Optical limiting by nonlinear tuning of resonance in metamaterial absorbers

Metamaterial resonant absorbers (MRA) have intense local field enhancements that can be used to elicit large nonlinear responses. An MRA, composed of gold disks separated by a ZnS thin film from an underlying gold layer, shows optical limiting for the reflectivity of 8 ps pulses at 1064 nm due to the Kerr nonlinearity of gold and ZnS. Fluorescence from multiphoton absorption due to large fields localized in the ZnS layer is measured, and the effective χ⁽³⁾ of the layer is enhanced by 3 orders of magnitude compared to bare ZnS thin films. Self-consistent nonlinear electromagnetic simulations confirm that the nonlinear absorption is caused by a shift of the resonance with increasing intensity.