Curved Laser Beams Could Help Tame Lightning 184
Urchin writes "Laser beams just gained a new property — they can curve through space. That's what happens when ultrashort laser pulses pass through a phase pattern mask and a lens, which together shift the most intense region of the beam from the center to the right-hand side. The asymmetry in the pulse causes it to drift progressively further to the right along an arc as it travels. The laser beam is so intense that it ionizes the air it passes through to create a curved plasma channel. Those kinds of channels can be up to 100 meters long — direct them at thunderclouds and they could first trigger lightning to spark and then act as a convenient but short-lived lightning rod to guide it safely to the ground, according to some researchers."
Re:Direct them at people ... (Score:1, Informative)
Re:And they taunted Raiden II (Score:4, Informative)
http://en.wikipedia.org/wiki/File:Rdft0004.png [wikipedia.org]
Re:Filament propagation. (Score:5, Informative)
I can't really imagine a practical use for this (a lightning rod seems like a much cheaper solution) but it's pretty nifty science.
Then You are not imagining hard enough. Cheaper or not cheaper, it depends on the height of the lightning rod. Higher the tip, wider the safety zone - we could save on individual lightning rods and current surge ducts. Eventually, maybe we could tap on the charged layers of atmosphere and drain them to harvest energy. Perhaps we could "puncture" (short circuit) cumulonimbus clouds in controlled fashion and thus trigger hailstorms before they encroach crop-farming areas. We could use very high plasma columns as SLF vertical ground plane antennas. We could form free-space atmospheric plasma channels to be used as very high voltage/low current power lines bridging across great distances without a single power line tower in between. We could tase tanks on the field, warships on the sea and even airplanes in the air (using two opposite high voltage sources from two distant points simultaneously). We could also tase civilians, steel-frame buildings etc. but I hope we wouldn't. We could create giant radius induction loops in the air for whichever purpose. Ah, if only Tesla was still with us today, he would probably found myriad of cool applications for this ...
Re: "they can curve through space" (Score:3, Informative)
"they can curve through space"
Errr...no...
" The laser beam is so intense that it ionizes the air..."
Do I need to point out the obvious incompatibility between the two statements?
This is what high energy "space war" lasers--or more precisely the beam aiming/focusing systems--have been fighting with for a long time when dealing with the atmosphere. Send a very high powered beam through the atmosphere... You get ionization and heating. The center of the beam heats/ionizes more rapidly. That causes defocusing or "thermal bloom". Air (wind) traveling through the beam has a greater distance to travel through the center of the beam than at the edges, resulting in greater heating/ionization, the resulting change in density across the beam surface causes the beam to bend.
You've basically got hold of one end of a string--looking down a beam path that's constantly wiggling around--and constantly trying to correct for the intervening atmospheric effects to keep the beam on target by manipulating one end of a string. Which is why we still don't have effective anti-missile laser systems.
That said, for the purposes descibed in TFA, this should be much simpler and much more feasible.
Well-known problem with high-power optics (Score:5, Informative)
Normally the refractive index of a material is quoted as a constant. However, light radiation will slightly distort the electron levels of the material they are passing through, and this will have effect the refractive index. Normally this effect is very tiny. However, if you design high-power lasers, then it can become a nuisance. If you have a bright spot to your beam, then this will locally raise the refractive index. This will, in turn, cause the light to come to a line focus, which raises the intensity even more. If you do not design high-power optics to account for this, then a flat, uniform beam of light can spontaneously divide into a set of filamentary hot spots, which can smash your expensive optics.
There is another process, more usually associated with high-power ion beams. An ion beam that travels a long distance in air can twist like a garden hose squirting water. The ion beam heats up the air it is passing through, which creates a kind of pipe through the air as the hot atoms move away. This is a nuisance if you want to make the beam go in a straight line. One way of keeping an ion-beam weapon firing straight is to put a laser pre-pulse to heat a straight line through the air for the ion beam to travel down.
Re:No more "Don't taze me, bro!" ? (Score:3, Informative)
Actually, the opposite has already been used, there is a very bulky taser that instead of using darts (I think you're talking about stun guns, right?) uses lasers to ionize a path. With this tech you could make it curve and zap those geeks from a distance.
The utility (Score:3, Informative)
I used to work on this technology. The justification for it is really simple. If you could prevent just one lightning induced internet or power outage the amount of money saved would more than pay for all the research to date.
Under conditions When it works these systems are more effective than lightning rods. But to make these things ubiquitously functional and dependable is not a simple matter.
The airy beam decribed here I believe is just a variation of the old axiconic focus concept. With an axicon the beam only "looks like" it is bending. But the light does not bend per se. What is happeing is that one creates a fresnel lens and adjusts each lens segment to focus at a different foci. If you do this densly enhough the foci merge into a line. the light passing through one foci immediately diverges and does not pass through the next focii. That next focii is formed by diffenent rays. But to the viewer it looks like a continuous filament.
This is distict from soliton filmamentation. In this kind of filmentation the light realy does self-induce a light guide that allows an extended filemanet like focus. It's not unreasonable to imagine that a clever person could design an assymetric filament that would propagate it's light guide into an arc.
The description of the system uses language draw from both genre's of filament production, so it's not really clear which they are doing. This is understandable since due to the destructive nature of the filaments it's really really hard to insert monitoring equipment into the beam to actually determine which way the light is propagating. In many cases it's likely a little bit of both. some self containment fed by some axiconic focusing to replenish the beam as it loses energy.
In any cast the end result is a conduction channel.
Like lightning rods sometimes the purpose of the conduction channel is not to seed a lighting path but rather to cause conduction to drain the charge separation that is creating the conditions for lighting. indeed originally lightning rods were placed in large arrays to deplete the stored energy and prevent lightining rather than be sacrificial guides that preferentially attract lightning.
While either technique is good at preventing lightings lethal effects of causing fires. with electronics it is better to just never have lightining bolt at all, as our electronic systems fon't do well when the ground plane suddenly surges to a million volts.