250mw red to white flashes.

[Gazoo]

Of course I have seen it too and have always wondered exactly what causes it. And I can see it when burning through a floppy, but it is very easy to see on the paper part of a paper match. Could it be the projection of the mirror faucets or have something to do with that?

 

[BlueFusion]

[quote author=Benm link=1204963819/0#5 date=1204993136]It IS just heat, nothing special about it. When you focus 200 mW of light on a tiny spot on that cigarette, that part just heats up to the point of thermal emission. The goggles make this visible on camera, as the red light is blocked out for the most part and thus the blackbody radiation of the target becomes more visible.

I think you'd find it very difficult to reproduce this effect using for example a black anodized heatsink as the target - it just doest heat up enough.

The effect has nothing to do with 'overloading' your eyes, the inner workings of the eye are such that you will always see red as red, all the way up to the point where the intensity will damage your eyes. This is completely different from a camera, where it is quite usual to overload the sensor and make the dot look white with a red corona around it.

Well, I don't know if I agree with the IR from heat explanation cause I can see it with my naked eye. however, I was UNABLE to produce the effect on a black heatsink as you suggested. so your explanation has merit. I believe that this is from intense heat from the laser that part I can believe and I certainly am not arguing with you not having the knowledge to form a hypothesis.[/quote]

Actually Kenom he's talking about heating the material to the point it emits VISIBLE light.
Think of getting metal red hot. It actually makes sense now he points it out...
When any material gets hot enough, the electrons in its constituent atoms become excited and jump to a higher electron shell. When they fall back down again, they emit a photon.

This really does make sense. And like I was telling you kenom, the red light is totally blocked by the goggles which would make the other light (the blackbody radiation from the material) more visible.



My previous theory was that the red blocking goggles made the camera sensor / eyes more sensitive to the red from the laser by depriving it of any other red light, thus making the laser spot overexposed and thus white.

 

[Benm]

Perhaps 'white hot' would better explain what is happening here. If you look at it without a filter, you (or your camera) will always see a lot of red light from the laser itself, and the effect is less pronounced.

When using a filter that blocks out the red from the laser, you will only see light emitted at shorter wavelengths from hot spots on the target. The image though the filter should look cyan if the target is glowing white hot, since the red from the glow is also eliminated by the filter (provided it doesnt pass any red at all).

When using CO2 lasers the filter can be such that it passes all visible light, and you'd see only red/orange/white emitted from hot pieces of target material.

 

[MarioMaster]

yeah i'm pretty sure you're just heating it up to the point at which it gives off light as Schrecken said, is much like a lightbulb filament

 

[Switch]

yeah i'm pretty sure you're just heating it up to the point at which it gives off light as Schrecken said, is much like a lightbulb filament

Yea but if you burn a floppy with a lighter it doesn't emit any light unless it bursts into flame, but no white glow : I still think that small area gets a lot of energy that it cannot dissipate it fast enough and cannot reflect enough of it so it absorbs it and turns to plasma :-/

 

[Benm]

Well, it does heat up in a very small spot, and glows white, so far you're right.

Plasma is a term for materials where the bulk properties stem from free electrons rather than electrons interating with the closest nucleus. At normal pressure this requires temperatures far beyond what we see happening here.

 

[CL_]

hummm, so i wonder what it is, and every day i realize how many science geeks there are here, im in good company ;D

 

[knimrod]

[quote author=MarioMaster link=1204963819/15#19 date=1205085958]yeah i'm pretty sure you're just heating it up to the point at which it gives off light as Schrecken said, is much like a lightbulb filament

Yea but if you burn a floppy with a lighter it doesn't emit any light unless it bursts into flame, but no white glow  :  I still think that small area gets a lot of energy that it cannot dissipate it fast enough and cannot reflect enough of it so it absorbs it and turns to plasma :-/[/quote]

Want plasma? Make a flame.. A flame is at least partially plasma. But what you see in those white flashes is indeed incandescence.

 

[CL_]

i saw this one dude who lit a match, put it uder a jar, put it in a microwave and it looked awesome!!!

 

[styropyro]

i saw this one dude who lit a match, put it uder a jar, put it in a microwave and it looked awesome!!!

OT but, you can do the same thing with grapes. Cut a grape almost in half so that a little piece of skin holds the two haves of the grape together. Stick it in a microwave and enjoy the show. Sometimes you just get a tiny flame, but sometimes you get huge fireballs that go to the top of the microwave.

 

[CL_]

ya, i saw a video of that too

 

[Cyparagon]

Want plasma? Make a flame.. A flame is at least partially plasma.

Care to source that?

 

[Benm]

Common flames are not plasmas, really. The light from a candle flame is a result of incandescent soot particles and electronic transitions form C2 and CH fragments resulting from the combustion. Flames that burn clean usually dont produce much light at all (like a bunsen burner with the air valve open).

But you already have plasma's in your house - tube lights, the backlight of your LCD screens...

 

[knimrod]

I believe the boundary region of a flame is a form of plasma.  Plasma consists of a collection of free-moving electrons and ions - atoms that have lost electrons...  

I'm no authority but that's what I remember from my physics studies..

Ask an astrophysicist: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971007b.html  

 

[bob12345]

[quote author=MarioMaster link=1204963819/15#19 date=1205085958]yeah i'm pretty sure you're just heating it up to the point at which it gives off light as Schrecken said, is much like a lightbulb filament

Yea but if you burn a floppy with a lighter it doesn't emit any light unless it bursts into flame, but no white glow : I still think that small area gets a lot of energy that it cannot dissipate it fast enough and cannot reflect enough of it so it absorbs it and turns to plasma :-/[/quote]


That is because a floppy is made from polymers, i.e. very long chains of hydrogen and carbon atoms. Burning that will only split the links between those chains and eventually disintegrate the chains themselves. On the other hand, heating up something with a rigid, regular lattice structure (such as a metal, or most common forms of carbon) will cause it to emit the blackbody spectrum depending on, of course, temperature. The reason being, that it turns out that lattice vibrations themselves (when treated mathematically, you call them phonons) can in turn emit photons of a generally wider range of frequencies when releasing energy.

That, or camera effects would be the reason for a 'white glow'.

 

[Benm]

Interesting, but the lattice story doesnt really hold up in practical situations. Take for example a load of molten metal, which emits a good deal of blackbody radiation when hot enough, but obviously lacks any lattice since its liquid.