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关键词： 测量   法拉第效应   磁光特性   法拉第旋转镜   费尔德常数   双折射  

摘要： 为了解决随机线性双折射对光纤磁光特性测量的影响,采用旋转光纤(SF)结合法拉第旋转镜(FRM)的测量方法,研究了FRM对旋转光纤磁光特性测量的影响。首先,从理论方面研究旋转光纤与FRM的引入如何减小光纤中的随机线性双折射对磁光特性测量的影响,并搭建基于FRM的旋转光纤磁光特性测试系统。当光源波长为1310 nm时,FRM作用前的旋转光纤费尔德常数都比未旋转光纤的大,且旋转光纤的节距越短,费尔德常数越大。特别是旋转光纤的节距为1.0 mm时,其费尔德常数为0.8304 rad/(T·m),比未旋转光纤的费尔德常数[0.8029 rad/(T·m)]增大了约3.43%。当测试系统加入FRM后,不同光纤的费尔德常数测量值相较于未使用FRM的光纤费尔德常数测量值都有一定幅度的增大,尤其相比于节距为1.0 mm时的旋转光纤更进一步提高了7.50%,并且在FRM作用前后不同光纤费尔德常数测量值的均方差分别为0.99%和0.61%,说明FRM的引入提高了掺杂光纤费尔德常数的测量精度与稳定性。

关键词： 混凝土面板堆石坝   渗漏监测   温度示踪法   光纤光栅   降温曲线  

摘要： 面板开裂导致渗漏是混凝土面板堆石坝最常见的病害之一,严重时甚至会引起溃坝事故。为了准确定位混凝土面板渗漏位置,提出了基于光纤布拉格光栅(FBG)传感技术的点热源(PHS)渗漏监测方法,利用点热源(PHS)在垫层中的降温特性来进行面板渗漏监测。为验证该方法的有效性,设计了混凝土面板堆石坝渗漏监测的模型试验,考虑渗漏通道位置、数量及蓄水水位影响,分别开展了六种不同工况下的渗漏监测试验,根据PHS的降温时程曲线定义渗漏判别指标,然后利用判别指标的分布定位面板渗漏位置。试验结果表明:越靠近面板渗漏位置,得到的判别指标变化越显著,对于渗漏更为敏感。通过相邻FBG监测结果能够确定渗漏发生的范围。识别结果与实际渗漏状态吻合,验证了该方法的可行性。

关键词： Ronchi光栅检测   像差   剩余反射   条纹对比度  

摘要： 为指导大口径非球面反射镜的精磨至抛光过程的加工,设计了Ronchi光栅检测系统。采用零位补偿器替代补偿光栅的设计制作,既能用Ronchi法对粗加工过程检测,也能用于干涉仪检测;模拟Ronchi检测过程中条纹形状与对应面型像差的关系,通过判断条纹形状对加工过程进行指导;针对某600mm口径的双曲面反射镜,设计了Ronchi光栅检测系统、零位补偿系统、成像系统。分析检测系统元件剩余反射对成像结果的影响,并提出相应的解决方案。分析表明,在Ronchi光栅检测光路中,分光棱镜表面5%剩余反射相对0.1%剩余反射,像面暗条纹的照度值增量大于30倍,条纹明暗对比度下降,难以分辨;光栅剩余反射大于3%时条纹中心产生亮斑,亮斑照度与条纹照度值比大于5倍。通过优化系统结构,降低元件表面剩余反射,提高了像面条纹对比度。将Ronchi检测系统用于双曲面镜抛光过程的检测,测得双曲面粗抛光后RMS值为0.042λ,PV值为0.291λ,可有效指导非球面的精磨与粗抛光过程。

关键词： 常态化   期末考试   自我说服   竞争对手   高中   同桌  

摘要： 高中时,我的同桌是最令我胆寒的人:下午期末考试完毕,晚上他还默默去自习——我的竞争对手啊,连半天都不让人休息。我的心都要碎了。可怕之处在于,他风轻云淡,平静如水。一切发生得如此自然,不需自我说服,不需心理建设……

关键词： 激光应用  

ISBN: (纸本)9787312055164

摘要： 本书阐述了激光钠导星的特性以及大气湍流对激光钠导星的影响。根据激光钠导星的产生和波前探测的顺序，对激光的上行传输、激光与大气中间层钠原子的作用及激光钠导星光波大气传输成像进行研究，主要分析了激光钠导星的亮度特性、闪烁特性、光斑特性及其光波传输成像和回波光子数的计算等。

关键词： Terahertz waves  

摘要： Terahertz (THz) wave has broad application prospects because of its many unique properties. However, due to the relative lag in the development of related materials and devices, there are still many limitations in the practical application of terahertz technology. Metamaterials and metasurfaces can effectively manipulate the phase, amplitude, and polarization of terahertz waves, providing many new possibilities for the development of terahertz technology. One of its important functions is to reflect incident waves in non-specular directions through phase discontinuities, commonly known as generalized Snell's law. However, most of the previously reported anomalous reflection devices are relatively inefficient and have limitations in practical applications. To solve this problem, we propose a terahertz metasurface anomalous reflector that reflects normal incident light to a 40° direction without changing its polarization. We theoretically expound the idea of improving efficiency and demonstrate its effectiveness through numerical simulation. We construct a metasurface using all-dielectric materials to eliminate material losses and exploiting the coupling of different Bloch waves to provide a non-local response, the operating efficiency of the device can be increased to more than 99%. In addition, our design concept can be generalized to polarization-independent devices and could be useful for other similar devices. This work has the potential to be applied to practical terahertz devices such as terahertz lasers and terahertz cavity resonators. © 2023 Chinese Society of Astronautics. All rights reserved.

摘要： The polarisation properties of light are often used as a means of information transfer, as well as in assessing the structural and compositional properties of ma- terials. In many practical situations, however, the propagation of polarised light is impeded by random scattering, which tends to scramble the information content of the underlying fields. Theoretical study of the random scattering of light is an old, complex field of research, in which approximate, numerical methods are often favoured over exact mathematical analysis. Random matrix theory, in which systems are modelled using random scattering matrices, has uncovered universal properties of wide classes of random media, most notably in the field of quantum scattering. Despite also finding success in optics, a random matrix theory of polarised light has yet to be pursued. In this thesis we apply the notion of random matrices to develop statistical techniques for modelling the random scattering of polarised light. We present a full derivation of the symmetries of the vectorial scattering and transfer matrices that describe dielectric scattering media, including the scattering of evanescent wave components. We then consider the circular ensembles as a simple random matrix model and explore its implications for the scattering of polarised light. Moving be- yond elementary models, a rigorous, statistical theory of the scattering matrix for discrete random media is presented, and exact mathematical results are derived in certain special cases. A numerical simulation method for studying scattering matri- ces describing random media of arbitrary thickness is then developed and validated against known physical phenomena. Finally, the techniques developed within this thesis are applied to the problem of the recovery of polarisation information within light that has propagated through a random medium.

关键词： 先兆子痫   二甲双胍   扩散张量成像   认知功能  

摘要： 目的 探讨先兆子痫(PE)大鼠二甲双胍治疗前后扩散张量成像(DTI)量化指标各向异性分数(FA)值与认知功能的相关性.方法 42只孕鼠随机分为对照组、PE组和治疗组,每组2个亚组.产后10 d及1个月行水迷宫实验和MRI检查,随后取脑HE染色.使用逃避潜伏期评估认知功能,DTI测量前皮层额颞岛叶区域、后皮层枕顶叶区和海马区的FA值,将各区域FA值与逃避潜伏期进行Pearson相关分析.结果 产后10 d及1个月,PE组上述区域FA值均较对照组降低,治疗组FA值较PE组增高,除海马区外,余上述差异均有统计学意义(P＜0.05);PE组产后1个月上述区域FA值均显著低于产后10 d(P＜0.05),治疗组产后1个月海马FA值较产后10 d显著增高(P＜0.05).产后10 d及1个月,PE组潜伏期较对照组延长,治疗组较PE组缩短;PE组产后1个月潜伏期较产后10 d延长,上述差异均有统计学意义.相关性分析提示上述区域FA值和潜伏期呈显著负相关.HE染色发现PE组海马神经元变性,治疗组变性神经元数量明显减少.结论 PE大鼠产后出现FA值降低及认知功能障碍,随时间加重,二甲双胍治疗后可逆转,前皮层额颞岛叶区域、后皮层枕顶叶区及海马区的FA值与认知功能障碍指标呈显著负相关.

摘要： 中国科学技术大学高能核物理课题组与美国布鲁克海文国家实验室、山东大学等单位的联合研究团队,在STAR国际合作组中发挥主导作用,首次在高能重离子碰撞过程中以不稳定粒子——短寿命矢量介子(ρ0)为实体,实现了费米尺度的单粒子双缝干涉实验,并利用该过程的线性偏振特征观测到极化空间的干涉现象.该研究成果2023年1月4日发表于《科学进展》.