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Directed-energy weapon

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A directed-energy weapon is a type of energy weapon that directs energy in a particular direction by a means other than a projectile. It transfers energy to a target for a desired effect. Some of these weapons are real or practicable; some are science fiction. The energy is in various forms:-

See energy weapon for non-directional energy weapons.

Some of these weapons are known as death rays or rayguns and are usually portrayed as projecting energy at a person or object in order to kill or destroy. The projected energy can come in many forms, such as a particle beam, laser, or radiation stream. Other forms are described later in this article. So far, weapons described as rayguns are all fictional (or non-functional toys and film props).

Some lethal directed-energy weapons are under active research and development, but most examples of such weapons appear in science fiction.

Types of directed-energy weapons are:-

Ordinary light

  • A flashlight directs light in the visible spectrum but it operates at such low power as to be generally harmless.
  • Some searchlights are bright enough to cause permanent or temporary blindness.
  • There is said to exist a real non-lethal weapon that disorients a target by shooting disorienting lighting patterns at the eyes.

Lasers

Lasers are very well known in science fiction as a type of raygun. In the real world, lasers are often used for sighting, ranging and targeting for guns; but the laser beam is not the source of the weapon's firepower.

There is research on real lasers as dazzling non-lethal weapons.

Laser weapons usually generate brief high-energy pulses. A million joules delivered as a laser pulse is roughly the same energy as 200g of high explosive, and has the same basic effect on a target. The primary damage mechanism is mechanical shear, caused by reaction (like a rocket) when the surface of the target is explosively evaporated.

Most existing weaponized lasers are gas dynamic lasers. Fuel, or a powerful turbine, pushes the lasing media through a circuit or series of orifices. The high-pressures and heating cause the medium to form a plasma and lase. A big difficulty with these systems is preserving the high-precision mirrors and windows of the laser resonating cavity. Most systems use a low-powered "oscillator" laser to generate a coherent wave, and then amplify it. Some experimental laser amplifiers do not use windows or mirrors, but have open orifices, which cannot be destroyed by high energies.

Problems with lasers

Blooming

Laser beams begin to cause plasma breakdown in air at power densities of around a megajoule per square centimeter. The laser beam is not visible, unless there is air, water or smoke present to scatter its light, or the heating of the air by the laser creates a path, or contrail, made of plasma. A laser beam can be effectively transmitted through the atmosphere a long distance without being absorbed because the air heated by the laser in the path of the beam becomes ionized plasma which undergoes thermodynamic expansion. This creates a plasma vacuum channel through the air that the beam passes through. In addition, some frequencies of laser light are not easily absorbed by air.

There are several ways to inhibit blooming:

  • The most promising is to distribute the beam over a large mirror that focuses the power on the target, to keep energy density in the air too low for blooming to happen. But this needs a large, very precise, very expensive, fragile mirror, mounted somewhat like a searchlight, requiring bulky machinery to slew the mirror to aim the laser.
  • A phased array. For the usual laser wavelengths this method would need billions of micrometre-size antennas, and no way to make these is known. Phased arrays could theoretically also perform phase-conjugate amplification (see below).
  • A very short pulse that finishes before blooming interferes.
  • A phase-conjugate laser system. Here, a "finder" or "guide" laser illuminates the target. Any mirror-like ("specular") points on the target reflect light that is sensed by the weapon's primary amplifier. The weapon-power amplifier then amplifies inverted waves in a positive feedback loop, destroying the target with shockwaves as the specular regions evaporate. This avoids the blooming problem because the waves from the target passed through the blooming, and therefore show the most conductive optical path; this automatically corrects for the distortions caused by blooming. Experimental systems using this method usually use special chemicals to form a "phase conjugate mirror". In most systems, the mirror overheats dramatically at weaponized powers.
  • Trying to induce a shockwave that evacuates the path between the target and the weapon. Without air in the laser's path, blooming will not occur. However, it is difficult to achieve the amount of power needed to blast the air out of the way.

Evaporated target material shading the target

Another problem with weaponized lasers is that the evaporated material from the surface of the target begins to shade the surface. There are several approaches to this problem:

  • One is to induce a standing shockwave in the ablation cloud. The shockwave then continues to perform damage.
  • Another scheme is to scan the target faster than the shockwave.
  • Another theoretical possibility is to induce plasmic optical mixing at the target. In this scheme, the transparency of the target's ablation cloud to one laser is modulated by another laser, perhaps by tuning the laser to the absorption spectra of the ablation cloud, and inducing population inversion in the cloud. The other laser then induces local lasing in the ablation cloud. The beat frequency that results can induce frequencies that penetrate the ablation cloud.

High power consumption

One major problem with laser weapons (and directed-energy weapons in general) is their high energy requirements. Existing methods of storing, conducting, transforming and directing energy are inadequate to produce a convenient hand-held weapon. Existing lasers need much energy and bulky cooling equipment because they are inefficient and waste much energy as heat.

This problem of storing and/or supplying energy in the form of electricity is offset in chemical lasers by using energy released in a suitable chemical reaction instead of electrical energy. Chemical oxygen iodine laser (hydrogen peroxide with iodine) and deuterium fluoride laser (atomic fluorine reacting with deuterium) are two examples of laser types capable of megawatt-range output of a continuous beam. Storing and transporting the chemical fuel presents its own problems with these lasers, and the problems of cooling and overall inefficiency remain.

The beam being absorbed by obscuration in the air

A laser beam or particle beam passing through air can be absorbed or scattered by rain, snow, dust, fog, smoke, or suchlike that a bullet would easily brush aside.

Electrolaser

An electrolaser lets blooming occur, and then sends a powerful electric current down the conducting ionized track of plasma so formed, somewhat like lightning. It functions as a giant high energy long-distance version of the Taser or Stun gun.

Alternating current is sent through a series of step-up transformers, increasing the voltage and decreasing the amperage. The final voltage may be between 108 and 109 volts. This current is fed into the laser beam. To complete the electric circuit, there should be either a second laser beam, or a ground return from the target to the last transformer in the step-up series. This electric arc could kill or incapacitate a human target through electrocution. Any electric or electronic devices in the target may be seriously damaged, disabled or destroyed. Because it relies on the blooming effect, there must be air or some other gas between the electrolaser weapon and the target.

Electrolasers often occur in science fiction and videogames.

Microwave lasers

Microwave lasers are called masers. Microwave guns powerful enough to injure humans are possible.

  • Active Denial System is a microwave laser, to heat the water in the target's skin and thus cause incapacitating pain. Being developed by the Air Force Research Laboratory in New Mexico by researchers working with Raytheon for riot-control duty in Iraq. While intended to cause severe pain while leaving no lasting damage, there has yet to be testing for long-term side effects of exposure to the microwave beam. It can destroy electronics.

Low-powered lasers

There is an imitation shotgun which fires a low-powered laser beam at a target which is covered with reflective 90° corners designed to send the beam back where it came from to be detected by a detector on the gun. This is only for target practice without using up ammunition; it has the disadvantage (for a shotgun user) that the beam travels at the speed of light and in a straight line, without teaching the shooter to allow for the effects of wind deflecting the fired shot and the target moving while the shot travels.

THEL

THEL (Tactical High Energy Laser) is a weaponized deuterium fluoride laser developed in a joint research project of Israel and the US. It is designed to shoot down aircraft and missiles.

Airborne Laser

The U.S. Air Force's Airborne Laser, or Airborne tactical laser, is a plan to mount a CO2 gas laser or COIL chemical laser on a modified Boeing 747 and use it to shoot down missiles. [2]

Ultraviolet laser

HSV Technologies of San Diego is developing a laser weapon to paralyze animals (testing for later use on humans) by an electric charge generated by the laser beam. It is described as an ultraviolet laser and not an electrolaser.

Tactical considerations

Lasers have two advantages:

  • They can hit whatever they see, at the speed of light.
  • Some lasers run on electricity, which can be cheaply generated, reducing the need for expensive ammunition.

Since lasers can defeat artillery and missile attacks, any group fielding an effective laser system will gain decisive advantages in ground, air and space combat. Under radar control, lasers have shot artillery shells in flight, including mortar rounds. This suggests that a primary application of lasers should be as part of a defensive system. Before a projectile can hit a target, it must become visible to the target.

The main difficulty with currently practical lasers is the high expense and fragility of their mirrors and mirror-pointing systems.

Some believe that mirrors or other countermeasures can reduce the effectiveness of high energy lasers. This has not been demonstrated. Small defects in mirrors absorb energy, and the defects rapidly expand across the surface. Protective mirroring on the outside of a target is liable to damage and getting dirty, much more than a mirror shut away inside a laser's mechanism.

Electric beam in a vacuum

In a vacuum (e.g. in space), an electric discharge can travel a potentially unlimited distance at a velocity slightly slower than the speed of light. This is because there is no significant electric resistance to the flow of electric current in a vacuum. This would make such devices useful to fry the electrical and electronic parts of satellites and spacecraft. However, in a vacuum the electric current cannot ride a laser beam, and some other means must be used to keep the electron beam on track and to prevent it from dispersing: see particle beam.

Particle beam weapons

Particle beam weapons include charged and neutral, endoatmospheric and exoatmospheric. Particle beams as beam weapons are theoretically possible, but practical weapons have not been demonstrated. Certain types of particle beams have the advantage of being self-focusing in the atmosphere.

Blooming is not limited to lasers, but is also a problem in particle beam weapons. Energy that would otherwise be focused on the target spreads out; the beam becomes less effective.

  • Thermal blooming occurs in both charged and neutral particle beams, and occurs when particles bump into one another under the effects of thermal vibration, or bump into air molecules. It is likely that a particle beam (except electrolasers) fired into air will make merely a short hot flame like a blowtorch.
  • Electrical blooming occurs only in charged particle beams, as ions of like charge repel one another.

Plasma weapons

Plasma weapons fire a beam or bolt of plasma, which is excited matter consisting of electrons and also protons or nuclei. Examples are:

  • The MARAUDER (Magnetically Accelerated Ring to Achieve Ultra-high Directed Energy and Radiation). See this link for more details; the antiaircraft potential of such a system is mentioned.
  • This article explains theories about ball lightning, which may be a type of plasma, which if weaponized could produce beam weapons guided in the same sense as an ATGM

The plasma rifle is a staple of science fiction. There may have been influence from the real plasma torch used to cut metal.

Pulse rifle

The pulse rifle is a fictional weapon occasionally used in science fiction. In some of its occurrences, (e.g. Aliens) it is a projectile weapon. The rifle in Aliens was said to use caseless ammunition, which is a current-generation technology used in actual weapons such as the Heckler & Koch G11 rifle. Caseless ammunition propels a bullet down a rifled barrel as a result of the combustion of gunpowder, just as regular cased ammunition does. Thus, this sort of "pulse rifle" is not a directed-energy weapon. In some of its incarnations (e.g. the Lost in Space movie) the "pulse rifle" is a directed-energy weapon. whose mode of operation has not been conclusively and consistently explained.

Sonic and ultrasonic beam weapons

See Sonic weaponry.

Rayguns: directed-energy weapons in fiction

See Raygun.

History

Mythology

Before modern technology developed, many mythologies described gods or demons using weapons that make lightning, such as Jupiter's and Zeus's thunderbolt, Thor's hammer Mjolnir, and the Hindu god Indra's spear (the vajrā).

Ancient inventors

According to mythology, the concept of the "burning mirror" or death ray began with Archimedes who created such a mirror with an adjustable focal length to track and set fire to the Roman fleet as it invaded Syracuse. Historians, however, acknowledge that the earliest accounts of the battle did not mention a "burning mirror" and that only Archimedes' ingenuity combined with a way to hurl fire were relevant to the victory. A Byzantine writer hundreds of years later is suggested to have imagined this 2200-year-old death ray, which is attributed to Archimedes. While the MythBusters television program was unsuccessful at creating this "death ray", others have since successfully built other versions. An experiment by students at MIT showed that a mirror-based weapon was at least possible, though the practicality of such a weapon was not established.[3]

A Greek called Diocles supposedly invented the parabolic mirror.

Grindell-Matthews

After the astonishing technological advancement during World War I, many such schemes began to appear credible. Harry Grindell-Matthews tried to sell such a ray to the British Air Ministry after that war. He failed to appear to demonstrate his apparatus, however. It was apparently taken to France but has not resurfaced, leading to various conspiracy theory ideas about what might have happened to it, or who might have developed it later. Radar may be a by-product of this research.

Tesla

Nikola Tesla generated the first large scale artificial electric lightning discharges during the 1890s. He invented Tesla coils, transformers, and alternating electric current generators. He was an early pioneer of electronic radio and television technology.

He worked on a real Death ray in the early 1900's. He designed it in 1942, and offered the US War Department the secrets of his "teleforce" weapon on January 5 1943, but was assumed to be crazy. Tesla then offered his device to several European countries.

Records which recently turned up in Russia showed that his proposed "death ray" was based on a narrow stream of atomic clusters of liquid mercury or tungsten accelerated by high voltage, probably produced by a huge Tesla Coil. If so, this weapon can be classed as a particle beam or as an electromagnetic-powered projectile gun, depending on the size of the projectiles.

When he died in 1943, a prototype compact version of the "death ray" called an "Anti-Tank gun" was in a trunk in the basement of his hotel. Immediately after he died, a Russian spy raided the room and the safe containing the schematics of the "death ray". The FBI never found any of the important parts of the schematics nor the trunk with the prototype, as far as we know. Schematics of the projector nozzle have surfaced, though. The U. S. Government classified his electron particle beam weapon design as secret until the 1980s.

See the document Ventura, Timothy, "Tesla Death Ray Reconstruction", 1994. It is in PDF format. It theorizes that Tesla's weapon fired a powerful beam of a special sort of electromagnetic radiation which caused the target to pick up a high electric charge, which then attracted destructive lightning-type electric arcs from the area around. The document is purely hypothetical with no experimentation.

Tesla theorized on the use of UV light to ionize a plasma path through the air to a target for his electron particle beam weapon. However, UV lasers were not invented until the 1960s.

Nazis

In the later phases of WWII, Nazi Germany increasingly put its hopes on research into technologically revolutionary secret weapons.

Among the directed-energy weapons the Nazis investigated were sonic weaponry, using parabolic reflectors to project sound waves of destructive force.

This Nazi research also included searching in India in the hope that some of the powerful weapons and flying craft described in the Mahabharata were the real products of a supposed ancient technologization, rather than mythology based on lightning and other destructive natural forces.

Star Wars

In the 1980s, Ronald Reagan revived the idea as a matter for public funding with his Strategic Defense Initiative program, which was immediately nicknamed "Star Wars", due to its objective to put weapons in space. It was proposed that lasers, perhaps including space-based X-ray lasers, could destroy ICBMs in flight. The program was heavily criticized on both theoretical and practical grounds. It is not clear whether this was part of a general plan to facilitate the collapse of the Soviet Union by misdirecting the Soviets into investing in research that had no practical outputs (this was a common Cold War strategy on both sides).

Enthusiasm for these ideas, and the arms race they implied, waned in the 1990s. Research proceeded, however, and by 2003, this led to the THEL project, which is described above.

Energy devices which may be confused with directed-energy weapons

The term electroshock gun includes two sorts of weapons, but neither of these is a directed-energy weapon, despite its name:-

  • Electric shock prod: it administers an electric shock on contact. It is not strictly a gun, as it does not cause any effect at a distance.
  • Guns which fire an electrified projectile.

The real thermic lance is not a gun. Occasionally science fiction authors misuse the name "thermic lance" to mean a raygun.

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