Abstract
Terahertz lens constitutes a vital component in terahertz systems, enabling high-resolution biosensing, biological imaging, and the detection of concealed details. Metasurfaces have been extensively employed in designing terahertz metalenses to mitigate the constraints of traditional bulky refractive lenses, owing to their adaptability and compact nature. Nevertheless, the high phase dispersion of their constituent units severely limits their applicability due to chromatic/spherical aberration, while the diffraction limit constrains the achievable imaging resolution. Consequently, the realization of achromatic super-resolution terahertz metalenses with a wide field of view (FOV) presents a challenging and urgently needed endeavor. In this study, we propose an innovative method for designing terahertz metalenses. The required phase distribution of the metalens is translated into a refractive index (RI) profile with a specific thickness, achieved through meticulously designed gradient metamaterials. Our designed terahertz metalens can realize achromatic super-resolution focusing with a high numerical aperture (NA) of 0.57 across the 0.2 to 0.9 THz range and is fabricated using 3D printing technology. Submillimeter features separated by approximately 0.2 mm can be resolved with high precision, such as epoxy-resin-impregnated woven glass fabric within FR4 panels and fibrous tissue on leaves, with a corresponding FOV of 900. Our approach offers a feasible and cost-effective means to obtain super-resolution achromatic terahertz metalens with a large FOV, which holds great potential for applications in non-destructive testing, biomedical imaging, and the realization of various terahertz metadevices.