High-Numerical-Aperture, 3D-Printed All-Dielectric Harmonic Diffraction Metalens in the Sub-THz Frequency Range

Abstract

Terahertz (THz) optical devices have emerged as critical tools across diverse applications, owing to the distinctive properties of THz radiation. The ability of THz waves to penetrate nonconductive materials enables numerous nondestructive testing applications, while their characteristic interaction with molecular vibrations produces unique spectral fingerprints, facilitating precise material identification and quantification. Moreover, the low photon energy of THz radiation makes it particularly suitable for biological inspection without sample damage. Despite these advantages, conventional THz devices, including emitters and detectors, remain bulky, impeding their miniaturization and integration. THz metalenses offer a promising solution by enabling wavefront control in compact, planar architectures. However, their reliance on electromagnetic diffraction introduces significant dispersion, presenting substantial challenges for implementation in the inherently broadband THz regime, which often spans multiple octaves. Herein, an advanced all-dielectric metalens operating at dual-frequency harmonics in the sub-THz regime is demonstrated. The lens, fabricated using commercial 3D printing technology, enables rapid prototyping and cost-effective manufacturing. This metalens achieves a numerical aperture of 0.86 (50 mm diameter, 15 mm focal length) at both 150 and 300 GHz. This development represents a significant advancement toward implementing higher-order metasurface elements in the THz regime.