Why??!?!!!!

[swimminsurfer256]

Just curious, why does laser light disappear around an open flame? It then continues as if unhindered afterwards. I don't have a picture of it as I am at work but I've seen it many times and thought I'd finally ask.



*edit* just took this video:



Messed it up because the power supply fan was blowing air on the match the first time. Blocked it with a white box and you can see it!

From 1:06 on is the main "ooooh..." part

 

[JBTexas]

Maybe the heat (incl. radiant heat) from the flame interferes with scattering. Maybe the dust particles in the area say "YYOOWWWowww!" and whiz up towards the ceiling really fast.

Or, just an optical thing, with the way our eyes work.

EDIT:

An experiment - in the same situation, blow smoke / make fog / put a steaming pot of water close by, and see what happens?

 

[swimminsurfer256]

Maybe the heat (incl. radiant heat) from the flame interferes with scattering. Maybe the dust particles in the area say "YYOOWWWowww!" and whiz up towards the ceiling really fast.

Or, just an optical thing, with the way our eyes work.

EDIT:

An experiment - in the same situation, blow smoke / make fog / put a steaming pot of water close by, and see what happens?

Here's one of pyro's really old video where you can kind of see the effect at :28. He's doing it with smoke in the room too (obviously).

 

[JBTexas]

Dunno, from the vid, (even at 0:28), I can't tell if it's just the match (stick) that is obscuring the beam.

Maybe the beam just gets jealous, stomps off in a rage into some other dimension briefly, and then decides to come back, realizing that it was just put off by a lowly incoherent flame.

 

[swimminsurfer256]

Dunno, from the vid, (even at 0:28), I can't tell if it's just the match (stick) that is obscuring the beam.

Maybe the beam just gets jealous, stomps off in a rage into some other dimension briefly, and then decides to come back, realizing that it was just put off by a lowly incoherent flame.

Look at :33 it's a better example.

I like that explanation I think I'll go with that :thanks:

 

[JBTexas]

AH! Okay, at about 00:33 I saw it.

Looks like a "gap" "chopped out" from the beam, for maybe an inch, inch and a half?

It was right over a lit match...

I'd say that its maybe a refraction thing? A column of hot, rarified, quickly-rising air, again, interferring with scattering? Like a teardrop shaped lense. The index of refraction changing from the "normal room air" to the "hotass match air". And probably the beam is too strong to be COMPLETELY wiped out from it; the effect is JUST ENOUGH to wipe out scattering. So the rest of the beam... and probably the spot on the wall... might be a LITTLE "wavy/distorted" (we can't see in the vid).

 

[daguin]

There are no particles "floating around" inside the flame to reflect or scatter the light toward your eye. It is just moving coherently forward. If the light does not come toward your eye, you cannot see it. The light is still there inside the flame. You just cannot see it.

Peace,
dave

 

[JBTexas]

Daguin... look again, at about 00:33 or so in the vid.

Briefly, OVER THE FLAME, (not IN the flame), there IS an odd "segment" that seems to be "chopped out" of the beam.

It IS weird, once you notice it.

 

[swimminsurfer256]

There are no particles "floating around" inside the flame to reflect or scatter the light toward your eye. It is just moving coherently forward. If the light does not come toward your eye, you cannot see it. The light is still there inside the flame. You just cannot see it.

Peace,
dave

So... what you're telling me is not only are Star Wars space battle scenes inaccurate because you wouldn't be able to hear the action, but you also wouldn't be able to see the action either??



And JBTexas, I think you were right in that the heat scatters the particles so there are no particles there...? Perhaps?

 

[Ra1nfade]

Yes, well I dont know about not being able to see it in space as there is a lot of particles floating around in space. Maybe equivilant to dust floating around in a room.

But that is correct if there is nothing to reflect to light you cannot see the beam

 

[JBTexas]

swimminsurfer... and yes, but also again it might be a REFRACTION thing... I get "that feeling" when I see the gap in the vid... like maybe some kind of "virtual lens" floating in the same space as the beam. Maybe kills the scattering, but NOT strong enough to strongly affect the beam.

 

[swimminsurfer256]

I'll snap some pictures when I get home. And also there aren't anywhere near as many particles in average space as there are in our atmosphere!

 

[Ra1nfade]

Your probably right,

I'm not sure off the name for the effect but to sort of "visualize" Have you ever seen how heat distorts light when its rising from the pavement or rolling out the top of a car? They may be the effect thats causing this.

Its the same effect that creates a mirage I just can't remeber waht its called...

 

[jeffreythe00]

Could it possibly have anything to do with heat? Example: When heat rises off objects like hot pavement or a heater or even an oven you can see through it but its all distorted?

I guess what I am saying is could it be that heat distorts light enough to make visible coherent invisible?

 

[qumefox]

I think the term is 'thermal lensing' Kind of like mirages or heat distortion off a parking lot or road.

I don't think that's what's happening here. I think it's just a combination of a) change in contrast.. flame is brighter than the beam, and b) expanding heat plume of the freshly lit match pushing the particulate away from it, leaving nothing to scatter the light towards your eyes/camera.

I just tried it with a lighter and a 445 and I saw no 'breaks' around a stable lit flame in a normal environment. (no smoke)

 

[swimminsurfer256]

I think the term is 'thermal lensing' Kind of like mirages or heat distortion off a parking lot or road.

I don't think that's what's happening here. I think it's just a combination of a) change in contrast.. flame is brighter than the beam, and b) expanding heat plume of the freshly lit match pushing the particulate away from it, leaving nothing to scatter the light towards your eyes/camera.

I just tried it with a lighter and a 445 and I saw no 'breaks' around a stable lit flame in a normal environment. (no smoke)

Try it with a match instead (not sure what the main difference would be... wood vs butane?). I've seen it constantly when doing burning videos even when holding the match there!