
Pulsed terawatt lasers have surprising effects when shone through the air (2006) - kungfudoi
http://www.americanscientist.org/issues/feature/2006/2/filaments-of-light/99999
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reallydontask
I spent countless hours of my PhD trying to get the White light continuum
stable enough to do measurements with.

Our laser wasn't powerful enough to use air as medium, so we would use
sapphire (very good, stable and predictable), Calcium Fluoride (absolutely
bloody terrible, but it did give out a lot more UV light) and water (never got
any measurements out of that, so unstable)

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rdtsc
> using pulsed lasers to trigger and guide high-voltage discharges over
> several meters in the laboratory.

There is no way the military have seen that and haven't thought "I bet we can
use that to fry our enemies"

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aaron-santos
I love the idea of generating two parallel beams and leveraging the
conductivity of plasma as a sort of "wireless" taser. It's likely not feasible
(I'm guessing someone has tried it), and it would be interesting to know why.

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street
I suspect being hit by the beams might harm the victim, with the electricity
just being a bonus. I doubt the laser generators are cheap and portable as
well.

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rdtsc
It has an EMP potential to fry electronics probably.

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genericone
"... back-directed light is the result of partial self-reflection of the
forward-traveling beam..."

"the idea of using a high-intensity laser to ionize air along the beam, thus
forming a conducting channel of plasma"

Real life light sabers are within the realm of possibility with existing
technologies!

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tbrownaw
The kerr effect sounds interesting, even if it is air-only... what power
density would it take to get self-focusing in a vacuum by gravitational
lensing?

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kragen
The Kerr effect is present in many different transparent media, but not in
vacuum. You're probably right that sufficient power density would give rise to
self-focusing by gravitational lensing, but it seems like the necessary power
density would be very high — the gravitational acceleration needs to be a
substantial fraction of _c_ very frequently, like 0.001 _c_ over every
interval where diffraction gives you a divergence of one milliradian. A
narrower beam moves the escaping light you need to capture closer to the
center of mass of the beam, but also increases that divergence.

It isn't obvious to me how to calculate this. Can anyone help?

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spott
You likely couldn't get gravitational lensing, you would probably get pair
production first, which would screw with your energy density.

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noobermin
Yes, I'd think the Schwinger limit[0] would be reached first, which is
currently the dream of most of us in this field. The Irradiance for the
Schwinger limit is 10^29 W/cm^2.

By contrast, the planned ELI[1] experiment will have pulse with a intensity of
10^24 W/cm^2. The current state of the art lasers of high peak intensity is
~10^21 W/cm^2 (current record I believe is 10^22 W/cm^2). There are proposals
to getting to the Schwinger limit but they are still in the hypothetical
stage.

[0]
[https://en.wikipedia.org/wiki/Schwinger_limit](https://en.wikipedia.org/wiki/Schwinger_limit)

[1]
[https://en.wikipedia.org/wiki/Extreme_Light_Infrastructure](https://en.wikipedia.org/wiki/Extreme_Light_Infrastructure)

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saidajigumi
This, while quite interesting, also feels like a member of a nascent genre:
"XKCD What-If? citation trolling."

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tbrownaw
_That is, hiking the peak power of the laser pulses that are applied increases
the number of filaments that result without notably influencing the individual
intensity or the energy each filament carries._

So these filaments are basically quantized particles?

...and their pulse length of 70 femtoseconds would be about 0.02 mm, or not
too far off how wide the filaments are. I guess the proportions would be
similar to a pair of saucers with the rims stuck together.

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daveloyall
In case you missed it: Take a close look at the last photo, the one near the
text "control of lightning strikes".

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dmitrygr
Most interesting thing in the article: they can likely use pulsed lasers to
guide lightning!

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sametmax
Now the next question: does the laser consume more energy than the lightning
bring ? Because maybe we can use that to harness energy in storms.

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qb45
The big problem is building batteries that could absorb some buttload-Joules
of energy in a fraction of a second. IIRC some researchers tried (just with
metal rods instead of lasers) and all they got was expensive fireworks.

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ChuckMcM
Two words: Graphene Capacitors :-)

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sametmax
Graphene, the only hot new thing more versatile than USB-C.

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dozzie
But you certainly can use USB-C to store energy from lightnings!

