Focusing Local Electric Field Inside and Outside Gold Nanotube by Choosing the Incident Frequency

Quasi-static calculations show that both the intensity and direction patterns of local electric field in a long gold nanotube are tunable by the incident wavelength. At surface plasmon resonance (SPR) frequencies, the maximum electric field occurs in the gold wall, and focuses along the incident polarization direction at high-energy resonance, whereas focuses perpendicular to the incident polarization direction at low-energy resonance. In the off-resonance cases, the intensity distribution may be isotropic homogeneous by choosing an intervenient frequency between the two resonances, and be focused out of the nanotube along the incident polarization direction when the wavelength is sufficiently away from the resonances. These frequency dependent focus location of local field in gold nanotube will be an effective guide for the design of optoelectronic devices and biosensors by gold nanostructures.