Directed-energy weapon

A directed-energy weapon (DEW) is a type of weapon that emits energy in an aimed direction without the means of a projectile. It transfers energy to a target for a desired effect. Some of these weapons are real or in development; others are at present only science fiction.

The energy can come in various forms:

• Electromagnetic radiation (typically lasers or masers).
• Particles with mass (particle beam weapons).
• Sound (sonic weaponry)

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.

Some lethal directed-energy weapons are under active research and development, but most examples appear in science fiction (non-functional toys, film props or animation).

[edit] Tactical considerations and problems

Lasers have several main advantages over conventional weaponry:

• Laser beams travel at the speed of light, unlike projectile weapons, so there is no need in terrestrial applications to aim ahead to allow for the target moving while the shot travels as the transit time over such distances is virtually zero.
• The speed of delivery means that the target has no chance to detect or evade (in contrast with enemy aircraft targeted with anti-aircraft missiles), and that some third object does not have the time to accidentally move into the trajectory while the energy is delivered.
• Light's short transit time also nearly eliminates the influence of gravity, so long range projection does not require compensation for such. Other aspects such as wind speed can be ignored.
• Lasers can provide a level of pin-point accuracy that cannot be matched by a projectile.
• Some lasers run on electricity which can be cheaply generated, reducing the need for expensive and finite ammunition, possibly replacing it with smaller batteries that would hold many more shots. However, building portable electric power sources of sufficient energy capacity is a problem.
• Because light has a practically nil ratio (exactly 1 / c) of momentum to energy, lasers produce negligible recoil.
• Laser beams do not "betray" themselves when emitted, either by eyesight or by sound. Unlike missiles ( e.g. ICBMs) there is no system to track and contain them.
• Design of laser weapons does not have to consider forces that the classic ammunition causes during firing.
• The laser could have much longer range than firearms without need of a long barrel or rifling

Since lasers can theoretically 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 might be as part of a defensive system.

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 could easily be made less effective by incidental damage and by dust and dirt on its surface. However protective measures have been considered that would evaporate off the surface and reduce the intensity of the beam, such as ablative armor.