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British terahertz laser chip sets new record

Leeds University researchers have built a terahertz laser chip with output that exceeds records set by MIT and Vienna University of Technology.

A paper in Electronics Letters reports that the Leeds team exceeded 1W output power from a quantum cascade terahertz laser.

The new record more than doubles landmarks set by the Massachusetts Institute of Technology (MIT) and subsequently by a team from Vienna last year.

Terahertz waves can penetrate materials that block visible light and uses include monitoring pharmaceutical products, the remote sensing of chemical signatures of explosives in unopened envelopes, and the non-invasive detection of cancers in the human body. 

According to the university, one of the main challenges for scientists and engineers is making the lasers powerful and compact enough to be useful.

In a statement, Prof Edmund Linfield, Professor of Terahertz Electronics in the University’s School of Electronic and Electrical Engineering, said: ‘Although it is possible to build large instruments that generate powerful beams of terahertz radiation, these instruments are only useful for a limited set of applications. We need terahertz lasers that not only offer high power but are also portable and low cost.’

The quantum cascade terahertz lasers being developed by Leeds are a few square millimetres in size.

Professor Linfield said: ‘The process of making these lasers is extraordinarily delicate. Layers of different semiconductors such as gallium arsenide are built up one atomic monolayer at a time.

‘We control the thickness and composition of each individual layer very accurately and build up a semiconductor material of between typically 1,000 and 2,000 layers.

‘The record power of our new laser is due to the expertise that we have developed at Leeds in fabricating these layered semiconductors, together with our ability to engineer these materials subsequently into suitable and powerful laser devices.’

In October 2013, Vienna University of Technology announced that its researchers had broken the world record output power for quantum cascade terahertz lasers previously held by Massachusetts Institute of Technology (MIT). 

Readers' comments (2)

  • 100% increase on the state of the art is to be congratulated.
    Are there theoretical limits to the process used?
    Please keep the community updated on commercialisation opportunities.

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  • Leeds University’s Professor Edmund Linfield replies: There are no specific theoretical limits, and higher output powers should be possible. However, as in many opto-electronic devices, it is necessary to ensure efficient heat extraction from the active region, and this can be quite a challenging engineering problem, which researchers will need to address.

  • These chips comprise over 1000 'single atom monolayers' each individually deposited and so seems to indicate high unit cost unless a simple process of sequential and selective deposition can be developed.

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  • Leeds University’s Professor Edmund Linfield replies: The lasers are grown by a technique called 'molecular beam epitaxy'. Whilst researchers at Leeds have spent a considerable time optimising the process for terahertz quantum cascade lasers, the layer structures can be grown over a full three-inch semiconductor substrate (and this could be scaled up). Given that individual lasers are only a few millimetres in dimensions, it is potentially a mass-production technique, and hence unit costs can be low.

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