A Telecentric Offset Reflective Imaging System (TORIS) for Terahertz Imaging and Spectroscopy

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Abstract
Terahertz (THz) imaging has emerged as a promising technology in medical diagnostics, thanks to non-ionizing radiation and the high sensitivity of THz waves to water content. However, traditional THz imaging systems face challenges such as slow mechanical scanning, limited field-of-view, and poor telecentricity. To address these limitations, we present the telecentric offset reflective imaging system, a novel dual-mirror scanning design optimized for high-speed, distortion-free imaging. Utilizing a telecentric $f-\theta$ lens and ray-tracing and physical optics simulations, the system achieves uniform resolution across a 50×50 mm2 field of view without mechanical translation stages. The system demonstrates its capability through broadband spectral imaging of a USAF resolution test target across WR-2.2 (325 - 500 GHz) and WR-1.5 (500 - 700 GHz) rectangular waveguide frequency bands, achieving consistent beam focus and minimal distortion, with maximum deviation of 2.7$^{\circ }$ from normal incidence and beam waist of 2.1$\lambda$ at the edge of the field of view in WR- 1.5 frequency band. Additionally, the system's ability to monitor hydration dynamics is validated by imaging wet tissue paper, illustrating its sensitivity to temporal changes in water content. Further, in vivo imaging of human skin after capsaicin patch application reveals localized hydration variations influenced by biochemical responses and adhesive patch removal. These results confirm the scanner's potential for real-time hydration sensing and dermatological assessments. By providing high-resolution, real-time THz imaging, TORIS establishes a new standard in THz-based spectroscopy and imaging, with applications spanning clinical diagnostics, wound assessment, and material characterization.
Funding Information
  • Research Council of Finland (333576)

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