Look beyond the visible

Most machine vision systems are developed using visible light. That makes sense because most of the time we want to detect things that we can see with the naked eye. But interesting things happen when you go out into the infrared region of the spectrum.

Quick primer: visible light spans wavelengths from about 400nm up to 750nm. That’s from blue to red. As wavelengths get longer than 750nm we’re into the “infrared” region, which goes all the way up 1mm; the so-called “millimeter waves”. Now that’s a big range, so to make life easier scientists have divided the IR spectrum into three regions. There seems to be some dispute about the precise definitions, but in crude terms there’s Short Wave Infrared (SWIR,) which goes up to about 3,000nm, Mid-IR which covers the 3 to 30μm range, and Far-IR which is beyond 30μm.

The silicon sensors we use in our conventional machine vision cameras can’t detect anything past 1μm, but InGas detectors can go up to 3μm. So what can you see with InGas that you can’t see with a regular silicon CCD?

Well Sensors Unlimited Inc, part of Goodrich Corporation, have built a whole business around SWIR imaging, so if you visit their web site you’ll find plenty of examples. Some of the most interesting relate to the inspection of photovoltaic cells. For a short summary you light also like to read the article and watch the video, posted on Laser Focus World, (September 8, 2009.)

Now, a pop quiz: can you name one of the founders of Sensors Unlimited, and for a bonus point, what is his biggest claim to fame?