无机纳米粒子的二阶光学非线性研究进展

Study Progress in Second-Order Optical Nonlinearitis of Inorganic Nanoparticles

非相干的超瑞利散射(HRS)技术是20世纪90年代发展起来的用于测定分子发色团一阶超极化率β的有效工具。由于它与惯用的相干二次谐波发生(SHG)和电场诱导二次谐波发生(EFISHG)技术相比较,不受样品的尺寸、取向和/或电荷的限制,因此近四五年来被使用来测定无机纳米粒子的一阶超极化率,并取得了一些重要的结果。文章介绍了HRS技术的一般原理、实验装置及数据处理方法。根据目前报导的实验结果,并结合我们的工作,探讨了纳米粒子超瑞利散射的几种可能机制:表面贡献、类体相贡献、聚集体贡献、共振增强的贡献以及粒子表面静电场和溶剂场的贡献,其中特别强调了表面贡献。指出用HRS技术研究纳米粒子二阶光学非线性这一新的领域正逐步吸引越来越多的科学家的兴趣,将成为非线性光学和纳米科学交叉领域的一个热点。

Hyper-Rayleigh scattering(HRS)technique,an incoherent methodolo gy,is an effective tool developed at the beginning of the nineties for the determination of the first-order hyperpolarizabilityβvalue of molecular chro-mophores in solution or gas.Compare d with conventional coherent second harmonic generation(SHG)or with electric-field-induced SHG techni que,HRS technique is not constrained by the orientational,size,and /or charge restrictions,hence,in the past yea rs,it has been used to measure theβvalue of nanoscale particles and som e important results were obtained.In this paper,its simple principle,ex perimental setup,and data processing method are described.According to t he recent studies reported and our wo rk,some possible HRS mechanisms,such as surface contribution,bulk-like contribution,aggregate contr ibution,resonance enhancement,su rface static electric field,and solvent filed,a re explored.Especially,surface contribution is emphasized.The investigation of second-order nonlinear optical pro perties of nanoparticles with the HRS technique is an interdisciplinary field of nano-science and nonlinear optics,which is attracting more and more attentions of scientists.