A research group in Galway has won a €1 million contract from the European Space Agency to develop new ways to correct visual errors in orbiting space telescopes.
The technologies involved are also of value to more Earthbound applications, from sharper microscopic systems to correcting read errors in DVD players.
The technologies involved centre on optics and how to improve them, says Dr Nicholas Devaney of the applied optics research group within NUI Galway’s School of Physics.
“The basic idea is to measure [visual] aberrations in real time and correct them by adjusting something in the optics,” he says.
The simplest way to understand the challenge involved is to think of the “heat haze” you sometimes see above road surfaces on a warm sunny day.
The heat causes an object seen through the haze to shimmer and flicker, making it difficult to see any fine detail of the object.
The goal is to take the shimmer out of the picture by reading the visual error caused by the haze and correcting it to eliminate the distortion. In order for this to be of use in a real application such as a space telescope, this needs to be done in real time at very high adjustment speeds.
Even if one looks at a much easier error to fix, an image gone out of focus, it still takes some work to find a way to bring a distorted image back into clarity.
Yet that is the goal set by the Active Optics Correction Chain for Large Monolithic Mirrors project funded under the space agency’s Technology Research Programme.
Devaney is principal investigator on the project and he will work with research colleague Dr Alexander Goncharov to design and build a functioning “active optics” system that can be used in future space telescopes.
They will hire a post-doctoral fellow and will also have PhD students working on the project, but they are also subcontracting aspects of the research with colleagues at the Fraunhofer Institute for Applied Optics in Germany.
The word active in this case has a very specific meaning, Devaney says. Active optics might help correct image blurring in an orbiting telescope, automatically adjusting the image until it comes back into proper focus.
“This is similar to the way in which our eyes are capable of focusing on both distant objects and objects that are close to us by adjusting the shape of the lenses in our eyes,” he says.
“Active optics has not yet been used in space and it is necessary to develop it for future space telescopes,” he adds. “This technology has already been developed for telescopes on the ground.”
Many ground-based telescopes also employ another set of technologies to take optical distortion out of the picture called “adaptive optics”.
These techniques can correct for distorting atmospheric turbulence, allowing the telescope to gain a sharp view of distant galaxies and planets despite having to peer through a messy, disturbed atmosphere.
“With adaptive optics, you sample for aberrations and corrections up to 1,000 per second,” Devaney says, but the technology also helps to take sound distortion out of a CD or DVD player to eliminate the effects of wobble.
“The origins of this technology were the idea of an astronomer, Horace Babcock. He had an idea about correcting for atmospheric turbulence which lowers the resolution of a telescope,” he adds.
“If you can achieve this you could obtain the theoretical maximum resolution from a telescope.”
The problem for Babcock was there was no technology to achieve this in the 1950s when proposed. “We had to wait until the 1970s and technologies being developed by astronomers and by the military,” he says.
We have President Ronald Regan’s Star Wars initiative to thanks for some of the advances at the time. The optical technology helped in keeping an eye on enemy satellites but also opened up the possibility of using strongly focused ground- based laser beams to knock out satellites.
“To do this you needed to correct for aberrations,” Devaney says. “After the Cold War ended, all of this transferred to astronomy and now all major telescopes have adaptive optics systems.”
Different challenges present themselves once you move into space with an orbiting telescope. The idea is to use the largest reflecting mirror possible in order to see to the edge of the universe, and as a consequence they have to be thin and lightweight.
These large mirrors – the James Webb Space Telescope set for launch in 2018 has a 6.5 metre diameter mirror – distort due to the tug of gravity and other reasons, Devaney says.
“The future telescopes need to be lightweight and their mirrors need to be thin and easily deformed and this is why we need active optics to correct them.”
The plan is for the researchers to deliver a functioning active optics system for use in space, but it is certain that the technologies developed will filter back into ground-based applications as they have already for active and adaptive optics.
Devaney uses these advances in microscopy to achieve very high resolution images of the retina.
"In retinal imaging you are able to see the individual cones and rods [retinal cells] in vivo. Before adaptive optics you could not do this and needed biopsies. It allows you to detect eye diseases much earlier."
Other uses include optical communications, lasers used in welding and shaping surfaces and in high intensity laser applications such as generating power thorough fusion.
