A pseudo-planar metasurface for a polarization rotator

W. Zhang, W. M. Zhu, E. E. M. Chia, Z. X. Shen, H. Cai, Y. D. Gu, W. Ser, and A. Q. Liu 

Abstract

New demonstrations of effective interaction between light and artificially electromagnetic interface, or the metasurface, have stimulated intensive research interests on control of light to realize applications in beam steering, optical imaging and light focusing, etc. Here we reported a new type of planar metasurface of which every individual metamolecule is single metallic layer with stereo structure and the metasurface is name as Pseudo-Planar Metasurface (PPM). The metamolecule of the PPM is a chiral structure and therefore derives significant optical activity.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-22-9-10446&id=284135

Electrothermally actuated microelectromechanical systems based omega-ring terahertz metamaterial with polarization dependent characteristics

Chong Pei Ho, Prakash Pitchappa, Yu-Sheng Lin, Chia-Yi Huang, Piotr Kropelnicki and Chengkuo Lee

Abstract

We present the design, simulation, fabrication, and characterization of a continuously tunable Omega-ring terahertz metamaterial. The tunability of metamaterial is obtained by integratingmicroactuators into the metamaterial unit cell. Electrothermal actuation mechanism is used to provide higher tuning range, larger stroke, and enhanced repeatability. The maximum achieved tuning range for the resonant frequency is around 0.30 THz for the input power of 500 mW. This shows the potential of using electrothermally actuated microactuators based tunablemetamaterial design for application such as filters, absorbers, sensors, and spectral imagers.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://scitation.aip.org/content/aip/journal/apl/104/16/10.1063/1.4871999

Structural and chemical modification of nontronite associated with microbial Fe(III) reduction: Indicators of “illitization”

Tae-hee Kooa, Young-nam Jangb, Toshihiro Kogurec, Jae Hoon Kimd, Byung Cheol Parkd, Don Sunwooe, Jin-wook Kima,

Abstract

The smectite-to-illite reaction, termed illitization, is a ubiquitous process in siliciclastic sedimentary environments and plays a significant role in biogeochemical cycling, plant nutrition, petroleum maturation/migration, particle dispersion–aggregation, and contaminant uptake. The change in the redox state of structural Fe in smectite as a consequence of microbial Fe respiration, in part, controls the physicochemical properties of smectite, but knowledge of the chemical/structural modification at a nanoscale, particularly the reversibility of the structure and K fixation at various Fe-redox states that could control illitization, is limited. The present study focused on measuring indicators of illitization at a nanoscale, utilizing transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS) and terahertz time-domain spectroscopy (THz-TDS), as well as chemical analysis, including cation exchange capacity (CEC) and Fe(III) reduction. Nontronite (NAu-1) of the size fraction less than 0.2 m was inoculated with the Fe-reducing bacteria Shewanella oneidensis MR-1 in M1 medium with structural Fe(III) in NAu-1 as the sole electron acceptor and Na-lactate as the electron donor. Incubation continued for up to 12 months in an anaerobic chamber. Two sets of microbial structural Fe(III) reduction experiments were performed, and then one set was re-oxidized by bubbling pure oxygen gas through an autoclaved needle for 24 hours. The reaction was stopped at various time points by freezing the samples with liquid N₂. The extent of Fe(III) reduction reached 26%; 5% of residual Fe(II) was detected upon re-oxidation. TEM and X-ray diffraction (XRD) analyses confirmed the presence of an illite-like packet with collapsed 10-Å basal spacing in the Fe-reduced nontronite sample and permanently fixed K after long-term incubation. The proportion of K fixation in the interlayer increased with the extent of Fe(III) reduction and the amount of residual Fe(II) upon re-oxidation. The values of CEC increased corresponding to the extent of Fe(III) reduction; the CEC was not restored after re-oxidation, most likely due to the increase in residual Fe(II), secondary phase mineral (vivianite) precipitation, and permanent K fixation. Nondestructive THz-TDS depicted the chemical/structural modification of bioreduced nontronite and its reversibility. In the present study, true illite was not formed because of the low value of Al/Si; however, the progressive increase in K/(K + 2Ca) and Al/Si in the packets of 10-Å layers as well as the chemical/structural irreversibility upon re-oxidation with increasing incubation time strongly suggested illitization.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.sciencedirect.com/science/article/pii/S0009254114001880

From mm-wave to THz: Scalable Filter Design for Ultra-low Cost Applications

W. J. Otter, F. Hu, J. Hazell and S. Lucyszyn

Abstract

This paper shows simulated and measured results of ultra-low cost metal mesh filters in the millimetre-wave and THz bands. It provides a broad overview of the filters currently available and their suitability for ultra-low cost applications. We demonstrate scalable conventional metal mesh filters on standard 525 µm fused silica substrates. In additional, trapped-mode excitation is used to improve out-of-band rejection at higher frequencies. The measured results show that these filters are scalable in the THz range using cost-effective micromachining manufacturing. This potentially opens up the possibility of using metal mesh filters for ultra-low cost applications. 

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article:

https://workspace.imperial.ac.uk/opticalandsemidev/Public/Publications/2014_04_ARMMSb.pdf

Frequency Dependent Optical and Dielectric Properties of Zinc Sulfide in Terahertz Regime

Abstract

Frequency dependent optical and dielectric properties for several grades of chemical vapor deposited (CVD) zinc sulfide (standard, elemental, and multi-spectral) was performed using a terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.15 THz to 2.5 THz. Zinc sulfide exhibits low frequency vibrational modes characterized by the THz-TDS. Two low-frequency phonon resonance lines were revealed at 0.78, and 2.20 THz. These samples were also characterized in the GHz range using a backward wave oscillator (BWO) source quasi-optical spectrometer, and the data obtained by both approaches were compared. Experimental data were also compared with an undamped harmonic oscillator model. These results compare well with the literature values obtained using other methods.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.sciencedirect.com/science/article/pii/S1350449514000541

Advances in terahertz research - recent papers and publications

Technology Update: 

TeraView continues to support and promote fundamental and applied research within the terahertz field.

Each year the breadth and depth of interest in the area increases and TeraView is happy to help highlight these.

Below is a small selection of work from our customers and partners highlighting advances across a diverse range of application areas. These include work on; graphene, composite materials, explosives  and art conservation.

Chinese Academy of Sciences, Xi’an, China

Terahertz Spectral Investigation of Anhydrous and Monohydrated Glucose Using Terahertz Spectroscopy and Solid-State Theory

Woosuk University, Chonbuk, Republic of Korea

Influence of terahertz waves on the penetration in thick FRP composite materials

Chung-Ang University, Anseong, Republic of Korea

Foreign-body detection in dry food using continuous sub-terahertz wave imaging

University of Cambridge, Cambridge, United Kingdom

Low-Bias THz Amplitude Modulator Based on Split-Ring Resonators and Graphene

University College London, London, United Kingdom

Systematic study of terahertz time-domain spectra of historically informed black inks

Military University of Technology, Warsaw, Poland

Identification of concealed materials, including explosives, by terahertz reflection spectroscopy

To keep up to date with the latest articles and publications from TeraView, as well as gain access to an archive of all our publications, visit our website or our blog at:

Website: http://www.teraview.com/news/terahertz-publications/index.html

The Bartlett PhD Conference 2014

Tiphaine Bardon from University College London (UCL), who TeraView are currently hosting, has had an abstract accepted for an oral presentation at The Bartlett PhD Conference held on the 15th of April gathering staff and PhD students from The Bartlett faculty. The topic of the presentation will be:

"Undercover investigation of documents with terahertz"

Abstract

Archives and libraries can contain documents with pages painted over, glued together as a result of water damage, or extremely brittle and difficult to turn or unfold without damage. Yet, the twofold task of archives is to guarantee that their collections of historical records are preserved and that the information remains accessible and available to the public. Is there any alternative way to provide access to the textual information of these documents without damaging them? The answer might lie in airport security scanners, using terahertz technologies to identify and image drugs and explosives under clothing and through closed bottles. This research explores the following questions:

- if terahertz technologies enable to “see” through clothes, can they enable to “read” through pages of paper or parchment? Are all inks on all paper and parchment sheets readable with this technology, or are there combinations giving better contrast? How deep in a stack of sheets can we uncover inscriptions using terahertz imaging?

- if terahertz technologies enable to identify drugs, can they also identify chemical and physical degradation processes occurring in archival collections? Specifically, can this technology be used to non-invasively differentiate inscriptions written with corrosive inks from those written with inert inks?

The presentation will be filmed and later on uploaded on the faculty YouTube Channel: 

https://www.youtube.com/user/BartlettTV

For more information visit: 

http://www.bartlett.ucl.ac.uk/events/bartlett-phd-conference-2014

Abstract accepted for an oral presentation at the LACONA-X conference

Tiphaine Bardon from University College London (UCL), who TeraView are currently hosting, has had an abstract accepted for an oral presentation at the LACONA-X conference (Lasers in the Conservation of Artworks) held in the United Arab Emirates between the 9th and the 13th of June 2014, gathering both researchers, conservators and conservation scientists. 

The topic of the presentation will be "Contrast and readability in terahertz time-domain images of ink inscriptions: A comparative study of model and historical documents"


Tiphaine Bardon, Robert K. May, Bianca Jackson, Philip F. Taday, Gerrit De Bruin, Matija Strlič

Abstract

The terahertz range between 0.15 – 3 THz (i.e. 5 – 100 cm-1) has been made accessible due to the development of ultra-short pulse lasers, as the emission and reception of a radiation with such broad bandwidth in the high frequency domain rely on photoconductive semiconductors gated by femtosecond laser pulses.

Terahertz time-domain imaging can give in-depth contrasted images of each layer in a laminar structure, with a depth resolution of up to 30 μm and a penetration depth of a few mm in dry organic materials. The image contrast of a specific layer relies on the differences of absorption and dispersion of the terahertz pulse by the materials on each side of this layer. Documents are, in essence, laminar structures consisting of layers of support (paper or parchment), ink and air gaps. Terahertz time-domain imaging therefore represents an ideal tool for the study of historical documents, the condition of which may prevent their opening or excessive handling, provided that ink inscriptions and their surrounding support can be differentiated in the terahertz image.

This comparative spectroscopic and imaging study of various model inks on different supports demonstrates the independent and combined influence of the nature of both the ink and the support on the contrast of inscriptions seen in terahertz images. Lamp black pigment is found to intensively absorb terahertz radiation and, as a result, any inscription containing lamp black would show good contrast in terahertz images, regardless of the nature of the support. On the other hand, the refractive index of the red pigment vermilion varies greatly in the terahertz region and is similar to the refractive index of parchment at specific frequencies: the image contrast of vermilion inscriptions on parchment is therefore very frequency-dependent.

Other factors can influence the contrast in terahertz images of documents and are reported in the present work: the roughness of the support can induce scattering of the impinging terahertz radiation, the indentation left by a quill or a pen locally modifies both the surface profile and the density (and therefore the refractive index of the support), and the ink penetration into the support creates a refractive index gradient. Finally, good readability of ink inscriptions does not rely solely on the contrast of the image, but also on the spatial resolution of the imaging set-up with respect to the width of the ink inscriptions: spatial resolutions of different set-ups are discussed, together with the loss of spatial resolution when imaging deep into a stack of sheets, depending on the nature and thickness of the supports.

Improved interpretation of the contrast in terahertz images of historical documents is possible on the basis of these findings. As an example, terahertz imaging of an Ottoman document from the UCL Centre for Sustainable Heritage Historic Reference Material Collection, dating from 1870 AD, is discussed: the difference in contrast of two black inscriptions is discussed and corroborated by results of analysis with optical coherence tomography, attenuated Fourier-transform infrared spectroscopy and near-infrared spectroscopy.

Further information about the conference can be found on the conference website:

http://www.lacona10.org/