硫系玻璃在无热化长波红外广角镜头中的应用

设计了一种工作波段为8~12μm、有效焦距为5mm、F数为2、视场角为110°的无热化长波红外广角镜头.根据红外无热化光学设计的基本原理,用了常规红外材料硫化锌、硒化锌和硫系玻璃材料制备的六片镜片,通过合理地分配各个镜片的光焦度以及相互间空气间隔等参量,在全视场角为110°的范围内实现接近衍射极限的成像效果.为了更好地控制系统像差,设计利用了硫系玻璃易于精密模压制备非球面的优点,在两片硫系玻璃镜片上设计了3处非球面.设计结果显示:系统在-40℃~60℃的温度范围内均可实现品质良好的红外成像,光学调制函数全视场内均大于0.4,同时在110°视场角时畸变控制在5%以下;实现了在较大视场角条件下控制红外广角镜头的畸变以及系统无热化等设计要求.该系统体积紧凑、质量较轻,整体设计符合民用红外车载镜头的使用要求.     

Effect of the nucleating agent 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol on the γ phase content of propylene/ethylene copolymer

The influence of the concentration of a nucleating agent (NA), namely 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS), on the γ phase content in a propylene/ethylene copolymer was investigated by means of Differential Scanning Calorimetry (DSC), Wide-Angle X-ray Diffraction (WAXD), Small-Angle X-ray Scatter (SAXS) and Polarized Optical Microscopy (POM). It was found that the nucleated cPP showed two endothermic peaks, corresponding to the melt behaviors of α and γ crystal; both α and γ crystal forms were present in each lamella within the same spherulite; the γ phase developed on the edges of α phase lamellae rather than on the less favorable DMDBS nucleating agent; the γ content in the crystallized samples increased initially with increasing DMDBS concentration and reached a maximum, then decreased with further increment of NA concentration under the non-isothermal condition. We interpreted these results in terms of competition and deposition between α and γ crystals.     

相位光栅分离双波长宽角度光线的理论分析

使用衍射光栅的分色分光方式一般以平行光入射情况为讨论基础,对于非平行光入射的情况讨论较少.本文基于菲涅尔衍射理论和角谱理论,将球面波与平面波的衍射波场联系起来,从而在传播函数中引入角度参量,结合分数泰伯效应的理论基础,推导出双波长宽角度入射光线经相位光栅衍射后的波场分布函数,并对推导出的函数进行数值模拟,得到像面不同位置衍射波场分布.与平行光入射时的标准波场分布相比较,得到宽角度入射时的衍射波场的横向展宽量和偏移量.通过调节光栅台阶的宽度,改变衍射场的展宽和偏移,使各个单一波长的衍射波场宽度小于光栅周期的一半,从而减少双波长光衍射波场的混叠.同时本文给出波场宽度与光栅台阶宽度的变化关系,选取光栅面上多个位置作为台阶宽度的计算点,并对整个光栅的台阶宽度进行曲线拟合,得到可以使双波长宽角度入射光实现良好空间分离的光栅参量.该结果可用于各类宽角度入射光线的光谱分离场合,如双波长成像、液晶显示和液晶投影等.     

An ultra-thin dual-band wide-angle polarization-insensitive metamaterial absorber with near-unity absorbance

In this paper, a dual-band metamaterial absorber (MMA) with wide-angle and polarization-insensitivity is proposed. The MMA consists of two copper layers with a layer of FR-4 between them. And its top layer consists of a cross-shaped resonator and a square ring resonator. The calculation result demonstrates that there are two distinct absorption peaks, whose absorptivity are 99.933% at 3.8441 GHz and 99.99% at 9.1094 GHz. And its thickness is only 1.34% of the wavelength of the lowest absorption frequency. The dual-band MMA shows polarization-insensitivity for normal incident wave and shows high absorptivity in a wide incident angle for both TE and TM polarization wave. In addition, we discuss the working mechanism. The influences of main parameters on the dual-band MMA's absorption are also analyzed. The proposed ultra-thin MMA has simple structure and high absorptivity, which has many potential applications, such as thermal radiometer, detection sensor, stealth technology.     

Thermostimulated creep in amorphous polyolefins. I

The thermostimulated creep of two amorphous polyolefins having the repeating unit ─(CH₂)_mC(CH₃)2─, where m = 2 and 3, was investigated from 77° to 350°. Two relaxation processes are distinguished: a secondary relaxation is observed at 138 and 113°, respectively, for m = 2 and m = 3; a primary relaxation is found around the glass transition. These relaxations have been resolved in their elementary components. From the data acquired, the mechanical losses have been calculated and compared with data from an inverted torsional pendulum. The activation energy found for the secondary relaxation—0.26 eV at 138° K for the amorphous polyolefin with m = 2 and 0.19 eV at 113° K for the polyolefin with m = 3—confirms that this relaxation mode is associated with restricted backbone motion.     

Facile synthesis and properties of a new generation of soluble and thermally stable polyimides

A new diamine, 1,4-phenylene bis((E)-1-(4-chloro-3-aminobenzylidene) thiourea) (PCABT), containing phenylthiourea and azomethine groups was prepared from the reduction of dinitro compound, 1,4-phenylene bis((E)-1-(4-chloro-3-nitrobenzylidene)thiourea), PCNBT. The structures of resulting monomers were characterized by elemental analysis, FTIR, ¹H and ¹³C NMR techniques. Afterwards, this diamine was reacted with various aromatic dianhydrides (ODPA, BTDA and 6FDA) in glacial acetic acid to afford poly(phenylthiourea azomethine imide)s (PPTAIs) with η_inh of 1.59-1.66 dL/g, depending on the dianhydride used. The ensuing PPTAIs exhibited ample solubility in organic solvents (DMAc, DMF, DMSO and NMP) and were obtained in quantitative yields. Also, all polyimides were amorphous according to wide-angle X-ray determination. GPC measurements of polymers revealed M_w around 69,000-72,000. Moreover, thermogravimetric analyses indicated that PPTAIs were fairly stable up to 550 °C, and 10% weight loss temperatures were recorded in the range of 563-578 °C (N₂ atmosphere). Ultimately, these polyimides own high glass transition temperatures about 281-285 °C.     

The study of correction for chromatic aberrations of human eye with diffractive–refractive hybrid elements

A chromatic corrector with two refractive–diffractive hybrid elements is designed over a reasonable wide field-of-view of 7° to correct the chromatic aberrations of human eye. We investigate the performance of the corrector using several optical criteria in a comparison with the chromatic corrector with single refractive–diffractive element. Both the correctors can correct the longitudinal chromatic aberration (LCA) fairly. It is demonstrated that the chromatic corrector with single element introduces serious eccentric transverse chromatic aberration (TCA), which deteriorates the image quality at the edge field-of-view. On using the chromatic corrector with two refractive–diffractive elements, not only the LCA but also the TCA can be corrected very well. The designed chromatic corrector can be used to improve the retinal image quality and has potential application in the design of visual instruments.     

The effect of chemical treatment on the crystallinity of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were chemically treated using nitric acid solution for different time. Quantitative analysis of the crystallinity of the MWCNTs was performed by wide-angle X-ray diffraction (WAXD). The WAXD patterns were deconvoluted into the crystalline diffraction peaks and the amorphous scattering peaks. The introduction of a correction factor for the integrated peak intensity can enhance the computational accuracy of the crystallinity. With increasing the chemical treatment time, the crystallinity of MWCNTs first increases, and then decreases. When the chemical treatment time is equal to 2 h, the crystallinity of MWCNTs reaches the maximum of 85.9%. Moreover, the degree of order in the structures of chemically treated MWCNTs was further studied by thermogravimetric analysis (TGA) and high-resolution transmission electron microscopy (HRTEM). It was found that the external walls of chemically treated MWCNTs with high crystallinity consist of a series of perfectly continuous and straight graphite layers.     

Crystallization behavior of polyethers containing odd numbers of methylene spacers from the isotropic and liquid crystalline states

A series of thermotropic polyethers synthesized from 1-(4-hydroxyphenyl) - 2 - (2 - methyl - 4 - hydroxyphenyl) - ethane and α,ω-dibromo-n-alkanes with odd numbers of methylene units (MBPE-n = odd) shows monotropic mesophase behavior. In isothermal differential scanning calorimetry (DSC) experiments, two—sometimes even three—exothermic transition processes can be observed when the crystallization temperature is below the mesophase transition temperature, while only one exothermic process is present above the mesophase transition temperature. The melting behavior of the crystals grown from the mesophase and from the isotropic melt states is different. The crystals grown from the mesophase state exhibit a larger overall heat of transition and a higher transition temperature compared with those grown from the isotropic melt. This may be attributed to the molecular interfacial connections between the crystal and amorphous regions when MBPEs crystallize from the mesophase state. The difference in morphology between the crystals grown from the different states has also been studied with polarized light microscopy (PLM) and transmission electronic microscopy (TEM). The structures of the crystals grown from the different states are, however, the same, as evidenced through wide-angle X-ray diffraction (WAXD) measurements. From the banded morphology of MBPE samples observed from PLM, the defect textures observed through TEM and the results of WAXD experiments, this mesophase can be identified as a nematic liquid crystal state.     

Chain folding and the structure of nylon 6.6 spherulites

Following the assignment of the 1329 and 1224 cm^?1 infrared bands to chain-folded conformations in nylon 6.6 by Koenig et al. examination of the infrared spectra of positively birefringent and negatively birefringent spherulitic films has been made. The spectra indicate extensive regular folding in negative spherulites but fewer folds or less regular folding in the positive spherulite structure.

The assignment of the infrared fold bands to modes of vibration of the repeat unit is discussed with reference to the spectra of films with varying extents of N deuteration (normal 6.6, disordered regions deuterated, N deutero 6.6, disordered regions hydrogenated).

Electron micrographs of negative spherulites are analyzed with the infrared and previous evidence. We suggest they are built up of single-crystal lamellae of 0.2 to 0.3 μ lateral dimensions packed with a preferential orientation of the lamellae planes parallel to the radial direction but otherwise randomly oriented.