利用数值模拟研究表面增强相干反斯托克斯拉曼散射增强基底

Numerical simulation study of surface enhancement coherent anti-Stokes Raman scattering reinforced substrate

为表面增强相干反斯托克斯拉曼散射(surface enhancement coherent anti-Stokes Raman scattering,SECARS)提供具有高增强、稳定性好的等离激元增强基底是十分重要的.本文从实际出发,在理论上设计了一种新的SECARS基底,其可以利用结构自身的杂化共振与额外激发的电荷转移等离子体共振相互作用产生Fano共振,并通过调节电荷转移等离子体共振来改变Fano共振的波长位置.通过对L-色氨酸1557 cm^(-1)处的拉曼模式的数值模拟得到的数据表明,这种具有空间对称性的结构可以产生多个不依赖入射光偏振方向的高增强热点,这些热点处的信号相对于普通相干反斯托克斯拉曼散射(coherent anti-Stokes Raman scattering,CARS)信号,其增强因子普遍可以达到10^(12),最大处可达到10^(14).这种利用电荷转移等离子体来设计基底的方法可以在SECARS的实用性基底中得到应用并为其他非线性光学工艺的设计提供了新的思路.

Plasma nanostructures are of particular significance for serving as a substrate for spectroscopic detection and identification of individual molecules.By combining the excitation wavelength of the molecule with the resonance wavelength of the nanostructure,the sensitive single-molecule Raman detection can be achieved.A high and stable plasma substrate for coherent anti-Stokes Raman scattering(CARS)is very useful for developing the surface-enhanced coherent anti-Stokes Raman scattering(SECARS).In the plasma nanostructures,the strong coupling of plasmonic nanoparticles with an inter-particle gap smaller than the diameter of the individual nanoparticles results in the hybridization of the optical properties of these individual nanoparticles.There are also the charge transfer plasmons(CTP)appearing in conductive bridging nanoparticles.Their unique properties make linked nanosystems a suitable candidate for building artificial molecules,nanomotors,sensors,and other optoelectronic devices.In this work,we,starting from reality,theoretically design a new linked nanosystem SECARS substrate where Fano resonance can be generated by the plasmon hybridization(PH)model resonance and the charge transfer plasmon resonance.The introduction of charge transfer plasma improves the tunability of structural resonance.By adjusting the conductivity of the conductive junction,the wavelength of the charge transfer plasma resonance can be easily adjusted to change the wavelength position of the Fano resonance.The data obtained by numerical simulation of the Raman mode at 1557 cm^(-1) of L-tryptophan when a 1064 nm light source is used as the pump light show that this spatially symmetrical structure can generate multiple highenhancement hot spots that do not depend on the polarization direction of the incident light.Ordinary CARS signal can generally be enhanced by 10^(12),and its maximum can reach 10^(14).Due to the ultrastrong field enhancement and insensitive-to-polarization,this method of using charge transfer plasma to design a substrate can be used in the practical substrate of SECARS and provide new ideas for designing other nonlinear optical processes such as four wave mixing and stimulated Raman scattering.