Here is the new holographic camera that sees the invisible

Researchers at Northwestern University have invented synthetic wavelength holography, a complex name for a new photographic method that works by indirectly scattering coherent light onto hidden objects, which then scatter again and return to a device. Photo. From there, an algorithm reconstructs the scattered light signal to reveal the hidden objects. Thanks to its high temporal resolution, the method also has the potential to imagine fast-moving objects, such as hearts beating in the chest or cars spinning around a street corner. In short, he can also see the invisible.

The relatively new area of ​​research into imaging objects behind occlusions or scattering media is called line-of-sight imaging (NLoS). Compared to related NLoS imaging technologies, the Northwestern method is capable of rapidly acquiring full-field images of large areas with submillimeter accuracy. At this level of resolution, the computer camera could potentially see through the skin to see even the smallest capillaries at work.

The method has clear potential for non-invasive medical imaging, early warning navigation systems for automobiles, and industrial inspection in tightly confined spaces, but the researchers believe the potential applications are endless. “If you’ve ever tried to shine a flashlight through your hand, then you’ve experienced this phenomenon,” said Florian Willomitzer, lead author of the study. “You see a bright spot on the other side of your hand, but theoretically there should be a shadow cast by your bones, revealing the structure of the bones. Instead, the light passing through the bones is scattered throughout the tissue in all directions, completely blurring the image of the shadow.

Credit: Northwestern University
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The goal is therefore to intercept the scattered light in order to reconstitute the information inherent in its travel time to reveal the hidden object. But this presents its own challenge. “Nothing is faster than the speed of light, so if you want to measure the travel time of light with great precision then you need extremely fast detectors,” said Willomitzer. “Such detectors can be terribly expensive.”

To eliminate the need for fast detectors, Willomitzer and his colleagues combined light waves from two lasers to generate a synthetic light wave that can be specifically adapted for holographic imaging in different scattering scenarios. Over the years, there have been numerous attempts at NLoS imagery to retrieve images of hidden objects. But these methods usually have one or more problems. They have low resolution, an extremely small angular field of view, require time-consuming raster scanning, or require large probing areas to measure the scattered light signal.

The new technology, however, overcomes these problems and is the first method of imaging in corners and through diffusion media that combines high spatial resolution, high temporal resolution, a small probing area and a large field of view. angular. This means the camera can image small features in tightly confined spaces and hidden objects in large areas at high resolution, even when objects are in motion.