Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donations

Links below open in new window

ArcticMyst Security by Avery | Browser Hide by Avery

What is the longest wavelength of laser light you have seen?

Things

0
Joined
May 1, 2007
Messages
7,517
Points
0
I've never come across a 808nm diode that has emitted any other wavelengths than 808nm. Of course their wavelength drifts just like any other diode, but it's still only one. Any 808nm diode datasheet will tell you that, as majority have spectrometer readings. It's purely your eyes ability (or lack of) to see IR light, a camera is far superior.
 
Last edited:





Joined
Sep 20, 2013
Messages
17,993
Points
113
I don't recall seeing the speckle, but it has been some time since I looked at it. I have a spectroscope that I might be able to use between the camera and the dot, but since the infrared camera is monochromatic as all are, it might be hard to do. I was just hoping there was something you could site to back up this claim.
 

Things

0
Joined
May 1, 2007
Messages
7,517
Points
0
OK, take this random C-mount 808nm diode from Osram for example, here's the datasheet:

http://www.osram-os.com/Graphics/XPic7/00083664_0.pdf/SPL CG81-2S.pdf

Page 4 has a graph of it's spectral emission - total flatline except at 808nm. Of course without knowing what diode you actually have, you'll probably be unable to find a datasheet for it and would have to actually measure it.

You'll probably struggle to see speckle on such a low power IR laser, seeing as how difficult it is to even see the dot. Provided you could prevent it from washing out the image on a camera you may be able to see it that way. That said, "LED" emissions from a diode can't be collimated unlike the actual laser emission itself, so you can pretty much guarantee that the beam is purely 808nm (thus why it's better to do spectral readings at a distance from the laser aperture).
 
Last edited:
Joined
Dec 11, 2011
Messages
4,364
Points
83
I've checked 808nm diodes with diffraction gratings and cameras (both with 808nm blocking filters and IR-pass filters) in the past. There's no detectable stray visible emission.

The beam will look wider on camera because the eye requires a higher power density threshold to perceive it and what you're "seeing" is the spacial distribution plot of the irradiance across the cross section. The camera's threshold is much lower so it perceives the entire beam/spot. This is akin to demodulating FM with an AM receiver by tuning to the edge of the broadcast frequency and relying on the nonlinearity of the receiver (slope detection).
 
Joined
Sep 20, 2013
Messages
17,993
Points
113
I checked the Osram sheet and it showed a perfect 808nm plot, but was only from 790nm to 830nm. That leaves out a whole lot of spectrum. But, I will accept your and Sig's explanation. It was at a distance of about 2 meters that this was detected. I didn't think that 808nm was within the visual acuity of most people.
 

Things

0
Joined
May 1, 2007
Messages
7,517
Points
0
Technically "red" ends at about 750nm - so if you consider the "visible" spectrum as purely colours we can observe that have a perceivable difference to other colours, then yeah, you could say that. Though from what I've read on these forums over the years most people mention being able to see 808nm, and simply describe it as a dim red.

If you are able to measure your laser then it'd be interesting to see - though I'd be willing to put bets on it being purely 808nm coherent emission :)

I know the old PS3 KES 405nm diodes were famous for having a slight yellow emission - but it wasn't coherent, simply "LED" emission for lack of a more technical term.
 
Last edited:
Joined
Jun 22, 2011
Messages
2,431
Points
83
I can see the speckles on 780nm, 808nm and 850nm IR lasers just fine. Can't see the speckles properly on camera, though.
 
Joined
Sep 30, 2010
Messages
12
Points
0
I was looking up some laser information, stumbled across this site, and remembered that this is where I posted an insane self-experiment four years ago that I'm lucky to still have full eyesight after.

In short, I looked directly into a 980 nm laser diode that was advertised as <5 mW (although in my stupidity I never tested it). I did indeed see a deep red pinprick in the center surrounded by a cyan glow that I presume was frequency-doubled 490 nm light. I risked my eyesight a second time by putting a cheap 750 nm IR-pass camera filter in front of the laser and looking again; the deep red light was clear as it was previously, but there was no cyan glow. So I'm pretty sure I saw 980 nm near IR light and 490 nm frequency-doubled cyan light.

Luckily for me, my right eye still works fine; no vision loss. This was nowhere near certain, as everybody who replied to my thread tried to warn me to no avail. I neither regret nor recommend this amateur "experiment" but it is fun to say that I've seen 980 nm light, and that I've seen two octaves of light simultaneously. On the other hand, the 980 nm spot was totally invisible as a diffuse reflection from a white wall - only directly shining a laser into my eye enabled me to see it. I got lucky; please nobody ever do this again. But I wrote about it here: http://laserpointerforums.com/f40/slightly-crazy-980-nm-laser-experiment-56198.html

This is the second most dangerous sciencey thing I've done. Only the time I made what I called "Hell's Mountain Dew", about six months later, eclipses it. Specifically, I went outside on a deck and, while holding my breath, added formic acid (~95%) to sulfuric acid (98%) in a glass beaker on a scale. The HCOOH rapidly decomposes to CO and H2O. I ran back inside, started breathing again, and observed the rate that the mass of the mixture fell to determine how quickly CO was being outgassed. Over a quarter of the HCOOH in an equal-volume mixture decomposes to CO within the first minute or so. I repeated this several times, until I was stopped by the scale failing because of corrosion from splattered sulfuric acid. The deck also took some damage, as did my clothing: I ruined at least three shirts and two pairs of jeans. I did at least wear safety goggles and gloves, but that and breath-holding were all the safety measures I felt like taking.

The sulfuric acid bubbles, violently at first, with carbon monoxide, which slowly subsides over the next half hour or so until it looks like Mountain Dew, if Mountain Dew were concentrated sulfuric acid rather than dilute citric and phosphoric acids and the bubbles were CO rather than CO2.

Thankfully, my backyard "experiments" did not earn me a Darwin Award. But yes, I have seen 980 nm laser light, and it is beautiful if incredibly dangerous.
 
Last edited:
Joined
Jun 22, 2011
Messages
2,431
Points
83
It was probably your experiment that triggered the other IR-viewing posts. Other members have confirmed the 490nm line, including me and The LED Museum:
http://laserpointerforums.com/f52/possible-cheap-2-line-980nm-490nm-pen-90391.html
http://laserpointerforums.com/f52/review-980p-100-bl-980nm-laser-pen-91218.html

There might be a way to perform your experiment safely. One would have to find a IR filter that passes about 1% @ 980nm. Then it's only a matter of metering the laser to make sure it's <1mW. If the 490nm washes it out the IR filter would have to be stacked with a visible light filter.

Another option would be buying a low power 980nm diode and underdriving it, but then the "LED" emissions might mess up the results.

BTW, what did the red color look like? 650nm? or "duller"?
 
Last edited:
Joined
May 6, 2013
Messages
178
Points
0
Luckily for me, my right eye still works fine; no vision loss.

I'm the one who revived the topic. I was already researching human vision in the near infrared on my own, and was amazed to find someone else had thought of the same thing.

I hope your eye is okay.

New interest: single-photon vision.
 

Benm

0
Joined
Aug 16, 2007
Messages
7,896
Points
113
To me 808 nm is surely visible - reflected of a piece of paper placed in front of a 808 nm pump diode. Is is, however, very very dim. Considering this pump was blasting out 500 mW or and the reflection on the paper seemed very dim (perhaps comparable to 0.1 mW of 650 nm).

Perhaps i'm saying this one time too many, but DO NOT LOOK INTO IR DIODES, EVER.

Generally it considered that 5 mW diodes are more or less safe to use, but that is because you will blink when hit in the eye with a blindingly bright light. As the IR does not appear bright at all you will not have a blink reflex either.

You could probably stare straight into a 808 collimated beam outputting 50 mW for an extended period of time. It will not seem to be bright at all, but it does almost the same amount of damage a 50 mW 532 nm beam does - which is so bright you will blink, but about 10 times too slow to prevent damage.
 
Joined
Jan 29, 2014
Messages
12,031
Points
113
Scary, I did something like that last year, I ordered some low power red lasers and when a package came from China I was happy it finally came, put some batteries in but it didn't put out any light, nothing when I pointed at the wall. I then at an angle looked into the end of the laser pointer about two and a half feet away and saw some dim red coming out of the tube when I realized it wasn't the red 5mw pointer, it was the 300mw 808nm pointer, I've seen that dim red color before! Crap....

Still scares me when I think about it, maybe I was hit by it but the focus was so far out I only received a small portion of the power due to beam spreading, that was probably far more likely as later I had to turn the lens quite a bit to focus it to burn something.

Later that day, I was burning plastic with this same laser and a week later my low power red laser came that had the same kind of host, very closely resembling the 808nm laser I could have blinded myself with. It was easy to confuse shipments, nothing was in English except my address.
 
Last edited:
Joined
Sep 20, 2013
Messages
17,993
Points
113
WOW! I have never been tempted in the slightest to look into a collimated laser, no matter what the power was. Now, a beam that has been diffused by a biconcave lens is another thing. That is perfectly safe to observe if you allow for the inverse of the square law. In fact it is pretty much a must when setting up a hologram optical bench and trying to get the reference beam and the object beam to be of a 1:4 ratio.
 
Joined
Jan 29, 2014
Messages
12,031
Points
113
I'm afraid to even look at the raw output of any laser diode unless diffuse enough and low power enough, but I am qualifying the statement with a lot of enough's. People sometimes forget, even without a lens in front of the diode, it can become a tight low divergence beam when going through the lens in your eye.
 




Top