FEATURE TERAHERTZ


doing terahertz research. They were either developing sources or sensors. However, over the past few years our sales have been split between research and industry. This is a sure sign of an evolving market. It parallels the growth of the x-ray market years ago; it started more as a lab curiosity, but they are realising they can do some pretty incredible things with it.’ Dooley pointed to the advantages of the technology: ‘The beauty of terahertz radiation, and the reason it will replace x-rays in certain areas, is that it is non-photoionising. It doesn’t damage materials.’ This


Terahertz


radiation is non- photoionising. It doesn’t damage materials, and has many other benefits’


has benefits for medical fields, industrial inspection, and security that typically use x-rays, which is photoionising and can damage biological tissue. As Linfield stated: ‘In terms of causing damage, terahertz frequency is much less energy per photon, which means it doesn’t cause as much damage on collision with a surface. Each photon is probing the material; more power means more photons means better signal.’


A major practical application of terahertz radiation is in airport security checks, where the detection technique is time-domain spectroscopy or broadband spectroscopy. Ben Agate, laser sales and service engineer at Photonic Solutions, described a German project to try to surmount the difficulties of portability of terahertz technology by building a more mobile terahertz detector system. The project, carried out between


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the University of Marburg and Menlo Systems, uses time-domain spectroscopy. The system is able to analyse material, even through a bottle, and indicate whether a substance is safe or not in a matter of seconds. Agate explained that the Marburg-Menlo system ‘is a


handheld device connected by a fibre to a laser source that is on wheels. So it is effectively portable where the handheld device emits and receives terahertz radiation.’ However, the way in which the


Marburg-Menlo system generates the terahertz radiation differs from


the method used by the Leeds University team. At the present moment, Agate pointed out, ‘one of the most common way of creating terahertz radiation is by using an indium gallium arsenide chip pumped with ultrafast pulsed lasers. The Menlo system uses a


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APRIL 2014 l ELECTRO OPTICS 15


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