Design of a Reflective Aspherical Surface of a Compact Beam-Shaping Device

A compact beam-shaping device with a reflective aspherical surface is proposed. The device converts a circular symmetric Gaussian beam from a laser into a uniform distribution on a target plane. The device consists of a laser, a reflective aspherical surface formed on the base plane inclined by 45° against the optical axis, and a spacer. The surface is designed for an optical device used as a transmitter of indoor wireless optical communication, which is one of the promising applications. The designed surface is obtained by approximation using polynomial. Beam shaping of a simulated surface and a uniform intensity distribution on the target plane is obtained. The intensity distribution generated by the surface is numerically simulated and evaluated if the surface is misaligned. It is clarified that the generated distribution is tolerable for the misalignment.     

光纤激光器反馈耦合损耗分析

将双包层光纤基模LP01模近似表示为拉盖尔-高斯光束的线性叠加,前六阶的拉盖尔-高斯光束包含了LP01模能量的99.99％.利用拉盖尔-高斯光束的传输特性计算了腔镜分别为球面镜和透镜加平面反射镜时的反馈耦合损耗.结果表明,腔镜为球面镜时,只有当球面镜和到达球面镜光束的曲率半径匹配时才能获得最小的耦合损耗,特别是当平面镜紧贴光纤端面时,耦合损耗为0;当腔镜为透镜加平面反射镜时,将平面镜放置在透镜焦平面时获得最小反馈耦合损耗为0.25％.     

Optical imaging system with a waveguide

The problem of image transmission through a waveguide is considered. The transfer function of a step rectangular waveguide is obtained, and it is concluded that direct image transmission is possible over large distances without significant loss of quality. An optical system with a waveguide in which an image is formed with a single objective is proposed. The process of image transmission through a step planar dielectric waveguide is experimentally investigated, and the influence of parameters of the waveguide on the resulting image is revealed. The conditions for image transmission through waveguides of other types are discussed.     

Detailed field model for DH stripe lasers

The field problem for DH stripe lasers is solved, using a two-dimensional model; the field variation perpendicular to the junction plane is found from a slab model, whereas the transverse variation is calculated using a method applicable to any complex permittivity profile. The origin of transverse variations in the permittivity is described by including current spreading, temperature variations and the carrier profile. The permittivity is used directly and not fitted by a parabola or a step. The fact that a large fraction of the intensity may be propagating in then-andp-layers, is taken into account by introduction of an effective permittivity. The model is applied to a practical example, and the threshold current is found as a function of active-layer thickness and stripe width. It is described how the model can be used both below and above the threshold.     

Computational Study of MHD Equilibrium of Noncircular Tokamak Reactor Plasmas

The MHD equilibrium and stability of noncircular tokamak plasmas limited by a separatrix is studied for reactor size systems. A typical example with a plasma current of 15.8 MA and major radius of 8.1 is presented. The required vertical field is generated by a set of discrete external coils and no conducting shell is included. The detailed equilibrium shape is calculated numerically for a vertical elongated plasma with two stagnation points symmetrically located above and below the midplane as would be required for a system with a poloidal divertor. The plasma height to width ratio is 2, the plasma shape factor is 1.6 and poloidal ? is 2.2. The plasma is locally stable. The general stability criteria with respect to quasi-rigid motions (special kink modes) are calculated numerically and found to be satisfied. Size scaling and the engineering constraints are discussed.     

Canonical quantisation in non-Abelian background fields

The canonical quantisation of Yang-Mills theory in a local background gauge is presented. The theory is shown to possess a BRS-supersymmetry, and the associated conserved charge is used to define a subsidiary condition on physical states. The Furry approximation is introduced, and an explicit example of the method in the case of a uniform external field strength is presented. The particle production rate is calculated, and the connection with the proper time formalism established. The results do not agree with those obtained by symmation of the corresponding perturbation series.     

Resonantly enhanced strip-line technique to measure microwave permeability of thin films

The sensitivity of a reflective single-port strip-line technique is increased by 10-20 times by amplification of a measured reflectivity response at a set of resonance frequencies. The resonant behavior is organized by connecting the strip cell to a network analyzer through a capacitor with a long coaxial cable. The capacitance defines the amplification; the cable length defines the resonance frequencies. S-parameters of the coaxial-to-strip junction and the field inhomogeneity inside the cell are accounted for by a reference measurement of sample with known constitutive parameters. Two methods for permeability calculation are suggested. The fist method is based on the comparison of Lorentzian parameters of resonance reflectivity curves. The second method is based on numerical solution of Fresnel's equation. The enhancement is essential at low-frequency part of the band, where the cell reflectivity is close to unity and the sensitivity of non-resonant technique is poor. The technique sensitivity is estimated by permeability measurements of Al stripes with different cross-section.     

Distribution corresponding to classical thermodynamics

A distribution corresponding to classical thermodynamics is constructed. The concept of degrees of freedom is generalized and a concept of temperature-dependent number of collective degrees of freedom is introduced. A relationship between the theory of numbers and mesoscopic physics is established. A geometric interpretation of spinodal as a curve of maximum entropy and as a catastrophe in a quasi-static Caratheodory process is given. A concept of local ideal gas is introduced. The phase transition of fluids to a dispersed system is determined. The distribution obtained is numerically compared with the distribution for a van der Waals gas in the Hougen-Watson diagram.     

Quenching Properties of an Arc in a Double Flow with a Vortex

The effect of a vortex in a gas flow on an air-blast arc is investigated. The radial density of a vortex in the compressible flow is evaluated with a simple model. The experiments show that the width of a low pressure channel on the axis of the nozzle is comparable to the theoretical values. The measured electric field strength profile is strongly influenced by the presence of such a vortex. In addition, the thermal interrupting capability is drastically lowered by vortex superimposed on the axial gas flow.     

Clausius-Mossotti-Type relation for planar monolayers

The dielectric properties of a quasi-two-dimensional molecular monolayer are analyzed. The dielectric function of the monolayer is expressed in terms of molecular polarizability and monolayer characteristics. The expression is analogous to the well-known Clausius-Mossotti equation for three-dimensional systems. The response of the monolayer to an external field is calculated. The case of a planar array of nanoparticles is also considered. The solution is obtained in the framework of a local-field theory.     

可调频高功率宽谱微波的产生和辐射

 设计了一种可调谐频率的高功率宽谱微波辐射装置,装置由可调谐长度的1/4波长低阻同轴谐振器、环形开关、电容耦合器和宽谱辐射天线组成,中心频率调谐为200～400 MHz。低阻传输线与环形开关构成1/4波长短路谐振器,它产生的宽谱微波振荡通过耦合器耦合到宽谱辐射天线上辐射,而耦合器由集中电容与分布电感组成,实现宽谱微波在频率调谐范围内以较为一致的耦合度提取微波能量。通过转动螺杆滑动安装在同轴谐振器内芯上的环形开关,达到改变谐振频率的目的。最后,将可调频宽谱辐射装置与输出电压为500 kV的Tesla变压器脉冲功率源联试,得到200～400 MHz宽谱微波辐射,辐射因子为95～130 kV,频谱百分比带宽为10%～30%。     

面向等离子体合成射流应用的微秒脉冲源研制

为了产生高能等离子体合成射流,设计了一台面向等离子体合成射流应用的微秒脉冲源,输出电压为10 kV,重复频率为100 Hz,可承受高达250 A的放电电流。详细介绍了微秒脉冲源的工作原理,比较了不同放电电容对脉冲变压器原边电流及输出电压的影响。进一步将所设计的微秒脉冲源成功应用于等离子体合成射流实验中,研究了不同间距对等离子体合成射流的影响,比较了有无放电电容条件下的能量消耗率。实验结果表明:不同放电电容在相同激励器间距的条件下,击穿电压基本相同;击穿电压随激励器间距增大而增大。有放电电容能产生较大的放电电流,且电流值随电容值的增大而增大。有放电电容条件下的能量消耗率比无放电电容要高,易于产生高能的等离子体合成射流。     

Poisson brackets and the Feynman problem

A derivation of a pair of Maxwell equations which is based on the concept of a Poisson structure on a manifold is given. The idea is geometric in character, and is extended to a generalized algebra. The special case of the dynamics for a particle in a Yang-Mills field is obtained as a consequence of the generalized case.     

On reflection from a suddenly created plasma half-space: transientsolution

The reflection by a suddenly created plasma half-space of a time-harmonic plane electromagnetic wave propagating in free space is considered. The problem involves a temporal discontinuity, a spatial discontinuity, and a dispersive medium. The steady-state solution is obtained by considering the basic features of the scattering processes due to each of the discontinuities in terms of analogous transmission-line models. The electric field of the reflected wave consists of two components. One component (called component A) is of the same frequency as the incident wave frequency and is due to the spatial discontinuity. The other component (called component B) is of a different frequency and arises because of the temporal discontinuity. The B component is damped out even if the plasma is only slightly lossy. The damping rate of the B component is calculated. The transient solution is obtained through the use of Laplace transforms. The solution is given in terms of Bessel-like functions. The limiting value of this solution is shown to agree with the steady-state solution. Numerical results illustrating the transient effects are for two typical cases     

Duality relations in the nonlinear percolation problem: Theory and numerical simulation

The problem of a nonlinear current flow in a heterophase medium formed by a random mixture of linear and nonlinear phases is investigated. The duality relation is derived for the critical indices describing the effective response of a heterogeneous system. The critical index is calculated at the percolation threshold (for equal concentrations of the phases). The nonlinear percolation problem is simulated numerically for degrees k = 3, 5, and 7 of the nonlinear phase. The existence of a duality relation for critical indices is established in a range of phase concentrations.     

Three Gaussian beam heterodyne interferometer for surface profiling

A novel three Gaussian beam interferometric technique for profiling optical smooth surfaces is presented. The technique is based on the heterodinization of three Gaussian beams, two of them with the same temporal frequency. The first beam is used as a probe beam after being focused and reflected from the surface under test. The second beam is reflected from a reference surface. The third beam is obtained from the first diffraction order of a Bragg cell and thus, it is shifted in its temporal frequency. The three beams are coherently added at the sensitive plane of a photodetector that integrates the overall intensity of the beams. We show analytically that the electrical signal at the output of the photodetector consists of a temporal carrier whose amplitude is a sinusoidal function of the local topography. We include the measurement of the topography of a sample consisting in a blazed-reflecting grating calibrated by means of an atomic force microscope.     

Critical dynamics and fluctuations for a mean-field model of cooperative behavior

The main objective of this paper is to examine in some detail the dynamics and fluctuations in the critical situation for a simple model exhibiting bistable macroscopic behavior. The model under consideration is a dynamic model of a collection of anharmonic oscillators in a two-well potential together with an attractive mean-field interaction. The system is studied in the limit as the number of oscillators goes to infinity. The limit is described by a nonlinear partial differential equation and the existence of a phase transition for this limiting system is established. The main result deals with the fluctuations at the critical point in the limit as the number of oscillators goes to infinity. It is established that these fluctuations are non-Gaussian and occur at a time scale slower than the noncritical fluctuations. The method used is based on the perturbation theory for Markov processes developed by Papanicolaou, Stroock, and Varadhan adapted to the context of probability-measure-valued processes.     

Relaxation properties of weakly coupled classical systems

The relaxation properties of a small classical system weakly coupled to a large classical system which acts as a heat bath are described using a generalized Fokker-Planck equation. The Fokker-Planck equation is derived in general using a modification of the elimination of fast variables techniques previously described. The specific example in which the small system is a harmonic oscillator linearly coupled to the heat bath is treated in detail and it is demonstrated that there is a dynamic frequency shift as well as a statistical shift of the oscillator frequency.     

Bose-Einstein condensation and the glassy state

The distinction between a classical glass and a classical liquid is difficult, since both are disordered. The difference is in the fact that a glass is frozen while the liquid is not. In this Letter an equilibrium measure is suggested that distinguishes between a glass and a liquid. The choice of this measure is based on the idea that in a system which is not frozen symmetry under permutation of particles is physically relevant, because particles can be permuted by actual physical motion. This is not the case in a frozen system. In this Letter it is shown how to generalize naturally the quantum mechanical concept of Bose condensed fraction to classical systems in order to distinguish between the glass and the liquid. It is finite in the liquid and zero in the frozen state. The actual value of the condensed fraction in the liquid may serve also as a measure of the glassiness in the liquid.