Compact broadband thermal absorbers based on plasmonic fractal metasurfaces

The ability to efficiently absorb thermal radiation within a small material volume is crucial for the realization of compact and high-spatial resolution thermal imagers. Here, we propose and experimentally demonstrate a compact plasmonic metasurface for broadband absorption in the 6-14 μm wavelength range. As opposed to previous works, our metasurface leverages strongly localized electromagnetic modes to achieve high absorption within a compact form factor. We numerically investigate the spectral response of finite arrays of fractals and show that the absorption enhancement provided by arrays with greater than 6 × 6 fractals covering a total area of only 30 × 30 μm² is similar to that of an infinitely periodic array. Furthermore, we experimentally validate our metasurface's absorption enhancement and demonstrate a good qualitative agreement between the measured and simulated spectral responses. Owing to its ability to achieve broadband absorption enhancement in a compact footprint, our metasurface provides new avenues, to the best of our knowledge, for the realization of next-generation infrared sensors and bolometers.