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Gas Discharges And Thermal Imaging

Gas Discharges And Thermal Imaging by Joseph W. Spencer
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It is often refreshing and surprisingly useful to research topics that you had previously overlooked. In this issue gas discharges come under the spotlight. We include papers that describe how gas discharges and plasmas may be analysed, and also a paper (refer to p. 56) that shows how gas discharges (sparks) can be used for generating very high energy acoustic pulses for use underwater for sub-bottom profiling. We also see how algorithms derived from the world of image processing have been used for removing noise from electric discharge data (refer to p. 41) and how this same filtering procedure can be applied to a very wide range of data acquisition problems. Every now and then a new area of technology opens up and you immediately know that it is destined to have a profound impact. Lasers are one example and they in turn have led to the development of the entirely new field of Terahertz or T-ray imaging (refer to p. 20). ‘‘Terahertz’’ refers to a band in the electromagnetic spectrum that lies between infrared and radio. Just as X-rays have a shorter wavelength than visible light, T-rays wavelengths are longer. This area of the spectrum has always been there of course, but until recently it has been difficult and very expensive to actually generate T-rays, and so they have remained very much in a technology backwater.

Lasers are key to this new development as T-rays are produced by firing a near-IR laser pulse at a semiconductor optical switching device. Like X-rays they pass through some materials easily but are attenuated by others and can therefore be used much like X-rays for medical and security applications. It is always useful to have a variety of tools at your disposals and one major advantage that T-rays have over X-rays is that being nonionising they are far less hazardous to use. Getting images beyond the visible spectrum is also the topic of ourTutorialwhich deals with the very latest developments in infrared imaging. The early days of pyroelectric vidicons are now giving way to very exotic semiconductors and ferroelectric devices. Not only are the resolutions available from such devices increasing all the time but also the temperatures at which they can operate are getting closer to ambient levels. Devices that had previous required liquid nitrogen cooling can now be operated at 110 K which can be achieved with low cost, and much more user friendly, thermoelectric cooling. In the future it is hoped that operation at 190 K will be possible.

In much the same way that I do not believe anyone would have anticipated a fraction of the applications that have been found for lasers. I also suspect that the future will have much the same to say about Terahertz imaging.

Clive Loughlin

Previously published in: Sensor Review, Volume 23, Number 1, 2002

Emerald Publishing Limited; Read online
Title: Gas Discharges And Thermal Imaging
Author: Joseph W. Spencer

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