A compact T-branch beam splitter based on anomalous reflection in two-dimensional photonic crystals

We project a compact T-branch beam splitter with a micron scale using a two-dimensional (2D) photonic crystal (PC). For TE polarization, one light beam can be split into two sub-beams along opposite directions. The propagating directions of the two splitting beams remain unchanged when the incident angle varies in a certain range. Coupled-mode theory is used to analyze the truncating interface structure in order to investigate the energy loss of the splitter. Simulation results and theoretical analysis show that choosing an appropriate location of the truncating interface (PC-air interface) is very important for obtaining high efficiency due to the effect of defect modes. The most advantage of this kind of beam splitter is being fabricated and integrated easily.     

A new method of relative radiometric calibration for hyperspectral imaging based on skylight monitor

Optical and Quantum Electronics - ZnO thin films were deposited onto aluminium substrates at different substrate temperatures from 300 to 450 °C by chemical vapour deposition method...     

利用海底反射信号进行地声参数反演的方法

针对现有反演方法的缺点,提出了一种基于海底反射信号的地声参数高分辨反演方法.它利用短距离声源在不同深度上发射宽带线性调频信号,采用垂直阵进行接收,首先通过匹配滤波方法提取多径到达信息,然后利用海底反射损失曲线,反演海底表层的声速和密度,最后利用浅底层反射信号估计沉积层参数.由于海水中直达波受到内波的强烈影响,选择海底表面反射作为参考,用以可靠地计算浅底层反射的相对到达时间和幅度,从而估计出沉积层的厚度、速度和衰减系数.通过海上实验,验证了利用浅底层反射信号反演参数的有效性. 关键词： 海底参数 反演 浅底层反射信号     

一种新型投影曝光调焦方法

为研究大面积激光投影光刻的调焦,利用Zemax光学设计软件模拟离焦对光程差（OPD）和调制传递函数（MTF）的影响,分析二者对投影曝光图形质量的影响,给出系统最大的离焦量值。提出一种利用显微镜的调焦方法,分析此方法的调焦误差主要来自于显微镜景深,根据景深表达式和系统最大离焦量值,选择一款景深不大于系统最大离焦量的显微镜来构建调焦系统,并基于该调焦系统进行光刻实验。实验结果表明:利用该方法对投影成像光刻进行调焦,无论是否离焦,边缘视场与中心视场的MTF均有差异,分辨率也有差异,但这种差异不影响光刻图形的质量。     

一种基于新型偏振干涉成像光谱仪的目标偏振信息探测新方法

提出了一种采用基于视场补偿型Savart偏光镜的新型偏振干涉成像光谱仪对二维目标偏振信息进行空间遥感探测的新原理和新方法.在新型偏振干涉成像光谱仪光学系统不变的情况下,通过旋转偏振干涉仪分别测出了三个不同角度下像面上各像点的光强值,反演出了二维面目标的斯托克斯矢量,并给出了各像点偏振度和偏振方向的理论表达式.采用计算机模拟实验对该探测原理和方法进行了验证,所得结果与理论完全符合.从理论和实践上扩展了干涉成像光谱仪的探测功能,与目前国内外所研究的成像光谱仪相比,该成像光谱仪既能同时探测目标二维空间信息和一维光谱信息,又提供了一种获得目标偏振信息的手段和方法.     

A new subdivision technique for grating based on CMOS microscopic imaging

We propose a new subdivision technique directly subdividing the grating stripe by using complementary metal-oxide semiconductor (CMOS) microscopic imaging system combined with image processing. The corresponding optical system, subdivision principle, and image processing methods are illuminated. The relations of systemic resolution to subdivision number, grating period, magnifying power and tilt angle are theoretically discussed and experimentally checked on the Abbe comparator. The measurement precision for displacement of the proposed subdivision system is tested in the range of 5 mm and the maximum displacement error is less than 0.4μm. The factors contributing to the systemic error are also discussed.     

A new method based on the harmonic balance method for nonlinear oscillators

The harmonic balance (HB) method as an analytical approach is widely used for nonlinear oscillators, in which the initial conditions are generally simplified by setting velocity or displacement to be zero. Based on HB, we establish a new theory to address nonlinear conservative systems with arbitrary initial conditions, and deduce a set of over-determined algebraic equations. Since these deduced algebraic equations are not solved directly, a minimization problem is constructed instead and an iterative algorithm is employed to seek the minimization point. Taking Duffing and Duffing-harmonic equations as numerical examples, we find that these attained solutions are not only with high degree of accuracy, but also uniformly valid in the whole solution domain.     

一种基于时频分析的逆合成孔径声呐的距离-瞬时多普勒成像方法

传统距离-多普勒逆合成孔径成像方法是基于匀速转动的目标模型之上的,然而当目标机动时,由于目标各散射点多普勒效应的差异及投影平面的变化,距离-多普勒成像可能会失效。本文运用时频分析的方法,提出了一种新的距离-瞬时多普勒成像的方法,改善了原方法对机动目标的成像效果。实测的结果表明了该方法行之有效。     

A new method of spatial compounding imaging

A new method of spatial compound imaging is presented that improves image quality without the usual requirement to decrease the frame rate. The new method of imaging utilizes three transducers for data acquisition. The transducer located at the center of the transducer system is a phased array probe that acts as both transmitter and receiver. The other transducers are unfocused pistons that act only as receivers. Envelope data acquired by each transducer are combined to form a final image with improved quality (speckle contrast, target detectability and lateral resolution). It is shown that the improvement in speckle contrast depends on the correlation between individual images acquired by the transducers. The effective aperture approach is used for analytic estimation of the correlation between images in order to optimize the lateral separation between transducers. Using simulations, several compounding strategies have been performed to find the strategy that maximizes image quality. The central frequency of 2.5 MHz is used in simulations. Quantitative analysis of simulated B-mode images shows that the new method of imaging efficiently improves visibility, detectability, and lateral resolution of low contrast regions. The image frame rate is preserved because multiple scans are not required for the spatial compounding.     

Infrared vibration spectroscopy of molecular adsorbates on tungsten using reflection inelastic electron scattering

The observation of adsorbate vibrational energies in the range, 30 ?, hv_vib ? 1000 meV, by electron-energy-loss spectroscopy, provides detailed information on the geometry of atomic and molecular complexes. The “surface normal dipole selection rule”, is discussed and illustrated with results obtained for CO and C₂H₂ adsorption on the principal low-index faces of tungsten, viz.: W(100), W(110) and W(111) using a high-resolution electron reflection spectrometer. Specifically, the behaviour of chemisorbedd diatomic carbon monoxide and polyatomic acetylene is compared as a function of coverage and surface crystallography. Comparison is made with the spectral information obtained by reflection infrared spectroscopy and recent ultraviolet photoelectron spectroscopy studies of the chemisorption binding energies. The energy loss spectra are discussed in terms of current adsorbate models and the possible formation of “distorted rehybridized surface molecular complexes” based on molecular orbital theories of organometallic compounds.     

New type of Y-branch power splitter and beam expander based on eliminating anomalous reflection effect

We propose a new type of Y-branch power splitter and beam expander with scales of microns in two- dimensional （2D） photonic crystals （PCs） by drilling air holes in a silicon slice. Its functionality and performance are numerically investigated and simulated by finite-difference time-domain （FDTD） method. Simulation results show that the splitter can split a TE polarized light beam into two parallel sub-beams and the distance between them is tunable by changing the parameters of the splitter, while the expander can expand a narrow beam into a wider one, which is realized in an integrated optical circuit. The proposed device is based on the avoiding of anomalous reflection effect and the coupling transmission of defect modes of the interfaces.     

A new subdivision method for grating-based displacement sensor using imaging array

A new subdivision method for grating-based displacement sensor was proposed in the present study, which takes advantages of imaging array's high resolution and pixels’ good uniformity in the space. In this method, the magnified grating image is received by imaging array and grating pitch is directly subdivided by pixels, which is quite different from that moiré fringe is subdivided by complex subsequent circuits in moiré-type displacement sensor. The displacement is statistically calculated by using the whole grating image, which greatly eliminates the errors arising from illumination, electrical signals’ fluctuation, grating defect, and so on. Therefore, the subdivision method is easy to obtain signal with high signal-to-noise ratio, insensitive to some external factors, and able to attain high measurement precision with low cost. In this paper, the principle of subdivision method was illuminated, the systemic resolution was theoretically discussed, the measurement precision was experimentally checked, and the uncertainty of measurement was analyzed. The subdivision system consisted of the grating with 20-μm pitch and the CMOS image sensor with the pixels of 1280×1024 had the resolution of 0.04 μm, and the maximum displacement error was less than 0.4 μm, which has been tested in the Abbe comparator platform.     

A new approach for extracting phase effect based on in-line X-ray phase imaging

In clinical applications, the X-ray spectra from tungsten are continuous, and include both attenuation and phase effects for in-line X-ray imaging. A new approach for extracting the pure phase effect from the mixed images is presented. In this work, a normalized imaging formula independent of the light intensity is derived for the polychromatic case. Taking both photoelectric and Compton interactions into account, the attenuation effects at 70 and 50 kVp for borosilicate pyrex, air, and water are accurately calculated and shown to be stable across these substances. The attenuation effect at the interface can be greatly weakened by the subtraction of the attenuation effects of two normalized images, thus revealing details of the phase effect. The experimental results show that this approach is valid.     

基于周期结构负反射的远场增强成像研究

远场高分辨率成像是近几年来声学和光学领域的研究焦点之一, 倏逝波无法在介质中传播成为将高分辨率成像带入远场的最大困难.本文提出了一种均匀排列的散射钢柱构成的超构散射体成像方式, 利用周期结构负反射现象将倏逝波信息转化为可传播波来增强成像.有限元数值模拟被用来研究和验证该方案的可行性, 结果显示波长3.4 mm的声波可以在20 cm外的远场获得大约0.6个波长的成像分辨能力. 通过减小散射体的晶格常数有希望达到更高分辨率成像.     

基于非均匀螺旋线数据和布雷格曼迭代的快速磁共振成像方法

数据采集时间长是制约磁共振成像技术发展的重要瓶颈.为了解决这一问题, 本文基于压缩感知成像理论, 提出了一种结合非均匀螺旋线磁共振数据采集序列和布雷格曼迭代重建的快速磁共振成像方法, 通过欠采样缩短数据采集时间.欠采样引起混迭伪影则通过非均匀螺旋线欠采样特性和布雷格曼迭代重建去除.水模磁共振成像实验和在体磁共振成像实验结果表明: 欠采样情况下, 所提出的方法能有效去除欠采样导致的混迭伪影, 获得的图像结构信息完整的成像结果, 在缩短采样时间的同时, 具有较高的准确度. 关键词： 磁共振成像 非均匀螺旋线 全变分 布雷格曼迭代     

A novel method for non-destructive Compton scatter imaging based on the genetic algorithm

Compton scattering tomography is widely used in numerous applications such as biomedical imaging, nondestructive industrial testing and environmental survey, etc. This paper proposes the use of the genetic algorithm (GA), which utilizes bio-inspired mathematical models, to construct an image of the insides of a test object via the scattered photons, from a voxel within the object. A NaI(Tl) scintillation detector and a 185 MBq ¹³⁷Cs gamma ray source were used in the experimental measurements. The obtained results show that the proposed GA based method performs well in constructing images of objects.     

A new method for removing impulse noise based on noise space characteristic

This paper proposes a new method for eliminating impulse noise. Based on the space characteristic of object and noise, three kinds of basic noise patterns are introduced to describe noise and detect noise candidates. Correspondingly, noise removal operators are presented to remove the impulse noise. Extensive experiment results have shown that the proposed method is better than some of the state-of-the-art methods.