Phaser emitter
From Memory Alpha, the free Star Trek reference.
A phaser emitter is a key component in starship and hand-held phasers. The emitter is equivalent to the "barrel of a gun", as it is the focal point where the phaser beam (à la "the bullet") is fired from.
[edit] Ship-mounted
From the 2260s to the late 2290s. These devices were connected to the ship's power systems and the emitter itself was built outside the hull while the main part of the device remained inside the hull and presumably accessible for maintenance and repair. (Star Trek II: The Wrath of Khan)
The emitters are arrangeable into Phaser banks in any number arrangements. The normal arrangement is two emitters to a bank, but as many as four could be placed in one bank to add more firepower. The large power requirement to operate such multiple banks usually limits the design to groups of two emitters.
The last known phaser emitter design before phaser arrays were introduced was the type-8 phaser system, which was still in use by the 2370s, long after the Federation-wide conversion to arrays. (TNG: "Preemptive Strike")
In 2372 the deflector of the USS Defiant was modified to perform as a single-shot phaser emitter when the ship was under attack from a Jem'Hadar attack ship in the atmosphere of a class J gas giant. (DS9: "Starship Down")
In 2375, Nog, acting as a representative of Miles O'Brien, bought a phaser emitter from the USS Musashi in a convoluted trade that also involved the USS Sentinel, to eventually acquire a graviton stabilizer. (DS9: "Treachery, Faith and the Great River")
[edit] Hand-weapons
Phaser emitters form part of the main component of hand phasers.
