- Directed-energy weapon
A directed-energy weapon (DEW) emits energy in an aimed direction without the means of a projectile. It transfers energy to a target for a desired effect. Intended effects may be non-lethal or lethal. Some such weapons are real, or are under active research and development.
The energy can come in various forms:
- Electromagnetic radiation, in lasers or masers
- Particles with mass, in particle beam weapons
- Sound, in sonic weapons
In science fiction, these weapons are sometimes known as death rays or rayguns and are usually portrayed as projecting energy at a person or object to kill or destroy. Many modern examples of science fiction have more specific names for directed energy weapons, due to research advances.
- 1 Operational advantages
- 2 Problems and considerations
- 3 Lasers
- 4 Particle beam weapons
- 5 Sonic weapons
- 6 History
- 7 Non-lethal weapons
- 8 See also
- 9 Notes
- 10 References
- 11 External links
Laser weapons could have several main advantages over conventional weaponry:
- Laser beams travel at the speed of light, so there is no need (except over very long distances) for users to compensate for target movement when firing over long distances. Consequently, evading a laser after it has been fired is impossible.
- Light does not have mass, so is little influenced by gravity, so that long range projection requires little compensation. Other aspects such as wind speed can be neglected at most times, unless shooting through clouds.
- Lasers can change focusing configuration to provide an active area that can be much smaller or larger than projectile weaponry.
- Given a sufficient power source, laser weapons could essentially have limitless ammunition.
- Because light has a practically nil ratio (exactly 1 / c) of momentum to energy, lasers produce negligible recoil.
- The operational range of a laser weapon can be much larger than that of a ballistic weapon, depending on atmospheric conditions and power level.
Modern ballistic weapons commonly feature systems to counter many undesirable side-effects mentioned for them in the above comparison. As such it follows that laser weapons' advantage over ballistics could end up more about elegance and cost.
Problems and considerations
Laser beams begin to cause plasma breakdown in the air at energy densities of around a megajoule per cubic centimeter. This effect, called "blooming," causes the laser to defocus and disperse energy into the atmosphere. Blooming can be more severe if there is fog, smoke, or dust in the air.
- Spread the beam across a large, curved mirror that focuses the power on the target, to keep energy density en route too low for blooming to happen. This requires a large, very precise, fragile mirror, mounted somewhat like a searchlight, requiring bulky machinery to slew the mirror to aim the laser.
- Use a phased array. For typical laser wavelengths this method requires billions of micrometre-size antennae. No way to make these is known. However, carbon nanotubes have been proposed. Phased arrays could theoretically also perform phase-conjugate amplification (see below). Phased arrays do not require mirrors or lenses, can be made flat and thus do not require a turret-like system (as in "spread beam") to be aimed, though range will suffer at extreme angles (that is, the angle the beam forms to the surface of the phased array).
- Use 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 then amplifies inverted waves in a positive feedback loop, destroying the target with shockwaves as the specular regions evaporate. This avoids blooming 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 weapon-useful power levels.
- Use a very short pulse that finishes before blooming interferes.
- Focus multiple lasers of relatively low power on a single target.
Evaporated target material
Another problem with weaponized lasers is that the evaporated material from the target's surface begins to shade. There are several approaches to this problem:
- Induce a standing shockwave in the ablation cloud. The shockwave then continues to perform damage.
- Scan the target faster than the shockwave propagates
- Induce plasmic optical mixing at the target. Modulate the transparency of the target's ablation cloud to one laser 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 electric energy requirements. Existing methods of storing, conducting, transforming, and directing energy are inadequate to produce a convenient hand-held weapon. Existing lasers waste much energy as heat, requiring still-bulky cooling equipment to avoid overheating damage. Air cooling could yield an unacceptable delay between shots. These problems, which severely limit laser weapon practicality at present, might be offset by:
- Cheap high-temperature superconductors to make the weapon more efficient.
- More convenient high volume electricity storage/generation. Part of the energy could be used to cool the device.
Chemical lasers use energy from a suitable chemical reaction instead. Chemical oxygen iodine laser (hydrogen peroxide with iodine) and deuterium fluoride laser (atomic fluorine reacting with deuterium) are two laser types capable of megawatt-range continuous beam output. Managing chemical fuel presents other problems, so the problems of cooling and overall inefficiency remain.
This problem could also be lessened if the weapon were mounted either at a defensive position near a power plant, or on board a large, possibly nuclear powered, water-going ship. A ship would have the advantage of water for cooling.
A laser beam or particle beam passing through air can be absorbed or scattered by rain, snow, dust, fog, smoke, or similar visual obstructions that a bullet would easily penetrate. This effect adds to blooming problems and makes the dissipation of energy into the atmosphere worse.
The wasted energy can disrupt cloud development since the impact wave creates a "tunneling effect". Engineers from MIT and the U.S. Army are looking into using this effect for precipitation management.
Lack of indirect fire capabilities
Indirect fire, as used in artillery warfare, can reach a target behind a hill, but is not feasible with line-of-sight DEWs. Possible alternatives are to mount the lasers (or perhaps just reflectors) on airborne or space-based platforms.
Lasers are often used for sighting, ranging and targeting for guns; but the laser beam is not the source of the weapon's firepower.
Laser weapons usually generate brief high-energy pulses. A one megajoule laser pulse delivers roughly the same energy as 200 grams of high explosive, and has the same basic effect on a target. The primary damage mechanism is mechanical shear, caused by reaction 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 major 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.
Specific examples include:
- The Zeus laser weapon is the first laser and the first energy weapon of any type to be given actual use on a battlefield. It is used for neutralizing mines and unexploded ordnance.
- Laser Area Defense System.
- The Mid-Infrared Advanced Chemical Laser (MIRACL) is an experimental U.S. Navy deuterium fluoride laser and was tested against an Air Force satellite in 1997.
- In 2011, the U.S. Navy began to test the Maritime Laser Demonstrator (MLD), a laser for use aboard its warships.  
- Personnel Halting and Stimulation Response, or PHaSR, is a non-lethal hand-held weapon developed by the United States Air Force  Its purpose is to "dazzle" or stun a target. It was developed by Air Force's Directed Energy Directorate.
- Tactical High Energy Laser (THEL) is a weaponized deuterium fluoride laser developed in a joint research project by Israel and the U.S. It is designed to shoot down aircraft and missiles. See also National missile defense.
- The U.S. Air Force's Airborne Laser, or Advanced Tactical Laser, is a plan to mount a CO2 gas laser or COIL chemical laser on a modified Boeing 747 to shoot down missiles.
- Northrop Grumman has announced the availability of a high-energy solid-state laser weapon system that they call FIRESTRIKE. The system is modular, using 15 kW modules that can be combined to provide various levels of power.
- Portable Efficient Laser Testbed (PELT)
- Laser AirCraft CounterMeasures (ACCM)
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.
On January 25, 2007 the US Army unveiled a device mountable on a small armored vehicle (Humvee). It resembles a planar array. It can make people feel as if the skin temperature is around 130 °F (54 °C) from around 500 yards (460 m) away. Full scale production of such a weapon was not expected until at least 2010. It is probably most usefully deployed as an Active Denial System.
Microwave guns powerful enough to injure humans are possible:
- Active Denial System is a millimeter wave source that heats the water in the target's skin and thus causes incapacitating pain. It is being used by the U.S. Air Force Research Laboratory and Raytheon for riot-control duty. Though intended to cause severe pain while leaving no lasting damage, some concern has been voiced as to whether the system could cause irreversible damage to the eyes. There has yet to be testing for long-term side effects of exposure to the microwave beam. It can also destroy unshielded electronics. The device comes in various sizes including attached to a humvee.
- Vigilant Eagle is an airport defense system that directs high-frequency microwaves towards any projectile that is fired at an aircraft. The system consists of a missile–detecting and tracking subsystem (MDT), a command and control system, and a scanning array. The MDT is a fixed grid of passive infrared (IR) cameras. The command and control system determines the missile launch point. The scanning array projects microwaves that disrupt the surface-to-air missile's guidance system, deflecting it from the aircraft.
- Bofors HPM Blackout is a versatile and compact stand alone High Power Microwave system suitable for evaluation, research and as a decision tool for microwave effects and/or protection. With this system a realistic perspective is possible with regard to tactical adaptation and the generated level of microwave radiation. Bofors HPM Blackout has proven destructive effects at considerable distance against a broad field of COTS equipment.
Pulsed Energy Projectile
Pulsed Energy Projectile or PEP systems emit an infrared laser pulse which creates rapidly expanding plasma at the target. The resulting sound, shock and electromagnetic waves stun the target and cause pain and temporary paralysis. The weapon is under development and is intended as a non-lethal weapon in crowd control.
Particle beam weapons
Particle beam weapons can use charged or neutral particles, and can be either endoatmospheric or 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 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.
- Electrical blooming occurs only in charged particle beams, as ions of like charge repel one another.
The MARAUDER (Magnetically Accelerated Ring to Achieve Ultra-high Directed Energy and Radiation) used the Shiva Star project (a high energy capacitor bank which provided the means to test weapons and other devices requiring brief and extremely large amounts of energy) to accelerate a toroid of plasma at a significant percentage of the speed of light.
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 destroy 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.
Speed of the weapon
The speed of the energy weapon is determined by the density of the beam. If it is very dense then it is very powerful, but a particle beam moves much slower than the speed of light. Its speed is determined by mass, power, density, or particle/energy density.
Cavitation, which affects gas nuclei in human tissue, and heating can result from exposure to ultrasound and can damage tissue and organs. Studies have found that exposure to high intensity ultrasound at frequencies from 700 kHz to 3.6 MHz can cause lung and intestinal damage in mice. Heart rate patterns following vibroacoustic stimulation have resulted in serious arterial flutter and bradycardia. Researchers have concluded that generating pain through the auditory system using high intensity sound risked permanent hearing damage.
A multi-organization research program involved high intensity audible sound experiments on human subjects. Extra-aural (unrelated to hearing) bioeffects on various internal organs and the central nervous system included auditory shifts, vibrotactile sensitivity change, muscle contraction, cardiovascular function change, central nervous system effects, vestibular (inner ear) effects, and chest wall/lung tissue effects. Researchers found that low frequency sonar exposure could result in significant cavitations, hypothermia, and tissue shearing. Follow-on experiments were not recommended.
Tests performed on mice show the threshold for both lung and liver damage occurs at about 184 dB. Damage increases rapidly as intensity is increased. Noise-induced neurological disturbances in humans exposed to continuous low frequency tones for durations longer than 15 minutes involved development of immediate and long term problems affecting brain tissue. The symptoms resembled those of individuals who had suffered minor head injuries. One theory for a causal mechanism is that the prolonged sound exposure resulted in enough mechanical strain to brain tissue to induce an encephalopathy.
According to legend, the concept of the "burning mirror" or death ray began with Archimedes who created a mirror with an adjustable focal length (or more likely, a series of mirrors focused on a common point) to focus sunlight on ships of the Roman fleet as they invaded Syracuse, setting them on fire. Historians point out that the earliest accounts of the battle did not mention a "burning mirror", but merely stated that Archimedes's ingenuity combined with a way to hurl fire were relevant to the victory. Some attempts to replicate this feat have had some success (though not on any of three attempts by the MythBusters television program). In particular, an experiment by students at MIT showed that a mirror-based weapon was at least possible, if not necessarily practical.
In 1935 the British Air Ministry asked Robert Watson-Watt of the Radio Research Station whether a "death ray" was possible. He and colleague Arnold Wilkins quickly concluded that it was not feasible, but as a consequence suggested using radio for the detection of aircraft and this started the development of radar in Britain. See: History of radar#Robert Watson-Watt.
Engine-stopping rays, urban legend made real
Engine-stopping rays are a variant that occurs in fiction and myth. Such stories were circulating in Britain around 1938. The tales varied but in general terms told of tourists whose car engine suddenly died and were then approached by a German soldier who told them that they had to wait. The soldier returned a short time later to say that the engine would now work and the tourists drove off. A possible origin of some of these stories arises from the testing of the television transmitter in Feldberg, Germany. Because electrical noise from car engines would interfere with field strength measurements, sentries would stop all traffic in the vicinity for the twenty minutes or so needed for a test. A distorted retelling of the events might give rise to the idea that a transmission killed the engine.
A shoulder-mounted engine-stopping weapon was a central plot element in episode 303 of BBC espionage drama serial Spooks, in which it was referred to as an "engine killer".
Modern car engines are not mechanically, but electronically controlled. Disabling the electronics can indeed stop the engine. This has been implemented in OnStar, which has a remote control feature, but this is not a weapon. See also electromagnetic pulse (EMP), which is known for its engine-stopping effect, but is an undirected energy weapon.
Nikola Tesla (1856–1943) was a noted inventor, scientist and electrical engineer. He invented Tesla coils, transformers, alternating current electrical generators and was the first early pioneer of radio technology. Tesla worked on plans for a directed-energy weapon from the early 1900s until his death. In 1937, Tesla composed a treatise entitled The Art of Projecting Concentrated Non-dispersive Energy through the Natural Media concerning charged particle beams.
German World War II experimental weapons
Among the directed-energy weapons the Nazis investigated were X-Ray Beam Weapons developed under Heinz Schmellenmeier, Richard Gans and Fritz Houtermans. They built an electron accelerator called Rheotron (invented by Max Steenbeck at Siemens-Schuckert in the 1930s, these were later called Betatrons by the Americans) to generate hard X ray synchrotron beams for the Reichsluftfahrtministerium (RLM). The intent was to pre-ionize ignition in Aircraft engines and hence serve as anti-aircraft DEW and bring planes down into the reach of the FLAK. The Rheotron was captured by the Americans in Burggrub on April 14, 1945.
The Third Reich further developed sonic weaponry, using parabolic reflectors to project sound waves of destructive force. Microwave Weapons were investigated together with the Japanese.
Strategic Defense Initiative
In the 1980s, U.S. President Ronald Reagan proposed the Strategic Defense Initiative (SDI) program, which was nicknamed Star Wars. It suggested that lasers, perhaps space-based X-ray lasers, could destroy ICBMs in flight. Though the strategic missile defense concept has continued to the present under the Missile Defense Agency, most of the directed-energy weapon concepts were shelved.
During the Iraq War, electromagnetic weapons, including high power microwaves were used by the U.S. military to disrupt and destroy the Iraqi electronic systems and may have been used for other purposes[which?]. Types and magnitudes of exposure to electromagnetic fields are unknown.
The TECOM Technology Symposium in 1997 concluded on non-lethal weapons, “Determining the target effects on personnel is the greatest challenge to the testing community,” primarily because "the potential of injury and death severely limits human tests."
Also, "directed energy weapons that target the central nervous system and cause neurophysiological disorders may violate the Certain Conventional Weapons Convention of 1980. Weapons that go beyond non-lethal intentions and cause “superfluous injury or unnecessary suffering” may also violate the Protocol I to the Geneva Conventions of 1977."
Some common bio-effects of non-lethal electromagnetic weapons include:
Interference with breathing poses the most significant, potentially lethal results.
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