A new imaging technique might one day help physicians peer into human tissue and behind bones, let mechanics inspect moving machinery such as airplane turbines for tiny defects, or enable automated vehicles to see through dense fog or around blind corners. A study detailed in Nature Communications shows how the process, called synthetic wavelength holography, can capture detailed and nearly instant snapshots of objects hidden from view.
Light scatters when it bounces around a corner or travels through a cloudy material, says Atul Ingle, an electrical engineer at Portland State University who was not involved in the study. To see what lies on the other side of such obstacles, he says, “you need to undo the scattering and resolve the [hidden] structures with very high resolution.” The technique overcomes those challenges at frame rates fast enough for video, Ingle adds.
The process involves firing laser beams with slightly different wavelengths past obstructions—be it off a wall or through some translucent material—to strike a hidden target. The wavelengths that reflect back are captured and superimposed to produce an interference pattern that reveals the distances of objects hidden from direct view. This process draws from a technique called interferometry, which scientists have used to precisely measure the size and shape of stars and cell structures. Other forms of “non-line-of-sight” imaging struggle with simultaneous speed, high resolution and broad field of view. “Our method combines all these attributes at the same time in one method,” says Northwestern University physicist Florian Willomitzer, lead author on the new study.
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