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 $23\text{−}\mathrm{nm}$-thin strips of $100–500\mathrm{nm}$ widths placed on quartz and covered with index-matching oil are in excellent agreement with theoretical predictions.

Figure 1

(Color online) Scattering cross section vs wavelength for a plane $p$-polarized wave incident on a gold nano-strip of thickness $t$ and width $w$ embedded in glass. For $w=67–155$ and $479\mathrm{nm}$, and the quasistatic (QS) case, the incident wave propagates along the $y$ axis. For $w=217$ and $306\mathrm{nm}$, the incident wave propagates at 45° relative to the $x$ axis.

Figure 2

(Color online) Reflection phase versus strip thickness $t$ according to Eq. (1) for a gold nanostrip surrounded by air for various resonance orders and the wavelengths 600, 700, and $800\mathrm{nm}$.

Figure 3

(Color online) Same as in Fig. 2 but for a gold strip surrounded by glass.

Figure 4

(Color online) (a) Schematic of the experimental setup for reflection spectroscopy along with exemplary (b) SEM and (c) dark-field images from an area with $500\text{−}\mathrm{nm}$-wide and $23\text{−}\mathrm{nm}$-thick gold strip resonators on a quartz substrate.

Figure 5

(Color online) Measured and calculated scattering spectra for $17\text{−}\mathrm{nm}$-thin gold strips of different widths $w$ placed on quartz and covered by index-matching oil.

Figure 6

(Color online) Same as Fig. 5 but for gold strips of thickness $23\mathrm{nm}$.