超强激光场物理学

首先,评述了超强激光场的理论结果;其次,描述了超短光脉冲在密的气体和光学介质传播中的自作用;第三,评述了强场离化无碰撞等离子体中高度离化的离子产生,及高功率超短激光脉冲巨大强度的电场可用于电子加速;第四,分析了超短声脉冲和无线电脉冲的产生和应用,讨论了在不同条件下,激光辐射谐波和 Ｘ 射线激光的产生,进一步评述了超强激光脉冲与凝聚靶相互作用可以产生接近星体物质参数的高温、超密、强磁场和巨大压力等离子体;最后,简要叙述了激光激发核、核反应,高能电子─光子相互作用的可能效应及可能进行的实验。     

激光与固体靶相互作用中低密度预等离子体对高能电子产生的影响

 对线极化、圆极化的超短超强激光脉冲与靶前有一段低密度预等离子体的固体靶的相互作用进行了理论和粒子模拟研究。激光通过有质动力加速机制加速预等离子体中的电子，研究了电子获得的最大能量随激光强度和预等离子体密度的变化。当激光脉冲与靶直接作用时，靶中的电子由于J×B机制而得到加速，所获得的能量比预等离子体中电子低。研究表明，在超短超强激光脉冲与固体靶相互作用中，预等离子体的存在有利于高能电子的产生。     

粒子模拟程序的发展及其在激光等离子体相互作用研究中的应用

介绍针对超短超强激光脉冲与等离子体相互作用研究的多维粒子模拟程序KLAP.在其一维程序KLAP1D中,考虑场电离、碰撞离化及两体碰撞效应后,程序可以用于研究短脉冲激光与中性物质的相互作用.在其三维程序KLAP3D中,为了研究加速能量达GeV的长距离激光尾波场加速问题,程序采用移动窗口技术,使得模拟尺度可以达到厘米量级.同时介绍了利用KLAP程序得到的有关THz辐射、激光与中性气体相互作用中的脉冲及离化波前演化、激光固体靶作用中表面电子加速及激光尾波场加速的研究实例.     

激光等离子体二维相对论电磁粒子模拟

研制了激光等离子体二维相对论电磁粒子模拟程序(2DCIC)。追踪几万甚至百万个模拟粒子在外加激光场和自洽场中运动,自洽地计算电荷和电流密度,求解完全的Maxwel方程,电子的相对论运动方程和离子的牛顿运动方程,辅以灵活的诊断研究波-波,波-粒子相互作用的发生、发展和饱和的细节以及时间演化规律。激光可以正入射,也可以斜入射;等离子体可以是均匀密度,也可以具有密度梯度;为了节约机时,还发展了并行运算。物理模型参数可调,既适用于研究激光聚变等离子体相互作用,也适用于超短脉冲超强激光等离子体相互作用和其它等离子体问题。经过多次试算检验,对等离子体平衡态进行了计算研究,对于超短脉冲超强激光的传播也进行了初步模拟计算。     

激光尾波场中光子加速研究

在SILEX-Ⅰ激光装置上,测量了超短超强激光脉冲与稀薄等离子体相互作用之后的透射谱. 实验中发现,激光尾波场产生的密度扰动导致等离子体折射率随时间空间不断变化,导致光子的加速/减速. 透射谱上主要表现为激光频率谱峰的劈裂和随密度变化的展宽,没有发现与前向受激拉曼散射或自调制不稳定性相联系的边频波. 同时,利用LPIC++无碰撞粒子模拟程序模拟了超短超强激光与稀薄等离子体相互作用后的透射谱,模拟结果也发现了明显的光子加速过程. 关键词： 超短超强激光脉冲 透射谱 光子加速/减速     

超热电子的产生与定向发射

在超短超强激光与等离子体相互作用的过程中，等离子体中的一部分电子通过各种机制吸收能量转变成为高能的超热电子．它们不仅是惯性约束核聚变“快点火”过程中的能量载体，对激光脉冲在等离子体中的传输、能量沉积、转化等一系列过程也都发挥着重要的作用．文章对超短超强激光与等离子体相互作用过程中超热电子产生的主要物理机制以及影响超热电子定向发射的因素进行了介绍．     

超短超强激光在稀薄等离子体中的自聚焦传输

 开展超短超强激光与次稠密等离子体相互作用实验,采用探针光对激光等离子体相互作用区域进行阴影成像,研究了不同激光功率与临界功率比值及不同激光脉冲长度与等离子体波波长比值下的激光在次稠密等离子体中的自聚焦传输。结果表明:相对论效应是超短脉冲在次稠密等离子体中的主要自聚焦机制,激光功率与临界功率比值是影响超短脉冲在次稠密等离子体中形成自聚焦的关键条件。     

激光聚变快点火机理研究

对超强超短激光等离子体相互作用和快点火机理及其物理可行性进行了理论和数值模拟研究.研制了二维和二维半粒子云模拟程序,数值模拟了超强超短激光脉冲在非均匀等离子体中的传播.提出快点火穿孔速度和深度以及用于快点火的超强超短激光器的初步指标 关键词： 超强超短激光等离子体相互作用 快点火机理 粒子云模拟     

薄膜靶整形强激光脉冲的理论分析和数值模拟

超强超短脉冲激光广泛应用于粒子加速以及新型X射线辐射源产生。较长的激光脉冲上升前沿直接影响激光应用效果。等离子体薄膜靶作为新型光学介质开关,可以有效降低超强激光脉冲前沿上升时间,优化激光等离子体相互作用参数。采用一维理论分析和粒子模拟方法研究了等离子体薄膜靶实现超强激光脉冲整形的机制。研究结果表明,薄膜靶通过对激光脉冲的非线性调制,可有效实现脉宽缩短和脉冲陡化;对比单层靶调制结果,选择参数优化的双层靶,可进一步优化脉冲整形效果,获得更短脉宽和更高振幅的激光脉冲;对于峰值振幅高于薄膜靶击穿阈值的超强激光,脉冲上升前沿可得到明显陡化,薄膜靶的击穿是产生这种脉冲整形效果的直接原因。     

激光入射角对靶面方向超热电子发射的影响

实验研究了超短超强激光脉冲与薄膜靶相互作用中产生的超热电子角分布随激光入射角的变化.在靶面方向观测到一束方向性很好的高能超热电子.该高能超热电子束的电子数目随着激光入射角的增大而增大.对结果的分析表明，表面准静态磁场是导致表面电子产生的主要原因. 关键词： 超热电子 表面准静态磁场 超强激光脉冲与等离子体相互作用     

Terahertz emission in tenuous gases irradiated by ultrashort laser pulses

Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scaling with the laser amplitude within a large range is also discussed.     

Terahertz emission in tenuous gases irradiated by ultrashort laser pulses

Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scaling with the laser amplitude within a large range is also discussed.     

Generation of XUV attosecond pulses in the process of atomic ionization by few-cycle laser radiation

Ionization of a model two-electron atom in the presence of a strong field of ultrashort laser pulses is investigated using the numerical integration of the nonstationary Schrödinger equation, which describes the dynamics of a quantum system in the presence of an electromagnetic wave. The features of two-electron ionization in the presence of one-and two-cycle pulses are analyzed. The suppression of double ionization in the presence of ultrashort laser pulses related to a finite-time interelectron energy exchange upon the laser action is demonstrated. The features of the generation of high-order harmonics and single XUV attosecond pulses are studied for the atomic ionization by few-cycle laser pulses. The parameters of the laser pulse are optimized for the effective generation of a single XUV attosecond pulse.     

Formation and dynamics of a plasma in superstrong laser fields including radiative and quantum electrodynamics effects

Studies of phenomena accompanying the interaction of superstrong electromagnetic fields with matter, in particular, the generation of an electron–positron plasma, acceleration of electrons and ions, and the generation of hard electromagnetic radiation are briefly reviewed. The possibility of using thin films to initiate quantum electrodynamics cascades in the field of converging laser pulses is analyzed. A model is developed to describe the formation of a plasma cavity behind a laser pulse in the transversely inhomogeneous plasma and the generation of betatron radiation by electrons accelerated in this cavity. Features of the generation of gamma radiation, as well as the effect of quantum electrodynamics effects on the acceleration of ions, at the interaction of intense laser pulses with solid targets are studied.     

Evidence for rescattering in intense, femtosecond laser interactions with a negative ion

It is now well established that energetic electron emission, nonsequential ionization, and high harmonic generation, produced during the interaction of intense, femtosecond laser pulses with atoms (and atomic positive ions), can be explained by invoking rescattering of the active electron in the laser field, the so-called rescattering mechanism. In contrast for negative ions, the role of rescattering has not been established experimentally. By irradiating F- ions with ultrashort laser pulses, F+ ion yields as a function of intensity for both linearly and circularly polarized light have been measured. We find that, at intensities well below saturation for F+ production by sequential ionization, there is a small but significant enhancement in the yield for the case of linearly polarized light, providing the first clear experimental evidence for the existence of the rescattering mechanism in negative ions.     

Electric field enhancement at multiple densities in laser-irradiated nanotube plasma

The electric field enhancement inside a nanotube irradiated by intense ultrashort laser pulse (?1?ps) is calculated. The hollowness of the nanotubes determines the field enhancement and the electron density at which such structures exhibit resonance. The electric field in a nanotube plasma is shown to be resonantly enhanced at multiple densities during the two phases of interaction: the ionization phase and the hydrodynamic expansion phase. It is further shown that by a proper choice of hollowness of the nanotubes, a continued occurrence of the resonance over a longer time can be achieved. These properties make nanotubes efficient absorbers of intense ultrashort laser pulses.     

Peculiarities of the ionization of many-electron systems and generation of attosecond pulses in ultrashort laser fields

The ionization of a model two-electron atom in the field of a strong ultrashort laser pulse is studied by numerical integration of the nonstationary Schrödinger equation describing the dynamics of a quantum system in the field of an electromagnetic wave. Pecularities of the two-electron ionization are analyzed for pulses whose duration amounts to one to two periods of oscillation of the electric field of the wave at different frequencies of the incident radiation. For extremely short pulses, the double ionization is found to be suppressed. This effect is caused by the finiteness of the interelectron energy exchange time during the laser action. Peculiarities of the generation of high-order harmonics and single XUV attosecond pulses upon ionization of atoms by laser pulses, whose duration is within one to two optical cycles, are investigated.     

超短脉冲强激光与团簇的相互作用

超短脉冲强激光与团簇的相互作用已被证明能够产生能量高达ＭｅＶ量级的高能离子和中子以及非常强的Ｘ射线辐射。广阔好原子团簇在超短脉冲强激光场的作用下的加热、电离和膨胀等机制,对这种相互作用的深入研究可能会对激光核聚变和Ｘ射线激光等应用领域产生重大影响。