Engineering the Complex-Valued Constitutive Parameters of Metamaterials for Perfect Absorption

We theoretically studied how to directly engineer the constitutive parameters of metamaterials for perfect absorbers of electromagnetic waves. As an example, we numerically investigated the necessary refractive index n and extinction coefficient k and the relative permittivity epsilon and permeability mu of a metamaterial anti-reflection layer, which could cancel the reflection from a hydrogenated amorphous silicon (alpha-Si:H) thin film on a metal substrate, within the visible wavelength range from 300 to 800 nm. We found that the metamaterial anti-reflection layer should have a negative refractive index (n < 0) for short-wavelength visible light but have a positive refractive index (n > 0) for long-wavelength visible light. The relative permittivity epsilon and permeability mu could be fitted by the Lorentz model, which exhibited electric and magnetic resonances, respectively.