Binary diffractive beam splitters with arbitrary diffraction angles

Diffractive optical beam splitters designed with iterative Fourier transform type algorithms can produce only certain diffraction angles given by the spatial frequencies used for the computations, which are multiples of a certain base spatial frequency. We have developed a design algorithm that overcomes this limitation and can be used to compute binary diffractive elements with arbitrary diffraction angles. The simulated and experimentally measured properties of optical elements producing beam arrays in circular arrangements are presented and discussed.     

Rigorous electromagnetic analysis of dual-closed-surface microlens arrays

In this paper, we investigated the focal performance of the dual-closed-surface microlens arrays (DCSMAs) based on rigorous electromagnetic theory and boundary element method (BEM) in the case of TE polarization. The DCSMAs are designed with different substrate thickness and different distance between microlenses. DCSMAs designed according to different wavelengths are surveyed. The DCSMAs with different incident angles are also studied. Several focusing performance measures, such as the focal spot size, the focal position on the preset focal plane, the diffraction efficiency and the normalized transmitted power, are presented. Numerical results indicate the DCSMAs with different parameters can implement focusing beams and the focal performance of DCSMAs is easily influenced by the substrate thickness and the incident wavelength. Furthermore, the optimal thickness for the maximal diffraction efficiency of the DCSMAs is given. It is expected that the DCSMAs may be used as a parallel processing device in micro-optics systems.     

Autocatalytic redox fabrication and magnetic studies of Co-Ni-P alloy nanowire arrays

Uniform and large-scale Co-Ni-P alloy nanowire arrays have been fabricated by autocatalytic redox reaction in an anodic alumina membrane (AAM). The images of Co-Ni-P alloy nanowire arrays and single nanowires are obtained by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that the Co-Ni-P nanowire arrays are amorphous in structure. The magnetic property of Co-Ni-P nanowire arrays is characterized using a vibrating sample magnetometer (VSM). The hysteresis loops show that the easily magnetized direction of Co-Ni-P nanowire arrays is parallel to the nanowire arrays and that it has obvious magnetic anisotropy as a result of the shape anisotropy.     

Direct measurement of the delay time for a neutron in a crystal in the case of the Laue diffraction

The dynamical Laue diffraction has been studied for a direct beam diffracted from a thin (～3.5 cm) α-quartz crystal at the Bragg angles close to 90°. It is shown that diffraction occurs at Bragg angles up to 87°. The time-of-flight method is used to measure the time of the neutron presence in the crystal under the diffraction conditions. The time delay for a scattered neutron inside the crystal predicted earlier for the Bragg angles close to 90° confirmed experimentally. The effective velocity of the neutron propagation in a crystal measured at the incident-neutron velocity of 810 m/s and the diffraction angle of 87° equals (43±1) m/s. The result obtained confirms the possibility of increasing, by an order of magnitude, the sensitivity of the diffraction method of determining the dipole moment of a neutron at Bragg angles close to 90° predicted earlier theoretically.     

Diffraction of electromagnetic waves by concave circumferential surfaces: Application for hybrid reflector antennas

A particular problem of diffraction of electromagnetic waves by an ideally conducting hemispherical reflector and model problems of excitation of an ideally conducting hemisphere by a current ring have been solved. Designs of hybrid reflector antennas and diffraction arrays on the basis of reflectors with a circular profile are proposed. Designs of packaged exciters of hybrid reflector antennas and diffraction arrays have been developed.     

Electroless synthesis of large scale Co-Zn-P nanowire arrays and the magnetic behaviour

Co-Zn-P nanowire arrays have been synthesized by electroless deposition in an anodic alumina membrane (AAM). The images of Co-Zn-P nanowire arrays and single nanowires are obtained by both scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that Co-Zn-P nanowire arrays are amorphous in structure. The hysteresis loops characterized by a vibrating sample magnetometer (VSM) show that the easily magnetized direction of Co-Zn-P nanowire arrays is parallel to the nanowire arrays and that there exhibits clearly a magnetic anisotropy as a result of the shape anisotropy.     

Diffraction of electromagnetic radiation near an interface between discrete positive and negative refractive media

The discrete diffraction of electromagnetic waves near the interface between two different media formed by waveguide arrays is studied. One of the arrays consists of waveguides made of a positive index material; the other, of waveguides made of a negative index material. The refraction of a beam resulting from diffraction at the interface obeys an analog of Snell’s law.     

Influence of vertex angles on the extraordinary optical transmission characteristics of triangular and bow-tie-shaped apertures

The influence of vertex angles on the extraordinary optical transmission (EOT) characteristics of isosceles triangular apertures is numerically investigated with a three-dimensional finite-difference time-domain (FDTD) method. It has been found that the resonant peak characteristics are dependent on the vertex angles of triangular aperture (TA) and the polarized directions of incident light. The resonant peak amplitude is dramatically decreased, when the vertex angle is increased. A blue-shift/red-shift phenomenon is observed in both of the two cases. Detailed studies indicate that the transmission peak characteristics are due to the effects of localized surface plasmon modes excited along the sidewalls and Fabry–Pérot-like resonance. The EOT performance of TA arrays is compared with that of the rectangular aperture arrays. In addition, a bow-tie-shaped aperture (BTA) can be recognized as two overlapped TAs. The EOT properties of BTA with varying bow angles are also studied and analyzed.     

用于并行激光直写的连续深浮雕衍射透镜阵列研究

研究了一种用于并行激光直写的连续深浮雕衍射透镜阵列方法.该方法采用连续浮雕衍射透镜阵列替换传统并行激光直写中的物镜阵列,在兼顾系统分辨力基础上,克服了波带片等衍射透镜阵列衍射效率低的缺点|同时因采用深浮雕结构优化环带宽度,可降低阵列的制作难度.针对并行激光直写系统阵列F/#小的特点,在建立连续深浮雕衍射透镜阵列非旁轴近似聚焦模型基础上,设计、制作和测试了波长为441.6 nm,F/#为7.5的连续深浮雕衍射透镜阵阵列.测试结果表明：该阵列的衍射效率优于70%,远高于波带片阵列的40%.     

High-efficiency arrays of any desired optical beams using modified grating-based elements

High efficiency grating-based diffractive elements were previously proposed in order to generate desired arrays of various optical beams. The elements enable us to generate a diversity of arrays of optical beams in desired shapes, so that the arrays produced by the method are homogeneous, uniform and lacking of unwanted higher diffraction orders. In this technique a modulated grating is used to restructure Fresnel zone plate or zone plate-based elements to get modified grating-based elements. To examine the method, a variety of rectangular arrays of optical spots and annular beams are created by the ordinary and modified elements. It is shown that the arrays generated by the modified elements are much more uniform than the same arrays produced by the ordinary ones. In addition to the uniformity of the arrays, the unwanted higher diffraction orders are also totally eliminated. This article exploits simulation and experimental studies in order to demonstrate the functionality of the proposed technique as a multi functional high-efficiency beam shaping.     

Synthesis of the vertically aligned carbon hexagonal nanoprism arrays and their application for field emission

A simple approach is demonstrated for effectively growing large-area vertically aligned carbon hexagonal nanoprism arrays on molybdenum substrates by the catalyst-assisted pulsed laser deposition techniques. The carbon hexagonal nanoprisms have uniform shape and length, almost aligned vertically on the substrate, and the average diameters are about 30 nm. The internal angles of the nanoprisms present 60°. The vertically aligned nanorods have also been obtained for a comparison in the presence of catalyst Fe. The sample with vertically aligned carbon hexagonal nanoprism arrays exhibits better field emission behaviors than that with aligned carbon nanorod arrays.     

The transient scattering mechanism of dipole array with reflector

The transient backscattering mechanisms of a dipole array with reflector have been investigated from different aspects： time-domain, frequency-domain, and combined time-frequency domain, using 4 × 8 dipole arrays with reflector as an example. The data of scattering from the arrays under the incidence of Gaussian pulses are obtained by finite differential time domain method. The influences of the array structural parameters, incident wave parameters, and incident angles on the waveforms, spectrum, and time-frequency representations of the backscattered fields of the arrays are analysed and conclusions are drawn. From these characteristics and conclusions, it is possible to deduce the array structure inversely from the backscattered field.     

EXPERIMENTAL STUDY OF DIFFRACTIVE PROPERTIES OF WAVELENGTH-SIZED SINGLE GROOVE IN Si-Si3N4 SUBSTRATE

Experimental results are presented for the diffractive properties of wavelength-sized single groove in Si-Si₃N₄ substrate. The experimental results show that the diffraction of wavelength-sized single grooves in a non-perfectly conducting material is more complex than that of perfectly conducting material. The diffraction intensities change with the change of polarization angle of the incident light. The diffraction intensities for TM polarization light are larger as the groove width is larger. The diffraction intensities of TM polarization light decrease gradually and that of TE polarization light increase gradually when the groove width is close to the wavelength of the incident light. The variations of diffraction intensities are quite different not only for various grooves with different widths but also for different diffraction angles for the same groove. Although the intensity variation of each diffraction order has a very regular sinusoidal dependence on the polarization angles of the incident light, the variation phase of each diffraction order is not all the same.     

Diffraction management

By using the diffraction properties of waveguide arrays, we propose a scheme to produce structures with designed diffraction. We fabricated arrays with reduced, canceled, and even reversed diffraction. Results of experiments with such waveguides are presented and compared with the predictions made by coupled-mode theory.     

菲涅耳微透镜列阵衍射效率的测试与分析

归纳了目前二元位相型菲涅耳微透镜列阵衍射效率测试中所用各种衍射效率的不同定义，提出规范定义的建议。并设计了测量衍射效率的系统，方法简单易行，适于测试具有微小单元尺寸的菲涅耳微透镜列阵的衍射效率。     

完整布拉格反射型晶体衍射特性的理论研究

利用x射线衍射动力学理论研究了完整布拉格反射型晶体衍射特性,给出晶体衍射强度分布图,并计算了完整晶体积分反射强度和衍射强度分布半高宽。结果表明:在相同的能量下,不同类型晶体的衍射强度分布不同;在相同的布拉格角条件下,不同类型晶体积分反射强度和衍射强度分布半高宽也不同;当布拉格角大于45°时,晶体的积分反射强度与衍射强度分布的半高宽随着布拉格角的增大而迅速增大。     

小F数衍射微透镜阵列光学性能研究

本文基于小光点扫描,在国内首次提出了一种测试小F数衍射微透镜阵列光学性能的方法.利用光通信用半导体激光器和探测器建立了一套测试系统,并对所研制的大阵列,小单元尺寸的多相位菲涅耳衍射微透镜阵列的衍射效率和点扩散函数进行了测试.结果表明,衍射微透镜实际衍射光斑比理论衍射受限光斑扩展不大,8相位和16相位石英微透镜的衍射效率分别高达80.2%和87.5%,说明本实验室对多相位的设计理论和制作工艺已基本掌握,满足应用的要求.     

The effect of substrate on magnetic properties of Co/Cu multilayer nanowire arrays

Ordered Co/Cu multilayer nanowire arrays have been fabricated into anodic aluminium oxide templates with Ag and Cu substrate by direct current electrodeposition. This paper studies the morphology, structure and magnetic properties by transmission electron microscopy, selective area electron diffraction, x-ray diffraction, and vibrating sample magnetometer. X-ray diffraction patterns reveal that both as-deposited nanowire arrays films exhibit face-centred cubic structure. Magnetic measurements indicate that the easy magnetization direction of Co/Cu multilayer nanowire arrays films on Ag substrate is perpendicular to the long axis of nanowire, whereas the easy magnetization direction of the sample with Cu substrate is parallel to the long axis of nanowire. The change of easy magnetization direction attributed to different substrates, and the magnetic properties of the nanowire arrays are discussed.     

Effect of recording conditions on the anisotropic diffraction of volume holographic gratings

The anisotropic Bragg diffraction of the volume holographic gratings in photorefractive crystals are investigated based on the model of anisotropic coupled-wave theory. The effect of the initial intensity ratio and the recording angles of the two recording waves on the anisotropic Bragg diffraction properties is discussed. It is shown that both the ratio of the initial intensity and the incident angles of the recording waves are selective action for the anisotropic Bragg diffraction efficiency of the volume holographic gratings, while these two recording conditions are not selective action for the isotropic Bragg diffraction. Furthermore, the Bragg phase matching condition of anisotropic diffraction is analyzed when the recording angles change.     

A measurement technique for optical fibre break angles

An apparatus which determines optical fibre break angles by a diffraction technique is described. The device measures break angles to an accuracy of 0.15° and is shown to be useful in the evaluation and optimization of breaking machines as well as in the study of properties dependent on the end angle of the fibre in a system.