Didn’t think a laser could retain this much power after traveling through many inches of water. But it looks like this 150mW laser somehow managed to do it. The target is flash paper, not regular paper which may have a bit to do with it but it is impressive regardless! Anyone think this is not real or staged somehow?
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I = 1/d^2 which means the further away it is the less intense but the distance squared.
Water is transparent which means light passes through it.(tho some is reflected just not as much as other things)
After that distance the lasers beam would be a lot less intense but the energy would still be transferred through the water although some would be lost.
So it seems plausible. 😀 feel free to correct I’m pretty sure I screwed that up some where but I’m not sure.
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If water was ideally transparent, you were right. But water is not pure, thus we can see the laser going through it. So traveling through water also disperses a bit of it. Nice experiment.
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I think that equation is for ordinary light from a light bulb that spreads out trough the room. Laser light doesn’t do that it keeps on going in a strait line, only loss is the dust in the air it hits and in this case the not pure water. Also the walls of the glass might take some light too.
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I was hoping that the paper would be under the water… oh well.
Anyways, the equation in 1 is for non-coherent light / divergence. As we can see this laser has a very fine beam and little if any divergence. And it was striking a black mark on the paper, which results in a lot of energy being transferred to the paper. I have an 80mw that will light black matches, cause (black) paper / electrical tape to smoke, or pop balloons from a few inches, so I would believe that this 2x as powerful laser could ignite flashpaper (279* F, below even matchheads) even through the water.
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I think Joe said it…
There is a black mark on the paper which would help to actually heat up the paper enough to ignite.
Powerful lasers are fun, but remember boys & girls, they are not “Toys”!!! (Well, at least not for kids).
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typicaly estimated “Loss of Energy” of light passing through glass is 4%.
Well let’s look what we have here:
1.: Laserbeam goes into glass(-4%)
2.: Laserbeam leaves inner glass and enters water (-4%)
3.: The Laser passes the water (I have no idea!! – lets guess -4%, maybe more/less)
4.: Laserbeam enters second inner side of the glass (-4%)
5.: Laser exits glass (-4%)
all in sum could make -20% “Loss of Energy” ..
this would result in 120mW koherent light-energy remaining!
According to Joe’s post this would be enough.