随机分布的多圆孔的夫琅禾费衍射场分布研究

采用蒙特卡罗方法先对随机分布的多圆孔构成的衍射屏进行了分析计算,并与单个圆孔的衍射场进行了比较,结果表明,多圆孔的衍射场与单个小圆孔的衍射场有相同的条纹形状和条纹半径,但多圆孔衍射场的能量比单个圆孔的衍射场能量明显增加,同时场强变化不均匀,有叠加噪声的效果,在衍射艾里斑的中心处有一个强亮点.然后对大圆孔内随机分布着的小圆屏构成的衍射屏进行分析,得到了与多圆孔衍射类似的结论,这些结论与实验结果一致.     

圆形余弦光栅菲涅耳衍射场的研究

基于波前相因子判断法并考虑到圆光栅孔径的影响,揭示了圆形余弦光栅的衍射场含有3种成分,它们是均受限于圆形孔径的平面衍射波、发散球面衍射波和会聚球面衍射波;分别给出了这3种衍射场的积分表达式,进而导出了沿轴的衍射场复振幅分布的3个公式,并显示了相应的沿轴衍射场实振幅分布曲线,得到了实焦斑的横向半值线宽和轴向半值线宽公式.本研究为圆形余弦光栅用于聚焦和成像技术进一步提供了一个理论基础.     

部分偏振部分相干光光栅衍射场的偏振特性和角相关研究

为了研究部分偏振部分相干光光栅衍射场的衍射特性.利用部分偏振部分相干光的光束相干-偏振(BCP)矩阵,推导出了部分偏振部分相干光通过任意偏振光栅后,衍射场的偏振度及场中衍射级次角相关的一般解析表达式.以部分偏振的高斯-谢尔模型光束(PGSM)为例,数值分析了偏振光栅TE和TM波的复振幅透过率、入射光束的光学参量对衍射场偏振度和场中各衍射级次的角相关的影响.计算结果表明,部分相干光透过偏振光栅后的其衍射光场是一非均匀、周期变化的部分偏振相干光场;场中对称级次的角相干值对应相等,且随衍射级次序数的增大而缓慢递减至零.     

平面透射光栅的菲涅耳衍射

从标量场的菲涅耳衍射理论出发,研究了球面波入射平面透射光栅的衍射场,导出菲涅耳衍射场的复振幅分布,并得到光栅菲涅耳衍射角的计算公式．结果表明,在理想情况下菲涅耳衍射的每一级衍射波都是一个球面波;在对菲涅耳衍射角进行新的定义后,衍射角的计算仍然可以采用夫琅禾费衍射的光栅方程．     

无衍射光的干涉实验与理论分析

分析了两束无衍射光的干涉场分布形式和干涉条纹轨迹。将一束单色光入射两小孔产生的两束相干光照射轴锥镜,在轴锥镜后将产生两束无衍射光。根据单束倾斜光入射轴锥镜的无衍射理论,分析出这两束无衍射光产生的干涉场为每束无衍射光的无衍射场的线性叠加。利用零阶贝塞尔函数的零点公式,推导出两束无衍射光的干涉条纹的轨迹为双曲线。计算结果表明,干涉场中两中心的间距与两孔实际的间距和干涉场距轴锥镜的距离成正比。实验结果与理论仿真相一致。     

利用TeO2减少多模光纤出射场散斑干扰的研究

 为了减少多模光纤出射光场的散斑干扰,提出了把声光布拉格衍射效应所形成的不同衍射级耦合到多模光纤中,由于衍射级具有不同的偏振态,消弱了光场相干条件,进而在出射光场中消弱了散斑场的对比度,并通过对改变声场频率后得到的散斑场对比度的分析,证实了利用各向异性晶体TeO2能够控制散斑场对比度,改善出射场的高斯分布,得出了可以利用布拉格衍射效应减少散斑场干扰的可能性。     

菲涅耳轴上衍射场的计算

给出了一种计算菲涅耳衍射的方法,它既能比较精确地计算轴上的衍射场,也能用来近似地估算轴外的衍射场。     

线性扫频影响超短光脉冲远域衍射场分布的理论分析

本文分析了具有线性扫频高斯型超短光脉冲衍射场的能量分布,教学计算结果显示了线性扫频对衍射场的影响.通过衍射分析可以获得光脉冲的信息.     

水基磁性液体的场诱导光衍射特性的研究

设计了一套用于研究磁性液体的场诱导静态和动态光衍射特性的实验装置.通过在样品的后方放置一个适当孔径的光阑,实现了定量研究其衍射特性的目的.采用沿衍射方向移动光阑的方法定量地研究了衍射光的空间分布.设计了一个指数衰减函数用来拟合动态衍射实验的数据,获得动态衍射的特征时间.以两种不同浓度的表面包覆型水基氧化铁磁性液体样品为例,定量地实验研究了其场诱导光衍射特性与外磁场强度和样品浓度的关系.结果表明,磁性液体的场诱导结构对光的静态和动态衍射与外磁场的强度和磁性液体的浓度有关.其静态衍射与外磁场强度呈非单调的关系|其动态衍射的特征时间与外磁场的强度成反比,与磁性液体的浓度成正比.对实验中观察到的场诱导静态和动态衍射特性的物理机理进行了详细的分析.     

水基磁性液体的场诱导光衍射特性的研究

设计了一套用于研究磁性液体的场诱导静态和动态光衍射特性的实验装置.通过在样品的后方放置一个适当孔径的光阑,实现了定量研究其衍射特性的目的.采用沿衍射方向移动光阑的方法定量地研究了衍射光的空间分布.设计了一个指数衰减函数用来拟合动态衍射实验的数据,获得动态衍射的特征时间.以两种不同浓度的表面包覆型水基氧化铁磁性液体样品为例,定量地实验研究了其场诱导光衍射特性与外磁场强度和样品浓度的关系.结果表明,磁性液体的场诱导结构对光的静态和动态衍射与外磁场的强度和磁性液体的浓度有关.其静态衍射与外磁场强度呈非单调的关系;其动态衍射的特征时间与外磁场的强度成反比,与磁性液体的浓度成正比.对实验中观察到的场诱导静态和动态衍射特性的物理机理进行了详细的分析.     

First-order reversal curves of magnetic recording tapes

The interaction and its variation between magnetic grains in two kinds of magnetic recording tapes are investigated by first-order reversal curves(FORC) and the δM method.The composition and microstructure of the samples are characterised by x-ray diffraction and scanning electron microscope.The FORC diagram can provide more accurate information of the interaction and its variation,but the δM curves cannot.The positive interaction field and the large variation of the interaction field have opposite effects on the δM curve.     

Giant magnetocaloric effect in Tb5Ge2-xSi2-xMn2x compounds

The crystal structure,magnetic and magnetocaloric characteristics of the pseduo ternary compounds of Tb5Ge2 xSi2 xMn2x(0 ≤ 2x ≤ 0.1) were investigated by x-ray powder diffraction and magnetization measurements.The x-ray powder diffraction results show that all compounds preserve the monoclinic phase as the majority phase and all the synthesized compounds were observed to be ferromagnetic from magnetization measurements.Magnetic phase transitions were interpreted in terms of Landau theory.Maximum isothermal magnetic entropy change value(20.84 J.kg-1.K-1) was found for Tb5Ge1.95Si1.95Mn0.1 at around 123 K in the magnetic field change of 5 T.     

Growth temperature dependent evolutions of microstructural, optical and magnetic properties of Zn0.75Co0.25O films

Zn0.75Co0.25O films are fabricated via reactive electron beam evaporation. The influence of growth temperature on the microstructural, optical and magnetic properties of Zn0.75Co0.25O films is investigated by using x-ray diffraction, selected area electron diffraction, field emission scanning electron microscope, high resolution transmitting electron microscope, photoluminescence （PL）, field dependent and temperature dependent DC magnetization, and x-ray photoelectron spectroscopy （XPS）. It is shown that Zn0.75Co0.25O films grown at low temperatures （250-350℃） are of single-phase wurtzite structure. Films synthesized at 300 or 350℃ reveal room temperature （RT） ferromagnetism （FM）, while su for 250℃ fabricated films is found above 56 K. PL and XPS investigations show favour towards the perspective that the O-vacancy induced spin-split impurity band mechanism is responsible for the formation of RT FM of Zn0.75Co0.25O film, while the superparamagnetism of 250℃ fabricated film is attributed to the small size effect of nanoparticles in Zn0.75Co0.25O film.     

Field electron emission from bunchy flake-like nano-carbonfilms

<正>This paper reports that bunchy flake-like nano-graphite crystallite films(BNGCFs) were deposited on Si substrates by using the microwave chemical vapour deposition technique.Furthermore the BNGCFs were characterized by x-ray diffraction spectra,scanning electron microscopy,Raman spectra and field emission(FE)Ⅰ—Ⅴmeasurements,and a lowest turn-on field of 1.5 V/μm,and a high average emission current density of 30mA/cm~2 at a macroscopic electric field of 8.0 V/μm.were obtained.The J—E data did not follow the original Fowler-Nordheim(F—N) relation since they were not well represented in the F-N plot by a straight line.A model considering the F-N mechanism,and the statistic effects of FE tip structures has been applied successfully to explain all the FE data observed for E < 8.8 V/μm.     

Incommensurate-commensurate magnetic phase transition in double tungstate Li2Co(WO4)2

Magnetic susceptibility, specific heat, and neutron powder diffraction measurements have been performed on polycrystalline Li$_{2}$Co(WO$_{4}$)$_{2}$ samples. Under zero magnetic field, two successive magnetic transitions at $T_{\rm N1}\sim 9.4$ K and $T_{\rm N2}\sim 7.4$ K are observed. The magnetic ordering temperatures gradually decrease as the magnetic field increases. Neutron diffraction reveals that Li$_{2}$Co(WO$_{4}$)$_{2}$ enters an incommensurate magnetic state with a temperature dependent $\bm k$ between $T_{\rm N1}$ and $T_{\rm N2}$. The magnetic propagation vector locks-in to a commensurate value $\bm k = (1/2, 1/4, 1/4)$ below $T_{\rm N2}$. The antiferromagnetic structure is refined at 1.7 K with Co$^{2+}$ magnetic moment 2.8(1) $\mu_{\rm B}$, consistent with our first-principles calculations.     

Effect of fabrication conditions on the properties of indium tin oxide powders

This paper reports that indium tin oxide （ITO） crystalline powders are prepared by coprecipitation method. Fabrication conditions mainly as sintering temperature and Sn doping content are correlated with the phase, microstructure, infrared emissivity c and powder resistivity of indium tin oxides by means of x-ray diffraction, Fourier transform infrared, and transmission electron microscope. The optimum sintering temperature of 1350℃ and Sn doping content 6～8wt% are determined. The application of ITO in the military camouflage field is proposed.     

Compound diffractive telescope system: design, straylight analysis, and optical test

The compound diffractive telescope is a novel space optical system which combines the structure of compound eyes with diffractive optics and so it has a lighter weight, a wider field of view (FOV), a lower cost as well as looser fabrication tolerance. In this paper, the design of a compound diffractive telescope composed of one primary lens and twenty-one eyepieces is introduced. Then the influence of diffraction orders on the performance of the system is analysed. A modified phase function model of diffractive optics is proposed to analyse the modulation transfer function (MTF) curves for 0 FOV, which provides a more accurate prediction of the performance of the system. In addition, an optimized mechanism is also proposed to suppress stray light. The star image and resolution tests show that the system can achieve diffraction limit imaging within ±2 of FOV and ±4 mm of eccentricity. Finally, a series of pictures of an object are taken from different channels, and the splicing of pictures from adjacent FOVs is demonstrated. In summary, the designed system has been proved to have great potential applications.     

MgB2超导体掺Au的研究

分析不同烧结温度及时间和不同掺金量的名义组分为Mg1-xAuxB2样品的X射线衍射图后发现，很难得到单相的Mg1-xAuxB2样品，名义组分为Mg1-xAuxB2（x=1/16,2/16,0.146)的样品都是多相混合物，X射线衍射图显示主要是Au和Mg的化合物，样品的起始超导转变温度仍然由MgB2决定。     

Holographically recorded reverse-mode transmission gratings in polymer-dispersed liquid crystal cells

We have synthesized one-dimensionally structured and switchable reverse-mode transmission gratings in polymer-dispersed liquid crystalline materials by holographic exposure technique using the 540 nm wavelength from a solid-state laser. These structures offer the potential for electrically switchable diffractive optical elements, whose functionality can be switched on by applied electric fields. We present results for the diffraction efficiency (η) as functions of curing-time, intensity of the writing-beams, polarizations of the writing, as well as probe beams, and frequency of the electric field. For exposure times much shorter than the time needed for complete-cure of the grating structure, η increases upon application of the electric field; for an electric field of 14 MV/m @1.1 kHz, we observe $\frac{\Delta\eta}{\eta}\sim 1100\%$ with switching time constant of ～15 ms.     

全息聚合物弥散液晶材料衍射特性的优化

研究了影响全息聚合物弥散液晶(HPDLC)衍射效率的主要因素，分析了衍射效率与聚合物单体的选择、曝光强度、曝光时间、液晶含量及温度的依赖关系，从而找到最佳条件，使衍射特性得到优化.目前测得的最大衍射效率为802%.实验中还研究了扫描电镜(SEM)观察下HPDLC的表面形貌.