Slightly crazy 980 nm laser experiment

[lasersbee]

There are different frequencies used by TV Remote manufacturers...
I've seen the dim glow of the IR LED in TV remotes and Video security
Camera IR ilumination... Those are 850nm LEDs...
I can also easily see 808nm Laser light..

But in ALL Laser cases I look at those wavelength by observing the light
reflected off of a diffused mat surface...

NOT DIRECTLY INTO MY EYE in the case of the Lasers...

So basically you're just curious about the sensitivity of your own eyes...

BTW... here is a link to an IR Indicator Card... You can probably find
others less expensive...

Sears: Appliances, Tools, Electronics, Apparel and more from Craftsman, Kenmore, Diehard and other Leading Brands


Jerry

 

[Benm]

I think almost everyone can see 808, and since its a laser, the output bandwidth of those pump diodes is pretty small. Realistically, you probably dont want to get in a situation where you can see 808, and certainly not when it appears bright.

The apparent brightness of 808nm compared to 635nm is in the order of a factor 100.000 less. By the time it seems as bright as a cat toy, you will be setting things on fire.

 

[Leodahsan]

got a reflex of a 980nm (100mw) directly in my eye, on lab. just for 1sec, and just 10mw entered my eye. My head started to hurt, after 2~3 minutes, and after 30 minutes or so it stopped. I had to damage in my vision (NEVER POINT ANY LASER IN YOUR EYES, NOT EVEN TO TRY IT, YOU WILL REGRET IT...)

 

[Markus Unread]

I got an "eyeburn" from a 405nm diode, bare and unfocused, in less than a second. The afterburn did go away in about a week but I was really lucky. I could very easily have had that little bar pattern permanently etched into mt eye.

Remember that a very bright point source can damage your eyes - doesn't even need to be coherent.

@Laserbee: Thanks for the IR card reference! It's good to know the right search terms!
Amazon.com: Petra 72-6772 Infrared Indicator Card: Electronics
http://www.fadfusion.com/selection.php?product_item_number=30383000550

 

[Vaporizer]

You really have to be joking to want to look into any laser, IR or whatever! Ok, so you see a dim red on remote controls, so what? Your "experiment" has nothing to gain and your eyesight to lose forever.

I've built micro rc models for yrs. Many were/are IR control. We had some challenges with flying in gymnasiums that had sodium vapor lights or during normal daylight. It's what we called invisible fog. The ambient IR light washes out the pulsed signal. Ok, so lets build the strongest IR tx with the best IR LED's we can find. 10* spread so its point and shoot. I set a rx with a small white led to illuminate as the "target" when it detected enough light to trigger the rx's control. Took the selected LEDs outside after dark, maxed current, and let them run while walking away from them. The strongest LED would be made into a bank of LEDs later on for the tx. One IR LED would trigger the rx at 183'. Yes feet! You shouldn't be looking directly into that LED up close IMHO.
And you want to look into an IR laser or know how long it takes to damage your eye?

You are an idiot. That's the nicest way I can put it after you have been so strongly warned and still seem persistent.

I know direct viewing of a laser (even the glass reflections that I actually do plan on looking at) is a very different beast - that is risky, but I think I can learn something interesting from it.

I think so too...........Braille.

 

[HaloBlu]

I think so too...........Braille.

:crackup:

 

[Benm]

Remember that a very bright point source can damage your eyes - doesn't even need to be coherent.

Sure thing, like the arc when welding, but also just the sun. The latter happens especially often when there is a solar eclipse. People peer into it, which is fine when its sun is completely eclipsed, but get their eyes damaged at the start of the end of the eclipse.

And when it concerns IR leds: If they were visible, they would be insanely bright. Most of them have better efficiency than visible leds. You wouldn't peer directly into a bright visible led, so its only logical you shouldn't do that with IR leds either. Use a camera to test if they are working

 

[Vaporizer]

Benm, I think you are referring to the "Diamond Ring Effect"
It seems apparent he is not going to listen to reason or ppl more knowledgeable that he is.
This should be moved to the "I plan to intentionally injure myself Fail thread because I'm an idiot" area.

 

[Benm]

It is part of it, but even when the eclipse passes beyond that point, many people keep looking directly for a couple of seconds, as the rim of the sun re-appears. Having seen the whole thing in person i can say its absolutely mesmerizing to see, but also important to notice when to re-apply safety glasses.

At the time i was in bulgaria, and the locals used welding masks to gauge the progess of the eclipse (even while it was not even half way there). That was actually a smart move on their part, lacking eye protection intended for observing eclipses.

As far as people ignoring fair warning: i'm all fine with that, if you have been warned and still proceed with a dangerous plan, you sit on the blisters, and/or lean braille. As long as it doesnt encourage others to repeat the same stupidity, i wont whine about it... and if i do, learning braille seems to take quite some time, so i'll be prepared for any 'feedback'

 

[00Giorge]

Benm, I think you are referring to the "Diamond Ring Effect"
It seems apparent he is not going to listen to reason or ppl more knowledgeable that he is.
This should be moved to the "I plan to intentionally injure myself Fail thread because I'm an idiot" area.

I agree, fail thread for stupidity! :banghead:

It sounds like no matter what we say he is going to do it anyway!

Intensity of a 1 mW Laser versus the Sun
Here is a comparison between the maximum intensity on the retina of the Sun and the beam from a 1 mW HeNe laser. (Adapted from one of Simon Waldman's optics lectures.)
Standard Sun:


Maximum intensity of sunlight at ground level (directly overhead, no smog, etc.) = 1 kW/m2 or 1 mW/mm2.

Assuming pupil diameter is 2 mm (i.e., radius of 1 mm), the area is approximately 3 mm2. So, the power of the sunlight through the pupil = 3 mW.

Focal length of eye's lens = approximately 22 mm. Angular size of Sun from Earth = 0.5 degree = 9 mR. Thus, diameter of image formed = 22 mm x 9 mR = 0.2 mm and the area of image = 0.03 mm2.

The intensity of the Sun on the retina (Power/Area) = 3 mW/0.03 mm2 = 100 mW/mm2.
Typical 1 mW HeNe laser (or laser pointer):


Power (P) = 1 mW, wavelength (l) = 633 nm, radius of beam (w) = 1 mm, focal length of eye (f) = 22 mm. So, the diameter of spot = (2 x f x l)/(w x pi) = 9 x 10-3 mm and the area of spot = 6 x 10-5 mm2.

The power density of the HeNe laser on the retina is 1 mW/(6 x 10-5 mm2) = 16,667 mW/mm2 = 16.667 watts/mm2.
So the 1 mW laser has the potential to produce an intensity on the retina 167 times that of direct sunlight! But there are many more factors to consider in determining the real risk of damage. In addition to those noted below, the actual focal point when looking at a laser at close range will not be at the retina so the spot size will most likely be much larger than the diffraction limit of the calculation. Even if the spot from the laser beam is smaller, natural eye movements or movement of the source (e.g., some moron waving a laser pointer) will result in it hitting any given point for a shorter time than the larger spot from the Sun (which usually doesn't move very quickly).

But, at least, perhaps you'll now have a bit more respect for that little HeNe laser or laser pointer!


The real problem behind this is that it is assumed that the power density is the significant factor in the thermal damage mechanism. The ability of the retina to dissipate heat is not dependent on the area covered, but the periphery (circumference) of the exposed area! The blood vessels are in the retina and not the sclera (the surface under the retina) - it is the blood flow that dissipates the heat and so can only act on the *edge* not the middle of the exposed area. In circumference terms, the ratio drops to 7 times. Furthermore because the larger spot is less efficient at dissipating heat, the effective power delivered by the laser beam is only about 2 times greater than that of the spot formed by the sun.

 

[Wallydraigle]

Dear Darwin, merciful father, please watch over and protect this combination of genes from harm, for it knows not what it does. And if you see fit, supreme father, to gather it back into your loving embrace, please help us to know that the removal of this genetic legacy is for the good of the species, and to always keep this truth in our hearts, or whatever circulatory organ we might develop over the eons. For as surely as we brought nothing into this world, so we can take nothing out. Adenine to thymine, guanine to cytosine, forever and ever or until new base pairs arise. Amen.

 

[Benm]

Its a pretty small beam at 2 mm diameter - something to expect from HeNes or DPSS, but not direct diode lasers. The fact that the projected image of the sun is larger may contribute to making it less dangerous than a laser, though i am not sure at which point power density becomes more problematic than raw power.

Blood flow obviously helps in cooling, but at a certain point the thermal resistance between the retina and the blood vessels becomes too large to overcome regardless of how fast the blood flows. From that point on its only power density that determines damage, but i suspect that we'll be far above MPE levels before that happens.

 

[00Giorge]

Its a pretty small beam at 2 mm diameter - something to expect from HeNes or DPSS, but not direct diode lasers. The fact that the projected image of the sun is larger may contribute to making it less dangerous than a laser, though i am not sure at which point power density becomes more problematic than raw power.

Blood flow obviously helps in cooling, but at a certain point the thermal resistance between the retina and the blood vessels becomes too large to overcome regardless of how fast the blood flows. From that point on its only power density that determines damage, but i suspect that we'll be far above MPE levels before that happens.

It was just something that I read a while back when I was reading up on eye damage after I accidentally caught a laser reflection. Just thought it might help to get the point across.:tinfoil:

But the way it has been going so far I think we are getting a better response from the squirrel that's out in the tree f#%@ing with my cat.

 

[Trajork]

Thanks everybody for putting up with my sheer recklessness. I'm happy to report that I did this and nothing bad happened.

It showed up yesterday and I hooked it up to a couple of batteries. Then I took it to a dark room and shined it off the wall. Not surprisingly, I wasn't able to detect anything with my eye. I made sure it worked by viewing it with a digital camera - there was a dot there, with the bluish color I've seen previously by using it to observe 940 nm LEDs. I unfocused the beam and tried to see anything off a glass surface - no dice either. So I then did the stupid thing and looked directly into the beam for ~1-2 seconds. What I saw was pretty interesting - a red spot in the center surrounded by a cyan glow. I repeated the experiment with a 750 nm filter in the way, which took out the cyan leaving only the red spot. So my eye (only the right one - left was covered) was subjected to two exposures of no more than 2 seconds or so.

This was enough to satisfy me. I did one last, much safer test to ensure the laser was the advertised wavelength. I shined it through a diffraction grating and marked the resulting spots on the wall, which I observed with the camera, with a pen. Then I compared it with spots from my other lasers (wavelengths 405, 532, and 650 nm), and fit a line to the results. Sure enough, it was 980 to within my uncertainty.

I did this all yesterday, and I have observed no visual disturbances in my right eye. Reading ability is unaffected compared to my left, and enough time has elapsed (16 hours) that any retinal burn would be obvious by now. What I did was dangerous and irresponsible, but again probably not more so than staring for even longer at focused laser pointers (a stupid thing I did as a kid many times after I first got my hands on a laser pointer, as I'm sure you're all not surprised to hear).

A couple of things about this interested me. First of all, the human eye does indeed have nonzero sensitivity to light even at nearly a full micron of wavelength. Granted, the sensitivity is so low that you have to be as stupid as me to see it, but it's there all the same. I later uncovered a paper ("Visual sensitivity of the human eye to infrared laser radiation", Sliney et. al., 1976) where researchers actually did shine low-powered lasers into subjects' eyes. They noted that there was some sensitivity even at 1064 nm. Most interestingly of all, although continuous 1064 nm was seen as red, a pulsed 1060 nm laser appeared green because of frequency doubling within the human eye.

Frequency doubling leads me to another question - could the cyan glow I saw around the laser spot have to do with frequency doubling somewhere within the laser? Frequency doubling would give me 490 nm light, which would be cyan. Or is something else probably going on here?

Anyway, again, thanks to everybody for dealing with me. Just because it was interesting doesn't mean it was a remotely good idea, and I won't be doing that sort of thing again. I just really wanted to satisfy my curiosity.

Now, off to go shine it at an airplane... JUST KIDDING!

 

[00Giorge]

You just went beyond stupid!! :banghead::toilet:

I was right about the squirrel out in the tree!

 

[Vaporizer]

Sir, you ARE an IDIOT. A damn lucky one at that.
I should put a bounty for a laser vasectomy on you using no anesthetic.
I'm still relativity new here, but why you haven't been banned I haven't a clue.
People coming to LPF do not need to read your recklessness on this forum.
I think this thread should be deleted forever.

My .02 cents is in.....no more here for me.