Nonlinear Near-Field Optics of Fractal Thin Films

本文研究了分形薄膜中的非线性近场光学过程，即自仿射表面和二维随机金属-介电薄膜。研究的非线性光学过程包括：克尔型非线性折射和吸收、近简并四波混频以及二次谐波和高次谐波的产生。分形薄膜的集体光学激发导致“热点”，这些“热点”在空间上被远远大于斑点大小的距离分开。这些空间局部化的“热点”代表了分形膜的特征模态。计算了分形薄膜上局部（近场）非线性光谱的空间分布。通过将光子扫描隧道显微镜的尖端放置在表面的不同点并改变波长，可以在实验上获得这些光谱。得到了分形膜的局部结构和这些纳米尺度随机区域的共振频率的重要信息。通过对非线性近区场的统计分析，例如通过两点相关函数，研究分形膜不同点产生的非线性场的相位和振幅相关特性。PI的理论研究为单分子和分子尺度材料的非线性光谱学的发展做出了贡献。＊＊＊

9810183 Shalaev This proposal is concerned with nonlinear near field optical processes in fractal thin films, namely self-affine surfaces and 2d random metal-dielectric films. Nonlinear optical processes to be investigated include: Kerr-type nonlinear refraction and absorption, nearly-degenerate four wave mixing, and second and higher harmonic generation. Collective optical excitations of fractal thin films lead to "hot" spots which are separated in space by distances much larger than the spot size. These spatially localized "hot spots" represent the eigenmodes of a fractal film. Spatial distributions of the local (near-field) nonlinear spectra on a fractal thin film will be calculated. These spectra are experimentally accessible by parking a tip of a photon scanning tunneling microscope at different points on the surface and varying the wavelength. Important information are obtained about the local configurations of a fractal film and the resonance frequencies of these nm-scale random areas of the film. Phase and amplitude correlation properties of the nonlinear fields generated from different spots of a fractal film will be studied by analyzing the statistics of the nonlinear near-zone fields, e.g., through two-point correlation functions. %%% The PI's theoretical research contributes to the development of a nonlinear optical spectroscopy of single molecules and materials of dimensions on the scale of molecules. ***