Mixed plasmons coupling for expanding the bandwidth of near-perfect absorption at visible frequencies.

We theoretically investigate the electromagnetic response of mixed-size sub-wavelength square hole array (M-SHA) combined with thick metal layer (TML). Near-perfect absorption with bandwidth about 17nm is firstly observed. Field distribution and dispersion relationship indicate that mixed surface plasmons (M-SPs) coupling is supported by MSHA and TML. The absorption band is proved to be dominated by M-SPs coupling. (C) 2009 Optical Society of America