My, what bright, glowing optical fibers you have.

One of my online compatriots recently explained a quick and easy way to do some IR photography. I felt compelled to try, and it was pretty easy. Cheap webcams are the most direct way to do this for a few reasons:

— they’re cheap. If you mess it up, you’re only out a few simoleans.

— they have manual focus. Modifying an autofocus camera requires you replace the IR filter with a glass plate, because removing it changes the optical path length. It’s a much trickier operation.

— it’s usually a fast modification

Just remove the lens — some of them simply unscrew — and check to see if the filter is mounted on the back. (If not, you’ll have to take the assembly apart. No biggie, though, it’s likely just one or two screws. You’ll need a jeweler’s screwdriver, probably phillips-head). Pop the filter off with a small screwdriver or equivalent; the filter may not survive in one piece, so don’t go into this expecting it to survive. Reassemble. You’re done. If the filter isn’t there, it’ll be covering the CCD/CMOS chip, but my extensive data (three points) says that it’s mounted on the back of the lens.

Plug it in to your computer and start taking pictures.

Expectations: This isn’t thermal imaging, so don’t expect bodies to show up glowing. Silicon, the element of choice, has a pretty sharp cutoff starting at about 950 nm, so what you’ll see in the near-IR. Something would have to be about 3000 K to be peaked at that wavelength and thermal images of body temperature targets peak between 9 and 10 microns. Also, the images will be small, since cheap webcams generally run only about a megapixel.

I just happen to have access to several infrared lasers (852 nm and 780 nm, the images use the latter), to give extreme examples of what you can see. This first picture is a laser table with the room lights off. You can see scattered light from several optical components, as well as light emanating from two optical fibers — not all of the light gets coupled into the fibers, and you’re seeing some of what leaks out (some probably in the wrong mode, since these are single-mode fibers, and the bending probably contributes)

In this second photo, there are two images of the same scene, taken with the room lights on. On the left, some shutters are shut, and on the right they are open, and you can see two fibers lit up. Also note the cylinder to the left — that’s a vapor cell with rubidium gas in it, set up for spectroscopy for servo-locking the laser. The laser is on resonance, so you can see the fluorescence as the beam passes through it.

As you can see, there’s quite a lot of scattered light, so normally this is encased in opaque plexiglass. None of the bright features shown are visible with the naked eye.