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Article

Investigations on Practical Issues in Solid Immersion Lens Based Sub-Wavelength Terahertz Imaging Technique: System Stability Verification and Interference Pattern Removal

Terahertz Research Section, Electronics and Telecommunications Research Institute, Daejeon 34129, Korea
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Academic Editors: Maris Bauer and Fabian Friederich
Sensors 2021, 21(21), 6990; https://doi.org/10.3390/s21216990
Received: 2 September 2021 / Revised: 19 October 2021 / Accepted: 19 October 2021 / Published: 21 October 2021
(This article belongs to the Special Issue Terahertz and Millimeter Wave Sensing and Applications)
Terahertz (THz) imaging techniques are attractive for a wide range of applications, such as non-destructive testing, biological sensing, and security imaging. We investigate practical issues in THz imaging systems based on a solid immersion lens (SIL). The system stability in terms of longitudinal misalignment of the SIL is experimentally verified by showing that the diffraction-limited sub-wavelength beam size (0.7 λ) is maintained as long as the SIL is axially located within the depth-of-focus (~13 λ) of the objective lens. The origin of the fringe patterns, which are undesirable but inevitable in THz imaging systems that use continuous waves, is analytically studied, and a method for minimizing the interference patterns is proposed. By combining two THz images obtained at different axial positions of the object and separated by λ/4, the interference patterns are significantly reduced, and the information hidden under the interference patterns is unveiled. The broad applicability of the proposed method is demonstrated by imaging objects with different surface profiles. Our work proves that the resolution of conventional THz imaging systems can easily be enhanced by simply inserting a SIL in front of the object with high tolerance in the longitudinal misalignment and provides a method enabling THz imaging for objects with different surface profiles. View Full-Text
Keywords: terahertz; sub-wavelength imaging; interference pattern removal; contact-free measurement; non-destructive testing terahertz; sub-wavelength imaging; interference pattern removal; contact-free measurement; non-destructive testing
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MDPI and ACS Style

Choi, D.-H.; Shin, J.-H.; Lee, I.-M.; Park, K.H. Investigations on Practical Issues in Solid Immersion Lens Based Sub-Wavelength Terahertz Imaging Technique: System Stability Verification and Interference Pattern Removal. Sensors 2021, 21, 6990. https://doi.org/10.3390/s21216990

AMA Style

Choi D-H, Shin J-H, Lee I-M, Park KH. Investigations on Practical Issues in Solid Immersion Lens Based Sub-Wavelength Terahertz Imaging Technique: System Stability Verification and Interference Pattern Removal. Sensors. 2021; 21(21):6990. https://doi.org/10.3390/s21216990

Chicago/Turabian Style

Choi, Da-Hye, Jun-Hwan Shin, Il-Min Lee, and Kyung H. Park 2021. "Investigations on Practical Issues in Solid Immersion Lens Based Sub-Wavelength Terahertz Imaging Technique: System Stability Verification and Interference Pattern Removal" Sensors 21, no. 21: 6990. https://doi.org/10.3390/s21216990

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