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Slightly crazy 980 nm laser experiment

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Toke

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This is just too dumb, Ebay have no shortage of IR leds for such tests.
 





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Hmmm... I was fascinated at first. Now i do think what you did was stupid. I'm sure that it will have done some damage, even if that damage is not noticeable. You shouldn't have stared for that long!

But all that aside, i'm intrigued. I am doing a presentation later in the year on diode lasers to people in my school, and (should you permit) i will mention this (along with a whole bunch of warnings not to do it).

Soo... going to try UV next?

(That was a joke! Don't do any more experiments!)
 

Benm

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Well - you had been warned plenty of times, and chose to ignore it all. I cannot condone your experiments, but at least you took the chance of getting some information and weigh the risks to some degree.

Reminds be of the early researchers in radioactivity, who noticed that some sources created flashes of light within their eye, even with their eyelids closed. I'm sure that led to a couple of brain tumors, but who knows they realized the risk to some degree and tried anyway.

As for the cyan light observed: I dont see any reasonable mechanism that could account for frequency doubling in the eye. Perhaps your L and S photoreceptors are also sensitive to this wavelength. I suggest you do not attempt to find out.

If the cyan is somehow emitted by the laser, you could observe that through IR blocking filters just as well. I'd suggest setting up a couple of IR filters in a row so you get a huge OD for IR, and then observe using a camera in a dark environment.
 
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Hmmm... I was fascinated at first. Now i do think what you did was stupid. I'm sure that it will have done some damage, even if that damage is not noticeable. You shouldn't have stared for that long!

But all that aside, i'm intrigued. I am doing a presentation later in the year on diode lasers to people in my school, and (should you permit) i will mention this (along with a whole bunch of warnings not to do it).

Soo... going to try UV next?

(That was a joke! Don't do any more experiments!)

Yeah, I exposed myself to it longer than I intended, and I'm lucky it hasn't done anything noticeable. I'm certainly not going to play any more visual Russian Roulette. And by all means mention this at your school - as long as a random idiot from the internet is a good enough source!

Benm said:
As for the cyan light observed: I dont see any reasonable mechanism that could account for frequency doubling in the eye. Perhaps your L and S photoreceptors are also sensitive to this wavelength. I suggest you do not attempt to find out.

If the cyan is somehow emitted by the laser, you could observe that through IR blocking filters just as well. I'd suggest setting up a couple of IR filters in a row so you get a huge OD for IR, and then observe using a camera in a dark environment.
That gives me an idea - perhaps I could use a spectroscope with a camera in front of it to see if that wavelength is really right around 490 nm. I don't think my S or M photoreceptors could be sensitive to 980 nm because I'd have seen some sort of composite color, rather than a deep red spot surrounded by a cyan glow. Do you think that something the light passes through in the laser might result in very weak frequency doubling, within the laser? I too doubt that a continuous laser beam could cause frequency doubling in the eye, so I'm wondering if it's some property of the laser itself.
 

Benm

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I highly doubt the frequency doubling theory, but i suppose its easy enough to find out using a spectrometer and/or IR filters - the latter to determine that anything non-ir comes out, the first to measure its wavelength.
 
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he could still type with his remaining good eye

It doesn't work. I try every day. They just don't protrude enough.

drowsy_2_080228_ms.jpg
 

rev0

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I recall reading somewhere (perhaps Sam's Laser FAQ) that lasers act unintentionally as LEDs sometimes, and can emit other wavelengths. Sometimes these other wavelengths will be much more visible in comparison to the IR wavelength and dominate (so, inadvertent LED activity in the red/near IR might be happening with these longer wavelength lasers, or even cyan as you mentioned). This would be worth researching, and I'll see if I can find that information again.

Edit: Woohoo, found it: http://www.repairfaq.org/sam/laserdio.htm#diovon1

Excerpt:
Sam's Laser FAQ said:
Here are a variety of comments on whether light perceived as originating from near-IR laser diodes - those with wavelengths shorter than about 1,000 nm - is actually due to the actual lasing line or just the much broader spontaneous (LED) emission. For some types of laser diodes, it may be a combination. But various experiments are described below with Ti:Sapphire and dye lasers that show clear visibility of near-IR wavelengths beyond 800 nm.
...
According to the official 'standard observer' photopic response of the human eye, the long wave cutoff is a gradual one. Sensitivity roughly halves for each 10 nm further into the infrared. This trend holds close to true enough 'officially' from 700 to at least 780 nm.

It seems as if a small spot is usually (maybe only barely) visible to dark-adapted eyes in a dark room with eye-safe levels of any wavelength up to around 880 to 900 nm, maybe 950 nm for brief viewing. (If your eye's long wave sensitivity is not below average!)

But you may not want to push your luck. A milliwatt of IR can permanently cook a spot of your retina, maybe within a couple seconds, and with no pain or warning. Prolonged focusing of any quantity of light over 0.4 microwatt onto a single point on the retina is potentially damaging, although several microwatts won't do damage in only seconds.
 
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Benm

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LED emission as a side effect is not uncommon, but its usually at a lower energy (i.e. longer wavelength) than the laser emission. For example, blue and bluray laser diodes can emit a visible yellow when driven at very low current (far below the threshold). This yellow is also produced when lasing, but simply overwhelmed by the laser light.
 
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Similar technology that offers an explanation - White LEDs without the use of a phosphor:

AOP_L-513NPWC-30D_die.jpg


"This InGaN p-n junction emits white light without the need for any phosphor. The emission spectrum of this device is composed of two relatively narrow spectral bands in the blue and yellow which originates from the material's regions having low and high indium concentration, respectively. The emission strengths of these peaks depend on the junction current, the yellow emission being relatively stronger at low current, resulting is a warm white appearance as shown here. "

Source
 

Morgan

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Our new best friend the 445nm diodes from the Casios apparently emit green and violet light that can be collimated at low level. It's mentioned over at PL but I can't remember if these emissions happen above or below the 445 lasing threshold. I haven't tried it myself yet but it's on my list...

I'm actually surprised this thread went on for as long as it did. Even more surprised it went on for as long as it did without a post from LRSFAQ! Where are you Steve? I'd love to see what you had to say on this subject!

M
:)
 
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What would be the problem, if using proper safety goggles, of doing a time lapse wall pic with the laser being shot through a prism to split these colors? The main color will probably try to burnout the image, but a flat black divider could block the cameras view of the main color allowing the other colors to be visible and not washed out. If they are that low in intensity, I doubt they'd make it through abt any filter.
I think it would be an interesting test if anyone has a prism handy.
 
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Thanks for the replies! I took a look at Sam's Laser FAQ and noticed this comment:

Some months ago we receiveed a batch of 980 nm laser diodes (modules) with light emission at two wavelengths: One as expected at 980 nm (50 mW) and another very low power emission at around 670 nm (few 10 uW).

That's interesting, although I don't think it would explain the red I saw, since I used an IR-pass filter to get rid of <750 nm light for my second exposure. I still saw red, but not cyan. I've verified this filter works a couple ways: looking through it at nearby foliage - sure enough, the foliage is much brighter than everything else nearby, since plants reflect IR even while they absorb red - and that a 650 nm laser doesn't produce any spot on the wall when passed through the filter.

As for the cyan though, possibly something bizarre is happening causing cyan LED-like emission from the laser diode? Obviously it would only have to be a billionth or so as powerful as the 980 nm light to evoke a similar response from my eye. Hopefully my camera can pick up the secondary wavelength and how spread out it is, once I the cheap spectroscope I ordered shows up (I don't have the money for a more sophisticated spectrometer). It would be visible by eye too, but I'm unwilling to risk my eye again.
 
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...As for the laser being over spec, I suppose I find it unlikely that it would be, say, 20 mW instead of 5. It's supposed to be class IIIa, so that would run afoul of labeling requirements, and wouldn't it be more expensive for them to produce a higher output anyway? If I don't get my hands on a meter, I'll at least compare it to my 940 nm LED and a 780 nm laser which I know to be dim by viewing the spot against a wall with a digital camera, to get some crude qualitative idea as to the power output...

I've purchased a number of "CDRH Class IIIa" (<5mW) laser pointers off of a popular auction website in recent months, and ***EVERY ONE*** of them measured well over 10mW (Class IIIb specs) -- and MOST of them measured between 40mW and 60mW!!!
patch.gif


So you really can't trust the labelling.
 
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I've purchased a number of "CDRH Class IIIa" (<5mW) laser pointers off of a popular auction website in recent months, and ***EVERY ONE*** of them measured well over 10mW (Class IIIb specs) -- and MOST of them measured between 40mW and 60mW!!!
patch.gif


So you really can't trust the labelling.



Were they green? If so, I suspect the extra power comes from the lack of an IR filter letting out a portion of the IR pump. I didn't realize until recently that they lack filters, that is potentially very dangerous since many safety glasses for green lasers pass IR.
 
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Were they green? If so, I suspect the extra power comes from the lack of an IR filter letting out a portion of the IR pump. I didn't realize until recently that they lack filters, that is potentially very dangerous since many safety glasses for green lasers pass IR.

Nope, these were all directly-injected violet diode lasers, which by their very nature, generate zero (0) IR or NIR radiation.
 
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