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Laser Blooming

by Kalrag
Tags: blooming, laser
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Dec13-10, 09:16 AM
P: 100
Alright, I have sources (Wikipedia) that say that when a Laser hits a certain intensity it "blooms" and creates a plasma (around a megajoule). How does a Laser acheive this and how big is the laser? Can anyone help me?
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Dec13-10, 03:16 PM
P: 58
Hi, Kalrag,

I'm not exactly sure what info you're looking for, but I'll try to answer your questions. A high-energy-density laser, fired through the atmosphere, will superheat the air at some critical point (~1 megajoule per cm3) and create a plasma (atoms of gas stripped of electrons) which essentially absorbs/scatters the beam and prevents it from reaching its target at full intensity. It isn't so much the absolute power output of the laser, (although it would have to be fairly high), but the energy concentration of the beam. Solutions include spreading out the energy density of the beam using a mirror, or--as is most often used--pulsing the beam on and off very quickly so that the heated air can dissipate between each pulse. As Wikipedia states, the effect is most pronounced when the air is not clear (fog/smog/etc.) as the particles absorb more energy and more quickly heat up the surrounding environment.

Does that help?
Dec13-10, 03:24 PM
P: 100
Yes that does help. Thanks for posting, But I would still like more. LikeIf it could create a sustained beam of plasma or something like that.

Dec13-10, 03:31 PM
P: 58
Laser Blooming

The plasma is not so much a beam as a cloud that forms and diffuses the coherent laser beam. It would be greatest near the source of the beam, and peter out as the beam lost energy further away. As long as the laser was operating with a power that passed the point of 'blooming', the plasma would remain. A beam of plasma would be difficult to produce and maintain in the atmosphere at any distance, but it is routinely used to cut metal and other materials at short range--it's known as a plasma torch.
Dr Lots-o'watts
Dec13-10, 07:40 PM
P: 674
It's important to note that the threshold should be stated in megajoules/cm3 (not just "megajoules"). This means a much weaker laser can be used, as long as the focusing point is correspondingly less. Some common-sized lab lasers can cause air breakdown, and PLD ( is becoming a widespread method of producing thin films out of laser-induced plasmas.
Dec14-10, 08:46 AM
P: 100
Also, I read that I is a good electrical connductor. Is this true?
Dr Lots-o'watts
Dec14-10, 11:41 AM
P: 674
"I" is a good electrical conductor? I'm not sure I understand.
Apr21-13, 01:12 AM
P: 1
you could have multiple small lasers focus on a point, and move the focal point back and forth along a linear axis, and make a "Plasma column"

Look @ Zeropto


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