Laser System Sees through Walls by Object Reconstruction
The unpredictable behavior of photons bouncing off objects and walls inside a room, inspired researchers from the Massachusetts Institute of Technology (MIT), Harvard University, the University of Wisconsin, and Rice University. They combined the bouncing photons with sophisticated optics to allow them to “see” what’s hidden around the corner. This technique, Detailed in a paper published in the journal Optics Express, the technique, could one day prove very useful in disaster recovery situations, in addition to non-invasive biomedical imaging applications.
“Imagine photons as particles bouncing right off the walls and down a corridor and around a corner—the ones that hit an object are reflected back. When this happens, we can use the data about the time they take to move around and bounce back to get information about geometry,” says Otkrist Gupta, lead author of the paper and MIT graduate student.
Trillions of Cycles per Second 2-D Streak Camera
Using advanced optics in the form of an ultrafast laser and a 2-D streak camera, both of which operate on the order of trillions of cycles per second, the team exploited being able to capture billions of images per second to demonstrate the technology’s ability to “see” objects by analyzing the light moving around a corner or through water bottle.
Streak cameras image formation is determined by the time profile of the incoming photons. “This type of imaging provides us with a very good idea of how long each of the photons takes to bounce and come back. If there’s something around the corner, the photons come back sooner and arrive earlier in time” says Gupta. “We’re actually capturing and counting photons. Each image we shoot has three or fewer photons in it. And we take lots of images very quickly to create ‘streak’ images, which help us determine the distance traveled by the photons in centimeters. Once we collect that data, we can infer the basic geometry of the hidden object and a 3-D picture emerges.”
Numerous prospective applications are waiting for this technology. Among the more straightforward are disaster recovery situations. “Say you have a house collapsing and need to know if anyone is inside, our technology would be useful. It’s ideal for use in nearly any disaster-type situation, especially fires, in which you need to find out what’s going on inside and around corners—but don’t want to risk sending someone inside because of dangerous or hazardous conditions. You could use this technology to greatly reduce risking rescue workers’ lives,” Gupta explains.
Non-Invasive Testing is Next
It’s also quite likely that the technology could be used as a type of non-invasive biomedical imaging to “see” what’s going on beneath a patient’s skin. That’s what the researchers plan to investigate now.
Gupta anticipates that it will probably be at least another five to 10 years before the technology becomes commercially available—based on the typical timeframe research and development (R&D) demonstrations take to reach a product launch.
So what kinds of applications can you think of for this system? I’ll bet the military has a few good ideas.