Optical Bistability,Instability and Optical Computing

The formation of a cone-type light beam structure in an amplifying medium exhibiting the Kerr-type non-linearity and two-photon absorption is considered. The dependences of the relative diameter, contrast, and the position of the origin of a filamentary light region (that formed on the beam axis) on the active medium parameters are investigated. The effects of additional factors, such as a dielectric tube covering the active medium cylinder, the inhomogeneity of the medium amplification in the cross-section, and a saturable absorber mixed with the active medium on the light propagation pattern, are also discussed. Here, it is shown that a cone-type light beam structure is highly stable under the influence of such factors. It is noted that picosecond and sub-picosecond spectroscopy, including the study of multiphoton transitions and the measurement of the Kerr-type non-linearity constant in a medium on observation of a cone-type light beam structure, are possible.     

Diffraction of cylinders with longitudinal surface structures

We present a model to determine the light scattered by a metallic cylinder with longitudinal structures when the cylinder is illuminated by a Gaussian light beam in oblique incidence. The model is based on an approximate solution to the Helmholtz-Kirchhoff integral by means of the stationary-phase method. We have studied the variations of the diffraction pattern in terms of the size of the defect and other geometrical parameters. The width of the beam and the misalignment between the beam and the cylinder have also been considered, as well as the optical properties of the surface.     

Scattering of light from arbitrarily oriented finite cylinders

An iterative approach to the scattering of light from a finite dielectric cylinder first developed by Shifrin and extended by Acquista is applied to cases where the phase shift is <2, and the cylinder is arbitrarily oriented. It is found that the first 2 orders of the iteration converge to within 1% when the aspect ratio (length/diameter) of the cylinder is as small as 20. The results are compared to the exact theory for infinite cylinders, and the effects of finite size are calculated and discussed.     

Focal shift of a focused partially coherent Laguerre-Gaussian beam of all orders

Abstract

We explore the focusing properties of a partially coherent Laguerre–Gaussian (LG) beam of all orders, particularly the focal shift (i.e. the shift of the actual focal plane away from the geometrical focal plane). We derive the analytical expressions for the average intensity and the effective beam width of a focused partially coherent LG beam, and we adopt the minimum effective beam width instead of the conventional maximum on-axis intensity to determine the actual focal plane. It is found that the focused beam shape, minimum effective beam width and the focal shift of a focused partially coherent LG beam are determined by its initial coherence width, radial mode order and azimuthal mode order (i.e. topological charge) together. Our results may be useful for optical trapping and micro-fabrication, where precise focal position and prescribed beam shape are required.     

Three-dimensional diffraction of a thin metallic cylinder illuminated in conical incidence: application to diameter estimation

We present a model to determine the far-field diffraction pattern of a metallic cylinder of infinite length when it is illuminated in oblique incidence. This model is based on the Helmholtz-Kirchhoff integral using the Beckmann conditions for reflection. It considers the three-dimensional nature of the diffracting object as well as the material of which the cylinder is made. This model shows that the diffraction orders are placed in a cone of light. The amplitude at the far field can be divided into three terms: the first term accounts for Babinet's principle, that is, the contribution of the cylinder projection; the second term accounts for the three dimensionality of the cylinder; and the third term accounts for the material of which the cylinder is made. This model is applied to the diameter estimation of the cylinder. Since the amplitude of the Babinet contribution is much larger than the light reflected by the surface, the cylinder diameter can be obtained in a simple way. With this approximation, the locations of the diffraction minima do not vary when the cylinder is inclined. On the other hand, when the reflected light is considered the location of the minima and, hence, the estimation of the diameter, varies. Also, a modification of the diffraction minima is produced by the material of which the cylinder is made. Experimental results are also obtained that corroborate the theoretical approach.     

SiCp/Al复合材料薄壁回转体变形的仿真分析

运用有限元仿真软件ABAQUS对体积分数为56%的SiCp/Al复合材料薄壁回转体在静载荷作用下的应力、变形及应变进行了仿真研究,研究了载荷施加位置、外径和壁厚对SiCp/Al复合材料圆筒薄壁件的应力、变形及应变的影响规律。结果表明:在其他条件一致的情况下,回转体的外径越小、壁厚越大、受力点距离施加全约束的一端越近,回转体受到外载荷引起的最大应力、最大变形及最大应变越小。薄壁回转体工件的壁厚对工件最大应力、最大变形及最大应变的影响最为显著。当壁厚增加到1mm以上时,最大应力、最大变形及最大应变的变化不明显。     

Working-point control method for readout of dynamic phase changes in interferometric fiber-optic sensors by tuning the laser frequency

A simple but reliable method, namely the working-point control by tuning the laser frequency, for the dynamic phase shift measurement in a passive homodyne interferometric fiber-optic sensor is proposed. A dc voltage calculated from the photodetector output is applied to the light source to control the interferometer at the condition of maximum sensitivity. Then the signal's phase shift can be obtained from the components of zero and fundamental frequencies. To test the method, an all polarization-maintaining Mach-Zehnder interferometer with a piezoelectric ceramic (PbZrTiO(3), or PZT) cylinder in one arm is constructed. The experimental results show that the simulation signal's phase shift generated by the PZT cylinder can be read out correctly with the method. It has the advantages of simplicities of operation, no-active element in the sensing head, and large operating bandwidth. It can be used for readout of dynamic phase shifts in various interferometric fiber-optic sensors.     

A 100 nm thick InGaN/GaN multiple quantum-well column-crystallized thin film deposited on Si(111) substrate and its micromachining

A 100?nm thick InGaN/GaN multiple quantum-well column-crystallized thin film was deposited on Si(111) substrate, with InN as the interlayer, by molecular beam epitaxy. The diameter of the column crystal is about 40?nm. Transmission electron microscopy images showed clear five-period well layers. Photoluminescence measurements demonstrated a wide emission wavelength from about 500 to 800?nm with the full width at half maximum of 107?nm at room temperature. An unusual photoluminescence peak position shift was observed from the optical measurement. The selected area electron diffraction image demonstrated the hexagonal wurtzite structure of the column crystal. A self-supported GaN-based active subwavelength grating was proposed, and the active subwavelength grating structure was fabricated from the InGaN/GaN quantum-well thin film by a Si micromachining process.     

基于粒子群优化算法的螺旋钻机变幅机构铰点位置优化

螺旋钻机变幅机构铰点位置是影响变幅机构性能的关键因素之一,它对变幅油缸最大油压、变幅机构各铰点最大受力、活动钻桅起柱时间等变幅机构主要性能参数都有决定性影响。针对传统设计方法对获取最佳铰点位置需要反复试算、耗时长、效率低且难以精确定位的不足,为了快速、高效、准确地获取最优铰点位置,以变幅机构的活动钻桅为研究对象,在分析变幅机构结构和工作原理的基础上,建立了变幅机构力学模型,并将变幅油缸的油压作为目标函数,以变幅机构的结构限制和油缸制造工艺要求确定约束条件。基于粒子群优化算法,结合MATLAB对目标函数进行运算分析,以变幅油缸的最大油压最小为目标确定了变幅机构最优铰点位置。铰点位置优化后,变幅油缸最大油压降低了9.2%,变幅机构各铰点最大受力降低了9.1%~9.2%,变幅机构性能明显得到提升。该研究提供了一种快速可行的铰点位置优化方法,对变幅机构的优化设计具有实际参考意义。     

鱼雷质心配重纠偏技术的实现

为了快速找到最佳配重组合，使鱼雷在完成配重后的实际质心尽可能地接受理想位置，提出了实际质心矢量和配重矢量的概念，从而将静力学问题转化为相对容易处理的几何学问题。设计了配重矢量表，通过查表法可以快速地寻求最佳配重组合，并提出了最大配重误差的评价方法。     

Effect of Electron Beam Orientation on Exit Wave Function via Simulation of Electron Dynamic Diffraction

Based on the electron dynamic diffraction, phase shift of the exit wave function vs misorientation of the incident electron beam from the exact zone axis has been calculated for the [001] oriented copper. The result shows that the peak of phase shift is the maximum at the atom position as the electron beam along the exact [001] zone axis, and the peak value of phase shift decreases as increases of the misorientation. At small misorientation, i.e. less than 5 degree, change of the phase shift is minimal. The peak value of phase shift decreases significantly when the incident beam deviates form the zone axis over 10 degree and the exit wave has a planar configuration as the misoriention angle arrives -17 degree. The effect of this phase shift characteristics on the information extracted from the hologram has also been considered.     

A Compact Fiber-Optic Flow Velocity Sensor Based on a Twin-Core Fiber Michelson Interferometer

A novel fiber-optic flow velocity sensor based on a twin-core fiber Michelson interferometer has been proposed and demonstrated. The sensor only is a segment of twin-core fiber acting as cylinder cantilever beam. The force exerted on the cylinder by the slow flow speeds of order mm/s of the fluid with unknown velocity bends the fiber, which corresponds to the shift of the phase of the twin-core in-fiber integrated Michelson interferometer.     

Axial tolerance in the position of aberration compensators placed in a converging beam

To perform a null test of aspherical surfaces we used a computer-generated hologram or a lens or a mirror compensator to compensate the aspherical aberration. When compensating in a convergent light beam the axial position of this hologram or compensator is critical. A holographic compensator to be used in the convergent beam of light was designed and constructed. We have established some relations to determine the tolerance in the axial positioning of these compensators.     

Taper array in silica glass for beam splitting

We proposed taper array in silica glass for beam splitting which was fabricated by water-assisted femtosecond laser direct writing technology and the subsequent heat treatment. We divided the array into many fabricating cells which were executed automatically in sequences as specified by the program that contained the information for the three-dimensional stage movements. Each cell could fabricated a rectangular cylinder. The size and distribution of the rectangular cylinder could be controlled by adjusting the position of the fabricating cells. Then the heat treatment should be used to reshape the rectangular cylinders into taper array. The experimental results show that the taper periodic microstructures in silica glass are uniform and smooth, and the tapers can divide the incident light into beam array. The results demonstrated that the combination of the water-assisted femtosecond laser direct writing technology and the heat treatment is accessible and practical for the high quality micro-optical elements. These micro-optical elements will have potential applications in fluorescence detection and beam splitter.     

光重心法在光纤位置检测中的精度研究与应用

为了确保LAMOST(大天区面积多目标光纤光谱天文望远镜)系统准确运转,需要对其焦面板上光纤的位置进行检测.本文即从实际应用的角度出发,阐述了光重心法在LAMOST光纤位置检测中的精度问题.在理论分析的基础上结合实验,具体研究光斑尺寸、相机光圈、光纤端面的发光强度等检测条件,并详细分析了它们与光重心法自身精度的关系.另外,还揭示了因光强变化而产生的"重心偏移"现象.最终,依据实验结果,为实际检测提供了一个最佳的测量条件.     

二维数字阵列光电位置敏感器件新式结构研究

简要阐述光电位置敏感器件的特点、工作原理,根据光电位置敏感器件的原理和光电位置方程,分析了背景光与测量精度的关系.在此基础上,利用低峰探测仪的双极性三极管将像素M(i,j)的行与列位线联系起来,用来检测最大光强度的像素,显示出最低输出电压,使位线与其输出电压相对应;采用分布图像的峰值检波器来模拟预处理光电信号,通过数字转换得到图像的重心位置;采用集中平行的模拟计算估算射到感光区的光分布的重心,并通过时钟比较器得到数字化图像.给出了检测位置的二维光电传感器阵列、显示与图像数量的平方根成正比功耗关系式以及几个重要结论.     

一维PSD定位精度的实验研究

本文根据实验研究测试了一维(二象限)PSD的线性特性,光斑大小和光束倾斜对PSD定位精度的影响,同时分析了其它一些因素的影响。实验表明,1mm直径的He—Ne激光束定位精度2.5μm,光斑越大,倾斜角越大,PSD的定位精度越低。PSD的线性性除与入射光能量有关外,还与后续处理电路有关。     

Principles of local sound velocity and attenuation measurementsusing transmission acoustic microscope

Fundamentals of transmission acoustic microscopy as applied to measurements of sound velocities and attenuation in thin specimens and films are discussed. The method is based on measuring the output signal A as a function of a distance z between the radiating and the receiving lenses in the two-lens focusing system of the transmission microscope. It is proposed to measure the A(z) dependence twice: initially without a specimen, and then in the presence of it. When a specimen is absent, maximum of the A(z)-curve arises in the confocal position of the lenses. In the presence of an object, the main peak of the curve is shifted, and its magnitude diminishes. Measuring the changes makes it possible to determine local values of sound velocities and attenuation. For data interpretation a theory of formation of the output signal in the two-lens focusing system was developed. The relationship between the peak shift and the ratio of sound velocities in a specimen and a couplant contains a correction depending on beam angle aperture     

摆杆式操作机钳杆平升降缓冲刚度与阻尼研究

针对摆杆式锻造操作机钳杆吊挂系统的液压缸与蓄能器组合缓冲装置,以平升降运动为例,提出基于动力学理论分析获得缓冲刚度与阻尼的思路,据设备结构形式简化吊挂系统的物理模型,利用拉格朗日法分析平升降运动的动能及势能,建立吊挂系统平升降动力学模型。以50 kN操作机为例,在Matlab中求解动力学方程,获得缓冲装置刚度及阻尼对吊杆摆动角、工件质心位置、钳杆摆角的变化规律,分析刚度及阻尼对平升降运动的影响,提出确定缓冲装置刚度及阻尼的方法,为摆杆式锻造操作机缓冲装置油缸与蓄能器设计提供理论依据。     

Effect of beam size parameters on internal fields in an infinite cylinder irradiated by an elliptical Gaussian beam

The scattered and internal fields of an infinite, homogeneous cylinder illuminated by a linearly polarized beam depend on the following parameters: the object size parameter of the cylinder (ka, where k=2pi/lambda, lambda is the wavelength of the incident beam in the surrounding medium, and a is the radius of cylinder), the complex relative refractive index of the object, the beam size parameters (komega(1) and komega(2), where omega(1), omega(2) are the representative beam dimensions), the angle between the cylinder axis and the Poynting vector of the incident wave, and the angle between the plane of polarization and the plane of incidence. Only when the dimensions of the beam are much greater than the cylinder diameter, and hence the portion of the beam interacting with the cylinder is essentially uniform, can the plane-wave solution be used in computing the scattered and internal fields. Hence a rigorous electromagnetic approach like the generalized Lorenz-Mie theory for spheres is used to study the effect of beam size parameters on the internal fields in an infinite cylinder irradiated by elliptical Gaussian beams. The significant effects of beam size parameters on the internal fields in an infinite cylinder are presented using specific cases of (1) resonance effects in a glass cylinder (ka=45.726, transverse-electric mode 53,3) and (2) a cylindrical microchannel (ka approximately 760) irradiated by a 632.8 nm laser beam.