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The dependence of emission direction of fast electrons on the laser intensity has been investigated. The experimental results show that, at nonrelativistic laser intensities, the emission of fast electrons is mainly in the polarization plane. With the increase of the laser intensity, fast electrons emit towards the laser propagation direction from laser polarization direction. At relativistic laser intensities, fast electrons move away from the laser polarization plane, closely to the reflection direction of the incident laser beam. 相似文献
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采用一维粒子模拟(PIC)方法,研究了相对论效应对P偏振激光斜入射非均匀等离子体时产生的共振吸收的影响. 计算表明,弱相对论情况下,在临界面附近产生的电子等离子体波的相对论非线性效应占主要作用;随着入射光场的逐渐增大,吸收率逐渐降低. 当入射光强超过3.7×1017W/cm2时,由于超短激光脉冲本身在等离子体中产生相对论效应、等离子体波破裂效应,以及参量不稳定过程激发等,吸收系数随着激光强度又开始增加. 固定等离子体密度标长,取不同的激光入射角、电子初始温度,相对论效应对吸收系数的影响是一致的.
关键词:
激光等离子体
相对论效应
共振吸收
粒子模拟 相似文献
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高功率超短超强激光脉冲的诞生开启了相对论非线性光学、高强场物理、新型激光聚变、实验室天体物理等前沿领域.近年来,随着数拍瓦级乃至更高峰值功率激光装置的建成,超强激光与等离子体相互作用进入到一个全新的高强场范畴.这种极强激光场与等离子体相互作用蕴含着丰富的物理过程,除了经典的波与粒子作用、相对论效应、有质动力效应等非线性物理过程外,量子电动力学(QED)效应变得格外重要,例如辐射阻尼效应、正负电子对产生、强伽马射线辐射、QED级联、真空极化等.本文主要介绍我们近年来在极端强激光场与等离子体相互作用中激发的QED效应以及伴随的超亮强伽马射线辐射和稠密正负电子对产生等方面的研究进展. 相似文献
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A survey on the mechanisms of powerful terahertz (THz) radiation from laser plasmas is presented.Firstly,an analytical model is described,showing that a transverse net current formed in a plasma can be converted into THz radiations at the plasma oscillation frequency.This theory is applied to explain THz generation in a gas driven by two-color laser pulses.It is also applied to THz generation in a tenuous plasma driven by a chirped laser pulse,a few-cycle laser pulse,a DC/AC bias electric field.These are well verified by particle-in-cell simulations,demonstrating that THz radiations produced in these approaches are nearly single-cycles and linear polarized.In the chirped laser scheme and the few-cycle laser scheme,THz radiations with the peak field strength of tens of MV/cm and the peak power of gigawatt can be achieved with the incident laser intensity less than 10 17 W/cm 2. 相似文献
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通过二维粒子模拟(particle-in-cell)方法研究了强激光与亚临界密度等离子体相互作用中的近前向光子加速机制.该机制利用强激光在亚临界密度气体传输过程中的电离效应产生在纵向和横向上密度分布不均匀的电子等离子体.在纵向上,入射激光电离氦气产生一个陡峭的电子密度前沿分布.在密度前沿处,入射激光与电子等离子体波作用发生近前向散射.散射光频率较激光频率增大,在频谱中产生了第一个特征峰.在横向上,密度不均匀造成电子等离子体波具有不同的相速度并与入射激光相互作用,使入射激光发生近前向散射,在频谱中产生了第2个特征峰.由于密度分布的不均匀性较电子等离子体波的密度扰动大得多,因此基于微扰理论的散射模型和色散关系,如受激拉曼散射,无法解释频谱中两个特征峰的出现.进一步研究发现:在密度不均匀的情况下,入射激光、电子等离子体波和散射光三者之间仍满足动量和能量守恒的三波耦合关系.这能够解释两个特征峰对应的频率和强度增长过程.该研究对于强激光在亚临界密度气体传输过程中的频谱演化具有重要参考意义. 相似文献
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理论研究和数值模拟发现入射光和反射光在低密度等离子体中形成的干涉场可以产生深度的等离子体密度调制. 对于中等强度的入射光,譬如1015W/cm2 ,产生密度调制的时间尺度在几十个光周期的范围. 这样的等离子体密度调制可以起类似布拉格反射镜的 作用,使得后面的入射光在临界面以下的区域产生相位反射. 因为密度调制的周期是光在等 离子体中波长的一半,其产生的反射率可以接近100%. 相位反射也可以在不均匀的低密度 等离子体中产生,它可以极大地减少等离子体对光的吸收,因此在惯性约束核聚变中需要考 虑到它的影响.
关键词:
相位反射
密度调制
激光等离子体
粒子模拟 相似文献
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Generation of Broadband High Harmonics through Linear Mode Conversion in Inhomogeneous Plasmas 下载免费PDF全文
The generation of high order harmonics from an inhomogeneous ovderdense plasma target irradiated by an ultrashort intense laser pulse is studied by numerical simulation. During such interaction, ultrafast electron bunches are generated and excite electron plasma oscillations as they pass through the overdense target. These plasma oscillations will emit high-frequency electromagnetic emission by linear mode conversion. Instead of the integer harmonies generation, the emission appears with a broadband and even continuous spectrum corresponding to the electron plasma frequency range of the inhomogeneous plasma density. 相似文献