IR is a wide band, and there are many types of IR lasers, with outputs
from about 720 nanometeters to 1500 nanometers, and beyond. I'm going to
assume the lower end of the spectrum, near visible light, as this is
more typical of the output of diode lasers.
In this case, some common photographic filters are available for this.
An RM72 is designed to cut at 720 nanometers; an RM90 at 900 nanometers,
and so forth. (Different filter makers use different letter prefixes.
Kodak uses a numbering system that does not uniquely identify the cut; a
Wratten 87C cuts at 800nm for example.) All of these allow some visible
light. You might try a higher filter to cut more visible light.
You'll find these at online photo shops. Gelatin filters are the
cheapest. You might also consider simply hacking an old IR remote, the
kind that has a dark filter over its LED.
Now as a warning: I experimented with lasers throughout the 80s. I
wasn't careful enough when handling IR lasers, and to this day, I have
several dark spots in my eyes. The lesions are permanent. FWIW, I think
it's better to use a visible light laser if your robot will be among
people. At least then people know to avert their eyes. You can work out
methods for looking for just the bright red dot (which looks like a
white dot on a B/W camera).
I forgot to mention that many color Webcams (like color camcorders)
incorporate IR blocking filters. This prevents the camera from showing
"false colors." Under some types of lighting, for instance, a color
Webcam without an IR blocking filter will show lots of skin
discoloration, veins, and so forth. Not pleasant.
Though some IR still gets through -- you can see this by flashing a TV
remote control into the camera -- you willl probably want to remove the
IR blocking filter in order to allow as much of the infrared as
possible. The design of some Webcams makes this difficult, where the
lens and imager are basically one unit. The filter looks like a clear or
slightly tinted piece of plastic. On some really cheap Webcams, the IR
blocking filter is part of the lens, and cannot be removed.
A black/white camera will not have an IR blocking filter, but there
aren't many B/W Webcams these days. You can try a B/W surveillance
camera, which come with both composite video outputs and USB. You can
get a composite video to USB adapter if needed. This approach will be
I have some.
Start with a IR laser and matching filter. Try Jameco for the laser, you
need to find one that lists the frequency so you can get the filter. Edmond
Sci is a nother place. Also Powertech. Most CCD elements can pick up the
IR, the filter is to cut out the visable spectrum.
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