Terahertz Electronics and Photonics (Professor Shen)
 

Since my appointment at the University of Liverpool in June 2007, I have made a number of progresses in the development of terahertz imaging and optical coherency tomography (OCT) technologies, in particular in the exploitation of their applications in industry and science. I have developed links across disciplines, between Electrical Engineering and Electronics, Physics, Pharmaceutical and Medical. Additionally we have strong links with the Daresbury Laboratory where we are developing new terahertz imaging modalities, supported by an EPSRC critic mass grant  which is led by Prof. Peter Weightman of Physics Department.

The terahertz (THz) region of the electromagnetic spectrum spans the frequency range between the mid-infrared and the millimetre/microwave (300 GHz – 30 THz). THz technology has advantages of being non-ionizing, non-destructive, and able to image at depth [1][2]. Traditionally the exploitation of this THz spectral region has been difficult owing to the lack of suitable source and detector. There has therefore been considerable interest in the development of THz technology. Over the last ten years or so, THz technology has advanced considerably with both THz spectroscopy and THz imaging instruments now commercially available. In the near-infrared region, optical coherence tomography (OCT) has also proven to be a non-invasive and cross-sectional imaging technique that permits, for example, three-dimensional (3D) images with micrometre resolution to be obtained from within the retina. Our researches focus at the development of novel THz imaging and OCT technologies in the context of material characterization and 3D non-destructive testing.

The principal research interests and scientific achievements include:

Terahertz devices: We demonstrated an ultra-broadband photoconductive THz antenna with a novel configuration which allows the generation and detection of ultrafast THz pulses with the highest bandwidth ever reported for photoconductive antennas [3], [4], [5]. A number of research groups have since used this technique to perform routine THz spectroscopic measurements in an extended spectral coverage of up to 8 THz. Currently we are working on more powerful and efficient THz emitters/receivers (in collaboration with Prof. Huang) [6], and also on possible energy harvesting using THz electronics (in collaboration with Prof. Hall and Prof. Huang of EEE Department) [7].

Security Applications: THz technology has the potential to make a significant impact in the security screening (e.g., detecting and identifying concealed threat objectives). We reported the first THz spectroscopy and chemical mapping of explosives ever realized using a reflection configuration [8]. This represents a significant advance toward developing a practical THz system for security screening of explosives. This work has been cited by more than 340 times since 2005, a good indication of the impact of this work.

Pharmaceutical Applications: As a collaboration between Liverpool University and TeraView Ltd. (Cambridge, UK) we performed the first thorough experimental and theoretical investigation of the use of THz pulsed imaging for non-destructive inspection of pharmaceutical tablets. Of particular significance we developed novel methods for extracting critical attributes of pharmaceutical products from the measured THz data [9]. The algorithms developed in this work have been widely used by major pharmaceutical companies and research institutes [10]–[15]. Recently through a TSB-funded project we have demonstrated further the world-first THz system for real-time online monitoring of pharmaceutical coating processes [16], [17].

Compressed Sensing: Prof. Daniel Mittleman at Rice University and Dr. Shen’s group at Liverpool University are the first two research groups who pioneered the compressed THz imaging work. In collaboration with Brunel, Cambridge, Leeds and Liverpool University, we demonstrated for the first time that both the spatial distribution and the spectral characteristics of a sample could be obtained by compressive THz pulsed imaging. Compared with conventional THz pulsed imaging, no raster scanning of the object is required, and ten times fewer THz spectra need be taken, making it ideal for real time terahertz imaging applications [18] [19].

  1. Novel OCT configuration: we have developed a high-resolution spectral domain OCT [20] [21] and a full-field time-domain OCT system [22] for analysing pharmaceutical tablet and small pellet coatings, respectively.  Recently we are collaborating with Dr. Zheng and Prof. Harding of Department of Eye and Vision Science, aiming to develop ultrasensitive OCT imaging system for the diagnosis and management of eye diseases.

Further details could be found at: https://www.liverpool.ac.uk/electrical-engineering-and-electronics/staff/yaochun-shen/

References:

[1]J. A. Zeitler and Y.-C. Shen, “Industrial Applications of Terahertz Imaging,” in Terahertz Spectroscopy and Imaging, K.-E. Peiponen, A. Zeitler, and M. Kuwata-Gonokami, Eds. Springer Berlin Heidelberg, 2013, pp. 451–489.

[2]D. Saeedkia, Handbook of Terahertz Technology for Imaging, Sensing, and Communications. Woodhead Publishing Limited, 2013.

[3]Y.-C. Shen, P. C. Upadhya, H. E. Beere, E. H. Linfield, A. G. Davies, I. S. Gregory, C. Baker, W. R. Tribe, and M. J. Evans, “Generation and detection of ultrabroadband terahertz radiation using photoconductive emitters and receivers,” Appl. Phys. Lett., vol. 85, no. 2, pp. 164–166, 2004.

[4]Y.-C. Shen, P. C. Upadhya, E. H. Linfield, H. E. Beere, and A. G. Davies, “Ultrabroadband terahertz radiation from low-temperature-grown GaAs photoconductive emitters,” Appl. Phys. Lett., vol. 83, no. 15, pp. 3117–3119, 2003.

[5]Y. C. Shen, P. C. Upadhya, E. H. Linfield, H. E. Beere, and A. G. Davies, “Terahertz generation from coherent optical phonons in a biased GaAs photoconductive emitter,” Phys. Rev. B, vol. 69, no. 23, p. 235325, Jun. 2004.

[6]N. Khiabani, Y. Huang, Y. Shen, and S. J. Boyes, “Theoretical Modeling of a Photoconductive Antenna in a Terahertz Pulsed System,” IEEE Trans. Antennas Propag., vol. 61, no. 4, pp. 1538–1546, 2013.

[7]S. Hall, I. Z. Mitrovic, N. Sedghi, Y. C. Shen, Y. Huang, and J. F. Ralph, “Harvesting Using THz Electronics,” in Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting, 2013.

[8]Y.-C. Shen, T. Lo, P. F. Taday, B. E. Cole, W. R. Tribe, and M. C. Kemp, “Detection and identification of explosives using terahertz pulsed spectroscopic imaging,” Appl. Phys. Lett., vol. 86, no. 24, pp. 241116–241116–3, 2005.

[9]Y.-C. Shen and P. F. Taday, “Development and Application of Terahertz Pulsed Imaging for Nondestructive Inspection of Pharmaceutical Tablet,” IEEE J. Sel. Top. Quantum Electron., vol. 14, no. 2, pp. 407–415, 2008.

[10]R. P. Cogdill, R. N. Forcht, Y. Shen, P. F. Taday, J. R. Creekmore, C. A. Anderson, and J. K. D. Iii, “Comparison of Terahertz Pulse Imaging and Near-Infrared Spectroscopy for Rapid, Non-Destructive Analysis of Tablet Coating Thickness and Uniformity,” J. Pharm. Innov., vol. 2, no. 1–2, pp. 29–36, Oct. 2007.

[11]R. P. Cogdill, S. M. Short, R. Forcht, Z. Shi, Y. Shen, P. F. Taday, C. A. Anderson, and J. K. Drennen, “An efficient method-development strategy for quantitative chemical imaging using terahertz pulse spectroscopy,” J. Pharm. Innov., vol. 1, no. 1, pp. 63–75, Sep. 2006.

[12]L. Ho, Y. Cuppok, S. Muschert, K. C. Gordon, M. Pepper, Y. Shen, F. Siepmann, J. Siepmann, P. F. Taday, and T. Rades, “Effects of film coating thickness and drug layer uniformity on in vitro drug release from sustained-release coated pellets: A case study using terahertz pulsed imaging,” Int. J. Pharm., vol. 382, no. 1–2, pp. 151–159, Dec. 2009.

[13]L. Ho, R. Müller, M. Römer, K. C. Gordon, J. Heinämäki, P. Kleinebudde, M. Pepper, T. Rades, Y. C. Shen, C. J. Strachan, P. F. Taday, and J. A. Zeitler, “Analysis of sustained-release tablet film coats using terahertz pulsed imaging,” J. Controlled Release, vol. 119, no. 3, pp. 253–261, Jun. 2007.

[14]L. Ho, R. Müller, K. C. Gordon, P. Kleinebudde, M. Pepper, T. Rades, Y. Shen, P. F. Taday, and J. A. Zeitler, “Monitoring the film coating unit operation and predicting drug dissolution using terahertz pulsed imaging,” J. Pharm. Sci., vol. 98, no. 12, pp. 4866–4876, 2009.

[15]L. Ho, R. Müller, C. Krüger, K. C. Gordon, P. Kleinebudde, M. Pepper, T. Rades, Y. Shen, P. F. Taday, and J. A. Zeitler, “Investigating dissolution performance critical areas on coated tablets: A case study using terahertz pulsed imaging,” J. Pharm. Sci., vol. 99, no. 1, pp. 392–402, 2010.

[16]R. K. May, M. J. Evans, S. Zhong, I. Warr, L. F. Gladden, Y. Shen, and J. A. Zeitler, “Terahertz in-line sensor for direct coating thickness measurement of individual tablets during film coating in real-time,” J. Pharm. Sci., vol. 100, no. 4, pp. 1535–1544, 2011.

[17]Y.-C. Shen, “Terahertz pulsed spectroscopy and imaging for pharmaceutical applications: A review,” Int. J. Pharm., vol. 417, no. 1–2, pp. 48–60, Sep. 2011.

[18]Y. C. Shen, L. Gan, M. Stringer, A. Burnett, K. Tych, H. Shen, J. E. Cunningham, E. P. J. Parrott, J. A. Zeitler, L. F. Gladden, E. H. Linfield, and A. G. Davies, “Terahertz pulsed spectroscopic imaging using optimized binary masks,” Appl. Phys. Lett., vol. 95, no. 23, p. 231112, Dec. 2009.

[19]H. Shen, L. Gan, N. Newman, Y. Dong, C. Li, Y. Huang, and Y. C. Shen, “Spinning disk for compressive imaging,” Opt. Lett., vol. 37, no. 1, pp. 46–48, Jan. 2012.

[20]S. Zhong, H. Shen, and Y. Shen, “Real-time monitoring of structural vibration using spectral-domain optical coherence tomography,” Opt. Lasers Eng., vol. 49, no. 1, pp. 127–131, Jan. 2011.

[21]S. Zhong, Y.-C. Shen, L. Ho, R. K. May, J. A. Zeitler, M. Evans, P. F. Taday, M. Pepper, T. Rades, K. C. Gordon, R. Müller, and P. Kleinebudde, “Non-destructive quantification of pharmaceutical tablet coatings using terahertz pulsed imaging and optical coherence tomography,” Opt. Lasers Eng., vol. 49, no. 3, pp. 361–365, Mar. 2011.

[22]C. Li, J. A. Zeitler, Y. Dong, and Y. C. Shen, “Nondestructive evaluation of Polymer Coating Structures on Pharmaceutical Pellets using Full Field Optical Coherence Tomography,” J. Pharm. Sci., 2014 (http://onlinelibrary.wiley.com/doi/10.1002/jps.23764/abstract).