Structural stability and electrical properties of AIB2-type MnB2 under high pressureStructural stability and electrical properties of AIB2-type MnB2 under high pressureStructural stability and electrical properties of AIB2-type MnB2 under high pressureStructural stability and electrical properties of AIB2-type MnB2 under high pressure

The structural stability and electrical properties of A1B2-type MnB2 were studied based on high pressure angle- dispersive x-ray diffraction, in situ electrical resistivity measured in a diamond anvil cell （DAC） and first-principles calcu- lations under high pressure. The x-ray diffraction results show that the structure of A1B2-type MnB2 remains stable up to 42.6 GPa. From the equation of state of MnB2, we obtained a bulk modulus value of 169.9~3.7 GPa with a fixed pressure derivative of 4, which indicates that A1B2-type MnB2 is a hard and incompressible material. The electrical resistance un- dergoes a transition at about 19.3 GPa, which can be explained by a transition of manganese 3d electrons from localization to delocalization under high pressure.     

灵巧型离轴三反光学系统设计

基于同轴三反射光学系统基本原理,将孔径光阑和视场适当偏心,设计了一个灵巧型多光谱离轴三反光学系统,系统焦距1 200 mm,并对设计结果进行了像质评价。实验结果表明:系统在可见波段（0.486 m ~0.656 m）80 lp/mm空间频率下MTF0.5,中波波段（3 m ~5 m）15 lp/mm空间频率下MTF0.35,全波段范围内最大RMS为2.096 m。系统中面型采用二次非球面,且整个系统仅有孔径光阑偏心,3个反射镜位置均无偏心和倾斜,降低了加工成本及装调难度。     

In-situ high pressure X-ray diffraction studies of orthoferrite SmFeO_3

The high-pressure behaviors of SmFeO3 are investigated by angle-dispersive synchrotron X-ray powder diffraction under a pressure of up to 40.3 GPa at room temperature. The crystal structure of SmFeO3 remains stable at up to the highest pressure. The different pressure coefficients of the normalized axial compressibility are obtained to be βa = 0.60 × 10-3 GPa-1,βb = 0.79 × 10-3 GPa-1, βc = 1.28 × 10-3 GPa- 1, and the bulk modulus （B0） is determined to be 293（3） GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. Furthermore, the larger compressibility of the FeO6 octahedra suggests the evolution of the orthorhombic structure towards higher symmetry configuration at high pressures.     

标准状态下氮气在0.145～2.058μm的色散特性

为了研究氮气在宽光谱范围内的色散特性,基于气体色散理论,在标准条件下(温度为293.15K,气压为101325Pa),利用二阶Sellmeier公式和最小二乘法拟合得到氮气在0.145～2.058μm波长范围内的色散公式。该公式在全波段范围内的不确定度约为2.1×10-7,与原始测量数据的准确度一致。与现有色散公式相比,该公式的适用波长范围更宽,可提供氮气在0.27～0.47μm波段更多的折射率信息,具有较广泛的适用性。通过实验测量氮气在633nm处的折射率验证了该公式的有效性。     

A Novel Tunable Dual-frequency Laser with Large Frequency Difference

This paper proposed a novel tunable dual frequency laser with large frequency difference,which used LD to pump the Nd∶YAG microchip in the end surface and put the liquid pressure on the radial direction of the crystal by a pressure-transporting thin film. As a result of the stress birefringence, there was a mode splitting phenomenon of the microchip laser longitudinal mode. Both theoretical analysis and experiments indicated that there is a directly proportional relation between the frequency difference and the pressure, so the tunable frequency difference could be obtained when the pressure was changed. A large frequency difference of about 3.4 GHz with linear tunable relation was achieved in the experiment,so it can be a practical light source for the absolute distance interferometry.     

Optical Feedback Characteristics in He-Ne Dual Frequency Lasers

Optical feedback characteristics in He-Ne dual frequency lasers are studied systematically in different feedback power ratios with a variable attenuator. Feedback power ratios vary from 0.010 up to 0.998. Five distinct regimes of self-interference effects are found and defined as regimes Ⅰ, Ⅱ,Ⅲ,Ⅳand Ⅴ. Accordingly, five optical feedback levels have been put forward in He-Ne dual frequency lasers. Strong mode competitions are observed in regimes Ⅲ and Ⅳ. In regime Ⅴ, multiple feedback effects are investigated. The basic theoretical analysis is also presented. Our results can advance the research of self-mixing interferometer and displacement sensor of He-Ne orthogonally polarized dual frequency lasers.     

一类低反射率分形膜系的设计

讨论了一类分形电磁波吸收膜层的设计.基于一种简化模型解析计算了膜系反射率,并得出了一系列选择膜层材料以降低反射率的判据.对由这些判据所选的一些理想和实际材料所构成的膜系的反射率进行了数值模拟.结果表明,符合材料判据构成的分形膜系的反射率会随分形级数的增加而逐渐降低.最低的平均反射率为0.01. 关键词： 分形 薄膜系 电磁波吸收     

载荷和纳米MoS2添加剂含量对圆形锤头-棒料的摩擦磨损特性及其机理分析

针对精密下料中圆形锤头与棒料之间弧状接触面剧烈的摩擦磨损问题,借助WTM-2E型可控气氛摩擦磨损试验仪,利用GCr15钢块-45钢柱摩擦副在纳米MoS₂添加剂质量分数为0%、0.1%、0.2%、0.3%、0.4%、0.5%和0.7%等七种润滑工况下,重点对不同载荷下摩擦磨损试验进行分析;采用扫描电子显微镜观察了GCr15钢块磨损表面形貌,采用能量色散谱仪(EDS)分析了GCr15钢块磨损表面成分,并探讨了其润滑抗磨及自修复机理. 结果表明:随着载荷增加,摩擦接触应力变大,摩擦系数和磨损量呈上升趋势,磨损表面形态由轻微磨粒磨损转变为黏着磨损. 同时加入的MoS₂添加剂的质量分数并非越高越好,摩擦系数和磨损量随MoS₂添加剂质量分数的升高呈现先减小后增大趋势,且MoS₂添加剂质量分数在0.1%~0.3%范围内时减摩抗磨效果较好. 通过对比不同润滑条件下摩擦副因摩擦磨损而产生的噪声、振动速度和温升,进一步定量确定出纳米MoS₂添加剂质量分数为0.1%时,可以最大程度地降低摩擦副的损耗.      

芴与苯并硒化二唑共聚物的电子结构和光谱性质的理论研究

用密度泛函B3LYP方法对低聚体(DEF-BSeD)n(n=1~4)[其中9,9二乙基芴(DEF)单元与苯并硒化二唑(BSeD)单元的摩尔比分别为1∶1和2∶1]进行全优化, 计算电离能(PI)、电子亲和势(EA)和能隙(ΔH-L), 在基态结构的基础上用TD-DFT和ZINDO方法计算激发能和电子吸收光谱, 并利用外推法得到高聚物的相应性质. 从外推结果看出, 随着聚合物中BSeD比例的增大, 聚合物的最低单激发能呈减小的趋势, 最大电子吸收光谱红移. 用CIS方法优化得到单体的S1激发态结构, 计算结果表明, 激发态的结构更趋近于平面构型.     

几种新型LD泵浦Nd∶YAG双频激光器

介绍了几种LD泵浦Nd∶YAG双频激光器 ,均应用双折射原理实现。一类是利用自然双折射效应 ,在激光谐振腔内加入自然双折射元件 ;另一类则是对YAG晶片加压力 ,使YAG晶片本身成为应力双折射元件。由于双折射效应使激光在谐振腔内产生偏振方向互相垂直的寻常光 (o光 )和非寻常光 (e光 )两种成分。因为o光和e光在双折射元件中有着不同的折射率 ,因此一个激光谐振腔变成了具有两个物理长度的谐振腔 ,从而产生双频激光。改变自然双折射元件或对YAG晶片施加的压力 ,可调谐频差。实验中获得 10 9Hz量级的大频差 ,合成波长可到几十毫米 ,适用于绝对距离干涉测量