High Resolution Terahertz (THz) Imaging

• Published in: Optik (Stuttgart) 2024-11, Vol.315, p.172002, Article 172002
• Main Authors: Aalam, Uzair, Singh, Khushboo, Bandyopadhyay, Aparajita, Sengupta, Amartya
• Format: Article
• Language: English
• Subjects: Near field imaging; Optical design; Spectroscopy; Subwavelength resolution; Terahertz
• ISSN: 0030-4026
• DOI: 10.1016/j.ijleo.2024.172002

Terahertz (THz) imaging is essential for non-contact and non-destructive testing due to its ability to penetrate numerous materials. Typically, the sample is raster-scanned through the beam waist of a confocal optical setup to generate an image in a single-pixel detection scheme. However, the spatial resolution achieved using such imaging configurations remains no less than millimeters, restricting the application of THz imaging. Here in this work, a simple hollow-core metal waveguide (HCMWG) based terahertz imaging setup has been designed and implemented in transmission configuration to record THz hyperspectral images of a sample. The sample is kept in the near-field range of the HCMWG to exploit the THz electric field confinement of the guided mode toward attaining high-resolution imaging. The THz images are acquired by raster scanning the sample in front of the HCMWG output aperture using a single-pixel detection setup. Additionally, spectroscopic sensing using the same setup has been shown by extracting the absorption spectrum of a chemical compound. Further, a plant leaf is used as a sample to demonstrate the applicability of this technique, where the highly resolved transmitted THz image is acquired using the proposed setup. This image is compared with the image recorded using a conventional confocal lens-based THz optical setup. The results show that the technique can resolve subwavelength features (approx. 0.8λ) of the sample under study while preserving spectroscopic information.