Image storage based on circular-polarization holography in an azobenzene side-chain liquid-crystalline polymer

Image storage was investigated in a liquid-crystalline azobenzene polymer film based on circular-polarization holographic recording. An image was stored in pure polarization holograms using two orthogonal circularly polarized 532 nm beams and was reconstructed with a 633 nm beam. The polarization holograms showed high stability and a high diffraction efficiency of 31.8%. Moreover, the polarization holograms could convert arbitrary probe polarization state into circular polarization, and the diffraction efficiency was dependent on the probe polarization state, which was favorable for controlling the reconstructed images.     

Experimental and theoretical study of skylight polarization transmitted through Snell's window of a flat water surface

The celestial polarization pattern may be scrambled by refraction at the air-water interface. This polarization pattern was examined in shallow waters with a submersible polarimeter, and it was calculated by using land measurements ('semiempirical predictions') and models of the skylight polarization. Semiempirically predicted and measured e-vector orientations were significantly similar. Conversely, predicted percent polarization was correlated but lower than measurements. Percent polarization depended on wavelength, where at high sun altitudes maximal percent polarization generally appeared in the UV and red spectral regions. The wavelength dependency of polarization may lead to differential spectral sensitivity in polarization-sensitive animals according to time and type of activity.     

Vectorial four-wave mixing due to optical Kerr effect in polycrystalline CdTe

We study experimentally the polarization properties of the wave generated by means of degenerate four-wave mixing in polycrystalline CdTe using forward-box phase matching configuration and picosecond laser pulses with a wavelength of 1064 nm. The dependencies of the wave polarization generated due to the optical Kerr effect on the polarization combinations of the input beams are presented. We show that diffracted light polarization depends on the polarization of both recording beams, and the effect of each recording beam on the diffracted beam polarization is different depending on the mutual position of the recording beams and the probe beam. It was found that virtually any polarization of the generated beam could be obtained by proper choice of the recording and probe beam polarization. These results could make the polycrystalline media with third-order non-linearity a cheap and effective alternative to single crystals in non-linear devices for ultrafast all-optical control of polarization.     

新型偏振特性因子及其传递关系的研究

偏振遥感图像通常可以采用强度、偏振度、偏振角或HIS柱形彩色空间表征目标偏振特性.本文通过建立光束在多层介质中传递的简单模型,找到一种新型偏振特性因子.此偏振特性因子所成图像是偏振度图像和偏振角图像信息复合的结果,其实质反映了偏振光束中的线偏振光的光强相对含量及它的偏振角方向.对伪装过的车牌进行偏振成像,实验表明此偏振特性因子可以用于特定环境下的伪装辨别.     

Twilight polarization and optical depth of stratospheric aerosols over Beijing after the Pinatubo volcanic eruption

After the volcanic eruption of Mt. Pinatubo the degree of polarization of skylight during twilight over Beijing was monitored with a polarimeter aimed at the local zenith. We analyze the effect of changes in the scattering coefficient of atmospheric aerosols for the case of multiple scattering on skylight polarization at the zenith and then discuss the evolution of skylight polarization over Beijing during the posteruption period. As a reference and for comparison we also discuss the evolution of the aerosol optical depth retrieved from the combination of skylight polarization and backscattering ratio measured by the polarimeter and a lidar for the period beginning with the eruption of Mt. Pinatubo through the end of 1993. The contributions of atmospheric aerosols at different altitudes to the ground-observed twilight polarization depend on the solar zenith angle. For larger solar zenith angles, the skylight polarization is mostly sensitive to aerosol variations in the upper layer that range from 15 to 30 km. The twilight polarization at the zenith from June 1991 to mid-1994 shows different features for three periods: (1) From October 1991 to February 1992, volcanic dust traveled to mid-latitudes, and the degree of polarization decreased substantially. (2) From February 1992 to November 1993, volcanic dust was dispersed the minimum degree of polarization at the solar zenith angle of 93.5 degrees disappeared and the maximum increased. In addition, polarization for solar zenith angles less than 90 degrees also increased. (3) From November 1993 to May 1994, most of the volcanic dust had fallen off, the atmosphere was restored to the background state, and the skylight polarization approached the preeruption condition.     

316L不锈钢在海水中的阴极极化行为研究

为了探索316L不锈钢阴极保护有效控制电位,利用动电位极化曲线及恒电位极化法研究了316L不锈钢在天然海水和模拟闭塞液中的阴极极化行为,通过失重法研究了不同电位恒电位极化对316L不锈钢在模拟闭塞液中腐蚀控制的效果.研究表明:316L不锈钢在海水中适宜的阴极保护电位为-0.6～-0.9 V(vs.SCE),模拟闭塞液中...     

Three-dimensional imaging of microspheres with confocal and conventional polarization microscopes

We experimentally studied the three-dimensional imaging of the microspheres by using confocal and conventional scanning polarization microscopes. Because of the field amplitude averaging effect of the confocal system, the polarization of the detected signals is mainly parallel to the initial polarization. As a result, the signal intensity from the microspheres in the confocal polarization microscope with a crossed analyzer was found to be weaker than that in the conventional system. Based on a vector approach that takes the polarization into account and on the image formations of the two systems, theoretical expressions are given that agree well with the experimental results.     

Phase field simulations of a permeable crack parallel to the original polarization direction in a ferroelectric mono-domain

Two-dimensional phase field simulations of polarization switching-induced toughening of an electrically permeable crack parallel to the original polarization direction in a ferroelectric mono-domain were conducted based on the time-dependent Ginzburg-Landau equation. The mono-domain represented a small vicinity region of the crick tip and the crack was loaded by nominal applied mechanical and/or electrical tip fields. The simulation results show that a wing-shaped switched zone is formed forwards from the crack tip under applied loading, which is different from the backward wing-shaped switched zone for a permeable crack perpendicular to the original polarization direction. The mechanical load to induce a same size of switched zone for a crack parallel to the original polarization is much lower than that for a crack perpendicular to the original polarization direction. Consequently, the polarization switching-induced toughening for a crack parallel to the original polarization, which was characterized by the local J-integral, behaves differently from that of a permeable crack perpendicular to the original polarization direction.     

基于AOTF的高光谱偏振成像系统设计

为获得目标和场景的偏振信息,提高目标识别和地物探测的准确度,设计了基于液晶相位可变延迟器(LCVR)和声光可调滤波器(AOTF)的高光谱偏振成像探测系统。首先介绍了偏振成像探测的原理,然后给出了探测系统的结构,并对其光学系统的各元件进行了合理的参数分配,最后利用编制的信息处理软件对系统采集的高光谱偏振图像进行了处理,处理结果能够反映出目标的光谱特性和偏振特性,对于复杂背景下的目标探测与识别具有重要的应用价值。     

State-dependent pyroelectric and thermal expansion coefficients in a PZT rectangular parallelepiped after compressive loading and unloading

A poled lead titanate zirconate rectangular parallelepiped was subject to compressive stress loading and unloading. After reaching a specific polarization, stress is removed and temperature is increased. Longitudinal polarization and longitudinal and transverse strains are measured during the temperature rise. A false contribution of leakage current to measured polarization is removed. From measured polarization and strains, pyroelectric and thermal expansion coefficients are evaluated. Dependence of the two thermal properties on remnant state variables is investigated. The evolution of remnant strains with relative remnant polarization is also discussed and compared with a previous work.     

B30铜镍合金在海水中的电化学行为

B30铜镍合金具有优良的耐海水腐蚀性能,但在海水中形成的表面膜对其自身的电化学行为有影响,过去对此研究不多.采用交流阻抗、线性极化、动电位极化、循环阳极极化等方法研究了B30铜镍合金表面在海水中形成的氧化膜对其自身腐蚀电化学行为的影响,采用原子力显微镜(AFM)对氧化膜的结构进行了分析.结果表明:B30铜镍合金在海水中浸泡72 h后,表面能够生成一层完整致密的氧化膜;表面膜使B30铜镍合金在海水中的阻抗值随浸泡时间的延长先增大后减小,而且能够降低其极化电流密度以及瞬时腐蚀速率;随着浸泡时间的延长,B30铜镍合金在海水中的点蚀倾向加重.     

Storage time effect on free charge relaxation of amorphous poly (ethylene terephthalate)

Using thermally stimulated depolarization currents of PET-a electrets formed by the windowing polarization technique, the effect of the storage time previous to depolarization on the free charge relaxation, , has been studied. It was noted that the temperature at which the relaxation maximum appears increases with the storage time, whereas the intensity of the maximum decreases. This behaviour depends on both the polarization temperature and the polarizing field. It was also observed that there is a polarization temperature, the optimal polarization temperature, for which the relaxation maximum temperature does not depend on the polarizing field.     

小温差情况下温度梯度铁电材料零极化偏移现象的理论验证

采用平均场近似下的横场伊辛模型理论,引入描述铁电畸变的分布函数,同时考虑量子起伏效应,研究了温度梯度铁电材料的极化偏移特性,重点针对小温差情况下温度梯度铁电材料极化偏移消失的实验现象进行了理论验证。研究表明,温度梯度的存在导致了材料内部的极化强度的梯度分布,量子起伏效应对温度梯度铁电材料的性质有十分重要的影响,本工作关于温度梯度铁电材料极化偏移的研究结果与实验研究取得了定性一致的结论。当同时在考虑铁电畸变和量子起伏效应时,小温差情况下温度梯度铁电材料极化偏移消失的实验现象得以验证。     

Anomalous celestial polarization caused by forest fire smoke: why do some insects become visually disoriented under smoky skies?

The effects of forest fire smoke on sky polarization and animal orientation are practically unknown. Using full-sky imaging polarimetry, we therefore measured the celestial polarization pattern under a smoky sky in Fairbanks, Alaska, during the forest fire season in August 2005. It is quantitatively documented here that the celestial polarization, a sky attribute that is necessary for orientation of many polarization-sensitive animal species, above Fairbanks on 17 August 2005 was in several aspects anomalous due to the forest fire smoke: (i) The pattern of the degree of linear polarization p of the reddish smoky sky differed considerably from that of the corresponding clear blue sky. (ii) Due to the smoke, p of skylight was drastically reduced (p(max)相似文献   

Electrochemical impedance spectroscopy investigation on indium tin oxide films under cathodic polarization in NaOH solution

The electrochemical corrosion behaviors of indium tin oxide (ITO) films under the cathodic polarization in 0.1 M NaOH solution were investigated by electrochemical impedance spectroscopy. The as-received and the cathodically polarized ITO films were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction for morphological, compositional and structural studies. The results showed that ITO films underwent a corrosion process during the cathodic polarization and the main component of the corrosion products was body-centered cubic indium. The electrochemical impedance parameters were related to the effect of the cathodic polarization on the ITO specimens. The capacitance of ITO specimens increased, while the charge transfer resistance and the inductance decreased with the increase of the polarization time. The proposed mechanism indicated that the corrosion products (metallic indium) were firstly formed during the cathodic polarization and then absorbed on the surface of the ITO film. As the surface was gradually covered by indium particles, the corrosion process was suppressed.     

电极极化对铝合金应力腐蚀断裂敏感性的影响

为了探讨极化对铝合金应力腐蚀断裂(SCC)敏感性的影响,采用慢应变速率拉伸技术研究了不同恒电位极化条件下7075T6,7075T7351,7075RRA铝合金的应力腐蚀行为.结果表明,在-1 200～-735 mV(vs SCE)电位范围内,无论是阳极极化还是阴极极化,甚至弱极化,都会增加7075铝合金在3.5% NaCl溶液中的应力腐蚀断裂敏感性,无论哪一种热处理状态的7075铝合金在极化电位下的ISSRT均明显高于腐蚀电位下的ISSRT.同时,有阴极极化时ISSRT值随电极极化增强而减小,阳极极化时ISSRT 值有随电极极化增强而增大的趋势.但不同热处理状态的7075铝合金受极化电位的影响程度不同.由此认为,阳极溶解和氢效应都是导致7075铝合金应力腐蚀开裂的重要因素,电化学保护方法并不适用于7075铝合金应力腐蚀断裂的防护.     

Effect of crystal and domain orientation on the visible-light photochemical reduction of Ag on BiFeO₃

The reduction of silver from an aqueous solution on BiFeO? surfaces, activated by visible light, was investigated as a function of crystal and ferroelectric domain orientation. When excited by light with energy between 2.53 and 2.70 eV, BiFeO? photochemically reduces silver cations from solution in patterns corresponding to the underlying ferroelectric domain structure. Silver is preferentially reduced on domains with a positive polarization directed toward the surface. The amount of reduced silver depends on whether the component of the domain polarization normal to the surface is positive or negative, but is relatively insensitive to the crystal orientation. It is concluded that the ferroelectric polarization decreases electron drift to the surface in domains with a negative polarization, causing spatially selective photochemical behavior, and that the direction of the polarization is more important than the amplitude.     

Effect of temperature on polarization reversal of strontium-doped lead zirconate titanate (PSZT) ceramics

The effect of temperature on polarization reversal of strontium-doped lead zirconate titanate ceramics was studied. The piezoelectric properties viz. dielectric constant and piezoelectric coupling coefficient, were used for polarization reversal characteristic. These properties and apparent coercive field were measured during polarization reversal at different temperatures. Results indicated that at higher temperature apparent coercive field decreased. Polarization reversal and further polarization reversal was quite asymmetric. After polarization reversal, dielectric constant was found to increase at all temperatures while piezoelectric coupling coefficient increased above the temperature of polarization. The trend shown by dielectric constant indicates that at 25°C, 1·5 kV/mm field can be applied safely to this material without much compromising the properties. D.c. field of 3·0 kV/mm and 100°C temperature can be predicted as poling parameters from their effect on k_p{\bf \textit{k}}_{{\bf p}}. Apparent coercive field has shown non-linear relationship with temperature. It was of exponential decay type.     

Ferroelectric properties of ultrathin films of Nylon 11

Ferroelectric properties of ultrathin films of Nylon 11 were investigated. The thickness was in the range of 25 to 55 nm. Ferroelectric response was largely affected by thermal annealing and following cooling conditions. Thermal annealing at higher temperature followed by quenching in liquid nitrogen gave larger remanent polarization and smoother surface, whereas cooling down in an ambient atmosphere caused smaller remanent polarization and rough surface. Surface roughness strongly affected the polarization reversal and remanent polarization. Hydrogen bonding in crystal was also significantly related to the polarization reversal and thus remanent polarization.     

TGS和GTGS热释电晶体的热力学模型模拟曲线

通过热力学推导,建立了零电场下热释电晶体的极化与温度的方程。由热释电系数的定义,对热释电晶体的极化方程对温度求导,得出由热力学模型建立的热释电方程。并对热释电晶体硫酸三甘氨酸（TGS）和掺胍TGS（GLTGS）的实验曲线进行了模拟,该理论基本符合。