Mesoscale lens design impact on sub-wavelength terahertz imaging resolution

Abstract

[EN]Terahertz (THz) technology has garnered significant interest due to its unique capability to penetrate non-metallic materials and deliver detailed spectral data, making it highly adaptable for applications such as medical imaging, security screening, quality assurance, and high-speed communications [1]. However, conventional THz imaging systems often face limitations in spatial resolution due to the diffraction limit imposed by their relative long wavelengths. This constraint poses a significant challenge in developing practical THz imaging and detection systems for real-world use [2]. To address these limitations, various methods to enhance THz detection have been reported [3]. One particularly promising approach is the so-called terajet effect [4-9], which employs mesoscale dielectric particles, with dimensions comparable to the wavelength, to focus THz waves beyond the diffraction limit. This method is akin to the photonic nanojet effect observed in the visible spectrum but adapted for THz frequencies [6]. The terajet effect creates a tightly focused, high-intensity beam that significantly enhances the localization of the electromagnetic field [4]. By concentrating THz beams into sub-wavelength regions, this effect not only improves field localization but also boosts detector sensitivity, offering a potential solution to the resolution challenges of traditional THz systems. Previous research has primarily focused on simple geometries like spheres [7] and cuboids [8], while these studies have explored a particular lens geometry, a systematic experimental comparison of different shapes of lenses across multiple frequencies has not been explored yet. This report aims to address that gap by systematically studying the impact of lens shape and size on the terajet effect by fabricating and testing PTFE lenses of various geometries at frequencies of 0.15 THz and 0.3 THz. Our findings suggest that optimizing THz imaging and detection systems requires tailored lens designs, as there is no one-size-fits-all solution. This work provides valuable insights into enhancing THz imaging and detection through strategic lens design.