Interference effect of dual cylindrical microlenses with the closed boundary in dielectric incident space

The focal characteristics of closed-boundary cylindrical microlenses with dielectric incident space are investigated based on rigorous electromagnetic theory and the boundary element method. For single cylindrical microlens, focal performance is improved with the use of the dielectric incident space, for instance, its diffraction efficiency can be increased. Moreover, the interference effect of dual cylindrical microlenses embedded in a uniform dielectric material is studied in detail. Numerical results reveal that the interference effect between the dual microlenses can be suppressed substantially by the dielectric incident material environment. The interference effect can also be depressed by adjusting some other parameters, such as the distance between the dual microlenses, and the incident wavelength.     

Effect of illumination types on focusing performance of closed-boundary cylindrical microlenses

The effect of illumination types on closed-boundary cylindrical microlenses (CBCMs) is investigated by rigorous electromagnetic theory and boundary element method. As a result, the focusing performance of CBCMs with different illumination types are different to each other, while the optics elements cannot be considered as pure phase element for small f-number.     

Broadband dispersion characteristics of diffractive microlenses based on the finite-difference time-domain method

The broadband dispersion characteristics of diffractive microlenses are studied using the finite-difference time-domain (FDTD) method. The distributions of the diffracted electric fields obtained through a diffractive microlens are presented for illumination wavelengths ranging from 0.35 to 1.30 μm, along with the corresponding broadband dispersion curves. It is shown that both the principal focal length and the diffracted order of the principal focal point are dependent on the illumination wavelengths. The broadband dispersion characteristics of a diffractive microlens may be used to optimise light coupling for a broadband optical fibre source.     

Rigorous electromagnetic analysis of metallic cylindrical focusing micromirrors with high diffraction efficiency, achromatic aberration and long focal depth

In this paper, we propose a kind of metallic cylindrical focusing micromirrors (MCFMs) with parabolic profiles, and the focal performance is investigated based on rigorous electromagnetic theory and the boundary element method (BEM). Numerical results by the BEM show that the proposed MCFM possesses a high diffraction efficiency and axially achromatic aberration. In addition, through designing a modulating phase function, the MCFM holds long focal depth and high transverse resolution simultaneously. It is believed that the MCFM should have wide application prospects in micro-optical systems, such as micro solar concentrators.     

Combined implementing the hole-drilling method and reflection hologram interferometry for residual stresses determination in cylindrical shells and tubes

Main features inherent in simplified approach to residual stresses determination in cylindrical shells and tubes, external diameter of which is not less than 60 mm, by combing the hole-drilling method and reflection hologram interferometry are discussed in detail. Initial experimental information in a form of hole diameter increments in principal stress directions is derived from high-quality reflection holograms recorded near cylindrical objects of intermediate curvature value. Converting measured parameters into required stress values is based on the transition model that corresponds to plane stress conditions of pure membrane type. The technique developed is capable of determining residual stress component values within 5% accuracy in an absence of stress gradients over the probe hole diameter when a type of residual stress field corresponds to the transition model adopted. The accuracy analysis involved is based on matrix formulation of conventionally direct problem and an assumption on a pure membrane character of residual stress field under study for thin-walled shell. Required error estimations in a case of inspecting thick-walled cylindrical tube are obtained by combining the above-mentioned approach and an analogy of reconstructed fringe patterns with actual and artificial interferograms, which follow from drilling blind hole of the same geometrical parameters in thick-walled plates. Experimental verification of the developed approach is founded upon a determination of actual stresses in thin-walled cylindrical shell and obtaining residual stress distributions at the proximity of welded joint in thick-walled cylindrical tube.     

Studies on conical and cylindrical resonators

Spectral features of conical and cylindrical Hartmann resonators are compared in this work through a systematic parametric study. Experiments have been conducted by varying the following parameters: stand-off distance, nozzle pressure ratio and cone angle. Resonance frequencies of conical cavities are found to be higher than those of cylindrical cavities of the same length. Low (∼kHz) and high frequency (∼10 kHz) modes are observed in the spectra. Low frequency modes show an oscillatory trend with stand-off distance. The high frequency tones are found to be independent of cavity geometry and cavity length, and are similar to jet impingement tones.     

Negative refraction and focusing of electromagnetic wave through two-dimensional photonic crystals

The negative refraction of electromagnetic waves in photonic crystals was recently demonstrated experimentally, and the physical properties were analyzed. Microsuperlenses based on two-dimensional photonic crystals were designed and the subwavelength images were observed. In this review, after providing a brief history of the research related to the above phenomena, we will summarize our research works in this field including the method of creating a negative refraction region, generating an absolute negative refraction, the focusing of unpolarized electromagnetic waves, and the effect of interface and disorder on the image by the two-dimensional photonic crystal flat lens. The discussion on the negative refraction and the focusing by high symmetric quasicrystals is also presented.     

调焦方式对测绘相机主点位置的影响

考虑测绘相机调焦会影响相机的主点位置,从而改变相机的内方位元素,降低立体测绘精度,故本文分析了空间相机常用的3种调焦方式（镜组调焦、平面反射镜调焦、焦面调焦）对测绘相机主点位置的影响。简要介绍3种调焦方式的工作原理,研究了理想情况下3种调焦方式对主点位置的影响。在考虑系统装凋误差的情况下,建立了主点位置变化量与调焦量之间的数学模型,通过实例计算得出焦面调焦易满足测绘相机主点定位精度〈0．2pixel,是最适合的调焦方式。最后,以某一型号相机调焦机构为实验对象,对平面反射镜方式对主点的位置变化进行了实验量测,结果证明了提出的主点位置变化量理论计算公式的准确性和分析得到的不同调焦方式对主点位置影响的正确性,该公式可以用于指导测绘相机调焦方式的选择,以满足高精度测绘的需要。     

基于Zemax的He-Ne激光光束聚焦物镜的设计

 为了得到一个合理的He-Ne激光光束聚焦物镜,采用以正前凸型为基础的高折射率双片结构,应用Zemax软件进行优化设计,获得了弥散斑直径为0.002mm的He-Ne激光聚焦物镜,该镜头只需校正轴上点球差。实验结果表明：设计的镜头比低折射率单片透镜得到的弥散圆直径更小,达到0.0019mm,球差被控制在-0.05mm～+0.05mm范围内,MTF曲线所围面积变大,中心点亮度增高,符合实际需要。     

基于ZEMAX的二次反射式激光聚焦系统设计与模拟

反射式激光聚焦系统使激光推力器具备了推力矢量控制能力,并且聚焦系统不存在球差,具有广阔的应用前景。针对三种二次反射聚焦方式,抛物面-双曲面、平面-抛物面、抛物面-平面,在建立的聚焦系统坐标系下,通过几何光学方法分析了两个反射面母线参数之间的数学关系,以及聚焦特征参数与两个反射面母线参数的关系,并建立了程序设计流程。针对特定的聚焦特征参数设计要求,在光学软件ZEMAX中进行了反射面的建模和聚焦效果的验证,为下一步开展聚焦性能的研究打下了基础。     

利用磁聚焦法测量电子比荷的误差分析

在利用磁聚焦法测量电子比荷的实验中,测量误差与示波管的加速电压和聚焦电压存在较大的相关性．通过对测量误差与电聚焦程度、加速电压和聚焦电压之间关系的分析,指出了误差产生的原因,给出了加速电压和聚焦电压的最佳取值范围．     

数字图像一阶矩的自动聚焦区域选择算法

聚焦区域选择是自动聚焦算法中的重要模块,直接影响评价函数曲线的尖锐性、准确性和稳定性。针对中心取窗和多点取窗等传统聚焦区域选择算法的局限性,提出了一种基于数字图像一阶矩的自动聚焦区域选择算法,它是通过图像灰度或边缘一阶矩定位聚焦区域的。传统聚焦区域选择是一种定点估计,实验证明一阶矩方式选择可以跟踪偏离中心的主体景物,是一种具有自适应性的前景位置估计算法,提高了聚焦精确度和速度。     

Numerical simulations of laser light guiding and focusing using an open hollow cone

An open hollow cone that can optically guide and focus a laser light into a small beam spot is proposed. The shaping and focusing effects are numerically demonstrated by finite-difference time-domain simulations. The results reveal that the cone-focused laser originates from the multi-beam interference and squeeze of two cone side walls acting like oblique targets. Moreover, the influences of oblique incident angle of laser light, cone angle and cone tip size on the focusing properties are discussed and the optimum cone geometry with cone angle of 16° and tip size of 4.5 wavelengths to achieve high energy concentration at the cone tip is also presented. It is shown that with an open hollow cone a laser light can be focused into a tiny highly localized beam spot of 1 µm diameter and keeps propagating forward for a distance of about 8 wavelengths with a tiny spot diameter remaining almost unchanged. The intensity almost increases up to twentyfold in a 1 µm focal spot.     

基于多重结构的平显视差仪中内调焦物镜设计

根据平显视差测量原理中自动调焦的要求,设计了一个相对孔径与调焦范围均较大的内调焦物镜。针对内调焦传统设计方法的不足,在对内调焦各镜组选型后将它们组合成为一个系统,采用多重数据结构设计的方法,对不同物距下的结构进行同时优化,从而解决了近距离的成像质量难以控制的问题。所设计的内调焦物镜在不同的物距下成像质量稳定,无穷远时光学传递函数(MTF)值在空间频率为120 lp/mm时轴上与轴外均达到0.4以上,物距在300 mm时轴上视场MTF为0.3,轴外视场弧矢MTF在0.3以上,子午MTF达到了0.2;相对畸变均控制在1%以内,有利于后续的图像处理工作。     

SNR analysis of the stripe illuminator based on linear emitter and cylindrical lens against solar irradiance

Achieving good signal-to-noise ratio (SNR) against solar illumination is a basic requirement for the light source of active vision sensors in outdoor applications. The article examines the high power stripe-lighting setup, constructed with a cylindrical lens and a rectangular emitting source placed at the focal line of the lens. This source type is capable of illuminating a very high total power because of the large surface size of the emitter; thus it is advantageous for outdoor applications. A detailed radiometric analysis of this setup is presented resulting in an integral for the calculation of the spatial irradiance distribution within the stripe. The achievable SNRs against solar illumination are calculated by applying the radiometric integral for different rectangular emitters built of LED arrays, laser diode arrays and incandescent sources. The article proposes stripe illuminators applying all the analyzed emitter types that are suitable for operation in direct sunshine.     

Analysis of radiative transport in a cylindrical enclosure—An application of the modified discrete ordinate method

Application of the modified discrete ordinate method (MDOM) proposed by Mishra et al. [Mishra SC, Roy HK, Misra N. Discrete ordinate method with a new and simple quadrature scheme. J Quant Spectrosc Radiat Transfer 2006;101:249-262.] has been extended for calculation of volumetric radiative information in a cylindrical enclosure. Radiatively, the medium inside a diffuse gray 1-D concentric cylinder is absorbing, emitting and scattering. Three types of problems, viz., an isothermal medium representing non-radiative equilibrium case, a non-isothermal medium representing radiative equilibrium situation and the case of a combined mode conduction and radiation heat transfer have been used to test the robustness of the MDOM. Temperature/emissive power and heat flux/energy flow rate distributions in the medium have been found for the effects of various parameters like the extinction coefficient, the scattering albedo, the boundary emissivity and the conduction-radiation parameter. To check the accuracy of the results of the MDOM, results have been compared with those available in the literature and also by obtaining the radiative information using the finite volume method. MDOM has been found to provide accurate results.     

非对称偏振分束光栅的矢量衍射优化设计

基于严格耦合波理论分析了一种非对称偏振分束光栅的设计。这种偏振分束光栅分别在1级和0级衍射级次上衍射TE和TM偏振波。介绍了利用遗传算法设计偏振分束光栅的方法,并给出了优化实例。仿真结果表明:在设计波长为1.55时,TE偏振波在1级的衍射效率大于93%,TM偏振波在0级的衍射效率大于99%,此时1级和0级的透射消光比分别达到了9914.1和46841.5。通过对设计结果的分析发现,该偏振分束光栅在设计波长附近100nm的波长范围内都具有较高的消光比(大于100),达到了较好的偏振分束效果。     

Study on sound transmission characteristics of a cylindrical shell using analytical and experimental models

A circular cylindrical cavity enclosed by a thin elastic shell is found in many practical devices such as expansion volume mufflers, hermetic compressors and aircraft cabins. Analytical and experimental studies are conducted in this work to understand the characteristics of sound transmission through the cylindrical wall of such a system. Using an infinitely long circular cylindrical shell subjected to a plane incident wave, an exact solution is obtained by solving the classical shell vibration equations and the acoustic wave equations simultaneously. Transmission losses obtained from the solution are compared to the transmission losses that are measured for a cylindrical shell of finite length and the same cross-sectional dimensions. The comparison suggests that the theoretical model can be used as an effective design tool despite considerable simplifications involved.     

基于麦克斯韦电磁场理论的神经元动力学响应与隐藏放电控制

钙、钾、钠等离子在细胞内连续泵送和传输时产生的时变电场不仅会影响神经元的放电活动,而且会诱导时变磁场去进一步调节细胞内离子的传播.根据麦克斯韦电磁场理论,时变的电场和磁场在细胞内外的电生理环境中会相互激发而产生电磁场.为了探究电磁场影响下的神经元放电节律转迁,本文在三维Hindmarsh-Rose(HR)神经元模型的基...     

Numerical solution of radiative and conductive heat transfer in concentric spherical and cylindrical media

A new technique is presented to improve the performance of the discrete ordinates method when solving the coupled conduction-radiation problems in spherical and cylindrical media. In this approach the angular derivative term of the discretized one-dimensional radiative transfer equation is derived from an expansion of the radiative intensity on the basis of Chebyshev polynomials. The set of resulting differential equations, obtained by the application of the S_N method, is numerically solved using the boundary value problem with the finite difference algorithm. Results are presented for the different independent parameters. Numerical results obtained using the Chebyshev transform method compare well with the benchmark approximate solutions. Moreover, the new technique can easily be applied to higher-order S_N calculations.