My laser makes a red lit dot in thin air...

[kernelpanic]

Hello All,

Wow! I just successfully reproduced this effect tonight. It's really very cool. I can only think of 2 competing explanations. Either-

1. The air is combusting at the focus of the beam and producing oxides of Nitrogen. ( N2 + O [ch8594] NO + N or
N + O2 [ch8594] NO + O ) (Possibly even using vapors of the plastic burned as a catalyst? i.e.- prompt NOx)

2. A plasma is being created.

I have no evidence either way, but my bet is on #1...

Regardless, it's a cool effect.

cheers,
kernelpanic

 

[Benm]

Post a video

I have serious doubts about either explanation though. There might be enough energy at the focal point to heat something up to plasma temperatures, but what is keeping that something in place remains a mystery.

As far as the nitrogen/oxygen explanation goes, there is not enough energy in the fotons to do that, no matter the intensity (until the point of dielectric breakdown).

Also, neither explains why the glowing 'ball' is the same color as the laser powering it - i reckon this should work similar for green or blu ray lasers, if they have the power?

 

[kernelpanic]

Post a video

I have serious doubts about either explanation though. There might be enough energy at the focal point to heat something up to plasma temperatures, but what is keeping that something in place remains a mystery.

As far as the nitrogen/oxygen explanation goes, there is not enough energy in the fotons to do that, no matter the intensity (until the point of dielectric breakdown).

Also, neither explains why the glowing 'ball' is the same color as the laser powering it - i reckon this should work similar for green or blu ray lasers, if they have the power?

I also was skeptical when I first read this thread. Hence my trying to reproduce the effect. I'm not really sure the 'dot' is the same color as the laser. The 'dot' will sit there for 10-20 seconds. When it stops, it winks out.

Since one has to burn something to initiate this effect, I doubt that straight Nitrogen combustion is happening. But many prompt NOx reactions involve cyanoacrylics which are very common in plastics...

Whatever it is, it's not just smoke at the focus. Some kind of reaction is occurring.

cheers,
kernelpanic

 

[lamborgini8]

Does this work with all laser colours? I might try it with my greenie tonight.

Does it still stay there when the laser is turned off?

 

[Low-Q]

Hi. Here is a long video in real closeup. 1 and a half minutes long, it is showing something very interesting - maybe even more interesting than the ball itself. The plasma balls are dancing back and forth in a streight line close to the focus point. One ball splits in two, or three, fuses together again. Very cool. I didn't see this without magnifying it. Please take a look Look close to the "aura" around the ball. it is showing that the ball is rotating a bit, or is in some unstable state that cause this "aura" to change.
http://www.youtube.com/watch?v=pHx5312UxII

@lamborgini8: The ball dissapears in the same moment the power is turned off. It also dissappear if I use something to partly shield the laser light.

Low-Q

 

[RA_pierce]

[quote author=Xplorer877 link=1229287299/20#29 date=1229511598][quote author=Low-Q link=1229287299/0#0 date=1229287299]Hi. I have a 635nm laser from a 16x DVD burner. When I focus this laser on a plastic piece, a red lit small dot remains in thin air for as long as the laser is activated - somtimes shorter time. So I wonder if someone knows what is happening. Is it plasma from platic vapour, or what is it?

I'm not allowed to post links here yet, but on youtube you can paste in these two lines at "YouTube dot com slash" to find the videos:

watch?v=9AzdMJSvuUU&NR=1

and

watch?v=ig_L3PnSuo0

br.

Low-Q

635nm? :-? How do you know it's 635nm? Which DVD burners containing 635nm diodes? I've never heard of that.
[/quote]Maybe I have to rethink about that... I assumed DVD lasers was 635nm - that is what I have heard. Actually both 650nm and 635nm. The red light is also orange red light - not that deep red light you get from 650 - 670nm lasers. I have to check, but as I remember I had a 635nm laser pointer once which had the same kind of "orangeish" red light.

Low-Q[/quote]


They are 650-670nm diodes.
I've never seen a +100mW 635nm single mode laser diode (although I'm sure they exist somewhere beyond my meager price range).
All the high power 635nm diodes I've seen are multimode and really expensive.

Cool video. I want to know if it works with all colors... I'm gonna try this with my green laser... When I get batteries... :-/

 

[bugattidude]

whered you get what ur burning?

(n i got 1st veiw on the video...  ;D)

 

[Benm]

I think the first video is more convincing, shows how the ball moves when you move the laser around - in the last one it could be smoke passing through and around the focal point.

Still, i havent seen anything like it, and wonder what the heck is going on there

 

[Spyderz20x6]

That is very strange :-?
I'm gonna go try it right now...

 

[Xplorer877]

I think I saw it briefly with my 650nm. What kind of plastic is it? I'm having trouble replicating this experiment.

-John

 

[hydrogenman15]

Is that...No its not....burning the air? :-?
Time to go try it...
--hydro15

 

[carulli]

the only thing I can think of is that the laser heats up the plastic and the air around it and starts ionizing the air, and when you take it away the ionization continues.

thats my theory anyway.

-Adam

I doubt its plasma, I think most gases gases ionise at a lot higher temperature than that but im probably wrong. Also isn't ionised nitrogen blue-purple not red?

 

[Low-Q]

I think the first video is more convincing, shows how the ball moves when you move the laser around - in the last one it could be smoke passing through and around the focal point.

Still, i havent seen anything like it, and wonder what the heck is going on there

I placed the optics for an old video projector on the table, and fixed the laser in its focal point. At the other end I put my camera in video mode with maximum zoom. I did this just to make sure I got a nice focus when recording close up.
I bet there is parts of smoke that gets stucked in the focal point, but the surrounding smoke dissappears quite quick, so I'm sure there is particles burning. If it was just smoke, you should see "><" like light pattern - but you don't. You only see that signle dot(s) in the focal point.

Where is the scientist when you need them? :'(

Br.

Low-Q

 

[Low-Q]

I think I saw it briefly with my 650nm. What kind of plastic is it? I'm having trouble replicating this experiment.

-John

I guess you need some power, and short, but also "clean" focus. If you want a "clean" focus, you can use a regular laser diode lens, but you have to invert the direction of the lens. These lenses are often flat on one side and convex on the other side, where the least convex or flat side is pointing towards the laser diode. Your focus lens however must have the least convex, or flat part, away from th laser apperture.

My diode isn't that can-looking one. Mine looks more like a black square transistor with one metal side. This metal side is a part of the laser cooling metal, and is soldered into an excess brass Yag crystal holder. This holder is then pressed very tight into the laser housing, ensuring good cooling. I use approx 3,35 Volts, and the laser doesnt get warm (just lukewarm after 1,5 - 2 minutes continous). I think I have a very good cooling when the diode is directly soldered into the can.

I use 3 lens corrective optics for the laser itself, and use an excess optics for a PC scanner to focus the parallell beam. These are very accurate optics, and the focal point will therfor be extremely small without optical errors you get from single lens optics.

Br.

Low-Q

 

[Things]

I just tried this with a few different plastics, and a LOC red runnning at about 420ma, and was unable to replicate it. Do you need the lights off to be able to see it? Around what temperature was it when you tried it ?

 

[drlava]

Cool effect, I'll have to give it a try. Does it work with the carbon from a pencil? Chunk of tire rubber? It sounds likt the lenses you are using allow a very small focal point, smaller than the typical plastic lens variety, I wonder is the multi-element glass aixiz variety is adequate?