基于环形光光内送粉激光熔覆温度场的数值模拟

针对"光束中空,光内送粉"的激光熔覆工艺方法,利用Ansys软件的参数化设计语言(APDL)建立了环形激光光斑连续移动加载的激光熔覆模型。通过计算该模型,可以掌握环形激光光内送粉激光熔覆过程中温度场的分布规律。计算结果表明,采用环形激光束加载时,熔池的最高温度区域的形状呈现出"马鞍形"。在基体纵切面上,熔池的高温区域分布呈不对称的"W"形,且高温区域主要分布在光斑中心往后;在基体横截面上,熔池的高温区域分布呈对称的"W"形,熔池中心温度低,两侧温度高,通过基体横断面等温线的分布能够判断熔覆层与基体的结合情况。位于扫描路径中心位置的点在激光束扫过其过程中会经历迅速升温、降温、升温、再迅速降温的急冷急热过程,且第二次升温高于第一次的温度值;位于光斑内外环之间的点在激光束扫过其过程中只有一次升温降温的过程,温度分布较均匀。     

带状电子注聚焦系统设计

通过理论分析、数值模拟和实验研究了PCM 结构聚焦椭圆带状电子注的可行性。利用三维PIC 粒子模拟软 件模拟了椭圆带状电子注在PCM 结构行程的周期磁场中的传输过程,结果显示：截面为10x0.4 mm2 的椭圆带状电子 注在12x0.8 mm2 的矩形通道中稳定长距离传输120mm 无截获。对PCM 聚焦结构的磁场进行了测试,测试结果与数 值模拟结果相符。实验并研究了该PCM 聚焦系统约束带状电子注的能力,测试用速调管的设计电压为75kV,在56.8kV 时的直流通过率达到52.1%,并随着工作电压的升高呈上升趋势。     

Multiply Reflected Gaussian Beams in a Circular Cross Section

A well-collimated beam reflected repeatedly within a circular cross section undergoes periodic focusing and defocusing. This behavior is of interest for tracking of beams around a type of acoustic surface wave disk delay line, and it also relates to beam monitoring after oblique injection into the endface of a multimode optical fiber. The problem is analyzed by considering first the field excited by an isotropic line source inside a dielectric cylinder, and then converting this to Gaussian beam excitation by assigning a complex value to the source coordinate location. Because the wavelength is small compared to the cylinder radius, ray-optical methods are employed to construct the solution, with inclusion of such novel ingredients as the lateral ray shift on a curved boundary. Results are obtained for the amplitude and phase of the ray and beam field and for such beam parameters as the location of the focus the minimum beam width and the rate of beam divergence between successive reflections.     

Azimuthally periodic electrostatically focused electron ribbon beams

Methods of enhancing transmission of ribbon-shaped electron beams undergoing circular motion in azimuthally periodic cylindrical electrostatic lenses are treated. Lens forces add to the naturally occurring curvature focusing to achieve this increase in beam transmission. Three basic configurations, differing only in the method of applying lens voltages, are treated: symmetrical focusing, deflection focusing, and asymmetric focusing (including inner and outer electrode segmentation). Expressions for beam perveance and rippling are derived from the paraxial-ray equation for thin electron ribbons advancing along a two-dimensional curved optical axis. The stiffness of azimuthally periodic electrostatically focused electron ribbons (i.e., the immunity of the beam to transverse disturbing forces) also receives attention. Mathematical extensions of the analysis to ribbon beams undergoing helical motion are discussed, and numerical results applicable to selected values of lens parameters are presented. Experimental results for an azimuthally periodic lens, constructed to test the analysis, are discussed in light of the theory developed.     

Hollow-beam focusing with electrostatic and periodic magnetic fields

A new method of focusing a hollow cylindrical electron beam is presented. The focusing system consists of a cylindrical center conductor inside the beam, a cylindrical outer conductor enclosing the beam, and a series of periodic magnets outside the tube. A radial electrostatic field between the conductors provides an outward force on the electrons. The periodic magnetic field produces an inward force on the electrons. The inward and outward forces can be adjusted to provide a balance of all the forces acting on the electrons at both boundaries of the beam by choosing the electric and magnetic fields properly. An approximate analysis has been made and is presented which gives necessary design information. A number of curves are presented which are useful in designing focusing systems of this type. Experimental results on a beam tester show that current transmission of over 90 per cent for perveance up to 11 micropervs can be obtained readily. The adjustments are not critical and the performance is very stable.     

直边衍射激光驻波场中铬原子的沉积特性研究

为了研究沉积基片对激光驻波场的影响,基于半经典理论,采用4阶龙格-库塔算法对直边衍射效应影响下铬原子的3维运动轨迹和3维沉积条纹结构进行了仿真。研究了激光束腰中心到反射镜的距离、高斯激光束腰半径对最终沉积过程的影响。结果表明,通过适当地调节实验参量,可以改变激光驻波场受到衍射效应的程度;当反射镜位于激光束腰截面处、高斯激光束腰半径为62.5μm时,纳米沉积条纹的质量最理想。这将为原子光刻实验提供有益的理论依据和数据信息。     

Equivalence of periodic magnetic field to uniform magnetic field in electron beam focusing

The general solution of the electron trajectory equation in a periodic magnetic field is derived in the form of series expansion, assuming laminar electron flow and small perturbation. It is concluded that if the cathode is not very heavily immersed in a magnetic field, beam focusing by a periodic magnetic field would be almost equivalent to that by a uniform magnetic field except near the unstable region. Under these restrictions, each focusing system would give almost the same beam ripple (in magnitude and phase) under the same injection conditions into the focusing system. It is also found that the first stable region of beam perturbation in the periodic magnetic field becomes narrower as the flux threading the cathode increases or the period of the magnetic field decreases, as far as linearization of the path equation is possible.     

Electron beam in the presence of a periodic magnetic field with allowance for the thermal velocities of electrons

Equations are derived to study the effect of the initial transverse thermal velocities of electrons on the configuration of an intense electron beam in an electron-optical system with a significant divergence for the case of the beam focusing by a periodic magnetic field. It is demonstrated that the minimization of the effect of thermal velocities of electrons in the electron-optical system with the given level of the periodic focusing field and the cathode radius and temperature and the limiting compression of the beam in the presence of such a field is reached with the shaping systems in which an optimal magnetic flux passes through the cathode and the flux depends on the parameters of the thermal beam and the focusing field.     

Transport of electron beams in periodic permanent-magnet focusing systems with nonharmonic distribution of the magnetic field

The results of the study of the transport of electron beams in periodic magnetic fields are presented for the case when the distribution of the magnetic field is essentially different from a sinusoidal distribution in different parts of the drift channel. An easy-to-implement nonharmonic distribution of the magnetic field is found. This distribution ensures a small ripple of the envelope of a high-intensity electron beam. The results of application of combined periodic permanent-magnet (PPM) focusing systems in high-powered pulse travelingwave tubes (TWT) are presented for the TWTs having a slow-wave structure that is superposed with the pole pieces of the PPM focusing systems.     

杂化矢量光场的研究进展（特邀）

偏振是光场的一个重要矢量属性。依据空间偏振分布的不同,可以将光场分为标量光场和矢量光场。其中,非均匀偏振分布的矢量光场在光场传播、聚焦、非线性效应等方面表现出一系列有趣的行为,对其进行深入研究具有重要的科学意义和应用价值。一种在同一波阵面上包含不同偏振态的杂化矢量光场,因其比普通矢量光场具有更丰富的偏振特性,自2010年被发现以来,在光通信、光学操控、量子通信等领域中展现诸多诱人的前景,目前已成为光学领域的一个研究热点。综述着重介绍了杂化矢量光的制备以及其在聚焦、传播和非线性光学等方面中的特性和应用。     

Theory of periodic electrostatic focusing of electron beams

A general theory of periodic electrostatic focusing structures in micowave tubes is presented. A general method for evaluating the properties of focusing systems is developed. The method is based on the use of the Action Function and is applicable to structures whose potential distribution can be found by the method of separable variables. It is shown that this approach can yield results similar to, but more exact, than those obtained by the classical paraxial ray equation. The basic and double-ring structures have been examined in detail. Parameters describing these structures are presented in graphical and tabular form. It is shown that for irrotational flow, a specific current distribution is required. The use of computer techniques for the solution of electron flow problems is discussed. A computer analysis has been developed and results obtained are discussed. The accuracy of the Action Function and the computer analyses has been verified experimentally. It has been shown that the focusing potentials predicted by the Action Function analysis are in good agreement with the experimental values. The computer analysis has also been shown to give results comparable with those obtained practically. Hollow beams of 3.85, 5.4, and 15.6 µP have been focused using the basic ring structure. In order to investigate the effect of unbalance of focusing and defocusing forces at the inner beam boundary, pinhole measurements have been made. It is shown that the ring structure focuses a hollow beam with some change in the beam cross section. The effect of the unbalance of forces is to transform the current density profile. Results indicate that the transformation is desirable since a beam of constant current density may be transformed to a distribution which approaches that required for irrotational flow.     

An investigation of the mechanism of total internal reflection in tropospheric microwave propagation

Some calculations are performed concerning the amplitude and phase fluctuations of a totally reflected monochromatic and homogeneous radio beam from a monotonically stratified tropospheric layer. In a first approximation the incident beam is considered to be collimated; the reflected beam is then also collimated but inhomngeneous along a cross section parallel to the interface. Next, a more realistic case is considered in which the incident beam is given by an angular bundle of rays corresponding to a certain radiation polar diagram of the transmitting source. Under this condition the totally reflected field presents a more complicated structure in space, since it manifests focusing or defocusing effects not only along the boundary of the layer but also with height from this interface. A numerical evaluation of these fluctuations with height is of special interest; in principle they may justify vertical space diversity efficiency in a number of typical cases concerning more especially obstructed microwave paths.     

Propagation of Light Beam through Lens-Like Media with Complex Permittivity

Primary characteristics of the light beam propagation through a complex-permittivity lens-like medium are investigated in more detail than in previous papers, with the help of approximate wave theory. Explicit general expressions for the spot size and the curvature of the phase front of a Gaussian beam as well as the real-valued ray transfer matrix are derived, and detailed numerical investigations are presented. The existence of a new type of propagation, in which the light beam propagates with constant amplitude of undulation, neither converging nor diverging, is pointed out. Furthermore, precise conditions are given for the occurence of convergent, divergent, and critical propagation, and the corresponding profiles of the real and imaginary parts of the complex permittivity in the transverse cross section are illustrated. The results of this paper will be useful for the evaluation of the effects of loss distributions inherent in practical optical fibers consisting of lens-like media, and also for the analysis or synthesis of laser resonators or amplifiers including a loss or gain distribution.     

The Conditions for Stable Sheet Electron Beams Transport in Periodic Permanent Magnet Fields

The stable focusing or transport of sheet electron beams is an essential technology for an emerging class of high-power high-frequency planar-structure microwave devices. This paper, in consideration of space-charge field and cyclotron motion, describes theoretical study and simulation on sheet beams transport in periodic permanent magnetic (PPM) fields. Based on the theoretical study, we obtain the clear conditions for the stable sheet beams transport in PPM field. And the three-dimensional simulations of the sheet beam transport are in good agreement with our theoretical study. Our research will be useful in further study and experimental.     

Second-harmonic generation in birefringent crystals by a Gaussian beam with an elliptical cross section

The theory of second-harmonic generation (SHG) in birefringent crystals by a Gaussian beam with an elliptical cross section is developed in the assumption of no depletion of the fundamental beam. This study reveals that the doubling efficiency at optimum elliptical focusing is higher than at optimum circular focusing.     

声光调制器换能器阵列远场声束特性研究

根据亥姆霍兹方程的远场解,为使声光调制器(AOM)换能器在输出平面上声压输出的分布模式较好,衍射光能的传输特性更好,该文研究并提出了换能器的远距离分布模型.基于该理论模型,仿真分析了远场声束截面声强分布、传输中心轴声强分布及声束束宽等换能器相关特性,并利用计算激光衍射效率的方案进行实验验证.实验表明,测试数据与该理论模型吻合,在90％的能量区域内,理论模型拟合测试数据的误差低于5％,实验条件下声光晶体在2.08 mm≤z≤3.43 mm(z为晶体中传输距离)范围内具有最佳模式转化效率.利用此模型可确定声光器件中晶体最优衍射率区域.     

Intense Sheet Electron Beam Transport in a Uniform Solenoidal Magnetic Field

In this paper, the transport of intense sheet electron beams in a uniform solenoidal magnetic field in high-power vacuum electronic devices is theoretically examined with the 3-D beam optics code MICHELLE. It is shown that a solenoidal magnetic field can be an effective transport mechanism for sheet electron beams, provided the beam tunnel is matched to the beam shape, and vice versa. The advantage of solenoidal magnetic field transport relative to periodic magnetic transport resides in the feasibility of transporting higher current density beams due to the higher average field strength achievable in practice and the lower susceptibility to field errors from mechanical misalignments. In addition, a solenoidally transported electron beam is not susceptible to voltage cutoff as in a periodic magnetic focusing system; hence, device efficiency is potentially higher.     

涡旋光束经双十字光阑的衍射特性研究

设计了一种新型的双十字狭缝光阑,对涡旋光束经过不同的双十字光阑后的衍射特性分别进行了理论模拟和实验分析。研究结果表明,涡旋光束经过双十字光阑后在远场的光强分布为矩形亮斑阵列,选择合适的双十字狭缝的宽、长及中心的位置,可以使图样中的亮斑更清晰;衍射图样的矩形亮斑阵列外围亮斑总个数除以2,即为人射涡旋光束的拓扑荷数的值。双...     

Ince-Gaussian矢量光场束腰位置对紧聚焦特性影响的研究

为了获得Ince-Gasussian矢量光场束腰位置对紧聚焦特性的影响规律,采用正交偏振的奇偶模式叠加理论和Richards-Wolf矢量衍射积分理论,对不同束腰位置的Ince-Gaussian矢量光场紧聚焦特性进行了研究。结果表明,在高数值孔径聚焦条件下,入射Ince-Gaussian矢量场的束腰距离透镜位置z_i在一定瑞利长度z_R范围内(z_i < 0.5z_R)改变时,其聚焦场的横向场结构即光强与偏振态分布,依然可以保持稳定;通过聚焦场相位结构分析,给出了在束腰距离透镜位置z_i超过一定瑞利长度z_R范围(z_i>0.5z_R)时,影响横向场结构不稳定的原因;聚焦场纵向偏振分量作为聚焦场的一个自由度,被证明可以用来构建更加丰富的矢量结构光场。此研究结果对复杂结构矢量光场在光学微操控与光信息存储方面的研究有重要参考价值。