We demonstrate that a self-complementary checkerboard-like metasurface worksas a broadband coherent perfect absorber (CPA) when symmetrically illuminatedby two counter-propagating incident waves. A theoretical analysis based on waveinterference and results of numerical simulations of the proposed metasurfaceare provided. In addition, we experimentally demonstrate the proposed CPA inthe terahertz regime by using a time-domain spectroscopy technique. We observethat the metasurface can work as a CPA below its lowest diffraction frequency.The size of the absorptive areas of the proposed CPA can be much smaller thanthe incident wavelength. Unlike conventional CPAs, the presented onesimultaneously achieves the broadband operation and energy concentration ofelectromagnetic waves at the deep-subwavelength scale.
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