Lasers cut a way to the stars

  • 20 January 2014
  • From the section Scotland
Media captionA laser is used to cut the photonic lantern - a glass circuit which can handle photons from the stars in new ways

Scottish researchers are using laser technology to help look further into space than ever before.

Today's astronomers are the heirs of Galileo.

Ever since he turned his telescope to the heavens, celestial light has been handled in fundamentally the same way: lenses, later mirrors and the odd diffraction grating.

Now a new generation of extremely large telescopes is on its way, including the European Extremely Large Telescope (E-ELT) which could be online around 2020. The E-ELT will have an aperture several times greater than previous telescopes.

But the bigger a telescope gets, the more light there is to analyse. Too much, in fact, for existing sensors to handle.

Image caption Dr John Davies says telescopes are getting bigger but that causes problems

"Astronomers have always wanted bigger and bigger telescopes," says Dr John Davies of the UK Astronomy Technology Centre at the Royal Observatory in Edinburgh.

"The problem is that as the telescopes get bigger, the instruments tend to get bigger as well.

"And soon those instruments are going to be unmanageably large."

Photonics holds out a solution. Think of an integrated circuit with electrons flowing through metal. Then replace the metal with glass and the electrons with photons, the individual particles of light.

One application is the photonic lantern - a glass circuit which can handle photons from the stars in new ways. Most importantly in the context of the new, bigger telescopes, each photonic lantern can be made smaller than existing instruments.

"Much, much smaller," according to Dr Davies.

"Which means we can probably make them cheaper, and also we can do more things at the same time."

Image caption Dr Robert Thomson says photonic lanterns break away from the constraints that conventional optics present

This is where Heriot-Watt University's Institute of Photonics and Quantum Sciences comes in.

In a darkened laboratory a powerful laser is cutting channels in a sliver of glass to create a photonic lantern.

Normally the laser would be producing infra-red light invisible to the human eye. For our benefit the beam has been tweaked into the visible spectrum.

Creating these photonic lanterns uses a new technique pioneered by STFC Advanced Fellow Dr Robert Thomson.

He says: "By moving that piece of glass through the laser focus we are actually able to directly write into the material optical circuits that guide light in an analogous way to the way in which electrical wires guide electrons."

The laser beam is not continuous. The technique uses ultra-short laser pulse each lasting just one million-millionth of a second.

They're not the shortest laser pulses yet achieved - those are down in the attosecond range, one-quintillionth of a second - but a million-millionth is the perfect pulse to create a photonic lantern.

Outside the lab, safety goggles off, Dr Thomson explains what photonic lanterns might mean for the new generation of extremely large telescopes.

"What that really allows us to do is break away from the constraints that conventional optics present.

"And by using photonic technologies we can really guide and mould the flow of the light from the telescope into the instrument.

"And that allows our instruments potentially to be much more efficient and much more stable."

One of the team's first lanterns has already been tested on the William Herschel Telescope in La Palma in the Canary Isles, in collaboration with a group from Durham University.

Heriot-Watt are describing it as a 'world first on-sky test' which has demonstrated improved stability and efficiency over traditional instruments.

The work is being supported by UK Science and Technology Facilities Council (STFC) and the EU. It involves Heriot-Watt, Durham, the University of Bath and the Leibniz Institute for Astrophysics near Berlin.

Image caption The Royal Observatory Edinburgh is the capital's stargazing centre

At the Royal Observatory Edinburgh, Dr John Davies says the new techniques will really come into their own when the extremely large telescopes see their first light at the beginning of the next decade.

"They can detect, we hope, planets around nearby stars," he says.

"We can also hope to detect galaxies right at the edge of the Universe."

Astronomy is the closest we get to time travel. Take Proxima Centauri, Earth's nearest known star. It's 4.24 light years away, which means we're seeing it as it looked just a shade over four years ago.

And the further away you look, the further back in time you are seeing.

The most distant - and therefore the oldest - galaxy yet observed has been dated to just 700 million years after the Big Bang. Given that the Big Bang was around 14 billion years ago that is pretty far back.

But combining photonic lanterns with an extremely large telescope should enable us to see even further back in time towards the dawn of the Universe.

You sense Galileo would have been impressed.