"Phaser" is an acronym for PHASed Energy Rectification. All phasers release an energy beam. Personal phasers can stun or kill an enemy. The stun setting can also be used for crowd control. Ship-mounted phasers can damage shields or other systems or even cut a vessel's hull.
Phasers are based on the Rapid Nadion Effect, whereby energy is passed through a special phaser crystal resulting in a discharge of nadion particles (often, the detection of nadion discharges is a key sign that a battle has recently taken place). Nadion particles have varying effects on the subatomic bonds of particles with which they interact, largely depending on the mass of the atom in question. To wit, dense starship hulls are more resistant to nadion discharges than is a humanoid lifeform. The disruptive effects of nadion discharges can be moderated to produce varying effects (discussed below), ranging from benign to extremely destructive.
Personal phasers come in three types. Phaser type-1s (hand phasers) are small and can be concealed easily. Phaser type-2s are larger and handheld. They have a similar emitter but have a longer handgrip, or a pistol grip, depending on the model. Phaser type-3s are also known as "phaser rifles." They have a longer barrel, a double-handed grip, and a stock. These weapons can fire beams or phaser pulses. Over centuries of use, there have been many models of the lightweight and effective phaser rifle.
Beyond these, phasers are usually mounted devices, such as the phaser type-4 used on Starfleet shuttlecraft and other small vehicles, all the way up to the phaser type-10 mounted in arrays on the hulls of Galaxy class starships.
Phasers can be made to overload, either deliberately or by sabotage. About sixty seconds after the overload started, the weapon would expend all of its remaining energy in an explosion capable of doing considerable damage to its surroundings. In 2266, Lenore Karidian attempted to murder James T. Kirk by hiding an overloading phaser in his cabin. In 2269, Kirk, McCoy, and Sulu were almost killed while on the Kalandan outpost planet, when its defensive computer fused the controls on Kirk's phaser, causing it to overload.
Phaser type-1s have eight settings:
- Light stun - knocks out humanoids for up to five minutes
- Stun - knocks out humanoids for up to fifteen minutes
- Heavy stun - humanoids put to sleep for about an hour
- Thermal effects - extensive neural damage and skin burns to humanoids; causes metals to retain heat if applied for over five seconds
- Thermal effects - severe skin burns to humanoids; can penetrate simple personal force fields
- Disruption effects - matter disassociates and deeply penetrates organic tissue; can heat objects
- Disruption effects - kills humanoids; disruption becomes widespread
- Disruption effects - maximum setting; vaporizes humanoid organisms
- Settings taken from issue 3 of "Star Trek: The Magazine," based on the system used for the Star Trek: The Next Generation Technical Manual, although we know the 23rd century versions have the same capabilities, as they were seen vaporizing also.
The phasers mounted aboard starships are considerably more powerful than those used by Starfleet personnel, owing to the increased power reserves available. Early phasers were mounted in banks of one or two emitters, firing in either pulses or beams. This phaser design was retained on Starfleet ships until the Ambassador-class, at which point phasers were installed in arrays of several (sometimes hundreds!) emitters. These arrays enhanced both firing arcs as well as overall phaser output, the design benefitting from force-coupling all of the emitters in the array for the final composite beam. With the launch of the Defiant-class, phasers were again redesigned to fire pulses, though this time benefiting from the advances made with phaser arrays. Pulse phasers typically discharge several emitters internally to emit the final composite nadion burst.
The phaser is often seen vaporizing or disintegrating matter. However insuffient heat seems to be released by the process to explain the effect in terms of complete combustion of carbon. For instance, if a person were instantly combusted into carbon-dioxide enough heat would be released to seriously injure or destroy objects within a radius of several meters.
In TOS the phaser was often seen vaporizing people when set to kill. This is likely because the visual effect was cheaper to do than to show the victim with a serious burn injury to his or her body.