Laser used to cool semiconductor

Next: the quantum physics case-mod

Boost IT visibility and business value

Lasers heat things up, right? – unless you happen to hit upon the right resonance, in which case it seems you can use lasers to cool things down.


Koji Usami carries out the experiments
at the Quantop laboratories at the Niels
Bohr Institute. Credit: Niels Bohr Institute

In an announcement that could be filed under either “counter-intuitive” or simply “wow”, scientists at Copenhagen University’s Niels Bohr institute have used a laser to cool a semiconductor membrane to -269°C.

The research, published in Nature Physics, extends a known quantum phenomenon to the macroscopic world. Focussed lasers have been used since the 1980s to cool atoms. In the current research, the group from the Niels Bohr Institute’s Quantop group wanted to try a similar trick in the macro world.

“It would mean entirely new possibilities for what is called optomechanics, the interaction between optical radiation … and a mechanical motion,” said Quantop’s head professor Eugene Polzik.

Here’s how it the cooling phenomenon happens for single atoms: if the atom is moving towards the laser, the photon striking the atom will slow it down; enough impacts will reduce its momentum to near-zero (at which point it would have a temperature of absolute zero).

There’s a problem, though: it only works for atoms traveling towards the laser. If the atom is traveling in the same direction as the laser, it will gain momentum instead (and heat up). Various techniques have been developed over the years to counter this; for the purposes of this discussion, I will stick with the simplest.

If the laser is tuned to just below the resonant frequency of the atom, the “head-on” photon is Doppler-shifted towards the resonant frequency. As a result, photons in that direction are absorbed just a little more strongly than photons headed in the same direction as the atom.

Making all this work for a complex material rather than a single atom is much harder – and that’s the breakthrough being claimed by the Niels Bohr researchers. Their choice of material is gallium arsenide, and since 2009, they have been working to create a semiconducting membrane with the right dimensions to use in their experiments.

The resulting membrane has an area of more than 1 square millimeter, but is only 160 nanometers thick. This, it seems, has the right resonant properties to be subjected to laser cooling, but at a macro rather than single-atom level.

Associate professor Koji Usami explains the experiement: “we let the membrane interact with the laser light in such a way that its mechanical movements affected the light that hit it.

“We carefully examined the physics and discovered that a certain oscillation mode of the membrane cooled from room temperature down to minus 269 degrees C, which was a result of the complex and fascinating interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances”.

Usami says the technique might be useful for cooling components in quantum computers, and could also be used to create new electrical or mechanical sensors. If the technique can be applied more widely, it could also replace cryogenic cooling in a variety of applications. ®

Gartner critical capabilities for enterprise endpoint backup

More from The Register

next story
Spanish launch goes titsup, we're off to the US of A
Gigantic toothless 'DRAGONS' dominated Earth's early skies
Gummy pterosaurs outlived toothy competitors
'Leccy racer whacks petrols in Oz race
ELMOFO rakes in two wins in sanctioned race
Ten points of stuff out of a five pound bag
Boffins ID freakish spine-smothered prehistoric critter: The CLAW gave it away
Bizarre-looking creature actually related to velvet worms
CRR-CRRRK, beep, beep: Mars space truck backs out of slippery sand trap
Curiosity finds new drilling target after course correction
But they'd lose a deathmatch against the coming Humvee-sized, armoured Arctic ones
Astronomers scramble for obs on new comet
Amateur gets fifth confirmed discovery
Boffins build CYBORG-MOTHRA but not for evil: For search & rescue
This tiny bio-bot will chew through your clothes then save your life
prev story


Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
7 Elements of Radically Simple OS Migration
Avoid the typical headaches of OS migration during your next project by learning about 7 elements of radically simple OS migration.
BYOD's dark side: Data protection
An endpoint data protection solution that adds value to the user and the organization so it can protect itself from data loss as well as leverage corporate data.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?