空间飞行器近尾区内场和密度空腔的研究

在静态极限下,通过傅里叶变换,研究了空间飞行器近尾区内等离子体与场之间的非稳态非线性相互作用,并进行了数值求解。数值模拟结果表明,在飞行器近尾区内会产生电磁孤波和密度空腔,由电场的塌缩现象可以探测到它们。因而通过探测电磁孤波和密度空腔的形状和强度,能够探寻具有隐身特性的飞行器。     

电子束短脉冲效应产生的相干辐射

在模空间里给出了自由电子激光线性区非定态自治方程，得到了由于电子束短脉冲效应产生相干辐射的条件并解释了文献［１］的实验结果。     

Superradiant free electron laser with space charge field

Linearized time dependent free electron laser equations with space charge field are solved for the space charge effects on the superradiant solution which now has a cosine square modulation on the intensity along the electron beam.     

大调制度下光折变运动光栅的微扰分析

利用“跳跃模型”讨论了大调制度下光折变材料对运动干涉条纹的非静态记录过程，给出了描述运动干涉条纹非静态记录时电荷密度波前三阶分量振幅的微分方程，以及前三阶空间电荷场的解析表达式.讨论了前三阶空间电荷场振幅改变量对干涉条纹运动速度的依赖关系，若扩散场不为零但较小时，施加较小的外电场能够实现对空间电荷场高阶分量选择性地增强.若扩散场较大(大于外加电场)，则不能实现对空间电荷场高阶分量选择性地增强. 关键词：     

[Russian Text Ignored]

The stability of the electromagnetic plasma confinement by powerful external s-polarized pump waves is considered. The parametric excitation of standing electromagnetic waves along the plasma boundary with frequencies close to the frequency of the pump wave leads to a periodic density modulation of the plasma boundary. The density disturbances along the direction of the external wave field are connected to the excitation of transverse p-polarized surface waves while the modulation in the direction perpendicular to the pump field are created by the parametric interaction between the external wave and s-polarized trapped leaking oscillations. Only when the leaking waves are excited the scale length of the modulation is larger than half the free space wave length of the incident radiation.     

基于石墨烯的宽带全光空间调制器

提出了单层石墨烯包裹微纳光纤的全光空间调制.石墨烯作为可饱和吸收体包裹在通过二氧化碳激光器加热制备的微纳光纤上,当信号光沿着微纳光纤传输时部分光将以倏逝场的形式沿着微纳光纤表面传递,并与石墨烯产生作用被吸收.同时将波长为808 nm的抽运光从空间垂直入射到石墨烯包裹的微纳光纤处,依据石墨烯的优先吸收特性,通过抽运光控制石墨烯对信号光的吸收,实现了宽带全光空间调制.在1095 nm波长处获得最大调制深度约为6 dB,调制带宽约为50 nm,调制速率约为1.5 kHz.空间全光调制器具有输出信号光“干净”的特点.与传统石墨烯微纳光纤全光调制器相比,输出端不需要对抽运光进行光学滤波而直接获得已调信号.该复合波导全光空间调制器以更为灵活、高效的方式打开了微纳超快信号处理的大门.     

Solutions,bifurcations and chaos of the nonlinear Schrodinger equation with weak damping

Using the wave packet theory,we obtain all the solutions of the weakly damped nonlinear Schrodinger equation.These solutions are the static solution,and solutions of planar wave,solitary wave,shock wave and elliptic function wave and chaos.The bifurcation phenomenon exists in both steady and non-steady solutions.The chaotic and periodic motions can coexist in a certain parametric space region.     

强外加电场与大调制度下光折变动力学光栅形成研究

强外加电场与大调制度在光折变效应的研究中已经得到了广泛应用。采用PDECOL算法,严格求解光折变带输运方程,得到外加电场时不同调制度下光折变晶体中随时间变化的空间电荷场、载流子浓度,并讨论了外加电场对它们的影响。通过将物质方程与耦合波方程联立数值求解,可得到光折变光栅形成过程中两波耦合增益系数以及光束条纹相位的变化。模拟结果表明,在强外加电场作用下,两束记录光之间的光强与相位耦合都得到了增强,而原有的解析式忽视了强外加电场与大调制度对空间电荷场相位耦合的影响,此时不再适用。同时发现折射率光栅与记录光束条纹均发生弯曲,并不再保持平行。     

One-body electron dynamics in a free electron laser

The free electron laser is analyzed by solving the one-body classical Lorentz force equation in the presence of periodic magnetic field and a plane electromagnetic wave. Phase space paths for electrons are related to those of a simple pendulum and describe laser gain, saturation, and coherent electron beam modulation.     

Finite-amplitude electrostatic waves im magneto-active plasmas

Summary Weakly nonlinear dispersive longitudinal waves in an infinite homogeneous collisionless plasma in the presence of an external constant and uniform magnetic field are considered. Under specific physical assumptions and for an arbitrary three-dimensional envelope modulation of a plane wave, a purely differential system is derived. Taking into account the effect of wave-wave and wave-particle interaction, the evolution of the modulation is described by a modified nonlinear Schr?dinger equation, coupled to the space perturbation charge densities. The generation of a static mode is described. As a particular case the electron waves are discussed and some special solutions, resorting to the theory of the perturbed solitions.     

Birefringence and absorption of infrared radiation in tunnel-coupled GaAs/AlGaAs quantum wells in a longitudinal electric field

Birefringence and absorption modulation under electron heating in a longitudinal electric field in the tunnel-coupled GaAs/AlGaAs quantum wells have been found and investigated in the spectral region corresponding to intersubband electron transitions. The observed phenomena are explained by electron heating in electric field and electron transfer in real space. The equilibrium absorption spectra at different lattice temperatures are analyzed.     

Ultracold molecule production via a resonant oscillating magnetic field

A novel atom-molecule conversion technique has been investigated. Ultracold 85Rb atoms sitting in a dc magnetic field near the 155 G Feshbach resonance are associated by applying a small sinusoidal oscillation to the magnetic field. There is resonant atom to molecule conversion when the modulation frequency closely matches the molecular binding energy. We observe that the atom to molecule conversion efficiency depends strongly on the frequency, amplitude, and duration of the applied modulation and on the phase space density of the sample. This technique offers high conversion efficiencies without the necessity of crossing or closely approaching the Feshbach resonance and allows precise spectroscopic measurements. Efficiencies of 55% have been observed for pure Bose-Einstein condensates.     

磁绝缘线振荡器中空间电荷的调制

 首次研究了磁绝缘线振荡器中射频场（包括辐射波场和空间电荷波场）对空间电荷的调制,得到了在饱和时谐波电流一阶分量的公式。这个公式表明：考虑空间电荷波时,在小信号和辐射波与空间电荷波同相的条件下,它将增强谐波电流。在大信号时,情况不确定;谐波电流一阶分量将随二极管上电压的增加而增加,随运行频率和饱和长度的增加而减少。     

外加电场对光折变高阶响应影响的微扰分析

应用微扰展开法了“跳跃模型”给出了空间电荷场前三阶分量随时间，外加电场等变化的解析表达式，同时讨论了外加电场对各阶空间电荷场建立的影响，当扩散与外加电场可比拟时，外加电场对空间电荷场的影响不大，随着空间电荷场阶数的提高，其达到最大饱和值所需的外加电磁越小，在外加电场作用下，空间电荷场各阶分量随时间呈振荡衰减，直到达到饱和，外加是场越大，振荡越强烈，周期越短，在考虑高阶分量的贡献后，空间电荷场的振荡     

Contraction of the space of electron drift in low-frequency bunchers

In the paper we theoretically investigate the mechanism by which the space of drift electrons is contracted in klystron-type bunchers which modulate the electron beam in ion accelerators, in particular to excite an rf field. The contraction of the drift length is effected through a decrease in the mean beam velocity in the field of an electrostatic lens or a metal tube and is based on the fact that the relative motion of velocity-modulated electrons are independent of the mean velocity of the electron beam in a weak modulation regime.     

埋入式光纤模式功率调制传感原理及实验研究——航天smart结构

对 Smart材料 /结构中的光纤传感原理进行了探讨 ,并进行了实验研究。这种新研制的传感器工作原理是基于模式功率调制。远场光强将反映结构内的变形场 ,亦即光纤受到外界加载或扰动后所产生的变形。最后提出了应用多模光纤在编织复合材料 Smart结构中进行远场光强测量的方案 ,建立了实验装置 ,给出了实验结果并进行了讨论。     

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.     

Symmetry and magnetic field driven transitions in the 2D triangular lattice compound RbFe(MoO4)2

The temperature versus magnetic field phase diagram of the 2D triangular lattice and multiferroic compound RbFe(MoO(4))(2) is analysed from the point of view of symmetry. The paramagnetic space group and its irreducible representations are used in order to obtain the magnetic symmetry of the possible modulated phases and characterize the restrictions imposed by this symmetry on the corresponding magnetic structures. Superspace symmetry is considered in the case of incommensurate phases. It is shown that the experimentally observed phases correspond to different isotropy subgroups originating in the same irreducible representation of the paramagnetic symmetry group. The relevant couplings between the primary transverse spin modulation and the electric polarization, the in-plane magnetization and the secondary longitudinal magnetic modulation are discussed. The mechanisms for the destabilization of the improper ferroelectric chiral phase and the origin of the different orientation of the spins with respect to the external field in the two collinear phases are analysed from a symmetry based perspective.     

Transport as a consequence of state-dependent diffusion

Overdamped particles subject to a drift in a force field with sinusoidal space dependence and also a sinusoidally modulated space-dependent diffusion, with the same period as the drift, experience a net driving force. The resulting current depends on the amplitude of the modulation of the diffusion and is a periodic function of the phase difference between the sinusoidal drift and the sinusoidal modulation of the diffusion. For small modulation amplitudes a particle subject to state-dependent noise behaves the same way as a particle subject to thermal noise but with a drift which, in addition to the sinusoidal term, contains a net force term.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

慢同步波行波管特性研究

 在传统行波管的放大过程中,随着电子纵向群聚的加深,由于空间电荷效应导致的非线性效应,影响了行波管的输出性能。介绍了一种新型的行波管并分析了其作用机理,分析了这种新型行波管慢波系统的结构及其色散特性,讨论了T形齿结构和梯形齿结构慢波系统几何尺寸对工作性能的影响。通过圆极化行波的高频横向电场调制电子束,导致电子束在空间的扭转,使得电子在放大过程中没有经过纵向群聚而处于减速场中,消除了非线性效应,提高了行波管的输出性能。