Frequency Range Optimization for Continuous Wave Terahertz Imaging

Abstract

With shorter wavelengths than microwaves and greater penetration depth than infrared light, waves in the terahertz spectrum offer unique material testing opportunities. Terahertz technology offers non-invasive and non-destructive testing in the form of spectroscopy and imaging. The most used systems for terahertz imaging are time-domain spectroscopy systems. However, frequency domain spectroscopy systems could offer excellent frequency resolution and be more suitable for biomedical applications. Terahertz imaging based on frequency domain spectroscopy systems is slow, and suffers from frequency tuning errors. A novel one-dimensional imaging principle is presented in this paper. In addition, frequency range optimization based on convolutional neural networks and occlusion sensitivity is utilized for frequency range optimization. Frequency range optimization is used to determine the optimal frequency range for data acquisition. The optimal frequency range or bandwidth should be wide enough for effective phase detection, and should be at the intersection of several spectral footprints in the observed medium. The intersection of spectral footprints is estimated using the proposed frequency range optimization algorithm based on a convolutional neural network and occlusion sensitivity algorithm. The proposed algorithm selects the most sensitive frequency band of THz spectrum automatically, and enables very fast acquisitions for object inspection and classification.

Terahertz Radiation from High Electron Mobility Avalanche Transit Time Sources Prospective for Biomedical Spectroscopy

“…A few of the remarkable advancements in recent times leading the prospective application of THz in biomedical spectroscopy include [45,46]: THz wound and diabetic injury screening [47]; spectroscopy and imaging for cancer diagnosis [48][49][50]; a THz time-domain spectral (THz-TDS) system for biological macromolecule detection [51]; biomolecular and pathogen detection [52] and evaluation of transdermal drug delivery [53]; identification of tumor mutation in the central nervous system [54,55]; and intraoperative neurodiagnostics [56]. Further advancement in THz biophotonics, materials and instrumentation [57][58][59]; tissue imaging techniques [60][61][62]; and applied computing algorithms [63] may also open up newer frontiers in THz biomedical applications. In the current work, the possibility of a compact yet powerful solid-state THz source promising for biomedical spectroscopy applications is reported.…”

Precise measurement of refractive index in the ambient environment using continuous-wave terahertz frequency-domain spectroscopy (THz-FDS)

“…On the other hand, tunable CW terahertz frequency-domain spectroscopy (THz-FDS) based on photomixing 9) has the advantages of low cost, high power and robustness. [10][11][12] Moreover, the combination of free-space beam splitting and mechanical delay lines is no longer necessary for the coherent detection of signals in THz-FDS, which makes the full fiber integration of the spectroscopy system in the industrial pipeline possible.…”