One Step Closer to Laser Weaponry and Power Transport
For years scientists, writers, and politicians have spoken of the weapon of the future, lasers that could knock a plane out of the sky, transport power long distance or work as remote detection sensors. And yet, this technology is not within our grasp – but it is however one significant step closer. New research published in the journal American Physical Society shows how a series of short laser pulses could lead to medium to high power laser bursts over kilometres of distance.
Classical waveguides (ie. optical fibres) are typically relied upon to ensure beam transportation, but suffer from two limitations: they can be damaged by high-energy or high-power pulses and can tolerate no more than 1 joule per square centimetre in short 100 femtosecond pulses. A convenient and fascinating solution was found to this issue; it was shown through simulation and then experiment that in air, a beam (filament) will ionize the air immediately around it which gives rise to a self-generated self-focusing effect which keeps the filament in focus over long distances. However, there were still a few issues to sort out. The filaments could travel a distance of up to 1 kilometre but carry no more than approximately one watt – much less energy than most proposed technologies would call for. Computer simulations have shown that if four filaments are created in a square pattern (see above) with femtosecond pulses that the sound waves created by the thermal energy of each filament would create an area of high-density air which lasts up to a millisecond and is ideal for acting as a waveguide. Using this method it was shown in the laboratory that a 110millijoule pulse of green light can be transported efficiently through 70cm of air. It is thought that if longer laser pulses could carry the same energy without disrupting the thermal column then the pulse could carry 10s of joules of energy - many factors above the 1milijoule carried by each filament in previous experiments.
At this stage the technology has the immediate application of effectively carrying power of a distance of a few meters, however for such things as cavity-free lasing and atmospheric laser communication will require more work on keeping the filaments parallel, stable and uniform over long distances. It is also speculated that in the future, this technology could be put to use in implementing filament-based lightning protection, an idea which was proposed more than 15 years ago but never came to bear fruit.