Thermally Induced Nonlinear Optical Absorption in Metamaterial Perfect Absorbers

TL;DR

This study demonstrates a metamaterial perfect absorber with nonlinear optical properties induced by heating, showing power-dependent saturation and high damage resistance at high laser intensities.

Contribution

It introduces a novel tri-layer metamaterial absorber with nonlinear optical absorption caused by thermal effects, fabricated using laser lithography.

Findings

Peak absorbance at 1090 nm

Nonlinear absorption depends on average power

Resistant to damage at 25 MW/cm2

Abstract

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.