Tracking novelty filter at 780 nm based on a photorefractive polymer in a two-beam coupling geometry

We have constructed an all-optical tracking novelty filter based on the dynamic holographic properties of an efficient and fast infrared-sensitive photorefractive polymer. The photorefractive polymer was used in a two-beam coupling geometry. The polymer had a gain coefficient of 175 cm(-1) at a wavelength of 780 nm and an applied field of 72 V/mum. In contrast to what has been observed in photorefractive crystals, the gain coefficient and the filter contrast are largely independent of the writing beam's intensity ratio. We show images of a swinging pendulum observed through the novelty filter.     

光折变聚合物材料的研究进展

与无机光折变晶体相比,光折变聚合物材料具有非线性光学系数大,响应时间快,成本低廉,制备灵活等优点,成为近代研究的热点。综述了光折变聚合物材料的发展状况,并分析了当前工作所面临的问题及发展前景。     

Refractive index of polycrystalline submicrometer polymer thin films: Thickness dependence

Dielectric films used in insulating applications are becoming consistently thinner, hence the thickness of thin and ultathin films is an important design parameter. There exists a need for characterizing and understanding the thickness dependence of properties of films. The refractive index for low dielectric polytetrafluoroethylene crystalline submicrometer thin films is investigated by using an optical spectrometer coupled with a hot stage to monitor their thickness-dependent behavior. It is demonstrated that the refractive index has a strong dependence on film thickness, which can be related to the microstructure and morphology of the film as characterized by Fourier transform infrared spectroscopy and scanning electron microscopy.     

Creep of polymer composites

A model incorporating a modified thermal activation theory is presented to model and predict creep of polymer composites. Results are presented of the successful application of this model to predict creep of a unidirectional, continuous-carbon-fiber-reinforced polymer composite (AS4/3501-6) and its epoxy matrix, over a wide range of stress (10–80% of ultimate tensile strength) and temperature (295–433 K). From an analysis of model parameters, it is concluded that the reinforcing carbon fibers do not alter the creep mechanism but do alter the creep behavior of the epoxy matrix, resulting in reductions in creep rate and in the magnitude of creep.     

Influence of geometry on polychromatic speckle contrast

Understanding speckle behavior is very important in speckle metrology application. The contrast of a polychromatic speckle depends not only on surface roughness and the coherence length of a light source, as shown in previous works, but also on optical geometry. We applied the Fresnel approach of diffraction theory for the free-space geometry and derived a simple analytical relationship between contrast, coherence length, size of illuminated spot, and distances between source, object, and observation plane. The effect of contrast reduction is found to be significant for low-coherence light sources.     

Digital holographic data storage in a high-performance photorefractive polymer composite

Binary information in the form of a 256 x 256 pixel array has been stored holographically within a polymeric photorefractive composite of 130-mum thickness. Devices used consisted of 55-wt. % organic chromophore 1-(2?-ethylhexyloxy)-2, 5-dimethyl-4-(4?nitrophenylazo) benzene and up to 11.2-wt. % 2, 4, 7-trinitro-9-fluorenone (TNF) dispersed within a poly(N-vinyl carbazole) matrix. In a degenerate four-wave mixing arrangement, the refractive-index modulation and speed were 10(-3) and 200 ms, respectively. The high TNF concentration leads to short digital hologram recording times of 2 s without detriment in optical quality. Although not yet optimized, a figure of merit, M#, for holographic storage in this composite has been measured to be 0.017, and this is estimated to reach 0.18 in a revised experimental geometry.     

Novel optical photorefractive storage-retrieval system using speckle coding technique in beam-fanning geometry

Abstract

An encoding technique based on speckle random patterns as carrier together with the beam-fanning concept is introduced to realize photo-refractive optical volume holographic memory. The set-up is based on beam-fanning geometry employing a single input beam in a BaTiO₃ crystal. Retrieval of information from this kind of memory system is very sensitive to code matching. Therefore, in the case of multiple storage, the cross-talk is minimized. The preliminary experimental results are presented with their possible applications in increasing the information storage capacity of volume holographic memories, with resultant reduced cross-talk. A dual-channel optical processor has also been realized wherein object information together with its contrast reversed version are obtained at the output channels simultaneously.     

晶须/聚合物基复合材料的研究

综述了钛酸钾晶须、硼酸铝晶须、氧化锌晶须及有机晶须等在改性聚合物基复合材料中的研究概况,分析了这几种晶须在改性热塑性树脂基体的机械性能、热性能、摩擦磨损方面的应用,并讨论了影响复合材料性能的主要因素,提出了复合材料制备中存在的主要问题,及复合材料的制备工艺对晶须的表面改性研究是这一领域中的重要研究方向。     

凹凸棒/聚合物复合材料研究进展

本文综述了国内外凹凸棒/聚合物复合材料研究进展,指出了存在的问题,展望了凹凸棒/聚合物复合材料应用前景,并分析了以后需要深入研究的方向.     

聚合物复合材料摩擦学研究进展

综述了聚合物复合材料的摩擦学研究概况,分析了不同填充材料及其含量、纤维填充材料方向及环境等因素对聚合物复合材料摩擦学性能的影响,指出不同填充材料对提高基体耐磨性的影响不同,且其提高基体耐磨性的机理也不同。     

Thermal diffusivity of antifriction polymer composites

We have studied the thermal diffusivity of a series of polymer composites based on poly(2,6-dimethyl-1,4-phenyleneoxide) (PDPO) and filled with copper and aluminum powders, SiC and TiO₂ whiskers, and comminuted carbon, poly(amidobenzimidazole) (PABI), and glass fibers. An increase in the thermal diffusivity of PDPO upon the introduction of a filler is explained by the formation of boundary layers in the polymer matrix near the filler particles, where the polymer molecules are oriented parallel to the particle surface. The boundary layer thickness varies from 1 to 60 μm, depending on the filler type. It is established that the thermal diffusivity of the composite exponentially decreases with increasing mean distance between particles of the filler.     

聚合物基导电复合材料研究进展

本文介绍了聚合物基导电复合材料的种类、用途及导电机理。并对碳系填料填充聚合物基导电复合材料及金属系填料填充聚合物基导电复合材料的研究进展进行了综述 ,最后展望了聚合物基导电复合材料的发展趋势。     

Angular dependence of hygroelasticity in unidirectional glass-epoxy composites

Swelling and hygroelasticity of unidirectional glass fibre-reinforced epoxy composites in boiling water is studied with respect to the angle between the direction of orientation and the direction of measured dimensional change. The results are expressed in terms of the dependence of of a hygroelasticity coefficient. A very good agreement is observed between the experimental results and the theoretical equation, already verified in the case of the angular dependence of the coefficient of thermal expansion. This is taken as additional support for the analogy between thermoelastic and hygroelastic behaviour in composites. The experimental longitudinal and transverse hygroelasticity coefficients are found to be different from predictions based on Schapery's equation. However, it is shown that these equations can produce possible valid estimates of _L and _T provided the mechanical properties of the swollen constituent materials are used.     

聚合物基石墨烯纳米复合材料的研究进展

综述了聚合物基石墨烯及改性石墨烯纳米复合材料的研究进展.添加少量的石墨烯就可以显著提聚合物材料的各方面性能,因此,近年来石墨烯得到了学术界和工业界的高度关注,石墨烯、氧化石墨烯的改性,以及聚合物基石墨烯纳米复合材料被广泛研究.通过广泛的文献阅读对聚合物基石墨烯纳米复合材料的结构、制备方法以及性能进行了深入探讨.     

Time-dependent damage in carbon fibre-reinforced polymer composites

Time-dependent damage (matrix cracks) evolution in AS4/3501-6 cross-ply laminates was studied using constant strain rate and constant stress tests. First ply failure stress and strain as well as the matrix crack density at a given stress level were found to be strongly dependent on strain rate. Matrix crack density increased with creep time at a constant stress level. The compliance and creep rate of the laminate increased in the presence of these cracks. These results emphasize the importance of the knowledge of time-dependent damage evolution in a lamina/laminate of a polymer composite for reliable prediction of creep and creep rupture.