一种紧凑型电子脉冲脉宽对称调制技术

针对电子脉冲脉宽调制技术的需求,提出了一种紧凑型电子脉冲脉宽对称型调制技术,其核心是利用交变电场对电子脉冲空间各部分电子施以差别性能量调制以达到调制电子脉冲脉宽的目的。详细阐述了该技术的工作原理,包括交变电场的选择、脉冲压缩幅度的变量关系以及轴向磁场的聚焦约束作用,分别给出了不同类型调制电场设置下脉冲压缩调制和展宽调制所对应的约束条件及实施例。     

Optical second harmonic generation induced by picosecond terahertz pulses in centrosymmetric antiferromagnet NiO

Optical second harmonic generation at the photon energy of 2?ω = 2eV in the model centrosymmetric antiferromagnet NiO irradiated with picosecond terahertz pulses (0.4–2.5 THz) at room temperature is detected. The analysis of experimental results shows that induced optical second harmonic generation at the moment of the impact of a terahertz pulse arises through the electric dipole mechanism of the interaction of the electric field of a pump pulse with the electron subsystem of NiO. Temporal changes in optical second harmonic generation during 7 ps after the action of the pulse are also of an electric dipole origin and are determined by the effects of propagation of the terahertz pulse in a NiO platelet. Coherent oscillations of spins at the antiferromagnetic resonance frequency induced by the magnetic component of the terahertz pulse induce a relatively weak modulation of magnetic dipole optical second harmonic generation.     

Collective modes and the far-infrared absorption of the two-dimensional electron gas in a periodic quantizing magnetic field

We investigate the far-infrared (FIR) absorption of a two-dimensional electron gas in a periodically modulated quantizing magnetic field. The magnetic field varies along only one spatial direction and the external time-dependent electric field is linearly polarized along that axis. The mutual Coulomb interaction of the electrons is treated self-consistently in the ground state and in the absorption calculation within the Hartree approximation. The effects of the magnetic material on top of the heterostructure as a grating coupler is included in the time-dependent incident FIR electric field. We show that, similar to an electric modulation, the absorption can be directly correlated to the underlying electronic energy bands. In addition, the magnetic modulation leads to absorption spectra with a richer structure due to the quite different static response of the electron density to the modulation.     

Self-organized nanogratings in glass irradiated by ultrashort light pulses

Periodic nanostructures are observed inside silica glass after irradiation by a focused beam of a femtosecond Ti:sapphire laser. Backscattering electron images of the irradiated spot reveal a periodic structure of stripelike regions of approximately 20 nm width with a low oxygen concentration, which are aligned perpendicular to the laser polarization direction. These are the smallest embedded structures ever created by light. The period of self-organized grating structures can be controlled from approximately 140 to 320 nm by the pulse energy and the number of irradiated pulses. The phenomenon is interpreted in terms of interference between the incident light field and the electric field of the bulk electron plasma wave, resulting in the periodic modulation of electron plasma concentration and the structural changes in glass.     

Effect of air breakdown on microwave pulse energy transmission

The energy transmission of the long microwave pulse for the frequency of 2.45 GHz and 5.8 GHz is studied by using the electron fluid model, where the rate coefficients are deduced from the Boltzmann equation solver named BOLSIG+. The breakdown thresholds for different air pressures and incident pulse parameters are predicted, which show good agreement with the experimental data. Below the breakdown threshold, the transmitted pulse energy is proportional to the square of the incident electric field amplitude. When the incident electric field amplitude higher than the breakdown threshold increases,the transmitted pulse energy decreases monotonously at a high air pressure, while at a low air pressure it first decreases and then increases. We also compare the pulse energy transmission for the frequency of 2.45 GHz with the case of 5.8 GHz.     

无规频率调制对冷等离子体波碎的抑制作用

本文采用Kubo-Anderson过程描述对驱动场的无规频率调制,分析了其对不均匀冷等离子体波碎的抑制作用。在不考虑Bogoliubov非线性频移的情况下,导出适用于各种宽度频率调制下的波碎时间及波碎时快电子能量与最大局部电场方均值的表达式。并与实验结果符合。结果表明无规频率调制确实是抑制波碎与快电子能量的有效方法。 关键词：     

强激光场中真空极化效应

 通过求解狄拉克方程,对强激光场下真空极化问题进行了研究。理论计算结果表明：在仅随时间变化的电场下,要激发狄拉克海中负能级的电子,需要两个阈值条件,即激光场的电场强度大于等于10¹⁶ V/cm和激光场的持续时间大于等于10^-21 s。前者主要保证负能态电子有足够的能量跃迁到正能态,后者主要是保证电子在跃迁过程中动量亏损得以补偿。     

The Poole–Frenkel effect in a dielectric under nanosecond irradiation by an electron beam with moderate or high current density

Processes of electron trapping and detrapping determine in many respects intense processes arising in dielectric and delayed by 1–100 ns from the irradiation pulse of a high-power electron beam, such as electron emission, electric discharge in the bulk of the dielectric, flashover, and electric breakdown. A model of charged donor center ionization in a dielectric exposed to a strong electric field is constructed. The model takes into account 1) the energy spectrum of the charged donor center in the dielectric, 2) the semiclassical state density in the donor center, 3) spontaneous emission of phonons by the electron localized in the donor center, 4) increase in the kinetic energy of the electron (heating) in the external electric field, 5) electron tunneling through a potential barrier and its reflection from the barrier depending on the external field intensity, and 6) thermal fluctuations of energy of the electron localized in the donor center. The probability of charged donor center ionization in the dielectric per unit time is calculated. In weak fields, the field dependence of the ionization probability almost coincides with that for the Poole–Frenkel theory. In strong fields, the contribution of electron heating to the external electric field is the deciding factor. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 10–16, December, 2008.     

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。     

Nonlinear cross-phase modulation with intense single-cycle terahertz pulses

We have demonstrated nonlinear cross-phase modulation in electro-optic crystals using intense, single-cycle terahertz (THz) radiation. Individual THz pulses, generated by coherent transition radiation emitted by subpicosecond electron bunches, have peak energies of up to 100 microJ per pulse. The time-dependent electric field of the intense THz pulses induces cross-phase modulation in electro-optic crystals through the Pockels effect, leading to spectral shifting, broadening, and modulation of copropagating laser pulses. The observed THz-induced cross-phase modulation agrees well with a time-dependent phase-shift model.     

Complete temporal characterization of short optical pulses by simplified chronocyclic tomography

A new self-referencing technique to characterize the temporal electric field of a short optical pulse is presented. The group delay of the pulse is directly obtained from two projections of the Wigner-Ville function after rotation of the pulse in chronocyclic space. Implementation of the technique requires only quadratic temporal phase modulation and two spectrum measurements, from which the electric field is directly and unambiguously reconstructed without any assumption. A device based on these principles is used to characterize the electric field of a 2-ps optical pulse.     

变像管相机中空间电荷效应的统计动力学分析

 从Boltzmann积分微分方程出发推出了保守势场中电子数密度按势能的分布规律,即Boltzmann统计分布。以此为基础,从统计动力学的角度详细分析了变像管相机中超短电子脉冲内部的空间电荷效应,通过求解Poisson方程得出了表征空间电荷效应的两个特征参量：空间电荷密度分布函数和速度分布函数,并对其按电位的动态变化规律进行了定性讨论。结果表明,限制变像管中的低电位区域和其中光电子脉冲从高电位向低电位传输的区域都将有助于优化整个变像管的性能。同时也重新讨论了光电阴极附近强加速场对光电子脉冲时间弥散的抑制作用,最终确定了其物理机制为不等位区间中电子脉冲空间分布的高度集中性。     

On the feasibility of the coulomb explosion of a metal

The mechanism of the Coulomb explosion of a metal in an external pulsed electric field is discussed. In the case of a low-frequency field, when its frequency is lower than the frequency of electron collisions, it is impossible to reach the conditions of the Coulomb explosion of a metal if the field pulse duration is shorter than the time of electron energy relaxation upon elastic collisions, and the electron temperature is well above the Fermi energy and the work function. In the case of a high-frequency field, e.g., in a powerful pulse of ultraviolet laser radiation, the Coulomb explosion can occur if the field strength is well above the intraatomic field strength (i.e., when the laser power density is ≥10¹⁹ W/cm²).     

Lateral electron transport in high-intensity laser-irradiated foils diagnosed by ion emission

An experimental investigation of lateral electron transport in thin metallic foil targets irradiated by ultraintense (>or=10(19) W/cm2) laser pulses is reported. Two-dimensional spatially resolved ion emission measurements are used to quantify electric-field generation resulting from electron transport. The measurement of large electric fields ( approximately 0.1 TV/m) millimeters from the laser focus reveals that lateral energy transport continues long after the laser pulse has decayed. Numerical simulations confirm a very strong enhancement of electron density and electric field at the edges of the target.     

二次发射微波电子枪的倍增特性

 利用3DRun程序通过数值模拟计算，对二次发射微波电子枪的束流倍增特性作了研究。用1维模型计算了束流倍增与腔两极间距离以及腔中场强的关系，并详细给出了腔两极间距离为10mm,场强为5-4MV/m时出射电子纵向聚束及能量聚焦过程；利用3DRun程序研究了在高频场及粒子束本身空间电荷场的共同作用下，束流在3维运动过程中的倍增特性，计算了出射束流的发射度。通过计算表明：二次发射微波电子枪可以提供低发射度、高流强的电子束。     

铁电介质阴极电子枪

 给出并分析了铁电介质阴极电子枪的初步数值模拟和实验结果。实验表明其发射电子密度可达110A/cm²。该种电子枪产生的电流密度大于阴极发射电子初始能量为零时的空间电荷限制电流,PIC数值模拟结果表明可以通过给发射电子赋予一定的初始能量来解释这一现象,理论分析认为铁电介质阴极发射电子具有初始能量是合理的。     

Modeling the triggering of streamers in air by ultrashort laserpulses

The physical processes involved in the triggering of ionization waves (streamers) by ultrashort laser pulses, focused in air at 350 Torr and in a uniform electric field, are investigated by means of a one-dimensional (1-D) numerical model. The model describes the interaction of the laser pulse with air and takes into account many of the reactions in the laser-created plasma as well as the radial expansion of the plasma. Consequences of the model are that the threshold electric field for the appearance of streamers is an increasing function of the delay between the laser pulse and the electric field pulse and a decreasing function of the laser energy. Also, it appears that the electron temperature, the plasma density and radius, and the conduction of heat across the plasma boundaries play major roles in the capacity of the laser-created plasma to trigger streamers. The results of the model are compared with the available experimental data     

Impact of spatial modulation on the third harmonic wave propagation and far-field focal spot in frequency conversion system

Third harmonic generation (THG) of high power laser is discussed in KDP crystals utilized in frequency conversion systems of large laser facilities. The far-field focal spot of the third harmonic wave is presented based on numerical simulation of the nonlinear coupled-wave equations, in which the walk-off and paraxial diffraction are taken into account and the electric field of the fundamental wave (1053 nm, 1ω) pulse is phase and amplitude modulated in spatial domain. Impact of the modulation depth and frequency on the focal spot energy, the side lobes location and conversion efficiency are analyzed in detail. The results show that the side lobes location is equivalently determined by the modulation frequency of both phase modulation and amplitude modulation, while the energy-concentration is decreased mostly because of the 1ω modulation depth. Relatively, the phase modulation plays a more important role than the amplitude modulation in decreasing main lobe energy for different reasons. The phase modulation makes the energy flowing from the main lobe to side lobes, while amplitude modulation not only makes the energy flowing but also decreases tripling efficiency significantly.     

The influence of the surface electron layer on the energy spectrum of photoelectrons

The influence of the self-consistent electric field of a surface electron layer on the energy spectrum of photoelectrons emitted under the action of a picosecond laser pulse on a metallic target was determined.     

脉冲电场防治水生生物附着

为探究脉冲电场对防治水生生物附着效果的影响因素,确定有效防治附着生物所需的最低电场条件,搭建了脉冲电场试验平台,通过人工脉冲形成线产生近似方波的脉冲,统计不同条件下大型溞死亡率和形态结构发生的变化,通过函数拟合得到了脉冲电场诱导死亡率与电场强度、总等效处理时间、脉冲注入能量密度之间的函数关系,并以某干渠工程为例介绍了脉冲电场防治大型溞的参数选取原则和平台搭建方法。结果表明,脉冲电场对大型溞的处理效果与电场强度、总等效处理时间和脉冲注入能量密度都呈正相关关系。电场强度介于0.5～1.5 kV/cm之间时,电场强度每增加0.5 kV/cm,诱导死亡率增加35%左右。电场强度高于2.0 kV/cm、总等效处理时间大于900μs或脉冲注入能量密度高于80 J/L时,脉冲电场都可以产生80%以上的诱导死亡率。