Laser providing a electrical path of low resistance


by Fion
Tags: electrical, laser, path, providing, resistance
Fion
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#1
Sep7-06, 12:43 PM
P: 3
Hi, I have a few questions about ionizing lasers creating an electrical path that I'm hoping someone here might be able to answer.
Does anyone know what kind/power of laser would create a good path of low resistance for an electrical current? I am thinking through normal atmosphere, say up to about 4 feet or so. And does anyone know what kind of resistance there would be? Compared to say a normal metal path?
I have heard tell of an optical taser that uses laser beams to deliver it's current, instead of wires, has anyone else heard of such a thing?
If noone knows any answers here, would you be able to redirect me to a good place to find them?
Thanks for your help!

Fion
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Claude Bile
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#2
Sep7-06, 06:08 PM
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To cause an optical induced breakdown of air, you need a laser that has either;
- Very high average power.
- Very small focal spot.
- Very short pulse lengths.

To obtain optical breakdown over 4 feet of air, you need a long Rayleigh range which rules out a small focal spot, your best bet is a laser with a high average power (by high I mean in the 10's of kW).

I have never heard of using a laser to cause optical breakdown for the purpose of guiding electrical current, which is more of an indication of how impractically inefficent the process would be rather than whether it is possible or impossible. Basically you are using a big, expensive, power-guzzling laser to accomplish the same thing as an electric cord.

Claude.
Fion
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#3
Sep8-06, 10:18 AM
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Thanks Claude!
I just found an article about the taser I mentioned earlier, and I thought people might be interested... It gives some details about how this is done (creating plasma channels to conduct electricity).
But from reading it, it looksl like the 5 joule laser they mention is for the one with a 100 meter range. That is way more range then I am thinking, for my idea, I really don't want anyone to get tased like that, I just need the electrical channel. Do you have any idea what power (approximatly) a laser would be needed for the shorter distance I'm thinking? (up to about 4-6 feet). Also, do you know where I could find some documentation on how laser power is determined? Most of the lasers I see are rated by what looks like the size of the beam, and the mW it uses... I would just like to be able to compare lasers in terms of power and understand what it means. The article below was written 2 years ago, and I assume that laser technology has advanced since then, and such lasers would be smaller and cheaper...

Solid-state lasers
The gun has been designed for the US Marine Corps to use for crowd control and security purposes and is due out in 2005. It is based on early, unwieldy technology and has a range of only three metres, but an operator can debilitate multiple targets by sweeping it across them for "as long as there is an input power source," says Bitar.
XADS is also planning a more advanced weapon which it hopes will have a range of 100 metres or more. Instead of firing ionised gas, it will probably use a powerful laser to ionise the air itself. The idea has been around for decades, says LaVerne Schlie, a laser expert at the US Air Force Research Lab in Kirtland, New Mexico. It has only become practical with advances in high-power solid-state lasers.
"Before, it took a laser about the size of two trucks," says Schlie. "Now we can do it with something that fits on a tabletop."
The laser pulse must be very intense, but can be brief. So the makers of the weapons plan to use a UV laser to fire a 5-joule pulse lasting just 0.4 picoseconds - equating to a momentary power of more than 10 million megawatts.
This intense pulse - which is said not to harm the eyes - ionises the air, producing long, thread-like filaments of glowing plasma that can be sustained by repeating the pulse every few milliseconds. This plasma channel is then used to deliver a shock to the victims similar to a Taser's 50,000-volt, 26-watt shock.

Pasted from <http://www.newscientist.com/article.ns?id=dn6014>

berkeman
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#4
Sep8-06, 11:32 AM
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Laser providing a electrical path of low resistance


Quote Quote by Fion
I have heard tell of an optical taser that uses laser beams to deliver it's current, instead of wires, has anyone else heard of such a thing?
Nope. Science fiction or urban legend.
Fion
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#5
Sep8-06, 11:41 AM
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Refer to my last post...
berkeman
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Sep8-06, 11:50 AM
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Quote Quote by Fion
Refer to my last post...
Sorry, I missed that. However, after reading the article, the laser approach still seems like vaporware, IMO. And even some of the others don't sound very practical. There's a reason, after all, that a Taser fires more than one dart. None of the descriptions of the other technologies addressed that need...
Mk
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#7
Sep9-06, 11:14 AM
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The optical taser sounds like a terribly uneconomical idea. Lasers are already so inefficient, you want to use one as a gun?
AO eye 5
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#8
Sep9-06, 11:37 AM
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This should be related to your inquiry:

Lightning Control with Lasers; August 1997; Scientific American Magazine; by Diels, Bernstein, Stahlkopf, Zhao; 6 Page(s)

There should be similar investigations as well in the article (and around the time period), because an issue I had was interesting--lightning sprites.

Here's a link to the SciAm search page: Link.
Chronos
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#9
Sep9-06, 11:54 PM
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It would be gruesomely inefficient to conduct electricity in this manner.
Claude Bile
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#10
Sep10-06, 06:50 PM
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Quoted from the same NS article -

"..a 5-joule pulse lasting just 0.4 picoseconds - equating to a momentary power of more than 10 million megawatts. This intense pulse - which is said not to harm the eyes.."

I find this very hard to believe, which leads me to question the credibility of the whole article. It sounds less like an article of science, than a shameless plug for some weapons manufacturing companies.

Claude.
Mk
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#11
Sep11-06, 09:53 AM
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Quote Quote by Claude Bile
Quoted from the same NS article -

"..a 5-joule pulse lasting just 0.4 picoseconds - equating to a momentary power of more than 10 million megawatts. This intense pulse - which is said not to harm the eyes.."

I find this very hard to believe, which leads me to question the credibility of the whole article.
Well, bullets don't harm eyes unless they hit the eyes!


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