Reflecting gratings with narrow grooves exhibit multiple electromagnetic modes. Using a simple setup, surface plasmon (SP), cavity mode (CM) resonance shift, surface-enhanced fluorescence (SEF), and surface-enhanced Raman scattering signals can be measured, thus forming a multimodal sensing or imaging system. The nature of these modes is first analyzed using dispersion curves as a function of the wavelength, thickness, and period and then confirmed experimentally. For a thin (20 nm) enough grating, the resonant modes are shown to be mainly attributed to SP excitation. Increasing the grating thickness allows the excitation of CMs, and more importantly, coupling between the two resonant modes can take place under certain conditions, leading to a change in the sign of the radius of curvature of the CM branch near the SP wavelength. Field distribution calculations show an agreement with the dispersion curve analysis expressing the nature of the three mode field. Additionally, the SP wavelength was shown to separate between the cavity and diffraction mode branches. The resonant modes can be controlled by tuning the grating parameters and are shown to be spread over a wide spectral range. Experimental verification (sensing in the visible and infrared ranges and SEF experiments) of the observed phenomena is performed on a 154 nm thick silver grating with 1050 nm period fabricated using electron beam lithography. Multimodal systems are important to provide as much as possible information on the measured samples, such as the concentration of analytes and characterization of cells and tissue.

中文翻译：

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设计用于多模式传感的反射光栅的共振模式

具有窄槽的反射光栅表现出多种电磁模式。使用简单的设置，可以测量表面等离子体激元（SP），腔模（CM）共振位移，表面增强的荧光（SEF）和表面增强的拉曼散射信号，从而形成多模态传感或成像系统。首先使用色散曲线作为波长，厚度和周期的函数分析这些模式的性质，然后进行实验确认。对于足够薄（20 nm）的光栅，共振模式主要表现为SP激发。增大光栅厚度可以激发CM，更重要的是，两个谐振模式之间的耦合可以在某些条件下发生，从而导致SP波长附近CM支路的曲率半径符号发生变化。场分布计算表明与色散曲线分析的一致性，表示了三模场的性质。另外，显示出SP波长在腔和衍射模分支之间是分开的。谐振模式可以通过调整光栅参数来控制，并显示在很宽的光谱范围内。对观察到的现象的实验验证（在可见光和红外范围内进行感应以及SEF实验）是在154 nm厚的银光栅上进行的，该银光栅的周期为1050 nm，使用电子束光刻技术制造。多峰系统对于在被测样品上提供尽可能多的信息非常重要，例如分析物的浓度以及细胞和组织的特征。