散射对激光水下图像传输影响的理论分析

激光水下成像技术在国内外已经取得较为完善的成果，目前主要采用距离选通和同步扫描两种方法。我国近海沿岸水质比较浑浊．散射现象严重。本文在研究了激光在水下的传输特性的基础上，结合散射光的分布特性，分析了在激光水下成像技术中．散射效应对传输目标图像精度的影响，以便能够在浑水中实现宽视角、全景深、图像清晰度高等技术指标。     

湿度对气溶胶单粒子偏振特性的影响研究

气溶胶散射特性对大气辐射和气候研究有重要意义,为了解气溶胶在不同相对湿度下的散射特性,在米耶散射理论基础上建立湿度偏振模型,仿真分析不同湿度下3种气溶胶粒子的散射光强度和线偏振度变化。结果表明:湿度对气溶胶粒子的散射强度几乎没有影响,在后向散射角120°～150°区域,粒子偏振度随湿度的变化而变化;对130°和140°后向散射角的偏振度与湿度仿真,得到粒子偏振度随着湿度的增大而增大。仿真结果从理论上说明了利用散射光偏振特性分析湿度与气溶胶散射特性的关系是可行的。     

水下非均匀光场建立方法的理论研究

光在水中照明时,由于水介质和水中微粒的吸收和散射,光能量损耗很多,而且产生了严重的散射光,降低了成像质量.因此在水中,尤其是在浑水中进行水下观察时,必须解决散射光的问题.针对以上存在的问题,我们提出一种新的水下目标图像探测方法--非均匀光场水下目标图像探测方法,并在此基础上我们提出了一种理想的分布光场模式,即在水下三维空间坐标轴上按所在水介质光衰减规律分布的非均匀照明光场.该光场有效的降低了后向散射光的影响,能获得较远的水下探测距离.     

基于激光选通成像技术的水下远距离目标智能识别系统研究

由于水体对电磁波的吸收与散射,水下光学成像存在“看不远”和“看不清”的问题,而水下激光距离选通成像技术可以提高水下光学成像距离和图像对比度。该文介绍了以水下激光距离选通成像技术为基础的水下远距离目标智能识别系统研究。实验结果显示,成像距离超过7倍衰减长度。该研究结合深度学习算法,在功率受限的硬件条件下,实现了目标的准实时检测,检测速度达0.8 f/s。水下激光距离选通成像技术与深度学习算法的结合,有望实现水下光学成像“看得远”和“看得清”的同时,实现“看得快”和“看得准”。     

水体后向散射特性研究进展

后向散射系数是水体重要的固有光学量之一,是水色反演半分析模型的重要输入参数,与水体组分有着密切关系。回顾了近年来国内外有关水体后向散射特性的研究进展,主要包括纯水、浮游植物和悬浮泥沙等无机颗粒物的后向散射特性,以及不同颗粒物的后向散射光谱变化性等。此外,还阐述了后向散射系数的理论基础和测量方法,并探讨了影响水体后向散射特性的影响因子,最后提出了水体后向散射的研究方向和发展前景。     

一种基于前向散射雷达的车辆目标自动识别方法

研究了一种基于前向散射雷达的车辆目标自动识别方法:分析了前向散射雷达回波与目标速度、轮廓等目标特性之间的关系;提出了主瓣对齐的功率谱预处理方法,采用主成分分析方法分析了不同类别车辆的前向散射雷达功率谱的特性;提出了基于多元线性回归的目标特征提取方法,比较了K最近邻法和Bayes分类器对不同特征集的识别性能.实现结果表明,本文采用的特征提取方法显著改善了识别效果.     

水下激光引信回波功率研究

针对目前水下激光引信无法选取其激光器合适的发射功率,对水下激光引信的回波功率展开研究。为计算应用于相关海域的水下激光引信所需的激光发射功率,通过推导水下激光引信探测目标的回波功率方程,计算海水各成分对532 nm绿激光的衰减系数,最终获得水下激光引信探测给定距离时所需的发射脉冲激光峰值功率计算公式。对所得公式在不同海水参量条件下进行仿真计算,仿真结果表明:对于应用于一般较清洁海域的水下激光引信,选择峰值功率不小于10 kW的脉冲激光器就能够探测到10 m处的目标,满足激光近炸引信的使用要求。所得的仿真计算结果可为水下激光引信应用于不同海域时激光发射功率的选择提供理论依据。     

水下激光成像的图像预处理技术

激光水下成像技术是一项目前正在发展的先进技术,它集激光技术、通信技术、信号处理与识别和电子技术等于一体,具有广阔的应用前景.水体对光的"吸收"和"散射"效应给水下激光成像带来大量的背景噪声,是水下成像高噪声和低对比度的主要成因.距离选通成像技术是提高激光距离选通成像系统信噪比的有效方法,可以在一定程度上克服大量后向散射的影响,但成像质量仍然不好.为了进一步改善成像效果,就需要利用数字图像处理技术时水下成像进行后续加工.水下图像处理结果的好坏直接影响到特征提取和目标识别的成败.直方图均衡化、对比度增强、平滑滤波、图像锐化等都是有效的数字图像预处理方法,并且实验结果表明上述方法都是有效可行的.     

水下弹性球壳回波特性的仿真研究

水下弹性球壳回波特性的研究对水下目标特征提取和识别具有重要意义.利用弹性理论和分离变量法导出弹性球壳散射声场的Bayleigh简正级数解,得到其反向散射波形态函数.由形态函数计算了高斯脉冲入射到弹性球壳的回波波形,并建立了水下弹性球壳回波特性的数学模型.通过对弹性球壳形态函数和回波结构的仿真,分析比较了不同材料和不同厚度的弹性球壳形态函数和回波特性,并讨论了水下弹性球壳回波特性的影响因素.结果表明,水下弹性球壳的回波特性与球壳材料、球壳厚度和入射信号等因素有关.     

水下窄脉冲超宽带信号的传播特性仿真

超宽带信号具有分辨率高、截获概率低、穿透能力强等优点,将在水下目标探测、定位及通信等领域具有良好的应用前景;基于水下等离子体声源提出了窄脉冲超宽带信号产生方法,建立了以传播损失和海洋环境噪声为主要影响因素的超宽带脉冲传播信道模型;结合湖试实测数据,利用Matlab仿真软件和Welch谱分析法,仿真分析了不同频率的超宽带脉冲在水下传播不同距离后的功率谱密度以及传播特性;研究成果对水下等离子体超宽带脉冲的工程应用具有重要的参考价值,同时对水下等离子体超宽带脉冲声源的设计和研制也有一定的借鉴意义.     

Invited Paper: Surface‐emitting‐diode lasers and laser arrays for displays

Abstract— High‐power red, green, and blue laser light sources made from vertically emitting arrays of intracavity doubled IR lasers is reported. The emitted infrared light from a monolithic array of large‐aperture vertical cavity lasers is converted into visible light using a PPLN doubling crystal in an external cavity. A volume Bragg grating provides simultaneous feedback for all emitters in the array and sets the laser wavelength. Increased diffraction losses for higher‐order modes result in quasi‐Gaussian beams with excellent conversion efficiency. Green 532‐nm lasers with more than 5.8‐W visible power have been demonstrated at a base temperature of 40°C. Blue 465‐nm lasers with 4.4‐W power at 40°C are unmatched in performance and wavelength when compared to competing GaN‐based edge emitters. Typical wall‐plug efficiencies are higher than 8%. We have measured single‐emitter operating lifetimes to be more than 28,000 hours. Red lasers based on highly strained InGaAs achieve record laser powers of 2.0W at 618 nm in the same form factor as the green and blue lasers. Red single‐emitter lifetimes of more than 10,000 hours have been attained. The technology described in this paper delivers on a full suite of cost efficient and reliable red, green, and blue lasers that meet the demands of the display markets.     

Field emission properties of amorphous GaN ultrathin films fabricated by pulsed laser deposition

Amorphous gallium nitride (a-GaN) films with thicknesses of 5 and 300 nm are deposited on n-Si (100) substrates by pulsed laser deposition (PLD), and their field emission (FE) properties are studied. It shows that compared with thicker (300 nm) a-GaN film, better FE performance is obtained on ultrathin (5 nm) a-GaN film with a threshold field of 0.78 V/μm, which is the lowest value ever reported. Furthermore, the current density reaches 42 mA/cm2 when the applied field is 3.72 V/μm. These experimental resul...     

Optical micro-paddle beam deflection measurement for electrostatic mechanical testing of nano-scale thin film application to MEMS

The authors describe their design for a paddle-like cantilever beam sample to relieve non-uniform stress distribution in beam-bending tests of the mechanical properties of thin film applications to MEMS. We added the sample to a custom-designed system equipped with an electrostatic panel and optical interferometer. The system overcomes problems associated with using nano-indentation for testing, and reduces errors tied to the amount of contact force required to bend the beam. Accurate paddle cantilever beam deflection was obtained using a four-step phase-shifting process with a Michelson interferometer. Film strain was determined using a simple force equilibrium equation. Residual stresses were measured at −41.3 MPa for 150 nm silver film, −3.2 MPa for 150 nm gold film, and −16.8 MPa for 150 nm copper film. We observed residual stresses for copper films at different thicknesses. The results indicate high tensile stress forms during the early deposition stage for thin copper film due to grain coalescence, and a decrease in stress with an increase in film thickness. In copper films with thicknesses greater than 153 nm, lattice relaxation associated with the surface mobility of metallic atoms changed residual stress from tension to compression.     

RETRACTED ARTICLE: Z-scan approach for measuring a threshold of two-photon photopolymerization

A technique is suggested to measure a threshold of two-photon initiated photopolymerisation involving Z-scan of a thin film of sensitive material along the focusing axis of the laser beam. The condition of reaching the threshold when gradually increasing the light intensity by moving the film towards the focal spot of the beam is defined as that with minimal intensity at which polymerization occurs. The occurrence of the polymerization is detected by interferometric effect inside the transmitted beam itself, which is due to interference of the wave going through the polymerization area and the wave going around it. The technique is demonstrated for measurements employing Nd:YAG laser in nanosecond regime with fundamental frequency 1064 nm and its harmonic of 532 nm, as well as with pumped by its third harmonic optical parametric oscillator. Threshold data are presented for particular systems, indicating threshold of 5 GW/cm² for a system based on Rose Bengal exposed by 1064 nm nanosecondpulsed radiation and 0.05 GW/cm² for Darocur initiators exposed to 532 nm. The text was submitted by the author in English.     

Effect of physical vapor deposition metallic thin films on micro injection molded weld line mechanical properties

Micro injection molded polymeric parts coated with functional thin films/layers show off the promising applications in microsystems area. But the unfavorable and unavoidable defect of weld line in micro injection molding part leads to detrimental mechanical and surface properties. The possibility of the functional thin film for enhancing micro injection molded weld lines was investigated. Two typical coating materials (aluminum and titanium) with various film thicknesses (400, 600, 800 nm) were deposited on one side of the micro injection molded weld line tensile sample via physical vapor deposition (PVD) method. The coated micro weld line samples were characterized by tensile tests. The results show that PVD films of aluminum and titanium can reinforce the strength and stiffness of micro injection molded weld line, even at thin thickness levels. But when the film thickness is increasing, the weaker adhesion between metallic films and polymers decreased the PVD films’ enhancing performance for micro weld line mechanical properties due to the degradation of polymers related to longer time exposure under high temperature.     

Microstructural and electrical properties of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT) epitaxial films grown on Si substrates

Epitaxially grown PMN-PT thin films using the PMN-PT single crystal targets were prepared at 550 °C on appropriate buffer layers of LSCO/CeO₂/YSZ deposited on a Si substrate using pulsed laser deposition. The micro-structural and the electrical properties of the films were investigated as a function of the film thickness. The PMN-PT films with the thickness from 200 to 600 nm exhibited an epitaxial nature with a pure perovskite structure. On the other hand, the films above 700 nm included a pyrochlore phase embedded in the perovskite structure although they exhibited an epitaxial nature. A pyrochlore phase included in the films above 700 nm thickness decreased the dielectric constant and the ferroelectric properties of the PMN-PT films.     

Microcrystalline‐silicon thin films by physical vapor deposition for wide‐area low‐temperature polysilicon production

A sputtered microcrystalline‐silicon thin film deposited on unannealed Corning Code 1737 glass has been shown to transform to polycrystalline material after excimer‐laser annealing at low energy densities, and below the full‐melt threshold. The homogeneous large‐grain polysilicon films obtained show promise for high‐yield manufacturing of large‐area LTPS displays. The material properties of the films will be presented and the properties of devices fabricated in the films will be discussed.     

Laser‐irradiated zinc oxide thin‐film transistors fabricated by solution processing

Abstract— This study investigates the effects of subjecting zinc oxide (ZnO) thin films to laser irradiation. The optical, structural, and electrical properties of the as‐deposited and laser‐irradiated films at different laser energies were studied. The transmittances without/with laser irradiation showed a net increase from 85 to 92% (@550 nm) for 250‐nm ZnO films, indicating an improvement in sample crystal linity. In addition, laser treatment decreased the ZnO band gap. Composition structure analysis shows that the crystallinity increased when the laser energy increased. Thin‐film transistors (TFTs) with a ZnO active layer were fabricated. The mobility of as‐deposited ZnO TFT devices (0.19 cm²/V‐sec) increased more than 2.5 times for ZnO of unirradiated laser treatment (0.49 cm²/V‐sec).     

Nonlinear properties of aluminum‐doped zinc sulfide under IR excitation

Abstract— Second harmonic generation (SHG) in ZnS‐based materials is reported. ZnS, ZnS:Cu, Br, and ZnS:Cu, Al, Br samples were studied. Phosphor powders were subjected to 30‐mJ pulses from YAG:Nd infrared laser. The wavelength of the generated green emission was 532 nm, exactly one‐half that of incident laser light (1064 nm). However, the non‐linear dependence of the emission intensity on pump intensity was observed only for the ZnS:Cu, Al, Br powder. It is concluded that aluminum co‐doping is crucial for the non‐linear properties.     

Ga‐doped zinc oxide: An attractive potential substitute for ITO,large‐area coating,and control of electrical and optical properties on glass and polymer substrates

Abstract— Ga‐doped ZnO (GZO) films with thicknesses of 30–560 nm were prepared on glass substrates at 200°C by ion plating with direct‐current arc discharge. The dependences of the characteristics of GZO films on thickness were investigated. All the polycrystalline GZO films, which showed high transmittance in the visible region, were ZnO crystallites with a wurtzite structure highly oriented along the (0002) plane. The resistivity, ρ, of GZO films decreases with increasing film thickness. The highest ρ achieved is 4.4 × 10⁻⁴ Ω‐cm with a carrier concentration, n, of 7.6 × 10²⁰ cm⁻³ and a Hall mobility, μ, of 18.5 cm²/V‐sec, determined by Hall effect measurement for the GZO films with a thickness of 30 nm, and the lowest ρ is 1.8 × 10⁻⁴ Ω‐cm with n = 1.1 × 10²¹ cm⁻³ and μ = 31.7 m²/V‐sec for the GZO film with a thickness of 560 nm. In addition, highly transparent GZO films with thicknesses of 12–300 nm were fabricated on unheated polymethyl methacrylate (PMMA). The ρ of these transparent GZO films decreased from 20 to 4 × 10⁻⁴ Ω‐cm with film thickness.