聚酰亚胺LB膜上液晶表面锚定的研究

通过测试光延迟研究了聚酰亚胺ＬＢ膜的光学各向异性，分析了在ＬＢ膜成膜过程中成膜分子的流动取向特性，并研究了液晶的表面锚定能，分析了ＬＢ膜上液晶的取向机制．聚酰亚胺ＬＢ膜的链段的取向程度较强摩擦情形的聚酰亚胺表面的链段取向要差．强摩擦的聚酰亚胺会比聚酰亚胺ＬＢ膜具有更好的排列液晶分子的能力．ＬＢ膜的流动取向模式使得聚酰亚胺成膜分子沿拉伸方向形成一定的有序排列，并诱导液晶分子定向排列，液晶和聚合物分子相互作用是液晶表面排列的主要动力 关键词：     

LB膜技术在液晶取向中的应用

本文以ＬＢ膜技术研究了向列相液晶的取向机理。选择了四种不同金属的可溶性酞菁化合物ＭＰｃ－Ｒ４作为取向材料，拉制成ＬＢ膜，诱导向列相正性液晶Ｅ－７。通过对菁酞ＬＢ膜的表征和液晶取向及电光性能的研究，认为液晶的取向是由分子间的相互作用力决定的。     

用于液晶取向的掺偶氮类染料的光诱导取向膜

介绍了一种使用聚酰亚胺和偶氮类染料进行液晶光诱导取向技术,深入研究了代号为SY04包含两个偶氮基团的新偶氮类染料.通过对取向膜偏振吸收光谱的分析,讨论了这种混合材料光诱导取向机理.由于聚酰亚胺良好的成膜性使得这种光诱导取向膜具有很好的稳定性,偶氮类染料的引入使得液晶表面取向更加有序,从而获得了响应快速,电光特性优良的液晶盒.这种取向膜材料同时具有很好的热稳定性及抗紫外稳定性.     

聚合温度及铁电液晶有序度对单体转化率的影响

采用琉醇和丙烯酸的混合物作为反应单体,利用红外光谱仪检测反应前后单体的C=C双键吸收峰的变化,研究了温度对单体转化率的影响。制备了单体含量为10%的聚合物稳定铁电液晶器件,研究了铁电液晶有序度对单体的影响。实验表明:随着温度的增加单体的转化率增加,随着铁电液晶有序度的增加单体的转化率增加;在铁电液晶中单体的转化率主要受有序度的影响;制备聚合物稳定铁电液晶器件最佳的聚合条件为近晶A相(SmA)下聚合。     

单体浓度对聚合物稳定铁电液晶稳定性的影响

制备了不同单体浓度的聚合物稳定铁电液晶器件,测试了震动实验和热稳定实验前后样品的排列织构、电光特性和对比度.用原子力显微镜研究了各样品的聚合物形貌,表明在器件内部形成了沿摩擦方向延伸的聚合物网络,并且随着单体含量的增加聚合物网络更加致密.由于聚合物网络体锚定的引入,使得铁电液晶分子在外力和温度场下的运动受到限制,聚合物体锚定的增强使聚合物稳定铁电液晶的稳定性也逐渐提高.实验结果表明,单体含量为4％时,聚合物稳定铁电液晶的抗震性和热稳定性良好,电光曲线为无阈值“V”字型,对比度达150∶1.     

垂直排列液晶盒中反铁电液晶TFMHxPOCBC-D2偏振红外光谱研究

本文通过偏振红外吸收光谱研究了铁电与反铁电液晶分子TFMHxPOCBC-D     

聚酰亚胺LB膜的研究：Ⅰ聚酰胺酸N,N—二甲基十八胺前聚物的LB膜

聚酰胺酸Ｎ，Ｎ－二甲基十八胺是制备本身不具备两亲性的聚酰亚胺ＬＢ膜的前聚物。合成制备了均苯四酸二酐－４，４’－二胺基二苯酸Ｎ，Ｎ－二甲基十八胺，研究了它单分子膜的各异性，比较了伯胺和叔胺膜的不同，并用低角Ｘ射线衍射研究这前聚物ＬＢ膜分子的详细排列。     

聚酰亚胺膜上液晶表面锚定强度的研究

研究了取向剂聚酰亚胺上摩擦强度与液晶的表面锚定强度的关系,分析了液晶的表面锚定强度与液晶分子表面预倾角的关系,并运用空间相互作用模型及表面沟槽理论进行了对比分析,认为液晶分子的表面排列机理主要是聚合物与液晶分子的空间相互作用力。 关键词：     

垂直排列液晶盒中反铁电液晶TFMHxPOCBC-D2偏振红外光谱研究

本文通过偏振红外吸收光谱研究了铁电与反铁电液晶分子TFMHxPOCBC-D₂(4-(trifluoromethylhexy-3-d₂ carbonyl)phenyl 4′-octyloxybiphenyl caboxylate)在垂直排列取向液晶盒中CD₂基团绕手征性烷基链转动的受阻行为.实验结果显示CD₂的偏振红外吸收在Sm-C相不同于Sm-C_A相.建立了一个CD₂转动受阻模型,在这一模型的基础上,对CD₂的偏振红外吸收进行了模拟计算,较好地解释了CD₂红外吸收在铁电和反铁电液晶相下的行为差异,得到了CD₂基团绕手征性烷基链转动受阻的结论. 关键词： 反铁电液晶 红外光谱 受阻转动     

分层蒸镀制备聚酰亚胺自支撑膜及其特性研究

 采用分层蒸镀法，在玻璃基片上依次蒸镀二氨基二苯醚（ODA）和均苯四甲酸二酐（PMDA）两种单体，然后在空气环境中对样品进行不同温度和时间的热亚胺化处理，使二者在交界面上反应生成聚酰亚胺。经加热150 ℃ 1 h然后经350 ℃ 2 h处理的样品，在脱膜后能制备出直径1.8 cm，厚度为100 nm的聚酰亚胺自支撑薄膜。用FTIR测量了自支撑薄膜的红外光谱，特征吸收峰的分析表明薄膜已基本上完全亚胺化。用原子力显微镜分析了浮法玻璃衬底上聚酰亚胺薄膜的表面形貌，结果表明以ODA作为内层制备的膜层表面更光滑平整。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.