INNOVATION July-August 2018

A bove : At the heart of an adaptive optics system is the deformable mirror. This mirror, from the 10-metre W. M. Keck Observatory telescope in Hawaii, is only six inches wide, but can change shape 2,000 times per second to compensate for atmospheric turbulence. P hoto credit : W. M. K eck O bservatory P revious page T op : Adaptive optics needs a strong, stable reference point—usually a bright star. If astronomers don’t have one, they make one by exciting sodium atoms to create an artificial star. P hoto credit : S ean G oebel /W. M. K eck O bservatory

per second at hundreds of different points. In astronomy, this makes atmospheric turbulence considerably less troublesome; in ophthalmology, it enables high-resolution analysis of the retina at the cellular level, and the ability to predict eye diseases long before they occur. Earth’s atmospheric turbulence has frustrated astronomers since Galileo. Dr. Colin Bradley, P.Eng., is a professor of mechanical engineering at the University of Victoria, and is heavily involved in astronomical optics and the Thirty Meter Telescope in particular. Dr. Bradley says that the nature of the atmospheric turbulence presents a complicated challenge to astronomers. “There’s different types of turbulence at different altitudes. The layer immediately above a telescope, you get a mixing of warmer and cooler air, and the result is [that the turbulence is] like a stream or a river,” he says. “That layer forms whirlpools, so you get this mixing and refracting of light, and different pockets and columns of light,” he says. “Think of light as a sheet of paper, a flat piece of paper that travels perfectly through space, until the final 30 kilometers,” he says. Once it hits Earth’s atmosphere, that fragile sheet of light is no match for turbulence. One of the reasons the Hubble Telescope was launched nearly 550 kilometers into orbit was to capture starlight from outside the violent effects of the our atmosphere. But Hubble’s got drawbacks. “[Hubble’s] diameter is so small that it’s got limited use. [The 2.4-metre diameter primary mirror] as a light collection bucket is very small.” And space telescopes

like Hubble are notoriously expensive; in 2010, Hubble’s to-date cumulative costs were estimated to be about US$10 billion. And Hubble requires a costly NASA mission and spacewalk just to tinker with it. (With the retirement of NASA’s space shuttles in 2011, no more manned Hubble missions are planned.) That’s why adaptive optics has essentially revolutionized ground-based astronomy, and is poised to revolutionize ophthalmology as well. An adaptive optics system can complete the sample/analyze/ correct routine up to thousands of times each second to produce images that can observe fine details of even faint objects far into space. “In effect, you are putting a massive telescope into space,” says Dr. Bradley. Adaptive optics proved irresistible to astronomers, and have become relatively commonplace on larger telescopes. Many telescopes that were designed before adaptive optics was available have since undergone retrofits. One of the first was the 8.1-metre Gemini North in Hawaii, whose 2002 ALTAIR adaptive optics retrofit was designed and built in Victoria, BC, at the Herzberg Astronomy and Astrophysics Research Centre. More recently, adaptive optics have begun to have a major impact in ophthalmology. Dr. Marinko Sarunic, P.Eng.’s retinal scanner uses adaptive optics to correct for light refractions that even the most powerful microscopes can’t fix. In eye clinics, adaptive optics is the newcomer that is braced to help clinicians detect abnormal blood vessels long before they cause damage. j

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