A new imaging technique could one day help doctors peer into human tissue and behind bones, enable mechanics to inspect moving machinery such as airplane turbines for tiny flaws, or enable automated vehicles to see through thick fog or blind corners. A detailed study in Nature Communication shows how the process, called synthetic wavelength holography, can capture detailed, near-instantaneous snapshots of objects hidden in plain sight.
Light scatters when it bounces around a corner or passes through 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 these obstacles, he says, “you have to cancel the scatter and solve the [hidden] very high resolution structures. The technique overcomes these challenges at frame rates fast enough for video, Ingle adds.
The process involves shooting laser beams with slightly different wavelengths past obstacles, whether on a wall or through translucent material, to hit a hidden target. The reflected wavelengths are captured and superimposed to produce an interference pattern that reveals the distances of objects hidden from direct view. This process is inspired by a technique called interferometry, which scientists have used to precisely measure the size and shape of stars and cellular structures. Other forms of “no line of sight” imaging struggle with simultaneous speed, high resolution, and wide field of view. “Our method combines all of these attributes at the same time in a single method,” says Northwestern University physicist Florian Willomitzer, lead author of the new study.
Willomitzer and his colleagues demonstrated that they could capture images of millimeter letters beyond corners as well as through blurry plastic plates. While previous imaging methods iteratively scanned thousands of pixels to compose a scene, this process only required two exposures (each taking just 23 milliseconds to capture) to scan a near-hemispherical field of view.
Combining this technique with ultrasound imaging could eventually allow doctors to see around bones or see tiny blood vessels under the skin, Ingle suggests. The two researchers say, however, that more work and testing is needed to turn this vision into reality. Probing a slab of living tissue is harder than looking through thin plastic, but in 10 years or more, Ingle says, this research could yield a practical, commercially available way to look beyond the line of sight. .