INNOVATION July-August 2018

F E A T U R E

WHAT I S A DA P T I V E O P T I C S ?

E veryone has seen twinkling stars. The twinkling is actually atmospheric turbulence: parallel wavefronts of light that are twisted and distorted by colliding air densities, caused by differing air temperatures. Light travels undisturbed through space until it passes through Earth’s atmosphere and encounters this turbulence—similar to airplane turbulence or heat waves shimmering above asphalt. The result is that stars look like a fuzzy, blobby mess by the time their light reaches us on the ground. Ophthalmologists encounter similar image problems. They call them “abberations”: light refractions caused by the cornea, lens, and fluid from inside the eye itself. These aberrations blur eye scans, especially deep into tissue at the back of the eye, and prevent clinicians from seeing progressive cell-level eye damage. Adaptive optics detects light turbulence (in astronomy) and aberrations (in ophthalmology), samples and analyzes them in real-time, and feeds the results to a powerful computer that calculates the optimal way to insert corrections into the light path. Those corrections are then fed to a sophisticated mirror called a “deformable mirror”—a little like a funhouse mirror, but smaller, and able to change shape thousands of times

Adaptive optics at work in astronomy. These images were taken from the W. M. Keck Observatory in 2004. On the left, Saturn and Uranus are shown with the telescope's adaptive optics system turned off; on the right, with the system turned on. Photo: Heidi B. Hammel and Imke de Pater, and the W. M. Keck Observatory

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I N N O V A T I O N