Slow-plasmon resonant-nanostrip antennas: Analysis and demonstration

Resonant scattering by gold nanostrip antennas due to constructive interference of counterpropagating slow surface plasmon polaritons (SPPs) is analyzed, including the quasistatic limit of ultrasmall antennas, and experimentally demonstrated. The phase of slow SPP reflection by strip ends is found from scattering spectra revealing the influence of non-SPP field components. Experimental scattering spectra of gold 17- and 23-nm-thin strips of 100-500 nm widths placed on quartz and covered with index-matching oil are in excellent agreement with theoretical predictions.