期望最大化算法近场被动定位技术研究

本文介绍了一种对近场声源的距离和方位参数的确定性最大似然估计方法。直接的对近场声源参数的最大似然估计产生了复杂的多参数优化问题,我们在实际采样数据(非完全数据)和假设数据(完全数据)等方面重新构建这个问题,最后提出运用期望最大化迭代方法获得最大似然估计。期望最大化算法将观测数据分解,然后对于最优化问题,运用有效的计算措施单独估计每个信号成分的参数。这种算法的应用性和有效性通过一定的仿真得到了验证。     

近场扫描光学显微镜及其探针技术研究新进展

对近场扫描光学显微技术(NSOM)研究与应用新进展作了概括介绍,较详细地阐述了NSOM的关键部件——探针技术的发展,并对NSOM的前景作了展望。     

Implications in the interpretation of plane-wave expansions in lossy media and the need for a generalized definition

Plane-wave expansions (PWEs) based on Fourier transform and their physical interpretation are discussed for the case of homogeneous and isotropic lossy media. Albeit being mathematically correct, standard Fourier-based definition leads to nonphysical properties, such as the absence of homogeneous plane waves, lack of dissipation along transversal directions and inaccurate identification of single plane waves. Generalizing the PWE definition using Laplace transform, which amounts to switching to complex spectral variables, is shown to solve these issues, reinstating physical consistency. This approach no longer leads to a unique PWE for a field distribution, as it allows an infinite number of equivalent definitions, implying that the interpretation of the individual components of a PWE as physical plane waves does not appear as justified. The multiplicity of the generalized definitions is illustrated by applying it to the near-field radiation of an elementary electric dipole, for different choices of Laplace cuts, showing the main differences in the generalized PWEs.     

苝聚集体随机激光的近场散射增强

本文通过物理模拟发现苝聚集体纳米粒子有很强的近场散射. 苝聚集体由异丁基取代聚倍半硅氧烷(POSS)苝(DPP)构成,其理论模拟得到的近场散射增强被实验证实. 同时,由聚集体的二硫化碳溶液激发出相干随机激光. 近场增强源自于通过化学键连接的POSS基团,相干随机激光源自于苝发射团. 本文通过分子设计发展出一种新的随机激光体系,为后续一系列交叉研究打开了大门,相关交叉研究主要涵盖无序光子学的分子设计等领域.     

Feasibility analysis of solid immersion lens-based dual-layer near-field recording optics with a numerical aperture of 1.84

A dual-layer near-field recording (NFR) optical system with a high numerical aperture (NA) of 1.84 was designed by appropriate cover and spacing layer selection, using layers with refractive indices of 2.0. The designed aplanatic imaging optics exhibited additional aberrations in the multi-layered stack, mainly due to the air-gap and spacer layer. Given optics designed only to compensate for aberrations caused by a 2-μm-thick cover-layer, a 3-μm-thick spacer layer induces 96.2 mλ_rms and 6.5 mλ_rms of spherical aberration and defocus, respectively. A complete electric field calculation analysis for the inside of the multi-layer stack verified that diffraction-limited spot quality can be ensured on the recording layer with phase-only correction. As the aberration caused by the multi-layered stack cannot be corrected perfectly, due to the high oscillation of the aberration function along the radial direction in the exit pupil, three different types of liquid crystal (LC) electrodes were considered for practical implementation. Of the three phase-correction methods, the approximate linear phase-correction method was the most tolerant of axis decenter from the optical axis, providing acceptable diffraction-limited correction performance.     

分层背景2维FDTD中斜入射平面波的引入

 对于分层介质中目标散射的时域有限差分（FDTD）计算,在分层背景中引入斜入射平面波源是一个难点。在2维Maxwell方程基础上,导出TM和TE模下含有斜入射角度的１维Maxwell方程,并用它在分层介质中连接边界上模拟斜入射平面波源,克服了分层背景时域有限差分计算斜入射平面波引入的困难。对熔石英表面覆盖薄膜的分层光学元件进行平面波斜入射时域有限差分计算结果表明,电磁波在各层内形成完好的平面波推进,验证了这种斜入射平面波添加方式的正确性。并通过对含气泡的缺陷模型的计算,来阐述这种入射波添加方式的应用。     

Optical characterization of chiral plasmonic nanostructures

Chiral plasmonic nanomaterials can have circular dichroism and optical rotatory dispersion effects orders of magnitude larger than those observed in ordinary chiral molecules. Understanding this fascinating class of materials has proved challenging and has motivated several research groups to develop entirely new experimental techniques for characterizing chirality driven optical properties. In this review, we first describe the classical method of circular dichroism which measures linear, far-field responses from an ensemble population. We then go on to describe several of the more recently developed methods to probe chiral nanostructures as they expand into the domains of non-linear, near-field, and single particle measurements including spatially and spectrally resolved techniques.     

Characterization on Modification and Biocompatibility of PCL Scaffold Prepared with Near-field Direct-writing Melt Electrospinning

In this study, orthogonal experiments were designed to explore the optimal process parameters for preparing polycaprolactone(PCL) scaffolds by the near-field direct-writing melt electrospinning(NFDWMES) technology. Based on the optimal process parameters, the PCL scaffolds with different thicknesses, gaps and structures were manufactured and the corresponding hydrophilicities were characterized. The PCL scaffolds were modified by chitosan (CS) and hyaluronic acid(HA) to improve biocompatibility and hydrophilicity. Both Fourier transform infrared spectroscopy(FTIR) analysis and antibacterial experimental results show that the chitosan and hyaluronic acid adhere to the surface of PCL scaffolds, sugges-ting that the modification plays a positive role in biocompatibility and antibacterial effect. The PCL scaffolds were then employed as a carrier to culture cells. The morphology and distribution of the cells observed by a fluorescence microscope demonstrate that the mo-dified PCL scaffolds have good biocompatibility, and the porous structure of the scaffolds is conducive to adhesion and deep growth of cells.     

近场拉曼光谱在纳米结构表征中的应用

近场拉曼光谱是近场光学领域中的新型技术,因其可对纳米结构进行光谱表征而备受科学研究者的关注。 文章从光学的角度简述了将近场光学与拉曼光谱相结合成为近场拉曼光谱的原理,介绍了近场拉曼光谱技术的优势,详细阐述了近场拉曼光谱在单壁碳纳米管、生物样品、热电晶体、染料分子等纳米结构表征中的应用,展现了近场拉曼光谱技术广阔的应用前景。