Nonparaxial propagation of a partially coherent dark hollow beam

Based on the generalized Raleigh-Sommerfeld diffraction integral, an analytical nonparaxial propagation formula of a partially coherent dark hollow beam (DHB) in free space is derived. The paraxial approximation is dealt with as a special case of our general result. By using the derived formula, the nonparaxial propagation properties of DHBs are studied and are compared with the paraxial results. It is shown that the nonparaxiality properties of a partially coherent DHB are closely related to its initial beam parameters (i.e., beam waist size, wavelength, coherence length, dark size) and the propagation distance.     

Simulation and fabrication of THz waveguides with silicon wafer by using eye-shaped pillars as building blocks

Silicon-based photonic crystal is a promising material for terahertz (THz) waveguide due to its high refractive index contrast. In this work, we introduce eye-shaped pillars as the feature building blocks for two-dimensional (2D) photonic crystals. The simulation study shows that larger TE mode band gaps (PBGs) can be created by the arrangement of dielectric eye-shaped pillars in air. The reflective spectra demonstrate that there are complex PBGs, where the peak position and intensity can be changed by varying the parameter e. Moreover, the peak of reflective spectra exhibits an obvious blue shift with the increase of incidence angle of light. When the vacant space in the structure is filled by polystyrene (PS) microspheres of 2 μm in diameter, the peak intensity of reflective spectra reduces significantly compared with that without PS microspheres, which suggests that this design can act as a sensor in the fields of biology, agriculture or medicine.     

基于抽取和连续投影算法的可见近红外光谱变量筛选

大多数短波CCD硅检测器为2 048或3 648像元,相邻波长间隔小,预处理算法对其适用性差.本文在600.09～980.47 nm光谱范围内,采用等间隔抽取方法重构光谱矩阵.经不同光谱预处理后,分别采用遗传算法(GA)和连续投影算法(SPA),筛选偏最小二乘法(PLS)建模变量.采用留一法交叉验证评价模型的预测能力,...     

钶铁矿型MnNb2O6的熔盐法合成、钒掺杂与磁性研究

采用了熔盐法新工艺制备了纯相与掺钒的MnNb₂O₆粉晶,利用X射线衍射仪(XRD),扫描电子显微镜(SEM),能谱分析(EDX),透射电子显微镜(TEM)、高分辨透射电镜(HRTEM)和电子衍射(SAED)分析了其物相、形貌及微结构.结果表明合成产物为正交晶系钶铁矿型MnNb₂O₆;在不同的熔盐中合成出了棒状、片状与长方体形貌的纯相产物.讨论了温度与掺杂对结构与形貌的影响,HRTEM与SAED分析表明了产物的各向异性生 关键词： 熔盐法 结构与形貌 掺杂 反铁磁性     

High spatial resolution distributed strain sensor based on linear chirped fiber Bragg grating and fiber loop ringdown spectroscopy

A simple sensor system for high spatial resolution distributed strain field measurement is proposed and demonstrated experimentally. The fiber loop ringdown technique combined with a linear chirped fiber Bragg grating is used to realize the high spatial resolution. A proof-of-concept distributed strain sensor with 2?mm spatial resolution is realized. The sensor network is also explored and researched experimentally. The proposed technique suggests a broad range of applications for real-time distributed physical parameter sensing, such as strain or temperature.     

Scattering-induced changes in the temporal coherence length and the pulse duration of a partially coherent plane-wave pulse

The scattering of a partially coherent plane-wave pulse on a Gaussian-correlated, quasi-homogeneous random medium is investigated. The analytical expressions for the temporal coherence length and the pulse duration of the scattered field are derived. We demonstrate that the scattering-induced changes in the temporal coherence length and the pulse duration may be used to determine the correlation function of the scattering potential of the medium.     

Experimental study of the focusing properties of a Gaussian Schell-model vortex beam

We carry out an experimental and theoretical study of the focusing properties of a Gaussian Schell-model (GSM) vortex beam. It is found that we can shape the beam profile of the focused GSM vortex beam by varying its initial spatial coherence width. Focused dark hollow, flat-topped, and Gaussian beam spots can be obtained in our experiment, which will be useful for trapping particles. The experimental results agree well with the theoretical results.     

Indirect measurement of the intensity of incident light by the light transmission fluctuation method

The light transmission fluctuation method is a simple and useful method for in situ and in-line measurement of particle size and concentration. To accomplish the measurement, it is necessary to know the intensity of incident light or background signal I(0). However, measuring I(0) during in-line applications is hard. In this Letter, an algorithm is proposed to indirectly measure I(0) based on the variation of transmitted light signals. Experiments have been carried out to verify the algorithm and the maximum deviation between premeasured I(0) and indirectly measured I(0)' is less than 2.5%.     

Optical properties of a planar metamaterial with chiral symmetry breaking

The optical properties of a planar metamaterial with gammadion-shaped chiral symmetry breaking holes array have been investigated both theoretically and experimentally. The results indicate that the introduction of the chiral symmetry breaking causes the split of the transmission peak and exerts large influence on the optical rotation and circular dichroism. Our metamaterials might have potential applications in future design of plasmonic devices.     

Facile synthesis and characterization of SnTe films

In this paper, we reported a novel, simple, and cost-effective route to SnTe films. The films were prepared by a chemical bath method, at room temperature and ambient pressure, using conventional chemicals as starting materials with or without surfactant. The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy, respectively. The SnTe film deposited without surfactant consists of nanoparticles (∼100 nm). The film deposited using polyethyleneglycol (PEG) as the surfactant consists of nanoparticles with size of ∼25 nm, whereas the film deposited using polyvinylpyrrolidone (PVP) as the surfactant consists of rough rod-like nanostructures (∼50 in diameter and ∼500 nm in length), besides nanoparticles (∼40-180 nm). The SnTe film deposited with PEG is smoother and denser. The formation mechanism of the SnTe films was proposed.