  Near perfect infrared light absorption at multi-spectral wavelengths has been
experimentally demonstrated by using multiplexed metal square plasmon resonance
structures. Optical power absorption over 95% has been observed in dual-band
metamaterial absorbers at two separate wavelengths and optical power absorption
over 92.5% has been observed in triple-band metamaterial absorbers at three
separate wavelengths. The peak absorption wavelengths are primarily determined
by the sizes of the metal squares in the multiplexed structures. Electrical
field distributions in the middle of the dielectric spacer layer were
calculated at the peak absorption wavelengths. It is shown that strong light
absorption corresponds to the local quadrupole plasmon resonance modes in the
metamaterial structures.
