Abstract

Tip-enhancement has become an essential technique to achieve an extremely high spatial resolution beyond the diffraction limit of the light in probe scanning microscopy [1,2]. However, the reproducibility in obtaining an extraordinary large enhancement of the electromagnetic field is not high [3]. There have been a number of reported FDTD calculations for a variety of metallic structures with different shapes, sizes, alignments and materials of particles and tips. Although intense fields have been shown as hot spots in those calculations, such high values are not necessarily reproduced in real experiments. A plausible reason comes from the fundamental nature of the resonance modes of surface plasmons that the spectral band narrows as the field intensity increases. Unlike the lasing resonator pumped with a gain medium, plasmonic enhancement effect is a linear process, thus, a strong enhancement comes with a price of spectral bandwidth, which means Raman lines can be easily detuned from the bandwidth of the plasmonic system [4].

© 2014 Japan Society of Applied Physics, Optical Society of America