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am I actually seeing IR light?

Crazlaser

Crazlaser

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So I was bored today and started playing with my 800mw 980nm laser. I noticed in darkness I can see a dark grayish blue dot on the wall at close range if I move the laser slowly. Other than this the laser is not visible. Am I actually seeing the 980nm light? I have been lead to believe only 808nm is possibly visible and 980nm is far to long of a wl to see at all. But after seeing the dot I'm thinking that at these powers, 980nm might be slightly visible after all. It was really dim, by really dim I mean barely visible at all, your eyes have to adjust to the darkness and be really close to the dot.
 





Radim

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Hi Sean, good to see you here again. It was discussed in some thread recently. There was mentioned in one post that even 1064 nm might be visible for some people. I did not read the study linked yet. But gray-blue look... Hmm...
 
Crazlaser

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Radim said:
Hi Sean, good to see you here again. It was discussed in some thread recently. There was mentioned in one post that even 1064 nm might be visible for some people. I did not read the study linked yet. But gray-blue look... Hmm...
Click to expand...
Been quite busy with school lately.

Oh, do you have a link by any chance?
 
CurtisOliver

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Interesting, people usually see IR as red still. But I have noticed an optical effect myself once, but not with IR. If light becomes so dim that you can only just about perceive it, you lose the colour and just get a grey faint light. I'm also wondering whether or not it could be something to do with IR fluorescence. I admit I'm a little bit puzzled by your findings but these are my thoughts.
 
Radim

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I would expect the fluorescence to be even more red. Just look on my "rainbow" laser in that another thread. There is just original 405 nm, some gap and wavelengths below. However some other effect might be there... Maybe it is just because of brain adjustment. As it cannot assign right color to it? There are many interesting things - what I've noticed with 405 nm for example. It just creates not only a bit blurry dot, but kind of other circle of dots around as I (and not only me) perceive it. These wavelengths in tails seems the most interesting to me due to various special characteristics.
 
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CurtisOliver

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I couldn't remember the process that I was thinking of. I have just found it however. Double-excitation, where it is possible for the sum of two longer wavelengths to fluoresce and output a shorter wavelength.
 
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Radim

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CurtisOliver said:
I couldn't remember the process that I was thinking of. I have just found it however. Double-excitation, where it is possible for the sum of two longer wavelengths to fluoresce and output a shorter wavelength.
Click to expand...

Yes, basically this happens in frequency doubling crystals, or not? But in the case Sean described I assume it is not - he did not mention material hit would be somehow special.

Maybe diachi will know.
 
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CurtisOliver

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SHG isn't quite the same process, but I can see what you are getting at. It most likely is just a anomaly of the human brain, but it sure would be interesting to find out why.
 
Radim

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Ah, you are right. My mistake. Sorry about that. That's when I write before I think. :D
 
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CurtisOliver

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To be fair, both are TPA (Two Photon Absorption) based processes, just how they achieve it is slightly different. So you wasn't far off with your thinking at all. ;)
And you don't have to apologise, we all get things wrong. :whistle:
Take a look at this image. Double Excitation seems to take the name more commonly of two-photon fluorescence. How simple. :p

1photonv2photon1.png
 
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CurtisOliver

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That was the sort of picture I wanted to find earlier. :p
If I knew it was as simple as searching 'two-photon' fluorescence I would of had it ages ago. :eek::rolleyes:
 
Cyparagon

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IR appears red. If you're seeing a grey or blue, that is likely spontaneous emission from the laser diode.
 
Radim

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Thanks. Makes sense - do you have some link for more reading about that?
 
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