Digital Infrared Holography

When firefighters go looking for victims trapped inside a burning building, they often encounter rooms and hallways filled with thick, blinding smoke. If no flames are present, a rescuer can use an infrared camera to spot the heat signatures of warm, living bodies. But in the midst of a raging inferno, heat from the flames will overwhelm the camera’s sensors and obscure nearby objects.

Researchers in Italy may have found a solution: a digital imaging system that captures infrared signals in 3-D and converts them to holographic video in real-time, thus allowing firefighters to distinguish flames from heat-emitting objects behind them.

Here’s a demonstration video the researchers made to show the system in action (right), compared with a standard infrared camera (left):

The imaging system generates video using the basic principles of holography, which are explained nicely in a press release accompanying the study:

To create a hologram, such as those typically seen on credit cards, a laser beam is split into two (an object beam and a reference beam). The object beam is shone onto the object being imaged. When the reflected object beam and the reference beam are recombined, they create an interference pattern that encodes the 3-D image.

How Holography Works

The researcher used an infrared laser, which sends out longer wavelengths of light than a laser operating in the visible spectrum, for two reasons: first, visible light can’t penetrate a smoke-filled room, while infrared light gets through with little scattering; second, laser beams of longer wavelength recombine to form a larger interference pattern, allowing the system to generate large, human-size holograms.

In order to turn a single static into a video, the infrared laser sends out repeated, pulsed beams. Each pulsed beam recombines to form a new 3-D image.

The imaging system would be a major improvement to regular infrared cameras, but before it’s ready for action, the researchers need to figure out a way to combine the laser source and camera into a single set-up.