Asian Journal of Physics Vol 32, Nos 5 – 8 (2023) 253-264

A brief introduction of THz interferometry, confocal, and digital holography

Min Wan
School of Electrical and Electronic Engineering
College of Architecture and Engineering, University College Dublin, Belfield, Dublin 4, Ireland.
Dedicated in memory of Prof John Sheridan

The THz imaging plays an important role in developing of THz applications, e.g., security check, biomedical imaging, and non-destructive inspection. THz instrumentation has improved significantly in recent decades making real time broadband THz imaging possible. In this paper, special attention has been paid to several THz imaging techniques using optical engineering principles: (a) a high-resolution, high-precision THz interferometry system; (b) implementation and calibration of a continuous wave THz transmission confocal (3D) imaging system; (c) continuous wave THz in-line digital holographic system with homodyne and heterodyne detection. Modelling, characterization, and data processing are discussed. We provide perspectives on THz technological challenges and its prospects. © Anita Publications. All rights reserved.
Keywords: Terahertz, Imaging, Interferometry, Confocal, Digital Holography.

Peer Review Information
Method: Single- anonymous; Screened for Plagiarism? Yes
Buy this Article in Print © Anita Publications. All rights reserve


  1. Bründermann E, Hübers H.-W, Kimmitt M F, Terahertz Techniques, Springer, 2012.
  2. Lee S, Principles of Terahertz science and technology, Springer Science & Business Media, 2009.
  3. Wei J, Olaya D, Karasik B S, Pereverzev S V, Sergeev A V, Gershenson M E, Ultrasensitive hot-electron nanobolometers for terahertz astrophysics, Nat Nanotechnol, 3(2008)496–500.
  4. Zhi C, Ma X, Zhang B, Zhang Y, Niu Z, Kuang N, Chen W, Li L, Li S, A survey on terahertz communications, China Commun, 16(2019)1–35.
  5. Gong A, Qiu Y, Chen X, Zhao Z, Xia L, Shao Y, Biomedical applications of terahertz technology, Appl Spectrosc Rev, 55(2020)418–438.
  6. Feng H, An D, Tu H, Bu W, Wang W, Zhang Y, Zhang H, Meng X, Wei W, Gao B, Wu S, A passive video-rate terahertz human body imager with real-time calibration for security applications, Appl Phys B, 126(2020)143;
  7. Wietzke S, Jördens C, Krumbholz N, Baudrit B, Bastian M, Koch M, Terahertz imaging: a new non-destructive technique for the quality control of plastic weld joints, Journal of the European Optical Society-Rapid Publications, 1–5 (2007) 07013; doi. 10.2971/jeos.2007.07013.
  8. Anton S S, Jackson J B, Bakunov M I, Menu M, Mourou G A, Terahertz time-domain imaging of hidden defects in wooden artworks: application to a Russian icon painting, Appl Opt, 53(2014)1033–1038.
  9. Pavlov G, Hübers H W, Riemann H, Zhukavin R K, Orlova E E, Shastin V N, Terahertz optically pumped Si: Sb laser, J Appl Phys, 92(2022)5632–5634.
  10. Demers J R, Logan R T, Brown E R, An optically integrated coherent frequency domain THz spectrometer with signal-to-noise ratio up to 80 dB, Microwave Photonics 92–95 (2007).
  11. Williams B S, Terahertz quantum-cascade lasers, Nat Photonics, 1(2007)517–525.
  12. Starikov E, Shiktorov P, Gruzinskis V, Physical mechanisms for terahertz generation, Mater Sci Forum, 297 (1999)271–278.
  13. Bhan R K, Saxena R S, Jalwania C R, Lomash S K, Uncooled infrared microbolometer arrays and their characterisation techniques, Def Sci J, 59(2009)580–589.
  14. Nguyen D T, Simoens F, Ouvrier-Buffet J L, Meilhan J, Coutaz J L, Broadband THz uncooled antenna-coupled microbolometer array—electromagnetic design, simulations and measurements, IEEE Trans Terahertz Sci Technol, 2(2012)299–305.
  15. Fujiwara M, Hirao T, Kawada M, Shibai H, Matsuura S, Kaneda H, Patrashin M, Nakagawa T, Development of a gallium-doped germanium far-infrared photoconductor direct hybrid two-dimensional array, Appl Opt, 42(2003) 2166–2173.
  16. Komiyama S, Single-photon detectors in the terahertz range, IEEE J Sel Top, 17(2010)54–66.
  17. Sizov F, Rogalski A, THz detectors, Prog Quantum Electron, 34(2010)278–347.s
  18. Tauk R, Teppe F, Boubanga S, Coquillat D, Knap W, Meziani Y M, Gallon C, Boeuf F, Skotnicki T, Fenouillet-Beranger C, Plasma wave detection of terahertz radiation by silicon field effects transistors: Responsivity and noise equivalent power, Appl Phys Letts, 89(2006)253511;
  19. Wan M, Yuan H, Čibiraitė D, Healy J J, Roskos H G, Sheridan J T, Terahertz spectrum detection based on interferometry, Digital Holography & 3-D Imaging 2019, Th3A.40 (2019).
  20. Deninger A J, Göbel T, Schönherr D, Kinder T, Roggenbuck A, Köberle M, Lison F, Müller-Wirts T, Meissner P, Precisely tunable continuous-wave terahertz source with interferometric frequency control, Rev Sci Instrum, 79,  (2008) 044702:
  21. Salhi M A, Pupeza I, Koch M, Confocal THz laser microscope, J Infrared Millim Terahertz Waves, 31(2010)358–366.
  22. Zinov’ev N N, Andrianov A V, Confocal terahertz imaging, Appl Phys Lett, 95(2009)011114;
  23. de Cumis U S, Xu J, Masini L, Degl’Innocenti R, Pingue P, Beltram F, Tredicucci A, Vitiello M S, Benedetti P A, Beere H E, Ritchie D A, Terahertz confocal microscopy with a quantum cascade laser source, Opt Express, 20(2012)21924–21931.
  24. Ciano C, Flammini M, Giliberti V, Calvani P, DelRe E, Talarico F, Torre M, Missori M, Ortolani M, Confocal Imaging at 0.3 THz with depth resolution of a painted wood artwork for the identification of buried thin metal foils, IEEE Trans. Terahertz Sci Technol, 8(2018)390–396.
  25. Wan M, Yuan H, Healy J J,  Sheridan J T, Terahertz confocal imaging: Polarization and sectioning characteristics, Opt Lasers Eng, 387(2020)169–201.
  26. Wan M, Healy J J, Sheridan J T, Terahertz phase imaging and biomedical applications, Opt Laser Technol, 122(2020)105859;
  27. Wang D, Ma D, Li K, Zhang Y, Zhao J, Wang Y, Rong L, Dynamic full-field reflective index distribution measurements using total internal reflection terahertz digital holography, Photonics Res, 10(2022)289–296.
  28. Petrov N V, Perraud J, Chopard A, Guillet J, Smolyanskaya O A, Mounaix P, Terahertz phase retrieval imaging in reflection, Opt Lett, 45(2020)4168–4171.
  29. Yuan H, Wan M, Lisauskas A, Sheridan J T, Roskos H G, 300-GHz holography with heterodyne detection, in Digital Holography and Three-Dimensional Imaging 2019, OSA Technical Digest, Th3A.21, (2019).
  30. Wan W, Yuan H, Čibiraitė D, Cassidy D, Lisauskas A, Healy J J, Roskos H G, Krozer V, Sheridan J T, Terahertz quantitative metrology using 300 GHz in-line digital holography, Proc SPIE 11030, Holography: Advances and Modern Trends VI, 110300R (2019).
  31. Zdanevicius J, Bauer M, Boppel S, Palenskis V, Lisauskas A, Krozer V, Roskos H G, Camera for high-speed THz imaging, J Infrared Milli Terahz Wave, 36(2015)986–997