Solid State Laser - Weapon

(CBS) U.S. scientists are on the verge of creating a laser weapon that could give American forces an awesome advantage on the battlefield, but would also raise tough questions for Pentagon war planners, a newspaper reports.

After 40 years of work, the Pentagon may have a solid-state laser in its arsenal within a decade, reports the Oakland Tribune.

Compared to the chemical lasers now in use by America's military, solid-state lasers would be compact and efficient — perhaps running off the engine of an Army Humvee or an Air Force F-16.

Solid-state lasers would also be deadly. In a recent demonstration at Lawrence Livermore National Laboratory — one of three sites of research on a solid-state laser — a test-fired laser emitted 400 pulses of light in two seconds, drilling through an inch of steel, the Tribune reported.

Once fully developed, the Tribune reports, solid-state lasers could shoot down mortars and artillery shells, explode ordnance in enemy depots and even wipe out ballistic missiles 500 miles away. They would strike with incredible speed and could be retargeted instantly.

Contrary to science fiction, the lasers will not be visible streams of light. Instead, targets will simply explode. Troops will not point and shoot lasers, because they will most likely have to react to dangers and targets moving too fast for a human response. Nor will lasers be holster-sized — the smallest to date is the size of a commercial jetliner.

Making lasers smaller is one reason for moving from chemical lasers — which require a larger mass of chemicals to generate more power — to solid-state lasers, which use electricity to generate a beam. According to the Tribune, Northrup Grumman is trying to reduce the size of one laser to fit in a single C-130 cargo plane.

But once the technical problems are solved, strategic issues will loom large, posing questions that, so far, the Pentagon has not answered.

For example, it is unclear if the U.S. would use the laser to target people or restrict its use to hitting inanimate targets. It is not known whether lasers would be employed to defend or attack satellites.

How will U.S. doctrine accommodate a weapon that can strike without detection possibly hundreds of miles away at relatively little cost? Since no other country is anywhere near developing a militarized solid-state laser, under what circumstances would the U.S. use it in a war?

In most cases, the "law of war" requires discrimination and proportionality. While a laser could do a better job of discriminating between troops and civilians, it is unclear that its use could be proportional to any enemy threat.

The military already uses several types of lasers. Some guide bombs and missiles. An experimental system, the Tactical High Energy Laser, has been used to shoot down missiles in demonstrations.

The national missile defense system includes work on an Airborne Laser that would be mounted on a freighter aircraft and used to shoot down ballistic missiles in flight.

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The Solid-state laser
A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid such as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but are generally considered as a separate class from solid-state lasers (see Semiconductor laser).

Solid-state media
Generally, the active medium of a solid-state laser consists of a glass or crystalline host material to which is added a dopant such as neodymium, chromium, erbium, or other ions. Many of the common dopants are rare earth elements, because the excited states of such ions are not strongly coupled with thermal vibrations of the crystalline lattice (phonons), and the lasing threshold can be reached at relatively low brightness of pump.

There are many hundreds of solid-state media in which laser action has been achieved, but relatively few types are in widespread use. Of these, probably the most common type is neodymium-doped YAG. Neodymium-doped glass (Nd:glass) and ytterbium-doped glasses and ceramics are used in solid-state lasers at extremely high power (terawatt scale), high energy (megajoules) multiple beam systems for inertial confinement fusion. Titanium-doped sapphire is also widely used for its broad tunability.

The first material used for lasing was ruby. Ruby lasers are still used for some applications, but are not common due to their low efficiency. Er:YAG lasers lase in the mid-infrared.

Pumping
Solid state lasing media are typically optically pumped, using either a flashlamp or arc lamp, or by laser diodes. Diode-pumped solid-state lasers tend to be much more efficient, and have become much more common as the cost of high power semiconductor lasers has decreased.

Applications
Solid-state lasers are being developed as optional weapons for the F-35 Lightning II, and are reaching near-operational status.

Source: wikipedia