Thursday, 21 August 2014
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Method could provide internal cooling mechanism for lasers

Scientists in Austria have designed a way to create a laser powered by heat rather than light or electricity.

The idea, from researchers at Innsbruck University, could provide an internal cooling mechanism for certain types of lasers and other electronic equipment by harnessing the heat they produce rather than dissipating it.

The proposal involves reversing an issue with in-quantum cascade lasers — semiconductor-based devices that emit infrared radiation — where the movement of electrons inside the laser that causes it to emit light also produces heat.

These lasers amplify electrical energy to produce a beam of infrared light by passing the electrons through a repeated pattern of specially designed semiconductor layers, according to researcher Helmut Ritsch, head of Innsbruck’s Institute for Theoretical Physics.

‘The electrons are transferred through this structure in a specific series of tunnelling processes and quantum leaps, emitting coherent light particles,’ he said in a statement. ‘Between these layers, the electrons collide with other particles, which heats the laser.’

When too much heat is produced, it prevents the laser from emitting light, so strong cooling mechanisms are usually required to make it work.

Ritsch and PhD student Kathrin Sandner, whose work was recently published in the journal Physical Review Letters, have come up with the idea of modifying the thickness of the semiconductor layers so that the temperature difference between them can drive the movement of electrons.

‘A crucial part is to spatially separate the cold and warm areas in the laser,’ said Sandner. ‘In such a temperature-gradient-driven laser, electrons are thermally excited in the warm area and then tunnel into the cooler area where photons are emitted.’

This produces a circuit where light particles are emitted and heat is absorbed from the system simultaneously. The researchers believe this concept could be used to produce lasers powered only by heat and provide the cooling mechanism for existing quantum cascade lasers.

‘Apart from the conceptual elegance of this idea, a completely new way may open up of using heat in microchips in a beneficial way instead of having to dissipate it by cooling,’ said Ritsch.


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