Plasmon-polariton nano-strip resonators: from visible to infra-red.

Dispersion of the resonant properties exhibited by silver and gold nano-strips in a wide range of wavelengths is considered. The tunability and Q-factor of scattering resonances as well as the field enhancement achieved at strip terminations are analyzed in the wavelength range from visible to near infrared (400-1700 nm), confirming that the resonant behaviour is dominated by dispersion properties of short-range surface-plasmon polaritons (SR-SPPs) propagating along the strip. It is found that, while the Q-factor decreases for longer wavelengths due to the SR-SPP dispersion curve moving closer to the light line, the field enhancement depending also on the metal susceptibility magnitude remains largely unaffected. The results obtained are also used to estimate the phase change involved in the SR-SPP reflection by strip terminations.