Abstract-Total Internal Reflection Geometry: Exploiting Total Internal Reflection Geometry for Terahertz Devices and Enhanced Sample Characterization

Qiushuo Sun, Xuequan Chen, Xudong Liu, Rayko I. Stantchev, Emma Pickwell‐MacPherson

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900535

To promote potential applications of terahertz (THz) technology, more advanced functional THz devices with high performance are needed, including modulators, polarizers, lenses, wave retarders, and antireflection coatings. This work summarizes recent progress in THz components built on functional materials including graphene, vanadium dioxide, and metamaterials. The key message is that, while the choice of materials used in such devices is important, the geometry in which they are employed also has a significant effect on the performance achieved. In particular, devices operating in total internal reflection geometry are reviewed, and it is explained how this geometry is able to be exploited to achieve a variety of THz devices with broadband operation.

Abstract-Exploiting Total Internal Reflection Geometry for Terahertz Devices and Enhanced Sample Characterization

Qiushuo Sun, Xuequan Chen, Xudong Liu, Rayko I. Stantchev 

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900535

To promote potential applications of terahertz (THz) technology, more advanced functional THz devices with high performance are needed, including modulators, polarizers, lenses, wave retarders, and antireflection coatings. This work summarizes recent progress in THz components built on functional materials including graphene, vanadium dioxide, and metamaterials. The key message is that, while the choice of materials used in such devices is important, the geometry in which they are employed also has a significant effect on the performance achieved. In particular, devices operating in total internal reflection geometry are reviewed, and it is explained how this geometry is able to be exploited to achieve a variety of THz devices with broadband operation.

Abstract-Graphene controlled Brewster angle device for ultra broadband terahertz modulation

Zefeng Chen, Xuequan Chen, Li Tao, Kun Chen, Mingzhu Long, Xudong Liu, Keyou Yan, Rayko I. Stantchev, Emma Pickwell-MacPherson, Jian-Bin Xu

https://www.nature.com/articles/s41467-018-07367-8


Terahertz modulators with high tunability of both intensity and phase are essential for effective control of electromagnetic properties. Due to the underlying physics behind existing approaches there is still a lack of broadband devices able to achieve deep modulation. Here, we demonstrate the effect of tunable Brewster angle controlled by graphene, and develop a highly-tunable solid-state graphene/quartz modulator based on this mechanism. The Brewster angle of the device can be tuned by varying the conductivity of the graphene through an electrical gate. In this way, we achieve near perfect intensity modulation with spectrally flat modulation depth of 99.3 to 99.9 percent and phase tunability of up to 140 degree in the frequency range from 0.5 to 1.6 THz. Different from using electromagnetic resonance effects (for example, metamaterials), this principle ensures that our device can operate in ultra-broadband. Thus it is an effective principle for terahertz modulation.

Abstract-THz in vivo measurements: the effects of pressure on skin reflectivity

Jiarui Wang, Rayko I. Stantchev, Qiushuo Sun, Tor-Wo Chiu, Anil T. Ahuja, and Emma Pickwell MacPherson

Fig. 1 Experimental setup and stratified media model illustration. (a) The THz beam is focused onto the top interface of the quartz window, and the reflected signal is collected and then detected by a photoconductive antenna. (b) Schematic illustration of the layers within human skin: each layer has a different permittivity. The hydration profile of skin is approximately linear in the SC and epidermis, and constant in the dermis.

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-12-6467

Terahertz (THz) light is non-ionizing and highly sensitive to subtle changes in water concentration which can be indicative of disease. The short THz penetration depth in bio-samples restricts in vivo measurements to be in a reflection geometry and the sample is often placed onto an imaging window. Upon contacting the imaging window, occlusion and compression of the skin affect the THz response. If not appropriately controlled, this could cause misleading results. In this work, we investigate and quantify how the applied pressure affects the THz response of skin and employ a stratified model to help understand the mechanisms at play. This work will enable future THz studies to have a more rigorous experimental protocol, which in turn will facilitate research in various potential biomedical applications under investigation.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Subwavelength hyperspectral THz studies of articular cartilage

 Rayko I. Stantchev, Jessica C. Mansfield, Ryan S. Edginton, Peter Hobson, Francesca Palombo,  Euan Hendry,

https://www.nature.com/articles/s41598-018-25057-9

Terahertz-spectroscopy probes dynamics and spectral response of collective vibrational modes in condensed phase, which can yield insight into composition and topology. However, due to the long wavelengths employed (λ = 300 μm at 1THz), diffraction limited imaging is typically restricted to spatial resolutions around a millimeter. Here, we demonstrate a new form of subwavelength hyperspectral, polarization-resolved THz imaging which employs an optical pattern projected onto a 6 μm-thin silicon wafer to achieve near-field modulation of a co-incident THz pulse. By placing near-field scatterers, one can measure the interaction of object with the evanescent THz fields. Further, by measuring the temporal evolution of the THz field a sample’s permittivity can be extracted with 65 μm spatial resolution due to the presence of evanescent fields. Here, we present the first application of this new approach to articular cartilage. We show that the THz permittivity in this material varies progressively from the superficial zone to the deep layer, and that this correlates with a change in orientation of the collagen fibrils that compose the extracellular matrix (ECM) of the tissue. Our approach enables direct interrogation of the sample’s biophysical properties, in this case concerning the structure and permittivity of collagen fibrils and their anisotropic organisation in connective tissue.

Abstract-Compressed sensing with near-field THz radiation

Rayko I. Stantchev, David B. Phillips, Peter Hobson, Samuel M. Hornett, Miles J. Padgett, and Euan Hendry

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-4-8-989&origin=search

We demonstrate a form of near-field terahertz (THz) imaging that is compatible with compressed sensing algorithms. By spatially photomodulating THz pulses using a set of shaped binary optical patterns and employing a 6-μm-thick silicon wafer, we are able to reconstruct THz images of an object placed on the exit interface of the wafer. A single-element detector is used to measure the electric field amplitude of transmitted THz radiation for each projected pattern, with the ultra-thin wafer allowing us to access the THz evanescent near fields to achieve a spatial resolution of ∼9  μm$\sim 9\mathrm{\mu m}$ (𝜆/45$\lambda /45$ at 0.75 THz). We conclude by experimentally improving the image rate by a factor of ∼3$\sim 3$ by undersampling the object with adaptive and compressed sensing algorithms.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.