TEA co2 laser turns air into plasma

[Event_Horizon]

Thought you guys might find this interesting. Yesterday in the lab at school we got to play around with a Lumonics TEA-203 CO2 laser. It's has been somewhat modified so we could put in our own gas mix at various pressures to examine the effects of the E/P ratio of TEA laser. Anyways, this laser fires pulses up to six joules each at a speed of about 1 Hz maximum. Now, this isn't really very impressive normally because the beam is about 1.5 inches in diameter, but when a focusing optic is placed into the beam, the power is so great that it actually turns the air into a plasma at the focal point. It looks like a spark in midair along with a LOUD snap. Videos below:

Here is the laser firing
http://www.youtube.com/watch?v=6N-mz0krcmk

Here is the laser firing into a piece of paper
http://www.youtube.com/watch?v=dqBIHXQEQ4U

I was actually a part of the first lab group to use this laser since it was repaired. So remember, you saw it here first!

EDIT: Some pictures. That's me firing the laser in the background of the second one And the last one caught a burst of microsecond flames that the burn paper emitted when the laser hit.

 

[Hemlock_Mike]

I've done that plasma in air using a small NdYAG laser. It chipped my lens on both sides doing it
That laser must have an electronic switch rather than a spark gap -- It's quiet. Air cooled?

Mike

 

[FrothyChimp]

That is slick! Six joules is a ton of power. Dielectric breakdown of air is something you don't see in laser demonstrations very often but is a clear demonstration of power.

 

[Event_Horizon]

The laser is triggered using a Thyratron instead of a spark gap. It goes from open circuit to closed circuit in about 5 nanoseconds   and it's almost completely silent when you fire it without the focusing optic there. All you hear is a quiet click inside and that's it. And the whole thing is air cooled, there are two small fans at either end. Since it can only fire about once a second and it's a pretty efficient laser (CO2) there isn't all that much heat to dissipate. The reason it can only fire at 1Hz is because the power supply runs off a standard 120V outlet so the capacitors need at least 1 second to charge up for the shot.

 

[laserwanabe]

very cool, it shoots through paper like nothing.

I would like to see a piece of a 2 by 4 get burnt.

 

[rocketparrotlet]

What is the power of this laser, and the pulse duration?

6 joules is not a lot of energy, really. About enough to heat 1 gram of water 1.5 degrees C. How can 6 joules burn something like this?

-Mark

 

[digital_blue]

What is the power of this laser, and the pulse duration?

6 joules is not a lot of energy, really.  About enough to heat 1 gram of water 1.5 degrees C.  How can 6 joules burn something like this?

-Mark

6 Joules pulsed is equivalent to watts of power... My 30uJ averages about 50mw...

 

[rocketparrotlet]

[quote author=rocketparrotlet link=1235073092/0#5 date=1235078998]What is the power of this laser, and the pulse duration?

6 joules is not a lot of energy, really.  About enough to heat 1 gram of water 1.5 degrees C.  How can 6 joules burn something like this?

-Mark

6 Joules pulsed is equivalent to watts of power... My 30uJ averages about 50mw...[/quote]

Apples to oranges. Watts is a measure of power, while joules is a measure of energy. Power=energy/time

1 W = 1 J/sec.

-Mark

 

[FrothyChimp]

1 gram of water is what, 1cm[sup]3[/sup]? If the beam cross section is 1cm x 1cm then yeah it would provide the energy to heat the water by 1.5 degree C in the duration of the pulse. Now focus that beam down to say 100um and the energy density goes through the roof. Now you are ripping the electrons off of oxygen/nitrogen.

 

[Benm]

Breakdown in mid-air is still an amazing sight. I've seen it demonstrated long ago, but it's still sort of mesmerizing to watch it zap away like that.

Also, 6 joule pulses, one a second, is still a pretty decent 6 watts average... but if you manage to discharge that in 10 microseconds its over half a megawatt peak.. keep your hands out of there

 

[Hemlock_Mike]

as the Chimp says -- 6 joules is a bunch...... He isn't joking.
In short pulses, 6J can get to over 100,000 watts Peak.

Mike

 

[Cyparagon]

The beam profile looks identical to my CO[sub]2[/sub] - donut with a dot in the middle. Why was the beam able to ionize air but not penetrate paper?

6 joules is not a lot of energy, really.  About enough to heat 1 gram of water 1.5 degrees C.  How can 6 joules burn something like this?

Apples to oranges.

Yeah, that pretty much says it. You're taking this out of context. It's like saying "your laser is only 10 watts? I have a 100W light bulb here"

How long would it take your "200mw long die open can" laser to heat a gram of water 1.5 degrees?

 

[Event_Horizon]

The beam was penetrating the paper. just made small holes.

According to measurements taken by the laser specialist guy at school, the maximum power output of this laser is 15J per pulse and the average pulse duration is 170 nanoseconds (FWHM). Even at 6J per pulse that comes to over 35 MEGAWATTS   Even ONE joule per pulse gives you almost 6 million watts.

So yeah, 35 million watts focused down to an area about 1mm across. You can see why it makes the air explode.  

Edited first post with some pictures too.

 

[Hemlock_Mike]

Numbers like these are hard for some to understand.  Add a Q switch and watch the peak power !!!!
Is that a ZnSe lens in front?? It looks a little amber.

Mike

 

[Event_Horizon]

That is indeed a ZnSe lens. All the CO2 lasers in the lab at school use ZnSe optics because they are much easier to align using a HeNe then opaque materials like Germanium!

 

[Cyparagon]

The beam was penetrating the paper. just made small holes.

I see. So the burn marks were just beam scatter?

Edited first post with some pictures too.

Do I see a spectra physics argon laser back there?