1,720,983 research outputs found
Terahertz calculations for the Australian synchrotron
Full text linkThe development of terahertz radiation (T-rays) is spurring new applications in spectroscopy and imaging. To maximize the use of T-rays in more applications, a high average terahertz power is needed. Rather than using fast diodes or laser sources, this paper will show that a synchrotron can generate high average power T-rays. This is achieved by creating an electron bunch in the synchrotron ring with high intensity in the terahertz frequency region via Thomson scattering.Chien Aun Chan, Samuel P. Mickan, Gwyn P. Williams, and Derek Abbot
Fibre laser doppler vibrometry system for target recognition
Full text linkVibrations from a target provide a difficult to mask target signature. Vibrometry shows potential for long-range target identification whilst a fibre implementation may lead to a smaller, more compact system when compared with an equivalent solid-state source solution. A prototype fibre LDV system and electronic demodulation scheme using low-cost telecommunications components is described and tested. The aim of the system is to remove the velocity component of a target signature for target identification purposes. Signal processing methods and signature measurements are described which demonstrate the utility of the system for target recognition.Michael P. Mathers, Samuel P. Mickan, Werner Fabian and Tim McKayhttp://spie.org/x648.html?product_id=58231
Simulation of terahertz radiation in stratified media
No full text© 2006 COPYRIGHT SPIE--The International Society for Optical EngineeringThe reflection characteristic of terahertz radiation (T-rays) in stratified media is being explored through the use of computer models. When T-rays are reflected off a sample, the measured T-ray signal contains coherent spectroscopic information about the sample. In the time domain, this spectroscopic information becomes the time response of the sample-a useful method for determining layer thickness and the number of interfaces in the sample. In order to confidently determine thickness and interfaces, the propagation characteristic of T-rays in a stratified medium needs to be understood. Internal reflections, interference, and water absorption within the layers can significantly alter the T-ray signal. This paper reports on a study of T-ray propagation in tissue layers inside the head, in reflection mode. Simulated results are presented and discussed.Gretel M. Png, Samuel P. Mickan, and Derek Abbot
Terahertz phase contrast imaging
Full text link© 2005 COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.Terahertz imaging is presently in its exploratory stage. Although plots of time versus terahertz amplitude, and frequency versus terahertz magnitude are some of the most common ways of analyzing terahertz data, no standard rendering technique has been established. While existing methods are indispensable, improvements to how terahertz data is rendered and analyzed should be explored so that new techniques can complement existing ones and/or provide a means of displaying new information that existing methods cannot. This paper reports on one solution to terahertz imaging: an implementation of a new form of phase contrast imaging, which is based on a well-established technique for optical microscopy. This will provide us with a further way of interpreting information from terahertz imaging systems.Gretel M. Png, Samuel P. Mickan, Tamath J. Rainsford, and Derek Abbot
Review of THz near-field methods
No full textTerahertz (THz) imaging offers many attractive advantages over existing modalities especially in its ability to obtain spectroscopic information. In particular, THz spectra are extremely sensitive to small changes of the molecular structure and different isomeric and intermolecular configurations. With a comparatively longer wavelength (0.3 mm at 1 THz), THz images suffer from the problem of low spatial resolution, as determined by Rayleigh's criterion and proves to be a major limitation. This paper reviews the existing THz near-field methods and recent developments for identifying potential areas of research.Hungyen Lin, Bernd M. Fischer, Samuel P. Mickan, and Derek Abbot
Retrofittable antireflection coatings for T-rays
No full textCopyright © 2007 Wiley Periodicals, Inc., A Wiley Company The definitive version may be found at www.wiley.comT-ray reflection loss at a window's surface is reduced by means of a quarter-wave antireflection coating. Because T-ray wavelengths are much longer than visible wavelengths, the antireflection layer for T-rays is much larger than the layers typically used in optics. This creates an interesting opportunity for retrofittable antireflection layers. In the experiment, an antireflection coating made from ordinary polyethylene sheets is pressed onto the surfaces of a silicon window in the way that rapid replacement of the rettroflttable coating is possible. Measured by terahertz time-domain spectroscopy (THz-TDS), the coated window shows enhancement of the transmittance within a range of T-ray frequencies. © 2007 Wiley Periodicals, Inc.Withawat Withayachumnankul, Bernd M. Fischer, Samuel P. Mickan, Derek Abbot
Low-cost optoelectronic devices to measure velocity of detonation
Full text linkVelocity of Detonation (VoD) is an important measured characteristic parameter of explosive materials. When new explosives are developed, their VoD must be determined. Devices used to measure VoD are always destroyed in the process, however replacing these devices represents a considerable cost in the characterisation of new explosives. This paper reports the design and performance of three low-cost implementations of a point-to-point VoD measurement system, two using optical fibre and a third using piezoelectric polymers (PolyVinyliDine Flouride, PVDF). The devices were designed for short charges used under controlled laboratory conditions and were tested using the common explosive 'Composition B'. These new devices are a fraction of the cost of currently available VoD sensors and show promise in achieving comparable accuracy. Their future development will dramatically reduce the cost of testing and aid the characterisation of new explosives.Edwin M. Chan, Vivian Lee, Samuel P. Mickan and Phil J. Davieshttp://spie.org/x648.html?product_id=58223
2-D wavelet segmentation in 3-D T-ray tomography
Full text linkCopyright © 2007 IEEEIn this letter, segmentation techniques for terahertz (T-ray) computed tomographic (CT) imaging are investigated. A set of linear image fusion and novel wavelet scale correlation segmentation techniques is adopted to achieve material discrimination within a 3-D object. The methods are applied to a T-ray CT image dataset taken from a plastic vial containing a plastic tube. This setup simulates the imaging of a simple nested organic structure, which provides an indication of the potential for using T-ray CT imaging to achieve T-ray pulsed signal classification of heterogeneous layersXiaoxia Yin, Brian W.-H. Ng, Bradley Ferguson, Samuel P. Mickan and Derek Abbot
Ab initio molecular orbital theory: a tool for THz spectroscopic investigation
No full text© 2006 COPYRIGHT SPIE--The International Society for Optical EngineeringTerahertz spectroscopy, which investigates the electromagnetic spectrum of samples between 0.1 and 10 THz, allows not only for exploration of molecular structures but also of molecular dynamics. One difficulty in performing THz spectroscopy is that the data can be noisy and difficult to interpret. Ab initio molecular modelling has recently become more and more useful in the prediction of, for example, molecular structures, dynamic states and isomeric forms. Since the structure of biomolecules is closely related to their functionality there are broad ranging applications in biomedicine, for example in DNA sensing. An a priori knowledge of the expected THz spectra allows for improved experimentation. There is a growing and recognised need for THz spectroscopic databases to be created and made available along with classifiers that are able to effectively detect a specific substance. We show, for a specific example, the 9-cis and all-trans retinal isomers, how ab initio molecular orbital calculations and quantum chemical modelling programs, such as Gamess, can aid in this endeavour.Inke Jones, Tamath J. Rainsford, Samuel P. Mickan, and Derek Abbot
Molecular and structural preservation of dehydrated bio-tissue for THz spectroscopy
Full text link© 2006 COPYRIGHT SPIE--The International Society for Optical EngineeringTerahertz transmission through freshly excised biological tissue is limited by the tissue's high water content. Tissue fixation methods that remove water, such as fixation in Formalin, destroy the structural information of proteins hence are not suitable for THz applications. Dehydration is one possible method for revealing the tissue's underlying molecular structure and components. In this study, we measured the THz responses over time of dehydrating fresh, necrotic and lyophilized rat tissue. Our results show that as expected, THz absorption increases dramatically with drying and tissue freshness can be maintained through lyophilization. Dehydrated biological tissue with retained molecular structure can be useful for future laser-based THz wave molecular analysis.Gretel M. Png, Jin Wook Choi, Ian Guest, Brian W.-H. Ng, Samuel P. Mickan, Derek Abbott, and Xi-Cheng Zhan
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