金属光栅表面增强拉曼散射的偏振依赖性研究

Polarization-Dependent Surface-Enhanced Raman Scattering from Metallic Gratings

表面增强拉曼散射的机理主要来源于金属表面等离子体共振所产生的电磁场增强,因而基底的电磁特性决定了其增强的性能。本文以干涉光刻方法制作的大面积均匀性一维纳米光栅为增强基底,从实验和理论上探究其表面增强拉曼散射的偏振依赖特性。本文使用苯硫酚作为探针分子,并采用633nm和785nm两种波长作为激发光源,开展了等离子体共振与非共振状态下金属光栅表面增强拉曼光谱的偏振依赖特性实验研究,并通过时域有限差分法对光栅电磁特性进行分析。研究发现,光栅表面的电场无论是否激发表面等离子体共振,其电场随入射光偏振方向都会呈现出sin函数的规律性变化,拉曼光谱的峰值强度则呈sin2函数的变化规律;此外,表面等离子体共振会进一步加大拉曼光谱的偏振依赖性。

The main mechanism of surface enhancement Raman scattering is the enhancement of electromagnetic field generated by surface plasma resonance.In this paper,one-dimensional large area and uniform nano-grating structure was fabricated as surface-enhanced Raman scattering substrate by using the interference lithography technique.The polarization dependence of surface-enhanced Raman spectra was explored experimentally and theoretically.Benzenethiol was employed as Raman probe molecule to characterize the polarization dependence of the SERS signals on the surface of the metallic grating.Both 633 nm and 785 nm wavelengths were adopted as the excitation source to achieve the plasma resonance and nonresonant states,and SERS spectrum polarization dependence characteristic curves were obtained.The electromagnetic properties of the gold grating were analyzed by finite difference time domain.The electric field intensity profiles can be fitted by sin functions.And the intensity profiles of SERS spectra of benzenethiol were well fitted with sin^2 functions.The polarization dependence of the surface-enhanced Raman spectra has been extensively discussed experimentally and theoretically,which has a certain effect on the further refinement of the surface-enhanced Raman spectroscopy theory.