Figure 3.

Experimental and modeled extinction cross sections of single particle (A), dimer (B), and tetramer chains (C): the spectra in the lower frames were modeled via GMMT for corresponding chain types consisting of 10 repeat units each. Blue curves in the experimental spectra illustrate the nongrating case for transversal polarization. FDTD modeled surface charge images of a single particle chain (D): the upper plot (1) features the dipolar transversal mode D (electric polarization vector E perpendicular to particle line, wave vector k perpendicular to particle line). The lower plot highlights the longitudinal subradiant and superradiant modes (2, 3). Black lines indicate the surface charge density integrated along the particle chain and perpendicular to it, respectively. Modeled surface charge images of a dimer chain (E): the left graph shows the transversal modes, namely, a dipolar D (5) and a quadrupolar Q_T coupling mode (4). The right graph displays the longitudinal quadrupolar coupling mode Q_L (6) and the radiant longitudinal modes (7, 8). The surface charge intensities were adjusted for better clarity.