Terahertz Super-Resolution Imaging Based on Subwavelength Metallic Grating

With the ability to penetrate to the most nonpolarized materials, terahertz (THz) imaging technologies show great potentials when it comes to nondestructive testing and biomedical sensing. But the resolutions of conventional THz imaging systems are constrained by the diffraction limit. To overcome this, evanescent harmonics decaying in space must be enhanced or transformed into propagating harmonics for far-field super-resolution imaging. Here, we demonstrate that the far-field super-resolution imaging in a broad THz frequency range can be realized by an ultrathin fan-shaped metallic grating. The rigorous mode-expansion theory is used to analyze the transmission of both propagating and evanescent harmonics inside the grating. We also find that a flat subwavelength metallic grating working in canalization regime has similar performance as a negative-index superlens. Both the near-field and far-field superlenses are experimentally verified by scaled models.