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can an IR dot cause afterimage or damage

I'd say damage from a reflection like that is not very likely. By the time you get to a dangerous intensity on a matte surface, you'll probably see some light... from the wallpaper catching flame.
 





I'm just wondering if I burn, say blue or black matte paper without goggles could my eyes be damaged if it's a foot away. Or even if it's white. The laser is 980nm 800mw, I know I shouldn't be using it without goggles, I'm just curious as to the effects. I thoroughly went through Sam's Laser FAQ yesterday and couldn't find an exact answer.
 
Crazlaser said:
I'm just wondering if I burn, say blue or black matte paper without goggles could my eyes be damaged if it's a foot away. Or even if it's white. The laser is 980nm 800mw, I know I shouldn't be using it without goggles, I'm just curious as to the effects. I thoroughly went through Sam's Laser FAQ yesterday and couldn't find an exact answer.
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I'm not recommending you do it, but you'd likely be OK.

I've done it myself, with slightly more power at 808nm. Very dangerous though. Do not recommend. It's a big risk.
 
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If you consider the surface to be really matte, you can calculate the risk to be acceptable. This is quite a bit of an assumption though.

It's a bit like calculating that it would be eye safe to look into the filament of a 100 watt incandescent lightbulb from a foot away: it probably is, but i would not recommend doing that.

It would also be safe to look directly into a 0.1 mW red laser for eternity, but i would not suggest doing that either.

I'd apply common sense here: even if calculations say something is safe, don't do it when it's uncomfortable, or if you are not absolutely sure it is safe. Assuming a surface to be matte could be a big mistake here. Especially things like paper can have a coating on it that makes it quite reflective at certain angles when it's actually "glossy" paper that doesn't appear to be that glossy at all.
 
I don't intend on doing it, just wondering. I suppose however that a surface could be determined to be matte by shining a visible laser at it.
 
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Okay so this may sound gory but I must ask, what would happen if you actually stared into a 800mw 980nm laser? Would you immediately feel pain or something or your eyes blur? Would you just stop seeing out of that eye?
 
Don't try the CW high power IR spot on the wall thing without proper goggles. The power levels for damage are actually a bit less then a similar visible spot in some cases due to retinal adsorption of the IR as the wavelength gets longer. Only way to be sure something is safe over a few tens of mW is to measure the scatter using a calibrated photodiode, measure the distance to the eye, and calculate using accepted formulas and tables.. Some materials have a more "specular" or mirror-like scatter then others. Others scatter with a cosine function for power vs angle, therefore a measurement is needed. I'd make the argument for safety glasses with ANY IR laser of any significant power... Cant see it, and whipping it around the room is very imprecise compared to a visible spot where your eye offers "position feedback". If your a "burner" the situation is quite worse as you can't find the focal point easily.

In many cases a cheap black and white CCD or CMOS security camera "sees" it quite well, although many cell phones and web cams (especially some Apple products I have ) now have filters on the camera that block near IR.

Near IR is IDENTICAL to visible light for all practical purposes.

I'm an ILDA Certified LSO and the day job involves tunable lasers...

Steve
 
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