Abstract-Warping effect-induced optical absorbance increment of topological insulator films for THz photodetectors with high signal-to-noise ratio

http://pubs.rsc.org/en/Content/ArticleLanding/2014/NR/C3NR06506E#!divAbstract

J. M. Shao,^a   H. Li^a and   G. W. Yang*^a  

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*

Corresponding authors

^a

State Key Laboratory of Optoelectronic Materials and Technologies, Institute of Optoelectronic and Functional Composite Materials, Nanotechnology Research Center, School of Physics & Engineering, Sun Yat-sen University, Guangzhou 510275, P.R. China
E-mail: stsygw@mail.sysu.edu.cn

Nanoscale, 2014, Advance Article

DOI: 10.1039/C3NR06506E
Received 08 Dec 2013, Accepted 13 Jan 2014
First published online 27 Feb 2014

Strong optical absorbance makes topological insulator (TI) surfaces a promising high-performance photodetector in the terahertz (THz) to infrared frequency range. Here, we study the optical absorbance of more realistic TI films with hexagonal warping effect using the Fermi's golden rules. It was found that when the warping term is λ ≠ 0, the absorbance is no longer a universal value as that of graphene or ideal Dirac cone, but increases monotonously with the photon energy. The increment is positively correlated with the parameter λ/v_F³ where v_F is the Fermi velocity. The relative signal-to-noise ratio (SNR) of the TI film working as a photoresistor-type photodetector is significantly enhanced by the warping effect-induced absorbance increment. These investigations provide useful information for developing TI-based photodetectors with high SNR in the range of THz to infrared frequency.

Evaluation of Coating Properties of Enteric-Coated Tablets Using Terahertz Pulsed Imaging

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• Masahiro Niwa 1 
• Yasuhiro Hiraishi 1 
• Katsuhide Terada 2

http://www.pharmagateway.net/ArticlePage.aspx?DOI=10.1007/s11095-014-1314-6
Purpose

Enteric coatings are used to reduce gastrointestinal side effects and control the release properties of oral medications. Although widely used, the effect of formulation and process conditions on physicochemical and functional properties of enteric coatings remains unclear.

Methods

Terahertz pulsed imaging (TPI) was employed to evaluate the coat properties of enteric coated tablets (ECTs) with various acid resistance. Other analytic methods, such as loss on drying, scanning electron microscopy and X-ray computed tomography were then used to validate the relationships established among 4 TPI-derived parameters and the physicochemical properties of enteric coatings.

Results

Weight gain measurement did not provide any information to assess acid resistance of enteric coating, whereas four TPI-derived parameters non-destructively reflected the coating properties such as thickness, coat uniformity, density, and water distribution, allowing the identification of the causes of poor acid resistance in certain ECT batches using a single measurement. These parameters also revealed the effect of coating conditions; in particular, coating under dry conditions led to less dense and nonuniform coatings with poor acid resistance.

Conclusion

We demonstrated the utility of TPI to identify structural defects within ECTs with poor acid resistance. TPI-derived parameters can aid in formulation development and quality control of ECTs.

Abstract-10 aJ-level sensing of nanosecond pulse below 10 THz by frequency upconversion detection via DAST crystal: more than a 4 K bolometer

Feng Qi, Shuzhen Fan, Takashi Notake, Koji Nawata, Takeshi Matsukawa, Yuma Takida, and Hiroaki Minamide  »View Author Affiliations

Optics Letters, Vol. 39, Issue 5, pp. 1294-1297 (2014)
http://dx.doi.org/10.1364/OL.39.001294

10 aJ-level sensing of nanosecond pulse below 10 THz by frequency upconversion detection via DAST crystal: more than a 4 K bolometer

By using frequency upconversion detection of terahertz (THz) waves via 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal with an optimized frequency conversion process, ultrahigh sensitivity has been achieved. Direct comparisons with a 4 K bolometer were implemented. By using a simple positive intrinsic negative (PIN) diode without either electrical amplification or optical amplification, frequency upconversion detection can compete with the commercial 4 K bolometer, while by replacing the PIN diode with an avalanche photo diode (APD), it performs more than three orders better than the 4 K bolometer. Based on power calibration, the minimum detectable THz pulse energy is in the order of 10 aJ (9–25 aJ) at 4.3 THz, with a pulse duration of 6 ns. Thus, the minimum number of THz photons that can be detected is down to the order of 103 at room temperature. The current THz detection system gives a noise equivalent power (NEP) in the order of 100  fW/Hz1/2 (50–128  fW/Hz1/2). Moreover, by switching current optical detectors, the dynamic range is over six orders.

© 2014 Optical Society of America

Abstract-Mode manipulation and near-THz absorptions in binary grating-graphene layer structures

Yuan H, Yang H, Liu P, Jiang X, Sun X.

http://www.ncbi.nlm.nih.gov/pubmed/24559407

The excitation and absorption properties of grating coupled graphene surface plasmons were studied. It was found that whether a mode can be excited is mainly determined by the frequency of incident light and the duty ratio of gratings. In the structure consisting graphene bilayer, a blueshift of the excitation frequency existed when the distance between neighbor graphene layer were decreased gradually. In graphene-grating multilayer structures, a strong absorption (approximately 90% at maximum) was found in near-THz range.

Abstract-Terahertz Radiation via Ultrafast Manipulation of Thermoelectric Conversion in Thermoelectric Thin Films

1. Kouhei Takahashi^*, 
2. Tsutomu Kanno,
3. Akihiro Sakai, 
4. Hiromasa Tamaki, 
5. Hideo Kusada, 
6. Yuka Yamada

Article first published online: 26 FEB 2014

http://onlinelibrary.wiley.com/doi/10.1002/adom.201400009/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false

DOI: 10.1002/adom.201400009

An ultrafast terahertz functionality of thermoelectric materials is shown. Femtosecond laser heating results in terahertz emission from thermoelectric Bi₂Te₃ thin films in a non-standard manner. The results manifest an ultrafast build-up of the thermal diffusion current on the picosecond order, which is useful for the development of high-speed optoelectronic thermoelectric devices.

Abstract-High-speed terahertz imaging toward food quality inspection

Gyeongsik Ok, Kisang Park, Hyun Jung Kim, Hyang Sook Chun, and Sung-Wook Choi  
»View Author Affiliations

Applied Optics, Vol. 53, Issue 7, pp. 1406-1412 (2014)
http://dx.doi.org/10.1364/AO.53.001406

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-53-7-1406

In contrast to conventional x-ray food inspection systems that have difficulty in detecting low-density materials, a terahertz imaging system can even identify insects and plastics embedded in a food matrix. A reflection-mode continuous-wave terahertz imaging system was therefore developed for application to food quality inspection, which requires fast, compact, and low-cost detection. High-speed operation of the terahertz imaging system was achieved through the use of a beam-steering tool. A reasonable compromise between the spatial resolution and the scan length of an aspheric f-theta scanning lens could be achieved by optimizing the lens parameters.

© 2014 Optical Society of America

Findings from University of Cambridge Yields New Data on Pharmaceutical Research and Biopharmaceuticals

http://www.hispanicbusiness.com/2014/2/26/findings_from_university_of_cambridge_yields.htm

By a News Reporter-Staff News Editor at Drug Week -- New research on Drugs and Therapies is the subject of a report. According to news reporting originating in Cambridge, United Kingdom, by NewsRx journalists, research stated, "In this study, terahertz pulsed imaging (TPI) was employed to investigate the effect of the coating equipment (fluid bed and drum coater) on the structure of the applied film coating and subsequent dissolution behaviour. Six tablets from every batch coated with the same delayed release coating formulation under recommended process conditions (provided by the coating polymer supplier) were mapped individually to evaluate the effect of coating device on critical coating characteristics (coating thickness, surface morphology and density)."

The news reporters obtained a quote from the research from the University of Cambridge, "Although the traditional coating quality parameter (weight gain) indicated no differences between both batches, TPI analysis revealed a lower mean coating thickness (Cr) for tablets coated in the drum coater compared to fluid bed coated tablets (p < 0.05). Moreover, drum coated tablets showed a more pronounced CT variation between the two sides and the centre band of the biconvex tablets, with the cr around the centre band being 22.5% thinner than the top and bottom sides for the drum coated tablets and 12.5% thinner for fluid bed coated tablets. The TPI analysis suggested a denser coating for the drum coated tablets. Dissolution testing confirmed that the film coating density, was the drug release governing factor, with faster drug release for tablets coated in the fluid bed coater (98 +/- 4% after 6 h) compared to drum coated tablets (72 +/- 6% after 6 h)."

According to the news reporters, the research concluded: "Overall, TPI investigation revealed substantial differences in the applied film coating quality between tablets coated in the two coaters, which in turn correlated with the subsequent dissolution performance."

For more information on this research see: Evaluating the effect of coating equipment on tablet film quality using terahertz pulsed imaging. European Journal of Pharmaceutics and Biopharmaceutics, 2013;85(3):1095-1102. European Journal of Pharmaceutics and Biopharmaceutics can be contacted at: Elsevier Science Bv, PO Box 211, 1000 AeAmsterdam, Netherlands. (Elsevier - www.elsevier.com; European Journal of Pharmaceutics and Biopharmaceutics -www.elsevier.com/wps/product/cws_home/600120)

Our news correspondents report that additional information may be obtained by contacting M. Haaser, University of Cambridge, Dept. of Chem Engn & Biotechnol, Cambridge, United Kingdom. Additional authors for this research includeK. Naelapaa, K.C. Gordon, M. Pepper, J. Rantanen, C.J. Strachan, P.F. Taday, J.A. Zeitler and T. Rades (see also Drugs and Therapies).

Seminar-Long Wavelength Single Pixel Imaging with Metamaterial Spatial Light Modulators

ECE Seminar or Event Long Wavelength Single Pixel Imaging with Metamaterial Spatial Light Modulators Willie Padilla http://www.eecs.umich.edu/eecs/etc/events/showevent.cgi?306 Associate Professor Department of Physics Boston College

Tuesday, March 11, 2014 10:00am - 11:00am 1008 EECS

About the Event "Metamaterials are a design paradigm for the construction of novel composites, where exotic electromagnetic properties arise from geometry rather than chemistry. From negative refractive index to cloaking and perfect lenses to perfect absorbers, metamaterials have demonstrated an extraordinary ability to extend the electromagnetic response of materials. As the underlying physics of these fascinating materials continues to be uncovered, much effort is now shifting toward demonstration of novel applications. I will present the design, fabrication, and demonstration of active metamaterials that function as a real-time tunable, spectrally sensitive spatial masks for use in THz imaging with only a single pixel detector."

Biography I received both my MS and PhD degrees in Physics from UC San Diego, and my thesis work, completed in 2004, was for investigation of the THz, infrared, optical and magneto-optic properties of novel materials utilizing various spectroscopic methods, including Fourier transform spectroscopy and ellipsometry. Materials studied include high temperature superconductors, pyrochlores, and artificial metamaterials. I was an author on the “discovery” paper on “left-handed” or Negative Index (NI) materials, and a main contributor to demonstrating artificial magnetic response at THz frequencies. I was awarded a Director’s Postdoctoral Fellowship from Los Alamos National Laboratory and worked in the laboratory for ultrafast optics in MST-CINT. My postdoctoral work at Los Alamos focused on terahertz time domain spectroscopy of novel materials. I am an Associate Professor of Physics at Boston College - now in my sixth year. In 2007 I was awarded a Young Investigator Program from the Office of Naval Research – a young faculty award – and a Presidential Early Career Award for Scientists and Engineers (PECASE) in 2011. In 2013 I was elected a Kavli Frontiers of Science Fellow. My research interests are primarily directed towards simulating, fabricating and measuring metamaterials at microwave, THz, and infrared frequencies and the characterization of high temperature superconductors. I am an expert in infrared, terahertz time domain, microwave, and magneto-optical spectroscopy.

Additional Information Contact: Linda Scovel Phone: 763-3260 Email: lscovel@umich.edu Sponsor: ECE Open to: Public

EMCORE Corporation : Patent Application Titled "Method and Apparatus for Analyzing, Identifying Or Imaging a Target" Published Online

http://www.4-traders.com/EMCORE-CORPORATION-10020198/news/EMCORE-Corporation--Patent-Application-Titled-Method-and-Apparatus-for-Analyzing-Identifying-Or-I-18009524/

By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors Logan, Ronald T. (Pasadena, CA); Demers, Joseph R. (North Hollywood, CA), filed on October 15, 2013, was made available online on February 20, 2014.

The assignee for this patent application is Emcore Corporation.

Reporters obtained the following quote from the background information supplied by the inventors: "The invention relates to microwave, millimeter wave and submillimeter wave spectroscopy systems and components and in particular to an apparatus and method for accurately adjusting the frequency of one or both of the optical beams used in a transceiver for terahertz spectroscopy.

"Terahertz devices and systems generally employ electromagnetic energy between 300 GHz and 3 terahertz (3 THz), or wavelengths from 100 to 1000 microns (0.1 to 1.0 millimeters), which is also referred to as the submillimeter or far-infrared region of the electromagnetic spectrum.

"One important application of terahertz systems is THz spectroscopy. Terahertz spectroscopy presents many new instrumentation and measurement applications since certain compounds and objects can be identified and characterized by a frequency-dependent absorption, dispersion, and/or reflection of terahertz signals which pass through or are reflected from the compound or object.

"The generation of terahertz radiation by photomixing is a method of generating quasi-optical signals using an optical-heterodyne converter or photomixer. Typical photomixer devices include low-temperature-grown (LTG) GaAs semiconductor devices, which have been used to generate coherent radiation at frequencies up to 5 THz. The spectroscopy system typically uses two single frequency tunable lasers, such as diode lasers, to generate two optical laser beams which are directed at the surface of the photomixer. By photoconductive mixing of the two beams in the semiconductor material, a terahertz difference frequency between the two optical laser frequencies is generated. In particular, a first laser generates radiation at a first frequency and a second laser generates radiation at a second frequency. The difference frequency, equal to the difference between the first and the second laser frequencies, is swept by the user from microwave through terahertz frequencies by changing the temperature of the lasers, which coarsely changes the frequency of one or both lasers. Other types of tuning mechanisms exist, such as distributed-Bragg-reflector diode lasers with multiple electrodes, grating-loaded external cavities, etc. A terahertz transmitter includes a first photomixer that is optically coupled to the first and the second light source. A first radiative element or antenna is electrically coupled to the first photomixer. In operation, the first antenna radiates a terahertz signal generated by the first photomixer at the difference frequency. A receiver includes a second antenna positioned to receive the signal from the target radiated by the first antenna. The second antenna generates a time varying voltage proportional to the terahertz return signal. A second photomixer is electrically coupled to the second antenna and is optically coupled to the first and the second light source. The second photomixer generates a homodyne downconverted current signal in response to the time varying voltage generated by the second antenna. The downconverted signal is a measurement of the absorption or reflection of the material at each terahertz frequency. This is useful, for example, when used in conjunction with computer processing to identify unknown samples by comparing measured results to a library of reference spectra. This apparatus may also be used to characterize the frequency response characteristics of passive or active components and devices such as waveguides, filters, amplifiers, mixers, diodes, and the like designed to work at terahertz frequencies."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "1. Objects of the Invention

"It is an object of the present invention to provide an improved frequency domain terahertz spectrometer using two continuously tunable semiconductor lasers with the relative frequency of the optical beam applied to respective source and detector photoconductive switches being electronically adjustable.

"It is another object of the present invention to provide a terahertz spectrometer for the identification of a target spectrum with high resolution and detection sensitivity of absorption bands of interest by producing CW radiation in one or more frequency bands, and 'fine tuning' the terahertz radiation in at least some of those bands to identify a spectral signature.

"It is also another object of the present invention to mitigate the interference effect in a frequency domain terahertz spectrometer with finely controllable frequency.

"It is an object of the present invention to provide a method for independently coarsely and finely adjusting the frequency difference between two source lasers forming a composite optical beam used in a frequency domain terahertz spectrometer.

"It is another object of the present invention to provide a method for adjusting the frequency of a laser in a terahertz spectrometer using photoconductive switches to provide more accurate frequency specificity and resolution by 'fine tuning' the terahertz radiation in a frequency band of interest using a reference oscillator.

"It is also another object of the present invention to provide a terahertz spectrometer with adjustable resolution of the order of Hz or 10's of Hz at specific frequency bands or absorption regions of interest.

"It is another object of the present invention to provide a method for adjusting the frequency of a laser in a terahertz spectrometer using photoconductive switches to provide more accurate frequency specificity and resolution by first 'coarsely tuning', and then subsequently 'fine tuning' the terahertz radiation in a frequency band of interest.

"It is another object of the present invention to provide a method for adjusting the frequency of a laser in a terahertz spectrometer using photoconductive switches to provide more accurate frequency specificity and resolution by 'fine tuning' the terahertz radiation in a frequency band of interest.

"It is still another object of the present invention to provide a self-contained, field portable terahertz spectrometer system in a highly compact configuration capable of identifying or imaging an object utilizing a laser with an electronically adjustable or controllable frequency.

"It is still another object of the present invention to provide a field portable terahertz spectrometer system with separately packaged source and detector heads which may be manually positioned by the operator.

"Some implementations may achieve fewer than all of the foregoing objects.

"2. Features of the Invention

"Briefly, and in general terms, the present disclosure provides an apparatus for analyzing, identifying or imaging a target, including a first housing including first and second lasers having tunable frequencies and coupled to first and second optical fibers respectively; a second housing including (i) a first photoconductive switch activated by an optical beam from the first optical fiber for producing electromagnetic radiation in a range of frequencies greater than 100 GHz, and (ii) a radiator for directing said radiation to a target; and a third housing including (i) a receiver for acquiring electromagnetic radiation in a range of frequencies greater than 100 GHz from the target, and (ii) a second photoconductive switch activated by an optical beam from the second optical fiber and coupled to the electromagnetic radiation from the receiver and functioning to generate an electrical signal representative of some characteristic of the target.

"In another aspect, the disclosure provides an apparatus for analyzing, identifying or imaging an object, including a source of CW signals in a range of frequencies greater than 100 GHz directed to said object; and a detector for acquiring spectral information reflected from or transmitted through said object and performing a heterodyne downconversion for generating an electrical signal representative of some characteristics of the object.

"In another aspect, the disclosure provides a method for analyzing, identifying or imaging an object, including generating CW signals in a range of frequencies lying above 100 GHz and directing them to said object; and acquiring spectral information reflected from or transmitted through said object and performing a heterodyne downconversion for generating an electrical signal representative of some characteristics of the object.

"In another aspect, the disclosure provides a method for analyzing, identifying or imaging a target by providing first and second lasers having first and second output beams respectively having different frequencies; frequency shifting the first output beam to produce a third beam; generating a CW radiative beam using a first photoconductive switch in the range of frequencies greater than 100 GHz from the first and third beams; causing the CW radiative beam to be substantially simultaneously focused on or through the target; combining the first beam and the second beam into a composite fourth beam; acquiring a spectral information signal from said target using a second photoconductive switch activated by said composite fourth beam; and generating an electrical signal representative of a characteristic of said target using said spectral information signal and said composite fourth beam.

"In another aspect, the disclosure provides a method comprising providing first and second lasers having tunable frequencies for producing a first optical beam and a second optical beam respectively with different frequencies; frequency shifting or modulating the first optical beam to produce a finely adjustable frequency shifted third optical beam; producing a composite fourth beam from the second and the third optical beams; producing a composite fifth beam from the first and the second optical beams; coupling the fourth optical beam to a first photoconductive switch for producing a CW radiative beam in a range of frequencies greater than 100 GHz; directing the CW radiative beam to be focused on or through a target; and detecting the radiative beam reflected from or transmitted through the target by a second photoconductive switch coupled to the composite fifth optical beam; and generating an electrical signal representative of some characteristic of the target.

"In another aspect, the disclosure provides a method for terahertz spectroscopy including sweeping a source of CW radiative beams over a range of frequencies greater than 100 GHz, including a first photoconductive switch activated by a first composite optical laser beam; directing the radiative beam to be focused on a target; and acquiring spectral information from the target by a second photoconductive switch coupled to a second composite optical beam; and finely adjusting the frequency difference between the first composite beam and the second composite optical beam by a frequency modulator in the path of one of the first and second optical beams used to generate the first composite optical beam, for generating additional electrical signals representative of some characteristic of the target in a selected frequency band.

"In another aspect, the disclosure provides a method for terahertz spectroscopy including sweeping a source of CW radiative beams in one or more predetermined frequency bands lying in a range of frequencies greater than 100 GHz; acquiring spectral information from the target; and processing the spectral information to determine the presence of a specific spectral signature to identify a compound of interest.

"In another aspect, the disclosure provides a method for identifying a compound in a target using terahertz spectroscopy by storing a spectral signature of the predetermined compound; sweeping a CW radiative beam over at least one frequency band in the range of frequencies greater than 100 GHz; directing the radiative beam to a target; acquiring spectral information from the target; and determining whether the spectral signature of the predetermined compound is present in the acquired spectral information by tuning the frequency of the CW radiative beam in frequency increments of less than 100 MHz in the frequency region of the spectral signature.

"Some implementations or embodiments may incorporate or implement fewer of the aspects or features noted in the foregoing summaries.

"Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description as well as by practice of the invention. While the invention is described below with reference to preferred embodiments, it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional applications modifications and embodiments in other fields, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of utility.

Novel laser produces random mid-infrared light for improved imaging applications

Random lasers remove speckling while maintaining brightness and could be used for applications where imaging quality is important, such as checking mail or airport security. Credit: Tomasz Wyszołmirski/iStock/Thinkstock

http://phys.org/news/2014-02-laser-random-mid-infrared-imaging-applications.html#jCp

Most lasers produce coherent light, meaning that the light waves are perfectly synchronized with each other. Spatially coherent waves, however, can interfere with one another and produce speckles in an image. With this in mind, scientists are turning to so-called random lasers, which not only show promise for applications such as biological and environmental imaging, but also mimic natural, disordered scattering from objects such as clouds.

Hou Kun Liang and co-workers at the A*STAR Singapore Institute of Manufacturing Technology and Nanyang Technological University, Singapore, have now developed a random laser that emits light in the mid-infrared range1. Moreover, the random laser is driven by electricity, making it more suitable for practical applications.

"Most random lasers are driven by optical pumping—this requires another laser to excite the random media," says Liang. "With electrical pumping we can make the laser smaller, less complex and cheaper."

The researchers modified a design known as a quantum cascade laser that contains several thin layers of compound semiconductors. When an external voltage is applied, electrons are driven across the layers and emit photons at every step. The frequency of the emitted light can be controlled by adjusting the thickness of the layers.

"A quantum cascade laser is like an electron reservoir," says Liang. "After an electron relaxes to a lower energy level, instead of becoming inactive, it flows to the subsequent active region where it is 're-used'. This is important for our laser, because loss in the mid-infrared region is high, and so we need a high gain to compensate for it."

Crucially, Liang and co-workers used plasma etching to create a random pattern of small holes—each only three micrometers in diameter—on the top surface of their laser. This design causes the laser light to be randomly scattered before it is emitted through the holes.

Currently, the random laser must be cooled to very low temperatures using liquid nitrogen to maximize the gain, but Liang and co-workers anticipate that their design can be improved to reduce the loss of mid-infrared radiation at room temperature. Liang also points out that their design gives them great freedom to explore other laser frequencies.

"For example, terahertz lasers can penetrate thick plastics and papers and, unlike X-rays, are harmless to humans. These lasers could be used for applications, such as checking mail or airport security, where imaging quality is important—a random laser would remove speckling while maintaining brightness."

 Explore further: Harnessing randomness to improve lasers

More information: Liang, H. K., Meng, B., Liang, G., Tao, J., Chong, Y. et al. "Electrically pumped mid-infrared random lasers." Advanced Materials 25, 6859–6863 (2013). DOI: 10.1002/adma.201303122

Journal reference: Advanced Materials 

Better remote-sensing explosive detectors: The beginning of the end of full-body scanners?

http://www.sciencecodex.com/better_remotesensing_explosive_detectors_the_beginning_of_the_end_of_fullbody_scanners-128644

Standing in a full-body scanner at an airport isn't fun, and the process adds time and stress to a journey. It also raises privacy concerns. Researchers now report in ACS' The Journal of Physical Chemistry Letters a more precise and direct method for using that "terahertz" (THz) technology to detect explosives from greater distances. The advance could ultimately lead to detectors that survey a wider area of an airport without the need for full-body scanners.

R. Kosloff and colleagues explain that using THz spectroscopy by itself is challenging for sensing far-away explosives. This technology uses beams of electromagnetic radiation that lie between microwaves, like those used in kitchen ovens, and the infrared rays used in TV remote controls. In addition to screening people for explosives, it is used at drug companies for quality-control purposes and, most recently, to study the layers of paint of ancient works of art. With recent advances, the technique is becoming a strong candidate for detecting substances from a distance. Other researchers have developed remote-sensing THz instruments, but they combine it with a second method to identify substances. Kosloff's group aimed to use THz directly to eventually develop even better remote sensors.

They developed a computational tool and used it to successfully identify two explosives, RDX and TATP, with THz data directly. RDX is a component of plastic explosives, and TATP is an explosive found in the shoes of the "shoe bomber" in 2009. "The ability to perform experimentally and simulate multidimensional spectroscopy should significantly enhance the screening ability of THz spectroscopy," say the researchers.

Source: American Chemical Society

Abstract & Presentation-From NMR to Terahertz Probing Wood-Water Interactions

http://www.unbc.ca/events/11492/nmr-terahertz-probing-wood-water-interactions

Date:

28 Feb 2014 - 2:30pm to 3:30pm

Location:

5-174 (UNBC Library Building)

Campus:

Prince George

Presented by:

Dr. Ian Hartley, Professor ESM/Physics (UNBC)

Sponsored by:

UNBC Department of Physics and IEEE Northern BC subsection

Abstract

The structure of wood is one of the most complex natural biomaterials to study. Many physical properties are modified with the presence of water at the anatomical level that influences its behavior as a building material or as a musical instrument component. Most wood products are in environments of low and/or high humidities, and, therefore,  to completely understand the role water plays, it is important to investigate the interaction of water with the wood material at the molecular level. This can be accomplished with several experimental techniques, including proton nuclear magnetic resonance (NMR) and terahertz (THz)spectroscopy among others. In this talk, results will be presented of experiments that use those techniques that help to tell the story of the mechanisms of wood-water interaction, namely of the different types of water present in wood.

Bio

Dr. Ian Hartley is Professor in the Ecosystem and Science Program, with joint appointment in Department of Physics. He holds a BSc in Physics and MScF in Wood Science from the University of New Brunswick and a PhD in Wood Physics from the University of British Columbia. Prior to coming to UNBC, he was an Assistant Professor of Forest Products at Mississippi State University. He is a Fellow of the Institute of Materials, Metals and Mining (Britain) and held Adjunct Professor appointment in the Department of Physics at the University of Waterloo. At UNBC, Dr. Hartley teaches forest products and wood science courses, and supervises graduate students in the of wood-water interaction at a molecular level for solid wood and composite materials. Dr. Hartley has published over 50 journal and technical articles and has made over 50 presentations at conferences and other technical sessions. He has research collaborations with UBC, FPInnovations (CT Imaging Centre; Evalutree), University of Waterloo, University of Tennessee, Auburn State University and Louisiana State University. At the UNBC 2007 Convocation, Dr. Hartley was awarded the Excellence in Teaching Award.

ian_hartley_-_feb_28_2014.pdf

Contact Information

Dr. Matthew Reid

Phone: 250-960-6622

- See more at: http://www.unbc.ca/events/11492/nmr-terahertz-probing-wood-water-interactions#sthash.DncDbMoB.dpufhttp://www.unbc.ca/events/11492/nmr-terahertz-probing-wood-water-interactions

Abstract-Modifying the polarization state of terahertz radiation using anisotropic twin-domains in LaAlO3

J. Lloyd-Hughes, S. P. P. Jones, E. Castro-Camus, K. I. Doig, and J. L. MacManus-Driscoll  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-39-5-1121

Optics Letters, Vol. 39, Issue 5, pp. 1121-1124 (2014)
http://dx.doi.org/10.1364/OL.39.001121

Polarization-resolved terahertz (THz) time-domain spectroscopy was utilized to examine the complex refractive index of lanthanum aluminate (LaAlO3), a rhombohedrally distorted perovskite that exhibits crystallographic twin domains. The uniaxial anisotropy of the refractive index was quantified. The ellipticity of THz radiation pulses after transmission through single domains indicated that LaAlO3 can be used as a quarter- or half-wave plate. The effective anisotropy of [001]-oriented LaAlO3 was found to be reduced when the material exhibited multiple, narrow twin domains.

© 2014 Optical Society of America