Highly efficient terahertz dark-field imaging system with 3D-printed components
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Date
2025
Authors
Chung, B.A.
Lees, H.
Ibrahim, M.
Headland, D.
Withayachumnankul, W.
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JPhys Photonics, 2025; 7(2):025012-1-025012-13
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Bryce Chung, Harrison Lees, Matthew Ibrahim, Daniel Headland, and Withawat Withayachumnankul
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Abstract
Non-destructive testing and evaluation of targets with low contrast and sub-wavelength features tends to be challenging. By illuminating the target off-axis, dark-field imaging techniques can resolve diffracted or scattered features that are typically challenging to discern with conventional bright-field imaging, which relies on specular reflection exclusively. Traditional dark-field methods achieve off-axis illumination by blocking the central portion of the incident beam, but this unfortunately incurs significant power losses of up to 99%. This level of power loss is unfavorable at terahertz frequencies where source power is relatively scarce. To address this, we propose a terahertz dark-field imaging system that makes use of a double axicon beam expander to create an annular beam, which is then focused down upon the target through an objective. The system permits simultaneous bright- and dark-field imaging in reflection without modifying the optical train, making greater use of raster scan time while achieving an average transmission efficiency of 33.15% and bright-field spatial resolution of 0.391 lp mm‾¹ The proposed dark-field imaging system is able to enhance the detection of fine features such as growth rings in wood, superficial imperfections on bulk materials, and defects in fiberglass. This approach to achieve dark-field imaging will be valuable for biomedical imaging at the terahertz range that harbors interesting molecular vibration activities.
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© 2025 The Author(s). Published by IOP Publishing Ltd. Original Content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.