Flat surface-plasmon-polariton bands and resonant optical absorption on short-pitch metal gratings

The dispersion curves of surface plasmon polaritons (SPP's) on short-pitch metal gratings consisting of an array of narrow Gaussian grooves are calcul ated. Very flat SPP bands (large band gaps) are observed in the frequency r egion where the electromagnetic wavelength is much larger than the grating pitch and grating depth. These flat SPP bands originate from the coupled SP P modes localized in the narrow grating grooves. The interaction between SP P modes and free radiation broadens the SPP modes inside the light line and also leads to strong anticrossings wherever the flat SPP bands cross the l ight line. Excitation of the SPP modes on these zero-order gratings by inci dent electromagnetic radiation may result in strong resonant absorption. Th e line shape of the resonant absorption is explained in terms of the radiat ive broadening and thermal broadening of the SPP modes. [S0163-1829(99)0261 9-3].