The laser guns are becoming a reality

Solid state lasers are approaching the battlefield. However, cramming all that technology into something the size of Captain Kirk's phaser gun (from Star Trek) is still far out in the realm of science fiction.

Stephen Ashley, "Scientific American"

The beam rifle, which has long been used as one of the mainstays of science fiction stories, may join the range of weapons of the US military in the coming years. Engineers at several defense companies have successfully tested key experimental components of truck-sized "laser cannon" systems capable of launching a laser beam from an aircraft, battleship or armored vehicle and eliminating targets many kilometers away - even through dust or fog.

High-power lasers -- power measured in the hundreds or thousands of kilowatts -- have several advantages over conventional ballistic weapons, says Mark Nice, director of the US Department of Defense's Joint High Energy Laser Technology Bureau in Albuquerque, New Mexico. "The lasers are capable of providing highly accurate attack capabilities at the speed of light, which will cause little, if any, secondary damage," says Nees.

In the past, the skeptics joked about overly optimistic forecasts and said that "the laser is the weapon of the future, and will always remain so," but this time it seems that these weapons are becoming a reality. "The industry is right on the brink of producing defensive and offensive directed energy weapons," says Nees.

In the past year, researchers at the companies Northrop-Grumman, Textron, Raytheon and the American Livermore National Laboratory, funded by the US Air Force, Army and Navy, have made considerable progress in researching a crystalline solid-state laser, which operates directly on electricity.

A solid-state laser with a power of more than 100 kilowatts, installed on a ground vehicle, and connected to an electric generator, a fuel cell or a battery array can provide an almost "infinite cartridge" of cheap shots, which can destroy in flight shells, mortar bombs, rockets and missiles from a distance of five to eight kilometers. Such a system could also dazzle electro-optical and infrared sensors on the battlefield, helping soldiers neutralize mines and improvised explosive devices from a safe distance.

The key to this high-energy device is the compliment medium, the material that amplifies the laser's photons. In the laser diodes found in DVD players and other consumer electronics, layers of semiconductor material amplify the light after excitation from an electric current.

Jackie Gish, Director of Directed Energy Technologies and Products at Northrop-Grumman Space Technologies, explains that the medium used in a crystalline solid-state laser is a square (or rectangular) tile several centimeters thick. The tiles are made of a hard ceramic material, such as yttrium-aluminum-garnet (garnet), doped with the rare element neodymium. But instead of electrical excitation, the praise medium is stimulated by optical pumping through arrays of laser diodes. In general, the larger the tile, the greater the power.

Each research team has its own ways of connecting several tiles together to create "chains" of lasers that produce tens of kilowatts of power, says John Bones, vice president of applied technology at Textron Systems. In the coming year, the engineers plan to group these chains coordinated, in series or in parallel, to reach hundreds of kilowatts - the average threshold power for use in military laser applications.

Other key performance goals, according to Niss, are an operational activation time of 300 seconds (enough for multiple laser shots), a system for converting electrical energy to optical energy with an efficiency of more than 17%, and above all a high "beam quality" (actually, a focused beam) to ensure Let enough photons reach the target and heat its surface to a temperature that will destroy, explode or tilt it off its course.

If the laser tiles meet these goals, their use on the battlefield depends on the success of their integration into operational weapons systems that will be small enough to be mounted on vehicles, Bones explains. A crystalline solid-state laser weapon would need, in addition to a renewable electricity source of more than 1,000 kilowatts, also a cooling device that would prevent the tiles from getting hot and causing the beam to distort.

Also, a device will be required for the direction of the beam that will place the photons on the target - most likely a large and portable mirror with adaptive or changeable optics that will compensate for atmospheric distortions, which will be able to be detected using a "sensor" of a low-power laser beam. And finally, the direction of the system will rely on a radar or optical marking system, which will locate the intended targets and track them.

Effective beam-based weapons will revolutionize warfare, no less. However, compressing all this technology into something the size of Captain Kirk's phaser gun (from "Star Trek") is still far out in the world of science fiction.

Fatal reactions

The US military has already developed one type of powerful laser: a directed energy device driven by the power of chemical reactions. These devices, which are much more powerful than solid state lasers, operate at powers of megawatts and are called chemical oxygen-iodine lasers (COILs).

But these lasers are large and can only be operated as long as the reacting materials do not decay. Nevertheless, US Department of Defense contractors are preparing to install them on planes. A Boeing 747 model aircraft will carry a COIL system called "Airborne Laser YAL-A1", and is intended for protection against flying objects, mainly ballistic missiles. And an AC-130 model cargo plane will carry the "advanced tactical laser", designed for precise air-to-ground attacks.

From the August-September issue of "Scientific American"