Death ray

From Academic Kids

The concept of a death ray is generally portrayed as some form of directed energy weapon that projects energy at a person or object in order to kill or destroy them. For science fiction weapons, see raygun.

Contents

History

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. It is worth noting that the Myth Busters television program attempted to replicate this idea, but found it highly impractical, partly due to the possiblity of the power source (the sun) being useable at night or on a cloudy day.


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 worked on an actual Death ray in the early 1900's and at the time of his death. He 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. At the time of his death, a prototype compact version of the "death ray" called an "Anti-Tank gun" was located in a trunk in the basement of his hotel. Immediatly after his death a Russian spy had 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.

Nazis

In the later phases of WWII, Nazi Germany put its hopes on research for technologically revolutionary secret weapons. Through the 1930s the atomic bomb and radiological weapon were proposed, and the related, more selective, surgical idea of a death ray was probably more appealing than wanton and horrific destruction by such means. This belief intensified in the 1940s after Hiroshima and Nagasaki proved the undesirable physical and political fallout of such weapons of mass destruction.

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. Lasers could destroy ICBMs in flight. The program had limited success but there were numerous attempts to find practical death ray technologies. 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. By this point, science fiction was more interested in the very real potential of personal-scale biological warfare, chemical warfare, robots, artificial intelligence and nanotechnology to kill selected individuals - without necessarily having to come directly into their sights to do so. The Project for the New American Century, for instance, noted that genetically-selective plagues might become a politically useful tool.

Research proceeded, however, and by 2003, the Tactical High Energy Laser project, a joint research project of Israel and the US, has demonstrated a weaponized laser with substantial practical antiaircraft and anti-missile abilities.

Other projects

On a more limited scale, there is research on lasers as dazzling non-lethal weapons, and weapons of projected sound waves.

Research and development

A death ray weapon is under active research and development, but most examples of such weapons appear in science fiction. The difficulty in creating a death ray is that most weapons work not by transferring energy, but by matter causing physical damage at the point of impact. To reproduce this amount of damage requires large amounts of energy, and this is difficult to implement in a hand weapon. The goal is a death ray that would fire a particle beam or laser or radiation stream sufficiently powerful to kill humans.

How they work

Laser

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 speaker, push 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. They have open orifices, which cannot be destroyed by high energies.

Laser weapons begin to cause plasma breakdown in air at densities around a megajoule per square centimeter. This leads to "blooming" in which the interaction of the laser with the air causes the laser to defocus. The laser beam becomes visible, with speckles or a solid bar of plasma appearing in the air.

There are a number of techniques that could overcome blooming.

The most promising is to use relatively low energies, distributed over a large mirror that focuses the power on a distance target. SInce the energy never exceeds breakdown, the air never blooms, and defocusing is reduced. The disadvantage of current implementations is that there is a large, very precise, very expensive, fragile mirror, mounted something like a searchlight. Since the mirror is relatively heavy, the machinery to slew the mirror is relatively expensive.

A less expensive method might be to use a phased-array. This method is currently impractical because the phased-array would require billions of one-micrometre antennas, and no construction methods are known. Phased arrays could theroretically perform phase-conjugate amplification, as well (see below).

Another promising method is to adjust the timing of the pulse so that the energy hits the target before the blooming interferes.

Another is a phase-conjugate laser system. In this scheme, a "finder" or "guide" laser illuminates the target. 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. The phase-conjugation system therefore automatically corrects for the distortions induced 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.

Another antiblooming system attempts to induce a shockwave that evacuates the path between the target and the weapon. With no air in the laser's path, blooming is impossible. It is difficult to achieve the high instantaneous powers needed to blast the air out of the way.

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 contiues 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.

Particle beams

These are theoretically possible, but practical weapons have not been demonstrated.

Sonic beams

The U.S. DOD has demonstrated phased arrays of infrasonic emitters. The weapon usually consists of a siren that sounds at about 7Hz. The output from the siren's interrupter is routed (by pipes) to an array of open emitters. The emitters are usually one wavelength apart.

At this frequency, armor, concrete walls and other common building materials vibrate, and therefore provide no defense.

The frequency is chosen to be near the resonant frequency of internal organs, and induces illness, deafness and internal injuries.

The resulting weapon is large, (the size of a truck), fragile, aims at the speed of sound, and has a substantially shorter range than missiles or artillery shells. Shells move faster than the speed of sound, so artillery can win by shooting after the infrasonic weapon turns on, but before the sound arrives.

Additionally, mechanical "diode walls" to convert the oscillating air into a steady flow have been demonstrated. Although not common at this time, they could be mass-produced and would provide an effective countermeasure.

Doctrine

Lasers have two advantages. The main one is tactical-- they can hit whatever they see, and do so at the speed of light. Another secondary advantage is that some lasers operate from electricity, and therefore utilize a wide variety of inexpensive energy sources, 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 persons believe that mirrors or other countermeasures can reduce the effectivity of high energy lasers. This has not been demonstrated. Small defects in practical mirrors absorb energy, and the defects rapidly expand across the surface.

See also

External link

ja:殺人光線

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