  A metamaterial perfect absorber consisting of a tri-layer (Al/ZnS/Al)
metal-dielectric-metal system with top aluminium nano-disks is fabricated by
laser-interference lithography and lift-off processing. The metamaterial
absorber had peak resonant absorbance at 1090 nm and showed nonlinear
absorption for 600ps laser pulses at 1064 nm wavelength. A nonlinear saturation
of reflectance was measured to be dependent on the average laser power incident
and not the peak laser intensity. The nonlinear behaviour is shown to arise
from the heating due to the absorbed radiation and photo-thermal changes in the
dielectric properties of aluminium. The metamaterial absorber is seen to be
damage resistant at large laser intensities of 25 MW/cm2.
