A novel all-fiber micro-displacement sensor based on long period grating and tip structure

A novel high sensitivity all-fiber micro-displacement sensor is proposed and experimentally demonstrated. This sensor consists of a long period fiber gating and a fiber tip, which is achieved only by a commercial arc discharge fusion splicer, and thus possesses a lower cost. The wavelength sensitivity of the proposed sensor could be up to 934 pm/μm,which is four times higher than that of the long period fiber grating （LPFG） with an air cavity structure. The intensitychange sensitivity is - 1.973 dB/μm.     

Mechanochemical activation of mixtures of wolframite (FeWO4) with carbon,studied by 57Fe Mössbauer spectroscopy

The effect of mechanochemical activation (high-energy grinding) on mixtures of natural FeWO₄ with two forms of carbon has been investigated by X-ray powder diffraction and Mössbauer spectroscopy. The crystallinity of the mechanically activated mixtures, which have previously been found to exhibit enhanced reactivity as precursors for carbothermal production of tungsten carbide, is shown by X-ray powder diffraction to decrease on grinding, but without detectable formation of new crystalline phases. Mössbauer spectroscopy shows that the grinding process is accompanied by the appearance of an unexpected new singlet resonance, attributed to the formation of dilute FeC regions. The Mössbauer spectra also show that mechanochemical activation under the present conditions results in progressive oxidation of the Fe²⁺ in the wolframite to Fe³⁺; this oxidation is more marked in wolframite ground in the absence of carbon, suggesting that the latter exerts an oxygen-scavenging effect on the system. Similar results are obtained irrespective of whether the carbon source is activated carbon or graphite. The crystallization of iron tungsten carbides on subsequent heating of the ground mixtures in argon suggests that the regions identified by Mössbauer spectroscopy as containing iron–carbon interactions may also be associated with tungsten.     

个体眼模型的横向色差随外置光阑偏心和视场的变化

为了研究外界因素,如人工光阑偏心和轴外物点所引入人眼横向色差的变化规律,构建了个体眼模型。由角膜地形图计算了8只人眼视轴与光轴的夹角。依据实际测得的角膜地形图数据、人眼波像差、眼轴数据以及计算的视轴与光轴间夹角,运用ZEMAX光学设计软件构建了考虑视轴方向的个体化眼模型。基于这些眼模型,研究了外置人工光阑相对视轴偏移在中心凹附近所引入的横向色差变化规律,讨论了在420～700nm边缘横向色差随入射视场角的变化规律。研究表明,横向色差随人工光阑的偏移量线性增加,增加的速率为5.46～5.95(′)/mm,平均值为5.7(′)/mm,但8只人眼存在一定的个体差异。在鼻侧和颞侧20°视场范围内,8只人眼的横向色差平均以0.36(′)/(°)的速率随视场角增加而增加,不同个体的增长速率有所差别,变化范围为0.32～0.44(′)/(°)。另外,横向色差在长波段的变化要比短波段处缓慢。由于横向色差随外置光阑偏移和视场有较大的增长,因此,在视网膜成像系统和现代头盔系统的设计中应当考虑横向色差的影响。     

飞秒激光直写金属反射光栅的实验研究

提出了利用800 nm的飞秒激光在Ni金属表面直写反射型衍射光栅的新方法.研究了激光刻写速度、激光功率以及光栅周期等实验参数与直写出的反射光栅衍射效率的关系.在现有实验条件下,由50 fS激光脉冲单光束直写获得的Ni质金属反射光栅的一级衍射效率η为7.47%.     

基于离散四元数余弦变换的彩色图像数字水印技术

将离散四元数余弦变换(DQCT)应用于彩色图像的数字水印技术中,提出了一种在彩色图像中嵌入水印的新技术。应用四元数理论把彩色图像作为一整体进行余弦变换,在彩色宿主图像的DQCT域中实现彩色水印图像的嵌入。实验表明,该方法具有较好的抗压缩能力,对高斯噪声、椒盐噪声和缩放攻击具有较好的鲁棒性。     

CdSeS量子点的光学非线性特性研究

以Nd:YAG锁模激光器二倍频532 nm的激光作激发光,利用Z-扫描技术研究了CdSeS量子点的光学非线性特性.实验结果表明,CdSeS量子点在532 nm光激发下具有很大的非线性吸收效应,吸收光谱和荧光光谱表明,CdSeS量子点的非线性吸收效应来自于双光子吸收.与已经有报道的量子点相比较发现CdSeS量子点产生双光子吸收效应的阈值为1.36 GW/cm2,非线性折射率达10-8 esu量级,平均双光子吸收截面为25 960GM.CdSeS量子点的这些优异光学非线性特性可使其广泛地应用在生物成像、荧光标记、全光光开关及光限幅等方面.     

一种新的基于魔方变换的数字图像置乱加密算法

提出一种基于魔方变换的数字图像置乱加密算法,突破了传统的不改变图像像素值、仅通过重新排列图像像素点的位置实现图像置乱加密的方法,在三维空间上实现了对图像数据的置乱加密,打破了原有图像的所有特征.提出了一种新的密钥与魔方变化的编码对应法则,使该加密算法的加密密钥不受类型、大小的限制,具有密钥空间大的特点.仿真结果表明,该算法具有很好的加密、解密结果.     

LDA泵浦Cr4+:YAG被动调QNd:YAG激光器实验研究

采用300W准连续激光二极管阵列LDA端面泵浦Nd:YAG晶体,微柱透镜和透镜导管耦合,Cr4 :YAG可饱和吸收体被动调Q,实现调Q脉冲输出,激光腔长4.5cm,Cr4 :YAG晶体初始透过率Tcr=73.2%,泵浦能量63.48mJ,输出单脉冲激光,脉冲宽度10ns,单脉冲能量3.42mJ,输出脉冲被调制并产生明显尾脉冲现象,分析了原因,说明调制脉冲是由于空间电磁辐射干扰,Cr4 :YAG晶体的慢恢复可饱和吸收特性导致尾脉冲产生。