Electrochemically Constructed Porous Metal Rugate Filters as Polarization-independent Perfect Absorbers in the Visible-IR Regime

We propose on the numerical design and electrochemical fabrication of perfect absorbers at the visible-IR regime based on porous metal rugate filters whose porosity oscillates sinusoidally along the film thickness direction. Preliminary simulation study indicates that perfect absorption efficiencies can be achieved for variable resonance wavelengths at normal incidence in the visible-IR regime by adjusting the structural parameters, particularly by setting the initial phase of the porosity sine wave to be 0 (this finding is counter-intuitive because dielectric rugate filters are generally used to realize high reflectivity, instead of high absorption, at the resonance wavelengths). The proposed metal rugate filter design is significantly different from the main-stream approach that utilizes planar periodic metal structures built on the device surface, and is promising for realizing perfect absorption efficiency for both TE and TM polarizations. Moreover, unlike the conventional designs which usually contain an insulating dielectric spacer layer, the proposed design of perfect absorbers utilizes only metals (e.g., nickel) as the building components and thus potentially enables more functionality, e.g., high conductivity, and more applications, e.g., for absorptive electrodes.We further propose to fabricate this novel type of absorbers by combining the wellestablished solution-based techniques of electrodeposition and dealloying. The proposed fabrication method is highly compatible with various substrate geometries (e.g., cylinders) and large sample sizes and are amenable to low-cost automated manufacturing.