By Spencer Ackerman, June 1, 2011
The Navy has a dream: to strap their shipdecks with laser cannons. The biggest obstacle is an awfully ironic one: sea air wreaks havoc on laser beams.
For lasers to work optimally, a beam of concentrated light needs to pass in a straight line at a target. But sea air is packed full of crud, from dense water particles to salt molecules and regular pollution. All that diminishes what’s called the “fluence” of a beam — the amount of radiated light it puts on a target; its zapping power, in other words. The traditional way to compensate for atmospheric distortions — with a “guide star” beam that tells you how much water and brine is in the air – hasn’t been effective enough. All attempts to burn through that crud with higher-powered energy weapons have flopped.
So now the Navy is taking a new approach, asking businesses to make the sea air safe for lasers.
In a new solicitation, called “Atmospheric Aerosol Mitigation for High Energy Laser Propagation,” the Navy suggests using “optical (electromagnetic) technologies” to cut down on the resistance that a beam of light traveling through the salty air will face. One option to preserve and expand fluence might be to use a “continuous wave” laser — an energy weapon that keeps blasting and blasting and blasting. Another choice: ultra short pulse lasers that fire so quickly, they burn a channel in the air.
How? According to the solicitation, the key method here is to “mitigate the absorption/scattering behavior of aerosol content within the beam path.” That would suggest the need to make the particles in the way of your laser beam less dense. Essentially, the task here is to clear the air – or at least make the air less likely to soak up your laser’s power. That’s why the potential commercial applications here include a greater ability to “study environmental effects and impacts of in situ gases and chemistry not normally associated with local environments.” It sure would be great for checking out pollution content.
It would also be extremely cost-effective for the Navy. The chief answer the Navy’s biggest brains have for the problem of sea air density is to weaponize the most ginormous laser of all. A Free Electron Laser, unlike all other lasers, can generate a beam of light from multiple wavelengths across the light spectrum, allowing technicians to find the wavelength that best fits the atmospheric density of a particular plot of ocean. (Which means you wouldn’t need all these other mitigation gimmicks.) Powerful? Certainly — it’s even used to find God’s own energy supply. But hardly efficient: the project’s been in development for 15 years, and it won’t be fielded aboard a ship, optimistically, for ten more.
That said, the Navy’s laser research is starting to pay off. Last month, the Maritime Laser Demonstrator — a regular ol’ solid state laser — on board a decommissioned destroyer disabled a small motorboat from a mile away, across choppy California waters. That beam was a mere 15 kilowatts. Imagine how much damage it could inflict through clearer air.