  Highly confined "spoof" surface plasmon-like (SSP) modes are theoretically
predicted to exist in a perforated metal film coated with a thin dielectric
layer. Strong modes confinement results from the additional waveguiding by the
layer. Spectral characteristics, field distribution, and lifetime of these SSPs
are tunable by the holes' size and shape. SSPs exist both above and below the
light line, offering two classes of applications: "perfect" far-field
absorption and to efficient emission into guided modes. It is experimentally
shown that these plasmon-like modes can turn thin, weakly-absorbing
semiconductor films into perfect absorbers.
