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Old 02-19-2013, 01:17 PM #1
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Default Air ionization with handheld laser- possible?

I really want to build a laser that is capable of causeing air ionization in a pointer sized package. I'm thinking somesort of q switched diode pumped solid state laser. The plasma would only need to form at the focal point of the lens that I would use with the device. I've seen some similar devices that are textbook sized, but I want to know if its possible to make somehing smaller. Also important is that it has a high repition rate <500 Hz. Over 1000 Hz would be great. Don't worry very much about power requirement, I just care about the compactness. I want to ask on these forums before I spend all my time trying to understand how to make one.


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Old 02-19-2013, 04:10 PM #2
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Default Re: Air ionization with handheld laser- possible?

What do you plan to do with the plasma point?

Even if it were possible, its still a laser. Not just a spark in the air. The goggles you would be required to wear for the q-switched system (remember I said kW) would cost as much as a couple college textbooks.

If what you want is breakdown in air - I would suggest a gas stove ignitor, or a cockroft-walton multiplier. I hate to say it, but high voltages alone would be less likely to hurt you, than if they were coupled with a kW nanosecond pulse beaming out of your hand.

Some things were never a good idea to let happen. Honey on a slice of pizza, that little light bulb in the freezer that always goes out, giving an engineer extra spending cash, putting a q-switched beam in someone's hand - its all the same!
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Old 02-19-2013, 06:21 PM #3
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Default Re: Air ionization with handheld laser- possible?

Please don't be concerned! I'm not planning on doing anything nefarious. Honestly, I just find the entire phenomenon fascinating. Right now I'm more concered if it is possible. No, I am not attempting to make a laser gun. And I've heard more than enough horror stories to make me aware of the importance of proper eye protection.

If it is possible, then how do you think something like that would work? I know this is going to be a long list, but it would great if someone who knows their stuff could answer a few of these.questions:
-what matters more in air breakdown: peak power density or peak energy density
-what is the power/energy density required for air breakdown?
-what controls a q switched laser's peak power and peak energy?
-what controls a q switched laser's repetition frequency?

Thanks meatball for your time and input.
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Old 02-19-2013, 06:52 PM #4
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Default Re: Air ionization with handheld laser- possible?

I have heard of people achieving air breakdown using an SSY-1 which is a small flashlamp pumped Nd:YAG laser. That could be done into something maybe the size of a Laserglow Hercules type body.

However, the SSY-1 probably won't last very long pumping that much power into it and the amount of energy required to fire an SSY-1 at joule level pulses with a rep rate of 1KHz would be far beyond what any portable solution would offer. Not to mention the lamp would melt itself in short order as well.

So no, it's not possible

For air breakdown peak power density is more important, hence a q-switched system would be mandatory.

Peak power and energy are a function of the laser's pulse duration and output energy. A laser firing a 1J pulse in 10ms is much lower peak power than say a 0.5J pulse at 1ms pulse duration.

Repetition frequency mainly depends on how powerful your charging circuit is and how much cooling the laser assembly has.

As an example, for a while I had an Eclipse Holmium:YAG laser which fired ~1J pulses at about 10Hz. The laser head was cooled with chilled deionized water and required 240v mains power. The lights in the room dimmed when the laser was firing.
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Old 02-22-2013, 03:25 PM #5
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Default Re: Air ionization with handheld laser- possible?

It sounds improbable, but I have two ideas.
1: shorten pulse duration. If it is possible to build a system with shorter pulse durations while outputting the same amout of energy, then the peak power would rise. From what I can tell, ssy-1 lasers seem to have a relatively long pulse duration when compared to some passively q-switched lasers I have seen.
2: change the wavelenth. Perhaps by making the lassr emit in the ultraviolet range, one could.increase the ionization efficiency.

Also, I decided to deal with the size constraints and I would settle with a sytem that produces ionization in a book sized package. This seems more reasonable than my previous idea of a pointer sized laser.
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Old 02-22-2013, 03:33 PM #6
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Default Re: Air ionization with handheld laser- possible?

I just came across this scientific paper. From what I can gather from the abstract, it seems to describe exactly what I'm looking for. The size is about the size of my palm. The only thing I'm not sure about is the repetition rate. I'm planning to buy the paper soon.
Here's the paper:
IEEE Xplore - Passively Q-switched Nd:YAG microchip laser over 1-MW peak output power for micro drilling

How do you guys think this thing works?
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Old 02-22-2013, 05:48 PM #7
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Default Re: Air ionization with handheld laser- possible?

The site doesn't really give much info without paying money for the PDF, active q-switching will definitely get you into the pulse durations you would want, but again power supply and cooling requirements for the joules alone will be large to get air breakdown level pulses at the rep rate you are requesting.
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Old 02-22-2013, 09:40 PM #8
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Default Re: Air ionization with handheld laser- possible?

Quote:
Originally Posted by SirRej View Post
It sounds improbable, but I have two ideas.
1: shorten pulse duration. If it is possible to build a system with shorter pulse durations while outputting the same amout of energy, then the peak power would rise. From what I can tell, ssy-1 lasers seem to have a relatively long pulse duration when compared to some passively q-switched lasers I have seen.
2: change the wavelenth. Perhaps by making the lassr emit in the ultraviolet range, one could.increase the ionization efficiency.

Also, I decided to deal with the size constraints and I would settle with a sytem that produces ionization in a book sized package. This seems more reasonable than my previous idea of a pointer sized laser.
SSY-1s are known for packing a punch for their size. It doesn't seem to make much sense to install a passive q-switch on anything any smaller, though it is done anyways.
You can get narrower pulses from a femtosecond laser (i.e. YAG pumped Ti:S), but the shorter the pulse, the wider the band of frequencies that it must carry. When you become less monochromatic, your smallest possible focal point gets bigger. There is a point where power density could be optimized as a function of pulse width and center wavelength, but I do not know what expressions you would use to do that.

So yes, going shorter on wavelength makes a smaller focal point given good optics and good beam profile.

Excimers are deeper UV, but can have a strange beam profile - something like a 445nm diode stripe but bigger.

This goes without portability in consideration, but I would guess a 355nm tripled, q-switched YAG would be a good area to look. But hey, when you can have kW CW from another setup, why bother with anything else?
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Old 02-23-2013, 02:26 PM #9
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Default Re: Air ionization with handheld laser- possible?

What would you say the threshold power density for laser air ionization is? I know the value changes with wavelength and air quality. This pdf seems to describe alot of the mathematics, but I haven't dug through it yet.
http://www.google.com/url?sa=t&sourc...-yczB_euRjLEqw

Also, I have also been looking at microchip lasers. A lot of these setups seem to provide high peak powers with an extremely compact setup. I mentioned an example in my previous post, and I am guessing the repetition rate was around 100Hz. What do you think about microchip lasers? They seem to be a upgrade from the ssy-1.

Since a smaller wavelength would be better, I want to figure out how to get that kind of output. I know Nd:YAG lasers can be made to output in the uv, but they are fairly inefficient. Are there any other options that are solid state?
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Old 02-23-2013, 06:05 PM #10
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Default Re: Air ionization with handheld laser- possible?

That threshold can depend on wavelength, air pressure, and what kind of breakdown you are looking for.

Some light reading:

Air ionization & lasers
http://www.jlab.org/FEL/LPC/05lpc-mao.pdf
http://legolas.ece.wisc.edu/papers/Magesh_1.pdf
Sam's Laser FAQ - Items of Interest

Other UV solid state? That would bring you back to YAGs which are diode pumped rather than flashpumped. A DPSS if you will. I'm you can find a fiber laser which could do the job, but hey you'll find that most of your high peak power options are indeed solid state - including microchip types.
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Old 02-24-2013, 12:50 AM #11
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Exclamation Re: Air ionization with handheld laser- possible?

Quote:
Originally Posted by Meatball View Post
That threshold can depend on wavelength, air pressure, and what kind of breakdown you are looking for.

Some light reading:

Air ionization & lasers
http://www.jlab.org/FEL/LPC/05lpc-mao.pdf
http://legolas.ece.wisc.edu/papers/Magesh_1.pdf
Sam's Laser FAQ - Items of Interest

Other UV solid state? That would bring you back to YAGs which are diode pumped rather than flashpumped. A DPSS if you will. I'm you can find a fiber laser which could do the job, but hey you'll find that most of your high peak power options are indeed solid state - including microchip types.
All very interesting reading. I recall, that there was an experimental area denial system that used a Q-switched laser to create a charge path. System used a YAG as it's medium. Shots were repeatable up to 30-50Hz.
It was designed to deliver some 100's Kvdc.
The device was supposed to be portable. I think the cost scared off investors.
Anyways...
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Last edited by Seoul_lasers; 02-24-2013 at 12:53 AM.
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Old 03-01-2013, 10:01 AM #12
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Default Re: Air ionization with handheld laser- possible?

it depends what kind of ionization you want if you want to make ozon then u need power.. other than that its kind of flash photolysis.. you have to find the exact electron band wavelength if you go up or down a notch it won't work

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