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Curved Laser Beams Could Help Tame Lightning
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."
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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 ...
"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.
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.