Nanocomposites in Microstructures: Optical Studies

小粒子分形聚集体中的偶极共振可能局域于亚波长空间区域，从而导致局域场的增强。局部场增强，反过来，导致线性和非线性光学过程的增强。将聚集体掺杂到微腔（如液体微滴）中，由于被微腔谐振模式捕获，进一步增加了局部场。纳米粒子-微腔复合材料具有独特的特性，包括极大的线性和非线性光学敏感性，分形特征模对激发激光的频率和偏振以及微腔共振结构的依赖性强。纳米复合材料的研究将有助于深入了解形貌对光谱特性的影响。复合材料本身在光子学、信息技术、信号处理、气溶胶科学和遥感方面具有潜在的应用前景。本项目将开展各种光学效应的实验和理论研究，包括线性和非线性拉曼散射、荧光和激光，以及其他三阶过程，包括简并四波混频；其他更基础的研究将包括安德森局域化和腔量子电动力学。小颗粒的聚集体广泛存在于自然界中，也可以在实验室中制造出来。在形成过程中，许多这些聚集体形成泡沫结构，具有所谓的“尺度不变性”，也就是说，当它们在很大的尺寸范围内观察时，它们具有相同的外观。这种聚集体是“分形”的例子，包括常见的材料，如烟雾、泡沫、聚合物和DNA。该复合材料的第二组分以简单的雨滴（即小的球形液滴）为例。复合材料本身由含有分形包体的液滴组成，可能是自然形成的，也可能是特定实验室程序的结果。最近的一些实验和理论研究表明，这些复合材料具有不寻常的光学特性，这是由于每个组成部分（即分形聚集体和微液滴）都具有所谓的电磁共振。电磁共振是许多不寻常的光学现象的原因，通常会导致共振系统发出的光的放大。一般的理论观点认为复合材料应该表现出增强的共振行为，它们在信息技术、信号处理和大气监测等不同领域有许多潜在的应用。在这个项目中，pi将对这些新型复合材料进行实验和理论研究。＊＊＊

w:\awards\awards96\*.doc 9623663 Armstrong Dipolar resonances in small-particle fractal aggregates may be localized in sub-wavelength spatial regions, leading to enhanced local fields. Local field enhancements, in turn, result in the enhancement of both linear and nonlinear optical processes. Doping the aggregates into microcavities (e.g., liquid microdroplets) further increases the local fields because of trapping by mirocavity resonant modes. Nanoparticle-microcavity composites are expected to possess unique characteristics including extremely large linear and nonlinear optical susceptibilities and strong dependence of the fractal eigenmodes on the frequency and polarization of the exciting laser and on the structure of the microcavity resonances. Investigations of nanocomposite materials will provide insight into the effect of morphology on spectral properties. The composites themselves have potential applications to photonics, information technology, signal processing, aerosol science, and remote sensing. This project will carry out experimental and theoretical studies of a variety of optical effects including linear and nonlinear Raman scattering, fluorescence and lasing, and other third-order processes including degenerate four-wave mixing; other, more fundamental, studies will include Anderson localization and cavity quantum electrodynamics. %%% Aggregates of small particles are widely found in nature and may also be fabricated in the laboratory. In the process of formation many of these aggregates form frothy structures that possess so called "scale invariance", that is, they have the same appearance when viewed over a wide range of sizes. Such aggregates are examples of "fractals" and include commonly occurring, materials such as smokes, foams, polymers, and DNA. A second constituent of the composite is exempli fied by the simple raindrop (that is, a small, spherical liquid droplet). The composite material itself, consisting of liquid droplets containing fractal aggregate inclusions, may form naturally or may be the result of a specific laboratory procedure. A number of recent experimental and theoretical studies suggests that these composite materials possess unusual optical properties, resulting from the fact that each constituent (i.e., the fractal aggregate and the microdroplet) possess so-called electromagnetic resonances. Electromagnetic resonances are responsible for many unusual optical phenomena and generally lead to an amplification of the light emitted by the resonant system. General theoretical arguments suggest that the composite materials should exhibit enhanced resonance behavior, they have many potential applications to such diverse fields as information technology, signal processing, and atmospheric monitoring. In this project, the PIs will carry out both experimental and theoretical investigations of these novel composite materials. ***