畸变光束的焦斑质心位置

 为分析振幅和相位发生畸变情况下光束焦斑质心位置所受的影响，以光波标量衍射理论中的夫琅和费衍射公式为基础，根据光斑强度分布一阶矩质心位置的定义，推导了直接依赖于光束近场复振幅分布的焦斑质心位置的一般表达式。进一步推导了焦斑质心位置对光束近场强度分布和相位斜率分布的依赖关系式，并对该式清晰的物理意义进行了阐述。利用焦斑质心位置表达式，可分析和确定由于振幅调制和相位畸变导致的质心位置偏移。最后，对无相位畸变和存在低阶泽尼克相位畸变情况下的简单畸变光束进行了相应的分析讨论。     

Fractional derivative applied to the retrieval of phase distribution from an interferogram

This paper proposes a new method for determining the phase distribution of a 2D fringe pattern using 2D fractional derivatives. The fractional derivative of order?r (real 0??r??3), in the ?? direction (????[0,2??]) is defined by the Fourier transform and its inverse and gives as result a phase distribution. The fractional derivative of order r produces a phase displacement of r??/2 without significantly changes in normalized amplitude distribution. There are optimum values of r and ?? for which the phase distribution given by the fractional derivative represents the phase distribution for the fringe pattern. Also, we demonstrate the usefulness of a method based on four fractional derivatives to determine the phase and intensity distribution from a single interferogram and highlights small objects located in the fringe pattern. We demonstrate the proposed method using both numerical simulated and experimental interferograms.     

A new analysis for extending the measurement range of the retardation-modulated differential interference contrast (RM-DIC) microscope

While considering measurements of grating-type samples with the retardation-modulated differential interference contrast (RM-DIC) microscope, we found a problem of phase objects. The problem is that smaller measured values than the actual phase distribution are obtained when phase objects are beyond the weak phase approximation range. We analyze the image characteristics of phase objects and show that the problem is caused by the effect of an image component which is proportional to the square of the phase distribution.To overcome this disadvantage, we propose a new analysis method named self phase-correction (SPC). The SPC method corrects the phase distribution of the first order approximation under the weak phase condition and obtains the actual phase distribution of an object’s phase beyond the weak phase approximation range. We propose a two-image SPC method and a three-image SPC method for the RM-DIC microscope, and examine the suitability of these methods.We confirm that the three-image SPC method effectively overcomes the problem, and that the measurement range of the RM-DIC microscope can thus be extended to a half-wavelength phase difference.     

Construction of the Phasing System for BEPCⅡ Linac

In order to get high beam quality, a RF distribution system is required, with minimal phase drifts and errors in the BEPCⅡ linac. The additional installation of phase reference cables and monitoring equipments and stable RF distribution for BEPC linac are finished. The master oscillator is chosen to offer RF signal with low phase noise and a stable phase distribution system is built to deliver RF signal to each klystron. A phase and amplitude detector is constructed to measure the phase precisely and an IΦA unit is used for a phase shifter. Control software based on EPICS is used to connect all the units of the system, and a phasing method based on BPM is adopted to optimize the phase of each klystron. Now the phasing system is installed and tested in the klystron gallery of the BEPCⅡ linac.     

Totally symmetric order parameter in the framework of the phenomenological theory of phase transitions: Ferroelastics

A new approach is proposed for constructing the phenomenological theory of phase transitions. The approach is based on the classical Landau theory with allowance made for the order parameter that corresponds to changes in the charge distribution probability density of a crystal and does not affect the symmetry of the high-symmetry phase. It is demonstrated that this approach makes it possible to describe phase transitions in terms of a nonequilibrium polynomial Landau potential of degree four in the components of the order parameters. The capabilities of the proposed approach are illustrated with three systems that undergo ferroelastic phase transitions.     

Effects of the randomly distributed magnetic field on the phase diagrams of Ising nanowire I: Discrete distributions

The effect of the random magnetic field distribution on the phase diagrams and ground state magnetizations of Ising nanowire is investigated using effective field theory with correlations. Trimodal distribution has been chosen as a random magnetic field distribution. The variation of the phase diagrams with that distribution parameters has been obtained and some interesting results have been found such as reentrant behavior and first order transitions. Also for the trimodal distribution, ground state magnetizations for different distribution parameters have been determined which can be regarded as separate partially ordered phases of the system.     

The study of phase matching of nonlinear waves in microdroplets

In this paper, the internal field distribution of higher order MDRs of water droplets is calculated and the result shows that the higher order MDRs should dominate the nonlinear couple process. Furthermore, the phase matching required for four-wave mixing (FWM) process in the droplet is interpreted as the concept of angular momentum conservation. The slight mismatch in angular momentum leads to significant improvement of phase matching than that in optical cell.     

焦斑二阶矩半径与光束近场分布的关系

为分析光束振幅畸变和相位畸变对其焦斑二阶矩半径的影响,以光波标量衍射理论中的夫琅和费衍射公式为基础,根据光斑二阶矩半径的定义,推导了直接依赖于光束近场复振幅分布的焦斑二阶矩半径的一般表达式,并进一步推导了直接依赖于光束近场强度分布和相位分布的焦斑二阶矩半径和焦斑二阶矩角半径的表达式.结果表明:畸变光束的焦斑二阶矩角半径...     

Phase compensation of laser beam modes

A technique is described for improving the propagation characteristics of high order laser beam modes. A thin phase plate inserted in the beam forces all portions of the wave front to oscillate in phase and yields a substantial improvement in the far field intensity distribution. Depending on the mode order, the peak intensity at a distant target may be readily increased by more than a factor of ten.     

Spherical mirror estimation with phase diversity method

In order to verify the phase diversity wavefront detector system by using its own light source to complete the wavefront estimation task independently, this paper sets up estimation spherical mirror shape of experiment platform with the method of phase diversity. Phase diverisity method collects shorter exposure image at the same time in the focal plane and away from the focal plane, calculates the distribution of wavefront solutions and recovers the target based on known defocus, so as to realize the estimation of large mirror aberration. In order to further validate the phase diversity measurement method, the phase diversity measurement results with high accuracy ZYGO interferometer measurement results are compared. Experimental results demonstrate that agreement is obtained among the errors distribution, PV value and RMS value of ZYGO interferometer, so the phase diversity method can effectively estimate the mirror aberration, which shows the feasibility and accuracy of phase diversity method.     

加性噪声对激光一级相变类比的影响

从单模激光场的增益－噪声模型出发,导出了激光场定态强度分布函数,研究了定态分布函数的极值点随加性噪声、乘性噪声和注入信号的变化情况。结果表明,乘性噪声是使激光系统出现一级相变类比的关键因素,注入信号使相变行为减弱,而加性噪声却使得定态分布中极值点的数量和位置出现来回跳跃式变化。     

基于数字非线性锁相环的相干态相位估计

基于量子理论获取相位参数的导航机制,理论上可以突破经典物理极限对导航精度的限制.利用量子零拍探测对相干态光场相位进行测量时,通常需要相位与之正交的本振光才能使测量精度达到量子标准极限.由于导航信号相位的高非线性特点,想要利用传统的线性锁相环获取完全满足条件的本振光具有一定的难度.为此,本文设计了一种基于容积准则的非线性锁相环,实现了在非正交本振光的条件下对相干态相位进行精确测量的功能.首先,利用相干态的Wigner函数推导了其相位在量子零拍探测的输出结果,设计了量子相位估计的非线性数字锁相环框架.然后基于正交单纯形容积准则设计了非线性滤波算法实现锁相环功能,该锁相环通过对本振相位进行多次状态更新,最终实现非线性迭代估计.实验结果表明,本文方法突破了本振光相位需与相干态相位正交的局限性,避免了传统量子锁相环方法引入的线性化误差,实现了对相干态相位的准确、稳定估计.     

小波变换轮廓术在双频光栅条纹中的应用

为了解决非连续物体三维面形测量中所存在的非连续相位解包问题,采用计算机生成的两频率之比为一无理数的电子光栅作为空间载频光栅条纹投影到待测物体表面。另外结合伽博小波变换分析的相位解调原理,在一幅变形双频光栅图像中分析得到两个频率各自所对应的包络相位分布,并且应用钟金钢等所提出的双频条纹查表法进行解包得到确定的调制相位分布。提出的双频光栅-小波变换-查表相位解包法很好地解决了傅里叶变换轮廓术,以及连续相位解包法在非连续物体三维面形测量中所存在的问题。给出了详细完整的理论推导过程、计算机模拟以及实验验证,证实了该方法的可行性。     

光强非均匀分布对波前曲率传感器的影响

为了将波前曲率传感器用于涉及激光波前的领域,理论分析了非均匀光强入射条件下的曲率传感器测量信号。用菲涅耳衍射公式,数值计算了相位分布为前10阶泽尼克多项式,光强为高斯分布和正态随机分布闪烁的曲率传感器信号,并和相同相位分布,光强均匀情况下的传感器信号比较。分析表明光强非均匀分布给波前曲率传感器测量信号带来了一定的误差。光强高斯分布对散焦相差的曲率信号影响较大,信号百分比误差达到25%,对其他相差的曲率信号影响很小;对于有正态随机分布闪烁的光强分布,信号百分比误差与正态随机分布的均方差成线性关系。在一定条件下,波前曲率传感器也能够用于光强非均匀分布的领域。     

The maximum entropy principle for non-equilibrium phase transitions: Determination of order parameters,slaved modes,and emerging patterns

The maximum entropy principle allows one to make guesses on the distribution function of systems by maximizing the information entropy under given constraints. In a previous paper we succeeded to formulate appropriate constraints for systems undergoing nonequilibrium phase transitions, but we had to confine our treatment to the order parameters. In this paper we describe a formalism which does not require any a priori knowledge on the order parameters but rather allows us to determine these as well as the slaved modes and the emerging patterns. The method is applicable also to non-physical systems such as neural nets. Our approach allows us to reconsider the Landau theory of phase transitions from a new point of view. A guess is made on the Fokker-Planck equation underlying the processes which give rise to stationary distribution functions of a single order parameter.     

水下高斯界面背向散射超声散斑场的相位奇异

为了精确描述超声散斑场的特性,提出了采用计算机模拟产生超声散斑场的方法.利用模拟产生的高斯相关随机表面,获得了这类表面远场超声散斑场,同时得到了声强分布和相位分布.与实验产生的散斑场进行对比,建立了超声散斑场接收的实验系统,取与计算模拟相同的参数,获得了实验散斑场.通过对比发现:计算机模拟产生的超声散斑场相位存在奇异点,奇异点周围相位分布类似漩涡,计算机模拟产生的散斑场与实验得到的散斑场强度分布相似,强度值比实验产生的散斑场强度大,携带有用信息的高亮散斑较多,暗点较少,更利于研究和分析.     

Scattering of surface polaritons in the vicinity of phase transition points

In the region of phase transitions the intensity of dielectric permeability fluctuations increases due to fluctuations of the order parameter. This can lead to the decrease in the length of propagation of surface polaritons and also it can influence the angular distribution of light reflected from the medium surface. In this paper the scattering of surface polaritons by the order parameter fluctuations is considered in conditions when the surface polariton is propagating along the surface of the metal coated with a thin dielectric film near the phase transition point in this film and for the case when the film is absent and the phase transition occurs in the whole substrate volume.     

基于涡流脉冲相位热成像的金属材料裂纹检测

涡流热成像可以对金属材料表面、近表面缺陷进行快速准确的检测。采用涡流热成像与脉冲相位分析相结合的方法,针对裂纹附近相位谱的分布规律及温度场对相位谱的影响关系问题,分别对带有上表面裂纹和下表面裂纹的45#钢料进行感应加热仿真和实验分析。结果表明,相位谱分布与温度大小无关,只与温度变化趋势有关,相位谱图对不均匀加热有很好的抑制作用,可以扩大裂纹的检测范围,当频率低于12.5 Hz时能够清晰地识别裂纹。结合实验验证了仿真结论的正确性,为下一步利用相位信息实现缺陷的定量检测提供参考。     

Finite-size scaling analysis of isotropic-polar phase transitions in an amphiphilic fluid

We present Monte Carlo simulations of the isotropic-polar (IP) phase transition in an amphiphilic fluid carried out in the isothermal-isobaric ensemble. Our model consists of Lennard-Jones spheres where the attractive part of the potential is modified by an orientation-dependent function. This function gives rise to an angle dependence of the intermolecular attractions corresponding to that characteristic of point dipoles. Our data show a substantial system-size dependence of the dipolar order parameter. We analyze the system-size dependence in terms of the order-parameter distribution and a cumulant involving its first and second moments. The order parameter, its distribution, and susceptibility observe the scaling behavior characteristic of the 3D Ising universality class. Because of this scaling behavior and because all cumulants have a common intersection irrespective of system size we conclude that the IP phase transition is continuous. Considering pressures 1.3 ≤ P ≤ 3.0 we demonstrate that a line of continuous phase transitions exists which is analogous to the Curie line in systems exhibiting a ferroelectric transition. Our results are qualitatively consistent with Landau's theory of continuous phase transitions.     

Influence of the phase coherence length on ballistic transport

The characteristic length scales for the transport in disordered metals are discussed. Based on a phenomenological model of phase randomising scattering processes, the influence of the phase coherence length on the conductance of ballistic systems is studied. It is argued that the frequency dependence of the conductance of quasi-one dimensional systems can be used in order to determine not only the statistical average but the whole distribution function of the phase coherence length. Various cases of distributions, the -function, the exponential, and the Gamma distribution, are discussed. It is shown that due to quantum coherence effects deviations from the classical (Drude) behavior of the conductance exist. For independent scattering processes the probability distribution function is given by the Poisson distribution function. In this case an expression for the conductance can be derived which contains the ballistic transport, and the result for the exponential distribution.