Its very greeeeeeeeen

[rszemeti]

Right, I actually read your PDF ... so here goes.

Lets take a 60W YAG laser ruuning into a piece of wood ...

According to your PDF, the author gives a CW limit of 5mW/cm2 as the incident damage threshold at the eye.

So, I am assuming:

output power 60W
reflectivity of the lump of wood, 10%
dispersal, semi-isotropic
distance of viewer to target: 2 metres.

which gives, incident power at the eye of the viewer: 47 uW/cm2 ... err .. yes, microwatts, 47x 10-6 ... or put another way 1/100th of the damage level, or what we call "safe" ... 100:1 is a fair safety margin don't you think?

Even if you assume say 50% reflection, 1/4 sphere dispersal, its still well below the damage threshold. specular reflections are of course a diffewrent matter .. avoid shiny surfaces, and in particular, avoid highly IR reflective surface, like photcopier paper!

Game, set and match?

[White-Light]

you run up your laser and burn your Kitchen cabinets well thats dangerous.

Not really, they're non reflective and it was a static beam. It was my fault for not realising the potential of the beam to burn wood at that moment in time.

[planters]

I now think I have a pretty good idea of how a troll works. Not so inflammatory that the posts are dismissed out of hand, but persistent and mildly disagreeable. What is the purpose of suggesting that laser safety should be treated in so caviler a fashion when it does not in any way interfere with the use and enjoyment of the lasers being discussed on this forum? Just because the power levels of the lasers used in entertainment projectors are significantly lower than those generated by some big,greasy, industrial, shrouded even invisible cutter does not mean they are less interesting. Or that the individuals discussing them do not posses some pretty impressive credentials and experience. If you want one of those big'ol lasers, just go buy one and burn some stuff, but then what? If you use these industrial lasers for legitimate manufacturing, that's cool, but that's too much like work and not that interesting. If you are pushing the envelope with new ideas or applications or state of the art lasers...well then THAT would be interesting and let's hear about it. Otherwise, please...

[steve-o]

Yeah I was thinking the very same thing earlier today when "troll-shit" was mentioned in the first pages of this thread.. heh . exactly right .

[dsli_jon]

Game, set and match?

No, a) We were discussing YAG-dangers to skin / hazards of Class IV NIR lasers in-general, not specifically your 'example', which, b) I think your math is wrong, but I don't have the time to prove it, right now, especially since c) you're forgetting to factor-in the exponential power-density increase to the retina, by the lens of the eye, which can even 'collimate' scattered-reflection / burn the retina, if-in sufficient-quantities.. you might wish to re-read Page 6 and re-try your math-excersize, since it's the retina, not cornea, we're most-concerned with...

Nonetheless, imo, my point has been made, all you had to do was simply 'qualify' your statements, like 'IN MY OPINION (not real-world data) 60W OF YAG NIR IS "NOT VERY DANGEROUS", BUT THOSE NOT-EXPERIENCED WITH HI-POWER, ESPECIALLY INVISIBLE LASER RADIATION SHOULD NOT GO PLAYING WITH IT', etc, etc, and we'd be done... additionally, since I've no further time for this, (..and, with some of your statements, above, I'm beginning to think Doc, et al were right... ) lemme give you this back:



...and bid you farewell... ...at least till I can put some video in your face..

later, taco..
j

[Stuka]

Just a quick FYI-

rzsmeti isnt a troll and i *think* (although i may be wrong) the comment about an infant holding a lens is a complete joke. This guy has talked to Steve, has some extensive knowledge of these Lasers and has alot of years/experience under his belt. Im glad we all think about safety here, but i think we tend to jump on people WAAAAY too quickly here about the whole safety factor. We all know lasers are dangerous but come on...they arent nuclear weapons like some of you make them out to be.

just my 2 cents. Although with the economy, its more like 1.4 cents.

-Marc

I don't know Marc -

For the first time, I'm going to have to disagree with you -

This dude's increasing "so what if someone gets hurt" attitude - and the issues that will obviously raise with most of us - reminds me more and more of a certain instigating troll that has been "cluebyfour'ed" from this forum under several different names in the past year, as well as similarities to a certain "dj" that pretty much drew universal despise here before he met the same fate.

His obvious experience with high-power lasers is rapidly being overshadowed by the fact that he comes across as not much more than an arrogant prick, with little regard for the example he might be setting or the fact that that he seems to find laser-induced injuries quite humorous.

Pretty sure that is NOT the example we generally try to set on this forum...

[rszemeti]

No, a) We were discussing YAG-dangers to skin / hazards of Class IV NIR lasers in-general, not specifically your 'example', which, b) I think your math is wrong, but I don't have the time to prove it, right now, especially since c) you're forgetting to factor-in the exponential power-density increase to the retina, by the lens of the eye, which can even 'collimate' scattered-reflection / burn the retina, if-in sufficient-quantities.. you might wish to re-read Page 6 and re-try your math-excersize, since it's the retina, not cornea, we're most-concerned with...

Nope sorry, the incident levels I quoted are correct, ie 5mw/cm2 are for energy delevidered to the eye is the damage threshold for YAG, the damage threshold at the retina is ~10kw/cm2 if you read it .. the guy even gives the example of sunlight of 100mw/cm2 becoming 6.2kW cm2 at the retina .. 5mw per cm is indeed low, but providing you are not the sort of person who goes around staring into beams or bouncing them reflective surfaces, just being a couple of meters away from a taret being illuminated by a beam should do it ... assuming 10% refelctivity, which is typical for wood, you are going to get 6W bouncing off ... and 6W spread over say, 1m square (just to make the calculation easier) which is 10,000 cm2 .. is already 0.6mW/cm2 or 1/10th of the damage level ... in reallity, the light is going to scatter all over the workshop, not just a sqaure metre, power densities will be even lower. Sure, if you are dumb enough to bounce it off a highly reflective surface and you get a flash, well ... its going to end up with someone losing an eye isnt it ..

Sure, if you catch a full on reflection, its going to cause damage .. but, thats where experience comes in, knowing which bits are safe to burn without glasses (wood, fire bricks) and which are not (metal, photocopier paper)

If you want to talk about skin thresholds .. look at page 11 ... NdYAG is 28W/cm2 .. 28 watts ... thats for a >1 second exposure .. which backs up practical experience that I can move my hand out of the way of an un-focused 60W yag fast enough to save physical injury.

Like I said, 200mw laser pointers are not dangerous .. you'd have to be an idiot to point them at someone, if a collimated beam lands on someones eye, they are going to suffer damage for sure .. simply handling them sensibly renders them harmless .. you can turn one on in your living room with a reasonable expectation of coming out alive and uncharred. You can hold your finger in front of one and expect to have the same number of fingers at the end of it. For this reason I call them "not dangerous" ... want to try that trick with the Lumonics? ... or a 5kW CO2? you'll torch the living room and lose body parts, now those I would call dangerous.

Still, I'll leave you all with this video posted on YouTube by a professional laser display operator, properly licensed in Germany who clearly understands these things a lot better than me ... high power 532nm around Germany ... 8 to 16W ... "enough to cut through arm-thick steel" apparently ... I better go, I just remembered i left a HeNe on, it might have burnt through some bricks by now!

[gashead]

Like I said, 200mw laser pointers are not dangerous .. you'd have to be an idiot to point them at someone, if a collimated beam lands on someones eye, they are going to suffer damage for sure .. simply handling them sensibly renders them harmless .. you can turn one on in your living room with a reasonable expectation of coming out alive and uncharred. You can hold your finger in front of one and expect to have the same number of fingers at the end of it. For this reason I call them "not dangerous" ... want to try that trick with the Lumonics? ... or a 5kW CO2? you'll torch the living room and lose body parts, now those I would call dangerous.

Gidday!

I think you're missing the general point that the majority of people who handle 200mw laser pointers (or even higher powers, Wicked Arctic springs to mind) *ARE* idiots and generally this is why people on PL are so safety aware.

The idiots with the laser pointers who decide to point them at themselves, other people, vehicles of all kinds, animals, etc.. don't seem to realise the danger they put themselves and others in. (It's just light.. what harm can it do?!?! Now hand me some more Buckfast!!)

I've been to many a club where dick heads have brought along their pointers and decide to behave inappropriately with them and it infuriates me because I only imagine it will get harder for Laserists who do conduct themselves in a safe and correct manner to continue to do so.

I don't think anyone disputes that CO2's at those power levels are dangerous, but likewise YAG's at their typical power levels are dangerous *in the wrong hands* (see the Russian incident) http://www.laserist.org/2008-07_Russian-incident.htm

It's great to have a new member on the forum whom has such knowledge of Photonics, but to be honest this looks to be turning into a pissing competition and there really is no need for that.

Cheers,

Nige.

[rszemeti]

Well, if certain members were less offensive and could take off their traffic-wardens hats for a while it might all calm down

if you are correct in that "the majority of people who handle 200mw laser pointers *ARE* idiots" and that covers the larger part of the readeship of this forum, I am clearly in the wrong place .. I was hoping this was for laser enthusiasts, eg people who had actually built some sort of laser (no, gluing a diode to a battery does not count) and had an understanding of laser physics, pretty much like the old alt.lasers newsgroup .. if its just a collection of kiddies waving laser pens around, then fair enough, i can see how anyting over 1mw might be dangerous ... in which case I am clearly in the wrong place.

[LaNeK779]

... in which case I am clearly in the wrong place.

stick around and find out

things are a bit "strange" lately, but i guess this has something to do with pre-christmass depression and other psychological stuff.
it will sort itself out soon, we do talk "lazors" from time to time.