Using un-used spectrum ...

Terahertz laser chip. Credit: University of Leeds

Spectrum, the range of frequencies (and wavelengths) of an electromagnetic field, is usually considered as scarce, however it is not scarce per sé. What is scarce is the usable spectrum and its usability depends on a variety of factors: the propagation characteristics (the shorter the wavelength, i.e. the higher the frequency, the more information potentially carried but the more tricky the propagation, the longer the wavelength the longer the antenna needed to capture it and so on), the absorption in the ambient, and, of course, the technology required to manage it.

So far engineers have managed to deal with spectrum in the GHz (and below) range and in the 10-100 THz range (that is usually addressed in terms of nm wavelength .... since it is the range where light is involved). 

The range of THz has been neglected because of technical difficulties in managing these frequencies, laying between microwaves and infrared. This range is particularly interesting since the electromagnetic field in this range is able to go through matter although slightly interacting with it. As such it can be used to detect anomalies in materials, including body tissues leading, as an example to the detection of cancers.

Researchers at the University of Leeds have been able to develop an efficient laser, with an emission power around 1 W, representing a 100% increase in power with respect to the one previously developed at MIT, that can be used in practical applications.

The laser is embedded in a chip only a few square mm, made up by 1,000-2,000 layers, each one a few atoms thick. Actually, it is by finely controlling the thickness of each layer that it is possible to create the laser working at 3.1 THz. The production process is very complex and this explains why it took so long before creating such a laser.

The potential applications are many, from detecting specific chemicals (like traces of explosive) to specific micro structures, such as cancerous cells.

As it is the case with most sensors, the chip can provide raw data. It is up to the software to analyse them and make sense out of them.

Author - Roberto Saracco

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