Theoretical Localized Electric Field Enhancement in Tip-Enhanced Spectroscopy Using Multi-Order Radially Polarized Modes
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Multi-order radially polarized modes (RPMs), including Bessel-Gaussian, Gaussian, Super Gaussian, and multi-order hollow Gaussian are respectively utilized as the illumination laser to achieve tip-enhanced spectroscopy (TES). Based on the vector diffraction theory and finite difference time domain (FDTD) analysis, we achieve the optimization of RPM illuminated TES system, including the focal spot size, focal depth, and electric field enhancement factor, in which the focal spot size of 5th order hollow Gaussian RPM is smallest (0.54λ) and the focusing depth of super Gaussian RPM is longest (4.71λ). Specially, it is found that the multi-order hollow Gaussian RPM illuminated TES system with the tip cone angle of 45° reveals better focusing ability and 40~60-fold electric field enhancement factor compared to the linearly polarized mode (LPM) illuminated TES system. These results will supply a useful reference for spectral signal enhancement of TES system.
KeywordsRadially polarized mode (RPM) Tip-enhanced spectroscopy (TES) Finite difference time domain (FDTD) Electric field enhancement factor
This work was supported by National Natural Science Foundation of China grants (Nos. 61575069, 61475048, 61275015).
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