Uncooled thermal imaging

Posted March 9, 2006

Infrared detectors sensitive around human body temperature are great to have, but they're troublesome to build because they usually require active cooling. These guys have a clever mechanism for passively converting infrared radiation into a normal optical signal that an off-the-shelf camera can read, with no cooling required.

The way it works, as I understand it, is simply to build a narrowband interferometric filter out of a material with a large thermal expansion coefficient. Hmmm, that was a bit of a mouthful... the point is that as the material heats up, it changes the spacing between its layers, which means that lets a slightly different light wavelength through, changing color effectively. So all you have to do is put this at the focal plane of your camera, shine a reference light through it, and take an image of that: as the filter heats up according to what's in the scene, it'll become lighter or darker at your reference wavelength, letting you see the heat image with a regular camera.

A clever technique, and one which I suspect has a lot more general applicability in other fields... can you find a material which shrinks and expands in response to, say, a certain chemical, or magnetic fields, or air pressure? Then there's an easy way to extract the signal optically with this sort of method. As it is, though, just having cheap infrared cameras will be cool enough.

Note: at the time of writing the Redshift Systems server was down, but hopefully that's just temporary.