It isn't easy to see through the smoke and flames in a burning building, but it’s crucial for emergency responders like firefighters, who need to be able to tell if people are trapped inside. To solve the problem, researchers at Italy’s National Institute of Optics have come up with a technique that one-ups conventional infrared camera technology by ditching an optical lens in favor of a laser, using infrared light to build a clear picture of what’s happening inside. The results were published in Optics Express.

Scientists were able to build a holographic model of someone standing past the fire

If you were to look inside a burning building through the lens of an ordinary thermographic camera, radiation from the flames could completely obscure anything inside, making it difficult or impossible to confirm if anyone needs rescuing. In their experiments, the scientists were able to build a holographic model of someone standing past the fire by shining infrared laser light inside the room, then combining the scattered laser light bouncing back out with light from a reference beam. The resulting interference pattern was then decoded to build a hologram.

The images can be processed quickly enough to create a nearly real-time video

The big advantage over conventional thermographic cameras is that because the light hitting the sensor is unfocused, even if some of the sensor’s pixels are saturated by the radiation from the flames, an image can still be reassembled from what’s left over. Sample a couple of times and combine everything with numerical methods, and you can get a remarkably sharp image, like the ones pictured above right. The researchers say that the images can even be processed quickly enough to create a nearly real-time video of a burning room’s interior. And the same principle also works to see through smoke — the soot particles in the air hardly scatter the IR light, thanks to its long wavelength.

Lens_versus_lensless

The team says that its infrared digital holographic (IRDH) system could be mounted on a tripod, giving first responders a live view of what’s happening inside a burning building, and that IR light's long wavelength makes hologram recording resistant to vibrations — an important consideration outside the laboratory. In the paper's introduction, the researchers point out that US fire departments respond to about 1.6 million fire calls a year, mostly domestic house fires, resulting in some 3,000 deaths. They are hopeful that their findings "can open a route for making an imaging technique available that is able to see through fire and possibly to give a completely new chance for saving human lives."