近场光学中的分子动力学研究以及在生物医学中的应用(摘要)

近年来 ,国际学术界正在利用光与分子间的相互作用 ,积极地展开生物学、医学诊断等领域的研究 .人们试图利用光的特性对生物分子的光机能特性进行系统的研究 ,从中掌握其规律 ,应用到生物医学和医学诊断等领域 .尤其是在对生物分子 (如生物代谢分子、免疫分子和 DNA遗传基因等 )的检测和医学诊断过程中 ,怎样有效地提高检测灵敏度、简化繁琐的操作过程始终是光学、分子生物学和生物医学等交叉学科领域中的重要课题 .“近场光学中的分子动力学研究以及在生物医学中的应用”是以光学应用为中心 ,结合物理学、化学和生物学等学科展开的基础和应用研究 .该研究以光、纳米和生物分子三者间相互作用的基础研究为背景 ,从理论和实验上论证了纳米分散系中生物分子与金属纳米粒子相互作用过程以及系统静电平衡机理和近场中分子动力学现象之间的关系 ;光与金属纳米微粒子相互作用过程中纳米近场现象以及纳米近场的能量分布规律 ;生物分子在光、纳米近场作用下的分子动力学增强散射的机理以及分子动力学增强共鸣散射的规律 .同时 ,本文提出了纳米近场中的生物医学诊断新方法 :“纳米分散系中的近红外免疫反应动力学增强分光法”、“纳米分散系中的生化学免疫反应动力学共鸣增强分光法”以及“DNA分子检测方法”     

光纤探针型近场光镊光强分布特性的数值模拟

光纤探针型近场光镊是近场光学领域中的新型技术,因其可对纳米尺度微粒直接进行捕获和操纵而受到广泛关注,其光纤探针尖端的近场分布特性影响着纳米粒子捕获及操纵的成败探针金属膜外侧电磁场由光波在针尖小孔处衍射而成,根据夫朗和费衍射公式分析了圆形纳米小孔的光波衍射图样,运用时域有限差分法（FDTD）研究了均匀平面波垂直入射于镀膜光纤探针的近场分布,比较了不同锥角、不同出射孔径、不同金属膜厚度及不同入射波长的近场分布情况,并对不同情况下的通光效率进行了分析。通过对各参数的计算与比较,结果表明,当锥角越大、孔径越大、镀合适膜厚并且入射波长越小时,探针尖端的出射光强越大并具有较大的通光效率     

中科院力学所建成纳米检测光学测试系统

“纳米检测光学测试系统”由光谱椭偏仪（Spec Ellipsometer）和近场光学显微镜（SNOM）组成，前者以相敏和光谱的优势为二维纳米材料、多层纳米介质和生物分子膜层的定量光谱分析提供了高灵敏和高精度的检测手段；后者的光探针提供了表征纳米尺度微观光学性质和无扰动探测柔性生物分子及其相互作用的能力，两者的有机结合提供了一种跨尺度光学检测平台。     

近场光镊与AFM探针复合的光阱力分析

本文针对纳米材料的纳米操作,提出了一种复合激光近场光镊与AFM探针进行纳米操作的方法,并基于动量守恒原理,采用三维时域有限差分方法建立了该方案中激光近场对纳米微粒的作用力模型,分析了各轴向光阱力的分布情况,讨论了两探针间距离、针尖材料的电导率、入射平面光场的偏振方向、入射角和波长等参数对近场光阱力的影响.结果表明:位于...     

纳米尺度铁电畴的扫描力显微镜成像研究进展

扫描力显微镜(SFM)作为一种新型的超分辨率近场扫描探针显微仪器正日益受到各学科领域的高度重视.在铁电材料领域,SFM是开展纳米尺度铁电畴结构成像、纳米尺度畴结构控制及纳米尺度微区的铁电性、介电性、压电性等特性研究的潜在的强有力的研究工具.本文就纳米尺度铁电畴的扫描力显微镜的成像原理的研究进展作一综述.     

我国纳米标准样品研究进展

纳米科技的迅猛发展促进了纳米测量技术的创新并对其不断提出更高的要求.在纳米尺度上对物质的结构、光、电、磁、力等物理化学性质进行测量时易受外界因素的干扰,而纳米标准物质/标准样品的应用能够在纳米测量技术的不确定性评估、验证新测量技术的可靠性等方面发挥重要作用.本文对我国所研制的、具有国际水平的纳米尺度测量用和功能特性纳米标准物质/标准样品的研究进展进行了扼要介绍.     

蝴蝶结形天线和天线阵列在纳米领域的应用

纳米天线具有广阔的前景,在介绍蝴蝶结形纳米天线和纳米天线阵列的基本构造和工作原理的基础上,综述其在多个科技前沿领域的应用。     

一种2.4GHz印刷单极天线的电磁辐射特性研究

建立了2.4 GHz单极天线的电磁辐射特性仿真模型,分析了天线的远场辐射方向图、辐射效率、实际增益等性能参数特性,研究了天线长度和高度与电磁辐射的关系.根据仿真的远场辐射特性与近场的对应关系设计了印刷单极天线,实测了其近场辐射特性.仿真和实验结果表明:所设计的天线具有最优的电磁辐射特性,为实际2.4 GHz天线设计提供了理论依据和实验指导.     

扫描近场光学显微技术在半导体材料表征领域应用的研究进展

半导体材料及其光电器件如激光器、探测器以及高速微波器件有着广阔的应用前景。半导体材料的结构和缺陷特性对器件性能起着至关重要的影响,然而对材料进行纳米尺度下的检测、表征无论是理论上还是技术和设备上都需要深入研究和发展,因此扫描近场光学显微技术在半导体材料表征领域有着无可替代的地位。扫描近场光学显微技术突破了传统光学显微技术的衍射分辨率极限的限制,具有超高空间分辨率、超高探测灵敏度等特点,并且是一种非接触性探测,具有无损伤性。简要介绍了扫描近场光学显微镜的原理及在半导体材料研究中的应用,包括量子阱结构中的位错及缺陷的表征,半导体器件的表面复合速率及扩散长度的纳米表征,以及半导体薄膜中的缺陷分布的检测。探讨了目前相关研究领域存在的主要问题,并对其发展趋势和前景进行了展望。     

我国首例飞秒时间分辨近场光学系统成功实现

北京大学物理学院张家森教授等人在今年6月出版的《物理学报》上，发表了题为“飞秒时间分辨近场光学系统实现及其应用”的论文。这是国内首例实现飞秒光脉冲和近场光学显微镜相结合，成功实现了三维空间加一维时间的四维高分辨光谱，从而为研究介观尺度下的超快物理过程提供了有力的工具。在国际上，     

Near-field photochemical imaging of noble metal nanostructures

The sub-diffraction imaging of the optical near-field in nanostructures, based on a photochemical technique, is reported. A photosensitive azobenzene-dye polymer is spin coated onto lithographic structures and is subsequently irradiated with laser light. Photoinduced mass transport creates topographic modifications at the polymer film surface that are then measured with atomic force microscopy (AFM). The AFM images correlate with rigorous theoretical calculations of the near-field intensities for a range of different nanostructures and illumination polarizations. This approach is a first step toward additional methods for resolving confined optical near fields, which can augment scanning probe methodologies for high spatial resolution of optical near fields.     

Electrically connected resonant optical antennas

Electrically connected resonant optical antennas hold promise for the realization of highly efficient nanoscale electro-plasmonic devices that rely on a combination of electric fields and local near-field intensity enhancement. Here we demonstrate the feasibility of such a concept by attaching leads to the arms of a two-wire antenna at positions of minimal near-field intensity with negligible influence on the antenna resonance. White-light scattering experiments in accordance with simulations show that the optical tunability of connected antennas is fully retained. Analysis of the electric properties demonstrates that in the antenna gaps direct current (DC) electric fields of 10(8) V/m can consistently be achieved and maintained over extended periods of time without noticeable damage.     

Ultrashort pulse propagation in near-field periodic diffractive structures by use of rigorous coupled-wave analysis

We present a method for near-field analysis of ultrashort optical pulse propagation in periodic structures-including subwavelength and resonant grating structures-based on the integration of Fourier spectrum decomposition and rigorous coupled-wave analysis (RCWA). We discuss the spectral decomposition, including considerations for computational efficiency, the application of the RCWA method to compute the internal and external fields of the structure, and the synthesis of the resulting fields to obtain the time-domain solution. We apply this tool to the analysis of two photonic structures: (1) a nanostructured polarization-selective mirror that exhibits the desired broadband performance characteristics when operated at the design wavelength but yields strongly diminished polarization selectivity and modulation of the pulse envelope at an offset wave-length and (2) a two-mode coupled waveguide structure that produces from one incident pulse two transmitted pulses whose temporal separation depends on the waveguide geometry. In both examples, we apply our new modeling tool to investigate the near fields and find that near-field effects are critical in determining the performance characteristics of nanostructured devices. Furthermore, detailed observation and understanding of near-field phenomena in nanostructures may be applied to the design of novel photonic devices.     

Visualization of localized intense optical fields in single gold-nanoparticle assemblies and ultrasensitive Raman active sites

We demonstrate visualization of localized intense electromagnetic fields in real space in well-tailored dimeric and trimeric gold nanospheres by using near-field optical techniques. With two-photon induced luminescence and Raman measurements, we show that the electric field is confined at an interstitial site in the aggregate. We also demonstrate optical switching operations for the electric-field localized sites in the trimer structure.     

Modal approximation for the electromagnetic field of a near-field optical probe

A formalism is given in which the optical field generated by a near-field optical aperture is described as an analytic expansion over a complete set of optical modes. This vectoral solution preserves the divergent behavior of the near field and the dipolar nature of the far field. Numerical calculation of the fields requires only evaluation of a well behaved, one-dimensional integral. The formalism is directly applicable to experiments in near-field scanning optical microscopy when relatively flat samples are evaluated.     

Field localization in very small aperture lasers studied by apertureless near-field microscopy

Localized surface plasmon polaritons (SSPs) have been observed on very small aperture lasers using apertureless near-field microscopy. Fields around multiple apertures are shown to result from interferences of SPP point sources at each aperture and optical fields. The near-field optical pattern around a single aperture indicates the interference of SPPs with their scattered counterparts. Near-field measurements also confirmed a preferred orientation of the rectangular aperture waveguide for the signal localization in very small aperture lasers.     

Adiabatic nanofocusing scattering-type optical nanoscopy of individual gold nanoparticles

We explore imaging of local electromagnetic fields in the vicinity of metallic nanoparticles using a grating-coupled scattering-type near-field scanning optical microscope. In this microscope, propagating surface plasmon polariton wavepackets are launched onto smooth gold tapers where they are adiabatically focused toward the nanometer-sized taper apex. We report two-dimensional raster-scanned optical images showing pronounced near-field contrast and demonstrating sub-30 nm resolution imaging of localized surface plasmon polariton fields of spherical and elliptical nanoparticles. By comparison to three-dimensional finite-difference time domain simulations, we conclude that virtually background-free near-field imaging is achieved. The microscope combines deep subwavelength resolution, high local field intensities and a straightforward imaging contrast, making it interesting for a variety of applications in linear and nonlinear nanospectroscopy.     

Field enhancement in apertureless near-field scanning optical microscopy.

The near field of an apertureless near-field scanning optical microscopy probe is investigated with a multiple-multipole technique to obtain optical fields in the vicinity of a silicon probe tip and a glass substrate. The results demonstrate that electric field enhancements of >15 relative to the incident fields can be achieved near a silicon tip, implying intensity enhancements of several orders of magnitude. This enhancement arises both from the antenna effect of the elongated probe and from a proximity effect when the probe is near the substrate surface and its image dipoles play a role.     

Diffraction by a subwavelength-sized aperture in a metal plane.

We present an experimental study on the diffraction of light by an aperture small compared with the wavelength. The aperture is illuminated by laser light guided in a metal-clad tapered optical fiber. We investigate different orientations of the aperture in the plane: normal to the cleaved plane, oblique to the cleaved plane, and off-center. We measure the far-field, two-dimensional intensity distributions of the diffracted light as functions of angle coordinates theta and phi in a full half-space for various polarization states and analyze the patterns by using low-order multipole fields. We also examine the near- and far-field effects of placing small periodic corrugations near the aperture, focusing on the role of surface-wave excitations. We measure the near-field intensity distributions near the aperture with a near-field scanning optical microscope and discuss their relation to the far-field diffracted fields.     

Photocurrent mapping of near-field optical antenna resonances

An increasing number of photonics applications make use of nanoscale optical antennas that exhibit a strong, resonant interaction with photons of a specific frequency. The resonant properties of such antennas are conventionally characterized by far-field light-scattering techniques. However, many applications require quantitative knowledge of the near-field behaviour, and existing local field measurement techniques provide only relative, rather than absolute, data. Here, we demonstrate a photodetector platform that uses a silicon-on-insulator substrate to spectrally and spatially map the absolute values of enhanced fields near any type of optical antenna by transducing local electric fields into photocurrent. We are able to quantify the resonant optical and materials properties of nanoscale (～50?nm) and wavelength-scale (～1?μm) metallic antennas as well as high-refractive-index semiconductor antennas. The data agree well with light-scattering measurements, full-field simulations and intuitive resonator models.