Theoretical analysis of gold nano-strip gap plasmon resonators

Gold gap plasmon resonators consisting of two nm-thin and submicron-wide gold strips separated by a nm-thin air or quartz gap are considered. Scattering resonances and resonant fields are related to a model of resonances being due to counter-propagating gap plasmon polaritons forming standing waves. A small gap (similar to 10 nm) is found to result in small resonance peaks in scattering spectra but large electric field magnitude enhancement (similar to 20), whereas a large gap (similar to 100 nm) is found to result in more pronounced scattering peaks but smaller field enhancement. Design curves are presented that allow construction of gap plasmon resonators with any desired resonance wavelength in the range from the visible to the infrared, including telecom wavelengths. The relation between resonance wavelength and resonator width is close to being linear. The field magnitude enhancement mid between the gold strips is systematically investigated versus gap size and wavelength.