How non-line-of-sight (NLoS) imaging is changing the way we view the world

On November 17th, 2021, Science Daily posted an article about a publication made in Nature Communications, a well-recognized scientific journal, titled: “Fast non-line-of-sight imaging with high-resolution and wide field of view using synthetic wavelength holography.” This new medical technology, developed by Northwestern University in Evanston, Illinois, is termed non-line-of-sight (NLoS) imaging because it uses scattered light that is eventually recombined to generate an image of an object through, behind, or around an obstacle/occlusion. Florian Willomitzer, the lead author of the publication, explained how the used of scattered light works for imaging:


“Seeing around a corner versus imaging an organ inside the human body might seem like very different challenges, but Willomitzer said they are actually closely related. "If you have ever tried to shine a flashlight through your hand, then you have experienced this phenomenon. 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 bones' structure. Instead, the light that passes the bones gets scattered within the tissue in all directions, completely blurring out the shadow image." 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.”


However, the newfound challenge of capturing this light has been the fact that the speed of light is so fast that “very expensive” detectors are needed to detect it. To overcome this obstacle these Northwestern University researchers have used tailored waves and walls to successfully create holographic images. Tailored waves involve merging two lasers to generate a synthetic light instead of traditional light, which can be adjusted situationally and captured with normal detectors. Meanwhile, by using walls as mirrors they can create straight lights paths to an object of interest through other obstacles or around corners to create the holographic image.