此 时的流体力学状态. 关键词： 有质动力 密度调制 双流双温流体力学模型 单流模型     

磁约束飞秒激光诱导铜等离子体特性研究

建立磁约束飞秒激光诱导铜等离子体辐射光谱采集系统,通过发射光谱法分析磁约束效应对飞秒激光诱导铜等离子体特性的影响.在强度为0.67T的稳磁场约束下,等离子体辐射连续谱和分立谱均有增强,分立谱线增强更显著;铜原子上能级越高,其辐射的原子谱线增强因子越大,具有最高上能级的Cu I 507.6nm增强因子最大,为2.8;等离子体铜原子谱线持续时间明显延长,在等离子体演化初期,谱线增强显著,在较大延时,谱线增强迅速减弱;等离子体电子温度和电子密度均有提高.     

激光加速质子束对电磁孤立子的照相模拟研究

激光在次稠密等离子中传输, 由于频率下移而被俘获, 从而产生电磁孤立子. 根据先前理论及PIC 模拟给出的孤立子的演化过程, 对不同阶段孤立子的电磁场分布进行了建模. 使用Geant4蒙特卡罗程序, 模拟研究了激光加速产生的能量为几个MeV的质子束对后孤立子的照相. 分析了质子能量, 质子源尺寸等因素对照相结果的影响, 并利用了TNSA加速产生质子束的分幅特性, 开展了时间分辨的孤立子照相模拟研究. 模拟给出的质子照相结果验证了文献中给出的孤立子静电场模型, 为以后在实验上探测孤立子提供了理论依据. 关键词： 超短激光 质子照相 孤立子 蒙特卡罗方法     

Enhanced electron trapping by a static longitudinal magnetic field in laser wakefield acceleration

An externally applied longitudinal magnetic field was found to enhance the particle trapping in the laser wakefield acceleration. When a static magnetic field of a few tens of tesla is applied in parallel with the propagation direction of a driving laser pulse, it is shown from two-dimensional particle-in-cell simulations that total charge of the trapped beam and its maximum energy increase. The analysis of electron trajectories strongly suggests that the enhanced trapping originates from the suppression of the transverse motion by the magnetic field. The enhanced trapping by the magnetic field was observed consistently for various values of the plasma density, the amplitude of the laser pulse and pulse spot size.     

Interplay of parallel electric field and trapped electrons in kappa-Maxwellian auroral plasma for EMEC instability

In this paper, propagation characteristics of electromagnetic electron cyclotron(EMEC) waves based on kappa-Maxwellian distribution have been investigated to invoke the interplay of the electric field parallel to the Earth's magnetic field and auroral trapped electrons. The dispersion relation for EMEC waves in kappa-Maxwellian distributed plasma has been derived using the contribution of the parallel electric field and trapped electron speed. Numerical results show that the presence of the electric field has a stimulating effect on growth rate, which is more pronounced at low values of wave number. It is also observed that as the threshold value of trapped electron speed is surpassed, it dominates the effect of the parallel electric field and EMEC instability is enhanced significantly. The electric field acts as another source of free energy, and growth can be obtained even in the absence of trapped electron drift speed and for very small values of temperature anisotropy. Thus the present study reveals the interplay of the parallel electric field and trapped electron speed on the excitation of EMEC waves in the auroral region.     

飞秒激光固体靶相互作用中超热电子的输运特性

 实验研究了在100 TW掺钛宝石超短超强脉冲激光装置上完成的飞秒激光-固体靶相互作用中超热电子的输运特性，获得了超热电子的能谱、产额、注量及超热电子在靶内输运能量沉积范围。测量结果表明:超热电子的注量和总能量随靶厚度的增加而减少，超热电子约80％的能量主要沉积在靶内的前约一个激光脉冲宽度的范围内，且能量沉积范围随激光脉冲宽度的增加而增加，这主要是静电场的影响所致。     

Trapping and Acceleration of Electron Bunches Generated by a Laser Pulse Moving through the Sharp Plasma Boundary

The formation and acceleration of electron bunches resulting from the self-injection of electrons into the wake wave from the laser pulse moving through a sharp plasma boundary are investigated in one-dimensional geometry. It is shown that electron trapping in the accelerating wakefield is governed by the electron energy and has a threshold character. The acceleration of the trapped bunch is numerically simulated.     

激光等离子体相互作用中的两级质子加速（英文）北大核心CSCD

研究了激光辐射压驱动的两级质子加速的相关问题。当超短超强激光脉冲与处在背景等离子体前方的薄固体平靶相互作用时,在固体靶后部形成一个电子层-离子层组成的双层结构。在激光的不断推进下,双层结构在背景等离子体里以一定速度传播,可以看成运动在背景等离子体中的电场。这样,在背景等离子体中的质子被这个运动电场捕获并能加速到很高的能量。通过二维PIC模拟方法和理论分析研究了质子加速的相关问题。研究结果表明,被加速质子的最大能量达到20GeV。     

Observation of Raman forward scattering and electron accelerationin the relativistic regime

Raman forward scattering (RFS) is observed in the interaction of a high intensity (>10¹⁸ W/cm²) short pulse (<1 ps) laser with an underdense plasma (n_e~10¹⁹ cm ^-3). Electrons are trapped and accelerated up to 44 MeV by the high-amplitude plasma wave produced by RFS. The laser spectrum is strongly modulated by the interaction, showing sidebands at the plasma frequency. Furthermore, as the quiver velocity of the electrons in the high electric field of the laser beam becomes relativistic, various effects are observed which can be attributed to the variation of electron mass with laser intensity     

Excitation of an upper hybrid wave by two intense laser beams and particle acceleration

This Letter presents an investigation of the excitation of an upper hybrid wave (UHW) by cross focusing of two intense laser beams in a collisionless hot magnetoplasma, when relativistic and ponderomotive nonlinearities are operative. The electric vectors of the two beams are polarized along uniform static magnetic field and the beams propagate perpendicular to the static magnetic field. Analytical expressions for the beam width of the laser beams, electric vector and power of the excited UHW and energy gain have been obtained. The UHW generation at the difference frequency and particle acceleration has also been studied. The nonlinear coupling between intense laser beams and UHW is so strong that UHW gets excited and a large fraction of the laser beam energy gets transferred to UHW and this UHW accelerates electrons. It has been shown that the presence of a magnetic field affects significantly the power of the UHW and energy gain by the electron in the presence of the UHW.     

Vacuum heating evaluation for plasmas of exponentially decreasing density profile

Ultra-short pulse lasers have opened a regime of laser-plasma interaction where plasmas have scale lengths shorter than the laser wavelength and allow the possibility of generating near-solid density plasmas. The interaction of high-intensity laser beams with sharply bounded high-density and small scale length plasmas is considered. Absorption of the laser energy associated with the mechanism of dragging electrons out of the plasma into the vacuum and sending them back into the plasma with the electric field component along the density gradient, so called vacuum heating, is studied. An exponentially decreasing electron density profile is assumed. The vector potential of the electromagnetic field propagating through the plasma is calculated and the behaviour of the electric and magnetic components of the electromagnetic field is studied. The fraction of laser power absorbed in this process is calculated and plotted versus the laser beam incidence angle, illumination energy, and the plasma scale length.     

Photoinscription of Bragg gratings within a germanosilicate fiber subjected to a high static electric field

The kinetics of Bragg grating growth in germanosilicate fibers subjected to a high static electric field are compared with those obtained without any electric field. The gratings were written by exposure of the fiber core to laser light at 244 or 193 nm. These experiments gave some clues about the mechanisms responsible for both the photosensitivity in germanosilicate fibers and the nonlinear second-order UV-induced susceptibility in silica glasses. The refractive-index modulation proved to be significantly higher in the fibers subjected to an electric field. Furthermore, the change in the fiber's mean effective refractive index as a function of exposure time was not monotonic. This evolution can be explained by the assumption that some electric-field-induced diffusion of electron trapped centers [Ge(1) and Ge(2)] from the fiber core is involved.