Proceedings Article | 11 March 2024
KEYWORDS: Terahertz radiation, Waveguides, Near field, Metals, Silver, Optical transmission, Near field optics, Copper, Spectroscopy, Principal component analysis
Terahertz (THz) waves possess unique abilities which drive applications in non-destructive characterization, spectroscopy, non-contact conductivity measurement, and through-packaging detection, to name a few. However, its relatively large wavelength restricts its applicability to image the subwavelength features of a material. In recent years, traditional near field imaging techniques, aperture-based, tip-assisted, etc., are being employed where the scattered near-field terahertz radiation is collected, which is not diffraction-limited, and, therefore, is able to resolve subwavelength features. In this work, we have investigated hollow-core metal waveguides (HCMWGs) made of copper and silver for their application in terahertz near field imaging. It is vital to understand the transmission characteristics of these guiding structures to deliver the terahertz power close to the sample and then collect the near-field scattered radiation. Therefore, we recorded the transmission efficiency of the HCMWGs of inner diameters 3.0 mm, 2.0 mm, and 1.5 mm using a time domain spectroscopic setup. We noted that the transmitted electric field profile was highly dependent on the positioning of the launching-lens and collecting-lens along the optical axis, and the transmission maxima showed two peaks. Furthermore, it was noted that the smaller the diameter of the HCMWG, the lesser the working distance of the collecting-lens. Using these profiles, we could design an optical arrangement for transmission-based terahertz near field imaging by employing 1.5 mm inner diameter silver hollow-core metal waveguide.
