I want to detect a hit from a laser pointer, or something similar. The pickup area needs to be about 16 by 16 inch. Wondering if anybody has used a thick piece of plastic, with a detector possibly looking at it from the side. — Looking for ideas.
It will be very difficult to distinguish the laser light from the background, unless the laser beam is modulated, for example at 40 kHz.
Thanks, and I agree
Doing it that way is an interesting approach. It may work if you etch the plastic sheet to scatter enough light so the 90 degree detector can pick it up.
An alternate method would be to use a large lens with a detector at the focal point. Perhaps a large Fresnel lens might work. I have a couple that are about 8" or so.
I did a project like this once, but the detection area was only about 1" square. Photodiodes that size are expensive!!!.
Thanks lyndon. You are along one of the ideas I plan on experimenting with. Playing, in my head so far, about etching or scratching with sand-paper. If that is done on the front, and then attach or spray on an aluminum coating on the back, there may be enough light redirected to squirt out sideways. As far as using a Fresnel lens, I want to keep it fairly thin, so having a lens of some type would make it thicker or deeper than I am hoping for.
Fresnel lenses are thinner than regular spherical lenses because of their special geometry. But the focal point distance does not change much.
https://en.wikipedia.org/wiki/Fresnel_lens
They are available in foil sticker form for using on car windscreens or windows. Also, they are sometimes used on transparent covers to magnify computer monitors. Or that was a cheap way to get large views in the past. So finding a 16 inch size might still be a posibility.
Worth checking and find out what focal lengths are. Worked with them way back on a special project, before they were so widely used on motion detection lights. Similar use, but not for turning on lights. Do you know of a good source? Someone like Digi-key or Allied carry them? Will have to do some digging.
Hey Valen, did some quick checking on Fresnel lenses and they look like a possibility. The price has sure dropped since I did any research on them. Will be checking focal lengths when I have more time. (Just came in for a bit from shoveling snow) If I can find what I am looking for, I would expect a much better signal to noise ratio than the direction I was going. TNX
Bern:
Anchor Optical Supply is a good place for cheap(er) optics. I think I got mine years ago from Ax Man, a local surplus dealer.