Even though the figure in red lies hidden, out of the direct line of sight of the figure in green, radiation naturally emitted by the concealed figure at submillimeter wavelengths betrays its presence. At these long wavelengths, many types of walls act as partial mirrors, reflecting the light into view of the green figure.
Credit: NIST
A new way of imaging concealed objects, devised by a researcher at the National Institute of Standards and Technology (NIST) and his colleagues, might take all the fun out of hide-and-seek, but could also help save lives.
Imaging scenes that lie outside an observer’s direct line of sight could greatly enhance search and rescue missions, such as finding a lost child in an abandoned factory, as well as military and police surveillance operations, such as exposing a hidden terrorist or enemy stronghold. The ability to see around corners and reconstruct a full image of a hidden object or obstacle in real time also could someday improve robotic vision and the safety and accuracy of self-driving cars. (At present, the prototype method cannot create an image instantaneously.)
Most conventional methods used to image objects behind an obstruction use an external source of light — ultra-short pulses of visible or infrared laser light, for example. The light source initially illuminates a wall that scatters the light into the concealed region. When the light strikes a hidden object, the object re-scatters some of the light back to the wall where it can be detected.
However, imaging hidden objects using only visible and infrared light is challenging. At those relatively short wavelengths, a typical wall — no matter how smooth to the human touch — presents itself as a rough surface and scatters incoming light in all directions. It therefor ..
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