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Old 03-01-2015, 02:57 AM #1
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Default Air/Nitrogen ionization using lasers

Hello,

I've been looking for a while but I cant find much information about this topic.

Lets say I have a ND:YAG Multimode laser of 532 nm and its Q-switch (if anyone can explain what Q switch means that will be awesome) and it produces 25mj per pulse at 1 kHz and peak pulse power of 385 kW.

I want to ionize Air or Nitrogen using this laser (I'm trying to make a laser triggered spark gap, basically 2 electrodes one at HV and the other is Ground, the problem is self break down, thats why I'm trying to trigger it using a laser, so the break down voltage doesn't change from every time I run the experiment).

Here is what I understand, Laser will give energy to the molecules of gas, and if this energy is sufficient this molecule will get ionized.. and if I have enough energy to ionize a certain number of molecules I will be able to trigger the electrodes at the voltage I want.

Would the laser I have work? if yes how can I tell if a laser will work? Also if you can explain to me the process because I think I dont understand it correctly that will be great.
(extra info:the distance between the 2 electrodes is around 1 cm, and the radius of the spherical electrodes is 1 cm)

I need your help.



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Old 03-01-2015, 05:01 AM #2
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Default Re: Air/Nitrogen ionization using lasers

I'm almost certain 25mJ is not enough to ionize air.

Why green and not IR?

What is this spark gap part of?

Is this absurd level of complexity really needed? You should learn a thing or two about thyratrons before you try something this silly.
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Old 03-01-2015, 05:12 AM #3
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Default Re: Air/Nitrogen ionization using lasers

I remember doing some research on this a few years ago for shits and giggles, there was sure enough pretty solid reporting from declassified government docs that green is actually pretty damned efficient at air ionization, as far as wavelength goes. Only thing that was better was deep UV. That being said it is a hell of a lot easier to produce IR in the energies needed than anything else, so while the light itself is more efficient at the task, the means of creating the light is not.

Anyway, see: http://loa.ensta-paristech.fr/ilm/up...13303_2014.pdf

They used 300mJ in 1pS....
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Old 03-01-2015, 05:17 AM #4
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Default Re: Air/Nitrogen ionization using lasers

In addition to the inherently decreased reliability of adding a doubler to the resonator, you lose over half the light converting to green.
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Old 03-01-2015, 09:19 AM #5
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Default Re: Air/Nitrogen ionization using lasers

Quote:
Originally Posted by Cyparagon View Post
I'm almost certain 25mJ is not enough to ionize air.

Why green and not IR?

What is this spark gap part of?

Is this absurd level of complexity really needed? You should learn a thing or two about thyratrons before you try something this silly.
I'm a sophomore student, and I'm trying hard to learn.
My university have 532 ND:YAG (25 mj at 1 kHZ) and 1064 ND:YAG (2 mj at 10 kHZ). So I have to work with what they have.
The spark gap is part of a Marx bank (Voltage multiplier using capacitors).
I will read about thyratrons, Thanks for your advice.

Thanks,
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Old 03-01-2015, 09:26 AM #6
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Default Re: Air/Nitrogen ionization using lasers

Quote:
Originally Posted by Sigurthr View Post
I remember doing some research on this a few years ago for shits and giggles, there was sure enough pretty solid reporting from declassified government docs that green is actually pretty damned efficient at air ionization, as far as wavelength goes. Only thing that was better was deep UV. That being said it is a hell of a lot easier to produce IR in the energies needed than anything else, so while the light itself is more efficient at the task, the means of creating the light is not.

Anyway, see: http://loa.ensta-paristech.fr/ilm/up...13303_2014.pdf

They used 300mJ in 1pS....
Thank you for sharing this paper with me, I will read it.
300mJ in 1 pS, I dont think the laser we have will work then. The lowest mJ laser to Ionize air I saw was 250 mJ, I didnt see anyone who used lower Energy than that to Ionize air. People say shorter wave lengths Ionize better, but I'm dont understand why.
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Old 03-01-2015, 10:35 PM #7
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Default Re: Air/Nitrogen ionization using lasers

Quote:
Originally Posted by aelshafiey View Post
People say shorter wave lengths Ionize better, but I'm dont understand why.
Per photon they do, simply because the photons are more energetic (wavelength inversely proportional to energy).

One thing to consider; increase the energy density using a short focal length focusing lens. Air breakdown occurs at a certain energy density level - kW/mm^2, if you decrease the spot size you increase your energy density, perhaps enough to reach the threshold.
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Old 03-02-2015, 01:54 AM #8
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Default Re: Air/Nitrogen ionization using lasers

Quote:
Originally Posted by Sigurthr View Post
Per photon they do, simply because the photons are more energetic (wavelength inversely proportional to energy).

One thing to consider; increase the energy density using a short focal length focusing lens. Air breakdown occurs at a certain energy density level - kW/mm^2, if you decrease the spot size you increase your energy density, perhaps enough to reach the threshold.
Awesome, that make sense now.
Do you know what does a Q-switch mean?
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Old 03-02-2015, 02:24 AM #9
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Default Re: Air/Nitrogen ionization using lasers

Q switches are optoelectronic/passive optical devices incorporated into certain lasers that allow a build up of energy and then a release at opportune time. Think of it as a slowly trickling stream of water from your faucet. You can try to wash your hair under it as is, or you can use a bucket to collect the water, and then dump the entire bucket over your head to fully rinse out your hair at once. The q switch does similar, releasing pulses of light at light higher amplitudes than if the laser ran continuously.
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