New holographic camera sees around corners and through skin

A new holographic camera that can see around corners and through scattering media like our skin has been developed by Northwestern University researchers.

The new method of imaging is called synthetic wavelength holography and it works by indirectly scattering coherent light onto hidden objects, which then scatters again and travels back to a camera. From there, an algorithm reconstructs the scattered light signal to reveal the hidden objects. Due to its high temporal resolution, the method also has potential to image fast-moving objects, such as the beating heart through the chest or speeding cars around a street corner. The study will be published on Nov. 17 in the journal Nature Communications.

This new field of research is called non-line-of-sight (NLoS) imaging. Compared to related NLoS imaging technologies, the Northwestern method can rapidly capture full-field images of large areas with submillimeter precision. With this level of resolution, the computational camera could potentially image through the skin to see even the tiniest capillaries at work.

While the method has obvious potential for noninvasive medical imaging, early-warning navigation systems for automobiles and industrial inspection in tightly confined spaces, the researchers believe potential applications are endless.

Seeing around a corner versus imaging an organ inside the human body might seem like very different challenges, but scientists say that they are actually closely related. Both deal with scattering media, in which light hits an object and scatters in a manner that a direct image of the object can no longer be seen.

The goal, then, is to intercept the scattered light in order to reconstruct the inherent information about its time of travel to reveal the hidden object. But that presents its own challenge.

To eliminate the need for fast detectors, researchers merged light waves from two lasers in order to generate a synthetic light wave that can be specifically tailored to holographic imaging in different scattering scenarios.

Over the years, there have been many NLoS imaging attempts to recover images of hidden objects. But these methods typically have one or more problems. They either have low resolution, an extremely small angular field of regard, require a time-consuming raster scan or need large probing areas to measure the scattered light signal.

The new technology, however, overcomes these issues and is the first method for imaging around corners and through scattering media that combines high spatial resolution, high temporal resolution, a small probing area and a large angular field of view. This means that the camera can image tiny features in tightly confined spaces as well as hidden objects in large areas with high resolution — even when the objects are moving.

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